Motor control system

Abstract

A motor control system for a vehicle comprises an inverter driver 302,303 configured to generate an electrical signal for controlling a motor 304,305. An inverter controller 301 is configured to gener

Description

This invention relates to a motor control system for a vehicle. A typical motor control system might implement a combination of control functions, pulse-width modulation and gate driving. For example, during operation, voltage demands may be modulated into pulses and the resulting waveform may be used to drive gate drivers, which provide current to the motor windings. Pulse-width modulated (PWM) waveforms are particularly suited to running inertial loads like motors. Their inertia causes them to react slowly to any changes in an input signal, so they are not readily affected by the rapidly-switched discrete pulses of a PWM signal. One straightforward way of generating a pulse-width modulated wave is to use a comparator configured to receive a sine wave and a sawtooth wave as inputs (or any other suitable comparison circuit), and to output either a maximum circuit voltage or a minimum circuit voltage depending on which of its two inputs has the higher value at a particular clocking instant. The voltage demands that are modulated into PWM waveforms will typically represent the speed required of the motor at a given time instant, and feedback from how previous voltage demands have been reflected in motor performance. Various feedback mechanisms may be provided to adjust the PWM waveforms so that the desired motor performance is achieved. For example, sensors may give information on winding currents, motor position and speed etc. The behaviour of electric motors can be modelled mathematically. This modelling tends to be complex as the variables that affect the behaviour of the system, such as induced voltages, currents and flux linkages, change continuously as the electric circuit is in relative motion. For such complicated analysis, mathematical transformations are often used to decouple variables and refer time-varying quantities to a common frame of reference. A typical motor control system will therefore include components that are capable of performing the required 21 06 24 calculations, such as e.g. processors or dedicated Proportional-Integral (PI) inverter controllers. A typical motor control system may therefore include a combination of relatively simple circuitry with components that are capable of complex control calculations. The combination may also have to meet various physical requirements. For example, the motor control system is often co-located with the motor. This requires the motor control system to be capable of operating in a hostile environment, and to be packaged in as small and flexible a way as possible (because there is typically restricted space around the motor in a vehicle). There is a need for an improved motor control system. According to one embodiment, there is provided a motor control system for a vehicle comprising an inverter driver configured to generate an electrical signal for controlling a motor, an inverter controller configured to generate a command for controlling the inverter driver and a communication interface configured to communicate the command from the inverter controller to the inverter driver, thereby enabling the inverter controller to be spaced apart from the inverter driver in the vehicle. The communication interface may be capable of communicating data between the inverter controller and a component that is not the inverter driver. The command may control the inverter driver to generate a pulse-width modulated signal for controlling the motor. The communication interface may be configured to communicate feedback data from the inverter driver to the inverter controller. The feedback data may comprise data relating to an operation of the motor. The inverter controller and the inverter driver may be configured to exchange data over the communication interface in accordance with a priority system that classifies some data as being of higher priority than other data, and to exchange data in order of its respective priority in the priority system. The priority system may classify data relating to the actuation of the motor as being relatively high priority data. The priority system may classify data from sensors and / or flags as being relatively low priority data. The inverter controller is configured to, during one Pulse Width Modulation Cycle: receive data relating to actuation of the motor from the inverter driver, calculate actuation requirements for a future Pulse Width Modulation cycle in dependence on that data and transmit the actuation requirements to the inverter driver. The inverter driver may be configured to, during a first Pulse Width Modulation cycle, record data relating to the actuation of the motor and to, during a second Pulse Width Modulation cycle, transmit that data to the inverter controller. The inverter controller may be configured to, during the second Pulse Width Modulation cycle, transmit a command to the inverter driver that comprises actuation requirements for a future Pulse Width Modulation Cycle. The inverter driver may be configured to, during a third Pulse Width Modulation cycle, generate an electrical signal for controlling the motor in dependence on the command from the inverter controller. The inverter driver is configured to record low-priority data during the first Pulse Width Modulation cycle, and to transmit the low-priority data to the inverter controller after the data relating to actuation of the motor. The vehicle may comprise a plurality of motors and the motor control system comprises a plurality of inverter drivers, each configured to generate an electrical signal for controlling a respective one of the plurality of motors, and the inverter controller is configured to generate commands for controlling each of the plurality of inverter drivers. The inverter controller may be capable of generating the commands, in dependence on data received from the plurality of inverter drivers, sufficiently quickly for synchronisation of the operation of the plurality of motors not to be required. The communication interface may have sufficient bandwidth for synchronisation of the operation of the plurality of motors not to be required. The inverter controller may be configured to, in response to receiving data relating to actuation of a motor from one of the plurality of inverter drivers during a Pulse Width Modulation Cycle of that inverter driver, transmit actuation requirements for that motor to that inverter driver during the same Pulse Width Modulation Cycle. The communication interface may be capable of supporting multiple communication channels, and the inverter controller is configured to communicate with each of the plurality of inverter drivers over a respective one of those channels. The communication interface may be configured to arrange data to be communicated between inverter controller and inverter driver into a series of data packets. The communication interface may be configured to arrange data to be communicated between inverter controller and inverter driver into one or more frames. The communication interface may be configured to, when neither the inverter driver nor the inverter controller has data to exchange, communicate a continuous stream of bits between the inverter controller and inverter driver. The communication interface may be configured to encrypt data for exchanging over the communication interface. The communication interface may comprise a physical link between the inverter controller and the inverter driver. The physical link may comprise one or more individual links, and the communication interface is configured to exchange duplicate data over those individual links. The inverter driver may be configured to be located near the motor. The inverter controller may be configured to be located remotely from the motor. The inverter controller may be configured to be located in a part of the vehicle that, during operation of the vehicle, experiences a less hostile environment than a part of the vehicle where the motor is located. The inverter controller may be configured to be located in a part of the vehicle that, during operation of the vehicle, experiences a lower ambient temperature than a part of the vehicle where the motor is located. The inverter controller may be configured to be located in a part of the vehicle in which space is less restricted than in a part of the vehicle where the motor is located. The communication interface may be a serial communication link. The communication interface may be a high-speed communication link. According to another embodiment, there is provided a method for controlling a motor in a vehicle comprising an inverter controller generating a command for controlling an inverter driver, a communication interface communicating the command from the inverter controller to the inverter driver, thereby enabling the inverter controller to be spaced apart from the inverter driver in the vehicle and the inverter driver generating an electrical signal for controlling the motor in dependence on the command. According to another embodiment, there is provided a motor control system comprising an inverter driver configured to generate an electrical signal for controlling a motor, an inverter controller configured to generate a command for controlling the inverter driver and a communication interface configured to communicate the command from the inverter controller to the inverter driver, and which is also capable of communicating data between the inverter control and a component that is not the inverter driver. According to another embodiment, there is provided a method for controlling a motor comprising: an inverter controller generating a command for controlling an inverter driver; a communication interface communicating the command from the inverter controller to the inverter driver; the inverter driver generating an electrical signal for controlling the motor in dependence on the command; and the communication interface communicating data between the inverter control and a component that is not the inverter driver. The present invention will now be described by way of example with reference to the accompanying drawings. In the drawings: Figure 1 shows an example of a motor control system; Figures 2a and b show control-feedback paths in a conventional motor control system and a motor control system as described herein; Figure 3 shows an example of a motor control system positioned within a vehicle; Figure 4 shows an example of an inverter controller configured to control multiple motors; Figure 5 shows an example of a method for controlling a motor; Figure 6 shows an example of a method for controlling a motor; Figure 7 shows an example of three Pulse Width Modulated waveforms; Figure 8 shows the timing of a Pulse Width Modulated cycle; and Figure 9 shows an inverter driver and a inverter controller exchanging data during three consecutive Pulse Width Modulated cycles. An example of a motor control system is shown in Figure 1. The motor control system is shown generally at 101. The motor control system comprises an inverter driver 102. The inverter driver is configured to generate an electrical signal for controlling a motor. The inverter driver is connected to a inverter controller 103 via a communication interface 104. The communication interface is configured to carry commands from the inverter controller to the inverter driver. The communication interface may be a boundary across which the inverter driver and the inverter controller can exchange information. The interface could comprise a wired or wireless connection. Suitably it comprises a physical connection between the two components provided by, for example, copper wire or fibre optic cables. The communication interface may be configured to provide serial and / or parallel communications. Data may be encoded for robust transmission compatible with the transmission medium. Data may be encrypted for data security, correctness and efficiency. Suitably the interface is capable of high-speed data communication. The communication interface replaces the direct connection that conventionally links the controller and the driver in an inverter. An example of this is illustrated in Figures 2a and b. Figure 2a shows the conventional arrangement: inverter 201 comprises a local controller 202 that provides driver 203 with direct physical control signals. Figure 2b shows an arrangement in which the local inverter control has been removed to central controller 205. The direct connection has been replaced by communication interface 207, which in this example is a high-speed communication link. Arrows 206 and 208 show the respective control feedback paths in a conventional arrangement (206) and the new arrangement (208). The control-feedback path has been altered to run between the driver, motor and the centralised controller 205, rather than between the driver, motor and a local controller specific to that driver / motor combination. In one aspect the removing the control functionality from the inverter to a separate, dedicated controller may enable the inverter controller to communicate with both the inverter driver and a component that is not the inverter driver. This may save duplicating control functions across multiple controllers and enable more sophisticated control strategies to be enacted across multiple devices. In another aspect, removing the control functionality from the inverter driver 102 may enable the inverter controller to control one or more operations of the inverter driver whilst being spaced apart from the inverter driver in a vehicle. The inverter controller 103 and the inverter driver can be physically separate components of the system and can be placed at a distance from each other. They can be located in different parts of the vehicle, which may place different physical restrictions on them. For example, one part of the vehicle may be subject to greater space restrictions than the other, or a harsher ambient environment during vehicle operation. The vehicle may be anything that is suitable for transporting people or cargo. The vehicle may have wheels, which may be driven by motors, but non-wheeled applications are also envisaged. For example, the vehicle might be a vertical take-off and landing vehicle that uses electric motors (e-VTOL). Inverter driver 102 may be configured to control the speed and / or torque of an electric motor. It may do this by generating a pulse-width modulated (PWM) signal that rapidly switches between two or more different DC voltages. Removing the inverter controller from the inverter driver may allow it to be smaller, lighter and cheaper. The inverter driver can be a relatively “dumb” device comprising drivers, power switches and sensors. Removing the control functions may enable a higher power density, allowing tighter / more flexible packaging of the high voltage inverter driver components. This may make it easier to physically integrate with other vehicle components, such as a motor. The inverter controller may be hosted on a domain inverter controller. During vehicle operation, the part of the vehicle where the motor is located is typically a high temperature, high voltage environment. The inverter controller may be located at a distance from the inverter driver, reducing the functions that are hosted in the “hostile” environment and removing some environmental constraints from the inverter controller design. Figure 3 shows an example of a motor control system within a vehicle. In this example the system comprises a inverter controller 301 and two inverter drivers 302, 303. The communication interface is shown at 314, 315. The vehicle is shown from above and is represented by its wheels (306-309), two axles (310-313) and motors (304, 305). In this example the vehicle has a motor for each axle. Each motor has its own respective inverter driver. Figure 3 shows the physical separation between the inverter controller 301 and the two inverter drivers 302, 303. In Figure 3 these are shown as stand-alone components, but they may also be integrated within the motor or axle. In this example the central inverter controller controls multiple inverter drivers and their respective PWM lines 316, 317 (which convey the PWM actuation signals to the motors 304, 305). The result is a distributed system divided between domain control and local actuation. The “inverter driver” has been split into a gate driver / power module function (in the inverter driver) and motor control (in the inverter controller). A single inverter controller saves duplicating motor control functions. It also provides a single point of control for all motors, enabling motor operation to be coordinated or synchronised. In one example the communication interface between the inverter controller and the inverter driver may comprise more than one physical link. An example is shown in Figure 4. In Figure 4, inverter controller 401 is connected to a plurality of inverter drivers 402, 403 (which could be more than two). The inverter drivers are in turn connected to a respective motor 404, 405. The inverter drivers are connected to the inverter controller via two physical links 406, 407. The inverter controller and the inverter drivers may exchange information over both links. Suitably the same information may be exchanged over both links, with secondary link 407 providing redundancy in case of a failure or malfunction in primary link 406, or in case of data corruption (e.g. due to electromagnetic compatibility (EMC) issues). An overview of a method for controlling a motor in a vehicle is shown in Figure 5. The method comprises the inverter controller generating a command for the inverter driver (step S501), the communication interface carrying the command from the inverter controller to the inverter driver (step S502) and the inverter driver generating an electrical signal for controlling the motor in dependence on the command (step S503). An overview of a method in which the inverter controller communicates with more than just the inverter driver is shown in Figure 6. In step S601 the controller generates a command, which is carried to the inverter driver by the communication interface (step S602). The inverter driver generates an electrical signal for controlling the motor (step S603), and the controller is able to communicate data with another component (step S604). Inverter drivers are typically configured to simulate a low frequency, analogue signal by rapidly switching DC voltages in pulses. Inertial loads like motors react slowly to any changes in an input signal, effectively causing the rapidly switched pulses of a PWM signal to appear as an approximate sine wave. The inverter drivers generate the pulses at defined time intervals. This time interval can be termed the “PWM cycle”. The “duty cycle” is the proportion of time during the PWM cycle that the voltage is high. This is shown in Figure 7, which shows three PWM waveforms. Each waveform has the same PWM cycle, but different duty cycles. Waveform 701 has a 25% duty cycle, waveform 702 has a 50% duty cycle and waveform 703 has a 75% duty cycle. The duration of each PWM cycle in a vehicle would typically be a multiple of the motor fundamental frequency. The duration of each PWM cycle may be variable to achieve motor and / or inverter efficiency. For example, typical values might range between 10ps (corresponding to 100kHz operation) and 250 ps (corresponding to 4kHz operation). Figure 8 shows the timed events that may be associated with a PWM cycle of an inverter driver. Here Tperiod represents the PWM cycle (801). U, V and W represent the three electrical signals that are generated for actuating the three windings of the motor. (In some applications the motor may have more than three windings. The number of windings could be 6 or more.) The timing signals control when these electrical signals can respectively go high or low, with a deadtime of tdead separating the “high” and “low” switching times to avoid transistor cross-conduction and shoot-through currents. The inverter driver may comprise sensors for detecting data relating to the actuation of the motor. For example, an ADC may sample the currents generated in the motor windings while a resolver may provide velocity and position feedback. Such sensors may be analogue devices that essentially operate continuously, so the inverter driver may sample them at predetermined time instants. This is illustrated in Figure 8 by sampling instants tADC and tresoiver (805, 806). The communication link between the inverter controller and the inverter driver enables them to exchange data. This data could have a range of different uses, e.g. it could vary from urgent instructions from the inverter controller to sensor data from the inverter driver. For example, the timed events illustrated in Figure 6 may be executed by the inverter driver in response to commands it receives from the inverter controller. The data exchanged over the communication link may vary in importance. The inverter controller and inverter driver may therefore be configured to follow a predetermined priority system that classifies some data as being of higher importance than other data. For example, under such a priority system, data relating to the actuation of the motor may be classified as high priority data. Such data might include, for example, commands from the inverter controller requiring the inverter driver to drive the motor with a particular PWM signal. It may also encompass data from the inverter driver relating to the performance of the motor, e.g. winding currents and / or sensor data regarding the speed or position of the motor. Low priority data might be sensor data relating to less important parts of inverter driver operation or flag data that indicates non-critical faults. Data relating to actuation of the motor is of such importance that the system may be configured to process and respond to it within a predetermined period of time. For example, the inverter controller may be configured to receive motor actuation data from an inverter driver, process it and send out the appropriate command to the inverter driver to adjust / maintain motor operation within one PWM cycle. If an inverter driver sends actuation data relating to one PWM cycle (cycle 1) to the inverter controller as soon as it is available (which will be during cycle 2), by the end of that cycle (cycle 2) it preferably receives back from the inverter controller instructions for actuating the motor during the next cycle (cycle 3). An example of this is shown in Figure 9. In this example, the inverter driver 901 is generating a PWM signal 903 with a PWM cycle 904. It records actuation data during one cycle 905 and transmits this data to the inverter controller 902 as soon as it is available 906. The inverter controller receives this data 907, calculates new actuation requirements in dependence on it (908) and transmits an actuation command to the inverter driver 909 during one cycle. The inverter driver preferably receives the actuation command 910 in time to implement it for the next cycle 911. Preferably this process is repeated continuously so that, during the second cycle of Figure 9, the inverter driver continues recording actuation data it will transmit to the inverter controller at the start of cycle 3, and so on. Figure 9 shows high-priority actuation data being exchanged between the inverter controller and the inverter driver, but lower priority data may also be exchanged. The lower priority data is suitably transmitted after the high-priority data. The following gives an example of how additional data may be fitted in, to give a complete priority system. During each PWM cycle, information may be exchanged between the inverter controller and the inverter driver in the following order: 1. The inverter driver may finish acquiring its PWM-synchronous measurements from the end of the previous PWM cycle 2. The inverter driver may communicate these high-priority PWM-synchronous measurements to the inverter controller as soon as they are available. These high-priority measurements might include data that relates to the actuation of the motor. This feedback is used to generate commands for controlling the motor. For example: • DC link voltage • 3 x phase currents • Resolver angular position / speed (sin / cos) 3. The inverter controller may then use these high-priority measurements to calculate the actuation requirements for the following PWM cycle. Meanwhile, the inverter driver may communicate some additional low-priority non-synchronous measurements to the inverter controller. These low-priority measurements might include, for example: • Communication link status flags and counts • Gate driver fault status • Phase over-current and over-voltage faults • Power Module fault status • Internal supply voltages • Internal temperatures 4. Once its PWM calculations have completed, the inverter controller may communicate its actuation demands to the inverter driver (for execution during the following PWM cycle). These high-priority demands might include, for example: • PWM period • Timings for each Power Module • ADC sampling time • Resolver sampling time The information exchange set out above is preferably completed within one PWM cycle. Preferably no practical restrictions are placed on the motor control strategies by the separation of the inverter driver and the control functions. The motor control system may be capable of synchronisation operation of the motors but for most implementations where the vehicle has multiple motors (and so multiple inverter drivers) it is preferred that there is no requirement for this to be the case. The communication exchanges described above and illustrated in Figure 7 are preferably completed for each inverter driver, in every one of its respective PWM cycles, regardless of the phasing between the inverter drivers. The communication link preferably has sufficient bandwidth to enable inverter controller to communicate with all inverter drivers in a timely manner so that the “single PWM cycle” requirement can be maintained for all inverter drivers. Likewise, the inverter controller preferably has the processing capacity to be able to calculate the actuation requirements for each inverter driver during the appropriate PWM cycle. The communication interface suitably comprises the physical link between the inverter controller and the inverter driver(s) and also an appropriate receiver / transmitter circuitry within the inverter controller and inverter driver(s). The physical link between the inverter controller and the inverter driver(s) suitably provides a high-speed connection. Preferably it offers sufficient bandwidth, and integrity, to permit high precision motor control. It should also support multi-channel operation. The receiver / transmitter circuitry suitably provides the inverter controller and inverter driver(s) with the functionality to physically exchange data over the physical link. The inverter controller and the inverter driver(s) may exchange data packets. For example, each packet might contain any of the following: • a payload (e.g. an instruction or simply data to be exchanged); • an identifier associated with the payload (e.g. sensor data, instruction etc); • a priority level; or • an identifier associated with a particular inverter driver. The communication interface may organise the data packets into a frame structure for transmission. Multi-channel operation may be provided by time-division multiplexing. For example, each frame may be divided into a plurality of time slots, with each time slot representing one logical channel. The inverter drivers may be assigned a particular time slot by the inverter controller, or they may be configured to “listen” to every packet but only act on those containing their particular identifier. Every frame is suitably duplicated across the primary and secondary links. The communication interface may encrypt the data frames. For example, encryption may be achieved using a CRC polynomial. This polynomial is optimum for achieving a Hamming distance of 3 over a wide variety of payload sizes. Preferably this enables a Bit Error Rate (BER) of no more than 10-10, to meet a target of meeting the highest Automotive Safety Integrity Level (ASIL) of D. Between frames, a continuous stream of data symbols may be transmitted, resulting in an alternating pattern of Os and 1s at the physical layer. This type of encoding allows clock data recovery (CDR) in the receivers (at the inverter controller and inverter driver) to acquire and maintain bit synchronisation. Implementing the inverter driver as a distributed system, in which motor control is hosted remotely from the inverter driver may offer several benefits: • It improves isolation between high voltage and low voltage components with the high voltage components being restricted to the inverter driver. • It minimises the number of components located in a hostile environment close to the motor. • It allows centralised control of multiple motors. • It reduces the overall component count in vehicles with multiple motors. • It offers improved packaging options, with the reduced number of inverter driver components able to be more tightly packaged around the motor or axle. • It offers the potential for very fine (< 100ns) level of synchronisation between inverters. This may improve, for example, DC bus ripple by enabling the motors to be run slightly out of phase. In some embodiments, some or all of the procedures described herein may be performed wholly or partly in hardware. In some implementations, the inverter controller (for example) may be implemented by a processor acting under software control. Any such software is preferably stored on a non-transient computer readable medium, such as a memory (RAM, cache, FLASH, ROM, hard disk etc.) or other storage means (USB stick, FLASH, ROM, CD, disk etc). The applicant hereby discloses in isolation each individual feature described herein and any combination of two or more such features, to the extent that such features or combinations are capable of being carried out based on the present specification as a whole in the light of the common general knowledge of a person skilled in the art, irrespective of whether such features or combinations of features solve any problems disclosed herein, and without limitation to the scope of the claims. The applicant indicates that aspects of the present invention may consist of any such individual feature or combination of features. In view of the foregoing description, it will be evident to a person skilled in the art that various modifications may be made within the scope of the invention.

Claims

1. A motor control system for a vehicle comprising:an inverter driver configured to generate an electrical signal for controlling a motor;an inverter controller configured to generate a command for controlling the inverter driver; anda communication interface configured to communicate the command from the inverter controller to the inverter driver, thereby enabling the inverter controller to be spaced apart from the inverter driver in the vehicle;wherein the inverter controller is configured to, during one Pulse Width Modulation Cycle:receive data relating to actuation of the motor from the inverter driver;calculate actuation requirements for a future Pulse Width Modulationcycle in dependence on that data;transmit the actuation requirements to the inverter driver;record low-priority data during the first Pulse Width Modulation cycle;andtransmit the low-priority data to the inverter controller after the data relating to actuation of the motor.

2. A motor control system as claimed in claim 1, wherein the communication interface is capable of communicating data between the inverter controller and a component that is not the inverter driver.

3. A motor control system as claimed in claim 1 or 2, wherein the command controls the inverter driver to generate one or more pulse-width modulated signals for controlling the motor.

4. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to communicate feedback data from the inverter driver to the inverter controller.

5. A motor control system as claimed in any preceding claim, wherein the feedback data comprises data relating to an operation of the motor and / or the inverter driver.

6. A motor control system as claimed in any preceding claim, wherein the inverter controller and the inverter driver are configured to exchange data over the communication interface in accordance with a priority system that classifies some data as being of higher priority than other data, and to exchange data in order of its respective priority in the priority system.

7. A motor control system as claimed in claim 5, wherein the priority system classifies data relating to the actuation of the motor as being relatively high priority data.

8. A motor control system as claimed in claim 5 or 6, wherein the priority system classifies data from sensors and / or flags as being relatively low priority data.

9. A motor control system as claimed in any preceding claim, wherein the inverter driver is configured to, during a first Pulse Width Modulation cycle, record data relating to the actuation of the motor and to, during a second Pulse Width Modulation cycle, transmit that data to the inverter controller.

10. A motor control system as claimed in claim 9, wherein the inverter controller is configured to, during the second Pulse Width Modulation cycle, transmit a command to the inverter driver that comprises actuation requirements for a future Pulse Width Modulation Cycle.

11. A motor control system as claimed in claim 10, wherein the inverter driver is configured to, during a third Pulse Width Modulation cycle, generate an electrical signal for controlling the motor in dependence on the command from the inverter controller.

12. A motor control system as claimed in any preceding claim, wherein the vehicle comprises a plurality of motors and the motor control system comprises aplurality of inverter drivers, each configured to generate one or more electrical signals for controlling a respective one of the plurality of motors, and the inverter controller is configured to generate commands for controlling each of the plurality of inverter drivers.

13. A motor control system as claimed in claim 12, wherein the inverter controller is capable of generating the commands, in dependence on data received from the plurality of inverter drivers, sufficiently quickly for synchronisation of the operation of the plurality of motors not to be required.

14. A motor control system as claimed in claim 12 or, wherein the communication interface has sufficient bandwidth for synchronisation of the operation of the plurality of motors not to be required.

15. A motor control system as claimed in any of claims 12 to 14, wherein the inverter controller is configured to, in response to receiving data relating to actuation of a motor from one of the plurality of inverter drivers during a Pulse Width Modulation Cycle of that inverter driver, transmit actuation requirements for that motor to that inverter driver during the same Pulse Width Modulation Cycle.

16. A motor control system as claimed in any of claims 12 to 14, wherein the communication interface is capable of supporting multiple communication channels, and the inverter controller is configured to communicate with each of the plurality of inverter drivers over one or more of the multiple communication channels that are allocated to that respective inverter driver.

17. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to arrange data to be communicated between inverter controller and inverter driver into a series of data packets.

18. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to arrange data to be communicated between inverter controller and inverter driver into one or more frames.

19. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to, when neither the inverter driver nor the inverter controller has data to exchange, communicate a continuous stream of bits between the inverter controller and inverter driver.

20. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to encrypt data for exchanging over the communication interface.

21. A motor control system as claimed in any preceding claim, wherein the communication interface is configured to encode data for exchanging over the communication interface.

22. A motor control system as claimed in any preceding claim, wherein the communication interface comprises a physical link between the inverter controller and the inverter driver.

23. A motor control system as claimed in any preceding claim, wherein the physical link comprises one or more individual links, and the communication interface is configured to exchange duplicate data over those individual links.

24. A motor control system as claimed in any preceding claim, wherein the communication interface is a serial communication link.

25. A motor control system as claimed in any preceding claim, wherein the communication interface is a parallel communication link.

26. A motor control system as claimed in any preceding claim, wherein the communication interface is a high-speed communication link.

27. A method for controlling a motor in a vehicle comprising:an inverter controller generating a command for controlling an inverter driver;a communication interface communicating the command from the inverter controller to the inverter driver, thereby enabling the inverter controller to be spaced apart from the inverter driver in the vehicle; andthe inverter driver generating an electrical signal for controlling the motor in dependence on the command;wherein the inverter controller, during one Pulse Width ModulationCycle:receives data relating to actuation of the motor from the inverter driver;calculates actuation requirements for a future Pulse Width Modulation cycle in dependence on that data;transmits the actuation requirements to the inverter driver;records low-priority data during the first Pulse Width Modulation cycle;andtransmits the low-priority data to the inverter controller after the data relating to actuation of the motor.

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