Energy storage system charge-discharge seamless switching control method and related device

Abstract

This invention discloses a seamless switching control method and related equipment for charging and discharging of an energy storage system. Based on a traditional dq rotating coordinate system architecture with dual closed-loop control of grid-side voltage and current, the method samples grid-side current and voltage, and combines this with grid phase angle information obtained from a phase-locked loop. During transient switching, the method controls the commutation of the three-phase grid currents, using the two phases most recently crossing zero as the start and end times of the switching. The other phase satisfies the three-phase instantaneous current balance constraint, achieving seamless switching of the grid-side current at the zero-crossing point. Compared with existing methods, this method requires no additional hardware, offers higher waveform quality, shorter switching time, and effectively improves the charging and discharging response speed of the energy storage system.

Description

Technical Field

[0001] This invention belongs to the field of grid connection control technology for oilfield power grid energy storage systems with new energy access, specifically involving a seamless switching control method for charging and discharging of an energy storage system and related equipment. Background Technology

[0002] With the high proportion of distributed photovoltaic power integrated into oilfield power grids, its randomness, volatility, and "double high" characteristics pose severe challenges to the safe and stable operation of traditional power systems. Energy storage systems, as a key means to address grid load fluctuations and the integration of new energy sources, are also crucial for the transformation and development of new power systems. Energy storage converters, as the core equipment of energy storage systems, undertake the important task of bidirectional energy flow and power conversion between the grid and energy storage batteries. Therefore, it is necessary to study the core control strategies of energy storage systems in conjunction with the characteristics of grid operation, ensuring both independent operation in discharge and charging modes and seamless switching between charging and discharging.

[0003] Researchers have proposed several solutions for charge / discharge switching technology in energy storage systems. Early methods often involved a shutdown-restart switching approach. While this resulted in minimal waveform distortion during the switching process, it was time-consuming and required manual intervention. Furthermore, based on the inner and outer loop design of the energy storage converter, some scholars proposed a variable DC electromotive force switching method. This method achieves switching by altering the DC bus voltage through a series DC power supply. This method is faster than the restart method but requires electrical operation, and the current change is not adjustable. Finally, variable current switching is a classic approach, achieving charge / discharge switching by changing the current command in the control loop. This method has been continuously improved. Existing literature, such as "Dai Meizhi. Research on Control and Switching Strategy of Bidirectional Energy Storage Inverter [D]. University of Electronic Science and Technology of China, 2016", and "Jin Wentao, Xu Shaohua, Zhang Delong, et al. Application and Response Time Test of MW-level Battery Energy Storage System in Grid-connected Photovoltaic Power Station. High Voltage Engineering, 2017, 43(7): 2425-2432", proposes a linear soft switching method; literature, such as "Chen Xuhai, Chen Yanlian, Chen Jiaqiao, et al. PCS Charge and Discharge Switching Control Based on Equal Inductance Energy Change Rate [J]. Power Electronics Technology, 2021, 55(01): 22-25", proposes a switching method based on the inductance energy change rate; however, these switching methods all have a contradiction between switching time and current quality, with switching time ranging from tens to hundreds of milliseconds. Summary of the Invention

[0004] The purpose of this invention is to provide a seamless switching control method and related equipment for charging and discharging in an energy storage system, so as to solve the technical problem of slow charging and discharging switching speed in existing energy storage systems.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A method for seamless switching control of charging and discharging in an energy storage system includes the following steps: The energy storage system receives a charge / discharge switching command and, based on the grid-side current phase angle information, determines the two phase currents that are most recently zero-crossing among the three-phase grid-side currents as the start and end times of the switching, while the other phase current satisfies the three-phase instantaneous current balance constraint condition. Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component calculated from the grid-side current value are used as current commands to achieve seamless switching of grid-side current zero crossing point in the energy storage system.

[0006] Furthermore, the grid-side current phase angle information is obtained through a phase-locked loop.

[0007] Furthermore, the d-axis current component and the q-axis current component are used as current command inputs to the current loop, and control signals are output through the current loop.

[0008] Furthermore, the three-phase instantaneous current balance constraint condition is as follows:

[0009] In the formula, Let a be the phase current. For phase b current, This represents the c-phase current.

[0010] Furthermore, among the three-phase currents on the grid side, the two phases that have most recently crossed zero are phase a and phase c. When neither phase a nor phase c has crossed zero, the three-phase currents on the grid side maintain their original theoretical values.

[0011] Furthermore, when phase a crosses zero and phase c does not cross zero, phase b satisfies the instantaneous current balance constraint condition.

[0012] Furthermore, the overall switching time for the seamless switching of the grid-side current at the zero-crossing point of the energy storage system is one-third of the power grid frequency cycle.

[0013] Furthermore, the overall time for seamless switching of the grid-side current zero-crossing point of the energy storage system is obtained by determining the start and end times of the switching through phase locking.

[0014] Secondly, a seamless charging and discharging switching controller for an energy storage system includes a judgment module and a switching calculation module, wherein: Judgment module: Used for the energy storage system to receive charge and discharge switching commands, and to determine the two phase currents that are most recently zero-crossing among the three phase currents on the grid side as the start and end times of switching based on the grid side current phase angle information, and the other phase current satisfies the three-phase instantaneous current balance constraint condition. Calculation and switching module: Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component are calculated based on the grid-side current value. The d-axis current component and q-axis current component are used as current commands to realize seamless switching of grid-side current zero crossing point of energy storage system.

[0015] Thirdly, a terminal device includes a memory, a processor, and a switching algorithm program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the switching algorithm.

[0016] Compared with the prior art, the present invention has the following beneficial technical effects: This invention provides a seamless switching control method for charging and discharging in an energy storage system. Based on the traditional dual closed-loop control system architecture of grid-side voltage and current in a dq rotating coordinate system, it samples the grid-side current and voltage and combines the grid phase angle information obtained by the phase-locked loop. During transient switching, it controls the commutation of the three-phase current on the grid side, taking the two phases that are most recently zero-crossing as the start and end times of the switching. The other phase satisfies the three-phase instantaneous current balance constraint condition, realizing seamless switching of the grid-side current at the zero-crossing point of the energy storage system. Compared with existing methods, it does not require additional hardware equipment, has higher waveform quality, faster switching speed, and effectively improves the charging and discharging response speed of the energy storage system.

[0017] This invention proposes a charging and discharging control method for energy storage systems based on seamless switching of grid-side current at zero crossing points. Building upon variable current switching technology, it achieves sequential switching of grid-side phase current at zero crossing points, enabling rapid switching between charging and discharging states. Simultaneously, it allows for free control of current magnitude, effectively suppressing grid-side current surges and oscillations, and achieving seamless and smooth switching.

[0018] Furthermore, the overall switching time for seamless switching of grid-side current at zero crossing point in the energy storage system is one-third of the power grid frequency cycle, which is significantly reduced compared to the switching time of existing technologies. Attached Figure Description

[0019] Figure 1 This is a flowchart of a seamless switching control method for charging and discharging of an energy storage system according to an embodiment of the present invention; Figure 2 The diagram shows an improved zero-crossing seamless switching control method for the grid-side current inner loop of an energy storage system based on the traditional dq rotating coordinate system. Figure 3 This is a schematic diagram of the switching simulation waveform from a grid-side charging current of 150A to a discharging current of 200A under direct current step switching. Figure 4 A schematic diagram of the switching simulation waveform from 150A grid-side charging current to 200A grid-side discharging current under linear current switching conditions; Figure 5A schematic diagram of the switching simulation waveform of phase a being charged from 150A current to 200A current and discharged from the grid side under the condition of zero crossing of phase a first; Figure 6 A schematic diagram of the simulation waveforms for the reference values ​​of the d-axis component and the q-axis component of the current; Figure 7 This document outlines the charging and discharging control method for an energy storage system based on seamless switching at grid-side zero crossings. Detailed Implementation

[0020] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] In the description of this invention, it should be understood that the terms "comprising" and "including" indicate the presence of the described features, integrals, steps, operations, elements and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or collections thereof.

[0022] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise.

[0023] It should be understood that although terms such as first, second, third, etc., may be used in the embodiments of the present invention to describe the preset range, these preset ranges should not be limited to these terms. These terms are only used to distinguish the preset ranges from one another. For example, without departing from the scope of the embodiments of the present invention, the first preset range may also be referred to as the second preset range, and similarly, the second preset range may also be referred to as the first preset range.

[0024] Depending on the context, the word "if" as used here can be interpreted as "when," "when," "in response to determination," or "in response to detection." Similarly, depending on the context, the phrase "if determination" or "if detection (of the stated condition or event)" can be interpreted as "when determination," "in response to determination," "when detection (of the stated condition or event)," or "in response to detection (of the stated condition or event)."

[0025] Definitions: Phase-locked loop (PLL): A typical feedback control circuit that uses an externally input reference signal to control the frequency and phase of the internal oscillation signal, thereby achieving automatic tracking of the output signal frequency to the input signal frequency.

[0026] A current loop is a device that can detect changes in current on a wire in real time and transmit this information to a processing device for processing, judgment, or control. It is usually based on a current sensor and combined with signal processing, transmission, and reception modules to achieve accurate measurement and monitoring of current in a circuit.

[0027] The present invention will now be described in further detail with reference to the accompanying drawings: like Figure 1 As shown, a seamless switching control method for charging and discharging in an energy storage system includes the following steps: Step 1: The energy storage system receives the charge / discharge switching command. Based on the grid-side current phase angle information, it determines the two grid-side currents that most recently cross zero as the start and end times of the switching. The other grid-side current satisfies the three-phase instantaneous current balance constraint condition. Specifically, during zero-crossing switching, a transient asymmetry in the three-phase currents may occur, and the unity power factor operation will no longer be satisfied during the switching time, meaning the reactive current will not be zero. This invention employs two-phase zero-crossing switching, with the other phase determining its command value based on the instantaneous current balance principle to ensure the sum of the three-phase currents is zero. This process is achieved by changing the reference values ​​of the active and reactive currents. Specifically, the grid-side currents of the two phases most recently crossing zero are determined based on the current phase angle information.

[0028] After receiving the charge / discharge switching command, the system locks the phase according to the phase-locked loop. Determine the start time of the switch. and the end time of the switch .

[0029] Step 2: Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component calculated from the grid-side current value are used as current commands to achieve seamless switching of grid-side current zero crossing point of the energy storage system. Specifically, the dual-closed-loop control system in the dq rotating coordinate system employs two feedback loops to control the input current and output voltage respectively. The outer loop is a voltage feedback loop, and the inner loop is a current feedback loop. The output signal of the outer loop serves as the command signal for the inner loop. By adjusting the voltage through the outer loop, the inner loop can control the current, enabling it to track the target current command value in real time.

[0030] As an embodiment of the present invention, the d-axis current component and the q-axis current component are used as current command inputs to the current loop, and control signals are output through the current loop.

[0031] In another embodiment of the present invention, based on the traditional dq rotating coordinate system dual closed-loop control system architecture for grid-side voltage and current, the grid-side current and voltage are sampled, and combined with the grid phase angle information obtained by the phase-locked loop, the three-phase current of the grid side is commutated and controlled respectively during the transient switching process. The two phases that are most recently zero-crossing are used as the start and end times of the switching, and the other phase satisfies the three-phase instantaneous current balance constraint condition, so as to realize seamless switching of the grid-side current zero-crossing point of the energy storage system.

[0032] The d-axis and q-axis current components, calculated based on the grid-side current values, are used as the current command input current loop, including: Define the instantaneous grid-side current during the charging state of an energy storage system: (1) Where: Im is the grid-connected current amplitude before the energy storage system switches over.

[0033] Based on the abc-dq coordinate transformation, the active current in the dq coordinate system is obtained. With reactive current : (2) In a three-phase three-wire system, the three-phase currents follow the principle of instantaneous balance: (3) During zero-crossing switching, a transient asymmetry in the three-phase currents may occur, and the unity power factor operation will no longer be satisfied during the switching time, meaning the reactive current will not be zero. This invention employs two-phase zero-crossing switching, with the other phase determining its command value based on the instantaneous current balance principle to ensure the sum of the three-phase currents is zero. This process is achieved by changing the reference values ​​of the active and reactive currents. After receiving the charge / discharge switching command, the system locks the phase using a phase-locked loop. Determine the start time of the switch. and the end time of the switch .

[0034] Upon receiving a switching command, such as phase In the interval or Then phase a current is the first phase to cross zero and is detected. or At time a, the current is reversed. The next phase zero-crossing current is phase c, so the current of phase c remains unchanged, and the current of phase b, as the adjustment phase, satisfies the relationship of equation (3) in real time. The theoretical instantaneous current value is expressed as: (4) in: This represents the grid-connected current amplitude after the energy storage system switches over.

[0035] At this time, active current With reactive current satisfy: (5) Phase change Afterwards, phase c crosses zero, and the currents of all three phases are the instantaneous values ​​after the switching: (6) The switching process maintains the active and reactive current commands at each stage according to the theoretically calculated values ​​mentioned above, thus achieving the charging and discharging switching strategy. The entire command switching time is one-third of the power grid frequency cycle, approximately 6.67ms.

[0036] If a switching command is received, phase In the interval or Then the current in phase b is the first phase to cross zero, and it is detected. or At time b, the phase is reversed. The next phase zero-crossing current is phase a, then the phase a current remains unchanged, and the phase c current acts as the adjustment phase, satisfying the relationship of equation (3) in real time. The theoretical instantaneous current value is expressed as: (7) Phase change After that, phase a crosses zero, and the currents of all three phases are the instantaneous values ​​of the currents after switching, as in equation (6).

[0037] If a switching command is received, phase In the interval or Then the current in phase c is the first phase to cross zero and is detected. or At time c, the phase is reversed. The next phase zero-crossing current is phase b, so the phase b current remains unchanged, and the phase a current acts as the adjustment phase, satisfying the relationship of equation (3) in real time. The theoretical instantaneous current value is expressed as: (8) Phase change After that, phase b crosses zero, and the currents of all three phases are the instantaneous values ​​of the currents after switching, as in equation (6).

[0038] In another embodiment of the invention, such as Figure 7 The diagram shown is a flowchart of a charging and discharging control method for an energy storage system based on seamless switching of grid-side current zero crossing. The following section, in conjunction with the attached diagram, illustrates this method. Figure 4 The present invention will be further described in detail with reference to the embodiments. The specific steps are as follows: Step 1: After receiving the charge / discharge switching command, if the phase... In the interval Then phase a current is the first phase to cross zero and is detected. Previously, the three-phase currents remained at their original theoretical values: (1) The theoretical values ​​of active current and reactive current satisfy: (2) See Figure 2 , Figure 2 This is a schematic diagram of the current control for a grid-connected energy storage converter. The inner current loop input includes the active current reference value. With reactive current reference value By decoupling control, the control voltage is input to the modulation module to achieve grid-side current control. The current reference value is selected by the switching module based on the phase. The theoretical value calculated by equation (2) is... , Input as a current loop reference value: (3) Step 2: Located in the interval At this point, the phase a current has already crossed zero, while the phase c current has not yet crossed zero. During this stage, it is necessary to satisfy the following conditions: the phase a current is reversed, the phase c current remains unchanged, and the phase b current meets the instantaneous balance requirement. (4) The theoretical values ​​of active current and reactive current satisfy: (5) The theoretical value calculated by equation (5) , Input as a current loop reference value: (6) Step 3: At this point, the c-phase current crosses zero, and all three-phase currents begin to switch, with a phase difference of 180° from before the switch. The three-phase currents satisfy the following: (7) The theoretical values ​​of active current and reactive current satisfy: (8) The theoretical value calculated by equation (5) , Input as a current loop reference value: (9) During the process, all three phase currents are continuous, phases a and c achieve zero-crossing switching, and phase b changes in accordance with the magnitude of the currents in phases a and c. The switching instant from step 2 to step 3... It also meets the continuity requirement: (10) Based on the above steps, the simulation results are as follows: Figure 3 As shown, the initial operating condition is a charging mode with a grid-side current amplitude of 150A, i.e., step 1; switching begins at 0.2s, proceeding to step 2; after 6.67ms, switching is complete, and step 3 is implemented. The switching process is characterized by continuous and smooth current flow and fast switching speed. The current reference commands input in the three stages of the switching process are as follows: Figure 7 Therefore, this invention effectively improves the charging and discharging response speed of energy storage systems and has broad application prospects in fields such as new energy distributed power generation systems.

[0039] Those skilled in the art will understand that various aspects of the present invention can be implemented as systems, methods, or program products. Therefore, various aspects of the present invention can be specifically implemented in the following forms: a completely hardware implementation, a completely software implementation (including firmware, microcode, etc.), or a combination of hardware and software aspects, collectively referred to herein as a "circuit," "module," or "platform."

[0040] In another embodiment of the present invention, a seamless charging and discharging switching controller for an energy storage system is also provided, comprising a judgment module and a switching calculation module, wherein: Judgment module: Used for the energy storage system to receive charge and discharge switching commands, and to determine the two phase currents that are most recently zero-crossing among the three phase currents on the grid side as the start and end times of switching based on the grid side current phase angle information, and the other phase current satisfies the three-phase instantaneous current balance constraint condition. Calculation and switching module: Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component are calculated based on the grid-side current value. The d-axis current component and q-axis current component are used as current commands to realize seamless switching of grid-side current zero crossing point of energy storage system.

[0041] An embodiment of the present invention provides a terminal device comprising: a processor, a memory, and an algorithm program stored in the memory and executable on the processor. When the processor executes the algorithm program, it implements the steps in the various method embodiments described above. Alternatively, when the processor executes the algorithm program, it implements the functions of each module / unit in the various device embodiments described above.

[0042] The algorithm program can be divided into one or more modules / units, which are stored in the memory and executed by the processor to complete the present invention.

[0043] The processor may be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0044] The memory can be used to store the algorithm program and / or modules. The processor implements various functions of the terminal device by running or executing the algorithm program and / or modules stored in the memory, and by calling the data stored in the memory.

[0045] The above content is only for illustrating the technical concept of the present invention and should not be construed as limiting the scope of protection of the present invention. Any modifications made to the technical solution based on the technical concept proposed in this invention shall fall within the scope of protection of the claims of this invention.

Claims

1. A method for seamless switching control of charging and discharging in an energy storage system, characterized in that, Includes the following steps: The energy storage system receives a charge / discharge switching command and, based on the grid-side current phase angle information, determines the two phase currents that are most recently zero-crossing among the three-phase grid-side currents as the start and end times of the switching, while the other phase current satisfies the three-phase instantaneous current balance constraint condition. Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component calculated from the grid-side current value are used as current commands to achieve seamless switching of grid-side current zero crossing point in the energy storage system.

2. The seamless switching control method for charging and discharging of an energy storage system according to claim 1, characterized in that, The grid-side current phase angle information is obtained through a phase-locked loop.

3. The seamless switching control method for charging and discharging of an energy storage system according to claim 1, characterized in that, The d-axis current component and the q-axis current component are used as current command inputs to the current loop, and control signals are output through the current loop.

4. The seamless switching control method for charging and discharging of an energy storage system according to claim 1, characterized in that, The three-phase instantaneous current balance constraint condition is as follows: In the formula, Let a be the phase current. For phase b current, This represents the current in phase c.

5. The seamless switching control method for charging and discharging of an energy storage system according to claim 1, characterized in that, The two phases that most recently crossed zero in the grid-side three-phase current are phase a and phase c. When neither phase a nor phase c has crossed zero, the grid-side three-phase current maintains its original theoretical value.

6. The seamless switching control method for charging and discharging of an energy storage system according to claim 5, characterized in that, When phase a crosses zero and phase c does not cross zero, phase b satisfies the instantaneous current balance constraint condition.

7. The seamless switching control method for charging and discharging of an energy storage system according to claim 1, characterized in that, The overall time for seamless switching of the grid-side current at the zero-crossing point of the energy storage system is one-third of the power grid frequency cycle.

8. The seamless switching control method for charging and discharging of an energy storage system according to claim 7, characterized in that, The overall time for seamless switching of the grid-side current at the zero-crossing point of the energy storage system is obtained by determining the start and end times of the switching through phase locking.

9. A seamless charging and discharging switching controller for an energy storage system, characterized in that, It includes a judgment module and a calculation switching module, wherein: Judgment module: Used for the energy storage system to receive charge and discharge switching commands, and to determine the two phase currents that are most recently zero-crossing among the three phase currents on the grid side as the start and end times of switching based on the grid side current phase angle information, and the other phase current satisfies the three-phase instantaneous current balance constraint condition. Calculation and switching module: Based on the dual closed-loop control system architecture of grid-side voltage and current in the dq rotating coordinate system, the d-axis current component and q-axis current component are calculated based on the grid-side current value. The d-axis current component and q-axis current component are used as current commands to realize seamless switching of grid-side current zero crossing point of energy storage system.

10. A terminal device, comprising a memory, a processor, and a switching algorithm program stored in the memory and executable on the processor, characterized in that, When the processor executes the algorithm program, it implements the steps of the method as described in any one of claims 1-7.

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