JPS6334715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an induction motor control device, and more particularly to an induction motor control device suitable for driving an induction motor using a plurality of frequency converters.

Figure 1 is a system diagram of a control device for an induction motor using a conventional self-excited frequency converter.
1 is a three-layer AC power supply; 12 is a current detector that detects the primary current _I1 of the induction motor 16; 13 is a forward converter that converts the three-phase AC power supply 11 into a variable DC power supply;
4 is a DC reactor that smoothes the DC current obtained by the forward converter 13, and 15 is a self-excited type that converts DC power into AC power with a variable frequency f and applies this AC power to an induction motor 16 to rotate it. A frequency converter, 17 a current control circuit for controlling the primary current I ₁ , 20 a primary voltage V ₁ of the induction motor 16
21 is an acceleration limiting circuit that limits the acceleration of the speed reference 22; 18 is a pulse that uses the signal given by the acceleration limiting circuit 21 to issue an ignition command to the self-excited frequency converter 15; An oscillation circuit 19 indicates the primary voltage V ₁ of the induction motor 16
This is a voltage detector that detects.

In this configuration, when controlling the induction motor, a firing command is given to the self-excited frequency converter 15 by the pulse oscillation circuit 18 in accordance with the signal set by the speed reference 22, and the DC current is changed to an AC of variable frequency f. Meanwhile, the primary voltage V ₁ of the induction motor ₁₆ is controlled by applying a signal set by the speed reference 22 to the voltage control circuit 20 . A closed loop control is performed in which the voltage detector 19 feeds back the primary voltage _V1 . Furthermore, a current control system is provided in this minor loop, and one of the induction motors 16
The next current I ₁ is controlled by a forward converter 13 .

In other words, this control system has a primary voltage V ₁ and a frequency f
A well-known control method is used to control the ratio V ₁ /f so that it remains approximately constant. However, this control method is considered unsuitable for cases such as rapid reversible operation, precise speed control, or cases where load fluctuations are large, and there has been a strong demand for a control system that can handle these situations. .

Therefore, an object of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to provide a new induction motor that can stably operate an AC motor even when performing rapid reversible operation or precise speed control, and even when load fluctuations are large. to provide control equipment.

Hereinafter, the present invention will be explained in more detail with reference to the drawings.

FIG. 2 is a vector diagram showing the principle of the induction motor control device according to the present invention, where the horizontal axis is d, the vertical axis is q, I ₁ is the primary current, I ₂ is the secondary current, and φ ₂
is the secondary magnetic flux, ω is the angular frequency of the secondary magnetic flux φ ₂ , ω _n is the angular frequency of the secondary conductor, M is the mutual inductance between the primary and secondary, L ₂ is the secondary leakage inductance, I ₀
corresponds to the excitation current that creates the secondary magnetic flux φ ₂ .

As shown in Figure 2, when driving an induction motor, the secondary conductor of the induction motor has a secondary current component I _2q orthogonal to the secondary magnetic flux φ ₂ due to the speed electromotive force and a secondary magnetic flux φ ₂ due to magnetic flux changes. A secondary current component I _2d parallel to flows. Furthermore, if the secondary magnetic flux φ ₂ and the angular frequency of the secondary conductor are ω and ω _n , respectively, and the secondary resistance is R ₂ , then I _2q = −(ω − ω _n )/R ₂ ×φ ₂ = −1/ R ₂ ×ω _S …(1) I _2d = 1/R ₂ ×dφ ₂ /dt …(2). However, ω _S =ω−ω _n …(3) where ω _S is the slip angular frequency. Expressing the above relationship in terms of primary current, I _1q = L ₂ /M×1/R ₂ ×ω _S ×φ ₂ …(4) I _1d =φ ₂ /M×(1+L ₂ /R ₂・d/dt ) …(5) I ₁ =L ₂ /M×(I ₀ −I ₂ ) …(6). However, L ₂ is the secondary leakage inductance,
M is the mutual inductance between the primary and secondary, and I ₀ is the excitation current that creates the secondary magnetic flux φ ₂ . On the other hand, since the generated torque τ is τ=−I _2q ×φ ₂ (7), it becomes τ=M/L ₂ ×I _1q ×φ ₂ (8). To summarize the above, torque τ is proportional to I _1q , magnetic flux φ ₂ is directly controlled by I _1d , and control performance equivalent to that of a DC machine can be obtained. Based on this basic principle, embodiments of the present invention will be described in detail below.

FIG. 3 is a system diagram of a control device for an induction motor according to an embodiment of the present invention, in which 11 ₁ and 11 ₂ are three-phase AC power supplies, and 12 ₁ and 12 ₂ are primary currents I of the induction motor 16. Current detector that detects ₁ , 13 ₁ , 13 ₂
14 1 and 14 2 are forward converters that convert the three-phase AC power supplies 11 ₁ and 11 ₂ into variable DC power supplies; 14 ₁ and 14 ₂ are DC reactors that smooth the DC current of the DC power supplies _;
15 ₂ is a separately excited and self-excited frequency converter that converts the DC power source into an AC power source with a variable frequency f; 17
₁ and 17 ₂ are current control circuits that control the input currents of the forward converters 13 ₁ and 13 ₂ ; 30 is an induction motor 16;
A pulse oscillator detects the angular frequency ω _n1 of the rotor corresponding to the angular frequency ω _n of the secondary conductor, 29 is the rotational speed of the induction motor 16, and the angular frequency ω _n of the secondary conductor is
36 is a secondary magnetic flux reference, and this signal corresponds to the field current reference signal of a separately excited DC motor, for example, and the reference value is normally kept constant so that the rated excitation current flows. However, when field-weakening current control is used as in a DC motor, the secondary magnetic flux standard 3 is automatically set as soon as the primary voltage or rotational speed of the induction motor exceeds a certain value.
Automatic field weakening control can also be performed by reducing 6. 34 is a secondary magnetic flux control circuit, and 35 is fed back the output signal of the secondary magnetic flux control circuit 34, and compares the secondary magnetic flux signal φ ₂₁ with a secondary magnetic flux reference signal to determine the d-axis component I _1d of the primary current. To control (5)
33 is a divider that divides the output signal I _1q of the speed control circuit 29 by the feedback signal φ ₂₁ of the operation circuit 35 to obtain the slip angular frequency ω _S1 ; 32 is a divider an adder for adding the output signal ω _S1 of 33 and the output signal ω _n1 of the pulse oscillator 30; 31 is applied with an output signal expressed as a primary frequency reference (ω _S1 +ω _n1 =ω ₁ ) of the adder 32; 25 is an arithmetic logic circuit that receives the output signal of the two-phase oscillation logic circuit 31 and outputs a commutation timing command to the separately excited frequency converter ₁₅₁ ; 24 is an induction motor 1;
a voltage phase detector that detects the phase of the primary voltage of 6;
23 is a pulse oscillation circuit that gives a firing command to the separately excited frequency converter ₁₅₁ according to the commutation timing command of the arithmetic logic circuit 25; 26 is a control advance angle β;
27 is a multiplier, and 28 is a divider.

Now, in this configuration, the rotational speed and the angular frequency ω _n of the secondary conductor of the induction motor 16 are controlled by the speed control circuit 29, but the speed control circuit 29 controls the secondary magnetic flux signal φ ₂₁ . The output signal is based on the q-axis component _I1q of the primary current. In this case, from equation (8), if this output signal is used as a torque reference, I _1q =L ₂ /M×τ/φ ₂ (9). However, since L ₂ /M is a constant, I _1q ∝τ/φ ₂ (10). Further, this output signal will be controlled by the angular frequency ω _n of the secondary conductor.

On the other hand, the output signal of the divider 33 is expressed as ω _S when formula (4) is expressed as ω _S =I _1q /(L ₂ /M×1/R ₁ ×φ ₂ ) (11). , L ₂ /M×1/R ₁ are constants, ω _S ∝I _1q /φ ₂ (12), resulting in a signal proportional to I _1q /φ ₂₁ .

The output signal of the two-phase oscillation logic circuit 31 is not only applied to the arithmetic logic circuit 25, but also applied to the pulse oscillation circuit 18 that generates a firing command for the self-excited frequency converter ₁₅₂ to control it. . Further, the arithmetic logic circuit 25 determines the control advance angle β according to the output signal of the voltage phase detector 24.
An analog signal related to the function is generated and applied to the function generating circuit 26. Furthermore, the commutation timing command of the logic circuit 25 is always based on the primary voltage.
Separately excited frequency converter 1 by control advance angle β from V ₁
5 The output current of ₁ is advanced to stabilize commutation.

On the other hand, when the output signal of the function generation circuit 26 is applied to the divider 28 and the multiplier 27, the output signal of the divider 28 generates a current reference signal of I _P ,
The output signal of multiplier 27 generates a current reference signal of I _P sinβ. The output signal of the divider 28 controls the current of the first forward converter ₁₃₁ , and the separately excited frequency converter 1
5 Controls the magnitude of the output current I _P of ₁ . On the other hand, the output signal of the multiplier 27 is added to the d-axis component reference _I1d of the primary current explained earlier to become the current reference signal of _IQ ,
This output signal controls the current of the second forward converter 13 ₂ to control the magnitude of the output current _IQ of the self-excited frequency converter 15 ₂ .

By controlling the induction motor 16 with the configuration described above, control characteristics as shown in the vector diagram of FIG. 4 can be obtained.

Next, the output current I _P of the separately excited frequency converter 15 ₁
Let I _P cosβ be the torque component current, and let the difference between the output current I _Q of the self-excited frequency converter 15 ₂ and I _P sinβ of the output current I _P of the separately excited frequency converter 15 ₁ be the magnetic flux component current. , the fundamental vector diagram of FIG. 2 is obtained.
This corresponds to the part indicated by the bold line in FIG.

This function can be expressed as the following formula.

I _1q = I _P cosβ (13) I _1d = I _Q −I _P sinβ (14) The vector line shown in bold in FIG. 4 is equivalent to the vector line in FIG. 2. In other words, the torque τ is proportional to the output current I _P cos β of the separately excited frequency converter 15 ₁ ,
The magnetic flux φ ₂ is the output current I _Q of the self-excited frequency converter 15 ₂
−I _P sin β can be directly controlled. On the other hand, since the controlled object is an induction motor and there is no armature reaction, the control advance angle β needs to be advanced from the primary voltage V ₁ by an amount that turns off the thyristor element. Additionally, the turn-off time of a thyristor element is generally several hundred μsec.
Therefore, I _P cosβ≒I _P …(19) I _Q −I _P sinβ≒I _Q …(20) Therefore, the torque component current can be converted using a separately excited frequency converter that can supply a leading current. Since it is possible to obtain a magnetic flux component current with a self-excited frequency converter that can supply a delayed current,
If the combined current is fed to an induction motor, control performance equivalent to that of a DC motor can be achieved. Moreover, the self-excited frequency converter only needs to supply the magnetic flux component, that is, the excitation part of the induction motor, and can be made smaller.The self-excited frequency converter can drive the induction motor almost only with the separately excited frequency converter, so it is stable. It is possible to perform the following driving.

As described above, according to the present invention, with a relatively simple configuration, it is possible to perform rapid reversible operation and precise speed control of an induction motor, and to perform speed control of an AC motor with large load fluctuations. Thus, it is possible to obtain a new induction motor control device that can be effectively applied to the above.

[Brief explanation of the drawing]

Fig. 1 is a system diagram of a conventional induction motor control device, Fig. 2 is a vector diagram showing the principle of an induction motor control device according to the present invention, and Fig. 3 is a system diagram of an induction motor control device according to an embodiment of the present invention. FIG. 4, a system diagram of the control device, is a vector diagram illustrating control characteristics in the configuration shown in FIG. 11, 11 ₁ , 11 ₂ ... 3-phase AC power supply, 12,
12 ₁ , 12 ₂ ... Current detector, 13, 13 ₁ , 1
3 ₂ ... Forward converter, 15 ... Frequency converter, 15 ₁
... Separately excited frequency converter, 15 ₂ ... Self-excited frequency converter, 16 ... Induction motor, 29 ... Speed control circuit, 36 ... Magnetic flux control circuit.

Claims (1)

[Claims] 1 A separately excited frequency converter that supplies a torque current component I _1q to the induction motor, a self-excited frequency converter that is connected in parallel to this and supplies an exciting current component I _1d , and detects the phase of the primary voltage of the induction motor. and calculating a sin β signal and a cos β signal corresponding to a control advance angle β of the separately excited frequency converter that is advanced by a predetermined phase from the primary voltage phase of the induction motor detected by the detection means. means for receiving the magnetic flux reference signal of the induction motor as an input and calculating a reference signal for the excitation current component _I1d ; Torque current component
means for calculating a reference signal for I _1q ; and means for calculating a reference signal for output current I _P of the self-excited frequency converter from the output signal of the means and the cos β signal;
A control device for an induction motor, comprising means for adding the output signal of the means and a reference signal of the excitation current component I _1d .