CN103529347B - A kind of cascade inverter H-bridge unit fault detection method based on frequency analysis - Google Patents

Abstract

The invention discloses a kind of cascaded inverter H-bridge unit short circuit failure detection method based on switching frequency frequency analysis, the method is based on the frequency analysis to output phase voltage, be applicable to phase-shifting carrier wave PWM mode, be divided into harmonic wave near output AC voltage sampling, switching frequency to extract and process, breakdown judge and localization of fault three parts.Cascaded inverter three-phase output voltage through low-pass filtering and A/D sampling, obtains characteristic harmonics by discrete Fourier transformation respectively; The comparative result of characteristic harmonics amplitude and fault threshold is as the foundation of breakdown judge, and wherein fault threshold is obtained through series of computation by command voltage.Localization of fault is then determined by the phase angle range of switching frequency place harmonic wave.The method only need gather inverter and export three-phase voltage, without the need to increasing other hardware circuits, can be cost-saving and raise the efficiency, and have stronger application power, the research for cascaded inverter real-time fault detection aspect has using value.

Description

A kind of cascade inverter H-bridge unit fault 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 industry and the development of 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 device.

Cascaded inverter is structurally easy to modular implementation, and has comparatively low switching losses and harmonic wave.But owing to which employs the structure of multiple H-bridge unit series connection, its structural complexity and control complexity add its possibility broken down.Cascaded inverter is often applied to the important events such as aerogenerator, electric power electric transformer, is but processed timely and effectively if it breaks down, and its consequence brought is very serious.This just has higher requirement to the redundancy of cascaded inverter, and the prerequisite of redundancy is fault detect, comprises breakdown judge and localization of fault, can judge whether cascaded inverter breaks down, and determine location of fault according to certain feature.

The fault detect of H bridge cascaded inverter can be achieved by increasing additional hardware circuit methods, such as each H-bridge unit be outgoing side installing voltage sensor, but the method not only considerably increases cost, and increase system complexity, reduce the reliability of device.In software approach, considerably less for cascaded inverter fault detect aspect research, consider that each H-bridge unit in the single-phase chain link of cascaded inverter is due to triangular carrier respectively phase shift certain angle, the harmonic wave at the switching frequency place in the output voltage waveforms of so each H-bridge unit also can distinguish phase shift certain angle, according to the analysis of the single-phase output voltage to cascaded inverter, obtain the harmonic amplitude near switching frequency and phase angle, can carry out judging to the H-bridge unit short trouble of cascaded inverter and locate.

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 cascade inverter H-bridge unit fault 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 mode, the method can carry out breakdown judge and location under the prerequisite not increasing hardware circuit, improves the redundancy of device.

Technical scheme: for solving the problems of the technologies described above, the invention provides a kind of cascade inverter H-bridge unit fault detection method based on frequency analysis, the method comprises the steps:

Step 1: output AC voltage is sampled:

Step 1.1: the three-phase voltage utilizing voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, and namely x=a, b, c, a, b, c are three-phase symbol; By described simulating signal v _xocarry out filtering by low-pass filter, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swfor the switching frequency of 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), wherein 0≤k≤N-1, N is the number of sampled point in a power frequency period;

Step 2: near switching frequency, harmonic wave extracts and process:

Step 2.1: calculate described discrete signal v _xk () is at H-bridge unit output voltage switching frequency f _swneighbouring 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)}

Wherein n _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f gets in every phase institute _swneighbouring 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 be multiplied with 1/N respectively and turn to exponential form, obtaining each phase switching frequency f _swneighbouring multiple harmonic, is designated as wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, and 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.

Step 2.3: harmonic wave near compute switch frequency; At described sequence of complex numbers in, one that gets amplitude maximum, be designated as namely characteristic harmonics near phase voltage switching frequency is exported as cascaded inverter; Wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, | C _xsw| be characteristic harmonics amplitude, namely for m subharmonic amplitude, for characteristic harmonics phase angle.

Step 3: breakdown judge 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=1,2 ..., n, f ₀for power frequency 50Hz, f _swfor H-bridge unit output voltage switching frequency; X phase with reference to switching frequency harmonic wave is $C_{\mathrm{xsw}}^{*}=\frac{{2v}_{\mathrm{dc}}}{\mathrm{\π}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sin \left(\mathrm{\πM}\frac{v_{\mathrm{xi}}^{*}}{v_{\mathrm{xm}}^{*}}\right)e^{j(i-1)\mathrm{\Δ\Φ}},$ Wherein v _dcfor single H bridge DC side voltage, for command voltage amplitude, i=1,2 ..., n, M are modulation ratio, the fault threshold of ΔΦ=2 π/n, x phase $\left|C_{\mathrm{xth}}\right|=\left|C_{\mathrm{xsw}}^{*}\right|+0.05v_{\mathrm{dc}};$

Step 3.2: breakdown judge; By characteristic harmonics near described cascaded inverter x phase output voltage switching frequency amplitude | C _xsw| with fault threshold | C _xth| compare, if | C _xsw| >|C _xth|, be then judged to be that x phase breaks down, otherwise be normal operation;

Step 3.3: localization of fault; If be judged as that H-bridge unit short trouble occurs inverter x phase in t, get the f calculated in described step 2.2 _swplace's harmonic wave phase angle localization of fault criterion is: if i-th H-bridge unit breaks down, then drop on in scope, wherein t ₀for first the H-bridge unit triangular carrier v of x phase before t _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 simulating, can conveniently realize, without the need to configuring the hardware detecting circuit of additional complexity;

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

(3) compared to the fault detection capability of IGBT Drive Protecting Circuit, there is wider sensing range.

Accompanying drawing explanation

Fig. 1 is H-bridge unit cascade combining inverter structural drawing;

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

Fig. 3 is fault detection method block diagram.

Embodiment

Below in conjunction with accompanying drawing the present invention done and further explain.

A kind of cascade inverter H-bridge unit fault detection method based on frequency analysis provided by the invention, the method comprises the steps:

Step 1: output AC voltage is sampled:

Step 1.1: the three-phase voltage utilizing voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, and namely x=a, b, c, a, b, c are three-phase symbol; By described simulating signal v _xocarry out filtering by low-pass filter, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swfor the switching frequency of 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), wherein 0≤k≤N-1, N is the number of sampled point in a power frequency period;

Step 2: near switching frequency, harmonic wave extracts and process:

Step 2.1: calculate described discrete signal v _xk () is at H-bridge unit output voltage switching frequency f _swneighbouring 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)}

Wherein n _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f gets in every phase institute _swneighbouring 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 be multiplied with 1/N respectively and turn to exponential form, obtaining each phase switching frequency f _swneighbouring multiple harmonic, is designated as wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, and 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.

Step 2.3: harmonic wave near compute switch frequency; At described sequence of complex numbers in, one that gets amplitude maximum, be designated as namely characteristic harmonics near phase voltage switching frequency is exported as cascaded inverter; Wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, | C _xsw| be characteristic harmonics amplitude, namely for m subharmonic amplitude, for characteristic harmonics phase angle.

Step 3: breakdown judge 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=1,2 ..., n, f ₀for power frequency 50Hz, f _swfor H-bridge unit output voltage switching frequency; X phase with reference to switching frequency harmonic wave is $C_{\mathrm{xsw}}^{*}=\frac{{2v}_{\mathrm{dc}}}{\mathrm{\π}}\underset{i=1}{\overset{n}{\mathrm{\Σ}}}\sin \left(\mathrm{\πM}\frac{v_{\mathrm{xi}}^{*}}{v_{\mathrm{xm}}^{*}}\right)e^{j(i-1)\mathrm{\Δ\Φ}},$ Wherein v _dcfor single H bridge DC side voltage, for command voltage amplitude, i=1,2 ..., n, M are modulation ratio, the fault threshold of ΔΦ=2 π/n, x phase $\left|C_{\mathrm{xth}}\right|=\left|C_{\mathrm{xsw}}^{*}\right|+0.05v_{\mathrm{dc}};$

Step 3.2: breakdown judge; By characteristic harmonics near described cascaded inverter x phase output voltage switching frequency amplitude | C _xsw| with fault threshold | C _xth| compare, if | C _xsw| >|C _xth|, be then judged to be that x phase breaks down, otherwise be normal operation;

Step 3.3: localization of fault; If be judged as that H-bridge unit short trouble occurs inverter x phase in t, get the f calculated in described step 2.2 _swplace's harmonic wave phase angle localization of fault criterion is: if i-th H-bridge unit breaks down, then drop on in scope, wherein t ₀for first the H-bridge unit triangular carrier v of x phase before t _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 cascaded inverter H-bridge unit short trouble that the present invention is used under phase-shifting carrier wave PWM mode detects, and Fig. 1 is the cascade combining inverter structural drawing of Y-connection, to be wherein respectively single-phasely in series by N number of H-bridge unit 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 often has n H-bridge unit mutually, then every phase output voltage is at switching frequency f _swthe harmonic wave v at place _swthe switching frequency harmonic wave v exported by each H-bridge unit _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, the v when inverter normally runs _swbe zero; When there being certain H-bridge unit short circuit, 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 a practical situation, v _swand non-vanishing, therefore a threshold value should be set and be used for judging whether to break down, when this threshold value can prevent command voltage from changing, erroneous judgement occur simultaneously.And when breaking down in a practical situation, 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 through low-pass filter filtering, then through A/D sampling, obtain dis-crete sample values v _x(k); Single H-bridge unit switching frequency f is obtained again by discrete Fourier transformation _swneighbouring multiple harmonic, is designated as in this harmonic sequence, the harmonic wave choosing amplitude maximum is as the characteristic harmonics near cascaded inverter x phase output voltage switching frequency.The threshold value of short trouble | C _xth| by command voltage obtain through computing, breakdown judge is greater than fault threshold according to for characteristic harmonics amplitude, and localization of fault is then the f according to output voltage _sw/ f ₀the phase angle of subharmonic by localization of fault to certain H-bridge unit concrete.

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., based on a cascade inverter H-bridge unit fault detection method for frequency analysis, it is characterized in that, the method comprises the steps:

Step 1: output AC voltage is sampled:

Step 1.1: the three-phase voltage utilizing voltage sensor to gather cascaded inverter is v _xo, wherein x represents x phase, and namely x=a, b, c, a, b, c are three-phase symbol; By described simulating signal v _xocarry out filtering by low-pass filter, filtered signal is v ' _xo, the cutoff frequency f of low-pass filter _lp=3f _sw, f _swfor the switching frequency of 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), wherein 0≤k≤N-1, N is the number of sampled point in a power frequency period;

Step 2: near switching frequency, harmonic wave extracts and process:

Step 2.1: calculate described discrete signal v _xk () is at H-bridge unit output voltage switching frequency f _swneighbouring 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)}

Wherein n _sw=f _sw/ f ₀, n _swfor the number of times of switching frequency harmonic wave, f gets in every phase institute _swneighbouring harmonic wave number is 2n ₀+ 1; H-bridge unit output voltage switching frequency f _sw, f ₀=50Hz; n ₀an integer, f ₀be a fixed value be 50Hz;

Step 2.2: calculate harmonic amplitude and phase angle; The result of described x phase voltage discrete Fourier transformation be multiplied with 1/N respectively and turn to exponential form, obtaining each phase switching frequency f _swneighbouring multiple harmonic, is designated as wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, and 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;

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

Step 2.3: harmonic wave near compute switch frequency; At described sequence of complex numbers in, one that gets amplitude maximum, be designated as namely characteristic harmonics near phase voltage switching frequency is exported as cascaded inverter; Wherein x represents x phase, and x=a, b, c, a, b, c are three-phase symbol, | C _xsw| be characteristic harmonics amplitude, namely for m subharmonic amplitude, for characteristic harmonics phase angle;

Step 3: breakdown judge 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=1,2 ..., n, f ₀for power frequency 50Hz, f _swfor H-bridge unit output voltage switching frequency; X phase with reference to switching frequency harmonic wave is wherein v _dcfor single H bridge DC side voltage, for command voltage amplitude, i=1,2 ..., n, M are modulation ratio, the fault threshold of ΔΦ=2 π/n, x phase $\left|C_{xth}\right|=\left|C_{xsw}^{*}\right|+0.05v_{dc};$

Step 3.2: breakdown judge; By characteristic harmonics near described cascaded inverter x phase output voltage switching frequency amplitude | C _xsw| with fault threshold | C _xth| compare, if | C _xsw| >|C _xth|, be then judged to be that x phase breaks down, otherwise be normal operation;

Step 3.3: localization of fault; If be judged as that H-bridge unit short trouble occurs inverter x phase in t, in described step 2.2, obtain switching frequency f _swneighbouring multiple harmonic get wherein m=n _swthat be its phase angle is localization of fault criterion is: if i-th H-bridge unit breaks down, then drop on in scope, wherein t ₀for first the H-bridge unit triangular carrier v of x phase before t _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.