JPH06233578A - Device for controlling minimum input operating speed of three-phase induction motor - Google Patents

Abstract

PURPOSE:To minimize the input of a motor with reference to various loads and to maximize the efficiency of the device wherein the output of a minimum input operation device is input and the motor is driven by its terminal voltage and frequency. CONSTITUTION:When an apparatus is connected to a three-phase induction motor 18 to which a load has been connected, the pressure drop signal of a pressure sensor 22 is input to a minimum output operation device 26 when the discharge amount of a pump 20 as a load for the motor 18 is increased, a corresponding frequency (f) is output to a conversion device 12, the number of revolutions of the motor 18 is increased and a drop in a discharge pressure is supplemented. Then, an increase in a rotational speed is input to the minimum input operation device 26 as the output of an operation device 16 or a detector 8, and it is checked whether set values of a terminal voltage V and the frequency (f) which minimize the input are preserved or not. When they are not preserved, a setting operation is performed, a set value is output to the exchange device, and data is preserved. When the discharge pressure of the pump 20 is increased, a reverse operation is performed, and the motor is always operated in a minimum input state.

Description

Detailed Description of the Invention

[0001]

[Industrial application] Regarding speed control of induction motors,
Set the terminal voltage and frequency to always operate with the minimum input at the arbitrary axis output at the arbitrary speed, perform the calculation and the setting, save the data at the same time, and directly calculate the terminal voltage and the frequency from the saved data. The minimum input operating speed that is set, and calculates and displays the input, generated torque and shaft output, efficiency while driving the motor, and displays the detected terminal voltage, current, rotation speed and shaft torque. The present invention relates to a control device.

[0002]

2. Description of the Related Art Conventionally, the operation of an AC motor has been targeted at a constant voltage, constant frequency commercial power source, and its rating is designed so that the maximum efficiency can be obtained under a full load or 80% load condition. It is well known that the efficiency is greatly reduced in the operation under load. Therefore, as one method, there is a method such as a control of the rotation speed, in which the conversion ratio between the frequency and the terminal voltage is kept constant and is controlled based on the idea of a commercial power source.

[0003]

However, since this method is not carried out based on the idea of the minimum input operation, there are cases in which the efficiency is not necessarily improved with respect to changes in the load. It is an object of the present invention to provide an input minimum operating speed control device for a three-phase induction motor that can minimize the motor input for various loads and maximize the efficiency.

[0004]

A minimum input operating speed control device for a three-phase induction motor according to the present invention is a voltage / current detection device for detecting a phase current and a phase voltage of a stator winding of a three-phase induction motor. , A magnetic flux calculation device that calculates the phase magnetic flux of the stator winding from the phase current and the phase voltage detected by the detection device or a magnetic flux detection device that directly detects the phase magnetic flux, and the rotation speed and the shaft torque of the induction motor. A detector for detecting, the phase current and phase voltage detected by the detection device, and the instantaneous input of the induction motor is calculated from the magnetic flux detected or calculated by the magnetic flux detection device or the magnetic flux calculation device, and the instantaneous torque generated is calculated. In addition to the calculation, the calculator that calculates the shaft output from the instantaneous torque and the rotation speed, the instantaneous input from the calculator, the shaft output, the speed command of the sensor installed in the load, etc. A minimum input arithmetic device for arithmetically setting and outputting the minimum input terminal voltage and frequency of the electric motor, and a voltage / frequency variable conversion device for inputting the output of the minimum input arithmetic device and driving the electric motor by the terminal voltage and frequency. It is characterized by that.

Further, in the minimum input operating speed control device for a three-phase induction motor according to the present invention, a minimum input terminal voltage at the shaft output calculated for various loads of the motor is supplied to the minimum input calculation device. It is characterized by having a learning function that saves frequency data.

Further, the minimum input operating speed control device for a three-phase induction motor according to the present invention is such that the minimum input terminal device and frequency at the shaft output calculated for the same load of the electric motor with respect to the minimum input arithmetic device. The feature is that it has a learning function to save the data.

Furthermore, the minimum input operating speed control device for a three-phase induction motor according to the present invention is such that, for various loads of the induction motor, the minimum input calculating device calculates the calculation input for each rotation speed and the motor output. The terminal voltage and frequency should be set directly from the saved data of the terminal voltage and frequency to minimize the above, and the calculated data should be saved for the load of the motor where the data is not saved. Also, for the same load of the electric motor, the terminal voltage and frequency are directly set from the stored data of the terminal voltage and frequency for minimizing the operation input for each rotation speed by the minimum input operation device. For the load of the motor for which the data is not saved, the calculated data is saved, and the input and Click, and motor shaft output, the display and operation efficiency and the detected terminal voltage, current, is characterized by causing the display of the rotational speed and the shaft torque.

[0008]

With the configuration described above, when this device is connected to a three-phase induction motor to which a load is connected, the voltage / current detection device detects the phase current and phase voltage of the stator winding. The magnetic flux calculator calculates the phase magnetic flux of the stator winding from the phase current and the phase voltage. In the case of the magnetic flux detection device, the phase magnetic flux is directly detected. Furthermore, the calculator calculates the instantaneous input of the induction motor from the previously detected phase current and phase voltage and the calculated magnetic flux, and also calculates the generated instantaneous torque. The shaft output is calculated from the rotation speed of the induction motor detected by the detector. Next, the minimum input arithmetic unit calculates and sets the minimum input terminal voltage and frequency of the electric motor based on the instantaneous input from the arithmetic unit, the shaft output, and the speed command of the sensor installed in the load, and outputs. This output is input to the voltage / frequency variable converter, and the motor is driven by the terminal voltage and frequency.

The minimum input arithmetic unit has a learning function in addition to arithmetically setting the minimum input terminal voltage and frequency of the electric motor, and has a minimum input terminal in the shaft output calculated for various loads of the electric motor. It stores voltage and frequency data, and also saves the minimum input terminal voltage and frequency data for the shaft output calculated for the same load of the motor. Then, the terminal voltage and frequency are set directly from the stored data, and the calculation and display of the motor input, generated torque, and motor shaft output, efficiency, and the detected terminal voltage, current, rotation speed and shaft are also performed. The torque is displayed.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. In Figure 1, initially the power frequency f ₁ and a constant performs speed control of the rotational speed N _1, the induction motor is TL ₁
It is assumed that the load torque of is applied. Since the zero phase voltage and zero phase current do not exist in the input P of this induction motor during normal normal operation, each phase voltage v _a (t) of the stator winding,
Two phase voltages v _a (t), v in v _b (t), v _c (t)
The instantaneous values of the two phase currents i _a (t) and i _b (t) in _b (t) and each phase current i _a (t), i _b (t) and i _c (t) are detected and It is possible to directly perform the calculation based on the equation (1) shown in FIG.

[0011] _{P = v a (t) ·} i a (t) + v b (t) · i b (t) + v c (t) · i c (t) = v a (t) [2i _a (t) + i _b (t)] + v _b (t) _{[i a (t) + 2i b} (t) ] ..... (1)

Therefore, when the rotation speed N ₁ is constant, the input P
It is possible to set the terminal voltage and frequency that minimize the In this case, in FIG. 1, the terminal voltage of V ₄ is V ₃ or less.
Then, it becomes impossible to control the speed at the rotation speed N ₁ , and the rotation speed decreases. Thus, when the load of the motor is used with the same load of TL ₁ or TL ₂ , the terminal voltage V and the frequency f which are the minimum input for each rotation speed are calculated without detecting the shaft output. The setting is made and the data is saved. Further, when the electric motor is loaded with the same load, the terminal voltage V and the frequency f are directly set from the stored data to enable speed control with the minimum input.

However, various loads TL ₁ , TL _2, ...
When a variable load and the like are applied to the same induction motor, the power supply frequency f ₁ is _first made constant and speed control is performed so that the rotation speed N _{1 is} constant. Next, the axis output for each load is calculated, the terminal voltage V and the frequency f at which the input of each axis output is minimized are calculated and set, and the data is saved. Further, when the electric motor is loaded with an arbitrary load, the terminal voltage V and the frequency f are directly set from the stored data to perform the speed with the minimum input. For a load for which data has not been saved, the terminal voltage V and frequency f for which the input is minimized are calculated and set, and the data is saved. Here, the shaft output is obtained from the product (ωτ) of the motor torque (τ) and the angular velocity (ω), and the torque of the motor is determined by the existence of normal zero-phase current and zero-phase magnetic flux in addition to the shaft torque detector of the motor. The instantaneous torque during normal operation that cannot be obtained can be obtained from the following equation (2).

[0014] τ _e (t) = √3n × _{[Ψ a (t) · i b} (t) -Ψ b (t) · i a (t) ] ..... (2) where, n: very Logarithm

That is, the three-phase magnetic flux Ψ _a (t) of the fixed winding,
Ψ _b (t) , Ψ _c (t) of two-phase magnetic flux Ψ
_a (t), Ψ _b (t) and the two-phase current i among the three-phase currents
_The instantaneous values of _a (t) and _ib (t) can be detected and directly calculated based on the equation (2). As a method of obtaining each phase magnetic flux of the stator winding, a method of directly obtaining from a search coil or a Hall element, etc. and the following (3 _1,2,3 ) between the phase voltage of the induction motor and each phase magnetic flux Since the voltage equation holds, the equation (4 _1,2,3 ) is derived, and a method of obtaining the magnetic flux of each phase from the calculation of the equation (4) is possible.

V _a (t) = R ^S · i _a (t) + p Ψ _a (t) (3 ₁ ) v _b (t) = R ^S · i _b (t) + p Ψ _b (t) (3 ₂ ) v _c (t) = R ^S · i _c (t) + p Ψ _c (t) (3 ₃ ) where R ^S : each of the stator windings Phase resistance, p: Differential operator

[0017] From the above _{equation, Ψ a (t) = ∫} {v a (t) -R S · i a (t)} dt ···· (4 1) Ψ b (t) = ∫ {v b ( _{^{t) -R S · i b (}} t)} dt ···· (4 2) Ψ c (t) = ∫ {v c (t) -R S · i c (t)} dt ···· ( 4 ₃ ) is obtained, and the two-phase magnetic flux Ψ _a (t), based on the equation (4),
Ψ _b (t) is calculated, and the instantaneous torque generated by the electric motor is obtained from equation (2).

FIG. 2 shows a block diagram in which the input minimum operating speed control device of the embodiment of the present invention is connected to a three-phase induction motor in a state where a load is connected. In the figure, 10
Is a commercial power supply, 12 is a voltage / frequency variable converter, 14 is a voltage / current detector for each phase voltage and each phase current of the induction motor, 16 is an input P and an instantaneous torque τ _e from the detection values of the detector 14. Along with this, it is an arithmetic unit for obtaining the shaft output from the instantaneous torque and the rotation speed of the electric motor detected by the detector 24. Reference numeral 18 is an induction motor that is operated by using the voltage / frequency variable conversion device 12 as a power source, and 20 is a load that is driven by the shaft output of the electric motor 18, such as a pump, and the amount of water discharged changes depending on the usage state. If so, this affects the discharge pressure, and it is necessary to maintain a constant pressure, and the pressure sensor 22 for this purpose issues a speed command. Reference numeral 24 is a detector that detects the rotation speed and the shaft torque of the electric motor and calculates the shaft output.

Reference numeral 26 is a minimum input arithmetic unit for inputting the speed command from the pressure sensor 22, the motor rotation speed and the shaft output of the detector 24, and the motor input and the shaft output of 16 and initially at the frequency f ₁ . The converter controls the set values of the terminal voltage V and the frequency f at which the input is minimized by performing the speed control of the speed command N ₁ and searching the stored data of the terminal voltage V and the frequency f at which the input P is minimized. 12 is output. If the data is not stored, the terminal voltage V and the frequency f at which the electric motor input is minimized are set and calculated, the set values are output to the converter 12, and the data is stored. In addition, it also has the function of calculating and displaying the input, generated torque, shaft output, and efficiency of the motor when the motor is operating with the minimum input, and also displaying the detected terminal voltage, current, rotation speed and shaft torque. is there.

Next, this operation will be described. If it is assumed that the discharge amount of the pump 20 of the load of the electric motor 18 has increased, the signal of the pressure decrease of the pressure sensor 22 becomes a signal in the speed command increasing direction and is input to the minimum output computing device 26. The frequency f corresponding to this is output from the arithmetic unit 26 to the converter 12. For this reason, the rotation speed of the electric motor 18 increases, and the decrease in discharge pressure due to the increase in discharge amount is compensated. In this case, of course, it is desirable that the rate of change between the frequency and the voltage of the converter 12 be set at a constant ratio as is conventionally done in this type of apparatus. Next, the increase of the rotation speed changes the output of the shaft and becomes the output of the calculator 16 or the detector 8 and is input to the minimum input calculator 26. In the speed control of the current speed command, the arithmetic unit 26 searches whether or not the set values of the terminal voltage V and the frequency f at which the motor input becomes the minimum are stored, and when not stored, the terminal having the minimum input is obtained. The setting calculation of the voltage V and the frequency f is performed, the set values are output to the conversion device 12, and the data is saved.
Further, calculation and display of the input, generated torque, shaft output, and efficiency of the motor while the motor is operating with the minimum input, and the detected terminal voltage, current, rotation speed and shaft torque are displayed.

If the amount of water used decreases and the discharge pressure of the pump 20 rises, the reverse operation is performed and the induction motor 18 is always operated in the minimum input state. Therefore, the heat loss of the induction motor 18 is always the minimum, which is optimum for energy saving operation.

As described above, the variable speed operation of the electric motor by the voltage / frequency variable converter is economically easy to use due to the development of the power semiconductor element, and the power source frequency is controlled by the load and the minimum input is controlled by the terminal voltage control. Driving can save a lot of power consumption. Needless to say, even if the frequency is constant with the commercial power supply, the variable voltage regulator controls the terminal voltage as described above, so that the operation is always performed with the minimum input.

[0023]

As described above, according to the present invention,
Since the operation at the minimum input can be performed by controlling the power supply frequency by the load and controlling the terminal voltage, it is possible to greatly reduce the power consumption.

[Brief description of drawings]

FIG. 1 is a diagram showing a torque-speed curve for each terminal voltage of an electric motor.

FIG. 2 is a block diagram of an embodiment of the present invention.

[Explanation of symbols]

10 Commercial power supply 12 Voltage / frequency variable converter 14 Voltage / current detector 16 Calculator of motor input and shaft output of instantaneous torque 18 Induction motor 20 Load of motor 22 Pressure sensor and speed command device 24 Rotation speed and shaft torque of motor For detecting the axis and computing the axis output 26 Minimum input computing device

Claims (4)

[Claims] 1. A voltage / current detecting device for detecting a phase current and a phase voltage of a stator winding of a three-phase induction motor; and a stator winding of the stator winding based on the phase current and the phase voltage detected by the detecting device. A magnetic flux calculation device that calculates the phase magnetic flux or a magnetic flux detection device that directly detects the phase magnetic flux, a detector that detects the rotation speed and shaft torque of the induction motor and that calculates the shaft output, and a phase current detected by the detection device. And the phase voltage and the magnetic flux detected or calculated by the magnetic flux detection device or the magnetic flux calculation device to calculate the instantaneous input of the induction motor and the generated instantaneous torque, and the shaft output from the instantaneous torque and the rotational speed. The minimum input terminal voltage and frequency of the motor are calculated based on the calculation unit, the instantaneous input from the calculation unit, the shaft output, and the speed command of the sensor installed in the load. A three-phase induction motor characterized by comprising: a minimum input arithmetic unit for setting and outputting; and a voltage / frequency variable conversion unit for inputting the output of the minimum input arithmetic unit and driving the motor by the terminal voltage and frequency thereof. Input minimum operating speed controller. 2. The minimum input calculation device is provided with a learning function for storing data of a minimum input terminal voltage and a frequency at a shaft output calculated for various loads of an electric motor. An input minimum operating speed control device for a three-phase induction motor according to claim 1. 3. The minimum input computing device is provided with a learning function for storing data of the minimum input terminal voltage and frequency of the shaft output calculated for the same load of the electric motor. Item 3. A minimum input operating speed control device for a three-phase induction motor according to item 1. 4. For various loads of an induction motor, the minimum input arithmetic device directly outputs the stored terminal voltage and frequency data to minimize the arithmetic input for each rotation speed and motor output. Set the voltage and frequency, save the calculated data for the load of the motor that has not saved the data, and use the minimum input calculation device for each rotation speed for the same load of the motor. With respect to the load of the motor for which the data is not saved, the terminal voltage and frequency are set directly from the saved data of the terminal voltage and frequency for minimizing the calculation input. Saves the calculated data, calculates and displays the motor input, generated torque, motor shaft output, efficiency, and detected terminal voltage. The minimum input operating speed control device for a three-phase induction motor according to claim 1, wherein the display of pressure, current, rotational speed and shaft torque is performed.