JPS61288796A - Controlling method for current control type inverter in ac servo motor - Google Patents

Abstract

PURPOSE:To suppress harmonic waves which affect influence to torque ripple or noise in normal state by executing switching for suppressing a high frequency by a current control type PWM inverter. CONSTITUTION:To always reduce the change rate (dDELTAi1/dt) of a deviation current DELTAi1 between a current i1 flowing through an AC servo motor and a command current i1* in a controller using a current control type PWM inverter, the term vector e0 of a voltage/current equation represented in an equation of the motor [where V/(k) is an inverter output voltage vector] is aimed at, the range of the vector e0 is detected in a vector diagram of the equation, and it is controlled to select an output voltage only from 4 modes of the vertexes of a triangle to which the vector e0 belongs. In this case, the coordinates axis of the current deviation of the phase is displaced at 30 deg., and the sign of the differentiated value is detected to obtain a range to which the vector e0 belongs.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention provides a current control comb-shaped P in an AC servo motor.
W M (Pulse Width Modula mouth
(n. Pulse Width Modulation) Inverter control methods, particularly those that suppress harmonics, can be used as a method for driving control motors of industrial robots and other automatic machine tools.

[Background technology and its problems]

A high-performance servo system for an AC motor is required to reduce torque ripple and noise in its steady state.

In order to satisfy this requirement, it is necessary to reduce the harmonic components of the current, and for this purpose, it is necessary to perform switching to suppress the harmonics using a current controlled PWM inverter.

As a method to achieve this, conventional methods have been proposed in which a certain tolerance range of the deviation current vector between the current flowing through the motor and the command current is considered, and the motor with the minimum average switching frequency is selected (for example, , J. Holt
z at alH″A Predictive Con
troller for the 5tator Cu
rrent Vector of＾CMachines
Fed from a 5w1tched Volt
age 5source in Conf, Rec, 19
83 Annu, Meet, IPHC; see).

Although this method is excellent in theory, it has the drawback that the circuit for carrying out the method is extremely complex, and it lacks versatility in terms of cost and various other aspects for general industrial use. There is.

In addition, various other methods have been proposed (for example, G., Pfaff et al.
nd Expert Illental Re5ults
of a Brush 1ess AC5ervo-
11rive”in Conf, Rec, 19B21
7th Annu, Meet, IEEEIAS%
D, M, Brod at alB “Current
Control of VSl-PWM Inver
ters″in Conf, Rec, 1984 An
nual.

Meet, IEEE IAS), these also have almost the same drawbacks as mentioned above, and there has been a strong desire for the emergence of a versatile control method that can be generally used for industrial robots and other applications.

[Purpose of the invention]

An object of the present invention is to provide a method for controlling a current-controlled PWM inverter in an AC servo motor, which can suppress harmonics without performing complicated calculations and requires a relatively simple control circuit. .

[Means and effects for solving the problems] The present invention has the following features:
Focusing on the rate of change of the deviation current (∆it) between the current (i)) flowing through the AC servo motor using a current-controlled PWM inverter and the command current (1bi) - the term eo in the voltage-current equation of the motor, Detect which region eo belongs to in the vector diagram of the voltage-current equation, and
In a control method in which the output voltage is selected only from the four modes corresponding to the vertices of the triangle to which
, ΔY and ΔZ, by detecting the signs of these differential values, it is possible to detect which region eo belongs to, and to detect harmonics that affect torque ripple or noise in a steady state This makes it possible to suppress current.

〔Example〕

1 to 10 are diagrams for explaining the present invention in detail.

Now, consider a load having internal induced voltage, inductance, and resistance as shown in FIG. This voltage-current equation is = O, l, -, 7 VtK) = JE (Vu + aVv + (QVw),
(4 a=eXP(-j”/3)
””△II-II-II
It is given by (6). However, ill: current command vector 11: current vector Δ11: deviation current vector e: internally induced voltage vector V(k): represents the inharter output voltage vector. (1)
In the formula, holds true and the following formula is obtained.

There are eight switching states, and k=0.7 is a zero voltage mode in which three sets are short-circuited at the top and bottom. Moreover, a vector diagram is shown in FIG.

Since the left side of equation (8) is the rate of change of the deviation current, a mode with a small rate of change (dΔi+/dt) of the deviation current may be selected to provide a switching arrangement that suppresses harmonics.

In order to follow the current, an output voltage V (k) that generates dΔft/dt that is 180 degrees 0 phase different from the deviation current Δ11 is required. Δ11 shown in Figure 3
In this case, current tracking becomes possible by selecting an output voltage that generates the dΔ11/dt component shown by the thick line in the opposite direction. On the other hand, considering that the inverter output voltage is in seven states including zero voltage, the deviation current vector is detected in a 6° range as shown in FIG. Here, since the deviation current of each phase is located as shown in the figure, it can be easily detected by a comparator.

In order to suppress harmonic components, it is necessary to select a mode with small dΔi+/dt (including zero voltage mode).

Therefore, it is detected which region eo belongs to, indicated by r, rr, . Much dΔi
+/dt is small and we want to follow the current, so we set 4 modes (zero voltage is 2
Select the output voltage only from mode). This is shown in Table 1.

V (k) limited by Table 1eo. Also, FIG. 5 shows dΔ11/dt when it is in the 0wt region of co and is at the center of gravity of an equilateral triangle as a representative example. FIG. 6 also shows L dΔil/dt and the area of the deviation current vector shown earlier (FIG. 4). In this case, in order to follow the current in the four triangular modes, select =2 when the deviation current Δ11 is in ■, ■,
, select =1 when it is in ■, and select = when it is in ■,■.
o+7 (select the one with fewer switching times). In addition, eO is ■、■、■TEHAL
dΔi+/dt is the difference shown in FIG. On the other hand, in ■, ■, and ■, the phase is delayed by 60°, as shown in FIG. The above is considered for all regions in Table 2 Modes where harmonics can be suppressed Also, when Δ11 is inside the hexagon in FIG. 4, switching is not performed and the output voltage is maintained. From this, the switching frequency fsw is determined by the width Δε of the hexagon.

From equation (8), eo is delayed by 30 degrees, and its new coordinate axes are ΔX, Δy, and Δ, which can be shown in FIG. Therefore (a)k-0,7
When (V (k) = 0), the differential dΔ of ΔX, Δy, Δ2
By detecting the signs of x/dt, dΔy/dt, and dΔz/dt, it is uniquely determined to which region eo belongs.

(b) k=1,2. ..., 6 (V(k)≠0) As described above, in this method, the switching state is determined only from the four modes at the vertices of the triangle to which eo belongs. Therefore, when V (1) is output, it can be considered that eo belongs to either ■ or @. Therefore, from FIG. 8, it can be determined from the sign of dΔz/dt. Thinking similarly about other modes,
The results are shown in Table 3. EO detection method (1-correct, 〇-
Although eO can be detected by the above method, the differential signal is easily influenced by noise. Therefore, let's consider how eo actually behaves. eo in steady state (switching method that can suppress harmonics is not used in transient state)
Since equation (7) holds true, equation (9) is defined.

On the other hand, the current command is °element −exp(−jωt)
(12')"-, Jwl eXP(-jwt)
(13), ・t, so substitute it into equation (9) to obtain the following equation.

50= A exp (j φ−ja+t)
(14) From this, it can be seen that eo has a phase relationship delayed by φ with respect to the current command, and rotates at the same angular velocity ω. Therefore, the output edge of co, P, F (L
owPass Filter), it is possible to remove the influence of noise generated by the differential circuit, etc.

In the case of alternating current, position detection is performed, so eo can be easily calculated. Based on equations (14) and (15), the circuit configuration diagram is shown in FIG.

Next, experimental results will be shown in which a permanent magnet synchronous motor was controlled using the above-described control method and a conventional control method using a comparator.

The servo system used in this experiment to carry out the above embodiment is shown in FIG. 10, and the ratings of the permanent magnet synchronous motor are shown in Table 5.

Table 5 Ratings of permanent magnet synchronous motors Figures 11 and 12 are shown in the above experiment, respectively.
The results show the results of measuring the current response in a steady state using an oscilloscope. Figure 11 shows the case where fo = OH2, and Figure 11 (a) shows the result of measuring the current response in the conventional control method.
FIG. 1(b) shows the case using the method of the above embodiment. In the figure, the vertical axis indicates current (A), and each scale in the figure is 6A, and the horizontal axis indicates time (ms), and each scale in the figure is 'l m s.

Moreover, FIG. 12 shows the case where fo=20Hz, and the 12th
Figure (a) is the same as Figure 12 (b) when using the conventional control method.
1 and 2 respectively show the cases according to the method of the above embodiment.

In the figure, the vertical axis indicates current (A), and one scale in the figure is 6A, and the horizontal axis indicates time (ms), and one scale in the figure is 5 ms.

In both the method of the embodiment and the conventional method, feedback control of Δε is performed so that the switching frequency fsw=2KH2.

In this case, in the method of the embodiment shown in FIG. 11(b), when fo=OHz, the dead time of the main circuit is
The sw is limited to about 800 HE.

As is clear from FIGS. 11 and 12, the harmonic current is significantly suppressed compared to the previous one.

Furthermore, FIG. 13 shows the measurement results of the relationship between the rotational speed and noise during no-load operation using the method of the present embodiment and the conventional method.

In the figure, the vertical axis is the noise (db), and the horizontal axis is the rotation speed (rpm).

In FIG. 13, curve (2) is the case where the conventional method is used, and curve (2) is the case where the method of this embodiment is used.

As is clear from FIG. 13, the noise produced by the method of this embodiment is extremely small compared to the conventional method, especially in the low speed range.

This is because eo is small in the low speed region, so the zero voltage mode greatly contributes to noise reduction.

Note that the reason why the noise relatively increases in the high speed M range is because eO increases and hemostasis in the zero voltage mode increases t.

In this way, according to the control method of this embodiment, harmonic current is effectively suppressed, so torque ripple and noise are small.

In addition, the control method of this embodiment focuses on the deviation current Δil and selects the switching mode from only the current command 11'' and the current, so it does not depend on the motor load constant and does not need to know the motor load constant. do not have.

Furthermore, there is no complicated calculation and the control circuit is simple.

For this reason, the control method of this embodiment has the advantage of being extremely versatile.

〔Effect of the invention〕

As detailed above, in the present invention, harmonics in a steady state are suppressed because eO is included, there is less torque ripple and noise, and the control circuit can be simplified because there is no complicated calculation. Furthermore, since it does not depend on the load constant, it has excellent effects such as being highly versatile.

[Brief explanation of the drawing]

FIGS. 1 to 10 are diagrams for explaining the present invention in detail, and FIGS. 11 to 12 show cases in which a permanent magnet synchronous motor is controlled by the control method of the embodiment of the present invention and a case in which the conventional control method is used. Figure 13 shows the measurement results of noise when the permanent magnet synchronous motor is controlled by the control method of the embodiment of the present invention and by the conventional control method. FIG.

Claims (2)

[Claims] (1) Voltage-current equation of AC servo motor using current-controlled PWM inverter ▲ There are mathematical formulas, chemical formulas, tables, etc. ▼ where K = 0, 1, ..., 7 ▲ Mathematical formulas, chemical formulas, tables, etc. ▼ Δi1=i1^*-i1, where i1^* is the current command vector i1 is the current vector Δi1 is the deviation current vector ■ is the internal induced voltage vector ■ is the first term on the right side of the inverter output voltage vector If the fourth term is expressed as ▲There are mathematical formulas, chemical formulas, tables, etc.▼, and the voltage-current equation is expressed as ▲There are mathematical formulas, chemical formulas, tables, etc.▼, detect the region to which ■o belongs, and In a control method in which the dΔi1/dt is always made small by selecting the output voltage only from the four modes corresponding to the vertices of the triangle to which ■o belongs in the vector diagram of the equation (III), the equation (III) In the vector diagram, the new coordinate axes that are delayed by 30 degrees from the coordinate axes of the current deviation of each phase are ΔX, ΔY, Δ
Current control in an AC servo motor characterized by finding the differential values of ΔX, ΔY and ΔZ of each inverter and detecting the sign of this differential value when Z is ▲There are mathematical formulas, chemical formulas, tables, etc.▼ Control method of type PWM inverter. (2) In claim 1, considering that i1^*=i^*exp(-jωt) =-jωi^*exp(-Jωt) (V), the formula (II) ■o=Aexp(jφ−jωt) (VI) φ=ta obtained by substituting the above equation (V) into
n×(ωLi^*)/(Ri^*+e) (VII) However, ■=e exp(-jωt) (VIII) Current in an AC servo motor characterized by determining the above ■o by calculating the formula Control method of controlled PWM inverter.