OSTI OAI (U.S. Department of Energy Office of Scientific and Technical Information), Dec 12, 2022
Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents... more Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.
Power System Network Reduction for Power Hardware-in-the-Loop Simulation
2021 IEEE Kansas Power and Energy Conference (KPEC), 2021
This paper proposes single-port equivalent and two-port equivalent network reduction methods to r... more This paper proposes single-port equivalent and two-port equivalent network reduction methods to respectively reduce single-port and two-port areas in a large power network. Parameters of the reduced systems are rigorously derived, which guarantees that the electrical quantities at the port(s) remain unchanged over the reduction, including voltage magnitude and phase and active and reactive power injections into the area to be reduced. The proposed techniques are applied to reduce a practical Maui grid, where the total numbers of buses, lines and transformers are respectively reduced from 212, 106 and 108 to 45, 30 and 13. Dynamic behaviors between the full model and the reduced model are compared in detail to illustrate the efficacy and accuracy of the proposed network reduction.
2016 IEEE Energy Conversion Congress and Exposition (ECCE), 2016
The total inertia stored in all rotating masses (synchronous generators, induction motors, etc.) ... more The total inertia stored in all rotating masses (synchronous generators, induction motors, etc.) connected to a power system grid is an essential force that keeps the system stable after disturbances. Power systems have been experiencing reduced inertia during the past few decades [1]. This trend will continue as the level of renewable generation (e.g., wind and solar) increases. Wind power plants (WPPs) and other renewable power plants with power electronic interfaces are capable of delivering frequency response (both droop and/or inertial response) by a control action; thus, the reduction in available online inertia can be compensated by designing the plant control to include frequency response. The source of energy to be delivered as inertial response is determined by the type of generation (wind, photovoltaic, concentrating solar power, etc.) and the control strategy chosen. The importance of providing ancillary services to ensure frequency control within a power system is evidenced from many recent publications with different perspectives (manufacturer, system operator, regulator, etc.) [2]-[6]. This paper is intended to provide operators with a method for the real-time assessment of the available inertia of a WPP. This is critical to managing power system stability and the reserve margin. In many states, modern WPPs are required to provide ancillary services (e.g., frequency regulation via governor response and inertial response) to the grid. This paper describes the method of estimating the available inertia and the profile of the forecasted response from a WPP.
2020 Clemson University Power Systems Conference (PSC)
Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents... more Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.
Hawaiian Electric Advanced Inverter Test Plan - Result Summary
This presentation is intended to share the results of lab testing of five PV inverters with the H... more This presentation is intended to share the results of lab testing of five PV inverters with the Hawaiian Electric Companies and other stakeholders and interested parties. The tests included baseline testing of advanced inverter grid support functions, as well as distribution circuit-level tests to examine the impact of the PV inverters on simulated distribution feeders using power hardware-in-the-loop (PHIL) techniques. hardware-in-the-loop (PHIL) techniques.
This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.n... more This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. U.S. Department of Energy (DOE) reports produced after 1991 and a growing number of pre-1991 documents are available free via www.OSTI.gov.
IEEE Journal of Emerging and Selected Topics in Power Electronics, 2017
As deployment of power electronic coupled generation such as photovoltaic (PV) systems increases,... more As deployment of power electronic coupled generation such as photovoltaic (PV) systems increases, grid operators have shown increasing interest in calling on inverter-coupled generation to help mitigate frequency contingency events by rapidly surging active power into the grid. When responding to contingency events, the faster the active power is provided, the more effective it may be for arresting the frequency event. This paper proposes a predictive PV inverter control method for very fast and accurate control of active power. This rapid active power control method will increase the effectiveness of various higherlevel controls designed to mitigate grid frequency contingency events, including fast power-frequency droop, inertia emulation, and fast frequency response, without the need for energy storage. The rapid active power control method, coupled with a maximum power point estimation method, is implemented in a prototype PV inverter connected to a PV array. The prototype inverter's response to various frequency events is experimentally confirmed to be fast (beginning within 2 line cycles and completing within 4.5 line cycles of a severe test event) and accurate (below 2% steady-state error).
2016 IEEE Energy Conversion Congress and Exposition (ECCE), 2016
Wind power plants and other renewable power plants with power electronic interfaces are capable o... more Wind power plants and other renewable power plants with power electronic interfaces are capable of delivering frequency response (both governor and/or inertial response) to the grid by a control action; thus, the reduction of available online inertia as conventional power plants are retired can be compensated by designing renewable power plant controls to include frequency response. The source of energy to be delivered as inertial response is determined by the type of generation and control strategy chosen. The cost of energy storage is expected to drop over time, and global research activities on energy storage are very active, funded both by the private industry and governments. Different industry sectors (e.g., transportation, energy) are the major drivers of the recent storage research and development. This work investigates the opportunities and capabilities of deploying energy storage in renewable power plants. In particular, we focus on wind power plants with doubly-fed induction generators, or Type 3 wind turbine generator (WTGs). We find that the total output power of a system with Type 3 WTGs with energy storage can deliver a power boost during inertial response that is up to 45% higher than one without energy storage without affecting the torque limit, thus enabling an effective delivery of ancillary services to the grid.
Ground Fault Overvoltage with Inverter-Interfaced Distributed Energy Resources
IEEE Transactions on Power Delivery, 2017
Ground fault overvoltage can occur in situations in which a four-wire distribution circuit is ene... more Ground fault overvoltage can occur in situations in which a four-wire distribution circuit is energized by an ungrounded voltage source during a single-phase-to-ground fault. The phenomenon is well documented with ungrounded synchronous machines, but there is considerable discussion about whether inverters cause this phenomenon and, consequently, whether inverters require effective grounding. This paper examines the overvoltages that can be supported by inverters during single-phase-to ground faults via theory, simulation, and experiment. It identifies the relevant physical mechanisms, quantifies expected levels of overvoltage, and makes recommendations for optimal mitigation. It concludes that under many circumstances, effective grounding of inverters is not necessary to prevent ground fault overvoltage.
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Papers by Andy Hoke