The present invention relates to motor control devices for controlling a synchronous motor and methods of calculating a correction torque coefficient in the motor control devices.
In a speed control of a synchronous motor, a conversion coefficient that expresses a relationship between a torque command and actual torque that is actually output from the motor is generally called a torque constant. In general, the torque constant is a fixed value that does not change with speed or current and configures a speed control system. However, the actual torque constant is not always fixed. The torque constant may not be fixed due to an influence of current flowing in the motor and a current control circuit.
PTL1 discloses a conventional method as a technical measure to cope with it. PTL1 has a means to measure actual output torque relative to the torque command by actually driving the motor, and correct the torque command. PTL1 controls the motor using this corrected torque command, so as to keep a fixed torque constant.
However, the above conventional method can correct the torque constant according to motor specifications, but cannot correct an influence of individual differences, such as variation in motor production and variation in characteristic of electronic components in a drive circuit.
PTL1 Japanese Patent Unexamined Publication No. H11-191990
A motor control device of the present invention includes a speed control part for controlling a motor rotation speed, and a torque correction means for suppressing variation in torque constant due to individual differences of motors. This eliminates influence of torque variation in individual motors and thus achieves high-precision torque control.
Exemplary embodiments of the present invention are described below with reference to drawings. The exemplary embodiments described herein are illustrative and not restrictive, and the scope of the present invention is not limited thereto.
As shown in
In motor control device 10 shown in
In addition, in the exemplary embodiment, brushless motor 100 has built-in circuit components 48p that function as motor control device 10 in synchronous motor 40. These circuit components 48p are mounted on circuit board 48b. For example, a switching element configuring inverter 23 is mounted on circuit board 48b. Still more, position detector 51 for detecting a rotating position of rotor 41 is disposed facing permanent magnet 43 of rotor 41. In this structure, three-phase AC voltage from inverter 23 is applied to motor coil 47 of each phase to energizing and drive motor coils 47, and rotor 41 rotates while being rotatably supported by bearing 44.
In brushless motor 100 as configured above, motor control device 10 includes current detector 31, torque converter 32, speed operation part 52, speed control part 53, torque command corrector 54, and current control part 55 in the exemplary embodiment shown in
Next, in motor control device 10 in
Current detector 31 detects current flowing when drive voltage Vdr, which is AC drive voltage, is applied to motor coil 47, and outputs it as motor current Idet to torque converter 32. Torque converter 32 performs unit conversion of motor current Idet detected by current detector 31 to torque, and outputs it as detected torque iq to current control part 55. Current control part 55 calculates voltage command Vc such that deviation between torque command iq*(crr) after correction and detected torque iq becomes zero, and outputs it to three-phase inverter 23. In other words, current control part 55 generates voltage command Vc for driving motor coils 47 of synchronous motor 40 based on corrected torque command iq*(crr) and detected motor current Idet. Then, inverter 23 generates drive voltage Vdr based on voltage command Vc, and generated drive voltage Vdr is applied to motor coil 47.
Next, the structure and operation of aforementioned torque command corrector 54 are further detailed.
As is known by a d-q axis in motor vector control, the d axis is an axis in a magnetic flux direction of permanent magnet 43 of rotor 41 in brushless motor 100, and the q axis is an axis whose phase is advanced for 90 degrees in the rotating direction from the d axis. When current in the d axis is d-axis current id, current in the q axis is q-axis current iq, d-axis inductance of motor coil 47 is Ld, q-axis inductance is Lq, induced voltage constant of synchronous motor is Ke, and the number of pole pairs is Pn; torque T of brushless motor 100 is expressed with Formula 1 below.
Formula 1
T=P
n
{K
e
i
q+(Ld−Ld)idiq} (1)
One of the most popular control methods that have been employed in brushless motors is the id=0 control to keep the d-axis current at 0. In this case, a current vector moves on the q axis according to the load state. It is apparent from Formula 1 that reluctance torque Tr=0 when d-axis current id=0. Generated torque thus becomes only magnet torque Tm. In this case, Formula 1 is transformed to Formula 2 below. It is apparent from Formula 2 that the torque is proportional only to q-axis current iq. Accordingly, linear control of torque becomes easy.
Formula 2
Tm=PnKeiq (2)
Formula 3 can be transformed to obtain induced voltage constant Ke in Formula 4 below.
On the other hand, torque Tstd of a reference motor whose induced voltage constant Kstd is already known is expressed with Formula 5 below based on Formula 2.
When torque Tsmp1 and induced voltage constant Ksmp1 of a mass-produced motor are assigned to Formula 5, Formula 6 below is obtained.
Based on Formula 4, when (std is unloaded speed on applying voltage Va to the reference motor, induced voltage constant Kstd is expressed with Formula 7 below.
When Csmp1 is unloaded speed on applying voltage Va to a mass-produced motor under the same conditions, induced voltage constant Ksmp1 is expressed with Formula 8 below.
Following Formula 9 is obtained by assigning Formulae 7 and 8 to Formula 6.
It is apparent from the above that a torque value same as that of the reference motor is obtained by multiplying q-axis current iq by ωsmp1/ωstd in the mass-produced motor. Here, correction torque coefficient C(crr) of torque command corrector 54 is this ωsmp1/ωstd, which is a ratio between unloaded speed ωsmp1 of the mass-produced motor and unloaded speed ωstd of the reference motor.
As described above, torque command corrector 54 is provided as a torque correction means in the exemplary embodiment to correct torque command iq* output from speed controller 53, using correction torque coefficient C(crr). This correction of torque command (q-axis current command) eliminates torque variation due to individual differences of motors and enables to keep a fixed torque constant.
More specifically, the maximum speed in the unloaded state is measured in advance by applying a predetermined voltage to a motor coil of the reference motor with known torque constant as a standard motor. Then, the maximum speed in the unloaded state of all motors is measured under the same conditions in a mass production process. Correction torque coefficient C(crr) for correcting torque is then calculated based on that speed and the speed of the standard motor, i.e., ωsmp1/ωstd, which is a ratio between unloaded speed ωstd on applying a predetermined voltage to the motor coil of the standard motor in the unloaded state and unloaded speed ωsmp1 on applying predetermined voltage to motor coil 47 of synchronous motor 40 in the unloaded state. Torque command iq* is multiplied by correction torque coefficient C(crr) to correct the torque constant. This method for correcting torque constant in the exemplary embodiment can improve variation in motor torque. As for specific example, correction torque coefficient C(crr) based on the maximum unloaded speed measured in the mass production process may be stored in a storage part, such as a memory, for correction by torque command corrector 54.
The above description refers to a correction method using correction torque coefficient C(crr) based on unloaded speed when an applied voltage to the motor coil is fixed to be constant. However, correction torque coefficient Cv(crr) based on an applied voltage value when the motor speed is fixed to be constant may be used for correction as the torque correction means.
In this case, correction torque coefficient Cv(crr) is calculated as follows.
From Formula 4, induced voltage constant Kstd is expressed with Formula 10 below on applying voltage Vstd to rotate the reference motor at predetermined speed ωa.
On applying voltage Vsmp1 to rotate the mass-produced motor at predetermined speed ωa under the same conditions, induced voltage constant Ksmp1 is expressed with Formula 11 below.
By assigning Formulae 10 and 11 to Formula 6, Formula 12 below is obtained.
As described above, torque variation due to individual differences of motors can be corrected by multiplying torque command (q-axis current command) iq* of the mass-produced motor by correction torque coefficient Cv(crr), which is Vstd/Vsmp1. In other words, correction torque coefficient Cv(crr) may be Vstd/Vsmp1, which is a ratio between voltage Vstd applied to the motor coil when the reference motor with known torque constant is rotated at a predetermined speed and voltage Vsmp1 applied to motor coil 47 when each brushless motor 100 is rotated at the same predetermined speed in the unloaded state.
In the exemplary embodiment, corrected torque command iq*(crr), which is corrected torque, is used only in current control part 55. However, it may be used in other controller or arithmetic operation.
In
On the other hand, torque converter 32 performs unit conversion of motor current Idet detected by current detector 31 to torque, and outputs it as detected torque iq. Detected torque corrector 33 corrects detected torque iq, using correction torque coefficient Cd(crr), and sends corrected torque ig(crr) obtained to current control part 55. In the exemplary embodiment, detected torque corrector 33 is provided to further correct the detected torque based on detected motor current Idet, so as to keep a fixed torque constant.
Current control part 55 calculates voltage command Vc that achieves zero deviation between torque command iq* and corrected torque ig(crr), and outputs it to three-phase inverter 23.
Here, with respect to correction by detected torque corrector 33, a torque value same as that of the reference motor is achieved by multiplying detected torque (detected q-axis current) by correction torque coefficient C(crr)=ωsmp1/ωstd, as in Formula 9 in the first exemplary embodiment. In the exemplary embodiment, detected torque iq is corrected to eliminate torque variation due to individual differences of motors and keep a fixed torque constant.
In the exemplary embodiment, torque variation due to individual differences of motors can also be corrected by multiplying detected torque (detected q-axis current) by corrected torque coefficient Cdv(crr)=Vstd/Vsmp1, as in Formula 12 in the first exemplary embodiment.
As described above, the motor control device of the present invention can solve torque variation due to individual differences of motors, and is thus applicable to general motor control devices having a speed control part (including current minor loop), such as of a servo motor.
10, 11 Motor control device
20 AC power source
21 Rectifying circuit
22 Smoothing capacitor
23 Inverter
31 Current detector
32 Torque converter
33 Detected torque corrector
40 Synchronous motor
41 Rotor
42 Shaft
43 Permanent magnet
44 Bearing
45 Stator
46 Stator core
47 Motor coil
48
b Circuit board
48
p Circuit component
51 Position detector
52 Speed operation part
53 Speed control part
54 Torque command corrector
54
x Multiplier
55 Current control part
100, 101 Brushless motor
Number | Date | Country | Kind |
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2015-013835 | Jan 2015 | JP | national |
This application is a divisional of U.S. application Ser. No. 15/325,309, filed Jan. 10, 2017, which is the U.S. National Phase of International Application No. PCT/JP2016/000363, filed on Jan. 26, 2016, which in turn claims the benefit of Japanese Application No. 2015-013835, filed Jan. 28, 2015, the disclosures of which are incorporated by reference herein.
Number | Date | Country | |
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Parent | 15325309 | Jan 2017 | US |
Child | 16287601 | US |