Synchrophasor-based monitoring, control, and protection for distributed energy resources

Abstract

The proliferation of distributed energy resources (DERs) are transforming the landscape of today's electrical grid. Non-conventional DERs such as photovoltaic systems, Battery Energy Storage Systems (BESS), and wind turbines exhibit strikingly different dynamics when compared to traditional energy sources driven by synchronous generators, due to their power electronic interfaces with the grid. Thus, a modern electrical grid that utilizes these new energy resources, would require a reconfigurable, fast, accurate, and time critical monitoring, protection and control framework in order to operate harmoniously and resiliently. Synchrophasor technology and Phasor Measurement Units (PMUs) provide a unique, time-critical, accurate, reliable and standardized framework for power system measurements under these new energy resources. This thesis proposes a synchrophasor-based monitoring, management, protection, and control architecture for power systems with DERs. The usage of PMUs and synchrophasor technology is appropriate for such applications, because they provide accurately time-stamped measurements for power network management functions such as monitoring and control. This approach proposes substantial benefits as compared to conventional supervisory control and data acquisition (SCADA) systems in terms of accuracy, reliability and speed. Because, it is logistically impossible to operate and test the proposed architecture in a real-life power system, real-time hardware-in-the-loop (HIL) simulators are used to mimic the behavior of a power system, containing multiple DERs such as photovoltaic systems, BESSs, and diesel generators. During this process, different types of real-time hardware-in-the-loop (HIL) simulator hardware were explored and their performances were compared. The proposed synchrophasor-based network management and control infrastructure uses deterministic real-time embedded systems with Field Programmable Gate Arrays (FPGA) for data acquisition and timing-management, and real-time processors are utilized for networking and inter-communication purposes. To test the resiliency of the proposed architecture, additional network traffic generator hardware were connected to the communication network that houses the controller and the PMUs. Through the course of experimentation, multi-platform homogeneous real-time simulation models were developed for photovoltaic cells and Li-ion batteries. In the domains of power system protection, controller-hardware-in-the-loop (CHIL) experiments were performed to investigate whether traditional protection methods are suitable for the integration of inverter based DERs. These experiments revealed that unlike traditional plants with synchronous generators, grounding transformers are not required in order to protect inverter based DERs from ground-fault overvoltages (GFOV) under single-line-to-ground (SLG) faults. However, most utilities are still reluctant to abandon the inclusion of grounding transformers. Thus, this observation has the potential to reduce the cost for planning and implementing DER based substations significantly, if adopted by the operators. To perform all these experiments seamlessly within a real-time digital power system simulation ecosystem, a laboratory architecture featuring networking, timing and electrical functionalities was standardized and experiments were performed on it. One such key experiment featured the design and implementation of a synchrophasor synchronization gateway and controller (SSGC) hardware. This hardware has the functionalities to parse multiple synchrophasor streams in real-time, compute and monitor their respective network delays, and provide supplementary control functionalities based on the information retrieved from those synchrophasor streams. This hardware was utilized to monitor and control a microgrid (containing BESS and PV systems) running on a real-time simulator. To test the resilience of this proposed hardware, its communication network was tampered with external hardware, and its performance was analyzed under such conditions.