The Wisconsin Electric Machines and Power Electronics Consortium (WEMPEC) is an internationally renowned power electronics and electric machines research group located at UW–Madison. With the support of more than 80 corporate sponsors, WEMPEC's team of professors, graduate students and international scholars work together to research and develop the newest technologies and techniques in electric machines, power electronics, actuators, sensors, drives, motion control and drive applications.

Several technologies that were developed using WEMPEC funding are available for licensing through WARF. These technologies include improved power converters, semiconductor modules, electric machines and more.


New Rotor Magnet Configuration Delivers Greater Efficiency at a Lower Price

UW–Madison researchers have developed a streamlined sinusoidal rotor magnet design for interior permanent magnet machines.

By altering the classic rectangular block design for embedded magnet stacks in favor of a sinusoidal, axially varied orientation, researchers have increased the efficiency of rotors in IPMMs in a twofold fashion: Not only does this new design reduce the amount of magnet material necessary for rotor production, but it also provides an optimized distribution of flux that significantly reduces torque pulsation and spatial harmonics. The new design is easy to manufacture and is complementary to rotors already in existence.

Axial Flux-Switching Permanent Magnet Machine for High Speed Operation

UW–Madison researchers have developed a new axial FSPM machine that can be run at high speed with less fundamental frequency required, therefore overcoming one of the largest barriers to adoption. The new design features innovative axial flux topologies with offset rotor and/or stator structures.

Lighter, Cheaper Multilevel Converter for Adjustable Speed Drives

UW–Madison researchers have developed a new multilevel converter design that does not require any extra capacitors, diodes or isolated voltage sources. This reduces costs, size and insulation requirements compared to conventional multilevel converters.

The new design is based on two multiphase inverters electrically coupled in series. The key feature is that they share the same input source (e.g., a single rectifier, DC grid or batteries). Other designs require separate isolated voltage sources. In this design, the output AC terminals of the inverters power different groups of machine windings, and the total output voltage is combined inside the machine without additional components.

Induction Motor Wastes Less Power

UW–Madison researchers have developed a method to control the supply of reactive power to/from an induction motor so that it operates at approximately unity (1:1) power factor. In other words, the motor consumes voltage and current in phase from the terminals of the electric grid.

In essence, multiphase voltage from the grid is applied to one side of the motor’s open stator windings. A processor receives this voltage and determines its phase. At the same time, stator currents are measured from the second side of open windings and converted to a type of reference frame having voltage on one axis. Based on this reference frame, a second output voltage signal is determined and applied to the second side of open windings.

Semiconductor Interconnect Design for Small, Inexpensive, Integrated Current Sensing with Improved Reliability

UW–Madison researchers have developed a design for integrated current sensing that is comprised of semiconductor interconnects with a loop configuration, instead of a straight bar, and point magnetic field detectors specially located to detect current flowing in the interconnect from DC to high frequency (MHz). Giant magnetoresistive (GMR) detectors serve as these point-field detectors.

Permanent Magnet Synchronous Motor Self-Sensing Drive System

UW-Madison researchers have developed a permanent magnet synchronous motor system that enables position sensorless rotor position estimation, which has been demonstrated to be effective even when a smooth cylindrical permanent magnet is positioned on the surface of the rotor. The system includes a rotor with a permanent magnet surface providing multiple angularly spaced magnetic poles and a stator fitting around the rotor so that the rotor can rotate within the stator. Within the stator, angularly spaced teeth extend inward toward the rotor, and electrically conductive coils are wound around at least some of the teeth to apply a magnetic field to the teeth. The system also may employ concentrated windings that will accentuate the stator-based saliency detected by the system. 

The power electronic drive attached to the motor not only provides the basic power conversion input, but also injects an electrical excitation signal into the coils at a frequency higher than the primary power conversion drive frequency. The primary power conversion input frequency is controlled to produce torque and thereby control rotation of the rotor. The superimposed high frequency injected signal is used to track rotor position by detecting variations in the injected signal that are functionally related to the rotor position and to the magnetic saturation of the stator teeth caused by the rotor magnetic fields.

This injection-based, saliency tracking method permits position sensorless operation for SPMSMs having little to no saliency on the rotor, eliminating the need for the inclusion of a separate position sensor in such systems. The system also is adaptable to a wide range of stator designs.

Power Conditioning Architecture for Wind Turbine

UW-Madison researchers have developed a viable solution that allows DFIG wind turbines connected to the grid to ride through a voltage sag. The turbines need converters, such as a DC/AC inverter, to change the power generated into a form that is compatible with the utility grid. In a conventional DFIG wind turbine, the grid-side converter is connected in parallel with the stator windings of the generator. This approach has the converter connected in series instead. The DC voltage bus of the converter is fed from the induction generator rotor windings through a second, machine-side converter. Connecting the grid-side converter in series allows continuous control of shaft torque and power delivered to the grid even during grid faults, enabling inherent voltage sag ride-through capability.

Device and Method for Reducing the Electromagnetic Interference (EMI) Generated by Power Converters

UW-Madison researchers have developed a hybrid filter device that more effectively reduces EMI produced by switching power converters, especially those involving high power densities, high switching frequencies and short transition intervals. The device consists of an active filter that works in conjunction with a passive filter. It targets EMI, resulting from the parasitic capacitive coupling paths that high frequency signals often find through various circuit elements, particularly in the common mode, or ground, paths.

Field Controlled Axial Flux Permanent Magnet Electrical Machine

UW-Madison researchers have developed an electrical machine that combines a variable DC coil excitation with permanent magnet excitation to control the flux in a cost-effective manner. This design modifies the multiple-rotor, multiple-stator, axial-flux permanent magnet machine by adding one or two DC field windings to control the air gap flux and to provide a path for the DC flux through a modification of the rotor structure. The resulting field-controlled, axial-flux, surface-mounted permanent magnet machine offers a less expensive and more readily implemented flux control.

Dual-Rotor, Radial-Flux, Toroidally-Wound, Permanent Magnet Machine with High Efficiency and High Torque Density

UW-Madison researchers have developed a machine topology suitable for high speed applications that simultaneously exhibits high efficiency and high torque density. Their dual-rotor, radial-flux, toroidally-wound, permanent magnet machine also employs inexpensive ferrite magnets, making these machines inexpensive to produce.

High Performance Active Gate Drive for IGBTs

UW–Madison researchers have developed an active gate drive circuit for driving high power IGBTs that incorporates three separately controlled stages. The new design optimizes switching performance for turn-on, turn-off and all operating conditions.

The circuit includes a semiconductor switch connected in series with a low resistance gate turn-on or turn-off resistor between the voltage supply line and the gate input line, and a parallel connected bipolar transistor. After receiving a turn-on signal, the switch provides low resistance rapid charging to the gate during a first stage, controlled current charging during a second stage and, thirdly, a rapid, low resistance final charging while the signal is present. Turning off the IGBT follows a similar pattern for discharging.

Quality High Voltage Output by Hybrid Multilevel Power Converter

UW–Madison researchers have developed a hybrid multilevel converter that provides high voltage output waveforms with good spectral characteristics. The design takes advantage of the operating features of both high speed and high voltage switches, like IGBTs and GTOs, respectively.

Amenable to various multilevel structures, the preferred design is a modified H-bridge inverter that may be used to synthesize a quality single or multiphase high voltage AC waveform. Specifically, the converter includes multiple DC voltage sources providing different voltage levels in a connected series of H-bridge inverters. The lowest voltage level inverter is modulated at a high frequency (exploiting IGBT capabilities) while the higher voltage inverters are modulated to provide a low frequency stepped waveform (exploiting GTO capabilities). The high and low frequency pulse width and waveform combine for improved spectral characteristics.

Short Circuit Protection of Power Switching Devices

UW–Madison researchers have developed a high power semiconductor switching device with a gate terminal that controls current flow between the power terminals of the device. A first fault signal is provided if the current flow path of the device exceeds a selected level; similarly, a second fault signal is triggered if the voltage across the power terminals exceeds a given level. When either the first or second fault signal is provided, the gate terminal is limited to a selected control level, which intermediates the full-on and full-off current levels of the switching device.
For more information about the technologies in this portfolio, contact Emily Bauer at or 608.262.8638.