Control method of interconnected converters based on VSG in AC / DC hybrid microgrid

Abstract

This invention discloses a VSG-based interconnected converter control method in an AC / DC hybrid microgrid. The method establishes a frequency control loop and a voltage / current loop for the interconnected converter. The frequency control loop includes transient damping and inertia. The inertia is the integral of the difference between the active power reference value and the actual output power value of the interconnected converter. The active power reference value is calculated based on the per-unit value of the AC bus frequency plus its change, the per-unit value of the DC bus voltage plus its change, and the steady-state damping coefficient. The dynamic virtual impedance in the voltage / current loop is set to ensure that the per-unit values ​​of the maximum values ​​of the AC bus frequency change rate and the DC bus voltage change rate are consistent. This invention coordinates power transmission between AC and DC subgrids by setting a steady-state damping coefficient to ensure that the interconnected converter transmits power with a set precision in steady state. It also optimizes the dynamic characteristics of the AC bus frequency and DC bus voltage during load surges by adding transient damping and setting virtual impedance.

Description

Technical Field

[0001] This invention relates to the field of AC / DC hybrid microgrid control technology, and more specifically to a VSG-based interconnected converter control method applied in AC / DC hybrid microgrids. Background Technology

[0002] To meet green and environmental protection requirements, an increasing number of distributed generators (DGs) are being integrated into the power system in the form of microgrids. Since DGs are mostly DC power sources, and an increasing number of loads require DC power, connecting them through a DC microgrid can reduce energy losses during DC-AC conversion. However, existing distribution networks are predominantly AC systems, making a complete reconstruction of DC microgrids impractical. Therefore, to reduce energy losses while fully utilizing the existing AC distribution network, hybrid AC-DC microgrids are currently recognized as one of the feasible solutions.

[0003] In AC / DC hybrid microgrids, selecting a suitable control strategy for the interlinking converter (ILC) is crucial for stable system operation. The control strategy for ILCs is typically a bidirectional droop control method, which unifies the AC frequency and DC voltage using a formula and compares the unified values ​​to determine the power flow direction. However, the droop control strategy has a very short dynamic response time, and with the increase of distributed generation in the microgrid, it reduces the virtual inertia of the hybrid microgrid system, affecting system stability. Furthermore, traditional control strategies only focus on the steady-state characteristics of the ILC, neglecting its dynamic characteristics. To address the lack of inertia in hybrid microgrid systems and provide inertia support for the AC bus frequency, ILCs often employ Virtual Synchronous Generator (VSG) control. However, the AC and DC subgrids themselves also have a certain inertia; when the two inertias are mismatched, frequency oscillations or even instability can occur. Moreover, while VSG control of the ILC can improve dynamic characteristics, it may also introduce errors in the power transmitted by the ILC in steady state, resulting in inaccuracy. Meanwhile, after the subnets are interconnected, the dynamic characteristics of AC frequency and DC voltage will be coupled through ILC. When the load changes suddenly, the AC bus frequency change rate and DC bus voltage change rate under the independent operation of the subnets can meet the constraints, but after interconnection, they may exceed the threshold. Summary of the Invention

[0004] To overcome the shortcomings of the existing technology, this invention provides a VSG-based interconnected converter control method for AC / DC hybrid microgrids. It employs VSG control and virtual impedance design that incorporates AC bus frequency and DC bus voltage variations, combined with transient damping control, enabling precise power transmission in the ILC during steady-state operation and power coordination between AC and DC subgrids. It also optimizes the dynamic processes of AC bus frequency and DC bus voltage.

[0005] The present invention adopts the following technical solution to solve the technical problem:

[0006] The characteristics of the VSG-based interconnected converter control method in AC / DC hybrid microgrids of this invention are:

[0007] Set up the frequency control loop and voltage and current loop of the interconnected converter;

[0008] The frequency control loop of the interconnected converter contains transient damping and inertia. The inertia is the integral of the difference between the active power reference value and the actual output power value of the interconnected converter. The active power reference value is based on the AC bus frequency plus its per-unit value, the DC bus voltage plus its per-unit value, and the steady-state damping coefficient K. P Calculated;

[0009] The interconnected converter voltage and current loop contains a dynamic virtual impedance. The dynamic virtual impedance is set based on the AC / DC subnet inertia, the AC bus frequency change rate threshold, and the DC bus voltage change rate threshold, with the goal of making the per-unit values ​​of the maximum AC bus frequency change rate and the DC bus voltage change rate consistent.

[0010] By setting a steady-state damping coefficient, the interconnected converters can transmit power with a set accuracy in steady state, thus coordinating power between AC and DC sub-networks; this is achieved by adding transient damping and setting a virtual impedance X. v Reduce output power overshoot and oscillation during load surges, thereby optimizing AC bus frequency and DC bus voltage.

[0011] The VSG-based interconnected converter control method in the AC / DC hybrid microgrid of this invention is carried out according to the following process:

[0012] Step 1: Calculate the reference value P of the active power of the interconnected converter using equation (1). ILC_ref :

[0013]

[0014] In formula (1):

[0015] K P Let be the steady-state damping coefficient, (·) p.u. Indicates per-unit;

[0016] U dc To detect the obtained DC bus voltage in real time, ΔU dc This represents the change in DC bus voltage.

[0017] w ilc To detect the AC bus frequency in real time, Δw ilc This refers to the change in AC bus frequency.

[0018] And there are:

[0019] in:

[0020] P ILC To monitor the transmitted power of the interconnected converter in real time;

[0021] m w m is the droop coefficient of the AC subnet. v This represents the droop factor of the DC subnet.

[0022] Step 2: The real-time measured power P of the interconnected converter is then converted into the power output of the interconnected converter. ILC The frequency control loop is introduced through negative feedback, and the active power reference value P of the interconnected converter is used. ILC_ref Compare, and then eliminate P through integration. ILC and P ILC_ref To reduce the error and achieve a reference value P for the active power of the interconnected converter. ILC_ref Tracking;

[0023] Step 3: Obtain the parameters of each line through detection, including: AC subnet virtual inertia J. ac The virtual inertia of the DC subnet J dc AC subnet line impedance X ac Interconnected converter line impedance X ILC The AC bus frequency change rate and DC bus voltage change rate are used as parameters. Based on the grid connection standards, given parameters are obtained, including the AC bus frequency change rate threshold and the DC bus voltage change rate threshold. The virtual impedance X is then calculated based on these line parameters and the given parameters. v The virtual impedance X v It is added to the voltage and current loop of the interconnected converter as a dynamic virtual impedance;

[0024] Step 4: Obtain the frequency w generated under the control of the AC subnet VSG via communication. ac The frequency w ac Transient damping control is performed by introducing negative feedback into the frequency control loop of the interconnected converter. The transient power P generated by the transient damping control is calculated by equation (2). e for:

[0025] P e=K e (w ilc -w ac (2)

[0026] In equation (2): K e This is the transient damping coefficient;

[0027] Transient power P e A frequency control loop is added in the form of positive feedback to improve the dynamic characteristics of the AC / DC hybrid microgrid and suppress power oscillations.

[0028] The characteristic of the VSG-based interconnected converter control method in the AC / DC hybrid microgrid of this invention is that the inertia contained in the frequency control loop of the interconnected converter has the inertia form shown in equation (3):

[0029]

[0030] In formula (3):

[0031] J1 is the virtual inertia constant of the interconnected converter; w N This is the rated value for the AC bus frequency.

[0032] The characteristic of the VSG-based interconnected converter control method in the AC / DC hybrid microgrid of this invention also lies in the fact that the steady-state damping coefficient K in the frequency control loop of the interconnected converter is... P It is obtained by calculation from equation (4):

[0033]

[0034] In equation (4):

[0035] P dcN P is the rated power of the DC subgrid. acN This refers to the rated power of the AC subnet.

[0036] The characteristic of the VSG-based interconnected converter control method in the AC / DC hybrid microgrid of this invention also lies in: the virtual impedance X v Calculated from equation (5):

[0037]

[0038] In equation (5):

[0039] f ac The AC bus frequency in an AC / DC hybrid microgrid;

[0040] The threshold for the rate of change of AC bus frequency in a hybrid AC / DC microgrid;

[0041] This is the threshold value for the rate of change of DC bus voltage in an AC / DC hybrid microgrid.

[0042] The characteristic of the VSG-based interconnected converter control method in AC / DC hybrid microgrids of this invention is also that: in equation (1), (·) p.u. The per-unit representation is calculated according to equation (6):

[0043]

[0044] In equation (6): γ pu Per-unit values ​​representing characteristic quantities of AC / DC hybrid microgrids; γ max and γ min A one-to-one correspondence represents the maximum and minimum allowable values ​​of characteristic quantities of a hybrid AC / DC microgrid.

[0045] Compared with existing technologies, the beneficial effects of this invention are reflected in:

[0046] 1. This invention incorporates the variation of AC / DC hybrid microgrid characteristic quantities into the VSG control loop of the interconnected converter, which can provide inertia for the AC frequency and achieve accurate power transmission in steady state.

[0047] 2. This invention designs virtual impedance according to constraints, so that the rate of change of AC bus frequency and DC bus voltage does not exceed the threshold when the load changes suddenly; at the same time, transient damping is added to the frequency control link to effectively reduce overshoot and suppress oscillation in the dynamic process. Attached Figure Description

[0048] Figure 1 This is the AC / DC hybrid microgrid topology in this invention;

[0049] Figure 2 This is a control block diagram of the VSG-based interconnected converter in this invention;

[0050] Figure 3 This refers to the output power of the AC / DC subgrid under VSG control with varying parameters in this invention.

[0051] Figure 4 This refers to the output power of the AC / DC subgrid under VSG control without any changes in the present invention.

[0052] Figure 5 This refers to the output power of the AC / DC subnet when virtual impedance and transient damping are added in this invention;

[0053] Figure 6 This refers to the rate of change of characteristic quantities of the AC / DC hybrid microgrid when virtual impedance and transient damping are added in this invention;

[0054] Figure 7This refers to the rate of change of characteristic quantities of the AC / DC hybrid microgrid without the addition of virtual impedance and transient damping in this invention;

[0055] Table 1 shows the given parameters for the AC / DC hybrid microgrid model in this invention. Detailed Implementation

[0056] See Figure 1 and Figure 2 In this embodiment, the control method for the interconnected converter based on VSG in the AC / DC hybrid microgrid is as follows: An interconnected converter frequency control loop and an interconnected converter voltage-current loop are set up. The interconnected converter frequency control loop contains transient damping and inertia. The inertia is the integral of the difference between the active power reference value and the actual output power value of the interconnected converter. The active power reference value is based on the per-unit value of the AC bus frequency plus its change, the per-unit value of the DC bus voltage plus its change, and the steady-state damping coefficient K. P Calculations show that the interconnected converter voltage and current loop contains dynamic virtual impedance. The dynamic virtual impedance is set based on the AC / DC subnet inertia, the AC bus frequency change rate threshold, and the DC bus voltage change rate threshold, aiming to ensure that the per-unit values ​​of the maximum AC bus frequency change rate and the DC bus voltage change rate are consistent. By setting the steady-state damping coefficient, the interconnected converter transmits power with a set accuracy in steady state, thus coordinating power between the AC and DC subnets. This is achieved by adding transient damping and setting the virtual impedance X. v Reduce output power overshoot and oscillation during load surges, thereby optimizing AC bus frequency and DC bus voltage.

[0057] In practice, the VSG-based interconnected converter control method in AC / DC hybrid microgrids is carried out as follows:

[0058] Step 1: Calculate the reference value P of the active power of the interconnected converter using equation (1). ILC_ref :

[0059] P ILC_ref =K P ((U dc +ΔU dc ) p.u. -(w ilc +Δw ilc ) p.u. (1)

[0060] In formula (1):

[0061] K P Let be the steady-state damping coefficient, (·) p.u. Indicates per-unit;

[0062] U dc To detect the obtained DC bus voltage in real time, ΔU dcThis represents the change in DC bus voltage.

[0063] w ilc To detect the AC bus frequency in real time, Δw ilc This refers to the change in AC bus frequency.

[0064] And there are:

[0065] Where: P ILC To detect the transmitted power of the interconnected converter in real time; m w m is the droop coefficient of the AC subnet. v This represents the droop factor of the DC subnet.

[0066] Step 2: The real-time measured power P of the interconnected converter is then converted into the power output of the interconnected converter. ILC The frequency control loop is introduced through negative feedback, and the active power reference value P of the interconnected converter is used. ILC_ref Compare, and then eliminate P through integration. ILC and P ILC_ref To reduce the error and achieve a reference value P for the active power of the interconnected converter. ILC_ref Tracking;

[0067] Step 3: Obtain the parameters of each line through detection, including: AC subnet virtual inertia J. ac The virtual inertia of the DC subnet J dc AC subnet line impedance X ac Interconnected converter line impedance X ILC The AC bus frequency change rate and DC bus voltage change rate are calculated. Based on the grid connection standards, various given parameters are obtained, including the AC bus frequency change rate threshold and the DC bus voltage change rate threshold. The virtual impedance X is then calculated based on the line parameters and the given parameters. v , virtual impedance X v It is added to the voltage and current loop of the interconnected converter as a dynamic virtual impedance;

[0068] Step 4: Obtain the frequency w generated under the control of the AC subnet VSG via communication. ac , frequency w ac Transient damping control is performed by introducing negative feedback into the frequency control loop of the interconnected converter. The transient power P generated by the transient damping control is calculated by equation (2). e for:

[0069] P e =K e (w ilc -w ac (2)

[0070] In equation (2): K e This is the transient damping coefficient;

[0071] Transient power P e A frequency control loop is added in the form of positive feedback to improve the dynamic characteristics of the AC / DC hybrid microgrid and suppress power oscillations.

[0072] The corresponding technical measures in this embodiment also include:

[0073] The inertia contained in the frequency control loop of the interconnected converter has the inertia form shown in equation (3):

[0074]

[0075] In equation (3): J1 is the virtual inertia constant of the interconnected converter; w N This is the rated value for the AC bus frequency.

[0076] In steady state Equation (3) simplifies to equation (3-1):

[0077]

[0078] The ΔU represented by equation (1-1) dc and Δw ilc Substitute the calculation formula into equation (3-1), and based on m w With the rated power and m of the AC subnet v The relationship between the rated power of the DC subgrid and the DC subgrid is given by equation (3-2):

[0079]

[0080] In equation (3-2):

[0081] P dcN P is the rated power of the DC subgrid. acN This refers to the rated power of the AC subnet.

[0082] When the output power of the AC and DC subgrids is ideally distributed according to their respective capacities, the per-unit values ​​of the characteristic quantities of the AC / DC hybrid microgrid are the same, as shown in equation (3-3):

[0083] (U dc ) p.u. =(w ilc ) p.u. (3-3)

[0084] Therefore, substituting equation (3-3) into equation (3-2) yields the steady-state damping coefficient K in the frequency control loop of the interconnected converter under ideal conditions. P It is characterized by equation (4), and K is obtained by calculating using equation (4). P :

[0085]

[0086] Virtual impedance X v Calculated from equation (5):

[0087]

[0088] In equation (5):

[0089] f ac The AC bus frequency in a hybrid AC / DC microgrid;

[0090] The threshold for the rate of change of AC bus frequency in a hybrid AC / DC microgrid;

[0091] This is the threshold value for the rate of change of DC bus voltage in an AC / DC hybrid microgrid.

[0092] During load surges, the VSG control of the interconnected converter and the AC subnet is not yet active, therefore the instantaneous output power distribution relationship of the AC and DC subnets is as shown in equation (5-1):

[0093]

[0094] In equation (5-1):

[0095] P ac_trans For the instantaneous output power of the AC subnet, P dc_trans This refers to the instantaneous output power of the DC subgrid.

[0096] From equation (5-1), it can be seen that changing the virtual impedance X v It can change the instantaneous output power distribution relationship. And according to the VSG control equations of the AC / DC subnet, P can be obtained. dc_trans With DC bus voltage change rate and P ac_trans The relationship with the rate of change of AC bus frequency is shown in equation (5-2):

[0097]

[0098] In equation (5-2): The rate of change of AC bus frequency in a hybrid AC / DC microgrid; This represents the rate of change of DC bus voltage in an AC / DC hybrid microgrid.

[0099] Substituting equation (5-2) into equation (5-1), and based on the design objective of virtual impedance being to make the per-unit value of the AC bus frequency change rate the same as the per-unit value of the DC bus voltage change rate, the calculation formula of the virtual impedance represented by equation (5) can be derived.

[0100] In equation (1), (·) p.u. The per-unit representation is calculated according to equation (6):

[0101]

[0102] In equation (6): γ pu Per-unit values ​​representing characteristic quantities of AC / DC hybrid microgrids; γ max and γ min A one-to-one correspondence represents the maximum and minimum allowable values ​​of characteristic quantities of a hybrid AC / DC microgrid.

[0103] To verify the effectiveness of the method of the present invention, an isolated AC / DC hybrid microgrid model was built in Matlab / Simulink. The given parameters of the model are shown in Table 1:

[0104] Table 1. Given parameters for the AC / DC hybrid microgrid model:

[0105] Parameter Description numerical values Parameter Description numerical values <![CDATA[Rated power P of the DC subnet dcN > 20kW <![CDATA[Rated power P of the AC subnet acN > 20kW <![CDATA[Rated DC bus voltage U dcN > 700V <![CDATA[Rated frequency w of AC busbar N > 100πrad / s <![CDATA[DC subnet droop coefficient m v > 30V / 20kW <![CDATA[AC subnet droop coefficient m w > 1Hz / 20kW <![CDATA[DC subnet virtual inertia J dc > <![CDATA[0.038kg·m 2 ]]> <![CDATA[Virtual inertia constant J1 of ILC]]> <![CDATA[0.8kg·m 2 ]]> AC subnet line impedance 0.1+j0.3π ILC line impedance 0.1+j0.3π

[0106] AC / DC hybrid microgrid topology such as Figure 1 As shown, the system consists of a DC microgrid, an AC microgrid, and interconnected converters connecting the AC and DC buses. The DC subgrid is composed of DC / DC converters controlled by virtual DC motors, while the AC subgrid is equivalent to a DC / AC inverter controlled by a virtual synchronous generator. Initially, the DC subgrid is unloaded, and the AC subgrid load is 10kW. The AC and DC subgrid capacities are set to be the same, both at 20kW.

[0107] Interconnected converters adopt, for example Figure 2 The control strategy shown in this embodiment incorporates the AC bus frequency change and DC bus voltage change into the power reference value of the VSG control loop of the ILC, which can achieve the balance of AC and DC sub-networks when the load fluctuates. Figure 3 The output power P of the AC subnet under VSG control with varying parameters ac and DC subgrid output power P dc At this point, the two output powers are evenly divided according to the subgrid capacity, each being 5kW, with no error. Figure 4 The output power of the AC / DC subgrid under VSG control without any changes is shown below. In this case, the AC subgrid output power is 2.5kW and the DC subgrid output power is 7.5kW. The power output is not evenly distributed according to the subgrid capacity to support the AC subgrid load, failing to achieve power coordination between the AC and DC subgrids. In severe cases, the output power of the AC and DC subgrids may exceed their capacity, which is unacceptable. Therefore, incorporating the variation of AC / DC hybrid microgrid characteristic quantities into the VSG control loop can eliminate errors in the power coordination and allocation of the AC / DC subgrids, achieving precise power transmission between the interconnected converters in steady state.

[0108] Figure 5The output power of the AC / DC subnet is calculated based on VSG control with the addition of virtual impedance and transient damping control. At this point, the system does not generate overshoot or oscillation, and the AC / DC subnet quickly stabilizes. The output power in steady state is the theoretical value of 5kW. Figure 6 The per-unit values ​​of the AC bus frequency change rate and DC bus voltage change rate are given when virtual impedance and transient damping control are added under VSG control. At this time, the per-unit values ​​of both change rates are -0.6, while the per-unit values ​​of the AC bus frequency change rate threshold and the DC bus voltage change rate threshold are both -1. Therefore, neither change rate exceeds the threshold, and the virtual impedance design target is achieved, that is, the per-unit values ​​of the two change rates are the same. Figure 7 These are the per-unit values ​​of the AC bus frequency change rate and the DC bus voltage change rate under VSG control without adding virtual impedance and transient damping. At this point, the per-unit value of the AC bus frequency change rate exceeds the threshold of -1, approximately -1.25, indicating that the AC bus frequency change rate does not meet the grid connection standard. Figure 3 and Figure 5 By comparing the output power of the AC and DC subnetworks, it can be found that... Figure 3 Without virtual impedance and transient damping control, the system exhibits overshoot and oscillation, with a significant overshoot of approximately 100%. Furthermore, the AC subgrid output power sometimes falls below zero during transient processes, indicating circulating current, which is detrimental to the stable operation of the AC / DC hybrid microgrid. Therefore, incorporating virtual impedance and transient damping control into the VSG-based interconnected converter can suppress system oscillations during load surges and optimize the system's dynamic performance under such conditions.

[0109] This invention overcomes the shortcomings of existing interconnected converter VSG control, which only focuses on steady-state characteristics. It enables the ILC to accurately transmit power in steady state, allowing the AC and DC subgrids to jointly support the load according to their respective capacities. Furthermore, it optimizes the dynamic processes of AC bus frequency and DC bus voltage during load surges. Simulations have verified the effectiveness of this invention.

Claims

1. A VSG-based interconnected converter control method in an AC / DC hybrid microgrid, characterized by: The interconnected converter is configured with a frequency control loop and a voltage and current loop. The frequency control loop includes transient damping and inertia. The inertia is the integral of the difference between the active power reference value and the actual output power value of the interconnected converter. The active power reference value is based on the AC bus frequency plus its per-unit value, the DC bus voltage plus its per-unit value, and the steady-state damping coefficient K. P The calculations show that the interconnected converter voltage and current loop contains a dynamic virtual impedance. This dynamic virtual impedance is set based on the AC / DC subnet inertia, the AC bus frequency change rate threshold, and the DC bus voltage change rate threshold, with the goal of aligning the per-unit values ​​of the maximum AC bus frequency change rate and the maximum DC bus voltage change rate. By setting a steady-state damping coefficient, the interconnected converter transmits power with a set precision in steady state, thus coordinating power between the AC and DC subnets. This is achieved by adding transient damping and setting the virtual impedance X. v Reduce output power overshoot and oscillation during load surges, thereby optimizing AC bus frequency and DC bus voltage; The steady-state damping coefficient K in the frequency control loop of the interconnected converter P It is obtained by calculation from equation (4): In equation (4): P dcN P is the rated power of the DC subgrid. acN The rated power of the AC subnet; The virtual impedance X v Calculated from equation (5): In equation (5): f ac The AC bus frequency in a hybrid AC / DC microgrid; The threshold for the rate of change of AC bus frequency in a hybrid AC / DC microgrid; This is the threshold value for the rate of change of DC bus voltage in an AC / DC hybrid microgrid.

2. The VSG-based interconnected converter control method in an AC / DC hybrid microgrid according to claim 1, characterized in that: Follow these steps: Step 1: Calculate the reference value P of the active power of the interconnected converter using equation (1). ILC_ref : P ILC_ref =K P ((AT dc +ΔU dc ) p.u. -(In ilc +Δw ilc ) p.u. ) (1) In formula (1): K P Let be the steady-state damping coefficient, (·) p.u. Indicates per-unit; U dc To detect the obtained DC bus voltage in real time, ΔU dc This represents the change in DC bus voltage. w ilc To detect the AC bus frequency in real time, Δw ilc This refers to the change in AC bus frequency. And there are: in: P ILC To monitor the transmitted power of the interconnected converter in real time; m w m is the droop coefficient of the AC subnet. v This represents the droop factor of the DC subnet. Step 2: The real-time measured power P of the interconnected converter is then converted into the power output of the interconnected converter. ILC The frequency control loop is introduced through negative feedback, and the active power reference value P of the interconnected converter is used. ILC_ref Compare, and then eliminate P through integration. ILC and P ILC_ref To reduce the error and achieve a reference value P for the active power of the interconnected converter. ILC_ref Tracking; Step 3: Obtain the parameters of each line through detection, including: AC subnet virtual inertia J. ac The virtual inertia of the DC subnet J dc AC subnet line impedance X ac Interconnected converter line impedance X ILC The AC bus frequency change rate and DC bus voltage change rate are used as parameters. Based on the grid connection standards, given parameters are obtained, including the AC bus frequency change rate threshold and the DC bus voltage change rate threshold. The virtual impedance X is then calculated based on these line parameters and the given parameters. v The virtual impedance X v It is added to the voltage and current loop of the interconnected converter as a dynamic virtual impedance; Step 4: Obtain the frequency w generated under the control of the AC subnet VSG via communication. ac The frequency w ac Transient damping control is performed by introducing negative feedback into the frequency control loop of the interconnected converter. The transient power P generated by the transient damping control is calculated by equation (2). e for: P e =K e (w ilc -w ac ) (2) In equation (2): K e This is the transient damping coefficient; Transient power P e A frequency control loop is added in the form of positive feedback to improve the dynamic characteristics of the AC / DC hybrid microgrid and suppress power oscillations.

3. The VSG-based interconnected converter control method in an AC / DC hybrid microgrid according to claim 2, characterized in that: The inertia contained in the frequency control loop of the interconnected converter has the inertia form shown in equation (3): In formula (3): J1 is the virtual inertia constant of the interconnected converter; w N This is the rated value for the AC bus frequency.

4. The VSG-based interconnected converter control method in an AC / DC hybrid microgrid according to claim 2, characterized in that: In equation (1), (·) p.u. The per-unit representation is calculated according to equation (6): In equation (6): γ pu Per-unit values ​​representing characteristic quantities of AC / DC hybrid microgrids; γ max and γ min A one-to-one correspondence represents the maximum and minimum allowable values ​​of characteristic quantities of a hybrid AC / DC microgrid.

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