JPH11122965A - Electric motor control device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric motor control device for achieving a control system with large control resolution by using an inexpensive D/A converter and a simple circuit. SOLUTION: An electric motor control device has a CPU for outputting a digital current command, a D/A converter for converting the current command into an analog signal, a power amplifier for receiving the signal and supplying current corresponding to the current command to an electric motor, and a means for compressing and expanding a signal 15 provided between the CPU and the power amplifier. In this case, the means for compressing and expanding the signal consists of a plurality of analog switches 31 and 32 and an operation amplifier 43. When the current command of the CPU (or a torque command) crosses a specific threshold, the analog switches 31 and 32 are switched so as to switch the gain of the operation amplifier 43.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor control device for driving a motor, and more particularly, to a method for controlling a current command of a CPU to a D / D.
The present invention relates to a motor control device that supplies electric power to a motor via a power amplifier after converting the signal into an analog signal with an A converter, and controls the position and speed of the motor, torque or thrust.

[0002]

2. Description of the Related Art As one of conventional motor control devices, there is one that realizes a control system having a large control resolution while using a mass-produced inexpensive D / A converter.
No. 773. The prior art will be described with reference to FIG. FIG. 3 is a block diagram of a motor control system including the above-described conventional motor control device. In the figure, a CPU 10 sends a digital speed command via a logarithmic converter 11 at regular intervals to a D / A converter 12 in order to move a movable table or the like to a command position specified in advance.
Output to A reversible counter 12 counts the pulses of the pulse generator 71 and detects the current position of the electric motor 60. The CPU 10 reads the signal when necessary and calculates the deviation between the command position and the current position. The CPU 10 outputs a speed command proportional to this deviation, thereby stabilizing the position control loop. The logarithmic converter 11 performs logarithmic conversion of the digital speed command of the CPU 10, and compresses and outputs the speed command as the input speed command increases. The compressed speed command is converted into an analog signal via the D / A converter 20, and the inverse logarithmic converter 21 performs the reverse conversion of the logarithmic converter 30. As the input speed command is increased by the antilogarithmic converter 21, the speed command is expanded,
Is returned to an analog signal corresponding to the speed command. As described above, since the speed command is compressed and D / A converted,
The number of bits of the / A converter 20 can be greatly reduced. Next, the difference between the signal of the antilogarithmic converter 21 and the signal of the tachogenerator 70 is obtained by the subtractor 22 and output to the drive circuit 50.
Is supplied with power and is driven. In this conventional example, D / A
The logarithmic converter 11 is provided before the converter 20, and the D / A
It is characterized in that an antilogarithmic converter 21 is provided at the subsequent stage of the converter 20, and a control system with a large speed resolution can be realized by using a mass-produced inexpensive D / A converter with a relatively small number of bits. It can be realized.

[0003]

However, in the conventional device, since the speed loop is constituted by an analog circuit,
Vibration suppression control used when problems such as vibration and load fluctuation occur.
There is a problem that a control method such as an observer cannot be easily incorporated. Therefore, an object of the present invention is to use a mass-produced inexpensive D / A converter even when a control system such as a vibration suppression control / observer can be easily incorporated and a speed loop is configured by a digital circuit. It is an object of the present invention to provide a motor control device capable of realizing a control system having a large control resolution.

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a CPU which calculates a current command for each phase corresponding to a field pole and outputs a digital current command, and converts the current command into an analog signal. A D / A converter for converting the signal into a signal;
A power amplifier for receiving a signal from the converter and supplying a current corresponding to the current command to the motor, and a signal compression / expansion means provided between the CPU and the power amplifier for controlling the motor. In the motor control device, the signal compression / expansion means includes a plurality of analog switches and an operational amplifier, and switches the analog switch when the current command of the CPU crosses a predetermined threshold value, and switches the gain of the operational amplifier. It was characterized by. Further, instead of the current command of the CPU with the torque command, C
When the torque command of the PU crosses a predetermined threshold value, the analog switch is switched, and the gain of the operational amplifier is switched. According to the present invention, when the torque (thrust) command of the CPU exceeds the threshold value, that is, when the current command cannot be output by the D / A converter, the torque (thrust) command is set to 1 / gain (compression). When the same D / A converter is used in order to return the signal corresponding to the current command calculated by the CPU, the analog switch is switched from the CPU to the one that multiplies (extends) the input signal of the operational amplifier circuit by the gain. If the control resolution can be increased and the same control resolution is required, a less expensive D / A converter having a smaller number of bits of the D / A converter can be used.
Since the compression / expansion of the current command is used, the speed loop can be configured digitally, and control methods such as vibration suppression control and observer can be easily incorporated.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram of a motor control system including a motor control device according to the present invention, in which the motor has three phases. In the figure, a CPU 1 moves a movable table or the like to a command position instructed in advance by an electric motor 6.
Converts the digital current command into the D / A converter 2 at regular intervals.
Output to In the CPU 1, a position loop and a speed loop are formed, and a torque command which is an output of the speed loop, that is, a thrust command is calculated. Then, the signal of the position sensor 7 such as a linear scale is fetched as the current position, and the motor 6 is referred to by referring to the SIN table prepared in advance in the memory.
The current command of each phase corresponding to the field pole is calculated. The compressed current command of the CPU 1 is transmitted to the analog switch 3 and the OP.
The original current command is expanded by the amplifier circuit 4. In the power amplifier 5, a current sensor detects the current of each phase and feeds back its signal to form a current loop.
When a current command output from the OP amplifier circuit 4 is input to the power amplifier 5, the power is converted and power is supplied to the motor 6, and the position, speed, and current of the motor 6 are controlled. Next, means for increasing the current resolution, which is a main part of the present invention, will be described in detail with reference to FIG. FIG. 2 is a diagram showing details of the analog switch 3 and the OP amplifier circuit 4 in FIG.
2 shows a circuit for one phase of the electric motor 6. For simplicity,
An example in which a ± 15 bit (± 32768), ± 5V / full scale (hereinafter referred to as FS) D / A converter is used for ± 13 bits (± 8192) and the gain of the power amplifier 5 is 1 A / V. Is shown. When the thrust command data is larger than 8191 (hereinafter, referred to as gain high), that is, when the output cannot be performed by the ± 13-bit D / A converter, the CPU 1 multiplies the thrust command data by 1/16 and the D / A converter 2 Output to At this time, the first analog switch 31 is set to the CPU 1
Is selected by the switching signal. First analog switch 3
When 1 is selected, the first system 8 (gain 16 times) becomes the current command flow. When the thrust command data is 8192, the thrust command data is set to 512 (= 8192/16), and D /
The output of the A converter 2 is 78.125 mV (= 5V × 512)
/ 32768), and the output signal of the OP amplifier circuit 4 is 1.2
5V (= 78.125 mV × 16), and after power conversion by the power amplifier 5, 1.25 A (= 1.25 V
× 1) is supplied to the electric motor 6. When the thrust command data is 65536, the thrust command data is 4096 (= 65
536/16), and the output of the D / A converter 2 is 625
mV (= 5V × 4096/32768), the output signal of the OP amplifier circuit 4 becomes 10V (= 625mV × 16), and after the power is converted by the power amplifier 5, 10A (=
A rated current of 10 V × 1) is supplied to the motor 6. On the other hand, when the thrust command data is smaller than 4096 (hereinafter referred to as gain low), that is, when a current command can be output with a margin with a ± 13-bit D / A converter, CP
The thrust command data is output from U1 to the D / A converter 2 as it is, that is, as it is at 1 time. At this time, the second analog switch 32 is selected by a switching signal of the CPU 1. When the second analog switch 32 is selected, the second system 9 (1x gain) of the OP amplifier circuit 4 becomes a current command flow. When the thrust command data is 4096, the thrust command data is input to the D / A converter 2 as 4096 (= 4096 × 1), and the output of the D / A converter 2 is 625 mV (= 5V × 1).
4096/32768), the output signal of the OP amplifier circuit 4 becomes 625 mV (= 625 mV × 1), and after the power is converted by the power amplifier 5, 625 mA (= 625 mV)
× 1) is supplied to the electric motor 6. When the thrust command data has the minimum value of 1, the thrust command data is input to the D / A converter 2 as 1 (= 1 × 1), and the output of the D / A converter 2 is 0.15 mV (= 5V / 32768). , The output signal of the OP amplifier circuit 4 becomes 0.15 mV (= 0.15 mV × 1).
A current of mA (= 0.15 mV × 1) is supplied to the motor 6. A resistor is mounted so that the gain ratio of the OP amplifier circuit 4 is gain high: gain low = 16: 1.
When the thrust command data has an intermediate value between the gain high and the gain low (4097 to 8191), the command switching gain maintains the previous state, and this width is used as the hysteresis width.
Therefore, a certain threshold value (thrust command data 4 in this embodiment)
096, 8192) and gain high: gain low = 16:
By switching at a ratio of 1, the current control range becomes
0.15 mA: 10 A = 1: 66666. If there are no constraints such as output voltage limitation of the OP amplifier circuit here, the current control range can be up to 1: 133333.
The current control range when switching is not performed is 0.15
mA: 1.25A = 1: 8333. Gain high:
The gain-low ratio can be easily and freely set as required by the resistance ratio of the OP amplifier circuit 4 and software.
Basically, it is possible to extend the current control range by this ratio times as compared with the case where switching is not performed.

[0006]

As described above, according to the present invention, when the same D / A converter is used, the resolution of the current control can be increased, and when the resolution of the current control is the same, the D / A converter can be used. An inexpensive D / A converter having a smaller number of bits of the A converter can be used, and a high-performance control device can be provided at low cost. In addition, since the current command is compressed and expanded, a speed loop can be configured by a digital circuit, and a motor control device that can easily incorporate a control method such as vibration suppression control or an observer can be provided. There is also an effect.

[Brief description of the drawings]

FIG. 1 is a block diagram of a motor control system including a motor control device of the present invention.

FIG. 2 is a schematic diagram of a main circuit of the motor control device of the present invention.

FIG. 3 is a block diagram of a conventional motor control system.

[Explanation of symbols]

 1, 10 CPU 2, 20 D / A converter 3 Analog switch 31 First analog switch 32 Second analog switch 4 OP amplifier circuit 43 Operational amplifier 5 Power amplifier 6, 60 Motor 7, 71 Position sensor 8 First system 9 Second system 11 Logarithmic converter 12 Reversible counter 21 Antilogarithmic converter 22 Subtractor 50 Drive circuit 70 Tach generator

Claims (2)

[Claims] 1. A CPU for calculating a current command of each phase corresponding to a field pole and outputting a digital current command, a D / A converter for converting the current command into an analog signal, and a D / A conversion A power amplifier that receives a signal from the power supply and supplies a current corresponding to the current command to the motor; and a signal compression / expansion unit provided between the CPU and the power amplifier to control the motor. In the motor control device, the signal compression / expansion means includes a plurality of analog switches and an operational amplifier, and switches the analog switches when a current command of the CPU crosses a predetermined threshold value.
An electric motor control device, wherein the gain of the operational amplifier is switched. 2. The method according to claim 1, wherein the current command of the CPU is replaced with a torque command, and when the torque command of the CPU crosses a predetermined threshold, the analog switch is switched and the gain of the operational amplifier is switched. Characteristic motor control device.