180-DEGREE THREE PHASE INVERTER WITH SIMULATION

The inverters are used to convert DC power into AC power. There are several types of inverter available. Click on below link to know more about different types of inverter.

https://circuitdigest.com/tutorial/different-types-of-inverters

According to the mode of operation, three-phase inverters are classified into two types; 180-degree mode and 120-degree mode. Before going to classification, revise the circuit diagram of a three-phase inverter and it is as shown in below figure.

Circuit diagram of three-phase inverter:

As we can see in the circuit diagram, three phase star connected load is connected and output is measured at the load. One arm for each phase means we have a total of three arms. For switching purpose, we can use MOSFET or IGBT or any other power electronics switches according to the application.

When the upper switch of any phase is in conduction mode (ON), at that time positive half cycle of that phase appears in the output. When the lower switch of any phase is in conduction mode (ON), at that time negative half cycle of that phase appears in the output. In one arm two switches are available and these two switches never conduct at the same time. If this happens than DC source will short-circuit.

In the 180-degree mode of operation of the three-phase inverter, all switches conduct for 180-degree. In other words, MOSFET will ON for 180-degree and OFF for 180-degree of one cycle and the pulse width is 50% of the period.

Simulation in MATLAB/SIMULINK:

This is the simulation of three-phase inverter. The circuit diagram of 180-degree and 120-degree is same. The only difference is in the GATE pulse of switches. Here in this blog, we will discuss 180-degree inverter.

The gate pulse of 1 & 4, 3 & 6 and 5 & 2 are totally opposite in this mode of operation. When MOSFET-1 is ON at that same time MOSFET-4 is OFF.

Switching of MOSFET:

How to generate this gate pulse?

The screenshot of MATLAB for gate pulse generator is below image.

Gate pulse generator:

Vab = Va0 – Vb0

Vbc = Vb0 – Vc0

Vca = Vc0 – Va0

The peak value of phase voltage (Va0) is 2Vs/3 and the peak value of line voltage is Vs. where Vs is the DC supply voltage. The waveform of the 180 degrees is as shown in below figure. This is a book image. We will compare this image with simulation results at the end of this blog.

Waveform of 180-degree inverter:

How to set pulse width in the pulse generator. You have to create gate pulse only for MOSFET 1,3 and 5 and toggle it with the help of NOT gate and give it to MOSFET 6, 2 and 4. Now, the question is how to generate gate pulse for 1, 3 and 5. For that, we will use the PULSE GENERATOR. For 50Hz output signal, the time period is 20 msec and amplitude is 1 for all pulse generator. For 180-degree inverter mode, the pulse width is 50%.

Phase delay for one signal is 0 sec and this signal is for phase-A and MOSFET-1. It is clear in the above table that, there is 120-degree phase delay between these two signals. So, phase delay for phase B and MOSFET-3 is 120-degree or (2e-3)*2/3. Now for the third signal, the phase delay is 60-degree or (2e-3)*1/6 and this signal is for MOSFET-5.

By this way, we have three signals. For the other three signals we will use NOT gate and inverse this signals as shown in the above screenshot.                                      

Output waveform:

from above figure we can see that, for DC supply of Vs = 100V, the peak phase voltage Va0 is (2*100)/3=66.6V and the peak phase voltage Vab = 100V. This result is same as book waveform. If you need this simulation you can contact me or comment in this blog.

Thanks for reading.