Is the UPC a Resonant DC-link converter?
A. Although the UPC has a superficial resemblance to resonant DC-link converters, it is not such a converter. Note that those converters have line filter inductors between the switches and the input/output, as these are voltage source converters, whereas the UPC has line filter capacitors, as it is a current sourced converter (an AC current source, not a DC current source as is usually done). Also, although the UPC link has partial-resonant intervals, and the link is an inductor in parallel with a capacitor, the link is not operated resonantly. The link waveform is not sinusoidal as the resonant DC link waveform is. Most importantly, the UPC may be operated without a link capacitor, as it only serves to provide soft switching, whereas the resonant DC link converter cannot operate without its link capacitor. Resonant link converters suffer from only being able to control switching at discreet intervals given by the resonant frequency, which causes poor PWM waveforms and I/O filter ringi
