Simulation of 3 phase inverter operating in 120 degree mode in MATLAB | SIMULINK | With Design

Summary

In this video, the creator explains how a three-phase inverter operates in 120-degree mode, highlighting key differences from 180-degree mode, such as the number of conducting switches at any time. The video walks through the design process, calculations for phase and line voltages, and provides a detailed MATLAB simulation tutorial. The simulation setup involves using MOSFETs, pulse generators, and measuring line and phase voltages. Viewers will also learn about common mistakes in simulation setups and how to measure RMS values effectively, along with an overview of the resulting waveforms and troubleshooting tips.

Takeaways

• 😀 The video covers the operation of a three-phase inverter in 120-degree mode, comparing it with 180-degree mode.
• 😀 In 120-degree mode, two switches conduct at a time, unlike 180-degree mode where three switches conduct.
• 😀 The phase voltage in 120-degree mode is a quasi-square wave, while the line voltage exhibits a stepped waveform.
• 😀 Each switch conducts for 120 degrees before turning off in 120-degree mode, ensuring equal switching intervals.
• 😀 The RMS value of line voltage in the design is 16.968 volts, while the phase voltage is 9.79 volts, calculated using a 24V DC supply.
• 😀 MATLAB Simulink is used for the simulation, where triggering angles must be converted from degrees to seconds for accurate timing.
• 😀 A detailed process is given for setting up the Simulink model, including adding blocks like MOSFET switches, pulse generators, and voltage measurement tools.
• 😀 The pulse generator block is configured with a pulse width of 33.33% to ensure each switch conducts for 120 degrees.
• 😀 The video emphasizes the importance of correctly configuring the pulse delay values for each MOSFET switch to achieve the desired waveform.
• 😀 After running the simulation, the expected values for line and phase voltages are achieved, and the output waveforms are analyzed for correctness.
• 😀 Common simulation issues, like small spikes during switch transitions, are explained and considered normal in the context of the simulation.

Q & A

What is the key difference between a three-phase inverter operating in 120-degree mode and 180-degree mode?

In the 120-degree mode, only two switches conduct at a time, whereas in the 180-degree mode, three switches are conducting simultaneously. This results in different switching patterns and waveforms for each mode.

Why is the mode called '120-degree' mode?

It is called 120-degree mode because each switch conducts for exactly 120 degrees before turning off, ensuring a 120-degree separation between the switching cycles of each MOSFET.

How is the phase voltage in a three-phase inverter related to the line voltage?

The phase voltage is obtained by dividing the line voltage by the square root of 3. In this example, the line voltage is 16.97V, so the phase voltage is calculated as approximately 9.79V.

What is the significance of the firing angle in the simulation of the inverter?

The firing angle determines when each MOSFET switch is triggered during the cycle. In MATLAB, these angles are entered in seconds instead of degrees, with a conversion factor based on the system's frequency.

How do you convert firing angles from degrees to seconds in MATLAB?

In MATLAB, firing angles are entered in seconds. For a 50Hz system, 360 degrees corresponds to 0.02 seconds, meaning each degree corresponds to 5.55 x 10^-5 seconds. This is used to convert the degree-based firing angles to time delays in the simulation.

What blocks are needed for the simulation in MATLAB/Simulink?

The key components required include a power block, DC voltage source, MOSFET switches, pulse generator, series RLC load, RMS measurement block, and display blocks for monitoring the output.

Why are MOSFET switches used instead of thyristors in the simulation?

MOSFETs are used instead of thyristors because they do not require a commutation circuit to turn off. This simplifies the simulation process, as MOSFETs can be turned off directly by the control signal.

How is the pulse width for each switch determined in the simulation?

The pulse width is set to 33.33% because each MOSFET switch must conduct for 120 degrees out of the 360-degree cycle. This is calculated by dividing 360 by 3, which gives 120 degrees, corresponding to 33.33% of the full cycle duration.

What is the cause of the sharp spikes seen in the waveform output during the simulation?

The sharp spikes occur due to the transitions between the switching states. When one MOSFET turns off and the next one turns on, the transition is not instantaneous, causing brief spikes in the waveform.

What steps should be taken if the RMS measurement block shows incorrect results?

Ensure that the correct RMS measurement block is selected and connected properly. Be careful not to use the wrong block from the library, and double-check the voltage and frequency settings to match the design parameters.