JPH0740796B2 - Secondary control method for induction machine - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method for a wound induction motor capable of secondary excitation control, and more particularly to an induction machine suitable for variable speed drive of a pump, a fan, or the like. Regarding control method.

[Background of the Invention]

Conventionally, as this type of control device, for example, a so-called SELVIUS device described in the literature, “Power Electronics” written by Shota Miyairi, Maruzen, p.170-171 is known. However, this device requires an inverse converter and a transformer with a large capacity in order to change the speed in a wide range from the stop time to the rated speed, and the power factor of the inverse converter is low. There was a drawback that the circuit was complicated.

In addition, Eat Z. A., B.D. 96 (197
5), H.S., 5.239-242, by Fick et al., “Bahn Stromrichter Mitt Guten”.
Rice Tungsfactor "(ETZ-A, Bd.96 (1975),
H.Sz, 5.239−242, Fick. “Bahn−Stromrichter mit gute
m Leistungsfactor ") has a chip before the drive inverter of an AC electric motor, and the input current of a diode rectifier that converts AC from an overhead contact wire into DC is Use a sine wave and have the same phase as the AC input voltage (power factor 1.
Although the power factor is improved by controlling it to 0), the inverter and the chip still have to have a large capacity corresponding to the capacity of the motor, and the power factor of the motor cannot be improved. there were.

[Object of the Invention]

The object of the present invention is to eliminate the above-mentioned drawbacks of the prior art and to make the capacity of the converter necessary for speed control smaller than the capacity of the electric motor, and to include the power factor of the electric motor in the entire system. Another object of the present invention is to provide a speed control method by the secondary excitation method of an induction machine capable of improving the power factor.

[Outline of Invention]

In order to achieve this object, the present invention, in a system in which the secondary current of the induction machine is chip-controlled to perform speed control, the secondary current is amplitude-modulated in synchronization with the secondary induced voltage. It is characterized in that the secondary current waveform of the induction machine is controlled by.

Example of Invention

Hereinafter, the secondary control method of the induction machine according to the present invention will be described in detail with reference to the illustrated embodiments.

FIG. 1 is an embodiment of the present invention. In the figure, reference numeral 1 is a rotor winding having orthogonal biaxial windings, and four sets of slip rings and brushes make two sets of secondary windings independent of each other. A winding type induction motor (hereinafter referred to as an induction machine) which is designed to be taken out as a circuit, 2 is a diode rectifier, 3 is a gate turn-off thyristor, a self-extinguishing type switching element such as a transistor (hereinafter referred to as GTO). ), 4 is a reverse current blocking diode, 5 is a capacitor, 6
Is a thyristor inverse converter for regenerating the secondary power of the induction machine 1 into an AC power source, 7 is a DC reactor for suppressing fluctuations in the input current of the inverse converter 6, and 8 is a transformer. Reference numeral 9 is a speed detector directly connected to the induction machine 1, and 10 is a speed command circuit. Reference numeral 11 denotes a speed controller that amplifies the deviation between the signal from the speed detector 9 and the speed command signal and outputs a current command signal. 1
Reference numerals 2 and 13 are current detectors, and 14 is a circuit for obtaining the absolute value of the signal of the current detector 12. Reference numeral 15 is a secondary current waveform command circuit, which is described in detail in FIG. 17 is the current command signal sent from the secondary current type command circuit 15 and the current detector
This is a comparator with hysteresis characteristics that compares the absolute value signal of the output of 12 or the output signal of the current detector 13 and outputs the ON / OFF control signal of GTO3. 18 is a gate amplifier, 19
Is a control circuit for controlling the inverse converter 6 in a constant firing phase. There is one set corresponding to the other rotor winding of the induction machine, which is the same as the components 2 to 4, 12 to 15, 17, and 18 described above, but the configuration is the same as that described above, and therefore the description will be omitted. Omit it.

Next, the operation will be described.

The GTO 3 is on / off controlled according to the output signal of the comparator 17. That is, the comparator 17 compares the current command signal with the current detection signal, and outputs a signal for turning off GTO3 when the latter increases by a predetermined value or more compared to the former, on the contrary, the latter compared to the former. When it is less than the specified value, a signal to turn on GTO3 is output.

Thus, while GTO3 is on, the DC current I _d is GT
It flows through O3 and through diode 4 when it is off. The current I _d1 flowing through the diode 4 charges the capacitor 5 and serves to increase the voltage V _co of the capacitor. As a result, when a difference is generated between the DC input voltage of the inverse converter 6 and the capacitor 5, the current flows from the capacitor 5 to the inverse converter 6. Since the inverse converter 6 is controlled by the ignition control circuit 19 at a constant ignition phase, its DC input voltage is almost constant. Therefore, the voltage of the capacitor 5 is also equal to the voltage of the inverse converter 6 in average value, and is held substantially constant.

By the way, when the GTO3 is turned on, the direct current increases due to this, and the magnetic energy stored in the circuit through which this current flows increases. Next, when GTO3 is turned off, this magnetic energy is released and the capacitor 5 is charged.
That is, it can be seen that the circuit formed by the GTO 3, the diode 4 and the capacitor 5 has a function of converting the fluctuating secondary voltage, that is, the output voltage of the diode rectifier 2 into a constant voltage direct current. As a matter of course, if the circuit loss is ignored, the power transmitted to the inverse converter side becomes equal to the secondary power of the induction machine 1. Therefore, for a load such as a pump or a fan whose torque changes with the square of the rotation speed, the power handled by the inverse converter 6 is 1/6 of the motor output.

Next, the reason for this will be described in more detail.

As is well known, the secondary voltage of an induction motor is proportional to slip and the secondary current is proportional to torque.

Therefore, when the load of the electric motor is a pump or fan and the load torque is proportional to the square of the rotation speed as described above, the secondary power P ₂ (secondary voltage × secondary current) of ).

P ₂ = S ・ E ₂₀・ (1-S) ²・ I ₂₀ ………… (a) where S: Slip E ₂₀ : Secondary voltage at S = 1 I ₂₀ : Rated speed (S≈0 ) Then the secondary power P _{2 with} respect to the slip S,
From the condition that the differential dP ₂ / dS becomes 0, that is, dP ₂ / dS = (1-4S + 3S ² ) ・ E ₂₀・ I ₂₀ = 0, try to find the maximum value _2m of this secondary power P _2. , (S = 1/3), the following equation (c) is obtained.

P _2m = _4/27 × (E ₂₀ · I ₂₀ ) …… (c) where (E ₂₀ · I ₂₀ ) is the secondary input at the time of rating, and the induction motor loss (iron loss, copper Loss) is ignored, it is approximately equal to the rated output of the induction motor.

Therefore, the secondary power P ₂ of the induction motor is as small as 4/27 of the rated output, that is, 1/6.

However, since the secondary voltage of the induction motor changes in proportion to the slip, in the case where the diode rectifier is simply connected to the secondary circuit as in the prior art SELVIUS device, the output voltage of the rectifier is reduced. The slip voltage also changes in proportion to the slip, and the input voltage of the thyristor converter (inverter) for regenerating the secondary power to the AC power supply side also changes.

Therefore, the converter must be able to operate even when this input voltage reaches its maximum value. And
This maximum value is (S =
Since it is 1), it becomes the above-mentioned secondary voltage E ₂₀ .

On the other hand, the secondary current of the induction motor becomes maximum at the time of rating (at the time of rating), but since this current flows through the diode rectifier to the converter as it is, the converter has the maximum input current. It is necessary to be able to operate even when it is.

Therefore, in the conventional technology, as the capacity of the converter required there, it is necessary to correspond to the maximum power determined by the product of the maximum value of the secondary voltage and the maximum value of the secondary current of the induction motor. , For example, as described above, when the induction motor is started, that is, (S = 1), the secondary voltage is E ₂₀ ,
And since the secondary current becomes I ₂₀ , it is eventually equal to the rated power, and therefore almost equal to the rated output, even though the maximum secondary power of the induction motor is only 1/6 of the rated value. Capacity is needed.

On the other hand, in the present invention, as described above, the chopper circuit composed of the GTO 3, the diode 4, and the capacitor 5 is provided, which is controlled as described above to change according to the slip of the induction machine 1. Since the secondary voltage, that is, the output voltage of the diode rectifier 2 is converted into a direct current having a constant voltage substantially equal to the rated secondary voltage, the inverse converter 6 is always operated at a constant voltage. The input voltage is maintained at a value approximately equal to the rated secondary voltage.

At this time, the current flowing through the inverse converter 6 is proportional to the secondary power of the induction machine 1 and inversely proportional to the DC voltage (= voltage of the capacitor 5), so that the input voltage is kept at the rated voltage. As long as it is present, the input power of the inverse converter 6 will not become larger than the rated secondary power of the induction machine 1.

Therefore, the capacity (equipment capacity) of the inverse converter 6 is 1/6 of that in the conventional technique. And again, this result
The capacity of the transformer 8 that handles the power of the inverse converter 6 is also 1/6.
It will be done.

Further, since the inverse converter 6 is controlled with a constant ignition phase, the power factor is always maintained at a constant high value. From these facts, the capacity of the inverse converter 6 and the transformer 8 is about 20% of the motor output, and the capacity can be reduced.

Next, FIG. 2 shows an embodiment of the secondary current waveform command circuit 15,
Hereinafter, FIG. 2 will be described.

The secondary voltage V ₂ generated in the secondary winding of the induction machine is passed through the integrator 21 and converted into the secondary magnetic flux Φ ₂ . This secondary magnetic flux Φ ₂ is A / D
The converter 22 converts the digital amount. Based on the Φ ₂ , signals I _2A and I _2B having a relationship to be described later with the secondary voltage V ₂ are read from read-only memories (hereinafter referred to as ROMs) 23 and 24, and their values are D / A converters 5, Input to 26 to output waveforms I _2A and I _2B .

Here, since the amplitude of the waveform of Φ ₂ needs to be always constant, the following arithmetic processing is performed between the integrator 21 and the A / D converter 22.

Here, Φ ₂₁ is an output signal of the integrator 21, and Φ ₂₂ is a signal obtained by integrating the secondary voltage of the other rotor winding (the side connected to the diode rectifier 2 ′) by the same integrator. ,
Φ _21N and Φ _22N are amplitude constant signals of Φ ₂₁ and Φ ₂₂ . Note that Φ ₂₁ and Φ ₂₂ are expressed by the following equations.

Φ ₂₁ = | Φ ₂ | cos (ω ₂ t + θ) ……… (3) Φ ₂₂ = | Φ ₂ | sin (ω ₂ t + θ) ……… (4) where ω ₂ is the angular frequency of the secondary voltage. Is.

In FIG. 2, the D / A converters 25 and 26 have a multiplication function and can change the amplitudes of the waveforms I _2A and I _2B in proportion to the input reference signal. Incidentally, such a D / A converter is well known. A current command signal (hereinafter, τ command) from the speed controller 11 is added to the D / A converter 26 as a reference signal. Also D /
A signal corresponding to the τ command or an independent signal (hereinafter, _IE command) is added to the A converter 25. In this way
The signals I _2A and I _2B synchronized with the secondary voltage V ₂ are taken out and added to form a waveform I _2C .

Then, the current command signal I _2d is generated through the absolute value circuit 27. This becomes the output of the secondary current waveform command circuit 15 as a command signal for controlling the output current of the diode rectifier 2, and it is compared with the current detection signal, and GTO3 is turned on and off according to the deviation as described above. Control.

Next, the principle of the power factor correction method by controlling the secondary current waveform will be described with reference to FIG. In the figure, (a) to (c) show the relationship between the voltage V ₂ and the current I ₂ in the diode rectifier 2,
(A) lag current, (b) in-phase (power factor = 1.0),
(C) is a case of a lead current (excitation current compensation of the electric motor). Either operation is possible by controlling the output current of the diode rectifier 2 as shown by the broken line in the figure. Therefore, in order to improve the power factor of the entire device including the improvement of the electric power factor of the electric motor, the secondary current I ₂ may be advanced and flowed with respect to the secondary voltage V ₂ as shown in (c). This is the principle of the present invention.

FIGS. 3D to 3F show a method of synthesizing the secondary current waveform in this embodiment. I _2B shown in (d) is a fundamental wave component,
It is a component that contributes to torque, and its magnitude changes according to the above-mentioned τ command. I _2A shown in (e) is a waveform obtained by reversing the polarity of the double-frequency waveform with respect to the fundamental wave every half cycle of the fundamental wave, and its magnitude changes according to the _IE command. I _2A contains a fundamental wave component having a 90-degree advanced phase with respect to the fundamental wave. The waveform I _2C shown in (f) is the waveforms I _2B and I _2A.
, Which is similar to the waveform of I ₂ shown in (c).

Therefore, the secondary current waveform command circuit 15 performs the above-mentioned waveform synthesis. That is, the A / D converter 22 outputs the phase angle amount of the secondary magnetic flux φ ₂ as a digital signal. ROM23, 24
Inputs the phase angle and outputs a value corresponding to the phase angle. The output signal is the reference signal (constant amplitude) of the waveforms I _2B and I _2A , and as described above, in the / A converters 25 and 26,
Amplitude modulation is performed by the τ command and the _IE command, and waveforms I _2B and I _2A are obtained. Further, by adding these, a signal having a waveform I _2C shown in FIG. 3 (f) is produced, and thereafter, an absolute value signal I _2d of this signal is outputted, whereby the waveform shown in FIG. 3 (c) is produced. Make the secondary current of I ₂ available. That is, as a result, the output current I _d of the diode rectifier 2 is controlled in proportion to the signal I _2d as described above, and as a result, the secondary current I ₂ becomes proportional to the I _2C . is there.

As is clear from FIG. 3 (c), the current I ₂ has a fundamental wave component having a lead phase with respect to the secondary voltage V ₂ , and as a result, the magnetic flux of the motor from the secondary side of the induction machine 1 is increased. The exciting current (reactive current) related to the generation can be supplied, and as a result, the exciting current (reactive current) from the primary side of the induction machine 1 decreases, and the power factor on the primary side of the induction machine 1 can be improved. it can.

This will further To supplement the explanation, as described above, the current command signal I _2d and the current detection signal by the comparator 17 | compares the detection signal to the command signal _{I 2d | | I 2 I 2} | a predetermined When it is increased by the value, GTO3 is turned off, and on the contrary, the command signal I
_When the detection signal | I ₂ | decreases by a specified value for _2d, GTO3
Is turned on.

Here, when GTO3 is turned on, the output side of the diode rectifiers 2, 2'is short-circuited, so that the output current increases, and conversely, when GTO3 is turned off, the output current decreases.

Therefore, as a result, the output currents of the diode rectifiers 2 and 2'will be controlled following the command value of the current command signal I _2d , and as shown in FIG.
Depending on _2d , the phase of the secondary current with respect to the phase of the secondary voltage can be arbitrarily controlled to be the same phase or the advanced phase.

Therefore, if the lead phase is controlled now, the induction machine 1
Is equivalent to the excitation current being supplied to the induction machine 1 itself from the secondary side, and the excitation current supplied from the primary side of the induction machine 1 is reduced by that amount, so the power factor of the induction machine 1 is reduced. (Primary side) can be improved.

When controlled to the same phase, the excitation current cannot be supplied from the secondary side, but at least the negative excitation current is not supplied, so the power factor is reduced. Instead, it can maintain a high power factor.

On the other hand, as described above, since the inverse converter 6 is controlled with a constant ignition phase, it operates under a constant high power factor, and therefore the power factor is not reduced.

Therefore, according to this embodiment, the entire device can always be operated at a high power factor.

In the conventional SELVIUS device, in the rated operating condition,
Since the DC input voltage of the inverse converter becomes approximately 0 V, the ignition phase α of the inverse converter becomes approximately 90 °, and as a result, its power factor becomes almost zero. Further, at this time, since the rated current is flowing through the inverse converter, the reactive power in the inverse converter is large, and the power factor of the entire device is greatly reduced.

By the way, when the GTO3 is turned on, the secondary side of the induction machine 1 is short-circuited, but the secondary current at this time is
The rate of change is limited by the leakage inductance existing in the induction machine 1 and increases with a predetermined time constant. Therefore, by appropriately selecting the switching frequency of GTO3, an appropriate current value can be maintained, and there is no risk of an overcurrent state.

In addition, at this time, current pulsation is involved, but this can also be suppressed within a predetermined allowable range by selecting a high switching frequency of GTO3 described above. The secondary current of the machine 1 follows the current command signal and is controlled in a substantially sinusoidal shape, so there is no risk of a reduction in the power factor.

Further, since the sinusoidal secondary current is obtained in this manner, torque pulsation is small, and harmonic components appearing in the AC power supply can be suppressed.

It is needless to say that a reactor may be inserted in the output side of the diode rectifiers 2 and 2 ', as is well known, and in this case, the pulsation of the current can be suppressed more sufficiently.

Here, the reason why the signals I _2A and I _2B are independently generated by using the two ROMs 23 and 24 and the D / A 25 and 26 and the signal I _2C is obtained by adding these signals is that the torque command τ and This is because the torque and the power factor can be arbitrarily controlled by the command I _E.

The same operation is performed in the circuit corresponding to the other rotor winding of the induction machine 1. However,
Since the phase of the secondary voltage differs by 90 degrees with respect to the other winding, the only difference is that the phase of the secondary current is also controlled to differ by 90 degrees.

As described above, according to this embodiment, the converter can be made to have a small capacity, and at the same time, the electric power factor of the electric motor can be improved and the power factor of the AC power supply system can be improved.

By the way, in the above-described embodiment, the case where the ordinary winding type induction machine with the brush and the slip ring is used as the induction machine 1, the present invention is not limited to this, and the induction machine capable of the secondary excitation. Any motor will do. That is, a brushless induction machine that continues two induction machines, and a stator winding having a different number of poles is wound around a common stator core as shown in Fig. 4, and the number of rotor bars is fixed to two. A brushless induction machine with a special configuration having the sum of the numbers of poles of the child winding may be used. This FIG. 4 is proposed in Japanese Patent Laid-Open No. 59-129588. Reference numeral 30 represents the entire brushless induction machine, and the stator 28 has a main winding 31 and an exciting winding 32 having different numbers of poles. The rotor 29 is provided with one winding, and the rotor 29 is provided with the above-mentioned number of bars 33.

FIG. 5 shows another embodiment of the secondary current waveform command circuit 15 described above. 1 is the same induction machine as in FIG. 1, 51 is a pulse oscillator for detecting the rotation angle, and 52 is a pulse signal of the oscillator 51. , 53 is a mono-multi that extracts a pulse signal synchronized with the AC power supply voltage, 54 is an oscillator that outputs a pulse signal of a constant frequency, 55 is a pulse signal of the oscillator 54, and the reset signal is generated by the mono-multi 53 signal. A counter that performs an operation, 56 is a subtracter that subtracts the output of the counter 52 from the output of the counter 55, and 57 and 58 are the signals I _2A and I ₂ based on the output of the subtractor 56.
It is a ROM that reads out signals synchronized with the secondary voltage similar to _2B . Others are the same as in FIG.

First, the counter 55 counts the pulse signal of the oscillator 54,
Since the reset is performed by the signal of the mono-multi 53, this count value is related to the phase of the power supply voltage. On the other hand, the counter 52 counts the pulse signal of the oscillator 51, and at the same time, the pulse signal from the oscillator 51 is reset once per rotation, so that the count value is related to the rotation angle phase. In the subtractor 56, these count values are subtracted, and a signal having a value related to the phase of the secondary voltage is taken out. Therefore, based on the signal, the memory 5
From 7,58, the waveform synchronized with the secondary voltage can be read out in the same manner as the above-mentioned embodiment, and the same operation can be performed.

Next, FIG. 6 shows another embodiment of the present invention. In the embodiment, the induction machine 1 having the orthogonal biaxial windings in which the rotor windings are insulated from each other is used. In this embodiment, an ordinary winding type induction machine having three-phase windings is used, and the diode rectifier 2 is placed between one line of the rotor winding and the diode rectifier 2'is placed between the other lines. In addition to using two independent reverse converters 6 and 6'and a transformer 8'having two independent windings on the secondary side, the secondary power of the induction machine 1 is used as an AC power source. It is designed to regenerate.

Therefore, also in this embodiment, the same operation can be obtained by controlling each output current in the same manner as in the embodiment of FIG. 1 on the basis of the phase of each AC input voltage of the diode rectifiers 2 and 2 '. As a result, the configuration becomes somewhat complicated by using the two inverse converters 6 and 6'and the transformer 8'having two independent windings on the secondary side.
Similar to the embodiment of FIG. 1, the capacity of the inverse converters 6 and 6'and the transformer 8'is small, and the power factor can be improved sufficiently. In addition, in this embodiment, as the induction machine 1, a winding type induction machine of a normal type having a three-phase rotor winding can be used, and the effect of suppressing an increase in cost can be obtained. .

In the embodiment of FIG. 6, two inverse converters 6,
6'is used, the total capacity thereof may be 1/6 as in the case of the embodiment of FIG. 1, so that each capacity is half that of the embodiment of FIG. That is, 1 /
The effect of requiring only 12 and therefore a small capacity can be obtained as in the embodiment of FIG.

In the above embodiments, a chopper circuit is required, and the electric power handled by this is the product of the maximum value of the secondary voltage and the maximum value of the secondary current, so a considerable capacity is required,
Since the main constituent element of this chopper circuit is one GTO3, the cost is small as compared with the capacity, and therefore the effects of the present invention described above are not lost.

〔The invention's effect〕

As described above, according to the present invention, since the secondary current waveform of the induction machine can be controlled and the exciting current can be supplied from the secondary side at this time, the power factor of the induction machine can be arbitrarily controlled. This makes it possible to easily provide a secondary control method for an induction machine that is useful for improving the power factor on the power supply side, excluding the drawbacks of the prior art.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an embodiment of a secondary control method for an induction machine according to the present invention, FIG. 2 is a circuit diagram showing an embodiment of a secondary current waveform command circuit according to the present invention, and FIG. ) ~ (F)
Is a waveform diagram for explaining the operation, FIG. 4 is an explanatory diagram showing an example of a brushless induction machine, FIG. 5 is a circuit diagram showing another embodiment of the secondary current waveform command circuit, and FIG. 6 is a diagram showing the present invention. It is a circuit diagram which shows another Example. 1 …… Induction machine, 2 …… Diode rectifier, 3 …… GTO, 4 ……
Reverse blocking diode, 6 ... Inverting converter, 7 ... Reactor, 8 ... Transformer, 9 ... Speed detector, 10 ... Speed command circuit,
11 …… Speed controller, 12, 13 …… Current detector, 14 …… Absolute value circuit, 15 …… Secondary current waveform command circuit, 17 …… Comparator with hysteresis characteristic, 18 …… Gate amplifier, 19… … Ignition control circuit.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hisaya Sasamoto 3-1-1 Sachimachi, Hitachi City, Ibaraki Prefecture Hitachi Research Laboratory Hitachi Research Laboratory (72) Inventor Sadahiko Niwa 3-chome, Hitachi City, Ibaraki Prefecture No. 1 Stock company Hitachi Ltd. Hitachi factory (56) Reference JP-A-53-72121 (JP, A)

Claims (2)

[Claims] 1. A speed control method by secondary control of a wound-type induction machine, comprising a plurality of single-phase input diode rectifiers, the AC input side of which is connected to the secondary winding of the induction machine, and the DC output of each rectifier. A chopper circuit is connected to the side, and by controlling the chopper, the DC side output current of the rectifier and the instantaneous value of the secondary current of the induction machine are controlled in synchronization with the secondary voltage of the induction machine. Characteristic induction motor secondary control method. 2. A speed control method for secondary control of a wound-type induction machine, comprising a plurality of single-phase input diode rectifiers, the AC input side of which is connected to the secondary winding of the induction machine, and the DC output of each rectifier. Side, a chopper circuit is connected, the instantaneous value of the DC side output current of the rectifier is controlled in synchronization with the secondary voltage of the induction machine by the control of the chopper, and the secondary current of the induction machine is set to a substantially sine wave. When considering, the phase angle is 0 ° to 90
The current values from ° and 180 ° to 270 ° are generally larger than the pure sine wave, and the current values from 90 ° to 180 ° and 270 ° to 360 ° are smaller than the pure sine wave. A secondary control method for an induction machine, comprising: