JP5952009B2 - Electric power steering device - Google Patents

Description

  According to the present invention, when a vehicle is steered by an operation member such as a steering handle (steering wheel), the power of a motor (electric motor) is transmitted to the steering system (steering system) as a steering assist force (steering assist force), and the operation by the driver is performed. More particularly, the present invention relates to an electric power steering device that reduces torque ripple of the motor.

  Conventionally, in an electric power steering apparatus, a three-phase brushless motor (hereinafter also simply referred to as a motor) has been adopted as the motor, and when driving this three-phase brushless motor, three phases of U phase, V phase, and W phase are used. Among the phase coils, the current of the two-phase coil is detected, and the current of the remaining one-phase coil is calculated by calculation (Patent Document 1).

  As a sensor for detecting the current of the coil, a sensor using a Hall effect (Hall sensor) or the like is used as schematically shown in FIG.

  In the Hall sensor 2, a coil (conductive wire) 4 is passed through a partially cut ring-shaped magnetic core 3. The Hall element 5 to which the control current is passed is arranged and fixed at the cutting portion. The magnetic flux (magnetic field) at the cut portion of the magnetic core 3 that changes in accordance with the change in the current (detection current) I flowing through the coil 4 to be detected is caused to be sensed by the magnetosensitive surface of the Hall element 5, By amplifying the voltage generated according to the strength of the magnetic field by the amplifier 6, the Hall sensor 2 can detect the output voltage V corresponding to the detection current I, and eventually the detection current I.

Japanese Patent No. 3849979 (FIG. 2, [0034])

  By the way, the motor in the electric power steering apparatus is set with a target current (referred to as target current It) based on the steering torque of the driver, and current feedback control is performed so that the detected current I becomes equal to the target current It. Is done.

  However, even if current feedback control is performed so that the detected current I becomes equal to the target current It, torque ripple is generated in the motor, and noise and noise are generated in the electric power steering device due to the torque ripple. In addition, there may be a problem that the steering feeling deteriorates.

  The present invention has been made in consideration of such problems, and by investigating the cause of torque ripple in the motor and reducing the torque ripple, the generation of the abnormal noise and noise is suppressed. And it aims at providing the electric power steering device which makes it possible to eliminate the malfunction which the said steering feeling deteriorates.

An electric power steering apparatus according to the present invention sets a target torque supplied to a three-phase motor based on a steering torque detector that detects a steering torque of a driver and the steering torque detected by the steering torque detector. A target current setting unit; first and second current detection units (for example, U-phase and V-phase current sensors 56 and 57 in the embodiment) that detect two- phase currents of the motor ; and the target current setting unit. An electric power steering apparatus comprising: a target current set by the first and second detected currents detected by the first and second current detecting units; and a motor driving unit that drives the motor based on the first and second detected currents. And it has the following characteristics (1)-( 4 ).

(1) The first and second detection currents include first and second actual currents actually flowing in the two phases (for example, the actual current Iu indicated by the solid line in FIG. 4A as the first actual current, 2, the first and second phase delay amounts (for example, the first phase delay amount is θd1 in FIG. 4A and the second phase delay amount is a graph). ΘA2) of 5A is included, and the first and second detected currents detected by the first and second current detectors are reduced so that a difference between the first and second phase delay amounts is reduced . or further comprising a detection current phase correction unit that corrects a phase of the second detection current, the motor drive unit, said target current set by the target electric current setting unit, a first corrected by the detected current phase correction unit And the second correction detection current. And features.

According to this invention, the motor driving unit detects the target current set by the target current setting unit and the first and second detections detected by the first and second current detection units by the detection current phase correction unit. The motor is driven based on the first and second corrected detection currents in which the phase of the first or second detection current is corrected so that the difference between the first and second phase delay amounts of the current is reduced . Therefore, it is possible to reduce the torque ripple of the motor that occurs due to the phase lag amount (difference) between the first and second current detection units included in the first and second detection currents. The reason why torque ripple occurs due to the phase lag amount (difference) will be described later.

In this case , the corrected detection currents of the remaining phases can be calculated (estimated) from the first and second correction detection currents obtained by correcting the different phase delay amounts of the first and second detection currents of the two phases.

( 2 ) In the invention having the above feature (1 ) , the detected current phase correcting unit has a small phase lag among the first and second detected currents detected by the first and second current detecting units. The correction is performed to increase the phase delay amount of the detection current.

According to the present invention, since to carry out the correction of increasing the phase delay of the current detect phase delay is less, the high-frequency component of the same time to reduce the torque ripple, the in detected current phase delay is small noise Can be attenuated.

( 3 ) In the invention having the above feature (1 ) , the detected current phase correcting unit has a large phase lag among the first and second detected currents detected by the first and second current detecting units. The correction is performed to reduce the phase delay amount of the detection current.

According to the present invention, since to perform correction to reduce the phase delay of the current detect phase lag has the size, of the first and second current detection unit, generating a large current detector of the phase lag As a result, the torque ripple can be reduced, and at the same time, the first and second corrected detection currents can follow the target current more quickly.

( 4 ) In the invention having any one of the above features (1) to ( 3 ), the motor further includes a motor rotation direction detection unit that detects the rotation direction of the motor, and the detected current phase correction unit includes the motor rotation direction. Based on the rotation direction of the motor detected by the detector, the phase delay amount of at least one of the first and second detected currents detected by the first and second current detectors. The correction amount is determined.

According to this invention, at least one of the first and second detection currents detected by the first and second current detection units based on the rotation direction of the motor detected by the motor rotation direction detection unit. since so as to determine a correction amount of the phase delay of detection current, it is possible to determine a correction amount in accordance with the phase delay of the detection current which changes according to the switching of the rotating direction of the motor.

According to this invention, the motor drive unit has the target current set by the target current setting unit and the first and second phases of the first and second detection currents detected by the first and second current detection units. Since the motor is driven based on the first and second corrected detection currents, in which the phase of the first or second detection current is corrected by the detection current phase correction unit so that the difference in the delay amount is reduced , It is possible to reduce torque ripple of the motor that occurs due to the phase lag amount (difference) between the first and second current detection units included in the first and second detection currents.

  By reducing the torque ripple, noise and noise generated in the electric power steering apparatus can be suppressed, and deterioration of the steering feeling can be prevented to obtain a light steering feeling.

  In addition, the detection current (correction detection current) of the remaining phase can be calculated (estimated) from the correction detection current obtained by correcting the phase lag amount in which each of the detection currents of at least two phases in the three-phase motor current is corrected.

It is a lineblock diagram of the electric power steering device concerning one embodiment of this invention. It is a block diagram of a motor control system provided with a control apparatus and a motor drive control apparatus in the electric power steering apparatus of the example of FIG. It is a block diagram of the detection electric current phase correction | amendment part which concerns on the principal part of this embodiment. FIG. 4A is a waveform diagram showing a U-phase actual current and a U-phase detection current. FIG. 4B is a Lissajous waveform diagram based on the U-phase actual current and the U-phase detection current. FIG. 5A is a waveform diagram showing a V-phase actual current and a V-phase detection current. FIG. 5B is a Lissajous waveform diagram based on the V-phase actual current and the V-phase detection current. It is a wave form diagram which shows a torque ripple etc. when the detection current of the two-phase current sensor from which a phase delay amount differs is not correct | amended by the detection current phase correction | amendment part. It is explanatory drawing which shows the comparison table for comparing and explaining each quantity by the presence or absence of phase correction including an fc setting table. FIG. 8A is a waveform diagram obtained as a result of performing phase correction so that the phase lag amount of the detected current is the same as that of the U phase with respect to the V-phase actual current. FIG. 8B is a Lissajous waveform diagram based on the actual current and the corrected detection current of FIG. 8A. It is a wave form diagram which shows a torque ripple etc. at the time of correct | amending the detection current of the two-phase current sensor from which a phase delay amount differs with a detection current phase correction | amendment part. It is a wave form diagram which shows the example of calculation of a phase current and a motor torque when there is no current phase error. It is a wave form diagram which shows the example of calculation of a phase current and motor torque when there exists a current phase error. It is a block diagram of the detection electric current phase correction | amendment part which concerns on another Example. It is a circuit diagram which shows the example of a current sensor.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a configuration diagram of an electric power steering apparatus 10 according to an embodiment of the present invention.

  An electric power steering device 10 mounted on a vehicle (not shown) is configured to give a torque (auxiliary torque) for assisting a steering torque given by a driver to a steering shaft 14 connected to a steering handle 12. Is done.

  An upper end of the steering shaft 14 is connected to the steering handle 12, and a pinion 16 is attached to the lower end. A rack shaft 20 provided with a rack 18 that meshes with the pinion 16 is disposed. A rack and pinion mechanism 22 is formed by the pinion 16 and the rack 18. Tie rods 24 are provided at both ends of the rack shaft 20, and front wheels (steered wheels) 26 are attached to the outer ends of the tie rods 24.

  A motor (brushless motor) 30 is provided for the steering shaft 14 via a power transmission mechanism 28 that is a speed reduction mechanism. The motor 30 outputs a rotational force for assisting the steering torque. This rotational force is increased as the auxiliary torque via the power transmission mechanism 28 and is given to the steering shaft 14.

  A steering torque sensor 32 is also provided on the steering shaft 14. The steering torque sensor 32 detects the magnitude and direction of the steering torque applied to the steering shaft 14 when the steering torque generated by the driver operating the steering handle 12 is applied to the steering shaft 14, and the detected steering torque is detected. The steering torque Ts, which is an electrical signal corresponding to the magnitude of, and the direction are output. The steering torque sensor 32 is configured using, for example, a torsion bar.

  The steering shaft 14 further detects a steering angle by the rotation of the steering shaft 14, that is, a steering angle including a steering direction, and outputs a steering angle θs that is an electric signal corresponding to the detected steering angle. Is provided.

  A vehicle equipped with the electric power steering device 10 is provided with a vehicle speed sensor 36 that detects and outputs a vehicle speed Vs that is an electric signal corresponding to the traveling speed of the vehicle.

  Furthermore, the electric power steering device 10 includes a motor drive control device 42 including a control device 40. The above-described steering torque sensor 32, rudder angle sensor 34, vehicle speed sensor 36, motor 30, and rotation angle sensor 38 to be described later are electrically connected to a motor drive control device 42 including the control device 40.

  FIG. 2 is a configuration diagram of a motor control system 50 including a motor drive control device 42 including a control device (motor control device) 40 that controls the drive of the motor 30 of the electric power steering device 10 shown in FIG.

  The control device 40 is an ECU (Electronic Control Unit), and the ECU includes a CPU, a ROM, a RAM, a microcomputer having an input / output interface such as an A / D converter and a D / A converter, a timer, and the like. The CPU of the microcomputer operates as various functional units (various functional means) by executing programs stored in the ROM based on various inputs.

  The motor 30 is driven and controlled by the motor drive control device 42 by vector control based on the dq-axis current component.

  The motor 30 detects a rotation angle of the rotor of the motor 30, and detects and outputs a rotor rotation angle, which is an electric signal, that is, a state quantity related to the rotation angle of the magnetic pole of the rotor from a predetermined reference rotation position. The rotation angle sensor 38 is provided.

  An RD (resolver / digital) converter 46 in the control device 40 outputs the rotor rotation angle θm of the motor 30 and the rotation speed of the motor 30 from the output of the rotation angle sensor 38 (also referred to as motor rotation speed, motor rotation speed, or rotation speed). Nm is output as a digital signal. Since the rotational speed Nm is positive or negative, the rotational speed Nm substantially includes the rotational direction Dm of the motor 30. The rotation direction Dm is either the clockwise direction CW (Clockwise) or the counterclockwise direction CCW (Counterclockwise).

  The motor drive control device 42 includes a steering torque Ts from the steering torque sensor 32, a steering angle θs from the steering angle sensor 34, a vehicle speed Vs from the vehicle speed sensor 36, and a motor rotation angle (from the RD converter 46). Motor current Im {U, V, W, three-phase phase current (U-phase current: also referred to as U-phase actual current) Iu, phase current (V-phase) Current: also referred to as V-phase actual current) Iv, phase current (W-phase current: also referred to as W-phase actual current) Iw} voltage (phase voltages) Vu, Vv, and Vw for outputting to motor 30 To do.

  In this case, the electric power steering device 10 converts the electric power supplied from the battery 60 based on the PWM signals of the U, V, and W phases from the PWM conversion unit 52 constituting the control device 40 into, for example, an FET full bridge configuration. By driving the motor 30 by performing power conversion (direct current → three-phase alternating current conversion) by the inverter 54, and performing vector control by energizing each winding of the motor 30 with sine wave phase currents Iu, Iv, Iw, Generate auxiliary torque. As described above, the auxiliary torque of the motor 30 assists the driver's operation of the steering handle 12.

  Of the three-phase actual currents Iu, Iv, and Iw that constitute the motor current Im (Iu, Iv, Iw) that actually flows through the motor 30, the magnitude and direction of flow of the U-phase actual current Iu and the V-phase actual current Iv are the motor current. Sensors (hereinafter referred to as current sensors) 56 and 57 respectively detect the currents Iu ′ and Iv ′ as electrical signals, and supply them to the detected current phase correction unit 62.

The detection current phase correction unit 62 corrects the phase delay amount of the U-phase detection current Iu ′ and the V-phase detection current Iv ′ detected by the current sensors 56 and 57, and corrects the U-phase correction detection currents Iu ^* and V The phase correction detection current Iv ^* is fed back to the dq converter 58.

Calculation unit 59, the correction detection current ^Iu *, Iv ^* from W-phase corrected detected current Iw ^* calculated by the following equation (1) (estimate), the correction detection current Iw ^* current feedback output to the dq conversion section 58 To do.
Iw ^* = − Iu ^* −Iv ^* (1)

The dq conversion unit 58 performs dq conversion from the corrected detection current (phase current) Iu ^* , Iv ^* , Iw ^* .

  The dq coordinate in the vector control is, for example, in the motor 30 having a two-pole rotor, the magnetic flux direction of the field pole by the permanent magnet is defined as the d axis (field axis), and the direction orthogonal to the d axis is the q axis (torque axis). ), Which rotates in synchronization with the rotor of the motor 30.

  The control device 40 gives a current phase with reference to the q axis, and as a current command for an AC signal supplied from the inverter 54 to each phase of the motor 30, the d axis current id and q axis that are DC signals are used. A current iq is applied.

  The control device 40 controls the motor 30 according to the command torque Tmcom by vector control described in a two-phase rotating magnetic field coordinate system (dq coordinate system). That is, the steering torque Ts applied to the steering handle 12 is detected by the steering torque sensor 32, and the motor 30 is vector-controlled so that the assist torque corresponding to the detected steering torque Ts is obtained, thereby assisting manual steering. .

  Basically, the basic operations of the control device 40 and the motor drive control device 42 that are configured and operate as described above will be described below in relation to the electric power steering device 10 while explaining more detailed configurations.

  First, in the command torque calculation unit 67, the control device 40 detects the steering torque Ts detected and output by the steering torque sensor 32, the steering angular velocity dθs / dt calculated from the steering angle θs detected and output by the steering angle sensor 34, The command torque Tmcom is obtained based on the vehicle speed Vs detected by the vehicle speed sensor 36 and output. From the command torque Tmcom, the target current It of the motor current Im is set in the target current setting unit 68 and is output to the q-axis target current setting unit 70.

  The q-axis target current setting unit 70 sets a q-axis current command value iqcom that is a torque current command value based on the target current It. On the other hand, the d-axis target current setting unit 72 sets the d-axis current command value idcom, which is a field weakening current command value, to a reference value (here, 0 value).

On the other hand, the three-phase correction detection currents Iu ^* , Iv ^* , Iw ^{* of} the motor 30 detected by the current sensors 56, 57 and corrected by the detection current phase correction unit 62 are based on the rotor rotation angle θm, and the dq conversion unit 58. Is converted into a d-axis current and a q-axis current, and a d-axis actual current value idr and a q-axis actual current value iqr are obtained.

  The subtracting unit 84 calculates a deviation Δiq between the q-axis current command value iqcom and the q-axis actual current value iqr subjected to current feedback.

  The adder 86 adds the d-axis current Id (<0) set by the d-axis current setting unit 61, which is a field weakening current setting unit, to the d-axis current command value idcom (= 0), thereby adding the d-axis. The current target value idt (<0) is calculated.

  The subtraction unit 88 calculates a deviation Δid between the d-axis current target value idt and the d-axis actual current value idr that has been current-feedbacked.

  The PI calculation units 80 and 82 execute a P (Proportional) control process and an I (Integral) control process on the d-axis current deviation Δid and the q-axis current deviation Δiq, and the d-axis current deviation Δid and q A d-axis command voltage Vdcom and a q-axis command voltage Vqcom that attempt to bring the shaft current deviation Δiq close to 0 are calculated and output to the dq inverse conversion unit 90.

  The dq inverse transformation unit 90 performs dq inverse transformation on the d-axis command voltage Vdcom and the q-axis command voltage Vqcom on the dq coordinate by using the rotor angle θm, and the Uq on the three-phase AC coordinate that is the stationary coordinate. The phase AC command voltage Vu, the V phase AC command voltage Vv, and the W phase AC command voltage Vw are converted.

  The PWM conversion unit 52 switches each phase AC command voltage Vu, Vv, Vw to a switching command (that is, a pulse width modulation signal) composed of pulses for driving each switching element of the inverter 54 on / off by pulse width modulation (PWM). ). Note that the duty of each pulse is stored in the PWM converter 52 in advance.

  The inverter 54 is driven by each pulse width modulation signal, and the corresponding phase currents Iu, Iv, Iw are supplied to the respective windings of the stator of the motor 30, so that a rotating magnetic field is generated and the rotor (rotor) of the motor 30 is generated. ) Rotates.

  The field weakening current Id (negative value) set by the d-axis current setting unit 61 is, as is well known (for example, Patent Document 1), a region where the q-axis command voltage Vqcom is large, and the q-axis actual current value iqr is It is set to flow independently in a small region and a region where the motor rotational speed Nm is large, and field weakening is performed. For example, the motor rotational speed Nm is controlled to increase in the low torque region of the motor 30. The

  Next, the configuration and operation (torque ripple reduction operation) of the detected current phase correction unit 62 according to the main part of the present invention will be described.

  FIG. 3 is a configuration diagram of the detection current phase correction unit 62 according to this embodiment. The detection current phase correction unit 62 includes a U-phase detection current phase correction unit (also simply referred to as a U-phase phase correction unit) 62u formed of a U-phase correction low-pass filter (LPF) having a cutoff frequency fcu, and a cutoff frequency. A V-phase detection current phase correction unit (simply referred to as a V-phase phase correction unit) 62v composed of a low-pass filter (LPF) for V-phase phase correction having fcv, and the cut-off frequencies fcu and fcv from the RD converter 46. Phase correction amounts set in the low-pass filters of the U-phase phase correction unit 62u and the V-phase phase correction unit 62v with reference to a cutoff frequency setting table (fc setting table) 63 based on the rotation direction Dm of the supplied motor 30 And a setting unit 64.

  An analog signal detection current Iu ′ detected by the current sensor 56 is converted into a digital signal detection current Iu ′ by an A / D converter (not shown) and supplied to the input port of the U-phase correction unit 62u.

  The analog signal detection current Iv ′ detected by the current sensor 57 is converted into a digital signal detection current Iv ′ by an A / D converter (not shown) and supplied to the input port of the V-phase correction unit 62v.

The corrected detection currents Iu ^* and Iv ^* after correction corrected by the U-phase correction unit 62u and the V-phase correction unit 62v are output from the output ports of the U-phase correction unit 62u and the V-phase correction unit 62v. The data is supplied to the dq converter 58 and the calculator 59.

  Here, the current sensor 56 for detecting the U-phase detection current Iu ′ from the U-phase actual current Iu and the current sensor 57 for detecting the V-phase detection current Iv ′ from the V-phase actual current Iu are shown in FIG. The hall sensor 2 having the configuration is used.

[Explanation of Torque Ripple Generation Reason and Torque Ripple Reduction Technique]
First, the reason why torque ripple occurs will be described.

  The detected currents Iu ′ and Iv ′ of the current sensors 56 and 57 using the Hall sensor 2 include U-phase actual current Iu and V-phase actual current Iv flowing in the U-phase coil and the V-phase coil of the motor 30, respectively. On the other hand, it has been found that a phase delay is included, and the phase delay amount may be different between the U-phase and V-phase current sensors 56 and 57.

  FIG. 4A shows a waveform diagram in which the U-phase detection current Iu ′ detected by the current sensor 56 is delayed by the phase delay amount θd1 with respect to the U-phase actual current Iu each of which is a sine wave. Shows the Lissajous waveform measurement result in the range of ± 4 [A] of the U-phase actual current Iu and the U-phase detection current Iu ′ having a maximum value of about 66 [A].

  FIG. 5A shows a waveform diagram in which the V-phase detection current Iv ′ detected by the current sensor 57 is delayed by the phase delay amount θd2 with respect to the V-phase actual current Iv, each of which is a sine wave. Indicates a Lissajous waveform measurement result in a range of ± 4 [A] of the sine wave V-phase actual current Iv and the V-phase detection current Iv ′ having a maximum value of about 66 [A].

  Here, the detected currents Iu ′ and Iv ′ are detected by relatively inexpensive current sensors 56 and 57 using the hall sensor 2 built in the motor drive control device 42, and the actual currents Iu and Iv are illustrated. An external current sensor that does not flow, for example, a high-accuracy, wide-band, high-current current probe, particularly a current sensor whose phase delay amount is negligibly small compared to the phase delay amounts θd1 and θd2, flows to the output line from the inverter 54 The actual currents Iu and Iv are detected in the vicinity of the entrance 30u and 30v of the motor 30 (see FIG. 2). By connecting these detected waveforms to the external measuring device with the U-phase actual current Iu as the X-axis and the U-phase detected current Iu ′ as the Y-axis, the U-phase actual current Iu is displayed on the display of the external measuring device. And a Lissajous waveform measurement result (FIG. 4B) of the U-phase detection current Iu ′. Similarly, the V waveform actual current Iv as the X axis and the V phase detection current Iv ′ as the Y axis are connected to the external measurement device, and the V phase actual current is displayed on the display of the external measurement device. Lissajous waveform measurement results (FIG. 5B) of the current Iv and the V-phase detection current Iv ′ are obtained.

  From the Lissajous waveform measurement results of the U-phase actual current Iu and the U-phase detection current Iu ′ in FIG. 4B, the phase delay amount θd1 of the U-phase current sensor 56 is equivalent to approximately 2 [A] in terms of current, and the V-phase in FIG. From the Lissajous waveform measurement results of the actual current Iv and the V-phase detection current Iv ′, it was found that the phase delay amount θd2 of the V-phase current sensor 57 is equivalent to approximately 0.5 [A] in terms of current.

In this case, the phase delay amount θd1 [deg] of the U phase is calculated by the following equation (2), and the phase delay amount θd2 [deg] of the V phase is calculated by the following equation (3).
arcsin (2/132) ≈0.9 [deg] (2)
arcsin (0.5 / 132) ≈0.2 [deg] (3)

  6 shows the waveform of the torque ripple Tma when the detection current phase correction unit 62 does not correct the detection current Iu ′ and the detection current Iv ′ of the two-phase current sensors 56 and 57 having different phase delay amounts θd1 and θd2. Show.

  In the torque ripple Tma, the magnitude (amplitude, peak-to-peak value) of the second-order component torque ripple Tma2 [Nm] having an electric angle θ [deg] and a frequency twice the detection currents Iu ′ and Iv ′. 0.07 [Nm] exists, and the torque ripple Tma2 of this secondary component is a cause of vibration and noise generated in the electric power steering apparatus 10, and is a main cause of deterioration of steering feeling. I found out.

  The torque ripple Tma waveform of FIG. 6 includes a sixth-order component in addition to the second-order component, but the sixth-order component has a relatively small amplitude and a high frequency. This is not the main cause of deterioration of steering feeling.

  In this case, the difference between the phase lag amount θd1 and the phase lag amount θd2 is the current in the U phase and the V phase depending on the layout (arrangement position) of the current sensors 56 and 57 arranged in the motor drive control device 42 which is an ECU. It has also been found that the sensor 56 and 57 are caused by different influences of the external magnetic field. However, since it is necessary to arrange the current sensors 56 and 57 in a limited space in the motor drive control device 42, it is possible to arrange the current sensors 56 and 57 so as not to be affected by the external magnetic field. Difficult in terms of cost and mountability. The external magnetic field is an external magnetic field mainly generated from the inverter 54 which is a drive circuit of the motor 30. When the rotation direction Dm of the motor 30 is reversed, the phase delay amount θd1 of the current sensors 57 and 58 and the phase delay are obtained. It was also found that the quantity θd2 was reversed.

  The above explanation is an explanation of the reason for the occurrence of torque ripple.

  Next, a method for reducing torque ripple will be described.

  Basically, it is understood that the secondary torque ripple Tma2 can be reduced if the phase lag amount θd1 and the phase lag amount θd2 generated in the current sensors 57 and 58 are set to the same value.

  In this embodiment, the phase delay amount [deg] of the low-pass filter is used in order to manipulate the phase delay amount. Therefore, the cutoff frequency fc of the fc setting table 63 stored in the phase correction amount setting unit 64 is also exchanged according to the rotation direction Dm.

  FIG. 7 is a comparison table 65 including the fc setting table 63 for comparing and explaining each amount depending on the presence or absence of phase correction.

  In the fc setting table 63, when the rotation direction Dm of the motor 30 is the clockwise direction CW, the low-pass filter of the U-phase correction unit 62u (in this embodiment, as an example, a first-order low-pass filter) is set. The U-phase cutoff frequency fcu is set to 1900 [Hz], and the V-phase cutoff frequency fcv is set to 1700 [Hz]. With this setting, a phase delay amount corresponding to about 1.5 [A] is given to the V-phase detection current Iv ′ by fcv = 1700 [Hz] with respect to the torque ripple Tma2 of the second order component at the electrical angle θ. Therefore, when fcu = 1900 [Hz], the U-phase detection current Iu ′ hardly gives the phase delay amount.

  The frequency of the secondary torque ripple Tma2 is about 100 to 400 [Hz], the current frequency is about 50 to 200 [Hz], which is half that, and the phase error correction amount is 0.2 to 0.7 [Hz]. deg].

  In addition, since any of the detection currents Iu ′ and Iv ′ is low pass filtered, high frequency noise can be removed.

Therefore, the phase difference between the U-phase correction detection current Iu ^* and the V-phase correction detection current Iv ^* , which is the detection current after phase correction, is equivalent to 0 [A], and the correction detection current Iu ^* and the correction detection current Iv By calculating (estimating) the corrected detection current Iw ^* of the W phase by the following equation (1) using the calculation unit 59 using ^* , the corrected detection current Iu ^* , the correction detection current Iv ^*, and the correction detection current Each Iw ^* has a phase difference of exactly 120 [deg].
Iw ^* = − Iu ^* −Iv ^* (1)

  FIG. 8A shows that the phase delay amount θd2 (see FIG. 5B) of the detected current Iv ′ with respect to the V-phase actual current Iv is the same as the U-phase in order to reduce the secondary torque ripple Tma2 at the electrical angle θ. A waveform is shown as a result of performing phase correction by the V-phase correction unit 62v so as to be the delay amount θd1. If phase correction is performed in this way, as shown in FIG. 8B, the phase delay amount θd2 is converted into current from the Lissajous waveform measurement results of the corrected V-phase currents Iv (actual current) and Iv ′ (corrected detection current). It can be seen that this is equivalent to 2 [A], and the phase delay amount θd1 (2 [A] in terms of current) equivalent to that of the U phase is found.

  FIG. 9 shows a waveform of the torque ripple Tmb after the detection current Iu ′ and the detection current Iv ′ of the two-phase current sensors 56 and 57 having different phase delay amounts θd1 and θd2 are corrected by the detection current phase correction unit 62. Yes.

In the torque ripple Tmb, the magnitude (amplitude, peak-to-peak value) of the second-order component torque ripple Tma2 [Nm] having an electrical angle θ [deg] and a frequency twice the correction detection currents Iu ^* and Iv ^*. However, it is reduced to approximately 0.04 [Nm]. By reducing the torque ripple Tma (FIG. 6) to the torque ripple Tmb (FIG. 9), vibrations and abnormal noises generated in the electric power steering apparatus 10 can be suppressed, and a light steering feeling can be realized.

  The above explanation is an explanation of a method for reducing torque ripple.

[Theoretical study of secondary torque ripple in electrical angle caused by current phase error]
In this theoretical examination section, for convenience of understanding, the above-mentioned symbols such as Iu and Iu ′ are used in duplicate. Therefore, the symbols used in this theoretical study section may have different meanings outside this section.

  First, the torque ripple when there is no phase error in the phase current will be described.

In this theoretical examination, the currents of the three phases are Iu, Iv, and Iw, and the rotating magnetic flux is Bu, Bv, and Bw, and are shown in the following equations (4) to (9). However, in the formulas (4) to (9), I represents the current amplitude, B represents the magnetic flux amplitude, and θ represents the motor electrical angle.
Iu = Isin θ (4)
Iv = Isin (θ + 120 °) (5)
Iw = Isin (θ−120 °) (6)
Bu = Bsin θ (7)
Bv = Bsin (θ + 120 °) (8)
Bw = Bsin (θ−120 °) (9)

At this time, the motor torque Tm can be expressed by the following equation (10). K is a proportionality constant.
Tm = K (Iu · Bu + Iv · Bv + Iw · Bw)
= (3/2) KIB (10)

  Therefore, a constant motor torque Tm can be obtained without depending on the electrical angle θ.

  FIG. 10 shows a calculation example of phase currents Iu, Iv, Iw and motor torque Tm when I = 66 [A] and KIB = (4/3) [Nm] as an example. From FIG. 10, when the current phase difference error Δθ is 0 [deg], the motor torque Tm is constant as Tm = (3/2) × (4/3) = 2 [Nm], and the torque ripple It turns out that does not occur.

  Next, torque ripple when the phase current has a phase error will be described.

When there is a phase error in the phase current, the currents (detection currents) detected by the current sensors 56 and 57 are Iu ′, Iv ′, and Iw ′. However, the W-phase detection current Iw ′ is calculated from the U-phase detection current Iu ′ and the V-phase detection current Iv ′. Since the rotating magnetic flux is not related to the phase error of the current sensor, the equations of the magnetic fluxes Bu, Bv, Bw can be used as they are. These are shown in the following formulas (11) to (16). However, in the equations (11) to (16), I is the current amplitude, B is the magnetic flux amplitude, θ is the motor electrical angle, and Δθ is the phase error that occurs in the detected current Iu ′.
Iu ′ = Isin (θ + Δθ) (11)
Iv ′ = Isin (θ + 120) (12)
Iw ′ = − Iu′−Iv ′ (13)
Bu = Bsin θ (14)
Bv = Bsin (θ + 120) (15)
Bw = Bsin (θ−120) (16)

At this time, the motor torque Tm ′ can be expressed by the following equation (17). K is a proportionality constant.
Tm ′ = K (Iu ′ · Bu + Iv ′ · Bv + Iw ′ · Bw) (17)

  As an example, FIG. 11 shows phase currents Iu ′, Iv ′, Iw ′, and motor torque Tm when I = 66 [A], KIB = (4/3) [Nm], and Δθ = 1 [deg]. A calculation example of ′ is shown. FIG. 11 shows that when the current phase difference error Δθ is not 0 [deg], a secondary torque ripple is generated in the motor torque Tm ′ with respect to the electrical angle θ.

  This secondary torque ripple is reduced or suppressed as in the above-described embodiment.

  The above explanation is a theoretical examination of the second order torque ripple caused by the current phase error.

[Summary of Embodiment]
According to the embodiment described above, in the electric power steering apparatus 10 that drives and controls the three-phase motor 30 according to the steering torque Ts by the driver's operation of the steering handle 12, the steering torque detection unit that detects the steering torque Ts. As a steering torque sensor 32, a target current setting unit 68 for setting a target current It to be supplied to the motor 30 based on the steering torque Ts detected by the steering torque sensor 32, currents Iu of at least two phases of the motor 30, Based on current sensors 56 and 57 as current detection units for detecting Iv, target current It set by target current setting unit 68, and detection currents Iu ′ and Iv ′ detected by current sensors 56 and 57. And an electric power steering apparatus 10 including an inverter 54 as a motor driving unit for driving the motor 30. There are, have the following technical characteristics [1] to [5].

[1] A detection current phase correction unit 62 that corrects the phase delay amounts θd1 and θd2 of the detection currents Iu ′ and Iv ′ detected by the current sensors 56 and 57 is further provided. The inverter 54 includes a target current setting unit. 68 based on the target current It set by 68 and the corrected detected currents Iu ^* and Iv ^{* obtained} by correcting the detected currents Iu ′ and Iv ′ detected by the current sensors 56 and 57 by the detected current phase correcting unit 62. 30 is driven.

In this way, the inverter 54 corrects and detects the target current It set by the target current setting unit 68 and the detected currents Iu ′ and Iv ′ detected by the current sensors 56 and 57 by the detected current phase correcting unit 62. Since the motor 30 is driven based on the currents Iu ^* and Iv ^* , the difference between the phase delay amount θd1 and the phase delay amount θ2 of the current sensors 56 and 57 included in the detection currents Iu ′ and Iv ′. The torque ripple of the motor 30 generated due to the above can be reduced.

In this case, at least two phase detection currents Iu ′ and Iv ′ having different phase lag amounts θd1 and θd2 are corrected from the corrected detection currents Iu ^* and Iv ^{* obtained} by correcting either or one of the detected currents (correction) of the remaining phases. Detection current) can be calculated (estimated) as Iw ^* = − Iu ^* −Iv ^* .

   [2] More specifically, the detected current phase correcting unit 62 corrects so that the difference between the phase delay amounts θd1 and θd2 of the detected currents Iu ′ and Iv ′ of the respective phases detected by the current sensors 56 and 57 is reduced. It is preferable to do. Since the phases of the detection currents Iu ′ and Iv ′ are corrected so as to reduce the difference between the phase delay amounts θd1 and θd2 of the detection currents Iu ′ and Iv ′ of each phase, the torque ripple of the motor 30 can be accurately reduced. Can do.

  [3] It should be noted that the detected current phase correcting unit 62 has a phase delay amount θd2 of the detected current Iv ′ of the phase having a small phase lag among the detected currents Iu ′ and Iv ′ of the respective phases detected by the current sensors 56 and 57. By performing the correction to increase the torque ripple, it is possible to reduce the torque ripple and attenuate the noise of the high frequency component in the detection currents Iu ′ and Iv ′.

  [4] Conversely, the detection current phase correction unit 62, as shown in the detection current phase correction unit 62h according to another embodiment shown in FIG. 12, has a high-pass filter (HPF) for U-phase correction having a cutoff frequency fcuh. V phase detection current phase correction unit (which is also referred to simply as a U phase phase correction unit) 62 uh and a V phase phase correction high-pass filter (HPF) having a cut-off frequency fcvh. (Simply referred to as a V-phase phase correction unit) 62vh and the cutoff frequencies fcuh and fcvh are referred to a cutoff frequency setting table (fc setting table) 63h based on the rotational direction Dm of the motor 30 supplied from the RD converter 46. And a phase correction amount setting unit 64h set for each high-pass filter of the U phase phase correction unit 62uh and the V phase phase correction unit 62vh. It may be.

In this case, among the detected currents Iu ′ and Iv ′ of the phases detected by the current sensors 56 and 57, correction is performed to reduce the phase delay amount θd1 of the detected current Iu ′ of the phase having a large phase lag. Since the detection delay amount generated in the current detectors 56 and 57 can be reduced, as a result, the torque ripple is reduced, and at the same time, the corrected detection currents Iu ^* , Iv ^* and Iw ^* are set to the target current It more quickly. Can be followed.

  Instead of using the low-pass filter and the high-pass filter, the detection current phase correction units 62 and 62h instead of the technical features [4] and [5] described above may use a phase lag compensation filter, a phase lead compensation filter, or A phase lead / lag compensation filter or the like can also be used.

  What is necessary is just to select suitably the order of various filters, the kind of filter, a cutoff frequency, etc. according to the difference of the phase delay amount of the current sensors 56 and 57 which generate | occur | produce based on the performance and layout of the current sensors 56 and 57.

  [5] The detected current phase correction units 62 and 62h are detected by the current sensors 56 and 57 based on the rotation direction Dm (CW, CCW) of the motor 30 detected by the RD converter 46 as the motor rotation direction detection unit. Since the phase lag correction amount of at least one phase of the detected currents Iu ′ and Iv ′ of each phase is determined, the rotation direction Dm (CW, CCW) of the motor 30 is switched. A correction amount corresponding to the phase delay amounts θd1 and θd2 of the detection currents Iu ′ and Iv ′ that change accordingly can be determined.

  The present invention is not limited to the above-described embodiment. For example, current sensors are provided in each of the U phase, the V phase, and the W phase so that the phase correction amounts are aligned so as to approach each other. Various configurations can be adopted on the basis of the description.

DESCRIPTION OF SYMBOLS 2 ... Hall sensor 5 ... Hall element 10 ... Electric power steering device 12 ... Steering handle 30 ... Motor 32 ... Steering torque sensor 34 ... Steering angle sensor 38 ... Rotation angle sensor 40 ... Control device 42 ... Motor drive control device 46 ... RD Converter 50 ... Motor control system 56, 57 ... Motor current sensor (current sensor)
62, 62h ... detected current phase correction unit 62u, 62uh ... U phase phase correction unit 62v, 62vh ... V phase phase correction unit 63, 63h ... fc setting table 64, 64h ... phase correction amount setting unit 65 ... comparison table 68 ... target Current setting section

Claims (4)

A steering torque detector for detecting the steering torque of the driver;
A target current setting unit that sets a target current to be supplied to a three-phase motor based on the steering torque detected by the steering torque detection unit;
First and second current detectors for detecting two- phase currents of the motor , respectively;
A motor drive unit that drives the motor based on the target current set by the target current setting unit and the first and second detection currents detected by the first and second current detection units;
An electric power steering apparatus comprising:
The first and second detection currents include first and second phase delay amounts with respect to the first and second actual currents actually flowing in the two phases, respectively.
The first and second detection currents include first and second phase delays that are phase delay amounts of the first and second actual currents flowing in the two phases with respect to the first and second actual phases. Amount is included,
The phase of the first or second detection current is corrected so that the difference between the first and second phase delay amounts of the first and second detection currents detected by the first and second current detection units is reduced. A detection current phase correction unit;
The motor drive unit is
The electric power steering device characterized in that the motor is driven based on the target current set by the target current setting unit and the first and second corrected detected currents corrected by the detected current phase correcting unit. . The electric power steering apparatus according to claim 1 ,
The detected current phase correction unit is
An electric power steering apparatus characterized by performing correction to increase a phase lag amount of a detected current having a small phase lag among the first and second detected currents detected by the first and second current detectors. The electric power steering apparatus according to claim 1 ,
The detected current phase correction unit is
An electric power steering apparatus, wherein correction is performed to reduce a phase lag amount of a detected current having a large phase lag among the first and second detected currents detected by the first and second current detectors. The electric power steering apparatus according to any one of claims 1 to 3 ,
A motor rotation direction detector for detecting the rotation direction of the motor;
The detected current phase correction unit is
Based on the rotation direction of the motor detected by the motor rotation direction detection unit, the at least one detection current of the first and second detection currents detected by the first and second current detection units. An electric power steering apparatus characterized by determining a correction amount of a phase delay amount.

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