Neville McNeill

An Experimental Investigation of the Tradeoff between Switching Losses and EMI Generation With Hard-Switched All-Si, Si-SiC, and All-SiC Device Combinations

Silicon carbide (SiC) switching power devices (MOSFETs, JFETs) of 1200 V rating are now commercially available, and in conjunction with SiC diodes, they offer substantially reduced switching losses relative to silicon (Si) insulated gate bipolar transistors (IGBTs) paired with fast-recovery diodes. Low-voltage industrial variable-speed drives are a key application for 1200 V devices, and there is great interest in the replacement of the Si IGBTs and diodes that presently dominate in this application with SiC-based devices. However, much of the performance benefit of SiC-based devices is due to their increased switching speeds ( di/dt, dv/ dt), which raises the issues of increased electromagnetic interference (EMI) generation and detrimental effects on the reliability of inverter-fed electrical machines. In this paper, the tradeoff between switching losses and the high-frequency spectral amplitude of the device switching waveforms is quantified experimentally for all-Si, Si-SiC, and all-SiC device combinations. While exploiting the full switching-speed capability of SiC-based devices results in significantly increased EMI generation, the all-SiC combination provides a 70% reduction in switching losses relative to all-Si when operated at comparable dv/dt. It is also shown that the loss-EMI tradeoff obtained with the Si-SiC device combination can be significantly improved by driving the IGBT with a modified gate voltage profile.

Investigation of Proximity Losses in a High Speed Brushless Permanent Magnet Motor

This paper presents a finite element investigation into the proximity losses in brushless AC permanent magnet motors used in hybrid/electric vehicle applications. The proximity effect in winding conductors is as a result of eddy-currents caused by magnetic fields generated by nearby conductors. This paper considers the influence of the conductor shape and disposition on the losses for a given stator lamination. Several structures of the winding are analysed and compared in respect to the loss and AC resistance. The analysis shows that the proximity losses can be significantly reduced through an appropriate choice of conductor shape and winding technique. The calculated results have been validated experimentally on the machine prototype for three different winding arrangements

Performance Analysis and Thermal Modeling of a High-Energy-Density Prebiased Inductor

This paper presents a methodology for analyzing the thermal performance of compact planar wound components. A high-energy-density prebiased choke is used to demonstrate and validate the proposed approach. Loss predictions from electromagnetic finite-element analyses are coupled to an equivalent lumped-circuit thermal model and used to determine the operating thermal envelope for the wound component. Results from the proposed method are directly compared with test measurements taken from the prototype choke and are shown to be in good agreement. A sensitivity analysis indicates that copper loss is the dominant component in such devices and that AC resistance effects are more prominent than core loss.

High-speed resonant gate driver with controlled peak gate voltage for silicon carbide MOSFETs

Parasitic inductance in the gate path of a Silicon Carbide MOSFET places an upper limit upon the switching speeds achievable from these devices, resulting in unnecessarily high switching losses due to the introduction of damping resistance into the gate path. A method to reduce switching losses is proposed, using a resonant gate driver to absorb parasitic inductance in the gate path, enabling the gate resistor to be removed. The gate voltage is maintained at the desired level using a feedback loop. Experimental results for a 1200 V Silicon Carbide MOSFET gate driver are presented, demonstrating switching loss of 230 µJ at 800 V, 10 A. This represents a 20% reduction in switching losses in comparison to conventional gate drive methods.

A First Approach to a Design Method for Resonant Gate Driver Architectures

This paper proposes a general circuit model and design method for resonant gate drivers. Topologies in the literature are analyzed by dividing each switching transient into up to five energy transfer stages, for which general analytical equations are derived. A general resonant gate driver circuit model is presented. Several reviewed topologies are identified as unique combinations of current paths within this circuit model, providing a basis for classification. This establishes a relationship between topology performance and architecture, which is verified experimentally using a reconfigurable test circuit.

High-Speed Resonant Gate Driver With Controlled Peak Gate Voltage for Silicon Carbide MOSFETs

Parasitic inductance in the gate path of a Silicon Carbide MOSFET places an upper limit upon the switching speeds achievable from these devices, resulting in unnecessarily high switching losses due to the introduction of damping resistance into the gate path. A method to reduce switching losses is proposed, using a resonant gate driver to absorb parasitic inductance in the gate path, enabling the gate resistor to be removed. The gate voltage is maintained at the desired level using a feedback loop. Experimental results for a 1200 V Silicon Carbide MOSFET gate driver are presented, demonstrating switching loss of 230 μJ at 800 V, 10 A. This represents a 20% reduction in switching losses in comparison to conventional gate drive methods.

A new soft-switching technique using a modified PWM scheme requiring no extra hardware

A new soft-switching PWM scheme for a three-phase, AC-DC, step-down unity power factor converter is described. The main advantage of the scheme is that it requires no additional hardware components to achieve a combination of zero current and voltage turn-off and zero and reduced voltage turn-on. The scheme relies on the repositioning of the PWM pulses within the carrier period to obtain natural commutation from one switching device to the next. The theoretical reduction in the total switching losses is mathematically shown to be 42% compared with the standard center-aligned PWM scheme used with the converter. A PSpice/sup TM/ simulation of the new scheme reveals soft-switching waveforms. Practical results are given to support the simulation results and heat-sink temperature rise results show a reduction in heat-sink temperature rise for the new scheme compared to the old.

Performance of a Prototype Traveling-Wave Actuator Made From a Dielectric Elastomer

The primary aim of the research is to demonstrate the fabrication and operation of a traveling wave actuator made from a silicone dielectric elastomer. Multiple folded stack configurations of a silicone are assembled to create individually controllable regions in a single device, allowing a traveling-wave pattern of electrical stimuli to be applied to each active region. The prototype actuator is sandwiched between two friction surfaces allowing motion in response to the traveling wave. A number of issues related to the research and development of the prototype actuator are considered, including traveling-wave principle, folded stack design, actuator fabrication, and electrical control. A prototype is tested with a bespoke multiple-channel high-voltage converter to assess the performance characteristics of stroke, force, and frequency. Practical velocities and forces are achieved; however, a number of challenges are discussed in order to increase performance to comparable levels exhibited by commercial actuators with high-force long-stroke capabilities.

Low-cost high-bandwidth current transducer for automotive applications

Electric actuators in automotive systems may require a current transducer for control purposes. A low-cost non-invasive transducer design based around a current transformer (CT) is described in this letter. The problem of droop in the output signal is addressed by controlling the CTs secondary terminal voltage in response to the core flux change. This is detected using a tertiary flux-change sense winding. The circuit is suited for use in high-temperature automotive environments. The bandwidth of the circuit is high allowing it to be used in peak current mode or hysteresis control schemes. Operation when sensing a 100-A current pulse of 10-ms duration is demonstrated

Design of a high-temperature pre-biased line choke for power electronics applications

Chokes are important elements in many power electronics circuits, for example in boost converters and current source inverters. Minimizing the chokes volume and mass is desirable in many applications. This paper considers using a permanent magnet to pre-bias the chokes core flux as a means of reducing its volume/weight. A methodology for designing a biased choke is presented and potential benefits are quantified through tests taken from a prototype device.