Active Methods for Addressing the Instability Problem between Constant Power Loads and their LC Input Filters in DC Power Systems

Abstract

Constant power loads (CPLs) have negative impedance characteristic. This characteristic can degrade the stability margin of the whole system when the CPL operates with other circuits, typically, an LC input filter. The stability of the CPL and the LC input filter can be determined by the impedance stability criterion. Many active methods have been proposed to stabilize the interaction between LC input filters and CPLs. Compared with the mature study of active methods for stabilization of inverter based CPLs and LC input filters, there are few active methods proposed for stabilization of DC/DC converter based CPLs and LC input filters. Due to the difference between inverter based CPLs and DC/DC converter based CPLs in power stage dynamics and feedback controllers, applying the active methods for inverter based CPLs directly to DC/DC converter based CPLs may not achieve an optimal performance or may not even work. To address this problem, in the thesis, an optimal active method is proposed for DC/DC converters under voltage mode control. The proposed methods can increase a larger stability margin and simultaneously have smaller audio susceptibility than the existing methods. The thesis also proposed another active method for DC/DC converters under current mode control. The proposed method results in a larger stability margin than the existing method. This thesis also contributes to the stabilization of LC input filters and CPLs from source side converters. The main advantage of this method is that it eliminates the drawback of the active stabilization method via adding a feedforward loop which enlarges the system audio susceptibility. The limitation of this method is that the upstream converter requires a wide bandwidth output voltage regulation.