A power system power flow optimization control method containing multi-direct current common grounding electrode

Abstract

This invention discloses a power flow optimization control method for a power system with multiple DC shared grounding electrodes, belonging to the field of power system stability and control. The method includes the following steps: S1: Establishing the AC / DC hybrid system topology, constructing an AC / DC equivalent model with shared grounding electrodes, and completing component parameter calculations and per-unit value reduction; S2: Establishing a power flow optimization model under normal operating conditions, setting objective functions, AC / DC power flow equality constraints, inequality constraints, and upper and lower limit constraints for variables; S3: Under unipolar operating conditions, establishing a power flow optimization model with minimum load shedding as the objective, adding grounding electrode current constraints to the original normal operating constraints; S4: Solving the AC / DC hybrid system power flow model with multiple DC shared grounding electrodes based on the actual operating conditions of the system, outputting the optimal operating scheme and control settings for the system under normal or unipolar operating conditions, including generator output, DC control variable setpoints, and DC power distribution. This method can achieve coordinated operation and reasonable distribution of grounding electrode current among multiple DC transmission lines in an AC / DC hybrid system, improving the safety and stability of the AC / DC hybrid system under different operating conditions.

Description

Technical Field

[0001] This invention relates to the field of power system stability and control, and specifically to a power flow optimization control method for a power system with multiple DC shared grounding electrodes. Background Technology

[0002] With the transformation of the global energy structure and the centralized integration of large-scale renewable energy, traditional AC power grids are gradually evolving into AC / DC hybrid systems. In large receiving-end power systems, to meet the demand for long-distance, high-capacity inter-regional power transmission, multiple DC transmission lines often converge at the same high-load center, thus forming a multi-infeed AC / DC hybrid receiving-end power grid. While this complex system topology significantly improves the interconnection and allocation capabilities of inter-regional energy, it also leads to increasingly severe electromagnetic and electromechanical interactions between different DC transmission channels. In actual engineering construction and planning, to save transmission corridor resources, reduce the difficulty of substation site selection, and significantly reduce infrastructure construction and operation and maintenance costs, adjacent DC transmission projects generally adopt a shared grounding electrode design. This physical architecture of multiple DC lines sharing a grounding electrode makes the superposition and distribution law of grounding currents at each converter station and the thermoelectric tolerance characteristics of the shared grounding device directly become the key physical boundaries restricting the operational safety of the entire receiving-end power system.

[0003] To achieve steady-state power flow distribution and economical operation in AC / DC hybrid systems, several optimization and control strategies have been proposed in existing technologies. For example, Chinese patent document CN108134401A discloses a multi-objective power flow optimization and control method for AC / DC hybrid systems. This prior art mainly collects the operating status data of the AC / DC power grid from the dispatch control center and establishes a multi-objective optimal power flow mathematical model with the objectives of minimizing network losses, minimizing system voltage deviation, and maximizing static voltage stability margin. In the solution process, this scheme uses the equivalent injected power method to handle the power correction of system nodes by the DC power flow controller, and finally adjusts the operating parameters of the converter station and the DC power flow controller by coordinating the issuance of commands. Under normal steady-state operating conditions, this scheme provides a computational framework for optimizing network losses and improving voltage distribution in AC / DC systems including DC power flow controllers. However, the method model of this prior art has significant limitations: its mathematical model and constraints are entirely based on the system being in an ideal normal bipolar operating state, and the research object does not cover the complex large power grid scenario of mixed parallel operation of grid commutated converters and modular multilevel converters. Even more critically, this existing technology does not address the crucial engineering reality of shared grounding electrodes in multi-terminal DC transmission projects, and therefore is completely unable to meet the power flow control requirements when the system's operating state undergoes sudden changes.

[0004] In actual receiving-end power grids with multiple DC transmission lines sharing a common grounding electrode, DC transmission lines typically operate in a bipolar symmetrical mode under normal conditions. The positive and negative conductors transmit power symmetrically, theoretically making the unbalanced current flowing into the common grounding electrode close to zero, which helps extend the service life of the grounding device. However, when the power grid encounters extreme weather, equipment insulation breakdown leading to a single-pole short circuit, grounding fault, or a single-sided converter equipment failure, if the conventional steady-state optimization strategy of the aforementioned existing technologies is still followed, the current at the faulty pole will rapidly increase, easily triggering widespread equipment cascading damage. To suppress fault propagation, in engineering practice, it is usually necessary to block the protection action of the faulty pole, forcing the DC transmission system to passively switch to a single-pole return line operation mode. Under this single-pole operation condition, all DC current from the non-faulty poles cannot return through their own poles but is forced to transfer entirely to the common grounding electrode and form a return loop through the ground. This drastic topology switch causes the total ground current of the common grounding electrode to rise exponentially, easily exceeding the maximum allowable continuous operating current limit designed for the grounding electrode. If the grounding electrode fails due to thermal overload or the surrounding step voltage exceeds the limit significantly, it will cause devastating damage to the safe power supply of the receiving-end power grid. The aforementioned existing technologies lack a mode discrimination mechanism for unipolar operating conditions when constructing the optimization model, and their constraint set does not include a safety limit formula for the shared grounding electrode current. Therefore, when facing such faults, their algorithms not only fail to provide effective control measures to minimize power outage losses, but may also cause model divergence or issue control commands that violate physical safety boundaries, forcing dispatchers to rely on manual experience to take blind and large-scale load shedding measures. This not only severely impacts the economic efficiency of the receiving-end power grid but also greatly increases the safety risks of the power system. Therefore, a power flow optimization control method is needed that can ensure both economic efficiency and efficient absorption of renewable energy during normal operation in complex AC / DC hybrid structures, while adaptively identifying unipolar operating conditions and strictly adhering to the grounding current safety limit, thereby minimizing the total load loss in emergency situations. Summary of the Invention

[0005] Firstly, in view of the shortcomings of the existing technology, this invention proposes a power flow optimization control method for power systems with multiple DC shared grounding electrodes. This method is used to achieve a power flow optimization control method that can ensure both economic efficiency and efficient absorption of renewable energy during normal operation under complex AC / DC hybrid structures, while also adaptively identifying single-pole operating conditions and strictly adhering to the grounding current safety limit, thereby minimizing the total load loss of the system in emergency situations.

[0006] The objective of this invention can be achieved through the following technical solutions: A power flow optimization control method for a power system with multiple DC shared grounding electrodes includes the following steps: The system component parameters and actual operating condition data of the AC / DC hybrid system are obtained, and the obtained system component parameters are uniformly converted into per-unit data. The AC / DC hybrid system includes an AC system, an LCC DC transmission line, an MMC DC transmission line, and a common grounding electrode connecting the two types of DC transmission lines. Based on the actual operating condition data, determine whether the AC / DC hybrid system is in a unipolar operating state; In response to the absence of a unipolar operating state in the AC / DC hybrid system, the per-unit data and the optimization variables are input into the power flow optimization model under normal operation for solution. In response to the existence of a unipolar operating state in the AC / DC hybrid system, the per-unit data, the optimization variables, and the newly added characterization nodes are... Variables of actual active load The input is fed into a power flow optimization model with the objective of minimizing load loss for solution. Obtain the optimization variables or the representation nodes after the solution has converged. The actual active load variable values ​​are used to generate and output the power system control setting data with multiple DC common grounding electrodes under the corresponding operating conditions. The control setting data includes generator output values, DC control variable setting values, and DC power distribution values.

[0007] Secondly, in view of the shortcomings of the prior art, this invention proposes a computer-readable storage medium to realize a power flow optimization control method that can ensure both economic efficiency and efficient absorption of renewable energy during normal operation under complex AC / DC hybrid structures, while also adaptively identifying unipolar operating conditions and strictly adhering to the grounding current safety limit, thereby minimizing the total system load loss in emergency situations.

[0008] The objective of this invention can be achieved through the following technical solutions: A computer-readable storage medium storing instructions that, when executed, enable a power flow optimization control method for a power system containing multiple DC shared grounding electrodes, as described in the first aspect.

[0009] Beneficial effects: This invention constructs an adaptive power flow optimization control architecture that takes into account both steady-state optimization during normal operation and extreme-state regulation during unipolar faults. When the system encounters sudden states such as unipolar blockage, it can automatically and smoothly switch from a conventional optimization mode oriented towards power generation cost or renewable energy consumption to an emergency optimization mode oriented towards survival and supply assurance. This underlying switching mechanism of the state machine changes the passive situation of traditional dispatching that relies too much on human experience and blindly cuts off loads when facing unipolar operating conditions, and significantly improves the dynamic response capability and self-healing resilience of multi-feed receiving-end power grids under complex and sudden operating conditions. This invention uses the physical safety boundary of the shared grounding electrode in multiple DC systems as a mathematical constraint. When dealing with single-pole operation, this method not only introduces variables characterizing the actual active load of the system as new optimization variables into the solver, establishing a new mathematical model with the goal of minimizing the total load loss of the entire network, but also forcibly superimposes an upper limit constraint on the grounding electrode current to limit the unbalanced current return of non-faulty poles. This optimization mechanism, which deeply couples the underlying thermoelectric tolerance limit of equipment with the system operating state, enables the system to maximize the potential for cross-regional mutual support between non-faulty DC channels and AC networks when redistributing power flow and issuing control commands, under the physical premise of ensuring that the shared grounding electrode does not experience thermal overload and that the step voltage is within the safe threshold. This precisely guides the dispatching system to perform precise load shedding operations within the smallest possible range, thereby ensuring the absolute safety of core physical equipment while minimizing the social and economic losses caused by power outages. This invention constructs AC / DC equivalence and constraints, accurately mapping both the AC / DC power coupling relationship of LCC converter stations and the strict power closed-loop equations considering internal active and reactive power losses in MMC converter stations into equal and inequality boundary conditions in the optimization solver. This improves the convergence determinism and optimization efficiency of the underlying solution algorithm when facing large matrices and high-dimensional nonlinear equations. This not only makes the method perfectly compatible with complex large power grid configurations covering pure LCC, pure MMC, and even deep AC / DC coupling, but also ensures that the final output generator output, DC control variable setpoints, and DC power allocation values ​​have extremely high engineering feasibility and control accuracy. Attached Figure Description

[0010] Figure 1 This is a flowchart illustrating the specific method in a particular embodiment of the present invention; Figure 2 This is a system topology diagram in a specific embodiment of the present invention; Figure 3 This is a comparison of the power generation costs of Scheme 1 and Scheme 2 in a specific embodiment 1 of the present invention; Figure 4 This is a comparison of the new energy consumption results between Scheme 1 and Scheme 3 in a specific embodiment 1 of the present invention; Figure 5 This is a comparison of node load loss results between Scheme 1 and Scheme 2 in specific embodiment 2 of the present invention. Detailed Implementation

[0011] Example 1: Power flow optimization control under normal operating conditions of a power system with multiple DC shared grounding electrodes This embodiment applies to power flow optimization and control settings of the receiving-end power grid under normal operating (bipolar symmetrical) conditions. The goal is to achieve any one of the following objectives while satisfying equipment and safety constraints: minimum system network loss, minimum generation cost, or maximum renewable energy absorption. The core approach involves setting AC system operating constraints, LCC DC operating constraints, MMC DC operating constraints, and DC network power and voltage balance equations on a unified AC / DC hybrid system model. Upper and lower limits are imposed on the optimization variables, allowing the solution results to be directly converted into control setpoints. The specific process is as follows: Figure 1 As shown.

[0012] S1. Establish the topology of the AC / DC hybrid system, construct the AC / DC equivalent model with a common grounding electrode, and complete the calculation and reduction of component parameters; In this embodiment, the AC / DC hybrid system topology is first established as follows: Figure 2 As shown, based on the IEEE 39-bus standard AC test system, two types of DC transmission channels are introduced to form an AC / DC hybrid system structure that includes LCC and MMC converters.

[0013] S1.1: Establish the topology of the AC / DC hybrid system and unify the per-unit value benchmarks for both AC and DC systems. in: These are the AC reference power, reference voltage, reference current, and reference impedance, respectively. These are the DC reference power, reference voltage, reference current, and reference resistance, respectively.

[0014] In this embodiment, the per-unit reference power is unified on both the AC and DC sides. Reference voltage Correspondingly, the reference current and reference impedance are calculated as follows: S1.2: Establish a power flow model for an AC / DC hybrid system based on the type of converter and its connection method. 1) LCC DC transmission lines: The control variables of LCC converter stations include DC voltage. U dc DC current I dc Control angle θ Converter turns ratio k T In power flow calculation, the DC side of the LCC node is equivalent to the AC PQ node.

[0015] In this embodiment, lines 4-5 are LCC DC lines, and the LCC converter stations at nodes 4 and 5 respectively adopt stable current generation.I dc 、k T Control and positioning U dc 、k T In the control system, nodes 4 and 5 are equivalent to PQ nodes.

[0016] 2) MMC DC transmission lines: The control variables of the MMC converter station include DC voltage. U dc Active power on the AC side of the converter P s Reactive power on the AC side of the converter Q s AC side voltage U s Depending on the type of AC node it is connected to, the DC side of the MMC node is equivalent to an AC PQ node or PV node in power flow calculation.

[0017] In this embodiment, lines 13-14, 22-21, 22-23, and 25-26 are MMC DC lines, and each node adopts a fixed-point configuration. P s , Q s In the control system, each node is equivalent to a PQ node.

[0018] 3) LCC-MMC Hybrid DC: A passive node BB is introduced between the LCC and MMC circuits. The BB node is a virtual node, and its DC power satisfies the formula: The BB node voltage is equal to the specified DC node voltage, and the BB node does not exchange power with the AC system and cannot be used as a balancing station. It is necessary to select any converter station in the MMC system as a balancing station to handle the unbalanced power.

[0019] S1.3: Calculate the total grounding current of the shared grounding electrode in, n The number of converters connected to this grounding electrode. I i For the first i The grounding current component of each converter is determined by the operating state of the bipolar system in which the converter is located. Let the converter... i The positive line current of the DC system is The negative line current is (Both take the amplitude of the actual flow direction), then the first iThe current component injected into the common ground electrode by each converter is the imbalance between the positive and negative currents, that is: Under the single-polarity return line operation condition (assuming the negative electrode is out of service), then At this time, the grounding current component Under normal bipolar symmetric operating conditions, ,but In this embodiment, LCC line 4-5 and MMC line 13-14 share a common grounding electrode. Under normal bipolar symmetrical operation conditions, the currents of each electrode cancel each other out, and the theoretical value of the grounding electrode current is close to zero.

[0020] S1.4 forms a set of parameters for solving the problem, including: AC side state variables, generator active / reactive power and upper and lower limits, line transmission power flow and upper and lower limits; DC side voltage, current, power and DC node control variables and upper and lower limits, etc.

[0021] S2. Establish a power flow optimization model and objective function under normal operating conditions, and set AC / DC power flow equality constraints and variable upper and lower limit constraints.

[0022] Based on the AC / DC hybrid system topology and parameter set established in step S1, a power flow optimization mathematical model is constructed for normal system operation. The core objective of this model is to optimize the system's operational economy or renewable energy absorption capacity while satisfying AC / DC power balance and equipment operation constraints. The model consists of three parts: optimization variables, objective function, and constraints, as described below: In this embodiment, the optimization variables include: 1) Optimization variable for AC system: node voltage amplitude U Node voltage phase angles except for slack nodes θ Generator node active power P G Reactive power of generator nodes Q G ; 2) Optimization variables for LCC DC transmission lines: DC voltage U dc DC current I dc Control angle cosine cosδ Power factor cosφ Converter turns ratio k T ; 3) Optimization variables for MMC DC transmission lines: Active power on the AC side of the converter. P s No power on the AC side of the converter Q s.

[0023] In this embodiment, the objective function for optimizing the model can be selected from the following: 1) Minimizes system network loss in, For generator power, For load power, For the number of generators, This represents the load quantity.

[0024] 2) Generator has the lowest cost. in, C 0 , C 1 , C 2 This represents the generator cost coefficient. In this embodiment, the generator cost parameter... C 0 = 0.2 C 1 = 0.3 C 2 = 0.01.

[0025] 3) Maximum absorption of new energy In this embodiment, taking wind power grid connection as an example, nodes 33 and 39 are set as wind turbine nodes. To maximize the absorption of new energy, the objective function is: in, Predicting the output of wind turbine units. For actual wind turbine output, This refers to the number of wind turbine units.

[0026] The constraints include operational constraints for the AC system, LCC system, and MMC system, as well as upper and lower bound constraints for all variables.

[0027] 1) Operating constraints of the AC system Each node in an AC power system needs to satisfy active and reactive power balance, that is: in, N This represents the total number of nodes in the system. U i θ i For nodes i Voltage amplitude and phase angle; G ij , B ij For nodes i, j The electrical conductivity and susceptance between them; For nodes i, j The phase angle difference between them.

[0028] Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, These are the upper and lower limits of the node voltage amplitude, respectively; These are the upper and lower limits of the node voltage phase angle, respectively; These are the upper and lower limits of the generator's output active power, respectively. These represent the upper and lower limits of the generator's output reactive power.

[0029] For wind turbine units, the actual wind turbine node output have: in, These represent the upper and lower limits of the actual output of the wind turbine generators. In this embodiment, the upper and lower limits of the actual output of the wind turbine generators connected to nodes 33 and 39 are 1200MW and 0MW, respectively.

[0030] For line power transmission P ij have: in, The lines are respectively ij Upper and lower limits of power transmission.

[0031] 2) Operational constraints of LCC DC transmission lines The nodes connected to the LCC converter need to satisfy active and reactive power balance, that is: Among them, the active power flowing from the AC system into the DC transmission line reactive power They respectively satisfy: in, , They are nodes i DC side voltage and current, For nodes i The power factor angle on the AC side of the converter.

[0032] The voltage balance equation must be satisfied on both sides of the node connected to the LCC converter, that is: in, For nodes i Converter turns ratio; For nodes i AC side voltage; For nodes i Converter control angle; For nodes i Converter reactance; It is a constant, taken as 0.995.

[0033] For DC power flow, the DC network equations are satisfied, namely: in, This refers to power loss during DC transmission. Each satisfies .

[0034] Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, They are nodes i DC-side voltage amplitude upper and lower limits; They are nodes i DC side current amplitude upper and lower limits; They are nodes i Upper and lower limits of the cosine of the converter control angle; They are nodes i upper and lower limits of power factor They are nodes i Converter turns ratio upper and lower limits.

[0035] For DC line transmission power have: in, DC lines ij Upper and lower limits of power transmission.

[0036] In this embodiment, the LCC converter stations at nodes 4 and 5 respectively adopt a fixed-line configuration. I dc 、k T Control and positioning U dc 、k T control, I dc Range 0~2.0 pu, U dc Range 2.1~2.3 pu,k T Range 0.8~1.2.

[0037] 3) Operational constraints of MMC DC transmission lines The nodes connected to the MMC converter need to satisfy active and reactive power balance, that is: For the MMC node, considering the converter losses during power transfer from the AC system to the DC transmission line, the power balance equation is: in, They are nodes i The active and reactive power losses of the MMC converter are calculated using the following formulas: in, These are the equivalent resistance and equivalent reactance of the MMC converter station, respectively.

[0038] For DC power flow, the DC network equations are satisfied, namely: in, p For the number of operating poles and nodes of a DC transmission line. i The DC-side voltage satisfies the voltage balance equation, that is: in, DC node i, j The electrical conductance between them This represents the total number of nodes in the DC network. They respectively satisfy: Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, They are nodes i AC active power measurement upper and lower limits; They are nodes i AC reactive power measurement upper and lower limits.

[0039] For DC line transmission power have: in, DC lines ij Upper and lower limits of power transmission.

[0040] In this embodiment, each node of the MMC DC transmission line adopts a fixed... P s , Q s Control, active power P s Range -600~600MW, reactive power Q s Range -800~800MVar.

[0041] like Figure 1 As shown, after step S2, it is necessary to determine whether the system is operating with a single pole. In this embodiment, the power system with multiple DC shared grounding electrodes is under normal operating conditions and does not operate with a single pole; therefore, step S3 is skipped, and the process proceeds directly to step S4. S4. Output the power system operation scheme and control settings with multiple DC shared grounding electrodes, including generator output, DC control variable setpoints, DC power distribution, etc.

[0042] In this embodiment, the fmincon function of Matlab is used to solve the optimization model, and the optimization results are verified using Matpower and MatACDC power flow solving tools. To verify the effectiveness of the proposed power flow optimization control method for power systems with multiple DC shared grounding electrodes during normal operation, this example will set up three schemes for numerical analysis and compare their implementation effects.

[0043] Option 1: Do not adopt an optimized control strategy; Option 2: Adopt an optimized control strategy, with the objective function being to minimize power generation costs; Option 3: Adopt an optimized control strategy, with the objective function being to maximize the consumption of new energy sources.

[0044] Simulations were performed using the three schemes described above. The optimized control strategy of Scheme 2, obtained using the control strategy proposed in this invention, controls the generator set and DC variables, as shown in Tables 1 and 2, respectively.

[0045] Table 1 Generator output settings for Scheme 2 Table 2 DC variable settings for Scheme 2 Calculate the optimized power generation cost and the original power generation cost of the system as follows: Figure 3 The comparison shown.

[0046] Depend on Figure 3It can be concluded that the optimized total power generation cost is approximately 61.22% of the original power generation cost of the system, proving that the power flow optimization control method for power systems with multiple DC shared grounding electrodes can effectively reduce the power generation cost of the power system under normal operating conditions, which is conducive to the economical operation of the power grid.

[0047] The optimized control strategy of Scheme 3 for the control of generator set and DC variables is shown in Table 3 and Table 4, respectively.

[0048] Table 3 Generator output settings for Scheme 3 Table 4 DC variable settings for Scheme 3 The optimized renewable energy output is compared with the original renewable energy output level of the system, such as... Figure 4 As shown.

[0049] Depend on Figure 4 It can be concluded that the output level of the optimized new energy units increased by 19.87%, proving that the power flow optimization control method for power systems with multiple DC shared grounding electrodes proposed in this invention can effectively improve the absorption capacity of new energy and reduce the waste of power resources under normal operating conditions.

[0050] Example 2: Power flow optimization control under unipolar operation conditions in a power system with multiple DC shared grounding electrodes This embodiment addresses the scenario where two or more DC channels share a grounding electrode in the receiving-end power grid. A power flow optimization model for an AC / DC hybrid system is established, verifying that under unipolar operation, this optimized control strategy can significantly reduce the total system load shedding and improve power flow distribution while meeting grounding electrode safety constraints. To ensure reproducibility, the following sections provide system configuration, model and constraints, solution process, and comparative examples.

[0051] First, following steps S1 and S2 of Example 1, the topology of the AC / DC hybrid system is established, a unified per-unit value benchmark is set, and a power flow optimization model for normal operation is constructed. Power balance constraints and operating boundary conditions are set for the AC system, LCC DC transmission lines, and MMC DC transmission lines. For example... Figure 1 As shown, after determining that the system is in a unipolar operating state, step S3 is executed. S3: Under unipolar operation conditions, establish a power flow optimization model with the goal of minimizing load loss, inherit the constraints during normal operation, and add ground electrode current constraints.

[0052] Specifically, the newly added optimization variable is the active power load of the power system. P L The revised objective function is now minimum load loss; new constraints include power system load constraints and grounding electrode current constraints.

[0053] The objective function of the optimization model for a power system with multiple DC shared grounding electrodes operating under single-pole conditions is: in, For nodes i Initial active load, For nodes i Actual active load Add new constraints: The active power load of a power system has upper and lower limits, namely: The grounding electrode current has upper and lower limits, namely: in, This is the maximum current allowed to flow through the grounding electrode.

[0054] In this embodiment, when the system enters the single-pole operation mode, the DC current flows back from the non-faulty pole through the grounding pole to form the ground current. If it is operated directly, the grounding pole current will exceed the limit. Therefore, the model limits the grounding current through constraint (33) and, together with the load adjustable constraint (32), ensures that the system achieves minimum load reduction within the current limit.

[0055] Depend on Figure 1 It can be seen that after solving the optimized power flow under unipolar operation conditions, step S4 is executed. The output includes the power system operation scheme and control settings with multiple DC shared grounding electrodes, including generator output, DC control variable setpoints, DC power distribution, etc.

[0056] In this embodiment, the fmincon function of Matlab is used to solve the optimization model, and the optimization results are verified using Matpower and MatACDC power flow solving tools. To verify the effectiveness of the proposed power flow optimization control method for power systems with multiple DC shared grounding electrodes under unipolar operation conditions, this example will set up two schemes for numerical analysis and compare their implementation effects.

[0057] Option 1: For AC / DC hybrid systems operating under unipolar conditions, adopt the power flow optimization control method for power systems with multiple DC shared grounding electrodes proposed in this invention. Option 2: For AC / DC hybrid systems operating under unipolar conditions, an average distribution of grounding current is adopted as the control method.

[0058] Simulations were performed using the three schemes described above. The optimized control strategy of Scheme 1, obtained using the control strategy proposed in this invention, controls the generator set and DC variables, as shown in Tables 5 and 6, respectively.

[0059] Table 5 Generator output settings for Scheme 1 Table 6 DC Variable Settings for Scheme 1 The load loss conditions of each node under control strategies Scheme 1 and Scheme 2 are compared, such as... Figure 5 As shown.

[0060] Depend on Figure 5 It can be concluded that the total load loss using the minimum load loss optimization control strategy is only 62.6% of the total load loss under the Scheme 2 control strategy. This proves that the power flow optimization control method for power systems with multiple DC shared grounding electrodes proposed in this invention can effectively reduce the load attenuation of the system under single-pole operation conditions, and provides an effective control scheme for single-pole blocking faults occurring in AC / DC hybrid systems with shared grounding electrodes.

[0061] Example 3: This invention also provides a computer-readable storage medium storing computer instructions or computer programs. Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by computer instructions instructing related underlying hardware devices (e.g., computing control devices deployed in power system dispatch centers or processors in servers). The computer instructions can be stored statically or dynamically in this computer-readable storage medium. When the instructions are read and executed by the corresponding processor, all data processing and machine control logic in the power system flow optimization control method with multiple DC shared grounding electrodes proposed in the foregoing embodiments can be implemented.

[0062] Specifically, when the instruction is executed, the computing control device can sequentially perform the following operation process: acquire system component parameters and actual operating condition data of the AC / DC hybrid power grid and perform unified per-unit value calculation using reference data; extract underlying optimization variables including AC system, LCC DC transmission line, and MMC DC transmission line; determine whether the system has been triggered to unipolar operation state based on the actual operating condition data state machine; when not in unipolar operation state, input the per-unit value data and optimization variables into the normal operation condition power flow optimization model constrained by power balance equation constraints, line transmission inequality constraints, and variable upper and lower limit constraints for conventional iterative optimization; when unipolar operation state is identified, seamlessly introduce variables representing actual active load, automatically switch to the power flow optimization model with minimum load shedding as the objective for solving, and rigidly superimpose power system load constraints and safety current limit constraints for limiting the current flowing through the common grounding electrode on the basis of inheriting normal operation constraints; finally obtain the optimization convergence value, generate and output underlying power system control setting data including generator output, DC control variable setpoints, and DC power allocation.

[0063] During the implementation of this project, the computer-readable storage medium may include, but is not limited to: read-only memory (ROM), random access memory (RAM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), magnetic random access memory (FRAM), flash memory, magnetic surface memory, optical disc, or CD-ROM, and other non-volatile or volatile machine-readable media capable of storing program code. By compiling and solidifying the underlying physical boundary constraints, multi-objective optimization mathematical model, and polar state protection logic for the common grounding electrode of the AC / DC hybrid system into the aforementioned storage medium, the technical solution of this invention can be seamlessly embedded into the existing power grid energy management system (EMS) or wide area control system (WAMS) in a pure machine instruction flow manner. This enables the power grid master station control system to perform fully automated adaptive optimization and precise fixed-point load shedding real-time control under extreme fault conditions such as complex single-pole blocking without significantly modifying the existing primary power grid hardware. This ensures the perfect implementation and execution of the core patented algorithm in actual industrial scheduling scenarios.

Claims

1. A power flow optimization control method for a power system containing multiple DC shared grounding electrodes, characterized in that, Includes the following steps: The system component parameters and actual operating condition data of the AC / DC hybrid system are obtained, and the obtained system component parameters are uniformly converted into per-unit data. The AC / DC hybrid system includes an AC system, an LCC DC transmission line, an MMC DC transmission line, and a common grounding electrode connecting the two types of DC transmission lines. Based on the actual operating condition data, determine whether the AC / DC hybrid system is in a unipolar operating state; In response to the absence of a unipolar operating state in the AC / DC hybrid system, the per-unit data and the optimization variables are input into the power flow optimization model under normal operation for solution. In response to the existence of a unipolar operating state in the AC / DC hybrid system, the per-unit data, the optimization variables, and the newly added characterization nodes are... Variables of actual active load The input is fed into a power flow optimization model with the objective of minimizing load loss for solution. Obtain the optimization variables or the representation nodes after the solution has converged. The actual active load variable values ​​are used to generate and output the power system control setting data with multiple DC common grounding electrodes under the corresponding operating conditions. The control setting data includes generator output values, DC control variable setting values, and DC power distribution values.

2. The power flow optimization control method for a power system with multiple DC shared grounding electrodes according to claim 1, characterized in that, Acquire system component parameters and actual operating condition data of the AC / DC hybrid system, and uniformly convert the acquired system component parameters into per-unit data, including: Step S1.1: Establish the topology of the AC / DC hybrid system and unify the per-unit value benchmarks for the AC and DC systems; in: These are the AC reference power, reference voltage, reference current, and reference impedance, respectively. These are the DC reference power, reference voltage, reference current, and reference resistance, respectively. The reference current and reference impedance are calculated as follows: Step S1.2: Establish a power flow model for the AC / DC hybrid system. The DC component of the AC / DC hybrid system power flow model includes LCC DC transmission lines, MMC DC transmission lines, and LCC-MMC hybrid DC transmission lines. 1) LCC DC transmission line: The control variables of the LCC converter station include DC voltage. U dc DC current I dc Control angle θ Converter turns ratio k T In power flow calculation, the DC side of the LCC node is equivalent to the AC PQ node; 2) MMC DC transmission lines: The control variables of the MMC converter station include DC voltage. U dc Active power on the AC side of the converter P s Reactive power on the AC side of the converter Q s AC side voltage U s Depending on the type of AC node connected to it, the DC side of the MMC node is equivalent to an AC PQ node or PV node in the power flow calculation. 3) LCC-MMC Hybrid DC: A passive node BB is introduced between the LCC circuit and the MMC circuit. The BB node is a virtual node, and the DC power of the BB node satisfies the formula: The BB node voltage is equal to the specified DC node voltage, and the BB node does not exchange power with the AC system and cannot be used as a balancing station. It is necessary to select any converter station in the MMC system as a balancing station to handle unbalanced power. Step S1.3: Calculate the total grounding current of the common grounding electrode. : in, n The number of converters connected to this grounding electrode. I i For the first i The grounding current component of each converter is determined by the operating state of the bipolar system in which the converter is located. Let the converter... i The positive line current of the DC system is The negative line current is Then the first i The current component injected into the common ground electrode by each converter is the imbalance between the positive and negative currents, that is: Under the single-maximum cyclic operation condition, then At this time, the grounding current component Under normal bipolar symmetric operating conditions, ,but ; Step S1.4: Form a parameter set for solving the problem. Use per-unit data as the parameter set. The parameter set includes: AC side state variables, generator active / reactive power and upper and lower limits, line transmission power flow and upper and lower limits; DC side voltage, current, power and DC node control variables and upper and lower limits.

3. The power flow optimization control method for a power system with multiple DC shared grounding electrodes as described in claim 1, characterized in that, The power flow optimization model during normal operation includes: optimization variables, objective function, and constraints; The optimization variables include: 1) Optimization variable for AC system: node voltage amplitude U Node voltage phase angles except for slack nodes θ Generator node active power P G Reactive power of generator nodes Q G ; 2) Optimization variables for LCC DC transmission lines: DC voltage U dc DC current I dc Control angle cosine cosδ Power factor cosφ Converter turns ratio k T ; 3) Optimization variables for MMC DC transmission lines: Active power on the AC side of the converter. P s Reactive power on the AC side of the converter Q s ; The objective function includes minimizing system network loss, minimizing generator cost, and maximizing renewable energy consumption. The constraints include AC system operation constraints, LCC DC transmission line operation constraints, and MMC DC transmission line operation constraints.

4. The power flow optimization control method for a power system with multiple DC shared grounding electrodes according to claim 3, characterized in that, The objective function includes minimizing system network losses, minimizing generator costs, and maximizing renewable energy consumption, including: 1) Minimal network loss in the system in, For generator power, For load power, For the number of generators, For the number of loads; 2) Generator has the lowest cost in, C 0 , C 1 , C 2 This is the generator cost coefficient; 3) Maximum absorption of new energy To maximize the absorption of new energy sources, the objective function is: in, Predicting the output of wind turbine units. For actual wind turbine output, This refers to the number of wind turbine units.

5. The power flow optimization control method for a power system with multiple DC shared grounding electrodes according to claim 3, characterized in that, The operating constraints of the communication system include: Each node in an AC power system needs to satisfy active and reactive power balance, that is: in, N This represents the total number of nodes in the system. U i θ i For nodes i Voltage amplitude and phase angle; G ij , B ij For nodes i, j The electrical conductivity and susceptance between them; For nodes i, j The phase angle difference between them; Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, These are the upper and lower limits of the node voltage amplitude, respectively; These are the upper and lower limits of the node voltage phase angle, respectively; These are the upper and lower limits of the generator's output active power, respectively. These are the upper and lower limits of the generator's output reactive power, respectively. For wind turbine units, the actual wind turbine node output have: in, These are the upper and lower limits of the actual output of the wind turbine; For line power transmission P ij have: in, The lines are respectively ij Upper and lower limits of power transmission.

6. The power flow optimization control method for a power system with multiple DC shared grounding electrodes according to claim 3, characterized in that, The operational constraints of the LCC DC transmission line include: The nodes connected to the LCC converter need to satisfy active and reactive power balance, that is: Among them, the active power flowing from the AC system into the DC transmission line reactive power They respectively satisfy: in, , They are nodes i DC side voltage and current, For nodes i The power factor angle on the AC side of the converter; The voltage balance equation must be satisfied on both sides of the node connected to the LCC converter, that is: in, For nodes i Converter turns ratio; For nodes i AC side voltage; For nodes i Converter control angle; For nodes i Converter reactance; It is a constant; For DC power flow, the DC network equations are satisfied, namely: in, This refers to power loss during DC transmission. Each satisfies ; Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, They are nodes i DC-side voltage amplitude upper and lower limits; They are nodes i DC side current amplitude upper and lower limits; They are nodes i Upper and lower limits of the cosine of the converter control angle; They are nodes i upper and lower limits of power factor They are nodes i Upper and lower limits of converter turns ratio; For DC line transmission power have: in, DC lines ij Upper and lower limits of power transmission.

7. The power flow optimization control method for a power system with multiple DC shared grounding electrodes according to claim 3, characterized in that, The operating constraints of the MMC DC transmission line include: The nodes connected to the MMC converter need to satisfy active and reactive power balance, that is: For the MMC node, considering the converter losses during power transfer from the AC system to the DC transmission line, the power balance equation is: in, They are nodes i The active and reactive power losses of the MMC converter are calculated using the following formulas: in, These are the equivalent resistance and equivalent reactance of the MMC converter station, respectively. For DC power flow, the DC network equations are satisfied, namely: in, p For the number of operating poles and nodes of a DC transmission line. i The DC-side voltage satisfies the voltage balance equation, that is: in, DC node i, j The electrical conductance between them; This represents the total number of nodes in the DC network. They respectively satisfy: Each variable needs to satisfy the corresponding inequality constraints; for the optimization variables, we have: in, They are nodes i AC active power measurement upper and lower limits; They are nodes i AC reactive power measurement upper and lower limits; For DC line transmission power have: in, DC lines ij Upper and lower limits of power transmission.

8. The power flow optimization control method for a power system with multiple DC shared grounding electrodes as described in claim 1, characterized in that, In response to the existence of a unipolar operating state in the AC / DC hybrid system, the per-unit data, the optimization variables, and the newly added characterization nodes are... Variables of actual active load The input is fed into a power flow optimization model with the objective of minimizing load loss for solution, including: The power flow optimization model adds new constraints, including power system load constraints and grounding electrode current constraints. The objective function of the power flow optimization model is: in, For nodes i Initial active load, For nodes i Actual active load; of which, The active power load of a power system has upper and lower limits, namely: The grounding electrode current has upper and lower limits, namely: in, This is the maximum current allowed to flow through the grounding electrode.

9. A computer-readable storage medium storing instructions, characterized in that, When the instruction is executed, it can realize the power flow optimization control method for a power system with multiple DC shared grounding electrodes as described in any one of claims 1 to 8.

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