JPH01303063A - Pulse width modulation controller for inverter - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a pulse width modulation control device for an inverter, and particularly relates to an improvement in a device that increases the carrier frequency and performs precise waveform control.

(Prior art) In recent years, MOSFETs have been used as high-speed switching devices.
Elements such as (metal oxide film gate field effect transistors) have appeared, and if they are adopted for pulse width modulation control of inverters, precise waveform control becomes possible, reducing electromagnetic noise and increasing motor efficiency. It has become possible to obtain the effect of

Therefore, conventionally, high carrier frequencies (e.g. 20 KHz) have been achieved by providing analog control circuits or using dedicated digital circuit hardware or high-speed arithmetic units such as DSP.
There is a known device that enables pulse width modulation control by , thereby ensuring the above-mentioned effect of reducing electromagnetic noise and the like. (For example, in the proceedings of the National Conference of the Industrial Application Division of the Institute of Electrical Engineers of Japan in 1986,
"Application of High Frequency Switching to General-purpose Inverters", presenter Chihiro Toshi, etc.).

(Problems to be Solved by the Invention) However, the above-mentioned conventional devices have disadvantages such as complicated circuits, complicated various adjustments, and high costs.

Therefore, it may be possible to use a co-chip microcomputer (hereinafter referred to as a microcomputer), which is inexpensive and has a simple circuit configuration. The calculation time is long, for example, about 200 μs, and the carrier frequency remains at about 5 KHz at maximum. For this reason, pulse width modulation control using a high frequency (20 KII z or higher) carrier frequency is generally difficult.

The present invention has been made in view of the above, and its purpose is to create a situation that is apparently equivalent to raising the carrier frequency, without using a single-chip microcontroller.
A low-cost and simple circuit), the X1 configuration enables pulse width modulation control at an equivalently high carrier frequency, and achieves effects such as reducing electromagnetic noise and increasing motor efficiency through precise waveform control. be.

(Means for Solving the Problems) In order to achieve the above object, the present invention changes the generation algorithm of the PWM control pattern (that is, the ON time of a plurality of switching elements in preparation for in/beta), and
Even if the calculation time (calculation cycle) of the WM control pattern is long,
The calculated ON time of each switching element is divided into a plurality of pulses to equivalently raise the gear frequency by 2.

In that case, when the 01V1 time of each switching element is equally divided into equal-width pulses, as shown in FIG. Reproducibility will decrease slightly. On the other hand, when the ON time of each switching element is divided into a plurality of pulses with unequal widths, as shown in FIG. Although reproducibility can be ensured, the calculation and processing time becomes longer due to the division into unequal widths, resulting in a disadvantage that the effect of increasing the carrier frequency is reduced by that amount.

Therefore, in the present invention, the mode of division of the ON time is not fixed, but can be switched between division into equal-width pulses and division into unequal-width pulses as appropriate, thereby ensuring good reproducibility of the signal wave. Therefore, the purpose is to shorten the computation and processing time required to divide the ON time of the switching elements as much as possible, and perform pulse width modulation control using a sufficiently high carrier frequency.

The specific solution includes a bridge circuit (4) connected to a three-phase winding (2) and having a plurality of switching elements (Tra) to (Trc) as shown in FIGS. 1 and 2. , each switching element (T
The present invention is based on a pulse width modulation control device for an inverter, which pulse width modulates a direct current by 0N10FF operation of ra) - (Trc') and applies a three-phase AC voltage to the two-phase winding (2). As shown in FIG. 6, FIG. 7, FIG. 11, and FIG. 15, each of the switching elements (rra) to (Trc") is
a calculation means (10) for calculating the ON time of , and each switching element (Tra) calculated by the calculation means (10);
A dividing means (11) for dividing the ON time of ~(Trc') into a plurality of equal-width pulses or unequal-width pulses according to the rate of change of the ON time, and the dividing means (1]). Each of the above switching elements (Tra) with a plurality of pulses
The configuration includes a control means (12) for controlling ON of .about.(Trc').

(Function) With the above configuration, in the present invention, the ON time (pw
M control pattern) is repeatedly calculated every calculation cycle according to the carrier frequency □ wave number of the calculation means (10), and the ON of each switching element (Tra) to (Trc') is
Since the time is divided into a plurality of pulses (for example, 4 pulses) by the dividing means (1]), the carrier frequency is multiplied by the number of divisions, resulting in an equivalently high carrier frequency (for example, 20 pulses).
The situation will be the same as if pulse width modulation control was performed at KIIz). As a result, when each of the switching elements (Tra) to (Trc') is turned ON by the control means (12) using each of the divided pulses, a precise Sendai waveform close to a sine wave is obtained, and electromagnetic noise is generated. is effectively reduced, and the motor efficiency is effectively increased.

Here, the carrier frequency of pulse width modulation control is the normal value (
(approximately 5KHz) and takes a long calculation time] Even a chip microcontroller can sufficiently calculate the PWM control pattern.
Pulse width modulation control using a high carrier frequency can be performed at low cost and with a simple circuit configuration.

Furthermore, the switching element (T
The division of the ON time of ra) - (Trc') can be appropriately selected between division into equal-width pulses and division into unequal-width pulses depending on the rate of change of the ON time, so that each switching element ( When the rate of change in the ON time of Tra) to (Trc') is large, division into unequal width pulses can be selected to ensure good reproducibility of the signal wave, and when the rate of change in the ON time is small, division into unequal width pulses can be selected. By selecting division into pulses, the calculation and processing time can be shortened, and the calculation cycle can be set to a short time. As a result, it is possible to equivalently perform pulse width modulation control using a sufficiently high carrier frequency while ensuring good reproducibility of the waveform of the signal wave.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

1 and 2 show a pulse width modulation (hereinafter abbreviated as PWM) control device for an inverter according to the present invention. In each figure, (1) has three windings (2a), (2b),
(2c) is an induction motor having a three-phase winding (2) with Y-connection; (3) is a voltage type inverter connected to the induction motor (]); A transistor bridge circuit (4) connected to the three-phase winding (2) of the induction motor (1) is provided, and the bridge circuit (4) includes free-wheeling diodes (Da) to (Dc'), respectively.
Multiple (six) transistors (switching elements) such as MOSFETs (Tra), (Tra') having
, (Trb) , (Trb'), (Trc) , (T
rc'). Facing the inverter (3),
A DC voltage is applied from a rectifier (6) that rectifies the three-phase AC of the three-phase power supply (5).

In addition, (8) is the ON time of the six transistors (Tra)-(Trc') of the bridge circuit (4), exactly p
This is a one-chip microcomputer that forms a wM control pattern, and the microcomputer (8) includes each of the transistors (Tr).
a) -(Trc') is equipped with a base dry/< (8a) that operates 0N10FF, and the microcomputer (
8) ll:, J: transistor (Tra) −(T
The direct current is pulse width modulated by 0N10FF control of rc').

Next, the formation of a PWM control pattern by the microcomputer (8) will be explained.

In general, this PWM control pattern is formed by determining a PWM control pattern so that the locus of time integration of the output voltage approaches a circular locus.

To explain this in detail, first, let the potentials of the output terminals of the inverter (3) be va, vb, and vc, and the potential of the neutral point of the three-phase winding (2) be vl, and the output defined by the following formula Consider the voltage vector vP1 and the time integral neP of the voltage vector Vp.

YP = J”, - fva +a 2 conflict vb +d -vc
l However, O=eJ2/3°" ap=, l'Vpdt Now, the angular frequency (V
+ is the effective value of the fundamental wave voltage) When the voltage vector vP and its time integral P are applied, the voltage vector vP and its time integral P draw a circular locus on the complex plane.

On the other hand, in the voltage source inverter (3), one of the transistors in each phase arm is always in the ON state, so for convenience, the ON state on the + side is set to "1", and the ON state on the - side is set to "0".
'', and the C phase, b phase, and C phase are rlO], J, r
o], ], J, etc., there are eight states of the inverter (3). The voltage vector of each state ￥p (
P = 0 to 7) is the size or f 10,000 d (Vd is the rectifier (6
), and its direction is the direction shown in FIG. Here, Vo and V7 are zero vectors as Vo =V7 =O.

” - Time integral Jp of distribution voltage vector is dλp /dt
-vP, the time integral ap when driving the inverter (3) is 1Vpl=iVd in the direction of the voltage vector Vp.
It moves at the speed of (however, it stops if the vector is zero).

From the following, the PWM control pattern of the voltage source inverter (3) is such that the voltage vector vp is set so that the vector locus in the complex plane of the time integral Jp of the voltage vector moves along the circumference of the specified radius R at an angular velocity ω. Select and decide as appropriate. (
The designated radius R is R=V, /ω, where the effective value of the line voltage of the fundamental wave voltage is V1% and the angular frequency is ω.

That is, for example, as shown in FIG. 4, the angle φ is 0≦φ≦π
In the range of /3, using the voltage vector ■4, Vo-1] − and a zero vector (for example MO), it remains at the point PO for a time τ0 (this state is indicated by the symbol 0), and then,
Consider the case where (1) 4 is taken for a time τ4 to reach a point q1, and Vo is further taken for a time τ6 to reach a point P1. In this case, in ΔPoq+P+, pop,=V,-T.

po Q+ = JT7'f Vd ・r4q+ P+
= J"2πVd ・τG and τ○+τ4+τ6−To, so by solving the above equation, the voltage vector I・le within the period To is 4゜vO,
Time to take vO τ4. τG and τ○ can be obtained.

T4/To =ks -8jn(π/3-φ0)τ
6/TO==11(s conflict sjnφ○ TO/To −1−k s −5jn(φ O→−π
/3)・・(3) Where, kS is the voltage control rate, and ks = JYV+ / Vd.

Equation (3) above is a relational expression in the range of angle φ or 0≦φ≦π/3, but in other sections, since the inverter (3) performs a symmetrical triad operation, the following equation is expressed. By replacing each symbol as shown in Table 1, a relational expression in the range 0≦φ≦2π can be obtained.

114 - Next, 0N10 of each transistor (Tra) - (Trc') based on the time τ of the voltage vector in equation (3).
Find the FT' pattern (PWM control pattern). In this case, the relationship between the voltage vector time τ and the PWM control pattern changes depending on the order in which the voltage vectors are taken, so for the sake of simplicity, the same pattern is repeated in each period TO, and 0N10F of the transistor in
Adding the constraint that F switching is only done once, PWM
The control patterns are represented by the four patterns shown in Fig. 5 (a) to (d) (in the figure, τ" is the O of the + side transistor.
N time, and τ- indicates the ON time of one side transistor, respectively).

In this embodiment, the PWM control pattern shown in FIG. In the voltage source inverter (3), the PWM control pattern is uniquely determined by knowing the name of the transistor that turns on at the beginning of the period TO and the time at which it turns off. Referring to figure (a), the PWM control pattern is determined by the following formula when the angle φ is in the range of 0≦φ≦π/3.

ra/To =1-JT・(V+/Vd)・5i
n(φ0+ π/3) rb /To =l JT・(■thad)・S]nφ
0τc/To-1 (always ON) (4) Relational expression (4) for the PWM control pattern in the range of O≦φ≦π/3 can be obtained by replacing each symbol in the same manner as above. ba0
The relational expression is within the range of ≦φ≦2π.

Next, the operation of the 1-chip microcontroller (8) is shown in Figures 6 and 7.
This will be explained based on the control flow shown in the figure with reference to FIG.

For convenience of explanation, each transistor (Tra) to (Tr
First, the case where the ON time of c') is divided into a plurality of equal width pulses will be explained.

The control flow in FIG. 6 is as follows for each transistor (Tra)-(
This is a calculation flow of the ON time (PWM control pattern) of Trc'), and the control flow of FIG. 7 is a flow of actually QN control of each transistor (Tra) to (Trc'). First, the control flow in FIG. 6 will be explained. This control flow is repeated every calculation period To (for example, 200 μs) corresponding to the carrier frequency (for example, 5 KHz), and in step SAI, the phase ωt (=φ0) of the output voltage is changed. and output voltage amplitude V], in step SA2, the ON time τ(n+1
) is calculated.

After that, in step SA3, the ON time τ(
n+1) by a preset number N (for example, 4),
Each ON time τ(n+1) is divided into a plurality of N (4) pulses τ'(n+1)(τ' (n+1) = τ(n+1-)
)/4).

Then, in step SA4, this divided pulse τ''(n
+1. ) is stored in one switching time register for each phase (in a voltage source inverter, one transistor in each phase arm is always in the ON state, so one transistor for each phase is sufficient) as shown in Figure 9. , return.

In addition, in the control flow shown in FIG. 7, the repetition period T○゛ is faster than the calculation period To shown in FIG. 6, and the ON time τ
According to the number of divisions N (4 pieces) of (n+1), To'-T○
/N (The number of divisions N is preferably selected to be N=2" (nrl, 2...), which allows division to be performed only by shifting.) Therefore, as shown in FIG. After the divided pulse τ' (n+1) is stored in the switching time register of each phase in the control flow, as shown in FIG.
During the next calculation cycle To, the contents of the switching time register are input in step S'BI, and the corresponding transistor (
Tra) to (Trc') are turned on and the process returns.

Therefore, in the calculation flow of the PWM control pattern shown in FIG. 6, in steps SAI and SA2, each transistor (switching element ) (Tra) to (Trc') constitutes a calculation means (10) configured to calculate ON time τ(n+1).

Next, each transistor (Tra) to (Trc”) is turned on.
The case where time is divided into a plurality of unequal width pulses will be explained based on FIGS. 10 to 14.

In other words, this division into unequal width pulses is achieved by linear interpolation (
(linear interpolation).

This will be explained in detail. In the control flow shown in FIG. 10, calculation processing is performed in the period To period, and in step SCI, the phase ω of the Sendai voltage is
and the amplitude V] are input, and at the same time, in step S02, the results of the previous calculation of the ON time τ(n-J,) (pulse divided into four) of each transistor (Tra) to (Trc'') are input.

After that, in step sC3, each transistor (Tra) of this time is determined based on the relational expression (4) of the PWM control pattern.
(Trc') ONN time (n) is calculated, and this ONN time (n) is calculated.
A divided pulse τ゛(n) divided into a plurality of N (4 pieces) is calculated from time τ(n), and then, in step SC4, the divided pulse τ of each transistor (Tra) to (Trc') is calculated.
According to the difference between the previous time and this time, the previous divided pulse τ'
An interpolated value Δτnl of (n-1) is calculated based on the following formula.

Δrn, = l r'(n) −r'(n-1)
l/NN; Number of divisions: N=4 -19 = Then, step SCS
Then, for each divided pulse τ'(n-1), sequentially from the second one Δτ, 2・Δτ, 3・Δτn−1 as n−],
n-], and in step Sc6, each divided pulse is stored in a plurality of N (N-4,) switching time registers, and in step SC7, each divided pulse τ' is added.
Store (n-1) and return.

In addition, the control flow in Figure 1] is as shown in Figure 12, from the period 1゛○ during which the divided pulse τ゛ is calculated and stored, to the second period T.
Each transistor (Tra
) to (Trc") are ON-controlled, and the control period T○" is 1./N (N is the number of divisions) of the calculation period To of the control flow shown in FIG.

In this control flow, as shown in FIG. 13, in step SDI, each mutually divided pulse τ□ stored in the first switching time register is read, and then in step SD2, the switching time register is reset, and in step So3.
Then, use the read divided pulse r'(n-1) to control each transistor (Tra) - (Trc') = 20 - ON and return, and thereafter, control cycle T is controlled in the same manner.
The mutually exclusive divided pulses stored in the 2nd, 3rd, and 4th switching time registers are read in order for each o', and each transistor (Tra) to (Trc') is turned on.
Repeat control.

Therefore, FIG. 15 shows each transistor (Tra) to (T
Whether the ON time of rc') is divided into equal width pulses or unequal width pulses is appropriately selected depending on the rate of change of the ON time.

In this embodiment, each transistor (Tra) to (Tr
According to the rate of change of the ON time of c'), that is, the phase of the signal wave, division into 11 equal-width pulses (control flow in Figures 6 and 7) and division into unequal-width pulses (10th pulse) are performed. Figure and 1st
Unlike the control flow shown in Figure 1),
By using the symmetry of the voltage vector I, each transistor (
Tra) - (Trc calculation of 01V1 time and its division into multiple N (N-4) all angles O≦φ≦2π
We are trying to further reduce the calculation time by performing the same calculations.

In other words, as can be seen from the relational expression (4) of the PWM control pattern, when the angle φ○ is in the range of 0≦φ○≦π/3, the ON time τa of the transistor is less than 5 inches as shown in FIG. (
φ0+π/3), and the rate of change in the ON time is small, so good waveform reproducibility is ensured while dividing into equal width pulses with short calculation time. In addition, since the ON time τl of the transistor is in the range S1nφ0 and the rate of change of the ON time is large, we will adopt division into unequal width pulses to ensure good waveform reproducibility. . Considering the above, the angle φ0 is set to 0≦φ0
In order to expand the range to ≦2π, the entire interval is divided into 6 intervals at intervals of π/3, and the result is shown in Table 2 below.

= 23 - FIG. 15 shows a configuration of the above with a single chip microcomputer (8). In the same figure, (15) is the phase ωt
(1G) is a section information calculation circuit that determines the section N in Table 2 above by calculation 1, and (1G) inputs the section signal N and phase ωt from the section information calculation circuit (15), and calculates the voltage vector from the symmetry of the voltage vector. , the angle φ0 is 0≦φ0 in the entire interval N (N-0 to 5)
In order to unify the range of ≦π/3, the angle calculation circuit calculates using the following formula (% formula %), (17) is the angle calculation circuit (
The angle φ○ calculated in 16) and the effective value V1 of the fundamental wave voltage
is input, the ON time of each transistor (Tra) to (Trc') is calculated based on the relational expression (4) of the PWM control pattern, and the pulse division is performed to divide this ON time into a plurality of equal width pulses. It is a circuit. Further, (18) is an unequal width pulse calculation circuit, and the unequal width pulse calculation circuit (18) is configured to operate each transistor (Tra) to (Trc') calculated by the pulse division circuit ('7). ON time of
and the divided equal-width pulses, as well as the section signal N from the section information calculation circuit (15), and the transistors to be divided into unequal-width pulses based on the section -24=N in Table 2 above. By understanding the ON time of (Tra) to (Trc') (that is, the function of 5inO to Sinπ/3 in Table 2), calculate only the ON time to be divided into unequal width pulses as shown in Figure 10 and 1 above. - Divide into a plurality of unequal width pulses by the same operation as the control flow shown in Figure 1, and send the divided unequal width pulses and the equal width pulses equally divided by the pulse division circuit (17) to the pace driver (18a). It has a function to output to.

Therefore, the unequal width pulse calculation circuit (18) calculates the ON time τ of each transistor (Tra) to (Trc') calculated by the calculation means (J, 0) of FIG.
When the rate of change is small (in Fig. 14, the angle φ0 is Sin π/3-3in (φo+π
/3), the pulse is divided into a plurality of N (N=4) equal-width pulses τ', and when the rate of change in ON time is large (
In Fig. 14, when the angle φ0 is in the range of 5jnO to Sinπ/3), a plurality of N (N=4) unequal width pulses ((τ
It constitutes a dividing means (1]) configured to divide the signal into two parts (°+Δτ) (τ゛+2·Δτ>...). Furthermore, top-2
5= According to the control flow shown in FIG. 7 and the control flow shown in FIG.
) constitutes a control means (12) configured to turn on each of the transistors (Tra) to (Trc') using equal-width pulses and unequal-width pulses.

Therefore, in the above embodiment, p W M :I
i! In the control pattern calculation flow (Fig. 6), each l transistor (T
The ON time τ of ra) to (Trc') is calculated by the calculation means (1o)
After calculating each ON time τ, dividing means (]
J) is divided into a plurality of N (four) pulses τ゛, and these divided pulses τ° are stored in the switching time registers of each phase of a, b, and c.

Then, in the subsequent period To, as shown in FIGS. 8 and 12, the ON time τ of each transistor (Tra) to (Trc") is calculated and divided as described above again in this period TO At the same time, in this current period TO, the divided pulse τ in the switching time register of each phase of a, b, and c obtained in the previous period To is calculated for each cycle of T o /N (-1" o '). □With this, each corresponding transistor (Tra) - (Trc') is controlled to be turned on by the control means (12), so the conventional type as shown in FIG. 18 (one in which 09 time is not divided into multiple pulses) Compared to , the frequency of the high frequency component can be increased, and the carrier frequency can be equivalently multiplied by the number of divisions of 09 hours N (N = 4), and the original carrier frequency (5KHz) can be increased to a high carrier frequency (20KHz). I can do something. In addition, in FIGS. 8 and 18, 0 of the + side transistor of each phase is shown.
This is a description of the case where 9 hours are calculated.

Here, the original carrier frequency (5Kl+z), that is, the calculation period T O (200 μs) for 09 hours, is a sufficient period for calculating the PWM control pattern with one chip microcomputer (8), so High carrier frequency (20KH) while using chip microcontroller (8)
Enables PWM control at low speeds (about Z), making the circuit configuration simple at low cost, and precisely controlling the waveform of the three-phase sum alternating current wave to the induction motor () by taking advantage of the capabilities of high-speed switching elements such as MOSFETs. It is possible to reduce electromagnetic noise and increase motor efficiency.

Furthermore, if a carrier frequency (5 KHz) comparable to that of the conventional method is sufficient, the calculation time of the chip microcomputer (8) can be shortened, and the processing capacity beyond PWM control can be increased.

Moreover, as shown in FIG. 14, the division of 09 hours by the dividing means (1) is performed by unequal width pulses in the range where the rate of change of 09 hours is large, and the division pulse τ□ is the first period T' When output at 0, the next cycle T゛○ is a divided pulse that is larger than this divided pulse by the interpolation value Δτ. Since the control cycle 1゛○ is repeated (see Fig. 12), Compared to the case of using equal-width pulses as shown in Figure 17 (a), the waveform is Good reproducibility can be ensured.

In addition, in the range where the rate of change is small for 09 hours, the change is small, so even if division is performed using equal width pulses, the reproducibility of the waveform for the average value 7 of the output voltage is as shown in Figure 17 (b). The interpolation value Δτ can be secured almost as well as when using non-uniform width pulses, and the interpolation value Δτ can be maintained by dividing the 09 hours by equal width pulses within a range where the rate of change in the 09 hours is small.
The calculation time required for the calculation becomes unnecessary. Therefore, while ensuring good waveform reproducibility, computation and processing time can be saved and PWM control using a higher carrier frequency can be achieved accordingly.

For deer, how do you calculate the PWM control pattern? Utilizing the symmetry of the W pressure vector, the entire range of angle ωt is 0≦ωt≦2π
After that, based on Table 2, you can easily determine whether it is 014 hours that should be divided into equal-width pulses or 09 hours that should be divided into equal-width pulses, so you can perform calculations that are suitable for microcontrollers. In addition to processing, it is possible to further simplify calculations and processing.

Further, FIG. 16 shows a modification example in which, instead of fixing the division number N of each transistor (Tra) to (Trc') to the set value (N-4) in the above embodiment, each transistor (Tr
It was changed as appropriate according to the rate of change of a) to (Trc') for 09 hours.

29 In other words, in the angular range with a large rate of change at 09 hours, the number of divisions N in the period To is set to N-8, and in the angular range with a small rate of change at 09 hours, the number of divisions N in the period T Orl] is set to N-8. is set to the normal N-4. Therefore, as can be seen from the figure, while reducing the computation and processing time of the microcomputer (8) in the angular range with a small rate of change at 09 hours, the reproducibility of the waveform in the angular range with a large rate of change at 09 hours can be improved. You can improve even more.

Note that the part that converts the contents of the switching time registers of each phase into pulse widths may be processed by external hardware such as pulse width modulation ICs.

Furthermore, if the configuration is as shown in FIGS. 9 and 13,
Even when the carrier frequency changes due to a change in the switching element, it is sufficient to change only the dividing means (11) and the control means (12). Furthermore, if the switching time register is shared with the register of the pulse width control section (step 5B2), the process of step SBI in FIG. 7 can be omitted.

Furthermore, whether the calculation period in the calculation flow of the PWM control pattern] ゛○ is uniquely determined by the time required to actually calculate the PWM control pattern (including division of ON time) or The period To' of ON control of the transistors in the control flow of FIG. 11 is determined according to the desired carrier frequency, and for this purpose, the number of divisions of the ON time of each transistor is N(T).

/To') may be set to an appropriate value.

In addition, in the above embodiment, the PWM control pattern was determined based on the relational expression (4) when using voltage vector control, but it was also determined based on the relational expression when using other PWM control methods such as the triangular wave comparison method. Of course, it is also good.

(Effects of the Invention) As explained above, according to the pulse width modulation control device for an inverter of the present invention, the ON time of the switching element that is repeatedly calculated at the calculation cycle according to the carrier frequency is changed by the rate of change of the ON time. The pulse is divided into a plurality of equal-width pulses or unequal-width pulses in accordance with
Even when it takes a relatively long time to calculate time, the carrier frequency can be equivalently increased, and even when using a low-cost, simple-circuit-configured single-chip microcontroller, for example, three-phase AC waveforms can be accurately converted into waveforms. It is possible to reduce electromagnetic noise and increase motor efficiency. Furthermore, by performing division using unequal width pulses when the rate of change in the ON time is large, and performing division using equal width pulses when the rate of change in the ON time is small, while ensuring good reproducibility of the signal waveform, The calculation and processing time of the PWM control pattern by the microcomputer can be effectively shortened, and pulse width modulation control at a higher carrier frequency can be performed.

[Brief explanation of the drawing]

Figures 1 to 16 show embodiments of the present invention. Figure 1 is a general schematic diagram, Figure 2 is an electric circuit diagram, and Figure 3 shows various states of the voltage source inverter using eight types of voltage vectors. The displayed explanatory diagrams, Fig. 4, are explanatory diagrams of voltage vector control to bring the locus of the time integral of the voltage vector on the complex plane closer to a circular locus, and Figs. 5 (a) to (d) respectively. 0≦ of angle φ
An explanatory diagram of the types of PWM control patterns that can be taken within the range of φ≦π/3, FIGS. 6 and 7 are 0N10PI' with equal width pulses for each transistor by a 1-chip microcomputer, respectively.
A flowchart diagram showing the control, FIG. 8 is an explanatory diagram in which the carrier frequency is equivalently increased by equally dividing the ON time of the transistor, FIG. 9 is an explanatory diagram of the operation when dividing into equal width pulses, and FIGS. FIG. 11 is a flowchart showing 0N10FF control with unequal width pulses for each transistor,
Figure 12 is an explanatory diagram of the state of interpolation of each divided pulse when divided into unequal width pulses, Figure 13 is an explanatory diagram of the operation when divided into unequal width pulses, and Figure 14 is an illustration of the interpolation of each divided pulse when divided into unequal width pulses. An explanatory diagram showing the angular range of the signal wave for selecting division and division with unequal widths. Figure 15 shows the case where the signal wave is divided into equal-width pulses and unequal-width pulses as appropriate depending on the rate of change of the ON time of the transistor. FIG. 16 is an explanatory diagram of the case where the number of divisions of the ON time is changed in accordance with the change in the ON time of the transistor. Further, FIGS. 17(a) and 17(b) are explanatory diagrams showing the state of waveform reproducibility when dividing into equal width pulses and when dividing into unequal width pulses, respectively. Furthermore, FIG. 18 is an explanatory diagram showing a conventional example. (2)... Three-phase winding, (3) Voltage source inverter, (4)... Bridge circuit, (Tra) to (Trc'
)...transistor, (8)...1 chip microcomputer,
(10)・Calculating means, (11)...Dividing means, (12
)...control means.

Claims (2)

[Claims] (1) A bridge circuit (4) connected to the three-phase winding (2) and having a plurality of switching elements (Tra) to (Trc'), each switching element (Tra) of the bridge circuit (4) This is a pulse width modulation control device for an inverter, which applies a three-phase AC voltage to the three-phase winding (2) by pulse width modulating the DC by ON/OFF operation of ~(Trc'), a calculation means (10) for calculating the ON time of each of the switching elements (Tra) to (Trc') at a calculation period corresponding to the calculation period;
10) Each switching element (Tra) ~ (
dividing means (11) for dividing the ON time of Trc') into a plurality of equal width pulses or unequal width pulses according to the rate of change of the ON time; Each of the above switching elements (Tra) to (Trc
1. A pulse width modulation control device for an inverter, comprising: control means (12) for controlling ON of the inverter. (2) The dividing means (11) divides each switching element (T
The inverter according to claim (1), wherein when the rate of change in the ON time of ra) to (Trc') is large, the pulse is divided into unequal width pulses, and when the rate of change in the ON time is small, the pulse is divided into equal width pulses. Pulse width modulation control device.