Control of a Doubly-fed Induction Generator with an Indirect Matrix Converter with changing DC voltage

In this paper a control strategy for a Doubly-Fed Induction Generator (DFIG) using an Indirect Matrix Converter (IMC), which consists of an input side matrix converter and an output side voltage source converter (VSI), is presented. The capability of the input converter to generate different virtual DC link voltage levels is exploited and commutation of the VSI using these reduced voltages is shown for operating points where the required output voltage is low in magnitude, without deteriorating the performance of machine current control. This method leads to a reduction in the commutation losses in the output converter and reduced common mode voltage. For the input converter soft switching commutation is obtained synchronizing the input and output PWM patterns. This strategy is applicable in DFIG applications because the required rotor voltage decreases as the DFIG speed gets closer to synchronous speed. The strategy is experimentally validated in a 2kW rig.