Voltage source network construction control method for enhancing asymmetric fault ride-through of new energy cluster

Abstract

The application belongs to the technical field of voltage source network construction control, and provides a voltage source network construction control method for enhancing asymmetric fault ride-through of new energy clusters, which comprises the following steps: constructing a new energy cluster grid-connected system and configuring a grid-side converter control framework; designing a network construction control outer ring to realize active support for the power grid through a frequency ring and a reactive power ring; designing a virtual impedance adaptive adjustment mechanism to dynamically correct a voltage reference value according to a current deviation; performing positive and negative sequence coordinated control to realize accurate control through current priority allocation and double sequence current loops; and managing the energy on the DC side according to a pry bar circuit to maintain stable DC voltage during the fault. The voltage source network construction control method for enhancing asymmetric fault ride-through of new energy clusters realizes safe and stable operation of the new energy cluster under asymmetric fault conditions through the organic combination of multiple control levels such as the network construction control outer ring, the adaptive virtual impedance ring and the positive and negative sequence coordinated control.

Description

Technical Field

[0001] This invention relates to the field of voltage source grid construction control technology, and in particular to a voltage source grid construction control method for enhancing asymmetric fault ride-through in new energy clusters. Background Technology

[0002] With the advancement of the "dual carbon" target, the proportion of renewable energy generation in the power system continues to increase. Renewable energy clusters are connected to the grid via power electronic converters, and their dynamic characteristics differ significantly from those of traditional synchronous generators. When asymmetrical faults occur in the grid, renewable energy clusters face severe fault ride-through challenges, which has become a key technical bottleneck restricting large-scale grid connection of renewable energy.

[0003] Existing renewable energy grid-connected control technologies mainly employ a grid-following control strategy, which relies on grid voltage to provide phase and frequency references. When an asymmetrical fault occurs in the grid, grid-following control presents the following prominent problems: Insufficient grid support capacity: Grid-connected converters are essentially controlled current source characteristics. During faults, they cannot actively support the grid voltage and cannot provide inertial and damping support for the system, resulting in a decrease in grid stability.

[0004] Weak ability to handle asymmetrical faults: When asymmetrical faults such as single-phase grounding or two-phase short circuits occur in the power grid, a severe imbalance in the positive and negative sequence components of the voltage at the grid connection point occurs. Traditional control strategies are unable to effectively coordinate the distribution of positive and negative sequence currents, which can easily lead to the overcurrent protection of the converter tripping and disconnecting it from the grid, thus affecting the fault ride-through performance.

[0005] Severe DC-side voltage fluctuations: Asymmetrical faults can generate double-frequency power fluctuations on the DC side, causing severe DC voltage fluctuations. When the DC voltage exceeds the safe range, the converter is forced to shut down.

[0006] Inflexible reactive power support response: Existing control strategies have limited reactive power regulation capabilities during faults, making it difficult to dynamically adjust reactive power output according to the degree of voltage drop, and thus failing to meet the stringent requirements of power grid regulations for reactive power support during faults.

[0007] In recent years, grid-based control technology has attracted attention because it can simulate the characteristics of synchronous generators. However, existing grid-based control schemes still have problems when dealing with asymmetrical faults, such as insufficient positive and negative sequence coordinated control, poor adaptability due to fixed virtual impedance parameters, and lack of DC-side energy management mechanisms. These issues make it difficult to meet the safe and stable operation requirements of new energy clusters under complex fault conditions.

[0008] Therefore, there is an urgent need to develop a voltage source grid control method that can enhance the asymmetric fault ride-through capability of new energy clusters in order to solve the above-mentioned technical problems. Summary of the Invention

[0009] Therefore, one objective of this invention is to propose a voltage source network control method to enhance the asymmetric fault ride-through of new energy clusters, so as to solve the problems mentioned in the background art and overcome the shortcomings of the prior art.

[0010] To achieve the above objectives, the present invention provides a voltage source grid control method for enhancing asymmetric fault ride-through in new energy clusters, comprising: Construct a new energy cluster grid-connected system and configure a grid-side converter control framework; The outer loop of the grid control system is designed to provide active support to the power grid through frequency loop and reactive power loop. Design a virtual impedance adaptive adjustment mechanism to dynamically correct the voltage reference value based on the current deviation; Positive and negative sequence coordinated control is performed, and precise control is achieved through current priority allocation and dual-sequence current loop; DC-side energy management is performed using the crowbar circuit to maintain DC voltage stability during faults.

[0011] Preferably, the new energy cluster grid-connected system includes a new energy cluster, a crowbar circuit, a DC capacitor, a grid-side converter, and an AC power grid connected in sequence. The grid-side converter includes a grid control outer loop, a virtual impedance loop, a positive sequence voltage and current loop, and a negative sequence current loop. The outer loop of the network control includes a frequency loop and a reactive power loop, and the positive sequence voltage and current loop includes a positive sequence voltage loop and a positive sequence current loop.

[0012] Preferably, the frequency loop normalizes and squares the DC voltage signal, subtracts it from 1, passes it through a lead-lag stage and a gain stage, and adds a feedforward value to obtain the synchronization frequency. The frequency loop expression is as follows: ; ; in, For synchronization frequency, Here, m is the feedforward value, and m is the weighting coefficient. DC voltage This is the rated DC voltage. This is the DC voltage tracking coefficient. The inertia coefficient, The damping coefficient is... For synchronization phase angle, For the Laplace operator.

[0013] Preferably, the reactive power loop calculates the difference between the reactive power command value and the actual reactive power value, normalizes the difference, adds the rated value of the phase voltage amplitude after PI control, obtains the voltage amplitude reference value, and performs amplitude limiting. The reactive power loop expression is as follows: ; ; in, This is a reference value for voltage amplitude. This is the reactive power command value. This represents the actual reactive power value. This is the system power rating. Pass functions to the PI controller. This is the rated voltage at the grid connection point. The voltage amplitude at the grid connection point. Filter inductor, This is the maximum allowable current value for the converter.

[0014] Preferably, the reactive power command value is set according to the degree of voltage drop or rise. Specifically, ; ; ; ; in, The positive sequence d-axis voltage at the grid connection point. The rated effective value of the grid connection point voltage. This is the effective value of the grid connection point voltage. This represents the converter capacity during a fault.

[0015] Preferably, the virtual impedance loop corrects the voltage amplitude reference value during a fault. The positive sequence dq axis voltage reference value is expressed as: ; ; in, This is the reference value for the positive-sequence d-axis voltage. This is the reference value for the positive-sequence q-axis voltage. This refers to the positive sequence d-axis current flowing from the grid connection point to the AC power grid. This refers to the positive sequence q-axis current flowing from the grid connection point to the AC power grid. For virtual inductance, For virtual resistance; The value of the virtual impedance is determined during a fault based on the difference between the current value and the rated current value, as expressed below: ; ; in, For virtual resistivity, The impedance ratio, This is the rated current. This refers to the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor.

[0016] Preferably, the positive sequence voltage and current loop is provided with a positive sequence current limiting module, and the negative sequence current loop is provided with a negative sequence current limiting module. When the current amplitude exceeds the preset maximum current value, the current limiting module limits the current reference values ​​of the positive sequence voltage and current loop and the negative sequence current loop. The maximum current values ​​for positive and negative sequences satisfy: ; in, This is the maximum current value in the positive sequence. The maximum current value is the negative sequence value.

[0017] Preferably, a positive sequence current limiting module is provided between the positive sequence voltage loop and the positive sequence current loop, which outputs a saturation current reference value when the current exceeds a specific threshold. The positive sequence voltage loop is as follows: ; ; in, and These are the reference current values ​​before limiting on the positive sequence d-axis and q-axis, respectively. The positive-sequence d-axis grid connection point voltage. This represents the positive-sequence q-axis grid connection point voltage. For filtering inductors; The positive sequence current limiting module is as follows: ; in, This is the reference value for the positive sequence d-axis or q-axis current after limiting. This is the reference value for the positive sequence d-axis or q-axis current before limiting; The positive sequence current loop is as follows: ; ; in, and These are the d-axis and q-axis positive sequence modulation voltages of the grid-side converter, respectively. This represents the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor. This is the reference value for the positive sequence d-axis current after limiting. This is the reference value for the positive sequence q-axis current after limiting.

[0018] Preferably, the negative sequence current loop is divided into two types, controlling the three-phase current balance and suppressing active power second harmonic fluctuations, depending on the control objective. When the control objective is to maintain three-phase current balance, the current reference values ​​are as follows: ; in, and These are the negative sequence d-axis and q-axis current reference values ​​when the three-phase current balance is controlled independently; When the control objective is to suppress active power frequency second harmonic fluctuations, the current reference values ​​are as follows: ; in, and These are the negative sequence d-axis and q-axis current reference values ​​when the active power second harmonic fluctuation is balanced independently; The negative sequence current reference value is determined by setting a weight. The two types of control objectives are determined uniformly: ; in, and These are the negative-sequence d-axis and q-axis current reference values ​​that combine the two control objectives; The negative sequence current limiting module is as follows: ; in, This is the reference value for the negative sequence d-axis or q-axis current after limiting. This is the reference value for the negative sequence d-axis or q-axis current before limiting; The negative sequence current loop is as follows: ; ; in, and These are the negative sequence modulation voltages of the d-axis and q-axis of the grid-side converter, respectively. and These are the negative sequence d-axis and q-axis current reference values ​​after limiting, respectively. This refers to the negative sequence q-axis current of the filter inductor. This represents the negative sequence current along the d-axis of the filter inductor.

[0019] Preferably, the priority allocation includes: First strategy: Prioritize positive sequence current, allocating existing current margin to the positive sequence current to keep it at its maximum value. When the positive sequence current has not reached its maximum value, the remaining margin of the negative sequence current will be limited. ; or The second strategy prioritizes negative-sequence current, allocating existing current margin to it to keep it at its maximum value. When the negative-sequence current has not reached its maximum value, the remaining margin of the positive-sequence current will be limited. ; in, It is a positive sequence current. It is a negative sequence current.

[0020] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: This invention employs a voltage source to construct the outer control loop, and actively supports the power grid through a frequency loop and a reactive power loop. The frequency loop introduces DC voltage feedback and lead-lag elements to simulate the inertia and damping characteristics of a synchronous generator, enabling it to actively adjust the synchronization frequency during faults and provide frequency support for the power grid. The reactive power loop dynamically adjusts the voltage amplitude reference value according to the voltage deviation at the grid connection point, achieving effective support for the grid voltage and significantly improving system stability.

[0021] This invention designs a positive and negative sequence current priority allocation strategy, which can flexibly select to prioritize the processing of positive sequence current or negative sequence current according to the fault type, and achieve optimal allocation of positive and negative sequence current within the current capacity range of the converter. It can choose to ensure the balance of three-phase current or suppress the second harmonic fluctuation of active power.

[0022] This invention designs a segmented reactive power reference value generation strategy based on the degree of voltage dips or rises. Within different voltage deviation ranges, it automatically adjusts reactive power output to meet power grid regulations and improve voltage support during fault periods.

[0023] This invention designs an adaptive virtual impedance mechanism, where virtual resistance and virtual inductance can be automatically adjusted based on the deviation between the current value and the rated current value. During a fault, the virtual impedance changes with the current, effectively suppressing fault current surges, improving the system's dynamic response characteristics, and enhancing the control system's adaptability to different fault conditions.

[0024] The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters in this invention achieves safe and stable operation of new energy clusters under asymmetric fault conditions by organically combining multiple control levels such as the grid control outer loop, the adaptive virtual impedance loop, and the positive and negative sequence coordinated control.

[0025] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0026] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 This is a schematic flowchart of the method of the present invention; Figure 2 This is a schematic diagram of the structure of a new energy cluster grid-connected system according to an embodiment of the present invention; Figure 3 This is a control block diagram of the grid-side converter according to an embodiment of the present invention; Figure 4 The following are relevant waveform diagrams for testing symmetrical low-voltage faults in a power grid according to an embodiment of the present invention; Figure 5 The waveform diagrams are relevant to the single-phase voltage fault test of the power grid in the embodiment of the present invention. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] like Figures 1-5 As shown in the figure, an embodiment of the present invention provides a voltage source grid control method for enhancing asymmetric fault ride-through in new energy clusters, comprising: S1: Construct a new energy cluster grid-connected system and configure the grid-side converter control framework.

[0029] The new energy cluster grid connection system adopted in this invention has the following main structure: Figure 2 As shown, it includes a new energy cluster, a crowbar circuit, a DC capacitor, a grid-side converter, and an AC power grid connected in sequence. The control block diagram of the grid-side converter used in this invention is shown below. Figure 3 As shown, the network includes an outer control loop, a virtual impedance loop, a positive-sequence voltage and current loop, and a negative-sequence current loop. The outer control loop includes a frequency loop and a reactive power loop. The positive-sequence voltage and current loop includes a positive-sequence voltage loop and a positive-sequence current loop.

[0030] S2: Design the outer loop of the grid control system to provide active support to the power grid through the frequency loop and the reactive power loop.

[0031] The grid control outer loop of this invention comprises two parts: a frequency loop and a reactive power loop. The frequency loop first converts the DC voltage signal... Standardize and square the result, subtract it from 1, and then pass it through a lead / lag stage and a gain stage. Add feedforward value Finally, the synchronization frequency is obtained. The frequency loop expression is as follows: ; ; in, For synchronization frequency, Here, m is the feedforward value, and m is the weighting coefficient. DC voltage This is the rated DC voltage. This is the DC voltage tracking coefficient. The inertia coefficient, The damping coefficient is... For synchronization phase angle, For the Laplace operator.

[0032] The reactive power loop first sets the reactive power command value Compared with actual reactive power The difference is calculated, and the difference is normalized. After passing through a PI controller, the rated value of the phase voltage amplitude is added to obtain the voltage amplitude reference value. And limit the amplitude; the reactive power loop expression is as follows: ; ; in, This is a reference value for voltage amplitude. This is the reactive power command value. This represents the actual reactive power value. This is the system power rating. Pass functions to the PI controller. The rated line voltage at the grid connection point. The voltage amplitude at the grid connection point. Filter inductor, This is the maximum allowable current value for the converter.

[0033] reactive power command value Depending on the degree of voltage drop or rise, it can be set as follows: ; ; ; ; in, The positive sequence d-axis voltage at the grid connection point. The rated effective value of the grid connection point voltage. This is the effective value of the grid connection point voltage. This represents the converter capacity during a fault.

[0034] The frequency loop of this invention achieves dynamic frequency adjustment by processing the squared DC voltage and combining it with lead-lag elements, simulating the characteristics of a synchronous generator. The reactive power loop sets reactive power command values ​​in segments according to the degree of voltage deviation at the grid connection point, thereby achieving a wide range of reactive power support capabilities.

[0035] S3: Design a virtual impedance adaptive adjustment mechanism to dynamically correct the voltage reference value based on the current deviation.

[0036] The virtual impedance loop corrects the voltage amplitude reference value during a fault, and the positive sequence dq-axis voltage reference value... and It can be represented as: ; ; in, This is the reference value for the positive-sequence d-axis voltage. This is the reference value for the positive-sequence q-axis voltage. This refers to the positive sequence d-axis current flowing from the grid connection point to the AC power grid. This refers to the positive sequence q-axis current flowing from the grid connection point to the AC power grid. For virtual inductance, This is a virtual resistor.

[0037] The virtual impedance can adaptively change during a fault, and its value is determined by the difference between the current value and the rated current value, as expressed below: ; ; in, For virtual resistivity, The impedance ratio, This is the rated current. This refers to the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor.

[0038] The adaptive virtual impedance mechanism of this invention dynamically adjusts the values ​​of virtual resistance and virtual inductance based on the deviation between the current current and the rated current, thereby enhancing the system's adaptability to different fault conditions.

[0039] S4: Perform positive and negative sequence coordinated control, and achieve precise control through current priority allocation and dual-sequence current loop.

[0040] Each of the positive and negative sequence voltage and current loops includes a current limiting module; that is, the positive sequence voltage and current loop has a positive sequence current limiting module, and the negative sequence current loop has a negative sequence current limiting module. When the current amplitude exceeds the preset maximum current value (imax), the current limiting module will limit the reference values ​​of the positive and negative sequence currents. The maximum current values ​​for the positive and negative sequences are... and Requirements must be met: ; in, This is the maximum current value in the positive sequence. The maximum current value is the negative sequence value.

[0041] Under this requirement, the priority of positive and negative sequence currents can be selected, and the sequence current can be adjusted and prioritized according to the fault type. The first strategy prioritizes positive sequence current, allocating the existing current margin to the positive sequence current to fix it at its maximum value. When the positive sequence current The negative sequence current has not reached its maximum value. The remaining margin will be limited.

[0042] ; The second strategy prioritizes negative-sequence current, allocating existing current margin to positive-sequence current to fix it at its maximum value. When negative sequence current The maximum value has not been reached; positive sequence current. The remaining margin will be limited.

[0043] ; The dual-sequence current loop is an integrated control loop consisting of a positive-sequence voltage-current loop and a negative-sequence current loop. A positive-sequence current limiting module is set between the positive-sequence voltage loop and the positive-sequence current loop. When the current exceeds a specific threshold, a saturation current reference value is output. The selected current limiting does not prioritize any particular axis. The positive-sequence voltage loop is represented as follows: ; ; in, and These are the reference current values ​​before limiting on the positive sequence d-axis and q-axis, respectively. The positive-sequence d-axis grid connection point voltage. This represents the positive-sequence q-axis grid connection point voltage. For filtering inductors; The positive sequence current limiting module is represented as follows: ; in, This is the reference value for the positive sequence d-axis or q-axis current after limiting. This is the reference value for the positive sequence d-axis or q-axis current before limiting; The positive sequence current loop is represented as follows: ; ; in, and These are the d-axis and q-axis positive sequence modulation voltages of the grid-side converter, respectively. This represents the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor. This is the reference value for the positive sequence d-axis current after limiting. This is the reference value for the positive sequence q-axis current after limiting.

[0044] The negative sequence loop only sets up a current loop. Depending on the control objective, it can be divided into two categories: controlling three-phase current balance and suppressing active power second harmonic fluctuations. Weights can be set accordingly. The two types of control objectives are unified. The reference value for controlling the three-phase current balance is expressed as follows: ; in, and These are the negative sequence d-axis and q-axis current reference values ​​when the three-phase current balance is controlled independently; The reference values ​​for suppressing active power frequency second harmonic fluctuations are as follows: ; in, and These are the negative sequence d-axis and q-axis current reference values ​​when the active power second harmonic fluctuation is balanced, respectively. and These are the reference values ​​for the positive sequence d-axis and q-axis currents before limiting, respectively. The negative sequence current reference value is expressed as follows: ; in, and These are the negative-sequence d-axis and q-axis current reference values ​​that combine the two control objectives; The negative sequence current limiting module is represented as follows: ; In the formula, This is the reference value for the negative sequence d-axis or q-axis current after limiting; This is the reference value for the negative sequence d-axis or q-axis current before limiting. This is the reference value for the negative sequence d-axis or q-axis current before limiting; The negative sequence current loop is represented as follows: ; ; in, and These are the negative sequence modulation voltages of the d-axis and q-axis of the grid-side converter, respectively. and These are the negative sequence d-axis and q-axis current reference values ​​after limiting, respectively. This refers to the negative sequence q-axis current of the filter inductor. This represents the negative sequence current along the d-axis of the filter inductor.

[0045] The positive and negative sequence current priority allocation strategy of this invention proposes two priority allocation schemes that can be flexibly selected according to the fault type, so as to achieve optimal coordinated control of positive and negative sequence currents under the premise of satisfying the current capacity constraints of the converter.

[0046] The negative sequence current control of this invention adopts two control objectives, "three-phase current balance" and "active power second harmonic suppression", with weighted coefficients to unify the two control objectives, thereby realizing flexible switching of control objectives.

[0047] S5: Perform DC-side energy management based on the crowbar circuit to maintain DC voltage stability during faults.

[0048] By introducing a crowbar circuit on the DC side, unbalanced energy across the DC side can be absorbed during a fault, maintaining the DC voltage at a constant value. The control expression is as follows: ; In the formula, The coefficient of motion for the crowbar circuit. Modulate the signal for the crowbar circuit. This is the reference value for DC voltage.

[0049] The introduction of the crowbar circuit in this invention solves the problem of DC voltage fluctuations during faults and forms a complete energy management scheme with the grid-side converter control.

[0050] The present invention provides a voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters, which enables new energy units to have the ability to ride through both symmetrical and asymmetric voltage faults.

[0051] In one embodiment, a symmetrical low-voltage fault test of the power grid was performed, in which the three-phase voltage dropped to 0.2 pu for 625 ms. Figure 4 (a) is the positive sequence voltage at the grid connection point. Waveform; Figure 4 (b) is the DC voltage Waveform; Figure 4 (c) represents active power. Waveform; Figure 4 (d) represents reactive power. Waveform; Figure 4 (e) is the voltage waveform of phase A. ; Figure 4 (f) shows the waveform of phase A current. .Depend on Figure 4 It can be seen that under the action of reactive power support, the PCC voltage rises to 0.33 pu, the DC voltage is maintained within a safe range under the control of the crowbar, and the AC current can maintain three-phase balance and stabilize within 1.2 pu.

[0052] In one embodiment, a single-phase voltage fault test of the power grid was performed. The voltage of phase A dropped to 0.2 pu for 625 ms. Figure 5 (a) is the positive sequence voltage at the grid connection point. Waveform; Figure 5 (b) is the DC voltage Waveform; Figure 5 (c) represents active power. Waveform; Figure 5 (d) represents reactive power. Waveform; Figure 5 (e) shows the three-phase voltage waveform. ; Figure 5 (f) shows the three-phase current waveform. .Depend on Figure 5 It can be seen that under the action of reactive power support, the DC voltage is maintained within a safe range under the control of the crowbar, and the AC current can maintain three-phase balance and stabilize below 1.2 pu. Among these, and for Figure 5 The blue curve in (e) and for Figure 5 The orange curve in (e) and for Figure 5 (e) is the red curve.

[0053] Depend on Figure 4 and Figure 5 It can be seen that the present invention effectively supports the grid voltage, and can comprehensively ensure the requirements of three-phase current balance and suppress active power fluctuations, and can maintain DC voltage stability and effectively suppress fault current surges.

[0054] Existing technologies mostly employ grid-following control strategies, lacking active support capabilities and struggling to effectively coordinate positive and negative sequence current distribution during asymmetrical faults. Fixed virtual impedance parameters result in poor adaptability, and a DC-side energy management mechanism is lacking. This invention achieves active grid support through grid-following control, coordinates positive and negative sequence control through a priority allocation strategy, enhances system flexibility through an adaptive mechanism, and addresses energy management issues through a crowbar circuit, thereby improving the asymmetrical fault ride-through capability of renewable energy clusters.

[0055] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0056] It will be readily understood by those skilled in the art that this invention includes any combination of the inventive description and specific embodiments outlined in the foregoing specification, as well as the various parts shown in the accompanying drawings. Due to space limitations and for the sake of brevity, not all of these combinations have been described in detail. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

[0057] Although embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters, characterized in that, include: Construct a new energy cluster grid-connected system and configure a grid-side converter control framework; The outer loop of the grid control system is designed to provide active support to the power grid through frequency loop and reactive power loop. Design a virtual impedance adaptive adjustment mechanism to dynamically correct the voltage reference value based on the current deviation; Positive and negative sequence coordinated control is performed, and precise control is achieved through current priority allocation and dual-sequence current loop; A crowbar circuit is introduced for DC-side energy management to maintain DC voltage stability during faults.

2. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 1, characterized in that, The new energy cluster grid-connected system includes a new energy cluster, a crowbar circuit, a DC capacitor, a grid-side converter, and an AC power grid connected in sequence. The grid-side converter includes a grid control outer loop, a virtual impedance loop, a positive sequence voltage and current loop, and a negative sequence current loop. The outer loop of the network control includes a frequency loop and a reactive power loop, and the positive sequence voltage and current loop includes a positive sequence voltage loop and a positive sequence current loop.

3. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 2, characterized in that, The frequency loop normalizes and squares the DC voltage signal, subtracts it from 1, passes it through a lead-lag stage and a gain stage, and adds a feedforward value to obtain the synchronization frequency. The frequency loop expression is as follows: ； ； in, For synchronization frequency, Here, m is the feedforward value, and m is the weighting coefficient. DC voltage This is the rated DC voltage. This is the DC voltage tracking coefficient. The inertia coefficient, The damping coefficient is... For synchronization phase angle, For the Laplace operator.

4. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 1, characterized in that, The reactive power loop calculates the difference between the reactive power command value and the actual reactive power value, normalizes the difference, adds the rated value of the phase voltage amplitude after PI control, obtains the voltage amplitude reference value, and performs amplitude limiting. The reactive power loop expression is as follows: ； ； in, This is a reference value for voltage amplitude. This is the reactive power command value. This represents the actual reactive power value. This is the system power rating. Pass functions to the PI controller. This is the rated voltage at the grid connection point. The voltage amplitude at the grid connection point. Filter inductor, This is the maximum allowable current value for the converter.

5. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 4, characterized in that, The reactive power command value is set according to the degree of voltage drop or rise. Specifically, ； ； ； ； in, The positive sequence d-axis voltage at the grid connection point. The rated effective value of the grid connection point voltage. This is the effective value of the grid connection point voltage. This represents the converter capacity during a fault.

6. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 2, characterized in that, The virtual impedance loop corrects the voltage amplitude reference value during a fault. The positive sequence dq axis voltage reference value is expressed as: ； ； in, This is the reference value for the positive-sequence d-axis voltage. This is the reference value for the positive-sequence q-axis voltage. This refers to the positive sequence d-axis current flowing from the grid connection point to the AC power grid. This refers to the positive sequence q-axis current flowing from the grid connection point to the AC power grid. For virtual inductance, For virtual resistance; The value of the virtual impedance is determined during a fault based on the difference between the current value and the rated current value, as expressed below: ； ； in, For virtual resistivity, The impedance ratio, This is the rated current. This refers to the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor.

7. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 2, characterized in that, The positive sequence voltage and current loop is equipped with a positive sequence current limiting module, and the negative sequence current loop is equipped with a negative sequence current limiting module. When the current amplitude exceeds the preset maximum current value, the current limiting module limits the current reference value of the positive sequence voltage and current loop and the negative sequence current loop. The maximum current values ​​for positive and negative sequences satisfy: ； in, This is the maximum current value in the positive sequence. The maximum current value is the negative sequence value.

8. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 2, characterized in that, A positive sequence current limiting module is set between the positive sequence voltage loop and the positive sequence current loop. When the current exceeds a specific threshold, a saturation current reference value is output. The positive sequence voltage loop is as follows: ； ； in, and These are the reference current values ​​before limiting on the positive sequence d-axis and q-axis, respectively. The positive-sequence d-axis grid connection point voltage. This represents the positive-sequence q-axis grid connection point voltage. For filtering inductors; The positive sequence current limiting module is as follows: ； in, This is the reference value for the positive sequence d-axis or q-axis current after limiting. This is the reference value for the positive sequence d-axis or q-axis current before limiting; The positive sequence current loop is as follows: ； ； in, and These are the d-axis and q-axis positive sequence modulation voltages of the grid-side converter, respectively. This represents the positive sequence current along the d-axis of the filter inductor. This represents the positive sequence q-axis current of the filter inductor. This is the reference value for the positive sequence d-axis current after limiting. This is the reference value for the positive sequence q-axis current after limiting.

9. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 2, characterized in that, The negative sequence current loop is divided into two types based on different control objectives: controlling the balance of three-phase current and suppressing active power second harmonic fluctuations. When the control objective is to maintain three-phase current balance, the current reference values ​​are as follows: ； in, and These are the negative sequence d-axis and q-axis current reference values ​​when the three-phase current balance is controlled independently; When the control objective is to suppress active power frequency second harmonic fluctuations, the current reference values ​​are as follows: ； in, and These are the negative sequence d-axis and q-axis current reference values ​​when the active power second harmonic fluctuation is balanced, respectively. and These are the reference values ​​for the positive sequence d-axis and q-axis currents before limiting, respectively. The negative sequence current reference value is determined by setting a weight. The two types of control objectives are determined uniformly: ； in, and These are the negative-sequence d-axis and q-axis current reference values ​​that combine the two control objectives; The negative sequence current limiting module is as follows: ； in, This is the reference value for the negative sequence d-axis or q-axis current after limiting. This is the reference value for the negative sequence d-axis or q-axis current before limiting; The negative sequence current loop is as follows: ； ； in, and These are the negative sequence modulation voltages of the d-axis and q-axis of the grid-side converter, respectively. and These are the negative sequence d-axis and q-axis current reference values ​​after limiting, respectively. This refers to the negative sequence q-axis current of the filter inductor. This represents the negative sequence current along the d-axis of the filter inductor.

10. The voltage source grid control method for enhancing the asymmetric fault ride-through capability of new energy clusters as described in claim 1, characterized in that, The current priority allocation includes: First strategy: Prioritize positive sequence current, allocating existing current margin to the positive sequence current to keep it at its maximum value. When the positive sequence current has not reached its maximum value, the remaining margin of the negative sequence current is limited. ； The second strategy prioritizes negative-sequence current, allocating existing current margin to it to keep it at its maximum value. When the negative-sequence current has not reached its maximum value, the remaining margin of the positive-sequence current is limited. ； in, It is a positive sequence current. It is a negative sequence current.

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