A Framework for Future Power Systems

在世界范围内，发电主要通过使用传统涡轮发电机(TG)机组的传统发电厂进行。与化石燃料发电厂相关的环境问题和温室气体排放，以及对电力能源的持续需求增加，表明可再生能源在电网中的渗透率不断增加，例如风能和太阳能光伏发电厂。在未来，即使是大多数传统的基于化石燃料的TG发电机组也将被可再生能源取代，因为它们的寿命即将结束。因此，可再生能源的渗透深度将不可避免地不断增加，最终电网将接近甚至100%由可再生能源供电。与直接并网的传统发电机组不同，可再生发电机组的共同特点是它们是变流器接口(CI)机组，即通过电子变流器连接到电网。此外，电网中的许多其他子系统和设备，例如高压直流(HVDC)换流站、储能单元和无功补偿器，也是CI单元。因此，从长远来看，电网中CI机组处理的电力与TG机组产生的电力的比率将大幅增加，因此电网的运行、控制和保护要求将由CI机组决定。这一趋势使得现有的传统电网的运行、控制和保护策略发生了重大变化，这些策略是在过去几十年中根据TG机组的特点而开发的，因此既不能最好地利用CI机组的特点，也不能保证CI机组高渗透率下未来电网的稳定性和安全性。这些关切虽然得到了利益攸关方的承认，但既没有得到充分的了解、调查，也没有得到充分的阐述，因此没有制定系统的解决办法和补救措施。遗留电网的资产是在过去几十年里开发出来的，价值数十亿美元。因此，根据传播和信息单位的特点，不能拆除现有的网格并用新的网格取而代之。因此，需要制定操作、控制和保护策略，以随着CI单位渗透率的增加而动态适应和适应传统网格的不断发展。本次拨款申请的研发重点是未来电网的系统级控制。研究的目标是：i)开发用于分析和离线/实时仿真工具的模型，以调查和揭示未来电网动态现象的本质；ii)开发能够适应不断变化的电网复杂性并系统地解决稳定性问题的控制策略；以及iii)随着CI单元渗透率的增加，使电网的资产利用率达到最佳。

Worldwide, electrical power generation is predominantly through legacy power plants that use conventional turbine-generator (TG) units. The environmental issues and green-house gas emissions associated with the fossil-fueled power plants and the ongoing increase in  demand for the electrical energy indicate continuous increase in the penetration of renewables, e.g., wind and solar-PV power plants, in the power grid. In the future, even most of the legacy fossil-fuel TG-based generation units will be replaced by renewables as they approach the end of their life-spans. Thus, inevitably the penetration-depth of renewables will gradually and continuously increase and eventually the grid will be supplied close to or even at 100% by renewables. In contrast to the conventional TG units which are directly connected to the grid, the common characteristic of renewable generation units is that they are converter-interfaced (CI) units, i.e., connected to the grid by electronic converters. Furthermore, many other subsystems and apparatus within the grid, e.g., high-voltage direct-current (HVDC) converter stations, energy storage units, and reactive power compensators, are also CI units. Thus, in the long run, the ratio of electric power handled by CI units to the power generated by TG units in a grid will substantially increase and consequently the operation, control and protection requirements of the grid will be dictated by the CI units. This trend entails a major departure from the current operation, control, and protection strategies of the existing legacy grid which have been developed within the past several decades based on the characteristics of TG units, and therefore can neither best utilize the features of CI units, guarantee stability, nor security of the future grid under high penetration of CI units. These concerns although acknowledged by stakeholders, have been neither fully understood, investigated, nor formulated, and thus no systematic solutions and remedial measures have been developed. The legacy grid's asset which has been developed in the past several decades is worth billions of dollars. Thus the existing grid cannot be dismantled and replaced by a new grid based on the characteristics of CI units. Therefore, there is a need to develop operation, control, and protection strategies to dynamically accommodate and adapt to the continuous evolution of the legacy grid as the penetration of CI units increases. The R&D focus of this grant application is on the system-level controls of the future grid. The research objectives are to i) develop models for analytical and off-line/real-time simulation tools to investigate and reveal the nature of the dynamic phenomena of the future grid, ii) develop control strategies that can adapt to the evolving grid complexities and systematically address stability issues, and iii) enable best asset utilization of the grid as the penetration of CI units increases.