Analysis of a voltage clamp quasi-resonant DC-link used in high frequency DC-AC converters

To increase power density in power converters we can increase the switching frequency as this enables the use of smaller capacitors and inductors. However, this technique has the disadvantage of increasing power loss in the switches. We can solve this problem by using a quasi-resonant circuit in the inverter DC link (RDCL). This circuit reduces its output voltage when the inverter switches switch. This is therefore performed at zero voltage and the switching power losses are zero. RDCL is used before a DC/AC converter, and so its behaviour must be characterised for reference in the control design. This characterisation is also used for adopting the RDCL output impedance and the inverter input in order to improve the system dynamic response. In this work, we present the results of the behavioural analysis of a resonant DC-link structure. It is based on the structure described in [S.Y.R. Hui et el., January 1996]. The resonance frequency was increased to 1.5 MHz and this enabled the use of RDCL in combination with inverters switching at 200 kHz. As a result the magnetic component requirement was strict. Different simulations were made and a 1 kW prototype was built to monitor the behaviour under different conditions.