An evaluation of the DC-link capacitor heating in adjustable speed drive systems with different utility interface options

In this paper, an evaluation of DC-link capacitor heating in adjustable speed drive systems with different utility interface options is presented. The evaluation is based on the level of ripple currents DC-link capacitors can endure that lead to self-heating and reduction of capacitors´ operating life. Three popular utility interface options for ASD systems are considered for evaluation. First, a standard six-pulse diode rectifier with and without DC-link inductor is examined. Second, an active PWM rectifier, which draws nearly sinusoidal current from the utility, is studied. Third, an auto-connected 12-pulse rectifier system for utility interface is analyzed. A new term capacitor heating factor (CHF) based on the dependence of ESR on frequency is introduced and is computed for various utility interface options and the results are compared. A mathematical procedure is outlined to analytically compute the capacitor ripple current and hence heating. Simulation and experimental results are presented to verify analytical calculation. Finally, a relative comparison of capacitor heating as a function of utility interface options is presented