Resilient Power Systems Inc. — Department of Energy SBIR Phase I: 16d

Description

Presently, most renewable installations are treated as a convenience, not as a critical resource. But as dependency on renewables increases, these resources become critical and the need for them to continue operating during harsh grid and weather-related conditions is crucial. The current commercial practice is to use 3-phase low voltage power converters and step-up transformers for connection to distribution grid. As solar farms installations have increased, utilities have witnessed an increase in distribution line problems. The cause of these problems is largely due to the large number of step-up transformers and low voltage converter output filters. The step-up transformers require large inrush current during energization hence when the solar converters trip-off during harsh weather or fault events, reconnecting the installation to grid must be managed carefully and often requires expensive coordination and cause lost revenue. The low voltage converter output filters contribute to troublesome instability in the grid during fault events. NERC and IEEE standards require grid tie medium voltage equipment to withstand 2X rated voltage. To remove obstacles for high penetration of solar energy into nation’s grid, solar converters capable of connecting directly to medium voltage feeders with large overvoltage capability and no passive filters that can withstand harsh weather-related events (i.e., hurricanes, floods, lightnings) have become a necessity and not an option. To address the above issues, a rugged, modular, scalable up to 34.5kV low-cost multi-port converter with isolated high frequency transformer that eliminates the troublesome step-up transformer and output filter with 2X withstand voltage rating and no-inrush current is proposed. The proposed technology not only survives normal power line conditions but continues to operate satisfactory in harsh electrical and weather events. The proposed technology uses heavy duty weatherproof enclosure that can withstand up to 2 feet of flood water without shutting down. Besides, the proposed technology will have 250% overload capacity for one second that can be used to supply reactive fault current during short circuit to reduce voltage dips to prevent other grid equipment to trip. The converter will integrate efficient electrical energy storage through an isolated dc port which provides flexibility for different batteries (or hydrogen electrolysis) without interfering with the reliability or performance of the solar production. Besides, it provides an isolated port for local loads. Not only this converter increases system efficiency and eliminates power line problems and provide reactive volt-ampere compensation, but it also costs less than a low voltage solar converter + storage converter + output filter + step-up transformer. During Phase I, team will: (1) develop control algorithms and feedback systems for zero voltage switching in multi-level converter; (2) characterizing of nanocrystalline magnetic materials and developing closed form loss calculation model for high frequency transformer and optimization of the design; (3) build simulation models and perform analysis for weather- related transient events including evaluating impact of lightning, low and high voltage and fault ride-through, grid-forming and islanding functionalities; (4) developing smart inverter functionalities specified in IEEE 1547-2018. These functions include reactive power and voltage support, monitoring and control, scheduling, bulk system reliability and frequency support, and other advanced distributed functions. (5) carrying out commercialization feasibility study including cost analysis versus performance. The proposed technology will reduce the cost of solar energy production and will remove obstacles for high penetration of solar energy into nation’s grid. During Phase II and III, team plan to build pilot-scale prototype and perform validations under laboratory conditions as well as to demonstrate and validate the actual system performance in the field and develop manufacturing and testing plans.