Advanced HVDC Converter Applications in the Modern Power Grid

高压直流输电正变得越来越重要。发电机通常是交流发电机，大多数负载也是交流发电机。高压直流输电系统通过将交流电压转换为直流电压，然后再转换回交流电压，将这些电压连接在一起。与交流输电相比，高压直流输电降低了损耗，不要求发送端和接收端交流网络同步。因此，它被视为将可再生能源从偏远地区(如偏远的风电场)输送到遥远的负荷中心的首选方式。**传统上，线路换向转换器(LCC)一直是唯一一种能够处理大功率额定功率的AC-DC转换设备。它的缺点是在失真或欠电压条件下工作不佳。然而，另外两种类型的变流器--电压源变流器(VSC)和电容换向变流器(CCC)--最近被引入，它们不容易受到这个问题的影响。随着高压直流输电在电网中的普及，不同类型的高压直流输电换流站(如LCC、VSC等)的可能性越来越大。将在很近的地方终止，并相互干扰。由此产生的系统被称为多馈入高压直流系统。利用先进的计算机模拟工具，我打算研究这种转换器间相互作用对各种网络参数的敏感性，以期建立转换器放置的指导原则。我和我的团队希望开发出改进的控制算法，将这种互动降至最低。我们研究的另一个目标是开发技术来估计VSC转换器的损耗，以确定使损耗最小化的操作条件。**这项研究的重要成果将是为多馈入高压直流系统和直流电网开发研究方法、建模工具和改进设计。这将有望产生更强大的电力传输方案，能够安全、高效和可靠地运行。

High Voltage Direct Current (HVDC) transmission is growing in importance. Power generators are usually ac (alternating current) generators, and most loads are also ac. The HVDC transmission system connects these together by transforming the ac voltage to dc and then back to ac. In comparison with ac transmission, HVDC has reduced losses and does not require the sending and receiving end ac networks to be synchronized. Consequently it is seen as a preferred means to transport renewable energy from remote locations such as remote wind farms, to distant load centres. **Conventionally, the Line Commutated Converter (LCC) has been the only type of ac-dc converting equipment to handle large power ratings. Its drawback is that it works poorly under distortion or under-voltage conditions. However, two other types of converter, the Voltage Sourced Converter (VSC) and the Capacitor Commutated Converter (CCC) have recently been introduced and are not susceptible to this problem. As HVDC penetration in the network grows, it is more and more likely that HVDC converters of different types (i.e. LCC, VSC, etc.) will terminate in close proximity and interfere adversely with each other. The resulting system is referred to as a multi-infeed HVDC system. Using advanced computer simulation tools, I intend to investigate the sensitivity of such inter-converter interactions to various network parameters, with a view to establishing guidelines for converter placement. My team and I hope to develop improved control algorithms that would minimize such interaction. Another objective of our research is to develop techniques to estimate the losses in VSC converters, with a view to determining the operating conditions under which these are minimized. **The significant outcome of this research will be the development of study methods, modelling tools and improved designs for multi-infeed HVDC systems and dc grids. This will hopefully result in more robust power transmission schemes that can operate securely, efficiently and reliably.**********