Study of Harmonics and THD of Nine Phase PWM Inverter Drive with CLC Filter for motor drive applications

Transcription

1 International Journal of Electronics Engineering Research. ISSN Volume 9, Number 3 (2017) pp Research India Publications Study of Harmonics and THD of Nine Phase PWM Inverter Drive with CLC Filter for motor drive applications Dr. Manjesh* 1 and Nilima Siddhartha Dabhade 1 1 Bangalore University, Karnataka, India. Abstract Most of the applications 60% of loads are motor driven loads, more than 90% of these loads are used for industrial applications. Many applications use three phase motor drive which limits torque density. Multiphase motor drives are better solutions for high torque density and heavy loads. In this work a Nine Phase Inverter is designed to drive nine phase load, along with fundamental frequency the load consist of harmonics. These harmonics are higher than fundamental frequencies and cause total harmonic distortion (THD) which enhances the current harmonics and generates heat in the load. Many techniques are used to suppress the harmonics to minimize the heat in the load. A common technique is employed in this paper to minimize THD by constructing CLC filter in the PWM inverter and simulated using Simulink/Matlab, the results are compared with the normal Nine Phase inverter. Index Terms: Harmonics, Nine Phase Inverter, CLC filter, Nine phase Induction Motor, Matlab/Simulink. INTRODUCTION Three phase drives are generally used for heavy torque loads, if the phases are increased beyond three phase then it is more advantageous. The main advantages of constructing a multiphase motor in place of a 3-phase motor is due to density of high torque, minimization ripples, better noise suppression, smoother torque and reduction of the torque ripple magnitude [1]. To drive the multiphase motor multi phase inverters are used, multiphase drives are best examples for high torque motor drives like aviation, hybrid electric cars, traction and battery-operated electric vehicles.

2 370 Dr. Manjesh and Nilima Siddhartha Dabhade NINE PHASE INDUCTION MOTOR DRIVE N phase Asynchronous machines have n number of stator windings obtained by 360⁰/n phase. Therefore 9-phase synchronous motor has 9-stator windings displaced by 40⁰ phase shift. Rotor windings use squirrel cage, the 9-phase synchronous motor is fed by 9-phase inverter. 9-phase synchronous motor drive is fed by 9-Phase inverter presented in Fig There are 9-push pull drives, each drive is triggered by PWM signal. Thus there are 9- PWM trigger signals which are 40 out of phase with each other. The PWM trigger signals drive IGBT (Insulated-Gate Bipolar Transistor) switches. All the switches operated for a period of Fig Schematic diagram of 9-Phase synchronous Motor fed by 9- Phase NINE PHASE INVERTERS Inverter. The PWM inverter is commonly used for motor drive applications in industries, speed of the asynchronous motor can be varied by pulse width modulation method. Most of the inverters use power MOSFET s or IGBT s as semiconductor switching devices. The PWM inverter topology is constructed with two semiconductor devices connected in series, in each PWM inverter leg the ON and OFF operation can be performed with upper and lower switch alternatively. The arms of PWM inverter depending on linear and nonlinear phase load applications [1-10]. The Nine phase inverter is constructed with nine legs and eighteen switches as shown in Fig Fig Topology of Nine Phase Inverter

3 Study of Harmonics and THD of Nine Phase PWM Inverter Drive with CLC Filter 371 The control signals to the inverter switches are pulse width modulated (PWM) signals which are generated through pulse generators. The magnitude of generated pulse depending on modulation index, as the modulation index approaches unity, the harmonic content can be minimize. Reducing THD is very important in power electronics systems. Harmonics are the sinusoidal frequencies of voltage and current of fundamental power supply frequency (50HZ). The main reason for the presence of harmonics in the power electronic AC circuit is to use of nonlinear loads. Power of harmonic frequencies will not provide any additional energy nor influences any mechanical torque at the output of inverter, but this frequency of harmonics dissipated as heat in the load which affects the power factor and switching losses. THD is the percentage of harmonic magnitudes at the output of the inverter which affects the efficiency of an inverter. Third order harmonic is the most dominant harmonic frequency which belongs to 3rd order of 50Hz i.e. 150Hz, also amplitude of harmonic is 34.70% of the input power. Suppression of third harmonic can improve the efficiency of an inverter. Nonlinear loads are the major challenge in the field of power electronics, the gradual impact of nonlinear parameters on load generates additional harmonic frequencies which affect the power factor. The power rectifiers and PWM inverters are employed to operate the nonlinear loads and Filters are the best option to overcome this distortion. Filters are the circuits which block the unwanted frequency components of different harmonics, passive filters are easy to construct but at lower frequencies the values of the components are high. The Nine Phase PWM Inverter Drive does not contain even harmonics and only odd harmonics are present, as 3 rd harmonic is the most prominent harmonic, the presented schematic design is used to reduce 3 rd harmonic by using passive filters [11-13]. NINE PHASE INVERTERS WITH PASSIVE FILTER The Block diagram of PWM 9-phase inverter using CLC filter and R-load in each phase is as shown in the Fig Fig Block diagram of 9-phase inverter with CLC filter and R load

4 372 Dr. Manjesh and Nilima Siddhartha Dabhade The Presented schematic is designed with the CLC filters arranged with the combination of two capacitors and an inductor. It provides better minimization of harmonics in the 9-phase inverter compare to other filter techniques. The main significance of using CLC filter scheme at the inverter output is to reduce unwanted harmonics with fewer ripples at the output and low distortion in reactive output power. Resonant frequency of the circuit with CLC-filter scheme can be obtained by 1 f0 = 2π LC Where fo is the frequency of resonance, L is an Inductor and C is a capacitor. The filter scheme has been constructed using Equation1, resonance frequency has been taken as 150Hz to eliminate 3 rd harmonic (3x50Hz). The values of inductor and capacitor has been designed accordingly are L= 1.12µH and C1=C2= 1000mF. (1) Fig Schematic of 9-phase inverter drive with CLC filter The complete setup is shown in Fig CLC filter is fixed at the output of the inverter with nine-phase star load, where C1 to C18= 1000mf and L1-L8= 1.12µH. SIMULATION RESULTS The results obtained using 9-phase inverter with and without filter are shown in Fig and Fig Waveforms are generated for line voltage and line current. Simulation work carried out for 9-phase by connecting CLC filter at the output of the inverter and measured the parameters, also the same circuit is used to obtain the parameters without using the filter scheme. The inverter drives studied and simulated for rated frequency 50Hz. The results obtained are analyzed for harmonics and (THD).

5 Study of Harmonics and THD of Nine Phase PWM Inverter Drive with CLC Filter 373 Fig Individual line Voltage/ Current waveforms without filters Fig Individual voltage / current waveforms with CLC filter Fig and Fig shows the FFT analysis of normal 9-Phase Inverter for 50Hz using CLC filter scheme respectively. The comparison of percentage of reduction in THD of traditional inverter and with CLC filter scheme is presented in Table.1.1. Tremendous change in presence of odd harmonics with and without CLC filter for f= 50Hz is shown as in Table.1.2. Fig FFT analysis of normal 9-phase inverter for 50 Hz

6 374 Dr. Manjesh and Nilima Siddhartha Dabhade Fig FFT analysis of 9-inverter with CLC filter for 50 Hz The parameters used for simulation work with frequency f= 50 Hz, Vdc= 100v, THD in % is presented in table 1.1 Table 1.1 Comparison of THD without filters and with CLC filter for frequency 50 Hz Modes THD % Without CLC Filter 48.93% With CLC Filter 28.83% At fundamental frequency f= 50 Hz, Vdc= 100v, THD % comparison for nth harmonics is as shown in table 1.2. Table.1.2. THD profile without and with CLC filter for frequency 50 Hz Harmonics Without Filter THD % With Filter THD % 3 rd 34.70% 0.38% 7 th 16.92% 12.56% 9 th 0.00% 0.77% 11 th 11.85% 4.78% 13 th 10.34% 2.85% 17 th 8.05% 1.20% 19 th 0.00% 0.96%

7 Study of Harmonics and THD of Nine Phase PWM Inverter Drive with CLC Filter 375 CONCLUSION A nine phase Inerter drive is constructed using Simulink/Matlab to study the harmonics and THD of the 9-phase inverter. The results obtained using Nine Phase Inverter without filter and with CLC filter has been compared. It is observed that the harmonics and percentage in Total Harmonics Distortion (THD) at the 9-phase inverter output is found to be less using CLC filter. In future this work can be used to drive 9-phase asynchronous motor for stator winding temperature analysis. REFERENCES: [1] G.K.Singh, Multi phase Induction Machine Drive research survey, Elect power syst. Res, vol62,pp ,2002 [2] B. Bose, power Electronics and AC drives Englewood cliffs, N prentice Hall,1986. [3] E. Levi, M. Jones, S. N. Vukosavic, H. A. Toliyat, A Five-Phase Two- Machine Vector Controlled Induction Motor Drive Supplied from a Single Inverter, EPE Journal Vol. 14 no 3 August 2004 [4] M. Jones and E. Levi, A literature survey of state-of-the-art in multiphase ac drives, in Proc. 37th Int. UPEC, Stafford, U.K., 2002, pp [5] E. Levi, R. Bojoi, F. Profumo, H. A. Toliyat, and S. Williamson, Multiphase induction motor drives-a technology status review, IET Elect. Power Appl., vol. 1, no. 4, pp , Jul [6] E. Levi, Multi-phase machines for variable speed applications,, EEE Trans. Ind. Electron., vol. 55, no. 5, pp , May [7] K. P. Prasad Rao, B. Krishna Veni, D. Ravithej, FIVE-LEG INVERTER for FIVE-PHASE SUPPLY, International Journal of Engineering Trends and Technology- Volume3Issue [8] Shaikh Moinoddin, Atif Iqbal and Elmahdi M. Elsherif Five-phase induction motor drive for weak and remote grid system,, International Journal of Engineering, Science and Technology Vol. 2, No. 2, 2010, pp [9] Five-Phase Induction Motor Drive System Fed from Five-Phase Matrix- Converter, Proceedings of the IEEE 15th International Middle East Power Systems Conference (MEPCON 12), Alexandria University, Egypt, December 23-25, 2012, Paper ID 302, pp [10] A. Reznik, M.Godoy Simões, Ahmed Al-Durra, S. M. Muyeen, LCL Filter Design and Performance Analysis for Grid Interconnected Systems, [11] Parikshith.B.C, Dr.Vinod John, Higher Order Output Filter Design for Grid Connected Power Converters, Fifteenth National Power Systems Conference (NPSC), IIT Bombay, December 2008

8 376 Dr. Manjesh and Nilima Siddhartha Dabhade [12] Khaled H. Ahmed, Stephen J. Finney and Barry W. Williams, Passive Filter Design for Three-Phase Inverter Interfacing in Distributed Generation, Electrical Power Quality and Utilisation, Journal Vol. XIII, No. 2, 2007 [13] Kuldeep Kumar Srivastava, Saquib Shakil, Anand Vardhan Pandey, Harmonics & Its Mitigation Technique by Passive Shunt Filter, International Journal of Soft Computing and Engineering (IJSCE), ISSN: , Volume-3, Issue-2, May 2013.