Cost-Effective Grid-Connected Inverter for a Micro Combined Heat and Power System

This paper proposes a novel, cost-effective grid-connected inverter for a domestic micro combined heat and power system. A high-frequency (~12 000 r/min), high-voltage (~425 Vdc) brushless dc machine is used as the generator. The output of the generator is injected into the grid through a novel grid-connected inverter, utilizing a digital algorithm for the implementation of a constant frequency hysteresis current control. This allows a simplified output filter with smaller components to be employed. A grid synchronization method has also been designed, based on a low-pass filter and a microcontroller to optimize/tune the output power factor. The proposed method is successfully applied to a 500-W, 230-V, 50-Hz grid-connected voltage-source inverter (VSI) prototype, where the output of the VSI has been demonstrated to comply with the operating regulations for domestic distributed power generation systems.