基于虚拟电阻的P-V下垂系数计算方法

doi:10.12204/j.issn.1000-7229.2021.04.012

摘要/Abstract

摘要：

现有研究有很多针对多端柔性直流下垂系数的计算方法,但是鲜有基于虚拟电阻的下垂系数计算方法。参考I-V下垂控制策略,提出了一种基于虚拟电阻的P-V下垂控制策略。首先,在放射型直流电网中,分析了换流站直流端口电压与公共母线电压之间的关系。通过设置虚拟电阻得出换流站桥臂电压和直流端口电压的关系,并根据P-V下垂控制策略,推导出基于虚拟电阻的P-V下垂系数计算方法。随后,分析了该下垂系数计算方法存在极限运行状态下无法计算的问题,并提出了对应的解决方法,完善了控制策略。最后,在仿真软件中搭建了一个6端放射型柔性直流电网仿真模型,分别对比例下垂控制、自适应下垂控制和基于虚拟电阻的下垂控制策略进行仿真验证。通过对比发现,提出的基于虚拟电阻的P-V下垂控制策略有直流电压偏差较小、功率分配较为合理的特点。

关键词: 直流电网, 虚拟电阻, 下垂控制, 放射型系统

Abstract:

Many studies about multi-terminal VSC systems are concentrated on calculating droop control coefficients. However, few methods have been used to obtain the coefficients applying the virtual resistance. According to the I-V droop control, a new P-V droop control method based on virtual resistance is proposed. Firstly, the relationship between the voltage on the DC side of VSC stations and the voltage of the common bus is analyzed in a radial DC system. Then, the relationship between VSC arm voltage and the DC voltage is obtained by imposing a virtual resistance. Considering the P-V droop equation, the method for calculating coefficients is given. Thereafter, the calculation limitations of the proposed method in extreme operating conditions are analyzed, and the resolvent is proposed which improves the control strategy. Finally, three types of control strategies, i.e., the ratio droop control, the adaptive droop control and the droop control based on virtual resistance, are simulated on a six-terminal radial VSC system. Simulation results show that, the proposed method has the advantages of smaller deviation of dc-side voltage and reasonable power distribution.

Key words: DC grid, virtual resistance, droop control, radial system

中图分类号:

TM734

曹昕, 韩民晓, 张明洋, 魏炜. 基于虚拟电阻的P-V下垂系数计算方法[J]. 电力建设, 2021, 42(4): 105-112.

CAO Xin, HAN Minxiao, ZHANG Mingyang, WEI Wei. A Method for Calculating P-V Droop Coefficients Based on Virtual Resistance[J]. ELECTRIC POWER CONSTRUCTION, 2021, 42(4): 105-112.

图/表 8

图1 放射型直流电网拓扑

Fig.1 Radial topology of DC system

图2 直流系统当前状态和目标状态的等效模型

Fig.2 Equivalent model of DC system under present status and target status

图3 基于虚拟电阻的P-V下垂控制

Fig.3 P-V droop control based on virtual resistance

图4 6端放射型柔性直流系统

Fig.4 6-termianl radial VSC system

表1 各换流站在仿真开始时控制策略

Table 1 Control strategy of the convertersm when simulation begins

图5 三种下垂系数下的逆变站有功功率

Fig.5 Active power of the inverters based on three kinds of droop control coefficients

图6 三种下垂系数下VSC4和VSC6的直流电压

Fig.6 DC-side voltage of VSC4 and VSC6 based on three kinds of droop control coefficients

图7 VSC4和VSC6的下垂系数

Fig.7 Droop control coefficients of VSC4 and VSC6

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