Research On Interaction Issues Of Nonlinear Subsystems In Distributed Power System

Distributed power systems (DPS) are widely utilized in existing industrial applications. The resulting complex nonlinear dynamics of power electronic circuits can cause system interactions,leading to instability,power quality and other system problems. Interaction theory and technology has been an important research subject to ensure DPS successful integration and operation. The dissertation mainly focus on three key issues related, including input/output impedance standardization of dc/dc converters,two-port network features with their applications of dc/dc converters as well as modeling methodology and its application in both subsystem and system level.The thesis presents an overview of the research history and state of art at first, and several typical interaction problems and challenges in practice are demonstrated. Then the dissertation introduces a systematic analysis tool based on two-port network model. It is not only a theoretical extension of impedance-based system analysis method but also can be applied to analyze and integrate such complex systems.Efforts are made in methodology for two-port network model. A PWM switch unified average model that covers CCM, DCM and FCCM modes is proposed, which lays a fundation for analysis and applications of the dissertation.This work investigates closed loop impedance characteristics of voltage control and average current control buck converters in continuous/discontinuous current modes, from view points of outer loop crossover frequency and phase margin. The resulting models help impedance standard design procedures which is improved with load converters'input capacitors included.At the same time, converter's two-port network models and their applications are discussed. Based on cross output impedance concept, a methodology is proposed to evaluate control-loop interaction in a multi-output dc-dc converter with magamp post-regulators. Two corresponding solutions are also presented. Zero-crossing distortion problem occurs in high line frequency(360-800Hz) applications is analyzed and solved, with an input admittance model of an average current mode control boost PFC rectifier. A novel method based on output current back gain Ai(s) is also proposed for input current low frequency ripple cancellation performace evaluation with different control approaches in a two-stage single phase inverter system. In addition, LC resonant filter added in dc bus is generalized as an approach, which clamps the twice line frequency current ripple in dc link. Another solution is proposed with active band elimination filter in control circuit. The two-stage inverter achieves constant power operation with these methods. Subsystems of aeronautical secondary power supply system is built with the PWM switch unified average model, including a non-isolated buck converte,a bi-directional buck/boost converter(BDC) and etc. It is pointed out that a buck/boost BDC is also a synchronous buck converter, and power flow in two directions could be achieved only with the main switch in buck mode. Different poles and zeros in the main power stage reveal the operational modes transfer. Its control loops design criterion is also presented. At last a DPS system model is implemented, simulation results and analysis verify the modeling approach and foregoing interaction theory.Detailed simulation and experimental results are provided to verify the works studied in this dissertation. These works provide theoretical and technical basis for DPS design and optimization.