201O 2nd International Conference on Mechanical and Electronics Engineering (ICMEE 2010)
Computer Implemented Model of Single Switched Single-Phase Parallel Active Power Filter
R. Baharom, M. K. Hamzah, N.R. Hamzah & N.F. Nik Ismail
A.S. Abu Hasim Faculty of Electrical Engineering Universiti Pertahanan Nasional Malaysia, 57000 Kuala Lumpur, Malaysia
Faculty of Electrical Engineering Universiti Teknologi MARA Malaysia 40450 Shah Alam, Selangor, Malaysia
[email protected]
Abstract-This paper is concerned on a parallel active power filter for harmonic compensation of a single-phase system feeding non-linear load.
An active current wave-shaping
technique is proposed to mitigate the distortion current by injecting equal but opposite current to shape the pulsating nature of the supply current to a sinusoidal form and in-time phase with the supply voltage. In the proposed work only one power switch is employed to minimize cost, reduce switching stress and losses. The behaviour and operation of the proposed filter structure was examined through computer simulation.
Keywords- Active Power
Filter;
Rectifier;
Pulse
Width
Modulation; Boost Circuit.
I.
could however be extended into multiphase systems in the future. This work propose a new parallel connected active power filter topology using bridge-rectifier circuit incorporating boost technique with reduced number of switches for implementation. The supply current is targeted with an almost sinusoidal and in-phase with the supply voltage that could lead to satisfY IEEE 519 using simple control algorithm. A standard proportional integral (PI) control was also employed to implement active pulse width modulation (APWM) for control of boost rectifier used for APF function. Selected simulation results are presented. II.
INTRODUCTION
A typical power electronic system is normally used as an interface between a load and supply comprising a power converter, a load/source, a control unit and can be generally classified in terms of basic functions, namely; AC-AC conversion, AC-DC conversion (rectifier), DC-DC conversion and DC-AC conversion. Amongst all of these types single-phase power electronics converter, AC-DC converter (rectifier) is by far the widest in applications ranging from industrial drives to low-powered portable equipments [1, 2, 3]. The use of these converters; using power switching devices inadvertently results with a non sinusoidal current being drawn from the supply, containing harmful harmonic components which are then fed back to the supply system creating various problems. As a result, several standards such as IEEE 519 have been developed to limit damages with solutions of power quality problems and there have been considerable interests in developments of solutions in various forms. One of the most common methods to suppress the harmonics is by using passive filter; with many drawbacks that includes; their inability to compensate random frequency variations in the current with associated tuning and parallel resonance problems. To improve, converter based solutions; called active power filter (APF) are proposed in various configurations. For a more complete solution; hybrid arrangements are more comprehensive with digital techniques at the heart of their control that is both compact and simple. Many researchers have focused on the single-phase topology due to its widespread use; which will be the focus of this paper. It
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ACTIVE POWER FILTER
A typical single phase diode bridge rectifier circuit with APF function using boost technique which is employed a single switch is as shown in Figure 1, with three major components; a) diode bridge rectifier circuit, b) boost inductor and c) current control loop (CCL) connected to a switch as shown in Figure 2. A non-linear load is represented by a resistor shunted by a capacitor. Basic boost rectifier equivalent circuit during charging and discharging is illustrated as shown in Figure 3 and 4. An active power filter is designed to maintain a sinusoidal input current through proper control. Compensation current is injected into the system to improve the supply current waveform into a form that is continuous, sinusoidal and in phase (near unity power factor) with the supply voltage; illustrated as in Figure 5. III.
BOOST RECTIFIER CIRCUIT
Implementation of active power filter function is to force the supply current to follow the reference current (desired signal). The rectifier is controlled to have a sinusoidal line current with high power factor through compensation algorithm. This is designed in the CCL that generates active pulse width modulation (APWM) for boost technique control used for APF function; facilitated by observing the supply current waveform and making corrections using current compensation techniques. The CCL (Figure 7) has three elements; a) Subtractor, b) Proportional Integral (PI) controller and c) PWM generator. The supply current waveform is subtracted (using subtractor) from reference current; the resultant error represents the modulation signal
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that is used to control the charging and discharging of the inductor as a current source for compensation purposes. IV.
(1)
PROPOSED ACTIVE POWER FILTER
The APF circuit consists of a main supply connected to a non-linear load as shown in Figure 5. RC parallel circuit connected to a single-phase rectifier circuit represents the non-linear load while the inductor represents a simple input filter. The proposed APF is placed across the main supply just before the filter. It can be clearly seen that the APF is in parallel with the non-linear load and the passive filter forming a PAPF comprising a control loop and a compensating circuit. The compensating circuit, in turn, consists of a circuit whose components are similar to that of the non-linear load but with the addition of one active power switching device (IGBT) is used. Note that the employment of only one active power switching device enables to simplifY the compensation scheme and contributes to low switch stress and losses. The IGBT is controlled by the control loop, which consists of a peak detector and a Supply Current Control Loop (SCCL). The peak detector is connected to a point just after the main supply terminal before the APF and the load. The components in the SCCL are as shown in Figure 7. The PWM technique is used to synthesize the injected current (see Figure 6). The controlling output of the SCCL provides gating signals to the IGBT, which in tum, provides the switching functions to compensate the distorted supply current into a sinusoidal form. V.
the mains voltage is a pure sine-wave. It can be represented as;
iL(t)= � )n sin (nllX+Bn )
(2)
iL (t) = I I sin (ax + BI ) + L In sin (nllX + Bn )
(3)
n =l
n=2
(4)
iL (t) = ILp sin (aJI) + I Lq cos (aJI) + LIn sin (naJI + B. } n iF{t)
=
Iif sin {ax ) - ILp sin {ax ) - ILq cos{ax ) -
I/n n=2 sin{nax+0)
iAt)=-ILqcos{ax)-i)nsi n=2 n{nax+O)
(6) (7) (8)
where,
ILp = ILl cosBI realpartof iLl(t) I Lq = I Ll sin BI;reactive part of iLl (t)
�)n n=2 sin{nax+On );distortion component
: peak source voltage : angular frequency of the fundamental � : phase of the nth order harmonic of the load current
vp (0
OPERATION OF ACTIVE POWER FILTER
The proposed APF injects the required current into the system. When switch is turned on, diode D is reversed biased thus the output stage is isolated as in Figure 8(a). The input supplies the energy to the inductor, L, causes inductor current to linearly increase. The energy stored in the inductor can be used for compensation purposes. When the switch is turned off, as shown in the equivalent circuit of Figure 8(b), there exists a change in current. Since the current in the inductor cannot change instantaneously, voltage in the inductor reverses its polarity in an attempt to maintain constant current. At this stage, the current will flow through the inductor L, diode D, and the reactive component (RC) in the APF. Control is required in the design such that the inductor does not completely discharge the energy so that some residual energy remains in the inductor. Thus; when the power switch is turned on, the current ramp rides on a pedestal with a magnitude proportional to the residual energy in the core. Energy stored in the inductor is then used for charging the output capacitor and hence energy is transferred. Due to this requirement in operation, the boost voltage VL must always be greater than the DC supply voltage VS since the APF is intended to inject an opposite reactive current into the system. VI.
(5)
=2
THEORETICAL TREATMENT
Detailed analysis of Boost Rectifier operation [12] is restated mathematically here for completeness assuming that
VII.
PWM TECHNIQUE AND CONTROL
Of the many PWM strategies available, the sinusoidal PWM method is proposed for this work. To compensate for random variations in the waveform active pulse width modulation (APWM) technique [1] is proposed. The APWM operates by comparing the error signal that was used to determine a new magnitude with the carrier signal to produce the required PWM control. This is done by changing the modulation ratio of the PWM (defined as the amplitude ratio of the modulating signal to the carrier signal); thus changing the width of pulse in accordance to the error detected. The higher the switching capacity of the converter circuit, the more harmonics components that could be injected thus cancelling the distortion components in the supply current. A proportional integral (PI) control algorithm is used to regulate the error. VIII. SIMULATION MODEL Using Figure 5, the proposed system is simulated as shown using MATLAB/Simulink model of Figure 9; showing the model of parallel active filter connected to the non-linear load and Figure 10 the model of the compensating circuit. Initially a bridge-rectifier is investigated to determine the extent of distortion without APF. This is then followed by
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implementation APF function. The rectifier was supplied by 40 V (pk-pk) voltage source to a 3000 pure resistive load with an output DC capacitor filter of 1000 JlF. IX.
RESULTS AND DISCUSSION
Figures 11 through 13 were selected results obtained from simulations, illustrating the pulsating supply current and the final corrected current as a result of employing the proposed APF. Observe that Figure 11 shows that the current is leading the voltage supply indicating capacitive load. The APF provides current injection for correction as shown in Figure 12. These results with improvements to the input current waveform as shown in Figure 13; in-phase current are observed. Analysis of the waveform as shown in Figures 14 through 16 found the total harmonic distortion (THD) is approximately at 150.32% with a power factor of 0.59 leading. When subjected to compensation, the waveform is now continuous, almost sinusoidal and in phase with the supply voltage. The THD level is reduced to 4.20 % with almost unity power factor operation achieved. X.
CONCLUSION
The paper presented has shown that the use of single switch topology for PAPF is sufficient to reduce the input current distortions and achieve unity power factor operation in a single-phase capacitor filtered bridge-rectifier system. This is done by injecting equal but opposite current to shape the pUlsating supply current into a sinusoidal form with almost unity power factor which could lead to designs that could comply standard harmonic requirements as specified by IEEE 519. ACKNOWLEDGMENT
Financial support from Ministry of Higher Education (MoRE) Malaysia FRGS Grant No: 600-RMVSTIFRGS 5/3/Fst (130/2010) is gratefully acknowledged for implementation of this project. Financial assistance of
Universiti Teknologi acknowledged.
MARA
Malaysia is also gratefully
REFERENCES [I]
R Akagi "Active harmonics filters", Proceedings of the lEE, VoL93, No.l2, Dec. 2005, pg 2128
[2]
F.Z. Peng, R Akagi, "A new approach to harmonics compensation in power system - A combine system of shunt passive and series active filters", lEE Transactions on Industry Application, VoL26, No.6, NovlDec 1990.
[3]
H. Rudnick, 1. Dixon and L. Moran, "Active power filters as a solution to power quality problems in distribution networks", IEEE Power and Energy Magazine, Sept/Oct 2003
[4]
F.z. Peng, "Application issues of active power filters", IEEE Industry Applications Magazine, Sept/Oct 1998.
[5]
R Akagi, "New trends in active filters for power conditioning", IEEE Transactions on Industry Applications, VoL32, No.6, NovlDec 1996, pp. 1312
[6]
John C. Salmon, "Technique for minimizing the input current distortion of current-controlled single phase boost rectifier", lEE Transaction on Power Electronics. VoL8.NoA. October 1993
[7]
R. Blundell, L. Kupka, S. Spiteri, "AC-DC converter with unity power factor and minimum harmonic content of line current: design considerations", lEE Proc.-Electr. Power AppJ., VoL 145, No.6, November 1998
[8]
Zhaoan Wang, Qun Wang, Weizheng Yao And Jinjun Liu, "A series active power filter (APF adopting hybrid control approach)", IEEE Transactions On Power Electronics, VoL 16, No. 3, May 2001
[9]
RS. Athab and PK Shadhu Khan, "Single-Switch Single-Phase Boost Power Factor Correction with Harmonics Current Reduction", 1st IEEE International Power and Energy Conference, PECon '06, 28-29 Nov. 2006, pp. 447-452
[10] Y. Hayashi, N. Satao and K. Takahashi, "A Novel Control of a Current-Source Active Filter for AC Power System Harmonics Compensation", IEEE Trans. Indus. App. , VoU7, Issue 2, Page(s):380-385, March/April 1997 [II] Faridz, A.; Ghafar, A.; Fadzil Saidon, M.; "Simulation Evaluations of a Single-phase Half-bridge Active Power Filter Employing Fuzzy Logic Control", IEEE International Conference on Power Electronics and Drives Systems, 2005. PEDS 2005. Volume 2, 28-01 Nov. 2005 Page(s):1019 - 1023 [12] K. Chatterjee, B. G. Fernandes and G. K. Dubey, "An Instantaneous Reactive Volt-Ampere Compensator and Harmonic Suppressor System", IEEE Trans. On Power Electronics, VoL14, No.2, March 1999, pp.381-392
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Figure 2. Diode bridge rectifier with current control loop
Figure I. Rectifier boost converter circuit
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1 Figure 4. Equivalent circuit during turn 'OFF'
Figure 3. Equivalent circuit during turn 'ON' Non.linear Load
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Figure 5. Proposed APF System
Figure 7. Layout of supply current control loop (SCCL)
is(l)
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idl)
(b)
Figure 8. Equivalent circuit of the system when (a) switch is "ON" (b) switch is "OFF"
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2010 2nd International Conference on Mechanical and Electronics Engineering (ICMEE 2010)
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Figure II. Supply Voltage and Current of Non-linear Loads
Figure 12. Supply, Injection and Load current Fundamental (50Hz)
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Figure 14, Harmonics spectrum after Compensation
THO Spectrum
THO Spectrum
120
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100 80
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- Standard
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Number of Harmonics
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Figure 15. THD spectrum of Non-linear Load Current
Figure 16. THD spectrum after APF Implementation
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