John Stanley Glaser

Small-signal analysis of frequency-controlled electronic ballasts

This paper presents analytical tools aimed at improving and simplifying the development of frequency-controlled dimming electronic ballasts. A modified phasor transformation is proposed that converts a frequency-modulated signal into an equivalent time-varying phasor. The proposed transformation is applied to develop a complete small-signal phasor model of the LCC resonant ballast, which explicitly models the effect of the frequency modulation on the envelopes of the outputs. A Spice-compatible implementation of the model is presented that facilitates ac analysis of the ballast in addition to envelope transient simulation, and is verified through comparison of experimental and simulation results. A closed-form solution of the control-to-output current transfer function for the ballast-resistor system is presented, along with key observations of the pole locations and low-frequency gain that facilitate simple and intuitive compensator design. The effects of lamp dynamics on the controller design are discussed, followed by a design example for the feedback controller.

Recent advances in silicon carbide MOSFET power devices

Emerging silicon carbide (SiC) MOSFET power devices promise to displace silicon IGBTs from the majority of challenging power electronics applications by enabling superior efficiency and power density, as well as capability to operate at higher temperatures. This paper reports on the recent progress in development of 1200V SiC power MOSFETs. Two different chip sizes were fabricated and tested: 15A (0.225cm×0.45cm) and 30A (0.45cm×0.45cm) devices. First, the 30A MOSFETs were packaged as discrete components and static and switching measurements were performed. The device blocking voltage was 1200V and typical on-resistance was less than 50 mΩ with gate-source voltages of 0V and 20V, respectively. The total switching losses were 0.6 mJ, over five times lower than the competing devices. Next, a buck converter was built for evaluating long-term stability of the MOSFETs and typical switching waveforms are presented. Finally, the 15A MOSFETs were used for fabrication of 150A all-SiC modules. The module on-resistance values were in the range of 10 mQ, resulting in the best-in-class on-state voltage values of 1.5V at nominal current. The module switching losses were 2.3 mJ during turn-on and 1 mJ during turn-off, also significantly better than competing designs. The results validate performance advantages of the SiC MOSFETs, moving them a step closer to power electronics applications.

Output plane analysis of load-sharing in multiple-module converter systems

This paper explores the origin of the DC current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems. Both problems may be studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems. Furthermore, a broad class of converters whose output voltage is load-dependent, i.e., those that have a moderate value of output resistance, all exhibit good voltage- and current-sharing characteristics. Such converters are often suitable for a/spl times/b arrays of converters that can meet a large range of power-conversion requirements. The output planes of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A simple small-signal model of the modular converter system is developed. Experimental confirmation of load sharing and the small-signal model is given for the clamped series resonant converter and the series resonant converter for various configurations of four converters. >

Direct comparison of silicon and silicon carbide power transistors in high-frequency hard-switched applications

RECENT progress in wide bandgap power (WBG) switches shows great potential. Silicon carbide (SiC) is a promising material for power devices with breakdown voltages of several hundred volts up to 10 kV. SiC Schottky power diodes have achieved widespread commercial acceptance. Recently, much progress has been made on active SiC switches, including JFETs, thyristors, BJTs, IGBTs, and MOSFETs. Many a great promise has been made, and wondrous claims abound, but the question remains: will they live up to the hype? We explore this question for the class of high-frequency, hard-switched converters with input voltages of up to 600 VDC and power throughputs in the kilowatt range. Experimental evidence shows that both superior efficiency and higher power density may be obtained via the use of SiC MOSFETs. A direct comparison is made using silicon power devices (IGBTs and MOSFETs) and SiC MOSFETs in a 200 kHz, 6 kW, 600 V hard-switched converter. The losses are measured and conduction and switching losses of the active devices are estimated. Total losses can be reduced by a factor of 2–5 by substitution of SiC MOSFETs for Si active power devices.

A 500 W push-pull dc-dc power converter with a 30 MHz switching frequency

DESIGNERS of power conversion circuits are under relentless pressure to increase power density while maintaining high efficiency. Increased switching frequency is a primary path to higher power density. Prior work has shown that the use of switching frequencies in the VHF band (30 MHz-300 MHz) are a viable path to the achievement of gains in power density. A promising topology for VHF operation is the voltage-fed Class EF2 (Class Φ2) inverter based topology, where the use of controlled impedance at the switching frequency and its 2nd and 3rd harmonics provides both full soft switching and substantially reduced voltage stress compared to topologies such as Class E. However, such converters contain multiple resonant elements, and the tuning of the converter can be complicated due in part to the interaction of said elements. It is proposed that a push-pull version of the Class EF2 inverter can alleviate some of these difficulties. In particular, it is shown that odd and even frequency components can be independently tuned without interaction, and furthermore that center-tapped inductors may be used to reduce the total volume occupied by said inductors. The benefits include simplified design and increased power density. Evidence is presented in the form of a push-pull Class EF2 (Class Φ2) unregulated 500 W prototype dc-dc converter with a 30 MHz switching frequency, an input voltage 150 VDC, and an output voltage of 65 VDC. This converter has an efficiency of > 81% under nominal conditions, including gate drive power.

Application of a constant-output-power converter in multiple-module converter systems

The origins of the current-sharing problem of parallel-converter systems and the dual problem of voltage sharing in series-converter systems are explored. Both problems are studied by examining the output plane (output current versus output voltage) of a particular converter. It is shown that strict current source behavior is unnecessary for good current sharing in parallel-converter systems, and that converters which behave neither as current nor as voltage sources can share a load equally in an a*b array of converters. One class of converters useful in such systems is that characterized by constant output power (e.g., the clamped series resonant converter). Furthermore, it is shown that constant output power converters are a subset of a broad class of converters whose output voltage is load-dependent, all of which exhibit particular load-sharing good voltage- and current-sharing characteristics. The characteristics of discontinuous mode PWM converters as well as conventional and clamped series resonant converters are examined in detail. A small-signal model of the modular converter system is developed. Experimental results are given.<<ETX>>

Direct modeling of envelope dynamics in resonant inverters

This paper provides a direct dynamic modeling approach for envelope signals in resonant inverters driven by modulated inputs (AM or FM). Based on the sinusoidal approximation, this approach decomposes the modulated input into its fundamental component plus two dominant sidebands. The system response is then found by the summation of the responses to the three individual inputs. Following this conception, the small signal transfer functions for envelope signals in a resonant inverter are then derived. Some simple but useful results for these transfer functions are presented, which link the transfer functions of envelope signals to the transfer functions of the resonant tank and simplify hand calculations. This modeling approach is verified with simulation and experimental results by studying the dynamic responses of output current envelope to bus voltage and switching frequency.

13.56 MHz High Density DC–DC Converter With PCB Inductors

This paper presents the design and implementation of a high density 150–200 V to 28 V, 200–400 W resonant dc–dc converter with embedded inductors. The converter has a switching frequency of 13.56 MHz and uses air-core toroidal inductors fabricated with printed circuit board (PCB) technology. Implementing toroidal inductors with the PCB reduces inductance variation. Hence, the tuning and implementation of the converter are simplified while achieving high levels of performance and power density. By not using magnetic cores, the inductors also maintain stable values over a wide temperature range. Moreover, the paper discusses the tradeoffs between simplicity and performance of implementing a hard-switched gate drive at megahertz switching frequencies. We describe the advantages of resonant power converter topologies in applications requiring high density and high performance in demanding environmental conditions.

3.3kV SiC MOSFETs designed for low on-resistance and fast switching

This paper discusses the latest developments in the optimization and fabrication of 3.3kV SiC vertical DMOSFETs. The devices show superior on-state and switching losses compared to the even the latest generation of 3.3kV fast Si IGBTs and promise to extend the upper switching frequency of high-voltage power conversion systems beyond several tens of kHz without the need to increase part count with 3-level converter stacks of faster 1.7kV IGBTs.

Dynamic analysis of frequency-controlled electronic ballasts

This paper presents analytical tools aimed at improving and simplifying the development of frequency-controlled dimming electronic ballasts. A modified phasor transformation is proposed that converts a frequency-modulated signal into an equivalent time-varying phasor. The proposed transformation is applied to develop a complete small-signal phasor model of the LCC resonant ballast, which explicitly models the effect of the frequency modulation on the envelopes of the outputs. A Spice-compatible implementation of the model is presented that facilitates AC analysis of the ballast in addition to envelope transient simulation, and is verified through comparison of experimental and simulation results. A closed-form solution of the control-to-output current transfer function for the ballast-resistor system is presented, along with key observations of the pole locations and low-frequency gain that facilitate simple and intuitive compensator design. Finally a design example for the feedback controller is given to verify the theoretical analysis.