A method for controlling on-grid and off-grid switching of energy storage converter

Abstract

The present invention relates to a control method for switching an energy storage converter from grid to off-grid, comprising detecting the working state of the energy storage converter; when the working state of the energy storage converter is a grid-connected working state, detecting whether the three-phase grid voltage is less than a limit value, if so, using the phase angle and amplitude of the three-phase grid voltage of the energy storage converter in the grid-connected working state as the phase angle and amplitude of the three-phase grid voltage in the off-grid working state, so as to realize a smooth transition of the energy storage converter from the grid-connected working state to the off-grid working state; when the working state of the energy storage converter is an off-grid working state, detecting whether the three-phase grid voltage during off-grid operation is greater than a limit value, if so, controlling the difference between the off-grid voltage phase angle and the three-phase grid voltage phase angle in the off-grid working state to be within a specified range, so as to realize the switching of the energy storage converter from the off-grid working state to the grid-connected working state. It can realize the stable switching of the on-grid and off-grid modes of the system, and improve the stability and reliability of the energy storage device when it is working.

Description

Technical Field

[0001] The present invention relates to the technical field of high-voltage energy storage, and in particular to a method for controlling on-grid and off-grid switching of an energy storage converter. Background Art

[0002] The high-voltage energy storage converter is a key device in the high-voltage energy storage system. When a distribution network failure occurs, or the host computer issues an off-grid command, the high-voltage energy storage converter needs to transition from the grid-connected mode to the off-grid mode to ensure operation in an island state; when the distribution network failure is eliminated, the high-voltage energy storage system needs to transition from the off-grid mode to the grid-connected mode to improve the power supply reliability of the power grid.

[0003] In the prior art, the input voltage of the high-voltage energy storage inverter is as high as 1000V. When switching from the grid-connected operation mode to the off-grid operation mode, the energy storage inverter operates unstably and the grid voltage is prone to sudden changes, which will cause the energy storage inverter to operate unstably and ultimately affect the power supply quality on the load side of the energy storage inverter. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a method for controlling on-grid and off-grid switching of an energy storage converter, which can achieve stable switching of the on-grid and off-grid modes of the system and improve the stability and reliability of the energy storage device during operation.

[0005] To solve the above technical problems, the present invention provides a method for controlling on-grid and off-grid switching of an energy storage inverter, comprising: detecting the working state of the energy storage inverter; when the working state of the energy storage inverter is the on-grid working state, detecting whether the three-phase grid voltage of the energy storage inverter when the energy storage inverter is on-grid operating is less than a limit value, and if so, using the phase angle and amplitude of the three-phase grid voltage of the energy storage inverter in the on-grid working state as the phase angle and amplitude of the three-phase grid voltage of the energy storage inverter in the off-grid working state, so as to achieve a smooth transition of the energy storage inverter from the on-grid working state to the off-grid working state; when the working state of the energy storage inverter is the off-grid working state, detecting whether the three-phase grid voltage of the energy storage inverter when the energy storage inverter is off-grid operating is greater than a limit value, and if so, controlling the difference between the off-grid voltage phase angle of the energy storage inverter in the off-grid working state and the three-phase grid voltage phase angle to be within a specified range, so as to achieve a stable switching of the energy storage inverter from the off-grid working state to the on-grid working state.

[0006] As a preferred method, "the energy storage inverter smoothly transitions from the grid-connected working state to the off-grid working state" specifically includes the following steps: S101, the energy storage inverter operates in the grid-connected working state and enters the grid-connected control loop; S102, obtains the limit value of the three-phase grid voltage; determines whether the three-phase grid voltage of the energy storage inverter in the grid-connected working state is less than the limit value, and if so, proceeds to the next step; S103, switches the energy storage inverter to the off-grid working state for operation.

[0007] Preferably, the limit value of the three-phase grid voltage is set to 80V.

[0008] Preferably, between S102 and S103, it also includes: when the energy storage inverter operates in the grid-connected control loop, detecting and saving the three-phase grid voltage phase angle and amplitude; disconnecting the relay in the grid-connected control loop, converting the grid-connected control loop into an off-grid control loop; using the three-phase grid voltage phase angle and amplitude in the grid-connected control loop as the three-phase grid voltage phase angle and amplitude in the off-grid control loop.

[0009] As a preferred embodiment, "the energy storage inverter stably switches from an off-grid working state to a grid-connected working state", specifically includes the following steps: S201, the energy storage inverter operates in an off-grid working state and enters an off-grid control loop; S202, obtains a limit value of the three-phase grid voltage; determines whether the three-phase grid voltage of the energy storage inverter in the off-grid working state is greater than the limit value, and if so, proceeds to the next step; S203, the energy storage inverter switches to a grid-connected working state to operate.

[0010] Preferably, the limit value of the three-phase grid voltage is set to 80V.

[0011] Preferably, the S203 and S203 also include: when the energy storage inverter is operating in the off-grid control loop, obtaining the off-grid voltage phase angle and the three-phase grid voltage phase angle; setting the difference range between the off-grid voltage phase angle and the three-phase grid voltage phase angle; calculating the difference between the off-grid voltage phase angle and the three-phase grid voltage phase angle, and determining whether the difference is within the difference range; if the difference is within the difference range, converting the off-grid control loop to a grid-connected control loop; if the difference is not within the difference range, adjusting the off-grid voltage and the three-phase grid voltage.

[0012] Preferably, the difference range is set to 0-30V.

[0013] Preferably, the three-phase grid voltage phase angle of the energy storage converter in an off-grid working state is obtained according to a decoupling software phase-locking method of a dual synchronous coordinate system.

[0014] As a preferred method, "obtaining the phase angle of the three-phase grid voltage when the energy storage inverter is in an off-grid working state" specifically includes: when the energy storage inverter is in an off-grid working state, detecting the three-phase grid voltage; subjecting the three-phase grid voltage in the off-grid working state to Clark transformation and Park transformation to obtain the positive-sequence voltage and negative-sequence voltage of the three-phase grid; processing the positive-sequence voltage and negative-sequence voltage of the three-phase grid by a decoupling method of a dual synchronous coordinate system to obtain the phase angle of the three-phase grid voltage.

[0015] The above technical solution of the present invention has the following advantages compared with the prior art:

[0016] 1. The energy storage inverter of the present invention can quickly switch between the two operating modes of grid-connected and off-grid, and can operate in both grid-connected mode and off-grid mode. It integrates the advantages and disadvantages of grid-connected inverters and off-grid inverters.

[0017] 2. When the energy storage AC device of the present invention switches from a grid-connected working state to an off-grid working state, the phase angle and amplitude of the three-phase grid voltage can be used as the phase angle and amplitude of the three-phase grid voltage of the energy storage converter in the off-grid working state; the output current will not fluctuate, and the energy storage AC device can switch smoothly from the grid-connected working state to the off-grid working state.

[0018] 3. When the energy storage AC device of the present invention switches from an off-grid working state to a grid-connected working state, it can control the difference between the off-grid voltage phase angle of the energy storage converter in the off-grid working state and the three-phase grid voltage phase angle within a specified range, thereby improving the working stability of the energy storage converter and the power supply reliability of the microgrid. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments of the present invention in conjunction with the accompanying drawings, wherein:

[0020] Figure 1 A schematic diagram of a process of switching the energy storage converter from a grid-connected working state to an off-grid working state;

[0021] Figure 2 It is a schematic diagram of a flow chart of switching the energy storage converter of the present invention from an off-grid working state to a grid-connected working state. DETAILED DESCRIPTION

[0022] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0023] Reference Figure 1-2 As shown, the present invention discloses a method for controlling on-grid and off-grid switching of an energy storage converter, comprising:

[0024] The energy storage converter switches from the grid-connected working state to the off-grid working state and the energy storage converter switches from the off-grid working state to the grid-connected working state.

[0025] When the energy storage converter switches from an off-grid working state to a grid-connected working state, the specific steps include:

[0026] Step 101: The energy storage converter enters the grid-connected control loop to enable the energy storage converter to operate in a grid-connected working state.

[0027] Step 102: Obtain a limit value of the three-phase grid voltage. The limit value of the three-phase grid voltage is preferably 80V.

[0028] Obtain the three-phase grid voltage value when the energy storage converter is running in the grid-connected working state. Determine whether the three-phase grid voltage of the energy storage converter in the grid-connected working state is less than the above limit value, if so, proceed to the next step.

[0029] Step 103: Switch the energy storage converter to an off-grid operating state.

[0030] Preferably, when the three-phase grid voltage of the energy storage inverter in the grid-connected working state is not less than the limit value, the above-mentioned energy storage inverter still operates in the grid-connected working state. Furthermore, between the steps 102 and 103, it also includes: when the above-mentioned energy storage inverter operates in the grid-connected control loop, the phase angle and amplitude of the three-phase grid voltage at this time are detected and saved. The relevant parameters are initialized, and the relay in the grid-connected control loop is disconnected at the same time to realize the conversion of the grid-connected control loop to the off-grid control loop. The phase angle and amplitude of the three-phase grid voltage of the energy storage inverter in the grid-connected working state are used as the phase angle and amplitude of the three-phase grid voltage of the energy storage inverter in the off-grid working state, and the bus clamping voltage control method is used to prevent the voltage on the bus capacitor from abruptly changing, so as to realize the smooth transition of the energy storage inverter from the grid-connected working state to the off-grid working state.

[0031] When the energy storage converter switches from an off-grid working state to a grid-connected working state, the following steps are specifically included:

[0032] Step 201: The energy storage converter enters an off-grid control loop, so that the energy storage converter operates in an off-grid working state.

[0033] Step 202: Obtain a limit value of the three-phase grid voltage when the energy storage converter is operating in an off-grid working state. The limit value of the three-phase grid voltage is preferably 80V.

[0034] Obtain the three-phase grid voltage value when the energy storage converter is operating in an off-grid working state. Determine whether the three-phase grid voltage of the energy storage converter in an off-grid working state is greater than the above-mentioned limit value, and if so, proceed to the next step.

[0035] Step 203: The energy storage converter switches to a grid-connected working state for operation.

[0036] Preferably, if the three-phase grid voltage of the energy storage converter in the off-grid working state is not greater than the above-mentioned limit value, the energy storage converter continues to operate in the off-grid working state.

[0037] Further preferably, the above step 202 and step 203 further include: when the energy storage converter operates in the off-grid control loop, obtaining the off-grid voltage phase angle and the three-phase grid voltage phase angle.

[0038] The difference range between the off-grid voltage phase angle and the three-phase grid voltage phase angle is set. Preferably, the difference range is 0-30V.

[0039] The difference between the off-grid voltage phase angle and the three-phase grid voltage phase angle is calculated and it is determined whether the difference is within the difference range. If the difference is within the difference range, the off-grid control loop is converted to a grid-connected control loop. If the difference is not within the difference range, the off-grid voltage and the three-phase grid voltage are adjusted so that the difference satisfies the difference range.

[0040] Among them, according to the decoupling software phase-locking method of the dual synchronous coordinate system, the three-phase grid voltage phase angle of the energy storage converter in the off-grid working state is obtained. When the three-phase grid voltage phase angle of the energy storage converter in the off-grid working state is obtained, it specifically includes: when the energy storage converter is in the off-grid working state, the three-phase grid voltage is detected.

[0041] The positive sequence voltage is obtained by Clark and Park transformation. and Negative sequence voltage and Using the decoupling method of dual synchronous coordinate systems, we can obtain Among them, the above is the voltage positive sequence d-axis component, is the voltage positive sequence q-axis component, is the voltage negative sequence d-axis component, is the negative sequence q-axis component of voltage. is the voltage positive sequence d-axis component after decoupling, is the voltage positive sequence q-axis component after decoupling, is the voltage negative sequence d-axis component after decoupling, is the negative-sequence q-axis component of the voltage after decoupling.

[0042] Using the formula Obtain the angular frequency w, and then according to the formula dθ=wdt, θ=(w1+w2+w3+…)*dt, obtain the real-time phase angle of the three-phase power grid. Among them, kp is the proportional coefficient, ki is the integral coefficient, dθ is the phase angle per unit time, θ is the real-time phase angle of the three-phase power grid, and w1, w2, w3 are the angular frequencies.

[0043] After the phase synchronization is successful, the instantaneous values ​​of the off-grid voltage phase angle and the three-phase grid voltage phase angle are compared. If the difference between the two is within the specified range, the grid relay is connected and the grid-connected control loop is entered.

[0044] Preferably, when the energy storage inverter switches from the off-grid mode to the grid-connected mode, the phase angle of the off-grid voltage and the phase angle of the three-phase grid voltage are gradually approached to suppress oscillation during the operation of the energy storage inverter system, thereby achieving stable switching of the system's grid-connected and off-grid modes and improving the stability and reliability of the energy storage device during operation.

[0045] Example

[0046] In the actual operation of the microgrid, in the grid-connected mode, the grid-connected control loop is entered, and the frequency of the control loop is selected as 20kHz. When the real-time three-phase grid voltage effective value is detected to be less than 40V, it is considered to enter the off-grid state. At the same time, the current phase angle and amplitude of the three-phase grid voltage are saved, the battery and off-grid voltage loop and current loop PI (proportional and integral) parameters are initialized, and the grid-connected relay is disconnected. The current phase angle of the three-phase grid voltage is used as the phase angle of the off-grid voltage, and the amplitude of the three-phase grid voltage is used as the amplitude of the off-grid voltage.

[0047] The step size of the phase angle in the off-grid state is fixed. When the phase angle exceeds 360 degrees, the phase angle starts to participate in the control from 0. When the three-phase grid voltage is detected to be greater than 80V, it is considered to enter the grid-connected mode. The off-grid phase angle and the grid phase angle are detected in real time. The grid phase angle is realized by the decoupling software phase-locking method based on the dual synchronous coordinate system. The off-grid phase angle is compared with the phase angle of the three-phase grid. The instantaneous value ΔU of the three-phase grid voltage and the off-grid voltage is compared. d . Where ΔU d =U Grid -U EPS (U Grid is the instantaneous value of the grid voltage, U EPS is the instantaneous value of the off-grid voltage) If the difference between the two is ΔU d Within the specified range, the grid relay is merged and enters the grid control loop. In the process of grid-connection and off-grid switching, the bus clamp voltage control method is added. When the difference between the bus capacitor voltage and the reference voltage of the bus capacitor is greater than 30V, it means that the system is unstable and needs to be adjusted to control the difference within 30V.

[0048] Those skilled in the art will appreciate that the embodiments of the present application may be provided as methods, systems, or computer program products. Therefore, the present application may adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application may adopt the form of a computer program product implemented in one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) that include computer-usable program code.

[0049] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the embodiments of the present application. It should be understood that each process and / or box in the flowchart and / or block diagram, as well as the combination of the processes and / or boxes in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to generate a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1 A process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0050] These computer program instructions may also be stored in a computer-readable memory capable of directing a computer or other programmable data processing device to operate in a specific manner, so that the instructions stored in the computer-readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 A process or multiple processes and / or boxes Figure 1 A function specified in one or more boxes.

[0051] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operating steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing instructions for implementing the process. Figure 1 A process or multiple processes and / or boxes Figure 1 The steps for the functions specified in one or more boxes.

[0052] Obviously, the above embodiments are merely examples for clear explanation and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the protection scope of the invention.

Claims

1. A method for controlling on-grid and off-grid switching of an energy storage converter, characterized in that: include: Detect the working status of the energy storage converter; When the working state of the energy storage converter is the grid-connected working state, it is detected whether the three-phase grid voltage of the energy storage converter is less than the limit value when the energy storage converter is in grid-connected operation. If so, the phase angle and amplitude of the three-phase grid voltage of the energy storage converter in the grid-connected working state are used as the phase angle and amplitude of the three-phase grid voltage of the energy storage converter in the off-grid working state, so as to realize the smooth transition of the energy storage converter from the grid-connected working state to the off-grid working state; When the working state of the energy storage converter is an off-grid working state, it is detected whether the three-phase grid voltage of the energy storage converter is greater than the limit value when the energy storage converter is in off-grid operation. If so, the difference between the off-grid voltage phase angle of the energy storage converter and the three-phase grid voltage phase angle in the off-grid working state is controlled to be within a specified range, so as to realize the stable switching of the energy storage converter from the off-grid working state to the grid-connected working state; Wherein, "the energy storage converter smoothly transitions from the grid-connected working state to the off-grid working state" includes the following steps: S101, the energy storage converter operates in a grid-connected working state and enters a grid-connected control loop; S102, obtaining a limit value of the three-phase grid voltage; determining whether the three-phase grid voltage of the energy storage converter in the grid-connected working state is less than the limit value, and if so, performing the following steps: Detecting the phase angle and amplitude of the three-phase grid voltage when the energy storage converter operates in the grid-connected control loop; Disconnecting the relay in the grid-connected control loop to convert the grid-connected control loop into an off-grid control loop; The phase angle and amplitude of the three-phase grid voltage in the grid-connected control loop are used as the phase angle and amplitude of the three-phase grid voltage in the off-grid control loop; S103, switching the energy storage converter to operate in an off-grid working state; "The energy storage converter stably switches from an off-grid working state to a grid-connected working state", comprising the following steps: S201, the energy storage converter operates in an off-grid working state and enters an off-grid control loop; S202, obtaining a limit value of the three-phase grid voltage; determining whether the three-phase grid voltage of the energy storage converter in the off-grid working state is greater than the limit value, and if so, performing the following steps: When the energy storage converter operates in the off-grid control loop, obtaining the off-grid voltage phase angle and the three-phase grid voltage phase angle; Setting a difference range between the off-grid voltage phase angle and the three-phase grid voltage phase angle; After synchronizing the off-grid voltage phase angle and the three-phase grid voltage phase angle, calculating the difference between the instantaneous values ​​of the off-grid voltage phase angle and the three-phase grid voltage phase angle, and determining whether the difference is within the difference range; If the difference is within the difference range, the off-grid control loop is converted into a grid-connected control loop; if the difference is not within the difference range, the off-grid voltage and the three-phase grid voltage are adjusted until the difference between the off-grid voltage phase angle and the three-phase grid voltage phase angle falls within the difference range; S203, the energy storage converter is switched to a grid-connected working state and operates; Obtaining the three-phase grid voltage phase angle in an off-grid working state comprises the following steps: Detecting the three-phase grid voltage of the energy storage converter when it is in an off-grid working state; The three-phase grid voltage in the off-grid working state is subjected to Clark transformation and Park transformation to obtain a positive sequence voltage and a negative sequence voltage of the three-phase grid voltage; The positive-sequence voltage and the negative-sequence voltage are processed by a decoupling method of a dual synchronous coordinate system to obtain a phase angle of the three-phase grid voltage; When the phase angle of the three-phase grid voltage exceeds 360 degrees, the phase angle of the three-phase grid voltage is controlled starting from 0; Among them, the limit value of the three-phase grid voltage is set to 80V; the difference range is set to 0-30V.

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