JPH02202392A - Current control system for ac synchronous servo motor - Google Patents

Abstract

PURPOSE:To eliminate non-linearity and to facilitate control by subtracting the product of motor phase current and coil phase resistance from a phase voltage to be fed to a motor, then multiplying the difference by the reciprocal of the gain of a power amplifier, thereafter adding thus obtained product to a phase voltage command, and inputting to the power amplifier. CONSTITUTION:A feedback circuit 20 comprises a transfer function 21 for multiplying the phase current ic by the phase resistance R of coil, and a transfer function 22 for subtracting the output of the transfer function 21 from the phase voltage er' of a servo motor and multiplying the difference by the reciprocal of the gain G3 of a power amplifier, where the output from the transfer function 22 is added to a phase voltage command er and fed to the power amplifier. In the current control loop, each control block for the phase voltage command er and the phase current ic has constant factor and linear characteristic. In other words, when the feedback circuit 20 is provided additionally, current control system for the AC synchronous servo motor has linear characteristic and thereby influence of inductance variable with the electrical angle of rotor can be eliminated.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a current control method for a synchronous AC (alternating current) servo motor.

In the case of a conventional three-phase synchronous AC servo motor, a block diagram of a speed control loop is generally represented as shown in FIG.

In FIG. 5, the speed loop compensation circuit 1 has a speed command V
c and the voltage corresponding to the actual speed of the servo motor from the frequency/voltage converter 9, that is, the speed deviation, is amplified, outputs a torque command Tc, and multipliers 2U, 2V, 2Vlt and the torque command, U, V, W phase sine wave signal generation circuit 8U, 8V
, the electrical angle θ of the servo motor rotor output from 8W
The phase current commands 1r (U), 1r (V), ir4) are output by multiplying the phase current commands by a sine wave signal with a phase shift of 2π/3 according to the phase current. The current loop compensation circuits 3U, 3V, and 3W each receive phase current commands i r (U), i r (V), i
r(W) and the corresponding phase currents i c(U), i c(V), detected by current detectors 5U, 5V, 5W,
The difference from i c (W), that is, the current deviation, is amplified, and the phase voltage commands er (U), er (V), and er (W) are sent to power amplifiers 4U and 4V, respectively.

Output to 4W.

The power amplifiers 4U, 4V, and 4W are composed only of transistor PWM circuits, and have a phase voltage command er(U).

e r(V), e r(14) are received, and the phase voltage e
r'(U).

The servo motor 6 is driven by applying er' (V) and er' (v) to each phase of the servo motor 6.

The frequency/voltage converter 9 converts the output of the pulse coder 7 attached to the servo motor 6 from frequency to voltage,
It outputs a voltage according to the actual speed of the servo motor 6, and
The sine wave signal generating circuits 8u, sv, and aw each output a sine wave signal whose phase is shifted by 2π/3 according to the electrical angle θ of the rotor from the rotor position detected by the pulse coder 7.

Note that G1(S) is the transfer function of the speed loop compensation circuit,
G2(S) is a current loop compensation circuit 3U.

It is a transfer function of 3V and 3W. Furthermore, G3 is the gain of the power amplifiers 4U, 4V, and 4W.

The structure and operation of the speed control loop of the synchronous AC servo motor described above are conventionally known, and detailed explanation will be omitted.

In FIG. 5, the one-phase current control loop is extracted and explained in detail, resulting in the block diagram shown in FIG. 6.

In FIG. 6, 1o means a motor section, and if the interlinkage magnetic flux of the winding of the relevant phase is Φ, and the phase resistance of the coil is R, then the phase voltage er' applied to the relevant phase of the servo motor 6 and the phase The following equation (1) holds true for the current ic.

(d/dt), Φ1R-ic=er'-
= − (1) When the equation (1) is transformed, the following equation (2) is obtained.

c= (er' −(d/dt) −Φ) −(1/R
) ・(2) On the other hand, the inductance of the coil is L(θ
), the magnetic flux linkage Φ is expressed by the following equation (3).

Φ=L(θ) iC (3) And since the inductance (θ) changes depending on the rotor electrical angle θ, from the above equations (2) and (3), the motor A block diagram of the section 10 is shown in FIG.

That is, the phase current ic is obtained by subtracting the differential value of the flux linkage Φ, which is the output of the transfer function 14, from the phase voltage er' and dividing it by the phase resistance R of the coil (transfer function 11). The alternating magnetic flux Φ is calculated by multiplying the coil inductance (θ) (transfer function 12) according to the rotor electrical angle θ by the phase current IC (13
) u can be found.

As is clear from the block diagram of FIG. 6, since the coil inductance L(θ) changes with the rotor electrical angle θ, this control system is not a constant coefficient but nonlinear.

Problems to be Solved by the Invention As mentioned above, the conventional control system for synchronous AC servo motors is non-linear, resulting in poor control system stability. It was difficult to control the driving rotation. Furthermore, since it is nonlinear, increasing the gain always causes oscillation, making it difficult to increase the gain of the control system.

The ratio of the maximum value (θ) max and the minimum value (θ) win of the coil inductance (θ) which changes with the rotor electrical angle θ (L(θ)max/L(θ)Illin) is based on the permanent magnet synchronous motor type and In a coil-excited synchronous motor type synchronous AC servo motor, the nonlinearity is often about 2 or less, so this nonlinearity does not have a large effect on the stability of the entire system.

However, in a variable reluctance type AC servo motor, the above ratio (L(θ)wax/L(θ)Illin
) has a correlation with the output torque, and since this value is designed to be as large as possible, it is often a value of about 7 to 10. Therefore, in the case of a variable reluctance type AC servo motor, the above nonlinearity is This greatly affects the stability of the entire control system.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a current control method that eliminates the above-mentioned nonlinearity and facilitates control in current control of a synchronous AC servo motor.

Means for Solving the Problems The present invention subtracts, for each phase of a synchronous AC servo motor, a value obtained by multiplying the phase current of the motor by the phase resistance of the coil from the phase voltage input to the motor, and calculates the subtracted value. The problem was solved by linearizing the current control system by providing a feedback circuit that adds the value obtained by multiplying by the reciprocal of the power amplifier gain to the phase voltage command and inputs it to the power amplifier.

Operation FIG. 1 is a block diagram for one phase of a current control loop of a synchronous AC servo motor, explaining the principle of operation of the present invention, and a block diagram of a conventional current control loop shown in FIG. 6. Compared to this, a feedback circuit 20 is added.

That is, the feedback circuit has a transfer function 21 that multiplies the phase current; A transfer function 22 is multiplied by a reciprocal, and the output of the transfer function 22 is added to the phase voltage command er and input to the power amplifier.

In the above current control loop, if we organize the block diagram from the phase voltage command er to the phase current iC, (er+(e
r'-R-ic) -(1/G3))G3=er'・
...(4) When formula (4) above is rearranged, c=G3(1/R)-er ...(5), and the block diagram in Fig. 1 is as shown in Fig. 2. It can be rewritten as a block diagram.

As is clear from the block diagram shown in FIG. 2, each control block of this current control system all has constant coefficients and is linear.

That is, by adding the feedback circuit 20, the synchronous type A
The current control system of the C servo motor is linear, and the influence of the inductance L(θ), which varies depending on the electrical angle of the rotor, can be eliminated.

Embodiment FIG. 3 is a main circuit diagram according to the present invention of a motor drive control section of an embodiment in which the present invention is applied to a variable reluctance type AC servo motor, and FIG. 4 is a three-phase variable reluctance type AC servo motor.
FIG. 2 is a schematic cross-sectional view showing a mechanical arrangement relationship between a stator core in a servo motor and a salient pole rotor provided inside the stator core with a small gap therebetween.

First, referring to FIG. 4, a variable reluctance type AC servo motor 30 according to an embodiment of the present invention has a stator 32
and a rotor 34 provided inside thereof, and six stator magnetic pole portions 328 to 32f of the former stator 32.
In contrast, the latter rotor 34 is held by a rotation bearing mounted on a motor shaft (not shown) through a minute gap, and is configured to be rotatable. Since the rotating rotor 34 is of a non-permanent magnet type, it is formed as a laminated structure of iron plates, and has four salient pole parts 34a to 34d.
It is designed as a polar rotor.

On the other hand, the stator 32 has an excitation winding I! surrounding each of the 11 pole parts 32a to 32f. 4136 is provided, and in this embodiment, excitation currents of three different phases, beam phase, ■ phase, and W phase, which are out of phase with each other, flow through these excitation windings, and the stator magnetic pole portion 328
~32f are configured to form stator poles by sequentially magnetizing diametrically opposed stator pole portions passing through the center of the stator 32, e.g.
a and 32d form the same polarity. The principle of rotation of the non-permanent 30 is well known, and as described above, the stator magnetic pole portions 32a to 32f (32a:32d).

When the three sets (32b:32e, 32c:32f) are alternately excited and magnetized to form 1if1 pole, a magnetic flux flow is formed that penetrates from the stator side to the rotor side through the gap, and therefore, the stator 32 and Rotational torque is generated between the rotors 34 due to the action of the magnetic attraction force, and the rotors 34 rotate. In the state shown in FIG. 4, stator magnetic pole parts 32a and 32d
For the pair of salient poles 34a and 34G of the rotor 34,
are directly facing each other, and if the stator magnetic pole portions 32b, 32e or 32G, 32f that are not in the directly facing state are excited and magnetized, the salient poles 34b, 34d of the rotor 34 rotate toward the directly facing position. It is. In addition, the rotor 34
34a to 34d and the magnetic pole parts 328 to 32f of the stator 32, that is, the reluctance of each phase varies greatly depending on the electrical angle θ of the rotor 34, and as described above, the maximum inductance L(θ)max and the minimum Ratio of inductance L(θ)min θ)max/L(θ)m1
0 is configured to be about 7 to 10.

The drive control section of the variable reluctance type AC servo motor shown in FIG. 3 shows only the main parts related to the present invention.
In the same circuit, capacitor C is a capacitor for taking out DC output provided in a forward conversion circuit that converts AC input from a 3-phase AC power supply into DC, and is a capacitor that forms part 00929 of the motor drive circuit in the subsequent stage. It is. The DC output from this capacitor C is the stator excitation winding 3 mentioned above.
Windings 36a and 36d of U phase, ■ phase, and W phase in 6.

Transistors Tr1 to Tr6 and diodes D1 to D6 form an inverter circuit that converts signals 36b and 36e, 36G and 36f into well-known PWM output waves to excite them, respectively.
The signal is supplied as a pulse wave to a motor drive circuit 38 equipped with the following. That is, the on/off order of the transistors Tr1 to Tr6 is selectively controlled by the external inverter control circuit 70, and depending on the on/off of the transistors Tr1 to Tr6, the DC voltage pulse waveform from the 00929 section is applied, and the corresponding An excitation N current flows through the windings 36a to 36f of the stator 32. Stator windings 368 to 36 for each phase above
As is well known, each of f is a circuit element having a DC resistance component and an inductance component.

The motor drive circuit 38 further includes current detectors 408 to 400 connected in series to the excitation windings of each phase.
Phase current ic(U), ic(V) of each phase.

c(W). The outputs of these current detectors 40a to 40G are the feedback circuits 50U, 50V, 5 corresponding to the feedback circuit 20 in the block diagram of FIG.
Input 0W, 50U and 50 inputs, respectively, and feedback circuits 50U and 50
V, 50W, the corresponding phase voltage e r '(U), e
r'(V) and e r'(W) have been input.

The feedback circuit 50U amplifies the phase voltage 1c (U) detected by the current detector 40a by the coil resistance R, and outputs -R-ic.
(U), and the phase voltage e r '(
U) minus the output value of the amplifier 51U is amplified by the reciprocal of the gain G3 of the power amplifier (motor drive circuit 18), and the output -(er'(U)-R-i C(Ll
))-(1/G3). In addition, the feedback circuit of the ■ phase and W phase is 50V, 50W.
has the same configuration, and the details are omitted in FIG. 3.

Further, the outputs of the feedback circuit 50U, 50V, 50W (7) are input to the adder circuits 60U, 60V, 60W, respectively.

Sarah 1. ,,L, Lera addition circuit 60U, 60V, 60
W is the phase voltage command e created in the same way as before.
Voltages whose polarities are reversed by amplifiers 61U, 61V, and 61W are input to r(II), e r(V), and e r(W), respectively, and feed back circuits 50U and 50V.

50W output and phase voltage command e r(U), e r(
V).

Add each of e r (W) to er+ (er'
-Rc)(1/G3)) and is output to the inverter control circuit 70. The inverter control circuit 70 receives these signals and controls the transistors Tr1:Tr2゜Tr3:Tr4, Tr5: in the excitation winding circuit of each phase of the stator 32.
The servo motor 30 is driven by turning each phase of the Tr 6 on and off.

That is, in this embodiment, variable reluctance type A
Feedback circuit 5C1 in conventional drive control circuit of C servo motor
1,50V, 50W and addition circuit 60U, 60V, 60
W etc. are added, and for each phase, the voltage amplified by the coil resistance R is subtracted from the phase voltage er' to the voltage corresponding to the phase voltage ic, and this difference voltage is amplified by the reciprocal of the gain G3 of the current control loop, By adding to the phase voltage command er, for each phase,
By adopting a configuration that allows linear control as shown in the block diagram shown in FIG. 1, a linear system as shown in FIG. 2 is constructed.

In addition, in the above embodiment, an example in which the present invention is applied to a variable reluctance type AC servo motor whose inductance largely fluctuates depending on the electrical angle of the rotor has been described; Permanent magnet synchronous electric type.

Of course, it can also be applied to a coil-excited synchronous motor type).

In addition, in the above embodiment, the feedback circuits 50U, 50V, 50
W etc. are configured with hardware, but in the case of a software servo, the 9JX principle shown in the feedback circuit 20 in Fig. 1 is implemented in software using a digital signal processor that performs servo control. l! l! It is also possible to do it in a logical manner.

Furthermore, although a three-phase motor was described in the above embodiment, it is clear that the present invention can also be applied to a synchronous type AC servo motor other than three-phase motors.

Effects of the Invention In the present invention, in a synchronous AC servo motor,
Since the nonlinear part of the current control loop caused by inductance fluctuations is linearized by providing a feedback circuit, a stable system can be obtained and the gains of the control system such as position control loop gain and speed control loop gain can be increased. It is possible to obtain high level determination accuracy.

Further, since there is no non-linear portion, control becomes easy, and torque fluctuations and speed fluctuations are eliminated, and smooth rotation of the servo motor without vibration can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of one phase of the current control loop of a synchronous AC servo motor, which explains the operation and principle of the present invention.
FIG. 2 is a block diagram after rearranging and modifying the block diagram in FIG. The circuit diagram, Figure 4, shows the same variable lactance type A.
FIG. 5 is a schematic sectional view showing the mechanical arrangement relationship between the stator core and the salient pole rotor provided inside the stator core through a small gap in the C servo motor. A block diagram of the speed control loop, FIG. 6 is a block diagram of the current control loop for one phase in FIG. 5. 10... Block diagram of motor section, 20... Block diagram of feedback circuit, 3o... Variable reluctance type AC servo motor, 32
...Stator, 32a to 32f...Stator magnetic pole part, 3
4... Rotor, 348-34d... Rotor salient pole part,
36a to 36f...Each phase stator winding, 38...Drive circuit, 40a to 40C...Current detector, 50U to 50
W...Feedback circuit, 51U...Amplifier, 52U...
Amplifier, 60U~60W...addition circuit. Figure 4 Figure 2 Curse

Claims (2)

[Claims] (1) In the current control method of a synchronous AC servo motor, for each phase, the value obtained by multiplying the motor phase current by the coil phase resistance is subtracted from the phase voltage input to the motor, and the subtracted value is applied to the power amplifier. A current control method for a synchronous AC servo motor, characterized in that a value obtained by multiplying by the reciprocal of a gain is added to a phase voltage command and input to a power amplifier. (2) The current control system for a synchronous AC servo motor according to claim 1, wherein the synchronous AC servo motor is a variable reluctance type AC servo motor.