Direct current/direct current converter for a fuel cell system

Abstract

Fuel cell systems and control methods including a fuel cell and a second energy source, such as a battery that is adapted to supplement the fuel cell. In addition, the fuel cell system utilizes a single bipolar switching module, such as an IGBT six pack module that is configured to implement a DC / DC converter, such as a DC / DC boost converter, for both the fuel cell and the battery. The fuel cell system also makes use of a controller that is configured to control either or both of input current and output voltage of the DC / DC converter.

Description

CROSS REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of co-pending U.S. utility application entitled, “DIRECT CURRENT / DIRECT CURRENT CONVERTER FOR A FUEL CELL SYSTEM,” having Ser. No. 10 / 346,561, filed Jan. 16, 2003, which is entirely incorporated herein by reference, which claims the benefit of provisional application having Ser. No. 60 / 319,701, filed Jan. 16, 2002.BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present fuel cell systems and control methods relate generally to direct current-to-direct current (DC / DC) converters, and more particularly to using a DC / DC converter with both a fuel cell and a second energy source. [0004] 2. Description of the Related Art [0005] In an application utilizing an energy source, such as a fuel cell, the quality of power or the regulation of the direct current (DC) bus is an issue. For example, a fuel cell is typically not able to respond immediately to peaks in demand. A further issue in su...

AI Technical Summary

Benefits of technology

[0007] In a further aspect of the present fuel cell systems and control methods, a DC / DC converter with independent control of DC / DC converter input current and output voltage is used, which increases system efficiency.

[0009] An embodiment of the present fuel cell systems and control methods provides a DC / DC converter that utilizes one leg of an insulated gate bipolar transistor (IGBT) six pack module to provide bi-directional DC / DC conversion between a battery pack and an inverter DC bus. The other two legs of the IGBT six pack module provide DC / DC conversion between a fuel cell and the inverter DC bus. This achieves optimization of best use of the power stage to provide lower system cost topologies by utilizing the IGBT six pack module configuration. The battery pack can also supply power during fuel cell outages. One or two legs of the IGBT six pack module can be added in parallel to the battery leg by using a contactor or switch to increase power conversion capability.

[0011] The IGBT six pack module has, for example, three IGBT legs that are configured to boost the DC voltage from the fuel cell and the battery to the DC bus capacitor bank and load. In addition, one of the three IGBT legs of the module is configured to provide for bi-directional DC / DC conversion for the battery. A first switch (alternatively referred to herein as a contactor) is adapted to connect the other two of the three IGBT legs to the battery to provide two additional DC / DC converter legs to the battery for a high power load. The first switch is also adapted for switching to a fuel cell position to provide two legs of the IGBT six pack module to boost the fuel cell voltage when the fuel cell is the primary energy source. A second switch (alternatively referred to herein as a contactor) is adapted to disconnect the battery from the DC / DC converter.

[0012] The present fuel cell systems and control methods also make use of a controller that is configured to control either or both of input current and output voltage of the DC / DC converter. The controller is configured to control the input current of the DC / DC converter by controlling a duty cycle of two fuel cell legs of the IGBT six pack module. The controller is configured to control the output voltage of the DC / DC converter by controlling a battery pack leg of the IGBT module and employing a bi-directional capability of the IGBT module. In addition, the controller is configured to simultaneously control either or both of the input current and output voltage of the DC / DC converter by controlling a flow of power to and from the battery to maintain an average state of charge of the battery, whereby the battery can deliver or absorb a required level of power.

Problems solved by technology

In an application utilizing an energy source, such as a fuel cell, the quality of power or the regulation of the direct current (DC) bus is an issue.

For example, a fuel cell is typically not able to respond immediately to peaks in demand.

A further issue in such an application is that the fuel cell may be subject to power outages which are unacceptable in an uninterruptible power supply (UPS) application.

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