An inertia time constant estimation method suitable for hybrid direct current microgrid

Abstract

The application belongs to the technical field of time constant estimation, and particularly relates to an inertia time constant estimation method suitable for a hybrid DC microgrid, and steps include: for low-pass filter droop control and virtual synchronous machine control, an equivalent mapping relationship between control parameters is established; for a hybrid DC microgrid containing m low-pass filter droop control converters and n virtual synchronous machine control converters, an equivalent inertia model of the hybrid DC microgrid is established, and an equivalent mapping relationship between control parameters of the hybrid DC microgrid and the equivalent inertia model is established; a time-domain response analytical expression of a DC voltage of the equivalent inertia model is established; according to the time-domain response analytical expression of the DC voltage of the equivalent inertia model, an inertia time constant estimation formula is obtained, so as to estimate the inertia time constant, and further obtain a virtual inertia response time of the hybrid DC microgrid. The application can more accurately reflect the virtual inertia characteristics of the hybrid DC microgrid.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of time constant estimation, and particularly relates to an inertia time constant estimation method suitable for a hybrid DC microgrid. BACKGROUND

[0002] With the rapid development of new energy such as photovoltaic, wind turbine and energy storage and the increase of DC load proportion, the DC microgrid is gradually becoming a research hotspot in the academic and industrial circles. However, photovoltaic, energy storage and DC load need to be connected to the DC microgrid through a converter, and the isolation of the converter causes the DC microgrid to have low inertia and weak damping characteristics. In the future, the inertia time constant will be an important index for evaluating the virtual inertia of the DC microgrid, and how to accurately obtain the inertia time constant of the DC microgrid will become increasingly important.

[0003] For a DC microgrid with low-pass filter droop control, the document Impact of virtual inertia on DC grid stability with constant power loads studies the influence of virtual inertia control parameters on system stability. For a DC microgrid with virtual synchronous machine control, the document DC microgrid wind and storage inertia coordination control strategy qualitatively studies the influence of control parameters on the virtual inertia of the DC voltage through the unit step response curve of the transfer function. The documents Adaptive virtual inertia control of DC microgrid based on droop curve intercept adjustment and Inertia emulation in droop-based DC microgrids with equivalent converter impedance reshaping respectively study the influence of control parameter changes on the virtual inertia of the DC microgrid through the measured value of the virtual inertia time constant of the time domain simulation or experimental results, but do not give a theoretical estimation method of the inertia time constant of the DC microgrid.

[0004] From the above analysis, for a hybrid DC microgrid containing low-pass filter droop control and virtual synchronous machine control, the existing research is difficult to directly and quantitatively evaluate the virtual inertia of the hybrid DC microgrid. Therefore, it is necessary to establish a DC voltage time domain response analytical expression and an inertia time constant estimation formula that can directly and quantitatively evaluate the virtual inertia of the hybrid DC microgrid. SUMMARY

[0005] In view of the deficiencies in the above prior art, the purpose of the present application is to provide an inertia time constant estimation method suitable for a hybrid DC microgrid, which can more accurately reflect the virtual inertia characteristics of the hybrid DC microgrid.

[0006] To achieve the above object, the application provides an inertia time constant estimation method suitable for a hybrid DC micro-grid, comprising the following steps:

[0007] S1, for low-pass filter droop control and virtual synchronous machine control, an equivalent mapping relationship of control parameters between the two is established;

[0008] S2, for a hybrid DC micro-grid containing m low-pass filter droop control converters and n virtual synchronous machine control converters, an equivalent inertia model of the hybrid DC micro-grid is established, and an equivalent mapping relationship of control parameters between the hybrid DC micro-grid and the equivalent inertia model is established;

[0009] S3, a DC voltage time domain response analytical expression of the equivalent inertia model is established;

[0010] S4, according to the DC voltage time domain response analytical expression of the equivalent inertia model, an inertia time constant estimation formula is obtained to estimate the inertia time constant, and further obtain the virtual inertia response time of the hybrid DC micro-grid.

[0011] As a preferred scheme of the application, in S1, the process of establishing the equivalent mapping relationship of control parameters is that, for the yth converter adopting low-pass filter droop control, the virtual inertia time domain response equation thereof is:

[0012] (1);

[0013] In the formula, is the DC voltage of the hybrid DC micro-grid at t; is the droop coefficient of the yth converter; is the low-pass filter cutoff frequency of the yth converter; is the output current of the yth converter at t; is the voltage reference value of the yth converter at t; e is a natural constant;

[0014] For the yth converter adopting virtual synchronous machine control, the virtual inertia time domain response equation thereof is:

[0015] (2);

[0016] In the formula, is the virtual inertia coefficient of the yth converter; is the virtual damping coefficient of the yth converter;

[0017] The equivalent mapping relationship between the droop coefficient and the virtual damping coefficient is represented as:

[0018] (3);

[0019] The equivalent mapping relationship between the low-pass filter cutoff frequency and the virtual inertia coefficient is expressed as:

[0020] (4).

[0021] As a preferred scheme of the present application, the process of establishing the equivalent inertia model of the hybrid DC microgrid in S2 is:

[0022] S2.1, convert the n virtual synchronous machine controlled converters into n low-pass filter droop controlled converters through the equivalent mapping relationship established in S1, then for the hybrid DC microgrid containing m low-pass filter droop controlled converters and n virtual synchronous machine controlled converters, convert it into a DC microgrid containing m low-pass filter droop controlled converters;

[0023] S2.2, sum the output currents of all converters, and the sum should be equal to the load current, thereby establishing the equivalent inertia model of the hybrid DC microgrid, and the time domain response equation is expressed as:

[0024] (5);

[0025] In the formula, is the load current of the hybrid DC microgrid at time t;

[0026] S2.3, rewrite the time domain response equation of the equivalent inertia model as:

[0027] (6);

[0028] In the formula, is the equivalent droop coefficient; is the equivalent cutoff frequency; is the equivalent voltage reference value of the hybrid DC microgrid at time t.

[0029] As a preferred scheme of the present application, the process of establishing the equivalent inertia model of the hybrid DC microgrid and the control parameter equivalent mapping relationship between the equivalent inertia model is:

[0030] (7);

[0031] For the cutoff frequency equivalent mapping relationship between the hybrid DC microgrid and the equivalent inertia model, it is expressed as:

[0032] (8).

[0033] As a preferred scheme of the present application, in the S3, the process of establishing the direct current voltage time domain response analytic expression of the equivalent inertia model is:

[0034] S3.1, defining variables is as follows:

[0035] (9);

[0036] Combining , formula (6) is further rewritten as:

[0037] (10);

[0038] Defining a historical moment , assuming that the hybrid direct current micro-grid has been in a steady state operation state before moment, when the load power occurs a step disturbance, the direct current voltage time domain response analytic expression of the equivalent inertia model is established as:

[0039] (11);

[0040] In the formula, is the initial value of the direct current voltage at moment; is the steady state value of the direct current voltage when the time variable tends to ∞; is the steady state component of the direct current voltage at t moment; is the transient component of the direct current voltage at t moment.

[0041] As a preferred scheme of the present application, in the S4, the method for obtaining the inertia time constant estimation formula is that, since formula (11) and the full response equation of the first order RC circuit have consistency in mathematical form, the estimation formula of the inertia time constant of the equivalent inertia model is as follows:

[0042] (12).

[0043] As a preferred scheme of the present application, in the S4, the virtual inertia response time of the hybrid direct current micro-grid is set.

[0044] As a preferred scheme of the present application, based on the PLECS software, the simulation model of the hybrid direct current micro-grid is built, and the estimation result of the inertia time constant is verified by using the relative error , which is expressed as:

[0045] (13);

[0046] In the formula, is the DC voltage simulation value at time t; is the DC voltage theoretical value at time t;

[0047] When is less than the set threshold value, the verification is valid.

[0048] The algorithm related to the present application can be executed by an electronic device, which includes a memory, a processor, and a computer program stored on the memory and executable on the processor, and the above-mentioned algorithm calculation is realized by executing the software on the processor.

[0049] The present application has the beneficial effects of:

[0050] The present application converts the hybrid DC microgrid into an equivalent inertia model by establishing the equivalent mapping relationship of control parameters between the low-pass filter droop control and the virtual synchronous machine control, and then deduces the time-domain response analytical expression of the DC voltage and the inertia time constant estimation formula, thereby filling the gap of the theoretical estimation method of the inertia time constant of the hybrid DC microgrid in the existing research.

[0051] The experimental results show that the equivalent inertia model is basically consistent with the simulation results of the actual hybrid DC microgrid, the theoretical estimated value of the inertia time constant is highly consistent with the measured value, and the relative error of the time-domain response analytical expression of the DC voltage is less than 3%, which fully proves the feasibility and accuracy of the present application in theory and practice, and provides a reliable, efficient and convenient method for the estimation of the inertia time constant of the hybrid DC microgrid. BRIEF DESCRIPTION OF DRAWINGS

[0052] Figure 1 is the flow principle diagram of the present application;

[0053] Figure 2 is the topological graph of the hybrid DC microgrid in the verification process of the present application;

[0054] Figure 3 is the topological graph of the equivalent inertia model in the verification process of the present application;

[0055] Figure 4 is the simulation result of the hybrid DC microgrid at the first inertia parameter scene in the verification process of the present application;

[0056] Figure 5 is the simulation result of the equivalent inertia model at the first inertia parameter scene in the verification process of the present application;

[0057] Figure 6 is the simulation result of the hybrid DC microgrid at the second inertia parameter scene in the verification process of the present application;

[0058] Figure 7This is the simulation result of the equivalent inertia model in the second inertial parameter scenario during the verification process of this invention;

[0059] Figure 8 This is the simulation result of the hybrid DC microgrid in the third inertial parameter scenario during the verification process of this invention;

[0060] Figure 9 This is the simulation result of the equivalent inertia model in the third inertial parameter scenario during the verification process of this invention. Detailed Implementation

[0061] The embodiments of the present invention will be further described below with reference to the accompanying drawings:

[0062] like Figure 1 As shown, a method for estimating the inertial time constant suitable for hybrid DC microgrids includes the following steps:

[0063] S1. For low-pass filter droop control and virtual synchronous machine control (two classic virtual inertial control methods), establish the equivalent mapping relationship of control parameters between the two.

[0064] S2. For a hybrid DC microgrid containing m low-pass filter droop control converters and n virtual synchronous machine control converters, establish an equivalent inertia model of the hybrid DC microgrid and establish an equivalent mapping relationship of control parameters between the hybrid DC microgrid and the equivalent inertia model.

[0065] S3. Establish the analytical expression of the DC voltage time-domain response of the equivalent inertia model;

[0066] S4. Based on the analytical expression of the DC voltage time domain response of the equivalent inertia model, the inertia time constant estimation formula is obtained. This formula is used to estimate the inertia time constant and further obtain the virtual inertia response time of the hybrid DC microgrid.

[0067] Existing research typically employs two classic virtual inertial control methods—low-pass filter droop control and virtual synchronous machine control—to enhance the virtual inertia of DC microgrids. This embodiment takes a hybrid DC microgrid containing these two typical virtual inertial controls as the research object and establishes an equivalent mapping relationship between the two virtual inertial controls.

[0068] In S1, the process of establishing the equivalent mapping relationship of control parameters is as follows: For the y-th converter using low-pass filter droop control, its virtual inertial time-domain response equation is:

[0069] (1);

[0070] In the formula, Let be the DC voltage of the hybrid DC microgrid at time t; Let be the droop coefficient of the y-th converter; Let be the low-pass filter cutoff frequency of the y-th converter; Let y be the output current of the y-th converter at time t; Let be the voltage reference value of the y-th converter at time t; e is the natural constant;

[0071] For the y-th converter controlled by a virtual synchronous machine, its virtual inertial time-domain response equation is:

[0072] (2);

[0073] In the formula, Let be the virtual inertia coefficient of the y-th converter; Let be the virtual damping coefficient of the y-th converter;

[0074] Low-pass filter droop control and virtual synchronizer control are equivalent. The equivalent mapping relationship between the droop coefficient and the virtual damping coefficient is expressed as:

[0075] (3);

[0076] The equivalent mapping relationship between the low-pass filter cutoff frequency and the virtual inertia coefficient is expressed as:

[0077] (4).

[0078] In S2, the process of establishing the equivalent inertia model of the hybrid DC microgrid is as follows:

[0079] S2.1. Convert the n virtual synchronous machine controlled converters into n low-pass filter droop controlled converters through the equivalent mapping relationship established in S1. Then, for a hybrid DC microgrid containing m low-pass filter droop controlled converters and n virtual synchronous machine controlled converters, convert it into a system containing m low-pass filter droop controlled converters and n virtual synchronous machine controlled converters. A DC microgrid with a low-pass filter droop control converter;

[0080] S2.2 Summing the output currents of all converters, the sum should equal the load current. Since the response time scale of the voltage-current dual-loop control and filter circuits is much smaller than that of the low-pass filter droop control, the virtual inertia characteristics of the hybrid DC microgrid are primarily determined by the low-pass filter droop control. Therefore, the influence of factors such as the voltage-current dual-loop control and filter circuits on the virtual inertia of the DC microgrid can be ignored. Based on this, an equivalent inertia model of the hybrid DC microgrid is established, and its time-domain response equation is expressed as:

[0081] (5);

[0082] In the formula, The hybrid DC microgrid is the load current of the hybrid DC microgrid at time t;

[0083] S2.3. The time-domain response equation of the equivalent inertia model is rewritten as follows:

[0084] (6);

[0085] In the formula, This is the equivalent droop coefficient; This is the equivalent cutoff frequency; This is the reference value of the equivalent voltage of the hybrid DC microgrid at time t.

[0086] The process of establishing the equivalent mapping relationship of control parameters between the hybrid DC microgrid and the equivalent inertia model is as follows: The equivalent mapping relationship of the droop coefficient between the hybrid DC microgrid and the equivalent inertia model can be expressed as:

[0087] (7);

[0088] The cutoff frequency equivalent mapping relationship between the hybrid DC microgrid and the equivalent inertia model can be expressed as:

[0089] (8).

[0090] In S3, the process of establishing the analytical expression for the DC voltage time-domain response of the equivalent inertia model is as follows:

[0091] S3.1 Defining Variables It is in the following form:

[0092] (9);

[0093] Combination Equation (6) can be further rewritten as:

[0094] (10);

[0095] Define a historical moment Assuming a hybrid DC microgrid in It was already in a steady-state operation before that time. When the load power experiences a step disturbance, the analytical expression for the DC voltage time-domain response of the equivalent inertia model is established:

[0096] (11);

[0097] In the formula, for The initial value of the DC voltage at time t; This represents the steady-state value of the DC voltage as the time variable approaches infinity. Let be the steady-state component of the DC voltage at time t; Let be the transient component of the DC voltage at time t. This analytical expression shows that the dynamic response of the DC voltage exhibits a typical first-order exponential decay characteristic.

[0098] In S4, the method for obtaining the inertial time constant estimation formula is as follows: Since equation (11) is consistent with the total response equation of a first-order RC circuit in mathematical form, the inertial time constant of the equivalent inertia model is established. The estimation formula is as follows:

[0099] (12).

[0100] According to equation (12), the inertial time constant is... It is a function of all droop coefficients, cutoff frequencies, and virtual inertia coefficients within the hybrid DC microgrid. Assuming the hybrid DC microgrid is in... It has reached steady state before the specified time, and in Power disturbances occur constantly. At this time, the transient component of the DC voltage... The initial value is After experiencing an inertial time constant Afterwards, the transient component of the DC voltage decayed to 36.8% of its initial value (i.e., a decay of 63.2%). When time... and At that time, the transient component of the DC voltage further decayed to 13.5% and 5% of its initial value. According to the principle of automatic control, the transient component of the DC voltage... Theoretically, it would take an infinitely long time to fully decay; however, in engineering practice, it is generally considered that the decay occurs when the time reaches a certain threshold. At that time, the transition process has basically ended. For conservative reasons, this embodiment adopts... Virtual inertial response time as a hybrid DC microgrid ,Right now .

[0101] A simulation model of a hybrid DC microgrid was built using PLECS software, and the relative error was utilized. The estimation results of the inertial time constant are verified and expressed as follows:

[0102] (13);

[0103] In the formula, The simulated DC voltage value at time t; Let be the theoretical value of the DC voltage at time t;

[0104] when The verification is valid when the percentage is less than the set threshold (3%).

[0105] The verification process is as follows:

[0106] A system was built using PLECS software, such as Figure 2 The hybrid DC microgrid switching model shown uses low-pass filter droop control for the first and second converters, and virtual synchronous machine control for the third and fourth converters.

[0107] exist Figure 2 middle, Let be the output current of the first converter at time t. The droop factor for the first converter. This is the low-pass filter cutoff frequency of the first converter. Here is the reference voltage value for the first converter at time t. Let be the output current of the second converter at time t. The droop factor for the second converter. This is the low-pass filter cutoff frequency of the second converter. Here is the reference voltage value for the second converter at time t. Let be the output current of the third converter at time t. The virtual inertia coefficient of the third converter. This represents the virtual damping coefficient of the third converter. Here is the reference voltage value for the third converter at time t. Let be the output current of the fourth converter at time t. The virtual inertia coefficient of the fourth converter. This is the virtual damping coefficient for the fourth converter. This is the voltage reference value for the fourth converter at time t. Let be the load power of the hybrid DC microgrid at time t.

[0108] The equivalent inertia model of a hybrid DC microgrid is as follows: Figure 3 As shown. In Figure 3 middle, This is the equivalent output current of the equivalent inertia model.

[0109] when , , , The inertial time constant can be calculated using equation (12). Let this be denoted as the first inertial parameter scenario. At t=1s, the load power jumps from 12kW to 14kW. The simulation results of the hybrid DC microgrid and its equivalent inertia model in the first inertial parameter scenario are as follows: Figure 4 and Figure 5 As shown. According to Figure 4 andFigure 5 As can be seen, the simulation results of the hybrid DC microgrid and its equivalent inertia model are in good agreement, verifying the accuracy of the equivalent inertia model. Figure 4 It can be seen that the measured value of the virtual inertial response time in the simulation results of the first inertial parameter scenario is 7.5s, which is the inertial time constant. The measured value was 1.5s, which is basically consistent with the theoretical estimate of 1.5s, verifying the correctness of the method proposed in this embodiment. Calculated from equation (11), the theoretical values ​​of the DC voltage at t=2.5s, 4.0s, and 5.5s are 391.285V, 390.980V, and 390.869V, respectively; Figure 4 The measured DC voltage values ​​at t=2.5s, 4.0s, and 5.5s are 391.302V, 390.994V, and 390.877V, respectively. By dividing the difference between the measured and theoretical DC voltage values ​​by the transient component of the DC voltage, the relative errors at t=2.5s, 4.0s, and 5.5s are calculated to be 1.270%, 1.076%, and 0.651%, respectively, verifying the effectiveness of the analytical expression for the DC voltage time-domain response.

[0110] when , , , The inertial time constant can be calculated using equation (12). This is denoted as the second inertial parameter scenario. At t=1s, the load power jumps from 12kW to 14kW. The simulation results of the hybrid DC microgrid and its equivalent inertia model in the second inertial parameter scenario are as follows: Figure 6 and Figure 7 As shown. According to Figure 6 and Figure 7 As can be seen, the simulation results of the hybrid DC microgrid and its equivalent inertia model are basically in agreement, further verifying the accuracy of the equivalent inertia model. Figure 6 It can be seen that the measured value of the virtual inertial response time in the simulation results of the second inertial parameter scenario is 12.5s, which is the inertial time constant. The measured value was 2.5s, which is basically consistent with the theoretical estimate of 2.5s, further verifying the correctness of the method proposed in this embodiment. Calculated from equation (11), the theoretical values ​​of the DC voltage at t=3.5s, 6.0s, and 8.5s are 391.285V, 390.980V, and 390.869V, respectively; Figure 6It can be seen that the measured values of the DC voltage at t=3.5s, 6.0s and 8.5s are 391.300V, 390.993V and 390.876V respectively. The relative errors of the DC voltage at t=3.5s, 6.0s and 8.5s are 1.117%, 0.999% and 0.574% respectively by dividing the difference between the measured value and the theoretical value of the DC voltage by the transient component of the DC voltage, which verifies the effectiveness of the time-domain response analytical expression of the DC voltage again.

[0111] When , , , , the inertia time constant can be calculated by formula (12), which is referred to as the third inertia parameter scenario. At t=1s, the load power is stepped from 12kW to 14kW, and the simulation results of the hybrid DC microgrid and its equivalent inertia model in the third inertia parameter scenario are shown in Figure 8 and Figure 9 . According to Figure 8 and Figure 9 , the simulation results of the hybrid DC microgrid and its equivalent inertia model are also basically consistent, which verifies the accuracy of the equivalent inertia model again. According to Figure 8 , the measured value of the virtual inertia response time of the simulation result of the third inertia parameter scenario is 15.0s, that is, the measured value of the inertia time constant is 3.0s, which is basically consistent with the theoretical estimated value 3.0s, which verifies the correctness of the method proposed in this embodiment again. According to formula (11), the theoretical values of the DC voltage at t=4.0s, 7.0s and 10.0s are 391.285V, 390.980V and 390.869V respectively; according to Figure 8 , the measured values of the DC voltage at t=4.0s, 7.0s and 10.0s are 391.299V, 390.992V and 390.719V respectively. The relative errors of the DC voltage at t=4.0s, 7.0s and 10.0s are 1.041%, 0.923% and 0.574% respectively by dividing the difference between the measured value and the theoretical value of the DC voltage by the transient component of the DC voltage, which verifies the effectiveness of the time-domain response analytical expression of the DC voltage again.

[0112] The results of multiple groups of comparisons show that the relative errors between the measured values and the theoretical values of the DC voltage are all less than 3%, which verifies the effectiveness of the method proposed in this embodiment.

Claims

1. A method for estimating the inertia time constant suitable for hybrid DC microgrid characterized by The method comprises the following steps: S1, for low-pass filter droop control and virtual synchronous machine control, establishing the equivalent mapping relationship between the control parameters; S2, for a hybrid DC microgrid comprising m low-pass filter droop control converters and n virtual synchronous machine control converters, establishing an equivalent inertia model of the hybrid DC microgrid, and establishing the equivalent mapping relationship between the control parameters of the hybrid DC microgrid and the equivalent inertia model; The process of establishing the equivalent inertia model of the hybrid DC microgrid is as follows: S2.1, convert the n virtual synchronous machine controlled converters to n low-pass filter droop controlled converters through the equivalent mapping relationship established in S1, then for the hybrid DC microgrid containing m low-pass filter droop controlled converters and n virtual synchronous machine controlled converters, convert it to a DC microgrid containing m low-pass filter droop controlled converters; S2.2, summing the output currents of all converters, and the sum should be equal to the load current, so as to establish the equivalent inertia model of the hybrid DC microgrid, and the time domain response equation is expressed as: （5）； In the formula, is the load current of the hybrid DC microgrid at time t; is the DC voltage of the hybrid DC microgrid at time t; is the droop coefficient of the yth converter; is the voltage reference value of the yth converter at time t; is the low-pass filter cutoff frequency of the yth converter; S2.3, rewriting the time domain response equation of the equivalent inertia model as: （6）； In the formula, is the equivalent droop coefficient; is the equivalent cut-off frequency; is the equivalent voltage reference value of the hybrid DC microgrid at time t; S3, establishing a DC voltage time domain response analytical expression of the equivalent inertia model; S4, according to the DC voltage time domain response analytical expression of the equivalent inertia model, obtaining an inertia time constant estimation formula to estimate the inertia time constant and further obtain the virtual inertia response time of the hybrid DC microgrid.

2. The method for estimating the inertia time constant suitable for hybrid DC microgrid according to claim 1, characterized in that, In S1, the process of establishing the equivalent mapping relationship of the control parameters is as follows: for the yth converter adopting low-pass filter droop control, the virtual inertia time domain response equation is: （1）； In the formula, Iy(t) is the output current of the yth converter at time t; e is the natural constant; For the yth converter adopting virtual synchronous machine control, the virtual inertia time domain response equation is: （2）； wherein is the virtual inertia coefficient of the yth converter; is the virtual damping coefficient of the yth converter; The equivalent mapping relationship between the droop coefficient and the virtual damping coefficient is expressed as: （3）； The equivalent mapping relationship between the low-pass filter cutoff frequency and the virtual inertia coefficient is expressed as: （4）。 3. The method for estimating the inertia time constant suitable for hybrid DC microgrid according to claim 2, characterized in that, The process of establishing the equivalent mapping relationship between the control parameters of the hybrid DC microgrid and the equivalent inertia model is as follows: for the droop coefficient equivalent mapping relationship between the hybrid DC microgrid and the equivalent inertia model, it is expressed as: （7）； For the cutoff frequency equivalent mapping relationship between the hybrid DC microgrid and the equivalent inertia model, it is expressed as: （8）。 4. The method for estimating the inertia time constant suitable for hybrid DC microgrid according to claim 3, characterized in that, In S3, the process of establishing the DC voltage time domain response analytical expression of the equivalent inertia model is as follows: S3.1, define variables of the form: （9）； in combination with Equation (6) is further rewritten as: （10）； Defining a historical time instant Assuming that the hybrid DC microgrid is in a steady-state operation before the time instant When the load power has a step disturbance at the time instant The analytical expression of the DC voltage time-domain response of the equivalent inertia model is established. （11）； wherein is the initial value of the DC voltage at time t = 0; is the initial value of the DC voltage at time t = 0; is the steady state value of the DC voltage for time t = ∞; is the steady state component of the DC voltage at time t; is the transient component of the DC voltage at time t.

5. The method for estimating the inertia time constant suitable for hybrid DC microgrid of claim 4, wherein, In S4, the method for obtaining the inertial time constant estimation formula is as follows: since equation (11) is consistent with the total response equation of a first-order RC circuit in mathematical form, the inertial time constant of the equivalent inertia model is established. The estimation formula is as follows: （12）。 6. The method for estimating the inertia time constant suitable for hybrid DC microgrid according to claim 5, characterized in that, In the S4, a virtual inertia response time of the hybrid DC microgrid is set .

7. The method for estimating the inertia time constant suitable for hybrid DC microgrid of claim 4, wherein, The simulation model of hybrid DC microgrid is built based on PLECS software, and the relative error The estimation result of the inertia time constant is verified, which is expressed as: （13）； In the formula, is the DC voltage simulation value at time t; is the DC voltage theoretical value at time t; When The verification is valid when the value is less than the set threshold.

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