Development of Different Control techniques for Shunt Active Power Filter
Kranthi Kumar Vanukuru
Research Scholar, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

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[email protected] Pakkiraiah
Associate Professor, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

[email protected] – Extensive use of the Non-linear elements like power electronic devices, circuits with inductor and capacitor are effecting the quality of power. All non-linear loads induces harmonics into the system. Shunt active power filters (SAPF) are used to improve the power quality by reducing the harmonics under specified levels along with improving the power factor. This paper deals with the development of different control methods for power quality improvement in shunt active power filter. Apart from other familiar existence techniques, four different methods are developed, first constant instantaneous power control by using the Instantaneous active reactive power theory, second sinusoidal current control method by using phase locked loop control, third Fryze current control with a positive sequence detector, and fourth Synchronous Reference Frame theory (DQ). Bridge rectifier with RL load is considered. SAPF controlled by mentioned controlling techniques were implemented by using MATLAB/Simulink environment. Simulation results are obtained with wave forms for different controlling techniques for SAPF. Total harmonic distortion (THD) data of all four cases are tabulated and discussed. By analyzing all the simulation results, it comes out that Synchronous Reference Frame method gives good results.
Keywords – Shunt Active Power Filter (SAPF), Constant Instantaneous Power Method (CIP), Sinusoidal Current Control Strategy with Phase Locked Loop (SCC), Synchronous Reference Frame (DQ), Positive Sequence Detector (PSD).

Introduction
The utilization of power electronic devices has been enormously increased now a days, major industries with different equipment, loads in the distribution system creates lot of disturbances to the current waveforms, causing distortion in the waveform. Non-linear loads causes disturbances to the other users and causes interference in Telecommunication networks. Compensation control scheme was developed to limit the effect of non-linear loads 1. Rapid technical advances in power electronics and micro-electronics such as uninterrupted power supplies, personal computers, and various other consumer electronics draw highly distorted current from the grid. A large harmonic currents flows in phases in case three phase loads, and flows through neutral wire in case of single phase loads. A constant-hysteresis, tolerance-band controller is developed to protect the other users from the adverse effects of these loads 2. Shunt active power filter is designed to achieve reactive power compensation to bring the power factor near to the unity. Feedback control law with analytically tuned PI controller is used in APF 3. Various controlling techniques are developed for APF, mathematical modelling of synchronous reference frame approach is proposed to eliminate harmonics and to compensate reactive power of non-linear load in three phase systems 4. Measuring the all variables for power quality analysis at each every point is not economical. Therefore, an efficient algorithm has been prepared to make the system observable. So that the overview of the power quality can be observed by managers of utility companies. Algorithm evaluate the power in distribution network and make available for the power quality process 5. Harmonics caused by the non-linear loads has an effect on the other users, efficiency of the transmission lines and responsible for malfunctioning of the protective relays. Kalman filter and the artificial neural network algorithm was developed for the protection of the transmission line 6.

There are various control algorithms for shunt active power filter to reduce the harmonics in non-linear loads. Synchronous source current detection method, instantaneous active reactive power theory, I cos Ø theory and power balance theories are discussed and analysed the results of all the four methodologies 7. PQ theory was developed for APF for reactive power compensation and current harmonic reduction. It improves the efficiency of the system and brings the power factor nearer to the unity. APF with PQ theory will also eliminates the oscillations in active power. Thereby, end user will get constant instantaneous active power 8. Shunt active power filter with sinusoidal source current control strategy has been discussed. This method balances the voltage fluctuations and voltage imbalances in the power supply 9. Fryze current control method for active power filter is one of the efficient method of control. A positive sequence detector was introduced in this method. The reference currents are generated by using the Fryze current minimization algorithm and hysteresis current controller generates the switching signal for voltage source inverter 10. A comparative study of three control methods for APF was discussed. From the obtained results, it has been observed that the current harmonics are reduced considerably to bring the value down to meet the IEEE standards. Now, in this paper, one more technique ‘synchronous reference frame’ (DQ) is introduced. Results shows that this method is effectively reduces the harmonic level in the given distribution system.

II.BASIC OPERATION OF SHUNT ACTIVE POWER FILTER
Fig.1 shows fundamental block diagram of SAPF with source, nonlinear load. Where isa, isb, isc are source currents, ila, ilb, ilc are line currents and ica, icb, icc are compensating currents.

Fig.1. Block diagram of Shunt Active Power Filter
The reference current calculation block represents any of three methods mentioned above. In this block inputs are line voltages and line currents which are used to generate the reference current I*C. The error signal obtained by comparing I*C and IC is fed to PWM converter. The output of PWM converter are six gate signals which in turn applied to VSI. The VSI circulates the compensating current ‘IC’ through capacitor.
In VSI these switching process generates switching losses also. Those switching losses are fed by p? loss , which has been generated by comparing actual VDC and reference V*DC voltage. In between them there is PI controller which track the IC current. For generating gate pulses, Hysteresis band current control method has selected.
These pulses are fed into six switches of VSI. ON and OFF process of six switches allow to flow the IC current. So the PI controller track to change the gate pulses until IC becomes equal to I*C.

III.TECHNIQUES FOR SHUNT ACTIVE POWER FILTER
Four techniques are considered here, one is Constant Instantaneous Power (CIP), second is Sinusoidal Current Control (SCC), third one is Synchronous Reference Frame Theory (DQ), and fourth one is Generalized Fryze Current Control.

Constant Instantaneous Power Technique (CIP)
This technique used Clarke transformation 8 for converting a, b, c three phase axis values to alpha-beta two phase axis.

Fig.2. Block diagram of CIP method
The key thing for separation these all things is that we can eliminate any power out of four (p, p,q, q). So we are flowing the current in such a way that controls the different power.

In CIP technique we selected p and whole q (q+ q) for elimination so that there are no harmonics in source current because all oscillating part of power has been eliminated. But only in balanced supply case. In unbalanced and/or disturbed supply voltage it will give bad result as we will see in simulation result. All the discussion of above has simply given in fig.2.
B.Sinusoidal Current Control Technique with Phase Locked Loop (SCC)
This method is modification of CIP method. This method is very useful when there is distortion and /or unbalance from supply side. Positive sequence detection block determine sequence and give only positive sequence voltage as output.

1685925131572000Fundamental positive sequence diagram(PSD) is given in fig.4. Here supply voltages transformed into alpha beta axis. And currents are fed into PLL block and that currents are used for calculation of instantaneous power p` and q`. By applying these powers to two low pass butterworth filters with cut off frequencies 50Hz. Which gives p?? and q ?. These powers and alpha- beta currents are fed to alpha-beta voltage calculation block with equation that shown in fi.4.

Fig.3. Block diagram of SCC strategy
so we have finally pure sine wave which have positive sequence.

Fig.4. Block diagram of PSD
Here in PLL circuit block PI controller decides w. then integrator block gives wt which gives two 90-degree phase shift alpha and beta currents. In Sinusoidal Current Control technique, the key operation is inside the PSD and PLL blocks. In distortion and/or unbalance supply condition this method gives best result that we will discuss in simulation result later.

Synchronous Reference Frame Theory (DQ)
In the proposed controller with the existing phase (considered ? phase), other orthogonal fictitious phase is created which is considered as ? phase. This orthogonal ? phase generation has been done with the quarter cycle time delay method. Generation of ?-? quadrature phases resembles the Clarke’s transformation in three phase theory. Accordingly this ? and ? instantaneous values are transformed into synchronous reference frame (SRF) based d-q components. Here Clarke and then Park transformation is implemented where the reference angle is obtained through single phase PLL. In order to obtain the fundamental positive sequence component of distorted PCC voltage due to presence of nonlinear load, the variable dc value along d axis due to presence of nonlinear load has been kept constant with the application of Moving-Average Filter (MAF)

Fig.5. Block diagram of DQ
GeneralizedFryzeCurrentsMinimization Technique (Fryze)
Plus point of this method is that it does not require Clarke transformation. So it is very simple compared with previous two methods. It directly calculates instantaneous voltage and current for each phase.

Fig.6 represent diagram for Fryze method. In that also Gloss has added same as p? loss in above two methods which supply the switching losses for VSI. Reference current are fed into PWM block to generate gate pulses. Fryze methods draws less value of RMS current for same power compared with other two methods. But it has some higher THD in source current that we will see in simulation result. So we can say that this is the second best method for out of three.

Fig.6. Block diagram of FRYZE current control strategy
IV.SIMULATION RESULTS
Above discussed all three methods are performed in MATLAB 2016a software for different operating condition.

MATLAB/Simulink of SAPF

System Data for simulation
TABLE I.PARAMETERS FOR SIMULATION
Vsupply (L-L) 400 V
Load (RL) R=150 ohm, L=0.5mH
Frequency 50Hz
Smoothing reactor 8mH with 0.02 ohm resistor
DC capacitance 1000 micro F
Reference DC voltage 600 V
Load current (peak) ~ 3A (peak)
Line parameter(RL) R=0.1 ohm, L=2mH
TABLE II.%THD FOR DIFFERENT TECHNIQUES
Technique % THD
Constant Instantaneous Power 3.39
Sinusoidal Current Control 3.26
Fryze Current Control 3.16
Synchronous Reference Frame 3.12
V.CONCLUSION
A non-linear load is supplied by the three phase power supply and shunt active power filter is used. Constant instantaneous power method, sinusoidal current control method, Fryze current control technique, and synchronous reference frame methods for active power filter are developed in MATLAB/Simulink environment. The shunt active power filter effectively eliminates the unwanted harmonic content introduced by the non-linear load in the distribution systems.

Source current and compensating currents for all methods are plotted. It is observed that each and every technique is effective in reducing the harmonic content. Results shows that the % THD is under 5 % in all the control methodologies.

From the analysis, it shows that % THD is equal to 3.12 % in synchronous reference frame method, which is superior to the remaining three methods. Finally the proposed control methods for shunt active power filter smoothens the current waveform, voltage imbalance, reduces the % THD of the source current, improves the power factor to the unity, and overall efficiency of the distribution system is improved.REFERENCES
1 Instantaneous power theory and application to power conditioning by Hirofumi Akagi,Edson Hirokaju,Mauricio Aredes.IEEE press, A john wiley and sons publication.

2 Power Quality Problems and Mitigation Techeniques,First edision,by Bhim singh,Ambrish Chandra,and Kamal Al Hadad 2015 Johm wiley and sons publication.

3 Power Quality by C.Sanakaran CRC press.

4 Thomas’Calculation 11th edision by Weir and Maurice D, Pearson publication.

5 An Advanced Current Control Strategy for Three Phase Shunt Active Power Filters by Quoc Nam Trinth And Hong Hee Lee,Senior member ,IEEE.IEEEtransactiononindustrialelectronics vol.60no.12december 2013
6 An Implementation of an Adaptive Control Algorythm for a Three Phase ShuntActive Filter. By Bhim Singh, Senior Member,IEEE and Jitendra Solanki, IEEE Transaction on industrial electronics vol,56 no,8 aug 2009.

7 MPOSO based optimal control of SAPF using variable structure fuzzy logic sliding mode controller for hybrid(PV-FC-Wind-Battery) energy utilization scheme by Adel A.A.Elgammal,Mohammed F.Elinaggar.IET renewable power generation
8 Circuit Analysis of AC power system vol 1by Edith Clarke joh wiley and sons publication.

9 Application of shunt active power filter for harmonic reduction and reactive power compensation in three phase four wire system. By Leonardo.B. Campanhol, Sergio A Olivia da Silva, Alessandro Goedtel. IET Power Electron.2014 vol.7.Iss,pp.2825-2836 DOI : 10.1049/iet-pel.2014.0027

Development of Different Control techniques for Shunt Active Power Filter
Kranthi Kumar Vanukuru
Research Scholar, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

[email protected] Pakkiraiah
Associate Professor, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

[email protected] – Extensive use of the Non-linear elements like power electronic devices, circuits with inductor and capacitor are effecting the quality of power. All non-linear loads induces harmonics into the system. Shunt active power filters (SAPF) are used to improve the power quality by reducing the harmonics under specified levels along with improving the power factor. This paper deals with the development of different control methods for power quality improvement in shunt active power filter. Apart from other familiar existence techniques, four different methods are developed, first constant instantaneous power control by using the Instantaneous active reactive power theory, second sinusoidal current control method by using phase locked loop control, third Fryze current control with a positive sequence detector, and fourth Synchronous Reference Frame theory (DQ). Bridge rectifier with RL load is considered. SAPF controlled by mentioned controlling techniques were implemented by using MATLAB/Simulink environment. Simulation results are obtained with wave forms for different controlling techniques for SAPF. Total harmonic distortion (THD) data of all four cases are tabulated and discussed. By analyzing all the simulation results, it comes out that Synchronous Reference Frame method gives good results.
Keywords – Shunt Active Power Filter (SAPF), Constant Instantaneous Power Method (CIP), Sinusoidal Current Control Strategy with Phase Locked Loop (SCC), Synchronous Reference Frame (DQ), Positive Sequence Detector (PSD).

Introduction
The utilization of power electronic devices has been enormously increased now a days, major industries with different equipment, loads in the distribution system creates lot of disturbances to the current waveforms, causing distortion in the waveform. Non-linear loads causes disturbances to the other users and causes interference in Telecommunication networks. Compensation control scheme was developed to limit the effect of non-linear loads 1. Rapid technical advances in power electronics and micro-electronics such as uninterrupted power supplies, personal computers, and various other consumer electronics draw highly distorted current from the grid. A large harmonic currents flows in phases in case three phase loads, and flows through neutral wire in case of single phase loads. A constant-hysteresis, tolerance-band controller is developed to protect the other users from the adverse effects of these loads 2. Shunt active power filter is designed to achieve reactive power compensation to bring the power factor near to the unity. Feedback control law with analytically tuned PI controller is used in APF 3. Various controlling techniques are developed for APF, mathematical modelling of synchronous reference frame approach is proposed to eliminate harmonics and to compensate reactive power of non-linear load in three phase systems 4. Measuring the all variables for power quality analysis at each every point is not economical. Therefore, an efficient algorithm has been prepared to make the system observable. So that the overview of the power quality can be observed by managers of utility companies. Algorithm evaluate the power in distribution network and make available for the power quality process 5. Harmonics caused by the non-linear loads has an effect on the other users, efficiency of the transmission lines and responsible for malfunctioning of the protective relays. Kalman filter and the artificial neural network algorithm was developed for the protection of the transmission line 6.

There are various control algorithms for shunt active power filter to reduce the harmonics in non-linear loads. Synchronous source current detection method, instantaneous active reactive power theory, I cos Ø theory and power balance theories are discussed and analysed the results of all the four methodologies 7. PQ theory was developed for APF for reactive power compensation and current harmonic reduction. It improves the efficiency of the system and brings the power factor nearer to the unity. APF with PQ theory will also eliminates the oscillations in active power. Thereby, end user will get constant instantaneous active power 8. Shunt active power filter with sinusoidal source current control strategy has been discussed. This method balances the voltage fluctuations and voltage imbalances in the power supply 9. Fryze current control method for active power filter is one of the efficient method of control. A positive sequence detector was introduced in this method. The reference currents are generated by using the Fryze current minimization algorithm and hysteresis current controller generates the switching signal for voltage source inverter 10. A comparative study of three control methods for APF was discussed. From the obtained results, it has been observed that the current harmonics are reduced considerably to bring the value down to meet the IEEE standards. Now, in this paper, one more technique ‘synchronous reference frame’ (DQ) is introduced. Results shows that this method is effectively reduces the harmonic level in the given distribution system.

II.BASIC OPERATION OF SHUNT ACTIVE POWER FILTER
Fig.1 shows fundamental block diagram of SAPF with source, nonlinear load. Where isa, isb, isc are source currents, ila, ilb, ilc are line currents and ica, icb, icc are compensating currents.

Fig.1. Block diagram of Shunt Active Power Filter
The reference current calculation block represents any of three methods mentioned above. In this block inputs are line voltages and line currents which are used to generate the reference current I*C. The error signal obtained by comparing I*C and IC is fed to PWM converter. The output of PWM converter are six gate signals which in turn applied to VSI. The VSI circulates the compensating current ‘IC’ through capacitor.
In VSI these switching process generates switching losses also. Those switching losses are fed by p? loss , which has been generated by comparing actual VDC and reference V*DC voltage. In between them there is PI controller which track the IC current. For generating gate pulses, Hysteresis band current control method has selected.
These pulses are fed into six switches of VSI. ON and OFF process of six switches allow to flow the IC current. So the PI controller track to change the gate pulses until IC becomes equal to I*C.

III.TECHNIQUES FOR SHUNT ACTIVE POWER FILTER
Four techniques are considered here, one is Constant Instantaneous Power (CIP), second is Sinusoidal Current Control (SCC), third one is Synchronous Reference Frame Theory (DQ), and fourth one is Generalized Fryze Current Control.

Constant Instantaneous Power Technique (CIP)
This technique used Clarke transformation 8 for converting a, b, c three phase axis values to alpha-beta two phase axis.

Fig.2. Block diagram of CIP method
The key thing for separation these all things is that we can eliminate any power out of four (p, p,q, q). So we are flowing the current in such a way that controls the different power.

In CIP technique we selected p and whole q (q+ q) for elimination so that there are no harmonics in source current because all oscillating part of power has been eliminated. But only in balanced supply case. In unbalanced and/or disturbed supply voltage it will give bad result as we will see in simulation result. All the discussion of above has simply given in fig.2.
B.Sinusoidal Current Control Technique with Phase Locked Loop (SCC)
This method is modification of CIP method. This method is very useful when there is distortion and /or unbalance from supply side. Positive sequence detection block determine sequence and give only positive sequence voltage as output.

1685925131572000Fundamental positive sequence diagram(PSD) is given in fig.4. Here supply voltages transformed into alpha beta axis. And currents are fed into PLL block and that currents are used for calculation of instantaneous power p` and q`. By applying these powers to two low pass butterworth filters with cut off frequencies 50Hz. Which gives p?? and q ?. These powers and alpha- beta currents are fed to alpha-beta voltage calculation block with equation that shown in fi.4.

Fig.3. Block diagram of SCC strategy
so we have finally pure sine wave which have positive sequence.

Fig.4. Block diagram of PSD
Here in PLL circuit block PI controller decides w. then integrator block gives wt which gives two 90-degree phase shift alpha and beta currents. In Sinusoidal Current Control technique, the key operation is inside the PSD and PLL blocks. In distortion and/or unbalance supply condition this method gives best result that we will discuss in simulation result later.

Synchronous Reference Frame Theory (DQ)
In the proposed controller with the existing phase (considered ? phase), other orthogonal fictitious phase is created which is considered as ? phase. This orthogonal ? phase generation has been done with the quarter cycle time delay method. Generation of ?-? quadrature phases resembles the Clarke’s transformation in three phase theory. Accordingly this ? and ? instantaneous values are transformed into synchronous reference frame (SRF) based d-q components. Here Clarke and then Park transformation is implemented where the reference angle is obtained through single phase PLL. In order to obtain the fundamental positive sequence component of distorted PCC voltage due to presence of nonlinear load, the variable dc value along d axis due to presence of nonlinear load has been kept constant with the application of Moving-Average Filter (MAF)

Fig.5. Block diagram of DQ
GeneralizedFryzeCurrentsMinimization Technique (Fryze)
Plus point of this method is that it does not require Clarke transformation. So it is very simple compared with previous two methods. It directly calculates instantaneous voltage and current for each phase.

Fig.6 represent diagram for Fryze method. In that also Gloss has added same as p? loss in above two methods which supply the switching losses for VSI. Reference current are fed into PWM block to generate gate pulses. Fryze methods draws less value of RMS current for same power compared with other two methods. But it has some higher THD in source current that we will see in simulation result. So we can say that this is the second best method for out of three.

Fig.6. Block diagram of FRYZE current control strategy
IV.SIMULATION RESULTS
Above discussed all three methods are performed in MATLAB 2016a software for different operating condition.

MATLAB/Simulink of SAPF

System Data for simulation
TABLE I.PARAMETERS FOR SIMULATION
Vsupply (L-L) 400 V
Load (RL) R=150 ohm, L=0.5mH
Frequency 50Hz
Smoothing reactor 8mH with 0.02 ohm resistor
DC capacitance 1000 micro F
Reference DC voltage 600 V
Load current (peak) ~ 3A (peak)
Line parameter(RL) R=0.1 ohm, L=2mH
TABLE II.%THD FOR DIFFERENT TECHNIQUES
Technique % THD
Constant Instantaneous Power 3.39
Sinusoidal Current Control 3.26
Fryze Current Control 3.16
Synchronous Reference Frame 3.12
V.CONCLUSION
A non-linear load is supplied by the three phase power supply and shunt active power filter is used. Constant instantaneous power method, sinusoidal current control method, Fryze current control technique, and synchronous reference frame methods for active power filter are developed in MATLAB/Simulink environment. The shunt active power filter effectively eliminates the unwanted harmonic content introduced by the non-linear load in the distribution systems.

Source current and compensating currents for all methods are plotted. It is observed that each and every technique is effective in reducing the harmonic content. Results shows that the % THD is under 5 % in all the control methodologies.

From the analysis, it shows that % THD is equal to 3.12 % in synchronous reference frame method, which is superior to the remaining three methods. Finally the proposed control methods for shunt active power filter smoothens the current waveform, voltage imbalance, reduces the % THD of the source current, improves the power factor to the unity, and overall efficiency of the distribution system is improved.REFERENCES
1 Instantaneous power theory and application to power conditioning by Hirofumi Akagi,Edson Hirokaju,Mauricio Aredes.IEEE press, A john wiley and sons publication.

2 Power Quality Problems and Mitigation Techeniques,First edision,by Bhim singh,Ambrish Chandra,and Kamal Al Hadad 2015 Johm wiley and sons publication.

3 Power Quality by C.Sanakaran CRC press.

4 Thomas’Calculation 11th edision by Weir and Maurice D, Pearson publication.

5 An Advanced Current Control Strategy for Three Phase Shunt Active Power Filters by Quoc Nam Trinth And Hong Hee Lee,Senior member ,IEEE.IEEEtransactiononindustrialelectronics vol.60no.12december 2013
6 An Implementation of an Adaptive Control Algorythm for a Three Phase ShuntActive Filter. By Bhim Singh, Senior Member,IEEE and Jitendra Solanki, IEEE Transaction on industrial electronics vol,56 no,8 aug 2009.

7 MPOSO based optimal control of SAPF using variable structure fuzzy logic sliding mode controller for hybrid(PV-FC-Wind-Battery) energy utilization scheme by Adel A.A.Elgammal,Mohammed F.Elinaggar.IET renewable power generation
8 Circuit Analysis of AC power system vol 1by Edith Clarke joh wiley and sons publication.

9 Application of shunt active power filter for harmonic reduction and reactive power compensation in three phase four wire system. By Leonardo.B. Campanhol, Sergio A Olivia da Silva, Alessandro Goedtel. IET Power Electron.2014 vol.7.Iss,pp.2825-2836 DOI : 10.1049/iet-pel.2014.0027

Development of Different Control techniques for Shunt Active Power Filter
Kranthi Kumar Vanukuru
Research Scholar, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

We Will Write a Custom Essay Specifically
For You For Only $13.90/page!


order now

[email protected] Pakkiraiah
Associate Professor, Dept. of EEE
KLEF, Deemed to be University.

Guntur Dt. – 522 502, India.

[email protected] – Extensive use of the Non-linear elements like power electronic devices, circuits with inductor and capacitor are effecting the quality of power. All non-linear loads induces harmonics into the system. Shunt active power filters (SAPF) are used to improve the power quality by reducing the harmonics under specified levels along with improving the power factor. This paper deals with the development of different control methods for power quality improvement in shunt active power filter. Apart from other familiar existence techniques, four different methods are developed, first constant instantaneous power control by using the Instantaneous active reactive power theory, second sinusoidal current control method by using phase locked loop control, third Fryze current control with a positive sequence detector, and fourth Synchronous Reference Frame theory (DQ). Bridge rectifier with RL load is considered. SAPF controlled by mentioned controlling techniques were implemented by using MATLAB/Simulink environment. Simulation results are obtained with wave forms for different controlling techniques for SAPF. Total harmonic distortion (THD) data of all four cases are tabulated and discussed. By analyzing all the simulation results, it comes out that Synchronous Reference Frame method gives good results.
Keywords – Shunt Active Power Filter (SAPF), Constant Instantaneous Power Method (CIP), Sinusoidal Current Control Strategy with Phase Locked Loop (SCC), Synchronous Reference Frame (DQ), Positive Sequence Detector (PSD).

Introduction
The utilization of power electronic devices has been enormously increased now a days, major industries with different equipment, loads in the distribution system creates lot of disturbances to the current waveforms, causing distortion in the waveform. Non-linear loads causes disturbances to the other users and causes interference in Telecommunication networks. Compensation control scheme was developed to limit the effect of non-linear loads 1. Rapid technical advances in power electronics and micro-electronics such as uninterrupted power supplies, personal computers, and various other consumer electronics draw highly distorted current from the grid. A large harmonic currents flows in phases in case three phase loads, and flows through neutral wire in case of single phase loads. A constant-hysteresis, tolerance-band controller is developed to protect the other users from the adverse effects of these loads 2. Shunt active power filter is designed to achieve reactive power compensation to bring the power factor near to the unity. Feedback control law with analytically tuned PI controller is used in APF 3. Various controlling techniques are developed for APF, mathematical modelling of synchronous reference frame approach is proposed to eliminate harmonics and to compensate reactive power of non-linear load in three phase systems 4. Measuring the all variables for power quality analysis at each every point is not economical. Therefore, an efficient algorithm has been prepared to make the system observable. So that the overview of the power quality can be observed by managers of utility companies. Algorithm evaluate the power in distribution network and make available for the power quality process 5. Harmonics caused by the non-linear loads has an effect on the other users, efficiency of the transmission lines and responsible for malfunctioning of the protective relays. Kalman filter and the artificial neural network algorithm was developed for the protection of the transmission line 6.

There are various control algorithms for shunt active power filter to reduce the harmonics in non-linear loads. Synchronous source current detection method, instantaneous active reactive power theory, I cos Ø theory and power balance theories are discussed and analysed the results of all the four methodologies 7. PQ theory was developed for APF for reactive power compensation and current harmonic reduction. It improves the efficiency of the system and brings the power factor nearer to the unity. APF with PQ theory will also eliminates the oscillations in active power. Thereby, end user will get constant instantaneous active power 8. Shunt active power filter with sinusoidal source current control strategy has been discussed. This method balances the voltage fluctuations and voltage imbalances in the power supply 9. Fryze current control method for active power filter is one of the efficient method of control. A positive sequence detector was introduced in this method. The reference currents are generated by using the Fryze current minimization algorithm and hysteresis current controller generates the switching signal for voltage source inverter 10. A comparative study of three control methods for APF was discussed. From the obtained results, it has been observed that the current harmonics are reduced considerably to bring the value down to meet the IEEE standards. Now, in this paper, one more technique ‘synchronous reference frame’ (DQ) is introduced. Results shows that this method is effectively reduces the harmonic level in the given distribution system.

II.BASIC OPERATION OF SHUNT ACTIVE POWER FILTER
Fig.1 shows the Basic block diagram of SAPF. When the Rectifier type load is connected to the three phase supply, harmonics are induced in rectifier load and it affects source current. SAPF is used to supress the harmonics in source current by injecting compensating currents from VSI. Switching pulses of a VSI are given by the HCC by comparing the actual and reference compensating currents. Reference currents are generated from different control strategies by providing source voltage and load current. Switching losses are generated by PI controller by comparing the actual and reference Vdc values.

Fig.1. Block diagram of Shunt Active Power Filter
III.TECHNIQUES FOR SHUNT ACTIVE POWER FILTER
Four techniques are considered here, one is Constant Instantaneous Power (CIP), second is Sinusoidal Current Control (SCC), third one is Generalized Fryze Current Control theory, and fourth one is Synchronous Reference Frame (DQ) theory.

Constant Instantaneous Power Technique (CIP)
The p-q theory consists of alpha beta zero transformation. It converts 3-phase voltages and currents to the corresponding alpha beta zero reference frame. These phase voltages and currents on the alpha beta zero axis will define the instantaneous active (p) and reactive (q) power. The reference compensating currents can be obtained from active (p) and reactive (q) power. The reference compensating currents are compared with the actual compensating current generated at the inverter output and the error signals obtained are used to generate the gating pulses for the 3-phase inverter by HCC as shown in Fig.2.

Fig.2. Block diagram of CIP method
B.Sinusoidal Current Control Technique with Phase Locked Loop (SCC)
This method is modification of CIP method. Positive sequence voltages are given as CIP source voltage input, which are generated from the positive sequence detector as shown in Fig.3. In Fig.4, The control strategy of PSD is given, which improves the system performance. Phase Locked Loop (PLL) is shown in Fig.5. PLL calculates the I?/, I?/ for getting instantaneous power p and q from source voltages.

Fig.3. Block diagram of SCC strategy

Fig.4. Block diagram of PSD

Fig.5. Block diagram of PLL
Generalized Fryze Currents Minimization Technique (Fryze)
The proposed FCC is presented in Fig.6. Power is calculated from the source voltages and load currents. P loss is added to the calculated power and multiplied with the source voltages in order to get the active currents. The difference between the actual currents and load currents gives the compensating current values.

Fig.6. Block diagram of Fryze
Synchronous Reference Frame (DQ) method.

DQ method is shown in Fig.7. Compensating currents are calculated by comparing the actual and reference currents. Reference currents are generated from the direct and quadrature axis load currents. Low pass filter is used to remove the fluctuation in current.

Fig.7. Block diagram of DQ method.

IV.SIMULATION RESULTS
All the four methods considered in this paper are developed in MATLAB 2015a software. A balanced three phase source supplies power to the non-linear load. Non-linear load consists of bridge rectifier along with RL load. Basic active power filter is connected to the line through a circuit breaker. In the APF, switching signals for VSI are generated by the CIP method, SCC method, FCC method, and DQ method separately. Fig.8 shows the working model of the proposed method.

MATLAB/Simulink of SAPF

Fig.8. MATLAB/Simulink model.

System Parameters
A three phase, 400 V, 50 Hz source is given to the load consists of a bride rectifier and RL load, R=150 ?, and L=0.5 mH. Smoothing reactor is having 8 mH inductance with 0.02 ? resistance. The value of DC capacitance is 1500 ?F, and the Reference DC voltage is 600 V. Line parameters are, 0.1 ? resistance and 2 mH inductance. The peak value of load current is approximately 3 ampere.

Simulation waveforms
(i) Source current without APF: Source current waveform is affected by the non-linear load when it is operated without APF. Fig.9 (a) shows the distortion in Is affected by the IL, (b) shows the harmonic content in Source current

Fig.9 (a) Load current (IL) and Source current (Is) (b) % THD of Source current (Is)
(ii) Power Factor (PF):
TABLE I.PF without APF and with APF by using CIP control method:
Without APF With APF
(iii) Source Current (Is) and Compensating Current (Ic):
TABLE II:Source current and Compensating current for Different Techniques:
Sl. No. Method Source Current Compensating Current
01 CIP
02 SCC
03 FCC
04 DQ
TABLE III.%THD FOR DIFFERENT TECHNIQUES
Technique % THD
Constant Instantaneous Power (CIP) 3.39
Sinusoidal Current Control (SCC) 3.26
Fryze Current Control (FCC) 3.16
Synchronous Reference Frame (DQ) 3.12
V.CONCLUSION
A non-linear load is supplied by the three phase power supply and shunt active power filter is used. Constant instantaneous power method, sinusoidal current control method, Fryze current control technique, and synchronous reference frame methods for active power filter are developed in MATLAB/Simulink environment. The shunt active power filter effectively eliminates the unwanted harmonic content introduced by the non-linear load in the distribution systems.

Source current and compensating currents for all methods are plotted. It is observed that each and every technique is effective in reducing the harmonic content. Results shows that the % THD is under 5 % in all the control methodologies.

From the analysis, it shows that % THD is equal to 3.12 % in synchronous reference frame method, which is superior to the remaining three methods. Finally the proposed control methods for shunt active power filter smoothens the current waveform, voltage imbalance, reduces the % THD of the source current, improves the power factor to the unity, and overall efficiency of the distribution system is improved.

REFERENCES:
1 R. K. Tripahi, Ch. Pratap Singh, “Power quality control of unregulated non-linear loads”, 2010 International Conference on Power, Control and Embedded Systems, 978-1-4244-8542-0/10©2010 IEEE
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3 Ramos G.A., Costa-Castello R., Olm J.M. (2013) Shunt Active Power Filter. In: Digital Repetitive Control under Varying Frequency Conditions. Lecture Notes in Control and Information Sciences, vol 446. Springer, Berlin, Heidelberg.

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8 Anand Panchbhai, Shreya Parmar, Nikunj Prajapati, “Shunt Active Filter for Harmonic And Reactive, Power Compensation Using p-q Theory, 2017 International Conference on Power and Embedded Drive Control (ICPEDC), 16-18 March 2017, Electronic ISBN: 978-1-5090-4679-9.

9 Hirofumi Akagi, Edson Hirokazu Watanabe, Mauricio Aredes, “Instantaneous Power Theory and Applications to Power Conditioning”, IEEE Press, John Wiley & Sons, Inc. Publication, pp. 137-145.

10 Manish Kr. Singh, Jayanti Chaudhary, “Fryze Current Controller Based Active Power Filter”, Third International Conference on Advances in Control and Optimization of Dynamical Systems, March 13-15, 2014, pp. 794-800.

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