Research On Control Strategy For UPFC With Two Stage Matrix Converter

With the rapid development of the society and economy, the modern power grid has become one of the world’s largest and most complex artificial systems.It gradually formed a giant power system using grid interconnection, and laid a solid foundation for long-distance transmission of energy, not only improves the reliability of power supply system, but also achieve the optimal allocation of power resources and economies of scale. To ensure the safe operation and power quality of modern power grid, Flexible AC Transmission Systems(FACTS) was invented, which controls many aspects of the entire transmission system, including the phase voltage, phase angle, power flow. FACTS can improve the power system’s security、stability and flexibility.Unified Power Flow Controller is a new generation of flexible AC transmission devices, having has the most powerful features, the greatest potential in all FACTS devices. And two-stage matrix converter as a new type of power electronic devices has superior electrical properties:the energy can flow in both directions; input power factor is controllable; stable output performance, can fully meet the needs of the unified power flow controller. Compared to the traditional unified power flow controller device, the two-stage matrix converter without DC link capacitor not only makes the system structure become compact and size become smaller, reduction, but also saves the cost of the device, improves the reliability of the system.Firstly, the basic structure of the two-stage matrix converter is introduced in the paper, analyzes the rectifier stage and inverter stage of the control strategy and its low-frequency switching function, and then the UPFC with two-stage matrix converter is studied. The main research object is the two-stage matrix converter’s inverter in the unified power flow controller series side. A mathematical model in three-phase stationary coordinate system is built, and coordinate transformation to the two-phase stationary coordinate system, then the model uses dual loop control strategy:the voltage loop and current loop. To achieve the current and voltage decoupling control, the model uses PI controller. Base on this the paper puts forward a predictive current control strategy for UPFC with two stage matrix converter series side. In every sampling cycle, according to the quality function, this strategy will use the sign of the given active and reactive power and the eight different predictive values of current produced by two stage matrix converter inverter stage to determine the switching signal in the next sampling period, to control the line trend. Derive predictive control strategy can quickly adjust the line power flow, and effectively improve the system dynamic and static performance. At last, the system model is built in MATLAB simulation to verify the correctness of the above discussion.And a TSMC experimental platform is built, using the DSP2812, prove the correctness of the double space vector modulation strategy.