Custom Power Supply

[mlambru]

I need a power supply for the load of 10KW, which will feed it with the alternative currency, but by pulses of 2 KHz. The power in the load will be regulated by regulating the duty cycle of pulses. Control pulses can be generated by PC or programmable controller, as the power in the load should vary depending on the time/date. Can you propose a diagram for such a device? What switching power elements to use - say power transistors, MOSFET SSR, whatever? Maybe exist ready blocks, which can be used to assemble such a device?

 

[(*steve*)]

So you want a 10kW AC PWM power supply? AC and PWM don't really go hand in hand.

What voltage?

Is the load purely resistive?

What is your power source? (i.e mains, or some existing DC source -- maybe a bank of lead acid batteries for example)

What is your skill level (i.e. what power electronics have you designed and built previously)

 

[mlambru]

240V, mains, load resistive.
I'm electricity generation engineer, electronics is not my field. Thus ready made device for me is the best - say some functional blocks on DIN rail to connect together.
I have a task in hand and have to find a solution, thus any help appreciated.

 

[NickS]

I think you are talking about something like a Thyristor dimmer for lighting, except you want to control it electronically right.

The way the dimmer works is it turns on for just a portion of the sinusoidal half wave(if that makes any sense see pic HERE). I know there are ready made blocks for lighting applications but I am not sure of any that can deal with 10kW.

 

[mlambru]

The principle of the dimmer is similar.
The difference is that dimmer switch only once per 1/2 wave, thus working at 100 Hz, but I want to switch at 2 KHz, making small pulses, only envelope curve of which will be normal AC sunwave. And to regulate electronically I want not the phase of switching, like in dimming, but the duty cycle of the pulses.
Thus my power device, which should switch on/off quickly, should be something like MOSFET, or similar. Thyristor will not suite, as it only switch off during 0 voltage in the load.

 

[Resqueline]

Not that I know, but this sounds to me like something you'd find in stage lighting equipment. I'm sure there are modules that dims by PWM nowadays (MOSFET/ IGBT).

 

[NickS]

Ok I see what you are talking about. We made a similar circuit for driving an electro-surgical knife but the power requirements were different.

We used a UCC27324 to drive our MOSFET(60R099) which drove a transformer from a 200V rail at a frequency of about 50kHz(produced by our uC). We also used a massive heat sink with fan to keep the FET cool at 120W. You may need to consider multiple FET's in parallel to handle the heat.

 

[mlambru]

If possible, send me please a diagram and parts list to see.

 

[NickS]

I don't think I can or I may be in violation of IP rights but if you lookup the datasheets for the UCC27324 you will see an example of how it functions(it is just a FET driver)
The MOSFET Use will depend on your load. Like I said we were driving a transformer, thus our schematic may not be suited to your load anyway. We attachet the source to ground the gate to the driver and the load sat between the 200VDC rail and the drain of our FET(we also had an LC tank and snubber circuit that you probably would not use).

As for the clock signal that is a whole different animal. It sounds like your clock will have variable duty cycle but constant frequency so it is possible to design an analog circuit to suit your needs but you would be better off using a micro controller which means writing some basic code too.

 

[mlambru]

Thank you for the explanations. I think what you described is the circuit I need.
Probably to use a pair of 60R045. Logical level signal is not a problem.
But unfortunately with my level of experience to try to design a concrete diagram myself is not a good idea. To build it I need exact diagram and layout, or best of all - where to buy as a ready block.

 

[NickS]

The other issue you face is that you are using AC. So the switcher has to work bi polar. I have not seen this done.

Have you considered something like a variac? It is just an adjustable transformer. So instead of chopping the mains in and out you could just reduce the amplitude to some fraction of full level. We have one with a knob on top and it works great.

 

[mlambru]

No, my task defined exactly, and can not be changed.
I do need AC, but I understood MOSFET can do it.
Probably 27324 + 2 x 60R045 is workable variant - just need to be designed correctly - what I can not do myself.
Probably other variants exist. For example, what do you think about using ready made idustrial MOSFET SSR?

 

[NickS]

Perhaps but I have never used a bipolar SSR before so I am probably not the right person to help you on that(at high power little details can make a big deal).