CN101237145B - M-series modulation and variance judgement based parallel network active alone island detection system and method - Google Patents

Abstract

The invention relates to a synchronization active type islanding detection system and a method based on M sequence modulation and variance estimation. The detection system comprises a synchronization inverter, a synchronization switch, a voltage Hall sensor arranged on a synchronization communal join point, a digital signal processor connected with the synchronization inverter, the synchronization switch and the voltage Hall sensor. The detection method is to utilize the pseudo-random signal M sequence of the communication technique, modulate the modulation wave of the inverter according to the distribution law of the M sequence, so as to make the output have the characteristics of the M sequence, and thus the output signals also have the characteristics of random signals. During synchronizing, the voltage of the synchronization communal join point is controlled by a power network and the randomness is small; therefore the obtained variance value of the random sequence is very small; when islanding, the voltage of the synchronization communal join point is determined by the output of the inverter, the output of the inverter is modulated through the digital signal processor and have the characteristics of the random signals, so the variance value is significantly increased. During detecting, a variance threshold value is set, and islanding can be determined when the detected variance is more than the threshold value. The synchronization active type islanding detection system and the method has the advantages of simple arithmetic, low cost, small effects to harmonic waves of the output power and small islanding detection blind zone.

Description

Parallel network active alone island detection system and method based on M sequence modulation and variance judgement

Technical field

The present invention relates to a kind of parallel network active alone island detection system and method based on M sequence modulation and variance judgement.

Background technology

The development and use of new forms of energy such as photovoltaic generation, wind power generation are constantly developed, and future will occur the distributed generation system of more being made up of regenerative resource.These distributed generation systems are connected in parallel on the electrical network use, can realize the complimentary between distributed generation system and electrical network, but distributed generation system is connected in parallel on the electrical network and brings many potential safety hazards to electrical network, and island detection is exactly one of them important technology.Usually the island detection method that adopts has electric power system end detection method and power converter end detection method.Electric power system end detection method cost is higher.Power converter end detection method is divided into two classes again: passive type and active.The passive type detection algorithm is simple and be easy to realization, but has bigger detection blind area; Active detection method roughly has detection methods such as active frequency interference, slip-frequency drift, reactive power variation, Voltage unbalance current harmonics and correlation technique at present, and active frequency interferences detects and causes harmonic wave to increase; Slip-frequency drift detection method detects at pure resistor load or under resonance condition and lost efficacy; Reactive power change-detection method not only can cause harmonic wave to increase, and when having a plurality of distributed generation system in the electrical network, the idle phase mutual interference of variation also can cause detecting lost efficacy; The detection method algorithm of Voltage unbalance current harmonics detection method and correlation technique is too complicated, is unsuitable for practical application.

Summary of the invention

The objective of the invention is to provides a kind of parallel network active alone island detection system and method based on M sequence modulation and variance judgement at the defective that prior art exists, adopt this detection method can reduce the blind area of island detection, and this modulator approach is little to the harmonic effects that electrical network brings.In addition, this detection system does not change the hardware configuration of former combining inverter, and algorithm is simple, cost is low, output quality of power supply height.

For achieving the above object, the present invention adopts following technical proposals:

A kind of parallel network active alone island detection system based on M sequence modulation and variance judgement comprises combining inverter and the switch that is incorporated into the power networks, and it is characterized in that the be incorporated into the power networks public tie point P of combining inverter output behind the switch that is incorporated into the power networks _CCOn voltage hall sensor is installed, by a digital signal processor connect described combining inverter, switch and voltage hall sensor are incorporated into the power networks, the modulating wave of combining inverter (2) is pressed pseudo-random signal M sequence modulation by described digital signal processor, thereby the output that makes combining inverter (2) has the feature of M sequence, the voltage signal of gathering according to voltage hall sensor again, doing variance according to the data of sampling calculates, if variance yields surpasses threshold value, then judge isolated island, control combining inverter then and the switch that is incorporated into the power networks.Digital signal processor is by A/D conversion chip 1 P of fixed time sampling at each power frequency period _CCPoint voltage is through obtaining N P behind the N continuous power frequency period _CCThe point voltage sampled data is calculated these data and is obtained variance yields.When being incorporated into the power networks, because P _CCPoint voltage is controlled by electrical network, and randomness is little, and the random sequence variance yields that is obtained is very little, and during isolated island, P _CCPoint voltage is controlled by inverter output, and inverter output is subjected to digital signal processor to modulate the characteristics with random signal, so variance yields will increase greatly.Set a variance threshold values during detection, can be judged as isolated island above threshold value when detecting variance.

In the above-mentioned active alone island detection hardware device of judging with variance based on the M sequence modulation, described digital signal processor adopts the DSP2407 or the DSP2812 of TI company.Combining inverter builds up the H bridge by the IGBT pipe and realizes that voltage sensor adopts the voltage hall sensor of LEM, and switch S 1 adopts gate-controlled switch.

A kind of parallel network active alone island detection method based on M sequence modulation and variance judgement, adopt above-mentioned parallel network active alone island detection system to detect based on M sequence modulation and variance judgement, it is characterized in that adopting the pseudo-random signal M sequence of mechanics of communication, the regularity of distribution according to the M sequence is modulated the combining inverter modulating wave, so that output also has the feature of M sequence, thereby output signal also has the characteristics of random signal; By the be incorporated into the power networks voltage signal of public tie point of voltage hall sensor timing sampling, do variance according to the data of sampling and calculate simultaneously,, then be judged to be isolated island if variance yields surpasses thresholding.The modulation step of above-mentioned combining inverter modulating wave is as follows:

1. get 5 grades of M sequences, get 31 random binary elements, be respectively: 0000011100100010101111011010011;

2. with these 31 elements as a table storage in presetting form, the definition address variable of tabling look-up takes out a M sequential element at every turn when tabling look-up, the address variable of tabling look-up after tabling look-up adds 1, address value increases at 32 o'clock and is reset to 0;

3. table look-up when inverter sinusoidal modulation wave positive going zeror crossing point and take out current M sequential element, element is 1 o'clock, and then the modulation depth with current combining inverter multiply by coefficient 1.04, and element is 0 o'clock, then changes coefficient into 0.96.Combining inverter modulating wave after the modulation is shown below:

Wherein m is a modulation depth, and ω is the line voltage frequency, and a is current M sequential element value.

Above-mentioned variance calculation procedure is as follows:

1. digital signal processor is by the be incorporated into the power networks magnitude of voltage of public tie point of the fixed time sampling of the 5ms of voltage hall sensor after the beginning of each power frequency period positive going zeror crossing point;

2. the mathematic expectaion of digital signal processor calculating sampling N the data of coming

Δ E is a residual error;

3. digital signal processor calculates variance

4. digital signal processor compares with the variance of calculating according to the variance threshold values that is provided with, if exceed threshold value, then is judged as isolated island.

The present invention compared with prior art, have following conspicuous outstanding substantive distinguishing features and remarkable advantage: the present invention be a kind of be the island detection method that combining inverter is controlled of core with digital signal processor (DSP), it does not change the hardware configuration of original combining inverter, only on software, adopt the pseudo-random signal M sequence of mechanics of communication, the regularity of distribution according to the M sequence is modulated the inverter modulating wave, so that output also has the characteristic of M sequence, thereby output signal also has the characteristics of random signal, this modulator approach is simple and practical, and the harmonic wave of output waveform is little; Variance is calculated on algorithm and is simplified greatly than the algorithm that adopts correlation technique simultaneously, and the programming that is easy to digital signal processor realizes.Software algorithm of the present invention is simple, cost is low, and little to the harmonic effects of output electric energy, the island detection blind area is little.

Description of drawings

Fig. 1 is the parallel network active alone island detection system method structured flowchart that the present invention is based on M sequence modulation and variance judgement.

Fig. 2 is based on the modulation algorithm flow chart of M sequence modulation.

Fig. 3 is an algorithm flow chart of judging isolated island with variance

Fig. 4 is the system topological figure when being incorporated into the power networks with isolated island.

Embodiment

Details are as follows in conjunction with the accompanying drawings for the preferred embodiments of the present invention:

Referring to Fig. 1, this parallel network active alone island detection system based on M sequence modulation and variance judgement comprises combining inverter (2) and the switch that is incorporated into the power networks (4), the be incorporated into the power networks public tie point P of combining inverter (2) output behind the switch that is incorporated into the power networks (4) _CCThe voltage hall sensor of last installation (3), connect described combining inverter (2), the switch that is incorporated into the power networks (4) and voltage hall sensor (3) by a digital signal processor (1), described digital signal processor (1) carries out the pseudo-random signal modulation, the voltage signal of gathering according to voltage hall sensor (3) carries out isolated island and calculates back control combining inverter (2) and the switch that is incorporated into the power networks (4) again.Digital signal processor (1) adopts the DSP2407 or the DSP2812 of TI company, and it is by modulation algorithm module output modulation signal.Combining inverter (2) builds up the H bridge by the IGBT power tube and realizes the public tie point (P that is incorporated into the power networks of inverter output end _CC) voltage hall sensor (3) go up to be installed, digital signal processor (1) is incorporated into the power networks or the island state control switch (4) that is incorporated into the power networks according to current.Because the inverter modulating wave is pressed pseudo-random signal M sequence modulation by digital signal processor, thereby inverter output also has the rule of random signal.The be incorporated into the power networks voltage signal of public tie point of fixed time after each power frequency period zero crossing begins sampling, digital signal processor carries out variance to sampled signal and calculates, and obtains variance yields, and this value and setting threshold relatively can be detected isolated island.

This is based on the parallel network active alone island detection method of M sequence modulation and variance judgement, detect in above-mentioned detection system, adopt the pseudo-random signal M sequence of mechanics of communication, the regularity of distribution according to the M sequence is modulated combining inverter (2) modulating wave, so that output also has the feature of M sequence, thereby output signal also has the characteristics of random signal; Simultaneously by voltage hall sensor (3) the timing sampling public tie point P that is incorporated into the power networks _CCVoltage signal, do variance according to the data of sampling and calculate, if variance yields surpasses thresholding, then be judged to be isolated island.The above-mentioned modulation step to combining inverter (2) modulating wave is as follows:

1. get 5 grades of M sequences, get 31 random binary elements, be respectively: 0000011100100010101111011010011;

2. with these 31 elements as a table storage in presetting form, the definition address variable of tabling look-up takes out a M sequential element at every turn when tabling look-up, the address variable of tabling look-up after tabling look-up adds 1, address value increases at 32 o'clock and is reset to 0;

3. table look-up when inverter sinusoidal modulation wave positive going zeror crossing point and take out current M sequential element, element is 1 o'clock, and then the modulation depth with current combining inverter multiply by coefficient 1.04, and element is 0 o'clock, then changes coefficient into 0.96.Combining inverter modulating wave after the modulation is shown below:

Wherein m is a modulation depth, and ω is the line voltage frequency, and a is current M sequential element value.

The control flow of modulating wave is referring to Fig. 2.

The step that above-mentioned variance is calculated is as follows:

1. digital signal processor is by the be incorporated into the power networks magnitude of voltage of public tie point of the fixed time sampling of the 5ms of voltage hall sensor after the beginning of each power frequency period positive going zeror crossing point;

2. the mathematic expectaion of digital signal processor calculating sampling N the data of coming

Δ E is a residual error;

3. digital signal processor calculates variance

4. digital signal processor compares with the variance of calculating according to the variance threshold values that is provided with, if exceed threshold value, then is judged as isolated island.

Variance judges that the control flow of isolated island is referring to Fig. 3.

The active alone island detection method principle of judging with variance based on the M sequence modulation is summarized as follows:

As Fig. 4, Fig. 4 (a) is the topological diagram of distributed grid-connected system, and Fig. 4 (b) is the topological diagram of distributed generation system under the isolated island situation.

u _d(t) and e _Pcc(t) represent combining inverter output voltage and the voltage of public tie point (Pcc) of being incorporated into the power networks, e respectively ₀(t) be line voltage.u _d(t) and e _Pcc(t) expression formula is:

u _d(t)＝U _d(t)cos(2πft+θ _d) (1)

e _PCC(t)＝E _PCC(t)cos(2πft+θ _r)

(2)

U wherein _d(t) and E _Pcc(t) be respectively u _d(t) and e _Pcc(t) amplitude, θ _dAnd θ _rBe u _d(t) and e _Pcc(t) initial phase, f are work frequencies.If with U _d(t) and E _Pcc(t) be decomposed into the stack of a stable quantity and a change at random amount, shown in (3), (4):

U _d(t)＝U _d0+ΔU _d(t) (3)

E _PCC(t)＝E _PCC0+ΔE _PCC(t) (4)

U _D0And E _Pcc0Be stable quantity, Δ U _d(t) and Δ E _PCC(t) be time dependent change at random amount.

When being incorporated into the power networks, because net capacity is very big, e _Pcc(t) be controlled by e ₀(t), Δ E _PCC(t) randomness is very little; When isolated island occurs, e _Pcc(t) directly be controlled by u _d(t), if Δ U _d(t) has the characteristic (as white noise) of random signal, then Δ E _PCC(t) stochastic behaviour obviously presents, and changes as variance.Thereby the detection of isolated island can be converted on the signal stochastic behaviour and analyzes.

Yet, make Δ U _d(t) have certain characteristics at random, need handle accordingly the sinusoidal modulation wave of combining inverter, the present invention introduces pseudo-random signal (M sequence) commonly used in the mechanics of communication.The M sequence is a kind of pseudo random sequence commonly used in the Digital Signal Processing, and it has 3 important characteristics:

1. in each cycle, code element 1 has more now once than code element 0, has balance;

2. in each cycle, have 2 ⁿ-1 element distance of swimming, wherein the distance of swimming number of the distance of swimming of code element 1 and code element 0 respectively accounts for half;

3. M sequence { a _nAnd its displacement sequence { a _nThe exclusive-OR of-t} is still another displacement sequence in the M sequence.

Three characteristics of this of M sequence have determined that the M sequence has good white noise character, are the pseudo noise sequence of narrow sense, and are easy to generate and duplicate.Tell about the modulator approach of M sequence below.

5 grades of linear feedback shift register networks are adopted in the generation of M sequence, form by 5 d type flip flops and an XOR gate, the output of the 5th and the 3rd d type flip flop is as the input of XOR gate, the output of XOR gate is as the input of first d type flip flop, can obtain 5 grades of M sequences, totally 31 elements are respectively:

0000011100100010101111011010011

The regularity of distribution by these 31 elements, the modulating wave of inverter is done corresponding conversion, its implementation is: earlier with these 31 elements as a table storage in form, when inverter sinusoidal modulation wave positive going zeror crossing point, take out current M sequential element, element is 1 o'clock, then current modulation depth be multiply by coefficient 1.04, element is 0 o'clock, and coefficient changes 0.96 into.The inverter modulating wave is shown below.

$f\left(t\right)=\left\{\begin{array}{cc}1.04m\·\sin \left(\mathrm{\ωt}\right)& a=1\\ 0.96m\·\sin \left(\mathrm{\ωt}\right)& a=0\end{array}\right.---\left(5\right)$

Wherein m is a modulation depth, and ω is the line voltage frequency, and a is current M sequential element value.

Then the combining inverter output voltage is:

$U_{\mathrm{invert}}=\left\{\begin{array}{cc}1.04\·U_m\sin \left(\mathrm{\ωt}\right)& a=1\\ 0.96\·U_m\sin \left(\mathrm{\ωt}\right)& a=0\end{array}\right.---\left(6\right)$

When giving local load, the voltage that Pcc is ordered is when independently-powered:

$e_{\mathrm{PCC}}=\left\{\begin{array}{cc}1.04\·E_m\sin (\mathrm{\ωt}+\mathrm{\θ})& a=1\\ 0.96\·E_m\sin (\mathrm{\ωt}+\mathrm{\θ})& a=0\end{array}\right.---\left(7\right)$

Voltage signal of fixed time sampling in each power frequency period that Pcc is ordered, 31 cycles of continuous sampling obtain 31 data E _PCC(1), E _PCC(2) ..., E _PCC(31), can obtain random sequence Δ E _PCC(N) 31 sample data { Δ E _PCC(1), Δ E _PCC(2) ..., Δ E _PCC(31) }, wherein

Definition random sequence Δ E _PCC(N) mathematic expectaion is:

$u_{{\mathrm{\ΔE}}_{\mathrm{PCC}}}=\frac{1}{31}\underset{i=1}{\overset{31}{\mathrm{\Σ}}}\mathrm{\Δ}{E}_{\mathrm{Pcc}}\left(i\right)---\left(8\right)$

Random sequence Δ E then _PCC(N) variance is:

${\mathrm{\σ}}_{{\mathrm{\ΔE}}_{\mathrm{PCC}}}^2=\frac{1}{31}\underset{i=1}{\overset{31}{\mathrm{\Σ}}}{[{\mathrm{\ΔE}}_{\mathrm{PCC}}\left(i\right)-u_{{\mathrm{\ΔE}}_{\mathrm{PCC}}}]}^2---\left(9\right)$

In the formula, N=31 is the duration of M sequence, and when generating electricity by way of merging two or more grid systems, the Pcc point voltage is controlled by line voltage, and change in voltage is little, so Δ E (i) trends towards 0, its mathematic expectaion also trends towards zero, and variance is very little; When isolated island occurred, the Pcc point voltage was controlled by inverter output voltage and has the characteristic of M sequence, and the random law of M sequence modulation appears in Δ E (i), and its mathematic expectaion trends towards zero by the characteristic of M sequence, knows that by formula (9) variance then enlarges markedly.A variance threshold values can be set during island detection, isolated island can be judged as above threshold value when detecting variance.

Claims (4)

1. the parallel network active alone island detection system based on M sequence and variance judgement comprises combining inverter (2) and the switch that is incorporated into the power networks (4), it is characterized in that the be incorporated into the power networks public tie point (P of combining inverter (2) output behind the switch that is incorporated into the power networks (4) _CC) on voltage hall sensor (3) is installed, connect described combining inverter (2) by a digital signal processor (1), switch (4) and voltage hall sensor (3) are incorporated into the power networks, the modulating wave of combining inverter (2) is pressed pseudo-random signal M sequence modulation by described digital signal processor (1), thereby the output that makes combining inverter (2) has the feature of M sequence, the voltage signal of gathering according to voltage hall sensor (3) again, doing variance according to the data of sampling calculates, if variance yields surpasses threshold value, then be judged to be isolated island, control combining inverter (2) and the switch that is incorporated into the power networks (4) then.

2. parallel network active alone island detection method of judging based on M sequence modulation and variance, adopt the parallel network active alone island detection system based on M sequence modulation and variance judgement according to claim 1 to detect, it is characterized in that adopting the pseudo-random signal M sequence of mechanics of communication, the regularity of distribution according to the M sequence is modulated combining inverter (2) modulating wave, so that output also has the feature of M sequence, thereby output signal also has the characteristics of random signal; By the be incorporated into the power networks voltage signal of public tie point (Pcc) of voltage hall sensor (3) timing sampling, do variance according to the data of sampling and calculate simultaneously,, then be judged to be isolated island if variance yields surpasses threshold value.

3. according to right 2 described parallel network active alone island detection methods based on M sequence modulation and variance judgement, the modulation step of the described combining inverter of its feature (2) modulating wave is as follows:

1. get 5 grades of M sequences, get 31 random binary elements, be respectively:

0000011100100010101111011010011；

2. with these 31 elements as a table storage in presetting form, the definition address variable of tabling look-up takes out a M sequential element at every turn when tabling look-up, the address variable of tabling look-up after tabling look-up adds 1, address value increases at 32 o'clock and is reset to 0;

3. when combining inverter (2) sinusoidal modulation wave positive going zeror crossing point, table look-up and take out current M sequential element, element is 1 o'clock, then the modulation depth with current combining inverter multiply by coefficient 1.04, element is 0 o'clock, then change coefficient into 0.96, the combining inverter after the modulation (2) modulating wave is shown below:

Wherein m is a modulation depth, and ω is the line voltage frequency, and a is current M sequential element value.

4. according to right 2 described parallel network active alone island detection methods, it is characterized in that the step of variance calculating is as follows based on M sequence modulation and variance judgement:

1. digital signal processor (1) is by the be incorporated into the power networks magnitude of voltage of public tie point of the fixed time sampling of the 5ms of voltage hall sensor (3) after the beginning of each power frequency period positive going zeror crossing point;

2. the mathematic expectaion of digital signal processor (1) calculating sampling N the data of coming

Δ E is a residual error;

3. digital signal processor (1) calculates variance

4. digital signal processor (1) compares with the variance of calculating according to the variance threshold values that is provided with, if exceed threshold value, then is judged as isolated island.

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