A method and system for analyzing the operating characteristics of a receiving system with cascading instability

Abstract

The present invention discloses a method and system for analyzing the operating characteristics of the cascading instability of a receiving system, and belongs to the technical field of power systems. The method of the present invention comprises: establishing a simulation model of an AC / DC hybrid receiving system, and performing a simulation operation of the AC / DC hybrid receiving system according to the simulation model to obtain a simulation result; and determining whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving system based on the simulation result. The present invention strictly controls the operating boundary conditions of each sub-region of the receiving system, and can avoid disordered and repeated work when adjusting the required power grid operation mode, so that the simulation results are more intuitive and clear and have analytical significance.

Description

Technical Field

[0001] The present invention relates to the technical field of power systems, and more particularly, to a method and system for analyzing the cascading instability operating characteristics of a receiving-end system. Background Art

[0002] Due to the uneven distribution of energy centers and loads in China, line commutated converter-based high voltage direct current (LCC-HVDC) transmission technology has rapidly developed due to its advantages such as long transmission distances and large power transmission capacity. With the successive commissioning of ultra-high voltage and ultra-high voltage direct current (UHVDC) projects, hybrid AC / DC systems are becoming increasingly common, with multiple DC grids transmitting or receiving in the same direction exhibiting a "strong DC, weak AC" characteristic. my country's Central China Power Grid, East China Power Grid, and Southern Power Grid all feature system structures with multiple DC feeds.

[0003] After a grid fault occurs, multiple DC circuits may be significantly impacted simultaneously, increasing the risk of simultaneous or sequential DC blockages. This can severely impact the AC system and threaten the safe and stable operation of hybrid AC / DC systems. Therefore, it is necessary to rapidly identify and analyze strongly correlated faults and accident chains, addressing the frequent AC / DC coupling issues in hybrid AC / DC systems, to avoid the large-scale power flow shifts and power imbalances caused by potential DC blockages.

[0004] Because DC transmission relies on coordinated AC / DC grid operation, grid operational characteristics are typically analyzed within a specific subregion. Traditional analysis methods simplify the AC / DC receiving system analysis by disconnecting the interconnecting lines between subregions in the receiving system, eliminating the fault transmission path after a system failure. However, this approach fails to accurately analyze the post-fault transmission process and influencing factors of the AC / DC hybrid receiving system. Summary of the Invention

[0005] To address the above issues, the present invention proposes a method for analyzing the operating characteristics of a receiving system with cascading instability, comprising:

[0006] Establishing a simulation model of an AC / DC hybrid receiving-end system, and performing a simulation run of the AC / DC hybrid receiving-end system based on the simulation model to obtain a simulation result; the simulation run includes:

[0007] Determine the system operation mode of the AC / DC hybrid receiving system;

[0008] Based on the system operation mode, a risk scan is conducted on the AC / DC hybrid receiving-end system by region to determine the greatest fault risk affecting the operation of the power grid in each region;

[0009] Determine the fault that has the greatest impact on the operation of the power grid in each region based on the fault risk;

[0010] Adjusting the grid operation mode of any regional grid in each region to a critical instability operation mode according to the largest operating fault in the grid;

[0011] Based on the simulation results, determine whether there is operating characteristic of cascading instability in the AC / DC hybrid receiving end system.

[0012] Optionally, determine the system operation mode of the AC / DC hybrid receiving-end system, specifically:

[0013] Determine the maximum operating range of DC power, startup mode and load conditions in each area of the AC / DC hybrid receiving system, determine the interconnection line transmission power between each area based on the maximum operating range of DC power, startup mode and load conditions, and determine the system operation mode of the AC / DC hybrid receiving system based on the interconnection line transmission power.

[0014] Optionally, the failure risk is at least one of the following: three-period N-1 failure and three-period N-2 failure.

[0015] Optionally, adjusting the grid operation mode of any regional power grid in each area to a critical instability operation mode according to the largest operating fault in the grid, specifically includes:

[0016] Selecting any regional power grid in each area of the AC / DC hybrid receiving-end system as a starting point for adjusting the operating mode, changing the load and system spinning reserve of the any regional power grid, wherein the load and system spinning reserve are equal, and switching capacitors and reactors within a preset range of busbars for the any regional power grid to determine a critical instability operating mode of the any regional power grid;

[0017] According to the largest fault in the power grid, the sub-regional power grid in any regional power grid is adjusted to the critical stable operating condition.

[0018] Optionally, determine the operating characteristics of the AC / DC hybrid receiving-end system that may cause cascading instability, including:

[0019] Monitor the bus voltage, unit power angle, and power exchange of the interconnecting lines between different areas in each area of the AC / DC hybrid receiving system;

[0020] Based on the bus voltage, the unit power angle, and the power exchange conditions of the tie lines between the areas, it is determined whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system.

[0021] Optionally, determine whether there are operating characteristics of cascading instability in the AC / DC hybrid receiving-end system, as follows:

[0022] Determine whether a low voltage problem exists in one area or multiple areas of the AC / DC hybrid receiving system based on the bus voltage;

[0023] Determine based on the bus voltage whether voltage collapse occurs in certain areas of the AC / DC hybrid receiving system or in the entire network;

[0024] Determine whether the power angles of all units in the AC / DC hybrid receiving system are in sync, partially out of sync, or the entire network is out of sync;

[0025] According to the power exchange situation of the inter-area tie lines in each area of the AC / DC hybrid receiving end system, it is determined that the inter-area tie lines are not disconnected, partially disconnected, or completely disconnected;

[0026] If a low voltage problem exists in a certain area, the power angles of all generators in the entire network are not out of step, and the tie lines between the areas are not disconnected, then it is determined that the low voltage operation problem exists only in the certain area of the AC / DC hybrid receiving end system;

[0027] If low voltage problems exist in certain areas, the power angles of the generators in the entire network are partially out of step, and the tie lines between the areas are partially disconnected, it is determined that only regional low voltage operation characteristics exist in the AC / DC hybrid receiving-end system, and the sequence and causal relationship of the chain accidents can be determined based on the inter-area bus voltage drop time sequence;

[0028] If voltage collapse occurs in certain areas, the generator power angles in the entire grid are partially out of sync, and the interconnecting lines between areas are partially disconnected, it is determined that only regional voltage collapse exists in the AC / DC hybrid receiving system. The sequence of chain accidents and the causal relationship can be determined based on the inter-area bus voltage drop time sequence.

[0029] If a voltage collapse problem occurs in the entire network, the power angles of all units in the network are out of step and the interconnection lines between regions are disconnected, it is determined that only a regional voltage collapse problem exists in the AC / DC hybrid receiving system, and the sequence and causal relationship of the chain accident are determined based on the timing of the inter-regional bus voltage drops.

[0030] The present invention also proposes a system for analyzing the operating characteristics of the receiving system in a chain-like instability state, comprising:

[0031] The simulation operation unit establishes a simulation model of the AC / DC hybrid receiving end system and performs a simulation operation of the AC / DC hybrid receiving end system based on the simulation model to obtain a simulation result; the simulation operation includes:

[0032] Determine the system operation mode of the AC / DC hybrid receiving system;

[0033] Based on the system operation mode, a risk scan is conducted on the AC / DC hybrid receiving-end system by region to determine the greatest fault risk affecting the operation of the power grid in each region;

[0034] Determine the fault that has the greatest impact on the operation of the power grid in each region based on the fault risk;

[0035] Adjusting the grid operation mode of any regional grid in each region to a critical instability operation mode according to the largest operating fault in the grid;

[0036] The analysis unit determines whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system based on the simulation results.

[0037] Optionally, determine the system operation mode of the AC / DC hybrid receiving-end system, specifically:

[0038] Determine the maximum operating range of DC power, startup mode and load conditions in each area of the AC / DC hybrid receiving system, determine the interconnection line transmission power between each area based on the maximum operating range of DC power, startup mode and load conditions, and determine the system operation mode of the AC / DC hybrid receiving system based on the interconnection line transmission power.

[0039] Optionally, the failure risk is at least one of the following: three-period N-1 failure and three-period N-2 failure.

[0040] Optionally, adjusting the grid operation mode of any regional power grid in each area to a critical instability operation mode according to the largest operating fault in the grid, specifically includes:

[0041] Selecting any regional power grid in each area of the AC / DC hybrid receiving-end system as a starting point for adjusting the operating mode, changing the load and system spinning reserve of the any regional power grid, wherein the load and system spinning reserve are equal, and switching capacitors and reactors within a preset range of busbars for the any regional power grid to determine a critical instability operating mode of the any regional power grid;

[0042] According to the largest fault in the power grid, the sub-regional power grid in any regional power grid is adjusted to the critical stable operating condition.

[0043] Optionally, determine the operating characteristics of the AC / DC hybrid receiving-end system that may cause cascading instability, including:

[0044] Monitor the bus voltage, unit power angle, and power exchange of the interconnecting lines between different areas in each area of the AC / DC hybrid receiving system;

[0045] Based on the bus voltage, the unit power angle, and the power exchange conditions of the tie lines between the areas, it is determined whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system.

[0046] Optionally, determine whether there are operating characteristics of cascading instability in the AC / DC hybrid receiving-end system, as follows:

[0047] Determine whether a low voltage problem exists in one area or multiple areas of the AC / DC hybrid receiving system based on the bus voltage;

[0048] Determine based on the bus voltage whether voltage collapse occurs in certain areas of the AC / DC hybrid receiving system or in the entire network;

[0049] Determine whether the power angles of all units in the AC / DC hybrid receiving system are in sync, partially out of sync, or the entire network is out of sync;

[0050] According to the power exchange situation of the inter-area tie lines in each area of the AC / DC hybrid receiving end system, it is determined that the inter-area tie lines are not disconnected, partially disconnected, or completely disconnected;

[0051] If a low voltage problem exists in a certain area, the power angles of all generators in the entire network are not out of step, and the tie lines between the areas are not disconnected, then it is determined that the low voltage operation problem exists only in the certain area of the AC / DC hybrid receiving end system;

[0052] If low voltage problems exist in certain areas, the power angles of the generators in the entire network are partially out of step, and the tie lines between the areas are partially disconnected, it is determined that only regional low voltage operation characteristics exist in the AC / DC hybrid receiving-end system, and the sequence and causal relationship of the chain accidents can be determined based on the inter-area bus voltage drop time sequence;

[0053] If voltage collapse occurs in certain areas, the generator power angles in the entire grid are partially out of sync, and the interconnecting lines between areas are partially disconnected, it is determined that only regional voltage collapse exists in the AC / DC hybrid receiving system. The sequence of chain accidents and the causal relationship can be determined based on the inter-area bus voltage drop time sequence.

[0054] If a voltage collapse problem occurs in the entire network, the power angles of all units in the network are out of step and the interconnection lines between regions are disconnected, it is determined that only a regional voltage collapse problem exists in the AC / DC hybrid receiving system, and the sequence and causal relationship of the chain accident are determined based on the timing of the inter-regional bus voltage drops.

[0055] The advantages of the present invention are:

[0056] (1) The present invention strictly controls the operating boundary conditions of each sub-region of the receiving system and can avoid disorder and duplication of work when adjusting the required grid operation mode, making the simulation results more intuitive, clear and analytically meaningful;

[0057] (2) The present invention can not only obtain the key factors affecting the transient stability of a multi-input receiving-end system, but also derive the time sequence and correlation relationship of the instability of each sub-region caused by the fault, which is suitable for providing a method for solving system safety and stability analysis in actual engineering;

[0058] (3) The present invention verifies the accuracy of the characteristic analysis method of multiple DC-fed receiving-end systems through the analysis results of multiple receiving-end systems and their derived operating modes, showing that the method has strong practicality in engineering analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 is a flow chart of an embodiment of the method of the present invention;

[0060] Figure 2 This is a diagram of the grid structure of the Z area in the embodiment of the method of the present invention;

[0061] Figure 3 This is a timing curve diagram of voltage drops in various provinces after a most serious three-phase N-1 fault in province A in an embodiment of the method of the present invention;

[0062] Figure 4 This is a bus voltage curve diagram of province D in an embodiment of the method of the present invention;

[0063] Figure 5 This is a bus voltage curve diagram of Province B in an embodiment of the method of the present invention;

[0064] Figure 6 This is a curve diagram of bus voltage in province C in an embodiment of the method of the present invention;

[0065] Figure 7 This is a bus voltage curve diagram of province A in an embodiment of the method of the present invention;

[0066] Figure 8 This is a power angle curve diagram of the D-unit in the embodiment of the method of the present invention;

[0067] Figure 9 This is a power angle curve diagram of unit B in the embodiment of the method of the present invention;

[0068] Figure 10 This is a power angle curve diagram of the C-saving unit in the embodiment of the method of the present invention;

[0069] Figure 11 This is a power angle curve diagram of unit A in the embodiment of the method of the present invention;

[0070] Figure 12 This is an active power curve of line I between Province C and Province D in an embodiment of the method of the present invention;

[0071] Figure 13 This is an active power curve of the C Province-D Province connection II line in the embodiment of the method of the present invention;

[0072] Figure 14 This is an active power curve of the C Province-D Province connection line III in the embodiment of the method of the present invention;

[0073] Figure 15This is an active power curve of line I between Province B and Province D in an embodiment of the method of the present invention;

[0074] Figure 16 This is an active power curve of the B-Province D connection line II in the embodiment of the method of the present invention;

[0075] Figure 17 This is a timing curve diagram of voltage drops in various provinces after a most serious three-phase N-1 fault in province A in an embodiment of the method of the present invention;

[0076] Figure 18 This is a bus voltage curve diagram of province D in an embodiment of the method of the present invention;

[0077] Figure 19 This is a bus voltage curve diagram of Province B in an embodiment of the method of the present invention;

[0078] Figure 20 This is a curve diagram of bus voltage in province C in an embodiment of the method of the present invention;

[0079] Figure 21 This is a bus voltage curve diagram of province A in an embodiment of the method of the present invention;

[0080] Figure 22 This is a power angle curve diagram of the D-unit in the embodiment of the method of the present invention;

[0081] Figure 23 This is a power angle curve diagram of unit B in the embodiment of the method of the present invention;

[0082] Figure 24 This is a power angle curve diagram of the C-saving unit in the embodiment of the method of the present invention;

[0083] Figure 25 This is a power angle curve diagram of unit A in the embodiment of the method of the present invention;

[0084] Figure 26 This is an active power curve of line I between Province C and Province D in an embodiment of the method of the present invention;

[0085] Figure 27 This is an active power curve of the C Province-D Province connection II line in the embodiment of the method of the present invention;

[0086] Figure 28 This is an active power curve of line III of the Province C-Province D tie line in an embodiment of the method of the present invention;

[0087] Figure 29 This is an active power curve of line I of the B-province-D province tie line in an embodiment of the method of the present invention;

[0088] Figure 30 This is an active power curve of line II of the B-province-D province tie line in an embodiment of the method of the present invention;

[0089] Figure 31 This is a graph showing active power curves of the Province A-Province D tie line after the most serious fault in Province A occurs in different startup modes in Province A in an embodiment of the method of the present invention;

[0090] Figure 32 This is a bus voltage curve diagram of Province D after the most serious fault in Province A occurs in different startup modes in Province A in an embodiment of the method of the present invention;

[0091] Figure 33 It is a structural diagram of the system of the present invention. DETAILED DESCRIPTION

[0092] Exemplary embodiments of the present invention will now be described with reference to the accompanying drawings. However, the present invention may be embodied in many different forms and is not limited to the embodiments described herein. These embodiments are provided to provide a thorough and complete disclosure of the present invention and to fully convey the scope of the present invention to those skilled in the art. The terminology used in the exemplary embodiments shown in the accompanying drawings is not intended to limit the present invention. In the accompanying drawings, identical elements are denoted by the same reference numerals.

[0093] Unless otherwise specified, the terms used herein (including technical terms) have the meanings commonly understood by those skilled in the art. In addition, it is understood that terms defined in commonly used dictionaries should be understood to have the same meanings as those in the context of the relevant fields, and should not be understood as idealized or overly formal meanings.

[0094] The present invention will be further described below in conjunction with embodiments:

[0095] The present invention proposes a method for analyzing the cascading instability operating characteristics of the receiving system. Figure 1 Shown, including:

[0096] 1. Determine the transmission power of each inter-area tie line based on the maximum operating range of DC power, startup mode, and load conditions in each area, and then determine the operating mode of the receiving system;

[0097] 2. Based on the established system operation mode, perform a risk scan of the entire AC system by region to identify the fault risks that have the greatest impact on the grid operation characteristics in each region. These fault risks are risks existing in the entire AC system, including: three-period N-1 faults and three-period N-2 faults.

[0098] 3. Identify the faults that have the greatest impact on the operational characteristics of the power grid in each region;

[0099] 4. Adjust the operation mode of each regional power grid to the critical instability operation mode according to the known faults in step 3 above. The adjustment method is as follows:

[0100] 1) Select a regional power grid A as the research object and the starting point for adjusting the operating mode. By changing the load in the region and the equivalent system spinning reserve, and switching capacitors and reactors around the busbar, the regional power grid A is guaranteed to operate at the same voltage level under different operating modes. The critical instability operating mode of region A is then determined.

[0101] 2) Based on the regional grid faults identified in step 3, adjust the sub-regional grid of the next adjacent region A to a critically stable operating condition. Then, use the faults of the selected regional grid A again to verify whether the region is operating in a critically unstable condition.

[0102] 3) According to adjustment method 2), adjust the remaining sub-regions' power grid modes one by one to critical stability conditions, and determine whether only region A in the entire network is operating in a critical instability condition. If only region A is operating in a critical instability condition, proceed to step 5. Otherwise, return to adjustment method 1), readjust region A to a critical instability condition, and repeat method 2) until only region A in the entire network is operating in a critical instability condition. At this point, the power flow adjustment is complete.

[0103] 5. Based on the simulation results output in step 4, when only a certain area of the entire network is operating under critical instability conditions, it is necessary to determine whether the entire network system has cascading instability characteristics caused by a certain area. It is necessary to monitor the bus voltage, unit power angle, and active power exchange of the tie lines between regions in each area. The judgment rules can be divided into the following:

[0104] 5-1) If the simulation results show that only one area has a low voltage problem, the power angle of the entire network is not out of step, and the tie lines between sub-areas are not disconnected, it can be determined that the low voltage operation problem only exists in a certain area of the multi-infeed receiving system;

[0105] 5-2) If the simulation results show low voltage problems in certain areas, power angle desynchronization of units in some areas, and disconnection problems in certain inter-area tie lines, it can be determined that the multi-input receiving system only has regional low voltage operation characteristics. The sequence and causal relationship of the chain accident can be determined based on the inter-area bus voltage drop time sequence;

[0106] 5-3) If the simulation results show voltage collapse in certain areas, power angle desynchronization in some areas, and disconnection of certain inter-area tie lines, it can be determined that only regional voltage collapse exists in the multi-input receiving system. The sequence of the chain events and the causal relationship can be determined based on the inter-area bus voltage drop timing.

[0107] 5-4) If the simulation results show a network-wide voltage collapse, a loss of power angle across all generators, and disconnection of all inter-regional tie lines, it can be determined that the multi-input receiving system only has a regional voltage collapse problem. The sequence and causal relationship of the chain reaction can be determined based on the timing of the inter-regional bus voltage drops.

[0108] The present invention can be realized by simply following the calculation process and analysis method, is simple and easy to implement, and can be adopted in analyzing the operating characteristics of a multi-DC feed-in receiving-end system to significantly improve the analysis efficiency, save manpower and material resources, and quickly determine the system operating characteristics.

[0109] The following is based on the structure of a regional power grid at the end of 2021, including the 2021 power grid data uniformly provided by the State Grid Dispatching and Control Center. Taking the transient safety and stability issues of the Z regional power grid as the research object, simulation calculations are performed under different startup and operation modes in Province A.

[0110] The calculation program used was the power system comprehensive analysis program PSASP7.61.06 (Windows version) of the China Electric Power Research Institute.

[0111] By the end of 2021, Figure 2 As shown, after the interprovincial UHV ring network in Region Z was sequentially put into operation, the level of DC power transmission fed into the Region Z grid was significantly improved, and the electrical connection between the four provinces in Region Z was further strengthened. The voltage stability issues that existed in the four provinces in the original Region Z grid could, under severe conditions, be triggered by a single fault, leading to cascading voltage stability issues across the entire region. This paper analyzes the impact of a single fault in Province A on the operating characteristics of the Region Z grid based on two calculation examples, assuming the grid in Province A has a startup capacity of 14 million kilowatts and 18 million kilowatts, respectively.

[0112] 1) Instability mode 1 (Province A starts 14 million kilowatts)

[0113] The operation mode of the power grids in each province is as follows: Province A starts up 14 million kilowatts, a certain DC in Province A is 4.5 million kilowatts, and Province A sends out 3.7 million kilowatts of AC, there are 0 phase-shifting units, and 8% (1.12 million kilowatts) of the units in Province A are in standby; Province B has a load of 15.13 million kilowatts, Province B starts up 6.58 million kilowatts, a certain DC in Province B is 4 million kilowatts, Province B receives 4.8 million kilowatts of AC, and Province B has 1.34 million kilowatts of units in standby, with 1 phase-shifting unit; Province D has a load of 32.04 million kilowatts, Province D starts up 37.53 million kilowatts, Province C sends 3.1 million kilowatts to Province D, and the western part of Province D sends 5.8 million kilowatts to the eastern section of Province D, and Province D meets the minimum start-up requirement, and a certain DC in Province D is 3 million kilowatts. By applying the adjustment of the receiving-end system operation mode proposed by the present invention, only the power grid in Province A operates in a critical instability state after being affected by a certain most serious three-permanent N-1 fault in Province A, such as Figure 3 As shown in Figure 2, the power grids of the other three provinces in region Z are all operating in critical stability conditions.

[0114] By comparing the lowest bus voltage values in each provincial power grid, such as Figure 4-7 As shown in the figure, it can be concluded that only the voltage of the power grid in Province A oscillates around 0.4pu after the fault and cannot recover over time. At this time, there is no chain instability in the power grid in Region Z.

[0115] Then, by comparing the power angle differences of the generators in each province’s power grid, Figure 8-11 As shown in the figure, it can be concluded that only the power angle of the units in the power grid of Province A loses synchronization with the power angles of the units in other provinces after the fault occurs. At this time, there is no chain instability in the power grid of Region Z.

[0116] Finally, we compare the inter-provincial interconnection line power after the most serious Sanyong N-1 fault in Province A. Figure 12-16 As shown in the figure, it can be further confirmed that the inter-provincial interconnection lines of the Z region power grid were not disconnected after the fault. Therefore, it can be concluded that under this operating mode in the Z region, the fault of the power grid in Province A only caused the voltage instability of the power grid in Province A, and the other three provinces and three networks were not affected.

[0117] 2) Instability Mode 2 (Province A starts generating 18 million kilowatts)

[0118] The operation modes of the power grids in each province are as follows: Province A has 18 million kilowatts of started-up power, a certain DC power plant in Province A has 4.5 million kilowatts, Province A has 3.7 million kilowatts of AC power exported, there are 0 phase-shifting units, and 5% (900,000 kilowatts) of units in Province A are in standby mode; Province B has a load of 15.13 million kilowatts, Province B has 6.58 million kilowatts of started-up power, a certain DC power plant in Province B has 4 million kilowatts, Province B receives 4.8 million kilowatts of AC power, Province B has 1.34 million kilowatts of units in standby mode, and there is 1 phase-shifting unit; Province D has a load of 32.04 million kilowatts, Province D has 37.53 million kilowatts of started-up power, Province C has 3.1 million kilowatts transmitted to Province D, and the western part of Province D has 5.8 million kilowatts transmitted to the eastern section of Province D. Province D meets the minimum start-up requirement, and a certain DC power plant in Province D has 3 million kilowatts. By applying the adjustment of the receiving-end system operation mode proposed in the present invention, only the power grid in Province A operates in a critical instability state after suffering from the most serious three-permanent N-1 fault in Province A, while the power grids in the other three provinces in Region Z all operate in critical stability conditions.

[0119] By comparing the lowest bus voltage values in the power grids of various provinces, it can be concluded that the power grid in region Z experienced voltage instability after being hit by the most serious Sanyong N-1 fault in Province A. At this time, the power grid in region Z experienced a chain instability of the entire network.

[0120] like Figure 17 As shown, the voltage drop sequence of each province's power grid can be found to be Province A-Province D-Province C-Province B, and from Figure 17-21 It can be seen that the voltage instability problem only exists in the southern part of the power grid in Province C.

[0121] By comparing the power angle differences of the generators in each province’s power grid, it can be concluded that the power angles of the generators in each province’s power grid in region Z are out of sync with the power angles of the generators in other provinces after a fault occurs. Figure 22-25As shown in the figure, at this time, the power grid in area Z is experiencing a chain-linked instability.

[0122] Finally, we compare the inter-provincial interconnection line power after the most serious Sanyong N-1 fault in Province A. Figure 26-30 As shown in Figure 1, after the fault, the active power of the inter-provincial tie lines oscillates and exchanges at 0pu, thus determining that the inter-provincial tie lines of the Z region power grid are disconnected, causing the voltage of the entire Z region power grid to become unstable.

[0123] By comparing the power of the same inter-provincial tie line and the bus voltage value in the same region under different startup modes in Province A, it can be concluded that the same fault under different operating boundaries of the power grid in Province A will have different impacts on the operating characteristics of the entire Z region power grid. Figure 31 As shown in the figure, when Province A starts generating 14 million kilowatts, the active power of the Province A-Province D tie line reaches -14pu at 1.7s, and there is still active power exchange in the tie line; however, when Province A starts generating 18 million kilowatts, the active power of the Province A-Province D tie line reaches -15.5pu due to a fault, and then the active power of the tie line is zero, indicating that the tie line is disconnected due to a fault. Figure 32 It can be seen that when Province A starts up at 14 million kilowatts, the voltage of Province D can be restored to 0.8pu after the Sanyong N-1 fault in Province A. However, when Province A starts up at 18 million kilowatts, the voltage in Province D becomes unstable and cannot be restored.

[0124] Through the proposed method for adjusting the grid operation mode, it is determined whether there is a cascading instability pattern in the Z region grid and the engineering practicability of the proposed analysis method is verified according to the analysis method provided by the present invention.

[0125] The present invention also proposes a system 200 for analyzing the cascading instability operating characteristics of a receiving system. Figure 33 Shown, including:

[0126] The simulation operation unit 201 establishes a simulation model of the AC / DC hybrid receiving-end system and performs a simulation operation of the AC / DC hybrid receiving-end system based on the simulation model to obtain a simulation result. The simulation operation includes:

[0127] Determine the system operation mode of the AC / DC hybrid receiving system;

[0128] Based on the system operation mode, a risk scan is conducted on the AC / DC hybrid receiving-end system by region to determine the greatest fault risk affecting the operation of the power grid in each region;

[0129] Determine the fault that has the greatest impact on the operation of the power grid in each region based on the fault risk;

[0130] Adjusting the grid operation mode of any regional grid in each region to a critical instability operation mode according to the largest operating fault in the grid;

[0131] The analyzing unit 202 determines whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system based on the simulation results.

[0132] Among them, the system operation mode of the AC / DC hybrid receiving end system is determined as follows:

[0133] Determine the maximum operating range of DC power, startup mode and load conditions in each area of the AC / DC hybrid receiving system, determine the interconnection line transmission power between each area based on the maximum operating range of DC power, startup mode and load conditions, and determine the system operation mode of the AC / DC hybrid receiving system based on the interconnection line transmission power.

[0134] The failure risk is at least one of the following: a three-way N-1 failure and a three-way N-2 failure.

[0135] The operation mode of the power grid in any of the regions is adjusted to a critical instability operation mode according to the largest operating fault in the power grid, specifically including:

[0136] Selecting any regional power grid in each area of the AC / DC hybrid receiving-end system as a starting point for adjusting the operating mode, changing the load and system spinning reserve of the any regional power grid, wherein the load and system spinning reserve are equal, and switching capacitors and reactors within a preset range of busbars for the any regional power grid to determine a critical instability operating mode of the any regional power grid;

[0137] According to the largest fault in the power grid, the sub-regional power grid in any regional power grid is adjusted to the critical stable operating condition.

[0138] The operational characteristics of the AC / DC hybrid receiving-end system that may cause cascading instability are determined as follows:

[0139] Monitor the bus voltage, unit power angle, and power exchange of the interconnecting lines between different areas in each area of the AC / DC hybrid receiving system;

[0140] Based on the bus voltage, the unit power angle, and the power exchange conditions of the tie lines between the areas, it is determined whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system.

[0141] The operational characteristics for determining whether there is cascading instability in the AC / DC hybrid receiving-end system are as follows:

[0142] Determine whether a low voltage problem exists in one area or multiple areas of the AC / DC hybrid receiving system based on the bus voltage;

[0143] Determine based on the bus voltage whether voltage collapse occurs in certain areas of the AC / DC hybrid receiving system or in the entire network;

[0144] Determine whether the power angles of all units in the AC / DC hybrid receiving system are in sync, partially out of sync, or the entire network is out of sync;

[0145] According to the power exchange situation of the inter-area tie lines in each area of the AC / DC hybrid receiving end system, it is determined that the inter-area tie lines are not disconnected, partially disconnected, or completely disconnected;

[0146] If a low voltage problem exists in a certain area, the power angles of all generators in the entire network are not out of step, and the tie lines between the areas are not disconnected, then it is determined that the low voltage operation problem exists only in the certain area of the AC / DC hybrid receiving end system;

[0147] If low voltage problems exist in certain areas, the power angles of the generators in the entire network are partially out of step, and the tie lines between the areas are partially disconnected, it is determined that only regional low voltage operation characteristics exist in the AC / DC hybrid receiving-end system, and the sequence and causal relationship of the chain accidents can be determined based on the inter-area bus voltage drop time sequence;

[0148] If voltage collapse occurs in certain areas, the generator power angles in the entire grid are partially out of sync, and the interconnecting lines between areas are partially disconnected, it is determined that only regional voltage collapse exists in the AC / DC hybrid receiving system. The sequence of chain accidents and the causal relationship can be determined based on the inter-area bus voltage drop time sequence.

[0149] If a voltage collapse problem occurs in the entire network, the power angles of all units in the network are out of step and the interconnection lines between regions are disconnected, it is determined that only a regional voltage collapse problem exists in the AC / DC hybrid receiving system, and the sequence and causal relationship of the chain accident are determined based on the timing of the inter-regional bus voltage drops.

[0150] The advantages of the present invention are:

[0151] (1) The present invention strictly controls the operating boundary conditions of each sub-region of the receiving system and can avoid disorder and duplication of work when adjusting the required grid operation mode, making the simulation results more intuitive, clear and analytically meaningful;

[0152] (2) The present invention can not only obtain the key factors affecting the transient stability of a multi-input receiving-end system, but also derive the time sequence and correlation relationship of the instability of each sub-region caused by the fault, which is suitable for providing a method for solving system safety and stability analysis in actual engineering;

[0153] (3) The present invention verifies the accuracy of the characteristic analysis method of multiple DC-fed receiving-end systems through the analysis results of multiple receiving-end systems and their derived operating modes, showing that the method has strong practicality in engineering analysis.

[0154] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code. The scheme in the embodiment of the present application can be implemented in various computer languages, for example, object-oriented programming language Java and literal translation scripting language JavaScript, etc.

[0155] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the steps in the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0156] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0157] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0158] Although the preferred embodiments of the present application have been described, those skilled in the art may make additional changes and modifications to these embodiments once they have learned the basic creative concept. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present application.

[0159] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A method for analyzing the operating characteristics of a receiving system cascading instability, the method comprising: Establishing a simulation model of an AC / DC hybrid receiving-end system, and performing a simulation run of the AC / DC hybrid receiving-end system based on the simulation model to obtain simulation results; The simulation operation includes: Determine the system operation mode of the AC / DC hybrid receiving system; Based on the system operation mode, a risk scan is conducted on the AC / DC hybrid receiving-end system by region to determine the greatest fault risk affecting the operation of the power grid in each region; Determine the fault that has the greatest impact on the operation of the power grid in each region based on the fault risk; Adjusting the grid operation mode of any regional grid in each region to a critical instability operation mode according to the largest operating fault in the grid; Based on the simulation results, determine whether there is a cascading instability in the AC / DC hybrid receiving-end system; The step of adjusting the grid operation mode of any regional grid in each area to a critical instability operation mode according to the largest operating fault in the grid specifically includes: Selecting any regional power grid in each area of the AC / DC hybrid receiving-end system as a starting point for adjusting the operating mode, changing the load and system spinning reserve of the any regional power grid, wherein the load and system spinning reserve are equal, and switching capacitors and reactors within a preset range of busbars for the any regional power grid to determine a critical instability operating mode of the any regional power grid; Adjust the sub-regional grid in any regional grid to a critical stable operating condition based on the largest operating fault in the grid; The operation characteristics of determining whether the AC / DC hybrid receiving-end system has cascading instability include: Monitor the bus voltage, unit power angle, and power exchange of the interconnecting lines between different areas in each area of the AC / DC hybrid receiving system; Determine whether there is a cascading instability operating characteristic in the AC / DC hybrid receiving-end system based on the bus voltage, the unit power angle, and the power exchange status of the tie lines between the regions; The operational characteristics for determining whether there is cascading instability in the AC / DC hybrid receiving-end system are as follows: Determine whether a low voltage problem exists in one area or multiple areas of the AC / DC hybrid receiving system based on the bus voltage; Determine based on the bus voltage whether voltage collapse occurs in certain areas of the AC / DC hybrid receiving system or in the entire network; Determine whether the power angles of all units in the AC / DC hybrid receiving system are in sync, partially out of sync, or the entire network is out of sync; According to the power exchange situation of the inter-area tie lines in each area of the AC / DC hybrid receiving end system, it is determined that the inter-area tie lines are not disconnected, partially disconnected, or completely disconnected; If a low voltage problem exists in a certain area, the power angles of all generators in the entire network are not out of step, and the tie lines between the areas are not disconnected, then it is determined that the low voltage operation problem exists only in the certain area of the AC / DC hybrid receiving end system; If low voltage problems exist in certain areas, the power angles of the generators in the entire network are partially out of step, and the tie lines between the areas are partially disconnected, it is determined that only regional low voltage operation characteristics exist in the AC / DC hybrid receiving-end system, and the sequence and causal relationship of the chain accidents can be determined based on the inter-area bus voltage drop time sequence; If voltage collapse occurs in certain areas, the generator power angles in the entire grid are partially out of sync, and the interconnecting lines between areas are partially disconnected, it is determined that only regional voltage collapse exists in the AC / DC hybrid receiving system. The sequence of chain accidents and the causal relationship can be determined based on the inter-area bus voltage drop time sequence. If a voltage collapse problem occurs in the entire network, the power angles of all units in the network are out of step and the interconnection lines between regions are disconnected, it is determined that only a regional voltage collapse problem exists in the AC / DC hybrid receiving system, and the sequence and causal relationship of the chain accident are determined based on the timing of the inter-regional bus voltage drops.

2. The method according to claim 1, wherein determining the system operation mode of the AC / DC hybrid receiving-end system comprises: Determine the maximum operating range of DC power, startup mode and load conditions in each area of the AC / DC hybrid receiving system, determine the interconnection line transmission power between each area based on the maximum operating range of DC power, startup mode and load conditions, and determine the system operation mode of the AC / DC hybrid receiving system based on the interconnection line transmission power.

3. The method according to claim 1, wherein the failure risk is at least one of the following: a three-way N-1 failure and a three-way N-2 failure.

4. A system for analyzing the operational characteristics of a receiving system in a cascading instability event, the system comprising: A simulation operation unit is configured to establish a simulation model of the AC / DC hybrid receiving-end system and perform a simulation operation of the AC / DC hybrid receiving-end system based on the simulation model to obtain a simulation result; The simulation operation includes: Determine the system operation mode of the AC / DC hybrid receiving system; Based on the system operation mode, a risk scan is conducted on the AC / DC hybrid receiving-end system by region to determine the greatest fault risk affecting the operation of the power grid in each region; Determine the fault that has the greatest impact on the operation of the power grid in each region based on the fault risk; Adjusting the grid operation mode of any regional grid in each region to a critical instability operation mode according to the largest operating fault in the grid; The analysis unit determines whether there is an operating characteristic of cascading instability in the AC / DC hybrid receiving-end system based on the simulation results; The step of adjusting the grid operation mode of any regional grid in each area to a critical instability operation mode according to the largest operating fault in the grid specifically includes: Selecting any regional power grid in each area of the AC / DC hybrid receiving-end system as a starting point for adjusting the operating mode, changing the load and system spinning reserve of the any regional power grid, wherein the load and system spinning reserve are equal, and switching capacitors and reactors within a preset range of busbars for the any regional power grid to determine a critical instability operating mode of the any regional power grid; Adjust the sub-regional grid in any regional grid to a critical stable operating condition based on the largest operating fault in the grid; The operation characteristics of determining whether the AC / DC hybrid receiving-end system has cascading instability include: Monitor the bus voltage, unit power angle, and power exchange of the interconnecting lines between different areas in each area of the AC / DC hybrid receiving system; Determine whether there is a cascading instability operating characteristic in the AC / DC hybrid receiving-end system based on the bus voltage, the unit power angle, and the power exchange status of the tie lines between the regions; The operational characteristics for determining whether there is cascading instability in the AC / DC hybrid receiving-end system are as follows: Determine whether a low voltage problem exists in one area or multiple areas of the AC / DC hybrid receiving system based on the bus voltage; Determine based on the bus voltage whether voltage collapse occurs in certain areas of the AC / DC hybrid receiving system or in the entire network; Determine whether the power angles of all units in the AC / DC hybrid receiving system are in sync, partially out of sync, or the entire network is out of sync; According to the power exchange situation of the inter-area tie lines in each area of the AC / DC hybrid receiving end system, it is determined that the inter-area tie lines are not disconnected, partially disconnected, or completely disconnected; If a low voltage problem exists in a certain area, the power angles of all generators in the entire network are not out of step, and the tie lines between the areas are not disconnected, then it is determined that the low voltage operation problem exists only in the certain area of the AC / DC hybrid receiving end system; If low voltage problems exist in certain areas, the power angles of the generators in the entire network are partially out of step, and the tie lines between the areas are partially disconnected, it is determined that only regional low voltage operation characteristics exist in the AC / DC hybrid receiving-end system, and the sequence and causal relationship of the chain accidents can be determined based on the inter-area bus voltage drop time sequence; If voltage collapse occurs in certain areas, the generator power angles in the entire grid are partially out of sync, and the interconnecting lines between areas are partially disconnected, it is determined that only regional voltage collapse exists in the AC / DC hybrid receiving system. The sequence of chain accidents and the causal relationship can be determined based on the inter-area bus voltage drop time sequence. If a voltage collapse problem occurs in the entire network, the power angles of all units in the network are out of step and the interconnection lines between regions are disconnected, it is determined that only a regional voltage collapse problem exists in the AC / DC hybrid receiving system, and the sequence and causal relationship of the chain accident are determined based on the timing of the inter-regional bus voltage drops.

5. The system according to claim 4, wherein determining the system operation mode of the AC / DC hybrid receiving-end system comprises: Determine the maximum operating range of DC power, startup mode and load conditions in each area of the AC / DC hybrid receiving system, determine the interconnection line transmission power between each area based on the maximum operating range of DC power, startup mode and load conditions, and determine the system operation mode of the AC / DC hybrid receiving system based on the interconnection line transmission power. 6 . The system according to claim 4 , wherein the failure risk is at least one of the following: a triple-N-1 failure and a triple-N-2 failure.

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