Research On The Technologies Of Three-Phase PWM Rectifier Suitable For Variable Frequency Adjustable Speed Devices

The PWM rectifier can be applicated to the frequency control system to implement bi-directional power flow, for its advantages of unit power factor control, low harmonics and fast dynamic response. It can not only reduce the harmonic pollution to the power line, but also save enegy. The mathematical model and control strategy of PWM rectifier are studied in this paper, the random PWM technology based on Markov chain is used in order to reduce the high-frequency noise and electromagnetic interference of PWM rectifier, and its nonlinear phenomenon is analyzed. The circuit topology, mathematical model and control strategy of PWM rectifier are studied for the three-level PWM rectifier.The topology and working modes of three-phase two-level PWM rectifier are analyzed, and the low-frequency time-domain model and the high-frequency time-domain model are established. For the rectifying state, a novel dual single-input single-output (DSISO) model based on twelve intervals is proposed. In this model, the a-axis model andβ-axis equivalent model are shown to be similar to two traditional single-phase boost converters, which is much easier to analyze three-phase PWM rectifier. Based on this model, the small signal model is derived, the control-to-output transfer function is deduced, and a detailed analysis of the parameter conditions required for system stability is presented. Meanwhile, the control strategy is analyzed to determine switching control signals in a switching period. Simulation and experimental results confirm the validity of the DSISO model and its control strategy. In order to simplify the system structure and increase reliability, a novel control strategy without AC voltage sensors based on the twelve interval DSISO model for the PWM rectifier is proposed. An interval self-synchronous controller is design, and the interval can be selected correctly according to the assigned physical quantity. Simulation results confirm the validity of the control strategy without AC voltage sensors.In order to sovle the problem of unidirectional power flow for the DSISO model based on twelve intervals, a DSISO model based on six intervals is proposed, and the three-phase PWM rectifier is equivalent to two single-phase full-bridge PWM rectifiers, which can implement bi-directional power flow. Based on the DSISO model and space vector modulation, the control strategy is analyzed to determine switching control signals in a switching period. The resisitor experiment, motor experiment without load, and motor experiment with load are carried out, and the experimental results confirm the validity of the DSISO model based on six intervals and its control strategy.The work principle of Markov process and Markov chain is studied, and the two-state Markov chain and three-state Markov chain are analyzed in detail. A novel random PWM technology of PWM rectifier based on two-state Markov chain is proposed, and the random cycle values can be evenly distributed around the cycle expectations. And therefore, the input current spectrum is also distributed evenly and the high-frequency noise and electromagnetic interference of PWM rectifier are reduced. Compared to the conventional random PWM, the input current ripples are reduced. The new algorithm solves the contradiction between time-domain and frequency-domain caused in the conventional random PWM. The simulation and experimental results verify the validity of the novel algorithm.The novel topologies of three-level PWM rectifier are studied, and the mathematical model and working modes of four-line three-arm three-level NPCPWM rectifier and the three-phase two-arm three-level NPC PWM rectifier are analyzed. For the three-phase two-arm three-level NPC PWM rectifier, a novel DSISO model based on a-P stationary reference frame is proposed, in which the a-axis andβ-axis equivalent model are shown to be similar to two traditional single-phase boost converters. Switching strategy is analyzed to determine switching control signals in a switching period based on space vector modulation and volt-second characteristic. The simulation results verify the validity of three-phase two-arm three-level PWM rectifier and its DSISO control strategy.According to the DSISO model based on six intervals, the nonlinear characteristics of PWM rectifier are studied in detail with phase-space reconstructing algorithm. Quantitative chaos analysis is implemented by phase graph and power spectrum, and qualitative chaos analysis is implemented by calculating the maximum Lyapunov exponent and correlation dimension. By analysis, calculation and simulation, the chaotic characteristics of PWM rectifier are verified.