Performance analysis of active damped small DC-link capacitor based drive for unbalanced input voltage supply

A small DC-link capacitor based drive is presented in this paper. The drive shows negative impedance instability at operating points with high power load. A phase portrait is presented for input filter states which exhibit a limit cycle. When the drive is operated with unbalanced input supply voltages, the rectified voltage contains all even harmonics frequencies. However, it is shown that the dominant harmonic component of the DC-link voltage is decided by the limit cycle instead of the input filter resonance frequency. An active damping technique is used to stabilize the operating point. The responses of the DC-link voltage with and without active damping are presented. The low order harmonics components are reduced with the increase in the gain of the active damping term. The experimental results for the DC-link voltage, input phase currents, and machine phase current are presented.