Study On Two Stage Matrix Converter And Its Control Stratgy

Due to reduced number of switchings and much simple control strategy compared to conventional matrix converter(CMC), two-stage matrix converter(TSMC) is a novel matrix converter with huge development potentials. But in applications, all kinds of no-ideal operation conditions and disturbances will deteriorate output performances of TSMC, so the advantages of TSMC can't be fully demonstrated. Therefore, How to improve output performance by eliminating influences of no-ideal conditions and disturbances has become an urgent problem to be resolved. Based on the study of space vector modulation strategy of TSMC, this paper made deep investigation on output voltage control strategy of TSMC, which include: open-loop modulation strategy and closed-loop control strategy. The main works include:In this paper, the widely employed space vector modulation(SVM) strategy without zero vector at rectifier stage was modified to overcome its lack capabilities in adjusting input power factor. At the same time, a dual SVM and its simplified strategy was proposed, the low frequent switching function of which was derived. By introducing the low frequent switching function, the no-linear and discontinuous switching circuit of TSMC can be changed into a linear and continuous system in the form of transformation relationship, which make it easy to design and analyze TSMC system.The conventional space vector modulation can't reduce the influence imposed on the output of two-stage matrix converter(TSMC) by abnormal input voltages. To overcome this shortcoming, a new method was proposed to describe the abnormal input voltages, a concept of anti-disturbance vector was introduced and added to the rectifier modulation vector to improve the output waveforms. Analysis and simulation show that the proposed strategy is easily to implement and can effectively reduce the output harmonic components under abnormal input voltages. In this paper, the steady model of TSMC based on synchronous rotating coordinate(dq coordinate) was set up by dq transformation., Based on dq steady model, the power characteristics of TSMC is analyzed, and an idea of computing control variables was proposed, which resolved the problem that control variables are difficult to be determined when multi-control requirements need to be satisfied at the same time. The analysis and computing method is theoretically significant to design and control TSMC system.Closed-loop control by introducing the instant value feedback of output voltage is a reasonable method to guarantee the output performance of TSMC by restraining multi disturbances. In this paper, inverter stage of TSMC is regarded as controlled object, input disturbances are regarded as DC disturbances. The mathematics model of inverter stage was set up on three phase static coordinate, based on which the compound vector model of inverter stage was set up, which simplifies the model from a multi-input/ multi-output system to an equivalent single-input/single-output system. Based on these models, three closed-loop control strategies of output voltage for TSMC were deeply investigated.Closed-loop control strategy employing PI controller on single synchronous rotating coordinate(positive sequence dq coordinate) for TSMC was proposed, according to its lack capability in controlling unbalanced load disturbance, a closed-loop control method based on dual synchronous rotating coordinate (dual sequence dq coordinate)was proposed, which employed two groups of PI controller: one is on the positive sequence dq coordinate, the other is on negative sequence dq coordinate, to control the positive sequence and negative sequence components of output voltage respectively. Simulation results show that PI control on single dq coordinate can effectively restrain disturbances such as input voltage sags,load changes. etc, and PI control on dual sequence dq coordinate can guarantee high performance of output voltage under unbalanced load disturbance.Repetitive control technology is an effective method to restrain periodical disturbances. In this paper, Repetitive control was firstly introduced into TSMC control. In order to overcome the defect of repetitive controller in dynamic response, repetitive controller and PI controller are combined into a compound controller. Additionally, the problem of conventional repetitive controller is pointed out and a modifed one was proposed: In order to avoid the influence of no-periodical disturbances imposed on the control action of repetitive controller, the error caused by no-periodical disturbance is identified and discarded. Simulation results show significant effects on harmonics control with repetitive controller and feasibility of the modified compound controller.According to non-linearity, multi-variables and strong coupling characteristics of TSMC, a closed-loop control strategy of output voltage based on Auto-disturbance rejection control(ADRC) was proposed, in which ADRC is used to dynamically observe and compensate internal/external disturbances of TSMC system. Simulation results show good dynamic and steady performances of ADRC control under no ideal operation conditions and disturbances. Under same disturbances, ADRC presents not only much better dynamics performance compared to PI controller, but also strong capabilities in harmonics control, which guaranteed higher steady performance in no-ideal operation conditions, such as abnormal input and unbalanced load.