DC-Link Capacitor Sizing in HEV/EV e-Drive Power Electronic System from Stability Viewpoint

Selection of the DC-link capacitance value in an HEV/EV e-Drive power electronic system depends on numerous factors including required voltage/current ratings of the capacitor, power dissipation, thermal limitation, energy storage capacity and impact on system stability. A challenge arises from the capacitance value selection based on DC-link stability due to the influence of multiple hardware parameters, control parameters, operating conditions and cross-coupling effects among them. This paper discusses an impedance-based methodology to determine the minimum required DC-link capacitance value that can enable stable operation of the system in this multi-dimensional variable space. A broad landscape of the minimum capacitance values is also presented to provide insights on the sensitivity of system stability to operating conditions. The target example considered is an HEV e-Drive power electronic system consisting of one bidirectional dc/dc converter and two three-phase electric machine drive inverters, sharing a common dc-link. Since PWM power converters are nonlinear, the system stability is analyzed using operating point dependent, small-signal models. A set of assumptions is made to simplify the modeling and analysis procedure. Representative results from ongoing hardware experimental studies are also provided to show a reasonable correlation between results obtained from the model and the hardware experimental observations.