A method for calculating the equivalent virtual inertia time constant of energy storage device

Abstract

A method for calculating the equivalent virtual inertia time constant of an energy storage device defines the energy storage virtual inertia time constant under the energy storage additional differential inertia control, and quantitatively characterizes its value through analysis. Combined with the energy storage inverter control model, the ratio relationship between the rate of change of the energy storage charge state and the change of the system synchronous angular velocity during the inertial response process is explored, and the ratio is substituted into the definition formula of the energy storage virtual inertia time constant to obtain the complex frequency domain expression of the inertia time constant, and then the time domain value is obtained through Laplace inverse transformation. The equivalent virtual inertia time constant of the energy storage device in the present invention has obvious dynamic time-varying characteristics, which is significantly different from the characteristics of the synchronous unit with a constant inertia time constant; it lays an important foundation for further research on the dynamic frequency characteristics of power systems containing energy storage virtual inertia control.

Description

Technical Field

[0001] The present invention relates to the technical field of dynamic frequency characteristic analysis of power systems, and in particular to a method for calculating the equivalent virtual inertia time constant of an energy storage device. Background Art

[0002] Utilizing the rapid power regulation capabilities of electrochemical energy storage devices to participate in system frequency regulation is one of the key application technologies of energy storage. In recent years, with the vigorous development of new energy sources, system inertia levels have continued to decrease. Energy storage devices employ additional virtual inertia control to change their output active power to release energy for inertial response, thereby increasing system inertia and improving the system's dynamic frequency characteristics. Energy storage actively participates in the system's inertial response, changing the system's equivalent inertial time constant from known to unknown, and the system's dynamic frequency characteristics will also change. Quantitatively characterizing the inertial response capability of energy storage and calculating the expression for its virtual inertial time constant are key to studying these issues. Currently, a complete expression for the virtual inertial time constant of energy storage has not yet been obtained. Summary of the Invention

[0003] The present invention proposes a method for calculating the equivalent virtual inertia time constant of an energy storage device. By calculating the equivalent virtual inertia time constant of an energy storage device, an important foundation is laid for further research on related issues such as the dynamic frequency characteristics of power systems containing energy storage virtual inertia control.

[0004] The technical solution adopted by the present invention is:

[0005] A method for calculating the equivalent virtual inertia time constant of an energy storage device comprises the following steps:

[0006] Step 1: Introduce the typical differential inertia control method and define the virtual inertia time constant expression of the energy storage device:

[0007] ;

[0008] Where: ω e ,△ ω e are the synchronous angular velocity and angular velocity variation of the power system respectively; u B 、 S B are the rated voltage and rated capacity of the energy storage device respectively; Q N is the rated capacity of the energy storage device when fully charged; γ soc ´ is the rate of change of the state of charge of the energy storage device;

[0009] A typical differential inertia control method utilizes a grid frequency differential signal to generate an active power reference and power response based on the frequency change rate and inertia control gain, thus implementing energy storage inertia control. Under differential inertia control, the energy storage device possesses inertial response capability, enabling the definition of a virtual inertia time constant for the energy storage device.

[0010] Step 2: According to the virtual inertia time constant expression of the energy storage device defined in step 1, if we want to quantitatively solve H BESS , needs to be further solved The ratio relationship between

[0011] Step 3: According to step 2, , substitute into step 1, and then calculate H BESS The complex frequency domain value of

[0012] Step 4: Bring in relevant parameters and calculate through inverse Laplace transform H BESS The time-frequency domain values ​​of .

[0013] The relevant parameters specifically refer to the parameters in the following formula (8), including the controller gain K df , rated voltage of the energy storage device u B , rated capacity S B , the direct axis component of the voltage on the grid-connected side of the energy storage u d , the synchronous angular velocity of the power system ω e and the filter time constant T 1. T 2.

[0014] In step 2, the ratio of the charge state change rate of the energy storage device to the change in the synchronous angular velocity of the power system is The expression is:

[0015] (6);

[0016] In formula (6): K df is the differential inertia controller gain; T 1. T 2 is the filter time constant; u d is the direct-axis component of the voltage on the grid-connected side of the energy storage; s is the complex frequency domain operator.

[0017] In formula (6), 5400 is calculated based on the energy storage inverter control model. For details, please refer to the attached figure in the specification. Figure 4 , 1 / 5400=(1 / 3600)*(2 / 3), where 3600 is the conversion unit between hours and seconds in the model, and 2 / 3 is the coefficient of the expression for the relationship between the active power reference value of the energy storage inverter and the d-axis reference current.

[0018] In the step 3, the H BESS The complex frequency domain value expression of is:

[0019] (7);

[0020] In formula (7), 5400 is calculated based on the energy storage inverter control model. For details, please refer to the attached figure in the specification. Figure 4 , 1 / 5400=(1 / 3600)*(2 / 3), where 3600 is the conversion unit between hours and seconds in the model, and 2 / 3 is the coefficient of the expression for the relationship between the active power reference value of the energy storage inverter and the d-axis reference current.

[0021] In the step 4, the H BESS The time-frequency domain value expression of is:

[0022]

[0023] in: ; ; .

[0024] In formula (8): is a constant, K 1. K 2 is the coefficient of the Laplace transform partial fraction expansion, ω e is the synchronous angular velocity of the power system.

[0025] In the parameter expression of K, 10800 is obtained by 5400*2 in formula (7), which is formula (6) Substitute the energy stored in step 1 into H BESS Definition Calculated.

[0026] The present invention provides a method for calculating the equivalent virtual inertia time constant of an energy storage device, and the technical effects are as follows:

[0027] 1) Under the premise of adding differential inertia control to the energy storage device, the present invention calculates the energy storage equivalent virtual inertia time constant. Unlike the synchronous unit with a constant inertia time constant, the energy storage virtual inertia time constant in the present invention has obvious dynamic time-varying characteristics, and the calculation result is more accurate.

[0028] 2) The equivalent virtual inertia time constant of the energy storage device in this invention exhibits significant dynamic time-varying characteristics, significantly different from the constant inertia time constant characteristic of synchronous generators. This invention lays an important foundation for further research on the dynamic frequency characteristics of power systems with virtual inertia control using energy storage. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Flowchart of an embodiment of the present invention.

[0030] Figure 2 This is the virtual inertia control model diagram of the energy storage device.

[0031] Figure 3 This is the inverter control model diagram of the energy storage device.

[0032] Figure 4 This is the transfer function model diagram of the energy storage device with virtual inertia control.

[0033] Figure 5 Schematic diagram of the independent microgrid structure.

[0034] Figure 6 This is a comparison chart of the calculated and simulated values ​​of the virtual inertia time constant of the energy storage device. DETAILED DESCRIPTION

[0035] A method for calculating the equivalent virtual inertia time constant of an energy storage device defines the virtual inertia time constant of energy storage under the control of energy storage with additional differential inertia, and quantitatively characterizes its value through analysis. Combined with the energy storage inverter control model, the ratio relationship between the rate of change of energy storage charge state and the change of system synchronous angular velocity during the inertial response process is explored, and the ratio is substituted into the definition formula of the virtual inertia time constant of energy storage to obtain the complex frequency domain expression of the inertia time constant, and then the time domain value is obtained through Laplace inverse transformation. Finally, the accuracy of the calculation of the virtual inertia time constant of energy storage is verified through a calculation example system. The specific flow chart of the implementation of the present invention is as follows: Figure 1 As shown, the following steps are included:

[0036] Step 1: Express the energy released by the energy storage device during the frequency response process in a form similar to the rotational kinetic energy of the synchronous generator, and obtain:

[0037] (1);

[0038] In formula (1): u B 、i B ( t ) , γ soc 、 Q N They are the rated voltage, discharge current, state of charge and rated capacity of the energy storage device in the fully charged state; S B is the rated capacity of the energy storage device; p n 、 J vir_B are the pole pairs and virtual moment of inertia of the equivalent synchronous generator respectively; ω e is the synchronous angular velocity of the power system.

[0039] From the above formula we can get:

[0040] (2);

[0041] The definition of the virtual inertia time constant of energy storage is further obtained:

[0042] (3);

[0043] In formula (3): ω e is the change in angular velocity of the power system; γ soc ´ is the rate of change of the state of charge of the energy storage device.

[0044] Step 2: Find the quantitative solution H BESS , further discussion is needed The ratio relationship between Figure 2 The virtual inertia control model of the energy storage device can be obtained:

[0045] (4);

[0046] according to Figure 3 Based on the energy storage device inverter control model, the relationship between the active power reference value of the energy storage inverter and the d-axis reference current is as follows:

[0047] (5);

[0048] Further analysis reveals the relationship between the rate of change of energy storage charge state and the change of synchronous angular velocity: Figure 4 As shown by Figure 4 We can get:

[0049] (6);

[0050] In the above formula: K df is the differential inertia controller gain; T 1. T 2 is the filter time constant; u d is the direct-axis component of the voltage on the grid-connected side of the energy storage; s is the complex frequency domain operator.

[0051] Step 3: From step 2 Substitute the calculated result into step 1 H BESS The definition of , we can get H BESS The complex frequency domain expression of is:

[0052] (7);

[0053] In formula (7), we can set K = u B ω e / (10800 u d S B ), through analysis, we can know that the discriminant of the denominator polynomial is △≥0, that is, the denominator polynomial has two simple roots.

[0054] Step 4: H BESS Perform inverse Laplace transform on the complex frequency domain expression of H BESS Time domain expression:

[0055]

[0056] In formula (8): ; .

[0057] In Matlab / simulink environment, build Figure 5 The independent microgrid system model shown in the figure verifies H BESS ( t ) The calculation results are correct. The power configuration capacity and parameters in the microgrid system are shown in Table 1.

[0058] Table 1 Microgrid configuration

[0059]

[0060] t=15s, set the sudden load L2 to simulate the frequency disturbance under the power shortage of the system. Compare the frequency response dynamic process of the energy storage device H BESS ( t ) calculated value and simulation value, such as Figure 6 As shown. Among them, H BESS ( t ) simulation value is extracted by the virtual inertial response process of energy storage γ soc ´ / △ ω e , and put it into formula (3) to calculate, H BESS ( t ) calculated value, obtained by formula (8) and substituting relevant parameters.

[0061] from Figure 6 It can be seen that according to the definition, derivation and calculation of the present invention, H BESS ( t ) values ​​are generally consistent with the simulation values, indicating that H BESS ( t )The calculated value is more accurate. In addition, Figure 6 in H BESS ( t ) curve has obvious dynamic time-varying characteristics, which is significantly different from the characteristics of synchronous units with constant inertia time constant, laying an important foundation for further research on the dynamic frequency characteristics of power systems with virtual inertia control containing energy storage.

Claims

1. A method for calculating the equivalent virtual inertia time constant of an energy storage device, characterized in that The following steps are involved: Step 1: Define the virtual inertia time constant expression of the energy storage device: ； Where: ω e ,△ ω e are the synchronous angular velocity and angular velocity variation of the power system respectively; u B 、 S B are the rated voltage and rated capacity of the energy storage device respectively; Q N is the rated capacity of the energy storage device when fully charged; γ soc ´ is the rate of change of the state of charge of the energy storage device; Step 2: Solve The ratio relationship between Step 3: According to step 2, , substitute into step 1, and then calculate H BESS The complex frequency domain value of Step 4: Calculate by inverse Laplace transform H BESS The time-frequency domain values ​​of .

2. The method for calculating the equivalent virtual inertia time constant of an energy storage device according to claim 1, wherein: In step 2, the ratio of the charge state change rate of the energy storage device to the change in the synchronous angular velocity of the power system is The expression is: （6）； In formula (6): K df is the differential inertia controller gain; T 1. T 2 is the filter time constant; u d is the direct-axis component of the voltage on the grid-connected side of the energy storage; s is the complex frequency domain operator.

3. The method for calculating the equivalent virtual inertia time constant of an energy storage device according to claim 2, wherein: In the step 3, the H BESS The complex frequency domain value expression of is: （7）。 4. The method for calculating the equivalent virtual inertia time constant of an energy storage device according to claim 3, wherein: In the step 4, the H BESS The time-frequency domain value expression of is: in: ; ; ; In formula (8): is a constant, K 1. K 2 is the coefficient of the Laplace transform partial fraction expansion, ω e is the synchronous angular velocity of the power system.

Images