Method, system and equipment for controlling low voltage ride through of network-forming converter and medium

Abstract

The invention discloses a low voltage ride through control method, system and device for a network-forming converter and a medium, and the method comprises the steps: collecting the PCC voltage of a grid-connected point of the network-forming converter, and judging the size relation between the PCC voltage and a preset threshold voltage; when the size relation between the PCC voltage and the preset threshold voltage meets the triggering low voltage ride through control condition, the first logic switch S1 is controlled to be switched to 1, and the active power reference value Pref is given again; and meanwhile, the second logic switch S2 and the third logic switch S3 are controlled to be switched to 1, the reactive power reference value Qref is given again, and the PCC voltage is subjected to feedforward operation. The method is not only suitable for single reactive loop control, but also capable of injecting reactive current according to standard low-pass requirements and maintaining network construction characteristics at the same time, has better reactive dynamic response capability and control precision, can realize current sharing among multiple machines, reduces power deviation in a transient process, and improves the reliability of the system. Therefore, the reliable operation of the converter during the low-voltage ride-through period is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of grid-type converter control, and in particular relates to a low voltage ride-through control method, system, device and medium for a grid-type converter. Background Art

[0002] The "dual high" characteristics of future power systems, characterized by a high proportion of renewable energy and a high proportion of power electronic equipment, are becoming increasingly evident. Increasing the proportion of renewable energy generation connected to the power grid through power electronic equipment such as converters has become a top priority for development in the power sector, implying the urgent need for a high degree of power electronics in the power system. To achieve a stable grid-connected renewable energy system, the control design of grid-connected converters must be fully addressed. Currently, there are two basic control modes: current source mode and voltage source mode. However, traditional current source converter control methods cannot support grid voltage and cannot operate independently off-grid, making them difficult to adapt to the "dual high" characteristics of future power systems. Therefore, grid-connected converters with voltage source characteristics, adaptable to various operating conditions, and providing voltage and frequency support for power systems have become a research focus.

[0003] Typical network control can be divided into the outer loop (electromechanical part) and the inner loop (electromagnetic part). For the outer loop, its control methods mainly include droop control and virtual synchronous generator (VSG) control. Its control structure is as follows: Figure 1 As shown in Figure 2. In the active-frequency control component, droop control simulates the droop characteristics of traditional generators to control the system and achieve equal distribution of active and reactive power. However, traditional droop control does not simulate the inertia component, which means it lacks inertial support for the power system. The VSG control strategy simulates the rotor characteristics of synchronous generators and introduces a swing equation into the control equation, thereby adding virtual inertia to the system. This allows the system to provide inertial support to the grid voltage and frequency during sudden changes in operating conditions, thereby suppressing fluctuations. For the inner loop, typical control schemes include control based on the reactive power loop, single-loop control based on voltage amplitude, and control based on voltage / current dual loops. Control based on voltage / current dual loops is widely used due to its better current regulation capability, higher power quality, and better compatibility with grid-following control. However, this control scheme has high model complexity and requires multiple controllers to work together. Grid-connected converters that utilize voltage-reactive power reverse droop and a single reactive inner loop structure have better parameter robustness, lower model complexity, smaller bus voltage offsets, and more balanced reactive power distribution than classical methods. [1] .

[0004] With the rapid development and increasing penetration of renewable energy generation technologies such as wind and photovoltaic power, the inertia and stability of power systems are gradually decreasing, and the dynamic characteristics during grid faults are becoming more complex. In this context, ensuring that the converter can continue to operate on the grid during grid voltage sags or faults while providing the necessary reactive power support has become one of the core technical indicators of grid-connected converters. To address this, domestic and foreign scholars have proposed low-voltage ride-through control strategies suitable for grid-connected converters, which can be roughly divided into the following three categories:

[0005] 1) Switch the control structure to the grid-following mode during the fault period. This type of method is simple to implement. For example, [2] and literature [3] A fault ride-through control strategy based on mode switching is proposed. It can transform the grid-forming control mode into the grid-following control mode during the grid fault period, and return to the voltage control mode after the fault is eliminated, thereby achieving flexible current control during the grid fault period. It has the advantages of simple implementation and significant current limiting effect. However, this control mode switching can cause system oscillation, transient overcurrent and other problems, and it is difficult to quickly restore the stable operation state after the fault is cleared. To improve the stability of the switching process, the literature [4] A reference value memory retention strategy is proposed to achieve smooth switching by saving the operating parameters before the fault and reloading them when the fault is restored. However, this method requires memorizing a large number of physical quantities, making it difficult to apply in practice, and the droop characteristics will be lost during the fault. [5] and literature [6] Transient shocks are reduced by optimizing switching logic, but these methods rely on phase-locked loops (PLLs) to achieve synchronous switching, which introduces additional stability risks under weak grid conditions. [7] .literature [8] While the proposed switch to PQ control mode avoids transient issues, it still fails to address the inherent flaws of the grid-following control mode. While the grid-following mode offers significant advantages in fault current limiting, this control strategy loses its key advantage of voltage support capability and introduces new challenges such as phase-locked loop (PLL) dependency and poor grid stability.

[0006] 2) Low voltage ride-through strategy based on virtual impedance: It aims to limit the fault current by increasing the equivalent output impedance. [9] A fault current limiter based on virtual impedance is proposed, which can effectively suppress overcurrent and eliminate system oscillation, but it does not consider the power angle stability problem during voltage sag.

[10] and literature

[11] They further proposed a virtual impedance design method that comprehensively considers reactive power demand, overcurrent limitation, and power angle stability. This method obtained a feasible domain of virtual impedance values ​​that satisfied multiple constraints. By optimizing the dynamic characteristics of the virtual impedance, they effectively addressed the limitations of traditional virtual impedance optimization in improving transient power angle stability. However, the design process of such methods is relatively complex, and their application in practical engineering projects faces many challenges.

[0007] 3) Low voltage ride-through strategy based on voltage / power reference value adjustment.

[0008] Some studies have focused on the reactive current injection during low voltage ride-through, for example,

[12] and literature

[13] The proposed scheme can adjust the reactive power command according to the standard requirements during low voltage ride-through. Although it can meet the requirements of reactive current injection, it does not fully utilize the overcurrent capacity of the grid-connected converter and cannot achieve the maximum support for the PCC voltage.

[14] Combined voltage regulation and reactive power injection, but its reactive power injection does not comply with the standard requirements and is not specially designed for overcurrent limitation;

[15] A three-phase independent control strategy was proposed. Although it can achieve flexible control, the additional current controller also increases the complexity of the control structure. Another part of the research focuses on the transient stability during low voltage ride-through.

[16] and literature

[17] Power reference optimization ensures power angle stability but insufficient voltage support;

[18] A control strategy to keep the converter in grid-type mode during fault ride-through is proposed, but it cannot cope with asymmetric fault scenarios and has difficulty meeting the maximum allowable current injection requirements;

[19] Extension to asymmetric faults but limited overcurrent control.

[0009] Based on the above discussion, under the existing grid-type converter low voltage ride-through standard system, most grid-type converter low voltage ride-through solutions are difficult to take into account the reactive current injection and grid characteristic maintenance required by the standard, and there is currently no research on the grid-type converter low voltage ride-through control strategy based on single reactive loop control.

[0010] Related Literature:

[0011] [1] J.Liu, H.Bevrani, and T.Ise, "A design-oriented QV response modeling approach for grid-forming distributed generators considering different operation modes," IEEE J.Emerg.Sel.Topics Power Electron., vol.10, no.1, pp.387-401, Feb.2022.

[0012] [2]KOOureilidis and CSDemoulias.A fault clearing method inconverter-dominated microgrids with conventional protection means[J].IEEETransactions on Power Electronics, 2016,31(6):4628–4640.

[0013] [3]H.Wu and

[0014] [4] Fang Zhixue, Su Jianhui, Wang Huafeng, Shi Yong, Xu Huadian. Low voltage ride-through control strategy for microgrid inverters[J]. Automation of Electric Power Systems, 2019, 43(2): 143-149161.

[0015] [5]Chen Tianyi,Chen Laijun and Zheng Tianwen.Low voltage ride throughcontrol method of virtual synchronous generator based on mode smoothswitching[J].Power System Technology,2016,40(7):2134–2140.

[0016] [6]K.Shi,W.Song,P.Xu,R.Liu,Z.Fang and Y.Ji.Low-Voltage Ride-ThroughControl Strategy for a Virtual Synchronous Generator Based on SmoothSwitching[J].IEEE Access,2018,6:2703–2711.

[0017] [7]R.Rosso,M.Andresen,S.Engelken and M.Liserre.Analysis of theinteraction among power converters through their synchronization mechanism[J].IEEE Transactions on Power Electronics,2019,34(12):12321–12332.

[0018] [8]H.Wang,Q.Zhang,D.Wu and J.Zhang.Advanced Current-Droop Control forStorage Converters for Fault Ride-Through Enhancement[J].IEEE Journal ofEmerging and Selected Topics in Power Electronics,2020,8(3):2461–2474.

[0019] [9]

[0020]

[10] Liu Hang, Wang Yue, Liu Yonghui, Peng Yang, Li Mingxuan, Lei Wanjun. VSG low voltage ride-through strategy based on quantitative design of virtual impedance [J]. High Voltage Technology, 2022, 48(1): 245-256

[0021]

[11] M.Li et al.Analysis and Improvement of Large-DisturbanceStability for Grid-Connected VSG Based on Output Impedance Optimization[J]. IEEE Transactions on Power Electronics, 2022, 37(8):9807–9826.

[0022]

[12] MAGarnica López,JLGarcía de J. Miret, M. Castilla and R. Guzmán. Control Strategy for Grid-Connected Three-Phase Inverters During Voltage Sags to Meet Grid Codes and to Maximize Power Delivery Capability[J]. IEEE Transactions on Power Electronics, 2018, 33(11):9360–9374.

[0023]

[13] D.I.Brandao,F.E.G.Mendes,R.V.Ferreira,S.M.Silva andI.A.Pires.Active and Reactive Power Injection Strategies for Three-PhaseFour-Wire Inverters During Symmetrical / Asymmetrical Voltage Sags[J].IEEETransactions on Industry Applications,2019,55(3):2347–2355.

[0024]

[14] W.Si and J.Fang.Transient Stability Improvement of Grid-FormingConverters Through Voltage Amplitude Regulation and Reactive Power Injection[J].IEEE Transactions on Power Electronics,2023,38(10):12116–12125.

[0025]

[15] S.Maganti and N.P.Padhy.An Advanced Control Strategy for a WeakGrid-Connected DG for Enhancing Voltage Support During Co-occurrence of Sagand Swell[J].IEEE Transactions on Power Electronics,2024,39(1):1644–1655.

[0026]

[16] Z.Shuai,C.Shen,X.Liu,Z.Li and Z.J.Shen.Transient angle stabilityof virtual synchronous generators using Lyapunov's direct method[J].IEEETransactions on Smart Grid,2019,10(4):4648–4661.

[0027]

[17] Li Qinghui,Ge Pingjuan,Xiao Fan,et al.Study on fault ride-throughmethod of VSG based on power angle and current flexible regulation[J].Proceedings of the CSEE,2020,40(7):2071–2080,2387.

[0028]

[18] T.Liu,

[0029]

[19] K.Sun, W.Yao, J.Wen and L.Jiang.A Two-Stage Simultaneous ControlScheme for the Transient Angle Stability of VSG Considering CurrentLimitation and Voltage Support[J]. IEEE Transactions on Power Systems, 2022, 37(3):2137–2150. Summary of the Invention

[0030] The purpose of the present invention is to address the problems in the above-mentioned prior art and provide a low voltage ride-through control method, system, equipment and medium for a grid-type converter, which is not only suitable for single reactive loop control, but can also inject reactive current according to standard low voltage ride-through requirements while maintaining grid characteristics, has better reactive dynamic response capability and control accuracy, can achieve current balancing among multiple machines, reduces power deviation in transient processes, and thus ensures reliable operation of the converter during low voltage ride-through.

[0031] In order to achieve the above object, the present invention has the following technical solutions:

[0032] In a first aspect, an embodiment of the present invention provides a low voltage ride-through control method for a grid-connected converter, comprising:

[0033] The PCC voltage of the grid-connected point of the grid-type converter is collected to determine the magnitude relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-type converter is based on VSG control and has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P ref Set the first logic switch S1; the QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part, in the VQ droop part about the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3;

[0034] When the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition, the first logic switch S1 is controlled to switch to 1, and the active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

[0035] As a preferred solution, the preset threshold voltage is 0.85 times the per-unit value; the collected three-phase PCC voltage of the grid-type converter is subjected to Clark transformation, and the PCC voltage amplitude and phase angle are synthesized, and the PCC voltage amplitude is normalized; when the normalized PCC voltage is less than 0.85 times the per-unit value, the low voltage ride-through control condition is met.

[0036] As a preferred solution, the grid-type converter low voltage ride-through control method further includes collecting the three-phase output current of the grid-type converter, performing Clark transformation on the collected three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and normalizing the output current amplitude;

[0037] Active power reference value P ref And reactive power reference value Q ref When re-given, the standard reactive current injection instruction is converted into a reactive power instruction. The standard reactive current injection instruction conforms to the following expression:

[0038]

[0039] Where: I Q is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

[0040] As a preferred solution, the step of converting the standard reactive current injection instruction into a reactive power instruction complies with the national standard requirements, which is "Technical Requirements for Energy Storage Converters of Electrochemical Energy Storage Systems [S]. GB / T34120-2023".

[0041] As a preferred solution, when the QV control part of the grid-type converter adopts single reactive loop control, the reactive power output is adjusted by the Q controller, the single reactive loop control is combined with the low voltage ride-through standard requirements, and a mapping relationship between reactive power and reactive current in the single reactive loop control is established;

[0042] In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as:

[0043] Q out =V d I q -V q I d =V pcc I q

[0044] The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is:

[0045] Q out =V α I β -V β I α

[0046] If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows:

[0047] Q out =V α I β -V β I α .

[0048] As a preferred solution, the active power reference value P ref And reactive power reference value Q ref When re-given, follow the following expression:

[0049]

[0050] Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point;

[0051] By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

[0052] As a preferred solution, the P-ω control part of the grid-type converter can ensure that the grid-type converter maintains transient stability during a grid voltage drop;

[0053] The QV control part of the grid-type converter can ensure that the grid-type converter provides sufficient reactive power support according to the voltage drop degree to meet the standard requirements.

[0054] As a preferred solution, during the low voltage ride-through period, the actual voltage per unit value V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

[0055] As a preferred solution, the virtual impedance part of the grid-type converter performs overcurrent protection, and the introduced virtual impedance includes two parts: a virtual resistance and a virtual inductance.

[0056] As a preferred solution, the grid-type converter low voltage ride-through control method is suitable for multi-machine coordinated low voltage ride-through, achieving current balancing among multiple machines without relying on communication, and reducing power deviation during transient processes.

[0057] In a second aspect, a grid-type converter low voltage ride-through control system is provided, comprising:

[0058] The grid-connected point voltage acquisition and logic switch setting module is used to collect the grid-connected point PCC voltage of the grid-connected converter and judge the size relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-connected converter is based on VSG control and has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P refSet the first logic switch S1; the QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part, in the VQ droop part about the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3;

[0059] The logic switch switching and low voltage ride-through module is used to control the first logic switch S1 to switch to 1 when the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition. The active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

[0060] As a preferred solution, the threshold voltage preset for the logic switch switching and low voltage ride-through module is 0.85 times the per-unit value;

[0061] The grid connection point voltage acquisition and logic switch setting module performs Clark transformation on the collected three-phase PCC voltage of the grid-connected converter, synthesizes the PCC voltage amplitude and phase angle, and performs per-unit processing on the PCC voltage amplitude;

[0062] When the logic switch switching and low voltage ride-through module determines that the PCC voltage after per-unit processing is less than 0.85 times the per-unit value, the low voltage ride-through control condition is triggered.

[0063] As a preferred solution, the grid-type converter low voltage ride-through control system further includes a three-phase output current acquisition module for acquiring the three-phase output current of the grid-type converter, performing Clark transformation on the acquired three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and normalizing the output current amplitude; the logic switch switching and low voltage ride-through module re-sets the active power reference value P ref and reactive power reference value Q ref When the standard reactive current injection instruction is converted into a reactive power instruction, the standard reactive current injection instruction conforms to the following expression:

[0064]

[0065] Where: I Q is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

[0066] As a preferred solution, the logic switch switching and low voltage ride-through module converts the standard reactive current injection instruction into a reactive power instruction in accordance with the national standard requirements, which are "Technical Requirements for Energy Storage Converters of Electrochemical Energy Storage Systems [S]. GB / T 34120-2023".

[0067] As a preferred solution, the logic switch switching and low voltage ride-through module, when the QV control part of the grid-type converter adopts single reactive loop control, adjusts the reactive power output through the Q controller, combines the single reactive loop control with the low voltage ride-through standard requirements, and establishes a mapping relationship between reactive power and reactive current in the single reactive loop control;

[0068] In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as:

[0069] Q out =V d I q -V q I d =V pcc I q

[0070] The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is:

[0071] Q out =V α I β -V β I α

[0072] If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows:

[0073] Q out =V α I β -V β I α .

[0074] As a preferred solution, the logic switch switching and low voltage ride-through module re-set the active power reference value P according to the following expression ref And reactive power reference value Q ref:

[0075]

[0076] Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point;

[0077] By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

[0078] As a preferred solution, the logic switch switches and the low voltage ride-through module changes the actual voltage per unit value V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

[0079] In a third aspect, an electronic device is provided, comprising a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement the low voltage ride-through control method for a grid-type converter.

[0080] In a fourth aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the low voltage ride-through control method of the grid-type converter is implemented.

[0081] Compared with the prior art, the first aspect of the present invention has at least the following beneficial effects:

[0082] The low voltage ride-through control method for a grid-type converter proposed in the present invention enables the grid-type converter to achieve stable power regulation during the low voltage ride-through process, while maintaining the grid characteristics and accurately injecting reactive current. The method of the present invention is not only applicable to single reactive loop control, but can also inject reactive current in accordance with standard low voltage ride-through requirements while maintaining grid characteristics. Compared to traditional methods, the method of the present invention has superior reactive dynamic response capability and control accuracy, can achieve current balancing among multiple machines, and reduce power deviation during transient processes, thereby ensuring the reliable operation of the converter during low voltage ride-through.

[0083] Furthermore, the reactive current injection requirements during low voltage ride-through required by the national standard are equivalently converted into reactive power requirements, which not only ensures that reactive current is injected according to the standard reactive injection requirements during low voltage ride-through, but also solves the compatibility problem between the reactive current injection requirements and the single reactive loop control.

[0084] Furthermore, through precise reactive power injection strategies, voltage support is continuously provided to the grid during low voltage ride-through, effectively maintaining the grid-forming operation characteristics of the converter and enhancing the stability of the system in fault conditions.

[0085] Furthermore, due to the use of PCC voltage feedforward and single reactive loop control, the reactive response speed is accelerated. Compared with traditional methods, the method of the present invention has better reactive dynamic response capability and control accuracy.

[0086] Furthermore, by resetting the power reference value of the converter according to the PCC voltage during low voltage ride-through, the control method of the present invention can be effectively extended to collaborative low voltage ride-through between multiple machines, and current balancing between multiple machines can be achieved without relying on communication, thereby reducing power deviation during transient processes.

[0087] It can be understood that the beneficial effects of the second to fourth aspects mentioned above can be found in the relevant description of the first aspect mentioned above, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0088] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments or descriptions of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0089] Figure 1 This is a typical control structure diagram of a grid-type converter;

[0090] Figure 2 The schematic diagram of the P-ω control structure of a typical control scheme for a grid-type converter is shown in Figure 2.

[0091] Figure 3 The schematic diagram of the QV control structure of a typical control scheme for a grid-type converter is shown below.

[0092] Figure 4 This is a schematic diagram of the structure of the P-ω control part of the low voltage ride-through control method for a grid-type converter according to an embodiment of the present invention;

[0093] Figure 5 This is a schematic structural diagram of the QV control part of the low voltage ride-through control method for a grid-type converter according to an embodiment of the present invention;

[0094] Figure 6(a) is a simulation circuit diagram of a voltage drop occurring when a single grid-connected converter is connected to the grid;

[0095] Figure 6(b) is a simulation circuit diagram of a voltage drop in a grid-type converter system with two parallel machines;

[0096] FIG7( a ) is a comparison curve of the dynamic characteristics of the method according to the embodiment of the present invention and the existing method when the voltage drops to 0.7 pu under the condition of single machine grid connection when the short circuit ratio SCR=11;

[0097] FIG7( b ) is a comparison curve of the dynamic characteristics of the method according to the embodiment of the present invention and the existing method when the voltage drops to 0.3 pu under the condition of single machine grid connection when the short circuit ratio SCR=11;

[0098] FIG8( a ) is a comparison curve of the dynamic characteristics of the method according to the embodiment of the present invention and the existing method when the voltage drops to 0.7 pu under the condition of a single machine connected to the grid with a short circuit ratio SCR=2;

[0099] FIG8( b ) is a comparison curve of the dynamic characteristics of the method according to the embodiment of the present invention and the existing method when the voltage drops to 0.3 pu under the condition of single machine grid connection when the short circuit ratio SCR=2;

[0100] FIG9( a ) is a graph showing the dynamic response characteristics of the method according to an embodiment of the present invention when the voltage drops to 0.7 pu under the grid-connected condition of a dual-machine parallel grid-connected converter system with a short-circuit ratio SCR=11;

[0101] FIG9( b ) is a graph showing the dynamic response characteristics of the method according to an embodiment of the present invention when the voltage drops to 0.3 pu under the grid-connected condition of a dual-machine parallel grid-connected converter system with a short-circuit ratio SCR=11;

[0102] FIG10( a ) is a graph showing the dynamic response characteristics of a method according to an embodiment of the present invention when the voltage drops to 0.7 pu under the grid-connected condition of a dual-machine parallel grid-connected converter system with a short-circuit ratio SCR=2;

[0103] FIG10( b ) is a dynamic response characteristic curve diagram of the method according to an embodiment of the present invention when the voltage drops to 0.3 pu under the grid-connected condition of the dual-machine parallel grid-connected converter system with a short-circuit ratio SCR=2.

[0104] Parameter explanation:

[0105] E ref -virtual internal potential; L tran 、R subtran - Transient virtual current limiting inductor, sub-transient virtual current limiting resistor;

[0106] P0-active power command; P in -Virtual shaft power; P out- Output active power;

[0107] S base -Rated capacity; V base -Rated voltage; V pcc -PCC voltage;

[0108] X ls 、X f 、X line -Virtual reactance, filter reactance, line reactance;

[0109] ω0-rated angular frequency; ω m -virtual rotor angular frequency; I out - output current;

[0110] P ref - Active power reference value; P' ref - Active power reference value during low voltage ride-through;

[0111] Q ref -Reactive power reference value; Q' ref -Reactive power reference value during low voltage ride-through. DETAILED DESCRIPTION

[0112] In the following description, specific details such as specific system structures and techniques are provided for purposes of illustration rather than limitation to facilitate a thorough understanding of the embodiments of the present application. However, it will be apparent to those skilled in the art that the present application may be implemented in other embodiments without these specific details. In other cases, detailed descriptions of well-known systems, devices, circuits, and methods are omitted to avoid obscuring the description of the present application with unnecessary detail.

[0113] With the rapid development and increasing penetration of renewable energy generation technologies such as wind and photovoltaic power, the inertia and stability of power systems are gradually decreasing, and the dynamic characteristics of grid faults are becoming more complex. In this context, low voltage ride-through (LVRT) capability—ensuring the converter's continued grid-connected operation during grid voltage sags or faults while providing necessary reactive power support—has become a core technical requirement for grid-connected converters. Existing research on LVRT control strategies primarily focuses on three technical approaches, each with its own unique characteristics but significant limitations. Mode switching (grid-connected / grid-following switching), while offering a simple control structure and ease of current limiting, faces inherent drawbacks such as switching transients, stability risks, and loss of voltage support capability. Virtual impedance technology, while achieving overcurrent suppression through impedance adjustment, suffers from limitations in reactive current injection and engineering applicability. Voltage / power reference value adjustment strategies, while maintaining grid-connected characteristics, face challenges such as current limiting and standard reactive current injection. These studies highlight a core dilemma facing current LVRT technologies in grid-connected converters: how to balance standard reactive current injection with maintaining grid-connected characteristics. Furthermore, most research focuses on voltage / current dual-loop control, lacking research on low voltage ride-through (LVRT) for grid-connected converters based on a single reactive loop. Therefore, the present invention combines the standard reactive current injection requirements for LVRT with single reactive loop control to propose a LVRT control strategy for grid-connected converters that balances standard reactive current injection with maintaining grid characteristics.

[0114] This invention proposes a method for controlling low voltage ride-through of a grid-type converter, guided by a method for controlling reactive current injection and grid-forming characteristics that can take into account both the standard requirements and the maintenance of grid-forming characteristics. The method of the invention is not only applicable to single reactive loop control, but can also inject reactive current according to standard low voltage ride-through requirements while maintaining grid-forming characteristics. Compared to traditional methods, the method of the invention has superior reactive dynamic response capability and control accuracy, can achieve current balancing among multiple machines, and reduces power deviation during transient processes, thereby ensuring the reliable operation of the converter during low voltage ride-through.

[0115] Typical control schemes for grid-type converters are as follows: Figure 1 The P-ω control part is based on VSG control, including speed regulator, virtual inertia and virtual damping term based on state feedback control, as shown in Figure 2 The QV control part includes VQ droop and reactive power loop-based control, as shown in Figure 3 As shown. Since the power line between the converter and the public bus of the power grid is mainly resistive and inductive, power coupling problems will occur. Therefore, it is necessary to add a virtual inductor L lsAdjust the line impedance characteristics to make it inductive, thereby achieving decoupling control between active and reactive power. Since a voltage drop will be generated on the added virtual inductor, the final modulation voltage V pwm The virtual internal potential E is required minus the voltage drop across the virtual inductor.

[0116] See also Figure 4 and Figure 5 The low voltage ride-through control method of a grid-connected converter according to an embodiment of the present invention mainly includes:

[0117] S1, collect the PCC voltage of the grid-connected point of the grid-type converter, and judge the relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-type converter is based on VSG control, which has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P ref Set the first logic switch S1; the QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part, in the VQ droop part about the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3;

[0118] S2: When the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition, the first logic switch S1 is controlled to switch to 1, and the active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

[0119] The PCC (Point of Common Connection) is typically the interface between the power system and the load. The PCC voltage, or voltage level at this interface, is directly related to the stability of the power system and the quality of power supply to the load. The stability of the PCC voltage is crucial to the operation of the power system. Voltage fluctuations or sags can lead to serious consequences, such as equipment damage and production interruptions. Therefore, proper voltage control and management are essential to ensure PCC voltage stability and safe operation in the power system.

[0120] In the field of motor control, P-ω control (usually referring to speed-power or speed-torque control) is often combined with PWM (pulse width modulation) technology. P-ω control regulates the motor's speed or power, while PWM technology achieves precise voltage or current output. P-ω control controls the output power (P) by adjusting the motor's speed (ω). In permanent magnet synchronous motors (PMSMs), speed regulation is often combined with field-of-control (FOC) technology. This decomposes the motor's current into its excitation and torque components, enabling independent control of speed and torque.

[0121] The QV control strategy is based on the reactive-voltage (QV) relationship. QV control adjusts the system's reactive power according to the voltage level at the network connection point, exhibiting QV characteristics. Its core objective is to maintain voltage stability at the point of common connection (PCC) by regulating reactive power output. For example, when the voltage drops, the system increases reactive power output to boost the voltage; conversely, when the voltage drops, reactive power is reduced. This control approach is closely related to the reactive-voltage droop characteristic of droop control. By simulating the regulation characteristics of synchronous generators, it achieves a dynamic balance between voltage and reactive power.

[0122] In one possible implementation, the threshold voltage preset in the embodiment of the present invention is 0.85 times the per-unit value. Clark transform is performed on the collected three-phase PCC voltage of the grid-connected converter to synthesize the PCC voltage amplitude and phase angle, and the PCC voltage amplitude is normalized. When the normalized PCC voltage is less than 0.85 times the per-unit value (per unit, pu), the low voltage ride-through control condition is triggered. Per-unit value is a relative unit system used in power system analysis and calculations.

[0123] The per-unit value is the ratio of an actual physical quantity to its reference value (or rated value) and is dimensionless.

[0124] In one possible implementation, the low voltage ride-through control method for a grid-type converter according to an embodiment of the present invention further includes collecting the three-phase output current of the grid-type converter, performing Clark transformation on the collected three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and normalizing the output current amplitude.

[0125] The Clark transform (also known as the αβ transform) is a commonly used coordinate transformation method in fields such as motor control and power system analysis. It converts physical quantities (such as voltage and current) in a three-phase stationary coordinate system (abc) to a two-phase stationary coordinate system (αβ). Its core purpose is to simplify the analysis and control of three-phase systems and decouple the three-phase coupled variables into two independent variables.

[0126] Furthermore, the step of converting the standard reactive current injection instruction into a reactive power instruction in the embodiment of the present invention complies with the national standard requirements, which is "Technical Requirements for Energy Storage Converters of Electrochemical Energy Storage Systems [S]. GB / T 34120-2023".

[0127] In order to utilize the reactive power support capability of grid-type converters during low voltage ride-through, the national standard "Technical Requirements for Energy Storage Converters for Electrochemical Energy Storage Systems [S]. GB / T 34120-2023" puts forward clear requirements for reactive current injection.

[0128] The active power reference value P in the embodiment of the present invention ref And reactive power reference value Q ref When re-given, the standard reactive current injection instruction is converted into a reactive power instruction. The standard reactive current injection instruction conforms to the following expression:

[0129]

[0130] Where: I Q is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

[0131] When the QV control portion of the grid-type converter adopts single reactive loop control, precise regulation of reactive power output is achieved through the Q controller, which has the inherent advantages of fast reactive response and accurate command following compared to other solutions. However, the single reactive loop control scheme is based on the αβ coordinate system for physical quantity decomposition and control, and it lacks a clear q-axis current component similar to the dq coordinate system to directly represent the reactive current. Therefore, it is necessary to combine single reactive loop control with the requirements of the low voltage ride-through standard by establishing a mapping relationship between reactive power and reactive current in the single reactive loop control.

[0132] In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as:

[0133] Q out βV d I q -V q I d βV pcc I q

[0134] The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is:

[0135] Q out =V α I β -V β I α

[0136] If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows:

[0137] Q out =V α I β -V β I α

[0138] Therefore, combined with the requirements of the low voltage ride-through standard, the active power reference value P of the grid-connected converter based on single reactive loop control during the low voltage ride-through period is ref And reactive power reference value Q ref When re-given, follow the following expression:

[0139]

[0140] Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point;

[0141] By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

[0142] The P-ω control part of the current-given grid-type converter low voltage ride-through control method proposed in the embodiment of the present invention is as follows: Figure 4 As shown in the figure, it ensures that the converter can maintain transient stability during grid voltage sag; the QV control part is as follows Figure 5 As shown, this ensures that the converter can provide sufficient reactive power support according to the degree of voltage drop to meet the standard requirements.

[0143] In a possible implementation, during the low voltage ride-through period, the actual voltage per unit value V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

[0144] In a possible implementation, a virtual impedance part of the grid-type converter performs overcurrent protection, and the introduced virtual impedance includes two parts: a virtual resistor and a virtual inductor, which are integrated into the virtual impedance part of the reactive-voltage control link.

[0145] Through the low voltage ride-through control method for a grid-type converter according to the embodiment of the present invention, the grid-type converter can achieve stable power regulation during the low voltage ride-through process, taking into account both the maintenance of the grid characteristics and the accurate injection of reactive current. pcc As a feedforward compensation to increase the response speed of the reactive power loop, it is worth noting that in actual systems, direct measurement of the PCC voltage is difficult due to the distance of the transmission line. Therefore, the PCC voltage estimation method is applied in the control to improve the adaptability of the control and measurement reliability. If the actual system has high-precision PCC voltage measurement capabilities, the measured data can be directly used instead of the estimated value to further improve control accuracy and dynamic performance.

[0146] The technical advantages of the grid-type converter low voltage ride-through control method of the present invention are: 1. It converts the reactive current injection requirement during low voltage ride-through, as required by the national standard, into a reactive power requirement. This not only ensures that reactive current is injected according to the standard reactive injection requirement during low voltage ride-through, but also resolves the compatibility issue between the reactive current injection requirement and single reactive loop control. 2. Through a precise reactive power injection strategy, voltage support is continuously provided to the grid during low voltage ride-through, effectively maintaining the grid-type operating characteristics of the converter and enhancing system stability under fault conditions. 3. Due to the use of PCC voltage feedforward and single reactive loop control, the reactive power response speed is further accelerated. Compared with traditional methods, the present invention method has superior reactive dynamic response capability and control accuracy. 4. By resetting the converter power reference value based on the PCC voltage during low voltage ride-through, the present invention method can be effectively extended to coordinated low voltage ride-through between multiple machines, achieving current balancing between multiple machines without relying on communication, and reducing power deviation during transient processes.

[0147] Another embodiment of the present invention further provides a grid-connected converter low voltage ride-through control system, comprising:

[0148] The grid-connected point voltage acquisition and logic switch setting module is used to collect the grid-connected point PCC voltage of the grid-connected converter and judge the size relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-connected converter is based on VSG control and has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P ref Set the first logic switch S1; the QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part, in the VQ droop part about the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3;

[0149] The logic switch switching and low voltage ride-through module is used to control the first logic switch S1 to switch to 1 when the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition. The active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

[0150] In one possible implementation, the threshold voltage preset by the logic switch switching and low voltage ride-through module is 0.85 times the per-unit value; the grid connection point voltage acquisition and logic switch setting module performs Clark transformation on the collected three-phase PCC voltage of the grid-connected converter, synthesizes the PCC voltage amplitude and phase angle, and performs per-unit processing on the PCC voltage amplitude;

[0151] When the logic switch switching and low voltage ride-through module determines that the PCC voltage after per-unit processing is less than 0.85 times the per-unit value, the low voltage ride-through control condition is triggered.

[0152] In a possible embodiment, the grid-type converter low voltage ride-through control system further includes a three-phase output current acquisition module for acquiring the three-phase output current of the grid-type converter, performing Clark transformation on the acquired three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and normalizing the output current amplitude; the logic switch switching and low voltage ride-through module re-sets the active power reference value P ref and reactive power reference value Q ref When the standard reactive current injection instruction is converted into a reactive power instruction, the standard reactive current injection instruction conforms to the following expression:

[0153]

[0154] Where: IQ is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

[0155] In one possible implementation, the logic switch switching and low voltage ride-through module converts the standard reactive current injection instruction into a reactive power instruction in accordance with the national standard requirements, which are "Technical Requirements for Energy Storage Converters for Electrochemical Energy Storage Systems [S]. GB / T 34120-2023".

[0156] In one possible implementation, the logic switch switching and low voltage ride-through module, when the QV control part of the grid-type converter adopts single reactive loop control, adjusts the reactive power output through the Q controller, combines the single reactive loop control with the low voltage ride-through standard requirements, and establishes a mapping relationship between reactive power and reactive current in the single reactive loop control;

[0157] In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as:

[0158] Q out =V d I q -V q I d =V pcc I q

[0159] The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is:

[0160] Q out =V α I β -V β I α

[0161] If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows:

[0162] Q out =V α I β -V β Iα .

[0163] In a possible implementation, the logic switch switching and low voltage ride-through module resets the active power reference value P according to the following expression: ref And reactive power reference value Q ref :

[0164]

[0165] Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point;

[0166] By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

[0167] In a possible implementation, the logic switch switching and low voltage ride-through module converts the actual voltage per unit value V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

[0168] Through the control strategy proposed in the embodiment of the present invention, the grid-type converter can achieve stable power regulation during the low voltage ride-through process, taking into account both the maintenance of grid characteristics and accurate reactive current injection. pcc As feedforward compensation to increase the response speed of the reactive power loop. In actual systems, due to the influence of the distance of the transmission line, it is difficult to directly measure the PCC voltage, so PCC voltage estimation is used in the control to improve the adaptability of the control and the reliability of the measurement. If the actual system has high-precision PCC voltage measurement capabilities, the measured data can be directly used instead of the estimated value to improve the control accuracy and dynamic performance. In addition, to ensure the safe operation of the system under complex working conditions, a precise current limiting strategy based on fuzzy-regulated adaptive virtual impedance is integrated into the reactive-voltage control. This collaborative control scheme enables the grid-type converter to have stronger overcurrent protection capabilities while meeting the low voltage ride-through requirements, providing double guarantees for its reliable operation.

[0169] The embodiments of the present invention are not only applicable to single reactive loop control but can also inject reactive current in accordance with standard low-throughput requirements while maintaining grid-connected characteristics. Figures 7(a), 7(b) and 8(a), 8(b) show a comparison of the dynamic characteristics of the present invention's embodiment with existing methods when the voltage drops to 0.7 pu and 0.3 pu under single-machine grid-connected conditions with short-circuit ratios SCR = 11 and SCR = 2. Compared to traditional methods, the present invention's embodiment has superior reactive dynamic response capability and control accuracy.

[0170] Please refer to Figures 7(a) and 7(b). It can be seen from the figures that under strong grid conditions, when the grid voltage drops to 0.7 pu, the proposed low voltage ride-through control strategy outperforms existing methods in terms of reactive dynamic response speed and can accurately inject reactive current in strict accordance with LVRT standards. When the grid voltage drops to 0.3 pu, the reactive regulation capability of the existing control strategy further deteriorates, requiring a longer regulation time. In contrast, the strategy proposed in the present invention can still maintain a fast reactive dynamic response speed under more severe grid voltage drop conditions while ensuring accurate reactive current injection.

[0171] Refer to Figures 8(a) and 8(b). As can be seen from the figures, under weak grid conditions, when the grid voltage drops to 0.7 pu, the reactive power dynamic response speed of the existing control strategy decreases further compared to strong grid conditions, and overshoot occurs prematurely during reactive power regulation. As shown in the figure, when the grid voltage further drops to 0.3 pu, although overshoot decreases, the regulation time increases and control accuracy deviates, resulting in the PCC voltage being unable to be supported in a timely manner. However, the control strategy proposed in this invention is not affected by changes in grid strength.

[0172] As shown in Figures 9(a), 9(b) and 10(a), 10(b), the dynamic response characteristic curves of the method of the embodiment of the present invention when the voltage drops to 0.7pu and 0.3pu under the grid-connected conditions of a dual-machine parallel grid-connected converter system are shown when the short-circuit ratio SCR = 11 and SCR = 2. The simulation results further demonstrate that the low voltage ride-through control strategy proposed in the embodiment of the present invention is not only applicable to the low voltage ride-through scenario of a single grid-connected converter, but can also be effectively expanded to the coordinated low voltage ride-through of two converters of different capacities. Both grid-connected converters can inject reactive current according to the low voltage ride-through standard, while ensuring the precise distribution of reactive power between the two converters and eliminating transient differences.

[0173] Another embodiment of the present invention further provides an electronic device, including a processor and a memory, wherein the processor is configured to execute a computer program stored in the memory to implement the grid-connected converter low voltage ride-through control method.

[0174] Another embodiment of the present invention further provides a computer-readable storage medium, wherein the computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the low voltage ride-through control method of the grid-type converter is implemented.

[0175] The computer program includes computer program code, which may be in source code form, object code form, executable file or some intermediate form. The computer-readable storage medium may include: any entity or device, medium, USB flash drive, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electric carrier signal, telecommunication signal and software distribution medium that can carry the computer program code. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals. For ease of explanation, the above content only shows the part related to the embodiment of the present invention. For specific technical details not disclosed, please refer to the method part of the embodiment of the present invention. The computer-readable storage medium is non-transitory and can be stored in a storage device formed by various electronic devices, and can implement the execution process recorded in the method of the embodiment of the present invention.

[0176] Those skilled in the art will appreciate that embodiments of the present invention may be provided as methods, systems, or computer program products. Thus, the present invention may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention may take the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0177] The present invention is described with reference to flowcharts and / or block diagrams of methods, devices (systems) and computer program products according to embodiments of the present invention. It should be understood that each process and / or block in the flowcharts and / or block diagrams, as well as combinations of processes and / or blocks in the flowcharts and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowcharts and / or block diagrams. Figure 1 a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0178] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0179] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0180] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, ordinary technicians in the field should understand that the specific implementation methods of the present invention can still be modified or replaced by equivalents. Any modification or equivalent replacement that does not depart from the spirit and scope of the present invention should be covered by the scope of protection of the claims of the present invention.

Claims

1. A low voltage ride-through control method for a grid-connected converter, characterized in that: include: The PCC voltage of the grid-connected point of the grid-type converter is collected to determine the magnitude relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-type converter is based on VSG control and has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P ref Setting a first logic switch S1; The QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part. In the VQ droop part, the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3; When the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition, the first logic switch S1 is controlled to switch to 1, and the active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

2. The low voltage ride-through control method for a grid-connected converter according to claim 1, characterized in that: The preset threshold voltage is 0.85 times the per-unit value; Clark transformation is performed on the collected three-phase PCC voltage of the grid-type converter, and the PCC voltage amplitude and phase angle are synthesized, and the PCC voltage amplitude is normalized; When the normalized PCC voltage is less than 0.85 times the per-unit value, the low voltage ride-through control condition is met.

3. The low voltage ride-through control method for a grid-connected converter according to claim 2, characterized in that: The method also includes collecting the three-phase output current of the grid-type converter, performing Clark transformation on the collected three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and performing per-unit processing on the output current amplitude; Active power reference value P ref And reactive power reference value Q ref When re-given, the standard reactive current injection instruction is converted into a reactive power instruction. The standard reactive current injection instruction conforms to the following expression: Where: I Q is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

4. The low voltage ride-through control method for a grid-connected converter according to claim 3, characterized in that: The step of converting the standard reactive current injection instruction into a reactive power instruction complies with the national standard requirements, which is "Technical Requirements for Energy Storage Converters for Electrochemical Energy Storage Systems [S]. GB / T 34120-2023".

5. The low voltage ride through control method for a grid-connected converter according to claim 3, characterized in that: When the QV control part of the grid-type converter adopts single reactive loop control, the reactive power output is adjusted by the Q controller, the single reactive loop control is combined with the low voltage ride-through standard requirements, and a mapping relationship between reactive power and reactive current in the single reactive loop control is established; In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as: Q out βV d I q -V q I d βV pcc I q The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is: Q out =V α I β -V β I α If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows: Q out =V α I β -V β I α 。 6. The low voltage ride-through control method for a grid-connected converter according to claim 5, characterized in that: The active power reference value P ref And reactive power reference value Q ref When re-given, follow the following expression: Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point; By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

7. The low voltage ride through control method for a grid-connected converter according to claim 1, characterized in that: The P-ω control part of the grid-type converter can ensure that the grid-type converter maintains transient stability during the grid voltage drop; The QV control part of the grid-type converter can ensure that the grid-type converter provides sufficient reactive power support according to the voltage drop degree to meet the standard requirements.

8. The low voltage ride through control method for a grid-connected converter according to claim 1, characterized in that: During the low voltage ride-through period, the actual voltage per unit value of the grid connection point is V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

9. The low voltage ride through control method for a grid-connected converter according to claim 1, characterized in that: The virtual impedance part of the grid-type converter performs overcurrent protection, and the introduced virtual impedance includes two parts: a virtual resistance and a virtual inductance.

10. The low voltage ride through control method for a grid-connected converter according to claim 1, characterized in that: It is suitable for multi-machine coordinated low-power consumption, and can achieve current balancing among multiple machines without relying on communication, thereby reducing power deviation during transient processes.

11. A grid-type converter low voltage ride-through control system, characterized in that: include: The grid-connected point voltage acquisition and logic switch setting module is used to collect the grid-connected point PCC voltage of the grid-connected converter and judge the size relationship between the PCC voltage and the preset threshold voltage. The P-ω control part of the grid-connected converter is based on VSG control and has a speed regulator, a swing equation and a damping part. In the speed regulator part, the active power reference value P ref Setting a first logic switch S1; The QV control part of the grid-type converter includes PCC voltage estimation, VQ droop, Q controller and virtual impedance part. In the VQ droop part, the reactive power reference value Q ref Set the second logic switch S2, about the rated voltage V of the Q controller base Setting a third logic switch S3; The logic switch switching and low voltage ride-through module is used to control the first logic switch S1 to switch to 1 when the magnitude relationship between the PCC voltage and the preset threshold voltage meets the low voltage ride-through control condition. The active power reference value P ref Reset; at the same time, control the second logic switch S2 and the third logic switch S3 to switch to 1, the reactive power reference value Q ref Reset and feed forward the PCC voltage.

12. The grid-type converter low voltage ride-through control system according to claim 11, characterized in that: The threshold voltage of the logic switch switching and low voltage ride-through module is preset to 0.85 times the per unit value; The grid connection point voltage acquisition and logic switch setting module performs Clark transformation on the collected three-phase PCC voltage of the grid-connected converter, synthesizes the PCC voltage amplitude and phase angle, and performs per-unit processing on the PCC voltage amplitude; When the logic switch switching and low voltage ride-through module determines that the PCC voltage after per-unit processing is less than 0.85 times the per-unit value, the low voltage ride-through control condition is triggered.

13. The grid-type converter low voltage ride-through control system according to claim 12, characterized in that: It also includes a three-phase output current acquisition module for collecting the three-phase output current of the grid-type converter, performing Clark transformation on the collected three-phase output current of the grid-type converter, synthesizing the output current amplitude and phase angle, and normalizing the output current amplitude; the logic switch switching and low voltage ride-through module is used to re-set the active power reference value P ref and reactive power reference value Q ref When the standard reactive current injection instruction is converted into a reactive power instruction, the standard reactive current injection instruction conforms to the following expression: Where: I Q is the reactive current per unit value that the grid-type converter needs to output, I N is the per-unit value of the rated output current of the AC port of the grid-type converter, V pcc It is the per-unit value of the actual voltage at the grid connection point.

14. The grid-type converter low voltage ride-through control system according to claim 13, characterized in that: The logic switch switching and low voltage ride-through module converts the standard reactive current injection instruction into a reactive power instruction in accordance with the national standard requirements, which are "Technical Requirements for Energy Storage Converters for Electrochemical Energy Storage Systems [S]. GB / T 34120-2023".

15. The grid-type converter low voltage ride-through control system according to claim 13, characterized in that: When the QV control part of the grid-type converter adopts single reactive loop control, the Q controller is used to adjust the reactive power output, combining the single reactive loop control with the low voltage ride-through standard requirements, and establishing a mapping relationship between reactive power and reactive current in the single reactive loop control. In the synchronously rotating dq coordinate system, it is assumed that the d-axis is aligned with the PCC voltage vector, that is, V d =V pcc , V q =0, the reactive power injected into PCC is expressed as: Q out =V d I q -V q I d =V pcc I q The synchronous rotating dq coordinate system is converted to the two-phase stationary αβ coordinate system through Park inverse transformation. At this time, the reactive power expression injected into the PCC voltage is: Q out =V α I β -V β I α If the voltage vector falls completely on the α axis, the direction of the reactive current is the same as V pcc The phasor direction is 90°, that is, V α =V pcc , V β =0, then the simplified relationship is as follows: Q out =V α I β -V β I α 。 16. The grid-type converter low voltage ride-through control system according to claim 15, characterized in that: The logic switch switching and low voltage ride-through module resets the active power reference value P according to the following expression ref And reactive power reference value Q ref : Where: Q ref With P ref are the reactive power reference value and active power reference value of the grid-connected converter at rated operation, Q′ ref and P′ ref are the reactive power reference value and active power reference value of the grid-type converter during low voltage ride-through, S base is the rated capacity of the grid-type converter, V pcc is the per-unit voltage of the actual grid connection point; By giving active power command values ​​and reactive power command values ​​of the grid-connected converter during the low voltage ride-through period corresponding to different grid-connected point voltage amplitudes, the grid-connected converter outputs power according to the re-given commands.

17. The grid-type converter low voltage ride-through control system according to claim 11, characterized in that: During the low voltage ride-through period, the logic switch switching and low voltage ride-through module will set the actual voltage per unit value V pcc Feedforward compensation is applied to the reactive-voltage control link to synthesize a new virtual internal potential, thereby speeding up the response of the reactive control loop.

18. An electronic device, characterized in that: The method comprises a processor and a memory, wherein the processor is used to execute a computer program stored in the memory to implement the low voltage ride-through control method of the grid-type converter according to any one of claims 1 to 10.

19. A computer-readable storage medium, characterized in that The computer-readable storage medium stores at least one instruction, and when the at least one instruction is executed by a processor, the low voltage ride-through control method for a grid-type converter according to any one of claims 1 to 10 is implemented.

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