Study of Control Strategies for Shunt Active Power Filter for Harmonics Suppression

ABSTRACT:  

Excessive use of nonlinear and time varying devices results in harmonic currents in the secondary distribution system. The suppression of harmonics is a dominant issue and one of the practical ways to compensate harmonics is shunt active power filter (SAPF). The core part of the SAPF is control techniques used for reference current generation. This paper presents a comprehensive study of three control strategies namely instantaneous reactive power (p – q) theory, synchronous reference frame (SRF) theory and instantaneous active and reactive current (id - iq) component method for SAPF in a three phase three wire distribution system. These three control methods aims to compensate harmonics, reactive power and load unbalance under sinusoidal balanced supply voltage conditions. Simulation results present a relative investigation of three control techniques based on current THD and load unbalance.

KEYWORDS:

1.      Harmonics

2.      Hysteresis band current control (HBCC)

3.      Id - iq method

4.      Nonlinear loads

5.      P – q theory

6.      Shunt active power filter

7.      SRF theory

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. SAPF connected to distribution grid

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of SAPF with p-q theory under nonlinear balanced

load (a) Source voltage (b) Load current (c) Source current after filtering

(d) Compensation current.

Fig. 3. Simulation results of SAPF with id-iq method under nonlinear

balanced load (a) Source current after filtering (b) Compensation current

Fig. 4. Simulation results of SAPF with id-iq method under nonlinear

unbalanced load (a) Source voltage (b) Load current (c) Source current

after filtering (d) Compensation current.

Fig. 5. Dynamic performance of SAPF during load change with id-iq method

(a)     Load current (b) Source current (c) Compensation current.

Fig. 6. (a) Source voltage (V) and load current (A) (b) Source voltage (V)

and source current (A) (c) Compensation current (d) Reactive power

demand of the load (e) Reactive power supplied by the SAPF (f)

Reactive power supplied by the source.

CONCLUSION:

The harmonic distortions exist in the distribution system due to the massive use of power electronic based nonlinear loads. Harmonic distortions can result in serious problems such as increase in current, reactive VAs, VAs, power factor reduction and increase in losses. The SAPF with three control strategies viz. p-q theory, SRF theory and id-iq method has been studied in this paper. The simulation has been carried out for different load scenarios and the THD, percentage of individual dominant harmonics has also observed. From the simulation analysis, it is observed that the SAPF giving quite reasonably good performance in compensating harmonics, reactive power and load unbalance. Among the three control techniques, it is noticed that the id-iq method gives reasonably better performance in terms of current THD.

 REFERENCES:

[1] S. Rahmani, N. Mendalek, and K. Al-Haddad, "Experimental design of a nonlinear control technique for three-phase shunt active power filter," IEEE Trans. Ind. Electron, vol. 57, no. 10, pp. 3364-3375, Oct. 2010.

[2] IEEE Recommended Practice and Requirements for Harmonic Control in Electric Power Systems - Redline," IEEE Std 519-2014 (Revision of IEEE Std 519-1992) - Redline , pp.1-213, June 11 2014.

[3] S. Senini and P. J. Wolfs, “Hybrid active filter for harmonically unbalanced three phase three wire railway traction loads,” IEEE Trans. Power Electron., vol. 15, no. 4, pp. 702–710, Jul. 2000.

[4] S. Rahmani, K. Al-Haddad, H. Y. Kanaan, and B. Singh,

“Implementation and simulation of a modified PWM with two current control techniques applied to a single-phase shunt hybrid power filter,” Proc. Inst. Elect. Eng. Electr. Power Appl., vol. 153, no. 3, pp. 317–326, May 2006.

[5] B. Singh, K. Al-Haddad, and A. Chandra, "A review of active filters for power quality improvement," IEEE Trans. Ind. Electron, vol. 46, no. 5, pp. 960-971, Oct 1999.

Harmonic Mitigation by SRF Theory Based Active Power Filter using Adaptive Hysteresis Control

ABSTRACT:  

Power quality is an all-encompassing concept for a multitude of individual types of power system disturbances. The presence of harmonics in power supply network poses a severe  power quality problem that results in greater power losses in the distribution system, interference problems in communication systems and, sometimes, in operation failures of electronic equipment. Shunt active power filters are employed to suppress the current harmonics and reduce the total harmonic distortion (THD). The voltage source inverter (VSI) is the core of an active power filter. The hysteresis current control is a method of controlling the VSI. Hysteresis control can be either of fixed band type or adaptive band type. In this paper, Synchronous Reference Frame (SRF) theory is implemented for the generation of reference current signals for the controller. This paper investigates the effectiveness of the proposed model in harmonics currents mitigation by simulating a model of a three-phase three wire shunt active power filter based on adaptive hysteresis current control and SRF theory. Simulation results indicate that the proposed active power filter can restrain harmonics of electrical source current effectively

KEYWORDS:

1.      Synchronous reference frame theory

2.      Adaptive hysteresis control

3.      Harmonic mitigation

4.      Shunt active filter

5.      Voltage source inverter

SOFTWARE: MATLAB/SIMULINK

BLOCK DIAGRAM:

Fig. 1. Reference Current Generation Block

 EXPECTED SIMULATION RESULTS:

Fig. 2. Nonlinear Load Currents

Fig. 3. Compensating APF Currents

Fig.4.Source currents after compensation

Fig.5. Harmonic analysis of source current with Adaptive Hysteresis Band

CONCLUSION:

In the adaptive band hysteresis control, the switching  frequency is nearly constant with respect to the system parameters and defined switching frequency. However, at low switching frequency case, the tracking is not as good as the one in high switching frequency. Obviously, a decrease in switching frequency results in an increase in the hysteresis bandwidth that causes the free operation of current error in a  wider range. This higher low-frequency error, in turn, will lead to higher low order harmonics in the source current, and hence higher THD. Based on the above facts, the switching frequency should be kept as high as possible for better performances of adaptive band hysteresis current control.

The developed model has the following advantages:

(i)                 Simplification of the power conversion circuit can be achieved.

(ii)               (ii) Under the developed model, the performance of control strategy can be effectively examined without long simulation run time and convergence problem.

REFERENCES:

[I] L. A Moran, J. W. Dixon, "Active Filters", Chapter 33 in "Power Electronics Handbook", Academic Press, August 200 I, pp. 829-841.

[2] IEEE Recommended Practices and Requirements for Harmonic Control in Electrical Power Systems, IEEE Standard 519-1992, 1993

[3] Singh, 8.; Chandra, A; AI-Haddad K. "Computer-Aided Modeling and Simulation of Active Power Filters", Electric Power Components and Systems, 27: 11, 1227 -1241,1999

[4] L. Moran, 1. Dixon, J. Espinoza, R. Wallace "Using Active Power Filters to Improve Power Quality", 5th Brasilian Power Electronics Conference, COBEP'99, 19-23 September 1999, pp 501-511.

[5] Massoud, AM. ; Finney, SJ.; Williams, B.W. "Review of harmonic current extraction techniques for an active power filter", 11^th International Conference on Harmonics and Quality of Power, pp 154 - 159,12-15 Sept. 2004

A Multilevel Inverter Structure based on Combination of Switched-Capacitors and DC Sources

ABSTRACT:  

This paper presents a switched-capacitor multilevel inverter (SCMLI) combined with multiple asymmetric DC sources. The main advantage of proposed inverter with similar cascaded MLIs is reducing the number of isolated DC sources and replacing them with capacitors. A self-balanced asymmetrical charging pattern is introduced in order to boost the voltage and create more voltage levels. Number of circuit components such as active switches, diodes, capacitors, drivers and DC sources reduces in proposed structure. This multi-stage hybrid MLI increases the total voltage of used DC sources by multiple charging of the capacitors stage by stage. A bipolar output voltage can be inherently achieved in this structure without using single phase H-bridge inverter which was used in traditional SCMLIs to generate negative voltage levels. This eliminates requirements of high voltage rating elements to achieve negative voltage levels. A 55-level step-up output voltage (27 positive levels, a zero level and 27 negative levels) are achieved by a 3-stage system which uses only 3 asymmetrical DC sources (with amplitude of 1Vin, 2Vin and 3Vin) and 7 capacitors (self-balanced as multiples of 1Vin). MATLAB/SIMULINK simulation results and experimental tests are given to validate the performance of proposed circuit.

KEYWORDS:

1.      Multi-level inverter

2.      Switched-capacitor

3.      Bipolar converter

4.      Asymmetrical

5.      Self-balancing

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig (1) Three stage structure of the proposed inverter

EXPECTED SIMULATION RESULTS:

Fig (2) Waveform of the output voltage in (a) 50Hz and pure resistive load (b)

the inset graphs of voltage and current

Fig (3) waveform of the output voltage in 50Hz with resistive-inductive load

Fig (4) Capacitor’s voltage in 50Hz (a) middle stage (b) last stage

CONCLUSION:

In this paper, a multilevel inverter based on combination of multiple DC sources and switched-capacitors is presented. Unlike traditional converters which used H-bridge cell to produce negative voltage that the switches should withstand maximum output AC voltage, the suggested structure has the ability of generating bipolar voltage (positive, zero and negative), inherently. Operating principle of the proposed SCMLI in charging and discharging is carried out. Also, evaluation of reliability has been done and because of high number of redundancy, there has been many alternative switching states which help the proposed structure operate correctly even in fault conditions. For confirming the superiority than others, a comprehensive comparison in case of number of devices and efficiency is carried out and shows that the proposed topology has better performance than others. For validating the performance, simulation and experimental results are brought under introduced offline PWM control method.

REFERENCES:

[1] L. G. Franquelo, J. Rodriguez, J. I. Leon, S. Kouro, R. Portillo, and M. A. M. Prats, “The age of multilevel converters arrives,” IEEE Trans. Ind. Electron. Mag., vol. 2, no. 2, pp. 28–39, June, 2008.

[2] M. Saeedifard, P. M. Barbosa and P. K. Steimer,”Operation and Control of a Hybrid seven Level Converter,” IEEE Trans. Power Electron., vol. 27, no.2, pp. 652–660, February, 2012.

[3] A. Nami. “A New Multilevel Converter Configuration for High Power High Quality Application,” PhD Thesis, Queensland University of Technology, 2010.

[4] V. Dargahi, A. K. Sadigh, M. Abarzadeh, S. Eskandari and K. Corzine, “A new family of modular multilevel converter based on modified flying capacitor multicell converters IEEE Trans. Power Electron., vol. 30, no.

1, pp. 138-147, January, 2015.

[5] I. López, S. Ceballos, J. Pou, J. Zaragoza, J. Andreu, I. Kortabarria and V. G. Agelidis,” Modulation strategy for multiphase Neutral-Point Clamped converters,” IEEE Trans. Power Electron., vol. 31, no. 2, pp. 928–941, March, 2015.

A Highly Efficient and Reliable Inverter Configuration Based Cascaded Multi-Level Inverter for PV Systems

 ABSTRACT:  

 This paper presents an improved Cascaded Multi-Level Inverter (CMLI) based on a highly efficient and reliable configuration for the minimization of the leakage current. Apart from a reduced switch count, the proposed scheme has additional features of low switching and conduction losses. The proposed topology with the given PWM technique reduces the high-frequency voltage transitions in the terminal and common-mode voltages. Avoiding high-frequency voltage transitions achieves the minimization of the leakage current and reduction in the size of EMI filters. Furthermore, the extension of the proposed CMLI along with the PWM technique for 2m+1 levels is also presented, where m represents the number of Photo Voltaic (PV) sources. The proposed PWM technique requires only a single carrier wave for all 2m+1 levels of operation. The Total Harmonic Distortion (THD) of the grid current for the proposed CMLI meets the requirements of IEEE 1547 standard. A comparison of the proposed CMLI with the existing PV Multi-Level Inverter (MLI) topologies is also presented in the paper. Complete details of the analysis of PV terminal and common-mode voltages of the proposed CMLI using switching function concept, simulations, and experimental results are presented in the paper.

KEYWORDS:

1.      Cascaded multi-level inverter

2.       Leakage current

3.      Common-mode voltage

4.      Terminal voltage

SOFTWARE: MATLAB/SIMULINK

CIRCUIT DIAGRAM:

Fig. 1. Proposed five-level grid-connected CMLI with PV and parasitic elements.

 EXPECTED SIMULATION RESULTS:

Fig. 2. Simulation results of proposed five-level CMLI showing the waveforms of : (a) output voltage vuv; (b) grid current iac; (c) terminal voltage vxg; (d) terminal voltage vyg; (e) terminal voltage vzg; (f) leakage current ileak; (g) common-mode voltage vcm.

Fig. 3. Proposed five-level CMLI integrated with MPPT. The subplots give waveforms of : (a) voltage VPV1; (b) voltage VPV2; (c) current IPV1; (d) current IPV2; (e) power PPV1; (f) power PPV2; (g) resultant modulation index ma; (h) output power POUT; (i) modified reference wave vref_modified; (j) inverter output voltage vab.

 CONCLUSION:

In this paper, an improved five-level CMLI with low switch count for the minimization of leakage current in a transformerless PV system is proposed. The proposed CMLI minimizes the leakage current by eliminating the high-frequency transitions in the terminal and common-mode

voltages. The proposed topology also has reduced conduction and switching losses which makes it possible to operate the CMLI at high switching frequency. Furthermore, the solution for generalized 2m+1 levels CMLI is also presented in the paper. The given PWM technique requires only one carrier wave for the generation of 2m+1 levels. The operation, analysis of terminal and common-mode voltages for the CMLI is also presented in the paper. The simulation and experimental results validate the analysis carried out in this paper. The MPPT algorithm is also integrated with the proposed five-level CMLI to extract the maximum power from the PV panels. The proposed CMLI is also compared with the other existing MLI topologies in Table V to show its advantages.

 REFERENCES:

[1] Y. Tang, W. Yao, P.C. Loh and F. Blaabjerg, "Highly Reliable Transformerless Photovoltaic Inverters With Leakage Current and Pulsating Power Elimination," IEEE Trans. Ind. Elect., vol. 63, no. 2, pp. 1016-1026, Feb. 2016.

[2] W. Li, Y. Gu, H. Luo, W. Cui, X. He and C. Xia, "Topology Review and Derivation Methodology of Single-Phase Transformerless Photovoltaic Inverters for Leakage Current Suppression," IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4537-4551, July 2015.

[3] J. Ji, W. Wu, Y. He, Z. Lin, F. Blaabjerg and H. S. H. Chung, "A Simple Differential Mode EMI Suppressor for the LLCL-Filter-Based Single-Phase Grid-Tied Transformerless Inverter," IEEE Trans. Ind. Elect., vol. 62, no. 7, pp. 4141-4147, July 2015.

[4] Y. Bae and R.Y.Kim, "Suppression of Common-Mode Voltage Using a Multicentral Photovoltaic Inverter Topology With Synchronized PWM," IEEE Trans. Ind. Elect., vol. 61, no. 9, pp. 4722-4733, Sept. 2014.

[5] N. Vazquez, M. Rosas, C. Hernandez, E. Vazquez and F. J. Perez-Pinal, "A New Common-Mode Transformerless Photovoltaic Inverter," IEEE Trans. Ind. Elect., vol. 62, no. 10, pp. 6381-6391, Oct. 2015.