Design and implementation of an inverter output LC filter used for dv/dt reduction

This paper presents the design and analysis of a LC output filter for use with IGBT-based motor drive inverters. The LC filter is used to limit the rate of rise of the inverter output voltage and reduce common mode noise to the motor. In typical applications where dv/dt is limited to 100-500 V//spl mu/s, the resonant frequency of the filter is above the switching frequency. A diode bridge must therefore be used to clamp the resonant voltage. Resistors are also used to help dissipate the energy stored in the resonant circuit. Crucial to the design of the filter is the handling of the additional losses in the filter. The paper describes the design considerations for such a filter for use in a 460 V induction motor drive. The losses in the circuit are estimated to show the limitations of the filter. Experimental results illustrate the control of dv/dt at the inverter terminals, and the reduced peak voltage at the motor end of a long cable.