Variable Phase PWM

Purpose

Generate PWM signals with variable phase shift

Library

Control / Modulators

Description

The Variable Phase PWM block can generate phase-shifted PWM signals.

The block offers different regular sampling methods for the modulation index if the parameter Carrier type is set to Symmetrical (carrier counts up/down). If double edge sampling is used, the modulation index is updated at the minimum and maximum of the carrier. The regular sampling methods are visualized in the Symmetrical PWM block. For a Sawtooth (carrier counts up) Carrier type, the modulation index is updated when the carrier reaches the minimum.

The \(ph\) input is only sampled when the carrier of the internal master channel reaches the minimum, regardless of the Carrier type. The figure below illustrates the sampling of the \(ph\) input. The sampling instant is indicated by a solid black dot. The phase shift of the channels are always relative to the internal master channel.

../../_images/var_phase_pwm_sawtooth.svg — Fig. 188 Variable phase PWM with sawtooth carrier

../../_images/var_phase_pwm_symmetrical.svg — Fig. 189 Variable phase PWM with symmetrical carrier

Inputs and Outputs

The input \(m\) is the modulation index, \(ph\) the phase shift in per unit \((\mathrm{p.u.})\), and the output \(s\) is the switching function. If the modulation index is a vector, the switching function and the \(ph\) input are also a vector of the same width. The output \(s\) of a channel goes to the on-state if the modulation index \(m\) of the respective channel is greater than the carrier.

m: A scalar or vector representing the modulation index. If the modulation is a scalar signal and the \(ph\) input a vector, the output is a vector of the same width as the \(ph\) input. In this case, all output channels will have an identical modulation index.
ph: A vector representing the phase shift of each output in respect to the internal master channel, in per unit \((\mathrm{p.u.})\).

Parameters

Carrier type: Specifies the carrier type. Sawtooth (carrier counts up) and Symmetrical (carrier counts up/down) counter modes are supported.
Modulation index sampling: The Regular Sampling method of the modulation index lets you choose among single update at either min or max, and double update at both min and max of the carrier. This parameter is made visible if the Carrier type parameter is set to Symmetrical (carrier counts up/down).
Carrier frequency: The frequency of the carrier signal, in hertz \((\mathrm{Hz})\).
Carrier limits [min max]: The range of the carrier. The default is [-1 1].
Output values [off on]: Values of the switching function in off-state and on-state. The default is [-1 1].

Probe Signals

Master max event: Outputs a rising edge if the internal master carrier reaches the maximum value.
Master min event (phase sampling point): Outputs a rising edge if the internal master carrier reaches the minimum value. This instant also describes the point in time when a new phase value of each channel is sampled.
Master carrier: Outputs the carrier signal for each channel.
Max event: Outputs a rising edge if the carrier reaches the maximum value.
Min event: Outputs a rising edge if the carrier reaches the minimum value.
Carrier: Outputs the carrier signal for each channel.