A method and apparatus for implementing fault ride-through control strategy in a photovoltaic-storage combined power generation system

Abstract

This invention discloses a method and apparatus for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system. The method includes: under normal grid-connected operation of the photovoltaic-storage combined power generation system, the photovoltaic inverter adopts a pre-set maximum power point tracking control strategy, and the energy storage converter adopts a constant power control strategy to achieve stable operation; under the condition of an asymmetrical fault occurring in the grid-connected photovoltaic-storage combined power generation system, the photovoltaic inverter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter to achieve fault ride-through; the energy storage converter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter to support fault ride-through, and adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and more specifically, to a method and apparatus for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system. Background Technology

[0002] In recent years, photovoltaic (PV) energy, as a renewable energy source, has been connected to the grid on a large scale. At the same time, in order to address power quality issues such as grid voltage fluctuations caused by the intermittency, randomness, and volatility of PV output, constructing a PV-storage combined power generation system based on energy storage technology has become one of the effective means to solve the PV grid connection problem.

[0003] Furthermore, asymmetrical faults frequently occur during actual grid operation, causing asymmetrical voltage drops at the grid connection point of photovoltaic (PV) power generation systems. In this situation, on the one hand, the poor tolerance of power electronic device interfaces may lead to PV power generation systems disconnecting from the grid, hindering the effective utilization of renewable energy; on the other hand, the presence of negative-sequence components will cause fluctuations in the output power of the PV power generation system, resulting in second harmonics in the DC-side voltage of the PV inverter. Therefore, an asymmetrical fault ride-through control strategy that can ensure the PV power generation system does not disconnect from the grid and eliminate the impact of negative-sequence components on the PV power generation system urgently needs research. Existing research on inverter asymmetrical fault ride-through control strategies mainly focuses on: simultaneously supplying reactive power to the grid to support voltage and supplying active power to reduce instantaneous power imbalance, while suppressing the inverter's output negative-sequence current to reduce the DC-side second harmonic content and suppress output power fluctuations. However, suppressing negative-sequence current reduces the short-circuit current level of the PV power generation system, thus affecting the sensitivity of relay protection. In addition, some studies have focused on enabling photovoltaic power generation systems to simultaneously achieve four control objectives: voltage support, active power oscillation constraint, inverter output current limiting, and active power output. However, the combined constraint of multiple objectives will significantly reduce the voltage support capability and the effect of reducing instantaneous active power imbalance of the photovoltaic power generation system. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a method and apparatus for implementing fault ride-through control strategies in a photovoltaic-storage combined power generation system.

[0005] According to one aspect of the present invention, a method for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system is provided, comprising:

[0006] Under normal grid-connected operation of the photovoltaic-storage combined power generation system, the photovoltaic inverter adopts a pre-set maximum power point tracking control strategy, and the energy storage converter adopts a constant power control strategy to achieve stable operation.

[0007] In the event of an asymmetrical fault during grid connection of the photovoltaic-storage combined power generation system, the photovoltaic inverter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter, thereby achieving fault ride-through.

[0008] The energy storage converter outputs active and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter to support fault ride-through, and adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

[0009] Optionally, the photovoltaic inverter employs a pre-set maximum power point tracking control strategy, including:

[0010] The d-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system is obtained by the maximum power point tracking strategy.

[0011] By setting the q-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system to a preset threshold, the grid-connected and normal operation of the photovoltaic-storage combined power generation system can be achieved.

[0012] Optionally, the energy storage converter employs a constant power control strategy, including:

[0013] The positive sequence components of the energy storage converter are set as the voltage and current themselves;

[0014] The difference between the active power dispatch command value of the energy storage converter and the active power output value of the photovoltaic inverter is used as the reference value of the active power output of the energy storage converter.

[0015] The difference between the reactive power dispatch command value of the energy storage converter and the reactive power output value of the photovoltaic inverter is used as the reference value for the active power output of the energy storage converter and the reference value for the reactive power output.

[0016] Optionally, the expression for the actual reactive current reference value of the photovoltaic inverter during fault ride-through is:

[0017]

[0018] The expression for the actual active current reference value of a photovoltaic inverter is:

[0019]

[0020] In the formula, This is the actual reactive current reference value for the photovoltaic inverter. I is the actual active current reference value of the photovoltaic inverter. PVN This refers to the rated output current of the photovoltaic inverter. This is the per-unit value of the positive sequence voltage for PCC.

[0021] Optionally, the expression for the actual reactive current reference value of the energy storage converter during fault ride-through is:

[0022]

[0023] The expression for the actual active current reference value of the energy storage converter is:

[0024]

[0025] In the formula, This is the actual reactive current reference value for the energy storage converter. I is the actual active current reference value of the energy storage converter. ESN This refers to the rated output current of the energy storage converter. This is the per-unit value of the positive sequence voltage for PCC.

[0026] Alternatively, the implementation scheme of the negative sequence voltage compensation control strategy is as follows:

[0027] The pre-set negative sequence virtual conductance is multiplied by the PCC negative sequence voltage of the energy storage converter, and the energy storage converter is controlled to track the product and output a negative sequence current.

[0028] Based on the negative sequence current, a quasi-PR current controller is adopted to make the negative sequence control loop of the energy storage current device equivalent to the negative sequence virtual conductance.

[0029] The negative sequence virtual conductance is connected in series with the negative sequence equivalent impedance from the grid-side fault point to the grid connection point to reduce the negative sequence voltage at the grid connection point.

[0030] Alternatively, the design scheme for negative sequence virtual conductance is as follows:

[0031] The design incorporates a negative-sequence virtual conductance that adaptively adjusts based on the remaining rechargeable and dischargeable capacity of the energy storage battery to prevent overcharging or over-discharging.

[0032] The negative sequence virtual conductance is adaptively adjusted based on the voltage imbalance at the grid connection point.

[0033] The maximum value of the negative sequence virtual conductance is determined based on the maximum limit value of the output current of the energy storage current device.

[0034] According to another aspect of the present invention, a device for implementing a fault ride-through control strategy for a photovoltaic-storage combined power generation system is provided, comprising:

[0035] The first module is used to ensure stable operation of the photovoltaic inverter and the energy storage converter under the normal grid-connected operation of the photovoltaic-storage combined power generation system.

[0036] The second module is used to enable the photovoltaic inverter to output active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter in the event of an asymmetrical fault in the grid connection of the photovoltaic-storage combined power generation system, thereby achieving fault ride-through.

[0037] The third module is used by the energy storage converter to output active and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter, to support fault ride-through, and adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

[0038] According to another aspect of the present invention, a computer-readable storage medium is provided, the storage medium storing a computer program for performing the methods described in any of the above aspects of the present invention.

[0039] According to another aspect of the present invention, an electronic device is provided, the electronic device comprising: a processor; a memory for storing executable instructions of the processor; the processor being configured to read the executable instructions from the memory and execute the instructions to implement the method described in any of the preceding aspects of the present invention.

[0040] Therefore, this invention proposes a fault ride-through control strategy for a photovoltaic-storage combined power generation system under asymmetrical voltage dips. In the event of an asymmetrical grid-connected fault, the photovoltaic inverter outputs active and reactive power based on its actual reactive current reference values ​​and actual active current reference values ​​to achieve fault ride-through. The energy storage converter outputs active and reactive power based on its actual reactive current reference values ​​and actual active current reference values ​​to support fault ride-through. Furthermore, a negative-sequence voltage compensation control strategy is employed to reduce the impact of PCC negative-sequence voltage on the photovoltaic inverter, further addressing the fault ride-through issues of photovoltaic power generation systems under asymmetrical voltage dips, as well as the power output fluctuations and second harmonics in the DC-side voltage caused by negative-sequence components. The fault ride-through control strategy provided in this application enables the photovoltaic power generation system to output reactive power according to grid-connected standards during voltage dips. Attached Figure Description

[0041] Exemplary embodiments of the present invention can be more fully understood by referring to the following figures:

[0042] Figure 1 This is a flowchart illustrating the implementation method of the fault ride-through control strategy for a photovoltaic-storage combined power generation system provided in an exemplary embodiment of the present invention.

[0043] Figure 2 This is a grid-connected topology diagram of a photovoltaic-storage combined power generation system provided in an exemplary embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram of a photovoltaic inverter control strategy provided in an exemplary embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of an energy storage converter control strategy provided in an exemplary embodiment of the present invention;

[0046] Figure 5 This is another flowchart illustrating the implementation method of the fault ride-through control strategy for a photovoltaic-storage combined power generation system provided in an exemplary embodiment of the present invention;

[0047] Figure 6 This is a block diagram of positive sequence current control for an energy storage converter provided in an exemplary embodiment of the present invention;

[0048] Figure 7 This is an equivalent block diagram of the negative sequence control loop of an energy storage converter provided in an exemplary embodiment of the present invention;

[0049] Figure 8 This is an equivalent block diagram of the negative sequence control loop of an energy storage converter provided in an exemplary embodiment of the present invention;

[0050] Figure 9 This is a schematic diagram of the Norton equivalent circuit of the negative sequence control loop provided in an exemplary embodiment of the present invention;

[0051] Figure 10a This is a Bode plot of the negative-order closed-loop transfer function provided in an exemplary embodiment of the present invention;

[0052] Figure 10b This is a negative-order output admittance Bode plot provided by an exemplary embodiment of the present invention;

[0053] Figure 11 This is a schematic diagram of the equivalent circuit for negative sequence voltage compensation of a single energy storage converter provided in an exemplary embodiment of the present invention;

[0054] Figure 12 This is a schematic diagram of the equivalent circuit for negative sequence voltage compensation of n energy storage converters provided in an exemplary embodiment of the present invention;

[0055] Figure 13 This is a schematic diagram of the structure of a device for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system, provided in an exemplary embodiment of the present invention.

[0056] Figure 14 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. Detailed Implementation

[0057] Hereinafter, exemplary embodiments according to the present invention will be described in detail with reference to the accompanying drawings. Obviously, the described embodiments are merely some embodiments of the present invention, and not all embodiments of the present invention. It should be understood that the present invention is not limited to the exemplary embodiments described herein.

[0058] It should be noted that, unless otherwise specifically stated, the relative arrangement, numerical expressions, and values ​​of the components and steps described in these embodiments do not limit the scope of the invention.

[0059] Those skilled in the art will understand that the terms "first," "second," etc., in the embodiments of the present invention are only used to distinguish different steps, devices, or modules, and do not represent any specific technical meaning, nor do they indicate a necessary logical order between them.

[0060] It should also be understood that in the embodiments of the present invention, "multiple" can refer to two or more, and "at least one" can refer to one, two or more.

[0061] It should also be understood that any component, data or structure mentioned in the embodiments of the present invention can generally be understood as one or more unless explicitly defined or given contrary instructions in the context.

[0062] Furthermore, the term "and / or" in this invention is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. Additionally, the character " / " in this invention generally indicates that the preceding and following related objects have an "or" relationship.

[0063] It should also be understood that the description of the various embodiments in this invention emphasizes the differences between the various embodiments, and the similarities or similarities can be referred to each other. For the sake of brevity, they will not be described in detail.

[0064] At the same time, it should be understood that, for ease of description, the dimensions of the various parts shown in the accompanying drawings are not drawn according to actual scale.

[0065] The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the invention or its application or use.

[0066] Techniques, methods, and equipment known to those skilled in the art may not be discussed in detail, but where appropriate, they should be considered part of the specification.

[0067] It should be noted that similar labels and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be discussed further in subsequent figures.

[0068] The embodiments of this invention can be applied to electronic devices such as terminal devices, computer systems, and servers, and can operate together with a wide range of other general-purpose or special-purpose computing system environments or configurations. Well-known examples of terminal devices, computing systems, environments, and / or configurations suitable for use with electronic devices such as terminal devices, computer systems, and servers include, but are not limited to: personal computer systems, server computer systems, thin clients, thick clients, handheld or laptop devices, microprocessor-based systems, set-top boxes, programmable consumer electronics, network PCs, minicomputer systems, mainframe computer systems, and distributed cloud computing environments including any of the above systems, etc.

[0069] Electronic devices such as terminal devices, computer systems, and servers can be described in the general context of computer system executable instructions (such as program modules) executed by a computer system. Typically, program modules can include routines, programs, object programs, components, logic, data structures, etc., which perform specific tasks or implement specific abstract data types. Computer systems / servers can be implemented in distributed cloud computing environments, where tasks are executed by remote processing devices linked through communication networks. In distributed cloud computing environments, program modules can reside on local or remote computing system storage media, including storage devices.

[0070] Exemplary methods

[0071] Figure 1 This is a flowchart illustrating a method for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system according to an exemplary embodiment of the present invention. This embodiment can be applied to electronic devices, such as… Figure 1 As shown, the fault ride-through control strategy implementation method 100 for a photovoltaic-storage combined power generation system includes the following steps:

[0072] Step 101: Under the normal grid-connected operation of the photovoltaic-storage combined power generation system, the photovoltaic inverter adopts a pre-set maximum power point tracking control strategy, and the energy storage converter adopts a constant power control strategy to achieve stable operation.

[0073] Step 102: In the event of an asymmetrical fault in the grid connection of the photovoltaic-storage combined power generation system, the photovoltaic inverter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter to achieve fault ride-through.

[0074] The fault ride-through is difficult. The energy storage converter outputs active and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter to support fault ride-through. It also adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

[0075] Optionally, the photovoltaic inverter employs a pre-set maximum power point tracking control strategy, including:

[0076] The d-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system is obtained by the maximum power point tracking strategy.

[0077] By setting the q-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system to a preset threshold, the grid-connected and normal operation of the photovoltaic-storage combined power generation system can be achieved.

[0078] Optionally, the energy storage converter employs a constant power control strategy, including:

[0079] The positive sequence components of the energy storage converter are set as the voltage and current themselves;

[0080] The difference between the active power dispatch command value of the energy storage converter and the active power output value of the photovoltaic inverter is used as the reference value of the active power output of the energy storage converter.

[0081] The difference between the reactive power dispatch command value of the energy storage converter and the reactive power output value of the photovoltaic inverter is used as the reference value for the active power output of the energy storage converter and the reference value for the reactive power output.

[0082] Optionally, the expression for the actual reactive current reference value of the photovoltaic inverter during fault ride-through is:

[0083]

[0084] The expression for the actual active current reference value of a photovoltaic inverter is:

[0085]

[0086] In the formula, This is the actual reactive current reference value for the photovoltaic inverter. I is the actual active current reference value of the photovoltaic inverter. PVN This refers to the rated output current of the photovoltaic inverter. This is the per-unit value of the positive sequence voltage for PCC.

[0087] Optionally, the expression for the actual reactive current reference value of the energy storage converter during fault ride-through is:

[0088]

[0089] The expression for the actual active current reference value of the energy storage converter is:

[0090]

[0091] In the formula, This is the actual reactive current reference value for the energy storage converter. I is the actual active current reference value of the energy storage converter. ESN This refers to the rated output current of the energy storage converter. This is the per-unit value of the positive sequence voltage for PCC.

[0092] Alternatively, the implementation scheme of the negative sequence voltage compensation control strategy is as follows:

[0093] The pre-set negative sequence virtual conductance is multiplied by the PCC negative sequence voltage of the energy storage converter, and the energy storage converter is controlled to track the product and output a negative sequence current.

[0094] Based on the negative sequence current, a quasi-PR current controller is adopted to make the negative sequence control loop of the energy storage current device equivalent to the negative sequence virtual conductance.

[0095] The negative sequence virtual conductance is connected in series with the negative sequence equivalent impedance from the grid-side fault point to the grid connection point to reduce the negative sequence voltage at the grid connection point.

[0096] Alternatively, the design scheme for negative sequence virtual conductance is as follows:

[0097] The design incorporates a negative-sequence virtual conductance that adaptively adjusts based on the remaining rechargeable and dischargeable capacity of the energy storage battery to prevent overcharging or over-discharging.

[0098] The negative sequence virtual conductance is adaptively adjusted based on the voltage imbalance at the grid connection point.

[0099] The maximum value of the negative sequence virtual conductance is determined based on the maximum limit value of the output current of the energy storage current device.

[0100] Specifically, to further address the problem of asymmetrical voltage dips at the grid connection point and improve the operational stability of photovoltaic power generation systems, this invention proposes a novel fault ride-through control strategy for photovoltaic-storage combined power generation systems under asymmetrical voltage dips. The proposed control strategy utilizes an energy storage converter to compensate for the negative sequence voltage at the grid connection point, thereby eliminating the adverse effects of negative sequence voltage on the photovoltaic power generation system. This ensures the photovoltaic power generation system outputs active and reactive power to reduce power imbalance and achieve voltage support.

[0101] The purpose of this invention is to achieve fault ride-through of photovoltaic (PV) power generation systems under asymmetrical voltage dips and to solve the problems of output power fluctuations and second harmonics in DC-side voltage caused by negative-sequence components. To achieve this goal, this invention proposes a fault ride-through control strategy for PV-storage combined power generation systems under asymmetrical voltage dips. This control strategy enables the PV power generation system to output reactive power according to grid connection standards during voltage dips and to utilize remaining capacity to output active power. Furthermore, this strategy controls the energy storage converter to output a certain amount of active and reactive power to provide support, and introduces a negative-sequence virtual conductance control loop to utilize the synergistic effect of multiple parallel energy storage converters to compensate for the negative-sequence voltage at the grid connection point, thereby reducing the adverse effects caused by negative-sequence components.

[0102] Specifically, it includes the following aspects:

[0103] (1) Fault ride-through control strategy for photovoltaic-storage combined power generation system

[0104] Figure 2 This is a system structure diagram consisting of n photovoltaic and energy storage units connected in parallel via a transformer. The proposed control strategies for the photovoltaic inverter and energy storage converter are as follows: Figure 3 , Figure 4 As shown, Figure 5 This is the overall control flowchart. Figure 3 middle, These represent the positive-sequence dq-axis components of the three-phase output current from the photovoltaic inverter after Park transformation. These are the positive-sequence dq-axis components of the three-phase voltage at the point of common coupling (PCC) after Park transformation. These are the reference values ​​for the positive sequence components of the photovoltaic inverter output current along the dq axis in a synchronous rotating coordinate system.

[0105] exist Figure 4 middle, These represent the positive-sequence dq-axis components of the three-phase output current from the energy storage converter after Park transformation. These are the reference values ​​for the positive sequence components of the energy storage converter output current along the dq axis in a synchronous rotating coordinate system, P. ref Q ref These are the reference values ​​for the active and reactive power outputs of the energy storage converter, respectively. The negative sequence control loop is as follows: Figure 4 As shown in the dashed box. The αβ-axis component of the PCC negative sequence voltage after Clarke transformation under asymmetrical voltage drop conditions. The αβ-axis component of the three-phase negative sequence current output by the energy storage converter after Clarke transformation. The reference value for the αβ axis component of the negative sequence current output by the energy storage converter in a two-phase stationary coordinate system. This is the introduced negative-order virtual conductance.

[0106] When the system is operating normally, switch S1 is closed, and the photovoltaic inverter adopts the maximum power point tracking (MPPT) control strategy. Obtained by MPPT control, Set it to 0.

[0107] Simultaneously, with switch S2 closed, the voltage and current contain no negative sequence components, and the negative sequence control loop is inactive. The positive sequence components are the voltage and current themselves. The energy storage converter adopts a constant power control strategy, P refQ ref The difference between the active and reactive power dispatch command values ​​and the active and reactive power output values ​​of the photovoltaic inverter is used as a reference value for the active and reactive power output of the energy storage converter, thereby smoothing out the output power fluctuations of the photovoltaic power generation system.

[0108] When an asymmetrical voltage drop occurs at the grid connection point, switch S1 opens, and the photovoltaic inverter outputs active and reactive power according to the active and reactive current reference values ​​to achieve fault ride-through. During fault ride-through, the actual reactive current reference value of the photovoltaic inverter... The expression is:

[0109]

[0110] In the formula: I PVN This refers to the rated output current of the photovoltaic inverter. This is the per-unit value of the positive sequence voltage for PCC.

[0111] Due to limitations imposed by the inverter's maximum output current and reactive power priority output, the actual active current reference value of the photovoltaic inverter... The expression can be set as:

[0112]

[0113] Photovoltaic inverters control the positive sequence component of the current. The output active and reactive power are controlled by the energy storage converter. The negative sequence component has a negligible impact on the photovoltaic inverter after compensation by the energy storage converter, so its effect is not considered. Therefore, the photovoltaic inverter controls the output active and reactive power by controlling the actual reactive current reference value and the actual active current reference value.

[0114] Simultaneously, switch S2 opens, and the energy storage converter outputs a certain amount of active and reactive power according to the active and reactive current reference values ​​to support fault ride-through. During fault ride-through, the reactive current reference value of the energy storage converter... The expression is:

[0115]

[0116] In the formula: I ESN This is the rated output current of the energy storage converter.

[0117] Actual active current reference value of energy storage converter The expression is:

[0118]

[0119] At this time, the energy storage converter prioritizes supplying a certain amount of reactive power to the grid to support the voltage, and also supplies a certain amount of active power to reduce the degree of instantaneous power imbalance. Furthermore, the negative sequence control loop comes into play, employing a negative sequence voltage compensation control strategy based on adaptive negative sequence virtual conductance to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter. Thus, the energy storage converter controls the output active and reactive power by controlling the actual reactive current reference values ​​and the actual active current reference values.

[0120] (2) Principle of Negative Sequence Voltage Compensation Control Strategy for Energy Storage Converter

[0121] In the positive sequence control loop of the energy storage converter, the following is adopted: Figure 6 The current decoupling control strategy shown in the dashed box has the following relationship between the positive sequence components of voltage and current in a two-phase rotating coordinate system:

[0122]

[0123] In the formula: These are the positive sequence dq-axis components of the energy storage converter output voltage, k p k i These are the proportional and integral control coefficients of the PI controller, respectively.

[0124] As shown in equation (5), the equivalent block diagram of the positive sequence control loop of the energy storage converter is as follows: Figure 7 As shown, The transfer function for the positive sequence current controller is given, using a PI controller, G. PWM This is a coefficient representing the voltage conversion and power transmission functions of the converter.

[0125] The equivalent block diagram of the negative sequence control loop of the energy storage converter is as follows: Figure 8 As shown, For the negative sequence current controller transfer function. This is the negative sequence component of the PCC voltage. (From...) Figure 8 The negative sequence output current can be derived. The expression is:

[0126]

[0127] In the formula: G N (s) is the closed-loop transfer function of the negative sequence output current of the energy storage converter. This is the negative sequence equivalent output admittance of the energy storage converter.

[0128] From equation (6), the Norton equivalent circuit of the negative sequence control loop of the energy storage converter can be obtained as follows: Figure 9 As shown. To accurately track the αβ axis current, the negative sequence current controller employs a quasi-PR controller, the expression of which is:

[0129]

[0130] In the formula: k P1 k R1 These are the proportional adjustment coefficient and the resonant gain coefficient, respectively, where ω0 is the resonant frequency of the quasi-PR controller, and ω c is the resonant bandwidth at the resonant frequency.

[0131] design So that G N (s) and The values ​​at the fundamental angular frequency points are approximately 1 and 0, respectively, G N (s) and Bode diagram as shown Figure 10a and 10b As shown, let the negative sequence current reference value be... If the value is 0, then the negative sequence current of the energy storage output in equation (6) is 0. The expression can be simplified to:

[0132]

[0133] From equation (8), we can see that the output value of the energy storage converter is a negative sequence current, the magnitude of which depends on the product of the negative sequence virtual conductance and the PCC negative sequence voltage.

[0134] Combination Figure 9 According to the analysis of equation (8), the energy storage converter with negative sequence voltage compensation control strategy is equivalent to a negative sequence virtual conductance. The equivalent circuit for negative sequence voltage compensation obtained by connecting a single energy storage converter to a PCC is as follows: Figure 11 As shown, The equivalent negative sequence voltage source at the fault point. It is the equivalent negative sequence impedance of the line between the fault point and the PCC.

[0135] Depend on Figure 11 The PCC negative sequence voltage with compensation by a single energy storage converter can be obtained. for:

[0136]

[0137] From equation (9), it can be seen that the negative sequence virtual conductance The larger the value, the smaller the negative sequence voltage of the PCC, and the better the negative sequence voltage compensation effect. At the same time, the energy storage converter also absorbs a larger negative sequence current. However, considering the current limiting problem of the energy storage converter, the negative sequence virtual conductance should be designed reasonably.

[0138] Depend on Figure 2It can be seen that in actual operation, multiple photovoltaic-storage combined power generation systems operate in parallel and collaboratively. There are n energy storage converters connected to the PCC operating simultaneously, all employing a negative sequence voltage compensation control strategy. The equivalent circuit for negative sequence voltage compensation of the n energy storage converters can be obtained as follows: Figure 12 As shown.

[0139] Depend on Figure 12 The PCC negative sequence voltage can be obtained by using n energy storage converters for compensation. for:

[0140]

[0141] As shown in equation (10), the negative sequence voltage compensation effect of PCC at this time depends on the sum of the equivalent negative sequence virtual conductance of n energy storage converters. Compared with the connection of a single energy storage converter, the increased total virtual conductance can further weaken the negative sequence voltage. As can be seen from the above, both the negative sequence voltage compensation effect and the magnitude of the negative sequence current output by the energy storage converter are affected by the negative sequence virtual conductance. Next, the negative sequence virtual conductance will be analyzed and designed.

[0142] (3) Adaptive negative sequence virtual conductance design

[0143] First, during fault ride-through, the energy storage battery outputs negative sequence current to compensate for the negative sequence voltage. To prevent the battery from being damaged by overcharging or over-discharging due to the compensation for the negative sequence voltage, the remaining rechargeable and dischargeable capacity of each energy storage battery needs to be determined by combining the current value of the energy storage battery's state-of-charge (SOC) and its current rate of change.

[0144] Define the remaining rechargeable and dischargeable capacity coefficient K of the i-th energy storage battery. SOCi for:

[0145]

[0146] Where: SOC i Let be the current SOC of the i-th energy storage battery, 0.2 be the lower limit of the energy storage battery SOC, and 0.8 be the upper limit of the energy storage battery SOC.

[0147] As can be seen from equation (11), when the energy storage battery is in the charging state but SOC≥0.8, or in the discharging state but SOC≤0.2, the remaining chargeable and discharge capacity coefficient of the energy storage battery is designed to be 0, so that it does not participate in the negative sequence voltage compensation circuit, and prevents the energy storage battery from being damaged by overcharging and over-discharging.

[0148] Secondly, the negative sequence voltage of PCC is related to the type and location of grid-side asymmetrical faults, and its magnitude can be represented by the voltage imbalance. The design of the negative sequence virtual conductance should meet the requirements of the energy storage converter to adaptively adjust the output of the negative sequence voltage compensation according to the PCC voltage imbalance.

[0149] Define the voltage unbalance coefficient η at PCC as:

[0150]

[0151] In the formula: This is the positive sequence voltage of PCC.

[0152] The negative sequence virtual conductance of the i-th energy storage converter is then adjusted by subtracting η from 0 and passing the result through a proportional controller. It can be set as:

[0153]

[0154] In the formula: k p2 This is the proportional control coefficient of the proportional controller.

[0155] The result adjusted by the proportional controller is multiplied by a coefficient K. SOCi / ∑K SOCj As the negative sequence virtual conductance value of the i-th energy storage converter, each energy storage converter adjusts the output of the negative sequence voltage compensation circuit according to the remaining chargeable and dischargeable capacity of the energy storage battery, and causes the energy storage converter with a remaining chargeable and dischargeable capacity of the energy storage battery to exit the negative sequence voltage compensation circuit, so as to avoid overcharging and over-discharging of the energy storage battery.

[0156] Finally, the energy storage converter outputs positive-sequence current based on the degree of drop in the positive-sequence voltage of the PCC. Since the negative-sequence voltage of the PCC is measurable, the negative-sequence current output by the energy storage converter depends on the negative-sequence virtual conductance. To ensure that the current output by each phase of the energy storage converter does not exceed the maximum limit, the negative-sequence virtual conductance should be limited, and its maximum value should be determined.

[0157] The maximum negative sequence virtual conductance of the i-th energy storage converter satisfy:

[0158]

[0159] In the formula: It represents the maximum value of the negative sequence current phasor magnitude output by the i-th energy storage converter.

[0160] Define the positive and negative sequence A-phase current phasors of the i-th energy storage converter. for:

[0161]

[0162] In the formula: These are the positive and negative sequence A-phase current phasor magnitudes of the i-th energy storage converter, θ and θ, respectively. Pi θ Ni The positive and negative sequence A-phase current phasors and phase angles of the i-th energy storage converter are respectively.

[0163] The three-phase output current of the energy storage converter must not exceed the maximum limit value I. ESmax Therefore corresponding The following condition must be met:

[0164]

[0165] By combining equations (14) to (16), the maximum negative sequence virtual conductance of the i-th energy storage converter can be obtained.

[0166] Therefore, this invention proposes a fault ride-through control strategy for photovoltaic-storage combined power generation systems under asymmetrical voltage dips, further addressing the issues of fault ride-through in photovoltaic power generation systems under asymmetrical voltage dips, as well as the output power fluctuations of photovoltaic power generation systems caused by negative sequence components and the presence of second harmonics in the DC-side voltage. First, during fault ride-through, the photovoltaic inverter, while meeting relevant standard requirements for reactive power output, maximizes active power output without causing overcurrent in the inverter. This supports the grid connection voltage and reduces instantaneous active power imbalance. Second, the energy storage converter provides a certain amount of active and reactive power support and adopts a negative-sequence voltage compensation strategy based on adaptive negative-sequence virtual conductance to eliminate the impact of negative-sequence components on the photovoltaic inverter. Third, the design of the negative-sequence virtual conductance considers the remaining rechargeable and dischargeable capacity of the energy storage battery. The negative-sequence voltage compensation output of the energy storage battery is adjusted according to the remaining rechargeable and dischargeable capacity to avoid overcharging and over-discharging of the energy storage battery. In addition, the negative-sequence virtual conductance is adaptively adjusted based on the grid connection voltage imbalance to maximize the compensation of negative-sequence voltage. Finally, a maximum limit value for the negative-sequence virtual conductance is designed to ensure that the three-phase output current of the energy storage converter does not exceed the maximum limit value.

[0167] Exemplary device

[0168] Figure 13 This is a schematic diagram of the structure of a device for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system, provided in an exemplary embodiment of the present invention. Figure 13 As shown, the device 1300 includes:

[0169] The first module 1310 is used to ensure stable operation of the photovoltaic inverter and the energy storage converter under the normal grid-connected operation of the photovoltaic-storage combined power generation system.

[0170] The second module 1320 is used to enable the photovoltaic inverter to output active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter in the event of an asymmetrical fault in the grid connection of the photovoltaic-storage combined power generation system, thereby achieving fault ride-through.

[0171] The third module, 1330, is used by the energy storage converter to output active and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter, supporting fault ride-through. It also adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

[0172] Optionally, the first employing module 1310 includes:

[0173] The synchronization submodule is used to obtain the d-axis component of the photovoltaic inverter's output current in the synchronous rotating coordinate system using the maximum power point tracking strategy.

[0174] The first setting submodule is used to set the q-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system to a preset threshold, so as to realize the grid-connected normal operation of the photovoltaic-storage combined power generation system.

[0175] Optionally, the first employing module 1310 includes:

[0176] The second setting submodule is used to set the positive sequence components of the energy storage converter to the voltage and current themselves.

[0177] The first submodule is used to take the difference between the active power dispatch command value of the energy storage converter and the active power output value of the photovoltaic inverter as the reference value of the active power output of the energy storage converter.

[0178] The second submodule is used to take the difference between the reactive power dispatch command value of the energy storage converter and the reactive power output value of the photovoltaic inverter as the reference value of the active power output of the energy storage converter and the reference value of the reactive power.

[0179] Optionally, the expression for the actual reactive current reference value of the photovoltaic inverter during fault ride-through is:

[0180]

[0181] The expression for the actual active current reference value of a photovoltaic inverter is:

[0182]

[0183] In the formula, This is the actual reactive current reference value for the photovoltaic inverter. I is the actual active current reference value of the photovoltaic inverter. PVN This refers to the rated output current of the photovoltaic inverter. This is the per-unit value of the positive sequence voltage for PCC.

[0184] Optionally, the expression for the actual reactive current reference value of the energy storage converter during fault ride-through is:

[0185]

[0186] The expression for the actual active current reference value of the energy storage converter is:

[0187]

[0188] In the formula, This is the actual reactive current reference value for the energy storage converter. I is the actual active current reference value of the energy storage converter. ESN This refers to the rated output current of the energy storage converter. This is the per-unit value of the positive sequence voltage for PCC.

[0189] Alternatively, the implementation scheme of the negative sequence voltage compensation control strategy is as follows:

[0190] The pre-set negative sequence virtual conductance is multiplied by the PCC negative sequence voltage of the energy storage converter, and the energy storage converter is controlled to track the product and output a negative sequence current.

[0191] Based on the negative sequence current, a quasi-PR current controller is adopted to make the negative sequence control loop of the energy storage current device equivalent to the negative sequence virtual conductance.

[0192] The negative sequence virtual conductance is connected in series with the negative sequence equivalent impedance from the grid-side fault point to the grid connection point to reduce the negative sequence voltage at the grid connection point.

[0193] Alternatively, the design scheme for negative sequence virtual conductance is as follows:

[0194] The design incorporates a negative-sequence virtual conductance that adaptively adjusts based on the remaining rechargeable and dischargeable capacity of the energy storage battery to prevent overcharging or over-discharging.

[0195] The negative sequence virtual conductance is adaptively adjusted based on the voltage imbalance at the grid connection point.

[0196] The maximum value of the negative sequence virtual conductance is determined based on the maximum limit value of the output current of the energy storage current device.

[0197] Exemplary electronic devices

[0198] Figure 14 This is the structure of an electronic device provided in an exemplary embodiment of the present invention. For example... Figure 14 As shown, the electronic device 140 includes one or more processors 141 and memory 142.

[0199] The processor 141 may be a central processing unit (CPU) or other form of processing unit with data processing capabilities and / or instruction execution capabilities, and may control other components in the electronic device to perform desired functions.

[0200] The memory 142 may include one or more computer program products, which may include various forms of computer-readable storage media, such as volatile memory and / or non-volatile memory. The volatile memory may include, for example, random access memory (RAM) and / or cache memory. The non-volatile memory may include, for example, read-only memory (ROM), hard disk, flash memory, etc. One or more computer program instructions may be stored on the computer-readable storage medium, and the processor 141 may execute the program instructions to implement the methods of the software programs of the various embodiments of the present invention described above, and / or other desired functions. In one example, the electronic device may also include an input device 143 and an output device 144, these components being interconnected via a bus system and / or other forms of connection mechanisms (not shown).

[0201] In addition, the input device 143 may also include, for example, a keyboard, a mouse, etc.

[0202] The output device 144 can output various information to the outside. The output device 144 may include, for example, a display, a speaker, a printer, and a communication network and its connected remote output devices, etc.

[0203] Of course, for the sake of simplicity, Figure 14 Only some of the components of the electronic device relevant to the present invention are shown, omitting components such as buses, input / output interfaces, etc. In addition, the electronic device may include any other suitable components depending on the specific application.

[0204] Exemplary computer program products and computer-readable storage media

[0205] In addition to the methods and apparatus described above, embodiments of the present invention may also be computer program products, which include computer program instructions that, when executed by a processor, cause the processor to perform the steps in the methods according to various embodiments of the present invention described in the "Exemplary Methods" section above.

[0206] The computer program product can be written in any combination of one or more programming languages ​​to perform the operations of the embodiments of the present invention. The programming languages ​​include object-oriented programming languages ​​such as Java and C++, as well as conventional procedural programming languages ​​such as C or similar languages. The program code can be executed entirely on the user's computing device, partially on the user's computing device, as a standalone software package, partially on the user's computing device and partially on a remote computing device, or entirely on a remote computing device or server.

[0207] Furthermore, embodiments of the present invention may also be computer-readable storage media storing computer program instructions thereon, which, when executed by a processor, cause the processor to perform the steps of the methods for information mining of historical change records according to various embodiments of the present invention as described in the "Exemplary Methods" section above.

[0208] The computer-readable storage medium may be any combination of one or more readable media. A readable medium may be a readable signal medium or a readable storage medium. A readable storage medium may be, for example, an electrical, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or any combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: an electrical connection having one or more wires, a portable disk, a hard disk, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), optical fiber, portable compact disk read-only memory (CD-ROM), optical storage device, magnetic storage device, or any suitable combination thereof.

[0209] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0210] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For system embodiments, since they largely correspond to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments.

[0211] The block diagrams of devices, systems, devices, and systems involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, systems, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0212] The methods and systems of the present invention may be implemented in many ways. For example, they may be implemented by software, hardware, firmware, or any combination of software, hardware, and firmware. The above-described order of steps for the methods is for illustrative purposes only, and the steps of the methods of the present invention are not limited to the order specifically described above unless otherwise specifically stated. Furthermore, in some embodiments, the present invention may also be implemented as a program recorded on a recording medium, the program comprising machine-readable instructions for implementing the methods according to the present invention. Thus, the present invention also covers recording media storing programs for performing the methods according to the present invention.

[0213] It should also be noted that in the systems, apparatus, and methods of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered equivalents of the present invention. The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0214] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A method for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system, characterized in that, include: Under normal grid-connected operation of the photovoltaic-storage combined power generation system, the photovoltaic inverter adopts a pre-set maximum power point tracking control strategy, and the energy storage converter adopts a constant power control strategy to achieve stable operation. In the event of an asymmetrical fault during grid connection of the photovoltaic-storage combined power generation system, the photovoltaic inverter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter, thereby achieving fault ride-through. The energy storage converter outputs active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the energy storage converter to support fault ride-through, and adopts a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter. The implementation scheme of the negative sequence voltage compensation control strategy is as follows: The pre-set negative sequence virtual conductance is multiplied by the PCC negative sequence voltage of the energy storage converter, and the energy storage converter is controlled to track the product and output a negative sequence current. Based on the negative sequence current, a quasi-PR current controller is used to make the negative sequence control loop of the energy storage converter equivalent to the negative sequence virtual conductance. The negative sequence virtual conductance is connected in series with the negative sequence equivalent impedance from the grid-side fault point to the grid connection point to weaken the negative sequence voltage at the grid connection point.

2. The method according to claim 1, characterized in that, The photovoltaic inverter employs a pre-set maximum power point tracking control strategy, including: The d-axis component of the output current of the photovoltaic inverter in the synchronous rotating coordinate system is obtained by the maximum power point tracking strategy. The output current of the photovoltaic inverter in the synchronous rotating coordinate system is set to a preset threshold to realize the grid-connected normal operation of the photovoltaic-storage combined power generation system.

3. The method according to claim 1, characterized in that, The energy storage converter employs a constant power control strategy, including: The positive sequence components of the energy storage converter are set as the voltage and current themselves. The difference between the active power dispatch command value of the energy storage converter and the active power output value of the photovoltaic inverter is used as the reference value of the active power output by the energy storage converter. The difference between the reactive power dispatch command value of the energy storage converter and the reactive power output value of the photovoltaic inverter is used as the reference value of the reactive power output by the energy storage converter.

4. The method according to claim 1, characterized in that, The expression for the actual reactive current reference value of the photovoltaic inverter during fault ride-through is: （1） The expression for the actual active current reference value of the photovoltaic inverter is: （2） In the formula, i PPVqref is the actual reactive current reference value of the photovoltaic inverter. i PPVdref is the actual active current reference value of the photovoltaic inverter. I PVN This refers to the rated output current of the photovoltaic inverter. U P*PCC is the per-unit value of the positive sequence voltage of PCC.

5. The method according to claim 1, characterized in that, The expression for the actual reactive current reference value of the energy storage converter during fault ride-through is: （3） The expression for the actual active current reference value of the energy storage converter is: （4） In the formula, i PESqref is the actual reactive current reference value of the energy storage converter. i PESdref is the actual active current reference value of the energy storage converter. I ESN This refers to the rated output current of the energy storage converter. U P*PCC is the per-unit value of the positive sequence voltage of PCC.

6. The method according to claim 1, characterized in that, The design scheme for the negative sequence virtual conductance is as follows: The design incorporates a negative-sequence virtual conductance that adaptively adjusts based on the remaining rechargeable and dischargeable capacity of the energy storage battery to prevent overcharging or over-discharging. The negative sequence virtual conductance is adaptively adjusted based on the voltage imbalance at the grid connection point. The maximum value of the negative sequence virtual conductance is determined based on the maximum limit value of the output current of the energy storage current device.

7. A device for implementing a fault ride-through control strategy in a photovoltaic-storage combined power generation system, used to implement the method described in any one of claims 1-6, characterized in that, include: The first module is used to ensure stable operation of the photovoltaic inverter and the energy storage converter under the normal grid-connected operation of the photovoltaic-storage combined power generation system. The second module is used to enable the photovoltaic inverter to output active power and reactive power based on the actual reactive current reference value and the actual active current reference value of the photovoltaic inverter in the event of an asymmetrical fault in the grid connection of the photovoltaic-storage combined power generation system, thereby achieving fault ride-through. The third module is used by the energy storage converter to output active power and reactive power according to the actual reactive current reference value and the actual active current reference value of the energy storage converter, to support fault ride-through, and to adopt a negative sequence voltage compensation control strategy to reduce the impact of PCC negative sequence voltage on the photovoltaic inverter.

8. A computer-readable storage medium, characterized in that, The storage medium stores a computer program for performing the method described in any one of claims 1-6.

9. An electronic device, characterized in that, The electronic device includes: processor; Memory used to store the processor's executable instructions; The processor is configured to read the executable instructions from the memory and execute the instructions to implement the method described in any one of claims 1-6.

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