Research On Symbolic Analysis Of Switched Circuit And Its Engineering Applications

Power electronic (PE) is based on switched circuit (SC) theory and widely used in economy of energy transformation, transmission, utilization and control so as to improve the efficiency and effects of energy utilization and control. PE system is a complex system engineering concerning multi-discipline cross of switch circuit, analog/digital circuit, computer, automatic control, materials science and technology, etc. therefore, only by making full use of computer aided simulation technique, can the PE design cost be cut thus efficiency be improved. SC, include PE and piece-wise linear (PWL) circuit, is typical strong nonlinear circuit. It is commonly regarded as very difficult to analyze and design due to SC analysis has two difficulties:excess long simulation time and non-convergence problem, and to which there has no idea solution yet. In this dissertation, a new symbolic based analysis method for SC analysis is proposed to solve these two difficulties. The main researches and contributions are presented as follows:(1) Great variety of practical SC or PWL circuits is first formulated to ideal switches modeling and their analysis is turned out to be the ideal diodes'working states determina-tion hence laid the foundation for developing SC's unified and generalized mathematical model and solving algorithms.(2) A symbolic-based SC analysis method (SSCAM) is proposed and importance characteristics of SC solution are analyzed so as to provide a reliable basis for constructing SC simulation programme. SSCAM regards the switch as a symbolic time-varying resistor RQD with value 0 or oo, and the SC's s-domain general solution F(RQD, s) is obtained. By performing limitation and inverse-Laplace transformation to F(RQD, s) with the switch-states, the SC's t-domain solution f(t) can be easily obtained. F(RQD,s) can be repeatedly applied to the switch working state (SWS) determination, whereas a correct f(t) is valid until next SWS, therefore, solving the circuit equations isn't needed during or after the switches variation and save the simulation time. Besides, SSCAM can well handle the Dirac impulse occurred at the instant of switch-state change, hence overcome the non-convergence problem; also, the analytical expression f(t) can help the circuit designer to get insight the SC's working mechanism, better evaluate the circuit properties and modify the circuit design.(3) Using Matlab/Maple symbolic math toolbox, a symbolic aided analysis programme for SC was developed and key technique details of programming are introduced. By simu- lating two working modes of a typical DC-AC inverter, the SSCAM's characteristics and panorama are shown; SSCAM can be easily and efficiently put into practical application.(4) An improved genetic algorithm (iGA) was proposed to handle the SWS determina-tion which consumes most of the total simulation time (≈90%). This iGA adopts population crowding technique, adaptive mutation and specific point induced mutation technique, etc. and successfully overcome the inherent premature convergence problem of common GA and result in iGA quickly converge to correct switch-states solution. Numerical simulation results shown that iGA needs only 16% of the circuit analysis times of enumeration method (EM) hence has much more analysis efficiency over EM; unlike conventional linear com-plementary problem algorithm, iGA has no dimension disaster problem and is more suitable for relatively large-scale SC analysis.(5) Using SABER simulation, a BUCK type high-voltage switching power supply for electron beam accelerating of electronic beam welder (EBW) was designed to replace the tradictional one which has bad efficiency, the feasibility of SSCAM is also partly verified meanwhile. An effective current-limited measure was introduced through the analysis of surge current generating mechanism; a feedforward PID control algorithm was suggested to meet the system's control requirements according to its open and closed loop behaviours. Simulation and experiment results had verified the feasibility of the system design and thus provide a technique to improve our country's EB technical level.