Control system and method for assisting thermal power frequency modulation by energy storage system

Abstract

The invention discloses a control system and method for assisting thermal power frequency modulation by an energy storage system, and relates to the technical field of power system and inverter control, and the system comprises a power calculation module, a main unit current support control module, an inter-phase adjustment module, a slave unit virtual impedance control module, a current amplitude compensation module, a main unit energy storage control module and a slave unit energy storage control module. A master-slave structure is combined with virtual impedance control, the output voltage of each energy storage sub-module is accurately adjusted while the current consistency is ensured, adaptive power distribution among multiple modules is realized, power distribution based on the SOC state and a current amplitude compensation mechanism driven by the interphase SOC are introduced, and the adaptive power distribution among multiple modules is realized. The charge state of each energy storage unit can be dynamically balanced in the system operation process, the overall service life of the energy storage system is prolonged, the utilization efficiency of the energy storage system is improved, and the problem that in the prior art, multi-module cooperation, electric quantity balance, three-phase coordination and system robustness are difficult to meet the requirement for high-performance energy storage networking control of a novel electric power system is solved.

Description

Technical Field

[0001] The present invention relates to the field of power systems and inverter control technology, and in particular to a control system and method for energy storage system-assisted thermal power frequency regulation. Background Art

[0002] With the continuous increase in the penetration rate of renewable energy, the output of traditional thermal power units has declined significantly, the system inertia of the power system has gradually weakened, and the frequency regulation capability has significantly degraded. Especially in scenarios with a high proportion of photovoltaic access, the system frequency is increasingly affected by intermittent disturbances, the steady-state frequency deviation increases, and traditional thermal power units are unable to meet the tasks of rapid frequency response and inertial support. Therefore, there is an urgent need to build a new energy storage grid construction solution with rapid regulation and frequency support capabilities. Among them, high-voltage direct-mounted grid construction energy storage systems are particularly suitable for joint operation with large thermal power units due to their direct access to high-voltage busbars, fast response, and high regulation accuracy. Representative examples include high-voltage direct-mounted three-phase cascaded H-bridge energy storage systems. However, the grid construction control of energy storage systems under high-voltage direct-mounted conditions is highly complex, with higher control accuracy and stability requirements, and coordinated control faces significant challenges.

[0003] Currently, high-voltage, direct-mounted, three-phase cascaded H-bridge energy storage systems still face coordination and control challenges under grid-connected operating conditions. The main issues are as follows:

[0004] First, the series output of the energy storage modules requires consistent current, and there is a lack of flexible module-level power regulation capabilities, making it difficult to achieve flexible power distribution among multiple modules while meeting the consistent current constraint; second, the overall frequency support capability of the system is limited, and the response is delayed, which cannot meet the inertial support requirements after a high proportion of new energy is connected; third, the state of charge (SOC) between modules is inconsistent, which may lead to a "short board effect" that limits the overall operating performance of the system; fourth, when the three-phase system operates independently, there are problems such as frequency drift, uneven power distribution and energy imbalance between phases.

[0005] To overcome the above problems, grid-type energy storage control solutions have been proposed in the prior art, mainly including three categories:

[0006] (1) Voltage-type virtual synchronous generation control (VSG) scheme: By building a voltage controller similar to a synchronous generator to simulate inertia and damping response, it is suitable for centralized high-power energy storage scenarios; limitations: multi-module coordination is difficult, module response speed is limited, and adaptability is poor; it is difficult to achieve independent regulation and energy balance between modules;

[0007] (2) Current-type grid-following control scheme (GFL): uses a phase-locked loop to extract the grid phase and frequency, and controls the energy storage output with a current reference; limitations: relies on high-precision sensing devices and has weak anti-interference capabilities; sensing delays can easily cause frequency drift and stability degradation; lacks multi-module power distribution and SOC balancing mechanisms;

[0008] (3) Master-slave network control scheme: Some studies have proposed using a master unit to regulate voltage and slave units to follow a current reference, but they do not systematically introduce phase synchronization and energy balance control. Furthermore, the master unit and the grid synchronization rely on a phase-locked loop, which is not very robust. Limitations: Phase imbalance and three-phase power dynamic imbalance are ignored, resulting in a coarse control granularity for the overall system, making it impossible to achieve fine-grained distributed control.

[0009] In summary, these solutions have obvious deficiencies in multi-module collaboration, power balancing, three-phase coordination, and system robustness, making it difficult to meet the comprehensive needs of new power systems for high-performance energy storage network control, especially thermal power frequency regulation. Therefore, there is an urgent need for a control system and method for energy storage system-assisted thermal power frequency regulation to intelligently dispatch power supply to solve the above technical problems and provide protection and defense for large-scale power grid security. Summary of the Invention

[0010] In response to the above technical problems in related technologies, the present invention proposes a control system and method for an energy storage system to assist thermal power frequency regulation. The energy storage system parameters are designed from three aspects: frequency response capability, power regulation range and SOC regulation margin to solve the above problems.

[0011] In a first aspect, the present invention provides a control system for an energy storage system assisting thermal power frequency regulation, wherein the energy storage system is a three-phase cascade H-bridge energy storage system, comprising an A-phase system, a B-phase system, and a C-phase system, wherein each phase is composed of a linear impedance and N series-connected energy storage submodules, forming an overall series three-phase structure incorporated into a public power grid; the energy storage submodules have the same structure, including a filter circuit, an energy storage converter, and an energy storage unit; the topmost energy storage submodule of each phase of the three-phase energy storage system serves as the master unit of each phase, and the other N-1 energy storage submodules serve as slave units of each phase; and the energy storage system comprises the following modules:

[0012] A power calculation module is used to sample and calculate the active power output of each phase system and the reactive power output of each phase system;

[0013] The master unit current support control module is used to calculate the output current frequency and amplitude of each phase master unit based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment through virtual inertia calculation and the first PI controller. Each phase master unit sends the two as the current phase reference to all slave units of the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases;

[0014] The interphase regulation module is used to calculate the sinusoidal signal of the AC current of each phase according to the phase angle of the output current of each phase system, and perform phase angle compensation on the output current phase angle of each phase system to obtain the equivalent phase angle variable of each phase and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount according to the equivalent phase angle variable of each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent;

[0015] The slave unit virtual impedance control module is used to combine the current phase reference sent by the master unit received by the slave unit with the cascade power distribution coefficient and use virtual impedance control to adjust the output voltage of the slave unit;

[0016] The current amplitude compensation module is used to correct the current active power of each phase according to the output active power of each phase system and the average value of the SOC of each phase to obtain the corrected active power of each phase, and calculate the current amplitude compensation component of each phase according to the corrected active power of each phase and inject it into the calculation of the output current amplitude of the main unit;

[0017] The main unit energy storage control module is used to generate a main unit PWM signal by using the proportional resonant controller to adjust the state of the energy storage converter corresponding to the main unit by combining the sinusoidal signal of each phase AC current and the current of each phase of the public grid;

[0018] The slave unit energy storage control module is used to generate a slave unit PWM signal through voltage and current dual closed-loop control by comparing the output voltage reference of each phase system slave unit with the each phase current of the public grid and the output voltage of each phase system slave unit to adjust the state of the energy storage converter corresponding to the slave unit.

[0019] Specifically, the formulas for calculating the virtual inertia and the first PI controller are as shown in formula (2):

[0020]

[0021] in, is the output current frequency of the x-phase main unit; I x is the output current amplitude of the x-phase main unit; P x The output active power of the x-phase system; Q x is the output reactive power of the x-phase system; H is the virtual inertia time constant; D is the virtual damping coefficient; Indicates that the x-phase system is at the standard frequency fn The system output active power reference; Indicates that the x-phase system is at the standard frequency f n The system output reactive power reference; Δf x Indicates the phase angle balance adjustment value of phase x; I * is the system rated current amplitude; is the reactive power regulation proportional coefficient; is the reactive power regulation integral coefficient; s represents the Laplace operator; Indicates the output current frequency of the x-phase main unit The derivative of the time variable t; ΔI x is the x-phase current amplitude compensation component; x∈{A,B,C}.

[0022] Specifically, the calculation formula for calculating the sinusoidal signal of each phase AC current according to the phase angle of each phase system output current in the phase regulation module is shown in formula (4):

[0023]

[0024] in, is the current sinusoidal signal conversion function, which is used to combine the current amplitude and phase into a sinusoidal signal. is the x-phase AC current sinusoidal signal; δ B I is the output current phase angle of the B phase system; δ C I Output current phase angle for the C-phase system.

[0025] Specifically, according to formula (5), the phase angle compensation of the output current phase angle of each phase system is performed to obtain the equivalent phase angle variable of each phase:

[0026]

[0027] in is the equivalent phase angle variable of phase A after phase angle compensation; is the equivalent phase angle variable of phase B after phase angle compensation; is the equivalent phase angle variable of phase C after phase angle compensation; δ A I is the output current phase angle of phase A system; δ B I is the output current phase angle of the B phase system; δ C I Output current phase angle for the C-phase system.

[0028] Specifically, each phase main unit calculates the interphase phase angle balance adjustment amount according to the equivalent phase angle variable of each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three-phase phase consistent based on formula (6):

[0029]

[0030] Where Δf x Indicates the phase angle balance adjustment value of phase x; Ω={A,B,C}, used to represent the set of subscripts of the three phases A, B, and C; k p and k I is the frequency adjustment coefficient, k p k is the frequency adjustment coefficient of inter-phase synchronous control; I is the frequency adjustment coefficient for phase-to-phase synchronization control; Represents the set of all equivalent phase angle variables; ultimately, the phase angle balance adjustment value Δf of phase x is x Formula (2) is passed to the main unit current support control module.

[0031] Specifically, the expression for the virtual impedance control adjustment is shown in formula (7):

[0032]

[0033] Among them, i x Indicates the x-phase system output current; V x represents the output voltage reference of the x-phase slave unit; s represents the Laplace operator; x represents the phase, x∈{A,B,C}; I x is the output current amplitude of the x-phase main unit; represents the magnitude of the x-phase virtual resistance; g(s) is the second-order transfer function; Indicates the virtual impedance of the slave unit; represents the active power required by phase x, which is calculated according to formula (8):

[0034]

[0035] Specifically, the second-order transfer function g(s) is implemented based on formula (9):

[0036]

[0037] in, is the x-phase angle frequency, that is f n is the standard frequency; Indicates the cascade power distribution coefficient of each unit in phase x.

[0038] Specifically, the current active power of each phase is corrected according to the output active power of each phase system and the average value of the SOC of each phase to obtain the corrected active power of each phase based on formula (11). Formula (11) is as follows:

[0039]

[0040] Among them, P x is the output active power of the x-phase system; P' x is the corrected active power of phase x; is the average SOC value of phase x, n is the number of all energy storage units in the x-phase system; x∈{A,B,C}; k soc is the SOC phase balance ratio coefficient.

[0041] Specifically, the calculation formula for calculating the current amplitude compensation component of each phase based on the corrected active power of each phase is shown in formula (12):

[0042]

[0043] Among them, ΔI x is the x-phase current amplitude compensation component; k0 is the proportional coefficient of current compensation control; is the average value of the three-phase corrected active power; sgn() is the sign function.

[0044] In a second aspect, the present invention provides a control method for energy storage system-assisted thermal power frequency regulation, based on a control system for energy storage system-assisted thermal power frequency regulation according to any one of the first aspects, comprising the following steps:

[0045] S1, sampling and calculating each phase system output active power and each phase system output reactive power;

[0046] S2. Based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment amount, the virtual inertia calculation and the first PI controller are used to calculate the output current frequency and the output current amplitude of each phase master unit. Each phase master unit sends the two as the current phase reference to all slave units in the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases;

[0047] S3. Calculate the AC current sinusoidal signal of each phase based on the output current phase angle of each phase system, perform phase angle compensation on the output current phase angle of each phase system to obtain an equivalent phase angle variable for each phase, and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount based on the equivalent phase angle variable for each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent in phase.

[0048] S4, the slave unit receives the current phase reference sent by the master unit and combines it with the cascade power distribution coefficient, and uses virtual impedance control to adjust the output voltage of the slave unit;

[0049] S5. Correcting the current active power of each phase according to the system output active power of each phase and the average SOC value of each phase to obtain the corrected active power of each phase, and calculating the current amplitude compensation component of each phase according to the corrected active power of each phase, and injecting the resulting compensation component into the calculation of the output current amplitude of the main unit;

[0050] S6. Using the sinusoidal signal of each phase AC current and the current of each phase of the public grid through a proportional resonant controller to generate a main unit PWM signal to adjust the state of the energy storage converter corresponding to the main unit;

[0051] S7. The output voltage reference of each phase system slave unit is combined with each phase current of the public grid and the output voltage of each phase system slave unit through voltage and current dual closed-loop control to generate a slave unit PWM signal to adjust the state of the energy storage converter corresponding to the slave unit.

[0052] The control system and method for the energy storage system-assisted thermal power frequency regulation of the present invention can effectively assist in regulating the thermal power ramp rate under high-proportion penetration of new energy, thereby improving the frequency regulation capability of the entire power system under high-proportion penetration of new energy.

[0053] Compared with the prior art, the present invention has the following significant improvements:

[0054] 1) Stronger multi-module power regulation capability

[0055] Compared with the traditional voltage-type VSG and current-type GFL solutions that cannot achieve flexible module-level power adjustment, the present invention adopts a master-slave structure combined with virtual impedance control, which can accurately adjust the output voltage of each energy storage sub-module while ensuring current consistency, thereby realizing adaptive power distribution among multiple modules.

[0056] 2) Equipped with a complete SOC balancing mechanism

[0057] Unlike existing control methods that do not consider or only partially consider energy balance, the present invention introduces a power allocation factor based on the SOC state and a current amplitude compensation mechanism driven by the phase-to-phase SOC in the three-phase system. This can dynamically balance the charge state of each energy storage unit during system operation, thereby improving the overall life and utilization efficiency of the energy storage system.

[0058] 3) Better system-level frequency support capability

[0059] The present invention introduces a virtual inertia link in the master unit to enable the energy storage system to have frequency dynamic response characteristics; at the same time, the slave unit improves the system disturbance suppression capability through a dynamically optimized second-order controller, and the overall frequency support performance is significantly better than the voltage-type VSG slow response solution and the current-type GFL easy-to-instability solution.

[0060] 4) Outstanding inter-phase coordination ability

[0061] Traditional solutions often neglect three-phase coordinated control, which can easily lead to power imbalance and phase angle drift. This invention, by constructing an interphase phase angle adjustment variable and a current compensation injection strategy based on SOC differences, achieves interphase power coordination and synchronous control of a three-phase system under the constraint of current consistency for the first time, effectively suppressing dynamic three-phase imbalance.

[0062] 5) Clear structure and easy engineering implementation

[0063] The solution of the present invention adopts a layered architecture of master-slave + phase control, with clear functional division of labor and low coupling between controllers, which is suitable for distributed deployment and modular expansion of actual projects. At the same time, the solution has low dependence on sensor accuracy and external power grid, has greater robustness and field adaptability, and conducts more reasonable and intelligent scheduling of power supply, providing better protection and defense for large-scale power grid security. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0065] Figure 1 This is a control block diagram of a control system for an energy storage system assisting thermal power frequency regulation provided by an embodiment of the present invention;

[0066] Figure 2 This is a schematic diagram of the main unit current support control using phase A as an example provided by an embodiment of the present invention;

[0067] Figure 3 1 is a schematic diagram of slave unit virtual impedance control using phase A as an example provided by an embodiment of the present invention;

[0068] Figure 4 This is a schematic diagram of a control method for energy storage system-assisted thermal power frequency regulation provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0069] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention are within the scope of protection of the present invention.

[0070] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature identified as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "plurality" means two or more, unless otherwise specifically defined.

[0071] The embodiment of the present invention provides a control method and system for an energy storage system to assist thermal power frequency regulation, in a preferred but non-limiting implementation manner of the present invention.

[0072] Example 1.

[0073] refer to Figure 1 This embodiment provides a schematic diagram of a control system for an energy storage system assisting thermal power frequency regulation. The energy storage system is a three-phase cascade H-bridge energy storage system, wherein the three phases include phase A, phase B, and phase C. The energy storage system includes an A-phase system, a B-phase system, and a C-phase system. Each phase is composed of a linear impedance and N series-connected energy storage submodules, forming an overall series three-phase structure that is incorporated into a public power grid. N is a positive integer greater than 1.

[0074] The utility grid provides a voltage amplitude V g and phase angle θ g , as a synchronization reference between the three phases of general energy storage system control;

[0075] In traditional power systems, a phase-locked loop (PLL) is generally used to track the phase and frequency of the utility grid in real time to provide a synchronization reference signal for the control system. For example, by measuring the zero crossing point of the utility grid or using complex algorithms (such as synchronous frame phase-locked loop), the PLL outputs a phase angle θ that is in phase with the utility grid. g and voltage amplitude V g , as a benchmark for subsequent control (such as current control, power regulation); that is, the traditional power system requires real-time information of the public grid (voltage amplitude V g and phase angle θ g ) to achieve synchronization, otherwise the phase and amplitude of the output current or the power output cannot be accurately controlled, which may lead to grid connection failure or low power transmission efficiency; the control method of this embodiment realizes phase-locked loop-free control between the three phases of the power grid, and does not require real-time tracking of the grid voltage reference (voltage amplitude V g and phase angle θ g This technology not only simplifies system design but also improves dynamic response, reliability, and adaptability. It is particularly suitable for scenarios with high synchronization requirements and complex grid conditions, such as renewable energy grid integration and microgrids.

[0076] The A-phase system, the B-phase system, and the C-phase system are connected to the public power grid respectively, responsible for converting the DC power of the energy storage unit into AC power and feeding it back to the grid;

[0077] The energy storage submodules have the same structure, and both include a filtering circuit, an energy storage converter, and an energy storage unit. After the energy storage unit is connected to the energy storage converter, it is connected to the public power grid through the filtering circuit. The filtering circuit contains an inductor L and a capacitor C, which are used to filter and stabilize the output voltage. Each energy storage converter includes an SOC measuring device, a voltage sampling device, and a current sampling device. The SOC measuring device is used to collect the remaining power of the energy storage unit, that is, the real-time SOC status of the energy storage unit. The voltage sampling device is used to sample the voltage of the energy storage submodule, and the current sampling device is used to sample the current of the energy storage submodule. The sampling frequency is 10kHz. That is, each energy storage submodule is equipped with independent SOC measurement, voltage, and current sampling functions.

[0078] The energy storage submodule adopts an IGBT full-bridge structure that supports SVPWM control and has dual closed-loop control of voltage and current;

[0079] The energy storage unit is a battery or other energy storage device used to store and release electrical energy. The energy storage unit is connected to the controller via a DC link to provide or absorb DC power.

[0080] The Power Conversion System (PCS) is the core device that connects the energy storage unit to the grid, enabling bidirectional power conversion. Its main functions and features include: converting battery DC power to AC power (discharging) or grid AC power to DC power (charging), supporting flexible AC / DC conversion; receiving control commands through communication, regulating the grid's active and reactive power, and balancing load and grid interaction;

[0081] In this system, energy storage submodules are connected in series to form a single, directly connected high-voltage grid. While this structure achieves uniform current output, it also introduces the following control difficulties:

[0082] 1) All modules must output the same current, otherwise inconsistent current will cause module imbalance or even overvoltage and overcurrent faults;

[0083] 2) How to coordinate the synchronization and power distribution issues of each module;

[0084] 3) Power regulation must take into account the SOC balance target to avoid the "short board effect" in series modules;

[0085] 4) It can suppress current when the grid voltage fluctuates.

[0086] This embodiment proposes a hierarchical and hierarchical collaborative control strategy based on "current control + virtual impedance control + interphase coordinated control". For each phase, the top-level energy storage submodule is selected as the master unit. The master unit adopts the current-type support control method to be responsible for current control. The remaining energy storage submodules are used as slave units. The slave units adopt the virtual impedance control method. The interphase behavior control adopts interphase phase supplementation control and interphase current compensation control, which are used for three-phase phase balance adjustment and three-phase interphase SOC balance control, respectively.

[0087] In this embodiment, the topmost energy storage submodule of each phase of the three-phase energy storage system is used as the master unit of each phase, and the other N-1 energy storage submodules are used as slave units of each phase;

[0088] For example, in this embodiment, N is 10, and the energy storage submodules in the A-phase system are divided and numbered from 1 from top to bottom according to the series connection order of the energy storage submodules, namely, the 1st energy storage submodule of phase A, the 2nd energy storage submodule of phase A, ..., the 10th energy storage submodule of phase A. Then, the 1st energy storage submodule of phase A is used as the master unit of the A-phase system, and the 2nd to 10th energy storage submodules of phase A are used as slave units of the A-phase system.

[0089] The division rules of energy storage submodules in the B-phase system and the C-phase system are the same as those in the A-phase system, namely:

[0090] The first energy storage submodule of phase B is used as the master unit of the phase B system, and the second to tenth energy storage submodules of phase B are used as slave units of the phase B system;

[0091] The first energy storage submodule of phase C is used as the master unit of the phase C system, and the second to tenth energy storage submodules of phase C are used as slave units of the phase C system.

[0092] The output voltage of the first energy storage submodule of phase A is v A1 , the output voltage of the second energy storage submodule of phase A is v A2 , the output current of the Nth energy storage submodule of phase A is v AN Because the energy storage submodules in the series system share current, the output current of the energy storage submodules in the A phase system is consistent, both are i A ;

[0093] i A is the A-phase current of the public grid, and the A-phase voltage of the public grid is equal to the output voltage of each energy storage submodule in A phase (v A1 , v A2 ,...,v AN ) is the cumulative sum of .

[0094] The input current and input voltage of each energy storage submodule of the B-phase system and the C-phase system are similar to those of the A-phase system, namely:

[0095] The output voltage of the first energy storage submodule of phase B is v B1 , the output voltage of the second energy storage submodule of phase B is v B2 , the output current of the Nth energy storage submodule of phase B is v BN Because the energy storage submodules in the series system share current, the output current of the energy storage submodules in the B phase system is consistent, both are i B ;

[0096] i B is the B-phase current of the public grid, and the B-phase voltage of the public grid is equal to the output voltage of each B-phase energy storage submodule (v B1 , v B2 ,...,v BN ) is the cumulative sum of .

[0097] The output voltage of the first energy storage submodule of phase C is v C1 , the output voltage of the second energy storage submodule of phase C is v C2 , the output current of the Nth energy storage submodule of phase C is v CN Because the energy storage submodules in the series system share current, the output current of the energy storage submodules in the C phase system is consistent, both are i C ;

[0098] i C is the C-phase current of the public grid, and the C-phase voltage of the public grid is equal to the output voltage of each C-phase energy storage submodule (v C1 , v C2 ,...,v CN ) is the cumulative sum of .

[0099] Each energy storage submodule includes a unit controller, that is, each phase system includes 1 master unit controller and N-1 slave unit controllers;

[0100] Each phase system master unit controller is responsible for coordinating the operation of the entire system. Each phase system master unit controller communicates with other phase system master unit controllers through inter-phase communication messages. Each phase system master unit controller sends its own inter-phase communication messages to other phase system master unit controllers and receives inter-phase communication messages sent by other phase system master unit controllers. The inter-phase communication messages include: A phase corrected active power P' A ; Corrected active power P' of phase B B ; Corrected active power P' of phase C C ; A phase equivalent phase angle variable B-phase equivalent phase angle variable C-phase equivalent phase angle variable

[0101] For example, the A-phase system main unit controller corrects the active power P' of phase A. A Equivalent phase angle variable to phase A It is sent to the B-phase system main unit controller and the C-phase system main unit controller, and also receives the B-phase corrected active power P' sent by the B-phase system main unit controller. A Equivalent phase angle variable to phase B and the C-phase corrected active power P' sent by the C-phase system master unit controller C Equivalent phase angle variable to phase C

[0102] The master unit communicates with each phase slave unit controller to receive the slave unit SOC information sent by the slave unit and calculate the average SOC of each phase. And send the master controller instructions to the slave unit controller;

[0103] Average SOC value of each phase The calculation formula is: n is the number of all energy storage units in phase x; x∈{A,B,C} is used to represent three phases;

[0104] The main controller instructions include the main unit output current frequency Main unit output current amplitude I x And the average SOC of each phase To the slave unit controller; where x represents the phase, x∈{A,B,C};

[0105] The main unit controller also controls the charging and discharging process of the energy storage unit in the main unit and adjusts the output current and voltage through signals;

[0106] Each slave unit has a slave unit controller, which is responsible for controlling the corresponding energy storage unit and receiving the master controller instructions sent by each phase master unit controller. It adjusts the charging and discharging process according to the master controller instructions and sends the slave unit SOC information back to the master unit controller.

[0107] Inter-phase communication (interaction between master units) is mainly used to adjust inter-phase coordination, including inter-phase synchronization and inter-phase SOC balance; intra-phase communication (interaction between master units and slave units) is mainly used to synchronize the units within the phase, inertial support, and intra-phase SOC balance;

[0108] Both inter-phase communication (e.g., between the A-phase master unit and the B-phase master unit) and intra-phase communication (e.g., between the A-phase master unit and the A-phase slave unit) use wired communication and are implemented through serial communication technology. This is existing technology and will not be repeated here.

[0109] d in the figure AThe signal is the duty cycle control signal output by the A-phase main unit controller, which is used to adjust the switching state of the IGBT in the energy storage converter (PCS). Ai represents the duty cycle control signal output by the i-th slave unit controller of phase A;

[0110] In power electronics systems, the switching states of IGBTs (insulated gate bipolar transistors) in PSCs include two operating modes: on (ON) and off (OFF). These two states are controlled by the gate voltage. By controlling the switching state of the IGBT, precise regulation of current and voltage is achieved, thereby meeting the operating requirements of the power electronics system.

[0111] A general controller first obtains a reference value (such as a target current or voltage), compares the reference value with the actual value, passes it through a current loop or voltage loop controller, and then converts it into a normalized duty cycle signal through a modulation strategy (such as SPWM or SVPWM).

[0112] The master unit controller is a current VSG controller; the slave unit controller is a virtual impedance controller;

[0113] The VSG controller (Virtual Synchronous Generator Controller) is a control strategy used to simulate the characteristics of synchronous generators. It is mainly used in renewable energy power generation systems (such as wind power and photovoltaic power generation) and energy storage systems to enhance the inertia and stability of the system.

[0114] The energy storage system has the ability to form a grid and operate; the control system acts on the energy storage system;

[0115] The control system includes the following modules:

[0116] A power calculation module is used to sample and calculate the active power output of each phase system and the reactive power output of each phase system;

[0117] Specifically, the system output active power P per phase x And each phase system output reactive power Q x The output voltage v collected by each phase main unit x and the output current i x The calculation expression is shown in formula (1):

[0118]

[0119] Where s represents the Laplace operator, Indicates v x The 90° lag angle can be determined by v xAfter Hilbert transform, we can get: τ is the time constant of the low-pass filter, which is generally set to 0.008s~0.03s; the parameter x in the formula is used to represent the three-phase number, x∈{A,B,C}; that is, i x Indicates the x-phase system output current; v x Indicates the x-phase system output voltage;

[0120] Specifically, the system output active power P per phase x Including the A phase system output reactive power P A , B phase system output reactive power P B And the C phase system output reactive power P C ; Each phase system output reactive power Q x Including phase A system reactive power Q A , B phase system reactive power Q B And C phase system reactive power Q C ;

[0121] The output voltage v x The output current i is obtained by collecting the voltage signal of the voltage sampling device of each phase main unit, generally collecting the voltage signal of the two ends of the capacitor C; x The current is collected by the current sampling device of each phase main unit, generally collecting the current signal at both ends of the inductor L;

[0122] For example, the output voltage of the A phase system is v A With the output current i A The voltage sampling device and current sampling device of the phase A main unit are used to collect the data. The overall output reactive power and active power of phase A are obtained by calculation. The expressions are as follows:

[0123]

[0124] Similarly, the collection of output current and output voltage of the B-phase system and the C-phase system and the calculation of active power and reactive power are similar to those of the A-phase system and will not be repeated here.

[0125] Figure 1 in i A is the A-phase system output current, v A is the output voltage of the phase A system, v A2 ,…,v An Indicates the output voltage of the A-phase system slave unit.

[0126] The master unit current value support control module is used to calculate the output current frequency and amplitude of each phase master unit based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment through virtual inertia calculation and the first PI controller. Each phase master unit sends the two as the current phase reference to all slave units of the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases;

[0127] The formulas for calculating the virtual inertia and the PI controller are shown in formula (2):

[0128]

[0129] in, is the output current frequency of the x-phase main unit; I x is the output current amplitude of the x-phase main unit; P x The output active power of the x-phase system; Q x is the output reactive power of the x-phase system; H is the virtual inertia time constant, whose value is related to the energy storage capacity and the allowable frequency change rate of the system. In this embodiment, its value is 0.039; D is the virtual damping coefficient, whose value is related to the energy storage capacity and the allowable frequency deviation range. In this embodiment, its value is 80; Indicates that the x-phase system is at the standard frequency f n The output active power reference of the lower system is generally determined by the preset value according to the grid demand; Indicates that the x-phase system is at the standard frequency f n The system output reactive power reference is generally a preset value determined by the grid demand (if the grid does not require a reactive power reference value, it is set to 0); Δf x Indicates the phase angle balance adjustment value of phase x; I x * is the rated current amplitude of the x-phase system, which can be calculated based on Divide by the rated grid voltage to obtain; and is the frequency adjustment coefficient, is the reactive power regulation proportional coefficient; is the reactive power regulation integral coefficient; s represents the Laplace operator; standard frequency f n The default is 50Hz; Indicates the output current frequency of the x-phase main unit The derivative of the time variable t, that is, the rate of change of frequency (ROCOF); ΔI x is the x-phase current amplitude compensation component; x represents the phase, x∈{A,B,C};

[0130] The first formula in formula (2) is for virtual inertia calculation; the second formula in formula (2) is for calculating the output current amplitude reference. The first PI controller is used for system reactive power regulation and control, and adjusts the output current amplitude reference size according to the system reactive power.

[0131] The PI controller generates a control signal to adjust the controlled object by performing proportional and integral operations on the system's error signal, so that the system output is as close to the expected value as possible.

[0132] In the second formula (2), Indicates the error between the reference value and the actual value of reactive power; is the first PI controller; is the proportional coefficient, which performs proportional operation on the error, quickly responds to the change of the error, and produces a control component proportional to the error size; The integral link in the time domain calculates the accumulated error over time to eliminate the steady-state error of the system. Through the combined effect of proportion and integration, the first PI controller adjusts the output current amplitude of the main unit I x , so that it is close to the expected value to achieve accurate control of reactive power, that is, formula (2) The second formula is the embodiment of the calculation of the first PI controller;

[0133] Each phase main unit calculates the main unit output current frequency of each phase And the main unit output current amplitude I x , and then the output current frequency of each phase main unit And the main unit output current amplitude I x The master unit of each phase also calculates the average SOC value of each phase based on the SOC information of all energy storage subsystems in each phase (the master unit SOC information and the SOC information of all slave units). Send to all other slave units in the same phase at the same time;

[0134] Specifically, the main unit outputs current frequency Including the output current frequency of the A phase main unit B-phase main unit output current frequency And the output current frequency of the C phase main unit The main unit output current amplitude I x Including the output current amplitude of the A phase main unit I A , B phase main unit output current amplitude I B And the output current amplitude of the C phase main unit I C ;

[0135] refer to Figure 2 , Figure 2Schematic diagram of the A-phase main unit current VSG controller; specifically, the calculation formula corresponding to the A-phase main unit output current frequency and the A-phase main unit output current amplitude is as follows:

[0136]

[0137] Where Δf A Indicates the inter-phase balance adjustment value of phase A; Indicates the output current frequency of the A-phase main unit; I A * is the rated current amplitude of the A-phase system; I A Indicates the output current amplitude of the main unit of the A-phase system; Indicates that the A phase system is at the standard frequency f n The system output active power reference; Indicates that the A phase system is at the standard frequency f n The lower system output reactive power reference; is the reactive power regulation proportional coefficient of the phase A system, and its value is 0.0006; is the reactive power regulation integral coefficient of the A-phase system, and its value is 0.0005; Express The derivative with respect to the time variable t;

[0138] Specifically, the calculation formula corresponding to the output current frequency of the B-phase main unit and the output current amplitude of the B-phase main unit is as follows:

[0139]

[0140] Where Δf B Indicates the interphase balance adjustment value of phase B; Indicates the output current frequency of the B-phase main unit; I B * is the rated current amplitude of the B phase system; I B Indicates the output current amplitude of the main unit of the B-phase system; Indicates the phase system at the standard frequency f n The system output active power reference; Indicates that the B phase system is at the standard frequency f n The lower system output reactive power reference; is the reactive power regulation proportional coefficient of the phase B system, and its value is 0.0006; is the reactive power regulation integral coefficient of the B phase system, and its value is 0.0005; Express The derivative with respect to the time variable t;

[0141] Specifically, the calculation formula corresponding to the output current frequency of the C-phase main unit and the output current amplitude of the C-phase main unit is as follows:

[0142]

[0143] Where Δf C Indicates the inter-phase balance adjustment value of phase C; Indicates the output current frequency of the C-phase main unit; I C * is the rated current amplitude of the C phase system; I C Indicates the output current amplitude of the main unit of the C phase system; Indicates that the C phase system is at the standard frequency f n The system output active power reference; Indicates that the C phase system is at the standard frequency f n The lower system output reactive power reference; is the reactive power regulation proportional coefficient of the C-phase system, and its value is 0.0006; is the reactive power regulation integral coefficient of the C phase system, and its value is 0.0005; Express The derivative with respect to the time variable t;

[0144] The interphase regulation module is used to calculate the sinusoidal signal of the AC current of each phase according to the phase angle of the output current of each phase system, and perform phase angle compensation on the output current phase angle of each phase system to obtain the equivalent phase angle variable of each phase and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount according to the equivalent phase angle variable of each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent;

[0145] Output phase angle of each phase The main unit controller outputs the current frequency of each phase of the main unit The integral is obtained as shown in formula (3):

[0146]

[0147] That is, the output phase angle of the A-phase system is δ A I , the output phase angle of the B-phase system is δ B I , the output phase angle of the C-phase system is δ C I ;

[0148] Since each phase operates independently, achieving coordinated control of the entire system requires addressing two key issues: 1) interphase synchronization; and 2) interphase power distribution. In this solution, the control method for each phase is the same, so the overall system output, i.e., the overall output frequency and amplitude of the energy storage system, can be determined:

[0149] Each phase AC current sinusoidal signal calculated by the main unit of each phase system include As shown in formula (4):

[0150]

[0151] in, is the current sinusoidal signal conversion function, which is used to combine the current amplitude and phase into a sinusoidal signal. is the x-phase AC current sinusoidal signal; that is, is the A-phase AC current sinusoidal signal; is the B-phase AC current sinusoidal signal; is the C-phase AC current sinusoidal signal; δ A I , δ B I , δ C I are the output current phase angles of each phase system calculated by the A, B, and C phase system main unit controllers using formula (3); δ A I is the output current phase angle of phase A system; δ B I is the output current phase angle of the B phase system; δ C I is the output current phase angle of the C phase system; I A I is the output current amplitude of the main current unit of the A phase system, which is also the current flowing through all units in this string of phase A; B I is the output current amplitude of the main unit of the B phase system, which is also the current flowing through all units in this string of phase B; C The output current amplitude of the main current unit of the C phase system is also the current flowing through all units in this string of phase C;

[0152] In order to eliminate the fixed phase difference of 2 / 3π (rad) of the three-phase current, the output current phase angle of each phase is compensated by formula (5) with phase A as the reference to obtain the equivalent phase angle variable of each phase; formula (5) is as follows:

[0153]

[0154] in is the equivalent phase angle variable of phase A after phase angle compensation; is the equivalent phase angle variable of phase B after phase angle compensation; is the equivalent phase angle variable of phase C after phase angle compensation; each phase master unit controller transmits the equivalent phase angle variable of the phase system after phase angle compensation to other phase master unit controllers;

[0155] For example, the A-phase master unit controller converts the phase angle compensated A-phase equivalent phase angle variable The B-phase main unit controller and the C-phase main unit controller are transmitted to the B-phase main unit controller and the C-phase main unit controller; similarly, the B-phase main unit controller converts the phase angle compensated B-phase equivalent phase angle variable The controller of the C-phase main unit transmits the phase angle compensation equivalent phase angle variable of the C-phase to the A-phase main unit controller and the C-phase main unit controller; the C-phase main unit controller transmits the phase angle compensation equivalent phase angle variable of the C-phase to the A-phase main unit controller and the C-phase main unit controller. Passed to the A-phase main unit controller and the B-phase main unit controller;

[0156] The second PI controller is used to adjust the system frequency output of each phase to make the three phases consistent, as shown in formula (6):

[0157]

[0158] Where Δf x Indicates the phase angle balance adjustment value of phase x; Ω={A,B,C}, used to represent the set of subscripts of the three phases A, B, and C; k p and k I is the frequency adjustment coefficient, k p k is the inter-phase synchronous control frequency adjustment coefficient, which is 1.3 in this embodiment. I is the inter-phase synchronous control frequency adjustment coefficient, which is 2.5 in this embodiment; Represents the set of all equivalent phase angle variables; ultimately, the phase angle balance adjustment value Δf of phase x is x Formula (2) passed to the main unit current support control module;

[0159] Formula (6) first calculates It means calculating the sum of the phase differences between the other two phases and the x phase. This sum of phase differences reflects the overall phase difference between the x phase and the other two phases.

[0160] Then, the sum of the phase differences is passed through the second PI controller (k P +k I / s) for processing, the proportional part k p Directly multiplying the sum of the phase differences produces an adjustment proportional to the current phase difference; the integral part k I / s integrates the sum of the phase differences to generate an adjustment amount that accumulates over time and is used to eliminate steady-state errors;

[0161] The final Δf x It is used to adjust the frequency output of the x-phase system. By adjusting the frequency output, the speed of phase change is changed, so that the three-phase phases tend to be consistent.

[0162] The steady state of formula (6) is That is, when δ AI =δ B I +2π / 3=δ C I -2π / 3 meets the three-phase balance requirement of the system. Since the phase is the integral of the frequency, if the steady-state phase is balanced, the frequency will definitely be synchronized. Therefore, the frequency synchronization between the phases of the three-phase system can be maintained by formula (6), while also maintaining the phase balance of the three-phase system.

[0163] The slave unit virtual impedance control module is used to combine the current phase reference sent by the master unit received by the slave unit with the cascade power distribution coefficient and use virtual impedance control to adjust the output voltage of the slave unit;

[0164] refer to Figure 3 , Figure 3 This is a schematic diagram of the virtual impedance control of the A-phase slave unit. Since the output current of the energy storage submodule in each phase system is consistent, the current phase reference (the output current frequency of the master unit) And the main unit output current amplitude I x ) can be used to control the slave unit. The slave unit adopts a virtual impedance control method that does not require synchronization and adjusts the output voltage according to the current reference power and system current information. The expression is shown in formula (7):

[0165]

[0166] Among them, V x represents the output voltage reference of the x-phase slave unit; s represents the Laplace operator; x represents the phase, x∈{A,B,C}; Indicates the active power required by phase x; I x is the output current amplitude of the x-phase main unit; represents the magnitude of the x-phase virtual resistance; g(s) is a second-order transfer function, which is used to optimize the dynamic response of the system and improve the stability of the system; Indicates the virtual impedance of the slave unit;

[0167] Among them, the active power required by phase x is According to formula (8), we can get:

[0168]

[0169] Where H is the virtual inertia time constant, D is the virtual damping coefficient; s represents the Laplace operator; f is the output current frequency of the x-phase main unit; n It is the standard frequency, usually 50Hz;

[0170] The second-order transfer function g(s) is implemented based on formula (9):

[0171]

[0172] Where x represents the phase, x∈{A,B,C}; is the x-phase angle frequency, that is f n is the standard frequency; The cascade power allocation coefficient for each unit in phase x needs to be determined based on the real-time SOC status of each energy storage unit in each phase system. This allows the output power to be adjusted based on the real-time SOC status, thereby achieving SOC balance among each energy storage unit in the phase.

[0173] Cascade power distribution coefficient of each unit in phase x According to formula (10), we can get:

[0174]

[0175] in, Indicates the remaining capacity of the i-th energy storage unit in phase x, i.e., the real-time SOC state of the energy storage unit. The value of can be directly read after estimation based on the BMS system of the energy storage unit; n represents the number of all energy storage units in phase x, i represents the sequence number of the energy storage units from top to bottom in each phase, the sequence number of the energy storage unit of the master unit is 1, the sequence number of the energy storage unit of the first slave unit is 2, ..., the sequence number of the energy storage unit of the N-1th slave unit is N;

[0176] The current amplitude compensation module is used to correct the current active power of each phase according to the output active power of each phase system and the average value of the SOC of each phase to obtain the corrected active power of each phase, and calculate the current amplitude compensation component of each phase according to the corrected active power of each phase and inject it into the calculation of the output current amplitude of the main unit;

[0177] Since each phase system operates independently, in order to achieve overall coordinated control of the system, the following two issues need to be addressed: (1) inter-phase power distribution; (2) inter-phase SOC balance adjustment.

[0178] In order to further achieve power coordination and SOC balance among the three-phase systems, this embodiment introduces a current amplitude compensation control strategy: This strategy constructs a corrected power expression based on the average SOC value of each phase to correct the current active power of each phase, thereby obtaining the corrected active power of each phase, and calculates the current amplitude compensation component of each phase based on the corrected active power of each phase. The injection formula (2) is used to calculate the output current amplitude of the main unit I x In the calculation, the energy flow between the three phases is dynamically adjusted to achieve inter-phase SOC balance, thereby achieving active power coordination and smooth energy balance among the three phases.

[0179] The corrected active power of each phase is obtained by correcting the current active power of each phase according to the current active power of each phase and the average SOC value of each phase. The corrected active power of each phase is obtained based on formula (11). Formula (11) is as follows:

[0180]

[0181] Among them, P x is the output active power of the x-phase system, that is, the current active power of the x-phase system; P' x is the corrected active power of phase x; is the average SOC value of phase x, n is the number of all energy storage units in the x-phase system; x∈{A,B,C} is used to represent three phases; k soc The SOC phase balance ratio coefficient can generally be selected between 0.01 and 0.1 of the rated power. The larger the value, the faster the SOC convergence speed. Too large a value will also affect stability.

[0182] The calculation of the current amplitude compensation component of each phase based on the corrected active power of each phase is shown in formula (12):

[0183]

[0184] Among them, ΔI x is the x-phase current amplitude compensation component; k0 is the proportional coefficient of current compensation control, which needs to be selected based on power, current and system stability. In this embodiment, k0 is between 1.4e-4 and 2.86e-4; is the average value of the three-phase corrected active power, that is sgn() is the sign function.

[0185] SOC is defined as follows:

[0186]

[0187] in, represents the SOC (remaining capacity) of the i-th energy storage unit in the x-phase system, where represents the initial remaining capacity of the i-th energy storage unit in the x-phase system, represents the output current of the DC side of the i-th energy storage unit in the x-phase system, Indicates the capacity of the i-th energy storage unit in the x-phase system, which can be found in the battery module data sheet; It represents the maximum energy sum of the i-th energy storage unit of the x-phase system, through Multiplying it by the DC side output voltage can get; P xi represents the output active power of the i-th energy storage unit in the x-phase system;

[0188] Because power and SOC are closely related, power disturbance changes will also lead to SOC imbalance. If the power distribution is unbalanced, the SOC of some energy storage units will be too high or too low, thus affecting the overall performance and life of the system. Introducing SOC feedback regulation can balance the SOC of each energy storage unit and avoid overcharging or over-discharging.

[0189] formula is the current adjustment formula, and its control significance is that in the discharge mode, P x >0, Too big, Then ΔI x When the value is positive, the output current amplitude of the phase system increases, forcing the discharge power of the phase system to increase and speed up the SOC decrease. In the charging mode, P x <0, when Too big, Then ΔI x When it is positive, the output current amplitude of the phase system decreases, forcing the charging power of the phase system to decrease and slowing down the SOC rising speed.

[0190] The main unit energy storage control module is used to generate a main unit PWM signal by combining the sinusoidal signal of each phase AC current and the current of each phase of the public grid through a proportional resonant controller to adjust the switching state of the IGBT in the energy storage converter corresponding to the main unit;

[0191] The AC current sinusoidal signal of each phase and the current per phase of the public grid i x As the input signal, it is sent to the proportional resonant controller, which processes and calculates the difference of the input signal to generate the main unit PWM signal d x The duty cycle of this signal will be adjusted according to the change of the input signal to achieve precise control of the energy storage converter; the generated d x The signal is used to adjust the switching state of the IGBT in the energy storage converter corresponding to the main unit. As the core switching device of the energy storage converter, the switching state of the IGBT directly determines the output voltage and current of the converter. Therefore, by adjusting the switching state of the IGBT, the flow of electric energy between the energy storage system and the public power grid can be controlled, such as realizing the charging (absorbing electric energy from the grid) or discharging (transmitting electric energy to the grid) of the energy storage system, while ensuring the quality and stability of the output current.

[0192] A proportional resonant (PR) controller is a controller used to track AC signals and eliminate harmonics of specific frequencies. It is particularly suitable for fields such as power electronics and motor control. The proportional resonant controller adds a resonant link to the traditional proportional control, enabling it to achieve high-precision tracking of signals of specific frequencies while suppressing harmonic interference. This is existing technology and will not be described in detail here.

[0193] The slave unit energy storage control module is used to generate a slave unit PWM signal through voltage and current dual closed-loop control by comparing the output voltage reference of each phase system slave unit with the each phase current of the public grid and the output voltage of each phase system slave unit to adjust the switching state of the IGBT in the energy storage converter corresponding to the slave unit.

[0194] The dual closed-loop control input includes the control of each phase system based on two key input quantities (the output voltage reference V x The current per phase of the public grid i x ) and the actual output voltage v of each phase system from the unit Ai , the output voltage reference V x The voltage output target that the system expects to achieve is set, and the current per phase of the utility grid i x And each phase system output voltage v Ai It provides real-time operating status information of the system; voltage and current dual closed-loop control is a common control strategy, which includes voltage loop and current loop. The voltage loop mainly ensures the stability of the output voltage, making it close to the output voltage reference V x The current loop is used to quickly respond to current changes and improve the dynamic performance of the system. Through the synergy of these two closed loops, the system can accurately adjust the control quantity based on the real-time feedback of voltage and current information; the output of the dual closed loop control is used to adjust the slave unit PWM signal d Ai The duty cycle of the PWM signal determines the ratio of the on and off time of the IGBT. By adjusting the duty cycle of dAi, the switching state of the IGBT can be controlled, that is, the generated PWM signal d Ai It is used to adjust the switching state of the IGBT in the energy storage converter, and the switching state of the IGBT directly affects the output voltage and current of the energy storage converter, thereby realizing the control of the power interaction between the energy storage system and the public power grid, such as realizing the charging and discharging functions of the energy storage system, and maintaining the stability of the output voltage and good power quality.

[0195] Dual voltage-current closed-loop control is a high-performance control strategy widely used in power electronics systems (such as inverters, frequency converters, and motor drives). It achieves precise and rapid system regulation through nested voltage and current loops. The strategy consists of an outer loop (voltage loop) and an inner loop (current loop). The outer loop uses the output voltage as the controlled variable and uses a PI controller to compare the error between the target voltage and the actual voltage to output a current reference value. The inner loop (current loop) uses the current as the controlled variable and receives the current reference value output by the voltage loop. A PI controller is used to rapidly adjust the actual current to track the current reference value. Dual voltage-current closed-loop control works in tandem with the inner loop, which is responsible for rapid current regulation, while the outer loop manages the steady-state accuracy of the voltage. These two loops work together to improve overall performance, ensuring stable system output voltage and current. This is prior art and will not be further elaborated here.

[0196] This embodiment also includes a protection and warning module, which is used to set overvoltage protection and undervoltage protection for each energy storage submodule and set SOC upper and lower limit thresholds. When the remaining power of the energy storage unit is lower than the SOC lower limit threshold or higher than the SOC upper limit threshold, the individual energy storage submodule immediately enters a protection state and reports the abnormality. When an abnormality occurs in the communication between the master unit and the slave unit in the phase or the voltage and current exceed the limit, the individual energy storage submodule immediately enters a protection state and reports the abnormality.

[0197] Generally, after entering the protection state, two response strategies can be adopted: first, activate the reserved redundant unit to replace the abnormal module to ensure continuous system operation; second, use the proposed control method to dynamically redistribute power among the remaining units to achieve functional compensation. If the power allocation reaches the system limit and still cannot meet operational requirements, a shutdown maintenance mechanism is triggered to ensure system safety.

[0198] In addition, it should be noted that when all controls are normal, the SOC of all energy storage units is consistent, and there will be no problem of any energy storage unit exceeding the limit.

[0199] This example is based on a three-phase cascaded H-bridge energy storage system with a rated capacity of 100MW and a voltage level of 15.75kV. The overvoltage protection of each energy storage submodule is set to 1800V, and the undervoltage protection is set to 1200V. In this example, the upper and lower SOC thresholds of the energy storage unit are set to 95% and 10%. When a communication anomaly or voltage or current exceeds the limit occurs, the module immediately enters the protection state and reports the anomaly.

[0200] The control strategy of this embodiment does not rely on a traditional phase-locked loop (PLL) for synchronization signal extraction. Instead, the master unit naturally establishes synchronization with the grid or phase-to-phase reference through current support control, while the slave units achieve adaptive synchronization using virtual impedance adjustment, effectively avoiding control uncertainty caused by phase-lock instability and sensing errors. Furthermore, because the system is essentially a current-mode control framework with inherent current limiting capabilities, it can operate stably even in weak grids or scenarios with large line impedance variations, significantly reducing the risk of overcurrent and providing excellent distributed deployment capabilities and field engineering feasibility.

[0201] Example 2.

[0202] refer to Figure 4 This embodiment provides a control method for energy storage system-assisted thermal power frequency regulation, based on the control system for energy storage system-assisted thermal power frequency regulation described in Example 1, including the following steps:

[0203] S1, sampling and calculating each phase system output active power and each phase system output reactive power;

[0204] S2. Based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment amount, the virtual inertia calculation and the first PI controller are used to calculate the output current frequency and the output current amplitude of each phase master unit. Each phase master unit sends the two as the current phase reference to all slave units in the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases;

[0205] S3. Calculate the AC current sinusoidal signal of each phase based on the output current phase angle of each phase system, perform phase angle compensation on the output current phase angle of each phase system to obtain an equivalent phase angle variable for each phase, and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount based on the equivalent phase angle variable for each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent in phase.

[0206] S4, the slave unit receives the current phase reference sent by the master unit and combines it with the cascade power distribution coefficient, and uses virtual impedance control to adjust the output voltage of the slave unit;

[0207] S5. Correcting the current active power of each phase according to the system output active power of each phase and the average SOC value of each phase to obtain the corrected active power of each phase, and calculating the current amplitude compensation component of each phase according to the corrected active power of each phase, and injecting the resulting compensation component into the calculation of the output current amplitude of the main unit;

[0208] S6. Using the sinusoidal signal of each phase AC current and the current of each phase of the public grid through a proportional resonant controller to generate a main unit PWM signal to adjust the state of the energy storage converter corresponding to the main unit;

[0209] S7. The output voltage reference of each phase system slave unit is combined with each phase current of the public grid and the output voltage of each phase system slave unit through voltage and current dual closed-loop control to generate a slave unit PWM signal to adjust the state of the energy storage converter corresponding to the slave unit.

[0210] As described in the background technology, due to the long-term low-load operation of thermal power plants under high renewable energy penetration, the frequency regulation capability of the entire power system is reduced. Due to the limitations on the thermal power ramp rate, the system lacks inertial support. The control system and method of the energy storage system provided in the embodiments of the present invention can effectively assist in regulating the thermal power ramp rate under high renewable energy penetration, thereby improving the frequency regulation capability of the entire power system under high renewable energy penetration.

[0211] Compared with the prior art, the embodiments of the present invention have the following significant improvements:

[0212] 1) Stronger multi-module power regulation capability

[0213] Compared with the traditional voltage-type VSG and current-type GFL solutions that cannot achieve flexible module-level power adjustment, this embodiment adopts a master-slave structure combined with virtual impedance control. While ensuring current consistency, it can accurately adjust the output voltage of each energy storage sub-module and realize adaptive power distribution among multiple modules.

[0214] 2) Equipped with a complete SOC balancing mechanism

[0215] Unlike existing control methods that do not consider or only partially consider energy balance, this embodiment introduces a power allocation factor based on the SOC state and a current amplitude compensation mechanism driven by the phase-to-phase SOC in the three-phase system. This can dynamically balance the charge state of each energy storage unit during system operation, thereby improving the overall lifespan and utilization efficiency of the energy storage system.

[0216] 3) Better system-level frequency support capability

[0217] This embodiment introduces a virtual inertia link in the master unit to give the energy storage system a frequency dynamic response characteristic. At the same time, the slave unit improves the system's disturbance suppression capability through a dynamically optimized second-order controller. The overall frequency support performance is significantly better than the voltage-type VSG slow-response solution and the current-type GFL prone-to-instability solution.

[0218] 4) Outstanding inter-phase coordination ability

[0219] Traditional solutions often neglect three-phase coordinated control, which can easily lead to power imbalance and phase angle drift. This embodiment, by constructing an interphase phase angle adjustment variable and a current compensation injection strategy based on SOC differences, achieves interphase power coordination and synchronous control of a three-phase system under the constraint of current consistency for the first time, effectively suppressing dynamic three-phase imbalance.

[0220] 5) Clear structure and easy engineering implementation

[0221] The solution in this embodiment adopts a layered architecture of master-slave + phase control, with clear functional division of labor and low coupling between controllers, making it suitable for distributed deployment and modular expansion in actual projects. At the same time, the solution has low dependence on sensor accuracy and external power grids, has greater robustness and field adaptability, and implements more reasonable and intelligent scheduling of power supply, providing better protection and defense for large-scale power grid security.

[0222] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A control system for energy storage system-assisted thermal power frequency regulation, characterized in that: The energy storage system is a three-phase cascade H-bridge energy storage system, comprising an A-phase system, a B-phase system, and a C-phase system. Each phase is composed of a linear impedance and N series-connected energy storage submodules, forming an overall series three-phase structure that is incorporated into the public power grid. The energy storage submodules have the same structure, including a filter circuit, an energy storage converter, and an energy storage unit. The topmost energy storage submodule of each phase of the energy storage system serves as the master unit of each phase, and the other N-1 energy storage submodules serve as slave units of each phase. The system comprises the following modules: A power calculation module is used to sample and calculate the active power output of each phase system and the reactive power output of each phase system; The master unit current support control module is used to calculate the output current frequency and amplitude of each phase master unit based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment through virtual inertia calculation and the first PI controller. Each phase master unit sends the two as the current phase reference to all slave units of the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases; The interphase regulation module is used to calculate the sinusoidal signal of the AC current of each phase according to the phase angle of the output current of each phase system, and perform phase angle compensation on the output current phase angle of each phase system to obtain the equivalent phase angle variable of each phase and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount according to the equivalent phase angle variable of each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent; The slave unit virtual impedance control module is used to combine the current phase reference sent by the master unit received by the slave unit with the cascade power distribution coefficient and use virtual impedance control to adjust the output voltage of the slave unit; The current amplitude compensation module is used to correct the current active power of each phase according to the output active power of each phase system and the average value of the SOC of each phase to obtain the corrected active power of each phase, and calculate the current amplitude compensation component of each phase according to the corrected active power of each phase and inject it into the calculation of the output current amplitude of the main unit; The main unit energy storage control module is used to generate a main unit PWM signal by using the proportional resonant controller to adjust the state of the energy storage converter corresponding to the main unit by combining the sinusoidal signal of each phase AC current and the current of each phase of the public grid; The slave unit energy storage control module is used to generate a slave unit PWM signal through voltage and current dual closed-loop control by comparing the output voltage reference of each phase system slave unit with the each phase current of the public grid and the output voltage of each phase system slave unit to adjust the state of the energy storage converter corresponding to the slave unit.

2. The control system according to claim 1, characterized in that: The formula for calculating the virtual inertia and the first PI controller is shown in formula (2): in, is the output current frequency of the x-phase main unit; I x is the output current amplitude of the x-phase main unit; P x The output active power of the x-phase system; Q x is the output reactive power of the x-phase system; H is the virtual inertia time constant; D is the virtual damping coefficient; Indicates that the x-phase system is at the standard frequency f n The system output active power reference; Indicates that the x-phase system is at the standard frequency f n The system output reactive power reference; Δf x Indicates the phase angle balance adjustment value of phase x; I * is the system rated current amplitude; is the reactive power regulation proportional coefficient; is the reactive power regulation integral coefficient; s represents the Laplace operator; Indicates the output current frequency of the x-phase main unit The derivative of the time variable t; ΔI x is the x-phase current amplitude compensation component; x∈{A,B,C}.

3. The control system according to claim 2, characterized in that: The calculation formula for calculating the sinusoidal signal of each phase AC current in the phase regulation module according to the phase angle of the output current of each phase system is shown in formula (4): in, is the current sinusoidal signal conversion function, which is used to combine the current amplitude and phase into a sinusoidal signal. is the x-phase AC current sinusoidal signal; δ A I is the output current phase angle of phase A system; δ B I is the output current phase angle of the B phase system; δ C I Output current phase angle for the C-phase system.

4. The control system according to claim 1, characterized in that: According to formula (5), the phase angle of the output current phase angle of each phase system is compensated to obtain the equivalent phase angle variable of each phase: in is the equivalent phase angle variable of phase A after phase angle compensation; is the equivalent phase angle variable of phase B after phase angle compensation; is the equivalent phase angle variable of phase C after phase angle compensation; δ A I Output current phase angle for phase A system; δ B I Output current phase angle for phase B system; δ C I Output current phase angle for the C-phase system.

5. The control system according to claim 4, characterized in that: Each phase master unit calculates the phase angle balance adjustment value based on the equivalent phase angle variable of each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent based on formula (6): Where Δf x Indicates the phase angle balance adjustment value of phase x; Ω={A,B,C}; k p k is the frequency adjustment coefficient of inter-phase synchronous control; I is the frequency adjustment coefficient for phase-to-phase synchronization control; Represents the set of all equivalent phase angle variables; ultimately, the phase angle balance adjustment value Δf of phase x is x Formula (2) is passed to the main unit current support control module.

6. The control system according to claim 2, characterized in that: The expression of the virtual impedance control adjustment is shown in formula (7): Among them, i x Indicates the x-phase system output current; V x represents the output voltage reference of the x-phase slave unit; s represents the Laplace operator; x represents the phase, x∈{A,B,C}; represents the magnitude of the x-phase virtual resistance; g(s) is the second-order transfer function; Indicates the virtual impedance of the slave unit; represents the active power required by phase x, which is calculated according to formula (8):

7. The control system according to claim 6, characterized in that: The second-order transfer function g(s) is implemented based on formula (9): in, is the x-phase angle frequency, that is Indicates the cascade power distribution coefficient of each unit in phase x.

8. The control system according to claim 1, characterized in that: The corrected active power of each phase is obtained by correcting the current active power of each phase according to the system output active power of each phase and the average value of the SOC of each phase. The corrected active power of each phase is obtained based on formula (11). Formula (11) is as follows: Among them, P x is the output active power of the x-phase system; P' x is the corrected active power of phase x; is the average SOC value of phase x, n is the number of all energy storage units in the x-phase system; x∈{A,B,C}; k soc is the SOC phase balance ratio coefficient.

9. The control system according to claim 8, characterized in that: The calculation formula for calculating the current amplitude compensation component of each phase based on the corrected active power of each phase is shown in formula (12): Among them, ΔI x is the x-phase current amplitude compensation component; k0 is the proportional coefficient of current compensation control; is the average value of the three-phase corrected active power; sgn() is the sign function.

10. A control method for energy storage system-assisted thermal power frequency regulation, based on the control system for energy storage system-assisted thermal power frequency regulation according to any one of claims 1 to 9, characterized in that: The following steps are involved: S1, sampling and calculating each phase system output active power and each phase system output reactive power; S2. Based on the active power output of each phase system, the reactive power output of each phase system, and the phase angle balance adjustment amount, the virtual inertia calculation and the first PI controller are used to calculate the output current frequency and the output current amplitude of each phase master unit. Each phase master unit sends the two as the current phase reference to all slave units in the phase, and calculates the corrected active power of each phase and the equivalent phase angle variable of each phase and sends them to the master units of other phases; S3. Calculate the AC current sinusoidal signal of each phase based on the output current phase angle of each phase system, perform phase angle compensation on the output current phase angle of each phase system to obtain an equivalent phase angle variable for each phase, and send it to other phase master units. Each phase master unit calculates the interphase phase angle balancing adjustment amount based on the equivalent phase angle variable for each phase and adjusts the frequency output of each phase system based on the second PI controller to make the three phases consistent in phase. S4, the slave unit receives the current phase reference sent by the master unit and combines it with the cascade power distribution coefficient, and uses virtual impedance control to adjust the output voltage of the slave unit; S5. Correcting the current active power of each phase according to the system output active power of each phase and the average SOC value of each phase to obtain the corrected active power of each phase, and calculating the current amplitude compensation component of each phase according to the corrected active power of each phase, and injecting the resulting compensation component into the calculation of the output current amplitude of the main unit; S6. Using the sinusoidal signal of each phase AC current and the current of each phase of the public grid through a proportional resonant controller to generate a main unit PWM signal to adjust the state of the energy storage converter corresponding to the main unit; S7. The output voltage reference of each phase system slave unit is combined with each phase current of the public grid and the output voltage of each phase system slave unit through voltage and current dual closed-loop control to generate a slave unit PWM signal to adjust the state of the energy storage converter corresponding to the slave unit.

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