Method and system for detecting a failed current sensor in a three-phase machine

A method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine is disclosed. The method may include detecting one or more failed current sensor by determining if an absolute value of a sum of the phase currents of the motor is below an open circuit value. The method may also include determining which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the sum of the phase currents of the motor is not below the open circuit value. The method may further include estimating the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

TECHNICAL FIELD

This application relates to a power converter control method and system, and more particularly, to a method and system for detecting a failed current sensor, and estimating a value for the failed current sensor, in a three-phase machine.

BACKGROUND

Power converters/inverters are commonly used in a machine for motor control. Power converters/inverters usually include a plurality of power transistors, and these power transistors may be switched on and off to modulate an output voltage from the power converter/inverter. Knowing the state of the current or voltage of each phase of the motor allows for a power converter/inverter to be controlled to produce a controlled power waveform to the motor. Sensors are often deployed to detect the current associated with each phase of the motor. If one or more sensors are producing incorrect current values, the commands and changes in voltage to control the AC motor will not match the actual state of the AC motor, potentially leading to a loss of motor control.

Because accurate detection of phase current is critical to ensuring synchronous operation of the motor, precision sensors are typically provided for each phase of the motor. Some conventional sensor control strategies provide back-up phase current detection schemes, should one or more sensors fail or otherwise become inaccurate or unreliable. Many such sensor control strategies often include a method to detect the failure of one or more of the sensors. A conventional control strategy may first detect if a sensor has failed by summing the detected current for each phase of the AC motor. If the sum is not zero, each detected current may be compared against an estimate value for the current of that phase of the AC motor. A sensor has failed when the detected current for that sensor does not match the estimated current of that sensor. If a current sensor has failed, and an alternate way to control the inputs to an AC motor is not available, the motor may have to be shut down. Therefore, in order to ensure proper operation of the motor in the event of a sensor failure, a relatively simple, inexpensive motor control strategy that can detect a sensor failure and compensate for such failure may be desirable.

One device and method for failure detection in electric vehicles is described in U.S. Pat. No. 5,357,181 to Mutoh et al. (“the '181 patent”). The '181 patent describes a device or method that may detect if one or more current sensors are failing, and provide an alternate way to control the motor to compensate for the failed sensor(s). The system of the '181 patent uses a predetermined maximum current error value, which defines a maximum total current level permitted on the system. The sum of the three phase currents is then compared to this error value to monitor the operating condition of the current sensors. If the summation is below this value, the sensors are in normal condition. If the summation exceeds the error value, the disorder in output from excessive input deviation of current control (the estimate and the sensed signal) is checked at the current control system of each phase. The current sensor of the phase at which a disorder is found is determined to be failing. If only one out of three current sensors is failing, the device or method estimates the current of the failing current sensor by using the two normal current sensors. If two or more current sensors are found to be failing, the motor is controlled based on the AC current reference.

Although the device and method of the '181 patent may provide a method of determining if a current sensor has failed and estimating a value for the failed current sensor, it may include several disadvantages. Specifically, the device and method of the '181 patent may require a large number of components, rendering the system unnecessarily costly and unduly complex. Additionally, because the device and method of the '181 patent maintain an estimate of the current of each phase to aid in the detection of disorder in output from excessive input deviation, small errors in one or more current sensors may cause the estimate of one or more current sensors to drift and, in the event of a current sensor failure, the wrong sensor or sensors may be determined to have failed. Furthermore, the device and method of the '181 patent may not re-qualify a current sensor that has been determined to have failed if that current sensor later begins to perform normally. Thus, in order to facilitate accurate and reliable motor control, a motor control sensor strategy that can detect and accurately correct for a failed sensor, while reducing the cost and complexity of the AC motor control sensor strategy by decreasing the amount of processing and the number of sensors required, is desirable.

The disclosed system and method are directed to improvements in the existing technology.

SUMMARY

In accordance with one aspect, the present disclosure is directed toward a method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine. The method may include detecting one or more failed current sensor by determining if an absolute value of a sum of the phase currents of the motor is below an open circuit value. The method may also include determining which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the sum of the phase currents of the motor is not below the open circuit value. The method may further include estimating the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

According to another aspect, the present disclosure is directed toward a system for detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine. The system may include at least one three-phase machine and at least one sensor deployed per phase of each three-phase machine. The system may further include a controller electrically coupled to the at least one three-phase machine. The controller may be configured to detect one or more failed current sensor. The controller may be configured to determine if an absolute value of a sum of the phase currents of the three-phase machine is below an open circuit value. The controller may also be configured to determine which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the absolute value of the sum of the phase currents of the three-phase machine is not below the open circuit value. The controller may be further configured to estimate the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

In accordance with yet another aspect, the present disclosure is directed toward a machine. The machine may include a power source and at least one motor, each motor having at least two phases and a current sensor associated with each phase of the motor. The machine may also include a controller electrically coupled to the at least one motor. The controller may be configured to detect one or more failed current sensor. The controller may be configured to determine if an absolute value of a sum of the phase currents of the motor is below an open circuit value. The controller may also be configured to determine which phase currents are approximately zero, for each phase current associated with each phase of the motor, if the absolute value of the sum of the phase currents of the motor is not below the open circuit value. The controller may be further configured to estimate the phase current for the failed current sensor by determining the phase current value for the failed current sensor, that when added to the actual phase currents of the remaining current sensors, will make the sum of all the phase currents equal to approximately zero.

DETAILED DESCRIPTION

FIG. 1provides a block diagram of a machine in accordance with an exemplary embodiment of the present disclosure. Machine100may include, among other things, a power source110, a power electronics system120, a traction system130, and a control system140. Machine100, as the term is used herein, refers to a fixed or mobile machine that may perform some type of operation associated with a particular industry, such as mining, construction, farming, etc. Examples of machines include trucks, cranes, earth moving vehicles, mining vehicles, backhoes, material handling equipment, farming equipment, and on-highway vehicles.

Power source110may include various components configured to provide electric power for use by one or more systems of machine100. Power source110may include a prime mover101and a generator102driven by prime mover101. Prime mover101may be a combustion engine, such as, for example, a diesel engine, or may be a hybrid motor. Generator102may be an AC generator, otherwise known as an alternator, that generates alternating current by rotating a coil in the magnetic field or by rotating a magnetic field within a stationary coil. Alternatively, power source110may include any other suitable device for providing an electrical power output such as, for example, a battery, a fuel cell, or any other type of power source configured to provide electrical power to machine100.

Power electronics system120may include at least one power converter. Examples of power converters may include a power inverter that converts DC current to AC power and a power rectifier that converts AC current to DC power. Each power converter may have at least one phase, and each phase may include at least one power transistor. Each power transistor may be switched on and off by its corresponding gate driving circuit. The power transistors may be switched according to a switching scheme, such as a pulse width modulation (PWM), to modulate the voltage that is output from the power converter. While three-phase machine may indicate a machine using three-phase power, three-phase machine may also include machines with multiples of three phases, i.e., for example, a six-phase machine, or a nine-phase machine.

Power electronics system120may be electrically coupled to power source110via a first set of conductors, and to traction system130via a second set of conductors. Traction system130may include at least one electric load, such as an electric motor. Power electronics system120may be configured to convert power provided by power source110into power forms appropriate for consumption by traction system130. Power electronics system120, for example, may include a power rectifier to convert AC voltage supplied by power source110to a DC voltage output, and may further include a power inverter to convert the DC voltage to an AC voltage of a certain waveform. Power electronics system120may provide voltage and/or current outputs to drive traction system130and/or control system140.

Traction system130may include at least one electric load, such as an electric motor for one or more ground-engaging devices for propelling machine100. The at least one electric load may be directly coupled to power source110, or may be coupled to power source110via the power electronics system120. Each electric load may have at least one phase and may be connected with a power converter with an equal number of phases in the power electronics system120. One example of the electric load may be an electric motor, such as an AC induction motor, a brushless DC motor, a stepper motor, a linear motor, or any other type of motor.

Control system140may be coupled to power electronics system120and configured to provide gate driving signals to the power transistors based on a pre-programmed switching scheme. Control system140may be an integral part of power electronics system120, or, alternatively, control system140may be external to power electronics system120, for example, as part of a separate electronic control module (ECM) associated with machine100. Control system140may also be coupled to traction system130and/or power source110to perform one or more control functions. Control system140may be further coupled to generator102to perform one or more control functions. Control system140may further be configured to receive feedback from a plurality of points in the circuit and adjust the control signals based on the feedback. For example, control system140may be configured to communicate with current sensors150associated with the power electronics system120, generator102, and/or traction system130, determine the current of each phase of a motor or the generator, determine if any of current sensors150have failed, determine appropriate control signals based on current sensor150measurements, and send the control signals to power electronics system120.

Control system140may be configured to detect one or more failed current sensors and estimate a phase current for one failed current sensor on a three-phase machine. According to one embodiment, control system140may be configured to detect a failed current sensor by determining if the sum of the phase currents of a motor is below an open circuit value. If the sum of the phase currents of a motor is below an open circuit value the sensors are operating normally, but if the sum of the phase currents of a motor is above an open circuit value, one or more current sensors150may have failed. Because the sum of currents of the phases of a properly operating three-phase machine should ideally be approximately zero, a non-zero sum may be indicative of a problem (either with the motor or with a current sensor150associated therewith). The open circuit value is the maximum allowable value of the sum of the phase currents of the phases of a properly operating three-phase machine. If the sum of the phase currents of the motor is not below the open circuit value, control system140may be configured to determine which phase currents are approximately zero, for each phase current associated with each phase of the motor. Control system140may be further configured to estimate a phase current for the failed current sensor by determining a phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors150may make the sum of all the phase currents approximately equal to zero.

Machine100may include two or more current sensors150deployed among power electronics system120and a traction system130. Current sensors150may detect or monitor the phase currents associated with a phase of a three-phase machine, and may report those phase currents as an analog or discrete value to control system140or other controllers on machine100. In one exemplary embodiment, current sensors150may be deployed to detect the phase current of each phase of a motor, and automatically report the detected values to control system140. Current sensors150may provide information associated with an operational condition, such as, for example, the magnitude of a phase current, the frequency of a phase current, the polarity of the phase current and a complete profile of the phase current as a function of time or frequency. Current sensor150measurements may be indicative of the characteristics of the electric loads that power electronics system120drives, for example, traction system130.

Detecting one or more failed current sensors and estimating a phase current for one failed current sensor may help prevent a motor from being damaged or rendered inoperative. For instance, when the control signals that are delivered to a power converter produce an AC voltage waveform not appropriate for a three-phase machine, the motor may be damaged or rendered inoperative. This may occur when one or more of current sensors150has failed and control system140is no longer receiving correct inputs. When control system140is not receiving correct inputs, control system140may send controls to the power converter which may produce an irregular or uncontrolled output to drive the three-phase machine. The irregular or uncontrolled output from the power converter may damage other power components connected in the circuit. For example, power source110, power electronics system120, and/or traction system130may contain highly sensitive electronic circuits, which may be damaged by an irregular or uncontrolled output.

FIG. 2provides a diagrammatic illustration of a control system140, in accordance with an exemplary embodiment of the present disclosure. As illustrated inFIG. 2, control system140may include one or more hardware components and/or software applications that cooperate to monitor, analyze, and/or control performance or operation of one or more machines100. Control system140may include any computing system configured to receive, analyze, transmit, and/or distribute performance data associated with machine100.

Control system140may include hardware and/or software components that perform processes consistent with certain disclosed embodiments. For example, as illustrated inFIG. 2, control system140may include a central processing unit (CPU)201; one or more computer-readable memory devices such as storage device202, a random access memory (RAM)203, and a read-only memory (ROM)204; a display unit205; an input/output (IO) device206; and/or a motor control module207. The components described above are exemplary and not intended to be limiting. Furthermore, it is contemplated that control system140may include alternative and/or additional components than those listed above, such as, for example, one or more field-programmable gate arrays (FPGAs).

CPU201may be one or more processors that execute instructions and process data to perform one or more processes consistent with certain disclosed embodiments. For instance, CPU201may execute software that enables control system140to request and/or receive performance data from current sensors150on machine100. CPU201may also execute software that stores collected performance data in storage device202. In addition, CPU201may execute software that enables control system140to analyze performance data collected from machine100and detect one or more failed current sensor and estimate a phase current for the failed current sensor on a three-phase machine. According to one embodiment, CPU201may access computer program instructions stored in memory. CPU201may then execute sequences of computer program instructions stored in computer-readable medium devices such as, for example, a storage device202, RAM203, and/or ROM204to perform methods consistent with certain disclosed embodiments, as will be described below.

One or more computer-readable medium devices may include storage devices202, RAM203, ROM204, and/or any other magnetic, electronic, flash, or optical data computer-readable medium devices configured to store information, instructions, and/or program code used by CPU201of control system140. Storage devices202may include magnetic hard-drives, optical disc drives, floppy drives, flash drives, or any other such information storing device. RAM203may include any dynamic storage device for storing information and instructions by CPU201. RAM203also may be used for storing temporary variables or other intermediate information during execution of instructions to be executed by CPU201. During operation, some or all portions of an operating system (not shown) may be loaded into RAM203. In addition, ROM204may include any static storage device for storing information and instructions by CPU201.

Display unit205may include a display including a graphical user interface (GUI) for outputting information on a monitor. Display unit205may include one or more displays that may be useful in testing and/or troubleshooting control system140and/or motor control module207. I/O device206may include one or more components configured to communicate information associated with control system140. For example, I/O device206may include an integrated keyboard and mouse to allow a user to input commands or instructions for control system140. I/O devices206may include one or more peripheral devices, such as, for example, printers, cameras, disk drives, microphones, speaker systems, electronic tablets, bar code readers, or any other suitable type of I/O device206.

Control system140may include a hardware or software motor control module207configured to receive/collect certain performance data from current sensors150, and detect, based on the received performance data, one or more failed current sensor and estimate a phase current for the failed current sensor on a three-phase machine. Motor control module207may be implemented or partially implemented on a FPGA. The FPGA may relieve CPU201of some of the processing burden of implementing the disclosed method and system. The FPGA may execute the method and system every cycle that current sensors150sample the phase current for a respective phase. Motor control module207may be further configured to detect a failed current sensor by determining if the absolute value of the sum of the phase currents of a motor is below an open circuit value. If the sum of the phase currents of a motor is below an open circuit value the sensors are operating normally, but if the sum of the phase currents of a motor is above an open circuit value, one or more current sensors150may have failed. If the sum of the phase currents of the motor is not below the open circuit value, motor control module207may be configured to determine which phase currents are approximately zero, for each phase current associated with each phase of the motor. Motor control module207may be further configured to estimate a phase current for the failed current sensor by determining a phase current value for the failed current sensor, that when added to the phase currents of the remaining current sensors150, may make the sum of all the phase currents approximately equal to zero.

FIG. 3illustrates a flowchart300depicting an exemplary method for detecting one or more failed current sensor and estimating a phase current for the failed current sensor on a three-phase machine. As illustrated inFIG. 3, predetermined variables may be loaded from control system140on machine100(Step305). For example, motor control module207of control system140may contain one or more predetermined variables used in the method. Some exemplary embodiments of predetermined variables may include an open circuit value, a value for “approximately zero”, a first delay, a second delay, and a predetermined number of times in a row that may be used to determine when an irresolvable sensor failure has occurred. The values assigned to these predetermined variables may be machine-dependant.

According to one exemplary embodiment, the open circuit value may be a predetermined and/or user-defined value to which the absolute value of the sum of the phase currents is compared. The open-circuit value may serve as a benchmark by which control system140determines whether the sum of the phase currents of the motor can be estimated as approximately zero. For example, in large motors the open circuit value may be set to 50 amps. In other examples, the open circuit value may be as low as a few amps in a small motor, and may be much higher in a large motor, such as 300 amps. In other examples, the open circuit value may be a percentage of the expected maximum current of a phase, such as 25 percent. The percentage may be much lower, perhaps a few percent, or may range as high as 40 percent.

According to another exemplary embodiment, a phase current or a summation of phase currents may be compared to a number, such as, approximately zero. Because the sum of all phase currents in a balanced, three-phase machine should be at or near zero, the phase current or summation of phase currents may be compared with a threshold current value of approximately zero. In some cases, particularly where the energizing current required to drive the motor is on the order of several hundred Amps, 10 to 20 Amps may be considered “approximately zero”, for the purposes of phase current detection. In other examples, approximately zero may be as low as one amp in a small motor, and may be much higher in a large motor, such as a 100 amps. In other examples, approximately zero may be a percentage of the expected maximum current of a phase, such as 10 percent. The percentage may be much lower, perhaps one percent, or may range as high as 20 percent.

According to another exemplary embodiment, a first delay may be a time duration between the execution of two steps, depending on the fall time of the open sensor or the decay time based on the ECM circuit. First delay may be between 100 microseconds and one millisecond. Second delay may be a time duration associated with the time a properly working current sensor150reading approximately zero may need to no longer read an approximately zero value. Second delay may be greater than the time it would take a phase current to cross the approximately zero magnitude range. Second delay may be less than the time it would take a phase current to once again enter the approximately zero magnitude range. In one exemplary embodiment, in a 60 hertz motor, second delay may be as little as 500 microseconds and as long as 6 milliseconds. Second delay may have a smaller lower bound and/or a higher upper bound, depending on with width of the approximately zero range, and the frequency of the waveform to the motor.

According to another exemplary embodiment, control system140may be configured to detect the number of times in a row that two or more current sensors150indicate that they are approximately zero simultaneously. For example, because current sensors150may be configured to detect a threshold range about “absolute” zero, there may be situations where one current sensor150is within the approximate zero range, while another current sensor150may have failed. Thus, there may be situation where more than one current sensor150appears to be in the “approximately zero” state, which may generate a “false positive” indication that two or more of the phases of the motor are not operating appropriately. Consequently, control system140may be configured to identify and count such erroneous “false positives.” If the number of consecutive “false positives” exceeds a predetermined user-defined threshold, such as, a predetermined number of times in a row, control system140may provide an indication that a problems exists with two or more current sensors150. A predetermined number of times in a row may be as low as twice, and may be as high as 20 or 30.

Once the predetermined variables are loaded, the values of the actual phase currents may be collected from current sensors150on machine100(Step310). For example, motor control module207of control system140may receive/collect the values of the actual phase currents for a motor in traction system130or each power converter in power electronics system120. According to one embodiment, current sensors150may provide the sampled values for the phase currents to an FPGA, which may execute one or more of the steps described below. According to another embodiment, motor control module207may automatically receive the actual phase current values from a performance diagnostic system that may be monitoring one or more systems on machine100. Alternatively or additionally, motor control module207may provide a data request to each current sensor150or performance diagnostic system and receive actual phase current values from each current sensor150or performance diagnostic system in response to the request.

Once phase current values have been collected, one or more flexible variables may be determined from the phase currents (Step315). According to one embodiment, after collection of actual phase current values, motor control module207may determine one or more flexible variables from phase currents. For example, the open circuit value may be calculated based on the phase currents measured in Step310. In one exemplary embodiment, the open circuit value may be a percentage of the maximum value of the largest magnitude of the phase currents, such as 25 percent. The percentage may be much lower, perhaps a few percent, or may range as high as 40 percent.

Once the flexible variables have been determined, the absolute value of the sum of the actual phase currents may be calculated (Step320). According to one embodiment, after the flexible variables have been determined, motor control module207may calculate the absolute value of the sum of the actual phase currents.

Once the sum of the actual phase currents has been determined, control system140may determine whether the absolute value of the sum of the actual phase currents is below an open circuit value (Step325). According to one embodiment, if the absolute value of the sum of the actual phase currents is less than the open circuit value, motor control module207may determine if one or more phase current values are approximately zero. Under ideal conditions, the summation of the phase currents of a three-phase machine would be zero. But due to noise, sensor error, system imbalances, and interference, the summation of the phase currents in a three-phase machine may be close to zero, but not exactly zero. A threshold value is needed, under which the summation may be assumed to be zero, and above which, the summation may be assumed to be non-zero. The threshold value for Step325is the open circuit value from either Step305or Step315. If the absolute value of the sum of the actual phase currents is less than the open circuit value, Step330may be executed. In contrast, if the absolute value of the sum of the actual phase currents is equal to or greater than the open circuit value, Step335may be executed.

If the absolute value of the sum of the actual phase currents is less than the open circuit value, control system140may wait for the next current sensor sample time (Step330). According to one embodiment, motor control module207may wait for the next current sensor sample time and then execute Step310. The sampling frequency of current sensors150may be between 5 kHz and 40 kHz. In one exemplary embodiment, the sampling frequency of current sensors150may be 20 kHz.

If the absolute value of the sum of the actual phase currents is equal to or greater than the open circuit value, control system140may wait a first delay time (Step335). As discussed above, a first delay may be a time duration between the execution of two steps, depending on the fall time of the open sensor or the decay time based on the ECM circuit. First delay time may be the time needed for a current sensor150that has failed to read approximately zero. In one embodiment, when the absolute value of the sum of the actual phase currents is equal to or greater than the open circuit value, the failed current sensor may not yet read zero, as the failed current sensor may take some time to decay to a zero reading.

Once control system140has waited a first delay time, control system140may determine the phases of the motor for which the phase currents are approximately zero (Step340). According to one embodiment, after a first delay time, motor control module207may determine which phase currents are approximately zero. Under ideal conditions a failed current sensor may have a value of zero. But due to noise and interference, the value of the failed current sensor may be close to zero, but not exactly zero. A threshold value is needed, under which the current sensor may be assumed to be zero, and above which, the value of current sensor150may be assumed to be non-zero. The threshold value for Step340is the approximately zero value from Step305.

Once the phase currents that are approximately zero have been determined, control system140may determine whether only one phase current is approximately zero (Step345). According to one embodiment, if there is one failed current sensor reading approximately zero, and there are no phase currents properly at the zero crossing point, control system140may determine the failed current sensors. In the case where only one phase current is approximately zero, current sensor150corresponding to the zero value may be identified as a failed sensor. If no current sensors150have registered a phase current of approximately zero, then the failed current sensor may be producing a non-zero value. If two or more current sensors150register a phase current of approximately zero, either two or more current sensors150may have failed, or a current sensor150may have failed and another current sensor is at a zero-crossing point. If less than one or more than one phase currents is approximately zero, Step350may be executed. In contrast, if one phase current is approximately zero, Step365may be executed.

If less than one or more than one phase current is approximately zero, control system140may wait a second delay time (Step350). A second delay may include a time duration sufficient to ensure that a zero reading from a valid current sensor150is not improperly identified as a sensor failure (at or near a proper zero crossing of the phase current of the motor). In one embodiment, when more than one current sensor150value is approximately zero, motor control module207may wait a second delay time to allow those phase currents to move away from zero before re-executing Step345. In another embodiment, if no current sensors150are approximately zero, but the absolute value of the actual phase currents is equal to or greater than the open circuit value, either the failed current sensor has not yet decayed to zero, of the failure is not of an open circuit type. In these cases, either additional time is needed to allow the failed current sensor to decay to zero, or the loop created by Steps340to355may declare an irresolvable current sensor failure after executing a predetermined number of times in a row.

Once control system140has waited a second delay time, control system140may determine if the number of times Step340and345has been executed is greater than a predetermined number of times (Step355). If Steps340and345have been performed too many times in a row, it may be an indication that two or more current sensors150have failed, or that the failed current sensor is producing a non-zero value. If the number of times Step340and345has been executed is greater than a predetermined number of times, motor control module207may next execute Step360. If the number of times Step340and345has been executed is less than or equal to a predetermined number of times, motor control module207may next execute Step340.

If the number of times Step340and345has been executed is greater than a predetermined number of times, control system140may determine that an irresolvable current sensor failure has occurred (Step360). According to one embodiment, motor control module207may declare an irresolvable current sensor failure. Either two or more current sensors150have failed, or the failed current sensor is producing a non-zero value. If the failed current sensor is producing a non-zero value, it may indicate a non-open circuit current sensor failure. Motor control module207may shut down the motor, or may initiate other preprogrammed health and welfare measures to prevent the motor from becoming uncontrolled.

If one phase current is approximately zero, control system140may estimate a phase current for the failed current sensor (Step365). According to one embodiment, motor control module207may estimate a phase current for the failed current sensor. An estimated phase current for the failed current sensor may be selected such that the summation of the estimated phase current and the valid actual phase currents may be approximately zero. Under ideal conditions, the summation of the estimated phase current and the valid actual phase currents may have a value of zero. But due to noise and interference, which may not be symmetrically distributed about zero, it may be desirable to bias the estimation by several amps. Such a bias may be as low as a fraction of an amp, and as high as 20 amps.

Once control system140has estimated a phase current for the failed current sensor, control system140may continue to estimate the phase current each time a sample is taken for the failed current sensor (Step370). The phase current of the failed current sensor may continue to be estimated by motor control module207until the failed current sensor passes a requalification check. The Steps ofFIG. 3may continue to be executed with the phase current for the failed current sensor provided by the estimate. If an additional current sensor150is then detected as a failure, an irresolvable current sensor failure may have occurred.

Control system140may be configured to store relevant performance data and other information in storage device202. The information stored may include one or more of the values of the actual phase currents, flexible variables, estimated phase currents, date, time, motor, and power converter. The stored data may be stored in a permanent file, or may be stored in revolving buffer, which can be transferred to a permanent file in the event of an anomaly associated with power electronics system120or control system140.

While certain aspects and features associated with the method described above may be described as being performed by one or more particular components of control system140, it is contemplated that these features may be performed by any suitable computing system. Specifically, one or more of these features may be performed by a suitably programmed FPGA. Furthermore, the order of steps inFIG. 3is exemplary only and certain steps may be performed before, after, or substantially simultaneously with other steps illustrated inFIG. 3. For example, in some embodiments, Step350and Step355may be preformed in reverse order. In another example, Step335may be unnecessary, as once a current sensor150has failed, the remaining phase currents may be rapidly driven off the zero crossing point.

Another possible variation on the steps ofFIG. 3includes if less than one or more than one phase current is approximately zero in Step345, control system140may periodically repeat Step345until either one phase current is approximately zero, and then next perform Step365, or the currents destabilize and the motor is automatically shut down.

FIG. 4illustrates a flowchart400depicting an exemplary method for requalifying a failed current sensor on a three-phase machine. As illustrated inFIG. 4, one or more predetermined variables may be loaded from control system140on machine100(Step405). Step405may be essentially the same as Step305, and the similar details will not be repeated. Step405may additionally load a selected integer. A selected integer may be a number compared to a counter to determine if a failed current sensor may be requalified. A selected integer may be as low as two, and may be as high as 100. In an alternate embodiment, Step405may load from storage device202the predetermined variables loaded by Step305.

Once the predetermined variables are loaded, the values of the actual phase currents may be collected from current sensors150on a machine100(Step410). Step410may be essentially the same as Step310, and the similar details will not be repeated. In an alternate embodiment, Step410may load from storage device202the data loaded by Step310.

Once phase current values have been collected, flexible variables may be determined from the actual phase currents (Step415). Step415may be essentially the same as Step315, and the similar details will not be repeated. In an alternate embodiment, Step415may load from storage device202the data loaded by Step315.

Once the flexible variables have been determined, the absolute value of the sum of the actual phase currents may be calculated (Step420). According to one embodiment, after the flexible variables have been determined, motor control module207may calculate the absolute value of the sum of the actual phase currents. Step420may be essentially the same as Step320, and the similar details will not be repeated. In an alternate embodiment, Step420may load from storage device202the data calculated by Step320.

Once the sum of the actual phase currents has been determined, whether the absolute value of the sum of the actual phase currents is below an open circuit value may be determined (Step425). Step425may be essentially the same as Step325, and the similar details will not be repeated. If the absolute value of the sum of the actual phase currents is less than the open circuit value, motor control module207may next execute Step430. If the absolute value of the sum of the actual phase currents is equal to or greater than the open circuit value, motor control module207may next execute Step435.

If the absolute value of the sum of the actual phase currents is less than the open circuit value, control system140may determine if the phase current of the failed current sensor is approximately zero (Step430). If the actual phase current of the failed current sensor is approximately zero, motor control module207may next execute Step435. If the actual phase current of the failed current sensor is greater than approximately zero, motor control module207may next execute Step450.

If the absolute value of the sum of the actual phase currents is greater than or equal to the open circuit value, or the actual phase current of the failed current sensor is approximately zero, control system140may decrement a counter (Step435). The counter may be an integer tracker. The counter may be used to determine when a failed current sensor has produced correct values a sufficient number of times to requalify a current sensor150and thus start using readings from current sensor150instead of an estimate of the phase current for that current sensor150.

Once the counter has been decremented, control system140may determine if the counter is less than zero (Step440). The counter is a measure of how accurate a failed current sensor has recently been. To requalify a failed current sensor, current sensor150may need to have been accurate for several sensor samples, that is, a time period long enough to show current sensor150is now working correctly. In most cases, requiring current sensor150to work correctly for as long a time period as current sensor150had failed is unnecessary. This is accomplished by not allowing the counter to go negative. If the counter is less than zero, motor control module207may next execute Step445. If the counter is greater than or equal to zero, motor control module207may next execute Step410.

If the counter is less than zero, control system140may reset the counter to zero (Step445). Once the counter has been reset, and a new sample is available from current sensors150, Step410may be executed next. If the absolute value of the sum of the actual phase currents is less than the open circuit value and the actual phase current of the failed current sensor is greater than approximately zero, control system140may increment a counter (Step450).

Once control system140has incremented a counter, control system140may determine if the counter is greater than the selected integer (Step455). As discussed above, the selected integer was determined to give sufficient valid phase current sensor reads before requalifying a failed current sensor. If the counter is less than or equal to the selected integer, Step410may be executed. In contrast, if the counter is greater than the selected integer, Step460may be executed.

If the counter is greater than the selected integer, control system140may requalify the failed current sensor (Step460). According to one embodiment, when current sensor150has been requalified, motor control module207may stop estimating the phase current value of the failed current sensor and start using the actual phase current value of current sensor150to control the motor.

In another embodiment, the process of flowchart400may include comparing the actual phase current from the failed current sensor to the estimate phase current for the failed current sensor. In one example, this additional check might be an additional step and comparison between Step430and Step450. If the actual phase current and the estimated phase current are not within some predetermined and/or user defined range of each other, motor control module207would next execute Step435. If the actual phase current and the estimated phase current are within some predetermined and/or user defined range of each other, motor control module207might next execute Step450.

Control system140may also be configured to store relevant performance data and other information in the storage device202. The information stored may include one or more of the values of the actual phase currents, flexible variables, the present counter value, estimated phase currents, date, time, motor, and power converter. The stored data may be stored in a permanent file, or may be stored in revolving buffer, which can be transferred to a permanent file in the event of an anomaly associated with power electronics system120or control system140.

While certain aspects and features associated with the method described above may be described as being performed by one or more particular components of control system140, it is contemplated that these features may be performed by any suitable computing system. Furthermore, the order of steps inFIG. 4is exemplary only and certain steps may be performed before, after, or substantially simultaneously with other steps illustrated inFIG. 4.

INDUSTRIAL APPLICABILITY

Methods and systems consistent with the disclosed embodiments may provide a solution for detecting a failed current sensor and estimating a phase current for the failed current sensor. A control system140that employs the processes and features described herein may determine if the sum of the phase currents provided by current sensors150is less than an open circuit value. If the sum of the phase currents is not less than an open circuit value, control system140may determine which phase current values are approximately zero. If only one phase current is consistently approximately zero, and is not reading other values, that current sensor150may have failed. A phase current may be estimated for the failed current sensor by choosing an estimated phase current that may make the sum of the estimated phase current and the other actual phase currents approximately zero. Although the disclosed embodiments are described in connection with a motor and a power converter on machine100, they may be applicable to any power converter that supplies a motor where it may be advantageous to provide a three-phase machine open current sensor detection and estimation strategy.

The presently disclosed system and method of detecting one or more failed current sensor and estimating a phase current for the failed current sensor may have several advantages. For example, the systems and methods described herein may provide a way to quickly determine if a current sensor150has failed and if an estimate can be generated for the phase current of the failed current sensor. The motor may be operable with a failed current sensor because an estimate for that phase current may be reliably substituted for the failed sensor.

Additionally, the disclosed system and method provide a robust way to determine which current sensors150may have failed by focusing on the zero crossings. A current sensor150that has not failed may be quickly driven off a zero value as the power converter responds to the erroneous values created by the failed current sensor. The failed current sensor may be detected and an estimate used in its place to bring the motor back under control.

Further, the disclosed system and method may provide a way to requalify a current sensor150that has been previously identified as having failed. If the failed current sensor starts to operate normally, after being requalified, current sensor150may no longer be treated as failed, the estimating may stop, and if another current sensor150fails, the motor may not have to be shut down.