﻿ 特高压直流故障对新能源送端电网暂态过电压作用机理

特高压直流故障对新能源送端电网暂态过电压作用机理Mechanism of UHVDC Fault on Transient Overvoltage of New Energy Grid

Abstract: With the continuous increase in the scale of new energy access to the power grid, UHVDC transmission becomes an important way to absorb it. Meanwhile, UHVDC faults causing transient overvoltage in the power grid of new energy delivery directly threaten the safe operation of new energy, which has become an urgent problem to be solved at present. Therefore, based on the background of Qishao UHVDC power supply network, this paper analyzes the mechanism of UHVDC fault on the transient overvoltage of new energy power supply network, and puts forward the control strategy for the transient overvoltage. Firstly, the equivalent model of new energy through DC is established. Secondly, the mechanism of UHVDC fault on transient overvoltage of power grid is analyzed. Based on this, the control strategy of transient overvoltage of power grid of new energy is proposed. Finally, the effectiveness of the control strategy is verified by simulation of Qishao UHVDC power grid.

1. 引言

2. 新能源经直流外送等效模型

Figure 1. Equivalent model of new energy DC outgoing terminal

$\left\{\begin{array}{l}{P}_{L1}={P}_{W}\\ {Q}_{L1}={Q}_{W}-{Q}_{l1}\end{array}$ (1)

${Q}_{l1}=\frac{{P}_{L1}^{2}+{Q}_{L1}^{2}}{{U}_{D}^{2}}{X}_{L1}$ (2)

$\left\{\begin{array}{l}{P}_{L2}={P}_{L1}-{P}_{D}\\ {Q}_{L2}={Q}_{W}-{Q}_{D}-\left({Q}_{l1}+{Q}_{l2}\right)+{Q}_{f}={Q}_{W}-\left({Q}_{l1}+{Q}_{l2}\right)\end{array}$ (3)

${Q}_{l2}=\frac{{P}_{L2}^{2}+{Q}_{L2}^{2}}{{U}_{S}^{2}}{X}_{L2}$ (4)

$\left\{\begin{array}{l}{P}_{L1}^{f}={P}_{L1}+\Delta {P}_{W}^{f}\\ {Q}_{L1}^{f}={Q}_{L1}+\Delta {Q}_{W}^{f}-\Delta {Q}_{l1}^{f}\\ {P}_{L2}^{f}={P}_{L2}+\Delta {P}_{W}^{f}-\Delta {P}_{D}^{f}\\ {Q}_{L2}^{f}={Q}_{L2}+\Delta {Q}_{W}^{f}+\left({Q}_{f}-\Delta {Q}_{D}^{f}\right)-\left(\Delta {Q}_{l1}^{f}+\Delta {Q}_{l2}^{f}\right)\end{array}$ (5)

Figure 2. Voltage vector diagram during failure

$\left\{\begin{array}{l}\Delta {U}_{S}^{f}=\frac{{Q}_{L2}^{f}{X}_{L2}}{{U}_{S}}\\ \delta {U}_{S}^{f}=\frac{{P}_{L2}^{f}{X}_{L2}}{{U}_{S}}\\ {U}_{D}^{f}=\sqrt{{\left({U}_{S}+\Delta {U}_{S}^{f}\right)}^{2}+{\left(\delta {U}_{S}^{f}\right)}^{2}}\end{array}$ (6)

$\left\{\begin{array}{l}\Delta {U}_{D}^{f}=\frac{{Q}_{L1}^{f}{X}_{L1}}{{U}_{D}^{f}}\\ \delta {U}_{D}^{f}=\frac{{P}_{L1}^{f}{X}_{L1}}{{U}_{D}^{f}}\\ {U}_{W}^{f}=\sqrt{{\left({U}_{D}^{f}+\Delta {U}_{D}^{f}\right)}^{2}+{\left(\delta {U}_{D}^{f}\right)}^{2}}\end{array}$ (7)

3. 特高压直流故障对送端电网暂态过电压的作用机理

3.1. 特高压直流换相失败/闭锁对送端电网暂态过电压作用机理

Figure 3. AC bus voltage of rectifier station

Figure 4. AC bus voltage of wind farm

3.1.1. 直流换相失败

3.1.2. 直流闭锁

3.1.3. 整流站出口近区短路

3.2. 造成暂态过电压的主要因素

Figure 5. Active and reactive power output of the doubly-fed fan at the feed end of the rectifier station

$\Delta {Q}_{W}=1.5\left(0.9-{U}_{W}^{f}\right){Q}_{WN}$ (8)

${Q}_{f}={\lambda }_{D}{P}_{D}$ (9)

4. 新能源直流送端电网暂态过电压控制策略

4.1. 整流站调相机控制策略

${Q}_{ref}={Q}_{f}-\underset{i=1}{\overset{N}{\sum }}{n}_{i}{Q}_{fli}$ (11)

Figure 6. Reactive power coordination control strategy with the camera in rectifier station

4.2. 风电场SVC控制策略

5. 实例仿真验证

5.1. 仿真背景

Figure 7. Topological diagram of Qishao DC wind power plant

5.2. 暂态电压分布式控制策略仿真验证

Figure 8. AC bus voltage of commutation failure rectifier station under different control strategies

Figure 9. Bus voltage of Qiaowan wind power plant due to failure of commutation with different control strategies

Figure 10. Commutation failure of different control strategies dry busbar voltage in north wind power plant

6. 结论

1) 直流换相失败对直流送端电网近区风电场暂态压升的影响最为严重。

2) 直流换相失败时，送端暂态电压呈现先降低后升高的现象，期间风机低压穿越增加的无功出力与整流站滤波器盈余的大量无功是引起送端电网暂态过电压的主要因素。

3) 对整流站调相机和风电场SVC进行分布式控制可有效抑制直流故障引起的暂态过电压，仿真计算验证了控制策略的有效性。

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