Modulation techniques for quasi resonant DC link PWM converters

The performance limitations of the quasi-resonant DC link inverter at very low load current are discussed. It is shown that substantial benefits can be obtained by suitable improvements in modulation strategy, without affecting the power circuit structure. Further substantial benefits can be obtained by introducing an intermediate phase voltage status, allowed by the converter structure, which is valid at low load current. This gives an extra degree of freedom, thus overcoming all practical limitations to the working range of this kind of converter. The proposed solutions are of general validity, and can be applied to different modulation techniques (both analog and digital), irrespective of operating conditions. Converter performance was simulated in a wide range of situations. Efficient and reliable operation was demonstrated by extensive experimental tests