Engines & Power Electronics : Power converters

Engines & Power Electronics Portfolios


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.

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.

Auxiliary Resonant Commutated Pole (ARCP) Current Source Converter

UW–Madison researchers have developed an auxiliary resonant commutated pole (ARCP) current source converter that controls power from a source to a three-phase load, e.g., a motor. It uses special pulse patterns and auxiliary commutation units and includes a current source rectifier, a DC link inductor, a current source inverter and a firing and control circuit. The converter exploits the benefits of soft switching, i.e., switching at zero voltages or currents, and pulse width modulation.

Improved Multilevel Inverter System

UW–Madison researchers have developed a multilevel inverter system for use in high voltage, high power applications. The system comprises at least three DC bus capacitors, an inverter, a control means and a rectifier; it also may include one or more transformers. The controller is connected to the switching devices of the inverter. After receiving signals indicating the load currents and the voltages across the DC bus capacitors, the controller provides a selected output waveform at the output lines. The system enables an inverter of four levels or higher to achieve desired output voltage generation while obtaining link voltage balancing at higher modulation depths. This reduces costs and improves the performance of the drive.