JPS63117684A - Controller for motor - Google Patents

Abstract

PURPOSE:To eliminate an improper start of a motor by limiting a winding current to a higher value at the time of starting. CONSTITUTION:When a drive operating circuit 12 is turned ON, a microproces sor 9 feeds a control signal to an inverter 7 to control the operation of a motor 8. A transistor Q10 is turned ON at the time of starting, and a resistor R17 is connected in parallel with a resistor R15. Thus, a limiting current at the time of starting by a limiter 17 is set to a higher value to supply a sufficient winding current. When the start is completed to set the rotating speed of the motor 8 to a predetermined value or higher, the transistor Q10 is turned OFF, the limiting current by the limiter 17 is set to a lower value to become a slightly larger value than the maximum rated current of the motor 8.

Description

Detailed Description of the Invention (a) Field of Industrial Application This invention relates to a motor control device that uses an inverter circuit that converts DC output to AC output and controls the rotation speed by changing the voltage applied to the inverter circuit. .

(B) Prior art A conventional electric motor control device is disclosed in Japanese Patent Application Laid-open No. 54-755, for example.
As disclosed in Publication No. 27, the voltage applied to a DC motor is controlled using the active region of a high-power transistor, and the operation of the high-power transistor is controlled when the current flowing through the high-power transistor exceeds a limit current. It is known to limit and protect this transistor.

(c) Problems to be solved by the invention By the way, in the above-mentioned control device, the limiting current is set at a constant value, so if the limiting current is set to a low value, the limiter will operate with the starting current of the tgj machine, and the electric motor will In addition, if the limit current is set high to match the starting current, the choke can withstand even when a large current close to the limit current flows continuously. This method requires the use of coils and power elements, which increases the size and cost of the device.

This invention was made in view of the above facts,
It is an object of the present invention to prevent starting failure at the time of starting, and to enable the use of small and inexpensive circuit elements.

(d) Means for Solving the Problems This invention includes a switching circuit that intermittently outputs a DC voltage based on an on-off switching signal, and a smoothing circuit that smoothes the output of this switching circuit into a DC output. , an inverter circuit that converts DC output of a smoothing circuit into AC output, which consists of multiple switching elements connected in a bridge configuration, an electric motor driven by the output of this inverter circuit, and an electric motor based on the rotation angle of the rotor of this motor. an inverter control circuit that controls the operation of the switching element;
a DC output control circuit that changes the on-off time of the switching signal using a control signal output from the inverter control circuit; and a limiter circuit that turns off the switching signal when the motor winding current exceeds the limit current. This limiter circuit has a configuration in which the limiting current at the time of starting is set to be larger than the limiting current after starting.

(f) Effect With this configuration, the limiting current can be set high according to the starting current at the time of starting, and the limiter circuit is prevented from operating with the current during normal starting, thereby reducing the drop in the applied voltage. This prevents startup failures caused by Furthermore, after starting, the limiting current can be set to a low value according to the maximum rated current of the motor, so there is no need to use power elements or choke coils in the smoothing circuit that have a large continuous withstand current, and the circuit elements can be made smaller. This makes it possible to reduce the cost.

(F) Embodiments The present invention will be described in detail below based on embodiments shown in the drawings.

In the figure, a DC power supply circuit 3 is configured that outputs a DC voltage of approximately 142V from an AC power supply 1, a full-wave rectifier 2, and a smoothing capacitor C1, and a resistor R is connected in parallel with the smoothing capacitor C1.
1 and a control power supply circuit 4 consisting of a constant voltage diode 2D
is provided.

Reference numeral 5 denotes a switching circuit that connects and disconnects the DC output of the DC power supply circuit 3 based on an on-off switching signal, and includes transistors Ql, Q2 . Q3, resistance R2, R3, R
4, R5 and a flywheel diode D1. The smoothing circuit 6 includes a choke coil L and a smoothing capacitor C2, and converts intermittent output into a smoothed DC output.

7 is an inverter circuit, which includes six switching elements (
Transistors) Q4 to Q9 and diodes D2 to D7 are connected in a three-phase bridge configuration, and DC output is converted to AC output by the on-off operation of these switching elements. , 8 are three-phase brushless motors, which are driven by the output of the inverter circuit 7. Note that when using a single-phase brushless motor, a single-phase inverter circuit may be used.

Reference numeral 9 denotes a microprocessor as an inverter control circuit, which includes an inverter control section 11 that outputs control signals from 1 to 6 to the inverter circuit 7 to output terminals based on the signal from the rotational position detection circuit 10; and an operation operation circuit 12. a rotation speed control unit 13 that controls the start/stop and rotation speed of the electric motor 8 based on input signals from the rotation speed calculation unit 14 that calculates the rotation speed of the electric motor 8 based on signals from the rotational position detection circuit; It has

Reference numeral 15 denotes an integrated circuit that accommodates a DC output control circuit 16, a limiter circuit 17, and a logic circuit 18. The DC output control circuit 16 is connected to resistors R10 and R11, in which a voltage based on the DC output of the smoothing circuit 6 and a voltage signal supplied from 7 to KIO via the resistance ladder circuit 19 are superimposed on the output terminal of the microprocessor 9. Voltage VA at point A and integrated circuit 15
It outputs an on-off switching signal according to the difference between the constant voltage v and the voltage (■) at the connection point B of the resistors R12 and R13 supplied with a constant voltage (I), and when (■) becomes larger than vIl, the switching signal is output. The off time becomes longer than the on time, and conversely, when vA becomes smaller than Vs, the on time becomes longer than the off time. Further, the limiter circuit 17 is connected to the connection point between the inverter circuit 7 and the resistor R14 and the voltage VC (voltage proportional to the winding current I of the motor 8) at the connection point C between the resistors R15 and R16, which is supplied with a constant voltage V. A transistor Q10 and a resistor are connected in parallel with the resistor R15 to which a voltage signal is supplied from the output terminal Kll of the microprocessor 9. A DC circuit of R17 is provided. The logic circuit 18 gives priority to the OFF switching signal of the limiter circuit 17 over the ON-OFF switching signal of the DC output control circuit 16, and the switching circuit 5
This is supplied to the base of transistor Q3.

In addition, the microprocessor 9 operates when the rotation speed of the electric motor 8 is 40.
When it is less than 0r, p, m, an L output is generated from the output terminal Kll to turn on the transistor QIO, and 400r, p,
When the voltage is greater than or equal to m, an H output is generated from the output terminal Kll to turn off the transistor QIO.

When the operation operation circuit 12 is turned on, the microprocessor 9 sends a control signal to the inverter circuit 7 to control the operation of the electric motor 8. Also, based on the speed setting signal of the driving operation circuit 12, a control signal is sent to the resistance ladder circuit 19,
Change the voltage at connection point A. Then, the DC output control circuit 16 inputs the voltages at points A and B and supplies an on-off switching signal to the switching circuit 5.
Smoothing circuit 6 so that the rotation speed of electric motor 8 becomes the set rotation speed.
DC output is adjusted. Further, the limiter circuit 17 compares the voltages at point 0 and point D, and when the winding current exceeds the limit current, turns off the switching signal to limit the winding current.

In this embodiment, the transistor Q10 is turned on at the time of starting, and
Since resistor R17 is connected in parallel to resistor R15,
The limiting current ILI at the time of starting by the limiter circuit 17 is set high and becomes larger than the normal starting current. Therefore, during normal starting, the limiter circuit 17 does not operate to turn off the switching signal, and there is no fear that the electric motor 8 will start incorrectly. In addition, when the starting is completed and the rotation speed reaches 400r, p, m or more, the transistor QIO
is turned off, the current limit by the limiter circuit 17 is set to a low value (ILX<It+) and becomes a value slightly larger than the maximum rated current of the motor 8. As a result, the motor 8 becomes locked or overloaded, and the winding current decreases to IL! When the limiter circuit 17 turns off the switching signal, the transistor Q of the switching circuit 5
1 and the switching elements of the inverter circuit 7.

Note that when starting, there is a risk that the permanent magnet of the rotor of the motor 8 may be demagnetized, so the microprocessor 9 sets a low speed control signal so that the voltage applied to the motor 8 is low regardless of the set speed. The starting current is kept low.

(g) Effects of the Invention Since the present invention is configured as described above, it is possible to limit the winding current at the time of starting to a high value to prevent starting failures, and also to reduce the winding current after starting. It is useful because it can protect circuit elements by restricting it to the eyes, and it can reduce the size and cost of circuit elements and devices.

[Brief explanation of the drawing]

The figure is an electrical circuit diagram of a motor control device showing an embodiment of the present invention. 5... Switching circuit, 6... Smoothing circuit,
7... Inverter circuit, 8... Electric motor,
9...Microprocessor (inverter control circuit),
16... DC output control circuit, 17... Limiter circuit.

Claims (1)

[Claims] (1) A switching circuit that intermittently outputs a DC voltage based on an on-off switching signal, a smoothing circuit that converts the output of this switching circuit into a smoothed DC output, and multiple switching elements connected in a bridge configuration. An inverter circuit that converts the DC output of a smoothing circuit into an AC output, an electric motor driven by the output of this inverter circuit, and an inverter control circuit that controls the operation of a switching element based on the rotation angle of a rotor of this electric motor. , a DC output control circuit that changes the on-off time of the switching signal using a control signal output from the inverter control circuit, and a limiter circuit that turns off the switching signal when the motor winding current exceeds a limit current. A control device for an electric motor, characterized in that the limit current at the time of starting by the limiter circuit is set larger than the limit current after starting.