JPH04183297A - Load detector for motor - Google Patents

Abstract

PURPOSE:To eliminate necessity of an exclusive use power source having a simple structure by supplying a current corresponding to a load of a motor if an AC voltage is output from a speed controller to drive the motor. CONSTITUTION:If an AC voltage is output from an inverter 1 to drive an induction motor 2, a current corresponding to the load of the motor 2 flows, the current is detected by a current transformer 3, converted into a microscopic current, which is, in turn, converted into a voltage according to a rule of E=I.R by a resistor 4. The converted voltage is converted from an AC to a DC (pulsating current) by a rectifier 5, further converted a DC voltage having a small ripple by a smoothing capacitor 6, and applied to a relay coil 9 of a relay 8 through a variable resistor 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a load detection device for an AC motor.

[Conventional technology] In recent years, cargo handling equipment such as cranes and hoists,
Various types of industrial machinery such as fans and pumps use induction motors as drive devices, and the induction motors are driven by inverters in order to save energy, reduce the size and weight of equipment, and simplify maintenance. .

In such a drive device, the load acting on the induction motor is detected and the inverter is controlled according to the load so that the output characteristics of the induction motor or the constant output characteristics are achieved.

The following methods are available for detecting the load acting on this induction motor.

■ A method that uses a current and power converter to detect the load through microcomputer calculations.

■ A method that uses a power converter and detects the load using a comparator.

■ A method that uses a current converter and detects the load with a comparator.

[Problems to be Solved by the Invention] However, each of the above-mentioned systems has the following problems.

Although the method described in item (2) can provide accurate constant output characteristics, the device configuration is complicated and expensive.

In the method described in item (2), the power converter used as the load detection means is expensive, and a dedicated power source for the comparator is required, resulting in an increase in the size of the device.

Similarly to the method described in item (2), the method described in item (2) also requires a dedicated power source for the comparator, which increases the size of the device.

The present invention solves the above-mentioned problems, and aims to provide a load detection device for an electric motor that has a simple structure and does not require a dedicated power source.

[Means for Solving the Problems] The present invention includes a current transformer that detects a current flowing corresponding to the load of the motor when an alternating current voltage is applied to the motor from a speed control device and converts it into a minute current; A resistor that converts the minute current output from the current regulator into voltage, a rectifier that converts the AC voltage output from the resistor into DC voltage, and a relay coil is excited by the DC voltage output from the rectifier. The relay includes a relay having a relay contact that is activated when the relay coil is activated, and a Zener diode to prevent the voltage applied to the relay coil from exceeding an allowable voltage value.

[Operation] When an AC voltage is output from the speed control device to drive the electric motor, a current corresponding to the load of the motor flows, this current is detected by a current transformer and converted to a minute current, and the minute current is Current is converted to voltage by a resistor, and the converted voltage is further converted from alternating current to direct current by a rectifier.
Applied to the relay coil of the relay.

In such a state, if the load acting on the motor is small, the current flowing through the motor is also small, and the voltage applied to the relay coil is a small value that does not reach the operating voltage of the relay coil, so the relay contact is in a steady state.

On the other hand, as the load acting on the motor increases, the value of the current flowing through the motor also increases, and when the voltage value applied to the relay coil or the operating voltage value of the relay coil is reached, the relay contact becomes activated.

[Example] Hereinafter, the present invention will be described in detail based on the drawings.

FIG. 1 shows an embodiment of the present invention. In the figure, 1 is an inverter that applies AC voltage to the induction motor 2 to drive the induction motor 2, and 3 is an inverter that drives the induction motor 2 by applying an AC voltage to the induction motor 2. a current transformer that detects a current flowing corresponding to the load of the induction motor 2 and converts it into a minute current, 4 a resistor that converts the minute current output from the current transformer 3 into voltage, and 5 a resistor. A rectifier that converts the AC voltage output from 4 into a DC voltage, 6 a smoothing capacitor that converts the ripple-containing DC (pulsating current) output from the rectifier 5 into a DC voltage with less ripple, and 7 a smoothing capacitor 6. A variable resistor 8 is a signal output relay that adjusts the voltage value of the converted DC voltage, and the relay coil 9 of the relay 8 has a
The DC voltage output from the variable resistor 7 is applied, and when the DC voltage is applied and the relay coil 9 is excited, the relay contact JO of the relay 8 is opened.

Furthermore, the current flowing to the induction motor 2 becomes large.
A Zener diode is used to prevent the voltage value from exceeding the permissible voltage value of the relay coil 9 when the voltage output from the resistor 4 becomes high.A Zener diode 12 is used to prevent overcurrent from flowing through the Zener diode ll. current limiting resistor,
H, 14 is a signal circuit that connects the relay contact IO and the high-speed command circuit of the inverter I.

When the relay contact 10 is closed, the inverter 1 applies voltage to the induction type i machine 2 so that the high speed command circuit is in operation and the induction motor 2 is driven at high rotation and low torque, and When the relay contact 10 is opened, the high-speed command circuit is not activated, and a voltage is applied to the induction motor 2 so that the induction motor 2 is driven at low rotation and high torque.

In the above configuration, when an AC voltage is output from the inverter 1 to drive the induction motor 2, the induction motor 2
A current corresponding to the load flows, this current is detected by the current transformer 3 and converted into a minute current, and the minute current is passed through the resistor 4.
It is converted into voltage according to the -I-R law.

The converted voltage is converted from AC to DC (pulsating current) by a rectifier 5, further converted to a DC voltage with less ripple by a smoothing capacitor 6, and applied to a relay coil 9 of a relay 8 via a variable resistor 7. Ru.

In such a state, when the load acting on the induction motor 2 is small, the current value flowing through the induction motor 2 is also small, and the voltage value applied to the relay coil 9 is small enough to not reach the operating voltage value of the relay coil 9. value, the relay contact 10 remains closed and the high speed command circuit of the inverter l is activated.

Therefore, the inverter l applies a voltage to the induction motor 2 so that the induction motor 2 is driven at high rotation and low torque.

On the other hand, as the load acting on the induction motor 2 increases, the current value flowing through the induction motor 2 also increases, and the voltage value applied to the relay coil 9 or the operating voltage value of the relay coil 9 is reached, and the relay contact IO opens. The high-speed command circuit of inverter l will no longer operate.

Therefore, the inverter 1 applies a voltage to the induction motor 2 so that the induction motor 2 is driven at low rotation and high torque.

As described above, in the present invention, when a voltage is applied from the inverter 1 to the induction motor 2, the current flowing corresponding to the load of the induction motor 2 is detected and converted into a minute current, and the minute current is converted into a DC voltage. Since the voltage is converted into the voltage and then applied to the relay coil to activate the relay contacts, the structure of the device is simple, the device can be made smaller and less expensive, and there is no need for a dedicated power source.

The load detection device for an electric motor of the present invention is not limited to the above-described embodiments, but is configured such that the relay contacts of the relay are open in a steady state and closed in an operating state, and the inverter is The present invention may be applied within the scope of the present invention, such as changing the operation of a high-speed command circuit according to a relay, applying to a speed control device for a 4-AC motor other than an inverter, or applying to a motor other than an induction motor. Of course, various changes can be made.

[Effects of the Invention] As explained above, the motor load detection device of the present invention can achieve various excellent effects as described below.

■ When voltage is applied from the speed control device to the motor, the current flowing corresponding to the load of the motor is detected and converted into a minute current, and the minute current is converted into a DC voltage and then applied to the relay coil. Since relay contacts are operated, the structure of the device is simple, the device can be made smaller and less expensive, and a dedicated power source is not required.

■ The device is small and does not require a dedicated power source, so it can be easily installed in existing drive equipment.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram of an embodiment of the present invention. In the figure, 1 is an inverter (speed control device), 2 is an induction motor (motor), 3 is a current transformer, 4 is a resistor, 5 is a rectifier, 6
7 is a smoothing capacitor, 7 is a variable resistor, 8 is a relay, 9 is a relay coil, IO is a relay contact, and 11 is a Zener diode.

Claims (1)

[Claims] 1) A current transformer that detects the current flowing corresponding to the load of the motor when an AC voltage is applied to the motor from the speed control device and converts it into a minute current, and a current transformer that converts the minute current output from the current transformer into a voltage. a rectifier that converts an alternating current voltage output from the resistor into a direct current voltage, and a relay having a relay contact that operates when the relay coil is excited by the direct current voltage output from the rectifier. and a Zener diode for preventing a voltage value applied to the relay coil from exceeding an allowable voltage value.