Multilevel inverter (5 level) based variable frequency drive

Concept:

Important parts :

            1. Induction motor (0.5hp, 230V, 1.5A)

            2. Mosfets / IGBTs based on the machine voltage and current ratings.
            3. No. of  DC power supplies (depends on no. of levels).
                               Two power supplies - two mosfet bridges for 3 level
                               Four power supplies - four mosfet bridges for 5 level

            4. Each power supply consists of a rectifier bridge, filter capacitor and a fuse.
            5. Each power supply will be conncetd to the MOSFET bridge.
            6. The MOSFET bridges should be coonected to the power supplies.(The following Figure is for 9 level)

            7. 89s52 microcontroller is programmed in my project according to the switching logic of
                Cascaded inverter.

            8. The signals from MC will be given to the mosfet bridges through the optocoupler unit.
            9. Optocoupler unit requires seperate power supplies. A multiwinding transformer is used in
                my project to excite the optocoupler transistor.

We have re-wound the transformer as per our requirements. We just disassembled a transformer and calculated the number of turns required and then fixed it back.

We have done an experiment to see the stress experienced by the switches for the 0.5hp induction motor. We build a capacitor based potential divider to design diode clamped inverter. The diode clamped inverter is my next project and probably it will be a three phase drive.

This multilevel inverter is tested with a resistive load. Two transformers are used as the main power supplies. each 12V. The filtered output gave 18V for each bridge. The three levels are 0v 18v 36v.