Electric power conversion systems – Current conversion – Including an a.c.-d.c.-a.c. converter
Reexamination Certificate
2000-07-20
2001-12-18
Patel, Rajnikant B. (Department: 2838)
Electric power conversion systems
Current conversion
Including an a.c.-d.c.-a.c. converter
C363S132000, C318S434000
Reexamination Certificate
active
06331941
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates generally to the detection of shorts in various electrical circuits and more particularly to a method and apparatus for detecting shorts with a lower risk of damaging the circuits during a detection procedure.
It is often desirable to test power conversion circuits for integrity. Generally, a “power conversion circuit” refers to any circuit that renders a change in electrical power, such as a step-up transformer, a step-down transformer, an inverter, a rectifier, a switching bridge, or the like. Power conversion circuits find applications in many devices, such as AC motor drives for example. Typically in an AC motor drive, three phase AC power is converted to DC power and conversion circuits, such as bridges, are coupled between positive and negative DC buses. The conversion circuits are operated in a predetermined manner to generate a reasonable facsimile of AC power having the desired voltage and frequency using various techniques, such as pulse width modulation. Many power conversion circuits comprise complex semiconductor circuits that must be manufactured under very precise conditions and are subject to defects or failure due to overloading.
Of particular importance in many power conversion circuits is avoidance of shorts. Of course, shorts may cause the power conversion device to malfunction. Further, shorts in power conversion devices can cause damage to other components coupled to the power conversion device, such as motors, and may even cause physical harm to nearby personnel due to electrical shock or explosion. Accordingly, power conversion circuits and other electrical circuits are often subjected to short circuit test procedures after assembly.
It is known to accomplish short circuit testing of power conversion circuits by charging the DC bus and subsequently firing the gates of the circuit elements of interest in sequence while observing for symptoms of a short. However, this procedure has disadvantages. First, the timing of firing the various gates must be executed precisely or the results of the test procedure will not be accurate. It is difficult in a practical sense to achieve the required timing precision. Second, if the DC bus is charged beyond a relatively low level when the gates are fired, the bus capacitors will discharge at a very high current level, often in excess of the ratings of the circuit elements such as integrated gate commutated thyristors (IGCTs). Of course, such currents can damage the circuit elements. For these reasons, the short circuit test procedure described above is difficult to apply and often destructive.
BRIEF SUMMARY OF THE INVENTION
A first aspect of the invention is a method of testing an electrical circuit between two DC buses for shorts, comprising the steps of gating selected elements of the circuit, activating a DC bus charger coupled to the DC buses while the circuit is gated, detecting a level of charge of the DC buses over time as a result of the activating step to determine if the circuit is shorted, and discharging the DC buses after the detecting step.
A second aspect of the invention is an apparatus for testing an electrical circuit between two DC buses for shorts, comprising means for gating selected elements of the circuit, means for activating a DC bus charger while the circuit is gated, means for detecting a level of charge of the DC buses over time as a result of the DC bus charger to determine if the circuit is shorted, and means for selectively discharging the DC buses.
A third aspect of the invention is a short circuit test cell comprising a positive DC bus, a negative DC bus, a neutral DC bus, an electrical circuit connected between the positive DC bus and the negative DC bus, a DC bus charger coupled to the positive DC bus and the negative DC bus, a discharge circuit coupled to the positive DC bus and the negative DC bus, the discharge circuit including a switch coupled between the positive DC bus and the neutral DC bus and a switch coupled between the negative DC bus and the neutral DC bus, and a controller operatively coupled to the electrical circuit, the DC bus charger, and the discharge circuit. The controller is operative to selectively gate the electrical circuit, operate the DC bus charger, and detect a charge on the DC bus in response to activation of the DC bus charger. The controller also is operative to activate the discharge circuit to discharge the DC bus between gating operations.
A fourth aspect of the invention is an AC motor drive comprising, a converter section, a positive DC bus, a negative DC bus, a neutral DC bus, an inverter section having bridges connected between the positive DC bus and the negative DC bus, a DC bus charger coupled to the positive DC bus and a controller operatively coupled to the bridges, the DC bus charger, and the discharge circuit. The controller is operative to selectively gate the bridges, operate the DC bus charger, and detect a charge on the DC bus in response to activation of the DC bus charger. The controller also is operative to activate the discharge circuit to discharge the DC bus between gating operations.
REFERENCES:
patent: 4720776 (1988-01-01), Guyeska et al.
patent: 5631813 (1997-05-01), Ikeshita
patent: WO 90/07813 (1990-07-01), None
Duncan, Esq. Kevin T.
General Electric Company
Horton Esq. Carl B.
Hunton & Williams
Patel Rajnikant B.
LandOfFree
Short circuit detection method and apparatus and motor drive... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Short circuit detection method and apparatus and motor drive..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Short circuit detection method and apparatus and motor drive... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2564792