JPS5992774A - Pwm controlling method for inverter - Google Patents

Abstract

PURPOSE:To enhance the output of an inverter while suppressing the generation of low order harmonic wave by performing a sinusoidal PWM when a voltage reference value is low, and sequentially shifting from the sinusoidal PWM to a rectangular PWM when the voltage reference value is higher than the DC power source voltage. CONSTITUTION:The set voltage of the output frequency given by an output frequency setter 1 is converted by a V/F converter 2 into a frequency, which is then inputted to a microcomputer 100. A timing signal from the microcomputer 100 is applied to the microcomputer 101, which provides necessary data to output a PWM signal. The sinusoidal PWM is performed while the peak value of the AC output voltage is lower than the voltage of a DC power source, and gradually shifted to a rectangular PWM when the AC voltage of the peak value higher than the voltage of the DC power source is outputted.

Description

[Detailed Description of the Invention] [Technical Field of the Invention] The present invention provides an inverter PWM
yn) Z row control method, especially sine wave PWM
1] Control method (related to 2) in which the voltage range of the output voltage is expanded by sequentially partially shifting to rectangular wave PWM when the output voltage due to 12 is saturated.

[Technical background of the invention and its problems]

Generally, the PWM inverter shown in Figure 1 is often used for variable speed (pivotal) electric power, and the sine wave PWM method is used to reduce the special C low 111 wave. .

With the advancement of microcomputers (hereinafter referred to as microcomputers), the use of microcomputers in control circuits has progressed, and it has become possible to use microcomputers for PWM operation.

As one of the applications of microcontrollers to T'WM, the present inventor previously published a patent application No. 76635/1983 to develop a pulse generator that outputs a sinusoidal PWM voltage that does not contain low harmonics over a wide range of output frequencies. A width control method was proposed.

The outline is as follows.

As shown in Figure 2, three-phase sine wave cliff output city, pressure VU
In order to obtain V+VVW+VWU, each phase potential EU+EV+Ew with respect to the DC voltage neutral point is PWM controlled as shown.

That is, in the interval ■, the V-phase positive side transistor VPT is turned off and the negative side transistor VNT is turned on, so that EV=E, (as m- becomes, EU+Ew rises to EV j,
V1J+Iz7L (θ+30°)2 and υL:,
6-1θ] is controlled by f2 PWM so that it becomes 2, and one phase is fixed at 12 or −j − in sequential intervals ■ to ■, and the other two phases are 1:lJ-like in PW
M control is performed, thereby obtaining a three-note string wave output with a wave height of 11D-0.

FIG. 3 shows the circuit configuration for carrying out the above-mentioned pulse mid-section 1, in which the A microcomputer 100 and the B microcomputer 100
1 for example Intel 8048A and 804 respectively
1 can be used.

In FIG. 3C, the output frequency setter 1 is set to 54. The setting voltage of the output frequency f that can be maintained is 6×n in VF converter 2.
It is changed to the frequency of xPXf by 4Q and inputted to the A microcomputer 100, where it is divided into '/n to generate a modulation frequency of 6·P-f, that is, two interrupt timing signals are generated every 60 degrees of electrical angle. do.

On the other hand, the output of the frequency setter 1 provides a voltage reference signal a via a function generator 12.

When the A-th interrupt timing occurs, the A microcomputer jumps to the interrupt routine, and the s ('-'i)-th interrupt routine causes a total of 9. The data required for the B microcomputer to output the PWM signal is given at a timing such that the pulse is in the middle of the second pulse.

This data exchange takes place over the time Tr of one round of the modulation frequency.
Finish with half of n.

Therefore, the A microcomputer calculates the data to be given to the B microcomputer during the remaining half of the time (2) when the next re-entry timing is given.

After that, the OB microcontroller returns to the main routine, which waits for the next interrupt timing to be given and measures the time until the interrupt timing is determined. PWM according to the timing and data given from microcomputer 3 ('j is output, and the second half uses the data given in the first half again to create the timing on the B microcomputer itself.
WM (Outputs number s.

By sharing the functions between the two microcomputers A and B, there is enough time to perform calculations during the pulse.

Therefore, the fourth electrical angle θAl”l: (A-1) the city 5
It is obtained from the air angle θA-1 using the following (1) 2.

θA −θ rule + △θ −−−−
------- (1) On the other hand, the time between interrupt timings, that is, Δθ, is determined by mil as a count value Tffl in the main routine.

This measured value Tm, electrical angle θA and AD converter 1]
f5 from the voltage base Iφσ (-=-) given via
dr.

U-phase and w-phase pulses rl''rsl'r0 are calculated using the following equations (2) and (8).

”:a””L(θa+30°) ・Tm −−−−−
---(2) TO= (1-c, e, aθa
−Tm−−−−−−−(81 Therefore, the average voltage between Tl
−−−−−−−−−−−L41M j−1 α～・θa −−−−−−−−−−
-(5) 7M, and by kneading, sine wave PWM is performed. 1. The output voltage is approximated as a sine wave, and a is changed from zero to 1. C. 2. Therefore, the peak value V of the fundamental wave of the line voltage is changed from zero to DC voltage Ed, up to Sij! I can control it.

However, the peak value of the fundamental wave cannot be made higher than Ejc.

In other words, in Fig. 2 1-, the line voltage Vuvid period ■
At the end of (θA = 60°), it becomes maximum (j4.i v,
When voltage reference a = l, Tll, ? A=600-[1itn(θle+30°)・
Tm3e4=6oO=Tm---------
-----(61), and a constant AC pressure with wave position value Edc is obtained.

Therefore, the maximum value d' of the output voltage is determined by the DC voltage PQdc.

When the motor is operated with an inverter that rectifies the AC constant pressure and uses it as a DC power source as shown in Figure 1ζ2, the DC voltage Ed
changes depending on the load.

Excerpt: 1. For example, 3-phase 200v AC voltage flowing Jz x
A sine wave PWM inverter using 200v to 282v as a DC power source has a maximum output of 200V, ignoring the voltage drop of the elements.
It is possible to output an AC voltage of
Since the voltage drops to approximately 0V, the inverter output voltage actually decreases further due to the voltage drop within the inverter elements and the delay time required to keep the elements fired.

On the other hand, the rectangular wave PWM has a higher content of low-order harmonics than the sine wave PWM, but the fundamental wave voltage is higher and a three-phase AC voltage can be obtained.

[Purpose of the invention]

The present invention performs sine wave PWM while the peak value of the AC output voltage is lower than the 14 current power supply voltage, and ■i current fJ4.
: When outputting an AC voltage with a wave peak value higher than the source voltage, the inverter's PWM control gradually shifts to C2 square wave PWM, thereby expanding the output voltage range while suppressing the generation of lower harmonics. The purpose is to provide a method.

[Summary of the invention]

The present invention sets an output voltage reference α for the output frequency f and the maximum sine wave PWM output voltage, and controls the output frequency of the inverter at the set frequency f (2) and the modulation period for the maximum sine wave PWM output voltage. T during the pulse as a function of electrical angle θA, (θA) to a-T
p(θA) is calculated, and the smaller of a-Tp(θ4) calculated above and TI, l during the modulation period is set as pulse 1 in each variable EIt3 period, and the output 1b and pressure are controlled. This is an inverter PWM control force method in which when the sine wave PWM output voltage reaches the maximum value, the inverter's PWM control force method is sequentially converted into a rectangular wave PWM.

[Embodiments of the invention]

An embodiment of the present invention is shown in the flowchart of FIG.

The hardware lecture of the present invention is the same as shown in Fig. 3, and the present invention
Control during pulses in WM is performed using a sine wave PWM while the voltage reference a is smaller than 1, and when it becomes larger than 1, it is partially sequentially brought closer to a rectangular wave PWM l1.

Figure 5 shows W phase [T during two paired pulses. Two control Cs are shown, and similar control can be performed for other phases in accordance with their waveforms.

In FIG. 5, it is assumed that all the data necessary for pulse width calculation has been prepared in step (1), and step (2)
), calculate Tc' during the second sine wave pulse for each timing A using the following equation (7).

To': a-ceriθA-, Tm-
-------1--(7) However, the above T. ' is calculated without considering the actual pulse interval T, and when a>1, Q'C+6Jθa>1 may be obtained, so there is a dispute. '>'rm may occur.

However, the pulse width at the end of the day is the pulse interval T. The pulse r used for the actual 'I'tA cannot be made larger.
l] To it step +81-. (Determined in step 51 using the following equation (8).

T in the next 1st step (6). Output pulse 1j''
Then, in the second step (7), set 4 to A+1' and perform timing A +1 += Tweet same IN, and then sequentially perform pulse width control by C2.

FIG. 6 shows an example of the relationship between Ta';T41 and To.

This (2, therefore, a' cv, 6θA is 0 to 1''!, sine wave PWM is performed, and when %D6AθA exceeds 1, To is saturated and becomes constant 'i6.Tm, 11 stones from the center of the output waveform. The primary pulses are connected and gradually transition to a (-square wave).

When all the pulses are saturated, they become complete rectangular waves, and a π AC voltage with a peak value J times (approximately 1.1 times) the DC voltage Ed is generated.

In this case, the transition from sine wave to square wave is sequentially partial (1
Therefore, there is no shock unlike when directly switching the PWM mode from a sine wave to a rectangular wave f2.

In addition, the flowchart in FIG. 5 is shown in general (1) and (2), including other cases. Instead of 2θ ⋅T, it is sufficient to calculate in advance Tp (θA) during the pulse with respect to the electrical angle θ^ for each modulation period of the valley phase when the maximum sine wave output voltage of the sine wave PWM is generated.

〔Effect of the invention〕

As explained above, according to the present invention, when the voltage reference value is low, the sine wave PWM is performed, and when the voltage reference value is higher than the DC'g\TJW voltage, the lii-order sine wave pwy+ By shifting from to square wave PWM, it is possible to suppress or suppress the generation of low-order harmonics while also converting the counterflow output 1↓.
A PWM control method for an inverter is adopted.

[Brief explanation of the drawing]

Fig. 1 is a circuit diagram showing the general configuration of an inverter to which the present invention is applied, Fig. 2 is a 1i: positive waveform diagram of each phase in sine wave AWM-2, g1 x 3 Fig. PWM il]ll Grapes]
FIG. 4 is a block diagram showing the configuration of the circuit, FIG. 4 is a diagram showing the pulse It in FW'M control, and FIG.
1. Frequency setter 2. VF converter 11 A
D converter 12 Function generator 100 A microcomputer 101B microcomputer PS AC power supply REO
Rectifier UPT~WNT) Transistor ■ External power to induction 1 Fig. 1 Fig. 2 θ° θ° 6oI' 12o6
1aoj 2ao”
J (110″″ 3n6 Fig. 3 Fig. 4 Fig. 5 Fig. 6

Claims (1)

[Claims] An output voltage reference a is set with the output frequency f and the maximum sine wave PWM output voltage as 1, and the output frequency of the impark is controlled at the set frequency ft2, and the ti air angle θA
Pulse rl corresponding to]T, (OA) to a・Tp(O
A) is calculated, and the above calculated a-Tp (OA) and Shun =
PwMfI111η marked method for an inverter, characterized in that the output voltage is controlled by using the smaller of rr and Tm during one station period as the pulse width in each modulation period.