Virginia Tech®home

Power Electronics

ECE researchers are developing a SiC- and GaN-based high-frequency rectifier system, which is expected to cut back on data center energy consumption.

Power electronics is an enabling technology for all electronic devices—from the power grid to nanoscale devices. Power electronics can enable efficient alternative energy sources, low-cost electric vehicles, lower power data centers, deep space exploration, and more. Improvements in power electronics, whether to the size, cost, or functionality of power electronics devices, can improve our environment, economy, security, and capabilities.

Highlighted Research

Data centers are costly in terms of both the money and resources they require to operate. One way ECE researchers are lowering these costs is by developing a 48 V LLC converter that achieves 98.8% efficiency with a power density of 600 W/in3. 48 V architectures can attain highly efficient power delivery, but are often large and expensive—considerations mitigated by this new converter.

Applications such as renewable energy, deep space exploration, and naval systems require smaller components than traditional medium voltage systems. These systems require medium voltage power conversion capable of high voltage and high density—which is not possible with conventional silicon technology. Our researchers are addressing this need with innovative 10 kV silicon-carbide (SiC) MOSFET packages that are rugged, compact, and capable of operating at high temperatures.

Medium voltage power devices are found in the power grid, renewable energy processing, industrial motor drives, and electric transportation. To improve their energy processing, these applications require low on-resistance, high switching speed, and high breakdown voltage—a combination not found in traditional silicon devices, or even newer silicon-carbide (SiC) devices. ECE researchers are taking these devices a step farther using Gallium Nitride (GaN), which is traditionally used in lower voltage applications. With new device designs, these researchers are bringing the benefits of GaN to critical medium voltage applications.

Electric motors consume a large portion of global energy—a portion that will grow with the electric vehicle market. Our researchers are developing models for permanent magnet synchronous machines (PMSMs) using small-signal, terminal-behavioral, three-port networks. These models will provide opportunities for in-situ observations and stability assessments for both the electrical and mechanical interfaces. 

Medium voltage DC circuit breakers are vital for applications like charging stations and power delivery in aircraft and ships. Both solid-state and hybrid DC circuit breakers require a power electronic interrupter (PEI) for arcless breaking operation. Conventional PEI systems are bulky and expensive with limited breaking voltage. Our researchers are meeting this challenge with a modular-based PEI that stacks identical low voltage PEI cells.

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.

Other Research Topics

  • Power electronic packaging and materials 
  • Packaging of power semiconductor devices and modules 
  • Material synthesis for die bonding, electrical insulation, and magnetic components 
  • Reliability of power semiconductor packages 
  • Wide-bandgap power semiconductors modules