CN103529347A - Cascade inverter H-bridge unit fault detecting method based on harmonic analysis - Google Patents

Abstract

The invention discloses a cascade inverter H-bridge unit short circuit fault detecting method based on harmonic analysis of switching frequency, which is suitable for a carrier phase-shifting PWM (pulse width modulation) manner based on the harmonic analysis to output phase voltage and comprises three parts, namely output alternating voltage sampling, extracting and processing of harmonic wave close to the switching frequency, and fault judging and fault locating. Three-phase output voltage of a cascade inverter is respectively subjected to low-pass filtering and A/D (analog-to-digital conversion) sampling, and is subjected to discrete Fourier transformation to obtain characteristic harmonic; a comparison result of the characteristic harmonic amplitude and a fault threshold is utilized as the evidence of fault judging, wherein the fault threshold is obtained by carrying out a series of calculation on command voltage. The fault locating is determined through a phase angle range of the harmonic of the switching frequency. According to the cascade inverter H-bridge unit short circuit fault detecting method based on the harmonic analysis of the switching frequency, which is disclosed by the invention, the three-phase output voltage of the inverter is collected, and no other hardware circuit is additionally arranged, so that the cost is reduced, and the efficiency is improved; the application capability is strong, and the application value in the study on the real time fault detection of the cascade inverter exists.

Description

A kind of cascaded inverter H bridge cell failure detection method based on frequency analysis

Technical field

The invention belongs to the applied technical field of high-voltage and high-power power electronic technology in electric system, relate to the phase-shifting carrier wave PWM(width modulation based on switching frequency frequency analysis) cascaded inverter H bridge unit short circuit failure detection method under mode.

Background technology

In recent years, along with the development of industry with power technology, H bridge cascade structure becomes the focus of research in fields such as parallel network reverse, energy storage, electric power electric transformers.H bridge cascaded inverter has the advantages such as power capacity is large, switching device stress is little, harmonic content is low, is therefore widely used in various electric devices.

Cascaded inverter is structurally easy to modular implementation, and has compared with low switching losses and harmonic wave.But because it has adopted the structure of a plurality of H bridge units in series, its structural complexity and control complicacy have increased its possibility breaking down.Cascaded inverter is often applied to the important events such as aerogenerator, electric power electric transformer, if it breaks down and is but processed timely and effectively, its consequence of bringing is very serious.This just has higher requirement to the redundancy of cascaded inverter, and the prerequisite of redundancy is fault detect, comprises fault judgement and localization of fault, can judge whether cascaded inverter breaks down according to certain feature, and definite location of fault.

The fault detect of H bridge cascaded inverter can be achieved by increasing additional hardware circuit methods, it in each H bridge unit, is for example outgoing side installing voltage sensor, but the method has not only increased cost greatly, and has strengthened system complexity, reduced the reliability of device.Aspect software approach, considerably less for cascaded inverter fault detect aspect research, consider each H bridge unit in the single-phase chain link of cascaded inverter due to triangular carrier respectively phase shift certain angle, the harmonic wave at the switching frequency place in the output voltage waveforms of each H bridge unit also can be distinguished phase shift certain angle so, according to the analysis to the single-phase output voltage of cascaded inverter, obtain switching frequency neighbouring harmonic amplitude and phase angle, can judge and location the H bridge unit short trouble of cascaded inverter.

Summary of the invention

Goal of the invention: for the problem of above-mentioned cascaded inverter fault detect, the object of the invention is to propose a kind of cascaded inverter H bridge cell failure detection method based on frequency analysis, the method be based on switching frequency frequency analysis for the cascaded inverter H bridge unit short circuit failure detection method under phase-shifting carrier wave PWM modulation system, the method can be carried out fault judgement and location under the prerequisite that does not increase hardware circuit, improves the redundancy of device.

Technical scheme: for solving the problems of the technologies described above, the invention provides a kind of cascaded inverter H bridge cell failure detection method based on frequency analysis, the method comprises the steps:

Step 1: output AC voltage sampling:

Step 1.1: the three-phase voltage that utilizes voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, i.e. x=a, and b, c, a, b, c is three-phase symbol; By described simulating signal v _xoby low-pass filter, carry out filtering, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swswitching frequency for cascaded inverter H bridge unit output voltage;

Step 1.2, to described filtered simulating signal v ' _xocarry out A/D sampling, sample frequency f _sfor H bridge unit output voltage switching frequency f _swintegral multiple, sampling gained discrete signal be designated as v _x(k), 0≤k≤N-1 wherein, N is the number of sampled point in a power frequency period;

Near step 2: switching frequency, harmonic wave extracts and processes:

Step 2.1: calculate described discrete signal v _x(k) at H bridge unit output voltage switching frequency f _swnear discrete Fourier transformation result, is designated as:

{V _x(n _sw-n ₀),V _x(n _sw-n ₀+1),…,V _x(n _sw),…,V _x(n _sw+n ₀)}

N wherein _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f that every phase is got _swnear harmonic wave number is 2n ₀+ 1; H bridge unit output voltage switching frequency f _sw, f ₀=50Hz.

Step 2.2: calculate harmonic amplitude and phase angle; The result of described x phase voltage discrete Fourier transformation is multiplied each other with 1/N respectively and turns to exponential form, obtain each phase switching frequency f _swnear multiple harmonic, is designated as

wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, m is overtone order, i.e. m=n _sw-n ₀, n _sw-n ₀+ 1 ..., n _sw+ n ₀,

for m subharmonic amplitude,

for m subharmonic phase angle.

Near step 2.3: harmonic wave compute switch frequency; At described sequence of complex numbers

in, get amplitude maximum one, be designated as

as near characteristic harmonics cascaded inverter output phase voltage switching frequency; Wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, | C _xsw| be characteristic harmonics amplitude,

for m subharmonic amplitude,

for characteristic harmonics phase angle.

Step 3: fault judgement and localization of fault;

Step 3.1: calculate fault threshold; Cascaded inverter x phase command voltage is

will

phase shift angle obtains n voltage signal amount

n is the number of every phase H bridge unit, i=1, and 2 ..., n, f ₀for power frequency 50Hz, f _swfor H bridge unit output voltage switching frequency; X with reference to switching frequency harmonic wave is $C_{\mathrm{xsw}}^{*}=\frac{{2v}_{\mathrm{dc}}}{\mathrm{\π}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sin \left(\mathrm{\πM}\frac{v_{\mathrm{xi}}^{*}}{v_{\mathrm{xm}}^{*}}\right)e^{j(i-1)\mathrm{\Δ\Φ}},$ V wherein _dcfor single H bridge DC side voltage, for command voltage amplitude, i=1,2 ..., n, M is modulation ratio, ΔΦ=2 π/n, the fault threshold of x phase $\left|C_{\mathrm{xth}}\right|=\left|C_{\mathrm{xsw}}^{*}\right|+0.05v_{\mathrm{dc}};$

Step 3.2: fault judgement; By near characteristic harmonics described cascaded inverter x phase output voltage switching frequency amplitude | C _xsw| with fault threshold | C _xth| relatively, if | C _xsw|>| C _xth|, be judged to be x and break down mutually, otherwise be normal operation;

Step 3.3: localization of fault; If be constantly judged as inverter x at t, there is mutually H bridge unit short trouble, get the f calculating in described step 2.2 _swplace's harmonic wave phase angle

localization of fault criterion is: if i H bridge unit breaks down,

drop on

in scope, t wherein ₀for t constantly before x first H bridge unit triangular carrier v mutually _cx1for the moment of maximal value or minimum value, t _sw=1/f _sw,

for low-pass filter in described step 1.1 is at f _swthe phase shift at place.

Beneficial effect:

(1) this method mainly relies on software to realize, and can conveniently realize, without the hardware detecting circuit of configuration additional complexity;

(2) this method detection failure quick and precisely, can carry out localization of fault again fast, as the prerequisite of device redundancey technology, can be fault subsequent process scheme and provides safeguard;

(3) fault detection capability than IGBT Drive Protecting Circuit has wider sensing range.

Accompanying drawing explanation

Fig. 1 is the unit cascaded combining inverter structural drawing of H bridge;

Fig. 2 is each unit switch frequency harmonics phasor graph of single-phase chain link;

Fig. 3 is fault detection method block diagram.

Embodiment

Below in conjunction with accompanying drawing, the present invention is done further and explained.

A kind of cascaded inverter H bridge cell failure detection method based on frequency analysis provided by the invention, the method comprises the steps:

Step 1: output AC voltage sampling:

Step 1.1: the three-phase voltage that utilizes voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, i.e. x=a, and b, c, a, b, c is three-phase symbol; By described simulating signal v _xoby low-pass filter, carry out filtering, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swswitching frequency for cascaded inverter H bridge unit output voltage;

Step 1.2, to described filtered simulating signal v ' _xocarry out A/D sampling, sample frequency f _sfor H bridge unit output voltage switching frequency f _swintegral multiple, sampling gained discrete signal be designated as v _x(k), 0≤k≤N-1 wherein, N is the number of sampled point in a power frequency period;

Near step 2: switching frequency, harmonic wave extracts and processes:

Step 2.1: calculate described discrete signal v _x(k) at H bridge unit output voltage switching frequency f _swnear discrete Fourier transformation result, is designated as:

{V _x(n _sw-n ₀),V _x(n _sw-n ₀+1),…,V _x(n _sw),…,V _x(n _sw+n ₀)}

N wherein _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f that every phase is got _swnear harmonic wave number is 2n ₀+ 1; H bridge unit output voltage switching frequency f _sw, f ₀=50Hz;

Step 2.2: calculate harmonic amplitude and phase angle; The result of described x phase voltage discrete Fourier transformation is multiplied each other with 1/N respectively and turns to exponential form, obtain each phase switching frequency f _swnear multiple harmonic, is designated as

wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, m is overtone order, i.e. m=n _sw-n ₀, n _sw-n ₀+ 1 ..., n _sw+ n ₀,

for m subharmonic amplitude,

for m subharmonic phase angle.

Near step 2.3: harmonic wave compute switch frequency; At described sequence of complex numbers

in, get amplitude maximum one, be designated as as near characteristic harmonics cascaded inverter output phase voltage switching frequency; Wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, | C _xsw| be characteristic harmonics amplitude,

for m subharmonic amplitude, for characteristic harmonics phase angle.

Step 3: fault judgement and localization of fault;

Step 3.1: calculate fault threshold; Cascaded inverter x phase command voltage is

will

phase shift angle obtains n voltage signal amount

n is the number of every phase H bridge unit, i=1, and 2 ..., n, f ₀for power frequency 50Hz, f _swfor H bridge unit output voltage switching frequency; X with reference to switching frequency harmonic wave is $C_{\mathrm{xsw}}^{*}=\frac{{2v}_{\mathrm{dc}}}{\mathrm{\π}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sin \left(\mathrm{\πM}\frac{v_{\mathrm{xi}}^{*}}{v_{\mathrm{xm}}^{*}}\right)e^{j(i-1)\mathrm{\Δ\Φ}},$ V wherein _dcfor single H bridge DC side voltage,

for command voltage amplitude, i=1,2 ..., n, M is modulation ratio, ΔΦ=2 π/n, the fault threshold of x phase $\left|C_{\mathrm{xth}}\right|=\left|C_{\mathrm{xsw}}^{*}\right|+0.05v_{\mathrm{dc}};$

Step 3.2: fault judgement; By near characteristic harmonics described cascaded inverter x phase output voltage switching frequency

amplitude | C _xsw| with fault threshold | C _xth| relatively, if | C _xsw|>| C _xth|, be judged to be x and break down mutually, otherwise be normal operation;

Step 3.3: localization of fault; If be constantly judged as inverter x at t, there is mutually H bridge unit short trouble, get the f calculating in described step 2.2 _swplace's harmonic wave phase angle

localization of fault criterion is: if i H bridge unit breaks down,

drop on

in scope, t wherein ₀for t constantly before x first H bridge unit triangular carrier v mutually _cx1for the moment of maximal value or minimum value, t _sw=1/f _sw,

for low-pass filter in described step 1.1 is at f _swthe phase shift at place.

The present invention detects for the cascaded inverter H bridge unit short trouble under phase-shifting carrier wave PWM modulation system, the cascade combining inverter structural drawing that Fig. 1 is Y-connection, and wherein each is single-phasely formed by N H bridge units in series respectively, adopts Y-connection between three-phase.In addition, the present invention is also applicable to triangle connected mode.

As shown in Figure 2, if cascaded inverter is every, have mutually a n H bridge unit, every phase output voltage is at switching frequency f _swthe harmonic wave v at place _swthe switching frequency harmonic wave v by each H bridge unit output _sw1, v _sw2..., v _swnbe formed by stacking:

${\stackrel{\·}{v}}_{\mathrm{sw}}=\underset{x=1}{\overset{n}{\mathrm{\Σ}}}{\stackrel{\·}{v}}_{\mathrm{swx}}---\left(1\right)$

Due to the phase shift of each unit PWM triangular carrier, v _sw1, v _sw2..., v _swnbetween also differ certain angle, its phasor graph is as shown in Figure 2 a.In theory, v when inverter normally moves _swbe zero; When having the short circuit of certain H bridge unit, phasor graph is (unit 1 short circuit) as shown in Figure 2 b, now v _swnon-vanishing, size equals v _sw1amplitude, phase place and v _sw1on the contrary.In actual conditions, v _swand non-vanishing, therefore a threshold value should be set and be used for judging whether to break down, this threshold value can prevent that when command voltage from changing, erroneous judgement occurring breaks simultaneously.And while breaking down in actual conditions, the harmonic wave that amplitude is larger is not just at switching frequency place, but near switching frequency.

As shown in Figure 3, the single-phase output voltage v of cascaded inverter _xofirst pass through low-pass filter filtering, then through A/D sampling, obtain discrete sampling value v _x(k); By discrete Fourier transformation, obtain single H bridge unit switch frequency f again _swnear multiple harmonic, is designated as

in this harmonic sequence, the harmonic wave of choosing amplitude maximum is

as near characteristic harmonics cascaded inverter x phase output voltage switching frequency.The threshold value of short trouble | C _xth| by command voltage

through computing, obtain, fault basis for estimation is that characteristic harmonics amplitude is greater than fault threshold, and localization of fault is the f according to output voltage _sw/ f ₀the phase angle of subharmonic arrives concrete certain H bridge unit by localization of fault.

The above is only the preferred embodiment of the present invention; it should be pointed out that for those skilled in the art, under the premise without departing from the principles of the invention; can also make some improvements and modifications, these improvements and modifications also should be considered as protection scope of the present invention.

Claims (1)

1. the cascaded inverter H bridge cell failure detection method based on frequency analysis, is characterized in that, the method comprises the steps:

Step 1: output AC voltage sampling:

Step 1.1: the three-phase voltage that utilizes voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, i.e. x=a, and b, c, a, b, c is three-phase symbol; By described simulating signal v _xoby low-pass filter, carry out filtering, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swswitching frequency for cascaded inverter H bridge unit output voltage;

Step 1.2, to described filtered simulating signal v ' _xocarry out A/D sampling, sample frequency f _sfor H bridge unit output voltage switching frequency f _swintegral multiple, sampling gained discrete signal be designated as v _x(k), 0≤k≤N-1 wherein, N is the number of sampled point in a power frequency period;

Near step 2: switching frequency, harmonic wave extracts and processes:

Step 2.1: calculate described discrete signal v _x(k) at H bridge unit output voltage switching frequency f _swnear discrete Fourier transformation result, is designated as:

{V _x(n _sw-n ₀),V _x(n _sw-n ₀+1),…,V _x(n _sw),…,V _x(n _sw+n ₀)}

N wherein _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f that every phase is got _swnear harmonic wave number is 2n ₀+ 1; H bridge unit output voltage switching frequency f _sw, f ₀=50Hz;

Step 2.2: calculate harmonic amplitude and phase angle; The result of described x phase voltage discrete Fourier transformation is multiplied each other with 1/N respectively and turns to exponential form, obtain each phase switching frequency f _swnear multiple harmonic, is designated as

wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, m is overtone order, i.e. m=n _sw-n ₀, n _sw-n ₀+ 1 ..., n _sw+ n ₀,

for m subharmonic amplitude, for m subharmonic phase angle;

Near step 2.3: harmonic wave compute switch frequency; At described sequence of complex numbers

in, get amplitude maximum one, be designated as

as near characteristic harmonics cascaded inverter output phase voltage switching frequency; Wherein x represents x phase, x=a, and b, c, a, b, c is three-phase symbol, | C _xsw| be characteristic harmonics amplitude,

for m subharmonic amplitude,

for characteristic harmonics phase angle;

Step 3: fault judgement and localization of fault;

Step 3.1: calculate fault threshold; Cascaded inverter x phase command voltage is

will

phase shift angle obtains n voltage signal amount

n is the number of every phase H bridge unit, i=1, and 2 ..., n, f ₀for power frequency 50Hz, f _swfor H bridge unit output voltage switching frequency; X with reference to switching frequency harmonic wave is $C_{\mathrm{xsw}}^{*}=\frac{{2v}_{\mathrm{dc}}}{\mathrm{\π}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sin \left(\mathrm{\πM}\frac{v_{\mathrm{xi}}^{*}}{v_{\mathrm{xm}}^{*}}\right)e^{j(i-1)\mathrm{\Δ\Φ}},$ V wherein _dcfor single H bridge DC side voltage,

for command voltage amplitude, i=1,2 ..., n, M is modulation ratio, ΔΦ=2 π/n, the fault threshold of x phase $\left|C_{\mathrm{xth}}\right|=\left|C_{\mathrm{xsw}}^{*}\right|+0.05v_{\mathrm{dc}};$

Step 3.2: fault judgement; By near characteristic harmonics described cascaded inverter x phase output voltage switching frequency

amplitude | C _xsw| with fault threshold | C _xth| relatively, if | C _xsw|>| C _xth|, be judged to be x and break down mutually, otherwise be normal operation;

Step 3.3: localization of fault; If be constantly judged as inverter x at t, there is mutually H bridge unit short trouble, get the f calculating in described step 2.2 _swplace's harmonic wave

phase angle

localization of fault criterion is: if i H bridge unit breaks down,

drop on in scope, t wherein ₀for t constantly before x first H bridge unit triangular carrier v mutually _cx1for the moment of maximal value or minimum value, t _sw=1/f _sw,

for low-pass filter in described step 1.1 is at f _swthe phase shift at place.

Images