JPS6218986A - Motor controller - Google Patents

Abstract

PURPOSE:To prevent a motor from overheating without stopping the operation by controlling so that the effective value of an input current does not exceed the limiting value at accelerating and constant-speed operating time. CONSTITUTION:The present current is detected by a current transformer 4, and a current effective value calculator 8 calculates the effective current value. The present speed is detected on the basis of a signal from a position sensor 2. Whether it is accelerating is judged from the detected result; if the accelerating, the effective current value is compared with the effective current value limitation at the present speed, and if arriving at the limitation, the acceleration is temporarily stopped for the prescribed time. If in constant-speed operation, the effective current value is compared with the effective current limitation at present time, and if arriving at the limitation, the speed is decelerated by the prescribed amount.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a motor control device, and more particularly to a motor control device suitable for variable speed control of a motor that drives a fan, pump, etc. having square load characteristics. .

(Technical Background of the Invention) In recent years, when driving loads such as fans and pumps, AC variable speed drive units (hereinafter referred to as V
A system is adopted in which variable speed operation is performed over a wide range using VVF (VVF).

FIG. 8 is a system diagram of a conventional motor control device for variable speed control of an AC motor. As shown in the figure, an electric motor 1 that drives loads such as fans and pumps is operated at variable speed by a VVVF 3. A position sensor 2 is attached to the electric motor 1 and is used as a commutation control signal for the VVVF 3.

The primary side of VVVF3 is connected to AC power supply via current transformer 4.
is connected. On the other hand, an overcurrent relay 5 that stops the operation of the VVVF 3 in the event of an overcurrent is connected to the secondary side of the current transformer 4. The VVVF 3 performs variable speed operation based on the speed reference set by the speed reference control device 6.

In such a conventional motor control device, if the primary current value of VVVF 3 exceeds the rated value, the temperature of the motor 1 will exceed the permissible value if the motor 1 is operated or accelerated. A control method is adopted in which the overcurrent relay 5 detects an overcurrent in the primary side current through the flow device 4, and the VVVF 3 is turned off to stop the motor 1.

[Problems with blue technology]

As mentioned above, conventional electric motor control devices stop operation when the current value exceeds the rated value. ! Since a control method that protects 11 is adopted, the stoppage causes a decrease in operational efficiency, resulting in a large economic loss. Also, depending on the nature of the load, stopping may be dangerous, so there has been a strong demand for a system that protects the electric motor 1 without stopping it.

In addition, if the motor 1 is self-cooled, the cooling effect changes depending on the rotation speed, so in order to protect the motor 1 from overheating in all variable speed ranges, it is necessary to check whether the motor current exceeds the rated value. Merely checking this has the disadvantage that effective overheating protection cannot be achieved.

[Purpose of the invention]

Therefore, the purpose of the present invention is to ensure maximum operating efficiency by protecting the motor from overheating without stopping it, and for self-cooled motors, to enable effective overheating protection over the entire variable speed range. An object of the present invention is to provide an electric motor control device that provides the following characteristics.

[Summary of the invention]

In order to achieve the above object, the present invention provides a setting means for setting the limit value of the effective current value in the entire variable speed range of a motor operated at variable speed, and a setting means for measuring the input current of the motor at fixed time intervals. a calculation means for calculating an effective value, and when the effective value of the input current calculated by this calculation means reaches the limit value of the current effective value set by the setting means during constant speed operation, deceleration is performed by a certain amount, and acceleration is performed. The present invention provides a motor control device characterized in that it includes a control means for interrupting acceleration for a certain period of time when the effective current value reaches a limit value.

[Embodiments of the invention]

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

FIG. 1 is a system diagram of a motor control device according to an embodiment of the present invention. In the figure, an RMS current calculation device 8 calculates the effective value (RMS) current of the input current from the input current value to the VVVF 3 detected by the current transformer 4. Current comparison υ
The J control device 7 receives an input RMS current from the RMS current calculation device 8, receives a speed signal from the position sensor 2, and sends a control signal to the speed reference control device 6.

On the other hand, FIG. 2 is a characteristic diagram showing an example of load characteristics of a fan, a pump, etc. driven by the electric motor 1 operated at variable speed by the electric motor control device of this embodiment. As is clear from the figure, fans, pumps, etc. are loads with decreasing torque characteristics, where the load torque decreases as the rotation speed decreases if the load condition, that is, the condition of the damper, stator vane, valve, etc., is constant. It is.

Further, FIG. 3 is a characteristic diagram showing the RMS current limit value according to the rotational speed of the self-cooled ratio fIJ machine operated at variable speed by the electric motor control device of this embodiment. As shown in the figure, the cooling effect of the self-cooled electric motor changes depending on its rotation speed, and the RMS current is limited due to its heat capacity, so the limit value OL of the RMS current is set. can do.

FIG. 4 shows a current chart in which the primary current supplied to the VVVF 3 is measured at regular time intervals. VV
V, F To explain in detail the calculation method of the effective value of the input current, that is, the input RMSt current, input is the sampling time (seconds), i is the current value (ampere), and t is the sampling pitch (seconds). In other words, did you sample at a pitch of t seconds per sampling time of 1 second? li style i
is calculated, and the root mean square current is calculated as 8MS current.

Here, data updating of current i within sampling time T seconds will be explained with reference to FIG. 4. First, at sampling time T(1), current 11-in is calculated at a sampling pitch of t1-1°. In the next cycle, the sampling time shifts to T(2), and the current 20+11~i is applied at a sampling pitch of 1-1, and the current is set to 2 at sampling time T(3).
n+1 is a current i33 with a sampling pitch of 1 −1
Similarly, at sampling time T(4)n+2, ff114 is applied to n+2 to 1 with a sampling pitch of 1 −1.
The data of current i is sequentially divided into 4n+ as n+3 i ~ 1.
3 Calculate the input iRMs current while updating.

The operation of this embodiment will be explained based on the above-mentioned device configuration, load characteristics, and motor conditions with reference to the control flowchart shown in FIG.

First, block 51) detects the current current from current transformer 4.
, the RMS current calculation device 8 calculates the RMS current IR (block 52), and the current speed is detected based on the signal from the position sensor dimension -2 (block 53). Based on the detection result, it is determined whether or not acceleration is being performed (block 54). If acceleration is being performed, the 8MS current (IR) at the current speed and the
A comparison is made with the current limit value CL (blocks 55 and 56).
), if the limit value is reached, the acceleration is interrupted for a certain period of time (block 57), and if the limit value is not reached, the acceleration is continued (block 57).
block 58). On the other hand, if the judgment in block 54 is that the vehicle is not accelerating, that is, it is driving at a constant speed, then the
MS current (■,) and RMS? A comparison is made with the i4 flow limit value CL (blocks 59 and 60), and if the limit value is reached, the speed is lowered to a certain level (block 61), and at the same time an abnormality display is displayed and an alarm is issued (block 62). On the other hand, if the limit value has not been reached, constant speed operation is continued at the set speed (block 63), so that acceleration and constant speed operation are performed within the RMS current limit value in any state. Control becomes possible, and heating of the electric motor 1 can be protected.

In addition, in the above-mentioned action, 8MS current (I
When R) reaches the RMS current limit value C, acceleration is interrupted, and during constant speed operation, when the 8MS current (IR) reaches the RMS current limit value C, the speed is reduced by a certain amount. Although the case is illustrated, closed loop control as described below may also be performed.

For example, Fig. 6 shows a control flowchart during acceleration.
The S current (IR) is compared with the RMS current limit value OL (block 64.65), and if the limit value has not been reached, acceleration operation is performed at the specified acceleration rate (block 66).
. On the other hand, if the limit value has been reached, the acceleration rate is decreased (block 67) and the acceleration is continued for a certain period of time (block 68).
), 7171ffRMSffil (IR) limit 1i
aCLc7) Ratio M (block 69.70), if the limit value has been reached, reduce the acceleration rate again and accelerate for a certain period of time (block 71), repeat this control RMS
If the ffi flow (IR) becomes smaller than the limit (iaCL), the acceleration operation continues at the current acceleration rate (block 72).
.

On the other hand, Fig. 7 is a control flowchart during constant speed operation, and as shown in the figure, the control during constant speed operation is similar to that during acceleration, by comparing the 8MS current (11) and the RMS current limit value OL. Then, if the limit value has not been reached, constant speed operation is performed at the set speed (block 75). On the other hand, when the limit value is reached, reduce the speed by a certain amount (block 76) and operate at a constant speed for a certain period of time (block 77).
, compare the RMS current (IR) and the limit value CL again (
If the limit value has been reached (blocks 78, 79), the amount of speed reduction is increased again and constant speed operation is performed for a certain period of time (block 80). When this control is repeated and the RMS current (1) becomes less than the limit value CL, the speed reduction is stopped and constant speed operation is continued at the current speed (block 81).

J3, as the electric motor 1 to be controlled, a synchronous motor may be used to perform variable speed and constant speed operation with VVVF3, and an induction motor may be used as the electric motor 11 to perform similar operation. .

On the other hand, when using a DC motor as the motor, VV
Of course, the same effect can be obtained by using a DC Leonard control device in place of VF3.

〔Effect of the invention〕

As described above, according to the present invention, during acceleration and constant speed operation, the RMS current limit value is set and control is performed so that the input RMS current does not exceed the limit value, so that the operation cannot be stopped. Therefore, it is possible to provide a motor control device that can protect the motor from overheating without any problems and can operate at maximum efficiency.

[Brief explanation of drawings]

FIG. 1 is a system diagram of a motor control device according to an embodiment of the present invention; FIG. 2 is a characteristic diagram showing an example of load characteristics of a load driven by a motor operated by the motor control device of FIG. 1; Fig. 3 is a characteristic diagram showing the RMS current limit value of a self-cooling type '#J machine operated at variable speed by the electric motor control device shown in Fig. 1, and Fig. 4 is an input current of the motor control device shown in Fig. 1. 5 is a flowchart explaining the operation of the configuration of FIG. 1; FIGS. 6 and 7 are flowcharts explaining other operations of the configuration of FIG. 1; FIG. 8 is a system diagram of a conventional motor control I device. 1...Electric motor, 2...Position sensor, 3...
- Variable speed drive device, 4... Current transformer, 5... Overcurrent relay, 6... Speed reference control device, 7... Current comparison control device, 8... RMS current calculation device. Figure 1 Rotation angle -〉 (olo) Figure 2 Figure 3 Figure 4 Figure 8

Claims (1)

[Claims] 1. Setting means for setting the limit value of the effective current value in the entire variable speed range of the motor operated at variable speed; a calculating means for calculating, and when the effective value of the input current calculated by the calculating means reaches the limit value of the effective current value set by the setting means during constant speed operation, decelerating by a certain amount; An electric control device comprising: control means for interrupting acceleration for a certain period of time when the limit value of the effective current value is reached during acceleration. 2. The motor control device according to claim 1, wherein the motor is a synchronous motor. 3. The electric motor control device according to claim 1, wherein the electric motor is an induction motor. 4. The motor control device according to claim 1, wherein the motor is a DC motor driven by a DC Leonard control device.