Repetitive control of power conversion system from a distributed generator to the utility grid

An AC-DC-AC converter is employed as an interface between a distributed generator and the utility grid. A corresponding control system for the converter is proposed to offer good waveform quality of a local grid where a large proportion of the load is non-linear, and to regulate the exported power as well. The control system consists of two nested loops. In the inner loop, a voltage controller based on repetitive control and H^∞ control is used to achieve good waveform tracking. Decoupling control is used in the outer loop to control active power (P) and reactive power (Q) accurately and independently. A PLL (phase-locked loop) is used to synchronise the conversion system It also identifies the fundamental frequency voltage magnitude of the utility grid and generates quadrature voltage signals which are used for the control system.