The Study Of Control Strategy For Three-phase AC-DC Matrix Rectifier On Output Voltage And Power Factor

The rectifier is widely used in communication power supplies, household appliances, uninterrupted power supplies(UPS), frequency converters of motor drives, converters of wind power generation, battery chargers etc. However, traditional rectification methods, adopting phase control or non-control rectification, consume a large amount of reactive power. Such traditional rectifiers input harmonic current into the grid, which greatly influences the efficiency and quality of the power source. The three-phase AC-DC matrix rectifier(MR), an ideal rectifying device deduced by the three-phase AC-AC matrix converter, has many desirable features: operating in all four quadrants of operation, no need for a large capacitor using space on the DC side, safe current commutation, sinusoidal current input, power factor regulation, small size, and long life span. However, space vector modulation(SVM), the conventional modulation algorithm for the MR, is open-loop control. Thus, applying convention SVM on MR, the DC output of MR is susceptible to voltage disturbance at the power supply. An input filter is necessary for the MR, in order to improve the main input current quality. Unfortunately, the presence of an input filter results in a displacement angle between input voltage and input current at the main power supply, which degrades the input power factor tremendously. The problems mentioned above hinder the industrial application of the MR.In this dissertation, the control strategy of the matrix rectifier is studied by theoretical deduction, Matlab simulation analysis and experimental verification. The research contents are as follows:Focusing on the problem that the DC output voltage of the MR is susceptible to the disturbance of the AC supply, this dissertation is put forward a control algorithm based on the sliding mode control(SMC) for the DC output voltage. Firstly, a mathematical model of MR and its control algorithm SVM are presented. Secondly, the switching function is designed based on SMC strategy. Then, three expressions of the control function are deduced according to the accessibility conditions of the generalized sliding mode. Meanwhile, the influence of three kinds of control functions on the chattering is analyzed. Further, the matching conditions of the uncertain sliding mode control of the matrix rectifier are studied. Finally, both computer simulations and prototype experiments are carried out. The results show that the DC output voltage of the MR is stable and its dynamic response is fast. This proposed control algorithm is resistant to disturbance and perturbation.Based on the instantaneous power theory, a control algorithm for the input power factor(IPF) using SMC is presented. Firstly, the problems of input reactive power and open-loop compensation are analyzed by using static characteristics of the MR, and the mathematical model of IPF is established based on the theory of instantaneous power. Then, the switching function is designed based on SMC strategy, the expressions of two kinds of control functions are derived based on the generalized sliding mode reachability condition, and the influence of two kinds of control functions on the chattering is analyzed. Moreover, the matching condition of the sliding mode control of the IPF angle control is given. Finally, based on mechanism analysis and theoretical study, the computer simulations and prototype experiments show that applying the SMC can get effective, controlled, and robust harmonic current waves on grid.Under the conditions of DC voltage and load wide variation, adopting separate control algorithm of output voltage and reactive power might lead to malfunction of the MR. Consequently, an adaptive sliding mode control method is proposed based on the DC output voltage and IPF. Firstly, an analysis of the static characteristics and failure working mechanism of the MR is presented, and a control system based on the d-q coordinate system is given. Then, an adaptive control function is used to compensate the IPF angle so as to guarantee the DC output voltage. Finally, computing simulations and prototype experiments verify the proposed compensation algorithm. The experimental result shows that using the given control algorithm, the MR can still work in wide load variation range.As demonstrated in the research of control algorithm, the MR can obtain DC output voltage and a unity power factor, and it has several advantages, including less DC output ripple voltage, less input harmonics current, and a fast dynamic response. The research findings of this paper provide support for the industrial application of MR.