特高压直流输电系统直流闭锁故障及交流系统短路故障引起的暂态过电压,对系统稳定性造成严重冲击.量化评估交直流系统暂态性能指标,对确定交直流电力系统规划设计和调度运行具有指导意义.对交流系统暂态过电压机理进行分析,推导出基于无功补偿和短路比的暂态过电压计算方法,基于系统短路比与补偿电容和交流滤波器参数的比值定义了暂态电压评估指标Rr.研究表明,随着该暂态电压评估指标Rr减小,系统故障后送端换流母线暂态电压升高,受端也会发生不同程度的换相失败.最后,基于国际大电网会议直流标准测试系统,验证了所提指标的有效性.

With the increasing penetration of wind power, wind turbine is required to have fault ride through capability during grid fault. To improve the direct current (DC) voltage suppression effect of traditional high voltage ride through (HVRT) control scheme with regard to chopper resistance, this paper proposes an HVRT control strategy based on dynamic chopper resistance calculation method considering surplus active power, DC voltage limit and reactive current. The simulation results show that the proposed strategy can suppress the DC voltage increment more effectively and avoid the trip-off accident of wind turbines by dynamically adjusting the chopper resistance for the duration of high-voltage fault.

During the recovery process of commutation failure, the current command repeatedly enters and exits the voltage dependent current order limiter (VDCOL) control because of the interaction between the DC regulation speed and the AC voltage recovery rate, causing the DC power to oscillate continuously. Concerning this problem, a transient stability analysis method of VDCOL control based on energy variation rate is proposed. Firstly, the paper analyzes the VDCOL control during the recovery process of commutation failure and constructs the voltage recovery equation of the receiving-end power grid. Secondly, according to the model of receiving-end power grid and voltage recovery equation, the energy function is established, and the transient stability of the system during the recovery process of commutation failure is revealed based on the analysis of energy variation rate of DC terminal (in VDCOL control) and other components. Finally, the transient energy trend of the receiving-end power grid is analyzed by building a commutation failure and recovery simulation, and the simulation results illustrate the effectiveness of the proposed transient stability analysis method.

The commutation failure of high voltage direct current (HVDC) systems could lead to unstable operation of the alternating current/direct current (AC/DC) hybrid power grid. The commutation voltage distortion caused by harmonics is a considerable but unclear factor of commutation failure. According to the control switching process of HVDC systems, the commutation voltage-time area method is employed to analyze and reveal the influence mechanism of harmonic components of commutation voltage on first and subsequent commutation failures. Considering the distortion characteristics of AC voltage, a predictive commutation failure suppression strategy considering multiple harmonics of commutation voltage is proposed. In this strategy, the new extinction angle and the zero-crossing offset angle after voltage distortion are calculated considering the harmonic components so as to obtain the compensation margin of the lag trigger angle by combining the correction margin with the voltage change rate. Moreover, the tuning method of parameters of extinction angle and voltage prediction variables are provided. Finally, a case study based on CIGRE standard HVDC system is performed and analyzed by using power systems computer-aided design (PSCAD) software. Compared with the International Council on Large Electric systems (CIGRE) standard test model and traditional commutation failure prevention (CFPREV) control model, the results verify that the proposed strategy can effectively reduce the risk of first and subsequent commutation failures and improve the sensitivity of CFPREV control.