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REALIZATION OF CASCADED H-BRIDGE 5-LEVEL MULTILEVE L
INVERTER AS DYNAMIC VOLTAGE RESTORER
1P.SURENDRA BABU &2 BV. SANKER RAM 1Department of Electrical and Electronics Engineering ,VRS &YRN College of Engineering and
Technology, Chirala, A.P,India 2Department of Electrical and Electronics Engineering ,JNTU College of Engineering,Hyderabad,
A.P,India
ABSTRACT
Modern industrial devices are mostly based on electronic devices such as programmable logic
controllers and electronic drives. The electronic devices are very sensitive to disturbances and become
less tolerant to power quality problems such as voltage sags, swells and harmonics. Due to the power
quality issues like voltage sag, voltage swell, unbalanced voltage, voltage flickering, Interruptions etc.
load side voltage is not constant. The main requirement of any system is to maintain load side voltage
constant. Among the entire power quality issues, voltage sag and voltage swell occupy a major role. So
my project deals with compensating voltage sag, voltage swell and Interruption at load side using 5-level
multi level inverter as a Dynamic Voltage Restorer.
KEYWORDS : Controller Design using p-q theory, Multi-level inverter, Dynamic Voltage Restorer (DVR),
Three-phase cascaded H bridge inverter.
INTRODUCTION
Modern power electronics have contributed a great deal to the development of new powerful
applications and industrial solutions. But at the same time, these advances have increased the harmonic
contamination present in line currents, which ends up distorting the voltage waveforms. Some power
electronics applications, such as diode power rectifiers, thyristor converters and static VAR
compensators (SVCs) are clear examples. This has encouraged the development of passive and active
filters, which are intended to block all non-fundamental current components. Passive filters have many
disadvantages, such as weight, volume, frequency tuning, and cost making their implementation
sometimes unpractical. On the other hand, different configurations of pulse width-modulated (PWM)
inverters have been implemented as active power filters (APF) to compensate harmonic currents.
Nevertheless, these devices have shown to produce a series of problems in related equipment when
operated at high frequencies, such as circulating currents, dielectric stress, overvoltage and corona
discharge. Multilevel inverters can work as amplitude modulation and PWM and this fact makes the
outputs of the converter very much cleaner [1], [3]. This way of operation allows having almost perfect
currents and good voltage waveforms, eliminating most of the undesirable harmonics. The series
connection of several bridges allows working with much higher voltages and the stepped voltage
Bipolar Transistors (IGBT), and Integrated Gate Commutated Thyristors (IGCT). Each type has its own
benefits and drawbacks. The IGCT is a recent compact device with enhanced performance and reliability
that allows building VSC with very large power ratings. Because of the highly sophisticated converter
design with IGCTs, the DVR can compensate dips which are beyond the capability of the past DVRs
using conventional devices. The purpose of storage devices is to supply the necessary energy to the VSC
via a dc link for the generation of injected voltages. The different kinds of energy storage devices are
Superconductive magnetic energy storage (SMES), batteries and capacitance.
P.Surendra Babu & BV. Sanker Ram 18
DC CHARGING CIRCUIT
The DC Charging Circuit has two main tasks.
1. The first task is to charge the energy source after a sag compensation event.
2. The second task is to maintain dc link voltage at the nominal dc link voltage
3.2.5 Control and Protection:
The control mechanism of the general configuration typically consists of hardware with
programmable logic. All protective functions of the DVR should be implemented in the software.
Differential current protection of the transformer, or short circuit current on the customer load side are
only two examples of many protection functions possibility.
EQUATIONS RELATED TO DVR
Fig. 4 Equivalent circuit diagram of DVR
The system impedance ZTH depends on the fault level of the load bus. When the system voltage
(VTH) drops, the DVR injects a series voltage VDVR through the injection transformer so that the desired
load voltage magnitude VL can be maintained. The series injected voltage of the DVR can be written as
Where
VL : The desired load voltage magnitude
ZTH : The load impedance
IL : The load current
VTH : The system voltage during fault condition
CARRIER PHASE SHIFTING PULSE WIDTH MODULATION
A so-called phase-shift sinusoidal pulse width modulation (PS-SPWM)switching scheme is proposed
to operate the switches in the system.Optimum harmonic cancellation is achieved by phase shifting each
carrier by
(k-1) π/n,
19 Realization of Cascaded H-Bridge 5-Level Multilevel Inverter as Dynamic Voltage Restorer
Where k is the kth inverter,n is the number of series-connected single phase inverters
n= (L-1)/2 where L is the number of switched DC levels that can be achieved in each phase leg. In this paper to
obtain a five level multilevel inverter four carriers of triangular in nature are used and eachcarrier is phase shifted by 90º [19]. These carriers are compared with the reference sinusoidal waveform as shown in Fig.
MAT LAB/SIMULINK MODEL
Voltage Sag
Fig. 5.1 Simulink diagram of open loop system for voltage sag
Fig. 5.2 Load Voltage Waveform
P.Surendra Babu & BV. Sanker Ram 20
Fig. 5.3 Simulink diagram of closed loop system for voltage sag
Fig. 5.4 Load Voltage waveform
Fig. 5.5 Compensator Voltage Waveform
Fig 5.1 shows the simulink diagram of open loop system for voltage sag. Fig 5.2 shows the load
voltage waveform in which voltage sag is created from 0.1 to 0.3 seconds by adding an extra RL Load i,e
voltage level is below 90% of the rated voltage and above 10% of the rated voltage according to IEEE
std l159-1995. Fig 5.3 shows the simulink diagram of closed loop system using Dynamic Voltage
Restorer where the reference voltages are generated by using PQ theory. By observing Fig 5.4 we can
say that voltage sag is eliminated by using Dynamic Voltage Restorer so as to maintain load voltage
constant. Fig 5.5 shows the voltage waveforms generated by the compensator during voltage sag so as to
maintain load voltage constant.
21 Realization of Cascaded H-Bridge 5-Level Multilevel Inverter as Dynamic Voltage Restorer
VOLTAGE SWELL
Fig. 5.6 Simulink Diagram of Open Loop System for voltage swell
Fig. 5.7 Load Voltage Waveform
Fig. 5.8 Simulink diagram of closed loop control system for voltage swell
P.Surendra Babu & BV. Sanker Ram 22
Fig. 5.9 Load Voltage waveform
Fig 5.6 shows open loop simulink diagram for voltage swell. Fig 5.7 shows the load voltage
wave form for voltage swell which is created by adding an extra capacitor bank from 0.1 sec to 0.4
seconds i,e voltage level is above 110% of the rated voltage according to IEEE std l159-1995. Fig 5.8
shows the simulink diagram of closed loop system using dynamic voltage Restorer for elimination of
voltage swell where the reference voltages are generated using PQ theory. Fig 5.9 shows the load voltage
wave form where voltage swell is mitigated to maintain constant voltage at load side.
INTERRUPTION
Fig. 5.10 Simulink Diagram of Open Loop System for Voltage Interruption
23 Realization of Cascaded H-Bridge 5-Level Multilevel Inverter as Dynamic Voltage Restorer
Fig. 5.11 Load Voltage Due to Occurrence of LG Fault
Fig. 5.12 Load Voltage Due to Occurrence of LLG Fault
Fig. 5.13 Load Voltage Due to Occurrence of LLL Fault
P.Surendra Babu & BV. Sanker Ram 24
Fig 6.14 Simulink Diagram of Closed Loop System for Voltage Interruption
Fig 5.15 Load Voltage for LG Fault
Fig 5.16 Load Voltage for LLG Fault
25 Realization of Cascaded H-Bridge 5-Level Multilevel Inverter as Dynamic Voltage Restorer
Fig 5.17 Load Voltage for LLL Fault
Fig 5.18 Compensator Voltage of DVR during LLL fault
Fig 5.10 shows the simulink diagram of open loop system for interruption. One method of
getting interruption in the system is by creating faults and faults were created in the system by using
three phase fault block present in simulink library. Fig 5.11 to Fig 5.13 shows the load voltage wave
forms for LG, LLG, LLL faults where voltage magnitude is below 10% of the rated voltage during
faulted condition i,e from 0.1 sec to 0.3 sec according to IEEE std l159-1995. Fig 5.14 shows the
simulink diagram of closed loop system using Dynamic voltage Restorer for elimination of Interruption
present in the system. By observing Fig 5.15 to Fig 5.17 load voltage is maintained constant by
elimination of LG, LLG, LLL faults taken place in the system using Dynamic voltage Restorer and Fig
5.18 shows the compensator voltage generated by DVR during LLL fault duration.
P.Surendra Babu & BV. Sanker Ram 26
CONCLUSIONS
In this paper cascade H-Bridge five level multilevel inverter is implemented as Dynamic
Voltage Restorer to compensate voltage sag, voltage swell, interruption. Closed loop control of Dynamic
Voltage Restorer is designed for better regulation of the load voltage. Reference signal is generated using
PQ theory for closed loop control. Sag, Swell and interruption are compensated using Dynamic Voltage
Restorer and MATLAB simulations are carried for the above to maintain load voltage constant.
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27 Realization of Cascaded H-Bridge 5-Level Multilevel Inverter as Dynamic Voltage Restorer
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Mr.P.SURENDRA BABU is currently working as Associate Professor & HOD, EEE in VRS &
YRN College of Engineering & Technology, Chirala. He completed his B.Tech in the year 2002 at JNTU
Anantapur. He completed his M.Tech in the year 2007 at JNTU Hyderabad. He has over 10 years of
teaching experience in various positions. His research areas include Facts Devices ,Power Systems.