Total Harmonic Distortion Analysis of Multilevel Inverter Fed To Induction Motor Drive With PV-Battery Hybrid System

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1 CH. Anusha Int. Journal of Enineerin Research and Applications IN : 48-96, Vol. 4, Issue 1( Part 3), ecember 014, pp REEARCH ARTICLE OPEN ACCE Total Harmonic istortion Analysis of Multilevel Inverter Fed To Induction Motor rive With PV-Battery Hybrid ystem CH. Anusha 1, ri P.anthi Kumar, 1 P.G.tudent ept. of EEE, NIE Collee, Macherla, Associate Professor, ept. of EEE, NIE Collee, Macherla. ABTRACT This paper presents the control of a multilevel inverter supplied by a Photovoltaic (PV) panel and a batteries bank. It is well known that the power quality of multilevel inverter sinals depends on their number of levels. However, the question that arises is whether there is a limit beyond which it is not necessary to increase the number of level. This question is addressed in this paper. Three, nine and fifteen-level converters are studied. The harmonics content of the output sinals are analyzed. A simplified Pulse Width Modulation (PWM) method for a multilevel inverter that supplied an induction motor is developed. The controller equations are such that the PWM pulses are enerated automatically for any number of levels. The effectiveness of the propose method is evaluated in simulation. Matlab / imulink is used to implement the control alorithm and simulate the system. I. INTROUCTION Nowadays, the industry requires power equipment increasinly hih, in the meawatt rane. The rapid evolutions of semiconductor devices manufacturin technoloies and the desiner's orientation have enabled the development of new structures of converters (inverters) with a reat performance compared to conventional structures. o, these new technoloies of semiconductor are more suited to hih power applications and they enable the desin of multilevel inverters. The constraints due to commutation phenomena are also reduced and each component supports a much smaller fraction of the C-bus voltae when the number of levels is hiher. For this reason, the switches support more hih reverse voltaes in hihpower applications and the converter output sinals are with ood spectral qualities. Thus, the usin of this type of inverter, associated with a judicious control of power components, allows deletin some harmonics. Amon the control alorithms proposed in the literature in this field, the PWM, appears most promisin. It offers reat flexibility in optimizin the desin and it is well suited for diital implementation. It also helps to maximize the available power. The main advantae of multilevel inverters is that the output voltae can be enerated with a low harmonics. Thus it is admitted that the harmonics decrease proportionately to the inverter level. For these reasons, the multilevel inverters are preferred for hih power applications. However, there is no shortae of disadvantaes. Their control is much more complex and the techniques are still not widely used in industry. In this paper, modelin and simulation of a multilevel inverter usin Neutral- Point-Clamped (NPC) inverters have been performed with motor load usin imulink/ MATLAB proram. In the first section multilevel inverter control strateies are presented before to detail a study of seven-level inverter in the second section. Total Harmonic istortion (TH) is discussed in the third section. The aim is to hihliht the limit at which the multilevel inverters are no loner effective in reducin output voltae harmonics. II. Photovoltaic and Battery Enery Generation: Photovoltaic (PV) systems are stand-alone power enerators that have ood environmental footprints. The modelin and the Maximum Power Point Trackin (MPPT) control stratey for a PV system are developed. In the latter, the control stratey that is presented is based only on the measurement of the PV current to track the maximum power. A batteries bank is added to the C-bus to ensure the eneretic autonomy of the system. A Proportional-Interal (PI) controller is used to reulate the C-bus voltae V dc at a constant value. As a consequence the batteries compensate for the difference between the power supplied by the PV system and the power needed by the induction motor. The batteries are chared when the PV power exceeds the motor demand. 169 P a e

2 CH. Anusha Int. Journal of Enineerin Research and Applications IN : 48-96, Vol. 4, Issue 1( Part 3), ecember 014, pp Fi. : Three-level three phase inverter Fi. 1. Induction motor driven by PV-batteries standalone system usin a controlled multilevel inverter III. Multilevel Inverter Control trateies: A. The three-level inverter control stratey Fi. shows a three-phase three-level inverter. It has three arms. Each arm has four switches. Every switch is connected in antiparallel with a diode. This pararaph describes the operation of one of the les shown at Fi. 3. The voltae V ao between the phase "a" and the neutral point O is defined entirely by the switches position (0 open or 1 closed ). witch sets [ 11, 13 ], and [ 1, 14 ] have complementary positions. When [ 11, 13 ], are open [ 1, 14 ] are closed. The three-level NPC inverter is mostly used for medium-voltae hih-power applications. In this converter, the number of commutation sequences ( eq ) is equal to 4 = 16., where 4 stands for the number of switches per arm and is the number of state per switch (0, 1). V dc is the C-bus voltae. Only three commutation sequences are possible. They are represented at Table 1. Fi. 3 shows the confiurations of the inverter s arm which correspond to the three possible commutation sequences: -equence 1: 11, 1 conduct and 13, 14 open (Fi. 3.a). V ao = V dc /. -equence : 1, 13 conduct and 11, 14 open (Fi. 3.b). V ao = 0. -equence 3: 13, 14 conduct and 11, 1 open (Fi. 3.c). V ao = V dc /. equences 1, and 3 are applied in this order periodically. A pulse width modulation is used to control the switches. Consider Fi. 3 and Fi. 4, the reference voltae V ra is compared to the positive and neative sawtooth carrier V cx and V cy respectively. The comparator output is sent to the switches (Insulated Gate Bipolar Transistor or IGBT) to enerate the machine phase voltae. a. equence 1 b. equence c. equence 3 Fi. 3: ifferent possible confiurations for one arm Fi. 4: Three-level PWM control method TABLE 1: equences of control vectors.no [ 11, 1, 13, 14 ] V ao 1 [1100] V ao [0110] V ao =0 3 [0011] V ao the same as the reference voltae V ra frequency. The inverter output voltaes are written as follow (1): 170 P a e

3 CH. Anusha Int. Journal of Enineerin Research and Applications IN : 48-96, Vol. 4, Issue 1( Part 3), ecember 014, pp V ao = 1 3 V bo = 1 3 V co = 1 3 V ab V ca V bc V ab V ca V bc (1) Modulation index (m a ) is defined by (): m a = A r () (n 1)A c where A r and A c are the peak to peak value of V ao and V c respectively. B. The hiher level inverter control stratey Calculation of carrier : A bipolar sawtooth carrier is illustrated at Fiure 6. The voltaes V cx and V cy have the expression iven by equation (4): Fi. 5: Principle PWM multilevel inverter control The previous study for the three-level voltae inverter is now extended to hiher level inverters. For an n-level inverter, it is possible to determine the number of components that are needed per arm (number of switches, diodes, carrier, etc). Numbers of inverter components calculation: efine eq as the number of commutation sequence possibilities. is the number of secondary voltae sources. K stands for the number of switches per phase. is the number of diodes loop includin the diode switches per phase. C represents the manitude of the voltae across each capacitor and P is the number of carriers. The followin equations provide how these quantities are calculated and table shows the values for several multilevel inverters. eq = (n1) = P = n 1 K = (n 1) (3) = 4n 6 C = V dc n 1 TABLE : equence of the control Vectors Fi. 6: iaram of the induction motor control principle based on the multilevel inverter h V cx = V cx 1 1 x= h V cy = V cy 1 1 x=0 (4) Calculation of reference voltaes: The balanced three-phase reference voltae is iven by(5): V ra t = A r sin πf r t V r : V rb t = A r sin πf r t π 3 (5) V rc t = A r sin πf r t 4π 3 where V r is the three phase reference voltae Calculation of the comparator: The comparator uses the reference and carrier sinals to enerate a binary sinal accordin to the followin equation: 171 P a e

4 - CH. Anusha Int. Journal of Enineerin Research and Applications IN : 48-96, Vol. 4, Issue 1( Part 3), ecember 014, pp If V r V cx => T xm = 1 If V r < V cx => T xm = 0 If V r V cy => T ym = 1 (6) If V r > V cy => T ym = 0 where matrices T xm andt ym are the comparator output. Calculation of the adder : The parameter T k is the difference between T xm and T ym. It is therefore calculated as follows. T k = T xm T ym (7) Calculation of inverter control vectors: The eneration of the pulse vector that control the inverter is very important. The pulse vector can be enerated by applyin the G n vector for each T k accordin equation (8). The inverter output voltae V k is iven by equation (9). If T k = n 1 i => G 1 = G = G 3 = G n = (8) V k = h i V n 1 dc (9) where h = n 1, i = {0,1,.., n} and G n is 1X(n-1) vector. It contains 1X(n-1) zero vector and 1X(n-1) ones vector. IV. imulink Circuit and Results: Ramp1 Fi. 8: imulink iaram of PV Array Fuel flow rate (lpm) <Utilization (%) [O(Yellow); H(Maenta)]> <tack consumption (lpm) [Air(Yellow); Fuel(Maenta)]> <tack Efficiency (%)> cope1 <Voltae> <Current> m cope ramp Ramp_Fr w FuelFr 1 Fr_re_in Fr_re_out witch Flow rate selector - Fuel Cell tack _ f low rate Current Flow rate reulator Fi 9 : imulink iaram of Fuel Cell iscrete, Ts = 5e-005 s. powerui [L1a] [La] [L3a] Fi 10: Input Voltae C1 L1a [L1a] A 1 [L1b] [Lb] [L3b] L1c [L1c] L1b L1d [L1b] [L1d] B 1 C-C Va a A La [La] Pv model A Vb b B Lc Lb Ld L3a [Lc] [Lb] [Ld] [L3a] BATTERY _ 1 _1 [L1c] [Lc] [L3c] Vc B Van Vbn C Vcn outae Neutral Voltaes c C LP filter nd order Filtered Line voltaes L3c L3b L3d [L3c] [L3b] [L3d] C-C1 C [L1d] [Ld] [L3d] Line voltaes 180 deree pulses Fi. 7: imulink Circuit of the proposed ystem Fi 11: Multilevel output Voltae without filter 17 P a e

5 Ma (% of Fundamental) CH. Anusha Int. Journal of Enineerin Research and Applications IN : 48-96, Vol. 4, Issue 1( Part 3), ecember 014, pp Fi 1: Multilevel output voltae with filter Total Harmonic istortion Analysis of Multilevel Inverter The main criterion for assessin the quality of the voltae delivered by an inverter is the Total Harmonic istortion (TH). This section will be devoted to analyzin the inverters performance accordin to their number level. Level three, seven inverters will be considered. The oal is to see if the low order harmonics amplitude will decrease when the number of level increases. The inverter is usually followed by a low pass filter since hiher frequency harmonics are easy to filter. This means that the performance of multilevel inverters can be improved by cancellin or reducin lower order harmonics. Lower order harmonics enerate the most important currents when an inductive load is used. The TH is a ratio between the Root Mean quare (RM) of the harmonics and the fundamental sinal. For an inverter that has a fundamental output voltae V 1 and harmonics V, V 3,..., we define the TH as follows: TH = N V k k elected sinal: 5 cycles. FFT window (in red): cycles Time (s) Fundamental (50Hz) = 30., TH= 0.55% Frequency (Hz) V 1 (10) Fi 13: TH of the Multilevel Inverter Voltae (0.55%) V.CONCLUION In this paper, a eneral multilevel PWM control alorithm for n-level inverter has been modeled and simulated usin Matlab /imulink. This alorithm can enerate automatically PWM pulses for any level of inverter by chanin only a parameter n which is the number of inverter level. imulation of 3, 9, and fifteen level inverter connected to induction motor has been performed and the enerated sinals TH is analysed. The system is supplied by a PV panel and batteries bank. That ives enery autonomy to the system. imulation results ive a better quality of stator current in terms of low harmonics, thus reducin the adverse effects on of the machine life and eventually the electrical network which supplies it. Base to TH analyze for three different index of modulation, we have also hihlihted that at fifteen-level, the harmonics are very low. These latter can be easily eliminated with a simple low-pass filter. o it is not necessary to continue increasin the inverter level. REFERENCE [1] R. Teodorescu, F. Beaabjer, Multilevel converters A survey, Proc. EPE'99, pp [] Z. Yan, M. Jia, "An Interation PWM tratey for Hih- Frequency Link Matrix Converter With Adaptive Commutation in One tep Based on e- Re-Couplin Idea ", Industrial Electronics, IEEE Transactions on, Vol. 59, pp , 01. [3] Wu, F.J., "inle-phase three-level PWM scheme suitable for implementation with P", Electronics Letters, Vol. 47, pp , 011 [4].G. Holmes, and P.M. Brendan, Opportunities for harmonic cancellation with carrier based PWM for two level and multilevel cascaded inverters, IEEE Trans. on Industry Applications, Vol.37, No., pp , 001. [5] L. Li, C. ariusz, and Y. Liu, Multilevel space vector PWM technique based on phase-shift harmonic suppression Applied Power Electronics Conference and Exposition (APEC), Vol.1, pp , 000. [6] L. M. Tolbert, "Multilevel Converters for Lare Electric rives", IEEE Trans. on Ind. Application, Vol. 35, pp , [7]. Nin-Yi, W. Man-Chun, and H. Yin-uo, Application of a three level NPC inverter as a three-phase four-wire power quality compensator by eneralized 3VM IEEE Trans. Power Electron., vol. 1, no., pp , Mar [8] M. A. Tankari, M.B.Camara, B. akyo, C. Nichita, Ultracapacitors and Batteries control for Power Fluctuations mitiation in Wind-PV-iesel Hybrid ystem, Int. Conf. EVER'11, Monte-Carlo, Mars 011. [9] M. A. Tankari, M.B.Camara, B. akyo, C-bus Voltae Control in Multi-sources ystem Battery and upercapacitors, the 37 th Annual Conf. of the IEEE Industrial Electronics ociety IECON, Melbourne - Australia, Nov P a e