并联换流器高压直流输电系统控制策略

随着中国高压直流输电技术的发展,在直流工程分期建设和融冰方式运行方面,并联换流器结构受到越来越多的关注。文中详细分析了并联结构的四端直流输电系统特点,提出了整流站定直流电流控制、逆变站定直流电压控制且附加直流电流平衡控制功能的多端直流系统协调配合方式。该方式不仅最大程度地保持了双并联直流系统的相对独立性,简化了多端直流系统控制策略的设计,而且可以实现并联换流器间功率的灵活分配。由于换流器的并联和解并联是系统运行的关键技术,文中提出了详细的第二换流器解锁及第一换流器闭锁控制策略,并基于PSCAD/EMTDC搭建了四端并联直流系统的详细控制策略模型,验证了所提控制策略的有效性。

Control Strategies for HVDC Transmission System with Parallel Connection of Converters

With the development of high voltage direct current (HVDC) transmission technology in China,parallel converters are drawing ever-increasing attention to their structure. The HVDC transmission system with parallelly connected converters is particularly advantageous when the transmission is built by stages or in the de-icing operation mode. The characteristics of a 4-terminal HVDC system with parallel converters are analyzed at length. A new multi-terminal dc system coordinated mode is proposed for rectifier control of DC current and inverter control of DC voltage. And an additional special DC balancing control function is applied to avoid an unambiguous operating DC voltage. This coordinated mode has not only retained the relative independence of the bi-parallelly connected DC system as best it can, but also it has simplified the control system design for the 4-terminal HVDC transmission. In addition, it is now possible to realize flexible power allotment between parallelly connected converters. De-blocking the second valve and blocking the first valve being of special interest for parallel operation, methods of doing this are also described. Finally, a case study of 4-terminal HVDC system with parallelly connected converters has validated the control strategies using PSCAD/EMTDC. This work is supported by State Grid Corporation of China.