A fixed frequency ZVS high power, PWM SMR converter with zero to rated load variation capability

Typical 6-12 kW switched-mode rectifier (SMR) converters operate at switching frequencies of about 40 kHz, employ FET switches, and utilize pulse width modulation (PWM) power control techniques. These operating conditions create a harsh PWM switching environment which makes the switching to conduction loss ratio approximately 3 to 1, and complicates the task of EMI suppression. A zero-voltage switching (ZVS) SMR high power circuit that improves overall converter efficiency by significantly reducing switching losses while moderately increasing conduction losses is presented. A feature of the proposed converter is that ZVS fixed frequency operation is possible, even with the primary of the transformer disconnected. The modes of circuit operation are presented and analyzed. The feasibility of the proposed converter is demonstrated with experimental results on a 7 kW prototype unit