Control method of network following / constructing new energy LCC-HVDC grid-connected system, electronic equipment and storage medium

Abstract

The invention relates to the technical field of power grid control, in particular to a control method of a network following / constructing new energy LCC-HVDC grid-connected system, electronic equipment and a storage medium. System optimization control is realized through six key steps: firstly, obtaining basic parameters such as a network construction new energy capacity ratio and a system short-circuit ratio; secondly, calculating reactive vacancy of the system; then determining a system working mode; establishing a new energy mathematical model; a cooperative control strategy is obtained; and finally formulating a high-low penetration control strategy. Therefore, a complete control closed loop is established, and a systematic solution is formed from parameter acquisition to strategy execution. And the advantages of the following network type new energy and the constructed network type new energy are integrated, so that the high efficiency of the following network type new energy is reserved, and the power grid supporting capability of the constructed network type new energy is also realized.

Description

Technical Field

[0001] This invention relates to the field of power grid control technology, specifically to a control method, electronic device, and storage medium for a grid-connected / grid-connected new energy LCC-HVDC system. Background Technology

[0002] Driven by the "dual carbon" goals, the penetration rate of new energy sources in the power system is continuously increasing, and ultra-high voltage direct current transmission (LCC-HVDC) has become an important way to transmit new energy. Existing projects generally adopt a hybrid transmission-end architecture of "new energy + thermal power," relying on synchronous power sources for voltage support and inertia response. While this ensures stable system operation, it restricts the full utilization of clean energy. The development of grid-forming new energy technologies provides a new approach for grid connection of pure new energy sources. By autonomously constructing AC voltage by simulating the characteristics of synchronous generators, it is expected to break through the dependence on traditional synchronous power sources.

[0003] Current research on grid connection of renewable energy via LCC-HVDC mainly revolves around two schemes: one is to enhance system support capabilities by adding synchronous condensers, energy storage, and other equipment; the other is to optimize the sending-end grid topology. While these schemes can improve system stability, they still rely on synchronous power sources or additional equipment, failing to achieve grid connection entirely based on renewable energy. Existing research has attempted to construct pure renewable energy systems using grid-connected converters, but under low short-circuit ratio conditions, problems such as insufficient voltage stability and reduced economic efficiency exist, hindering their practical application.

[0004] Therefore, how to construct a 100% renewable energy LCC-HVDC grid-connected system with high stability and high economic efficiency has become a key issue that urgently needs to be addressed. Existing research still has shortcomings in system architecture design and control strategy optimization, and new technical routes need to be explored to overcome the technical bottlenecks of pure renewable energy grid connection. Summary of the Invention

[0005] To avoid and overcome the technical problems existing in the prior art, this invention provides a control method, electronic equipment, and storage medium for a grid-connected / grid-connected renewable energy LCC-HVDC system. This invention retains the high efficiency of grid-connected renewable energy while also possessing the grid support capabilities of grid-connected renewable energy.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A control method for a grid-connected / grid-connected renewable energy system via an LCC-HVDC includes the following steps:

[0008] S1. Obtain the grid-connected new energy capacity ratio and grid-connected system short-circuit ratio;

[0009] S2. Calculate the reactive power deficit of the grid-connected system;

[0010] S3. Obtain the operating mode of the grid-connected system;

[0011] S4. Construct mathematical models for grid-connected new energy and grid-connected new energy;

[0012] S5. Obtain the coordinated control strategy for grid-connected new energy and grid-connected new energy;

[0013] S6. Obtain the high-low voltage transmission control strategy for grid-connected systems.

[0014] As a further aspect of the present invention: the grid-connected renewable energy capacity ratio ξ i It is represented as follows:

[0015] ξ i =S GFj / ST i ;

[0016] In the formula, S Ti S represents the total fixed capacity of new energy sources. GFj The total rated capacity of new energy sources for grid construction;

[0017] The formula for calculating the short-circuit ratio of a grid-connected system is as follows:

[0018]

[0019] In the formula, ML SCR This represents the short-circuit ratio of the grid-connected system; (1-ξ) GFL,i ξ represents the weighting coefficient of the i-th grid-connected new energy source; GFM,j S represents the weighting coefficient of the j-th renewable energy source in the grid; GFL,i S represents the equivalent short-circuit capacity of the i-th grid-connected new energy source; GFM,j S represents the equivalent short-circuit capacity of the j-th grid-connected renewable energy source; total S represents the total capacity of new energy sources; grid This indicates the inherent short-circuit capacity on the power grid side.

[0020] As a further aspect of the present invention, the reactive power deficit is calculated as follows:

[0021] Q q =-Q C +Q L +Q T +Q LCC-HVDC ;

[0022] In the formula, Q q For the system reactive power deficit, Q C The reactive power for charging transmission lines, Q L Q represents the reactive power loss of the transmission line. T Q represents the reactive power loss of the transformer.LCC-HVDC For the reactive power demand of DC transmission systems;

[0023]

[0024] In the formula, P dc It is DC transmission power; α is the converter power factor, α is the rectifier-side firing angle, and μ is the commutation overlap angle.

[0025] As a further aspect of the present invention: the critical value of reactive power in a grid-connected system is determined by the following formula:

[0026]

[0027] In the formula, ΔQ ML ΔU represents the change in reactive power. ML U represents the voltage change in a grid-connected system. N This indicates the rated voltage of the grid-connected system.

[0028] As a further aspect of the present invention: In the grid-connected system operating mode: n grid-connected renewable energy sources and m grid-connected renewable energy sources are stepped up by a step-up transformer and then converge at the PCC bus; the grid-connected system converts the converged power into DC power for transmission, and the m grid-connected renewable energy sources provide commutation voltage for the grid-connected system; the n grid-connected renewable energy sources operate in maximum power point tracking mode; simultaneously, the capacity Q of the grid-connected renewable energy sources is locked out. S =|-Q C +Q L +Q T +Q LCC-HVDC -ΔQ ML As the basis for the blocking capacity of the new energy generator-side converter, the grid-connected / connected new energy needs to calculate the active and reactive power output of the grid-connected new energy based on the light intensity and wind speed using the MPPT module. If the grid-connected new energy unit stops operating, the grid-connected new energy generator-side converter will be blocked, and the grid-side converter will be switched to constant voltage control.

[0029] As a further aspect of the present invention, the mathematical model for grid-connected new energy control is as follows:

[0030]

[0031] In the formula, ω1 and ω n These are the actual and given values ​​of the active power loop output angular frequency, respectively; P ref P and Q represent the given and actual values ​​of active power, respectively; ref Q and J represent the given and actual values ​​of reactive power, respectively; J and D... p These represent the virtual inertia and droop factor of the active loop, respectively; K and D q These are the inertia coefficient and droop coefficient of the reactive power loop, respectively; Ki1 U is the reactive power loop integral coefficient; ref U and E are the reference value and amplitude of the output voltage of the grid-type converter, respectively; GF To construct the virtual internal electromotive force of new energy sources in the grid;

[0032] The mathematical model for mesh control is shown below:

[0033]

[0034] In the formula, ω pll ω is the output angular frequency of the phase-locked loop (PLL). g ω1 is the grid angular frequency of the PLL; ω2 is the rated angular frequency; θ is the voltage. pll The output phase of the PLL; s is the differential operator, K p.pll and K i,pll These are the proportional coefficient and integral coefficient of the phase-locked loop, respectively.

[0035] As a further aspect of the present invention, the cooperative control strategy is expressed as follows:

[0036] Coordinated control of grid-connected and grid-connected new energy sources can improve the stability and adaptability of grid-connected converters in scenarios with high new energy penetration. Therefore, weighting is allocated according to the capacity ratio of grid-connected new energy sources, and the weighting coefficients are adaptively adjusted based on the short-circuit ratio of the grid-connected system. When the MLSCR is high, the grid-connected system operates in a PLL synchronization-dominated mode, and conversely, when the MLSCR is low, the grid-connected system operates in a power synchronization-dominated mode. The current signals required by the converter are allocated according to the MLSCR and sent to the grid-connected control calculation unit and the grid-connected control calculation unit, respectively. The two control calculation units calculate their respective modulation waves, and finally, the modulation signals of the grid-connected / grid-connected new energy converters are weighted to obtain the switching signals of the converters.

[0037] As a further aspect of the present invention, the grid-connected system's coordinated high-low voltage transmission control strategy is expressed as follows:

[0038] When a system failure occurs, the maximum reactive current limit of the grid-connected renewable energy power supply is:

[0039]

[0040] In the formula, i GLqmax For the active current of the grid-connected converter of new energy power sources; P NS The active power output to the grid by the new energy grid-connected converter; I Lim The maximum allowable current for grid-connected converters of new energy sources; I GLd U represents the d-axis current of the grid-connected converter for new energy sources. g Voltage at the grid connection point for new energy sources;

[0041] When constructing grid-connected renewable energy power sources, power angle stability must be considered to avoid system instability during faults. The relationship between the output power and power angle of a grid-connected converter is shown below:

[0042]

[0043] In the formula, P GM and Q GM These represent the output active and reactive power of the grid converter, respectively; E GM Z is the internal potential of the grid converter; Σ θ is the synchronous reactance; θ is the Z Σ The impedance angle; δ is the power angle, which is usually in the range of 0° < δ < 90°;

[0044] As can be seen from the active current, during a fault, the reactive power output of the grid-connected converter can be changed by increasing the reactive current of the grid-connected renewable energy source along the q-axis, thereby supporting the grid voltage; according to The reactive power deficit of the system is determined by the degree of voltage drop at the fault point, and the reactive power regulation capability of the grid-side converter is used to provide the reactive power required for the continuous operation of the new energy grid-connected system.

[0045] Using a limiting power angle of 90° as the boundary for the power angle stability of the grid-connected renewable energy system, the power angle stability of the grid-connected renewable energy system during a fault is determined. If the boundary condition is met, the grid-connected converter is switched to a grid-following control mode based on current phasor synchronization, and synchronization is achieved by tracking the grid voltage through a backup phase-locked loop. Considering the capacity difference between grid-connected and grid-connected renewable energy units, the grid-side reactive power compensation capacity undertaken by grid-connected and grid-connected renewable energy units should be proportionally allocated according to their own capacity, as shown below:

[0046]

[0047] In the formula, This indicates the reactive power command value of the grid-connected new energy system.

[0048] Regarding the transient recovery overvoltage problem of renewable energy, and considering the reactive power of renewable energy connected to the grid / connected grid causing the grid connection point voltage to reach 1.3 per unit (pu) and the fluctuation characteristics of renewable energy output, which can lead to renewable energy disconnection and system instability or even collapse, the controller parameters are adjusted online in real time through input and output data to suppress transient overvoltage problems at the millisecond level, as shown below:

[0049]

[0050] In the formula, λ is a weighting factor used to limit the variation of the control input; y *(k+1) represents the desired output signal of the system at time k+1; y(k) represents the output signal of the system at time k; u(k) and u(k-1) are the inputs of the system at times k and k-1, respectively; ψ c (k) is the pseudo-partial derivative of the system; ρ∈(0,1] is the step size factor, which mainly makes the control algorithm more general.

[0051] An electronic device includes a processor, an input device, an output device, and a memory, wherein the processor, input device, output device, and memory are connected in sequence, the memory is used to store a computer program, the computer program includes program instructions, and the processor is configured to call the program instructions to execute a control method for a grid-connected / grid-connected new energy system via LCC-HVDC as described above.

[0052] A storage medium storing a computer program, the computer program including program instructions, which, when executed by a processor, cause the processor to perform a control method for a grid-connected / grid-connected new energy system via an LCC-HVDC, as described above.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] 1. This invention achieves optimized system control through six key steps: First, it acquires basic parameters such as the capacity ratio of grid-connected renewable energy and the system short-circuit ratio; second, it calculates the system reactive power deficit; third, it determines the system operating mode; fourth, it establishes a mathematical model for renewable energy; fifth, it acquires a coordinated control strategy; and finally, it formulates a high-voltage and low-voltage transmission control strategy. This establishes a complete control closed loop, forming a systematic solution from parameter acquisition to strategy execution. It also integrates the advantages of both grid-connected and grid-connected renewable energy, retaining the high efficiency of grid-connected renewable energy while possessing the grid support capabilities of grid-connected renewable energy.

[0055] 2. A rigorous mathematical formula clearly defines the calculation methods for the grid-connected renewable energy capacity allocation ratio and the multi-level short-circuit ratio (MLSCR) of the grid-connected system. The capacity allocation ratio is expressed as the ratio of the total rated capacity of grid-connected renewable energy to the total capacity of renewable energy, accurately reflecting the proportion of grid-connected equipment in the system. The calculation formula for the multi-level short-circuit ratio innovatively introduces a weighting coefficient, which represents the contribution of grid-connected and grid-connected renewable energy to the system's short-circuit capacity. Therefore, it has the following significant advantages: 1) The proposed calculation formula has clear physical meaning, accurately quantifying the differentiated impact of different renewable energy types on grid strength; 2) The introduction of the weighting coefficient makes the calculation results more accurate, providing a reliable basis for the formulation of subsequent control strategies; 3) The formula design has good scalability and can be applied to complex grid-connected systems containing multiple renewable energy units; 4) It directly relates to the inherent short-circuit capacity of the grid side, facilitating practical engineering applications and on-site commissioning.

[0056] 3. This study comprehensively considers key factors such as the reactive power of transmission line charging, line reactive power loss, transformer reactive power loss, and the reactive power demand of the LCC-HVDC DC transmission system. In particular, for the reactive power demand of the DC system, it innovatively establishes a precise mathematical relationship between DC transmission power, converter power factor, rectifier-side firing angle, and commutation overlap angle, thus offering the following advantages: 1) Comprehensiveness: For the first time, the reactive power demand of the LCC-HVDC system is incorporated into the overall calculation, overcoming the shortcomings of traditional methods that only consider AC system parameters; 2) Accuracy: By introducing DC system-specific parameters such as firing angle and commutation overlap angle, the calculation accuracy is significantly improved; 3) Practicality: The model output results can be directly used for the formulation of subsequent voltage control strategies, providing a quantitative basis for system reactive power compensation; 4) Foresight: It lays a theoretical foundation for system stability analysis in scenarios with a high proportion of new energy access.

[0057] 4. The formula for determining the critical value of reactive power establishes a differential relationship between the change in reactive power and the change in voltage, thus achieving a precise description of the system stability boundary. The rated voltage introduced in the formula serves as a benchmark parameter, ensuring the universality of the criterion and offering the following advantages: 1) Fast response: Real-time monitoring of system state changes through the differential relationship enables millisecond-level reactive power regulation; 2) Preventive control: Timely control measures can be taken before voltage instability, effectively preventing system collapse; 3) Strong adaptability: Applicable to grid-connected systems of different voltage levels and scales; 4) Engineering practicality: The formula is concise, parameters are easy to obtain, and it is convenient to promote and apply in practical engineering. This critical value determination method provides an important technical means for voltage stability control of new energy grid-connected systems.

[0058] 5. The operating mode and intelligent interlocking mechanism of the grid-connected system include a system architecture where n grid-connected renewable energy units and m grid-connected renewable energy units converge at the PCC bus after passing through a step-up transformer; the key function of grid-connected renewable energy units providing commutation voltage; the control strategy for grid-connected renewable energy units operating in maximum power point tracking mode; and an intelligent interlocking mechanism based on reactive power deficit calculation. This system offers the following advantages: 1) Innovative system architecture: By rationally configuring the ratio of grid-connected and grid-connected renewable energy units, an optimal balance between economy and stability is achieved; 2) Clear functional division: Fully leveraging the technical advantages of different types of renewable energy units, with grid-connected units responsible for voltage support and grid-connected units focusing on power output; 3) Intelligent interlocking algorithm: Dynamically adjusting the number of operating units based on real-time calculated reactive power deficit, ensuring system stability while avoiding resource waste; 4) Fault response capability: Supporting grid-side converters to switch to constant voltage control mode, significantly improving the system's anti-disturbance capability. This solution provides a complete solution for building a highly reliable renewable energy grid-connected system.

[0059] 6. For grid-connected renewable energy sources, the model simulates the active-frequency characteristics of synchronous generators using parameters such as virtual inertia and droop coefficient, and employs an integral element to achieve reactive-voltage regulation. The grid-following model focuses on improving the phase-locked loop (PLL) design, enhancing synchronization accuracy through a proportional-integral (PI) element. It offers the following advantages: 1) Strong physical equivalence: The grid-connected model accurately reproduces the dynamic characteristics of the synchronous generator, contributing to grid stability; 2) Superior control performance: The optimized PLL in the grid-following model exhibits faster response speed and higher synchronization accuracy; 3) Parameter decoupling: The active and reactive power loops are designed independently, greatly simplifying the controller parameter tuning process; 4) Engineering practicality: The model structure is clear and facilitates digital implementation. These models lay a solid foundation for the development of subsequent control strategies.

[0060] 7. The collaborative control strategy dynamically adjusts the weighting of grid-connected and grid-connected control based on the real-time calculated short-circuit ratio (MLSCR): PLL synchronization-dominated mode is used at high short-circuit ratios, while switching to power synchronization-dominated mode is used at low short-circuit ratios. Technically, the acquired current signals are intelligently allocated and fed into two types of control calculation units, ultimately generating the converter switching signal through weighted summation. The breakthroughs of this strategy are: 1) Strong adaptability: Automatically optimizes the control mode based on grid conditions; 2) Fast response speed: Integrates the advantages of both control types to improve dynamic performance; 3) Good stability: The weighted algorithm ensures smooth transition and avoids mode switching shocks; 4) High practicality: The algorithm has a moderate computational load and is easy to implement in engineering. This collaborative control strategy effectively solves the system stability problem under high penetration rates of new energy sources.

[0061] 8. The high-low voltage ride-through coordinated control strategy includes: reactive current limit calculation for grid-connected renewable energy, power angle stability criterion for grid-connected renewable energy, reactive power compensation allocation principle during faults, and transient overvoltage suppression algorithm. It has the following advantages: 1) Dual-machine coordination: Grid-connected units provide reactive power support, while grid-connected units ensure power angle stability; 2) Clear safety boundary: A 90° power angle is used as the stability threshold; 3) Intelligent allocation: Reactive power compensation responsibility is allocated according to capacity ratio; 4) Advanced algorithm: A data-driven parameter self-adjustment method is used to suppress overvoltage. This scheme enables the system to have excellent fault ride-through capability, with a voltage support response time of less than 100ms and significant overvoltage suppression effect.

[0062] 9. The electronic device includes a processor, input / output devices, and memory, capable of executing complex control algorithms in real time. The storage medium stores the control program and supports multi-platform deployment. It has the following advantages: 1) It achieves a leap from technological innovation to product implementation; 2) It boasts powerful computing performance, meeting millisecond-level real-time control requirements; 3) It has good system compatibility, facilitating upgrades and maintenance; 4) It has broad industrialization prospects, providing a standard solution for the research and development of new energy grid-connected equipment. Through these two claims, the entire technical solution meets the conditions for commercial promotion and application. Attached Figure Description

[0063] Figure 1 For grid-connected / constructed new energy sources, the LCC-HVDC grid-connected system is used.

[0064] Figure 2 This is a flowchart of the control method of the present invention.

[0065] Figure 3 Diagram of the control structure during the steady-state period of grid-connected / grid-constructed renewable energy.

[0066] Figure 4 Diagram showing the integrated control structure for grid-connected / grid-connected new energy synchronous links.

[0067] Figure 5 Diagram showing the integrated control structure for grid-connected / grid-connected new energy modulation links.

[0068] Figure 6 High-low voltage control strategy for grid-connected / constructed new energy grid-connected systems.

[0069] Figure 7 This is a transient control structure diagram for switching from network construction mode to network following mode.

[0070] Figure 8 A schematic diagram of a multi-strategy voltage ride-through device for grid-connected / grid-connected new energy systems via LCC-HVDC.

[0071] Figure 9 This is a schematic diagram of the structure of the electronic device of the present invention.

[0072] In the diagram: 400, electronic device; 410, processor; 420, memory; 430, storage medium. Detailed Implementation

[0073] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] In this embodiment, as Figure 1 As shown, there are n grid-connected renewable energy generating units, m grid-connected renewable energy generating units, and an LCC DC transmission system. The number of any grid-connected renewable energy generating unit is denoted as i, i = 1, ..., n; and the number of any grid-connected renewable energy generating unit is denoted as j, j = 1, ..., m.

[0075] The control method for grid-connected / grid-connected new energy sources via the LCC-HVDC grid-connected system is as follows:

[0076] I. Establish a grid-connected system topology that includes grid-connected / grid-connected new energy sources and conventional high-voltage direct current transmission;

[0077] S11. Obtain the grid-connected / grid-connected renewable energy capacity ratio

[0078] The ratio of grid-connected renewable energy capacity to total renewable energy capacity is defined as the grid-connected renewable energy capacity ratio ξ. i As shown in formula (1):

[0079] ξ i =S GFj / S Ti (1)

[0080] In the formula, S Ti S represents the total fixed capacity of new energy sources. GFj The total rated capacity of new energy sources for grid construction.

[0081] The short-circuit ratio of grid-connected / constructed new energy systems is affected by the control mode. Traditional short-circuit ratio calculation does not consider the dynamic contribution difference of new energy control mode to short-circuit capacity, making it difficult to accurately assess the strength of high-proportion new energy systems. Therefore, a short-circuit ratio (MLSCR) calculation method based on grid-connected / constructed capacity identification is proposed to quantify the stability margin of grid-connected / constructed new energy systems. The short-circuit ratio is used to evaluate the system voltage support strength before and after the access of new energy to the grid, and the analytical relationship between the grid capacity ratio and the system strength is obtained. The expression of MLSCR is shown in formula (2).

[0082]

[0083] In the formula, ML SCR This represents the short-circuit ratio of the grid-connected system; (1-ξ) GFL,i ξ represents the weighting coefficient of the i-th grid-connected renewable energy source, used to quantify the contribution of grid-connected / integrated renewable energy sources to the short-circuit current; GFM,j S represents the weighting coefficient of the j-th renewable energy source in the grid; GFL,i S represents the equivalent short-circuit capacity of the i-th grid-connected new energy source; GFM,j S represents the equivalent short-circuit capacity of the j-th grid-connected renewable energy source; total S represents the total capacity of new energy sources; grid This represents the inherent short-circuit capacity on the grid side. Generally, the minimum generalized short-circuit ratio that the LCC-HVDC can provide for stable commutation voltage is 5. If it is desired to increase the MLSCR to λ (λ>5), the grid-connected / network-connected capacity ratio can be determined according to formulas (1) and (2).

[0084] S12. Calculate the reactive power deficit of the renewable energy grid-connected system.

[0085] The capacity of grid-connected and grid-connected renewable energy sources in the system is determined according to formulas (1) and (2). The reactive power deficit of the grid-connected / grid-connected renewable energy system is closely related to the type of wind turbine, the topology of the wind farm collection line, the parameters of submarine AC cables of different voltage levels, and the reactive power control strategy in the system. It is mainly divided into the following four parts:

[0086] Q q =-Q C +Q L +Q T +Q LCC-HVDC (3)

[0087] In the formula, Q q For the system reactive power deficit, Q C The reactive power for charging transmission lines, Q L Q represents the reactive power loss of the transmission line. T Q represents the reactive power loss of the transformer. LCC-HVDC For the reactive power demand of DC transmission systems;

[0088]

[0089] In the formula, P dc It is DC transmission power; α is the converter power factor, α is the rectifier-side firing angle, and μ is the commutation overlap angle.

[0090] The QLCC-HVDC is provided by a sending-end filter and a reactive power compensator to ensure that reactive power during system disturbances or faults does not cause overvoltage at the new energy grid connection point. Therefore, there is a critical value for the reactive power of the system. When the upper limit of the reactive power of the system is lower than this critical value, the voltage rise caused by reactive power will not cause equipment damage. This critical value is shown in formula (5).

[0091]

[0092] In the formula, ΔQ ML ΔU represents the change in reactive power. ML U represents the voltage change in a grid-connected system. N This indicates the rated voltage of the grid-connected system.

[0093] By blocking the generator-side converter of the new energy source and only putting the grid-side converter into operation, the new energy source can operate in a constant voltage control mode. The grid-connected new energy capacity that needs to be blocked is shown in formula (6):

[0094] Q S =|-Q C +Q L +Q T +Q LCC-HVDC -ΔQ ML| (6)

[0095] Among them, Q S Blocked grid-connected renewable energy capacity.

[0096] S13. Obtain the working mode of the grid-connected / grid-connected new energy system via LCC-HVDC.

[0097] The power from n grid-connected renewable energy sources and m grid-connected renewable energy sources is stepped up by a step-up transformer and then converges at the PCC bus. The LCC-HVDC system converts the converged power into DC for transmission. The m grid-connected renewable energy sources enhance the system strength to provide a stable commutation voltage. The n grid-connected renewable energy sources operate in maximum power point tracking (MPPT). Tracking (MPPT) mode to improve energy utilization; determine the grid-connected / network-connected capacity ratio according to step S11, and select appropriate AC collection voltage and DC voltage based on conductor current carrying capacity and economic constraints; at the same time, formula (6) serves as the basis for the blocking capacity of the new energy generator side converter. The grid-connected / network-connected new energy needs to calculate the active power and reactive power output of the grid-connected new energy according to the light intensity and wind speed, and determine the grid-connected new energy generator unit to stop. Then, the grid-connected new energy generator side is blocked, and the grid-side converter is switched to constant voltage control to improve system stability; under normal circumstances, the system adopts grid-connected control mode under strong grid conditions to improve the utilization rate of new energy; under weak grid conditions, it switches to network-connected control mode to improve the stability under weak grid conditions and provide certain support capabilities for the grid; the control structure diagram during steady state is as follows Figure 3 As shown;

[0098] II. Establish a grid-connected / grid-connected new energy control strategy suitable for building stable commutation voltage during steady-state periods and a high-low ride-through control strategy that coordinates grid-connected / grid-connected operations during transient periods.

[0099] S21. Construct mathematical models for grid-connected new energy and grid-connected new energy.

[0100] The mathematical model for grid-connected new energy control is shown in formula (7):

[0101]

[0102] In the formula, ω1 and ω n These are the actual and given values ​​of the active power loop output angular frequency, respectively; P ref P and Q represent the given and actual values ​​of active power, respectively; ref Q and J represent the given and actual values ​​of reactive power, respectively; J and D... p These represent the virtual inertia and droop factor of the active loop, respectively; K and D q These are the inertia coefficient and droop coefficient of the reactive power loop, respectively; K i1 U is the reactive power loop integral coefficient;ref U and E are the reference value and amplitude of the output voltage of the grid-type converter, respectively; GF To construct the virtual internal electromotive force of new energy sources in the grid.

[0103] The mathematical model for mesh control is shown in equation (8):

[0104]

[0105] In the formula, ω pll ω is the output angular frequency of the phase-locked loop (PLL). g ω1 is the grid angular frequency of the PLL; ω2 is the rated angular frequency; θ is the voltage. pll The output phase of the PLL; s is the differential operator, K p.pll and K i,pll These are the proportional coefficient and integral coefficient of the phase-locked loop, respectively.

[0106] S22. Obtain the coordinated control strategy for grid-connected new energy and grid-connected new energy.

[0107] Coordinated control of grid-connected new energy and grid-connected new energy can improve the stability and adaptability of grid-connected converters in scenarios with high penetration of new energy to a certain extent. The grid-connected control mode locks the phase of the grid through PLL, thereby achieving synchronization with the grid and controlling the grid-connected current. The grid-connected control mode relies on methods such as power synchronization, virtual synchronous machine control, matching control and DC voltage synchronization to achieve synchronization with the grid without PLL. Therefore, a fusion method of power synchronization loop and phase-locked loop based on short-circuit ratio constraint is adopted, and the weight is allocated according to formula (1), and the weighting coefficient is adaptively adjusted according to formula (2). When MLSCR is high, the system operates in the PLL synchronization-dominated mode, and when MLSCR is low, the system operates in the power synchronization-dominated mode. The fusion control structure diagram of grid-connected / grid-connected new energy synchronization link is shown in Figure 1. Figure 4 As shown;

[0108] The integrated control structure diagram of the grid / grid-based new energy modulation link is shown below. Figure 5 As shown; where i 1ab These are the actual current values ​​for the two modes after current distribution; P set1 Q set1 These are the active and reactive power settings for the network-type control mode; P set2 Q set2 These are the active and reactive power settings for the grid-type control mode; e dq1 e dq2The modulation waves calculated in the dq coordinate system are the two modes respectively; k1 and k2 are the weighting coefficients of the two modulation waves respectively; the method is to equate the grid-connected / grid-connected renewable energy control to a virtual system that combines grid-connected renewable energy and grid-connected renewable energy. The current signal required by the converter is distributed according to MLSCR and sent to the grid-connected control calculation unit and the grid-connected control calculation unit respectively. The two control calculation units calculate the modulation waves respectively, and finally the grid-connected / grid-connected modulation signals are weighted to obtain the switching signal of the converter.

[0109] S23. Obtain the high-low crossover control strategy for grid-connected / constructed new energy grid-connected systems.

[0110] When a system failure occurs, the maximum output reactive current limit value i of the grid-connected new energy power supply GLqmax for:

[0111]

[0112] In the formula, i GLqmax For the active current of the grid-connected converter of new energy power sources; P NS The active power output to the grid by the new energy grid-connected converter; I Lim The maximum allowable current for grid-connected converters of new energy sources; I GLd U represents the d-axis current of the grid-connected converter for new energy sources. g The voltage at the grid connection point of the new energy source is given. As can be seen from formula (9), the maximum reactive current of the new energy source connected to the grid is affected by the output active power of the grid-connected converter, the grid connection point voltage, and the maximum allowable current of the grid-connected converter. The maximum allowable current of the grid-connected converter is usually a constant value.

[0113] When a system failure occurs, the grid-connected new energy power supply needs to consider the power angle stability to avoid system instability during the failure period. The relationship between the output power and power angle of the grid-connected converter is shown in formula (10):

[0114]

[0115] In the formula, P GM and Q GM These represent the output active and reactive power of the grid converter, respectively; E GM Z is the internal potential of the grid converter; ∑ θ is the synchronous reactance; θ is the Z ∑ The impedance angle; δ is the power angle, which is usually 0° < δ < 90°.

[0116] As can be seen from formula (9), during the fault period, the reactive power output of the grid-connected converter can be changed by increasing the reactive current of the grid-connected new energy q-axis, thereby supporting the grid voltage. According to formula (11), the reactive power deficit of the system can be determined by the degree of voltage drop at the fault point. The reactive power regulation capability of the grid-side converter can be used to provide the reactive power required for the continuous operation of the new energy grid-connected system.

[0117]

[0118] The increase in reactive power output by the grid-connected converter causes a drop in the voltage at the grid connection point of the new energy source, which in turn causes a drop in the active power output of the converter, resulting in a deviation between the actual output power and the reference value, and causing a problem with the power angle stability. Therefore, the limit power angle of 90° is used as the boundary of the power angle stability of the grid-connected new energy source system to judge the power angle stability of the grid-connected new energy source during the fault period. If the boundary condition is reached, the grid-connected converter is switched to the grid-following control mode based on current phasor synchronization, and synchronization is achieved by tracking the grid voltage through the backup phase-locked loop. Considering the capacity difference between the grid-connected and grid-connected new energy units, the grid-side reactive power compensation capacity undertaken by the grid-connected and grid-connected new energy units should be proportionally allocated according to their own capacity size, as shown in formula (12).

[0119]

[0120] In the formula, This indicates the reactive power command value of the grid-connected new energy system.

[0121] For the problem of transient recovery overvoltage of new energy sources, considering the reactive power of new energy sources connected to the grid / connected grid reversed to the grid connection point voltage reaching 1.3 per unit value pu and the power output fluctuation characteristics of new energy sources, which cause new energy sources to disconnect from the grid and cause system disorder or even collapse, a model-free adaptive control algorithm is proposed. The controller parameters are adjusted online through real-time input and output data to suppress the transient overvoltage problem in milliseconds, as shown in formula (13):

[0122]

[0123] In the formula, λ is a weighting factor used to limit the variation of the control input; y * (k+1) represents the desired output signal of the system at time k+1; y(k) represents the output signal of the system at time k; u(k) and u(k-1) are the inputs of the system at times k and k-1, respectively; ψ c (k) is the pseudo-partial derivative of the system; ρ∈(0,1] is the step size factor, which mainly makes the control algorithm more general.

[0124] Model-free adaptive control directly utilizes input and output data, avoiding complex modeling processes. It is suitable for complex nonlinear, time-varying, and strongly coupled systems. Based on the operating status of grid-connected / grid-connected renewable energy sources, it updates pseudo-partial derivatives and control laws in real time, automatically adapting to parameter changes and external disturbances to form a closed-loop adjustment. The high and low voltage ride-through strategy control diagram for grid-connected / grid-connected renewable energy systems is shown below. Figure 6 As shown, the transient control structure diagram for switching from network construction mode to network following mode during the transient period is as follows: Figure 7 As shown.

[0125] This invention also includes a control device for a grid-connected / grid-connected new energy system via LCC-HVDC, using the method described above, such as... Figure 8 As shown, it includes:

[0126] Establish a grid-connected system model for new energy sources connected to the grid / connected to the grid via LCC-HVDC, calculate the total capacity of new energy sources connected to the grid / connected to the grid and the short-circuit ratio required for LCC commutation, so as to obtain the capacity ratio of new energy sources connected to the grid / connected to the grid.

[0127] The MPPT calculation module is used to calculate the power output of grid-connected renewable energy in real time, which serves as a blocking signal on the generator side to determine the grid-connected / grid-connected ratio of the system under this environmental condition, so as to ensure that a stable commutation voltage can be provided for the LCC.

[0128] The voltage ride-through module selects an appropriate multi-strategy coordinated voltage ride-through strategy combination scheme to address the voltage drop of the renewable energy grid-connected system under different operating conditions and faults, ensuring that the power angle of the grid-connected renewable energy does not become unstable, thereby enhancing the transient stability of the grid-connected / grid-connected renewable energy system via LCC-HVDC.

[0129] See Figure 9 The diagram shown is a structural schematic of an electronic device provided in an embodiment of this application. An electronic device 400 provided in this application includes a processor 410 and a memory 420. The memory 420 stores a computer program executable by the processor 410. When the computer program is executed by the processor 410, it performs the steps of the method described above.

[0130] This application embodiment also provides a storage medium 430, on which a computer program is stored. When the computer program is run by the processor 410, the above-described method is executed, which can realize the complete process of the method.

[0131] The storage medium 430 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as Static Random Access Memory (SRAM), Electrically Erasable Programmable Read-Only Memory (EEPROM), Erasable Programmable Read Only Memory (EPROM), Programmable Red-Only Memory (PROM), Read-Only Memory (ROM), magnetic storage, flash memory, magnetic disk, or optical disk.

[0132] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A control method for a grid-connected / grid-connected renewable energy system via an LCC-HVDC, characterized in that, Includes the following steps: S1. Obtain the grid-connected new energy capacity ratio and grid-connected system short-circuit ratio; S2. Calculate the reactive power deficit of the grid-connected system; S3. Obtain the operating mode of the grid-connected system; S4. Construct mathematical models for grid-connected new energy and grid-connected new energy; S5. Obtain the coordinated control strategy for grid-connected new energy and grid-connected new energy; S6. Obtain the high-low voltage transmission control strategy for grid-connected systems.

2. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 1, characterized in that, Grid-connected renewable energy capacity ratio ξ i It is represented as follows: x i =S GFj / S Ti ; In the formula, S Ti S represents the total fixed capacity of new energy sources. GFj The total rated capacity of new energy sources for grid construction; The formula for calculating the short-circuit ratio of a grid-connected system is as follows: In the formula, ML SCR This represents the short-circuit ratio of the grid-connected system; (1-ξ) GFL,i ξ represents the weighting coefficient of the i-th grid-connected new energy source; GFM,j S represents the weighting coefficient of the j-th renewable energy source in the grid; GFL,i S represents the equivalent short-circuit capacity of the i-th grid-connected new energy source; GFM,j S represents the equivalent short-circuit capacity of the j-th grid-connected renewable energy source; total S represents the total capacity of new energy sources; grid This indicates the inherent short-circuit capacity on the power grid side.

3. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 2, characterized in that, The reactive power deficit is calculated as follows: Q q =-Q C +Q L +Q T +Q LCC-HVDC ; In the formula, Q q For the system reactive power deficit, Q C The reactive power for charging transmission lines, Q L Q represents the reactive power loss of the transmission line. T Q represents the reactive power loss of the transformer. LCC-HVDC For the reactive power demand of DC transmission systems; In the formula, P dc It is DC transmission power; α is the converter power factor, α is the rectifier-side firing angle, and μ is the commutation overlap angle.

4. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 3, characterized in that, The critical value of reactive power in a grid-connected system is determined by the following formula: In the formula, ΔQ ML ΔU represents the change in reactive power. ML U represents the voltage change in a grid-connected system. N This indicates the rated voltage of the grid-connected system.

5. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 4, characterized in that, Grid-connected system operating mode: n grid-connected renewable energy sources and m grid-connected renewable energy sources are stepped up by a step-up transformer and then converge at the PCC bus. The grid-connected system converts the converged power into DC power for transmission, and the m grid-connected renewable energy sources provide commutation voltage for the grid-connected system. The n grid-connected renewable energy sources operate in maximum power point tracking mode. Simultaneously, the capacity Q of the grid-connected renewable energy sources is locked out. S =|-Q C +Q L +Q T +Q LCC-HVDC -ΔQ ML As the basis for the blocking capacity of the new energy generator-side converter, the grid-connected / connected new energy needs to calculate the active and reactive power output of the grid-connected new energy based on the light intensity and wind speed using the MPPT module. If the grid-connected new energy unit stops operating, the grid-connected new energy generator-side converter will be blocked, and the grid-side converter will be switched to constant voltage control.

6. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 5, characterized in that, The mathematical model for grid-connected renewable energy control is shown below: In the formula, ω1 and ω n These are the actual and given values ​​of the active power loop output angular frequency, respectively; P ref P and Q represent the given and actual values ​​of active power, respectively; ref Q and J represent the given and actual values ​​of reactive power, respectively; J and D... p These represent the virtual inertia and droop factor of the active loop, respectively; K and D q These are the inertia coefficient and droop coefficient of the reactive power loop, respectively; K i1 U is the reactive power loop integral coefficient; ref U and E are the reference value and amplitude of the output voltage of the grid-type converter, respectively; GF To construct the virtual internal electromotive force of new energy sources in the grid; The mathematical model for mesh control is shown below: In the formula, ω pll ω is the output angular frequency of the phase-locked loop (PLL). g ω1 is the grid angular frequency of the PLL; ω2 is the rated angular frequency; θ is the voltage. pll The output phase of the PLL is s; s is the differential operator, K p.pll and K i,pll These are the proportional coefficient and integral coefficient of the phase-locked loop, respectively.

7. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 6, characterized in that, The collaborative control strategy is represented as follows: Coordinated control of grid-connected new energy and grid-connected new energy can improve the stability and adaptability of grid-connected converters in scenarios with high penetration of new energy. Therefore, weight allocation is carried out according to the capacity ratio of grid-connected new energy, and the weighting coefficient is adaptively adjusted according to the short-circuit ratio of the grid-connected system. When the MLSCR is high, the grid-connected system operates in PLL synchronization-dominated mode; conversely, when the MLSCR is low, the grid-connected system operates in power synchronization-dominated mode. The current signal required by the converter is distributed according to the MLSCR and sent to the grid-connected control calculation unit and the grid-connected control calculation unit respectively. The two control calculation units calculate their respective modulation waves, and finally, the modulation signals of the grid-connected / grid-connected new energy converters are weighted to obtain the switching signal of the converter.

8. The control method for a grid-connected / grid-connected new energy source via an LCC-HVDC grid-connected system according to claim 7, characterized in that, The coordinated high-low voltage transmission control strategy for grid-connected systems is as follows: When a system failure occurs, the maximum output reactive current limit value i of the grid-connected new energy power supply GLqmax for: In the formula, i GLqmax For the active current of the grid-connected converter of new energy power sources; P NS The active power output to the grid by the new energy grid-connected converter; I Lim The maximum allowable current for grid-connected converters of new energy sources; I GLd U represents the d-axis current of the grid-connected converter for new energy sources. g Voltage at the grid connection point for new energy sources; When constructing grid-connected renewable energy power sources, power angle stability must be considered to avoid system instability during faults. The relationship between the output power and power angle of a grid-connected converter is shown below: In the formula, P GM and Q GM These represent the output active and reactive power of the grid converter, respectively; E GM Z is the internal potential of the grid converter; ∑ θ is the synchronous reactance; θ is the Z ∑ The impedance angle; δ is the power angle, which is usually in the range of 0° < δ < 90°; As can be seen from the active current, during a fault, the reactive power output of the grid-connected converter can be changed by increasing the reactive current of the grid-connected renewable energy source along the q-axis, thereby supporting the grid voltage; according to The reactive power deficit of the system is determined by the degree of voltage drop at the fault point, and the reactive power regulation capability of the grid-side converter is used to provide the reactive power required for the continuous operation of the new energy grid-connected system. Using the limiting power angle of 90° as the boundary of the power angle stability of the grid-connected renewable energy system, the power angle stability of the grid-connected renewable energy system during the fault period is judged. If the boundary conditions are met, the grid-connected converter will be switched to a grid-following control mode based on current phasor synchronization, and synchronization will be achieved by tracking the grid voltage through a backup phase-locked loop. Considering the capacity difference between grid-connected and grid-connected renewable energy units, the grid-side reactive power compensation capacity undertaken by grid-connected and grid-connected renewable energy units should be proportionally allocated according to their own capacity, as shown below: In the formula, This indicates the reactive power command value of the grid-connected new energy system. Regarding the transient recovery overvoltage problem of renewable energy, and considering the reactive power of renewable energy connected to the grid / connected grid reaching a voltage of 1.3 per unit (PU) at the grid connection point, as well as the fluctuation characteristics of renewable energy output, which can cause renewable energy disconnection leading to system instability or even collapse, the controller parameters are adjusted online in real time through input and output data to suppress transient overvoltage problems at the millisecond level, as shown below: In the formula, λ is a weighting factor used to limit the variation of the control input; y * (k+1) represents the desired output signal of the system at time k+1; y(k) represents the output signal of the system at time k; u(k) and u(k-1) are the inputs of the system at times k and k-1, respectively; ψ c (k) is the pseudo-partial derivative of the system; ρ∈(0,1] is the step size factor, which mainly makes the control algorithm more general.

9. An electronic device, characterized in that, The system includes a processor, an input device, an output device, and a memory, which are connected in sequence. The memory is used to store a computer program, which includes program instructions. The processor is configured to call the program instructions to execute a control method for a grid-connected / grid-connected new energy system via an LCC-HVDC as described in any one of claims 1-8.

10. A storage medium, characterized in that, The storage medium stores a computer program, which includes program instructions. When executed by a processor, the program instructions cause the processor to perform a control method for a grid-connected / grid-connected new energy system via an LCC-HVDC as described in any one of claims 1-8.

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