# Pulse Width Modulation Sinewave

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#### SanjayEV

I've got a solar-powered 3-phase inverter/ The electricity comes in pulse width modulation. It powers a 3-phase motor without any problem. But the control panel only agrees with 1-phase electricity.

How can I change this to work and power the control panel?

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#### BrennanB12

Sanjay,

If you're on the hunt for or need a Pure Sine inverter, you will need to modulate the PWM sinusoidally at a high frequency (usually 100KHz plus more). But then you'll want to filter it with an L-C circuit.

Most standard power electronic textbooks will show you how to do this.

Not quite sure what your tolerances are and what sort of control scheme you'll need. But if you let us know, I or someone on here, might be able to help. It's an interesting issue to work through.

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#### Robin14

Because it is a solar-powered inverter, the PWM keeps the total o/p power within a certain scope.

When it's bright out, the duty cycle is lower than 50%. With grayer conditions, more than 50%.

I'm also thinking that you should convert the square or rectangular wave itself to sine — that is, the PWM signal itself is not being modulated by a sine wave that needs to be extracted from it.

Unless you know by how much the duty cycle varies between different light conditions, you cannot say for sure if it can be converted to a sine wave. For example, if it is between, say, 50 +/-5%, we can probably convert it to a sine wave (with a few details/ issues possibly)

But if the duty cycle variation is more, you cannot convert it to a pure sine wave.

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But also —
A sine wave has a constant DC offset or mean value (usually zero).

But a sine wave generated from PWM will have a net mean value that will vary based on the on/off time of the PWM wave.

If the duty cycle variation is within +/-5%, you will get a pseudo-sine wave that has a net mean value that will vary by that much.

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#### RobinJohnson

Once you convert it to sine wave, the total power available will also be reduced. This is because the peak value of the sine wave will be limited to that squared wave.

However, now the RMS value will now be 0.707 times the peak. This will get worse for AC if the duty cycle is not at the very least 50%.

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#### Haree

The power is primarily dictated by the load and the inverter's job is to keep the voltage regulated to either 230V/120V (this depends on where you are).

As you know, the voltage must be regulated. We can’t do it by varying the duty cycle on the inverter end as we will be invariably changing the output voltage as well.

#### ron simpson

I've got a solar-powered 3-phase inverter/ The electricity comes in pulse width modulation. It powers a 3-phase motor without any problem. But the control panel only agrees with 1-phase electricity.
Do I understand? You have a 3 phase inverter. You have a 1 phase control panel. Is that right?

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#### SanjayEV

Yes. 1 phase control panel.