Research On New Non-PWM Power Unit High-Voltage Frequency Converter

With the development of the VVVF technology, the high-voltage frequency converter used for large-capacity transmission has been widely applied. High-voltage motors can be achieved stepless speed regulation under the help of high-voltage converter, as a result, the motor speed control not only meet the needs of production process, but also can save energy and reduce production costs. Since the Robicon company of the United States released the first generation of perfect harmony high voltage converter in 1994, this kind of converter has been a leader on the markets of Europe, the United States, Japan, China and other countries because of its good performance, high reliability and simple maintenance. Compared to the traditional high voltage frequency converter, the perfect harmony high voltage converter is superior in performance, reliability guarantees, as well as manufacturing processes.However, so far the rectifier of the power unit in this perfect harmony high voltage converter is made of one-way diodes and the control strategy of the inverter is the traditional PWM strategy, which lead to high swiching frequency, large swiching power loss and system's energy irreversible. In order to cut back energy-losing, reduce the pollution of power grid and prevent the electromagnetic interference, this paper introduced a new kind of high voltage frequency converter, namely the Non-PWM power unit high voltage frequency converter. The input section of the Non-PWM power unit composed of three-phase controllable rectifier bridge made of thyristor; the output section composed of IGBT inverter bridges. The pulse control strategy is to control pulse frequency based on expected voltage output frequency, so as to realize no system high frequency and avoid the PWM strategy. This can lower the production costs, reduce the pollution of power grid and the electromagnetic interference.The development of high-voltage converter is a high investment and high risk project, mainly including the design of the control system and the main circuit of high voltage converter, and also a complex of multidisciplinary and high-tech. The author deeply researched the principle of new Non-PWM power unit, selected and designed the IGBT drive circuit and designed the control system of the converter and simulated the entire high voltage frequency converter. The content of this paper are as follows:1. Outlined the development of high-voltage frequency converters and its application, pointed out the existing problems and the significance of this research; 2. Described the structure and principle of work of traditional multi-level high voltage frequency converter and its interior's traditional PWM power unit, based on this has explained the new Non-PWM power unit, and introduced the circuit structure, the principle of work as well as the superiority of the new Non-PWM power unit;3. Discussed the overall program design of Non-PWM power unit high voltage frequency converter, including the selection and design of IGBT driver circuit; the design of input part, the power conversion part, detecting and protecting part as well as the control and interface part;4. The design of the control system;5. Simulated the entire high voltage frequency converter: modeling the pulse, the three-phase power, power unit, one-phase model and the whole converter; simulated each model and analyzed the experimental data.