Study On The Control System Of Active Neutral-point-clamped Five-level Converter

The high-voltage converter and its control system with high efficiency, high performance, high reliability, are the key to solve the problem of low efficiency in the field of motor system. Some detailed research mainly focusing on topology, build pressure method, modulation algorithm and control system design have been in-depth studied in this dissertation by taking the active neutral-point-clamped(ANPC) five-level converter as the research object.By analyzing the structural characteristics of the ANPC five-level converter topology and the relationship between its output five levels and eight switching states, the principle of switching between the different switching states was given. The effect of IGBT voltage stress has been analyzed when the voltages of the dc-link capacitor and the flying capacitor with normal and abnormal operating conditions, the prerequisite for stable operation of the systerm was obtained. For the voltage balance control of the flying capacitor, the corresponding control strategy was also given.A general capacitor voltage buildup method for ANPC five-level rectifier was proposed after the topological structure characteristics being analyzed. This method is that the capacitor voltage was buildup by controlling some IGBTs open or off only with a pre-charging transformer. The formula of capacitor voltage buildup is deduced after analyzing of the characteristics about the capacitor voltage buildup circuits in different stages. The surface of the relationship among the capacitor voltage buildup speed, the equivalent pre-charge resistance and the capacitor capacity was given.A new SVPWM algorithm based on line voltage coordinate was studied to overcome shortcomings of the traditional algorithm. Through coordinate transformation,steps of determine basic vectors and the solution about the basic vector corresponding action time are simplified. To take the ANPC-5L inverter as a research object, by analyzing the single-phase topology of the ANPC-5L inverter and its working principle, the neutral-point voltage balancing control method of the ANPC-5L inverter was studied. An effective control method of the neutral-point is proposed by selecting the switch sequence of the reference voltage vector in the triangle and controlling the reuse vector function of time, a decouple method and a balancing control of the floating capacitor voltage and the neutral-point voltage balance are achieved. The high common-mode voltage will affect the service life of motor and reduce the reliability of the system especially in high-voltage converter. The common-mode voltage is also reduced by choosing the right switching state. For the shortcomings of new SVPWM control algorithm computation time is not fixed, an optimization algorithm of reducing the SVPWM control algorithm processor computing time greatly is proposed.In order to reduce system losses, improve system efficiency, achieve optimal control system. ANPC five-level PWM inverter model predictive control technology was studied. Mathematical model of ANPC five-level PWM inverter and discrete predictive model was established by analyzing the five-level converter model predictive control characteristics. The model predictive control strategy of ANPC five-level PWM rectifier was proposed with the design method of predictive controller giving. An ANPC five-level PWM rectifier fixed-frequency predictive control strategy was proposed by the basic idea of predictive control, then the principle of fixed-frequency predictive control and implementation are also given detailedly.To further improve the five-level ANPC converter control system performance in industry, a hardware system of back-to-back ANPC five-level control was designed, so that it can meet the design requirements to achieve the related control algorithms and high-speed communication. Secondly, in order to solve the over-voltage problem at the motor side caused by using long cable between the inverter with the motor, a du/dt output filter with its parameters and the design method were given. In order to achieve real-time data communication between the control systerms of the five-level ANPC converter, a high-speed serial communication system based on high-speed optical fiber was designed, modularized design for program can improve the readability and portability of the program. Finally, the reliability and the validity of the design of hardware system, control system and communication system were proved by building an ANPC five-level converter induction motor vector control system.