Project Name: Modular Wide-Bandgap String Inverters for Low-Cost Medium-Voltage Transformerless PV Systems
Funding Opportunity: Advanced Power Electronics Designs for Solar Applications
SETO Subprogram: Systems Integration
Location: Seattle, WA
SETO Award Amount: $2.9 million
Awardee Cost Share: $710,000

This project team will build a low-cost, medium-voltage photovoltaic (PV) string inverter without using step-up transformers to increase voltage. The inverter will consist of modular circuit-plus-control (C2) blocks with an integrated power converter and local controller. Together, the new circuit designs and control strategies will yield high efficiency and easier interconnection for use in next-generation commercial and utility-scale PV systems.


The team will use wide-bandgap (WBG) power electronics and distributed, decentralized controls to produce stackable, lightweight converter blocks. The bandgap is a measure of energy that signifies the distance between an electron’s starting point and the point it has to move to in order to conduct electricity. The inverter will use silicon carbide devices to enable series-connected C2 blocks to directly convert direct current (DC) to three-phase alternating current (AC) at medium voltages and multi-megawatt power levels. The team will validate the system using the National Renewable Energy Laboratory’s Controllable Grid Interface, a controllable power converter that can emulate a medium-voltage grid point of interconnection under utility- and commercial-scale voltages. The team will also present a framework for a low levelized cost of energy that paves the way for a market transition plan.


String-level photovoltaic DC inputs eliminate the need for combiner boxes and reduce the complexity of DC-side wiring. By using WBG devices, the elimination of bulky line-frequency transformers simplifies AC-side wiring. Each C2 block will be fabricated on high-voltage printed circuit boards to enable automated, low-cost, high-throughput manufacturing. The inverter’s design will lower energy costs and installation costs while increasing PV system efficiency by operating at medium voltage and eliminating low-frequency transformers.

Power Electronics – University of Washington
Illustration courtesy of the University of Washington.