Self-adaptive zero sequence suppression network construction type composite control method and self-adaptive zero sequence suppression network construction type composite control system

Abstract

The invention relates to the technical field of power distribution networks, in particular to a self-adaptive zero-sequence suppression network construction type composite control method and system, and the method comprises the steps: collecting three-phase network voltage data according to the operation condition of a power distribution network, and recognizing the fault type; if the fault type is identified to be an asymmetric fault working condition, executing a corresponding zero-sequence suppression control strategy according to the transmission direction of the zero-sequence component; and if the fault type is identified to be a symmetric drop fault condition or a power grid dynamic fluctuation condition, executing a network construction type control strategy. Through the control method and system, the risk of maloperation can be reduced, and the effect of suppressing the zero-sequence voltage and the zero-sequence current at the same time can be achieved. Meanwhile, a suppression control strategy for transmitting a direct-current side common-mode component to an alternating-current side and a strategy for carrying out control processing on fault working conditions except an asymmetric fault working condition are provided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution networks, in particular to a network-structured composite control method and system for adaptive zero sequence suppression. BACKGROUND

[0002] With the increase of new energy access and the increase of network structure complexity, the local power distribution network presents the characteristics of weak grid strength and poor power quality. The classic phase-locked loop and positive and negative sequence control used in the existing grid-connected control cannot adapt to the impedance dynamic changes of the weak power distribution network, causing a series of problems such as frequency fluctuation. At the same time, the zero sequence current existing in the unbalanced power distribution network can cause common-mode voltage, which has great harm to the safe and stable operation of the power distribution network.

[0003] In the prior art, a Chinese patent application with the publication number CN115720043A and the publication date of February 28, 2023 is disclosed, and the technical solution disclosed in the patent document is as follows: A fault discrimination and zero sequence suppression method and system for a non-coupled variable power distribution network, which utilizes the amplitude difference characteristics of the zero sequence component of the AC voltage of each MMC converter caused by zero sequence current closed-loop control, to accurately and quickly locate the fault station. The conditions for distinguishing the fault station and the non-fault station are obtained by comprehensive comparison of the working conditions of each end, and the working conditions of each end can be mutually referenced to avoid the failure to timely identify and locate faults or misjudgment due to the inadaptability of the distinguishing conditions to the actual working conditions, thereby improving the reliability of fault discrimination. According to the different characteristics of the fault station and the non-fault station, different zero sequence voltage feed-forward suppression modes are set, and two different and replaceable suppression conditions are set for the zero sequence voltage feed-forward suppression of the non-fault station.

[0004] In the actual use process of the above technical solution, since the collected data is the AC zero sequence voltage at the converter, if other faults occur at the converter or the converter itself fails, the identification in the technical solution may be misjudged, resulting in protection misoperation. Moreover, the technical solution does not consider the transmission of zero sequence components from the DC side to the AC side, nor does it consider the control and processing of fault conditions other than asymmetric fault conditions. SUMMARY

[0005] To solve the above technical problems, the present application proposes a network-structured composite control method and system for adaptive zero sequence suppression, which can reduce the risk of misoperation and achieve the effect of simultaneous suppression of zero sequence voltage and zero sequence current. Meanwhile, the present application also proposes an inhibition control strategy for the transmission of common-mode components from the DC side to the AC side and a strategy for controlling and processing fault conditions other than asymmetric fault conditions.

[0006] The present application is achieved by adopting the following technical solutions: A network-structured composite control method with adaptive zero sequence suppression, comprising the following steps: Step S1. According to the operation condition of the power distribution network, collect three-phase power grid voltage data, and identify the fault type; Step S2. If the identified fault type is an asymmetric fault condition, perform the corresponding zero sequence suppression control strategy according to the transmission direction of the zero sequence component; if the identified fault type is a symmetric drop fault condition or a power grid dynamic fluctuation condition, perform the network-structured control strategy.

[0007] The fault type identification method is to detect the positive sequence component of the power grid voltage , calculate the maximum value of the three-phase power grid voltage amplitude ; if , it is judged that the fault type is an asymmetric fault condition; if , it is judged that the fault type is a symmetric fault condition or a power grid dynamic fluctuation condition; in the formula, is the voltage rated value.

[0008] The zero sequence suppression strategy comprises the following steps: Step S 211 . Separate positive and negative zero sequences, separate zero sequence components, positive sequence components and negative sequence components; Step S 212 . According to the transmission direction of the zero sequence component, the corresponding control is performed on the zero sequence component; the positive sequence component and the negative sequence component are controlled independently; Step S 213 . SPWM modulation.

[0009] According to the transmission direction of the zero sequence component, the corresponding control is performed on the zero sequence component, which specifically refers to: If the zero sequence component is transmitted from the alternating current side to the direct current side, the zero sequence component of the virtual potential is controlled as follows: , , If the zero sequence component is transmitted from the direct current side to the alternating current side, the zero sequence component of the virtual potential is controlled as follows: , , In the above formula, is the zero sequence component of the three-phase alternating current voltage, is the virtual voltage, R is the equivalent resistance of the bridge arm, L is the equivalent inductance of the bridge arm, is the zero sequence component of the three-phase alternating current, is the phase power grid voltage amplitude, is an initial phase of the phase voltage, is an angular velocity, is a time.

[0010] The network configuration type control strategy specifically comprises the following steps: Step S 221 . Real-time adjustment of the adjustable droop coefficient of each end according to the size of the active power fluctuation range; Step S 222 . According to the optimized adjustable droop coefficient, the system frequency and the DC voltage are coupled, and the voltage and power are closed-loop controlled; Step S 223 . Closed-loop control of the current; Step S 224 . SPWM modulation.

[0011] The adjustment method of the adjustable droop coefficient is: , In the formula, is the initial value of the adjustable coefficient, is the droop coefficient adjustment amount; U dcmax is the upper limit of the DC voltage, and P is the actual output power, P set is the preset power deviation size, is the rated value of the DC voltage, is the active power rated value, is the adjustable droop coefficient with power distribution.

[0012] The method for closed-loop control of the voltage and power is: , , In the formula, J is the virtual moment of inertia, and are the active power reference value and the rated value respectively, ω is the angular velocity, is the rated angular velocity of the power grid, and are the DC voltage reference value and the rated value respectively, is the inertia coefficient, is the adjustable droop coefficient with power distribution, C is the total capacitance value of the DC side, is the difference between the actual power and the rated power.

[0013] Closed-loop control of the current specifically refers to: employing a differential-mode voltage triggering mechanism to introduce current feedback control; when the current negative feedback controller uses PI regulation, constructing a differential-mode voltage for current loop tracking control. , Equation; where, This represents the differential voltage adjustment value along the d-axis. This represents the differential voltage adjustment value in the q-axis direction.

[0014] Differential-mode voltage of the constructed current loop tracking control , The equation is: , In the formula, and These are the d-axis and q-axis components of the grid current, respectively. and These are the reference values ​​for the d-axis and q-axis components of the grid current, respectively. and These are the d-axis and q-axis components of the grid voltage, respectively. The rated angular velocity of the power grid, 、 and 、 These are the coefficients of the proportional and integral elements, respectively; L is the grid-side inductance; and S is the state equation variable.

[0015] An adaptive zero-sequence suppression network-type composite control system includes: The fault type identification unit is used to identify the fault type based on the collected three-phase power grid voltage data; The zero-sequence suppression control unit is used to execute the corresponding zero-sequence suppression control strategy according to the asymmetric fault condition and the transmission direction of the zero-sequence component. The grid-type control unit is used to execute grid-type control strategies based on symmetrical drop fault conditions or grid dynamic fluctuation conditions.

[0016] The zero-sequence suppression control unit includes: The positive and negative zero sequence separation module is used to extract the zero sequence component, positive sequence component, and negative sequence component; The separation control module is used to control the zero-sequence component according to the propagation direction of the zero-sequence component and generate corresponding control signals. The zero-sequence control loop is used to suppress the zero-sequence component based on the control signal given by the separation and control module. The positive sequence control loop is used to control the positive sequence components; The negative sequence control loop is used to control the negative sequence components. The SPWM modulation module is used to synthesize the output signals of the zero-sequence control loop, positive-sequence control loop, and negative-sequence control loop. After SPWM modulation, the final control command is generated to trigger the pulse signal.

[0017] The network-type control unit includes: The coefficient optimization module is used to adjust the adjustable droop coefficients at each end in real time according to the magnitude of the active power fluctuation range. The voltage-power loop is used to couple the system frequency with the DC voltage based on the optimized adjustable droop coefficient, and to perform closed-loop control of voltage and power. A current loop is used for closed-loop control of the current. The SPWM modulation module is used to synthesize the output signals of the voltage-power loop and the current loop. After SPWM modulation, the final control command is generated to trigger the pulse signal.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This method and system can formulate corresponding control strategies based on different fault types, including zero-sequence suppression control strategies and grid-based control strategies. When performing zero-sequence suppression control, starting from the relationship between zero-sequence voltage and zero-sequence current, a zero-sequence component suppression strategy is proposed by combining direct suppression of zero-sequence current with leading control of zero-sequence voltage, achieving the effect of simultaneously suppressing zero-sequence voltage and zero-sequence current. Simultaneously, a suppression control strategy for the transmission of DC-side common-mode components to the AC side is proposed. Through this zero-sequence suppression method, the transmission of zero-sequence components from faulty feeders to non-faulty feeders is blocked. Compared with traditional grid-based control methods, this method improves the power support capability of flexible interconnection equipment and enhances system stability.

[0019] 2. In this invention, the grid-side voltage is used as the criterion when identifying fault types, which can reduce the risk of device malfunction and has higher reliability.

[0020] 3. In this invention, the adjustable droop coefficients at each end can be adjusted in real time according to the magnitude of the active power fluctuation range. This allows for adjustment of power distribution capabilities at each end. As the power fluctuation range increases, the droop coefficient decreases accordingly, improving the system's power distribution capability. Simultaneously, the synchronous machine rotor motion equation and the DC capacitor dynamic equation are introduced to couple the system frequency with the DC voltage, providing inertial support for the connected weak power grid system and contributing to enhanced frequency stability. Attached Figure Description

[0021] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments, wherein: Figure 1 This is a schematic diagram of the system structure in this invention; Figure 2 Flowchart of the zero sequence suppression control strategy in the present application; Figure 3 Flowchart of the network configuration type control strategy in the present application. DETAILED DESCRIPTION

[0022] Embodiment 1 As a basic embodiment of the present application, the present application comprises a network configuration type composite control method with adaptive zero sequence suppression, comprising the following steps: Step S1. According to the operation condition of the power distribution network, three-phase power grid voltage data are collected, and the fault type is identified. The fault type includes asymmetric fault condition, symmetric drop fault condition and power grid dynamic fluctuation condition.

[0023] Step S2. If the identified fault type is asymmetric fault condition, the corresponding zero sequence suppression control strategy is executed according to the transmission direction of the zero sequence component. If the identified fault type is symmetric drop fault condition or power grid dynamic fluctuation condition, the network configuration type control strategy is executed.

[0024] Embodiment 2 As a preferred embodiment of the present application, the present application comprises a network configuration type composite control method with adaptive zero sequence suppression, comprising the following steps: Step S1. According to the operation condition of the power distribution network, three-phase power grid voltage data are collected, and the fault type is identified. Specifically, the identification method of the fault type is: detecting the positive sequence component of the power grid voltage , calculating the maximum value of the three-phase power grid voltage amplitude . If , it is judged that the fault type is asymmetric fault condition. If , it is judged that the fault type is symmetric fault condition or power grid dynamic fluctuation condition. Wherein, is the voltage rated value.

[0025] Step S2. If the identified fault type is asymmetric fault condition, the corresponding zero sequence suppression control strategy is executed according to the transmission direction of the zero sequence component. If the identified fault type is symmetric drop fault condition or power grid dynamic fluctuation condition, the network configuration type control strategy is executed.

[0026] Specifically, the zero sequence suppression strategy comprises the following steps: Step S 211 . Positive and negative zero sequence separation, separating zero sequence component, positive sequence component and negative sequence component.

[0027] Step S 212 . According to the transmission direction of the zero sequence component, the zero sequence component is controlled correspondingly. The positive sequence component and the negative sequence component are controlled independently.

[0028] Step S 213 .SPWM modulation.

[0029] The network configuration type control strategy specifically comprises the following steps: Step S 221 . Real-time adjustment of the adjustable droop coefficient of each end according to the size of the active power fluctuation range.

[0030] Step S 222 . According to the optimized adjustable droop coefficient, the system frequency is coupled with the DC voltage, and the voltage and power are closed-loop controlled.

[0031] Step S 223 . Closed-loop control of the current.

[0032] Step S 224 .SPWM modulation.

[0033] Embodiment 3 As another preferred embodiment of the present application, the present application comprises a network configuration type composite control method with adaptive zero sequence suppression, comprising the following steps: Step S1. According to the operation condition of the power distribution network, three-phase grid voltage data are collected, and the fault type is identified.

[0034] Step S2. If the identified fault type is an asymmetric fault condition, according to the transmission direction of the zero sequence component, the corresponding zero sequence suppression control strategy is executed. If the identified fault type is a symmetric drop fault condition or a grid dynamic fluctuation condition, the network configuration type control strategy is executed.

[0035] Specifically, the zero sequence suppression strategy comprises the following steps: Step S 211 . Positive and negative zero sequence separation, separating the zero sequence component, the positive sequence component and the negative sequence component.

[0036] Step S 212 . According to the transmission direction of the zero sequence component, the zero sequence component is controlled correspondingly; the positive sequence component and the negative sequence component are controlled independently.

[0037] Among them, according to the transmission direction of the zero sequence component, the zero sequence component is controlled correspondingly specifically as follows: If the zero sequence component is transmitted from the AC side to the DC side, the zero sequence component of the virtual potential is controlled as follows: , , If the zero sequence component is transmitted from the DC side to the AC side, the zero sequence component of the virtual potential is controlled as follows: , , In the above formula, wherein, is a three-phase alternating voltage zero sequence component, is a virtual voltage, R is a bridge arm equivalent resistance, L is a bridge arm equivalent inductance, is a three-phase alternating current zero sequence component, is a phase grid voltage amplitude, is a phase voltage initial phase, is an angular velocity, is a time.

[0038] Step S 213 .SPWM modulation.

[0039] The network construction type control strategy specifically comprises the following steps: Step S 221 . Real-time adjustment of the adjustable droop coefficient of each end according to the size of the active power fluctuation range.

[0040] Step S 222 . According to the optimized adjustable droop coefficient, the system frequency and the DC voltage are coupled, and the voltage and power are closed-loop controlled.

[0041] Step S 223 . Closed-loop control of the current. Specifically, a differential mode voltage triggering mechanism is adopted, and current feedback control is introduced; when the current negative feedback controller adopts PI regulation, the differential mode voltage , equation is constructed for current loop tracking control; wherein, represents the differential mode voltage adjustment value in the d-axis direction, represents the differential mode voltage adjustment value in the q-axis direction.

[0042] Step S 224 .SPWM modulation.

[0043] Embodiment 4 As another preferred embodiment of the present application, the present application comprises a network construction type composite control method with adaptive zero sequence suppression, comprising the following steps: Step S1. According to the operating condition of the distribution network, three-phase grid voltage data is collected, and the fault type is identified. Specifically, it comprises the following steps: Step S 11 . The A-phase, B-phase and C-phase grid voltage drop amplitudes are respectively ε1 U g , ε2 U g and ε3 Ug , 0≤ε1, ε2, ε3≤1, the three-phase grid voltage instantaneous value is, satisfying: , In the formula, ε1, ε2, ε3 are percentage coefficients of three-phase voltage drop, and 0≤ε1, ε2, ε3≤1; U g is a phase grid voltage amplitude; , and are three-phase grid voltage instantaneous values respectively; ω is an electrical angular velocity.

[0044] Step S 12 . Obtain u α and u β components by Clark transformation, and further obtain three-phase grid voltage equivalent amplitude expression: , The expressions of A, B, C and D in the above formula are as follows: , In the formula, u α and u β are Clark transformation quantities; is a three-phase grid voltage equivalent amplitude.

[0045] Step S 13 . Detect the positive sequence component of grid voltage , and according to the maximum value of three-phase grid voltage amplitude calculated above , set the voltage rated value as , judge the fault type: If , judge the fault type as asymmetric fault condition. If , judge the fault type as symmetric fault condition or grid dynamic fluctuation condition.

[0046] Step S2. If the fault type is identified as asymmetric fault condition, execute the corresponding zero sequence suppression control strategy according to the transmission direction of zero sequence component. If the fault type is identified as symmetric drop fault condition or grid dynamic fluctuation condition, execute the network type control strategy.

[0047] The transmission direction of zero sequence component includes transmission from alternating current side to direct current side and transmission from direct current side to alternating current side. Referring to the description attached Figure 2 , the zero sequence suppression strategy includes the following steps: Step S 211. Positive, negative and zero sequence separation, separating zero sequence component, positive sequence component and negative sequence component. Specifically, using symmetrical component method, separating positive sequence component, negative sequence component and zero sequence component: , In the formula: , And The positive sequence component, negative sequence component and zero sequence component of three-phase alternating current respectively; , And The positive sequence component, negative sequence component and zero sequence component of three-phase alternating current respectively; , And The positive sequence component, negative sequence component and zero sequence component of virtual potential respectively; The virtual voltage; R The equivalent resistance of bridge arm, L The equivalent inductance of bridge arm.

[0048] Step S 212 . According to the transmission direction of zero sequence component, the corresponding control is carried out on zero sequence component. Specifically, if the zero sequence component is transmitted from the alternating current side to the direct current side, the zero sequence component of virtual potential The following control is made: , , If the zero sequence component is transmitted from the direct current side to the alternating current side, the zero sequence component of virtual potential The following control is made: , , In the above formula, The phase grid voltage amplitude, The initial phase of phase voltage, The angular velocity, The time.

[0049] The positive sequence component and the negative sequence component are controlled independently.

[0050] Step S 213 . SPWM modulation is used to synthesize the above output signal. After SPWM modulation, the final control instruction is generated, the trigger pulse signal is generated, the power electronic device is driven, and the effective suppression of zero sequence component is realized.

[0051] Referring to the description attached Figure 3 , the network construction type control strategy specifically includes the following steps: Step S 221. Real-time adjustment of adjustable droop coefficient of each terminal according to the size of active power fluctuation range. Among them, the adjustment method of adjustable droop coefficient is: , In the formula, is the initial value of the adjustable coefficient, is the droop coefficient adjustment amount; U dcmax is the upper limit of DC voltage, P is the actual output power, P set is the preset power deviation size, is the rated value of DC voltage, is the active power rated value, is the adjustable droop coefficient with power distribution.

[0052] Step S 222 . According to the optimized adjustable droop coefficient, the system frequency and the DC voltage are coupled, and the voltage and power are closed-loop controlled. Specifically, according to the mechanical rotation equation of the synchronous generator, the voltage and power can be closed-loop controlled: , , In the formula, J is the virtual moment of inertia, and are the active power reference value and the rated value respectively, ω is the angular velocity, is the rated angular velocity of the power grid, and are the DC voltage reference value and the rated value respectively, is the inertia coefficient, is the adjustable droop coefficient with power distribution, C is the total capacitance value of the DC side, is the difference between the actual power and the rated power.

[0053] Step S 223 . Closed-loop control of current: in order to make the control amount output by voltage-power control accurately trigger pulse, differential mode voltage trigger mechanism is adopted, and current feedback control is introduced; when the current negative feedback controller adopts PI regulation, the differential mode voltage , equation of current loop tracking control is constructed; wherein, represents the differential mode voltage adjustment value in the d-axis direction, represents the differential mode voltage adjustment value in the q-axis direction.

[0054] The differential mode voltage , equation of current loop tracking control constructed is: , wherein, and are the d-axis and q-axis components of the grid current, and are the reference values of the d-axis and q-axis components of the grid current, and are the d-axis and q-axis components of the grid voltage, is the grid rated angular velocity, 、 and 、 are the proportional and integral gains, L is the grid-side inductance, and S is the state equation variable.

[0055] Step S 224 SPWM modulation. The output signals are synthesized to generate the final control command after SPWM modulation, trigger the pulse signal, drive the power electronic device, and realize stable operation of the system.

[0056] Embodiment 5 As another preferred embodiment of the present application, the present application includes a network configuration type composite control system with adaptive zero sequence suppression, which can realize the control method described in any one of embodiments 1 to 4, and the control system is described in detail with reference to the accompanying drawings. Figure 1 , the control system comprises: a fault type identification unit for identifying the fault type according to the collected three-phase grid voltage data.

[0057] a zero sequence suppression control unit for executing corresponding zero sequence suppression control strategies according to the asymmetric fault condition and the transmission direction of the zero sequence component. Specifically, the zero sequence suppression control unit comprises: a positive and negative zero sequence separation module for separating the zero sequence component, the positive sequence component and the negative sequence component; a separation control module for controlling the zero sequence component according to the transmission direction of the zero sequence component to generate a corresponding control signal; a zero sequence control loop for suppressing the zero sequence component according to the control signal given by the separation control module; a positive sequence control loop for controlling the positive sequence component; a negative sequence control loop for controlling the negative sequence component; an SPWM modulation module for synthesizing the output signals of the zero sequence control loop, the positive sequence control loop and the negative sequence control loop, generating the final control command after SPWM modulation, and triggering the pulse signal.

[0058] A network-constructing control unit is configured to execute a network-constructing control strategy according to a symmetrical drop-out fault condition or a power grid dynamic fluctuation condition. The network-constructing control unit comprises: A coefficient optimization module is configured to adjust the adjustable droop coefficients of each terminal in real time according to the size of the active power fluctuation range; A voltage-power loop is configured to couple the system frequency and the DC voltage according to the optimized adjustable droop coefficients, and to perform closed-loop control on the voltage and the power; A current loop is configured to perform closed-loop control on the current; An SPWM modulation module is configured to synthesize the output signals of the voltage-power loop and the current loop, and to generate final control instructions after SPWM modulation, and to trigger pulse signals.

[0059] When it is detected that the power grid voltage is an asymmetrical drop-out fault, the switch S1 is opened and the switch S2 is closed, and at this time, the zero sequence suppression control strategy is executed; when it is detected that the power grid is dynamically fluctuating or a symmetrical drop-out fault occurs, the switch S1 is closed and the switch S2 is opened, and at this time, the network-constructing control strategy is executed.

[0060] In summary, various corresponding transformation schemes made by those skilled in the art after reading the present application without creative mental effort according to the technical solutions and technical concepts of the present application all belong to the scope of protection of the present application.

Claims

1. A network configuration type composite control method of adaptive zero sequence suppression, characterized in that: The method comprises the following steps: Step S1. According to the operation condition of the power distribution network, three-phase grid voltage data are collected, and a fault type is identified; Step S2. If the identified fault type is an asymmetric fault condition, a corresponding zero-sequence suppression control strategy is executed according to the transmission direction of the zero-sequence component; if the identified fault type is a symmetric drop fault condition or a grid dynamic fluctuation condition, a network-forming control strategy is executed.

2. The network configuration type composite control method with adaptive zero sequence suppression according to claim 1, characterized in that: The fault type identification method comprises the steps of detecting positive sequence component of grid voltage , calculating maximum value of three-phase grid voltage amplitude ; if , judging that the fault type is asymmetric fault condition; if , judging that the fault type is symmetric fault condition or grid dynamic fluctuation condition; in the formula, is voltage rated value.

3. The network configuration type composite control method with adaptive zero sequence suppression according to claim 1, characterized in that: The zero-sequence suppression strategy comprises the following steps: Step S 211 . Positive and negative zero sequence separation, separating zero sequence component, positive sequence component and negative sequence component; Step S 212 . According to the transmission direction of the zero sequence component, the zero sequence component is controlled correspondingly; the positive sequence component and the negative sequence component are controlled independently respectively; Step S 213 SPWM modulation.

4. The network configuration type composite control method with adaptive zero sequence suppression according to claim 3, characterized in that: According to the transmission direction of the zero-sequence component, the zero-sequence component is controlled in correspondence, and the specific control is as follows: If the zero sequence component is transferred from the AC side to the DC side, the zero sequence component of the virtual potential The following control is performed: ， ， If the zero sequence component is transferred from the DC side to the AC side, the zero sequence component of the virtual potential The following control is performed: ， ， in the above formulae, is the zero sequence component of the three-phase alternating voltage, is the virtual voltage, R is the bridge arm equivalent resistance, L is the bridge arm equivalent inductance, is the zero sequence component of the three-phase alternating current, is the phase network voltage amplitude, is the initial phase of the phase voltage, is the angular velocity, is the time.

5. The network configuration type composite control method of claim 1 or 3, wherein: The network-forming control strategy specifically comprises the following steps: Step S 221 . Real-time adjustment of each terminal adjustable droop coefficient according to the size of active power fluctuation range; Step S 222 . According to the optimized adjustable droop coefficient, the system frequency is coupled with the direct current voltage, and the voltage and power are closed-loop controlled. Step S 223 . closed loop control of the current; Step S 224 SPWM modulation.

6. The network configuration type composite control method of claim 5, wherein: The adjustment method of the adjustable droop coefficient is as follows: ， In the formula, is the initial value of the adjustable coefficient, is the droop coefficient adjustment amount; U dcmax is the upper limit of the DC voltage, and P is the actual output power, P set is the preset power deviation size, is the rated value of the DC voltage, is the active power rated value, is the adjustable droop coefficient with power distribution.

7. The network configuration type composite control method of claim 6, wherein: The method for closed-loop control of voltage and power is as follows: ， ， wherein, J is a virtual moment of inertia, and are respectively an active power reference value and a rated value, ω is an angular velocity, is a grid rated angular velocity, and are respectively a DC voltage reference value and a rated value, is an inertia coefficient, is an adjustable droop coefficient with power distribution, C is a total capacitance value of the DC side, is a difference between an actual power and a rated power.

8. The network configuration type composite control method with adaptive zero sequence suppression according to claim 5, characterized in that: The closed-loop control of the current specifically refers to: adopting a differential mode voltage trigger mechanism, introducing current feedback control; when a PI regulation is adopted for the current negative feedback controller, a differential mode voltage equation for tracking control of the current loop is constructed , , wherein, represents a differential mode voltage adjustment value in the d-axis direction, represents a differential mode voltage adjustment value in the q-axis direction.

9. The network configuration type composite control method with adaptive zero sequence suppression according to claim 8, characterized in that: A constructed current loop tracks the control of differential mode voltage , The equation is: ， wherein and are the d- and q-axis components of the grid current, and are the reference values of the d- and q-axis components of the grid current, and are the d- and q-axis components of the grid voltage, is the grid rated angular velocity, 、 and 、 are the proportional and integral gains, L is the grid-side inductance, and S are the state equation variables.

10. A networked composite control system with adaptive zero sequence rejection, characterized by: Comprise: A fault type identification unit is configured to identify a fault type according to collected three-phase grid voltage data; A zero-sequence suppression control unit is configured to execute a corresponding zero-sequence suppression control strategy according to an asymmetric fault condition and the transmission direction of a zero-sequence component; A network-forming control unit is configured to execute a network-forming control strategy according to a symmetric drop fault condition or a grid dynamic fluctuation condition.

11. The networked composite control system with adaptive zero-phase sequence rejection of claim 10, wherein: The zero-sequence suppression control unit comprises: A positive and negative zero-sequence separation module is configured to extract a zero-sequence component, a positive-sequence component and a negative-sequence component; A separation regulation and control module is configured to control the zero-sequence component in correspondence according to the transmission direction of the zero-sequence component, and generate a corresponding control signal; A zero-sequence control loop is configured to suppress the zero-sequence component according to the control signal given by the separation regulation and control module; A positive-sequence control loop is configured to control the positive-sequence component; A negative-sequence control loop is configured to control the negative-sequence component; An SPWM modulation module is configured to synthesize the output signals of the zero-sequence control loop, the positive-sequence control loop and the negative-sequence control loop, generate a final control instruction after SPWM modulation, and trigger a pulse signal.

12. The networked composite control system with adaptive zero phase sequence rejection of claim 10, wherein: The network-forming control unit comprises: A coefficient optimization module is configured to adjust the adjustable droop coefficient of each end in real time according to the size of the active power fluctuation range; A voltage-power loop is configured to couple the system frequency and the DC voltage according to the optimized adjustable droop coefficient, and perform closed-loop control of voltage and power; A current loop is configured to perform closed-loop control of current; An SPWM modulation module is configured to synthesize the output signals of the voltage-power loop and the current loop, generate a final control instruction after SPWM modulation, and trigger a pulse signal.

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