Adaptive soc equalization control method in black start process of energy storage system

Abstract

The application discloses a self-adaptive SOC equalization control method in a black start process of an energy storage system. Compared with the prior art, the application has the following beneficial effects: compared with the traditional black start control strategy of the energy storage system, the method disclosed by the application effectively realizes SOC balancing and power sharing of different energy storage units in the energy storage system by using a self-adaptive SOC equalization strategy. The application provides an energy storage system capacity configuration strategy in the black start process and a safety threshold of charging and discharging power of each energy storage unit of the energy storage system. The method disclosed by the application improves the stability and reliability of the black start process of the energy storage system.

Description

Technical Field

[0001] This invention relates to an adaptive SOC equalization control method considering the black start process of an energy storage system, belonging to the field of energy storage system operation and control technology. Background Technology

[0002] With continuous economic development and a gradually expanding population, overall electricity consumption is increasing at an average annual rate of 5%. To meet the electricity needs of social development, the power system is gradually expanding in scale, with interconnected internal subsystems, and increasingly complex network structures and dynamic behaviors. This increased complexity reduces the system's stability margin to some extent. When the system suffers from multiple complex faults due to high-risk natural disasters, the probability of power outages increases. Major power outages cause enormous losses to the social economy and people's daily lives. After a power outage, the system needs to have the ability to quickly restore regional power supply to minimize losses.

[0003] Black start is defined as the process of gradually restoring the power supply capacity of a system by utilizing its own generating units without the assistance of external systems after a power outage. The black start process mainly involves the automatic restart of the black start power supply in the event of a system fault or a complete power outage. The black start power supply ignites the auxiliary generators of the main generator set, which in turn restart the main generator set, gradually restoring the load.

[0004] The black-start power source determines the performance of the system during the black-start process. Compared to traditional black-start diesel generators, energy storage systems offer greater regulation range, faster dynamic response, lower starting power, faster load recovery, more revenue streams (AGC frequency regulation, peak shaving, etc.), and are more economical and environmentally friendly. Energy storage systems are becoming the primary choice for black-start power sources.

[0005] When an energy storage system participates in black start, the energy storage units within the system generally adopt a master-slave control structure. The master energy storage unit uses a constant voltage and frequency (VF) control strategy, while the slave energy storage units use a constant power and quality (PQ) control strategy. The master energy storage unit provides stable voltage and frequency support for the black start process.

[0006] During black start, inconsistencies in the State of Charge (SOC) of different energy storage units within an energy storage system can cause some units to overcharge and discharge, leading to the shutdown of some units and system black start failure. Therefore, researching SOC balancing strategies for the black start process of energy storage systems is of great significance for improving the black start stability of energy storage systems. Summary of the Invention

[0007] The purpose of this invention is to study and analyze the adaptive SOC equalization control strategy for energy storage systems as black-start power sources during the process of starting auxiliary loads in thermal power plants.

[0008] To achieve the above objectives, the technical solution of the present invention provides an adaptive SOC equalization control method during the black start process of an energy storage system, characterized by comprising the following steps:

[0009] At the start of black start, the energy storage unit with the highest SOC value among all energy storage units is selected as the main energy storage unit, and its droop factor is set to the lowest, denoted as R. master The remaining energy storage units serve as slave energy storage units, forming a total of N groups of slave energy storage units;

[0010] During the discharge process, the droop coefficient R of the i-th energy storage unit i Calculate using the following formula:

[0011]

[0012] During the charging process, the droop coefficient R of the i-th energy storage unit i Calculate using the following formula:

[0013]

[0014] In the formula: master is the identifier of the master energy storage unit, i is the identifier of the slave energy storage unit, and n is the SOC index;

[0015] p is the SOC equalization speed amplification factor;

[0016] β is the power-equalization acceleration factor;

[0017] α is the SOC equalization rate contraction factor, where: during discharge, the SOC equalization rate contraction factor α is adaptively adjusted according to the following formula:

[0018]

[0019] During charging, the SOC equalization speed contraction factor α is adaptively adjusted according to the following formula:

[0020]

[0021] SOC master State of charge of the primary energy storage unit; State of charge of SOCi is the i-th slave energy storage unit.

[0022] Preferably, let τ be the maximum droop ratio between energy storage units in the energy storage system, where τ equals R max To determine the droop factor corresponding to the energy storage unit with the minimum charge / discharge power from the energy storage units, the maximum droop factor ratio τ is designed to satisfy... To ensure that the charging and discharging power between the various energy storage units in the energy storage system remains stable within a reasonable range, where P... bound The rated upper limit of the discharge power of the main energy storage unit, P demand ε represents the active power demand of the black start load, and ε is the safety margin parameter.

[0023] Preferably, the initial capacity of the energy storage system during the black start process is configured as follows:

[0024]

[0025] In the formula: E i The rated capacity of the i-th energy storage unit; The initial state of charge of the i-th energy storage unit; η is the charge / discharge efficiency of the i-th energy storage unit; ΔP% is the line loss ratio; P net t represents the net load requirement for black start; t represents the duration of black start.

[0026] Compared with prior art solutions, the present invention has the following advantages:

[0027] 1. Compared with the traditional black-start control strategy of energy storage system, the method disclosed in this invention effectively realizes the SOC balance and power distribution of different energy storage units in the energy storage system by using an adaptive SOC balancing strategy.

[0028] 2. This invention provides a capacity configuration strategy for the energy storage system during black start and a safe threshold for the charging and discharging power of each energy storage unit in the energy storage system.

[0029] 3. The method disclosed in this invention improves the stability and reliability of the black start process of the energy storage system. Attached Figure Description

[0030] Figure 1 The influence of various parameters of the adaptive SOC control strategy is illustrated.

[0031] Figure 2 The process of the present invention is illustrated. Detailed Implementation

[0032] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0033] Consider the Pf and QV droop characteristic curves of the energy storage unit during the black start process, as shown in equations (1) and (2) below:

[0034]

[0035]

[0036] Equation (1) is the output Pf curve of the i-th energy storage unit on the inverter side, where: f is the real-time frequency of the system grid; f 0 The system's no-load frequency is 50Hz; P i (f 0 R represents the active power output of the inverter of the i-th energy storage unit at the system's no-load frequency. i P is the droop coefficient of the i-th energy storage unit; i The active power output of the i-th energy storage unit is N; N is the number of energy storage units connected in parallel.

[0037] Equation (2) is the QV curve of the inverter side output of the i-th energy storage unit, where: V i V is the output voltage on the inverter side of the i-th energy storage unit; i 0 Q is the no-load bus voltage of the i-th energy storage unit; i (V i n ) represents the reactive power output of the inverter of the i-th energy storage unit under no-load voltage; m i Q is the droop coefficient of the i-th energy storage unit; i The reactive power output is the output side of the inverter of the i-th energy storage unit.

[0038] At the parallel connection point of each energy storage unit, the frequency is a global variable, and the node voltage is a local-global variable. Therefore, V i =V j =...=V n =V. Under no-load conditions, P1(f) 0 )=P2(f 0 )=...=P n (f 0 ) = 0, Q1(V1 0 )=Q2(V2 0 )=...=Q n (V n 0 = 0. Combining equations (1) and (2) and simplifying, we can see the relationship between the power reference value of each energy storage unit controller and the droop coefficient, as shown in equations (3) and (4):

[0039] P i R i =P j R j =...=P N R N (3)

[0040] Qi m i =Q j m j =...=Q N m N (4)

[0041] By utilizing the relationship between power and droop coefficient, the power of each parallel energy storage unit can be rationally allocated. This embodiment uses the relationship between active power P and droop coefficient R for demonstration; the method for demonstrating reactive power is the same and will not be repeated here.

[0042] Assume the active power demand of the black start load is P. demand If there are N energy storage units, then:

[0043]

[0044] Furthermore, we can obtain:

[0045]

[0046] In equation (6), the reference value P for power distribution of each energy storage unit in parallel state is... i With the droop coefficient R i Inversely proportional.

[0047] To effectively achieve a balance between the state of charge (SOC) and power distribution during the charging and discharging processes of each energy storage unit in the energy storage system, inspired by equation (6), the SOC is calculated for the discharging process. i With P i Proportional, SOC i With R i Inversely proportional. Therefore, designing a reasonable SOC... i With R i By establishing a functional mapping relationship, SOC balancing and power distribution during the energy storage charging and discharging process can be achieved.

[0048] At the same time, establish SOC i With R i The mapping relationship requires the establishment of centralized communication equipment to collect the state of charge (SOC) of each energy storage unit at high frequency at each moment. The real-time SOC calculation method is not the focus of this invention, so the general ampere-hour method is used to calculate the SOC value of each energy storage unit at the sampling moment, as shown in the following formula (7):

[0049]

[0050] In equation (7), SOC i (k) represents the state of charge of the i-th energy storage unit at sampling time k; Let A and C be the DC current output by the i-th energy storage unit at sampling time k. iΔt is the rated capacity of the i-th energy storage unit, Ah; Δt is the sampling interval, s.

[0051] Therefore, the adaptive SOC equilibrium strategy algorithm designed in this embodiment includes the following:

[0052] At the start of black start, the energy storage unit with the highest SOC value is selected as the main energy storage unit, and its droop factor R is set. master To minimize this, in this embodiment, R master Set to 1, and the remaining energy storage units are set as slave energy storage units. During the discharge process, the droop coefficient R of the i-th slave energy storage unit... i Calculated according to formula (8); during the charging process, the droop coefficient R of the i-th energy storage unit. i Calculate according to formula (9).

[0053]

[0054]

[0055] In equations (8) and (9): master is the identifier of the master energy storage unit, and i is the identifier of the slave energy storage unit. n is the SOC index; p is the SOC equalization speed amplification factor; α is the SOC equalization speed contraction factor; and β is the power equalization acceleration factor.

[0056] The effects of each parameter are shown in the table below. Figure 1 , Figure 1 The vertical axis represents the power ratio. It reflects the maximum charge and discharge power ratio of multiple energy storage units connected in parallel in the energy storage system. For a detailed analysis, see equation (14).

[0057] In equations (8) and (9): during the discharge process, the SOC equalization speed contraction factor α is adaptively adjusted according to equation (10); during the charging process, the SOC equalization speed contraction factor α is adaptively adjusted according to equation (11).

[0058]

[0059]

[0060] SOC master State of charge of the primary energy storage unit; State of charge of SOCi is the i-th slave energy storage unit.

[0061] Adjusting different parameters can achieve different power distributions, thereby realizing the SOC (State of Charge) balance of each energy storage unit in the energy storage system. The power ratio affects the SOC balance speed of each energy storage unit and can be adjusted as needed according to specific project requirements.

[0062] Design the safe threshold for the charging and discharging power of the energy storage unit (the following discussion takes the discharge process of the energy storage system as the background, and the only difference in the design of the charging process scheme is the sign).

[0063] Sag coefficient R i The droop coefficient affects the power distribution of the energy storage unit during charging and discharging, therefore it is necessary to study and analyze the relationship between the droop coefficient and the upper and lower limits of the energy storage unit's charging and discharging power. Based on equations (8) and (9), the droop coefficient R of the energy storage unit... i The droop factor R of the main energy storage unit master It can be seen that the droop coefficient of the main energy storage unit is the smallest during the charging and discharging process, corresponding to the charging and discharging power P. master maximum.

[0064] Using equation (5), we can obtain the charging and discharging power of the energy storage unit. If the charging and discharging power of the main energy storage meets the upper and lower limits, then the secondary energy storage will naturally meet the limits. Therefore, it is necessary to analyze how to configure parameters to ensure that the charging and discharging power of the main energy storage does not exceed the limits.

[0065] From equation (6), we can obtain:

[0066]

[0067]

[0068] In equations (12) and (13), R max This is the droop coefficient corresponding to the energy storage unit with the smallest charging and discharging power among N energy storage units.

[0069]

[0070] make Equal to τ, from equation (12) we get:

[0071]

[0072] In equation (15), P bound τ is the rated upper limit of the main energy storage discharge power; τ is the maximum droop ratio between each energy storage unit in the energy storage system.

[0073] The maximum value of τ is shown in equation (16):

[0074]

[0075] In the actual operation of the control system, N and P bound Given a fixed parameter, P demand This represents the actual black-start load requirements. In large-scale systems, P demandData needs to be acquired through communication, which poses risks such as data communication delay and data sampling error. In order to ensure the safety and stability of the black start operation process, a safety margin parameter ε is set. In this embodiment, the value is 5%, resulting in equation (17).

[0076]

[0077] By combining equation (14) and reasonably designing the parameter τ to meet the requirements of equation (17), the charging and discharging power between each energy storage unit of the energy storage system can be kept within a reasonable range.

[0078] Black start total capacity configuration strategy for energy storage systems

[0079] The capacity configuration of the energy storage system needs to be reasonable to ensure the stability of black start. This invention configures the initial capacity of the energy storage system during the black start process using equation (18).

[0080]

[0081] In equation (18): E i The rated capacity of the i-th energy storage unit is Wh; Let A be the initial state of charge of the i-th energy storage unit; η be the charge / discharge efficiency of the i-th energy storage unit; ΔP% be the line loss ratio; P net W represents the net load requirement for black start; t represents the duration of black start, in hours.

Claims

1. An adaptive SOC equalization control method during the black start process of an energy storage system, characterized in that, Includes the following steps: At the start of black start, the energy storage unit with the highest SOC value among all energy storage units is selected as the main energy storage unit, and its droop factor is set to the lowest value. The remaining energy storage units serve as slave energy storage units, forming a total of N groups of slave energy storage units; During the discharge process, the droop coefficient R of the i-th energy storage unit i Calculate using the following formula: During the charging process, the droop coefficient R of the i-th energy storage unit i Calculate using the following formula: In the formula, master is the identifier of the master energy storage unit, i is the identifier of the slave energy storage unit, and n is the SOC index; p is the SOC equalization speed amplification factor; The power-equalization acceleration factor; Here, SOC equalization rate contraction factor is the factor that determines the SOC equalization rate contraction during discharge. Adaptive adjustment according to the following formula: During charging, the SOC equalization speed contraction factor Adaptive adjustment according to the following formula: State of charge of the main energy storage unit; This represents the state of charge of the i-th energy storage unit.

2. The adaptive SOC equalization control method for the black start process of an energy storage system as described in claim 1, characterized in that, Let the maximum droop ratio between the energy storage units in the energy storage system be... , equal R max To determine the droop factor corresponding to the energy storage unit with the lowest charge / discharge power from the energy storage units, the maximum droop factor ratio is designed. Make it satisfy To ensure that the charging and discharging power between the various energy storage units in the energy storage system remains stable within a reasonable range, the formula is as follows: The rated upper limit of the discharge power of the main energy storage unit. The active power requirement for black start load. This is a safety margin parameter.

3. The adaptive SOC equalization control method for the black start process of an energy storage system as described in claim 1, characterized in that, The initial capacity of the energy storage system during the black start process is configured as follows: In the formula: The rated capacity of the i-th energy storage unit; This represents the initial state of charge of the i-th energy storage unit; Let i be the charging and discharging efficiency of the i-th energy storage unit; This represents the line loss ratio; t represents the net load requirement for black start; t represents the duration of black start.

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