Photovoltaic low voltage ride through rapid recovery control method and device

Abstract

The invention provides a photovoltaic low voltage ride through rapid recovery control method and device, and belongs to the field of power grids. The method is applied to a photovoltaic system. The photovoltaic system comprises a photovoltaic module, a direct-current converter and a photovoltaic inverter which are connected in sequence, and the photovoltaic inverter is connected to a power grid; the method comprises the following steps: acquiring power grid voltage in real time, and detecting whether the power grid voltage drops or not; when it is detected that the power grid voltage drops, reference reactive current and reference active current are determined according to the current power grid voltage; and performing loop control on the photovoltaic inverter according to the reference reactive current and the reference active current. According to the invention, when the power grid voltage drops, the inverter is directly controlled according to the power grid voltage to realize low-voltage penetration, the low-voltage penetration effect is good, additional equipment is not needed, and the cost is low.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power grid, and particularly relates to a photovoltaic low-voltage ride-through fast recovery control method and device. BACKGROUND

[0002] As one of the main sources of clean energy, photovoltaic power generation occupies an important position in clean energy power generation. When the power grid fails or is planned to be disconnected, the distributed power supply, energy storage device and load are independently operated, and at this time, the photovoltaic grid-connected power generation system is applied to the weak power grid scene. With the increasing penetration rate of renewable energy power generation such as photovoltaic, related problems also arise, such as off-grid accidents caused by equipment failure, which seriously affects the stability and reliability of the power grid. How to reasonably complete the low-voltage ride-through is of great significance to ensure the stable and reliable operation of the power grid.

[0003] In the prior art, the voltage of the DC bus is stabilized by simplifying the front-stage structure or adding additional equipment to complete the low-voltage ride-through, but the low-voltage ride-through effect is not good and the cost is high. SUMMARY

[0004] Embodiments of the present application provide a photovoltaic low-voltage ride-through fast recovery control method and device to solve the problem of poor effect and high cost in the prior art by simplifying the front-stage structure or adding additional equipment to achieve low-voltage ride-through.

[0005] In a first aspect, embodiments of the present application provide a photovoltaic low-voltage ride-through fast recovery control method applied to a photovoltaic system; the photovoltaic system comprises photovoltaic components, a DC converter and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to a power grid; the method comprises:

[0006] real-time acquisition of the power grid voltage and detection of whether the power grid voltage has dropped;

[0007] when the power grid voltage drop is detected, determining reference reactive current and reference active current according to the current power grid voltage;

[0008] loop control of the photovoltaic inverter according to the reference reactive current and the reference active current.

[0009] In a second aspect, embodiments of the present application provide a photovoltaic low-voltage ride-through fast recovery control device applied to a photovoltaic system; the photovoltaic system comprises photovoltaic components, a DC converter and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to a power grid; the device comprises:

[0010] a drop detection module for real-time acquisition of the power grid voltage and detection of whether the power grid voltage has dropped;

[0011] The reference current determination module is configured to determine the reference reactive current and the reference active current according to the current grid voltage when the grid voltage drop is detected.

[0012] The voltage loop control module is configured to perform loop control on the photovoltaic inverter according to the reference reactive current and the reference active current.

[0013] The embodiment of the present application provides a photovoltaic low-voltage ride-through fast recovery control method and device, and belongs to the field of power grids. The method is applied to a photovoltaic system; the photovoltaic system comprises photovoltaic components, a direct-current converter and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to a power grid; the photovoltaic low-voltage ride-through fast recovery control method comprises the following steps: acquiring a grid voltage in real time, and detecting whether the grid voltage drops; when the grid voltage drop is detected, determining a reference reactive current and a reference active current according to the current grid voltage; and performing loop control on the photovoltaic inverter according to the reference reactive current and the reference active current. In the embodiment of the present application, the inverter is directly controlled according to the grid voltage to realize low ride-through when the grid voltage drops, without the need of additionally installing equipment, so that the cost is low, and the low ride-through effect is good. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0015] Figure 1 is a structural schematic diagram of a photovoltaic system provided by the embodiment of the present application;

[0016] Figure 2 is an implementation flowchart of a photovoltaic low-voltage ride-through fast recovery control method provided by the embodiment of the present application;

[0017] Figure 3 is a control loop diagram of a photovoltaic inverter provided by the embodiment of the present application;

[0018] Figure 4 is a P-V curve diagram of a photovoltaic component;

[0019] Figure 5 is a control loop diagram of a direct-current converter provided by the embodiment of the present application;

[0020] Figure 6 is a low ride-through curve diagram of a photovoltaic component provided by the embodiment of the present application;

[0021] Figure 7 is a grid frequency control block diagram provided by the embodiment of the present application;

[0022] Figure 8 is a waveform diagram of the output voltage of the photovoltaic module corresponding to the control method in the prior art under working condition 2;

[0023] Figure 9 is a waveform diagram of the output power of the photovoltaic inverter corresponding to the control method in the prior art under working condition 2;

[0024] Figure 10 is a waveform diagram of the output voltage of the photovoltaic module corresponding to the control method provided by the embodiment of the present application under working condition 2;

[0025] Figure 11 is a waveform diagram of the output power of the photovoltaic inverter corresponding to the control method provided by the embodiment of the present application under working condition 2;

[0026] Figure 12 is a low-frequency penetration comparison diagram of the prior art and the control method provided by the embodiment of the present application under working condition 1;

[0027] Figure 13 is a structural schematic diagram of the photovoltaic low-voltage penetration rapid recovery control device provided by the embodiment of the present application. DETAILED DESCRIPTION

[0028] In the following description, specific details are set forth in order to provide a thorough understanding of the embodiments of the present application. However, persons skilled in the art will understand that the present application can be practiced in other embodiments that depart from these specific details. In other instances, detailed descriptions of well-known systems, apparatuses, circuits, and methods are omitted in order to not obscure the description of the present application with unnecessary detail.

[0029] In order to make the objects, technical solutions and advantages of the present application clearer, the following will be described by specific embodiments in conjunction with the accompanying drawings.

[0030] Figure 1 is an application scenario diagram of the photovoltaic low-voltage penetration rapid recovery control method provided by the embodiment of the present application. As shown in Figure 1 , the above photovoltaic low-voltage penetration rapid recovery control method is applied to a photovoltaic system; the photovoltaic system includes photovoltaic modules, a direct-current converter and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to a power grid.

[0031] Figure 2 is a flowchart of the implementation of the photovoltaic low-voltage penetration rapid recovery control method provided by the embodiment of the present application. The above photovoltaic low-voltage penetration rapid recovery control method includes:

[0032] S101: Real-time acquisition of the grid voltage, and detection of whether the grid voltage has dropped;

[0033] When the power system is in normal operation, the grid voltage operates at or above the rated voltage. In one possible implementation, S101 can include:

[0034] S1011: When it is detected that the grid voltage is below the rated grid voltage, it is determined that the grid voltage has a dip;

[0035] S1012: Otherwise, it is determined that the grid voltage is normal.

[0036] When the grid voltage is below the rated grid voltage, it is determined that the voltage has a dip, otherwise, it is normal.

[0037] S102: When it is detected that the grid voltage has a dip, then determine the reference reactive current and the reference active current according to the current grid voltage;

[0038] In one possible implementation, S102 can include:

[0039] S1021: Determine the reference reactive current according to the current grid voltage;

[0040] S1022: Determine the reference active current according to the reference reactive current.

[0041] In one possible implementation, S1021 can include:

[0042] 1. According to the current grid voltage, determine the reference reactive current in combination with the first formula;

[0043] The first formula can include:

[0044]

[0045] Determine the reference active current according to the reference reactive current in combination with the second formula;

[0046] Since the output current of the photovoltaic inverter should be below 1.1 times the current rated value I N , based on this, the definition of the second formula can include:

[0047]

[0048] wherein, is the reference reactive current, is the reference active current; I N is the current rated value; U N is the rated grid voltage, U is the current grid voltage; K q is a proportional coefficient, a constant.

[0049] In the embodiment of the present application, the reference reactive current is sent to the grid side more, to provide voltage support at the grid connection point; the reference active current is used to maintain the bus voltage stability. According to the voltage drop depth, the reference reactive current is determined. The more the voltage drop, the greater the reference reactive current, to compensate the reactive power of the power grid, so that the power grid quickly passes through the low wear.

[0050] Further, when the grid voltage is normal, the normal voltage ring is restored, and the reference active current and the reference reactive current are determined according to the DC bus voltage. The specific method is a conventional technical means, and details are not described here.

[0051] S103: Loop control is performed on the photovoltaic inverter according to the reference reactive current and the reference active current.

[0052] In a possible implementation, S103 can include:

[0053] S1031: Reference active voltage and reference reactive voltage are determined according to the reference reactive current and the reference active current;

[0054] S1032: The reference active voltage and the reference reactive voltage are modulated to generate a driving PWM wave of the photovoltaic inverter.

[0055] In the embodiment of the present application, the reference Figure 3 , the photovoltaic inverter adopts a double-loop control of voltage outer ring and current inner ring, the voltage outer ring outputs the reference reactive current and the reference active current, and the current inner ring generates the reference active voltage and the reference reactive voltage, and modulates to generate a driving PWM wave to control each switch tube in the photovoltaic inverter.

[0056] In a possible implementation, S1031 includes:

[0057] 1. The grid voltage and current are acquired in real time, and the grid voltage and current are calculated to obtain active current, reactive current, active voltage and reactive voltage;

[0058] Reference Figure 3 , the grid voltage and current are calculated to obtain active current, reactive current, active voltage and reactive voltage;

[0059] According to the instantaneous power theory, the active and reactive power of the inverter in the dq axis can be expressed as:

[0060]

[0061] Where, P is the active power output by the photovoltaic inverter; Q is the reactive power output by the photovoltaic inverter; u d is the d-axis voltage; u q is the q-axis voltage; i d is the active current; iq is the reactive current. Generally u q is 0, u d is the grid voltage.

[0062] The dq decoupling is realized by Park transformation. According to the rule of equal amplitude transformation, it is assumed that the a-axis in the αβ transformation is coincident with the a-axis in the abc transformation, and the transformation matrix from abc to αβ is obtained. Assuming that the A-phase is the reference voltage, the voltage expression is obtained.

[0063]

[0064] According to Kirchhoff's voltage law, the state equation in the three-phase stationary coordinate system can be obtained.

[0065]

[0066] The voltage applied to the filter is the voltage difference on both sides, and for the low-frequency condition, L = L f + L t That is, the filter is regarded as an inductive device. However, the independent variable of this equation is the alternating current, which is not easy to control, so it is converted into the direct current which is easy to control through mathematical transformation. That is, through the Clark transformation shown by the following formula, the abc three-phase coordinate system is converted into the αβ coordinate system.

[0067]

[0068] Based on the above, the following formula is obtained:

[0069]

[0070] When the control variable is reduced in this state, but u α , u β is still an alternating component, which is not easy to control. It needs to be further transformed, that is, it is converted into a direct current component through Park transformation.

[0071] It is assumed that the initial time θ = 0°, and the dq axis rotates at a speed of ω, and its transformation matrix is shown in the following formula:

[0072]

[0073] The voltage is transformed to obtain the following formula:

[0074]

[0075] As can be seen above, after two transformations, we convert three AC control variables into two DC control variables, greatly simplifying the control steps and difficulty. However, DC d-q axis coupling still exists. To address this, current state feedback is introduced, and the d-axis and q-axis currents are controlled separately. Simultaneously, the d-axis and q-axis components of the grid voltage are introduced as feedforward compensation, gradually improving the system's dynamic performance. The decoupling process actually injects a component containing information about the other axis into the output of the PI regulator for each axis current. This injected component is equal to the coupling generated by the controlled object in the opposite direction.

[0076] 2. Determine the reference active voltage and the reference reactive voltage based on the active current, reactive current, active voltage, reactive voltage, reference reactive current, and reference active current in combination with the third formula;

[0077] The third formula may include:

[0078]

[0079] Among them, u d and u q are the reference active voltage and the reference reactive voltage respectively; i d and i q are active current and reactive current respectively; and are the reference active current and the reference reactive current respectively; e d and e q are active voltage and reactive voltage respectively; ω is angular frequency, L is inductance, K p , K i , s are the current loop PI integral parameters.

[0080] refer to Figure 3 In an embodiment of the present invention, when the grid voltage drops, a reference reactive current and a reference active current are determined according to the current grid voltage, and the inverter is controlled. Different reactive power and active power are transmitted to the grid based on the voltage drop depth, and the inverter is used to compensate the grid for the corresponding reactive power, thereby achieving rapid recovery of the grid voltage and frequency, and quickly passing through the low-voltage drop, thereby improving the stability and reliability of the grid.

[0081] During normal grid operation without any faults, PV panels typically operate at maximum power. However, when a grid fault occurs and the voltage suddenly drops, the power generated by the PV panels cannot be delivered to the grid in a timely manner. This mismatch between the generated power and the output power of the PV panels causes power accumulation at the output of the PV panels, damaging the panels and the DC converter.

[0082] In a possible implementation, the above method may further include:

[0083] S104: Obtaining a photovoltaic output reference value output by the MPPT module (ie, an input reference value of the DC converter);

[0084] S105: Subtracting the actual input voltage of the DC converter and the feedback voltage error from the photovoltaic output reference value to obtain an input voltage error;

[0085] S106: Input the input voltage error into the PI controller to generate a driving PWM wave for the DC converter.

[0086] In the embodiment of the present invention, a feedback voltage error is added to the loop of the DC converter. During low voltage operation, the output power of the photovoltaic module is adjusted by the feedback voltage error so that the power of the photovoltaic module matches the output.

[0087] In a possible implementation, the above method may further include:

[0088] S107: When a grid voltage drop is detected, the current photovoltaic output reference value is recorded as a first voltage;

[0089] S108: Obtain the output power of the photovoltaic inverter at the current moment, and determine the target input voltage of the DC converter according to the output power, which is recorded as the second voltage;

[0090] S109: Subtract the second voltage from the first voltage to obtain a feedback voltage error.

[0091] During normal operation, the photovoltaic modules operate in MPPT mode and output the maximum power. Figure 4 . Figure 5 The control loop of the DC converter is shown. When the grid drops, the DC converter operates in MPPT mode. The photovoltaic output reference value at this time is the voltage corresponding to the maximum power.

[0092] At the same time, the target input voltage is calculated based on the output power of the photovoltaic inverter, so that the output power of the photovoltaic module when operating at the target input voltage matches the output power of the photovoltaic inverter. The first voltage minus the second voltage is the feedback voltage error. Figure 4 , that is, forcibly lowering the reference voltage of the photovoltaic loop to the target input voltage, reducing the output power of the photovoltaic module, so that the output power of the photovoltaic module matches the output power of the photovoltaic inverter, achieving power balance, and can quickly overcome the low-voltage wear.

[0093] Specifically, the calculation formula for the PV curve of a photovoltaic module at any illumination and temperature is as follows:

[0094]

[0095] Among them, I PV is the photovoltaic output current; U PVis the photovoltaic output voltage; I′ sc is the short-circuit current under normal working conditions; U′ oc is the open circuit voltage under normal working conditions; U′ MPP It is the maximum power point voltage under normal working conditions.

[0096] Based on the above formula, we can get Figure 4 The PV curve of a photovoltaic module is shown in the figure. In this embodiment of the present invention, since the PV curve of the photovoltaic module is steeper to the right of the maximum power point than to the left, that is, only a small change in voltage can achieve a larger power adjustment, the adjustment terminal voltage is increased to move the operating point to the right of the PV curve to achieve the purpose of matching the power generated by the photovoltaic module with the output power of the inverter.

[0097] In a possible implementation, the above method may further include:

[0098] S1010: When it is detected that the grid voltage returns to normal, the feedback voltage error is set to 0, and the output of the MPPT module is adjusted so that the output of the MPPT module is the first voltage.

[0099] When the grid returns to normal, the feedback voltage error is reset to zero, and the PV panels resume normal MPPT control, operating at maximum power and achieving maximum power output. At the same time, because the dip is so short, the PV curve barely changes. That is, the maximum power point before and after the dip are almost identical. Therefore, after the grid returns to normal, the MPPT module output can be directly adjusted to the output recorded before the dip, allowing the PV panels to quickly return to their maximum power point, achieving rapid power recovery and shortening the time it takes to recover from a low-voltage drop.

[0100] The above method will be described below with reference to specific embodiments.

[0101] As a power electronic device, a photovoltaic inverter does not have a rotating rotor like a synchronous generator. The power angle δ defined below is the phase angle difference between the voltage phasor output by the inverter and the grid voltage phasor. When the line resistance is ignored, the output power is:

[0102]

[0103] Among them, E is the inverter output voltage, U is the grid voltage, and X is the line reactance.

[0104] like Figure 6 As shown, under normal conditions, the photovoltaic inverter operates at point A. When a voltage sag occurs, the phase angle cannot change suddenly, and the operating state shifts to point B. At this time, the photovoltaic inverter power instruction changes from P ref becomes P LVRT, so that the operating point moves to point C; when the grid voltage returns to normal, the operating point moves to point D, and then shifts to the operating point A in the normal state. At this time, the output P pv is not the maximum value, P pv <P ref . The operating point will first reach point E, and gradually increase with the tracking of the MPPT until it returns to point A, and the entire process is A-B-C-D-E-A.

[0105] When the control method provided by the embodiment of the application is used, P pv will be reduced, the dynamic process directly reaches the maximum power, and the operating point of the photovoltaic inverter will directly transition from point D to point A. The entire dynamic process is A-B-C-D-A. As can be seen from the above, without losing stability, the control method provided by the embodiment of the application reduces the transient process time and reaches the stable operating state more quickly.

[0106] When the photovoltaic inverter is in a weak grid, the frequency of the grid will be affected by the power generated by the photovoltaic inverter. Generally, the active-frequency droop characteristic is used to analyze the influence of the unbalanced active power on the frequency, and the formula is as follows:

[0107] ΔP=K f (ω-ω n )

[0108] Wherein, K f is the active-frequency droop coefficient, ΔP is the difference between the injected grid power and the normal working set power of the grid, ω is the actual frequency of the grid, and ω n is the rated frequency of the grid.

[0109] The mathematical expression of the grid frequency control model is:

[0110]

[0111] Wherein, P m is the mechanical power, P e is the electromagnetic power, P ref is the active power reference value, D is the virtual damping coefficient, and J is the moment of inertia.

[0112] The grid frequency control block diagram is as follows: Figure 7where θ = ∫ωdt. When the difference between the power injected into the grid and the power set when the grid is working normally is positive, the frequency rises, and the actual frequency is higher than the rated frequency. Conversely, the frequency drops, and the actual frequency is lower than the rated frequency. During normal operation of the photovoltaic inverter, the grid frequency is the rated frequency. During low penetration, the grid frequency decreases due to the decrease in active power output by the photovoltaic, and the grid frequency will not return to the rated frequency until the device resumes normal operation. Therefore, the recovery speed after low penetration ends will affect the speed at which the grid frequency recovers. When the photovoltaic inverter resumes normal operation at a faster speed, the grid frequency will also recover to the rated frequency faster.

[0113] A 2kW photovoltaic source grid-connected experimental platform was built and experimental verification was performed. A grid simulator, load cabinet, RCP fast prototype controller, Aine AN531500-90 photovoltaic simulator, inverter, and other related equipment were used for the experiment.

[0114] The RCP fast prototype controller was used to control the corresponding hardware for the experiment. A related model was built using MATLAB / Simulink to generate a compilable file that was burned into the RCP to control the DC converter and photovoltaic inverter. The switching of the device and the monitoring and collection of related experimental data were performed by the host computer. The device was connected according to the topology, the DC converter (BOOST circuit) was connected to the front stage, the photovoltaic inverter was connected to the microgrid designed based on the VSG, and the experiment was performed with the grid simulator. The influence of reactive power output on grid drop was compared with the frequency change in the microgrid and strong grid. Figure 1

[0115] The photovoltaic MPP point terminal voltage was 320V, and the power was 2kW, i.e., the normal working mode. The working voltage was 350V, and the power was 0.5kW during low penetration. The DC side bus voltage was 600V, the filter inductance was 5mH, the filter capacitance was 470μF, the grid frequency was 50Hz, the current inner loop K p was 0.15, the current inner loop K i was 6, the outer loop K p was 0.1, and the outer loop K i was 0.8.

[0116] The grid voltage was set to drop to 0.5p.u. in the experimental condition.

[0117] Condition 1: The grid voltage drop experiment was performed under the traditional load shedding control. At t = 0.8s, the recovery from the low penetration process to the normal state began. At this time, the output power followed the MPPT algorithm, and the power gradually increased from the corresponding power during low penetration. The photovoltaic terminal voltage gradually decreased to the terminal voltage corresponding to the MPP point, and the control strategy also returned to normal.

[0118] ​Case 2: The method provided by the embodiment of the application is used to carry out the grid voltage drop experiment, and when t = 2.85s, the low penetration process is restored to the normal state by using the prior art control method, and the recovery time is about 1.6s, and the reference Figure 8 and Figure 9 The method provided by the embodiment of the application can make the direct current converter quickly return to the maximum power point, and then make the photovoltaic assembly quickly reach the maximum power output, and the recovery time is about 0.01s, and then the control strategy returns to normal. For details, please refer to Figure 10 and Figure 11 .

[0119] By comparing the changes of the photovoltaic terminal voltage during the low voltage penetration recovery under different control strategies, it can be known that in the case of using the traditional load shedding control, during the recovery process, the photovoltaic assembly voltage finds the MPP point again by the voltage disturbance method of the MPPT, and it needs a longer time of about 1.6s due to the action limitation of the direct current converter. However, the control method provided by the embodiment of the application does not need a long recovery time.

[0120] Because the output power of the photovoltaic panel is controlled by the terminal voltage, under the case 2, due to the voltage control of the MPPT algorithm, the photovoltaic power needs 1.6s to recover to the maximum value corresponding to the terminal voltage recovery process under this strategy. After using the improved MPPT control algorithm, the power recovers to the maximum output power faster, only 0.01s, which is much faster than the traditional control strategy.

[0121] During the recovery process, the recovery speed of the output power will affect the recovery speed of the simulated grid frequency, as shown in Figure 12 When the photovoltaic output power reaches the rated value, the grid frequency is 50Hz, and when the low penetration is over, the faster the inverter recovers to the active power in the normal working state, the faster the grid frequency recovers to the rated frequency of 50Hz. By using the traditional load shedding control, the power slowly recovers along with the photovoltaic terminal voltage, so that the recovery speed of the grid frequency is also reduced, and it needs t2 = 1.6s to reach the rated frequency. However, the control method provided by the embodiment of the application can quickly increase the power output, and then realize the supporting effect on the grid frequency, and the frequency recovery speed depends on the response coefficient of the grid system, which is t1 = 0.1s, much smaller than the recovery time of the traditional load shedding control.

[0122] In summary, when the photovoltaic power generation system uses the control method provided by the embodiment of the application, the low voltage penetration can be realized, and the transition from the low voltage penetration process to the normal maximum photovoltaic output mode can be realized faster, and it is also beneficial to the recovery of the grid frequency.

[0123] The control method provided in the embodiment of the present invention is also applicable to single-stage and isolated photovoltaic inverters. The only difference is the specific control loop of the photovoltaic inverter. However, as long as the output of the MPP point before the low-crossover can be recorded and stored, the recovery phase time can be shortened and the frequency recovery speed can be accelerated.

[0124] It should be understood that the size of the serial numbers of the steps in the above embodiments does not mean the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0125] The following are device embodiments of the present invention. For details not fully described therein, reference may be made to the corresponding method embodiments described above.

[0126] Figure 13 The following is a schematic diagram showing the structure of a photovoltaic low voltage ride-through fast recovery control device provided by an embodiment of the present invention. For ease of explanation, only the parts related to the embodiment of the present invention are shown, which are described in detail as follows:

[0127] like Figure 13 As shown, a photovoltaic low voltage ride-through rapid recovery control device is applied to a photovoltaic system; the photovoltaic system includes photovoltaic modules, a DC converter, and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to the power grid; the photovoltaic low voltage ride-through rapid recovery control device includes:

[0128] A drop detection module 21 is used to obtain the grid voltage in real time and detect whether the grid voltage drops;

[0129] A reference current determination module 22 is configured to determine a reference reactive current and a reference active current according to the current grid voltage when a grid voltage drop is detected;

[0130] The voltage loop control module 23 is used to perform loop control on the photovoltaic inverter according to the reference reactive current and the reference active current.

[0131] In a possible implementation, the reference current determination module 22 may include:

[0132] a first reference current determining unit, configured to determine a reference reactive current according to a current grid voltage;

[0133] The second reference current determining unit is configured to determine a reference active current according to a reference reactive current.

[0134] In a possible implementation, the first reference current determining unit may be specifically configured to: determine the reference reactive current according to the current grid voltage in combination with the first formula;

[0135] The first formula may include:

[0136]

[0137] determine the reference active current according to the reference reactive current and the second formula;

[0138] The second formula can include:

[0139]

[0140] wherein, is the reference reactive current, is the reference active current; I N is the current rating; U N is the grid voltage rating, U is the current grid voltage; K q is a proportional coefficient, a constant.

[0141] In a possible implementation, the voltage loop control module 23 can include:

[0142] a reference voltage determination unit configured to determine reference active voltage and reference reactive voltage according to the reference reactive current and the reference active current;

[0143] a drive wave generation unit configured to generate a drive PWM wave of the photovoltaic inverter by modulation according to the reference active voltage and the reference reactive voltage.

[0144] In a possible implementation, the reference voltage determination unit can include:

[0145] a solver unit configured to acquire the grid voltage and the current in real time, and solve the grid voltage and the current to obtain active current, reactive current, active voltage and reactive voltage;

[0146] a voltage output sub-unit configured to determine the reference active voltage and the reference reactive voltage according to the active current, the reactive current, the active voltage, the reactive voltage, the reference reactive current and the reference active current, and in combination with a third formula;

[0147] The third formula can include:

[0148]

[0149] wherein, u d and u q are the reference active voltage and the reference reactive voltage respectively; i d and i q are the active current and the reactive current respectively; and are the reference active current and the reference reactive current respectively; e d and e q are the active voltage and the reactive voltage respectively; ω is the angular frequency, L is the inductance, K pK i s is a current loop PI integral parameter.

[0150] In a possible implementation, the apparatus can further include:

[0151] an MPPT control module configured to acquire a photovoltaic output reference value output by the MPPT module;

[0152] an error calculation module configured to subtract an actual input voltage and a feedback voltage error of the DC converter from the photovoltaic output reference value to obtain an input voltage error;

[0153] a DC converter drive wave generation module configured to input the input voltage error into a PI controller to generate a drive PWM wave of the DC converter.

[0154] In a possible implementation, the apparatus can further include:

[0155] a voltage locking module configured to, when detecting a grid voltage sag, record a photovoltaic output reference value at a current time, denoted as a first voltage;

[0156] an input voltage calculation module configured to acquire an output power of the photovoltaic inverter at the current time, and determine a target input voltage of the DC converter according to the output power, denoted as a second voltage;

[0157] a feedback voltage error output module configured to subtract the second voltage from the first voltage to obtain a feedback voltage error.

[0158] In a possible implementation, the apparatus can further include:

[0159] a feedback voltage error zeroing module configured to, when detecting that the grid voltage returns to normal, set the feedback voltage error to 0, and adjust an output of the MPPT module, so that the output of the MPPT module is the first voltage.

[0160] In a possible implementation, the sag detection module 21 can be specifically configured to:

[0161] 1. when detecting that the grid voltage is lower than a rated value of the grid voltage, it is determined that the grid voltage has sagged;

[0162] 2. otherwise, it is determined that the grid voltage is normal.

[0163] In the foregoing examples, the description of each example focuses on different aspects, and parts not described or recorded in detail in a certain example can be referred to the relevant description of other examples.

[0164] Those of ordinary skill in the art can understand that the template, unit and algorithm steps of each example described in combination with the embodiments disclosed herein can be implemented in electronic hardware or a combination of computer software and electronic hardware. Whether the functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those of ordinary skill in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0165] If the modules / units are implemented in the form of software function units and sold or used as independent products, they can be stored in a computer readable storage medium. Based on this understanding, all or part of the processes in the above-mentioned embodiment methods can also be completed by a computer program instructing related hardware. The computer program can be stored in a computer readable storage medium, and when executed by a processor, the computer program can implement the steps of each photovoltaic low-voltage ride-through fast recovery control method embodiment. The computer program includes computer program code, which can be in the form of source code, object code, executable files or some intermediate forms, etc. The computer readable medium can include any entity or device capable of carrying computer program code, recording medium, U disk, mobile hard disk, magnetic disk, optical disk, computer memory, read-only memory, random access memory, electrical carrier signal, telecommunication signal and software distribution medium, etc.

[0166] The above embodiments are only used to illustrate the technical solutions of the present application, but not limit it; although the present application has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacements for some technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application, and should be included in the protection scope of the present application.

Claims

1. A photovoltaic low voltage ride-through rapid recovery control method, characterized in that: Applied to a photovoltaic system; the photovoltaic system includes a photovoltaic module, a DC converter and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to the power grid; the method includes: Acquire the grid voltage in real time and detect whether the grid voltage drops; When the grid voltage drops, a reference reactive current and a reference active current are determined according to the current grid voltage; The photovoltaic inverter is loop-controlled according to the reference reactive current and the reference active current.

2. The photovoltaic low voltage ride-through rapid recovery control method according to claim 1, characterized in that: The step of determining the reference reactive current and the reference active current according to the current grid voltage includes: Determining the reference reactive current according to the current grid voltage; The reference active current is determined according to the reference reactive current.

3. The photovoltaic low voltage ride-through rapid recovery control method according to claim 2, characterized in that: The determining the reference reactive current according to the current grid voltage includes: Determine the reference reactive current according to the current grid voltage and the first formula; The first formula includes: Determining the reference active current based on the reference reactive current and in combination with a second formula; The second formula includes: Among them, i q* is the reference reactive current, i d* is the reference active current; I N is the rated current; U N is the rated value of the grid voltage, U is the current grid voltage; K q is the proportional coefficient, a constant.

4. The photovoltaic low voltage ride-through rapid recovery control method according to claim 1, characterized in that: The performing loop control on the photovoltaic inverter according to the reference reactive current and the reference active current includes: Determining a reference active voltage and a reference reactive voltage according to the reference reactive current and the reference active current; Modulation is performed according to the reference active voltage and the reference reactive voltage to generate a driving PWM wave for the photovoltaic inverter.

5. The photovoltaic low voltage ride-through rapid recovery control method according to claim 4, characterized in that: The determining of a reference active voltage and a reference reactive voltage according to the reference reactive current and the reference active current includes: Obtaining grid voltage and current in real time, and solving the grid voltage and current to obtain active current, reactive current, active voltage, and reactive voltage; Determine the reference active voltage and the reference reactive voltage according to the active current, the reactive current, the active voltage, the reactive voltage, the reference reactive current and the reference active current in combination with a third formula; The third formula includes: Among them, u d and u q are the reference active voltage and the reference reactive voltage respectively; i d and i q are the active current and the reactive current respectively; i d* and i q* are the reference active current and the reference reactive current respectively; d and e q are the active voltage and the reactive voltage respectively; ω is the angular frequency, L is the inductance, K p , K i , s are the current loop PI integral parameters.

6. The photovoltaic low voltage ride-through rapid recovery control method according to any one of claims 1 to 5, characterized in that: The method further comprises: Get the photovoltaic output reference value output by the MPPT module; Subtracting the actual input voltage and feedback voltage error of the DC converter from the photovoltaic output reference value to obtain an input voltage error; The input voltage error is input into a PI controller to generate a driving PWM wave for the DC converter.

7. The photovoltaic low voltage ride-through rapid recovery control method according to claim 6, characterized in that: The method further comprises: When the grid voltage drops, the photovoltaic output reference value at the current moment is recorded as a first voltage; Obtaining the output power of the photovoltaic inverter at a current moment, and determining a target input voltage of the DC converter according to the output power, recorded as a second voltage; The feedback voltage error is obtained by subtracting the second voltage from the first voltage.

8. The photovoltaic low voltage ride-through rapid recovery control method according to claim 7, characterized in that: The method further comprises: When it is detected that the grid voltage returns to normal, the feedback voltage error is set to 0, and the output of the MPPT module is adjusted so that the output of the MPPT module is the first voltage.

9. The photovoltaic low voltage ride-through rapid recovery control method according to any one of claims 1 to 5, characterized in that: The detecting whether the grid voltage drops comprises: When it is detected that the grid voltage is lower than the grid voltage rated value, it is determined that the grid voltage has dropped; Otherwise, it is determined that the grid voltage is normal.

10. A photovoltaic low voltage ride-through rapid recovery control device, characterized in that: Applicable to a photovoltaic system; the photovoltaic system includes photovoltaic modules, a DC converter, and a photovoltaic inverter connected in sequence, and the photovoltaic inverter is connected to the power grid; the device includes: A drop detection module is used to obtain the grid voltage in real time and detect whether the grid voltage drops; A reference current determination module, configured to determine a reference reactive current and a reference active current according to the current grid voltage when a grid voltage drop is detected; A voltage loop control module is used to perform loop control on the photovoltaic inverter according to the reference reactive current and the reference active current.

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