Hybrid Filter System for Optimum Performance of Harmonics Mitigation Process

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1 Jurnal Elektro ELTEK Vol. 1, No. 2, 2010 IN: Hybrid ilter ystem for Optimum Performance of Harmonics Mitigation Process Awan Uji Krismanto and Yusuf Ismail Nakhoda Department of Electrical Engineering, Institut Teknologi Nasional Malang Abstract onventional passive filter was the most compensator used to overcome harmonics problem. Unfortunately, stand alone passive filter has some drawback related to resonance and antiresonance phenomena. Hybrid system filtering involves unt passive filter and series active power filter configuration proposed due to improve performance of stand alone passive filter. The proposed system yield better performance for harmonics mitigation process, THD value, increase efficiency and loading capacity hence the installation cost will decrease. PAD/ EMTD simulation employed to verify the performance of hybrid system filter. Keywords Harmonics, passive filter, hybrid, THD I. INTRODUTION Harmonics become a serious problem in power system since the significant increase usage of nonlinear load such as power electronic equipment for voltage and current conversion, motor drives, switching power supplies and other electronics devices. The main concern of harmonics effects are the appearance of voltage and current distortion waveform. These cause development of oscillation torque phenomena in electric motor, excessive heating and losses in transmission line and degradation of power quality. Many compensators have been proposed to overcome harmonics problem. Passive filter was the most compensator used for harmonics mitigation purpose. Unfortunately, passive filter has several drawback related to variation of impedance system. irst problem is that passive filter only tuned for specific harmonics source hence harmonics component coming from other sources would distort the voltage source waveform[1]. The second problem is anti resonance that appears between the source impedance and passive filter impedance producing harmonics amplifying phenomenon. To overcome this problem, hybrid filter method was proposed. Hybrid filter consist of unt and series filter installed to the grid. The main purpose of hybrid active filters is to reduce initial costs and to improve efficiency[2]. They are also used to improve the compensation characteristics of passive filters and alleviate any series or parallel resonance due to supply or load respectively. Practically, more viable and cost effective hybrid filter topologies have been developed than stand-alone active filters. They enable the use of significantly small rating active filters that is less than 5% of the load KVA compared to stand-alone parallel (25-30%) or series active filter solutions. High initial running cost and complexity are major drawbacks of this active harmonic filtering technique. This paper present hybrid filter modeling which consist of series active power filter combined with unt passive filter. ontrol of series active filter performed based on instantaneous p-q theory. Passive filter tuned for 5 th and 7 th order harmonics component. PAD/ EMTD used to verify performance of hybrid filter. II. BAI THEORY A. Hybrid ystem igure 1 ows a configuration diagram of a combined series active filter and unt passive filter[1]. The nonlinear load modeled by a thyristor rectifier. The unt passive filters consist of a 5 th and 7 th order harmonics filters, plus a high pass filter. Twelve IGBT switching devices, built three single phase voltage source inverters (VI), connected in series in each phase through a current transformer. This configuration compose series active power filter (AP). A PWM control block is designed so that the ac output voltage of the VI follows the references that are calculated by control block based on instantaneous p-q theory. V Ls VT Gain K + Vc - eries Active ilter PWM ontrol ircuit v* i is p q alculation of i i il 5 th 7 th High pass High Pass ilter G(s) hunt Passive ilter va vb vc Non Linear Load ps qs alculation of ps and qs isa isb isc igure 1. Hybrid ilter ystem onsist of eries Active ilter and hunt Passive ilter. In this hybrid filter, the function of the series AP is not to compensate for the harmonics voltages directly, but to enhance the unt passive filter characteristics by providing harmonics isolation. The series AP ould synthesize the active impedance presenting zero impedance at the fundamental frequency and a high resistance at the source or load harmonics frequency. In other words, the series AP ould provide high impedance for harmonics frequency. In fact, this active impedance is synthesized by the PWM switching control signal in VI. One important result of this 64

2 Jurnal Elektro ELTEK Vol. 1, No. 2, 2010 IN: configuration is that the series AP are much smaller in capacity than a conventional unt active power filter designed to filter directly the load harmonics currents. B. ompensation Principles or the simplicity, only one of the circuits in figure 1 presented in figure 2 which owed single phase equivalent circuit for the series active filter and unt passive filter. The harmonics current flowing in the source both the load harmonics current I is dependent on I and the source harmonics voltagev. It is given by equation: Z V I I (1) Z Z K Z Z K Where I 0 if K Z, Z (2) V sf X s V c V Z I h igure 2. ingle phase equivalent circuit for the series active filter and unt passive filter. With Z s is being magnitude of Z and Z the magnitude of Z. The first terms on the right hand side of (1) ows that the series AP operates as an active impedance. In fact, it acts as damping resistance which can eliminate the parallel resonance between unt passive filter and the source impedance. The second term means that the series AP acts as a blocking resistance, which can prevent the harmonics current produced by the source harmonics voltage from flowing into the unt passive filter. It is important to poit out that if the equivalent resistance K is much larger than the source impedance, variations in this impedance produce no effect on the filtering characteristic of the unt passive filter. onsequently, this reduces the source harmonics current to zero as own in (2). The output voltage of the series AP, which corresponds to the harmonics voltage across the equivalent resistance K in figure 2 is given by Z I V V KI K (3) Z Z K V I V Z if K Z, Z (4) Equation (4) ows clearly that the voltage rating of series active filter V is given by two factors: the first term in the right hand side of this equation, which is inversely proportional to the quality factor of the unt passive filter, and the second term that is equal to the source harmonics voltage. The harmonics voltage on the unt passive filter is given by K V Z h Z I A Z Z K (5) Z where Ais V Z Z K V h Z I if K Z, Z (6) The above equations ow that by choosing K Z,, no source harmonic voltage appears across Z the unt passive filter.. ontrol ircuit The control of series AP is based on a very simple equation: * v (7) Ki where i is the source harmonics current, which can be calculated based on the instantaneous p-q theory. or this calculation, the voltages in the load side (v a, v b, v c ) and the current in the source side ( i a, i b, i c ) have to be transformed into the transformation: 1 1 va v vb (8) v v c ia i ib (9) i i c 2 2 The real and imaginary power can be calculated by p v v i (10) q v v i By using a high pass filter, the oscillating component ~ p and q ~ can be extracted from p and q. In this paper, a first order, high pass filter with a cutoff frequency of 35 Hz is used. Then, the source harmonics current is calculated by i 1 0 ah v v ~ p ibh v v q ~ (11) ich The reference voltage for series AP given by (5) is compared with a triangular carrier waveform to produce the PWM switching pattern. With this control, the series AP operated as controlled voltage source. III. IMULATION AND REULT This paper performed hybrid filter simulation for harmonics mitigation purpose. The performance of hybrid filter would be analyzed through total harmonics distortion (THD), harmonics spectrum and waveform of source voltage and current. ondition of voltage and current in the system 65

3 urrent (A) Voltage (kv) urrent (A) Voltage (kv) Jurnal Elektro ELTEK Vol. 1, No. 2, 2010 IN: without filter, with passive filter and with hybrid filter compared in order to examine the redundancy performance of hybrid system. To verify the performance of the proposed configuration hybrid filter based instantaneous p-q theory algorithm, PAD/ EMTD used to simulate the proposed system. The system was three phases balanced system with 200V, 60Hz. Non linear load modeled by three phase controlled rectifier supplied inductive load (2.5Ω and 1mH). Load voltage and distorted current of the system without filter installation owed in figure Voltage and urrent before ilter Installation Time igure 3. Voltage and urrent before ilter Installation Voltage and current appear in the system before filter installation have non-sinusoidal waveform. It means that these waveforms contain of fundamental and high harmonics component. 3 Harmonics pectrum of ource Voltage - - Voltage and urrent after hunt Passive ilter Installation Time igure 5. Voltage and ource urrent after hunt Passive ilter Installation Harmonics spectrum of distorted voltage and source current owed that 5 th and 7 th order are the dominant order harmonics component. onventionally, unt passive filter are installed to suppress the dominant harmonics component hence the voltage and current waveform are improved. hunt passive filter consist of 5 th tuned passive filter and 7 th tuned passive filter. The unt passive parameters are given in Table 1. TABEL I PARAMETER O HUNT PAIVE ILTER Tuned R(Ω) L(H) () Q KVar 5 th th hunt passive filter installation caused the voltage and source current waveform improved indicated by more sinusoidal waveform and smaller notches appear in voltage waveform Harmonics pectrum of ource Voltage kv [1] Harmonics pectrum Of ource urrent kv [1] Harmonics pectrum Of ource urrent 3 A [1] igure 4. Harmonics pectrum of ource Voltage and urrent before ilter Installation Distorted voltage waveform has 21.6% THD value and distorted current waveform has 14.8% THD value. Detailed harmonics component contained in voltage and current waveform owed in harmonics spectrum term. Harmonics spectrum of voltage and current before filter installation owed in figure 4. A [1] igure 6. Harmonics pectrum of ource Voltage and urrent after hunt Passive ilter Installation The THD values after unt passive filter installation are 5.44% for voltage and 1.8% for source current. Voltage and source current waveform after unt passive filter installation owed in figure 5. It owed that dominant harmonics component i.e. 5 th and 7 th order harmonics have been suppressed. Harmonics spectrum of voltage and source 66

4 urrent (A) Votage (kv) Jurnal Elektro ELTEK Vol. 1, No. 2, 2010 IN: current after unt active power filter installation owed in figure 6. tand alone passive filter tuned at 5 th and 7 th doing well to suppress harmonics component at specific order. However, small distortion still appears in the voltage and current waveform due to higher order harmonics component remains. This problem solved by additional installation of series compensator device hence the system become hybrid configuration Harmonics pectrum of ource Voltage Voltage and ource urrent after Hybrid ystem Installation kv [1] Harmonics pectrum of ource urrent - Time igure 7. Voltage and ource urrent after Hybrid ilter Installation The proposed hybrid system consists of unt passive filter tuned at 5 th and 7 th order harmonics and series active power filter. Additional device; series active power filter used to improve stability of the power system and to minimize the voltage distortion thus performance of unt passive filter would get better. igure 7 owed voltage and source current waveform after installation of hybrid system. A [1] igure 8. Harmonics pectrum of Voltage and ource urrent after Hybrid ilter Installation TABEL II PERORMANE O THE YTEM WITH VARIOU ILTER ONIGURATION onfiguration Voltage Harmonics omponent urrent Harmonics omponent THD Value (%) 5th 7th 5th 7th V I Passive ilter 5th L R (H) (Ω) Passive ilter 7th L R (H) (Ω) Without ilter Passive ilter with Q = 70 Hybrid ilter with Q = 70 Hybrid ilter with Q = The voltage and current waveform have better ape compared with previous compensation method. Higher harmonics and voltage distortion suppressed due to series active filter installation. With hybrid filter proposed scheme, capacity of unt active filter can be decreased without generate any significant effects to the system performance hence the efficiency increased and installation cost of passive filter decreased. In this hybrid system two values of passive filter quality factor (Q) have been applied. or Q = 70, the THD value of voltage and source current are 2.29% and 0.713% respectively. or Q = 40, the THD value of voltage and source current are 2.3% and 2.5% respectively. Eventhough the THD value with smaller Q factor increased, however the values are well enough under 5% refers to the IEEE standard for THD value. Table 2 summarize the performance of the system before and after installation filter system contain passive filter and hybrid filter configuration. ompared to the previous filtering process that contain only unt passive filter, the voltage and source current have better result. These indicated by smaller THD value than using only unt passive filter. Voltage waveform has 2.29% THD value and source current has 0.713% THD value. The harmonics spectrum of voltage and source current owed in figure 8. IV. ONLUION Hybrid filter system involving unt passive filter and series active power filter was analyzed. The hybrid system owed better performance than stand alone unt passive filter. Additional series active power filter improve performance of unt passive filter, increasing efficiency, loading capacity and stability of the system. With the hybrid filtering system distorted voltage and harmonics current component have been suppressed yield smaller THD value compare with stand alone passive filtering system. 67

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