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Author Topic: A question for the grid inverter designers.  (Read 1881 times)
Alan
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« on: February 26, 2008, 02:02:07 PM »

A question for the grid inverter designers.

Most grid connect inverters use a H bridge fet or IGBT out put system to drive the grid connected transformer.
The two low side drivers are easy to drive because they are ground referenced. On low voltage inverters up to 50 V.D.C. driving the high side devices is straight forward.
With D.C. voltages up to 600 V.D.C. on the two high side devices a means of driving them that has suffient isolation is required. The IR2113 high / low side driver is one option.

The gate charge for the high-side MOSFET is provided by the bootstrap capacitor which is
charged by the 15 V supply through the bootstrap diode during the time when the device is off
(assuming that VS swings to ground during that time, as it does in most applications). Since the
capacitor is charged from a low voltage source the power consumed to drive the gate is small.
The input commands for the high-side channel have to be level-shifted from the level of COM to
whatever potential the tub is floating at which can be as high as 1200 V.D.C.

The point.
Systems seem to drive the high and low side fets / I.G.B.T devices with pulse width modulation.
   Would it not be possible to switch the high side fet on for one half cycle and pulse width modulate just the low side device for the same half cycle, reversing the H bridge configuration for the negative going cycle. I am trying to understand why the high and low sides need pulse width modulation. I have a system operational but can see a definitive advantage to having less switching operations on the high side.?

Regards

Alan
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Paulh_Boats
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« Reply #1 on: February 26, 2008, 04:25:29 PM »

Alan,

Can you PM or email a circuit?

-Paul
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