108 International Journal for Modern Trends in Science and Technology
Adaptive Fuzzy, Fuzzy PI and PI Controller based Shunt Active Power Filter for Harmonic Reduction
N. Manjula1 | A.Jawahar2 | J.Anusha3
1PG Student, EEE Department, SITAM, Visakhapatnam, AP, India
2,3Asst. Prof., EEE Department, SITAM, Visakhapatnam, AP, India
To Cite this Article
N.Manjula, A.Jawahar, J.Anusha, “Adaptive Fuzzy, Fuzzy PI and PI Controller based Shunt Active Power Filter for Harmonic Reduction”, International Journal for Modern Trends in Science and Technology, Vol. 02, Issue 11, 2016, pp.
108-115.
The present paper describes Adaptive Fuzzy logic and FuzzyPI and PIcontroller Shunt Active Power Filter (SAPF) designed for harmonic compensation and reactive power under variable conditions. Therefore the power quality can be increase efficiently by using this Shunt hybrid active power filter. The main purpose of this work is Fuzzy logic and PI controller based regulator, the shunt active power filter to compensate harmonics and reactive power by nonlinear load to enhance power quality is implemented for three wire system The various simulation results are presented under steady state conditions and performance of AdaptiveFuzzy and FuzzyPI and PIcontrollers is compared. Simulation results obtained show that the performance of Adaptivefuzzy controller is found to be better than Fuzzy PI and PI controller.
KEYWORDS: Shunt Active Power Filters (SAPF); DC Link Voltage, Adaptive fuzzy Logic ,Fuzzy pi ,Pi controller,VSI.
Copyright © 2016 International Journal for Modern Trends in Science and Technology All rights reserved.
I. INTRODUCTION
A power quality issue exists if any of the voltage, current or frequency various from sinusoidal nature occurs. Power quality issues are generally in commercial, industrial and utility networks as the power electronics appliance is normally used in these fields. These appliances produce harmonics and reactive power. It is very important to mitigate the dominant harmonics and therefore Total Harmonic Distortion (THD) below 11% as specified in IEEE 519 harmonic standard [1]. The effect of harmonic distortion is reduced by Active filter. To overcome this issue shunt Active Power Filter (SAPF) is brought into effect. Active power filter acts as harmonic current source to provide emphatic result to mitigate for harmonic currents as well as reactive power. It has the capacity to
inject harmonic. The paper is organized as current into the AC system with the same amplitude but in opposite phase of the load [2]. As the SAPF is complex with cost effective parameter control, the shunt active power filter has been preferable in the subject of harmonic solution.
Shunt active power filter gives the efficacious active filter, which implies the advantages to reduce the harmonics and reactive power shown in figure1.
Accuracy of this shunt active power filter is depending upon the estimate of harmonic current and production of reference current. Paper present a three phaseAdaptive Fuzzy logic andFUZZY PI and PIcontrolled shunt active power filter is proposed [3], [4], [5]. To create the shunt active power filter model more dynamic and robust in nature in this paper aAdaptive Fuzzy logic ABSTRACT
International Journal for Modern Trends in Science and Technology
Volume: 02, Issue No: 11, November 2016ISSN: 2455-3778 http://www.ijmtst.com
109 International Journal for Modern Trends in Science and Technology andFUZZY PI and PI controller have been used to
make an easy estimate of reference currents.
Low pass is used to generate fundamental from non-ideal voltage source. The extract fundamental currents are then subtracted from source current to calculate the reference signal i.e. harmonic current. The planned controller has self-learning with high accuracy and simple architecture and it can be successfully applied for harmonic filtering under different power system operating conditions.
Figure 1. Shunt Active Filter Configuration
II. PROPOSEDTOPOLOGY
Three phase shunt active power filter is used as prototype shown in figure 2. Shunt active Power filter is used produce mitigation current in opposite phase. Power circuit for SAPF is planned as An IGBT based three-phase voltage source inverter with DC storage capacitor for better mitigation of non-sinusoidal unbalanced /balanced loads.
Active power filter has three various control schemes; one is Adaptive Fuzzy logic controller that accounts for reference current production and a second Fuzzy PI controller for Direct Current voltage regulation. Adaptive Fuzzy logic and Fuzzy PI controller comprises three adaptive linear neurons to extract the fundamental components of the three phase voltages from non-sinusoidal supply [6]. The capacitors are planning to limit the DC voltage ripple to a particular value, typically 1 to 2 %. In this case the capacitor should be planned for the worst case. Since the shunt active filter will operate in several modes (balanced or unbalanced load), then the injection of mitigation current is complete in order to nullify or compensate the harmonic currents. Injection of this mitigation current gives enhanced power quality. The performance of the shunt active power filters is dependent to a great extent upon the method used for the estimate of reference current.
Figure 2. Proposed topology of shunt active power filter
III. CONTROLSTRATEGY A. Shunt Active Power Filter
In a present electrical distribution system, there has been a rapid increase of distorted loads, such as power supplies, domestic appliances, rectifier gear, and adjustable speed drives (ASD), etc. As the number of these loads rises, harmonic currents generate by these loads may become very significant. These harmonics could lead to a variety of different power system issues ,including the distorted voltage waveforms, gear overheating, malfunction in system protection, incorrect power flow metering, excessive neutral currents, light flicker etc. They have also decreased efficiency by drawing reactive current component of the distribution network [8]. In order to overcome these issues, active power filter (APFs) has been developed. The voltage-source- inverter (VSI)-based shunt active power filter has been used in present and known as a viable solution the control scheme, in which the necessary mitigating currents are determined by sensing line currents only, which is easy to implement. The system uses a conventional proportional plus integral (PI) controller for the generation of a reference current.
Basic Compensation Principal
APF A current regulated voltage source inverter with required passive equipments is used as an APF as shown in fig 1. It is controlled to supply /drawn compensated current from/to the utility, such that it reduces harmonic and reactive Current of the non-linear load. Therefore, the resulting total current drawn from the AC mains is sinusoidal. Ideally, the APF requirements to produce just sufficient reactive and harmonic current to compensate the non-linear loads in the line.
110 International Journal for Modern Trends in Science and Technology
Fig.3 Shunt Active Power Filter with Non – Linear Load
B. Reference Compensation Current Estimation The following equations explain the procedure used for reference compensation current calculations.
Let us consider
𝑖𝑠 𝑡 is the instantaneous source current, 𝑖𝑙(t ) is the instantaneous load current, and 𝑖𝑐(t) is the instantaneous compensating current Fig.3 according to Kirchhoff’s current law, the instantaneous currents can be written 𝑖𝑠 𝑡
𝑖𝑠 𝑡 =𝑖𝑙(t ) -𝑖𝑐(t)
Let the instantaneous source voltage be 𝑣(𝑡)=𝑣𝑚𝑠𝑖𝑛w𝑡
If a nonlinear load is applied, the load current will be Divided into two parts, 1st is the fundamental component and 2nd is the harmonic component and can be
Represented as
l(t)
i = ∞n=1InSin nωt + Øn = 𝐼1𝑆𝑖(𝑛𝜔𝑡+ Ø𝑛 ) + ∞n=2i2 𝑆𝑖𝑛(𝑛𝜔𝑡+ Ø𝑛)
The instantaneous load power can be given in terms of source voltage and load current as 𝑝𝐿( 𝑡) =𝑣𝑠 𝑡 ∗𝑖𝑙(𝑡)
=𝑉𝑚𝐼1𝑠𝑖𝑛2𝜔𝑡∗𝑐𝑜𝑠Ø𝑛+𝑉𝑚𝐼1𝑠𝑖𝑛𝜔𝑡∗𝑐𝑜𝑠𝜔𝑡∗𝑠𝑖𝑛Ø1+𝑉𝑚𝑠𝑖𝑛
𝜔𝑡∗ ∞n=2In𝑠𝑖𝑛 (𝑛𝜔𝑡+Ø𝑛) (1)
=𝑃𝑓 𝑡 +𝑃𝑟 𝑡 +𝑃ℎ(𝑡)
From Equation (1), real (fundamental) power is drawn by the load
𝑃𝑓 𝑡 =𝑉𝑚𝐼1𝑠𝑖𝑛2𝜔𝑡∗𝑐𝑜𝑠Ø𝑛=𝑉𝑠 𝑡 +𝐼(𝑡) (2) From Equation (2), the fundamental source current supplied
𝐼𝑠 𝑡 =𝑃(𝑡)𝑉𝑠(𝑡)=𝐼1𝑐𝑜𝑠Ø𝑛𝑠𝑖𝑛Ø𝑡=𝐼𝑚𝑠𝑖𝑛𝜔𝑡 Where 𝐼𝑠𝑚=𝐼1𝑐𝑜𝑠Ø1
Also, present are some switching losses in the PWM converter. Therefore, the utility must supply a small overhead for the capacitor leaking and converter switching losses in addition to the real power of the load. Hence, total peak current supplied by the supply
𝐼𝑠𝑝=𝐼𝑠𝑚+𝐼𝑠1 (3)
If the active filter provides the total reactive and harmonic power, then is(t) will be in phase with the utility voltage and will be sinusoidal. The active filter must provide the following compensation current:
𝑖𝑐 𝑡 =𝑖𝐿 𝑡 −𝑖𝑠(𝑡)
Hence, for the accurate and instantaneous compensation of reactive and harmonic power, it is necessary to calculate is(t), which the fundamental component of load current is. The main meaning of the control scheme is shown in figure 3 to maintain the sources current waveform Sinusoidal, identification of harmonic content, regulation of DC voltage and controlling system of SAPF is necessary which provides mitigating current to the power system as well as supply harmonic currents to the three phase variable load at the same instant. For the proper response of APF the extraction of the fundamental component of current of variable input, reference, current generation, DCvoltage regulation and injection of compensation currents is essential tasks [10].
These tasks could achieve only with the reference source current (I*sm), result in 3 phase reference supply currents (I*sa, I*sb, I*sc). The reference supply currents and sensed supply currents (Isa, Isb, Isc) are the inputs for the pulse generator, which generates the firing pulses for the gating signals to the IGBT’s of the active power filter.
Hysteresis current control is a method of controlling a voltage source inverter so that the output current is generated which follows a reference current waveform.
C. Fuzzy Logic Controller
The fuzzy control scheme as shown in Fig. 4 consists fuzzification, defuzzification, and decision making unit[20]. The change in error, input is error and the output is given to drive circuit to get the signal. The inputs get fuzzified within fuzzification block and send to decision making block to get the output by seeing the data sets and rule base. The output is given to defuzzification block to get the corresponding crisp values. They will be send to drive circuit to decide the signal.
Fig. 4 Fuzzy Control System
111 International Journal for Modern Trends in Science and Technology Fig. 5& 6shows the fuzzy inference system
consists membership functions and the method of decision making i.e. Mamdani. Here the membership functions are (i) error (e) (ii) change in error (ce) and (iii) output of FLC (o). The error is the difference between Vdc and Vdc,ref V . Change in Error is the derivatives of DC V .These two are the input membership functions and the output of the FLC is the output membership function.
Fig.5 Fuzzy Inference System
Fig. 6. Degree of Membership Functions of Error, Change in Error and Output
Fig. 6 shows Membership functions of Error, Change in Error and Output. It shows the minimum and maximum values of membership functions and the ranges of membership functions.
now only three membership functions are used small, medium and big for the ease of framing fuzzy inference system in all the membership functions.
These consist of data of the system how it behaves.
These require slip flops or storing devices.
D. Proportional Integral Controller
The Proportional value determines the reaction to the current error; the Integral determine the reaction based on the sum of recent errors. A comparison of the average and the reference values of the DC bus voltage for the shunt AF results in a
voltage error, which is fed to a proportional integral (PI) controller and the output of the PI controller is multiplied by the mains voltage waveform Vsa, Vsb, Vsc in order to obtain the supply reference currents isa*, isb*, isc*. A PI controller used to control the DC-bus voltage is shown in Figure 6 whose transfer function can be represent as 𝐻 𝑆 = 𝐾𝑝 + 𝐾𝑖𝑆
Where, kp is the proportional constant that determines the dynamic response of the DC-bus voltage control, and ki is he integration constant that determines it’s settling time.
Figure 7. PI controller for DC-bus voltage control
It can be noted that if kp and ki are large, DC-bus voltage regulation is dominant, and the steady state DC-bus voltage error is low. On the hand, if kp and ki are small, the real power unbalance gives little effect to the transient performance The computed three-phase supply reference currents are compared with the sensed supply currents and are given to a hysteresis current controller to generate the switching signals to the switches of the shunt AF which makes the supply currents follow its reference values [13].
E. Adaptive Fuzzy Controller
An adaptive control system is a system which adjusts automatically on-line the parameters of its controller, so as to maintain a satisfactory level of performance when the parameters of the system under control are unknown and/or time varying. In indirect adaptive fuzzy control, the fuzzy logic systems are used to model the plant. Then a controller is constructed assuming that the fuzzy logic system approximately represents the true plant.
Fig 7. Adaptive fuzzy controller
112 International Journal for Modern Trends in Science and Technology IV. RESULTS
The system parameters: Load resistance RL = 100WR, Load inductance LL=37mH, Supply Phase voltage = 240 V, Supply line parameters Rs =1W, Ls
= 3mH, Inverter DC bus capacitor =2000μF, Reference Voltage = 480V, Hysteresis band limit
=0.5A and Switching frequency =10 kHz, PI controller parameters are Ki =30, Kp = 0.5. The Active Power Filter with proposed Fuzzy logic and Pi controller was modelled and simulated in MATLAB.
The proposed controller simulated with balanced nonlinear loads with sinusoidal/distorted, balanced conditions of source voltages.
Waveforms of shunt active power filter without controller:
THD of source current 43.78%
Waveforms of shunt active power filter without controller:
Voltage vs Time
Waveforms of shunt active power filter without controller:
Current vs Time
Waveforms of shunt active power filter with pi controller:
THD of source current 28.34%
Waveforms of shunt active power filter with pi controller:
Voltage vs Time
113 International Journal for Modern Trends in Science and Technology Waveforms of shunt active power filter with pi
controller:
Current vs Time
Waveforms of shunt active power filter with fuzzy pi controller:
THD of source current 10.60%
Waveforms of shunt active power filter with fuzzy pi controller:
Voltage vs Time
Waveforms of shunt active power filter with fuzzy pi controller:
Current vs Time
Waveforms Of Shunt Active Power Filter With Adaptive Fuzzy Controller:
THD of source current 8.97%
Waveforms of shunt active power filter with adaptive fuzzy controller:
Voltage vs Time
114 International Journal for Modern Trends in Science and Technology Waveforms of shunt active power filter with
adaptive fuzzy controller:
Current vs Time
V. CONCLUSION
In this paper proposed PI, Adaptive Fuzzy Logic and Fuzzy PI controller was verified through simulation studies with MATLAB. Proposed controller supply accurately. The shunt APF with Adaptive fuzzy logic controller is capable of Reactive Power Compensation and Harmonic Reduction. The Fuzzy PI controller can also give Simulation results obtained show that the performance of Adaptive fuzzy controller is found to be better than Fuzzy PI and PI controller. This operation is not feasible practically, as it is difficult to change PI parameters with every load changes.
The Adaptive fuzzy logic controller is therefore more suitable for this cause.
ACKNOWLEDGMENT
The authors would like to express their gratitude to Dr.S.V.H Rajendra, Secretary, AlwarDasGroup of Educational Institutions, SriVBhaskar, Dean for their encouragement and support throughout the course of work. The authors are grateful to Principal, Sanketika Institute of Technology and Management, Dr.N.C.Anil, Head of EEE Department, Ch.Vishnu Chakravarthi and staff for providing the facilities for publication of the paper.
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