JPH0421386A - Motor controller - Google Patents

Abstract

PURPOSE:To exhibit transient capacity higher than rated capacity without sacrifice of motor protective function by operating an allowable current value based on correlation between a maximum allowable current value and a maximum allowable temperature value and then setting an allowable current value for a current reference based on the operation results. CONSTITUTION:An allowable current value curve K is set such that the maximum allowable current A and maximum allowable temperature C are in approximately reverse proportional relation within a range below the maximum allowable current A and maximum allowable temperature C. According to an allowable current curve K representing a relation between an allowable current IK and a motor temperature T detected through a temperature detector 22, an allowable current higher than a continuous rated current B and lower than a maximum allowable current A is set when the motor temperature T is low, and the allowable current IK decrease as the motor temperature T increases to be finally settled at the continuous rated current B of a motor 20. When the motor temperature exceeds the maximum allowable temperature C, the allowable current IK is brought to zero in order to stop the motor 20.

Description

[Detailed Description of the Invention] [Object of the Invention] (Industrial Application Field) The present invention provides a motor control device for controlling a motor current according to a current standard set so that the speed of the motor becomes a predetermined value. Regarding.

(Prior Art) A motor control device is provided with various protection devices to protect the motor from various failures. For example, overcurrent protection devices monitor the motor current to protect the motor from excessive current and cut off the power when a current exceeding a permissible value flows, and motor temperature control devices protect the motor from overheating or burnout. An example is an overheat protection device that monitors the temperature and shuts off the power when the temperature exceeds a permissible value. In such conventional protection devices, the current value or temperature value for cutting off the power source is generally uniquely determined in accordance with the continuous rating of the motor.

(Problems to be Solved by the Invention) The conventional motor protection devices described above are basically equipped with multiple types of single-function devices, and cannot be used when excessive current flows transiently, such as when starting a motor. Except for the following: - If the current exceeds the rated value or the temperature exceeds the allowable value, the power supply is shut off to prevent operation under such conditions.

However, for example, there are loads such as dehydrators, polishing equipment, and coolers that require a large amount of power when starting up, and then the power gradually decreases, and operations such as cargo handling, transportation equipment, and conveyance equipment. In the case of a load that operates infrequently and only for short periods of time, even if a transient overcurrent is detected, there is no need to immediately shut off the power, and even if the load continues to operate, there will be no result. In many cases, it is seen that there would have been no problem. Excessive suspension of motor operation is undesirable because it excessively reduces the operating efficiency of the equipment.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a motor control device that can transiently exhibit a capacity exceeding the rated value without impairing the motor protection function of protecting the motor from overcurrent and overheating.

[Structure of the invention]

(Means for Solving the Problems) In order to achieve the above object, the motor control device of the present invention has the following features:
The temperature of the electric motor is detected by the first means based on a correlation determined such that the two have a decreasing function within the range of the maximum allowable current value and the maximum allowable temperature value of the electric motor. A second means for determining an allowable current value for the detected motor temperature, and a third means for limiting the current reference to be less than or equal to the allowable current value determined by the second means. do.

(Function) Calculate the allowable current value for each motor temperature based on the correlation determined so that the two have a decreasing function within the range of the maximum allowable current value and the maximum allowable temperature value,
By setting the allowable current value for the current reference based on the calculation result, transient overload can be achieved within the range where the motor current does not reach the maximum allowable current value and the motor temperature does not reach the maximum allowable temperature value. This allows the motor to continue operating even in a state where such a condition occurs, and allows the motor to transiently exhibit performance exceeding its rating without impairing its original protective function of protecting the motor from burnout accidents.

(Embodiment) FIG. 1 shows an embodiment of a motor control device of the present invention.

The motor control device 10 shown in FIG. 1 is a device that controls the motor current so that the speed N of the motor 20 matches the speed command N 2 . The speed N of the electric motor 20 is detected by the speed detector 21, and the current setting circuit 11 is detected as speed feedback.
is input together with the speed command N. The current setting circuit 11 calculates a current reference for making the motor speed N match the speed command N 1 , that is, a current command I for making the speed deviation (N-N) zero, and inputs it to the comparison calculation circuit 12 . The motor current I detected by the current detector 16 is also input to the comparison calculation circuit 12 as current feedback. Comparison calculation circuit 12 converts motor current I into current command I.
A current reference that makes the current deviation (1-1) match zero, that is, makes the current deviation (1-1) zero, is output to the current limiting circuit 13.

On the other hand, the motor temperature T is detected by the temperature detector 22, and the protection calculation circuit 14 calculates the allowable current value IA each time based on this motor temperature T.

Ideally, the temperature detector 22 should detect the winding temperature of the electric motor 20, but it is also practical to install it on the frame, considering the possibility of applying it to electric motors that have already been completed as standard products. Temperature detection can be performed.

The current limiting circuit 13 controls the current reference, which is limited based on the current reference obtained by the comparison calculation circuit 12 and the allowable current value obtained by the protection calculation circuit 14, so that the motor current becomes less than or equal to the allowable current value. It is output to the amplifier circuit 15. Typically, the current limiting circuit 13 can be configured as a low value priority circuit that selectively outputs the smaller value of both inputs.

The power amplifier circuit 15 controls the motor current according to the current reference given from the current limit circuit 13.

The allowable current value IA determined by the protection calculation circuit 14 will be explained with reference to FIG.

In FIG. 2, the horizontal axis is the motor temperature T, and C indicates the maximum allowable temperature value corresponding to the motor continuous rated current value B. The vertical axis is the allowable current value IK of the motor, and A indicates the maximum allowable current value. When the motor temperature T exceeds the maximum allowable temperature value C or the maximum allowable current value A, the motor current is reduced to zero or an overheat protection device or overcurrent protection device (not shown) is installed in parallel. sends a trip signal to the power circuit breaker to cut off the power.

As can be seen from the allowable current value curve K in FIG. 2, the present invention is characterized in that the allowable current value IK is not constant but varies depending on the motor temperature T.

In other words, the allowable current value curve includes the maximum allowable current value A or less,
The allowable current value IK is determined to have a decreasing function relationship close to an inversely proportional function within a range below the maximum allowable temperature value C, and the allowable current value IK changes depending on the motor temperature T detected by the temperature detector 22. It is determined according to curve K.

According to the allowable current value curve K, when the motor temperature T is low,
An allowable current value larger than the continuous rated current value B is set, with the maximum allowable current value A as the limit, and as the motor temperature T increases, the allowable current value gradually decreases, and eventually the motor 20's Continuous rated current value B. Motor temperature T
rises and exceeds the maximum allowable temperature value C, the electric motor 20
In order to stop the current, the allowable current value IK is set to zero.

To find the allowable current value ■ based on the motor temperature T, use the function given in the form -f (T) based on experimental results, calculation results, or by adding empirical rules to them. It is also possible to calculate the value of T by substituting the value of T, but in some cases, the allowable current value curve K is represented by an appropriate number of points, and each point is expressed as (T,
IKI) , (T2. IK2) , ... (Tn,
It is also possible to store it as a table in the form of IKn), input the value of the motor temperature T, and read out the corresponding allowable current value IK.

The current limiting circuit 13 limits the current reference obtained by the comparison arithmetic circuit 12 so as not to exceed the allowable current value IK found by the protection arithmetic circuit 4, and transmits it to the power amplifier circuit 15.

By setting the allowable current value IK of the electric motor 20 as described above, when the temperature of the electric motor 20 is in a relatively low temperature state, that is, when it is in a state below the maximum allowable temperature value C, the controlled An overload condition can be created, thereby making it possible to derive performance from the electric motor 20 that exceeds the continuous rating. If the motor continues to operate in this way, the motor temperature may gradually rise.
In that case, the current limiting effect works according to the allowable current value curve K in FIG. 2, and the allowable current value IK gradually decreases, gradually shifting to continuous rated operation.

〔Effect of the invention〕

As described above, according to the present invention, when the temperature of the electric motor is lower than the maximum permissible temperature value, that is, when the temperature of the electric motor is lower than the maximum permissible temperature value, the transiently controlled overload state is activated. This enables the motor to operate in a transient manner, thereby drawing out transient performance from the motor that exceeds its continuous rating. Thereby, it is possible to avoid as much as possible a situation in which the operating efficiency of the equipment is excessively reduced.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of a motor control device according to the present invention, and FIG. 2 is a characteristic diagram showing the characteristics of the protection arithmetic circuit in FIG. 10... Motor control device, 11... Current setting circuit,
12... Comparison calculation circuit, 13... Current limiting circuit, 14
...Protection calculation circuit, 15...Power amplifier circuit, 16.
...Current detector, 20...Electric motor, 21...Speed detector, 22...Temperature pressure detector.

Claims (1)

[Scope of Claims] A motor control device that controls a motor current according to a current reference set so that the speed of the motor becomes a predetermined value, comprising: a first means for detecting a temperature of the motor; and a maximum permissible temperature of the motor. a second means for determining the permissible current value for the motor temperature detected by the first means, based on a correlation determined such that the current value and the maximum permissible temperature value have a decreasing function relationship; and third means for limiting the current reference to be less than or equal to the allowable current value determined by the second means.