This example shows the operation of a 2-MVA, 3-Level NPC inverter using Space-Vector Pulse-Width-Modulation (SVPWM) technique with neutral-point voltage control.
From an ideal 2400-Volt DC source, a 2-MVA, three-phase 3-level inverter delivers power to a 25-kV distribution system. A sine filter is used on the secondary side of the distribution transformer in order mitigate high-frequency harmonics generated by the inverter. The Sw1 ideal switch is used to create a major unbalance on the DC link.
The inverter is controlled in open-loop using an SVPWM 3-Level Generator block. The PWM switching frequency is set to 1620 Hz and the neutral-point voltage control gain is set to 0.04.
Run the simulation and observe waveforms on the VIdc Scope. We will notice that the neutral-point voltage control perform correctly when a large unbalance is created at 0.2 sec. Now double-click on the SVPWM generator block and set the proportional gain of the neutral-point voltage control to zero. Re-run the simulation and note that without neutral-point voltage control, the DC link unbalance increases rapidly.