JPH099494A - AC motor control device - Google Patents

Abstract

PURPOSE: To detect the temperature of the rotor of a motor and compute the value of secondary resistance by installing a phototransistor on the stator side in a position convenient for it to receive infrared rays generated from the coils of the rotor, and placing nearby a thermistor for detecting the temperature of primary coils. CONSTITUTION: A phototransistor 16 is installed on the stator of a three-phase induction motor 8. When a current is passed through secondary coils 11, the coils produce heat. This increases the temperature of a rotor 10, which then radiates infrared rays. Since the phototransistor 16 is disposed in a position convenient for it to receive the infrared rays, it detects the temperature of the rotor 10. When the temperature of the rotor 10 is increased, the resistance of the secondary coils 11 varies. The temperature of the secondary coils 11 is in proportion to that of the rotor 10; therefore, the resistance of the secondary coils 11 can be calculated from the temperature of the rotor. Even if the resistance of the secondary coils 11 is varied due to temperature, as a result, it is possible to continue intended efficiency-oriented, torque-oriented or high speed-oriented operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for applying an appropriate current or frequency from an inverter to a motor for efficient operation, and more particularly to an AC motor control device suitable for a battery forklift.

[0002]

2. Description of the Related Art Conventionally, temperature detection of a motor has been used to protect the motor. For example, as disclosed in Japanese Patent Laid-Open No. 54-10950, a warning is given and power is cut off.

However, the resistance value of the induction motor changes depending on the temperature of the coil and changes its characteristics.

Since the primary coil is directly subjected to the cooling of the motor, the temperature rise is small and the change in resistance value is small. Moreover, since the temperature of the coil can be directly measured by the thermistor, efficient operation can be performed with the changed characteristics.

However, since the secondary coil of the rotor is difficult to cool, the temperature rises greatly, and it is difficult to detect the temperature of the coil because the rotor is rotating.

When the temperature change of the secondary coil increases, the secondary resistance r2 of the equivalent circuit shown in FIG. 2 changes and the output changes. In order to operate the motor efficiently, it is necessary to detect and control the value of the secondary resistance r2.

Also, when the acceleration control of the motor is performed, it is necessary to detect the value of the secondary resistance r2 to control the increase of the current and the increase of the frequency.

[0008]

The object is to detect the temperature of the rotor and calculate the value of the secondary resistance r2.

[0009]

A phototransistor is set on the stator side of a motor and arranged so as to easily receive infrared rays generated from a coil portion of a rotor.

A thermistor for detecting the temperature of the primary coil is placed nearby.

[0011]

The heat generated from the coil portion of the rotor raises the temperature of the rotor. The phototransistor receives the infrared rays emitted from the rotor. Then, the temperature of the rotor is converted into an electric signal. The temperature of the rotor is equal to or some proportional to the resistance r2 of the secondary coil. Then, if the temperature of the rotor can be detected, the value of the secondary resistance r2 can be calculated.

Since some phototransistors are easily affected by temperature, the temperature of the primary coil is detected by a thermistor and the output of the phototransistor is corrected, so that an accurate temperature can be calculated.

[0013]

1 shows a block diagram of the temperature detection of the present invention.

A signal from the input circuit 1 is supplied from a control circuit 2 including a microcomputer to a sine wave of a command current and a command frequency to a current control circuit 3, and the current control circuit 3 feeds back the signal of the current sensor 4 to a feedback. Pulse waveform (PWM / pulse width modulation) is obtained by proportional control.
The gate drive circuit 5 applies an on / off signal to the switching element of the inverter 6. And the battery 7
Energizes the primary coil 9 of the three-phase induction motor 8. The rotor 10 has a secondary coil 11. A rotation sensor 12 is attached to the rotation shaft of the rotor 10 and is connected to the input circuit 1. The signals of the thermistor 13 and the accelerator 14 that detect the temperature of the primary coil 9 are also connected to the input circuit 1.

The constant voltage line 15 is connected to the phototransistor 16 via the resistor R1.

The phototransistor 16 is a three-phase induction motor 8
Attach to the fixed side (stator) of.

When a current flows through the secondary coil 11, heat is generated and the temperature of the rotor 10 rises. And it emits infrared rays.
The phototransistor 16 is set at a position where this infrared ray is easily received.

Therefore, the phototransistor 16 becomes the rotor 10
Detects the temperature of.

The signal of the phototransistor 16 is the input circuit 1
Connected to.

FIG. 3 shows a map of command current and command frequency during steady operation. If the command current is divided into one for excitation and one for torque current, it is useful for control that accelerates responsiveness during acceleration control.

The command frequency is determined by the number of rotations, the number of poles and slippage of the three-phase induction motor 8. That is, generally, the operation frequency to be prioritized is commanded by control called slip frequency control.

The horizontal axis represents the rotational speed of the three-phase induction motor 8.
The rotation frequency of the three-phase induction motor 8 has a one-to-one relationship with the synchronization frequency, and the command frequency is determined when slip is known. In performing the control, the rotational speed of the three-phase induction motor 8 is shown on the horizontal axis because the control is easy when the rotational speed of the three-phase induction motor 8 is used as a reference. The vertical axis represents the command current or the current in steady operation. As the opening degree of the accelerator 14 increases, the limit range is expanded from (A) to (B). Then, steady operation is performed at a point matching the load characteristics.

As the temperature of the rotor 10 rises, the resistance value of the secondary coil 11 changes. Then, the value of the map determined by priority of efficiency, priority of torque, or priority of high-speed operation changes.

Therefore, the temperature of the secondary coil 11 is equal to that of the rotor 1.
There is a certain proportional relationship with the temperature of 0, and the resistance value of the secondary coil 11 can be calculated at this temperature.

As a result, the value of the map determined by the priority of efficiency, the priority of torque, or the priority of high-speed operation in each operating state is corrected by changing the resistance value. Therefore, the operation with priority on efficiency, torque, or high-speed operation can be continued.

[0026]

[Effects of the Invention] Even if the resistance value of the secondary coil 11 changes depending on the temperature, the operation determined by the efficiency priority, the torque priority, or the high-speed operation priority is continued.

[Brief description of drawings]

FIG. 1 is a block diagram of temperature detection according to the present invention.

FIG. 2 is an equivalent circuit diagram of an induction motor.

FIG. 3 is an explanatory diagram of a command current and a command frequency.

[Explanation of symbols]

1 ... Input circuit, 2 ... Control circuit, 3 ... Current control circuit, 4 ...
Current sensor, 5 ... Gate drive circuit, 6 ... Inverter, 7 ... Battery, 8 ... Three-phase induction motor, 9 ... Primary coil, 10 ... Rotor, 11 ... Secondary coil, 12 ... Rotation sensor, 13 ... Thermistor, 14 ... Accelerator, 15 ... Constant voltage line, 16 ... Phototransistor.

Claims (1)

[Claims] 1. A battery, an inverter including a gate drive circuit, a motor, a control circuit including a microcomputer, and an input circuit for processing an electric signal of an accelerator pedal depression amount and an electric signal of a coil temperature detecting thermistor of the motor. In the AC motor control device, the light receiving surface of the phototransistor is directed to the coil side of the rotor of the motor, the phototransistor is installed on the stator side of the motor, and this signal is applied to the microcomputer via the input circuit. An AC motor control device characterized by the above.