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SPWM H-Bridge Output Issues [Giving Square Wave Output]

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Power_Pro123

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Hi All,
I have designed a basic H-Bridge circuit using the 20N60 Mosfets and 2 IR2110 gate drivers. I have successfully generated the spwm and applied to the driver to drive the H bridge. My H Bridge seems to work fine but it doesn't gives a spwm output, instead it gives me a square wave of 50Hz. Please help me in this issue. I have attached my results.
Vdc = HBridge input
HBridge Output
NewFile5.png

Output of gate driver to gates when Vdc is 0V
NewFile3.png

Output of gate driver when Vdc=10V [it disturbs the gate signal by shifting the gate signal spwm by Vdc volts provided at H Bridge input
NewFile4.png
 

Hi,

I assume all is working correctly, but your expectations are not.

A halfbridge for SPWM is a square wave with variable duty cycle, this is what I see.
To see a sine you need to connect a low pass filter at the output.

Klaus
 

I am expecting an output of this kind sir, how can i get this as highlighted in yellow ?
wJZxM.png
 

Hi,

This is what you have.
You just need to select the correct timebase and the correct (single shot) trigger at your scope.
At least this is my assumption.

Klaus
 

Your H-bridge creates a buck converter in one direction during one half of the cycle, then a buck converter in the opposite direction during the second half of the cycle. Your mosfets must switch on and off properly to create this action. In addition there's a chance the body diodes conduct upward as well.

It may be a good idea to get familiar with constructing a buck converter first. Single switching device. LC output stage. Your SPWM waveforms (post #1) are typical of correct shape, to produce one-half of a sinewave.
 

Sir is there any difference if the input switching signal is SPWM or square wave, because the output waveform for both the cases are the same.

Connecting a LC filter at the output for both types will give us a sine wave! Am I right with this concept?
 

The gate drive pattern doesn't look right. Do drive a reactive load, e.g. a LC filter, all 4 MOSFETs must be activated alternatingly during a sine half cycle. The intended output waveform in post #3 suggests an unipolar or "three level" modulation scheme, review literature about the required drive pattern.
 

Sir is there any difference if the input switching signal is SPWM or square wave, because the output waveform for both the cases are the same.

Connecting a LC filter at the output for both types will give us a sine wave! Am I right with this concept?

To some extent. To choose a plain 50 Hz square wave, then it does not need a buck converter arrangement but needs a different configuration at the output stage to create a sine shape.

Below is the SPWM driven buck converter (one half of a cycle). The LC filter is low-pass second order. Its values are chosen for a 100 ohm resistive load. They form a filter that smooths the jagged waveform to a sine shape.

Notice my carrier frequency is 1000 Hz (in order to make all the waveforms easy to view). By choosing a higher frequency for the carrier, then smaller LC values can be used.

SPWM opamp NPN top drives 10V buck converter (like half H-bridge).png
 
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