DC-link capacitor sizing in HEV/EV e-Drive Power Electronics System from Stability viewpoint 2020-01-0468
Selection of DC-link capacitance value in a HEV/EV e-Drive power electronics system depends on numerous factors including the capacitor’s required voltage/current ratings, power dissipation, thermal limitation, energy storage capacity, impact on system stability and so on. A significant challenge arises from capacitor selection based on DC-link stability due to the influence of multiple hardware parameters, control parameters, operating conditions and interaction effects among them. This paper introduces a methodology to determine the minimum required DC-link capacitance values that guarantee stable operation of the system in this multi-dimensional variable space. A broad landscape of the minimum capacitance values is also presented to provide valuable insights into the sensitivity of both hardware parameters and control parameters, on the overall system stability and understanding trade-offs and limits of these parameters. The target system example considered is a HEV e-Drive power electronics system consisting of one PWM DC/DC converter and two, three-phase PWM inverters, each inverter feeding an electrical machine. All the converters share the common dc-link at which the system stability is analyzed. Since the PWM converters are nonlinear, operating point dependent, small-signal models are used to analyze system stability. A set of assumptions is made to simplify the modeling and analysis procedure under different modes of converter and inverter operations. Discussion is included on how the insights obtained from the landscape are used for further model improvements/simplifications, in addition to identification and subsequent mitigation of critical operating regions within the torque-speed capability of respective machines. Representative results from experimental studies conducted on a HEV e-Drive power electronics system are also provided for validation purposes.