Power conversion in variable load applications

Details Power conversion in variable load applications Power conversion in variable load applications

2002-09-26

2004-10-05

Berhane, Adolf (Department: 2838)

Electricity: power supply or regulation systems

Output level responsive

Using a three or more terminal semiconductive device as the...

C363S089000

Reexamination Certificate

active

06801027

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates generally to power conversion systems and more specifically to power conversion in radar antenna systems.
BACKGROUND OF THE INVENTION
Proper management of power for a destination system, such as conditioning and distribution, often is critical to the operation of the destination system. However, many difficulties complicate the management of power in such systems. For one, many such destination systems include components having different requirements for the form of power supplied. Some components may require an alternating current (AC) electrical feed, others may require direct current (DC) power, and the voltage, current, and/or frequency requirements may differ for different components of the destination system. Another complication often present is that such destination systems often have variable load requirements, making it difficult for conventional power management and distribution systems to provide an adequate amount of power.
Power management is particularly critical in radar antenna systems, where additional difficulties and constraints often are introduced. For example, in addition to different power form requirements, many radar antenna systems, such as Active Aperture Array radar systems, have temporary, rapid increases, or “pulses”, in power consumption during periods of long pulse, high duty scan modes. As a result, the load requirement of the radar antenna varies both substantially and frequently. Likewise, because of the environment in which radar antenna systems typically operate, further consideration is made for the ease of mobility and the ability of the power distribution system to interface with a variety of power sources. Likewise, because of potential hostile actions by adversaries, these radar antenna systems often have certain requirements of the power distribution system with regards to defense, such as by requiring a minimized infrared signature.
Accordingly, various power management systems have been developed to address some or all of these difficulties. However, these known systems have a number of limitations. For one, these known systems typically include a single power source that provides all of the power for the system. Such an arrangement does not accommodate for a failure of the single power source and therefore does not provide redundancy. In response, some known power management/distribution systems include a second power source in parallel with a first power source. Although this arrangement provides redundancy, it too has inherent limitations. Either both power sources must be operational simultaneously, resulting in wasted power/fuel and/or increased operational costs, or only one power source is kept operational at a time, thereby minimizing waste but requiring some down time to switch between one power source to the other power source in the event of a failure or any necessary repairs/maintenance. As a result, degradation in the capability of the power distribution system to provide power generally causes degradation in the performance of the radar antenna system.
Another limitation of known power management systems arises in variable load applications. Conventional power management systems typically provide power at full capacity, thereby causing wasted power during periods of light duty by the destination system. For example, many radar antenna systems operate in a light duty mode a majority of the time and only operate at full capacity during periods of alert, such as when an unknown entity has been detected. Accordingly, to provide for these brief periods of high duty, known radar antenna power systems continuously provide power adequate for the full capacity operation of the radar antenna system, thereby wasting a significant amount of power during light duty periods.
Furthermore, many known power management systems employ power converters to convert power from a first form to power having a second form, such as from alternating current (AC) power to direct current (DC) power. These power converters typically receive power in the first form from one or more power sources, convert the power, and provide the converted power to a component of a system. To illustrate, many types of AC-DC converters include a universal front end where the AC mains typically range between 85 volts AC (VAC) and 265 VAC at between 50 and 60 hertz (Hz). These types of AC-DC converters typically rectify and capacitively filter the AC input to provide a low ripple DC buss to a DC-DC converter.
However, these known converter have a number of limitations. For one, these known converters typically have severe line current harmonics and therefore generally do not comply with Military Standard (MIL-STD) 1399. Also, the high voltage DC buss fed to the DC-DC converter generally is unregulated and fluctuates with line voltage, thereby placing the burden on the DC-DC converter to operate from a 2:1 line range. Furthermore, the output of these known AC-DC converters often are line regulated, requiring a relatively large voltage on the output rectifiers due to the necessary transformer turns ratio. This line regulation requirement often prohibits the optimization of the output state with lowest possible drop Schottky diodes, resulting in a less-than-optimal efficiency and higher power dissipations than otherwise.
Another limitation of many known relatively low voltage power converters is their lack of power factor correction (PFC). This lack of PFC often prevents the power circuitry from achieving optimum performance and meeting critical specifications of the load to which the power converter is connected. Higher voltage (typically above 300 VDC) AC-DC converters can implement PFC relatively easily, since boost or buck-boost style front end can be used to produce a relatively high intermediary voltage. However, the method most typically employed to convert this higher level intermediary voltage to a lower DC output voltage includes placing DC-DC converter in series with the AC-DC converter, thereby increasing the complexity, cost, and power dissipation of the power converter.
Additionally, known power converters typically are not adapted to change their output voltage relative to loading effects, such as a change in the load requirement of a load. Likewise, known power converters generally are incapable of preparing for a heavy load requirement before it occurs. As a result, either a single power converter is adapted to constantly supply an amount of power equivalent to the maximum load requirement of a load or multiple power converters constantly supply a total amount of power equivalent to the maximum load requirement, wasting power in either case. Alternatively, known power converters may be adapted provide only an adequate amount of power for average use. As a result, undesirable operation of the load may occur during heavy loads in excess of the average load requirement. Additional limitations of known power converters include: an inability to produce the desired DC output from a DC input; implementing only a fail signal for the status of the converter, rather than providing built-in test (BIT) or built-in test equipment (BITE) information.
Furthermore, many such power management systems, especially radar systems, make use of voltage regulators to provide a regulated voltage to the one or more loads. However, to account for any temporary increases, or “pulses,” in the power consumption by the load, these voltage regulators often include relatively large capacitive elements (e.g., capacitors) both at the input and the output of the voltage regulator to provide stored energy for use during these temporary increases in power consumption. While useful in compensating for the increased power consumption by the load and in preventing the voltage regulator from “dropping out,” these relatively large capacitors often prove cumbersome, both in the space they occupy and the cost of their implementation.
The size and cost of these capacitors is of particular significance in radar systems, which often utilize thousan

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