CN105896533B - A kind of active distribution network Static security assessment method - Google Patents

Abstract

The invention relates to a static security evaluation method for an active distribution network, the method comprising: inputting network parameters and wind and load data; performing static security evaluation for a certain branch fault in a certain period of time; performing load transfer; judging whether there is an isolated island. Control the power supply, if yes, analyze whether the power of the island is balanced; if unbalanced, perform load translation and load shedding operations; if balanced, perform power flow calculations, and analyze whether there is a limit violation, if so, perform active management, if not, record parameters; judge Whether the fault is repaired, if not, enter the next fault period, return to the judgment step, if so, judge whether the fault calculation of all branch periods has been completed; if completed, calculate the safety index according to the recorded parameters; if not complete, return Continue to analyze the next envisioned accident. Compared with the prior art, the present invention is characterized in that it integrates the activeness and initiative of the active distribution network, considers the timing characteristics of network operation, and has comprehensive analysis.

Description

A static security assessment method for active distribution network

technical field

The invention relates to the field of static security analysis of distribution networks, in particular to a static security analysis method for active distribution networks considering timing characteristics.

Background technique

The continuous growth of population, the sustainable development of economy and society, the continuous consumption of traditional fossil energy, and the increasingly serious environmental pollution have made sustainable, green and low-carbon development a new requirement for contemporary human development. In the context of the current ecological development, the field of electric energy must also follow the trend of sustainable development. For this reason, renewable energy power generation technology has received extensive attention and attention, and distributed generation (Distributed Generation, DG) has been connected to the distribution network in large numbers. However, due to the inherent intermittency and uncertainty of green distributed power sources such as wind turbines and photovoltaic arrays, extensive DG integration will have a series of impacts on the operation of the distribution network. A large number of DGs entering the network will change the power flow and voltage distribution of the network, increase the complexity of relay protection strategies, cause power quality problems in power supply, increase the difficulty of planning and scheduling, and affect the reliability and security of distribution networks. Although the introduction of energy storage technology and power electronics technology can overcome the negative impact caused by DG grid access to a certain extent, the distribution network still has insufficient intermittent energy consumption, poor compatibility, and network optimization operation capabilities. Insufficient, outdated dispatching methods, and low degree of source-network-load interaction. The large-scale and full utilization of renewable energy, the high-penetration integration of DG in the distribution network, and the strategic optimization and adjustment of the energy structure still face many difficulties. To this end, the Active Distribution Network (ADN) technology emerged as the times require, aiming to solve the problems of distribution network compatibility and large-scale application of intermittent renewable energy, improve the utilization rate of green energy, and optimize and adjust the primary energy structure. According to the definition given in the working report of the CIGRE C6.11 working group, the active distribution network is a distribution network that can comprehensively control distributed energy resources (Distributed Energy Resources, DER), and can use flexible network technology to achieve effective management of power flow. On the basis of its reasonable regulatory environment and access criteria, distributed energy bears a certain supporting role on the system. As a development model of the future intelligent distribution network, the active distribution network integrates distributed energy sources such as distributed power generation, distributed energy storage (ESS), controllable load (Controllable Load, CL), and relies on advanced Advanced information and communication technology and power electronics technology, coordinated control and active management of abundant controllable resources in the network, to achieve high compatibility and efficient use of renewable energy, optimize the operating status of the network, improve the utilization efficiency of power distribution assets, Delay investment in upgrading and transformation of distribution network, improve power supply quality, safety and reliability.

The static security analysis of the distribution network is to analyze the steady-state operation of the distribution network after the expected accident occurs, and to warn of accidents that will cause equipment overload, voltage over-limit, and load loss that threaten the safe operation of the network, and then evaluate the distribution network. level of security and identify weak links in system operation. For distribution network static security analysis and security assessment, many scholars have done relevant research and achieved certain results. The literature "Research on the Security Index of Distribution Network" and "Research on the Static Security Evaluation Index of Distribution Network Based on Risk Theory" established the security evaluation index for the static security analysis of distribution network and applied it to examples. The literature "Based on Backup Power Static Security Analysis of Distribution Network with Automatic Switch-on Device" considers the impact of automatic switch-on of backup power, and conducts a static security analysis of distribution network based on the N-1+M criterion, but none of the above documents takes distributed power into account. The literature "N-1 Safety Assessment of Distribution Network Based on Load Restoration Strategy" uses network reconfiguration to restore load power supply after a fault, and takes the load ratio of restored power supply as the safety index to conduct N-1 safety assessment on distribution network, but The analysis results are only for a certain operating state of the network, without considering the timing and fluctuation of load and wind and solar resources. The document "Hierarchical Risk Assessment of Transmission System Considering the Influence of Active Distribution Network." considered the influence of ADN in the safety assessment of the transmission network, but ignored the power flow constraints of the distribution network, and only considered the activeness of the ADN and its influence on the active distribution network. At the same time, it is believed that only wind turbines and photovoltaic islands can operate. In fact, intermittent power sources cannot support isolated power supply alone. The document "Security Assessment in Active Distribution Networks with Change in Weather Patterns" considers the influence of weather changes on component failures, and proposes a three-state weather model, which uses Monte Carlo simulation to deal with the uncertainty of system operating However, energy storage is not considered in the power balance of the island, nor is the sustainability of the island power supply considered.

Contents of the invention

The purpose of the present invention is to provide a static security evaluation method for an active power distribution network in view of the above problems.

For realizing the stated purpose of the present invention, the technical scheme of the present invention is as follows:

A static security assessment method for active distribution networks. This method integrates the activeness and initiative of active distribution networks, and considers the timing characteristics of network operation. Firstly, a component timing model for static security assessment of active distribution networks is established. Set the security evaluation index for the static security assessment of the active distribution network, and then analyze the expected accidents based on the above data considering the timing of the fault occurrence period and the network operation status during the fault period, and realize the static security evaluation of the active distribution network. The method includes the following steps:

(1) Input network parameters and wind load data;

(2) For the fault of the nth branch in the tth time period, perform a static safety assessment based on the network parameters, wind and load data and the established component timing model, specifically:

(a) Load transfer: restore load power supply through tie lines, and implement island operation mode for unrecoverable parts;

(b) For the island formed after the failure, analyze whether there is a stable and controllable power supply in the island as the main power supply for the island operation, if so, enter step (c), otherwise enter step (e);

(c) Analyze whether the power of the island is balanced, and if so, proceed to step (d); otherwise, perform load translation and load shedding operations until the power of the island is balanced, and proceed to step (d);

(d) Carry out the power flow calculation of the main distribution network and the isolated island, judge whether there is a voltage limit or power limit, if so, carry out active management until the limit is eliminated, if not, go to step (e);

(e) Record the outage load, outage time and remaining power of energy storage;

(f) Determine whether the fault is repaired, if so, enter step (3); otherwise enter the next fault period, return to step (b);

Among them, t=1,2..,T, n=1,2,...N, T is the total number of time periods, and N is the total number of branches;

(3) Judging whether the fault calculation of all branches and all time periods has been completed, if so, enter step (4); otherwise, increase t or n, return to step (2), and continue to analyze the next expected accident;

(4) Carry out index calculation and safety evaluation according to the recorded parameters and the set safety evaluation index.

The component timing model of the static security assessment of the active distribution network includes a wind turbine and photovoltaic timing model, a timing load model taking into account shiftable loads, and a timing model of energy storage.

In the fan and photovoltaic timing model, the fan timing model is:

Among them: P _WTr is the rated active power of the fan; parameter k ₁ =P _WTr /(v _r -v _ci ); parameter k ₂ =-k ₁ v _ci ; v is the wind speed; v _ci is the cut-in wind speed; v _r is the rated wind speed; v _co is the cut-out wind speed;

The PV timing model is:

P _PV = rAη

Among them: PP _PV is the active power output by the photovoltaic array; r is the light intensity; A is the total area of the photovoltaic array; η is the photoelectric conversion efficiency.

The time series load model considering the load that can be translated is:

P _t =P _Forecast,t -P _Shiftout,t

Among them: P _t is the shifted load value during the t period; P _{Forecast, t} is the load forecast value during the t period; P _{Shiftout, t} is the shiftable load shifted out during the t period:

Among them: M is the total number of load equipment types that can be shifted; x _{k, t, t} is the number of load equipment of type k _that should start power supply during time period t when it is removed from time period t; The power of the first period of its continuous working time; L is the maximum continuous working time of various types of translational load equipment; x _{k, tl, t} is the k-th category of translational load equipment that should start to supply power during the tl period when it is moved out of the t period number; P _k,1+l is the working power of the kth category of shiftable load equipment in the 1st+1 period of its continuous working time.

The time series model of the energy storage is:

Among them: P _{ESS, t} is the charge and discharge power of the battery during the t period, the discharge is positive, and the charge is negative; P _{Load, t} is the total load in the island during the t period; PDG _{, t} is the total output power of other power sources in the island during the t period; η _Dis is the discharge efficiency; η _Cha is the charging efficiency; S _SOC,t is the state of charge of the battery in the t period; ΔD _t is the duration of the t period; E _ESS is the rated capacity of the battery; the battery meets the following constraints during operation :

P _ESS,t ≤P _ESS,max

S _SOC,min ≤S _SOC,t ≤S _SOC,max

Among them: P _ESS,max is the maximum charge and discharge power allowed by the battery; S _SOC,max and S _SOC,min are the upper and lower limits of the state of charge, respectively.

In the step (a), the time-series change of the available capacity of the tie line is considered when load transfer is performed.

The security assessment indicators of the active distribution network static security assessment include power loss rate indicators, island power loss rate indicators, time period security indicators, branch security indicators and system comprehensive security indicators.

The expression of the power loss rate index is:

Among them: C _{ELR,t,n is} the power loss rate index of the fault of the nth branch in the t period; λ _n is the failure rate of the nth branch; L _n is the length of the nth branch; T _E is the evaluation time; t _D is the last period of fault duration; φ _F,d is the set of outage loads in period d; γ _i is the importance level factor of load i; S _d,i is the capacity of load i in period d; S _SL,d,i is the capacity of the i-th load that can be removed during the period d; ΔD _F,d,i is the outage time of the i-th load during the period d; φ _S,d is the set of system loads during the period d; ΔD _d is the duration of period d;

The island power loss rate index, its expression is:

Among them: C _IELR,t,n is the island energy loss rate index of the nth branch fault in period t; φ _IF,d is the set of island power outage loads in period d; φI _,d is the set of island loads in period d;

The safety index of the time period, its expression is:

Among them: C _S,t is the safety index of the tth time period; α ₁ and α ₂ are weight coefficients; N is the number of system branches;

The branch security index, its expression is:

Among them: C _S,n is the safety index of the nth branch; T is the time period of static safety analysis;

Described system comprehensive security index, its expression is:

Among them: C _SCS is the comprehensive safety index of the system; β ₁ and β ₂ are weight coefficients.

The active management includes load translation, DG active output reduction and reactive output control, transformer tap adjustment, reactive power compensation equipment control and load shedding.

Compared with the prior art, the present invention has the following beneficial effects:

(1) Static security assessment is carried out by combining the activeness of ADN (including distributed energy such as wind, wind and storage, which can be operated in an isolated manner after a failure to reduce the power outage load) and initiative (with active management capabilities, which can eliminate the risk of network over-limits) , the evaluation results are more accurate and reliable.

(2) Taking into account the timing fluctuation of wind and solar loads, the static safety analysis is carried out separately in different fault occurrence periods, so that the evaluation is more comprehensive.

(3) The timing characteristics of network operation during faults are considered, mainly including dynamic changes of network power flow, dynamic changes of network load shedding and sustainability of island power supply.

Description of drawings

Fig. 1 is a safety assessment flowchart of the present invention;

Figure 2 is a 37-node AND test example diagram;

Fig. 3 is the daily load curve diagram of distribution network;

Fig. 4 is a daily curve diagram of the ratio of the translational load to the total load of the distribution network;

Figure 5 is a graph of the maximum load allowed to be transferred to the tie line;

Figure 6 is a daily graph of scenery resources;

Fig. 7 is the period security index;

Fig. 8 is branch security index;

Fig. 9 is the power loss rate index of each branch fault in period 19;

Fig. 10 is the power loss rate index of branch 3 faults in each time period;

Figure 11 shows the time-period security indicators for different scenarios;

Figure 12 shows branch security indicators in different scenarios;

Fig. 13 is the period safety index of different analysis methods;

Figure 14 shows the branch safety indicators of different analysis methods.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is carried out on the premise of the technical solution of the present invention, and detailed implementation and specific operation process are given, but the protection scope of the present invention is not limited to the following embodiments.

This embodiment provides a static security assessment method for an active distribution network, which integrates the activeness and initiative of the active distribution network, considers the timing characteristics of network operation, and first establishes the components for the static security assessment of the active distribution network At the same time, the safety evaluation index of the static safety evaluation of the active distribution network is set, and then according to the above data, the time sequence of the fault occurrence period and the network operation state during the fault period is considered to carry out the expected accident analysis, and the static safety evaluation of the active distribution network is realized. Safety assessment.

1. Component timing model of active distribution network

ADN contains a wealth of controllable resources. Considering the timing fluctuation of wind and load, establishing the timing model of key components in ADN is the basic work of static security analysis.

(1) Timing model of wind turbine and photovoltaic

The relationship between the active power P _WT output by the wind turbine and the wind speed v can be expressed by the following piecewise function:

Among them: P _WTr is the rated active power of the fan; parameter k ₁ =P _WTr /(v _r -v _ci ); parameter k ₂ =-k ₁ v _ci ; v _ci is the cut-in wind speed; v _r is the rated wind speed; v _co is the cut-out wind speed.

The simplified calculation formula of the active power P _PV output by the photovoltaic array is:

P _PV =rAη (2)

Among them: r is the light intensity; A is the total area of the photovoltaic array; η is the photoelectric conversion efficiency.

Through wind resource forecasting, time-series wind speed and light intensity data of the time period to be analyzed (such as a day) can be obtained, combined with formula (1) (2), the time-series output data of wind turbines and photovoltaics can be obtained.

(2) Time-series load model considering shiftable load

Shiftable loads (SL) refer to the loads whose power supply time can be moved and adjusted according to the plan. There are a large number of friendly and controllable loads that can be shifted in ADN, especially the proportion of residential loads is relatively large. Load shifting technology is an effective load management and control technology, taking load shifting into account in static security analysis is beneficial to improve the security of ADN. After an accident occurs, when the power supply in the isolated island is insufficient or the network is in danger of over-limiting, load shifting can reduce the load demand of the network during the fault duration, thereby reducing load shedding and power loss, and improving network security.

In order to simplify the model and facilitate the analysis, the present invention assumes that: ADN has a higher degree of distribution automation and a shorter fault duration, and the maximum allowable delayed power supply time (generally taken as 6 hours) of the translational load is greater than the fault duration, so the The transfer of loads that can be shifted can be carried out after the fault is restored. During the fault period, it is only necessary to consider the removal of loads that can be shifted; only after the fault occurs, when the power supply in the island is insufficient or the network is in danger of exceeding the limit, load shifting is considered. ; For the purpose of improving safety, once the load has been shifted, remove as much of the shiftable load equipment as possible until the fault is repaired.

The calculation formula of the sequence load value taking into account the load that can be shifted during the fault period is as follows:

P _t =P _Forecast,t -P _Shiftout,t (3)

Among them: P _t is the shifted load value in t period; P _Forecast,t is the load forecast value in t period; P _Shiftout,t is the shiftable load out in t period. The shiftable load removed during the t period includes two parts: the shiftable load that has just been removed during the t period and the shiftable load that has been removed before the t period but is still within its continuous working time during the t period. The specific expression is:

Among them: M is the total number of load equipment types that can be shifted; x _{k, t, t} is the number of load equipment of type k _that should start power supply during time period t when it is removed from time period t; The power of the first period of its continuous working time; L is the maximum continuous working time of various types of translational load equipment; x _{k, tl, t} is the k-th category of translational load equipment that should start to supply power during the tl period when it is moved out of the t period number; P _k,1+l is the working power of the kth category of shiftable load equipment in the 1st+1 period of its continuous working time.

Time-series load data can be obtained from load forecasting. Combined with shiftable load forecasting and network operation during faults, the time-series load data including shiftable load can be obtained from formula (3) (4).

(3) Timing model of energy storage

In the static security analysis of ADN, energy storage is one of the core components that must be considered. As a flexible and controllable power source that can be both charged and discharged, the introduction of energy storage greatly improves the initiative of ADN.

The present invention adopts the storage battery as the energy storage device. Considering that the output of intermittent distributed power sources such as wind and solar is random and cannot support the stable operation of the island, during the fault period, the battery is regarded as the main power supply of the island, which mainly plays a role in maintaining the power balance of the island, and its access nodes are regarded as The balance node of the island, its output is determined by the load in the island and the output of other power sources:

Among them: P _ESS,t is the charge and discharge power of the battery during the t period (discharge is positive, charge is negative); P _Load,t is the total load in the island during the t period; PDG _,t is the total output power of other power sources in the island during the t period ; η _Dis is the discharge efficiency; η _Cha is the charging efficiency; S _SOC,t is the state of charge of the battery in the t period; ΔD _t is the duration of the t period; E _ESS is the rated capacity of the battery. For the purpose of protecting battery life and operating safety, the battery needs to meet the following constraints during operation:

P _ESS,t ≤P _ESS,max (7)

S _SOC,min ≤S _SOC,t ≤S _SOC,max (8)

Among them: P _ESS,max is the maximum charge and discharge power allowed by the battery; S _SOC,max and S _SOC,min are the upper and lower limits of the state of charge, respectively.

In addition, in order to facilitate the analysis of the problem, the present invention makes the following assumptions on the energy storage model: when there are multiple energy storages in the island, the one with the largest charging and discharging power is preferred as the main power supply, and the remaining energy storages provide power support to the island according to the demand; If the energy storage state of the balance node reaches the lower limit during discharge, the island will stop operating.

2. Security evaluation index for static security analysis of active distribution network

Static security analysis evaluates the security of the system by anticipating the voltage limit, power limit and load loss of the network after the accident occurs, provides early warning of dangerous accidents, and finds out the weak links of the system. In the ADN environment, the voltage limit and power limit can be eliminated through active management, so the safety of network operation after a fault is mainly evaluated by the load loss situation. Based on N-1 branch faults and comprehensive consideration of timing characteristics, the present invention establishes the safety evaluation index of ADN based on power loss.

(1) Power loss rate index

The power loss rate index comprehensively considers the failure rate and the severity of load power outage after a fault. The severity of load power outage is represented by the ratio of system power loss to the system's power supply. The index can quantitatively evaluate a certain fault that occurs in a certain period of time. The smaller the index value, the better the security. This index takes into account the change of the fault occurrence time period and the load change within the fault duration, which is time-sequential. For the fault of the nth branch that occurs during the t period, the expression of the power loss rate index is:

Among them: C _{ELR,t,n is} the power loss rate index of the fault of the nth branch in the t period; λ _n is the failure rate of the nth branch; L _n is the length of the nth branch; T _E is the evaluation time; t _D is the last period of fault duration; φ _F,d is the set of outage loads in period d; γ _i is the importance level factor of load i; S _d,i is the capacity of load i in period d; S _SL,d,i is the capacity of the i-th load that can be removed during the period d; ΔD _F,d,i is the outage time of the i-th load during the period d; φ _S,d is the set of system loads during the period d; ΔD _d is the duration of the period d.

(2) Island power loss rate index

Similarly, the island power loss rate index describes the severity of load outages in the island by the ratio of the power loss in the island during the fault period to the power supply of the island. This index is used to quantitatively evaluate the safety of the ADN island after a certain fault occurs in a certain period of time. Operating capability, the smaller the indicator value, the better the island security. For the fault of the nth branch that occurs during the t period, the expression of the island power loss rate index is:

Among them: C _IELR,t,n is the island energy loss rate index of the nth branch fault in period t; φ _IF,d is the set of island outage loads in period d; φ _I,d is the set of island loads in period d.

(3) Time-period safety indicators

For all branch faults that occur in a certain period, taking into account the average level and the maximum level, based on the energy loss rate and island energy loss rate indicators, a period security index is established, which can quantitatively evaluate the security of the system power supply in each period , to find weak periods of system operation. The safety index of the system operation in the period t is:

Among them: C _S,t is the safety index of the tth period; α ₁ and α ₂ are weight coefficients (taken as 0.7 and 0.3 in the present invention); N is the number of system branches.

(4) Branch safety index

For a certain branch fault that occurs in all time periods, from the perspective of the average value and the maximum value, comprehensively considering the energy loss rate and the island energy loss rate index, the branch safety index is established, and the safety index of each branch is quantitatively evaluated. Security, to identify weak branches of system operation. The safety index of the nth branch is:

Among them: C _S,n is the security index of the nth branch; T is the time period of static security analysis.

(5) System comprehensive security index

The comprehensive security index of the system combines the time period security and branch security indicators, taking into account the average level and the maximum level, and quantitatively evaluates the comprehensive security of the entire power distribution system. The expression is:

Among them: C _SCS is the comprehensive security index of the system; β ₁ and β ₂ are weight coefficients (taken as 0.5 and 0.5 in the present invention).

3. Static security assessment method for active distribution network

Based on the above models and indicators, the specific process of the active distribution network static security assessment method of the present invention is shown in Figure 1, specifically:

(1) Input network parameters and wind load data;

(2) For the fault of the nth branch in the tth time period, perform a static safety assessment based on the network parameters, wind and load data and the established component timing model, specifically:

(a) Load transfer: restore load power supply through tie lines, and implement island operation mode for unrecoverable parts;

(b) For the island formed after the failure, analyze whether there is a stable and controllable power supply in the island as the main power supply for the island operation, if so, enter step (c), otherwise enter step (e);

(c) Analyze whether the power of the island is balanced, and if so, proceed to step (d); otherwise, perform load translation and load shedding operations until the power of the island is balanced, and proceed to step (d);

(d) Carry out the power flow calculation of the main distribution network and the isolated island, judge whether there is a voltage limit or power limit, if so, carry out active management until the limit is eliminated, if not, go to step (e);

(e) Record the outage load, outage time and remaining power of energy storage;

(f) Determine whether the fault is repaired, if so, enter step (3); otherwise enter the next fault period, return to step (b);

Among them, t=1,2..,T, n=1,2,...N, T is the total number of time periods, and N is the total number of branches;

(3) Judging whether the fault calculation of all branches and all time periods has been completed, if so, enter step (4); otherwise, increase t or n, return to step (2), and continue to analyze the next expected accident;

(4) Carry out index calculation and safety evaluation according to the recorded parameters and the set safety evaluation index.

4. Application examples

The present invention establishes a 37-node radial ADN test example, as shown in FIG. 2 . The voltage level of the network is 10kV; node 0 is the low-voltage bus node of the substation, the on-load tap changer (110/10kV) has 17 taps, and the adjustable range of transformation ratio is ±8×1.25%; SVG of power compensation equipment, reactive power adjustable range -500kVar to +500kVar.

The loads include residential loads, industrial loads and commercial loads. Residential loads are the main ones. Nodes 1-29 are residential loads, nodes 30-33 are industrial loads, and nodes 34-36 are commercial loads. The specific parameters of the load are shown in Table 1, and the greater the important factor of the load, the more important the load. The overall daily load curve of the distribution network is shown in Figure 3.

Table 1 Node load parameters

This example only takes into account the shiftable loads among the residential loads. The shiftable loads consider three types of dryers, dishwashers, and washing machines. The specific power consumption characteristics and the number of equipment connected to the grid at each time period are shown in Table 2 , as shown in Table 3, the curve of the proportion of the load that can be translated in each period of the distribution network to the total load is shown in Figure 4.

Table 2 Electrical characteristics of load equipment that can be translated

Table 3 The number of parallel load equipment connected to the power grid in each period (unit: set)

Each branch line is a cable, the impedance per kilometer is 0.18+j0.09Ω, the maximum carrying capacity is 509A, the fault repair time is 4h, the failure rate is 0.04 times/a km, and the line length of each branch of the main feeder is 0.6km , the length of each branch line of the branch where nodes 16 and 26 are located is 0.4 km, and the length of each branch line of the branch where nodes 23, 30, and 34 are located is 0.3 km. The tie switch is mainly used for the load transfer of the branch where node 26 is located. The fluctuation curve of the maximum load allowed to be transferred is shown in Figure 5. The load that can be transferred by the tie line during the 18-21 period is relatively limited, and the rest of the time can be transferred to the branch. all loads.

Select the wind speed and light intensity data of a certain day in summer in a certain area to generate a daily curve of scenery resources as shown in Figure 6. The network includes several wind turbines, photovoltaics and energy storage, with a total penetration of wind and solar at about 48%. The cut-in wind speed of the fan is 2.5m/s, the rated wind speed is 12m/s, and the cut-out wind speed is 25m/s. The rated capacities of the fans connected to nodes 14, 20 and 35 are 300kW, 400kW and 300kW respectively. The photoelectric conversion efficiency of photovoltaics is 16%. The total areas of photovoltaics connected to nodes 14, 22 and 24 are 1875m ² , 2500m ² and 2500m ² respectively, and the rated capacities are 300kW, 400kW and 400kW respectively. The charging efficiency and discharging efficiency of the battery are 80% and 85% respectively, the upper and lower limits of the state of charge are 100% and 20% respectively, and the maximum charging and discharging power of the batteries connected to nodes 15, 22, and 33 are 750kW, 600kW, 400kW, the rated capacity is 1500kW·h, 1200kW·h, 800kW·h respectively.

For the above calculation example, considering the timing characteristics, taking into account ADN's island operation and active management capabilities, ADN static security analysis is carried out to find the weak periods and weak branches of system operation. Based on island power balance and network power flow constraints, active management operations such as load shifting and load shedding are carried out to obtain the power loss rate and island power loss rate indicators when each branch circuit fails at each time period, and then perform relevant statistical calculations to obtain The safety index of the outgoing period (as shown in Figure 7), the safety index of the branch (as shown in Figure 8) and the comprehensive safety index of the system.

The comprehensive safety index C _SCS of the system is 0.0069.

It can be seen from Figure 7 that the security of the network is relatively good during periods 5-11. The reason is that for faults occurring during these periods, the load does not reach the peak value during the duration of the fault, there are more shiftable loads available in the network, and the wind turbines and The photovoltaic output is large, so that the power supply in the island is relatively sufficient and the load shedding is small; during the period 18-21, the security of the network is poor, and the weakest period of the system is period 19. The load demand of the network is very large, the controllable load equipment is less, the photovoltaic power has gradually lost its power, and the available capacity of the tie line is limited. Security is weak. Aiming at the weakest period 19 of the system, the power loss rate index of each branch fault in this period is calculated, as shown in Figure 9, it can be seen that operators should pay special attention to the faults occurring upstream of the main feeder in period 19.

Analyzing Figure 8, it can be obtained that the safety of branches 12-15, 19-22, 28-29, and 32-33 is the best, and the high safety of branch 28-29 is due to the load transfer of the tie line when a fault occurs. The safety of the remaining branches is better because the isolated islands formed by the failure of these branches are small in scale, and there are sufficient distributed power sources and energy storage inside, which can safely and stably support the operation of the isolated islands, and can often avoid the occurrence of load shedding. ; The safety of the upstream branch of the main feeder is poor, and the weakest branch of the system is branch 3. Due to the radial structure of the network, once the upstream branch fails, a large-scale isolated island will be formed. In the case of low-level conditions, the isolated island can only use limited resources to run for a period of time, and it is difficult to maintain a reliable power supply for the isolated island during the entire fault duration. Sexual decline. For the weakest branch 3 of the system, the power loss rate index of the branch fault in each period is made, as shown in Figure 10, from which it can be seen that the fault of branch 3 occurring at night (17-21 time period) is the most dangerous and should cause Special attention of the operating staff.

The distributed energy of ADN includes: distributed power supply, distributed energy storage, controllable load, etc. In order to reflect the influence of these elements on the static security analysis of ADN, the following four scenarios (see Table 4) are constructed for static security analysis respectively. The results are shown in Figure 11, Figure 12, and Table 5.

Table 4 Different scenarios of static security analysis

Table 5 System comprehensive security indicators in different scenarios

Comparing the curves of Scenario 1 and Scenario 2, Scenario 3 and Scenario 4 in Figure 11 and Figure 12, it can be seen that the control of the shiftable load on the demand side can effectively improve the security of the system, and this improvement effect is more in the case of shiftable load equipment Most notable in the morning and noon hours. Compared with loads that can be shifted, distributed power sources and energy storage have a more substantial effect on improving system security. Comparing the curves of scenarios 1 and 3, and scenarios 2 and 4, it can be seen that the access of distributed power sources and energy storage makes the network With the ability of island operation, the power loss load of the system after a fault occurs is greatly reduced, and the safety is greatly improved. It can also be seen from Table 5 that with the network access of distributed energy and the increase of active resources available to the system, the power loss load of the system after the accident gradually decreases, and the overall security of the distribution network gradually increases. The above-mentioned diagrams and analysis discussions have also proved the effectiveness of the analysis method and evaluation index of the ADN static security analysis proposed by the present invention. Increased reliability of network security can go a long way.

In order to verify the necessity of considering the timing characteristics of network operation during faults in ADN static security analysis, two different methods are used for security analysis, and the results are shown in Figure 13 and Figure 14. Among them, the time-section method is a traditional method, which only considers the power balance and over-limit situation of the time section at the time of fault occurrence, and obtains the load shedding static value and safety index; The load shedding method and safety indicators are obtained based on the power balance and limit violations within the time period; the analysis scenarios are all scenario 4.

For the comprehensive safety index of the system, the calculation result of the time-section method is 0.0036, and the calculation result of the full-time method is 0.0069.

It can be seen from Figure 13 that if the time section method is used to focus only on the time section at the time when the fault occurs, the system security is excellent in the early morning and daytime periods when the net load is small. The main reason is that the analysis does not take into account the dynamic changes of the network operation , ignoring the sustainability of energy storage and power supply; on the other hand, the weakest period of the system has become the 21st period with the largest net load. Obviously, this analysis result is relatively one-sided. Combined with Figure 13, Figure 14 and comprehensive safety indicators, it can be seen that compared with the full-time method, the index value obtained by the time-section method is lower and the system security is better. The analysis results are too optimistic. The dynamic changes of network power flow and load shedding caused by fluctuations in wind, wind and load within time do not take into account the island power outage caused by the depletion of energy storage power. Above-mentioned analysis result and comparative discussion have shown the deficiency of the analysis method that only considers the time section at the time when the fault occurs and ignores the timing, and fully proves the necessity of considering the timing characteristics of network operation during the fault in the ADN static security analysis, and also verifies the present invention The scientific nature of the analytical method.

Claims (9)

1. A kind of 1. active distribution network Static security assessment method, which is characterized in that this method combines the active of active distribution network Property and initiative, it is contemplated that the temporal characteristics of the network operation initially set up the element sequence of active distribution network Static security assessment Model, while the safety evaluation index of active distribution network Static security assessment is set, then according to said elements temporal model Timing of both network operation state is envisioned during considering failure period of right time and failure with safety evaluation index Crash analysis, realizes the assessment to active distribution network static security, and this method comprises the following steps：

   (1) network parameter and honourable lotus data are inputted；

   (2) for the nth bar branch trouble of t-th of period, according to the network parameter and honourable lotus data and the member of foundation Part temporal model carries out Static security assessment, is specially：

   (a) load transfer is carried out：Recover load by interconnection to power, decoupled mode is performed to the part that can not recover；

   (b) to the isolated island formed after failure, analysis isolated island is interior to whether there is main power source of the stably and controllable power supply as islet operation, If then entering step (c), if otherwise entering step (e)；

   (c) whether the power for analyzing isolated island balances, if then entering step (d), if otherwise carrying out load translation and cutting load behaviour Make, until isolated island power-balance, enters step (d)；

   (d) Load flow calculation of main distribution net and isolated island is carried out, judges whether that voltage out-of-limit or power are out-of-limit, if then carrying out Active management, it is out-of-limit until eliminating, if otherwise entering step (e)；

   (e) power failure load, power off time and energy storage remaining capacity are recorded；

   (f) whether failure judgement repairs, if then entering step (3)；If otherwise into next failure period, return to step (b)；

   Wherein, t=1,2.., T, n=1,2 ... N, T are period sum, and N is branch sum；

   (3) judge whether to have completed all branches, the calculation of fault of all periods, if then entering step (4)；If otherwise to t Or n progressively increases operation, return to step (2) continues to analyze next forecast accident；

   (4) according to the parameter of record and set safety evaluation index into row index calculate and security evaluation.
2. 2. active distribution network Static security assessment method as described in claim 1, which is characterized in that the active distribution network is quiet The element sequence model of state security evaluation include the sequential load model of wind turbine and photovoltaic temporal model, meter and translatable load with The temporal model of energy storage.
3. 3. active distribution network Static security assessment method as claimed in claim 2, which is characterized in that when the wind turbine is with photovoltaic In sequence model, wind turbine temporal model is：

   <mrow> <msub> <mi>P</mi> <mrow> <mi>W</mi> <mi>T</mi> </mrow> </msub> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mrow> <mi>v</mi> <mo>&amp;le;</mo> <msub> <mi>v</mi> <mrow> <mi>c</mi> <mi>i</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mrow> <msub> <mi>k</mi> <mn>1</mn> </msub> <mi>v</mi> <mo>+</mo> <msub> <mi>k</mi> <mn>2</mn> </msub> </mrow> </mtd> <mtd> <mrow> <msub> <mi>v</mi> <mrow> <mi>c</mi> <mi>i</mi> </mrow> </msub> <mo>&amp;le;</mo> <mi>v</mi> <mo>&amp;le;</mo> <msub> <mi>v</mi> <mi>r</mi> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <msub> <mi>P</mi> <mrow> <mi>W</mi> <mi>T</mi> <mi>r</mi> </mrow> </msub> </mtd> <mtd> <mrow> <msub> <mi>v</mi> <mi>r</mi> </msub> <mo>&amp;le;</mo> <mi>v</mi> <mo>&amp;le;</mo> <msub> <mi>v</mi> <mrow> <mi>c</mi> <mi>o</mi> </mrow> </msub> </mrow> </mtd> </mtr> <mtr> <mtd> <mn>0</mn> </mtd> <mtd> <mrow> <msub> <mi>v</mi> <mrow> <mi>c</mi> <mi>o</mi> </mrow> </msub> <mo>&amp;le;</mo> <mi>v</mi> </mrow> </mtd> </mtr> </mtable> </mfenced> <mo>;</mo> </mrow>

   Wherein：P_WTFor the active power of wind-driven generator output, P_WTrFor the rated active power of wind turbine；Parameter k₁=P_WTr/(v_r- v_ci)；Parameter k₂=-k₁v_ci；V is wind speed；v_ciTo cut wind speed；v_rFor rated wind speed；v_coFor cut-out wind speed；

   Photovoltaic temporal model is：

   P_PV=rA η

   Wherein：P_PVFor the active power of photovoltaic array output；R is light intensity；A is the photovoltaic array gross area；η is imitated for opto-electronic conversion Rate.
4. 4. active distribution network Static security assessment method as claimed in claim 2, which is characterized in that the meter and translatable negative The sequential load model of lotus is：

   P_t=P_Forecast,t-P_Shiftout,t

   Wherein：P_tFor load value of the t periods after translation；P_Forecast,tFor the predicted load of t periods；P_Shiftout,tFor the t periods The translatable load removed：

   <mrow> <msub> <mi>P</mi> <mrow> <mi>S</mi> <mi>h</mi> <mi>i</mi> <mi>f</mi> <mi>t</mi> <mi>o</mi> <mi>u</mi> <mi>t</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>=</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <mrow> <msub> <mi>x</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <msub> <mi>P</mi> <mrow> <mi>k</mi> <mo>,</mo> <mn>1</mn> </mrow> </msub> </mrow> <mo>+</mo> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>l</mi> <mo>=</mo> <mn>1</mn> </mrow> <mrow> <mi>L</mi> <mo>-</mo> <mn>1</mn> </mrow> </munderover> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>k</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>M</mi> </munderover> <msub> <mi>x</mi> <mrow> <mi>k</mi> <mo>,</mo> <mi>t</mi> <mo>-</mo> <mi>l</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <msub> <mi>P</mi> <mrow> <mi>k</mi> <mo>,</mo> <mn>1</mn> <mo>+</mo> <mi>l</mi> </mrow> </msub> </mrow>

   Wherein：M is translatable load equipment type sum；x_k,t,tThe kth class that should start power supply for the t periods that the t periods remove can Translate load equipment number；P_k,1For the power of the translatable load equipment of kth class the 1st period in its continuous working period；L is The maximum continuous working period of all kinds of translatable load equipments；x_k,t-l,tIt should start the of power supply for the t-l periods that the t periods remove The translatable load equipment number of k classes；P_k,1+lFor the translatable load equipment of kth class in its continuous working period the 1+l period Operating power.
5. 5. active distribution network Static security assessment method as claimed in claim 2, which is characterized in that the sequential mould of the energy storage Type is：

   <mrow> <msub> <mi>P</mi> <mrow> <mi>E</mi> <mi>S</mi> <mi>S</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mfenced open = "{" close = ""> <mtable> <mtr> <mtd> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>L</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>P</mi> <mrow> <mi>D</mi> <mi>G</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>)</mo> <mo>/</mo> <msub> <mi>&amp;eta;</mi> <mrow> <mi>D</mi> <mi>i</mi> <mi>s</mi> </mrow> </msub> </mtd> </mtr> <mtr> <mtd> <mrow> <mo>(</mo> <msub> <mi>P</mi> <mrow> <mi>L</mi> <mi>o</mi> <mi>a</mi> <mi>d</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>P</mi> <mrow> <mi>D</mi> <mi>G</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>)</mo> <msub> <mi>&amp;eta;</mi> <mrow> <mi>C</mi> <mi>h</mi> <mi>a</mi> </mrow> </msub> </mrow> </mtd> </mtr> </mtable> </mfenced> </mrow>

   <mrow> <msub> <mi>S</mi> <mrow> <mi>S</mi> <mi>O</mi> <mi>C</mi> <mo>,</mo> <mi>t</mi> <mo>+</mo> <mn>1</mn> </mrow> </msub> <mo>=</mo> <msub> <mi>S</mi> <mrow> <mi>S</mi> <mi>O</mi> <mi>C</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>-</mo> <mfrac> <mrow> <msub> <mi>P</mi> <mrow> <mi>E</mi> <mi>S</mi> <mi>S</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <msub> <mi>&amp;Delta;D</mi> <mi>t</mi> </msub> </mrow> <msub> <mi>E</mi> <mrow> <mi>E</mi> <mi>S</mi> <mi>S</mi> </mrow> </msub> </mfrac> </mrow>

   Wherein：P_ESS,tFor t period accumulator cell charging and discharging power, discharge just, to be charged as bearing；P_Load,tAlways to be born in t period isolated islands Lotus；P_DG,tFor the gross output of other power supplys in t period isolated islands；η_DisFor discharging efficiency；η_ChaFor charge efficiency；S_SOC,tFor t The state-of-charge of period accumulator；ΔD_tFor the duration of t periods；E_ESSFor the rated capacity of accumulator；Accumulator is being run Meet following constraint in the process：

   P_ESS,t≤P_ESS,max

   S_SOC,min≤S_SOC,t≤S_SOC,max

   Wherein：P_ESS,maxThe maximum charge-discharge electric power allowed for accumulator；S_SOC,max、S_SOC,minRespectively state-of-charge bound.
6. 6. active distribution network Static security assessment method as described in claim 1, which is characterized in that in the step (a), into The timing variations of interconnection active volume are considered during row load transfer.
7. 7. active distribution network Static security assessment method as described in claim 1, which is characterized in that the active distribution network is quiet The safety evaluation index of state security evaluation includes electric quantity loss rate index, isolated island electric quantity loss rate index, time safety and refers to Mark, branch safety indexes and system general safety index.
8. 8. active distribution network Static security assessment method as claimed in claim 7, which is characterized in that the electric quantity loss rate refers to Marking expression formula is：

   <mrow> <msub> <mi>C</mi> <mrow> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>&amp;lambda;</mi> <mi>n</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>L</mi> <mi>n</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>T</mi> <mi>E</mi> </msub> <mfrac> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>d</mi> <mo>=</mo> <mi>t</mi> </mrow> <msub> <mi>t</mi> <mi>D</mi> </msub> </munderover> <munder> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>&amp;phi;</mi> <mrow> <mi>F</mi> <mo>,</mo> <mi>d</mi> </mrow> </msub> </mrow> </munder> <msub> <mi>&amp;gamma;</mi> <mi>i</mi> </msub> <mo>&amp;CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mrow> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>S</mi> <mrow> <mi>S</mi> <mi>L</mi> <mo>,</mo> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&amp;CenterDot;</mo> <msub> <mi>&amp;Delta;D</mi> <mrow> <mi>F</mi> <mo>,</mo> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> </mrow> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>d</mi> <mo>=</mo> <mi>t</mi> </mrow> <msub> <mi>t</mi> <mi>D</mi> </msub> </munderover> <munder> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>&amp;phi;</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>d</mi> </mrow> </msub> </mrow> </munder> <msub> <mi>&amp;gamma;</mi> <mi>i</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>S</mi> <mrow> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>&amp;Delta;D</mi> <mi>d</mi> </msub> </mrow> </mfrac> </mrow>

   Wherein：C_ELR,t,nFor the electric quantity loss rate index of t period nth bar branch troubles；λ_nFor the failure rate of nth bar branch；L_nFor The length of nth bar branch；T_EFor evaluation time；t_DFor the last one lasting period of failure；φ_F,dFor the power failure load of d periods Set；γ_iFor the important level factor of i-th of load；S_d,iFor the capacity of i-th of load of d periods；S_SL,d,iFor i-th of d periods Load contains the capacity of extensible load；ΔD_F,d,iFor the power off time of i-th of load of d periods；φ_S,dSystem for the d periods is born Lotus set；ΔD_dFor the duration of d periods；

   The isolated island electric quantity loss rate index, expression formula are：

   <mrow> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>=</mo> <msub> <mi>&amp;lambda;</mi> <mi>n</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>L</mi> <mi>n</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>T</mi> <mi>E</mi> </msub> <mfrac> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>d</mi> <mo>=</mo> <mi>t</mi> </mrow> <msub> <mi>t</mi> <mi>D</mi> </msub> </munderover> <munder> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>&amp;phi;</mi> <mrow> <mi>I</mi> <mi>F</mi> <mo>,</mo> <mi>d</mi> </mrow> </msub> </mrow> </munder> <msub> <mi>&amp;gamma;</mi> <mi>i</mi> </msub> <mo>&amp;CenterDot;</mo> <mrow> <mo>(</mo> <msub> <mi>S</mi> <mrow> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>-</mo> <msub> <mi>S</mi> <mrow> <mi>S</mi> <mi>L</mi> <mo>,</mo> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>)</mo> </mrow> <mo>&amp;CenterDot;</mo> <msub> <mi>&amp;Delta;D</mi> <mrow> <mi>F</mi> <mo>,</mo> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> </mrow> <mrow> <munderover> <mo>&amp;Sigma;</mo> <mrow> <mi>d</mi> <mo>=</mo> <mi>t</mi> </mrow> <msub> <mi>t</mi> <mi>D</mi> </msub> </munderover> <munder> <mo>&amp;Sigma;</mo> <mrow> <mi>i</mi> <mo>&amp;Element;</mo> <msub> <mi>&amp;phi;</mi> <mrow> <mn>1</mn> <mo>,</mo> <mi>d</mi> </mrow> </msub> </mrow> </munder> <msub> <mi>&amp;gamma;</mi> <mi>i</mi> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>S</mi> <mrow> <mi>d</mi> <mo>,</mo> <mi>i</mi> </mrow> </msub> <mo>&amp;CenterDot;</mo> <msub> <mi>&amp;Delta;D</mi> <mi>d</mi> </msub> </mrow> </mfrac> </mrow>

   Wherein：C_IELR,t,nFor the isolated island rate of energy loss index of t period nth bar branch troubles；φ_IF,dIsolated island for the d periods stops Electric load set；φ_I,dFor the isolated island load aggregation of d periods；

   The time safety index, expression formula are：

   <mrow> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>=</mo> <mfrac> <msub> <mi>&amp;alpha;</mi> <mn>1</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>N</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <msub> <mi>&amp;alpha;</mi> <mn>2</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>N</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> </mrow>

   Wherein：C_S,tFor the safety indexes of t-th of period；α₁、α₂For weight coefficient；N is system branch number；

   The branch safety indexes, expression formula are：

   <mrow> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>=</mo> <mfrac> <msub> <mi>&amp;alpha;</mi> <mn>1</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>T</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <msub> <mi>&amp;alpha;</mi> <mn>2</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>T</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>I</mi> <mi>E</mi> <mi>L</mi> <mi>R</mi> <mo>,</mo> <mi>t</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> </mrow>

   Wherein：C_S,nFor the safety indexes of nth bar branch；T is the when hop count of static security analysis；

   The system general safety index, expression formula are：

   <mrow> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mi>C</mi> <mi>S</mi> </mrow> </msub> <mo>=</mo> <mfrac> <msub> <mi>&amp;beta;</mi> <mn>1</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>T</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>t</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>T</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>t</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> <mo>+</mo> <mfrac> <msub> <mi>&amp;beta;</mi> <mn>2</mn> </msub> <mn>2</mn> </mfrac> <mrow> <mo>(</mo> <mfrac> <mn>1</mn> <mi>N</mi> </mfrac> <munderover> <mi>&amp;Sigma;</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>+</mo> <munderover> <mi>max</mi> <mrow> <mi>n</mi> <mo>=</mo> <mn>1</mn> </mrow> <mi>N</mi> </munderover> <mo>{</mo> <msub> <mi>C</mi> <mrow> <mi>S</mi> <mo>,</mo> <mi>n</mi> </mrow> </msub> <mo>}</mo> <mo>)</mo> </mrow> </mrow>

   Wherein：C_SCSFor system general safety index；β₁、β₂For weight coefficient.
9. 9. active distribution network Static security assessment method as described in claim 1, which is characterized in that the active management includes Load translates, DG active power outputs are cut down and idle control of contributing, load tap changer are adjusted, reactive-load compensation equipment is controlled and cut Load.