CHAPTER 4 POWER QUALITY ANALYSIS USING …shodhganga.inflibnet.ac.in/bitstream/10603/9783/8/08_chapter 3.pdfCLOSED LOOP REFERENCE CURRENT ESTIMATION TECHNIQUES ... (SDM) The Synchronous

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CHAPTER 4

POWER QUALITY ANALYSIS USING VARIOUS

CLOSED LOOP REFERENCE CURRENT

ESTIMATION TECHNIQUES

4.1 INTRODUCTION

Previous chapter analysed the SHAF based VSI for various PWM

techniques to reduce the %THD which didn’t consider the variation in load

current. Hence this chapter deals with the performance of closed loop control

which takes into account load current variation by various current estimation

techniques.

As shown in Figure 4.1, the reference signal to be processed by the

controller is the key component that ensures correct operation of AF. The

reference signal estimation is initiated through the detection of essential

voltage / current signals to gather accurate system variables information given

by Peng et al (1998). The voltage variables to be sensed are AC source

voltage, DC-bus voltage of the AF and voltage across the interfacing

transformer. Typical current variables are load current, AC source current,

compensation current and DC-link current of the AF proposed by Soares et al

(1997), (2000). Based on these system variable feedbacks, estimation of

reference signals in terms of voltage / current levels are carried out in

frequency-domain or time-domain.

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Numerous publications on the theories related to detection and

measurement of the various system variables for reference signals estimation

are reported. Figure 4.1 illustrates the considered reference signal estimation

techniques proposed by Motano et al (2002) and Gobrio et al (2008). This

section presents the considered reference signal estimation techniques,

providing for each of them a short description of their basic features.

Figure 4.1 Topology of reference signal estimation techniques

4.2 FREQUENCY DOMAIN APPROACHES

Reference signal estimation in frequency-domain is suitable for

both single and three phase systems. It is mainly derived from the principle of

Fourier analysis as follows:

Fourier Transform Techniques

In principle, either conventional Fourier Transform (FT) or Fast

Fourier Transform (FFT) is applied to the captured voltage / current signal.

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The harmonic components of the captured voltage / current signal are first

separated by eliminating the fundamental component. Inverse Fourier

Transform is then applied to estimate the compensation reference signal in the

time domain. The main drawback of this technique is the accompanying time

delay in the sampling of system variables and computation of Fourier

coefficients. This makes it impractical for real-time applications with

dynamically varying loads. Therefore, this technique is only suitable for

slowly varying load conditions. In order to make computation much faster,

some modifications were proposed and implemented. In this modified

Fourier-series scheme, only the fundamental component of current is

calculated and this is used to separate the total harmonic signal from the

sampled load current waveform.

4.3 TIME DOMAIN APPROACHES

Time-domain approaches are based on instantaneous estimation of

reference signal in the form of either voltage or current signal from distorted

and harmonic polluted voltage and current signals. These approaches are

applicable to both single-phase and three-phase systems except for the

Synchronous Detection Method and Synchronous Reference Frame theorem

which can only be adopted for three-phase systems.

4.3.1 Instantaneous Reactive Power Theory (p-q theory)

The instantaneous reactive power theory otherwise known as p-q

theory is proposed by Akagi et al (2007). This theorem is based on -0

transformation which transforms three-phase voltages and currents into the

-0 stationary reference frame. From these transformed quantities, the

instantaneous active and reactive power of the nonlinear load is calculated,

which consists of a DC component and an AC component. The AC

119

component is extracted using HPF and taking inverse transformation to obtain

the compensation reference signal in terms of either current or voltage. This

theorem is suitable only for a three-phase system and its operation takes place

under the assumption that the three-phase system voltage waveforms are

symmetrical and purely sinusoidal. If this technique is applied to

contaminated supplies, the resulting performance is proven to be poor. In

order to make the p-q theory applicable for a single-phase system, some

modifications in the original p-q theory was proposed and implemented by

Czarnecki (2004), (2006).

4.3.2 Synchronous Detection Method (SDM)

The Synchronous Detection Method is very similar to the p-q

theory. This technique is suitable only for a three-phase system and its

operation relies on the fact that three-phase currents are balanced. It is based

on the idea that the AF forces the source current to be sinusoidal and in phase

with the source voltage despite load variations. The average power is

calculated and divided equally between the three phases. The reference signal

is then synchronized relative to the source voltage for each phase as discussed

by Chen et al (1993). Although this technique is easy to implement, it suffers

from the fact that it depends to a great extent on the harmonics in the source

voltage.

4.3.3 Synchronous Reference Frame Theory (d-q theory)

This theorem relies on the Park’s Transformations to transform the

three phase system voltage and current variables into a synchronous rotating

frame. Active and reactive components of the three-phase system are

represented by direct and quadrature components respectively as given by

Bhattacharya et al (1995). In this theorem, the fundamental components are

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transformed into DC quantities which can be separated easily through

filtering. This theorem is applicable only to a three-phase system. The system

is very stable since the controller deals mainly with DC quantities. The

computation is instantaneous but incurs time delays in filtering the DC

quantities.

4.4 REFERENCE CURRENT ESTIMATION

The control scheme of a SHAF must calculate the current reference

waveform for each phase of the inverter, maintain the dc voltage constant, and

generate the inverter gating signals. The block diagram of the control scheme

of a SHAF is shown in Figure 4.2. The current reference circuit generates the

reference current required to compensate the load current harmonics and

reactive power, and also try to maintain constant the dc voltage across the

electrolytic capacitors.

There are many possibilities to implement this type of control and

the most popular of them will be explained in this section. Also, the

compensation effectiveness of an active power lter depends on its ability to

follow with a minimum error, time delay and the reference signal calculated

to compensate the distorted load current. Finally, the dc voltage control unit

must keep the total dc bus voltage constant and equal to a given reference

value. The dc voltage control is achieved by adjusting the small amount of

real power absorbed by the inverter. This small amount of real power is

adjusted by changing the amplitude of the fundamental component of the

reference current.

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Figure 4.2 Overall control system of the proposed SHAF

4.4.1 p-q CONTROL TECHNIQUE

The p-q theory formally known as “The Generalized Theory of the

Instantaneous Reactive Power in a Three-Phase Circuit” was first developed

by Akagi (1984). It is based on instantaneous values in three phase power

systems with or without a neutral wire, and is valid for steady state or

transitory operations, as well as for generic voltage and current waveforms.

The p-q theory consists of an algebraic transformation known as a Clarke

transformation of the three phase input voltages and the load harmonic

currents in the a-b-c coordinates to the – – 0 reference frame followed

by calculation of real and reactive instantaneous power components.

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0

1 1 1

2 2 2

2 1 11

3 2 2

3 30

2 2

a

b

c

v v

v v

v v

(4.1)

0

1 1 1

2 2 2

2 1 11

3 2 2

3 30

2 2

a

b

c

i i

i i

i i

(4.2)

0 0 00 0

0

0

p v i

p v v i

q v v i

(4.3)

' ' '

' ' '' 2 '2

'1

'

v i i p

v i i qi i (4.4)

'

'

'

'

'

1 0

2 1 3

3 2 2

1 3

a

b

c

vv

vv

v

(4.5)

Based on equations (4.1) to (4.5), the algebraic formula for

determining the instantaneous zero sequence power, instantaneous real power

and instantaneous imaginary power is shown in equation (4.6).

0 0 0p v i

123

p v i v i (4.6)

q v i v i

Figure 4.3 shows the interactions of each of the power components

within the power system and how each relates to one another.

‘ ’ is the average value of the instantaneous zero sequence power.

This corresponds to the power which is transferred from the power supply to

the load through the zero sequence components of voltage and current.

‘ ’ corresponds to the alternating power of the instantaneous zero

sequence power. This relates to the exchanged power between the power

supply and the load through the zero sequence components of voltage and

current. The zero sequence power only exists in three phase systems with a

neutral wire.

‘p’ is the mean value of the instantaneous real power. This

corresponds to the energy per unit time unity which is transferred from the

power supply to the load.

‘ ’ is an alternating value of the instantaneous real power. This

corresponds to the power which is exchanged between the power supply and

the load.

‘q’ is the instantaneous imaginary power. This corresponds to the

power that is exchanged between phases of the load. This component is not

constructive to the system and is accountable for undesirable current which

circulates between the system phases. The reactive power does not transfer

power from the supply to the load nor does it exchange power.

124

Figure 4.3 Power components of the p-q theory in – – 0 coordinate

From Figure 4.3, the only component of the power obtained

through the p-q theory that is desirable and constructive is the average real

power and the average zero sequence power. This is because power is

transferred from the supply to the load. The other components of the power

are less desirable and this can be compensated by the SHAF.

The control diagram for the SHAF controller is shown in Figure 4.4. An

important component to note is that the high- pass filter with a cut off

frequency of 50Hz. This filter receives the instantaneous real power from

equation (4.6) and filters all frequencies of power greater than the

fundamental. The output waveform is thus the harmonic power which is

recognized as containing only current harmonics.

2 2

1c

c

i v v p p

v v qv vi (4.7)

0

0

0

11 0

2

2 1 1 3

3 2 22

1 1 3

2 22

ca

cb

cc

i i

i i

i i

(4.8)

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The harmonic power output from the high pass filter together with

the reactive power is used in equation (4.7) to determine the alpha reference

and beta reference of the currents. These currents are then input to equation

(4.8) where the instantaneous current references to the PWM current control

are determined.

Figure 4.4 Control diagram for SHAF using p-q control theory

Since the SHAF is designed predominantly for current harmonic

mitigation, the harmonics present in the power waveform can be assumed to

be attributed solely by the current harmonics demanded by the non-linear

load. If one assumes that the voltage waveform is perfectly sinusoidal and

free from all harmonics, then this condition becomes true. If the three phase

voltage input to the controller is unbalanced or highly distorted, the reference

currents calculated would not completely filter the current harmonics

demanded by the non-linear load. This situation gives rise to the need of a

positive sequence voltage detector.

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4.4.2 Positive Sequence Voltage Detector

The positive sequence voltage detector shown in Figure 4.5 derives

the positive sequence fundamental signal from a three phase voltage signal

carried by the power line. The PLL control circuit tracks the positive

sequence voltage at the fundamental frequency of highly distorted and

unbalanced three phase signals. The synchronizing circuit determines

accurately the fundamental frequency of the system voltage and phase angle

of the measured signals which may be unbalanced and contain harmonics.

The fundamental frequency is used as an input to a sine wave generator that

produces three auxiliary signals, namely (ia', ib', ic') to be used as ‘fundamental

positive sequence currents’ along the detector. These currents together with

the line voltages are then input to a Clarke -0 transformation algorithm and

power calculation. Equation (4.1) shows the transformation matrix which

converts the phase voltages and phase currents into an appropriate reference

frame. Equation (4.3) determines the power values composed from the

fundamental positive sequence voltage and auxiliary currents.

The – - 0 voltage reference box of Figure 4.5 calculates the

alpha and beta reference voltages given by equation (4.4). Finally, the a-b-c

instantaneous values of the fundamental positive sequence voltage are

determined by the –0 inverse transformation box, without errors in the

amplitude or phase angle as shown in equation (4.5). The voltages calculated

from equation (4.5) are now considered as inputs to the main control circuit.

127

Figure 4.5 Block diagram of the fundamental positive sequence voltage

detector

Thus, the purpose of the positive sequence voltage detector is

justified as the active filter controller compensates the load current as if it

were connected directly to a perfectly balanced sinusoidal voltage source,

irrespective of whether the source is in fact unbalanced or highly distorted.

4.4.3 Synchronous Reference Frame Theory (d-q theory)

The d-q theory is based on a synchronous rotating frame derived

from the mains voltages with the use of a Phase Locked Loop (PLL). In this

theory, active filter currents are obtained from the instantaneous active and

reactive current components (iLd and iLq) of the nonlinear load in a two-step

procedure. In the first step, the load current in the a-b-c reference frame is

transformed to the reference frame. In the second step, these stationary

reference frame quantities are then transformed into synchronous reference

frame quantities based on the Park’s Transformation.

128

The relationship of the real and imaginary components of the

current space vector in the original stationary two-axis reference frame and

the new rotating reference frame is shown in Figure 4.6. In fact, the

transformation is the subset of d-q transformation.

A rotating coordinate system can be defined to enable the vector

representation to become a constant without any time variations. Thus, a d-q

coordinate system has been defined such that the‘d’ and ‘q’ axes rotate at an

angular frequency ‘ ’ in the plane. A balanced three-phase vector

representation in this rotating d-q coordinate system will now be constant

over all times and the angle ‘ ’ is a uniformly increasing function of time.

This transformation angle is sensitive to unbalanced and distorted main

voltage conditions so its change with respect to time may not be constant over

the main period.

Figure 4.6 Space vectors representation in the stationary and

synchronous frames

From Figure 4.6, the direct and quadrature current components can

be written as in equation (4.9):

129

Ldq Ld Lqi i ji . (4.9)

which can also be written in matrix form given by equation (4.10),

cos sin

sin cos

Ld L

Lq L

i i

i i (4.10)

where,

1tanv

v

The real component of the current space vector in this new

reference frame is the direct axis component (id) while the imaginary

component is called the quadrature axis component (iq). With vector rotation,

the direct voltage component and the quadrature voltage component are given

by equation (4.11):

2 2 , 0dq q

v v v v (4.11)

By using simple geometry, equation (4.11) is written in terms of the

stationary reference frame load voltage vectors given by equation (4.12):

2 2

1Ld L

Lq L

i v v i

i v v iv v (4.12)

The block diagram of this theory is given in Figure 4.7. In the

nonlinear load case, the instantaneous active and reactive load currents can

also be decomposed into oscillatory and average terms. Since the d and q axes

rotate at an angular frequency ‘ ’ (=2* *ffundamental) in the plane; the first

harmonic positive sequence current is transformed to a dc quantity and other

130

current components constitute the oscillatory parts. After removing the DC-

component of iLdq by using low pass filters, the compensation current is

obtained given by equation (4.13),

2 2

1c Ld

c Lq

I v v i

I v v iv v (4.13)

Figure 4.7 Block diagram of the instantaneous active and reactive

current method

4.4.3.1 Phase Locked Loop (PLL) Circuit

The PLL circuit tracks continuously the fundamental frequency of

the measured system voltages. The appropriate design of the PLL should

allow proper operation under distorted and unbalanced voltage waveforms

given by Arruda et al (2001). The PLL synchronizing circuit is shown in

Figure 4.8, which determines automatically the system frequency and the

phase angle of the fundamental positive sequence component of a three phase

input signal.

131

Figure 4.8 Block diagram of PLL circuit

4.4.4 Synchronous Detection Method (SDM)

Figure 4.9 shows the control circuit of an AF system using SDM.

The control circuit consists of an outer voltage control loop and two inner

current control loops. The outer control loop is used to maintain the capacitor

voltage constant and to determine the amplitude of the mains currents

required in an AF system. The SDM method is basically used for the

determination of amplitude of the source currents. In this algorithm, the

three-phase mains currents are assumed to be balanced after

compensation. The real power p(t) consumed by the load could be

calculated from the instantaneous voltages and load currents as given by

equation (4.14).

( )

( ) [ ( ) ( ) ( )] ( )

( )

la

sa sb sc lb

lc

i t

p t v t v t v t i t

i t

(4.14)

where, vsa(t), vsb(t), vsc(t) are the instantaneous values of supply voltages and

ila(t), ilb(t), ilc(t) are the instantaneous values of load currents.

132

Figure 4.9 represents the block diagram of the system. The real

power p(t) is sent to a low-pass filter to obtain its average dc value Pdc. The

required expressions are explained in the following section:

Figure 4.9 Block diagram of Synchronous Detection Method

The average value Pdc is determined by applying p (t) to a low pass

filter. The real power is then split into the three phases as given by the

equation (4.15),

dc sma

a

sma smb smc

P VP

V V V

dc smb

b

sma smb smc

P VP

V V V (4.15)

dc smc

c

sma smb smc

P VP

V V V

Thus for purely sinusoidal balanced supply voltages, Pa=Pb=Pc

given by equation (4.16),

3

dca b c

PP P P (4.16)

133

where,

22 2

sma sma sma smaa sa sa

V I V IP V I

2 a

sma

sma

PI

V

Thus the reference source currents for all the phase are given by

equation (4.17),

2

2 ( )( ) sa a

sa

sma

v t Pi t

V

2

2 ( )( ) sb b

sb

smb

v t Pi t

V (4.17)

2

2 ( )( ) sc c

sc

smc

v t Pi t

V

where, Vsma , Vsmb and Vsmc are the amplitudes of the supply voltages. The

compensation currents are then calculated using equation (4.18),

( ) ( ) ( )ca sa lai t i t i t

( ) ( ) ( )cb sb lbi t i t i t (4.18)

( ) ( ) ( )cc sc lc

i t i t i t

This method can be extensively used for compensation of reactive

power, current imbalance and mitigation of current harmonics. It can be

134

inferred as the simplest method as it requires minimum calculations.

However, this method suffers a drawback from individual harmonic detection

and its mitigation.

4.4.5 Perfect Harmonic Cancellation (PHC) Technique

The Perfect Harmonic Cancellation (PHC) technique can be

regarded as a modi cation of the three previous theories. Its objective is to

compensate all the harmonic currents and the fundamental reactive power

demanded by the load in addition to eliminating the imbalance. The source

current will therefore be in phase with the fundamental positive-sequence

component of the voltage at the Point of Common Coupling (PCC).

The reference source current will be given by as in equation (4.19),

1refi K v (4.19)

where, v1+ is the PCC voltage space vector with a single fundamental

positive- sequence component given by equation (4.20),

1 1 1( )s

P v Kv K v v v v (4.20)

The constant ‘K’ will be determined with the condition that the

above source power equals the dc component of the instantaneous active

power demanded by the load given by equation (4.21),

0

2 2

1 1

La Lp pK

v v (4.21)

Finally, the reference source current will be given by

equation (4.22),

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0

0

12 2

1 1

1

0ref

La L

ref

ref

ip p

i vv v

i v

(4.22)

where, and are the fundamental components of the load voltages and

can be obtained from the original voltages by means of two simple Band Pass

Filters (BPF). Also, Pdc is filtered from p(t) using a simple Low Pass Filter

(LPF). The block diagram of Perfect Harmonic Cancellation strategy (PHC) is

shown in Figure 4.10. Rational term in equation (4.22) is a constant and it can

be seen that after compensation, the currents will have the same shape as the

fundamental components of voltages in and axes. The desired currents

calculated using this method is symmetrical and sinusoidal.

Figure 4.10 Block diagram of Perfect Harmonic Cancellation Method

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4.5 SIMULATION RESULTS FOR VARIOUS CLOSE LOOP

REFERENCE CURRENT ESTIMATION TECHNIQUES

Simulation results for various close loop reference current

estimation techniques are given below in Tables 4.1 and 4.2 for two loads

namely Resistive load (R) and DC Motor load:

Table 4.1Simulation parameters for R-load

System Source voltage 230V

System frequency 50Hz

Source resistance(Rs) and Inductance(Ls) 0.1 , 0.03mH

Impedance upstream of the rectifier Rc and Lc 0.3 0.07mH

Load(three phase diode bridge rectifier) Rdc, Ldc

and Cdc

0.5 ,

0.3mH,470µF

DC link capacitor Cdc(ref) 1000µF

Reference voltage Vdc(ref) 500V

Active filter output inductance , Lf 4.5mH

Table 4.2 Simulation parameters for DC Motor Load

Power 5HP

Supply voltage 240V

Speed 1750rpm

Field excitation 300V

Torque 10 m

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4.5.1 Simulation results of p-q technique for R-load and DC motor

load

The simulation model for p-q algorithm for R load is shown in

Figure 4.11. Figures 4.12 to 4.14 show subsystem model for pulse generation,

reference current generation and active filter. Figure 4.15 shows the

simulation waveforms of source voltage, source current and load current

variations. Figure 4.16 shows the phase displacement between source voltage

and source current. Figures 4.17 and 4.18 give the DC link capacitor voltage

and %THD of VSI-SHAF based p-q technique for R-load.

Figure 4.11 Simulation Model for VSI-SHAF using p-q technique for

R-Load

138

Figure 4.12 Subsystem for pulse generation of p-q technique

Figure 4.13 Reference current generation circuit for p-q technique

139

Figure 4.14 Active Filter circuit for p-q technique

Figure 4.15 Simulation waveforms for source voltage, source current

and load current using p-q technique for R-load

140

Figure 4.16 Simulation waveform showing Phase displacement between

source voltage and source current for R-load

Figure 4.17 DC link capacitor voltage using p-q technique for R-load

141

Figure 4.18 %THD for VSI-SHAF using p-q technique for R-load

Figure 4.19 shows the simulation diagram of VSI-SHAF based p-q

technique for DC motor load. Figure 4.20 shows the waveforms of source

voltage, source current and load current and Figure 4.21gives the phase

displacement between source voltage and source current. Figures 4.22 and

4.23 show the DC link capacitor voltage and % THD.

Figure 4.19 Simulation Model for VSI-SHAF based p-q technique for

DC Motor Load

142

Figure 4.20 Simulation waveforms for source voltage, source current

and load current using p-q technique for DC Motor load

Figure 4.21 Simulation waveform showing Phase displacement between

source voltage and source current using pq technique for

DC motor load

143

Figure 4.22 DC link capacitor voltage using p-q technique for DC Motor

load

Figure 4.23 %THD for VSI-SHAF using p-q technique for DC Motor

Load

4.5.2 Simulation results of d-q technique for R-load and DC motor

load

The simulation model for d-q algorithm for R-load is shown in

Figure 4.24. Figure 4.25 shows pulse generation circuit and Figures 4.26 and

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4.27 show subsystems for d-q and inverse d-q transformations. Figures 4.28 to

4.30 show source voltage, source current and load current waveforms, DC

link capacitor voltage waveform and %THD.

Figure 4.24 Simulation Model for VSI-SHAF using d-q technique for R-

Load

Figure 4.25 Subsystem for pulse generation

145

Figure 4.26 Simulation diagram for d-q transformation (subsystem1)

Figure 4.27 Simulation diagram for inverse d-q transformation

(subsystem2)

146

Figure 4.28 Source voltage, source current and load current waveforms

for VSI-SHAF using d-q technique for R-Load

Figure 4.29 DC link Capacitor voltage for VSI-SHAF using d-q

technique for R-Load

147

Figure 4.30 %THD for VSI-SHAF using d-q technique for R-Load

Figure 4.31 shows the simulation diagram of VSI-SHAF based d-q


voltage, source current and load current, Figures 4.33 and 4.34 show the DC

link capacitor voltage and % THD.

Figure 4.31 Simulation Model for VSI-SHAF using d-q technique for

DC Motor Load

148


for VSI-SHAF using d-q technique for DC Motor Load

Figure 4.33 DC link Capacitor voltage for VSI-SHAF using d-q

technique for DC Motor Load

149

Figure 4.34 %THD for VSI-SHAF using d-q technique for DC motor

load

4.5.3 Simulation results of SDM technique for R-load and DC motor

load

The simulation model for SDM algorithm for R-load is shown in

Figure 4.35. Figures 4.36 and 4.37 show subsystem for pulse generation and

subsystem model. Figures 4.38 to 4.40 show source voltage, source current

and load current waveforms, dc link capacitor voltage and %THD.

150

Figure 4.35 Simulation Model for VSI-SHAF based SDM technique for

R-load

Figure 4.36 Simulation diagram for Pulse generation of SDM

151

Figure 4.37 Simulation diagram of Subsystem block in the pulse

generation for VSI-SHAF based SDM technique


for VSI-SHAF based SDM technique for R-load

152

Figure 4.39 DC link capacitor voltage for VSI-SHAF based SDM

technique for R-load

Figure 4.40 %THD for VSI-SHAF based SDM technique for R-load

Figure 4.41 shows the simulation diagram of VSI-SHAF based SDM


voltage, source current and load current, Figures 5.43 and 5.44 show the DC

link capacitor voltage and % THD.

153

Figure 4.41 Simulation Model for VSI-SHAF based SDM technique for

DC motor Load


for VSI-SHAF based SDM technique for DC motor Load

154

Figure 4.43 DC link capacitor voltage for VSI-SHAF based SDM

technique for DC Motor load

Figure 4.44 %THD for VSI-SHAF based SDM technique for DC motor

Load

4.5.4 Simulation results of PHC technique for R-load and DC motor

load

The simulation model for PHC algorithm for R-load is shown in

Figure 4.45. Figures 4.46 and 4.47 show pulse generation circuit of PHC

155

technique and simulation diagram for subsystem1 in the pulse generation

circuit. Figures 4.48 to 4.50 show source voltage, source current and load

current waveforms, dc link capacitor voltage and %THD.

Figure 4.45 Simulation Model for VSI-SHAF based PHC technique for

R-Load

Figure 4.46 Pulse generation circuit of PHC technique

156

Figure 4.47 Simulation diagram for subsystem1 of pulse generation

circuit of PHC technique


for VSI-SHAF based PHC technique for R-Load

157

Figure 4.49 DC link capacitor voltage for VSI-SHAF based PHC

technique for R-load

Figure 4.50 %THD for VSI-SHAF based PHC technique for R-Load

Figure 4.51 shows the simulation diagram of VSI-SHAF based

PHC technique for DC motor load. Figure 4.52 shows the waveforms of

source voltage, source current and load current, Figures 4.53 and 4.54 show

the DC link capacitor voltage and % THD.

158

Figure 4.51 Simulation Model for VSI-SHAF based PHC technique for

DC motor load


for VSI-SHAF based PHC technique for DC motor Load

159

Figure 4.53 DC link capacitor voltage for VSI-SHAF based PHC

technique for DC Motor load

Figure 4.54 %THD for VSI-SHAF based PHC technique for DC motor

Load

Tables 4.3 and 4.4 show the overall comparative results for various

closed loop reference current estimation techniques showing the variation of

real and reactive powers, power factor and %THD for Resistive load and DC

Motor load.

160

Table 4.3 Overall comparative results for various closed loop reference

current estimation techniques showing the variation of real

and reactive powers, power factor and %THD for Resistive

load

R-load

parameterWithout

filter

Close loop technique

p-q d-q SDM PHC

Real

power(P)2.18e5 2.371e5 2.417e5 2.46e5 2.563e5

Reactive

power(Q)4.45e4 4.404e4 2.676e4 1.342e4 9800

pf 0.92 0.9931 0.9941 0.9986 0.9992

%THD 13.15 9.28 8.95 7.46 4.89

Table 4.4 Overall comparative results for various closed loop reference

current estimation techniques showing the variations of real

and reactive powers, power factor and % THD for DC Motor

load

DC Motor load

parameterWithout

filter

Close loop technique

p-q d-q SDM PHC

Real

Power(P)8.099e4 8.22e4 8.5e4 1.054e5 1.56e5

Reactive

Power (Q)7.841e4 6.665e4 2.535e4 2.321e4 2.15e4

Power

factor (pf)0.65 0.8153 0.8339 0.8713 0.8865

% THD 95.89 9.03 7.19 5.95 4.15

161

Figures 4.55 to 4.58 show the graphical representation of

comparative analysis of various closed loop current estimation techniques

based on % THD and real and reactive power variation for Resistive load

and DC Motor load.

Figures 4.55 Graphical representation of % THD for closed loop

reference current estimation techniques for Resistive load

Figures 4.56 Graphical representation of % THD for closed loop

reference current estimation techniques for DC Motor load

162

Figures 4.57 Graphical representation of Real and Reactive power

variation for closed loop reference current estimation

techniques for Resistive load

Figures 4.58 Graphical representation of Real and Reactive powers for

closed loop reference current estimation techniques for DC

Motor load

163

4.6 CONCLUSION

Among the various closed loop reference current estimation

techniques, namely p-q, d-q, SDM and PHC, %THD for PHC is the least

(4.89% for R-load and 4.15% DC Motor load). Also it gives better load

balancing, better power factor and good reactive power compensation.

CHAPTER 4 POWER QUALITY ANALYSIS USING …shodhganga.inflibnet.ac.in/bitstream/10603/9783/8/08_chapter 3.pdfCLOSED LOOP REFERENCE CURRENT ESTIMATION TECHNIQUES ... (SDM) The Synchronous

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