Solar fed Induction Motor Drive with TIBC Converter and Voltage Multiplier Circuit

Transcription

1 Solar fed Induction Motor Drive with TIBC Converter and Voltage Multiplier Circuit Aiswarya s. Nair 1, Don Cyril Thomas 2 MTech 1, Assistant Professor 2, Department of Electrical and Electronics St. Joseph s College of Engineering and Technology Abstract- The paper proposes a new converter (Two Inductor Boost Converter -TIBC) to drive the induction motor in three phase supply. The peculiarity is that it has no batteries like chemical storage elements. The major points of TIBC are that it contains nonisolatedsnubber circuits and voltage doubler to achieve high voltage gain and low input current ripple. The main application of the system comes under photovoltaic water pumping system due to high life time and absence of electrolytic capacitors. The paper is modified with a new topology called Cockcroft-Walton voltage multiplier circuit. The entire system includes converter side and an inverter side. The inverter is three leg bridge inverter. The control of inverter is done using SPWM and Third Harmonic Injected SPWM and THD is compared. Keywords- photovoltaic (PV) cell, MPPT algorithm, TIBC converter, Three phase induction motor, THD detection, I. INTRODUCTION The use of Photovoltaic (PV) solar energy is one of the most efficient promising solution to the places where the unavailability of electric power rules come out for water consumption[1]. Instead of PV we can adopt lead acid batteries or dc motor to drive the water pump [2]. The batteries can operate only at rated power and maximum two years life span. In addition to the cost of installation and maintenance another drawback is the problem of battery replacement. The boost stage between PV module and the motor can be avoided by the use of low voltage dc motor. But the disadvantages come like it is not suitable for application in isolated areas, lower efficiency and higher maintenance cost compared to induction motor. Against all the challenging problems three phase induction motor [3] having higher efficiency, availability in local markets, greater robustness (maintenance need is minimum), autonomous operation (no specific training needed) as in Fig.1 is introduced. Fig.1. Simplified block diagram of the proposed system This paper deals with Section II, Modelling of PV cell is explained. In Section III, MPPT algorithm and in Section IV, proposed converter is analyzed. Section V, inverter circuit and control finally in Section VI, conclusion. First consideration is how to make a PV cell? II. PV MODEL Fig. 2.Solar cell model The Fig. 2 shows the equivalent circuit of the ideal PV cell. The voltage current characteristic of a solar cell is given as - [exp [q( V + I )/ K A]-1] ( V + I / ) (1) Light generated current or photo current 86

2 Cell saturation of dark current q- 1.6 C, electron charge K 1.38 J/K, Boltzmann s constant - Cell s working temperature A- Ideal factor A. Solar Module and Array Model Since a typical PV cell produces less than 2W at 0.5V the cells must be connected in series parallel configuration on a module to generate enough high power. The equivalent circuit for the solar model arranged in is shown in Fig. 3. parallel cells The cell s saturation current changes with the cell temperature which is written as = [ exp[ ] (4) Cell s reverse saturation current at standard solar radiation and reference temperature Band gap energy of the semiconductor used in the cell In the equation (4) (5) = (6) By substituting (6) in (5) (7) PV efficiency is insensitive to variation of since shunt resistance is inversely related with shunt leakage current to ground. So the simplified model of the PV solar cell is expressed by the equation (8) and is shown in Fig. 4. I = - [ exp[ -1] (8) = (9) Fig. 3. Equivalent circuit of solar array Now the terminal equation for the current as follows I = - [ exp [ -1] ) (2) The photo current mainly dependscell s working temperatureand on the solar insolation which can be written as =[ ( )]H (3) Fig. 4. Simplified model of solar array B. Implementation and Simulation Model A generalized PV model is made using Matlab/Simulink according to equation (1), (3), (8) and the basic circuit shown in Fig. 3. The unknown parameters (,, A) of the model can be obtained by equations (6), (7), (9). Cell s short-circuit current at 25ºC and 1 kw/ Cell s short circuit current temperature coefficient H solar insolation in kw/ Fig. 5. Masked PV model 87

3 Fig. 6. Subsystem 1. of PV model Fig. 7.P-V and I-V characteristics of PV module at reference temperature (25 ) and standard solar insolation(1 kw/sq.m.) III. MPPT ALGORITHM A PV array or generator will have one point on its current /voltage characteristic that points to maximum power output. This is called as the maximum power output or MPP. Directly connected system do not work at the MPP, because a significant amounts of available energy are wasted. A Pump controller (dc-dc converter) is required to better match the PV generator to the motor/pump set. This is called as MPPT. utilization efficiencies of up to 99% depending on weather conditions. The efficiency is marginally lower for rapidly Changing irradiance due to the energy loss during the confusion and recovery periods.but the INC algorithm is less confused by noise and system dynamics compared to the P&O algorithm. So in the following section detailed study of Perturb and Observe (P&O) algorithm is explained. Fig. 8. Mis match between resistive load andpv Source; current voltage curves In order to avoid this mis match in the two curves shown in Fig.8 and Fig.9 we use MPPT circuit shown in Fig. 10. MPPT algorithm offers significantly higher energy utilization efficiencies. But for more significant improvements in energy usage, more efficient MPPT control algorithms, that include the effects of insolation and temperature variation on the MPPT Voltage would be required.the INC, P&O algorithms offer higher energy Fig. 9.Mis match between resistive load and PV Source; power-voltage curves Fig. 10. Circuit diagram for PV system with MPPT control 88

4 A. Perturb and Observe (P&O) Algorithm The P&O MPPT algorithm is a simple algorithm that does not require previous knowledge of the PV generator characteristic or the measurement of solar intensity and cell temperature.in P&O algorithm system performance is affected by step size ( or ) and perturbation frequency ( ). With the addition of MPPT the powervoltage curves is as shown in Fig. 11. Fig.11.Behavior with reference voltage perturbation in theelevel. B. SIMULATION MODEL By P&O algorithm Matlab/Simulation is made with the voltage and current input from PV. In MPPTthe pulses are generated by fixed duty cycle control. Fig.12 MPPT Model IV. PROPOSED CONVERTER Fig. 1 represents an overview of the proposed system. From panel the energy produced is fed to the motor through a converter which is a dc-dc two inductor boost converter (TIBC) and a dc-ac three phase inverter to convert the dc voltage to three phase ac voltage. Instead of all conventional converters drawbacks [4][5][6] at last a modified TIBC topology is adopted [7] shown in Fig. 17 so that transformer turns ratio can be reduced. Fig. 13.Modified TIBC topology A. Operation Principle and Description The TIBC converter in Fig.13 includes two input inductors and and two active switches and. and are the antiparallel diodes of and respectively. The resonant tank includes a first resonant inductor and second resonant inductor and a resonant capacitor. is greater than which is performed by transformer s magnetizing inductance. Fig. 14 (a)-(f) shows the first six operation modes of the TIBC converter during half switching cycle. The corresponding theoretical waveform is also shown in Fig. 14 Mode 1 [ ; Fig. 14(a)]: At, and =0. From onwards is keeps off and is keep on. is absorbed in to and feeds the resonance tank..mode 2 [ ; Fig. 14(b)]: Both and conduct in this periods. Terminal A and B shorted and the rectifying diodes are still off. Mode 3 [ ; Fig. 14(c)]: Here goes negative and this mode is similar to mode2.it ends at when gets off. and come to their peaks.mode 4 [ ; Fig. 14(d)]: The only difference with mode 3 is that after is off the negative. flows through. At reaches zero again and mode 4 ends. By is still charged. At touches /2 and mode 5 ends.mode 6 [ ; fig 14(f)]: is on and is off from onwards. Since is forced on, at /2, is clamped. is charged by and transfers it s stored energy to the load. = -. This mode ends at when =. 89

5 Fig. 14.Operating modes and waveforms of the proposed converter. (a) Mode 1. (b) Mode 2. (c) Mode 3. (d) Mode 4. (e) Mode 5. (f) Mode 6. (g) Theoretical waveforms When higher dc voltages are needed cascade voltage multiplier circuits or cascade doubler circuits can be used. The former require too many supply and isolating transformers. The later are used when larger output voltages are needed without changing input transformer voltage level. Cockcroft-Walton voltage multiplier circuit uses single supply transformer by extending the simple voltage doubler. By Cockcroft Walton topology in TIBC as in Fig. 16 the output voltage is increased to V compared to simple voltage doubler as in Fig. 15. The transformer output in former is 100V and by voltage doubler it is 200V. C.Basic Design = = [ + 1] (10) = 2.25 and TIBC switching frequency = 100kH Inverter switching frequency = 7.7 khz, = 100 H Fig.15 Simulation model of Cockcroft topology Input Inductor Design = and (11) = (12) B.TIBC Converter with Modification Fig16. Output voltage in Double and Cockcroft topology V. INVERTER CIRCUITORY AND CONTROL Conventional three phase inverter system is used to invert the dc voltage to ac in the load. Control is done using three methods. PWM (Pulse Width Modulation), SPWM (Sinusoidal Pulse Width Modulation ), SPWM with third harmonic injection are the methods. A third harmonic waveform is injecting to the sinusoidal waveform sothat all harmonics are concentrated to third harmonics. A third harmonic filter is used to avoid these harmonics as the reduction of Total Harmonic Detection (THD).To eliminate third harmoni component Fig. 18. Masked model of inverter circuit = sin wt + Asin 3wt 90

6 REFERENCES Fig.19. Control Signals Fig.20. Entire system VI. CONCLUSION In this paper a dc-dc TIBC converter with photovoltaic energy as input, for water pumping is discussed. The TIBC converter is having the advantages like high robustness, autonomous operation, easy transformer flux balance,low cost, high life span and the main application comes under traction motor control, trolley cars and solar power application. This paper includes PV model, MPPT algorithm, TIBC converter with Cockcroft topology. [1] M. Chunting, M. B. R. Correa, and J. O. P. Pinto, The IEEE 2011 international future energy challenge Request for proposals, in Proc.IFEC, 2010, pp [2] M. A. Vitorino and M. B. R. Correa, High performance photovoltaic pumping system using induction motor, in Proc. Brazilian Power Elec-tron. Conf., 2009, pp [3] Tschanz, H. Lovatt, A. Vezzini, and V. Perrenoud, A multi-functional converter for a reduced cost, solar powered, water pump, in Proc. IEEEISIE, 2010, pp [4] W. Li, L. Fan, Y. Zhao, X. He, D. Xu, and B. Wu, High step-up and high efficiency fuel cell power generation system with active clamp flybackforwardconverter, IEEE Trans. Ind. Electron., vol. 59, no. 1, pp , Jan [5] R.-Y. Chen, T.-J. Liang, J.-F. Chen, R.-L. Lin, and K.-C. Tseng, Study and imp lementation of a current-fed fullbridge boost dc-dc converter with zero-current switching for high-voltage applications, IEEE Trans. Ind.Appl., vol. 44, no. 4, pp , Jul./Aug [6] Y. Jang and M. M. Jovanovic, New two-inductor boost converter with auxiliary transformer, in Proc. IEEE Appl. Power Electron. Conf. Expo., 2002, pp [7] Yuan, X. Yang, X. Zeng, J. Duan, J. Zhai, and D. Li, Analysis anddesign of a high step-up current-fed multiresonant dc-dc converter with low circulating energy and zero-current switching for all active switches, IEEE Trans. Ind. Electron., vol. 59, no. 2, pp ,Feb