JPH06237593A - Driving device of induction motor for polisher - Google Patents

Abstract

PURPOSE:To obtain a driving device of a polisher being so designed as to prevent an overcurrent from flowing through an electric light line of an input in any loaded state, by combining a variable-frequency inverter with a three- phase induction motor. CONSTITUTION:The number of revolutions of a motor 18 is detected by a revolutions detector 19 and a signal 20 thereof is inputted to an arithmetic unit 14. Meanwhile, a signal 13 set by a revolutions setting unit 12 is also inputted to the arithmetic unit 14. In the arithmetic unit 14, a voltage and a frequency are computed so that a torque be the maximum in a prescribed input current of the motor, by using the set number of revolutions and an intrinsic set number of revolutions of the motor, and they are inputted to a variable- frequency inverter 17. Thereby the motor is driven by a minimum current at any number of revolutions and thus a driving device of a polisher which can prevent an overcurrent from flowing through an electric light line of an input.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a drive device for a polisher induction motor, which is a combination of a polisher induction motor and a variable frequency inverter.

[0002]

2. Description of the Related Art Floor cleaning machines (hereinafter referred to as polishers)
Conventionally, an electric motor has been used for driving. In addition, since cleaning is not performed in a specific place, the power is mostly received from a single-phase power line that can be easily used anywhere. However, the single-phase electric motor has the following problems as compared with the general industrial 3-phase electric motor.

1) In principle, a starting device is required and a mechanical switch or the like is provided, so that maintenance is required and sparks are likely to cause electromagnetic interference.

2) Large starting current.

3) Both efficiency and power factor are low, and current during operation is large.

4) In principle, there is torque pulsation.

Moreover, since the capacity of the general electric power line is small,
Due to the above-mentioned problems, the breaker of the power line has fallen or a large voltage effect has occurred. Therefore, it cannot be used for a relatively large polisher. In addition, the brush at the bottom of the polisher starts turning around when the power is turned on, which poses a safety issue for workers.

In order to solve the above problems, Japanese Patent Laid-Open No. Sho 61-61
-1449427, single phase input-3
A three-phase induction motor equipped with a phase output type variable frequency inverter and having excellent characteristics is provided, which has a system of driving a polisher.

According to this method, the problems of the single-phase induction motor described above can be almost solved, and at the same time, there is an advantage that the rotation speed of the polisher can be changed steplessly because the variable frequency inverter is driven. However, since the V / f value is constant and the open loop control system uses a general inverter, some problems described below remain.

Next, a conventional technique will be described with reference to FIGS. FIG. 5 shows an equivalent circuit for one phase of the three-phase induction motor.
In the figure, f is the input frequency (inverter output frequency), V is the input voltage (inverter output voltage), i ₁ is the input current (inverter output current), R ₁ is the primary resistance, R ₂ is the primary conversion secondary resistance. , L ₁ is the primary leakage inductance, L ₂ is the primary leakage secondary leakage inductance, L ₀ is the excitation inductance, and S is the slip.

FIG. 6 shows a rotational speed-torque characteristic and a rotational speed-input current characteristic diagram of the three-phase induction motor when the three-phase induction motor is driven by open loop control with constant V / f. Curves 1 to 4 in the figure are V so as to supplement the primary voltage drop i ₁ (R ₁ + jωL ₁ ) caused by the primary resistance R ₁ , the primary leakage inductance L ₁ and the primary current i ₁ shown in FIG. / F value is an example of the rotation speed-torque characteristic with respect to the rotation speed command value, and curves 5 to 7 are examples of the rotation speed-torque characteristic when the V / f is not compensated. Also, the curves 8-11
Is a rotation speed-input current characteristic when V / f is compensated, and f _SM is a slip frequency peculiar to the electric motor when the induction motor has the maximum torque.

The following problems can be easily understood from FIG. That is, when the primary voltage drop is not compensated for, the torque decreases significantly as the set rotation speed decreases. This is because the ratio of the primary voltage drop increases as the rotation speed decreases, and the voltage applied to the excitation inductance L ₀ in the equivalent circuit of FIG. 5 decreases significantly. Also, 1
When the correction of the next voltage drop is performed, the torque does not decrease even if the set rotation speed is low, but the input current is large even when there is no load. This is because the compensating voltage is applied to the exciting inductance L ₀ almost as it is when the load is light.
This is because the exciting inductance causes magnetic saturation. Also, during operation at a certain set speed, an excessive input current flows when the electric motor is in a locked state due to overload or the like, or when the speed is significantly different from the set speed. This is because the inverter continues to output a constant set voltage and frequency regardless of the rotation speed of the electric motor.

As described above, in open loop control using a general inverter, there still remains a problem that the breaker of the power line breaks down due to overcurrent at the time of overload and a large voltage drop occurs. Also, the rotation is not stable due to the torque decrease at low rotation speed, and V /
When the f-value compensation is performed, there is also a problem that the electric motor is often overheated because the input current is large even when the load is light.

[0014]

SUMMARY OF THE INVENTION According to the present invention, in a polisher drive device, a variable frequency inverter and a three-phase induction motor are combined to detect the motor rotation speed, and the optimum value is determined from this, the motor constant and the set rotation speed. By calculating the voltage and frequency and supplying them to the electric motor, it is possible to maintain a stable rotation speed over the entire rotation speed range and to prevent overcurrent from flowing in the input power line under any load condition. To do.

[0015]

According to the present invention, in a polisher induction motor driven by a variable frequency inverter, a rotation speed detector for detecting the rotation speed of the induction motor and a rotation speed setting for setting the rotation speed. And a calculator in which a slip frequency capable of outputting the largest torque with respect to the current of the induction motor and a V / f value at which the gap magnetic flux of the induction motor is always constant are input in advance. Inputs the rotation speed of the induction motor to the calculator, thereby calculating and outputting the frequency and voltage using the slip frequency and the V / f value, and outputting these calculation outputs to the frequency command value and voltage of the inverter. By setting the command value, it is possible to always operate with the maximum torque with respect to the current of the induction motor regardless of the setting value of the rotation speed setting device.

[0016]

The signal from the rotation speed detector is input to the calculator. The calculator uses the set speed and the unique motor constant,
The voltage and frequency are calculated so that the torque is maximized at a given input current of the electric motor, and are input to the variable frequency inverter. This allows the motor to be driven with a minimum input current at any speed.
It is possible to suppress overcurrent from flowing through the input power line.

[0017]

FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, 12 is a rotation speed setting device, 13 is a setting signal, 14 is a calculator, 15 is a voltage command value, 17 is a variable frequency inverter, 18 is a polisher electric motor, 19 is a rotation speed detector, and 20 is a rotation speed signal. is there.

2 and 3 show the arithmetic operation of the arithmetic unit 14 in the block diagram of FIG. FIG. 2 shows the relationship between the slip frequency f _S and the motor rotation speed.
Curves 21 to 24 in the figure are slip frequency curves at each set rotation speed, and f _SM is a slip frequency at which the torque of the electric motor shown in FIG. 1 is maximum, and is a value peculiar to the electric motor. The torque of the electric motor increases with the increase of the slip frequency up to the slip frequency of f _SM shown in FIG. Therefore, the motor speed decreases. That is, as the load becomes heavier, if the slip frequency is gradually increased using the curve of FIG. 2, the torque gradually increases, the slip frequency becomes f _SM when the motor is locked, and the torque becomes maximum when the motor is locked. . In other words, the electric motor can be started with the maximum torque that the electric motor has. Where f is the inverter frequency, f _M is the frequency corresponding to the motor speed,
If f _S is the slip frequency, the above operation is represented by the following mathematical expression.

F = f _M + f _S Equation 1 From Equation 1, if the frequency f _M corresponding to the motor rotation speed decreases, the increase in the slip frequency f _S is small, and the inverter frequency f also decreases. , Excessive current does not flow to the motor even when the motor is locked.

Next, the block diagram of FIG. 1 will be described. The rotation speed signal 20 from the rotation speed detector 19 attached to the polisher induction motor 18 is taken into the calculator 14. The calculator 14 calculates the slip frequency f _{S according} to the setting signal 13 set by the rotation speed setting device 12, the rotation speed signal 20, and the slip frequency curve of FIG. This is achieved by determining the inverter frequency f using Equation 1 and inputting this as the frequency command value 16 to the variable frequency inverter 17. Each curve in FIG. 2 is obtained in advance by an experiment or a calculation using a motor constant.

FIG. 3 shows the relationship between the V / f value and the motor rotation speed. Curves 25 to 28 show V at each set rotation speed.
The relationship between the / f value and the motor rotation speed is shown. As previously mentioned,
When the motor rotation speed becomes low, the influence of the primary voltage drop becomes large, and the torque is greatly reduced. Therefore, it is necessary to compensate for this. That is, the primary voltage drop can be compensated by gradually increasing the V / f value according to each curve of FIG. 3 with the decrease of the motor rotation speed. In the figure (V
/ F) _M is the maximum V / f value, which is maximum when the motor is locked. (V / f) ₀ is a V / f value when there is no load, which is a relatively small value. The inverter output frequency f of V / f value is
Since it is determined using FIG. 2 as described above, the calculator 14 calculates only the inverter output voltage V from the setting signal 13, the motor rotation speed 20 and each V / f curve of FIG. This can be achieved by inputting the command value 15 to the variable frequency inverter 17. Each V / f in FIG.
The curves 25 to 28 have been previously obtained by experiments or calculations using motor constants. By doing so, the V / f value is adjusted according to the load state, so that appropriate compensation can be performed without magnetic saturation of the exciting inductance at the time of light load as described above, and the total number of revolutions can be reduced. Efficient over range.

FIG. 4 shows the experimental results of the present invention, and Table 1 shows the data of the induction motor used in this experiment.

[0023] Curves 29 to 31 in the figure each have a rotational speed setting of 300.
Torque-motor rotation speed characteristics at rpm, 1000 rpm and 1800 rpm, and curves 32 to 34 are motor input current-motor rotation characteristics with respect to the rotation speed setting. From the results, the torque is large and the rotation speed is stable even at low rotation speeds. Also in the following rotation speed setting,
It can be seen that the starting torque is the same and the maximum torque that the motor can output. Further, it can be seen that the electric motor input current is suppressed to a constant value and that value is also small.

[0024]

According to the present invention, the induction motor for a polisher is provided with a rotation speed detector, which is combined with a variable frequency inverter to drive the induction motor for a polisher with an optimum voltage according to the rotation speed of the motor and a variable frequency. The present invention provides a device, and compared with a conventional machine, 1) The starting torque is large and constant regardless of the rotation speed.

2) Even if the electric motor is overloaded (including when the electric motor is locked), no overcurrent flows through the electric motor.

3) The torque is large and the rotation is stable even at a low rotational speed.

4) Since the torque curve has no peak torque, it is easy for the worker to work.

It has excellent effects such as the above, and is considered to be most suitable for driving a motor for a polisher.

[Brief description of drawings]

FIG. 1 is a configuration block diagram showing an embodiment.

FIG. 2 is a calculation circuit diagram of a slip frequency and an electric motor rotation speed showing an embodiment.

FIG. 3 is a calculation circuit diagram of a V / f value and an electric motor rotation speed showing an embodiment.

FIG. 4 is a characteristic diagram showing an experimental result of an example.

FIG. 5 is an equivalent circuit diagram of a conventional technique for one phase of a three-phase induction motor.

FIG. 6 is a characteristic diagram of a conventional technique of rotation speed-torque and rotation speed-input current when a three-phase induction motor is driven by open loop control with a constant V / f value.

[Explanation of symbols]

1 to 11 ... Torque characteristic curve 12 ... Rotation speed setting device 13 ... Setting signal 14 ... Computing device 15 ... Voltage command value 16 ... Frequency command value 17 ... Variable frequency inverter 18 ... Induction motor for polisher 19 ... Rotation speed detector 20 ... Rotation speed signal 21-24 ... Slip frequency characteristic curve 25-28 ... V / f value characteristic curve 29-34 ...・ Torque characteristic curve V ・ ・ ・ Input voltage i ₁・ ・ ・ Input current R ₁・ ・ ・ Primary resistance R ₂・ ・ ・ Primary conversion secondary resistance L ₀・ ・ ・ Excitation inductance L ₁・ ・ ・ 1 Secondary leakage inductance L ₂・ ・ ・ Primary conversion secondary leakage inductance S ・ ・ ・ Slip f ・ ・ ・ Input frequency f _S・ ・ ・ Slip frequency f _M・ ・ ・ Frequency corresponding to the motor speed f _SM・ ・・ Slip frequency when the motor reaches maximum torque V / f ・ ・ ・ V / f value (V / f) _M・ ・ ・ Maximum V / f value (V / f) ₀・ ・ ・ V / f value without load

Claims (1)

[Claims] 1. In a polisher induction motor driven by a variable frequency inverter, a rotation speed detector for detecting the rotation speed of the induction motor, a rotation speed setting device for setting the rotation speed, and a current for the induction motor. A calculator having a slip frequency capable of outputting the largest torque and a V / f value with which the gap magnetic flux of the induction motor is always constant is input in advance, and the calculator calculates the rotation speed of the induction motor. By inputting to the calculator, the slip frequency and the V / f value are used to calculate and output the frequency and voltage,
By providing these operation outputs as the frequency command value and the voltage command value of the inverter, it is possible to always have a function of operating with the highest torque with respect to the current of the induction motor regardless of the setting values of the rotation speed setting device. Induction motor drive device for polisher.