SIMULATION RESULTS AND ANALYSIS - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9782/9/chapter-6.pdf · placed in parallel with the SAPF at the PCC in the proposed SHAF topology

Chapter 6 Simulation results and analysis 129

Ph.D Thesis submitted to Jawaharlal Nehru Technological University Anantapur, Anantapur.

CHAPTER 6

SIMULATION RESULTS AND ANALYSIS

6.1 INTRODUCTION

The MATLAB/Simulink simulation models of the proposed SHAF topology

for harmonic compensation in low and medium voltage power distribution systems

are discussed in chapters 4 and 5 respectively. The simulation results of LV test

system model are presented in section 6.2 and that of MV test system model are

presented and analysed in section 6.3 of this chapter.

In section 6.2, first the performance of the LV distribution system model

without any compensation is presented. Then, the LV test system performance with

shunt active filter compensation is presented followed by results of the LV test system

with proposed SHAF compensation for harmonic mitigation. The performance of

SAF and SHAF in reducing THDi is compared for low voltage test system. Using this

we are able to validate the effectiveness of the proposed SHAF compensation scheme.

In section 6.3 first the performance results of MV test system model without

any compensation are presented followed by the performance results of MV test

system with ACSLI based SAPF compensation and ACSLI based shunt hybrid active

power filter(SHAPF) compensation. The capability of the proposed ACSLISHAPF in

reducing THDI and improving power factor is evaluated. Finally, Total Harmonic

Distortion (THD) of source current with the proposed ACSLISHAPF and basic

ACSLISAPF are compared.



6.2 RESULTS OF HARMONIC MITIGATION IN LV TEST

SYSTEM

In this section performance results of low voltage test system simulink model

without any compensation developed in section 4.2 are presented first followed by

results with SAF compensation along with its controllers developed in section 4.4 and

with proposed SHAF compensation developed in section 4.3.

6.2.1 Results of LV test System without any Compensation

The simulink model of LV test system without any compensation is developed

in chapter 4, section 4.2. It consists of a three-phase full-bridge diode rectifier load

connected to the distribution system in order to obtain the distorted load current. The

results of simulation are shown in Fig. 6.1 including three phase load current

waveforms, three phase source current waveforms and three phase source voltage

waveforms without any type of compensation.

6.1(a)



6.1(b)

6.1(c)



6.1(d)

Fig. 6.1 Results of LV test system without any compensation: (a) Non linear load current

for three phases (b) Source current for three phases (c) Three phase source

voltages (d) Phase angle comparison between source voltage and source current

for phase-a.

As can be seen, the resulting load current is highly distorted. It deviates

significantly from a sinusoidal waveform. This distorted load current leads to

distortion in the source currents and source voltage waveform as seen in Fig. 6.1(b)

and Fig. 6.1(c) respectively. The distortion in the source voltage waveforms is due to

the presence of source inductor (Ls) and distorted currents drawn by the load. The

source voltage and currents for phase-a are shown in Fig. 6.1(d) in which it is

observed that source current is out of phase with source voltage leading to poor power

factor due to reactive currents taken by the nonlinear load.



6.2.2 Results of LV Test System with basic SAF Compensation

The basic configuration of SAF is shown in Fig. 6.2. The simulation results of

the basic shunt APF are shown in Fig. 6.3. When the SAPF is connected, the injected

compensation current (if) forces the source current (is) to become a near sinusoidal

waveform.

Fig. 6.2 SAPF Configuration.

Applying Kirchhoff’s Current Law (KCL) at the point of common coupling

(PCC), we get

is= iL- i f (6.1)

where ‘is’ is the source current after compensation, ‘iL’ is the load current and ‘if’ is

the compensation current. The ideal current source is controlled to inject a

compensation current (if ) such that it cancels out the reactive and harmonic parts of

load current. In other words, reference value of if is equivalent to the summation of

iL,q and iL,h :



𝑖𝑓∗

= iL,q+ iL,h (6.2)

Simulation based on Eqn.(6.2) is carried out to verify the effectiveness of the

𝑖𝑓∗

under ideal compensation condition. Fig. 6.3 shows the simulation results of this

analysis. It is seen that the source current (is) waveform is obtained mathematically by

subtracting if from iL using Eqn.(6.1). Therefore the source current shown in Fig. 6.3

has very less harmonic content and also as seen from Fig. 6.4 the source current

waveform is in phase with the source voltage (vs) waveform, resulting in near unity

power factor.

Fig. 6.3 Simulation results of LV system with basic SAPF compensation -load current,

SAPF compensation current and source current waveforms for phase– a.

From Fig. 6.3 the source current contains appreciable amount of lower order

harmonics. This is due to the unavoidable switching ripple of the compensation

current, the presence of source inductor (Ls) and large amount of harmonics drawn by



Nonlinear load . When harmonic frequency switching ripple is injected into the point

of common coupling (PCC), it corrupts the source voltage, load current and source

current waveforms.

Fig. 6.4 Source voltage and source current for phase–a

(a)



(b)

Fig. 6.5 (a) Three phase SAF compensation currents and b) Three phase source currents

of SAF compensated LV test system model.

The three phase SAF compensating currents and source currents of the test

system with SAF compensation are shown in Fig. 6.5. It is seen that due to SAF

compensating currents the source currents attained near sinusoidal form. The

performance of SAF mainly depends on the technique used for estimating reference

signal for compensating currents. The synchronous reference frame theory

performance results and fuzzy logic based DC bus voltage controller results are

presented in the following sections.

Results of Compensation Current Reference Estimation

Fig. 6.6 shows the estimated compensating reference currents in a-b-c

reference frame produced by d-q-0 theory based reference compensating current

estimator. As can be seen, the current waveforms are distorted. They deviate

significantly from sinusoidal waveform and resembles the harmonic content in the

source current. It can therefore be concluded that the application of d-q-0 theorem to



estimate the compensation current reference for the proposed SAF work very well.

Fig. 6.6. Compensation reference currents in a-b-c reference frame.

Results of Fuzzy Logic based DC Bus Voltage Control

Fig. 6.7 DC bus capacitor voltage.

0 0.5 1 1.5 20

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

Time (sec)

Cap

acito

r vo

ltage

(Vol

ts)



The DC bus capacitor voltage of SAF is shown in Fig. 6.7. From this Fig. 6.7,

it is seen that the DC bus capacitor voltage is maintained constant at reference value

of 4700V by using fuzzy logic controller. It has reached the steady state value after

0.5 sec.

6.2.3 Results of LV System Model with Proposed SHAF

Compensation

Section 6.2.2 clearly demonstrated that the harmonic distortion in the source

current is reduced significantly by the use of basic shunt APF. However, an

appreciable amount of harmonic content still remains in the source current

waveforms. To reduce the dominant 5th

and 7th

order harmonics, tuned passive filter is

placed in parallel with the SAPF at the PCC in the proposed SHAF topology. The

TPF provides a path for 5th

and 7th

order harmonics. The MATLAB/Simulink model

of test system with the proposed SHAF topology is developed in Chapter 4, section

4.3.

Fig. 6.8 shows the simulation results of test system model with the proposed

SHAF compensation. When SHAF is applied, the injected compensation current (if)

forces the source current (is) to become near sinusoidal waveform and in phase with

the source voltage waveform, resulting in unity power factor. Comparing to the

simulation results with only SAPF as shown in Fig. 6.3, the harmonic content in the

source current is greatly reduced. It can be concluded that the TPF provides a path for

the 5th

and 7th

order harmonics to flow. This is evident by the fact that harmonic

content present in the TPF current waveform as seen in Fig. 6.8. Hence, the filtering

performance of SAPF is improved by the proposed SHAF topology.



Fig. 6.8 Non linear load current, SAF compensation current, TPF current and source

current for phase-a of LV test system with proposed SHAF compensation.

The three phase SAF currents, TPF currents and source currents of LV test

system with proposed SHAF compensation are shown in Fig. 6.9.

(a)



(b)

(c)

Fig. 6.9 Three phase a) SAF currents b) TPF currents and c) Source currents of SHAF

compensated LV test system.

From Fig. 6.9. it is seen that due to compensation action of SAF current and

TPF current the source current reached near pure sinusoidal wave form.



Fig. 6.10 LV test system source voltage and source current comparison for phase-a with

SHAF compensation.

The Fig. 6.10 shows LV test system source voltage and current for phase-a

with proposed SHAF compensation. From the Fig. 6.10 it is seen the source voltage is

in phase with source current leading to unity power factor. Thus the performance of

proposed SHAF topology is superior to that of SAF compensation in improving

power factor. This is evident by comparing Fig. 6.4 and Fig. 6.10.

6.2.4 Harmonic Distortion Analysis for LV Test System

The THD is the most common indicator to determine the quality of AC

waveforms. Using the Fast Fourier Transform (FFT), the harmonic spectrum of the

source current under different compensation conditions are presented. Then, the THD

comparison is carried out for the simulation results. The harmonic spectrum of the

source current of LV test system without compensation is shown in Fig. 6.11. From



the spectra plot, it can be seen that the source current contains large amount of

harmonic current components of frequencies below 1 kHz and the THDi is 12.4%.

Fig. 6.11 Harmonic spectrum of phase-a load current of LV test system without any

compensation.

The Harmonic spectrum of the three phase source current with basic SAPF

compensation is shown in Fig. 6.12 for all three phases-a,b,c.

(a)



(b)

(c)

Fig. 6.12 Harmonic spectrum of source current with basic SAPF compensation

(a) Phase-a (b) Phase-b (c) Phase-c.



From Fig. 6.12 it is seen that the basic shunt APF successfully filters the

harmonic current components caused by the nonlinear load. This is evident by the

reduction of source current THD from 12.4% to nearly 2%, but still there are some

low order harmonics present in the source current harmonic spectrum.

Fig. 6.13 shows the harmonic spectrum of the source current with the

proposed SHAF compensation. It is seen that the THDI is reduced to 1.62%. In

comparison to Fig. 6.12, the source current harmonic spectrum is almost free of

harmonic components. This implies that the proposed SHAF compensates the

distorted source currents including dominant 5th

and 7th

order harmonics. The source

current THD comparison is carried for different compensations in Table 6.1.

(a)



(b)

(c)

Fig. 6.13 Harmonic spectrum of source current of LV test system with proposed SHAF

compensation (a) Phase-a (b) Phase-b (c) Phase-c.



Table 6.1 THD comparison of source current of LV test system for different

compensations.

Type of compensation

THDI (%)

Isa Isb Isc

Without compensation 12.4 12.4 12.4

With basic SAF Compensation

2 1.86 1.95

With proposed SHAF compensation 1.62 1.39 1.52

The source current THD is reduced from 12.4 % to 2 % with basic shunt APF.

With the proposed SHAF, the source current THD is further reduced to 1.62 %. Thus,

the harmonic filtering performance of the proposed SHAF topology is superior

compared to the basic shunt APF which is well below the harmonic limit imposed by

IEEE Standard 519.

6.3 RESULTS OF HARMONIC MITIGATION IN MV TEST

SYSTEM

This section presents the simulation results of the simulink model of the

proposed 7-level SHAF for harmonic mitigation in a MV distribution system

developed in chapter 5. It presents the simulation results of MV test system model

without any compensation in section 6.3.1 first, followed by the results of MV test

system with basic seven level SAPF in section 6.3.2 , followed by the results of MV

system with proposed 7-level SHAPF compensation in section 6.3.3. The Results of

performance of ACSLSAF are presented and analysed and then compared with the

results of the proposed ACSLSHAPF for mitigating harmonics in medium voltage test

system.



6.3.1 Results of MV Test System without any Compensation

(a)

(b)



(c)

(d)

Fig. 6.14 Simulation results of MV test system without compensation a) Three phase

nonlinear load currents b) Three phase source currents c) Three phase

source voltages d) Phase angle comparison between source voltage and

source current for phase-a.



The simulink model of medium voltage test system developed in chapter 5,

section 5.2 consists of a three-phase full-bridge diode rectifier load connected to a

three phase distribution source of voltage 4.5 kV(peak) in order to obtain the distorted

load current. Fig. 6.14 shows the simulation results of MV test system without any

compensation .

It shows three phase Load currents, source currents, source voltages, and

phase angle comparison between source voltage and source current waveforms of

phase-a. As can be seen, the resulting load current is highly distorted and deviated

significantly from sinusoidal waveform. This distorted load current leads to distortion

in the source current and source voltage waveforms. The distortion in the source

voltage waveform is due to the presence of source inductor (Ls) and distorted currents

drawn by the load. The source voltage and source current for phase-a are shown in

Fig. 6.14(d) in which it is seen that source current is out of phase with source voltage

leading to poor power factor.

6.3.2 Results of MV Test System with basic 7-Level SAPF

Compensation

This section presents the simulation results of MV test system model with

basic seven level SAPF compensation developed in Chapter 5, section 5.3. The

Fig. 6.15 shows the single phase and three phase seven level output voltage wave

forms of asymmetric cascaded inverter based SAPF.



(a)

(b)

Fig. 6.15 Seven level voltages generated by the asymmetric cascaded inverter for

(a) Phase-a (b) Phases a, b and c.

From this Fig. 6.15, it is evident that the reference current estimator and

CSFMCSH PWM method are worked satisfactorily and produced required gating

signals for asymmetric cascaded seven level inverter to generate required seven level

output voltage. The three phase compensating currents injected by ACSLI SAPF for

harmonic mitigation and three phase source currents after ACSLISAPF compensation

are shown in Fig. 6.16.



(a)

(b)

Fig. 6.16. (a)Three phase ACSLISAPF currents and (b) Three phase source currents

with ACSLI based SAPF compensation for MV test system.

From this Fig. 6.16, it is seen that the harmonic content in the source current is

very much reduced with SLI SAPF compensation and the wave form attained near

sinusoidal form compared to source current waveform without any compensation in

Fig. 6.14(b). The source current THD is also reduced from 12.4% to 3.51 % from

THD analysis given in section 6.3.4. For ease of comparison the load current, SAPF

compensating current and source currents for phase-a only are shown in Fig. 6.17,



when the MV test system is compensated with basic ACSLI based SAPF.

Fig. 6.17 Load current, filter current and source current for phase- a of MV test system

with ACSLI based SAPF compensation.

From the Fig. 6.17, it is observed that the load current is heavily distorted in

phase–a and the ACSLI based SAPF has injected suitable harmonic current to

compensate the load harmonics and hence the source current is almost pure

sinusoidal. Also the filter current is injected at the PCC such that source current is

sinusoidal and it is forced to be in phase with the voltage at the AC mains after

compensation of ACSLI based APF, leading to near unity power factor which is

evident from the Fig. 6.18.



Fig. 6.18 Phase angle comparison between source voltage and source current for

phase–a after compensation with ACSLISAF.

The performance of SAF mainly depends on the technique used for estimating

reference signal for compensating currents and the method adopted to generate gating

signals for voltage source inverter. The results of synchronous reference frame d-q

theory, fuzzy logic based DC bus voltage controller and CSFSHPWM are presented

in the following sections.

Results of d-q-0 Theory in SLISAPF compensation

In this section, the results of d-q theory based reference compensating current

estimator model are presented. Fig. 6.19 shows the estimated compensating reference

currents produced by d-q-0 theory estimator model in a-b-c reference frame. As can

be seen from Fig. 6.19(a) the estimated compensation current waveforms are distorted

showing the harmonic content in the load current. Figure 6.19(b) shows the reference

three phase current wave forms for PWM after subtracting with actual compensating

currents.



(a)

(b)

Fig. 6.19 (a) Compensation reference currents in a-b-c reference frame and b) Three

phase modulating signals for CSFSHPWM for ACSLISAPF compensation.



It can therefore be concluded that the application of d-q theorem to estimate

the compensation current reference for the proposed SAPF work very well.

Results of Fuzzy Logic based DC Bus Voltage Control

Fig. 6.20 DC bus capacitor voltage on LV cell.

The DC bus capacitor voltage is controlled by using fuzzy logic controller on

the LV cell of ACSLI as explained in section 5.3.2. The Fig. 6.20 shows the DC bus

capacitor voltage on LV cell. It is noted that the Fuzzy Logic Controller maintained

1.5 kV (LV cell) capacitor voltage constant.

Results of CSFSHPWM

The switching devices of each phase leg of ACSLI are controlled by

CSFSHPWM model developed in section 5.3.2 in which triangular carrier signals are

compared with reference sinusoidal signal generated by reference current estimator. A

small section of the adopted carrier signals and modulating signal for controlling two

H-bridges of phase-a of ACSLI are shown in Fig. 6.21 and the generated gating

signals are shown in Fig. 6.22.



Fig. 6.21 Carrier signals and reference signal for phase-a of CSFSHPWM.

Fig. 6.22 A small section of the gating signals for phase–a of ACSLI.



6.3.3 Results of MV Test System with proposed ACSLI based SHAPF

Compensation

This section presents the simulation results of the proposed ACSLI based

SHAPF compensated medium voltage system simulink model developed in chapter 5,

section 5.3. The nonlinear current load current is compensated using a three-phase

ACSLI based SHAF associated with d-q theory for compensating reference current

estimation and CSFMCSHPWM for generating gating signals.

Results of D-Q Theory Based Compensating Current Reference

Estimator in ACSLISHAPF Compensation

The reference currents estimated by d-q-0 theory based reference current

estimator in a-b-c reference frame are shown in Fig. 6.23.

Fig. 6.23 The reference compensating currents in a-b-c reference frame for ACSLI

based SHAPF compensation.



It is seen that the peak value of reference currents are less in this case

compared to reference currents in SAPF compensation shown in Fig. 6.19(a). This is

due to the absorption of 5th

and 7th

harmonic currents by the TPF connected in parallel

with the load in addition to SAPF in this hybrid filter. This is observed in a-b-c-

reference frame currents which proves the effectiveness of reference compensating

current estimator in evaluating the harmonic content in the load current.

Results of CSFSHPWM in ACSLISHAPF Compensation

The Fig. 6.24 shows the modulating signal generated and the triangular carrier

signals for phase–a in this topology.

Fig. 6.24 Modulating signal and the triangular carrier signals of CSFSHPWM of

phase–a in SHAPF compensation.

The seven level single phase and three phase output voltages of ACSLI in

SHAPF topology is shown in Fig. 6.25. It is seen that the seven level output voltage is

not disturbed due to the addition of TPF in ACSLI based SAPF model.



.

(a)

(b)

Fig. 6.25 Output voltage of ACSLI based SAF for a) Phase-a b) Three phases.

The three phase compensating currents injected by ACSLI based SAPF in

SHAPF topology is shown in Fig. 6.26 and the three phase TPF currents are shown in

Fig. 6.27. Due to these harmonic compensating currents the source current is free

from harmonics and is as shown in Fig. 6.28.



Fig. 6.26 Compensating three phase currents of ACSLI based SAF in SHAF topology.

Fig. 6.27 Three phase tuned passive filter currents in ACSLISHAF topology.

Fig. 6.28 Three phase source current of MV test system with ACSLI based SHAPF

compensation.



For the ease of comparison the load current, SAPF current, TPF current and

source current for phase-a are given Fig. 6.29.

Fig. 6.29 Load current, ACSLI based SAF current, tuned passive filter current and

source current for phase- a with ACSLI based SHAF compensation.

From the Fig. 6.29, it is seen that the combination of SAF current and tuned

passive filter current effectively compensated for the harmonics in the load current

and reduced the THD in source current from 12.4% to1.01% as presented in section

6.3.4.

6.3.4 Harmonic Distortion Analysis for MV Test System

In this section the harmonic spectrum of the source current using the FFT

under different compensation conditions are presented. Then, the THD comparison is

carried out for the simulation results. The spectrum of the source current without

compensation is shown in Fig. 6.30 for phase-a. From the spectra plot, it can be seen



that the source current contains large amount of harmonic current components of

frequencies below 1 kHz and the THD in source current is 12.4%. It is seen that the

most dominant are 5th

and 7th

order harmonics in the spectra plot.

Fig.6.30 Harmonic spectrum of phase–a source current of MV test system without any

compensation.

The spectrum of three phase source currents of MV test system with basic

ACSLISAPF compensation is shown in Fig. 6.31. The ACSLISAPF successfully

filtered the harmonic current components caused by the nonlinear load.



(a)

(b)



(c)

Fig. 6.31 Harmonic spectra of source currents of MV test system with ACSLISAPF

compensation a) For phase–a b) For phase-b and c) For phase-c.

Although the high frequency harmonic components (i.e. greater than 1 kHz)

are filtered significantly, appreciable amount of lower order harmonics still remain in

the source current spectrum. The most dominant are 5th

and 7th

order harmonics. To

eliminate these harmonics shunt tuned passive filters are connected in addition to

ACSLISAPF in the proposed hybrid filter. The source current harmonic spectrum of

MV test system with the proposed ACSLSHAPF compensation is shown in Fig. 6.32.



(a)

(b)



(c)

Fig. 6.32 Source current harmonic spectra of MV test system with ACSLISHAPF

compensation a) For phase –a b) For phase-b and c) For phase-c

From the Fig. 6.32, it is seen that the proposed ACSLISHAPF reduces the

THD in nonlinear load current well below the limit specified by IEEE. This implies

that the proposed hybrid APF effectively compensates the load current harmonics.

The source current THD is reduced from 12.4 % to 3.51 % with ACSLISAPF and

with the proposed ACSLISHAPF, the source current THD is further reduced to 1.01

%. Thus, the harmonic filtering performance of the proposed ACSLISHAF topology

is superior compared to the ACSLISAPF which is well below the harmonic limit

imposed by IEEE Standard 519. The source current THD comparison is carried out

for ACSLISAPF and ACSLISHAPF compensations in Table 6.2.



Table 6.2 THD comparison of source current of MV system for different compensations.

Type of compensation

THD (%)

Isa Isb Isc

Without compensation 12.4 12.4 12.4

With ACSLISAPF Compensation

3.51 3.28 3.44

With proposed ACSLISHAPF

compensation

1.01 1.29 1.25

6.3.5 Response of proposed ACSLI based SHAPF for 3-phase Fault

To test the ability and flexibility of the proposed three-phase ACSLI based

SHAPF configuration in compensating the current harmonics under dynamic

conditions a three phase fault is introduced at time 0.04s and cleared at time 0.072s in

the MV system model developed in chapter 5, section 5.4. The Fig. 6.33 shows the

load current, filter compensating current and source currents of ACSLISHAF

compensated test system with three phase fault.



(a)

(b)



(c)

Fig. 6.33 Three phase (a) Load Currents and b) Compensating currents and (c) Source

currents of ACSLISHAF compensated test system for three phase fault.

From the Fig. 6.33, it is seen that the distortion in source current is very less

compared to that of load current due to the presence of ACSLISHAPF compensation.

From the results the proposed ACSLI based SHAPF is capable of compensating

harmonics at the time of faults under dynamic conditions.

6.4 CONCLUSION

This chapter presented the results obtained from the simulations of SHAF

compensated LV test system and MV test system. Simulation and tests were

conducted aiming to illustrate the effectiveness of the proposed shunt hybrid APF in

harmonic mitigation in low voltage test system. The effectiveness of d-q theory in

estimating compensation reference current is demonstrated. In addition, the



effectiveness of fuzzy logic controller in maintaining DC bus voltage is discussed.

The simulation results are analysed and discussed. Finally, a detailed THD analysis on

source current spectrums is carried out to validate the harmonic filtering performance

of the proposed SHAPF topology in comparison to the basic SAPF compensation in

LV system.

The results of the proposed three-phase ACSLI based SHAPF shown that it

has compensated the distortion in the line current caused by nonlinear load in a

medium voltage distribution system. Based on the results, the proposed SHAPF

topology is capable of responding effectively to the harmonics caused by the three-

phase diode rectifier load. The total harmonic distortion of the source current without

compensation is high; about 12.4 % in each phase and THDi with SLI based SAPF is

3.51%. When compensation is made with the proposed ACSLISHAPF, the total

harmonic distortion is reduced to 1.01%, which is fairly good. Thus ACSLISHAPF

performance is superior compared to SLI based SAPF and has better response under

dynamic conditions.

Documents

SIMULATION RESULTS AND ANALYSIS - Shodhgangashodhganga.inflibnet.ac.in/bitstream/10603/9782/9/chapter-6.pdf · placed in parallel with the SAPF at the PCC in the proposed SHAF topology