Gui-Jia Su

A novel ZVS-ZCS bidirectional DC-DC converter for fuel cell and battery application

This paper presents a new zero-voltage-switching (ZVS) bidirectional dc-dc converter. Compared to the traditional full and half bridge bidirectional dc-dc converters for the similar applications, the new topology has the advantages of simple circuit topology with no total device rating (TDR) penalty, soft-switching implementation without additional devices, high efficiency and simple control. These advantages make the new converter promising for medium and high power applications especially for auxiliary power supply in fuel cell vehicles and power generation where the high power density, low cost, lightweight and high reliability power converters are required. The operating principle, theoretical analysis, and design guidelines are provided in this paper. The simulation and the experimental verifications are also presented.

Multilevel DC link inverter

This paper presents a new class of multilevel inverters based on a multilevel DC link (MLDCL) and a bridge inverter to reduce the number of switches, clamping diodes or capacitors. An MLDCL can be a diode-clamped phase leg, a flying capacitor phase leg, or cascaded half-bridge cells with each cell having its own DC source. Connecting one of the MLDCLs with a single-phase bridge inverter can form a multilevel voltage source inverter. The MLDCL provides a DC voltage with the shape of a staircase approximating the rectified shape of a commanded sinusoidal wave, with or without pulse width modulation, to the bridge inverter, which in turn alternates the polarity to produce an ac voltage. Compared with the cascaded H-bridge, diode-clamped and flying-capacitor multilevel inverters, the MLDCL inverters can significantly reduce the switch count as the number of voltage levels increases. For a given number of voltage levels, m, the required number of active switches is 2/spl times/(m-1) for the existing multilevel inverters but is m+3 for the MLDCL inverters. Simulation and experimental results are included to verify the operating principles of the MLDCL inverters.

Low-cost sensorless control of brushless DC motors with improved speed range

This paper presents a low-cost position sensorless control scheme for brushless dc motors. Rotor position information is extracted by indirectly sensing the back EMF from only one of the three motor-terminal voltages for a three-phase motor. Depending on the terminal voltage sensing locations, either a low-pass filter or a band-pass filter is used for position information retrieval. This leads to a significant reduction in the component count of the sensing circuit. The cost saving is further increased by coupling the sensing circuit with a single-chip microprocessor or digital signal processor for speed control. In addition, a look-up-table-based correction for the nonideal phase delay introduced by the filter is suggested to ensure accurate position detection even at low speed. This extends the operating speed range and improves motor efficiency. Experimental results are included to verify the proposed scheme.

A Multiphase, Modular, Bidirectional, Triple-Voltage DC–DC Converter for Hybrid and Fuel Cell Vehicle Power Systems

Electrical power systems in future hybrid and fuel cell vehicles may employ three voltage [14 V, 42 V, and high voltage (HV)] nets. These will be necessary to accommodate existing 14-V loads as well as efficiently handle new heavy loads at the 42-V net and a traction drive on the HV bus. A low-cost DC-DC converter was proposed for connecting the three voltage nets. It minimizes the number of switches and their associated gate driver components by using two half-bridges and a high-frequency transformer. Another salient feature is that the half bridge on the 42-V bus is also utilized to provide the 14-V bus by operating at duty ratios around an atypical value of 1/3. Moreover, it makes use of the parasitic capacitance of the switches and the transformer leakage inductance for soft switching. The use of half bridges makes the topology well suited for interleaved multiphase modular configurations as a means to increase the power level because the capacitor legs can be shared. This paper presents simulation and experimental results on an interleaved two-phase arrangement rated at 4.5 kW. Also discussed are the benefits of operating with an atypical duty ratio on the transformer and a preferred multiphase configuration to minimize capacitor ripple currents.

A Reduced-Part, Triple-Voltage DC–DC Converter for EV/HEV Power Management

Electrical power systems in future hybrid and fuel cell vehicles may consist of three voltage nets: 14 V, 42 V, and high voltage (>200 V) buses. A soft-switched, bidirectional dc-dc converter that uses only four switches was proposed for interconnecting the three nets. This paper presents a reduced-part dc-dc converter, which decreases the converter cost while retaining all the favorable features of the original topology. Experimental data are included to verify a simple power flow control scheme.

A low-cost, digitally-controlled charger for plug-in hybrid electric vehicles

In this paper, a low-cost onboard charger for plug-in hybrid electric vehicles (HEVs) is presented and verified experimentally. The idea is to utilize the already available main traction and auxiliary motors and associated power electronics systems of an HEV to construct the charger circuit instead of building a standalone charger. Compared to the latter, it enables significant cost, weight, and volume reductions. The topology was verified by modeling and experimental results on a 14 kW prototype.

A five-leg inverter for driving a traction motor and a compressor motor

This paper presents an integrated inverter for speed control of a traction motor and a compressor motor to reduce the compressor drive cost in electric vehicle/hybrid electric vehicle applications. The inverter comprises five phase-legs; three of which are for control of a three-phase traction motor and the remaining two for a two-phase compressor motor with three terminals. The common terminal of the two-phase motor is tied to the neutral point of the three-phase traction motor to eliminate the requirement of a third phase leg. Further component reduction is made possible by sharing the switching devices, dc bus filter capacitors, gate drive power supplies, and control circuit. Simulation and experimental results are included to verify that speed control of the two motors is independent from each other

Multilevel DC link inverter for brushless permanent magnet motors with very low inductance

Due to their long effective air gaps, permanent magnet motors tend to have low inductance. The use of ironless stator structure in present high power PM motors (several tens of kWs) reduces the inductance even further (<100 /spl mu/H). This low inductance imposes stringent current regulation demands for the inverter to obtain acceptable current ripple. An analysis of the current ripple for these low inductance brushless PM motors shows that a standard inverter with the most commonly used IGBT switching devices cannot meet the current regulation demands and will produce unacceptable current ripples due to the IGBTs limited switching frequency. This paper introduces a new multilevel DC link inverter, which can dramatically reduce the current ripple for brushless PM motor drives. The operating principle and design guidelines are included.

Optimum fuel cell utilization with multilevel DC-DC converters

Static characteristics of fuel cells show more than a 30% difference in the output voltage between no-load to full-load conditions. This inevitable decrease, which is caused by internal losses, reduces the utilization factor of the fuel cells at low loads. Additionally, the converters fed by these fuel cells have to be derated to accommodate higher input voltages at low currents. To increase the utilization of fuel cells and to avoid derating of semiconductors, this paper proposes a level reduction control using a multilevel DC-DC converter. Level reduction is done by inhibiting a certain number of fuel cells when the load current decreases. The inhibited fuel cells can be used in other applications such as charging batteries to further increase their utilization and the efficiency of the system.

A Three-Phase Bidirectional DC-DC Converter for Automotive Applications

This paper presents a three-phase soft-switching, bidirectional dc-dc converter for high-power automotive applications. The converter employs dual three-phase active bridges and operates with a novel asymmetrical but fixed duty cycle for the top and bottom switches of each phase leg. Simulation and experimental data on a 6-kW prototype are included to verify the novel operating and power flow control principles.