JPH01321866A - Control of pwm waveform of inverter - Google Patents

Abstract

PURPOSE:To shorten a processing time by employing a resistor, used for timer interruption, as an auxiliary resistor. CONSTITUTION:An inverter 17 is constituted of a DC power source 10 and semiconductor elements 11-16 to drive an induction motor 18. The inverter 17 is provided with an one-tip CPU 19 consisting of an A/D converter 22, a plurality of timers 23, a ROM 24, a RAM 25, a microprocessor 26 and the like. A PWM control waveform is outputted by timer interruption utilizing the one-tip CPU 19 and when a resistor, used for the timer interruption of PWM waveform output control, is used as an auxiliary resistor and a main resistor is switched to the auxiliary resistor upon interruption to effect the transfer of data for a timer processing the pulse width of the PWM output and the setting of starting, the auxiliary resistor is employed without passing the data through the RAM 25 thereby transferring the data and setting the starting. As a result, a processing time may be shortened and PWM control reduced in errors may be effected.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a PWM waveform control method for an inverter used for variable speed of a three-phase induction motor.

PRIOR ART As a conventional method for controlling the P'WM waveform of an inverter, there is a structure shown in FIG.

This configuration inputs the output frequency setting manually to the A/D converter 2, applies the output of the A/D converter 2 to the microprocessor 3, draws out the data of the pwV waveform pattern stored in the ROM 4, and then Apply the pwu waveform data obtained through the arithmetic processing in step 3 to the program timer 6,
3 phase from program timer 6')"H+ v+ *"
r * Ut g “t l ”! ') PW'' output is created and applied to the pace of transistors Tr and Tr6 of the inverter, but the PWM waveform in this case drops from H level to L level at regular intervals as shown in figure #c2. Therefore, the transistors Tr, , TI"s, Trs in the + arm of the inverter or the transistors Trt, TI4. in the - arm of the inverter. Trg is O at the same time
This resulted in problems with output current vibration and harmonic components. In order to solve this, this P
To create a WM waveform, use T7 as shown in ■ in Figure 4.
There is one that calculates pulses a and b every two cycles using a microprocessor 3, outputs them using a program timer 6 to obtain the waveform shown in ■, and synthesizes the PWM waveform using a flip-flop 8 as shown in Figure 4 ■. . This method uses 1 of a constant period T.
7. Output pulses with different widths every /2 intervals. Since the synthesis is performed by the flip-flop 8, the flip-flop circuit is required externally, and the printed circuit board for the control circuit is thick (which has the disadvantage of increasing costs).

Problems to be Solved by the Invention In order to improve the PWM output of the conventionally implemented configuration shown in FIG.
There is a method that uses a chip cpσ to control the PWM output, and this method has the advantage that the circuit configuration is simplified without requiring an external circuit for synthesizing the 2wM output for three phases.

As an example of PWM output control using 1-chip cpσ, we will explain a program using the type TMP900840 manufactured by Toshiba Corporation.Since the TMP900840 is equipped with an 8-bit interrupt timer and an 8-bit PWM output, the interrupt timer ( By performing interrupt processing at regular intervals using timer 0) and controlling the pvrM output mode (timer 1), it is possible to output a PWM waveform centered at c T / z every cycle T shown in FIG. 5. ■Pattern in Figure 5 is A
, mB.

In the case of , the ■ pattern is the waveform for a horse, and the pure vibration frequency at this time is IQ M H! ? If '@include same period le large - 204Ps, then if 4 interrupts are applied to one period of PWM output, the period of PWM output is T - 204X4:81
PWM with 6 units S and carrier frequency of approximately 1225HM
I get the output.

The timer interrupt processing program for obtaining a PWM output will be explained based on chart 70 in FIG. 6. In step @, the register is saved, in step [phase], timer 1 is stopped, and in step O, P? Data of rM period is set in the register of timer 1, and timer 1 is started at step [phase] or left in the stopped state. Assuming that the interrupt processing counter repeatedly counts TllTl+Tt*T3 as shown in FIG. 5, it is determined in step (2) whether the current interrupt counter is T, or 5.

PWM of T, %/'r3 in step O for T6
The output cover turns are collectively calculated and stored on the RAM, and in step [phase] PWM output data is set on the RAM based on the PWM output cover turns. At this time, assuming that the PfM output is 8 bits and has 256 types of patterns, 256 x 4 = 10
This can be easily processed by preparing a 24-byte table and comparing the table address with the pattern. As shown in the example table of FIG.

In the case of the @ pattern in Figure 5, from address A to address A+3 K O
+ AI - BI + Blt Prepare a table in which data is set, and if it is a pattern, start from address B ~
.

8L o, o, 131--4 A table is prepared, and in step [phase], the register saved in step [phase] is restored, and the interrupt processing is ended.

Next, after the interrupt processing is accepted by the interrupt timer (timer O), the processing program of TMP90 (!840 is explained using the 70-chart in FIG. The interrupt processing start address V of the interrupt accepted in step [phase] is moved to the program counter, and the interrupt is escaped in step O. Jump to the physical program.

In step O, the process returns after processing step [phase].

The processing time from when an interrupt is accepted until one interrupt processing program counter is counted is 4 pS. Figure 9 shows the relationship between the interrupt processing by the timer and the processing program in Figure 6 when outputting the PWM waveform in Figure 5 ■, and jumps to the interrupt processing program at a, 4 pB after the timer interrupt. Then, when register saving ■, timer stop ■, and timer 1 data transfer ■ in Fig. 6 are performed, and timer l start setting O is performed at point b, the output becomes L at point 0 after a time period based on data A at this time. Move from level to H level.

Figure 1O shows the case where the datum is large, and this time is al-
If the timer output is longer than the timer output, the timer is stopped at step A before the timer output moves from the L level to the H level, so it remains at the L level and does not shift to the E level, resulting in a waveform disturbance. Therefore, for data A, the time of a, -b becomes maximum, and a, -a, that is, T11-T, becomes shorter than the time t in Fig. 5, causing an error in the PIFM waveform, which causes a jump to the interrupt processing. This problem arises because of the processing time from when the timer is stopped to when the timer is started again.

Means for Solving the Problems In view of the above content Kfi, the present invention saves the timer interrupt processing owner register by making the register used for the timer interrupt an auxiliary register in the timer interrupt processing of PWM output. By switching between the main register and the auxiliary register, interrupt processing can be performed and the processing time can be shortened.

10 is a DC power supply, 11 to 16 are six semiconductor elements that constitute an inverter ■, 1B is an AC induction motor, ■
is the chip OPσ, 20, which controls the inverter F by PWM.
is an output frequency setting input and is applied to the input interface 21', 22 is an A/D converter, 23 is a plurality of timers for interrupts and PWM pulse width settings, and 24 is a ROM that stores program data and pulse width data. , 25 is a RAM for storing data, and 26 is a data 'OJ1. The arithmetic processing is performed by the child processing microprocessor, and 27 outputs the PWM IIJ output to the inverter (2) through the output/Turf Ace.

Next, regarding the processing method for obtaining PWM output according to the present invention @
Explaining based on the flowchart in FIG. 12, in step (2), the main register and the auxiliary register are switched, and the auxiliary register is used for the subsequent registers. At step O, timer l is stopped, and at step O, the data of timer 1 is set in the B register and transferred to the timer 1 register.
The state of timer 1 is set based on the start or stop setting of timer 1 set in the C register. Step 7 [
phase], O is the same process as steps ■ and ■ in Fig. 6, in which the data calculated in step @ is transferred to the auxiliary register B', the condition for starting or stopping the timer is transferred to the C register, and step At O, the main register and auxiliary register are switched and the 1st interrupt processing is finished. In this case, the time from jumping to interrupt processing at 5 to setting timer 1 data is as shown in tR13.
The conventional process shown in FIG. 6 requires 11.2 pEl, and the process shown in FIG. 12 according to the present invention requires 3.6 pEl, which is a reduction of 7.6 PS. The theoretical maximum value of timer 1 data is 204pF3, then 7.6/204X 100
== 3.7% of the data can be brought closer to the theoretical value, and a PWM waveform with fewer errors can be output.

Effects of the Invention The present invention aims to shorten the data processing time by effectively utilizing the registers used for PWM data processing in a device that uses a 1-chip CPU to output a PWM control waveform by a timer interrupt. There is an effect like.

(1) When setting the register used for the interrupt timer for PWM waveform output control as an auxiliary register, switching the main register to the auxiliary register at the time of one interrupt, and performing data transfer and activation settings for the timer that processes the pulse width of the PWM output. Since data transfer and startup settings are performed using an auxiliary register without passing the data through the RAM that temporarily stores it, processing time is shortened and PWM control with fewer errors is possible.

(2) Performs interrupt processing at regular intervals, and generates a PWM waveform in which the center of the cycle is the center of the pulse with a cycle that is an even multiple of the 9-interrupt processing time without the need for an external circuit. It is possible to construct an inverter with a simple and inexpensive 9-circuit configuration since it can be created using only the functions of T.

[Brief explanation of the drawing]

The figure shows an embodiment of the PWM waveform control method for an inverter according to the present invention, and FIGS. 1 to 10 show a conventional example. 6 is a PWM waveform diagram output from the control circuit 8, FIG. Figure 5 is a PWM output waveform diagram by a 1-chip CPU, Figure 6 is a flow chart of PWM output control by a 1-chip CPU, Figure 7 is a table example of a pw-t-output pattern, and Figure 8 is an interrupt processing diagram. Flow chart diagram No. 9
Figure 10 is a PfM waveform diagram for explaining the problem,
11 to 13 are diagrams showing the PWM waveform control method of the present invention. FIG. 11 is a block diagram showing the PWM output waveform control of the inverter, FIG. 12 is a flowchart of the PWM output, and FIG. 12 is a diagram comparing the processing time from jumping to the input processing until setting the data of timer 1. FIG. 2 is an inverter, 19 is a 1-chip CPU, 21 is an input interface, 23 is a timer, 26 is a microprocessor, and 27 is an output interface.

Claims (1)

[Claims] 1. A 1-chip CPU consisting of a memory circuit, a timer function, an input/output interface, and a microprocessor, and one of the timer functions of the 1-chip CPU performs PWM at regular intervals.
an interrupt processing means for setting the output mode of the output waveform; a means for making all the registers used for the interrupt processing auxiliary registers and switching from the main register at the time of an interrupt; A PWM waveform control method for an inverter in which the center of the cycle is the center of the PWM waveform pulse width.