Energy storage inverter power grid pre-charging control method and energy storage inverter system

Abstract

The invention discloses an energy storage inverter power grid pre-charging control method and an energy storage inverter system.The energy storage inverter power grid pre-charging control method comprises the steps that when it is detected that no direct-current power source is input into the energy storage inverter system, a pre-charging relay and a first live wire relay are closed, and a direct-current bus of an energy storage inverter is pre-charged through a power grid; the second live wire relay and the null line relay are kept disconnected; when the energy storage inverter meets the pre-charging completion condition, an adjusting loop is started, the adjusting loop is used for enabling the phase difference of the output voltage of the energy storage inverter to be transited to a second angle from a first angle, so that the phase difference of the output voltage of the energy storage inverter is close to the phase difference of the power grid side voltage, and the impact current at the moment of grid connection can be reduced; when the energy storage inverter meets the grid connection condition, the second live wire relay is closed, the pre-charging relay is disconnected, and the zero line relay is closed, so that the energy storage inverter is connected to the grid.

Description

Technical Field

[0001] This invention relates to the field of energy storage inverter technology, and in particular to a grid pre-charging control method for an energy storage inverter and an energy storage inverter system. Background Technology

[0002] In energy storage inverter systems, grid precharging is a crucial step in preventing damage to equipment components from instantaneous surge currents upon power-on and ensuring safe startup. Among these methods, resistor-based current-limiting precharging has become the mainstream technical solution in the industry due to its simple circuit topology, controllable cost, and high reliability.

[0003] In related technologies, grid pre-charging is typically completed during the soft-start phase of the inverter, which can be divided into three stages: startup, pre-charging, and grid connection. The startup stage involves controlling the corresponding relays to close and establish a pre-charging circuit based on pre-charging methods such as line voltage pre-charging or phase voltage pre-charging. The pre-charging stage involves the grid supplying power to the energy storage inverter to slowly raise the bus voltage. The grid connection stage involves closing the grid connection relay group after pre-charging is completed, enabling the energy storage inverter to connect to the grid.

[0004] However, between the pre-charging and grid-connection phases, directly closing the grid-connection relay group can easily generate a large inrush current in the circuit due to the phase or amplitude difference between the output voltage of the energy storage inverter and the grid voltage. This inrush current can not only cause disturbances to the grid but also damage the power devices, bus capacitors, and relay contacts inside the inverter. Over time, this can lead to reduced reliability and shortened lifespan of the energy storage inverter system.

[0005] Therefore, optimizing the pre-charging end and grid connection process to suppress the inrush current at the moment of grid connection has become an urgent problem to be solved. Summary of the Invention

[0006] One objective of this invention is to provide a grid pre-charge control method for energy storage inverters, thereby reducing the inrush current of the energy storage inverter at the moment of grid connection after pre-charging.

[0007] Another objective of this invention is to provide an energy storage inverter system that applies the above-mentioned energy storage inverter grid pre-charge control method.

[0008] To achieve at least one of the above objectives, the technical solution adopted by the present invention is as follows: a grid pre-charge control method for an energy storage inverter, comprising: closing a pre-charge relay and a first live wire relay to pre-charge the DC bus of the energy storage inverter using the grid, while keeping a second live wire relay and a neutral wire relay open; when the energy storage inverter meets the pre-charge completion conditions, starting an adjustment loop, wherein the adjustment loop is used to transition the phase difference of the output voltage of the energy storage inverter from a first angle to a second angle; when the energy storage inverter meets the grid connection conditions, closing the second live wire relay, opening the pre-charge relay, and closing the neutral wire relay to connect the energy storage inverter to the grid.

[0009] As a preferred embodiment, the regulation loop includes feedforward processing for generating a regulation signal, which is a weighted average of the voltage vector on the energy storage inverter side and the voltage vector on the grid side. By adjusting the weighting coefficient of the weighted average, the regulation signal enables the phase difference of the output voltage of the energy storage inverter to transition from a first angle to a second angle.

[0010] As a preferred embodiment, the adjustment signal includes, U adjd =(1-α)U invd +αU gd U adjq =(1-β)U invq +βU gq Among them, U adjd U is the adjusted d-axis feedforward voltage. adjq U is the adjusted q-axis feedforward voltage. invd U is the d-axis voltage on the energy storage inverter side. invq U is the q-axis voltage on the energy storage inverter side. gd U is the d-axis voltage on the grid side. gq Let α be the q-axis voltage on the grid side, and β be the weighting coefficients.

[0011] As a preferred embodiment, when the regulation loop is started, the initial values ​​of the weighting coefficients α and β are 0, and they are increased from 0 to 1 over several power frequency cycles, so that the phase difference of the output voltage of the energy storage inverter transitions from the first angle to the second angle.

[0012] As a preferred embodiment, the regulation loop further includes a bus voltage slow-start outer loop and a current inner loop. Through the bus voltage slow-start outer loop and the current inner loop, the energy storage inverter draws supplementary current from the grid. This supplementary current is used to maintain the DC bus voltage V. bus Stablize.

[0013] As a preferred embodiment, the bus voltage soft-start outer loop acts on the d-axis component, and the bus voltage soft-start outer loop includes a soft-start module, the input of which is the bus voltage V. bus The soft-start module can output the d-axis current reference value I.d * where the d-axis current reference value I d *It has an upper limit and a lower limit.

[0014] As a preferred embodiment, the inner current loop acts on both the d-axis and q-axis components. The inner current loop includes a first comparator, a first PI regulator, and a first adder, as well as a second comparator, a second PI regulator, and a second adder. The input to the first comparator is the d-axis current reference value I. d * and d-axis current value I d The output of the first comparator serves as the input of the first PI controller, and the output of the first PI controller and the adjustment signal together serve as the input of the first adder, which then outputs the d-axis control signal d. con The input to the second comparator is the q-axis current reference value I. q * and q-axis current value I q The output of the second comparator serves as the input of the second PI controller, and the output of the second PI controller and the adjustment signal together serve as the input of the second adder, which then outputs the q-axis control signal q. con .

[0015] As a preferred embodiment, the pre-charge completion condition is that the pre-charge time count value is greater than or equal to a preset time threshold, and the bus voltage V of the energy storage inverter is [value missing]. bus It is greater than or equal to the preset voltage threshold.

[0016] As a preferred embodiment, the grid connection condition is that the absolute value of the difference between the effective value of the output voltage of the energy storage inverter and the effective value of the grid-side voltage is less than or equal to a preset voltage difference value, and the bus voltage V of the energy storage inverter is... bus It is greater than or equal to the preset voltage threshold.

[0017] To achieve at least one of the above objectives, the technical solution adopted by the present invention is as follows: an energy storage inverter system, comprising: a grid-connected relay group, the grid-connected relay group including a first live wire relay, a second live wire relay, and a neutral wire relay connected between the output terminal of the energy storage inverter and the power grid; a pre-charge branch, the pre-charge branch being connected in parallel with the second live wire relay, the pre-charge branch including a pre-charge relay and a pre-charge resistor connected in series; and a controller, the controller being communicatively connected to the grid-connected relay group and the pre-charge relay, the controller being configured to store instructions and execute the energy storage inverter grid pre-charge control method as described above, to control the first live wire relay, the second live wire relay, the neutral wire relay, and the pre-charge relay to close or open respectively.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: After the energy storage inverter meets the pre-charge completion conditions, the adjustment loop is activated to make the phase difference of the output voltage of the energy storage inverter transition from the first phase angle to the second phase angle. As a result, the phase difference of the output voltage of the energy storage inverter is close to the phase difference of the grid side voltage, which can reduce the inrush current at the moment of grid connection. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of an energy storage inverter system according to some embodiments of this application.

[0020] Figure 2 This is a schematic diagram of a relay group and a precharge branch according to some embodiments of this application.

[0021] Figure 3 The voltage U of the existing 120° grid a Voltage U b and voltage U c A vector diagram.

[0022] Figure 4 The voltage U on the energy storage inverter side is based on the existing technology that uses line voltage pre-charging and is pre-charged by the 120° grid. a Voltage U b 'and voltage U c A vector diagram of '.

[0023] Figure 5 This is a flowchart of a grid pre-charge control method for an energy storage inverter according to some embodiments of this application.

[0024] Figure 6 This is a schematic diagram of an adjustment loop according to some embodiments of this application. Detailed Implementation

[0025] The present invention will now be further described in conjunction with specific embodiments. It should be noted that, without conflict, the various embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0026] It should be noted that the terms "first," "second," etc., in the specification and claims of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence.

[0027] The terms “comprising” and “having”, and any variations thereof, in the specification and claims of this application are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units that are explicitly listed, but may include other steps or units that are not explicitly listed or that are inherent to such process, method, product, or device.

[0028] For ease of understanding, this application will describe the following content using an energy storage inverter system. Figure 1 and Figure 2 As shown, the energy storage inverter system mainly includes a DC power supply, a bus capacitor bank, an inverter bridge arm, a grid-connected relay group, and a pre-charge branch. The bus capacitors C1 and C2 of the bus capacitor bank are connected in series and then in parallel with the DC power supply. Furthermore, the DC bus is connected to the power grid via the bus capacitor bank, the inverter bridge arm, and the grid-connected relay group. The grid-connected relay group includes a first live wire relay S1 located on the first live wire L1, a second live wire relay S2 located on the second live wire L2, and a neutral wire relay S3 located on the neutral wire N. N Furthermore, the pre-charge branch is connected in parallel with one of the relays in the grid-connected relay group, for example, in parallel with the second live wire relay S2. The pre-charge branch includes the pre-charge relay S... P and pre-charge resistor R P .

[0029] Specifically, as shown in Table 1, in the initial stage, the first live wire relay S1 and the precharge relay S are closed. P To construct a pre-charge circuit; after pre-charge is completed, sequentially close the second live wire relay S2 and open the pre-charge relay S. P and the closed neutral relay S N .

[0030] Table 1: Operation process of each relay during pre-charge

[0031] In Table 1, "1" represents the relay being engaged, and "0" represents the relay being disengaged. However, when using the line voltage pre-charge method, the DC bus voltage V... bus It may only reach near the peak value of the line voltage, i.e., the bus voltage V. bus The low voltage level leads to a large potential difference between the DC and AC sides of the energy storage inverter, which may cause safety hazards during grid connection and even affect the overall operation of the energy storage inverter system.

[0032] If a line voltage pre-charging method is used, and pre-charging is performed by a 120°C power grid, such as Figures 2-4 As shown, although the first live wire L1 of the energy storage inverter INV Second Fireline L2 INV The voltage U between c ', with the first live wire L1 of the 120° power grid AC Second Fireline L2 AC The voltage U between c They are equal, however, due to the neutral wire relay S during the pre-charging process... N Keeping it disconnected will cause the first live wire of the energy storage inverter and L1 to...INV Neutral line N INV The voltage U between a ', with the second line of fire L2 INV and zero line N INV The voltage U between b The vector angle is 180°; however, the first live wire L1 of the 120° power grid AC and zero line N AC The voltage U between a With the second line of fire L2 AC and zero line N AC The voltage between voltages U b The vector angle is 120°, which will cause voltage U a With voltage U a Unequal, voltage U b With voltage U b The values ​​are not equal, thus the neutral relay S is closed during the grid connection phase. N Inrush currents are easily generated at this time.

[0033] Based on the above, in order to reduce the inrush current during grid connection, this application provides a grid pre-charge control method for energy storage inverters, such as... Figure 5 As shown, it includes: a closed pre-charge relay S P The first live wire relay S1 is used to precharge the DC bus of the energy storage inverter using the power grid, and the second live wire relay S2 and the neutral wire relay S... N Keep disconnected. Furthermore, when the energy storage inverter meets the pre-charge completion conditions, the regulation loop is activated. This loop transitions the phase difference of the energy storage inverter's output voltage from the first angle to the second angle, thus making the phase difference of the energy storage inverter's output voltage closer to the phase difference of the grid-side voltage, reducing the inrush current during subsequent grid connection. Even further, when the energy storage inverter meets the grid connection conditions, the second live wire relay S2 is closed, and the pre-charge relay S1 is opened. P And close the neutral relay S N This is to enable the energy storage inverter to be connected to the grid.

[0034] It is understandable that after pre-charging, the phase difference of the energy storage inverter's output voltage can be smoothly and controllably transitioned from the first angle to the second angle through the adjustment loop. This allows the phase difference of the energy storage inverter's output voltage to be closer to the phase difference of the grid-side voltage before grid connection. This configuration can significantly suppress the inrush current during grid connection, thereby improving the reliability and safety of the energy storage inverter system after pre-charging before grid connection.

[0035] In a specific example, the first angle is 180° and the second angle is 120°. Specifically, after the energy storage inverter is pre-charged using a line voltage pre-charge method and pre-charged by the 120° grid, the voltage U can be adjusted through the regulating loop. a 'and voltage U b The vector angle smoothly transitions from 180° to 120°, which helps avoid closing the neutral relay S during the grid connection phase. N The time changes abruptly from 180° to 120°.

[0036] In some embodiments, the pre-charge completion condition is that the pre-charge time count value is greater than or equal to a preset time threshold, and the bus voltage V of the energy storage inverter is... bus It should be greater than or equal to the preset voltage threshold. This should be understood as achieving this by making the bus voltage V... bus Meeting a voltage threshold greater than or equal to the preset threshold helps ensure that bus capacitors C1 and C2 have sufficient voltage, providing better initial conditions for subsequent regulation loops. Furthermore, ensuring that the pre-charge time count value is greater than or equal to the preset time threshold helps prevent issues caused by bus voltage V... bus The instantaneous fluctuations can cause the regulation loop to be mistakenly activated, thereby improving the reliability of the pre-charge stage and ensuring that bus capacitors C1 and C2 are fully charged.

[0037] In some embodiments, the grid connection condition is that the absolute value of the difference between the effective value of the output voltage of the energy storage inverter and the effective value of the grid-side voltage is less than or equal to a preset voltage difference value, and the bus voltage V of the energy storage inverter is... bus It is greater than or equal to the preset voltage threshold.

[0038] It should be understood that the magnitude of the inrush current depends on the neutral relay S. N When closed, the instantaneous potential difference between the output voltage of the energy storage inverter and the grid voltage is determined by both the phase difference and the effective value. Through the aforementioned adjustment loop, the phase difference of the energy storage inverter's output voltage smoothly transitions from the first angle to the second angle, gradually approaching the phase difference of the grid voltage. Furthermore, by ensuring that the absolute value of the difference between the effective value of the energy storage inverter's output voltage and the effective value of the grid voltage is less than or equal to a preset voltage value, the difference between their effective values ​​is controlled within a small range. This, in turn, helps ensure the neutral relay S during grid connection. N The instantaneous potential difference between the two ends is close to 0, so as to reduce the neutral line relay S N The inrush current generated when the circuit is closed.

[0039] Furthermore, under grid-connected conditions, the bus voltage V of the energy storage inverter is still required. busMeeting a voltage threshold greater than or equal to the preset threshold helps ensure that bus capacitors C1 and C2 still have sufficient voltage when connected to the grid. This helps to avoid the energy storage inverter failing to connect to the grid due to insufficient DC side voltage, and also helps to avoid the energy storage inverter operating near the low-voltage critical state, which would cause increased power device losses. This improves the stability and reliability of the energy storage inverter system.

[0040] In some embodiments, the regulation loop includes feedforward processing for generating a regulation signal, which is a weighted average of the voltage vector on the energy storage inverter side and the voltage vector on the grid side. By adjusting the weighting coefficients of the weighted average, the regulation signal enables the phase difference of the output voltage of the energy storage inverter to transition from a first angle to a second angle.

[0041] It is understandable that if the grid-side voltage is directly used as the regulation signal, the phase difference of the energy storage inverter's output voltage will abruptly change from the first angle to the second angle when the regulation loop is started, resulting in significant harmonics. In this embodiment, by smoothly changing the weighting coefficients, the output of the regulation signal gradually transforms from the voltage vector on the energy storage inverter side to the voltage vector on the grid side. This allows the phase difference of the energy storage inverter's output voltage to smoothly transition from the first angle to the second angle, helping to avoid inrush currents caused by phase abrupt changes during grid connection and improving the safety of the energy storage inverter system and the grid. Furthermore, the regulation signal, as a feedforward quantity in the regulation loop, helps improve the response speed and stability of phase difference regulation.

[0042] In at least one embodiment, such as Figure 6 As shown, the adjustment signal includes, U adjd =(1-α)U invd +αU gd U adjq =(1-β)U invq +βU gq Among them, U adjd U is the adjusted d-axis feedforward voltage. adjq U is the adjusted q-axis feedforward voltage. invd U is the d-axis voltage on the energy storage inverter side. invq U is the q-axis voltage on the energy storage inverter side. gd U is the d-axis voltage on the grid side. gq Let α be the q-axis voltage on the grid side, and β be the weighting coefficients.

[0043] It should be understandable, U adjd Used to regulate the active component, U adjqThis setting is used to regulate the reactive component, which helps avoid coupling interference and simplifies the design of the controller for the energy storage inverter system. It is worth noting that the weighting coefficients α and β can be different. In other words, the variation trajectories of weighting coefficients α and β can be set separately according to the different characteristics of the active and reactive components, thereby improving the smoothness of the phase difference transition of the energy storage inverter's output voltage from the first angle to the second angle, making the regulation loop suitable for more complex grid-connected environments. Weighting coefficients α and β can also be the same; that is, their variation trajectories are consistent, which further simplifies the design of the controller for the energy storage inverter system. Those skilled in the art can adjust the variation trajectories of weighting coefficients α and β according to actual conditions, and such adjustments fall within the protection scope of this application.

[0044] In at least one embodiment, when the regulation loop is started, the initial values ​​of the weighting coefficients α and β are 0, and they are increased from 0 to 1 within several power frequency cycles, so that the phase difference of the output voltage of the energy storage inverter transitions from a first angle to a second angle. It should be understood that by increasing the weighting coefficients α and β from 0 to 1 after several power frequency cycles, the phase difference of the output voltage of the energy storage inverter can smoothly transition from the first angle to the second angle within tens to hundreds of milliseconds; in other words, the change of the output voltage of the energy storage inverter from the first angle to the second angle can be completed in a shorter time, thereby further improving grid connection efficiency while effectively suppressing the inrush current at the moment of grid connection.

[0045] Furthermore, setting the initial values ​​of weighting coefficients α and β to 0 and the final values ​​to 1 helps ensure that the regulation signal is entirely dominated by the output voltage of the energy storage inverter at the moment of start-up of the regulation loop, thereby helping to avoid abrupt changes. Setting the final values ​​of weighting coefficients α and β to 1 helps ensure that the phase difference of the output voltage of the energy storage inverter is consistent with or nearly consistent with the phase difference of the grid-side voltage when connected to the grid. It is worth mentioning that those skilled in the art can adjust the initial and final values ​​of weighting coefficients α and β according to actual conditions, and such adjustments fall within the protection scope of this application.

[0046] In some embodiments, such as Figure 6 As shown, the regulation loop also includes a bus voltage slow-start outer loop and a current inner loop. Through the bus voltage slow-start outer loop and the current inner loop, the energy storage inverter draws supplementary current from the grid. The supplementary current is used to maintain the DC bus voltage V. bus Stablize.

[0047] It is understandable that after the pre-charge is completed, during the operation of the regulating loop, the bus voltage V... busThe voltage may drop due to losses. However, in this application, by using the outer loop of bus voltage slow-start and the inner loop of current, the energy storage inverter can actively draw supplementary current from the grid to supply the DC bus, thereby helping to ensure that the bus voltage V of the energy storage inverter remains stable from the end of pre-charging to grid connection. bus Always keep it within a controllable range; in other words, it helps to keep the bus voltage V bus Maintain within a range greater than or equal to the preset voltage threshold.

[0048] In some embodiments, such as Figure 6 As shown, the bus voltage soft-start outer loop acts on the d-axis component. The bus voltage soft-start outer loop includes a soft-start module, and the input of the soft-start module is the bus voltage V. bus The soft-start module is able to output the d-axis current reference value I. d * where the d-axis current reference value I d *It has an upper limit and a lower limit.

[0049] It should be understood that the smooth-start module generates a smoothly varying d-axis current reference value I. d * This helps to avoid the problem caused by bus voltage V bus Sudden changes cause inrush current. Furthermore, by providing a reference value I for the d-axis current... d *Setting upper and lower limits allows control over the magnitude of the supplementary current drawn by the energy storage inverter from the grid, thereby helping to prevent hardware protection from being triggered due to overcurrent and improving the safety of the energy storage inverter system.

[0050] In at least one instance, the d-axis current reference value I d The lower limit value of * is 0A, which helps to prevent the energy storage inverter from feeding back into the grid before grid connection, and also helps to prevent the bus voltage V bus The continuous increase in current can lead to overvoltage risk. It is worth noting that those skilled in the art can adjust the d-axis current reference value I according to the actual situation. d The upper and lower limits of * are both within the scope of protection of this application.

[0051] In some embodiments, such as Figure 6 As shown, the inner current loop acts on both the d-axis and q-axis components. The inner current loop includes a first comparator, a first PI regulator, and a first adder, as well as a second comparator, a second PI regulator, and a second adder. Specifically, the input to the first comparator is the d-axis current reference value I. d * and d-axis current value I d The output of the first comparator serves as the input of the first PI controller. The output of the first PI controller and the adjustment signal together serve as the input of the first adder, which then outputs the d-axis control signal d. con The input to the second comparator is the q-axis current reference value I.q * and q-axis current value I q The output of the second comparator serves as the input of the second PI controller. The output of the second PI controller and the adjustment signal together serve as the input of the second adder, which then outputs the q-axis control signal q. con In at least one instance, the q-axis current reference value I q * is 0A.

[0052] It is understandable that this configuration enables decoupled control of the d-axis active component and the q-axis reactive component. While adjusting the phase difference of the output voltage of the energy storage inverter, it draws supplementary current from the grid through the inner current loop of the d-axis to maintain the bus voltage V. bus Stable. Furthermore, the output of the first PI regulator is combined with U through the first adder. adjd The output of the second PI regulator is superimposed and then added to U via a second adder. adjq The superposition allows the phase difference of the energy storage inverter's output voltage to smoothly transition from the first angle to the second angle, which helps to avoid the neutral relay S N The inrush current generated during closing. It is worth mentioning that, through feedforward processing, the lag of the first and second PI regulators can also be compensated, thereby enabling the energy storage inverter to meet grid connection conditions more quickly.

[0053] In at least one instance, such as Figure 6 As shown, a first limiting module is provided between the first PI regulator and the first adder, and a second limiting module is provided between the second PI regulator and the second adder. It should be understood that the first and second limiting modules respectively limit the output amplitude of the first and second PI regulators, thereby helping to avoid overshoot or oscillation caused by excessive integral accumulation, and improving the response performance of the inner current loop. It is worth mentioning that the first and second limiting modules are located before the first and second adders, respectively, which helps to avoid affecting the regulation signal, thus helping to ensure that the phase difference of the output voltage of the energy storage inverter smoothly transitions from the first angle to the second angle quickly.

[0054] In some embodiments, when there is no DC power input to the energy storage inverter, the above-described grid pre-charging method is adopted. No DC power input refers to situations such as the DC power supply being depleted or the energy storage inverter being in a dormant state. When DC power is available to the energy storage inverter, DC power is preferentially used to pre-charge bus capacitors C1 and C2 to improve grid connection efficiency and simplify the control process.

[0055] This application also provides an energy storage inverter system, including: a grid-connected relay group, the grid-connected relay group including a first live wire relay S1, a second live wire relay S2 and a neutral wire relay S3 connected between the output terminal of the energy storage inverter and the power grid. N The pre-charge branch is connected in parallel with the second live wire relay S2. The pre-charge branch includes a pre-charge relay S2 connected in series. P and pre-charge resistor R P ; Controller, controller with grid-connected relay group and pre-charge relay S P The communication connection is established, and the controller is configured to store instructions and execute the aforementioned energy storage inverter grid pre-charge control method to control the first live wire relay S1, the second live wire relay S2, and the neutral wire relay S3. N and precharge relay S P They can be closed or opened respectively.

[0056] It can be understood that through the above-mentioned grid pre-charge control method for energy storage inverters, after pre-charging, the phase difference of the output voltage of the energy storage inverter can be controllably and smoothly transitioned from the first angle to the second angle. Thus, before grid connection, the phase difference of the output voltage of the energy storage inverter can be closer to the phase difference of the grid voltage, which can suppress the inrush current at the moment of grid connection to a large extent, thereby improving the reliability and safety of the energy storage inverter system after pre-charging and grid connection.

[0057] In one specific embodiment, if the grid connection is performed directly without activating the regulating loop, the inrush current on the first live wire L1 is approximately 59.00A, and the inrush current on the neutral wire N is approximately 66.88A at the moment of grid connection. However, if the grid connection is performed using the aforementioned grid pre-charge control method for the energy storage inverter (i.e., activating the regulating loop before grid connection), the inrush current on the first live wire L1 is approximately 15.50A, and the inrush current on the neutral wire N is approximately 3.75A at the moment of grid connection. Therefore, the aforementioned grid pre-charge control method for the energy storage inverter effectively suppresses the inrush current of the energy storage inverter system at the moment of grid connection after grid pre-charge.

[0058] The basic principles, main features, and advantages of this invention have been described above. Those skilled in the art should understand that this invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely principles of the invention. Various changes and modifications can be made without departing from the spirit and scope of the invention, and all such changes and modifications fall within the scope of the invention as claimed. The scope of protection claimed by this invention is defined by the appended claims and their equivalents.

Claims

1. A grid pre-charge control method for an energy storage inverter, characterized in that, include: Close the precharge relay and the first live wire relay to precharge the DC bus of the energy storage inverter using the power grid, while the second live wire relay and the neutral wire relay remain open; When the energy storage inverter meets the pre-charge completion conditions, the adjustment loop is activated. The adjustment loop is used to transition the phase difference of the output voltage of the energy storage inverter from the first angle to the second angle. When the energy storage inverter meets the grid connection conditions, the second live wire relay is closed, the precharge relay is opened, and the neutral wire relay is closed to enable the energy storage inverter to be connected to the grid.

2. The grid pre-charge control method for energy storage inverters according to claim 1, characterized in that, The regulation loop includes feedforward processing for generating a regulation signal, which is a weighted average of the voltage vector on the energy storage inverter side and the voltage vector on the grid side. By adjusting the weighting coefficient of the weighted average, the regulation signal enables the phase difference of the output voltage of the energy storage inverter to transition from a first angle to a second angle.

3. The grid pre-charge control method for energy storage inverters according to claim 2, characterized in that, The adjustment signal includes, U adjd =(1-α)U invd +αU gd U adjq =(1-β)U invq +βU gq ; Among them, U adjd U is the adjusted d-axis feedforward voltage. adjq U is the adjusted q-axis feedforward voltage. invd U is the d-axis voltage on the energy storage inverter side. invq U is the q-axis voltage on the energy storage inverter side. gd U is the d-axis voltage on the grid side. gq Let α be the q-axis voltage on the grid side, and β be the weighting coefficients.

4. The grid pre-charge control method for energy storage inverters according to claim 3, characterized in that, When the regulation loop is started, the initial values ​​of the weighting coefficients α and β are 0, and they increase from 0 to 1 over several power frequency cycles, so that the phase difference of the output voltage of the energy storage inverter transitions from the first angle to the second angle.

5. The grid pre-charge control method for energy storage inverters according to claim 2, characterized in that, The regulation loop also includes a bus voltage slow-start outer loop and a current inner loop. Through these loops, the energy storage inverter draws supplementary current from the grid, which is used to maintain the DC bus voltage V. bus Stablize.

6. The grid pre-charge control method for energy storage inverters according to claim 5, characterized in that, The bus voltage slow-start outer loop acts on the d-axis component. The bus voltage slow-start outer loop includes a slow-start module, and the input of the slow-start module is the bus voltage V. bus The soft-start module can output the d-axis current reference value I. d * where the d-axis current reference value I d *It has an upper limit and a lower limit.

7. The grid pre-charge control method for energy storage inverters according to claim 6, characterized in that, The inner current loop acts on the d-axis and q-axis components. The inner current loop includes a first comparator, a first PI regulator, and a first adder, as well as a second comparator, a second PI regulator, and a second adder. The input to the first comparator is the d-axis current reference value I. d * and d-axis current value I d The output of the first comparator serves as the input of the first PI controller, and the output of the first PI controller and the adjustment signal together serve as the input of the first adder, which then outputs the d-axis control signal d. con The input to the second comparator is the q-axis current reference value I. q * and q-axis current value I q The output of the second comparator serves as the input of the second PI controller, and the output of the second PI controller and the adjustment signal together serve as the input of the second adder, which then outputs the q-axis control signal q. con .

8. The grid pre-charge control method for energy storage inverters according to any one of claims 1-7, characterized in that, The pre-charge completion condition is that the pre-charge time count value is greater than or equal to a preset time threshold, and the bus voltage V of the energy storage inverter is... bus It is greater than or equal to the preset voltage threshold.

9. The grid pre-charge control method for energy storage inverters according to any one of claims 1-7, characterized in that, The grid connection condition is that the absolute value of the difference between the effective value of the output voltage of the energy storage inverter and the effective value of the grid-side voltage is less than or equal to a preset voltage difference value, and the bus voltage V of the energy storage inverter is... bus It is greater than or equal to the preset voltage threshold.

10. An energy storage inverter system, characterized in that, include: A grid-connected relay group, comprising a first live wire relay, a second live wire relay, and a neutral wire relay connected between the output terminal of the energy storage inverter and the power grid; A pre-charge branch, wherein the pre-charge branch is connected in parallel with the second live wire relay, and the pre-charge branch includes a pre-charge relay and a pre-charge resistor connected in series; A controller is communicatively connected to the grid-connected relay group and the precharge relay. The controller is configured to store instructions and execute the grid precharge control method for the energy storage inverter as described in any one of claims 1-9, so as to control the first live wire relay, the second live wire relay, the neutral wire relay and the precharge relay to close or open respectively.

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