Engines & Power Electronics : Power converters

Engines & Power Electronics Portfolios


Integrated Capacitor, Inductor and Resistor for Use as a Power Converter Filter

UW–Madison researchers have developed a bus bar incorporating voltage rise time filtration. The filter makes use of the inductance of the bus bar and is augmented by a surrounding layer of high relative permeability material. This material also provides multiple layers that provide a necessary filter capacitance and damping resistance. The result is a compact form factor bus bar that also provides high-frequency filtering.

This technology builds on previous work by the researchers, extending their concept of an integrated inductor/capacitor to include resistance, as well as packaging into bus bars or cables for easy use. These passive components are often the largest and bulkiest components in the power electronic converter, and integration of these components represents an opportunity to make more compact, efficient and cost-effective energy conversion systems.

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.

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.

Combined Capacitor/Inductor with Improved Performance

UW–Madison researchers have now mitigated the problem of parasitic inductance. Their new design features a loop-back terminal structure that minimizes the net magnetic field induced by the capacitor current. In other words, the capacitor leads are routed back up through the middle of the core to cancel the increased inductance seen at the capacitor terminals.

Combined Capacitor/Inductor Reduces Circuit Bulk

A UW–Madison researcher has designed a combination capacitor/inductor configured to share energy storage volumes, thereby significantly reducing the bulk of devices. In essence, the capacitor incorporates into its layers a material of high magnetic permeability (e.g., iron or an iron alloy laminated with a nonferrous metal) so that it may fit into the inductor coil in place of the normal core.

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.

Reducing DC-DC Converter Loss for More Efficient Cars

UW–Madison researchers have developed a technique for reducing loss in DC-DC converters by estimating and selecting the best flux linkage trajectory to meet target output. This is accomplished rapidly, within the time it takes to sample the system at large (Ta).

The loss associated with each of the possible trajectories can be stored in the converter controller or may be calculated in real time. The trajectory with the least loss is selected and implemented using a deadbeat control law, which can accurately achieve the loss minimizing flux linkage trajectory.

New Capacitive Method for More Efficient Power Generation

A UW–Madison researcher has developed a varying capacitance rotating electrical machine for an improved power generation system. The design comprises a rotor, stators, a spring element and conductive plates. The device utilizes capacitive coupling that is obtained between rotating and stationary capacitor plates by allowing one plate to float on a cushion of fluid (either air or liquid). These “air bearings” allow for much smaller gaps between the plates than existing methods. When combined with high rotational speeds, they enable an increase in power density.

New Flexible Mechanical Structure for Improved Wireless Power Transmission

UW–Madison researchers have developed a wireless power transfer technique that uses opposing pairs of capacitor plates, eliminating many of the reliability and maintenance issues present in current designs. The design provides a mechanism to power the electromagnets in wound field synchronous machines by which power is transferred to the rotor via capacitive coupling. The device consists of a flexible plate structure and glides on a cushion of air while the system is in motion. The system comprises a rotor including at least one electrical coil, a conductor, an electrical rectifier and first, second, third and fourth capacitor plates. The device may further comprise a power generation circuit providing alternating current power to at least one electrical coil and a capacitance monitor to provide an output signal indicating velocity and/or position of the rotor.

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.

High-Speed Digital-to-Analog Converter

A pair of UW-Madison researchers has now created a digital-to-analog converter whose architecture is based on microwave circuit principles, rather than traditional digital circuits. The new architecture enables much faster operation: The researchers predict their design can attain processing speeds of 60 Giga-samples per second (Gs/s), while the fastest commercial DAC today operates at approximately 1.5 Gs/s. In addition, the device does not require an amplifier to achieve faster speeds, as do conventional converters.

Efficient Boost Rectifier Employing Half-Rated Semiconductor Devices

UW-Madison researchers have developed a half controlled rectifier that can deliver performance similar to that of a fully-rated, three-phase, pulse-width-modulated (PWM) rectifier, while allowing the ratings of the switches and diodes to be reduced to half the rated power. Because the semiconductors devices need only be rated for half of the rectifier’s peak current, they can be significantly less expensive than those used in conventional rectifiers. This rectifier also eliminates the typical problems seen in other half-controlled rectifiers, such as low-order even harmonics on both the AC and DC sides.

AC to AC Frequency Converters with a Three-Phase Isolated Vector Switching Structure

A UW-Madison researcher has developed an integrated power conversion process involving a multi-phase transformer and a multi-pole, three-phase switching structure to achieve AC to AC frequency conversion without an intermediate DC link. In essence, the transformer – already included in the system for isolation purposes – is made to serve double duty. It provides electrical isolation and voltage step up/step down, and it phase shifts the vector components of the waveforms to bring about frequency conversion.

Dual Bridge Matrix Converter for AC to AC Power Conversion

UW-Madison researchers have developed a novel dual bridge matrix converter that solves the commutation problems typically seen with conventional matrix converters. These new dual bridge converters possess the same characteristics as conventional matrix converters, including four-quadrant operation, a unity input power factor and high-quality voltage and current waveforms.

Inverter Configurations with Shoot-Through Immunity

UW-Madison researchers have developed a novel phase leg configuration that is inherently immune to shoot-through conditions. In the basic embodiment of this invention, the low-side switch acts like a master switch to control switching of the high-side switch. That is, whenever the low-side switch is on, the high-side switch is automatically forced off, and the high-side switch only begins to turn on when the low-side switch turns off. Thus, a short-circuit through both of the main switches is topologically inhibited and a single control signal for the low-side switch is enough to control the entire phase leg.

Adjustable Speed Drive For Single-Phase Induction Motors

UW-Madison researchers have developed a simple and inexpensive adjustable speed drive for use with low-cost, single-phase induction motors. The drive can operate in full-speed mode with high starting torque, and in at least one lower-speed mode suitable for applications such as fan motor drives.