JPS5972990A - Detecting method for induction electromotive force - Google Patents

Abstract

PURPOSE:To accurately detect the prescribed induction electromotive force without influence of the impedance drop by obtaining by claculating the orthogonal component of a voltage detecting signal to the magnetic flux phase signal. CONSTITUTION:A phase number changer 5 calculates 2-phase AC voltage detection signals V1alpha, V1beta, multipliers 6, 7 and an adder 9 detect induced electromotive force E, and the detected force E includes leakage impedance drop component in addition to the secondary inducted electromotive force E2 to be detected. It can be readily compensated by subtracting the resistance drop r1it corresponding component from the force E2 by using the torque current i*t.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for detecting induced electromotive force in an induction motor that is P-controlled by a frequency converter, and in particular has a method that reduces detection errors due to drop in leakage impedance of the motor windings. The present invention relates to an induced electromotive force detection method for detecting a required induced electromotive force with high precision.

[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 torque component current, excitation component current, and current, so each current component can be controlled in correspondence with the armature current and field current in the DC motor. Can be done. 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 the winding machines used in rolling lines, and since this requires constant output control to keep the motor output constant regardless of the rotation speed, it is necessary to effectively control the motor input power. be.

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. It is necessary to consider detection error. Conventionally, as an electromotive force detection method, a method has been 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, calculating the motor magnetic flux phase, and calculating the orthogonal component of the voltage detection signal to the magnetic flux phase signal. The reason is that it detects electric power.

[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 the command signal It of the torque component of the next current
5 is a phase number converter that converts the primary voltage detection signal (3-phase signal) detected by the voltage detector 20 into a 2-phase signal, 6 and 7 are 2-phase signals from an oscillator 8, which will be described later. 9 is an adder that adds the output signal of multiplier 6゜7 and outputs an induced electromotive force detection signal (DC signal). lo is an adder that takes out the deviation of the electromotive force. an adder; 11 is an electromotive force deviation amplification device that amplifies the electromotive force deviation;
12 is a divider that divides the torque component current command It by the excitation component current command 1m and obtains the slip frequency command f of the motor 2. 13 adds the frequency command f and the speed detection signal, and calculates the motor 2 by adding the frequency command f and the speed detection signal. Adder that outputs missing frequency command fIk, L4゜15
16 is a multiplier that multiplies the current command 1゜' or i,' 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 -order current instantaneous value command i1'''. , 17 is a current detector that detects the instantaneous value of the primary current, 1
Reference numeral 8 denotes a current controller that controls the converter 1 according to the deviation between the above-mentioned primary current command and the current detection signal, and controls the negative primary current according to the command value.

Next, its operation will be explained.

The divider 12 takes out a frequency command f according to the following equation.

Here, Ip2 is the motor secondary time constant. Next, in the adder 13, the slip frequency command f, the speed detection signal f,
is added and a primary frequency command f1'' is taken out.The oscillator 8 outputs a two-phase sine wave signal (cosωIt, sinω+1) with a frequency proportional to the primary frequency command f1.(1
), when the total υ frequency f of the motor 2 is controlled according to the relationship of equation 2, one of the two-phase sine wave signals has the same phase as the motor magnetic flux, and the other has a phase difference of 90 degrees with respect to the magnetic flux. becomes the calculation detection signal.

Next, the multipliers 14, 15 and the adder 16 perform the calculation shown in the following equation, and a negative current command 11'' is obtained.

11:l, CoSω+1 i*5to6)lt
-.'' (2) The current regulator 18 controls the frequency converter 1 so that the -order current II flows in proportion to the primary current command i. The current is controlled in the same way by calculating current command signals that differ by 120 degrees from the primary current command 1 by a circuit not shown.

As described above, the excitation component and torque addition component of the -order current are determined by the current command 1. , It, and the percent motive 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.

In the phase number converter 5, the two-phase AC voltage detection signal vlff
+vlβ is calculated according to the following equation.

Note that vU, vy, and vy are phase voltages, which are converted into two-phase signals for the purpose of simplifying the calculation f.

Next, the multiplier 6.7 and the adder 9 calculate the following equation to detect the induced electromotive force E.

E = -Vl, (sinωl+v, ,g(cos
ωIt) −f4) Here, sin ω, 1 and c
osω,1 is the output signal of the oscillator 8. In addition to the secondary induced electromotive force E2 to be detected, the induced electromotive force E thus detected includes a leakage impedance drop component as shown in the following equation.

E; E2+r11 t 10(t), t, l m ”
”” (5) Here, rl Knee-order resistance t1 Knee-order leakage inductance ω1 Knee-order angular frequency ft: ) Luke component current i: Excitation component current However, the leakage reactance drop in the third term on the right side is
Since E2>ω1t1i, it can be ignored. Also, the second term resistance drop rli is the primary frequency f
The degree of influence is large in the operating range where + is low, but this can be done by subtracting the induced electromotive force E2 by the resistance drop r, i, using the torque component current it, as shown by the broken line in Figure 1. It can be easily compensated.

Note that the signals obtained from the adder 9 are expressed as vI and l in equation (4) when the rotation direction of the motor (phase order of the -order current) is reversed.
and the polarity of v1β is reversed. Therefore, if necessary, an absolute value calculator is provided on the output side of the adder 9 or i, j: 19, and its output is added to the adder 10.

Since the motor input P is given by the following equation, P'':;
3 E 2・it・・・・・・・・・
- (6) By keeping E2 and It 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 the second factor. In addition, in FIG. 2, P2 is the motor magnetic flux.

B】=V (E2+ωI41m +v1it )2+(
ω1t2 + > 10) tI+t 'I1m)2
(7) Compared to the induced electromotive force E2 to be detected, the detection error becomes large due to the primary leakage impedance drops r+i+ and ω+l+i+ and the secondary leakage reactance drop ω1t21t. On the other hand, the detection voltage E in the detection method of the present invention is as shown in the figure, and the detection error of υ is smaller than that of the conventional voltage E+. This means that the excitation component 1. This can be understood from the fact that is 1/3 to 1/6 of the torque component It. Also,
Compared to the electromotive force E2, only rH1 and ω+t+i are errors, but rl't can be easily compensated for. Also, since ω+t+i-/Ez is always a nearly constant value, ω]! The effect of −+ i m is not harmful. This is because when controlling the induced electromotive force E2, the command value E'' is set to ω
If the command is increased by 1t1im, the induced electromotive force E
2 can be controlled to a predetermined value.

〔Effect of the invention〕

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

[Brief explanation of drawings]

FIG. 1 is a circuit configuration diagram showing an embodiment of the present invention, and FIG. 2 is a vector diagram for explaining the present invention. l...Frequency converter, 2...Induction motor, 6.7.
... Multiplier, 8... Oscillator. Funeral 2

Claims (1)

[Claims] 1. Detecting the terminal voltage of an induction motor driven by a frequency converter, calculating the magnetic flux phase of the induction motor, and calculating the orthogonal component υ of the voltage detection signal to the magnetic flux phase signal of the induction motor. A method for detecting induced electromotive force, characterized in that the induced electromotive force of an electric motor is detected.