JECET, June – August-2013; Vol.2.No.3, 558-566.
Journal of Environmental Science, Computer Science and Engineering & Technology
An International Peer Review E-3 Journal of Sciences and Technology
Available online at www.jecet.org Engineering & Technology
Research Article
JECET, June – August 2013; Vol.2.No.3, 558-566. 558
The Novel Approach of Matrix Converter Based Shunt Active Filter for Harmonic Load
Valsala.G. L*, Padma Suresh.L,
Electrical and Electronics Engineering, Noorul Islam University, Tamilnadu, India.
Received: 24 May 2013; Revised: 20 June 2013; Accepted: 24 June 2013
Abstract
:
This paper proposed a new shunt active filter, which based on a matrix converter without energy storage devices, to mitigate the current harmonics. By connecting the matrix converter output terminals to the load side, and the input side of matrix converter connected to a step up transformer to the supply side. Therefore, a matrix converter injects the compensation current point of common coupling, resulting in an efficient solution for mitigating current harmonics. Thus, the proposed topology has the ability to mitigate the current harmonics without energy storage elements. The space-vector modulation (SVM) used to control the matrix converter.Matlab/simulink based simulation results presented to validate the approach.
Key words: Matrix Converter, Shunt Active Filter, Harmonic Load, step-up transformer Matlab/Simulink
INTRODUCTION
Harmonic current pollution of three-phase electrical power systems is becoming a serious problem due to the wide use of nonlinear loads, such as diode or thyristor rectifiers and a vast variety of power electronics based appliances. Traditionally, passive LC filters have been used to eliminate the current harmonics and to improve the power factor. However, passive LC filters are bulky, load dependent
JECET, June – August 2013; Vol.2.No.3, 558-566. 559 and inflexible. They can also cause resonance problems to the system. The main currents after compensation are in phase with the supply voltages and can be expressed as shunt passive filters have following problems.
(i) The source impedance, which is not accurately known and varies with the system configuration, strongly influences filtering characteristics of the shunt passive filter.
(ii) Shunt passive filter may fall in series resonance with source impedance for harmonic voltages in source voltage.
Fig.1: Basic structure of active filter
(iii) There is a possibility of parallel resonance between source impedance and shunt passive Filter at a specific frequency at which even harmonic amplification may take place
In order to solve these problems, APFs have been reported and considered as a possible solution for reducing current harmonics and improving the power factor.
A
ctive power filters have being developed since 1983 . Since then, almost all controllers, developed by the authors, for active power line conditioners and FACTS controllers use the pq Theory, Lada et al1,. and expanded for three-phase four-wire systems in Gonda et al,2.. On the other hand, several works on active filter controllers based on synchronous reference frame transformation to pq TheoryDa Silva et al.3ANN based controllers Bhattacharyaet al. 4 and fuzzy control Gupta et al. 5 are developed.PWM techniques are use to drive the shunt active filter. The two most widely used PWM schemes for multilevel inverters are the carrier based sine-triangle PWM (SPWM) technique and the space vector PWM (SVPWM) technique.
Fig. 2: Fundamental representation of shunt active filter
JECET, June – August 2013; Vol.2.No.3, 558-566. 560 Drawback of active filter is the DC bus capacitor must be designed .it achieve two goals, i.e., to comply with the minimum ripple requirement of the dc bus voltage and to limit the DC bus voltage variation during load transients. To solve the preceding problems of shunt passive filters, shunt active filters using PWM inverters have been used in recent years. A shunt active filter is controlled in such a way so as to actively shape the source current into sinusoid by injecting the compensating current.
Figure 2 above shows the fundamental working principle of a shunt active filter. Zs is the source impedance, Iaf is the shunt active filter current, ILh is the load current, Vs is his supply voltage.
Difficulty in realizing a large rated PWM current source inverter, high initial cost & low efficiency as compared to shunt passive filters. Possibility of importing harmonics from other harmonic producing loads are the serious practical problems with the use of shunt active filters. Due to switching loss, capacitor leakage current, etc., the distribution source must provide not only the active power required by the load but also the additional power required by the VSI to maintain the DC-bus voltage constant. Unless these losses are regulated, the DC-bus voltage will drop steadily .Moreover VSC based converter produces more harmonics and switching losses high.
MATRIX CONVERTER
Fig. 3: Basic structure of matrix converter
Matrix converter was initially introduced as an AC Driver, due to its advantages may be used in voltage compensation applications.
Fig 4: Proposed shunt active filter
JECET, June – August 2013; Vol.2.No.3, 558-566. 561 The matrix converter has several advantages listed below:
• Sinusoidal input and output current waveforms with small distortion,
• Adjustable input power factor regardless of the load, generally with unity power factor,
• Bilateral transformation of energy,
• Elimination of energy storage components,
• high-efficiency and fast-response,
• Reduction of installation area and integration of more complex silicon structures in power modules,
• higher controllability,
• the number of phases on input and output sides are independent of each other,
• The waveform and the frequency on both sides are independent of each other,
• A matrix converter can reproduce any waveform without using any additional power hardware,
• It can be used as a full four-quadrant power supply without any additional power hardware,
• Elimination of temperature sensitive electrolytic dc-link capacitors, which results in higher reliability and higher operating temperature. a space vector modulation strategy which permits zero current commutation is employed to provide sinusoidal input and output currents for the Matrix Converter .
• Indirect matrix converter is used for active filtering purpose Ali Aghabeigi Heris et al,. (2012).but the drawback of indirect matrix converter is consist of high power transistor required.
PROPOSED SHUNT ACTIVE FILTER
In this paper proposes a matrix converter based shunt active filter instead of VSC based converter.
The proposed shunt active filter is designed using matrix converter is shown in figure4. Zsabc are the source impedance, labc is the smoothing inductor. Cf(abc) is the smoothing capacitor .one step up transformer is used for step up the matrix converter input voltage. So the matrix converter injects the significant current to PCC.
Fig. 5: proposed per phase equivalent diagram of the system
JECET, June – August 2013; Vol.2.No.3, 558-566. 562 In this paper, the step up transformer was simply modeled by a current source and the focus was put on the control of the input current for the active filtering function. Because matrix converter transfer ratio is limited to 0.876. The steps up transformer boost the voltage and increase the current flow for the filtering purpose. The two cascaded control loops used for control strategy. The inner loop controls the capacitor voltage, vc, and provides the current reference i’mc to the modulation block of the matrix converter. The outer loop controls the current, imc, injected into the grid at the PCC and provides the capacitor voltage vc reference to the inner loop.
CONTROL SYSTEM
The output terminal voltage and input terminal current of matrix converter consider the low frequency transformation function (1) and set a sinusoidal input voltage, as follows:
+ +
− +
+
=
) 3 / 2 cos(
) 3 / 2 cos(
) cos(
0 0
0 0
0 0
π α ω
π α ω
α ω t t
t V
vabc i (1)
+ +
− +
+
=
− +
=
=
) 3 / 2 cos(
) 3 / 2 cos(
) cos(
) ) 1 ( (
0 0
0 0
0 0
2 1
π α ω
π α ω
α ω t t
t qV
v D a aD v
D v
i
abc abc
ABC (2)
Where φ is the output (or load) angle. Using equation (2), the MC output currents can be written as follows:
{
+ +
− +
+
− +
+ +
− +
+
− =
=
) 3 / 2 cos(
) 3 / 2 cos(
) cos(
) 1 ( ) 3 / 2 cos(
) 3 / 2 cos(
) cos(
π ϕ ω
π ϕ ω
ϕ ω π
ϕ ω
π ϕ ω
ϕ ω
o i
o i
o i
o i
o i
i i ABC o
T abc
t t
t a
t t
t a qI i D i
(3)
Assume the desired input current to be
+ + +
− + +
+ +
=
) 3 / 2 cos(
) 3 / 2 cos(
) cos(
0 0 0
0 0 0
0 0 0
π ϕ α ω
π ϕ α ω
ϕ α ω t t
t I
iABC o
(4)
Where
ϕ
i is the input displacement angle.
+ + +
− + +
+ +
=
) 3 / 2 cos(
) 3 / 2 cos(
) cos(
π ϕ α ω
π ϕ α ω
ϕ α ω
i i i
i i i
i i i
abc i
t t
t I
i
(5)
Reference current generation: The load current is measured and transformed from the fixed abc- reference frame to the rotating dq-reference frame using relation (6) and the angle of the voltage at the Point of Common Coupling (PCC)
.
+
−
+
−
=
c b a
q d
i i i i
i
3) sin( 2 3) sin( 2 sin
3) cos( 2 3) cos( 2 cos 3 2
θ π θ π
θ
θ π θ π
θ (6)
Since the rotating dq-reference frame is based on the angle of the voltage at the PCC, the d and q load current components represent respectively the active and reactive components of the load current. The control objective is to compensate all the load current components except for the fundamental active
JECET, June – August 2013; Vol.2.No.3, 558-566. 563 load current component. Therefore, a High Pass Filter (HPF) is introduced to filter out the fundamental component of the active current. Only the harmonic and reactive components remain in the current reference. The active current that is produced by the transformer also needs to be added to the active current reference as the matrix converter. Finally are obtained the references d* mc, q * mc
and which are provided to the outer current control loop. All entities marked with asterisk are reference values as opposed to real/measured values.
Current control: The previous sections explained calculate the current references. To control the current we use eq. (7)
c pcc mc
f i v v
dt
L d = − (7)
When eq. (8) is converted into the rotating dq-reference frame, cross-coupling terms appear as shown in eq. (9) which must be compensated. When transforming to the rotating dq reference frame again cross coupling terms appear
−
−
−
=
−
−
d c
q c f q
mc d mc q mc
d mc q
c d c
f v
C v i
i i
i v
v dt C d
, , ,
, ,
,
'
' ω (8)
−
−
−
=
−
−
d mc
q mc f q c
d pcc c
q mc
d mc
f i
L i v
v v i
i dt L d
, , ,
,
0 ω (9)
Table- 1: Simulation parameter
Parameter value
vsource 440v
Ls 2mh
Pnon liner load 20kW
Lf 0.5mh
cf 20uf
Switching frequency 20kHz
Step up transformer 440/600v
SIMULATION RESULTS
Result for VSC based converter harmonic: in this work, three-phase matrix converter based shunt active filter is used to compensate the current harmonics. The source voltage is 440Vrms, 60Hz. Table 1 shows the proposed system main parameters. It includes source impedance parameters L and C values for passive branches used. The system has been simulated without filter, existing shunt active filter and the proposed matrix converter based active filter separately. In simulation studies, the results are specified before and after applying the matrix converter based active filter. In addition, the values for Total Harmonic Distortion before compensation and after compensation using without filter, existing shunt active filter and the proposed matrix converter filter are given .all the simulation is performed by the matlab simulink model in discrete form. The sample time of the discrete value is 3x10-4sec.figure 6 shows the total harmonic distortion of VSC based converter. Figure 6.a shows the
JECET, June – August 2013; Vol.2.No.3, 558-566. 564 voltage source converter, s output voltage. Figure 6(b) shows that its total harmonic distortion. It clearly displayed the total harmonics distortion is more than 100 %.
Fig. 6: Total harmonic distortion of VSC based converter
Result for matrix converter harmonic: Figure 6 shows the matrix converter output voltage and its harmonics. The matrix converter produces lower % of harmonic as shown in figure7(a)and its corresponding matrix converter voltage is show in figure 7(b).so the matrix converter produces the les harmonic compared the voltage source converters
Fig. 7: matrix converters and its total harmonics distortion (a) total harmonic distortion in % (b) matrix converter output voltage
Result For without shunt active filter compensation:
Fig. 8: Current harmonics and its THD
JECET, June – August 2013; Vol.2.No.3, 558-566. 565 (a) Supply voltage (b) supply current without compensation (c) total harmonics distortion of supply current Figure 8 shows the current harmonics and its total harmonics distortion. Figure 8. (a) Shows the supply voltage. The voltage is 440v.figure 8(b) shows the load current. At 0.25 sec the current is increases due to additional load. So the amplitude of current goes to increases. The figure 8.c shows the total harmonics of current. Here the value of THD is 30%.
Result For with conventional shunt active filter based compensation: Figure. 9 show the current harmonics mitigation using conventional shunt active filter. Figure 9(a) shows the supply voltage. It sinusoidal. The magnitude of supply voltage is 400 volts. Figure 9.(b)shows the supply current after compensation. This wave form also sinusoidal but it contains harmonics. Figure 9. (c) Shows the total harmonics distortion is 5%.the simulation time start 0.2sec to e.6 sec .the load s increased at 0.275bsec the harmonic level is increases, because of the shunt active filer capacitor.
Fig. 9: conventional shunt active filters based compensation; (a) Supply voltage (b) supply current after compensation (c) total harmonics distortion of supply current
Result For matrix converter based shunt active filter based compensation: Figure 10 shows the matrix converter based shunt active filter to mitigate the current harmonics efficiently compared to conventional technique. Figure 10. (a) Shows the supply voltage and the wave form is sinusoidal.figure10.(b)shows the wave form of current after proposed compensation. The wave for also sinusoidal and the harmonic content is Low/.figure 10. (c) Shows the total harmonic distortion level. The total harmonic distortion is 2% only. It is clear from figure 10.(c) that the current injected by the matrix converter compensates the harmonics of the nonlinear load.
The THD of the source current is reduced from 0% to 2%.
Fig.10: proposed matrix converter controlled shunt active filter based compensation(a) Supply voltage (b) supply current after proposed compensation (c) total harmonics distortion of supply
current
JECET, June – August 2013; Vol.2.No.3, 558-566. 566 Corresponding Author
:
Valsala.G. LElectrical and Electronics Engineering, Noorul Islam University, Tamilnadu , India CONCLUSION
In this paper was investigated the use of matrix converter based shunt active filtering. This paper analyzed the matrix converter and conventional voltage source converter based active filter and found that matrix converter produces less harmonics compared voltage source converter. Based on the simulation results the matrix converter based shunt active filter mitigates the current harmonics efficiently with low total harmonic distortion. The matrix converter proved to be efficient for active filtering purposes compared to conventional voltage source converter
REFERENCES
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2. J.M.Gonda,V.A. Adithya,S.S. David,. “Performance analysis of compensation current extraction techniques for 3Ф, 3-wire shunt active power filter under unbalanced supply”
International Conference on Power Systems, 2009, 1 – 6.
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