JPS5911270B2 - Control method of induction motor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a control system for digitally servo-controlling an induction motor.

(Background technology) In order to improve the servo performance by extending the slip frequency control of an induction motor, the stator excitation component (reactive component) and torque current component (effective component) 15 are derived from the load condition, and both of these components are A method has been proposed in which servo controllability equivalent to that of a DC shunt motor can be achieved even though it is an induction motor by synthesizing the stator current as each phase current command, but generally in the servo area, small capacity However, when applied to a large-capacity induction motor, the accuracy of speed detection generators and oscillators becomes a problem due to low slip, and digital processing is more advantageous than analog signal processing.

(Objective of the present invention) 25 The present invention performs all of the above-mentioned steps of processing digitally, making it possible to realize even higher servo controllability.

(Structure of the present invention) FIG. 1 is a block diagram showing an embodiment of the present invention, in which 301 is a two-phase induction motor, 2 is a pulse generator connected to the induction motor 1, 3 is a comparator, and the pulse generator 2 is connected to the induction motor 1. Feedback pulse Nfb generated according to the actual speed of electric motor 1 and speed command pulse Nref are compared, and the deviation is input to deviation counter 354.

5 is a slip frequency Ki2 calculation time, in which the optimum slip frequency is calculated every moment according to the contents of the deviation counter 4.

A waveform generator 6 generates a two-phase sine wave of an optimum driving frequency from the pulse Nfb generated by the pulse generator 2 and the slip frequency Ki2, and generates two sine waves each having a 90-phase difference.

7 and 8 are D/A converters (for example, multiplying D7A converters), which multiply the respective sine wave signals generated by the waveform generator 6 to calculate the torque current components (effective minute) to create a signal.

Since the two sine waves generated by the waveform generator 6 directly correspond to the stator excitation current components (reactive components) of each phase winding, these sine waves are transmitted to the multiplexing D/A converter 7,
By combining the output signals of 8 and 8 separately, a signal corresponding to each phase winding current can be obtained. 9 and 10 are current amplifiers having a predetermined amplification factor according to the capacity of the motor 1;
11 and 12 are CTs (current transformers) for the current minor loop.

(Embodiment) FIG. 2 shows a circuit embodying the embodiment of FIG. 1, which will be explained in further detail.

In the figure, the same symbols as in Figure 1 indicate the same parts.
13 is a rotation direction discrimination circuit, 14 to 18 are synchronous differentiating circuits,
1G to 18G are gates, M is rate multiplier, 1
FD and 2FD are frequency dividing circuits, BO is a bead oscillator, 1F,
2F is a low pass filter, and MSB is the sign bit of the deviation counter.

Note that the feedback pulse Nf of the pulse generator 2
As shown in FIG. 3, b consists of two-phase signals of A phase and B phase which are different in phase by 900 degrees, and from the phase relationship of these signals, the rotation direction of the electric motor 1 is clockwise Cw or counterclockwise Cc.
It is now possible to distinguish between w and w. Also, Figure 4 shows the second
The figure shows various clock pulses used in the circuit, and the reference clock φ. And this reference clock φ. 1 each
4-phase clock φ1, φ2, φ3, obtained by dividing the frequency by /4
φ4 and reference clock φ. The phase relationship between the clocks φ10 and φ30, which are obtained by dividing the frequency by 1/4 and have 180 clock phases different from each other, is shown. The feedback pulse Nfb is applied to the rotation direction discrimination circuit 13, which discriminates the rotation direction based on the phase relationship shown in FIG. Open gate 2G.

When the direction command DA is ``1'', the gate 3G is opened as a clockwise command, and when it is ``o'', the gate 4G is opened as a counterclockwise command, and the speed command pulse Nref is passed.
Therefore, the speed command pulse Nref is inputted to the DOWN input 41 of the deviation counter 4 through gates 3G, 5G and 7G depending on the rotation direction, for example, if the direction command DA is '1 clockwise). Also, when the direction command DAI) 5'0'l' (counterclockwise), the gate 4
G, 6G and 8G to the UP input 42.

The feedback pulse Nfb is input to the down input 41 of the deviation counter 4 through gates 1G, 5G and 7G when the rotation direction is counterclockwise, and is input through gates 2G, 6G and 8G when the rotation direction is clockwise. input to input 42; When the motor rotation direction is counterclockwise CCW, as shown in FIG. At 10G, the output φ1+θ is added to the clock φ, and is input to the waveform generator 6, and when the electric rotation direction is clockwise, the output b is synchronized with the clock φ,o from the synchronous differentiator circuit 16.
passes through gate 2G, and clock φ1 at gate 9G.
The output φ1−θ is inputted.

Such clock conversion is performed by the slip frequency calculation circuit 5.
Gates 11G, 12G, 13G, 14G are applied to the output of the rate multiplier M in
It is also used when adjusting the clock φ3.

If rotation in only one direction is required, pulse generator 2
Only one phase output is required, and a direction discrimination circuit is not required.

The slip frequency calculation circuit 5 includes a rate multiplier M that divides the oscillation frequency of the oscillator 0SC according to the absolute value of the output of the deviation counter 4.

Further, as shown in FIG. 6, the multiplying D/A converter 7 is composed of an adder circuit using an operational amplifier and an analog switch, 20 is an inverting circuit, 21, 2
2 is a logic inverter, 23, 24 and 25, 26, 27,
28 is an analog switch, and 29 is an operational amplifier.

Analog signal 1mβ from waveform generator 6 and inversion circuit 20
are connected to analog switches 25, 26, 27, and 28 via analog switches 23 and 24, one of which is turned on according to the code signal Yn,
Output of deviation counter 4 YO, Yl, Y2...Y
When any of n-2 becomes 1'', the corresponding analog switch is turned on.

Now, for example, among the outputs of the deviation counter 4, only YO is 15 and the others are 07, and if Yn=1, the analog switch 23 is turned on, the analog switch 25 is also turned on, and the other analog The switch is off.

Therefore, the relationship between analog signal 1mβ and output 12α[XO is I2α−? 1 mβ will cause n-2 hail.

In general, I2αCx−1mβ[YO2re+Yl2l+Y2
22+...+Yn-22n-2].

Note that the multiplying D/A converter 8 has a similar configuration, and the input 1mβ in FIG. 6 is set to Imα, Yn is set to Yn,
It is sufficient to replace the output 12α with I2β. Note that by adjusting the addition input resistance of the operational amplifier according to the output bit of the deviation counter 4, it is possible to obtain an analog output voltage proportional to the digital deviation amount.

Further, in order to obtain an analog code corresponding to the positive or negative value of the digital deviation amount, switching between an inverted signal and a non-inverted signal of the multiplicable input may be performed according to the sign of the sign bit MSB of the deviation counter 4. The waveform generator 6 that generates the two-phase sine wave can have various configurations, but in this example, the bead oscillator uses a reference frequency signal corresponding to the clock pulses φ1 and φ3, and a frequency signal corresponding to the motor rotation speed and rotation direction. A two-phase sine wave is generated by extracting the bead frequency signal from the frequency signal.

(Operation) First, when the motor is stationary, the direction command D
The operation when A is ``'O'', that is, counterclockwise (Ccw), will be described.

In this case, the speed command pulse Nref is
G, 8G and is applied to the up input 42 of the deviation counter (up down counter) 4.

Assuming that the deviation counter is composed of 8 bits, its output is (YO, Yl, Y2, Y3, Y4).
, Y5, Y6, Y7) = (1, 1, 1, 1, 1, 0, 0
, 0). This output is input to rate multiplier M and multiplying D/A converters 7 and 8. The rate multiplier M takes the output value of the deviation counter 4 as a rate input, and divides the oscillation frequency of the oscillator 0SC according to the rate input and sends out a divided output, thereby generating a pulse corresponding to the slip angle frequency. give a signal. At this time, the sign bit MS of the deviation counter
Since B is SO'', the gate 11G of the slip frequency calculation circuit 5 is opened, and the clock φ3 is output at the gate 14G.
and a pulse signal corresponding to the slip angular frequency, and the outputs of gates 10G and 14G are added at gate 15G to calculate φ1+φ3+Ki2. K
i2 is a pulse signal corresponding to the angular frequency and is synchronized with clock φ4. The output of the gate 15G is input to the frequency dividing circuit 1FD, and the frequency is divided by a frequency division ratio determined by the number of pulses generated per revolution of the pulse generator 2 connected to the motor.

That is, if the number of pulses generated by the pulse generator 2 is N [pulses/rotation] and the number of poles of the motor is P, then the frequency division ratio is 1.
/n is 1/n-1, which is 2N.

For example, if N-1000 [pulses/rotation] and P=4, then 1/n=1/500. Frequency divider circuit 1FD, 2FD
The outputs of the bead oscillators BO are Sln(ωt+ψ
) and Si
n(ωt+ψ)XSln(i)TllSln(ωt+ψ
)XCOS(l)t:-Slnψ+-Sln Primary current angular frequency φ
The cosine wave signal 1mβImcOsψ and the sine wave signal 1mβ−1mS1nψ (g)m corresponding to the excitation current command amplitude are constant).

Here, φ-θ+Ki2, ψ=fψαt. Note that when the motor is stationary, b=o, so the primary current angular frequency ψ is specific to the slip angular frequency.

Since the sign bit MSB of the deviation counter 4 is 0'' at this time, its inverted signal 1'' is input to the multiplier D/A converter 7.

If the multiplied value of the analog quantity and digital quantity in this case is determined to be negative, the multiplication D/A converter 7
The output 12α of is I2α=-12sinψ. Also,
A code signal of '0'' is input to the multiplication D/A converter 8, and the multiplication result at this time is positive, and the output is 1.
2β becomes I2β=I2COSψ. Here, I2 is a value proportional to the output deviation amount of the deviation counter, and is the torque current command width.

Current amplifiers 9 and 10 have primary current commands 1 and α, respectively.
=I2α+Imα, i1β+I2β+Imβ are added, and the motor starts rotating CCW.

Therefore, a feedback pulse Nfb (A-phase/B-phase pulse) of the pulse generator 2 is generated, and the gate 1G is opened by the output of the rotation direction discrimination circuit 13, and the clock φ2
The feedback pulse synchronized with is input to the down input 41 of the deviation counter 4, and the deviation amount begins to decrease.

Also, the feedback pulse Nf of the pulse generator 2
Since the pulse b corresponding to the pulse b is added to the clock φ1 at the gate 0G and applied to the gate 15G, the waveform generator 6
The frequency becomes even higher, and the motor rotation speed also increases.
As the motor rotation speed increases, the deviation amount of the deviation counter 4 gradually becomes smaller, and the slip frequency pulse Ki2 and torque current commands 12α and I2β also become smaller.
The motor speed reaches a certain equilibrium point.

Next, consider a case where the direction command DA is clockwise CW.

In this case, the command pulse Nref is for gates 3G, 5G, 7.
G to the down input 41 of the deviation counter 4.

Therefore, the sign bit MSB of the deviation counter becomes '12', the gate 12G of the slip frequency calculation circuit 5 is opened, and the rate multiplier M synchronized with the clock φ30 is activated.
The output of is applied to gate 13G. This signal is a pulse signal whose phase is opposite in synchronization with clock φ3,
A part of the clock φ3 is thinned out to create a pulse of φ3-Ki2. Therefore, at gate 15G,
A pulse of φ1+φ3-Ki2 is generated, and this pulse is input to the bead oscillator BO via the frequency dividing circuit 1FD.
A pulse obtained by dividing the frequency of the pulse φ1+φ3 by the frequency dividing circuit 2FD is input to the bead oscillator. Bead signals of these pulses are generated by a bead oscillator BO, and passed through low-pass filters 1F and 2F, respectively, Imα=ImcOsψ, I
A signal of mβ=-1 msi is obtained, and this signal gives a current that generates a rotating magnetic field in the CW direction of the motor, and the output of the multiply D/A converters 7 and 8 is 12α=I2sinψ.
, 12β=I2COSψ is a current command that generates a torque to rotate the motor in the CW direction. When the motor starts to rotate in the CW direction, the gate 2G is opened by the output of the rotation direction discrimination circuit 13, and the feedback pulse Nfb from the pulse generator 2 is applied to the gate 9G through the synchronous differentiator circuit 16 whose clock is φ10.

This pulse is a signal that synchronizes with the clock φ1 and reverses its phase, and operates to thin out the clock φ1, so a pulse of φ1+φ3-θ-Ki2 is output from the gate 15G, and the output angular wave number ψ of the waveform generator 6 is It becomes even higher, and the motor rotation speed also rises accordingly.

At the same time, the pulse from gate 2G is applied to the up input 42 of deviation counter 4, and the deviation amount begins to decrease. Since the output of the D/A converters 7 and 8 for generating torque of the electric motor is proportional to the deviation amount of the deviation counter 4, as the deviation amount decreases, the torque also decreases, and at the point where it is balanced with the load torque,
The deviation amount of the deviation counter 4 becomes constant, and the electric motor continues to rotate at a constant rotation speed according to the speed command pulse Nref. Gates 7G and 8G are for preventing the saturation of the deviation counter 4. For example, when the up count input is very large, when the deviation amount reaches the (n-1)th bit, the gate 17G is used to prevent the deviation counter 4 from saturating. The capacity (number of bits) of the deviation counter 4 can be reduced by lowering the 8G input to the '02 level, closing the gate, and not adding an up-count input.

In the above embodiment, a bead oscillator is used as a waveform generator, but a read-only memory ROM is used to store two-phase sine wave information, and pulse input corresponding to the motor rotation speed and slip frequency is used. It is also possible to specify an address in the ROM and extract that information to use as an excitation current command.

The same thing may be done using a shift register.

Also, the rate multiplier M is omitted, and the oscillator 0
By adding and subtracting pulses of a constant frequency from the oscillation frequency of the SC, an inverter with foot slip frequency control can be constructed.

As described above, since all signal processing is digitalized in the present invention, the carrier frequency of the two-phase oscillator can be increased and stabilized, so that the motor can always accelerate and accelerate at the optimum slip. It is possible to configure a drive system with steady operation and deceleration control, high precision and high speed response, and it can be easily connected to a computer, simplifying the system hardware configuration.

Furthermore, it is easy to apply to low-slip, large-capacity motors. For convenience of explanation, we have described the case of driving a two-phase induction motor, but it goes without saying that a known two-phase to three-phase converter can convert the current into three-phase AC and drive a three-phase induction motor. .

[Brief explanation of the drawing]

Fig. 1 is a block diagram of an embodiment of the present invention, Fig. 2 is a specific circuit diagram of the embodiment of Fig. 1, and Fig. 3 is a feedback pulse N.
fb signal waveform diagram, Figure 4 is a clock pulse waveform diagram,
FIG. 5 is an explanatory diagram of the output pulse of the gate 10G, and FIG. 6 is an explanatory diagram of the multiplication D/A converter. 1 is an electric motor, 2 is a pulse generator, 3 is a comparator, 4 is a deviation counter, 5 is a circuit for determining the slip frequency, 6 is a waveform generator, 7 and 8 are D/A converters, respectively, 9 and 10
11 and 12 are current amplifiers, CTll3 is a rotational direction discrimination circuit, Nfb is a feedback pulse, Nref is a speed command, DA is a direction command, and Ki2 is an axis corresponding to the slip frequency of the motor.

Claims (1)

[Claims] 1. A pulse generator 2 connected to an induction motor 1, a deviation counter 4 that counts the deviation between the output of the pulse generator 2 and a speed command value, and a slip frequency according to the contents of the deviation counter 4. a waveform generator 6 that generates a two-phase sine wave of a predetermined frequency from the output of the pulse generator 2 and the slip frequency, and a circuit 5 that calculates the content of the deviation counter 4 and the output of the waveform generator 6. The output of the waveform generator 6 is used as a stator excitation current component, the output of the D/A converters 7 and 8 is used as a torque current component, and both of these components are provided with D/A converters 7 and 8 for multiplying. An induction motor control method that supplies stator current to each phase of the induction motor 1 based on a combined value. 2. The waveform generator 6 comprises a beat oscillator that generates a beat angular frequency signal of a reference angular frequency signal and a signal obtained by adding or subtracting a primary current angular frequency signal to the reference angular frequency signal. control method for induction motor. 3. The control system for an induction motor according to claim 1, wherein the waveform generator 6 comprises a storage circuit in which waveforms are stored in advance.