A large motor starting voltage drop calculation method and system based on voltage stability margin

Abstract

The application discloses a large motor starting voltage drop calculation method and system based on voltage stability margin, comprising: abstracting the power grid topology into a static graph, and reconstructing the static graph according to the operation state of the power grid equipment to obtain the topology graph of the power grid under the current operation condition; searching the power supply path set constituted by the edge sequence from each power supply node to the node of the motor to be started on the topology graph; calculating the single power supply equivalent impedance and the multi-power supply parallel equivalent impedance to the motor node according to the power supply path set; calculating the bus voltage drop and the motor terminal voltage according to the equivalent path impedance of each power supply and the equivalent impedance of the multi-power supply parallel, obtaining the motor starting voltage drop percentage of the optimal path under the current power grid operation condition; and determining the large motor starting according to the voltage drop percentage. The application can adapt to the topology structure of a complex power grid, combine the actual power grid data, quickly calculate the voltage drop of the bus under multiple operation modes, and is high in accuracy.

Description

Technical Field

[0001] This invention relates to the field of power system automation, and in particular to a method and system for calculating the starting voltage drop of a large motor based on voltage stability margin. Background Technology

[0002] Large electric motors, as key power equipment in the industrial field, are widely used in petrochemical, steel metallurgy, transportation and other scenarios. The starting process of an electric motor refers to the process from when the motor starts to rotate until it reaches its rated speed. During this process, the starting current of the motor can typically reach 5-8 times the rated current. Such a huge inrush current will cause a significant voltage drop across the power grid impedance, which may lead to problems such as motor starting failure and protection malfunction in severe cases.

[0003] Currently, various research methods have been developed in the industry for calculating grid voltage and analyzing characteristics during the starting process of large electric motors. However, these methods have significant shortcomings in terms of grid topology adaptation, operation simulation, and engineering application efficiency. They cannot balance calculation accuracy and engineering practicality, and are difficult to adapt to the motor starting analysis needs of complex industrial power grids. The key technical defects of various mainstream methods are as follows:

[0004] Simplified formula method: Based on the approximate formula for short-circuit capacity, the entire power grid is simplified to a single short-circuit capacity parameter, completely ignoring the influence of the internal topology of the power grid on voltage distribution. It is suitable for simple radial distribution networks, but the error increases significantly for ring networks, multi-level power supply, or complex networks with reactive power compensation.

[0005] Equivalent circuit method: The instantaneous start-up of the motor is equivalent to the transient impedance connected to the motor terminal. The voltage distribution is solved by establishing a simple series circuit that includes the equivalent impedance of the power grid. However, it ignores the mutual coupling effects of other dynamic loads in the power grid, parallel equipment and the starting motor. It cannot truly reflect the dynamic characteristics of voltage fluctuation and current change during the entire motor start-up process. The calculation results are one-sided and have limited accuracy, making it difficult to support refined start-up characteristic analysis.

[0006] Time-domain simulation method: Detailed models are established using electromagnetic transient simulation software, and the entire startup process is simulated by solving differential equations. It has high accuracy, but the modeling is complex and time-consuming, with a single simulation taking several minutes to tens of minutes, resulting in poor engineering applicability. Summary of the Invention

[0007] Purpose of the invention: One of the purposes of this invention is to provide a method for calculating the starting voltage drop of large motors based on voltage stability margin, which can adapt to the complex topology of power grids, and, combined with actual power grid data, quickly calculate the bus voltage drop under various operating modes with high accuracy.

[0008] Another objective of this invention is to provide a system for calculating the starting voltage drop of a large electric motor based on voltage stability margin.

[0009] Technical Solution: To achieve the above objectives, the present invention provides a method for calculating the starting voltage drop of a large electric motor based on voltage stability margin, comprising the following steps:

[0010] S1. Abstract the power grid topology into a static graph, where nodes represent power grid equipment and edges represent electrical connection branches between nodes;

[0011] S2. Reconstruct the static diagram based on the operating status of the power grid equipment to obtain the topology diagram of the power grid under the current operating conditions;

[0012] S3. Search the topology graph for the set of power supply paths consisting of the edge sequences from each power node to the motor node to be started.

[0013] S4. Calculate the single-source equivalent impedance to the motor node based on the power supply path set. Equivalent impedance of multiple power sources in parallel ;

[0014] S5. Based on the equivalent path impedance of each power source Equivalent impedance in parallel with multiple power sources Calculate the bus voltage drop and motor terminal voltage To obtain the percentage of motor starting voltage drop for the optimal path under the current power grid operating conditions;

[0015] S6. Determine the starting status of large motors based on the voltage drop percentage.

[0016] Preferably, the nodes in S1 include: bus nodes, power supply nodes, motor nodes, load nodes, switchgear nodes, transformer nodes, and reactive power compensation nodes;

[0017] The reconstruction described in S2 includes: deleting the connection edge of the open switch in the static diagram, merging the nodes at both ends of the closed switch, and merging parallel branches.

[0018] Preferably, the step S3, which involves searching the topology graph for a set of power supply paths consisting of edge sequences from each power node to the node of the motor to be started, includes:

[0019] Set the initial cumulative electrical weighted path distance between all power nodes and motor nodes;

[0020] Establish a priority queue Add all power nodes to the priority queue Let the sorted index be... ;

[0021] Let the path expansion step index be... From the priority queue The highest priority power node is selected from the list. All adjacent edges of the current power node are traversed to obtain downstream nodes, and the cumulative electrically weighted path distance from the current power node to each downstream node is calculated. Then proceed to expand the downstream nodes of the next power node until the priority queue is reached. If empty, obtain the first step of the extended path for all power nodes and the cumulative electrically weighted path distance for downstream nodes;

[0022] Calculate the voltage sag caused by the motor node starting at each downstream node, retain the extended paths and downstream nodes whose calculated voltage sag does not exceed the maximum allowable transient voltage sag at the downstream node, and add the retained downstream nodes to a priority queue. Priority is determined based on the cumulative electrical weighted path distance value;

[0023] Will The nodes stored in priority queue Q are then expanded to the next step of path extension until the motor node is reached, resulting in a set of power supply paths originating from each power node:

[0024] , ,

[0025] in, Indicates power node Extending from the starting point to the motor node v m The edge sequence of the s-th path, Indicates power node Extending from the starting point to the motor node v m A subset of all path edge sequences; s is based on power nodes. Extended path index, Represents an integer greater than or equal to 1. This is the index of the power node.

[0026] Preferably, power node To node The cumulative electrical weighted path distance is calculated as follows:

[0027] ,

[0028] in, For power nodes For the edge The impedance magnitude of the represented branch; For the weighting coefficients, satisfying ;

[0029] For motor v m Starting current on the side Voltage drop sensitivity caused by the above:

[0030] ,

[0031] In the formula, This is the starting current of the motor. The reference current;

[0032] For power nodes Voltage stability margin:

[0033] ,

[0034] In the formula, For power nodes Operating voltage, For power nodes The minimum permissible steady-state voltage;

[0035] For power nodes Voltage stability margin penalty function:

[0036] ,

[0037] In the formula, This is the voltage stability margin warning threshold. This is the penalty coefficient.

[0038] Preferably, the motor is at the node The voltage calculation method during startup is as follows:

[0039] ,

[0040] in, For power node Up to the current expansion node The set of paths This is the variable ratio reduction coefficient.

[0041] Preferably, the single-supply equivalent impedance to the motor node described in S4 Represented as:

[0042] ,

[0043] in, For path impedance:

[0044] ,

[0045] branch road The impedance ratio reduction factor for line branches For transformer branches , To calculate the reference voltage, This is the rated voltage of the branch circuit;

[0046] The multi-power supply parallel equivalent impedance to the motor node Represented as:

[0047] .

[0048] Preferably, the motor terminal voltage in S5 is expressed as:

[0049] ,

[0050] The starting voltage drop is expressed as:

[0051] ,

[0052] The percentage of pressure drop is expressed as:

[0053] ,

[0054] in, Before starting the bus voltage, This is the rated voltage of the motor.

[0055] Preferably, S6 is based on the percentage of pressure drop. The starting determination for large electric motors includes: if the calculated voltage drop percentage... If the maximum allowable voltage drop limit for motor starting is met by the power grid, the large motor to be started will be started; otherwise, it will be started from the set of power supply paths. Select the optimal path combination Based on optimal path combination The corresponding power supply starts the large motor waiting to be started;

[0056] Among them, from the power supply path set Select the optimal path combination This includes: minimizing the equivalent parallel impedance The goal is to simultaneously satisfy the voltage sag constraints at each node. , For nodes Maximum permissible transient voltage drop For the motor at the node Voltage drop caused during startup.

[0057] Preferably, if the large motor to be started cannot start normally after executing S6, then the feasibility of starting the current motor is determined:

[0058] If the starting safety conditions are met, the output motor terminal voltage will be... Starting voltage drop ΔU, voltage drop percentage ;

[0059] If the startup safety conditions are not met, reactive power compensation devices are installed in the power grid to optimize the grid operation, including: establishing an optimization function.

[0060]

[0061]

[0062] in, For the first The activation status of the reactive power compensation device is 0 or 1, where 0 is deactivated and 1 is activated. F is the objective function for the total cost of activating the reactive power compensation device. U represents the motor terminal voltage with all reactive power compensation devices currently in operation. min This is the minimum permissible terminal voltage threshold for motor startup.

[0063] The optimal number of reactive power compensation devices can be obtained by solving the optimization function through enumeration or integer programming.

[0064] The large motor starting voltage drop calculation system based on voltage stability margin described in this invention includes the following modules:

[0065] Static graph construction module: used to abstract the power grid topology into a static graph, where nodes represent power grid equipment and edges represent electrical connection branches between nodes;

[0066] Topology generation module: used to reconstruct the static diagram based on the operating status of power grid equipment, and obtain the topology diagram of the power grid under the current operating conditions;

[0067] Power supply path set search module: used to search the topology graph for a set of power supply paths consisting of edge sequences from each power node to the node of the motor to be started;

[0068] Motor port equivalent impedance calculation module: used to calculate the single-source equivalent impedance to the motor node based on the set of power supply paths. Equivalent impedance of multiple power sources in parallel ;

[0069] Motor starting voltage drop data calculation module: used to calculate the voltage drop based on the equivalent path impedance of each power supply. Equivalent impedance in parallel with multiple power sources Calculate the bus voltage drop and motor terminal voltage To obtain the percentage of motor starting voltage drop for the optimal path under the current power grid operating conditions;

[0070] Motor start determination module: used to determine the start of large motors based on the voltage drop percentage.

[0071] Beneficial effects: The present invention has the following advantages: The present invention abstracts the power grid equipment and operating status into a topology diagram. Through path search and merging, it calculates the physical consistency of the equivalent impedance at the motor end, which can adapt to the topology of complex power grids. Combined with actual power grid data, it can quickly calculate the voltage drop of the bus under various operating modes with high accuracy. Attached Figure Description

[0072] Figure 1 This is a schematic diagram of the method flow of the present invention. Detailed Implementation

[0073] The technical solution of the present invention will be described in detail below with reference to the embodiments and accompanying drawings.

[0074] Example 1

[0075] This embodiment provides a method for calculating the starting voltage drop of a large electric motor based on voltage stability margin, such as... Figure 1 As shown, it includes the following:

[0076] I. Abstracting the power grid topology into a static graph G s (V s E s V s E represents the set of nodes that characterize power grid equipment. s This is the set of edges that characterize the electrical connection branches between nodes.

[0077] Among them, power grid equipment includes electrical equipment such as power grid busbars, power sources, lines, loads, switches, transformers, motors, and reactive power compensation devices, which are all industrial electrical equipment units used to realize the transmission, transformation, consumption, and regulation of electrical energy.

[0078] In this embodiment, the nodes include: bus node, power supply node, motor node, load node, switchgear node, transformer node, and reactive power compensation node.

[0079] An edge is an undirected edge, representing a physical electrical connection between electrical components in a power grid, such as lines, transformer branches, and various switch connections. The impedance of each edge is represented as follows: .

[0080] This embodiment further employs an adjacency list to store static graph information, and indexes are created for frequently queried fields such as node type, voltage level, and device ID, as shown in Tables 1 and 2.

[0081] Table 1 Node Types

[0082]

[0083] Table 2 Edge Types

[0084]

[0085] II. Reconstruct the static diagram G based on the operating status of the power grid equipment. s (V s E s ), obtain the topology G of the power grid under the current operating conditions. c (V c E c ).

[0086] The operating status of power grid equipment can be determined by the set C of operating mode configurations, which consists of the real-time operating conditions of the power grid, dispatching rules, and equipment commissioning / discharging status.

[0087] The representation of set C is as follows: ,in, For the set of switch states, For power output collection, The set of reactive power of the load. This refers to the set of taps for a transformer.

[0088] The aforementioned reconfiguration refers to the reconfiguration of the static diagram G under the current operating conditions, specifically the activation / deactivation status of the equipment and the on / off state of the switches. s (V s E s Topology updates and equivalent simplifications are performed, specifically including:

[0089] 1. Delete the connection edge of the disconnect switch: For each switch node, if the state is disconnected ( Then from the static graph G s (V s E s ) Delete the switch edge.

[0090] 2. Combine the nodes at both ends of the closed switch: For the state of closed ( If the switch edge is a certain value, then the two ends of the switch edge are merged into an equipotential point to form a new calculation node.

[0091] The merging rule is as follows: if nodes u and v are connected by a closed switch, then create a new node w to replace u and v, and update all edges connected to nodes u and v to the new node w.

[0092] 3. Merging Parallel Branches: For multiple parallel branches connecting the same pair of computing nodes, the parallel formula is used to merge them into a single equivalent branch:

[0093]

[0094] in Let n be the impedance of the i-th parallel branch, and n be the number of parallel branches.

[0095] III. In the topology graph G c Perform a voltage stability-weighted multi-source search to obtain the voltage from each power supply node to the node of the motor to be started. m The power supply path set P, consisting of edge sequences, specifically includes:

[0096] 1. Create an array, including: a cumulative electrical weighted path distance array. Array of nodes and edges for the most extended path and power supply voltage margin array ,in:

[0097] The Used to store data from the power node to the motor node. m The cumulative electrical weighted path distance is initialized to infinity;

[0098] The Used to record the downstream nodes and edges of the power nodes in the extended path.

[0099] The Used to store the voltage stability margin of each power node under the current operating mode, the calculation formula is:

[0100]

[0101] in For a certain power node Operating voltage, For power nodes Minimum allowable steady-state voltage This is the index of the power node, starting as an integer of 1.

[0102] 2. Configure all power supply nodes and motor nodes v m Initialize the cumulative electrical weighted path distance to 0 and calculate the initial voltage margin for each power node.

[0103] Construct a priority queue Q and enqueue all power nodes. All power nodes have the same initial priority, and there are no specific requirements for the initial order of arrangement within the queue.

[0104] 3. While priority queue Q is not empty, perform path expansion operations in a loop:

[0105] 3.1. Let the path expansion step index be... ,when At that time, from the priority queue The highest priority power node is displayed in the output, denoted as... , Indicates power node The sorting index after adding to priority queue Q, with an initial value of 1.

[0106] Traversing power nodes All adjacent edges ,in, for The adjacent downstream node, To be based on power nodes The index of the extended downstream nodes.

[0107] Calculate from power node To node Cumulative electrical weighted path distance:

[0108]

[0109] in, For the edge The impedance magnitude of the representative branch reflects the static electrical distance of the path. For the weighting coefficients, satisfying It is used to balance the effects of impedance distance, voltage drop sensitivity, and voltage margin on path selection.

[0110] For motor v m Starting current on the side The voltage drop sensitivity caused by the above is defined as:

[0111]

[0112] In the formula, This is the starting current of the motor. This is the reference current.

[0113] For power nodes Voltage stability margin:

[0114]

[0115] In the formula, For power nodes Operating voltage, For power nodes The lowest permissible steady-state voltage.

[0116] For power nodes The voltage stability margin penalty function is defined as:

[0117]

[0118] In the formula, This is the voltage stability margin warning threshold. This is a penalty coefficient; when the power node When the voltage stability margin is exhausted, the penalty value becomes infinite, thus achieving automatic path pruning.

[0119] 3.2, will Repeat step 3.1 until priority queue Q is empty, and obtain the first step extended path and cumulative electrical weighted path distance for all power nodes.

[0120] Estimate the motor at the node Voltage drop during startup :

[0121]

[0122] in, For power node Up to the current expansion node The set of paths For variable ratio reduction coefficients;

[0123] like ,in For nodes If the maximum permissible transient voltage drop occurs, then the path extension is accepted and updated. and and nodes Add to priority queue ;

[0124] like If the path does not meet the voltage constraint, it is immediately pruned, terminating further expansion in that direction.

[0125] All nodes that meet the conditions Add to priority queue Q, priority based on The value is determined, and the smaller the value, the higher the priority.

[0126] 3.3, will Increment by 1, and perform the next path extension on the nodes stored in priority queue Q, including: from the priority queue... The highest priority node is popped up. , Represents a node The sorting index after adding to priority queue Q, starting with a value of 1. Based on the index... It can quickly trace the source nodes, edges, expansion steps, and their associated power nodes.

[0127] Traversing nodes All adjacent edges ,in, For nodes The adjacent downstream node, This is the index for the downstream node. Calculate the sub-node index. To node Cumulative electrical weighted path distance .

[0128] Will Repeat this process until the priority queue Q is empty, and obtain the expansion path and cumulative electrically weighted path distance for all power nodes in the current expansion step;

[0129] Will satisfy nodes Add to priority queue Q, Continue adding 1 to proceed with the next step of path expansion until the path reaches the motor node v. m This yields the set P of power supply paths originating from each power node.

[0130] 4. Record the set of power supply paths , , Indicates power node Extending from the starting point to the motor node v m The edge sequence of the s-th path, Indicates power node Extending from the starting point to the motor node v m The subset of all path edge sequences is called the power supply sub-path subset; s is based on power supply nodes. Extended path index, Represents an integer greater than or equal to 1.

[0131] IV. Based on the power supply path set Calculate the single-source equivalent impedance to the motor node. Equivalent impedance of multiple power sources in parallel .

[0132] When k is greater than 1, it indicates that there are multiple power sources, and the equivalent impedances of each power source to the motor node are connected in parallel.

[0133] The equivalent impedance from a single power source to the motor node is expressed as:

[0134]

[0135] in, For path impedance:

[0136]

[0137] branch road The impedance ratio reduction factor for line branches For transformer branches , To calculate the reference voltage, This is the rated voltage of the branch circuit.

[0138] After parallel connection, the motor node v m Equivalent network impedance of the port Represented as:

[0139]

[0140] V. Based on the equivalent path impedance of each power source Equivalent impedance in parallel with multiple power sources Calculate the bus voltage drop ΔU and the motor terminal voltage U. m This yields the percentage of motor starting voltage drop for the optimal path under the current power grid operating conditions.

[0141] Motor terminal voltage:

[0142]

[0143] Start-up voltage drop:

[0144]

[0145] Pressure drop percentage:

[0146] in, Before starting the bus voltage, This is the rated voltage of the motor.

[0147] VI. Based on the percentage of pressure drop Perform start-up determination for large electric motors.

[0148] If the calculated pressure drop percentage If the maximum allowable voltage drop limit for motor starting is met by the power grid, the large motor to be started will be started directly; otherwise, it will be started from the set of power supply paths. Select the optimal path combination Based on optimal path combination The corresponding power supply starts the large motor waiting to be started.

[0149] From the set of power supply paths Select the optimal path combination This includes the following:

[0150] To minimize equivalent parallel impedance The goal is to simultaneously satisfy the voltage sag constraints at each node. From the set of power supply paths Each power supply path subset within Select the optimal path combination Specifically, it includes:

[0151] 1. Traverse all feasible power supply paths under each power source, sort them based on the path weighted distance and voltage stability margin penalty value, eliminate invalid paths that exceed voltage limits, and iteratively select the effective path combination with the minimum impedance.

[0152] 2. Path to Impedance Transition: Optimal Path Combination For a set of side sequences consisting of multiple branches, the equivalent path impedance of a single source is obtained by summing all branches within the combination according to the impedance reduction formula.

[0153] 3. Iterative calculation loop: Determine the optimal path combination Then, the equivalent impedance of a single power supply, the equivalent impedance of a multi-power supply parallel system, and the percentage of voltage drop during motor startup need to be recalculated sequentially to complete one round of voltage verification; if the voltage drop still does not meet the safety threshold, the path search step is returned to iteratively update the path combination.

[0154] 7. If the large motor to be started cannot start normally after performing step six, determine the feasibility of starting the current motor. If the starting safety conditions are met, output the voltage drop calculation result (including the motor terminal voltage). Starting voltage drop ΔU, voltage drop percentage Otherwise, a reactive power compensation device should be installed in the power grid.

[0155] Setting safety conditions for starting large motors: Preset the safe operating voltage threshold U of the power grid. th Motor starting allowable voltage deviation threshold ΔU th When the motor terminal voltage <ΔU th And the starting voltage drop ΔU < U th If so, the startup safety conditions are met.

[0156] When the startup safety conditions are not met, the power grid operation mode configuration is further optimized to minimize the reactive power compensation cost. The optimal motor startup scheme that balances grid voltage stability and equipment operation safety is then selected, specifically including:

[0157] Establish the optimization function:

[0158]

[0159]

[0160] in, For the first The activation status of the reactive power compensation device group (0 or 1, 0 for deactivation, 1 for activation), F is the objective function of the total cost of the reactive power compensation device, which is quantitatively represented by the number of devices activated. U is the motor terminal voltage when all reactive power compensation devices are in operation. min This is the lowest permissible terminal voltage threshold for motor startup.

[0161] The optimal number of reactive power compensation devices can be obtained by solving the optimization function through enumeration or integer programming.

[0162] The operating parameters of the power grid operation scheme after reactivating the optimal number of reactive power compensation devices include the motor terminal voltage. Starting voltage drop ΔU, voltage drop percentage Return to step six to perform a large motor starting determination until an optimal motor starting scheme that meets the grid voltage safety constraints is generated.

[0163] Example 2

[0164] Take, for example, a large petrochemical plant that is building a new production unit and needs to add an 8000kW high-voltage electric motor to drive the compressor.

[0165] I. Setting Operating Parameters

[0166] The petrochemical plant's power supply system adopts a 10kV dual-power-input, single-busbar segmented connection method. Power grid equipment parameters and status information are sourced from the SCADA system and equipment ledger database, and are uniformly converted to per-unit values. Abnormal data undergoes missing value compensation and consistency verification. Assume it operates as follows:

[0167] The 10kV busbar adopts a single busbar segmentation, with segment switch closure;

[0168] The 10kV Section I busbar is equipped with a capacitor bank of 2×2400kvar;

[0169] The 10kV II section busbar is equipped with a capacitor bank of 2×2400kvar;

[0170] Existing load: 4.2MW of 10kV I section and 3.8MW of 10kV II section.

[0171] II. Based on the operating parameters, a static graph is constructed. In this embodiment, the node definitions are shown in Table 3:

[0172] Table 3 Node Definitions

[0173]

[0174] The edge definitions in this embodiment are shown in Table 4:

[0175] Table 4 Edge Definitions

[0176]

[0177] 3. Reconstruct the topology graph from the static graph, including: deleting the relevant edges of G2 and T2; merging the nodes at both ends of the sectionalizing switch (merging 10kV I and II into one electrical node); and deleting the relevant edges of C2.

[0178] IV. Perform multi-source power supply path search on the topology graph.

[0179] The first power supply path P1 was obtained by searching the path using a multi-source algorithm: G1 → 35kV bus → T1 → 10kV bus → M1;

[0180] The second power supply path P2 is obtained using the Yen algorithm: G2→35kV bus→T2→10kV bus→M1.

[0181] 5. Based on the searched multi-source power supply paths, determine whether the motor meets the starting conditions.

[0182] 1. Calculate the equivalent impedance of the motor:

[0183]

[0184] 2. Initial operating voltage calculation: capacitors C1 and C2 are not connected, and power is supplied via dual paths.

[0185] The rated current of the motor is:

[0186]

[0187] The starting current is:

[0188]

[0189] After startup, the motor's terminal voltage is:

[0190]

[0191]

[0192]

[0193] Detection: Startup requirements not met!

[0194] VI. Constraint Optimization

[0195] After the capacitor is switched on, its equivalent impedance is connected in parallel to the 10kV busbar. The equivalent impedance is:

[0196]

[0197] In the formula, This represents the number of capacitor banks. The rated reference voltage of the 10kV busbar.

[0198] Constraints:

[0199] Voltage constraint: ;

[0200] Equipment capacity constraints: ; , These represent the actual number of capacitor banks connected at two different installation locations.

[0201] Objective function F: Minimize reactive power compensation input.

[0202] Enumerate all possible combinations (3×3=9 in total), as shown in Table 5.

[0203] Table 5 Design Scheme

[0204]

[0205] VI. Selection of the Optimal Solution:

[0206] According to Table 5, the schemes that satisfy the constraints include: ② to ⑨, and the schemes that minimize the objective function include: ② or ③ (F=1).

[0207] Therefore, the recommended option ② is: 1 group of capacitor C1 (1200kvar) is connected, capacitor C2 is not connected, total reactive power compensation: 1.2 Mvar, terminal voltage: 0.808 pu ≥ 0.80 pu.

[0208] This embodiment takes the starting analysis of an 8000kW motor in a petrochemical plant as an example to fully demonstrate the scenario where dual-path power supply still fails to meet the starting requirements:

[0209] 1. Dual-path power supply: G1 and G2 operate simultaneously, with 10kV segmented closure.

[0210] 2. Initial requirements not met: Due to the small short-circuit capacity of the system (200MVA / 180MVA) and the high starting multiple of the motor, even with dual-path power supply, the voltage is still only 0.79 pu.

[0211] 3. Constraint Optimization: By adding a small number of capacitors, the voltage was increased to 0.808 pu, meeting the requirements.

[0212] 4. Optimal Solution: Solution ② (C1 invests in 1 group, F=1) is the most economically optimal solution.

[0213] This embodiment demonstrates that even with dual-path power supply, reactive power compensation is still required to meet startup requirements when system conditions are poor, and the effectiveness of the method of this invention in finding the optimal compensation scheme.

Claims

1. A method for calculating the starting voltage drop of a large electric motor based on voltage stability margin, characterized in that, Includes the following steps: S1. Abstract the power grid topology into a static graph, where nodes represent power grid equipment and edges represent electrical connection branches between nodes; S2. Reconstruct the static diagram based on the operating status of the power grid equipment to obtain the topology diagram of the power grid under the current operating conditions; S3. Search the topology graph for the set of power supply paths consisting of the edge sequences from each power node to the motor node to be started. S4. Calculate the single-source equivalent impedance to the motor node based on the power supply path set. Equivalent impedance of multiple power sources in parallel ; S5. Based on the equivalent path impedance of each power source Equivalent impedance in parallel with multiple power sources Calculate the bus voltage drop and motor terminal voltage To obtain the percentage of motor starting voltage drop for the optimal path under the current power grid operating conditions; S6. Determine the starting status of large motors based on the voltage drop percentage.

2. The method for calculating the starting voltage drop of a large electric motor according to claim 1, characterized in that, The nodes mentioned in S1 include: bus nodes, power supply nodes, motor nodes, load nodes, switchgear nodes, transformer nodes, and reactive power compensation nodes; The reconstruction described in S2 includes: deleting the connection edge of the open switch in the static diagram, merging the nodes at both ends of the closed switch, and merging parallel branches.

3. The method for calculating the starting voltage drop of a large electric motor according to claim 1, characterized in that, The search in S3 for the set of power supply paths formed by the edge sequences from each power node to the node of the motor to be started on the topology graph includes: Set the initial cumulative electrical weighted path distance between all power nodes and motor nodes; Establish a priority queue Add all power nodes to the priority queue Let the sort index be... ; Let the path expansion step index be... From the priority queue The highest priority power node is selected from the list. All adjacent edges of the current power node are traversed to obtain downstream nodes, and the cumulative electrically weighted path distance from the current power node to each downstream node is calculated. Then proceed to expand the downstream nodes of the next power node until the priority queue is reached. If empty, obtain the first step of the extended path for all power nodes and the cumulative electrically weighted path distance for downstream nodes; Calculate the voltage sag caused by the motor node starting at each downstream node, retain the extended paths and downstream nodes whose calculated voltage sag does not exceed the maximum allowable transient voltage sag at the downstream node, and add the retained downstream nodes to a priority queue. Priority is determined based on the cumulative electrical weighted path distance value; Will The nodes stored in priority queue Q are then expanded to the next step of path extension until the motor node is reached, resulting in a set of power supply paths originating from each power node: ， ， in, Indicates power node Extending from the starting point to the motor node v m The edge sequence of the s-th path, Indicates power node Extending from the starting point to the motor node v m A subset of all path edge sequences; s is based on power nodes. Extended path index, Represents an integer greater than or equal to 1. This is the index of the power node.

4. The method for calculating the starting voltage drop of a large electric motor according to claim 3, characterized in that, Power Node To node The cumulative electrical weighted path distance is calculated as follows: ， in, For power nodes For the edge The impedance magnitude of the represented branch; Let be the weighting coefficient, satisfying ; For motor v m Starting current on the side Voltage drop sensitivity caused by the above: ， In the formula, This is the starting current of the motor. The reference current; For power nodes Voltage stability margin: ， In the formula, For power nodes Operating voltage, For power nodes The minimum permissible steady-state voltage; For power nodes Voltage stability margin penalty function: ， In the formula, This is the voltage stability margin warning threshold. This is the penalty coefficient.

5. The method for calculating the starting voltage drop of a large electric motor according to claim 4, characterized in that, The electric motor at the node The voltage calculation method during startup is as follows: ， in, For power node Up to the current expansion node The set of paths This is the variable ratio reduction coefficient.

6. The method for calculating the starting voltage drop of a large electric motor according to claim 3, characterized in that, The single-supply equivalent impedance to the motor node as described in S4 Represented as: ， in, For path impedance: ， branch road The impedance ratio reduction factor for line branches For transformer branches , To calculate the reference voltage, This is the rated voltage of the branch circuit; The multi-power supply parallel equivalent impedance to the motor node Represented as: 。 7. The method for calculating the starting voltage drop of a large electric motor according to claim 1, characterized in that, The motor terminal voltage mentioned in S5 is expressed as follows: ， The starting voltage drop is expressed as: ， The percentage of pressure drop is expressed as: ， in, Before starting the bus voltage, This is the rated voltage of the motor.

8. The method for calculating the starting voltage drop of a large electric motor according to claim 1, characterized in that, S6 states that the pressure drop percentage is used as a basis. The starting determination for large electric motors includes: if the calculated voltage drop percentage... If the maximum allowable voltage drop limit for motor starting is met by the power grid, the large motor to be started will be started; otherwise, it will be started from the set of power supply paths. Select the optimal path combination Based on optimal path combination The corresponding power supply starts the large motor waiting to be started; Among them, from the power supply path set Select the optimal path combination This includes: minimizing the equivalent parallel impedance The goal is to simultaneously satisfy the voltage sag constraints at each node. , For nodes Maximum permissible transient voltage drop For the motor at the node Voltage drop caused during startup.

9. The method for calculating the starting voltage drop of a large electric motor according to claim 1, characterized in that, If the large motor to be started fails to start normally after executing S6, then determine the feasibility of starting the current motor: If the starting safety conditions are met, the output motor terminal voltage will be... Starting voltage drop ΔU, voltage drop percentage ; If the startup safety conditions are not met, reactive power compensation devices are installed in the power grid to optimize the grid operation, including: establishing an optimization function. ， ， in, For the first The activation status of the reactive power compensation device is 0 or 1, where 0 is deactivated and 1 is activated. F is the objective function for the total cost of activating the reactive power compensation device. U represents the motor terminal voltage under the current reactive power compensation device operating condition. min This is the minimum permissible terminal voltage threshold for motor startup. The optimal number of reactive power compensation devices can be obtained by solving the optimization function through enumeration or integer programming.

10. A system for calculating the starting voltage drop of a large electric motor based on voltage stability margin, characterized in that, Includes the following modules: Static graph construction module: used to abstract the power grid topology into a static graph, where nodes represent power grid equipment and edges represent electrical connection branches between nodes; Topology generation module: used to reconstruct the static diagram based on the operating status of power grid equipment, and obtain the topology diagram of the power grid under the current operating conditions; Power supply path set search module: used to search the topology graph for a set of power supply paths consisting of edge sequences from each power node to the node of the motor to be started; Motor port equivalent impedance calculation module: used to calculate the single-source equivalent impedance to the motor node based on the set of power supply paths. Equivalent impedance of multiple power sources in parallel ; Motor starting voltage drop data calculation module: used to calculate the voltage drop based on the equivalent path impedance of each power supply. Equivalent impedance in parallel with multiple power sources Calculate the bus voltage drop and motor terminal voltage To obtain the percentage of motor starting voltage drop for the optimal path under the current power grid operating conditions; Motor start determination module: used to determine the start of large motors based on the voltage drop percentage.

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