PWM 5 level multilevel inverter

PWM 5 level multilevel inverter

Level-Shifted PWM for 5-Level Multilevel Inverter

Level-Shifted Pulse Width Modulation (LSPWM) is one of the most popular modulation methods for multilevel inverters because of its simplicity and effectiveness. In this scheme, multiple triangular carrier signals are used, which are shifted vertically (level-shifted) to generate gate pulses for the switches.

For a 5-level inverter, the output has 5 distinct voltage levels:

+Vdc,  +Vdc/2,  0,  −Vdc/2,  −Vdc+V_{dc}, \; +V_{dc}/2, \; 0, \; -V_{dc}/2, \; -V_{dc}+Vdc​,+Vdc​/2,0,−Vdc​/2,−Vdc​Principle of Operation

• A sinusoidal reference signal (modulating signal) is compared with four triangular carrier signals that are vertically shifted.
• Depending on which carrier the reference lies above or below, the inverter produces one of the five voltage levels.
• This results in a stepped output waveform that approximates a sinusoid with reduced harmonic distortion.

Carrier Arrangement Schemes for 5-Level Inverter

There are different ways to arrange the carrier signals in LSPWM:

1. Phase Disposition (PD-LSPWM)

• All carriers are in-phase and equally shifted in the vertical axis.
• Simple and commonly used for diode-clamped (NPC) inverters.

1. Phase Opposition Disposition (POD-LSPWM)

• Carriers above zero are in-phase, and carriers below zero are 180° phase-shifted.

1. Alternative Phase Opposition Disposition (APOD-LSPWM)

• Carriers are alternately phase-shifted by 180°.

Each scheme affects the harmonic spectrum of the output differently.Advantages of LSPWM

• Simple implementation → Easy to generate using digital controllers.
• Good harmonic performance for lower-order harmonics.
• Better DC bus utilization compared to single-carrier PWM.
• Suitable for high-level inverters (5-level, 7-level, etc.).

Applications

• Medium and high-voltage motor drives.
• Renewable energy systems (solar, wind integration).
• HVDC and FACTS controllers.
• UPS and aerospace converters.