Research On The Application In Wind Farm And Control Strategy Of A Novel Hybrid Controller For Power Quality And Fault Current

As the growth of the power load, the level of the grid short-circuit enhances unceasingly, which will lead to a serious impact on the normal operation of the load in power grid and power system by the short-circuit fault. How to take measures to limit the short circuit current rapidly becomes a problem to be solved as soon as possible. In addition, the power quality problem of the adjacent fault lines is increasingly highlighted, which will seriously affect the normal operation of the sensitive loads, such as computers, and also bring an immeasurable loss to the national economy. Considering the low utilization problems of fault current limiting device in the conventional methods, how to increase the utilization ratio of current limiting device and improve the system of power quality has become one of research hotspots at home and abroad. So a novel hybrid controller for power quality and fault current is proposed. Based on the analysis of its working principle, the control strategy of the system is put forward. And its application to the fault through of the squirrel-cage asynchronous machine(SCIG) of the wind farm has also been confirmed.Comparing the characteristics of various types of solid-state current limiting device, the topology structure and working mechanism of HPQFC system is proposed. After the introduction of the PWM rectifier, series voltage regulator, filter and solid-state current limiter, the working principle of the power quality management and the short circuit current limiting is analyzed. Fault detection method of HPQFC is proposed, comparing the conventional single phase detection algorithm based on the dq transform, confirming the breakdown of the voltage detection algorithm based on dq transform derivative. The judgement method of the fault current consists of the line current's instantaneous value and the current's rate and integral value. In the 10 k V power grid under different grounding systems, by analysis of the features of different types in short-circuit fault respectively, the control strategy of HPQFC is put forward in no grounding system and the arc suppression coil grounding system. The main control strategy is grid voltage feed-forward and load voltage outer loop and capacitive current double closed loop of the inner ring compound in no grounding system. Because of the arc suppression coil in the arc suppression coil grounding system, the double closed loop of compound control strategy is presented considering the saturation effect of coupling transformer and the factors such as voltage fluctuation of direct current capacity. The same fault current limiting control strategy is proposed as the similar fault transient characteristics in small current neutral grounding system.Finally, through the analysis of the transient process in the fault of the SCIG wind farms, comparing the defects of traditional fault through methods, the wind farm with HPQFC system model is established. Before the proposal of the working mode and control strategy of HPQFC system, the process of fault the fault's elimination are analyzed. The effectiveness and superiority of this method is verified by simulation.