A method and system for grid-forming energy storage power and battery state of charge control

Abstract

The application relates to the technical field of direct current conversion system control, in particular to a grid-connection type energy storage power and battery state of charge control method and system. The method comprises the following steps: setting a constant system rated angular frequency, generating a phase angle as a phase reference of a three-phase modulation wave through pure time integration; adaptively adjusting a time constant based on a battery state of charge and a photovoltaic active power change rate to generate a smooth sending power reference of a diode rectifier station; extracting an initial demand power and superimposing a battery state of charge dynamic penalty function to generate an active power reference instruction through dynamic asymmetric amplitude limiting; inputting a difference between the reference instruction and an actual output into a single-loop proportional integral controller to superimpose a steady-state feedforward regulation degree to obtain a regulation degree; generating a three-phase sinusoidal modulation wave in combination with the phase reference, and controlling a cascade H-bridge through a carrier phase-shifted pulse width modulation control. The application simplifies the control structure, eliminates loop coupling, avoids transient impact caused by mode hard switching, and improves weak grid operation stability.

Description

Technical Field

[0001] This application relates to the field of DC converter system control technology, specifically to a method and system for controlling the power and state of charge of grid-type energy storage and batteries. Background Technology

[0002] Large-scale renewable energy bases, exemplified by desert photovoltaic and deep-sea photovoltaic projects, are typically located far from load centers and in areas with extremely low short-circuit ratios in the power grid, exhibiting significant weak grid characteristics. Traditional AC transmission methods, limited by synchronization stability and reactive power / voltage control issues, struggle to meet the demands of large-scale, long-distance, and high-capacity power transmission. Against this backdrop, flexible DC transmission (VSC-HVDC) technology based on voltage source converters, with its independent active and reactive power control capabilities, black-start capability, and adaptability to weak grids, has become a crucial technology for renewable energy transmission. However, the sending-end converter station of this technology employs a fully controlled modular multilevel converter (MMC), whose converter valves consist of thousands of fully controlled IGBT sub-modules. This results in high costs, large footprints, and high operating losses, hindering the economic benefits of renewable energy bases.

[0003] To overcome the aforementioned economic bottlenecks, high-voltage direct current (DR-HVDC) transmission systems based on diode rectifiers have attracted attention in recent years. This technology uses passive twelve-pulse or twenty-four-pulse diode rectifier valves to replace expensive IGBT fully controlled sub-modules, utilizing the unidirectional conduction characteristics of diodes to achieve uncontrolled rectification from AC to DC. This reduces the construction cost of converter stations, decreases equipment size, and reduces operating losses. In applications where new energy is transmitted via DR-HVDC transmission systems using diode rectifiers, a grid-connected energy storage system is typically required on the AC side to provide the voltage amplitude and frequency support needed for commutation at the diode rectifier station, while also enabling the smoothing of photovoltaic power fluctuations and energy time-shift management.

[0004] However, existing grid-based energy storage control strategies have the following problems: First, existing grid-based control architectures, such as virtual synchronous generator control and traditional droop control, generally adopt a multi-nested cascaded control structure including phase-locked loops, voltage outer loops, and current inner loops. This results in high control dimensions and complex inter-loop coupling. When interacting nonlinearly with passive diode rectifier stations and facing weak grid short-circuit ratio conditions, it is prone to high-frequency resonance, control loop instability, and even large-scale grid disconnection accidents. Second, energy storage systems are subject to strict constraints on battery state of charge when smoothing photovoltaic power fluctuations. Existing energy management strategies typically use hard logic judgment to force a switch of the converter control mode when the battery state of charge reaches extreme states such as full charge or deep discharge. For example, they may forcibly switch from active power smoothing mode to pure reactive power compensation STATCOM mode. This hard mode switch can cause the integrator inside the controller to reset and the command to change abruptly, generating transient voltage and power surges on the AC bus, threatening the commutation safety of the rectifier station and the stable operation of the photovoltaic inverter. Summary of the Invention

[0005] The purpose of this application is to provide a method and system for controlling the power and state of charge of grid-connected energy storage, and to solve the problem that existing grid-connected energy storage control is prone to instability when interacting with passive diode rectifier stations and under conditions of weak grid short-circuit ratio.

[0006] The technical solution adopted by this application to solve its technical problem is: Firstly, a method for controlling the power and state of charge of grid-type energy storage is provided, which is applied to the power transmission system including grid-type energy storage system and diode rectifier station; The grid-type energy storage system adopts a cascaded H-bridge topology; the method includes: A constant system rated angular frequency is set, a phase angle is generated by pure time integration, and a phase reference for a three-phase modulated wave is generated based on the phase angle. The photovoltaic active power and battery state of charge are obtained. Based on the photovoltaic active power, the battery state of charge and the photovoltaic active power change rate adaptively adjusting the time constant, a smooth output power reference for the diode rectifier station is generated. Based on the photovoltaic active power and the smoothed power output benchmark, the initial demand power of the grid-type energy storage system is extracted, and the comprehensive reference power to be limited of the grid-type energy storage system is obtained by superimposing the dynamic penalty function of the battery state of charge. The integrated reference power to be limited is dynamically and asymmetrically limited to generate an active power reference command for the grid-type energy storage system. The actual output active power of the grid-type energy storage system is obtained. The difference between the active power reference command and the actual output active power is calculated and input into a single-loop proportional-integral controller. The regulation adjustment is solved and superimposed with the steady-state feedforward regulation to obtain the regulation. The modulation index is combined with the phase reference to generate a three-phase sinusoidal modulation wave, which is then modulated by carrier phase-shift pulse width modulation to generate a drive pulse to control the switching transistors of the cascaded H-bridge topology.

[0007] Furthermore, the transmission system is a photovoltaic transmission system rectified by diodes, comprising a photovoltaic power station, an AC collecting bus, a diode rectifier station and a receiving-end converter station connected in series, and the grid-type energy storage system is directly connected to the AC collecting bus.

[0008] Furthermore, the formula for calculating the phase angle is:

[0009] in, The phase angle is expressed in degrees (°). The system's rated angular frequency, in units of ; For time, the unit is ; The phase references of the three-phase modulated waves are respectively , , .

[0010] Furthermore, the adaptive time constant filtering includes: when At the same time, maintain the time constant. ; when and When, increase the time constant and ; when and When, decrease the time constant and ; when and When, decrease the time constant and ; when and When, increase the time constant and ; in, The battery is in its state of charge. This is the upper limit of the preset safe zone for the battery's state of charge; This is the preset lower limit of the safe zone for the battery's state of charge; The rate of change of photovoltaic active power, in units of ; The time constant is expressed in units of 1 / 250 Ω. ; The basic time constant, in units of ; The unit is the increase in photovoltaic active power. .

[0011] Furthermore, the calculation formula for the smoothed output power reference is as follows:

[0012] in, To smooth the power reference, the unit is... ; The time constant is expressed in units of 1 / 250 Ω. ; For the Laplace operator, the unit is . ; Photovoltaic active power, unit is .

[0013] Furthermore, the formula for calculating the initial power demand is as follows:

[0014] in, The initial power requirement is expressed in units of... ; The formula for calculating the dynamic penalty function of the battery state of charge is:

[0015] in, The dynamic penalty function for the battery's state of charge is expressed in units of... ; This is the penalty gain coefficient, in units of... ; This represents the optimal expected value of the battery's state of charge. The formula for calculating the integrated reference power to be limited is as follows:

[0016] in, To summarize the reference power to be limited, the unit is... .

[0017] Furthermore, the method for dynamically asymmetrically limiting the integrated reference power to be limited to generate an active power reference command for a grid-type energy storage system includes: when At that time, the formula for calculating the active power reference command is:

[0018] in, This represents the lower limit threshold of the battery's state of charge. This represents the high limit threshold for the battery's state of charge. This is a reference command for active power, and the unit is... ; This is the lower limit value of the limiter, in units of... ; This is the upper limit value of the limiter, in units of... ; when hour, Equal to the maximum allowable charging power, Equal to the maximum permissible discharge power; This is the lower limit of the high warning zone for battery state of charge. when hour, Follow The increase then decreases to 0. Equal to the maximum permissible discharge power; when hour, Equal to the maximum allowable charging power, Follow The decrease in decays to 0; This is the upper limit of the low warning zone for battery state of charge; when and At that time, or when and At that time, the forced active power reference command .

[0019] Furthermore, the formula for calculating the modulation intensity is as follows:

[0020] in, To adjust the system; For steady-state feedforward adjustment mechanism; This is the proportionality coefficient, and the unit is... ; This refers to the actual output active power, measured in units of... ; The integral coefficient is in units of 1 / 2 oz. ; For time, the unit is .

[0021] Furthermore, the calculation formula for the three-phase sinusoidal modulation wave is as follows:

[0022] in, The voltage of the modulated wave in phase a is expressed in units of . ; This is the phase b modulated wave voltage, and its unit is... ; This refers to the c-phase modulated wave voltage, with units of . .

[0023] Secondly, a grid-based energy storage power and battery state-of-charge control system is provided, including: The phase reference generation module is used to set a constant system rated angular frequency, generate a phase angle through pure time integration, and generate a phase reference for the three-phase modulated wave based on the phase angle. The smooth output power reference generation module is used to obtain the photovoltaic active power and the battery state of charge, and to generate a smooth output power reference for the diode rectifier station based on the photovoltaic active power, the battery state of charge and the photovoltaic active power change rate adaptively adjusting the time constant. The integrated reference power generation module is used to extract the initial demand power of the grid-type energy storage system based on the photovoltaic active power and the smoothed power output benchmark, and to obtain the integrated reference power to be limited of the grid-type energy storage system by superimposing the dynamic penalty function of battery state of charge. The active power reference command generation module is used to dynamically and asymmetrically limit the comprehensive reference power to be limited, and generate the active power reference command of the grid-type energy storage system. The regulation calculation module is used to obtain the actual output active power of the grid-type energy storage system, calculate the difference between the active power reference command and the actual output active power, input the difference into the single-loop proportional-integral controller, solve the regulation adjustment amount, and superimpose the steady-state feedforward regulation to obtain the regulation. The modulation wave generation module is used to combine the modulation index with the phase reference to generate a three-phase sinusoidal modulation wave, and generate a drive pulse through carrier phase-shift pulse width modulation to control the switching transistors of the cascaded H-bridge topology.

[0024] The beneficial effects of this application are: 1. This application abandons the multi-nested cascaded control structure of phase-locked loops, voltage outer loops, and current inner loops in traditional grid-connected control. Instead, it sets a constant system rated angular frequency and generates a phase angle through pure time integration. Based on this phase angle, a phase reference for the three-phase modulation wave is generated. Simultaneously, a single-loop proportional-integral controller is employed to directly generate the modulation command for pulse width modulation by superimposing the modulation adjustment of the power outer loop output with the steady-state feedforward modulation. This forms a unified active-voltage coupled control architecture where the modulation wave is directly generated by the power outer loop. This control architecture simplifies multi-loop nested control to single-loop PI control, significantly reducing the complexity of control dimensions and loop coupling. It fundamentally eliminates dynamic coupling and interaction between control loops, avoiding high-frequency resonance problems caused by overlapping bandwidths and accumulated phase delays in multiple loops. Especially when interacting nonlinearly with passive diode rectifier stations and facing weak grid short-circuit ratio conditions, it effectively suppresses the risk of control loop instability, significantly improves the operational stability of grid-connected energy storage under weak grid conditions, and reduces the risk of large-scale grid disconnection.

[0025] 2. This application generates a smooth power output reference for the diode rectifier station based on the adaptive adjustment time constant of photovoltaic active power, photovoltaic active power change rate and battery state of charge. This multi-factor collaborative adaptive adjustment mechanism ensures smooth power output while taking into account the dynamic response speed of the system and the safety of energy management. It effectively solves the contradiction of insufficient smoothing capability with small time constant and lag response with large time constant under fixed time constant, which can easily aggravate overcharging and over-discharging of energy storage. It also reduces the risk of energy storage saturation and secondary fluctuations in DC power output caused by unreasonable power reference.

[0026] 3. This application continuously corrects the initial demand power by superimposing a dynamic penalty function for the battery state of charge and uses dynamic asymmetric limiting to generate active power reference commands. This makes the generation and limiting process of power reference commands continuous and smooth. When the battery state of charge reaches its limit, there is no need to perform a hard switch of control mode, thereby avoiding the reset of the integrator inside the controller and sudden command changes. It effectively suppresses the transient voltage and power surges generated on the AC bus during mode switching, ensuring the commutation safety of the passive diode rectifier station and the stable operation of the photovoltaic power station.

[0027] 4. This application continuously corrects the initial power demand by superimposing a dynamic penalty function for the battery state of charge and uses dynamic asymmetric limiting to generate an active power reference command. This forms a pre-emptive soft guidance and flexible boundary constraint at the power demand level, making the generation and limiting process of the power reference command continuous and smooth. When the battery state of charge reaches its limit, there is no need to perform a hard switch of the control mode, thereby avoiding the reset of the controller's internal integrator and the sudden change of the command caused by the mode switch. This effectively suppresses the transient voltage and power surges on the AC bus, ensuring the commutation safety of the passive diode rectifier station and the stable operation of the photovoltaic power station.

[0028] 5. This application combines a grid-based control method with a cascaded H-bridge topology. By generating drive pulses through carrier phase-shift pulse width modulation, it achieves multi-level output while reducing the equivalent switching frequency and electromagnetic interference, thus improving the output voltage waveform quality. Furthermore, the modular structure of the cascaded H-bridge topology facilitates flexible series and parallel expansion based on the sending-end voltage level and power capacity requirements, enhancing the system's engineering applicability and maintainability, and helping to reduce the overall cost and footprint of the grid-based energy storage system. Attached Figure Description

[0029] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a schematic diagram of the overall hardware topology of the photovoltaic system rectified and transmitted via diodes provided in the embodiments of this application; Figure 2 This is a diagram illustrating the overall control strategy of a grid-type energy storage system provided in an embodiment of this application. Figure 3 This is a flowchart illustrating the generation of active power reference commands for a grid-type energy storage system provided in this application embodiment; Figure 4 This is a schematic diagram of the composition of the grid-type energy storage power and battery state of charge control system provided in the embodiments of this application.

[0031] Figure label: 1-Photovoltaic power station; 2-AC collecting bus; 3-Diode rectifier station; 4-Receiving-end converter station; 5-Grid-type energy storage system; 6-Filter; 7-High voltage DC transmission line; 8-Receiving-end power grid; 101-Phase reference generation module; 102-Smooth output power reference generation module; 103-Comprehensive reference power to be limited generation module; 104-Active power reference command generation module; 105-Modulation degree solving module; 106-Modulation wave generation module. Detailed Implementation

[0032] The embodiments of this application are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application.

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Unless otherwise specified, the embodiments and features in the embodiments of this application can be combined with each other.

[0034] In the description of this application, the terms "upper," "lower," "left," "right," "front," "rear," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Unless otherwise specified, the above-mentioned orientational descriptions can be flexibly set in actual application, provided that the relative positional relationships shown in the accompanying drawings are satisfied.

[0035] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "set up," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0036] See Figure 1This application provides a power transmission system, which is a photovoltaic power transmission system via diode rectification. It includes a photovoltaic power station 1, an AC collecting bus 2, a diode rectifier station 3, and a receiving-end converter station 4 connected in series. A grid-type energy storage system 5 is directly connected to the AC collecting bus 2, and a filter 6 is connected in parallel to the AC collecting bus 2 to suppress AC side harmonic disturbances. The diode rectifier station 3 and the receiving-end converter station 4 are electrically connected through a high-voltage DC transmission line 7, and the AC side of the receiving-end converter station 4 is connected to the receiving-end power grid 8.

[0037] Photovoltaic power station 1 includes a photovoltaic array and a photovoltaic inverter. The photovoltaic inverter can adopt conventional grid-connected or grid-connected control. The photovoltaic active power output of photovoltaic power station 1 is denoted as... Photovoltaic power station 1 connects to AC busbar 2 via an AC connection line. The three-phase AC voltage of AC busbar 2 is denoted as... The fundamental amplitude of AC bus 2 is denoted as The rated angular frequency of the transmitting system is denoted as . .

[0038] The grid-type energy storage system 5 is directly connected to the AC collection bus 2, employing a cascaded H-bridge converter (CHBC) topology to simultaneously provide AC voltage to both the photovoltaic power station 1 and the diode rectifier station 3. The state of charge (SOC) of the batteries in the grid-type energy storage system 5 is denoted as... The safe operating range for the battery's state of charge can be set from 10% to 90%. The active power output of the grid-type energy storage system 5 is denoted as... Discharging is positive, charging is negative. The modulation index of the three-phase modulated wave signal of the grid-type energy storage system 5 is denoted as […]. The phase angle of the three-phase modulated wave is denoted as .

[0039] The AC side of the passive diode rectifier station 3 is connected to the AC collecting bus 2, and includes a converter transformer, AC filter, reactive power compensation device, and 12-pulse or 24-pulse diode rectifier valve group. The DC output power of the diode rectifier station 3 is denoted as... The DC bus voltage is denoted as .

[0040] The receiving-end converter station 4 is connected to the diode rectifier station 3 via the high-voltage DC transmission line 7. It adopts a modular multilevel converter (MMC) and operates in constant DC voltage control mode to maintain a constant DC voltage for the entire system.

[0041] The control strategy of this application is based on the special physical power flow model of the DR-HVDC system. Since the receiving-end converter station 4 maintains the DC network voltage stability, the DC output power of the diode rectifier station 3 is... Presents the three-phase AC voltage on the AC side Strong correlation characteristics.

[0042] Neglecting the leakage reactance voltage drop of the converter transformer, the formula for calculating the output power of diode rectifier station 3 is as follows:

[0043] in, This refers to the DC output power, measured in units of... ; Equivalent DC impedance, unit is ; This is the DC bus voltage, in units of... ; This refers to three-phase AC voltage, and the unit is... .

[0044] Under the open-loop modulation strategy, the formulas for calculating the three-phase AC voltage and modulation degree are as follows:

[0045] in, This is a topology-dependent scaling factor, in units of... ; To adjust the system.

[0046] As can be seen from the above, the three-phase AC voltage With adjustment system Proportional to the modulation index, therefore, the DC power output is a monotonically increasing function of the modulation index, i.e.:

[0047] Meanwhile, neglecting line and converter losses, based on the conservation of fundamental active power at AC parallel nodes, the system satisfies the following power balance equation:

[0048] in, Photovoltaic active power, unit is ; The active power of energy storage is expressed in units of _____. ; This refers to the DC output power, measured in units of... .

[0049] Based on the above formula analysis, it can be concluded that by adjusting the modulation index of the grid-type energy storage system 5... This allows for direct control of the active power output of the entire power transmission system.

[0050] This application provides a method for controlling the power and state of charge of a grid-type energy storage system, applied to a power transmission system including a grid-type energy storage system 5 and a diode rectifier station 3. The grid-type energy storage system 5 adopts a cascaded H-bridge topology. See also... Figure 2 The underlying control of the grid-type energy storage system 5 completely eliminates the phase-locked loop, voltage outer loop, and current inner loop, and adopts a unified active-voltage coupling control architecture in which the modulation wave is directly generated by the power outer loop.

[0051] See Figure 2 , Figure 3 The control method includes the following steps: S1. Set a constant system rated angular frequency, generate the phase angle through pure time integration, and generate the phase reference of the three-phase modulated wave based on the phase angle.

[0052] Specifically, the formula for calculating the phase angle is:

[0053] in, The phase angle is expressed in degrees (°). The system's rated angular frequency, in units of ; For time, the unit is .

[0054] The generated phase angle , , They serve as the phase references for phases a, b, and c in the three-phase modulated wave, respectively.

[0055] Correspondingly, this step generates the phase reference by replacing the traditional phase-locked loop with pure time integration, fundamentally eliminating the bandwidth limitation, phase delay, and instability risks of the phase-locked loop under weak power grid and low short-circuit ratio conditions. At the same time, the setting of a constant angular frequency provides rigid commutation voltage frequency support for the passive diode rectifier station, ensuring that the rectifier valve has a stable and reliable commutation reference under various operating conditions, and significantly improving the frequency stability of the system under weak power grid and variable short-circuit ratio conditions.

[0056] S2. Obtain the photovoltaic active power and battery state of charge. Based on the photovoltaic active power, battery state of charge and photovoltaic active power change rate adaptive adjustment time constant, generate a smooth output power reference for the diode rectifier station.

[0057] Specifically, a safe zone for the battery state of charge of the grid-type energy storage system 5 is defined, and the following zone thresholds are set: This is the upper limit of the preset safe zone for the battery's state of charge, for example, 70%. This is the preset lower limit of the safe zone for the battery's state of charge, for example, 30%.

[0058] Adaptive adjustment methods for the time constant include: when At this time, the battery state of charge is in the safe zone, maintaining the time constant. .

[0059] when and At this time, the battery's state of charge deviates from the safe zone, increasing the time constant. and Under high power conditions, photovoltaic power surges, requiring energy storage to charge and absorb the surge. By automatically increasing the time constant, the filtered reference power follows the photovoltaic changes more slowly, thereby proactively reducing the charging demand of energy storage and slowing down the rate at which the battery's state of charge approaches its upper limit.

[0060] when and When the battery's state of charge deviates from the safe zone, the time constant is reduced. and In this state, photovoltaic power suddenly drops, requiring energy storage to discharge and support it. By automatically reducing the time constant, the energy storage is encouraged to discharge quickly and deeply, which not only smooths out the fluctuations but also indirectly causes the battery's state of charge to fall back to the preset safe range.

[0061] when and When the battery's state of charge deviates from the safe zone, the time constant is reduced. and Under low power conditions, the photovoltaic power surges, requiring energy storage to charge and absorb it. By automatically reducing the time constant, the filtered reference power can follow the photovoltaic changes more quickly, thereby increasing the charging demand of energy storage. This fully utilizes the opportunity when the photovoltaic output is sufficient to actively replenish the battery and promote the battery's state of charge to recover to the preset safe range as soon as possible.

[0062] when and At this time, the battery's state of charge deviates from the safe zone, increasing the time constant. and Under low power conditions, photovoltaic power drops suddenly, requiring energy storage to discharge to support it. By automatically increasing the time constant, the filtered reference power follows the photovoltaic changes more slowly, thereby actively reducing the discharge demand of energy storage, suppressing deep battery discharge, and slowing down the rate at which the battery's state of charge approaches its lower limit.

[0063] in, The battery is in its state of charge. The rate of change of photovoltaic active power, in units of ; The time constant is expressed in units of 1 / 250 Ω. ; The basic time constant, in units of ; The unit is the increase in photovoltaic active power. .

[0064] The formula for calculating the smoothed output power reference is:

[0065] in, To smooth the power delivery reference, the unit is... ; The time constant is expressed in units of 1 / 250 Ω. ; For the Laplace operator, the unit is . ; Photovoltaic active power, unit is .

[0066] Accordingly, this step involves constructing a two-dimensional adaptive time constant function. This system achieves dual-factor collaborative sensing of battery state of charge (SOC) and photovoltaic power change trends via time constant. When the SOC deviates from the preset safe zone, the system actively adjusts the time constant to slow down or accelerate the power reference tracking speed. This proactively reduces the charging demand of energy storage or encourages deep discharge while ensuring the smoothness of DC power output. It effectively solves the contradiction of insufficient smoothing capability with small time constants and lag in response with large time constants, which can easily exacerbate overcharging and over-discharging of energy storage. It also reduces the risk of energy storage saturation and secondary fluctuations in DC power output caused by an unreasonable power reference.

[0067] S3. Extract the initial demand power of the grid-type energy storage system based on the photovoltaic active power and smoothed power output benchmark, and obtain the comprehensive reference power to be limited by superimposing the battery state of charge dynamic penalty function.

[0068] Specifically, based on the nodal power balance equation, the formula for calculating the initial demand power of the grid-type energy storage system 5 for smoothing high-frequency fluctuations is as follows:

[0069] in, The initial power requirement is expressed in units of... .

[0070] To further enhance the system's active anti-limit-crossing capability, a dynamic penalty function for the battery's state of charge is constructed, and its calculation formula is as follows:

[0071] in, The dynamic penalty function for the battery's state of charge is expressed in units of... ; This is the penalty gain coefficient, in units of... ; This represents the optimal expected value of the battery's state of charge.

[0072] The formula for calculating the overall reference power to be limited is as follows:

[0073] in, To summarize the reference power to be limited, the unit is... .

[0074] Correspondingly, this step constructs a dynamic penalty term for the battery's state of charge using a cubic nonlinear function, so that in Within the central safety zone, the penalty term is almost zero, and the grid-type energy storage system performs its power smoothing task with full force. When the battery state of charge approaches the danger edge, the penalty term increases sharply and non-linearly, forcibly superimposing an auxiliary power command to pull the energy storage power back to the central zone. This soft guidance mechanism forms a proactive, flexible boundary constraint at the power demand level, actively suppressing the tendency of the battery state of charge to exceed the limit without relying on subsequent hard limiting, significantly reducing the probability of energy storage reaching its physical limits, and providing a smoother input signal for subsequent limiting stages.

[0075] S4. Dynamically and asymmetrically limit the integrated reference power to be limited to generate the active power reference command of the grid-type energy storage system 5.

[0076] Specifically, the battery state of charge of the grid-type energy storage system 5 is divided into a normal zone, a deep warning zone, and an extreme zone, and the following zoning thresholds are set: This is the lower limit threshold for the battery's state of charge, for example, 10%. This is the upper limit of the low warning zone for battery state of charge, for example, 20%; This is the lower limit of the high warning zone for battery state of charge, for example, 80%. This is the high limit threshold for the battery's state of charge, for example, 90%.

[0077] The method for dynamically and asymmetrically limiting the integrated reference power to be limited to generate an active power reference command for a grid-type energy storage system includes: when At that time, the formula for calculating the active power reference command is:

[0078] in, This is a reference command for active power, and the unit is... ; This is the lower limit value of the limiter, a negative number, corresponding to the charging power, and the unit is... ; This is the upper limit value of the limiter, a positive number, corresponding to the discharge power, and the unit is... .

[0079] The upper and lower limits of the limiter are not fixed to the rated power, but... The dynamic asymmetric adjustment rule for a continuous function is as follows: when At that time, the battery state of charge is in the normal range. Equal to the maximum allowable charging power, It equals the maximum allowable discharge power; the grid-type energy storage system 5 responds to power stabilization commands across the entire power range.

[0080] when At this time, the battery's state of charge enters the high charge warning zone. Maintain equal to the maximum allowable discharge power, while Follow The value increases and then decays linearly or non-linearly to 0. At this point... The reduction from the maximum allowable charging power to 0 means that as the battery's state of charge approaches the high limit threshold, the charging capacity of the grid-type energy storage system 5 is gradually tightened until charging is completely prohibited, thereby avoiding battery overcharging.

[0081] when At this time, the battery's state of charge enters the low battery warning zone. Maintain the maximum allowable charging power. Follow The decrease in [something] leads to a linear or non-linear decay to 0. At this point... The decay from the maximum allowable discharge power to 0 means that as the battery's state of charge approaches the low limit threshold, the discharge capacity of the grid-type energy storage system 5 is gradually tightened until discharge is completely prohibited, thereby avoiding deep over-discharge of the battery.

[0082] when and At that time, the battery's state of charge enters the high-charge extreme region; when and At this time, the battery state of charge enters the low-charge extreme region; in both cases, the active power reference command is forced. This means that any power flow that exacerbates the battery's state of charge exceeding its limits is completely prohibited. At this point, the grid-type energy storage system 5 is equivalent to a STATCOM, providing voltage only to the diode rectifier station 3. All the power generated by the photovoltaic system is then sent out through the diode rectifier station 3.

[0083] During the aforementioned dynamic asymmetric limiting process, the limiting boundary... and The switching is strictly based on real-time The value changes continuously and gradually, rather than through hard jumps based on a fixed threshold. Simultaneously, the limiting boundaries for the charging and discharging directions are adjusted independently and asymmetrically. Specifically, at high battery levels, charging capacity is prioritized while discharging capacity is preserved, and at low battery levels, discharging capacity is prioritized while charging capacity is preserved. This dynamic and asymmetrical dual characteristic ensures that the power reference command maintains a continuous and smooth transition as the battery's state of charge crosses the boundaries of each zone, fundamentally eliminating the command abrupt changes caused by hard logic switching in traditional mode switching.

[0084] Correspondingly, this step, in coordination with the dynamic penalty function for the battery state of charge in step S3, forms a dual protection mechanism at the power command level: pre-emptive soft guidance and boundary soft constraints. The cubic nonlinear penalty function in step S3 actively corrects the power demand when the battery state of charge deviates from the center, thus ensuring that the overall reference power to be limited is optimized. The system spontaneously tends towards a direction conducive to the recovery of the battery's state of charge; the dynamic asymmetric limiting in step S4 further flexibly trims the power command at the physical execution boundary. The combination of these two processes ensures that the generation and limiting process of the power reference command in the grid-type energy storage system 5 is continuous and smooth when the battery's state of charge approaches its limit, eliminating the need for hard switching of control modes and thus avoiding integrator resets and command abrupt changes within the controller.

[0085] S5. Obtain the actual output active power of the grid-type energy storage system, calculate the difference between the active power reference command and the actual output active power, input the difference into the single-loop proportional-integral controller, solve for the regulation adjustment amount, and superimpose the steady-state feedforward regulation to obtain the regulation.

[0086] Specifically, the formula for calculating the adjustment system is as follows:

[0087] in, To adjust the system; For steady-state feedforward adjustment mechanism; This is the proportionality coefficient, and the unit is... ; This refers to the actual output active power, measured in units of... ; The integral coefficient is in units of 1 / 2 oz. ; For time, the unit is .

[0088] To prevent overmodulation, upper and lower limits are set on the output of the PI controller, for example... .

[0089] Correspondingly, this step abandons the multi-nested structure of voltage outer loop and current inner loop in traditional grid-connected control. Instead, it uses a single-loop proportional-integral controller to directly map the power deviation into a modulation adjustment, which is then superimposed with the steady-state feedforward modulation to generate the final modulation command. This power outer loop-direct modulation architecture simplifies multi-loop nested control to single-loop control, significantly reducing the complexity of control dimensions and loop coupling. It fundamentally eliminates the dynamic coupling and interaction between control loops, avoiding high-frequency resonance problems caused by overlapping bandwidths and accumulated phase delays in multiple loops. Especially when interacting nonlinearly with passive diode rectifier stations and facing weak grid short-circuit ratio conditions, it effectively suppresses the risk of control loop instability and significantly improves the operational stability of grid-connected energy storage under weak grid conditions.

[0090] S6. The modulation index and phase reference are combined to generate a three-phase sinusoidal modulation wave, which is then modulated by carrier phase-shift pulse width modulation to generate a drive pulse to control the switching transistors of the cascaded H-bridge topology.

[0091] Specifically, the formula for calculating a three-phase sinusoidal modulated wave is as follows:

[0092] in, The voltage of the modulated wave in phase a is expressed in units of . ; This is the phase b modulated wave voltage, and its unit is... ; This refers to the c-phase modulated wave voltage, with units of . .

[0093] The three-phase modulated wave is directly fed into the carrier phase-shift pulse width modulation module to generate trigger pulses that drive the switching transistors of each stage of the cascaded H-bridge module.

[0094] Accordingly, this step combines the grid-based control method with the cascaded H-bridge topology. Through carrier phase-shift pulse width modulation, it achieves multi-level output while reducing the equivalent switching frequency and electromagnetic interference, improving the output voltage waveform quality, and providing a low-harmonic distortion commutation voltage for the passive diode rectifier station. Furthermore, the modular structure of the cascaded H-bridge topology facilitates flexible series and parallel expansion according to the sending-end voltage level and power capacity requirements, enhancing the system's engineering applicability and maintainability, and helping to reduce the overall cost and footprint of the grid-based energy storage system.

[0095] This application embodiment can divide the device and server into functional modules according to the above method examples. For example, each function can be divided into a separate functional module, or two or more functions can be integrated into one processing module. The integrated module can be implemented in hardware or as a software functional module. It should be noted that the module division in this application embodiment is illustrative and only represents one logical functional division. In actual implementation, there may be other division methods.

[0096] When dividing each function into modules according to its corresponding function. Figure 4 A schematic diagram of a possible composition of the control system involved in the above embodiments is shown.

[0097] See Figure 4 The grid-type energy storage power and battery state of charge control system provided in this application includes: a phase reference generation module 101, a smooth output power reference generation module 102, a comprehensive reference power generation module 103, an active power reference command generation module 104, a modulation scheme solving module 105, and a modulation wave generation module 106.

[0098] The phase reference generation module 101 is used to set a constant system rated angular frequency, generate a phase angle through pure time integration, and generate a phase reference for the three-phase modulated wave based on the phase angle.

[0099] The smooth power output reference generation module 102 is used to obtain the photovoltaic active power and the battery state of charge, and to generate the smooth power output reference of the diode rectifier station based on the photovoltaic active power, the battery state of charge and the photovoltaic active power change rate adaptively adjusting the time constant.

[0100] The integrated reference power generation module 103 is used to extract the initial demand power of the grid-type energy storage system based on the photovoltaic active power and smoothed power output benchmark, and obtain the integrated reference power of the grid-type energy storage system by superimposing the dynamic penalty function of battery state of charge.

[0101] The active power reference command generation module 104 is used to dynamically and asymmetrically limit the comprehensive reference power to be limited, and generate the active power reference command for the grid-type energy storage system.

[0102] The regulation calculation module 105 is used to obtain the actual output active power of the grid-type energy storage system, calculate the difference between the active power reference command and the actual output active power, input it into the single-loop proportional-integral controller, solve for the regulation adjustment amount, and superimpose the steady-state feedforward regulation to obtain the regulation.

[0103] The modulation wave generation module 106 is used to combine the modulation index with the phase reference to generate a three-phase sinusoidal modulation wave, which is then used to generate a drive pulse through carrier phase-shift pulse width modulation to control the switching transistors of the cascaded H-bridge topology.

[0104] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for controlling the power and state of charge of grid-type energy storage, applied to a power transmission system including a grid-type energy storage system and a diode rectifier station; Its features are, The grid-type energy storage system adopts a cascaded H-bridge topology; the method includes: A constant system rated angular frequency is set, a phase angle is generated by pure time integration, and a phase reference for a three-phase modulated wave is generated based on the phase angle; The photovoltaic active power and battery state of charge are obtained. Based on the photovoltaic active power, the battery state of charge and the photovoltaic active power change rate adaptively adjusting the time constant, a smooth output power reference for the diode rectifier station is generated. Based on the photovoltaic active power and the smoothed power output benchmark, the initial demand power of the grid-type energy storage system is extracted, and the comprehensive reference power to be limited of the grid-type energy storage system is obtained by superimposing the dynamic penalty function of the battery state of charge. The integrated reference power to be limited is dynamically and asymmetrically limited to generate an active power reference command for the grid-type energy storage system. The actual output active power of the grid-type energy storage system is obtained. The difference between the active power reference command and the actual output active power is calculated and input into a single-loop proportional-integral controller. The regulation adjustment is solved and superimposed with the steady-state feedforward regulation to obtain the regulation. The modulation index is combined with the phase reference to generate a three-phase sinusoidal modulation wave, which is then modulated by carrier phase-shift pulse width modulation to generate a drive pulse to control the switching transistors of the cascaded H-bridge topology.

2. The method for controlling the power and state of charge of grid-type energy storage according to claim 1, characterized in that, The power transmission system is a photovoltaic power transmission system rectified by diodes, which includes a photovoltaic power station, an AC collecting bus, a diode rectifier station and a receiving-end converter station connected in series. The grid-type energy storage system is directly connected to the AC collecting bus.

3. The method for controlling the power and state of charge of grid-type energy storage according to claim 1, characterized in that, The formula for calculating the phase angle is: in, The phase angle is expressed in degrees (°). The system's rated angular frequency, in units of ; For time, the unit is ; The phase references of the three-phase modulated waves are respectively , , .

4. The method for controlling the power and state of charge of grid-type energy storage according to claim 1, characterized in that, The adaptive adjustment method for the time constant includes: when At the same time, maintain the time constant. ; when and When, increase the time constant and ; when and When, decrease the time constant and ; when and When, decrease the time constant and ; when and When, increase the time constant and ; in, The battery is in its state of charge. This is the upper limit of the preset safe zone for the battery's state of charge; This is the preset lower limit of the safe zone for the battery's state of charge; The rate of change of photovoltaic active power, in units of ; The time constant is expressed in units of 1 / 250 Ω. ; The basic time constant, in units of ; The unit is the increase in photovoltaic active power. .

5. The method for controlling the power and state of charge of grid-type energy storage according to claim 4, characterized in that, The formula for calculating the smoothed power output reference is as follows: in, To smooth the power reference, the unit is... ; The time constant is expressed in units of 1 / 250 Ω. ; For the Laplace operator, the unit is . ; Photovoltaic active power, unit is .

6. The method for controlling the power and state of charge of grid-type energy storage according to claim 5, characterized in that, The formula for calculating the initial power demand is as follows: in, The initial power requirement is expressed in units of... ; The formula for calculating the dynamic penalty function of the battery state of charge is: in, The dynamic penalty function for the battery's state of charge is expressed in units of... ; This is the penalty gain coefficient, in units of... ; This represents the optimal expected value of the battery's state of charge. The formula for calculating the integrated reference power to be limited is as follows: in, To summarize the reference power to be limited, the unit is... .

7. The method for controlling the power and state of charge of grid-type energy storage according to claim 6, characterized in that, The method for dynamically and asymmetrically limiting the integrated reference power to be limited to generate an active power reference command for a grid-type energy storage system includes: when At that time, the formula for calculating the active power reference command is: in, This represents the lower limit threshold of the battery's state of charge. This represents the high limit threshold for the battery's state of charge. This is a reference command for active power, and the unit is... ; This is the lower limit value of the limiter, in units of... ; This is the upper limit value of the limiter, in units of... ; when hour, Equal to the maximum allowable charging power, Equal to the maximum permissible discharge power; This is the lower limit of the high warning zone for battery state of charge. when hour, Follow The increase then decreases to 0. Equal to the maximum permissible discharge power; when hour, Equal to the maximum allowable charging power, Follow The decrease in decays to 0; This is the upper limit of the low warning zone for battery state of charge; when and At that time, or when and At that time, the forced active power reference command .

8. The method for controlling the power and state of charge of grid-type energy storage according to claim 7, characterized in that, The formula for calculating the modulation index is: in, To adjust the system; For steady-state feedforward adjustment mechanism; This is the proportionality coefficient, and the unit is... ; This refers to the actual output active power, measured in units of... ; The integral coefficient is in units of 1 / 2 oz. ; For time, the unit is .

9. The method for controlling the power and state of charge of grid-type energy storage according to claim 8, characterized in that, The formula for calculating the three-phase sinusoidal modulation wave is as follows: in, The voltage of the modulated wave in phase a is expressed in units of . ; This is the phase b modulated wave voltage, and its unit is... ; This refers to the c-phase modulated wave voltage, with units of . .

10. A grid-type energy storage power and battery state-of-charge control system, characterized in that, include: The phase reference generation module is used to set a constant system rated angular frequency, generate a phase angle through pure time integration, and generate a phase reference for the three-phase modulated wave based on the phase angle. The smooth output power reference generation module is used to obtain the photovoltaic active power and the battery state of charge, and to generate a smooth output power reference for the diode rectifier station based on the photovoltaic active power, the battery state of charge and the photovoltaic active power change rate adaptively adjusting the time constant. The integrated reference power generation module is used to extract the initial demand power of the grid-type energy storage system based on the photovoltaic active power and the smoothed power output benchmark, and to obtain the integrated reference power to be limited of the grid-type energy storage system by superimposing the dynamic penalty function of battery state of charge. The active power reference command generation module is used to dynamically and asymmetrically limit the comprehensive reference power to be limited, and generate the active power reference command of the grid-type energy storage system. The regulation calculation module is used to obtain the actual output active power of the grid-type energy storage system, calculate the difference between the active power reference command and the actual output active power, input the difference into the single-loop proportional-integral controller, solve the regulation adjustment amount, and superimpose the steady-state feedforward regulation to obtain the regulation. The modulation wave generation module is used to combine the modulation index with the phase reference to generate a three-phase sinusoidal modulation wave, and generate a drive pulse through carrier phase-shift pulse width modulation to control the switching transistors of the cascaded H-bridge topology.

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