Pulse width modulation applied to voltage converters of power electronics

Static converters are power electronics devices which, through appropriate control, enable the flow of electrical energy between a generator and a receiver to be controlled. The flow of energy is made possible by the controlled closing and opening of the semiconductor switches that make up the conversion structure. The conversion function and the control of energy exchanges are achieved by adjusting the sequence of control commands for each switch. Pulse width modulation (PWM) is a technique for generating switch opening and closing commands. This control principle, implemented in the control architectures of power electronics devices, makes it possible to obtain controlled variations in voltage and current across the load. The state of the art is rich in examples of modulation schemes, which can be applied to all conversion structures.

This article explains the principle of pulse-width modulation and its application to common voltage conversion devices. Starting from a desired average voltage value at the load terminals, the modulation strategy generates the sequence of control commands to be applied to the switches, in order to achieve switched voltages whose average values over a switching period are equal to the references. The subject concerns switches whose control is based on a hard-switching mode, and therefore generates losses on each switch. The article discusses the generic principle for generating control commands from a power architecture typical of electrical energy conversion devices. Examples of application of the generic modulation scheme to common conversion architectures (series chopper, reversible chopper, single-phase and three-phase inverter) are then illustrated. A review of frequency tools for analyzing the switched signals produced is given. Finally, the article discusses the various indicators that can help in choosing a modulation strategy when several possibilities exist.

Readers will find a table of notations and acronyms at the end of the article.