Abstract:
A method and apparatus is disclosed for detecting one or more faults in a multi-phase alternator, wherein a phase sensing unit, comprising a star wound resistor assembly, senses each phase of the alternator and provides an indirect phase measure; further wherein a comparing unit, comprising an op amp, receives and compares each of the corresponding phase measures with a reference to provide a comparison result and wherein a fault detection unit receiving the comparison result and providing a fault condition signal in the case of a fault.

Description:
TECHNICAL FIELD  
       [0001]     This invention relates to the field of electronics. More precisely this invention pertains to detecting faults in multi-phase alternators.  
       BACKGROUND OF THE INVENTION  
       [0002]     Now referring to  FIG. 1 , there is shown a prior art embodiment of an apparatus  12  for detecting a fault in a multi-phase alternator  10 . In this embodiment, the multi-phase alternator  10  comprises 3 phases A, B and C which are star wound.  
         [0003]     The apparatus  12  comprises a comparing unit  16  comprising an operational amplifier  14 . A comparison is performed between a reference signal  18  and a voltage signal provided by a given phase, in this case phase A.  
         [0004]     In the case where a fault occurs at phase A, for instance, if phase A goes open circuit, the fault will be detected as the result of the comparison with the reference signal  18  will change. Unfortunately, if a fault occurs at phases B or C, it will remain undetected therefore creating potential electrical hazards.  
         [0005]     There is a need for a method and apparatus that will overcome the above-identified drawbacks.  
       SUMMARY OF THE INVENTION  
       [0006]     In one of its aspects, the present invention provides a method and apparatus for detecting one or more faults on a multi-phase alternator.  
         [0007]     According to an embodiment of the invention, there is provided a method for detecting a fault in a multi-phase alternator. The method comprises providing an indirect measure of at least two of the phases of the multi-phase alternator; comparing the indirect measure of the phases with a reference; and detecting a fault condition using the comparison.  
         [0008]     According to another embodiment of the invention, there is provided an apparatus for detecting a fault on a multi-phase alternator. The apparatus comprises a phase sensing unit for monitoring the multi-phase alternator and for reading a signal that indirectly measures at least two of the phases, thereby providing an indirect phase measure signal; and a comparing unit for receiving and comparing the indirect phase measure signal with a given reference signal to provide a comparison result signal indicative of the comparison; the comparison being used to detect the fault.  
         [0009]     According to another embodiment of the invention, the apparatus for detecting a fault on a multi-phase alternator comprises a phase sensing unit having a star wound resistor assembly comprising a plurality of resistors, each resistor being connected, at one end, to a corresponding phase of the multi-phase alternator and, at the other end, a common star point from which is read an indirect phase measure signal; and a comparing unit having an operational amplifier receiving the indirect phase measure signal and a reference signal and providing therefrom a comparison result signal indicative of the comparison; the comparison being used to detect the fault.  
         [0010]     Further details of these and other aspects of the present invention will be apparent from the detailed description and Figures included below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]     Reference is now made to the accompanying Figures depicting aspects of the present invention, in which:  
         [0012]      FIG. 1 . is an electronic schematics showing a prior art embodiment of an apparatus for detecting a fault on a single phase in a multi-phase alternator;  
         [0013]      FIG. 2 . is a block diagram showing an embodiment of an apparatus for detecting one or more faults in a multi-phase alternator;  
         [0014]      FIG. 3 . is a flowchart showing the steps for detection of a fault on a phase of a multi-phase alternator is detected according to the invention; and  
         [0015]      FIG. 4  is an electronic schematic showing a second embodiment of an apparatus for detecting one or more faults in a multi-phase alternator. 
     
    
       [0016]     It will be noted that throughout the appended drawings, like features are identified by like reference numerals.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]     Now referring to  FIG. 2 , there is shown an embodiment of an apparatus  22  for detecting one or more faults in a multi-phase alternator  20  comprising 3 phases A, B and C which are star wound.  
         [0018]     The apparatus  22  for detecting one or more faults in a multi-phase alternator  20  comprises a phase sensing unit  24 , a comparing unit  26  and a fault detection unit  28 . It is to be note that the apparatus  22  may be incorporated in a Electronic Engine Controller (EEC)  
         [0019]     More precisely, the phase sensing unit  24  receives a first voltage signal, a second voltage signal and a third voltage signal provided respectively by phase A, phase B and phase C. Using the voltage signals from phases A, B, and C, the phase sensing unit  24  provides an indirect phase measure signal.  
         [0020]     The comparing unit  26  receives the indirect phase measure signal provided by the phase sensing unit  24  and a reference signal and performs a comparison to provide a comparison result signal.  
         [0021]     The fault detection unit  28  receives the comparison result signal and provides a fault detection signal when a fault is detected.  
         [0022]     Now referring to  FIG. 3 , there is shown how the apparatus  22  for detecting one or more faults in a multi-phase alternator operates.  
         [0023]     According to step  30 , an indirect measure of at least two of the phases (in another embodiment it is an indirect measure of all the phases) of said multi-phase alternator is provided. Referring back to  FIG. 2 , the indirect measure of the phases of the multi-phase alternator is provided using the phase sensing unit  24 . The indirect phase measure signal comprises an indication of the measure of each phase of the multi-phase alternator. If there are no faults present then the balanced nature of the output voltage of a multi-phase alternator will present a phase sensing signal with a certain relationship to the reference signal. Whereas if there is a fault present then the unbalanced nature of the alternator output voltage will disturb this relationship in a detectable way.  
         [0024]     Referring to step  32  of  FIG. 3 , a comparison is performed between the indirect phase measure signal and a reference using the comparing unit  26  of  FIG. 2 . In fact, the comparing unit  26  receives the phase measure signal indicative of the measure of each phase of the multi-phase alternator and compares it with a reference signal. The comparing unit  26  provides a comparison result signal indicative of the result of the comparison.  
         [0025]     Referring to step  34  of  FIG. 3 , a fault condition is determined using the comparison result signal. The skilled addressee will appreciate that when a fault occurs, the comparison result signal will have a pattern indicative of the fault.  
         [0026]     Referring back to  FIG. 2 , the detection of the fault is performed by the fault detection unit  28  using the comparison result signal. In fact, the comparison result signal evolves over time according to a predefined pattern depending on various parameters such as rotation speed of the alternator, specifications of the phase element, etc., which is therefore expected when the multi-phase alternator operates in a normal mode. As soon as a fault occurs, the comparison result signal evolves over time according to another pattern which is indicative of the fault at any given phase of the multi-phase alternator.  
         [0027]     The fault detection unit  28  provides a fault detection signal. It will be appreciated that in one embodiment, the fault detection signal is only representative of a fault occurring without any further details.  
         [0028]     Now referring to  FIG. 4 , there is shown an embodiment of an apparatus  42  for detecting one or more faults on a phase in a multi-phase alternator according to one embodiment of the invention.  
         [0029]     The apparatus  42  comprises a phase sensing unit  44 , a comparing unit  46 , and a fault detection unit  49 .  
         [0030]     The phase sensing unit  44  comprises three resistors (i.e., a star wound resistor assembly) which create an artificial star point S. Each resistor is connected to a phase A, B and C of the multi-phase alternator. The value of the resistor is chosen base on at least the fact that it must be between a maximum which is low by comparison with the current drawn by the comparing unit, and a minimum which presents a trivial load on the alternator. In one embodiment, each resistor has a value of 1 kohms. The star point S therefore provides an indirect phase measure signal which comprises a measure of the voltage value of each phase A, B and C. In an embodiment, with no faults present, this voltage is approximately at the potential of the “0 volt DC supply”. When there is an open circuit fault on (say phase A, then this voltage is the mean of phases B and C.  
         [0031]     The comparing unit  46  receives the indirect phase measure signal. The comparing unit  46  comprises an operational amplifier  48 . The operational amplifier  48  receives the phase measure signal as well as a reference signal which is simply a given fraction between the positive DC supply and the 0 volt DC line obtained using resistances  52  and  54 . The operational amplifier  48  compares the received phase measure signal indicative of the measure of each phase as with the reference signal and thereby provides the comparison result signal to the monostable circuit  50  of the failure detection unit  49 . Using the comparison result signal, the monostable circuit  50  provides a fault condition signal indicative of a fault condition.  
         [0032]     While illustrated in the block diagrams as groups of discrete components communicating with each other via distinct data signal connections, it will be understood by those skilled in the art that the preferred embodiments may be provided by a combination of hardware and software components, with some components being implemented by a given function or operation of a hardware or software system, and many of the data paths illustrated being implemented by data communication within a computer application or operating system. The structure illustrated is thus provided for efficiency of teaching the present preferred embodiment.  
         [0033]     The above description is meant to be exemplary only, and one skilled in the art will recognize that further changes may be made to the embodiments described without departing from the scope of the invention disclosed. Still other modifications will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims.