JPS626437B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speed control device for a DC motor applied to a steel process line, etc., and in particular, the present invention relates to a speed control device for a DC motor applied to a steel process line, etc. By keeping the gain constant,
It is an object of the present invention to provide a control device that has good control performance during acceleration and deceleration and has very high stability. In general, a shared power supply system is adopted in steel process lines such as electric resistance welding pipe equipment and continuous plating equipment.
Each DC motor group as a roll drive motor for each stand is controlled at a predetermined speed by individual field control, and Figure 1 shows the specific configuration of this process line. In the figure, ₁₀ to 1n indicate the armatures of the DC motors that drive the rolls of each stand, and ₂₀ to 2n indicate the field windings thereof. ₃₀ to 3n are small generators for speed detection that extract the actual speed of each motor, and 4 is a reference motor _10.
A thyristor rectifier constructed by connecting thyristors in a pure bridge with a field power source is applied. Reference numeral 5 denotes a thyristor rectifier as a shared power source, and two sets of thyristor rectifiers connected in antiparallel are used to perform predetermined power running operation, regenerative operation, etc. Reference numeral 6 is a current detection current transformer for extracting the AC input current from the power supply side, 7 is a first comparison circuit that compares the speed command signal and the actual speed detection signal, and 8 is a speed control amplifier that performs these comparisons. The circuit 7→amplifier 8 constitutes a major loop speed control system. 9 is a second comparison circuit that compares the current setting signal and the current detection signal;
10 is a current control amplifier, 11 is a pulse generation circuit, and these comparison circuit 9, amplifier 10, and pulse generation circuit 11 constitute a minor loop current control system. With this configuration, predetermined control is performed to maintain the power supply voltage of the shared bus of _each motor group at the command value. Specifically, 12 ₁ to 12n are shunt resistors for taking out the armature current of each motor, 13 is a third comparison circuit that compares the speed setting command signal and the actual speed detection signal, and 14 is a speed control circuit. The comparator circuit 13 and the amplifier 14 constitute a speed control system of a measurer loop. 15 is a fourth comparison circuit that compares the current setting command signal and the armature current detection signal, and 16 is an amplifier for armature current control. These comparison circuits 15 and amplifier 16 form a minor loop armature current control system. is configured. 17 is a fifth signal that compares the field current setting command signal and the field current detection signal.
18 is a field current control amplifier,
Reference numeral 19 denotes a pulse generation circuit, and the comparison circuit 17, amplifier 18, and pulse generation circuit 19 constitute a minor loop field current control system. 20 is a thyristor rectifier serving as a variable power source for the field, and 21 is a current detecting current transformer for extracting field current. The field current control system has exactly the same circuit configuration even in other motor groups, for example, motor 1n in the figure.

The operation of the conventional device configured as described above is illustrated in the field current If-speed N characteristic diagram shown in FIG. 2, for example.
As is well known, up to the base rotation speed NB,
The field is strengthened so that the strongest field current IR can be passed through the field winding ₂₁ by the thyristor rectifier 20, while the bus voltage of the common bus, that is, the armature voltage of the motor group, is controlled by the thyristor rectifier 5. A predetermined armature voltage control is performed that is controlled according to the command value and raised to approximately the rated voltage value. When accelerating the motor speed to the rated rotation speed NR under such conditions, the field current If is controlled via the major loop speed control system and the minor loop current control system of the field control system, as shown in the characteristic diagram in Figure 2. A predetermined field control is performed to gradually narrow down the field current from the strongest field current IR to the weakest field current IB, and the rotation speed is accelerated to the rated rotation speed. It goes without saying that in this field control range, the armature voltage of the motor group is automatically controlled to a predetermined rated voltage by the thyristor rectifier 5 of the shared power supply. In this way, during steady state, a predetermined field control is performed for each motor individually via the field control system of each motor, and speed control or torque control is performed. However, the problem with this operating method is that the second In the characteristic diagram shown in the figure, in the armature voltage control range up to the base rotation speed NB, for example, even if the value of the field current If is changed, the rotation speed change range ΔN does not become very large, but it is higher than the base rotation speed NB. As is clear from the figure, in the field control range up to the rotation speed NR, even if the value of the field current If is slightly changed, the range of change in the rotation speed becomes a very large value. The value of is the weakest field current near the strongest field current IR.
It can be understood that the variation width ΔN of the rotational speed becomes large near IB, and at the same time, it can also be understood that the variation width of the rotational speed differs depending on the value of the field current. What this phenomenon means is that the loop gain of the control system is significantly different between the strong field control region and the weak field control region.In particular, the loop gain is the smallest in the strong field control region, and the loop gain is the smallest in the weak field control region. This means that the loop gain is largest near the highest field weakening current IB where the gain is large. In this way, the loop gain changes particularly in the field-weakening control region, so in the conventional device shown in Fig. 1, the field control system is adjusted based on the field-weakening control region in order to improve stability in the field-weakening control region, where the gain changes rapidly, for example. The loop gain is determined. Therefore, stable operation can be achieved in the field weakening control region, especially in the range where the change in gain is small, but stable operation cannot be expected at all near the maximum field weakening current IB where the change in gain is large. It becomes something that does not exist. Furthermore, in the field-strengthening control region, the loop gain of the control system is much smaller than in the field-weakening control region, so the response of the control system is poor and quick-response control cannot be performed. In this way, the difference in loop gain between the strong field control region and the weak field control region in individual motors not only causes problems in terms of controllability and responsiveness, but is especially important as shown in Figure 1. In the case of a shared power supply system, the above problems are combined with factors such as the fact that the field current-speed characteristics of individual motors are different, and the setting command amount given to the control system is different. Therefore, for example, between electric motors for driving rolls that are directly connected mechanically in a product material such as a steel bar,
Differences occur in the rotational speed and acceleration dN/dt during deceleration, resulting in tensile torque and pressing torque, which has fatal drawbacks such as damage to the product.

The present invention was invented in view of this point, and will be described in detail below based on the embodiment shown in FIG. The embodiment shown in Fig. 8 shows a specific circuit configuration diagram of the field control system using the motor ₁₁ shown in Fig. 1 as an example. The same reference numerals are given, and 22 is a bias amount setting device for setting the required bias amount;
3 is a sixth comparison circuit that compares the set bias amount and the field current detection signal, 24 is an amplifier with a limiter for amplifying the deviation amount from the comparison circuit, that is, the correction signal, and 25 is a gain correction circuit. A lower limiter setting device for setting the lower limit value of the signal, 25-2
7 is a maximum value derivation circuit for deriving the maximum value of the correction signal. These set values 22 to 25, the comparator circuit 23, the amplifier 24, and the maximum value deriving circuit constitute a function generating circuit that generates a gain correction signal, which is the main part of the present application, and the gain correction signal is shown in FIG. The output signals Y and V have such characteristics with respect to the field current If, and the output signal Y, which is this correction signal, is, for example, the field current If-velocity N shown in FIG.
First, a characteristic diagram of the rate of change ΔN of the motor speed N with respect to the rate of change ΔIf of the field current If is determined in the characteristic diagram, and this characteristic diagram of the rate of change ΔN/ΔIf is shown in Figure 3. The rate characteristics are obtained by tangential approximation using a straight line as shown in FIG. Note that in the characteristic diagram of FIG. 4, curve A directly represents the change rate ΔN/ΔIf characteristic of FIG. 3, and similarly, straight line B is a tangential approximation of the characteristic of A. The function generating circuit having the above configuration generates the gain correction signal obtained in this way, and the amplifier with limiter 24, for example, starts from the point of the strongest field current IR in the characteristic diagram of FIG. The required gain correction signal Y, V with the characteristics up to the point of current IB
The amplifier characteristics and the set value of the bias amount are defined in advance so as to generate the following. Further, the setting device 25 outputs the lower limit value of the correction signal.
The correspondence relationship between the lower limit limiter value and the amplifier output is defined in advance so that signals Y and V with required characteristics can be obtained in the field strength control region shown in FIG. 5. Returning again to the embodiment shown in FIG. 8, 28 is a division circuit. This circuit is a circuit that divides the field current command signal X given from the armature current control system by the correction signal Y. The characteristics of this calculation result are as follows. As shown in the characteristic diagram of FIG. 6, Z is a characteristic with respect to the Y axis, which is different from the rate of change characteristic of FIG. 3. 29 is the output Z=- of the arithmetic circuit
This is an amplifier circuit to temporarily amplify the field current command signal KX/Y.

To describe the operation of this embodiment configured as above, in the strong field control region until the motor speed reaches the base rotation speed NB, the actual speed detection signal of the motor is small compared to the speed setting command amount, so a minor loop occurs. The maximum motor current setting command amount is given to the armature current control system of the comparator circuit 15 →
28 through the path of the armature current control amplifier 16
The strongest field current command signal X is given to the dividing circuit. On the other hand, in the function generation circuit which is the main part of the present application, the actual detection signal of the field current and the 22
The bias amount setting signal given from the bias amount setting device is almost balanced, and the signal given from the lower limit limiter setting device 25 to the diode 27 is almost balanced compared to the signal given from the limiter amplifier 24 to the diode 26. The signal generated by
A gain correction signal Y ₁ corresponding to is inputted to 28 division circuits. Therefore, in the 28 division circuits, based on the input signals X and Y, -
A predetermined calculation KX/Y (where K is a constant) is performed, and the result of this calculation is once amplified by an amplifier circuit 29 and given as a required field current command to the field current control system of the minor loop. This field current command signal Z is the strongest field current command amount as shown in the characteristic diagram of Fig. 6, so in the strong field control region, the field current command signal Z is transmitted through the field current control system according to this strongest field current command. The field current is controlled by

Next, in the field weakening control region where the rotation speed is accelerated from the base rotation speed NB to the rated rotation speed NR, the balance between the set bias amount and the field current detection signal begins to collapse in the function generation circuit, causing an amount of deviation. The relationship between the signal obtained by amplifying this deviation amount and the lower limit limiter command signal is that the limiter command signal is smaller, so that the gain correction signal derived from the diode 26 is input to the divider circuit 28, and the limiter command signal is smaller. A predetermined division is performed between the signal X input in the division circuit and the field current command signal Y derived from the armature current control system, and the field current is controlled according to the command value based on the result of this calculation. In other words, the gain correction signal Y derived from the function generation circuit has a deviation amount between the bias setting amount and the field current detection signal that gradually increases depending on the value of the field current If, so the gain correction signal Y derived from the function generation circuit is As shown in the characteristic diagram in the figure, the field current increases linearly in inverse proportion to the decrease. On the other hand, in the major loop speed control system, the deviation between the speed setting command amount and the actual speed detection signal is large, and the 14 speed control amplifiers are still in a saturated state, and in the minor loop armature current control system, the acceleration torque In order to further increase
The armature current control amplifier No. 6 also maintains a substantially saturated state. Therefore, the signal Z output from the division circuit 28 gradually decreases according to the value of the field current as shown in the characteristic diagram of FIG. 6 by the amount that the signal Y derived from the function generation circuit increases. Go. The characteristic diagram shown in FIG. 7 shows the correspondence between the characteristics of the output signal Z of the divider circuit 28 and the ratio ΔN/ΔIf of minute changes in the actual motor. Similarly to the output signal characteristics of the circuit, B shows the characteristics of the ratio ΔN/ΔIf of minute changes, and as is clear from the characteristic diagram in Fig. 7, the actual motor characteristics are particularly in the field weakening control region. The minute change ΔN in the motor speed is larger than the minute change ΔIf in the field current, and as the field current If becomes smaller, the relative ratio gradually increases. The characteristics of the field current command signal Z output from the divider circuit No. 28 are completely opposite to the motor characteristics A described above, and are intended to suppress the increase in motor speed by the amount that the field current decreases. Therefore, equivalently, the loop gain of the control system is always constant, as the motor speed changes by the proportion that the field current changes.In particular, keeping this loop gain constant is due to field weakening control. Sometimes its effects are noticeable. Although this embodiment used a method in which the speed-field current characteristic of the motor was plotted at two points and approximated by a straight line as a gain correction signal, it is also possible to plot multiple points and perform a tangential approximation; in this case, Since the correction signal more closely approximates the motor characteristics, it is possible to realize a device with very good controllability. Furthermore, although the case has been described in which ΔN/ΔIf is linearly approximated as the gain correction signal, it is also possible to calculate the rate of change of the speed and field current through a differentiating circuit and use this directly. Furthermore, a minute change in the field current may be taken out and used directly as a gain correction signal.

As described above, in the present invention, predetermined field control is performed in the field strengthening control region and the field weakening control region, respectively, based on the correction signal that corrects the loop gain of the control system. It has various effects.

Since the loop gain of the control system is held constant during predetermined field control, very stable predetermined speed control or torque control can be performed over the entire operating range.

Based on the advantages mentioned above, the control performance especially during acceleration and deceleration can be improved, and when performing uniform speed control, etc., there is no tension torque, pressing torque, etc. between the rolls that are mechanically directly connected with the material. Since this process does not occur, productivity can be greatly increased.

Since a circuit that generates the speed-field current characteristic of the motor may be used as a gain correction signal that keeps the loop gain constant, the circuit configuration can be simplified and an economical device can be realized.

[Brief explanation of the drawing]

Figure 1 is a specific circuit configuration diagram showing the motor control system when speed control-torque control etc. are performed using a shared power supply system, Figure 2 is a characteristic diagram showing the speed-field current characteristics in that case, and Figure 3 is a characteristic diagram showing the speed-field current characteristics in that case. The figure shows the characteristic speed and ΔN/ΔIf according to the present application when the field current is slightly changed.
FIG. 4 is a characteristic diagram of the gain correction signal according to the present application when its characteristics are linearly approximated; FIG. 5 is a characteristic diagram showing the characteristics of the correction signal output from the gain correction system according to the present application; FIG. The figure is a characteristic diagram showing the characteristics of the field current command signal output from the divider circuit according to the present application, and Figure 7 is the minute change rate Δ of speed - field current.
FIG. 8 is a characteristic diagram showing the correspondence between the N/ΔIf characteristic and the field current command signal characteristic, and FIG. 8 is a specific circuit configuration diagram showing an embodiment according to the present invention. 13-15-17-23 is a comparison circuit, 14 is a speed control amplifier, 16 is an armature current control amplifier, 18 is a field current control amplifier, 19 is a pulse generation circuit, 20 is a field thyristor rectifier, 22
is a bias setting device, 24 is an amplifier with a limiter, 2
5 is a lower limit value setter, and 28 is a division circuit.

Claims (1)

[Claims] 1. A field control system in which the speed control system is a major loop, the first minor loop of the armature current control system is installed inside the major loop, and the second minor loop of the field current control system is installed inside the major loop. Until then, armature voltage control is performed on the field side with the strongest constant field control, and when accelerating from the base rotation speed to the rated rotation speed, the armature voltage is constant and field weakening control is performed on the field side. In this case, a correction system is provided that outputs the rate of change characteristic ΔN/ΔIf, which expresses the speed N-field current If characteristic of the motor as a minute rate of change, as a gain correction signal, and the correction output from this correction system is A signal X obtained by amplifying the armature current deviation amount derived from the armature current control system from the signal Y.
A speed control device for a DC motor, characterized in that a division circuit for dividing by is inserted into an armature current control system, and the output of the division circuit is given to the field control system as a field current command signal.