Control And Application Of Voltage Source PWN Converter

The production and consumption of electricity are two main key points in power system, and its efficiency and safety is very important in the development of power engineering. In nowadays, as the short of energy and the expansion of the power grid, stability and efficiency are always the focus in power system research.Inductive motor is the main consumer of power in the power system. Under the drive of frequency converter, it can produce huge regenerative energy which was always wasted through the break unit. This way is not cooperate with the strategy of construct energy saving society and reduce exhaust. And another aspect, with the construction of’west to east power transmission’and the connection of area grid, the problem of lack damping and low frequency oscillation became a serious problem. So the research on a new excitation system has its practical significance.The PWM converter of voltage source has been used more and more in power system because of its good controllability and flexible structure. This dissertation mainly studies on the usage of this kind converter in energy saving field:lift, oil pump unit and the excitation system as follows:First is the research on the basic theory of digital energy feedback device based on the voltage source converter, and talked about its process of design and implementation in details, include the design of main circuit, the calculation of component parameters, and the design of control circuit, peripheral circuit and control program. The experiment results indicated that, the device can adapt to the voltage’s big deviation and keep unit power factor; the voltage of feedback point can be adjust in a certain range. Through a long time operation in the lift field, the device worked well, and has no passive impact to the frequency converter. And its record indicated that after the installation of the energy feedback device, the lift has a remarkable energy saving effectThen this dissertation analyzed the beam pumping unit’s motion low in petroleum exploitation, and designed a dual PWM frequency converter; include the main circuit, control circuit, peripheral circuit and the control program. After the field operation, the device worked well with perfect performance:nearly unit power factor, zero reactive power, reduced line voltage drop, flexible speed adjusting. It can reduce much consumption of active power with no impact to the oil production. Through the professional testing, after the installation of the dual PWM frequency converter, the beam pump unit has a remarkable energy saving effect.Then the voltage source PWM converter was used in the excitation system:analyzed the principle of how the injected reactive current affects the electric power of generator compensates proper current will increase the damping of generator. And a control strategy of voltage source converter excitation system based on full controlled devices was designed, that using three phase full bridge PWM converter as exciter. The simulation results show that, this kind of voltage source converter excitation system can supply more damping to system through another way, and also increase the dynamic stability of the generator. The larger capacity of the compensation system, the more damping there will be.At last, this dissertation deduced a third-order model of this kind of excitation system. And with the main goal of controlling the rotor angle as well as the terminal voltage, a MIMO nonlinear control strategy was designed through this model. The simulation results show that, comparing to the linear control scheme (AVR+PSS), this nonlinear scheme has better effect in enhancing the system’s damping, with the compensation capacity increase, and better effect can be achieved; when system parameters changed, still has a good performance and better suitability.