JPH03215189A - Motor digital control device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to motor control, and more particularly to a digital current control device for a motor using a microcomputer.

BACKGROUND OF THE INVENTION In recent years, motor control devices are required to move smoothly and with high precision, such as in the control of industrial robots and NC machine tools, and for this reason, digital control using microcomputers has become widely used. In particular, as microcomputers become faster and more sophisticated, current control circuits that were conventionally constructed from analog circuits are now becoming digital.

An example of the conventional motor speed control device mentioned above will be described below with reference to the drawings.

FIG. 5 is a block diagram of a conventional motor digital control device. In Fig. 5, l represents the motor 2, as shown in Fig. 6, an inverter circuit consisting of a direct current and four transistors, 3 a current detector that detects the current flowing through the motor 1 and converts it into voltage, and 4 the current This is an A/D converter that converts the output voltage of the detector 3 into a digital value. 5 is a microcomputer equipped with a current command calculation means for calculating a current command value and a PWM calculation means for calculating the width of a PWM signal; 6 is a microcomputer 5
This is a PWM circuit that converts the PWM width obtained in the above into a PWM signal and outputs it to the inverter circuit 2. The circuit configuration of the PWM circuit 6 is shown in FIG. In Figure 7, 7 is IOMHZ
8 is a 10-bit counter that counts the output of clock circuit 7, and 9 is P of microcomputer 5.
10 bit latch holding WM width data, 10 is 10
Compare the values of bit counter 8 and 10 bit latch 9 and get 1
It is a 10-bit comparison circuit that outputs a PWM signal of "H" level when the 0-bit counter 8 is larger, and of "L" level otherwise.

The operation of the motor digital control device configured as described above will be described below.

Microcomputer 5 uses current command calculation and timer for 200μs
A PWM operation is executed for each ec. The current command calculation is to calculate a current command value to be applied to the motor 1 based on the rotational speed, position, etc. of the motor 1. The processing details of PWM calculation are explained in the 8th section.
As shown in the figure. In step 1, the microcomputer 5 calculates the current field value (1
,B). In step 2, the difference between the current command value (Io) and the current feedback value (IFB) is determined and used as the current deviation (Δl). In step 3, the cumulative value (ΣΔI) of the current deviation (ΔI) is calculated, and in step 4, the current deviation (ΔI) is calculated.
Multiplied by proportional gain (Kp) and current deviation (ΔI)
The sum of the cumulative value (ΣΔI) multiplied by the integral gain (Ki) is calculated and set as the PWM value (PA).

In step 5, the sign (positive/negative) of the PWM amplitude (PA) is outputted to the PWM circuit 6 as a direction signal and the absolute value (Pc) as the PWM width. The PWM circuit 6 receives the calculation result P of the microcomputer 5.

is held in the 10-bit latch 9.

If we plot the output of the lO bit counter 8 on the vertical axis and the time on the horizontal axis, we get 1001. as shown in Figure 9a. The waveform has a period of lsec.

If the PWM amplitude data held in the 10-bit latch 9 at this time is written in the figure as shown by the broken line, the PWM signal output from the 10-bit comparator 10 will be as shown in FIG. 9b. The PWM signal and the direction signal from the microcomputer 5 are input to the inverter circuit 2, and as shown in FIG. 10a, when the level is "H", Ql and Q4 are in a conductive state, while as shown in FIG. 10b, the direction signal is input to the inverter circuit 2. When the level is "L", Q2 and Q3 are in a conductive state, and current flows to the motor 1. In addition, the current flowing through the motor 1 is converted into current/lightning voltage by the current detector 3 and passed through the A/D converter 4 to a current feedback value (1,
B) is read into the microcomputer 5.

Problems to be Solved by the Invention However, in the above configuration, the current flowing to the motor lags behind the PWM signal due to the armature resistance and armature inductance of the motor. This causes the PWM signal to go “H”.
The level is 50% of the PWM signal period (100μsec)
As shown in FIG. 11a, if the current is less than 1, the current flowing to the motor always becomes zero when the PWM signal reaches the "H" level, and not much current flows. In contrast, the PWM signal “
Conversely, when the H'' level becomes 50% or higher, as shown in FIG. 11b, the current begins to flow more and more, and the PWM width changes or becomes thicker until the current is saturated.

Due to the nonlinearity between the PWM signal and the current flowing through the motor, there has been a problem in that it is difficult to flow the current according to the command value. In particular, if too much current flows when the PWM width becomes large, the PWM width becomes small in the next PWM calculation, and by repeating this, the current may oscillate.

In view of the above-mentioned problems, the present invention provides a digital control device for a motor that allows current to flow according to a command value without using a high-speed microcomputer.

Means for Solving the Problems In order to solve the above problems, the motor digital control device of the present invention uses PWM which is the calculation result of the PWM calculation means.
It is provided with gain changing means for calculating and changing the calculation parameters of the PWM calculation means from the time width of the signal.

Effects According to the present invention, the current is stably controlled by the gain changing means that changes the calculation parameters of the PWM calculation means based on the calculation results of the PWM calculation means, with the above-described configuration.

In other words, when the PWM width is large, the gain is lowered and the PWM
By increasing the gain when @ is small, current oscillation can be suppressed and stable control can be achieved.

Embodiment A digital control device for a motor according to an embodiment of the present invention will be described below with reference to the drawings. FIG. 1 shows the configuration of a motor digital control device in this embodiment. The configuration shown in FIG. 1 is the same as that shown in FIG. 14 is an A/D converter that converts the output voltage of the current detector 13 into a digital value. 15 is a microcomputer, and this microcomputer 15 includes a current command calculating means for calculating a current command value and a PWM signal for calculating the width of a PWM signal.
PW which is the calculation result of the calculation means and this PWM calculation means
A microcomputer 16 is equipped with gain changing means for calculating and changing calculation parameters of the PWM calculation means from the time width of the M signal; PW to output
It is an M circuit. The circuit configuration of the PWM circuit is also the same as that shown in FIG.

Microcomputer 15 uses current command calculation and timer to generate 200μ
PWM calculation is executed every sec. The current command calculation is to calculate a current command value to be applied to the motor 1 based on the rotational speed, position, etc. of the motor 1. FIG. 2 shows the contents of the PWM calculation.

The microcomputer 15 outputs A/
The current feed value (] which is the output of the D converter l4)
,,) is read. In step 2, the current is known and the value (1
) and the current feedback value (lFB)C and use it as the current deviation <ΔI). In step 3, calculate the cumulative value (ΣΔI) of the current deviation (ΔI), and in step 4
The current deviation (ΔI) multiplied by the proportional gain (Kp) and the cumulative value (ΣΔI) of the current deviation (ΔI) multiplied by the integral gain (
The sum of the products multiplied by Ki) is calculated and taken as the PWM value (PA). In step 5, the PWM circuit 1 uses the sign (positive/negative) of the PWM value (PA) as the direction signal and the absolute value (Po) as the PWM width.
Output to 6.

In step 6, the proportional gain (K,
o) and the integral gain (K, o) are multiplied by the gain (K also) obtained from the PWM width according to the table shown in Figure 3, and the new proportional gain (Kp) and integral gain (K i ) are calculated for the next PWM. Store for calculation. The PWM signal and the direction signal from the microcomputer 15 are input to the inverter circuit l2, and current flows through the motor 11. Further, the current flowing through the motor 1l is converted into a T current 7' voltage by the current detector 13, and is read into the microcomputer 15 through the A/D converter 314 as a T current feedback value (1,,).

To create the table shown in Figure 3, first plot the relationship between the PWM width and the current flowing through the motor 11 as shown in Figure 4, and then plot the curve as a quadratic function (
When the PWM width is 50% or more, it is approximated by a linear function (y = bx-c) (correctly X is P
WM width, y is current). A obtained in this way. b, c
If the PWM width is less than 50%, Kt = 1/2ax, P
When the WM width is 50% or more, if Kt is set close to 1/b, a table as shown in FIG. 3 will be created.

As described above, according to this embodiment, the proportional gain (K)
The new proportional gain (Kp) is obtained by multiplying the integral gain (K,,) by the gain (Kt) obtained from the table.
) and integral gain (Ki). By providing a gain changing means, it is possible to decrease the gain when the PWM width becomes large and increase the gain when the PWM width becomes small. Stable current control is possible over the entire width region.

In addition, in the above embodiment, the gain (K
t) was obtained from the table, but Kt is when x=O
Kt=1 When 0<x<0.5 Kt=1/2 a x
O. When 5≦X≦1, it can also be determined from a mathematical formula such as Kt=1/b.

Effects of the Invention As described above, the present invention includes gain changing means for calculating and changing the calculation parameters of the PWM calculation means from the PWM width which is the calculation result of the PWM calculation means, so that the PWM
Since the gain can be lowered when the M width is large and the gain can be increased when the PWM width is small, stable current control is possible and the motor can be rotated smoothly.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between motor currents in an embodiment of the present invention, FIG. 5 is a configuration diagram of a conventional motor digital control device, and FIG. 6 is a configuration diagram of an inverter circuit.
Figure 7 shows the PWM circuit Ka, b It P W
M signal waveform diagram, Figure 10a. A circuit diagram showing the state of current flowing through the motor due to conduction of the rt inverter circuit, FIG. 11a. b is a waveform diagram of the PWM signal and the current flowing through the motor. 11...Motor, 12...Inverter circuit, 13...Current detector, l4...
A/D converter, 15...Microcomputer, l6...
...PWM circuit.

Claims (1)

[Claims] a motor, an inverter circuit connected to the motor and consisting of a power supply and a switching element, a current detector that detects the current flowing through the motor, a current command calculation means that calculates a current command value to flow through the motor, and the current PWM calculation means for calculating a time width for controlling on/off of the switching elements of the inverter circuit from a current command value which is a calculation result of the command calculation means and a current feedback value which is an output of the current detector; In a motor digital control device comprising a PWM circuit that generates a PWM signal input to the inverter circuit from the calculation result of the PWM calculation means, the calculation parameter of the PWM calculation means is determined from the time width of the PWM signal which is the calculation result of the PWM calculation means. A digital control device for a motor, characterized in that it is equipped with gain changing means for calculating and changing the gain.