2012 IEEE International Conference on Power Electronics, Drives and Energy Systems December16-19, 2012, Bengaluru, India
Performance Comparison of Shunt Active Filter Interfacing Algorithm for Renewable Energy Sources Ilango K, Bhargav.A, Trivikram.A, Kavya.P.S, Mounika.G, and Manjula G. Nair* Department of Electrical and Electronics Engineering, Amrita Vishwa Vidyapeetham University, Amrita School of Engineering, Bengaluru, India.
[email protected],
[email protected]
Abstract— The renewable energy source interfacing with grid is the major issue in the electric utility side. The various types of grid interfacing converter topology have been proposed by researchers to improve quality of power and efficiency of the system. This paper focuses the shunt active filter interface for the renewable energy source with an efficient modified IcosΦ algorithm for controlling the grid /source side power flow and renewable energy power with linear static loads. The proposed shunt active filter interfacing algorithm is compared with the well known algorithm of Instantaneous Reactive Power Theory (IRPT) with modifications for reactive power compensation and real power control from the renewable energy source. The performance of the both the algorithms have been simulated and tested in MATLAB/Simulink.
Keywords— shunt active filter interface, performance comparison, reactive power compensation, power factor correction.
I.
INTRODUCTION
In this paper shunt active filter interface for renewable source is implemented with modifications in IcosΦ control algorithm reported in [1], for real power control from the source /grid side and renewable energy source side. The IcosΦ algorithm has been proved for harmonic, reactive and unbalances compensation in a three phase system with balanced/unbalanced source and load conditions [1]. In this work the performance of proposed modified IcosΦ algorithm is compared with the modified IRPT algorithm for shunt active filter interfacing for renewable energy source which delivering power to the static linear load. In general the renewable energy source is requires power electronic converters for power conditioning and interfacing with utility grid. The power conditioning converter and interfacing converter involves complex control circuits and also leads to bulkier system with increased switching losses, higher implementation cost. The renewable energy sources are used in various applications, based on the applications different types of configuration of topologies have been proposed by various researchers. The commonly used topologies such separately connected systems, micro-grids, multi-port converter are reported in [3], shunt active filter interface with p-q theory reported in [2, 4]. II.
PROPOSED CONFIGURATION FOR RENEWABLE ENERGY SOURCE
978-1-4673-4508-8/12/$31.00 ©2012 IEEE
The Fig.1 shows the schematic diagram of the proposed shunt active filter interface configuration for the renewable energy source. Here, the star connected three phase source symbolizes as the source/grid to the linear RL load, the output from the renewable energy source is considered as a DC output, which is connected across DC link capacitor of the shunt active filter. The grid power supply is controlled by the proposed algorithm, which along with the renewable energy source handles the total power requirement of the load. The configuration consists of source /grid of 400V, 50Hz and two linear RL loads of L1 and L2 with different power factor conditions. These loads are switched at different intervals, based on power factor condition these loads are drawing real power and reactive power. The shunt active filter is designed to provide the reactive power compensation, power factor correction along with the real power exchange to utility grid. The reasons for preferring a shunt active filter interfacing with proposed control algorithm is superior in functionality characteristics, faster performance cost effective for practical implementation and has ability to provide both active and reactive power support ,thereby providing flexible voltage control for power quality improvement.
Fig.1. Proposed Shunt Active Filter Interface for renewable energy source
III. A.
PROPOSED CONTROL ALGORITHMS
Concept of Modified IcosΦ Algorithm A regular shunt active filter is capable of providing only the reactive power support and harmonic current compensation, where as the real power requirements are met
by the source/grid by maintaining the power factor close to unity. Here, the modified IcosΦ control algorithm is more advantageous because it uses the assistance of shunt active filter to provide the real power support from the renewable energy source along with the conventional reactive power support and harmonic current compensation of a regular shunt active filter. The concept of modified control algorithm evolved from IcosΦ control algorithm reported in [1],where the source /grid is required to supply only the fraction of active portion of the load current as determined by the controller. The reference compensation currents for the shunt active filter are deduced as the difference between the actual load current and the desired source current in each phase .i.e. I a (comp ) = I La - I sa ( ref ) ; I b(comp ) = I L - I sb( ref ) ; b
I Lc (comp ) = I Lc - I sc ( ref ) ; (1) where, the desired (reference) source currents in the three phases are given as,
I sa (ref ) = K I s (ref ) × U a =K I s (ref ) sinω t I sb( ref ) = K I s ( ref ) × U b = K I s ( ref ) sin(ω t - 120°) I sc ( ref ) = K I s ( ref ) × U c = K I s ( ref ) sin(ω t + 120°) (2) where K is the load factor which determines how much real power has to be supplied by the source/grid. Ua, Ub, and Uc are the unit amplitude templates of the phase to ground source voltages in the three phases respectively. U a = 1.sin ω t ; U b = 1.sin(ω t - 120°); U c = 1.sin(ω t + 120°); (3) The magnitude of the desired source current Is(ref ) can be expressed as the magnitude of the real component of the fundamental load current in the respective phases .i.e. for phase ‘a’ it can be written as I = Re(I ) .A zero crossing s(ref )
La
detector (ZCD) is used to detect the negative going zero crossing of the corresponding phase voltage. The ZCD has been designed with a tolerance of 5% to ensure that any oscillations around the zero-crossing are taken care of. The phase-shifted fundamental current goes as the “sample” input and the ZCD output pulse goes as the “hold” input to the “sample and hold” circuit whose output is the . This magnitude is multiplied with magnitude IcosΦ = I s(ref )
unit amplitude sine wave in phase with input voltage and also desired fraction which determines how much real power is supplied by the source. The difference between load current and reference source current gives the reference filter current. This reference filter current and actual filter current are given to a hysteresis controller to get required the pulses for the shunt active filter.
Concept of Modified IRPT Control Algorithm In this algorithm proposed by Akagi [5], the instantaneous imaginary power, which is a new electrical quantity, is introduced in three phase circuits. The three phase mains voltages and load currents of the system are sensed and converted into the α-β (two) phase plane using Park’s transformation. B.
1 ⎡ ⎡eα ⎤ 2 1 − 2 − ⎢ = ⎢ ⎥ 3 3 ⎢0 − ⎢⎣eβ ⎥⎦ ⎣ 2
⎤ ⎡ea ⎤ ⎥ ⎢e ⎥ 3 ⎥⎢ b⎥ 2 ⎦ ⎣⎢ ec ⎦⎥
1
2
(4)
Where ea , eb , e c are the three phase mains voltages.
1 ⎡ ⎡iLα ⎤ 2 1 − 2 − ⎢ ⎢i ⎥ = 3 3 ⎢0 − ⎣ Lβ ⎦ ⎣ 2
⎤ ⎡iL a ⎤ 2 ⎥⎢ ⎥ iLb ⎢ ⎥ 3 ⎥ 2 ⎦ ⎢⎣ iLc ⎥⎦
1
(5)
where I La , I Lb , I Lc are the three-phase load currents. The instantaneous real power p L and the instantaneous imaginary power q L consumed by load current are derived as, p L = eα i Lα + eβ i Lβ ; and q L = e α i Lβ - eβ i Lα (6) p L and q L are made up of a DC and an AC component, so that they may be expressed by ~ ~ p L = p L + p L ; and q L = q L + q L (7)
The reference filter currents are determined using the expression given below, ~ ~ * * p f = p L + (1 - k) p L ; and q f = q L + q L (8) where k is the load factor which determines the amount of real power supplied by the source. This is the modification in IRPT proposed by the authors to bring the control of real power from the renewable energy source. For the purpose of current harmonic suppression and of reactive power compensation, the AC term of p L , fraction of DC term of p L and all the terms of q L must be compensated by the active power filter. Hence, the reference signal of the compensation current in the d-q axes can be represented as -1 ⎡iCα ⎤ ⎡ eα eβ ⎤ ⎡p f * ⎤ (9) ⎢i ⎥ = ⎢-e ⎥ ⎢ *⎥ ⎣ Cβ ⎦ ⎣ β eα ⎦ ⎢⎣q f ⎥⎦ Applying inverse Park’s transformation on the above signals gives the three-phase reference compensation currents as,
⎡ ⎡iC * ⎤ ⎢ 0 ⎢ a* ⎥ 2⎢ 1 ⎢iCb ⎥ = 3⎢ 2 ⎢i ⎥ ⎢- 1 ⎢⎣ Cc* ⎥⎦ ⎣ 2 IV.
⎤ ⎥ ⎡i ⎤ 3 ⎥ Cα 2 ⎥ ⎢i ⎥ ⎣ Cβ ⎦ 3 ⎥ 2⎦ 0
(10)
SIMULATION OF SHUNT ACTIVE FILTER INTERFACING ALOGORITHMS FOR RENEWABLE ENERGY SOURCE
The earlier described system, three phase grid is supplying linear RL-load (L1and L2) with shunt active filter interface for renewable energy source has been done using MATLAB/Simulink. For the simulation purpose the renewable energy source output is considered as a rectified DC voltage source connected to DC link of shunt active filter to provide the real power support for the load. The following section explains the performance of proposed algorithms with and without shunt active filter interface
A.
Simulation Results without Shunt Active Filter Interfacing Three phase grid is supplying linear RL-loads of L1and L2. The second load is switched on at t= 0.15sec, the total real and reactive power drawn by these loads is supplied by the source.
Fig.2.Three phase voltages source /grid side
Fig.3.Three phase currents of source /grid side
Fig.5.Three phase load currents of RL linear Load
Fig.2, Fig.3 are the voltage and current wave forms of the three phase system, taken at the source and Fig.4, Fig.5 are voltage and current wave forms measured at load side of the system. From Fig.5 one can easily understand the second load is switched on after the time t= 0.15sec and current magnitude changed to higher level. This current is lagging the source voltage by some angle based on reactive power requirement of linear dynamic loads.
B.
Simulation Results with Shunt Active Filter Interfacing Algorithms The shunt active filter acts as an effective interfacing link between the renewable energy source and grid system. The shunt active filter performs the role of delivering the required amount of reactive power and power factor correction, which works with modified IcosΦ and modified IRPT algorithm generated pulses from the controller circuit. In addition to merely being an interfacing unit, another imperative function of shunt active filter is ability to exchange real power from the renewable energy source to load and grid. But a small amount of power loss will take place in the shunt active filter unit under lightly load conditions. These cases have been proven in the simulation analysis and the results are tabulated in Table I and Table .II. Table I provides the information for modified IcosΦ controller based shunt active filter performance and Table II provides performance of the modified IRPT controller based interfacing. The simulation results of the two linear RL loads switched on at different instants are given below. Fig.6 shows the active and the reactive power drawn by dynamic linear RL loads of L1 and L2. Fig.7 shows the active and reactive power supplied by the three phase source/ grid. Fig.8shows the real and reactive power supported by the renewable energy source through the shunt active filter.
Fig.4. Three phase load voltages of RL linear Load Fig.6. Active and Reactive power drawn by dynamic linear loads
Fig .7.Active and reactive power supplied by source/grid
Fig.10. Modified IRPT Controller performance comprising of load current, source voltage, reference and actual current of shunt active filter interface
Fig.11. shows the phase ‘a’ source /grid voltage and source current after compensation. From this one can easily understand the source voltage and source currents are in phase and thereby the power factor is virtually equal to unity hence it is proven that the power factor of the three phase system is improved using the modified IcosΦ controller.
Fig.8. Real and reactive power supported by shunt active filter at PCC
Fig.9. shows the performance of modified IcosΦ controller with source voltage and load current along with reference current and actual shunt active filter current for reactive power compensation and power factor correction.
Fig .11. Source voltage and source current of phase-a afer compensation using modified Icosφ controller.
Fig.12 shows the phase ‘a’ source /grid voltage and source current after the compensation. The power factor is improved using modified IRPT algorithm based shunt active filter interface ,but when compared to the performance of the modified IcosΦ control algorithm based shunt active filter gives better performance results in less power loss and faster, efficient control .Hence validating the superiority of the modified IcosΦ control algorithm based shunt active filter for the renewable energy source. Fig.9. Modified IcosΦ controller performance comprising source voltage, load current, reference and actual current of shunt active filter interface
Fig.10. shows performance of Modified IRPT controller with load current, source voltage, along with the reference current and actual current of shunt active filter interface for the linear loads which has been switched on at above mentioned time periods of less than 0.15sec and greater than 0.15 sec. Fig.12.Source voltage and current of phase –a for p.f verification using Modified IRPT controller.
V.
CONCLUSION
This paper focuses the performance comparison of the proposed modified IcosΦ control algorithm and modified Instantaneous Reactive Power Theory (IRPT) algorithm for shunt active filter interface for the renewable energy source .Both the algorithm has been developed and simulated in MATLAB/SIMULINK environment. The proposed modified IcosΦ algorithm and modified IRPT control algorithm have ability to provide the power factor correction, reactive power compensation along with real power support from the renewable energy source. It has also been proven that the modified IcosΦ algorithm is a feasible fast acting effective solution for a linear dynamically varying RL load system. The shunt active filter interface for renewable energy is found to be an effective interface between the grid and load. ACKNOWLEDGMENT This work has been funded by DST SERC under Fast Track Scheme for Young Scientists No: 100/IFD/2769. The authors are also grateful to Amrita Vishwa Vidyapeetham University, Amrita School of Engineering, Bengaluru campus for extending support for the progress of the project. REFERENCES [1] G. Bhuvaneswari, Manjula G. Nair, “Design, Simulation and Analog Circuit Implementation of a Three – Phase Shunt Active Filter Using the IcosΦ Algorithm”, IEEE Transactions on Power Delivery April 2008. [2] J. G. Pinto, R. Pregitzer, Luis F. C. Monteiro, Joao L. Afonso, “3-Phase 4-Wire Shunt Active Power Filter with Renewable Energy Interface”. [3] Joseph A. Carr, Juan Carlos Balda, H. Alan Mantooth, “A Survey of Systems to Integrate Distributed Energy Recourses and Energy Storage on the Utility Grid”, IEEE Energy 2030 Atlanta, Georgia, USA, 17-18 November 2008 [4] L. G. B. Rolim, A. Ortiz, M. Aredes, R. Pregitzer, J. G. Pinto, Joao L. Afonso, “Custom Power Interfaces for Renewable Energy Sources”, 1-4244-0755-9/07 IEEE 2007. [5] H. Akagi, Y. Kanazawa and A. Nabae, “Instantaneous Reactive Power Compensators comprising Switching Devices without Energy Storage Component”, IEEE Transac. on Industry Applications, 1984. [6] H. L. Jou, “Performance Comparison of the three – phase active – power – filter algorithms”, IEE Proc. Vol. 142. No. 6, November 1995. [7] Marta Molinas, Jon Are Suu and Tore Undeland “Improved grid interface of induction generators for renewable energy by use of STATCOM” 1-4244-0632-3/07 IEEE 2007. [8] Samira Dib, Brahim Ferdi, Chellali Benachaiba “Wind Energy Conversion Using Shunt Active Power Filter” Journal of Scientific Research Nov. vol. 2 .2010
[9] Thomas S. Basso, and Richard DeBlasio, “IEEE 1547 Series of Standards: Interconnection Issues” IEEE Transaction Power Electronics, Vol.19, No.5, Sep 2004 [10] E. Belenguer, H. Beltrán, N. Aparicio, ‘Distributed Generation Power Inverters as Shunt Active Power Filters for Losses Minimization in the Distribution Network’ IEEE 18787-0435- 2/06 2006. [11] Ismail H. Altas, ‘A Novel Active Filter Strategy for Power Mitigation and Quality Enhancements in a Stand-Alone WECS’ IEEE 0-7773-9442-5/03 2009. [12] K.J.P. Macken, ‘Active filtering and load balancing with small wind energy systems’. IEEE 0-7803-7671-41021517.00 02002. [13] W. Kramer, S. Chakraborty, B. Kroposki, and H. Thomas “Advanced Power Electronic Interfaces for Distributed Energy Systems”, Technical Report NREL/TP-581-42672 March 2008. [14] Benjamin Kroposki, Christopher Pink, Richard DeBlasio, ‘Benefits of Power Electronic Interfaces for Distributed Energy Systems’, IEEE 1-4244-0493-2/06 2006.
POWER SHARING BETWEEN SOURCE AND RENEWABLE ENERGY USING MODIFIED ICOSΦ CONTROL ALGORITHM
TABLE I. LF
1/4
1/2
3/4
1
p.f
Power drawn by load PL(kW) L1 L1+L2 5.19 10.38 5.587 11.175 5.587 11.175 5.587 11.175 5.587 11.175 5.19 10.35 5.587 11.175 5.587 11.175 5.587 11.175 5.587 11.175 5.191 10.38 5.587 11.175 5.587 11.175 5.587 11.175 5.587 11.175 5.191 10.382 5.587 11.175 5.587 11.175 5.587 11.175 5.587 11.175
0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9
TABLE II.
Lf
pf
1/4
1/2
3/4
1
QL(kVar) L1 L1+L2 11.8 23.6 7.387 14.774 5.515 11.03 3.600 7.100 2.673 5.347 11.8 23.6 7.387 14.774 5.515 11.031 3.594 7.188 2.673 5.347 11.8 23.4 7.387 14.774 5.515 11.031 3.595 7.189 2.673 5.347 11.8 23.6 7.387 14.774 5.515 11.031 3.594 7.189 2.673 5.347
L1 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587 5.587
L1+L2 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175 11.175
PS(kW) L1 L1+L2 1.974 15.737 2.139 4.055 1.90 3.163 5.385 10.1 5.368 10.00 3.010 17.05 3.600 6.745 4.468 8.625 3.000 5.416 5.368 10.06 4.100 19.18 5.008 9.674 4.211 7.822 4.166 7.746 4.157 7.674 5.194 20.926 6.372 12.466 5.385 10.205 5.384 10.105 5.368 10.06
QS(kVar) L1 L1+L2 -0.05 3.887 -0.037 -0.0745 -0.050 -0.119 0 0 0 0 0 3.9 0 0 0.050 0.104 -0.0575 -0.06 0 0 0 4.257 0 0 0 0 -0.030 -0.0625 -0.02 -0.0525 0 4.42 -0.014 -0.062 -0.050 -0.02 -0.015 -0.02 -0.019 -0.043
Power provided by renewable energy source via shunt active filter interface PRES(kW) QRES(kVar) L1 L1+L2 L1 L1+L2 3.217 -5.356 11.85 19.716 3.448 7.120 7.424 14.85 3.680 8.000 5.568 11.15 0.2 1.070 3.600 7.100 0.220 1.17 2.673 5.347 2.18 -6.6 11.84 19.63 2.00 4.43 7.387 14.774 1.118 2.55 5.411 10.926 2.588 5.758 3.650 7.250 0.220 1.114 2.673 5.347 1.085 -8.8 11.8 19.34 0.578 1.500 7.388 14.75 1.376 3.352 5.515 11.104 1.421 3.428 3.625 7.251 1.430 3.500 2.694 5.400 0 -10.544 11.8 19.184 -0.785 -1.291 7.400 14.712 0.204 0.969 5.564 11.041 0.204 1.069 3.610 7.208 0.219 1.114 2.692 5.390
POWER SHARING BETWEEN SOURCE AND RENEWABLE ENERGY USING MODIFIED IRPT CONTROL ALGORITHM
Power drawn by load PL(kW)
0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9 0.4 0.6 0.7 0.8 0.9
Power supplied by source/grid
Power supplied by source(grid)
QL(kVar) L1 12.705 7.387 5.515 3.595 2.673 12.705 7.387 5.515 3.595 2.673 12.705 7.387 5.515 3.595 2.673 12.705 7.387 5.515 3.595 2.673
L1+L2 25.408 14.774 11.03 7.189 5.347 25.408 14.774 11.03 7.189 5.647 25.4 14.774 11.03 7.189 5.347 25.4 14.774 11.03 7.189 5.347
PS(kW) L1 6.1 6.0 5.8 5.65 5.64 4.8 4.5 4.35 4.29 4.35 3.35 3.0 3.0 2.85 2.825 2.00 1.5 1.6 1.68 1.55
L1+L2 25 10.8 10.2 10.00 10.00 23.3 8.3 7.5 7.35 7.05 20.5 5.25 4.85 4.4 4.3 18.00 2.5 1.8 1.55 1.60
QS(kVar) L1 -0.075 -0.085 -0.025 -0.075 -0.075 -0.125 -0.125 -0.050 -0.025 -0.175 -0.150 -0.175 -0.125 -0.075 -0.100 -0.125 -0.200 -0.200 -0.125 -0.100
L1+L2 6.225 -0.025 -0.125 -0.125 -0.025 6.00 -0.125 -0.200 -0.150 -0.200 5.650 -0.225 -0.275 -0.250 -0.250 5.25 -0.300 -0.340 -0.275 -0.350
Power provided by renewable energy source via shunt active filter interface PRES(kW) QRES(kVar) L1 -0.5 -0.35 -0.30 -0.1 -0.1 0.6 1.0 1.2 1.3 1.25 2.2 2.5 2.6 2.7 2.75 3.6 4.0 4.0 4.0 4.0
L1+L2 -13.8 0.225 0.775 1.2 1.25 -11.3 3.0 3.6 3.85 4.00 -9.35 6.0 6.3 6.75 6.85 -6.95 8.55 9.4 9.6 9.55
L1 12.8 7.5 5.5 3.65 2.74 12.8 7.52 5.5 3.62 2.85 12.8 7.6 5.6 3.65 2.75 12.8 7.6 5.7 3.7 2.76
L1+L2 19 14.8 11.12 7.3 5.35 19.4 14.9 11.2 7.35 5.55 19.7 14.94 11.3 7.43 5.60 20.00 15.1 11.2 7.45 5.70
