Method for improving reclosing success rate of weak-connected local power grid considering new energy

Abstract

The present invention relates to the technical field of reclosing of local power grids. To solve the technical problem of how to effectively improve the success probability of reclosing, the present invention provides a method for improving the success rate of reclosing of a weakly-connected local power grid considering new energy, which includes: collecting the active power and reactive power of each new energy power station and the main tie line in real time; when the circuit breaker on the main tie line trips, the weakly-connected local power grid forms an island system that independently supplies power to the load. A power balance control strategy is adopted to suppress voltage and frequency fluctuations in the island system, so that the island system operates stably; the power balance control strategy is based on the active power and reactive power on the main tie line at ΔT before the circuit breaker trips as the sum of the output adjustment amounts of each new energy power station in the island system; when the circuit breaker on the main tie line recloses, the weakly-connected local power grid and the power system jointly supply power to the load, and each new energy power station in the weakly-connected local power grid is controlled to return to the output state before the circuit breaker trips.

Description

Technical Field

[0001] The present invention relates to the technical field of reclosing of local power grids, and particularly to a method for improving the success rate of reclosing of a weak-connected local power grid considering new energy. Background Art

[0002] At present, new energy grid connection technology has made remarkable development, but still faces problems such as weak new energy transmission grids and low success rates of reclosing operations. Most power system faults are transient faults. To improve the power supply reliability of the power system, faulty lines will automatically perform reclosing. However, for a weak-connected local power grid containing new energy (a "weak-connected local power grid" refers to a power grid with low transmission capacity of the tie line with the power system and few numbers of tie lines), due to the low inertia of the system and large voltage and frequency change rates caused by power imbalance, it is easy to lose voltage and frequency stability before reclosing, resulting in a significant reduction in the success rate of reclosing of the outgoing lines of the weak-connected local power grid dominated by new energy. This situation becomes more and more serious with the increase in the proportion of new energy. After the local isolated network, due to power imbalance and further weakening of the inertia of the local isolated network system, it is difficult to stabilize the voltage and frequency. New energy units are extremely likely to trip out of the network due to repeatedly entering and exiting high and low voltage ride-through during voltage fluctuations and due to insufficient frequency adaptability during frequency fluctuations, resulting in the collapse of the local power grid.

[0003] However, at present, the primary frequency regulation and virtual inertia control of new energy still adopt a limiting scheme. The power of the outgoing line fluctuates in a large range in the positive and negative directions with the volatility of the new energy power. The original relatively fixed high and low cycle scheme is difficult to maintain the stability of the local isolated network, and the voltage and frequency of the local power grid fluctuate greatly and exceed the normal operation range. Then, after reclosing, since the voltage and frequency of the local power grid exceed the normal operation range, the protection action will be triggered again, and the circuit breaker will permanently trip after reclosing, resulting in the failure of reclosing. Summary of the Invention

[0004] The purpose of the present invention is to solve the problems existing in the above-mentioned prior art, and provide a method for improving the success rate of reclosing of a weak-connected local power grid considering new energy, which can effectively improve the success probability of reclosing.

[0005] The present invention is realized by the following technical solutions: A method for improving the success rate of reclosing of a weak-connected local power grid considering new energy, characterized by comprising the following steps:

[0006] Real-time collect the active power and reactive power of each new energy station in the weak-connected local power grid, as well as the active power and reactive power on the main tie line between the weak-connected local power grid and the power system;

[0007] When the circuit breaker on the main tie line trips, the weakly-connected local power grid forms an island system that independently supplies power to the load. Voltage and frequency fluctuations in the island system are suppressed through a power balance control strategy, ensuring stable operation of the island system. The power balance control strategy uses the active and reactive power on the main tie line at a time ΔT before the circuit breaker trips as the total adjustment amount of the output of each new energy power station in the island system, thereby suppressing voltage and frequency fluctuations caused by surpluses or shortages of active and reactive power.

[0008] After the circuit breaker on the main tie line recloses, the weakly-connected local power grid and the power system jointly supply power to the load, and each new energy power station in the weakly-connected local power grid is controlled to resume its output state before the circuit breaker tripped.

[0009] Furthermore, the power balance control strategy includes a first objective function and system operation constraints, with the minimum number of adjustment stations as the first objective function:

[0010]

[0011] In the formula, N e is the total number of new energy power stations in the weakly-connected local power grid; E i is the state of the new energy power station after adjustment, is the state of the new energy power station after adjustment, and the initial value is 0, i ∈ {1, 2,......N e}; if the active power output or reactive power output of the i-th new energy power station changes before and after adjustment, then If there is no change, then

[0012] Furthermore, the power balance control strategy also includes a second objective function and new energy power station profit constraints, with the minimum adjustment cost as the second objective function:

[0013]

[0014] In the formula, α j is the cost per unit active power adjustment of the j-th new energy power station, β k is the cost per unit reactive power adjustment of the k-th new energy power station; W m is the set of new energy power stations with changed active power output after adjustment; W n is the set of new energy power stations with changed reactive power output after adjustment.

[0015] Furthermore, under system operation constraints and new energy power station profit constraints, a genetic algorithm is used to jointly solve the first objective function and the second objective function to obtain the optimal power adjustment strategy for new energy power stations in the weakly-connected local power grid.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0017] 1. The method proposed by the present invention can effectively suppress the voltage and frequency fluctuations of the weak local power grid during faults, and avoid the protection action being triggered again due to the voltage and frequency of the local power grid exceeding the normal operation range after reclosing, resulting in the permanent tripping of the circuit breaker and the failure of reclosing. Therefore, the success rate of reclosing can be greatly improved.

[0018] 2. The present invention can also effectively improve the operation reliability of the weak-connected local power grid in the new power system, enhance the ability of the local power grid mainly composed of new energy to cope with instantaneous faults, ensure the continuous power supply of the local power grid, and avoid the situation of the local power grid becoming an island or collapsing due to high-failure instantaneous faults.

[0019] 3. Under the system operation constraint conditions and the profit constraint of the new energy power station, the genetic algorithm is used to jointly solve the first objective function and the second objective function to obtain the optimal power adjustment strategy of the new energy power station in the weak-connected local power grid. It not only meets the requirement of improving the success rate of reclosing, but also has economy. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 is the power grid system architecture diagram;

[0021] Figure 2 is the flowchart for implementing the power balance control strategy. DETAILED DESCRIPTION OF THE INVENTION

[0022] (I) Line Structure and Overall Process

[0023] To better illustrate the technical solution of the present invention, the line structure of the power grid system is first described. Refer to Figure 1 As shown, the weak-connected local power grid includes multiple new energy power stations and loads (only two are shown in the figure). There is a new energy power station monitoring system in the new energy power station, from which the current active power output P ec and reactive power output Q ec of the new energy power station can be obtained, as well as its maximum active and reactive power output capacities P emax , Q emax . The weak-connected local power grid is connected to substation A in the power system through substation B and the tie line AB (main tie line).

[0024] The P ec , Q ec , P emax , Q emax obtained from the monitoring systems of each new energy power stationIt is sent to the substation (Substation B) where the local grid-side protection device is located in real time via optical fiber or GPRS. At the same time, the active and reactive powers P l and Q l of the main transmission line are obtained in real time from the tie-line protection device (in Substation A), and P l and Q l are defined as positive when the power flow direction is from the power system to the weakly-connected local grid, and P l and Q l are defined as negative when the power flow direction is from the weakly-connected local grid to the power system, and they are stored and recorded.

[0025] When an instantaneous fault occurs on the tie-line and causes the line breaker to trip, before the breaker recloses, the weakly-connected local grid becomes an island system. At this time, the active and reactive powers in this island system will become unbalanced, resulting in voltage and frequency fluctuations in the island system, reducing the success rate of breaker reclosing. In severe cases, it will also cause new energy units to trip off the grid due to fluctuations, further exacerbating the power imbalance, resulting in a vicious cycle, and ultimately leading to the collapse of the entire island system. At this time, the present invention adjusts the active and reactive power outputs of new energy power stations to achieve real-time matching of active and reactive powers during reclosing, suppress voltage and frequency fluctuations in the weakly-connected local grid, greatly improve the success rate of reclosing, effectively ensure the reliable power supply of the weakly-connected local grid, and avoid the occurrence of power grid accidents.

[0026] The method proposed by the present invention will be specifically described below. Referring to Figure 2 shown, a method for improving the reclosing success rate of a weakly-connected local grid considering new energy includes the following steps:

[0027] Real-time collect the active and reactive powers of each new energy power station in the weakly-connected local grid, as well as the active and reactive powers on the main transmission line between the weakly-connected local grid and the power system;

[0028] When the breaker on the main transmission line trips, the weakly-connected local grid forms an island system that independently supplies power to the load. Voltage and frequency fluctuations in the island system are suppressed through a power balance control strategy, making the island system operate stably. The power balance control strategy uses the active and reactive powers on the main transmission line at ΔT moments before the breaker trips as the total adjustment amount of the output of each new energy power station in the island system, so as to suppress voltage and frequency fluctuations caused by surplus or deficit of active and reactive powers. When a power grid fault trips, the fault recorder can record 5 - 10 cycles before the fault occurs. One cycle is 20 ms, so the fault recorder can record 100 - 200 ms before the fault occurs. Therefore, the power value at the start of the fault recorder, that is, 100 - 200 ms before the breaker trips, is selected as the power that the island system needs to increase / decrease. ΔT is preferably 200 ms.

[0029] After the circuit breaker on the main tie line recloses, the weak-connected local power grid and the power system jointly supply power to the load. Control the output of each new energy power station in the weak-connected local power grid to return to the output state before the circuit breaker trips, and the entire power system returns to the stable operation state before the fault, so as to prevent the reclosing failure caused by the permanent tripping of the circuit breaker due to the unstable operation of the weak-connected local power grid after reclosing.

[0030] (2) Power balance control strategy

[0031] 2.1) The first objective function and system operation constraints

[0032] Starting from the rapidity and stability of adjustment response, the power adjustment response times of each power station may not be exactly the same. The more new energy power stations participate in the adjustment, the more likely problems such as power oscillation will occur. Therefore, it is hoped to achieve power balance in the island system with the fewest adjustment stations. The power balance control strategy includes the first objective function and system operation constraints, and takes the fewest adjustment stations as the first objective function:

[0033]

[0034] In the formula, N e is the total number of new energy power stations in the weak-connected local power grid; E i is the state of the new energy power station after adjustment, is the state of the new energy power station after adjustment, and the initial value is 0, i ∈ {1, 2,......N e}; if the active power or reactive power of the i-th new energy power station changes before and after adjustment, then If there is no change, then

[0035] The system operation constraints include power balance constraints, that is, the sum of the output adjustment amounts of each new energy power station is equal to the active power and reactive power on the main tie line at ΔT before the circuit breaker trips:

[0036]

[0037]

[0038] In the formula, P l is the active power on the main tie line at ΔT before the circuit breaker trips; Q l is the reactive power on the main tie line at ΔT before the circuit breaker trips; P l is W m is the set of new energy power stations with changed active power output after adjustment, is the adjusted active power of the j-th new energy power station with changed active power output; is the active power of the new energy field before the change in the active power output of the j-th one; W n is the set of new energy power stations where the reactive power output changes after adjustment, is the reactive power of the new energy field after the change in the reactive power output of the k-th one; The reactive power of the new energy field before the change in the reactive power output of the k-th one.

[0039] The system operation constraint conditions also include the new energy power station capacity constraint, that is, the active and reactive powers of each new energy power station in the weakly-connected local power grid after adjustment should simultaneously meet their minimum and maximum output limits:

[0040]

[0041] In the formula, are the minimum and maximum output active powers of the i-th new energy power station respectively; are the minimum and maximum output reactive powers of the i-th new energy power station respectively; is the active power of the i-th new energy power station after adjustment, is the reactive power of the i-th new energy power station after adjustment.

[0042] The system operation constraint conditions also include the line current-carrying capacity constraint, that is, the active power of the new energy power station where the active power output changes after adjustment does not exceed the maximum allowable transmission power of the branch connection line (i.e., Figure 1 the connection line between the new energy power station and the system in

[0043]

[0044] In the formula, is the active power of the j-th new energy power station where the active power output changes after adjustment, is the maximum allowable transmission power of the branch connection line of the j-th new energy power station.

[0045] As the basic adjustment plan, the optimal power adjustment strategy is obtained by solving the first objective function under the system operation constraint conditions, that is, the new energy power stations in the weakly-connected local power grid that need to change the active and reactive power outputs and their corresponding power increase and decrease amounts are sent to the corresponding new energy power stations respectively. The fast power adjustment device of the new energy power station quickly increases or decreases the corresponding power according to the required adjusted active power and reactive power.

[0046] 2.2) The second objective function and system operation constraint conditions

[0047] From an economic perspective, on the basis of the least number of power stations participating in power adjustment, grid operators always hope to achieve the adjustment goal at the lowest cost. Therefore, the power balance control strategy also includes a second objective function and a profit constraint for new energy power stations, and takes the least adjustment cost as the second objective function:

[0048]

[0049] In the formula, α j is the cost of unit active power adjustment of the j-th new energy power station, and β k is the cost of unit reactive power adjustment of the k-th new energy power station; W m is the set of new energy power stations with changed active power output after adjustment; W n is the set of new energy power stations with changed reactive power output after adjustment.

[0050] The profit constraint for new energy power stations means that the power adjustment cost of new energy power stations should not be greater than their income in the 24 hours before the fault moment:

[0051]

[0052] In the formula, G r is the income of the r-th new energy power station with changed active power output and / or reactive power output in 24 hours since the fault moment; r ∈ W m ∪W n , W m is the set of new energy power stations with changed active power output after adjustment; W n is the set of new energy power stations with changed reactive power output after adjustment.

[0053] As an upgraded adjustment plan, under the system operation constraint conditions and the profit constraint of new energy power stations, the genetic algorithm is used to jointly solve the first objective function and the second objective function to obtain the optimal power adjustment strategy for new energy power stations in a weakly-connected local power grid. The active power and reactive power required to be adjusted by each new energy power station in the optimal power adjustment strategy are respectively sent to the corresponding new energy power station, and the fast power adjustment device of the new energy power station quickly increases or decreases the corresponding power according to the required active power and reactive power.

[0054] The above technical solution is only one implementation manner of the present invention. For those skilled in the art, on the basis of the disclosed principle of the present invention, it is very easy to make various types of improvements or deformations, not limited to the technical solution described in the above specific embodiments of the present invention. Therefore, the foregoing description is only preferred and does not have a restrictive meaning.

Claims

1. A method for improving the reclosing success rate of a weakly-connected local power grid considering new energy, characterized in that: The steps include: Real-time collecting the active power and reactive power of each new energy power station in the weakly-connected local power grid, as well as the active power and reactive power on the main tie line between the weakly-connected local power grid and the power system; When the circuit breaker on the main tie line trips, the weakly-connected local power grid forms an island system that independently supplies power to the load. Voltage and frequency fluctuations of the island system are suppressed through a power balance control strategy, enabling the stable operation of the island system. The power balance control strategy uses the active power and reactive power on the main tie line at ΔT moments before the circuit breaker trips as the sum of the output adjustment amounts of each new energy power station in the island system, thereby suppressing voltage and frequency fluctuations caused by surplus or deficit of active power and reactive power. Among them, the power balance control strategy includes a first objective function and system operation constraint conditions, and takes the minimum number of adjustment stations as the first objective function: Where N e is the total number of new energy power stations in the weakly-connected local power grid; E i is the status of the new energy power station after adjustment, E i 0 is the status of the new energy power station after adjustment, and the initial value is 0, i ∈ {1, 2,...... N e}; if the active power output or reactive power output of the i-th new energy power station changes before and after adjustment, then if there is no change, then The power balance control strategy also includes a second objective function and new energy power station profit constraints, and takes the minimum adjustment cost as the second objective function: Where, α j is the cost of unit active power adjustment of the j-th new energy power station, and β k is the cost of unit reactive power adjustment of the k-th new energy power station; W m is the set of new energy power stations with changed active power output after adjustment; W n is the set of new energy power stations with changed reactive power output after adjustment, is the adjusted active power of the j-th new energy power station with changed active power output; is the active power of the j-th new energy power station with changed active power output before adjustment; Q e ′ ck is the adjusted reactive power of the k-th new energy power station with changed reactive power output; is the reactive power of the k-th new energy power station with changed reactive power output before adjustment; Under the system operation constraint conditions and new energy power station profit constraints, the genetic algorithm is used to jointly solve the first objective function and the second objective function to obtain the optimal power adjustment strategy of the new energy power stations in the weakly-connected local power grid; When the circuit breaker on the main tie line recloses, the weakly-connected local power grid and the power system jointly supply power to the load, and each new energy power station in the weakly-connected local power grid is controlled to return to the output state before the circuit breaker trips.

2. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 1, wherein: The system operation constraint conditions include power balance constraints, that is, the sum of the output adjustment amounts of each new energy power station is equal to the active power and reactive power on the main tie line at ΔT moments before the circuit breaker trips: Wherein, P l is the active power on the main tie line at the moment of ΔT before the circuit breaker trips; Q l is the reactive power on the main tie line at the moment of ΔT before the circuit breaker trips; W m is the set of new energy power stations where the adjusted active power output changes, is the adjusted active power of the j-th new energy power station where the active power output changes; is the active power of the j-th new energy power station where the active power output changes before adjustment; W n is the set of new energy power stations where the adjusted reactive power output changes, is the adjusted reactive power of the k-th new energy power station where the reactive power output changes; is the reactive power of the k-th new energy power station where the reactive power output changes before adjustment.

3. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 2, characterized in that: ΔT is 100 - 200 ms.

4. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 2, characterized in that: The system operation constraint conditions also include new energy power station capacity constraints, that is, the active power and reactive power of each new energy power station in the adjusted weakly-connected local power grid should simultaneously meet its minimum and maximum output limits: Where, P emini and P emaxi are respectively the minimum and maximum active power outputs of the i-th new energy power station; are respectively the minimum and maximum reactive power outputs of the i-th new energy power station; is the adjusted active power of the i-th new energy power station, is the adjusted reactive power of the i-th new energy power station.

5. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 4, characterized in that: The system operation constraint conditions also include line current-carrying capacity constraints, that is, the active power of the new energy power stations with changed active power output after adjustment does not exceed the maximum allowable transmission power of the branch tie line connecting them to the weakly-connected local power grid: In the formula, is the active power of the j-th new energy power station where the adjusted active power output changes, is the maximum allowable transmission power of the branch tie line of the j-th new energy power station.

6. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 1, characterized in that: The new energy power station profit constraint, that is, the output adjustment cost of the new energy power station should not be greater than its income in the 24 hours before the fault moment: where G r is the revenue of the r-th new energy power station with changed adjusted active power output and / or reactive power output within 24 hours since the fault moment; r ∈ W m UW n ,W m is the set of new energy power stations with changed adjusted active power output, and W n is the set of new energy power stations with changed adjusted reactive power output.

7. The method for improving the reclosing success rate of a weakly-connected local power grid considering a lifting meter and new energy according to claim 1, characterized in that: The required active power and reactive power for adjustment of each new energy power station in the optimal power adjustment strategy are respectively sent to the corresponding new energy power station, and the fast power adjustment device of the new energy power station quickly increases or decreases the corresponding power according to the required active power and reactive power for adjustment.

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