A method for improving stability of a direct-current interconnected microgrid

Abstract

The application belongs to the field of electric power information technology, and discloses a method for improving stability of a direct-current interconnected microgrid, which is suitable for an interconnected microgrid system composed of an alternating-current subnetwork, a rectifier, a direct-current line, an inverter and a filter circuit. On the basis of constructing a small signal model of the interconnected microgrid system, the application solves characteristic roots thereof, determines an effective range of filter parameters on the rectifier side and the inverter side through trajectories of the characteristic roots, and determines an optimal interval of the filter parameters on the rectifier side and the inverter side according to real-time operation conditions of the system. The application can consider stability improvement in combination with design requirements of the filter parameters, and improves the stability of operation of the interconnected microgrid system in a manner of filter parameter optimization design without increasing auxiliary control measures.

Description

Technical Field

[0001] This invention belongs to the field of power information technology, and in particular relates to a method for improving the stability of DC interconnected microgrids. Background Technology

[0002] As conventional energy reserves continue to dwindle, scholars are conducting in-depth research on microgrids, which consist of distributed power sources, loads, and power electronic devices. However, single microgrids suffer from limited capacity, weak regulation capabilities, and insufficient utilization efficiency. To address these issues, scholars have proposed the concept of interconnected multi-microgrids, which aims to interconnect multiple small-capacity microgrids through specific methods and rules.

[0003] Currently, AC and DC interconnection are commonly used methods for interconnecting microgrids. However, AC interconnection suffers from problems such as lack of electrical isolation and low accuracy of tie-line power control. DC interconnection can better solve these problems. DC interconnection uses interconnected converters, DC lines, and filter circuits for connection. With the in-depth development and research of DC interconnected microgrids, their stability will inevitably become the primary condition for the safe and reliable operation of interconnected microgrid systems.

[0004] Existing methods for improving stability mainly involve constructing a small-signal model of the system and optimizing the values ​​of parameters such as the PI controller, line inductance, and droop coefficient based on the eigenvalue locus. However, stability analysis neglects the impact of filtering parameters on stability, and fails to consider the different effects of the rectifier and inverter sides on stability. Furthermore, existing filtering parameter designs focus more on power quality and economic requirements, without considering the stability of the system. Therefore, it is necessary to study the correctness of filtering parameter settings from a stability perspective. Summary of the Invention

[0005] The purpose of this invention is to provide a method for improving the stability of DC interconnected microgrids, in order to solve the technical problem of not setting filter parameters from the perspective of system stability.

[0006] To address the aforementioned technical problems, the present invention provides a specific technical solution for improving the stability of DC interconnected microgrids as follows:

[0007] A method for improving the stability of a DC-connected microgrid includes a DC-connected microgrid consisting of two AC subgrids, a rectifier-side filter circuit and a rectifier-side converter, an inverter-side filter circuit and an inverter-side converter, and DC lines. The AC subgrids contain multiple micro-sources, which are simulated using an ideal DC power supply and controller. The rectifier-side converter employs constant DC voltage control, and the inverter-side converter employs a constant power control strategy. The method constructs a complete small-signal model of the DC-connected microgrid, solves for eigenvalues, analyzes the effective range of filter parameters through eigenvalue trajectory analysis, and rationally sets the optimal range of filter parameters according to the real-time operating conditions of the system. The method specifically includes the following steps:

[0008] Step 1: Construct a small-signal model of the rectifier side containing an AC subnet, filter circuit, and controller;

[0009] Step 2: Construct a small-signal model of the inverter side containing an AC subnet, filter circuit, and controller;

[0010] Step 3: Construct a small-signal model of the DC line;

[0011] Step 4: Based on steps 1-3, construct a complete small-signal model of a DC interconnected microgrid;

[0012] Step 5: Solve for the eigenvalues ​​of the small-signal model, analyze the effective range of the filtering parameters through the eigenvalue trajectory, and reasonably set the optimal range of the filtering parameters according to the real-time operating conditions of the system.

[0013] Furthermore, the rectifier-side small-signal model constructed in step 1 is specifically as follows:

[0014]

[0015] In the formula, Δx resys =[Δi Ad Δi Aq Δu f1q Δu f1d Δi 1d Δi 1q Δx1 Δx 2d Δx 2q Δu 1d Δu 1q ] T B vo1 =[0]; B vo2 =[0-1 0]; B vo3 =[1];Δx dc =[Δi dc Δu dc1 Δudc2 ] T ; L A R A u A θ represents the equivalent internal inductance, resistance, voltage, and phase of subnet A; C f1 L f1 For the capacitors and inductors of the filter circuit; i Ad i Aq i 1d i 1q Let be the d-axis and q-axis current components before and after filtering, respectively; u f1d u f1q ;u 1d u 1q These represent the d-axis and q-axis voltage components before and after filtering, respectively; ω is the angular frequency; R1 is the line resistance; x1 is the voltage outer loop state variable; x 2d x 2q These are the d-axis and q-axis state variables of the inner current loop, respectively; u dref This is the reference value for the DC bus voltage; u dc1 This refers to the actual DC voltage output from the rectifier side; u dc2 This refers to the actual DC voltage output from the inverter side; i dc For DC line current; k p1 k i1 k is the proportional-integral coefficient of the voltage outer-loop PI regulator. p2 k i2 ;k p3 k i3 These represent the proportional-integral coefficients of the d-axis and q-axis PI regulators in the inner current loop controller; T is the converter switching cycle; K s This represents the converter's amplification factor.

[0016] Furthermore, the inverter-side small-signal model constructed in step 2 is specifically as follows:

[0017]

[0018] In the formula, Δx insys =[Δi Bd Δi Bq Δu f2q Δu f2d Δi 2d Δi 2q Δx 3d Δx 3q Δu 2d Δu 2q ] T ; B insys =[0]; G po1 =[0]; L B R B u B θ represents the equivalent internal inductance, resistance, voltage, and phase of subnet B; C f2 L f2 For the capacitors and inductors of the filter circuit; i Bd i Bq i 2d i 2q Let be the d-axis and q-axis current components before and after filtering, respectively; u f2d u f2q ;u 2d u 2q These represent the d-axis and q-axis voltage components before and after filtering, respectively; R2 is the inverter-side line resistance; x 3d x 3q These are the d-axis and q-axis state variables of the power outer loop, respectively; P ref Q ref For active and reactive power reference values; k p4 k i4 ;k p5 k i5 These are the proportional-integral coefficients of the d-axis and q-axis PI regulators of the inner current loop controller; U f2d This represents the steady-state voltage component along the d-axis before filtering.

[0019] Furthermore, the small-signal model of the DC line constructed in step 3 is specifically as follows:

[0020]

[0021] in

[0022]

[0023]

[0024] L dc R dc These are the DC line inductance and resistance; C1 and C2 are the rectifier and inverter capacitors, respectively; U 1d U 1q I 1d I 1q These are the steady-state components of the d-axis voltage and current after rectifier-side filtering; U 2d U 2q I2d I 2q These are the steady-state components of the d-axis voltage and current after filtering on the inverter side; U dc1 U dc2 This refers to the steady-state DC voltage output from the rectifier and inverter sides.

[0025] Furthermore, the complete DC interconnected microgrid model constructed in step 4 based on equations (1) to (3) is specifically as follows:

[0026]

[0027] In the formula, Δx sys =[Δx resys Δx insys Δx dc ] T ;

[0028] Furthermore, step 5 includes the following specific steps:

[0029] When the filter parameters undergo a directional change, if the system eigenvalues ​​move from the left half-plane to the right half-plane of the complex plane, and at a certain parameter value, the eigenvalues ​​cross the imaginary axis into the right half-plane, the system is in an unstable state, indicating that the directional change of the parameters at this time is not conducive to the stability of the system. If the system eigenvalues ​​always move from the left half-plane of the complex plane, it indicates that the directional change of the parameters can improve the stability of the system. If the system eigenvalues ​​always remain in the left half-plane of the complex plane and do not move into the right half-plane with the parameter change, the system remains in a stable state, indicating that the change of the parameters does not affect the stability of the system. Based on this, the effective range of the filter parameters is determined, and the optimal range of the filter parameters is set based on the original parameter design and the real-time operating conditions of the system.

[0030] The method for improving the stability of DC interconnected microgrids according to the present invention has the following advantages: the present invention can take into account the stability improvement requirements in combination with the filter parameter design requirements, and improve the stability of the interconnected microgrid system operation through the filter parameter optimization design without adding auxiliary control measures. Attached Figure Description

[0031] Figure 1 This is a block diagram of the DC interconnected microgrid structure of the present invention;

[0032] Figure 2 Small-signal block diagram for constant DC voltage;

[0033] Figure 3 Block diagram for constant power small signal;

[0034] Figure 4For stability flowchart;

[0035] Figure 5 This is the root locus diagram of the dominant characteristic roots when the rectifier-side capacitance changes;

[0036] Figure 6 This is the root locus diagram of the dominant characteristic roots when the rectifier-side inductance changes;

[0037] Figure 7 This is the root locus diagram of the dominant characteristic roots when the inverter-side capacitance changes;

[0038] Figure 8 This is the root locus diagram of the dominant characteristic roots when the inductance on the inverter side changes. Detailed Implementation

[0039] To better understand the purpose, structure, and function of this invention, the following detailed description of a method for improving the stability of a DC interconnected microgrid, in conjunction with the accompanying drawings, is provided.

[0040] like Figure 1 As shown, the DC interconnected microgrid of the present invention consists of two AC subgrids, a rectifier-side filter circuit and converter, an inverter-side filter circuit and converter, and DC lines. The AC subgrids contain multiple micro-sources, which are simulated using an ideal DC power supply and controller; the rectifier-side converter employs constant DC voltage control, and the inverter-side converter employs a constant power control strategy.

[0041] like Figure 4 As shown, a method for improving the stability of a DC interconnected microgrid according to the present invention includes the following steps:

[0042] Step 1: Construct a small-signal model of the rectifier side containing an AC subnet, filter circuit, and controller;

[0043] 1) By Figure 1 The mathematical model of the rectifier-side AC subnet and filter circuit can be obtained as follows:

[0044]

[0045] In the formula, L A R A u A θ represents the equivalent internal inductance, resistance, voltage, and phase of subnet A; C f1 L f1 For the capacitors and inductors of the filter circuit; i Ad i Aq i 1d i 1q Let be the d-axis and q-axis current components before and after filtering, respectively; u f1d u f1q u 1d u1q R1 represents the d-axis and q-axis voltage components before and after filtering, respectively; ω represents the angular frequency; and R1 represents the line resistance.

[0046] 2) To maintain the stability of the DC bus voltage, the rectifier-side converter adopts a constant DC voltage control strategy, based on... Figure 2 The differential equations for the outer loop state variables of the voltage can be obtained as follows:

[0047]

[0048] In the formula, x1 is the voltage outer loop state variable; u dref This is the reference value for the DC bus voltage; u dc1 This is the actual DC voltage output from the rectifier side.

[0049] The voltage outer loop output equation is

[0050]

[0051] In the formula, i 1dref i 1qref This is the reference value for the inner loop current; k p1 k i1 This represents the proportional-integral coefficient of the voltage outer loop PI regulator.

[0052] according to Figure 2 The differential equations for the state variables of the inner current loop can be obtained as follows:

[0053]

[0054] In the formula, x 2d x 2q These are the d-axis and q-axis state variables of the inner current loop, respectively.

[0055] according to Figure 2 The reference voltage equation for the inner current loop output can be obtained as follows:

[0056]

[0057] In the formula, The inner loop output voltage d, q axis reference value; k p2 k i2 ;k p3 k i3 These are the proportional-integral coefficients of the d-axis and q-axis PI regulators of the current inner loop controller, respectively.

[0058] 3) Combining equations (1) to (6), and considering the inertia of the converter, a complete small-signal model of the rectifier side is constructed as follows:

[0059]

[0060] In the formula, Δx resys =[Δi Ad Δi Aq Δu f1q Δu f1d Δi 1d Δi 1q Δx1 Δx 2d Δx 2q Δu 1d Δu 1q ] T B vo2 =[0 -10]; B vo3 =[1]; B vo1 =[0];Δx dc =[Δi dc Δu dc1 Δu dc2 ] T ; u dc2 This refers to the actual DC voltage output from the inverter side; i dc K represents the DC line current; T represents the converter switching cycle; K represents the DC line current. s This represents the converter's amplification factor.

[0061] Step 2: Construct a small-signal model of the inverter side containing an AC subnet, filter circuit, and controller;

[0062] 1) By Figure 1 The mathematical model of the inverter-side AC subnet and filter circuit can be obtained as follows:

[0063]

[0064] In the formula, L B R B u B θ represents the equivalent internal inductance, resistance, voltage, and phase of subnet B; C f2 L f2 For the capacitors and inductors of the filter circuit; i Bd i Bq i 2d i 2q Let be the d-axis and q-axis current components before and after filtering, respectively; u f2d u f2q u 2d u 2q These represent the d-axis and q-axis voltage components before and after filtering, respectively; R2 is the inverter-side line resistance.

[0065] 2) To achieve specified power mutual assistance in interconnected microgrids, the inverter-side converter adopts a constant power control strategy, such as... Figure 3 As shown, the differential equation for the power outer loop state variables is:

[0066]

[0067] In the formula, x 3d x 3q These are the d-axis and q-axis state variables of the power outer loop, respectively; P ref Q ref These are reference values ​​for active and reactive power.

[0068] The output equation of the power outer loop is:

[0069]

[0070] In the formula, i 2dref i 2qref These are the reference values ​​for the outer loop current and the inner loop current of the power circuit.

[0071] The output voltage equation is:

[0072]

[0073] In the formula, The inner loop output voltage d, q axis reference value; k p4 k i4 ;k p5 k i5 These are the proportional-integral coefficients of the d-axis and q-axis PI regulators of the current inner loop controller, respectively.

[0074] Combining equations (8) to (11), and considering the inertia of the converter, a complete small-signal model of the inverter side can be obtained:

[0075]

[0076] In the formula, Δx insys =[Δi Bd Δi Bq Δu f2q Δu f2d Δi 2d Δi 2q Δx 3d Δx 3q Δu 2d Δu 2q ] T ; B insys =[0]; G po1 =[0]; U f2d This represents the steady-state voltage component along the d-axis before filtering.

[0077] Step 3: Construct a small-signal model of a DC line;

[0078] according to Figure 1 The mathematical model of the DC line can be obtained as follows:

[0079]

[0080] In the formula, L dc R dc These are the DC line inductance and resistance, respectively; C1 and C2 are the rectifier and inverter capacitors, respectively.

[0081] Linearizing the above equation yields the small-signal model of a DC line.

[0082]

[0083] in U 1d U 1q ;I 1d I 1q These are the steady-state components of the d-axis voltage and current after rectifier-side filtering; U 2d U 2q ;I 2d I 2q These are the steady-state components of the d-axis voltage and current after filtering on the inverter side; U dc1 U dc2 This refers to the steady-state DC voltage output from the rectifier and inverter sides.

[0084] Step 4: Based on steps 1-3, construct a complete small-signal model of a DC interconnected microgrid;

[0085] A complete small-signal model of a DC interconnected microgrid can be constructed based on equations (7), (12), and (14). This model contains 24 state variables and 3 input variables.

[0086]

[0087] In the formula, Δx sys =[Δx resys Δx insys Δx dc ] T ;

[0088]

[0089] Step 5: Using the small-signal model of the DC interconnected microgrid constructed in Step 4, solve for the eigenvalues ​​of the small-signal model. Analyze the impact of the filter parameters on stability on the rectifier side and the inverter converter through the eigenvalue locus analysis, and determine the effective range of the filter parameters respectively. Then, based on the original filter parameter design, consider factors such as filtering effect and economy, and rationally set the optimal range of filter parameters according to the real-time operating conditions of the system, thereby improving the stability of the DC interconnected microgrid system.

[0090] Example

[0091] like Figure 1 As shown, the DC interconnected microgrid consists of an AC subgrid, DC lines, and converters. The rectifier-side converters employ constant DC voltage control, while the inverter-side converters employ constant power control. Under initial operating conditions, the component parameters R... A and R B 0.1Ω, L A and L B The current is 0.0015H, the line resistance R1 is 2Ω, R2 is 1Ω, the DC line capacitances C1 and C2 are both 0.0047F, and the resistance R... dc The inductance is 1Ω, and the inductance is L. dc =0.08H, k p1 For 20, k i1 For 50, k p2 and k p3 For 10, k i2 and k i3 For 100, k p4 and k p5 For 15, k i4 and k i5 The value is 100. Based on the small-signal model and initial operating parameters, analyze the impact of the filtering parameters on system stability:

[0092] (1) Analysis of the impact of rectifier-side capacitor on system stability

[0093] The rectifier-side capacitor is increased from 0.00002F to 0.004F, while other parameters remain at their initial steady-state values. Figure 5 It can be seen that increasing the capacitance on the rectifier side causes the characteristic roots to move towards the right half of the complex plane, gradually approaching the imaginary axis, thus weakening the system stability. When the rectifier capacitance increases to 0.004F, the characteristic roots enter the right half-plane, and the system is in an unstable state. It can be determined that when the rectifier capacitance is less than 0.004F, the system can remain stable, and within this range, reducing the capacitance value can improve the stability of the interconnected microgrid.

[0094] (2) Analysis of the impact of rectifier-side inductance on system stability

[0095] The inductance on the rectifier side is increased from 0.00004H to 0.0034H, while other parameters remain at their initial steady-state values. Figure 6 It can be seen that increasing the inductance on the rectifier side causes the eigenvalues ​​to gradually move from the right half-plane of the complex plane closer to the imaginary axis, weakening the system's stability. When the rectifier inductance value is 0.0034H, the eigenvalues ​​enter the right half-plane, and the system is in an unstable state. It can be determined that when the rectifier inductance is less than 0.0034H, the system can remain stable, and within this range, reducing the inductance value can improve the stability of the interconnected microgrid.

[0096] (3) Analysis of the impact of the inverter-side capacitor on system stability

[0097] The capacitor was increased from 0.0001F to 0.7F. Figure 7 It is evident that as the inverter-side capacitance increases, the eigenvalues ​​exhibit different shift trends; some eigenvalues ​​move towards the left half of the complex plane, while others move towards the right half. However, as the capacitance continues to increase, the eigenvalues ​​remain in the left half of the complex plane and do not fall into the right half. This demonstrates that the inverter capacitance has no impact on the stability of the interconnected microgrid system.

[0098] (4) Analysis of the impact of the inductance on the inverter side on system stability

[0099] The inductance increases from 0.0004H to 10H, from Figure 8 It is evident that as the inductance on the inverter side increases, the movement trends of the eigenvalues ​​differ. Some eigenvalues ​​move towards the left half of the complex plane, while others move towards the right half. As the inductance value continues to increase, the eigenvalues ​​remain in the left half of the complex plane and do not fall into the right half. This demonstrates that the inductance on the inverter side does not affect the stability of the DC interconnected microgrid system.

[0100] Further optimize the filter parameters by setting the optimal range. As mentioned above, reducing the inductance and capacitor on the rectifier side within this range can improve system stability. However, based on the existing parameter settings, the filtering effect must be considered, and the filter parameters should not be too small. Therefore, the capacitor and inductor on the rectifier side should be set to no less than 0.0002F and 0.0006H, respectively. For the inverter side, considering both filtering effect and economic factors, the inductor and capacitor should not be too small or too large; they can be selected to be similar to the values ​​of the capacitor and inductor on the rectifier side. Therefore, based on the existing filter parameter design requirements and the real-time operating conditions of the system, the optimal range for the capacitor on both the rectifier and inverter sides can be set to greater than 0.0002F and less than 0.0008F; the inductor can be set to greater than 0.0006H and less than 0.001H.

[0101] In summary, this invention constructs a complete small-signal model by integrating the rectifier side, inverter side, and DC lines, solves for the eigenvalues ​​of the small-signal model, analyzes the influence of rectifier and inverter converter filter parameters on stability through eigenvalue trajectory analysis, thereby determining the effective range of filter parameters. Based on the original parameter design, considering factors such as filtering effect and economy, and combined with the real-time operating conditions of the system, the optimal range of filter parameters is further rationally set to improve the stability of the DC interconnected microgrid system.

[0102] It is understood that the present invention has been described through some embodiments, and those skilled in the art will recognize that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of the invention. Furthermore, under the teachings of the present invention, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of the invention. Therefore, the present invention is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of the present invention.

Claims

1. A method for improving the stability of a DC-connected microgrid, wherein the DC-connected microgrid comprises two AC subgrids, a rectifier-side filter circuit and a rectifier-side converter, an inverter-side filter circuit and an inverter-side converter, and a DC line; the AC subgrids contain multiple micro-sources, which are simulated using an ideal DC power supply and controller; the rectifier-side converter employs constant DC voltage control, and the inverter-side converter employs a constant power control strategy; characterized in that... The method involves constructing a complete small-signal model of a DC interconnected microgrid, solving for eigenvalues, analyzing the effective range of filter parameters through eigenvalue trajectory analysis, and rationally setting the optimal range of filter parameters based on the real-time operating conditions of the system. The method specifically includes the following steps: Step 1: Construct a small-signal model of the rectifier side containing an AC subnet, filter circuit, and controller; Step 2: Construct a small-signal model of the inverter side containing an AC subnet, filter circuit, and controller; Step 3: Construct a small-signal model of the DC line; Step 4: Based on steps 1-3, construct a complete small-signal model of a DC interconnected microgrid; Step 5: Solve for the eigenvalues ​​of the small-signal model, analyze the effective range of the filtering parameters through the eigenvalue trajectory, and set the optimal range of the filtering parameters reasonably according to the real-time operating conditions of the system. When the filter parameters undergo a directional change, if the system eigenvalues ​​move from the left half-plane to the right half-plane of the complex plane, and at a certain parameter value, the eigenvalues ​​cross the imaginary axis and enter the right half-plane, the system is in an unstable state, indicating that the directional change of the parameters at this time is not conducive to the stability of the system; if the system eigenvalues ​​always move from the left half-plane of the complex plane, it indicates that the directional change of the parameters can improve the stability of the system; if the system eigenvalues ​​always remain in the left half-plane of the complex plane and do not enter the right half-plane with the change of the parameters, the system is always in a stable state, indicating that the change of the parameters does not affect the stability of the system. This determines the effective range of the filtering parameters, and based on the original parameter design, combined with the real-time operating conditions of the system, the optimal range of the filtering parameters is set.

2. The method for improving the stability of DC interconnected microgrids according to claim 1, characterized in that, The rectifier-side small-signal model constructed in step 1 is specifically as follows: （1） In the formula, ; ; ; ; ; ; ; ; ; ; ; , ; ; ; ; ; ; ; ; , The equivalent internal inductance and resistance of subnet A; , For the capacitors and inductors of the filter circuit; , ; , Let be the d-axis and q-axis current components before and after filtering, respectively; , ; , These are the d-axis and q-axis voltage components before and after filtering, respectively; ω is the angular frequency. Line resistance; For voltage outer loop state variables; , These are the d-axis and q-axis state variables of the inner current loop, respectively. This is the reference value for the DC bus voltage; This is the actual DC voltage output from the rectifier side; This is the actual DC voltage output from the inverter side; This refers to the DC line current. , The proportional-integral coefficient of the voltage outer loop PI regulator; , ; , These represent the proportional-integral coefficients of the d-axis and q-axis PI regulators in the inner current loop controller; T is the converter switching cycle; K s This represents the converter's amplification factor.

3. The method for improving the stability of DC interconnected microgrids according to claim 2, characterized in that, The inverter-side small-signal model constructed in step 2 is specifically as follows: (2) In the formula, ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; , For the equivalent internal inductance and resistance of subnet B; , For the capacitors and inductors of the filter circuit; , ; , Let be the d-axis and q-axis current components before and after filtering, respectively; , ; , These are the d-axis and q-axis voltage components before and after filtering, respectively. The inverter-side line resistance; , These are the d-axis and q-axis state variables of the power outer loop, respectively. , These are reference values ​​for active and reactive power. , ; , These are the proportional-integral coefficients of the d-axis and q-axis PI regulators of the current inner loop controller, respectively. This represents the steady-state voltage component along the d-axis before filtering.

4. The method for improving the stability of DC interconnected microgrids according to claim 3, characterized in that, The DC line small-signal model constructed in step 3 is specifically as follows: （3） in ; ; ; ; , These are the inductance and resistance of a DC line, respectively. , These are the capacitors on the rectifier side and the inverter side, respectively. , , , These are the steady-state components of the d-axis voltage and current after filtering on the rectifier side. , , , These are the steady-state components of the d- and q-axis voltage and current after filtering on the inverter side. , This refers to the steady-state DC voltage output from the rectifier and inverter sides.

5. The method for improving the stability of DC interconnected microgrids according to claim 4, characterized in that, The complete DC interconnected microgrid model constructed in step 4 based on equations (1) to (3) is as follows: （4） In the formula, ; ; ; .

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