Control of active and reactive powers in three phase inverters for grid-tied photovoltaic systems under unbalanced voltages

This paper presents an analysis of two algorithms used to control the active and reactive powers in three phase inverters for grid-tied photovoltaic systems under unbalanced voltages in the Point of Common Coupling (PCC). The algorithms are focused on injecting balanced currents to the grid despite the voltage unbalances. The analysed algorithms are composed of two control loops: the reference signal generation and the current controller. One of the algorithms generates the reference currents in the abc coordinates and the inverter firing pulses are obtained by using a Dead-Beat controller. The other algorithm calculates the reference current in the dq0 coordinates and considers a Proportional-Integral control technique to generate the firing pulses. The synchronization of the reference signals is made by a Kalman filter in both algorithms. This filter estimates the positive sequence component of the PCC voltages in order to obtain balanced reference currents. The performance of the algorithms is verified through simulations in PSIM and the results were compared based on the following parameters: the Total Harmonic Distortion (THD) of the injected currents and the mean square errors in the active power, the reactive power and the injected currents.