Research On Problems Of STATCOM To Improve Voltage Stability Of Wind Farms

The development and utilization of renewable energy become imminent whenthe environment of China deteriorates gradually along with the development ofnational economy. Wind energy is rapidly expanding as one of the most maturetechnology in the renewable energy field. Because of the characteristic of randomnessand intermittence, wind farm will influence the voltage stability of the power systemwhen it is connected to the power system extensively. Wind farm is generallyconnected to the power system at the weak point. Therefore, the insufficient reactivepower may affect the voltage stability of power grid, even cause the voltage tocollapse. Static synchronous compensator (STATCOM) can dynamically add theinductive or capacitive reactive power to the grid, which will rapidly suppress thevoltage disturbance. So, it is very suitable for the wind farm reactive powercompensation. However, the problems about the control strategy, the main circuitmodulation technology, the location and the capacity optimization of STATCOM inwind power system need further in-depth study.The traditional control strategy is difficult to quickly and accurately suppressthe wind farm voltage fluctuation due to the strong coupling of inverter, the core ofSTATCOM. The linear automatic rejection control (LADRC) is applied to the currentdecoupling of d、q axis of the inverter in the paper. The method has the better rapidityand robustness than the PI control does and the parameterized method is used todetermine the parameters for the controller, which can simplified the control systemand convenient for the practical engineering application.According to the characteristics of the micro grid system including wind power,the different points with ordinary wind power system are analyzed theoretically. Thepaper points out that the voltage fluctuation is easily affected by the active powerfluctuation in this power system. A new control strategy based on STATCOM/SMESsystem is designed. The EXPMA is used to produce the active power commandsignals and improve the voltage stability of wind power system on the basis ofLADRC decoupling control.In order to solve the harmonics generated by the power electronic devices, anew chaos sequence based on Chebyshev chaotic sequence and infinite chaoticsequence is built. On the basis of this new method, a new RFPWM modulation strategy is proposed to improve running performance and reduce the harmonic contentand electromagnetic noise.In the study of three problems above, an optimization method of location andcapacity of STATCOM based on particle swarm optimization (PSO) and continuouspower flow (CPF) is designed for the economic problems. Considering the multipleSTATCOM investment, a new objective function is proposed which takes the nodeload parameters, the capacity, and the voltage level as the indexes. The results provethat the method can reduce the investment and improve other indicators of the system.For the voltage stability control of wind power system, the development of thecompensation equipment modulation technology, the optimization of multiple reactivepower compensation equipments, as well as the development of wind power, theresearch have theoretical significance and practical value.