Research On Control Technique Of Matrix Converter And Its Application

The matrix converter is a high efficiency, high power density, and high reliability direct AC/AC power converter without any bulky DC link component. It can provide sinusoidal output current and input current, adjustable input power factor, and regeneration capability; and it's very attractive in areas where volume, efficiency and reliability are of importance. Widespread, systematic, and in-depth studies have been focused on the modulation algorithm and the commutation strategy of the matrix converter, and the key technologies for its application in induction motor drive system. These studies have provided theoretical and technological foundation for the development and application of the matrix converter.In this paper, the 3φ/3φdirect matrix converter is studied. The direct space vector modulation (DSVM) algorithm and indirect space vector modulation (ISVM) are analyzed, and it has been found they are identical modulation algorithms. The concept of modulation vector is proposed, and an implementation method for ISVM is proposed based on the modulation vector, thus the calculation process is simplified. The input/output characteristic of the matrix converter is analyzed based on the modulation vectors, and the output voltage/current distortion of the matrix converter is investigated. A compensation method for unbalanced and non-sinusoidal input voltages is proposed based on real-time adjustment of the modulation vectors. The input current characteristics of the matrix converter under unbalanced input voltage is analyzed, and two input current control methods under unbalanced input current condition is investigated.A voltage-based variable-step safety commutation strategy is proposed. In this method, the two-step commutation is utilized to realize uncritical commutations (commutation between input phases with unclear relative voltage), and four-step commutation is utilized to realize critical commutations (commutation between input phases with clear relative voltage); and the short-circuit problem of the voltage-based commutation strategy in critical intervals is solved. The voltage-based commutation strategy is then implemented with space vector modulation (SVM) algorithm, and it has been found that the four-step critical commutation can be all avoid by selecting four SVM switching patterns, thus all-two-step commutation is realized. In order to prevent the commutation processes from being interrupted when the duty cycles of the active vectors are low, the modulation method which uses both the triple-zero-vector switching pattern (TZVSP) and the single-zero-vector switching pattern (SZVSP) is proposed. The calculation of the maximum duty cycle of the commutation time is investigated. With the selected commutation time, the Extend and Abandon approaches are no longer needed, and the output voltage/current waveform quality are improved.The matrix converter is then implemented with the induction motor to realize a high performance AC drive system. The control scheme of the motor drive system is presented based on rotor-flux-oriented vector control strategy. A decoupled stator current control strategy is proposed; and the PI regulators for stator current loop, flux loop, and speed loop are designed based on classical control theory. The bidirectional power flow mechanism of the matrix converter is analyzed for the first time, it has found the direction of power flow can only be controlled by the difference between the output voltage of the matrix converter and the back-electromotive force (Back-EMF), regardless of the input current displacement angle.The output voltage error caused by voltage-based commutation process is analyzed. It was point out for the first time that the output capacitance of the switching device and the parasitic capacitor of the matrix converter will affect the output voltage error caused by forced commutation process. This effect could reduce the total output voltage error caused by commutation process, and it makes the output voltage error relate to not only the direction of the load current, but also the magnitude of the load current. The voltage error caused by voltage-based commutation process is obtained considering the switching pattern, and then the general function of total voltage error is obtained considering the on-state voltage drop of the switching devices. A nonlinear commutation method is then proposed based on modification of the reference output voltage. With the proposed compensation method, the linearity of the matrix converter is improved, and the output voltage/current quality in low modulation index condition is improved. The nonlinear commutation method is then implemented in the matrix converter induction motor drive system, the low-speed performance is improved. A 5.5 kW matrix converter prototype has been developed in this paper. And then the matrix converter induction motor drive system was constructed based on the prototype. The design methods of the main circuit, gate driver circuit, control unit, measurement circuit, and over-current protection circuit are detailed analyzed. The requirements for the input filter of the matrix converter are investigated, and the design criteria are presented. The validity of the matrix converter prototype design and the control methods proposed in this paper are verified by experiments.