Low voltage ride through control method and device for two-stage grid-connected photovoltaic inverter

Abstract

This application relates to a low-voltage ride-through control method, apparatus, and equipment for a two-stage grid-connected photovoltaic inverter. By using valve-side reference data obtained from a first and second control method (both capable of controlling positive and negative sequence voltage and current) respectively, the positive and negative sequence voltages are controlled, exhibiting voltage source characteristics externally. It also controls the positive and negative sequence currents to flexibly manage fault currents. Through the coordinated control strategies of the front-stage boost circuit and the rear-stage inverter circuit, the low-voltage ride-through of the two-stage grid-connected photovoltaic inverter achieves a balance of photovoltaic output power during faults and a smooth transition back to grid-connected control after a fault. This solves the technical problem of large currents that can occur after a fault in existing power systems using photovoltaic inverters in grid-connected control technology, potentially jeopardizing power system operation.

Description

Technical Field

[0001] This application relates to the field of new energy control technology, and in particular to a low voltage ride-through control method, device and equipment for a two-stage grid-type photovoltaic inverter. Background Technology

[0002] In recent years, new energy power generation has received high attention in energy development strategies and has developed rapidly. A high proportion of new energy is integrated into the power system through power electronic devices. Under traditional operating modes, the power system lacks the characteristics of synchronous generators, leading to reduced inertia and decreased frequency stability. To address these issues, the concept of grid-based control has been proposed. By simulating the operating characteristics of synchronous generators to a certain extent, this improves the ability of new energy to support the frequency and voltage of the power system.

[0003] The application of grid-based control technology in photovoltaic inverters can improve the support capacity of power systems. However, it can also generate significant fault currents during external AC system failures, jeopardizing inverter safety. Therefore, it is necessary to study fault current suppression and fault ride-through strategies for grid-based photovoltaic inverters to ensure their safe and stable operation. Summary of the Invention

[0004] This application provides a low-voltage ride-through control method, apparatus, and equipment for a two-stage grid-type photovoltaic inverter, which addresses the technical problem that a fault in the application of photovoltaic inverters in grid-type control technology in existing power systems can generate a large current that endangers the operation of the power system.

[0005] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0006] A low-voltage ride-through control method for a two-stage grid-connected photovoltaic inverter, the two-stage grid-connected photovoltaic inverter including a front-end boost circuit and a rear-end inverter circuit, the low-voltage ride-through control method comprising the following steps:

[0007] Obtain the electrical quantity parameters of a two-stage grid-type photovoltaic inverter, including the actual reactive power value, rated AC voltage value, AC voltage amplitude, maximum withstand current value, and rated current value.

[0008] The control signal for low voltage ride-through in the two-stage grid-type photovoltaic inverter is determined based on the AC voltage amplitude.

[0009] If the control signal is 0, the first valve-side reference data is obtained by using the first control method based on the actual value of reactive power and the rated value of AC voltage, and the operation of the downstream inverter circuit is controlled based on the first valve-side reference data; the operation of the upstream boost circuit is controlled by using the maximum power point tracking mode.

[0010] If the control signal is 1, the second valve-side reference data is obtained by using the second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value. The operation of the downstream inverter circuit is controlled based on the second valve-side reference data. The operation of the upstream boost circuit is controlled by using the DC voltage mode.

[0011] Preferably, obtaining the first valve-side reference data using the first control method based on the actual reactive power value and the rated AC voltage value includes:

[0012] A voltage reference value is obtained by using a network-based algorithm based on the actual value of reactive power and the rated value of AC voltage.

[0013] The voltage reference value is subjected to amplitude limiting processing through a positive sequence voltage loop and a negative sequence voltage loop to obtain a first positive sequence current reference value and a first negative sequence current reference value.

[0014] The first positive sequence current reference value and the first negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and the first negative sequence valve side reference voltage.

[0015] The first valve-side reference data includes a first positive-sequence valve-side reference voltage and a first negative-sequence valve-side reference voltage.

[0016] Preferably, obtaining the second valve-side reference data using the second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value includes:

[0017] Based on the control signal being 1, obtain the reference value of the d-axis positive sequence current before the fault of the two-stage grid-type photovoltaic inverter.

[0018] A voltage reference value is obtained by using a network-based algorithm based on the actual reactive power value and the rated AC voltage value; the voltage reference value is then subjected to amplitude limiting processing through a positive-sequence voltage loop and a negative-sequence voltage loop; and a second positive-sequence current reference value and a second negative-sequence current reference value are calculated and determined based on the d-axis positive-sequence current reference value, the AC voltage amplitude, the maximum withstand current value, and the rated current value.

[0019] The second positive sequence current reference value and the second negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and the second negative sequence valve side reference voltage.

[0020] The second valve-side reference data includes a second positive-sequence valve-side reference voltage and a second negative-sequence valve-side reference voltage.

[0021] Preferably, determining the low-voltage ride-through control signal in the two-stage grid-type photovoltaic inverter based on the AC voltage amplitude includes: if the AC voltage amplitude is less than the voltage threshold value, the control signal is 1, indicating that a fault has occurred in the power system where the two-stage grid-type photovoltaic inverter is located; if the AC voltage amplitude is not less than the voltage threshold value, the control signal is 0, indicating that no fault has occurred in the power system where the two-stage grid-type photovoltaic inverter is located.

[0022] Preferably, the low voltage ride-through control method for the two-stage grid-type photovoltaic inverter includes: if the fault is cleared, controlling the AC voltage amplitude to be no less than the voltage threshold value, and restoring the second positive sequence current reference value and the second negative sequence current reference value in the second control mode to the state before the fault according to the slope ratio; at the same time, switching the DC voltage mode controlling the operation of the front-stage boost circuit to the maximum power point tracking mode.

[0023] This application also provides a low voltage ride-through control device for a two-stage grid-type photovoltaic inverter. The two-stage grid-type photovoltaic inverter includes a front-stage boost circuit and a rear-stage inverter circuit. The low voltage ride-through control device includes a parameter acquisition module, a control judgment module, a first execution module, and a second execution module.

[0024] The parameter acquisition module is used to acquire the electrical quantity parameters of the two-stage grid-type photovoltaic inverter. The electrical quantity parameters include the actual value of reactive power, the rated value of AC voltage, the amplitude of AC voltage, the maximum withstand current value, and the rated current value.

[0025] The control judgment module is used to determine the low voltage ride-through control signal in the two-stage grid-type photovoltaic inverter based on the AC voltage amplitude.

[0026] The first execution module is configured to obtain first valve-side reference data based on the actual reactive power value and the rated AC voltage value using a first control method when the control signal is 0, control the operation of the downstream inverter circuit based on the first valve-side reference data, and control the operation of the upstream boost circuit using maximum power point tracking mode.

[0027] The second execution module is used to obtain second valve-side reference data by adopting a second control method based on the control signal being 1, the AC voltage amplitude, the maximum withstand current value, and the rated current value, and to control the operation of the downstream inverter circuit based on the second valve-side reference data; and to control the operation of the upstream boost circuit by adopting a DC voltage mode.

[0028] Preferably, the first execution module includes a first calculation submodule, a first processing submodule, and a second processing submodule;

[0029] The first calculation submodule is used to calculate the voltage reference value based on the actual value of reactive power and the rated value of AC voltage using a network-type algorithm;

[0030] The first processing submodule is used to perform amplitude limiting processing on the voltage reference value through a positive sequence voltage loop and a negative sequence voltage loop to obtain a first positive sequence current reference value and a first negative sequence current reference value;

[0031] The second processing submodule is used to process the first positive sequence current reference value and the first negative sequence current reference value with corresponding positive sequence current loop and coordinate transformation and negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and first negative sequence valve side reference voltage.

[0032] The first valve-side reference data includes a first positive-sequence valve-side reference voltage and a first negative-sequence valve-side reference voltage.

[0033] Preferably, the second execution module includes a data acquisition submodule, a second calculation submodule, and a third processing submodule;

[0034] The data acquisition submodule is used to acquire the reference value of the d-axis positive sequence current before the fault of the two-stage grid-type photovoltaic inverter based on the control signal being 1.

[0035] The second calculation submodule is used to calculate a voltage reference value based on the actual reactive power value and the rated AC voltage value using a network-based algorithm; to perform amplitude limiting processing on the voltage reference value through a positive-sequence voltage loop and a negative-sequence voltage loop; and to calculate and determine a second positive-sequence current reference value and a second negative-sequence current reference value based on the d-axis positive-sequence current reference value, the AC voltage amplitude, the maximum withstand current value, and the rated current value.

[0036] The third processing submodule is used to process the second positive sequence current reference value and the second negative sequence current reference value with corresponding positive sequence current loop and coordinate transformation and negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and second negative sequence valve side reference voltage.

[0037] The second valve-side reference data includes a second positive-sequence valve-side reference voltage and a second negative-sequence valve-side reference voltage.

[0038] Preferably, the low voltage ride-through control device of the two-stage grid-type photovoltaic inverter includes a fault clearing module. The fault clearing module is used to control the AC voltage amplitude to be no less than the voltage threshold value according to the fault clearing, and restore the second positive sequence current reference value and the second negative sequence current reference value in the second control mode to the state before the fault according to the slope ratio; at the same time, it switches the DC voltage mode controlling the operation of the front-stage boost circuit to the maximum power point tracking mode.

[0039] This application also provides a terminal device, including a processor and a memory;

[0040] The memory is used to store program code and transmit the program code to the processor;

[0041] The processor is used to execute the low voltage ride-through control method for the two-stage grid-type photovoltaic inverter described above, according to the instructions in the program code.

[0042] As can be seen from the above technical solutions, the embodiments of this application have the following advantages: The low voltage ride-through control method, device, and equipment for a two-stage grid-type photovoltaic inverter include: acquiring electrical quantity parameters of the two-stage grid-type photovoltaic inverter; determining the low voltage ride-through control signal in the two-stage grid-type photovoltaic inverter based on the AC voltage amplitude; if the control signal is 0, obtaining first valve-side reference data using a first control method based on the actual reactive power value and the rated AC voltage value, and controlling the operation of the subsequent inverter circuit based on the first valve-side reference data; controlling the operation of the front-stage boost circuit using maximum power point tracking mode; if the control signal is 1, obtaining second valve-side reference data using a second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value, and controlling the operation of the subsequent inverter circuit based on the second valve-side reference data; and controlling the operation of the front-stage boost circuit using DC voltage mode. This low-voltage ride-through control method for a two-stage grid-connected photovoltaic inverter uses valve-side reference data obtained from a first and a second control mode, which have the capability to control both positive and negative sequence voltage and current, to control the positive and negative sequence voltages, thus presenting voltage source characteristics. It also controls the positive and negative sequence currents to flexibly control fault currents. The low-voltage ride-through of the two-stage grid-connected photovoltaic inverter is achieved through the coordination of the front-stage boost circuit and the control strategy of the back-stage inverter circuit. This ensures the balance of photovoltaic output power during faults and a smooth transition back to grid-connected control after a fault. This solves the technical problem that existing power systems using photovoltaic inverters in grid-connected control technology will generate large currents that endanger the operation of the power system after a fault. Attached Figure Description

[0043] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0044] Figure 1 This is a flowchart illustrating the steps of the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter as described in the embodiments of this application.

[0045] Figure 2 This is a control framework diagram of the low voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application;

[0046] Figure 3 This is a control framework diagram of the grid-type algorithm in the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application;

[0047] Figure 4 This is a voltage loop diagram of the grid-type algorithm in the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application;

[0048] Figure 5 This is a current loop diagram of the grid-type algorithm in the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application;

[0049] Figure 6 This is a frame diagram of the low voltage ride-through control device for a two-stage grid-type photovoltaic inverter according to an embodiment of this application. Detailed Implementation

[0050] To make the inventive objectives, features, and advantages of this application more apparent and understandable, the technical solutions in the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0051] This application provides a low-voltage ride-through control method, apparatus, and device for a two-stage grid-connected photovoltaic inverter. When the two-stage grid-connected photovoltaic inverter is operating normally, a voltage reference value is obtained through a grid-connected algorithm, and first valve-side reference data is obtained through positive and negative sequence voltage loops and positive and negative sequence current loops to control the two-stage grid-connected photovoltaic inverter. When the two-stage grid-connected photovoltaic inverter experiences AC-side symmetrical or asymmetrical faults, in the initial stage of the fault, output limiting through positive and negative sequence voltage loops is used to suppress instantaneous current spikes. During the fault period, flexible control of the fault current is achieved by setting positive and negative sequence current reference values, and the output power of the two-stage grid-connected photovoltaic inverter is balanced through DC voltage control mode. After the fault, a smooth transition from positive and negative sequence current control back to grid-connected control is achieved. This solves the technical problem that in existing power systems using photovoltaic inverters in grid-connected control technology, large currents are generated after a fault, endangering the operation of the power system.

[0052] Example 1:

[0053] Figure 1 This is a flowchart illustrating the steps of the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter as described in an embodiment of this application.

[0054] like Figure 1 As shown in the figure, this application provides a low-voltage ride-through control method for a two-stage grid-connected photovoltaic inverter. The two-stage grid-connected photovoltaic inverter includes a front-end boost circuit and a rear-end inverter circuit. The low-voltage ride-through control method includes the following steps:

[0055] S1. Obtain the electrical parameters of the two-stage grid-type photovoltaic inverter. The electrical parameters include the actual reactive power, rated AC voltage, AC voltage amplitude, maximum withstand current, and rated current.

[0056] It should be noted that the electrical parameters of the two-stage grid-type photovoltaic inverter obtained in step S1 provide data for subsequent steps. In this embodiment, the front-stage boost circuit is mainly used to control the output voltage of the two-stage grid-type photovoltaic inverter, and the rear-stage inverter circuit is mainly used to convert DC to three-phase AC. The front-stage boost circuit can be referred to as the front-stage DC / DC circuit, and the rear-stage inverter circuit can also be referred to as the rear-stage VSC circuit.

[0057] S2. Determine the low-voltage ride-through control signal in a two-stage grid-type photovoltaic inverter based on the AC voltage amplitude.

[0058] It should be noted that in step S2, the AC voltage amplitude obtained in step S1 can be used to determine whether the two-stage grid-type photovoltaic inverter has failed, and then the control signal for controlling the low voltage ride-through of the two-stage grid-type photovoltaic inverter is determined based on whether a failure has occurred.

[0059] Furthermore, the control signal for low-voltage ride-through in a two-stage grid-connected photovoltaic inverter, determined based on the AC voltage amplitude, includes: if the AC voltage amplitude is less than the voltage threshold, the control signal is 1, indicating a fault has occurred in the power system where the two-stage grid-connected photovoltaic inverter is located; if the AC voltage amplitude is not less than the voltage threshold, the control signal is 0, indicating that no fault has occurred in the power system where the two-stage grid-connected photovoltaic inverter is located.

[0060] Figure 2 This is a control framework diagram of the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application. Figure 3 This is a control framework diagram of the grid-type algorithm in the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in the embodiments of this application.

[0061] S3. If the control signal is 0, the first valve-side reference data is obtained by using the first control method based on the actual value of reactive power and the rated value of AC voltage, and the operation of the downstream inverter circuit is controlled based on the first valve-side reference data; the operation of the upstream boost circuit is controlled by using the maximum power point tracking mode.

[0062] It should be noted that in step S3, based on a control signal of 0 and the actual reactive power value and rated AC voltage obtained in step S1, a first valve-side reference data is obtained using the first control method. This first valve-side reference data is used to control the operation of the subsequent inverter circuit and the maximum power point tracking (MPPT) mode is used to control the operation of the preceding boost circuit, thus achieving low-voltage ride-through control of the two-stage grid-type photovoltaic inverter. In this embodiment, during the process of controlling the operation of the subsequent inverter circuit based on the first valve-side reference data, a trigger pulse signal is first obtained through a modulation stage based on the first valve-side reference data. Then, the operation of the subsequent inverter circuit is controlled based on the trigger pulse signal. The modulation stage can employ PWM modulation, a relatively common technique in the field. The maximum power point tracking mode is also a relatively common technique in the field; therefore, the details of the modulation stage and the maximum power point tracking mode will not be elaborated here.

[0063] like Figure 2 As shown, further, the first valve-side reference data obtained using the first control method based on the actual reactive power value and the rated AC voltage value includes:

[0064] The voltage reference value is obtained by using a network-based algorithm based on the actual reactive power value and the rated AC voltage value.

[0065] The voltage reference value is limited by positive sequence voltage loop and negative sequence voltage loop to obtain the first positive sequence current reference value and the first negative sequence current reference value;

[0066] The first positive sequence current reference value and the first negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and the first negative sequence valve side reference voltage.

[0067] The first valve-side reference data includes the first positive-sequence valve-side reference voltage and the first negative-sequence valve-side reference voltage.

[0068] In the embodiments of this application, such as Figure 3 As shown, the voltage reference value calculated using the network-based algorithm includes: first, comparing the actual reactive power value Q with the reactive power reference value Q. ref The difference between the two values ​​is calculated to obtain the reactive power difference; the reactive power difference is then compared with the first control parameter M of the network-type algorithm. q Multiply to obtain the adjusted reactive power; then multiply the adjusted reactive power with the rated AC voltage V.acN The voltage reference value V is obtained by superposition processing. acref .

[0069] It should be noted that, as Figure 3 As shown, the grid-type algorithm also includes: obtaining the actual DC voltage value u of the two-stage grid-type photovoltaic inverter. dc DC voltage reference value u dcref And the AC rated angular frequency ω0, the actual DC voltage value u dc With DC voltage reference value u dcref The difference calculated between them and the second control parameter M of the network algorithm dc Multiplying these yields the adjusted voltage; this adjusted voltage is then superimposed onto the AC rated angular frequency ω0 and integrated by a 1 / s integrator to obtain the phase angle θ. θ is used as the reference angle for the positive-sequence abc / dq coordinate transformation and the inverse positive-sequence dq / abc coordinate transformation, while -θ is used as the reference angle for the negative-sequence abc / dq coordinate transformation and the inverse negative-sequence dq / abc coordinate transformation.

[0070] Figure 4 This is a voltage loop diagram of the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in this application embodiment. Figure 4 This is a current loop diagram of the grid-type algorithm in the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter described in this application embodiment. Figure 4 In the middle, L f A filter inductor configured on the AC side of a two-stage grid-type photovoltaic inverter.

[0071] like Figure 4 As shown in this embodiment, the voltage reference value is limited by a positive-sequence voltage loop and a negative-sequence voltage loop to obtain the first positive-sequence current reference value and the first negative-sequence current reference value, which include:

[0072] Obtain the positive sequence component u of the d-axis voltage at the connection point between the two-stage grid-connected photovoltaic inverter and the power system. dP q-axis voltage positive sequence component u qP d-axis voltage negative sequence component u dN and the negative sequence component of the q-axis voltage u qN ;

[0073] In the positive sequence voltage loop, the voltage reference value V acref With the positive sequence component of the d-axis voltage u dP Through comparison, PI integral control, and amplitude limiting, the d-axis positive sequence current reference value i is obtained. dPref For the positive sequence component of the q-axis voltage u qP By comparing with 0, performing PI integral control, and limiting control, the q-axis positive sequence current reference value i is obtained. qPref ;

[0074] In the negative sequence voltage loop, for the negative sequence component u of the d-axis voltage dN By comparing with 0, performing PI integral control, and limiting, the d-axis negative sequence current reference value i is obtained. dNref ; for the negative sequence component of the q-axis voltage u qN By comparing with 0, performing PI integral control, and limiting, the q-axis negative sequence current reference value i is obtained. qNref ;

[0075] The first positive sequence current reference value includes the d-axis positive sequence current reference value i. dPref and q-axis positive sequence current reference value i qPref The first negative sequence current reference value includes the d-axis negative sequence current reference value i. dNref and q-axis negative sequence current reference value i qNref .

[0076] It should be noted that the parameters for the limiting process include the maximum limiting value i of the d-axis output of the positive sequence voltage loop. dPLim The maximum limit value i of the q-axis output of the positive sequence voltage loop qPLim The maximum limit value i of the d-axis output of the negative sequence voltage loop dNLim The maximum limit value i of the q-axis output of the negative sequence voltage loop pNLim .

[0077] like Figure 5 As shown in the embodiments of this application, the first positive sequence current reference value and the first negative sequence current reference value are processed by corresponding positive sequence current loop and coordinate transformation and negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve-side reference voltage and first negative sequence valve-side reference voltage, including:

[0078] Obtain the positive sequence component i of the measured d-axis current at the outlet of a two-stage grid-connected photovoltaic inverter. dP q-axis measured positive sequence current component i qP d-axis measured negative sequence current component i dN and the negative sequence component of the measured current along the q-axis i qN ;

[0079] In the positive sequence current loop, the d-axis positive sequence current reference value i dPref The positive sequence component of the measured current along the d-axis i dP Through comparison, PI control, and coordinate transformation, the d-axis positive sequence valve side reference voltage component u is obtained. cdP ; For the q-axis positive sequence current reference value i qPref The positive sequence component of the measured current along the q-axis, i qP Through comparison, PI control, and coordinate transformation, the q-axis positive sequence valve side reference voltage component u is obtained. cqP ;

[0080] In the positive sequence current loop, the negative sequence current reference value i along the d-axis is... dNref The negative sequence component of the measured current along the d-axis i dN Through comparison, PI control, and coordinate transformation, the d-axis negative sequence valve-side reference voltage component u is obtained. cdN ; Reference value i for negative sequence current on the q-axis qNref The negative sequence component of the measured q-axis current i qN Through comparison, PI control, and coordinate transformation, the q-axis negative sequence valve-side reference voltage component u is obtained. cqN ;

[0081] The first positive sequence valve-side reference voltage includes the d-axis positive sequence valve-side reference voltage component u. cdP and the q-axis positive sequence valve side reference voltage component u cqP The first negative sequence valve-side reference voltage includes the d-axis negative sequence valve-side reference voltage component u. cdN and the q-axis negative sequence valve side reference voltage component u cqN .

[0082] S4. If the control signal is 1, the second valve-side reference data is obtained by using the second control method based on the AC voltage amplitude, the maximum withstand current value and the rated current value. The operation of the subsequent inverter circuit is controlled based on the second valve-side reference data. The operation of the preceding boost circuit is controlled by using the DC voltage mode.

[0083] It should be noted that if the control signal is 1, indicating a symmetrical or asymmetrical ground fault in the power system where the two-stage grid-type photovoltaic inverter is located, then the operation of the downstream inverter circuit needs to be controlled using the second valve-side reference data obtained by the second control method; the operation of the upstream boost circuit is controlled using DC voltage mode. In this embodiment, DC voltage mode is a relatively common technical means in the field, therefore, the content of DC voltage mode will not be described in detail here.

[0084] Furthermore, the second valve-side reference data obtained using the second control method based on the AC voltage amplitude, maximum withstand current value, and rated current value includes:

[0085] The reference value of the positive sequence current of the d-axis before the fault of the two-stage grid-type photovoltaic inverter is obtained based on the control signal of 1.

[0086] The voltage reference value is obtained by using a network-type algorithm based on the actual value of reactive power and the rated value of AC voltage. The voltage reference value is then subjected to amplitude limiting through positive sequence voltage loop and negative sequence voltage loop. The second positive sequence current reference value and the second negative sequence current reference value are calculated and determined based on the d-axis positive sequence current reference value, AC voltage amplitude, maximum withstand current value and rated current value.

[0087] The second positive sequence current reference value and the second negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and the second negative sequence valve side reference voltage.

[0088] The second valve-side reference data includes the second positive-sequence valve-side reference voltage and the second negative-sequence valve-side reference voltage.

[0089] In this embodiment, there is a certain time delay between the occurrence of a fault in the power system where the two-stage grid-connected photovoltaic inverter is located and the implementation of measures to control the fault current, resulting in a fault current spike. Therefore, the second control method of the low-voltage ride-through control method for this two-stage grid-connected photovoltaic inverter can also adopt the first control method, which limits the voltage based on the voltage reference value through the output of the positive-sequence voltage loop and the negative-sequence voltage loop. This can suppress the current spike before the fault current control measures take effect (i.e., when the second control method takes effect), thus suppressing the instantaneous current spike during the fault. This allows the low-voltage ride-through control method for the two-stage grid-connected photovoltaic inverter to effectively suppress instantaneous current spikes in the early stages of a fault by setting output limits for the positive and negative-sequence voltage loops. This ensures that the output current reference value is limited to the maximum current value that the two-stage grid-connected photovoltaic inverter can withstand.

[0090] In this embodiment of the application, the parameters for the limiting processing can be represented by Expression 1, which is:

[0091]

[0092] In the formula, i MAX This refers to the maximum current that a two-stage grid-type photovoltaic inverter can withstand, which can be set according to the actual capacity of the equipment. Among the parameters for limiting processing, the maximum limiting value i of the d-axis output of the positive sequence voltage loop is included. dPLim The maximum limit value i of the q-axis output of the positive sequence voltage loop qPLim The maximum limit value i of the d-axis output of the negative sequence voltage loop dNLim The maximum limit value i of the q-axis output of the negative sequence voltage loop pNLim In this embodiment, i in expression one dPLim =i MAX The d-axis current can be from 0 to i MAX Internal changes, residual margin Apply current to the q-axis to limit the amplitude.

[0093] In this embodiment, the low-voltage ride-through control method for the two-stage grid-type photovoltaic inverter uses a current reference formula to calculate and determine the second positive-sequence current reference value and the second negative-sequence current reference value based on the d-axis positive-sequence current reference value, AC voltage amplitude, maximum withstand current value, and rated current value. The current reference formula is:

[0094]

[0095]

[0096] i dNref '=0

[0097] i qNref '=0

[0098] In the formula, i d0 U is the reference value of the positive sequence d-axis current before the fault. T I represents the amplitude of the AC voltage. N This is the rated current value. Specifically, when a three-phase or two-phase short circuit occurs in the AC power grid of the power system where the two-stage grid-connected photovoltaic inverter is located, U... T Line voltage; when a single-phase short circuit occurs in the AC grid of the power system where the two-stage grid-connected photovoltaic inverter is located, U T The phase voltage threshold for low-voltage ride-through can be set to 0.9pu. pu is the per-unit value of the power system voltage in which the two-stage grid-connected photovoltaic inverter is located. The second positive sequence current reference value includes the d-axis positive sequence current reference value i. dPref ′ and q-axis positive sequence current reference values ​​i qPref The second negative sequence current reference value includes the d-axis negative sequence current reference value i. dNref ′ and q-axis negative sequence current reference values ​​i qNref '。d-axis positive sequence current reference value i dPref The value of ′ is from i d0 and The minimum value between.

[0099] It should be noted that in the second control method, the second positive-sequence current reference value and the second negative-sequence current reference value are processed using corresponding positive-sequence current loops and coordinate transformations, and the corresponding second positive-sequence valve-side reference voltage and second negative-sequence valve-side reference voltage are obtained using the same principle as in the first control method. The second valve-side reference data can be obtained by referring to the data processing process of the positive-sequence current loop and negative-sequence current loop in the first control method. In this embodiment, the low-through current reference value (including the second positive-sequence current reference value and the second negative-sequence current reference value) is sent to the positive-sequence current loop and the negative-sequence current loop to control the positive-sequence and negative-sequence fault currents respectively. At the same time, the front-end boost circuit switches from the maximum power point tracking mode (MPPT control loop) to the DC voltage mode to achieve DC voltage control and automatic balancing of photovoltaic output power during the fault period. Specifically, when the control mode is 1, the grid configuration algorithm, positive-sequence voltage loop, and negative-sequence voltage loop of the downstream inverter circuit are locked to keep its output at the value before the fault, and the maximum power point tracking mode of the front-end boost circuit is locked to keep its output at the value before the fault.

[0100] This application provides a low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter. The method includes: acquiring electrical parameters of the two-stage grid-type photovoltaic inverter; determining a low-voltage ride-through control signal in the two-stage grid-type photovoltaic inverter based on the AC voltage amplitude; if the control signal is 0, obtaining first valve-side reference data using a first control method based on the actual reactive power value and the rated AC voltage value, and controlling the operation of the subsequent inverter circuit based on the first valve-side reference data; controlling the operation of the preceding boost circuit using maximum power point tracking mode; if the control signal is 1, obtaining second valve-side reference data using a second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value, and controlling the operation of the subsequent inverter circuit based on the second valve-side reference data; and controlling the operation of the preceding boost circuit using DC voltage mode. This low-voltage ride-through control method for a two-stage grid-connected photovoltaic inverter uses valve-side reference data obtained from a first and a second control mode, which have the capability to control both positive and negative sequence voltage and current, to control the positive and negative sequence voltages, thus presenting voltage source characteristics. It also controls the positive and negative sequence currents to flexibly control fault currents. The low-voltage ride-through of the two-stage grid-connected photovoltaic inverter is achieved through the coordination of the front-stage boost circuit and the control strategy of the back-stage inverter circuit. This ensures the balance of photovoltaic output power during faults and a smooth transition back to grid-connected control after a fault. This solves the technical problem that existing power systems using photovoltaic inverters in grid-connected control technology will generate large currents that endanger the operation of the power system after a fault.

[0101] In one embodiment of this application, the low voltage ride-through control method of the two-stage grid-type photovoltaic inverter includes: if the fault is cleared, controlling the AC voltage amplitude to be no less than the voltage threshold value, and restoring the second positive sequence current reference value and the second negative sequence current reference value in the second control mode to the state before the fault according to the slope ratio; at the same time, switching the DC voltage mode controlling the operation of the front-stage boost circuit to the maximum power point tracking mode.

[0102] It should be noted that the slope ratio can be set according to requirements, for example, the slope ratio should not be less than 30% of the rated current. If the fault is cleared, and the control AC voltage amplitude is not less than the voltage threshold value, the control signal is 0, and the reference values ​​of the positive sequence current loop and the negative sequence current loop are restored to the values ​​before the fault according to the slope ratio; the maximum power point tracking mode (also known as the MPPT control loop) output is opened, and the DC voltage mode of the front-stage boost circuit is switched back to the maximum power point tracking mode control. At the same time, the network algorithm and the positive and negative sequence voltage loop outputs of the rear-stage inverter circuit are reopened.

[0103] Example 2:

[0104] Figure 6 This is a frame diagram of the low voltage ride-through control device for a two-stage grid-type photovoltaic inverter according to an embodiment of this application.

[0105] like Figure 6 As shown, this application embodiment also provides a low voltage ride-through control device for a two-stage grid-type photovoltaic inverter. The two-stage grid-type photovoltaic inverter includes a front-stage boost circuit and a rear-stage inverter circuit. The low voltage ride-through control device includes a parameter acquisition module 10, a control judgment module 20, a first execution module 30, and a second execution module 40.

[0106] The parameter acquisition module 10 is used to acquire the electrical quantity parameters of the two-stage grid-type photovoltaic inverter. The electrical quantity parameters include the actual value of reactive power, the rated value of AC voltage, the amplitude of AC voltage, the maximum withstand current value, and the rated current value.

[0107] Control and judgment module 20 is used to determine the low voltage ride-through control signal in a two-stage grid-type photovoltaic inverter based on the AC voltage amplitude;

[0108] The first execution module 30 is used to obtain first valve-side reference data based on the actual value of reactive power and the rated value of AC voltage when the control signal is 0, and to control the operation of the downstream inverter circuit based on the first valve-side reference data; and to control the operation of the upstream boost circuit using the maximum power point tracking mode.

[0109] The second execution module 40 is used to obtain second valve-side reference data according to the second control method based on the control signal being 1, the AC voltage amplitude, the maximum withstand current value, and the rated current value, and to control the operation of the downstream inverter circuit according to the second valve-side reference data; and to control the operation of the upstream boost circuit using DC voltage mode.

[0110] In this embodiment of the application, the first execution module 30 includes a first calculation submodule, a first processing submodule, and a second processing submodule;

[0111] The first calculation submodule is used to calculate the voltage reference value based on the actual value of reactive power and the rated value of AC voltage using a network-type algorithm.

[0112] The first processing submodule is used to perform amplitude limiting processing on the voltage reference value through the positive sequence voltage loop and the negative sequence voltage loop to obtain the first positive sequence current reference value and the first negative sequence current reference value;

[0113] The second processing submodule is used to process the first positive sequence current reference value and the first negative sequence current reference value with the corresponding positive sequence current loop, coordinate transformation and negative sequence current loop, coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and first negative sequence valve side reference voltage.

[0114] The first valve-side reference data includes the first positive-sequence valve-side reference voltage and the first negative-sequence valve-side reference voltage.

[0115] In this embodiment of the application, the second execution module 40 includes a data acquisition submodule, a second calculation submodule, and a third processing submodule;

[0116] The data acquisition submodule is used to acquire the reference value of the d-axis positive sequence current before the fault of the two-stage grid-type photovoltaic inverter based on the control signal being 1.

[0117] The second calculation submodule is used to calculate the voltage reference value based on the actual value of reactive power and the rated value of AC voltage using a network-type algorithm; to perform amplitude limiting processing on the voltage reference value through positive sequence voltage loop and negative sequence voltage loop; and to calculate and determine the second positive sequence current reference value and the second negative sequence current reference value based on the d-axis positive sequence current reference value, AC voltage amplitude, maximum withstand current value and rated current value.

[0118] The third processing submodule is used to process the second positive sequence current reference value and the second negative sequence current reference value with the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and the second negative sequence valve side reference voltage.

[0119] The second valve-side reference data includes the second positive-sequence valve-side reference voltage and the second negative-sequence valve-side reference voltage.

[0120] In this embodiment, the low voltage ride-through control device of the two-stage grid-type photovoltaic inverter includes a fault clearing module. The fault clearing module is used to control the AC voltage amplitude to be no less than the voltage threshold value according to the fault clearing, and restore the second positive sequence current reference value and the second negative sequence current reference value in the second control mode to the state before the fault according to the slope ratio; at the same time, it switches the DC voltage mode controlling the operation of the front-stage boost circuit to the maximum power point tracking mode.

[0121] It should be noted that the modules in the device of Embodiment 2 correspond to the steps in the method of Embodiment 1. The low voltage ride-through control method of the two-stage grid-type photovoltaic inverter has been described in detail in Embodiment 1, and the content of the modules in the device will not be described in detail in this Embodiment 2.

[0122] Example 3:

[0123] This application provides a terminal device, including a processor and a memory;

[0124] Memory is used to store program code and transfer the program code to the processor;

[0125] The processor is used to execute the low-voltage ride-through control method for the two-stage grid-type photovoltaic inverter described above, according to the instructions in the program code.

[0126] It should be noted that the processor is used to execute the steps in the above-described embodiment of a low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter according to the instructions in the program code. Alternatively, when the processor executes the computer program, it implements the functions of each module / unit in the above-described system / device embodiments.

[0127] For example, a computer program can be divided into one or more modules / units, one or more of which are stored in memory and executed by a processor to complete this application. One or more modules / units can be a series of computer program instruction segments capable of performing a specific function, which describe the execution process of the computer program in a terminal device.

[0128] Terminal devices can be computing devices such as desktop computers, laptops, handheld computers, and cloud servers. Terminal devices may include, but are not limited to, processors and memory. Those skilled in the art will understand that this does not constitute a limitation on the terminal device, which may include more or fewer components than illustrated, or combinations of certain components, or different components. For example, a terminal device may also include input / output devices, network access devices, buses, etc.

[0129] The processor referred to can be a Central Processing Unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. A general-purpose processor can be a microprocessor or any conventional processor.

[0130] Memory can be an internal storage unit of a terminal device, such as a hard drive or RAM. Memory can also be an external storage device, such as a plug-in hard drive, SmartMedia Card (SMC), Secure Digital (SD) card, or Flash Card. Furthermore, memory can include both internal and external storage units. Memory is used to store computer programs and other programs and data required by the terminal device. Memory can also be used to temporarily store data that has been output or will be output.

[0131] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0132] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0133] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0134] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0135] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0136] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter, characterized in that, The two-stage grid-connected photovoltaic inverter includes a front-stage boost circuit and a rear-stage inverter circuit. The low-voltage ride-through control method includes the following steps: Obtain the electrical quantity parameters of a two-stage grid-type photovoltaic inverter, including the actual reactive power value, rated AC voltage value, AC voltage amplitude, maximum withstand current value, and rated current value. The control signal for low voltage ride-through in the two-stage grid-type photovoltaic inverter is determined based on the AC voltage amplitude. If the control signal is 0, the first valve-side reference data is obtained by using the first control method based on the actual value of reactive power and the rated value of AC voltage, and the operation of the downstream inverter circuit is controlled based on the first valve-side reference data; the operation of the upstream boost circuit is controlled by using the maximum power point tracking mode. If the control signal is 1, the second valve-side reference data is obtained using the second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value. The operation of the downstream inverter circuit is controlled based on the second valve-side reference data. The operation of the upstream boost circuit is controlled using DC voltage mode. The first valve-side reference data obtained using the first control method based on the actual reactive power value and the rated AC voltage value includes: A voltage reference value is obtained by using a network-based algorithm based on the actual value of reactive power and the rated value of AC voltage. The voltage reference value is subjected to amplitude limiting processing through a positive sequence voltage loop and a negative sequence voltage loop to obtain a first positive sequence current reference value and a first negative sequence current reference value. The first positive sequence current reference value and the first negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and the first negative sequence valve side reference voltage. The first valve-side reference data includes a first positive-sequence valve-side reference voltage and a first negative-sequence valve-side reference voltage.

2. The low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter according to claim 1, characterized in that, The second valve-side reference data obtained using the second control method based on the AC voltage amplitude, the maximum withstand current value, and the rated current value includes: Based on the control signal being 1, obtain the reference value of the d-axis positive sequence current before the fault of the two-stage grid-type photovoltaic inverter. A voltage reference value is obtained by using a network-based algorithm based on the actual reactive power value and the rated AC voltage value; the voltage reference value is then subjected to amplitude limiting processing through a positive-sequence voltage loop and a negative-sequence voltage loop; and a second positive-sequence current reference value and a second negative-sequence current reference value are calculated and determined based on the d-axis positive-sequence current reference value, the AC voltage amplitude, the maximum withstand current value, and the rated current value. The second positive sequence current reference value and the second negative sequence current reference value are processed by the corresponding positive sequence current loop and coordinate transformation and the negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and the second negative sequence valve side reference voltage. The second valve-side reference data includes a second positive-sequence valve-side reference voltage and a second negative-sequence valve-side reference voltage.

3. The low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter according to claim 1, characterized in that, The control signal for low-voltage ride-through in the two-stage grid-type photovoltaic inverter is determined based on the AC voltage amplitude. If the AC voltage amplitude is less than the voltage threshold value, the control signal is 1, indicating that a fault has occurred in the power system where the two-stage grid-type photovoltaic inverter is located. If the AC voltage amplitude is not less than the voltage threshold value, the control signal is 0, indicating that no fault has occurred in the power system where the two-stage grid-type photovoltaic inverter is located.

4. The low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter according to claim 3, characterized in that, include: If the fault is cleared, the AC voltage amplitude is controlled to be no less than the voltage threshold value, and the second positive sequence current reference value and the second negative sequence current reference value in the second control mode are restored to the state before the fault according to the slope ratio; at the same time, the DC voltage mode controlling the operation of the front-stage boost circuit is switched to the maximum power point tracking mode.

5. A low-voltage ride-through control device for a two-stage grid-type photovoltaic inverter, characterized in that, The two-stage grid-type photovoltaic inverter includes a front-stage boost circuit and a back-stage inverter circuit. The low-voltage ride-through control device includes a parameter acquisition module, a control judgment module, a first execution module, and a second execution module. The parameter acquisition module is used to acquire the electrical quantity parameters of the two-stage grid-type photovoltaic inverter. The electrical quantity parameters include the actual value of reactive power, the rated value of AC voltage, the amplitude of AC voltage, the maximum withstand current value, and the rated current value. The control judgment module is used to determine the low voltage ride-through control signal in the two-stage grid-type photovoltaic inverter based on the AC voltage amplitude. The first execution module is configured to obtain first valve-side reference data based on the actual reactive power value and the rated AC voltage value using a first control method when the control signal is 0, control the operation of the downstream inverter circuit based on the first valve-side reference data, and control the operation of the upstream boost circuit using maximum power point tracking mode. The second execution module is configured to obtain second valve-side reference data based on the control signal being 1, the AC voltage amplitude, the maximum withstand current value, and the rated current value using a second control method; control the operation of the downstream inverter circuit based on the second valve-side reference data; and control the operation of the upstream boost circuit using a DC voltage mode. The first execution module includes a first calculation submodule, a first processing submodule, and a second processing submodule; The first calculation submodule is used to calculate the voltage reference value based on the actual value of reactive power and the rated value of AC voltage using a network-type algorithm; The first processing submodule is used to perform amplitude limiting processing on the voltage reference value through a positive sequence voltage loop and a negative sequence voltage loop to obtain a first positive sequence current reference value and a first negative sequence current reference value; The second processing submodule is used to process the first positive sequence current reference value and the first negative sequence current reference value with corresponding positive sequence current loop and coordinate transformation and negative sequence current loop and coordinate transformation to obtain the corresponding first positive sequence valve side reference voltage and first negative sequence valve side reference voltage. The first valve-side reference data includes a first positive-sequence valve-side reference voltage and a first negative-sequence valve-side reference voltage.

6. The low-voltage ride-through control device for a two-stage grid-type photovoltaic inverter according to claim 5, characterized in that, The second execution module includes a data acquisition submodule, a second calculation submodule, and a third processing submodule; The data acquisition submodule is used to acquire the reference value of the d-axis positive sequence current before the fault of the two-stage grid-type photovoltaic inverter based on the control signal being 1. The second calculation submodule is used to calculate the voltage reference value based on the actual value of reactive power and the rated value of AC voltage using a network-type algorithm; The voltage reference value is limited by positive-sequence voltage loop and negative-sequence voltage loop; and the second positive-sequence current reference value and the second negative-sequence current reference value are calculated and determined based on the d-axis positive-sequence current reference value, the AC voltage amplitude, the maximum withstand current value and the rated current value. The third processing submodule is used to process the second positive sequence current reference value and the second negative sequence current reference value with corresponding positive sequence current loop and coordinate transformation and negative sequence current loop and coordinate transformation to obtain the corresponding second positive sequence valve side reference voltage and second negative sequence valve side reference voltage. The second valve-side reference data includes a second positive-sequence valve-side reference voltage and a second negative-sequence valve-side reference voltage.

7. The low-voltage ride-through control device for a two-stage grid-type photovoltaic inverter according to claim 5, characterized in that, The system includes a fault clearing module, which controls the AC voltage amplitude to be no less than the voltage threshold value according to the fault clearing, and restores the second positive sequence current reference value and the second negative sequence current reference value in the second control mode to the state before the fault according to the slope ratio; at the same time, it switches the DC voltage mode controlling the operation of the front-stage boost circuit to the maximum power point tracking mode.

8. A terminal device, characterized in that, Including the processor and memory; The memory is used to store program code and transmit the program code to the processor; The processor is configured to execute the low-voltage ride-through control method for a two-stage grid-type photovoltaic inverter as described in any one of claims 1-4, according to the instructions in the program code.

Images