This paper details the optimization of inductive power transfer (IPT) coil systems with respect to efficiency $\eta $ and area-related power density $\alpha $ as required in electric vehicle applications. Based on analytical calculations and finite-element models, which are discussed and experimentally verified in detail, generally valid design guidelines for high-power IPT systems are derived, and the $\eta $ - $\alpha $ -Pareto optimization of a scaled 5kW prototype system is presented. Experiments demonstrate a dc-to-dc conversion efficiency of more than 96.5% at a power density of 1.47kW/dm $^{2}$ with coils of 210mm diameter/52mm air gap, including the losses in the resonant capacitors and the power converter. Field measurements validate the predicted stray field with a calculation error of less than 10%.

Modeling and $\eta $ - $\alpha $ -Pareto Optimization of Inductive Power Transfer Coils for Electric Vehicles

Wide bandgap (WBG) device-based power electronics converters are more efficient and lightweight than silicon-based converters. WBG devices are an enabling technology for many motor drive applications and new classes of compact and efficient motors. This paper reviews the potential applications and advances enabled by WBG devices in ac motor drives. Industrial motor drive products using WBG devices are reviewed, and the benefits are highlighted. This paper also discusses the technical challenges, converter design considerations, and design tradeoffs in realizing the full potential of WBG devices in motor drives. There is a tradeoff between high switching frequency and other issues such as high dv/dt and electromagnetic interference. The problems of high common mode currents and bearing and insulation damage, which are caused by high dv/dt , and the reliability of WBG devices are discussed.

Wide Bandgap Devices in AC Electric Drives: Opportunities and Challenges

Silicon-Carbide (SiC) MOSFETs, due to material properties, are designed with smaller thickness in the gate oxide and a higher electric field compared to Si MOSFETs. Consequently, the SiC MOSFETs have a worse reliability which causes higher leakage currents during instantaneous abnormal operating conditions. This paper investigates the reliability issues of the SiC MOSFET gate oxide under standard short-circuit test conditions. In this paper, 1200-V SiC MOSFETs are newly modeled, and also their short-circuit sustainability (tolerance) have been studied at different drain-source and gate-source voltages. A hardware tester circuit was designed and developed to test the devices under such extreme circuit conditions. Then, the gate reliability of SiC MOSFET devices have been compared to that of Si power devices of similar ratings. The results reveal a higher reduction in the instantaneous gate-source voltage of SiC MOSFETs compared to that of Si devices under the same operating conditions. The gate-voltage reduction phenomenon results from the higher leakage currents through the gate. Furthermore, it was found that the gate-source voltage reduction during the test depends on the gate structures. The gate voltage reduction of SiC MOSFETs with planar gate is higher than that of MOSFETs with shield planar gate. As the pulse duration increases in short-circuit tests, the leakage current in the gate-source of SiC devices increases. The results show that even though the SiC MOSFETs are very capable of processing long pulses and high power in the drain-source, the gate-source side is highly degraded by these pulses in the test. Moreover, whenever a small number of the short-circuit tests are applied, the gate structure of SiC MOSFETs becomes broken while the drain-source is still able to block the dc-link voltage. The paper concludes that the short-circuit reliability of the gate was found to be worse compared with commercial Si devices with similar rating.

Gate Oxide Reliability Issues of SiC MOSFETs Under Short-Circuit Operation

Power module packaging technologies have been experiencing extensive changes as the novel silicon carbide (SiC) power devices with superior performance become commercially available. This article presents an overview of power module packaging technologies in this transition, with an emphasis on the challenges that current standard packaging face, requirements that future power module packaging needs to fulfill, and recent advances on packaging technologies. The standard power module structure, which is a widely used current practice to package SiC devices, is reviewed, and the reasons why novel packaging technologies should be developed are described in this article. The packaging challenges associated with high-speed switching, thermal management, high-temperature operation, and high-voltage isolation are explained in detail. Recent advances on technologies, which try to address the limitations of standard packaging, both in packaging elements and package structure are summarized. The trend toward novel soft-switching power converters gave rise to problems regarding package designs of unconventional module configuration. Potential applications areas, such as aerospace applications, introduce low-temperature challenges to SiC packaging. Key issues in these emerging areas are highlighted.

A Review of SiC Power Module Packaging Technologies: Challenges, Advances, and Emerging Issues

Wide-bandgap (WBG) power semiconductor devices have become increasingly popular due to their superior characteristics compared to their Si counterparts. However, their fast switching speed and the ability to operate at high frequencies brought new challenges, among which the electromagnetic interference (EMI) is one of the major concerns. Many works investigated the structures of WBG power devices and their switching performance. In some cases, the conductive or radiated EMI was measured. However, the EMI-related topics, including their influence on noise sources, noise propagation paths, EMI reduction techniques, and EMC reliability issues, have not yet been systematically summarized for WBG devices. In this article, the literature on EMI research in power electronics systems with WBG devices is reviewed. Characteristics of WBG devices as EMI noise sources are reviewed. EMI propagation paths, near-field coupling, and radiated EMI are surveyed. EMI reduction techniques are categorized and reviewed. Specifically, the EMI-related reliability issues are discussed, and solutions and guidelines are presented.

A Survey of EMI Research in Power Electronics Systems With Wide-Bandgap Semiconductor Devices

This work presents an automated design procedure for series parallel resonant converters (LCC) employed in electrostatic precipitator (ESP) power supplies, which reduces the designer effort significantly. The requirements for the power supplies in ESP applications and means to derive an accurate mathematical model of the LCC converter, such as the power loss from commercial insulated-gate bipolar transistors, are described in detail in this paper. The converter parameters, such as resonant tank elements, are selected in order to improve the overall efficiency of the system, when a typical ESP energization operation range is considered. The analysis comprises two different control strategies: the conventional variable frequency control and the dual control. Both control strategies are analyzed by comparing semiconductor losses of five commercial modules. Finally, the circuit operation and design are verified with a 60 kW LCC resonant converter test setup.

Automated Design of a High-Power High-Frequency LCC Resonant Converter for Electrostatic Precipitators

Two different dynamic effects influencing the insulated gate bipolar transistor (IGBT) losses in soft-switching converters are demonstrated. The first one, the Dynamic tail-charge effect shows that the tail charge is dependent not only on the absolute value of the current at turn-off, but also on the dynamics of the current. This effect may have a significant impact on the optimization of zero-current-switching converters. The Dynamic conduction losses originate from the conductivity modulation lag of the IGBT. It is shown by experiments that the on-state losses depend on the operating frequency. Different methods to accurately determine the on-state losses are evaluated. It was found that the best method is an indirect measurement, where the stray inductance is identified by the use of an oscillating circuit. The experiments are performed under a sinusoidal current excitation at a fixed amplitude (150 A) for different frequencies (up to 104 kHz). The switching devices used are IGBT modules rated 300-400 A/1200 V in a bridge-leg configuration. From the experiments performed, it is found that IGBTs of a modern punch-though (PT) designs have the lowest losses in the series-loaded resonant converters studied in this paper.

On Dynamic Effects Influencing IGBT Losses in Soft-Switching Converters

Soft-switching converters equipped with insulated gate bipolar transistors (IGBTs) in silicon (Si) have to be dimensioned with respect to additional losses due to the dynamic conduction losses originating from the conductivity modulation lag. Replacing the IGBTs with emerging silicon carbide (SiC) transistors could reduce not only the dynamic conduction losses but also other loss components of the IGBTs. In the present paper, therefore, several types of SiC transistors are compared to a state-of-the-art 1200-V Si IGBT. First, the conduction losses with sinusoidal current at a fixed amplitude (150 A) are investigated at different frequencies up to 200 kHz. It was found that the SiC transistors showed no signs of dynamic conduction losses in the studied frequency range. Second, the SiC transistors were compared to the Si IGBT in a realistic soft-switching converter test system. Using a calorimetric approach, it was found that all SiC transistors showed loss reductions of more than 50%. In some cases loss reductions of 65% were achieved even if the chip area of the SiC transistor was only 11% of that of the Si IGBT. It was concluded that by increasing the chip area to a third of the Si IGBT, the SiC vertical trench junction field-effect transistor could yield a loss reduction of approximately 90%. The reverse conduction capability of the channel of unipolar devices is also identified to be an important property for loss reductions. A majority of the new SiC devices are challenging from a gate/base driver point-of-view. This aspect must also be taken into consideration when making new designs of soft-switching converters using new SiC transistors.

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An Experimental Evaluation of SiC Switches in Soft-Switching Converters

A Voltage Source Converter (VSC) (10) with Neutral-Point-Clamped (NPC) topology with one or more phases, comprises an intermediate DC circuit having at least a first and a second capacitance connected in series between a positive terminal and a negative terminal, providing a central tap terminal between both capacitances, and at least one sub-circuit for generating one phase of an alternating voltage, each sub-circuit comprising an AC terminal for supplying a pulsed voltage; a circuit arrangement of the form of a conventional NPC converter, with a first series connection of at least two switches between said AC terminal and said positive terminal, a second series connection of at least two switches between said AC terminal said negative terminal, and switchable connections from said central tap terminal to the centers of both two-switch series connections; and additional first and second auxiliary switches assigned to said two-switch series connections.

Voltage source converter (VSC) with neutral-point-clamped (NPC) topology and method for operating such voltage source converter

Commercially available Silicon Carbide (SiC) MOSFET power modules often have a design based on existing packages previously used for silicon insulated-gate bipolar transistors. However, these packages are not optimized to take advantage of the SiC benefits, such as, high switching speeds and high-temperature operation. The package of a half-bridge SiC MOSFET module has been modeled and the parasitic elements have been extracted. The model is validated through experiments. An analysis of the impact of these parasitic elements on the gate-source voltage on the chip has been performed for both low switching speeds and high switching speeds. These results reveal potential reliability issues for the gate-oxide if higher switching speeds are targeted.

Per Ranstad

Papers

Automated Design of a High-Power High-Frequency LCC Resonant Converter for Electrostatic Precipitators

On Dynamic Effects Influencing IGBT Losses in Soft-Switching Converters

An Experimental Evaluation of SiC Switches in Soft-Switching Converters

Voltage source converter (VSC) with neutral-point-clamped (NPC) topology and method for operating such voltage source converter

Analysis of parasitic elements of SiC power modules with special emphasis on reliability issues