Patent Application
20070063708
This invention relates to auto-transformer rectifier units and more particularly to a circuit for detecting a failed diode in a rectifier.
In some power system architectures, including aircraft applications, rectifier circuits are used to convert AC power to DC power. These power system architectures may also include a transformer, in which case the combined unit is referred to as a transformer rectifier unit. If the transformer is a non-isolating type, then it is called an auto-transformer rectifier unit (ATRU).
One known ATRU applies a three-phase AC input to a transformer circuit. Nine nodes on the transformer are each connected to a high or positive rail by a diode and to a low or negative rail by another diode in the rectifier circuit. If one of these diodes fails (i.e. provides an open circuit), then the DC power provided will be degraded. It is desirable to detect the failure of any of the diodes in the rectifier circuit.
The present invention provides a circuit for detecting an open diode in a rectifier of the type described above, particularly a rectifier incorporated into an auto-transformer rectifier unit of the type described above. The open diode detection circuit includes a plurality of first diodes each connecting one of the nodes of the transformer (i.e., one of the inputs to the rectifier) to a high rail in the detection circuit. Each of the nodes is also connected to a low rail in the detection circuit by another diode. The high rail of the detector circuit is then compared to the high rail of the rectifier circuit while the low rail of the detector circuit is compared to the low rail of the rectifier circuit. One comparator compares the high rails and generates a signal if the high rails differ by a certain margin, while another comparator compares the low rails and generates a signal if they differ by more than a certain margin.
In operation, if one of the high diodes fails (open), the high rail in the rectifier circuit will be lower than the high rail in the detection circuit. The comparator will detect that the difference between the high rails exceeds the threshold and generate a signal indicating the failure of a diode in the rectifier circuit.
Similarly, if one of the low diodes in the rectifier circuit fails (open), the low rail will have a voltage that is not as negative as the low rail of the detection circuit. The comparator will detect that the difference in voltage exceeds the threshold and generate an indication that a diode has failed.
Other advantages of the present invention can be understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:
A power system 20 is illustrated in
The rectifier 30 includes a plurality of first or high diodes 36, each connecting one of the nodes 1-9 of the transformer 28 to a high rail 38 in the rectifier 30. The rectifier 30 also includes a plurality of second or low diodes 37 connecting each of the nodes 1-9 to a low rail 40. Capacitors 32 may further smooth the signal by connecting the high rail 38 to the low rail 40 and by connecting the rails 38, 40 to ground.
The detector 22 includes a plurality of first or high diodes 36 each connecting one of the nodes 1-9 to a high rail 48 in the detector 22. The detector 22 further includes a plurality of second or low diodes 47 each connecting one of the nodes 1-9 to a low rail 50 of the detector 22. It should be noted that while the high diodes 36 and low diodes 37 of the rectifier 30 are large, high current, high power diodes, the high diodes 46 and low diodes 47 of the detector 22 are small, low power, low current diodes.
The detector further includes a first comparator 52 coupled to the high rail 38 of the rectifier 30 and the high rail 48 of the detector 22. The comparator 52 may be an opto-coupler having an LED that flashes based upon any voltage difference between the high rails 38, 48 that exceeds a threshold.
Similarly, a second comparator 54 is coupled between the low rails 40, 50. The second comparator 54 may also include an opto-coupler having an LED which indicates when the voltage difference between the low rails 40, 50 exceeds a threshold. The outputs of the comparators 52, 54 may be OR-ed as shown to simply indicate that any of the diodes, high or low, has failed.
In operation, as each node 1-9 goes high, its associated high diode 36 switches on and supplies high voltage to the high rail 38 of the rectifier 30. When the node 1-9 of the transformer 28 goes low, its associated low diode 37 switches on, thereby pulling the low rail 40 negative.
The detector 22 operates similarly. When any of the nodes 1-9 is high, its associated high diode 46 switches on and drives the high rail 48 high. When any node goes low, its associated low diode 47 switches on, thereby pulling low rail 50 of the detector 22 low.
While the high diodes 36 and low diodes 37 of the rectifier 30 are operational, the high rail 38 of the rectifier 30 will have equal voltage to the high rail 48 to the detector 22. The first comparator 52 will not see a voltage difference exceeding the threshold and will therefore not turn on. Similarly, the voltage on the low rail 40 will substantially equal the low voltage on the low rail 50 of the detector 22, and the second comparator 54 will therefore not see a voltage difference that exceeds the threshold and will therefore not switch on.
In the event that one of the high diodes 36 fails open, the high rail 38 of the rectifier 30 will not be connected to that associated node at that time and will therefore have a voltage that is lower that it would if the high diode 36 had not failed. Since the high rail 48 of the detector 22 will be connected to that same node by a high diode 46 at that time, the first comparator 52 will detect the difference in voltage between the high rail 38 of the rectifier 30 and the high rail 48 of the detector 22 and switch on, thereby giving an indication that a high diode 36 in the rectifier 30 has failed. The first comparator 52 will flash its indicator each time that associated node goes high. Alternatively, the output of the first comparator 52 can be coupled to a latch or capacitor in order to hold its output on in the event of a failure of one of the diodes.
Similarly, if one of the low diodes 37 in the rectifier 30 should fail, the low rail 40 of the rectifier will not be connected to that associated node in the transformer 28. However, since the low rail 50 in the detector 22 will be connected to the node by its associated low diode 37, the low rail 50 in the detector 22 will be pulled low. At that time, the voltages on the low rail 40 in the rectifier 30 and on the low rail 50 of the detector 22 will differ by an amount exceeding the threshold and the second comparator 54 will indicate that a low diode 37 has failed. Again, the output of the second comparator 54 can be latched and/or otherwise held.
Thus, the detector 22 of the present invention provides a simple, inexpensive circuit for detecting a failure of a diode 36, 37 in a rectifier 30. In particular, as illustrated, this detector 22 is particularly useful in the auto-transformer rectifier unit 24.
In accordance with the provisions of the patent statutes and jurisprudence, exemplary configurations described above are considered to represent a preferred embodiment of the invention. However, it should be noted that the invention can be practiced otherwise than as specifically illustrated and described without departing from its spirit or scope. Alphanumeric identifiers in method steps are for ease of reference in dependent claims and do not signify a required sequence unless otherwise indicated in the claim.
