An Active Common-Mode Voltage Canceler for PWM Converters in Wind-Turbine Doubly-Fed Induction Generators

Wind energy integration in power grids is increasing day by day to reduce the use of fossil fuels, and consequently greenhouse gas emissions. Using the pulse-width modulated (PWM) power converters in wind turbine generators, specifically in doubly-fed induction generators, results in generating a common-mode voltage (CMV). This common-mode voltage causes a flow of common-mode current (CMC) that leaks through the stray capacitances in the generator structure. These currents impose a voltage on the generator bearing which may deteriorate them. In the current work, an active common-mode voltage canceler (ACMVC) is developed to eliminate the CMV produced by a PWM converter. The ACMVC generates a compensating voltage at the converter terminals to eliminate the CMV with a subsequent reduction of the voltage stress on the generator bearing. This compensating voltage has the same amplitude as CMV, but opposite polarity. A simulation of the ACMVC model is performed using the PSCAD/EMTDC (Electromagnetic Transient Design and Control) software package. Results confirm the effectiveness of ACMVC in canceling not only the CMV but the CMC and bearing voltage as well. In addition, the relationship between the rise time of CMV and the peak value of CMC is investigated.