Research on modifying inverter controls in utility-scale renewables to emulate synchronous-generator voltages/currents under faults to retain existing protection infrastructure

为了应对气候危机，利用风能和太阳能等可再生资源发电至关重要。这些资源主要在大规模时是经济的，而且往往位于远离都市地区的地方，因此需要输电线路。在这些传输线上安装了保护继电器，以检测由照明或其他短路引起的故障，并断开故障线路。现有的保护设备是为发电厂使用煤和天然气等传统能源发电而设计的。然而，这种保护基础设施将无法与可再生能源发电中使用的现有控制方法一起工作。随着许多州选择向100%可再生能源发电迈进，所有现有的保护继电器都需要更换。这项研究的目的是通过控制基于可再生能源的发电，使其在发生故障时模仿传统发电，从而使现有的保护设备（如继电器）在发电从传统能源向可再生能源转变的过程中继续使用。这将避免招致全系统升级保护基础设施的巨额费用。所建议的方法是基于首先确定已发生的故障类型，然后采取适当的行动，使现有的继电器像在传统源的情况下一样工作。这项研究将是保持可再生能源低成本的一个非常重要的步骤，以提高它们对公用事业电网的渗透。它将在保护传输基础设施的关键领域推进知识的变革，并成为硬件设备制造商使用的规范。这项研究是在电力电子，电力系统和控制的交叉点，对下一代电力工程师将非常有教育意义。该提案的目标是找到一种解决方案，以满足增强公用事业规模可再生能源整合的现实和迫切需求。现有的公用事业规模的可再生资源逆变器，如光伏和风能，即使在不平衡故障期间也能产生平衡的三相电流。然而，通常使用的保护继电器依赖于产生的不平衡电流，例如传统发电厂的同步发电机在不平衡故障期间产生的不平衡电流。随着这种基于逆变器的资源越来越多地渗透到100%可再生能源的目标，现有的保护方案将不起作用。提出的研究是在故障期间注入适当的不平衡电流，以便继续使用现有的输电保护基础设施，而不必承担全系统升级保护基础设施的巨大成本。所提出的方法是基于首先识别已经发生的故障类型，然后注入适当的电流使继电器运行，只知道逆变器终端电压和变压器绕组配置。所提出的控制方案是基于模拟传统发电机在故障期间经过时间考验的行为，因此不需要修改现有的保护基础设施，即逆变器仅根据本地测量值运行。本研究将通过软件仿真和硬件验证来深入研究和开发控制方案。该研究还将检查这种控制对逆变器组件的影响。技术转让的目的是使控制方案成为一种规范，可以由输电系统所有者和独立电力生产商强制执行，而后者又会要求逆变器制造商强制执行。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

For combating the climate crisis, generating electricity from renewable resources, such as wind and solar, is essential. These resources are economical primarily in large scales and are often located far away from the metropolitan areas, hence need transmission lines. Protective relays are installed on these transmission lines to detect faults caused either by lighting or other short circuits, and disconnect faulted lines. The existing protection equipment is designed for electricity that is generated in power plants using conventional sources such as coal and natural gas. However, this protection infrastructure will not work with the existing control methods used in renewables-based generation. With many states opting to move towards hundred-percent generation by renewables, all existing protective relays will need to be replaced. The objective of the proposed research is to allow the existing protection equipment, such as relays, to continue to be used even as the electricity generation transitions from conventional sources to renewables, by controlling the renewable-based generation such that it emulates the conventional generation in the event of a fault. This will avoid incurring the huge cost of the system-wide upgrade of the protection infrastructure. The proposed approach is based on first determining the type of fault that has occurred and then to take appropriate action such that the existing relays perform as they do in the case of conventional sources. This research will be a very important step in keeping the cost of renewables low in order to enhance their penetration into the utility grid. It will be transformative in advancing knowledge in the critical field of protecting the transmission infrastructure and becoming a norm used by hardware equipment manufacturers. This research is at the intersection of power electronics, power systems, and controls, and will be very educational for the next generation of power engineers.The objective of this proposal is to find a solution to the real and immediate need to enhance the integration of utility-scale renewables. Existing inverters of utility-scale renewable resources, such as PVs and wind, are controlled to generate balanced three-phase currents even during unbalanced faults. However, to operate, the commonly-used protection relays depend upon unbalanced currents that are generated, such as by the synchronous generators of conventional power plants during unbalanced faults. With the increasing penetration of such inverter-based resources, toward the goal of hundred-percent renewables, the existing protection schemes will not work. The proposed research is on injecting appropriate unbalanced current during faults so that the use of the existing transmission-protection infrastructure continues, without having to incur the huge cost of the system-wide upgrade of the protection infrastructure. The proposed approach is based on first identifying the type of fault that has occurred and then to inject the appropriate currents to make the relays operate, knowing only the inverter terminal voltages and the transformer-winding configuration. The proposed control scheme is based on emulating the time-tested behavior of conventional generators during faults, thus requiring no modifications in the existing protection infrastructure, i.e., the inverters operate based solely based on local measurements. This research will thoroughly investigate and develop the control scheme by software emulation and hardware verification. The research will also examine the impact of this control on the inverter components. The aim of the technology transfer is that the control scheme becomes a norm that can be mandated by transmission-system owners and independent power producers, who in turn, would require it of inverter manufacturers.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.