Comparison of continuous and transition mode in a PV-booster with GaN-transistors and switching frequencies up to 250 kHz

A 1.8 kW boost converter for a PV-inverter with a switching frequency up to 250 kHz is analyzed. The boost converter consists of two parallel legs and the hardware is built so that chokes and semiconductors can be exchanged easily. Two different operating modes, the Continuous Induction Current Mode (CICM) with a fixed switching frequency of f_S = 250 kHz and the Transition Mode (TM) with a variable switching frequency are compared. The basic operation principles are explained and efficiency measurements on real hardware under different conditions (output power, semiconductors (GaN/Si)) are shown. An improved version of the Transition Mode is developed which leads to higher efficiencies. Exceptional efficiencies of η_{max, CICM} = 98.2 % in CICM at f_S = 250 kHz and η_{max, eTM} = 98.7 % in enhanced TM are obtained.