March 22, 2010 - Loss of One Phase of a Three-Phase Rectifier

What happens if one phase of a three-phase rectifier is lost? Will the rectifier keep working in single-phase mode with sinusoidal phase current? Of course it depends on the converter topology and the control.

Researcher from the Power Electronic Systems Lab., ETH Zurich, worked on such a feature and the control some time ago, and implemented this in the three-phase AC/DC Vienna Rectifier (it's available as technology package).

You can test the behavior of a three-phase rectifier in case of phase loss online. Click the orange rectangle in the left side bar of this page. Java 1.6 has to be installed on your computer to make this work.

 
Fig. 1: 10kW Three-Phase AC/DC converter (Vienna Rectifier). 

As you can see, the system can handle the loss. Please note that the voltage- and current controllers have not been correctly designed - it's just a 'quick-and-dirty' approach to demonstrate phase-loss.

 
Fig. 2: Simulation of losing one phase: Converter switches into single-phase mode with increased input currents. Currents are still sinusoidal. After phase loss you see voltage oscillations with twice the mains frequency (power flow is not constant any longer).  

But how to handle the increased phase current? In the online simulation you can see clearly the increased current amplitudes. If the current is too high it might destroy the power switches.

The strategy implemented in the prototype is simple: If the system operates at lower power (66% rated power or lower) the current increase can be handled. Otherwise, the rectifier stops operation. Alternatively, one could over-dimension the rectifier to handle over-current in case of phase loss, but this might be a very bad idea if system cost is an issue. Basically, the strategy must be defined by user and/or application.