VOLTAGE SOURCE INVERTER (VSI) USING PWM SIGNAL GENERATED BY MICROCONTROLLER FOR THREE-PHASE INDUCTION MOTOR CONTROL

VSI in this project is using rectification and Inverter to convert dc-to-ac voltage. 3 phase gate IGBT is controlled by 3 phase HPWM techniques generated by Microcontroller. The speed of motor can be adjusted by pressing button at microcontroller part. By using PWM technique, the current used is efficiently reduced which means less power is consumed to run the motor compared to the system without PWM.

Methodology

Firstly, the circuit diagram is drawn using ISIS Proteus software as shown in figure above which include microcontroller PIC18F4431, speed control button, LCD display and optocouplers.

For the coding part, Picbasic Pro compiler is used to generate three-phase PWM signal. This compiler is assisted by MicroCode Studio for the compiling of the coding.   

After the coding is compiled, transfer it into microcontroller in ISIS Proteus software to generate the PWM signal. The signal is observed using digital oscilloscope inside the software. The finalized coding is then transferred into real microcontroller using PicKit2 software.

Hardware

The real project circuit is divided into four part, microcontroller, LCD, optocouplers and gate driver connected as shown in figures.

Microcontroller of PIC18F4431 is used to generate three-phase PWM signal. The PIC18F4431 is mounted on the SK40C and supply with 5V. The upper part jumper is connected to the optocoupler circuit whereas the lower part jumper connects to the LCD screen.

IR2130 is used as the gate driver to turn IGBT on and off and supplied by 15V. The input of driver from pin 2 until pin 7 is connected to the output of the optocoupler and the output of driver is then connected to the input of IGBT circuit.

Three set of IGBT are used as inverter that converts DC voltages into AC voltages. The input comes from gate driver circuit and the three-phase output is connected to the motor.  

Result

Figure at below shows the high side PWM output from the gate driver. A maximum voltage of about 25V and minimum voltage of 14V is recorded. The mean voltage of 11V is provided for three-phase high PWM signal.

High side PWM output (gate driver)

High and low side PWM ( gate driver)

The output of PWM signal which the upper signal (yellow) is the high signal and lower signal (blue) is the low signal. The deadtime is created when the signal pass through the gate driver circuit. the deadtime is 22 -60 ns.

Single phase IGBT output voltage signal 

When the three-phase output of the IGBT is connected to the motor input, it successfully turns on the motor and the speed can be adjusted by pressing the increase or decrease button at microcontroller input part. Some voltages and current are measured during the motor is running.

	PWM	Without PWM
Current	0.048	0.255

The table shows that by using PWM technique, the current used can be efficiently reduced which directly means less power is consumed. Whereas the system without PWM, more current is required to run the motor which means it is less efficient since more power is used. Hence, PWM technique is preferred compare to system without PWM.