JPH01177890A - Current controller for motor - Google Patents

Abstract

PURPOSE:To increase the speed of response by adding a field forward compensating element to a minor loop controlling the rate of change of currents. CONSTITUTION:In a current control circuit 5, the difference of a mean current command value I0 and mean currents I1 detected by a mean current detector 12 is taken, and the difference is used as the current change rate command I2 of a minor loop through a first compensating element 7. In the minor loop, the difference of the command I2 and an output I3 from a current change rate detector 6 is input to a second compensating element 8, and employed as a voltage command to a gate pulse generator 3. A third compensating element 9 is mounted to the minor loop, and a second voltage command to the gate pulse generator 3 from the current change rate command I2 is formed. The two voltage commands are added, and a final voltage command VP to the gate pulse generator 3 is acquired.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a current control device for a motor, and particularly to a current control device suitable for controlling a DC motor in which commands and disturbances are frequently changed.

[Conventional technology]

A current control device for a DC motor is particularly required to have good response characteristics to the commands and disturbances when current commands and disturbances are frequently applied to the motor. A control device for this purpose is disclosed in Japanese Patent Publication No. 57-58875, in which a measure loop for controlling the average current is used.
Double-loop control is performed with a minor loop that controls the current rate of change. This allows the gain of the major loop to be set larger by compensating for the nonlinearity of the motor and current converter using the minor loop, thereby improving the control accuracy of the average current.

[Problem to be solved by the invention]

Since the conventional technology uses only feedback control,
For stabilization, it is necessary to use an integral element, and it is not possible to compensate for the first-order lag element that occurs as an electrical characteristic of the motor. Therefore, when the current command changes in a stepwise manner, the motor current should normally increase immediately, but it usually starts increasing with a delay of 3 to 4 ms. This sets the target response time to 10 mS as recently
If you try to do so, it will result in a fatal delay time.

An object of the present invention is to provide a current control device for a motor that can compensate for this -order lag characteristic and obtain current response performance with almost no lag time.

[Means to solve the problem]

The purpose of the above is to input a current change rate command to a minor loop that controls current change rate control, and a feedforward compensation element connected so that its output is added to the current change rate control output of the minor loop. This is achieved by adding .

[Effect]

Since the control system using the feedforward compensation element does not include a delay due to minor loop control, the command voltage corresponding to the command change can be immediately output to the gate pulse generation circuit, and the response speed can be increased.

〔Example〕

An embodiment of the present invention will be described below. FIG. 1 shows an embodiment in which the present invention is applied to a current control system of a DC motor, in which the current of a DC motor 1 supplied from a power converter 2 consisting of a thyristor or the like is controlled by a current control circuit 5. It is adjusted by the gate pulse generation circuit. The current control circuit 5 has an average current detection circuit 12. Current change detection circuit 6. First compensation element for major loop 7. It consists of a second compensation element 8 for the minor loop and a third compensation element 9 which is a feature of the invention.

The average current command value Io to the current control circuit 5 is determined by the average current detected from the output of the current detector 4 by the average current detection circuit 12. This becomes the loop current change rate command I2. In the minor loop, the difference between this command I2 and the output T3 of the current change rate detection circuit 6 is input to the second compensation element 8, and becomes a voltage command to the gate pulse generator 3. Up to this point, the device is the same as the conventional device, but in the present invention, a third compensation element 9 is provided in this minor loop to generate the second voltage command to the gate pulse generator 3 from the current change rate command I2. , this compensation means feedforward compensation of the current rate of change control system. The two voltage commands are added to obtain the final voltage command Vp to the gate pulse generator 3. Gate pulse generator 3 generates a pulse signal that operates power converter 2 .

FIG. 2 is a block diagram representing the control system of FIG. 1. In the figure, EMF is the induced voltage of the motor, and the transfer function 10 of the motor is the first-order lag element (1/R) / (
1+ Te a ), the gain 11 of the power converter is a constant F
A transfer function corresponding to the equipment of FIG. 1 is shown, which is denoted by C, and other elements have the same numbers as those given in the same figure. Among these, especially the transfer function 09 of the third compensation element 9 is Go2Geo(1/Kp)(R/Fc)(1+T
e s )/(Tcas) (1). When the current control circuit 5 is configured with a digital device, the value according to the theoretical formula cannot be obtained, so
In order to adjust this, it is multiplied by a constant G9o, which is a function or constant included in the transfer function of all other elements. In the following, it will be shown that a high-speed response can be obtained by setting the transfer function 09 as equation (1).

FIG. 3 is an equivalent circuit in which element 6 in FIG. 2 is moved outside the minor loop to form element 13. 1 point P in this circuit
When determining the transfer function G C1 between 2 and P3, Gc1=G/(1+GH)=(1/H)(1/(1+1
/GH))...(2) However, G=Kp(1/R)(1/(1+Te5))Fc '''
(3) H=Tcd/Tcr
...(4). Using this transfer function GCI,
Figure 3 can be expressed as shown in Figure 4. Furthermore, in this figure 4, point P
If we find the transfer function GC2 between 1 and P3 and organize it, we get (
From equations 1) to (4), GC2=(GI?+ 1/(Tcrs))・Gci=(
1/Tc11g)X(1+K(HTes) Goo)/
(1+K(1+Tc5))...(5) However, = RTcr/(KpFcTei) '・
- (6). If FIG. 4 is further simplified using this G c z, the equivalent circuit shown in FIG. 5 can be obtained. Therefore, if the gain Goo of the compensation element 9 is adjusted to approximately 1, then from equation (5), GC2=1/Tca s
''(7), and since the element Gc2 can be made into a complete integral system, a control response that does not include a delay element can be obtained.

〔Effect of the invention〕

According to the present invention, since the first-order lag characteristic of the electric motor can be compensated for by the added feedforward element, it is possible to speed up responsiveness to commands and to obtain control performance with less fluctuation in response to external disturbances.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing one embodiment of the present invention, and Fig. 2 is a circuit diagram showing an embodiment of the present invention.
The block diagram in the figure and FIGS. 3 to 5 are developed views of FIG. 2. DESCRIPTION OF SYMBOLS 1... Electric motor, 2... Current converter, 3... Gate pulse generator, 5... Current control circuit, 7... First compensation element, 8... Second compensation element , 9...Third compensation element.

Claims (1)

[Claims] 1. A first current control system that outputs a first command for controlling the average value of the detected motor current to match the current command, and a time rate of change of the detected motor current that matches the first command. and a second current control system that outputs a second command for controlling the motor current, and controls the motor current by adjusting the output voltage of a power conversion means that supplies the motor current according to the second command. The current control device is characterized in that a compensation element receiving the first command as an input is provided to compensate for the first-order lag characteristic of the electric motor, and the output of the element is added to the second command. Electric motor current control device.