Photovoltaic power distribution network operation control method and system based on mode switching

Abstract

This invention provides a photovoltaic power distribution network operation control method and system based on mode switching. The control method specifically involves: real-time acquisition of reactive power and frequency of the photovoltaic power distribution network; calculation of the reactive power change rate and frequency change rate based on a sliding window; determining the target control mode for the energy storage device and the collaborative control mode for the reactive power compensation device based on the operation control objective when both exceed corresponding preset thresholds; switching the energy storage device to the target control mode and the collaborative control mode for the reactive power compensation device by superimposing additional control quantities when mode switching is triggered based on a state judgment matrix; setting the current control weights of the two types of devices based on distributed priority, and coordinating the output power of the energy storage device and the reactive power compensation device through these control weights. This invention effectively improves the accuracy and safety of operation control through the joint criterion of reactive power and frequency change rates and the soft switching mechanism by superimposing additional control quantities.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power distribution network operation control technology, and in particular to a photovoltaic power distribution network operation control method and system based on mode switching. Background Technology

[0002] As the penetration rate of distributed photovoltaic (PV) power in county-level distribution networks continues to increase, the intermittent and random nature of PV power output has led to increasingly prominent problems such as voltage fluctuations, reactive power imbalance, and insufficient system inertia. To adapt to different operating scenarios such as grid-connected steady-state, disturbance transient, and fault ride-through, energy storage devices and reactive power compensation devices are typically configured with multiple control modes, including PQ control, constant voltage control, voltage-frequency control, and virtual synchronous machine control, to ensure stable grid operation through dynamic mode switching.

[0003] Current distribution network mode switching control schemes mostly rely on instantaneous sampled values ​​of single electrical quantities such as voltage amplitude and frequency offset as triggering criteria. Although some schemes introduce a single rate of change index to optimize trigger sensitivity, in actual operation, such single electrical quantities or single index criteria are easily affected by short-term disturbances such as instantaneous fluctuations in photovoltaic output and random load impacts, frequently resulting in false triggering and malfunctions, leading to low accuracy in mode switching. Furthermore, during the execution of mode switching, most adopt a hard switching method with direct control structure switching. At the moment of switching, the control parameters and output reference quantities undergo a step change, which generates significant current spikes and high-frequency resonances in actual operation, causing transient voltage drops. This impacts the safety of power electronic equipment and the transient stability of the power grid, failing to guarantee the safe operation of the power grid. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of current photovoltaic distribution network operation control schemes, such as the reliance on a single trigger for mode switching which easily leads to malfunctions, and the tendency for sudden hard switching to generate transient impacts, resulting in insufficient accuracy and safety of operation control. This invention provides a photovoltaic distribution network operation control method and system based on mode switching. By using a joint criterion of reactive power and frequency change rates, it accurately identifies real operational disturbances to reduce the false trigger rate. Furthermore, by using a soft switching mechanism with superimposed additional control quantities, it suppresses current spikes and high-frequency resonances during the switching process, mitigating transient impacts and thereby improving the accuracy and safety of operation control.

[0005] The objective of this invention is achieved through the following technical solution: The photovoltaic distribution network operation control method based on mode switching includes: Real-time acquisition of reactive power and frequency of photovoltaic power distribution network, and calculation of reactive power change rate and frequency change rate based on sliding window; When both the rate of change of reactive power and the rate of change of frequency exceed the corresponding preset thresholds, the target control mode of the energy storage device is determined in combination with the operation control objectives, and the coordinated control mode of the reactive power compensation device is matched according to the target control mode. The mode switching trigger is determined based on the state judgment matrix. When the mode switching is triggered, the energy storage device is switched to the target control mode by superimposing additional control quantities, and the reactive power compensation device is switched to the cooperative control mode. The current control weights of energy storage devices and reactive power compensation devices are set based on distributed priority, and the output power of energy storage devices and reactive power compensation devices are coordinated through the control weights.

[0006] Furthermore, the step of determining the target control mode of the energy storage device in conjunction with the operation control objectives, and matching the cooperative control mode of the reactive power compensation device according to the target control mode, includes: Based on the active power regulation requirements, frequency support requirements, and voltage stability requirements corresponding to the operation control objectives, the corresponding target control mode of the energy storage device is selected. Based on the reactive power regulation requirements corresponding to the selected target control mode, a coordinated control mode for the reactive power compensation device is matched.

[0007] Furthermore, the target control modes of the energy storage device include PQ control mode, constant voltage control mode, voltage frequency control mode and virtual synchronous machine control mode, and the cooperative control modes of the reactive power compensation device include constant reactive power control mode and constant voltage control mode.

[0008] Furthermore, the matching of the reactive power compensation device's cooperative control mode based on the reactive power regulation demand corresponding to the selected target control mode includes: When the selected target control mode is PQ control mode or virtual synchronous machine control mode, the coordinated control mode of the matching reactive power compensation device is constant voltage control mode. When the selected target control mode is constant voltage control mode or voltage frequency control mode, the coordinated control mode of the matching reactive power compensation device is constant reactive power control mode.

[0009] Furthermore, the step of switching the energy storage device to the target control mode by superimposing additional control quantities includes: The additional control quantities include a second-order feedforward damping term and an equivalent virtual impedance; During mode switching, the second-order feedforward damping term is superimposed on the reference angular velocity signal input terminal of the frequency control loop of the energy storage device; The equivalent virtual impedance, consisting of a virtual resistor and a virtual inductor connected in series, is superimposed onto the output control circuit of the energy storage device.

[0010] Furthermore, the setting of the current control weights for energy storage devices and reactive power compensation devices based on distributed priority includes: The baseline control weights of energy storage devices and reactive power compensation devices are matched based on preset distributed priority matching. Based on the ratio of real-time frequency deviation to preset frequency deviation threshold, the control weight adjustment coefficient of the energy storage device is determined, and the current control weight of the energy storage device is determined in combination with the corresponding benchmark control weight. Based on the ratio of real-time voltage deviation to preset voltage deviation threshold, the control weight adjustment coefficient of the reactive power compensation device is determined, and the current control weight of the reactive power compensation device is determined in combination with the corresponding benchmark control weight.

[0011] Furthermore, the process of generating the state judgment matrix is ​​as follows: Real-time acquisition of control signals, frequency change rate, and number of switching actions, and simultaneous acquisition of low voltage ride-through flag and communication failure flag; The acquired control signal status, frequency change rate, number of device switching actions, low voltage ride-through flag, and communication failure flag are used as matrix elements to form a status judgment matrix according to a preset arrangement rule.

[0012] Furthermore, the mode switching trigger judgment based on the state judgment matrix includes: The values ​​of each element in the state judgment matrix are updated in real time, and the mode switching judgment output value is calculated by combining the preset judgment rules. When the mode switching judgment output value reaches the preset switching threshold, the mode switching is triggered, and the corresponding mode switching command is output to the energy storage device and the reactive power compensation device.

[0013] Furthermore, when coordinating the output power of energy storage devices and reactive power compensation devices through control weights, the following is also performed: Real-time acquisition of the SOC of energy storage devices, and matching to determine the current SOC operating range and power limit of the energy storage devices; Collect the load power at adjacent times and calculate the power change amplitude, and determine the current energy storage charging and discharging priority of the energy storage device in combination with the current SOC operating range; Based on the corresponding energy storage charging and discharging priorities and power limits, constraints are set on the output power of the energy storage device determined by the control weight coordination.

[0014] A photovoltaic distribution network operation control system based on mode switching, used to execute any of the above-mentioned operation control methods, including: The data monitoring module is used to collect reactive power and frequency of the photovoltaic distribution network in real time, and calculate the rate of change of reactive power and the rate of change of frequency based on a sliding window. The mode switching judgment module is used to judge the mode change based on the reactive power change rate and frequency change rate, and when judging the mode change, it matches the corresponding control mode of the energy storage device and the reactive power compensation device. At the same time, it performs mode switching trigger judgment based on the state judgment matrix. The mode switching module is used to switch the energy storage device to the target control mode by superimposing additional control quantities after determining that a mode switching is triggered, and to switch the reactive power compensation device to the cooperative control mode. The output regulation module is used to set the current control weights of the energy storage device and the reactive power compensation device according to the distributed priority, and to coordinate the output power of the energy storage device and the reactive power compensation device through the control weights.

[0015] The beneficial effects of this invention are: Mode switching is determined by a dual criterion of reactive power change rate and frequency change rate to filter out short-term disturbances such as instantaneous fluctuations in photovoltaic output and random load surges, reducing the probability of false triggering and malfunctions. Simultaneously, a state judgment matrix is ​​introduced for switching trigger judgment to cover extreme operating scenarios such as communication failures and low-voltage ride-throughs, ensuring the accuracy of mode switching. Furthermore, a soft switching mechanism with superimposed additional control quantities is employed during the switching process to mitigate transient voltage drops and power surges at the moment of switching, preventing power electronic devices from experiencing excessive stress and ensuring grid transient stability and equipment operational safety during mode switching. Attached Figure Description

[0016] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0018] Example: Photovoltaic distribution network operation control methods based on mode switching, such as Figure 1 As shown, it includes: Real-time acquisition of reactive power and frequency of photovoltaic power distribution network, and calculation of reactive power change rate and frequency change rate based on sliding window; When both the rate of change of reactive power and the rate of change of frequency exceed the corresponding preset thresholds, the target control mode of the energy storage device is determined in combination with the operation control objectives, and the coordinated control mode of the reactive power compensation device is matched according to the target control mode. The mode switching trigger is determined based on the state judgment matrix. When the mode switching is triggered, the energy storage device is switched to the target control mode by superimposing additional control quantities, and the reactive power compensation device is switched to the cooperative control mode. The current control weights of energy storage devices and reactive power compensation devices are set based on distributed priority, and the output power of energy storage devices and reactive power compensation devices are coordinated through the control weights.

[0019] First, reactive power and frequency operation data of the distribution network are collected in real time. A sliding window mechanism is used to statistically process the sampled data to calculate the rate of change of reactive power and the rate of change of frequency. The sliding window statistics can smooth out instantaneous sampling fluctuations, filter out data spikes caused by random jumps in photovoltaic output and instantaneous load impacts, and avoid interference from single-moment sampling anomalies in the judgment results.

[0020] Using reactive power and frequency as the two types of change rates as the basis for judgment can comprehensively reflect the degree of system disturbance from the perspective of active and reactive power coupling. Compared with a single electrical quantity criterion, it is more in line with the actual operating state of the system, thereby improving the accuracy of mode switching.

[0021] When the rate of change of reactive power and the rate of change of frequency both exceed their respective preset thresholds, a continuous operational disturbance is determined. At this time, the target control mode of the energy storage device is determined in combination with the operation control objectives, and the corresponding collaborative control mode of the reactive power compensation device is matched. The appropriate control logic is assigned to the two types of devices according to the actual control requirements, so as to realize the dynamic adaptation of the control mode under different operating scenarios.

[0022] After completing mode matching, the trigger for mode switching is further determined based on the state judgment matrix. The state judgment matrix can perform multi-dimensional comprehensive verification of the grid operating state to supplement the dual-rate criterion and further ensure the reliability of the switching trigger. When determining the trigger for mode switching, the energy storage device and reactive power compensation device are smoothly switched to the corresponding control mode by superimposing additional control quantities. This avoids parameter jumps caused by direct changes in the control structure, effectively suppresses current spikes and high-frequency resonances at the moment of switching, alleviates transient voltage fluctuations, reduces the impact of the mode switching process on grid operation and power electronic equipment, and achieves smooth mode switching with low disturbance.

[0023] During the mode switching process and subsequent steady-state operation, weight regulation is further performed based on distributed priority. This allows for dynamic adjustment of the output ratio of the two types of equipment according to the type and degree of system disturbances, thereby achieving optimized allocation of regulation resources, avoiding control target conflicts among multiple devices, further mitigating switching transient disturbances, and ensuring voltage and frequency stability of the power grid.

[0024] Among them, considering that the raw data collected during the operation of the power grid is easily affected by factors such as instantaneous fluctuations in photovoltaic output, random load switching, and on-site electromagnetic interference, there are high-frequency glitches and random jumps. If the rate of change is directly calculated based on the instantaneous sampled value, the anomaly of single-point data will be amplified, resulting in frequent false exceedances of the rate of change and triggering false mode switching.

[0025] Therefore, after synchronously collecting the instantaneous reactive power and system frequency values ​​at the photovoltaic distribution network connection point using measurement equipment such as distribution terminals and synchronous phasor measurement units, a sliding window averaging method is used for preprocessing, and the corresponding reactive power change rate and frequency change rate are calculated. These reactive power change rates and frequency change rates are then used as the criteria for mode change judgment, avoiding random fluctuation interference caused by a single change rate criterion and ensuring the accuracy of switching triggering.

[0026] In the preprocessing using sliding window averaging, a fixed-duration sliding window is first preset, with the window's sliding step size consistent with the sampling period of the original data. Whenever new sampled data is added to the buffer queue, the sliding window moves forward one step along the time axis, extracting all reactive power and frequency sampling points within the current window's coverage area. An arithmetic mean is then performed on all sampled values ​​within the window to obtain the smoothed reactive power and frequency values ​​corresponding to the current window, forming a continuous smooth data sequence as the window slides.

[0027] Based on the smoothed data sequence output by the sliding window, the smoothed values ​​corresponding to two adjacent windows are extracted. The difference between the smoothed values ​​is divided by the time interval of the window sliding to calculate the reactive power change rate and frequency change rate at the current moment. Alternatively, the smoothed data points within the current window are linearly fitted using the least squares method, and the slope of the fitted line is taken as the change rate of the corresponding electrical quantity.

[0028] After calculating the reactive power change rate and frequency change rate, a second-order judgment is performed, comparing the reactive power change rate and frequency change rate with the corresponding change judgment thresholds to determine whether there is a continuous overall operating state deviation.

[0029] If both the rate of change of reactive power and the rate of change of frequency exceed the corresponding change judgment threshold, a continuous disturbance is judged to exist, thereby triggering subsequent judgments to ensure the accuracy of the switching trigger.

[0030] Second-order judgments based on reactive power change rate and frequency change rate can only determine the existence of a persistent disturbance requiring control mode adjustment, but cannot distinguish the dominant type and severity of the disturbance. In actual operation, simultaneous exceedance of both rates may correspond to various scenarios, such as a sudden drop in photovoltaic output causing a combined active and reactive power disturbance, a transient impact caused by large load switching, or the distribution network entering an islanded state after being disconnected from the grid. The control requirements differ under different scenarios, and the corresponding optimal control modes also differ. Therefore, it is necessary to further determine the control requirements in conjunction with the operational control objectives to select an appropriate energy storage control mode and ensure control effectiveness.

[0031] Meanwhile, considering that both energy storage devices and reactive power compensation devices have reactive power regulation capabilities, if only the mode switching of the energy storage device is triggered without matching the coordinated mode of the reactive power compensation device, the two types of devices may simultaneously perform voltage regulation, leading to overlapping control targets, mutual cancellation of reactive power output, or even oscillation. This could also result in regulation blind spots, causing insufficient voltage or frequency support. Therefore, based on the selected control mode of the energy storage device, the control mode of the reactive power compensation device should be further adjusted to ensure effective regulation.

[0032] Specifically, determining the target control mode of the energy storage device by combining the operation control objectives, and matching the cooperative control mode of the reactive power compensation device according to the target control mode, includes: Based on the active power regulation requirements, frequency support requirements, and voltage stability requirements corresponding to the operation control objectives, the corresponding target control mode of the energy storage device is selected. Based on the reactive power regulation requirements corresponding to the selected target control mode, a coordinated control mode for the reactive power compensation device is matched.

[0033] The target control modes of the energy storage device include PQ control mode, constant voltage control mode, voltage frequency control mode and virtual synchronous machine control mode, and the cooperative control modes of the reactive power compensation device include constant reactive power control mode and constant voltage control mode.

[0034] PQ control mode refers to a control mode in which energy storage devices output constant active power P and reactive power Q according to externally set commands. It has the advantages of high regulation accuracy and good stability, but it lacks the ability to adapt to voltage disturbances and is difficult to meet voltage support requirements. Especially when the voltage at the end of the distribution area fluctuates drastically, using PQ control mode may result in passive grid disconnection or power surge.

[0035] Therefore, when the power grid is in a steady-state operation and the optimization objective is to execute the fixed output of active and reactive power according to the dispatch instructions, that is, when there is no additional frequency support requirement and voltage stability requirement, the PQ control mode is selected.

[0036] Constant voltage mode refers to the control mode of energy storage equipment that aims to maintain the stability of the bus voltage. By comparing the real-time measured voltage with the set value, the corresponding reactive power output is adjusted according to the PI control algorithm to achieve the control purpose. It has the advantages of sensitive response and active local voltage adjustment.

[0037] Therefore, when the power grid is in a grid-connected steady-state operation and the optimization objective is to maintain the stability of the bus voltage and control voltage fluctuations, that is, when there is a need for voltage stability but no need for frequency support, the constant voltage control mode is selected.

[0038] The voltage and frequency control mode is mainly used in islanded operation scenarios. When the photovoltaic distribution network loses the support of the upper-level grid, the energy storage device can replace the traditional power source to maintain the voltage and frequency of the photovoltaic distribution network through the voltage and frequency control mode.

[0039] Therefore, when the power grid is in an islanded state and the optimization objective is to independently maintain the voltage and frequency reference of the local power grid, and there are additional frequency support and voltage stability requirements, the voltage and frequency control mode is selected. The energy storage device acts as the main power source to establish and maintain the voltage and frequency reference values ​​of the local power grid, ensuring continuous power supply to the load.

[0040] The virtual synchronous machine control mode is suitable for high-penetration new energy systems with insufficient inertia and easy voltage instability. Its essence is to mathematically map the mechanical-electromagnetic dynamic characteristics of the synchronous generator to the control of the energy storage device, so as to realize the dynamic and stable regulation of frequency and voltage, and has the advantage of good dynamic response performance.

[0041] Therefore, when the power grid is in a transient disturbance operation state, and the optimization objective is to provide virtual inertia support and suppress rapid frequency fluctuations, and there are additional frequency support and voltage stability requirements, the virtual synchronous machine control mode is selected. The energy storage device simulates the output characteristics of a synchronous generator by introducing virtual inertia and damping, thereby mitigating frequency drops and voltage fluctuations.

[0042] The reactive power compensation device only has the ability to quickly and continuously regulate reactive power. It lacks the hardware and control logic for bidirectional regulation of active power, virtual inertia simulation, and islanded voltage and frequency stabilization. It does not support modes that require active power coordinated regulation, such as PQ control, voltage and frequency control, and virtual synchronous machine control. It can only carry out control around reactive power. Therefore, the reactive power compensation device is only equipped with constant voltage control mode and constant reactive power control mode.

[0043] After selecting the target control mode for the energy storage device, a coordinated control mode for the reactive power compensation device is further matched based on the reactive power regulation requirements corresponding to the selected target control mode, including: When the selected target control mode is PQ control mode or virtual synchronous machine control mode, the coordinated control mode of the matching reactive power compensation device is constant voltage control mode. When the selected target control mode is constant voltage control mode or voltage frequency control mode, the coordinated control mode of the matching reactive power compensation device is constant reactive power control mode.

[0044] When the target control mode of the energy storage device is PQ control mode or virtual synchronous machine control mode, the reactive power regulation of the energy storage device is only used to coordinate with the active power output or provide transient damping support, and does not perform steady-state voltage regulation. At this time, the matching reactive power compensation device is in constant voltage control mode, and the reactive power compensation device performs steady-state bus voltage regulation, while the energy storage device provides transient reactive power supplementation, thereby achieving coordinated voltage regulation between steady state and transient states.

[0045] When the target control mode of the energy storage device is constant voltage control mode or voltage frequency control mode, the energy storage device has already undertaken voltage-dominated control or voltage frequency reference establishment. At this time, the matching reactive power compensation device is in constant reactive power control mode. The reactive power compensation device outputs fixed reactive power according to the preset value to avoid forming a closed loop conflict with the voltage control loop of the energy storage device and prevent reactive circulating current and voltage oscillation.

[0046] Considering that the dual-rate criterion is based solely on reactive power and frequency, it can only reflect the electrical operating trend of the power grid and cannot detect special operating conditions that are not electrical quantities, such as fault ride-through and communication anomalies. These conditions impose mandatory constraints on mode switching. For example, during low-voltage ride-through, equipment must remain connected to the grid and provide reactive power support. Even if both frequency and reactive power change rates exceed limits, arbitrarily switching control modes is prohibited, otherwise it will lead to abnormal disconnection of equipment from the grid and expand the scope of the fault. In the case of communication failure, the main control layer and the device layer lose connection and cannot reliably issue switching commands and synchronization status. Forcibly executing mode switching will also lead to the loss of control logic for multiple devices. Moreover, the dual-rate criterion only focuses on the operating status of the power grid and does not consider the operating losses and health constraints of the equipment itself. Mode switching is accompanied by dynamic adjustments to the control structure and power output. If switching is frequent, it will continuously apply electrical and mechanical stress to the power devices and switching contacts of the converter, accelerating the aging of the devices.

[0047] Therefore, by further combining other influencing factors besides the dual-rate criterion to construct a state judgment matrix, the mode switching trigger is judged to ensure that the switch is officially executed only when there is a real and continuous disturbance and the equipment and communication are in normal condition, thereby further improving the accuracy of the trigger judgment.

[0048] Specifically, the process of generating the state judgment matrix is ​​as follows: Real-time acquisition of control signals, frequency change rate, and number of switching actions, and simultaneous acquisition of low voltage ride-through flag and communication failure flag; The acquired control signal status, frequency change rate, number of device switching actions, low voltage ride-through flag, and communication failure flag are used as matrix elements to form a status judgment matrix according to a preset arrangement rule.

[0049] For control signal status, the current mode control command status and the preparation completion feedback signals of each device target mode are collected in real time through the control interaction link of energy storage device and reactive power compensation device, and quantified into discrete state quantities to characterize the validity of the current control link command and the device preparation status.

[0050] For the rate of frequency change, the real-time rate of frequency change value calculated by sliding window averaging is directly reused as the quantization input for the degree of disturbance.

[0051] For the number of device switching actions, the local action counting module of the energy storage device and the reactive power compensation device counts the cumulative number of mode switching actions within a preset statistical period, which is used to constrain the frequent switching actions of the device.

[0052] The low voltage ride-through flag and communication failure flag are obtained by reading the corresponding status flags of the grid connection point and communication link, respectively. The low voltage ride-through flag is used to identify whether the power grid is in fault ride-through condition, and the communication failure flag is used to identify whether the communication link of the energy storage device and the reactive power compensation device is normal. It is updated to the set state when it is in the corresponding abnormal condition, and to the reset state under normal conditions.

[0053] After all elements have been collected, the control signal status, frequency change rate, number of device switching actions, low voltage ride-through flag, and communication failure flag are sequentially filled into the corresponding positions as matrix elements according to a pre-set fixed arrangement rule, forming a fixed-dimensional state judgment matrix. The fixed arrangement rule can be set according to actual needs.

[0054] Then, based on the state judgment matrix, mode switching trigger judgment is performed, including: The values ​​of each element in the state judgment matrix are updated in real time, and the mode switching judgment output value is calculated by combining the preset judgment rules. When the mode switching judgment output value reaches the preset switching threshold, the mode switching is triggered, and the corresponding mode switching command is output to the energy storage device and the reactive power compensation device.

[0055] The update period of the state judgment matrix is ​​consistent with the sampling period of the original data. Each time sampling and element value update is completed, a state judgment matrix for the current moment is generated.

[0056] Based on the current state of the matrix, the values ​​of each matrix element are normalized according to the preset normalization mapping logic corresponding to each type of matrix element. The normalized values ​​are then multiplied by the corresponding preset weight coefficients and summed to obtain a single discrimination output value.

[0057] Among them, the status flag element is normalized to 1 under normal operating conditions and normalized to 0 when it is set abnormally, so as to realize the switching interlocking under abnormal operating conditions.

[0058] For analog elements of frequency change rate, normalization is performed based on a preset frequency change judgment threshold. When the real-time value reaches the threshold, the normalization value is 1; otherwise, the value is linearly taken according to the ratio of the real-time value to the threshold.

[0059] The number of switching actions is counted as a quantity element. It is reverse normalized based on the preset upper limit of the number of switching actions per unit time. When the cumulative number is 0, the normalization value is 1, and when the upper limit is reached, the normalization value is 0, thereby limiting the frequent operation of the device.

[0060] After calculating the mode switching discrimination output value of the state judgment matrix, it is compared with a preset switching threshold. When the discrimination output value reaches the preset switching threshold, it is determined that all execution conditions for mode switching are met, and a switching command for the corresponding target mode is output to the energy storage device and the reactive power compensation device, initiating the soft switching process. When the discrimination output value does not reach the preset switching threshold, it is determined that the current switching execution conditions are not met, the switching command is blocked, and the current control mode of the equipment remains unchanged. The preset switching threshold can be set according to actual needs.

[0061] Considering that the traditional hard switching method requires direct switching between two independent control loops, the control parameters, reference inputs and closed-loop transfer functions will all change abruptly at the moment of switching, which is equivalent to applying a step disturbance. This will inevitably cause a sudden jump in output power, grid current spikes and high-frequency resonance, which will in turn cause a drop in bus transient voltage. This will not only cause excessive electrical stress on the converter power devices and accelerate device aging, but also deteriorate the transient power quality of the grid. In severe cases, it may even trigger protection actions and cause the equipment to disconnect from the grid.

[0062] Therefore, instead of directly changing the control structure to complete the mode transition, the difference in control characteristics between the target control mode and the current mode is transformed into a smoothly injectable auxiliary control component based on the current control loop of the energy storage device. This auxiliary control component is then superimposed on the corresponding node of the original control loop, achieving mode transition without interrupting the continuity of closed-loop control.

[0063] Specifically, the step of switching the energy storage device to the target control mode by superimposing additional control quantities includes: The additional control quantities include a second-order feedforward damping term and an equivalent virtual impedance; During mode switching, the second-order feedforward damping term is superimposed on the reference angular velocity signal input terminal of the frequency control loop of the energy storage device; The equivalent virtual impedance, consisting of a virtual resistor and a virtual inductor connected in series, is superimposed onto the output control circuit of the energy storage device.

[0064] The second-order feedforward damping term is superimposed on the reference angular velocity input of the frequency control loop to actively increase the damping characteristics, counteract the high-frequency oscillation components excited by changes in control parameters during the switching process, accelerate the attenuation of the transient process, and avoid continuous resonance.

[0065] The equivalent virtual impedance, which is formed by the series connection of the virtual resistor and the virtual inductor, is superimposed on the output control loop. This is done by changing the output impedance characteristics to limit the rate of change of the output current during switching, smoothing out current spikes, and avoiding power oscillations caused by sudden changes in output impedance.

[0066] After the mode switching command is triggered, a switching transition phase with a preset duration is first entered. The transition duration can be set according to the actual operating conditions of the distribution network. During the switching transition phase, additional control quantities are injected into the two control nodes of the energy storage device simultaneously, and both adopt a smooth and gradual input method. Without reconstructing the original control loop structure, the switching transient disturbances are suppressed from the input side and output loop side of the control loop, respectively.

[0067] The second-order feedforward damping term is superimposed in series to the reference angular velocity signal input terminal of the energy storage device's frequency control loop. After the original reference angular velocity signal undergoes second-order damping correction processing, it is then sent to the subsequent frequency control loop. The expression for the transfer function of the second-order damping correction is as follows: ; in, Indicates frequency control loop The original reference angular velocity signal, Indicates frequency control loop The output reference angular velocity signal after second-order damping correction Indicates frequency control loop The feedforward damping time constant, Indicates frequency control loop The filtering time constant.

[0068] The transfer function provides phase lead correction through the first-order differential term of the numerator and introduces damping characteristics through the second-order inertial term of the denominator. The combination of the two can suppress the high-frequency oscillation component in the reference angular velocity signal without changing the steady-state reference value, offset the transient oscillation of the frequency loop caused by changes in the control structure during mode switching, and accelerate the decay rate of the transient process.

[0069] Before the mode switch is triggered, the second-order damping correction stage is in bypass mode, and the reference angular velocity signal is directly fed into the frequency control loop. This is equivalent to the damping time constant being 0, and the correction stage does not apply damping. After the mode switch command is issued, a preset switching transition phase is entered. During the transition period, the value of the damping time constant is gradually increased linearly, smoothly increasing from 0 to the preset rated value. Correspondingly, the strength of the second-order damping correction stage gradually increases, and the correction degree of the reference angular velocity signal deepens synchronously with the switching process, avoiding the introduction of new disturbances. After the mode switch transition is completed and the system enters a steady state, the second-order damping stage can be continuously engaged to continuously suppress high-frequency disturbances in the system, or its parameters can be gradually reduced to exit operation, reducing the phase delay of the steady-state control stage.

[0070] The equivalent virtual impedance, composed of a virtual resistor and a virtual inductor connected in series, is superimposed on the output control circuit of the energy storage device. This effectively simulates the electrical characteristics of the series impedance at the output port by correcting the output voltage reference value. Specifically, the instantaneous output current value of the energy storage converter is first acquired in real time. The impedance voltage drop corresponding to the virtual resistor and the virtual inductor are calculated separately. The sum of these two voltage drops yields the total virtual impedance voltage drop compensation. At the voltage reference node of the output control circuit, the original output voltage reference value is subtracted from this total voltage drop compensation. The corrected voltage reference value is then sent to the subsequent pulse width modulation stage, thus completing the equivalent superposition of the virtual impedance. Before mode switching is triggered, both the virtual resistor and virtual inductor values ​​are 0, and the equivalent virtual impedance is not activated. After mode switching is triggered, within the transition time synchronized with the second-order damping stage, the virtual resistor and virtual inductor values ​​increase linearly from 0 to their respective preset rated values. After the switching transition ends, the virtual impedance can be maintained in operation or gradually deactivated according to the external characteristic requirements of the target control mode to avoid additional steady-state voltage drop losses caused by continuous operation.

[0071] After completing the matching and switching of control modes, only the control logic type of a single device can be determined. If the fixed output allocation before the switch is still followed, it will be difficult to adapt to disturbance scenarios of different severity levels, and problems such as redundant adjustment resources or insufficient support capacity may occur.

[0072] Therefore, after the preset switching transition time ends, the additional control quantity is gradually put into operation and enters a stable state. After determining that both the energy storage device and the reactive power compensation device have been stably switched to the corresponding control mode, the control weights of the two types of devices are set based on distributed priority to achieve dynamic matching of disturbance degree and adjustment intensity.

[0073] Specifically, the setting of the current control weights for energy storage devices and reactive power compensation devices based on distributed priority includes: The baseline control weights of energy storage devices and reactive power compensation devices are matched based on preset distributed priority matching. Based on the ratio of real-time frequency deviation to preset frequency deviation threshold, the control weight adjustment coefficient of the energy storage device is determined, and the current control weight of the energy storage device is determined in combination with the corresponding benchmark control weight. Based on the ratio of real-time voltage deviation to preset voltage deviation threshold, the control weight adjustment coefficient of the reactive power compensation device is determined, and the current control weight of the reactive power compensation device is determined in combination with the corresponding benchmark control weight.

[0074] Before operation control, the baseline control weights of the two types of equipment are set in advance according to the distributed priority division rule that energy storage equipment takes priority in frequency support and active power regulation, and reactive power compensation devices take priority in voltage stability and reactive power compensation. The set baseline weights are the initial adjustment coefficients when the photovoltaic distribution network is in rated operating condition and there are no additional frequency support and voltage stability requirements, and correspond to the basic response strength of the two types of equipment to the corresponding control tasks under steady-state operation.

[0075] For energy storage devices, the actual frequency value at the grid connection point of the distribution network is collected in real time. The difference between this value and the rated frequency of the grid is used to obtain the real-time frequency deviation. The absolute value of the deviation is then compared with a preset frequency deviation threshold to obtain the control weight adjustment coefficient for the energy storage device. When the real-time frequency deviation does not exceed the preset frequency deviation threshold, the control weight adjustment coefficient is set to 1, and the energy storage device maintains its baseline control weight. When the real-time frequency deviation exceeds the preset frequency deviation threshold, the control weight adjustment coefficient increases synchronously with the increase of the deviation ratio. Multiplying the baseline control weight by this adjustment coefficient yields the current control weight of the energy storage device. Simultaneously, a weight upper limit is preset to avoid exceeding the device's rated regulation capacity. The larger the frequency deviation, the higher the control weight of the energy storage device, and the greater the proportion of frequency regulation tasks it undertakes.

[0076] For reactive power compensation devices, the actual bus voltage value at the distribution network connection point is synchronously collected. The difference between this and the rated voltage of the grid is used to obtain the real-time voltage deviation. The absolute value of the deviation is then compared with a preset voltage deviation threshold to calculate the control weight adjustment coefficient for the reactive power compensation device. When the real-time voltage deviation does not exceed the preset voltage deviation threshold, the control weight adjustment coefficient is set to 1, and the reactive power compensation device maintains its baseline control weight. When the real-time voltage deviation exceeds the preset voltage deviation threshold, the control weight adjustment coefficient increases synchronously with the increase in the deviation ratio. Multiplying the baseline control weight by this adjustment coefficient yields the current control weight of the reactive power compensation device. Similarly, a corresponding upper limit value is preset to constrain the adjustment range. The larger the voltage deviation, the higher the control weight of the reactive power compensation device, and the greater the proportion of voltage and reactive power regulation tasks it undertakes.

[0077] Furthermore, based on the operating parameters of the distribution network and the rated capacity of the equipment, the total frequency regulation baseline demand and the total voltage regulation baseline demand are set in advance. The total frequency regulation baseline demand is the total active power regulation required to smooth out the frequency deviation when it reaches the threshold, which is undertaken by the energy storage equipment. The total voltage regulation baseline demand is the total reactive power regulation required to smooth out the voltage deviation when it reaches the threshold, which is undertaken by the reactive power compensation device.

[0078] During real-time operation, the total frequency regulation baseline demand is multiplied by the current control weight of the energy storage device to obtain the active power regulation increment that the energy storage device needs to perform under the current operating condition, which is then added to the basic set amplitude of the active power regulation command under the corresponding target control mode. Similarly, the total voltage regulation baseline demand is multiplied by the current control weight of the reactive power compensation device to obtain the reactive power regulation increment that the device needs to perform under the current operating condition, which is then added to the basic set amplitude of the reactive power regulation command under the corresponding control mode.

[0079] The final generated control commands are sent to the corresponding devices for execution. The energy storage devices perform frequency support according to the adjusted active power commands, and the reactive power compensation devices perform voltage support according to the adjusted reactive power commands.

[0080] However, if the current voltage or frequency deviation exceeds the adjustment capability of the corresponding device, the support control weight of another device can be set according to the excess, so that the missing amount can be supplemented by the other device.

[0081] Considering that the control weight is set only from the perspective of the degree of grid disturbance and does not cover the operating boundary of the energy storage device battery itself, if its SOC is in the extreme range of near full charge or deep discharge, the full charge and discharge command will still be output according to the weight, which will trigger the battery protection shutdown and even cause permanent damage to the battery.

[0082] Therefore, when coordinating the output power of energy storage devices and reactive power compensation devices through control weights, the following is also performed: Real-time acquisition of the SOC of energy storage devices, and matching to determine the current SOC operating range and power limit of the energy storage devices; Collect the load power at adjacent times and calculate the power change amplitude, and determine the current energy storage charging and discharging priority of the energy storage device in combination with the current SOC operating range; Based on the corresponding energy storage charging and discharging priorities and power limits, constraints are set on the output power of the energy storage device determined by the control weight coordination.

[0083] The SOC range of the energy storage battery is pre-divided into multiple operating ranges, including a normal charge / discharge range, a charge-limited range, a discharge-limited range, a prohibited charging range, and a prohibited discharging range. For each range, an allowable upper limit for charge / discharge power is set. The closer the SOC is to the upper or lower limit of full charge or discharge, the lower the corresponding charge / discharge power limit. In extreme ranges, charging and discharging in the corresponding direction are directly prohibited. The current SOC value of the energy storage battery pack is collected in real time, matched to the corresponding operating range, and the upper limits of charging and discharging power for that range are read as the active power constraint boundaries for the current energy storage device.

[0084] The system collects the active power value of the local load in the distribution network at a fixed control cycle, calculates the load power difference between the current and previous time points, obtains the load power change amplitude and direction, and determines the charging and discharging priority based on the current State of Charge (SOC) operating range. When the load power is increasing and the SOC is within the allowable discharge range, the discharge priority is increased and the charging priority is decreased to prioritize ensuring the discharge support capacity of energy storage. When the load power is decreasing and the SOC is within the allowable charging range, the charging priority is increased and the discharge priority is decreased to prioritize utilizing the surplus power of the grid to complete the energy storage charging. When the SOC is in the prohibited charging or prohibited discharging range, the priority in the corresponding direction is directly locked to the lowest, and the corresponding charging and discharging actions are prohibited.

[0085] The initial output power command of the energy storage, calculated by the control weight, is matched and verified with the current power limit and charging / discharging priority. If the discharge power of the initial command exceeds the current discharge power limit, the command is clipped according to the discharge power limit. If the charging power of the initial command exceeds the current charging power limit, the command is clipped according to the charging power limit. If the charging / discharging priority determines that the corresponding direction of action is currently prohibited, the power command of the corresponding direction is corrected to 0.

[0086] Furthermore, during the correction process, the active component demand for frequency regulation is prioritized within the power limit range, and the remaining converter capacity is redistributed to the reactive component supported by voltage, ensuring the regulation effect.

[0087] Another aspect of this embodiment provides a photovoltaic distribution network operation control system based on mode switching, including: The data monitoring module is used to collect reactive power and frequency of the photovoltaic distribution network in real time, and calculate the rate of change of reactive power and the rate of change of frequency based on a sliding window. The mode switching judgment module is used to judge the mode change based on the reactive power change rate and frequency change rate, and when judging the mode change, it matches the corresponding control mode of the energy storage device and the reactive power compensation device. At the same time, it performs mode switching trigger judgment based on the state judgment matrix. The mode switching module is used to switch the energy storage device to the target control mode by superimposing additional control quantities after determining that a mode switching is triggered, and to switch the reactive power compensation device to the cooperative control mode. The output regulation module is used to set the current control weights of the energy storage device and the reactive power compensation device according to the distributed priority, and to coordinate the output power of the energy storage device and the reactive power compensation device through the control weights.

[0088] The data monitoring module is connected to the mode switching judgment module, the mode switching module is connected to the mode switching judgment module, the mode switching module is connected to the energy storage device and the reactive power compensation device, and the output adjustment module is connected to the mode switching judgment module, the energy storage device and the reactive power compensation device.

[0089] The embodiments described above are merely preferred embodiments of the present invention and are not intended to limit the present invention in any way. Other variations and modifications are possible without departing from the technical solutions described in the claims.

Claims

1. A photovoltaic distribution network operation control method based on mode switching, characterized in that, include: Real-time acquisition of reactive power and frequency of photovoltaic power distribution network, and calculation of reactive power change rate and frequency change rate based on sliding window; When both the rate of change of reactive power and the rate of change of frequency exceed the corresponding preset thresholds, the target control mode of the energy storage device is determined in combination with the operation control objectives, and the coordinated control mode of the reactive power compensation device is matched according to the target control mode. The mode switching trigger is determined based on the state judgment matrix. When the mode switching is triggered, the energy storage device is switched to the target control mode by superimposing additional control quantities, and the reactive power compensation device is switched to the cooperative control mode. The current control weights of energy storage devices and reactive power compensation devices are set based on distributed priority, and the output power of energy storage devices and reactive power compensation devices are coordinated through the control weights.

2. The photovoltaic distribution network operation control method based on mode switching according to claim 1, characterized in that, The process of determining the target control mode of the energy storage device by combining the operational control objectives, and matching the cooperative control mode of the reactive power compensation device according to the target control mode, includes: Based on the active power regulation requirements, frequency support requirements, and voltage stability requirements corresponding to the operation control objectives, the corresponding target control mode of the energy storage device is selected. Based on the reactive power regulation requirements corresponding to the selected target control mode, a coordinated control mode for the reactive power compensation device is matched.

3. The photovoltaic distribution network operation control method based on mode switching according to claim 2, characterized in that, The target control modes of the energy storage device include PQ control mode, constant voltage control mode, voltage frequency control mode and virtual synchronous machine control mode, and the cooperative control modes of the reactive power compensation device include constant reactive power control mode and constant voltage control mode.

4. The photovoltaic distribution network operation control method based on mode switching according to claim 3, characterized in that, The coordinated control mode for matching reactive power compensation devices based on the reactive power regulation demand corresponding to the selected target control mode includes: When the selected target control mode is PQ control mode or virtual synchronous machine control mode, the coordinated control mode of the matching reactive power compensation device is constant voltage control mode. When the selected target control mode is constant voltage control mode or voltage frequency control mode, the coordinated control mode of the matching reactive power compensation device is constant reactive power control mode.

5. The photovoltaic distribution network operation control method based on mode switching according to claim 1, characterized in that, The method of switching the energy storage device to the target control mode by superimposing additional control quantities includes: The additional control quantities include a second-order feedforward damping term and an equivalent virtual impedance; During mode switching, the second-order feedforward damping term is superimposed on the reference angular velocity signal input terminal of the frequency control loop of the energy storage device; The equivalent virtual impedance, consisting of a virtual resistor and a virtual inductor connected in series, is superimposed onto the output control circuit of the energy storage device.

6. The photovoltaic distribution network operation control method based on mode switching according to claim 1, characterized in that, The method of setting the current control weights of energy storage devices and reactive power compensation devices based on distributed priority includes: The baseline control weights of energy storage devices and reactive power compensation devices are matched based on preset distributed priority matching. Based on the ratio of real-time frequency deviation to preset frequency deviation threshold, the control weight adjustment coefficient of the energy storage device is determined, and the current control weight of the energy storage device is determined in combination with the corresponding benchmark control weight. Based on the ratio of real-time voltage deviation to preset voltage deviation threshold, the control weight adjustment coefficient of the reactive power compensation device is determined, and the current control weight of the reactive power compensation device is determined in combination with the corresponding benchmark control weight.

7. The photovoltaic distribution network operation control method based on mode switching according to claim 1, characterized in that, The process of generating the state judgment matrix is ​​as follows: Real-time acquisition of control signals, frequency change rate, and number of switching actions, and simultaneous acquisition of low voltage ride-through flag and communication failure flag; The acquired control signal status, frequency change rate, number of device switching actions, low voltage ride-through flag, and communication failure flag are used as matrix elements to form a status judgment matrix according to a preset arrangement rule.

8. The photovoltaic distribution network operation control method based on mode switching according to claim 7, characterized in that, The mode switching trigger judgment based on the state judgment matrix includes: The values ​​of each element in the state judgment matrix are updated in real time, and the mode switching judgment output value is calculated by combining the preset judgment rules. When the mode switching judgment output value reaches the preset switching threshold, the mode switching is triggered, and the corresponding mode switching command is output to the energy storage device and the reactive power compensation device.

9. The photovoltaic distribution network operation control method based on mode switching according to claim 1, characterized in that, When coordinating the output power of energy storage devices and reactive power compensation devices through control weights, the following is also performed: Real-time acquisition of the SOC of energy storage devices, and matching to determine the current SOC operating range and power limit of the energy storage devices; Collect the load power at adjacent times and calculate the power change amplitude, and determine the current energy storage charging and discharging priority of the energy storage device in combination with the current SOC operating range; Based on the corresponding energy storage charging and discharging priorities and power limits, constraints are set on the output power of the energy storage device determined by the control weight coordination.

10. A photovoltaic distribution network operation control system based on mode switching, used to execute the operation control method according to any one of claims 1 to 9, characterized in that, include: The data monitoring module is used to collect reactive power and frequency of the photovoltaic distribution network in real time, and calculate the rate of change of reactive power and the rate of change of frequency based on a sliding window. The mode switching judgment module is used to judge the mode change based on the reactive power change rate and frequency change rate, and when judging the mode change, it matches the corresponding control mode of the energy storage device and the reactive power compensation device. At the same time, it performs mode switching trigger judgment based on the state judgment matrix. The mode switching module is used to switch the energy storage device to the target control mode by superimposing additional control quantities after determining that a mode switching is triggered, and to switch the reactive power compensation device to the cooperative control mode. The output regulation module is used to set the current control weights of the energy storage device and the reactive power compensation device according to the distributed priority, and to coordinate the output power of the energy storage device and the reactive power compensation device through the control weights.

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