new DVR

DYNAMIC VOLTAGE RESTORER

A ThesisSubmitted for the degree of

BACHELOR OF ENGINEERING

From

OSMANIA UNIVERSITY

Hyderabad, India

BY

Syed Saad Ahmed Quadri (04-07-2033)

Shoaib Ahmed (04-07-20042)

Syed Rameez Khaja (04-07-2033)

Department of

Electrical and Electronics Engineering

Muffakham Jah College of

Engineering And Technology

Hyderabad 500 032

2009-10

viii

DEDICATED

To

Almighty Allah and Our Parents

viii

DECLARATION

We hereby declare that we are the only authors of this thesis. I authorize Muffakham Jah

College of Engineering and Technology to lend this thesis to other institutions or

individuals for the purpose of scholarly research.

ACKNOWLEDGMENTS

We would like to take this opportunity to express our deep sense of gratitude and

profound feeling of admiration to our thesis supervisor Mrs. Fabia Akbar and many

thanks to Mr. KRM Rao HOD Electrical and Electronics Department MJCET,

Mr. Venkat Rao, HOD, Bio Medical Department Osmania University, and all our

Professors. We would also like to use this opportunity to thank our friends and also the

students from Erciyes University, especially Miss. Sevda Çıtak, for their support and help

at various points of our project fruition.

Abstract

Power quality problems encompass a wide range of disturbances such as voltage

sags/swells, flicker, harmonic distortions, impulsive transients and interruptions. Though

the impact of these disturbances causes minimal financial impact on residential areas, this

is not the case for industries that are heavily automated. A brief disturbance in the form

of voltage sag could cause the failure or malfunction of a single stage of a continuous

process and may cause heavy financial losses, apart from the damage to the machinery.

Voltage sags last until electrical network faults are cleared, and range from a few

milliseconds to several seconds. There are a number of methods to over come voltage

sags. One approach is to use dynamic voltage restorers with energy storage. The dynamic

voltage restorer with lead acid battery is an attractive way to provide excellent dynamic

voltage compensation capability as well as being economical when compared to shunt

connected devices.

The DVR is a custom power device that is connected in series with distribution

system. The DVR employs IGBTS to maintain the voltage applied to the load by

injecting output voltages, whose magnitudes, phase and frequency can be controlled.

These voltages are injected in synchronism with the voltages in the distribution systems,

to mitigate the voltage problems. In the proposed project, a DVR circuit is designed and

developed, and the performance of the same can be shown as wave forms on a CRO. The

circuit works on a 230V load

TABLE OF CONTENTS

Acknowledgements i

Abstract ii

List of Figures iv

List of Tables v

Notations and Abbreviations vi

1 Introduction 1

1.1 What is this template? 1

1.2 Organization of this template. 1

2 Review of Related Literature 2

3 Methods 3

4 Results and Interpretations 4

5 Summary and Conclusion 5

Bibliography 6

Appendix 7

LIST OF FIGURES

LIST OF TABLES

NOTATIONS/ABBREVIATIONS

Chapter 1

Introduction

The technological advancements have proven a path to the modern industries to extract

and develop the innovative technologies within the limits of their industries for the

fulfillment of their industrial goals. And their ultimate objective is to optimize the

production while minimizing the production cost and thereby achieving maximized

profits while ensuring continuous production throughout the period.

As such a stable supply of un-interruptible power has to be guaranteed during the

production process. The reason for demanding high quality power is basically the modern

manufacturing and process equipment, which operates at high efficiency, requires high

quality defect free power supply for the successful operation of their machines. More

precisely most of those machine components are designed to be very sensitive for the

power supply variations. Adjustable speed drives, automation devices, power electronic

components are examples for such equipments.

Failure to provide the required quality power output may sometimes cause complete

shutdown of the industries which will make a major financial loss to the industry

concerned .Thus the industries always demands for high quality power from the supplier

or the utility. But the blame due to degraded quality cannot be solely put on to the hands

of the utility itself. It has been found out most of the conditions that can disrupt the

process are generated within the industry itself. For example, most of the non-linear loads

within the industries cause transients which can affect the reliability of the power supply

7

[8,9]. Following shows some abnormal electrical conditions caused both in the utility end

and the customer end that can disrupt a process.

1. Voltage sags

2. Phase outages

3. Voltage interruptions

4. Transients due to Lighting loads, capacitor switching, non linear loads, etc..

5. Harmonics

As a result of above abnormalities the industries may undergo burned-out motors, lost

data on volatile memories, erroneous motion of robotics, unnecessary downtime,

increased maintenance costs and burning core materials especially in plastic industries,

paper mills & semiconductor plants.

Among those power quality abnormalities voltage sags and surges or simply the

fluctuating voltage situations are considered to be one of the most frequent type of

abnormality. Those are also identified as short term under/over voltage conditions that

can last from a fraction of a cycle to few cycles. Motor start up, lightning strikes, fault

clearing, power factor switching is considered as the reasons for fluctuating voltage

conditions.

As the power quality problems are originated from utility and customer side, the solutions

should come from both and are named as utility based solutions and customer based

solutions respectively. The best examples for those two types of solutions are FACTS

devices (Flexible AC Transmission Systems) and Custom power devices. FACTS devices

are those controlled by the utility, whereas the Custom power devices are operated,

maintained and controlled by the customer itself and installed at the customer premises

Both the FACTS devices and Custom power devices are based on solid state power

electronic components .As the new technologies emerged, the manufacturing cost and the

reliability of those solid state devices are improved; hence the protection devices which

incorporate such solid state devices can be purchased at a reasonable price with better

performance than the other electrical or pneumatic devices available in the market.

Uninterruptible Power Supplies (UPS), Dynamic Voltage Restorers (DVR) and Active

Power Filters (APF) are examples for commonly used custom power devices. Among

those APF is used to mitigate harmonic problems occurring due to non-linear loading

conditions, whereas UPS and DVR are used to compensate for voltage sag and surge

conditions.

In this thesis the control of a Dynamic voltage restorer for single phase voltage sags has

been studied. Voltage sag may occur from single phase to three phases. But it has been

identified single phase voltage sags are the commonest and most frequent in India.

Therefore the industries that use three phase supply will undergo several interruptions

during their production process and they are compelled to use some form of voltage

compensation equipment. In this research it was found that the most common voltage

compensation equipment used in India is the UPS; though it’s considered to be an

expensive alternative to move towards a full UPS system. This is the basic reason to carry

out this research in that particular area and focused into single phase voltage sags.

The wave forms are clearly shown on CRO, and the associated operation of the circuit is

explained in the following chapters.

Once the DVR is connected to the system, the phase angle of this reference signal is

synchronized with the supply voltage phase angle by continuously monitoring the

reference phase angle using a look up table. Then by comparing this reference voltage

waveform with the measured voltage waveform, any occurrence of voltage abnormalities

was detected as an error. As the system detect any voltage sags as error, the power circuit

in the DVR generates a voltage waveform to compensate for the voltage sag. The design

of the power circuit parameters and the control circuit is discussed in the preceding

chapters in detail.

One problem was notified as the internal voltage drop of the DVR and it responds when

harmonics presents in the supply voltage by becoming the injected voltage being non

sinusoidal even under normal operating conditions. However at the normal operating

conditions, the injected voltage becomes less and their affect on the load voltage due to

distortion is less. Therefore this thesis has contributed a strong knowledge to the research

and development targeting industrial application to compensate the single-phase voltage

sags.

The basic flow of this report is as follows. Chapter 2 is about the Literature review, which

will describe the basic operation, structure. This chapter will give the reader a general

idea about the Dynamic Voltage restorer and its functionality.

Chapter 3 describes the

The were illustrated and discussed under Chapter 4.

Chapter 5 will give the reader some hints about further development proposals of this

new control technique and further the technical limitations found during the research

work. Chapter 6 is the conclusion

Chapter 2

Review of Related Literature

2.1 Power quality related problems in the distribution network

Together with the technological developments, maintaining the power quality is one of

the major requirements, the electricity consumers are demanding of. The reason is

modern technology demands for an un-interrupted, high quality electricity supply for the

successful operation of voltage sensitive devices such as advanced control, automation,

precise manufacturing techniques. Power quality may be degraded due to both the

transmission and the distribution side abnormalities.

The abnormalities in the distribution system are load switching, motor starting, load

variations and non-linear loads whereas lightning and system faults can be regarded as

transmission abnormalities. To overcome the power quality related problems occurring in

the transmission system, FACTS (Flexible AC Transmission System) devices play a

major role. These are also referred to as Utility based solutions. Similarly Custom Power

devices, which normally targeted to sensitive equipped customers, are used to overcome

power quality problems in the distribution network. One of the main advantages of the

FACTS devices is that they allow for increased controllability and optimum loading of

the lines without exceeding the thermal limits. Whereas Custom Power devices ensure a

greater reliability and a better quality of power flow to the load centers in the distribution

system by successfully compensating for voltage sags/dips, surges, harmonic distortions,

interruptions and flicker, which are the frequent problems associated with distribution

lines.

However, failure of such custom power devices cause equipment failing, mal operations,

tripping of protective relays and ultimately plant shut downs, which results huge financial

loss to the industry .Therefore proper design of control and selection of the custom power

device is very important.

2.1 Voltage sags and surges

The most frequent power quality associated problem in the distribution network is

voltage sags and surges and are shown in Figure 2.1 below.

Figure 2.1: top left, top right bottom left bottom right

- Voltage sag occurs at the zero crossing point & without a phase shift - Voltage surge

occurs at zero crossing point & without a phase shift - Voltage sag not at the zero

crossing point & without a phase shift - Voltage sag at zero crossing point with a phase

shift.

Voltage sag/surge can simply be defined as a sudden increase/decrease in the rms voltage

with duration of half a cycle to few cycles. In addition to the magnitude change of the

supply voltage, there can be a phase shift during the voltage sag / surge as shown in

Figure 2.1. The magnitude of the voltage sag will depend on the fault type and the

location and also on the fault impedance .The duration of the fault depends on the

performance of the relevant protective device. Further it has been found that the voltage

sags with magnitude 70% of the nominal value are more common than the complete

outages. Sags and surges can be identified by the voltage magnitude and the time

duration it prevails. IEEE 5191992, IEEE 1159-1995 describes it as in Table 2.1 [10]

Table 2.1 : IEEE definitions for the voltage sags and swells

For a particular disturbance (voltage sag or swell), if the voltage and time duration it

remains is within the range given in Table 2.1, the custom power devices are the

optimized solution to overcome the problem and compensate for the abnormality during

the time period it prevails [16].

2.2 Custom Power Devices

The most common custom power devices to compensate for the voltage sags and swells

are the Uninterruptible Power Supplies (UPS), Dynamic Voltage Restorers (DVR) and

Active Power Filters (APF) with voltage sag compensation facility. Among those the

UPS is the well known. DVRs and APFs are less popular due to the fact that they are still

in the developing stage, even though they are highly efficient and cost effective than

UPSs [3,14,21]. But as a result of the rapid development in the power electronic industry

and low cost power electronic devices will make the DVRs and APFs much popular

among the industries in the near future [1,22]. DVR and APF are normally used to

eliminate two different types of abnormalities that affect the power quality. They are

discussed based on two different load situations namely linear loads and non-linear loads.

The load is considered to be a linear when both the dependent variable and the

independent variable shows linear changes to each other. Resistor is the best example for

a linear device. The non-linear load on the other hand does not show a linear change.

Capacitors and inductors are examples for non-linear devices.

(a) When the supply voltage/current consists of abnormalities, while the load is

linear: In this case the custom power device together with the defected supply should be

capable of supplying a defect free voltage/current to the load. To be precise the device

should be able to supply the missing voltage/current component of the source. A reliable

device that can be used for the above case (for voltage abnormalities) is the DVR. It

compensates for voltage sags/swells either by injecting or absorbing real and reactive

power [15].

(b) Power supplied is in normal condition with a non linear load: When non-linear

loads are connected to the system, the supply current also becomes non-linear and this

will cause harmonic problems in the supply waveform. In such situation to make the

supply current as sinusoidal, a shunt APF is connected [8]. This APF injects/absorbs a

current to make the supply current sinusoidal. Hence the supply treats both the non-linear

load and the APF as a single load, which draws a fundamental sinusoidal current [23,24].

Figures 2.2a and b show the basic function of the DVR and the shunt APF.

Figure 2.2a & b: Basic operation of DVR (left) and APF (right)

From Figures 2.2a, b and the references it is clear that the DVR is series connected to the

power line, while APF is shunt connected. Among the custom power devices, UPS and

DVR can be considered as the devices that inject a voltage waveform to the distribution

line. When comparing the UPS and DVR; the UPS is always supplying the full voltage to

the load irrespective of whether the wave form is distorted or not. Consequently the UPS

is always operating at its full power whereas the DVR injects only the difference between

the pre-sag and the sagged voltage and that also only during the sagged period. Thus

DVR operating losses and the required power rating are very low compared to the UPS.

Hence DVR is considered as a power efficient device compared to the UPS.

Chapter 3

DYNAMIC VOLTAGE RESTORER HARD WARE

DESIGN

DYNAMIC VOLTAGE RESTORER HARD WARE DESIGN

The actual dynamic voltage restorer basically consists of:

a) Single phase voltage source bridge inverter.

b) Micro controller circuit.

c) Opto coupler and driver circuits

d) Coupling network

e) Inverter driving circuitry

f) Isolated power supplies

3.1 Structure of DVR

The DVR basically consists of a power circuit and a control circuit. Control circuit is

used to derive the parameters (magnitude, frequency, phase shift, etc…) of the control

signal that has to be injected by the DVR. Based on the control signal, the injected

voltage is generated by the switches in the power circuit. Further power circuit describes

the basic structure of the DVR and is discussed in this section. Power circuit mainly

comprising of five units as in Figure 2.3 and the function and the requirement of each

unit is discussed below .

Figure 3.1: DVR Power circuit Block Diagram

3.2 BLOCK DIAGRAM

The basic block diagram of the proposed DVR system is as shown in the figure.

In the block diagram, the 230V, 50 HZ supply is isolated by means of a 1:1(230/230),

150VA isolation transformer. This isolated voltage is treated as the line voltage, which

supplies power to the load, through simulated line impedance. The simulated line

impedance is simply a wire wound resistor. To have maximum effect of voltage drop

across the line impedance, the resistance value considered is of very high value, in this

case it is 66 Ohms. The resistance 66 Ohm is obtained by connecting two 33 Ohms

10Watt resistors in series. After this simulated line impedance, a switch is connected,

through which the load can be connected or disconnected. In the return path, the DVR

output is connected, by means of the output winding of the coupling transformer,

developed. This output from the DVR is connected in series with the load, and mitigates

the line impedance effects, i.e. in this case the voltage drop caused by it.

The DVR circuit has to check the load voltage and need to be connected to the micro

controller circuit and correct the voltage if there is any shortage or excess when compared

to a reference voltage, by injecting appropriate voltage into the circuit by means of the

coupling network. As the micro controller can read voltages only between 0 and 5V. But,

the single phase voltage can have a peak voltage of 230√2 V at peak point during the

positive half cycle and -230√2 V during the negative half cycle. As this voltage cannot be

directly fed to the micro controller circuit, this voltage is attenuated to 2.5V at peak

points by means of a potential divider. The potential divider is basically a resistor divider

network, with resistors R1 and R2 as shown in the figure. One of these resistor values is

arbitrarily chosen and the other value is calculated, as explained below.

Initially, the R2 value is assumed and is 1.8KΩ. The supply peak voltage, output

voltage, R1 and R2 values are related by the following equation.

(R2÷ (R1+R2))×230√2 = 2.2 V

Here, the R1 value is calculated and is 2.6k

The output voltage is considered to be 2.2V, instead of 5V that can be accepted by

the micro controller circuit. The micro controller has to sense both positive and negative

voltages, and the range it can accept is only 0 to 5V. Thus, for positive and negative

peaks if 2.5 V is generated as the output, then if 2.5 V is added then the output remains in

the range of 0 to 5V. But, the input supply voltage can have a value more than 230V rms.

In order to accommodate the excess voltages, instead of 2.5 V for peak voltages 2.2V is

generated. Thus, another 0.3 V is there to meet the higher voltages, if occurred.

The load in the present circuit is a 60 Watts lamp load. If the lamp load is not

connected, the output of the isolation transformer does not have any drop, and the full

voltage appears across the sensing circuit, and there is no need of any correction by the

DVR circuit. When the load is connected, the lamp glows and current flows through the

simulated line impedance, and there is an appreciable voltage drop across the line

impedance, and this drop in voltage need to be injected by the DVR circuit. How, this

voltage is injected is explained below.

The micro controller circuit along with its program detects the voltage reduction

or excess and provides triggering pulses to the power switches, which are connected to

form a single phase bridge inverter. The inverter generates a voltage in such a manner, so

that the resultant voltage across the load is simply the required 230V. The micro

controller continuously monitors the load voltage and the corrective action is taken so

that the voltage is always in the specified limits. The micro controller provides only 5V

pulses and they cannot drive the power switches directly as it requires the necessary

isolation. The isolation can be provided either by means of pulse transformers or by

means of Opto isolators. In the present project opto isolators are used, as they can provide

the triggering pulses at maximum frequency. The opto couplers also require the isolated

power supplies to trigger the power devices.

The power supply block provides the necessary power supply voltages to the

respective modules. The power supply circuit module works on AC mains through

necessary step-down transformer.

The design details and the circuit operation is explained In the coming units.

3.3 Energy Storage Unit

Energy storage device is used to supply the real power requirement for the

compensation during voltage sag. Flywheels, Lead acid batteries, Superconducting

magnetic energy storage (SMES) and Super-Capacitors can be used as energy storage

devices [3,11,13]. For DC drives such as SMES, batteries and capacitors, ac to dc

conversion devices (solid state inverters) are needed to deliver power, whereas for others,

ac to ac conversion is required. The maximum compensation ability of the DVR for

particular voltage sag is dependent on the amount of the active power supplied by the

energy storage devices [8,13]. Lead acid batteries are popular among the others owing to

its high response during charging and discharging. But the discharge rate is dependent on

the chemical reaction rate of the battery so that the available energy inside the battery is

determined by its discharge rate [11,21].

3.4 By-pass switch

Since the DVR is a series connected device, any fault current that occurs due to a fault in

the downstream will flow through the inverter circuit. The power electronic components

in the inverter circuit are normally rated to the load current as they are expensive to be

overrated. Therefore to protect the inverter from high currents, a by-pass switch (crowbar

circuit) is incorporated to by-pass the inverter circuit [9,11]. Basically the crowbar circuit

senses the current flowing in the distribution circuit and if it is beyond the inverter

current rating the circuit bypasses the DVR circuit components (DC Source, inverter and

the filter) thus eliminating high currents flowing through the inverter side. When the

supply current is in normal condition the crowbar circuit will become inactive [8].

3.6 Voltage injection transformers

The high voltage side of the injection transformer is connected in series to the

distribution line, while the low voltage side is connected to the DVR power circuit. For a

three-phase DVR, three single-phase or three-phase voltage injection transformers can be

connected to the distribution line, and for single phase DVR one single-phase transformer

is connected .The basic function of the injection transformer is to increase the voltage

supplied by the filtered VSI output to the desired level while isolating the DVR circuit

from the distribution network. The transformer winding ratio is pre-determined according

to the voltage required in the secondary side of the transformer (generally this is kept

equal to the supply voltage to allow the DVR to compensate for full voltage sag) .A

higher transformer winding ratio will increase the primary side current, which will

adversely affect the performance of the power electronic devices connected in the VSI.

The rating of the injection transformer is an important factor when deciding the DVR

performance, since it limits the maximum compensation ability of the DVR. Further the

leakage inductance of the transformer brings to a low value to reduce the voltage drop

across the transformer. In order to reduce the saturation of the injection transformer under

normal operating conditions it is designed to handle a flux which is higher than the

normal maximum flux requirement. The winding configuration of the injection

transformer mainly depends on the upstream distribution transformer. If the distribution

transformer is connected in Δ-Y with the grounded neutral, during an unbalance fault or

an earth fault in the high voltage side, there will not be any zero sequence currents flow

in to the secondary. Thus the DVR needs to compensate only the positive and negative

sequence components. As such, an injection transformer which allows only positive and

negative sequence components is adequate. Consequently the delta/open configuration

can be used (shown in Figure 2.8-left). Further this winding configuration allows the

maximum utilization of the DC link voltage. For any other winding configurations (such

as star/star earthed) of the distribution transformer, during an unbalance fault all three

sequence components (positive, negative and zero) flow to the secondary side. Therefore

the star/open configuration (Figure 2.8-right) should be used for the injection

transformers, which can pass all the sequence components.

3.7 Single Phase Voltage Bridge Inverter

The dynamic voltage restorer concept uses power electronics to produce a voltage either

in phase or out of phase with mains voltage and is added to the supply voltage in order to

keep the load voltage essentially constant. These dynamic voltage restorer circuits are

relatively new and a number of different topologies are being proposed. Within each

topology, there are issues of required component ratings and methods of rating the overall

ratings for the loads to be compensated. The voltage source inverter is one such

configuration. In the present project the voltage source inverter is used and is controlled

in a specified manner, in order to control the voltage sags and swells.

The voltage source inverter is the heart of the DVR. There are two types of power circuits

applicable to single / three-phase DVR circuits; a voltage-source PWM converter

equipped with a dc capacitor, which is shown in Fig. 4 (a), and a current-source PWM

converter equipped with a dc inductor, which is shown in Fig. 4 (b). These are similar to

the power circuits used for ac motor drives. They are, however, different in their behavior

because DVR circuits act as Non-sinusoidal current or voltage sources.

Fig.4. Power circuits applicable to active filters: a) Voltage-source PWM converter

and b) current-source PWM converter.

Voltage source is preferred to current-source PWM converter because the voltage source

PWM converter is higher in efficiency; lower in cost, and smaller in physical size than

the current-source PWM converter, particularly in terms of comparison between the dc

capacitor and the dc inductor.

Moreover, the IGBT module that is now available from the market is more

suitable for the voltage-source PWM converter because a free-wheeling diode is

connected in anti-parallel with each IGBT. This means that the IGBT does not need to

provide the capability of reverse blocking in itself, thus bringing more flexibility to

device design in a compromise among conducting and switching losses and short-circuit

capability than the reverse-blocking IGBT. On the other hand, the current-source PWM

converter requires either series connection of a traditional IGBT and a reverse-blocking

diode as shown in Fig. 4 (b), or the reverse-blocking IGBT that leads to more

complicated device design and fabrication, and slightly worse device characteristics than

the traditional IGBT without reverse-blocking capability. In fact, almost all DVR circuits

that have been put into practical, commercial application in developed countries have

adopted the voltage-source PWM converter equipped with the DC-filter capacitor as the

power circuit, i.e. shown in fig.4 (a).

The voltage source inverter used in the DVR circuit makes the induction of required

voltage with required phase possible. This inverter uses dc capacitors as the supply and

can switch at a high frequency to generate a signal which will mitigate the voltage sags

and swells across the load.

The DVR circuit needs to provide real power to mitigate the voltage sags and swells

across the load. The amount of voltage to be mitigated and the amount of power to be

delivered to the load, decides the voltage and current rating of the inverter. The inverter

requires to be fed by a source to meet these requirements. Therefore, the Dc capacitors

and the filter components must be rated based on the power to be injected into the load

circuit to mitigate the voltage fluctuations.

The voltage waveform for mitigating the voltage variations in the load circuit is achieved

with the voltage source inverter, coupling transformer and an interfacing filter. The

coupling transformer needs to transfer energy from the voltage source inverter to the load

and at the same time need to provide low impedance on the load side, so that the

transformer winding itself doesn’t provide a voltage drop across the load. The voltage

source inverter also works at very high frequencies, thus a ferrite core based transformer

is designed and implemented. The transformer basically consists of 200 turns on the

primary side that is on the inverter side. The load side the transformer has 800 turns.

Thus, the transformer has a step-up nature, and the voltage applied by the inverter is

stepped up by 4 times and is applied to the load, in order to mitigate the voltage

variations. The transformer secondary side a capacitor filter is provided to smoothen and

filter out the high frequency components in the voltage into the load circuit. The rest of

the filter provides smoothing and isolation for high frequency components. The desired

voltage waveform to be injected is obtained by accurately controlling the switching of the

insulated gate bipolar transistors (IGBTs) in the inverter. Control of the voltage wave

shape is limited by the switching frequency of the inverter and by the available driving

voltage across the interfacing inductance.

When the inverter is not injecting any voltage into the load circuit, there is a small

ac voltage induced into the primary side of the transformer, due to current flow on the

secondary side of the transformer. The inverter IGBTs are with reverse diodes, and the

voltage gets rectified and charges the inverter supply capacitor. But, the inverter supply is

derived from a second transformer, and is always higher than the induced voltage. So, the

transformer does not load the mains supply, during the normal operating conditions.

Figure 4.a shows the basic topology of a full-bridge inverter for single-phase DVR circuit

output. This configuration is often called an H-bridge, due to the arrangement of the

power switches and the load. The inverter can deliver and accept both real and reactive

power. The inverter has two legs, left and right. Each leg consists of two power control

devices (here IGBTs) connected in series. The injection transformer is connected between

the midpoints of the two-phase legs. Each power control device has a diode connected in

anti parallel to it. The diodes provide an alternate path for the load current if the power

switches are turned off. Control of the circuit is accomplished by varying the turn on time

of the upper and lower IGBT of each inverter leg, with the provision of never turning on

both at the same time, to avoid a short circuit of the DC bus. In fact, modern drivers will

not allow this to happen, even if the controller would erroneously command both devices

to be turned on. The controller will therefore alternate the turn on commands for the

upper and lower switch, i.e., turn the upper switch on and the lower switch off, and vice

versa. The driver circuit will typically add some additional blanking time (typically 500

to 1000 ns) during the switch transitions to avoid any overlap in the conduction intervals.

The circuit of the single-phase voltage source bridge inverter is built around power

IGBTS (IGBT-25N120), because the working voltage of the circuit is only around 640V,

and the current that can be carried by the elements is less than 1Ampere. The inverter

switching current is very small because the load current it self is around 1 Amp with

200W lamp load, out of that the entire voltage can not be under mitigating voltage, and is

not required to be compensated for. These devices are triggered by the micro controller,

in such a way that the voltage sags and swells are removed from the sensitive load circuit,

which were introduced by the current flow through the line impedance. The micro

controller is programmed in such a way to identify the voltage to be injected and is also

programmed to generate the required triggering pulses for the voltage source inverter

switching devices (IGBT-25N120). The triggering pulses generated by the micro

controller can not be used to trigger the devices, as it requires isolation. Thus the

triggering pulses are applied to the opto-isolator and driving circuits. The output of the

voltage source inverter is coupled to the load circuit in series to the load by means of the

interfacing circuit.

Each power device in the inverter is protected from transients by means of a suitable

snubber circuit. The snubber circuit is just an resistor – capacitor series combination

connected across each and every power device. This snubber protects the power device

from the voltage and current transients.

3.8 Micro controller circuit

The micro controller circuit is the heart of the system, and is responsible for generating

the reference voltage waveform from the voltage waveform that is sampled from the

sensing network; it has obtained from the reference voltage sensing circuit. This

reference voltage waveform is generated keeping the zero crossing as the reference to

maintain the phase relationship of the load and correcting voltage. The micro controller

takes the zero crossing point as the reference and calculates the sample by sample the

voltage values, and are compared with the actual load voltage value sensed from the

potential divider network through the ADC of the micro controller, and based on the

comparison, the bridge inverter elements are triggered to compensate for the voltage

deviation from the reference value. As the voltage induced through the coupling

transformer, generated by the bridge inverter, the resulted voltage across the load will be

a pure sinusoid of required voltage. The sinusoid voltage purity can be improved by

increasing the switching frequency of the inverter power devices. This frequency is again

dependent on the micro controller operating frequency, and also on the coupling

transformer.

There are many different control methods that can be used to generate the compensating

voltage that mitigates the voltage variations in the load voltage. They are distinguished by

how the voltage reference signal is derived from the measured quantities.

The basic features needed with a micro controller for this application are:

Two analog inputs, one analog input pin for reading the actual load voltage. This

input is obtained from the potential divider network connected across the load,

processed by an op-amp circuit, to meet the requirements of the ADC of the micro

controller. For better performance the minimum number of bits required may be a

minimum of 10bits. The second ASDC is used to sense the reference, in the

present case the reference is also generated by sensing the voltage at the

transformer secondary itself, before the line impedance. In the practical situations,

it is not possible, in practical situations, this voltage is generated by using

different software techniques.

Approximately 4k-8k ROM space for the basic application software, which is to

be developed during the project implementation.

Two output pins to drive the inverter switching elements.

Minimum of 256 bytes of internal RAM.

A 16-bit timer/counter with compare-match function to generate the required

reference voltage waveform.

Apart from these features, it is also required to have the following additional features, to

make the product a full fledged commercial product.

Additional analog input pins, to sense temperature, current, etc., for operating the

DVR circuit in safe limits. These inputs can be used as protective inputs.

Additional digital inputs to sense the other inputs that can be generated either

from the sensors or to detect the status of the switching elements, using intelligent

triggering circuits.

Additional 11-12 I/O lines to interface a 162 character LCD for displaying the

essential values, such as the actual load voltage, injected voltage etc.,

Additional 3-4 I/O lines to indicate the fault conditions through LEDs.

Additional ROM/RAM memory space to incorporate PID controller algorithm for

better performance characteristics.

A serial communication port for interacting with master controller, if any etc.

Most of the present day micro controllers from different manufacturers satisfy these

requirements.

Apart from these standard features, in order to use the micro controllers, especially to

write the developed code into ROM of the micro controller, the necessary software and

hardware support from the micro controller manufacturer, commonly referred as

developmental tools.

All these features (present and additional requirements) , are available with Renesas

R8C-1A controller with the following features.

CPU configuration for the application.

Facility to develop the programs and also verify them.

On-chip clock structure, interrupt facilities.

All the on-chip peripherals including ports, timer/counters, communication

facilities.

Facilities are available to use all the features of the selected micro controllers

without any physical hardware.

Also plenty of external embedded modules are simulated for the application.

Range of Plain Point LEDs and Seven Segment LED options.

LCD modules in many configurations.

Momentary ON keys.

A variety of keypads upto 4 X 8 key matrix.

Toggle switches.

All modes of on chip serial port communication facility.

IIC components including RTC, EEPROMs.

SPI Bus based EEPROM devices.

PIN DIAGRAM:

The operational features of the micro controller along with the software instructions were

provided in the “Annexure-A”. The internal block diagram of the micro controller is

provided in fig.5.

Any micro processor or micro controller requires clock for its operation. Most of them

are having built in oscillators, and only a crystal of appropriate frequency has to be

connected across the terminals provided in the IC. The R8C-1A is designed to operate at

20MHz. So the crystal connected is 20MHz, and is connected across the specified pins as

shown in fig.6.

In the case of power On or whenever the CPU enters into an endless loop or a program of

an unknown destination, the CPU has to be resetted. In order to achieve, both power on

and manual reset, the circuit is to be connected as shown in fig.7

In the circuit, the minimum RC values must be chosen in such a way that at least a low

signal of four clock signals are to be kept on a Reset pin after the stabilization of circuit

power.

3.8.1 A/D CONVERTER:

The A/D converter consists of one 10-bit successive approximation A/D converter circuit

with a capacitive coupling amplifier. The analog input shares the pins with P1_0 to P1_3.

Therefore, when using these pins, ensure the corresponding port direction bits are set to

“0” (input mode).

When not using the A/D converter, set the VCUT bit in the ADCON1 register to “0”

(Vref unconnected), so that no current will flow from the VREF pin into the resistor

ladder, helping to reduce the power consumption of the chip. The result of A/D

conversion is stored in the AD register.

3.8.2 PERFORMANCE OF A/D CONVERTER

Table 3.7: Performance of A/D converter

Analog input voltage does not depend on use of sample and hold function. When

the analog input voltage exceeds the reference voltage, the A/D conversion result

will be 3FFh in 10-bit mode and FFh in 8-bit mode.

The frequency of φAD must be 10 MHz or below.

Without sample and hold function, the φAD frequency should be 250 kHz or

above.

With the sample and hold function, the φAD frequency should be 1 MHz or

above.

In repeat mode, only 8-bit mode can be used.

3.9 TIMER

The microcontroller contains two 8-bit timers with 8-bit prescaler and a 16-bit

timer. The two 8-bit timers with the 8-bit prescaler contain Timer X and Timer Z. These

timers contain a reload register to memorize the default value of the counter. The 16-bit

timer is Timer C which contains the input capture and output compare. All these timers

operate independently. The count source for each timer is the operating clock that

regulates the timing of timer operations such as counting and reloading.

Timer c ,an example is given below:

Timer C is a 16-bit timer. Figure 14.23 shows the Block Diagram of Timer C. Figure

14.24 shows the Block Diagram of CMP Waveform Generation Unit. Figure 14.25 shows

the Block Diagram of CMP Waveform Output Unit. Timer C has two modes: input

capture mode and output compare mode. Figure 14.26 to 14.29 show the Timer C

associated registers.

3.10 OPTO-COUPLER AND GATE DRIVER CIRCUIT

The output form the micro controller is provided by the circuit is not sufficient to

drive the IGBT gates. They usually require a +12 volts at the gate with respect to emitter

to make it ON at the same time in order make it OFF it requires to apply a -12V at the

gate, and this is not directly possible with the outputs from the micro controller. For this

reason a suitable driver circuit is designed to provide the required signal to make the

IGBT ON or OFF. The circuit also cannot directly drive the IGBT, because of shock

hazards and also because of the isolation problem. For this reason opto isolation is used.

Opto couplers are capable of transferring an electrical signal between two circuits

while electrically isolating the circuits from each other. They generally consist of an

infrared LED, light emitting section at the input and a silicon photo detector at the output.

The input for opto couplers can be either AC or DC, which can drive the LED. The

output can be a photocell, photodiode, phototransistor, or photo Darlington. Photocells

are light-dependent resistors. They are used to detect changes in light intensity.

Photodiodes are a two-electrode, radiation-sensitive junction formed in a semiconductor

material in which the reverse current varies with illumination. A phototransistor is a

bipolar transistor used as a photo detector. It provides current at its output that is

proportional to light intensity at its input. The low-level input light current is amplified

by the current gain (beta) of the transistor. A photo Darlington is a pair of bipolar

transistors connected in a Darlington configuration to provide very high current gain and

often used as the photo detector section of an opto coupler.

Important performance specifications to consider when searching for opto

couplers include isolation voltage, rise time, collector emitter breakdown voltage,

resistance on, and operating temperature. Isolation voltage specifies the input-to-output

voltage withstanding capability of an optically coupled isolator. Rise time is the time that

elapses while a pulse waveform increases from 10% to 90% of its maximum value.

Collector emitter breakdown voltage refers to the voltage at which a transistor, biased in

the normal direction with no optical or electrical input to the base, will conduct a

specified current much higher than the normal leakage currents that occur at lower

voltages. The resistance on refers to the resistance of the opto coupler when activated.

Operating temperature is the temperature range the opto coupler is designed to operate in.

Mounting options for opto couplers include surface mount, flat pack, and through hole

(plug-in). In Surface Mount Technology (SMT), components are mounted on printed

circuit boards by soldering the component leads or terminals to the top surface of the

board. A flat pack is an IC package with gull wing or flat leads on two or four sides. In

Through Hole Technology (THT), opto couplers are mounted on printed circuit boards by

inserting component leads through holes in the board and then soldering.

The circuit diagram of the IGBT driver is shown in fig.6

Fig. 6: IGBT drive circuit

When the LED in the opto-coupler is OFF there is no light falling on the

phototransistor. The phototransistor is under OFF condition and the +12 V output appears

at the IGBT gate and emitter of the IGBT is directly connected to the 0V terminal of the

opto coupler power supply. When the LED is made ON by providing ‘1’ signal at the

input makes the LED ON, which makes the phototransistor ON. Because of this, the

IGBT gate is provided with a -12V, which make the IGBT OFF.

This way the IGBT is made ON and OFF by the signal provided by the micro

controller circuit. The micro controller output pins has to drive two opto coupler inputs,

one the top element of one of the arms, and the other to drive the bottom element of the

other arm. The micro controller output pins cannot drive this much of load. For this

reason, the micro controller out pins are connected to a buffer driver circuit, which is

basically an AND gate IC 7408. The AND gate output is used to drive the opto coupler

inputs. The AND gate output is very small current and is less than few milli amps. This

out put is not sufficient to drive the opto couplers. For this reason 555 timer IC is used,

which provide a maximum of 100 mamps. But, the 555 timer IC inverts the output, for

that reason the And gate outputs are given to NOT gates and the NOT gate in turn drives

the 555 IC. The output from the 555 IC is used to drive the opto couplers.

The micro controller provides a logic 1 for the entire positive half cycle in case of

error in voltage and similarly in the negative half cycle on the other pin. If these pulses

are directly used to drive the inverter, the inverter provides 50- Hz output. This output to

be injected into the power circuit requires a 50Hz transformer. This transformer becomes

bulky and also poses several other problems. For all the reasons, it is always preferred to

increase the operating frequency. This is done by using another 555 IC in astable mode.

These pulses are AND operated with micro controller otputs and are used to drive the

bridge inverter.

3.11 Coupling network

The voltage waveform for mitigating the voltage variations in the load circuit is

achieved with the voltage source inverter, coupling transformer and an interfacing filter.

The coupling transformer needs to transfer energy from the voltage source inverter to the

load and at the same time need to provide low impedance on the load side, so that the

transformer winding itself doesn’t provide a voltage drop across the load. The voltage

source inverter also works at very high frequencies, thus a ferrite core based transformer

is designed and implemented. The transformer basically consists of 200 turns on the

primary side that is on the inverter side. The load side the transformer has 800 turns.

Thus, the transformer has a step-up nature, and the voltage applied by the inverter is

stepped up by 4 times and is applied to the load, in order to mitigate the voltage

variations. The transformer secondary side a capacitor filter is provided to smoothen and

filter out the high frequency components in the voltage into the load circuit. The rest of

the filter provides smoothing and isolation for high frequency components. The desired

voltage waveform to be injected is obtained by accurately controlling the switching of the

insulated gate bipolar transistors (IGBTs) in the inverter. Control of the voltage wave

shape is limited by the switching frequency of the inverter and by the available driving

voltage across the interfacing transformer.

The driving voltage across the interfacing transformer secondary determines the

maximum dv/dt that can be achieved by the DVR circuit. This is important because

relatively high values of dv/dt may be needed to cancel higher order spikes. At the same

time to smoothen out the induced voltage pulses a capacitor is connected across the load.

If very high value capacitor is connected, the voltage spike reduces to a small voltage

step, and if very low capacitor is connected, the spiky nature of the induced voltage

remains. Therefore, there is a tradeoff involved in sizing the capacitor, and are just 0.22

micro farads.

3.12 Inverter Driving circuitry and Design of isolated power supply

In order to trigger the IGBTs, it is required to apply a +12volts pulse to make it

turn ‘ON’ and –12 volts pulse to turn it ‘OFF’, to the gate with respect to its emitter.

Even if GND (0v) potential is applied to gate, then also one can turn off the IGBT. But

the device turn off time will becomes longer. In order to reduce the turn off time, it is

advised to apply -12 volt pulse to the gate. To provide these pulses to the power device

gate with respect to the emitter, it is required to have a + / -12 volt power supply.

Apart from this, there are altogether four power MOSFETs in the proposed

inverter circuit and all the power MOSFETs sources are not at the same potential. Thus in

order to provide triggering pulses to each and every MOSFET, it is required to have four

isolated power supplies of ± 12 volts which can be used to apply trigger pulses to the

respective MOSFETs. But fortunately the bottom two MOSFETs are at the same

potential and thus all the two bottom power devices do not require two isolated power

supplies and in fact one power supply can be used for the bottom devices.

With this, the triggering pulse circuit requires three numbers of isolated ±12 volts

power supplies and out of which two can be used to apply triggering pulses to two

switching devices and the other supply is used to provide triggering pulses for all the two

bottom devices. This sort of power supplies can be generated in many numbers of ways.

All the techniques can be broadly classified as 50 Hz transformers based or SMPS based.

In the first method, the 230 volts, 50 Hz supply is used to power the primary of the

transformer. The transformer consists of 6 numbers of isolated secondaries. Each

secondary winding provides 15-0-15-volt output which can be used to generate positive

or negative voltage supplies with rectifier and filter circuits. Though the circuit is simple,

the circuit mainly has certain problems. The main problem is the inter layer capacitance

between windings. If the inter layer capacitance is high it will lead to improper isolation

between the triggering pulse power supplies which restricts the power voltage that can be

used along with power switches.

In the SMPS mode of power supplies 12 to 18 volts dc supply is used to power

the circuit. The circuit basically consists of an oscillator driving push pull devices that

powers the primary of the SMPS transformer. This produces a very high frequency

magnetic flux, which is used to induce voltage in the secondary windings. The secondary

winding is used to produce 15-0-15 volt output which is rectified and filtered to be used

for triggering circuit.

The circuit diagram is as shown in the fig. The circuit is powered by a 12-V

power supply derived from mains my means of a step down transformer and associated

rectifier and filter circuits. This DC supply is applied to the circuit. This DC supply is

converted to a very high frequency AC supply, by means of the two transistors and the

associated feedback circuit with them. The circuit is basically an astable mutivibrator,

driving the transformer in the push-pull mode. The secondary side of the ferrite cored

transformer consists of 3 no.s of isolated 15-0-15 windings. These secondary voltages are

rectified by means of rectifiers with capacitor filter. This provides the required outputs,

which can be used to drive the opto-coupler secondary side, which is meant for driving

the IGBT gate.

3.13 Isolated power Supplies for filter elements

Three different power supplies are required, to provide power to various blocks of

the over-all DVR circuit.

The micro controller requires basically a 5-V supply. But, the op-amp circuit

associated with the potential divider circuit requires a ±12 volts supply. This supply is

generated from a step-down transformer connected to the mains. The circuit is as shown

in the fig.

The DVR inverter requires a separate power supply, and this is generated from

another step-down transformer, and the circuit is shown in the fig.,

Another 12-V supply is generated using another step-down transformer, which is

mainly to power the isolated power generator circuit. This circuit is shown in the fig.,

3.14 Design of Instrument power supply

With any micro controller based equipment, power supply is an essential item,

which takes the input AC (230v, 50Hz) and converts the same into DC voltages of

specified values, required by the other circuits of the equipment, such as micro controller,

sensor amplifier, opto-coupler etc. Sometimes only a single power supply of value +5v is

sufficient. But in some cases both positive and negative voltages of specified values are

to be derived, because of the circuit involved; where as in other cases, different values of

the voltages may be required. This is entirely dependent on the other circuits of the

system.

In the proposed DC motor speed control circuit, Hitachi H8/300H-3664 micro

controller is used and the associated digital circuit requires a 5v regulated power supply

for its operation. But in order to drive the IGBT, it is required to provide an isolation

between the micro controller and the IGBT gate drive circuit. To provide the isolation,

two techniques can be used, one is a pulse transformer and second is an opto –isolator. In

the pulse transformer, the output pulse shape is not properly maintained and will have

voltage spikes at raising and falling edges of the driving pulse. For which, the IGBT is

very sensitive and may get damaged. To avoid this situation, opto-isolators are preferred.

With the opto –isolator, a second power supply is required in order to power up the

secondary side of the opto-isolator. The second power supply is completely isolated from

the 5v supply. The same supply can also be used to provide the feedback signal to the

micro controller i.e., the back EMF across the armature is attenuated and used to provide

a feed back to the micro controller, through another opto-isolator working in a linear

range. To operate this opto-isolator also the power supply needed is achieved from the

second power supply.

The circuit diagram of the desired power supply is as shown in fig.4.

Fig.4: Instrument Power Supply

In the circuit, a step down transformer of rating 230v primary with the isolated

secondary is used. One secondary winding provides an 8v ac output, with a current

capacity of 500mA, and the other winding provides 15:0:15v (i.e. center tapped

secondary) with a current capacity of 500mA.

The secondary winding-1, voltage is rectified by using a bridge rectifier. This is followed

by a capacitor filter to remove the ripple.

The secondary winding-2, voltages are rectified, by using two center tapped full wave

rectifiers, one providing positive voltage and the other providing the negative voltage.

The positive and negative voltages are again filtered by using two capacitor filters as

shown in fig.4.

In these instrument power supplies, the filter sections can be either or L sections, but

these sections are not normally needed in low power, low voltage applications and only a

single capacitor is sufficient. The internal impedance of the secondary winding is

sufficient to limit the current during the initial surge. The capacitor value should be of

very high value for low ripple. Thus, a capacitor of 1000f with a working voltage of 18v

is sufficient, but with a factor of safety the working voltage is considered as 35v.

The filtered DC output from secondary winding-1, without any load has a value of

10v to 12v with normal input supply of 230v AC. The input voltage may fluctuate over a

wide range practically. To accommodate these ranges a higher initial output, which is

more than 12v is considered. The regulator itself requires 2v higher than its regulated

output, i.e., 7v is needed for getting 5v. In order to accommodate the voltage fluctuations

on the lower side of 230v, another 5v additional voltage is considered.

This voltage is fed to a three pin regulator 7805, which basically provides an

output of 5v irrespective of its input supply, provided the input is greater than 7v. But, at

the maximum input voltage, it should not exceed 32v, and as it is, it never happens,

unless the input supply voltage is greater then 400v, and is of rare nature. The output of

this regulator is connected with a small capacitor of 0.1f (between output and ground).

This capacitor improves the noise immunity. This output drives the micro controller.

The filtered DC output from secondary winding-2, is also connected to a three pin

positive regulator, 7812 to obtain +12v and a three pin negative regulator 7912, to obtain

–12v. These supplies are used to power the IGBT/power MOSFET gate drive circuits.

The three pin regulators are very handy and are widely used by industry in order

to get regulated dc power supplies. These regulators are having built in features such as

over voltage, over current limitations and also thermal shut down. Thus, because of these

protection mechanisms these devices provide all the options required for an ideal

regulator.

This is the basic power supply module, which is designed and used with the circuit.

3.15 Inverter power supply:

In the practical situations the inverter is powered by an auxiliary power supply. In

the present project this power supply is provided with a power supply derived from

another transformer of 15-0-15 transformer. This output is rectified and filtered and then

provided to the inverter as power supply.

3.16 Complete Circuit Diagram

The total circuit diagram of the DVR is given below

The DVR circuit consists of two parts. The first part, being the power control circuit and

the second part being the actual control circuit. The power control circuit basically

consists of an isolation transformer, which provides 230volts isolated voltage and is

applied to a lamp load in series with simulated line impedance. The circuit also includes

DVR coupling transformer secondary side is also included. The reference voltage is

sensed by means of a potential divider which is situated near to the transformer secondary

and the second sensor circuit is situated near the load, which senses the actual voltage.

These are two voltages are fed to the control circuit.

The reference voltage and actual voltage are need to fed to the micro controller’s ADC

inputs. These inputs can handle only voltage in the range of 0 to 5v. But the sensed

voltages are having both positive and negative voltages and by means of the potential

divider network , The voltages are adjusted in such a way that the voltages are below

+2.5v in the positive half cycle and -2.5v during the negative half cycle. The op-amp

circuit is designed in such a manner to add 2.5v to these values, So that the entire signal

shifts to a range of 0 to 5 volts, so that the micro controller can sense both the voltages.

The 2.5v reference is also generated by means of 5v regulated power supply and using

two equivalent resistors in series, the center point voltage is take as reference.

The micro controller reads the two analog signals in succession and compares them. If

the load voltage is having any dip during positive half cycle, the micro controller

provides a ‘1’on one of the port pins. Similarly the micro controller reads the voltages

during the negative half cycle and if there is any voltage dip at load side a ‘1’ is provided

on the other port pins. The micro controller just reads the two voltages and compares and

if any dip during positive half cycle a ‘1’ is provided on one of the port pins and similarly

during the negative half cycle also. The reading comparison continuous and the operator

is kept in a loop. Thus the micro controller provides a ‘1’ on one of the port pins during

positive half cycle and a ‘1’ on the other port pins during negative half cycle. Thus a ‘1’

indicates the error.

In case of error a ‘1’ is provided continuously for one complete half cycle, thus making

the cycle the 50Hz one. If the inverter elements are kept on for entire 10ms period if leads

to a short circuit, because the coupling transformer is designed to handle high frequency.

In order to suit this requirement, the micro controller output is ANDed with high

frequency clock generator by means of a 555 timer IC. The 555 timer IC is working in

astable mode and provides 10k HZ output. Thus the AND gates outputs are a high

frequency clock during the error during a positive are negative half cycle i.e. one gate

provides clock during the positive half cycle if error is there, and similarly the other gate

provides clock during the negative half cycle if error is there.

The AND gate outputs are provided to 2 NOT gates. The NOT gate itself may not be able

to drive the opto couplers. In order to increase the driving capability of the circuit the

output of the not gate is provided to a 555 IC. The 555 IC can provided a maximum of

300ma sinking and sourcing capability and can drive the opto couplers. The opto couplers

in turn drive the power MOSFETs.

The inverter MOSFET elements are connected in single phase bridge format. The single

phase bridge is power by under power supply again derived from the another transformer

this power supply is derived from a transformer with a secondary voltage of 30v. This

voltage is rectified and filtered and this voltage is fed to the bridge inverter as power

supply. The bridge inverter power MOSFET sources are not at the same potential so

these isolated power supplies need to be generated. This isolated power supplies are

generated using the an astable multi-vibrator built around BDBP transistors, driving a

ferrite cored transformer. The ferrite transformer is having 3 isolated secondary

windings, with center tap facility. By using these windings, the isolated voltage are

derived. This voltages are rectified and filtered and positive or negative voltages are

acquired. These voltages are used to drive the opto coupler photo transistor. So that when

the MOSFET need to be ON, at 12v is applied and when need to be OFF a -12v is applied

to the gate.

The output from the bridge inverter is applied to the ferrite cored coupling transformer.

The secondary of ferrite cored coupling transformer is connected to the power line to

mitigate the voltage values. The secondary voltage need to be filter and applied to the line

circuits. But the present case, filter is not used. If filter is used the voltage gets smoothed

and the smooth voltage is applied to mitigate the voltage sags.

Chapter 4

DVR CODE

/

***********************************************************************/

/* */

/* FILE :varpwm.c */

/* DATE :Wed, Jun 10, 2009 */

/* DESCRIPTION :Main Program */

/* CPU TYPE :Other */

/* */

/* This file is generated by Renesas Project Generator (Ver.4.0). */

/* */

/

***********************************************************************/

#include "sfr_r81B.h" //Definition of R8C/13 SFR

#include "config.h" //Declaration of interrupts and functions

#define enable1 p1_0

#define enable2 p1_1

unsigned char i=89,x=1,y=1;

unsigned char

a[]=0x0000,0x0001,0x0002,0x0002,0x0003,0x0004,0x0005,0x0006,0x0007,0x0009,0x

000a,0x000c,0x000d,0x000f,0x0010,0x0012,0x0013,0x0015,0x0016,0x0018,0x0019,0x0

01b,0x001c,0x001e,0x001f,0x0021,0x0022,0x0024,0x0025,0x0027,

0x0028,0x002a,0x002b,0x002d,0x002e,0x0030,0x0031,0x0033,0x0034,0x0036,0x0037,

0x0039,0x003a,0x003c,0x003d,0x003f,0x0040,0x0042,0x0043,0x0045,0x0046,0x0048,0

x0049,0x004b,0x004c,0x004e,0x004f,0x0051,0x0052,

0x0054,0x0055,0x0057,0x0058,0x005a,0x005b,0x005d,0x005e,0x0060,0x0061,0x0063,

0x0064,0x0066,0x0067,0x0069,0x006a,0x006c,0x006d,0x006f,0x0070,0x0072,0x0073,0

x0075,0x0076,0x0078,0x0079,0x007b,0x007b,0x007c,

0x007c,0x007d;

void compare0(void)

enable1=1;

ir_cmp0ic=0;

asm("REIT");

void compare1(void)

enable1=0;

ir_cmp1ic=0;

if(x==1)

i--; //i++;

tm0=a[i];//0x003d;

tm1=0x007d;//0x007c;

if((a[i]==0x0000)|(x==2))

tm0=a[i];//0x003d;

tm1=0x007d;//0x007c;

x=2;

if(i==89)

x=1;

if(y==1)

enable2=1;

else

enable2=0;

y=0;

y++;

i++;//i--;

asm("REIT");

void main()

asm("FCLR I"); //Interrupt disable

prc0=1; //Protect off

//**************************************

// CPU Clock Setting

//**************************************

//Note: Include asm("nop")for oscillator's stabilization period after clock setting is

done.

//User may set on-chip oscillator to off when Main Clock is selected.(cm14=1)

cm05=0;cm13=1;cm14=0; //Main Clock selected(cm0 bit 5, cm1 bit 3

and 4, ocd bit 2)

cm15=1; //High Drive Capacity selected(CM1 bit 5)

ocd2=0; //Main Clock selected(ocd bit 2)

cm16=0;cm17=0;cm06=0; //Divide by 8 selected(cm0 bit 5)

prc0=0; //Protect on

init(); //Inital setting

asm("FSET I"); //Interrupt enabled

asm("NOP");

cmp0ic=1;

cmp1ic=1;

tcc00=1;

enable2=0;

while(1);

void init(void)

//**************************************

// Port1 Setting

//**************************************

pd1=0x03; // Port P1 direction register

drr=0x00; // Port P1 drive capacity control register

pd1_0=1;

pd1_1=1;

//**************************************

// Timer C Setting

//**************************************

//Note:At the end of Timer C Setting, set tcc00=1 to start timer C counting.

//To use high-speed on-chip oscillator as timer c count source, make sure

HR00=1(high-speed on-chip oscillator on).

//Set CMP output pins(P10-P12,P30-P32) to output(under output compare mode).

//Set P33/INT3/TCIN pin to input(under input capture mode).

//Set INT3 to input when selecting INT3 as measurement pulse.

tm0=a[89];

tm1=0x007d;

tcc0=0x9a;

tcc1=0xbc;

tcout=0x01;

ir_cmp0ic=0;

ir_cmp1ic=0;

//**************************************

// ADC Setting

//**************************************

//Note:For 8-bit resolution, when conversion finished, read AD result at AD

register(00C0H).

//Note:For 10-bit resolution, when conversion finished, read AD result at AD

register(00C0H,00C1H).

//Set AN8 pin to input port direction

vcut=1;adgsel0=1;ch0=0;ch1=0;ch2=1; //Port P1 group: AN8 is

selected(adcon0 bit 0-3)

md=0; //One-shot mode selected(adcon0 bit 3)

cks1=1; cks0=0; //fad selected(adcon1 bit 2)

bits=1; //10-bit mode selected(adcon1 bit 1)

smp=0; //Without sample and hold selected(adcon2 bit 0)

adst=1; //A/D conversion starts(adcon0 bit 6)

ir_adic=0;

Chapter 5

Summary and Conclusion

In the Present Project Dynamic Voltage Restorer has been Designed and Developed. The

Developed Dynamic Voltage Restorer is evaluated using small loads. In order to Reduce

the Voltage across the Load, and Simulated line Impedance is used. As the load Current

Passes through the line Impedance, Results in a Voltage Drop across it, Thus Reducing

the Voltage across the load. This reduction in voltage is restored back by using the DVR

Circuit that is developed. The wave form which is seen on a CRO Include, The Normal

Voltage wave form without any Deduction in Voltage that is Possible when load is not

connected. The second wave form is the line voltage across the load; When DVR is kept

in OFF mode. This clearly indicates the reduction in Voltage across the load, Due to the

load current flow to the Simulated line Impedance. The hide wave form is the load

voltage, when the load is connected and DVR is made on. This wave form clearly

indicates that the DVR is injecting a Voltage Into the line in a manner so as to mitigate

the reduction voltage i.e voltage sag caused by simulated line impedance. This waveform

clearly indicates that the developed system is working satisfactorily for the specification

it has been designed for.

Though the subject is satisfactorily working, the system is only a

primitive one, which demonstrated the functionality and working of a DVR. The system

can be further improved by implementing adding advanced control and sensing

techniques and methods.

In the present circuit the reference voltage wave form is the transformer

secondary voltage before it is passed through the simulated line impedance. This is not

the practical simulation, as the line length is usually very large, and it is highly

impossible to sense the voltage at the starting point of a transmission line. Instead, the

voltage can be sensed at the load point itself and from that the reference voltage can be

generated. This requires special Algorithms using DSP Techniques or dedicated ASIC

devices, which are meant for generating the reference wave forms, from the load voltage.

In our model the micro controller simply acquires the reference and actual voltages

and are compare to establish the error and the output is used to control the inverter in

such a manner to increase the output voltage to the required value. There are different

algorithms available to implement the control. Better control techniques can be

implemented.

The total system has to be protected from faults such as over currents, over

voltages and temperatures. The micro controller can be programmed to detect these faults

and safely turn off the system in case of faults.

Bibliography

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Supply voltage Vref Vcontrol Load voltage

Supply voltage Vcontrol Vinjected Load voltage Load current

[7] N.H.Woodley, “Field experience with Dynamic Voltage Restorer

(DVR MV) Systems”, Power Engineering Society Winter Meeting

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