IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS, VOL. 47, NO. 5, SEPTEMBER/OCTOBER 2011 2075 Integrated Differential-Mode and Common-Mode Filter to Mitigate the Effects of Long Motor Leads on AC Drives Rangarajan M. Tallam, Senior Member, IEEE, Gary L. Skibinski, Todd A. Shudarek, and Richard A. Lukaszewski, Senior Member, IEEE Abstract—Pulsewidth-modulated (PWM) ac drives generate high differential-mode (DM) motor voltages due to the reflected wave phenomenon. The common-mode (CM) voltage produced by a PWM inverter also has fast transitions that result in high peak currents to ground. For low-power ac drives, this can present several issues, such as pump-up of the dc bus and failure of the power module due to high instantaneous currents that are often undetected because of the typical sampling algorithm used. In this paper, existing drive output filter solutions are reviewed, and a new filter design is presented, which has integrated DM and CM im- pedance with damping matched to typical cable surge impedance. This eliminates reflections of both DM and CM traveling waves and also reduces peak cable charging currents. Experimental re- sults are provided to demonstrate that the new filter has improved performance to reduce motor DM and CM voltages and drive output CM current, thus mitigating the issues specifically seen with low-power ac drives. Complete design details for the filter and a particular implementation of the integrated DM and CM reactor are also presented. Index Terms—AC drives, common mode, differential mode, pulsewidth modulation (PWM), reflected wave. I. I NTRODUCTION I T IS WELL KNOWN that, with long motor leads, pulsewidth-modulated (PWM) ac drives generate high differential-mode (DM) voltages at the motor terminals [1]. In addition, the common-mode (CM) voltage produced by an ac drive has fast transitions, resulting in high peak cable charging currents. For low-power drives, this presents several issues: pump-up of the dc bus voltage [2] occurs particularly when the drive is lightly loaded; high repetitive peak cable charging currents can lead to overcurrent trips or power module failure. Hence, the maximum lead length permissible between drive and motor is severely limited by cable charging current. Several different drive filter topologies have been proposed in the literature to mitigate the effect of long motor leads [3]–[5]. Manuscript received October 4, 2010; revised November 30, 2010 and February 26, 2011; accepted April 5, 2011. Date of publication July 7, 2011; date of current version September 21, 2011. Paper 2010-IDC-385.R2, presented at the 2010 IEEE Energy Conversion Congress and Exposition, Atlanta, GA, September 12–16, and approved for publication in the IEEE TRANSACTIONS ON INDUSTRY APPLICATIONS by the Industrial Drives Committee of the IEEE Industry Applications Society. R. M. Tallam, G. L. Skibinski, and R. A. Lukaszewski are with Rockwell Automation, Mequon, WI 53092 USA (e-mail: rmtallam@ra.rockwell.com; glskibinski@ra.rockwell.com; ralukaszewski@ra.rockwell.com). T. A. Shudarek is with the MTE, Menomonee Falls, WI 53051 USA (e-mail: tashudarek@cramercoil.com). Digital Object Identifier 10.1109/TIA.2011.2161431 Most of these filters address only DM motor voltage ring-up. The reflected wave is damped by using a resistor matched to the DM cable surge impedance. Some filters include separate CM impedance [4] to reduce peak cable charging currents—a typical implementation is placing the three-phase leads through a set of CM cores—but little or no damping results in ring-up of the motor terminal CM voltage and undamped oscillations in the CM current. In this paper, a new drive output filter topology is proposed, which has integrated DM and CM impedance, with damp- ing resistance matched to typical cable surge impedance for both modes. This eliminates the reflections of DM and CM traveling waves and consequently reduces peak line–line and line–ground cable charging currents and peak motor DM and CM voltages. The damping of motor CM voltage also reduces the peak voltage across the motor bearings. Experimental results are provided to demonstrate that the new filter has improved performance to reduce motor DM and CM voltages and drive output CM current, thus mitigating the issues specifically seen with low-power ac drives. Analytical design equations for the filter inductance, resistance, and power loss are provided. In addition, design details for a particular implementation of the integrated DM and CM reactor that was used in the experimental tests are also presented. II. I SSUES FOR LOW-POWER AC DRIVES WITH LONG MOTOR LEADS In addition to the high DM motor voltages that occur due to the reflected wave effect, the CM voltage generated by ac drives presents several issues, particularly for low-power ac drives. A. Cable Charging Current Due to the fast rise time of the PWM voltage pulses, large spikes of current flow through the line–line and line–ground cable capacitances at every switching transition. This current is superimposed on the normal-mode motor currents. At low fundamental output frequencies, the dwell time on the active switching states is small; this results in nearly simultaneous switching on all three phases and step change in CM volt- age equal to the dc-bus voltage, resulting in high peak cable charging currents. If the peak current exceeds the instantaneous peak rating of the drive, an overcurrent trip occurs. While the overcurrent detection circuitry is implemented with analog 0093-9994/$26.00 © 2011 IEEE