CN104393597A - Electric power system UFLS (under frequency load shedding) optimization method considering probabilities and risks - Google Patents

Abstract

The invention relates to a load shedding method for nodes in an electric power system, in particular to an electric power system UFLS (under frequency load shedding) optimization method considering probabilities and risks. The method comprises steps as follows: step one, considering the probabilities to determine fault states of the system; step two, determining the lower frequency limit of the system in each fault state; step three, determining the load shedding amount of the j<th> node in the i<th> fault state with an optimal power flow algorithm; step four, determining frequency segments with a clustering method; step five, performing UFLS scheme optimization according to a frequency segment fault set; step six, determining the mounting position and the load shedding amount of a UFLS device of the system according to an optimization result obtained in step five. According to the method, the system element reliability is considered, and the UFLS setting scheme of the system is determined through risk assessments on consequences caused by faults. By the aid of the determined scheme, economic losses caused by the system load shedding can be minimized, the frequency restoration effect of the system can be guaranteed, and the electric power system UFLS optimization method has a bright prospect.

Description

Take into account the electric power system UFLS optimization method of probability and risk

Technical field

The present invention relates to the load off-load method of electric power system interior joint, be specially the electric power system UFLS optimization method taking into account probability and risk.

Background technology

When meritorious disappearance appears in electric power system, because the imbalance between supply and demand can make system frequency occur declining, if reserve capacity cannot make the fast quick-recovery of system frequency, then system crash may be made.By the three lines of defence that frequency automatic load-reducing device is electric power netting safe running, its Main Function is exactly when especially big abnormal accident occurring and causing serious active power vacancy, can before system frequency collapse, rapidly according to predetermined control strategy, excise a part of load, with " sacrifice local and save the overall situation from damage ", to ensure system safety operation and the uninterrupted power supply to responsible consumer.Make system can recover the balance of active power soon, frequency is tended towards stability, to avoid the generation of large area blackout.

Frequency and the sequence of movement of the action of Load Shedding According To Frequency (UFLS) device adopt the method for presetting usually, when there is accident in electric power system, if power shortage is less, and when having sufficient spinning reserve capacity in system, system frequency is through the decline of a bit of time, along with the startup of spinning reserve capacity, frequency can return to rated value; If when reserve capacity etc. can not meet power shortage, frequency keeps declines, and when frequency decrease is to the first order (wheel) operating frequency of Load Shedding According To Frequency, Load Shedding According To Frequency device action, excises a part of unessential load automatically; If the load of excision just in time equals power shortage, then frequency can return to rated value; Otherwise the action successively of follow-up each round, until system frequency again settles out or occurs ging up, this process just can terminate.For preventing frequency to be parked between certain two level wiper frequency, being provided with particular stage and returning to allowed band to make system frequency.It is in fact the method applying " Approach by inchmeal " by frequency loadshedding equipment, adopt the method for time delay between at different levels, rapidly the power shortage of calculation system in time, and disconnect corresponding user, to reach the stable of system frequency, make the object that operator on duty can process calmly.Electric power system by frequency automatic load-reducing device for prevent frequency accident decline and avoid the further expansion of accident to be very fruitful.

Usual China takes 7 round UFLS schemes, no matter the running status of the scale of electrical network and actual components, and the UFLS operating frequency that unified employing is identical.And it is actual in electrical network is larger, even if frequency departure is very little, also need to excise very large load, to meet system frequency vacancy, if arrange identical frequency operating value, bulk power grid will be made to need the multiple low frequency load shedding equipment of action at short notice, excise larger load, this can cause new impact again to electrical network, and due to electrical network comparatively large, the UFLS round of its larger frequency departure arranged may use never.And for minor scale power net, it occurs that the probability of larger frequency departure is higher, the round action effect of its lower frequency deviation arranged is not obvious.

Simultaneously, according to existing scheme, when determining low frequency load shedding equipment installation site, the maximum power vacancy that may occur according to system is determined, but do not consider the position of fault that this power shortage occurs, but operating experience shows, when system malfunctions, when excising identical load but excise place difference, the operational effect difference for electric power system is very large.

Therefore, how according to the actual conditions determination low frequency load shedding equipment round segment frequence value of electrical network, and the position that selecting system low frequency load shedding equipment is installed is very important.

Summary of the invention

The present invention effectively can not solve in order to the method for the installation site and round segment frequence value that solve existing setting low frequency load shedding equipment the problem that power system frequency declines, and provides the electric power system UFLS optimization method taking into account probability and risk.Adopt the method, for its frequency departure that may occur of given electrical network analysis, determine the frequency segmentation round of this electrical network, and according to ensureing the operating scheme that system optimal runs under various failure condition, determine installation site and the load resection of low frequency load shedding equipment.

The present invention adopts following technical scheme to realize: the electric power system UFLS optimization method taking into account probability and risk, comprises the following steps:

S1: according to power system component RELIABILITY INDEX, the malfunction of electric power system is determined in sampling, determines x kind malfunction altogether, and wherein, the probability of i-th malfunction generation is λ _i, i=1 ... x; Due to main certainty annuity cutting load value, this part mainly considers the malfunction of generator failure and main interconnection;

S2: the malfunction determined according to S1, adopts transient stability analysis method, determines the frequency values f of electric power system under i-th malfunction _i, i=1 ... x;

S3: adopt Algorithms for Optimal Power Flow Problems, make the cutting load amount cost under i-th malfunction for the whole network cutting load cost and Web-based exercise minimum time, obtain the cutting load amount Δ PD of a jth node in electric power system _ij, wherein p _jfor the unit of electrical energy benefit of node j, n is electric power system nodes, and pr is electricity price, for electric power system network loss;

S4: adopt clustering method, by frequency values f _ibe divided into m section, i=1 ... x, the frequency segmentation fault set of kth section is D _k, k=1 ... m;

S5: according to frequency segmentation fault set D _k, by malfunction Classified optimization, make $F_1=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}|u_j{\mathrm{PD}}_j-\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}}|$ With $F_2=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i(\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{PD}}_j-\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}})/K_a$ Obtain minimum value, obtain the low frequency load shedding equipment setting mark u of node j _j, wherein PD _jfor the UFLS set amount of node j, uj equals 0 or 1, K _afor system frequency response coefficient, F1 is the deviation between UFLS set amount and cutting load amount, and F2 is the system frequency deviation that the difference of UFLS set amount and cutting load amount causes, k=1 ... m;

S6: the UFLS mark uj of the node j drawn according to S5, at the node sets low frequency load shedding equipment of uj=1, UFLS set amount is PD _j, the operating frequency value of its correspondence is D _krespective frequencies value.

The electric power system UFLS optimization method taking into account probability and risk provided by the invention is when the UFLS set amount of certainty annuity frequency segmentation value and each node, consider possibility and its probability occurred, the consequence caused of element failure in electric power system, consider the optimum cutting load value that cost is determined, thus the UFLS setting program obtained can ensure electric power system, and the economic loss that causes of cutting load is minimum in most cases, and the frequency retrieval value of electric power system is best.

Embodiment

Take into account the electric power system UFLS optimization method of probability and risk, comprise the following steps:

S1: according to power system component RELIABILITY INDEX, the malfunction of electric power system is determined in sampling, determines x kind malfunction altogether, and wherein, the probability of i-th malfunction generation is λ _i, i=1 ... x;

S2: the malfunction determined according to S1, adopts transient stability analysis method, determines the frequency values f of electric power system under i-th malfunction _i, i=1 ... x;

S3: adopt Algorithms for Optimal Power Flow Problems, make the cutting load amount cost under i-th malfunction for the whole network cutting load cost and Web-based exercise minimum time, obtain the cutting load amount Δ PD of a jth node in electric power system _ij, wherein p _jfor the unit of electrical energy benefit of node j, n is electric power system nodes, and pr is electricity price, for electric power system network loss;

S4: adopt clustering method, by frequency values f _ibe divided into m section, i=1 ... x, the frequency segmentation fault set of kth section is D _k, k=1 ... m;

S5: according to frequency segmentation fault set D _k, by malfunction Classified optimization, make $F_1=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}|u_j{\mathrm{PD}}_j-\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}}|$ With $F_2=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i(\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{PD}}_j-\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}})/K_a$ Obtain minimum value, obtain the low frequency load shedding equipment setting mark u of node j _j, wherein PD _jfor the UFLS set amount of node j, uj equals 0 or 1, K _afor system frequency response coefficient, F1 is the deviation between UFLS set amount and cutting load amount, and F2 is the system frequency deviation that the difference of UFLS set amount and cutting load amount causes, k=1 ... m;

S6: at the node sets low frequency load shedding equipment of uj=1, UFLS set amount is PD _j, the operating frequency value of its correspondence is frequency segmentation fault set D _krespective frequencies value.

Claims (1)

1. take into account the electric power system UFLS optimization method of probability and risk, it is characterized in that comprising the following steps:

S1: according to power system component RELIABILITY INDEX, the malfunction of electric power system is determined in sampling, determines x kind malfunction altogether, and wherein, the probability of i-th malfunction generation is λ _i, i=1 ... x;

S2: the malfunction determined according to S1, adopts transient stability analysis method, determines the frequency values f of electric power system under i-th malfunction _i, i=1 ... x;

S3: adopt Algorithms for Optimal Power Flow Problems, make the cutting load amount cost under i-th malfunction for the whole network cutting load cost and Web-based exercise minimum time, obtain the cutting load amount △ PD of a jth node in electric power system _ij, wherein p _jfor the unit of electrical energy benefit of node j, n is electric power system nodes, and pr is electricity price, for electric power system network loss;

S4: adopt clustering method, by frequency values f _ibe divided into m section, i=1 ... x, the frequency segmentation fault set of kth section is D _k, k=1 ... m;

S5: according to frequency segmentation fault set D _k, by malfunction Classified optimization, make $F_1=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}|u_j{\mathrm{PD}}_j-\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}}|$ With $F_2=\underset{i\&Element;D_k}{\mathrm{\&Sigma;}}{\mathrm{\&lambda;}}_i(\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}{\mathrm{PD}}_j-\underset{j=1}{\overset{n}{\mathrm{\&Sigma;}}}\mathrm{\&Delta;}{\mathrm{PD}}_{\mathrm{ij}})/K_{\mathrm{\&alpha;}}$ Obtain minimum value, obtain the low frequency load shedding equipment setting mark u of node j _j, wherein PD _jfor the UFLS set amount of node j, uj equals 0 or 1, K _afor system frequency response coefficient, F1 is the deviation between UFLS set amount and cutting load amount, and F2 is the system frequency deviation that the difference of UFLS set amount and cutting load amount causes, k=1 ... m;

S6: at the node sets low frequency load shedding equipment of uj=1, UFLS set amount is PD _j, the operating frequency value of its correspondence is frequency segmentation fault set D _krespective frequencies value.