GB2495089A

GB2495089A - Vehicle fail-safe electric motor controller

Info

Publication number: GB2495089A
Application number: GB1116622.0A
Authority: GB
Inventors: Phil Eagleton
Original assignee: Sevcon Ltd
Current assignee: Sevcon Ltd
Priority date: 2011-09-27
Filing date: 2011-09-27
Publication date: 2013-04-03
Anticipated expiration: 2031-09-27
Also published as: GB2495089B; GB201116622D0

Abstract

An electric motor controller comprises: a health indicator 18 providing an output signal to indicate operation of a power provider such as inverter 16; a failsafe 20 that receives a health indicator signal from another electric motor controller, and a controller 12 that controls operation of power provider 16 based on the indicator signal from said other electric motor controller. The controller may only activate the inverter if an indicator signal is received in response to a parameter of the signal such as its voltage level, frequency, phase amplitude and duty cycle. The health indicator signal may be a square wave and only provided if the motor controller is operating safely, which can include that controller components are operating and a signal from another component is consistent with safe vehicle operation. The health indicator signal can be based on operational parameters of the controller such as the direction of DC currents of the controller or another controller; a key switch voltage; temperature of inverter power transistors or the controller; and speed and resolver measurements. The power supply to a first electric traction motor may be controlled based on a comparison of the drive direction the motor controller with the drive direction of a second motor controller. The drive direction may be sensed by sensing the direction of the supply current to each controller.

Description

Motor Controller The present invention relates to the motor controllers for the control of electric motors such as may be used in electric vehicles.

The need to reduce carbon emissions associated with transport is widely recognised. To address this need electric vehicles are becoming increasingly common.

The use of electric motors enables vehicle designers to simplify the drive line of a vehicle.

For example each driven wheel in a vehicle may be driven directly by an electric motor dedicated only to that wheel. In addition to simplified construction, it is recognised that such independent control of the wheels of a vehicle can provide certain other advantages.

In particular, the manoeuvrability of the vehicle may be substantially greater than in vehicles lacking such independent control of driven wheels.

It is generally preferred to provide independent power supply inverters for each motor in a vehicle and the inventors in the present case have appreciated that, whilst it provides many advantages the independent control of different wheels of a vehicle also presents certain challenges. For example, if the power supply inverter associated with some (but not all) of the wheels malfunctions whilst a vehicle is in motion the vehicle may be caused to swerve or even to spin.

Aspects and examples of the invention are set out in the claims and aim to address at least a part of the above described problem.

Examples of the invention will now be described in detail, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a very schematic view of an electric vehicle; Figure 2 shows a motor controller; Figure 3 shows a configuration of two motor controllers with an external control unit; Figure 4 shows two interconnected motor controllers; Figure 5 shows an example combining features of Figures 3 and 4.

Figure 1 shows a vehicle 100 having four wheels 102, 104, 106, 108. Wheels 106 and 108 are opposite each other towards the front of the vehicle. Wheels 102 and 104 are opposite each other towards the rear of the vehicle 100.

Wheel 102 is coupled to electric motor 101, which in turn is electrically coupled to motor controller 2. Wheel 104 is coupled to electric motor 103 which in turn is electrically coupled to motor controller 2. Vehicle control unit 126 is coupled to both of the motor controllers 2, 2'.

The electric motors 101, 103 are operable to drive the wheels 101, 103 independently of one another under the control of controllers 2, 2. The vehicle control unit 126 provides control signals to controllers 2, 2' to control movement of the vehicle by driving the motors 101, 103.

Although shown as rear wheel drive the vehicle 100 may be front wheel drive. In addition, although the vehicle 100 is shown as a two wheel drive vehicle examples of the invention may be applied to four wheel drive vehicles. The vehicle control unit 126 may be coupled to the controllers 2, 2' by a control bus such as a controller area network, CAN-bus.

Figure 2 shows a motor controller 2 comprising a control means 12 coupled to a local current monitor 10 and a remote current monitor 14. The motor controller comprises a power provider 16 which is coupled to an external fail safe 20 and to the control means 12.

The control means 12 is also coupled to a health indicator 18.

In Figure 2 power supply input connections (e.g. battery connections) and AC power output connections are not shown. Power supply connections are discussed in more detail below with reference to Figure 4.

The power provider 16 includes an insulated gate bipolar transistor, IGBT, inverter and is operable to provide a pulse width modulated power output to an electric motor based on a direct current, DC, power supply. The power provider can be disabled by a shutdown signal from the control means 12 or as a result of the failsafe 20 disconnecting the power electronics (e.g. the PWM drive) of the power provider 16. When the output of the failsafe is in the enabling state, it turns on a transistor circuit (not shown) which controls the supply of power to the PWM drive circuits of the power provider 16. When the output of the failsafe 20 is in the disabling state, it turns off the transistor circuit thereby deactivating the PWM drive.

The local current monitor 10 is operable to sense current drawn from the DC power supply by the power provider 16 and provides a sense output signal to the control means 12 based on the sensed current flow. This local current monitor 10 is operable to provide an estimate of output torque from a motor driven by the power provider 16 and can be used to check whether the controller is providing energy to the motor (e.g. operating in a drive mode) or if the motor is returning energy to the controller (as in a regenerative brake mode). The remote current monitor 14 is operable to be coupled to sense current drawn by a power provider of another motor controller, similar to motor controller 2.

The health indicator 18 is operable to provide a heartbeat output signal at its output coupling dependent upon a determination that the other components of the motor controller, 10, 12, 14, 16, 18, 20 are functioning correctly and that the signal from the remote current monitor 14 is consistent with safe operation of the vehicle. The heartbeat signal is a sequence of square-wave pulses having a selected amplitude, frequency and duty-cycle. If the heartbeat signal is acceptable then the failsafe 20 produces a signal which enables the power provider. If the heartbeat signal is not acceptable then the output of the failsafe circuit disables the power provider 16.

It will be understood that the output of the failsafe is combined with other signals in the system, for example the inverse of the shutdown signal from the control means 12, so that all such signals must be in the enabling state to enable the power provider 16 and so that any such signal in the disabling state will cause the power provider to be disabled. A means to prevent the power provider 16 from re-enabling for a period of time after it has been disabled is provided. Determination of correct function is based on checking the range and in some cases transient behaviour of signals associated with the various component blocks.

In the example of Figure 2 the heartbeat signal comprises a pulsed (square wave) signal.

The failsafe 20 is operable to receive a heartbeat signal from an external system and to provide an enable signal to the power provider 16. The failsafe 20 is configured to provide an enable signal to the power provider 16 in the event that it receives a heartbeat signal and the power provider is arranged such that it cannot be activated in the absence of an enable signal from the failsafe, for example the power supply to the power provider may be configured such that, in the absence of an enable signal the power supply to the power provider 16 is disconnected. In addition to or as an alternative to a failsafe, the failsafe 20 may also comprise a detecting means configured such that in the event that it does not receive a heartbeat signal it causes the power provider to taper or reduce or to otherwise modify its power output to a safe level. In some cases the power provider or the failsafe may include a timer configured to prevent the power provider friom being re-enabled for a selected time after it has been disabled. Alternatively or in addition, the failsafe or the power provider may be arranged to signal to the control means 12 that action has been taken to disable the power provider.

The control means 12 is a control device, such as a microprocessor, configured to control operation of the other components of the controller 2. For example, the control means 12 is configured to compare the local current sensed by the local current monitor 10 with the current sensed by the remote current monitor 14. Based on this comparison the control means 12 is configured to control the power provider 16. For example, in the event that the direction of the current sensed by the local current monitor 10 does not match the direction of the current sensed by the remote current monitor 14 the control means is configured to shut down the power provider. This could relate to a situation in which one of the motors is engaged in regenerative braking. Note that the reversal of battery current in the reversed motor will be transient. If the situation persists then regenerative braking will end. The reversed motor could start to drive in the opposite direction and battery current would then go back to the original sense.

In operation the power provider 16 provides an AC power output signal for an electric traction motor provided that: (a) the failsafe 20 provides an enable signal to the power provider 16 indicating that the failsafe 20 is receiving a valid heartbeat signal; and (b) the control means does not provide a shut down signal to the power provider. The health indicator 18 provides an output heartbeat signal (e.g. to be received by another controller) in the event that it determines that the other components 10, 12, 14, 16, 18,20 of the motor controller are functioning correctly and that the signal from the remote current monitor 14 is consistent with safe operation of the vehicle, e.g. to ensure that the motors are driving in the same direction (or that they are driving in a selected direction or to ensure that the speed or torque of the motor is within a selected range, for example a range based on the speed or torque of another motor. In some cases the power provider is configured to check that the remote motor's direction of rotation is consistent with safe operation. For example, where the power provider is coupled to a controller area network bus (CANbus) of a vehicle then speed information from the remote monitor may be read from the CANbus to perform this check. Although the power provider 16 has been described as comprising an IGBT inverter other types of inverter may be used, for example the inverter may comprise IG-FETs, MOS-FETs, BJTs or other types of voltage controlled impedances. Coupling between components of the system may be direct or indirect and, where appropriate, may be provided by wireless couplings and/or through other components of the system. Although, for the purposes of explaining the invention components of the system have been shown as discrete units, this is merely exemplary and similar functionality may be provided in a smaller number of functional units, a single integrated unit, or the functionality may be further distributed/subdivided between a greater number of functional units.

The failsafe circuit could be implemented using digital or analogue electronics. The heartbeat signal is described as a sequence of square-wave pulses having a selected amplitude, frequency and duty-cycle. However other waveforms such as sinusoids or sawtooth waveforms may be used. In addition, one or more of the amplitude, frequency and duty cycle may not be used. For example the heartbeat may simply be based on the frequency of the signal or its amplitude or the duty cycle. In some cases a combination of two or more of these parameters may be used.

Figure 3 shows the motor controller 2 of Figure 2 (in which like reference numerals indicate like elements) in use with a second similar motor controller 2' and an external safety monitor 26. To assist understanding of the example of Figure 3, elements which are not directly relevant to the example are shown only in broken lines; these or other elements may be omitted.

The external fail safe 20 of the motor controller 2 is coupled to the health indicator 18' of the second motor controller 2' by a switching unit 24. The external fail safe 20' of the second motor controller 2' is coupled to the health indicator 18 of the motor controller 2' by the switching unit 24. The switching unit 24 is coupled to the external safety monitor 26. The external safety monitor 26 may be provided by a control unit such as the vehicle control unit 126 of Figure 1.

The switching unit 24 is controllable by the external safety monitor 26 to couple/decouple the failsafe 20 of the motor controller 2 to the health indicator 18' of the second motor controller 2'. The switching unit 24 is also controllable by the external safety monitor 26 to couple/decouple the failsafe 20' of the second motor controller 2' to the health indicator 18 of the motor controller 2.

In operation the external safety monitor 26 and/or the health indicator 18 monitors safety parameters of the vehicle such as; the current sense of each motor controller 2, 2'; the key switch voltage (e.g. the supply voltage to the control electronics, as opposed to the supply voltage of the main power stage); the temperature of the power transistors (IGBTs) of each controller; the temperature of the control logic of each controller; the voltage and/or temperature of DC link tracks; ADC calibration voltages; analogue inputs; supply voltage (Vcc) monitors (for monitoring programmable and fixed supply voltages); speed feedback measurements (such as sin-cos encoder data; resolver measurements); other digital inputs and motor PlC inputs. These are merely examples of parameters which can be monitored, some or all of them may not be used in practice and/or other additional safety parameters may be monitored. Fault detection may be performed by comparing one or more of these parameters with selected threshold values or selected ranges or by comparing sampled values of a parameter over a time interval to measure its transient behaviour, for example the rate of change of one or more of these parameters may be compared with a selected threshold level or a selected range; the thresholds and ranges may be selected based on stored (e.g. predetermined) values or may be determined on the fly based on other parameters.

The external safety monitor 26 is operable to detect a fault condition based on monitoring of one or more of these safety parameters and to control the switching unit 24 in response.

For example, in the event that the external safety monitor detects a fault it can control the switching unit 24 to decouple the failsafe 20' of the second motor controller 2' from the health indicator 18 of the motor controller 2 and/or to decouple the failsafe 20 of the first motor controller 2 from the health indicator 18' of the second motor controller 2'. In response to disconnection of the health indicator 18, 18' from the failsafe 20, 20' the controllers will shut down. For the configuration where 18' is connected to 20 and 18 is connected to 20' then both controllers will be shut down as a result of failure of one controller.

Figure 4 shows another example of the motor controller 2 of Figure 2 (in which like reference numerals indicate like elements) in use with a second similar motor controller 2'.

To assist understanding of the example of Figure 4, elements which are not directly relevant to the example are shown only in broken lines and connections which are not directly relevant have been omitted.

The local current monitor 10 of motor controller 2 is electrically coupled in series between the positive battery terminal B+ of a battery 200 and the power provider 16 of motor controller 2. The remote current sense module of the second motor controller 2' is electrically coupled in series between the power provider 16 of the first motor controller 2 and the negative battery terminal B-of the battery 200. The local current monitor 10' of motor controller 2' is electrically coupled in series between the positive battery terminal B+ of a battery 200 and the power provider 16' of motor controller 2'. The remote current sense module of the first motor controller 2 is electrically coupled in series between the power provider 16' of the motor controller 2' and the negative battery terminal B-of the battery 200. In this way the remote current monitor 14 of controller 2 is coupled to monitor the sense of the current drawn by the power provider 16' of motor controller 2' and the remote current monitor 14' of controller 2' is coupled to monitor the sense of the current drawn by the power provider 16 of motor controller 2. Thus, each controller 2, 2' is arranged to monitor the sense of the current drawn or generated by the other motor controller.

In some examples according to Figure 4, to provide a paired controller interlock the failsafe of the motor controller 2 is coupled to the health indicator 18' of the second motor controller 2'. The external fail safe 20' of the second motor controller 2' is coupled to the health indicator 18 of the motor controller 2'.

Although they are shown as being connected as series current measurement devices the current monitor 10, 10', 14, 14' may be provided by inductive or Hall Effect current transducers which need not be conductively coupled to the power supply lines and/or maybe provided by other current sensing devices such as current sensing transistors. In some examples the current monitors may also be configured to monitor current magnitude as well as or instead of current direction.

Figure 5 uses the same reference numerals as Figure 3 and Figure 4 to indicate like elements and shows an example which uses components of Figure 3 and Figure 4 in combination. In Figure 5 the switching unit 24 and the external safety monitor 26 are shown in broken lines to indicate that the failsafe 20 of the controller 2 may be coupled to the health indicator 18' of controller 2' without the presence of a switching unit; likewise, the failsafe 20' of the controller 2' may be coupled to the health indicator 18 of controller 2 without the presence of a switching unit. In some cases the failsafe input on controller 2 and 2' can be supplied directly by the external safety monitor 26 with the health signal generated by controllers 2 and 2' being monitored by the external safety monitor 26.lt is intended that one or more features of any of the examples described above and/or defined in the appended claims may be omitted and/or combined with one or more features of any of the other examples. The methods described herein may be implemented in hardware middleware or software or any combination thereof. In addition, examples of the invention comprise computer readable storage media and computer program products operable to program a processor to perform any of the methods described herein and in particular to configure a processor to perform one or more of the functions carried out by the control means 12, the failsafe 20, or the health indicator 18 as described hereinabove.

Claims

<claim-text>Claims 1. An electric motor controller comprising: a health indicator for providing an output signal to indicate operation of a power provider; and, a failsafe, comprising signal receiving means for receiving a health indicator signal from another electric motor controller, and a control means arranged to control operation of said power provider based on the indicator signal from said other electric motor controller.</claim-text> <claim-text>2. The electric motor controller of claim 1 in which the failsafe is configured to enable activation of the power provider based on the indicator signal.</claim-text> <claim-text>3. The electric motor controller of claim 1 or 2 in which the failsafe is configured not to enable activation of the power provider if the indicator signal is not received.</claim-text> <claim-text>4. The electric motor controller of any preceding claim in which the failsafe is configured to activate the power provider in response to receiving the indicator signal.</claim-text> <claim-text>5. The electric motor controller of any preceding claim in which the control means is configured to determine at least one parameter of the indicator signal and to control the power provider based on the at least one parameter.</claim-text> <claim-text>6. The electric motor controller of claim 5 in which the at least one parameter comprises one of: a DC voltage level; a frequency; a phase; peak to peak amplitude; RMS amplitude; and a duty cycle.</claim-text> <claim-text>7. The electric motor controller of any preceding claim in which the health indicator is configured to provide a time varying output signal to indicate operation of the power provider.</claim-text> <claim-text>8. The electric motor controller of claim 7 in which the time varying signal comprises a pulsed output signal such as a square wave.</claim-text> <claim-text>9. The electric motor controller of any preceding claim in which the health indicator is configured to provide the indicator signal only in the event that it is determined that the electric motor controller is operating safely, for example based on a determination that components of the motor controller are functioning and!or that the signal from another similar controller is consistent with safe operation of a vehicle.</claim-text> <claim-text>10. The electric motor controller of any preceding claim in which the health indicator is configured to provide the indicator signal based on a determination of at least one operational parameter.</claim-text> <claim-text>11. The electric motor controller of claim 10 in which the at least one operational parameter is selected from a list comprising: the direction of a DC current of the motor controller; the direction of a DC current of the other motor controller; a key switch voltage; the temperature of the power transistors (IGBTs) of the controller; the temperature of control logic of the controller; the voltage and/or temperature of DC link tracks associated with the controller; ADC calibration voltages; analogue inputs; one or more programmable or non-programmable supply voltage (Vcc) monitors; sin-cos encoder data; resolver measurements; speed feedback measurements; other digital inputs and motor PTC inputs.</claim-text> <claim-text>12. The electric motor controller of claim 11 or 12 in which the determination comprises comparing the at least one operational parameter with a threshold value.</claim-text> <claim-text>13. The electric motor controller of any preceding claim further comprising the power provider, wherein the power provider is operable to provide a power supply for an electric traction motor; 14. An electric motor controller comprising a control means configured to control the power supply of a first electric traction motor based on a comparison of the drive direction of the electric motor controller with the drive direction of a second electric motor controller.15. The electric motor controller of claim 14 comprising a comparer operable to compare the drive direction of the electric motor controller with the drive direction of said second electric motor controller.16. The electric motor controller of claims 14 or 15 comprising at least one of: a sensor for sensing the drive direction of the electric motor controller; and a sensor for sensing the drive direction of said second electric motor controller.17. The electric motor controller of claim 15 or 16 in which sensing drive direction comprises sensing the direction of a power supply current of the electric motor controller.18. The electric motor controller of any of claims 14 to 17 comprising a power provider for providing a power supply for said first electric traction motor. -ii-19. The electric motor controller of any of claims 13 to 17 having the features of any of claims ito 12.20. An electric motor controller substantially as described herein with reference to Figure 2.21. A combination comprising an electric motor and an electric motor controller according to any preceding claim.22. A combination comprising two electric motor controllers according to any of claims 1 to 20.23. A combination of electric motor controllers substantially as described herein with reference to any one of Figure 3, Figure 4 or Figure 5.24. A drive apparatus for an electric vehicle comprising a combination according to any of claims 20 to 22.25. A vehicle comprising an electric motor controller according to any of claims ito 20, a combination according to any of claims 21 to 23, or a drive apparatus according to claim 24.26. A method of operating an electric motor controller, the method comprising operating an electric motor in the manner defined in any one of claims 1 to 20.27. A method of operating an electric motor controller substantially as described herein with reference to any one of Figures 2 to 5.28. A computer program product comprising program instructions operable to program a processor of an electric motor controller to control an electric motor by providing a drive signal to the electric motor based on monitoring a supply current of a second electric motor controller.29. A computer program product comprising program instructions operable to program a processor of an electric motor controller to control an electric motor by providing a drive signal to the electric motor in dependence upon a control signal from a second electric motor controller.30. A computer program product according to claim 28 or 29 in which the program instructions are operable to program a processor of an electric motor controller to operate in the manner defined in any one of claims 1 to 20.Amendment to the claims gave been filed as follows Claims 1. An electric motor controller comprising: a control means configured to control the power supply of a first electric traction motor based on a comparison of the drive direction of the electric motor controller with the drive direction of a second electric motor controller, at least one of: a sensor for sensing the drive direction of the electric motor controller; and a sensor for sensing the drive direction of said second electric motor controller; wherein sensing drive direction comprises sensing the direction of a power supply current.
2. The electric motor controller ot claim 1 comprising a comparer operable to compare the drive direction ot the electric motor controller with the drive direction of said second electric motor controller.Ct',J
3. The electric motor controller of claim 1 or 2 comprising a power provider for providing a power supply for said first electric traction motor.N-0
4. An electric motor controller according to claim 1 comprising: a health indicator for providing an output signal to indicate operation of a power provider; and, a failsafe, comprising signal receiving means for receiving a health indicator signal from another electric motor controller, and a control means arranged to control operation of said power provider based on the indicator signal from said other electric motor controller.
5. The electric motor controller of claim 4 in which the failsafe is configured to enable activation of the power provider based on the indicator signal.
6. The electric motor controller of claim 4 or 5 in which the failsafe is configured not to enable activation of the power provider if the indicator signal is not received.
7. The electric motor controller of any preceding claim in which the failsafe is configured to activate the power provider in response to receiving the indicator signal.
8. The electric motor controller of any of claims 4 to 7 in which the control means is configured to determine at least one parameter of the indicator signal and to control the power provider based on the at least one parameter.
9. The electric motor controller of claim 8 in which the at least one parameter comprises one of: a DC voltage level; a frequency; a phase; peak to peak amplitude; RMS amplitude; and a duty cycle.
10. The electric motor controller of any of claims 4 to 9 in which the health indicator is configured to provide a time varying output signal to indicate operation of the power provider.
11. The electric motor controller of claim 10 in which the time varying signal comprises a pulsed output signal such as a square wave.
12. The electric motor controller of any of claims 4 to 11 in which the health indicator is configured to provide the indicator signal only in the event that it is determined that the electric motor controller is operating safely, for example based C'SJ on a determination that components of the motor controller are functioning and/or r. .. . that the signal from another similar controller is consistent with sate operation of a I'." vehicle.
13. The electric motor controller of any of claims 4 to 12 in which the health (%J indicator is configured to provide the indicator signal based on a determination of at least one operational parameter.
14. The electric motor controller of claim 13 in which the at least one operational parameter is selected from a list comprising: the direction of a DC current of the motor controller; the direction of a DC current of the other motor controller; a key switch voltage; the temperature of the power transistors (IGBTs) of the controller; the temperature of control logic of the controller; the voltage and/or temperature of DC link tracks associated with the controller; ADC calibration voltages; analogue inputs; one or more programmable or non-programmable supply voltage (Vcc) monitors; sin-cos encoder data; resolver measurements; speed feedback measurements; other digital inputs and motor FTC inputs.
15. The electric motor controller of claim 13 or 14 in which the determination comprises comparing the at least one operational parameter with a threshold value.
16. The electric motor controller of any claims 4 to 14 further comprising the power provider, wherein the power provider is operable to provide a power supply for an electric traction motor;
17. An electric motor controller substantially as described herein with reference to Figure 2.
18. A combination comprising an electric motor and an electric motor controller according to any preceding claim.
19. A combination comprising two electric motor controllers according to any of claims ito 17.
20. A combination of electric motor controllers substantially as described herein with reference to any one of Figure 3, Figure 4 or Figure 5.
21. A drive apparatus for an electric vehicle comprising a combination according to any of claims 17 to 19.C'J
22. A vehicle comprising an electric motor controller according to any of claims 1 to 17, a combination according to any of claims 17 to 20, or a drive apparatus I''." according to claim 21.
23. A method of operating an electric motor controller, the method comprising (sJ operating an electric motor in the manner defined in any one of claims 1 to 17.
24. A method of operating an electric motor controller substantially as described herein with reference to any one of Figures 2 to 5.</claim-text>