Abstract:
A power electronics system configured to determine a condition of a winding insulation is disclosed. The system may include at least one capacitor, and a first resistance coupled to the at least one capacitor. The system may further include a plurality of electronic switching devices coupled to at least the first resistance and the at least one capacitor, wherein the plurality of electronic switching devices are configured to selectively couple the at least one capacitor to a power source to charge the at least one capacitor during a first time interval and selectively couple the at least one capacitor to a second resistance during a second time interval. The system may further include a voltage measuring device configured to detect a change in voltage at a terminal of the at least one capacitor in response to the selective coupling of the at least one capacitor to the second resistance. The system may further include a computing system configured to determine a condition of the insulation based on the detection.

Description:
TECHNICAL FIELD 
     The present disclosure relates generally to a system and method for testing insulation that surrounds an electric conductor, and more particularly, to a system and method for testing winding insulation resistance in an electric powertrain. 
     BACKGROUND 
     The use of electric motors is becoming increasingly popular in powertrain systems due, in large part, to their relatively high efficiency, responsiveness, and environmental cleanliness when compared with conventional powertrain systems that rely solely on internal combustion engine drive technology. In order to generate electric fields large enough to produce the relatively high output torque required of modern powertrain systems, these electric motors may be subjected to extremely high current levels. If not properly isolated and contained, current may be allowed to “leak” into other electrical circuits or systems, potentially decreasing motor and, ultimately, powertrain performance. If undetected, current leakage may cause serious damage to sensitive electronics and electric systems associated with a machine. 
     One common cause of a breach of electrical isolation, potentially leading to current leakage, may be a deterioration in insulation that surrounds the phase windings in the electric motor. Such deterioration may lead to breakdown in isolation between electric phases and/or between one or more phases and ground, potentially resulting in a short-circuit condition that may cause, for example, an arc-fault. Consequently, an accurate system and method for detecting deterioration in conductor insulation may be required. 
     Some systems and methods for determining the structural integrity of winding insulation in an electric powertrain may require the dismantling of the powertrain in order to test the resistance of the winding insulation. Such manual methods may increase maintenance costs and require significant machine downtime. Thus, accurately detecting insulation wear in an electric machine, while minimizing repair costs and machine downtime, may also be required. 
     One system for accurately determining the structural integrity of motor winding insulation, while reducing downtime and maintenance costs, is set forth in U.S. Pat. No. 4,766,387 (the &#39;387 patent) issued to Browne et al. The &#39;387 patent discloses a system for measuring the insulation resistance of a winding of a polyphase motor. The system includes a motor winding insulation resistance measuring circuit and a switching mechanism that allows for each motor winding to be coupled to a separate phase power source and the circuit. The insulation measuring circuit is then used to measure the resistance of a winding&#39;s insulation to ground while the motor is operating. 
     Because the &#39;387 patent may provide a solution for determining a breach in the structural integrity of winding insulators during operation of the motor without requiring dismantling and manual inspection/testing of each insulator, it may limit machine downtime and maintenance costs associated with manual inspection techniques in certain situations. However, the complexity and customized nature of the system disclosed in the &#39;387 patent, as well as the process of connecting the circuit to the motor, may make the system difficult to operate. 
     The disclosed system and method is directed to overcoming one or more of the shortcomings set forth above. 
     SUMMARY 
     An aspect of the present disclosure is directed to a power electronics system configured to determine a condition of a winding insulation. The system may include at least one capacitor, and a first resistance coupled to the at least one capacitor. The system may further include a plurality of electronic switching devices coupled to at least the first resistance and the at least one capacitor, wherein the plurality of electronic switching devices are configured to selectively couple the at least one capacitor to a power source to charge the at least one capacitor during a first time interval and selectively couple the at least one capacitor to a second resistance during a second time interval. The system may further include a voltage measuring device configured to detect a change in voltage at a terminal of the at least one capacitor in response to the selective coupling of the at least one capacitor to the second resistance. The system may further include a computing system configured to determine a condition of the insulation based on the detection. 
     Another aspect of the present disclosure is directed to a method for determining a condition of a winding insulation. The method may include discharging at least one capacitor. The method may further include selectively coupling the at least one capacitor to a resistance while the at least one capacitor is discharging. The method may further include detecting a change in voltage at a terminal of the at least one capacitor in response to the coupling of the at least one capacitor to the resistance. The method may further include determining, based on the detection, a condition of the winding insulation. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagrammatic illustration of an exemplary disclosed machine; 
         FIG. 2  is a diagrammatic illustration of an exemplary electrical powertrain for the machine of  FIG. 1 ; 
         FIG. 3A  is an exemplary plot illustrating a discharge rate of a capacitor corresponding to a first winding insulation resistance; 
         FIG. 3B  is an exemplary plot illustrating a discharge rate of a capacitor corresponding to a second winding insulation resistance; 
         FIG. 4  is an exemplary plot illustrating a substantially instantaneous change in voltage corresponding to a first winding insulation resistance; and 
         FIG. 5  is an exemplary method for determining the structural and/or electrical integrity of winding insulation associated with the electric powertrain of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates an exemplary machine  100 . Machine  100  may be a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, machine  100  may be an earth moving machine such as an excavator, a dozer, a loader, a backhoe, a motor grader, or any other earth moving machine. It is contemplated that machine  100  may embody a machine different than that illustrated in  FIG. 1 . For example, machine  100  may be an on-highway or off-highway vehicle such as a haul truck, a rail transport vehicle, a mobile rail car mover, or any other type of machine. 
     Machine  100  may include a linkage system  102 , a tool  104  attachable to linkage system  102 , and an operator interface  106 . Operator interface  106  may be configured to receive input from a machine operator indicative of a desired movement of machine  100 . Specifically, operator interface  106  may include an operator interface device  108  and an electronic control module  110 . In one embodiment, operator interface device  108  may be a multi-axis joystick located to one side of an operator station. Operator interface device  108  may be a proportional-type controller configured to position and/or manipulate linkage system  102  and/or tool  104  by producing and directing an interface device position signal to electronic control module  110 . The interface device position signal may be indicative of a desired movement of tool  104 . It is contemplated that additional and/or different operator interface devices may be included within operator interface  106  such as, for example, wheels, knobs, push-pull devices, switches, pedals, and/or other such operator interface devices. 
     Electronic control module  110  may be a computing system that include one or more components configured to perform system controls such as, for example, a memory, a secondary storage device, and a processor. One skilled in the art will appreciate that electronic control module  110  may contain additional and/or different components than those listed above. For example, electronic control module  110  may include one or more other components or subsystems such as, for example, power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and/or any other suitable circuit for aiding in the control of one or more systems of machine  100 . 
     Machine  100  may further include a traction device  112  and an electric powertrain system  200 . Traction device  112  may include one or more ground-engaging devices for maneuvering, moving, or otherwise positioning machine  100  to facilitate the performance of one or more tasks associated with machine  100 . Traction device  112  may include, for example, tracks, wheels, belts, or any other suitable device that facilitate maneuvering and movement of machine  100 . 
     Electric powertrain system  200  may include one or more components and subsystems that cooperate to perform one or more operations associated with machine  100 . More specifically, electric powertrain system  200  may include electrical, mechanical, and electro-mechanical components associated with an electrical drivetrain system of machine  100 . Additionally, according to exemplary embodiments described herein, electric powertrain system  200  may be configured to monitor operational parameters associated with the electrical components of electric powertrain system  200  and identify certain conditions that may be indicative of excessive wear and/or degradation of the structural integrity associated with the insulation that surrounds conductors of the electric components. 
       FIG. 2  illustrates an exemplary electric powertrain system  200  consistent with the present disclosure. Electric powertrain system  200  may include at least one engine  202 , at least one generator  204 , at least one motor  208 , and at least one power electronics (PE) module  210 . PE module  210  may contain a resistor  212 , a resistor  214 , a capacitor  216 , and a plurality of electronic switching devices (ESD) electrically coupling generator  204  and motor  208 . The plurality of ESDs located within PE module  210  may include ESD  218 , ESD  220 , ESD  222 , ESD  224 , ESD  226 , ESD  228 , ESD  230 , ESD  232 , ESD  234 , ESD  236 , ESD  238 , and ESD  240 , collectively referred to herein as ESDs  218 - 240 . It is contemplated that PE module  210  may contain additional and/or different components than those listed above. For example, PE module  210  may further contain an additional resistor in parallel with capacitor  216 . The additional resistor may be configured to assist in the discharging of capacitor  216  when PE module  210  is turned off. 
     Engine  202  may be any device configured to output mechanical energy. In one example, engine  202  may be an internal combustion engine having multiple subsystems (not shown) that cooperate to produce a mechanical power output. One skilled in the art will recognize that engine  202  may be any type of internal combustion engine such as, for example, a gasoline or diesel-powered engine. The subsystems included within engine  202  may include, for example, a fuel system (not shown), an air induction system (not shown), an exhaust system (not shown), a lubrication system (not shown), a cooling system (not shown), and/or any other appropriate system(s). Engine  202  may be coupled to generator  204  via a shaft (not shown) and may be configured to provide mechanical energy to generator  204 . 
     Generator  204  may embody any device that is configured to receive mechanical power from engine  202  and convert at least a portion of the mechanical power into electrical energy. For example, generator  204  may convert a torque provided by a rotating shaft associated with engine  202  to rotate one or more coils of wire (i.e., windings) within a magnetic field, thereby inducing a current in the coil. Generator  204  may include, for example, an alternating current synchronous generator, an induction generator, a permanent-magnet generator, a switched-reluctance generator, or any other generator capable of converting mechanical power into electrical power. It is contemplated that engine  202  and generator  204  may be replaced by a single device or multiple devices that can output electrical energy (e.g., batteries, fuel cells, hybrid engines, etc). 
     Motor  208  may include multiple components that interact to convert electrical energy to mechanical energy. For example, motor  208  may include an output shaft (not shown), and, as electrical power is supplied from generator  204  to motor  208  via PE module  210 , motor  208  may generate a torque, which may be delivered to one or more components of machine  100  through the output shaft. The output shaft may be coupled to traction device  112  of machine  100  to deliver torque generated by the motor  208  to traction device  112  to propel machine  100 . PE module  210  may be an electronic device configured to convert, condition, and/or regulate the production, and/or flow of electrical power in electric powertrain system  200 . For example, PE module  210  may convert and regulate the production and/or flow of electrical power in electric powertrain system  200  by being configured to receive an input of fixed or variable frequency alternating current (AC) from generator  204  and output a fixed or variable frequency AC and/or direct current (DC) from the AC input. PE module  210  may power condition the flow of an electrical current from generator  204  by ensuring the electrical current is balanced, appropriately-phased, and sinusoidal. 
     ESDs  218 - 240  may be configured to allow the flow of electrical current from generator  204  to motor  208  via PE module  210 . For example, if all of ESDs  218 - 240  are open, no current will flow from generator  204  to motor  208  via PE module  210 . However, if an appropriate number of ESDs  218 - 240  are closed (e.g., ESD  226  and ESD  224 ), electrical current may flow to motor  208  via PE module  210 , thereby allowing motor  208  to produce a mechanical power output in response to the electrical current input. 
     ESDs  218 - 240  may comprise any device, or combination of devices, configured to operate as an electrically-controlled switch. For example, ESDs  218 - 240  may comprise transistors and diodes. The transistors may include one or more transistors such as, for example, bipolar junction transistors and/or filed-effect transistors. 
     Resistors  212 ,  214  may each comprise a resistive material that controls electrical current in PE module  210  by being configured to produce a voltage drop across their respective resistance. Resistors  212 ,  214  may have any desired resistance. For example, it is contemplated that resistors  212 ,  214  may both have a resistance value of 1 megohm. 
     Capacitor  216  may be an electronic device that stores energy in an electric field between a plurality of conductors. For example, capacitor  216  may comprise any one of, or a combination of, metalized paper capacitors, PET film or mylar film capacitors, polystyrene capacitors, metalized mica or silver mica capacitors, class-II high dielectric strength type ceramic capacitors, aluminum electrolytic capacitors, and/or any other suitable capacitor. Capacitor  216  may have any desired capacitance such as, for example, 5000 μF. 
     As stated previously, electric powertrain system  200  may be configured to determine the structural integrity of winding insulation located within generator  204  and/or motor  208 . For example, it is contemplated that a maintenance computer  250  and an alarm  252  ( FIG. 2 ) may be coupled to machine  100 . The maintenance computer  250  may be used to initiate a winding insulation resistance test procedure that results in engine  202  and generator  204  being used to produce a voltage across capacitor  216  (i.e., charge capacitor  216 ). It is further contemplated that a voltage measuring device  242  may be electrically coupled to capacitor  216 . The maintenance computer  250  may use the voltage measuring device  242  to measure the voltage across the terminals of capacitor  216 . 
     When all of ESDs  218 - 240  are open (i.e., no current is allowed to flow from generator  204  to motor  208  via PE module  210 ), capacitor  216  may discharge at a first rate τ=RC, where R corresponds to the resistance of resistor  212  and resistor  214 , and C corresponds to the capacitance of capacitor  216 . 
     At any time during the discharge of capacitor  216 , one of ESDs  218 - 228  may be closed, thus allowing electrical current to flow from PE module  210  to motor  208 . The electrical current flowing from PE module  210  to motor  208  may force capacitor  216  to discharge at a second rate τ 2 =R new C, where C corresponds to the capacitance of capacitor  216 , and, if ESD  226  is closed, R new  corresponds to the resistance of resistor  212 , resistor  214 , and the resistance of the winding insulation located within motor  208 . 
     Since dirt, moisture, physical abrasions, etc. may lower the resistance of the winding insulation, the change in discharge rate of capacitor  216 , and/or the value of τ 2 , when one of ESDs  218 - 228  is closed, may be used to determine the structural integrity of the winding insulation within motor  208 . 
     For example,  FIG. 3A  illustrates an exemplary plot of a voltage versus time discharge rate of capacitor  216  when resistor  212  has a resistance value of 1 megohm, resistor  214  has a resistance value of 1 megohm, and the winding insulation within motor  208  has a resistance value of 2 megohms. As illustrated in  FIG. 3A , at t=0, the voltage drop across capacitor  216  is approximately 500 volts (i.e., HV +  is positive 250 volts and HV −  is negative 250 volts). After t=0 all of ESDs  218 - 240  are opened and no electrical current is allowed to flow from generator  204  to motor  208 . Between t=0 and t=5 capacitor  216  has a discharge rate corresponding to the capacitance of capacitor  216  and the resistance of resistors  212 ,  214 . At t=5 ESD  226  may be closed, thus allowing electrical current to flow from PE module  210  to motor  208 . 
     As illustrated in  FIG. 3A , a substantially instantaneous change in voltage occurs corresponding to ESD  226  being closed at t=5. The substantially instantaneous change in voltage occurring at t=5 (i.e., when ESD  226  is closed) is a result of at least the winding insulation resistance of motor  208  being placed in parallel with resistor  212 .  FIG. 3A  illustrates that if the winding insulation resistance for motor  208  is 2 megohms, the substantially instantaneous change in voltage at HV +  and HV − , corresponding to closing ESD  226 , may be approximately 50 volts. 
       FIG. 3B  illustrates a similar set of circumstances as in  FIG. 3A . That is, at t=0 the voltage across capacitor  216  is approximately 500 volts, and after t=0 all of ESDs  218 - 240  are opened. However,  FIG. 3B  corresponds to a winding insulation resistance of 0.5 megohms, whereas  FIG. 3A  corresponds to a winding insulation resistance of 2 megohms. As illustrated in  FIG. 3B , when ESD  226  is closed at t=5, the substantially instantaneous change in voltage at HV +  and HV −  may be approximately 100 volts. Again, the substantially instantaneous change in voltage occurring at t=5 (i.e., when ESD  226  is closed) is a result of at least the winding insulation resistance of motor  208  being placed in parallel with resistor  212 . 
       FIG. 3B  illustrates that if the winding insulation resistance for motor  208  is 0.5 megohms, the substantially instantaneous change in voltage at HV +  and HV − , corresponding to closing ESD  226 , may be twice what it is when the motor  208  winding insulation resistance is 2 megohms. Again, since dirt, moisture, physical abrasions, etc. may lower the resistance of the winding insulation, a winding insulation resistance of 0.5 megohms may indicate a fault in the winding insulation, whereas a winding insulation resistance of 2.0 megohms may indicate that the winding insulation is functioning properly. Therefore, the amount of the substantially instantaneous change in voltage corresponding to closing one of ESD  218 - 228  may be used to determine the structural integrity of the winding insulation within motor  208 . 
     It is contemplated that, as an alternative to engine  202  and generator  204  being used to charge capacitor  216 , a direct current (DC) power-producing device (e.g., a battery) may supply power to capacitor  216  to aid in the determination of the structural integrity of the winding insulation. For example, a DC power producing device may be used to apply a first DC voltage (e.g., +250 volts) at HV +  and a second DC voltage (e.g., −250 volts) at HV − . After the DC voltage is applied at HV +  and HV − , an ESD (e.g., ESD  226 ) may be closed, thus causing a substantially instantaneous change in voltage at HV +  and HV − . 
     Illustrated in  FIG. 4  is an exemplary plot showing the substantially instantaneous change in voltage at HV +  and HV −  when ESD  226  is closed at t=5, and when the resistance of the winding insulation is 0.5 megohms. As illustrated in  FIG. 4 , a winding insulation resistance of 0.5 megohms corresponds to a substantially instantaneous change in voltage at HV +  of approximately 100 volts. Therefore, similar to the method described previously, the substantially instantaneous change in voltage at HV +  (and/or HV − ) may be used to determine the structural integrity of the winding insulation. 
     It is contemplated that the actual resistance of the winding insulation of motor  208  may be calculated using the time constant X (i.e., the discharge rate of capacitor  216 ). An operator and/or a maintenance technician may then compare the calculated resistance to a threshold resistance value to determine if the winding insulation of motor  208  needs to be replaced. For example, if the calculated resistance is relatively high (i.e., above the threshold resistance value), it may be determined that the winding insulation is operating appropriately. However, if the calculated resistance is relatively low (i.e., below the threshold resistance value), it may be determined that the winding insulation located within motor  208  needs to be replaced or repaired. 
     It is further contemplated that the structural integrity of the winding insulation associated with generator  204  may be determined substantially similar to the determination of the structural integrity of the winding insulation associated with motor  208 . For example, instead of closing ESD  226  at t=5, ESD  238  may be closed at t=5. In this way the structural integrity of the winding insulation associated with generator  204  may be determined through the substantially instantaneous change in voltage at a terminal of capacitor  216  and/or the time constant τ (i.e., the discharge rate of capacitor  216 ). 
     INDUSTRIAL APPLICABILITY 
     The disclosed system and method may be applicable where it is desired to minimize the cost and maximize the reliability of determining the structural integrity of winding insulation in an electric powertrain. The disclosed system and method may minimize the cost and simplify the operation of determining the structural integrity of winding insulation by allowing an operator and/or a maintenance technician to determine the structural integrity of winding insulation using components that are located within the powertrain, rather than connecting a customized circuit to a motor and/or a generator winding. The disclosed system and method may maximize the reliability of determining the structural integrity of winding insulation since few or no additional components are added to the powertrain. 
       FIG. 5  shows a flowchart  500  illustrating a method for determining the structural integrity of the winding insulation associated with electric powertrain system  200 .  FIG. 5  will be now be discussed in detail to illustrate the disclosed system and its operation. 
     As illustrated in flowchart  500 , determining the structural integrity of winding insulation associated with electric powertrain system  200  may include initiating a winding insulation test procedure (Step  502 ). The initiation of the winding insulation test procedure may be done through electronic control module  110  and/or a remote maintenance computing system that may be coupled to electric powertrain system  200 . After the winding insulation test procedure has been initiated, capacitor  216  may be charged to a value such as, for example, 500 volts (Step  504 ). It is contemplated that engine  202  and generator  204  may be used to charge capacitor  216 . Once the desired voltage is produced across capacitor  216 , all of ESDs  218 - 240  may be opened (Step  506 ), ensuring that capacitor  216  is discharging at a rate corresponding to τ=RC, where R corresponds to the resistance of resistor  212  and resistor  214 , and C corresponds to the capacitance of capacitor  216 . It is contemplated that as a first iteration of the process of flowchart  500 , capacitor  216  may be allowed to completely discharge as a calibration process in order to cancel effects of, for example, component degradation, tolerance, and environment. After a calibration discharge cycle, capacitor  216  may be charged again to a desired value (e.g., 500 volts) in preparation for closing one of ESDs  218 - 240 . 
     Again, once the desired voltage is produced across capacitor  216 , all of ESDs  218 - 240  may be opened (Step  506 ), ensuring that capacitor  216  is discharging at a rate corresponding to τ=RC, where R corresponds to the resistance of resistor  212  and resistor  214 , and C corresponds to the capacitance of capacitor  216 . As capacitor  216  discharges, one of ESDs  218 - 240  may be closed (Step  508 ). Closing one of ESDs  218 - 240  may result in introducing the generator  204  or motor  208  winding insulation resistance into PE module  210 , thus changing the discharge rate of capacitor  216 . According to one embodiment, the user may manually select which of ESDs to switch on, depending upon which one of generator  204  and motor  208  is to be tested. For example, if an operator and/or maintenance technician desires to know the structural integrity of the winding insulation associated with motor  208 , then ESD  226  may be closed, thereby allowing electrical current to flow from capacitor  216  to motor  208  (Step  508 ). If, however, an operator and/or maintenance technician desires to know the structural integrity of the winding insulation associated with generator  204 , then ESD  238  may be closed, thus allowing electrical current to flow from capacitor  216  to generator  204  (Step  508 ). 
     Once the desired ESD is closed, the resulting substantially instantaneous change in voltage at a terminal of capacitor  216  (i.e., HV +  and/or HV − ) may be measured by the voltage measuring device  242 . The amount of the substantially instantaneous change in voltage at a terminal of capacitor  216  may be used to determine the structural integrity of a winding insulation within electric powertrain system  200  (Step  510 ). For example, the winding insulation located within motor  208  may be working properly and may have a relatively high resistance. When ESD  226  is closed, the relatively high resistance of the winding insulation may prevent excess current leakage through a parasitic resistance, thus indicating a properly working winding insulation. Specifically, according to one embodiment, a properly working winding insulation may have a resistance of approximately 2 megohms. When, for example, ESD  226  is closed, the winding insulation resistance of approximately 2 megohms may cause a relatively low substantially instantaneous change in voltage to occur at HV + and HV − . 
     Conversely, the resistance associated with a typical damaged winding insulator may be approximately 0.5 megohms. Accordingly, when ESD  226  is closed, the winding insulation having a resistance of approximately 0.5 megohms may cause a relatively high substantially instantaneous change in voltage to occur at HV +  and HV − . Therefore, the amount of the substantially instantaneous change in voltage at a terminal of capacitor  216  may be indicative of the condition of the winding insulation in electric powertrain system  200 . 
     The winding insulation test method may include sending an alert to an operator and/or a maintenance technician in response to the test results. For example, if it is determined that the winding insulation is not working properly (Step  512 , No), an alert may be sent to an operator and/or a maintenance technician indicating the winding insulation is damaged (Step  514 ). However, if it is determined that the structural integrity of the winding insulation is sufficient (Step  512 , Yes), then an alert may be sent to an operator and/or a maintenance technician indicating the winding insulation is functioning properly (Step  516 ). The alerts may be audible alarms (e.g., generated by the alarm  252  shown in  FIG. 2 ), and/or flashing or steady light(s), or by any other appropriate means. 
     It is contemplated that an operator and/or a maintenance technician may calculate the actual resistance of the winding insulation of generator  204  and/or motor  208  using the time constant τ. An operator and/or maintenance technician may then use the calculated resistance to determine if the winding insulation of generator  204  and/or motor  208  needs to be replaced. For example, if the calculated resistance is relatively high, it may be determined that the winding insulation is operating appropriately. However, if the calculated resistance is relatively low, it may be determined that the winding insulation located within generator  204  and/or motor  208  needs to be replaced. An alert may then be sent to an operator and/or a maintenance technician corresponding to the structural integrity of the winding insulation. 
     It will be apparent to those skilled in the art that various modifications and variations can be made to the disclosed system and method. Other embodiments will be apparent to those skilled in the art from consideration of the specification and practice of the disclosed system and method. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.