Abstract:
A sensorless motor control device includes a magnetic pole position estimating unit that does not use a sensor to detect a magnetic pole position of a motor having a salient rotor, and overlays a high-frequency current on the motor to estimate the magnetic pole position of the rotor of the motor; and a high-frequency current control unit for changing a magnitude of the high-frequency current based on a magnitude of one of a torque and a current of the motor.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The disclosure of Japanese Patent Application No. 2008-327239 filed on Dec. 24, 2008 including the specification, drawings and abstract is incorporated herein by reference in its entirety. 
     BACKGROUND 
     The present invention relates to a drive control device for a motor, and specifically relates to a sensorless vector control device that calculates a position angle of a rotor based on a high-frequency current and a high-frequency voltage running through the motor for use as a position angle in a vector control computation. The sensorless motor control device of the present invention may be used, for example, in an electric vehicle (EV) that uses a motor to drive the wheels, as well as a hybrid electric vehicle (HEV) having a motor whose battery is recharged by driving the engine. 
     In Japanese Patent Application Publication No. JP-A-H11-299299, a harmonic current generated by a harmonic current generator  10  is overlaid on (added to) id of target currents id, iq on two axes of a motor vector control. A motor voltage is detected and a q-axis voltage is calculated from the voltage, and then differentiated. A positional error detector  15  calculates a positional error, after which a position angle of a targeted gap magnetic flux is calculated. In Japanese Patent Application Publication No. JP-A-2007-236015, an induced voltage of a motor is calculated based on a d-axis voltage command of a motor vector control, and d-axis and q-axis currents of the motor. A position computation then calculates a position angle θ based on the induced voltage. 
     SUMMARY 
     The position angle calculation using a high frequency focuses on orthogonal biaxial inductances Ld, Lq. However, power loss occurs in the motor due to the high-frequency current injected to the motor or the harmonic component in the motor current, and generates noise. In light of this, reducing the high-frequency current or the harmonic current is desirable, but a reduction would lower the S/N ratio in the Ld, Lq calculations and increase the error in the position angle calculation. 
     In small high-output motors often used as on-vehicle motors, higher torque (higher current) driving is accompanied by increased magnetic saturation, and reduces the saliency ratio (Lq/Ld) (the saliency ratio approaches 1), thus lowering the accuracy of the position angle calculation. In other words, as shown in  FIG. 5 , the orthogonal biaxial inductances Ld, Lq for the high-frequency current or the harmonic current are dynamic inductances that become the tangent angle of the I/φ curve of the stator. However, near the saturation region of the I/φ curve, that is, in the high torque (high current) region, Ld and Lq both approach zero and there is little change in Ld and Lq with respect to the high-low variation of a current I. This lowers the S/N ratio of the Ld, Lq calculation values based on the voltage and the high-frequency current or the harmonic current, which lowers the accuracy of the position angle calculation that uses Ld and Lq as parameters. 
     The present invention increases the accuracy of a position angle calculation ranging from a low torque (low current) to a high torque (high current), and suppresses power loss at low torque (low current). 
     (1) A sensorless motor control device includes a magnetic pole position estimating unit that does not use a sensor to detect a magnetic pole position of a motor having a salient rotor, and overlays a high-frequency current on the motor to estimate the magnetic pole position of the rotor of the motor. The sensorless motor control device further includes a high-frequency current control unit for changing a magnitude of the high-frequency current based on a magnitude of a torque or a current of the motor. 
     At a high torque with a large motor current value, the detection accuracy of the position angle deteriorates because of the small saliency ratio (Lq/Ld) caused by magnetic saturation. Conversely at a low torque with a small motor current value, the detection accuracy of the position angle can be secured because of the large saliency ratio (Lq/Ld). Therefore, based on the magnitude of the torque or current of the motor, the detection accuracy of the position angle can be improved while also suppressing power loss and noise, by changing the magnitude of the high-frequency or harmonic current used in the position angle calculation. 
     (2) In the sensorless motor control device according to (1) above, the high-frequency current control unit increases the high-frequency current in accordance with a larger magnitude of the torque or the current of the motor, and decreases the high-frequency current in accordance with a smaller magnitude of the torque or the current of the motor. 
     At a high torque with a large motor current value, power loss and noise increase due to the increased high-frequency or harmonic current used in the position angle calculation; however, the accuracy of the position angle calculation can be improved. Conversely at a low torque with a small motor current value, the detection accuracy of the position angle can be secured even with a reduced high-frequency or harmonic current, so power loss and noise can also be reduced. 
     (3) In the sensorless motor control device ( FIGS. 2 to 4 ) according to (2) above, the high-frequency current control unit includes a high-frequency generating unit for generating a high-frequency current signal; a table that is a collection of current level specification data that correspond to each value of the torque or the current of the motor; and a unit for generating the high-frequency current by amplifying the high-frequency current signal to a level specified by the current level specification data in the table that corresponds to the present torque or current. 
     Accordingly, the current level specification data can be acquired by accessing the table, and the high-frequency current can be easily generated. 
     (4) In the sensorless motor control device ( FIGS. 2 ,  4 ) according to (3) above, the current level specification data in the table is amplitude specification data, and the high-frequency current control unit generates a high-frequency current command value by amplifying an amplitude of the high-frequency current signal to an amplitude specified by the amplitude specification data. 
     Accordingly, the current level specification data can be acquired by accessing the table, and the high-frequency current command value can be easily generated. 
     (5) In the sensorless motor control device ( FIGS. 3 ,  5 ) according to (3) above, the current level specification data in the table is gain specification data, and the high-frequency current control unit generates a high-frequency current command value by amplifying the high-frequency current signal using a gain specified by the gain specification data. 
     (6) In the sensorless motor control device ( FIG. 2 ) according to any one of (3) to (5) above, the table is a collection of current level specification data that corresponds to each value of a target torque. 
     (7) In the sensorless motor control device ( FIG. 3 ) according to any one of (3) to (5) above, the table is a collection of current level specification data that corresponds to each value of an orthogonal biaxial target current. 
     (8) In the sensorless motor control device ( FIG. 4 ) according to any one of (3) to (5) above, the table is a collection of current level specification data that corresponds to each value of an orthogonal biaxial feedback current. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram that shows a constitution of an electrical system of a wheel drive apparatus according to a first embodiment of the present invention; 
         FIG. 2  is a block diagram that shows a functional configuration according to the first embodiment of a motor control device  30  shown in  FIG. 1 ; 
         FIG. 3  is a block diagram that shows a functional configuration according to a second embodiment of the motor control device  30  shown in  FIG. 1 ; 
         FIG. 4  is a block diagram that shows a functional configuration according to a third embodiment of the motor control device  30  shown in  FIG. 1 ; and 
         FIG. 5  is a graph that shows an outline of the relationship between magnetic flux and an energization current value of a stator in a synchronous motor with embedded permanent magnets. 
     
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
     Other objects and characteristics of the present invention will become clear from the embodiments described below with reference to the accompanying drawings. 
     First Embodiment 
       FIG. 1  shows an outline of a first embodiment according to the present invention. In this embodiment, an electric motor  10  to be controlled is installed in a vehicle and is a synchronous motor with embedded permanent magnets for rotationally driving a wheel. The permanent magnets are built into a rotor, and a stator has coils  11  to  13  of the three phases, U, V, and W. A voltage type inverter  16  supplies the electric motor  10  with power from an on-vehicle battery  17 . 
     The battery  17  is an accumulator in the vehicle and connects to a primary-side condenser  18  when an electric component in the vehicle is turned on. Together with the battery  17 , the primary-side condenser  18  forms a primary-side DC power supply. A voltage sensor  19  sends a voltage detection signal Vdc representing the voltage of the primary-side condenser  18  (voltage of the on-vehicle battery  17 ) to a motor control device  30 . In this embodiment, partial pressure resistance is used in the voltage sensor  19 . The positive electrode (+ line) of the primary-side DC power supply is connected to an end of a reactor  21  of a converter  20 . 
     The converter  20  further includes a pressure-increasing semiconductor switch  22 , which is a switching element for increasing pressure, that switches on and off between another end of the reactor  21  and the negative electrode (− line) of the primary-side DC power supply; a regenerative semiconductor switch  23 , which is a switching element for regeneration, that switches on and off between the other end of the reactor  21  and the positive electrode of a secondary-side condenser  27 ; and diodes  24 ,  25  that are connected in parallel to the respective semiconductor switches  22 ,  23 . 
     If the pressure-increasing semiconductor switch  22  is turned on (conductive), current flows from the primary-side DC power supply ( 17 ,  18 ) to the switch  22  through the reactor  21 , and the reactor  21  accumulates power accordingly. If the switch  22  is turned off (non-conductive), the reactor  21  sends a high-pressure discharge to the secondary-side condenser  27  through the diode  25 . In other words, a higher voltage than the voltage of the primary-side DC power supply is induced to charge the secondary-side condenser  27 . Repeatedly turning the switch  22  on and off enables continued high-pressure charging of the secondary-side condenser  27 . That is, the secondary-side condenser  27  is charged at a high voltage. Repeatedly switching between on and off in regular cycles increases the power accumulated by the reactor  21  depending on the length of the on period. Therefore, by adjusting the on time in a regular cycle (on-duty: ratio of the on time to the regular cycle), namely by performing a PWM control, the speed at which power is fed (feeding speed for power running) from the primary-side DC power supply  17 ,  18  to the secondary-side condenser  27  through the converter  20  can be adjusted. 
     If the regenerative semiconductor switch  23  is turned on (conductive), the accumulated power of the secondary-side condenser  27  is sent to the primary-side DC power supply  17 ,  18  through the switch  23  and the reactor  21  (reverse power supply: regeneration). In this case as well, by adjusting the on time of the switch  23  in a regular cycle, namely by performing a PWM control, the speed at which power is reverse-fed (feeding speed for regeneration) from the secondary-side condenser  27  to the primary-side DC power supply  17 ,  18  through the converter  20  can be adjusted. 
     The voltage type inverter  16  includes six switching transistors Tr 1  to Tr 6 . The transistors Tr 1  to Tr 6  are driven on (conductive) based on six drive signals generated in parallel by a drive circuit  29 . The DC voltage of the secondary-side condenser  27  (output voltage of the converter  20 , i.e., secondary voltage) is converted into three AC voltages whose phase difference is 2π/3, namely a three-phase AC voltage, and respectively applied to the three-phase (U-phase, V-phase, W-phase) stator coils  11  to  13  of the electric motor  10 . Thus, phase currents iU, iV, iW respectively flow to the stator coils  11  to  13  of the electric motor  10 , and rotate the rotor of the electric motor  10 . In order to increase the power supply performance for driving on and off (switching) the transistors Tr 1  to Tr 6  using a PWM pulse and suppress voltage surges, the secondary-side output line of the converter  20 , which is the input line of the inverter  16 , is connected to the high-capacity secondary-side condenser  27 . On the contrary, the primary-side condenser  18  forming the primary-side DC power supply is small, low-cost, and low-capacity. The capacity of the primary-side condenser  18  is considerably smaller than the capacity of the secondary-side condenser  27 . The voltage sensor  28  detects a secondary voltage Vuc of the converter  20  and sends the detection result to the motor control device  30 . The supply power line connected to the stator coils  11 ,  12  of the electric motor  10  is mounted with current sensors  14 ,  15  that use a hall IC. The current sensors  14 ,  15  respectively detect the phase currents iV, iW, and generate current detection signals (analog voltage) that are sent to the motor control device  30 . 
       FIG. 2  shows a functional configuration of the motor control device  30 . In the present embodiment, the motor control device  30  is an electronic control unit whose main body consists of a digital signal processor (DSP). The motor control device  30  includes interfaces (signal processing circuits) not shown in the drawing between itself and the drive circuit  29 , the current sensors  14 ,  15 , the primary voltage sensor  19 , and the secondary voltage sensor  28 , and further includes interfaces (communication circuits) not shown in the drawing between itself and a main controller of a vehicle running control system (not shown) in the vehicle. 
     Referring to  FIG. 2 , a position computation unit  45  calculates a rotation angle (magnetic pole position) θ of the rotor of the electric motor  10 , and a speed computation unit  46  calculates a rotation speed (angular speed) ω based on the rotation angle θ. To be more precise, the rotation angle and magnetic pole position of the rotor of the electric motor  10  are not the same; however, the two have a proportional relationship and the proportionality coefficient is determined by a magnetic pole number p of the electric motor  10 . Furthermore, although the rotation angle and the angular speed are not the same, the two have a proportional relationship and the proportionality coefficient is determined by the magnetic pole number p of the electric motor  10 . In the present specification, the rotation angle θ refers to the magnetic pole position. The rotation speed ω refers to the angular speed, and may also refer to the rotation speed. 
     The main controller of the vehicle running control system (not shown) sends a motor target torque TM* to a control device  30  of the motor control device  30 . Note that the main controller calculates a vehicle required torque TO* based on the vehicle speed and the throttle opening, generates the motor target torque TM* corresponding to the vehicle required torque TO*, and then sends the motor target torque TM* to the control device  30 . The control device  30  outputs a rotation speed ω [rpm] of the electric motor  10  to the main controller. 
     In accordance with a torque command limit  31 , the motor control device  30  reads out from a limit torque table (look-up table) a limit torque TM*max that corresponds to the rotation speed ω and an upper limit Vmax of the output voltage (secondary voltage) of the converter  20 . If the target torque TM* exceeds TM*max, TM*max is set as a target torque T*. If the target torque TM* is equal to or less than TM*max, the motor target torque TM* is set as the target torque T*. The motor target torque T* generated with such a limit added is sent to an output computation unit  32 , and also used in a secondary target voltage calculation. 
     Note that the limit torque table is a memory region in which the upper limit Vmax of the secondary voltage and voltage values in the range of the rotation speed are written as addresses, and the maximum torque capable of activating the electric motor  10  at each voltage value is written as TM*max. In the present embodiment, the limit torque table refers to a memory region of a RAM (not shown) in the control device  30 . The limit torque TM*max becomes larger as the upper limit Vmax of the secondary voltage increases, and smaller as the upper limit Vmax decreases. In addition, the limit torque TM*max becomes larger as the rotation speed ω decreases, and smaller as the rotation speed ω increases. 
     There is a nonvolatile memory inside the motor control device  30  that is written with the data TM*max of the limit torque table. When operating voltage is applied to the control device  30 , the control device  30  reads out TM*max from the nonvolatile memory and writes TM*max to the RAM over the course of initializing itself and a motor drive system shown in  FIG. 1 . It will be noted later on that there are a plurality of other similar look-up tables in the control device  30 . Like the limit torque table, these look-up tables also refer to memory regions on the RAM that are written with reference data in the nonvolatile memory. 
     The motor control device  30  determines whether power running or regeneration is to be performed based on the target torque T* and the rotation speed ω. The motor control device  30  reads out a secondary target voltage Vuc* assigned for the rotation speed ω of the electric motor  10  from a secondary target voltage table assigned for the target torque T* in a “power running” group if power running, and in a “regeneration” group if regeneration. The motor control device  30  then controls the converter  20  through the drive circuit  26  such that the secondary voltage detected by the sensor  28  matches the target voltage Vuc*. 
     Based on the output computation unit  32 , a motor current control  42 , and a voltage conversion unit  43 , the motor control device  30  performs a feedback control of the motor current using a vector control computation on a conventional d-q axis model in which the d-axis is the direction of a pair of magnetic poles in the rotor of the electric motor  10  and the q-axis is the direction perpendicular to the d-axis. The control device  30  digitally converts and reads the current detection signals iV, iW from the current sensors  14 ,  15 . In a current feedback computation unit  49 , the control device  30  uses a three-phase/two-phase conversion, which is a conventional conversion of fixed coordinates into rotating coordinates, to transform the three-phase current values iU, iV, iW of a fixed coordinate system into two-phase current values id, iq for the d-axis and q-axis of a rotating coordinate system. Note that iU+iV+iW=0, and iU is calculated based on this assumption. 
     A first high-efficiency torque curve table A, which is a look-up table, is used in the output computation unit  32 . The first high-efficiency torque curve table A is written with d-axis current values id that are linked to the motor speed ω and the motor target torque T*, and used to generate the target torques T* at each motor speed. 
     The output torque of the electric motor is set with respect to the values of the d-axis current id and the q-axis current iq. For one rotation speed, that is, at the same motor rotation speed, there are an infinite number of id, iq combinations for outputting the same torque, which are indicated on a constant torque curve. The id, iq combination with the highest efficiency of power use (least power consumption) on the constant torque curve is a high-efficiency torque point. A curve that connects the high-efficiency torque points on a plurality of torque curves is a high-efficiency torque curve that exists with respect to each rotation speed. The d-axis current id and the q-axis current iq for the position of the given motor target torque T* on the high-efficiency torque curve for the motor rotation speed are designated as target current values for biasing the electric motor  10 . The electric motor  10  thus outputs the target torque T* and such biasing of the motor results in a highly efficient use of motor power. 
     In the present embodiment, the high-efficiency torque curve is divided into two systems: the first high-efficiency torque curve A representing d-axis values, and a second high-efficiency torque curve B representing q-axis values. Furthermore, the first high-efficiency torque curve A is a pair of curves, with one applicable to the power running region and one applicable to the regeneration region; both represent the d-axis target current with respect to the motor rotation speed and the target torque. 
     The first high-efficiency torque curve table A is a memory region written with the target torque T* linked to the d-axis target currents in order to generate the target torque using the least power consumption, and is formed from a pair consisting of a power running table A1 for power running and a regeneration table A2 for regeneration. To determine which of the power running and regeneration tables is used, it is first determined whether power running or regeneration is to be performed based on the rotation speed co of the electric motor and the given target torque T*, and one of the tables is selected based on the determination result. 
     In a d-axis current command calculation within the output computation unit  32 , the control device  30  subtracts a d-axis field weakening current Δid from the d-axis current value id, which is read out from the first high-efficiency torque curve table A corresponding to the target torque T* determined by the torque command limit  31 . The control device  30  then calculates a d-axis target current id* as id*=−id−Δid. 
     A q-axis current command calculation uses the second high-efficiency torque curve table B that is in the output computation unit  32 . The second high-efficiency torque curve table B corrects the second high-efficiency torque curve B representing the q-axis values on the high-efficiency torque curve to a curve representing the q-axis target current after subtracting a q-axis field weakening current Δiq paired with the d-axis field weakening current Δid. The second high-efficiency torque curve table B then stores the data of the corrected second high-efficiency torque curve B. The second high-efficiency torque curve table B is a memory region written with the d-axis target currents linked to the target torque T* and the d-axis field weakening current Δid in order to generate the target torque using the least power consumption, that is, the target current values on a corrected second high-efficiency torque curve B. The second high-efficiency torque curve table B is also formed from a pair consisting of a power running table B1 for power running and a regeneration table B2 for regeneration. To determine which of the power running and regeneration tables is used, it is first determined whether power running or regeneration is to be performed based on the rotation speed ω of the electric motor and the target torque T*, and one of the tables is selected based on the determination result. 
     In the q-axis current command calculation, a q-axis target current iq* designated for the target torque T* and the d-axis field weakening current Δid is read from the second high-efficiency torque curve table B and set as the q-axis current command. 
     In the motor current control  42 , the motor control device  30  calculates a current difference δid between the d-axis target current id* and the d-axis current id, and a current difference δiq between the q-axis target current iq* and the q-axis current iq. A proportional control and integral control (PI computation of the feedback control) are performed based on the current differences δid, δiq. Based on such output, a d-axis voltage command value Vd* and a q-axis voltage command value Vq* are then calculated as output voltages in the voltage conversion unit  43 . 
     Next in a two-phase/three-phase conversion unit  47 , which performs a transformation of rotating coordinates into fixed coordinates, the target voltages Vd* and Vq* of a rotating coordinate system are transformed in accordance with the two-phase/three-phase conversion into three-phase target voltages VU*, VV*, VW* of a fixed coordinate system, and sent to a PWM pulse generator  48 . When the voltage control mode is two-phase modulation, the target voltages Vd* and Vq* are modulated into two-phase target voltages and sent to the PWM pulse generator  48 . When the PWM pulse generator  48  receives the phase target voltages, the PWM pulse generator  48  converts them into PWM pulses MU, MV, MW in order to output voltage at each target voltage value, and outputs the PWM pulses MU, MV, MW to the drive circuit  29  shown in  FIG. 1 . The drive circuit  29  generates six drive signals in parallel based on the PWM pulses MU, MV, MW, and the drive signals respectively turn on and off the transistors Tr 1  to Tr 6  of the voltage type inverter  16 . Thus, the phase target voltages are respectively applied and the phase currents iU, iV, iW flow to the stator coils  11  to  13  of the electric motor  10 . When the phase target voltages of the two-phase modulation mode are received, the PWM pulse generator generates PWM pulses for two phases and sets an on or off (constant voltage output) signal for the remaining phase. When the phase target voltages of a one-pulse modulation mode are received, an energization section signal that uses the phases for rectangular wave conduction is output. 
     Note that the field weakening current computation calculates a voltage saturation index m, which is a parameter used for a field weakening control. Namely, based on the d-axis voltage command value Vd* and the q-axis voltage command value Vq*, a voltage saturation calculation value ΔV is calculated as a value representing the degree of voltage saturation, and a field adjustment amount calculated. In the calculation of the field adjustment amount, if ΔV is integrated and an integrated value ΣΔV is positive, the integrated value ΣΔV is multiplied by the proportional coefficient to calculate the d-axis field weakening current Δid used in performing the field weakening control and set to a positive value. If the voltage saturation calculation value ΔV or the integrated value ΣΔV is zero or less, the adjustment value Aid and the integrated value ΣΔW are set to zero. The adjustment value Δid is used in the d-axis current command calculation and the q-axis current command calculation. 
     The position computation unit  45  calculates the rotation angle (magnetic pole position) θ of the rotor, i.e., a rotor position angle, using a position angle computation that uses the high-frequency-compatible orthogonal biaxial inductances Ld, Lq, based on high-frequency voltages Vdh*, Vqh* that are injected into (overlaid on) the three-phase current of the electric motor  10 . The calculated position angle θ is used in the speed computation unit  46  for calculating the motor rotation speed ω, and also used for phase conversion in the two-phase/three-phase conversion unit  47  and the three-phase/two-phase conversion unit  49 . 
     According to the present embodiment, in order to inject high-frequency current into the electric motor  10 , high-frequency current commands idh*, iqh* are first generated at a low level for a low target torque (low current value) in a high-frequency current control  33 A, and are increased to a higher level as the target torque increases. The high-frequency current commands idh*, iqh* are then added to the orthogonal biaxial target current values id*, iq* by addition-subtraction units  41   d ,  41   q . Thus, the injected high-frequency-compatible high-frequency voltages Vdh*, Vqh* are included in the output of the voltage conversion unit  43 . This is then extracted by a band pass filter  44 . The high-frequency voltages Vdh*, Vqh* (instantaneous values) extracted by the band pass filter  44  are applied to the position computation unit  45 , and the position computation unit  45  calculates and outputs the position angle θ corresponding to these values. 
     The high-frequency current control  33 A of the present embodiment includes a high-frequency generation unit  34 , which generates constant-amplitude current signals ido, iqo with a high frequency (500 Hz in the present example) for a pair of d-, q-axes, and also includes a high-frequency amplitude table (a data set in a region of the RAM)  35   a , which uses the values of target torques as addresses and the high-frequency amplitudes linked to each target torque as current level specification data. A high-frequency amplitude (target amplitude) linked to the target torque T* is read out from the table  35   a , and a multiplication (amplification) unit  36  amplifies the constant-amplification current signals ido, iqo to the target amplitude, and outputs these to the addition-subtraction units  41   d ,  41   q.    
     The high-frequency amplitude table  35   a  is written with high-frequency amplitudes whose level is higher for higher target torque values and lower for lower target torque values. Therefore, the position angle computation at a high torque (high current) has greater accuracy, and there is less power loss at a low torque (low current). 
     Note that in a modification of the present embodiment, the data in the high-frequency amplitude table  35   a  may be an amplitude gain instead of the high-frequency amplitude. The constant-amplification current signals ido, iqo may be amplified using an amplitude gain read out from the table  35   a  and then output to the addition-subtraction units  41   d ,  41   q . Likewise, an amplitude gain may also be used in modifications of second and third embodiments described next. 
     Second Embodiment 
       FIG. 3  shows a functional configuration of the motor control device  30  according to a second embodiment. In the second embodiment, the three-phase current of the motor is converted into the orthogonal biaxial d-axis current id and q-axis current iq in the three-phase/two-phase conversion unit  49 , and a vector resultant value of id, iq, that is, a target current value io having orthogonal two-axis coordinates, is calculated by a vector computation unit  37 . A table  35   b  uses the target current values io corresponding to the target torque T* as addresses and stores high-frequency amplitudes (target amplitudes) that are current level specification data. A high-frequency amplitude (target amplitude) linked to the current target current value io is read out from the table  35   b , and the multiplication (amplification) unit  36  amplifies the constant-amplification current signals ido, iqo to the target amplitude, and then outputs these to the addition-subtraction units  41   d ,  41   q . Other constitutions and functions of the second embodiment are identical to the first embodiment described above. 
     Third Embodiment 
       FIG. 4  shows a functional configuration of the motor control device  30  according to a third embodiment. A table  35   c  of a high-frequency current control  33 C uses motor current values (feedback values) as addresses and stores high-frequency amplitudes (target amplitudes) that are current level specification data. The three-phase current of the motor is converted by the current feedback computation (three-phase/two-phase conversion) unit  49  into the orthogonal biaxial values, d-axis current id and q-axis current iq. A vector resultant value of id, iq, that is, a motor current value (feedback current value) if having orthogonal two-axis coordinates, is calculated by a vector computation  50 . The calculation value (instantaneous value) is smoothed (converted into DC) by a low-pass filter  51 , and a high-frequency amplitude (target amplitude) corresponding to the calculation value (motor current value) is read out from the table  35   c . The multiplication (amplification) unit  36  amplifies the constant-amplification current signals ido, iqo to the target amplitude, and outputs these to the addition-subtraction units  41   d ,  41   q . Other constitutions and functions of the third embodiment are identical to the first embodiment described above.