Control of multi-functional grid-connected PV systems with load compensation under distorted and unbalanced grid voltages

This paper proposes a new algorithm in the natural abc coordinates used to control grid-connected photovoltaic (PV) systems with load compensation functionalities under distorted and unbalanced grid voltages. The control of the PV system is composed of three loops: The Maximum Power Point Tracker (MPPT), the reference signal generation, and the inverter controller. The contribution of the paper is presented in the signal generation algorithm, which is focused on the quality of the injected currents and the inclusion of load compensation functions (power factor correction, current harmonics mitigation, and load balancing). The proposed algorithm is based on the Fryze's theory and an adaptive Butterworth-Kalman filter, which estimates the fundamental positive-sequence component of the grid voltages and determines the current reference. An experimental prototype of a three-phase grid-connected PV system was implemented to evaluate the behaviour of the proposed controllers under distorted and unbalanced grid voltages. The experimental and simulation results show the good behaviour of the control algorithms, the achievement of the compensation goals and the outstanding performance of the system under disturbances in the grid voltages. ABSTRACT This paper proposes a new algorithm in the natural abc coordinates used to control grid-connected photovoltaic (PV) systems with load compensation functionalities under distorted and unbalanced grid voltages. The control of the PV system is composed of three loops: The Maximum Power Point Tracker (MPPT), the reference signal generation, and the inverter controller. The contribution of the paper is presented in the signal generation algorithm, which is focused on the quality of the injected currents and the inclusion of load compensation functions (power factor correction, current harmonics mitigation, and load balancing). The proposed algorithm is based on the Fryze's theory and an adaptive Butterworth-Kalman filter, which estimates the fundamental positive-sequence component of the grid voltages and determines the current reference. An experimental prototype of a three-phase grid-connected PV system was implemented to evaluate the behaviour of the proposed controllers under distorted and unbalanced grid voltages. The experimental and simulation results show the good behaviour of the control algorithms, the achievement of the compensation goals and the outstanding performance of the system under disturbances in the grid voltages.