Symmetrical PWM

Purpose

Generate PWM signal using symmetrical triangular carrier

Library

Control / Modulators

Description

2-level PWM generator with a symmetrical triangular carrier. The input m is the modulation index, and the output s is the switching function. 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 Converter (3ph) or the Ideal Converter (3ph). In these cases the modulation index must have a width of \(3\) according to the number of inverter legs.

The block offers different sampling methods for the modulation index. The next three figures illustrate Natural Sampling with carrier starting at minimum, center or maximum.

Fig. 181 Natural Sampling - carrier starting at minimum or center

Fig. 182 Natural Sampling - carrier starting at maximum

The next two figures illustrate Regular Sampling with single update, where the modulation index is updated only at minimum or the maximum of the carrier.

Fig. 183 Regular Sampling with single update

In the last figure, Regular Sampling with double update is illustrated, i.e. the modulation index is updated at both tips of the triangular carrier.

Fig. 184 Regular Sampling with double update

Parameters

Sampling

Select a sampling method. If you select Natural Sampling, the carrier signal may begin at mininum, center, or maximum at simulation start. The Regular Sampling method lets you choose among single update at either min or max, and double update at both min and max.

Carrier frequency

The frequency \(f\) of the triangular 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 triangular carrier. The default is [-1 1].

Output values

Values of the switching function in off-state and on-state. The default is [-1 1].