Z. John Shen

A self-powered ultra-fast DC solid state circuit breaker using a normally-on SiC JFET

This paper introduces a new self-powered solid state circuit breaker (SSCB) concept using a normally-on SiC JFET as the main static switch and a fast-starting isolated DC/DC converter as the protection driver. The new SSCB detects short circuit faults by sensing its drain-source voltage rise, and draws power from the fault condition to turn and hold off the SiC JFET. The new two-terminal SSCB can be directly placed in a circuit branch without requiring any external power supply or additional wiring. A unique low power isolated DC/DC converter is designed and optimized to provide a fast reaction to a short circuit event. The SSCB prototypes have experimentally demonstrated a fault current interruption capability up to 180 amperes at a DC bus voltage of 400 volts within 0.8 microseconds. DC circuit protection applications provide a unique market opportunity for wide bandgap power semiconductor devices outside the conventional focus on power electronic converter applications.

Droop control method for load share and voltage regulation in high-voltage microgrids

When the line impedance is considered in the microgrid, the accuracy of load sharing will decrease. In this paper, the impact of line impedance on the accuracy of load sharing is analyzed. A robust droop control for a high-voltage microgrid is proposed based on the signal detection on the high-voltage side of the coupling transformer. For a high-voltage microgrid, the equivalent impedance of coupling transformer connecting distributed generator with the grid is usually the dominate factor. Compared with the conventional droop control strategy, the proposed control method in this paper detects the feedback signal from the high-voltage side of the coupling transformer. The impact of line impedance on the load sharing accuracy can be mitigated significantly. The proposed droop control only changes the detection point of the feedback signal, thus it is easy to be implemented. The PSCAD/EMTDC simulation results show the effectiveness of the proposed robust droop control concept in load sharing and voltage regulation with highly accuracy.

Design and Analysis of DC Solid-State Circuit Breakers Using SiC JFETs

Protection against short-circuit faults remains a major technical challenge in increasingly popular dc power networks. This paper describes a new concept of a self-powered dc solid-state circuit breaker (SSCB) with one or more normally on SiC JFETs as the main static switch and a fast-starting isolated dc/dc converter as the protection driver. The new SSCB detects short-circuit faults by sensing its terminal voltage rise and draws power from the fault condition itself to turn and hold off the SiC switch. The new two-terminal SSCB can be directly placed in a circuit branch without requiring any external power supply or extra wiring. A low-power isolated dc/dc converter is designed and optimized to provide a fast reaction to a short-circuit fault. Unidirectional and bidirectional SSCB prototypes based on this design concept have been built. Repeated interruption of fault currents up to 180 A at a dc bus voltage of 400 V within 0.8 μs was experimentally demonstrated. DC circuit protection applications provide a unique market opportunity for wide-bandgap semiconductors, which are outside the conventional focus on power electronic converters.

Fault Analysis of Inverter-Interfaced Distributed Generators With Different Control Schemes

Diversification of control schemes adopted by inverter-interfaced distributed generators (IIDGs) leads to difficulties in fault current estimation in a microgrid, which might make preexisting protection systems invalid and threaten the safety of power electronic devices. It is therefore important to study fault characteristics of IIDGs. This paper investigates characteristics of fault current of IIDGs caused by both symmetrical and asymmetrical faults. Two kinds of widely used control modes, current control (constant current control and PQ control) and voltage control (V/F control and droop control), are under investigation to provide an intuitive comparison on fault current. In particular, a novel algorithm is proposed to calculate fault current of droop-controlled IIDGs. It is found that different limiters have great impacts on fault response of IIDGs and detailed research works are carried out to identify the effects in this paper. Simulation results based on PSCAD/EMTDC and calculation results based on MATLAB/Simulink verify the correctness of the proposed fault models.

A new characterization technique for extracting parasitic inductances of fast switching power MOSFETs using two-port vector network analyzer

This paper discusses a new technique to accurately characterize parasitic inductances of discrete fast switching MOSFETs based on S-parameters measurement using two-port vector network analyzer. The method is validated through case studies of 1200V SiC MOSFET in TO-247 and 30V silicon trench MOSFET in SO-8 package.

Fault discrimination using SiC JFET based self-powered solid state circuit breakers in a residential DC community microgrid

This paper identifies validates the use of ultra-fast SiC JFET based self-powered solid state circuit breakers (SSCBs) as the enabling protective device for a 340Vdc residential DC community microgrid. These SSCBs will be incorporated into a radial distribution system in order to enhance fault discrimination through autonomous operation. Because of the nature and characteristics of short circuit fault inception in DC microgrids, the time-current trip characteristics of protective devices must be several orders of magnitude of faster than conventional circuit breakers. The proposed SSCBs detect short circuit faults by sensing the sudden voltage rise between its two power terminals and draw power from the fault condition itself to turn off SiC JFETs and then coordinate with no load contacts can isolate the fault. Depending upon the location of the SSCBs in the microgrid either unidirectional or bidirectional implementations are incorporated. Cascaded SSCBs are tuned using a simple resistor change to enable fault discrimination between upstream high current feeds and downstream lower current branches. Operation of the SSCBs in these cascaded arrangements are validated both in simulation and with a hardware test platform. The target application is a residential DC microgrid that will be installed as part of a revitalization effort of an inner city Milwaukee neighborhood.

Extracting parasitic inductances of IGBT power modules with two-port S-parameter measurement

Parasitic inductances of IGBT power modules have a major influence in device operation and circuit performance. They often incur negative effects such as switching oscillations, EMI, extra power losses and stress on the devices. This paper proposes a technique to extract parasitic inductances of IGBT power modules based on two-port scattering (S) parameter measurement. Accurate values of the internal parasitic inductances can be obtained through a step by step analysis using the measured S-parameters. The new approach is experimentally validated with a case study of a commercial 600V IGBT half-bridge power module.

Failure modes and mechanism analysis of SiC MOSFET under short-circuit conditions

Abstract The preliminary characterization study and analysis of the short-circuit (SC) capability of SiC MOSFET have been reported in recent years. However, the failure modes of the SiC MOSFET under various SC conditions and their physical mechanisms are unclear. The purpose of this paper is to extensively investigate the SC ruggedness, failure modes and internal physical mechanisms of the SiC MOSFET. The influence of major limiting factors on the failure mode of the SiC MOSFET is experimentally studied, including gate drive voltage, DC bus voltage, case temperature and die sizing. Two SC failure mechanisms, the thermal runaway and gate interlayer dielectric breakdown of the SiC MOSFET are identified as the root reason of failure by means of microscopic failure analysis techniques.

Detection and identification of power switch failures for fault-tolerant operation of flying capacitor Buck-boost converters

Abstract Power switch failures have great influence for electronic converter. Prompt detection of power switchs failure and fault-tolerant operation of multilevel converters have extremely vital significance for high reliability electronic systems. The paper presents a new technique of detecting, identifying, and locating faults of switching devices in an N-Level Flying Capacitor Buck-Boost Converter (FCBBC). The characteristics of inductor current and flying capacitor voltage of FCBBC with different kinds of failure are analyzed. A new fault diagnosis algorithm is proposed to detect and identify the fault on basis of this information. Then the fault-tolerant operation method of the FCBBC is also discussed. The validity of the new control method is demonstrated in the control hardware by experiment result.

A New Characterization Technique for Extracting Parasitic Inductances of SiC Power MOSFETs in Discrete and Module Packages Based on Two-Port S-Parameters Measurement

The parasitic inductances of silicon carbide (SiC) power mosfets have a major influence on their operation and circuit performance. They incur negative effects such as switching oscillations, power losses, and electromagnetic interference noise. This paper introduces a new technique to accurately characterize the parasitic inductances of SiC power mosfets in both discrete packages and power modules based on two-port S-parameters measurement. By treating a power mosfet as a two-port network, we obtain the scattering (S) and impedance (Z) parameters from network analyzer measurement. These parameters, through detailed network analysis, provide more accurate values of the internal parasitic inductances than the commonly used single-port impedance measurement technique. The new approach is first verified with high-frequency circuit simulation and then applied in the case study of SiC power mosfets in a TO-247 discrete package and a half-bridge power module. In addition, a number of silicon power mosfets and IGBTs in TO-247, TO-220, D2PAK, DPAK, and SO-8 packages are also characterized for comparison. A comparison between the characterization results from the new two-port and the prior art one-port methods reveals a significant difference ranging from 12.6% to 93.9%.