JPS63283491A - Current control system for synchronizing servomotor - Google Patents

Abstract

PURPOSE:To increase an output torque, by a method wherein a minimum value among the angles of lead of a phase, which is capable of equalizing the value of maximum current capable of being conducted through a servomotor to an allowable current value, is operated based on an input voltage and the allowable current value in accordance with the rotating speed of the motor. CONSTITUTION:A position controller 1 outputs a speed command in accordance with a difference between a position command and a position signal. A speed control device 2 outputs a current command in accordance with the difference between the speed command and a speed signal. A current control device 3 controls a power circuit 4 in accordance with a difference between the current command and a current signal. In this case, the minimum value among the angles theta of lead of the phase of current, which is capable of increasing a current, conducted through a motor, is operated based on the power source voltage and the allowable current value when the speed of the motor has become higher than a speed, in which the terminal voltage of the motor arrives at the power source voltage or higher. When the angle theta is positive, the angle of lead is made theta while the angle of lead of the phase is nullified to control the phase of the current when the angle theta is negative.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a current control method for a synchronous servo motor, and in particular, the present invention relates to a current control method for a synchronous servo motor, and in particular, even if the rotational speed of the servo motor increases beyond a predetermined value, the maximum current that can flow through the servo motor increases. The present invention relates to a current control method for a synchronous servo motor that increases the output torque of the servo motor by making the current value equal to an allowable current value set for the servo motor.

[Conventional technology]

Generally, this type of synchronous servo motor is configured to receive a simulated AC voltage obtained by full-wave rectification of a three-phase AC power source and further pulse modulation (PWM).
When the rotational speed of the motor increases above a certain value, the current that can flow through the motor becomes limited by the input voltage from the power source.

In addition, the drive circuit of this type of synchronous servo motor is generally connected to a predetermined drive amplifier depending on the rating of the motor, and the allowable current value that can be passed through the motor is limited depending on the capacity of the drive amplifier. The current is normally set to several times the current required for the motor to produce its rated torque.

FIG. 10 shows the speed-torque characteristics of such a synchronous servo motor. If the allowable current value (effective value) of the motor set as described above is 1IIIa×, then Until the rotational speed ω of the motor reaches a predetermined value ω, the current of the motor can be increased to the allowable current value Imax, and therefore the output torque T of the motor is Kt−1max (where (KL is a torque constant) (the so-called current limit region where the output torque is determined by the allowable current value)
However, if the rotational speed ω of the motor exceeds the predetermined value ω1, the current that can flow through the motor is limited by the input voltage, and therefore cannot be increased to the allowable current value 1a+ax. When entering the voltage limit region, the output torque of the motor gradually decreases, and the rotational speed ω of the motor decreases.
When becomes 02 or more, the output torque becomes zero.

Here, the output torque T of the motor is T=Kt-1-cosθ (where Kt is the torque constant, c
osθ is expressed as power factor). Normally, especially when the phase control of the motor is not performed, θ=0 and the power factor is 1, but in the voltage restriction region as described above, the motor current must be increased to the above-mentioned allowable current value 1 wax. As a result, the output torque gradually decreases as described above.

Figure 11 shows the power supply voltage (DC conversion value) Vmax input to the synchronous servo motor and the terminal voltage V of the motor.
is a vector diagram showing the relationship between the rotational speed of the motor, ω, the back electromotive force constant (back electromotive force for one phase per unit rotational speed), and R the winding resistance of the motor (1 phase component) and L is the winding inductance (l phase component) of the motor, then the terminal voltage of the motor at a predetermined rotational speed ω is calculated by adding ω to the back electromotive force generated in the motor and the windings in the motor. It is a vectorial combination of the resistance and the voltage drop caused by the winding inductance, and it is clear that the terminal voltage V must be equal to or lower than the power supply voltage VmaxO value. Note that the solid line in the vector diagram above indicates that no phase control of the motor is performed (i.e., θ=0) as described above.
A vector diagram of the case is shown.

As is clear from the vector diagram of the solid line, as long as the rotational speed ω of the motor is small, even if the current of the motor is increased to the allowable current value 1 wax, the terminal voltage ■ will not be lower than the power supply voltage Vsax. (the vector of the terminal voltage ■ does not go outside the circle with the radius of the Vmax), but if the rotation speed exceeds the predetermined value ω1, the resulting back electromotive force As K ttz + increases, the terminal voltage V reaches the power supply voltage Vmax before the motor current reaches the allowable current value 1max, and it is impossible to further increase the motor current to the 1a+ax. become unable. (In other words, the vector of the terminal voltage V goes outside the circle whose radius is Vmax).

As a result, the output torque of the motor gradually decreases, and when the motor rotational speed increases to ω2 and the value of ω2 in the back electromotive force reaches the Vmax, no current can flow through the motor. , as a result, the above first
As shown in the θ diagram, the output torque T becomes 0.

[Problem that the invention seeks to solve]

In such conventional technology, when the rotational speed of the motor exceeds a predetermined value ω, as shown in FIG. There is a problem. Therefore, when the rotational speed of the motor increases to a predetermined value or more, by appropriately advancing the phase of the motor current by a predetermined expected value θ', the motor speed increases as shown by the dotted line in FIG. It is conceivable to increase the current that can flow to a certain extent (that is, even if the current is increased from 1 to ■', the vector of the terminal voltage V' at that time will be within a circle whose radius is Vmax), Even in this case, there is a problem in that the phase control is merely based on a prospective phase, and the increase in the current value, that is, the torque, is still insufficient.

The present invention was made in order to solve such problems, and each of the motors has an influence on the power supply voltage input to the motor, the allowable current set for the motor, and the terminal voltage of the motor. Considering the characteristics (i.e., back electromotive force constant, winding resistance, winding inductance, number of motor poles, etc.), the maximum current value that can flow through the motor is equal to the allowable current value Ill1ax (i.e., the motor The optimal phase advance angle θ (which allows the current to flow up to the allowable value Iwax) is calculated in real time according to the rotational speed of the motor, thereby increasing the output torque as much as possible regardless of the increase in the motor rotational speed. It is designed so that it can be increased.

Measures for Solving Problem c] In order to solve the above problem, the present invention also provides a method for controlling the voltage input to the synchronous servo motor and the allowable current value set for the synchronous servo motor. Then, calculate the minimum value of the phase advance angles that can make the maximum current value that can flow through the servo motor equal to the allowable current value according to the rotation speed of the motor, and calculate the calculated phase advance angle. A current control method for a synchronous servo motor is provided, which controls the phase of the current of the servo motor according to the current phase of the servo motor.

[For production]

According to the above configuration, during the rotational operation of the servo motor, the maximum current value that can flow through the servomotor can be made equal to the cough allowable current value (that is, during the rotational operation of the servomotor, the motor current is adjusted to the allowable coughing current value). current value)
The minimum value of the phase advance angle (i.e., the phase advance angle at which the power factor cos θ is maximum among the phase advance angles that satisfy the above conditions)
can be calculated in real time according to the rotation speed of the motor, and the output torque can be increased as much as possible according to the rotation speed of the motor.

〔Example〕

It is known that the following equation holds true regarding the control of a synchronous servo motor, and the present invention is also based on the use of the following equation. That is, Vsax≧
(K ω + (Rcosθ −k ω Lsin
θ)■)2+ (Rsinθ+ to ωLcosθ)! ■2
= (kω)”+(R”+(kωL)”)I”-2ω
/Y exit] Otsu tile door 1stn (θ-φ) - (1) further K
is the back electromotive force constant for one phase mentioned above, R is the winding resistance for one phase, L is the winding inductance for one phase, k is the number of motor poles, V wax is the power supply voltage (DC conversion value) T wax is the allowable current value (effective value), and θ is the phase advance angle of the current, and ω is the motor rotation speed.

Now, to explain the above equation (1), in the vector diagram shown in Fig. 3, the terminal voltage of the motor is equal to ω and the back electromotive force generated in the motor at a certain rotational speed ω. It is a vectorial combination of the voltage drops IR and IωL caused by the winding resistance and winding inductance in the motor (shown by the right side of equation (1) above), and the vector length of the terminal voltage is equal to the power supply voltage. (Voltage input to the motor) Inside the circle whose radius is Vsax (
or on its circumference). In the vector diagram of Fig. 3, the voltage drop caused by the above-mentioned inductance is indicated as ωL, but generally when the number of poles of the motor is k, the voltage drop caused by the inductance is ωLl.
(In other words, ω is the rotational speed expressed in electrical angle).

Here, in the present invention, in order to calculate the phase advance angle θ that can increase the current flowing through the motor to the allowable current value 1 wax at a certain motor rotation speed ω, the above (
In equation 1), the value of θ that satisfies the following equation (3) is calculated as Iwl+ax. That is, ...(3) Therefore, -.(4) In this way, the above conditions are satisfied (i.e., the I IIa
The phase advance angle θ that can flow up to the allowable current value rmax may be within a range that satisfies the above equation (4), but in this case, in the present invention, the phase advance angle By setting the minimum value of (that is, θ when the equality sign holds in equation (4) above) as the phase advance angle θ at the rotation speed ω, the power factor cos θ is made as large as possible, and Output torque (
In other words, the objective was to increase Kt - Imax - cos θ) as much as possible. Here, the value of θ (which changes depending on the rotational speed ω) is in the range of 0≦θ≦− as a practical matter, and if the above θ becomes a negative value at a certain rotational speed, the following As shown in Figure 4, there is a margin (
In other words, even if the motor current is increased to the allowable current value Iwax, the vector of the terminal voltage
In such a case, θ=0 and no phase control is performed.

Hereinafter, in the present invention, various aspects of controlling the phase of the motor current according to the motor rotation speed will be described with reference to FIGS. 4 to 6.

First, the rotation speed ω of the motor is in the range O≦ω≦ω (where ω is the value of ω obtained as θ=O in the equation (3) above), that is, the motor rotation speed is If the speed is lower than ω, as shown in FIG.
Even if it increases to llax, the vector of terminal voltage ■ exists inside a circle whose radius is Vmax, so the phase advance angle θ remains zero. In this case, the output torque can range up to Kt-IIlax, and acceleration can be achieved with respect to the load torque within that range.

Next, the rotational speed ω of the motor increases, and when ω1≦ω≦, as shown in FIG. By advancing the current phase up to the allowable current value r
o+ax, thereby increasing the output torque (Kt - Imax - CO3θ) as much as possible. In this case, the power factor cos θ itself is lower than when the phase control is not performed (that is, θ = 0), but the motor current can be increased to the allowable current value 1 wax, and (4) By employing the equation in the equation, the output torque can be increased as much as possible compared to the conventional technology by minimizing the decrease in the power factor, as shown in FIGS. 7 and 8 below. As shown in

Furthermore, when the rotational speed ω of the motor increases and becomes ω≧ω (a range in which no motor current can flow as shown in Fig. 10 if phase control is not performed), the 6th As shown in the figure, by advancing the current phase to a value of θ that satisfies the equation (4) above, the motor current can be increased to the allowable current value I n + ax, and within this rotation speed range. Also, as shown in FIGS. 7 and 8, the output torque can be increased as much as possible.

In this rotational speed range (ω>ωt), as is clear from Fig. 6, the value of the motor current is particularly small (that is, the load is too small), and the motor current cannot flow, that is, the terminal voltage There is a region where the vector cannot reach the circumference with the radius of V*ax, but excluding such a small current region, the above allowable current value I as the motor current
It is clear that up to wax can be achieved, and the output torque in this rotational speed range can be increased as much as possible while minimizing the drop in power factor.

FIG. 1 is a block diagram of a servo system to which the current control method of the present invention is applied. A position control signal for the servo motor 5 is output from the position control bag W1 according to the feedback signal, and then a position control signal for the servo motor 5 is output by the position control signal and the servo motor 5.
The servo motor 5 is controlled by the speed controller 2 by a speed feedback signal from the speed detector 6 which detects the speed of the servo motor 5.
A speed control signal is output to the servo motor 5, and a current control device is controlled by the speed control signal and a current feedback signal from a current detector (usually provided on the output side of the power circuit 4) that detects the current supplied to the servo motor 5. 3, the current (current value and phase) supplied to the servo motor 5 is controlled, and a predetermined drive current is supplied to the servo motor 5 via the power circuit (drive amplifier) 4.

In performing the above position control, speed control, and current control, for example, an RO in which a predetermined program is stored is used.
It is also possible to control by software using M,
In that case, in the present invention, when the value of the motor rotational speed ω becomes 01 or more, the value of the phase advance angle θ that satisfies the equation in the above equation (4) is determined, for example, as shown in FIG. The current phase of the motor is controlled by using a ROM in which a program is stored and performing calculations according to the program.

That is, FIG. 2 is a flowchart showing the processing procedure when performing current phase control according to the present invention. First, in step l, the motor rotation speed ω is input, and in step 2, the equation in equation (4) above is input. A phase lead angle θ that satisfies the formula is calculated, and if it is determined in step 3 that the calculated phase lead angle θ is θ>O, in step 4 the current phase is controlled by the phase lead angle θ, On the other hand, if the determination as to whether θ>0 in step 3 is negative, the phase advance angle θ is set to zero in step 5, and after setting the current phase in this way, a predetermined current is set in step 6. The command is output to the motor side.

FIGS. 7(a) and 7(b) show the speed-current characteristics and speed-torque characteristics of the motor when the present invention is applied, respectively, and the phase advance angle θ that satisfies the equal sign in equation (4) above.
By controlling the current phase according to
), regardless of the rotational speed of the motor, the motor current can flow up to the allowable current value 1max (that is, the current limit region) set for the motor. In this case, when the motor rotation speed ω exceeds ω, the above angle θ gradually increases (that is, the power factor cos θ gradually decreases), but the minimum value of the angle θ that satisfies the above equation (4) (that is, ( 4) By setting the angle θ) that satisfies the equation in the equation as the phase advance angle, the decrease in the power factor cos θ (that is, the decrease in the output torque based on the decrease in the power factor) is minimized, and the above-mentioned 10th Speed in the prior art shown in the figure -
Compared to the torque characteristics, it is possible to significantly increase the output torque at rotational speeds of 01 or higher (that is, in the voltage restriction region).

(See Figure 7(b)). In addition, when the motor rotation speed is 02 or higher, the motor current (and therefore the output torque)
As mentioned above, there is a region in which it is impossible to lower the current below a predetermined value (see the range of ω≧ω2 in Figures 7(a) and (b)), but as long as this region is excluded, the above-mentioned allowable current Figure 7 (b) shows how the motor current can flow up to the value Iwax and output torque within a specified range
) as shown.

An example of specific data when the present invention is applied is as follows.

That is, the electromotive force constant K -50V/1000 revolutions (1
The power supply voltage Vmax is 200 and 170 V (
When inputting the three-phase AC vibration medium value), when the phase advance control i11 according to the present invention is performed, the allowable current value I max for the acid motor regardless of the rotation speed of the motor
can be set to, for example, 40 amperes.

FIGS. 8(a) and 8(b) specifically show examples of speed-current characteristics and speed-torque characteristics, respectively, when phase lead control according to the present invention is performed on a motor having the above characteristic values. ing. That is, as shown in FIG. 8(a),
In the case of any of the above-mentioned power supply voltages, it is possible to flow a motor current up to 40 amperes, which is set as the allowable current value 1 wax of the motor, regardless of the rotation speed of the motor. As mentioned above, when the motor rotation speed exceeds the above ω2, a small current region occurs where no current can flow through the motor. The case where it is 200■ is shown. Furthermore, as shown in FIG. 8(b), when the motor rotation speed exceeds approximately 1000 rotations/synchronization, the speed-torque characteristic of the motor shifts from the so-called current limit region to the voltage limit region (the solid line indicates the power supply voltage 200 mm). In the case of , the dotted line is the power supply voltage 1
70V), by increasing the motor current to the permissible current value (40 amperes in this case), the decrease in output torque can be minimized despite the decrease in power factor due to the increase in phase advance angle θ. Compared to the speed-torque characteristic (shown in FIG. 9) when such phase control is not performed, the output torque in the voltage limited region can be greatly improved, and the motor rotation speed is approximately 2000 rpm. Even if the current exceeds the rotational torque ω2 (corresponding to the rotational torque ω2), it is possible to generate an output torque within a predetermined range, except for the above-mentioned small current region.

〔Effect of the invention〕

According to the present invention, even when the rotational speed of a synchronous servo motor increases and its output torque enters a region limited by the power supply voltage, the motor current is increased to the allowable current value set for the motor. Accordingly, it is possible to measure a large increase in output torque.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a servo system to which the current control method according to the present invention is applied; FIG. 2 is a flowchart when current phase control is performed using the current control method according to the present invention; FIG. is a general vector diagram showing the relationship between power supply voltage and terminal voltage for a servo motor to which the current control method according to the present invention is applied, and FIGS. 4, 5, and 6 are general vector diagrams according to the present invention. FIGS. 7(a) and 7(b) are vector diagrams showing the relationship between the power supply voltage and terminal voltage for the servo motor for various rotational speed ranges of the servo motor when the current control method is applied. Figures 8(a) and 8(b) show the speed-current characteristics and speed-torque characteristics of the servo motor when the present invention is applied, respectively. Figure 9, a diagram showing one specific example of flow characteristics and speed-torque characteristics, is similar to Figure 8 (b) above.
) is a diagram showing a specific example of the speed-torque characteristics of the servo motor when the conventional technology is applied, and FIG. Figure 11, which is a diagram showing general speed-torque characteristics, compares the relationship between the power supply voltage and terminal voltage for the servo motor when current phase control is not performed and when current phase control is performed. FIG. (Explanation of symbols) 1...Position control device, 2...Speed control device, 3.
...Current control device, 4...Power circuit, 5...Servo motor, 6...Speed detector, 7...Position detector. Figure 1 Figure 2 $3 Figure 4 [ Figure 5 Figure 6 Figure 7 (a) Figure 7 (b) Number of revolutions (r, p, m) Figure 8 (a) Number of revolutions ( r, p, m) Figure 8 (b) Number of revolutions (r, p, m) Figure 9

Claims (1)

[Claims] 1. Based on the voltage input to the synchronous servo motor and the allowable current value set for the synchronous servo motor, the maximum current value that can flow through the servo motor can be made equal to the allowable current value. A synchronous servo motor characterized in that the minimum value of the phase advance angles is calculated according to the rotation speed of the motor, and the phase of the current of the servo motor is controlled according to the calculated phase advance angle. current control method.