CN112072663B - Harmonic control method based on wavelet pulse width modulation and application - Google Patents

Harmonic control method based on wavelet pulse width modulation and application Download PDF

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CN112072663B
CN112072663B CN202010945847.2A CN202010945847A CN112072663B CN 112072663 B CN112072663 B CN 112072663B CN 202010945847 A CN202010945847 A CN 202010945847A CN 112072663 B CN112072663 B CN 112072663B
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modulation
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wavelet
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CN112072663A (en
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张慧
葛远喆
何怡刚
谢杰
徐磊
周锦涛
李其真
王安阳
周执昕
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Wuhan University WHU
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/084—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters using a control circuit common to several phases of a multi-phase system
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M1/00—Details of apparatus for conversion
    • H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
    • H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

The invention discloses a harmonic control method based on wavelet pulse width modulation, which can control single or multiple specific low-frequency harmonics and compensate or inhibit the low-frequency harmonics which are difficult to control in an electric power system. The method comprises the steps of carrying out non-uniform sampling on a limited number of modulated waves obtained by superposing fundamental waves and specific low-frequency harmonic waves, realizing reconstruction of modulated waveforms on the premise of meeting practical engineering application, namely calculating a scale factor according to the midpoint moment amplitude of a modulation function sampling interval, linearly amplifying the total area of all pulse sequences according to an impulse equivalence principle to enable the total area of all pulse sequences to be equal to the area of a modulation function in a fundamental wave period, and realizing control of the amplitude and the phase of the specific harmonic waves. The high-power grid-connected inverter can be used for controlling low-frequency specific harmonic waves needing compensation in a new energy power grid, the switching angle of the inverter can be calculated on line, and the method has the advantages of low switching frequency, low power loss, simple control algorithm, high direct-current voltage utilization rate, high modulation efficiency and the like.

Description

Harmonic control method based on wavelet pulse width modulation and application
Technical Field
The invention belongs to the field of harmonic detection and suppression of power systems, and particularly relates to a harmonic control method based on wavelet pulse width modulation and application thereof.
Background
With the development of industrial technology, more and more power electronic devices and new energy grid-connected systems, especially some nonlinear devices, are widely used. The productivity is greatly improved, the harmonic waves in the power grid are increased day by day, and the harmonic pollution is serious day by day. Therefore, modeling analysis on various harmonic sources is urgently needed, harmonic waves in a power grid are detected, and corresponding technical countermeasures for harmonic suppression are provided.
At present, the suppression of harmonic waves in an electric power system is mainly to detect the harmonic waves in the electric power system by using a proper harmonic wave detection method and then reduce the harmonic waves in the electric power system to a reasonable level by using an active filter or a reactive power compensation device through a certain control strategy. The related harmonic current compensation control can be summarized into two types: non-selective harmonic compensation and selective harmonic compensation. The former means that harmonic compensation instructions of the current controller come from residual harmonics and inter-harmonics which extract fundamental wave parts, and the latter means that selective harmonic compensation is respectively realized by detecting specific harmonics, so that the specific harmonics can be accurately controlled, low-order harmonics which are most harmful are pertinently treated, and the power quality can be better improved. The prior scholars propose that the inverter unit is used as a direct regulation unit for harmonic suppression, related selective harmonics are compensated in an amplitude modulation and phase modulation mode, and a good suppression effect is achieved.
At present, the PWM control techniques can be mainly classified into four major categories, i.e., carrier modulation PWM techniques, specific harmonic cancellation PWM techniques, space vector PWM techniques, and random PWM techniques. In recent years, canadian scholars.a.saleh actively explores in the aspect of wavelet PWM modulation technology for improving the modulation degree of fundamental wave voltage output by an inverter, namely, the control strategy based on non-binary discrete wavelet resolution analysis is used for realizing control signals of inverter switches, and the method has the advantages of simpler realization of a digital algorithm, higher voltage utilization rate of the inverter and smaller Total Harmonic Distortion (THD), but unfortunately, the existing wavelet PWM method does not consider the control of voltage harmonic information.
Disclosure of Invention
Aiming at the defects or improvement requirements of the prior art, the invention provides a harmonic control method based on wavelet pulse width modulation and application thereof, aiming at directly controlling specific harmonic in an electric power system, improving the stability of the electric power system and ensuring the safe operation of the electric power system.
To achieve the above object, according to one aspect of the present invention, there is provided a harmonic control method based on wavelet pulse width modulation, comprising:
(1) selecting a specific harmonic wave to be controlled as a modulation waveform to obtain the amplitude and phase information of the specific harmonic wave to be controlled;
(2) selecting a proper maximum sampling group number D, generating a series of equal-interval sampling moments according to the maximum sampling group number, calculating a Haar wavelet scale factor at each sampling moment according to the amplitude of a specific harmonic to be controlled at the current moment, and generating a series of wavelet pulse sequences with the same amplitude and different widths in a total period according to the values of the wavelet scale factor and the modulation degree;
(3) calculating the total area of the generated wavelet pulse sequence, obtaining a proportionality coefficient K according to the area of the specific harmonic wave to be controlled in a fundamental wave period, and expanding the width of each wavelet pulse by K times in an equal proportion;
(4) and driving the inverter switch by using the expanded wavelet pulse sequence to enable the inverter to generate required specific harmonic waves.
In some alternative embodiments, the specific method of step (2) is as follows:
(2.1) for the selected specific harmonic, converting it into a corresponding modulation value M according to its amplitudek，MkExpressing the modulation degree of the k-th harmonic wave, selecting the maximum sampling group number D required by modulation, and performing the modulation in a period time TmInternally generating D equal-interval sampling time tmidWherein, in the step (A),
Figure GDA0003322904560000021
d＝0,1,2,…,D-1；
(2.2) defining a modulation harmonic function y ═ f (t) according to the specific harmonic selected in the step (1), and enabling the modulation harmonic function y ═ f (t) to be ordered
Figure GDA0003322904560000031
Wherein A iskFor modulating the amplitude of each harmonic component in the wave, ω is the fundamental angular frequency, θkRepresenting the initial phase angle of the kth harmonic, n representing the number of harmonic components, each sampling instant tmidWhere a Haar wavelet scale factor j ═ f (t) is definedmid)|；
(2.3) at each sampling instant tmidSequentially generating a height of 1 and a width of
Figure GDA0003322904560000032
Is detected.
In some alternative embodiments, TmUsually taking the fundamental period, i.e. Tm＝0.02。
In some alternative embodiments, the specific method of step (3) is as follows:
(3.1) calculating the total area S of the D wavelet pulses generated in the step (2)1；
(3.2) calculating the harmonic function y ═ f (T) at a cycle time TmTotal area S enclosed by inner and time axes2Wherein, in the step (A),
Figure GDA0003322904560000033
(3.3) defining a modulation scale factor K ═ S2/S1In aEach sampling instant tmidAre sequentially regenerated to have a height of 1 and a width of
Figure GDA0003322904560000034
Is detected.
According to another aspect of the present invention, there is provided a harmonic control method based on wavelet pulse width modulation according to any one of the above methods, applied to any one of the following methods:
(1) the harmonic control method based on the wavelet pulse width modulation is adopted to control an inverter to generate fundamental waves;
(2) the harmonic control method based on wavelet pulse width modulation is adopted to control the inverter to generate a specific harmonic wave or a mixed wave formed by overlapping a plurality of subharmonics with any amplitude and phase.
According to another aspect of the invention, a computer-readable storage medium is provided, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of any of the above.
In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:
the harmonic control method based on wavelet pulse width modulation provided by the invention can realize direct control on certain harmonic waves which are difficult to control in an electric power system; the harmonic waves with specific amplitude and phase positions can be independently generated, the specific harmonic waves in the power grid are compensated through the series operation mode of the active power filter, a mixed wave with a plurality of harmonic waves superposed can be generated, for example, the fundamental waves are superposed with the low-order harmonic waves with certain amplitude values, and the accurate compensation of the power grid harmonic waves is realized through the parallel operation mode of the active power filter. The existing inverter wavelet modulation method controls the amplitude of the output voltage by controlling the modulation degree of the inverter, but cannot realize the precise control of the phase, and has larger amplitude control error under the condition of low modulation degree. Compared with the space vector PWM technology, the method has the advantages that the switching frequency is obviously lower, and the loss of the inverter switch is effectively reduced; compared with a specific harmonic elimination PWM technology, the method has the advantages of small calculated amount, more controllable low-order harmonics and the like; the method of the present invention can also be used to modulate fundamental, which has a lower total harmonic distortion rate compared to carrier PWM techniques.
Drawings
Fig. 1 is a schematic diagram of an inverter topology adopted in an embodiment of the present invention, where fig. 1(a) is a single-phase inverter and fig. 1(b) is a three-phase inverter;
fig. 2(a) is a wavelet pulse waveform diagram generated in one period when the maximum number of sampling groups D is 10 and the corresponding switching angle α1～α5；
Fig. 2(b) shows an inverter switching angle α when the maximum number of sampling groups D is 10 according to an embodiment of the present invention1～α5A three-dimensional graph related to the input fundamental wave modulation degree and phase change relation;
fig. 3 is an illustration of a wavelet pulse generation principle when the maximum number of sample groups D is 10 according to an embodiment of the present invention, where the modulation wave y is 0.8sin (ω t);
fig. 4 is a schematic flow chart of wavelet pulse width modulation adopted in the embodiment of the present invention;
FIG. 5 shows an input fundamental modulation M according to an embodiment of the present invention1In the interval [0,0.9]Each subharmonic modulation degree change diagram output by the inverter during internal change has the resolution of 0.05;
FIG. 6 shows an input seventh harmonic modulation degree M according to an embodiment of the present invention7In the interval [0,0.9]Each subharmonic modulation degree change diagram output by the inverter during internal change has the resolution of 0.05;
FIG. 7 shows an input fundamental modulation M according to an embodiment of the present invention10.8, fifth harmonic modulation degree M5Controlling the phase of the input fifth harmonic in the interval [0 DEG, 355 DEG ] to be 0.16]When the voltage is internally changed, the modulation degree change diagram of each subharmonic output by the inverter is 5 degrees;
FIG. 8 shows an input fundamental modulation M according to an embodiment of the present invention10.7, seventh harmonic modulation degree M7Controlling the input seventh harmonic phase at interval [0 deg. ° 355 deg. °]When the voltage is internally changed, the modulation degree change diagram of each subharmonic output by the inverter is 5 degrees;
FIG. 9 shows an input fundamental modulation M according to an embodiment of the present invention10.7, seventh harmonic modulation degree M7Controlling the input seventh harmonic phase to gradually increase from 0 degrees to 350 degrees, collecting the seventh harmonic phase output by the inverter once by taking 10 degrees as an increment unit, and obtaining 36 phase sampling points and an inverter theoretical output phase curve graph;
fig. 10 shows a maximum number of sample groups D equal to 10, and an input fundamental modulation degree M according to an embodiment of the present invention1When the phase is 0.05, controlling the phase of the input fundamental wave to gradually increase from 0 degrees to 350 degrees, acquiring the phase of the fundamental wave output by the inverter once by taking 10 degrees as an increment unit, and obtaining 36 phase sampling points and an inverter theoretical output phase curve graph;
fig. 11 is a graph showing the variation of the phase deviation value of the fundamental wave output from the inverter with respect to the modulation degree and the input phase of the fundamental wave, when the maximum number of sampling sets D is 20 according to the embodiment of the present invention;
FIG. 12 shows an input fifth harmonic modulation degree M according to an embodiment of the present invention5When the input fundamental wave modulation degree M is 0.05, the input fundamental wave modulation degree M is selected1Gradually increasing from 0 to 0.9, and obtaining a modulation degree change relation diagram of fundamental waves and fifth harmonics output by the inverter, wherein the resolution is 0.05;
FIG. 13 is a schematic diagram of a series harmonic voltage compensator for specific harmonic control of a three-phase AC power grid with superimposed harmonic voltage sources according to an embodiment of the present invention;
fig. 14 is a three-phase grid phase current waveform diagram (fig. 14 (a)) containing a certain amount of fifth harmonics and a frequency spectrum diagram (fig. 14 (b)) obtained after FFT analysis thereof according to an embodiment of the present invention, where a three-phase grid phase voltage is 220V, a fifth harmonic voltage source is three-phase symmetric, a fifth harmonic voltage amplitude is 34.3V, an a-phase is 270 °, a grid-side inductance-blocking load parameter R is 1 Ω, and L is 0.37mH, and a star connection method is adopted;
FIG. 15 is a three-phase grid phase current waveform (FIG. 15 (a)) obtained by series compensation of the grid using the method of the present invention to generate specific fifth harmonics and a frequency spectrum (FIG. 15 (b)) obtained by FFT analysis thereof, wherein the three-phase grid parameters are the same as those in FIG. 13, and DC side voltage U is showndDriving an IGBT switch by using a wavelet pulse with D-18, and modulating a harmonic function to y-sin (5 ω t); the filtering mode is RLC filtering, wherein the parameter L is 0.75mH, the parameter C is 0.54mF, and the parameter R is 1.18 omega;
if no special description is given, the following exemplary descriptions in fig. 5 to 12 all use single-phase inverters, and the inverter links the dc voltage Ud100V, and the maximum number of sampling groups D is 30.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
The invention provides a harmonic control method based on wavelet pulse width modulation, as shown in fig. 4, comprising the following steps:
(1) selecting a specific harmonic wave to be controlled to obtain the amplitude and phase information of the specific harmonic wave to be controlled;
in the embodiment of the present invention, step (1) may be implemented by:
selecting certain specific harmonics with higher content or difficult control in the power grid, obtaining amplitude and phase information of the harmonics by using a harmonic detection method, if the selected and controlled harmonics are seventh harmonics, extracting the seventh harmonics on the grid side by using a proper band-pass filter, and calculating the amplitude U of the harmonics by Sliding Discrete Fourier Transform (SDFT)kAnd phase angle thetakWherein the subscript k denotes the order of the harmonics, e.g. MkDenotes the k-th timeDegree of modulation of harmonic wave, thetakDenotes the initial phase angle of the k-th harmonic, as follows.
In order to facilitate comparison with other PWM methods, such as SVPWM and other modulation efficiency, the reference voltage quantity is defined as the maximum fundamental wave quantity 4U of the square wave pulse width modulation methoddVoltage modulation M of/pi, and thus k-th harmonickDefined by formula (1):
Figure GDA0003322904560000071
wherein, UdThe value of the DC side voltage of the inverter is shown.
The amplitude of the modulated wave is numerically equal to 4/times the modulation degree of the corresponding harmonic wave, i.e.:
Figure GDA0003322904560000072
(2) selecting a proper maximum sampling group number D, generating a series of equal-interval sampling moments according to the value D, calculating a Haar wavelet scale factor j according to the amplitude of the harmonic wave at the current moment at each sampling moment, and generating a series of wavelet pulse sequences with the same amplitude and different widths in the total period according to the value of j;
in the embodiment of the invention, the specific method of the step (2) is as follows:
(2.1) using the selected maximum number of sample groups D, during a cycle time TmInternally generating D equal-interval sampling time tmid：
Figure GDA0003322904560000073
Wherein D is 0,1,2, …, D-1. Defining the generated D sampling time points as
Figure GDA0003322904560000076
＝1,2,…,D。
And (2.2) according to the specific harmonic wave selected in the step (1), enabling the selected specific harmonic wave to be a modulation wave. Defining a harmonic function y ═ f (t):
Figure GDA0003322904560000074
wherein A iskFor modulating the amplitude of each harmonic component in the wave, ω is the fundamental angular frequency, e.g. 100 π, θkDenotes the initial phase angle of the k-th harmonic, and n denotes the number of harmonic components.
If only the fundamental wave and the seventh harmonic wave need to be controlled, let AkWhen 0(k ≠ 1,7), the modulation wave function is:
f(t)＝A1sin(ωt+θ1)+A7sin(7ωt+θ7) (5)
at the sampling time
Figure GDA0003322904560000075
Defining a Haar wavelet scale factor ji：
Figure GDA0003322904560000081
Wherein i ═ 1,2, …, D; as shown by reference numeral 301 in fig. 3, the maximum number of sample groups is defined as 10, and the input modulated wave is one akA fundamental wave of 0.8, 10 sampling instants t are generated within one periodmid. At each t in turnmidAnd sampling the modulation wave, wherein the height of the sampling pulse is the amplitude of the modulation wave at the sampling point, namely the value of the scale factor j at the sampling point.
(2.3) at each sampling instant tmidSequentially generating a wavelet pulse according to the value of j at each sampling time, and defining the width w of the ith wavelet pulseiComprises the following steps:
Figure GDA0003322904560000082
wherein i is 1,2, …, D.
(3) According to the principle that the pulse impulse is equal in effect, in order to enable PWM wave energy to replace modulated sine waves, the generated PWM waves and the modulated sine waves have the same energy, namely the area enclosed by the PWM waves and a time axis in the total period is equal to the area enclosed by the modulated sine waves and the time axis;
as shown by reference numeral 302 in fig. 3, a sine wave whose portion enclosed by the horizontal axis can be divided into five regions with different areas, as shown by reference numeral 303 in fig. 3, and the energy contained in each region can be equivalently replaced by rectangular pulses with equal areas. The total area of five rectangular pulses of the same amplitude and different widths shown as reference numeral 304 in fig. 3 is equal to the area of the sine waves shown as reference numerals 302 and 303, and thus is completely equivalent to the sine waves shown as reference numerals 302 and 303. According to (2.3) in the step (2), generating the total number D of rectangular pulses, the total area of which is smaller than the area of the modulation wave, i.e. the energy contained in the wavelet pulse to be generated is not equal to the energy contained in the modulation wave. Therefore, the width of the wavelet pulse needs to be increased in equal proportion, so that the total pulse area is equal to the modulation wave area (i.e. impulse). The implementation method comprises the steps of firstly calculating the total area of a generated pulse sequence, obtaining a proportionality coefficient K according to the area of a specific harmonic wave to be controlled in a total period, then linearly expanding the width of a wavelet pulse in an equal proportion mode, and generating a series of wavelet pulse sequences with the same amplitude and different widths in the total period again by combining scale factors, wherein the specific method comprises the following steps:
(3.1) calculating the total area of the generated pulse sequence:
Figure GDA0003322904560000091
wherein h is the pulse height, and h is 1; j is a function ofi(i-1, 2, …, D) are D scale factors generated by step (2), and if the maximum number of sample groups is defined as 10, the input modulated wave is a, as shown by reference numeral 305 in fig. 310.8 fundamental wave, 10 wavelet pulses are generated in one period according to step (2), which are symmetrical about the half-period center, so the areas of the first five wavelet pulses are equal to the areas of the last five wavelet pulses, and only the total area S 'of the first half-period wavelet pulses needs to be calculated'1(the area of the shaded portion in reference numeral 305), the total area S is obtained1：
Figure GDA0003322904560000092
Figure GDA0003322904560000093
(3.2) calculating the modulation wave function y ═ f (T) in a period time TmTotal area S enclosed by inner and time horizontal axes2The concrete formula is
Figure GDA0003322904560000094
If the input modulated wave has an amplitude A, as indicated by reference numeral 306 in FIG. 31Since 0.8 fundamental wave is symmetric about the center of the half period, it is only necessary to calculate the area S 'surrounded by the first half period modulated wave and the time axis'2(area of gray portion in reference numeral 303), the total area S can be obtained2：
Figure GDA0003322904560000095
Figure GDA0003322904560000096
(3.3) defining a proportionality coefficient K, wherein:
K＝S2/S1 (13)
the width of each wavelet pulse is increased to K times of the original width:
w′＝K·w (14)
in conjunction with equation (7), new wavelet pulse widths w' are obtained, each wavelet pulse width being
Figure GDA0003322904560000101
Wherein i is 1,2, …, D.
The purpose of increasing the width of the wavelet pulse in equal proportion is to make the generated wavelet pulse contain energy (impulse) equivalent to that of the modulation wave, so that the output of the inverter can reflect the amplitude of the modulation wave linearly, and the simplicity of controlling the amplitude of specific harmonic waves is improved. And (3) calculating the scale factor K in real time by using a proper numerical calculation method and DSP-TMS320F28335 developed by TI company, wherein the calculation time is not more than 0.01 ms.
(3.4) defining the turn-on and turn-off time of the inverter switch as td1And td2Due to td1And td2About the pulse midpoint tmidSymmetrically, the switch on time is the width w' of a wavelet pulse, so the following constraint equation can be obtained:
td1+td2＝2tmid (16)
td2-td1＝w′ (17)
combining equation (3) and equation (15), the inverter switching time t can be obtainedd1And td2：
Figure GDA0003322904560000102
Figure GDA0003322904560000103
As shown by reference numeral 307 in fig. 3, a single wavelet pulse before linear increase is a fringe part, the width is w, a single wavelet pulse after linear increase of the width by K times is a gray part (including a middle fringe part), and the rising edge and the falling edge of the pulse respectively correspond to the turn-on time t of the inverter switchd1And a turn-off time td2. After each wavelet pulse width is expanded by K times, the volt-second area of the sine-modulated wave shown as 301 in fig. 3 is made to be the same as the sum of the volt-second areas of the pulses shown as 308 because the wavelet pulse shown as 308 isAnd the modulation wave with the reference number of 301 meets the balance characteristic of pulse voltage volt-second, so that the corresponding voltage waveform output by the inverter is basically the same as the modulation wave expected to be controlled in a certain allowable engineering error range theoretically.
(3.5) switch V1～V6Controlling IGBT switch Q1～Q6Opening;
using a single-phase inverter as an example, V is operated1And V4Are complementary in on-off state, V2And V3The on-off states of (c) are also complementary. If time t satisfies td1≤t≤td2And when the harmonic function y ═ f (t) ≧ 0, then V1＝V3＝1，V2＝V 40, corresponding to inverter switch Q1And Q3Closed, Q2And Q4Turning off; if the harmonic function y ═ f (t) < 0 at this time, V1＝V3＝0，V2＝V 41, corresponding to inverter switch Q1And Q3Off, Q2And Q4Closing; if t > td2Then V is1＝V2＝V3＝V4And (5) corresponding to all the switches being turned off, and at the same time, d is d +1, obtaining a new scale factor according to the new displacement factor, and further calculating the switching-on and switching-off time t of the next inverter switchd1And td2。
And (3.6) returning to the step (3.5), and judging the on-off of the inverter switch again according to the value of t. T is gradually increased along with the sampling frequency until T is more than or equal to Tm. If the maximum number of sampling groups is defined as 10 and the input modulation wave is a fundamental wave with a modulation amplitude of 0.8, the 5 wavelet pulses generated in the first half period according to the above steps are shown as reference numeral 308 in fig. 3.
(4) The generated wavelet pulse sequence is used for driving the inverter switch to enable the inverter to generate the required specific harmonic voltage UL. When the maximum number of sampling sets is 10, the switching angle of the inverter is as shown in fig. 2 for different modulation degrees and preset initial phase angles. Fig. 2(a) is a schematic diagram of the switching angle, and fig. 2(b) is a three-dimensional diagram of the change of the switching angle.
In the embodiment of the present invention, the specific method of step (4) is as follows:
for single-phase inverters, using a switching function siRespectively control ViIs (i) ═ 1,2,3,4), where s2Lag s1Electrical angle 180 DEG, s1＝s3,s2＝s4(ii) a For three-phase inverters, using switching function siRespectively control ViIs (i) ═ 1,2, …,6), where s3Lag s1Electrical angle 120 °, s5Lag s3Electrical angle 120 °, s2、s4And s6Respectively with s1、s3And s5And (4) complementation. The inverter carries an inductive load, and finally specific harmonic voltage U at the load end is obtainedL. The specific topology is shown in fig. 1. Fig. 1(a) shows a control topology of a single-phase inverter, and fig. 1(b) shows a control topology of a three-phase inverter.
Fig. 5-11 are graphs illustrating the effect of controlling specific harmonics by the method of the present invention. In fig. 5, the low order harmonics are almost completely eliminated, and the output fundamental component varies linearly with the value of the desired modulation degree; in fig. 6, the output seventh harmonic component is linearly changed with the value of the desired modulation degree, and the remaining second harmonic is almost completely eliminated, which illustrates that the method of the present invention has a good control effect on the amplitude of the single harmonic; in fig. 7, the output fundamental component and the fifth harmonic component are almost constant with the variation of the input initial phase angle, and the content of the remaining sub-low frequency harmonics is small or close to zero; in fig. 8, the output fundamental component and the seventh harmonic component remain almost constant with the variation of the input initial phase angle, and the remaining low-frequency harmonics have little or nearly zero content; in fig. 9, when there are a lot of fundamental wave components, the phase of the output seventh harmonic component is almost equal to the initial phase angle of the input seventh harmonic, and is basically consistent with the theoretical output curve, which illustrates that the method of the present invention has better control effect for more than two kinds of harmonics, and fig. 12 is the same; in fig. 10, under the condition of low fundamental wave modulation degree, the phase of the output fundamental wave component is almost equal to the initial phase angle of the input seventh harmonic, and is basically consistent with the theoretical output curve, which illustrates that the method of the present invention has more precise control effect on the phase at the time of low modulation degree; fig. 11 is a three-dimensional graph of the phase deviation of the fundamental wave output, and it can be seen that the deviation value of the phase does not exceed 2 ° even in the case of a low modulation degree which is most disadvantageous to the control.
Driving the three-phase inverter in fig. 1(b) to compensate for specific harmonics in the power grid by using the method of the present invention, wherein fig. 13 is a compensation schematic diagram, fig. 14(a) is a power grid current waveform containing a certain fifth harmonic before compensation, and fig. 14(b) is an FFT analysis result thereof; fig. 15(a) is a compensated grid current waveform, which can be found to be smoother, and fig. 15(b) is an FFT analysis result thereof, which shows that the fifth harmonic content is significantly reduced. The method can be applied to compensation of low-frequency harmonic waves which are difficult to control in the power grid.
The present application also provides a computer-readable storage medium, such as a flash memory, a hard disk, a multimedia card, a card-type memory (e.g., SD or DX memory, etc.), a Random Access Memory (RAM), a Static Random Access Memory (SRAM), a read-only memory (ROM), an electrically erasable programmable read-only memory (EEPROM), a programmable read-only memory (PROM), a magnetic memory, a magnetic disk, an optical disk, a server, an App application mall, etc., on which a computer program is stored, which when executed by a processor implements the wavelet pulse width modulation-based harmonic control method in the method embodiments.
It should be noted that, according to the implementation requirement, each step/component described in the present application can be divided into more steps/components, and two or more steps/components or partial operations of the steps/components can be combined into new steps/components to achieve the purpose of the present invention.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.

Claims (6)

1. A harmonic control method based on wavelet pulse width modulation is characterized by comprising the following steps:
(1) selecting a specific harmonic wave to be controlled as a modulation waveform to obtain the amplitude and phase information of the specific harmonic wave to be controlled;
(2) selecting a maximum sampling group number D, generating a series of equal-interval sampling moments according to the maximum sampling group number, calculating a Haar wavelet scale factor at each sampling moment according to the amplitude of a specific harmonic to be controlled at the current moment, and generating a series of wavelet pulse sequences with the same amplitude and different widths in a total period according to the values of the wavelet scale factor and the modulation degree;
(3) calculating the total area of the generated wavelet pulse sequence, obtaining a proportionality coefficient K according to the area of the specific harmonic wave to be controlled in a fundamental wave period, and expanding the width of each wavelet pulse by K times in an equal proportion;
(4) and driving the inverter switch by using the expanded wavelet pulse sequence to enable the inverter to generate required specific harmonic waves.
2. The method according to claim 1, wherein the specific method of the step (2) is as follows:
(2.1) for the selected specific harmonic, converting it into a corresponding modulation value M according to its amplitudek，MkExpressing the modulation degree of the k-th harmonic wave, selecting the maximum sampling group number D required by modulation, and performing the modulation in a period time TmInternally generating D equal-interval sampling time tmidWherein, in the step (A),
Figure FDA0003435714900000011
Figure FDA0003435714900000012
(2.2) defining a modulation harmonic function y ═ f (t) according to the specific harmonic selected in the step (1), and enabling the modulation harmonic function y ═ f (t) to be ordered
Figure FDA0003435714900000013
Wherein A iskFor modulating the amplitude of each harmonic component in the wave, ω is the fundamental angular frequency, θkRepresenting the initial phase angle of the kth harmonic, n representing the number of harmonic components, each sampling instant tmidWhere a Haar wavelet scale factor j ═ f (t) is definedmid)|；
(2.3) at each sampling instant tmidSequentially generating a height of 1 and a width of
Figure FDA0003435714900000014
Is detected.
3. The method of claim 2, wherein T ismTaking the fundamental period, i.e. Tm＝0.02s。
4. The method according to claim 3, wherein the specific method of step (3) is as follows:
(3.1) calculating the total area S of the D wavelet pulses generated in the step (2)1；
(3.2) calculating the harmonic function y ═ f (T) at a cycle time TmTotal area S enclosed by inner and time axes2Wherein, in the step (A),
Figure FDA0003435714900000021
(3.3) defining a modulation scale factor K ═ S2/S1At each sampling instant tmidAre sequentially regenerated to have a height of 1 and a width of
Figure FDA0003435714900000022
Is detected.
5. The method of claim 4, applied to control an inverter to produce a fundamental wave, or to control an inverter to produce a mixed wave of a specific harmonic or several harmonics of arbitrary amplitude and phase superimposed on each other.
6. A computer-readable storage medium, on which a computer program is stored, which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 4.
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