I am designing a system for a 3.5 kW wind turbine that has a large input voltage range, from 0 up to say 750 VDC. The output voltage should not exceed 600 VDC. I would like to make a voltage limiting circuit. Do not worry I do not test any of this in my barn or backyard. I do my experiments in a university in a laboratory environment surrounded by professionals.
I came across some problems for this application:
I believe ideally the buck converter should do nothing (gets bypassed) up to 600 VDC. The reason is that operating the buck converter introduces energy loss which I want to avoid. Bypassing seems not to be very simple:
- Using a relay at this DC voltage there is a lot of arcing, a relay wears out quickly and it is also dangerous.
- Using a semiconductor such as a power MOSFET or IGBT requires high side switching. High side switching with a bootstrap circuit does not work if you would like to have the switch fully closed (duty cycle = 1). Using a charge pump is possible I believe, but the typical ICs go up to 60 VDC. I could design a high voltage charge pump. This is not my preferred choice since I think it is going to be difficult to properly and reliably control expensive and delicate power electronics.
- Perhaps using a P-channel MOSFET would be more do-able. The R_on resistance losses are bit higher but perhaps could be acceptable. However, they do not seem to be available for such high voltages.