JPS6216092A - Control method for inverter - Google Patents

Abstract

PURPOSE:To obtain a rotating field vector having high approximation to a reference rotating field vector by bringing timing for generating a unit vector to an intermediate value between a virtual rotating field vector up to that time and the next virtual rotating field vector. CONSTITUTION:A voltage command signal and a frequency command signal are inputted to a microcomputer 3, and a control signal for acquiring inverter outputs at voltage and frequency commanded. A memory M1 in which control data V1-V8 for control switches A1-C2 are written, a memory M2 in which data at sintheta are written, a memory M3 in which data at costheta are written, a memory M4 in which an operation formula for determining a point of time of the generation of a unit vector is written, and a memory M5 in which an operation formula employed for determining unit vectors V1'-V8' is written previously, are incorporated into the computer 3.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for controlling a three-phase inverter connected to a three-phase AC load.

[Conventional technology]

It is known to connect AC motors with variable frequency and voltage inverters. In addition, this impermanent PWM (
Pulse width modulation) control is also known. by the way,
When driving with a three-phase inverter Y P W M ml control to obtain an approximate sine wave, if each phase is modulated, it will be easily influenced by other phases, and optimum output cannot be obtained. R
In other words, the line voltage of the inverter output is determined by the difference in potential between each phase.

It is virtually impossible to simultaneously approximate each line voltage to a sine wave.

As a method to solve the above-mentioned drawbacks.

For example, there is a method of detecting the rotating magnetic field of the motor, finding the difference between the detected rotating magnetic field and the reference rotating magnetic field, and controlling the inverter so that the detected rotating magnetic field matches the reference rotating magnetic field. It is disclosed in Japanese Patent No. 59-25592.

[Help while the invention is trying to solve the problem]

According to the above method, it is possible to generate a magnetic field in the motor that approximates the reference rotating magnetic field, but the rotating magnetic field of the motor must be detected.

The configuration becomes complicated. Therefore, the applicant in this case filed a patent application filed in 1986.
-66259 proposed an inverter control method that can easily obtain a desired rotating magnetic field.

However, there is a need to further improve accuracy.

Therefore, an object of the present invention is to provide a method for easily obtaining a desired rotating magnetic field with high precision.

[Means to solve problem-obsessed problems]

In the present invention to achieve the above object.

In order to obtain a virtual rotating magnetic field vector that follows the reference rotating magnetic field vector, the c
Switch control is performed to generate two unit vectors and a zero vector. The timing of on/off control of the inverter switch to generate unit vector energy is as follows:
Determined at the point in time when the distance between the tip trajectory of the reference rotating magnetic field vector and the tip of the virtual oral magnetic field vector is equal to the distance between the tip trajectory of the reference rotating magnetic field vector and the tip of the vector obtained by adding the unit vector to the virtual rotating magnetic field vector. has been done. The control signal for the switch may be obtained by calculation, or may be obtained by obtaining it in advance, writing it into a memory, and reading it out by χ.

[For production]

In the conventional control method, in which unit vectors are added immediately based on the fact that the reference rotating magnetic field vector is ahead of the virtual rotating a-field vector, by adding unit vectors, the difference before addition is also an approximation to the reference rotating magnetic field vector. There was a period of bad sex. On the other hand, in the present invention, unit vectors are not generated until approximately halfway between the virtual rotating magnetic field vector before unit vector addition and the virtual rotating magnetic field vector after unit vector addition generate. Therefore, it is possible to obtain rotating magnetic field vectors that are highly similar to the reference rotating magnetic field vector.

〔Example〕

Next, an inverter device and a control method thereof according to an embodiment of the present invention will be described with reference to one drawing.

(Configuration of inverter device) FIG. 1 shows a three-phase inverter system.

In this Figure 1, (1) is the 1L current power supply, A+, ~b
BI-horse, C,, C, is a control switch consisting of a transistor, af), bridge-connected. (2) is a 3-phase AC fi motor with 9 loads, and the inverter p
,,B.

Connected to the C phase output line. (3) is a microcomputer (referred to as 9-lower microcomputer), which functions as an I/J control signal generation circuit for the inverter. This microcontroller (3) contains read-only memory (
This ROM is equipped with mIJ control switch/b" Ct 'l controlled tanu data V,
˜Memory M, in which Vs is prewritten.

a memory M into which data of sjnθ is preloaded;
, a memory M in which data of COSθ is stored in advance,
.

A memo υM4 in which arithmetic expressions for determining the occurrence of unit vectors are stored, a memory M in which arithmetic expressions used to determine unit vectors V, ~Vx are written in advance; has.

In addition to the above ROM, the microcomputer (3) also has a CPU and R
Of course, it also includes AM (not shown), etc. This microcomputer (
A voltage command signal and a frequency command signal are input to 3), and a control signal for obtaining an impulse output of the commanded voltage and frequency is generated. The microcomputer (3) sends the first . Second. Third
control signals A and B.

C is generated and supplied to the control switch Al s Bl * CI. I hated it. NOT circuit (41+51 (61 forms inverted signals of A, B, and C, and fltU control switches A, , B, , and C).

supplied to Lower control switch Atm Bs s
Cf is upper 1Il11f] Limit 1 switch At, Bs
, operates in the opposite direction to CI, so the control switch Al *
By specifying the operation of Bl s CI, the operation of the entire inverter can be specified. Therefore, in the following, the first. Second. and a third signal A.

B and C specify the control state of the inverter.

Note that control signals A, B, and C are at high level, that is, logical 1σ]
When the control switch AI, Blsc, is controlled to be on, and when it is at a low level, that is, logic O, the control switch AI is controlled to be on.
-=8+, C+ is controlled off.

(Explanation of Principle) FIG. 2 shows the relationship between the reference rotating magnetic field vector φS and the virtual rotating magnetic field vector φ using coordinates. In this figure, a shows the locus of the end point (tip) of the basic @time KK magnetic field vector φ3 corresponding to the ideal rotating magnetic field desired by the motor I''j;e, and φ is the virtual rotating a field introduced according to the present invention. The virtual rotating magnetic field vector φ follows the change in the angular position of the reference rotating magnetic field vector φS and is changed by degrees Celsius.

ffO, based on the error vector between the reference rotating magnetic field vector φS and the virtual rotating magnetic field vector φ, the unit pect magnetic field vector φ to be added is combined to determine a new virtual rotating magnetic field vector φ shown by a one-dot line. The virtual plane &fB field vector φ, which is determined sequentially, is determined along the one-circle locus a. Further, as the unit vector V, a vector specified in advance is used. NO Kai.

This unit vector V is the inverter's! This is a vector that can be generated by the on/off operation of IJ control switches A and %C.

Reference rotating magnetic field vector φ for obtaining circular locus a.

The coordinate data indicating 81. is stored in the memory 81. in the microcomputer (3).
is sequentially generated by sin θ of the memory M3 and COS θ of the memory M3. The incorrect virtual rotating magnetic field vector φθ) is determined by adding one selected unit vector V to the old virtual rotating magnetic field vector φ. When the coordinate data of the reference rotating magnetic field vector φS and the seated image data of the virtual rotating magnetic field vector are obtained, the unit vector to be used is determined by arithmetic processing based on this data, and the time point at which the unit vector is generated is determined. be done.

(Explanation of deuteron vector) FIG. 3 shows inverter control swings +A,,B,.

This shows the relationship between the C3σJ state and the voltage vector.

3-phase I/verter control switch (A, B, C
,) of 9), (100) (110) (OlO
)(011)(001)(101)(lill(000
]σ) There were 8 types! 1. The voltage vector in each state can be expressed by six space vectors V, ~V8 and two zero vectors v7 and v8 at 60 degree intervals, as shown in the third concavity. Switching mode (
8 voltage vectors) are combined to set the motor (2).
It is possible to generate a rotating magnetic field. Merely arranging six switching modes as shown in FIG. 3 in one cycle 3 (2π) is not suitable for practical use because there are many high temperature wave components. Therefore.

In the present invention, the virtual rotation FiFi FP vector φ is created using the unit vector corresponding to this voltage vector V
This virtual rotating magnetic field vector φ is compared with the reference intermediate rotating magnetic field vector φS for each of the multiple contacts provided during one cycle, and a control signal is determined.

(Principle of virtual rotating magnetic field vector) The virtual rotating magnetic field vector -σ) is determined by dividing A (1 period X2π of the circular locus a of the single rotating magnetic field vector φS) into 6, 1-6th section configuration ゛・j=shi1
This is done for each ward. Now, the first interval σ) l-1 center is θ=o' and 1 ~ (P4.9 First interval &J, 3π curve π from 30° to 310° has a corresponding L1., = σ)th 4
βj(τn) pressure pect η・V, 5\1. is the third
The city of the city 1 Evector ℃ "71, the same port, Ru. 1st
[Temporary 7t in the section! (b) Rotation・↓KutolgarekisuI) Sometimes, when comparing the voltages, ′・torV, IC tenkogto single 6i vector V; V3 'i @Add to the imaginary rotating magnetic field vector φ.Determined by the imaginary rotating magnetic field vector φ calculation. However, since this virtual rotating magnetic field vector φ is used to determine the control signals of the control switches of the inverter, the control switches A1 to C2
The voltage vector VpV in FIG. 3 is determined by the on/off state of the voltage vector VpV.

is used (determined by -. Therefore, φ and φS completely match tc.

Fig. 4 σ,) In the first section at °C, the virtual rotating magnetic field vector can be made to follow the 1-circle locus a well.
Two voltage vectors (V7, \'s (/c corresponding first and second σ) unit vectors V, , V, are not used.

After the death, the virtual world turned around, and I got ni!
As is clear from the small scale, there are two units: V2,
V3 l'7) ItI',',.

Knowledge, six vectors V7. Or use it for 8 and 1 yen 1111. traces a1, i7 ”, 'ei virtual (b) rotating magnetic field vector)
Increase the followability of A, 4, zero, 1) Add A2 to virtual 1': -1,...
+) means that the virtual rotation is stopped at the angular position of ff'N field vector 7. The meaning of 2 and 2 is 1, V: dv8'σ〉Irreko', si + 70, l'X difference na'i'゛) Kuimotoji Hoke (color 1j - (iQ ma , 1") ・Feast Figure 4・Deteiku [' Power day 〈. 60° 181
1; Self -○
f3;11-to(,Y,-・to 0°05. , ,
, I: (~] 20° te v, t v'-ym g t-+
, o'-60'-cv knee b: worn out.

Mr. V? The person who specifies the use of V8 and makes the same number of switching in the inverter: Nude. For example, in the interval from 0° to 60', (Cho-vector v, [01, unit vector V with + line in OF, 7' which is generated many times]) [pressure vector V.

(000)σ) Zero vector ~ls is selected.・
-Thank you for your help, V! The switching mode of 010) and the switching (- mode of Vstooo+) are adjacent to each other.
When the switch B1. Enter I'''l to switch on/off. 1″%
Oc'ku z stomach teha, v2 F1〕Q) &', +:
Hates Second No.22 ・V ga 23 ('f'(, Runo-hi, zero "t l-E ”"・Attle\'g! -,
11j) ic vs. Ar1, -t, b Ohek)'t-
N゛4 "i ゛゛, Yu I 4K; 蓼1 [τ5j regretful night 60
'-120' Ward 1'' 1 in 1 Sea (Ot l,
)'-Lis Ittenia,,F
-1,,+, is the th. ．． is selected ν1', t1 and 5)
．． 1 evil 2 L";, li'lj ・, -4 anti 2t shi
,,2 To...:,Question 6 4th,I] :Kj""-5"%732<)7 Tor V3(010) /:V4(0,[l)
To r'-? ',, %: 'hc,k -9-', 1
)Q (';I hekl-tq= N,),,', N
,,r; t,) Ijii, ,#,lt[f<b9
1-1 and below, similarly in the third section, the voltage vector V, (
011) and V, the unit vector V4 corresponding to (001) by 1j.

■, Full use 8. In the fourth interval, the unit vector V;, V, corresponding to the voltage pect, V, (OO1), V, +101) is formed using all! , in the 5th section, the voltage is 7kV6CIOI),! :V! <100.
) K'm corresponding Jl medium vector V6 m ''+ k is used to determine the vector V+ (1
00) Vt (110) K Determine using the corresponding unit vector V+, Vt k.

(Determination of unit vector A) FIG. 5 explains the determination of the unit vector in the first section. If the angular position of the reference rotating magnetic field s and the virtual m rotating magnetic field φ at T4 is known, the unit vector to be used can be determined based on the principle explained in FIG. In the case of the first interval, the unit vector) v2bvs is used.
-ru. 5th flesh tic, E..., virtual m-turning magnetic field vector 6υ) end point (Lk4] (iZ 14A)!
Persimmon Ka(x), *yA') is J), then this vector 44 i,? Unit vector V on the knee side, Gekaen 1
-The monument at point B becomes (XB e Y□), and it is temporary.
Gukutonoto φI/the other single A) f kuri (・ru V.

The value of the point C that has been added is (X(1!, yo)).The point B or C that may become the tip position of the new virtual rotating magnetic field vector is determined by calculation. After finding the locus mk of C, based on this, it is determined by calculation which one of the unit vectors vf and the other unit vector end point locus I) should be selected.

Next, I will explain this determination method 1 in detail. Reference rotating magnetic field (″
The angular position is changed to i microk, and the vector end point locus a of -f: changes. Therefore, the distance from the reference rotating magnetic field vector 68 to the point D (XD - yr:, ) to the point 1 point, the distance from the point B to the point 6 points, and the distance from the point C are calculated for each clock. At the point when the distance between 8 and 1 and the distance between B and 0 are almost equal, the unit vector V is calculated from the memo +7 to f in Figure 1.
, with ↓6-y) data V, (110) horizontally 4. ．．
Take notes! IM, a single vector according to the acid n formula of H? ·generate. In this example, the distance between A-0 and B-0
Since the point in time when the distance between A Dl's'l and the distance between C and Dl's'l and the distance between C and C0 are equal to each other is reached before the point in time when the distance between them becomes equal, only one unit vector V is selected. .

The unit vector V of 1m21.

Conventionally, the reference rotating magnetic field arrived near point 4a/')! Since we generated the unit vector V, V, 1 at the point -,
Although the difference between the virtual rotating magnetic field and the reference rotating magnetic field became large near the time when the unit vector was generated, the present invention
Since a unit vector is generated between the virtual rotating magnetic field vector of 51-go and the virtual rotating magnetic field vector after the unit vectors are fully added, the difference between the virtual m-turning magnetic field and the reference rotating magnetic field becomes small. In addition, in this example, the first section is missing 4
6 clocks (/(divide and generate intermediate vector k!
In this example, 22 unit vectors γ are generated in the first section.

Figure 6 (, ; Clock and intermediate vector generation and glue, 1
Person in charge? It is ¥). Figure 6 (D clock duck C,
Then, if ftl is made to coincide with the virtual 1hj rolling field pair φ and the reference rotating magnetic field vector $S, then -, ra! (S♂i16 Figure F, Ic spill as shown/) l・y
yv, generate sound.

1+'Of:v, ! ll a(I (='li
(:A,',i, (:,i rth 51st $43
As in 1... 1st and 1st invar 27 ha entered →, ~, )3. , (-21 "keep on, A,
,B, ,C, is kept off. FIG. 6 shows the state of the first section. The unit vectors generated in σ] are V and V. clock t. Then, determine how the virtual rotating magnetic field vector changes when V; also &''iv3iv3 is applied, and make the unit vector end point locus according to the principle explained in Fig. 5. Immediately, Fig. 6 In the case of , the zero vector remains 1 even when the clock t.

A unit vector,V,%,is generated at a clock,t,. ff
rlchi.

Switch AI -81*C1" controls A, 81 on, 01 off. At the same time, output voltage is controlled.

Adjust the on time T with the timer. After the on-time T ends, a zero vector is output. On-time T〉・If the on-time is made longer, the output voltage will be higher, and if it is made shorter, the output voltage will be lower. In this FIG. 6, clock 1. ．． 1. unit hec) V, '79
1+, 5 clocks t, then the unit vector Vp'7
generate. , -, there is a space between each leg as shown in Figure 6 (C1 (
Dl[F]W shows-■Mochi is 9 h t'. Output layer η
7 number σ) cycle vi′: rFigure 6 (PI =)) C that changes the clock period 7 and ((, I・−゛riθ) Circumference torque λ
-Can you change it, 5? The electrical ratio also changes due to π-.

(Formation of unit vectors) The unit vectors v; to v; necessary for calculating the virtual rotating magnetic field vector 1 are determined as follows. The unit vector used is v;~v! corresponds to the three-phase voltage vectors V, ~v8 shown in FIG. 3 phase (A.

The control data for the control switches A1 to C (A, B, C) with respect to the voltage vectors V and %V of B and CJ are stored in the microcomputer (3) and memory M and K8. That is, (100) corresponds to V, and (110
).

■, corresponding to +oxO), corresponding to Vt (01J]
, ~l, corresponds to (001), and V, corresponds to (]0
1) (111) corresponding to sV, (0
00 and 1 have been omitted. In addition, the content of the data (1
00) etc. is the output (ABC) of the microcontroller (3) K vs. TE
, 1 le. Follow, V, ~V8Gj V (A,
B, C) Can be expressed as te. It would be very convenient if this data could be used to determine the unit vector VI/. Data Vl (100) ~ V, (101
The Q-D coordinate data (vQ, VD) of the unit vector V, '%V, can be obtained by the following equation based on the following equation.

V = A ・B ・C・・ (2) l) 22 However,, A, B, Cf'! , f = l Vt
(100,) ~V.

Contents of (1,01) f100) to (101), that is, (A,
Corresponding to B, C), data V, +100) ~%7
゜ (101) If the content of σ is I+7), then σ is 1 or V
Substitute into the expression Q,,Vゎ, and if the content is $σ) then −
1 and substituted into the equations vl to V. As a result, in the case of a one-circle locus, the σ unit vector σI valley coordinate data becomes the following trace.

V, + 0, 2) V; tJa, 1) Vt (JT, -1) V, (0, -2) v; f -J3, -1) VS (-Ja, 1) Figure 7 shows this unit. Vector V: ~v; and coordinate data 7 are shown. The above formula 111F21 is the memory IM of the microcontroller (3)
, )K is written deviated, so the memo υM, the thus read data V, (100) ~ V, (101, > and the above equation are combined with ) (2) to create a unit vector V, ~ V
6. Use easy approximations. For example, the control signal (110) is used to obtain the unit vector V at clock t.
From this point on, the virtual rotating magnetic field vector φ
The value becomes the value obtained by adding the unit vector to the virtual rotating magnetic field vector φ up to that point, and this value is stored in the RAM.

(FIG. 8 σ) Embodiment Next, another embodiment of the present invention will be described with reference to FIG. 8. In FIG. 8, the calculations explained in the embodiments of FIGS. 1 to 7 are not performed every clock, but are calculated in advance at intervals of τ, and the results are written into the 2ROM, that is, read-only memory (101). The control signals in FIG. 6 ([31] are stored in the memory (10)
I will write it down. The old memory q has 46 addresses corresponding to the unit section (60°) shown in FIG. In this example, the first section σ] address 2.4.6.9.12.1
5. , 18, 21° 25. 30. 37 has a unit vector v
; Control signal data + 110, ) is written to address 10.1? , 22.26.29,32
, 35°38.41.43.45 has a unit vector V! Control signal data +010) is written to obtain .

Control signal data (111) or (000) for obtaining a zero vector is written in other addresses.

Therefore, when the control signal shown in FIG. 6 (same as shown in B) is read out from the memory 00 in FIG. 8 in synchronization with the clock shown in D, the inverter switch shown in FIG. A,
~C1 performs an on/off operation corresponding to this, and the same rotating magnetic field as the virtual rotating magnetic field vector φ obtained by calculation is obtained.

Note that the control signals (A, B
, C) are the output terminals ca, b,
c) and is output from OR gate u21 (131Q41
A N is supplied to the inverter switch through the gate t15+ubl[1η. AND gate [5
1t16+ (The output of Iη is the upper switch A in Figure 1.
le BIs c, control signal! 7. NOT circuit (
The output of 41i51 (6) is the lower switch At -8
2 @ C1's Ura j signal. CP LT (lt
The + output terminal d outputs 0 when all of the control signals (A1, B, C) are set to 1lll), and generates 1 when all of them are set to +000) during a period in which no unit vector is generated. A5. Connected to NAND gate α&.

The output terminal e of the old CPU is a timer output terminal, and generates an output that determines the pulse width of the control signal for generating a unit vector. FIrJ generates 0, that is, a low level output, corresponding to the on time T in FIG. koσ)
Output terminal e has three OR gates (121o:, α pull and 1
Since it is connected to the input of two NAND gates σ), when this σ) output is 1 or high level, the OR gate)
[21 (The output of 1141 is also 1, that is, high.
.

At this time, if the output terminal d is O, the NAND gate (18
The output of 1 becomes 1, that is, a high level, and as a result, all m of the outputs of the three AND gates u5]uIliIr1n correspond to the zero vector (111). On the other hand, during the period when the output terminal d is 1 and the output terminal e is 1, that is, at a high level, the NA
Since the output of ND gate a81 becomes 0, that is, low level,
The output of the three AND gates uiae becomes (000). Note that if T is changed by one hour, the output voltage value of the inverter changes. Also in FIG. 8, if the clock frequency is changed based on the f command signal, the output frequency of the inverter changes and the voltage value also changes.

Although we have explained the operation in the first section in Fig. 4, even after the second section, the unit vector used is only variable, so the first control signal (8, B, C
) data can be entered.

II+ control similar to that in the first section becomes possible. In the embodiment shown in FIG. 8, since the III-1 data is written in the memo IJ (101) through preliminary calculations, basic calculations for control are not necessary, and high-speed control is possible.

(Modified example) The invention is not limited to the embodiments described above.

For example, a first-order modification example is obtained as follows.

(at In the methods shown in FIGS. 1 and 8, the end point locus a of the reference rotating magnetic field vector φS is an elliptical locus.

To match this, the unit vector V, ~vote may be set to 5. It is desirable that the unit vector in this case does not include any fractions, as shown in FIG.

fbl Obtain 6 unit vectors and 2 zero vectors Put 8 types of control signals into 8 addresses by -1, specify a predetermined address with a predetermined clock, and use this clock to A required control signal may be output.

((+ In the method of determining the generation and generation of unit vectors by calculations in Figure 1, when a new virtual rotating magnetic field vector φ is obtained, immediately calculate the type and generation time of the next unit vector, and store this in memory. It may be written in advance and then generated when the first generation point has arrived.

〔Effect of the invention〕

As is clear from the above, in the present invention, the timing for generating the unit vector is set between the previous virtual rotating magnetic field vector and the next virtual rotating magnetic field vector.
A rotating magnetic field vector with little difference from the reference rotating magnetic field vector can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an inverter device according to an embodiment of the present invention. FIG. 2 is a vector diagram for explaining the present invention in detail. FIG. 3 is a vector diagram showing the relationship between the switch state of the three-phase inverter and the rotating magnetic field vector. Fourth, a vector diagram showing the arrangement of the sections, changes in the virtual rotation motherboard vector in the first section, and the selection range of the zero vector in principle. FIG. 5 is a vector diagram for explaining the control timing for generating a unit vector. Fig. 6 is a waveform diagram showing the states of each part in Fig. 1. Fig. 7 is a vector diagram showing the terminal locus of the reference rotating magnetic field vector or the unit vector in the case of a circle, and Fig. 8 is a diagram showing the unit vector in the case of a circle. A block diagram showing the inverter control circuit in the embodiment. Fig. 9 is a vector diagram showing the unit vector when the end point locus of the rotating magnetic field vector is an elliptical locus. tl+... is the source i2+... motor , (3+...
Microcomputer, φ... Virtual garden transformation world vector, φS...
Reference rotation arsenic vector. ■1 to V6...Unit vector. Agent Norihiro Takano Next ill cause Figure 2 Figure 3 ＼, e, = o”; V+ (100) ↓ V4 (011) 0, .180'

Claims (2)

[Claims] (1) In order to obtain a virtual rotating magnetic field vector (φ) that follows the reference rotating magnetic field vector (φ_S) in a three-phase AC load connected to a three-phase inverter, six unit vectors and a zero vector are determined, and the reference Rotating magnetic field vector (φ
_S) is divided into six equal parts, and in each section, two unit vectors and a zero vector are used to obtain the virtual rotating magnetic field vector. In the method, two unit vectors (V'_2) (
the end point position (x_A, y_A) of the virtual rotating magnetic field vector (φ) before adding one or the other of V_3), and adding the one unit vector (V_2) to the virtual rotating magnetic field vector (φ). The first obtained by
After addition of , the end point position of the virtual rotating magnetic field vector (x_B, y
_B) and the end point position (x
_C, y_C) are obtained in advance, and further, the end point position (x_A,
y_A), and a second distance to the end point position (x_B, y_B) of the virtual rotating magnetic field vector after the first addition.
and a third distance to the end point position (x_C, y_C) of the virtual rotating magnetic field vector after the second addition,
At or near the time when the first distance and the second distance become equal and the time when the first distance and the third distance become equal, A method for controlling an inverter, characterized in that the switch is controlled to generate unit vectors that are related to the point in time when they become equal. (2) In order to obtain a virtual rotating magnetic field vector (φ) that follows the reference rotating magnetic field vector (φ_S) in a three-phase AC load connected to a three-phase inverter, six unit vectors and a zero vector are determined, and the reference Rotating magnetic field vector (φ
When controlling the switch of the three-phase inverter on and off to obtain the virtual rotating magnetic field vector by dividing the angular position of _S) into six equal parts and using two unit vectors and a zero vector in each section, The end point position (x_A, y_A) of the virtual rotating magnetic field vector (φ) before adding one or the other of the two unit vectors (V'_2) (V'_3) in each section, and the virtual rotation The end point position (x_B, y_B) of the first added virtual rotating magnetic field vector obtained by adding the one unit vector (V_2) to the magnetic field vector (φ), and the virtual rotating magnetic field vector (φ) , the other unit vector (V'_3
) is obtained in advance by determining the end point position (x_C, y_C) of the second virtual rotating magnetic field vector after addition obtained by adding a first distance from to the end point position (x_A, y_A) of the virtual rotating magnetic field vector (φ), a second distance to the end point position (x_B, y_B) of the virtual rotating magnetic field vector after the first addition, and The end point position (x_C, y_
C), and calculate the first distance between the time when the first distance and the second distance become equal and the time when the first distance and the third distance become equal. A method of performing equivalent control by generating a unit vector related to the previous point of equality at or near the point of equality, the method comprising: controlling the switch corresponding to the unit vector required in each section; A method for controlling an inverter, characterized in that control data and data indicating a time point at which the control data is generated are written in advance in a memory, and the switch is controlled based on data read from the memory.