Efficiency Improvement of a Gas Engine Cogeneration System by Power Factor Control with an IGBT Rectifier

Improvement of the efficiency of a 1 kW household type gas engine cogeneration system is investigated. We propose two approaches. One is the power factor control of the synchronous generator by using an IGBT rectifier instead of a diode rectifier to improve the generator efficiency. This approach enables us to reduce the copper losses in the generator windings by reducing the reactive current, and also to reduce the harmonic torque of the generator by improving the current waveform. The other approach is application of a matrix converter to reduce the losses in the rectifier and inverter. Since this system connects the three-phase generator to the single-phase utility, the power pulsation due to the single-phase power must be treated. To solve this problem, we propose the new strategy that the power pulsation is absorbed by the inertia of the rotor of the generator in the case of application of the matrix converter that has no energy storage component. In order to realize this strategy, we investigate a new control method that the instantaneous three-phase power is synchronously modulated with the single-phase power pulsation. This paper describes the experimental results of the efficiency improvement of the generator by the power factor control using the IGBT rectifier, and the simulation result of the power modulation control using the three-phase/single-phase matrix converter.