Power Quality Improvement using Shunt Passive Filter

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1 Power Quality Improvement using Shunt Passive Filter Assistant Professor, Department of Electrical Engineering Bhutta Group of Institutions, India Abstract: The electricity supply would, ideally, show a perfect sinusoidal voltage at every point of the power network. In reality, it is almost impossible to accomplish such desirable conditions. Voltage and current waveforms deviate massively from a sinusoidal. These waveform deviations are described by the use of waveform distortion and usually called harmonic distortion. Even if harmonic distortion is a quite old phenomenon it today presents one of the main concerns for public utilities, distribution system operators as well as their end customers. Already in the first years of operation of power distribution networks, there were first disturbances.. The major concern at this time was the effect that harmonic distortion had for the electric machines itself. Another well-known issue was interference in the telephone lines. But in general it can be said that harmonic distortion in former times did not have the same dangerous potential like it has today. This paper presents the design and formulation of shunt passive filter to lower the harmonics and improve the power quality.. Key Words-Shunt Passive filter, Series Active filter, Hybrid filter I. Literature Background Enjeti et al., 1992), entitled Analysis and design of an active power filter to cancel harmonic currents in low voltage electric power distribution systems, presents active power filter design considerations used for improving current quality in low voltage electric power distribution systems. Among various types of filters, shunt active filter is used for current harmonics removal and improves the power quality in electric power distribution system. (Hirofumi Akagi et al.,1998), entitled The unified power quality conditioners: the integration of series-active and shunt-active filters, In this paper the main purpose of a UPQC is to compensate for voltage flicker/imbalance, reactive power, negative sequence current, and harmonics. In other words, the UPQC has the capability of improving power quality at the point of installation on power distribution systems or industrial power systems. This paper discusses the control strategy of the UPQC, with a focus on the flow of instantaneous active and reactive powers inside the UPQC. Singh, Bhim Al-Haddad et al., 1998), entitled Harmonic elimination, reactive power compensation and load balancing in three-phase, four-wire electric distribution systems supplying non-linear loads In this paper, a new control scheme of a three-phase active power filter (APF) is proposed to eliminate harmonics, to compensate reactive power and neutral currents and to remedy system unbalance, in a three-phase four-wire electric power distribution system, with unbalanced non-linear loads. The APF is realized using three single phase IGBT based PWM- VSI bridges with a common dc bus capacitor. (Bhim singh et al., 1999), entitled A review of active filters for power quality improvements, presents in this paper presents a comprehensive review of active filter (AF)

2 configurations, control strategies, selection of components, other related economic and technical considerations, and their selection for specific applications. It is aimed at providing a broad perspective on the status of AF technology to researchers and application engineers dealing with power quality issues. (Fujita et al., 2000),entitled A hybrid active filter for damping of harmonic resonance in industrial power system, explains the feature of passive filter and active filter in a combined way called hybrid filter for the elimination of harmonic resonance in industries. In a hybrid filter, active filter works for the elimination of voltage harmonics and passive filter is used for the elimination of current harmonics. (Adil M.and Al-Zamil et al.,2001), entitled A Passive Series, Active Shunt Filter for High Power Applications This paper presents a hybrid series passive/shunt active power filter system for high power nonlinear loads. This system is comprised of a three-phase shunt active filter and series ac line smoothing reactance installed in front of the target load. The proposed system significantly reduces the required shunt active filter bandwidth. The space-vector pulse width modulation (PWM) controller is based on a dead-beat control model. It is implemented digitally using a single 16-bit microcontroller. This controller requires only the supply current to be monitored, an approach different from conventional methods II. INTRODUCTION TO PASSIVE FILTERS The passive filters are used to mitigate power quality problems in six-pulse ac-dc converter with R-L load. Moreover, apart from mitigating the current harmonics, the passive filters also provide reactive power compensation, thereby, further improving the system performance. CLASSIFICATION OF PASSIVE FILTERS Depending on the connection of different passive components, the passive filters are classified as below: Passive series filter Passive shunt filter My scope of work is on shunt passive filter PASSIVE SHUNT FILTER Fig.1 shows the schematic diagram of a passive shunt filter connected at input ac mains of sixpulse ac-dc converter with R-L load. This is the most commonly used configuration of passive filters. In this configuration different branches of passive tuned filters (low pass and high pass) tuned for the more dominant harmonics are connected in parallel with the diode rectifier with RL load. It consists of a set of low pass tuned shunt filters tuned at 5th and 7th harmonic frequencies and high pass tuned for 11th harmonic frequency. This passive filter scheme helps in sinking the more dominant 5th and 7th and other higher order harmonics and thus prevents them from flowing into ac mains. The diversion of harmonic current in the passive filter is primarily governed by the source impedance available in the system. The higher value of source impedance offers better performance of the passive filter. 192

Figure 1Compensation Principle of Passive Shunt Filters A passive shunt filter mainly consists of several LCR branches each tuned at a particular frequency. Fig.

I S I l z s z l I F V S z sh V l Figure 2 Equivalent circuit diagram of a passive shunt filter CONTROL STATERGIES THE DUAL INSTANTANEOUS REACTIVE POWER THEORY SRF CONTROLLER The synchronous reference

3 Figure 1Compensation Principle of Passive Shunt Filters A passive shunt filter mainly consists of several LCR branches each tuned at a particular frequency. Fig.2 shows the equivalent circuit diagram of a passive tuned shunt filter. I S I l z s z l I F V S z sh V l Figure 2 Equivalent circuit diagram of a passive shunt filter CONTROL STATERGIES THE DUAL INSTANTANEOUS REACTIVE POWER THEORY SRF CONTROLLER The synchronous reference frame theory or d-q theory is based on time-domain reference signal estimation techniques. It performs the operation in steady-state or transient state as well as for generic voltage and current waveforms. It allows controlling the active power filters in real time system. Another important characteristic of this theory is the simplicity of the calculations, which 193

involves only algebraic calculation. The basic structure of SRF controller consists of direct (d-q) and inverse (d-q)- park transformations as shown in fig3.

4 involves only algebraic calculation. The basic structure of SRF controller consists of direct (d-q) and inverse (d-q)- park transformations as shown in fig3. These can useful for the evaluation of a specific harmonic component of the input signals. Figure 3 Synchronous d-q reference frame based compensation algorithm These three phase space vectors stationary coordinates are easily transformed into two axis dq rotating reference frame transformation. This algorithm facilitates deriving id-iq(rotating current coordinate) from three phase stationary coordinate load current ia.ib ic, as shown in equation. The d-q transformation output signals depend on the load current (fundamental and harmonic components) and the performance of the Phase Locked Loop (PLL). The PLL circuit provides the rotation speed (rad/sec) of the rotating reference frame, where ωt is set as fundamental frequency component. The PLL circuit provides sinѳ and cosѳ. The id-iq current are sent through low pass filter (LPF) for filtering the harmonic components of the load current, which allows only the fundamental frequency components. PQ THEORY The instantaneous reactive power theory is the most widely used as a control strategy for the APF. It is mainly applied to compensation equipment in parallel connection. This theory is based on a Clarke coordinate transformation from the phase coordinates (see figure 4). In a three-phase system voltage and current vectors can be defined by v=[ v a v b v c ] T i =[ i a i b i c ] - (1) 194

5 Figure 4 Transformation from the phase reference system (abc) to the (0αβ) system. Instantaneous reactive power theory (IRPT) uses the park transform, to generate two orthogonal rotating Vectors (α and β) from the three phase vectors (a, b and c). This transform is applied to the voltage and current and is given by eqn 2,3 = - (2) = - (3) By looking at instantaneous powers, the harmonic content can be visualized as a ripple upon a DC offset representing the fundamental power. By removing the DC offset and performing the inverse park transform the harmonic current can be determined The supply voltage and load current are transformed into αβ quantities. The instantaneous active and reactive powers p and q are calculated from the transformed voltage and current as given is = - (4) Which gives, Po= vo.io instantaneous zero sequence power p= + instantaneous real power q= instantaneous imaginary power 195

6 The instantaneous active and reactive powers are filtered to leave the AC components. The Compensating currents are determined by taking the inverse and is given by = (5) This current is then multiplied by gain (k) to produce PWM signal. THREE PHASE SYSTEM WITH DIODE RECTIFIER The power circuit is a three-phase system supplied by a sinusoidal balanced three-phase 415V source and 50 Hz frequency with a source inductance of 5.8 mh and a source resistance of 3.6Ω.The three phase system supply is given to a 15kW AC-DC Diode bridge rectifier feeding an RL load. The MATLAB Simulink model of the system is shown in Fig.5. The performance of diode bridge rectifier feeding an RL load without any filter in the system is shown in figure. The system has been simulated under nonlinear balanced source and balanced load conditions. The source current is highly distorted. THREE PHASE SYSTEM WITH PASSIVE FILTER The 5th and 7th order of shunt passive filters are designed to sink in respective harmonic currents. The capacitors for the passive filter are selected to supply the specified percentage of the reactive power requirement of the load. The MATLAB Simulink model of the system with passive filters is shown in Fig 6. The passive filter helps to reduce the major amount of distortions in source current. i.e., the passive filter sinks the 5th and 7th harmonic currents by providing a low impedance path. Table 1 gives the parameter values of passive filter components for compensation. TABLE 1. Parameter values of passive filter Harmonic Inductor Capacitor 5 th 13.5mH 30µF 7 th 6.5mH 50µF FIGURE 5. SIMULINK DIAGRAM OF THREE PHASE SYSTEM 196

7 FIGURE 6. SIMULINK DIAGRAM OF THREE PHASE SYSTEM WITH PASSIVE FILTER SIMULATION RESPONSE The system parameters considered for the study of Filter is given below in Table 2. COMPONENTS SPECIFICATIONS AC Source V s =415v, f=50hz, R s =3.6Ω,L S =5.8Mh Non Linear Load R L =40Ω, L L =50mH Passive Filter L 5 =13.5mH C 5 =30F, L 7 =6.75mH C 5 = 50F Table 2Specifications for Test System 197

Simulation Response without filters Simulation Response with Passive shunt filter SIMULATION RESPONSE WITHOUT FILTER

8 shows the waveforms of source voltage and current of the three phase system without compensating.

connected in parallel at the dc side.figure 5 shows the three source currents.

8 Simulation Response without filters Simulation Response with Passive shunt filter SIMULATION RESPONSE WITHOUT FILTER Figure-7 Waveforms of source voltage without filters Figure-8 Waveforms of source current without filters Figure 7 and 8 shows the waveforms of source voltage and current of the three phase system without compensating. The nonlinear unbalanced load consisted of three phase uncontrolled rectifiers with a capacitor and a resistor connected in parallel at the dc side.figure 5 shows the three source currents. The THD of the current measured is 23% and power factor measured is SIMULATION RESPONSE WITH SHUNT PASSIVE FILTER Figure-9 Waveforms of load voltage with shunt passive filter 198

9 Figure 10 Waveforms of load current with passive shunt filter Figure- 11 Waveforms of source voltage with passive shunt filter 199 Figure-12 Waveforms of source current with passive shunt filter

10 Figure 9 and 10 shows the waveforms of load voltage and current, Figure 11 and 12 shows the waveforms of source voltage and current. When the shunt passive filter is connected have a THD falls from 23.0% to 4.3%. The passive filter was only designed to compensate the source current harmonics; the reactive power was not taken into account. The power factor rises to 0.99 Conclusion This paper proposed shunt passive filter design to enhance the power quality in transmission and distribution system. REFERENCES Third EditionBhim Singh, Kamal Al-Haddad, Senior Member, IEEE, and Ambrish Chandra, Member, IEEE(1999) A Review of Active Filters for Power Quality Improvement IEEE Transactions Industrial Electronics, VOL. 46, NO. 5, OCTOBER Adil M. Al, -Zamil, Member, IEEE, and David A. Torrey, Member, IEEE(2001), A Passive Series, Active Shunt Filter for High Power Applications, Transactions of Power Electronics, Vol. 16 NO. 1, C. Nalini Kiran, Subhransu Sekhar Dash, S.Prema Latha (2011) A Few Aspects of Power Quality Improvement Using Shunt Active Power Filter International Journal of Scientific & Engineering Research Volume 2, Issue 5, May Jinn-Chang, Hurng-Liahng, Kuen-Der, Hsin-Hsing Hsiao (2012), Three-phase fourwire hybrid power filter using a smaller power converter Electric Power Systems Research 87 (2012) Mark F,Roger C.[2012] Electrical Power System Quality Tata Mc Graw-Hill BIOGRAPHY Name - Chamandeep kaur Designation-Assistant Professor in Bhutta College of Institutions, India Qualification-Btech (Electrical Engg) from Guru Nanak Dev Engineering College Mtech(power Engg) from Guru Nanak Dev Engineering College 200

Design and Simulation of Three Phase Shunt Active Power Filter Using SRF Theory

Advance in Electronic and Electric Engineering. ISSN 2231-1297, Volume 3, Number 6 (2013), pp. 651-660 Research India Publications http://www.ripublication.com/aeee.htm Design and Simulation of Three Phase