KR101789134B1

KR101789134B1 - Variable frequency modulation method for inverter

Info

Publication number: KR101789134B1
Application number: KR1020150136587A
Authority: KR
Inventors: 박성준; 황정구; 문정훈; 박성미
Original assignee: 전남대학교산학협력단
Priority date: 2015-09-25
Filing date: 2015-09-25
Publication date: 2017-10-31
Also published as: KR20170037746A

Abstract

More particularly, the present invention relates to a variable frequency modulation technique, in which the switching frequency is increased when the slope of the output voltage command value of the inverter is greater than a predetermined reference slope, And a variable frequency modulation technique capable of improving the efficiency of the inverter.

Description

[0001] The present invention relates to a variable frequency modulation method for an inverter,

More particularly, the present invention relates to a variable frequency modulation technique, in which the switching frequency when the slope of the output voltage command value of the inverter is smaller than the predetermined reference slope is made lower than the switching frequency when the slope is larger than the predetermined reference slope And a variable frequency modulation technique capable of improving the efficiency of the inverter by reducing the number of switching times.

Recently, the need for renewable energy is increasing due to depletion of fossil fuels and increase of carbon dioxide. Photovoltaic energy and wind energy account for most of renewable energy generation, and inverters are essential to convert this energy into electric energy, which is a necessary form.

Among the inverter modulation techniques, PWM technique has been studied as a key element of inverter for the past several years. The characteristics and performance of the inverter vary with the selection of these various PWM schemes.

1 is a view showing a conventional single-phase inverter. 1, a conventional single-phase inverter includes a switching unit 12 for converting an input power source 11 into an AC, and a filter unit 13 for smoothing the power output from the switching unit and supplying the power to a load do.

Generally, pulse width modulation (PWM) is used for single-phase inverter control. This pulse width modulation technique is a typical technique for improving the THD (total harmonic distortion) performance of the load current in the grid connection to be.

Basically, the pulse width modulation technique uses a sine wave comparison method, compares the output voltage of the setpoint with the triangular wave, and turns on / off each phase switch of the inverter according to the magnitude of the magnitude.

Here, the triangular wave refers to a reference signal generated in the switching controller. Unlike the optimum voltage modulation technique, the triangular wave is controlled in a unit of sampling time, and thus the dynamic characteristic is excellent.

On the other hand, the conventional modulation techniques can improve the THD performance, but increase the number of switching times of the switching unit 12, which results in an increase in switching loss and a decrease in efficiency.

It is an object of the present invention to provide a variable frequency modulation technique capable of reducing the switching loss and improving the efficiency of the inverter by reducing the number of switching times.

The objects of the present invention are not limited to the above-mentioned objects, and other objects not mentioned can be clearly understood by those skilled in the art from the following description.

According to an aspect of the present invention, there is provided a variable frequency modulation method for varying a switching frequency of an inverter and outputting an output voltage command value, the method comprising: dividing the switching frequency into at least two switching periods according to a magnitude of the output voltage command value; And outputting the output voltage command value by varying the switching frequency of the switching sections.

In a preferred embodiment of the present invention, the output voltage command value is output by making the switching frequency of the larger interval of the output voltage command value smaller than the switching frequency of the smaller interval of the output voltage command value.

In a preferred embodiment, the step of discriminating the switching periods comprises: setting a reference slope, which is a value obtained by dividing a peak value of the output voltage instruction value by a predetermined period value; And dividing an interval in which the tangential slope of the output voltage command value is larger than the reference slope and a smaller interval into the switching intervals.

In a preferred embodiment, the reference slope may be a value obtained by dividing the peak value by a quarter cycle.

The present invention further provides a computer program stored in a medium for executing the variable frequency modulation technique in combination with a switching controller of an inverter.

The present invention further provides an inverter controlled by a variable frequency modulation technique by a switching controller provided with the computer program.

The present invention has the following excellent effects.

According to the variable frequency modulation technique of the present invention, the switching frequency is decreased in a section where the output voltage command value is relatively larger, the switching frequency is increased in a section where the output voltage command value is relatively smaller, It is possible to remarkably reduce the power conversion efficiency of the inverter.

1 is a view for explaining a general inverter,
2 is a diagram for explaining a variable frequency modulation technique according to an embodiment of the present invention;
FIG. 3 is a diagram showing a waveform simulating a THD performance of a variable frequency modulation technique according to an embodiment of the present invention. Referring to FIG.

Although the terms used in the present invention have been selected as general terms that are widely used at present, there are some terms selected arbitrarily by the applicant in a specific case. In this case, the meaning described or used in the detailed description part of the invention The meaning must be grasped.

Hereinafter, the technical structure of the present invention will be described in detail with reference to preferred embodiments shown in the accompanying drawings.

However, the present invention is not limited to the embodiments described herein but may be embodied in other forms. Like reference numerals designate like elements throughout the specification.

The variable frequency modulation technique according to an embodiment of the present invention controls the switching operation of the inverter 10 to output an output voltage of a desired command value (hereinafter referred to as an 'output voltage command value').

In addition, the variable frequency modulation technique of the present invention is substantially performed by a switching controller (not shown) for controlling the switching operation of the switching unit 12. [

In addition, a computer program for performing the variable frequency modulation technique is installed in the switching controller.

The switching controller also refers to a wide range of computing devices, including general computers, microcontrollers, embedded devices, smart devices, and the like.

In addition, the switching controller may be provided separately from the inverter 10, and may be included in the inverter 10 and provided as one inverter system.

In addition, the computer program may be separately stored in a recording medium, and the recording medium may be designed and configured specifically for the present invention or may be known and used by those having ordinary skill in the computer software, Examples of the optical recording medium include a magnetic medium such as a hard disk, a floppy disk and a magnetic tape, an optical recording medium such as a CD and a DVD, a magnetic-optical recording medium capable of combining magnetic and optical recording, a ROM, Lt; RTI ID = 0.0 > and / or < / RTI >

In addition, the computer program may be a program consisting of program commands, local data files, local data structures, etc., alone or in combination, and may be executed by a computer using an interpreter or the like as well as machine code Can be a program woven with high-level language code

Hereinafter, a variable frequency modulation technique according to an embodiment of the present invention will be described in detail.

First, a variable frequency modulation technique according to an embodiment of the present invention distinguishes at least two switching periods according to the magnitude of the output voltage command value.

Referring to FIG. 2, the output voltage command value Vref is a sinusoidal waveform of period T and a peak value is Vp.

In addition, the switching sections are sections for varying the switching frequency, and set a reference slope, which is a value obtained by dividing the peak value Vp of the output voltage command value Vref by a predetermined period value.

In the present invention, the predetermined period value is set to T / 4, but it can be appropriately selected by the designer.

That is, the reference slope is a value obtained by dividing the peak value Vp by 1/4 period (

).

Next, based on the reference slope, the tangent slope of the output voltage instruction value (Vref)

(B,

), A section with small tangent slope (a,

), And the intervals a and b are referred to as a switching interval because they are intervals for different switching frequencies.

In other words, the switching period is a switching period a (hereinafter referred to as a 'second switching period') having a slope with a large slope around the reference slope (hereinafter referred to as a 'first switching period' .

In FIG. 2, the reference slope is set to one reference slope. However, the designer can set the reference slope to a plurality of reference slopes, and the plurality of switching intervals divided into the reference slopes are switched do.

Next, the switching frequencies of the switching sections a and b are different from each other to output the output voltage command value Vref.

In addition, the switching frequency of the first switching section (b) is greater than the switching frequency of the second switching section (a) among the switching sections to output the output voltage command value (Vref).

For example, the switching frequency of the first switching period (b) is set to be equal to the conventional switching frequency, and the switching frequency of the second switching period (a) is set to be higher than the switching frequency of the second switching period The number of switching times can be reduced.

If the reference slope is set to a plurality, the switching frequency is divided into three or more switching periods. In this case, the switching frequency is set to be lower as the slope is larger (the output voltage command value is larger).

In other words, the switching frequency is set to be gradually lowered to the switching period in which the slope is the smallest in the switching period in which the slope is greatest.

However, in this case, since the number of switching times increases and the switching loss increases as compared with switching by dividing into two switching sections, the number of switching sections and the switching loss are in a trade-off relationship with each other.

FIG. 3 is a simulation result of a simulation of a performance of a variable frequency modulation technique according to an embodiment of the present invention.

FIG. 3 (a) shows an inverter output voltage controlled by a conventional PWM modulation technique, FIG. 3 (b) shows an inverter output voltage controlled by the variable frequency modulation technique of the present invention, (D) is a waveform showing the switching periods divided by the reference slope.

Also, the switching frequency of the conventional PWM modulation scheme is set to 20 [kHz], and the switching frequency of the first switching period b is set to 20 [kHz] 2 The switching frequency (low switching frequency) of the switching section (a) is set to 15 [kHz].

The input voltage was set to 100 [V] and the load was set to 50 [OMEGA].

As a result of simulation, the THD of the variable frequency modulation technique according to an embodiment of the present invention is about 0.18% higher than that of the conventional PWM modulation technique, and the THD characteristic is slightly decreased, but the switching frequency is reduced by about 12.5% or more.

That is, although the THD characteristics are substantially similar, the number of switching times can be greatly reduced, so that the power conversion efficiency can be remarkably increased and the lifetime of the switching device can be prolonged.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, Various changes and modifications will be possible.

10: Inverter 11: Input power
12: switching section 13: filter section

Claims

delete

This is a variable frequency modulation technique that changes the switching frequency of the inverter and outputs the output voltage command value.
A value obtained by dividing the peak value V _p of the output voltage command value V _ref by 1/4 cycle

); &Lt; / RTI >
The slope of the output voltage command value (

, The tangential slope of the output voltage command value), and when the slope calculated by comparing the calculated slope with the reference slope is smaller than the reference slope (

) Is calculated when the calculated slope is greater than the reference slope (

), The number of switching times can be reduced.

A computer program stored in a medium for implementing the variable frequency modulation technique of claim 4 in combination with a switching controller of an inverter.

An inverter in which the computer program of claim 5 is controlled by a variable frequency modulation technique by a switching controller.