Overmodulation

(To be removed) Add third harmonic or triplen harmonic zero-sequence signal to three-phase signal

The Specialized Power Systems library will be removed in R2026a. Use the Simscape™ Electrical™ blocks and functions instead. For more information on updating your models, see Upgrade Specialized Power System Models to use Simscape Electrical Blocks.

Library

Simscape / Electrical / Specialized Power Systems / Power Electronics / Power Electronics Control

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Description

The Overmodulation block increases the linear region of a three-phase PWM generator by adding a third harmonic or triplen harmonic zero-sequence signal V₀ to the three-phase original reference signal U_ref. This zero-sequence signal does not appear in the line-to-line voltages.

A modulation index of up to 1.1547 (exact value = 2/sqrt(3)) can be used without pulse dropping.

The Overmodulation block implements three overmodulation techniques:

• The Third Harmonic overmodulation technique. In this technique the third-harmonic signal V0 subtracted from the original signal is calculated as

  $$V_0=\frac{\left|U\right|}{6}\times \sin \left[3\cdot (wt+\angle U)\right]$$

• The Flat Top overmodulation technique. In this technique the portion of the three-phase input signal exceeding values +/−1 is computed. The three resulting signals are then summed and removed from the original signal U_ref. The resulting modified signal U_ref* is therefore a flat-top three-phase signal that contains zero-sequence triplen-harmonics. The block outputs a value between −1 and 1.

• The Min-Max overmodulation technique. In this technique the minimum and maximum values of the three components of input signal U_ref are summed and divided by two, and then subtracted from the input signal. The resulting modified signal U_ref* also contains zero-sequence triplen-harmonics. The block outputs a value between −1 and 1.

Parameters

Overmodulation type

Select the overmodulation technique you want to apply to the Uref signal: Third harmonic (default), Flat top, or Min-Max.

Inputs and Outputs

Uref

The three-phase reference signal of three-phase PWM generator.

Uref*

The overmodulated three-phase signal of three-phase PWM generator.

Characteristics

Sample Time	Inherited
Scalar Expansion	No
Dimensionalized	Yes

Version History

Introduced in R2013a