Fast current-tracking control for grid-connected inverter with an LCL filter by sinusoidal compensation

A voltage source inverter with an LCL filter is often used for a utility interface to control its output current to a grid side because of its harmonic reduction advantages. The integral compensator is often used to reduce the steady-state errors. However, there is always a control delay due to sinusoidal variations. This paper proposes a digital sinusoidal compensator which is based on the internal model principle to realize a response with no deviation for a periodic sinusoidal reference input. It has a simple numerator and a denominator z² - 2zcosωT + 1 of a transfer function which is equal to the z function of a sinusoidal waveform of the angular frequency ω and the sample time T. Compensator and feedback gains of the inverter are determined by the dead-beat or the optimal control principle. For an utility interface inverter, it is necessary to detect the sinusoidal phase of the source voltage. A new digital technique is proposed and it is based on the least-mean-square (LMS) method. The proposed method is investigated for performances and it is validated through simulation and experimental results by a DSP control system.