JPH05316638A - Motor protective circuit - Google Patents

Abstract

PURPOSE:To automatically select and set the overheat protective level which is the optimum for a motor having an arbitrary capacity without relying on manual selecting and setting operations. CONSTITUTION:In the circuit which protects a motor operated by means of a power converter by maintaining the current of the motor at or lower than an overheat protective level, a means 200' which applied a DC voltage across the motor before operating the motor, means 203 and 1 which detects DC current which is made to flow to the motor due to the DC voltage, means 2 and 3 which discriminate the capacity of the motor from the detected value of the DC current, and means 4 and 5 which select and set the overheat protective level of the motor in accordance with the discriminated capacity of the motor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a motor protection circuit,
More specifically, the present invention relates to a motor protection circuit for protecting a motor driven by a power conversion device such as an inverter from overheating.

[0002]

2. Description of the Related Art Conventionally, a motor protection circuit of this type is known as shown in FIG. In FIG. 3, 1
00 is an AC power source, 200 is an inverter that performs AC / DC conversion and DC / AC conversion, 300 is a magnet contactor connected to the AC output side of the inverter 200, and 400.
Is a thermal relay, and 500 is a general-purpose motor. The operation is briefly described. The magnet contactor 300 is normally closed, and the motor 500 includes the thermal relay 40.
Current is supplied via 0. The overheat protection level of the motor 500 due to overcurrent (operation level of the thermal relay 400) is stored in advance in the device, and can be artificially selected and set by an operator by operating a switch, a key, a volume, or the like. When the current of the motor 500 exceeds the overheat protection level and the motor 500 becomes overheated, the thermal relay 400 operates to open the magnet contactor 300 and stop the power supply to the motor 500. As a result, the motor 500 can be protected from overcurrent or overheating.

[0003]

According to the above-mentioned conventional technique, since the overheat protection level of the motor 500 is artificially selected and set, the overheat protection may not be achieved and the motor 500 may burn due to a selection error. Further, when a plurality of motors having different capacities are switched to operate and a thermal relay is shared, the overheat protection level must be set every time the motors to be operated are switched. To avoid this complexity, it is necessary to install a thermal relay with a different operation level for each motor.
The size of the entire device was increased and the cost was increased.

The present invention has been made in order to solve the above problems, and an object thereof is to eliminate a motor damage accident due to an incorrect selection of an overheat protection level and to operate by switching a plurality of motors. However, it is an object of the present invention to provide a motor protection circuit that enables automatic setting of the overheat protection level, eliminates the complexity of selection and setting operations, and enables downsizing of the device and cost reduction.

[0005]

In order to achieve the above object, a first aspect of the present invention is a motor protection circuit for protecting a motor by maintaining a current of a motor operated by a power conversion device at an overheat protection level or less. A means for applying a direct current voltage to the motor before the motor is operated, a means for detecting a direct current flowing in the motor by the direct current voltage, a means for determining the capacity of the motor from the detected direct current current, and a means for determining the determined motor. And a means for selecting and setting the overheat protection level of the motor according to the capacity.

A second invention is the same as the first invention,
A means for determining the capacity of the motor from the detected DC current and a means for selecting and setting the overheat protection level of the motor according to the determined capacity of the motor are realized by the CPU and its program.

In each of the above inventions, it is desirable to use a power converter for motor operation as means for applying a DC voltage to the motor before the motor is operated.

[0008]

According to the first aspect of the invention, before the motor is operated by the power converter, a DC voltage is applied to the motor in advance to detect the DC current at that time. Since this DC current corresponds to the motor capacity, the motor capacity can be determined by storing the motor current data corresponding to the capacity in the memory and referring to it. After determining the motor capacity in this way, a known overheat protection level is automatically selected and set according to the motor capacity to prepare for the main operation.

According to the second aspect of the invention, the CPU operates so as to execute the capacity determination of the motor, the selection of the overheat protection level of the motor, and the setting processing according to a predetermined program.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows an embodiment of the first invention together with an inverter main circuit 200 'for driving a motor. First,
The inverter main circuit 200 'for driving a motor includes a DC voltage smoothing capacitor 201, a switching element 202 such as a three-phase bridge-connected power transistor, a current transformer 203 for detecting an AC output current, and the like. The AC / DC converter in the inverter main circuit 200 'is not shown. Further, 204 is a drive circuit for sending an ignition pulse to the switching element 202, 501 is a motor stator circuit to be protected against overheat, and R is a stator resistance.

The structure of the motor protection circuit of the present invention including the current transformer 203 will be described below. The output of the current transformer 203 is applied to the current detection circuit 1, and the output thereof is input to the motor capacity determination circuit 3. Reference numeral 2 is a motor current data memory, and the motor current data read from this memory 2 is also output from the current detection circuit 1 along with the motor capacity determination circuit
Has been entered in. The motor current data memory 2
As will be described later, the motor current when the direct current is passed through the stator circuit 501 prior to the operation of the motor is stored in association with the motor capacity. The output of the motor capacity determination circuit 3 is input to the overheat protection switching circuit 4,
The output is input to the overheat protection control circuit 5. A drive circuit 204 for driving the switching element 202 is connected to the control circuit 5.

Next, this operation will be described. First, in this embodiment, the driving circuit 204 causes the switching elements 202a, 20a
Turn on 2b. As a result, the DC voltage charged in the smoothing capacitor 201 is applied to the switching element 20 in the motor.
2a, 202b applied to the stator circuit 501
A DC current corresponding to the value of the stator resistance R flows through the. This current is assumed to correspond to the capacity of the motor and the current transformer 20
3 and the current detection circuit 1 detect and input to the motor capacity determination circuit 3.

The motor capacity determination circuit 3 compares the output of the current detection circuit 1 with the motor current data from the memory 2 to determine the capacity of the motor, and the determination output is input to the overheat protection switching circuit 4. .. Overheat protection switching circuit 4
Selects and sets the current overheat protection level according to the motor capacity based on the judgment output from the motor capacity judgment circuit 3. Then, the overheat protection control circuit 5 automatically selects the operation level according to the overheat protection level set by the overheat protection switching circuit 4.

Although not shown, the detection value of the motor current during operation is input to the overheat protection control circuit 5, and the current is compared with the operation level to the drive circuit 204. And outputs a control signal such as an operation stop. As described above, according to this embodiment, it is not necessary to artificially set the overheat protection level, and the motor capacity determination circuit 3, the overheat protection switching circuit 4 and the like automatically determine the motor capacity even when the motor capacity is different. Since the optimum overheat protection level is selected, the overheat protection level is automatically switched even when a plurality of motors are switched and operated, and there is no problem.

FIG. 2 shows an embodiment of the second invention.
In this embodiment, the functions of the motor capacity determination circuit 3, the overheat protection switching circuit 4, and the overheat protection control circuit 5 in the embodiment of FIG. 1 are realized by a CPU and its program. That is, in FIG. 2, the inverter main circuit 200 '
A resistor 205 is connected between the smoothing capacitor 201 and the bridge composed of the switching element 202,
The A / D converter 6 is connected to the resistor 205. CPU to the A / D converter 6 via a data bus
7 and the ROM 8 are connected, and the drive circuit 20 is connected to the CPU 7.
4 is connected.

To explain this operation, also in this embodiment, the switching elements 202a and 202b are driven by the drive circuit 204 before the motor 500 is driven by the inverter.
Turn on. As a result, the DC voltage charged in the smoothing capacitor 201 is applied to the switching element 2 of the motor 500.
A direct current corresponding to the resistance value of the stator flows through the stator circuit by being applied via 02a and 202b. This current is detected by the voltage value across the resistor 205 as corresponding to the capacity of the motor 500, and the analog detection signal is converted into a digital signal by the A / D converter 6 and input to the CPU 7.

The ROM 8 stores motor current data corresponding to the capacity of the motor 500, like the motor current memory 2 of the embodiment shown in FIG. The CPU 7 determines the capacity of the motor 500 from the output signal of the A / D converter 6 and the motor current data. Then, the overheat protection level corresponding to the motor capacity is read from the ROM 8 and the necessary overheat protection calculation is performed to select the operation level. Although not shown, the detected value of the motor current during operation is converted into a digital signal and input to the CPU 7, and the current is compared with the operation level to the drive circuit 204. Outputs control signals such as operation stop. According to this embodiment, the main functions such as the judgment of the motor capacity and the selection and setting of the overheat protection level are realized by the program, so that the circuit configuration can be further simplified.

In the above embodiment, the protection circuit for the motor driven by the three-phase inverter has been described, but the power converter for driving the motor is not limited to the three-phase inverter, but may be a single-phase inverter or a cyclo. It may be a converter or the like. Further, as a means for applying a DC voltage to the motor before operating the motor, it is preferable to use a power converter for operating the motor, but a separate DC power source may be used.

[0019]

As described above, according to the first aspect of the invention, the capacity determination of the motor and the selection and setting of the overheat protection level are automatically performed. There is no risk of motor burnout accidents,
The reliability of motor protection can be improved. At the same time, when switching between multiple motors to use, there is no need to set the overheat protection level each time, and since a thermal relay according to the number of motors is not required, the configuration can be simplified and the cost can be reduced. it can.

According to the second invention, in addition to the above effects,
It is possible to further simplify the structure than the first invention,
Since the specification can be changed according to the application system by changing the program, it has the effect of being versatile.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the first invention.

FIG. 2 is a block diagram showing an embodiment of the second invention.

FIG. 3 is a circuit diagram showing a conventional technique.

[Explanation of symbols]

 1 Current Detection Circuit 2 Motor Current Data Memory 3 Motor Capacity Judgment Circuit 4 Overheat Protection Switching Circuit 5 Overheat Protection Control Circuit 6 A / D Converter 7 CPU 8 ROM 200 'Inverter Main Circuit 203 Current Transformer 204 Drive Circuit 205 Resistance 500 Motor 501 Motor stator circuit

Claims (3)

[Claims] 1. A motor protection circuit for protecting a motor by maintaining a current of a motor operated by a power conversion device at an overheat protection level or less, and means for applying a DC voltage to the motor before the operation of the motor; A means for detecting a direct current flowing through the motor by a direct current voltage; a means for determining the motor capacity from the detected direct current value; and a means for selecting and setting the overheat protection level of the motor according to the judged motor capacity. A motor protection circuit comprising: 2. The motor protection circuit according to claim 1, wherein the means for determining the capacity of the motor from the detected value of the direct current and the means for selecting and setting the overheat protection level of the motor according to the capacity of the determined motor. Is realized by a CPU and its program. 3. The motor protection circuit according to claim 1, wherein the means for applying a DC voltage to the motor before the motor is operating is a power converter for operating the motor.