For the design of three phase inverter for three phase motor drive, which is better using low DC voltage (12 V or 24 V DC) for the inverter stage then step it up using three phase transformer, or using High DC voltage (220 V DC) directly in the inverter stage?
To use higher DC voltage for converter would be more economical and reliable as the low working current reduces copper loss and step up transformers could be eliminated and 220 volt reliable and efficient inverters are readily available in market, with advent in semiconductors technology……
I agree with the answer of Dr. Desai. However, there are trade-offs. As Dr. Desai explained, for the same power rating, using high DC voltage will allow the inverter to operate in low current. Hence, the conduction loss could be minimized. However, the component will have to have higher voltage ratings. the switches should have higher DC voltage blocking capacity while turned-off.
So, you have to consider different aspects- inverter topology, budget, converter size to design your converter.
I also agree with Dr. Desai, but for a different reason--it is not the copper losses which might dominate, but the transformer magnetic losses. That is a large voltage ratio you are considering (24 V DC to 220 VDC). This is probably too large to start with 24 V and use a boost inverter so you must use a transformer for the inverted AC waveform. But a main advantage of the three phase inverter is control offered by the high frequency PWM capability. A transformer will have large (probably unacceptable) losses at high (~20 kHz) frequencies. Therefore, use 220 VDC with 3-phase inverter for the reasons and copper AND magnetic losses. The voltage is not so high as to incur significant penalty for switch voltage blocking capability. Good luck!