Constant power loads in More Electric Vehicles - an overview

Power electronic converters are playing an ever increasingly important role in today´s electric vehicles. These regulated power electronic converters act as Constant Power Loads (CPLs) to the converters driving them. A CPL has a negative input impedance which results in a destabilising effect on closed-loop converters driving them. The use of power electronics in More Electric Vehicles (MEVs) is discussed, along with the CPLs they present and how they are modeled. Negative impedance instability is then discussed and the stability of various DC-DC converter topologies when loaded by CPLs is analyzed in both voltage-mode and current-mode control operating in Continuous Conduction Mode (CCM) and Discontinuous Conduction Mode (DCM). Finally, the currently proposed control strategies that can stabilize a power electronic converter are discussed.