Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
2000-09-01
2001-05-29
Sterrett, Jeffrey (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
C363S098000
Reexamination Certificate
active
06239997
ABSTRACT:
TECHNICAL FIELD
the present invention relates generally to a supplemental power source, and more particularly to a system and method for connecting and synchronizing a supplemental power source to a power grid.
BACKGROUND OF THE INVENTION
When a supplemental power source, such as a three-phase generator, is connected to a power grid, a small difference in the frequency, phase angle, or magnitude between the source and the grid can create very large over current. This is because the voltage source usually has very low impedance. The over current condition can trigger the power grid to “shut-down” or may damage circuit components.
Therefore, it is necessary when connecting a supplemental power source to a power grid to guarantee that the three phase output voltage of the power source has the same phase sequence, the same phase angle, and the same magnitude and frequency as the three phase voltage of the power grid. This is called synchronization of the power source and the power grid.
In the prior art, it is known to employ a phase lock loop technique to control the phase synchronization of the supplemental power source (SPS) and the power grid. Prior to the present application, this technology is basically a hard-wired configuration requiring hardware and associated hardware control technology. This technique requires separate phase and magnitude detecting circuits to control the voltage phase and magnitude of the supplemental power source. Extra circuitry is required to calculate the frequency of the supplemental power source or the power grid.
SUMMARY OF THE INVENTION
It is an object of the present invention to connect a supplemental power source to a power grid. It is another object of the present invention to synchronize the connection of a supplemental power source to a power grid.
It is a further object of the present invention to provide a software solution for connecting a supplemental power source to a power grid. It is still a further object of the present invention to detect the three phase voltages of the power grid, and to control the SPS voltage magnitude and phase to generate a more flexible method of connection.
In carrying out the above objects and other objects and features of the present invention, a software solution is provided for connecting a supplemental power supply to a power grid. The system and method of the present invention uses fewer devices and generates more useful information, i.e. phase sequence, phase angle, grid frequency, etc., for control while providing a faster response and increased flexibility for control.
The present invention is an electronic supplemental power supply having circuitry and controls for detecting grid voltage and current that are used to synchronize, and connect, the three-phase output voltages of the supplemental power supply with a power grid. Through these controls, the method of the present invention detects the three phase voltages of both the supplemental power supply and the power grid and converts the detected voltages into components on a d-q plane.
The converted values are controlled and transformed to eliminate output voltage errors and correct the actual three-phase output voltages from the supplemental power source so that they are as close as possible to the voltages of the power grid.
According to the method of the present invention, current regulators are used to eliminate the possibility of over current caused by voltage errors between the supplemental power source and the power grid.
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Ford Motor Company
Sterrett Jeffrey
Vick Karl
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