CN101794988B - Method for detecting piconet island state - Google Patents

Abstract

The invention discloses a method for detecting a piconet island state according to the self-characteristic of a piconet. The method comprises the following steps of: (1) detecting electrical characteristic value when the piconet runs; (2) judging whether the voltage at a load end is higher than the definite value or not, if yes, entering step (3), and if not, considering that the piconet is not in the island state; (3) judging whether the frequency changing rate is higher than the upper limit of the definite value or not, if yes, sending out a trip signal and then finishing, and if not, entering step (4); (4) detecting and judging whether the frequency changing rate is higher than the lower limit of the definite value or not, if yes, judging whether the phase difference is more than the phase difference setting valve or not, if yes, finishing the detection and sending out the trip signal, and if not entering step (5); and (5) after delaying for a period of time, judging whether the phase difference is more than the phase difference setting valve or not, if yes, sending out the trip signal, and if not, considering that the piconet is in the island state. Compared with the existing detection method, the method has the characteristics of rapid and reliable detection, and guarantees comparatively high anti-interference capability at the same time.

Description

A kind of detection method of piconet island state

Technical field

The invention belongs to the microgrid technology, be specifically related to the method that a kind of piconet island state detects, this method is a kind of integrated approach based on frequency change rate and phase changing capacity coordination judgement.

Background technology

Along with the raising and the develop rapidly of renewable and clean energy resource generation technology that society requires power supply reliability, microgrid has obtained increasing attention as a kind of new electrical network form, but the application of microgrid also faces a series of matter of science and technologys that need solutions.Wherein, because the piconet island effect that fault or disturbance cause is exactly a huge challenge.Under the prerequisite that present island effect utilization technology is not a very maturation, form isolated island hastily, will cause huge impact, also run counter to the highest criterion of power system security simultaneously the user.Therefore, must configuration island detection scheme in the microgrid, when detecting unplanned isolated island and take place, need break off distributed generator in the microgrid fast, in time, to guarantee the safety of electric power system.

Present piconet island detection method mainly is divided into based on the island detection method of communication and local island detection method.Wherein the island detection method based on communication can be divided into intertripping method and electric line carrier communication method again; And local island detection method mainly is divided into passive type island detection method and active alone island detection method.

In the island detection method based on communication, the intertripping method is simple and effectively concerning the feeder line that fixed topology is arranged, if but when a plurality of automatic switches and feeder line change in topology were arranged in the system, it is quite complicated that the intertripping method possibly become; The signal means of transportation of electric line carrier communication method electrification line needn't be considered the change of topological structure, carries out easily, but needs to use signal generator and step-down transformer, causes to detect that cost is high, cost is big.

The active alone island detection method detects island effect through injecting disturbance to electrical network according to corresponding system responses.But in microgrid, because many distributed generators need inject a plurality of interference, the interference of these injections influences each other, and certainly will influence the response of system, thereby has reduced the reliability that detects.

The passive type island detection method is to judge that through detecting different system parameterss whether isolated island produces, and this method need not system operation is exerted one's influence, thus noiseless to electrical network, the quality of power supply there is not influence.Its principle is that because the support of big electrical network, the voltage magnitude of system, phase place and frequency are invariable when microgrid is incorporated into the power networks with big electrical network; When because little electrical network and big electrical network break off is isolated island when taking place, the power that distributed generator provides in the microgrid is unequal with the power that load consumes, and makes voltage magnitude in the system, phase place and frequency change.Therefore just can whether isolated island take place interpretation through detecting voltage magnitude, phase place and frequency.

Passive type island detection commonly used has two kinds of methods; A kind of is the frequency change rate method; The principle of this method is when piconet island takes place; The power that distributed power source provides exists the power imbalance with the power that load consumes, and the power output of distributed generator changes the variation that causes the microgrid frequency.Relation between frequency change rate and the power amount of unbalance, can represent by formula (1):

$\frac{\mathrm{df}}{\mathrm{dt}}=-\frac{(P_L-P_{\mathrm{DG}})f_{\mathrm{<figure-callout\; id="2"\; label="n"\; filenames="HDA0000020264260000023.png"\; state="\{\{state\}\}">n</figure-callout>}}}{2{\mathrm{HP}}_{\mathrm{GN}}}---\left(1\right)$

Wherein, f is the actual frequency of microgrid, and t is the time of system, P _LBe the power that load consumes, P _DGBe the power output of distributed generator, f _nBe the rated frequency of system, H is the inertia time constant of distributed generator, P _GNRated power for distributed generator.

If given frequency change rate setting value f ' _Set, it is following to obtain the frequency change rate island detection method:

$\frac{\mathrm{df}}{\mathrm{dt}}\&GreaterEqual;f_{\mathrm{set}}^{\&prime;}---\left(2\right)$

When formula (2) when satisfying condition, can judge that microgrid gets into island state.It is little, highly sensitive that this method detects blind area, but in active power difference very hour, might get into and detect the dead band, and experience in system under the situation of big disturbance and be easy to generate erroneous judgement.

Another kind is a phase change method; The principle of this method is when piconet island takes place; Because generator electromotive force and set end voltage exist voltage drop and phase difference; Load that distributed generation system is born increases or reduces, with the phase difference increase that causes set end voltage and electromotive force accordingly or reduce.Utilize the variation of this phase difference can obtain following criterion:

Δθ≥α _set (3)

When formula (3) is set up, think that microgrid gets into island state.Δ θ is a load side voltage-phase variable quantity; α _SetSetting value for load side voltage-phase variable quantity.This method hour still can detect island state in active power difference, not influenced by system disturbance, but this method is when active power difference is big, and detection time is slow, can not satisfy the requirement of fast detecting.

Summary of the invention

The object of the present invention is to provide a kind of detection method of piconet island state, this detection method is quick, sensitive, and can prevent the erroneous judgement when system interference effectively.

The detection method of a kind of piconet island state provided by the invention is characterized in that, this method comprises the steps:

(1) microgrid is in service, measures the terminal voltage V of load, the running frequency f and the frequency change rate

of microgrid in real time

(2) judge that V is whether greater than the threshold value V of predefined load side voltage _Limit, if, then change step (3) over to, otherwise make trip signal trip=0, change step (6) over to;

(3) determination frequency rate of change

Whether greater than the setting value upper limit f ' of frequency change rate _Max, if then make trip signal trip=1, and change step (6) over to, otherwise change step (4) over to;

(4) determination frequency rate of change

Whether greater than the setting value lower limit f ' of frequency change rate _Min,, otherwise behind the time-delay t, change step (5) over to if then change step (5) over to;

(5) judge whether load side voltage-phase variation delta θ surpasses the threshold alpha of phase change relay _Set,, change step (6) over to if then make trip signal trip=1; Otherwise, make trip signal trip=0, change step (6) over to;

(6) when trip=0, think that then isolated island does not take place microgrid, sends block signal; When trip=1, the expression piconet island takes place, and sends trip signal; Change step (7) over to;

(7) detection of end.

The method that this method adopts determination frequency rate of change and phase changing capacity to combine, the frequency change rate method is fast sensitive when active power difference is big, and hour phase changing capacity method is fast sensitive in active power difference.This method that combines can detect piconet island state fast, delicately, and can prevent the erroneous judgement when system interference effectively under any situation.

Description of drawings

Fig. 1 is the flow chart of the inventive method;

Fig. 2 is the artificial circuit figure of instance;

Fig. 3 is the frequency change rate analogous diagram behind the instance isolated island;

Fig. 4 is the phase changing capacity analogous diagram behind the instance isolated island.

Embodiment

Below in conjunction with accompanying drawing and instance the present invention is done further detailed explanation.

Fig. 1 is the flow chart of the inventive method, and among the figure, V is the terminal voltage of load; V _LimitThe threshold value of load side voltage; F is the actual frequency of microgrid; T is the time of system; F ' _MaxThe setting value upper limit for frequency change rate; F ' _MinSetting value lower limit for frequency change rate; Δ θ is a load side voltage-phase variable quantity; α _SetSetting value for load side voltage-phase variable quantity; Trip is a trip signal, works as trip=0, and expression does not have isolated island to take place, and the circuit breaker that links to each other with distributed generator does not trip, and works as trip=1, and the circuit breaker trip that links to each other with distributed generator takes place the expression isolated island.

The practical implementation step of this method is following:

(1) microgrid is in service, measures the terminal voltage V of load, the running frequency f and the frequency change rate

of microgrid in real time

(2) judge that V is whether greater than the threshold value V of load side voltage _Limit(V _Limit85%-95% for the motor rated voltage), if, then change step (3) over to, otherwise make trip signal trip=0, change step (6) over to;

(3) determination frequency rate of change

Whether greater than the setting value upper limit f ' of frequency change rate _Max(f ' _MaxGenerally be set at 0.5Hz/s-1Hz/s), if then make trip signal trip=1, and change step (6) over to, otherwise change step (4) over to;

(4) determination frequency rate of change

Whether greater than the setting value lower limit f ' of frequency change rate _Min(f ' _MinGenerally be set at 0.1Hz/s-0.5Hz/s), if then change step (5) over to, otherwise behind the time-delay t (t generally is set at 0.3～3 second), change step (5) over to;

(5) judge whether load side voltage-phase variation delta θ surpasses the threshold alpha of phase change relay _Set(being made as 2 °～20 ° usually) if then make trip signal trip=1, changes step (6) over to; Otherwise, make trip signal trip=0, change step (6) over to;

(6) when trip=0, think that then isolated island does not take place microgrid, sends block signal; When trip=1, the expression piconet island takes place, and sends trip signal; Change step (7) over to;

(7) detection of end.

Instance:

Adopt PSCAD/EMTDC electromagnetic transient simulation software to set up artificial circuit as shown in Figure 2.

Main electrical network is the ideal source of 50MVA, and distributed power source DG adopts synchronous generator, and capacity is 5.4MVA, and active power is 4.6MW, reactive power 2.4Mvar, inertia coeffeicent 6.07s.Load 1 is adopted permanent power module with load 2, and its total active power is 6.0MW, and reactive power is 2.4Mvar.The rated frequency of system is 50Hz.

In this example, get V _Limit=0.93p.u, f ' _Min=0.2Hz/s, f ' _Max=0.5Hz/s, t=2S, α _Set=3 °.

When three-phase breaker BRKs1, BRKs2, BRK1, BRK2 close a floodgate; The microgrid stable operation of being incorporated into the power networks, after 7 seconds, three-phase breaker BRKs1 breaks off; Microgrid forms island state thus, this moment the microgrid frequency change rate that measures distinguish following Fig. 3 with phase changing capacity, shown in 4.

Among Fig. 3, frequency change rate is 0.2Hz/s when 7.05s, reaches the minimum frequency rate of change threshold of this method, when 7.15s, reaches 0.5Hz/s, can directly make island state according to this method and judge; Among Fig. 4, load side voltage-phase variable quantity is 3 ° at 7.43s, has reached the differentiation threshold value of this method, can make island state and judge.

The above is preferred embodiment of the present invention, but the present invention should not be confined to the disclosed content of this embodiment and accompanying drawing.So everyly do not break away from the equivalence of accomplishing under the disclosed spirit of the present invention or revise, all fall into the scope of the present invention's protection.

Claims (1)

1. the detection method of a piconet island state is characterized in that, this method comprises the steps:

(1) microgrid is in service, measures the terminal voltage V of load, the running frequency f and the frequency change rate

of microgrid in real time

(2) judge that V is whether greater than the threshold value V of predefined load side voltage _Limit, if, then change step (3) over to, otherwise make trip signal trip=0, change step (6) over to; Threshold value V _Limit85%-95% for the motor rated voltage;

(3) determination frequency rate of change

Whether greater than the setting value upper limit f ' of frequency change rate _Max, if then make trip signal trip=1, and change step (6) over to, otherwise change step (4) over to; Setting value upper limit f ' _MaxBe set at 0.5Hz/s-1Hz/s;

(4) determination frequency rate of change

Whether greater than the setting value lower limit f ' of frequency change rate _Min,, otherwise behind the time-delay t, change step (5) over to if then change step (5) over to; Setting value lower limit f ' _MinBe set at 0.1Hz/s-0.5Hz/s, time-delay t is set at 0.3～3 second;

(5) judge whether load side voltage-phase variation delta θ surpasses the threshold alpha of phase change relay _Set,, change step (6) over to if then make trip signal trip=1; Otherwise, make trip signal trip=0, change step (6) over to; Threshold alpha _SetBe made as 2 °～20 °;

(6) when trip=0, think that then isolated island does not take place microgrid, sends block signal; When trip=1, the expression piconet island takes place, and sends trip signal; Change step (7) over to;

(7) detection of end.

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