WO2011051729A2

WO2011051729A2 - Variable rotation speed motor control system and the method thereof

Info

Publication number: WO2011051729A2
Application number: PCT/GB2010/051826
Authority: WO
Inventors: Bin-Yen Ma
Original assignee: Ultra Motor Limited
Priority date: 2009-10-30
Filing date: 2010-11-01
Publication date: 2011-05-05
Also published as: WO2011051729A3

Abstract

An electric motor control system for an electric vehicle, comprising: a control module for receiving a throttle signal and one or more phase signals indicative of a phase angle of an electric motor, and for outputting a boost signal, a pulse width modulated (PWM) motor control signal and a phase advance signal; a DC/DC converter module arranged to receive the boost signal from the control module and to selectively increase a voltage of a motor power supply in response thereto; and a motor driver module arranged to receive the motor power supply and the phase advance signal and to output driving current to a plurality of windings of the electric motor; wherein the control module is arranged to determine a duty cycle of the PWN motor control signal, to selectively control the boost signal and phase advance signal for controlling an operating speed and torque of the motor according to the throttle signal and phase signals.

Description

VARIABLE ROTATION SPEED MOTOR CONTROL SYSTEM AND THE METHOD

THEREOF

FIELD OF THE INVENTION

[0001] The present invention relates to a variable rotation speed motor control system and the method thereof. The present invention is particularly suitable for applications where it is difficult to acquire high power supply voltage, such as electric vehicles.

BACKGROUND OF THE INVENTION

[0002] Currently, DC brushed and brushless electric motors are widely used in the propulsion systems of electric vehicles due to the ease in which torque and rotation speed are controlled. In the case of brushless motors, the electrical supply to the motor is typically a three-phase modulated supply. The output torque of the motor is proportional to the input current to the stator windings, but the maximum rotation speed of the motor is limited by the power supply voltage. However, in electric vehicles using storage batteries as the power supply, the power supply voltage is limited by the number of batteries that can be carried, and which are connected in series.

[0003] Fig. 1 shows a motor controller system in which the maximum motor output torque is determined by the motor windings, the magnetic circuit, and the driving current. Similarly, the maximum rotation speed is limited by the design of the motor 1 and the voltage of the battery 2, in which the fundamental torque output feature thereof can be shown as Fig. 2.

[0004] The motor control system of Fig. 1 shows a motor 1 , battery 2, pulse width modulation (PWM) control circuit 3, motor phase-current driver 4, rotation-speed/torque control 5, and a phase-current driver circuit 6.

[0005] Fig. 2 shows the output torque of a motor as a function of rotational speed of the motor, when operated at a constant phase-voltage.

[0006] The relationship between the output torque and the motor phase (line) current of a DC motor is:

T ( output torque ) = K_t ( constant of torque ) ^* l_a ( motor phase-current ) .

[0007] The relationship between the speed of rotation of the motor's rotor and the motor phase (supply) voltage is: ω ( rotational speed ) = Κ_ω ( constant of rotational speed ) ^* V_a ( motor phase-voltage ) [0008] Thus, to achieve sufficient torque output, it is necessary to provide sufficient phase- current. Otherwise, to increase the output torque of the motor, it would be necessary to use a mechanical reduction gearing. Although increasing the phase current elevates the output torque, it also increases the energy dissipated in the windings of the motor through to resistive loss (Joule heating), due to the resistance of the windings, which are commonly copper windings. The resistive loss in the windings is as follows:

P_c ( resistive loss ) = l_a ² ( motor phase-current ) x R_p ( winding resistance ) .

[0009] It is noted that the resistive loss is proportional to the square of the motor phase- current, and this heavily influences the efficiency of the motor. Furthermore, the loss may significantly elevate the temperature of the motor, and shorten the lifespan of the motor. Thus, for electric vehicles, a mechanical variable rotation speed system (e.g. variable ratio gear system) is desirable to achieve a wide range of torque and rotation speeds to simultaneously fulfill the demands of high torque and high speed. However, a mechanical variable speed system is costly and would require additional space to house the mechanical variable speed system. Alternatively, achieving higher rotation speed would require more series-connected batteries, in order to increase the supply voltage, and also it would require the pulse width modulation (PWM) control circuit 3 to be able to control the motor phase-current driver 4 to provide the motor windings with sufficiently large phase- current to generate sufficient output torque. The use of more batteries connected in series would require a more complex battery management system of the battery pack. Additionally, under low rotation speed and high current conditions, higher battery voltage would result in additional switching losses.

[0010] Therefore, to satisfy the demands of low-speed/high torque and high speed at the same time, a larger motor or a mechanical variable rotation speed system (e.g. variable ratio mechanical gearing system) would be needed, which may undesirably lead to increased weight and size, and additional costs.

[0011] It can be appreciated that the aforementioned problems limit the performance of electric vehicles. A motor controller able to replace the conventional mechanical variable rotation speed system and to use a lower power supply voltage with smaller size and lower cost would be very desirable in related industries.

[0012] The present invention seeks to address at least some of the aforementioned drawbacks found in conventional motor control systems. SUMMARY OF THE INVENTION

[0013] According to a first aspect of the present invention, there is provided an electric motor control system for an electric vehicle, comprising: a control module for receiving a throttle signal and one or more phase signals indicative of a phase angle of an electric motor, and for outputting a boost signal, a pulse width modulated (PWM) motor control signal and a phase advance signal; a DC/DC converter module arranged to receive the boost signal from the control module and to selectively increase a voltage of a motor power supply in response thereto; and a motor driver module arranged to receive the motor power supply and the phase advance signal and to output driving current to a plurality of windings of the electric motor; wherein the control module is arranged to determine a duty cycle of the PWM motor control signal, to selectively control the boost signal and phase advance signal for controlling an operating speed and torque of the motor according to the throttle signal and phase signals.

[0014] According to a second aspect of the present invention, there is provided a method of controlling an electric motor, comprising: receiving a throttle signal and one or more phase signals indicative of a phase angle of an electric motor; determining a duty cycle of a pulse-width-modulated motor control signal according to the throttle signal; selectively DC/DC converting a motor power supply in order to increase a voltage of the motor power supply such that a rotational speed of the motor increases in response thereto; and selectively advancing a phase angle of a driving current provided to a plurality of windings of the electric motor in response to the phase signals.

[0015] According to a third aspect of the present invention, there is provided an electric vehicle, comprising: an electric motor for driving the electric vehicle; a DC power supply having a power supply voltage; a motor controller arranged to receive a throttle signal and one or more phase signals indicative of a phase angle of an electric motor and to pulse- width-modulate (PWM) a driving current of the motor, wherein the controller comprises: a DC/DC converter module arranged to receive the power supply and to output a motor power supply selectively having a voltage greater than the power supply voltage; a motor driver module arranged to receive the motor supply and to output driving current to a plurality of windings of the electric motor; wherein the motor controller is arranged to determine a duty cycle of the PWM, the operation of the DC/DC converter and to phase advance the driving current of the electric motor to control an operating speed and torque of the motor according to the throttle signal and phase signals.

[0016] The control module may be arranged to selectively cause the DC/DC converter to increase the voltage of the motor power supply greater than a DC power supply voltage to increase a rotation speed of the electric motor.

[0017] The control module may control the boost signal in a stepwise manner to control the rotation speed of the electric motor.

[0018] The control module may be arranged to selectively output the phase advance signal to advance a phase of the driving current to the electric motor to increase the torque of the electric motor.

[0019] The control module may be arranged to output the boost signal and phase advance signal to increase a rotational speed of the electric motor and to increase an output torque of the electric motor at high rotational speeds.

[0020] One or more sensors may be provided for sensing the phase angle of the electric motor. The sensors may be Hall effect sensors.

[0021] The control module may be arranged to receive a motor speed signal indicative of a rotational speed of the motor and to selectively output the phase advance signal at least in part in response thereto.

[0022] The DC/DC converting may be selectively performed to increase the voltage of the motor power supply to greater than a power supply voltage, such that the rotational speed of the electric motor increases.

[0023] The DC/DC converting may increase the voltage of the motor power supply in a stepwise manner to control the rotation speed of the electric motor.

[0024] The phase angle of the driving current to the electric motor may be selectively advanced to increase a torque of the electric motor.

[0025] The DC/DC converting and phase angle advancing may be selectively performed to increase a rotational speed of the electric motor and to increase an output torque of the electric motor at high rotational speeds.

[0026] The method may comprise receiving a motor speed signal indicative of a rotational speed of the motor; and selectively DC/DC converting the motor power supply and advancing the phase angle at least in part in response thereto.

[0027] The motor controller may be arranged to one or more of: selectively cause the DC/DC converter to increase the voltage of the motor power supply to greater than the power supply voltage to increase a rotation speed of the electric motor; and/or advance the phase of the driving current to the electric motor to increase an output torque of the electric motor.

[0028] The DC power supply may be provided from a plurality of cells.

[0029] The motor may be arranged to drive a reduction gear for multiplying an output torque of the electric motor.

[0030] The objective of the present invention is to provide a variable rotation speed motor control system and the method thereof which enables a motor control system with low rotation speed high torque and wide operational range from low rotation speed to high rotation speed. [0031] Another objective of the present invention is to provide a variable rotation speed motor control system and the method thereof that is able to apply lower battery voltage and able to boost an input voltage (without series-connected batteries for the input voltage boost) when the motor speed raises to a sufficient level, as well as to apply the phase-shift technology using phase angle advancing, so as to keep a proper output torque at high rotation speed in response to the entire operating range.

[0032] To achieve the aforementioned objectives, the variable rotation speed motor control system and the method thereof comprises a status control module, a DC/DC boost converter module, a motor phase-current driver module, a motor, a phase-current detection module and a power supply module. The power supply module is configured to provide lower battery voltage and boost an input voltage by the DC/DC boost converter module when the motor rotation speed raises to a sufficient level (by mechanical reduction gear device, it is able to convert low torque-high rotation speed into high torque-low rotation speed; however, the maximum rotation speed would be affected unless a variable rotation speed mechanism is adapted), and also by the status control module which operates to apply the phase-shift technology using phase angle advancing, so as to keep a proper output torque at high rotation speed of the motor power system in the electric vehicle.

[0033] More specifically, as aforementioned, when the motor power system outputs a sufficient torque, it can be still kept within a proper efficiency range. Thus, by applying the DC/DC boost converter, it is able to properly raise the rotation speed to a desired range of operational rotation speed and improve the operational efficiency in the low rotation speed- high torque status, further ensuring sufficient operational rotation speed without a complex mechanical variable rotation speed system.

[0034] More specifically, the output voltage of the DC/DC boost converter module is adapted to be adjusted in accordance with target rotation speeds. Therefore, in the low rotation speed-high torque status, the system can operate under a lower voltage. In reference to the conventional technologies directly applying high voltage (i.e. more series- connected batteries) and operating under low rotation speed-high torque, the system of the present invention bears less switching loss and lower electrical stress. Meanwhile, the present invention is advantageous because by not continuously activating the DC/DC boost converter module, the system suffers fewer losses in the DC/DC boost converter module. When the motor rotation speed rises, the phase-current accordingly decreases and the motor control system operates under high voltage-low current conditions.

[0035] More specifically, the input voltage required by the motor phase-current driver module (i.e., the output voltage of the DC/DC boost converter module) may be affected by the motor characteristic parameters, rotation speed, temperature or even the magnitude of the intended output torque. In calculation, if all such factors need to be considered, it may increase operation loads in the control unit; suppose software operations, hardware reaction speed and even traffic factors interact with each other, then the issue of system instability may arise. Besides, due to manufacturing cost constraints, electric vehicles usually are not able to employ a powerful microcomputer or single chip to perform related complicated operations. Consequently, regarding the rotation speed of motor, when it is necessary to operate in an operational condition of higher rotation speed than originally required, the present invention needs only use the DC/DC boost converter module to increase the voltage of the power supply module and appropriately set the rotation speed magnetic hysteresis range upon accelerating or decelerating, based on a way that the switching voltage command rotation speed set-point in accelerating is higher than the switching voltage command rotation speed set-point in decelerating, so as to directly acquire the target value of the drive power voltage for the motor phase-current driver module; consequently, the present invention needs not to take other factors into account, but instead, by using a simple control method, it is possible to realize the aforementioned performance improvement with reduced cost.

[0036] More specifically, if it is intended that a further greater power output should be provided when a DC brushless motor operates in a range of higher rotation speed, then, in addition to the aforementioned application of the DC/DC boost converter module to increase the input voltage to the motor phase-current driver module, it is also possible to conjunctively apply the phase-shift technology of phase angle advancing such that, when the motor is kept above a certain rotation speed, a software program can be utilized to cause the motor to actively advance the drive for the next phase windings of the motor before the signal of the phase-shift point position sensor is generated, thereby achieving the effect of weak magnetic control and thus further extending about 30% of the motor operational rotation speed range.

[0037] More specifically, although the sensor-less phase-shift technology is employed by the present invention for achieving the feature of phase shift advancing, since such a function operates only within the high rotation speed range, greater rotational kinetic energy has been accumulated in the motor system at this moment, so no significant transient rotation speed variation may occur. Consequently, in comparison with activation at zero rotation speed or the application of sensor-less phase-shift technology throughout the entire process, the reliability can be significantly elevated.

[0038] The present invention may provide a variable rotation speed motor control system, comprising: a status control module, being connected to a DC/DC boost converter module, a motor phase-current driver module, a motor, and a phase-current detection module, in which the status control module is configured to effect PWM control, phase-shift control, and boost control, and when the motor rotation speed raises, the DC/DC boost converter module is configured to boost an input voltage to keep a proper torque output in high rotation speed; the DC/DC boost converter module, being connected to the status control module, the motor phase-current driver module, and the power supply module, and being configured to boost the input voltage provided by the power supply module to a target voltage required by the status control module, and then transfer the voltage to the motor phase-current driver module; the motor phase-current driver module, being connected to the status control module, the DC/DC boost converter module, and the motor, and being configured to receive the voltage provided by the DC/DC boost converter module and then output a driving current to the motor; the motor, being connected to the status control module, the motor phase-current driver module, and the phase-current detection module, in which the motor is configured to transmit phase and velocity signals to the status control module for controlling the status of motor; the phase-current detection module, being connected to the status control module, the motor, and the power supply module, and being configured to detect the driving current through the motor and feed a signal back to the status control module; the power supply module, being connected to the DC/DC boost converter module and the phase-current detection module, and being configured to provide a DC input voltage to the DC/DC boost converter module.

[0039] The status control module may be connected to a control command receiver for receiving the command of a motor rotation speed or a motor torque.

[0040] The status control module may comprise a PWM control circuit, a phase-shift control circuit, and a boost control circuit.

[0041] The motor may be selected from groups of a DC brush motor, a DC brushless motor, an AC motor, and a Hub motor.

[0042] The motor may be externally connected to a mechanical deceleration device for raising the output torque.

[0043] The power supply module may be a power supply apparatus being configured to provide a DC voltage.

[0044] The Hub motor may be configured to decelerate and increase the torque via an internal deceleration gear device, as well as when the Hub motor is configured to achieve the similar functions by increasing windings of the motor without the additional mechanical reduction gear device.

[0045] The present invention may provide a variable rotation speed motor controlling method, comprising the operation steps of: (1 ) designing a motor with a fixed value power voltage, a fixed value maximum torque, and a fixed value maximum rotation speed; (2) increasing the output torque by N times and decreasing the maximum rotation speed to 1/N times by an external N:1 mechanical reduction gear device; and (3) increasing the power voltage by N times by a DC/DC boost converter module to increase the motor rotation speed by N times for compensating the maximum output rotation speed.

[0046] The output of the DC/DC boost converter module may be adapted to adjust according to a target rotation speed, thereby, it is able to operate in lower operation voltage during low rotation speed and high torque.

[0047] The variable rotation speed motor controlling method may comprise the step of, considering a fixed power control mode, decreasing a phase-current when the rotation speed increases to operation the control system in a high voltage and low current operation condition.

[0048] The present invention may provide a variable rotation speed motor control system applicable for controlling and driving the motor actions of an electric vehicle, comprising: a status control module, which receives the rotation speed or rotation torque control command from outside, the phase and speed signals sent by the motor and the detection signal fed back from the motor phase-current detection module, determines the openness and phase-shift sequence of PWM based on the command or detection signal, and then outputs the control signal to a DC/DC boost converter module and the motor phase-current driver module such that the DC/DC boost converter module increases the output voltage according to the request or the motor phase-current driver module is enabled to achieve the function of phase-shift advancing based on the demand; a power supply module, which is a power supply apparatus allowing to provide DC voltage; a DC/DC boost converter module, in which, after the status control module determines the output voltage of the boost circuit based on the motor rotation speed, the DC/DC boost converter module increases the voltage input by the power supply module to the output voltage requested by the status control module and provides it to the motor phase-current driver module as the drive power source; a motor phase-current driver module, which receives the voltage provided by the DC/DC boost converter module and outputs the driving current to the motor windings inside the motor, and also receives the control signal input by the status control module; and a phase-current detection module, which detects the driving current flowing through the motor and transfers the signal back to the status control module.

[0049] The status control module may comprise a PWM control circuit, a phase-shift control circuit and a boost control circuit.

[0050] The power supply module may be a battery set.

[0051] The present invention may provide a variable rotation speed motor controlling method, comprising the following operation steps: (1 ) designing a motor with a power voltage of fixed value, a maximum torque of fixed value and a maximum rotation speed of fixed value; (2) increasing the output torque by N times and decreasing the maximum rotation speed to 1/N times by an external N:1 mechanical reduction gear device; (3) with regards to the rotation speed of the motor, increasing the voltage of the power supply module by using the DC/DC boost converter module where operations under an operational condition of higher rotation speed than the original rotation speed are required, and setting rotation speed magnetic hysteresis range upon accelerating or decelerating, thereby completing the setting for the drive power voltage in a way that the switching voltage command rotation speed set-point in accelerating is higher than the switching voltage command rotation speed set-point in decelerating; (4) in case it is intended to increase the motor rotation speed by N times, it is possible to raise the power voltage by N times with the DC/DC boost converter module so as to compensate the maximum output rotation speed.

[0052] The voltage output by the DC/DC boost converter module may be adjusted based on the target rotation speed, thereby operating at a lower operational voltage in a condition of low rotation speed high torque.

[0053] Considering a control mode of fixed power, as the rotation speed gradually rises, the phase-current may accordingly decrease, thus the motor control system operates in the operational condition of high voltage, low current.

[0054] In the case that it is intended to further accelerate the motor rotation speed to extend the operation range, it may be required to apply the phase-shift technology using phase angle advancing such that the motor actively advances the drive for the next phase windings of the motor before the signal of the phase-shift point position sensor is generated, thereby achieving the effect of weak magnetic control and further increasing the range of motor operational rotation speed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Fig. 1 shows a system architecture diagram of a conventional motor controller;

[0056] Fig. 2 shows a diagram for characteristics of a conventional motor torque output;

[0057] Fig. 3 show a system architecture diagram of a variable rotation speed motor control system and the method thereof according to the present invention;

[0058] Fig. 4 shows a diagram for characteristics of the motor torque output for a variable rotation speed motor control system according to the present invention which applies only the DC/DC boost converter module; and

[0059] Fig. 5 shows a diagram for characteristics of the motor torque output for a variable rotation speed motor control system according to the present invention which simultaneously applies both the DC/DC boost converter module as well as the feature of phase-shift advancing. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] Fig. 3 illustrates an electric motor arrangement comprising: an electric motor 11 , a power supply battery 12, a throttle 15, a detection module 16, and an. The electric motor control system 18 comprises a control module 13, a motor driver module 14, and a DC/DC boost converter module 17.

[0061] The a motor 1 1 , is internally configured with motor windings and has sensors (e.g. Hall sensors) that permit the detection of the phase and rotational speed of the rotor in the motor 1 1 and produce phase and rotational speed signals. The motor 1 1 may be one of a DC brushed motor, a DC brushless motor, and an AC motor.

[0062] The throttle 15 controls the rotation speed or output torque of the motor 11 , by providing a throttle signal to the control module 13. For example, the throttle may be a user operated control that is mounted on the handlebars of an electric bicycle that is driven by the electric motor invention illustrated in Fig. 3.

[0063] The control module 13 receives the throttle signal for governing the rotation speed or rotation torque of the motor 11 from the throttle 15. The control module 13 also receives the phase signals and rotational speed signals sent by the motor 1 1 , as well as the detection signal fed back from the motor phase-current detection module 16. The control module 13 determines the duty cycle and phase-shift sequence of the pulse width modulation (PWM) based on the throttle signal and/or the detection signal. The control module 13 also sends a boost control signal to the DC/DC boost converter module 17 to govern the amount by which the DC/DC boost converter module 17 increases the output voltage. Also the control module 13 sends a phase angle advance signal to the motor phase-current driver module 14 to govern the amount by which the motor driver module 14 advances (phase shifts) the phase angle of the its output.

[0064] The power supply module 12 is a battery (plurality of cells).

[0065] The DC/DC boost converter module 17, comprises a voltage step-up converter, receives an input voltage from the power supply module 12, and provides a boosted output voltage in accordance with the received boost signal from the control module 13. The level by which the input voltage is boosted to the output voltage is in correspondence with the boost signal. The level of voltage boost instructed by the boost signal is in correspondence with the motor rotation speed.

[0066] The motor phase-current driver module 14, which receives the voltage provided by the DC/DC boost converter module 17, outputs the driving current to the motor windings inside the motor 1 1. The driver module 14 comprises a multi-phase inverter circuit, and the driving current to the motor 11 is a multi-phase modulated driving current, e.g. producing a three-phase modulated driving current, which drives three phase-separated groups of motor windings within the motor 11 . The drive current drives the rotation of the motor 11 at the desired rotational speed. Accordingly, by use of at least the throttle signal from the throttle 15 the control module 13 provides a variable speed drive to the motor 11.

[0067] Additionally, the control module 13 governs the phase angle advance function of the motor driver module 14. When the phase angle advance function of the motor driver module 14 is enabled, the phases of the driving phase-currents to the motor 11 are phase- shifted forward. This phase-shifting has the effect of driving each of the motor windings ahead of when it would otherwise be driven, with respect to the rotational position of the rotor within the motor 11 . This has the effect of increasing the motor output torque, for the same driving phase-current. This phase angle advance of the driving phase-currents is particularly advantageous at high rotational speeds of the motor.

[0068] The phase-current detection module 16, which detects the driving current of the motor 11 and provides a detected signal back to the control module 13.

[0069] The control module 13 is internally configured with: (1 ) a PWM (Pulse Width Modulation) control circuit; (2) a phase-shift control circuit; and (3) a boost control circuit, the details of which are described as follows:

[0070] (1 ) The PWM control circuit determines the pulse width modulation applied to the driving currents, in order to control the output torque of motor 11 , since the output torque of the motor is directly proportional to the current input into the motor windings. A switching circuit within the boost converter 17 is provided within the circuit between the power supply module 12 and the motor 11 , and switches the current flowing into the motor windings, correspondingly controlling the motor output torque. The phase-current detection module 16 is configured to detect the motor phase-current and is used in a feedback loop by the control module 13 to determine the duty cycle of the pulse width modulation of the driving phase-currents, as applied by the switching circuit within the boost converter 17, to the motor 11 , in order to control the motor output torque.

[0071] (2) In operating a DC brushless motor, the phase angle of the rotor position relative to the motor windings is important, and is detected by sensors within the motor to enable the correct phase of the driving phase-currents to be applied to the motor. Conventionally the relative phase between the rotational position of the rotor in the motor and the phase with which the motor windings are driven is chosen to provide high efficiency of conversion from the electrical energy to the mechanical energy provided by to the driven system (e.g. propulsion of an electric bicycle). However, when enhanced torque is required, this can be provided by phase-shifting the driving phase-current forward, in order to advance the phase of the currents in the windings of the motor relative to the position of the rotor. The phase-shift control circuit of the control module 13 also determines the rotational speed of the rotor in the motor 11 from the input signal receive from sensors in the motor. [0072] (3) The boost control circuit is configured to determine the drive power voltage of the DC/DC boost converter module in correspondence with the rotation speed of the motor. Below a lower rotational speed threshold level the DC/DC boost converter is not used, in order to avoid unnecessary electrical losses, and the motor is controlled by choice of the PWM duty cycle. Above the lower rotational speed threshold, the boost converter is used, with the boost voltage being a generally linearly stepped increasing function of the rotational speed. The boost voltage is set according to a first linearly stepped function of the rotational speed during periods of increasing rotational speed, as is shown in Fig. 4 by the solid stepped line. However, during periods of decreasing rotational speed, the boost function is set according to a second linearly stepped function of the rotational speed as is also shown in Fig. 4 by the dashed stepped line. The first and second linearly stepped functions correspond, except that the second linearly stepped function is offset from the first linearly stepped function toward lower rotational speeds of the motor. This offset introduces an operational hysteresis into the boost control circuit, by which there is a region of constant boost voltage to provide stable maintenance of the motor (e.g. latched), to suppress any tendency of positive feedback in the feedback loop and to provide a tolerance range to variations in measurement of the rotational speed, e.g. due to mechanical vibrations affecting the signal produced by the motor phase sensors. Accordingly, the rotational speed at which the driving voltage provided by the boost converter switches to a particular boost voltage will be higher in the case of a decreasing rotational speed than in the case of an increasing rotational speed. The linearly stepped boost voltages in Fig. 4 are illustrated schematically, and in practice a larger number of boost voltage switching points may be used. The rotational speed trigger values and their corresponding boost voltage values are conveniently stored in a look-up table within the control module 13. The boost voltage increases with increasing rotational speed up to an upper rotational speed threshold.

[0073] (4) In the case of a DC brushless motor operating in at a high rotational speed range, the driving current may be forward phase-shifted. The phase-shift is such that the phase angle is advanced by a proportion of the period of the phase-current. For example, once the when the motor is operating at the maximum boost voltage, the output torque may be increased by advancing the phase of the driving phase-currents to the windings of the motor. The phase angle advance increases monotonically (e.g. linearly) with increasing rotational speed above the upper rotational speed threshold. Accordingly, Fig. 5 illustrates the increased range of the output torque as a function of rotational speed, when the phase angle advance is employed above the upper rotational speed threshold. The rotational speed and corresponding phase angles by which the driver-currents are forwards phase-shifted are conveniently stored in a further look-up table within the control module 13.

[0074] An example of the variable rotation speed electric motor control system according to the present invention is now described.

[0075] An electric vehicle (e.g. electric bicycle) has an arrangement of one or more batteries having a 48 V output voltage. Conventionally a 600 rpm motor would be required that is capable of a maximum output torque 120 Nm. However, with the variable rotation speed electric motor control system of the present invention, a lower torque motor can be used, that has a maximum output torque of 40 Nm and a maximum rotation speed of 600 rpm.

[0076] A power-train is formed in which a mechanical reduction gear device (deceleration gears) with a 3:1 ratio is coupled to the motor, and multiplies the output torque 3 times to 120 Nm, but at the cost of reducing the maximum rotation speed of the output from the power-train to 200 rpm. However, by boosting the battery supply voltage with the DC/DC voltage boost module, and by forward shifting the phase angle of the driving phase-current to the motor, it is achieve a maximum rotational speed from the power-train of 600 rpm

[0077] Operation of the boost voltage function is described in a period of acceleration and subsequent deceleration of the electric vehicle powered by the electric motor: Once the rotational speed of the motor reaches a lower threshold value (accelerating) of 500 rpm, the drive power voltage output from the DC/DC boost converter module is increased by 8 V, from 48 V (when the boost converter is not operated, and accordingly the voltage corresponds with the battery voltage) to 56 V. As acceleration continues to 600 rpm, this triggers boosting of the voltage by an additional 8 V, thus becoming 64V. This is repeated during the period of acceleration until a final voltage boost is triggered when the rotation speed of the motor reaches 1100 rpm, at which the output drive power voltage of the DC/DC converter module reaches 96 V, enabling the rotational speed of the electric motor to rise to 1200 rpm. When the motor rotational speed decelerates to 1050 rpm, this triggers a reduction in the output drive power voltage by 8 V, from 96 V to 88 V. This is repeated until the rotational speed of the motor reaches a lower rotational speed threshold level (decelerating) of 450 rpm, where the output drive power voltage of the DC/DC converter module becomes 48 V, and the voltage boosting operation is no longer performed.

[0078] Such an electric motor control scheme, in which the electric motor has a rotational speed of 1200 rpm when driven with a voltage of 96 V, may be used within a power-train having a 3:1 fixed ratio speed reduction gearing, producing a power-train output rotational speed of 400 rpm. In such an arrangement a power-train rotational speed of 600 rpm may be achieved through driving the electric motor at 1800 rpm with a voltage of 144 V. [0079] Operation of the phase angle advance function is described in a period of acceleration and subsequent deceleration: To further increase the rotation speed of the motor above 1800 rpm, the phase-shift technology using phase angle advancing can be applied, such that when the motor accelerates above 1700 rpm, a software program can be utilized to forward phase-shift the driving phase-currents to the motor, for example to advance the drive-phase by 10% of the period of the phase-shift point position sensor in the motor. This phase angle advance changes the magnetic interaction between the rotor and motor windings to increase the output torque. Similarly, such a drive approach of phase-shift advancing can be cancelled as the rotation speed of the motor decelerates below 1600 rpm.

[0080] Accordingly, by the method of the present invention a 48 V motor with 40 Nm output torque and 600 rpm original maximum rotation speed provide a power-train having an output of 120 Nm and 600 rpm rotation speed without requiring the addition of further batteries to increase the voltage of the power supply module. In particular, an N:1 deceleration ratio (provided by a mechanical reduction gear device) is applied to the motor in order to increase the output torque of the power-train, and the DC/DC boost converter to multiply the power supply voltage N times in order to compensate the desired maximum rotation speed, with additional enhancement of the output torque being provided by phase advancement of the driving phase-currents to the motor.

[0081] Conveniently, the invention is suitable for use with a hub motor that is provided with an internal reduction gear.

[0082] Advantageously the variable rotation speed motor control system and the method thereof of the present invention applies a motor control system with power boost function to increase the rotation speed of the motor power system in an electric vehicle to a desired value.

[0083] Advantageously, the motor control system and the method thereof of the present invention are able to apply a lower battery voltage and boost the input voltage (without the requirement to serially connect additional batteries to increase input voltage) to provide a the same rotation speed and output torque of the motor, in particular by increasing the rotational speed of the motor for which the output torque of the motor is maintained, thereby increasing the operational range of the motor.

[0084] Advantageously, calculation of the target value of input voltage required by the motor phase-current driver module (i.e., the output voltage of the DC/DC booster converter module) in the present invention is determined in accordance with first and second stepped functions of the rotational speed that increases with rotational speed, and are offset with respect to rotational speed to produce a hysteresis-like response in determining the rotational speed. Such an arrangement of switching points that differs between accelerating and decelerating provides that greater operational errors in the DC/DC booster converter module can be tolerated.

[0085] Advantageously, by use of the described phase-shift technology using phase angle advancing, particularly in the higher rotation speed range, the present invention enables a further increase in motor power output, in such higher rotation speed ranges. Compared with the motor power system not applying the present invention, the power output at intermediate/high rotation speed can be greatly elevated without significantly sacrificing the efficiency and torque demonstrated in the range of lower rotation speed. The aforementioned detailed descriptions are for explaining one preferred embodiment of the present invention, and the embodiment is by no means intended to limit the scope of the present invention. All effectively equivalent modifications or alternations made to the embodiment of the present invention without departing from the spirit of the present invention shall be included in the scope of the present invention.

[0086] Throughout the description and claims of this specification, the words "comprise" and "contain" and variations of them mean "including but not limited to", and they are not intended to (and do not) exclude other moieties, additives, components, integers or steps. Throughout the description and claims of this specification, the singular encompasses the plural unless the context otherwise requires. In particular, where the indefinite article is used, the specification is to be understood as contemplating plurality as well as singularity, unless the context requires otherwise.

[0087] Features, integers, characteristics, compounds, chemical moieties or groups described in conjunction with a particular aspect, embodiment or example of the invention are to be understood to be applicable to any other aspect, embodiment or example described herein unless incompatible therewith. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive. The invention is not restricted to the details of any foregoing embodiments. The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

[0088] The reader's attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

Claims

WHAT IS CLAIMED IS:

1 . An electric motor control system for an electric vehicle, comprising:

a control module for receiving a throttle signal and one or more phase signals indicative of a phase angle of an electric motor, and for outputting a boost signal, a pulse width modulated (PWM) motor control signal and a phase advance signal;

a DC/DC converter module arranged to receive the boost signal from the control module and to selectively increase a voltage of a motor power supply in response thereto; and

a motor driver module arranged to receive the motor power supply and the phase advance signal and to output driving current to a plurality of windings of the electric motor; wherein the control module is arranged to determine a duty cycle of the PWM motor control signal, to selectively control the boost signal and phase advance signal for controlling an operating speed and torque of the motor according to the throttle signal and phase signals.

2. The system of claim 1 , wherein the control module is arranged to selectively cause the DC/DC converter to increase the voltage of the motor power supply greater than a DC power supply voltage to increase a rotation speed of the electric motor.

3. The system of claim 2, wherein the control module controls the boost signal in a stepwise manner to control the rotation speed of the electric motor.

4. The system of any preceding claim, wherein the control module is arranged to selectively output the phase advance signal to advance a phase of the driving current to the electric motor to increase the torque of the electric motor.

5. The system of any preceding claim, wherein the control module is arranged to output the boost signal and phase advance signal to increase a rotational speed of the electric motor and to increase an output torque of the electric motor at high rotational speeds.

6. The system of any preceding claim, comprising one or more sensors for sensing the phase angle of the electric motor.

7. The system of claim 6, wherein the sensors are Hall effect sensors.

8. The system of any preceding claim, wherein the control module is arranged to receive a motor speed signal indicative of a rotational speed of the motor and to selectively output the phase advance signal at least in part in response thereto.

9. A method of controlling an electric motor, comprising:

receiving a throttle signal and one or more phase signals indicative of a phase angle of an electric motor;

determining a duty cycle of a pulse-width-modulated motor control signal according to the throttle signal;

selectively DC/DC converting a motor power supply in order to increase a voltage of the motor power supply such that a rotational speed of the motor increases in response thereto; and

selectively advancing a phase angle of a driving current provided to a plurality of windings of the electric motor in response to the phase signals.

10. The method of claim 9, wherein DC/DC converting is selectively performed to increase the voltage of the motor power supply to greater than a power supply voltage, such that the rotational speed of the electric motor increases.

11. The method of claim 10, wherein the DC/DC converting increases the voltage of the motor power supply in a stepwise manner to control the rotation speed of the electric motor.

12. The method of any one of claims 9 to 11 , wherein the phase angle of the driving current to the electric motor is selectively advanced to increase a torque of the electric motor.

13. The method of any one of claims 9 to 12, wherein the DC/DC converting and phase angle advancing are selectively performed to increase a rotational speed of the electric motor and to increase an output torque of the electric motor at high rotational speeds.

14. The method of any one of claims 9 to 13, comprising:

receiving a motor speed signal indicative of a rotational speed of the motor; and selectively DC/DC converting the motor power supply and advancing the phase angle at least in part in response thereto.

15. An electric vehicle, comprising:

an electric motor for driving the electric vehicle;

a DC power supply having a power supply voltage;

a motor controller arranged to receive a throttle signal and one or more phase signals indicative of a phase angle of an electric motor and to pulse-width-modulate (PWM) a driving current of the motor, wherein the controller comprises:

a DC/DC converter module arranged to receive the power supply and to output a motor power supply selectively having a voltage greater than the power supply voltage; a motor driver module arranged to receive the motor supply and to output driving current to a plurality of windings of the electric motor;

wherein the motor controller is arranged to determine a duty cycle of the PWM, the operation of the DC/DC converter and to phase advance the driving current of the electric motor to control an operating speed and torque of the motor according to the throttle signal and phase signals.

16. The vehicle of claim 15, wherein the motor controller is arranged to one or more of: selectively cause the DC/DC converter to increase the voltage of the motor power supply to greater than the power supply voltage to increase a rotation speed of the electric motor; and/or

advance the phase of the driving current to the electric motor to increase an output torque of the electric motor.

17. The vehicle of claim 15 or 16, wherein the DC power supply is provided from a plurality of cells.

18. The vehicle of any one of claims 15 to 17, wherein the motor is arranged to drive a reduction gear for multiplying an output torque of the electric motor.