Investigation on applications of random pwm controller based multi level inverter for grid connected renewable energy system

Abstract

quotBackground: Harmonic spectrum of line current on ac side of grid connected solar newlineinverter is function of solar irradiation, temperature and PWM method employed. Conventionally, and#64257;xed frequency PWM technique is used to control grid connected inverter using Linear Current Control. The and#64257;xed frequency PWM method has issues of side-band harmonics atmultiple of switching frequency and increased value of lower order harmonics. Random frequency PWM method has capability to overcome issues of harmonic present in and#64257;xed frequency method. newlineAim: To evaluate the performance of grid connected solar inverter and grid isolated solar inverter for THD, Spread spectrum with sine PWM, Pseudo random bit sequence(PRBS) PWM, Random carrier frequecy (RCF) PWM and space vector PWM (SVPWM) for two level and three level. newlineMethod: Simulation model of grid connected inverter is prepared in MATLAB® Simulink®. A two-level inverter was controlled by Sine PWM supplied by DC sources. DC source was replaced by Solar panel with appropriate Irradiation and Temperature control. Various MPPT techniques like incremental conductance, perturb and observe etc. were studied. A Solar inverter using two level and three level supplying R-L load in grid isolated mode was simulated. For grid connection, various current control methods are available in literature. A linear current control technique using PI controller is selected as it is easy to implement but has disadvantage of its poor response for harmonic compensation. Grid connected inverter using two and three level inverters were developed using sine PWM. A PRBS based RCF PWM method was realized for two and three level DCMLI grid connected inverter to vary the switching frequency with an aim to get spread spectrum characteristics. RCF PWM method for two level and Random carrier frequency space vector PWM(RCFSVPWM) method for three level was designed. Variation in frequency band and its effect on THD, Lower harmonics and Harmonics at multiple of switching frequency was studied.