JP3315332B2 - Inverter control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in an inverter control device for driving an induction motor, and particularly for controlling the speed by current feedback control.

[0002]

2. Description of the Related Art An application will be described below taking an elevator apparatus as an example. In elevators, it is necessary to perform a wide and smooth speed control from start to stop,
Therefore, current feedback control is performed. That is, the voltage command is operated so that the feedback current matches the current command of each phase, and the main transistor is driven by the PWM signal so that the voltage is applied to the induction motor according to the voltage command. .

In this case, the control characteristics greatly depend on the detection accuracy of the current detector. Generally, the current detector outputs a small signal, that is, an offset irrespective of the fact that the detected current is actually zero. For this reason, a command in which the offset is added or subtracted is always given to the control signal of the inverter. As a result, torque ripple due to the DC component occurs, the car vibrates, and the riding comfort deteriorates. Problems arise.

[0004]

For this reason, it is conceivable to use a high-performance current sensor to minimize the offset. However, a high-performance current sensor is expensive and leads to an increase in overall cost.

Further, a method of canceling the offset by considering the offset amount after stopping the inverter as zero in the next inverter operation has been considered. However, when an inexpensive current detector such as a Hall element is used,
Since the offset becomes different from the original value due to the influence of residual magnetic flux when the inverter stops, even if the offset amount after stopping the inverter is regarded as zero in the next operation, the original offset is completely Can not be canceled.

That is, the influence of the residual magnetic flux differs in magnitude and polarity depending on the current value and the current direction before the inverter stops due to its hysteresis characteristic, and the powering mode or the powering mode depends on the driving direction and the load condition in the car like an elevator. When the load condition is different from the regenerative mode every time, the influence of the residual magnetic flux added to and subtracted from the original offset also has a different value each time. Therefore, even if the above method is applied to an elevator and the offset amount when the inverter is stopped is regarded as zero in the next operation, the value is different from the original offset. It cannot be canceled completely, and as a result, torque ripple due to the DC component occurs.

SUMMARY OF THE INVENTION The present invention has been made to solve such a problem. An inexpensive current sensor such as a hall element is used for an elevator, and the offset value at the time of stopping the inverter is different each time due to the influence of residual magnetic flux. In such a case, the original offset can be reliably canceled with a simple configuration.

[0008]

SUMMARY OF THE INVENTION According to the present invention, when the elevator is operated a plurality of times (for example, about 10 times), the load in the car and the load driving direction during the operation vary, so the offset for each stop of the elevator during this time is varied. When the amounts are averaged, the effect of the residual magnetic flux is almost canceled, and only the original offset is left.Furthermore, taking into account the time elapsed until the next start, the offset correction means
It is to change according to the elapsed time.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, when it is detected that an elevator has stopped by a speed command signal or the like, an offset of a current detector is detected and its amount is stored. Furthermore, in order to remove the influence of the residual magnetic flux, the average value of the latest and latest offset amounts including the current offset amount is calculated, and the average value is used as the offset correction amount. Then, this offset correction amount is output as a correction signal at the time of the next startup. This is repeated each time the elevator stops, and the offset included in the detection signal of the current detector is canceled by this correction signal.

[0010] However, when the interval from the stop of the elevator to the next start-up is wide (about 3 minutes or more), the influence of the offset shift due to the temperature dependence is larger than the influence of the offset shift due to the residual magnetic flux. In this case, the offset value immediately before starting is used as it is as the offset correction amount.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the overall configuration of the present invention, wherein 1 is a three-phase AC power supply, 2 is a converter for converting an AC power supply to DC, 3 is a smoothing capacitor for smoothing the output of this converter, and 4 is a converter 2 An inverter for converting the output into an alternating current with a variable voltage and a variable frequency, 5 detects an output current of each phase of the output of the inverter 4, and outputs a current detector as a detection signal 5a. 5b converts this detection signal 5a to a correction signal described later. 1
The detection signal corrected by 7a, 6 is an induction motor fed by the inverter 4 to drive the elevator, 7 is a speed detector that outputs the actual speed of the car as a speed feedback signal 7a, and 8 is driven by the induction motor 6. The sheave of the hoisting machine, 9 is a main rope wound around the sheave 8, 10 is a car connected to the main rope 9, 11 is a counterweight, and 12 is a speed command for outputting an ideal speed command signal 12 a. Generator, 13
Is a current command generator that inputs a speed command signal 12a and a car speed feedback signal 7a and outputs a current command signal 13a.
4 is an ACR (current controller), 15 is a PWM circuit, and 16 is a base drive circuit.

Reference numeral 17 denotes a microcomputer as offset correction means, which detects an offset from the detection signal 5a every time the elevator stops and stores the value, and a storage means 18 for storing the value of the latest multiple offset amounts. Calculate the average value as the offset correction amount at the next startup,
And an offset correction amount calculating unit 19 that outputs the offset correction amount as a correction signal 17a.

In the above configuration, the speed command generator 1
When the speed command 12a is generated from 2, the current command generator 13 generates a current command signal 13a corresponding to the torque required by the induction motor 6 so that the elevator car 10 follows the speed command 12a. On the other hand, the current actually flowing through the induction motor 6 is detected by the current detector 5, and the detection signal 5a is corrected for the offset by the correction signal 17a calculated by the microcomputer 17 in a procedure described later, and the detection signal 5b Become.

Here, the procedure for calculating the offset correction amount in the microcomputer 17 will be described with reference to the flowchart of FIG.

This program starts when the elevator arrives at the destination floor and stops. First, in step S1, an offset is detected from the detection signal 5a when the elevator stops, and the value is stored. Next, in step S2, the latest 1
The average value of the zero offset amount is calculated, and the average value is replaced as it is with the value calculated at the previous stop as the offset correction amount. The offset correction amount may be output until the elevator starts and stops next time. However, as described above, when a predetermined time (for example, about three minutes) elapses after the car stops, the offset due to temperature dependence is output. Because the influence of the deviation becomes large, here, when three minutes or more have passed since the stop of the elevator, the offset value immediately before the next start-up is output as the offset correction amount as it is, instead of the offset correction amount calculated in step S2. ing.

That is, in step S3, it is confirmed whether three minutes have passed since the elevator stopped, and in step S4, it was confirmed that the operation of the elevator was started, and then the offset correction amount calculated in step S2 was corrected. The signal is output until the next stop of the elevator in step S5.

On the other hand, if three minutes or more have elapsed since the elevator was stopped, the latest offset at the present time is detected in steps S6 and S7, and when the elevator starts operating, the offset immediately before startup is used as a correction signal in step S8. Until the elevator stops.

Thereafter, when the same procedure is repeated every time the elevator stops, the offset correction amount is updated every time the elevator stops, and the effect of the residual magnetic flux is canceled regardless of the load condition. A value corresponding to the offset is calculated as the offset correction amount.

Returning to FIG. 1, as described above, the correction signal 17a
Signal 5b in which the original offset has been canceled
Is compared with the current command signal 13a.
The signal is amplified by R14, and pulse width modulation is performed by the PWM circuit 15 by comparison with a carrier signal. The base drive circuit 16 controls a switching element such as a transistor constituting an inverter according to the pulse width modulation signal. However, since the offset is canceled as described above, the output of the inverter does not generate a DC component. The desired AC power is supplied to the induction motor, and as a result, the elevator car 10 moves up and down following the speed command without generating vibration.

In the above description, the offset correction amount is calculated by averaging the amounts of the offsets for ten times. However, the number of offset corrections is not limited to this number, and the influence of the residual magnetic flux can be substantially reduced. Any number of times that are considered to be cancelled can be used. Also, the predetermined time is not limited to three minutes, and it is needless to say that the predetermined time may be any time in which the influence of the temperature dependence is considered to be large.

[0021]

According to the present invention, even if an inexpensive current detector such as a Hall element is used, the offset can be surely canceled without being affected by the residual magnetic flux, and the riding due to the occurrence of torque ripple can be achieved. Deterioration of comfort can be prevented.

Further, according to the present invention, even when the offset amount fluctuates due to aging or the like, the offset correction amount is updated accordingly, so that stable control can be performed for a long period of time. Further, when a predetermined time or more has elapsed from the stop of the elevator, the offset immediately before the next start is used as it is as the offset correction amount, so that the influence of the offset deviation due to temperature dependency can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of the present invention.

FIG. 2 is a flowchart showing a processing procedure of an offset correction unit in the present invention.

[Explanation of symbols]

 Reference Signs List 1 three-phase AC power supply 2 converter 3 smoothing capacitor 4 inverter 5 current detector 6 induction motor 10 car 12 speed command generator 13 current command generator 14 ACR 15 PWM circuit 16 base drive circuit 17 microcomputer 18 storage means 19 offset correction amount Calculation means

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-7095 (JP, A) JP-A-63-274398 (JP, A) JP-A-60-23268 (JP, A) JP-A-63-274 274390 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H02P 1/00-7/66 H02P 21/00 B66B 1/00-1/52 H02M 7/42-7/98 G01R 22/00 G01R 35/00

Claims (2)

(57) [Claims] 1. A a converter for converting AC power to DC,
An inverter control device comprising: an inverter that converts the output of the converter into an alternating current having a variable voltage and a variable frequency and supplies power to the induction motor; and an offset control unit that includes a current detector provided in each phase of the inverter output. The offset correction unit includes a storage unit that stores an offset amount of the current detector each time the operation of an intermittent load such as an elevator is stopped, and the latest multiple times when the elapsed time until the next startup is within a predetermined value. Is calculated as the offset correction amount at the next startup, and if the elapsed time until the next startup exceeds a predetermined value, the offset immediately before the startup is calculated as the offset correction amount at the next startup. An inverter control device comprising: a correction amount calculating unit. 2. The method according to claim 1, wherein the current detector is a sensor such as a Hall element.
The inverter control device according to claim 1, wherein