A collaborative operation and fault recovery method for flexible interconnected microgrids considering active disturbance suppression

Abstract

A method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression includes: collecting state information of each microgrid, calculating local frequency / voltage recovery control compensation; calculating the compensation required for power sharing of distributed power sources in each microgrid, and the adjustment amount of each SOP required for power sharing between interconnected microgrids; and calculating the V dc Current feedforward compensation and additional frequency control are introduced at the ‑Q / P‑Q ports to optimize transient performance. In the event of a fault, the SOP port converter connected to the de-energized microgrid applies outer-loop state following, phase angle maintenance, and current estimation compensation, followed by a switch to V / f control. This method achieves seamless restoration of the frequency and critical bus voltage across microgrids, as well as power balancing between and within microgrids, while ensuring the dynamic regulation performance of the SOP and system transient stability. Furthermore, in the event of a fault, SOP control mode can be smoothly switched to ensure continuous, safe, and reliable system operation.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid group operation control, and in particular to a method for coordinated operation and fault recovery of a flexible interconnected microgrid group taking active disturbance suppression into consideration. Background Art

[0002] As an improved method, the intelligent soft open point (SOP) is used to connect multiple geographically adjacent microgrids, helping to flexibly adjust the bidirectional power flow between microgrids and achieve efficient utilization of various adjustable resources on a larger scale. However, due to the asynchronous decoupling characteristics of the SOP, frequency and voltage disturbances cannot be directly transmitted between microgrids, and the frequency convergence value of each microgrid is no longer directly related to the active power sharing ratio. Most existing methods determine the exchanged active and reactive power by the voltage / frequency on both sides of the SOP. However, after the additional frequency / voltage secondary control is applied to each microgrid, the SOP transmission power drops to zero, greatly reducing the effectiveness of power sharing. In addition, the SOP DC bus voltage directly affects the system stability. It often fluctuates due to changes in the system operating state, which causes the SOP transmission instructions to change. Even under large transient disturbances, the system crashes due to DC bus voltage instability.

[0003] Furthermore, SOP can achieve millisecond-level fault isolation and emergency control mode switching, rapidly transferring power and restoring power while maintaining stable operation. A reliable SOP control mode switching strategy is key to providing self-healing capabilities for faulty areas. Otherwise, the fault can escalate or recur due to sudden changes in controller state or power imbalances after the switch.

[0004] In summary, it is necessary to study a hierarchical collaborative operation control strategy for a flexible interconnected microgrid group that takes into account the dynamic anti-interference characteristics of SOP, as well as a fault recovery method based on emergency smooth switching of the SOP control mode, to achieve local autonomy of each microgrid under normal operating conditions and flexible power mutual assistance between microgrids, while also ensuring rapid power supply restoration of power-off loads under fault conditions, and comprehensively improving the stability, reliability and flexibility of the system. Summary of the Invention

[0005] In view of the deficiencies and gaps in the existing technology, the present invention provides a method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression to solve the problems existing in the above-mentioned background technology.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] On the one hand, a method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression is provided, including:

[0008] Step A: Collect the state information of each microgrid and calculate the secondary control compensation required for local frequency / key bus voltage recovery based on the collected state information of each microgrid;

[0009] Step B: Based on the pinning concept, a two-layer communication network is established between and within microgrid groups. A distributed consensus algorithm is used to calculate the compensation required for the active / reactive power sharing of the distributed generation (DG) within each microgrid, as well as the various SOP adjustments required to achieve global power sharing. The compensation required for the DG active / reactive power sharing and the secondary control compensation in step A are then superimposed on the droop control equations of each DG to achieve autonomous control within each microgrid.

[0010] Step C: Add the SOP adjustment values ​​obtained in step B to the local control V dc -Q and PQ control ports, while introducing current feedforward compensation and additional frequency control loops in the two-port converters of each SOP, so that the SOP has active anti-disturbance characteristics when adjusting the global power balance;

[0011] Step D: If a fault causes a microgrid to completely lose power and cannot participate in the system coordinated operation according to the above steps, the outer loop state quantity following, phase angle maintenance and estimated current compensation control are applied to the SOP port converter connected to the power-lost side after the fault, and the PQ control mode is switched to V / f control to provide frequency / voltage support for the power-lost load.

[0012] Furthermore, in step A, the secondary control compensation amount is calculated through the following steps A01 to A02 to achieve frequency / key bus voltage recovery of each microgrid:

[0013] Step A01: Measure the frequency signal and key bus voltage in each microgrid, and construct the frequency / voltage secondary controller of each microgrid according to the following formula:

[0014]

[0015] Where, Ω ωk,i ,Φ vk,i are the i-th distributed generation DG in microgrid k k,i Frequency and voltage secondary control compensation amount; i=1,2,…,n k ; k=1,2,…,m; k ωk,i ,k vk,i is the integral coefficient; ω k,i and DG k,i Output angular frequency and rated angular frequency of microgrid k; u k,c and are the actual value and rated value of the key bus voltage of microgrid k; g vk,i Indicates DGk,i Whether to receive the microgrid k key bus voltage rating information, if received, g vk,i =1, otherwise, g vk,i =0, there is only one DG in each microgrid that can receive the information;

[0016] Step A02: Ω calculated in step A01 is respectively ωk,i ,Φ vk,i By adding it to the droop control equation of each DG, the frequency of each microgrid and the key bus voltage can be stably restored to the rated value.

[0017] Furthermore, the step B specifically includes:

[0018] Step B01: Taking microgrid k as an example, set n k A DG is divided into 1 pinning node and n k -1 non-pinning node, the m pinning nodes of the m microgrids jointly establish a distributed sparse communication network, recorded as the inter-group communication network; and the non-pinning nodes in the m microgrids each establish m distributed sparse communication networks, recorded as the intra-group communication network;

[0019] Step B02: Based on the intra-group communication network constructed in step B01, the DG active power equalization compensation amount in each microgrid is calculated using the pinning consistency algorithm as follows: and reactive power sharing compensation

[0020] Where, and is the integration coefficient; is the i-th microgrid k kh Non-pinned nodes The set of neighbor nodes of Non-binding in the intra-group communication network arrive Communication link weight; m k,pin P k,pin (n k,pin Q k,pin )and are respectively the DG restrained and non-restrained in microgrid k The product of the active (reactive) droop coefficient and its output active (reactive) power, and is proportional to their respective capacities; is the active and reactive power containment gain;

[0021] Step B03: The compensation amount obtained in step B02 is and By superimposing the active and reactive droop equations of the corresponding non-constrained DG in the microgrid, the DG in each microgrid can achieve uniform output according to capacity; Step B04: Based on the inter-group communication network constructed in Step B01, the average consistency algorithm is used to calculate the active adjustment amount Ω of each SOP required for global power sharing according to the following formula Pk,pin and reactive power regulation Φ Qk,pin :

[0022]

[0023] Where k Pk,pin and k Qk,pin is the integration coefficient; is the set of neighbor nodes that control DG in microgrid k; a kl is the weight of the communication link from microgrid l to microgrid k; the subscript l,pin represents the pinned DG variable in microgrid l;

[0024] Step B05: The adjustment value Ω obtained in step B04 is converted to Pk,pin and Φ Qk,pin The integral is added to the PQ port of the SOP corresponding to the microgrid where the DG is located to generate the active reference value P that the SOP needs to transmit between the interconnected microgrids. ref,kl and reactive reference value Q ref,kl :

[0025]

[0026] Among them, P 0,kl and Q 0,kl K is the initial transmission power setting value of the SOP connecting microgrid k and microgrid l; Pkl and K Qkl is the active and reactive transmission power regulation gain.

[0027] Furthermore, in step C, current feedforward compensation and additional frequency adjustment are introduced into the SOP two-port converter control loop, specifically comprising the following steps:

[0028] Step C01: Solve the compensation current d-axis component i that has a coupling relationship with the SOP transmission power reference value according to the following formula: dVk and the q-axis component i qVk :

[0029]

[0030] Where u dk,c ,u qk,c are the dq axis components of the key bus voltage in microgrid k respectively;

[0031] Step C02: Add the compensation amount obtained in step C01 to the V of SOP.dc -Q converter outer loop proportional-integral controller output current correction value, generate the current inner loop dq axis reference value i dkref and i qkref :

[0032]

[0033] Where k pVk ,k pQk ,k iVk ,k iQk is the proportional-integral controller parameter; V dcklref and V dckl are the reference value and actual value of the SOP DC bus voltage connected to microgrid k and microgrid l, respectively, Q kl For its actual transmission of reactive power, after applying current feedforward compensation, V dc -Q port has active power balancing capability to effectively suppress DC bus voltage fluctuations when the SOP transmission power command suddenly changes;

[0034] Step C03: For the PQ converter of the SOP, the frequency values ​​of the microgrids on both sides of the interconnection are normalized and then subtracted, and the frequency dynamic compensation value δ is obtained after integration. ω,kl :

[0035]

[0036] Where k S,kl is the integral coefficient; the subscripts k and l represent the corresponding frequency values ​​of the microgrid k and l respectively;

[0037] Step C04: Substitute the δ obtained in step C03 ω,kl Added to the active reference value P of the PQ converter power outer loop ref,kl , which can generate compensation at the moment the system operating state changes to improve the regulation performance of each SOP.

[0038] Furthermore, in step D, outer loop state quantity following, phase angle holding, and estimated current compensation control are applied to the SOP port converter connected to the power-off side after the fault, thereby switching the PQ control mode to V / f control, which specifically includes the following steps:

[0039] Step D01: Before switching the SOP control mode, the Vf controller input signal is set to the difference between the PQ control outer loop output current reference value and the Vf control voltage outer loop output adjustment value, so that the Vf controller output is continuously adjusted according to the PQ controller; when switching is required after a fault, the Vf controller input signal is set to the rated voltage / frequency and connected to the same current inner loop of the PQ control at the same time, so that the current inner loop reference value remains unchanged before and after switching, ensuring a smooth transition of the voltage reference modulation signal amplitude;

[0040] Step D02: During the SOP control mode switching process, the phase angle θ is maintained during the PQ control period. PQkl Based on this, the set phase angle θ of Vf control is obtained as follows: Vfkl :

[0041] θ Vfkl =2πf ref / s+θ PQkl

[0042] Where, f ref is the frequency reference value, s is the Laplace operator;

[0043] Step D03: At the moment of SOP control mode switching, according to the active power shortage ΔP of the power-off microgrid kL and reactive power shortage ΔQ kL , the steady-state value i of the inner current loop dq axis after switching is estimated as follows: dkl and i qkl :

[0044]

[0045] Among them, u d,Vref and u q,Vref They are the dq axis voltage reference values ​​output after the SOP port converter switches to V / f control, and the i dkl and i qkl By subtracting the current input to the V / f control inner loop from the dq axis current reference value, the dynamic regulation performance of the SOP control mode switching process can be improved to accelerate fault recovery.

[0046] The present invention designs a method for cooperative operation and fault recovery of flexible interconnected microgrid groups with active disturbance suppression. The power mutual control between microgrids is converted into flexible regulation of the transmission power of each SOP by exchanging power state information of the restraining nodes in the inter-group communication network. The frequency / voltage of each microgrid is independently controlled, and the frequency and key bus voltage are guaranteed to be restored without difference based on local state measurement. dc -Q and PQ control sides respectively introduce current feedforward compensation and additional frequency terms based on the transmission power reference value to suppress the transient disturbance of DC bus voltage caused by changes in system operating conditions, while improving the dynamic adjustment performance of SOP power. In order to ensure the continuous and reliable power supply to the power-lost microgrid load after the fault, the present invention also implements emergency smooth switching of SOP control mode by applying three measures of synchronous following of outer loop state quantity, switching phase angle adjustment, and supply and demand current estimation compensation to the power-lost side SOP port converter, thereby accelerating fault recovery. The present invention provides a new idea for deep mining the application of SOP in microgrid groups. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 is a flow chart of the control method of the present invention;

[0048] Figure 2 It is a flexible interconnected microgrid group simulation test system used in the embodiment of the present invention;

[0049] Figure 3 : is a frequency waveform diagram of each microgrid in an embodiment of the present invention;

[0050] Figure 4 : is a waveform diagram of the key bus voltage of each microgrid in an embodiment of the present invention;

[0051] Figure 5 1 is a waveform diagram of the active power output of each distributed power source in the microgrid group in an embodiment of the present invention;

[0052] Figure 6 1 is a waveform diagram of reactive power output by each distributed power source in a microgrid group in an embodiment of the present invention;

[0053] Figure 7 In the embodiment of the present invention, the SOP adopts the anti-interference strategy and the traditional control strategy respectively. 12 DC bus voltage waveform comparison chart;

[0054] Figure 8 1 is a comparison diagram of the frequency waveform of the fault microgrid when the SOP control mode smooth switching strategy and hard switching are respectively adopted in the embodiment of the present invention;

[0055] Figure 9 1. A comparison diagram of the voltage waveforms of the key busbars of the faulty microgrid when the SOP control mode smooth switching strategy and hard switching are respectively adopted in the embodiment of the present invention;

[0056] Figure 10 In the embodiment of the present invention, the SOP control mode smooth switching strategy and the hard switching SOP are respectively adopted. 12 Comparison of transmitted active power waveforms. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0058] like Figure 1 As shown, the embodiment of the present invention designs a method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression. In practical application, the method specifically includes the following steps:

[0059] Step A: Collect the state information of each microgrid, calculate the secondary control compensation required for local frequency / key bus voltage recovery based on the collected microgrid state information, and then proceed to step B;

[0060] Step B: Based on the concept of pinning, a two-layer communication network is established between and within microgrid groups. A distributed consensus algorithm is used to calculate the compensation required for active / reactive power sharing of the distributed generation (DG) within each microgrid, as well as the various SOP adjustments required to achieve global power sharing. The calculated power compensation and the frequency / voltage secondary control compensation in step A are then superimposed on the droop control equations of each DG. This achieves autonomous control within each microgrid, and then proceeds to step C.

[0061] Step C: Add the SOP adjustment values ​​obtained in step B to the local controlled V dc -Q and PQ control ports, and at the same time introduce current feedforward compensation and additional frequency control loops into the two-port converters of each SOP, so that the SOP has active anti-interference characteristics when adjusting the global power balance, and then enter step D;

[0062] Step D: If a fault causes a microgrid to completely lose power and cannot participate in the system collaborative operation according to the above steps, the outer loop state quantity following, phase angle maintenance and estimated current compensation control are applied to the SOP port converter connected to the power-lost side, and the converter control mode is switched to V / f control to provide frequency / voltage support for the power-lost load.

[0063] In the above step A, the compensation amount required for each microgrid to achieve local frequency / critical bus voltage regulation recovery is calculated through the following steps A01 to A02:

[0064] Step A01: Collect the frequency signal and key bus voltage in each microgrid, and construct the frequency / voltage secondary controller of each microgrid according to the following formula:

[0065]

[0066] Where, Ω ωk,i ,Φ vk,i are the i-th distributed generation DG in microgrid k k,i Frequency and voltage secondary control compensation amount; i=1,2,…,n k ; k=1,2,…,m; k ωk,i ,k vk,i is the integral coefficient; ω k,i and DG k,i Output angular frequency and rated angular frequency of microgrid k; u k,c and are the actual value and rated value of the key bus voltage of microgrid k; g vk,i Indicates DG k,i Whether to receive the microgrid k key bus voltage rating information, if received, g vk,i =1, otherwise, g vk,i = 0. There is only one DG in each microgrid that can receive this information.

[0067] Step A02: Ω calculated in step A01 (1) is converted to ωk,i ,Φ vk,i It is added to the active / reactive power equation of each DG droop control to stabilize and restore the frequency of each microgrid and the key bus voltage to the rated value.

[0068] In the above step B, steps B01 to B05 calculate the compensation amount of the DG power divided equally by capacity in each microgrid and the SOP adjustment amount required for power sharing between microgrids:

[0069] Step B01: Taking microgrid k as an example, set n k A DG is divided into 1 pinning node and n k -1 non-pinned node. Further, the m pinned nodes of the m microgrids jointly establish a distributed sparse communication network, which is recorded as the inter-group communication network; and the non-pinned nodes in the m microgrids respectively establish m distributed sparse communication networks, which are recorded as the intra-group communication network.

[0070] Step B02: Based on the intra-group communication network constructed in step B01, the DG active power equalization compensation amount in each microgrid is calculated using the pinning consistency algorithm as follows: and reactive power sharing compensation

[0071] Where, and is the integration coefficient; is the i-th microgrid k kh Non-pinned nodes The set of neighbor nodes of Non-binding in the group communication network arrive Communication link weight; m k,pin P k,pin (n k,pin Q k,pin )and are respectively the DG restrained and non-restrained in microgrid k The product of the active (reactive) droop coefficient and its output active (reactive) power, and is proportional to their respective capacities; are the active and reactive power restraint gains.

[0072] Step B03: Substitute the equation (2) in step B02 and They are respectively superimposed on the active / reactive droop equations of the non-constrained DGs in the corresponding microgrids to achieve uniform output of DGs in each microgrid according to their capacity.

[0073] Step B04: Based on the inter-group communication network constructed in step B01, the average consistency algorithm is used to calculate the active power regulation amount Ω of each SOP required for global power sharing according to the following formula: Pk,pin and reactive power regulation Φ Qk,pin :

[0074]

[0075] Where k Pk,pin and k Qk,pin is the integration coefficient; is the set of neighbor nodes that control DG in microgrid k; a kl is the weight of the communication link from microgrid l to microgrid k; the subscript l,pin represents the restraining DG variable in microgrid l.

[0076] Step B05: Substitute the adjustment value Ω obtained by equation (3) in step B04 into Pk,pin and Φ Qk,pin The integral is added to the PQ port of the SOP corresponding to the microgrid where the DG is located to generate the active reference value P that the SOP needs to transmit between the interconnected microgrids. ref,kl and reactive reference value Q ref,kl :

[0077]

[0078] Among them, P 0,kl and Q 0,kl K is the initial transmission power setting value of the SOP connecting microgrid k and microgrid l; Pkl and K Qkl is the active and reactive transmission power regulation gain.

[0079] In the above step C, current feedforward compensation and additional frequency regulation are introduced into the SOP two-port converter control loop from steps C01 to C04:

[0080] Step C01: Solve the compensation current d-axis component i associated with the SOP transmission power reference value as follows: dVk and the q-axis component i qVk :

[0081]

[0082] Among them, udk,c ,u qk,c are the dq axis components of the key bus voltage in microgrid k, respectively.

[0083] Step C02: Compare the compensation value obtained by equation (5) in step C01 with the V dc -Q converter outer loop proportional-integral controller output current correction value superposition, generate the current inner loop dq axis reference value i dkref and i qkref :

[0084]

[0085] Where k pVk ,k pQk ,k iVk ,k iQk is the proportional-integral controller parameter; V dcklref and V dckl are the reference value and actual value of the SOP DC bus voltage connected to microgrid k and microgrid l, respectively, Q kl It actually transmits reactive power. After applying current feedforward compensation, V dc The -Q port has active power balancing capability to effectively suppress DC bus voltage fluctuations when the SOP transmission power instruction changes suddenly.

[0086] Step C03: For the PQ converter of the SOP, the collected frequency values ​​of the microgrids on both sides of the interconnection are normalized and then subtracted, and the frequency dynamic compensation value δ is obtained after integration. ω,kl :

[0087]

[0088] Where k S,kl is the integral coefficient; the subscripts k and l represent the corresponding frequency values ​​of the microgrid k and l, respectively.

[0089] Step C04: Substitute the δ obtained in equation (7) in step C03 into ω,kl and the active reference value P of the PQ converter power outer loop ref,kl Superposition can generate compensation at the moment when the system operating state changes to improve the SOP adjustment performance.

[0090] In the above step D, the following steps D01 to D03 are performed on the SOP port converter on the power-off side after the fault to implement outer loop state quantity following, phase angle maintenance, and estimated current compensation to achieve smooth switching of the control mode:

[0091] Step D01: Before switching the SOP control mode, set the Vf controller input signal to the difference between the PQ control outer loop output current reference value and the Vf control voltage outer loop output adjustment value, so that the Vf controller output is continuously adjusted according to the PQ controller; after the fault, when switching is required, set the Vf controller input signal to the rated voltage / frequency and connect it to the same current inner loop of the PQ control at the same time, so that the current inner loop reference value remains unchanged before and after switching, and ensure a smooth transition of the voltage reference modulation signal amplitude.

[0092] Step D02: During the SOP control mode switching process, it is necessary to maintain the phase angle θ during the PQ control period PQkl Based on this, the set phase angle θ of Vf control is obtained as follows: Vfkl :

[0093] θ Vfkl =2πf ref / s+θ PQkl Formula (8)

[0094] Among them, f ref is the frequency reference value, and s is the Laplace operator.

[0095] Step D03: Based on the active power shortage ΔP of the power-off microgrid kL and reactive power shortage ΔQ kL , estimate the steady-state value i of the dq axis of the current inner loop controlled by Vf according to the following formula: dkl and i qkl :

[0096]

[0097] Among them, u d,Vref and u q,Vref are the dq axis voltage reference values ​​output after the SOP port converter switches to V / f control. dkl and i qkl By subtracting the current input to the V / f control inner loop from the dq axis current reference value, the dynamic regulation performance of the SOP control mode switching process can be improved to accelerate fault recovery.

[0098] Apply the above-mentioned technical solutions to practice, the simulation system is as follows Figure 2 As shown in the figure, three microgrids (MGs) are connected in sequence through two SOPs to form a microgrid group. Each MG contains three DGs with the same capacity. The impedance of each line in the system is different. 11 ,DG 21 ,DG 31To contain the nodes and form an inter-cluster communication network. The reference value of the DC bus voltage of each SOP is 800V, and the initial value of the transmission power is set to 0. According to the embodiment of the present invention, a system controller is established for the coordinated operation and fault recovery method of a flexible interconnected microgrid group with disturbance suppression, and a simulation test model is built based on the MATLAB / Simulink simulation platform to verify the control effect of the method of the present invention.

[0099] Corresponding to Figure 2 , set up two simulation conditions: normal operation and microgrid power failure. The system normal operation simulation condition is set as follows:

[0100] 1) At the initial moment, the local droop control of the DG in each microgrid and the anti-disturbance suppression strategy of the SOP are activated;

[0101] 2) At 2 seconds, activate the frequency / voltage local secondary control and DG power sharing secondary control in each microgrid;

[0102] 3) At 4 seconds, global power sharing control is activated;

[0103] 4) At 7 seconds, the load of microgrid 2 increases by 30kW+j15kVar.

[0104] Figures 3 to 7 Corresponding to the simulation results under normal operating conditions in this embodiment. Figure 3 The frequency waveform of each microgrid is shown in Figure 1. The horizontal axis represents time in seconds, and the vertical axis represents frequency in Hertz. Figure 4 The waveform diagram of the key bus voltage of each microgrid is shown in Figure 1. The horizontal axis represents time in seconds, and the vertical axis represents voltage in volts. Figure 5 The waveform of the active power output of DG in each microgrid is shown in Figure 1. The horizontal axis represents time in seconds, and the vertical axis represents active power in kilowatts. Figure 6 The waveform of reactive power output by DG in each microgrid is shown in Figure 1. The horizontal axis represents time (unit: seconds), and the vertical axis represents active power (unit: kvar). Figure 7 The SOP under the conditions of applying the disturbance suppression method of the present invention and the traditional method respectively 12 The DC bus voltage waveform comparison chart shows time on the horizontal axis in seconds and voltage on the vertical axis in volts. Figures 3 to 6It can be seen that within 0 to 2 seconds, the frequency and key bus voltage of each microgrid deviate from the rated value and are different from each other, which reflects the differential regulation characteristics of droop control. Since the capacity of each DG is the same, active power equalization can be automatically achieved in each microgrid, while reactive power equalization cannot be achieved due to inconsistent path impedance; after 2 seconds, when the DG secondary control is activated in each microgrid, the DG in each microgrid outputs power evenly according to capacity, realizing accurate equalization of active and reactive power; after the global power equalization control is activated in 4 seconds, each SOP relies on the inter-group communication network to generate a transmission power reference value, and quickly adjusts the power mutual assistance between microgrids to realize the global DG distribution of active and reactive power according to capacity; after the load of microgrid 2 increases in 7 seconds, each SOP quickly responds to the change in system operating conditions, generates a new transmission power reference value, and makes the global power reach the equalization state again. The frequency / key bus voltage of each microgrid recovers to the rated value after a brief fluctuation. During the entire simulation process, the overshoot of global power equalization is small, which reflects that the method of the present invention has good dynamic regulation characteristics. Figure 7 It can be seen that the traditional SOP control method has a significant increase in the DC bus voltage to adjust the power balance at the moment of load increase, and the maximum deviation reaches ±28V. In comparison, when the control of the present invention is applied, the DC bus voltage only produces very small fluctuations. The SOP can quickly adjust the transmission power to achieve regional balance, which effectively suppresses the adverse effects caused by the sudden change of SOP transmission power.

[0105] Corresponding to Figure 2 ,The microgrid power failure simulation conditions are set as follows:

[0106] 1) At the initial moment, the system operates normally, the local frequency / voltage control of each microgrid, the global power sharing control, and the SOP disturbance suppression strategy are all started, and the outer loop state quantity following control of the SOP is activated;

[0107] 2) At 1.5 seconds, all DGs in microgrid 1 exit due to faults;

[0108] 3) After 20 milliseconds, the system detects a fault and simultaneously 12 The port converter starts phase angle holding and current estimation compensation control, and switches the control mode from PQ to V / f control to provide emergency power supply for the load on the power-off side.

[0109] Figures 8 to 10 The corresponding simulation results are as follows: Figure 8 This is a comparison diagram of the frequency waveform of the fault microgrid 1 when the SOP control mode smooth switching strategy and hard switching are adopted respectively. The horizontal axis represents time, unit: second, and the vertical axis represents frequency, unit: Hertz. Figure 9This is a comparison diagram of the key bus voltage waveforms of the fault microgrid 1 when the SOP control mode smooth switching strategy and hard switching are adopted respectively. The horizontal axis represents time, unit: second, and the vertical axis represents voltage, unit: volt. Figure 10 The SOP control mode smooth switching strategy and hard switching SOP are used respectively. 12 Transmission active power waveform comparison chart, the horizontal axis represents time, unit: second, the vertical axis represents active power, unit: kilowatt. Figures 8 to 10 It can be seen that after the fault occurs at 2 seconds, due to the imbalance of source and load, the frequency / key bus voltage of microgrid 1 drops rapidly until the fault measurement SOP at 1.52 seconds. 12 The port converter switches to V / f control and provides frequency / voltage support to the faulty microgrid, allowing the corresponding frequency / critical bus voltage to return to the rated value. This quickly compensates for the power supply and demand shortfall within microgrid 1, providing continuous and reliable power supply to the power-destroying load. Compared to the traditional SOP's hard switching control mode after a fault, the proposed method has a smaller frequency / voltage impact at the switching moment, recovers to the rated value faster, and reduces the SOP power overshoot, highlighting the effectiveness and superiority of the present invention.

[0110] The present invention proposes a method for coordinated operation and fault recovery of flexible interconnected microgrids that takes active disturbance suppression into consideration. First, the method uses local state quantity measurement to achieve independent control of the frequency / voltage of each microgrid and zero-error recovery. At the same time, the tracking control of the non-constrained DG in the intra-group communication network is used to achieve equal distribution of DG power in each microgrid. The inter-group communication network flexibly regulates the transmission power of each SOP, thus achieving power mutual assistance between microgrids. Secondly, by using the V dc -Q and PQ control sides respectively introduce current feedforward compensation and additional frequency terms based on transmission power to suppress the transient disturbance of DC bus voltage caused by complex changes in system operating conditions, while improving the SOP power dynamic regulation performance and enhancing the system's operational stability. For the continuous and reliable power supply of power-lost loads after system failure, the present invention also realizes the emergency smooth switching of the SOP control mode by combining the three measures of synchronous following of outer loop state quantity, switching phase angle adjustment, and supply and demand current estimation compensation, accelerates fault recovery, and improves the elasticity and sustainability of flexible interconnected microgrid groups. The present invention provides a feasible and effective implementation plan for deep mining the application of SOP in microgrid groups.

[0111] Throughout this specification, references to terms such as "one embodiment," "example," or "specific example" indicate that the specific features, structures, materials, or characteristics described in conjunction with that embodiment or example are included in at least one embodiment or example of the present invention. In this specification, schematic representations of these terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in any one or more embodiments or examples.

[0112] The basic principles, main features, and advantages of the present invention are shown and described above. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and descriptions are merely illustrative of the principles of the present invention. Various changes and modifications may be made to the present invention without departing from the spirit and scope of the present invention, and such changes and modifications fall within the scope of the invention as claimed.

Claims

1. A method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression, characterized in that: include: Step A: Collect the state information of each microgrid and calculate the secondary control compensation required for local frequency / key bus voltage recovery based on the collected state information of each microgrid; Step B: Based on the pinning concept, a two-layer communication network is established between and within microgrid groups. A distributed consensus algorithm is used to calculate the compensation required for the active / reactive power sharing of the distributed generation (DG) within each microgrid, as well as the various SOP adjustments required to achieve global power sharing. The compensation required for the DG active / reactive power sharing and the secondary control compensation in step A are then superimposed on the droop control equations of each DG to achieve autonomous control within each microgrid. Step C: Add the SOP adjustment values ​​obtained in step B to the local control V dc -Q and PQ control ports, while introducing current feedforward compensation and additional frequency control loops in the two-port converters of each SOP, so that the SOP has active anti-disturbance characteristics when adjusting the global power balance; Step D: If a fault causes a microgrid to completely lose power and cannot participate in the system coordinated operation according to the above steps, the outer loop state quantity following, phase angle maintenance and estimated current compensation control are applied to the SOP port converter connected to the power-lost side after the fault, and the PQ control mode is switched to V / f control to provide frequency / voltage support for the power-lost load.

2. A method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression according to claim 1, characterized in that: In step A, the secondary control compensation amount is calculated through the following steps A01 to A02 to achieve frequency / key bus voltage recovery of each microgrid: Step A01: Measure the frequency signal and key bus voltage in each microgrid, and construct the frequency / voltage secondary controller of each microgrid according to the following formula: Where, Ω ωk,i ,Φ vk,i are the i-th distributed generation DG in microgrid k k,i Frequency and voltage secondary control compensation amount; i=1,2,…,n k ; k=1,2,…,m; k ωk,i ,k vk,i is the integral coefficient; ω k,i and ω k * ; respectively DG k,i Output angular frequency and rated angular frequency of microgrid k; u k,c and are the actual value and rated value of the key bus voltage of microgrid k; g vk,i Indicates DG k,i Whether to receive the microgrid k key bus voltage rating information, if received, g vk,i =1, otherwise, g vk,i =0, there is only one DG in each microgrid that can receive the information; Step A02: Ω calculated in step A01 is respectively ωk,i ,Φ vk,i By adding it to the droop control equation of each DG, the frequency of each microgrid and the key bus voltage can be stably restored to the rated value.

3. The method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression according to claim 1, characterized in that: The step B specifically includes: Step B01: Taking microgrid k as an example, set n k A DG is divided into 1 pinning node and n k -1 non-pinning node, the m pinning nodes of the m microgrids jointly establish a distributed sparse communication network, recorded as the inter-group communication network; and the non-pinning nodes in the m microgrids each establish m distributed sparse communication networks, recorded as the intra-group communication network; Step B02: Based on the intra-group communication network constructed in step B01, the DG active power equalization compensation amount in each microgrid is calculated using the pinning consistency algorithm as follows: and reactive power sharing compensation Where, and is the integration coefficient; is the i-th microgrid k kh Non-pinned nodes The set of neighbor nodes of Non-binding in the intra-group communication network arrive Communication link weight; m k,pin P k,pin (n k,pin Q k,pin )and are respectively the DG restrained and non-restrained in microgrid k The product of the active (reactive) droop coefficient and its output active (reactive) power, and is proportional to their respective capacities; is the active and reactive power containment gain; Step B03: The compensation amount obtained in step B02 is and By superimposing them on the active and reactive droop equations of the non-constrained DG in the corresponding microgrid, the DG in each microgrid can be uniformly output according to its capacity. Step B04: Based on the inter-group communication network constructed in step B01, the average consistency algorithm is used to calculate the active power regulation amount Ω of each SOP required for global power sharing according to the following formula: Pk,pin and reactive power regulation Φ Qk,pin : Where k Pk,pin and k Qk,pin is the integration coefficient; is the set of neighbor nodes that control DG in microgrid k; a kl is the weight of the communication link from microgrid l to microgrid k; the subscript l,pin represents the pinned DG variable in microgrid l; Step B05: The adjustment value Ω obtained in step B04 is converted to Pk,pin and Φ Qk,pin The integral is added to the PQ port of the SOP corresponding to the microgrid where the DG is located to generate the active reference value P that the SOP needs to transmit between the interconnected microgrids. ref,kl and reactive reference value Q ref,kl : Among them, P 0,kl and Q 0,kl K is the initial transmission power setting value of the SOP connecting microgrid k and microgrid l; Pkl and K Qkl is the active and reactive transmission power regulation gain.

4. The method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression according to claim 1, characterized in that: In step C, current feedforward compensation and additional frequency adjustment are introduced into the SOP two-port converter control loop, specifically comprising the following steps: Step C01: Solve the compensation current d-axis component i that has a coupling relationship with the SOP transmission power reference value according to the following formula: dVk and the q-axis component i qVk : Where u dk,c ,u qk,c are the dq axis components of the key bus voltage in microgrid k respectively; Step C02: Add the compensation amount obtained in step C01 to the V of SOP. dc -Q converter outer loop proportional-integral controller output current correction value, generate the current inner loop dq axis reference value i dkref and i qkref : Where k pVk ,k pQk ,k iVk ,k iQk is the proportional-integral controller parameter; V dcklref and V dckl are the reference value and actual value of the SOP DC bus voltage connected to microgrid k and microgrid l, respectively, Q kl For its actual transmission of reactive power, after applying current feedforward compensation, V dc -Q port has active power balancing capability to effectively suppress DC bus voltage fluctuations when the SOP transmission power command suddenly changes; Step C03: For the PQ converter of the SOP, the frequency values ​​of the microgrids on both sides of the interconnection are normalized and then subtracted, and the frequency dynamic compensation value δ is obtained after integration. ω,kl : Where k S,kl is the integral coefficient; the subscripts k and l represent the corresponding frequency values ​​of the microgrid k and l respectively; Step C04: Substitute the δ obtained in step C03 ω,kl Added to the active reference value P of the PQ converter power outer loop ref,kl , which can generate compensation at the moment the system operating state changes to improve the regulation performance of each SOP.

5. The method for coordinated operation and fault recovery of a flexible interconnected microgrid group considering active disturbance suppression according to claim 1, characterized in that: In step D, outer loop state quantity following, phase angle holding, and estimated current compensation control are applied to the SOP port converter connected to the power-off side after the fault, thereby switching the PQ control mode to V / f control. The steps specifically include the following: Step D01: Before switching the SOP control mode, the Vf controller input signal is set to the difference between the PQ control outer loop output current reference value and the Vf control voltage outer loop output adjustment value, so that the Vf controller output is continuously adjusted according to the PQ controller; when switching is required after a fault, the Vf controller input signal is set to the rated voltage / frequency and connected to the same current inner loop of the PQ control at the same time, so that the current inner loop reference value remains unchanged before and after switching, ensuring a smooth transition of the voltage reference modulation signal amplitude; Step D02: During the SOP control mode switching process, the phase angle θ is maintained during the PQ control period. PQkl Based on this, the set phase angle θ of Vf control is obtained as follows: Vfkl : i Vfkl =2πf ref / s+θ PQkl Where, f ref is the frequency reference value, s is the Laplace operator; Step D03: At the moment of SOP control mode switching, according to the active power shortage ΔP of the power-off microgrid kL and reactive power shortage ΔQ kL , the steady-state value i of the inner current loop dq axis after switching is estimated as follows: dkl and i qkl : Among them, u d,Vref and u q,Vref are the dq axis voltage reference values ​​output after the SOP port converter switches to V / f control, and the i dkl and i qkl By subtracting the current input to the V / f control inner loop from the dq axis current reference value, the dynamic regulation performance of the SOP control mode switching process can be improved to accelerate fault recovery.

Images