Electric power conversion systems – Current conversion – With condition responsive means to control the output...
Reexamination Certificate
1999-10-27
2001-03-20
Nguyen, Matthew (Department: 2838)
Electric power conversion systems
Current conversion
With condition responsive means to control the output...
Reexamination Certificate
active
06205042
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to voltage source inverters, such as are used in motor drive applications. More particularly, the present invention relates to a method and apparatus for determining an effective DC bus voltage present within a voltage source inverter.
Voltage source inverters (VSIs) are commonly used in motor drives and other applications to control the magnitude and frequencies of voltages in these systems. It is generally desirable to be able to obtain an accurate measure of the effective DC bus voltage present within a VSI, as such a measure is useful for monitoring, control, and to obtain optimal VSI performance in different operating conditions. However, a wide variety of VSI's are known, many of which have designs or bridge topologies which make it difficult to directly measure the effective DC bus voltage. For example, multi-level VSI bridges are known which contain multiple internal DC buses. Conventionally, such bridges require multiple voltage sensors for direct measurements of the bus voltages. This solution is impractical because it typically requires high cost sensors in order to achieve a relatively high level of voltage isolation, and because the use of multiple sensors places a significant I/O burden on the control circuitry associated with the VSI.
In view of the limitations of the techniques described above, it would be desirable to be able to determine the effective DC bus voltage present within a VSI without the need for direct bus voltage measurement. It would further be desirable to be able to determine the effective DC bus voltage of the VSI regardless of the topology of the VSI bridge. It would also be desirable to accurately determine effective DC bus voltage in both transient and steady state conditions.
BRIEF SUMMARY OF THE INVENTION
The problems and limitations described above are overcome, and additional advantages can be achieved, according to the exemplary embodiments of the present invention described below, which provide a technique for accurately determining a DC bus voltage in a VSI independent of bridge topology and in both transient and steady state conditions. The exemplary embodiments use variables readily available within the VSI to accurately determine the effective DC bus voltage. In one example, effective DC bus voltage is determined by measuring a first output voltage of the VSI and dividing the first output voltage by a modulation index of the VSI to determine a first effective DC voltage signal. In another example, the effective DC voltage can be determined from a stored energy and an effective capacitance of the VSI. In still another example, the techniques can be combined.
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Blasey Thomas M.
General Electric Company
Horton Carl B.
Hunton & Williams
Nguyen Matthew
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