Control method and device of power grid system

Abstract

The invention discloses a control method and device for a power grid system. The control method comprises the following steps: acquiring the voltage of the first end of a transformer; when the positive sequence component of the voltage is larger than or equal to a first threshold value and smaller than or equal to a third threshold value and the effective value of the voltage is larger than or equal to a second threshold value and smaller than or equal to a fourth threshold value, the power grid system is normal, otherwise, voltage fault ride-through occurs in the power grid system, and voltage fault ride-through is controlled; wherein the first threshold value is lt; a third threshold, a second threshold lt; and a fourth threshold. The control method can control the grid voltage fault ride-through of the inverter.

Description

Technical Field

[0001] This invention relates to the field of power system technology, and in particular to a control method and apparatus for a power grid system. Background Technology

[0002] As the penetration rate of new energy sources such as photovoltaic power generation in the power system continues to increase, the power grid is gradually evolving into a new type of power system centered on power electronic converters. This places higher demands on the reactive power support capabilities of equipment such as inverters when grid faults occur. Currently, relevant standards for inverter grid connection typically stipulate that inverters must be able to accurately control reactive or active current during grid fault ride-through to ensure the grid smoothly overcomes the fault.

[0003] Most existing fault ride-through control methods rely on detecting the voltage on the AC side of the inverter to determine if the grid is in a fault state, and then calculate the fault ride-through depth based on this result, thereby adjusting the power response characteristics. However, in practical applications, especially in string inverter scenarios, the inverter and the downstream transformer are connected via AC cables. Due to the transformer's own impedance and the parasitic impedance of the cables, there is a significant difference between the voltage detected at the inverter and the actual voltage on the grid side of the transformer. This difference may cause the inverter to fail to accurately and promptly trigger the ride-through control logic when a grid fault occurs, resulting in a power response that does not meet standard requirements. In severe cases, it may even lead to malfunctions or failure of the ride-through function. Summary of the Invention

[0004] In view of this, the main objective of the present invention is to provide a control method and apparatus for a power grid system.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows: a control method for a power grid system, the power grid system comprising: n inverters and a transformer, the n inverters being connected in parallel and electrically connected to a first terminal of the transformer, the second terminal of the transformer being electrically connected to the power grid, wherein the first terminal and the second terminal of the transformer are two different terminals; comprising the following steps: obtaining the voltage of the first terminal of the transformer. When the first threshold is less than or equal to the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

[0006] As an improvement to this embodiment of the invention, the phrase "the power grid system experienced a voltage fault ride-through" specifically includes: when the voltage... The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through; when the voltage... The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

[0007] As an improvement to this embodiment of the invention, the "voltage fault ride-through in the power grid system" specifically includes: the power grid system experiencing a voltage fault ride-through, generating active current. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

[0008] As an improvement to this embodiment of the invention, the "controlling the reactive current output of n inverters" Specifically, this includes: controlling the reactive current output of n inverters based on a current loop. .

[0009] As an improvement to an embodiment of the present invention ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

[0010] This invention also provides a control device for a power grid system, the power grid system comprising: n inverters and a transformer, the n inverters being connected in parallel and electrically connected to a first terminal of the transformer, and the second terminal of the transformer being electrically connected to the power grid, wherein the first terminal and the second terminal of the transformer are two different ends; the device includes: an information acquisition module for acquiring the voltage of the first terminal of the transformer. ; Processing module, used when the first threshold is ≤ the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

[0011] As an improvement to this embodiment of the invention, the processing module is further configured to: when the voltage The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through; when the voltage... The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

[0012] As an improvement to this embodiment of the invention, the processing module is further configured to: generate active current when a voltage fault ride-through occurs in the power grid system. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

[0013] As an improvement to this embodiment of the invention, the processing module is further configured to: control the reactive current output of n inverters based on the current loop. .

[0014] As an improvement to an embodiment of the present invention ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

[0015] The power grid system control method and apparatus provided in this embodiment of the invention have the following advantages: This embodiment of the invention discloses a power grid system control method and apparatus, the control method comprising: acquiring the voltage at a first terminal of the transformer. When the first threshold is less than or equal to the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is ≤ the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced voltage fault ride-through, and the voltage fault ride-through is controlled. The first threshold is < the third threshold, and the second threshold is < the fourth threshold. This control method can control the inverter's grid voltage fault ride-through. Attached Figure Description

[0016] Figure 1 This is a first structural diagram of the power grid system in the embodiment; Figure 2 This is a flowchart illustrating the control method of the power grid system in the embodiment; Figure 3 The transformer in the embodiment Equivalent circuit diagram; Figure 4 This is a second structural diagram of the power grid system in the embodiment; Figure 5 This is an equivalent circuit diagram of the power grid system in the embodiment; Figure 6 This is a schematic diagram illustrating the calculation principle of phasors in the embodiment. Detailed Implementation

[0017] The present invention will now be described in detail with reference to the embodiments shown in the accompanying drawings. However, these embodiments do not limit the present invention, and any structural, methodological, or functional modifications made by those skilled in the art based on these embodiments are included within the scope of protection of the present invention.

[0018] The following description and accompanying drawings fully illustrate specific embodiments described herein to enable those skilled in the art to practice them. Some embodiments may include or substitute parts and features of other embodiments. The scope of the embodiments herein encompasses the entire scope of the claims and all available equivalents thereof. Throughout this document, the terms “first,” “second,” etc., are used only to distinguish one element from another without requiring or implying any actual relationship or order between the elements. Indeed, a first element can also be referred to as a second element, and vice versa. Furthermore, the terms “comprising,” “including,” or any other variations thereof are intended to cover non-exclusive inclusion, such that a structure, apparatus, or device that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a structure, apparatus, or device. Without further limitation, an element defined by the phrase “comprising one…” does not exclude the presence of other identical elements in the structure, apparatus, or device that includes said element. The various embodiments described herein are presented in a progressive manner, with each embodiment focusing on its differences from other embodiments; similar or identical parts between embodiments can be referred to interchangeably.

[0019] The terms "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer" used in this document to indicate orientation or positional relationships are based on the orientation or positional relationships shown in the accompanying drawings and are used only for the convenience of describing this document and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention. In the description herein, unless otherwise specified and limited, the terms "installed," "connected," and "linked" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, or internal connections between two elements, or direct connections or indirect connections through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms according to the specific circumstances.

[0020] Embodiment 1 of the present invention provides a control method for a power grid system, the power grid system comprising: n inverters and a transformer, the n inverters being connected in parallel and electrically connected to a first terminal of the transformer, the second terminal of the transformer being electrically connected to the power grid, wherein the first terminal and the second terminal of the transformer are two different ends; like Figure 1 As shown, the system contains n inverters, inverter #1, inverter #2, ..., inverter #n connected in parallel, all supplying power to the grid. The electrical energy output from the inverters is collected, stepped up by a transformer, and finally fed into the grid. The grid voltage is... The inverter itself includes a main circuit, a filter, and a control unit. A current sampling unit is located between the AC side of the main circuit and the filter. This current sampling unit can collect the inverter output current, for example, the current of a single inverter. , ... The combined current from multiple inverters A voltage sampling unit is installed between the filter and the grid-connected side of the inverter. This voltage sampling unit can collect the voltage at the grid-connected port, i.e. The meaning of PCC is Point of Common Connection. The control unit, connected to the current and voltage sampling units, receives the collected current and voltage signals, providing a signal basis for subsequent inverter control (such as grid connection control and power regulation). Optionally, the inverter in this power grid system is connected to a photovoltaic power generation system.

[0021] The core logic of this control method is: the control unit relies on the collected current and voltage signals to adjust the output of each inverter, so that when multiple inverters are connected in parallel, they can stably and coordinately deliver power to the grid, while ensuring the quality of the grid-connected power (such as voltage, frequency, harmonics, etc. meet the grid requirements).

[0022] like Figure 2 As shown, it includes the following steps: Step 201: Obtain the voltage at the first terminal of the transformer. ; Step 202: When the first threshold is less than or equal to the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

[0023] In a three-phase power system, voltage (or current) changes may consist of symmetrical components (positive sequence, negative sequence, and zero sequence). The positive sequence component refers to the component in a symmetrical system obtained by decomposing the electrical quantities of an unbalanced three-phase system using the symmetrical component method. This component consists of three-phase quantities (voltage or current) of equal magnitude, with phases successively differing by 120° (A phase → B phase → C phase, each lagging by 120°), and the phase sequence is consistent with the phase sequence of the power grid during normal operation (usually ABC). During normal operation, voltage / current is primarily composed of positive sequence components. When an asymmetrical fault occurs in the power grid (such as single-phase grounding or two-phase short circuit), negative and zero sequence components appear. Changes in the positive sequence component (magnitude and phase) can reflect the symmetrical fault or overall voltage level of the power grid. By detecting the positive sequence component, it is possible to determine whether the power grid is experiencing a symmetrical fault (or whether the overall voltage is abnormal), because high / low voltage ride-through can be either a symmetrical fault (three-phase simultaneous high / low voltage) or a reflection of the overall voltage trend through the positive sequence component.

[0024] For sinusoidal alternating current (mains voltage is typically sinusoidal), the effective value is the equivalent direct current (DC) value describing its work capacity. That is, if alternating current and direct current pass through a resistor of the same resistance, and the heat generated is equal in the same amount of time, then the DC value is the effective value of the alternating current. The calculation formula (taking a sinusoidal voltage as an example): If the instantaneous voltage value is... ( If the maximum value is 0, then the effective value is 0. .

[0025] RMS voltage is the most commonly used voltage / current quantification indicator in engineering (for example, the rated voltage of the power grid, 220V and 380V, both refer to RMS values). By comparing the detected RMS voltage value with the set normal range threshold, it can be directly determined whether the voltage is too high (greater than the threshold) or too low (less than the threshold), thereby triggering the high / low voltage ride-through logic.

[0026] In grid fault ride-through, positive sequence components and RMS values ​​are complementary detection dimensions: If the grid has a symmetrical fault (three phases simultaneously at high / low voltage), the RMS value of the positive sequence component directly reflects the voltage anomaly, and can be used for judgment. If the grid has an asymmetrical fault (such as a single-phase fault), the positive sequence component reflects the voltage trend of the symmetrical part, while the RMS value can be combined with the situation of each phase to comprehensively judge whether the overall voltage exceeds the fault ride-through threshold. By combining the two, grid voltage faults can be identified more comprehensively and accurately, ensuring that the inverter triggers the correct ride-through control logic.

[0027] In this embodiment, "the power grid system experienced a voltage fault ride-through" specifically includes: When the voltage The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through. When the voltage The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

[0028] In this embodiment, "voltage fault ride-through occurred in the power grid system" specifically includes: the power grid system experienced a voltage fault ride-through, generating active current. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

[0029] Here, current is decomposed by impedance angle to achieve precise control of active and reactive currents, and the total current is decomposed by polar coordinates. Decomposed into active current and reactive current Among them, active current The component used to transmit active power (the actual consumption / transmission of electrical energy), reactive current. Used to support grid voltage and provide reactive power components; This is the total current amplitude output by the inverter (the total current that needs to be controlled during fault ride-through). This is the phase difference between the inverter output voltage and current (reflecting the current power factor). The impedance angle (calculated from the equivalent impedance of the transformer / cable, and needs to be dynamically adjusted during a fault in conjunction with the impedance characteristics of the power grid); The angle difference between the total current and the active / reactive decomposition reference is used to decompose the current in the "active-reactive" dimension by using the cosine and sine values ​​of this angle.

[0030] During grid voltage faults (such as low / high voltage ride-throughs), the grid requires reactive power support (to maintain voltage stability), therefore, adjustments are made... Its size allows it to actively inject / absorb reactive power into the power grid.

[0031] The control process consists of two steps: Step 1, current command calculation, where the inverter control unit first calculates the impedance angle of the current power grid. Substituting this into the above formula, we obtain the active current command. and reactive current command Step 2: Current loop execution control, based on the calculated... (Reactive current command) The inverter outputs the target reactive current to ultimately achieve power response control during fault periods.

[0032] Active current command Its core function is to control the active power output of the inverter, specifically: During grid faults (such as low / high voltage ride-through), the grid's active power transmission capacity may be limited. This can be addressed through control... The size of the inverter can be adjusted to control the active power output (active power) of the inverter to the grid. (V is the grid connection point voltage). If a fault causes the grid to be unable to carry excessive active power, the voltage can be reduced. To reduce active power output and avoid increasing the burden on the power grid; if the fault has a minor impact on active power transmission, it can be maintained. This ensures the stability of power supply and guarantees normal power transmission.

[0033] In conjunction with reactive power support, ensuring grid stability is crucial; the core requirement during fault periods is reactive power support (through...). (achieved), but active current Control is key to auxiliary stability; if If the current is too high, it will consume the inverter's output capacity (the inverter's total current). Due to hardware limitations, this limits the amount of data that can be used for reactive power support. Compressed; through proper control , can be Reserve sufficient output space to ensure the effectiveness of reactive power support, while avoiding inverter overload.

[0034] Power restoration after a fault is recovered can be achieved by gradually increasing the power output once the grid fault has been resolved. This allows the inverter's active power output to smoothly return to normal levels, preventing sudden changes in active power from causing secondary impacts on the power grid.

[0035] In this embodiment, the phrase "controlling the reactive current output of n inverters" is used. Specifically, this includes: controlling the reactive current output of n inverters based on a current loop. .

[0036] The core here is to use a "detection-comparison-adjustment" cycle to ensure that the actual reactive current output of the inverter precisely matches the pre-calculated reactive current command. .

[0037] The current loop is a fast-response closed-loop control system, and the key signals and components involved include: input signals and pre-calculated reactive current commands. (That is, the target value, obtained from the impedance angle formula mentioned above). Feedback signal, the actual reactive current feedback value output by the inverter. (Obtained in real time via a current sampling sensor). The controller, typically a PI (Proportional-Integral) controller (or a more advanced PR controller), handles the deviation between the command and feedback. The actuator, the main circuit of the inverter (such as switching devices like IGBTs), changes the output current by adjusting the switching state.

[0038] The operation of the current loop is a continuous cyclical process, with the following steps: Step 1, Deviation calculation, converting the reactive current command... Compared with actual feedback value By subtracting the values, we obtain the current deviation. Step 2: Adjust the controller to correct the deviation. The input is given to a PI controller, which calculates the corresponding voltage regulation signal based on the magnitude of the deviation (proportional element) and the accumulated value (integral element). (Used to adjust the inverter's output voltage). Step 3: Signal modulation and execution, converting the voltage regulation signal... The input PWM (Pulse Width Modulation) module generates drive signals for the inverter's switching devices, controlling the on / off times of devices such as IGBTs. Step 4: Feedback Update. The current sampling sensor detects new reactive current output in real time, using it as feedback value for the next cycle. The output is continuously corrected until the deviation between the actual reactive current and the command value is small enough.

[0039] During grid faults (such as low / high voltage ride-through), the core value of the current loop is to quickly and accurately track reactive current commands. During a fault, the power grid requires extremely fast response speed to reactive power support (typically on the order of milliseconds), and closed-loop control of the current loop must ensure this. It can quickly reach the target value; when the grid voltage fluctuates, the current loop can correct the output in real time to avoid the reactive current deviating from the command and ensure that the reactive power support effect of the grid meets the grid connection standards.

[0040] In this embodiment, ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

[0041] Here, the equivalent impedance of a transformer can be calculated based on the changes in the inverter's output voltage and current under different output power conditions. Alternatively, it can be calculated using the transformer's nameplate values. The following section describes how to calculate the equivalent impedance using the transformer's nameplate values. Type equivalent circuit such as Figure 3 As shown, the formula for calculating the short-circuit impedance is: ,in, This represents the percentage of short-circuit impedance. Rated line voltage, Rated capacity, short-circuit voltage percentage This refers to the percentage of the rated voltage relative to the rated voltage when a short circuit occurs on the secondary side of a transformer and a voltage of rated frequency is applied to the primary side, causing the winding to carry the rated current. The calculation formula is as follows: = (Short-circuit voltage / Rated voltage) × 100%.

[0042] short-circuit resistor The calculation formula is ,in, This refers to short-circuit losses (active power losses of electrical equipment under rated current). This is the rated current. The formula for calculating short-circuit reactance is: The formula for calculating the excitation impedance is: ,in, The no-load current percentage (the ratio of the current flowing under no-load conditions to the rated current) is the ratio of the input current to the rated load current when the equipment is under no-load conditions (no load connection). It typically expresses this as a percentage. It illustrates the relationship between the energy loss (mainly iron loss and mechanical loss) and the rated capacity of the equipment when there is no load. = (No-load current / Rated current) × 100%.

[0043] The formula for calculating the excitation resistance is: ,in, This refers to no-load loss, which is the active power loss during no-load operation. The formula for calculating the excitation reactance is: .

[0044] Considering that the excitation impedance is usually much greater than the short-circuit impedance, and ignoring the excitation impedance, the power grid system, after considering the transformer's influence, is as follows: Figure 4 As shown. If the output line impedance difference of the inverters is small, then N inverters are equivalent to one inverter, and the high-voltage side impedance of the transformer is referred to the low-voltage side, resulting in... Figure 5 Equivalent circuit of a power grid system.

[0045] The impedance angle is calculated based on the inverter's output current, output port voltage, and the transformer's equivalent impedance. (Specific location voltage...) Inverter output current and grid voltage The phasor diagram is as follows Figure 6 As shown. Definition and The included angle is the transformer impedance angle. , and The included angle is the power factor angle. .

[0046] by Using the reference axis, the following relationship is obtained. Further simplification yields, Solving for the impedance angle .

[0047] Transformer impedance angle Subject to inverter output current and power factor angle and grid voltage Influence.

[0048] Embodiment 2 of the present invention provides a control device for a power grid system. The power grid system includes n inverters and a transformer. The n inverters are connected in parallel and electrically connected to a first terminal of the transformer. The second terminal of the transformer is used for electrical connection to the power grid. In the transformer, the first terminal and the second terminal are two different ends. The device includes the following: an information acquisition module for acquiring the voltage of the first terminal of the transformer. ; Processing module, used when the first threshold is ≤ the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

[0049] In this embodiment, the processing module is further configured to: when the voltage The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through; when the voltage... The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

[0050] In this embodiment, the processing module is further configured to: generate active current when a voltage fault ride-through occurs in the power grid system. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

[0051] In this embodiment, the processing module is further configured to: control the reactive current output of n inverters based on the current loop. .

[0052] In this embodiment, ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

[0053] It should be noted that although the steps are described in a specific order above, it does not mean that the steps must be executed in the above specific order. In fact, some of these steps can be executed concurrently, or even in a different order, as long as the required function can be achieved.

[0054] This invention can be a system, method, and / or computer program product. A computer program product may include a readable storage medium having computer-readable program instructions loaded thereon for causing a processor to implement various aspects of the invention.

[0055] A readable storage medium can be a tangible device that holds and stores instructions for use by an instruction execution device. Readable storage media can include, for example, but not limited to, electrical storage devices, magnetic storage devices, optical storage devices, electromagnetic storage devices, semiconductor storage devices, or any suitable combination thereof. More specific examples (a non-exhaustive list) of readable storage media include: portable computer disks, hard disks, random access memory (RAM), read-only memory (ROM), erasable programmable read-only memory (EPROM or flash memory), static random access memory (SRAM), portable compact disc read-only memory (CD-ROM), digital multifunction disc (DVD), memory sticks, floppy disks, mechanical encoding devices, such as punch cards or recessed protrusions storing instructions thereon, and any suitable combination thereof.

[0056] The various embodiments of the present invention have been described above. These descriptions are exemplary and not exhaustive, nor are they limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is chosen to best explain the principles, practical application, or technical improvements to the embodiments in the market, or to enable others skilled in the art to understand the embodiments disclosed herein.

Claims

1. A control method for a power grid system, the power grid system comprising: n inverters and a transformer, wherein the n inverters are connected in parallel and electrically connected to a first terminal of the transformer, and a second terminal of the transformer is used for electrical connection to the power grid, wherein the first terminal and the second terminal of the transformer are two different terminals; characterized by comprising the following steps: Obtain the voltage at the first terminal of the transformer. ; When the first threshold is less than or equal to the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

2. The control method according to claim 1, characterized in that, The phrase "voltage fault ride-through occurred in the power grid system" specifically includes: When the voltage The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through. When the voltage The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

3. The control method according to claim 1, characterized in that, The phrase "voltage fault ride-through occurred in the power grid system" specifically includes: A voltage fault ride-through occurred in the power grid system, generating active current. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

4. The control method according to claim 3, characterized in that, The phrase "controlling the reactive current output of n inverters" is mentioned. Specifically, it includes: Based on current loop control of the reactive current output of n inverters .

5. The control method according to claim 3, characterized in that, ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

6. A control device for a power grid system, the power grid system comprising: The transformer comprises n inverters and a transformer, wherein the n inverters are connected in parallel and electrically connected to a first terminal of the transformer, and a second terminal of the transformer is used for electrical connection to the power grid, wherein the first terminal and the second terminal are two different ends of the transformer; characterized in that it includes the following device: The information acquisition module is used to acquire the voltage at the first terminal of the transformer. ; Processing module, used when the first threshold is ≤ the voltage The positive-order component is less than or equal to the third threshold and the second threshold is less than or equal to the voltage. When the effective value is less than or equal to the fourth threshold, the power grid system is normal; otherwise, the power grid system has experienced a voltage fault ride-through. Wherein, the first threshold is less than the third threshold, and the second threshold is less than the fourth threshold.

7. The control device according to claim 6, characterized in that, The processing module is also used for: When the voltage The positive sequence component > the first threshold or the voltage When the effective value is greater than the second threshold, the power grid system experiences a high-voltage ride-through. When the voltage The positive sequence component < the third threshold or the voltage When the effective value is less than the fourth threshold, the power grid system experiences a low-voltage ride-through.

8. The control device according to claim 6, characterized in that, The processing module is also used for: A voltage fault ride-through occurred in the power grid system, generating active current. and reactive current ,in, Let n be the total output current of n inverters. For the output voltage of n inverters Phase difference with current, The impedance angle is used to control the reactive current output of n inverters. .

9. The control device according to claim 8, characterized in that, The processing module is also used for: Based on current loop control of the reactive current output of n inverters .

10. The control device according to claim 8, characterized in that, ,in, This is the short-circuit resistance of the transformer. , This refers to the short-circuit loss of the transformer. This is the rated current of the transformer. Let n be the output currents of the inverters. For the short-circuit reactance of the transformer, , ,in, This represents the percentage of the transformer's short-circuit impedance. This is the rated line voltage of the transformer. This refers to the rated capacity of the transformer.

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