Hybrid energy storage thermal power generating unit frequency modulation strategy and system based on hierarchical adaptive control

Abstract

The embodiment of the invention provides a hybrid energy storage thermal power generating unit frequency modulation strategy and system based on hierarchical adaptive control, and the strategy comprises the steps: detecting the reserve capacity and hybrid energy storage charge state of a thermal power generating unit in real time, and obtaining an automatic power generation control instruction, obtaining interregional tie line exchange power and system frequency deviation, and calculating a regional control deviation frequency modulation instruction; the outer layer control is based on the relation between the residual energy of the hybrid energy storage system and a hybrid energy storage distribution scaling factor K, and self-adaptive distribution is carried out on a power grid real-time area control deviation frequency modulation instruction between the thermal power generating unit and the hybrid energy storage system; the inner layer control decomposes a regional control deviation signal distributed to the hybrid energy storage system between flywheel energy storage and battery energy storage, and calculates a rated output power instruction of each energy storage; a battery energy storage unit is divided into a charging sub-unit and a discharging sub-unit, and when any sub-unit reaches a state-of-charge boundary, a charging state and a discharging state are switched; and outputting the frequency modulation power instruction to the energy storage converter.

Description

Technical Field

[0001] Embodiments of the present disclosure belong to the technical field of hybrid energy storage assisting thermal power units to participate in power system frequency regulation, and specifically relate to a frequency regulation strategy and system for a hybrid energy storage thermal power unit based on hierarchical adaptive control. Background Art

[0002] The volatility and reverse peak shaving characteristics of new energy have had a significant impact on the stability of the power grid frequency and voltage, prompting the power grid to require more flexible regulation capabilities. Under the regulation of dynamic area control error (ACE), the automatic generation control (AGC) system of traditional thermal power units issues control commands to controllable units according to the ACE instruction to achieve rapid restoration of the power grid frequency. However, the frequent fluctuations and randomness of the ACE instruction, as well as the rapid change of the load, make it difficult for the traditional coordinated control system (CCS) mainly based on steady-state load response to meet the current requirements. In addition, thermal power units also have problems such as slow regulation rate and weak climbing ability.

[0003] The energy-type energy storage system has the advantage of large energy capacity and is suitable for long-term energy regulation, but its instantaneous power response is weak; while the power-type energy storage system has a strong instantaneous power response ability and is suitable for rapid power regulation, but its energy capacity is small. Therefore, introducing an energy storage system can significantly improve the execution effect of thermal power units on the power grid ACE instruction.

[0004] To solve the above problems, a hybrid energy storage system (HESS) composed of a flywheel energy storage and a battery energy storage is introduced to assist thermal power units in secondary frequency regulation. The existing control strategies for HESS to assist thermal power units mainly focus on the signal distribution of energy storage participating in system frequency regulation, and do not fully discuss the relationship between the frequency regulation instruction and the remaining energy of the system. At the same time, the power regulation instruction of the battery energy storage system mostly considers maintaining the state of charge (SOC), ignoring the balance between frequency regulation and SOC maintenance, as well as the impact of the depth of discharge (DOD) on the battery life, resulting in increased battery life loss due to frequent charge and discharge switching. Summary of the Invention

[0005] Embodiments of the present disclosure aim to at least solve one of the technical problems existing in the prior art, and provide a frequency regulation strategy and system for a hybrid energy storage thermal power unit based on hierarchical adaptive control.

[0006] In a first aspect of the embodiments of the present disclosure, a frequency regulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control is provided, which is characterized by including:

[0007] Real-time detect the standby capacity of thermal power units and the state of charge of hybrid energy storage, obtain the automatic generation control instructions from the power plant's distributed control system, obtain the tie-line exchange power between regions and the system frequency deviation, and calculate the area control error frequency modulation instructions;

[0008] The outer layer control is based on the relationship between the remaining energy of the hybrid energy storage system and the hybrid energy storage distribution ratio factor K, and adaptively distributes the real-time area control error frequency modulation instructions of the power grid between the thermal power unit and the hybrid energy storage system;

[0009] The inner layer control decomposes the area control error signal assigned to the hybrid energy storage system between the flywheel energy storage and the battery energy storage based on fuzzy control with variable time constant filtering, and calculates the rated output power instructions of each energy storage;

[0010] Divide the battery energy storage unit into a charging sub-unit and a discharging sub-unit that independently perform charging and discharging operations, and switch the charging and discharging states when any sub-unit reaches the state of charge boundary;

[0011] Output the frequency modulation power instruction to the energy storage converter, and repeat the execution until the power grid frequency is stable or the output of the thermal power unit approaches the automatic generation control instruction.

[0012] Optionally, based on the fact that the frequency modulation ability of the thermal power unit is negatively correlated with the hybrid energy storage distribution ratio factor K, select the hyperbolic tangent function as the adaptive adjustment function of the K value, and calculate the hybrid energy storage area control error signal distribution ratio factor based on the standby capacity of the thermal power unit.

[0013] Optionally, based on the fact that the frequency modulation ability of the hybrid energy storage system is positively correlated with the hybrid energy storage distribution ratio factor K, select the Logistic function as the adaptive adjustment function of the K value, and the hybrid energy storage area control error signal distribution ratio factor based on the state of charge feedback of the hybrid energy storage.

[0014] Optionally, the distribution ratio factor K is determined by the minimum value of the hyperbolic tangent function and the Logistic function.

[0015] Furthermore, it also includes: based on the standby capacity boundary of the thermal power unit and the state of charge boundary of the hybrid energy storage system, adjust the value of the distribution ratio factor K in real time.

[0016] Furthermore, it also includes: in the tie-line deviation control mode, calculate the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system according to the hybrid energy storage system distribution ratio factor K.

[0017] Optionally, the method for distributing the area control error frequency modulation instructions within the hybrid energy storage system includes:

[0018] Obtain the secondary frequency modulation signal of the hybrid energy storage system and the state of charge of each energy storage unit;

[0019] Analyze the current state of charge and response power of the flywheel energy storage through a fuzzy controller to determine the current adjustment amount T of the variable time constant i ;

[0020] Calculate the low-pass filter time constant T according to the adjustment amount T of the variable time constant i ;

[0021] Distribute the high-frequency and low-frequency signals after the frequency modulation command of the hybrid energy storage system is decomposed by the variable-time low-pass filter to the flywheel energy storage and the battery energy storage respectively, and calculate the frequency modulation signals of the flywheel energy storage and the battery energy storage after distribution

[0022] Calculate the output power command according to the area control deviation signals distributed to the flywheel energy storage and the battery energy storage

[0023] In a second aspect of the embodiments of the present disclosure, there is provided a computer-readable storage medium having a computer program stored thereon

[0024] When the computer program is executed by a processor, it can implement the above-mentioned frequency modulation strategy of the hybrid energy storage thermal power unit based on hierarchical adaptive control

[0025] In a third aspect of the embodiments of the present disclosure, there is provided a frequency modulation system for a hybrid energy storage thermal power unit based on hierarchical adaptive control. The frequency modulation system can operate the above-mentioned frequency modulation control strategy, including

[0026] A thermal power unit system, including a power plant distributed control system, a coordinated control system and a thermal power unit. Among them, the power plant distributed control system is configured to receive the area control deviation frequency modulation command sent by the grid dispatching center and generate an automatic generation control command

[0027] The coordinated control system adjusts the output load of the thermal power unit according to the automatic generation control command; the thermal power unit includes a boiler, a steam turbine, a governor and a generator, and is used to respond to the frequency modulation signal to change the main steam flow rate and output power

[0028] A hybrid energy storage system, including a flywheel energy storage, a battery energy storage and a control system. Among them, the flywheel energy storage unit includes an asynchronous motor, a filter circuit, a flywheel rotor and an inverter, and is used for short-term high-frequency power response; the battery energy storage is used for medium- and long-term power and energy support

[0029] Optionally, the thermal power unit system and the hybrid energy storage system are connected to the high-voltage bus of the power plant in a parallel operation mode, and their combined output power tracks the grid command; the flywheel energy storage and the battery energy storage are each independently connected to the grid through a DC / AC inverter

[0030] The beneficial effects of the embodiments of the present disclosure include

[0031] This application comprehensively considers the problems that the ACE frequency modulation command fluctuates frequently and randomly, resulting in insufficient regulation rate and weak climbing ability of thermal power units; the influence of the remaining energy of the system on the frequency modulation command; and the influence of the battery cycle times and discharge depth on the life of the battery energy storage system. A secondary frequency modulation control strategy for hybrid energy storage-assisted thermal power units based on hierarchical adaptive control in the ACE mode is proposed, including real-time detection of the standby capacity of thermal power units and the state of charge of hybrid energy storage, obtaining the AGC command and ACE frequency modulation command from the power plant DCS; the outer control adaptively distributes the ACE frequency modulation command between the thermal power unit and the hybrid energy storage system based on the relationship between the remaining energy of the system and the proportionality factor; the inner control decomposes the ACE signal allocated to the energy storage between the flywheel energy storage and the battery energy storage based on fuzzy control with variable time constants filtering; optimizes the actual output power of the battery energy storage, divides the battery energy storage system into two parts, and independently undertakes the charging and discharging tasks respectively when participating in frequency modulation; outputs the frequency modulation power command to the energy storage converter to control the charging and discharging power adjustment of the energy storage system, and repeats the above steps until the output of the thermal power unit gradually approaches the AGC command or the grid frequency is stable.

[0032] On the premise of satisfying the output boundary of the unit and the energy storage system and responding to the frequency, it reduces the frequency deviation, significantly improves the execution effect of the thermal power unit on the ACE frequency modulation command of the power grid; enables the hybrid energy storage system to reduce the number of charge and discharge switches of the battery energy storage while quickly and adaptively responding to the frequency modulation demand, and extends the service life of the battery energy storage; better coordinates the utility of the energy storage system and the conventional frequency modulation unit, and realizes the efficient and stable operation of the power grid frequency modulation. Description of the Drawings

[0033] Figure 1 It is a schematic flow chart of a frequency modulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control according to another embodiment of the present disclosure;

[0034] Figure 2 It is a schematic diagram of a secondary frequency modulation system for hybrid energy storage-assisted thermal power units in the ACE mode according to an embodiment of the present application;

[0035] Figure 3 It is a schematic flow chart of a secondary frequency modulation control strategy for hybrid energy storage-assisted thermal power units based on hierarchical adaptive control in the ACE mode according to an embodiment of the present application;

[0036] Figure 4 It is a schematic diagram of a hybrid energy storage frequency modulation command allocation control structure based on variable time constant low-order filtering control according to an embodiment of the present application. Detailed Embodiments

[0037] To enable those skilled in the art to better understand the technical solutions of the present disclosure, the present disclosure will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0038] The embodiments of the present application will be further described in detail below in conjunction with the accompanying drawings and examples. The detailed descriptions and drawings of the following examples are used to exemplarily illustrate the principles of the present application, but cannot be used to limit the scope of the present application, that is, the present application is not limited to the described embodiments. In the description of the present application, it should be noted that unless otherwise specified, the meaning of "a plurality" is two or more; the terms "upper", "lower", "left", "right", "inner", "outer", etc. indicate the orientation or positional relationship only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation of the present application. In addition, the terms "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" is not strictly vertical, but within the allowable error range. "Parallel" is not strictly parallel, but within the allowable error range.

[0039] In the description of the present application, it should also be noted that unless otherwise clearly specified and defined, the terms "installed", "connected", "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present application can be understood according to specific circumstances.

[0040] As Figure 1 shown, a frequency modulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control is characterized by including:

[0041] S101. Real-time detect the spare capacity of the thermal power unit and the state of charge of the hybrid energy storage, obtain the automatic generation control (AGC) instruction from the distributed control system (DCS) of the power plant, obtain the tie-line exchange power between regions and the system frequency deviation, and calculate the area control error (ACE) frequency modulation instruction.

[0042] S102. Based on the relationship between the remaining energy of the hybrid energy storage system and the hybrid energy storage distribution ratio factor K, the outer layer control adaptively distributes the real-time area control error (ACE) frequency modulation instruction of the power grid between the thermal power unit and the hybrid energy storage system.

[0043] S103. Based on the fuzzy control with variable time constant filtering, the inner layer control decomposes the area control error (ACE) signal allocated to the hybrid energy storage system between the flywheel energy storage and the battery energy storage, and calculates the rated output power instruction of each energy storage.

[0044] S104. Divide the battery energy storage unit into a charging sub-unit and a discharging sub-unit that independently perform charge and discharge operations, and switch the charge and discharge states when any sub-unit reaches the state of charge (SOC) boundary.

[0045] S105. Output a frequency modulation power command to the energy storage converter, and repeat the execution until the grid frequency is stable or the output of the thermal power unit approaches the automatic generation control (AGC) command.

[0046] In some embodiments, based on the fact that the frequency modulation ability of the thermal power unit is negatively correlated with the hybrid energy storage distribution ratio factor K, select the hyperbolic tangent function as the adaptive adjustment function of the K value, and calculate the hybrid energy storage area control error (ACE) signal distribution ratio factor based on the reserve capacity of the thermal power unit.

[0047] In some embodiments, based on the fact that the frequency modulation ability of the hybrid energy storage system is positively correlated with the hybrid energy storage distribution ratio factor K, select the Logistic function as the adaptive adjustment function of the K value, and distribute the ratio factor based on the hybrid energy storage area control error (ACE) signal feedback from the state of charge (SOC) of the hybrid energy storage.

[0048] In some embodiments, the distribution ratio factor K is determined by the minimum value of the hyperbolic tangent function and the Logistic function.

[0049] In some embodiments, it further includes: based on the reserve capacity boundary of the thermal power unit and the state of charge boundary of the hybrid energy storage system, adjust the value of the distribution ratio factor K in real time.

[0050] In some embodiments, it further includes: in the tie-line bias control (TBC) mode, calculate the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system according to the hybrid energy storage system distribution ratio factor K.

[0051] In some embodiments, the method for distributing the area control error (ACE) frequency modulation command in the hybrid energy storage system includes:

[0052] Obtain the secondary frequency modulation signal (Ace, H(s)) of the hybrid energy storage system and the state of charge of each energy storage unit.

[0053] Analyze the current state of charge and response power of the flywheel energy storage through a fuzzy controller to determine the current variable time constant adjustment amount T i 。

[0054] According to the variable time constant adjustment amount T i Calculate the low-pass filter time constant T.

[0055] The high- and low-frequency signals obtained by decomposing the frequency regulation command (Ace, HESS) of the hybrid energy storage system through variable-time low-pass filtering are respectively allocated to the flywheel energy storage and the battery energy storage, and the frequency regulation signals of the flywheel energy storage and the battery energy storage after allocation are calculated.

[0056] Calculate the output power command according to the area control error (ACE) signals allocated to the flywheel energy storage and the battery energy storage.

[0057] In some embodiments, the current variable time constant adjustment amount T is determined by analyzing the current state of charge and response power of the flywheel energy storage through a fuzzy controller i Including:

[0058] Fuzzy controller design principle:

[0059] When the SOC of the flywheel is at a low level, the flywheel needs to be charged at this time.

[0060] Assume that the ACE signal allocated to the flywheel is positive at this time, and the flywheel is charged with the current ACE signal. In order to quickly increase the flywheel SOC to a higher level, the variable time constant T must be increased i ;

[0061] Assume that the ACE signal allocated to the flywheel is negative at this time, then the flywheel does not output or reduces the power output, and the variable time constant adjustment amount T must be reduced i .

[0062] When the SOC of the flywheel is at a high level, the situation is opposite.

[0063] The fuzzy controller is specifically designed as:

[0064] The two input variables are S oc,F and ΔP F , the basic domain of S oc,F is [0, 1], the basic domain of ΔP F is [0, 1], and it is divided into 5 fuzzy sets: NB (negative large), NS (negative small), ZO (zero), PS (positive small), PB (positive large);

[0065] The domain of the variable time constant T i is [-2, 2], and it is divided into 5 fuzzy sets: NB (negative large), NS (negative small), ZO (zero), PS (positive small), PB (positive large);

[0066] The fuzzy control rules of T i are shown in Table 1 below.

[0067] In some embodiments, the optimization of the actual output power of the battery energy storage includes:

[0068] Determine the operating SOC range of the battery energy storage. Analyze the operating life at different depths of discharge (DOD) using the actual frequency regulation power data, and determine the SOC range with the best life extension effect.

[0069] Set the battery capacities of the charging and discharging parts to be equal, which is half of the single battery energy storage. Calculate the actual power of the batteries in the charging and discharging states considering the rated power, rated capacity, and SOC constraints of the battery energy storage;

[0070] When the SOC of the battery in the charging state reaches S oc,max or the SOC of the battery in the discharging state reaches S oc,min Convert the battery in the charging state to the discharging state, and convert the battery in the discharging state to the charging state.

[0071] The battery unit also needs to meet the power constraint and SOC operating constraint conditions during operation. If a certain battery cannot meet the frequency regulation power demand due to the rated power or rated capacity constraint, it is compensated by another battery.

[0072] Optionally, the method for solving the operating SOC range of the battery energy storage includes:

[0073] According to the number of cycles N at different DODs obtained from engineering tests, use a fifth-order function to fit the relationship curve between the number of cycles of the lithium battery and DOD;

[0074] Use the rain flow counting method to count the equivalent number of cycles at different DODs, and based on the relationship curve between the number of cycles and DOD and the equivalent cycle life method, convert the number of cycles N at different DODs to the equivalent number of cycles N' under full charge and discharge (i.e., D od = 1) and sum them up;

[0075] Compare with the number of cycles N1 obtained from the test under full charge and discharge to obtain the actual operating life T of the lithium battery B ;

[0076] Calculate the operating SOC boundary of the battery energy storage in the case of the DOD with the best life extension effect.

[0077] In some embodiments, the optimization of the actual output power of the battery energy storage includes:

[0078] Determine the operating SOC range of the battery energy storage. Analyze the operating life at different depths of discharge (DOD) using the actual frequency regulation power data, and determine the SOC range with the best life extension effect.

[0079] Set the battery capacities of the charging and discharging parts to be equal, which is half of the single battery energy storage. Calculate the actual power of the batteries in the charging and discharging states considering the rated power, rated capacity, and SOC constraints of the battery energy storage;

[0080] When the state of charge (SOC) of the battery in the charging state reaches S oc,max or the SOC of the battery in the discharging state reaches S oc,min the battery in the charging state is converted to the discharging state, and the battery in the discharging state is converted to the charging state.

[0081] During operation, the battery unit also needs to meet the power constraint and the SOC operation constraint conditions. If a certain battery cannot meet the frequency regulation power demand due to the rated power or rated capacity constraint, it is compensated by another battery.

[0082] The technical solution provided by the embodiment of the present application at least brings the following beneficial effects:

[0083] The present application comprehensively considers the problems that the regulation rate of thermal power units is insufficient and the climbing ability is weak due to the frequent fluctuation and strong randomness of the ACE frequency regulation command; the influence of the remaining energy of the system on the frequency regulation command; and the influence of the battery cycle times and the depth of discharge on the life of the battery energy storage system. A secondary frequency regulation control strategy for a hybrid energy storage auxiliary thermal power unit based on hierarchical adaptive control in the ACE mode is proposed, including real-time detection of the standby capacity of the thermal power unit and the state of charge of the hybrid energy storage, obtaining the AGC command and the ACE frequency regulation command from the power plant DCS; the outer layer control adaptively distributes the ACE frequency regulation command between the thermal power unit and the hybrid energy storage system based on the relationship between the remaining energy of the system and the proportionality factor; the inner layer control decomposes the ACE signal allocated to the energy storage between the flywheel energy storage and the battery energy storage based on fuzzy control with variable time constants; optimizes the actual output power of the battery energy storage, divides the battery energy storage system into two parts, and independently undertakes the charging and discharging tasks respectively when participating in frequency regulation; outputs the frequency regulation power command to the energy storage converter to control the charging and discharging power adjustment of the energy storage system, and repeats the above steps until the output of the thermal power unit gradually approaches the AGC command or the grid frequency is stable.

[0084] On the premise of meeting the output boundaries of the unit and the energy storage system and responding to the frequency, it reduces the frequency deviation, significantly improves the execution effect of the thermal power unit on the ACE frequency regulation command of the power grid; enables the hybrid energy storage system to reduce the number of charge and discharge switches of the battery energy storage while quickly and adaptively responding to the frequency regulation demand, and extends the service life of the battery energy storage; better coordinates the utility of the energy storage system and the conventional frequency regulation unit, and realizes the efficient and stable operation of the power grid frequency regulation.

[0085] An embodiment provided by the present application includes:

[0086] Figure 2 A schematic diagram of a secondary frequency regulation system for a hybrid energy storage auxiliary thermal power unit in the ACE mode according to an embodiment of the present application; as Figure 2As shown in the figure, the secondary frequency regulation system of a thermal power unit assisted by hybrid energy storage in ACE mode includes: a thermal power unit system and a hybrid energy storage system. Among them, the hybrid energy storage system does not change the original operation mode of the thermal power unit. The thermal power unit and the hybrid energy storage are in a parallel operation state, and the combined power of the unit power + energy storage power is used to track the grid command.

[0087] The thermal power unit system consists of a power plant DCS system, a CCS system, and a thermal power unit. Among them, the power plant DCS system is used to receive the ACE frequency regulation command sent by the grid dispatching center through the RTU and output the AGC command to the CCS system; the CCS system is used to adjust the output load of the unit; the thermal power unit consists of a boiler, a steam turbine, a governor, and a generator, and is used to adjust the steam turbine valve opening according to the frequency regulation signal, change the instantaneous main steam flow rate, and thus change the output power of the steam turbine to participate in the grid frequency regulation.

[0088] The hybrid energy storage system consists of a flywheel energy storage, a battery energy storage, and a control system. Among them, the flywheel energy storage consists of a filter circuit, an inverter, an asynchronous motor, and a flywheel rotor, and is used for short-term high-power and frequent charge and discharge scenarios; the battery energy storage is used for long-term power and energy support.

[0089] The connection method of the flywheel energy storage and the battery energy storage is to adopt a connection method with a common AC side topology containing a DC / AC inverter. Each uses a separate DC / AC inverter to connect to the grid side. In this case, when a certain DC / AC inverter fails, other energy storage units can still operate normally.

[0090] The hybrid energy storage is connected to the thermal power unit system by connecting to the high-voltage bus of the power plant. This connection method only requires that the high-voltage transformer of the thermal power plant can meet the access requirements of the energy storage system, and there is no need to transform the generator, resulting in lower project costs. In addition, it also avoids the problem of unit shutdown caused by the step-up and transformation failure of the energy storage system.

[0091] Figure 3 It is a schematic flow chart of a secondary frequency regulation control strategy for a hybrid energy storage assisted thermal power unit based on hierarchical adaptive control in ACE mode according to an embodiment of the present application. As Figure 3 shown, a secondary frequency regulation control strategy for a hybrid energy storage assisted thermal power unit based on hierarchical adaptive control in ACE mode is used to implement the secondary frequency regulation system of the hybrid energy storage assisted thermal power unit, including:

[0092] S1: Real-time detect the standby capacity of the thermal power unit and the state of charge of the hybrid energy storage, obtain the AGC command from the power plant DCS, and calculate the ACE frequency regulation command according to the tie-line exchange power between regions and the system frequency deviation;

[0093] Specifically, in the embodiments of the present disclosure, the tie-line frequency bias control (TBC) mode is adopted, and the calculation formula of the ACE signal of the regional frequency deviation is:

[0094] A ce (s)=ΔP t (s)+b1Δf(s) (1)

[0095] In the formula, A ce (s) is the regional power deviation; ΔP t (s) is the interchange power of the tie-line between regions; b1 is the frequency deviation coefficient; Δf(s) is the system frequency deviation;

[0096] S2 distributes the ACE signal between the thermal power unit and the hybrid energy storage, adjusts the proportionality factor K in real time considering the standby capacity boundary of the thermal power unit and the SOC boundary of the hybrid energy storage, and calculates the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system according to the proportionality factor K;

[0097] Among them, in the embodiments of the present disclosure, the calculation method of the proportionality factor for distributing the ACE signal of the hybrid energy storage based on the standby capacity of the thermal power unit is as follows:

[0098] The frequency modulation ability of the thermal power unit is negatively correlated with the proportionality factor K of the hybrid energy storage. Since the hyperbolic tangent function not only conforms to the characteristic of the low ramp rate of the thermal power unit but also can achieve the effect of smoothing the unit output. Therefore, the hyperbolic tangent function is selected as the adaptive adjustment function of the proportionality factor for distributing the ACE signal of the hybrid energy storage based on the standby capacity of the thermal power unit; the specific calculation formula is:

[0099]

[0100] In the formula: n is the adaptive parameter; K 1c and K 1d are the proportionality factors for distributing the ACE signal of the hybrid energy storage corresponding to the control of the throttle opening and closing of the thermal power unit when the frequency increases and decreases respectively; ΔP g is the feedback power of the thermal power unit.

[0101] In addition, in the embodiments of the present disclosure, the calculation method of the proportionality factor for distributing the ACE signal of the hybrid energy storage based on the SOC feedback of the hybrid energy storage is as follows:

[0102] The frequency modulation ability of the hybrid energy storage system is positively correlated with the proportionality factor K of the hybrid energy storage. Since the Logistic function conforms to the characteristic of the fast response of the energy storage system and can smoothly adjust the proportionality factor of the energy storage in real time. Therefore, the Logistic function is selected as the adaptive adjustment function of the proportionality factor for distributing the ACE signal of the hybrid energy storage based on the SOC feedback of the hybrid energy storage; the specific calculation formula is:

[0103]

[0104] Where: K 2c and K 2d are respectively the hybrid energy storage ACE allocation ratio factors during charging or discharging of the hybrid energy storage, P ec and P ed are respectively the average rated charging and discharging powers of the hybrid energy storage system; S oc,min , S oc,low , S oc,high , S oc,max are respectively the minimum value, lower value, higher value, and maximum value of the hybrid energy storage system S oc ; A and n are adaptive parameters;

[0105] Furthermore, in the embodiments of the present disclosure, in order to simultaneously satisfy these two output constraints, by calculating the ratio factors under the output of the thermal power unit and the SOC state of the hybrid energy storage at the same time, the minimum value under the two state constraints is selected as the actual hybrid energy storage ratio factor, and the calculation formula of the hybrid energy storage ratio factor is:

[0106]

[0107] Where K c,min and K d,min are respectively the adaptive ratio factors during charging and discharging.

[0108] Among them, in the embodiments of the present disclosure, the above calculation method for calculating the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system according to the ratio factor K is:

[0109] In the tie-line frequency bias control (TBC) mode, according to the hybrid energy storage system ratio factor K, calculate the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system, and the specific calculation formula is:

[0110] A ce,H (s) = KA ce (s) (5)

[0111] A ce,g (s) = (1 - K)A ce (s) (6)

[0112] Where, A ce,H (s) is the secondary frequency modulation signal of the hybrid energy storage system; A ce,g (s) is the secondary frequency modulation signal of the thermal power unit.

[0113] The S3 inner layer control decomposes the ACE signal allocated to the energy storage between the flywheel energy storage and the battery energy storage based on the variable time constant filtering fuzzy control, and calculates the output power commands of each energy storage;

[0114] Figure 4 It is a schematic diagram of a hybrid energy storage frequency modulation command allocation control structure based on variable time constant low-order filtering control provided according to an embodiment of the present application.

[0115] Specifically, in the embodiments of the present disclosure, the above-mentioned fuzzy control based on variable time constant filtering for allocating the ACE signal between hybrid energy storages includes the following steps:

[0116] Step a: Obtain the secondary frequency modulation signal A ce,H (s) of the hybrid energy storage system and the SOC of each energy storage;

[0117] Step b: Analyze the current state of charge and response power of the flywheel energy storage through a fuzzy controller to determine the current variable time constant adjustment amount T i .

[0118] Among them, in the embodiments of the present disclosure, the design principle of the above-mentioned fuzzy controller is:

[0119] When the SOC of the flywheel is at a low level, the flywheel needs to be charged at this time.

[0120] Assume that the ACE signal allocated to the flywheel is positive, and the flywheel is charged with the current ACE signal. In order to quickly increase the flywheel SOC to a higher level, the variable time constant T i ;

[0121] Assume that the ACE signal allocated to the flywheel is negative, then the flywheel does not output or reduces the power output, and the variable time constant adjustment amount T i .

[0122] When the SOC of the flywheel is at a high level, the situation is the opposite.

[0123] Furthermore, in the embodiments of the present disclosure, the above-mentioned variable time constant adjustment amount T i of the fuzzy controller is designed as:

[0124] The two input quantities are S oc,F and ΔP F , the basic domain of S oc,F is [0,1], the basic domain of ΔP F is [0,1], and it is divided into 5 fuzzy sets: NB (negative large), NS (negative small), ZO (zero), PS (positive small), PB (positive large);

[0125] The variable time constant T iThe universe of discourse is [-2, 2], which is divided into 5 fuzzy sets: NB (Negative Big), NS (Negative Small), ZO (Zero), PS (Positive Small), PB (Positive Big);

[0126] T i The fuzzy control rules are shown in Table 1.

[0127] Table 1 Variable time constant T i Fuzzy rules

[0128]

[0129]

[0130] Step c adjusts the variable time constant T i Calculate the time constant T of the low-pass filter;

[0131] Among them, in the embodiments of the present disclosure, the above time constant T calculation method is:

[0132] T = T0 + T i (7)

[0133] In the formula, T0 is the fixed time constant.

[0134] Step d assigns A ce,HESS The high- and low-frequency signals after the variable-time low-pass filter decomposition are respectively assigned to the flywheel and the lithium battery energy storage, and calculate the frequency modulation signal after the assignment;

[0135] Among them, in the embodiments of the present disclosure, the above frequency modulation signal calculation method is

[0136]

[0137] In the formula, Ace,BESS and Ace,F are the ACE signals of the battery energy storage and the flywheel energy storage respectively.

[0138] Step e calculates the output power command according to the ACE signals allocated to each energy storage.

[0139] Among them, in the embodiments of the present disclosure, the above output power command calculation method is:

[0140] P BESS = A ce,BESS G B (s) (10)

[0141] P F = A ce,F G F (s) (11)

[0142] In the formula, G B (s) and G F(s) are the first-order system transfer functions of the energy storage battery and the flywheel energy storage respectively.

[0143] S4 optimizes the actual output power of the battery energy storage. To reduce the impact of frequent charge and discharge switching on the battery life, the battery energy storage system is divided into two parts. When participating in frequency modulation, they independently undertake the charge and discharge tasks respectively. When the SOC of a certain battery reaches the SOC boundary, the charge and discharge states of the two batteries are switched.

[0144] Specifically, in the embodiments of the present disclosure, the optimization of the actual output power of the battery energy storage includes the following steps:

[0145] Step a calculates the operating SOC range of the battery energy storage according to the DOD with the best life extension effect.

[0146] Among them, in the embodiments of the present disclosure, the calculation method of the above DOD is:

[0147] For battery energy storage, DOD is the main factor affecting its operating life, and the number of cycles is a functional relationship with DOD. The actual frequency modulation power data is used to analyze the operating life at different depths of discharge (DOD), and the DOD with the best life extension effect is determined.

[0148] Furthermore, in the embodiments of the present disclosure, the relationship between the depth of discharge and the operating life is:

[0149] First, according to the number of cycles N at different DODs obtained from engineering tests, a fifth-order function is used to fit the lithium battery cycle number - DOD relationship curve:

[0150]

[0151] Furthermore, considering that the DOD of the battery is constantly changing during the frequency modulation process, therefore, the rain flow counting method is used to count the equivalent number of cycles at different DODs, and based on the cycle number - DOD relationship curve and the equivalent cycle life method, the number of cycles N at different DODs is converted to the equivalent number of cycles N' under full charge and discharge (i.e., D od = 1) and summed;

[0152] Finally, it is compared with the number of cycles N1 obtained from the test under full charge and discharge, and the actual operating life TB of the lithium battery is obtained as:

[0153] T B = N1 / ΣN′ (13)

[0154] Step b defines the DOD with the best life extension effect as D od , and calculates the operating SOC boundary of the battery energy storage;

[0155] Among them, in the embodiments of the present disclosure, the above-mentioned battery energy storage SOC boundary can be expressed as:

[0156] S oc,max =(1 + D od ) / 2 S oc,min =(1 - D od ) / 2 (14)

[0157] In the formula: S oc,max and S oc,min are respectively the upper and lower bounds of the battery energy storage operation SOC.

[0158] In step c, since the power instruction is independently executed during the operation process, the capacities of the two batteries are set to be equal, which is half of the single battery energy storage. Considering the rated power, rated capacity and SOC constraints of the battery energy storage, calculate the actual power of the battery in the charging and discharging states;

[0159] Among them, in the embodiments of the present disclosure, the actual powers of the batteries in the above-mentioned charging and discharging states can be respectively expressed as:

[0160]

[0161] In the formula: P c,BESS (t), P d,BESS (t) are respectively the actual power instructions of the batteries in the charging and discharging states; P BESS (t) is the reference power instruction; S oc,c (t - Δt), S oc,d (t - Δt) are respectively the SOCs of the batteries in the charging and discharging states at the previous moment; E is the rated capacity of the battery energy storage,

[0162] In step d, when the SOC of the battery in the charging state reaches S oc,max or the SOC of the battery in the discharging state reaches S oc,min , convert the battery in the charging state to the discharging state, and convert the battery in the discharging state to the charging state.

[0163] In step e, if a certain battery cannot meet the frequency regulation power demand due to rated power or rated capacity constraints, it is compensated by the other battery. In addition, the battery energy storage also needs to meet the power constraint and SOC operation constraint conditions during operation.

[0164] S5 outputs the frequency regulation power instructions of the flywheel energy storage and the battery energy storage to the energy storage converter to control the charging and discharging power adjustment of the energy storage system, and repeats the above steps until the output of the thermal power unit gradually approaches the AGC instruction or the grid frequency is stable, the output response of the energy storage system exits, and the energy storage system enters the charging mode in a timely manner to reserve energy for the next response process.

[0165] This application provides a computer-readable storage medium, on which a computer program is stored,

[0166] When the computer program is executed by a processor, it can implement the above-mentioned frequency modulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control.

[0167] This application provides a frequency modulation system for a hybrid energy storage thermal power unit based on hierarchical adaptive control. The frequency modulation system can operate the above-mentioned frequency modulation control strategy, and is characterized by including:

[0168] A thermal power unit system, including a plant distributed control system (DCS), a coordinated control system (CCS), and a thermal power unit. Among them, the plant distributed control system (DCS) is configured to receive a regional control error (ACE) frequency modulation instruction sent by a grid dispatching center and generate an automatic generation control (AGC) instruction;

[0169] The coordinated control system (CCS) adjusts the output load of the thermal power unit according to the automatic generation control (AGC) instruction; the thermal power unit includes a boiler, a steam turbine, a governor, and a generator, and is used to respond to a frequency modulation signal to change the main steam flow rate and output power;

[0170] A hybrid energy storage system (HESS), including a flywheel energy storage, a battery energy storage, and a control system. Among them, the flywheel energy storage unit includes an asynchronous motor, a filter circuit, a flywheel rotor, and an inverter, and is used for short-term high-frequency power response; the battery energy storage is used for medium- and long-term power and energy support.

[0171] In some embodiments, the thermal power unit system and the hybrid energy storage system are connected to the plant high-voltage bus in a parallel operation mode, and their combined output power tracks the grid instruction; the flywheel energy storage and the battery energy storage are each independently connected to the grid through a DC / AC inverter.

[0172] A specific frequency modulation system includes: a thermal power unit system and a hybrid energy storage system. Among them, the hybrid energy storage system does not change the original operation mode of the thermal power unit, the thermal power unit and the hybrid energy storage are in a parallel operation state, and the combined power of the unit power + energy storage power is used to track the grid instruction.

[0173] The thermal power unit system is composed of a plant DCS system, a CCS system, and a thermal power unit. Among them, the plant DCS system is used to receive the ACE frequency modulation instruction sent by the grid dispatching center through the RTU and output the AGC instruction to the CCS system; the CCS system is used to adjust the output load of the unit; the thermal power unit is composed of a boiler, a steam turbine, a governor, and a generator, and is used to adjust the steam turbine valve opening according to the frequency modulation signal, change the instantaneous main steam flow rate, and thus change the output power of the steam turbine to participate in grid frequency modulation.

[0174] The hybrid energy storage system consists of a flywheel energy storage, a battery energy storage, and a control system. The flywheel energy storage consists of a filter circuit, an inverter, an asynchronous motor, and a flywheel rotor, and is used for scenarios with short-term high power and frequent charge and discharge; the battery energy storage is used for power and energy support suitable for a longer time.

[0175] Optionally, the connection method of the flywheel energy storage and the battery energy storage is that each uses a separate DC / AC inverter to connect to the grid side. In this case, when a certain DC / AC inverter fails, other energy storage units can still operate normally.

[0176] In summary, the secondary frequency modulation control strategy of the hybrid energy storage assisting thermal power units based on hierarchical adaptive control in this application fully considers the influence of the remaining energy in the system on the frequency modulation command under the ACE mode and the influence of the depth of battery discharge on the service life of the energy storage. On the premise of satisfying the output boundary of the unit and the energy storage system and responding to the frequency, it significantly improves the execution effect of the thermal power unit on the grid ACE frequency modulation command; at the same time, it reduces the number of charge and discharge switches of the battery energy storage, prolongs its service life, and improves the reliability and stability of the hybrid energy storage system; it better coordinates the utility of the energy storage system and the frequency modulation thermal power unit, and realizes the efficient and stable operation of the grid frequency modulation.

[0177] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principles of the present disclosure. However, the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present disclosure, and these modifications and improvements are also regarded as the protection scope of the present disclosure.

Claims

1. A frequency regulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control, characterized in that, Including: Real-time detecting the standby capacity of the thermal power unit and the state of charge of the hybrid energy storage, obtaining the automatic generation control instruction from the power plant distributed control system, obtaining the tie-line exchange power between regions and the system frequency deviation, and calculating the area control error frequency modulation instruction; The outer layer control adaptively distributes the real-time area control error frequency modulation instruction of the power grid between the thermal power unit and the hybrid energy storage system based on the relationship between the remaining energy of the hybrid energy storage system and the hybrid energy storage distribution ratio factor K; The inner layer control decomposes the area control error signal distributed to the hybrid energy storage system between the flywheel energy storage and the battery energy storage based on the fuzzy control with variable time constant filtering, and calculates the rated output power instruction of each energy storage; The battery energy storage unit is divided into a charging sub-unit and a discharging sub-unit that independently perform charging and discharging operations, and the charging and discharging states are switched when any sub-unit reaches the state of charge boundary; Output the frequency modulation power instruction to the energy storage converter, and repeat the execution until the power grid frequency is stable or the output of the thermal power unit approaches the automatic generation control instruction.

2. The frequency regulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 1, wherein Based on the negative correlation between the frequency modulation ability of the thermal power unit and the hybrid energy storage distribution ratio factor K, the hyperbolic tangent function is selected as the adaptive adjustment function of the K value, and the hybrid energy storage area control error signal distribution ratio factor based on the standby capacity of the thermal power unit is calculated.

3. The frequency modulation strategy of the hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 2, wherein Based on the positive correlation between the frequency modulation ability of the hybrid energy storage system and the hybrid energy storage distribution ratio factor K, the Logistic function is selected as the adaptive adjustment function of the K value, and the hybrid energy storage area control error signal distribution ratio factor based on the state of charge feedback of the hybrid energy storage is calculated.

4. The frequency regulation strategy of the hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 3, wherein The distribution ratio factor K is determined by the minimum value of the hyperbolic tangent function and the Logistic function.

5. The frequency regulation strategy of the hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 1, wherein Also including: Based on the standby capacity boundary of the thermal power unit and the state of charge boundary of the hybrid energy storage system, the value of the distribution ratio factor K is adjusted in real time.

6. The frequency regulation strategy of the hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 1, wherein Also including: In the tie-line deviation control mode, the secondary frequency modulation signals of the thermal power unit and the hybrid energy storage system are calculated according to the hybrid energy storage system distribution ratio factor K.

7. The frequency modulation strategy for a hybrid energy storage thermal power unit based on hierarchical adaptive control according to claim 6, wherein The area control error frequency modulation instruction distribution method in the hybrid energy storage system includes: Obtaining the secondary frequency modulation signal of the hybrid energy storage system and the state of charge of each energy storage unit; Analyze the current state of charge and response power of the flywheel energy storage through a fuzzy controller to determine the current variable time constant adjustment amount T i ; Adjustment amount T according to variable time constant i Calculate the low-pass filter time constant T; The high-frequency and low-frequency signals obtained by decomposing the frequency modulation instruction of the hybrid energy storage system through variable-time low-pass filtering are respectively distributed to the flywheel energy storage and the battery energy storage, and the frequency modulation signals of the flywheel energy storage and the battery energy storage after distribution are calculated; Calculate the output power instruction according to the area control error signals distributed to the flywheel energy storage and the battery energy storage.

8. A computer-readable storage medium, on which a computer program is stored, characterized in that When the computer program is executed by a processor, it can implement the hybrid energy storage thermal power unit frequency modulation strategy based on hierarchical adaptive control according to any one of claims 1 to 7.

9. A hybrid energy storage thermal power unit frequency modulation system based on hierarchical adaptive control, the frequency modulation system being capable of operating the frequency modulation control strategy described in any one of claims 1-7, characterized in that, Including: The thermal power unit system includes a power plant distributed control system, a coordinated control system and a thermal power unit. Among them, the power plant distributed control system is configured to receive the area control error frequency modulation instruction sent by the power grid dispatching center and generate an automatic generation control instruction; The coordinated control system adjusts the output load of the thermal power unit according to the automatic generation control instruction; the thermal power unit includes a boiler, a steam turbine, a governor and a generator, and is used to respond to the frequency modulation signal to change the main steam flow rate and output power; The hybrid energy storage system includes a flywheel energy storage, a battery energy storage and a control system. Among them, the flywheel energy storage unit includes an asynchronous motor, a filter circuit, a flywheel rotor and an inverter, and is used for short-term high-frequency power response; the battery energy storage is used for medium- and long-term power and energy support.

10. The hybrid energy storage thermal power unit frequency modulation system based on hierarchical adaptive control according to claim 9, wherein, The thermal power unit system and the hybrid energy storage system are connected to the high-voltage bus of the power plant in a parallel operation mode, and their combined output power tracks the grid instruction; the flywheel energy storage and the battery energy storage are each independently connected to the grid through a DC / AC inverter.

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