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Symmetrical PWM

Purpose

PWM generator with symmetrical triangular carrier.

Library

Control / Modulators

Description

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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 2-Level IGBT Converter or the ideal 2-Level Converter. 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 figure below illustrates Natural Sampling.

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The following figures illustrate the different Regular Sampling methods. In the figure on the left, double edge sampling is used, i.e. the modulation index is updated at both tips of the triangular carrier. In the right figure, single edge sampling is employed. Here, the modulation index is updated only at the upper tips of the carrier.

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Parameters

Sampling
Select a sampling method. If you select Natural Sampling the carrier signal may begin with 0 or 1 at simulation start. The Regular Sampling method lets you choose between double edge or single edge sampling.
Carrier frequency
The frequency f   of the triangular carrier signal, in Hz.
Carrier offset
The time offset of the carrier signal, in p.u. of the carrier period.
Input limits
The range of the modulation index. The default is [-1 1].
Output values
Values of the switching function in off-state and on-state. The default is [-1 1].