ISSN 2348 2370 Vol.08,Issue.10, August-2016, Pages:1905-1910 www.ijatir.org Multilevel Inverter based Photovoltaic System with Distributed Generation System Fed Induction Motor Drive VENKATA V ANJANEYULU B 1, G.PRASANTH 2 1 PG Scholar, Dept of EEE, Avanthi Research & Technological Academy, Vizianagaram(Dt), AP, India, E-mail: vignesh9veeru@gmail.com. 2 Assistant Professor, Dept of EEE, Avanthi Research & Technological Academy, Vizianagaram(Dt), AP, India. E-mail: Prasant.oct26@gmail.com. Abstract: Solar energy is the most low cost, competition free, universal source of energy as sun shines throughout. This energy can be converted into useful electrical energy using photovoltaic technology. The effective operation of Induction motor is based on the choice of suitable converter-inverter system that is fed to Induction Motor. Converters like Buck, Boost and Buck-Boost converters are popularly used for photovoltaic systems. But these converters are limited to low power applications. For PV applications like pumping these converters could do a good job as pumping is carried out at high power. Thus a new push pull converter which is two switch topology can do justice by giving a high power throughout. The Induction Motors are the AC motors and hence from converter, an inverter system is also required to obtain an AC voltage. This inverter is chosen based on its advantages and it is fed to induction motor. To obtain optimum motor performance and to reduce total harmonic distortion of the inverter output waveform, we employed sinusoidal pulse width modulation (SPWM) technique based multilevel inverter for switching of inverter power circuit. In order to maximize the power output the system components of the photovoltaic system should be optimized. The proposed inverter can be replaced with multilevel inverter and is implemented MATLAB/SIMULATION software for better control of motor. development of new control algorithms. However, the cost, simplicity and flexibility of the overall drive system which are some of the most important factors did not get that much attention from the researchers [4-6]. That is why, despite tremendous research in this area, most of the developed control system failed to attract the industry. Thus, the main issue of this work is to develop a cost effective, simple and efficient high performance IM drive. Recently, some efforts have been made on the application of four switch Three Phase (FSTP) inverter for variable speed drives [7]. Some advantages of the FSTP inverter over the conventional SSTP inverter such as, reduced price due to reduction in number of switches, reduced switching losses, reduced number of interface circuits to supply logic signals for the switches, simpler control algorithms to generate logic signals, less chances of destroying the switches due to lesser contact among switches and less real time computational burden [8-10]. The traditional inverters are Voltage Source Inverter (VSI) and Current source Keywords: Wind Power, Distribution Network, Induction Generator, Reactive Power, Harmonics, and Power Quality. I. INTRODUCTION Many research works are focusing in the development of the efficient control algorithms for high performance variable speed induction motor (IM) drives. Induction motor has been operated as a work horse in the industry due to its easy build, high robustness and generally satisfactory efficiency. Recent development of high speed power semi-conductor devices, three phase inverters take part in the key role for variable speed AC motor drives [1-3]. Traditionally, Three Phase inverters with six switches (SSTP) have been commonly utilized for variable speed IM drives; this involves the losses of the six switches as well as the complexity of the control algorithms and interface circuits to generate six PWM logic signals. So far researchers mainly concentrated on the Fig.1. Block Diagram of Proposed Converter Five Level Inverter with Induction Motor Inverter (CSI), which consist of diode rectifier front end, DC link and Inverter Bridge. In order to improve power factor, either an AC inductor or DC inductor is normally used [11-13]. The DC link voltage is roughly equal to 1.35 times the line voltage and the Voltage source inverter is a buck converter that can only produce an AC voltage limited by the dc link voltage and the Voltage source inverter is a buck converter that can only produce an AC voltage limited by the dc link voltage. Because of this nature, the Voltage source inverter based PWM VSI and Copyright @ 2016 IJATIR. All rights reserved.
CSI are characterized by relatively low efficiency because of switching losses and considerable Electromagnetic Interference (EMI) generation [14]. Simple converter topology, Inherent four quadrant operation, Reliability, Motor friendly waveforms with low dv/dt. II. CONTROL STRATEGY In our proposed control strategy the RES is connected to a voltage source inverter (VSI) as a DC source. If the RES generates AC voltage, that can be connected to the VSI after rectifying it. The DC link capacitor acts as an isolator in between the converters (the rectifier and the inverter) providing the freedom for independent control of both the converters. The power from some of the less stable RES should be conditioned before connecting them to the VSI. The basic aspect of the control strategy has been discussed in [5]. The DC link (transfers the power from the RES to the grid. The control scheme is shown in Fig 2. Fig.2. Control Scheme The inverter output current, in this control scheme, is forced to follow the grid voltage. The grid voltage is converted to a unit vector template using a unity sine wave generator (basically an op-amp circuit designed for less than unity gain) and then this waveform is used as the reference current. The actual grid current is measured and compared with the reference current which is the unit sine wave obtained from the grid, and the pulses are generated according to the error between the actual current and the grid current [8, 15]. The unity vector templates are obtained from the grid voltage, here the synchronizing angle, tk lf the three phases is used to force the inverter output current to follow the grid voltage. The unit vector templates are represented as VENKATA V ANJANEYULU B, G.PRASANTH (1) (2) (3) These unit vector templates are sampled and fed to the microcontroller and compared with the actual grid currents la, Ib and Ie sampled from the grid directly. (6) Where, h is the hysteresis band provided. If all the three conditions of equations (4), (5) and (6) are satisfied then the upper switches of the three phase inverter are switched on. (9) If the three conditions of equations (7), (8) and (9) are satisfied, then the upper switches will be switched off and the lower switches will be switched on. In order to synchronize the RES to the grid the magnitude, the frequency and the phase of the voltages on the two sides should match [6]. The control scheme presented here easily manages these aspects. The reference current is obtained from the grid voltage. This helps the control scheme to generate switching pulses for the inverter such that the inverter output current is in the same phase and frequency as that of the grid voltage. Apart from the synchronization, the inverter output voltage should lead the grid voltage in order to achieve power transfer from the RES to the grid. As far as this control scheme is concerned the inverter output current is of the same phase as that of the grid current and also lags the inverter output voltage by an angle decided by the inductance in the circuit. Thus by default the inverter output voltage leads the grid voltage by the same angle. This makes the power transfer to the gird possible [11]. The control scheme using these equations thus provides switching pulses to the inverter in such a way that the inverter output current is forced to follow the reference current strictly. III. PHOTOVOLTAIC (PV) SYSTEM In the crystalline silicon PV module, the complex physics of the PV cell can be represented by the equivalent electrical circuit shown in Fig.3. For that equivalent circuit, a set of equations have been derived, based on standard theory, which allows the operation of a single solar cell to be simulated using data from manufacturers or field experiments. The series resistance RS represents the internal losses due to the current flow. Shunt resistance Rsh, in parallel with diode, this corresponds to the leakage current to the ground. The single exponential equation which models a PV cell is extracted from the physics of the PN junction and is widely agreed as echoing the behavior of the PV cell (4) (5) (7) (8)
Multilevel Inverter based Photovoltaic System with Distributed Generation System Fed Induction Motor Drive Fig.3. Equivalent Electrical Circuit of a PV Module (10) The number of PV modules connected in parallel and series in PV array are used in expression. The Vt is also defined in terms of the ideality factor of PN junction (n), Boltzmann s constant (KB), temperature of photovoltaic array (T), and the electron charge (q). Applied a dynamical electrical array reconfiguration (EAR) strategy on the photovoltaic (PV) generator of a grid-connected PV system based on a plant-oriented configuration, in order to improve its energy production when the operating conditions of the solar panels are different. The EAR strategy is carried out by inserting a controllable switching matrix between the PV generator and the central inverter, which allows the electrical reconnection of the available PV modules. Fig.4.Induction Motor Stator Winding: (a) General Arrangement (b) Arrangement for the Proposed Inverter. (14) Similarly voltage equitation for the remaining phases are (15) (16) Voltage equations in dq0 frame can be solved from the basic equations of induction motor IV. INDUCTION MOTOR In a conventional four pole induction motor, there are two sets of identical voltage profile windings will be present in the total phase winding. These two windings are connected in series as shown in fig.4 (a). For the proposed inverter these two identical voltage profile winding coils are disconnected, and the available four terminals are taken out, like shown in the fig.4 (b). Since these two windings are separated equally, stator resistance, Stator leakage inductance and the magnetizing inductance of each identical voltage profile windings are equal to the half of the normal induction motor shown in fig.4 (a). The voltage equitation for the stator winding is given by common dc link. Flux linkages are as follows (17) (11) (12) The effective voltage across the stator winding is the sum of the voltages across the two individual windings. (18) The expression for the electromagnetic torque in terms of dq0 axis currents is (13) The motor phase voltage can be achieved by substituting equations (11) and (12) in (13) Rotor speed in terms of Torque is (19)
VENKATA V ANJANEYULU B, G.PRASANTH (20) V. MATLAB MODELEING AND SIMULATION RESULTS Fig.9. Inverter Output Power for 190V DC Input. Fig.5. Matlab/Simulink Model of Proposed Grid Interfacing Inverter Fig.6. Simulation Results for Grid Side Voltages. Fig.10. Matlab/Simulink Model of Proposed PV Based Five Level Inverter Fed Induction Motor Drive. Fig.7. Inverter Output Power for 110V DC Input. Fig.11. Five Level Inverter Phase to Phase Voltage. Fig.8. Simulation Results for Grid Side Voltages.
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