Method, apparatus and article for motor control voltage dropout detection

A control subsystem for an electric motor determines whether power was interrupted, and delays torque production if power was interrupted. The control subsystem may employ two separate non-volatile memory locations, or alternatively a single non-volatile memory location.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This disclosure generally relates to electric motors, and particularly to the control of electric motors in electric motor driven systems, for example, electric vehicles.

2. Description of the Related Art

A large variety of applications employ electric motors. For example, electric vehicles such as electric vehicles with battery, super- or ultra-capacitors, fuel cell and/or hybrid power sources employ electric motors in the power train to drive the traction wheels of the vehicle. Such electric motor driven vehicles may also employ electric motors to drive auxiliary devices, such as fans, compressors, blowers, moving seats and/or windows. Many other applications exist for electric motors that are not transportation vehicle related.

Electric motors may be driven using alternating current (AC) or direct current (DC) electric power. In the case of a traction motor for an electric motor driven vehicle, the electric motor is typically driven using AC power. The AC power may be supplied from a DC power source such as a battery, super- or ultra-capacitor, and/or fuel cell system. Such systems employ an inverter to transform the DC power from the DC power source to AC power for driving the electric motor. Typically, the AC power is supplied as three phase AC power at a relatively high voltage (e.g., 24VAC–400VAC).

Most motor driven applications employ a control subsystem for controlling operation of the electric motor. The control subsystem may include a microprocessor and associated memory which typically require DC power at a relatively low voltage (e.g., 2.5V–5V). Consequently, many electric motor driven systems will employ a low voltage power supply (LVPS) to transform the high voltage DC power from the DC power source to a low voltage suitable for use with the control subsystem.

There are a large variety of control subsystems and control regimes suitable for the different electric motor driven applications. Even in the relatively limited field of electric motor driven vehicles, a large number of different control subsystems and control regimes have been proposed. In almost all instances of electric motor driven systems, it is possible that power to the control subsystem may be interrupted during normal operation. In electric motor driven vehicle applications, the power train is required to resume normal torque production after low voltage dropout interruptions lasting under several seconds, for example, during periods of high torque demand. Conventional approaches may produce motor control loop stability problems, resulting in current demand surges while attempting to command full torque from an electric motor with insufficient flux. An improved motor control subsystem and control regime to address this problem is desirable.

BRIEF SUMMARY OF THE INVENTION

In one aspect, a method of operating an electric motor driven system comprises determining if an interruption of power to the control subsystem controlling the electric motor has occurred during at least one ON/OFF cycle of the electric motor driven system; and delaying torque production of the electric motor if it is determined that an interruption of power to the electric motor has occurred during the at least one ON/OFF cycle of the electric motor. The method may further comprise storing in a first non-volatile memory location a value indicative of a number of times the control subsystem has executed a shut down procedure; and storing in a second non-volatile memory location a value indicative of a number of times that the control subsystem has started.

In another aspect, a method of operating an electric motor of a vehicle comprises in response to a start up of a controller, comparing a value stored in a first non-volatile memory location to a value stored in a second non-volatile memory location, the value stored in the first non-volatile memory location indicative of a number of times that the controller has executed a shut down procedure and the value in the second non-volatile memory location indicative of a number of times that the controller has started up; and delaying torque production of the electric motor if the value stored in the first non-volatile memory location is equal to the value stored in the second non-volatile memory location.

In a further aspect, a control subsystem for controlling operation of an electric motor of an electric motor driven system comprises means for determining if an interruption of power to the control subsystem controlling the electric motor has occurred during at least one ON/OFF cycle of the electric motor driven system; and means for delaying torque production of the electric motor if it is determined that an interruption of power to the electric motor has occurred during the at least one ON/OFF cycle of the electric motor. The control subsystem may further comprise a first non-volatile memory location to a value indicative of a number of times the control subsystem has executed a shut down procedure; and a second non-volatile memory location to store a value indicative of a number of times that the control subsystem has started, wherein the means for determining if an interruption of power to the control subsystem controlling the electric motor has occurred during at least one ON/OFF cycle of the electric motor driven system comprises means for comparing the value stored in the first non-volatile memory location to the value stored in the second non-volatile memory location.

In still a further aspect, a control subsystem for controlling an operation of an electric motor of an electric motor driven system comprises a first non-volatile memory location to store a value indicative of a number of times a controller has executed a shut down procedure; a second non-volatile memory location to store a value indicative of a number of times the controller has started up in an ON/OFF cycle; and a processor configured to increment the value indicative of the number of times the controller has executed the shut down procedure at each execution of the shut down procedure, and further configured to delay torque production if a defined relationship between the value stored in the first non-volatile memory location and the value stored in the second non-volatile memory location is satisfied.

In still a further aspect, a method of operating an electric motor driven system comprises checking a value stored in a first non-volatile memory location during a start up procedure, the value representing whether a shut down procedure has previously been completed; delaying torque production of the electric motor if the value stored in the first non-volatile memory location is equal to a first value; storing a second value to a first non-volatile memory location as part of a start up procedure; after storing the second value to the first non-volatile memory location as part of the start up procedure, enabling the electric motor; and if a shut down procedure is completed, storing the first value in the first non-volatile memory location at the end of the shut down procedure.

DETAILED DESCRIPTION OF THE INVENTION

In the following description, certain specific details are set forth in order to provide a thorough understanding of various embodiments of the present methods and systems. However, one skilled in the relevant art will recognize that the present methods and systems may be practiced without one or more of these specific details, or with other methods, components, materials, etc. In other instances, well known structures associated with electric motors, power subsystems, control subsystems, microprocessors, memories, and sensors have not been shown or described in detail to avoid unnecessarily obscuring descriptions of the embodiments of the present methods and systems.

The headings provided herein are for convenience only and do not interpret the scope or meaning of the claimed invention.

FIG. 1shows an electric motor driven vehicle2comprising an electric motor drive system4. The electric motor drive system4comprises an electric motor6, a power subsystem8and a control subsystem10.

The electric motor6provides drive torque to drive a set of wheels12of the electric motor driven vehicle2. A drive train14comprising a transaxle16and drive shaft18physically couples the electric motor6and the wheels12. The transaxle16includes gearing selected to provide appropriate torque and rotational speed ratios between the electric motor6and the wheels12. Some embodiments commonly referred to as “hybrids” may include an internal combustion engine (not shown). The internal combustion engine may be coupled to the drive train14in “parallel” with the electric motor drive system4. Alternatively, or additionally, the internal combustion engine may be coupled to drive a generator to supply power to the power subsystem8. The internal combustion engine in such embodiments are typically considered to be in “series” with the electric drive system4.

A vehicle with an internal combustion engine typically has a multi-speed transmission to provide appropriate torque at all speeds. The electric motor driven vehicle2can use a single speed transmission if the internal combustion engine is omitted, or if the internal combustion engine is provided in series with the electric drive system4. This is due to the mechanical simplicity of an electric motor6and the motor's resultant ability to deliver required driving torque over a much wider speed range than an internal combustion engine. Thus, transaxle16may be a single speed transaxle. Such a transaxle has considerable advantages of simplicity, reliability and relatively low cost.

The power subsystem8comprises a power source20that provides electric power for the electric motor6. The power source20may take any of a variety of forms. In transportation related applications, the power source20typically takes the form of one or more DC power sources capable of storing electric power, for example, a set of battery cells and/or super- or ultra-capacitors, and/or one or more DC power sources capable of producing electrical power, for example, a fuel cell stack. The electric motor driven vehicle2may or may not further comprise an internal combustion engine (not shown) physically coupled to the drive train, or coupled to drive a generator (not shown) to supply electrical power to the power source20and/or motor6. Thus, as used herein and in the claims, an electric motor driven system includes any device or system that is driven in whole or in part by an electric motor, with or without additional motors or engines.

The power subsystem8also comprises one or more circuits for conditioning the electrical power, generically known as converters which may comprise one or more rectifiers, inverters and/or step-up or step-down converters.

Where the electric motor6takes the form of an AC electric motor, the power subsystem8comprises an inverter22to transform DC power from the power source20to AC power to drive the electric motor6. Typically, the inverter22will take the form of a switch mode inverter. The inverter22may comprise a number of switching legs. For example, where the electric motor6is driven with three phase AC power, the inverter22may comprise three pairs of switching legs22a–22c, each leg operable to produce a respect phase (A, B, C) of the AC power. Each switching leg22a–22cmay comprise one or more upper switches and one or more lower switches, with anti-paralleled diodes. WhileFIG. 1illustrates the upper and lower switches of each leg22a–22cas each comprising a respective switch and anti-parallel diode, each may actually comprise multiple switches and anti-parallel diodes electrically coupled in parallel. The upper and lower switches may, for example, take the form of insulated gate bipolar transistors (IGBTs) or metal oxide semiconductor field effect transistors (MOSFETs).

In some embodiments, the inverter22may take the form of a bi-directional converter. For example, the inverter22may also function as a rectifier for converting three phase power produced by the electric motor6operating as a generator in a regenerative braking mode to DC power to be stored in the power source20, as is commonly understood by those of skill in the art. In some embodiments, the inverter22may function as a rectifier for converting AC power produced by a generator driven by an internal combustion engine of a hybrid, as is commonly understood by those of skill in the art.

The power subsystem8may further comprise a low voltage power supply (LVPS)24to transform power received from the power source20via a high power bus26into a form suitable for use with the control subsystem10. For example, the low voltage power supply24may step down the voltage of DC power supplied from the power source20, and/or may otherwise condition the power, supplying the low voltage power to the control subsystem10via a low voltage power bus28. For example, the low voltage power supply24may convert unregulated 12V battery power to regulated 5V power. Low voltage power supplies are commercially available from a large variety of commercial sources. While not illustrated, the power subsystem8may include one or more low power storage devices in addition to the power source20. These low power storage devices may, for example, comprise one or more battery cells and/or super- or ultra-capacitors coupled to supply a relatively intermediate level of power (e.g., 12V) to run various accessory items such as motors, seats, entertainment systems, etc. The low power storage devices may be coupled to supply power to the control subsystem10via the low voltage power supply24.

The control subsystem10may comprise a microprocessor-based device and/or a hardwired device, for example, an application specific integrated circuit (ASIC), having appropriate inputs, outputs, throughput, and/or memory and the like to perform the functions ascribed to it herein. The control subsystem10provides gating control signals30to control the switches of the inverter22. The control subsystem10also executes control logic for converting a torque demand signal Trefgenerated by a position of a throttle32such as a pedal sensor, into a current command for driving the electric motor6based on various operating characteristics of the electric motor drive system4. For example, current sensors34and rotational encoders36provide actual motor current signal I and drive train rotational speed signal ω to the control subsystem10. Voltage and/or current sensors38may provide DC bus voltage VBUSand/or bus current signals IBUSto the control subsystem10. The control subsystem10may also receive a Start/Stop signal KEY_SIGNAL that indicates whether the electric motor drive system4is in an ON organ OFF condition or state. For example, the Start/Stop signal KEY_SIGNAL may indicate whether a key has been turned into an ON or Start position or turned to an OFF or Stop position to start and stop operation of the electric motor drive system4, respectively. Thus, the Start/Stop signal KEY-SIGNAL defines an ON/OFF cycle for the electric motor drive system4, which may be a determined or user selected starting and stopping of system operation. The control subsystem10may provide a KEEP_ALIVE signal to the low voltage power supply24. The control subsystem10may receive a reset signal RESET from the low voltage power supply24.

FIG. 2shows the control subsystem10according to one illustrated embodiment. The control subsystem10comprises a microcontroller or microprocessor, collectively controller40, and memory such as an electronically erasable programmable read-only memory (EEPROM)42, flash memory44and random access memory (RAM)46. Flash memory44is typically less expensive the comparable sizes of EEPROM42. However, it typically takes longer to store data to flash memory44, since each cell of the flash memory44must be erased prior to being reprogrammed, and flash memory44can only be erased as a sector or block at a time.

The control subsystem10may also include an input/output (I/O) interface48, which may or may not include suitable buffers for buffering input and output Suitable low voltage power (e.g., 2.5 volt, 5 volt) is supplied to the controller40, EEPROM42, flash memory44and RAM46via the low voltage power bus28. Data and instructions are passed between the controller40and EEPROM42Via a first internal communications bus52. Data and instructions are passed between the controller40and the flash memory44and RAM46via a second internal communications bus54. Data and instructions are passed between the controller40and the I/O interface48via a third internal communications bus56. While illustrated as separate internal communications buses52,54,56, some embodiments may combine one or more internal communications buses52,54,56, or may use additional or different internal communications buses.

FIG. 3shows a method100of operating the electric motor drive system4according to one illustrated embodiment. The method100starts at102when power is applied to the control subsystem10. At104, the controller40of the control subsystem10executes a standard start up procedure. The standard start up procedure may be any of a number of existing start up procedures which determine whether the control subsystem10and/or various other subsystems are operational.

As a modification to the standard start up procedure, the controller40determines whether power has been interrupted during an ON/OFF cycle at106.

If the controller40determines that power has been interrupted during an ON/OFF cycle, the controller40delays torque production at108. The controller40may delay torque production of the electric motor6by delaying activation of one or more of the switches on the inverter22by way of the control signals30. After delaying torque production, the controller40enables the electric motor at110. The controller40may enable the electric motor6by activating of one or more of the switches on the inverter22by way of the control signals30.

If the controller40determines that power has not been interrupted during the ON/OFF cycle, the controller4immediately passes control to110to enable the electric motor6without delaying torque production.

At112, the controller40determines whether a shut down request has been received. If the controller40determines that a shut down request has not been received, the controller continues to enable the electric motor, returning to110. If the controller40determines that a shut down request has been received, the controller40executes a shut down procedure at114. The method100terminates at116, at the end of the shut down procedure114.

FIGS. 4A–4Bshows a method200of operating the electric motor drive system4according to another illustrated embodiment. The method200illustrates a particular embodiment of the method100(FIG. 3). The method200starts at202when power is applied to the control subsystem10. At204, the controller40of the control subsystem10executes a standard start up procedure.

As a modification to the standard start up procedure, the controller40of the control subsystem10compares a value stored in a second non-volatile memory location to a value stored in a first non-volatile memory location at205. The first non-volatile memory location may be a location in the flash memory44, while the second non-volatile memory location may be a location in the EEPROM42. This takes the relative speed of the EEPROM42with respect to the flash memory44, while balancing the relative cost of EEPROM42versus flash memory44. For example, the flash memory44may be used to store values during a controlled shut down since the shut down procedure can accommodate the relative slowness of storing data to flash memory44, while the EEPROM42may be used to store data during the start up where responsiveness is more important. Alternatively, in some embodiments the first and second memory locations may be respective locations in the same flash memory44or in the same EEPROM42. The control subsystem10may employ additional and/or different memory devices.

At206the controller40determines whether the value stored in the second non-volatile memory location is equal to the value stored in the first non-volatile memory location.

If the controller40determines that the value stored in the second non-volatile memory location is equal to the value stored in the first non-volatile memory location, the control subsystem10determines that power interruption has occurred and delays torque production. For example, the controller40may start a delay timer at207, executing a wait loop at208until the controller40determines that the delay timer is equal to a defined delay time at209. If however the controller40determines that the value stored in the second non-volatile memory location is not equal to the value stored in the first non-volatile memory location, then a power interruption has not occurred and the controller40passes control directly to211.

At211, the controller40sets the value stored in the second non-volatile memory location equal to the value stored in the first non-volatile memory location. At210, the controller40enables the electric motor6, for example, providing appropriate control signals30to the inverter22.

At212, the controller40determines whether a shut down request has been received. If the controller40determines that a shut down request has not been received, the controller40continues to enable the electric motor6returning to210. If the controller40determines that a shut down request has been received, the controller40executes a standard shut down procedure at214. As a modification to the standard shut down procedure, the controller40increments the value stored in the first non-volatile memory location at215. The method200terminates at216.

FIG. 5shows a portion of a method300which may be substituted for a portion of the method200. In particular, the controller40determines the difference between a value stored in the second non-volatile memory location and a value stored in the first non-volatile memory location at305. At306, the controller40determines whether the difference is equal to a defined value. For example, the controller40may determine whether the difference between the value stored in the second non-volatile memory location and the value stored in the first non-volatile memory location is equal to zero. These acts may be substituted for the acts205and206of method200, respectively.

FIG. 6shows a method400of operating the motor drive system4employing a single non-volatile memory location according to another illustrated embodiment. The method400starts at402when power is applied to the control subsystem10. At404, the controller40of the control subsystem10executes a standard start up procedure.

As a modification to the standard start up procedure, the controller40of the control subsystem10determines whether a value stored in a first non-volatile memory location is equal to a defined first value at406. The defined first value may, for example, be a logical TRUE, ON or 1. The first non-volatile memory location may be a location in the EEPROM42. Alternatively, the first non-volatile memory location may be a location in the flash memory44.

If the controller40determines that the value stored in a first non-volatile memory location is not equal to a defined first value, the controller40delays torque production at408, for example, by controlling the switches of the inverter22via the control signals30. After delaying torque production for the desired period, the controller40then passes control to411. If the controller40determines that the value stored in a first non-volatile memory location is equal to a defined first value, the controller40passes control directly to411.

At411, before enabling the electric motor6the controller40sets the value stored in the first non-volatile memory location equal to a first defined value, for example, zero (0). The first defined value indicates that the controller40has not yet executed the shut down procedure.

At410, the controller40enables the electric motor6, for example, providing appropriate control signals30to the inverter22.

At412, the controller40determines whether a shut down request has been received. If the controller40determines that a shut down request has not been received, the controller40continues to enable the electric motor6returning to410. If the controller40determines that a shut down request has been received, the controller40executes a standard shut down procedure at414. As a modification to the standard shut down procedure, at415the controller40sets the value stored in the first non-volatile memory location to a second defined value, for example one (1). The second defined value indicates that the controller40has completed the shut down procedure. The method400terminates at420.

One example of operation is discussed below. Other examples of operation will be apparent.

In operation there may be three cases of interest. In the first case, where a control subsystem10is new, the values of both non-volatile memory locations may be the same (e.g., 0000). A flag brownout_error may consequently be set, resulting in a delay in torque production. This should not present an problem since the electric motor drive system4is being tested, and will perform as desired in further operation.

On the next subsequent power up, the value in the first non-volatile memory location is 0001 and the value in the second non-volatile memory location is 0000. The flag brownout_error will be cleared since the values are different, and no delay in torque production will occur. The value of the second non-volatile memory is set equal to the value of the first non-volatile memory location and saved immediately, for example, to EEPROM42. This occurs during the initialization or start up procedure, for example, within approximately 500 m-seconds after power being applied to the control subsystem10, and before the electric motor6is enabled. During shut down, the value stored in the first non-volatile memory is incremented (e.g., 0001 to 0002).

Should power be interrupted before shut down is complete, upon application of power the control subsystem10restarts. During initialization or start up the values in both non-volatile memory locations are the same because the shut down procedure was not completed. The controller40sets the flag brownout_error, and torque production is consequently delayed.

The above description of illustrated embodiments, including what is described in the Abstract, is not intended to be exhaustive or to limit the invention to the precise forms disclosed. Although specific embodiments of and examples are described herein for illustrative purposes, various equivalent modifications can be made without departing from the spirit and scope of the invention, as will be recognized by those skilled in the relevant art. The teachings provided herein of the invention can be applied to other electric motor driven systems, not necessarily the exemplary electric motor driven vehicle generally described above.

The various embodiments described above can be combined to provide further embodiments. All of the U.S. patents, U.S. patent application publications, U.S. patent applications, foreign patents, foreign patent applications and non-patent publications referred to in this specification and/or listed in the Application Data Sheet, including but not limited to commonly assigned U.S. application Ser. No. 10/658,124 filed Sep. 9, 2003, are incorporated herein by reference, in their entirety. Aspects of the present methods and systems can be modified, if necessary, to employ systems, circuits and concepts of the various patents, applications and publications to provide yet further embodiments of the invention.

These and other changes can be made to the present methods and systems in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the invention to the specific embodiments disclosed in the specification and the claims, but should be construed to include all electric motor driven systems, electric motor drive systems, and methods that operated in accordance with the claims. Accordingly, the invention is not limited by the disclosure, but instead its scope is to be determined entirely by the following claims.