< h1 class="pgc-h-arrow-right" > team introduction</h1>
Rong Fei, born in 1978, graduated with a doctorate degree in electrical engineering, a doctoral supervisor of Hunan University, enjoys the special allowance of Chenxinggang, Yuelu Scholar of Hunan University, and his main research direction is power electronic converter technology and new energy power generation technology. In recent years, he has won 2 first prizes for scientific and technological progress at the provincial and ministerial levels; published more than 70 academic papers, including more than 40 SCI/EI articles, with a total frequency of more than 1,100 citations; 10 authorized invention patents, of which 2 have been transformed; 2 monographs and 1 translation. Reviewer of IEEE Transaction on Power Electronics, IEEE Transaction on Industrial Electronics, Renewable & Sustainable Energy Reviews, IEEE Trans on Industrial Informatics, National Natural Science Foundation of China, Project review expert of Hunan Provincial Science and Technology Department, Zhejiang Provincial Science and Technology Department, and Guangdong Provincial Science and Technology Department.
Li Peiyao: Master's degree candidate, whose research direction is optimal dispatch and operation of power systems. He has participated in projects such as the National Natural Science Foundation of China, the Natural Science Foundation of Hunan Province and the Science and Technology Project of China Southern Power Grid Co., Ltd.
<h1 class="pgc-h-arrow-right" > introduction</h1>
Based on the optimal power flow model, this paper proposes an active and reactive power coordinated control strategy suitable for doubly-fed wind farms, constructs a doubly-fed wind farm into an optimal power flow model based on the linear power flow equation, and combines the internal reactive power distribution strategy of the doubly-fed wind turbine, which can reduce the active loss generated by the doubly-fed wind turbine unit and the network loss generated by the wind farm collector line, thereby reducing the cumulative fatigue effect of converters and other equipment, and at the same time realizing the load-reducing operation of the doubly-fed wind farm and meeting the relevant guidelines for wind power grid connection.
< h1 class="pgc-h-arrow-right" > research background</h1>
With the rapid development of wind turbines in technology and structure, wind farms can provide a variety of auxiliary services for power systems while transmitting electrical energy, such as frequency, voltage support and reactive power compensation. Different from the traditional asynchronous wind turbine, the doubly-fed asynchronous induction wind turbine can transmit reactive power to the network side while realizing the reactive power decoupling control, so it has become a consensus to use DFIG's reactive power control capability in the wind farm to achieve real-time reactive power control of the wind farm.
< h1 class="pgc-h-arrow-right" > main content</h1>
The control block diagram of the active and reactive power coordination and optimization control of the doubly-fed wind farm is shown in Figure 1. Among them, the ARPCC controller is the active and reactive power coordination optimization controller in the doubly-fed wind farm, and the Pref WF and Qref WF are the reference values of the active power and reactive power that the doubly-fed wind farm should output from the power system dispatching center to the doubly-fed wind farm according to the grid demand.
After the controller receives the dispatch instruction, the measurement data of the wind farm feedback (including the current moment of the doubly-fed fan wind speed vi, the actual output of the active power PWT of the fan at the previous moment, i and the node voltage value ui) into the optimal loss target function, combined with the constraints, the secondary planning algorithm is used to calculate the objective function to obtain the required parameters of the doubly-fed fan Qs, i, Qg, i and PWT, i reference values, Qref s, i and Qref g in the figure, i are the reference value of the stator reactive power of the doubly-fed fan and the reference value of the reactive power of the network-side converter, pref WT, i is the reference value of the active power output of the doubly-fed fan at the current moment.
Figure 1 Active and reactive power coordination optimization control block diagram
In order to prove the control effect of the proposed active and reactive power coordination optimization control strategy (strategy 1), this paper builds a simulated doubly-fed wind farm with two feeders on the Matlab/Simulink simulation platform, each feeder consisting of 10×5MW DFIG wind turbines.
In addition, two optimal control strategies are used to compare with the proposed strategies, namely the coordinated optimal control strategy (strategy 2) and the proportional control strategy (strategy 3) that do not consider the loss of doubly-fed fan units.
The simulation time is set to 600s, Figure 2 is the total loss curve generated by the doubly-fed wind farm using different control strategies in the simulation platform, it can be seen that the loss value of strategy 1 proposed in this paper is always lower than that of the other two control strategies; Figure 3 is the loss reduction value of the doubly-fed wind farm adoption strategy 1 compared with the other two strategies. For example, when comparing strategy 1 and strategy 2, the total loss value of strategy 2 is subtracted from the total loss value of strategy 1 at the same time to obtain the value of the loss reduction of strategy 1.
Compared with strategy 2, the total loss value of the reduction fluctuates between 300kW and 400kW, and it can be calculated that the percentage of loss reduction ranges from 5% to 18%; compared with strategy 3, the degree of loss reduction gradually weakens after about 320s, and reaches stability around 400s, which is because at this time the wind farm changes from load reduction operation to full load operation, and the impact of active power on the loss of doubly-fed wind farms gradually increases.
As can be seen from Figure 3, when the doubly-fed wind farm is fully loaded, the use of strategy 1 can still reduce the power loss by about 200kW compared with strategy 3.
From the above simulation results, it can be seen that Strategy 1 can reduce the network loss of the wind farm and the unit loss of DFIG under different operating conditions of the wind farm, prolong the service life of the related devices, and at the same time realize the load reduction operation of the wind farm to meet the diversified needs of the wind farm operation.
Figure 2 Total loss of wind farm operating for a certain period of time using different control strategies
Figure 3 The loss reduction value of the wind farm using different strategies for a certain period of time
< h1 class="pgc-h-arrow-right" > conclusion</h1>
In this paper, a method for coordinated and coordinated optimization control of active and reactive power of doubly-fed wind farms is proposed, and the simulation results effectively prove that the method can reduce the total power loss of doubly-fed wind farms while distributing the active and reactive power of DFIG units inside the wind farm, so as to realize the load reduction operation of the wind farm and meet the operating needs of the wind farm under different conditions.
The advantages of this method are as follows:
1) This method constructs a doubly-fed wind farm into an optimal power flow model based on the linear power flow equation, and combines the reactive power optimization distribution strategy of the doubly-fed wind turbine, which can reduce the active loss generated by the doubly-fed wind turbine unit and the network loss generated by the wind farm collector line.
2) Compared with the separate control of active and reactive power, the proposed coordinated control strategy considers the influence of active and reactive power on power loss at the same time, so it can reduce the power loss of the wind farm by a larger margin, and can still reduce the power loss of the system when the load reduction is running, thereby prolonging the service life of the converter and other devices.
3) This method does not require additional equipment, it can distribute the active and reactive power of the doubly-fed wind turbine unit inside the wind farm, realize the load reduction operation of the doubly-fed wind farm, and meet the relevant guidelines for wind power grid connection.
<h1 class="pgc-h-arrow-right" > cite this article</h1>
RONG Fei, LI Peiyao, ZHOU Shijia. Coordinated and optimized control of active and reactive power for loss minimization of doubly-fed wind farms[J]. Transactions of China Electrotechnical Society, 2020, 35(3): 520-529. Rong Fei, Li Peiyao, Zhou Shijia. Coordinated Optimal Control with Loss Minimization for Active and Reactive Power of Doubly Fed Induction Generator-Based Wind Farm. Transactions of China Electrotechnical Society, 2020, 35(3): 520-529.