Design, Control, and Test of Emerging Grid-connected Converters Considering Grid Requirements

Power electronics plays a significant and non-substitutable role in the power system's ongoing revolution from the traditional centralized model to a decentralized system. However, many challenges need to be addressed, and this dissertation aims at addressing some of the challenges in power electronics-based grid applications.

To systematically evaluate the benefits of using medium voltage (MV) silicone carbide (SiC) devices in grid applications, benchmark design comparisons are conducted considering different grid applications, voltage levels, and power ratings.

The impact of grid requirements on MV SiC-based grid-connected converters is evaluated in a 13.8 kV/ 1 MW grid-connected converter design. Then, a 13.8 kV / 100 kW grid-connected converter prototype is designed and developed following the same design consideration. The converter performances and grid-side functions are tested with the designed MV test platform. An insulation structure is proposed for the MV filter inductor, which helps to shrink the overall inductor size and still maintain the grid insulation requirements. The grounding and parasitic capacitance impact on the MV device dynamic characterization and the converter power loss are analyzed. Approaches are proposed to reduce the power loss introduced by the parasitic capacitance loss of the MV transformer and the MV inductor.

To test the electrical performance of the flexible combined heat and power (CHP) system and the controller, a power electronics-based test platform is designed and developed. Different grid conditions, system mode transitions, system central controller, and the system performance during both the steady state and transients are tested.

To improve the low overcurrent capability of inverter-based resources (IBRs) and solve the corresponding issues, a grid strengthening IBR, combining an IBR and a co-located synchronous condenser, and its control are proposed. The proposed setup can provide comparable overcurrent capability as a synchronous generator, which is verified in the steady-state operation, single-unit operation considering different grid fault conditions, multi-unit operation, and transient stability performance. Also, it is concluded that the proposed setup does not have the transient stability issue.