COMPARATIVE STUDY OF DIFFERENT PWM CONTROL SCHEME FOR
THREE-PHASE THREE-WIRE SHUNT ACTIVE POWER FILTER
A.S.A HASIM
PROFESOR MADYA DR ZULKIFILIE BIN IBRAHIM
MD HAIRUL NIZAM BIN TALIB
Comparative Study of Different PWM Control Scheme for
Three-Phase Three -Wire Shunt Active Power Filter
A. S. A. Hasirn*, Z. Ibrahim** and M. H. N. Talib**
*
Department of Electrical, Faculty of Engineering, Universiti Perlahanan Nasional Malaysia, 57000 Kuala Lumpur, Malaysia**
Faculty of Electrical Engineering, Universiti Teknikal Malaysia Melaka, 76100 Durian Tunggal , Mel aka. Email: asyukJ l@y<1hoo.com, [email protected], hairulnizam@utem .edu .myAbs/met - lnshlnlancous rcacti\'C power theory was the most populnr control theory used when dealing with harmonics compensations. In conjunction with the inslant:mcous theory, switching signal gcncl"lltion techniques 1>lays nn imporhrnt role to ensure the corrl.'ct compensation sign:il injected in the system .. Therefore, this pnpcr discussed on comparati\'C study of five (:5) methods used in instnntnneous theory namely; /J-1/ method, modified
p-q, 11-f[ method, p-q-r merhod and vectorial with lhrce (3) types . of
signal gcncralion namely; carrier current control, hysteresis current control and space \•cctor modulation conlrol. Continuous rcducrions of lhc totnl harn1onics distortion (THD) arc expected at the supply current when :11lplicd diffc1·cnt types of switching technique. The compnrison was cx:1111ining using MATLAB/Sirnulinl1 (MLS) environment.
Kl(l'IV/lr1/s-instantaneous rcnctivc power theory, shunt Active Filter, switching signal gcncrntion
I. INTRODUCTION
Power electronics application is dependent on the use of power switching devices that inadvertently; results with a non-sinusoidal current being drawn from the supply, containing harmful harmonic components which are then fed back lo the supply system creating various problems. Various methods have been proposed in an effort to solve these problems. Amongst others is the use of passive filters connected in parallel with nonlinear loads [I], resulting with improvements in power factor and harmonic suppression [2}; designed to exhibit lower impedance al a tuned harmonics frequency [JJ. This approach is popular due lo its simplicity. reliability, efficiency and low cost
(4), but at the expense of providing incomplete solutions particularly when compensating random frequency variations in the current, tuning and parallel resonant problems.
In recent years, various active power filters (APF) configurntion with their respective control strategies have been proposed and have been recognized as a viable solution to the problem created by harmonics
r
1-4]. Control is most important element in the success of implementation of active power filter. The APF control is based on the instantaneous reactive power theory with difforent approaches [5-17]. The instantaneous reactive power theory was first introduced by Akagi et al. [7] for controlling of APFs. The control strategy derived from the p-q theory was efficient to reduced harmonics in the supply current hence provide the sinusoidal source currentwith same characteristic with voltage supply. Two formulations have been precursor from the origin p-q theory with great interesting contributions with respect to the original theory namely; modi lied p-q theory [I 0, 11] and p-q-r theory [ 14-16 ]. On the other hands, d-q theory [12, 13) and vecloria/ theory [18] were developed at the end of I 980's. This formulation was found obtaining identical result as compared to p-q theory in balance nonlinear load conditions.
This paper presents a comparative study of five harmonics detection algorithms incorporating with three different signal generations conditions. A brief description of each algorithm with necessary equation is explained in Section 11. Hence, switching generation of three types of switching techniques is briefly explained in Section Ill. The simulation results from the operations are compared in Matlab/simulink (MLS) environment presented in Section IV. Three-phase three-wire shunt APF circuit consists of main supply connected lo a non-linear load as shown in Figure I. Four esscntiat. ｾＱ＼ＺｩｭＧｾｩＱｴｳ＠ in the APF are namely; (i) signal conditioning, (ii) reforencc current generation, (iii) signal generation and (iv) three-phase inverter. The signal conditioning circuit used to provide accurate system information from the voltage and current from the grid. The reference current generator is used to generate the required harmonics current to be amplified · and injected into the lines, at the point of common coupling (pee). The switching generation for the inverter is generated at the controller circuit by comparing the reference current (i"*, iu*, i0*) with the injected currents (i0 • ib• ic).
f-igure I. Block Dingram of Shunt Active Power Filter
ｎｯｮｾ ｮ･｡ｲ＠
Load
II. INSTANTANEOUS REACTIVE POWER THEORY
This section discussed briefly about five (5) harmonics detection algorithms and relevant equations that have been studies.
A. p-q and Mod(fied p-q Formulation
The p-q theory transform the three-phase system voltages and current from phase coordinate to 0-a.-(J coordinates based on Clarke-Coordinate transformation, which represent by the following matrix {I);
l/
'z
Arz
ｦ
ＱＱｾ＠
[A]=
ｾＳＱＮ＠
:
V ._ [
sa]
-lh
Ash (1).,/3 / 2
-../3 /
2 Asewhere A can be either current or voltage. In the new coordinate system. three power terms arc expressed namely; zero-sequence instantaneous real power {p,J.
instantaneous real power (fJuJJ and instantaneous imaginary power (C/u1J.
(2)
Finally allows the expression or current as a function of power quantities
[
ia - - -iol
1｛ｖｾｰ＠
0 ip - ｖ Ｐ ｖｾｰ＠ Q0
(3)
Where; ｶｾｰ＠
=
ｶｾＫｶｦｦ＠On the other hand, the modified p-q formulation defines the instantaneous real power {p,J and instantaneous reactive power vector (q) as follmvs;
Pu= V0i0
+
Vaia+ Vpip
(j(t)
=
v
xi=
[qo qa qpy ( '1-)fl assume that the three instantaneous imaginary power q,,(t). q"(I). q1,(t) are not independent, where; v0q0
+
Vaqa+
Vpqp=
0.｛
ｾＺ｝＠
=
ｾ＠
｛ｾＺ＠ Ｍｾｰ＠
vt
-vO:a]
[:qq:P]
(5)
ip Vo-a-{J Vp Va -V0
Where; ｶｾＭ｡Ｍｰ＠
=
vJ+
ｶｾ＠+
vff (6) B. d-q TransformationThe transformation of d-q uses matrix
f
P] with O(t)OJI as the phase current transformation. For this case, OJ
represent the voltage fundamental wave pulsation. d-q formulation only works in the instantaneous active current id and instantaneous imaginary current iq. Park transformation is used to transform the supply current into stationary coordinate.
[
cos81 (t) [P] =
ft
-sin:1 (t)../2
cos82(t)
-sin82(t)
1
../2
C. p-q-r Form11/atio11
In this formula, current are translated from p-q-r coordinates by means or the following:
Vo Va Vp
r·1 ,
0 _ Vo-a-{J Vo-a-/3[i;
l
iq = - - - Vap Vap
ir. Vo-a-{3 Vo Va _ V0Vp Va{J
Vap Vap
D. Vectorial Form11/atio11
(7)
0-a.-[J to
(8)
The technique docs not need to undergo any transformation. Same power variable as original theory arc define in instantaneous imaginary power
q
(I) in phase coordinates.q(t)
=
vqi
=
ｾ＠ ｲｾＺ＠
=
::1
｛ｾＺ｝＠
=
Ciap(t)v3 .Va - Vb .. le
(9)
The equation that determines the currents are as follows;
｛
ｾＺＱ＠
=
p2ｲｾＺＱ＠
+
2.
ｰｾ＠ ｲｾＺＱ＠
+
2.
q2ｲｾＺ＠
=
::1
; V V .,/3 Vo V
.J3
V V - VJ'-C C 0 . a J.
(10)
111. SWITCHING TECHNIQUE
Switching technique can be divided into two categories: current control and voltage control. Carrier and hysteresis fall under current control while space vector fall under voltage control category. Briefly explanations of the switching techniques explain in the subsequence.
A. Carrier C11rre111 C'omrol
This method used to generate two switching function consists of positive and negative cycle or PWM as shown in Figure 2. The pulses arc the result of intersection between the error signals with f'requency of carrier signal. Furthermore, the switching fi·equency is also the carrier operating frequency. This method used in current control loop to force the actual current according to the reference.
[image:3.595.306.527.317.434.2]V(l)
B. Hysteresis Currelll Control
The earliest and most commonly proposed time-domain corrective technique is the hysteresis method [19, 20].
Preset upper and lower tolerance limits are compared to extracted error signal. No switching action is taken as long as the error is within the tolerance band. Switching action occurs when the errors leaves the tolerance band. These technique yields instantaneous and fast response controller
[21). The conditions of switching devices are tabulated below:
Switch Hysteresis Band (HB) Lower switch on ircr - iac1 < -1-!B
Upper switch on iref - i:ict > HB
[image:4.598.308.529.81.672.2]Switching Pattern
Figure 3. Mysteresis Method
C. Space Vector Modular ion
Space Vector Modulation has been widely use in APF system. This method have an advantages over carrier based such as lower Total harmonics Distortion (TI-ID), higher etriciency easier digital implementation and wider linear modulation range [22]. It is shown that in the linear range modulation. the index modulation wi II goes high and reduce the inverter DC link voltage in APF [23]. In implementation of SVM technique, there are TWO (2) rules that must be followed. First rule, each leg have two switches that cannot gated at the same time and at lease one switch must be turn "ON" due to the system inductance.
IV. MODELLING APF SYSTEM IN THREE-WIRE SYSTEM
To carry out the comparative analysis among live compensation strategies with different types of signal generations, a simulation platform has been design. Figure 4(a) shows the simulation scheme with control system for the APF in three-phase three-wire system. The non-linear load was constructed using lull bridge rectilier connected in parallel with a resistor and a capacitor as the load. AC link inductors use to attenuate the switching ripple hence prevent high harmonics switching frequency. In Figure 4 (b), (c) and (d) shows the harmonics detection algorithm for p-q. d-q and vectorial. While modified p-q and p-q-r
block diagram are based on p-q algorithm block with additional transformation needed. In the system low pass
filter used to obtain the ac components that arise due lo the harmonics ofthe load current.
L,
l.
(a)
IRPT Algorilhm for p·q
poss
filter
(b)
IRPT Algorithm for d-q
(c)
IRPT Algorilhm for vcc10rial
(d)
Figure 4. APF schematic diagram;
(a) Shunt APF layout scheme
(b) Block diagram of IRl'T algorithm for p-q
(c) 131ock diagram of IRPT algorithm for d-q
o,
o,
Tllree-Phase RecJifier
v..,_
(d) Block diagram or I RPT algorithm for rec/oriaf
[image:4.598.57.296.95.357.2]V. SIMULATION RESULT
This section presents the general simulation block diagram of' the shunt APF in MLS environment in Figure 5, while the simulation parameters are tabulated in Table 11.
·I
·l
:1 [image:5.597.303.526.101.172.2]l'igure S. Si111u!ation diagram of shunt API' in MLS environment
Table II
Simulation parameters of the APF
P;munctcl's Vnluc
Voltage Source 311 Vims
DC li11k Voltage (I·;") ./OOV
DC link capacilor, C fOOOµF
Non-linear Load !? ; fkD., C; /WOµF
load l11d11ctors (l1) /1111-/
Fi/Jer /11d11ctor (l1) 5111/1
2"' orda Bu1te111·or1'1ji/1er 201-1::
ln the simulation studies, the switching f'requency is set 20kHz for carrier and SYPWM. while the hysteresis band is set I 0% of the maximum current injected. Total harmonic distortion (THD) rrom the simulations was found achieve the standard l EEE 519 standard from each algorithm. Even though, the THD result different rrom each algorithm, however the waveforms show otherwise. Figure 6 and 7 shows the waveform or supply current after the compensation with different algorithm and switching generation. Whilst, the (phase b) corrected supply current, compensation current and load current shown in Figure 8. All results from the simulation are tabulated in Table llf.
Table Ill
THO AFTER THE COMPENSATIONS WITH SWITC'H!NG FREQUENCY
20kl-lz
After Compensntion Carrier Signnl {%THD) (%TllD) SVPWM
/Hf 4.79 2.43
Modified p-q 4.71 2.38
tl-q 4.81 2.40
p-q-r 4.78 2.20
Vectorial 4.80 2.35
THO AFTER THEC'OMPENSATtONS WITH 10%0F IWSTERESIS BAND
After Com11ensation llysteresis (%Tl!D)
/I-ff 2.50
i\fod ificd p-q 2.42
d-q 2.49
11-11-r 2.31
Vectorial 2.41
[image:5.597.64.288.164.298.2] [image:5.597.305.531.210.656.2]It clearly shown that in Table llL SVPWM offers the best reduction of harmonics compares to others switching techniques. High percentage of distortion exist in d-q algorithm when apply the carrier signal which effect the overall power is shown in Figure 7. On the other hands, Figure 8 shows the besl reduction or THD when applying SVPWM in p-q-r algorithm.
ｾ＠
:;
: l
Figure 6. Supply current a Iler compensation using carrier signal
·'·
Figure 7, Supply current aller compensation using SVPWM
'
•·I
ｾＭＭ
:vv\:- ·.·
h·-/\;'\\ · -,,
ｉｖｾ｜＠
--
ｾ［ｾＧ｜｜＠
.11:
d
V1JV
\Jl.,_il
'VJ·
VJ ,
'· ···--·· ·- t . . . 1 . -.· - -· .!- - -- - - --.1
' ·• , . , ·..;1 ,... <I, • ' I
•I f ｾ＠ i' ｾ＠
--- ｾ＠-·, 1 ｾＭＭ L --.,;f' •.
·! i: l,
Figure 8. Supply. comre11satio11 and load current a Iler compensation
Vl. CONCLUSION
[image:5.597.63.287.346.446.2]hysteresis and S VPWM for three-phase three-wire active shunt active power tilter system. From the simulation results, it can be concluded that all the control strategies combine with different types of switching techniques passed the Tl-ID requirement of IEEE 519 standard, which SVPWM switching techniques offer the best switching generation compares to another two techniques in terms of
Tl-ID and switching control.
[I J
f2] [3) [4] (5] [6] (7) [8) (9] [10] (llJ {12J [13J [14] (15)
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