Role of Active Clamp Circuit in a DC/AC Isolated Converter based on the principle of Pulsating DC Link

The operation of Active Clamp circuit is presented for an Isolated DC/AC Converter based on the principle of Pulsating DC link (PDL). This innovative two stage converter, made of a Phase Shifted Full Bridge and a Three Phase Inverter, is featured by the pulsating evolution of the voltage on the intermediate DC link resulting from the absence of the output filter of the first stage. The zero voltage phases of the PDL are used to achieve the Zero Voltage Transition (ZVT) for all the switches of the second stage. The Active Clamp circuit is used to clamp the voltage overshoots on the Pulsating DC link due to the parasitic inductance which resonates with stray capacitance of the converter. Moreover, the circuit permits the storage of the energy associated with the overvoltage and its restitution to the DC-link during the subsequent energizing phases. The role of the Active Clamp capacitor is discussed on the basis of a comprehensive simulation analysis and experimental data obtained from a 5kW prototype.