A three-phase four-wire unbalanced current compensation method and device based on photovoltaic converter margin

Abstract

The application relates to the technical field of power distribution control, in particular to a three-phase four-wire unbalanced current compensation method and device based on a photovoltaic converter margin, equipment, a medium and a program product. The method comprises the following steps: acquiring three-phase active power measurement values and three-phase reactive power measurement values of a photovoltaic grid-connected point; calculating three-phase power imbalance caused by a current load, and determining three-phase theoretical compensation currents for realizing complete compensation; acquiring a rated current limit value and a neutral line allowed current limit value of the photovoltaic converter; performing capacity constraint processing on the three-phase theoretical compensation currents to generate three-phase actual compensation current instructions meeting the capacity limitation of the converter; superimposing the three-phase actual compensation current instructions on grid-connected positive sequence current instructions of the photovoltaic converter to generate a final current inner loop reference value, and injecting the final current inner loop reference value into a converter current inner loop for tracking control, so that real-time suppression of negative sequence currents and zero sequence currents is realized. By adopting the method, active compensation of unbalanced currents can be realized.

Description

Technical Field

[0001] This application relates to the field of power distribution control technology, and in particular to a three-phase four-wire unbalanced current compensation method, device, equipment, medium, and program product based on the margin of photovoltaic converter. Background Technology

[0002] With the significant increase in three-phase and single-phase equipment in three-phase four-wire (3P-4W) low-voltage distribution networks, phase current imbalance poses a significant challenge to the efficient and safe operation of these networks. Problems caused by unbalanced current include impaired power quality, voltage imbalance, overheating of distribution transformers, neutral line overload, additional line losses, reduced distribution network capacity utilization, and malfunctioning protection relays. Traditional solutions often rely on Static Var Compensators (SVG) or Active Power Filters (APFs) for compensation, but these require dedicated equipment, resulting in high costs and insufficient flexibility.

[0003] Meanwhile, photovoltaics, as a common distributed power source, is typically used only for transmitting active power, and its capacity is redundant in most scenarios. Research shows that by modifying the control strategy of photovoltaic converters, unbalanced current can be managed using their remaining capacity without affecting active power output. However, existing methods are mostly limited to symmetrical three-phase three-wire systems, lacking sufficient compensation capability for neutral current in three-phase four-wire systems. Furthermore, traditional methods ignore the vector relationship between sequence components, treating only positive, negative, and zero-sequence currents as orthogonal. Moreover, existing compensation methods fail to distinguish between the different risk levels of neutral overload and phase overload in three-phase four-wire systems, leading to a contradiction between safety and effectiveness in the compensation strategy. Secondly, existing methods often employ fixed-ratio allocation or simple closed-loop feedback, failing to fully consider the converter's capacity constraints, which could lead to exceeding the converter's own capacity limits. Therefore, an adaptive optimal compensation method suitable for three-phase four-wire photovoltaic converters is needed. Summary of the Invention

[0004] Therefore, it is necessary to address the aforementioned technical problems by providing a three-phase four-wire unbalanced current compensation method, device, computer equipment, computer-readable storage medium, and computer program product that can actively compensate for unbalanced current by tapping the self-regulation potential of photovoltaic converters, while possessing renewable energy absorption capacity.

[0005] Firstly, this application provides a three-phase four-wire unbalanced current compensation method based on the margin of a photovoltaic converter. The method includes:

[0006] Obtain the three-phase active power and three-phase reactive power measurements at the photovoltaic grid connection point;

[0007] Based on the measured values ​​of the three-phase active power and the three-phase reactive power, calculate the three-phase power imbalance caused by the current load, and based on the three-phase power imbalance, determine the three-phase theoretical compensation current for achieving full compensation.

[0008] Obtain the rated current limit and neutral line allowable current limit of the photovoltaic converter;

[0009] Based on the rated current limit and the neutral line allowable current limit, the three-phase theoretical compensation current is subjected to capacity constraint processing to generate a three-phase actual compensation current command that meets the converter capacity limit.

[0010] The actual three-phase compensation current command is superimposed on the grid-connected positive sequence current command of the photovoltaic converter to generate the final current inner loop reference value, which is then injected into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

[0011] In one embodiment, determining the theoretical three-phase compensation current for achieving full compensation based on the three-phase power imbalance includes:

[0012] Based on the deviations between the measured active power values ​​and the measured reactive power values ​​of each phase, calculate the theoretical active power compensation power and theoretical reactive power compensation power required for each phase respectively.

[0013] Based on the theoretical active power compensation power and the theoretical reactive power compensation power, and combined with the positive sequence component of the grid connection point voltage, the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase are calculated respectively.

[0014] The theoretical active compensation current component and the theoretical reactive compensation current component of each phase are vector synthesized to obtain the theoretical compensation current of each phase.

[0015] In one embodiment, the photovoltaic converter includes a DC-DC stage and a DC-AC stage. When performing the method, no additional current sensor is added. Step A1 includes:

[0016] The DC-DC stage of the photovoltaic converter executes a preset maximum power point tracking algorithm to adjust the DC bus voltage according to the target power.

[0017] While performing phase-locking and DC bus voltage regulation, the DC-AC stage of the photovoltaic converter superimposes the actual three-phase compensation current command with the grid-connected positive sequence current command, and achieves current tracking control through a proportional resonant controller.

[0018] In one embodiment, before performing capacity constraint processing on the three-phase theoretical compensation current based on the rated current limit and the neutral line allowable current limit to generate a three-phase actual compensation current command that satisfies the converter capacity limit, the method further includes:

[0019] Obtain the currently available computing resource information for the photovoltaic converter;

[0020] Based on the computing resource information, determine whether the current computing power meets the optimal computing conditions. If it does, select the optimal computing strategy; otherwise, select the fast computing strategy.

[0021] In one embodiment, the step of determining whether the current computing power meets the optimal computing conditions based on the computing resource information, and selecting the optimal computing strategy if it does, and selecting the fast computing strategy if it does not, includes:

[0022] When the optimal calculation strategy is selected, the minimum weighted sum of the uncompensated negative-sequence current component and the zero-sequence current component is taken as the optimization objective.

[0023] The constraints are that the effective value of each phase current is not greater than the rated current limit and the effective value of the neutral current is not greater than the allowable neutral current limit.

[0024] The Lagrange multiplier method is used to jointly solve the optimization objective and the constraints to obtain the optimal allocation result of the compensation current for each phase, which is then output as the actual compensation current command for the three phases.

[0025] In one embodiment, the step of determining whether the current computing power meets the optimal computing conditions based on the computing resource information, and selecting the optimal computing strategy if it does, and selecting the fast computing strategy if it does not, includes:

[0026] When the fast calculation strategy is selected, the first type of scaling factor for ensuring that the current of each phase does not exceed the limit and the second type of scaling factor for ensuring that the neutral line current does not exceed the limit are calculated respectively.

[0027] Based on the second type of scaling factor, the first candidate value that satisfies the neutral line safety constraint is determined first, and then the minimum value among the first type of scaling factors is taken as the second candidate value for evaluating the phase current compensation potential.

[0028] The first candidate value and the second candidate value are compared, and the larger one is taken as the dynamic scaling factor. The three-phase theoretical compensation current is scaled proportionally using the dynamic scaling factor to obtain the three-phase actual compensation current command.

[0029] Secondly, this application also provides a three-phase four-wire unbalanced current compensation device based on the margin of a photovoltaic converter. The device includes:

[0030] The power measurement module is used to acquire the three-phase active power measurement value and the three-phase reactive power measurement value of the photovoltaic grid connection point;

[0031] The imbalance module is used to calculate the three-phase power imbalance caused by the current load based on the measured values ​​of the three-phase active power and the three-phase reactive power, and to determine the three-phase theoretical compensation current for achieving full compensation based on the three-phase power imbalance.

[0032] The current limiting module is used to obtain the rated current limit and the neutral line allowable current limit of the photovoltaic converter;

[0033] The compensation instruction module is used to perform capacity constraint processing on the three-phase theoretical compensation current according to the rated current limit and the neutral line allowable current limit, and generate a three-phase actual compensation current instruction that meets the converter capacity limit.

[0034] The compensation execution module is used to superimpose the actual three-phase compensation current command onto the grid-connected positive sequence current command of the photovoltaic converter, generate the final current inner loop reference value, and inject it into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

[0035] In one embodiment, the imbalance module is further configured to:

[0036] Based on the deviations between the measured active power values ​​and the measured reactive power values ​​of each phase, calculate the theoretical active power compensation power and theoretical reactive power compensation power required for each phase respectively.

[0037] Based on the theoretical active power compensation power and the theoretical reactive power compensation power, and combined with the positive sequence component of the grid connection point voltage, the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase are calculated respectively.

[0038] The theoretical active compensation current component and the theoretical reactive compensation current component of each phase are vector synthesized to obtain the theoretical compensation current of each phase.

[0039] In one embodiment, the photovoltaic converter includes a DC-DC stage and a DC-AC stage. When performing the method, no additional current sensor is added. The device also includes a current control module for:

[0040] The DC-DC stage of the photovoltaic converter executes a preset maximum power point tracking algorithm to adjust the DC bus voltage according to the target power.

[0041] While performing phase-locking and DC bus voltage regulation, the DC-AC stage of the photovoltaic converter superimposes the actual three-phase compensation current command with the grid-connected positive sequence current command, and achieves current tracking control through a proportional resonant controller.

[0042] In one embodiment, a calculation strategy module is included before the compensation instruction module, for:

[0043] Obtain the currently available computing resource information for the photovoltaic converter;

[0044] Based on the computing resource information, determine whether the current computing power meets the optimal computing conditions. If it does, select the optimal computing strategy; otherwise, select the fast computing strategy.

[0045] In one embodiment, the calculation strategy module is further configured to:

[0046] When the optimal calculation strategy is selected, the minimum weighted sum of the uncompensated negative-sequence current component and the zero-sequence current component is taken as the optimization objective.

[0047] The constraints are that the effective value of each phase current is not greater than the rated current limit and the effective value of the neutral current is not greater than the allowable neutral current limit.

[0048] The Lagrange multiplier method is used to jointly solve the optimization objective and the constraints to obtain the optimal allocation result of the compensation current for each phase, which is then output as the actual compensation current command for the three phases.

[0049] In one embodiment, the calculation strategy module is further configured to:

[0050] When the fast calculation strategy is selected, the first type of scaling factor for ensuring that the current of each phase does not exceed the limit and the second type of scaling factor for ensuring that the neutral line current does not exceed the limit are calculated respectively.

[0051] Based on the second type of scaling factor, the first candidate value that satisfies the neutral line safety constraint is determined first, and then the minimum value among the first type of scaling factors is taken as the second candidate value for evaluating the phase current compensation potential.

[0052] The first candidate value and the second candidate value are compared, and the larger one is taken as the dynamic scaling factor. The three-phase theoretical compensation current is scaled proportionally using the dynamic scaling factor to obtain the three-phase actual compensation current command.

[0053] Thirdly, this application also provides a computer device. The computer device includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the steps of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin as described in any embodiment of the first aspect.

[0054] Fourthly, this application also provides a computer-readable storage medium. The computer-readable storage medium stores a computer program thereon, which, when executed by a processor, implements the steps of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin as described in any embodiment of the first aspect.

[0055] Fifthly, this application also provides a computer program product. The computer program product includes a computer program that, when executed by a processor, implements the steps of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin as described in any embodiment of the first aspect.

[0056] The above-described method, apparatus, computer equipment, storage medium, and computer program product for compensating three-phase four-wire unbalanced current based on the margin of photovoltaic converters, derived through the technical features in the embodiments, can achieve the following beneficial effects to address the technical problems in the background art:

[0057] This application provides a three-phase four-wire unbalanced current compensation method based on the margin of photovoltaic converters. By fully utilizing the residual current capacity of the photovoltaic grid-connected converter, it effectively manages the three-phase unbalanced current and neutral line overload problems in low-voltage distribution networks without adding any additional sensors or hardware. The method first uses existing three-phase active and reactive power measurement data at the photovoltaic grid connection point to directly calculate the three-phase power imbalance caused by the current load and determine the theoretical compensation current required for complete compensation, thus avoiding the complex and inaccurate sequence component extraction process. Based on this, the rated current limit of the photovoltaic converter and the allowable current limit of the neutral line are obtained as hard constraints to perform capacity constraint processing on the theoretical compensation current, generating an actual compensation current command that effectively reduces negative-sequence and zero-sequence currents while strictly ensuring that each phase of the converter and the neutral line do not overload. Finally, this command is superimposed with the grid-connected positive-sequence current command and injected into the current inner loop for tracking control. The entire method ensures the normal operation of photovoltaic grid-connected power generation while achieving dynamic real-time management of local unbalanced current. It significantly reduces the negative sequence and zero sequence current components flowing to the grid, effectively alleviates problems such as neutral line overload, transformer overheating, and power quality degradation, and takes into account system operation safety, hardware economy, and compensation management effect, showing good engineering application prospects. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of this application or related technologies, the drawings used in the description of the embodiments of this application or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0059] Figure 1 This is a schematic diagram of the first process of a three-phase four-wire unbalanced current compensation method based on the margin of a photovoltaic converter in one embodiment.

[0060] Figure 2 This is a schematic diagram of the second process of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin in another embodiment.

[0061] Figure 3 This is a schematic diagram of the third process of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin in another embodiment.

[0062] Figure 4 This is a schematic diagram of the fourth process of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin in another embodiment.

[0063] Figure 5 This is a schematic diagram of the fifth process of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin in another embodiment;

[0064] Figure 6 This is a schematic diagram of the sixth process of a three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin in another embodiment;

[0065] Figure 7 This is a schematic diagram of a photovoltaic converter control architecture for implementing photovoltaic grid connection and unbalanced current compensation in a specific embodiment.

[0066] Figure 8 Here is a control block diagram of a photovoltaic converter in a specific embodiment;

[0067] Figure 9 This is a schematic diagram of voltage positive sequence, negative sequence, and zero sequence component extraction and phase-locked loop (PLL) circuitry in a specific embodiment.

[0068] Figure 10 This is a structural block diagram of a three-phase four-wire unbalanced current compensation device based on the margin of a photovoltaic converter in one embodiment.

[0069] Figure 11 This is an internal structural diagram of a computer device in one embodiment. Detailed Implementation

[0070] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0071] In one embodiment, such as Figure 1 As shown, a three-phase four-wire unbalanced current compensation method based on the margin of a photovoltaic converter is provided. This embodiment illustrates the application of this method to a terminal. It is understood that this method can also be applied to a server, and to a system including both a terminal and a server, and implemented through interaction between the terminal and the server. In this embodiment, the method includes the following steps:

[0072] Step 102: Obtain the three-phase active power measurement value and the three-phase reactive power measurement value of the photovoltaic grid connection point.

[0073] Step 104: Calculate the three-phase power imbalance caused by the current load based on the measured values ​​of the three-phase active power and the three-phase reactive power, and determine the three-phase theoretical compensation current for achieving full compensation based on the three-phase power imbalance.

[0074] Step 106: Obtain the rated current limit and neutral line allowable current limit of the photovoltaic converter.

[0075] Step 108: Based on the rated current limit and the neutral line allowable current limit, perform capacity constraint processing on the three-phase theoretical compensation current to generate a three-phase actual compensation current command that meets the converter capacity limit.

[0076] Step 1010: The actual three-phase compensation current command is superimposed on the grid-connected positive sequence current command of the photovoltaic converter to generate the final current inner loop reference value, and injected into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

[0077] In the above-mentioned three-phase four-wire unbalanced current compensation method based on the margin of photovoltaic converter, reasonable derivation is made in conjunction with the technical features in the embodiments, which achieves the beneficial effect of solving the technical problems raised in the background art:

[0078] This application provides a three-phase four-wire unbalanced current compensation method based on the margin of photovoltaic converters. By fully utilizing the residual current capacity of the photovoltaic grid-connected converter, it effectively manages the three-phase unbalanced current and neutral line overload problems in low-voltage distribution networks without adding any additional sensors or hardware. The method first uses existing three-phase active and reactive power measurement data at the photovoltaic grid connection point to directly calculate the three-phase power imbalance caused by the current load and determine the theoretical compensation current required for complete compensation, thus avoiding the complex and inaccurate sequence component extraction process. Based on this, the rated current limit of the photovoltaic converter and the allowable current limit of the neutral line are obtained as hard constraints to perform capacity constraint processing on the theoretical compensation current, generating an actual compensation current command that effectively reduces negative-sequence and zero-sequence currents while strictly ensuring that each phase of the converter and the neutral line do not overload. Finally, this command is superimposed with the grid-connected positive-sequence current command and injected into the current inner loop for tracking control. The entire method ensures the normal operation of photovoltaic grid-connected power generation while achieving dynamic real-time management of local unbalanced current. It significantly reduces the negative sequence and zero sequence current components flowing to the grid, effectively alleviates problems such as neutral line overload, transformer overheating, and power quality degradation, and takes into account system operation safety, hardware economy, and compensation management effect, showing good engineering application prospects.

[0079] In one embodiment, it can be as follows Figure 2 As shown, step 104 includes:

[0080] Step 202: Based on the deviations between the active power measurement values ​​and the reactive power measurement values ​​of each phase, calculate the theoretical active power compensation power and theoretical reactive power compensation power required for each phase respectively.

[0081] Step 204: Based on the theoretical active power compensation power and the theoretical reactive power compensation power, and combined with the positive sequence component of the grid connection point voltage, calculate the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase respectively.

[0082] Step 206: Perform vector synthesis of the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase to obtain the theoretical compensation current of each phase.

[0083] In this embodiment, the theoretical compensation current is calculated by directly using the existing three-phase active / reactive power measurement values ​​at the grid connection point. There is no need to extract the negative sequence and zero sequence current components or add additional current sensors. This simplifies the data processing flow while ensuring calculation accuracy, reduces system hardware costs and control complexity, and provides an accurate theoretical compensation benchmark for subsequent capacity constraint processing.

[0084] In one embodiment, it can be as follows Figure 3As shown, the photovoltaic converter includes a DC-DC stage and a DC-AC stage. When performing the method, no additional current sensor is added. The method includes:

[0085] Step 302: The DC-DC stage of the photovoltaic converter executes a preset maximum power point tracking algorithm to adjust the DC bus voltage according to the target power.

[0086] Step 304: While performing phase-locking and DC bus voltage regulation, the DC-AC stage of the photovoltaic converter superimposes the actual three-phase compensation current command with the grid-connected positive sequence current command, and realizes current tracking control through a proportional resonant controller.

[0087] In this embodiment, the DC-DC and DC-AC stages of the photovoltaic converter are controlled collaboratively, achieving joint operation of photovoltaic maximum power point tracking and unbalanced current compensation without adding additional current sensors. The DC-AC stage directly superimposes the compensation current command and the grid-connected positive sequence current command, and uses a proportional resonant controller for precise tracking. This allows the photovoltaic converter to simultaneously perform unbalanced current mitigation tasks while completing normal grid-connected power generation, fully leveraging the multi-functional potential of the photovoltaic equipment and improving equipment utilization and system integration.

[0088] In one embodiment, it can be as follows Figure 4 As shown, before step 104, the procedure further includes:

[0089] Step 402: Obtain the currently available computing resources information for the photovoltaic converter.

[0090] Step 404: Determine whether the current computing power meets the optimal computing conditions based on the computing resource information. If it does, select the optimal computing strategy; otherwise, select the fast computing strategy.

[0091] In this embodiment, based on the available local computing resources of the photovoltaic converter, an optimal computing strategy or a fast computing strategy is adaptively selected, enabling the method to flexibly adapt to different computing power platforms such as host computers and DSPs. When computing power is sufficient, the optimal strategy is used to pursue the best compensation effect; when computing power is limited, the fast strategy is switched to ensure the real-time performance of control. This achieves a dynamic balance between compensation performance and execution efficiency, significantly improving the applicability and engineering portability of the method across different hardware platforms.

[0092] In one embodiment, it can be as follows Figure 5 As shown, step 404 includes:

[0093] Step 502: When the optimal calculation strategy is selected, the minimum weighted sum of the uncompensated negative-sequence current component and the zero-sequence current component is taken as the optimization objective.

[0094] Step 504: The effective value of each phase current is not greater than the rated current limit and the effective value of the neutral current is not greater than the neutral allowable current limit as constraints.

[0095] Step 506: Use the Lagrange multiplier method to jointly solve the optimization objective and the constraints to obtain the optimal allocation result of the compensation current for each phase, which is then output as the actual compensation current command for the three phases.

[0096] In this embodiment, after selecting the optimal calculation strategy, the optimization objective is to minimize the weighted sum of uncompensated negative-sequence and zero-sequence currents. Constraints are set by the limits of each phase current and the neutral line current. A joint solution using the Lagrange multiplier method is then implemented to achieve the globally optimal allocation of compensation currents for each phase. This method, while ensuring that the converter is not overloaded, minimizes the negative-sequence and zero-sequence current components flowing to the grid, effectively improving the management of unbalanced currents. It is particularly suitable for applications with sufficient computing power and high requirements for compensation accuracy.

[0097] In one embodiment, it can be as follows Figure 6 As shown, step 404 includes:

[0098] Step 602: When the fast calculation strategy is selected, calculate the first type of scaling factor to ensure that the current of each phase does not exceed the limit and the second type of scaling factor to ensure that the neutral line current does not exceed the limit.

[0099] Step 604: Based on the second type of scaling factor, first candidate value that satisfies the neutral line safety constraint is determined first, and then the minimum value among the first type of scaling factors is taken as the second candidate value for evaluating the phase current compensation potential.

[0100] Step 606: Compare the first candidate value with the second candidate value, take the larger one as the dynamic scaling factor, and use the dynamic scaling factor to scale the three-phase theoretical compensation current proportionally to obtain the three-phase actual compensation current command.

[0101] In this embodiment, when selecting a fast calculation strategy, the scaling factors corresponding to the phase current constraints and neutral line current constraints are calculated separately. A two-stage decision logic of "neutral line priority" is used to determine the dynamic scaling factor. The second type of scaling factor is prioritized to ensure that the neutral line current does not exceed the limit. Then, the larger of the phase current potential assessment results is taken as the final scaling factor, thereby maximizing the utilization of the phase current compensation capacity while ensuring the absolute safety of the neutral line. This strategy does not require complex iterative optimization, is simple to calculate, and is highly efficient in execution, making it particularly suitable for real-time control platforms with limited computing power, such as DSPs.

[0102] In one specific embodiment, a three-phase four-wire unbalanced current compensation method based on the margin of a photovoltaic converter is provided, which includes the following steps:

[0103] S1, Collect the measured values ​​of three-phase active power and reactive power at the photovoltaic grid connection point, and calculate the three-phase power imbalance caused by the current load based on the power.

[0104] S2, based on instantaneous power theory, derives the three-phase theoretical compensation current under the condition of achieving full compensation;

[0105] S3, compare the theoretical compensation current with the rated current capability of the photovoltaic converter, and generate an executable compensation current reference value based on the converter capacity constraint;

[0106] S4 injects the obtained compensation current command into the inner current loop of the photovoltaic converter to achieve real-time suppression of negative sequence current and zero sequence current.

[0107] Furthermore, the photovoltaic converter includes a DC-DC stage and a DC-AC stage. The method achieves combined control of photovoltaic maximum power point tracking and unbalanced current compensation without adding any current sensors. A schematic diagram of the unified control architecture for the photovoltaic converter, realizing both grid connection and unbalanced current compensation, is shown below. Figure 1 As shown, the compensation current generation module, along with the supporting current tracking control strategy, voltage positive sequence component extraction, and phase-locked loop (PLL) circuit, are as follows: Figure 7 As shown in Figure 8, it specifically includes:

[0108] (1) The DC-DC stage executes the maximum power point tracking algorithm and adjusts the power to the DC bus according to the target power;

[0109] (2) While performing phase-locked loop and DC bus voltage regulation, the DC-AC stage generates the corresponding three-phase compensation current according to the unbalance compensation command and superimposes it with the grid-connected positive sequence current command to achieve current tracking through the proportional resonant controller.

[0110] Furthermore, the calculation of the compensation current in the embodiment does not require extracting the three-phase negative sequence current and zero sequence current components. Instead, it is based on the average active power and average reactive power of each phase to estimate the imbalance compensation requirement. The steps include:

[0111] (1) Utilize existing three-phase active and reactive power meters to measure the average active and reactive power of each phase flowing into the load. , , , , , .

[0112] (2) When the capacity limitation of the photovoltaic converter is not taken into account, the theoretical compensation power required to obtain full compensation based on the power deviation can be shown in the following equations (1) and (2):

[0113]

[0114] In this context, the subscript i represents phases A, B, and C of the three-phase system, and the superscript s represents the power required to achieve the theoretical compensation.

[0115] (3) According to the decomposition relationship of active current components and reactive current components on the P-axis and Q-axis, the compensation current is expressed as active compensation components and reactive compensation components as shown in equations (3) and (4) below:

[0116]

[0117] In this context, the subscript P represents the active current component of phase i, located on the active axis P. The P axis is in phase with the voltage vector of phase i (phases A, B, and C are respectively...). Similarly, the subscript Q represents the m-phase reactive current component, located on the reactive axis Q, which leads the P axis by 90 degrees. It is obtained by extracting the positive sequence component from the three-phase voltage flowing into the load through the Clarke transform.

[0118] Theoretically, the compensated phase current is derived from the positive sequence reference current ( ) and compensation current ( )composition. and Together they determine the active component of the phase current, that is, the current component in the same direction as the P-axis. and Together, they determine the reactive component of the phase current, that is, the current component in the same direction as the Q-axis.

[0119] Due to the capacity limitations of photovoltaic converters, complete compensation is theoretically impossible. Positive sequence current reference and... The sum may exceed the maximum allowable value of the phase current. Therefore, the actual compensation current command ( To avoid overcurrent. and The difference between them is defined as the uncompensated current, with the subscript un, as shown in equation (5) below.

[0120]

[0121] Furthermore, the unbalanced current compensation control method based on photovoltaic converters described in this embodiment includes the following specific steps for calculating the reference value of the photovoltaic converter compensation current:

[0122] Based on the local computing power of the photovoltaic converter, two different control strategies can be adopted: the optimal calculation strategy and the fast calculation strategy. The specific process includes:

[0123] (1) Optimal computation strategy

[0124] The goal of this control strategy is to minimize the negative-sequence and zero-sequence currents flowing to the grid and to limit the phase currents and neutral currents to within the currents allowed to pass through the converter.

[0125] (2) Fast calculation strategy

[0126] This control strategy is suitable for situations where the local computing power of the photovoltaic converter is insufficient. It directly performs calculations in the DSP of the photovoltaic converter controller, generates the reference value of the compensation current of the photovoltaic converter, and executes it. Compared with the optimal calculation strategy, although the fast calculation strategy cannot meet the control objective of minimizing the sum of the uncompensated negative sequence and zero sequence current components, it is simple to implement, can be executed in real time in the DSP, and meets the constraint that the effective value of the three-phase current does not exceed the limit.

[0127] Furthermore, the optimal calculation strategy described in this embodiment is executed on the local host computer or computer platform, with the objective function being to minimize the negative-sequence current component and the zero-sequence current component flowing to the power grid, while satisfying the constraint that the currents of each phase and the neutral line current do not exceed the limits. Specifically, this includes...

[0128] (1) Construct objective functions for the magnitudes of the negative-sequence and zero-sequence components of the three-phase current, minimizing the weighted sum of the uncompensated negative-sequence and zero-sequence current components. The objective of the control strategy is shown in the following equation:

[0129]

[0130] (2) Using the effective values ​​of the three-phase currents and the maximum allowable value of the neutral line current as constraints, and combining the characteristic that the compensation current does not change the sum of the positive sequence currents, constraint equations are established. The specific constraint equations are as follows: , , .

[0131] in and It is a three-phase current The negative and zero order components. This represents the maximum allowable current for the neutral line. and These are the weights corresponding to the negative and zero-order components.

[0132] Since the compensation current does not cause a change in the positive sequence current, the sum of the three-phase compensation currents for active power and reactive power is zero, as shown in equation (6):

[0133]

[0134] By using the relationship between positive sequence current and compensation current, and combining it with the above formula, the three-phase ( The theoretical current amplitude of ) is as shown in the following equation (7):

[0135]

[0136] The three-phase current can be decomposed into negative-sequence and zero-sequence currents, which can be written as shown in equations (8) and (9) below:

[0137]

[0138] Among them, let Then there is .

[0139] The neutral current is three times the zero-sequence current. Combining this with the phase relationship between active and reactive power currents, we can deduce... As shown in equation (10):

[0140]

[0141] And there are .

[0142] Substituting equations (8) and (9) into equation (5), the objective function is shown in equation (11) below:

[0143]

[0144] As shown in equation (12),

[0145]

[0146] (3) The objective function and constraint equations are solved by using the Lagrange multiplier method to obtain the optimal distribution of the compensation current amplitude of each phase.

[0147] The optimal solution is obtained by the Lagrange multiplier method, which includes the four variables in formula (11) and the four constraints in formulas (7) and (10). Since the unbalanced voltage is relatively small during normal operation, it is assumed here that the voltage of phase A is equal to... The phase difference between them can be ignored. Therefore, the compensation current command allocated to the three phases can be expressed as shown in equations (13) and (14) below:

[0148]

[0149] in:

[0150]

[0151] , The calculation formula is shown in equation (15) below:

[0152]

[0153] Furthermore, the fast calculation strategy described in this embodiment is executed within the DSP of the photovoltaic converter controller. It prioritizes low computational complexity and ease of real-time implementation, and innovatively introduces a neutral current-priority compensation sequence. A two-stage decision logic determines the dynamic scaling factor, effectively addressing the balance between neutral line safety and compensation effectiveness in a three-phase four-wire system while maintaining computational complexity. Specifically, this includes:

[0154] (1) Using the amplitude of the full compensation current as the reference value, set the scaling factor φ, and scale the full compensation current proportionally to obtain the reference value of the compensation current for each phase, as shown in the following formula (16):

[0155]

[0156] (2) The process of determining the dynamic scaling factor kd includes:

[0157] Calculate the scaling factor to ensure that the current in each phase does not exceed the limit. And a scaling factor to ensure the neutral current does not exceed the limit. These values ​​are the maximum allowable values ​​calculated for each phase according to formula (17). That is, the positive roots of a linear equation with one variable.

[0158] Phase 1 (Neutral Line Priority Constraint): Take Prioritize ensuring the safety of the neutral current;

[0159] Phase Two (Phase Current Capacity Assessment): Take To assess the overall compensation potential of the phase current;

[0160] Phase 3: Finalizing the dynamic scaling factor It can be represented by the following formula (17):

[0161]

[0162] The entire process of the compensation current generation module includes key solution steps such as local measurement, full compensation current calculation, optimal calculation strategy, and fast calculation strategy.

[0163] (3) When the grid operation status or the degree of load imbalance changes, the proportional coefficient k and the reference value of the compensation current are updated in real time, so as to improve the unbalanced current compensation effect as much as possible while ensuring that the converter current does not exceed the limit.

[0164] It should be understood that although the steps in the flowcharts of the embodiments described above are shown sequentially according to the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowcharts of the embodiments described above may include multiple steps or multiple stages. These steps or stages are not necessarily completed at the same time, but can be executed at different times. The execution order of these steps or stages is not necessarily sequential, but can be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.

[0165] Based on the same inventive concept, this application also provides a three-phase four-wire unbalanced current compensation device for implementing the aforementioned three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin. The solution provided by this device is similar to the solution described in the above method. Therefore, the specific limitations of one or more embodiments of a three-phase four-wire unbalanced current compensation device based on photovoltaic converter margin provided below can be found in the above-described limitations of the three-phase four-wire unbalanced current compensation method based on photovoltaic converter margin, and will not be repeated here.

[0166] In one embodiment, such as Figure 10 As shown, a three-phase four-wire unbalanced current compensation device based on the margin of a photovoltaic converter is provided, including: a power measurement module, an unbalance module, a current limiting module, a compensation command module, and a compensation execution module, wherein:

[0167] The power measurement module is used to acquire the three-phase active power measurement value and the three-phase reactive power measurement value of the photovoltaic grid connection point;

[0168] The imbalance module is used to calculate the three-phase power imbalance caused by the current load based on the measured values ​​of the three-phase active power and the three-phase reactive power, and to determine the three-phase theoretical compensation current for achieving full compensation based on the three-phase power imbalance.

[0169] The current limiting module is used to obtain the rated current limit and the neutral line allowable current limit of the photovoltaic converter;

[0170] The compensation instruction module is used to perform capacity constraint processing on the three-phase theoretical compensation current according to the rated current limit and the neutral line allowable current limit, and generate a three-phase actual compensation current instruction that meets the converter capacity limit.

[0171] The compensation execution module is used to superimpose the actual three-phase compensation current command onto the grid-connected positive sequence current command of the photovoltaic converter, generate the final current inner loop reference value, and inject it into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

[0172] In one embodiment, the imbalance module is further configured to:

[0173] Based on the deviations between the measured active power values ​​and the measured reactive power values ​​of each phase, calculate the theoretical active power compensation power and theoretical reactive power compensation power required for each phase respectively.

[0174] Based on the theoretical active power compensation power and the theoretical reactive power compensation power, and combined with the positive sequence component of the grid connection point voltage, the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase are calculated respectively.

[0175] The theoretical active compensation current component and the theoretical reactive compensation current component of each phase are vector synthesized to obtain the theoretical compensation current of each phase.

[0176] In one embodiment, the photovoltaic converter includes a DC-DC stage and a DC-AC stage. When performing the method, no additional current sensor is added. The device also includes a current control module for:

[0177] The DC-DC stage of the photovoltaic converter executes a preset maximum power point tracking algorithm to adjust the DC bus voltage according to the target power.

[0178] While performing phase-locking and DC bus voltage regulation, the DC-AC stage of the photovoltaic converter superimposes the actual three-phase compensation current command with the grid-connected positive sequence current command, and achieves current tracking control through a proportional resonant controller.

[0179] In one embodiment, a calculation strategy module is included before the compensation instruction module, for:

[0180] Obtain the currently available computing resource information for the photovoltaic converter;

[0181] Based on the computing resource information, determine whether the current computing power meets the optimal computing conditions. If it does, select the optimal computing strategy; otherwise, select the fast computing strategy.

[0182] In one embodiment, the calculation strategy module is further configured to:

[0183] When the optimal calculation strategy is selected, the minimum weighted sum of the uncompensated negative-sequence current component and the zero-sequence current component is taken as the optimization objective.

[0184] The constraints are that the effective value of each phase current is not greater than the rated current limit and the effective value of the neutral current is not greater than the allowable neutral current limit.

[0185] The Lagrange multiplier method is used to jointly solve the optimization objective and the constraints to obtain the optimal allocation result of the compensation current for each phase, which is then output as the actual compensation current command for the three phases.

[0186] In one embodiment, the calculation strategy module is further configured to:

[0187] When the fast calculation strategy is selected, the first type of scaling factor for ensuring that the current of each phase does not exceed the limit and the second type of scaling factor for ensuring that the neutral line current does not exceed the limit are calculated respectively.

[0188] Based on the second type of scaling factor, the first candidate value that satisfies the neutral line safety constraint is determined first, and then the minimum value among the first type of scaling factors is taken as the second candidate value for evaluating the phase current compensation potential.

[0189] The first candidate value and the second candidate value are compared, and the larger one is taken as the dynamic scaling factor. The three-phase theoretical compensation current is scaled proportionally using the dynamic scaling factor to obtain the three-phase actual compensation current command.

[0190] The modules in the aforementioned three-phase four-wire unbalanced current compensation device based on the margin of a photovoltaic converter can be implemented entirely or partially through software, hardware, or a combination thereof. These modules can be embedded in or independent of the processor in a computer device in hardware form, or stored in the memory of a computer device in software form, so that the processor can call and execute the operations corresponding to each module.

[0191] In one embodiment, a computer device is provided, which may be a terminal, and its internal structure diagram may be as follows: Figure 11As shown, the computer device includes a processor, memory, input / output interface, communication interface, display unit, and input device. The processor, memory, and input / output interface are connected via a system bus, and the communication interface, display unit, and input device are also connected to the system bus via the input / output interface. The processor provides computing and control capabilities. The memory includes non-volatile storage media and internal memory. The non-volatile storage media stores the operating system and computer programs. The internal memory provides an environment for the operation of the operating system and computer programs stored in the non-volatile storage media. The input / output interface is used for exchanging information between the processor and external devices. The communication interface is used for wired or wireless communication with external terminals; wireless communication can be achieved through Wi-Fi, mobile cellular networks, NFC (Near Field Communication), or other technologies. When executed by the processor, the computer program implements a three-phase four-wire unbalanced current compensation method based on the margin of a photovoltaic converter. The display unit is used to form a visually visible image and can be a display screen, projection device, or virtual reality imaging device. The display screen can be an LCD screen or an e-ink screen. The input device of the computer device can be a touch layer covering the display screen, or buttons, trackballs, or touchpads set on the casing of the computer device, or external keyboards, touchpads, or mice, etc.

[0192] Those skilled in the art will understand that Figure 11 The structure shown is merely a block diagram of a portion of the structure related to the present application and does not constitute a limitation on the computer device to which the present application is applied. Specific computer devices may include more or fewer components than those shown in the figure, or combine certain components, or have different component arrangements.

[0193] In one embodiment, a computer device is also provided, including a memory and a processor, wherein the memory stores a computer program, and the processor executes the computer program to implement the steps in the above method embodiments.

[0194] In one embodiment, a computer-readable storage medium is provided having a computer program stored thereon that, when executed by a processor, implements the steps in the above method embodiments.

[0195] In one embodiment, a computer program product is provided, including a computer program that, when executed by a processor, implements the steps in the above method embodiments.

[0196] It should be noted that the user information (including but not limited to user device information, user personal information, etc.) and data (including but not limited to data used for analysis, data stored, data displayed, etc.) involved in this application are all information and data authorized by the user or fully authorized by all parties, and the collection, use and processing of related data must comply with the relevant laws, regulations and standards of the relevant countries and regions.

[0197] Those skilled in the art will understand that all or part of the processes in the above embodiments can be implemented by a computer program instructing related hardware. The computer program can be stored in a non-volatile computer-readable storage medium, and when executed, it can include the processes of the embodiments described above. Any references to memory, databases, or other media used in the embodiments provided in this application can include at least one of non-volatile and volatile memory. Non-volatile memory can include read-only memory (ROM), magnetic tape, floppy disk, flash memory, optical memory, high-density embedded non-volatile memory, resistive random access memory (ReRAM), magnetic random access memory (MRAM), ferroelectric random access memory (FRAM), phase change memory (PCM), graphene memory, etc. Volatile memory can include random access memory (RAM) or external cache memory, etc. By way of illustration and not limitation, RAM can take many forms, such as Static Random Access Memory (SRAM) or Dynamic Random Access Memory (DRAM). The databases involved in the embodiments provided in this application may include at least one type of relational database and non-relational database. Non-relational databases may include, but are not limited to, blockchain-based distributed databases. The processors involved in the embodiments provided in this application may be general-purpose processors, central processing units, graphics processing units, digital signal processors, programmable logic devices, quantum computing-based data processing logic devices, etc., and are not limited to these.

[0198] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0199] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of this patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this application should be determined by the appended claims.

Claims

1. A method for compensating unbalanced current in a three-phase four-wire system based on the margin of a photovoltaic converter, characterized in that, The method includes: Obtain the three-phase active power and three-phase reactive power measurements at the photovoltaic grid connection point; Based on the measured values ​​of the three-phase active power and the three-phase reactive power, calculate the three-phase power imbalance caused by the current load, and based on the three-phase power imbalance, determine the three-phase theoretical compensation current for achieving full compensation. Obtain the rated current limit and neutral line allowable current limit of the photovoltaic converter; Based on the rated current limit and the neutral line allowable current limit, the three-phase theoretical compensation current is subjected to capacity constraint processing to generate a three-phase actual compensation current command that meets the converter capacity limit. The actual three-phase compensation current command is superimposed on the grid-connected positive sequence current command of the photovoltaic converter to generate the final current inner loop reference value, which is then injected into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

2. The method according to claim 1, characterized in that, The determination of the three-phase theoretical compensation current for achieving complete compensation based on the three-phase power imbalance includes: Based on the deviations between the measured active power values ​​and the measured reactive power values ​​of each phase, calculate the theoretical active power compensation power and theoretical reactive power compensation power required for each phase respectively. Based on the theoretical active power compensation power and the theoretical reactive power compensation power, and combined with the positive sequence component of the grid connection point voltage, the theoretical active power compensation current component and the theoretical reactive power compensation current component of each phase are calculated respectively. The theoretical active compensation current component and the theoretical reactive compensation current component of each phase are vector synthesized to obtain the theoretical compensation current of each phase.

3. The method according to claim 1, characterized in that, The photovoltaic converter includes a DC-DC stage and a DC-AC stage. When performing the method, no additional current sensor is added. The method also includes: The DC-DC stage of the photovoltaic converter executes a preset maximum power point tracking algorithm to adjust the DC bus voltage according to the target power. While performing phase-locking and DC bus voltage regulation, the DC-AC stage of the photovoltaic converter superimposes the actual three-phase compensation current command with the grid-connected positive sequence current command, and achieves current tracking control through a proportional resonant controller.

4. The method according to claim 1, characterized in that, Before generating a three-phase actual compensation current command that satisfies the converter capacity limit by performing capacity constraint processing on the three-phase theoretical compensation current based on the rated current limit and the neutral line allowable current limit, the process further includes: Obtain the currently available computing resource information for the photovoltaic converter; Based on the computing resource information, determine whether the current computing power meets the optimal computing conditions. If it does, select the optimal computing strategy; otherwise, select the fast computing strategy.

5. The method according to claim 4, characterized in that, The step of determining whether the current computing power meets the optimal computing conditions based on the computing resource information, and selecting the optimal computing strategy if it does, and selecting the fast computing strategy if it does not, includes: When the optimal calculation strategy is selected, the minimum weighted sum of the uncompensated negative-sequence current component and the zero-sequence current component is taken as the optimization objective. The constraints are that the effective value of each phase current is not greater than the rated current limit and the effective value of the neutral current is not greater than the allowable neutral current limit. The Lagrange multiplier method is used to jointly solve the optimization objective and the constraints to obtain the optimal allocation result of the compensation current for each phase, which is then output as the actual compensation current command for the three phases.

6. The method according to claim 4, characterized in that, The step of determining whether the current computing power meets the optimal computing conditions based on the computing resource information, and selecting the optimal computing strategy if it does, and selecting the fast computing strategy if it does not, includes: When the fast calculation strategy is selected, the first type of scaling factor for ensuring that the current of each phase does not exceed the limit and the second type of scaling factor for ensuring that the neutral line current does not exceed the limit are calculated respectively. Based on the second type of scaling factor, the first candidate value that satisfies the neutral line safety constraint is determined first, and then the minimum value among the first type of scaling factors is taken as the second candidate value for evaluating the phase current compensation potential. The first candidate value and the second candidate value are compared, and the larger one is taken as the dynamic scaling factor. The three-phase theoretical compensation current is scaled proportionally using the dynamic scaling factor to obtain the three-phase actual compensation current command.

7. A three-phase four-wire unbalanced current compensation device based on the margin of a photovoltaic converter, characterized in that, The device includes: The power measurement module is used to acquire the three-phase active power measurement value and the three-phase reactive power measurement value of the photovoltaic grid connection point; The imbalance module is used to calculate the three-phase power imbalance caused by the current load based on the measured values ​​of the three-phase active power and the three-phase reactive power, and to determine the three-phase theoretical compensation current for achieving full compensation based on the three-phase power imbalance. The current limiting module is used to obtain the rated current limit and the neutral line allowable current limit of the photovoltaic converter; The compensation instruction module is used to perform capacity constraint processing on the three-phase theoretical compensation current according to the rated current limit and the neutral line allowable current limit, and generate a three-phase actual compensation current instruction that meets the converter capacity limit. The compensation execution module is used to superimpose the actual three-phase compensation current command onto the grid-connected positive sequence current command of the photovoltaic converter, generate the final current inner loop reference value, and inject it into the converter current inner loop for tracking control, so as to achieve real-time suppression of negative sequence current and zero sequence current.

8. A computer device comprising a memory and a processor, wherein the memory stores a computer program, characterized in that, When the processor executes the computer program, it implements the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

10. A computer program product, comprising a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 6.

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