Power Electronics System Modelling

The use of modelling in the design of power electronics systems, both at a system and circuit level has become common place in the last thirty years. As computer processing power has become more inexpensive and the efforts of applied mathematics have produced ever more quickly converging, stable, non-linear solvers it has become easier to work with ever larger systems of coupled equations. Modelling across traditional domain boundaries and on large and small timescales within a single simulation setup is now a routine part of modern engineering design practice.

In this video I demonstrate a ‘first order’ work-up of a single phase to three phase power electronic converter in Matlab/Simulink.

The single phase side is connected to an idealised UK line source which is set in the ‘bar’ of an H bridge. The bridge is driven by sine wave pulse width modulation (SPWM) forming an active rectifier. A dual loop PI controller is used to realize unity power factor on the single phase side under steady state operating conditions in order to provide active power factor correction on the single phase line side.

On the three phase side, a six switch inverter is also driven by SPWM (although SVPWM would be a more common choice) with a fundamental frequency of 50 Hz. The three phase inverter drives a custom induction machine model which is the subject of another video linked in the end-card of the video above.

The DC bus is simply a capacitor without any parasitics.

The principle limitations of this model are related to second order effects such as: the lack of saturation in the induction machine, the lack of any gate drive hardware (because the MOSFET model doesn't require any), the lack of thermal effects, the ‘perfectness’ of the voltage source on the single phase side which is not realistic and most importantly the lack of current limiting during the start-up transient of the active rectifier. This simulation does not proffer an optimised design. Consideration has not been given to cost, volume or weight since these are physical engineering problems and this is a semi-idealised simulation.

With some tweaking and a few well chosen additions this model could be perfected to accurately model steady state and dynamic effects of a physical realization of this converter and machine system while maintaining a reasonable simulation time on a modern desktop PC.

Converters similar in design to this one are commonly sold as consumer electronics items for light industrial use where three phase is unavailable and its installation is prohibitively costly or in situations where the machine being driven must be mobile and the availability of a three phase supply is not guaranteed.

The overall schema could be easily re-designed to develop three phase to three phase, single phase to single phase or three phase to dual three phase, arrangements with frequency shifting properties. This may be desirable for example when testing aerospace or marine components running at 400 Hz or in 50 – 60 Hz conversion or simply to run a specialised electrical machine.

I am available for engineering design consultancy in all aspects of power electronics systems design, machine design, analogue and instrumentation system design, embedded & control systems engineering and other related fields. I may be contacted via LinkedIn, by email or through YouTube.