A high-permeability photovoltaic AC / DC flexible interconnection power flow reconstruction method and system

Abstract

The application belongs to the technical field of power distribution flow control, and discloses a high-penetration photovoltaic station area AC / DC flexible interconnection flow reconstruction method and system, which takes the decoupling control of phase power as a basic control loop, constructs three-level feedforward compensation channels for three typical coupling disturbances of DC voltage fluctuation, AC / DC harmonic coupling and control loop time delay, respectively offsets the interference of DC voltage fluctuation on output power, suppresses the mutual transmission of AC / DC side harmonics, and compensates the command deviation caused by the response time delay of the control loop, cooperates with the independent decoupling control architecture of the phase level and the branch level, and realizes the independent compensation operation of the power commands of each phase and each branch; thereby, the dynamic deviation between the actual output power and the reconstruction command is reduced, the coupling oscillation risk is avoided, a large voltage operation margin does not need to be reserved passively, the random fluctuation characteristics of high-penetration photovoltaic are adapted, and the actual execution effect of the flow reconstruction strategy and the system operation stability are improved.

Description

Technical Field

[0001] This invention belongs to the field of power distribution flow control technology, specifically a method and system for reconfiguring AC / DC flexible interconnection power flow in high-penetration photovoltaic power distribution areas. Background Technology

[0002] Flexible AC / DC interconnection technology is a core technological path to enhance the renewable energy absorption capacity of photovoltaic distribution areas and optimize power flow distribution. Existing technologies generally construct bidirectional power channels between adjacent distribution areas using voltage source converters, combined with steady-state power flow optimization algorithms to achieve power mutual assistance and operational performance optimization. However, in actual high-penetration photovoltaic operation scenarios, existing technologies still have the following technical problems: Current power flow reconfiguration is based on a steady-state AC / DC power flow model, assuming that the converter output power can track the command value without deviation. Sudden, random changes in high-penetration photovoltaic output can trigger nonlinear coupling effects such as DC bus voltage pulsations, AC / DC harmonic coupling, and control loop response delays. This leads to a continuous dynamic deviation between the actual output power and the reconfiguration command, causing network losses and voltage indicators to deviate from their theoretical optimal values ​​after reconfiguration. In severe cases, coupled oscillations can cause strategy failure. Existing solutions can only passively mitigate risks by increasing the voltage margin, failing to eliminate the fundamental impact of dynamic coupling at the model and control levels.

[0003] Existing systems generally adopt a binary control architecture that optimizes normal operation and isolates fault shutdowns, with power flow reconfiguration only enabled in fault-free steady-state scenarios. When local faults such as single-phase grounding or branch short circuits occur in a transformer area, the system directly triggers full-port blocking of the converter, interrupting the power regulation capability of the flexible interconnection. It is unable to maintain power flow reconfiguration and power mutual assistance in non-faulty areas during the fault handling transition phase. The regulatory value of the flexible interconnection device is limited to fault-free operating conditions, thus limiting the improvement in the reliability of transformer area power supply and the resilience of new energy consumption. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for reconfiguring AC / DC flexible interconnection in high-penetration photovoltaic power distribution areas, so as to solve one or more problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: a high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system, comprising the following modules: Furthermore, the sensing module synchronously collects the three-phase voltage, current, active / reactive power time-series data of the AC side of the transformer area, DC bus voltage ripple, transient pulsation components, power change data of distributed photovoltaic grid connection points, transformer winding temperature, overhead line ambient temperature and energization duration, switch status of each branch and IGBT drive pulse signal, and the switching quantities are recorded using an event-triggered method. The sensing module has a built-in transient disturbance identification algorithm to extract AC / DC coupled oscillation characteristic quantities, power sudden change slope and fault transient characteristic quantities, and distinguish the sources of disturbance as three types: photovoltaic power output fluctuation, harmonic interaction and branch fault. The collected data is aligned with timestamps, bad data is interpolated and corrected, and outliers are removed. Standardized operation datasets are generated by splitting the data by phase and branch, and the real-time thermal load limits of distribution transformers and overhead lines are simultaneously simulated.

[0006] Furthermore, the conversion module adopts a three-phase independent bridge arm voltage source converter topology. Each phase bridge arm adopts a three-level NPC structure. The rated voltage of the DC side bus is set to 750V. The three-phase AC control circuit is completely electrically decoupled. Each phase bridge arm is equipped with an independent current sampling unit, IGBT drive unit and DC current limiting buffer unit. The output signals of each sampling unit are uniformly connected to the sensing module. The DC side is equipped with multiple access branches with independent fuses, IGBT switching units and half-bridge voltage regulation units, which correspond to distributed photovoltaic access, energy storage access, DC load access and adjacent transformer interconnection channels, respectively. Each DC-side access branch is assigned a basic control priority based on its functional attributes and power supply importance. Fixed branches are divided into four levels, with priority from high to low as follows: distributed photovoltaic access branches, core DC load branches, adjacent transformer interconnection branches, and interruptible DC load branches. Energy storage branches are dynamically matched to their corresponding priority levels according to their operating status. Under discharge support status, they are assigned to the highest priority sequence, while under charging and consumption status, they are assigned to the same level as interruptible loads.

[0007] When a power imbalance occurs on the DC bus or a branch current limit is triggered, the branch power is adjusted in order of priority from low to high, with priority given to compressing the power supply to interruptible loads, and then the transmission capacity of the interconnection channel is adjusted; when there is a power surplus on the DC side, it is given priority to be allocated to the energy storage charging and transformer interconnection transmission channel, and the remaining capacity is then connected to the interruptible load for consumption.

[0008] The action threshold of each branch current limiting unit is matched with its priority. Lower priority branches have lower current limiting thresholds and are triggered for protection first, while higher priority branches have a larger short-term overload margin.

[0009] Each branch is equipped with an independent current limiting control unit, which supports independent current limiting, switching and protection of single phase and single branch. When a single branch or a single faulty phase operates, there is no need to trigger full port blocking, and the remaining phases and remaining branches maintain normal power transmission.

[0010] Furthermore, the control module uses phase-by-phase PQ decoupling control as the basic control loop, receives AC / DC coupling disturbance characteristics and power reference commands output by the sensing module, and constructs a three-level coupling disturbance feedforward compensation channel; the first level collects the DC bus voltage pulsation component and corrects the active power command value of each phase in real time to offset the interference of DC voltage fluctuations on the output power; the second level collects the harmonic coupling components of the AC / DC side of the converter and superimposes the harmonic cancellation command in the current inner loop to suppress AC / DC side harmonic coupling; the third level uses a first-order linear extrapolation method based on the photovoltaic power sudden change slope to predict the control loop time delay deviation and correct the current command value of each phase in advance; Feedforward compensation is executed independently for the power commands of each phase and branch, realizing decoupled control at the phase and branch levels.

[0011] Photovoltaic power sudden change delay prediction compensation formula: ; This represents the predicted photovoltaic power after a control cycle delay, used to correct the current commands for each phase in advance; the unit is kW. This represents the measured distributed photovoltaic output power at time t, in kW; The average slope of photovoltaic power variation is calculated from photovoltaic power data of 5 consecutive sampling periods through a sliding window, and the unit is kW / ms; T represents the total control loop delay, which includes the delay time of the entire process of sampling, calculation, and driving. It is equal to the duration of a complete control cycle and is measured in milliseconds (ms).

[0012] Furthermore, the support module receives the DC bus voltage change rate and photovoltaic output fluctuation amplitude data output by the sensing module, and executes the control logic in parallel with the control module to adaptively adjust the AC side virtual inertia coefficient and damping coefficient. Configure the DC-side virtual capacitor inertia control logic, link the rapid power throughput capability of the energy storage access branch, and build a three-level inertia support system of AC virtual inertia, DC virtual capacitor, and energy storage rapid response. The system is configured with bidirectional AC / DC disturbance blocking logic. When the amplitude of a disturbance on one side exceeds a set threshold, the disturbance component is smoothed out by the corresponding branch half-bridge voltage regulating unit, thus blocking the transmission path of the disturbance on the AC / DC side.

[0013] The bidirectional disturbance blocking function has built-in disturbance direction discrimination logic, which determines the source of the disturbance by comparing the occurrence sequence and change rate of the disturbance components; When the DC-side voltage disturbance occurs before the AC-side disturbance and changes at a faster rate, it is determined that the disturbance originates from the DC side. The focus is on smoothing the DC pulsation by adjusting the output voltage of the AC-side bridge arm and blocking the disturbance from being transmitted to the AC grid. When the AC side voltage disturbance occurs before the DC side and the corresponding phase voltage change is more significant, it is determined that the disturbance originates from the AC side. The focus is on smoothing the DC side fluctuation through the DC branch half-bridge voltage regulation unit to block the disturbance from being transmitted to the DC load and the photovoltaic side.

[0014] Furthermore, the fault reconstruction module locates the fault position based on the fault transient characteristic quantity output by the sensing module, performs fault handling by changing the independent switching capability of the phase level and branch level of the module, and uses the DC current mutation amount and voltage drop amplitude to form the initial judgment criterion for DC branch fault; on the basis of satisfying the initial judgment criterion on the corresponding side, the fault duration condition is superimposed to form the AC side fault confirmation criterion and the DC branch fault confirmation criterion respectively, and executes a three-level gradient fault handling process according to the criterion; In the first stage of fault diagnosis, the current limiting control unit of the faulty phase or branch is triggered to limit the fault current amplitude and maintain power transmission in the non-faulty area. In the second stage of fault confirmation, the faulty phase arm pulse is blocked, the IGBT switching unit of the faulty branch is disconnected, the power transmission channel of the non-faulty phase and non-faulty branch is retained, and the degraded power flow reconstruction algorithm is called simultaneously. In the third stage of fault isolation, the electrical isolation logic is executed to complete the reconstruction optimization of the non-faulty area. The remaining port capacity is checked based on the real-time thermal load limit of the equipment throughout the process.

[0015] After a single-fault phase arm is locked out of operation, the remaining two phase arms automatically switch to a two-phase coordinated voltage regulation mode. In the two-phase mode, the voltage regulation weight is dynamically allocated according to the actual load rate and thermal margin of the two phases. The phase with a lower load rate and more thermal margin undertakes more DC voltage regulation power.

[0016] The adjustment process maintains the two-phase independent control architecture, achieving natural coordination only through the global feedback of the DC bus voltage, without the need to add a dedicated inter-phase coupling control link. If either of the remaining two phases triggers a fault protection action again, the converter's full-port lockout protection will be immediately triggered, switching to a complete shutdown and isolation state.

[0017] Furthermore, the coordination module divides the operating modes according to the operating status output by the sensing module, coordinates the start-up and execution priorities of the control module, support module, and fault reconstruction module, and divides the operating modes into three categories: normal optimization state, disturbance transition state, and fault degradation state, which correspond to three levels of control time scales: second-level, millisecond-level, and millisecond-level fault handling and second-level degradation reconstruction, respectively. The triggering condition for the transition from the normal optimized state to the disturbance state is that the photovoltaic power sudden change slope exceeds the set threshold or the DC bus voltage ripple coefficient is greater than 2%. The condition for returning from the disturbance transition state to the normal optimized state is that the disturbance component is within the set threshold range for 10 consecutive control cycles. In the normal optimization state, execute the global power flow reconfiguration command; in the disturbance transition state, trigger coupled disturbance feedforward compensation control and inertia support control; in the fault degradation state, execute the gradient fault handling and degradation reconfiguration process; set the modal priority arbitration logic to execute control commands in the priority order of fault degradation state, disturbance transition state, and normal optimization state; The solution mode of the power flow reconfiguration module switches synchronously with the operating mode, matching the control time scale of the corresponding mode; in the normal optimization state, it performs full-dimensional global optimization, covering the control variables of all phases and all branches, and solves periodically according to the preset rolling step size to output a complete power allocation scheme.

[0018] During the disturbance transition state, the global optimization solution is paused, the current steady-state power command is maintained unchanged, all control resources are given way to fast control logic such as feedforward compensation and inertia support, and only the real-time verification of thermal load and voltage constraints is retained. When the risk of exceeding the limit occurs, a small power correction is performed.

[0019] In the fault-degraded state, global optimization is immediately terminated, and the system automatically switches to the degraded reconstruction solution mode. Optimization calculations are performed only on control variables in non-fault areas, and the solution step size is temporarily shortened to 30 seconds to quickly adapt to the post-fault operating state. After fault isolation is completed and the system operation is stable, the solution step size is gradually pulled back to the normal level to maintain steady-state optimization operation in the degraded mode.

[0020] A smooth transition element with inertia gradient is set between each mode. The control command switches gradually in a linear weighted manner. The weight coefficient of the target mode increases at a constant speed, while the weight coefficient of the original mode decreases at a constant speed. The virtual inertia, damping coefficient and power command slope are gradually adjusted. The mode switching is achieved by weighted superposition, which suppresses the power surge caused by mode switching.

[0021] Furthermore, the power flow reconstruction module receives the equipment thermal load limit, voltage limit and coupling deviation output by the sensing module, and combines the operation mode matching of the coordination module with the corresponding solution mode to construct the AC / DC flexible interconnection power flow optimization model for the transformer area, with the optimization objectives being the minimum transformer area network loss, the maximum photovoltaic absorption, and the minimum node voltage deviation. The thermal load limit of the equipment is calculated in real time based on the transformer winding temperature, ambient temperature, and energization duration. The thermal load limit is calculated iteratively based on the IEEE thermal balance equation. An energization duration correction coefficient is introduced to characterize the reduction effect of continuous current carrying on thermal load. The energization duration correction coefficient decays exponentially. Combined with the real-time output level of photovoltaic adjustment of the node voltage allowable deviation range, and combined with the dual time-varying characteristics of the equipment thermal load limit and the node voltage limit, a dual time-varying constraint dynamic feasible region is constructed. The AC / DC coupling power deviation is included in the robust uncertainty set and embedded into the constraint boundary of the optimization model. The feasible region is periodically updated using a rolling time-domain optimization framework, and the optimal power allocation scheme is solved using the original dual interior point method. It supports the degradation and reconfiguration solution of non-faulty phases and non-faulty branches, and the power control command obtained from the solution is sent to the control module, support module and transformation module.

[0022] The rolling time-domain optimization adopts a hot-start solution mechanism. When each optimization window starts solving, the power allocation scheme obtained from the previous window at the corresponding time is used as the initial iteration value. Based on this, fine-tuning optimization is performed in combination with the updated constraint boundary to shorten the solution time.

[0023] A rate-of-change constraint is set between the output commands of two adjacent optimization windows to limit the maximum amplitude of single-step power adjustment and avoid frequent jumps in power commands caused by small fluctuations in the optimization boundary. Under normal optimization conditions, the rate-of-change constraint is set at 2% of the rated power, and it is automatically narrowed to 1% under disturbance transition and fault degradation conditions.

[0024] The executability of the optimization solution process is verified synchronously. If the optimization result exceeds the equipment's adjustment capacity, it is automatically corrected according to the equipment's limit value and then issued, and the allocation scheme is readjusted in the next optimization window.

[0025] This invention also provides a method for reconfiguring AC / DC flexible interconnection in high-penetration photovoltaic power distribution areas, based on the above-mentioned system, including the following specific steps: S1. Synchronously collect three-phase electrical quantities on the AC side of the transformer area, transient components of the DC bus, distributed photovoltaic power output data, temperature parameters of distribution transformers and lines, status of branch switches and IGBT drive pulse signals, complete timestamp alignment, bad data interpolation correction and outlier removal, identify AC / DC coupling oscillation, power sudden change and fault transient characteristics, deduce real-time thermal load limits of equipment, and generate standardized operation datasets. S2. A three-phase independent bridge arm converter is used to achieve phase-by-phase electrical decoupling on the AC side. Multiple independent access branches are set on the DC side and equipped with switching units and current limiting control units to build independent power transmission channels at the phase and branch levels. This supports independent operation of single phase and single branch without triggering full-port blocking. S3. Based on phase-separated power decoupling control, DC voltage fluctuations are offset, harmonic coupling is suppressed, and control time delay deviations are compensated through a three-level coupling disturbance feedforward compensation channel. Simultaneously, the virtual inertia coefficient and damping coefficient are adjusted according to the DC bus voltage change rate and photovoltaic output fluctuation amplitude, and the energy storage access branch is linked to build an inertia support system to block the AC / DC bidirectional disturbance transmission path. S4. Based on transient electrical quantities, locate the fault location, perform fault handling in a three-level gradient of current limiting buffer, pulse blocking and branch disconnection, and electrical isolation, maintain power transmission in non-faulty areas, and complete the degraded power flow reconstruction in non-faulty areas in combination with equipment thermal load limits. S5. Divide the operation into three types of operating modes and match the corresponding control time scales. Arbitrate the execution order of each control logic according to priority and realize mode switching through inertia gradient transition. Construct an AC / DC power flow optimization model, combine the time-varying characteristics of equipment dynamic thermal load and voltage limit to construct a dynamic feasible region, incorporate AC / DC coupling power deviation to form robust constraints, and use rolling optimization to solve the optimal power allocation scheme.

[0026] The beneficial effects of this invention are as follows: 1. This invention uses phase-separated power decoupling control as the basic control loop. It constructs a three-level feedforward compensation channel to address three typical coupling disturbances: DC voltage fluctuations, AC / DC harmonic coupling, and control loop delay. This channel respectively cancels the interference of DC voltage fluctuations on output power, suppresses the mutual propagation of AC / DC harmonics, and compensates for command deviations caused by control loop response delays. Combined with an independent decoupling control architecture at the phase and branch levels, it achieves independent compensation calculations for power commands of each phase and branch. This reduces the dynamic deviation between the actual output power and the reconfiguration command, avoids the risk of coupled oscillations, eliminates the need for passively reserving excessive voltage operating margins, adapts to the random fluctuation characteristics of high-penetration photovoltaics, and improves the actual execution effect of the power flow reconfiguration strategy and the stability of system operation.

[0027] 2. This invention, through a three-phase independent bridge arm converter topology and a multi-channel DC independent access branch architecture, inherently possesses the capability for independent switching and current limiting protection of single phases and single branches. Combined with a three-level gradient fault handling process, it sequentially completes the entire process of current limiting buffering, fault unit pulse blocking and branch disconnection, and electrical isolation. Throughout the fault handling process, the normal power transmission channels of non-faulty phases and branches are maintained. Combined with the real-time thermal load limit verification of the remaining port capacity, it synchronously triggers degraded power flow reconstruction calculations to optimize power allocation. During the transition phase of fault handling, the power mutual assistance capability of flexible interconnection can still be retained, expanding the applicable operating conditions of flexible interconnection devices and improving the continuous power supply capability of the distribution area and the absorption resilience of high-penetration photovoltaics.

[0028] 3. This invention constructs a dual time-varying constraint dynamic feasible region based on the dynamic thermal load capacity of the equipment and the dynamic limit of the node voltage. The AC / DC coupling power deviation is incorporated into the robust uncertainty set and embedded into the constraint boundary of the optimization model. The feasible region is periodically updated through a rolling time-domain optimization framework, and the optimal power allocation scheme is solved. At the same time, three types of operating modes are matched with differentiated control time scales, and mode priority arbitration logic and inertia gradient smooth transition links are set to achieve shock-free smooth switching of different operating scenarios. Under the premise of ensuring the safe operation of the equipment, it can maximize the photovoltaic absorption level, reduce the active power grid loss in the distribution area, and smooth the node voltage deviation. Attached Figure Description

[0029] Figure 1 This is the main flowchart of AC / DC flexible interconnect power flow reconfiguration of the present invention; Figure 2 This is a flowchart of the three-level gradient fault handling sub-process of the present invention. Detailed Implementation

[0030] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0031] like Figures 1 to 2 As shown, this embodiment of the invention provides a high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system, including a sensing module, a conversion module, a control module, a support module, a fault reconfiguration module, a coordination module, and a power flow reconfiguration module. In this embodiment of the invention, the sensing module synchronously collects the three-phase voltage, current, and active / reactive power time-series data of the AC side of the distribution area, DC bus voltage ripple, transient pulsation components, power change data of the distributed photovoltaic grid-connected point, transformer winding temperature, overhead line ambient temperature and energization duration, and the status of each branch switch and IGBT drive pulse signal; the sampling frequency of AC side electrical quantities is set to 12.8kHz, the sampling frequency of DC side transient components is set to 51.2kHz, and the switching quantities are recorded using an event-triggered method; The sensing module has a built-in transient disturbance identification algorithm to extract AC / DC coupled oscillation characteristic quantities, power sudden change slope and fault transient characteristic quantities, and distinguish the sources of disturbance as three types: photovoltaic power output fluctuation, harmonic interaction and branch fault. The identification process adopts a hierarchical and progressive judgment logic. First, the short-term change features of electrical quantities are extracted through a 10-millisecond sliding window to complete the preliminary division between steady-state and transient operating conditions. After entering the transient judgment process, the exclusive feature sets of three types of disturbances are matched in sequence to complete the classification.

[0032] When making a judgment, the fault characteristics are checked first. When a step increase in phase current or branch current is detected, and the corresponding voltage drops synchronously, and the change exceeds the normal fluctuation range, it is first judged as a branch fault disturbance and the subsequent protection logic is immediately triggered. After eliminating fault characteristics, the harmonic characteristic dimension is verified. The characteristic harmonic content of AC side current and DC side voltage is analyzed. When the proportion of 3rd, 5th and 7th harmonics exceeds the reference threshold for multiple consecutive sampling cycles, and the active power does not have a continuous unidirectional sudden change, it is determined to be harmonic interactive disturbance. If there are no fault characteristics or obvious harmonic anomalies, but only continuous fluctuations in active power with a slope exceeding the steady-state threshold, it is judged as photovoltaic power output fluctuation disturbance; the three types of disturbance judgment results are accompanied by disturbance level labels.

[0033] The collected data is aligned with timestamps, bad data is interpolated and corrected, and outliers are removed. Standardized operation datasets are generated by splitting the data by phase and branch, and the real-time thermal load limits of distribution transformers and overhead lines are simultaneously simulated.

[0034] The thermal load limit simulation performs adaptability calculations for both distribution transformer windings and overhead line conductors. For both types of equipment, the real-time temperature data is used as the core input, and the maximum allowable current carrying capacity is iteratively calculated by combining the current carrying capacity, ambient temperature and continuous energization time.

[0035] The simulation process first calculates the real-time temperature rise rate of the equipment based on the difference between the current measured temperature and the ambient temperature, and then calculates the upper limit of steady-state current carrying capacity under the current temperature reference by combining the thermal balance characteristics. Next, a power-on duration correction coefficient is introduced to reduce the upper limit of steady-state current carrying capacity. The longer the continuous power-on duration, the lower the correction coefficient value, and the smaller the corresponding maximum allowable current carrying capacity, so as to avoid the equipment temperature rise exceeding the limit due to prolonged operation close to full load. For equipment that operates intermittently for short periods of time, the correction coefficient is increased according to the power-off cooling duration to release short-term overload capacity.

[0036] The simulation process incorporates equipment aging correction factors and makes minor conservative corrections to the thermal load limit based on the equipment's years of operation and historical overload records. The final result is updated every 30 seconds and pushed to the fault reconstruction and power flow optimization modules as constraint boundaries. When the equipment's thermal load exceeds 90%, a derating warning is automatically triggered, prompting the optimization module to reduce the power allocation quota of the corresponding port.

[0037] Formula for calculating the real-time thermal load limit of equipment: ; This represents the real-time thermal load limit of the equipment at time t, i.e., the maximum allowable flow rate of the equipment under the current conditions, expressed in A. The correction factor for the duration of power-on at time t ranges from 0.6 to 1.0 and is used to characterize the reduction effect of continuous current carrying on heat carrying capacity. The longer the continuous power-on time and the higher the equipment operating load rate, the lower the value of the factor. When the equipment is powered off and cooled, the factor gradually increases with the cooling time. This represents the baseline value of the correction factor during cold start, with a value of 1.0. This represents the correction coefficient and attenuation coefficient, which are positively correlated with the real-time load rate of the equipment. The higher the load rate, the faster the attenuation rate. This indicates the duration of continuous operation of the device when it is powered on, measured in seconds (s). This represents the upper limit of the steady-state current carrying capacity of the device, derived based on the current temperature conditions and calculated iteratively using the IEEE thermal balance equations. The unit is A. The measured temperature of the equipment (transformer winding / overhead line conductor) at time t is expressed in °C. This indicates the current ambient temperature, expressed in °C.

[0038] In this embodiment of the invention, the conversion module adopts a three-phase independent bridge arm voltage source converter topology. Each phase bridge arm adopts a three-level NPC structure. The rated voltage of the DC side bus is set to 750V. The three-phase AC control circuit is completely electrically decoupled. Each phase bridge arm is equipped with an independent current sampling unit, IGBT drive unit and DC current limiting buffer unit. The output signals of each sampling unit are uniformly connected to the sensing module to complete data collection. The DC side is equipped with multiple access branches with independent fuses, IGBT switching units and half-bridge voltage regulation units, which correspond to distributed photovoltaic access, energy storage access, DC load access and adjacent transformer interconnection channels, respectively. The AC / DC flexible interconnection device of adjacent transformer areas adopts a master-slave cooperative control architecture. During normal operation, one side of the device is responsible for maintaining the voltage stability of the interconnected DC bus, while the other side of the device adjusts the magnitude and direction of the interconnection power according to the power flow optimization command.

[0039] The power command of the interconnection channel is uniformly generated by the power flow reconfiguration module and dynamically adjusted according to the photovoltaic surplus, load gap and equipment carrying capacity of the two transformer substations. When one transformer substation experiences a large photovoltaic generation and insufficient local consumption, the interconnection transmission power is automatically increased to transmit the surplus photovoltaic to the adjacent transformer substation for consumption. When one transformer substation experiences a peak load and power supply gap, the backup capacity of the adjacent transformer substation is called back to supplement the power supply.

[0040] The interconnection channel is equipped with bidirectional power limits, which are dynamically adjusted based on the thermal load limits of the devices on both sides. It is also configured with undervoltage protection and communication interruption protection. When communication between the devices on both sides is interrupted, it automatically switches to droop control mode and automatically adjusts the interconnection power according to the DC bus voltage.

[0041] Each branch is equipped with an independent current limiting control unit, which supports independent current limiting, switching and protection of single phase and single branch. When a single branch or a single faulty phase operates, there is no need to trigger full port blocking, and the remaining phases and remaining branches maintain normal power transmission.

[0042] The current limiting control unit of each DC branch adopts a chopper-type current limiting architecture composed of fully controlled power electronic devices. Under normal operating conditions, the devices are in a fully conducting state, and the branch impedance is close to zero, so it will not cause additional loss and voltage drop to normal power transmission.

[0043] When the branch current is detected to exceed the corresponding current limiting threshold, the control unit immediately enters the high-frequency chopping working mode. By switching on and off at the microsecond level, the average duty cycle of the branch is dynamically adjusted to clamp the branch current within the set safety threshold range. This can suppress the peak value of the fault current in the initial stage of its rise, thus preventing the fault current from damaging the branch devices and the converter bridge arm.

[0044] The current limiting threshold is set with two levels of protection settings. The first level is the operating current limiting threshold, which is set to 1.2 times the rated current of the branch, and is used to limit the short-term overload operation of the branch. The second level is the fault current limiting threshold, which is set to 2 times the rated current of the branch, and is used to suppress the fault current in the initial fault judgment stage.

[0045] When the current limiting unit activates, it simultaneously sends a status feedback signal to the sensing module and the fault reconstruction module, triggering the subsequent fault feature identification and gradient handling process.

[0046] In this embodiment of the invention, the control module uses phase-separated PQ decoupling control as the basic control loop, receives AC / DC coupling disturbance characteristic quantities and power reference commands output by the sensing module, and constructs a three-level coupling disturbance feedforward compensation channel. Each phase of the AC circuit is independently configured with a dual closed-loop control architecture consisting of a power outer loop and a current inner loop. The power outer loop collects the AC phase voltage and phase current of the corresponding phase in real time, calculates the instantaneous active power and reactive power of the phase, performs difference calculations with the power command value of the corresponding phase, and outputs the reference command for the current inner loop through the proportional-integral regulator. The current inner loop adopts a quasi-proportional resonant control strategy to accurately track the power frequency current reference value and outputs the IGBT drive pulse signal for the corresponding phase bridge arm.

[0047] In view of the structural characteristics of the three-phase shared DC bus, the global average value of the DC bus voltage is introduced into each phase power loop as a reference quantity to offset the interference of the overall DC bus voltage fluctuation on the single-phase power calculation. Single-phase faults or single-phase power regulation do not affect the normal power transmission of non-faulty phases.

[0048] To address the structural characteristics of the three-phase independent bridge arms sharing a DC bus, a DC-side voltage balancing control loop is set up and executed in parallel with the power outer loop of each phase. The control loop collects the DC-side current of the three-phase bridge arms and the positive and negative voltages of the DC bus in real time, calculates the imbalance of the three-phase power input, and corrects the current distribution by fine-tuning the active power command of each phase when a single-phase power deviation causes DC-side current asymmetry, thereby controlling the imbalance of the three-phase DC-side current within 5% of the rated value.

[0049] The adjustment amount of the balance control is limited to within 5% of the rated active power of each phase, and only a small correction is made. It does not interfere with the normal operation of the main power control and feedforward compensation channel. At the same time, a dead zone threshold is set so that the adjustment will not be started when there is a small imbalance.

[0050] The first stage acquires the DC bus voltage pulsation component, and the control cycle is set to 10ms, which is consistent with the outer loop power control cycle. The active power command value of each phase is corrected in real time to offset the interference of DC voltage fluctuation on the output power. The second stage acquires the harmonic coupling components on the AC and DC sides of the converter, generates cancellation commands for the 3rd, 5th, and 7th low-order harmonics respectively, and superimposes the harmonic cancellation commands in the inner current loop to suppress harmonic coupling on the AC and DC sides. The third stage is based on the steep slope of photovoltaic power change, and uses a first-order linear extrapolation method to predict the control loop time delay deviation and correct the current command values ​​of each phase in advance. Each feedforward compensation channel is equipped with an independent signal processing unit and a limiting protection unit. The first-stage DC voltage fluctuation compensation channel first extracts the pulsating component in the DC bus voltage that is in the same frequency band as the power fluctuation through the bandpass filter unit, filters out DC bias and high-frequency noise interference, and then converts the voltage pulsation deviation into an active power correction amount according to a preset ratio, which is superimposed on the active power command of each phase. By adjusting the active power output, the power imbalance on the DC side is offset. The upper and lower limits of the compensation amount are both limited to 15% of the rated active power of the corresponding phase to avoid over-compensation causing reverse fluctuations.

[0051] The second-stage harmonic coupling compensation channel uses instantaneous reactive power detection to extract the characteristic harmonic components of each AC / DC side of the converter, generates harmonic current commands with equal amplitude and opposite phase in each phase, and directly superimposes them into the reference command of the current inner loop to cancel the harmonic components transmitted between the AC and DC sides. The compensation intensity of each harmonic can be dynamically adjusted according to the actual harmonic content.

[0052] The third-level control delay compensation channel uses photovoltaic power data from five consecutive sampling cycles to calculate the average change slope. It extrapolates the expected photovoltaic power value after one control cycle through first-order linear extrapolation, thereby correcting the current loop command in advance and offsetting the delay lag in the entire process of sampling, calculation, and driving of the control link. The slope calculation adopts a sliding window update method to filter out miscompensation caused by single-point power spikes.

[0053] All feedforward compensation quantities at each level are processed by a limiting circuit, with the limiting value set at 15% of the corresponding phase rated current. Feedforward compensation is executed independently for each phase and branch power command, achieving decoupled control at the phase and branch levels. The compensated current command is then sent to each phase drive circuit of the converter module.

[0054] In this embodiment of the invention, the support module receives the DC bus voltage change rate and photovoltaic output fluctuation amplitude data output by the sensing module, executes the control logic in parallel with the control module, collects the DC bus voltage change rate and photovoltaic output fluctuation amplitude in real time, and adaptively adjusts the AC side virtual inertia coefficient and damping coefficient. The virtual inertia coefficient is adjusted within the range of 0.2s to 2s, and the damping coefficient is adjusted synchronously with the inertia coefficient proportionally. The parameter adjustment adopts a graded gradient regulation scheme, which divides the DC bus voltage change rate and photovoltaic output fluctuation amplitude into three levels: light disturbance, medium disturbance and heavy disturbance. The higher value of the two levels is taken as the final regulation level.

[0055] Under the light disturbance setting, the virtual inertia coefficient is maintained at a baseline value in the range of 0.2s to 0.8s, and the damping coefficient is matched to a low damping level to ensure the system response speed. Under the medium disturbance setting, the virtual inertia coefficient is increased to the range of 0.8s to 1.5s, and the damping coefficient is increased accordingly to balance disturbance mitigation capability and response flexibility. Under the heavy disturbance setting, the virtual inertia coefficient is increased to the upper limit level in the range of 1.5s to 2s, and the damping coefficient is adjusted to the highest level to maximize the mitigation of power impact.

[0056] The gear shifting process is set with a gradual transition time of 100 milliseconds, and the parameters are adjusted gradually at a linear rate to avoid oscillations in the control output caused by step changes in parameters. At the same time, a gear shifting hysteresis is set to prevent frequent gear shifting at disturbance boundaries.

[0057] Configure the DC-side virtual capacitor inertia control logic, link the rapid power throughput capability of the energy storage access branch, and build a three-level inertia support system of AC virtual inertia, DC virtual capacitor, and energy storage rapid response. The three-tiered support system is deployed in a tiered and coordinated manner according to response speed and regulation capacity, with the response speed from fastest to slowest being AC virtual inertia, DC virtual capacitor, and energy storage branch.

[0058] In scenarios with small disturbances, only AC virtual inertia and DC virtual capacitor are used to work together to smooth out the power fluctuations. The virtual inertia and capacitor characteristics simulated by the control algorithm are used to offset the power fluctuations without having to adjust the energy storage unit, thus reducing the frequency of energy storage charging and discharging. When the disturbance amplitude rises to the medium disturbance level, and the adjustment margin of virtual inertia and virtual capacitance is insufficient, the energy storage branch is automatically triggered to participate in auxiliary support, and the power throughput fills the power difference in a short time. Once the disturbance drops to a minor disturbance level, first withdraw the energy storage branch support, then gradually reduce the virtual inertia and virtual capacitor parameters, withdrawing in reverse order of input.

[0059] The system is configured with bidirectional AC / DC disturbance blocking logic. When a single-sided voltage disturbance amplitude is detected to exceed ±5% of the rated voltage, the disturbance component is smoothed out by the corresponding branch half-bridge voltage regulating unit, blocking the conduction path of the disturbance on the AC / DC side. The inertia control command is synchronously applied to the energy storage branch and each phase bridge arm of the converter module, and the disturbance blocking signal is linked to the synchronous action of each branch half-bridge voltage regulating unit.

[0060] The half-bridge voltage regulation unit achieves disturbance suppression by dynamically adjusting the voltage amplitude at the branch access port. The control unit collects the voltage disturbance components on the AC side and DC side in real time, automatically determines the direction of the disturbance source, and adjusts the output voltage reference of the AC side bridge arm accordingly when the disturbance originates from the DC side to offset the AC side power fluctuation caused by DC voltage pulsation, thereby preventing disturbances such as photovoltaic output fluctuations and load changes on the DC side from being transmitted to the AC distribution network. When the disturbance originates from the AC side, adjust the access voltage amplitude of each DC branch to mitigate the impact of AC side voltage drops, flicker, and other disturbances on the DC bus and DC equipment, and block the transmission path of the disturbance to the DC side.

[0061] The response speed of the voltage regulating unit is synchronized with the current inner loop control cycle, enabling millisecond-level disturbance suppression. The operation process works in coordination with the inertia support system. First, the half-bridge voltage regulating unit completes rapid amplitude suppression, and then the three-stage inertia support system completes subsequent steady-state damping. The two work together to achieve rapid attenuation and complete isolation of disturbances. After the disturbance amplitude is lower than the threshold, the voltage regulating unit gradually exits and returns to the normal conduction state.

[0062] The coupled disturbance mitigation adopts a hierarchical collaborative response mechanism, which executes half-bridge voltage regulation blocking, feedforward compensation correction, and inertia support damping in order of response speed from fastest to slowest. In the initial stage of disturbance occurrence, the half-bridge voltage regulation unit completes the initial suppression of disturbance amplitude in microseconds to milliseconds, quickly blocking the cross-side transmission of disturbance; simultaneously, the three-level feedforward compensation channel is activated to correct power and current commands within a millisecond control cycle to offset the control deviation caused by disturbance. The inertia support system then follows up, suppressing subsequent oscillations of the disturbance and accelerating disturbance decay by adjusting the virtual inertia coefficient and damping coefficient. Three types of control logic operate in parallel but with staggered timing to avoid superimposed interference caused by simultaneous step inputs of multiple control quantities. A control quantity superposition limit is set, ensuring the sum of all dynamic corrections does not exceed 25% of the corresponding phase's rated current to prevent over-adjustment from causing new instability. The disturbance decay process is implemented in reverse order, first disabling feedforward compensation, then lowering the inertia support parameters, and finally disabling half-bridge voltage regulation to ensure a smooth and shock-free recovery process.

[0063] In this embodiment of the invention, the fault reconstruction module locates the fault position based on the fault transient characteristic quantity output by the sensing module, performs fault handling by transforming the independent switching capability of the phase level and branch level of the module, and uses the DC current mutation amount and voltage drop amplitude to form the initial judgment criterion for DC branch fault; on the basis of satisfying the initial judgment criterion on the corresponding side, the fault duration condition is superimposed to form the AC side fault confirmation criterion and the DC branch fault confirmation criterion respectively, and a three-level gradient fault handling process is executed according to the criterion; The initial threshold for judging the sudden change in current is set at 20% of the rated current of the corresponding branch. In practice, a floating threshold mechanism is adopted, which is dynamically adjusted according to the current load baseline. Under light load conditions, the threshold ratio is appropriately increased to avoid false triggering by small current fluctuations, and under heavy load conditions, the threshold ratio is appropriately reduced to ensure fault sensitivity. The initial threshold for judging voltage drop amplitude is set at 15% of the rated voltage, and the fault duration confirmation threshold is set at 20 milliseconds. This duration can avoid transient interference such as normal switching operations and lightning induction, and avoid erroneous disconnection caused by transient disturbances.

[0064] The three-level fault handling process is triggered in strict accordance with the hierarchical judgment criteria. When the initial fault judgment condition is triggered, it immediately enters the first-level current limiting state and starts the fault timer. When the cumulative fault duration reaches the confirmation threshold and the fault characteristics of current and voltage do not show any signs of abating, it automatically switches to the second-level fault clearing process, blocking the corresponding bridge arm pulse and disconnecting the fault branch switching unit. If the fault current is still not effectively suppressed after the second-level action, or if the temperature of the corresponding equipment continues to rise beyond the warning threshold, it will be further upgraded to the third level of complete electrical isolation, triggering the mechanical circuit breaker to trip and form a physical disconnection point.

[0065] The fault handling process continuously monitors the fault characteristic quantities. If the fault characteristics disappear and the electrical quantities return to the normal operating range at any handling level, the subsequent upgrade actions are immediately terminated. The fault control state is gradually exited in reverse order of handling: first, the current limiting control is released, then the branch switching is restored, and finally the bridge arm drive pulse is unlocked. Delay verification is set for each step of the recovery process.

[0066] The remaining port capacity verification covers three categories of objects: non-faulty phase bridge arms, remaining DC branches, and non-faulty transformer windings. It checks the matching degree between their thermal load limit and the current transmission power. If the verification fails, the power transmission limit of the non-faulty area is automatically lowered, and the non-core DC load and unnecessary transformer interconnection power are compressed in sequence according to the preset priority.

[0067] In the initial fault diagnosis stage, the current limiting control unit of the faulty phase or faulty branch is triggered to limit the fault current amplitude and maintain power transmission in the non-faulty area. In the second-level fault confirmation stage, the fault phase bridge arm pulse is blocked, the fault branch IGBT switching unit is disconnected, the power transmission channels of the non-fault phase and non-fault branch are retained, and the degraded power flow reconstruction algorithm is called synchronously. The algorithm automatically masks the control variables corresponding to the fault phase and fault branch. The downgrade and reconfiguration process first verifies the capacity of the remaining operating ports, recalculates the maximum transmittable power of non-faulty phases and branches based on the real-time thermal load limit of the equipment, allocates the remaining transmission capacity according to priority, prioritizes the absorption channel of distributed photovoltaic, secondly ensures the power mutual assistance needs of adjacent transformer areas, and finally adjusts the power supply of DC loads according to the remaining capacity.

[0068] Constraints are adjusted synchronously, and the allowable deviation range of node voltage is appropriately tightened to ±7% of the rated voltage to reserve more voltage margin to cope with the problem of reduced system anti-disturbance capability after a fault. The calculation frequency of equipment thermal load verification is increased from minutes to 30 seconds to track the temperature rise trend of the remaining equipment in real time and dynamically adjust the power allocation quota to maximize the use of remaining transmission capacity within the safe range of equipment.

[0069] If the remaining capacity after verification is insufficient to support the current load and photovoltaic consumption demand, interruptible DC loads will be cut off in sequence according to the preset load classification list.

[0070] The degraded power flow reconstruction is based on the global optimization model for adaptive mapping adjustment. First, the power control variables corresponding to the faulty phase and faulty branch are removed from the solution matrix, and the values ​​of the corresponding variables are locked to zero so that they do not participate in the optimization iteration.

[0071] The constraints are mapped and adjusted synchronously: the equipment thermal load constraint retains only the parameters of the remaining operating equipment, and the load quota of the original faulty unit is allocated to the remaining channels according to priority, giving priority to ensuring the transmission capacity of the photovoltaic access branch; the node voltage constraint covers the remaining operating AC phase nodes and DC nodes, and the upper and lower voltage limits are appropriately adjusted according to the voltage regulation capability of the remaining equipment; the DC bus voltage constraint appropriately narrows the operating range according to the number of remaining bridge arms, reducing the risk of voltage fluctuation under the condition of fewer bridge arms.

[0072] In the third-level fault isolation stage, the mechanical circuit breaker is triggered to open, forming a clear disconnection point. Electrical isolation logic is executed to complete the reconstruction and optimization of the non-faulty area. Throughout the process, the remaining port capacity is checked based on the real-time thermal load limit of the equipment to ensure that the non-faulty equipment operates in a safe range.

[0073] In this embodiment of the invention, the coordination module divides the operating modes according to the operating state quantity output by the sensing module, and coordinates the start-up and execution priorities of the control module, support module, and fault reconstruction module. It divides the operating modes into three categories: normal optimization state, disturbance transition state, and fault degradation state, which correspond to three levels of control time scales: second-level, millisecond-level, and millisecond-level fault handling and second-level degradation reconstruction, respectively. The triggering condition for the transition from the normal optimized state to the disturbance state is that the photovoltaic power sudden change slope exceeds the set threshold or the DC bus voltage ripple coefficient is greater than 2%. The condition for returning from the disturbance transition state to the normal optimized state is that the disturbance component is within the set threshold range for 10 consecutive control cycles. The threshold benchmark for the photovoltaic power sudden change slope is 10% per second of the rated installed photovoltaic power in the distribution area. The threshold setting is determined by combining the shock resistance capability of the distribution transformer in the distribution area and the voltage regulation margin of the node. In high-penetration distribution areas, the threshold can be appropriately lowered to trigger disturbance control in advance.

[0074] The slope calculation uses a sliding time window of 200 milliseconds and takes the average power change rate within the window as the criterion to filter out false sudden change signals caused by instantaneous power spikes, sampling noise, etc.

[0075] At the same time, a hysteresis band backlash mechanism is set, and the slope threshold for the return from the perturbation transition state to the normal optimized state is set to 5% of the rated power per second, so as to avoid frequent mode switching caused by the fluctuation of the perturbation amplitude near the trigger threshold.

[0076] In the normal optimization state, execute the global power flow reconfiguration command; in the disturbance transition state, trigger coupled disturbance feedforward compensation control and inertia support control; in the fault degradation state, execute the gradient fault handling and degradation reconfiguration process; set the modal priority arbitration logic to execute control commands in the priority order of fault degradation state, disturbance transition state, and normal optimization state; The modal priority arbitration logic is executed synchronously with the millisecond-level control cycle. In each control cycle, all running modes that meet the trigger conditions are first determined based on real-time running data, and then the highest priority mode is selected as the target running mode according to the preset priority sorting.

[0077] If the target mode is consistent with the current operating mode, the original control logic remains unchanged; if they are inconsistent, a smooth mode transition process is automatically initiated to avoid power surges caused by sudden changes in control commands. The transition process adopts a linear step-weighted mechanism, dividing the 200-millisecond transition duration into 20 step cycles. In each step cycle, the command weight is adjusted by 5%. The control command weight of the target mode gradually increases from 0 to 100%, while the control command weight of the original mode gradually decreases from 100% to 0. All control parameters, including power commands, virtual inertia coefficients, and damping coefficients, are output after being weighted and superimposed.

[0078] If a higher priority modal trigger condition is detected during the transition, the current transition process is immediately interrupted, the higher priority modality is directly switched to, and the transition timer is restarted; the return of the lower priority modality can only be triggered after the return condition is stably met for 10 consecutive control cycles.

[0079] A smooth transition stage with inertia gradient is set between each mode, with a transition time of 200ms. Control commands are switched gradually in a linear weighted manner. The weight coefficient of the target mode increases at a constant speed, while the weight coefficient of the original mode decreases at a constant speed. The virtual inertia, damping coefficient, and power command slope are adjusted gradually, and the mode switching is achieved by weighted superposition to suppress the power surge caused by mode switching. The mode switching command is synchronously sent to each control module.

[0080] In this embodiment of the invention, the power flow reconstruction module receives the equipment thermal load limit, voltage limit and coupling deviation output by the sensing module, and combines the operation mode matching of the coordination module with the corresponding solution mode to construct an AC / DC flexible interconnection power flow optimization model for the transformer area, with the optimization objectives being the minimum transformer area network loss, the maximum photovoltaic absorption, and the minimum node voltage deviation. The three optimization objectives adopt a dynamic hierarchical weighting mechanism, which automatically adjusts the weight ratio of each objective according to the real-time operating status of the system. Under normal light load conditions, the core optimization objective of maximizing photovoltaic absorption is assigned the highest weight, followed by minimizing grid loss in the distribution area, and the objective of node voltage deviation has the lowest weight, thereby maximizing the level of new energy absorption. When the node voltage operating value is close to the limit boundary, the weight ratio of the node voltage deviation target is automatically increased, and the voltage deviation is constrained first to ensure power supply quality; when the equipment load rate is close to the thermal load limit, the weight of the network loss optimization target is increased, and the equipment load and heat generation level are reduced by optimizing the power flow distribution.

[0081] The rolling time-domain optimization adopts a single-step landing and multi-step prediction execution method. In the multi-step power instructions obtained by each optimization window, only the instruction of the first step is issued and executed. When the next optimization window starts, the actual running state of the previous window is used as the initial boundary condition to resolve. At the same time, the instruction change rate constraint of the adjacent window is set to limit the upper limit of the power difference between the two optimization results.

[0082] Multi-objective function for power flow optimization in AC / DC flexible interconnected distribution areas: ; F represents the comprehensive objective value of multi-objective optimization, and the solution direction is minimization; The dynamic weighting coefficients of the three sub-objectives are adaptively adjusted according to the system's operating status. The photovoltaic absorption weight is the highest under normal light load conditions. When voltage exceeds the limit or equipment is overloaded, the weight of the corresponding objective is automatically increased, always adhering to the principle of safety first. This represents the total active power loss in the transformer area, including AC side line loss, converter loss, and DC side branch loss, in kW. This represents the total distributed photovoltaic power absorbed by the transformer area, in kW; since the optimization objective is to maximize photovoltaic absorption, this term is negative and included in the minimization objective function. N represents the total number of voltage nodes in the distribution area; This represents the effective value of the actual operating voltage of the i-th node, in V; Indicates the rated reference value of the node voltage, in volts (V). It represents the sum of the absolute values ​​of voltage deviations at all nodes in the transformer area, and is used to characterize the overall voltage quality of the transformer area.

[0083] The thermal load limit of the equipment is calculated in real time based on the transformer winding temperature, ambient temperature, and energization duration. The thermal load limit is calculated iteratively based on the IEEE thermal balance equation. An energization duration correction coefficient is introduced to characterize the reduction effect of continuous current carrying on thermal load. The energization duration correction coefficient decays exponentially. Combined with the real-time output level of photovoltaic power, the allowable deviation range of node voltage is adjusted. During periods of high power generation, the allowable deviation is increased to ±10% of the rated voltage, and during periods of light load, it is reduced to ±5%. Combining the dual time-varying characteristics of the equipment thermal load limit and the node voltage limit, a dynamic feasible region with dual time-varying constraints is constructed. The value of the power-on duration correction factor changes dynamically with the continuous power-on duration and load rate of the equipment. The longer the continuous power-on time and the higher the operating load rate, the lower the correction factor value and the greater the reduction in the thermal load limit of the equipment.

[0084] When the equipment operates in the light load range below the rated load, the correction coefficient decays at a slower rate, allowing for longer continuous operation; when the equipment is operating close to full load, the correction coefficient decays at a faster rate to prevent the temperature from exceeding the limit in a short period of time.

[0085] After the equipment is powered off or operates under reduced load, the correction factor gradually recovers over time. The recovery rate is positively correlated with the difference between the current equipment temperature and the ambient temperature; the larger the temperature difference, the faster the cooling and the faster the factor recovers, until it returns to the full reference value. The correction factor ranges from 0.6 to 1.0, with a minimum of 0.6.

[0086] The AC / DC coupling power deviation is included in the robust uncertainty set and embedded into the constraint boundary of the optimization model. The feasible region is periodically updated using a rolling time-domain optimization framework with a window length of 5 minutes and a solution step size of 1 minute. The optimal power allocation scheme is solved using the original dual interior point method. The solution supports the degradation and reconfiguration of non-faulty phases and non-faulty branches. The power control commands obtained from the solution are sent to the control module, support module, and transformation module.

[0087] The boundary of the robust uncertainty set is determined based on historical operating data statistics. The measured data of AC and DC coupling power deviation within the same period of the past 7 days are extracted. After removing extreme outliers using the box-line statistical method, the upper and lower deviation values ​​corresponding to the 95% confidence interval are taken as the initial boundary of the uncertainty set.

[0088] When optimizing the solution, the constraint boundary of the power exchange term is extended to the conservative side by the corresponding deviation amount. That is, on the basis of the original constraints of equipment capacity and voltage limit, a safety margin equal to the maximum value of coupling deviation is reserved. The optimized power allocation scheme can still meet all safety constraints.

[0089] The boundary of the uncertain set is updated synchronously with the rolling time-domain optimization window. In each optimization window, the recent deviation data is re-statistically analyzed and the boundary width is adjusted. Under normal optimization conditions, the boundary is appropriately shrunken to improve operational economy, while under perturbation transition conditions, the boundary is automatically expanded to enhance robustness.

[0090] The optimal power allocation command output by the power flow reconfiguration module is a steady-state command at the second level. After being processed by the command buffer unit, it is sent to the lower millisecond-level control loop. The command buffer unit adopts a slope limiting and step-by-step sending mechanism to evenly distribute the power difference between two adjacent optimization results to multiple control cycles for gradual adjustment. The change in command in each control cycle does not exceed 2% of the rated power, thus avoiding power surges caused by sudden changes in optimization commands.

[0091] The steady-state command serves as the reference value for the control loop. Both the feedforward compensation channel and the inertia support control are based on this reference value with dynamic corrections. The corrections are only used to smooth out short-term disturbances and do not change the power allocation ratio for steady-state optimization, ensuring that the smoothing of short-term disturbances is consistent with the long-term power flow optimization objective.

[0092] During the perturbation transition state, the instruction buffer unit automatically narrows the instruction change rate limit to prioritize system stability, and then gradually returns to the normal change rate after the system returns to the normal optimized state.

[0093] This invention also provides a method for reconfiguring AC / DC flexible interconnection in high-penetration photovoltaic power distribution areas, based on the above-described system, including the following specific steps: S1. Synchronously collect three-phase electrical quantities on the AC side of the transformer area, transient components of the DC bus, distributed photovoltaic power output data, temperature parameters of distribution transformers and lines, status of branch switches and IGBT drive pulse signals, complete timestamp alignment, bad data interpolation correction and outlier removal, identify AC / DC coupling oscillation, power sudden change and fault transient characteristics, deduce real-time thermal load limits of equipment, and generate standardized operation datasets. S2. A three-phase independent bridge arm converter is used to achieve phase-by-phase electrical decoupling on the AC side. Multiple independent access branches are set on the DC side and equipped with switching units and current limiting control units to build independent power transmission channels at the phase and branch levels. This supports independent operation of single phase and single branch without triggering full-port blocking. S3. Based on phase-separated power decoupling control, DC voltage fluctuations are offset, harmonic coupling is suppressed, and control time delay deviations are compensated through a three-level coupling disturbance feedforward compensation channel. Simultaneously, the virtual inertia coefficient and damping coefficient are adjusted according to the DC bus voltage change rate and photovoltaic output fluctuation amplitude, and the energy storage access branch is linked to build an inertia support system to block the AC / DC bidirectional disturbance transmission path. S4. Based on transient electrical quantities, locate the fault location, perform fault handling in a three-level gradient of current limiting buffer, pulse blocking and branch disconnection, and electrical isolation, maintain power transmission in non-faulty areas, and complete the degraded power flow reconstruction in non-faulty areas in combination with equipment thermal load limits. S5. Divide the operation into three types of operating modes and match the corresponding control time scales. Arbitrate the execution order of each control logic according to priority and realize mode switching through inertia gradient transition. Construct an AC / DC power flow optimization model, combine the time-varying characteristics of equipment dynamic thermal load and voltage limit to construct a dynamic feasible region, incorporate AC / DC coupling power deviation to form robust constraints, and use rolling optimization to solve the optimal power allocation scheme.

[0094] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0095] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-penetration photovoltaic power distribution area AC / DC flexible interconnection power flow reconfiguration system, characterized in that, Includes the following modules: The sensing module is used to collect AC / DC electrical quantities, photovoltaic operation data, equipment temperature and switch status in the transformer area, and output standardized operation datasets and real-time thermal load limits of the equipment. The converter module adopts a three-phase independent bridge arm voltage source converter topology, with electrical decoupling of each phase AC circuit and independent sampling and drive units configured for each phase bridge arm; the DC side is equipped with multiple independent access branches, and each branch is equipped with a switching unit and a current limiting control unit, supporting single-phase and single-branch independent switching and current limiting operations. The control module uses phase-separated power decoupling control as the basic control loop, constructs a feedforward compensation channel based on AC / DC coupling disturbance characteristics, independently performs compensation calculations on the power commands of each phase and branch, and outputs the corrected current control commands. The support module adjusts the virtual inertia coefficient and damping coefficient according to the DC bus voltage change rate and photovoltaic power output fluctuation amplitude, and links the DC side energy storage access branch to build an inertia support system to block the transmission path of disturbances on the AC and DC sides. The fault reconfiguration module identifies faulty phases and branches based on transient electrical quantity characteristics and executes fault handling procedures to maintain the power transmission channel in non-faulty areas. It also completes the degraded power flow reconfiguration in non-faulty areas by combining the real-time thermal load limit of the equipment. The collaboration module divides the operating modes according to the system's operating status and matches the corresponding control time scale. It sets mode priority arbitration logic to coordinate the execution order of each module and achieves smooth switching between different modes. The power flow reconfiguration module constructs a power flow optimization model for AC / DC flexible interconnected distribution areas. The optimization objectives are to minimize grid loss, maximize photovoltaic absorption, and minimize node voltage deviation. Constraints are constructed by combining the dynamic thermal load capacity of equipment and node voltage limits to solve for the optimal power allocation scheme.

2. The high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 1, characterized in that, The electrical quantities collected by the sensing module include AC three-phase voltage, current, and power time-series data, DC bus voltage ripple, transient pulsation components, and power change data at the distributed photovoltaic grid connection point; the collected status data include distribution transformer and line temperature parameters, branch switch status, and IGBT drive pulse signals. The sensing module has a built-in transient disturbance identification algorithm to extract transient features of AC / DC coupling oscillation, power sudden change and fault, and distinguish three types of disturbance sources: photovoltaic fluctuation, harmonic interaction and branch fault. It performs timestamp alignment, bad data correction and outlier removal on the collected data, and generates standardized operation datasets by phase and by branch.

3. The high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 2, characterized in that, Each phase arm of the converter module adopts a three-level NPC structure, with a rated DC bus voltage of 750V. Each phase arm is equipped with an independent current sampling, IGBT drive and DC current limiting buffer unit. The DC-side access branches correspond to the interconnection channels of photovoltaic, energy storage, DC load and adjacent transformer areas, and each branch is equipped with fuses, IGBT switching units and half-bridge voltage regulation units. When a single branch fault or a single faulty phase triggers the protection action, there is no need to trigger the full port blockade of the converter, and the remaining phases and remaining branches maintain normal power transmission.

4. A high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 3, characterized in that, The control module constructs a three-level coupling disturbance feedforward compensation channel; the first level collects the DC bus voltage pulsation component and corrects the active power command of each phase to offset DC voltage fluctuation interference. The second stage collects harmonic coupling components on both AC and DC sides, and superimposes harmonic cancellation commands on the inner current loop to suppress harmonic coupling. The third stage uses the photovoltaic power sudden change slope prediction control loop time delay deviation to correct the current command of each phase in advance; it independently performs feedforward compensation for the power command of each phase and each branch, realizing decoupled control between the phase level and the branch level.

5. A high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 4, characterized in that, The support module and the control module execute the control logic in parallel, adaptively adjusting the virtual inertia coefficient and damping coefficient on the AC side. Configure the DC-side virtual capacitor inertia control logic, link the energy storage branch, and based on the fast power throughput capability of the energy storage branch, construct a three-level inertia support system of AC virtual inertia, DC virtual capacitor, and fast energy storage response. The system is configured with bidirectional AC / DC disturbance blocking logic. When the amplitude of a disturbance on one side exceeds a set threshold, the disturbance is mitigated by a half-bridge voltage regulation unit, thus blocking the transmission path of the disturbance on the AC / DC side.

6. A high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 5, characterized in that, The fault reconstruction module uses current surge and voltage drop amplitude as the initial fault judgment criteria for DC branches, and uses phase current surge and phase voltage drop amplitude as the initial fault judgment criteria for AC fault phases. Based on the initial judgment criteria, the fault duration condition is superimposed to form the fault confirmation criteria for DC branch and AC fault phase respectively, and a three-level gradient fault handling process is executed. The first stage triggers the current limiting control unit to limit the fault current; the second stage blocks the drive pulse of the faulty phase bridge arm, disconnects the IGBT switching unit of the faulty branch, and synchronously calls the degraded power flow reconstruction algorithm; the third stage performs electrical isolation and completes the degraded power flow reconstruction optimization of the non-faulty area, and the remaining port capacity is verified based on the thermal load limit throughout the process.

7. A high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 6, characterized in that, The collaborative module divides the system into three operating modes based on the system's operating status: normal optimization state, disturbance transition state, and fault degradation state, and sequentially matches differentiated control time scales to the three operating modes. Normal optimization state is matched with a second-level scale, perturbation transition state is matched with a millisecond-level scale, and fault degradation state is matched with a hybrid scale that combines millisecond-level fault handling with second-level degradation and reconstruction. The mode priority arbitration logic is set up to coordinate the execution order of each module and achieve smooth switching between different modes. The mode priority is sorted from high to low according to the fault degradation state, disturbance transition state, and normal optimization state. An inertia gradient smooth transition link is set between each mode, and the control command is switched step by step in a linear weighted manner to suppress the power surge caused by mode switching.

8. A high-penetration photovoltaic power grid AC / DC flexible interconnection power flow reconfiguration system according to claim 7, characterized in that, The power flow reconfiguration module calculates the equipment thermal load limit in real time, and combines it with the photovoltaic real-time output adjustment node voltage allowable deviation range to construct a dynamic feasible domain with dual time-varying constraints of equipment thermal load and node voltage. The AC / DC coupling power deviation is included in the robust uncertainty set and embedded into the constraint boundary of the optimization model. The feasible region is updated using a rolling time-domain optimization framework. The power control command obtained from the solution is sent to the corresponding execution module, supporting the degradation and reconfiguration solution in non-faulty regions.

9. A method for reconfiguring AC / DC flexible interconnection power flow in a high-penetration photovoltaic power distribution area, based on the system described in any one of claims 1-8, characterized in that, The specific steps include the following: S1. Collect AC / DC electrical quantities, photovoltaic power output data, equipment temperature parameters and switch status of the transformer area, complete data preprocessing, identify disturbance and fault characteristics, deduce real-time thermal load limits of equipment, and generate standardized operation datasets. S2. A three-phase independent bridge arm converter is used to achieve phase-by-phase electrical decoupling on the AC side. Multiple independent access branches are set up on the DC side and equipped with switching units and current limiting control units to build independent power transmission channels at the phase and branch levels. S3. Based on phase-separated power decoupling control, AC / DC coupling disturbances are offset by a feedforward compensation channel; Simultaneously adjust the virtual inertia coefficient and damping coefficient, and link the energy storage branch to construct an inertia support system to block the transmission of AC and DC bidirectional disturbances; S4. Locate the fault location based on transient electrical quantities, perform fault handling according to gradient, maintain power transmission in non-faulty areas, and complete power flow reconstruction in non-faulty areas by combining equipment thermal load limits. S5. Divide the operating modes and match the corresponding control time scales, arbitrate the execution order of the control logic according to priority, and realize smooth mode switching; construct an AC / DC power flow optimization model and solve the optimal power allocation scheme in combination with time-varying constraints.

10. The method for AC / DC flexible interconnection power flow reconfiguration in a high-penetration photovoltaic power distribution area according to claim 9, characterized in that, In step S5, the thermal load limit of the equipment is calculated iteratively based on the thermal balance equation. A correction coefficient for the energizing duration is introduced to characterize the reduction effect of continuous current carrying on the thermal load capacity. A dynamic feasible region is constructed by combining the voltage deviation range of the photovoltaic output adjustment node. The AC / DC coupling power deviation is included in the robust uncertainty set and embedded into the constraint boundary. The optimal power allocation scheme is solved using a rolling time-domain optimization framework.

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