Fault ride-through period control method of photovoltaic inverter

Abstract

The invention provides a control method for a photovoltaic inverter in a fault ride-through period, and relates to the technical field of photovoltaic inverters. The method comprises the steps that reference voltage is collected, and the reference voltage is at least one of the positive sequence voltage, the minimum phase voltage and the maximum phase voltage of the alternating current side of the photovoltaic inverter; and determining that the photovoltaic inverter is in a fault ride-through state under the condition that the reference voltage continuously meets the fault ride-through condition within the first duration, and determining target active power and target reactive power of the photovoltaic inverter during the fault ride-through period based on a pre-established transient control model. According to the scheme provided by the embodiment of the invention, by establishing the modularized photovoltaic control model, complex and diversified inverter transient control logic is formatted and transparentized, diversified inverter control scenes and control strategies can be fitted, and conditions are provided for later model control parameter identification.

Description

Technical Field

[0001] This disclosure relates to the field of photovoltaic inverter technology, and in particular to a fault ride-through control method for photovoltaic inverters. Background Technology

[0002] In recent years, the penetration rate of photovoltaic power generation in power systems has increased significantly, and the number of power electronic components has continued to rise. This change has profoundly affected the dynamic characteristics of traditional power systems centered on synchronous machines. With the increasing complexity of new power systems, dispatching departments have placed more stringent requirements on relay protection for renewable energy power plants based on grid fault characteristics. In the research on fault characteristics and protection principles of inverter power sources, accurate transient models and key control parameters are crucial. Especially during the fault ride-through period of inverter power sources, the accuracy of control parameters directly affects the safe and stable operation of renewable energy units.

[0003] In related technologies, the control models for photovoltaic inverters are often black-box or gray-box systems, making it difficult to simulate and debug the control process. Therefore, there is an urgent need for a reliable control model for photovoltaic inverters with easily identifiable control parameters to meet the control requirements of photovoltaic inverters during fault ride-through. Summary of the Invention

[0004] To overcome the problems existing in related technologies, this disclosure provides a method for delineating risk zones in aquaculture and related equipment.

[0005] According to a first aspect of the present disclosure, a fault ride-through control method for a photovoltaic inverter is provided, comprising: A reference voltage is collected, wherein the reference voltage is at least one of the positive sequence voltage, minimum phase voltage, and maximum phase voltage on the AC side of the photovoltaic inverter; If the reference voltage continuously meets the fault ride-through condition within the first time period, it is determined that the photovoltaic inverter is in the fault ride-through state, and the target active power and target reactive power of the photovoltaic inverter during the fault ride-through period are determined based on the pre-established transient control model. The transient control model includes: a first active power control module, a first reactive power control module, an inverter current control and limiting module, and a photovoltaic power generation module. The first active power control module is used to determine the reference active power or reference active current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through. The first reactive power control module is used to determine the reference reactive power or reference reactive current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through. The inverter current control and limiting module is used to determine an active current reference value based on the reference active power when the first active power control module is used to determine the reference active power, and / or to determine a reactive current reference value based on the reference reactive power when the first reactive power control module is used to determine the reference reactive power. The photovoltaic power generation module is used to determine the target active power and target reactive power of the photovoltaic inverter based on the active current reference value and the reactive current reference value.

[0006] In some embodiments, the method further includes: If the reference voltage continuously meets the fault recovery conditions within the second time period, it is determined that the photovoltaic inverter is in a normal state, and based on the pre-established transient control model, the target active power and target reactive power of the photovoltaic inverter in the normal state are determined. The transient control model further includes: a second active power control module and a second reactive power control module; The second active power control module is used to determine the reference active power of the photovoltaic inverter according to the parameters of the photovoltaic inverter under normal conditions. The second reactive power control module is used to determine the reference reactive power of the photovoltaic inverter based on the parameters of the photovoltaic inverter under normal conditions.

[0007] In some embodiments, there are multiple first active power control modules, each corresponding to a different fault type; there are also multiple first reactive power control modules, each corresponding to a different fault type. The determination of the target active power and target reactive power of the photovoltaic inverter during fault ride-through, based on a pre-established transient control model, includes: Among multiple first active power control modules, determine the first active power control module corresponding to the current fault type, and among multiple first reactive power control modules, determine the first reactive power control module corresponding to the current fault type. Based on the first active power control module and the first reactive power control module corresponding to the fault type, and in conjunction with the inverter current control and limiting module and the photovoltaic power generation module, the target active power and target reactive power of the photovoltaic inverter during fault ride-through are determined.

[0008] In some embodiments, the transient control model further includes a frequency and inertia control module for adjusting the target active power of the photovoltaic inverter in response to changes in the frequency of the power grid.

[0009] In some embodiments, the method further includes: Construct a first active power control module comprising three stages: fault ride-through, fault recovery start point, and fault recovery process; In the case of the photovoltaic inverter during fault ride-through, the first active power control module is any one of the following: This corresponds to a control method based on a specified active power, used to generate a reference active power; where, For reference active power, This is the active power correction factor. This is the initial active power. To specify active power; This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the voltage correction factor. This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial active current. To specify the active current; This corresponds to a control method based on the initial active current, used to generate a reference active current; where, For reference active current, This is the initial active current; When the photovoltaic inverter is at the fault recovery starting point, the first active power control module is any of the following: This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the current correction factor. This is the initial active current. To specify the active current; This corresponds to a control method based on active current during a fault, used to generate a reference active current; where, For reference active current, This refers to the active current during the fault period; This corresponds to a control method based on active power during a fault, used to generate reference active power; where, For reference active power, This represents the active power during the fault period; When the photovoltaic inverter is in the fault recovery process, the first active power control module is any of the following: This corresponds to a control method based on a specified recovery slope, used to generate reference active power; where, For reference active power, For coefficients, This is the initial active power. This represents the active power during the fault period; This corresponds to a control method based on inertia curves, used to generate reference active power; where, For reference active power, This is the initial active power. The inertial time constant, It is a complex variable.

[0010] In some embodiments, the method further includes: Construct a first reactive power control module comprising three stages: fault ride-through, fault recovery start point, and fault recovery process; In the case of the photovoltaic inverter during fault ride-through, the first reactive power control module is any one of the following: This corresponds to a control method based on a specified reactive power, used to generate a reference reactive power; where, For reference reactive power, This is the reactive power correction factor. This is the initial reactive power. To specify reactive power; This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the voltage correction factor. For a specified voltage, This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial reactive current. To specify the reactive current; When the photovoltaic inverter is at the fault recovery starting point, the first reactive power control module is any of the following: This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the power correction factor. This is the initial reactive current. To specify the reactive current; This corresponds to a control method based on the initial reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the initial reactive current; This corresponds to a control method based on reactive power during a fault, used to generate a reference reactive current; where, For reference reactive power, This refers to the reactive power during the fault period; When the photovoltaic inverter is in the fault recovery process, the first reactive power control module is any of the following: This corresponds to a control method based on inertia curves, used to generate reference reactive power; where, For reference reactive power, This is the initial reactive power. The inertial time constant, It is a complex variable.

[0011] In some embodiments, the method further includes: The second active power control module is constructed in the following manner: ; in, For reference active power, This represents the actual active power at the maximum power point. For complex variables, is the time constant.

[0012] In some embodiments, the method further includes: The second reactive power control module can be constructed using any of the following methods: This corresponds to the constant power control mode; among which, For reference reactive power, This is a reactive power control command; This corresponds to the constant voltage control method; among which, For reference reactive power, This is the coefficient for the proportional element. For voltage measurement time constant, For reference voltage, For complex variables, For the target control voltage, It is reactive current. For line impedance, The coefficients of the integral element, It is a time constant; This corresponds to the constant power factor control mode; among which, For reference reactive power, For target active power, For reference power factor, For complex variables, is the time constant.

[0013] In some embodiments, the method further includes: Construct an inverter current control and limiting module that includes a reference active current conversion unit and a reference reactive current conversion unit; The reference active current conversion unit is any one of the following: ,in, For reference active current, For reference active power, This refers to the AC side voltage of the photovoltaic inverter. ,in, For reference active current, For complex variables, This is the active power control ratio coefficient. The active power control integral coefficient, For reference active power, The target active power; The reference reactive current conversion unit is any one of the following: ,in, For reference reactive current, For reference reactive power, This refers to the AC side voltage of the photovoltaic inverter. ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, The target reactive power; ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, For target reactive power, This refers to the AC side voltage of the photovoltaic inverter. This is the voltage control proportional coefficient. This is the reactive power control integral coefficient; ,in, For reference reactive current, For complex variables, This is the voltage control proportional coefficient. The integral coefficient for reactive power control. For reference voltage, This refers to the AC side voltage of the photovoltaic inverter.

[0014] In some embodiments, the method further includes: The photovoltaic power generation module is constructed in the following manner: ; in, This represents the actual active power at the maximum power point. As a reserve factor, The active power at the maximum power point. , For real-time irradiance, For reference irradiance, and These are the constants used in the calculation.

[0015] The solution provided in this disclosure establishes a modular photovoltaic control model, which formats and makes transparent the complex and diverse transient control logic of the inverter. This allows for the fitting of diverse inverter control scenarios and control strategies, and provides conditions for subsequent model control parameter identification. Attached Figure Description

[0016] Figure 1 This diagram illustrates the architecture of a photovoltaic inverter transient control model according to an embodiment of the present disclosure.

[0017] Figure 2 This diagram illustrates a flow chart of a fault ride-through control method for a photovoltaic inverter according to an embodiment of the present disclosure.

[0018] Figure 3 A schematic diagram of the fault passage state determination module in an embodiment of this disclosure is shown.

[0019] Figure 4 This diagram illustrates the time-segmentation of the fault-crossing process in an embodiment of the present disclosure.

[0020] Figure 5 A schematic diagram of the first active power control module in an embodiment of this disclosure is shown.

[0021] Figure 6 A schematic diagram of the first reactive power control module in an embodiment of this disclosure is shown.

[0022] Figure 7 A schematic diagram of the second active power control module in an embodiment of this disclosure is shown.

[0023] Figure 8 A schematic diagram of the second reactive power control module in an embodiment of this disclosure is shown.

[0024] Figure 9 A schematic diagram of the inverter current control and limiting module in an embodiment of this disclosure is shown.

[0025] Figure 10 A schematic diagram of a photovoltaic power generation module is shown in an embodiment of this disclosure.

[0026] Figure 11 A schematic diagram of the frequency and inertia control module in an embodiment of this disclosure is shown. Detailed Implementation

[0027] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numerals in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this disclosure as detailed in the appended claims.

[0028] The fault ride-through period of a photovoltaic inverter refers to the entire process from the occurrence of a grid fault (such as voltage dips / surges, frequency anomalies, etc.) to the completion of fault handling. The core objective during this period is to maintain the connection with the grid as much as possible while ensuring the safety of the photovoltaic inverter itself, actively adjust to support grid stability, and avoid the escalation of faults due to disorderly disconnection of equipment from the grid.

[0029] When a fault is detected, the control system needs to adjust the active and reactive power of the photovoltaic inverter to prevent line overload, support grid voltage, and facilitate fault recovery.

[0030] To facilitate understanding, we will first combine Figure 1 This document introduces an exemplary architecture of the transient control model in the embodiments of this disclosure. It is understood that this transient control model can be used to simulate the control strategy of a photovoltaic inverter during transient processes, particularly its behavior during fault ride-through.

[0031] Specifically, such as Figure 1As shown, the transient control model in this embodiment includes a fault ride-through state judgment model (WEV), an active power control module (WEU) under normal conditions, a reactive power control module (WEQ) under normal conditions, an active power control module (WLP) under fault ride-through conditions, a reactive power control module (WLQ) under fault ride-through conditions, an inverter current control and limiting module (WES), a photovoltaic power generation module (PSL), and a frequency and inertia control module (WAF & WAI).

[0032] The fault ride-through status determination module (WEV) can acquire the grid voltage and determine whether the grid is currently in a fault state based on the grid voltage level, so as to determine whether to adopt the control strategy under normal conditions or the control strategy under fault conditions.

[0033] The active power control module (WLP) under fault ride-through condition, also known as the first active power control module in the following text, is used to execute the corresponding active power control strategy when the power grid is in fault ride-through condition.

[0034] The reactive power control module (WLQ) under fault ride-through condition, also known as the first reactive power control module in the following text, is used to execute the corresponding reactive power control strategy when the power grid is in fault ride-through condition.

[0035] The active power control module (WEU) under normal conditions, also known as the second active power control module in the following text, is used to execute the corresponding active power control strategy when the power grid is in a normal state.

[0036] The reactive power control module under normal conditions (WEQ), also known as the second reactive power control module in the following text, is used to execute the corresponding reactive power control strategy when the power grid is in a normal state.

[0037] The inverter current control and limiting module (WES) is used to calculate the corresponding active and reactive current reference values ​​based on the power reference value. and It also limits the current to ensure that the inverter operates within a safe range.

[0038] A photovoltaic power generation module (PSL) is used to simulate the output characteristics of a photovoltaic unit and generate a target active power based on an input current reference value. and target reactive power .

[0039] The frequency and inertia control module (WAF & WAI) is used for frequency modulation and inertia response, and it can generate power adjustment signals. The power adjustment signal is then superimposed onto the active power control module to support the grid frequency.

[0040] The specific implementation methods of this disclosure will be described in detail below.

[0041] This disclosure provides a fault ride-through control method for a photovoltaic inverter, which can be executed by any electronic device.

[0042] Figure 2 This diagram illustrates a flow chart of a fault ride-through control method for a photovoltaic inverter according to an embodiment of the present disclosure, as shown below. Figure 2 As shown in the embodiments of this disclosure, the fault ride-through control method for photovoltaic inverters includes the following steps.

[0043] S201, acquires the reference voltage.

[0044] The reference voltage is at least one of the positive sequence voltage, minimum phase voltage, and maximum phase voltage on the AC side of the photovoltaic inverter.

[0045] S202, if the reference voltage continuously meets the fault ride-through condition within the first duration, determine that the photovoltaic inverter is in the fault ride-through state, and determine the target active power and target reactive power of the photovoltaic inverter during the fault ride-through period based on the pre-established transient control model.

[0046] The transient control model includes: a first active power control module, a first reactive power control module, an inverter current control and limiting module, and a photovoltaic power generation module.

[0047] The first active power control module is used to determine the reference active power or reference active current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through.

[0048] The first reactive power control module is used to determine the reference reactive power or reference reactive current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through.

[0049] The inverter current control and limiting module is used to determine an active current reference value based on the reference active power when the first active power control module determines the reference active power, and / or, when the first reactive power control module determines the reference reactive power, to determine a reactive current reference value based on the reference reactive power.

[0050] The photovoltaic power generation module is used to determine the target active power and target reactive power of the photovoltaic inverter based on the active current reference value and the reactive current reference value.

[0051] In some embodiments, if the reference voltage continuously meets the fault recovery conditions for a second duration, it can be determined that the photovoltaic inverter is in a normal state. At this time, the target active power and target reactive power of the photovoltaic inverter in the normal state can be determined based on a pre-established transient control model.

[0052] The transient control model also includes a second active power control module and a second reactive power control module.

[0053] The second active power control module is used to determine the reference active power of the photovoltaic inverter based on the parameters of the photovoltaic inverter under normal conditions.

[0054] The second reactive power control module is used to determine the reference reactive power of the photovoltaic inverter based on the parameters of the photovoltaic inverter under normal conditions.

[0055] Understandably, the transmission path of electrical quantities in the transient control model is similar regardless of whether the photovoltaic inverter is in fault ride-through or normal state. The difference lies in whether the first active power control module and the first reactive power control module are selected to generate the reference power or reference current (corresponding to the fault ride-through state), or whether the second active power control module and the second reactive power control module are selected to generate the reference power or reference current (corresponding to the normal state).

[0056] When the power generated by the power control module is the reference power, it needs to be further converted into a reference current by the inverter current control and limiting module. Regardless of whether it is fault ride-through or normal state, after obtaining the reference active current and reference reactive current, they can be input into the photovoltaic power generation module to obtain the target active power and target reactive power of the photovoltaic inverter.

[0057] In some embodiments, the reference voltage is at least one of the positive-sequence voltage, minimum phase voltage, and maximum phase voltage on the AC side of the photovoltaic inverter. The positive-sequence voltage, minimum phase voltage, and maximum phase voltage are important indicators for determining the system status. The positive-sequence voltage reflects the balance of the three-phase voltages in the system, while the maximum / minimum phase voltage is directly related to the overvoltage or undervoltage condition of the system. Changes in these parameters can intuitively reflect whether the system is in a healthy operating state or has entered a certain fault mode.

[0058] Positive sequence voltage is a symmetrical component in a three-phase circuit, used to describe the symmetrical balance of three-phase voltages. A decrease in positive sequence voltage usually indicates a system fault or load imbalance.

[0059] The maximum phase voltage refers to the voltage of the phase with the highest amplitude in a three-phase circuit. Under normal operation, the three phase voltage amplitudes are equal, and the maximum phase voltage equals the rated phase voltage. However, during a fault, the voltage of a certain phase may abnormally increase. For example, in a neutral-point ungrounded system, when a single-phase ground fault occurs, the voltage of the non-faulty phase will rise to the line voltage (approximately 1 / 3 of the phase voltage). (times), becoming the maximum phase voltage.

[0060] The minimum phase voltage refers to the voltage of the phase with the lowest amplitude in a three-phase circuit. Under normal operation, the minimum phase voltage is equal to the rated phase voltage, but when a fault occurs, the voltage of a certain phase may drop significantly. For example, when two phases are short-circuited, the voltage of the faulty phase will drop significantly, becoming the minimum phase voltage.

[0061] Based on this, please refer to Figure 3 The reference voltage is used as the positive sequence voltage. and minimum phase voltage For example, fault ride-through conditions could be Less than It can be Less than It can also be and All less than .in, This is the voltage threshold used to determine whether a fault ride-through state has been entered. Correspondingly, the fault recovery condition can be... Greater than It can be Greater than It can also be and All greater than .in, This is the voltage threshold used to determine when a system exits a fault-crossing state and returns to normal operation.

[0062] At the reference voltage If the fault ride-through conditions are continuously met within a given timeframe, the photovoltaic inverter is determined to have entered fault ride-through mode. At this point, the first active power control module (WLP) and the first reactive power control module (WLQ) can be selected to generate reference power or reference current. Meanwhile, when the reference voltage is... If the fault recovery conditions are met continuously within the specified time, and the photovoltaic inverter exits the fault ride-through state and returns to normal state, then the second active power control module (WEU) and the second reactive power control module (WEQ) can be selected to generate reference power or reference current.

[0063] Therefore, based on the monitoring of the reference voltage, the fault ride-through status judgment stage can quickly and accurately identify the current operating status of the photovoltaic system and make a decision on whether to execute the fault ride-through strategy accordingly. This disclosure, through the design of a complex pattern recognition and switching mechanism, enables the control method to possess high flexibility and response speed to cope with various possible fault scenarios.

[0064] Please refer to Figure 4 The fault ride-through process of a photovoltaic inverter can be divided into three phases: the fault ride-through period, the fault recovery start point, and the fault recovery process. These three phases correspond to... Figure 4 Different control strategies can be designed for A, B, and C based on their characteristics. Specifically, the first active power control module and the first reactive power control model can be designed in the following way.

[0065] Figure 5 A schematic diagram of the first active power control module in an embodiment of this disclosure is shown. Figure 5 In the diagram, FLG1 corresponds to the control mode during fault ride-through: 0 means no control; 1 means a control mode based on specified active power; 2 means a control mode based on specified active current; and 3 means a control mode based on the initial (before the fault) active current. FLG2 corresponds to the control mode at the fault recovery start point: 0 means no control; 1 means a control mode based on specified active current; 2 means a control mode based on active current during the fault; and 3 means a control mode based on active power during the fault. FLG3 corresponds to the control mode during the fault recovery process: 0 means no control; 1 means a control mode based on specified recovery slope; and 2 means a control mode based on inertia curve.

[0066] Specifically, a first active power control module can be constructed that includes three stages: fault ride-through, fault recovery start point, and fault recovery process.

[0067] In the case of the photovoltaic inverter during fault ride-through, the first active power control module is any one of the following: This corresponds to a control method based on a specified active power, used to generate a reference active power; where, For reference active power, This is the active power correction factor. This is the initial active power. To specify the active power.

[0068] This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the voltage correction factor. This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial active current. To specify the active current.

[0069] This corresponds to a control method based on the initial active current, used to generate a reference active current; where, For reference active current, This is the initial active current.

[0070] When the photovoltaic inverter is at the fault recovery starting point, the first active power control module is any of the following: This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the current correction factor. This is the initial active current. To specify the active current.

[0071] This corresponds to a control method based on active current during a fault, used to generate a reference active current; where, For reference active current, This represents the active current during the fault period.

[0072] This corresponds to a control method based on active power during a fault, used to generate reference active power; where, For reference active power, This represents the active power during the fault period.

[0073] When the photovoltaic inverter is in the fault recovery process, the first active power control module is any of the following: This corresponds to a control method based on a specified recovery slope, used to generate reference active power; where, For reference active power, For coefficients, This is the initial active power. This represents the active power during the fault period.

[0074] This corresponds to a control method based on inertia curves, used to generate reference active power; where, For reference active power, This is the initial active power. The inertial time constant, It is a complex variable.

[0075] Figure 6 A schematic diagram of the first reactive power control module in an embodiment of this disclosure is shown. Figure 6 In the diagram, FLG1 corresponds to the control mode during fault ride-through: 0 for no control; 1 for control based on specified reactive power; and 2 for control based on specified reactive current. FLG2 corresponds to the control mode at the fault recovery start point: 0 for no control; 1 for control based on specified reactive current; 2 for control based on initial (before the fault) reactive current; and 3 for control based on reactive power during the fault. FLG3 corresponds to the control mode during the fault recovery process: 0 for no control; and 1 for control based on the inertia curve.

[0076] Specifically, a first reactive power control module can be constructed that includes three stages: fault ride-through, fault recovery start point, and fault recovery process.

[0077] In the case of the photovoltaic inverter during fault ride-through, the first reactive power control module is any one of the following: This corresponds to a control method based on a specified reactive power, used to generate a reference reactive power; where, For reference reactive power, This is the reactive power correction factor. This is the initial reactive power. To specify reactive power.

[0078] This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the voltage correction factor. For a specified voltage, This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial reactive current. To specify the reactive current.

[0079] When the photovoltaic inverter is at the fault recovery starting point, the first reactive power control module is any of the following: This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the power correction factor. This is the initial reactive current. To specify the reactive current.

[0080] This corresponds to a control method based on the initial reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the initial reactive current.

[0081] This corresponds to a control method based on reactive power during a fault, used to generate a reference reactive current; where, For reference reactive power, This represents the reactive power during the fault period.

[0082] When the photovoltaic inverter is in the fault recovery process, the first reactive power control module is any of the following: This corresponds to a control method based on inertia curves, used to generate reference reactive power; where, For reference reactive power, This is the initial reactive power. The inertial time constant, It is a complex variable.

[0083] In some embodiments, there are multiple first active power control modules, each corresponding to a different fault type. There are also multiple first reactive power control modules, each corresponding to a different fault type. The fault types may include: low-voltage symmetrical (L), low-voltage asymmetrical (M), high-voltage symmetrical (H), and high-voltage asymmetrical (N), totaling four fault condition types.

[0084] Therefore, when executing S202 above, the first active power control module corresponding to the current fault type can be determined from among multiple first active power control modules, and the first reactive power control module corresponding to the current fault type can be determined from among multiple first reactive power control modules. Based on the first active power control module and the first reactive power control module corresponding to the fault type, combined with the inverter current control and limiting module and the photovoltaic power generation module, the target active power and target reactive power of the photovoltaic inverter during fault ride-through can be determined.

[0085] For example, Figure 7 A schematic diagram of the second active power control module in an embodiment of this disclosure is shown. Figure 7 As shown, the second active power control module can be constructed in the following manner: ; in, For reference active power, This represents the actual active power at the maximum power point. For complex variables, is the time constant.

[0086] In addition, Figure 7 middle, For maximum power limitation, As a minimum power limit, For the maximum rate of change, This represents the minimum rate of change.

[0087] By approximating the active power at the maximum power point as the active power command under normal operating conditions, sampling data with a delay element, and using numerical limiting and rate of change limiting for control, the active power control model can be simplified to the greatest extent.

[0088] For example, Figure 8 A schematic diagram of the second reactive power control module in an embodiment of this disclosure is shown. Figure 8 As shown, the second reactive power control module can be constructed in any of the following ways: This corresponds to the constant power control mode; among which, For reference reactive power, This is a reactive power control command.

[0089] This corresponds to the constant voltage control method; among which, For reference reactive power, This is the coefficient for the proportional element. For voltage measurement time constant, For reference voltage, For complex variables, For the target control voltage, It is reactive current. For line impedance, The coefficients of the integral element, is the time constant.

[0090] This corresponds to the constant power factor control mode; among which, For reference reactive power, For target active power, For reference power factor, For complex variables, is the time constant.

[0091] In addition, Figure 8 middle, This is the maximum limit for reactive power. This is the minimum limit for reactive power.

[0092] Figure 9 A schematic diagram of the inverter current control and limiting module in an embodiment of this disclosure is shown. The inverter current control and limiting module can perform relevant calculations and limiting of the current component based on the reference power output by the power control module, thereby converting the power command from the power control module into a current command. For example... Figure 9 As shown, an inverter current control and limiting module containing a reference active current conversion unit and a reference reactive current conversion unit can be constructed.

[0093] The reference active current conversion unit can be any of the following: ,in, For reference active current, For reference active power, This refers to the AC side voltage of the photovoltaic inverter.

[0094] ,in, For reference active current, For complex variables, This is the active power control ratio coefficient. The active power control integral coefficient, For reference active power, The target active power.

[0095] The reference reactive current conversion unit is any one of the following: ,in, For reference reactive current, For reference reactive power, This refers to the AC side voltage of the photovoltaic inverter.

[0096] ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, The target reactive power.

[0097] ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, For target reactive power, This refers to the AC side voltage of the photovoltaic inverter. This is the voltage control proportional coefficient. This is the reactive power control integral coefficient.

[0098] ,in, For reference reactive current, For complex variables, This is the voltage control proportional coefficient. The integral coefficient for reactive power control. For reference voltage, This refers to the AC side voltage of the photovoltaic inverter.

[0099] In addition, Figure 9 In the inverter current control and limiting module shown, The voltage upper limit (pu); The lower voltage limit (pu); The maximum active current limit (pu); Minimum active current limit (pu); The maximum limit of reactive current (pu); The minimum reactive current limit (pu) is used; FLAGP is used to select the calculation method for the reference active current conversion unit; FLAGQ is used to select the calculation method for the reference reactive current conversion unit.

[0100] Figure 10 A schematic diagram of a photovoltaic power generation module according to an embodiment of this disclosure is shown. For example, please refer to... Figure 10 Photovoltaic power generation modules can be constructed in the following ways: ; in, This represents the actual active power at the maximum power point. As a reserve factor, The active power at the maximum power point. , For real-time irradiance, For reference irradiance, and These are the constants used in the calculation.

[0101] The photovoltaic power generation module in this embodiment simplifies the photovoltaic array power generation model in related technologies, and can directly solve for the output power based on the solar irradiance (characterized by real-time irradiance). Since the transient control process is short, the temperature can be regarded as a constant value, and therefore the effect of temperature can be ignored.

[0102] In some embodiments, the transient control model further includes a frequency and inertia control module for adjusting the target active power of the photovoltaic inverter in response to changes in the frequency of the power grid.

[0103] Figure 11 A schematic diagram of a frequency and inertia control module in an embodiment of this disclosure is shown. Exemplarily, in... Figure 11 In the diagram, FLAGF represents the frequency control function switch; The frequency measurement time constant (s) is shared by frequency modulation and inertia control. The positive frequency deviation dead zone (Hz); The negative frequency deviation dead zone (Hz); This represents the maximum positive frequency deviation (pu, with the rated frequency as the reference). The maximum negative frequency deviation (pu, with the rated frequency as the reference); DPDF UP The power change rate (power pu / frequency pu, where the power per unit is based on the rated power and the frequency per unit is based on the rated frequency) corresponding to the positive frequency deviation; DPDF DN The power change rate corresponding to a negative frequency deviation (power pu / frequency pu, where the power per unit value is based on the rated power and the frequency per unit value is based on the rated frequency); DP max The upper limit of power variation (pu); DP min is the lower limit of power variation (pu). FLAGW is the inertia control switch; dbwi is the positive frequency deviation dead zone of inertia control (Hz); dbwi is the negative frequency deviation dead zone of inertia control (Hz). The first-order inertial time constant (s) for inertial control; This is the proportional coefficient for inertia control; The differential time constant (s) for inertia control; The upper limit of the change in inertia control power (pu); urlwi is the lower limit of the inertia control power change rate (pu); urlwi is the upper limit of the inertia control power change rate (pu / s); drlwi is the lower limit of the inertia control power change rate (pu / s). It is a complex variable.

[0104] During voltage ride-through, fluctuations in grid voltage may exceed normal ranges, potentially adversely affecting the operation of power generation equipment. To protect power generation equipment and ensure the safe and stable operation of the grid, the inverter itself features primary frequency regulation (fast frequency response), enabling it to rapidly adjust its power output in real time according to system conditions. Therefore, when the grid frequency changes, the inverter can quickly respond and adjust its output power to maintain grid frequency stability.

[0105] Other embodiments of this disclosure will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This disclosure is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not disclosed herein. The specification and examples are to be considered exemplary only, and the true scope and spirit of this disclosure are indicated by the appended claims.

Claims

1. A fault ride-through control method for a photovoltaic inverter, characterized in that, include: A reference voltage is collected, wherein the reference voltage is at least one of the positive sequence voltage, minimum phase voltage, and maximum phase voltage on the AC side of the photovoltaic inverter; If the reference voltage continuously meets the fault ride-through condition within the first time period, it is determined that the photovoltaic inverter is in the fault ride-through state, and the target active power and target reactive power of the photovoltaic inverter during the fault ride-through period are determined based on the pre-established transient control model. The transient control model includes: a first active power control module, a first reactive power control module, an inverter current control and limiting module, and a photovoltaic power generation module. The first active power control module is used to determine the reference active power or reference active current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through. The first reactive power control module is used to determine the reference reactive power or reference reactive current of the photovoltaic inverter based on the parameters of the photovoltaic inverter during fault ride-through. The inverter current control and limiting module is used to determine an active current reference value based on the reference active power when the first active power control module is used to determine the reference active power, and / or to determine a reactive current reference value based on the reference reactive power when the first reactive power control module is used to determine the reference reactive power. The photovoltaic power generation module is used to determine the target active power and target reactive power of the photovoltaic inverter based on the active current reference value and the reactive current reference value.

2. The method according to claim 1, characterized in that, The method further includes: If the reference voltage continuously meets the fault recovery conditions within the second time period, it is determined that the photovoltaic inverter is in a normal state, and based on the pre-established transient control model, the target active power and target reactive power of the photovoltaic inverter in the normal state are determined. The transient control model further includes: a second active power control module and a second reactive power control module; The second active power control module is used to determine the reference active power of the photovoltaic inverter according to the parameters of the photovoltaic inverter under normal conditions. The second reactive power control module is used to determine the reference reactive power of the photovoltaic inverter based on the parameters of the photovoltaic inverter under normal conditions.

3. The method according to claim 1, characterized in that, There are multiple first active power control modules, each corresponding to a different fault type; there are also multiple first reactive power control modules, each corresponding to a different fault type. The determination of the target active power and target reactive power of the photovoltaic inverter during fault ride-through, based on a pre-established transient control model, includes: Among multiple first active power control modules, determine the first active power control module corresponding to the current fault type, and among multiple first reactive power control modules, determine the first reactive power control module corresponding to the current fault type. Based on the first active power control module and the first reactive power control module corresponding to the fault type, and in conjunction with the inverter current control and limiting module and the photovoltaic power generation module, the target active power and target reactive power of the photovoltaic inverter during fault ride-through are determined.

4. The method according to claim 1, characterized in that, The transient control model also includes a frequency and inertia control module, used to adjust the target active power of the photovoltaic inverter in response to changes in the frequency of the power grid.

5. The method according to any one of claims 1 to 4, characterized in that, The method further includes: Construct a first active power control module comprising three stages: fault ride-through, fault recovery start point, and fault recovery process; In the case of the photovoltaic inverter during fault ride-through, the first active power control module is any one of the following: This corresponds to a control method based on a specified active power, used to generate a reference active power; where, For reference active power, This is the active power correction factor. This is the initial active power. To specify active power; This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the voltage correction factor. This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial active current. To specify the active current; This corresponds to a control method based on the initial active current, used to generate a reference active current; where, For reference active current, This is the initial active current; When the photovoltaic inverter is at the fault recovery starting point, the first active power control module is any of the following: This corresponds to a control method based on a specified active current, used to generate a reference active current; where, For reference active current, This is the current correction factor. This is the initial active current. To specify the active current; This corresponds to a control method based on active current during a fault, used to generate a reference active current; where, For reference active current, This refers to the active current during the fault period; This corresponds to a control method based on active power during a fault, used to generate reference active power; where, For reference active power, This represents the active power during the fault period; When the photovoltaic inverter is in the fault recovery process, the first active power control module is any of the following: This corresponds to a control method based on a specified recovery slope, used to generate reference active power; where, For reference active power, For coefficients, This is the initial active power. This represents the active power during the fault period; This corresponds to a control method based on inertia curves, used to generate reference active power; where, For reference active power, This is the initial active power. The inertial time constant, It is a complex variable.

6. The method according to any one of claims 1 to 4, characterized in that, The method further includes: Construct a first reactive power control module comprising three stages: fault ride-through, fault recovery start point, and fault recovery process; In the case of the photovoltaic inverter during fault ride-through, the first reactive power control module is any one of the following: This corresponds to a control method based on a specified reactive power, used to generate a reference reactive power; where, For reference reactive power, This is the reactive power correction factor. This is the initial reactive power. To specify reactive power; This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the voltage correction factor. For a specified voltage, This refers to the terminal voltage amplitude. This is the current correction factor. This is the initial reactive current. To specify the reactive current; When the photovoltaic inverter is at the fault recovery starting point, the first reactive power control module is any of the following: This corresponds to a control method based on a specified reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the power correction factor. This is the initial reactive current. To specify the reactive current; This corresponds to a control method based on the initial reactive current, used to generate a reference reactive current; where, For reference reactive current, This is the initial reactive current; This corresponds to a control method based on reactive power during a fault, used to generate a reference reactive current; where, For reference reactive power, This refers to the reactive power during the fault period; When the photovoltaic inverter is in the fault recovery process, the first reactive power control module is any of the following: This corresponds to a control method based on inertia curves, used to generate reference reactive power; where, For reference reactive power, This is the initial reactive power. The inertial time constant, It is a complex variable.

7. The method according to claim 2, characterized in that, The method further includes: The second active power control module is constructed in the following manner: ； in, For reference active power, This represents the actual active power at the maximum power point. For complex variables, is the time constant.

8. The method according to claim 2, characterized in that, The method further includes: The second reactive power control module can be constructed using any of the following methods: This corresponds to the constant power control mode; among which, For reference reactive power, This is a reactive power control command; This corresponds to the constant voltage control method; among which, For reference reactive power, This is the coefficient for the proportional element. For voltage measurement time constant, For reference voltage, For complex variables, For the target control voltage, It is reactive current. For line impedance, The coefficients of the integral element, It is a time constant; This corresponds to the constant power factor control mode; among which, For reference reactive power, For target active power, For reference power factor, For complex variables, is the time constant.

9. The method according to any one of claims 1 to 4, characterized in that, The method further includes: Construct an inverter current control and limiting module that includes a reference active current conversion unit and a reference reactive current conversion unit; The reference active current conversion unit is any one of the following: ,in, For reference active current, For reference active power, This refers to the AC side voltage of the photovoltaic inverter. ,in, For reference active current, For complex variables, This is the active power control ratio coefficient. The active power control integral coefficient, For reference active power, The target active power; The reference reactive current conversion unit is any one of the following: ,in, For reference reactive current, For reference reactive power, This refers to the AC side voltage of the photovoltaic inverter. ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, The target reactive power; ,in, For reference reactive current, For complex variables, This is the reactive power control proportional coefficient. The integral coefficient for reactive power control. For reference reactive power, For target reactive power, This refers to the AC side voltage of the photovoltaic inverter. This is the voltage control proportional coefficient. This is the reactive power control integral coefficient; ,in, For reference reactive current, For complex variables, This is the voltage control proportional coefficient. The integral coefficient for reactive power control. For reference voltage, This refers to the AC side voltage of the photovoltaic inverter.

10. The method according to any one of claims 1 to 4, characterized in that, The method further includes: The photovoltaic power generation module is constructed in the following manner: ； in, This represents the actual active power at the maximum power point. As a reserve factor, The active power at the maximum power point. , For real-time irradiance, For reference irradiance, and These are the constants used in the calculation.

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