SimPowerSystems

RMS

Measure the root mean square (RMS) value of a signal

Library

Extras/Measurements

Description

This block measures the root mean square value of an instantaneous current or voltage signal connected to the input of the block. The RMS value of the input signal is calculated over a running window of one cycle of the specified fundamental frequency.

Dialog Box and Parameters

Fundamental frequency (Hz)

The fundamental frequency, in hertz, of the input signal.

Example

In the psbcontrolvolt demo, the rms value of the voltage of the C capacitor is measured with a Voltage Measurement block and a RMS block. The Controlled Voltage Source block introduces a third harmonic (180 Hz) in the voltage at t = 0.4 seconds.

At the beginning of the simulation, the RMS block needs one cycle of the fundamental frequency (60Hz) to calculate the rms value of the voltage. At t = 0.4 seconds the rms value slightly increases because of the addition of the third harmonic in the signal. Again, the RMS block needs one cycle of the fundamental signal to stabilize and give the correct result.

PWM Generator

Saturable Transformer