Optimization Of Voltage Droop Control Parameters In MTDC System

In recent years, there has been an increased development of renewable energy resources to meet the ever increasing electric power demand and to reduce the environmental pollution caused by fossil fuels. Considering the environmental aspects, offshore wind power has become the most desired energy resources because of it is abundant in nature. Both from a technical and economic point of view, voltage source converter(MTDC system) based multi-terminal DC system provides the best solution to collect wind energy and transport it from the offshore to the demand center. However, the safety and economic aspects for MTDC system has not yet to be researched, and therefore it is systematically studied in this paper.Firstly, a novel reference voltage optimization method based on droop methodology is proposed for MTDC system. At the beginning, the voltage droop principle was analyzed based on the relationship between DC voltage and the active power output. Later, the constraint equations concerning the DC power flow as well as their control strategy are deduced. Then, a reference voltage optimization model in the droop control strategy was established, and later was solved using Lagrange rules. The efficiency and effectiveness of the proposed model have been verified via an experiment. The results demonstrate that the dynamic response of the reference voltage has been optimized and the power loss in the system has been minimized.Secondly, a brand new optimization method the slope parameter in droop control strategy is proposed. Based on the detailed analysis concerning control principle from the power grid perspective, a novel self-adaptive droop control methodology was presented. On the basis of that, a new optimization model for the slope parameter has been proposed as to better solve the overload problem existing in the convertor stations. In addition, the corresponding dynamic response for the slope parameters has been analyzed. The finished experiment proves that the proposed optimized model for the slope parameters can better allocate the system power to avoid the overload problems for the convertor stations. The overload problem was raised by the conventional droop control strategy and existed very often in real-life’s world.The model of the experiments in this paper has been established based on PSCAD/EMTDC. The voltage signal for the MTDC system has been optimized using the proposed reference voltage optimization method. Meanwhile, the slope of the droop control strategy has also been optimized using the proposed slope optimization method. The results for the proposed method have been compared to the resulted obtained from the conventional droop method. It is demonstrated that the effectiveness and efficiency of the proposed method has been improved a lot.Due to the fact that the security and system operation efficiency have strong associated with the slope parameters in droop control strategy, the proposed voltage optimization model as well as its solved optimization method can effectively reduce the system power loss, and so the efficiency of the system has been enhanced. Besides, the proposed slope optimization model and its optimization method in droop control strategy can avoid the overload problems existed in converter stations, and so the system security has been improved.