Active and Reactive Power Control of Single-Phase Two-Stage Grid-Tied PV System in dq-frame

Abstract

This thesis focuses on the boost converter and single phase VSI used with photovoltaic electricity generating systems in grid tied applications.A simple power control method is proposed.The control of time variant systems is more complicated compared to time invariant systems. However, by using suitable transformation techniques, time-variant systems (often vary sinusoidally with time) become time-invariant at the fundamental frequency, and are hence much easier to deal with. The direct application of transformation theory in single phase power systems is not possible without modification,and the d-q components would not be time-invariant in situations where harmonics, resonances or unbalance of system is present. The main objective is to address,the problems found with single-phase designs based on hysteresis controller in terms of cost, efficiency,power management and power quality. So a reliable single-phase inverter controller design based on voltage oriented control, with the implementation of direct quadrature reference frame has been proposed.As the first step the photovoltaic module is analyzed using SIMULINK software. By using MPPT extraction of maximum possible power from the PV can be done and feed this power to the inverter via boost converter, in which required magnitude of voltage can be acquired in steps. The second step, is the modelling of the single-phase inverter control using synchronous rotating frame. A mathematical analysis is conducted to determine the mechanism of the coupling that exists between the voltage phase and amplitude terms. The line frequency components of the feedback signals are transformed to time-invariant components, thus eliminating the ripple and reducing the computational burden associated with the controller stage.The inverter is control by bipolar sinusoidal pulse width modulation (SPWM) technique. Grid and VSI synchronization by SOGI-PLL is presented.By using SOGI generation of fictitious phase is presented. By park transform two-axis stationary (αβ) is converted into rotary (dq) frame. Finally, PI-controller based active and reactive power controller is implemented and the results areobtained using MATLAB/ SIMULINK.