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This paper describes the implementation of a four-pole neutral-point-clamped (NPC) three-phase inverter that produces virtually no common-mode voltage. The low common-mode voltage output is achieved by constraining the switch states of the NPC inverter to only those states that produce zero common-mode voltage in dead-time compensation, which enhances the capability of the circuit to produce low common-mode voltage by compensating common-mode voltages produced by reverse diode commutations. The low common-mode voltage performance is achieved at the expense of reduced voltage utilization and loss of dc-link voltage balance control. In order to overcome this limitation, a fourth pole and associated control are added to balance the upper and lower dc-link voltages. This paper describes the control implementations and simulation results compared to measured results used in tuning and commissioning of the system. A 450-V 78-kW system is implemented in hardware, and experimental results are provided, showing its differential mode transient and steady-state harmonic performance as well as its common-mode output voltage. Index Terms--Electromagnetic compatibility, grounding, power systems, pulse width modulated inverters.

A mathematical model that is developed for a generalized drive system, including common-mode passive and active elements, is used to explore the issues of paralleling soft-switched resonant dc-link drive systems. Differences between the modulation pattern for each drive system cause common voltage disturbances, which lead to significant circulating currents between the drive systems. Control methods for actively compensating for common-mode circulating currents or reducing the commonmode voltage disturbances are investigated. Practical modifications to the drive system controls are implemented to reduce the circulating currents between paralleled systems. Index Terms--Component, drive system modeling, electromagnetic interference (EMI), paralleling power converters, softswitched power converters.

A new six-phase 2.4-MVA soft-switched medium-voltage drive system utilizing series-stacked modules with low-voltage devices has been developed. The drive system combines a new soft-switched dc--dc converter with resonant dc-link inverter technology to deliver extremely low total harmoic distortion sinusoidal output, high power density, and high efficiency. The series-stacked configuration with the associated single-phase loading lead to unique power and control design challenges. Device selection, control of parasitic elements, sensing methods for converter control, custom magnetic component design, and clamping techniques have lead to a substantial improvement in device voltage utilization. The dc-dc converter controls must regulate the intermediate dc-bus voltage under single-phase loading while balancing transformer excitation and maintaining zero-voltage switching, among other tasks. Proper control of the resonant dc-link inverter requires the selection and tuning of the appropriate modulator and understanding its effect on the power circuit ratings. Index Terms--DC-DC converters, medium-voltage converter, multilevel converter, resonant dc link, sigma--delta modulation, soft switching.

This article identifies and validates the use of ultrafast silicon carbide (SiC) junction field effect transistor (JFET)-based self-powered solid-state circuit breakers (SSCBs) as the enabling protective device for a 340 Vdc 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 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 that 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 one of the SSCBs and three in cascaded arrangements are validated both in simulation and with a hardware test platform. Thermal impact on the SSCB is discussed as well. The target application is a residential dc microgrid that will be installed as part of a revitalization effort of an inner city Milwaukee neighborhood. [ABSTRACT FROM AUTHOR]

The suitability of a soft-switched actively clamped resonant dc-link (ACRDCL) inverter for low-output harmonic distortion/high-power-density power conversion is evaluated. Modulation and control techniques for achieving low-output harmonic distortion are described. Performance and power density of the ACRDCL inverter are maximized through the optimal design of the clamp circuit, resonant components, and output filter components. The ACRDCL inverter simulation and design are validated experimentally. For the same output kilovoltamperes, efficiency and harmonic performance as the ACRDCL inverter, hard-switched designs are compared. Methods to increase the power density of the ACRDCL are proposed, including the use of recently developed nonpunchthrough insulated gate bipolar transistors. Index Terms--Inverters, power electronics, power quality, resonant converters, soft-switched power converters.