International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 445
ISSN 2229-5518
Single Phase Shunt Active Filter with Fuzzy
Controller for Harmonic Mitigation
C L Anooja, N Leena
Abstract— This paper presents a single phase shunt active filter with fuzzy controller for harmonic mitigation .Shunt active filter is an efficient method for reducing harmonic content in power system. Instantaneous pq theory is used for the generation of reference controller signal and hysteresis controller is used for the production of gate signal. In this paper a comparative assessment of the performance of the conventional PI controller and fuzzy controller for harmonic mitigation is presented. Multilevel inverters are also discussed for harmonic mitigation. The simulation results show that the proposed fuzzy controller can give superior results with lower THD when compared to the PI controller. The results also validate that as the number of inverter level increases, the performance gets improved.
Index Terms— Harmonics, Total Harmonic Distrotion(THD),Multi inverter,Ffuzzy logic ,PI controller,Instantaneous P-Q theory,Hysteresis current control.
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ower electronic devices are widely used in domestic as well as industrial application. The main disadvantage of using these devices is that they cause harmonic pollution
in power system, and as a result they generate many adverse effects like reduction in the efficiency of the system, prema- ture failure of the electrical and electronic equipment’s, in- crease in power losses etc. Shunt active filter is one of the solu- tions for avoiding those types of problems created by the pres- ence of harmonics. Active filters with fuzzy controller are su- perior in filtering performance, smaller in physical size, and more flexible in application, compared to traditional harmon- ics mitigation method. The concept used in an active filter is the introduction of current components using power electron- ics to remove the harmonic distortions produced by the non- linear load. In order to obtain a clean sinusoidal supply cur- rent (Is) the shunt active filter has to keep on injecting com- pensating harmonic currents to cancel the current harmonics present in the nonlinear load. The block diagram is shown in fig.1. The control of inverter strategy has three stages. In the first stage, the supply voltage and current signals are meas- ured. In next stage, reference currents are generated based on instantaneous p-q theory. In the third stage, the gating signals for the power switches of inverter produced using hysteresis- based current control method.
The instantaneous real and reactive power can be calculat- ed in terms of α-β voltage and current signals. Harmonic ac- tive powers are separated from instantaneous active and reac- tive powers by using high-pass filters. The knowledge of har- monic active and reactive powers helps us to derive the com- pensating currents [1-4]. Hysteresis current controller can be used to generate the switching signals of the inverter switches [5].
• C L Anooja is currently pursuing masters degree program in power electronics and power system inM G University, India, PH-9747262825.
• N Leena is currently working as Asst.Prof in the Dept of EEE atFederal Insti- tute of Science and Technology ,Angamaly,India,
During non-switching operation, shunt filter charges dc ca- pacitor through the diodes to the maximum value of system voltage. The DC side of the inverter is connected to a capaci- tor. The DC capacitor provides a constant DC voltage and the real power necessary to cover the losses of the system. In the steady state, the real power supplied by the source should be equal to the real power demand of the load plus a small power to compensate the losses in the active filter. Thus, the DC ca- pacitor voltage can be maintained at a reference value. How- ever, when the load condition changes the real power balance between the mains and the load will be disturbed. The real power difference is to be compensated by the DC capacitor. This changes the DC capacitor voltage away from the refer- ence voltage. A PI controller is used to keep the constant volt- age across the capacitor by minimizing the error between the capacitor voltage and the reference voltage. But PI controller has its own disadvantages is that it needs a precise mathemat- ical model of the system lest the control operation of PI con- troller is not efficient and accurate. The conventional control- lers also fail to perform satisfactorily under varying condi- tions.This necessitated the usage of an intelligent control tech- nique.
In this paper, a fuzzy controller is used to overcome the problem say which problem. Multi-level inverter helps to re- duce the harmonic level observed in the conventional inverter and THD reduces with the increase of the number of levels of inverter [10-14]. Fig.2 shows a two-level, three-level and five- level inverter. Here a multilevel inverter is used as a shunt active filter.
The paper is organized as follows; Section II presents the control operation of inverter which contains reference current generation based on the single phase PQ theory, fuzzy control- ler and hysteresis current control for producing gate signal of power switches. The simulation results of the shunt active filter with conventional PI and the proposed fuzzy controller are provided in section III. Section IV presents the conclusion of this work.
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International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 446
ISSN 2229-5518
Due to the presence of power electronic devices, the supply current contain both fundamental component and harmonic component. When active filter is connected into the system, it injects the current which is equal to the harmonic component and cancel each other, supplying pure current composed of only fundamental component. Single phase PQ theory is suit- able for active filter control for reference current calculation. From the system, actual current and voltages are measured called by the ‘α’ component. These actual signals can be phase shifted by 90o, and called the ‘β’ component or pseudo com- ponent. By using ‘α-β’, components of voltage and current are used for the calculation of active and reactive power.
𝑝 𝑣𝛼 𝑣𝛽
𝑖𝛼
𝑝 + 𝑝
�𝑞� = �𝑣𝛽 −𝑣𝛼 � �𝑖𝛽 � = �
�………………(1)
Fig. 1. Block diagram of the system
The real and reactive power, consisting of harmonic and fundamental component, is separated by using a high pass filter. Fig.3 shows the block diagram for reference current generation.
𝑝� , 𝑞�= Active and reactive component corresponding to the harmonic component
𝑝 , 𝑞� = Active and reactive component corresponding to the fundamental component
Compensating reference current:
𝑐 𝑣𝛼 𝑣𝛽 −1
𝑝�
�𝑖𝑐 � = �𝑣𝛽 −𝑣𝛼 �
� � …………………………..(2)
𝑐 𝑐
𝑖𝛽 has no physical significance hence is discarded and 𝑖𝛼 is
only used as a compensation current
Fig. 2. Multi level inverter in two,three and five level configuration
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International Journal of Scientific & Engineering Research, Volume 4, Issue 9, September-2013 447
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The PI controller consists of a proportional term and an inte- gral term. Proportional value determines the reaction to the current error; the Integral determines the reaction based on the sum of recent errors. Ki and Ti are the proportional and the integral gains of the dc bus voltage PI controller. The Transfer function of Pi controller is
𝐺 (𝑠) = 𝐾 (1 + 1 ) ……………………………..(3)
𝑠𝑇𝑖
Here the values of proportional and integral gain taken as
0.345, Ti= 34.9 . PI controller need a precise mathematical mod-
el of the system otherwise the control operation of PI control-
ler is not efficient and accurate . If there are any changes oc-
curring in the system, the existing PI controller in the system is
not able to provide sufficient control of dc capacitor voltage
and as a result the THD value is not reduced.
Fig. 3. Block diagram of the system
Hysteresis controller is used independently for each phase and directly generates the switching signals for the switches of inverter. The error signal is the difference between the reference current and the actual current. If the error current exceeds the upper limit of the hysteresis band, the upper switch of the inverter arm is turned OFF and the lower switch is turned ON. If the error current crosses the lower limit of the hysteresis band, the lower switch of the inverter arm is turned OFF and the upper switch is turned ON. As a result, the current gets back into the hysteresis band as in fig.4.
The advantages of soft computing controllers are that they do not require an accurate mathematical model; it can work with imprecise inputs, can handle non-linearity, and are more ro- bust than conventional controllers.
The fuzzy controller has two inputs, one is error voltage of dc capacitor voltage and other is change of voltage (previous error – current error). These two inputs have seven Gaussian membership functions in linguistic terms, by using these func- tion the 49 ‘IF THEN’ rules were generated. Output of fuzzy controller is a nonfuzzy number and it is obtained by using
Centre of gravity method. The rule base of the fuzzy controller
is given in Table I. 
TABLE 1
RULES BASE OF FUZZY CONTROLLER
Error
∆𝑬
Fig. 4. Hysteresis band
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The THD analysis of a two level shunt active filter with PI controller and fuzzy controller are shown in fig 7 and 8. Fig 9 and 10 shows the THD analysis of three level shunt active fil- ter with PI and fuzzy controller. Five level active filter is con- nected to the system and THD analysis is done as shown in the fig 11 and 12.
Fig. 5. Fuzzy controller
Single phase shunt active filter is simulated with PI and fuzzy controller in different multilevel configurations. The system parameters used for simulation are given in Table.II.
TABLE 2
SIMULATION PARAMETERS
PARAMETERS VALUES
Supply voltage 230V Supply frequency 50Hz
Supply side inductor 5H Supply side resistor 0.1Ω Load resistor 20Ω Load inductor 0.1H Load capacitor 1mF
Reference capacitor
Voltage 300V
Fig. 6. Simulink diagram of the system
When sudden changes occur in the system, the PI controller alone is not sufficient for controlling the dc capacitor voltage. But in the case of fuzzy controller, the THD level reduces be- low the IEEE standard. As the number of levels of inverter increases, the THD is also reduced.
Here load is connected as a RL load through a diode rectifi- er. During the simulation another RC load is connected to the system through a circuit breaker. PI controller cannot give an efficient control action due to this sudden change in the sys- tem, but the fuzzy controller can reduce the THD during the changes. Fig 6 displays the Simulink block diagram of the sys- tem.
Fig. 7.T wo level shunt active filter with PI controller,THD=8.39%
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Fig.8.Two level shunt active filter with fuzzyI
controller,THD=5.68%
Fig.10.Three level shunt active filter with fuzzy controller,THD=4.47%
Fig.9.Three level shunt active filter with PI controller,THD=7.10% Fig.11.Five level shunt active filter with PI controller,THD=4.04%
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This paper demonstrates that fuzzy controller performs better than a PI controller for harmonic mitigation. Shunt active filter was simulated in two, three and five level configuration. From the simulation result analysis, it is clear that a fuzzy con- troller is able to provide much better response under varying load condition. Multilevel inverters were found to be very effective in reducing the THD of the system. Hence a multi- level inverter with a fuzzy controller can effectively reduce the THD of the system.
We would like to thank the management, principal, HOD (EEE) and others staff members of Federal Institute of Science and Technology, Angamaly for their support and guidance in carrying out this work.
Fig. 7.Five level shunt active filter with fuzzy controller,THD=1.61%
The simulation results of multi-level inverter are tabulated in Table III.
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TABLE 3
SIMULATION RESULTS
THD(%)
PI Fuzzy
Controller Controller
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Two level inverter 8.39 5.68
Three level inverter 7.10 4.47
Five level inverter 4.04 1.61
The above result shows that THD gets reduced significantly on using a fuzzy controller than with the conventional PI con- troller. In the two level configuration, the THD level is 8.39% with PI controller and gets reduced to 5.68% upon using a fuzzy controller instead of PI. Similarly, in three level inverter, the fuzzy controller reduces the THD by 4.94% whereas with the PI controller THD is 7.10%. In the case of five level config- uration with PI controller, the THD was 4.47% on the other hand a system with fuzzy controller reduces the THD to
1.61%.
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