Smooth switching method for control modes of multi-port flexible multi-state switch

Abstract

The invention discloses a control mode smooth switching method for a multi-port flexible multi-state switch, and the method comprises the steps: carrying out the Udc-Q control of any port of the flexible multi-state switch during grid-connected operation, and carrying out the PQ control of other ports; when a certain port is off-grid due to a feeder line fault, smoothly switching to a VSG control mode through state tracking control, and providing voltage and frequency support for a power-losing area; after the fault is cleared, the voltage amplitude, the phase and the frequency of the VSG are synchronized with a power grid through synchronous control, smooth grid connection is achieved, any port of the flexible multi-state switch comprises a grid-connected controller and an off-grid controller, Udc-Q control and PQ control in the grid-connected controller share a current loop and a reactive loop, and the switching complexity is reduced; the off-network controller adopts VSG control; in the state tracking control, the state tracking quantity is introduced into the inputs of different controllers in a negative feedback form, so that the bidirectional tracking of the output states of the controllers is realized. According to the invention, the cooperative control of the multi-port flexible multi-state switch and the smooth switching of any port control mode can be realized, and the transient impact at the switching moment is reduced.

Description

Technical Field

[0001] The present invention belongs to the field of flexible interconnection equipment control in distribution networks, and in particular relates to a control mode smooth switching method for a multi-port flexible multi-state switch. Background Art

[0002] With the widespread and decentralized integration of distributed energy resources into low-voltage distribution networks, traditional distribution networks are facing new challenges in terms of renewable energy consumption, power supply reliability, and power quality. Low-voltage distribution substations connect numerous power end users. In the event of a fault, traditional distribution networks struggle to transfer load to the affected area, failing to meet users' high demands for power reliability and continuity.

[0003] Flexible interconnection equipment based on flexible multi-state switches is a power electronic device that can flexibly connect different distribution areas and bidirectionally regulate power flows within each zone. This flexible interconnection technology enables electrical interconnection and power synergy between different distribution areas, enabling resource sharing and coordinated control. It effectively integrates and utilizes complex and variable distributed energy resources, maintaining continuous power supply for critical loads.

[0004] When a feeder failure occurs in the distribution network or equipment maintenance requires switching from grid-connected to off-grid mode, the flexible multi-state switch must be controlled according to the specific situation. In this case, the off-grid area is isolated from the main grid, while maintaining connectivity with other distribution zones via the flexible multi-state switch. The required power is provided by the port converter. However, with traditional switching methods, controller output jumps can cause large voltage and current fluctuations, significantly affecting frequency and power, and failing to meet the requirements for power supply stability and continuity. Therefore, ensuring a smooth transition during the mode switching process is crucial. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of traditional switching methods by proposing a method for smooth control mode switching of a multi-port flexible multi-state switch. This method addresses feeder fault conditions at different ports and ensures smooth switching under various operating conditions, thereby improving the system's anti-interference capabilities and power supply reliability.

[0006] To solve the above technical problems, the present invention adopts the following technical solution: a method for smoothly switching the control mode of a multi-port flexible multi-state switch, the method comprising the following steps:

[0007] Step S1, topological structure and mathematical model of flexible multi-state switch;

[0008] The flexible multi-state switch is a flexible interconnected device composed of fully controlled power electronic devices. It consists of at least three voltage source converters. The DC side is symmetrically connected through parallel capacitors, and the AC side is connected to the power grid through a distribution transformer. Based on the symmetrical structure of the flexible multi-state switch, the converter on one side of the port is modeled:

[0009] The mathematical model of the single-side port is established in the dq rotating coordinate system as shown below:

[0010]

[0011] Where i=1, 2, 3, which are port numbers; R and L are equivalent resistance and filter inductance; C and C are dc is the filter capacitor and DC side capacitor; i di 、i qi are the d-axis and q-axis components of the converter output current; E di 、E qi are the d and q axis components of the AC voltage; s di 、s qi are the d and q axis components of the switching function; ω is the angular frequency; U dc is the DC side voltage; i Edi 、i Eqi are the d and q axis components of the AC current;

[0012] The power flow of the flexible multi-state switch satisfies the following relationship:

[0013]

[0014] Where, P i is the active power of port i; I dci is the current flowing into the DC side from port i;

[0015] Step S2, control strategy modeling of the flexible multi-state switch;

[0016] Each port of the flexible multi-state switch includes a grid-connected controller and an off-grid controller, which can switch the control mode according to the operating state:

[0017] In normal grid-connected operation, PQ and U dc -Q control strategy regulates the power flow of the flexible multi-state switch and stabilizes the DC side voltage to ensure stable power transmission; when a fault occurs and the grid is disconnected, it switches to the VSG control strategy to ensure continuous power supply to critical loads.

[0018] The PQ and U dcThe -Q control strategy adopts a dual-loop control structure in the grid-connected controller, sharing the current inner loop and the reactive outer loop, with only the d-axis outer loop being different, thereby simplifying the controller structure and reducing the switching complexity; the VSG control strategy adopts a dual-loop control structure in the off-grid controller, with the outer loops being the active-frequency loop and the reactive-voltage loop, and the inner loop being the voltage-current dual closed loop.

[0019] Step S2.1, the PQ control, whose outer loop generates a set value based on the power demand of the flexible multi-state switch, and converts the difference between the power set value and the actual calculated value into d-axis and q-axis current reference values ​​through the PI controller:

[0020]

[0021] Where, I dref , I qref is the d-axis and q-axis current reference value; P ref , Q ref is the power setting value; P and Q are the active power and reactive power output by the port; K p , K i are the proportional coefficient and integral coefficient of the power outer loop; s is the complex variable in Laplace transform;

[0022] The inner loop generates a voltage reference based on the current reference and modulates the actual output voltage to ensure that the output current accurately follows the set value:

[0023]

[0024] Where: u d * 、u q * is the voltage reference value; K pi , K ii is the PI parameter of the current inner loop; I d , I q Output current for d-axis and q-axis; u d 、u q are the d-axis and q-axis voltages respectively.

[0025] Step S2.2, the U dc -Q control, its structure is similar to PQ control, both are double closed-loop structures, the outer loop generates the d-axis current reference value I through the PI controller according to the difference between the DC voltage set value and the actual value dref :

[0026]

[0027] Where: U dcref is the DC voltage setting value; K p,Udc , K i,Udcis the DC voltage outer loop PI parameter.

[0028] In step S2.3, the VSG control, whose active power-frequency loop dynamically adjusts the output voltage frequency to respond to active power fluctuations, achieves autonomous frequency stabilization, and establishes the virtual rotor motion equation:

[0029]

[0030] Where, Δω=ω-ω0 is the angular frequency deviation, ω0 is the rated angular frequency; P m 、P e is the mechanical power and electromagnetic power; J and D are the virtual inertia and damping;

[0031] Among them, P m The expression is as follows:

[0032] P m =(ω0-ω)D p +P ref (9)

[0033] Where: D p is the power frequency droop coefficient;

[0034] The reactive-voltage loop of the VSG adjusts the output voltage amplitude based on the reactive-voltage droop characteristics, maintains the voltage level in the power-off area, and establishes the virtual excitation control equation:

[0035] E=(Q ref -Q)D q +E0 (10)

[0036] Where: E0, E are the reference voltage and output voltage; D q is the reactive power droop coefficient.

[0037] Step S3: establishing a full-process mode smooth switching method based on the coordination of state tracking control and synchronous grid connection control;

[0038] The smooth switching method is based on state tracking control, which ensures that the output states of the off-grid controller and the grid-connected controller are consistent during the mode switching process when a feeder fails, thereby significantly reducing transient impacts;

[0039] After the fault is cleared, the voltage amplitude, phase and frequency of the VSG are synchronized with the grid through synchronous grid-connected control, which reduces the current impact at the time of grid connection and achieves smooth grid connection;

[0040] Dynamically adjust the mode switching process based on the operating mode of the faulty port to ensure smooth switching under different working conditions, improving the system's anti-interference ability and power supply reliability;

[0041] Step S3.1, the state tracking control is:

[0042] In the normal grid-connected operation state, the system maintains the connection between the grid-connected controller and the SPWM, and the logic variable i (i = 1 is PQ mode, i = 0 is U dc -Q mode) enables flexible switching between the two control strategies. Meanwhile, the off-grid controller remains disconnected from the SPWM. By comparing the voltage reference signal output by the grid-connected controller with the difference between its own output in real time, it forms tracking feedback after PI adjustment, ensuring that the off-grid controller output always follows the grid-connected controller, ensuring synchronization between the two.

[0043] When the feeder fault triggers the mode switch, the system first disconnects the grid-connected controller from the SPWM and connects the off-grid controller to the SPWM. During this process, the off-grid controller exits the tracking state of the grid-connected controller, and the grid-connected controller starts tracking the output voltage of the off-grid controller. Since the off-grid controller has been pre-synchronized with the output state of the grid-connected controller, the SPWM modulation signal can achieve a smooth transition, effectively avoiding the instantaneous impact of voltage and current, thereby completing the transition from PQ / U dc -Seamless switching from Q mode to VSG mode. This control strategy significantly reduces transient shocks and improves system operation stability.

[0044] Step S3.2, the synchronous grid-connected control is composed of amplitude synchronization control and phase synchronization control;

[0045] The amplitude synchronization control adjusts the difference between the grid and VSG voltage amplitudes through the PI controller to obtain the voltage correction value, which is input into the virtual excitation controller to dynamically adjust the output voltage amplitude of the VSG to keep it consistent with the grid;

[0046] The phase synchronization control adjusts the phase difference between the grid and the VSG through a phase-locked loop and a PI controller to obtain an angular velocity correction value, which is input into the virtual speed controller;

[0047] Establish synchronous control equation:

[0048]

[0049] Where: θ, θ g is the VSG output phase and grid phase; ΔE is the output of the VSG reactive-voltage loop; E g is the grid voltage amplitude; K pω , K iω , K pE , K pE are the PI coefficients of phase and amplitude;

[0050] Step S3.3, the mode smooth switching process is as follows:

[0051] When a feeder fault occurs on a port using PQ control in a flexible multi-state switch, the port is smoothly switched to VSG control to ensure continuous power supply to the passive network.

[0052] When using U dc When a feeder failure occurs on a port controlled by -Q, the port is first smoothly switched to VSG control; at the same time, the PQ control port with the largest capacity is selected from the remaining ports and switched to U dc -Q control, as a new voltage stabilization port, to maintain the stability of the DC side voltage of the flexible multi-state switch;

[0053] Establish the remaining capacity calculation equation:

[0054]

[0055] Where: S is the apparent power of the port converter; S max is the rated capacity of the port converter; S r is the remaining capacity of the port converter.

[0056] An electronic device comprises a memory, a processor and a computer program stored in the memory and runnable on the processor. When the processor executes the program, the control mode smooth switching method of the multi-port flexible multi-state switch is implemented.

[0057] A computer-readable storage medium stores computer instructions, which, when executed by a processor, implement the control mode smooth switching method of a multi-port flexible multi-state switch.

[0058] Beneficial effects:

[0059] Compared with the prior art, the present invention has the following effective effects:

[0060] 1. For feeder faults on the PQ port side, a state tracking control method is proposed. By matching the output states of the grid-connected controller and the off-grid controller in real time, a bidirectional state tracking mechanism is established. This effectively solves the transient impact problem existing in the traditional switching method and realizes smooth switching from PQ control to VSG control.

[0061] 2. Targeting U dc When the feeder fails on the -Q port side, a coordinated switching strategy is designed: on the one hand, the faulty port is switched to the VSG control mode, and on the other hand, the one with the largest capacity is selected from the remaining PQ ports and switched to the U dc -Q mode to maintain DC voltage stability; at the same time, by integrating PQ control and U dc -Q control dual-loop structure simplifies the control structure and reduces switching complexity;

[0062] 3. For the scenario of reconnecting to the grid after fault clearing, a voltage amplitude-phase synchronization module is embedded in the VSG control. Through dynamic adjustment, the grid connection deviation is suppressed within the specified range, realizing seamless switching from off-grid to grid connection. BRIEF DESCRIPTION OF THE DRAWINGS

[0063] Figure 1 is a flow chart of the present invention;

[0064] Figure 2 It is the overall control block diagram of the present invention;

[0065] Figure 3 This is the VSG synchronization control block diagram;

[0066] Figure 4 This is a flow chart for smooth mode switching. DETAILED DESCRIPTION

[0067] The present invention will be described in detail below with reference to the accompanying drawings.

[0068] Example: The control mode smooth switching method of a multi-port flexible multi-state switch described in the present invention has the following process: Figure 1 As shown, the specific steps include:

[0069] Step S1, topological structure and mathematical model of flexible multi-state switch;

[0070] The flexible multi-state switch is a flexible interconnected device composed of fully controlled power electronic devices. It consists of at least three voltage source converters. The DC side is symmetrically connected through parallel capacitors, and the AC side is connected to the power grid through a distribution transformer. Based on the symmetrical structure of the flexible multi-state switch, the converter on one side of the port is modeled:

[0071] The mathematical model of the single-side port is established in the dq rotating coordinate system as shown below:

[0072]

[0073] Where i=1, 2, 3, which are port numbers; R and L are equivalent resistance and filter inductance; C and C are dc is the filter capacitor and DC side capacitor; i di 、i qi are the d-axis and q-axis components of the converter output current; E di 、E qi are the d and q axis components of the AC voltage; s di 、s qi are the d and q axis components of the switching function; ω is the angular frequency; U dc is the DC side voltage; i Edi 、i Eqi are the d and q axis components of the AC current;

[0074] The power flow of the flexible multi-state switch satisfies the following relationship:

[0075]

[0076] Where, P i is the active power of port i; I dci is the current flowing into the DC side from port i;

[0077] Step S2, control strategy modeling of the flexible multi-state switch;

[0078] Each port of the flexible multi-state switch includes a grid-connected controller and an off-grid controller, which can switch the control mode according to the operating state. The overall control structure is as follows: Figure 2 As shown;

[0079] In normal grid-connected operation, PQ and U dc -Q control strategy regulates the power flow of the flexible multi-state switch and stabilizes the DC side voltage to ensure stable power transmission; when a fault occurs and the grid is disconnected, it switches to the VSG control strategy to ensure continuous power supply to critical loads.

[0080] The PQ and U dc The -Q control strategy adopts a dual-loop control structure in the grid-connected controller, sharing the current inner loop and the reactive outer loop, with only the d-axis outer loop being different, thereby simplifying the controller structure and reducing the switching complexity; the VSG control strategy adopts a dual-loop control structure in the off-grid controller, with the outer loops being the active-frequency loop and the reactive-voltage loop, and the inner loop being the voltage-current dual closed loop.

[0081] Step S2.1, the PQ control, whose outer loop generates a set value based on the power demand of the flexible multi-state switch, and converts the difference between the power set value and the actual calculated value into d-axis and q-axis current reference values ​​through the PI controller:

[0082]

[0083] Where, I dref , I qref is the d-axis and q-axis current reference value; P ref , Q ref is the power setting value; P and Q are the active power and reactive power output by the port; K p , K i are the proportional coefficient and integral coefficient of the power outer loop; s is the complex variable in Laplace transform;

[0084] The inner loop generates a voltage reference based on the current reference and modulates the actual output voltage to ensure that the output current accurately follows the set value:

[0085]

[0086] Where: u d * 、u q * is the voltage reference value; K pi , K ii is the PI parameter of the current inner loop; I d , I q Output current for d-axis and q-axis; u d 、u q are the d-axis and q-axis voltages respectively.

[0087] Step S2.2, the U dc -Q control, its structure is similar to PQ control, both are double closed-loop structures, the outer loop generates the d-axis current reference value I through the PI controller according to the difference between the DC voltage set value and the actual value dref :

[0088]

[0089] Where: U dcref is the DC voltage setting value; K p,Udc , K i,Udc is the DC voltage outer loop PI parameter.

[0090] In step S2.3, the VSG control, whose active power-frequency loop dynamically adjusts the output voltage frequency to respond to active power fluctuations, achieves autonomous frequency stabilization, and establishes the virtual rotor motion equation:

[0091]

[0092] Where, Δω=ω-ω0 is the angular frequency deviation, ω0 is the rated angular frequency; P m 、P e is the mechanical power and electromagnetic power; J and D are the virtual inertia and damping;

[0093] Among them, P m The expression is as follows:

[0094] P m =(ω0-ω)D p +P ref (9)

[0095] Where: D p is the power frequency droop coefficient;

[0096] The reactive-voltage loop of the VSG adjusts the output voltage amplitude based on the reactive-voltage droop characteristics, maintains the voltage level in the power-off area, and establishes the virtual excitation control equation:

[0097] E=(Q ref -Q)D q +E0 (10)

[0098] Where: E0, E are the reference voltage and output voltage; D q is the reactive power droop coefficient.

[0099] Step S3: establishing a full-process mode smooth switching method based on the coordination of state tracking control and synchronous grid connection control;

[0100] The smooth switching method is based on state tracking control, which ensures that the output states of the grid-connected controller and the off-grid controller are consistent during the mode switching process when a feeder fails, thereby significantly reducing transient impacts;

[0101] After the fault is cleared, the voltage amplitude, phase and frequency of the VSG are synchronized with the grid through synchronous grid-connected control, which reduces the current impact at the time of grid connection and achieves smooth grid connection;

[0102] Dynamically adjust the mode switching process based on the operating mode of the faulty port to ensure smooth switching under different working conditions, improving the system's anti-interference ability and power supply reliability;

[0103] Step S3.1, the state tracking control is as follows Figure 2 The state tracking part in the dotted box is shown in ( Figure 2 is the overall control block diagram), specifically:

[0104] In normal grid-connected operation, the system maintains the connection between the grid-connected controller and the SPWM, which satisfies the relationship:

[0105]

[0106] Where: are the d-axis and q-axis components of the modulation voltage finally input to the SPWM; The d-axis and q-axis components of the reference voltage output by the grid-connected controller;

[0107] The grid-connected controller can be connected through the logic variable i (i = 1 for PQ mode, i = 0 for U dc -Q mode) to achieve flexible switching between the two control strategies; at the same time, the off-grid controller is disconnected from the SPWM, Figure 2 Middle switch k d Closed, k c Disconnect, by comparing the difference between the voltage reference signal output by the grid-connected controller and its own output in real time, forming tracking feedback after PI adjustment, so that the output state of the off-grid controller always follows the grid-connected controller, ensuring that the two are synchronized;

[0108] When the feeder fault triggers the mode switching, the system first disconnects the grid-connected controller from the SPWM and connects the off-grid controller to the SPWM. d Disconnect, k c Closed, the off-grid controller exits the tracking state of the grid-connected controller, and the grid-connected controller starts to track the output voltage of the off-grid controller. Figure 2 Middle K c The switch on the left switches to the corresponding branch according to the value of i (i=1, the left switch is turned on to 1, i=0, the left switch is turned on to 0), preparing for the subsequent switch back to the original control mode. Since the off-grid controller has been pre-synchronized with the output state of the grid-connected controller, the SPWM modulation signal can achieve a smooth transition, effectively avoiding the instantaneous impact of voltage and current, thereby completing the transition from PQ / U dc -Seamless switching from Q mode to VSG mode. This control strategy significantly reduces transient shocks and improves system operation stability.

[0109] Step S3.2, the synchronous grid connection control is as follows Figure 3 As shown, it consists of amplitude synchronization control and phase synchronization control;

[0110] The amplitude synchronization control adjusts the difference between the grid and VSG voltage amplitudes through the PI controller to obtain the voltage correction value, which is input into the virtual excitation controller to dynamically adjust the output voltage amplitude of the VSG to keep it consistent with the grid;

[0111] The phase synchronization control adjusts the phase difference between the grid and the VSG through a phase-locked loop and a PI controller to obtain an angular velocity correction value, which is input into the virtual speed controller;

[0112] Establish synchronous control equation:

[0113]

[0114] Where: θ, θ g is the VSG output phase and the grid phase; ΔE is the output of the VSG reactive voltage loop; E g is the grid voltage amplitude; K pω , K iω , K pE , K pE are the PI coefficients of phase and amplitude;

[0115] Step S3.3, the mode smooth switching process is as follows Figure 4 As shown, specifically:

[0116] When a feeder fault occurs on a port using PQ control in a flexible multi-state switch, the port is smoothly switched to VSG control to ensure continuous power supply to the passive network.

[0117] When using U dc When a feeder failure occurs on a port controlled by -Q, the port is first smoothly switched to VSG control; at the same time, the PQ control port with the largest capacity is selected from the remaining ports and switched to U dc -Q control, as a new voltage stabilization port, to maintain the stability of the DC side voltage of the flexible multi-state switch;

[0118] Establish the remaining capacity calculation equation:

[0119]

[0120] Where: S is the apparent power of the port converter; S max is the rated capacity of the port converter; S r is the remaining capacity of the port converter.

[0121] It should be noted that the above embodiments are not intended to limit the scope of protection of the present invention, and equivalent changes or substitutions made on the basis of the above technical solutions fall within the scope of protection of the claims of the present invention.

Claims

1. A control mode smooth switching method for a multi-port flexible multi-state switch, characterized in that: The steps include: Step S1, topological structure and mathematical model of flexible multi-state switch; Step S2, control strategy modeling of the flexible multi-state switch; Step S3: Establish a full-process mode smooth switching method based on the coordination of state tracking control and synchronous grid-connected control.

2. The control mode smooth switching method of a multi-port flexible multi-state switch according to claim 1, characterized in that: Step S1, topological structure and mathematical model of flexible multi-state switch; The flexible multi-state switch is a flexible interconnected device composed of fully controlled power electronic devices. It consists of at least three voltage source converters. The DC side is symmetrically connected through parallel capacitors, and the AC side is connected to the grid through a distribution transformer. Based on the symmetrical structure of the flexible multi-state switch, the converter on one side of the switch is modeled: The mathematical model of the single-side port is established in the dq rotating coordinate system as shown below: Where i=1, 2, 3, which are port numbers; R and L are equivalent resistance and filter inductance; C and C are dc is the filter capacitor and DC side capacitor; i di 、i qi are the d-axis and q-axis components of the converter output current; E di 、E qi are the d and q axis components of the AC voltage; s di 、s qi are the d and q axis components of the switching function; ω is the angular frequency; U dc is the DC side voltage; i Edi 、i Eqi are the d and q axis components of the AC current; The power flow of the flexible multi-state switch satisfies the following relationship: Where, P i is the active power of port i; I dci is the current flowing into the DC side from port i.

3. The control mode smooth switching method of a multi-port flexible multi-state switch according to claim 1, characterized in that: Step S2, control strategy modeling of the flexible multi-state switch; Each port of the flexible multi-state switch contains a grid-connected controller and an off-grid controller, which can switch the control mode according to the operating status: In normal grid-connected operation, PQ and U dc -Q control strategy regulates the power flow of the flexible multi-state switch and stabilizes the DC side voltage to ensure stable power transmission; in the event of a fault and disconnection from the grid, it switches to the VSG control strategy to ensure continuous power supply to critical loads; Step S2.1, PQ control, its outer loop generates a set value based on the power demand of the flexible multi-state switch, and converts the difference between the power set value and the actual calculated value into the d-axis and q-axis current reference values ​​through the PI controller: Where, I dref , I qref is the d-axis and q-axis current reference value; P ref , Q ref is the power setting value; P and Q are the active power and reactive power output by the port; K p , K i are the proportional coefficient and integral coefficient of the power outer loop; s is the complex variable in Laplace transform; The inner loop generates a voltage reference based on the current reference and modulates the actual output voltage to ensure that the output current accurately follows the set value: Where: u d * 、u q * is the voltage reference value; K pi , K ii is the PI parameter of the current inner loop; I d , I q Output current for d-axis and q-axis; u d 、u q are the d-axis and q-axis voltages, respectively, Step S2.2, U dc -Q control is a double closed-loop structure. The outer loop generates the d-axis current reference value I through the PI controller according to the difference between the DC voltage set value and the actual value. dref : Where: U dcref is the DC voltage setting value; K p,Udc , K i,Udc is the DC voltage outer loop PI parameter; In step S2.3, VSG control, its active power-frequency loop dynamically adjusts the output voltage frequency to respond to active power fluctuations, achieves autonomous frequency stabilization, and establishes the virtual rotor motion equation: Where, Δω=ω-ω0 is the angular frequency deviation, ω0 is the rated angular frequency; P m 、P e is the mechanical power and electromagnetic power; J and D are the virtual inertia and damping; Among them, P m The expression is as follows: P m =(ω0-ω)D p +P ref (9) Where: D p is the power frequency droop coefficient; The reactive-voltage loop of the VSG adjusts the output voltage amplitude based on the reactive-voltage droop characteristics, maintains the voltage level in the power-off area, and establishes the virtual excitation control equation: E=(Q ref -Q)D q +E0 (10) Where: E0, E are the reference voltage and output voltage; D q is the reactive power droop coefficient.

4. The control mode smooth switching method of a multi-port flexible multi-state switch according to claim 1, characterized in that: Step S3: establishing a full-process mode smooth switching method based on the coordination of state tracking control and synchronous grid connection control; The smooth switching method is based on state tracking control. When a feeder fails, it ensures that the output states of the off-grid controller and the grid-connected controller are consistent during the mode switching process, thereby significantly reducing transient impacts. After the fault is cleared, the voltage amplitude, phase and frequency of the VSG are synchronized with the grid through synchronous grid-connected control, which reduces the current impact at the time of grid connection and achieves smooth grid connection; Dynamically adjust the mode switching process based on the operating mode of the faulty port to ensure smooth switching under different working conditions, improving the system's anti-interference ability and power supply reliability; Step S3.1, state tracking control is: In the normal grid-connected operation state, the system maintains the connection between the grid-connected controller and the SPWM, and the logic variable i (i = 1 is PQ mode, i = 0 is U dc -Q mode) realizes flexible switching between the two control strategies. At the same time, the off-grid controller and SPWM remain disconnected. It forms tracking feedback by comparing the voltage reference signal output by the grid-connected controller with the difference between its own output in real time, and forms tracking feedback after PI adjustment, so that the output state of the off-grid controller always follows the grid-connected controller, ensuring the synchronization of the two. When the feeder fault triggers the mode switch, the system first disconnects the grid-connected controller from the SPWM and connects the off-grid controller to the SPWM. During this process, the off-grid controller exits the tracking state of the grid-connected controller, and the grid-connected controller starts to track the output voltage of the off-grid controller. Since the off-grid controller has been pre-synchronized with the output state of the grid-connected controller, the SPWM modulation signal can achieve a smooth transition, effectively avoiding the instantaneous impact of voltage and current, thereby completing the transition from PQ / U dc -Seamless switching from Q mode to VSG mode, Step S3.2, synchronous grid-connected control consists of amplitude synchronization control and phase synchronization control; Amplitude synchronization control uses a PI controller to adjust the difference between the grid and VSG voltage amplitudes to obtain a voltage correction value, which is then input into the virtual excitation controller to dynamically adjust the output voltage amplitude of the VSG to keep it consistent with the grid. Phase synchronization control adjusts the phase difference between the grid and VSG through a phase-locked loop and a PI controller to obtain an angular velocity correction value, which is then input into the virtual speed controller. Establish synchronous control equation: Where: θ, θ g is the VSG output phase and grid phase; ΔE is the output of the VSG reactive-voltage loop; E g is the grid voltage amplitude; K pω , K iω , K pE , K pE are the PI coefficients of phase and amplitude; Step S3.3, the mode smooth switching process is as follows: When a feeder fault occurs on a port using PQ control in a flexible multi-state switch, the port is smoothly switched to VSG control to ensure continuous power supply to the passive network. When using U dc When a feeder failure occurs on a port controlled by -Q, the port is first smoothly switched to VSG control; at the same time, the PQ control port with the largest capacity is selected from the remaining ports and switched to U dc -Q control, as a new voltage stabilization port, to maintain the stability of the DC side voltage of the flexible multi-state switch; Establish the remaining capacity calculation equation: Where: S is the apparent power of the port converter; S max is the rated capacity of the port converter; S r is the remaining capacity of the port converter.

5. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein: When the processor executes the program, the control mode smooth switching method of the multi-port flexible multi-state switch according to any one of claims 1 to 4 is implemented.

6. A computer-readable storage medium having computer instructions stored thereon, characterized in that: When the computer instruction is executed by a processor, the control mode smooth switching method of the multi-port flexible multi-state switch according to any one of claims 1 to 4 is implemented.

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