Low-voltage distribution area flexible interconnection system and load rate equalization control method thereof

Abstract

This invention discloses a flexible interconnection system for low-voltage distribution transformer substations and its load factor balancing control method, belonging to the field of distribution network automation control technology. The method collects voltage and current data of target branches, forming voltage and current sampling sequences; filters these two types of sampling sequences to obtain filtered voltage and current sequences; calculates power fluctuations and branch load factors based on these sequences, and determines the safety margin coefficient for each target branch using preset parameters; then generates active power control commands based on the safety margin coefficient, voltage offset, and initial power scheduling plan, controlling the power regulation unit to perform power regulation. This method enables high-load-rate branches to reduce active power output and low-load-rate branches to undertake more regulation, thereby improving the load factor balancing effect of the distribution transformer substations and reducing the risk of sudden power command changes.

Description

Technical Field

[0001] This invention belongs to the field of power system and distribution network automation control technology, specifically relating to a low-voltage distribution substation flexible interconnection system and its load rate balancing control method. Background Technology

[0002] With the advancement of energy and transportation integration, the scale of new loads such as distributed photovoltaic (PV) power and electric vehicle charging facilities in low-voltage distribution transformer areas is continuously expanding. Low-voltage distribution transformer areas are gradually exhibiting operational characteristics of bidirectional source-load flow and increased volatility. Especially in areas with high PV penetration, localized power generation may exceed load demand during midday, leading to voltage increases and reverse power flow in the transformer area, potentially causing issues such as curtailment, voltage exceeding limits, and uneven branch load rates.

[0003] Currently, in low-voltage distribution substations and flexible interconnection systems, master-slave control or droop control strategies are commonly used to coordinate and control multiple converters. Master-slave control relies on a centralized scheduling and communication system, which carries the risk of communication delays and single points of failure. While droop control offers distributed control capabilities, it suffers from insufficient power allocation accuracy and steady-state voltage deviation. Furthermore, to ensure system operational safety, existing technologies typically incorporate fixed margin control, which reserves a certain safety margin based on equipment capacity or operating limits.

[0004] However, the aforementioned fixed margins are usually set based on experience and are difficult to adjust in real time according to changes in distributed power output and load conditions. In scenarios where renewable energy output fluctuates significantly, setting the margin too large may reduce equipment utilization, while setting it too small may increase operational risks, thereby limiting the energy absorption capacity of low-voltage distribution substations and the economic efficiency of system operation.

[0005] Therefore, a control method is needed to adjust the safety margin according to the operating status of the low-voltage distribution substation, so as to improve the power regulation capability of the flexible interconnection system while meeting voltage and current constraints. Summary of the Invention

[0006] Existing fixed margin control systems are difficult to adjust to changes in the operating status of low-voltage distribution transformer substations. Under complex operating conditions, this may lead to reduced equipment utilization and increase the risk of voltage overruns, branch overloads, or sudden power command changes when source load fluctuations increase. To solve the above technical problems, this invention provides a flexible interconnection system for low-voltage distribution transformer substations and its load rate balancing control method.

[0007] In a first aspect, the present invention provides a low-voltage distribution transformer area load rate balancing control method, which adopts the following technical solution:

[0008] This invention provides a load rate balancing control method for low-voltage distribution transformer areas, the method comprising:

[0009] Using pre-deployed acquisition units, voltage and current data are acquired in real time at acquisition nodes in the low-voltage distribution transformer area. The voltage data consists of three-phase instantaneous simulated voltage waveforms, and the current data consists of three-phase instantaneous simulated current waveforms. The processing unit synchronously samples the three-phase instantaneous simulated voltage and current waveforms to form voltage sampling sequences and current sampling sequences.

[0010] A sliding sampling window is set according to the sampling time sequence. The voltage sampling values ​​in the voltage sampling sequence and the current sampling values ​​in the current sampling sequence are smoothed to filter out pulse spikes, resulting in filtered voltage and current sequences.

[0011] The power sequence is calculated based on the filtered voltage and current sequences, and the power fluctuation is determined based on the power sequence. The real-time branch currents of multiple target branches are determined based on the filtered current sequences, and the branch load factor is determined by the ratio of the real-time branch current of each target branch to the corresponding branch current-carrying limit. Target branches are branches in the low-voltage distribution transformer area that participate in load factor balancing regulation, including at least one of the following: branches corresponding to the low-voltage side busbar of the distribution transformer, branches corresponding to the main branch box, and branches corresponding to the distributed photovoltaic grid connection point.

[0012] A safety margin calculation model is established, including power fluctuation correction terms and branch load rate correction terms. The safety margin coefficient for each target branch is calculated based on power fluctuation and branch load rate. This safety margin coefficient is then introduced as a margin correction term into the voltage-active power droop control equation. Combining the initial dispatched power plan for the target branch and the voltage offset of the local node corresponding to the target branch, active power control commands are generated for each target branch. Current reference values ​​are generated based on the active power control commands and reactive power control commands. Voltage reference values ​​are then generated based on the current reference values, and drive pulses are output based on the voltage reference values ​​to control the power regulation unit to perform power regulation.

[0013] Furthermore, using pre-deployed acquisition units, voltage and current data are acquired in real time at the acquisition nodes of the low-voltage distribution transformer area and converted into voltage and current sampling sequences by the processing unit, specifically including:

[0014] Voltage and current acquisition devices are installed at data acquisition nodes such as the low-voltage side busbar of the distribution transformer in the low-voltage distribution area, each main branch box, and major distributed photovoltaic grid-connected points. These devices continuously acquire the three-phase instantaneous analog voltage and current waveforms on the distribution lines, respectively. The acquired analog signals are sent to the pre-processing unit's signal conditioning circuit and then pass through an RC low-pass anti-aliasing filter to reduce high-frequency aliasing interference. The filtered analog signals are fed into independent parallel analog-to-digital converters (ADCs). The ADCs are time-triggered according to a preset sampling clock, with a sampling frequency set to 10kHz, meaning synchronous sampling is performed every 0.1 milliseconds. This converts the continuous three-phase instantaneous analog voltage and current waveforms into voltage and current sampling sequences, respectively. The voltage sampling sequence includes voltage sample values ​​recorded according to the sampling time sequence, and the current sampling sequence includes current sample values ​​recorded according to the same sampling time sequence. Both correspond to the same clock cycle and are written to a buffer array for subsequent filtering and power calculation by the control unit.

[0015] Furthermore, the filtering process specifically includes:

[0016] Low-voltage distribution substations typically connect multiple power electronic converters. These converters generate electromagnetic interference (EMI) during switching operations, which can introduce pulse spikes into the original voltage and current sampling sequences. Therefore, filtering is required for both sequences to eliminate these spikes and their impact on subsequent operations. Specifically, the control unit first extracts the voltage sample values ​​recorded according to the sampling clock from the voltage sampling sequence and the current sample values ​​recorded according to the same sampling clock from the current sampling sequence. These are then used to form the original voltage and current sequences according to their sampling time sequence. The control unit then sets a sliding sampling window according to the sampling time sequence to smooth both sequences, resulting in filtered voltage and current sequences.

[0017] Furthermore, the power sequence is calculated based on the filtered voltage and current sequences, and the power fluctuation is determined based on the power sequence, specifically including:

[0018] The control unit reads the voltage value in the filtered voltage sequence and the corresponding current value in the filtered current sequence at the same sampling time, calculates the power value at the corresponding sampling time, and calculates the power sequence according to the sampling time sequence.

[0019] For the operation characteristics of large-capacity energy storage devices switching between charging and discharging or multiple nonlinear loads changing simultaneously within a low-voltage distribution substation, the control unit controls the continuous N in the power sequence. s Perform a first-order forward difference operation on each sampling point and calculate N.s The power fluctuation, reflecting the amplitude of source load power variation, is calculated by taking the arithmetic mean of the absolute differences between -1 adjacent sampling points. The power fluctuation satisfies the following mathematical relationship:

[0020] ;

[0021] Among them, D p N represents the power fluctuation. s The width of the sliding sampling window and N s ≥2, P k P is the power value calculated from the filtered voltage and current values ​​at the k-th sampling time. k−1 The power value is calculated from the filtered voltage and current values ​​at the (k-1)th sampling time.

[0022] Furthermore, a safety margin calculation model including power fluctuation correction term and branch load rate correction term is established, and the safety margin coefficient is calculated based on the power fluctuation amount and the real-time branch current determined by the filtered current sequence. Specifically, after completing the calculation of the power fluctuation amount, the control unit reads the real-time branch current of each target branch in the low-voltage distribution area.

[0023] For each target branch, the control unit calculates the ratio of the effective value of the real-time branch current to the corresponding branch current limit, and determines this ratio as the branch load rate. The control unit obtains a preset reference margin coefficient, which is predetermined based on the target branch's current limit, the rated power of the power regulation unit, and the protection setting. The control unit uses power fluctuation as a fluctuation correction input and branch load rate as a current-carrying correction input, and calculates the corresponding safety margin coefficient for each target branch using the safety margin calculation model.

[0024] The safety margin calculation model includes a power fluctuation correction term and a branch load rate correction term; the safety margin calculation model satisfies the following calculation relationship:

[0025] ;

[0026] Among them, M d For multiple target branches, the corresponding safety margin factor, M, is calculated based on the branch load rate of each target branch. b K is the preset baseline margin factor. w D represents the volatility margin weight. p P is the power fluctuation quantity. r C is the rated active power capacity of the low-voltage distribution transformer area. w K is the fluctuation sensitivity constant. c For the current-carrying state weights, I tI represents the effective value of the real-time branch current of the target branch. m I represents the upper limit of the current carrying capacity of the branch corresponding to the target branch. t / I m The branch load factor is the target branch. The effective value of the real-time branch current is calculated from the filtered current sequence.

[0027] The safety margin coefficient output by the safety margin calculation model, after being subjected to amplitude limiting, satisfies 0. <M d <1.

[0028] The safety margin calculation model is executed separately for multiple target branches, enabling each target branch to generate a corresponding safety margin coefficient based on its own branch load rate. Unlike the method of uniformly reducing the total power of the entire distribution area, this invention adjusts the proportion of allowable output active power for each target branch separately to support load rate balance among multiple target branches.

[0029] Furthermore, the generation of active power control commands specifically includes: the control unit reads the real-time voltage value of the local node corresponding to the target branch from the filtered voltage sequence, and reads the rated voltage value of the local node from the pre-stored node rated parameter table. The control unit determines the voltage offset based on the difference between the real-time voltage value and the rated voltage value, and determines the droop support component based on the voltage offset and the preset voltage-active power droop coefficient.

[0030] The initial dispatch power plan for each target branch is adjusted according to the safety margin coefficient, and the adjusted initial dispatch power plan is superimposed with the droop support component to generate an active power control command. When the active power control command is positively directed to output active power to the low-voltage distribution transformer area, the active power control command satisfies the following relationship:

[0031] ;

[0032] Among them, P o For the active power control command corresponding to the target branch, P f M is the initial scheduling power plan corresponding to the target branch. d C represents the safety margin coefficient corresponding to the target branch. v V is the voltage-active droop factor. t V represents the real-time voltage value of the local node read from the filtered voltage sequence. n This is the rated voltage value corresponding to the local node, read from the node rating parameter table. The negative product of the voltage-active droop factor and the voltage offset is the droop support component.

[0033] The calculation formula is executed separately for each target branch. Target branches with higher load rates have larger safety margin coefficients, and their allowable output active power ratio is reduced; target branches with lower load rates have smaller safety margin coefficients, and their power adjustment space is increased.

[0034] After receiving the active power control command, a current reference value is generated based on the active power control command and the reactive power control command. A voltage reference value is generated based on the current reference value, and a drive pulse is output based on the voltage reference value. The drive pulse controls the power regulation unit to perform power regulation.

[0035] Secondly, this invention provides a flexible interconnection system for low-voltage distribution substations, employing the following technical solution:

[0036] A flexible interconnection system for low-voltage distribution substations includes:

[0037] The acquisition unit is used to acquire voltage and current data of each target branch within the low-voltage distribution substation area;

[0038] The processing unit is used to perform signal conditioning and synchronous sampling on voltage and current data, and record voltage and current sample values ​​in the same clock cycle to form voltage sampling sequence and current sampling sequence.

[0039] The control unit is used to calculate the safety margin coefficient based on the voltage sampling sequence and the current sampling sequence, and generate active power control commands using the safety margin coefficient, voltage offset, and initial power scheduling plan. Specifically, the voltage sampling sequence and the current sampling sequence are first filtered to obtain filtered voltage and current sequences. Then, the power fluctuation is calculated based on the filtered voltage and current sequences, and the branch load rate of each target branch is calculated based on the filtered current sequence. Next, the safety margin coefficient of each target branch is calculated based on the power fluctuation and the branch load rate. Finally, the active power control commands are generated based on the safety margin coefficient, the voltage offset of each target branch, and the initial power scheduling plan.

[0040] The power regulation unit is used to perform power regulation according to the active power control command;

[0041] The acquisition unit is connected to the processing unit, the processing unit is connected to the control unit, and the control unit is connected to the power regulation unit.

[0042] Furthermore, the processing unit includes a pre-signal conditioning circuit, an analog-to-digital converter, and a buffer array.

[0043] The pre-amplifier signal conditioning circuit is used to condition the voltage and current data; the analog-to-digital converter is used to synchronously sample the conditioned voltage and current data according to the same sampling clock; the buffer array is used to store the voltage sampling sequence and the current sampling sequence according to the sampling timing.

[0044] The pre-amplifier signal conditioning circuit is electrically connected to the analog-to-digital converter unit, and the analog-to-digital converter unit is communicatively connected to the buffer array.

[0045] Through the above system structure, voltage and current data are sequentially acquired, signal conditioned, synchronously sampled and buffered before being transmitted to the control unit. The control unit generates active power control commands for each target branch, and the power regulation unit executes power regulation.

[0046] The present invention has the following beneficial effects:

[0047] This invention constructs a safety margin calculation model including power fluctuation correction terms and branch load rate correction terms to reduce the problems of reduced equipment utilization or increased operational risks caused by fixed margin control. When the power fluctuation is small, the safety margin coefficient decreases, and the available power ratio increases accordingly. When the power fluctuation increases or the branch load rate of the target branch increases, the safety margin coefficient increases, and the safety margin reserve increases accordingly. Thus, the safety margin coefficient can change with the power fluctuation and branch load rate, and the power adjustment amount is allocated according to the branch load rate of each target branch. This method can increase the equivalent available transmission capacity of transformers and cables in low-voltage distribution substations within the existing equipment capacity range, improve the operational utilization of flexible interconnection systems, and reduce capacity idleness caused by excessive fixed margin.

[0048] This invention avoids the abrupt change in control quantity caused by threshold switching in traditional control strategies by introducing a safety margin coefficient into the voltage-active power droop control equation and setting continuous power fluctuation correction terms and branch load rate correction terms in the safety margin calculation model. Since both the power fluctuation correction term and the branch load rate correction term are continuous functions, the safety margin coefficient can change continuously, thereby reducing the risk of junction temperature fluctuations and thermal fatigue accumulation in the power switching module caused by sudden command changes, and reducing the thermal stress on the power switching devices. Attached Figure Description

[0049] Figure 1 This is a schematic diagram illustrating the working principle of the low-voltage distribution substation flexible interconnection system provided in this invention.

[0050] Figure 2 This is a flowchart of the low-voltage distribution transformer area load rate balancing control method provided in this invention. Detailed Implementation

[0051] The invention will be further described below with reference to examples.

[0052] like Figure 1 As shown, a flexible interconnection system for a low-voltage distribution substation includes a data acquisition unit, a processing unit, a control unit, and a power regulation unit. The data acquisition unit is communicatively connected to the processing unit, the processing unit is communicatively connected to the control unit, the control unit is communicatively connected to the power regulation unit, and the power regulation unit is electrically connected to the corresponding target branch within the low-voltage distribution substation.

[0053] In this invention, the acquisition unit is used to acquire voltage and current data of each target branch within the low-voltage distribution transformer area. The acquisition unit includes voltage acquisition devices and current acquisition devices installed at the low-voltage side busbar of the distribution transformer, the main branch box, and the distributed photovoltaic grid connection point. The voltage acquisition devices are used to acquire the three-phase instantaneous simulated voltage waveform of the target branch, and the current acquisition devices are used to acquire the three-phase instantaneous simulated current waveform of the target branch.

[0054] Each target branch is equipped with an independent data acquisition channel. The data acquisition channel is associated with the branch identifier and acquisition node of the corresponding target branch so that the acquired voltage and current data can be correlated with the corresponding target branch.

[0055] The processing unit is used to perform signal conditioning and synchronous sampling on the voltage and current data acquired by the acquisition unit, and to form voltage sampling sequences and current sampling sequences. The processing unit includes a pre-amplifier signal conditioning circuit, an analog-to-digital converter (ADC), and a buffer array. The pre-amplifier signal conditioning circuit is electrically connected to the ADC, and the ADC is communicatively connected to the buffer array.

[0056] The pre-amplifier signal conditioning circuit is used to perform anti-aliasing filtering and amplitude conditioning on the voltage and current data acquired by the acquisition unit; the analog-to-digital conversion unit is used to synchronously sample the voltage and current data after signal conditioning according to the same sampling clock, and convert the continuous analog signal into a digital signal; the buffer array is used to store the voltage and current sample values ​​corresponding to the same sampling time according to the sampling time sequence, so as to form the voltage sampling sequence and the current sampling sequence.

[0057] In this embodiment, the pre-amplifier signal conditioning circuit uses an RC low-pass anti-aliasing filter circuit, the analog-to-digital converter (ADC) unit uses an ADC with independent parallel sampling channels, and the buffer array uses a dual-port RAM buffer array. The ADC unit writes the voltage and current sample values ​​into the dual-port RAM buffer array according to a preset sampling clock, and the control unit reads the voltage and current sample sequences from the dual-port RAM buffer array.

[0058] The control unit is used to filter the voltage sampling sequence and current sampling sequence formed by the processing unit, calculate the power fluctuation based on the filtered voltage sequence and the filtered current sequence, calculate the branch load rate and safety margin coefficient of each target branch based on the filtered current sequence, and then generate active power control commands by combining the voltage offset of each target branch and the initial scheduling power plan.

[0059] In this embodiment, the control unit includes a main control DSP, which pre-stores a node rated parameter table and control parameters required for safety margin calculation. The node rated parameter table stores the rated voltage value corresponding to each local node and the upper limit of branch current carrying capacity corresponding to each target branch. The control unit reads the voltage sampling sequence and current sampling sequence from the processing unit, and performs filtering of the voltage sampling sequence and current sampling sequence, calculation of power fluctuation based on the filtered voltage sequence and filtered current sequence, calculation of branch load rate based on the filtered current sequence, calculation of safety margin coefficient, and generation of active power control commands in the main control DSP.

[0060] The power regulation unit receives active power control commands generated by the control unit and adjusts the active power of the corresponding target branch according to the active power control commands. In this embodiment, the power regulation unit adopts a converter unit, which includes an inner loop current regulator, a microprocessor, a pulse width modulation generator, and a bridge arm switch.

[0061] The inner-loop current regulator generates a current reference value based on the active power control command and the reactive power control command, and generates a voltage reference value based on the current reference value; the microprocessor determines the action time of the bridge arm switching transistor based on the voltage reference value; the pulse width modulation generator outputs complementary high and low level PWM drive pulses with dead-time protection, and uses the PWM drive pulses to control the on and off of the bridge arm switching transistors so that the power regulation unit performs power regulation.

[0062] In practical applications, the acquisition unit sends the acquired voltage and current data to the processing unit. The processing unit sequentially performs signal conditioning, synchronous sampling, and buffering of the voltage and current sampling sequences, and then sends the voltage and current sampling sequences to the control unit. The control unit generates active power control commands based on the operating status of each target branch, and the power regulation unit adjusts the active power exchange with the target branch according to the corresponding active power control commands.

[0063] When the load rate of the target branch increases, the control unit increases the safety margin coefficient corresponding to the target branch and reduces the proportion of active power allowed to be output by the target branch; when the load rate of the target branch decreases, the control unit reduces the safety margin coefficient corresponding to the target branch and increases the power adjustment space of the target branch, so that the load rates among multiple target branches tend to be balanced.

[0064] In this embodiment, the technical solutions involved in the present invention will be described from the perspective of application.

[0065] like Figure 2 As shown, the load balancing control of low-voltage distribution transformer areas is achieved through the following steps:

[0066] S1: Voltage and current data acquisition

[0067] Specifically, voltage and current acquisition devices are installed on the low-voltage side busbar of the distribution transformer in the low-voltage distribution area, on each main branch box, and on the main distributed photovoltaic grid connection points to continuously acquire the three-phase instantaneous simulated voltage waveform and the three-phase instantaneous simulated current waveform on the line.

[0068] The acquired analog signals are then fed into the pre-amplifier signal conditioning circuit of the processing unit. After passing through an RC low-pass anti-aliasing filter, they are fed into an independent parallel analog-to-digital converter (ADC). The ADC is time-triggered according to a preset sampling clock, with a sampling frequency set to 10kHz, meaning synchronous sampling is performed every 0.1ms. This converts the continuous three-phase instantaneous analog voltage waveform and the three-phase instantaneous analog current waveform into voltage sampling sequences and current sampling sequences, respectively. The voltage sampling sequence includes voltage sample values ​​recorded according to the sampling timing sequence, and the current sampling sequence includes current sample values ​​recorded according to the same sampling timing sequence. Both correspond to the same clock cycle and are cyclically pushed into the dual-port RAM buffer array for subsequent calls.

[0069] It should be noted that the data acquisition and sampling method in this embodiment is only one optional implementation. In practical applications, the data acquisition method, sampling frequency, and sampling accuracy for voltage and current can be determined based on the transformer substation capacity, line structure, and control cycle.

[0070] S2: Obtaining the filtered voltage and current sequences

[0071] Specifically, the voltage and current sampling sequences obtained in step S1 are denoised separately. Low-voltage distribution substations typically have multiple power electronic converters connected in the field. These power electronic converters generate electromagnetic interference (EMI) during switching operations, which can cause pulse spikes in the voltage and current sampling sequences. To avoid these interference-induced pulse spikes affecting the accuracy of subsequent safety margin coefficient calculations, the voltage and current sampling sequences need to be filtered separately.

[0072] In this embodiment, the control unit extracts voltage sample values ​​recorded according to the sampling clock from the voltage sampling sequence cached in RAM, and extracts current sample values ​​recorded according to the same sampling clock from the current sampling sequence cached in RAM, forming the original voltage sequence and the original current sequence respectively according to the sampling time sequence. The control unit constructs a sliding sampling window of fixed length and moves the sliding sampling window along the sampling time sequence. Within each sliding sampling window, the control unit calculates the voltage smoothing value corresponding to the center sampling point based on the voltage sample values ​​within the window, and calculates the current smoothing value corresponding to the center sampling point based on the current sample values ​​within the window. The control unit replaces the corresponding original sample values ​​with the voltage smoothing value and the current smoothing value respectively to obtain the filtered voltage sequence and the filtered current sequence. The above processing can filter out high-frequency pulse spikes and retain the effective change characteristics caused by load abrupt changes, thereby improving the consistency between power fluctuation and actual power change.

[0073] It should be noted that the filtering and denoising methods are not limited to the time-series filtering processing described above. Digital signal processing algorithms such as moving average filtering, Kalman filtering, or wavelet transform can be used to obtain filtered voltage and current sequences, as long as they can filter out high-frequency interference and preserve step change characteristics.

[0074] S3: Safety Margin Calculation

[0075] Specifically, after obtaining the filtered voltage and current sequences, the main DSP in the control unit first calculates the power sequence, and then determines the power fluctuation based on the power sequence. Unlike the fixed margin control method, the control unit calculates the safety margin coefficient corresponding to each target branch based on the power fluctuation and the real-time branch current of each target branch determined by the filtered current sequence.

[0076] First, the control unit reads the filtered voltage and current values ​​at the same sampling time and calculates the power value at the corresponding sampling time, forming a power sequence according to the sampling time sequence. For changes in active power caused by switching between energy storage charging and discharging in low-voltage distribution substations or sudden load changes, the control unit processes the continuous N values ​​in the power sequence... s Perform a difference operation on each sampling point and calculate N. sThe power fluctuation, reflecting the magnitude of the change in source load power, is calculated by taking the arithmetic mean of the absolute values ​​of the differences between -1 adjacent sampling points. The specific relationship is as follows:

[0077] ;

[0078] Among them, D p N represents the power fluctuation. s The width of the sliding sampling window and N s ≥2, P k P is the power value calculated from the filtered voltage and current values ​​at time k. k−1 The power value is calculated from the filtered voltage and current values ​​at time k-1.

[0079] After calculating the power fluctuation, the control unit uses it as the safety margin correction input. Combined with the real-time branch current carrying state, a safety margin calculation model including power fluctuation correction term and branch load rate correction term is established to calculate the safety margin coefficient.

[0080] In this embodiment, the control unit does not calculate the safety margin factor for a single branch, but rather reads the real-time branch current for multiple target branches within the low-voltage distribution transformer area. For each target branch, the control unit determines the branch load rate of the target branch based on the ratio of the effective value of the real-time branch current to the corresponding branch current limit.

[0081] The branch load rate serves as the input to the branch load rate correction term, enabling different target branches to form corresponding safety margin coefficients based on their own branch load rates. When power fluctuations increase, the power fluctuation correction term increases, and the safety margin coefficient increases accordingly to increase the safety margin reserve. When the branch load rate of a target branch increases, the branch load rate correction term increases, and the corresponding safety margin coefficient for that target branch increases, thereby reducing the proportion of active power allowed to be output by that target branch. The specific relationship is as follows:

[0082] ;

[0083] Among them, M d M is the safety margin coefficient corresponding to the target branch. b K is the preset baseline margin factor. w D represents the volatility margin weight. p P is the power fluctuation quantity. r C is the rated active power capacity of the low-voltage distribution transformer area. w K is the fluctuation sensitivity constant. c For the current-carrying state weights, I t I represents the effective value of the real-time branch current of the target branch. mI represents the upper limit of the current carrying capacity of the branch corresponding to the target branch. t / I m The branch load factor is the target branch. The effective value of the real-time branch current is calculated from the filtered current sequence.

[0084] It should be noted that the volatility margin weight K w The safety margin was determined through comparative experiments. First, a test platform including a photovoltaic simulation device, a load simulation device, a power regulation unit, and a control unit was built to determine the baseline safety margin under stable power conditions. Then, small, medium, and large power fluctuations were applied respectively, and the safety margin was gradually increased until the target branch did not experience overload, voltage over-limit, or power command abrupt change. Finally, the difference between the safety margin required under the maximum power fluctuation condition and the baseline safety margin was used as the basis for determining the fluctuation margin weight.

[0085] Fluctuation sensitivity constant C w The energy noise expansion factor is determined through graded power disturbance response experiments. Under the condition that the fluctuation margin weight remains unchanged, multiple levels of power disturbances from small to large are set, and multiple sets of fluctuation sensitivity constant test values ​​are established. Identical power fluctuation data are input into the control unit, and the changes in safety margin corresponding to each test value are compared. Test values ​​that overreact to normal small fluctuations or respond too slowly to severe fluctuations are eliminated, and test values ​​that can maintain stability under normal operating conditions and promptly improve the safety margin during significant power fluctuations are selected. This determination method is similar to the method used in the reference patent to obtain the energy noise expansion factor by comparing multiple sets of experimental values.

[0086] Current-carrying state weight K c The current-carrying capacity is determined through a step-load test on the branch. A test branch with the same conductor specifications, laying method, and protection settings as the target branch is selected. The load current is increased step by step, and conductor temperature rise, line voltage drop, protection margin, and remaining regulation capacity are recorded under different branch load rates. The safety margin is gradually increased under each load level until the branch current, conductor temperature rise, and protection device all meet safety requirements. The current-carrying state weight is determined based on the increase in safety margin corresponding to different branch load rates.

[0087] S4: Active power control command generation

[0088] Specifically, after the safety margin coefficient is calculated, the control unit inputs the safety margin coefficient into the active power control loop. In one embodiment, using the converter unit as the power regulation unit, the control unit generates and issues active power control commands. For each target branch, the control unit adjusts the initial scheduling power plan according to the corresponding safety margin coefficient and superimposes the droop support component determined based on the local node voltage offset to generate an active power control command for the power regulation unit to execute. The real-time voltage value of the local node is read from the filtered voltage sequence, and the rated voltage value of the local node is read from the node rated parameter table pre-stored by the control unit. When the active power control command is directed towards outputting active power to the low-voltage distribution transformer area, the specific relationship is as follows:

[0089] ;

[0090] Among them, P o For the active power control command corresponding to the target branch, P f M is the initial scheduling power plan corresponding to the target branch. d C represents the safety margin coefficient corresponding to the target branch. v V is the voltage-active droop factor. t V is the real-time voltage value of the local node corresponding to the target branch read from the filtered voltage sequence. n This is the rated voltage value corresponding to the local node, read from the node rating parameter table. The negative product of the voltage-active droop factor and the voltage offset is the droop support component.

[0091] It should be noted that the voltage-active power droop coefficient C v The parameters were determined through experiments on node voltage deviation and active power response. A programmable AC power supply was used to simulate different degrees of node voltage rise and fall, and multiple sets of voltage-active power droop coefficient test values ​​were set. The power regulation unit was controlled to adjust the active power according to each test value. Node voltage recovery time, maximum voltage deviation, branch current, and power command fluctuations were recorded. Test values ​​with insufficient voltage regulation capability or those prone to overcurrent or power oscillation were eliminated, and test values ​​that could quickly restore node voltage and ensure a stable power regulation process were selected. All the above parameters were calibrated and stored in the control unit before the system was put into operation.

[0092] After obtaining the active power control command for the target branch, the inner-loop current regulator in the power conditioning unit generates a current reference value in a rotating coordinate system based on the active power control command and the reactive power control command. The reactive power control command is either a preset reactive power control command or a reactive power control command generated by the reactive power voltage control loop. The inner-loop current regulator generates a voltage reference value in a rotating coordinate system based on the current reference value and obtains a reference voltage vector in a two-phase stationary coordinate system through coordinate transformation. When the power conditioning unit uses a converter unit, the microprocessor in the power conditioning unit calculates the action time of the three bridge arm switches through a pulse width modulation generator and outputs complementary high and low level PWM drive pulses with dead-time protection through an advanced timer.

[0093] Therefore, the control unit executes the voltage-active power droop control equation according to the target branch. For the target branch with a higher load rate, because its safety margin coefficient is larger, P... f ×(1−M d The term decreases, thereby reducing the active power output command corresponding to the target branch; for target branches with low load rates, the safety margin coefficient is smaller, causing P to decrease. f ×(1−M d The specified item retains a larger proportion of available power, thus allowing the target branch to handle more power regulation. Through the aforementioned differentiated instruction generation method, load balancing among multiple target branches is achieved.

Claims

1. A method for load rate balancing control of a low-voltage distribution transformer area, characterized in that, include: Collect voltage and current data of the target branch and form voltage sampling sequence and current sampling sequence; The voltage sampling sequence and the current sampling sequence are filtered respectively to obtain the filtered voltage sequence and the filtered current sequence. The power sequence is calculated based on the filtered voltage sequence and the filtered current sequence, and the power fluctuation is determined by the power sequence; the real-time branch current of each target branch is determined based on the filtered current sequence, and the branch load rate is determined by the ratio of the real-time branch current to the upper limit of the branch current. The safety margin coefficient for each target branch is calculated based on the power fluctuation and the branch load rate, wherein the safety margin coefficient is obtained by the following formula: ； In the formula, M d M is the safety margin coefficient corresponding to the target branch. b K is the preset baseline margin factor. w D represents the volatility margin weight. p P is the power fluctuation amount. r C is the rated active capacity of the low-voltage distribution transformer area. w K is the fluctuation sensitivity constant. c For the current-carrying state weights, I t I is the effective value of the real-time branch current of the target branch. m I is the upper limit of the current carrying capacity of the branch corresponding to the target branch. t / I m The branch load rate of the target branch; Based on the safety margin coefficient, the active power control command for the target branch is generated by combining the voltage offset and the initial scheduling power plan.

2. The low-voltage distribution transformer area load rate balancing control method according to claim 1, characterized in that, The operations for forming the voltage sampling sequence and the current sampling sequence include: Three-phase voltage and three-phase current waveforms are acquired at the acquisition nodes in the low-voltage distribution transformer area. The acquired three-phase voltage and three-phase current waveforms are conditioned and synchronously sampled. The voltage and current sample values ​​are recorded at the same clock cycle to form voltage and current sampling sequences for subsequent filtering and power calculation.

3. The low-voltage distribution transformer area load rate balancing control method according to claim 1, characterized in that, The filtering process includes: A sliding sampling window is set according to the sampling time sequence. Using multiple voltage sampling points and multiple current sampling points within the sliding sampling window, the voltage smoothing value and current smoothing value corresponding to the center sampling point are calculated respectively. The original voltage sampling value and the original current sampling value of the corresponding center sampling point are replaced by the voltage smoothing value and the current smoothing value respectively. The sliding sampling window is moved along the sampling time sequence to obtain the filtered voltage sequence and the filtered current sequence.

4. The low-voltage distribution transformer area load rate balancing control method according to claim 1, characterized in that, The calculation of the power fluctuation includes: The power sequence is calculated based on the filtered voltage sequence and the filtered current sequence. The change in power value at adjacent sampling times is calculated within the sliding sampling window, and the average of multiple changes is taken as the power fluctuation.

5. The low-voltage distribution transformer area load rate balancing control method according to claim 1, characterized in that, The calculation of the safety margin coefficient includes: The preset reference margin coefficient is a safety margin initial value predetermined based on the upper limit of the current carrying capacity of the target branch, the rated power of the power regulation unit, and the protection setting. The safety margin coefficient obtained according to the calculation formula is subjected to a limiting process to ensure that the safety margin coefficient satisfies 0. <M d <1.

6. The low-voltage distribution transformer area load rate balancing control method according to claim 5, characterized in that, The calculation of the safety margin factor also includes: When the load rate of the target branch increases, the safety margin factor of the target branch is increased; when the load rate of the target branch decreases, the safety margin factor of the target branch is decreased, so as to allocate the power adjustment amount according to the branch load rate.

7. The low-voltage distribution transformer area load rate balancing control method according to claim 1, characterized in that, The generation operation of the active power control command includes: The real-time voltage value of the local node corresponding to the target branch is read from the filtered voltage sequence, and the rated voltage value of the local node is read. The voltage offset is determined using the read real-time voltage value and the rated voltage value. The droop support component is determined according to the voltage offset and the preset voltage-active power droop coefficient. The initial scheduling power plan of the corresponding target branch is adjusted according to the safety margin coefficient, and the adjusted initial scheduling power plan is superimposed with the droop support component to generate the active power control command.

8. The low-voltage distribution transformer area load rate balancing control method according to claim 7, characterized in that, After generating the active power control command, the following operations are also included: A current reference value is generated based on the active power control command and the reactive power control command. A voltage reference value is generated based on the current reference value. A drive pulse is output based on the voltage reference value, and the power adjustment unit is controlled to perform power adjustment through the drive pulse.

9. A flexible interconnection system for low-voltage distribution substations, characterized in that, It includes a data acquisition unit, a processing unit, a control unit, and a power regulation unit that are connected in sequence via communication. The acquisition unit is used to acquire voltage and current data for each target branch; The processing unit is used to perform signal conditioning and synchronous sampling on the voltage data and the current data, and to form a voltage sampling sequence and a current sampling sequence. The control unit is used to calculate the safety margin coefficient based on the voltage sampling sequence and the current sampling sequence, and to generate active power control commands using the safety margin coefficient, voltage offset, and initial dispatch power plan; wherein, before calculating the safety margin coefficient, the control unit first filters the voltage sampling sequence and the current sampling sequence respectively, and calculates the power fluctuation based on the filtered voltage sequence and the filtered current sequence, and calculates the branch load rate based on the filtered current sequence; The power regulation unit is used to perform power regulation according to the active power control command.

10. A flexible interconnection system for low-voltage distribution transformer areas according to claim 9, characterized in that, The processing unit includes a pre-signal conditioning circuit, an analog-to-digital conversion unit, and a buffer array connected in sequence, which are used to perform signal conditioning and synchronous sampling on the voltage data and the current data, and to buffer the voltage sampling sequence and the current sampling sequence, respectively.

Images