Disturbance estimator based predictive current control of grid-connected inverters

ABSTRACT: The work presented in my thesis considers one of the modern discrete-time control approaches based on digital signal processing methods, that have been developed to improve the performance control of grid-connected three-phase inverters. Disturbance estimator based predictive current control of grid-connected inverters is proposed. For inverter modeling with respect to the design of current controllers, we choose the d-q synchronous reference frame to make it easier to understand and analyze. In accordance with the d-q system coordinate, we select the space vector pulse-width modulation (SVPWM) to implement the drive logic of the electronic switches, which is considered the best method used to generate the PWM control pulses because it provides a fixed switching frequency. Therefore, the distortion in the output voltage and current is to be less compared with the other PWM methods. In this thesis, we discuss the basics of grid-connected inverter modeling and analysis. In addition, all the equations have been derived in ( ) and ( ) reference frames. The simulations of predictive current control and disturbance estimator are discussed. In the simulation study, we obtain grid current waveforms in the steady-state and for step changes in the d-component of the reference current. The controlled grid current is observed to track the desired current with negligible differences. The grid angle is extracted via PLL using the estimated reactive disturbance component. Moreover, the abc dq stability of the disturbance estimator due to the parameter errors in the inductor filter is analyzed numerically regarding the estimator gains. The advantage of this strategy comes from the fact that grid voltage sensors are not required, thus we obtain a low-cost implementation with high performance and robustness. Keywords: Inverters, Predictive Current Control (PCC), d-q Synchronous Reference Frame, Space Vector (PWM). …………………………………………………………………………………………………………………………