Decoupling control of the active and reactive power for a three-phase inverter

We consider the control design of a grid-connected three-phase inverter which is meant to work with a small power generation unit. A two-level (nested) control system is presented. The inner control loop contains repetitive controllers which assure that the output voltage of each phase can track a sinusoidal reference voltage. These voltages are applied to the local loads, which are separated from the grid by small inductors. The outer control loop monitors the grid voltage and, based on given reference values for the active and reactive power injected into the grid, it generates three reference voltages for the inner control loop. The controller in the outer control loop consists of two parts: a power controller and a phase locked loop (PLL). This paper is about the design of the power controller, which involves decoupling the active and reactive power in order to control them independently and smoothly.