基于变下垂系数的风电全直流输电系统一次调频协调控制策略

风电场经直流汇集-直流送出的风电全直流输电系统中，直流系统的存在会解耦风电场和受端电网的频率耦合，在传统控制策略下对受端电网频率支撑能力弱。为此，提出一种针对风电全直流输电系统的一次调频变下垂协调控制策略。首先，提出基于Logistic函数的电压-频率变下垂频率传递策略，以直流系统电压为媒介，建立起电网频率与风电场功率的耦合关系。基于该频率传递策略，构建了由受端换流站的变下垂虚拟同步发电机(virtual synchronous generator, VSG)控制、直流升压站的改进双闭环控制及风力发电机的变下垂减载控制组成的风电全直流输电系统一次调频协调控制策略，实现系统无通信传递频率并参与电网一次调频。最后，利用Matlab/Simulink软件搭建风电全直流输电系统仿真模型，在不同工况下进行仿真验证。仿真结果表明，所提控制策略能使风电场在不依赖远端通信的情况下实现对电网的一次调频，同时，有效减小了调频过程中直流电压的波动幅度。

Primary frequency regulation coordination control strategy of a wind power all-DC transmission system based on variable droop coefficient

In the wind power all-DC transmission system of wind farm DC collection-DC transmission, the existence of the DC system will decouple the frequency connection between the wind farm and the power grid, and the frequency support ability is weak using the traditional control strategy. Therefore, a primary frequency regulation coordinated control strategy of a wind power all-DC transmission system based on variable droop is proposed. First, a voltage-frequency variable droop frequency transfer strategy based on the Logistic function is proposed, and the coupling relationship between the power grid frequency and the wind farm power is established with the DC system voltage as the medium. Based on this strategy, a primary frequency regulation coordinated control strategy of the wind power all-DC transmission system is contructed. It consists of variable droop virtual synchronous generator (VSG) control of the receiving converter station, the improved double closed-loop control of the DC booster station and the variable droop de-loading control of the wind turbine. This can realize system frequency transmission without communication and participate in power grid primary frequency regulation. Finally, Matlab/Simulink is used to build a simulation model of the system, and simulation verification is carried out in various working conditions. The simulation results show that the proposed control strategy enables the wind farm to achieve primary frequency regulation of the power grid without relying on remote communication, and effectively reduces the fluctuation amplitude of DC voltage in the process of frequency regulation.