JPS5941194A - Step-out preventing system for ac motor - Google Patents

Abstract

PURPOSE:To prevent the step-out of an AC machine in a full operation range by detecting the component crossing perpendicularly to the magnetic flux vector of a unit vector of a stator current and the parallel component and adding them to the instruction frequency value in the polarity for suppressing the variations. CONSTITUTION:3-phase AC voltages VR, VS, VT are detected by a voltage detector 10, and converted into alpha-beta orthogonal coordinates amounts Valpha, Vbeta by a 3-phase/2-phase converter 15. Currents iR, iS, iT are detected by a current detector 14, and converted into alpha-beta orthogonal coordinates amounts ialpha, ibeta by a 3-phase/2-phase converter 18. Perpendicularly crossing and parallel components A, B to the magnetic flux vector of the unit vector of the current are obtained through a magnetic flux arithmetic unit 16, a vector rotation unit 17 and a vector analyzer 19. The outputs dA'/dt and dB'/dt of a differentiating arithmetic unit 20 are added by an adder to the frequency instruction value.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention uses a current source inverter as a power conversion device for supplying power to an AC motor to be operated at variable speed, and controls the output voltage and output frequency of the inverter so that they are proportional to y. This invention relates to a method for preventing motor disturbances in an AC motor control system that operates an AC motor at variable speed.

FIG. 1 is a block diagram showing an AC motor control system to which the present invention is applied.

In the figure, the AC motor is a 4ti3 sum squirrel-cage rust conduction motor that is operated at variable speed, and the power converter that supplies power to this is a forward converter 2 connected to a three-phase power supply system 1, and an electric zero
This is a current source inverter consisting of an inverter section 3 connected to the inverter section 14, and a current smoothing reactor 5 interposed between the two. Incidentally, all commutation components and the like in the inverter section 3 are omitted from illustration.

In addition, 6 is a phase shifter for controlling the forward conversion section, 7t is a current detector, 8 is a current regulator, 9 is a voltage regulator, 19 is a voltage detection dK, 11 is a pulse distribution unit, and 12 is a voltage / 13 is a frequency converter and a speed setting device.

In the AC motor ff1lJ Qll system shown in Fig. 1, ζ-
;, the output voltage C1 set by the speed setting device 13 is
As the frequency command value, the voltage/frequency converter 12,
The output frequency of the current source inverter is guided through the distribution unit 11 to the Zyristor in the inverter section 3, and the output frequency of the current source inverter, and thus the rotational speed of the AC drive 42 motor 4, is controlled in an open loop manner.

On the other hand, the voltage regulator 9, the current regulator 8, and the phase shifter 6 for controlling the phase shifter form a closed loop together with the current detector 7 and the voltage detector 10, so that the output voltage and output frequency of the current source inverter are approximately proportional to each other. 5.4C1 forward conversion section 2 is controlled.

In this way, the control system shown in FIG. 1 enables variable speed control of the electric motor while keeping the magnitude of the electric motor magnetic flux constant g. However, such a control system is similar to the conventionally known control system. Since this is also a control system and no further explanation is necessary for understanding the present invention, the explanation will be omitted.

As a method for preventing disturbances in the AC motor in such a control system, a method as described in Japanese Patent Application Laid-Open No. 72119/1983 has been proposed. This method detects the amount corresponding to the motor power factor cosθ and adds the amount of change to the frequency command value with a polarity that minimizes the change in the power factor, thereby suppressing motor disturbances. It is a method.

However, in this method, when the power factor angle θ is large, that is, when the load is light, the power factor co
The change in sθ is large, and therefore the damping effect against the variation in the power factor cosθ is large, and disturbances can be suppressed, but when the power factor angle θ is small, disturbances cannot be suppressed sufficiently. This will be explained in more detail below with reference to FIG.

Figure 2 (A) shows a vector ■1 with a large power factor angle θ, and Figure 2 (B) shows a vector V2 with a small Fi power factor angle θ.
It shows. In FIG. 2(a), when the power factor angle of vector V1 changes from θ to (θ+Δθ), the change in power factor CO3θ corresponding to the change Δθ is Xl.

On the other hand, in FIG. 2 (b), when the power factor angle of vector V2 changes from θ by the same amount Δθ to (θ + Δθ), the change in power factor cos θ corresponding to the same change Δθ It is tix2. If you compare mud 2 diagrams (a) and (b), it is clear that xl)x2. .

In other words, it will be understood that even if the change Δθ in the power factor angle θ is the same, the resulting change υ1 in the power factor cos θ is larger as the initial power factor angle θ is larger, and smaller as the initial power factor angle θ is smaller. .

Under these circumstances, the conventional disturbance fjl1M prevention method has the drawback that it does not have a sufficient disturbance suppression effect when the power factor angle θ of the motor is small.

The present invention is as described above? This invention has been made to improve the shortcomings of the prior art, and therefore, it is an object of the present invention to provide sufficient power regardless of the power factor angle of the motor, whether large or small. It is an object of the present invention to provide a method for preventing disturbances in an AC motor that has an effect of suppressing disturbances.

Next, the principle of operation of the present invention will be explained with reference to FIG. Figure 3 shows the magnetic flux vector φ of the motor and the motor current vector i.
FIG. 2 is a vector diagram showing the relationship between

The present invention has been made by focusing on the fact that when the motor is out of order, the angle X formed by the motor current vector i with respect to the motor magnetic flux vector 7 (as shown in FIG. For disturbance, detect the change in angle X and use this to damp the vibration of angle
This is based on the recognition that this can be prevented by changing the frequency of the current supplied to the AC motor (output frequency of the N-flow inverter).

In FIG. 3, it is assumed that the angle X formed by the current vector [ with respect to the magnetic flux vector φ changes to (X + ΔX). At this time, for the angle change ΔxVC, 1co
Find the change in sx Δ(J)SX and the change in 4 sin X Δsin z, and calculate both changes (Δcosx, Δq
in
This is to suppress disturbances.

When the angle X formed with the angle X is small, the change Δcos x tit is small, but the change Δ5inx is large. Although it becomes smaller, Δcosx becomes larger.

Therefore, if both Δ5inx and ΔC03X are added to the output frequency command signal, regardless of the size of the angle
This makes it possible to effectively suppress disturbances.

This completes the explanation of the operating principle of the present invention, and next, one embodiment of the present invention will be described with reference to the drawings.

FIG. 4 is a block diagram showing one embodiment of the present invention. In this figure, the same parts as in FIG. 1 are given the same reference numerals. In addition, 15 and 18 are each 3-phase/
2-phase converter, 16 is a magnetic flux calculator, 17 is a vector rotator, 19Fi is a vector analyzer, 20 is a differential operator,
It is. In other words, the point of newly adding these circuits is
This is different from the control system shown in FIG.

Next, the circuit operation will be explained. First, the voltage detector 10 detects the 3-phase AC voltage VR9s, VT of the stain motor 4, and this voltage is converted by the 3-phase/2-phase converter 15 to the stator R-phase winding of the motor as a reference axis. α to do.

β is converted into orthogonal coordinate quantities ■α, Vβ.

Figure 5(a) shows the three-phase sinusoidal voltage waveform ■R9Vs, VT
, each instantaneous amount at time A is shown.

In Figure 5(b), the three phases of the stator (R, S, T)
The α axis is on the winding axis of the R phase, and the β axis is perpendicular to it, and each instantaneous quantity in Fig. 5 (a) is expressed as ■α on both axes.
,■β are converted into two phases and expressed to clarify the vector relationship of each member. Note that V corresponds to a spatial rotation vector, whose α-axis component is Vα and its β-axis component is β.

Such three-phase/two-phase conversion is a common means in vector control of an AC motor, and is carried out because it is more advantageous for control reasons to grasp the three-phase quantity as a spatial rotation vector.

Here, ■ α9vβ is expressed by the following equation.

Next, the current detector 14 detects the three-phase stator current 'R1iS11'T of the tit, y machine, and the three-phase/
The two-phase converter 18 converts the stain pressures Vα and ■β into α-β rectangular coordinates iα and iβ. Here, iα and iβ are expressed by the following equations.

iα and iβ are guided to the V'C magnetic flux compensator 16 along with the above-mentioned Vα and Vβ, and the orthogonal coordinate quantities φα and φβ of the rotor magnetic flux vector are outputted by the following calculations by the magnetic flux computation unit 161/U. .

Here, rl, m, tl, and 12' are the stator resistance, mutual inductance, -order leakage inductance, and secondary leakage inductance, respectively, in the T-type equivalent circuit of the induction motor. φα, φβ, iα, iβ are vector rotations u1
7, the vector rotator 17 outputs signals A and B for the next calculation.

As shown in FIG. 6, the angles with respect to each other are ψ.

(ψ+X,)? Let the l sizes be i and φ, respectively (4
) formula is as follows.

The nine signals A and B obtained in this way are vector analyzer 1.
9, the unit vector of the Shimi flow is converted into orthogonal and parallel components to the magnetic flux vector using the following calculation, for example.

These signals A', B' are processed by a differentiator n20. guided by.

FIG. 7 is a circuit diagram of an example of the differential calculator 20. In a current source inverter, the phase difference X (see FIG. 6) changes greatly each time the inverter commutates, so in order to smooth this, the signals A t:, l are sent to the filter 201. Next, it is led to a differentiating circuit 202 in order to extract only the changes of these 14 numbers.

dA' Next, returning to FIG. 4, the output of the differential calculator 20 is added to the frequency command value by an adder. The signal B' is also added.

With the configuration shown in FIG. 4, for example, when the load on the motor 4 is light, and therefore when the angular difference Under load, therefore, when the angular difference X is small,
The influence of the change in X appears largely on B'=cos)c.

Therefore, if both the changes in A' and B' are added to the frequency command value, the amount of addition n of the frequency command value - will be greater than a certain value regardless of the magnitude of the angular difference It is possible to properly damp the fluctuations in the angle difference X in the entire operating range from normal to heavy load, and it is possible to prevent disturbances.

In the above explanation, the output of the magnetic flux calculator 16 was the rotor magnetic flux vector, but in this invention, it is only necessary to know the fluctuation of the angle formed by the two vectors, the current vector and the magnetic flux vector, so the stator is used instead of the rotor magnetic flux. A magnetic flux vector may also be used. In that case, the input of the magnetic flux calculator 16 is ■α,
Since only Vβ is present, the output of the magnetic flux calculator 16 is as follows.

When implementing the magnetic flux calculator 16 that calculates equation (3) or equation (7), it is possible to use a −order lag filter for the integrator, or alternatively, to detect the oscillation of the angle formed by the two vectors. It is possible because it can be done. Also, for the same reason, a voltage vector can be used instead of the magnetic flux vector. In this case, the magnetic flux calculator has no effect, ■α, V/ is φα
, t guided directly to the vector rotator 17 instead of φβ
It's evening.

According to this invention, the component sin Because of the addition, disturbances in the AC motor can be prevented in the entire operating range from light loads to heavy loads.

It is thought that this invention can be applied not only to the variable speed operation of an induction machine using a current source inverter as described above, but also to a device using a voltage source inverter as a power converter and a device using a synchronous machine as an electric motor.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the AC motor control system that is the object of the present invention, and Fig. 2 shows the power factor (: O5 FIG. 3 is a vector diagram for explaining the operating principle of the present invention, FIG. 4 is a block diagram showing an embodiment of the present invention, and FIG. Three-phase AC waveform diagram, Figure 5(b) is a vector diagram showing the coordinate relationship of vector quantities, Elementary 6 diagram is a vector diagram showing the coordinate relationship between the magnetic flux vector and current vector, and Figure 7 is the same as in Figure 4. It is a circuit diagram showing an example of the differential calculator 20. Symbol explanation 1... Three-phase IF source system, 2... Forward conversion section, 3... Inverter section, 4...AC motor, 5...Current smooth sliding axle, 6...
. . . Forward conversion unit control cape phase shifter, 7 . . . Current detector, 8 . . . Current regulator, 9 . . . Voltage regulator, 10... ...Voltage detector, 11...
Pulse distribution unit, 12... Voltage/frequency converter, 13... Speed setting device, 14...
Phase current detector, 15, 18... 3-phase/2-phase converter, 16... Magnetic flux wave unit, 17... Vector rotator, 19 River... vector analyzer, 20
・・・・・・Differential calculator zero 1 Figure 2 vA (in (
b) t7IE3 figure 4) 511 (su I'ff5 figure (shi)

Claims (1)

[Claims] 1) As a power conversion device that supplies power to an AC motor that is operated at variable speed, it includes a forward converter that converts AC input voltage from a power supply into variable DC voltage and outputs it, and an inverse converter that converts DC input voltage to variable frequency AC. A current-source inverter is used, which includes an inverter section that supplies current to the AC motor, and an intermediate circuit including a current smoothing handle interposed between the forward conversion section and the inverter section. By applying an output frequency command signal to the inverter section and controlling the forward conversion section so that the output voltage and output frequency from the inverter section are proportional to y, the AC motor is operated at a variable speed. In the electric motor control system,
means for respectively detecting a first component perpendicular to a magnetic flux vector of a unit vector of an AC motor stator current and a second component parallel to the unit vector; and a differential output of the detected first component and a differential output of the second component. to the output frequency command signal, respectively, with a polarity such that the output frequency decreases when the first component or the second component increases. A method to prevent disturbances in electric motors.