International Journal of Pure and Applied Mathematics

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1 Volume 117 No , ISSN: (printed version); ISSN: (on-line version) url: doi: /ijpam.v117i8.15 ijpam.eu A NOVEL INTEGRATED APPROACH OF WIND ENERGY CONVERSION SYSTEMS WITH OPTIMIZED MATRIX CONVERTER FED GRID UNDER DIFFERENT LOAD CONDITIONS 1 Rajalakshmi D, 2 Kavitha R, 3 Geetha K 1,2 Faculty, Department of Electrical and Electronics Engg.,Kumaraguru College of Technology. 3 Professor, Department of Electronics and Communication Engg. Abstarct Matrix converter uses the different techniques to produce the high quality waveforms in the input and output side and also produces the desired output compared with Back to back converter. Genetic Algorithm based PI controller with Space vector modulation technique for Matrix converter under different load conditions fed in to grid are initially presented. This is to improve input power factor and to reduce the harmonics in the output of matrix converter in the integrated approach. The input power factor varies for different load conditions. So it is required to compare the performance under different loads. Results for light and high load conditions and compared results are presented. It is a practice to implement each Wind Energy generation system in wind mills connected to micro-grid with same AC-DC-AC converter technique. Key words: Matrix Converter, Total Harmonic Distortion, Lower order harmonics, Input Power Factor, Space Vector Modulation, PI controller,wecs INTRODUCTION As demand for energy savings have been increased in recent years, converters are being used in wide range of applications. The ranges of converter applications are further expanded due to demands for lower cost, smaller size and higher efficiency. AC to AC voltage converters operates essentially to regulate the output voltage. According to requirement and usage, the output voltage and frequency can be managed. Most of the topologies have emerged along with voltage regulation methods are linked to the development of the semiconductor devices. To convert AC input into variable AC output with variable frequency, various types of converters are used.there are Conventional AC-DC-AC converters, Cycloconverters and Matrix converters. A Matrix Converter is a device used for converting AC energy into AC energy directly without any intermediate dc link. The important feature of this device is to convert the magnitude as well as the frequency of the output into a desired magnitude and frequency. Matrix Converter switches arranged in array manner with nine bi-directional which are required to be commutated in the right way and sequence in order to minimize losses and produce the high quality input output waveforms and also the desired output. Advantages of MCs with other converter topologies have been discussed [1]- [5].The advantage of matrix converter is the absence of bulky reactive elements. These are subjected to ageing, and reduce the system reliability. Furthermore, Matrix converters provide nearly sinusoidal input and output waveforms, bidirectional power flow and controllable input power factor. Therefore MCs is a good alternative to voltage -source inverter (VSI) topology. It has inherent bi-directional energy flow capacity the input power factor can be fully controlled. It has a maximum input-output voltage transfer ratio of 0.87 for sinusoidal input and output waveforms. The modulation techniques used for matrix converters are mainly concentrates on safer operation of the switches and to get maximum voltage transfer ratio with better output. The various existing modulation techniques are Venturini method and Space Vector Modulation Techniques. Out of these techniques space vector modulation method is most widely used to get better voltage transfer ratio.the various modulation methods of MC are compared and finally it is concluded that the space vector modulation technique is the best solution to increases the voltage transfer ratio and to optimize the switching pattern through a suitable use of zero configuration. The matrix converter contributes to the realization of sinusoidal input current, bidirectional power flow and lack of bulky reactive elements [6]-[7]. THE BASIC TOPOLOGY OF MATRIX CONVERTER Figure.1 Matrix Converter The switching function of the switches, S kj (t) in the Matrix converter is defined as 1 when it is ON and defined as 0 when it is OFF., k ϵ {a,b,c} and j ϵ {A,B,C} (1) The constraint of the switches is expressed by the following equation (2), j ϵ {A,B,C} (2) In the matrix converter there are 27 different switching combinations with the above constraints for connecting output 73

2 phase to input phases if the above mentioned combinations can be analyzed in three groups from 512 possible combinations. The duty cycles of the switches are modulated for various voltage transfer ratio and it is increased from 0.5 to by using this modulation technique. This method uses 18 active switching combinations with 3 zero switching combinations to complete one full cycle. For each switching combinations, the input and output line voltages can be expressed in terms of space vectors as (4) Group1: The three input phases is directly connected to each output phase in turns with six switching combinations. Here the phase angle of output voltage vector and input voltage vector depend on each other. same condition is valid for current vectors too. Due to the phase angle of both the vectors cannot be controlled independently, these switching states are not used in the matrix converter with SVM technique. Group2: There are 18 switching combinations in this group in which the active voltage vector is created at variable amplitude and frequency. Amplitude of the output voltages depend on the chosen input line voltages. In this case, the phase angles of the output voltage space vector and the input voltage space vector are independent of each other. Similar condition is applicable for current vectors too. Group3: It having three switching combinations consists of zero vectors. In this case, all the output phases are connected to the same input phase. For balanced three-phase input voltages, the neutral voltage is equal to zero Mathematical the relationship of the input voltages can be expressed as V a + V b + V c = 0 The output phase voltage of the matrix converter is a product of the switching function and the input phase voltages given by Equation (5). = * (3) (5) The input line and output line currents can be written as, i i = 2/3(i a +i b e j2п/3 +i c e j4 П/3 ) = I i (6) i o = 2/3(i A +i B e j2п/3 +i C e j4 П/3 ) = I o (7) In this modulation technique the three phase quantities can be transformed to their equivalent two phase quantity either in synchronously rotating frame. From this two phase component, = the reference vector magnitude can be found and used for modulating the converter output. SVM treats the sinusoidal voltage as a constant amplitude vector rotating at constant frequency. This technique approximates the reference voltage Vref by a combination of the eight switching patterns (V 0 to V 7 ). For example if the reference voltage is located in sector 1, voltage vectors V 1, V 2, V 0 and V 7 would be selected and applied within a sampling period. MATRIX CONVERTER PERFORMANCE WITH PI CONTROLLER A.MATRIX CONVERTER FED GRID WITHOUT PI CONTROLLER The general circuit of the matrix converter is shown in Figure 1. The Matrix converter consist of nine bi-directional switches each comprises of two IGBTs connected in anti-parallel. The voltage and current rating of the device are 250V and 100A respectively. The output of Matrix Converter is connected to grid at point of common coupling. The Matrix converter (MC) fed grid with the phase voltage of 100V connected with load is shown in Figure 3. Figure.3 MC fed grid without PI controller The grid is composed of programmable voltage source of 100V phase-phase voltage with source inductance. The matrix converter is also supplying R-L load. The input current quality of Matrix converter is improved by an input filter and also reduces the input voltage distortion [13]-[14]. Input power factor is different for different load conditions. Under light load condition, it is poor and under normal or heavy output loads,it is nearly unity. So MC is analyzed with light load and normal load condition. Under any load condition, THD and lower order harmonics of load are also high in Matrix converter fed Grid. The above circuit of MC with SVM technique is modeled for different load condition using Matlab/Simulink and results are shown. Figure.4 Output voltage under light load condition Figure.2 Output voltage space vector Figure.5 Output current under light load condition The Figure 4 and 5 show the load side output voltage and current of Matrix converter fed grid without PI controller 74

3 under light load condition. The input power factor is Voltage THD (20.01%) and current THD (40.16%)are found using FFT analysis. Figure.10 Load voltage for Wind energy systems with conventional converters -1A load Figure.6 Output voltage under normal load condition. Figure.7 Output current under normal load condition The Figure 6 and 7 show the load side voltage and current of the matrix converter without PI controller under normal load condition. It is observed that there is no problem of input power factor(approximately 1) but high amount of THD values at load side voltages. Compared to light load condition, the voltage transfer gain is better. By FFT analysis it is observed that % of Voltage THD and 15.56% of current THD. Figure.11 Load current for Wind energy systems with conventional converters - 1A load From the above output voltage and current waveform it is proved that WECS with conventional converters had high voltage and current THD i. e 37.5% and 9.94% respectively under normal load,36.73% and 25.05% respectively under light load. But lower order harmonics are always less than 5%. Due to nature of wind system and DC link converter, inter harmonics are more and THD also increased. Input power factor is also poor and it is 0.57 under normal load and 0.48 under light load. B.RESULTS OF INTEGRATED APPROACH RESULTS WITH STANDARD APPROACH All the approaches are verified with same load (under normal load and light load), same specifications for grid and input used in previous section. Results are shown below. Figure.12 Load voltage for Wind energy systems with optimized converters - 10A load Figure.8 Load voltage for Wind energy systems with conventional converters -10A load Figure.13 Load current for Wind energy systems with optimized converters - 10A load Figure.9 Load current for Wind energy systems with conventional converters - 10A load Figure.14 Load voltage for Wind energy systems with optimized converters - 1A load) 75

4 Figure.15 Load current for Wind energy systems with optimized converters - 1A load When both the converters of wind systems are replaced with PI controller based MCs then input power factor is nearly unity and it is 0.98 for normal load and 0.94 under light load.voltage and current THD are reduced to 9.81% and 4.02% under normal load and 14.05% and 13.04% under light load condition. Lower order voltage and current harmonics are less than 0.35%.Performance of the system is improved but cost of the system will also be increased when more number of wind systems is used due to optimzation. Input power factor is also improved to 0.93 for normal load and 0.91 for light load. C.COMPARISON OF RESULTS Comparison of results of WECS with conventional converters, with optimized converters and integrated approach (combination of conventional and optimized converter) under different load condition are shown. Figure.20 Comparison of Input power factor Figure.16 Load voltage for integrated approach of Wind energy systems - 10A load Figure.21 Comparison of voltage and current THD Figure.17 Load current for integrated approach of Wind energy systems - 10A load Figure.18 Load voltage for integrated approach of wind energy systems - 1A load Figure.19 Load current for integrated approach of wind energy systems - 1A load Only 50% of wind systems are replaced with optimized PI controller based MCs to reduce the cost. Integrated approach in which one of wind system with conventional converter and other system with optimized MC (for 2 wind mills) is used then voltage and current THD is reduced to more than 40% compared to standard approach. Lower order harmonics are reduced to 0.7% which is nearly 5% in standard approach. From the above results it is proved that integrated approach provides a better result compared to the implementation of system with conventional converters in micro grid. System with only optimized MCs gives better results than a system with integrated approach. But cost is the factor then integrated approach will be chosen. CONCLUSION The optimized PI controller design for SVM technique of Matrix converter fed grid is presented. The results proved that introducing this optimized PI controller, input power factor under light load is improved and also THD and lower order harmonics are reduced at different loads. From the results of converter without PI controller, performance of the same system is more affected by at different load conditions. But this proposed work overcome the problem of reduction of input power factor under light load and increased harmonic distortion in the load side at different load condition. REFERENCE 1. Alesina and M. G. B. Venturini, Analysis and Design of Optimum Amplitude Nine-Switch Direct AC AC Converters, IEEE Transactions on Power Electronics,Vol. 4, pp , Thomas Friedli, Johann W.Kolar and Patrick W.Wheeler, Comparative Evaluation of Three Phase AC- AC Matrix Converter and Voltage DC-Link Back-to-Back Converter Systems, IEEE Transactions on Industrial Electronics, Vol.59, No.12, P. Wheeler, J. Clare, L. de Lillo, K. Bradley, M. Aten, C. Whitley, and G.Towers, A comparison of the reliability of a matrix converter and a controlled rectifier-inverter, in Proc. Eur. Conf. Power Electron. Appl., p. 7,

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