Comparative Evaluation of Various Single Phase

IEEE - International Conference On Advances In Engineering, S cience And Management (ICAES M -2012) March 30, 31, 2012 622

Comparative Evaluation of Various Single Phase Harmonic Filters for Non-Linear Load

P.MATHAN MOHANi; G.AMUTHAN 2 P.G. Scholar! ,M.E Power Electronics and Drives; Assistant Professor2

Department of Electrical and Electronics Engineering A. C. College of Engineering and Technology

Karaikudi-630004, Tamilnadu, India. Email:[email protected] no: +91-9940827699.

Abstract- Majority of loads draw non-sinusoidal current from the supply, resulting in the generation of current and voltage

harmonics. The presence of the harmonics leads to low

system efficiency, poor power factor, increased losses and reactive

power components of current from AC mains. In this

paper a comparative study of current harmonic compensation

using passive power filter, Shunt active power filter and hybrid

filter is made. In hybrid filter, two single tuned passive filters

are tuned

to compensate 3rd and 5th order harmonics and active power filter

compensates all remaining harmonic components which are not

compensated by passive filter. A voltage source inverter with

hysteresis current control is used to form an active power filter

and it is injecting equal but opposite current to mitigate the

distortion current to shape the supply current to a sinusoidal

form and in phase with the supply voltage. A simple PI de

bus voltage controller with reduced energy storage

capacitor is employed in the APF. A fixed non linear load is

simulated with various harmonic filters in MATLAB/Simulink

environment. The results show that use of Hybrid Filter

provides better performance simultaneously reducing the

required device rating.

Keywords- Passive Filter (PF), Active Power Filter (APF), Hybrid Active Power Filter (HAPF), Hysteresis Current

Control.

I. INTRODUCTION

HARMONI CS have existed in the power systems nearly since the very inception of ac interconnected power networks. The issue, however, added signi ficance due to ever-increasing use of equipment (residential, commercial, and industrial) sensitive to power system disturbances, energy conditioning and the related economic aspects, the increasing awareness of power quality and the deregulation The extensive use of power electronic devices to control different loads not only injects the harmonics but also draw substantial reactive power [1]. This unwanted distortion causes many adverse effects like additional heating, amplification of harmonics due to presence

of power factor correction capacitor banks, reduction of transmission system ef ficiency, overheating of distribution transformers, malfunctioning of electronic equipment, spurious operation of circuit breakers and relays, errors in measuring instruments, interference with communication and Control signals etc. The strict requirements of power quality at the input of the ac mains, several standards, have been developed and imposed on the consumers. The realization of these standards and guidelines such as IEEE- 519-1992/ IE C 61000 has attracted the attention of both utility and consumer to share their responsibilities, to keep the harmonics contamination within acceptable limits [9]. Harmonics problem are usually resolved by the use of conventional passive and active filters. Conventional passive filters, namely L C passive filters, possess the merits such as the simple structure, low cost and can compensate reactive power along with harmonics. Passive Filter based on resonant principle has many disadvantages, such as large size, fixed compensation, tuning problems etc. To overcome aforesaid problems, active filters came into picture to provide appropriate solution best suited to the compensation necessities under dynamic load conditions. However, APF topologies are not cost effective for high power applications due to their large rating and high switching frequency requirement of the PWM Inverter. This project describes a comparative evaluation of Passive Power Filter(PF),Shunt Active Power Filter(SAPF) and Hybrid Active Power Filter(HAPF) for single phase bridge rectifier with RL load. Simulation results show that the percentage of total harmonic distortion (%THD) of the source current after compensation is well below the permissible limit of 5% and reduce the device rms current rating of Active Power Filter.

I I. SYSTEM DESCRIPT ION

A schematic diagram of a Single-Phase HAPF which consists of an Active Filter in parallel with single tuned Passive Filter is shown in Fig. 1. A single-phase sinusoidal voltage source supplying power to nonlinear load which is connected in parallel with a current controlled APF and a single-tuned PF.

ISBN: 978-81-909042-2-3 2012 IEEE


Vs Rs i.

.iln

VL

1i.

i

TunedP.."We Filter

Fig. I Single Line Diagram of Proposed HAPF

RL L,L

A single-phase full bridge uncontrolled rectifier with R-L load on its dc-side is used as a nonlinear load. The APF consists of an inductor Lc and resistance Rc and a full bridge single phase IGBT or MOSFET based current controlled voltage source inverter with a self-charging capacitor Cdc' A hysteresis controller is used to obtain the PWM pulses to control the switches used in C C-VS I circuit. The Singletuned Passive Filters consist of fixed value inductors and capacitors are tuned to compensate 3rd and 5th order of harmonics [2].

I I I. CONTROL S CHEME

Fig. 2 shows the block diagram of an overall control scheme for the HAPF system. D C bus voltage and supply voltage and current are sensed to control the APF. A C source supplies fundamental active power component of load current and a fundamental component of a current to maintain average dc bus voltage to a constant value. The later component of source current is to supply losses in VSI such as switching loss, capacitor leakage current etc. in steady state and to recover stored energy on the dc bus capacitor during dynamic conditions. The sensed dc bus voltage of the APF along with its reference value are processed in the P- I voltage controller. The truncated output of the P- I controller is taken as peak of source current. A unit vector in phase with the source voltage is derived using its sensed value. The peak source current is multiplied with the unit vector to generate a reference sinusoidal unity power factor source current. The reference source current and sensed source current are processed in hysteresis current controller to derive gating signals for the MOSFETs of the APF. In response to these gating pulses, the APF impresses a PWM voltage to flow a current through filter inductor to meet the harmonic and reactive components of the load current. Since all the quantities such as dc bus voltage are symmetric and Periodic corresponding to the half cycle of the ac source, a corrective action is taken in each half cycle of the ac source resulting in fast dynamic response of the APF.

1_" .... _

___

_

---'

Fig. 2 Control Scheme of the APF

IV. BAS I C COMPENSA nON PRIN CIPLE

A. Shunt Active Power Filter Compensation Principle

The basic compensation principle of Shunt Active Filter is shown in the fig. 3 below. The SAPF is controlled to draw /supply the compensation current Ie which cancels the harmonics present in the source current Is. The compensating current will not affect the load current h. Conventionally four quadrants current controlled PWM-VSI is used as Shunt Active Power Filter [3].

Is = h-Ic (1) Ideal compensation requires the mains current to be sinusoidal and in phase with the source voltage, irrespective of the load current nature therefore the magnitude of source current alone need to be determined.

$our


ls

:----------R:. ---: tu .. u.u>f'r __ -;j-'-------'---------'

Fig. 4 Hannonic equivalent circuit of HAPF

The source and Passive Filter harmonic currents determined by following equation respectively

. (1 K ) ZF ..

':IJ = - lUI . ZF +ZS

Zs . iiiJ == l - K J ) .lUI '" Z,:;- +ZS

(2) can be

(3)

(4) Where ish and i Fh are the harmonic currents through source and PF respectively. For KA =1, the total harmonic current passed through APF and hence its rating is not reduced. When KA=O, no compensation through APF, only selected harmonics are compensated through passive filters and rest of the harmonics current is passed through supply source. Therefore, proper coordination between the active and passive filters is very important for reducing the rating of the APF. In the proposed technique the compensating frequency of the active filter is set to ignore the tuned frequencies of the passive filters. The passive filters are used for supplying reactive power and eliminating 3rd, 5th harmonics where as the APF eliminates all reaming harmonics [4] [ 5] [6].

V. CONTROL STRATEGIES

The proposed HAPF system is comprised of a passive filter, active power filter with hysteresis current controller and PI voltage controller are modeled separately and then joined together in order to simulate the HAPF system.

A. Passive Filter Control Strategy

As explained in introduction, a HAPF consists of an active filter with shunt connected single tuned passive filters for low order dominant harmonics. This section describes the design procedures for building single three phase passive filter using RL C elements [7]. The RL C values are determined based on the filter type and the following parameters:

(i) Reactive power at nominal voltage (ii) Tuning frequency (iii) Quality factor

If the conditions the resistance in reactors and dielectric losses in capacitors are neglected the total impedance of single-tuned

filter the impedance of PF for nth order harmonic is

z;, = + j(n( - :.,...., ) nc'-"-1

The resonance degree of single tuned filter is

1 1'1= -==

o;j4C;

(5)

(6)

The equivalent circuit and characteristics of single tuned passive filters Represents the following Fig. 5

T.illC

14 )CO Fig. 5 Equivalent Circuit and Impedance Characteristics of Single Tuned Pass ive fi Iter

B. Shunt Active Power Filter Control Strategy

Fig. 3 the instantaneous currents can be written as

is(t) = il(t) - Ic(t) Source voltage is given by

Vs (t) = Vs * sincot

(7)

(8)

If a nonlinear load is applied, then the load current will have a fundamental components and harmonic components, which can be represented as

00

iL(t) = L In sin (ncot+Q>n) n=1

00

idt) = Ilsin(cot+Q>I)+ L In sin (ncot+Q>n) n=1

The instantaneous load power can be given as

(9)

(10)

(11 )

pdt) = Y m II sin2cot *cos Q>I + Y m II sincot *coscot * sinQ>]

00

+ Ym sincot * L In sin (ncot+Q>n) n=2

From (12), the real power drawn by the load is

(12)

(13)

From (7) the source current supplied by the source, after compensation is

ISBN: 978-81-909042-2-3 2012 IEEE


There is also some switching losses in the P WM converter, and hence the utility must supply a small overhead for the capacitor leakage and converter switching losses in addition to real power of the load. The total peak current supplied by the source is

Isp = Ism + lsi (15)

If the Active Filter provides the total reactive and harmonic power, then is (t) will be in phase with the utility voltage and purely sinusoidal. At this time, the active filter must provide the following compensation current is

ic(t) = iLCt) - is(t) (16)

Hence, for accurate and instantaneous compensation of reactive and harmonic power it is necessary to estimate iL (t) i.e. the fundamental component of the load current is the reference current. The peak value of the reference current can be estimated by controlling the D C side capacitor voltage. Ideal compensation requires the mains current to be sinusoidal and in phase with source voltage, irrespective of the load current nature. The desired source currents, after compensation, can be given as

is*(t) = Isp * sin cot

Where Isp = I I cos I + ISL

(17)

It is the amplitude of the desired source current, while the phase angle can be obtained from the source voltages. Hence the waveform and phase of source current are known and only the magnitude of the source currents need to be determined. This peak value of the reference current has been estimated by regulating the D C side capacitor voltage of the PWM converter. This capacitor voltage is compared with a reference value and the error is processed in a PI controller. the output of the PI controller has been considered as the amplitude of the desired source current are estimated by multiplying this peak value with the unit sine vectors in phase with the source voltages.

B.i. Dc-Link Voltage Controller

The dc-link capacitor voltage is regulated to obtain the loss active power in the inverter circuit using an energy controller. The energy (Ede ) required by the dc-link capacitor to charge the capacitor from actual (Vde ) to the reference voltage ( Vdcrej) can be expressed as

1 2 2 Edc = - C" (V';o'''- -V.;() '1 ' 2 ., .. ' .. I. 0) On the other hand, the total energy (Edd delivered by the source will be

E",,= PsI COTe Equations (18) and (19) yields

VI. S IMULA nON RESULTS

(19)

(20)

The simulation is carried out in MA TLAB environment for single phase non-linear load without filter, PF, SAPF and HAPF respectively. System parameters chosen are given in Table 1.

TABLE I : SYSTEM PARAMETERS FOR SIMULATION

Parameters Value

S inusoidal source voltage(Vs) 230V(325V peak),50 Hz

S ource Impedance(Rs : Ls) 0.10:0.lmH

N on-Linear Load(Diode Bridge 7.50: 25 mH Rectifier) Impedance (RL : LL) (R3: L3: C3) 0.20: 16 mH: 70 J.lF

PF (R5: L5: C5) 0.25 0 : 9 mH: 45 J.lF Parameters Tuned frequencies 150Hz: 250Hz

Filter Impedance 0.0150: 3.5 mH APF (RC : LC)

Parameters DC-link capacitor Values (Vdcref: Cdc)

400V: 2000J.lF

Case 1) Simulation of Single Phase System without Filter

Fig. 6 shows the input voltage, input current and load current waveform of given non-linear load. The 3rd and 5th

order Harmonics values of source current are respectively 7.441 and 4.4 57. Current THD is 26.98%.

Fig. 6 (a) Input Voltage Waveform, (b) Input Current Waveform, (c) Load Current Waveform before compensation.

ISBN: 978-81-909042-2-3 2012 IEEE


Case 2) Simulation 0/ Single Phase System with Passive Filter

The simulation result with passive filter shows the 3rd order harmonic value of source current is reduced from 7.741 to 0.8643 and 5th harmonic value of source current is reduced from 4.4 57 to 0.31 52 and also % of current THD is reduced from 26.98% to 11.84%.

Fig. 7 (a) Input Voltage Wavefonn, (b) Input Current Waveform, (c) Load Current Waveform after Passive Filter Compensation.

Fig. 7 shows the input voltage, input current and load current waveforms after Passive Filter Compensation.

Case 3) Simulation o/Single Phase System with SAPF

The simulation result shows that the 3rd order harmonic value of source current is reduced from 7.741 to 0.4667 and 5th

order harmonic value of source current is reduced 4.4 57 to 0.1683.Source current after SAPF compensation is in phase with source voltage with 2.623% current THD.

Fig. 8 (a) Input Voltage Waveform, Load Current Waveform, Compensation current Waveform Compensation.

(b) Input Current Waveform, (c) (d) after SAPF

Fig. 8 shows the input voltage, input current and load current, Compensation current waveforms after shunt active power Filter.

Case 4) Simulation o/Single Phase System with HAPF

The performance of HAPF is analyzed under sinusoidal source voltage condition. The HAPF circuit is switched on at t=0. 5s.The simulation result shows that the 3rd and 5th order harmonic value of source current is reduced from 7.741 to 0.1464and 4.4 57 to 0.0902.Source current after HAPF compensation is in phase with source voltage with 1.641 % current THD.

8 Fig. 9 Simulation diagram of I system with HAPF

Fig. 9 shows the simulation circuits of single phase system of non-linear load with hybrid filter. Fig. 10 shows that the input voltage, input current, load current, Compensation current waveforms after hybrid Filter Compensation.

Fig. 10 (a) Input Voltage Waveform, (b) Input Current Waveform, (c) Load Current Waveform, (d) Compensation current Waveform after HAPF Compensation.

ISBN: 978-81-909042-2-3 2012 IEEE


Case 5) Device Current Waveform for SAPF and HAPF

The rms value of device current taken by SAPF is 7.66 5A and 6.3A for HAPF, which shows the significant reduction in rating of APF.

Fig. 11 Device Current Waveform for SAPF

Table 3 shows the % of THD and Power Factor of without Filter, PF, SAPF and HAPF. When compared to all methods the % of THD can be reduced to l.641 % and also Power Factor could be improved to 0.92 by HAPF.

By using Hybrid Active Power Filter, the current through Active Filter switching device is found to decrease as shown in Table 4.

VI I I. CONCLUSION

In order to reduce the rating of active power filter a control strategy which utilizes the advantages of both passive and active filter for nonlinear load compensation is presented in this paper. The control strategy not only reduces the rating of active filter but also improves the performance under distorted mains condition. It is predicted that the proposed control strategy of HAPF will be suitable for wherever a high rating nonlinear load is to be compensated. The THD of the source current after compensation is well below the permissible limit of 5%.

REFERENCES

[1] J. Arrillaga, M.H.J. Bollen, and N.R. Watson, "Power quality following

Fig. 12 Device Current Waveform for HAPF deregulation," Proceedings of the IEEE, vol. 88, no. 2, pp. 246-261,

VII. INFEREN CE

Comparison tables showing various performance parameters for without Filter, Passive Filter, Shunt Active Power Filter and Hybrid Active Power Filter are shown below for comparative evaluation.

TABLE 2: SOURCE CURRENT MAGNITUDE COMPARISON

Harmonic Magnitude Before Order

Compensation PF S APF HAPF

1st 36.50 35.66 36.12 36.13 3rd 7.448 0.8643 0.4667 0.1464 5th 4.457 0.3152 0.1683 0.0902

TABLE 3: COMPARISON OF% THD AND POWER FACTOR

SYS TEM % of THD POWER FACTOR Before Compensation 26.98 0.8389 Passive Power Filter 11.84 0.9123

Shunt Active Power Filter 2.159 0.9192 Hybrid Active Power Filter 1.641 0.9200

TABLE 4: COMPARISON OF DEVICE CURRENT

SYS TEM DEVICE RMS CURREN T

Shunt Active Power Filter 7.665 Hybrid Active Power Filter 6.300

Table 2 shows the magnitude of 3rd and 5th order harmonics are reduced signi ficantly in Hybrid Active Power Filter.

[2]

[3]

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[5] S.Z. Shuai, A. Luo, R. Fan et ai, "injection branch design of injection

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5,pp. 57-60, Jun 2007

[6] Yonghai Xu, Xiangning Xiao, Hao Liu, "Shunt Hybrid Filter for

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Transactions of China Electro technical Society, vol. 20, no. I , pp, 112-118,2005.

[7] X. Yo, "Algorithm for the Parameters of Double Tuned Filter,"

[8]

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ISBN: 978-81-909042-2-3 2012 IEEE

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Comparative Evaluation of Various Single Phase