Silicon Carbide Converters Research Articles

Planar Common-Mode EMI Filter Design and Optimization for High-Altitude 100-kW SiC Inverter/Rectifier System

Silicon-carbide (SiC) devices are receiving popularity for high-power converter systems in aircraft due to many advantages over silicon counterparts. However, the electromagnetic interference (EMI) problems are more serious with the SiC devices operating at higher switching speeds and higher switching frequencies. The common-mode (CM) EMI filter design of the high-power SiC converter is especially challenging for high-altitude applications due to the harsher requirements of insulation and heat dissipation. The optimization of the parameters and physical design of a CM EMI filter in a 100-kW SiC inverter/rectifier system operating at 50 000 ft is conducted in this article to obtain the highest power density. The effect of the switching frequency on the EMI filter volume and the total power density of the converter system is analyzed. The lower breakdown voltage of air and the higher thermal resistance of natural convection make the conventional design of the CM choke infeasible at high altitudes. A printed circuit board (PCB)-based planar CM choke is designed with the consideration of partial discharge (PD) and heat dissipation at the altitude of 50 000 ft. The structure of the CM choke is optimized with embedded electric-field shielding plates, which controls the electric-field intensity in the air below 300 V/mm. The PCB windings improve the efficiency of heat dissipation at high altitudes and reduce the profile of the CM choke. A Pareto optimization is conducted to minimize the size of the choke and the volume of the final design is only 155 cm3. The experimental results show that the CM noise is reduced effectively with the CM EMI filter. PD is not observed even at the altitude of 50 000 ft and the thermal performance is excellent with a current of 190 A. With the optimization and the dedicated design of the CM EMI filter, the power density of the converter system is up to 33.3 kW/L.

10 kV SiC MOSFET Based Medium Voltage Power Conditioning System for Asynchronous Microgrids

Distributed energy resources (DERs) and microgrids have seen tremendous growth and research activities in recent years. Flexible DERs and asynchronous microgrids (ASMG) can have many system-level benefits over fixed DERs and conventional microgrids. The key enabler for flexible DERs and ASMG is a power converter based power conditioning system (PCS) as the interface between DERs/microgrids and the medium voltage (MV) distribution grid. High voltage (HV, >3.3 kV) silicon carbide (SiC) based MV converter is now a promising solution for the PCS. This article presents development and testing of a 10 kV SiC MOSFET based MV PCS for 13.8 kV ASMG. MV PCS converter design addressing high dv/dt issue generated by fast switching of the 10 kV SiC MOSFET is presented. The developed PCS is successfully tested at 25 kV dc 13.8 kV ac voltages and 100 kVA power. Grid support functions are also demonstrated with the developed PCS prototype and hardware tests beds, validating HV SiC converter benefits for ASMG.

500 kW Forced Air-Cooled Silicon Carbide (SiC) Three-Phase DC/AC Converter With a Power Density of 1.246 MW/m3 and Efficiency >98.5%

There is a continuous demand for high-power, high-efficiency, and high-density converters in various existing and emerging applications such as large motor drives, electric vehicles, more electric aircraft, and utility applications. Compared with conventional silicon (Si) insulated gate bipolar transistors (IGBTs), silicon carbide (SiC) MOSFETs can have lower switching loss and higher frequency operation capabilities, which enables higher efficiency and higher power density at the converter level. Meanwhile, to achieve a high power rating such as 500 kW, how to extend the current capabilities of existing SiC power modules, the choice of parallel schemes, the selection of passive components, cooling and mechanical structure design pose clear challenges in maximizing the system power density and efficiency. This article presents a comprehensive design of the world-first air-cooled 500 kW SiC dc/ac three-phase converter, which achieves a record-high power density of 1.246 MW/m <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> (1.246 kW/L) and an efficiency over 98.5%. The converter has been tested in the experiment to the full power rating, which provides benchmark results for high power SiC converters and their applications.

Improved switching transient model suitable for power loss evaluation of SiC-based asymmetric H-bridge power converters in SRGs

This paper presented an improved switching transient model of silicon carbide (SiC)-based asymmetric H-bridge (AHB) power converter for a switched reluctance generator (SRG), which takes the nonlinear phase inductance of the SRG into consideration. First, a systematic mathematic derivation is carried out and the switching transient model is established. Second, the impact of the nonlinear phase inductance of the SRG on switching transients is verified by PSpice & Simulink co-simulations. Third, a power loss model is established by the transient model through PSpice & Simulink co-simulations. The model is conducted to indicate the power loss characteristics of the SiC-based AHB power converter. Simulation results indicate that the nonlinear phase inductance of the SRG is able to accelerate the switching speed of SiC-MOSFETs, and that the SiC converter is advantageous in terms of power loss. Experimental results illustrate that the established power loss model experiences high accuracy. In addition, SiC devices are able to strengthen the power density and efficiency of a converter while reducing its heat dissipation requirements.

Experimental Assessment of High Frequency Bearing Currents in an Induction Motor Driven by a SiC Inverter

Compared with silicon (Si) IGBTs, silicon carbide (SiC) MOSFETs have much faster switching speeds and high switching frequency operation capability, enabling compact and high-efficiency motor drive systems. However, the increased switching speed and frequency also cause increased-level of common-mode (CM) voltage with higher slew rates ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ). The CM voltage leads to machine leakage currents as well as bearing currents such as electric discharge machining (EDM) type current and capacitive-type ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dv</i> / <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">dt</i> ) current. These bearing currents can cause degradation or failure of motor bearings. In order to investigate the impact of SiC motor drives on the motor bearing currents, in this paper, the mechanism and modelling of bearing currents are analyzed first. Then, a direct measurement method is used to assess the bearing currents in the induction motor driven by the SiC converter. In the experiment, the number of EDM current events is counted and the amplitude of the capacitive-type of current is also examined under various switching speeds and frequencies of SiC devices. Furthermore, the bearing currents are also extensively tested under various bearing temperatures, motor speeds and dc-link voltages. The correlations between the bearing currents and various factors have been revealed in this paper.

SiC and GaN Devices With Cryogenic Cooling

This article presents the cryogenically cooled application for wide bandgap (WBG) semiconductor devices. Characteristics of silicon carbide (SiC) and gallium nitride (GaN) at cryogenic temperatures are illustrated. SiC MOSFETs exhibit increased on-state resistance and slower switching speed at cryogenic temperatures. However, cryogenic cooling provides low ambient temperature environment and thus enables the SiC converter to operate at lower junction temperature to achieve higher efficiency compared to room temperature cooling. A cryogenically cooled MW-level SiC inverter prototype is developed and demonstrated the feasibility of operating high-power SiC converter with cryogenic cooling. GaN HEMTs exhibit more than five times on-state resistance reduction and faster switching speed at cryogenic temperatures which makes GaN HEMTs an excellent candidate for cryogenic power electronics applications. The significantly reduced on-state resistance of GaN devices provides the possibility to operate them at a current level much higher than rated current at cryogenic temperatures. A GaN double pulse test (DPT) circuit is constructed and demonstrated that GaN HEMTs can operate at nearly four times of rated current at cryogenic temperatures. Challenges of utilizing WBG device with cryogenic cooling are discussed and summarized.

Opportunities, Challenges, and Potential Solutions in the Application of Fast-Switching SiC Power Devices and Converters

Power devices based on wide-bandgap material such as silicon carbide (SiC) can operate at higher switching speeds, higher voltages, and higher temperatures compared to those based on silicon material. This article highlights some opportunities brought by SiC devices in existing and emerging applications in terms of efficiency and power density improvement. While the opportunities are clear, there are also design challenges that must be met in order to realize their full potential. For example, the fast switching speeds and high dv/dt of SiC devices can cause increased electromagnetic interference, current overshoot, cross-talk effect, and have a negative impact on loads such as motors. This article presents several potential solutions to tackle the application challenges and to fully exploit the superior characteristics of SiC devices and converters while attenuating their negative side effects. This article provides an overview of recent SiC device research and development activities based on academic literature, work carried out by the authors and collaborators as well as input from industry. It aims to provide benchmark results and a timely and useful reference to accelerate the adoption and deployment of SiC devices and converters.

A Simplified Analytical Algorithm in abc Coordinate for the Three-Level SVPWM

Given the high complexity of the conventional three-level space-vector pulsewidth modulation (3L SVPWM), simplified SVPWM algorithms are usually adopted instead. However, existing simplifications for 3L SVPWM still have a large computation burden, which limits its applications, e.g., in high-switching-frequency silicon-carbide converters with a short computation period. In this letter, based on a typical simplified algorithm known as the center-aligned 3L SVPWM, a simplified analytical algorithm in abc coordinate is proposed. The reference-voltage-vector adjustment and the calculation of modulation waves are unified based on the center-aligned SVPWM. The modulation waves can be analytically derived by only eight simple equations, without sector determination, calculation, and assignment of dwell times. Consequently, the complexity of implementing the 3L SVPWM is significantly reduced.

Periodic variation in the effect of switching frequency on the harmonics of power electronic converters

Switching frequency is an important factor in the performance control of power electronic converters. It can help optimize switching losses, switching ripples and electromagnetic interference, especially for newly developed high-switching-frequency silicon carbide converters. Periodic variation in the switching-frequency methods has been developed for this purpose, especially the model-predictive variable switching-frequency pulse width modulation (VSFPWM) method. The effect of periodic switching-frequency variation on the harmonics of a converter using double Fourier analysis and simulations are investigated. This work verifies that the switching harmonics can be reduced by periodic variation in the switching frequency, and the low-frequency (baseband) harmonics only incur a slight change. The analysis provides a theoretical foundation for the application of VSFPWM in power electronic converters.

Comparison of Si and SiC EMI and Efficiency in a Two-Level Aerospace Motor Drive Application

Power electronics are crucial elements in more-electric aircraft (MEA) applications. Existing hardware is almost exclusively silicon (Si)-based. However, recent advances in semiconductor technology yielded silicon carbide (SiC) components with current ratings suitable for aerospace applications. These devices have much strength that can increase power density and improve performance over Si-based hardware. High switching speeds are characteristic of SiC devices, and there is much concern about their impact on electromagnetic interference (EMI). This may necessitate larger EMI filters to comply with EMI standards, which would decrease power density and negate some of SiC’s benefits. The following research explores the tradeoff between efficiency and EMI. It compares the performance of two high-power three-phase converters: one built from SiC MOSFETs and the other from Si IGBTs. The test setup consists of a 250-kW drive stand capable of sourcing and regeneratively sinking power as well as a 40-kVA aerospace rated machine. Experimental results are obtained at a bus voltage of 270-Vdc with power levels exceeding 1.5 p.u. The findings demonstrate comparable EMI performance for Si and SiC under MIL-STD-461 with the SiC converter achieving higher efficiency.

High Frequency Conducted EMI Investigation on Packaging and Modulation for a SiC-Based High Frequency Converter

Silicon carbide (SiC) devices have the advantages of high switching speed and high switching frequency, which can increase the power density, but electromagnetic interference (EMI) will increase along with higher switching frequency thus it can become a challenge for high-frequency converters. In order to clarify the influence factors of EMI noise in SiC converters and find the suppressing method, this paper investigated the conducted EMI in SiC-based high power density electronic systems from two aspects: packaging structures and modulation methods. For packaging investigation, this paper introduced parasitic parameters of power module into EMI analytical model, then defined transfer functions of EMI noise to analyze the influence of parasitic parameters on noise propagation path and further studied the impact of parasitic parameters on noise source by analyzing switching transient and frequency spectrum. Analysis and simulation are carried out based on a hybrid structure SiC power module and discrete SiC devices to verify the analysis. The influence of modulation on EMI is studied by analyzing and comparing two modulations: continuous current modulation (CCM) and triangle current modulation (TCM). To certify the analysis study, two 1.6-kW, 300-kHz switching-frequency synchronous buck converters are designed and tested. One is based on the hybrid packaging power module and the other is based on TO-247 packaged SiC devices, respectively. The result shows that the hybrid packaging module can suppress the common mode (CM) EMI by 10 dB, and has a suppression on differential mode (DM) EMI between 10 and 20 MHz. Moreover, TCM can increase DM EMI in low-frequency range but suppress it in the high-frequency range.

Silicon Carbide Converters and MEMS Devices for High-temperature Power Electronics: A Critical Review.

The significant advance of power electronics in today’s market is calling for high-performance power conversion systems and MEMS devices that can operate reliably in harsh environments, such as high working temperature. Silicon-carbide (SiC) power electronic devices are featured by the high junction temperature, low power losses, and excellent thermal stability, and thus are attractive to converters and MEMS devices applied in a high-temperature environment. This paper conducts an overview of high-temperature power electronics, with a focus on high-temperature converters and MEMS devices. The critical components, namely SiC power devices and modules, gate drives, and passive components, are introduced and comparatively analyzed regarding composition material, physical structure, and packaging technology. Then, the research and development directions of SiC-based high-temperature converters in the fields of motor drives, rectifier units, DC–DC converters are discussed, as well as MEMS devices. Finally, the existing technical challenges facing high-temperature power electronics are identified, including gate drives, current measurement, parameters matching between each component, and packaging technology.

Fractional proportional-resonant current controllers for voltage source converters

This paper proposes a novel fractional proportional-resonant controller, which applies fractional order calculus to the well-known proportional-resonant controllers. The focus of the study is the current control loop of voltage source converters. The main merit of the proposed fractional controller formulation lies into the use of fractional exponents in the integro-derivative parts obtaining a controller with an extra degree of freedom. This degree of freedom allows the phase delay to be improved for a wide frequency range in comparison with the conventional proportional-resonant controllers. Furthermore, the obtained controller results in a lower order transfer function that reduces the computational burden when multiple current frequencies have to be tracked. As fractional integro-derivative exponents are not directly implementable, five mathematical approaches are explored, selecting the Chareff’s approximation for the fractional controller operator’s implementation. A tuning procedure for such a controller is also addressed. The new controller formulation is validated in a 20kVA laboratory set-up based on a silicon-carbide converter, and it is implemented in a DSP. Two AC output converter’s configurations are considered to demonstrate the controllers’ tracking capability; short-circuited (balanced fault) output, and grid-connected operation. This last case is evaluated operating as active filter and delivering fundamental component to a non-ideal grid.

Electromagnetic Interference in Silicon Carbide DC-DC Converters

A comparison of radiated noise for Silicon and Silicon Carbide converters is presented. SiC JBS diodes were used in this evaluation to enable fast switching times, whilst minimizing the transistor junction temperature. Radiated electromagnetic-interference measurements showed the highest noise signature for the SiC JFET and lowest for the SiC MOSFET. The negative gate voltage requirement of the SiC MOSFET introduces up to 6 dBµV increase in radiated noise, due to the induced current in the high frequency resonant stray loop in the negative power plane of the gate drive. The SiC JFET and MOSFET have shown overall converter efficiencies of 96% and 95.5% respectively. This efficiency shows only a weak frequency dependence, in contrast to the CoolMOS/SiC JBS diode combination which demonstrated an efficiency drop from 95% to 92.5% when increasing the frequency from 100kHz to 250kHz.

Performance of a 25kW 700V Galvanically Isolated Bidirectional DC-DC Converter Using 1.2kV Silicon Carbide MOSFETs and Schottky Diodes

This paper presents the development and experimental evaluation of a 25kW, 700V galvanically isolated bidirectional converter based on silicon carbide (SiC) MOSFETs and Schottky diodes. Compared with a similarly rated silicon (Si) IGBT version, the SiC converter exhibits a 3% improvement in peak efficiency, 2.6 times reduction in total losses, and three times improvement in power density.

Efficiency Impact of Silicon Carbide Power Electronics for Modern Wind Turbine Full Scale Frequency Converter

Power electronics is an enabling technology found in most renewable energy generation systems. Because of its superior voltage blocking capabilities and fast switching speeds, silicon carbide (SiC) power electronics are considered for use in power conversion units in wind generation systems in this paper. The potential efficiency gains from the use of SiC devices in a wind generation system are explored by simulations, with the system modeling explained in detail. The performance of the SiC converter is analyzed and compared to its silicon counterpart at different wind speeds, temperatures, and switching frequencies. The quantitative results are based on SiC metal-oxide-semiconductor field-effect transistor (MOSFET) prototypes from Cree and modern Si insulated-gate bipolar transistor (IGBT) products. A conclusion is drawn that the SiC converters can improve the wind system power conversion efficiency and can reduce the system's size and cost due to the low-loss, high-frequency, and high-temperature properties of SiC devices, even for one-for-one replacement for Si devices.