Research On Control Technique For PWM Inverters Based On State-Space Theory

The important departments and electric equipments need more and more high qualitypower supply, but the utility power is stained strictly by harmonics which many electroniccomponents and nonlinear loads bring on. The conflict is quite evident. In recent years theresearches for high performance PWM inverter are taken more attention, and variouswaveform correction techniques have been proposed. Some of them have been appliedabroad, and the others are developing. This dissertation analyses performance andcontroller design method of some PWM inverter based on uniform state-space theory. Newsystemic theory basis for high quality PWM inverter design is provided. Novel controlschemes are proposed. Firstly, the continuous and discrete mathematical models of a single-phase PWMinverter are established, and their difference is compared. The influence of dead-time,PWM over modulation and nonlinear load on inverter output waveform is analyzed. With adiode rectifier load, the primary factor of output waveform distortion, output voltageharmonics are estimated. The mathematical models in abc and dq frame for three-phaseinverter are established. The concept of abcz-dqo three-dimension space frame is firstlyemployed so as to get mathematic and physical unification for two frames conversion.Those influence three-phase inverter performance are discussed. Inverter with single loop PID controller usually woks not very well. It is due to PIDcontroller parameters are not designed well. The design method of inverter instantaneousvoltage PID controller based on pole-assignment is proposed for the first time in this paper.Simulation and experimental results indicates that this PID controlled inverter provides fastdynamic response, low output THD with nonlinear load and nice static characteristics.Theoretically, control essence of the PID controlled inverter is expounded with state spaceconcept. The PID control scheme has advantage on circuit and cost, compared withdual-loop control inverter. The design method based on pole-assignment is employed to inverter voltage andcurrent dual-loop control system. Simulation analysis presents the dual-loop controlinverter has faster dynamic response, lower output THD with nonlinear load, compared toPID control inverter. Moreover, the output current limiting problem of single-phase andthree-phase inverter controller is discussed. Another characteristic of inverter innerinductor current loop and outer voltage loop control system is auto current limitingfunction. Three-phase inverter with dual-loop controllers in dq frame can keep sinusoidal IIIoutput waveform when limiting current. Dual-loop control scheme adapts to fulfill higherstandard inverter product. Some issues the controller designed based on pole-assignment faces in practice arestudied. The inverter robustness to system parameters variations is discussed. Two primaryinfluences of PWM process are analyzed. One is control delay, and the other is thatzero-sequence harmonics are introduced in three-phase inverter. They are necessary to beconsidered when design a control system. When feedback delay occurs, controller designand the change of system performance are introduced. Output unbalance of three-phase inverter is required to be restrained. The mechanismproducing unsymmetrical output voltages of a three-phase inverter under unbalanced operationis analyzed. As will be shown, the problem is related to not only controller characteristic but alsothe inherent nature of the inverter circuit. Design consideration is proposed to keep three-phaseoutput voltages of an inverter in symmetry. Theoretical analysis is confirmed well through bothsimulation and experimental results. In order to improve digital controller effect of inverter, a digital control schemes,increasing-state feedback digital control inverter, is firstly proposed in this paper. It can resolvethe problem that performance decline due to control syst...