Flywheel-battery hybrid energy storage control method and system for suppressing power oscillation of power grid

Abstract

This invention discloses a flywheel-battery hybrid energy storage method and system for suppressing grid power oscillations, relating to the field of power system stability control technology. It includes: acquiring the real-time rotor speed of the flywheel energy storage unit; generating a first power command based on the deviation from a preset rated speed; determining whether the real-time rotor speed is within a preset speed range; if it exceeds the limit, generating a second power command to control the battery energy storage unit to charge and discharge at a constant power; if it is within the range, generating a third power command based on the DC bus voltage deviation; and controlling the battery to execute the commands based on priority arbitration logic, with the second power command having higher priority than the third power command. This invention addresses the problems of existing centralized control architectures heavily relying on complex communication, experiencing response delays, and batteries suffering from shallow charging and discharging and rapidly declining lifespan due to frequent tracking of power oscillations.

Description

Technical Field

[0001] This invention relates to the field of power system stability control technology, and more specifically, to a flywheel-battery hybrid energy storage control method and system for suppressing grid power oscillations. Background Technology

[0002] The large-scale grid connection of renewable energy sources can easily trigger system power oscillations, directly threatening the stable operation of the power system. To effectively suppress power oscillations, the use of hybrid energy storage systems combining flywheels and batteries has become a key technical approach. Flywheel energy storage possesses high power density and extremely fast dynamic response characteristics, while battery energy storage has the advantage of high energy density. The complementary physical characteristics of the two can simultaneously meet the grid's dual requirements for rapid transient power throughput and long-term energy support.

[0003] For the coordinated control of flywheel-battery hybrid energy storage systems, the mainstream technical solutions generally adopt a centralized control architecture based on a central controller. This type of solution typically involves a central controller that centrally collects grid status signals, performs complex oscillation mode identification and power allocation calculations at the main control layer, and then relies on a high-speed communication network to send the calculated power commands for different frequency bands to the underlying converters of the flywheel and battery to enforce the coordinated command.

[0004] However, the aforementioned existing technologies have revealed significant limitations in practical engineering applications. First, the system heavily relies on a central controller and high-speed communication networks, which not only poses a single point of failure risk but also makes it difficult for unavoidable communication and computation time delays to maintain optimal matching between control actions and grid oscillation phases, thus weakening the damping effect. Second, under existing power distribution strategies, battery energy storage units need to frequently track low-frequency components in power oscillations, resulting in a continuous shallow charge and discharge state. This operating mode drastically accelerates battery aging and significantly shortens its cycle life. Furthermore, existing complex control algorithms typically contain a large number of parameters requiring precise tuning, exhibiting poor adaptability to changes in grid operating conditions and posing significant challenges to on-site commissioning. Summary of the Invention

[0005] To overcome the aforementioned deficiencies of the prior art, embodiments of the present invention provide a flywheel-battery hybrid energy storage control method for suppressing grid power oscillations. This method controls the flywheel to perform rapid damping response based on local real-time speed deviation, and combines a preset speed range with priority arbitration logic to ensure that the battery only performs state maintenance at constant power when the flywheel speed exceeds the limit. This solves the technical problems of existing centralized control architectures relying too heavily on complex communication networks, and batteries experiencing shallow charging and discharging and rapid lifespan degradation due to frequent tracking of power oscillations.

[0006] To achieve the above objectives, the present invention provides the following technical solution: A flywheel-battery hybrid energy storage control method for suppressing grid power oscillations includes the following steps: acquiring the real-time rotor speed of the flywheel energy storage unit, calculating the speed deviation from a preset rated speed, and generating a first power command based on the speed deviation; determining whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold; if it is below the lower threshold or above the upper threshold, generating a second power command to control the battery energy storage unit to operate at a constant discharge power or a constant charging power, respectively; if it is within the preset speed range, acquiring the DC bus voltage deviation and generating a third power command based on the voltage deviation; controlling the battery energy storage unit to execute the corresponding power command based on priority arbitration logic, wherein the second power command has a higher priority than the third power command.

[0007] In a preferred embodiment, before determining whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold, the method further includes: acquiring the moment of inertia of the flywheel energy storage unit and the target energy of the grid power oscillation; calculating the rated kinetic energy of the flywheel energy storage unit at the rated speed based on the moment of inertia and the rated speed; calculating the maximum allowable speed deviation threshold based on the target energy and the rated kinetic energy; and determining the upper and lower thresholds of the preset speed range based on the rated speed and the maximum speed deviation threshold.

[0008] In a preferred embodiment, the method further includes: monitoring the state of charge (SOC) of the battery energy storage unit; if the SOC is higher than a first preset threshold, increasing the rated speed at a preset adjustment rate; if the SOC is lower than a second preset threshold, decreasing the rated speed at a preset adjustment rate; wherein the preset adjustment rate is less than the dynamic response rate of the flywheel energy storage unit to dampen grid power oscillations.

[0009] In a preferred embodiment, generating the first power command based on the speed deviation includes: multiplying the speed deviation by a proportional control coefficient to obtain the first power command; wherein the value of the proportional control coefficient is less than twice the ratio of the moment of inertia of the flywheel energy storage unit to the sampling period of the control system.

[0010] In a preferred embodiment, generating a second power command for controlling the battery energy storage unit to operate at a constant discharge power or a constant charging power includes: setting a smoothing transition zone below a lower threshold and above an upper threshold; if the real-time rotor speed is within the smoothing transition zone, calculating the normalized distance between the real-time rotor speed and the corresponding threshold; inputting the normalized distance into a smoothing function to obtain a battery power smoothing component; and generating a continuously adjusted second power command based on the battery power smoothing component and the constant discharge power or constant charging power.

[0011] In a preferred embodiment, the process of controlling the battery energy storage unit to execute the corresponding power command based on priority arbitration logic further includes: obtaining the actual active power of the flywheel energy storage unit; performing first-order low-pass filtering on the actual active power to obtain a battery power feedforward compensation component; superimposing the battery power feedforward compensation component with the power command with the highest execution priority to obtain the final execution command of the battery energy storage unit; wherein, the filter time constant of the first-order low-pass filtering is greater than or equal to the equivalent power response time constant of the battery energy storage unit.

[0012] In a preferred embodiment, obtaining the real-time rotor speed of the flywheel energy storage unit includes: reading the real-time rotor position count value of the encoder; the real-time rotor speed is calculated using the following formula: ;in, This is the real-time rotor speed. This is the real-time rotor position count value. The number of pulses per encoder revolution. The sampling period.

[0013] In a preferred embodiment, obtaining the DC bus voltage deviation and generating a third power command based on the voltage deviation includes: obtaining the actual DC bus voltage value and the DC bus voltage setpoint, and calculating the difference between the two to obtain the voltage deviation; inputting the voltage deviation to a proportional-integral controller to generate a third power command; the calculation formula for the third power command is: ;in, This is the third power command. and These are the proportional and integral coefficients of the proportional-integral controller, respectively. This refers to the voltage deviation.

[0014] In a preferred embodiment, the step of inputting the normalized distance into a smoothing function to obtain the battery power smoothing component includes: processing the normalized distance using a cosine smoothing function, the calculation formula being: ;in, Let be the output value of the smoothing function, and x be the normalized distance. When the real-time rotor speed is in the softened transition zone below the lower threshold, the battery power softening component is: The product of the constant discharge power; when the real-time rotor speed is in the softening transition zone above the upper limit threshold, the battery power softening component is negative. The product of the constant charging power.

[0015] This invention provides a flywheel-battery hybrid energy storage control system for suppressing grid power oscillations, comprising: a flywheel energy storage unit, a battery energy storage unit, a DC bus, and a cooperative controller; the flywheel energy storage unit and the battery energy storage unit are connected in parallel to the DC bus via a power electronic converter, and the DC bus is connected to the power grid via a grid-connected converter; wherein, the DC side of the flywheel converter corresponding to the flywheel energy storage unit is connected to the DC bus; the battery converter corresponding to the battery energy storage unit is connected to the DC bus; the cooperative controller is configured to execute the following control logic: acquiring the real-time rotor speed of the flywheel energy storage unit, calculating and preset... The system calculates the speed deviation of the rated speed and generates a first power command based on the speed deviation; it determines whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold; if it is below the lower threshold or above the upper threshold, it generates a second power command to control the battery energy storage unit to operate at a constant discharge power or a constant charging power, respectively; if it is within the preset speed range, it acquires the DC bus voltage deviation and generates a third power command based on the voltage deviation; it controls the battery energy storage unit to execute the corresponding power command based on priority arbitration logic, and the second power command has a higher priority than the third power command.

[0016] The technical effects and advantages of the flywheel-battery hybrid energy storage control method for suppressing grid power oscillations in this invention are as follows: This invention generates the first power command directly based on the local real-time rotor speed deviation by controlling the flywheel energy storage unit. This transforms the flywheel's response to grid power oscillations into a rapid, spontaneous behavior based on physical quantities, eliminating reliance on complex upper-level communication and achieving a simplified and efficient control architecture. Simultaneously, the system innovatively utilizes upper and lower speed thresholds to schedule the battery energy storage unit. Only when the flywheel speed exceeds the limit is the battery triggered to charge and discharge at a defined constant power to maintain the flywheel's state. Within the safe flywheel speed range, the battery is allowed to perform routine smoothing tasks based on DC bus voltage deviations. Finally, with strict priority arbitration logic, the battery's "maintenance mode" for the flywheel is guaranteed to have absolute priority over the conventional "support mode." This method not only fundamentally guarantees the continuity and robustness of the flywheel's core vibration suppression function but also completely frees the battery from the shallow charge and discharge state caused by frequent power oscillation tracking, transforming it into a low-stress, intermittent constant-power operating mode. This significantly extends the battery's cycle life and substantially improves the overall lifecycle economics of the hybrid energy storage system. Attached Figure Description

[0017] Figure 1 A schematic diagram of the flywheel-battery hybrid energy storage control method for suppressing grid power oscillations provided in an embodiment of the present invention.

[0018] Figure 2A schematic diagram of a flywheel-battery hybrid energy storage control system for suppressing grid power oscillations, provided in an embodiment of the present invention. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1, Figure 1 The present invention provides a flywheel-battery hybrid energy storage control method for suppressing grid power oscillations, comprising the following steps: Step S1: Obtain the real-time rotor speed of the flywheel energy storage unit, calculate the speed deviation from the preset rated speed, and generate a first power command based on the speed deviation.

[0021] In this embodiment, the system first initializes the control parameters of the flywheel-battery hybrid energy storage system and collects the operating status data of the flywheel energy storage unit in real time. Specifically, the co-controller, as the control core of the system, is implemented using an embedded system based on a dual-core digital signal processor and periodically executes the control algorithm. The flywheel energy storage unit includes a mechanical energy storage body and a power electronic interface. It has a built-in high-precision absolute photoelectric encoder for real-time measurement of the rotor mechanical angle, and this signal is transmitted to the co-controller through a differential RS422 communication interface.

[0022] Furthermore, obtaining the real-time rotor speed of the flywheel energy storage unit includes: reading the real-time rotor position count value from the encoder; the calculation formula is: (1) in, This is the real-time rotor speed. This is the real-time rotor position count value. The number of pulses per encoder revolution. The sampling period.

[0023] In practice, one execution cycle of the speed measurement process within the collaborative controller is as follows: This is completed in the high-speed interrupt service routine. After the interrupt is triggered, the latest rotor position count value is first read from the quadrature encoder interface. The accurate real-time speed value is calculated using the improved M / T speed measurement method shown in formula (1). Subsequently, the speed deviation between the real-time rotor speed and the preset rated speed was calculated. The calculation formula is as follows: (2) in, It is the preset rated speed of the flywheel, which is a constant value and is the operating point that the flywheel is expected to maintain in steady state.

[0024] Furthermore, to prevent the flywheel from deviating from its optimal operating point for an extended period, the method further includes: monitoring the state of charge (SOC) of the battery energy storage unit; if the SOC is higher than a first preset threshold, increasing the rated speed at a preset adjustment rate; if the SOC is lower than a second preset threshold, decreasing the rated speed at a preset adjustment rate; wherein the preset adjustment rate is less than the dynamic response rate of the flywheel energy storage unit to dampen grid power oscillations.

[0025] In practical applications, the system energy balancing step takes one execution cycle. It is executed in the main loop task. The specific steps are as follows: Read the State of Charge (SOC) value reported by the battery management system through the controller local area network bus. If the SOC exceeds the preset high threshold (e.g., set to 85%), increase the rated speed setting of the flywheel at a slow rate to transfer energy from the battery to the flywheel; the calculation formula is: (3) Where k is the discrete time step index of the main loop of system energy balance, corresponding to the iteration calculation time of the kth energy balance logic; This is the adjustment rate coefficient for the rated speed of the flywheel; if the state of charge (SOC) is lower than a preset low threshold (e.g., set to 25%), the speed will decrease at the same rate. This is to transfer energy from the flywheel to the battery. Due to this slow rate... (e.g., 10 rpm / min) is much smaller than the dynamic response rate of the first control logic, thus ensuring that the adjustment process of the energy balance logic will not interfere with the flywheel energy storage unit's rapid damping response to grid power oscillations.

[0026] Further, generating the first power command based on the speed deviation includes: multiplying the speed deviation by a proportional control coefficient to obtain the first power command; wherein the value of the proportional control coefficient is less than the ratio of twice the moment of inertia of the flywheel energy storage unit to the sampling period of the control system. Specifically, this process is implemented by generating a power command proportional to the calculated deviation, the calculation formula of which is: (4) in, This is the first power command. This is the proportional control coefficient. For a first-order inertial element, to ensure system stability and provide sufficient stability margin, the proportional control coefficient must satisfy the following conditions: Where J is the moment of inertia of the flywheel. This is for controlling the cycle. For example, the cycle set in this embodiment is... and control cycle Under these conditions, the theoretical maximum proportional control coefficient is approximately To allow for sufficient stability margin, the actual selection can be... After the command is generated, the calculated first power command is limited to ensure that it does not exceed the safe operating range of the flywheel converter, and the final command value is output to the power control loop of the flywheel converter through a digital-to-analog converter to reduce the deviation.

[0027] This step uses the locally measured real-time speed deviation physical signal to directly generate a proportional power command within the underlying high-speed control loop. This transforms the flywheel energy storage unit's response to grid power disturbances into a rapid, spontaneous behavior based on physical inertia. Simultaneously, it is supplemented by slow energy balancing scheduling. By abandoning complex oscillation mode recognition algorithms and reliance on high-speed communication networks, it effectively ensures the robustness and continuity of the system's main damping function.

[0028] Step S2: Determine whether the real-time rotor speed is within a preset speed range defined by the lower threshold and the upper threshold.

[0029] In this embodiment, the system needs to determine in real time whether the flywheel's current kinetic energy margin is sufficient to independently cope with current grid fluctuations. Specifically, in an execution cycle of... In the main loop task, the system enters the battery maintenance logic's judgment phase, comparing the acquired real-time flywheel rotor speed with the upper and lower limits of the preset high-efficiency speed range (i.e., the preset speed range). This judgment logic is entirely based on the local, explicit physical signal of "whether the flywheel speed exceeds the limit," requiring no upper-level coordination or additional communication intervention. If the real-time rotor speed of the flywheel is lower than the lower threshold, the system determines that the current flywheel energy storage unit has insufficient energy; if the real-time rotor speed is higher than the upper threshold, the system determines that the flywheel energy storage unit has excess energy.

[0030] Before determining whether the real-time rotor speed is within the preset speed range defined by the lower and upper thresholds, the method further includes: acquiring the moment of inertia of the flywheel energy storage unit and the target energy of the grid power oscillation; calculating the rated kinetic energy of the flywheel energy storage unit at the rated speed based on the moment of inertia and rated speed; calculating the maximum allowable speed deviation threshold based on the target energy and rated kinetic energy; and determining the upper and lower thresholds of the preset speed range based on the rated speed and the maximum speed deviation threshold. The specific steps for obtaining the parameters of the high-efficiency speed range are as follows: First, parameter acquisition is performed to obtain the rotational inertia J of the flywheel energy storage unit and the preset rated speed. And the energy demand required to address typical power oscillation events in grid oscillation suppression. Then, the energy storage capacity of the flywheel at its rated speed, i.e., its rated kinetic energy, is calculated according to the formula. The formula for calculating the rated kinetic energy is: (5) Next, based on the principle of energy conservation, the maximum allowable speed deviation threshold is calculated. The speed deviation threshold is set based on energy margin requirements, and its value directly affects the flywheel energy storage unit's ability to cope with continuous power disturbances. The formula for calculating the maximum speed deviation threshold is: (6) In the formula, This refers to the energy demand required to address typical power grid oscillation events.

[0031] In this embodiment, for The energy requirement can be calculated. Finally, based on the preset rated speed... and the calculated maximum speed deviation threshold Set the upper limit threshold of the high-efficiency speed range (i.e., the preset speed range). and lower threshold The threshold calculation formula is as follows: (7) (8) This step establishes a limit-breaking judgment mechanism based on local rotational speed physical signals by scientifically quantifying the mathematical mapping relationship between the energy demand of typical oscillation events and the physical energy storage boundary of the flywheel. This accurately and reliably defines the safe operating boundary of the flywheel's ability to independently provide grid damping, providing a prerequisite judgment condition for subsequent automatic triggering of battery energy storage unit maintenance actions.

[0032] Step S3: If the value is below the lower threshold or above the upper threshold, a second power command is generated to control the battery energy storage unit to operate at a constant discharge power or a constant charging power, respectively. In this embodiment, when the flywheel speed exceeds its limit, it indicates that the flywheel energy has reached a bottleneck, and a battery unit needs to be introduced for high-power compensation. Specifically, the control logic within the co-controller includes a battery-driven flywheel maintenance mode. The goal of this mode is to ensure that the flywheel speed remains within a preset high-efficiency speed range, which is a prerequisite for the flywheel to continuously and effectively perform its main damping function. When it is determined that the flywheel energy storage unit has insufficient energy (i.e., the real-time rotor speed is below the lower threshold of the high-efficiency speed range), a second power command is generated to allow the battery energy storage unit to operate at a constant power to help the flywheel accelerate and recover. When it is determined that the flywheel energy storage unit has excess energy (i.e., the real-time rotor speed is above the upper threshold of the high-efficiency speed range), a second power command is generated to allow the battery energy storage unit to operate at a constant power to absorb excess energy and help the flywheel decelerate. The constant charging and discharging power of the battery... Based on the expected flywheel speed recovery time The required calculation formula is as follows: (9) in, To improve system efficiency, this method redefines the battery's role as a maintainer of the flywheel's operating state, forcibly locking the battery into an intermittent, deterministic, and low-stress operating mode, thus greatly extending battery life.

[0033] Furthermore, to avoid the impact of hard switching, the generation of a second power command for controlling the battery energy storage unit to operate at a constant discharge power or a constant charging power includes: setting a smooth transition zone below a lower threshold and above an upper threshold; if the real-time rotor speed is within the smooth transition zone, calculating the normalized distance between the real-time rotor speed and the corresponding threshold; inputting the normalized distance into a smoothing function to obtain a battery power smoothing component; and generating a continuously adjusted second power command based on the battery power smoothing component and the constant discharge power or constant charging power. In specific implementation, the above process optimizes the second control logic of the cooperative controller, aiming to eliminate DC bus power surges generated during mode switching and dynamic response by smoothing the battery power command. The steps are as follows: S301, first set the half-width of the smooth transition zone. The calculation formula is as follows: ,in This is the softening factor, and its value range is set to... If the current actual rotational speed of the flywheel is lower than the lower threshold, then the normalized distance is calculated using the following formula: If the actual rotational speed is higher than the upper threshold, the formula for calculating the normalized distance is: If the speed is within the high-efficiency speed range, then .

[0034] S302, further, the step of inputting the normalized distance into a smoothing function to obtain the battery power softening component includes: processing the normalized distance using a cosine smoothing function, the calculation formula being: ;in, The output value of the smoothing function. For normalized distance, and In practice, the control system will adjust the speed based on the flywheel's real-time rotor speed within different ranges, using a smoothing function. The output value is used to calculate the final battery power softening component through a piecewise function. The calculation formula for the battery power softening component is as follows: (10) in, Soften the battery power component; Set a constant charging power (positive value) for the battery. The set constant discharge power (negative value) of the battery. This represents the current actual rotational speed of the flywheel; and These are the lower and upper thresholds of the high-efficiency speed range, respectively. Through this piecewise function logic, when the real-time rotor speed is in the smooth transition zone below the lower threshold, the battery power smoothing component manifests as a smoothly increasing charging power; when the real-time rotor speed is in the smooth transition zone above the upper threshold, the battery power smoothing component manifests as a smoothly increasing reverse discharge power; and within the safety range, this smoothing component is strictly zero. Through the aforementioned smoothing function and the safety limiting processing of the normalized distance, the continuously changing battery power smoothing component is calculated. This mechanism ensures that the switching between "standby" and "maintenance" modes is no longer a step jump, but a continuous and smooth "soft start / soft stop," fundamentally eliminating the instantaneous power surge and voltage disturbance to the DC bus caused by control mode switching. Furthermore, because the energy balancing logic slowly adjusts the flywheel's preset rated speed, the system automatically recalculates the upper and lower limits of the high-efficiency speed range. This change causes the calculated normalized distance x to continuously change, thereby continuously adjusting the battery power smoothing component through the smoothing function, achieving a smooth energy balancing process without power command jumps.

[0035] This step introduces a smooth transition zone and a cosine smoothing function to continuously modify the constant power command triggered by physical over-limits. This not only ensures the reliable "bottom-line" maintenance of the battery when the flywheel energy exceeds the limit, but also completely eliminates the secondary electrical impact on the DC microgrid caused by hard mode switching, significantly improving the dynamic power quality and operating life of the hybrid energy storage system.

[0036] Step S4: If the speed is within the preset speed range, the voltage deviation of the DC bus is obtained, and a third power command is generated based on the voltage deviation.

[0037] In this embodiment, when the flywheel speed is within the safe range, the battery is primarily responsible for voltage stabilization, while the flywheel is responsible for the main power oscillation response. Specifically, when the real-time rotor speed of the flywheel is normal and within the high-efficiency speed range (i.e., the preset speed range), it indicates that the flywheel can independently complete the task of damping grid power oscillations. At this time, the battery energy storage unit enters the "support mode" for the grid. In this mode, even if the grid has a smoothing requirement, the battery's response is subordinate. This design forcibly locks the battery into an intermittent, deterministic, low-stress operating mode, completely eliminating the shallow charging and discharging and complex operating conditions caused by the need to frequently track power oscillation components in traditional strategies. At this time, the battery energy storage unit is controlled to perform grid power smoothing tasks based on the DC bus state parameters.

[0038] Further, the step of acquiring the DC bus voltage deviation and generating a third power command based on the voltage deviation includes: acquiring the actual DC bus voltage value and the DC bus voltage setpoint, and calculating the difference between the two to obtain the voltage deviation; inputting the voltage deviation to the proportional-integral controller to generate the third power command; the calculation formula is: (11) in, This is the third power command. and These are the proportional and integral coefficients of the proportional-integral controller, respectively. This refers to voltage deviation. The specific implementation steps are as follows: S401, the DC bus serves as a common DC coupling point, and its rated voltage (i.e., the DC bus voltage setting value) For example, it is set to 800V. During the main loop task, the system reads the actual value of the DC bus voltage sampled by the Hall voltage sensor through an analog-to-digital converter. .

[0039] S402, then the difference between the two is calculated to obtain the voltage deviation, and the calculation formula is: .

[0040] S403, finally, based on the DC bus voltage deviation A third power command for smoothing grid power is calculated by a slow proportional-integral controller. This instruction controls the battery's operation to stabilize the DC bus voltage.

[0041] This step, by releasing the battery's auxiliary voltage stabilization capability within the flywheel's safe operating range and combining it with slow proportional-integral control logic, achieves stable compensation for DC common bus voltage fluctuations without interfering with the flywheel's high-frequency physical damping response, thus clarifying the collaborative division of labor between the two energy storage media in a "dynamic-static combination".

[0042] Step S5: Based on priority arbitration logic, control the battery energy storage unit to execute the corresponding power command, and the priority of the second power command is higher than that of the third power command.

[0043] In this embodiment, the control system needs to coordinate multiple tasks of the battery under different operating conditions to prevent command conflicts. Specifically, the cooperative controller is configured with strict priority arbitration logic, which prioritizes the second power command used to maintain the flywheel speed (i.e., the battery power softening component). When the battery is busy performing grid auxiliary tasks, the "maintenance mode" command it represents has the highest priority. This logic eliminates the possibility of delaying the flywheel's recovery from its operating state due to the battery being busy performing grid auxiliary tasks, ensuring that the need to maintain the system's own core operating state takes absolute priority over providing auxiliary services for grid power smoothing.

[0044] Furthermore, the process of controlling the battery energy storage unit to execute the corresponding power command based on priority arbitration logic further includes: obtaining the actual active power of the flywheel energy storage unit; performing first-order low-pass filtering on the actual active power to obtain the battery power feedforward compensation component; superimposing the battery power feedforward compensation component with the power command with the highest execution priority to obtain the final execution command of the battery energy storage unit; wherein, the filter time constant of the first-order low-pass filtering is greater than or equal to the equivalent power response time constant of the battery energy storage unit. The specific steps are as follows: The system first obtains the current actual active power of the flywheel in real time. .right A first-order low-pass filter is performed to obtain the feedforward component, which is the battery power feedforward compensation component. The discretization iterative formula for the filter is: (12) in, , where is the filter coefficient of a first-order low-pass filter, dimensionless. To control the cycle, For discrete time step index of real-time power control; filter time constant Must meet .in, The equivalent power response time constant of the battery system (including the DC / DC converter) was determined through experimental measurements. Command fusion and output were then performed. Combine the battery power feedforward compensation component with the highest priority instruction (e.g., The total battery power command reference value is calculated by superimposing the values, using the following formula: Next, implement safety limiting: for Based on the battery's current state of charge (SOC) and physical limits, upper and lower limits are set to obtain the final executable instructions. Finally, output the result: The DC / DC converter sent to the battery energy storage unit performs the operation.

[0045] This step deeply optimizes the system's internal dynamic processes by introducing two core mechanisms: "command softening" and "power feedforward." A filter precisely matched to the battery's response capability generates feedforward compensation commands, enabling the battery to proactively and smoothly output a compensation amount that perfectly "keeps up" with the flywheel power changes. This achieves precise instantaneous power balance within the system, suppressing DC bus voltage fluctuations to extremely low levels and providing an extremely stable operating environment for the grid-side converter and other parallel equipment. The smooth power command further reduces current and voltage stress on the battery and power devices, providing additional benefits for their lifespan protection. Simultaneously, this mechanism integrates naturally and smoothly with "energy balancing logic," ensuring no command abrupt changes during long-term energy regulation, thereby comprehensively enhancing the system's dynamic quality, power quality, and long-term operational reliability.

[0046] Example 2, Figure 2 A flywheel-battery hybrid energy storage system for suppressing grid power oscillations is presented, comprising: a flywheel energy storage unit 100, a battery energy storage unit 200, a DC bus 300, and a cooperative controller 400; The flywheel energy storage unit 100 and the battery energy storage unit 200 are connected in parallel to the DC bus 300 via a power electronic converter, and the DC bus 300 is connected to the power grid via a grid-connected converter; wherein, the DC side of the flywheel converter corresponding to the flywheel energy storage unit 100 is connected to the DC bus 300; and the battery converter corresponding to the battery energy storage unit 200 is connected to the DC bus 300. The cooperative controller 400 is configured to execute the following control logic: The real-time rotor speed of the flywheel energy storage unit 100 is obtained, the speed deviation from the preset rated speed is calculated, and a first power command is generated based on the speed deviation. Determine whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold; If the value is below the lower threshold or above the upper threshold, a second power command is generated to control the battery energy storage unit 200 to operate at a constant discharge power or a constant charging power, respectively. If the speed is within the preset speed range, the voltage deviation of the DC bus 300 is obtained, and a third power command is generated based on the voltage deviation. The battery energy storage unit 200 is controlled to execute the corresponding power command based on the priority arbitration logic, and the priority of the second power command is higher than that of the third power command.

[0047] To illustrate the system's operation in detail, a transient three-phase short-circuit fault in the power grid is used as an example. At the moment of the fault (t=0ms), the grid voltage drops sharply, reducing the active power absorbed by the grid-connected converter 500, causing the DC bus 300 voltage to tend to rise. The flywheel main damping control loop (1ms period) immediately detects the increasing flywheel speed due to inertia, and the real-time speed deviation... The value becomes negative, and a negative first power command is calculated accordingly. Upon receiving the command, the flywheel converter controls the flywheel energy storage unit 100 to absorb active power from the DC bus 300, thereby suppressing the rise in DC bus 300 voltage and providing effective reactive power support to the grid to help restore voltage. If the fault persists, the flywheel speed continues to rise. When the main cycle task (cycle 10ms) detects the real-time speed... Exceeding the limit Immediately switch the battery storage unit 200 to maintenance discharge mode at a constant power. Discharge is supplied to DC bus 300 to absorb excess energy and help the flywheel decelerate. After the fault is cleared, the system's various state variables gradually return to steady state. The system has complete multi-level protection logic. For the flywheel energy storage unit 100, overspeed protection is provided: when the speed exceeds the first-level alarm value of 3500 rpm, the coordinating controller 400 will automatically reduce the proportional coefficient Kp to slow down the power response; when the speed exceeds the second-level protection value... At a certain rpm, an emergency shutdown sequence will be triggered. For the battery storage unit 200, its battery management system has multiple built-in protections for individual cell voltage, total current, and temperature, and is interlocked with the coordination controller 400. The DC bus 300 is equipped with overvoltage, undervoltage, and voltage imbalance protections. The coordination controller 400 continuously monitors all critical signals; any abnormality will trigger the corresponding fault handling procedure, including derating operation, mode switching, or orderly shutdown, to ensure system safety.

[0048] To objectively evaluate the performance advantages of the "flywheel-battery hybrid energy storage coordinated control system" described in this invention, a real-time digital simulation platform based on RT-LAB was built for this test to simulate power oscillation events under typical wind farm grid-connected scenarios. The test aims to quantitatively compare the performance differences between this invention and traditional centralized coordinated control strategies in three core dimensions: oscillation suppression effect, battery life protection, and system reliability.

[0049] Test prerequisites and conditions: Simulation platform: OPAL-RTOP4510, step size 50μs.

[0050] Power grid model: The modified IEEE 9-node system, with a 200MW wind farm connected at node 2.

[0051] Disturbance scenario: At t=5.0s, a short-circuit fault in the primary system of the power grid is simulated, which causes a low-frequency power oscillation of 0.8Hz lasting for about 10 seconds.

[0052] Comparison objects: This invention employs the aforementioned dual-logic local collaborative control.

[0053] Traditional technology employs a power distribution strategy based on bandpass filtering and a central coordinator. This strategy detects line power oscillation components, and the central controller calculates instructions: high-frequency components are allocated to the flywheel, and low-frequency components are allocated to the battery.

[0054] Parameters of the system under test (both must be kept consistent):

[0055] Comparison of test data and results: Table 1: Comparison of key indicators of oscillation suppression effect:

[0056] Table 2: Comparison of the impact of battery operating status on lifespan

[0057] Table 3: System Reliability and Communication Dependency Analysis

[0058] Table 4: Comparison of Control Performance Details

[0059] Comprehensive analysis of test results: Test data shows that the present invention is slightly superior to traditional technologies in terms of dynamic response speed and frequency support, especially in the initial stage of disturbance occurrence, where the flywheel's instinctive response based on physical characteristics demonstrates an unparalleled speed advantage. The steady-state suppression effects of both are comparable.

[0060] Battery life protection is the core highlight of this invention. Data clearly shows that this invention reduces the number of battery cycles and energy throughput by over 90%. This means the battery transforms from a "main player" to a "substitute," only needing to operate at a constant, "comfortable" power level when most critically needed. This will inevitably lead to an order-of-magnitude increase in battery life, significantly improving the overall lifecycle economics of hybrid energy storage systems.

[0061] This invention fundamentally eliminates the reliance on high-speed communication networks. Simulated communication interruption scenarios in the tests had no effect on this invention, while the comparative methods failed completely. This demonstrates that this invention possesses extremely high robustness and reliability in the face of the common risk of communication failure, making it particularly suitable for application in complex industrial environments.

[0062] The control logic of this invention is extremely simple, and the physical meaning of the parameters is clear, which greatly reduces the difficulty and cost of on-site debugging, maintenance, and optimization. In contrast, traditional methods have complex algorithms and are difficult to tune parameters.

[0063] Based on the rigorous real-time simulation tests and data analysis described above, the following conclusions can be drawn: The "flywheel-battery hybrid energy storage and collaborative control system" described in this invention maintains excellent oscillation suppression while exhibiting overwhelming advantages over traditional centralized coordinated control technologies in terms of battery life protection and system reliability. Its innovative division of labor—"flywheel as the main damper, battery as the maintenance provider"—is achieved through simple and reliable local control logic, effectively solving engineering pain points of traditional solutions such as complex control, strong communication dependence, and high battery losses. This fully verifies the invention's advanced nature, practicality, and significant economic benefits.

[0064] The above formulas are all dimensionless calculations. The formulas are derived from software simulations based on a large amount of collected data to obtain the most recent real-world results. The preset parameters in the formulas are set by those skilled in the art according to the actual situation.

[0065] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0066] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0067] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0068] 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 technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0069] In conclusion, 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 within the protection scope of the present invention.

Claims

1. A flywheel-battery hybrid energy storage control method for damping power oscillations in an electrical grid, characterized by, Includes the following steps: The real-time rotor speed of the flywheel energy storage unit is obtained, the speed deviation from the preset rated speed is calculated, and a first power command is generated based on the speed deviation. Determine whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold; If the value is below the lower threshold or above the upper threshold, a second power command is generated to control the battery energy storage unit to operate at a constant discharge power or a constant charging power, respectively. If the speed is within the preset speed range, the voltage deviation of the DC bus is obtained, and a third power command is generated based on the voltage deviation. The battery energy storage unit is controlled to execute the corresponding power command based on the priority arbitration logic, and the second power command has a higher priority than the third power command.

2. The method of claim 1, wherein, Before determining whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold, the method further includes: Obtain the rotational inertia of the flywheel energy storage unit and the target energy of grid power oscillation; Calculate the rated kinetic energy of the flywheel energy storage unit at the rated speed based on the moment of inertia and rated speed; Based on the target energy and rated kinetic energy, calculate the maximum allowable speed deviation threshold; Based on the rated speed and the maximum speed deviation threshold, the upper and lower thresholds of the preset speed range are determined.

3. The method of claim 1, wherein, Also includes: Monitor the state of charge of the battery energy storage unit; If the state of charge is higher than the first preset threshold, the rated speed is increased by a preset adjustment rate; If the state of charge is lower than the second preset threshold, the rated speed will be reduced by a preset adjustment rate. The preset adjustment rate is less than the dynamic response rate of the flywheel energy storage unit to dampen grid power oscillations.

4. The method according to claim 1, characterized in that, The generation of the first power command based on the speed deviation includes: Multiply the speed deviation by the proportional control coefficient to obtain the first power command; The value of the proportional control coefficient is less than twice the rotational inertia of the flywheel energy storage unit and the ratio of the sampling period of the control system.

5. The method according to claim 1, characterized in that, The generation of the second power command for controlling the battery energy storage unit to operate at a constant discharge power or a constant charge power includes: A smooth transition zone is set below the lower threshold and above the upper threshold, respectively; If the real-time rotor speed is within the softened transition zone, then calculate the normalized distance between the real-time rotor speed and the corresponding threshold. The normalized distance is input into the smoothing function to obtain the battery power smoothing component; Based on the battery power softening component and constant discharge power or constant charging power, a continuously adjusted second power command is generated.

6. The method according to claim 1, characterized in that, The process of controlling the battery energy storage unit to execute the corresponding power command based on priority arbitration logic also includes: Obtain the actual active power of the flywheel energy storage unit; The actual active power is processed by a first-order low-pass filter to obtain the battery power feedforward compensation component. The battery power feedforward compensation component is superimposed with the power command with the highest execution priority to obtain the final execution command of the battery energy storage unit. The filter time constant of the first-order low-pass filtering process is greater than or equal to the equivalent power response time constant of the battery energy storage unit.

7. The method according to claim 1, characterized in that, The step of obtaining the real-time rotor speed of the flywheel energy storage unit includes: Read the real-time rotor position count value from the encoder; The formula for calculating the real-time rotor speed is as follows: ； in, This is the real-time rotor speed. This is the real-time rotor position count value. The number of pulses per encoder revolution. The sampling period.

8. The method according to claim 1, characterized in that, The step of acquiring the voltage deviation of the DC bus and generating a third power command based on the voltage deviation includes: The actual value of the DC bus voltage and the set value of the DC bus voltage are obtained, and the difference between the two is calculated to obtain the voltage deviation. The voltage deviation is input to the proportional-integral controller to generate a third power command; The formula for calculating the third power command is: ； in, This is the third power command. and These are the proportional and integral coefficients of the proportional-integral controller, respectively. This refers to the voltage deviation.

9. The method according to claim 5, characterized in that, The step of inputting the normalized distance into a smoothing function to obtain the battery power smoothing component includes: The normalized distance is processed using a cosine smoothing function, and the calculation formula is as follows: ; in, Let be the output value of the smoothing function, and x be the normalized distance. ; When the real-time rotor speed is in the softened transition zone below the lower threshold, the battery power softening component is: The product of the constant discharge power; When the real-time rotor speed is in the softened transition zone above the upper limit threshold, the battery power softening component is negative. The product of the constant charging power.

10. A flywheel-battery hybrid energy storage system for suppressing grid power oscillations using the method described in any one of claims 1-9, characterized in that, include: The system comprises a flywheel energy storage unit, a battery energy storage unit, a DC bus, and a coordinated controller. The flywheel energy storage unit and the battery energy storage unit are connected in parallel to the DC bus via power electronic converters, and the DC bus is connected to the power grid via a grid-connected converter. The DC side of the flywheel converter corresponding to the flywheel energy storage unit is connected to the DC bus; the battery converter corresponding to the battery energy storage unit is connected to the DC bus. The collaborative controller is configured to execute the following control logic: The real-time rotor speed of the flywheel energy storage unit is obtained, the speed deviation from the preset rated speed is calculated, and a first power command is generated based on the speed deviation. Determine whether the real-time rotor speed is within a preset speed range defined by a lower threshold and an upper threshold; If the value is below the lower threshold or above the upper threshold, a second power command is generated to control the battery energy storage unit to operate at a constant discharge power or a constant charging power, respectively. If the speed is within the preset speed range, the voltage deviation of the DC bus is obtained, and a third power command is generated based on the voltage deviation. The battery energy storage unit is controlled to execute the corresponding power command based on the priority arbitration logic, and the second power command has a higher priority than the third power command.

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