Study On Bidirectional-Switch Power Electronics Converter

With the widely development of industry and economy, a series of new problems emerges, such as reactive power and harmonic pollutions on electric grid, converter inefficiency, serious electromagnetic emission and electromagnetic interference (EMI) problem, deteriorated environment, and energy crises. Under the background of energy saving and consumption reducing, employing power electronics bidirectional switch in AC/AC and AC/DC converter has become a hot topic in recent years. This system has several merits, for high power factor, energy bidirectional power flow, improving converter efficiency, high energy saving, simple control and low pollution of electric grid, and so on, with extensive application foreground.The dissertation mainly focuses on the research of power electronics bidirectional switch application and its control system. The dissertation firstly discusses the topologies, mathematic model, system performance and control strategy of AC direct converter and three-phase isolated matrix converter separately. The studies carried out in the dissertation and the corresponding results are as follow:(1) The dissertation proposes the AC/AC direct converter topology family using different forms of AC bi-directional power electronics switch in the DC direct base converter topology family to improve the performance of this converter. Based on the differences of the topologies, the operation principles and characteristics of a number of different types of converters: buck, boost, cuk, and so on.(2) Based on the voltage-fed or current-fed AC/AC direct converter topology family, the dissertation analyzes the four-step current commutation method based on the voltage or current direction, and proposes the novel two-step commutation method of combining current forecasting with complementary PWM. On the conditions that the current direction of the converter is as same as the voltage direction, the un-complementary PWM is used to realize the current freewheeling, otherwise the converter works on the complementary PWM condition. The dissertation proposes the method of the current-forecasting combined complementary PWM in the control of the novel AC/AC direct converter. Under this condition of the real current direction different with the forecasting current direction, the main switch and freewheeling switch use complementary PWM. (3) Based on the Buck AC/AC chopper for the sinusoidal-wave dipper module, the dissertation proposes the novel snubber circuit to reduce the reverse current of the diode in the bi-directional switches, then limits the di/dt and dv/dt. This novel sunnber circuit gives the low resistance passway to reduce the voltage spike and the switching loss, so as to add the total efficiency of the module. the paper proposes a novel LC filter to improve the performance of low or no load conditions, and also presents some improvements of main circuit design and the implementation of digital control scheme. Then the average-voltage and instantant-voltage dual-loop control system combined the duty cycle feedforward is proposed to improve the steady and dynamic performances of the whole system. And the simulation verifications are also carried out. The simulation results show the feasibility of the design and the control schme proposed in this paper.(4) Based on the average state-space model of three-phase current-fed rectifier, the mathematic models in abc three-phase reference frame and dq three-phase reference frame are analyzed in details. Then the steady state operation principles, control strategy and design criteria of three-phase current-fed rectifier are discussed in details. This paper analyzes the three-phase current space vector PWM modulation, and discusses the current usage ratio of three-phase current-fed converter. The current-fed control principle and method are proposed and discussed in detail, so as to give the thoeretical base for three-phase high-frequency isolated Buck rectifier.(5) The dissertation proposes and analyzes the parameter design of three-phase Buck bi-directional switches rectifier, based on the operation principle and mathtical model of three-phase Buck current-fed PWM rectifier.By using the state space averaging approach, the averaging model and control method are presented and deeply investigated. This dissertation proposed the whole digital control system, achieving the steady DC output voltage and good input current waveform with low current THD. This paper investigated the DC bias of the high-frequency transformer, firstly proposed the digital control of peak-current for balancing the magnetic DC bias of high-frequency transformer. Then the paper proposed digital dither method to reduce the steady output voltage ripples. The simulation and experiment testify the feasibility of the whole system.