JPH0413953B2 - - Google Patents

Description

[Detailed Description of the Invention] [Field of Application of the Invention] The present invention relates to a method for detecting the induced electromotive force of an induction motor that is suppressed by a frequency converter, and in particular, the detection error due to a drop in leakage impedance of the motor windings is small, and the required The present invention relates to an induced electromotive force detection method for detecting induced electromotive force with high accuracy.

[Prior Art] Vector control is known that can independently control the torque and magnetic flux of an AC motor according to each command signal. According to the vector control method, the motor current can be controlled by separating it into the torque component current and the excitation component current, so it is possible to control each current component by making it correspond to the armature current and field current in the DC motor. can. Therefore, various types of control that were previously performed exclusively by DC motors can now be performed by AC motors. One example of this is the control of winding machines used in rolling lines, but since this requires constant output control to keep the motor output constant regardless of the rotation speed, it is necessary to accurately control the motor input power. . By the way, the input power is proportional to the product of the induced electromotive force and the current in the motor, similar to a DC motor, but since the electromotive force is alternating current, when detecting it, it is necessary to detect it due to the drop in leakage impedance of the primary winding. Detection error must be taken into account. Conventionally,
As an electromotive force detection method, a method is used in which a motor voltage is detected, full-wave rectified, and extracted as a DC signal. However, there is a problem in that the drop in leakage impedance directly causes a detection error, making it impossible to perform accurate detection.

[Purpose of the invention]

An object of the present invention is to solve this problem, and to provide an induced electromotive force detection method that can detect induced electromotive force with high accuracy without being affected by leakage impedance drop.

[Summary of the invention]

The present invention is characterized by detecting the motor voltage and calculating the motor magnetic flux phase.
The required induced electromotive force is detected by calculating the orthogonal component of the voltage detection signal to the magnetic flux phase signal.

[Embodiments of the invention]

FIG. 1 shows an embodiment of the present invention.

In Fig. 1, 1 is a frequency converter that converts the commercial power supply voltage into alternating current with variable frequency and variable voltage, 2 is an induction motor, 3 is a speed detector, and 4 is a command signal for induced electromotive force according to the rotational speed of the motor. E ^* and a driving command circuit that outputs a command signal I _t ^* of the torque component of the primary current; 5 is a phase number converter that converts the primary voltage detection signal (three-phase signal) detected by the voltage detector 20 into a two-phase signal; , 6 and 7 are multipliers that multiply the two-phase signal by a magnetic flux phase signal from an oscillator 8, which will be described later. 9 adds the output signals of the multipliers 6 and 7, and outputs an induced electromotive force detection signal (DC signal). An adder, 10 is an adder for extracting the deviation of the electromotive force, 11 is an electromotive force deviation amplification device for amplifying the electromotive force deviation, and 12 is for dividing the torque component flow command i _t ^* by the excitation component current command i _n ^*. 13 is an adder _that adds the frequency command f _s ^{* and} the speed detection signal and outputs the motor primary frequency command f _i ^* ; 14; 1;
5 is a multiplier that multiplies the current command i _n ^* or i _t ^* by the magnetic flux phase signal, and 16 is an adder that adds the output signals of the multipliers 14 and 15 and outputs the instantaneous value command i _l ^* of the primary current. , 17 is a current detector that detects the instantaneous value of the primary current, and 18 is a current controller that controls the converter 1 according to the deviation between the aforementioned primary current command and the current detection signal, and controls the primary current according to the command value. It is.

Next, its operation will be explained.

The divider 12 calculates the slip frequency command according to the following formula:
f _a ^* is retrieved.

f _a ^* = 1/2πT ₂ · i _t ^* / i _n ^* (1) Here, T ₂ is the motor secondary time constant. Next, the adder 13 adds the slip frequency command f _s ^* and the speed detection signal _fr , and extracts the primary frequency command f ₁ ^* . The oscillator 8 generates a two-phase sine wave signal (cosω ₁ t, Sinω ₁ t) with a frequency proportional to the primary frequency command f ₁ ^*.
Output. When the slip frequency f _s of the motor 2 is controlled according to the relationship in equation (1), one of the two-phase sine wave signals is in phase with the motor magnetic flux, and the other is 90° with respect to the magnetic flux.
It becomes a signal of the degree phase difference, and becomes a calculation detection signal of the magnetic flux phase.

Next, the multipliers 14 and 15 and the adder 16 perform the calculation shown in the following equation, and the primary current command i ₁ ^* is extracted.

I ₁ ^* = i _n ^* cosωt−i _t ^* sinω ₁ t ………(2) The current regulator 18 sets the primary current i ₁ as the primary current command.
The frequency converter 1 is controlled so that the flow is proportional to i ₁ ^* . The other two phase currents of the motor phase currents are similarly controlled by calculating current command signals having phases different by 120 degrees from the primary current command i ₁ ^* by a circuit not shown.

As described above, the excitation and torque components of the primary current are controlled to be proportional to each of the current commands i _n ^* and i _t ^* , and the motor magnetic flux and torque are controlled. Such vector control operation is already well known.

Next, the operation of the main part of the present invention will be explained.
Two-phase AC voltage detection signal in phase number converter 5
v ₁ 〓 and v ₁ 〓 are calculated according to the following formula.

Note that v _U , v _V , and v _W are phase voltages, and the purpose of converting them into two-phase signals is to simplify calculations.

Next, the multipliers 6 and 7 and the adder 9 calculate the following equation to detect the induced electromotive force E.

E=−v ₁ 〓(sin ω ₁ t)+v ₁ 〓(cos ω ₁ t) (4) where sin ω ₁ t and cos ω ₁ t are the output signals of the oscillator 8. The induced electromotive force E detected in this way is 2 on the stator coordinates as shown in Figure 2.
It is obtained by converting the phase AC voltages v ₁ 〓, v ₁ 〓 to voltage on the rotor coordinates using the magnetic flux phase θ (= ω ₁ t), and the fundamental wave component of the output voltage is detected by the DC amount. be done. The detected induced electromotive force E includes a leakage impedance drop component in addition to the secondary induced electromotive force E ₂ to be detected, as shown in the following equation.

EE ₂ + r ₁ i _t + ω ₁ l ₁ i _n ………(5) where, r ₁ : Primary resistance l ₁ : Primary leakage inductance ω ₁ : Primary angular frequency i _t : Torque component current i _n : Excitation component current However, the leakage reactance drop in the third term on the right side can be ignored since generally E ₂ ≫ω ₁ l ₁ i _n . In addition, the resistance drop r ₁ i _t in the second term has a large influence in the operating range where the primary frequency f ₁ is low, but this can be explained by using the torque component current i _t ^* as shown by the broken line in Figure 1. Resistance drop from electromotive force E ₂
It can be easily compensated by subtracting the amount corresponding to r ₁ i _t .

Note that the signal obtained from the adder 9 becomes
The polarities of v ₁ 〓 and v ₁ 〓 are reversed. Therefore, if necessary, an absolute value calculator is provided on the output side of adder 9 or 19, and its output is added to adder 10.

Since the motor input P is given by the following equation, P3E ₂ ·i _t (6) By keeping E ₂ and i _t at predetermined values, the motor input P can be controlled to a predetermined value.

The induced electromotive force is detected as described above, and the vector diagram shown in Figure 2 explains why it can be detected with higher precision than the conventional method that detects the primary voltage and rectifies it to detect the induced electromotive force. I will explain using

In the conventional system that detects and rectifies the primary voltage to detect the induced electromotive force, the detected voltage _E1 is expressed by the following equation, as is clear from the vector diagram shown in FIG. In addition, in FIG. 2, φ ₂ is the motor magnetic flux.

E ₁ =√( ₂ + _{1 1 n} + _{1 t} ) ² + ( _{1
2 t} + _{1 1 t} − _{1 n} ) ² ………(7) Compared to the induced electromotive force E ₂ to be detected, the primary leakage impedance drop r ₁ i ₁ and ω ₁ l ₁ i ₁ and the secondary leakage reactance The detection error increases due to the drop ω ₁ l ₂ i _t . On the other hand, the detection voltage E in the detection method of the present invention is as shown in the figure, and has a smaller detection error than the conventional voltage _E1 . This can be understood from the fact that the excitation component i _n is 1/3 to 1/6 of the torque component i _t . Furthermore, compared to the electromotive force E ₂ , only r ₁ i _t and ω ₁ l ₁ i _n are errors, but r ₁ i _t can be easily compensated for. Moreover, since ω ₁ l ₁ i _n /E ₂ is always a substantially constant value, the influence of ω ₁ l ₁ i _n does not cause any real harm. because,
When controlling the induced electromotive force E ₂ , the command value E ^* is ω ₁ l _{1 i n}
This is because the induced electromotive force E ₂ can be controlled to a predetermined value by instructing it to be larger by that amount.

〔Effect of the invention〕

As explained above, according to the present invention, a required induced electromotive force can be detected with high accuracy without being affected by impedance drop.

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention;
FIG. 2 is a vector diagram for explaining the present invention. 1... Frequency converter, 2... Induction motor, 6,
7... Multiplier, 8... Oscillator.

Claims (1)

[Claims] 1. In a method for detecting induced electromotive force in a three-phase AC motor driven by a frequency converter that can vary the magnitude and frequency of the output voltage, the u-phase voltage component and the voltage component orthogonal thereto are detected from the output voltage of the frequency converter. , find the sine value and cosine value of the two-phase sine wave phase signal from the command signal of the output frequency of the frequency converter, and calculate the product value of the u-phase voltage component and the sine value, and the voltage orthogonal to the u-phase voltage component. A method for detecting induced electromotive force, characterized in that the induced electromotive force of the AC motor is detected from an added value of a component and a multiplication value of the cosine value.