Operation And Control Of The Induction Generator With Full Rated Converter Connected To DC Grid

As the global energy problem is becoming increasingly serious, more and more people pay attention to the development and utilization of clean, cheap, non-polluted new energy. DC grid is more suitable for the distributed energy resources compared with the traditional AC grid. At the same time, DC grid has the advantages of strong stability, no phase as long as reactive power, good power quality and small loss. This paper takes DC grid as the research object, and make a deep research on squirrel-cage induction wind system’s connection to DC grid, multi wind power DC power supply control mode, voltage optimization hierarchical scheme, power coordination strategies were studied. The main work and achieved results are shown as follows:(1) The dynamic model of the FRC-IG wind turbine is established firstly. Then, the working principle and control strategy of machine-side converter station and grid-connected converter is researched on. At last, a method of using DC/DC converter to connect FRC-IG with DC grid is proposed based on the function of FRC-IG’s structure and characteristics of the converter station.(2) Taking the fluctuation of wind speed, sudden increase or decrease of loads and exit operation of one or more wind turbines into consideration, a voltage optimization hierarchical control method is presented to give a certain dynamic support to the DC grid voltage. When DC grid is subjected to external disturbance, the method coordinate the control strategy of each converter according to the variety of DC grid’s voltage, the DC grid can find a new steady state through its own control. The voltage optimization hierarchical control method improves the regulating ability and system stability of DC grid’s voltage, at the same time, it ensures the safe and reliable operation of DC grid.(4) Research on the power coordination control mode of each converter within DC grid which includes the wind power generation unit, load unit and storage system. A multiple variables based power coordinated control strategy under multiple operation modes is proposed in this part Five operation modes and corresponding switching conditions are put forward according to the micro grid’s operation and the converter’s capacity, which avoids the overload of multiple converters, guarantees the smooth switch between multiple modes and lays the foundation for the further proposal of power coordinated control scheme. The proposed power coordinated control strategy based on the current of the grid-connected converter, SOC of the storage battery and the variation of the DC bus voltage not only enhances the power coordinated ability of each converter, but also keeps the DC voltage stable.(5) After completely building the simulation model of DC grid which contains FRC-IG wind power system, a simulation analysis about the voltage optimization hierarchical control and power coordinated control strategy is carried out. Finally, the results verify the feasibility and effectiveness of the proposed control strategy.