JP2009166770A - Electric power steering control device and motor drive controller - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce heat and radio noise generated during switching without changing over a recurrence frequency of a pulse signal, such as a PWM signal, used for switching control. <P>SOLUTION: An electric power steering control device is equipped with a motor drive circuit 24 that switches a current flowing to an electric coil independently provided for each phase of a three-phase brushless motor 12, independently for the phase, and with a controller 59 that generates a primary duty signal for driving the motor drive circuit 24 according to a predetermined drive command, for each phase, wherein a subtracter 61 is provided as a duty shift control unit which gives the same shift amount to primary duty signals Duty_abc for individual phases to generate secondary duty signals Duty_abc' for the individual phases, thereby driving the motor drive circuit 24 based on the secondary duty signals. Shifting a duty for one of the phases to 0% or 100% decreases the number of on/off times within a unit time to suppress heat generation. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electric power steering control device for applying a steering assist force to a steering mechanism of a vehicle such as an automobile using a multiphase AC motor having a plurality of independent electric coils, and a motor applicable to the electric power steering device. The present invention relates to a drive control device, and more particularly to an electric power steering control device and a motor drive control device that reduce heat generation and radio noise of electronic components such as an electric field transistor included in an inverter for driving a multiphase AC motor.

An electric power steering device used for a vehicle such as an automobile is generally configured as shown in FIG. That is, the steering force (steering torque) from the steering person with respect to the steering handle 1 shown in FIG. 9 is transmitted to the steering shaft 2 having the input shaft 2a and the output shaft 2b.
The steering shaft 2 has one end of the input shaft 2 a connected to the steering handle 1 and the other end connected to one end of the output shaft 2 b via the torque sensor 3.

  The steering force transmitted to the output shaft 2 b is transmitted to the lower shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown).

  Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

  An electric power steering device 10 that transmits a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The electric power steering device 10 includes a reduction gear 11 connected to the output shaft 2b, a three-phase brushless motor 12 connected to the reduction gear 11 as an electric motor that generates a steering assist force for the steering system, An electric power steering control device (hereinafter also referred to as a control unit) 20 for controlling the three-phase brushless motor 12 is mainly configured.

  The torque sensor 3 detects a steering torque applied to the steering handle 1 and transmitted to the input shaft 2a, and a torsion angle of a torsion bar (not shown) in which the steering torque is interposed between the input shaft 2a and the output shaft 2b. The displacement is converted into a displacement, and the torsional angular displacement is detected by, for example, a potentiometer.

  In addition, as shown in FIG. 10, the three-phase brushless motor 12 has one end of a U-phase electric coil Lu, a V-phase electric coil Lv, and a W-phase electric coil Lw connected to each other to form a star connection. The other ends of Lv and Lw are connected to the control unit 20, and motor drive currents Iu, Iv and Iw are individually supplied. In addition, the three-phase brushless motor 12 includes a rotor position detection circuit 13 including a resolver, a rotary encoder, and the like that detect the rotational position of the rotor.

  The control unit 20 receives the steering torque T detected by the torque sensor 3 and the vehicle speed detection value Vs detected by the vehicle speed sensor 21 and the rotor rotation angle θ detected by the rotor position detection circuit 13. Further, the motor drive current detection values Iud, Ivd, and the motor drive current detection values Iud, Ivd, which are output from the motor current detection circuit 22 for detecting the motor drive currents Iu, Iv, and Iw supplied to the phase electric coils Lu, Lv and Lw of the three-phase brushless motor Iwd is input.

  The control unit 20 calculates a steering assist target current value based on the steering torque T, the vehicle speed detection value Vs, and the rotor rotation angle θ, and outputs motor voltage command values Vu, Vv, and Vw. The control arithmetic unit 23, a motor drive circuit 24 composed of a field effect transistor (FET) for driving the three-phase brushless motor 12, and the phase voltage command values Vu, Vv and Vw output from the control arithmetic unit 23 And an FET gate drive circuit 25 for controlling the gate current of the field effect transistor of the motor drive circuit 24.

  The motor drive circuit 24 is a so-called inverter, and periodically switches (on / off) the power supplied from the power source to the electric coils for each phase of the three-phase brushless motor 12 in accordance with a duty-controlled pulse signal.

  The details of the control system of the control unit 20 are configured as shown in FIG. 11, for example. That is, the steering assist command calculation unit 251 calculates the steering current target value It based on the steering torque T detected by the torque sensor 3 and the vehicle speed detection value Vs detected by the vehicle speed sensor 21.

  On the other hand, the current command limit value calculation unit 252 calculates a current command limit value Iref_lim based on the motor rotation speed and the supply voltage. Then, the minimum value selection unit 253 compares the steering current target value It and the current command limit value Iref_lim, and outputs the smaller value as the current value Iref_min.

The d / q-axis current target value calculation unit 256 calculates a target value based on a known torque constant formula in order to keep the driving torque of the three-phase brushless motor 12 constant. More specifically, with respect to a vector model represented on two-axis coordinates composed of a q-axis corresponding to the rotational direction of the rotor of the three-phase brushless motor 12 and a radial d-axis orthogonal thereto, the torque Q-axis current target value iq and d-axis current target value id for controlling the current to be constant are calculated.
The d-axis current target value id is determined based on the current command value, the motor rotation speed, and the supply voltage.

The q-axis current target value iq and the d-axis current target value id calculated by the d / q-axis current target value calculation unit 256 are calculated with respect to the two-axis model, but the three-phase brushless that actually generates the steering assist force. Since the motor 12 is driven by a three-phase current, that is, by a force in the three axial directions, the 2-phase / 3-phase conversion unit 257 performs arithmetic conversion from two phases to three phases. That is, the two-phase / three-phase conversion unit 257 generates the three-phase current command value Iref_abc based on the q-axis current target value iq and the d-axis current target value id output from the d / q-axis current target value calculation unit 256. .
The three-phase current command value Iref_abc is composed of three independent command values Iref_a, Iref_b, and Iref_c for controlling the electric coil current for each phase.

  In the control system connected to the output side of the two-phase / three-phase converter 257, the amount of current Im_abc (three of Im_a, Im_b, and Im_c) flowing through the electric coil for each phase of the three-phase brushless motor 12 is detected. The current is feedback controlled for each phase. That is, the amount of current Im_abc flowing through the electric coil for each phase is controlled to coincide with the three-phase current command value Iref_abc. As a result, since the motor current follows the current command value, a predetermined torque is output from the three-phase brushless motor 12, and thus assist control is realized and steering assist force is applied to the steering mechanism. become.

  Actually, the current flowing through each electric coil of the three-phase brushless motor 12 is supplied by periodically repeating ON / OFF by switching of the inverter. Therefore, the amount of current is controlled by controlling the duty using the pulse signal in order to control this on / off. That is, the controller 259 generates a duty control signal Duty_abc based on the difference between the three-phase current command value Iref_abc and the current detection value Im_abc for each phase, and the PWM control unit 262 performs control based on the duty control signal Duty_abc. These three-phase pulse signals are generated and given to the motor drive circuit 24.

  In addition, about the technique of the conventional motor drive device which can be applied to the above-mentioned electric power steering apparatus, it is disclosed by patent document 2 and patent document 3, for example.

  By the way, in the electric power steering device as described above, low voltage and large current electricity is handled to drive and control a multiphase AC motor such as a three-phase brushless motor. There is a problem of growing. Further, in recent years, there is a tendency that a high output electric power steering apparatus capable of supporting a large vehicle such as an SUV (Sport Utility Vehicle) is strongly demanded from the market, and the problem of heat generation from the apparatus body is becoming remarkable. Yes, it is expected that measures for this will become even stricter. In addition, there is an increasing demand for downsizing of the main body of the electric power steering apparatus from the viewpoints of attachment, safety, and cost reduction.

  As a countermeasure against this heat generation, conventionally, in a device for controlling driving of this type of motor, a pulse signal (PWM) for controlling the switching of the transistor for the purpose of reducing the heat generation of the components of the switching transistor (FET, etc.). Signals) are known to have a variable repetition period.

  For example, in the prior art disclosed in Patent Document 1, a 20 kHz rectangular wave is used when the duty ratio of a pulse signal (PWM signal) is smaller than 90%, and a rectangular wave of 1 kHz and a duty ratio of 90 kHz are used when the duty ratio increases. A PWM signal synthesized using a 20 kHz rectangular wave fixed at% is generated. Thereby, it is supposed that the heat generation of the switching transistor when the duty ratio is large can be suppressed.

JP-A-6-30594 JP 2004-201487 A JP 2006-158198 A

  Here, it is considered that most of the heat generated in the device for controlling this type of motor is caused by a transistor that switches a current flowing in the electric coil of the motor. That is, when the transistor is switched on / off, a large electrical loss occurs in the transistor, and this is released as thermal energy, which leads to a problem of heat generation. Therefore, the amount of heat generation increases as the number of on / off operations per unit time increases.

  Therefore, if the technique disclosed in Patent Document 1 is adopted, a PWM signal is generated using a 1 kHz rectangular wave when the duty ratio is large, and therefore, compared with a case where only a 20 kHz rectangular wave is used, per unit time. The number of on / off operations can be reduced, and the amount of heat generated can be reduced.

  However, when a rectangular wave of 1 kHz is used as in Patent Document 1, the frequency of this signal is within the human audible frequency range, and therefore, from an element such as a motor controlled according to the cycle of this signal, There is a dislike that vibration (abnormal noise) is generated, which causes discomfort to users such as a steering person and a passenger. In addition, when the control is performed using a signal having a relatively low frequency such as 1 kHz, the followability with respect to the precise motor control is deteriorated, and the torque ripple of the motor may be generated.

  The present invention has been made in view of the above-described circumstances, and its object is to reduce heat generation and radio noise associated with switching without switching the repetition frequency of a pulse signal such as a PWM signal used for switching control. Thus, an object of the present invention is to provide an electric power steering control device and a motor drive control device capable of reducing the cost of the heat sink of the device and improving the safety of the device.

The above object of the present invention is achieved by the following configuration.
(1) Inverter for independently switching current flowing in an electric coil provided independently for each phase of the multiphase AC motor for each phase, and a primary duty signal for driving the inverter according to a predetermined drive command A multi-phase AC motor connected to a steering mechanism, and applying a steering assist force to the steering mechanism by controlling the multi-phase AC motor. An electric power steering control device,
Further comprising a duty shift control unit that generates the secondary duty signal for each phase by giving the same shift amount to the primary duty signal for each phase, respectively.
An electric power steering control device that drives the inverter based on the secondary duty signal.
(2) The electric power according to (1), wherein the duty shift control unit determines the shift amount based on a minimum value or a maximum value detected from the primary duty signal for each phase. Steering control device.
(3) The duty shift control unit
A minimum value detecting unit for detecting a minimum value from the primary duty signal for each phase;
A maximum value detector for detecting a maximum value from the primary duty signal for each phase;
A shift amount selection unit that determines the shift amount based on one of the minimum value detected by the minimum value detection unit and the maximum value detected by the maximum value detection unit. The electric power steering control device according to (1) above.
(4) The shift amount selection unit has a cycle longer than the cycle of the primary duty signal, and a first shift amount determined corresponding to the minimum value and a second shift determined corresponding to the maximum value. The electric power steering control device according to (3), wherein the shift amount is determined by periodically switching between the shift amount and the shift amount.
(5) In a motor drive control device for driving and controlling a multiphase AC motor,
An inverter that independently switches the current flowing in the electric coil provided independently for each phase of the multiphase AC motor for each phase;
A duty signal generator for generating a primary duty signal for driving the inverter according to a predetermined drive command for each phase;
A duty shift control unit that generates the secondary duty signal for each phase by giving the same shift amount to the primary duty signal for each phase, and the inverter based on the secondary duty signal. A motor drive control device for driving.
(6) The motor drive according to (5), wherein the duty shift control unit determines the shift amount based on a minimum value or a maximum value detected from the primary duty signal for each phase. Control device.
(7) The duty shift control unit
A minimum value detecting unit for detecting a minimum value from the primary duty signal for each phase;
A maximum value detector for detecting a maximum value from the primary duty signal for each phase;
A shift amount selection unit that determines the shift amount based on one of the minimum value detected by the minimum value detection unit and the maximum value detected by the maximum value detection unit. The motor drive control device according to (5) above.
(8) The shift amount selection unit has a cycle longer than the cycle of the primary duty signal, and a second shift determined corresponding to the first shift amount and the maximum value determined corresponding to the minimum value. (7) The motor drive control device according to (7), wherein the shift amount is determined by periodically and alternately switching the shift amount.

According to the configuration (1), the number of on / off times per unit time in the inverter can be reduced without switching the repetition frequency of a pulse signal such as a PWM signal used for switching control. The generated heat can be reduced, the cost of the heat sink of the apparatus can be suppressed, and the safety of the apparatus can be improved. For example, when driving a three-phase motor, in general duty control, the duty of the pulse signal of each phase is controlled as shown in FIG. In this case, the pulse signal for switching control of the high potential side and the low potential side for each phase of the electric coil is continuously turned on and off over the entire time axis as shown in FIG. 12, for example. As a result, the fluctuation of the power source current flowing from the power source to each electric coil repeatedly occurs at a rate of twice during one PWM cycle as shown in FIG. Therefore, by giving the same shift amount to the primary duty signal of each phase (for example, a signal whose duty changes as shown in FIG. 2A), for example, a signal as shown in FIG. Can be generated. In other words, since there is a section where the duty is 0% (or 100%) in the secondary duty signal, a section where the pulse signal on / off is interrupted occurs on any phase in the time axis as shown in FIG. By doing so, heat generation is suppressed. In this case, the fluctuation of the power supply current flowing from the power supply to each electric coil decreases, for example, at a rate of once during one PWM period as shown in FIG. Therefore, radio noise due to fluctuations in power supply current is reduced.
According to the configuration of (2) above, there is a secondary duty signal in which there is a section where the duty is 0% or 100% from the primary duty signal where the minimum value of the duty is greater than 0% and the maximum value is less than 100%. Can be generated. For example, when there are three-phase primary duty signals Duty_a (t), Duty_b (t), and Duty_c (t) that change according to time t (or rotation angle), these minimum values at each time point (t) Duty_min (t) is detected and used as the shift amount. In this case, if the secondary duty signal for each phase is calculated as Duty_a (t) −Duty_min (t), Duty_b (t) −Duty_min (t), Duty_c (t) −Duty_min (t), the secondary duty signal Is shifted to 0%. Conversely, when the maximum value of the three-phase primary duty signal is used as the shift amount, the maximum value of the secondary duty signal can be shifted to 100%.
According to the configuration of (3) above, when the shift amount selection unit determines the shift amount, either the minimum value detected by the minimum value detection unit or the maximum value detected by the maximum value detection unit is selected. Therefore, the operation for shifting the minimum value of the secondary duty signal to 0% and the operation for shifting the maximum value of the secondary duty signal to 100% can be switched as necessary.
According to the configuration of (4) above, since the shift amount selector switches the first shift amount corresponding to the minimum value and the second shift amount corresponding to the maximum value alternately and periodically, the secondary duty signal The operation in which the minimum value of 0 is 0% and the operation in which the maximum value of the secondary duty signal is 100% are alternately repeated. In both the operation in which the minimum value of the secondary duty signal is 0% and the operation in which the maximum value of the secondary duty signal is 100%, any of the plurality of switching elements existing in the inverter is fixed in the on state. Therefore, heat generation is concentrated on some switching elements. However, the switching element fixed in the ON state is periodically switched by alternately repeating the operation in which the minimum value of the secondary duty signal is 0% and the operation in which the maximum value of the secondary duty signal is 100%. Therefore, the distribution of heat generation can be averaged. By making this switching cycle longer than the cycle of the primary duty signal, the number of switching operations per unit time can be reduced.
According to the configuration of (5) above, as in the case of the electric power steering control device of (1) above, even if the repetition frequency of a pulse signal such as a PWM signal used for switching control is not switched, per unit time in the inverter. Since the number of times of turning on / off can be reduced, heat generated by switching can be reduced.
According to the configuration of the above (6), as in the case of the electric power steering control device of the above (2), the duty is derived from the primary duty signal in which the minimum value of the duty is greater than 0% and the maximum value is less than 100%. It is possible to generate a secondary duty signal in which there is a section in which becomes 0% or 100%.
According to the configuration of (7) above, as in the case of the electric power steering control device of (3) above, the minimum value detected by the minimum value detection unit when the shift amount selection unit determines the shift amount. Since either the value or the maximum value detected by the maximum value detection unit is selected, the operation of shifting the minimum value of the secondary duty signal to 0% and the maximum value of the secondary duty signal to 100% The operation can be switched as necessary.
According to the configuration of (8) above, as in the case of the electric power steering control device of (4), the shift amount selection unit corresponds to the first shift amount corresponding to the minimum value and the maximum value. Since the second shift amount is alternately and periodically switched, the operation in which the minimum value of the secondary duty signal is 0% and the operation in which the maximum value of the secondary duty signal is 100% are alternately repeated. Thus, the distribution of heat generation can be averaged.

  According to the present invention, the number of on / off operations per unit time in the inverter can be reduced without switching the repetition frequency of a pulse signal such as a PWM signal used for switching control. Therefore, the cost of the heat sink and the like of the apparatus can be reduced, and the safety of the apparatus can be improved. That is, using the shift amount determined based on the primary duty signal of each phase operating in a state where the minimum value of the duty is greater than 0% and the maximum value is less than 100%, the minimum value of the duty is 0. %, Or the secondary duty signal with the maximum duty value fixed at 100%, can reduce the number of times the switching element is turned on / off per unit time and suppress the switching heat generation of the switching element. become. In addition, the number of fluctuations of the power source flowing from the power source per unit time to each electric coil via each switch element is reduced, and radio noise due to the power source current is reduced.

A plurality of preferred embodiments of the electric power steering according to the present invention will be described below with reference to the drawings.
In the following embodiments, the case of an electric power steering control device will be described. Of course, if a multi-phase AC motor is used, various motor drive controls for controlling the drive of the multi-phase AC motor are used. The present invention can also be applied to an apparatus.

(First embodiment)
First, one specific embodiment relating to a control unit of an electric power steering apparatus according to the present invention will be described below with reference to FIGS.

  FIG. 1 is a block diagram showing the configuration of the electric power steering control device in the first embodiment, and FIG. 2 is a waveform diagram showing a specific example of a primary duty signal and a secondary duty signal generated by the circuit shown in FIG. FIG. 3 is a time chart showing a specific example of a pulse signal for driving each switching element generated by the circuit shown in FIG. 1, and FIG. 4 shows each pulse signal and power source shown in FIG. It is a time chart which shows the detail of the electric current which flows into each electric coil of a motor.

  In the present embodiment, it is assumed that the present invention is applied to an electric power steering control device having a configuration as shown in FIGS. 9 and 10 already described as a basic configuration. Of course, the present invention can also be applied to motor drive control devices other than the electric power steering control device, and if the electric power steering control device uses a multiphase AC motor, the configuration shown in FIG. It is not limited.

  As shown in FIG. 1, the overall configuration of the control system in the present embodiment includes a steering assist command calculation unit 51, a current command limit value calculation unit 52, a minimum value selection unit 53, an Iref / Id map 54, an induction A voltage map 55, a d / q-axis current target value calculation unit 56, a two-phase / three-phase conversion unit 57, a subtractor 58, a controller 59, a duty minimum value detector 60, a subtractor 61, The PWM control unit 62, the motor drive circuit 24, the power supply battery 64, and the three-phase brushless motor 12 are configured.

  The steering assist command calculation unit 51 calculates a steering current target value It based on the steering torque T detected by the torque sensor 3 and the vehicle speed detection value Vs detected by the vehicle speed sensor 21.

On the other hand, the current command limit value calculation unit 52 calculates a current command limit value Iref_lim based on the motor rotation speed and the supply voltage.
The motor rotation speed can be obtained, for example, by differentiating the output signal of a sensor (for example, the aforementioned rotor position detection circuit 13) that detects the rotation position of the rotor (rotor) of the three-phase brushless motor 12.

  The minimum value selection unit 53 compares the steering current target value It output from the steering assist command calculation unit 51 with the current command limit value Iref_lim output from the current command limit value calculation unit 52, and the smaller one of them. Is output as the current value Iref_min.

  The Iref / Id map 54 is a storage unit that holds information representing the correspondence relationship between the current command value Iref and the d-axis current. The induced voltage map 55 is a storage unit that holds information representing the correspondence between the electrical angle representing the rotational position of the rotor of the three-phase brushless motor 12 and the induced voltage.

The d / q-axis current target value calculation unit 56 calculates a target value based on a known torque constant formula in order to keep the driving torque of the three-phase brushless motor 12 constant. Specifically, with respect to a model of a vector represented on two-axis coordinates composed of a q-axis corresponding to the rotation direction of the rotor of the three-phase brushless motor 12 and a radial d-axis orthogonal to the q-axis, torque is calculated. A q-axis current target value iq and a d-axis current target value id for constant control are calculated.
The d-axis current target value id is determined based on the current command value, the motor rotation speed, and the supply voltage.

  Incidentally, the q-axis current target value iq and the d-axis current target value id calculated by the d / q-axis current target value calculation unit 56 are calculated for the two-axis model, but actually generate the steering assist force 3. Since the phase brushless motor 12 is driven by a three-phase current, that is, by a force in three axial directions, the two-phase / three-phase conversion section 57 is changed from the two-phase to the three-phase in order to convert from the two-axis to the three-axis. The arithmetic conversion is performed.

That is, the two-phase / three-phase converter 57 generates the three-phase current command value Iref_abc based on the q-axis current target value iq and the d-axis current target value id output from the d / q-axis current target value calculator 56. .
The three-phase current command value Iref_abc is composed of three independent command values Iref_a, Iref_b, and Iref_c that control the currents of the electric coils of the respective phases.

  In the control system connected to the output side of the two-phase / three-phase converter 57, the amount of current Im_abc (three of Im_a, Im_b, and Im_c) flowing through the electric coil of each phase of the three-phase brushless motor 12 is detected. , Feedback control of current for each phase. That is, the amount of current Im_abc flowing through the electric coil for each phase is controlled to coincide with the three-phase current command value Iref_abc. As a result, since the motor current follows the current command value, a predetermined torque is output from the three-phase brushless motor 12, and thus assist control is realized and steering assist force is applied to the steering mechanism. become.

  The subtractor 58 subtracts the result (difference: error amount) obtained by subtracting the detected current value Im_abc (three of Im_a, Im_b, Im_c) from each of the three-phase current command value Iref_abc (three of Iref_a, Iref_b, and Iref_c). This is given to the controller 59 every time.

  The controller 59 performs PI (proportional / integral) control or the like based on the signal input from the subtractor 58, and outputs a control amount as a three-phase primary duty signal Duty_abc (three of Duty_a, Duty_b, and Duty_c). To do. At this time, these primary duty signals periodically change up and down around a 50% duty as the electrical angle of the rotor of the three-phase brushless motor 12 changes as shown in FIG.

  The minimum duty detector 60 connected to the output of the controller 59 detects the minimum value Duty_min in the three-phase primary duty signals Duty_a, Duty_b, and Duty_c output by the controller 59 at each time point. Output it.

  The subtractor 61 subtracts the result of subtracting the minimum value Duty_min output from the minimum duty value detector 60 for each of the three-phase primary duty signals Duty_abc (Duty_a, Duty_b, Duty_c) output from the controller 59. Secondary duty signal Duty_abc ′ (three of Duty_a ′, Duty_b ′, and Duty_c ′). That is, “Duty_a−Duty_min” is set to Duty_a ′, “Duty_b−Duty_min” is set to Duty_b ′, and “Duty_c−Duty_min” is set to Duty_c ′. The next duty signal is Duty_abc ′.

  The PWM control unit 62 generates a three-phase pulse signal subjected to pulse width control (PWM) in accordance with the three-phase secondary duty signal (Duty_abc ′) output from the subtractor 61. Specific examples of these pulse signals are shown in FIG. That is, in the motor drive circuit 24 to be described later, since it is necessary to independently control the upper and lower two switching elements for each phase, six signals (a-UPPER, a-BOTTOM, b-UPPER, b-BOTTOM) , C-UPPER, d-BOTTOM). The repetition period (for example, 1/20 kHz) of these pulse signals is constant.

  The motor drive circuit 24 is a so-called inverter, and includes six independent transistors (FETs) Qva, Qua, Qwa, Qvb, Qub, Qwb as switching elements, for example, like the motor drive circuit 24 shown in FIG. The upper transistors Qva, Qua and Qwa are connected between the positive line of the power source and the electric coils of each phase, and the lower transistors Qvb, Qub and Qwb are connected to the electric coil of each phase and the negative side of the power source ( It is connected to the (earth) line.

  That is, the six signals (a-UPPER, a-BOTTOM, b-UPPER, b-BOTTOM, c-UPPER, and d-BOTTOM) shown in FIG. 3 are converted into the transistors (Qva, Qvb, Qua, In order to control the gate terminals of Qub, Qwa, and Qwb), the output from the PWM control unit 62 is input to the motor drive circuit 24.

  Therefore, the transistors Qva, Qvb, Qua, Qub, Qwa, Qwb of the motor drive circuit 24 are repeatedly turned on and off as shown in FIG. 3, and accordingly, the electric coils of the three-phase brushless motor 12 are supplied from the power supply battery 64. Current (the power source current shown in FIG. 4) flows. The amount of current in each electric coil is controlled by the duty of the pulse signal.

  By the way, if the primary duty signal Duty_abc (see FIG. 2A) output from the controller 59 is directly input to the PWM control unit 62 to generate a pulse signal, the entire time axis as shown in FIG. A pulse signal that repeatedly turns on and off at a constant cycle is generated continuously, and the power source current flowing from the power source to each electric coil of the three-phase brushless motor 12 has a PWM cycle (for example, 1/20 kHz as shown in FIG. 13). ) Is repeatedly turned on and off at a rate of twice during one period. Thus, when the number of on / off times per unit time is large, the amount of heat generated by switching of each switching element (FET or the like) increases. In addition, since the fluctuation cycle of the power supply current is short (half the PWM cycle), high-frequency radio noise is likely to occur.

  However, in the configuration shown in FIG. 1, since the subtractor 61 generates the secondary duty signal Duty_abc ′ from the primary duty signal using the minimum duty value Duty_min detected by the minimum duty value detector 60, the duty shift is performed. It can function as a control unit and suppress the above-described problems.

  For example, even when a primary duty signal that changes as shown in FIG. 2 (a) is output from the controller 59, the duty of the signal of either phase is temporary as shown in FIG. 2 (b). The secondary duty signal Duty_abc ′ that is fixed at 0% is supplied to the PWM controller 62, so that one of the three-phase pulse signals output from the PWM controller 62, that is, the duty of the secondary duty signal is The phase that has reached 0% is temporarily fixed to the on state or the off state, and any one of the switching elements in the motor drive circuit 24 is temporarily fixed to the on state or the off state. The

  As a result, as shown in FIG. 4, there is only one period in which the upper and lower switching elements are simultaneously turned on during one PWM period, and fluctuations in the power supply current flowing through each electric coil of the three-phase brushless motor 12 are also caused. This is only once during one PWM period, and is half that of the example shown in FIG.

  That is, the frequency corresponding to the fluctuation cycle of the power supply current can be lowered by shifting the duty using the subtractor 61 and generating the secondary duty signal. For example, when the basic frequency used for PWM control is 20 kHz, if a pulse signal is generated using a primary duty signal, the switched power supply current will vary at a frequency of 40 kHz, twice the basic frequency. By using the secondary duty signal, the fluctuation frequency of the power supply current can be lowered to 20 kHz. At a frequency of 40 kHz, radio noise is likely to be generated in the vicinity of the AM radio frequency band due to its harmonics, but radio noise can be reduced by lowering the fluctuation frequency of the power supply current to 20 kHz.

  Further, since the current flowing through the electric coils of each phase of the three-phase brushless motor 12 is determined by the power supply voltage applied between the motor terminals, the current flowing through the electric coils of the three-phase brushless motor 12 is Even if the duty shift processing is performed, there is no change. Further, since the terminal potential of the three-phase brushless motor 12 is proportional to the duty of the phase, even if the same value is subtracted from the duty of each terminal, the voltage between the terminals does not change. Therefore, there is no change in the phase current of the motor when the above-described duty shift processing is performed and when it is not performed.

  Therefore, according to the present embodiment, the number of on / off operations per unit time in the motor driving device 24 can be reduced without switching the repetition frequency of the pulse signal, and thus heat generated by the switching is reduced. Thus, the cost of the heat sink and the like of the electric power steering control device can be reduced, and the safety of the device can be improved. In addition, since the frequency is not used lower than that of the above-mentioned Patent Document 1, the follow-up performance to the motor control is not deteriorated, and the torque ripple of the three-phase brushless motor 12 is generated. Can be suppressed.

(Second Embodiment)
Another embodiment of the electric power steering control device of the present invention will be described below with reference to FIGS. 5 and 6.
FIG. 5 is a block diagram showing the configuration of the electric power steering control device in the second embodiment, and FIG. 6 is a waveform diagram showing a specific example of the secondary duty signal generated by the circuit shown in FIG.

This embodiment is a modification of the first embodiment, and the configuration of the control system is changed to the contents shown in FIG. 5 and is the same as the first embodiment except that the operation is slightly changed. In addition, the effects of the first embodiment are also provided.
In FIG. 5, elements corresponding to those of the first embodiment are denoted by the same reference numerals, and the description thereof is omitted or simplified.

  That is, the difference in configuration from the first embodiment is that, as shown in FIG. 5, the maximum duty value detector 65, the constant holding unit 66, the arithmetic unit between the output of the controller 59 and the input of the PWM control unit 62. 67 is provided.

  The constant holding unit 66 always outputs a constant corresponding to 100% duty. The maximum duty value detector 65 detects and outputs the maximum value Duty_max in the three-phase primary duty signals Duty_a, Duty_b, and Duty_c output by the controller 59 at each time point.

  The calculation unit 67 obtains a result obtained by subtracting the maximum value Duty_max output from the maximum duty value detector 65 from the 100% duty value output from the constant holding unit 66 as a shift amount, and obtains a three-phase primary output from the controller 59. The result of adding the shift amount is output as a three-phase secondary duty signal Duty_abc ′ for each of Duty_a, Duty_b, and Duty_c of the duty signal Duty_abc.

That is, the calculation unit 67 sets “Duty_a + (DUTYLIM−Duty_max)” to Duty_a ′, “Duty_b + (DUTYLIM−Duty_max)” to Duty_b ′, “Duty_c + (DUTYLIM−Duty_max)” to Duty_c ′, and all phases The result of shifting the duty to the plus side by the common shift amount DUTYLIM−Duty_max is used as the secondary duty signal Duty_abc ′ and functions as a duty shift control unit.
DUTYLIM is a duty value (100% duty value) at which the duty is 100%.

  Therefore, even when the signal as shown in FIG. 2A is output as the primary duty signal Duty_abc, the secondary duty signal Duty_abc ′ output from the calculation unit 67 shown in FIG. 5 is as shown in FIG. Shifted upward. That is, in this secondary duty signal Duty_abc ', the duty of any one phase signal is fixed at 100% as shown in FIG. 6, and the other phase signals are also shifted upward by the same shift amount.

  Since the PWM control unit 62 and the motor drive circuit 24 are controlled using such a secondary duty signal Duty_abc ′, the switching elements above and below the phase whose duty becomes 100% at each time point are temporarily turned on / off. Since the state does not change, the number of times of on / off switching per unit time is reduced as in the first embodiment, and the heat generation amount is reduced. Further, for example, occurrence of radio noise or the like is reduced.

(Third embodiment)
Another embodiment relating to the electric power steering control device of the present invention will be described below with reference to FIGS.
FIG. 7 is a block diagram showing the configuration of the electric power steering control device according to the third embodiment, and FIG. 8 is a waveform diagram showing a specific example of the secondary duty signal generated by the circuit shown in FIG.

The third embodiment is a modified example in which the first embodiment and the second embodiment are combined. The configuration of the control system is changed to the contents shown in FIG. 7, and the first embodiment except that the operation is slightly changed. It is the same as that of embodiment and 2nd Embodiment, and also has the effect of the above-mentioned 1st Embodiment and 2nd Embodiment similarly.
In FIG. 7, elements corresponding to those in the first embodiment and the second embodiment are denoted by the same reference numerals, and description thereof is omitted or simplified.
That is, the characteristic configuration in the third embodiment is that, as shown in FIG. 7, between the output of the controller 59 and the input of the PWM control unit 62, the minimum duty value detector 60, the maximum duty value detector 65, The constant holding unit 66, the calculation units 67B and 67C, and the switching unit 68 are provided.

  As in the first embodiment, the minimum duty detector 60 shown in FIG. 7 detects the minimum value Duty_min among the three-phase primary duty signals Duty_a, Duty_b, and Duty_c output by the controller 59 at each time point. And output it. On the other hand, the maximum duty value detector 65 detects the maximum value Duty_max among the three-phase primary duty signals Duty_a, Duty_b, and Duty_c output by the controller 59 at each time point, as in the second embodiment. Is output. The constant holding unit 66 constantly outputs a constant corresponding to 100% duty.

  The calculation unit 67B outputs a result obtained by subtracting the 100% duty value output from the constant holding unit 66 from the maximum duty value Duty_max output from the maximum duty value detector 65. The switching unit 68 is a switch that selects either the output of the minimum duty detector 60 or the output of the calculation unit 67B, and outputs the selected signal to the calculation unit 67C.

  The calculation unit 67C subtracts the output of the switching unit 68 (selected signal) from the three-phase primary duty signals Duty_a, Duty_b, and Duty_c output by the controller 59 at each time point. The next duty signal is output as Duty_abc '.

  Further, the switching unit 68 periodically and alternately selects two input signals (the output of the minimum duty value detector 60 and the output of the calculation unit 67B) in accordance with a binary signal that periodically changes at a predetermined frequency F1. . At this time, the frequency F1 is set to a frequency lower than the frequency corresponding to the PWM cycle of the pulse signal generated by the PWM control unit 62 (the cycle is longer than the PWM cycle).

That is, in the control system shown in FIG. 7, when the switching unit 68 selects the output of the minimum duty value detector 60, the minimum of the three-phase primary duty signal Duty_abc is obtained as in the first embodiment. When the result of shifting the value Duty_min to the minus side is output from the calculation unit 67C as the secondary duty signal Duty_abc ′, and the switching unit 68 selects the output of the calculation unit 67B, 3 as in the second embodiment. The result obtained by subtracting the maximum value Duty_max of the primary duty signal Duty_abc of the phase from the 100% duty value is used as a shift amount, and the result obtained by adding the shift amount DUTYLIM-Duty_max to the primary duty signal Duty_abc of each phase is obtained in three phases. Is output as a secondary duty signal Duty_abc ′.
Therefore, the processing method in the first embodiment and the processing method in the second embodiment are alternately selected.

  Therefore, even if the primary duty signals Duty_a, Duty_b, and Duty_c that change as shown in FIG. 2A are output from the controller 59, the secondary input to the PWM control unit 62 shown in FIG. The duty signal Duty_abc ′ changes as shown in FIG. 8, for example. That is, as shown in FIG. 8, a state in which the duty of any one-phase signal is 0% and a state in which the duty is 100% appear periodically.

  Here, in the operation of the first embodiment or the second embodiment, since there is a phase in which the duty of the secondary duty signal Duty_abc ′ is fixed to 0% or 100%, the switching element of the corresponding phase is in the ON state. As a result, a fixed state occurs, current flows intensively to the switching element in the on state, and heat generation also concentrates on the switching element.

However, in the third embodiment, as shown in FIG. 8, the state where the duty of any one phase signal is 0% and the state where the duty is 100% are periodically switched. Thus, the fixed state in the on state is avoided, and concentration of heat generation is prevented. That is, the effect of averaging the distribution of generated heat can be obtained.
In addition, further improvement in the heat generation distribution can be expected by appropriately changing the frequency F1 at which the switching unit 68 switches between the two signals.

  In the operation of the first embodiment or the second embodiment, when each switching element in the motor drive circuit 24 is short-circuited due to a failure and an abnormality that does not switch from the on state to the off state occurs, the failed switching While the occurrence of abnormality cannot be detected until an off signal is input to the element, in the third embodiment, the state where the duty becomes 0% and the state where the duty becomes 100% are periodically switched. It is possible to quickly detect the occurrence of.

  As described above, the present invention can be used as an electric power steering control device used in a vehicle or the like and a motor drive control device used in various other devices, and suppresses heat generation or radio noise. It is very useful for. In addition, since it is not necessary to switch the frequency used for the switching control of the motor drive device 24, there is an effect that it is possible to suppress the vibration of the frequency within the human audible frequency band, that is, the generation of abnormal noise.

This is the end of the description of specific embodiments. However, aspects of the present invention are not limited to these embodiments, and modifications, improvements, and the like can be made as appropriate.
For example, in each of the above-described embodiments, a three-phase brushless motor has been described. However, a multi-phase AC motor is not limited to the type of motor and the number of phases, and the motor is driven without departing from the concept of the present invention. It can be applied to various devices for controlling.

It is a block diagram which shows the structure of the electric power steering control apparatus in 1st Embodiment. It is a wave form diagram which shows the specific example of the primary duty signal and secondary duty signal which are produced | generated by the circuit shown in FIG. 2 is a time chart showing a specific example of a pulse signal for driving each switching element generated by the circuit shown in FIG. 1. It is a time chart which shows the detail of the electric current which flows into each electric coil of a motor from each pulse signal and power supply which were shown in FIG. It is a block diagram which shows the structure of the electric power steering control apparatus in 2nd Embodiment. FIG. 6 is a waveform diagram showing a specific example of a secondary duty signal generated by the circuit shown in FIG. 5. It is a block diagram which shows the structure of the electric power steering control apparatus in 3rd Embodiment. FIG. 8 is a waveform diagram showing a specific example of a secondary duty signal generated by the circuit shown in FIG. 7. It is a block diagram which shows the basic composition of the whole physical component of an electric power steering control apparatus. It is a block diagram which shows the basic composition regarding the electric circuit of the motor drive control apparatus used for an electric power steering control apparatus. It is a block diagram which shows the detail of the control system of the electric circuit shown in FIG. It is a time chart which shows the specific example of the pulse signal for switching electricity supply of each electric coil in the electric circuit shown in FIG. It is a time chart which shows the detail of the electric current which flows into each electric coil from the pulse signal and power supply which are shown in FIG.

Explanation of symbols

12 3-phase brushless motor (multi-phase AC motor)
24 Motor drive circuit (inverter)
51 Steering Auxiliary Command Calculation Unit 52 Current Command Limit Value Calculation Unit 53 Minimum Value Selection Unit 54 Iref / Id Map 55 Induced Voltage Map 56 d / q-axis Current Target Value Calculation Unit 57 2-phase / 3-phase Conversion Unit 58 Subtractor 59 Control (Duty signal generator)
60 Duty minimum value detector (minimum value detector)
61 Subtractor (duty shift control unit)
62 PWM control unit 64 Power supply battery 65 Duty maximum value detector (maximum value detection unit)
66 Constant holding unit 67, 67B, 67C Calculation unit (duty shift control unit)
68 Switching section (shift amount selection section)

Claims (8)

An inverter for independently switching current flowing in an electric coil provided independently for each phase of the multiphase AC motor for each phase, and a primary duty signal for driving the inverter in accordance with a predetermined drive command An electric power steering for providing a steering assist force to the steering mechanism by controlling the multiphase AC motor, and the multiphase AC motor is connected to a steering mechanism. A control device,
Further comprising a duty shift control unit that generates the secondary duty signal for each phase by giving the same shift amount to the primary duty signal for each phase, respectively.
An electric power steering control device that drives the inverter based on the secondary duty signal. 2. The electric power steering control according to claim 1, wherein the duty shift control unit determines the shift amount based on a minimum value or a maximum value detected from the primary duty signal for each phase. apparatus. The duty shift control unit
A minimum value detecting unit for detecting a minimum value from the primary duty signal for each phase;
A maximum value detector for detecting a maximum value from the primary duty signal for each phase;
A shift amount selection unit that determines the shift amount based on one of the minimum value detected by the minimum value detection unit and the maximum value detected by the maximum value detection unit. The electric power steering control device according to claim 1. The shift amount selection unit has a first shift amount determined corresponding to the minimum value and a second shift amount determined corresponding to the maximum value in a cycle longer than the cycle of the primary duty signal. The electric power steering control device according to claim 3, wherein the shift amount is determined by switching between and alternately. In a motor drive control device for driving and controlling a multiphase AC motor,
An inverter that independently switches the current flowing in the electric coil provided independently for each phase of the multiphase AC motor for each phase;
A duty signal generator for generating a primary duty signal for driving the inverter according to a predetermined drive command for each phase;
A duty shift control unit that generates the secondary duty signal for each phase by giving the same shift amount to the primary duty signal for each phase, and the inverter based on the secondary duty signal. A motor drive control device for driving. The motor drive control device according to claim 5, wherein the duty shift control unit determines the shift amount based on a minimum value or a maximum value detected from the primary duty signal for each phase. . The duty shift control unit
A minimum value detecting unit for detecting a minimum value from the primary duty signal for each phase;
A maximum value detector for detecting a maximum value from the primary duty signal for each phase;
A shift amount selection unit that determines the shift amount based on one of the minimum value detected by the minimum value detection unit and the maximum value detected by the maximum value detection unit. The motor drive control device according to claim 5. The shift amount selection unit has a first shift amount determined corresponding to the minimum value and a second shift amount determined corresponding to the maximum value in a cycle longer than the cycle of the primary duty signal. The motor drive control device according to claim 7, wherein the shift amount is determined by alternately switching between and.

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