JPH0789702B2 - Motor control device - Google Patents

Description

The present invention relates to an electric motor control device, and particularly to an electric motor control suitable for protecting an electric motor or a power conversion device that supplies electric power to the electric motor. Regarding the device.

(Prior Art) Generally, a motor control device is a device that controls the output of a power converter so that the output, speed or torque generated by the motor follows a set command value. It also has a protective function.

As a typical protection function, there is an overcurrent protection function for preventing an excessive current from flowing during a circuit short circuit time. This function detects the current flowing in the motor, and when this value exceeds a certain set value, it is detected as an overcurrent, and the circuit shorted by a circuit breaker, etc. is opened to prevent an excessive current from flowing in the circuit. is there. In the case of such overcurrent protection, since the protection target is a fault current such as a short circuit current, it is necessary to open the circuit instantaneously and cut off the current after the detection.

Another protection function is overload protection. Overload protection protects an electric motor or control device when an excessive load is continuously applied to the electric motor or control device. Generally, as the motor load increases,
To generate a torque corresponding to this load in the electric motor,
Increase the current flowing into the motor. Therefore, when an excessive load is continuously applied, a large current continuously flows through the electric motor. For this reason, the temperature inside the control device and the electric motor rises, but if this high temperature state continues for a long time,
For example, the insulation resistance of the control device and the electric motor may deteriorate, and the service life may be shortened. Therefore, in order to prevent such inconvenience, overload protection is performed.This overload protection instantly detects the case where an abnormally large current flows when overcurrent protection fails. In contrast to what is performed, it is performed by detecting the case where a large current that flows during normal operation continuously flows for a certain time or longer.

FIG. 3 is a block diagram of a known motor control device, and particularly illustrates an overload protection function.

In the configuration shown in the figure, the current flowing from the power converter 5 to the electric motor 1 via the circuit breaker 8 is detected by the current detecting means 2. The current signal detected by the current detecting means 2 is squared by the squaring means 3 and further averaged by the time averaging means 4.

By the way, the output of the time averaging means 4 squares the current signal,
Further, since the signal has a time average, it corresponds to the square of the effective value of the current signal. Therefore, the square root of this signal gives the effective value. That is, in the case of performing overload protection, the amount of heat generated in the electric motor 1 or the power converter 5 is monitored, so that the effective value of the current having an equivalent relationship with the amount of heat generation is obtained.

The effective value of this current is compared with the value set by the setting means 6 by the comparing means 7, and when the effective value of the detected current exceeds the set value, this is detected as an overload, and the circuit breaker 8
Is opened to cut off the electric current flowing through the electric motor 1,
Alternatively, the power converter 5 is protected.

In the case of the configuration shown in FIG. 3, by setting the effective value of the current which can be withstood by either the electric motor 1 or the power converter 5 which is thermally weak by the setting means 6, the electric motor 1 and the power converter 5 It is possible to protect both.

As mentioned above, the overload protection detects this when the effective current value exceeds the set value. Generally, since the motor 1 can withstand 100% continuous load, the set value is 100%. desirable. If set to 125%, 12
Up to 5% continuous load will be allowed.

On the other hand, electric motors have overload capacity. This is because, in addition to the load, torque may be required for a shorter time in order to accelerate or decelerate the electric motor. For example, if the motor speed is constant when a 100% load is applied, the motor current will be 100%, but more current needs to be passed to accelerate the motor. The current required to accelerate the electric motor varies depending on the rate of change in speed (acceleration or deceleration) and the time required for the change, but for example, a current of about 150% may be required. In this case, the electric current flowing through the electric motor may be 100% due to the load, 150% due to acceleration, and 250% in total. Therefore, as the overload capacity of the motor
Some allow for 60 seconds of 250% current.

(Problems to be Solved by the Invention) As described above, if the overload withstand amount is set, naturally, the overload should not be detected while the electric motor is operating within the overload withstand amount.

If the motor is rated for 100% continuous load and 250% -60% overload, 250% if the overload setting is 100%.
There is an inconvenience that the overload protection function operates during operation under load. On the other hand, if the overload setting is increased so that the overload protection function does not operate even if operated at 250% load for 60 seconds, this time, for example, 125% continuous load cannot detect overload and There is a problem that the protection function does not work.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide an electric motor control device capable of performing overload protection according to the usage state of the electric motor.

[Structure of Invention]

(Means for Solving Problems) The present invention relates to a power converter for supplying electric power to an electric motor, a current detecting means for detecting an output current of the power converter, and a detection current squared by the current detecting means. Setting means, and at least one time averaging means for time averaging the outputs of the calculating means to send a signal corresponding to the square of the effective current value, and the output of the time averaging means and a plurality of setting means. The present invention provides a motor control device including a plurality of comparing means for individually comparing a plurality of set values that have been set and outputting an output when the output of the time averaging means exceeds the set value.

(Operation) By performing overload detection of the electric motor under a plurality of conditions based on the above means, it is possible to perform appropriate overload protection of the electric motor in accordance with the usage state of the electric motor.

Embodiments Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram of an electric motor control device according to an embodiment of the present invention. As shown in the figure, the electric motor control device of the present embodiment includes an electric power converter 5 for supplying electric power to the electric motor 1 and a current detecting means 2 for detecting an output current of the electric power converter 5.
A square calculation means 3 for squaring the current signal obtained by the current detection means 2, and first and second time averaging means 41, 42 for time averaging the outputs of the square calculation means 3. It comprises first and second comparing means 71, 72 for comparing the outputs of these time averaging means 41, 42 with the set values of the first and second setting means 61, 62, respectively.

In such a configuration, the current detecting means 2 can be realized by a shunt, a DC CT (converter), or the like. The effective current value is obtained from the current signal detected by the current detecting means 2. The effective current value I _rms is Required by. Where I _rms is the effective value of the current, i
(T) is the magnitude of the current at time t. Further, T is a measurement time. The expression (1) means that time t = 0.
It means that the sum of squares of the magnitude of the current is taken in the time from t to t = T, this is averaged at the time T, and the square root is taken as the effective value.

When determining whether the load is overload, it is sufficient to determine whether the value of the equation (1) is greater than or equal to the set value, and therefore the square root of the equation (1) is not calculated, but the set value is set to 2 You can judge the overload by riding. Therefore, in this embodiment, The square of the effective value is calculated based on the following equation.

1, the square calculation means 3 calculates the {(i (t)} ² term of the equation (2), and the first and second time averaging means 41, 42 calculate the square. Output of means 3 {i (t)}
I ² _rms is calculated by inputting ² and taking the sum at each time T, and further dividing by T.

In the case of an electric motor having an overload tolerance of 250% -60 seconds, the first time averaging means 41 sets 60 seconds as the time T,
The effective value is calculated every second, and a value equivalent to 250% is set in the first setting means 61. Therefore, the effective value for 60 seconds is 250%
When it exceeds, the first comparison means 71 detects this and the circuit breaker 8 is opened by the output signal thereof to protect the electric motor 1.

On the other hand, the second time averaging means 42 sets 30 minutes as the time T, calculates the effective value every 30 minutes, and sets the second setting means 62.
Is set to a value equivalent to 100%. Therefore, when the effective value for 30 minutes exceeds 100%, this is detected by the second comparison means 72, and the circuit breaker 8 is opened by the output signal thereof to protect the electric motor 1.

As described above, overload detection based on a plurality of conditions by the first and second time averaging means 41, 42, the first and second setting means 61, 62 and the first and second comparing means 71, 72. By doing
An electric motor with a large overload capacity of 250% -60 seconds can be protected from overload of 100% or more during normal operation.

For example, the motor usage rating is 100% continuous load, 250% load
In the case of 60 seconds, the first time averaging means 41 calculates the time average for 60 seconds, outputs the square of the effective value for 60 seconds, and the first comparing means 71 calculates the square of the effective value for 60 seconds. 1 setting means
When the value set by 61 is exceeded, the circuit can be opened by the circuit breaker 8 to protect the power converter 5 and the electric motor 1. On the other hand, the second time averaging means 42 calculates the time average of 30 minutes, outputs the square of the effective value of 30 minutes, and the second comparing means 72 sets the square of the effective value of 30 minutes to the second setting. When the value set by the means 62 is exceeded, the circuit breaker 8 can open the circuit to protect the power converter 5 and the electric motor 1. Therefore, the first and second setting means 61, 6
If the set values of 2 are set to 250% and 100%, respectively, the overload is detected by the first comparing means 71 when the 250% load continues for 60 seconds or more, and, for example, 125
When the% load continues, the overload is detected by the second comparing means 72 after 30 minutes.

FIG. 2 is a block diagram of an electric motor control device according to another embodiment of the present invention. The configuration of FIG. 1 differs from that of FIG. 1 in that
The number of time averaging means 4 is one, the circuit breaker 8 is operated only by the output of the first comparing means 71, and the output of the second comparing means 72 is used only for the alarm signal 9.

In such a configuration, the time averaging means 4 is set to 5 minutes as the time T, and the effective value for 5 minutes is calculated. First, the second setting means 62 sets a value corresponding to an effective value of 100%, and when the effective value exceeds this value, the second comparing means 72 detects this and outputs the alarm signal 9 to the outside of the control device. Output. The alarm signal 9 informs the operator that the effective value is increasing, for example, by a lamp, and instructs the operator to reduce the load on the electric motor or stop the electric motor.

Still, if the effective value of the motor rises,
The first setting means 61 that sets a value equivalent to 130%
Of the electric motor 1 by opening the circuit breaker 8
Protect.

According to this configuration, the time averaging means 4 obtains a time average of 5 minutes, and when the square of the effective value exceeds, for example, 130% equivalent value by the first comparing means 71, the circuit breaker 8 is opened for protection. Can be done. Further, when the square of the effective value exceeds the 100% equivalent value by the second comparing means 72, the alarm signal 9 is output and the operator can reduce the load.

On the other hand, according to the present embodiment, particularly when a plurality of electric motors are moving in cooperation with each other, when one of the electric motors does not suddenly stop when an overload occurs, it is predicted that one electric motor will stop. There is an advantage that a plurality of electric motors can be stopped while cooperating with each other before stopping.

〔The invention's effect〕

As described above, according to the present invention, in order to protect the overload of the electric motor, the square of the effective value of the electric motor current, which directly represents the amount of heat generated that causes thermal destruction, is monitored to operate the electric motor. By having multiple comparison means corresponding to each state,
It is possible to provide an electric motor control device capable of overload protection suitable for the usage state of the electric motor.

[Brief description of drawings]

FIG. 1 is a block diagram of an electric motor control device according to an embodiment of the present invention, FIG. 2 is a block diagram of an electric motor control device according to another embodiment of the present invention, and FIG. 3 is a block of a known electric motor control device. It is a figure. 1 ... motor, 2 ... current detecting means, 3 ... square calculating means, 4,41,42 ... time averaging means, 5 ... power converter, 6,6
1,62 …… Setting means, 7,71,72 …… Comparison means, 8 …… Breaker.

Claims (3)

[Claims] 1. A power converter for supplying electric power to an electric motor, a current detecting means for detecting an output current of the power converter, a calculating means for squaring a detected current of the current detecting means, and a calculating means of the calculating means. At least one time averaging means for time averaging the outputs and transmitting a signal corresponding to the square of the current effective value;
And a plurality of comparing means for individually comparing the output of the time averaging means and a plurality of setting values set by a plurality of setting means, and for outputting an output when the output of the time averaging means exceeds the set value. A motor control device characterized by the above. 2. The electric motor control device according to claim 1, wherein the time averaging means is composed of a plurality of means in which different times are set. 3. The electric motor control device according to claim 1, wherein at least one of the plurality of comparing means is connected to a means for cutting off a current from the power converter to the electric motor.