Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2001-12-13
2003-03-25
Berhane, Adolf Deneke (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S132000, C363S017000
Reexamination Certificate
active
06538909
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates generally to AC/DC power converters and more particularly to a high efficiency AC/DC power converter operative to produce regulated DC output power with utility AC power as the input source.
2. Status of the Prior Art
In a conventional AC/DC converter, power is usually delivered to a DC load or multiple DC loads at a constant rate. Due to the fundamental nature of a single-phase AC source, power drawn from such a source has a pulsating nature with an average value equal to the output power plus losses incurred by the converter. Accordingly, the AC/DC converter must provide means for storing and retrieving energy during each half-cycle of the AC line.
In the conventional AC/DC converter, large value capacitors are used for energy storage. The voltage present on these capacitors determines the output voltage of the AC/DC converter and is regulated. In other words, the regulated output voltage of the AC/DC converter is a linear function of the capacitor voltage. When the conventional converter is used in universal input applications where the input line voltage can vary from 108 Vac to 264 Vac it is not feasible to maintain a regulated capacitor voltage. In order to mitigate the need for an AC/DC converter with a regulated output voltage and a wide range of input voltages, multiple AC/DC power converter designs have been developed. These are generally multiple designs of a dual power processing stage AC/DC converter. The first power processing stage is generally the voltage boost stage consisting of an AC rectified input followed by a choke-boosted converter. The choke-boosted converter has a capacitor output to provide for the energy storage described earlier.
The capacitor output presents an equivalent DC voltage source to the second power processing stage. The capacitor output, used for storing and retrieving energy, is generally a high capacitance capacitor or capacitors that are expensive and large in volume. The transformer turns ratio and the regulated output voltage of the first power processing stage defines the regulated output voltage of the AC/DC converter. The second power processing stage is a DC/DC converter with a transformer-rectified output.
In addition to providing regulated DC output voltage, the first power processing stage may provide for power factor correction (PFC). The second power processing stage accepts the regulated DC voltage from the first power processing stage and provides for input to output voltage amplification (via the transformer turns ratio) and galvanic isolation. Because of the large variations in utility voltages that exist in the global market place (i.e., 108 Vac to 264 Vac), a single conventional AC/DC converter design cannot process the full input voltage range and provide for the desired regulated output voltages. Accordingly, different converter designs are used to satisfy different portions of the input voltage range. As such, the AC/DC converter design for 120 Vac input will be different than that for 240 Vac input. Specifically, due to large variations in worldwide household and commercial AC power sources, multiple designs for the AC/DC converter are available. Furthermore, the desire for unity power factor by utility companies, the requirement for galvanic isolation for safety, and the large differences in application usage of power converter creates application specific designs. For example, conventional AC/DC power converters for battery chargers are designed for the specific application. The input voltage, as well as the output voltage requirements, are taken into considerations in the design process. Accordingly, the design of a conventional AC/DC converter for a given battery pack will change according to different AC input voltage sources.
The present invention addresses the above-mentioned deficiencies in AC/DC power converter designs by providing a single power converter design which can accept universal input voltages (i.e., 108 Vac to 264 Vac) and provide regulated DC output with a large voltage range. The invention is primarily an AC/DC power converter utilizing universal utility power to charge a battery pack. A battery pack is a group of batteries connected in series or series-parallel. The present invention operates using a single power processing stage, and provides power factor correction (PFC), input to output isolation (galvanic), and sine square output power. With the aid of relay(s) and a tapped transformer, the single stage AC/DC power converter of the present invention accepts input voltages of a global range (i.e., 108 Vac to 264 Vac) and provides regulated DC power with a large output voltage and power range capability, (i.e., 0 to 6 kW). The proposed invention provides constant power operation at large battery voltage range. For higher output power requirements, the multiple AC/DC power converters of the present invention can be operated in parallel or multiphase configuration without more effort than connecting the inputs and outputs accordingly. The AC/DC power converter of the present invention maintains a single design with higher efficiency, lower cost, and smaller volume than the conventional AC/DC power converters serving the same function.
SUMMARY OF THE INVENTION
In accordance with the present invention, there is provided a universal AC/DC power converter for generating regulated DC output power with large voltage range from a varying AC input voltage source of a global range (i.e., 108 Vac to 264 Vac). The AC/DC power converter has a single power processing stage, at least one relay in electrical communication with the output of the single power processing stage, a transformer in electrical communication with the relay, an output rectifier network in electrical communication with the output of the transformer, and a processor that contains the control for logic of the AC/DC power converter. The single power processing stage includes an input rectifier network to rectify the AC input voltage to a DC input voltage, and a voltage boost function to increase the DC input voltage to a higher regulated voltage defined herein as the boosted voltage. The boosted voltage is the regulated output voltage of the voltage boost function. The voltage boost function entails at least one inductor, at least one diode, at least four switching devices, an input current transducer, and the function of the processor. The four switching devices may be transistors such as power MOSFET's or IGBT's, and the input current transducer may be a sense resistor. In addition to the voltage boost function, the single power processing stage includes a voltage chop function that chops the boost voltage to form AC voltage. This AC voltage is in electrical communication with the transformer via the relays. The electrical components that make up the voltage chop function are some of the same components that make up the voltage boost function. For this reason the voltage boost function and the voltage chop function are defined as a single integrated power processing stage.
The relay (or relays) in electrical communication with the output of the single power processor stage is configured with at least two switching positions operated by the processor. The transformer (in electrical communication with the relays) has a primary winding and at least one secondary winding. The primary winding has at least two inputs operative to selectively vary the voltage generated on the secondary winding from the position of the relays. Alternatively, the relays can also be located on the secondary winding of the transformer without altering the intended function of the invention. Finally, an output rectifier network (in electrical communication with the transformer secondary winding) converts the AC voltage to DC voltage. The relays can selectively change the output DC voltage range of the AC/DC power converter by choosing the inputs of the transformer.
In accordance with the present invention, the AC/DC power converter includes a processor. The processor cont
Goodarzi Abas
Kang Don
Berhane Adolf Deneke
Enova Systems
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