By applying novel designs and integrating new materials and topologies, researchers are making electricity conversion more efficient, more reliable, and less expensive. This, in turn, is enabling applications from electric vehicles to microprocessors to reduce the use of electricity and its impact on the environment. The Center for Power Electronics (CPES) is a former NSF Engineering Research Center and has 80 industry members. The Future Energy Electronics Center (FEEC) is noted for its work with the U.S. Department of Energy and inverters that achieve more than 99 percent efficiency.
Jih-Sheng (Jason) Lai
Rolando P. Burgos
Fred C. Lee
Khai D. T. Ngo
Power electronics advances are helping to improve the efficiency of photovoltaic (PV) systems. In a major effort, FEEC researchers are adopting wide bandgap semiconductor devices for a PV microinverter to fit into a panel junction box. The microinverter is slated to achieve ultrahigh efficiency, high reliability, low cost, and long life. Instead of the conventional kilohertz-range operation, the microinverter operates at the megahertz range. This reduces the size and potting materials of the passive components. Zero-voltage and zero-current operation will eliminate switching loss, and a two-stage design helps avoid the use of electrolytic capac-itors. The size and cost reductions are important for continued commercialization of PV systems.
A CPES project recently developed an all SiC-MOSFET-based 40 kW commercial-scale PV inverter capable of operating in direct-to-line or transformerless mode. The inverter is capable of achieving 99 percent efficiency thanks to the use of triangular-conduction-mode (TCM) scheme, which ensures zero-voltage-switching (ZVS) at turn-on for all semiconductors.
Due to the increasing use of cloud computing, data centers will represent 10 percent of the total worldwide electrical power consumption by 2020. The conventional AC data center power architecture has multiple stages, which cause excessive power loss in power distribution. CPES researchers are developing a SiC- and GaN-based high-frequency rectifier system that eliminates the use of a bulky 60 Hz transformer, plus several series connected power stages common in data center architecture. This will greatly reduce power conversion loss. Copper use will be reduced by 90 percent, and distribution-related conduction loss will be reduced by a factor of 10. The proposed system is expected to save more than 15 percent of data center energy consumption.
Onboard chargers for electric vehicles (EVs) typically operate at less that 94 percent efficiency and low power density using silicon devices with very low switching frequencies. ECE researchers are developing a high-voltage (11 kW) bi-directional onboard charger to achieve more than 96 percent efficiency. With the help of high frequency operation, the charger will be well-suited for manufacturing automation, reducing the overall cost.
In another project, a team is developing an extremely fast recharger for EVs. In order for recharging times to be similar to refueling times for gasoline-powered autos, the charger must be at least 400 kW. Conventional fast chargers are 50 kW, and the Tesla maximum is currently 120 kW. The CPES team is developing a novel, compact, scalable, solid state transformer-based 400 kW extremely fast charger. The project will also provide a user-friendly DC voltage interface to external renewable generation systems and an Energy Storage System.
Exploring the boundaries that new GaN devices have in terms of power handling capability, CPES has developed an ultra-low-inductance 650 V 100 A switching cell using two paralleled 650 V 25 mΩ GaN e-HEMT devices with top-side thermal metallization from GaN Systems. This LLC converter demonstrated an efficiency exceeding 98 percent and a power density of 131 W/in3 (8 kW/L).
Voltage regulators have been widely used in computing system to deliver power from energy sources, such as a battery, to microprocessors. Today’s voltage regulator is usually constructed using discrete components and assembled on the motherboard. The discrete passive components, such as inductors and capacitors, are bulky and occupy a considerable footprint on the motherboard. An ECE team is developing a 20–50 MHz three-dimensional integrated voltage regulator for mobile devices. This will have a significant impact on power management solutions for smartphones and other mobile applications. It will help make the integrated voltage regulator a feasible approach to significantly reduce mobile devices power consumption, extending battery life and reducing electricity consumption.