Pure sine wave Inverter using pic microcontroller, power inverter, solar inverter and grid tie inverter are manufacture now a days in two ways:
- Switch mode power supply method
- Common method or old method
Diagrams below shows the difference between both methods.
Old/ common method using step up transformer:
In above diagrams both methods are used in inverters. But SMPS method is used in latest pure sine wave inverter. Because Switch mode power supplies are more efficient than old method. SMPS method have high efficiency, low harmonics distortion and low stand by losses. I will also discuss SMPS method in these tutorials on Pure sine wave inverter.
In first diagram two square wave outputs are used to drive MOSFETS of push pull converter. If you are generating square waves with microcontroller.Then you have to use mosfet driver like IR2210 to drive push pull converter mofets. You can also use pwm controller IC’s to generate two square wave. The advantage of using PWM controller IC’s is that you don’t have to used MOSFET driver. SG3525 PWM controller IC have built in mosfet driver using totem pole and another advantage is that one can easily implement feedback through these IC’s. I will explain SG3525 use in next tutorial.
Selection of mosfets depend on power rating of your inverter design. Commonly IRF3205 is used in most of inveters. Push pull topology is used due to its high power handling capability and we want to step up DC voltage from 12/24 volt to 311 volt ( peak of sine wave voltage). Chopper or high frequency transformer is used step up Dc voltage. Rectifier is used to rectify voltage into pure DC after chopper. Selection of diodes for rectifier circuit also depend on power rating of power inverter.One should check maximum forward current and voltage capability of diodes. It is better to use LC filter after rectifier circuit. But if you use capacitor of 400V , it will also work fine.
After rectification 311 volt output from Dc/dc to converter is fed to H bridge. H bridge is used to generate positive and negative cycle of AC voltage. H bridge switches selection also depend on power rating of power inverter. I have used IRF840 in my final year project “hybrid pure sine wave inveter”. IRF840 work fine by using proper heat sinks with them. SPWM (sinusoidal pulse width modulation) technique is used to generate pure sine wave ouput from inverter. PIC16F877A microcontroller is used to generate SPWM . These SPWM waves are fed to MOSFETS of H bridge. H bridge Mosfets are operated in such a way that a pulsating output is obtained from H bridge output. The generated SPWM is shown in figure below:
Output of H bridge is fed to LC filter to remove harmonics from output. Neat and clean sine wave output can be obtained by using proper LC filter. I have just try to give you brief overview of pure sine wave inverter or SMPS method pure sine wave inverter. Before making pure sine wave inverter one should keep these things in mind:
- Power electronics circuits are very complicated.
- You may have to make your circuits again and again to find issues.
- Components selection is very critical like MOSFETS, MOSFET drivers and LC Filter values selection
I have written complete articles on each block of SMPS base pure sine wave inverter. Click on following articles to learn about their use and ways to diagnose problems in thses circuits.
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