Phase-splitting vsg control method, device, medium and equipment for cascaded energy storage system

Abstract

The application relates to the field of power electronics and new energy grid connection technology, and discloses a kind of cascaded energy storage system's partial phase VSG control method, device, medium and equipment, cascaded energy storage system is star type cascaded H bridge topology structure, three-phase circuit is decoupled and equivalent as single-phase control unit, and partial phase VSG model is constructed based on circuit parameter;According to phase voltage current sampling value, calculate instantaneous power, input to active-frequency ring and reactive-voltage ring to generate initial voltage reference value and current given value;In current given value, superimpose the compensation amount of the reverse zero sequence component to obtain target current, carry out pulse width modulation to obtain switch driving signal;Based on switch driving signal control system operation, according to operating state information, determine stability margin, when the margin is lower than the preset threshold, adjust control ring parameter.The above-mentioned method realizes the fast, stable, adaptive control of cascaded energy storage system under unbalanced power grid condition.

Description

Technical Field

[0001] This invention relates to the field of power electronics and new energy grid connection technology, and in particular to a phase-separated VSG control method, device, medium and equipment for a cascaded energy storage system. Background Technology

[0002] With the deepening of the dual-carbon strategy, a new power system based on new energy sources is being built at an accelerated pace, and the grid-connected scale of renewable energy sources such as photovoltaics and wind power continues to expand. However, the inherent strong randomness, volatility, and intermittency of new energy power generation lead to the low inertia and weak damping characteristics of their grid-connected converters, which poses a severe challenge to the frequency stability and voltage support of the power grid. Cascaded H-bridge energy storage systems, with their modular structure and ease of achieving direct grid connection to medium and high voltage, have shown broad application prospects in the field of large-capacity energy storage. In the core control link, cascaded H-bridge energy storage converters widely adopt virtual synchronous generator (VSG) control technology. By simulating the inertia and damping response of synchronous generators, the active support capability of grid-connected converters for the power grid is enhanced, and the system operation stability is improved.

[0003] In actual engineering operations, the grid voltage often exhibits varying degrees of imbalance due to non-ideal operating conditions such as asymmetrical faults and load imbalances. To address this, existing VSG control strategies generally introduce positive and negative sequence component separation, such as the commonly used T / 4 delay method, to achieve independent control of positive and negative sequence components. However, such methods rely on a fixed calculation cycle to extract sequence components, causing control commands to lag behind the real-time changes in the grid state. Especially during transient processes, the inherent lag effect easily exacerbates power overshoot, leading to system oscillations or even instability, making it difficult to meet the application requirements of high dynamic response scenarios. At the same time, for star-connected cascaded H-bridge topologies, the structure itself does not provide a zero-sequence current path. When conventional phase-sequence control schemes are applied to this topology, they introduce additional zero-sequence components into the current commands of each phase, causing the control target to deviate, making it difficult to directly apply existing phase-sequence strategies. Although some research has attempted to improve this through zero-sequence voltage compensation or zero-sequence current correction, these methods still generally suffer from drawbacks such as slow dynamic response, complex control logic, and high computational overhead.

[0004] Therefore, a phase-sequence VSG control method that can realize a cascaded energy storage system with no delay and no zero-sequence interference is urgently needed. Summary of the Invention

[0005] In view of this, this application provides a phase-separated VSG control method, device, medium and equipment for a cascaded energy storage system. The main purpose is to solve the technical problems of existing VSG control strategies having control lag and zero-sequence interference under unbalanced grid conditions, resulting in poor transient stability and difficulty in being applied to star-cascaded H-bridge topologies.

[0006] According to a first aspect of the present invention, a phase-separated VSG control method for a cascaded energy storage system is provided, wherein the cascaded energy storage system is a star-cascaded H-bridge topology, comprising: The three-phase circuits of the star-cascaded H-bridge topology are decoupled and equivalent to three independent single-phase control units. A phase-separated virtual synchronous generator control model is constructed based on the circuit parameters of the single-phase control units. Based on the phase-splitting virtual synchronous generator control model, the instantaneous phase power is calculated according to the phase voltage sampling value and the phase current sampling value, and the instantaneous phase power is input to the active-frequency control loop and the reactive-voltage control loop respectively to generate an initial voltage reference value, and the corresponding current setpoint is generated according to the initial voltage reference value. The zero-sequence component in the current setpoint is detected, and a compensation amount opposite to the zero-sequence component is superimposed on the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. The target phase current setpoint is then used for pulse width modulation control to obtain a switch drive signal. The cascaded energy storage system is controlled based on the switch drive signal, and the stability margin is determined based on the operating status information of the cascaded energy storage system. When the stability margin is lower than a preset threshold, the control parameters of the active power-frequency control loop and / or the reactive power-voltage control loop are adjusted.

[0007] According to a second aspect of the present invention, a phase-separated VSG control device for a cascaded energy storage system is provided, wherein the cascaded energy storage system is a star-cascaded H-bridge topology, comprising: The phase-separated modeling module is used to decouple the three-phase circuit of the star-cascaded H-bridge topology and convert them into three independent single-phase control units, and to construct a phase-separated virtual synchronous generator control model based on the circuit parameters of the single-phase control units. The instruction generation module is used to calculate the instantaneous phase power based on the phase voltage sampling value and the phase current sampling value according to the phase-splitting virtual synchronous generator control model, and input the instantaneous phase power to the active-frequency control loop and the reactive-voltage control loop respectively to generate an initial voltage reference value, and generate a corresponding current setpoint based on the initial voltage reference value; The zero-sequence compensation module is used to detect the zero-sequence component in the current setpoint and superimpose a compensation amount that is opposite to the zero-sequence component into the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. The target phase current setpoint is used for pulse width modulation control to obtain a switch drive signal. The closed-loop control module is used to control the operation of the cascaded energy storage system based on the switch drive signal, and to determine the stability margin based on the operating status information of the cascaded energy storage system. When the stability margin is lower than a preset threshold, the control parameters of the active power-frequency control loop and / or the reactive power-voltage control loop are adjusted.

[0008] According to a third aspect of the present invention, a storage medium is provided on which a computer program is stored, which, when executed by a processor, implements the phase-separated VSG control method of the cascaded energy storage system described above.

[0009] According to a fourth aspect of the present invention, a computer device is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the program to implement the phase-separated VSG control method of the cascaded energy storage system described above.

[0010] This invention provides a phase-sequence VSG control method, device, medium, and equipment for a cascaded energy storage system. By decoupling the three-phase circuit of a star-cascaded H-bridge topology into three independent single-phase control units and constructing a phase-sequence virtual synchronous generator control model, it avoids dependence on a fixed calculation cycle and fundamentally eliminates the inherent control lag in the sequence component extraction stage, enabling control commands to follow grid state changes in real time. By detecting the zero-sequence component in the current setpoint and superimposing a reverse compensation amount to eliminate it, it solves the problem of control target deviation caused by the introduction of zero-sequence components in conventional phase-sequence control schemes in star topologies, making the phase-sequence control strategy directly applicable to star-cascaded H-bridge structures. By determining the stability margin based on operating state information and adaptively adjusting the control loop parameters when the value is below a preset threshold, a closed-loop control mechanism is formed from state perception to margin judgment and parameter adjustment. This mechanism can actively suppress power overshoot and system oscillation during transient processes, significantly improving the dynamic response speed and operational stability of the system under grid faults and unbalanced conditions. In summary, the above methods overcome the technical obstacles of slow dynamic response, poor topology adaptability, and insufficient transient stability of existing technologies, and realize fast, stable, and adaptive control of cascaded energy storage systems under unbalanced grid conditions.

[0011] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0012] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this application, illustrate exemplary embodiments of the invention and, together with their description, serve to explain the invention and do not constitute an undue limitation thereof. In the drawings: Figure 1 A schematic flowchart of a phase-separated VSG control method for a cascaded energy storage system provided in an embodiment of the present invention; Figure 2 A schematic flowchart of another phase-separated VSG control method for a cascaded energy storage system provided in an embodiment of the present invention; Figure 3 is a circuit diagram of the star-cascaded H-bridge topology in an embodiment of the present invention; Figure 4 This is a block diagram for calculating the three-phase current setpoint in an embodiment of the present invention; Figure 5 This is a diagram of a given current zero-sequence separation algorithm in an embodiment of the present invention; Figure 6 This is a phase separation control diagram based on zero-sequence separation in an embodiment of the present invention; Figure 7 This is the overall control block diagram of the phase-by-phase VSG control strategy for cascaded energy storage under unbalanced power grid in this embodiment of the invention; Figure 8 This is a block diagram of the VSG voltage and current loop frequency domain control in an embodiment of the present invention; Figure 9(a) is a Bode plot of the positive sequence output impedance of VSG in an embodiment of the present invention; Figure 9(b) is a Bode plot of the negative sequence output impedance of VSG in an embodiment of the present invention; Figure 10 This is the VSG equivalent small-signal circuit in the embodiment of the present invention; Figure 11(a) is a Bode plot of the positive sequence impedance of the VSG output in an embodiment of the present invention; Figure 11(b) is a Bode plot of the negative sequence impedance of the VSG output in an embodiment of the present invention; Figure 12(a) shows the Bode plot of the positive sequence VSG output impedance under the change of control parameter J in the embodiment of the present invention; Figure 12(b) shows the Bode plot of the output impedance of the negative sequence VSG under the change of control parameter J in the embodiment of the present invention; Figure 12(c) shows the Bode plot of the positive sequence VSG output impedance under the change of control parameter D in the embodiment of the present invention; Figure 12(d) shows the Bode plot of the output impedance of the negative sequence VSG under the change of control parameter D in the embodiment of the present invention; Figure 13(a) is a comparison diagram of positive sequence output impedance in an embodiment of the present invention; Figure 13(b) is a comparison diagram of negative sequence output impedance in an embodiment of the present invention; Figure 14(a) is a waveform diagram of the grid voltage when the single-phase grid voltage drops suddenly in an embodiment of the present invention; Figure 14(b) is a waveform diagram of the VSG output voltage when the single-phase grid voltage drops suddenly in an embodiment of the present invention; Figure 14(c) is a waveform diagram of the VSG output current when the single-phase grid voltage drops suddenly in an embodiment of the present invention; Figure 14(d) is a waveform diagram of the output active power when the single-phase grid voltage drops suddenly in an embodiment of the present invention; Figure 15(a) is a waveform diagram of the grid voltage when the three-phase grid voltage drops symmetrically in an embodiment of the present invention; Figure 15(b) is a waveform diagram of the VSG output voltage when the three-phase grid voltage drops symmetrically in an embodiment of the present invention; Figure 15(c) is a waveform diagram of the VSG output current when the three-phase grid voltage drops symmetrically in an embodiment of the present invention; Figure 15(d) is a waveform diagram of the output active power when the three-phase grid voltage drops symmetrically in an embodiment of the present invention; Figure 16(a) is a waveform diagram of the VSG output voltage when the three phases are under unbalanced load in an embodiment of the present invention; Figure 16(b) is a waveform diagram of the VSG output current when the three phases are under unbalanced load in an embodiment of the present invention; Figure 16(c) is a waveform diagram of the active / reactive power output of VSG when the three-phase system is under unbalanced load in an embodiment of the present invention. Figure 17 This diagram illustrates the structure of a phase-separated VSG control device for a cascaded energy storage system according to an embodiment of the present invention. Figure 18 A schematic diagram of the device structure of a computer device provided in an embodiment of the present invention is shown. Detailed Implementation

[0013] Exemplary embodiments of the present application will now be described in more detail with reference to the accompanying drawings. While exemplary embodiments of the present application are shown in the drawings, it should be understood that the present application may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the scope of the present application to those skilled in the art.

[0014] This application provides a phase-separated VSG control method for a cascaded energy storage system. The cascaded energy storage system has a star-cascaded H-bridge topology, such as... Figure 1 As shown, the method includes the following steps: 101. Decouple the three-phase circuit of the star-cascaded H-bridge topology and convert them into three independent single-phase control units. Construct a phase-separated virtual synchronous generator control model based on the circuit parameters of the single-phase control units.

[0015] Among them, the star-cascaded H-bridge topology refers to the energy storage converter structure that is connected to the power grid by cascading multiple H-bridge power units in a star configuration. Its three-phase circuits are connected to a common neutral point, and each phase is electrically coupled through this neutral point. The phase-separated virtual synchronous generator control model refers to using a single-phase circuit as the basic control unit, and equating each phase to an independent virtual synchronous generator. Each phase has independent power angle characteristics and excitation regulation characteristics, thereby realizing independent control of the voltage amplitude and frequency of each phase. Specifically, in this application, the three-phase circuit decoupling is to split the three-phase circuits that were originally coupled to each other through the common neutral point into three independent single-phase control channels at the control level. The control operations of each channel do not affect each other and are executed in parallel.

[0016] Specifically, when establishing the phase-separated virtual synchronous generator control model, the three-phase circuit is first separated at the control level according to the circuit structure of the star-cascaded H-bridge topology, so that phases A, B, and C correspond to three independent single-phase control units. Then, for each single-phase control unit, the corresponding circuit parameters are extracted, including the filter inductance value, filter capacitor value, line resistance value, and DC side voltage of the cascaded H-bridge. Based on these parameters, the electrical model of each phase virtual synchronous generator is constructed, and the stator voltage equation and rotor motion equation of each phase virtual synchronous generator are determined. This ensures that each phase has independent virtual inertia, virtual damping, and voltage regulation capabilities, providing a model basis for subsequent active-frequency control and reactive-voltage control of each phase.

[0017] In this embodiment, by decoupling the three-phase circuit and establishing a phase-sequence virtual synchronous generator control model, independent control of each phase can be achieved without relying on the separation of positive and negative sequence components. This directly avoids the fixed calculation cycle required by the traditional T / 4 delay method, fundamentally eliminating the inherent control lag in the sequence component extraction stage, and enabling control commands to follow the changes in grid status in real time. At the same time, the phase-sequence model completely decouples the regulation of voltage and power in each phase, and single-phase grid disturbances will not spread to other phases through the coupling mechanism, thereby enhancing the system's ability to resist single-phase faults. In addition, the model architecture based on the single-phase control unit also provides structural support for the subsequent independent execution of zero-sequence component detection and compensation in each phase, enabling the entire control scheme to adapt to the special structural constraints of the star-cascaded H-bridge topology.

[0018] 102. Based on the phase-separated virtual synchronous generator control model, the instantaneous phase power is calculated according to the phase voltage sampling value and the phase current sampling value. The instantaneous phase power is then input to the active-frequency control loop and the reactive-voltage control loop respectively to generate the initial voltage reference value. The corresponding current setpoint is generated according to the initial voltage reference value.

[0019] In this context, instantaneous phase power refers to the product of instantaneous voltage and instantaneous current in a single-phase circuit, including two components: instantaneous active power and instantaneous reactive power. The active-frequency control loop is a control loop that simulates the function of a synchronous generator speed governor. It adjusts the output frequency and phase angle of the virtual synchronous generator according to the active power deviation, enabling the converter to have inertia and primary frequency regulation capability. The reactive-voltage control loop is a control loop that simulates the function of a synchronous generator excitation regulator. It adjusts the output voltage amplitude of the virtual synchronous generator according to the reactive power deviation, enabling the converter to have voltage support capability. Specifically, in this application, the initial voltage reference value refers to the ideal voltage waveform signal output by the virtual synchronous generator model without subsequent correction, and the current setpoint refers to the target current command signal provided to the inner current loop to achieve effective tracking control of the output current.

[0020] Specifically, based on the phase-separated virtual synchronous generator control model, the instantaneous phase voltage and phase current values ​​of each single-phase control unit are first obtained through voltage and current sampling channels. These are then multiplied to obtain the instantaneous phase power value. The active and reactive components of the instantaneous power are then separated. Subsequently, the active power component is fed into the active-frequency control loop. Based on virtual inertia and virtual damping parameters, the control loop calculates the real-time angular frequency and phase angle offset of the virtual synchronous generator according to the deviation of the active power. The reactive power component is fed into the reactive-voltage control loop. Based on the deviation of the reactive power, the control loop calculates the voltage amplitude adjustment of the virtual synchronous generator. The calculated phase angle and voltage amplitude are then combined to generate the initial voltage reference value for this phase within the current control cycle. Based on this, the initial voltage reference value is compared with the current actual phase voltage sampling value. Proportional-integral control is performed on the difference between the two to generate the current setpoint corresponding to the difference, which serves as the tracking target for the subsequent current inner loop.

[0021] In this embodiment, by sending the active and reactive components of instantaneous power to their respective control loops for processing, a complete simulation of the inertia and damping characteristics of a virtual synchronous generator is achieved. This enables the cascaded energy storage system to have active frequency and voltage support capabilities, improving the low inertia and weak damping operation characteristics of the new energy grid-connected converter. Simultaneously, by using a phase-independent method to calculate the instantaneous power of each phase and adjust its own control loop, the active and reactive power of each phase can be independently controlled. When a voltage drop or phase change occurs in a phase of the grid, the control command only responds and adjusts within the corresponding phase, without affecting the control output of other phases through cross-coupling. This improves the system's adaptability to grid imbalance conditions and its dynamic response performance. Furthermore, by comparing the initial voltage reference value with the actual voltage sample value and executing proportional-integral control to obtain the current setpoint, an accurate tracking target is provided for the inner current loop, ensuring the coordination and unity of the voltage outer loop control accuracy and the current inner loop response speed.

[0022] 103. Detect the zero-sequence component in the current setpoint and superimpose a compensation amount that is opposite to the zero-sequence component into the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. Use the target phase current setpoint for pulse width modulation control to obtain the switch drive signal.

[0023] Among them, the zero-sequence component refers to the component with the same amplitude and phase in a three-phase system. It appears when the sum of the three-phase currents is not zero, reflecting the common-mode component in the three-phase current that cannot be explained by the positive-sequence and negative-sequence components. Specifically, in this application, the zero-sequence component in the current setpoint is generated by the independent adjustment of each phase after adopting phase-by-phase control. Its amplitude is equal to one-third of the sum of the three-phase current setpoints. The compensation amount refers to the reverse current value that is specially applied to cancel the zero-sequence component. Its amplitude is equal to the detected zero-sequence component value, and its direction is opposite to that of the zero-sequence component. The two superimposed can achieve complete cancellation of the zero-sequence component. Pulse width modulation control refers to comparing the target current setpoint with the actual current sampling value and generating a corresponding switching signal through a modulation strategy to control the conduction and cutoff of the power switching device.

[0024] Specifically, after obtaining the current setpoints for each phase, the three-phase current setpoints are first summed to obtain the total sum. Then, based on the principle of symmetrical component method, the sum is divided by three to extract the zero-sequence component contained in the current setpoint of this phase. Subsequently, a compensation amount equal in value but opposite in direction to the zero-sequence component is superimposed on each phase current setpoint. The compensation amount is the same in each phase, thereby completely canceling the zero-sequence component in each phase current setpoint, resulting in the target phase current setpoint after eliminating the zero-sequence component. Based on this, the difference between the target phase current setpoint and the current actual phase current sampling value is used as the current tracking error. After performing proportional-integral control on the error, a corresponding modulation wave signal is generated. The modulation wave is compared with the carrier wave to generate the drive signal of the corresponding power switching device, so as to control the output current of each phase of the cascaded energy storage system to track the target setpoint in real time.

[0025] In this embodiment, zero-sequence components are eliminated by superimposing reverse compensation on the current setpoint. This enables precise suppression of zero-sequence current without adding additional hardware circuitry, solving the problem that star-cascaded H-bridge topologies cannot directly apply phase-by-phase control due to the lack of a zero-sequence current path caused by structural limitations. This allows the phase-by-phase control strategy to be successfully transferred to star-cascaded H-bridge energy storage systems. Simultaneously, the compensation method acts directly on the current setpoint, without relying on indirect regulation of the modulation voltage, resulting in faster response and a simpler control structure. This avoids the drawbacks of existing zero-sequence voltage compensation methods, which require multiple coordinate transformations and complex calculations, effectively reducing the complexity and computational overhead of the control algorithm and facilitating engineering applications. Furthermore, by applying pulse width modulation control to the target phase current setpoint after eliminating the zero-sequence component, the sum of the three-phase output currents is ensured to be zero, eliminating the potential adverse effects of zero-sequence current on the power grid.

[0026] 104. Control the operation of the cascaded energy storage system based on the switch drive signal, and determine the stability margin based on the operating status information of the cascaded energy storage system. When the stability margin is lower than the preset threshold, adjust the control parameters of the active-frequency control loop and / or reactive-voltage control loop.

[0027] Among them, the operating status information refers to various electrical parameters and state variables that reflect the working status of the cascaded energy storage system during operation, including the output voltage, output current, active power, reactive power, frequency, phase angle, and DC side voltage of each phase. This information is obtained through sampling and calculation and is used to comprehensively perceive the current operating status of the system. The stability margin is a key indicator for measuring whether the system can maintain stable operation and the degree of stability after being disturbed. Specifically, it refers to the safety margin of the system from the stability boundary under a specific operating condition. The larger the value, the stronger the system's ability to resist disturbances. The smaller the value, the closer the system is to the instability boundary. The preset threshold is a safety limit value preset for the stability margin. It is used to determine whether the stability of the current operating status of the system meets the safety requirements. When the stability margin is lower than the threshold, it indicates that the system's stability reserve is insufficient and active control intervention is required. The control parameters of the active-frequency control loop and the reactive-voltage control loop refer to the adjustable coefficients that affect the response characteristics and stability of each control loop, including the virtual inertia coefficient, virtual damping coefficient, proportional coefficient, and integral coefficient.

[0028] Specifically, the switching drive signal output from the pulse width modulation stage is applied to the control terminals of each power switching device in the cascaded energy storage system, driving each phase cascaded H-bridge power unit to operate according to a predetermined switching sequence, realizing bidirectional energy conversion and grid-connected operation. During continuous system operation, various operating status information of the cascaded energy storage system is obtained in real time through sampling and calculation, including the output voltage, output current, active power, reactive power, and frequency of each phase, and the stability margin of the system under the current operating condition is determined according to preset calculation rules. When the stability margin is determined to be lower than the preset threshold, it indicates that the system has insufficient stability reserve under the current control parameters. At this time, the control parameters of the active-frequency control loop and / or reactive-voltage control loop are adaptively adjusted according to the preset adjustment strategy, including adjusting one or more of the virtual inertia coefficient, virtual damping coefficient, proportional coefficient, and integral coefficient, to increase the stability margin of the system under the corresponding operating condition to above the safe range, thus completing the closed-loop control of system stability.

[0029] In this embodiment, by determining the stability margin in real time during system operation and actively adjusting the control loop parameters when the margin is insufficient, a complete closed-loop control mechanism is formed, from state perception to margin judgment to parameter adjustment, ultimately achieving system optimization. This control mechanism enables the cascaded energy storage system to adaptively adjust the control strategy according to changes in grid operating conditions. When grid faults or disturbances cause a decrease in system stability, the system can actively intervene by adjusting key parameters such as virtual inertia and damping to enhance its ability to resist grid disturbances. This fundamentally suppresses power overshoot and system oscillations during transient processes, effectively avoiding the risk of system instability under adverse operating conditions due to fixed control parameters. It significantly improves the transient stability and dynamic response performance of the cascaded energy storage system under grid faults and unbalanced operating conditions.

[0030] This invention provides a phase-separated VSG control method for a cascaded energy storage system. By responding to the conduction signal generated when an effective electrical connection is formed between an external detection device and the target detection object, automatic start-up of screen recording is achieved. Screen recording initiation does not rely on manual clicks, and the start and stop of recording are controlled by the conduction signal received by the mobile terminal and the subsequent service process status. The recording timing cannot be manually selected or prematurely terminated, ensuring the integrity and objectivity of the recording process. The detection data collected in real-time by the external detection device is directly written into the pixel area corresponding to the original image frame in the form of pixel data. This writing operation is completed before compression encoding by the video encoder, making the detection data a component of the image pixel array. After encoding, the detection data and the screen recording are integrated into a unified whole. Since the detection data has been integrated with the screen at the pixel level before encoding, an inseparable binding relationship is formed between the two. There is no independent data file that can be replaced, nor can the subtitles that are superimposed later be removed or re-edited, thus ensuring the relevance and originality of the evidence. The accumulated hash value is continuously updated and stored in real time as the screen recording process progresses. Any data change at any moment during the screen recording process will produce a cascading reaction in the hash chain. Any tampering or deletion of local data can be detected in time. After the service is completed, the final accumulated hash value is written to the blockchain to achieve final solidification, eliminating the time window for local tampering or deletion and realizing trusted evidence storage throughout the entire process.

[0031] This application provides another method for phase-separated VSG control of cascaded energy storage systems, such as... Figure 2 As shown, it specifically includes: 201. Establish an equivalent model of star-shaped cascaded H-bridge energy storage phase VSG, and convert the three-phase system into three independent single-phase systems.

[0032] In one application scenario of this invention, when establishing the equivalent model of the star-cascaded H-bridge energy storage phase-separated VSG, phase-separated control is used to separate the star-cascaded H-bridge energy storage converter into three independent single-phase converters at the control level. Phase-separated control refers to splitting the three-phase circuit, which was originally coupled to each other through a common neutral point, into three independent single-phase control channels. Each channel performs its own voltage and current regulation. Each phase corresponds to three single-phase control units, namely phase A, phase B, and phase C. Each phase contains an independent filter inductor, filter capacitor, and cascaded H-bridge power unit. The common terminal of the filter inductor of each phase is connected to the neutral point of the power grid. The circuit parameters of each phase are independent and do not affect each other. Figures 3(a) and 3(b) show the structure diagram of the three single-phase circuits after phase-separated control and the equivalent circuit diagram of the three single-phase circuits, respectively. Figure 4The diagram below shows the calculation of the current setpoint when using phase-by-phase control. Specifically, firstly, reference values ​​for the three-phase voltages are generated using voltage-type VSG control. That is, each phase generates its initial voltage reference value based on its instantaneous power through the active-frequency control loop and the reactive-voltage control loop. Then, proportional-integral control is performed on the reference values ​​of the three-phase voltages to obtain the setpoint values ​​of the three-phase currents, which serve as the tracking targets for the inner loop of each phase current. Ideally, when the three-phase power grid and circuit parameters are perfectly symmetrical, the sum of the three-phase current setpoint values ​​is zero. Through the above phase-by-phase equivalence, grid disturbances or load changes occurring in one phase will not propagate to other phases through the coupling mechanism, significantly enhancing the system's ability to withstand single-phase faults. It also provides a structural basis for subsequent independent zero-sequence component detection and compensation for each phase, enabling the entire control scheme to adapt to the special structural constraints of the star-cascaded H-bridge topology.

[0033] 202. Generate independent current setpoints for each phase based on the phase split model.

[0034] Specifically, the phase voltage sampling values ​​include the inverter-side voltage sampling values ​​of the cascaded energy storage system and the voltage sampling values ​​of the virtual synchronous generator model; the phase current sampling values ​​include the inverter-side current sampling values ​​of the cascaded energy storage system and the current sampling values ​​of the virtual synchronous generator model.

[0035] In this embodiment, after establishing the phase-separated virtual synchronous generator control model, the voltage and current information of each single-phase control unit is first obtained through the sampling channel. The sampling values ​​specifically include the voltage and current sampling values ​​on the inverter side and the voltage and current sampling values ​​on the virtual synchronous generator model side. The inverter side sampling values ​​are used to reflect the actual output state of the power unit, and the VSG model side sampling values ​​are used to reflect the ideal output state of the virtual synchronous generator model. The two together constitute the data basis for subsequent power calculation and closed-loop control. Based on the above sampling values, the instantaneous power of each phase is calculated, and the active and reactive components of the instantaneous power of each phase are input to the active-frequency control loop and reactive-voltage control loop of this phase, respectively. The active-frequency control loop generates the real-time angular frequency and phase angle offset of the virtual synchronous generator according to the active power deviation, and the reactive-voltage control loop generates the voltage amplitude adjustment according to the reactive power deviation. The calculated phase angle and voltage amplitude are combined to generate the initial voltage reference value of each phase. Subsequently, proportional-integral control is performed on the initial voltage reference values ​​of each phase to obtain the corresponding current setpoints, which serve as the tracking targets for the inner current loop. When the three-phase power grid and circuit parameters are perfectly symmetrical, the sum of the three-phase current setpoints is zero. When the grid voltage does not meet the preset balance condition, the three-phase current setpoints contain positive-sequence, negative-sequence, and zero-sequence components, and the sum of the three-phase current setpoints is equal to three times the zero-sequence component. Therefore, the zero-sequence component in the current setpoints must be eliminated during phase-by-phase control.

[0036] 203. Implement phase-sequence VSG control for star-cascaded H-bridge energy storage converters based on zero-sequence separation. Eliminate zero-sequence components by using the given current zero-sequence separation method to achieve precise phase-sequence control.

[0037] Specifically, proportional-integral control is performed on the initial voltage reference value to obtain the current setpoint value of the corresponding phase; when the grid voltage meets the preset balance condition, the sum of the three-phase current setpoint values ​​is zero; when the grid voltage does not meet the preset balance condition, the three-phase current setpoint values ​​all include positive sequence components, negative sequence components and zero sequence components, and the sum of the three-phase current setpoint values ​​is equal to three times the zero sequence component.

[0038] Furthermore, the compensation amounts superimposed in the three-phase current setpoints are equal, and the sum of the three-phase target phase current setpoints is zero.

[0039] In this embodiment, because phase-by-phase control is used in the current setpoint generation stage, each phase is adjusted independently. When the grid voltage is unbalanced, the current setpoint of each phase will inevitably contain positive-sequence, negative-sequence, and zero-sequence components. At this time, the sum of the three-phase current setpoints is no longer zero, but equal to three times the zero-sequence component, i.e.

[0040] In the formula, (n=a, b, c) are the given values ​​for the three-phase current. , , (n=a, b, c) represent the positive sequence component, negative sequence component, and zero sequence component of the three-phase current, respectively.

[0041] At this time, the sum of the given values ​​of the three-phase currents is:

[0042] In the formula, This represents the zero-sequence component of the current.

[0043] Therefore, the star-cascaded H-bridge energy storage converter cannot be simply equivalent to three single-phase converters for control. The zero-sequence component in the current setpoint must be eliminated simultaneously with phase-by-phase control; otherwise, the presence of the zero-sequence component will cause the sum of the three-phase current setpoints to be non-zero, leading to deviation from the control objective and affecting the normal operation of the system. To eliminate the zero-sequence component, two methods can be used: one is to superimpose reverse zero-sequence voltages onto the three-phase modulation voltages, indirectly eliminating the zero-sequence component in the current setpoint through a voltage path; the other is to directly superimpose reverse zero-sequence currents onto the three-phase current setpoints, directly canceling the zero-sequence component. Compared to the modulation voltage zero-sequence separation method, the given current zero-sequence separation method acts directly on the current setpoint level, without the need for indirect conversion through a voltage link, resulting in a faster response speed. Therefore, this invention preferably adopts the given current zero-sequence separation method.

[0044] Specifically, let the sum of the three-phase current setpoints before zero-sequence separation be... I Lz After zero-sequence separation, the sum of the three-phase current setpoints is I L1 Specifically, it satisfies the following formula:

[0045]

[0046] In the formula, , , These are the current setpoints for phases a, b, and c, respectively, when zero-sequence separation is not performed; , , These are the current setpoints for phases a, b, and c after zero-sequence separation.

[0047] To eliminate the zero-sequence component in the given current and achieve phase-by-phase control, a reverse zero-sequence current is superimposed on the current setpoint of each phase, resulting in:

[0048] In the formula, , , It is the proportionality coefficient of the superimposed reverse zero-sequence current of each phase.

[0049] when + + When =1, we can obtain:

[0050] At this point, the sum of the three-phase given currents after zero-sequence separation is zero.

[0051] Theoretically, adding a reverse zero-sequence current to the current setpoint of each phase can completely eliminate the zero-sequence current in the three-phase current setpoint. Ignoring the differences in losses between phases, then... = = =1 / 3.

[0052] In summary, to achieve zero-sequence separation, the zero-sequence component contained in the current setpoint of each phase is first detected. Then, a compensation amount opposite in direction to the zero-sequence component is superimposed on the current setpoint of each phase. The superimposed compensation amounts for each phase are equal, thus making the sum of the three-phase current setpoints zero. Ignoring the differences in losses between phases, the superimposed compensation amount for each phase is one-third of the amplitude of the zero-sequence component contained in the phase current setpoint. Figure 5 This illustrates the specific implementation of the zero-order separation algorithm. Figure 6 This is a block diagram of phase-sequence control based on zero-sequence separation. Figure 7 The diagram shows the overall control block diagram of the phase-sequence VSG control strategy for cascaded energy storage under unbalanced power grids. Through the above zero-sequence separation process, phase-sequence control no longer requires complex steps such as sector judgment and amplitude calculation. The control structure is simple and the calculation is small. Theoretically, it can completely eliminate the zero-sequence component in the current setpoint, effectively avoiding system instability caused by factors such as amplitude calculation errors. At the same time, each phase of the system after phase-sequence control has independent voltage and current regulation capabilities, and can independently adjust the control output according to the operating conditions of each phase, thereby accurately adapting to the phase-sequence control requirements under unbalanced power grids.

[0053] 204. Perform phase-sequence VSG impedance modeling and stability analysis, establish positive and negative sequence impedance models, and use the Nyquist criterion to analyze system stability.

[0054] Specifically, a harmonic linearization method is used to inject a voltage disturbance signal into the grid side of the cascaded energy storage system, obtain the current response signal corresponding to the voltage disturbance signal, and establish the output impedance model of the cascaded energy storage system based on the ratio of the voltage disturbance signal to the current response signal; the stability margin of the cascaded energy storage system when interacting with the grid impedance is determined based on the output impedance model.

[0055] Furthermore, the output impedance model includes a positive-sequence output impedance model and a negative-sequence output impedance model. The positive-sequence output impedance model is obtained based on the voltage and current dual closed-loop control transfer function of the cascaded energy storage system, and the negative-sequence output impedance model is obtained from the positive-sequence output impedance model based on the frequency mapping relationship between the positive and negative-sequence impedances.

[0056] Furthermore, the stability margin includes positive-sequence stability margin and negative-sequence stability margin; the positive-sequence stability margin is output according to the positive-sequence output impedance model, and the negative-sequence stability margin is output according to the negative-sequence output impedance model.

[0057] In this embodiment, to analyze the operational stability of the cascaded energy storage system under a weak power grid after successful phase-splitting control, this application employs impedance analysis and uses a harmonic linearization method to establish the system's output impedance model. Considering the weak grid characteristics, the influence of grid impedance on system stability is not negligible. Frequency coupling effects are not considered during modeling. After phase-splitting control, the three-phase converter is equivalent to three independent and identical single-phase converters. Taking the A-phase single-phase converter as an example, a frequency f is applied on the grid side... p voltage disturbance V p The disturbance will generate a corresponding current response I in the system. p The output impedance is described by calculating the ratio of voltage disturbance to current response; after the disturbance is added, the output voltage of phase A... and output current The time-domain expressions are as follows:

[0058] In the formula, It is the time-domain expression of the fundamental voltage. This is the time-domain expression for the fundamental current, where ^ represents the small-signal component. and Frequency The amplitudes of the fundamental frequency voltage and fundamental frequency current. and Frequency The magnitude and initial phase angle of the positive-sequence disturbance voltage. and Frequency The amplitude and initial phase angle of the time-sequence disturbance current response. For frequency The initial phase angle of the time base wave current.

[0059] Rewriting the time-domain expression in the frequency domain yields the following equation:

[0060]

[0061] In the formula, frequency domain phasor , , , With time domain amplitude , , , The condition V1 = / 2, Vp=( / 2)e ±jφvp , =( / 2)e ±jφi1 Ip=( / 2)e ±jφip φvp, φi1, and φip are the initial phase angles of the disturbance voltage, fundamental current, and disturbance current response, respectively. ±jφ These correspond to the positive and negative frequency components in the frequency domain, respectively.

[0062] Further transforming the frequency domain expression to the αβ coordinate system, we get:

[0063]

[0064] Based on instantaneous power theory, the output active power of VSG is... P e and reactive power Q e The calculation is as follows:

[0065] In the formula, and The output voltage is respectively at shaft and Components on the axis, and The output current is respectively at shaft and Components on the axis.

[0066] Substituting the frequency domain expressions into the output active and reactive power of the VSG, the instantaneous active power disturbance can be expressed as:

[0067] In the formula, superscript It represents the conjugate of a complex number.

[0068] Considering that the output frequency of the VSG is forcibly synchronized to the grid frequency during grid-connected operation, with an allowable deviation of ±0.05Hz, the frequency regulation function of the virtual speed governor automatically fails under this condition. Therefore, the expression for the VSG output phase angle can be obtained as follows:

[0069] In the formula, s is the Laplace operator, M(s) is the frequency domain transfer function of the VSG rotor motion equation, which describes the response characteristics of the phase angle to the power deviation under the combined action of virtual inertia and damping, and P m P is the given power reference value for the VSG active-frequency loop. e The VSG electromagnetic power is the active component of the instantaneous power calculated from the sampled values. Where is the rated angular frequency of the VSG output, for example, 50Hz corresponds to 314.16 rad / s; D is the virtual damping coefficient used to simulate the damping winding's suppression of oscillations in a synchronous generator; J is the virtual inertia coefficient used to simulate the rotor inertia's resistance to frequency changes in a synchronous generator; P... m / and P e / These represent the virtual mechanical torque and electromagnetic torque, respectively, and the difference between them is related to the damping torque D. 0 together constitute the rotor motion balance relationship of VSG.

[0070] The disturbance signal will cause a response at the terminals of the power loop and participate in the generation of the reference voltage. After the disturbance is injected, the VSG output phase angle θ Phase angle of fundamental voltage θ 1 and disturbance phase angle Δ θ Composed of two parts, by transforming the VSG output phase angle to the frequency domain and substituting the instantaneous active power disturbance, the expression for the VSG output disturbance phase angle in the frequency domain can be obtained as follows:

[0071] Where Δθ is a small disturbance caused by harmonic disturbance, therefore the frequency domain expression of θ is:

[0072] Therefore, without considering frequency coupling, we can obtain:

[0073] In the formula, Output phase angle for VSG The expression in the frequency domain represents the frequency domain component of the phase angle at frequency f. This is the transfer function or composite coefficient of the power loop.

[0074] The reactive power output of a voltage-controlled VSG is determined by the voltage amplitude difference across the filter inductor. In actual devices, the filter inductor value is relatively small, resulting in a smaller voltage amplitude difference, which reduces voltage fluctuation at the VSG output. Therefore, in modeling and analysis, the amplitude obtained by the VSG reactive loop can be considered essentially constant. The A-phase reference voltage generated by the voltage-controlled VSG can then be expressed as:

[0075] In the formula, Let E be the disturbance component of the A-phase reference voltage in the frequency domain, and let E be the voltage amplitude output by the VSG reactive power loop.

[0076] Taking into account the existence of the voltage and current dual closed loops, the frequency domain control block diagram is as follows: Figure 8 As shown, the converter gain Kpwm Taking 1, the expression for the current loop PI controller Gi(s) is k. pi +k ii / s,k pi k is the proportionality coefficient. ii For the integral coefficient, the expression for the voltage loop PI controller Gu(s) is k. pu +k iu / s,k pu and k iu These are the proportional and integral coefficients, respectively, from which the voltage-current loop transfer function G can be obtained. ui (s) is:

[0077] In the formula, G ui (s) is the equivalent transfer function of the voltage-current loop, representing the transfer from the reference voltage u ref Frequency domain transfer relationship to the converter output voltage u , and These represent the filter inductance value, filter capacitor value, and equivalent series resistance of the filter inductance, respectively. A, B, C, D, and E are intermediate coefficients composed of system circuit parameters and control parameters, used to simplify the denominator polynomial of the transfer function.

[0078] After voltage and current control, the VSG output voltage is as follows:

[0079] Combining the A-phase reference voltage generated by the voltage-type VSG with the VSG output voltage, the positive sequence impedance can be expressed as:

[0080] In the formula, The initial phase angle of the fundamental current is represented by a complex exponential form, indicating the phase information of the fundamental current in the frequency domain.

[0081] Based on this, and according to the frequency mapping relationship between positive and negative sequence impedances, the negative sequence impedance of VSG can be obtained as follows:

[0082] The positive-sequence output impedance model of the VSG is shown in Figure 9(a), and the negative-sequence output impedance model of the VSG is shown in Figure 9(b). Figure 10 For the equivalent small-signal circuit of VSG, after obtaining the positive and negative sequence output impedance models, the Nyquist stability criterion is used to analyze the impedance ratio of the system to study the system stability. When the grid impedance Z gp (s) and VSG output impedance Z gnThe system is stable when the ratio of (s) satisfies the Nyquist stability criterion, that is, when the magnitudes of the grid impedance and the VSG output impedance intersect, it is determined whether the phase difference between the grid impedance and the VSG impedance is less than 180°, and the phase margin at the intersection point is:

[0083] In the formula, Z gp (f) and Z gn (f) represents the positive-sequence impedance and negative-sequence impedance of the power grid, respectively, Z p (f) and Z n (f) represents the positive-sequence output impedance and the negative-sequence output impedance of the VSG, respectively. This represents the phase margin at the corresponding frequency f.

[0084] As shown in Figure 11(a), the solid line represents the VSG output impedance, and the dashed line represents the grid impedance. The phase margins at intersections A and B are 103° and 123°, respectively, indicating that the system has good stability margins at these two intersections and can effectively cope with dynamic situations such as load changes and small fluctuations in grid voltage, reducing the occurrence of instability phenomena such as oscillations. The phase margin at intersection C is approximately 24°. Although the regulation capability is relatively weaker than at intersections A and B, the system still has a certain degree of stability and can maintain normal operation. As shown in Figure 11(b), the phase margin at intersection D is approximately 24°, and the system can also operate stably. Both the positive and negative sequence phase margins meet the impedance stability criterion, so the system can operate stably. In addition, the VSG output impedance model is affected by multiple control parameters. Under the premise of keeping the voltage and current control parameters constant and ignoring the influence of the reactive voltage loop, the influence of different VSG control parameters on the output impedance can be studied. As shown in Figure 12(a), keeping other parameters constant, in the low-frequency range, as the virtual inertia J increases, the amplitude of the positive sequence output impedance of the VSG increases and the phase decreases. In the mid-to-high frequency range, the amplitude and phase of the positive sequence output impedance are almost unaffected by J. The amplitude increases with the frequency, while the phase remains unchanged. As shown in Figure 12(b), in the low-frequency range, the amplitude and phase of the negative sequence output impedance decrease with the increase of J. The variation law in the mid-to-high frequency range is consistent with that of the positive sequence impedance. As shown in Figures 12(c) and 12(d), the amplitude and phase of the positive and negative sequence impedances are almost unaffected by the damping coefficient D. In the mid-to-high frequency range, the amplitude increases with the frequency, while the phase remains unchanged.

[0085] 205. Verify the control strategy through simulation.

[0086] To verify the accuracy of the established impedance model, a harmonic injection method was used for simulation. Under the conditions of an ideal power grid and stable grid-connected operation of the energy storage converter, a harmonic disturbance of a specific frequency was injected into the grid side. The output current will contain the current response of that frequency. FFT analysis was performed on the output current response to obtain the amplitude and phase of the harmonic current of that frequency. The output impedance of the energy storage converter at that frequency was obtained by dividing the disturbance voltage by the response current. By changing the injected harmonic frequency, the measurement characteristic curve of the output impedance can be obtained; as shown in Figures 13(a) and 13(b), the red solid line represents the VSG output impedance Z. pn The theoretical model is shown, with the black dotted line representing the simulation measurement results. The theoretical derivation values ​​are in good agreement with the simulation measurement results, verifying the accuracy of the established impedance model. When the single-phase grid voltage drops by 10%, the simulation results of the proposed phase-by-phase VSG control strategy are as follows: Figures 14(a) to 14(d) As shown, phase-by-phase control does not require separation of positive and negative sequences; the power of the faulty phase can be quickly adjusted by directly tracking the phase voltage. When the three-phase grid voltage drops symmetrically by 10%, such as Figures 15(a) to 15(d) As shown, phase-separated control directly responds to the symmetrical voltage drop of the three-phase system, while simultaneously limiting active power output more quickly through independent phase limiting, suppressing overshoot. This indicates that when the grid voltage undergoes a sudden change, the proposed control strategy can eliminate the inherent delay defect of the T / 4 delay method, significantly improving the system's stability and dynamic response speed during transient processes, making it more suitable for operating conditions with sudden grid voltage changes. When the three phases are equipped with an unbalanced load, such as... Figures 16(a) to 16(c) As shown, when the system switches from a balanced load to an unbalanced load under grid-connected operation in 0.5s, the peak reactive power of the system is about 15kVar. When the system switches to off-grid status in 0.7s, the VSG output voltage is close to balanced. This indicates that the proposed control strategy can effectively reduce the imbalance of the VSG output voltage and suppress the transient overshoot caused by the T / 4 delay. The overall dynamic response is faster and the accuracy is higher.

[0087] Furthermore, as Figure 1 In specific implementation of the method, this application provides a phase-separated VSG control device for a cascaded energy storage system, such as... Figure 17 As shown, the device includes: a phase-sequence modeling module 301, an instruction generation module 302, a zero-sequence compensation module 303, and a closed-loop control module 304.

[0088] The phase-separated modeling module 301 is used to decouple the three-phase circuit of the star-cascaded H-bridge topology and convert them into three independent single-phase control units, and to construct a phase-separated virtual synchronous generator control model based on the circuit parameters of the single-phase control units. The instruction generation module 302 is used to calculate the instantaneous phase power based on the phase voltage sampling value and the phase current sampling value according to the phase-separated virtual synchronous generator control model, and input the instantaneous phase power to the active-frequency control loop and the reactive-voltage control loop respectively to generate the initial voltage reference value, and generate the corresponding current setpoint value based on the initial voltage reference value; The zero-sequence compensation module 303 is used to detect the zero-sequence component in the current setpoint and superimpose a compensation amount that is opposite to the zero-sequence component into the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. The target phase current setpoint is used for pulse width modulation control to obtain the switch drive signal. The closed-loop control module 304 is used to control the operation of the cascaded energy storage system based on the switch drive signal, and to determine the stability margin based on the operating status information of the cascaded energy storage system. When the stability margin is lower than the preset threshold, the control parameters of the active-frequency control loop and / or reactive-voltage control loop are adjusted.

[0089] In specific application scenarios, the phase voltage sampling values ​​in the instruction generation module 302 include the inverter-side voltage sampling values ​​of the cascaded energy storage system and the voltage sampling values ​​of the virtual synchronous generator model; the phase current sampling values ​​include the inverter-side current sampling values ​​of the cascaded energy storage system and the current sampling values ​​of the virtual synchronous generator model.

[0090] In specific application scenarios, the instruction generation module 302 is specifically used to perform proportional-integral control on the initial voltage reference value to obtain the current setpoint value of the corresponding phase; when the grid voltage meets the preset balance condition, the sum of the three-phase current setpoint values ​​is zero; when the grid voltage does not meet the preset balance condition, the three-phase current setpoint values ​​all include positive sequence components, negative sequence components and zero sequence components, and the sum of the three-phase current setpoint values ​​is equal to three times the zero sequence component.

[0091] In specific application scenarios, the compensation amounts superimposed on the three-phase current setpoints in the instruction generation module 302 are equal, and the sum of the three-phase target phase current setpoints is zero.

[0092] In specific application scenarios, the closed-loop control module 304 is used to inject voltage disturbance signals into the grid side of the cascaded energy storage system using the harmonic linearization method, obtain the current response signal corresponding to the voltage disturbance signal, establish the output impedance model of the cascaded energy storage system based on the ratio of the voltage disturbance signal to the current response signal, and determine the stability margin of the cascaded energy storage system when interacting with the grid impedance based on the output impedance model.

[0093] In specific application scenarios, the output impedance model includes a positive-sequence output impedance model and a negative-sequence output impedance model; the closed-loop control module 304 is specifically used to obtain the positive-sequence output impedance model based on the voltage and current dual closed-loop control transfer function of the cascaded energy storage system, and to obtain the negative-sequence output impedance model from the positive-sequence output impedance model based on the frequency mapping relationship between the positive and negative-sequence impedances.

[0094] In specific application scenarios, the stability margin includes positive-sequence stability margin and negative-sequence stability margin; the closed-loop control module 304 is specifically used to output the positive-sequence stability margin according to the positive-sequence output impedance model and the negative-sequence stability margin according to the negative-sequence output impedance model.

[0095] It should be noted that other corresponding descriptions of the functional units involved in the phase-separated VSG control device of the cascaded energy storage system provided in this embodiment can be found in [reference]. Figure 1 and Figure 2 The corresponding descriptions in [the document] will not be repeated here.

[0096] Based on the above, Figure 1 and Figure 2 Accordingly, this embodiment also provides a storage medium storing a computer program that, when executed by a processor, implements the phase-separated VSG control method of the cascaded energy storage system described above.

[0097] Based on this understanding, the technical solution of this application can be embodied in the form of a software product. The software product can be stored in a non-volatile storage medium (such as CD-ROM, USB flash drive, mobile hard drive, etc.) and includes several instructions to enable a computer device (such as personal computer, server, or network device, etc.) to execute the phase-by-phase VSG control method of the cascaded energy storage system in various implementation scenarios of this application.

[0098] Based on the above, Figure 1 and Figure 2 The method shown, and Figure 17 The illustrated embodiment of the phase-separated VSG control device for the cascaded energy storage system, in order to achieve the above objectives, as shown... Figure 18 As shown, this embodiment also provides a physical device for phase-separated VSG control of cascaded energy storage. This device includes a communication bus, a processor, a memory, and a communication interface. It may also include input / output interfaces and a display device. The various functional units can communicate with each other via the bus. The memory stores a computer program, and the processor executes the program stored in the memory to perform the phase-separated VSG control method of the cascaded energy storage system described in the above embodiment.

[0099] Optionally, the physical device may also include a user interface, a network interface, a camera, radio frequency (RF) circuitry, sensors, audio circuitry, a Wi-Fi module, etc. The user interface may include a display screen, input units such as a keyboard, etc., and optional user interfaces may also include USB interfaces, card reader interfaces, etc. The network interface may optionally include standard wired interfaces, wireless interfaces (such as Wi-Fi interfaces), etc.

[0100] Those skilled in the art will understand that the cascaded energy storage phase-separated VSG control physical device structure provided in this embodiment does not constitute a limitation on the physical device, and may include more or fewer components, or combine certain components, or have different component arrangements.

[0101] The storage medium may also include an operating system and a network communication module. The operating system is a program that manages the hardware and software resources of the aforementioned physical device, supporting the operation of information processing programs and other software and / or programs. The network communication module is used to enable communication between the various components within the storage medium, as well as communication with other hardware and software in the information processing physical device.

[0102] Through the above description of the embodiments, those skilled in the art can clearly understand that this application can be implemented by means of software plus necessary general-purpose hardware platforms, or it can be implemented by hardware. By applying the technical solution of this application, by decoupling the three-phase circuit of the star-cascaded H-bridge topology into three independent single-phase control units and constructing a phase-separated virtual synchronous generator control model, the dependence on fixed calculation cycles is avoided, fundamentally eliminating the control lag inherent in the sequence component extraction stage, and enabling the control command to follow the changes in the grid state in real time; by detecting the zero-sequence component in the current setpoint and superimposing a reverse compensation amount to eliminate it, the problem of the control target deviation caused by the introduction of zero-sequence components in the star topology of conventional phase-separated control schemes is solved, and the phase-separated control strategy can be directly applied to the star-cascaded H-bridge structure; by determining the stability margin based on the operating state information and adaptively adjusting the control loop parameters when it is below the preset threshold, a closed-loop control mechanism from state perception to margin judgment to parameter adjustment is formed, which can actively suppress power overshoot and system oscillation in the transient process, and significantly improve the dynamic response speed and operating stability of the system under grid faults and unbalanced conditions. In summary, the above methods overcome the technical obstacles of slow dynamic response, poor topology adaptability, and insufficient transient stability of existing technologies, and realize fast, stable, and adaptive control of cascaded energy storage systems under unbalanced grid conditions.

[0103] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of a preferred embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing this application. Those skilled in the art will understand that the modules in the apparatus of the embodiment can be distributed within the apparatus of the embodiment as described, or can be modified to be located in one or more apparatuses different from this embodiment. The modules of the above-described embodiment can be combined into one module, or further divided into multiple sub-modules.

[0104] It should be noted that any AI models, software tools, or components not belonging to this company appearing in the embodiments of this application are merely illustrative examples and do not represent actual use. All user personal information involved in the embodiments of this application has been authorized (with the knowledge and consent) by the relevant parties or has been fully authorized by all parties, and the executing entity may obtain it through various legal and compliant means. The collection, storage, use, processing, transmission, provision, and disclosure of the information, data, and signals involved all comply with relevant laws and regulations and do not violate public order and good morals.

[0105] The serial numbers in this application are for descriptive purposes only and do not represent the superiority or inferiority of any particular implementation scenario. The above disclosures are merely a few specific implementation scenarios of this application; however, this application is not limited thereto, and any variations conceived by those skilled in the art should fall within the protection scope of this application.

Claims

1. A phase-separated VSG control method for a cascaded energy storage system, wherein the cascaded energy storage system is a star-cascaded H-bridge topology, characterized in that... include: The three-phase circuits of the star-cascaded H-bridge topology are decoupled and converted into three independent single-phase control units, respectively. A phase-separated virtual synchronous generator control model is then constructed based on the circuit parameters of the single-phase control units. Based on the phase-splitting virtual synchronous generator control model, the instantaneous phase power is calculated according to the phase voltage sampling value and the phase current sampling value, and the instantaneous phase power is input to the active-frequency control loop and the reactive-voltage control loop respectively to generate an initial voltage reference value, and the corresponding current setpoint is generated according to the initial voltage reference value. The zero-sequence component in the current setpoint is detected, and a compensation amount opposite to the zero-sequence component is superimposed on the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. The target phase current setpoint is then used for pulse width modulation control to obtain a switch drive signal. The cascaded energy storage system is controlled based on the switch drive signal, and the stability margin is determined based on the operating status information of the cascaded energy storage system. When the stability margin is lower than a preset threshold, the control parameters of the active power-frequency control loop and / or the reactive power-voltage control loop are adjusted.

2. The method according to claim 1, characterized in that, The phase voltage sampling values ​​include the inverter-side voltage sampling values ​​of the cascaded energy storage system and the voltage sampling values ​​of the virtual synchronous generator model side; The phase current sampling values ​​include the inverter-side current sampling values ​​of the cascaded energy storage system and the current sampling values ​​of the virtual synchronous generator model.

3. The method according to claim 1, characterized in that, The step of generating a corresponding current setpoint based on the initial voltage reference value includes: Proportional-integral control is performed on the initial voltage reference value to obtain the current setpoint for the corresponding phase; When the grid voltage meets the preset balance condition, the sum of the given current values ​​of the three phases is zero; When the grid voltage does not meet the preset balance condition, the current setpoints of the three phases all include a positive sequence component, a negative sequence component, and a zero sequence component, and the sum of the current setpoints of the three phases is equal to three times the zero sequence component.

4. The method according to claim 1, characterized in that, The compensation amounts superimposed on the current setpoints of the three phases are equal, and the sum of the target phase current setpoints of the three phases is zero.

5. The method according to claim 1, characterized in that, Determining the stability margin based on the operating status information of the cascaded energy storage system includes: A harmonic linearization method is used to inject a voltage disturbance signal into the grid side of the cascaded energy storage system, obtain the current response signal corresponding to the voltage disturbance signal, and establish the output impedance model of the cascaded energy storage system based on the ratio of the voltage disturbance signal to the current response signal. The stability margin of the cascaded energy storage system when interacting with grid impedance is determined based on the output impedance model.

6. The method according to claim 5, characterized in that, The output impedance model includes a positive-sequence output impedance model and a negative-sequence output impedance model; the step of establishing the output impedance model of the cascaded energy storage system based on the ratio of the voltage disturbance signal to the current response signal includes: The positive-sequence output impedance model is obtained based on the voltage and current dual closed-loop control transfer function of the cascaded energy storage system, and the negative-sequence output impedance model is obtained from the positive-sequence output impedance model based on the frequency mapping relationship between the positive and negative-sequence impedances.

7. The method according to claim 6, characterized in that, The stability margin includes positive-sequence stability margin and negative-sequence stability margin; the determination of the stability margin of the cascaded energy storage system when interacting with grid impedance based on the output impedance model includes: The positive-sequence stability margin is output based on the positive-sequence output impedance model, and the negative-sequence stability margin is output based on the negative-sequence output impedance model.

8. A phase-separated VSG control device for a cascaded energy storage system, wherein the cascaded energy storage system is a star-cascaded H-bridge topology, characterized in that... include: The phase-separated modeling module is used to decouple the three-phase circuit of the star-cascaded H-bridge topology and convert them into three independent single-phase control units, and to construct a phase-separated virtual synchronous generator control model based on the circuit parameters of the single-phase control units. The instruction generation module is used to calculate the instantaneous phase power based on the phase voltage sampling value and the phase current sampling value according to the phase-splitting virtual synchronous generator control model, and input the instantaneous phase power to the active-frequency control loop and the reactive-voltage control loop respectively to generate an initial voltage reference value, and generate a corresponding current setpoint based on the initial voltage reference value; The zero-sequence compensation module is used to detect the zero-sequence component in the current setpoint and superimpose a compensation amount that is opposite to the zero-sequence component into the current setpoint to obtain the target phase current setpoint after eliminating the zero-sequence component. The target phase current setpoint is used for pulse width modulation control to obtain a switch drive signal. The closed-loop control module is used to control the operation of the cascaded energy storage system based on the switch drive signal, and to determine the stability margin based on the operating status information of the cascaded energy storage system. When the stability margin is lower than a preset threshold, the control parameters of the active power-frequency control loop and / or the reactive power-voltage control loop are adjusted.

9. A storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

10. A computer device, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the computer program is executed by a processor, it implements the steps of the method according to any one of claims 1 to 7.

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