Abstract:
Problems associated with delta motors and motor controllers being subjected to the potentially damaging combination of extremely low motor torque and very high overcurrent conditions resulting from a single dead ended motor winding are eliminated in a motor controller that automatically inhibits operation of the delta motor upon detecting that the two leads of a single motor winding have both been connected to the supply lines for a single phase of a three phase power source.

Description:
FIELD OF THE INVENTION 
     This invention relates to motor controllers, and more particularly, to a controller for a delta motor that automatically detects when the two leads of a single motor winding are connected to the supply lines for a single phase of a three phase power source. 
     BACKGROUND OF THE INVENTION 
     A delta motor system typically includes a delta motor, a three phase power source and a motor controller. During start up, delta motors often experience potentially damaging high inrush currents and starting torques. This can adversely effect the performance of the motor drive and increase general wear and tear leading to higher maintenance costs. In addition, current peaks during motor startup can also cause voltage disturbances in the power supply. 
     Motor controllers are typically used to restrict the motor torque and reduce the high starting currents by controlling the application of voltage from the three phase power source to the delta motor. The motor controller generally includes a set of three control switches that are connected between the line voltage terminals of the three phase power source and each of the windings of the delta motor. The motor controller regulates the voltage from the three phase power source to the delta motor by selectively opening and closing the three control switches. The proper operation of the delta motor is dependent on the proper regulation of the control switches. 
     The motor controller&#39;s internal timing mechanisms are specifically designed to regulate the application of specific line voltages from the three phase power source to specific delta motor windings based on a predesignated wiring configuration. Conventional electrical leads are typically used to connect the delta motor windings to the control switches and to the line voltage terminals. Since the electrical leads providing connection to the delta motor terminals are not always clearly marked, mistakes in wiring the delta motor system are not uncommon. 
     A common wiring error where the two leads providing connection to a single winding are electrically coupled to a single line voltage terminal while the other two windings are connected in parallel across the remaining two line voltages terminals, is known as a single dead ended winding wiring configuration. In this configuration, the dead ended winding does not have any current flowing through it while the other two windings are subjected to lower motor torque and significantly higher current conditions. The lower motor torque in combination with the higher operating current can potentially damage both the delta motor and the motor controller. 
     Clearly it would be desirable to use a motor controller that automatically detects a single dead ended winding configuration so that the faulty wiring can be corrected prior to subjecting the delta motor and motor controller to the potentially damaging combination of low motor torque and high operating currents. The present invention seeks to achieve these objectives. 
     SUMMARY OF THE INVENTION 
     It is a principal object of this invention to provide a new and improved motor controller that automatically detects a fault condition when the two leads of a single motor winding have been connected to the supply lines of a single phase of a three phase power source. More specifically, it is an object of the invention to provide a motor controller that detects the fault condition prior to starting the delta motor so that the faulty wiring can be corrected prior to subjecting the delta motor and the motor controller to the potentially damaging combination of low motor torque and high operating currents. 
     An exemplary embodiment of the invention achieves the foregoing object in a motor controller for use in a motor system that includes a multiphase power source having three supply lines and a delta motor having three windings, each winding having a first lead and a second lead, where the first lead of each winding is intended for connection to a selected supply line. 
     The motor controller includes a plurality of switching means and an error detecting means. Each of the switching means is intended for connection between selected supply lines and the second leads of selected windings. The error detecting means is connected across each of the switching means and is operable to detect a fault condition if both the first and second leads of one of the windings are connected to a single one of the supply lines. An indicating means may be connected to the error detecting means for generating an indication in response to the fault condition. 
     In one embodiment, the plurality of switching means comprise solid state devices. 
     In another embodiment, the plurality of switching mean comprise SCRs or triacs. 
     In another form of the invention, the error detecting means may include a sensing means that is operably connected across each of the switching means and is operable to generate a plurality of outputs representative of the voltages across each of the switching means. 
     The error detecting means may also include a decoding means, connected to the sensing means, for detecting the fault condition. The decoding means identifies the fault condition if the voltages across the second and third switching means are synchronously both greater than or less than zero and the voltage across the first switching means is equal to zero; or if the voltages across the first and third switching means are synchronously both greater than or less than zero and the voltage across the second switching means is equal to zero; or if the voltage across the first and second switching means are synchronously both greater than or less than zero and the voltage across the third switching means is equal to zero. 
     Other objects and advantages of the invention will become apparent from the following specification taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a delta motor system including a prior art motor controller; 
     FIG. 2 illustrates the relationships between the delta motor windings, the line voltage terminals and the motor controller control switches necessary for proper motor controller operation; 
     FIG. 3 shows an example of a delta motor system wired in a single dead ended winding configuration where two leads providing connection to a single winding are connected to a single line voltage; 
     FIG. 4 depicts the motor controller according to the invention connected within a delta motor system; 
     FIG. 5 is a schematic representation of the sensing circuit; 
     FIG. 6 is a schematic representation of the decoding circuit; 
     FIG. 7 illustrates the waveforms for the digital signals representative of the voltages across the individual control switches relative to the line to line voltages for a correctly wired delta motor system; and 
     FIG. 8 illustrates the waveforms for the digital signals representative of the voltages across the individual control switches for a delta motor system for three different single dead ended winding configurations. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A diagram of a conventional delta motor system  10  including a prior art motor controller  12  is depicted in FIG.  1 . The delta motor system  10  typically consists of a three phase power source  14 , a delta motor  16  and a motor controller  12 . The motor controller  12  generally includes a set of three control switches S 1 , S 2 , S 3  for providing electrical connection between the line voltage terminals L 1 , L 2 , L 3  of the three phase power source  14  and the delta motor  16 . The motor controller  12  regulates the voltage applied to the delta motor  16  by selectively opening and closing the three control switches S 1 , S 2 , S 3 . The proper operation of the delta motor  16  is dependent upon the proper regulation of the control switches S 1 , S 2 , S 3 . 
     FIG. 2 illustrates in detail the necessary relationships between the delta motor windings W 1 , W 2 , W 3 , the line voltage terminals L 1 , L 2 , L 3  and the motor controller control switches S 1 , S 2 , S 3  for proper motor controller operation. The motor controller&#39;s internal timing mechanisms are specifically designed to regulate the application of the three phase voltage from the three phase power source  14  to the delta motor windings W 1 , W 2 , W 3  based on the illustrated wiring configuration. 
     The delta motor  16  consists of three windings W 1 , W 2 , W 3  arranged in a delta configuration. Each winding W 1 , W 2 , W 3  has a pair of associated motor terminals T 1  and T 4 , T 2  and T 5 , T 3  and T 6  respectively, that provide electrical connection to either side of each individual winding W 1 , W 2 , W 3 . Terminals T 1 , T 2  and T 3  are designated for connection to line voltage terminals L 1 , L 2  and L 3  respectively using the control switches S 1 , S 2  and S 3  respectively. Terminals T 4 , T 5  and T 6  are designated for connection to line voltage terminals L 2 , L 3  and L 1  respectively. 
     The overall layout of the control switches and the windings can be described as follows: control switch S 1  and winding W 1  are connected in series across line voltage terminals L 1  and L 2 ; control switch S 2  and winding W 2  are connected in series across line voltage terminals L 2  and L 3 ; and control switch S 3  and winding W 3  are connected in series across line voltage terminals L 3  and L 1 . It is essential that the motor terminals T 1 , T 2 , T 3 , T 4 , T 5 , T 6  be wired with the appropriate control switches S 1 , S 2 , S 3  across the appropriate line voltage terminals L 1 , L 2 , L 3  to enable the motor controller  12  to perform its motor torque restricting and current limiting functions. 
     Conventional leads are typically used to connect the delta motor windings W 1 , W 2 , W 3  to the control switches S 1 , S 2 , S 3  and the line voltage terminals L 1 , L 2 , L 3 . The electrical leads providing connection to the delta motor terminals T 1 , T 2 , T 3 , T 4 , T 5  and T 6  are not always clearly marked. As a result wiring mistakes during the installation process of the delta motor system  10  are not uncommon. 
     A common wiring error, known as a single dead ended winding configuration, occurs when the two leads of a single motor winding have been electrically coupled to the terminals of a single line voltage and the other two windings have been connected in parallel across the remaining line voltages&#39; terminals. Under these conditions, the dead ended winding will not have any current flowing through it while the other two windings will have a potentially damaging combination of very large currents and very low motor torques. 
     FIG. 3 depicts an example of a single dead ended winding configuration where the winding W 1  has been dead ended with no current flowing through it and windings W 2  and W 3  are connected in parallel and are running under overcurrent conditions. The illustrated single dead ended configuration can be described as follows: winding W 1  has both terminals T 1  and T 4  electrically coupled to line voltage terminal L 2  with control switch S 2  connected between terminal T 1  and line voltage terminal L 2 ; winding W 2  is electrically coupled across line voltage terminals L 1  and L 3  with control switch S 1  connected between terminal T 2  and line voltage terminal L 1 ; and winding W 3  is also electrically coupled across line voltage terminals L 1  and L 2  parallel to winding W 2  with control switch S 3  connected between terminal T 3  and line voltage terminal L 3 . 
     The motor controller  12  according to the invention includes an innovative error detection circuit  18 . An overview of the motor controller  12  as wired within a delta motor system  10  is depicted in FIG.  4 . The error detection circuit  18  is an integral part of the motor controller  12  and is electrically coupled to the line voltage terminals L 1 , L 2 , L 3  and to motor terminals T 1 , T 2 , T 3 , across each of the individual control switches S 1 , S 2 , S 3 . The error detection circuit  18  manipulates the voltage readings obtained from the line voltage terminals L 1 , L 2 , L 3  and the motor terminals T 1 , T 2 , T 3  prior to starting the delta motor  16  to determine if both ends of a single winding have been electrically coupled to the terminals of a single line voltage and generates a fault signal in response to detecting such a condition. 
     The controller circuit  20 , connected to each of the control switches S 1 , S 2 , S 3  and the error detection circuit  18 , controls the application of voltages from the three phase power source  14  to the delta motor  16  by controlling the operation of the control switches S 1 , S 2 , S 3 . The controller circuit  20  responds to the fault signal generated by the error detection circuit  18  by inhibiting operation of the delta motor  16 . In addition, the error detection circuit  18  also directs the fault signal to an indicator circuit, such as for example an LED  21 , that provides the user with notice of the single dead ended winding wiring error. 
     Solid state switches such as SCRs or triacs are used to perform the control switch S 1 , S 2 , S 3  functions in a preferred embodiment of the invention, however, the use of alternative switching mechanisms are also considered to be within the scope of the invention. In addition, in the illustrated embodiment, the controller circuit  20  comprises a programmed microcontroller. It should be noted that alternative hardware or software implementations of the controller circuit  20  are also within the spirit of the invention. 
     The error detection circuit  18  includes a sensing circuit  22 , shown in FIG. and a decoding circuit  24 , shown in FIG.  6 . The sensing circuit  22  accepts the three line voltages L 1 , L 2 , L 3  and the three voltages at the three motor terminals designated for control switch connections T 1 , T 2 , T 3  as inputs and generates a true signal for each of the following conditions that are found to be true: 
     Voltages Across Control Switches 
     Voltage (L 1 -T 1 )&gt;0 
     Voltage (L 2 -T 2 )&gt;0 
     Voltage (L 3 -T 3 )&gt;0 
     Voltage (L 1 -T 1 )=0 
     Voltage (L 2 -T 2 )=0 
     Voltage (L 3 -T 3 )=0 
     The sensing circuit  22  consists of three similar subcircuits  26 ,  28 ,  30 . The first subcircuit  26  consists of an amplifier A 1 , three comparators C 1 , C 2 , C 3  and an AND gate G 1 . The amplifier A 1  accepts the voltage at motor terminal T 1  as its negative input and the line voltage at terminal L 1  as its positive input and generates the difference between the two (L 1 -T 1 ), the voltage across control switch S 1 , as its output. This output (L 1 -T 1 ), is directed into the positive input of the first comparator C 1  and the negative input is connected to a ground signal. The comparator C 1  compares the input signal (L 1 -T 1 ), to the ground signal and generates a true signal when (L 1 -T 1 ), the voltage across control switch S 1 , is greater than zero. 
     The comparator C 2  accepts the amplifier A 1  output, (L 1 -T 1 ), as its negative input and a reference voltage +0.1 volts as its positive input and generates a true signal when (L 1 -T 1 ) is less than +0.1 volts. Comparator C 3  accepts the amplifier A 1  output, (L 1 -T 1 ), as its positive input and another reference voltage −0.1 volts as its negative input and issues a true signal when (L 1 -T 1 ) is greater than −0.1 volts. 
     The AND gate G 1  accepts the output from comparator C 2  indicating whether the voltage (L 1 -T 1 ) is less than +0.1 volts and the output from comparator C 3  indicating whether the voltage (L 1 -T 1 ) is greater than −0.1 volts as inputs and generates a true signal when both conditions are true, in other words when the voltage across the control switch S 1  is greater than −0.1 volts and less than +0.1 volts. The voltage across the control switch S 1 , (L 1 -T 1 ), is then assumed to be zero. 
     The second and third subcircuits  28 ,  30  operate similarly. The second subcircuit  28  accepts the voltages at the motor terminal T 2  and at the line voltage terminal L 2  as inputs and generates a first true signal when the voltage (L 2 -T 2 ), the voltage across control switch S 2 , is greater than zero and a second true signal when the voltage (L 2 -T 2 ) is between −0.1 volts and +0.1 volts. Similarly, the third subcircuit  30  accepts the voltages at motor terminal T 3  and at the line voltage terminal L 3  as inputs and generates a first true signal when the voltage (L 3 -T 3 ) across the control switch S 3  is greater than zero and a second true signal when the voltage (L 3 -T 3 ) is between the values −0.1 volts and +0.1 volts. 
     The decoding circuit  24 , shown in FIG. 6, accepts the digital output signals generated by the sensing circuit  22  and issues a true signal when a single dead ended winding configuration is detected. The decoding circuit  24  consists of three pairs of XNOR and AND gates and an OR gate G 8 . The three pairs of gates are: XNOR gate G 2  and AND gate G 3 ; XNOR gate G 4  and AND gate G 5 ; and XNOR gate G 6  and AND gate G 7 . The output generated by each of these pairs are input into the OR gate G 8 . 
     The operation of the first pair of gates, XNOR gate G 2  and AND gate G 3 , can be described as follows. The XNOR gate G 2  accepts the two signals indicating if the voltage (L 2 -T 2 ) and the voltage (L 3 -T 3 ) are both greater than or less than zero. Since the XNOR gate G 2  inverts its output, a true signal is issued when both voltages (L 2 -T 2 ) and (L 3 -T 3 ) are both greater than or less than zero. A true output at the XNOR gate G 2  indicates that the voltages across control switches S 2  and S 3  are in synch. 
     The AND gate G 3  then accepts the XNOR gate G 2  output and the signal indicating if the voltage (L 1 -T 1 ) is equal to zero as inputs. A true signal is generated by the AND gate G 3  when the voltage (L 1 -T 1 ), the voltage across the first control switch S 1 , is equal to zero and the voltage (L 2 -T 2 ) and (L 3 -T 3 ), the voltages across the second and third control switches S 2  an S 3  are in synch. An AND gate G 3  true signal indicates that the winding connected to the first control switch S 1  is in a single dead ended configuration. 
     The second pair of gates, XNOR gate G 4  and AND gate G 5 , manipulate the input signals indicating if the voltages (L 1 -T 1 ) and (L 3 -T 3 ) are both greater than or less than zero and the input signal indicating if the voltage (L 2 -T 2 ) is equal to zero in a similar manner. A true signal is generated at the output of AND gate G 5  when the voltages across control switches S 1  and S 3  are in synch and the voltage across S 2  is equal to zero indicating that the winding connected to the second control switch S 2  is the dead ended winding. 
     Similarly, the XNOR gate G 6  in the third pair also accepts the two signals indicating if the voltage (L 1 -T 1 ) and the voltage (L 2 -T 2 ) are both greater than or less than zero as inputs. The AND gate G 7  accepts the XNOR gate G 6  output and the signal indicating if the voltage (L 3 -T 3 ) is equal to zero as inputs. The AND gate G 7  generates a true output when the voltages across the first control switch S 1  and across the second control switch S 2  are in synch and the voltage across the third control switch S 3  is equal to zero indicating that the winding connected to the third control switch S 3  is in a single dead ended configuration. 
     The outputs generated by the three AND gates G 3 , G 5  and G 7  are all fed into the OR gate G 8  as inputs. The OR gate then generates a true signal or a fault signal if any one of the AND gate G 3 , G 5 , G 7  inputs are true indicating that one of the three windings W 1 , W 2  or W 3  has been wired in a dead ended configuration. The fault signal is then directed to the controller circuit  20  and the LED  21 . In a preferred embodiment of the invention, the logical functions shown in the decoding circuit  24  are performed by the microcontroller that implements the functions of the controller circuit  20 . While the illustrated embodiment focuses on a particular implementation of the error detection circuit, other equivalent hardware and software implementations of the logic disclosed also fall within the scope of the invention. 
     FIG. 7 illustrates the waveforms for the line to line voltages (L 1 ÷L 2 ), (L 2 -L 3 ) and (L 3 -L 1 ) and the digital signals showing when each of the voltages across the control switches (L 1 -T 1 ), (L 2 -T 2 ), (L 3 -T 3 ) are greater than zero for a correctly wired delta motor system  10 . The following observations can be made when the delta system  10  is correctly configured for operation: 
     (i) the first control switch S 1  is connected across line voltage terminals L 1  and L 2  and the voltage across the first control switch (L 1 -T 1 ), shown in FIG.  7 ( d ), and the line to line voltage (L 1 -L 2 ), shown in FIG.  7 ( a ), are synchronously greater than or less than zero; 
     (ii) the second control switch S 2  is connected across line voltage terminals L 2  and L 3  and the voltage across the second control switch (L 2 -T 2 ), shown in FIG.  7 ( e ), and the line to line voltage (L 2 -L 3 ), shown in FIG.  7 ( b ), are synchronously greater than or less than zero; and 
     (iii) the third control switch S 3  is connected across line voltage terminals L 3  and L 1  and the voltage across the third control switch (L 3 -T 3 ), shown in FIG.  7 ( f ), and the line to line voltage (L 3 -L 1 ), shown in FIG.  7 ( c ), are synchronously greater than or less than zero. 
     When the delta motor system  10  is configured in a single dead ended configuration, the relationships observed above are altered. FIG. 8 illustrates the waveforms for the digital signals representative of the voltages across the individual control switches (L 1 -T 1 ), (L 2 -T 2 ), (L 3 -T 3 ) for a delta motor system  10  wired in a single dead ended winding configuration relative to the line to line voltages (L 1 -L 2 ), (L 2 -L 3 ), (L 3 -L 1 ). These changed relationships are used by the decoding circuit  24  to identify the incorrect wiring configuration. 
     When the winding connected to the first control switch S 1  is dead ended, there is no current flowing through that winding or control switch S 1 . Since the voltage across the control switch (L 1 -T 1 ) is equal to zero, the digital signal indicating if the voltage (L 1 -T 1 ) is greater than zero is true, as shown in FIG.  8 ( d ). The other two windings and their associated control switches S 2  and S 3  are connected in parallel across line voltage terminals L 2  and L 3 . The digital signals representing when the voltages (L 2 -T 2 ) and (L 3 -T 3 ) are both greater than or less than zero are shown in FIGS.  8 ( e ) and ( f ) respectively and the waveform for line to line voltage (L 2 -L 3 ) is shown in FIG.  8 ( b ). Note that the voltages (L 2 -T 2 ) and (L 3 -T 3 ) across the two control switches S 2  and S 3  are in synch and if fact that they are in synch with the line to line voltage (L 2 -L 3 ). 
     When the winding connected to the second control switch S 2  is dead ended, comparable observations can be made regarding the relationships between the control switch voltages (L 1 -T 1 )—FIG.  8 ( g ), (L 2 -T 2 )—FIG.  8 ( h ), (L 3 -T 3 )—FIG.  8 ( i ) and the line to line voltage (L 3 -L 1 ) FIG.  8 ( c ). A similar analysis can be made when the winding connected to the third control switch S 3  is dead ended as can be seen by referring to FIG.  8 ( j ) for voltage (L 1 -T 1 ), FIG.  8 ( k ) for voltage (L 2 -T 2 ), FIG.  8 ( i ) for voltage (L 3 -T 3 ) and FIG.  8 ( a ) for (L 1 -L 2 ). 
     The motor controller  12  uses the error detection circuit  18  to determine if a delta motor winding is wired in a dead ended configuration. Upon detection of such a condition, the error detection circuit  18  generates a fault signal that is routed to an LED  21  to provide warning of the faulty wiring to the user and to the controller circuit  20  to inhibit operation of the delta motor  16 . It will be appreciated that since the entire error detection process occurs prior to actually operating the delta motor  16 , the delta motor  16  is never exposed to the potentially damaging combination of decreased motor torque and significant overcurrent conditions in the non dead ended windings. In addition, the motor controller  12  is also not placed at risk of damage. 
     The foregoing disclosure of specific embodiments is intended to be illustrative of the broad concepts comprehended by the invention.