JPH0789759B2 - Vector control current command generator - Google Patents

Description

The present invention relates to a current command generation circuit in vector control of an electric motor.

[Conventional technology and problems]

Vector control has become popular with the demand for high precision and high responsiveness of inverter drives of electric motors.

FIG. 4 shows a block diagram of vector control by the orthogonal coordinate system. This is a block diagram of the following (1) to (4).

T = K ₁ × I _m × I ₂ (1 formula) _{f 1 = f r + f s} ...... (3 _{equation) i 1 = i m + i} 2 ...... (4 type) i.e., expression (1) is input command I _2ref (2 primary current command),
This _indicates that Tokru is generated in proportion to I _mREF (excitation current command), and (2) to (4) are required to satisfy this (1). K ₁ is a constant.

(2 expression) of the slip frequency f _S is, which expresses that is inversely proportional to I _MREF proportional to I _2ref, slip frequency generator 1 of FIG. 4 corresponds to this.

(Formula 3) is the slip frequency f _S , 1 which is the characteristic of the induction motor.
Next current frequency f _1, and shows the relationship between the rotational frequency f _r, 1 primary frequency generator 2 corresponds to this. The output of the primary frequency generator 2 is a two-phase sine wave signal of constant amplitude used for vector calculation.

(Equation 4) is the vector quantity i in the multipliers 3 and 4 in FIG.
_{It is shown} that vector addition of _mREF and i _2REF results in the primary current command i _1REF .

The current controller 6 controls so that the primary current flows according to the current command i _1REF , and the signal for that is detected by the CT (current transformer) 8. Reference numeral 7 is an induction motor, and 9 is a speed detector directly connected to the induction motor 7.

As described above, if the constant K ₂ of (formula 2) determined by the motor constant is given and control is performed so that the current flows according to the command, the induction motor 7 generates the torque of (formula 1).

Also, when performing field weakening control for constant output control like a DC machine drive, the torque of (1 formula) is set to the rotation speed ratio.
Since it is _sufficient to _reduce N / N ₀ (where N> N ₀ ), I _mREF may be given as shown in FIG.

In the case of embodying this, if an analog multiplier is required for the field weakening function generator 10 and the multipliers 3 and 4, the accuracy is good, but the number of adjustment points increases, and the maintainability and stability deteriorate.

In addition, when the function generator 10 uses the line approximation, the accuracy deteriorates, and when the PWM (pulse width modulation) method using the switches for the multipliers 3 and 4 is used, the adjustment is lost, but the accuracy is reduced and the ripple voltage is reduced. Occurs.

Therefore, there is a need for a current command generation circuit that has improved accuracy and ripples and improved maintainability.

[Object of the Invention]

Here, the present invention overcomes the drawbacks of the conventional device and provides a current command circuit with improved accuracy and maintainability.
To that end.

[Outline of Invention]

In order to achieve the above object, the present invention, in vector control with field weakening control using a multi-pole resolver as a speed detector of an electric motor, uses a count and a DA converter to provide an unadjusted and highly accurate primary current command. It is a current command generating circuit characterized by being obtained.

〔Example〕

 First, the basic idea of the present invention will be shown.

Digitize to improve accuracy and maintainability.

Input signals such as I 2 _REF and N are all digital, and outputs are analog signals by DA converter.

Based on the above idea, the vector control current command circuit of the present invention is configured.

FIG. 1 is a block diagram showing a circuit configuration in one embodiment of the present invention.

In all the drawings, the same symbols represent the same or corresponding parts.

The slip frequency generator 1 is _{designed so that} when I _2REF and I _mREF are rated commands,
Generates a pulse signal with the rated slip frequency f _S of the motor.
10 is a function generator that generates the characteristics shown in FIG. 5, 11 and 12 are DA converters that convert a digital 8BIT signal to analog, 13
16 are DA converters constituting the multipliers 3 and 4 in FIG. 4, 17
Is a mixer that generates an average voltage of the output signal A of the slip frequency generator, 19 is two sets of low-pass filters that output the fundamental wave component corresponding to the output signal A, 20 is the output signal B of the low-pass filter 19, Is a primary frequency generator that adds the frequencies of the detection signals C and D from the resolver.

A circuit diagram of the function generator 10 is shown in FIG. Reference numeral 21 is a circuit for synchronizing the rotation speed pulse N with a clock, 22 is an 8BIT binary counter, 23 is a latch circuit, 24 is a frequency divider, and 25 and 26 are AND gates.

The counter 22 counts up, and continues counting until the signal E becomes "L" and the output of the AND gate 25 becomes "L". When the signal N'synchronized with the rotation speed pulse N becomes "H", the counter 22 performs a clear operation and all outputs are "L".

As a result, at low speed, since the count-up is faster than the signal N, the outputs of the counter 22 all become "H", and the output at the time of count-up is controlled by the AND gate 26 to the DA converters 11, 13 through the latch circuit 23. , 14 are provided, the clear pulse is output at a higher speed at a higher speed before the count-up is performed at an earlier timing. Therefore, at this time, the output of the counter 22 is given to the DA converters 11, 13 and 14 through the latch circuit 23 by the control of the AND gate 26 at a timing that becomes faster as the speed increases. That is, the synchronization circuit 21, the latch circuit 23,
The frequency divider 24 and the AND gates 25 and 26 count up the counter 22 when the rotation speed of the induction motor is less than or equal to the boundary rotation speed N ₀ , and the count value at the time of the count-up is used as the digital excitation current command value in the DA converter 11. The counter 22 functions as a first counter control circuit for the inverters 13, 13 and 14, and when the rotation speed of the induction motor is higher than the boundary rotation speed N ₀ , the counter 22
Second counter control circuit for giving the count value of the counter 22 as a digital excitation current command value to the DA converters 11, 13 and 14 before it is counted up and as the rotation speed of the induction motor increases. Will function as.

For example, assuming that the rotation speed pulse N is 3.6 KHz / 6000 rpm and the output signal of the frequency divider 24 is 230.4 KHz, the rotation speed N ₀ (the boundary rotation speed between the field constant region and the field weakening region) in FIG. Becomes The output of the counter 22 when N> N ₀ is Therefore, the characteristics shown in FIG. 5 are satisfied.

The primary frequency generation circuit 20 outputs signals E and F as shown in FIG. 3 with the signal B of the slip frequency and the signals C and D from the resolver. This signal is represented as:

The output signal G of the mixer 17 is _Vcc / 2.

Next, the DA converter 1 for the excitation current command that forms the multiplier
1, 13, 14 will be described.

When the signals G, F, E are applied to the voltage reference of the DA converters 11, 13, 14, the output is obtained using (Equation 5). And the α-phase and β-phase exciting currents I _mα and I _mβ are N> 1500rp
in m Becomes (Equation 11) and (Equation 12) show that the multiplier can be configured using the DA converters 11, 13, and 14.

α phase, beta-phase secondary origin I _2.alpha, for even I _2.beta, using the output signal of the DI converter 12, 15, 16 in the same manner _{I 2α = V DA12 -V DA16 =} -I 2REF V 0 sinωt ...... (13 _{formula) I 2β = V DA15 -V DA12} = -I 2REF V 0 sinωt ...... (14 expression), and it is possible to obtain a two-phase sine wave signal which is proportional to the secondary current command value I _2ref.

〔The invention's effect〕

As a result of the above, the following effects are recognized by the present invention.

Since there is no need for adjustment and setting, the reliability of the circuit can be improved.

By digitizing the signal processing and using a DA converter, a low ripple, high precision current command circuit can be configured. In particular, according to the present invention, a high-precision current command circuit can be configured by making the number of bits of the counter and the frequency of the clock for performing the counting operation sufficiently large.

The present invention thus makes a great contribution to the field.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of an embodiment of the present invention, FIG. 2 is a detailed diagram of a function generator 10, FIG. 3 is a time chart of a slip frequency signal, and FIG. 4 is a block diagram of orthogonal coordinate system vector control. FIG. 5 is a characteristic diagram of an excitation current command and a rotation speed during field weakening control, and FIG. 6 is an input / output signal relation diagram of the function generator. 1 ... Slip frequency generator, 2 ... Primary frequency generator,
3,4 …… Multiplier, 5 …… 90 ° phase shift circuit, 6 …… Current controller, 7 …… Induction motor, 8 …… CT, 9 …… Speed detector,
10 …… Function generator, 11 to 16 …… DA converter, 17 …… Mixer, 19 …… Low pass filter, 20 …… Primary frequency generator, 21 …… Synchronizing circuit, 22 …… Counter, 23… … Latch circuit, 24 …… divider, 25,26 …… and gate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Takasaki Inventor, Hideki Takashi, 2-13-1, Nishinomiya City, Yukuhashi City, Fukuoka Yasukawa Electric Co., Ltd. Inside the Yukuhashi Plant (56) Reference JP-A-59-110394 (JP, A)

Claims (1)

[Claims] 1. A vector controller with field weakening control for controlling a primary current of an induction motor according to a primary current command vector obtained by adding an exciting current command vector and a secondary current command vector, wherein a rotational speed of the induction motor is controlled. Input the output signal of the multi-pole resolver to detect, the rotation speed larger than the boundary rotation speed N ₀ between the field constant area and the field weakening area in the characteristics of the excitation current command value and the rotation speed during the field weakening control of the induction motor. Function generator that outputs a digital exciting current command value that is inversely proportional to the rotating speed by a number and becomes a constant value at a rotating speed of the boundary rotating speed N ₀ or less, a digital secondary current command value and the digital exciting current command value. The primary frequency signal is calculated from the slip frequency signal calculated from the secondary current command value I _2REF and the exciting current command value I _mREF, which are DA-converted respectively, and the output signal of the multipole resolver. And the output signal of the primary frequency generator and the digital secondary current command value and the exciting current command value are respectively multiplied to send out the secondary current command vector and the exciting current command vector. A DA converter, wherein the function generator is a counter that counts with a clock having a constant frequency higher than the rotation speed of the induction motor; and the counter when the rotation speed of the induction motor is the boundary rotation speed N ₀ or less. And a first counter control circuit for giving the DA converter a count value at the time of counting up as the digital excitation current command value, and the rotation speed of the induction motor is larger than the boundary rotation speed N ₀ , Before the counter counts up,
And a second counter control circuit for giving the DA converter a count value of the counter at a timing that becomes faster as the rotation speed of the induction motor increases, the vector control current. Command generation circuit.