Sawtooth PWM (3-Level)

Purpose

Generate 3-level PWM signal using sawtooth carriers

Library

Control / Modulators

Description

3-level PWM generator with a sawtooth carrier. The input m is the modulation index. The switching function s outputs either \(1\), \(0\) or \(-1\). If the modulation index is a vector, the switching function is also a vector of the same width.

The block can be used to control the IGBT 3-Level Converter (3ph) or the Ideal Converter (3ph). In these cases the modulation index must have a width of \(3\) to match the number of inverter legs.

Fig. 173 illustrate different sampling methods offered by the modulator block. In the left figure, Natural Sampling is used. The right figure shows Regular Sampling, i.e. the modulation index is updated at the vertical flanks of the carrier. In both figures carrier signals with rising ramps are employed.

../../_images/pwm3levelsaw.svg — Fig. 173 3-level sawtooth PWM waveforms

Parameters

Sampling: Choose between Natural and Regular Sampling.
Ramp: Choose between rising and falling ramps in the carrier signal.
Carrier frequency: The frequency \(f\) of the carrier signal, in hertz \((\mathrm{Hz})\).
Carrier phase shift: The time offset of the carrier signal, in per unit \((\mathrm{p.u.})\) of the carrier period.
Carrier limits: The range of the sawtooth carriers. The default is [-1 1].