JPH01190295A - Load torque detector and controller for induction motor - Google Patents

Abstract

PURPOSE:To enable load torque to be properly detected without being influenced by electrostriction, by finding a power-factor through the primary current and primary voltage of an induction motor, and by estimating the load torque through a deviation between said power-factor and a power-factor at the time of no-load. CONSTITUTION:Three-phase primary-current is detected by current detectors 30-32, and the detected current is inputted to a zero-phase detector 5. Zero-phase detecting signal from the zero-phase detector 5 is inputted to a phase difference detector 6. Besides, the zero-phase detecting signal from a PWM controlling circuit 14 and clock pulse from a V/F converter 13 is inputted to the phase difference detector 6. A phase difference obtained by the phase difference detector 6 is taken in a power factor arithmetic means 7, and a deviation between the power-factor found by the means 7 and a power-factor found by a power- factor arithmetic means 8 at the time of loading is found by an adding or subtracting unit 90. Based on the deviation, load torque is estimated.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a load torque detection device for an induction motor, and a control device for an induction motor using the torque detection device, and particularly to a control device for an induction motor using the torque detection device. The present invention relates to a device suitable for.

[Conventional technology]

As a conventional device for controlling torque according to load, for example, Japanese Patent Application Laid-open No. 183297/1983 is known.

This detects the magnitude of the load from the primary current and controls the torque of the motor by varying the frequency of the voltage applied to the motor in accordance with this value.

[Problem to be solved by the invention]

In conventional technology, the current flow is affected by the dead time of the PWM signal (the non-overlapping time between the gate signal of the positive arm and the gate signal of the negative arm, which is provided to prevent short circuits between the positive and negative arms of the inverter). Waveform distortion occurs,
On the other hand, no consideration was given to the fact that the magnitude of the current does not necessarily correspond to the load on a one-to-one basis. therefore,
There were problems such as not being able to apply the appropriate voltage to the motor according to the load, causing the motor to stall due to insufficient voltage, or the voltage becoming too high and causing overexcitation, causing the inverter to trip. .

SUMMARY OF THE INVENTION An object of the present invention is to provide a load torque detection device that can detect an appropriate load torque even if distortion occurs in the current, and furthermore, to provide an induction system that can perform efficient torque control using the detection device. To provide control devices for electric motors.

[Means to solve the problem]

The above purpose is to detect the power factor cos'p determined by the primary current and primary voltage flowing through the load applied to the motor, calculate the power factor CO8'l'O at no load from this power factor, and The magnitude of power factor deviation (CO3 (P-cos
'po) and controlling the terminal voltage of the motor according to this value.

[Effect]

The power factor cos 'f' obtained as described above is P
Even if the current is distorted due to the dead time of the WM signal, it changes as a function of increasing load. On the other hand, the power factor at no load co
Because of the primary resistance, s'7'o does not become zero even with no load, and increases as the inverter frequency becomes lower. However, from the power factor cosψ, the power factor at no load c
Deviation of power factor obtained by subtracting osψ0 (eos'p
-cosψ0) becomes zero at no load even if the inverter frequency changes, and increases almost in proportion to the load.

The present invention utilizes this point to detect the load torque, so that it can be properly detected without being affected by the current distortion.

Furthermore, in the control device of the present invention, since the inverter voltage to be supplied is controlled by the power factor deviation (cos ψ - cos ψ 0), an amount of voltage corresponding to the load can always be applied to the motor. Therefore, the motor may stall due to insufficient voltage, or become over-excited due to excessive voltage.
This can prevent the inverter from tripping.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First, the configuration shown in FIG. 1 will be explained. A DC power supply 1 is connected to a PWM inverter 2 to which a DC voltage Eo is input.

The PWM inverter 2 converts the DC voltage Eo into a variable voltage, variable frequency three-phase AC power source. The 3-phase power supply is P
The signal is input to an induction motor 4 connected to a WM inverter 2. Furthermore, the output terminal of PWM inverter 2 is connected to current detector 3.
Also connected to 0.31.32.

The output terminals of the current detectors 30, 31, 32 are connected to the input terminal of the zero-phase detector 5, and the three-phase primary current iupivH
iw is input. The output terminal of the zero-phase detector 5 is connected to the first input terminal of the phase difference detector 6, and the zero-phase signal C of the current of each phase is input. The second and third input terminals of the phase difference detector 6 are respectively connected to a PWM control circuit 14. It is connected to the output terminal of the V/F converter 13, and receives the clock signal a and the modulated wave zero phase signal S.

The output terminal of the phase difference detection circuit 6 is connected to the power factor calculation means 7, and one phase difference 4 is taken in by the power factor calculation means 7. The power factor calculation means 7 is connected to the plus side terminal of the adder/subtractor 90 and the power factor calculation means 8 during no-load. The automatic boost maximum frequency ωRO and the inverter angular frequency command ωR are input to the power factor calculation means 8 during no-load.

The output terminal of the power factor calculation means 8 at no-load is connected to the negative terminal of the adder/subtractor 90, and the power factor at no-load is cosψ
0 is input. The output terminal of the adder/subtractor 90 is connected to the amplifier 10
connected to the input terminal of An inverter angular frequency command (ωR) is further input to the amplifier 10, and the gain of the amplifier 1o is adjusted by the value of ωR.

The output terminal of the amplifier 10 is connected to one positive terminal of an adder 91, and the voltage command VR is input to the other positive terminal of the adder 91. The output terminal of the adder 91 is connected to one input terminal of the limiter 11.
The other input terminal of the voltage upper limit value is connected to the output section of the calculation means 12.

The inverter angular frequency command ωR is sent to the voltage upper limit value calculation means 12.
and a V/f pattern setting command are input.

The output terminal of the limiter 11 is connected to one input terminal of the PWM control circuit 14, and the other input terminal is connected to the output terminal of the V/F converter 13. Furthermore, the output terminal of the V/F converter 13 is also connected to the input terminal of the PWM control circuit 14. Then, the inverter angular frequency command ωR is input to the V/F converter 13.

The output terminal of the PWM control circuit 14 is connected to the gates of the positive side arm and the negative side arm (both are not shown) of each phase constituting the PWM inverter 2, and a PWM signal is input thereto.

Next, the operation of the circuit shown in FIG. 1 will be explained. Three-phase primary currents are detected by current detectors 30, 31, and 32.

When the current detected by the current detectors 30, 31, and 32 is input to the zero-phase detector 5, 0.2π of the current of each phase
Generate a differential pulse at the point in time. This differential pulse becomes a current zero phase detection signal C and is input to the phase difference detector 6. In addition, 0 and 2 of the three-phase modulated waves are output from the PWM control circuit 14.
A differential pulse synchronized with the phase of π is generated. This differential pulse becomes the zero phase detection signal of the modulated wave and is input to the phase difference detector 6. Furthermore, a V/F converter 1 is added to the phase difference detector 6.
Clock pulse a, which is output at three times, is input. The phase difference detector 6 converts the pulse interval (time difference) between the modulated wave zero phase detection signal and the current zero phase detection signal C into a clock pulse a.
Measure using. When the angular frequency ωR of the inverter changes, the pulse interval (time difference) between the pulse signal S and the pulse signal C changes, but the frequency of the clock pulse a also changes in proportion to the frequency of ωR. Therefore, the data obtained by counting the above-mentioned pulse intervals using the clock pulse a detects a phase difference ψ that is not affected by the frequency of the inverter.

The phase difference T obtained by the phase difference T detector 6 is taken into the power factor calculation means 7. The power factor calculation means 7 calculates the cosine function value cos ? corresponding to the phase difference T? seek.

Figure 2 shows the power factor cO8 determined by the method described above.
(Actually measured data on the relationship between P and point load. This shows the characteristics in a low speed range where the inverter frequency is 15 Hz or less.

FIG. 3 shows actually measured data on the relationship between the magnitude of the primary current and the load in such a low speed range.

It can be seen from FIG. 3 that the magnitude of the primary current is a bivalent function of the load. On the other hand, it can be seen that the power factor cos 'f' is an increasing function of the load and changes almost linearly with the load.

In the present invention, the load is estimated using the characteristics shown in FIG. It can be seen from FIG. 2 that as the inverter frequency decreases, the no-load power factor cosY'0 gradually approaches 1. When the power factor cos'+'o at no-load is determined using an equivalent circuit of an induction motor, it is given by equation (1).

However, 712 primary resistance Q11': excitation inductance Qt': secondary leakage inductance From equation (1), it can be seen that the power factor cos F o approaches 1 as the frequency decreases due to the influence of the primary resistance.

Therefore, the power factor cos? If the voltage is corrected using the value itself, the voltage will be corrected to increase as the inverter frequency decreases under no load. Therefore, in a region where the frequency of the inverter is low, the voltage becomes too large when there is no load, resulting in overexcitation. This phenomenon is avoided in the present invention as follows. That is, according to equation (1), the power factor c at no load for the inverter frequency ω1
Calculate os'7'o. Next, this power factor Co! 3'l'
Using O and the power factor cosψ obtained in the above process, (2
) is used to find the power factor deviation Δcos'+'.

Acos 'f' = (cos Lf - cos 'P
o) ”° (2) Ac obtained from formula (2)
With OS, even if the inverter frequency changes, it will always be zero under no-load conditions. And it changes almost proportionally to the load. Therefore, the magnitude of the load can be estimated from 800S'l'.

By the way, the slope of the function ΔC08(io) decreases as the inverter frequency decreases from the load characteristics of Acosψ shown in Figure 5.For this reason, if the voltage is corrected using the value of Δcosψ as it is, the inverter frequency will be low. In this region, it is not possible to apply proper voltage to the motor.

That is, in this case, the lower the inverter frequency, the greater the voltage drop due to the primary resistance, making it impossible to suppress the phenomenon that the gap magnetic flux decreases.

So as the inverter frequency decreases, the function Aco
Correct so that the slope of s(P becomes larger. Using the correction amount ΔV obtained in this way, (3), (4)
The voltage command VR is corrected based on the formula.

V*=V R+ΔV...
(3) ΔV=kv(Δcosψ) −
(4) However, kv: Gain that is corrected to decrease as the inverter frequency decreases In the embodiment of FIG. 1, the voltage command VR is corrected based on the above-mentioned concept. The details will be explained below.

In the embodiment shown in FIG. 1, calculation from equation (1) using the constants of the motor and the inverter frequency takes a long calculation time. Therefore, cos'po for automatic boost maximum frequency ωRO
Be sure to calculate and find the value in advance. The values thus obtained are stored in a memory table for each capacitance and number of poles, so that they can be retrieved from the memory table each time the capacitance and number of poles change. The no-load power factor calculation means 8 in FIG. 1 reads the no-load power factor cosψ0' for the automatic boost maximum frequency ωR from the memory, and linearly approximates equation (1) shown by the solid line in FIG. 5) Use equation to find the power factor cos'Po at no load at an inverter frequency ωl smaller than ωR.

CO8'l'O' of the motor actually being driven and cosψ0' stored in memory in advance are actually different. Therefore, it is preferable to perform no-load operation in advance at the inverter frequency ωRO and use the value obtained from the power factor calculation means 7. This case is shown in the embodiment.

The adder/subtractor 90 converts cos '1' and cos '
The power factor deviation Δcos'11' is determined using P o. The power factor deviation Acosψ is multiplied by a gain kv which is corrected in the amplifier 10 so that it increases as the inverter frequency decreases. The voltage correction amount ΔV obtained as a result is added to the voltage command VR by an adder 91, and becomes a voltage correction signal v.

The voltage correction signal v is inputted to the PWM control circuit 14 via the limiter 11. When the V/f pattern setting value is selected, the value of (V*)max corresponding to the inverter angular frequency ωR that corresponds to this Vlf value is calculated. In this way, depending on the V/f pattern setting value, (V*)max
The reason for making it variable is to be able to change the appropriate torque depending on the load.

The PWM control circuit 14 forms a PWM signal based on the voltage correction signal v and the inverter angular frequency command ωR. P
Since the method of forming the WM signal is well known in the past and any known technique may be used, the method will be omitted here.

In the above embodiment, the power factor CO8' is calculated from the phase difference between voltage and current.
l' was calculated, but this cos'p is the three-phase current lug
Using IV H1w, calculate the d-axis current component Iax + q#l current component qs obtained by converting the a-q axis coordinates according to equation (6), calculate the phase difference T from equation (7), and calculate the power factor CO
You may try to obtain 8ψ.

...(6) 'f' = π/ 2-tan(I qs/ I as
) = (7) [Effects of the Invention] According to the present invention, the magnitude of the load can be estimated regardless of the waveform of the current flowing through the motor. Further, by using the estimation, efficient torque control can be performed according to the load. That is, even if the two types of capacities of the electric motors change, the magnitude of the load can be easily estimated, making it possible to appropriately control the torque even with a general-purpose electric motor.

[Brief explanation of the drawing]

Figure 1 is a configuration diagram of an embodiment of the present invention, Figure 2 is the load characteristic of the power factor, Figure 3 is the load characteristic of the magnitude of the primary current, and Figure 4 is the frequency of the power factor at no load. Characteristics: Figure 5 shows the load characteristics of power factor deviation. 1...-DC power supply, 2...PWM inverter, 4...
... Induction motor, 5... Zero phase detector, 6... Phase difference detector, 7... Power factor calculation means, 8... Power factor calculation means at no load, 1o... Amplifier , 11... Limiter, 12... Voltage upper limit value calculation means, 30, 31, 32.
...Current detector, 90...Adder/subtractor, 91...Adder. Figure 1 Figure 2 Rin (%) Figure 3 Rin (%) Early 4 Figure Inno

Claims (1)

[Claims] 1. A device for detecting the torque of a load driven by an induction motor, comprising means for determining a power factor (cosψ) from a primary current and a primary voltage of the induction motor; Rate (c
A load torque detection device for an induction motor, comprising means for estimating the torque of the load from the deviation between the power factor (cosψ_0) at no-load and the power factor at no-load (cosψ_0). 2. An induction motor control device that controls the torque of an induction motor by varying the power supply voltage and frequency, comprising means for determining a power factor (cosψ) from the primary current and primary voltage of the induction motor; factor (cosψ) and power factor at no load (c
A control device for an induction motor, comprising means for increasing the power supply voltage of the induction motor according to the deviation from the current supply voltage osψ_0). 3. In claim 2, a correction gain (Kv) is set that increases when the frequency of the inverter decreases, and the power supply voltage is increased by passing the deviation through the correction gain (Kv). A control device for an induction motor, characterized in that: