Motor control

Abstract

The invention relates to an electric machine circuit incorporated into a control system for an electric machine, comprising: a current determination stage arranged for generating a current demand signal in response to a demand torque of the electric machine; a feedback loop comprising a detector stage comprising means for determining one or more operating values from the electric machine and a current controller configured for calculating an error signal using the one or more operating values from the detector stage and the current demand signal from the current determination stage; and a feed-forward path comprising a voltage controller configured for calculating a voltage demand signal from the current demand signal and one or more operating values from the electric machine, the voltage controller comprising a first bandwidth filter, and the current controller configured for combining the error signal and the voltage demand signal to calculate a voltage demand signal from the one or more operating values from the electric machine. A signal for the motor is generated.

Description

Technical Field

[0001] The invention relates to the improvement of a motor control circuit for an electric power steering system, and in particular to the control of a multi-phase brushless motor in the electric power steering system. Background Art

[0002] Control systems for PWM controlled motors typically use current sensors to measure the current through the motor windings or phases. The measured current is then converted to a stationary dq coordinate system and combined with a current demand signal, also in the dq coordinate system, representing the motor demand current, to produce an error signal.

[0003] The demand current in the electric power steering system is generated based on the motor demand torque. The torque demand signal is mainly a measurement of the amount of torque that the motor should apply to the steering wheel to help the driver turn the steering wheel. The error signal represents the difference between the demand current and the actual measured current. The error signal is fed into the controller, which generates a set of voltage demand signals (the voltage demand signals are also usually in the dq coordinate system) to represent the voltage to be applied to the motor to best push the error signal to zero. The dq voltage is then converted into a PWM signal for the motor phase based on the PWM strategy used. Therefore, the controller is used to change the phase voltage in an attempt to continuously minimize the amplitude of the error signal, thereby ensuring that the motor current is as close to the demand current as possible. Therefore, traditional controllers typically utilize a closed-loop current control system.

[0004] Applicants have recognized that these closed loop current control systems are susceptible to noise in the demand signal and in the motor phase current measurements from the sensors. In such systems, the noise will be passed on to the error signal, which, if not checked, will cause the current controller to react because the current controller cannot distinguish between noise and true error changes that it should track. In power steering systems, this can cause unwanted noise and steering wheel vibrations, which are known as "boom".

[0005] Figure 1 A widely known motor control circuit is shown, which is configured to compensate for sensor noise by filtering the error signal of the feedback control loop. By reducing the bandwidth of the current response, the reaction of such a system to changes in torque demand can be reduced. The present invention is intended to improve the problems associated with known motor control systems. Summary of the invention

[0006] A first aspect provides a motor circuit incorporated into a control system for a motor, wherein the motor circuit comprises:

[0007] a current determination stage arranged to generate a current demand signal in response to a demand torque of the motor;

[0008] Feedback loops, including:

[0009] a detector stage including means for determining one or more operating values ​​from the motor; and

[0010] a current controller configured to calculate an error signal using one or more operating values ​​from the detector stage and a current demand signal from the current determination stage; and

[0011] a feed-forward path including a voltage controller configured to calculate a voltage demand signal from the current demand signal and one or more operating values ​​from the motor,

[0012] wherein the voltage controller comprises a first bandwidth filter, and

[0013] The current controller is configured to combine the error signal and the voltage demand signal to generate a signal for the motor.

[0014] The error signal may be an error current signal representing a difference between the current demand signal and the motor operating current measured by a motor sensor.

[0015] The motor control circuit may include one or more motor sensors configured to provide one or more operating values ​​of the motor input to the voltage controller. For example, the motor control circuit may include a first motor sensor operable to measure the operating current of the motor. The motor control circuit may include a second motor sensor operable to measure the speed and / or position of the rotor relative to the stator.

[0016] The voltage controller may further include a steady-state model of the electric machine, the steady-state model being arranged to receive the current demand signal. The steady-state model of the electric machine may be configured to estimate an unfiltered voltage demand signal based on the current demand signal. The unfiltered voltage demand signal may be calculated by the steady-state model to produce a demand torque from the electric machine.

[0017] The voltage controller may be configured to feed an output from the steady-state model (eg, an unfiltered voltage demand) to a first bandwidth filter to form a voltage demand signal. The unfiltered voltage demand signal may be provided to the first bandwidth filter in a dq coordinate system.

[0018] The steady-state model may include a mathematical model of the motor, the mathematical model including characteristic parameters of the motor. The characteristic parameters of the motor may include any one of the following parameters or a combination thereof: resistance; d-axis inductance; and q-axis inductance.

[0019] The voltage controller may further comprise a back-EMF compensation stage arranged to receive operating values ​​from the motor sensor and calculate a back-EMF signal which is fed to the steady state model to compensate for the effects of the induced back-EMF. The operating values ​​received from the motor sensor may comprise a motor speed signal.

[0020] The voltage controller may include a filtered derivative stage arranged to receive at least a portion of the current demand signal. The voltage controller may be configured to feed the output from the filtered derivative stage and the steady state model to a bandwidth filter to form the voltage demand signal. Thus, the bandwidth filter may be configured to generate the voltage demand signal from the output of the filtered derivative stage and the steady state model.

[0021] The current demand signal may be represented in a dq axis coordinate system and formed from a q axis component and a d axis component.The filtered derivative stage may be arranged to receive the q axis component of the current demand signal but not arranged to receive the d axis component of the current demand signal.

[0022] The first bandwidth filter may include a first low pass filter. The first low pass filter may have a cutoff frequency greater than or equal to 460 Hz, 480 Hz, 500 Hz, 550 Hz, or 600 Hz. The first low pass filter may have a cutoff frequency less than 480 Hz, 500 Hz, 550 Hz, or 600 Hz.

[0023] The current controller may include a second bandwidth filter configured to filter one or more operating values ​​from the motor to produce a filtered operating value. The one or more operating values ​​from the motor, which the second bandwidth filter is arranged to filter, may include any one of the following or a combination thereof: vehicle speed; speed of the motor rotor relative to the motor stator; and / or position of the rotor relative to the stator. The current controller may be configured to calculate the error signal using the filtered operating value and the current demand signal.

[0024] The second bandwidth filter may include a second low pass filter. The second low pass filter may have a cutoff frequency less than or equal to 100 Hz, 80 Hz, 60 Hz, 50 Hz, or 40 Hz. The second low pass filter may have a cutoff frequency greater than 40 Hz, 50 Hz, 60 Hz, or 80 Hz.

[0025] The cut-off frequency of the low-pass filter may be defined as the frequency at which the output signal is below 70.7% of the input signal. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings, in which:

[0027] Figure 1 is a block diagram showing a known motor control circuit;

[0028] Figure 2 is a block diagram showing a motor control circuit according to the first aspect of the present disclosure; and

[0029] Figure 3 It is shown Figure 2 A block diagram of a portion of the motor control circuit. DETAILED DESCRIPTION

[0030] Figure 1 A block diagram of a known motor control circuit 1 for a power steering system is shown. The known circuit 1 includes a torque sensor (not shown) that measures the torque in the steering column and feeds the torque to a torque controller. The torque controller (not shown) calculates a torque demand signal 2 that represents the torque to be generated by the motor of the power steering system. The torque demand signal 2 is fed to a current determination stage 3 that is configured to convert the torque demand signal 2 into a current demand signal 4 in a fixed dq coordinate system based on known characteristics of the motor. The current demand signal 4 is fed to a current controller 5 that causes the motor to operate and provide the required torque. The torque is applied to the steering wheel shaft by the motor, making it easier for the driver to turn the steering wheel.

[0031] The known circuit 1 includes two closed-loop paths: a current controller loop 6 and a feedback controller loop 7. The current controller loop 6 includes a current sensor 61 that generates a current response signal 62 representing the actual current flowing in the motor. The current response signal 62 is then converted into a fixed dq coordinate system and fed to a subtractor 64 of the current controller 5 together with the current demand signal 4 to calculate a current error signal 8 representing the difference between the required dq current and the actual measured dq current. The current error signal 8 is then fed to the input of a proportional integral (PI) controller stage 81 (of the current controller 5), which converts the current error signal 8 in the dq coordinate system into a voltage error signal 82 in the dq coordinate system, which is then converted into a three-phase voltage UVW by a dq-UVW converter 83. The PWM converter 84 then converts the three-phase voltage UVW into a PWM voltage signal required for each phase of the motor using the selected SVM modulation technique. Therefore, the current controller loop 6 is configured to minimize the error associated with the current demand signal 4, which ensures that the current in the motor phase matches the demand current 4.

[0032] The feedback controller loop 7 includes a motor sensor 71 configured to provide one or more operating values ​​72 of the motor. For example, the motor sensor 71 can measure the speed and / or position of the rotor relative to the stator. These measurements can generate significant noise, especially if the motor sensor 71 includes a Hall sensor, whose position measurement often includes interference from external magnetic fields.

[0033] In order to minimize the effects of noise from the motor sensor 71, the working value 72 is filtered using a bandwidth filter 73 before being input to the PI controller stage 81 of the current controller 5. The current controller in the electric power steering (EPS) system requires a higher bandwidth to achieve the desired steering performance. The frequency of the bandwidth filter 73 is typically set at around 300-500 Hz to ensure the fast response time required for acceptable steering road feel. Unfortunately, a portion of the spectrum of the noise from the motor sensor 71 falls within the allowed frequency of the bandwidth filter 73, which is required for sufficient responsiveness. Therefore, for the known motor control circuit 1, a portion of the noise from the motor sensor 71 is fed to the current controller 5, which produces irregularities in the voltage signal for each phase of the motor. In a power steering system, this may manifest as unnecessary noise and / or steering wheel vibration (collectively referred to as "rumble"). The claimed invention is intended only to improve the rumble associated with existing motor control circuits.

[0034] Figure 2 A motor control circuit 100 according to a first aspect of the present disclosure is shown. The motor control circuit 100 is incorporated into a control system for a motor 11. The control system for the motor 110 includes a torque sensor (not shown) that measures the torque in the steering column and feeds the torque to a torque controller (not shown) of the control system. The torque controller calculates a torque demand signal 102 that represents the torque to be produced by the motor 110. In this example, the motor 110 is incorporated into a power steering system.

[0035] As in Figure 1 As shown in the previous example, Figure 2 The motor control circuit 100 includes a current determination stage 103 arranged to generate a current demand signal 104 in response to a torque demand of the motor 110 (i.e., in response to a torque demand signal 102). The current determination stage 103 is configured to convert the torque demand signal 102 into a current demand signal 104 in a fixed dq coordinate system based on known characteristics of the motor 110.

[0036] and Figure 1Compared with the previous example shown in , according to the first aspect of the present disclosure, the motor control circuit 100 includes a feedforward path including a voltage controller 140 .

[0037] The voltage controller 140 receives the current demand signal 104 and is configured to calculate a voltage demand signal 141, which represents the voltage to be provided to the motor phase to achieve the required torque of the motor 110. The voltage demand signal 141 (in the dq coordinate system) is then used to generate a three-phase voltage UVW through a dq-UVW converter 143. The PWM converter 144 then converts the three-phase voltage UVW into a PWM voltage signal required for each phase of the motor 110 using the selected SVM modulation technique. In an example where the motor control circuit 100 and the motor 110 form part of a power steering system, the PWM voltage signal causes the motor 110 to operate and provide the required torque to the steering wheel shaft, thereby making it easier for the driver to turn the steering wheel.

[0038] The motor control circuit 100 also includes two feedback loops: a current control loop 106 and a feedback control loop 107. The current control loop 106 includes a current controller 105 and a current sensor 161, which generates a current response signal 162 representing the actual current flowing in the motor 110. The current response signal 162 is then converted into a fixed dq coordinate system and fed into a subtractor 164 of the current controller 105 together with the current demand signal 104 to calculate a current error signal 108, which represents the difference between the demanded dq current and the actual measured dq current. The current error signal 108 is then fed to the input of a proportional-integral (PI) controller stage 181 (of the current controller 105), which converts the current error signal 108 in the dq coordinate system into a voltage error signal 182 in the dq coordinate system.

[0039] The voltage error signal 182 from the controller 105 and the voltage demand signal 141 from the voltage controller 140 are fed to an adder circuit which combines the two signals to provide a modified demand signal 142. Figure 2 As shown, the modified demand signal 142 (in the dq coordinate system) is converted into a three-phase voltage UVW by a dq-UVW converter 143, and finally causes the motor 110 to provide the required torque. Therefore, the motor control circuit 100 resolves the error between the demand response and the actual work value recorded from the motor 110.

[0040] The feedback control loop 107 comprises a detector stage 171 comprising means for determining one or more work values ​​from the motor 110. In this example, the means for determining one or more work values ​​172 from the motor 110 is a motor position sensor 171 arranged to measure the relative speed and position of the rotor and stator of the motor 110. The work values ​​172 measured by the motor position sensor 171 are input into a PI controller stage 181 of the voltage controller 140 and the current controller 105. The voltage controller 140 is configured for calculating the voltage demand signal 141 from the current demand signal 104 and the work value 172 of the motor 110.

[0041] The current controller 105 includes a bandwidth filter 173 that filters the signal representing the work value 172 of the motor 110 before it is input to the PI controller stage 181 of the current controller 105. Therefore, the current controller 105 is able to eliminate any steady-state errors or non-periodic errors associated with time-varying parameters (e.g., due to component expansion with increasing temperature or component wear over time).

[0042] In this example, the bandwidth filter 173 is a low pass filter, specifically a 50 Hz low pass filter. The bandwidth is lower than the noise on the current response signal 162 from the current sensor 161. Therefore, the bandwidth filter 173 does not propagate the noise and thus mitigates the rumble generated from this specific path.

[0043] Figure 3 There is shown a block diagram representing a voltage controller 140 of the motor control circuit 100. As previously mentioned, the voltage controller 140 forms part of a feed-forward path for estimating the voltage demand of the motor.

[0044] like Figure 3 As shown, the voltage controller 140 includes a steady-state model 210 (a mathematical model of the motor) provided with characteristic parameters of the motor, such as: resistance (R) 211; d-axis inductance (Ld) 212; q-axis inductance (Lq) 213; and motor speed 224. The steady-state model 210 is arranged to receive the current demand signal 104 and a signal representing the motor speed 224, and to estimate voltage demands 214a, 214b in the dq reference frame to produce a demand torque in the motor.

[0045] The voltage controller 140 also includes a back-EMF compensation stage 220, which receives operating values ​​from the motor sensor 171, in particular the motor speed signal 172', and calculates a back-EMF signal 223, which is fed to the steady-state model 210 to compensate for the rotor rotation resistance generated by the back-EMF. Since the voltage controller 140 also includes this purpose, the back-EMF compensation stage 220 is provided with a back-EMF constant (Ke) 221 for the motor and a number of pole pairs 122 for the motor.

[0046] The voltage demands 214a, 214b are fed through an output filter 230 to form the voltage demand signal 141. The output filter 230 includes a further bandwidth filter 231, which in this example is a 500 Hz low pass filter. Applicants have appreciated that a bandwidth of around 500 Hz is required to ensure adequate responsiveness to changes in torque demand for acceptable steering feel. Therefore, the use of a high frequency bandwidth filter (e.g., a 500 Hz, 550 Hz, or 600 Hz cutoff frequency) in the output filter 230 can advantageously ensure that the responsiveness of the motor control circuit 100 remains at an acceptable level while filtering out higher frequency noise that may cause rumble.

[0047] Applicants have recognized that rumble is typically only noticeable when the motor is stationary or spinning at low speeds. At these lower motor speeds, the phase current is nearly constant and manifests as rumble and vibration in the steering wheel. In contrast, when the motor is spinning, the phase current is sinusoidal and the noise fades as the current changes. At lower motor speeds, the d-axis current responsiveness does not play a significant role in the overall responsiveness of the motor control circuit 100 and is therefore not considered when ensuring the bandwidth required for the current response.

[0048] The voltage controller 140 includes a filtered derivative stage 240. The filtered derivative stage 240 provides a filtered derivative dynamic term 241 to the output filter 230 based on the q-axis component of the current demand signal 104. The filtered derivative dynamic term 241 can be used to achieve a desired bandwidth for the current response. The filtered derivative stage 240 can be used in a manner similar to, for example, Figure 1 The derivative stage 240 can also advantageously affect the frequency response of the motor control system 100, since large transient demands are often required to overcome the inductance in the motor and thus quickly obtain the required motor current.

[0049] Therefore, by using a feed-forward path including the voltage controller 140 , rumble can be mitigated or eliminated while maintaining the required bandwidth of the current response to allow for acceptable steering feel and dynamic response.

[0050] Reference Figure 2 and Figure 3 The motor control system 100 can be advantageously used in an electric power steering system, wherein the motor 110 applies assist torque to the steering shaft to assist the driver in turning the steering wheel. By improving noise propagation within the motor control system 100, rumble can be reduced, thereby improving steering road feel as perceived by an experienced driver.

Claims

1. A motor circuit incorporated into a control system for a motor, wherein: The motor circuit comprises: a current determination stage arranged to generate a current demand signal in response to a demand torque of the electric machine; A feedback loop, the feedback loop comprising: a detector stage comprising means for determining one or more operating values ​​from the motor; and a current controller configured to calculate an error signal using one or more operating values ​​from the detector stage and a current demand signal from the current determination stage; and a feed-forward path including a voltage controller configured to calculate a voltage demand signal from the current demand signal and one or more operating values ​​from the electric machine, wherein the voltage controller comprises a first bandwidth filter, and The current controller is configured to combine the error signal and the voltage demand signal to generate a signal for the motor.

2. The motor circuit according to claim 1, wherein: The voltage controller further comprises a steady state model of the electric machine, the steady state model being arranged for receiving the current demand signal, wherein the voltage controller is configured for feeding an output from the steady state model to the first bandwidth filter to form the voltage demand signal.

3. The motor circuit according to claim 2, wherein: The steady-state model includes a mathematical model of the motor, the mathematical model includes characteristic parameters of the motor, and the characteristic parameters of the motor include any one or a combination of the following parameters: resistance; d-axis inductance; q-axis inductance; and motor speed.

4. The motor circuit according to claim 2 or claim 3, wherein: The voltage controller further comprises a back-EMF compensation stage arranged to receive an operating value from a motor sensor and to calculate a back-EMF signal, the back-EMF signal being fed to the steady-state model to compensate for the effect of the induced back-EMF, optionally the operating value received from the motor sensor comprising a motor speed signal.

5. The motor circuit according to any one of claims 1 to 4, wherein: The voltage controller further comprises a filtered derivative stage arranged to receive at least a portion of the current demand signal, wherein the voltage controller is configured to feed the output from the filtered derivative stage and the steady-state model to the bandwidth filter to form the voltage demand signal.

6. The motor circuit according to claim 5, wherein: The current demand signal is represented in a dq axis coordinate system and is formed of a q axis component and a d axis component, and the filtered derivative stage is arranged to receive only the q axis component of the current demand signal and not the d axis component of the current demand signal.

7. The motor circuit according to any one of claims 1 to 6, wherein: The first bandwidth filter includes a first low pass filter having a cutoff frequency greater than or equal to 460 Hz, 480 Hz, 500 Hz, 550 Hz or 600 Hz.

8. The motor circuit according to any one of claims 1 to 7, wherein: The current controller comprises a second bandwidth filter arranged to filter the one or more operating values ​​from the motor to produce a filtered operating value, wherein the current controller is configured to calculate the error signal using the filtered operating value and the current demand signal, optionally, the second bandwidth filter is a low pass filter having a cut-off frequency less than or equal to 100 Hz, 80 Hz, 60 Hz, 50 Hz or 40 Hz.

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