CN205193210U

CN205193210U - Direct current trouble arc detection device

Info

Publication number: CN205193210U
Application number: CN201520669687.8U
Authority: CN
Inventors: 张玉林; 刘蓉; 张俊
Original assignee: SHANGHAI CHINT POWER SYSTEMS CO Ltd
Current assignee: SHANGHAI CHINT POWER SYSTEMS CO Ltd
Priority date: 2015-08-31
Filing date: 2015-08-31
Publication date: 2016-04-27
Anticipated expiration: 2025-08-31

Abstract

The utility model relates to a direct current trouble arc detection device, including impulse transformer, its characterized in that still includes band -pass filtering and amplifying circuit, AD sampling circuit and MCU processing unit, and wherein, impulse transformer's current output terminal links to each other with band -pass filtering and amplifying circuit's input, and AD sampling circuit's input is connected to band -pass filtering and amplifying circuit's output, and AD sampling circuit's output links to each other with MCU processing unit's input. To dc power converter field, the utility model provides a novel converter self characteristic is utilized to direct current trouble arc detection method, and the direct current highs all can produce noise signal in converter switching frequency's doubling of frequency department, utilizes this noise signal to carry out analytical calculation to the fault electric arc frequency spectrum to this comes the detection whether to break down electric arc.

Description

A kind of DC Line Fault electric arc detecting device

Technical field

The utility model proposes a kind of new method for DC Line Fault arc-detection, whether effective differentiation breaks down electric arc, report an error in time after the electric arc that breaks down being detected, improve security of system, the utility model can be applicable in DC power converter field, as UPS battery system, photovoltaic generating system etc.

Background technology

In recent years, along with the fast development such as clean energy resource, accumulator system, direct current power transformation system obtains very large development, because these system powers are large, voltage is high thus more easily produce fault electric arc.

Electric arc refers to the conductor flowing through big current, because the unreliable connection of joint or joint, wire insulation are degenerated, and the loose contact caused, between contact or contact and unreliable connection the between other conductors and the electric discharge phenomena that formed.Electric arc causes leading cause of fire in straight-flow system, and the generation of detecting electric arc promptly and accurately, directly affects the safety and reliability of straight-flow system.

Electric arc comprises series connection arcing and arcing in parallel, and the former refers to the arcing between cable, and the latter refers to that DC terminal is to electric discharge safely.What the utility model mainly solved is series connection arcing.

Photovoltaic generating system is exactly the DC application of this high-voltage large current.Along with the rapid growth of photovoltaic industry, the photovoltaic system equipment of installation gets more and more.The carelessness of the photovoltaic power generation equipment put into operation gradually in aging and artificial installation process brings challenges to the security of photovoltaic system.Photovoltaic system DC voltage can up to kilovolt on hundreds of with the configuration of photovoltaic panel, if produce fault electric arc, owing to not having zero crossing to protect, direct-current arc is more dangerous than alternating current arc.The photovoltaic panel of photovoltaic system is subject to sunlight prolonged exposure produce power, if produce fault electric arc and do not perceive in time and line disconnection, panel provides energy endlessly to electric arc, all huge damage can be caused to transmission line of electricity and photovoltaic apparatus itself, fire can be caused, threat to life safety time serious.

Based on safe and reliable consideration, increasing DC application proposes testing requirement to direct current arcing, and some has been forced to require to perform, as U.S.'s electrician regulation NEC2011 version starts to require for photovoltaic power generating system device arc fault detecting circuit breaker.For in NEC about the requirement of DC Line Fault arc-detection, UL1699B standard gives detailed regulation.This regulation requires should provide visual alarm prompt when inverter detects fault electric arc, and this alarm can not be removed automatically.After power cut-off re-powers, this alarm should still show, and manually must remove inverter could grid-connected work.Inverter need have the manual self-checking function of fault electric arc, visual interface must be had to point out when inverter performs self-inspection, if self-inspection is not passed through, must manually remove, otherwise this alarm is preserved, and still exists after power-off restarting.UL1699B has also done closed specification requirement to guard time and external environment etc.

On the one hand, reliably arc-detection is extremely important beyond doubt to the security of straight-flow system accurately, on the other hand, how to avoid detecting unit by mistake detecting be also the difficult point in reality.As U.S. NEC2011 requirement, after detecting unit sends arcing alarm, photovoltaic DC-to-AC converter need stop generating electricity and wait for that operating personnel detect and manually remove and just allow to continue to generate electricity by way of merging two or more grid systems, and therefore detecting can cause photovoltaic generating system frequently to shut down by mistake, influential system gene-ration revenue.

Detection common is at present as follows:

1, the radio frequency noise produced based on arcing judges

In WO95/25374, after occurring according to DC current electric arc, the radio frequency noise of certain frequency range can be produced, noise signal is received by radio-frequency (RF) Receiving Device, and carry out certain scaling down processing, the noise amplitude before and after occurring according to electric arc judges, thus whether detecting electric arc occurs.

Because power electronic equipment itself can produce noise, and electronic equipment uses increasingly extensive, and therefore this scheme cannot avoid detecting by mistake, and multiple equipment runs simultaneously, cannot accurately judge and locate the position that electric arc produces.

2, based on the detection of DC current high fdrequency component amplitude change

Nationalinstrument company DC current spectral magnitude of giving chapter and verse judges

The principle of this scheme, the principle bringing high frequency noise to a certain degree after producing according to direct-current arc to electric current equally, but detection mode is by gathering DC current and carrying out fast Fourier decomposition (FFT) to it, thus obtain the amplitude versus frequency characte of electric current, by judging that electric arc produces the amplitude difference of certain frequency band of front and back, judge whether electric arc produces.

This scheme is relatively accurate owing to detecting, with low cost and be widely adopted.But shortcoming is to be limited by equally the noise jamming that Power Electronic Circuit itself and surrounding devices bring, and comparatively greatly, this scheme just cannot use or frequently report by mistake the noise signal in the DC current of equipment itself.

Summary of the invention

The purpose of this utility model is to provide one can avoid detecting by mistake, and can not be limited by the series connection arcing detection method of the noise jamming that Power Electronic Circuit itself is brought with surrounding devices.

In order to achieve the above object, the technical solution of the utility model there is provided a kind of DC Line Fault electric arc detecting device, comprise pulse transformer, it is characterized in that, also comprise bandpass filtering amplifying circuit, AD sample circuit and MCU processing unit, wherein, the current output terminal of pulse transformer is connected with the input end of bandpass filtering amplifying circuit, the output terminal of bandpass filtering amplifying circuit connects the input end of AD sample circuit, and the output terminal of AD sample circuit is connected with the input end of MCU processing unit

For DC power converter field, the utility model proposes a kind of new DC Line Fault arc method for measuring, utilize transducer self-characteristic, DC current high fdrequency component all can produce noise signal at the frequency multiplication place of converter switches frequency, utilize this noise signal to carry out analytical calculation to fault electric arc frequency spectrum, detect with this electric arc that whether breaks down.

Accompanying drawing explanation

Fig. 1 is conventional BOOST circuit;

Fig. 2 is the drive singal of BOOST circuit;

Fig. 3 is amplitude-versus-frequency curve when there is not electric arc;

Fig. 4 is amplitude-versus-frequency curve when there is electric arc;

Fig. 5 is for photovoltaic DC-to-AC converter, and the method utilizing the utility model to provide carries out the embodiment of arc-detection;

Fig. 6 is the process flow diagram of MCU processing section;

Fig. 7 is overview flow chart of the present utility model.

Embodiment

For making the utility model become apparent, hereby with preferred embodiment, and accompanying drawing is coordinated to be described in detail below.

A kind of device that the utility model proposes is based on the direct-current arc detection method in conjunction with converters self character.Current converters is mostly PWM (pulsewidthmodulation) high frequency chopping principle, the high frequency of switching device is utilized to switch (being generally a few kHz ~ 500Hz), DC current is chopped into DC pulse pulse current, this frequency range in switching frequency place and switching frequency multiple of such DC current can produce the signal compared to neighbouring frequency higher magnitude.And when electric arc produces, because the frequency spectrum of electric current is by integral raising, the switching frequency of transducer itself and the noise amplitude of multiple frequency thereof then change relatively little compared to neighbouring frequency range.

Be described for conventional BOOST circuit as shown in Figure 1.Switch Q is HF switch, and its drive singal is shown in Vgs in Fig. 2, and inductive current and input current are i respectively _land i _in.From waveform, input direct-current electric current contains abundant switching frequency time noise.

FFT is carried out to input current, the amplitude versus frequency characte of input current can be obtained as shown in Figure 3, for switching frequency 16kH, can find out, in the frequency band of F1 ~ F2, the noise peak D1 of switching frequency 16kHz far above the mean value D2 in frequency band, at the frequency multiplication place of 16kHz, as 32kHz, 48kHz, also there is same situation.

In frequency band F1 ~ F2, definition D3 is the difference of peak value D1 and average D2, then the ratio D3/D2 of quantization parameter D3 and D2 then can be used to judge whether electric arc occurs, and when without electric arc, D3/D2 is larger.

After electric arc produces, the FFT amplitude versus frequency characte of input current as shown in Figure 4, can be found out, the amplitude of entirety is raised by the high frequency noise produced due to electric arc, and the peak value D1 in the frequency band comprising switching frequency and frequency multiplication reduces greatly relative to mean value D2 in frequency band.

From analyzing above, for high-frequency power electronic transducer, the electric current amplitude versus frequency characte after electric arc produces has two obvious characteristics:

1, in some frequency range, amplitude is obviously raised;

2, near switching frequency and frequency multiplication thereof, to be flooded by arc hissing due to the high-frequency signal amplitude of transducer itself or relative peak obviously diminishes, namely this noise in switching frequency and frequency multiplication place thereof of switch converters is constant, but other frequency ranges become large due to arc hissing;

According to above analysis, the arc-detection process that the utility model proposes is as follows:

1, input current is sampled, filtering and FFT, obtain the amplitude versus frequency characte of electric current high fdrequency component;

2, according to the switching characteristic selection and comparison frequency range of transducer self, judge whether amplitude becomes large;

3, selected one or more frequency range comprising switching frequency or multiple frequency, calculates the maximal value D1 in frequency range and mean value D2, utilize average after there is electric arc to become large and phenomenon that maximal value is substantially constant through logical calculated, judge whether electric arc occurs.

For photovoltaic DC-to-AC converter, provide a kind of embodiment utilizing the utility model to carry out arc-detection below:

1) DC current is through pulse transformer, bandpass filter, and AD converter and the sampling of MCU processor obtain current data, as Fig. 5.

2) MCU processing section, then sampled data is FFT through Chinese woods window, and time domain is converted to frequency domain, carrying out mathematical logic process after calculating high-frequency signal amplitude, as Fig. 6.

3) mathematical logic processing section mainly utilizes the noise signal that machine self-characteristic produces, and the noise signal of machine is mainly at the frequency multiplication place of machine switching frequency, and Fig. 4 is the frequency spectrum of electric arc of breaking down, and Fig. 3 is the frequency spectrum of electric arc of not breaking down.

Example machine switching frequency 16k in figure, whether no matter arc fault machine occur as shown in frequency spectrum obvious noise signal near 16k, 32k, 48k.

Near selecting frequency multiplication based on above 2 MCU, frequency range processes, as Fig. 3 and Fig. 4 can select 27k-37k and 43k-53k two frequency ranges to process respectively.Composition graphs 7, processing procedure following (marking D1 in Fig. 3, D2, D3)

The sliding average of Y number in step one, calculating frequency range, alternative maximal value D1.In the utility model, directly do not use running mean maximal value by maximal value, thus interference is taken into account, utilize the filtering that running mean acquires a certain degree.

Step 2, remove a certain proportion of high level in frequency range and low value and be left value and average D2.

Step 3, deduct D2 with maximal value D1 and try to achieve difference D3.

Step 4, try to achieve number percent D4 with difference D3 divided by average D2, add up the number X of 10 medium and small number percent D4 in threshold value T1 of data, if X is greater than threshold value T2, then have electric arc to occur, otherwise, occur without electric arc.

This algorithm with only to judge in a certain frequency range compared with amplitude size advantageously: first, difference D3 when there is arc fault is less than difference D3 when not there is arc fault; Secondly, average D2 when there is arc fault is greater than average D2 when not there is arc fault; Finally, with D3 divided by D2, when there is arc fault, the less and denominator of molecule is larger, and institute's value is certainly less, more favourable differentiation.

The utility model is considered to use this noise signal from following 2: first: during generation arc fault, overall spectrum amplitude is raised; Second: frequency multiplication place peak amplitude is substantially constant.

Claims

1. a DC Line Fault electric arc detecting device, comprise pulse transformer, it is characterized in that, also comprise bandpass filtering amplifying circuit, AD sample circuit and MCU processing unit, wherein, the current output terminal of pulse transformer is connected with the input end of bandpass filtering amplifying circuit, and the output terminal of bandpass filtering amplifying circuit connects the input end of AD sample circuit, and the output terminal of AD sample circuit is connected with the input end of MCU processing unit.