Reactive Power Compensation of LC Coupling Hybrid Active Power Filters by DC Link Voltage Controls

Transcription

1 Volume-5, Issue-5, October-2015 International Journal of Engineering and Management Research Page Number: Reactive Power Compensation of C Coupling Hybrid Active Power Filters by DC ink Voltage Controls B. akshmi Devi 1, M.. Dwarakanad 2 1 Post Graduate Student, Department of Electrical and Electronics Engineering, Global College of Engineering & Technology, Kadapa, YSR District, AP INDIA 2 HOD, Associate Professor, Department of Electrical and Electronics Engineering, Global College of Engineering & Technology, Kadapa, YSR District, AP INDIA ABSTRACT Now-a-days with the advancement of technology, the demand for electric power is increasing at an exponential rate. Many consumer appliances demand quality power continuously for their operation. The performance of the end user equipment is heavily dependent on the quality of power supplied to it. But the quality of power delivered to the end user is affected by various external and internal factors. They are like voltage and frequency variations, faults, outages etc. These power quality problems reduce the life time and efficiency of the equipment. Thus, to enhance the performance of the consumer equipment and also the overall performance of the system these problems should be mitigated. In this project a hybrid filter which is a combination of series active filter and shunt passive filter is studied. This project presents the control strategy to control the filter in such a way that the harmonics are reduced. The proposed control strategy is simulated in MATAB SIMUINK and the results are presented. Keywords--- Active power filters (APFs), dc-link voltage control, hybrid active power filters (HAPFs), passive power filters (PPFs),reactive power control I. INTRODUCTION Electrical energy is the most efficient and popular form of energy and the modern society is heavily dependent on the electric supply. The life cannot be imagined without the supply of electricity. At the same time the quality of the electric power supplied is also very important for the efficient functioning of the end user equipment. The term power quality became most prominent in the power sector and both the electric power supply company and the end users are concerned about it [1]. The quality of power delivered to the consumers depends on the voltage and frequency ranges of the power. If there is any deviation in the voltage and frequency of the electric power delivered from that of the standard values then the quality of power delivered is affected. Now-a-days with the advancement in technology there is a drastic improvement in the semi-conductor devices. With this development and advantages, the semiconductor devices got a permanent place in the power sector helping to ease the control of overall system. Moreover, most of the loads are also semi-conductor based equipment. But the semi-conductor devices are non-linear in nature and draws non-linear current from the source. And also the semi-conductor devices are involved in power conversion, which is either AC to DC or from DC to AC. This power conversion contains lot of switching operations which may introduce discontinuity in the current. Due to this discontinuity and non-linearity, harmonics are present which affect the quality of power delivered to the end user. In order to maintain the quality of power delivered, the harmonics should be filtered out. Thus, a device named Filter is used which serves this purpose. There are many filter topologies in the literature like- active, passive and hybrid. In this project the use of hybrid power filters for the improvement of electric power quality is studied and analyzed. 1.1 Filter Classification The different filters present in the literature are classified into three basic types. They are Active Filters and Passive Filters and Hybrid filter. Each type has its own 129 Copyright Vandana Publications. All Rights Reserved.

2 sub classification. Fig. 1 shows the detailed classification of the filters. another filter topology which is a combination of passive filter and APF known as Hybrid Filter. Figure 1: Classification of Filters II. METHODOOGY Power Quality Problems: The quality of power is affected when there is any deviation in the voltage, current or frequency [6]. The common problems that affect the sensitivity of the equipment are- Power Surges Transients Frequency Variation Electrical ine Noise Brownouts or Blackouts Power System Faults Improper grounding affect The main affect caused by these problems is the production of harmonics. The presence of harmonics deteriorates the quality of power and may damage the end user equipment. These harmonics causes the heating of underground cables, insulation failure, reduces the lifetime of the equipment, increases the losses etc. Solutions to Power Quality Problems: The most effective solution to improve the power quality is the use of filters to reduce harmonics. The basic idea of using a filter is explained in Fig. 2, where the filter injects a compensating current that compensates the harmonics in load current. There are different filter topologies in the literature such as- active, passive, hybrid. The passive power filters are used to filter out a particular order harmonics and has the problem of parallel resonance. The other solution is the use of Active Power Filter (APF). There are different types of APF like series APF, shunt APF. The shunt APF is costly and is not used for large systems. The series APF works as a harmonic isolator and used to reduce the negative-sequence voltage. There is Fig 2: Hybrid filter Advantages of Hybrid Power Filter: Hybrid Filter is a combination of series and shunt filters. Among the various available combinations, activepassive combination is effective as it has the advantages of both active and passive filters. The characteristics of the passive filter are improved [5], avoiding the problems of series and parallel resonances. The series APF with a shunt connected passive filter is widely used due to the above advantages. Thus, the control of series APF with shunt connected passive filter is studied and analyzed in this project for the improvement of electric power quality. 130 Copyright Vandana Publications. All Rights Reserved. III. SIMUATION RESUTS WITH BAANCED OAD The proposed control strategy is simulated with a non-linear balanced load and the performance of the system is analyzed. The system data is given in Table-I. TABE-I SYSTEM PARAMETERS System Parameter Value

3 Voltage Switching Frequency Source Inductance 100 V 20 KHz 5.8 Mh Source Resistance 3.6Ω Turns ratio of coupling Transformer 1:1 The series APF is connected through a coupling transformer whose turn s ratio is 1:1. A passive filter is connected at PCC to eliminate fifth and seventh order harmonics. Also a ripple filter is also connected at the output of the VSI. The values of these filters along with load values are given in Table-II. diagrams with R and RC loads are shown in Fig. 3 and Fig. 4 respectively. The MATAB SIMUINK results are presented shows the load current which is nothing but the source current of phase- a without any compensation. The THD of this current hich is too high (27.75%) exceeding the IEEE standards. To filter the harmonics at first only the passive filter is connected and the source current waveform under this condition. When both active and passive filters are connected together, the harmonics are still reduced and the source current is almost sinusoidal. Now the THD of the current is very less (1.3%) and the harmonic analysis. The use of active power filter increases the performance of the system and the overall power factor is also improved. In addition, the characteristics of the passive filter are also improved and the 5th and 7th order harmonics are greatly reduced. The corresponding simulation results with RC load. TABE-II FITER PARAMETERS FITER PARAMETER VAUE Mh C5 30 µf m C7 30 µf r 13.5 mh Cr 50 µf R 25 Ω 55 mh C 22oo µf The filter impedance should be less than the system impedance for effective filtering. The simulation is carried out under three conditions- with the actual system parameters, by increasing the impedance of C filter more than source impedance and by changing the load values. Also the simulation is carried out with different loads- R and RC. 3.1 With the Actual System Parameters: With the system parameters in table-i, the proposed control strategy is simulated and the circuit Fig 3: Simulation Diagram with R-oad 131 Copyright Vandana Publications. All Rights Reserved.

4 improving the quality of electric power delivered to the end user. TABE-IV COPMARISON OF SOURCE CURRENT THD UNDER UNBAANCED OAD NAME THD Phase a Phase b Phase c P.F source current without filter 22.75% 35.0% 37.6% passive filter 4.5% 4.3% 5.1% both filter 1.4% 1.1% 1.3% 0.99 both filter and source impedance of 1.3 ohm and 2.34 mh 1.8% 1.5% 2.1% 0.99 IV. Fig 4: Simulation Diagram with RC-oad SIMUATION RESUTS WITH UNBAANCED OAD The power system may experience unbalanced load conditions at many times. Thus, the behavior of the proposed control strategy is analyzed by simulating it under unbalanced loading conditions. Here the unbalanced load is created by connecting three single-phase uncontrolled rectifiers with capacitor and resistor in parallel on the DC side. The load values are given Table- III. TABE-III VAUES IN UNBAANCED CONDITION OAD Phase C R Phase a 2200µF 16.67Ω Phase b 2200µF 25Ω Phase c 2200µF 50Ω 4.1 Comparative Study Under Unbalanced oad Condition: A comparative study of the three phase source current THD during unbalanced load at various operating conditions is presented in Table-V. From these results it is clear that the proposed control strategy works better at almost all operating conditions and thus helps in V. CONCUSION The demand for electric power is increasing at an exponential rate and at the same time the quality of power delivered became the most prominent issue in the power sector. Thus, the reduction of harmonics and improving the power factor of the system is of utmost important. In this project a solution to improve the electric power quality by the use of Active Power Filter is discussed. The work done in this project can be further extended such new improvements can be found. The feasible options are to simulate the proposed control strategy with grid faults and study the behavior of APF in power quality improvement and To implement the control strategy using Artificial Intelligence (AI) techniques. REFERENCES [1] Awad, H.; Bollen, M. H J, "Power electronics for power quality improvements," Industrial Electronics, ISIE ' IEEEInternational Symposium on, vol.2, no., pp.1129,1136 vol. 2, 9-11 June2003 doi: /ISIE [2] Singh, Bhim; Al-Haddad, K.; Chandra, A., "A review of active filters for power quality improvement," Industrial Electronics, IEEE Transactions on, vol.46, no.5, pp.960,971, Oct 1999 doi: / [3] Rivas, D.; Moran,.; Dixon, J.W.; Espinoza, J.R., "Improving passive filter compensation performance with active techniques" Industrial electronics, IEEE Transactions on, vol.50, no.1, pp.161, Copyright Vandana Publications. All Rights Reserved.

5 [4] Herrera, R.S.; Salmeron, P., "Instantaneous Reactive Power Theory: A Comparative Evaluation of Different Formulations," Power Delivery, IEEETransactions on, vol.22, no.1, pp.595,604, Jan doi: /tpwrd [5] Salmeron, P.; itran, S.P., "Improvement of the Electric Power Quality Using Series Active and Shunt Passive Filters," Power Delivery, IEEETransactions on, vol.25, no.2, pp.1058,1067, April 2010 doi: /tpwrd [6] M H J Bollen, Understanding Po11 er Quality Problenis Voltage Sagsandlnterruptions, New York, IEEE Press, 1999 [7] Axente, N. G. Jayanti, M.Basu, and M. F. Conlon, A 12 kva DSP-controlled laboratory prototype UPQC capable of mitigating unbalance in source voltage and load current, IEEE Trans. Power Electron., vol. 25, no. 6, pp , Jun [8] 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 , Oct [9] J. W. Dixon, G. Venegas, and. A. Moran, A series active power filter based on a sinusoidal current-controlled voltage-source inverter, IEEETrans. Ind. Electron., vol. 44, no. 5, pp , Oct [10] F. Z. Peng and D. J. Adams, Harmonics sources and filtering approaches, in Proc. Industry Applications Conf., Oct. 1999, vol. 1, pp [11] J. K. Phipps, J.P. Nelson, P. K. Sen, Power Quality and Harmonic Distortion on Distribution Systems, in IEEE Trans. on Ind. Appl., vol. 30, No 2, March/April 1994, pp Copyright Vandana Publications. All Rights Reserved.