提升多直流馈入系统中高压直流交流故障支撑能力的基础理论与关键技术

AC fault support capability of HVDC (High voltage direct current) have significant influence on the safe operation of system with multiple DC infeed, and there are some problems in HVDC in the case of AC fault, such as poor controllability of commutation, active and reactive power, and uncontrollability of harmonics. The basic theories and key technologies related to HVDC controllability in the case of AC fault, such as synchronous phase locked loop and phase control of converter, commutation failure, harmonic active suppression, active power transfer capability, and reactive power quantitative control in AC fault recovery process, will be studied in this project considering HVDC self-performance and space-time characteristic of system with multiple DC infeed. Firstly, the time domain model and frequency domain model for HVDC considering asymmetrical AC voltage will be built, and the operating range and control stability of converter under various working conditions will be analyzed. Then, the tests will be carried out by the CIGRE Benchmark Model and practical engineering model for HVDC respectively in PSCAD/EMTDC. Finally, the results will be compared with the field cases on the test platform composed of actual HVDC control protection devices and RTDS (Real-Time Digital Simulator). After the success of the project, the continuous commutation failure during AC faults in the HVDC multi-infeed system can be avoided, the active power transmission capacity during AC fault can be enhanced, the decoupling and quantitative control can be realized for active and reactive power during AC fault recovery, and the AC fault support capability of HVDC will be significantly promoted. The key outputs will provide the core technical support for the safe operation of the huge AC/DC hybrid power system in China.

高压直流的交流故障支撑能力对多直流馈入系统安全运行有重要影响，现有直流在交流故障时存在换相失败、有功和无功可控性差，谐波不可控等问题。本项目从直流自身可控性和多直流馈入系统时空特性对交流故障时直流的控制能力进行研究，包括：交流故障时电压锁相和换流器触发相位控制、换相失败控制、交直流侧谐波主动控制、直流有功输送能力提升、故障恢复过程中有功无功解耦和无功定量控制。首先建立包括交流电压不对称的直流时域和频域模型，对各工况下换流器的运行范围和控制稳定性进行理论分析，进而在PSCAD/EMTDC中利用直流CIGRE标准模型和工程模型进行测试，最后在实际控制保护设备和实时数字仿真器组成的测试平台中与现场案例进行对比。研究成果能够在交流故障时避免直流发生连续换相失败，增强有功输送能力，实现故障恢复过程中无功定量控制，提升交流故障时直流对电网稳定的支撑能力，为我国交直流混联电网安全运行提供核心技术支撑。

高压直流在交流故障过程中支撑能力对多直流馈入系统安全运行有非常重要的影响，现有高压直流在交流故障时存在换相失败可控性差、有功可控性差、无功可控性差、谐波不可控等问题。本项目对交流故障时高压直流的可控性和可控能力开展了研究，研究内容包括：交流故障期间换流器触发相位控制、换相失败控制、交直流侧谐波抑制、交流故障持续期间有功输送能力、交流故障恢复过程无功功率控制等。主要研究成果包括：1）提出一种可减小动态偏差和缩短响应时间的新型锁相环；2）提出一种可减小首次换相失败概率的控制方法；3）提出一种能够有效降低后续换相失败概率的新型分相同步触发控制； 4）提出一种适用于换流器不对称运行条件的开关函数模型；5）提出一种高压直流控制器参数优化整定方法；6）提出一种基于换流站定无功控制的VDCOL替代方法；7）提出一种基于换相电压相位检测的交流故障恢复策略。上述研究成果可有效降低多直流馈入系统中交流故障引起的高压直流发生换相失败的概率，增强交流故障持续期间高压直流系统的有功输送能力，实现故障恢复过程中换流器有功和无功的解耦控制，提升高压直流对交流故障的支撑能力，为我国交直流混联电网的安全运行提供技术支撑。