Question

A three-phase 5-level Modular Multilevel Converter based on the half-bridge Submodules (SMS) is connected to a constant DC source of 2000 V on its DC side and a three-phase RL load at its AC side. Develop a simulation program for Sine-Triangle PWM strategy to control the converter. Set the modulation index to 0.95. Make sure that the SM capacitor voltage balancing task with the Sine-Triangle PWM. Make sure that you apply initial charge to your SM capacitor voltages. Run your simulation program and carry out the following tasks:

Adjust the load RL values such that the load current is 100 A at power factor of 0.9 and output frequency of 50 Hz. Draw the line-line voltage Vab and circulating current (only for three ac-side cycles) as well as the harmonic spectrum of the circulating current and comment on the results. The load is Y connected.

Answer 1

The student's task involves developing a simulation program to control a three-phase 5-level MMC using a Sine-Triangle PWM strategy, ensuring proper voltage balancing and achieving specific load characteristics.

Step-by-step explanation:

The student is asked to develop a simulation program for a Sine-Triangle Pulse Width Modulation (PWM) strategy to control a three-phase 5-level Modular Multilevel Converter (MMC) with half-bridge Submodules (SMs). This converter is connected to a 2000V DC source and a three-phase RL load. The simulation must include a detail such as the SM capacitor voltage balancing task and applying an initial charge to the SM capacitor voltages. With a modulation index set to 0.95, the program should simulate the converter's performance, including the adjustment of load RL values to achieve a load current of 100 A, at a power factor of 0.9 and an output frequency of 50 Hz. The simulation should also produce graphs for the line-line voltage Vab, the circulating current, and the harmonic spectrum of the circulating current, providing insights about the results observed.