Rct Systems, Inc. — Department of Energy SBIR Phase II: C50-17a

Description

Statement of the Problem or Situation that is Being Addressed As of 2020, the US has over 100 MW of wind energy capacity installed into the electric grid. In Europe, wind energy accounts for more than 44% of all new power installations, representing 11% of Europe’s total electricity demand. Installations all over the world are expected to increase at an exponential rate, driving the need for higher efficiency and lower cost systems. One method to address these needs is to make ever larger electric machines that are more cost effective to manufacture and maintain. As an example of this, GE recently installed the Halidate-X wind turbine, the largest of its kind rated at 12 MW. However, this turbine system still utilizes legacy low-voltage (LV) silicon (Si) based devices for the power electronic interface between the wind turbine and the utility grid. Furthermore, galvanic isolation between these components is still realized with century old 60 Hz transformers. To truly enable significant installation potential of offshore wind energy systems, a more power dense, lightweight, and cost-effective power electronic conversion system (PCS) is required.Statement of How this Problem or Situation is Being Addressed The goal of this proposal is to develop a 6.5kV medium voltage (MV) silicon carbide (SiC) based PCS capable of interfacing to >69 kV utility grid and emerging MW scale wind turbines. To this end, RCT Systems (RCT) proposes utilizing a SiC based Power Electronic Building Block (PEBB) utilizing GE’s 6.5 kV module housing, Power-Overlay technology, and State of the Art GeneSiC 6.5 kV SiC dies. RCT proposed approach and commercial partners (GE and GeneSiC) will produce additional market competition at both the 6.5 kV module level, as well as the 6.5 kV die manufacturing, lowering overall costs to consumers and allowing for the development of a cost effect MV-based SiC PEBB. The proposed PEBB will be composed of multiple GE 6.5 kV modules configured in a full-bridge converter. This PEBB then interfaces to a 6.5 kV and 1.7 kV based zero-voltage-switching DC-DC converter that provides galvanic isolation and a regulated output voltage. These building blocks will be utilized to develop the >69 kV grid interface (series stacked CHB building blocks), for a power rating of >3 MW per phase, for a total power rating of >10 MW. The proposed converter architecture can be further scaled for varying interface grid voltages (>69 kV), wind turbine interface voltages (13.8 kV), or power levels through a scaled converter architecture. The proposed Phase II team of RCT, UA, GE Aviation, and GeneSiC provide a component- to-system collection of experts to develop the proposed PCS.What was done in Phase I Phase I developed a detailed electro-thermal model of the proposed dual-stage PCS that investigated system control algorithms, floating DC bus balancing approaches, and max SiC device switching frequency for long lifetime (25-30 yrs) and 140 deg. C max junction temperature. Additionally, 1.7 kV and 6.5 kV SiC modules were characterized, initial datasheets developed, and an LTSpice model developed, which allowedfor system level trade studies to be completed. Lastly, an IEEE manuscript was completed and accepted to the 2021 Electric Ships Technology Symposium.What is Planned for the Phase II The Phase II will build upon the models and SiC module characterization work performed in Phase I. Specifically, working with GE Aviation, the Phase II will build multiple 6.5 kV SiC modules for full characterization testing at UA, and incorporation into a Power Electronic Building Block (PEBB) at RCT. The 6.5 kV modules will be built with GeneSiC 6.5 kV SiC dies, demonstrating a 2nd source of 6.5 kV dies (Cree and GeneSiC) and 2nd source of 6.5 kV module suppliers (GE and Wolfspeed). This approach will increase market competition, and lower overall costs for the 6.5 kV SiC modules, as well as RCTs MV PCS.Commercial Applications and Other Benefits Elimination of bulky 60 Hz transformers and the simplification of power conversion system will reduce the cost and size of this critical component of offshore wind turbine systems, in turn reducing the cost and footprint of the entire system, or allowing for greater capacity in the same footprint. The use of the proposed power electronic building block will also be useful for distributed energy sources such as grid-tied energy storage systems and/or solar power systems, both of which require this type of converter to interface their generated output to the utility grid.