JPS6091870A - Generating method of pwm signal of inverter - Google Patents

Abstract

PURPOSE:To obtain a PWM signal which becomes an accurate sinusoidal current by an inexpensive circuit by accurately calculating by the software processing of a microcomputer the current flowing time of a switching mode in a short time. CONSTITUTION:A timer 17 interrupts an MPU13 and inputs a phase (theta) and an angular velocity command (omega). Then, the output voltage ratio KH corresponding to (omega) is obtained from a ROM14c. Then, the current conduction rate deltaA and deltaA+B of the switching mode of the ROM14a are calculated by the microcomputer with the counted value of the counter 11 as an address. Then, when TA and TA+B are set to the timer 17, one shot pulse width is outputted. The gate signals of three types of the output port are switched by the output signal of the decoder 18 to produce a PWM signal.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a method for generating a pulse width modulated signal for generating a gate signal for an inverter in an AC motor variable speed drive system.

[Background of the Invention]" Conventionally, digitally, FIG. 1 shows an AC motor variable speed drive system, where 1 is a DC power supply, 2 is an inverter, and
It is an IP conductive motor. Pulse width modulation (hereinafter referred to as PW'M')
There are various methods of generating signals, but as shown in Figure 2 (a), the trajectory of the two switching mode vectors ■A + ■B and the line-to-section relaxation pressure composite vector becomes a circle depending on the phase θ. The example shown in Fig. 3 has been announced as a device that allows current to flow in this manner.

As shown in Figure 2(b), the switching mode is divided into eight modes, so as shown in Figure 2(a), there are yA and ■B switching modes corresponding to the phase. The specific control method is explained in the third section.
This will be explained using figures.

Numeral 4 is a counter which counts the number of sets of taroks proportional to the frequency, and the launched output from the launch circuit 5 becomes the phase θ. Also, this becomes an upper address command for the ROM6.

On the other hand, the reference clock is counted by a counter and becomes a lower address command for the ROM8. Also, the voltage command becomes the upper address command of the OM8, and the trapezoidal wave signal e is generated.

is output and becomes the lower address of ROM6.

Therefore, a pattern for outputting a trapezoidal wave signal eak corresponding to the voltage command and the time which is the output of the counter is stored in the ROM 8, and the switching mode (Ll++ V" + W") is set according to the edO value and the phase θ. This is a method for outputting data using hardware. In this way, in the conventional example, the switching mode eROM sequentially outputs signals in response to voltage commands, phases, etc. so that the ratio of the vector ■A + I'B as shown in FIG. 2(a) is achieved. Therefore, if the voltage command is 26 bits, the capacity of ROM8 is 16 bits.
(byte (216) capacity in i4)
LOM is required. On the other hand, In, 0M6 also requires 64 byte capacity, and commercially available 8 byte) ROM also requires 16 byte capacity.
As a result, the cost of the control circuit increases.

Note that 7 is a counter.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for obtaining a PWM signal that is a highly accurate sinusoidal current using an inexpensive control circuit.

[Summary of the invention]

The key points of the present invention are the three-phase switching mode in which the locus of the line voltage composite vector draws a circle in accordance with the phase θ, and the ratio of its conduction time. For the cycle T8, all microcontrollers calculate the current flow time corresponding to the switching mode from the contents of the table and the ratio KH of the inverter output voltage, and set it to the program timer, and set the switching mode to the output port of the microcontroller. The purpose is to generate a PWM signal that becomes a sine wave current by setting it.

[Embodiments of the invention]

The present invention will be explained below. Figure 2 (a) As shown in K, the tangent vector (length t) of the circle corresponding to the phase θ.
If the switching vectors are divided into two switching vectors ffA and VB, and their lengths are kth and ts, then ILI and Lll for the phase θ in the 00 to 60- section are expressed by equations (1) and (2), and L A + The tBD value LA+B is expressed by equation (3).

th = −−L Ilx sinθ・・・・・・
... Song... (1) Mu'"-ni' (3cos O-s"fJ)-°-°-゛(2) sin θ LA+s-Lwa (-+cosU), river,, ,,,(3
) Then, if the value at the point θ=300 where lk+B is maximum is taken as the ratio 1, then the ratios δA and δA4 of t^ and tA+B
-B is expressed by equations (4) and (5), and when plotted in a 60° interval from all oO, it becomes as shown in Fig. 4. Therefore, it can be seen that it is preferable to conduct the current at a ratio as shown in FIG. 4 with respect to the phase θ.

δ1=Sinθ 0.001.091. ,,． 00.1
．． ,,,(4) Also, one person in Figure 4 and LA + in ROM.
n ratio of 6 people.

1>A+B An interval from 0° to 60° is stored as a function of kθ.

Note that if this is drawn in a 360° section, the switching mode and conduction ratio will be as shown in the 51st switching mode, and the switching mode will change every 60° section.

Next, control of the inverter output voltage will be described using FIG.

yA and N for every arbitrary sampling period Ts.

When conducting current with a vector of 0
, 0, 0). Therefore, the output voltage ratio KH shown in equation (6) is expressed as the ratio of the voltage application period TA+T11 when θ=30° and the sampling period T8.

KH=■3/VcN...Song...Song (6) In other words, as shown in Figure 5, this is an example of outputting an inverter output pressure n that is 1/2 of the rated output voltage VCN, and when the phase is θ. ha/11 A
Term fee (0, 1, 1) mode, TB period (0, 0, 1)
It can be seen that the output deviation of the mode during the Tc period (0, 0, 0) is good.

Further, the value TA+B of TA and TB is expressed by equations (7) and (8).

TA=TI]XKHXδA ・・・・・・・・・(7)
TA+s='l'sX K HXδA×B・・・・・・
(8) A circuit according to an embodiment of the present invention is shown in FIG. 6, and software processing 'f of the microcomputer is shown in FIG. 9 is a frequency setter, 10 is a V/F converter, 11 is a counter, and 12 is an A/F converter.
D converter, 13 is a microprocessor, 14a is a storage ROM (/JδA, δA+n) in FIG.
, 1 bit of the 3bltXTc section of the 'l'B section has a total capacity of 6 bytes, which is 17 bits. Further, 14C stores the output voltage ratio KH to the angular velocity ω. or,
Reference numeral 15 is an output port of the microcomputer, and the contents of the ROM 14b are output. Furthermore, 16 is a commercially available one-chip microcomputer, and a block indicated by a broken line is built into one. Next, 17 is a commercially available program timer, 18 is a decoder circuit, 19a,
19b and 1gc are 3-state buffers.

Next, the operation will be explained using the software processing shown in FIG.

Timer 17 outputs MPIJ1 every gate signal output period T8.
Generates an interrupt to 3. Therefore, in interrupt processing, first,
Input the phase θ and angular velocity command ω.

After this, the output voltage ratio KH corresponding to ω is stored in the ROM14C.
Tangle. Next, the output of the counter 11 is as shown in FIG.
represents a phase of 60° from Oo.

Therefore, as this count value all at Vs)(,0M1
4a switching mode conduction ratio δA and charge,
The flow time TA and 'l'A are calculated by a ten-nk microcomputer using equations (7) and (8). On the other hand, 60 shown in No. 51 Ne1
The switching mode at ° intervals is determined by using the upper 3 bits of the count value in Figure 8 as the relative address from 0M14b,
Set to output port 15.

Next, when TA and 'l'A+++ are set in the timer 17, the one shot pulse width shown in the time chart of FIG. 9 is output. Therefore, the output signal of the decoder 18 is used as the output port 3a! All gate signals of the same type are switched, and the PWM@ signal is created.

According to embodiments of the invention) IOM 1.1(a), (
The capacity by adding b) and (c) is less than the number of bytes, and
Since the PWM generation circuit can be constructed from only a one-chip microcomputer, a programmable timer, a decoder, and a three-state bumper, the control circuit is much cheaper than conventional circuits. Further, the conduction time in the switching mode is calculated by software processing of a microcomputer, and even if the number of voltage and phase dits increases, the control circuit ti remains the same and a highly accurate PWM signal can be output.

Next, as another example, when the sampling period Ts is constant, l1lB in equations (7) and (8) becomes a constant, so instead of the function of δ people and δA + B shown in FIG.
×δA and T s X a to 4n'k ROM 14
a VCf-j can shorten the software processing time shown in Figure 7, and as a result, T
It is possible to make st=200 μs. As a result, the switching frequency can be increased to about 5KH2, and the current ripple of the motor can be sufficiently reduced.

Furthermore, although this embodiment has been described using an asynchronous method in which switching is performed at a constant period T8, in the case of a synchronous method in which switching is performed at every fixed phase angle Δθ, the method described in this embodiment can be achieved by setting the time of Δθ to Ts. can be applied as is.

[Effects of the Invention] According to the present invention, since the PWM signal generation circuit portion can be constructed with a small number of parts and inexpensive elements, an inexpensive inverter control circuit can be provided.

In addition, the calculation of the conduction time in the switching mode can be performed with high accuracy and in a short time using software processing by the microcomputer, so the switching frequency can be made sufficiently large, and a more accurate PWM signal that becomes a sine wave current can be output. be able to.

[Brief explanation of drawings]

Fig. 1 is a diagram of an AC tortoise motor variable speed drive system to which the present invention is applied, Fig. 2 is an explanatory diagram of switching mode vectors, Fig. 3 is a conventional circuit configuration diagram, and Fig. 4 is a diagram to which the present invention is applied. FIG. 5 is an explanatory diagram of the inverter output voltage control of the present invention.
Fig. 6 is a circuit diagram showing one embodiment of the present invention, and Fig. 7 is a circuit diagram showing an embodiment of the present invention.
Microcomputer software processing flowchart shown in 1 Philosophy, No. 8
The figure shows the operation waveform of the counter shown in Figure 6.
3 is an operation time chart of the circuit shown in the figure. 2... Three-phase inverter, 3... Fat conductor motor, 13
...Counter, 14...Microgross? , 14
a. 14b, 14C...ROM, 15...Digital output board, 16...1 chip microcomputer, 17...Program timer, 18...Decoder, 19a, 19b
. 1,300 days (gaps are also 6 figures, house 1 figure is full, 8 figure names are q figures)

Claims (1)

[Claims] 1. In a PWM signal generation method for an inverter for fully variable speed of an AC motor, the 60° and 60° A ROM that stores the interval switching mode, a ROM that stores the inverter output voltage ratio KH according to the frequency command (JM), a microcomputer that calculates the conduction time of the switching mode, and a pulse width that corresponds to the conduction time. and a program timer for outputting, the flow time is calculated from the product of the laminar flow ratio, the output voltage ratio K1-1, and the output cycle Ts of the switching mode, and is set in the program timer, and the switching mode is controlled by the microcomputer. A PWM signal generation method for an inverter, characterized in that by setting the output port, a PWM signal is generated such that the locus of the line-to-line voltage composite vector of the inverter draws a circle. 2. Claim 1 In the above, the relationship between the conduction ratios δA and δA+B in the switching mode is δA=SInθ, δA+B''/TCO8θ
+sin θ)/2.