Trapezium current mode (TPCM) boundary operation for single phase grid-tied inverter

A novel modulation technique for single phase grid-tied inverter is proposed in this paper. In normal discontinuous current mode (DCM) operation, the output current becomes distorted due to the resonant between parasitic output capacitors of switching devices and inductor during zero current periods if no current control method is applied. This low frequency distortion can be improved in the boundary conduction mode (BCM), however, the switching frequency in BCM operation varies in the main period, which may result in higher switching loss and inductor loss. The proposed trapezium current mode (TPCM) boundary operation enables to achieved boundary in the entire switching period without using variable switching frequency operation and the low frequency distortion in output current can be effectively improved. The operation principle, circuit analytical model, modulation strategy and design considerations are presented. A 400W prototype is fabricated to validate the proposed modulation technique.