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

[Power_Pro123]

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


Output of gate driver to gates when Vdc is 0V


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

 

[KlausST]

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

 

[Power_Pro123]

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

 

[KlausST]

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

 

[BradtheRad]

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.

 

[Power_Pro123]

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?

 

[FvM]

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.

 

[BradtheRad]

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.