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.


Vernier Permanent Magnet Machines with High Torque Density

UW–Madison researchers have developed a VPM rotor geometry that improves torque density and power factor by routing the stator flux in a way that boosts it. The new, single barrier design comprises an iron section with an air barrier near the rotor core to guide the stator magnet flux in a desirable path. This was created for the spoke-type configuration topology, where the magnets are aligned similar to the spokes of a bicycle wheel in the rotor. This design solution boosts the flux without compromising performance or cost.

Converter Control with Reduced Link Capacitor

Building on their work, the researchers have now developed an improved modulation method that allows for the use of conventional switches. This new method tightly integrates the control of the source and loads, which is not traditionally done with current methods.

Reducing the energy at the DC bus led the inventors to modify how the source and load are controlled. Their method determines the switching intervals of the various solid state switching devices of the power conversion system in an integrated fashion and places them within each switching period in a particular sequence. This is determined by the desired voltage and current waveforms such that the stiffness of the DC link can be maintained without large amounts of energy storage, or additional voltage penalty compared to conventional approaches. New parameters for the source and load integration are factored into the controller algorithms.

Wound Field Synchronous Machines with Enhanced Saliency, Performance

UW–Madison researchers have designed a modified rotor structure for salient pole WFSMs that enhances saliency and leads to better performance (peak motoring power/torque capability) using the same amount of input current.

Compared to conventional designs, the new rotor structure features a flux barrier gap made of a low cost polymer that enlarges the reactance Xd - Xq, differential between rotor axes. Based on the particular end use, three different barrier designs could be employed (single barrier, multilayer barrier or axial laminated).

Inverter for Common Mode Voltage Cancellation

UW–Madison researchers have developed inverter topology in which the CM voltage is 100 percent cancelled. Instead of the two switches in series (as found in conventional designs) the new ‘balanced inverter’ features three switches in series wherein the upper and lower switches of each phase-leg are rated at half the DC bus voltage.

The half-rated switches turn on and off simultaneously. The middle switch of each phase-leg operates complementarily with the other two, and is rated at the full DC bus voltage. This essentially replaces one full voltage-rated switch with two half-rated switches on the top and bottom of each phase.

The new topology cancels the total CM voltage by generating two equal-amplitude, opposite-signed CM voltages on the two sets of three windings. Hence, the whole machine remains at ground potential, and no current will flow to the ground. In addition, to take advantage of the six AC terminals of the balanced inverter, the three phase motor windings need to be equally separated as two sets of windings. This can be done by reconfiguring the series connected machine windings, which is particularly convenient for dual-voltage 9-lead machines.

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.
For more information about the technologies in this portfolio, contact Emily Bauer at or 608.960.9842.