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

Amr Zalhaf,Mazen Abdel-Salam,Mahmoud Ahmed

doi:10.3390/en12040691

Amr Zalhaf, Mazen Abdel-Salam + Show 1 more

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https://doi.org/10.3390/en12040691

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Abstract

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.

Highlights

With the increase of carrier frequency in pulse-width modulated (PWM) converters driving an AC motor, leakage currents with a frequency in the range from 100 kHz to several megahertz flow to earth via stray capacitors inside the motor
In the following subsections we will discuss the effect of the integration of the active common-mode voltage canceler (ACMVC) on the common-mode voltage, the common-mode current and the shaft voltage
Simulation produced by aby three-phase converter connected to the rotor winding of aofDFIG

Summary

Introduction

With the increase of carrier frequency in pulse-width modulated (PWM) converters driving an AC motor, leakage currents with a frequency in the range from 100 kHz to several megahertz flow to earth via stray capacitors inside the motor. These currents build up the so-called common-mode voltage (CMV) between the rotor neutral point and the ground. These currents may influence adversely motor control circuits and result in incorrect operation of zero-sequence relays. A common-mode choke connected in series between the terminals of the converter and motor terminals has been used to reduce the unwanted leakage current [3,4]

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