Precise zero-crossing switching method for low-voltage switch cabinet

Abstract

The application discloses a precise zero-crossing switching method of a low-voltage switch cabinet, comprising the following steps: (1) real-time sampling and zero-crossing capture: when the intelligent capacitor switches the capacitor group each time, the voltage across the switching switch is quantitatively collected in real time through front-end sampling, the zero-crossing moment of the voltage is latched by a zero-crossing capture unit, and a main control chip synchronously senses the voltage waveform across the switching switch and the driving voltage state; (2) characteristic matching and switching calculation: an action time compensation model is constructed to calculate the advance sending amount of the switching control signal, the accurate switching moment after compensation is obtained, the optimized closing and opening driving parameters are matched, and the switching switch is controlled to perform zero-crossing switching; and (3) dynamic iterative correction: after each switching is completed, the actual action time of the switching, the deviation between the actual switching point and the zero-crossing point, and the current / voltage change characteristics when the switch is closed are collected, the action time compensation model is updated, and the optimal closing and opening driving parameters are fitted and generated.

Description

Technical Field

[0001] This invention relates to the field of low-voltage switchgear technology, and in particular to a precise zero-crossing switching method for low-voltage switchgear. Background Technology

[0002] In low-voltage complete sets of power distribution equipment, intelligent capacitors are the core components for reactive power compensation, and zero-crossing switching control of capacitor switching switches is a key technology for suppressing inrush current, reducing contact arcing, and ensuring the stable operation of the compensation system.

[0003] Existing methods for zero-crossing switching of smart capacitors generally employ fixed action time parameters for advance compensation, failing to optimize parameter matching based on the actual electromagnetic-mechanical coupling characteristics of the switching devices. Furthermore, they do not adequately consider the impact of ambient temperature, operating voltage, and switch fatigue aging on the action time delay. After long-term operation, the mechanical and electromagnetic characteristics of the switch drift, and the deviation between the fixed compensation and the actual action time delay continuously increases. This leads to a significant deviation of the switching point from the true voltage zero-crossing point, causing problems such as excessive inrush current, contact arcing and erosion, and switch malfunctions. Ultimately, this results in an increased failure rate of the switching switch, a shortened capacitor lifespan, and directly impacts the operational reliability and maintenance costs of the low-voltage reactive power compensation system.

[0004] Therefore, there is an urgent need for a precise zero-crossing switching method for low-voltage switchgear that can dynamically adapt to changes in switch characteristics and has higher switching accuracy. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a precise zero-crossing switching method for low-voltage switchgear. This precise zero-crossing switching method for low-voltage switchgear can dynamically adapt to changes in switch characteristics, match the optimal operating parameters of the switch, and achieve precise zero-crossing switching.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A precise zero-crossing switching method for low-voltage switchgear, characterized by comprising the following steps: (1) Real-time sampling and zero-crossing capture: The intelligent capacitor of the low-voltage switch cabinet has a built-in sampling front-end, a zero-crossing capture unit and a main control chip; each time the intelligent capacitor switches the capacitor bank, the voltage at both ends of the switching switch is quantized and collected in real time through the sampling front-end, the zero-crossing capture unit latches the zero-crossing moment of the voltage, and the main control chip synchronously senses the voltage waveform and driving voltage status at both ends of the switching switch. (2) Characteristic matching and switching calculation: Combine the voltage zero crossing time, voltage waveform, driving voltage state in step (1) with the electromagnetic-mechanical action time delay characteristics of the switching switch itself. Based on the pre-built action time compensation model, calculate the advance issuance amount of the switching control signal to obtain the accurate switching time after compensation. Then match the optimized closing and opening driving parameters to control the switching switch to perform zero crossing switching. (3) Dynamic Iterative Correction: After each switching is completed, the actual action time of this switching, the deviation between the actual switching point and the zero crossing point, and the current / voltage change characteristics when the switch is closed are collected. The action time compensation model is iteratively updated through the "trial and error-learning" mechanism, and the optimal closing and opening driving parameters for the next switching are fitted and generated for the next round of zero crossing switching control.

[0007] In step (1) above, the sampling front end refers to the part of the circuit closest to the signal source being measured in the signal acquisition link. In the smart capacitor, the voltage across the relay is not directly converted into a weak signal type and transmitted to the chip. Instead, the circuit directly analyzes the voltage and only transmits high / low levels as signals indicating whether the signal has crossed zero.

[0008] In step (1) above, the circuit of the zero-crossing capture unit achieves precise latching of the voltage zero-crossing point at the microsecond level, providing a reliable time reference.

[0009] In step (2) above, the electromagnetic-mechanical action delay characteristics of the switching switch itself are combined with the pre-calibrated time compensation curve / two-dimensional compensation calibration surface to calculate the advance issuance amount of the switching control signal, so as to ensure that the contact of the switching switch completes the action at the voltage zero crossing point, thereby offsetting the switching deviation caused by the action delay of the switching switch in principle.

[0010] In step (3) above, after each switching is completed, the actual action time of this switching, the deviation between the actual switching point and the zero crossing point, and the current and voltage change characteristics are collected. The closing and opening drive parameters of the next time are iteratively corrected through the self-learning mechanism, and the characteristic drift caused by switch aging, temperature change and voltage fluctuation is automatically adapted to achieve self-maintaining zero crossing accuracy throughout the entire life cycle.

[0011] In the preferred embodiment, in step (1), the zero-crossing capture unit accurately obtains the voltage zero-crossing moment through a comparison circuit: (1-1) Raw signal input: The power frequency AC voltage at both ends of the switching switch is used as the raw input signal and sent to the detection link to provide the raw sampling object for subsequent zero-crossing detection; (1-2) Voltage divider / current limiting conditioning circuit processing: The high-voltage AC signal is linearly attenuated by a resistor voltage divider and current limiting network, reducing the grid-level high-voltage signal to the safe input range allowed by the operational amplifier device; (1-3) Voltage follower buffer isolation: A voltage follower composed of operational amplifiers is used as an intermediate buffer stage, and impedance isolation is achieved by utilizing its high input impedance and low output impedance characteristics. (1-4) Zero-crossing comparator core shaping: The zero-crossing comparator circuit is used as the core unit. The comparator reference terminal is connected to the 0V ground reference. The input sinusoidal AC signal is compared with the 0V reference in real time. The output is high level during the positive half-cycle of AC and low level during the negative half-cycle. The continuous sine wave is directly converted into a square wave signal synchronized with the power frequency, thus completing the zero-crossing shaping of the analog sine wave signal into a digital jumping signal. (1-5) RC filtering + Schmitt shaping debouncing: First, the high-frequency noise, glitches and power grid interference superimposed on the square wave signal are filtered out by the RC filter network. Then, the square wave is shaped twice by the Schmitt trigger to eliminate the output oscillation and multiple jumps caused by noise jitter of the comparator, and the output is a clean square wave with steep edges and no noise. (1-6) Level conversion: The shaped square wave signal is passed through a level conversion circuit to match the signal amplitude to the rated operating level of the main control chip's IO port, so as to achieve level compatibility between the detection circuit and the main control chip and obtain a standard square wave; (1-7) MCU hardware capture: The obtained standard square wave is sent to the MCU timer capture unit of the main control chip. The hardware capture channel captures the rising edge and falling edge of the square wave in real time and records the zero-crossing time register value. The moment of the transition edge is the precise zero-crossing time of the voltage.

[0012] The above steps (1-3) include voltage follower buffer isolation: a voltage follower composed of operational amplifiers is used as an intermediate buffer stage. Its high input impedance and low output impedance characteristics are used to achieve impedance isolation, completely avoiding the interference of the load effect of the subsequent circuit on the voltage division accuracy of the preceding stage, ensuring the amplitude accuracy and phase authenticity of the sampled signal, and preventing the introduction of zero-crossing phase error due to load bias.

[0013] The RC filtering and Schmitt shaping debouncing steps (1-5) above can ensure that each zero-crossing point corresponds to a unique transition edge, thus eliminating false triggering at the hardware level.

[0014] The above step (1) completes zero-crossing shaping through hardware comparison circuit, avoiding the calculation delay and quantization error of software sampling; the main control chip only needs to capture the square wave transition edge, and the time resolution can reach the microsecond level, improving the accuracy of the zero-crossing reference from the source.

[0015] In the preferred embodiment, in step (2), the action time compensation model is constructed using the full-condition test matrix and accelerated aging type test before leaving the factory, according to the following steps: (2-1) Initial operating condition acquisition: After receiving the switching trigger command, the current real-time operating condition parameters are first read, including ambient temperature T, bus voltage V and cumulative number of switch actions N; at the same time, the zero-crossing capture unit is started to monitor the voltage waveform in real time. (2-2) Reference zero-crossing time locking: The zero-crossing capture unit determines whether the next zero-crossing time T0 of the voltage has been latched: if not latched, it waits for the interrupt trigger signal of the hardware comparator; if latched, it acquires and latches the reference zero-crossing time T0. (2-3) Reference action delay query: Using ambient temperature T and bus voltage V as input variables, query the pre-constructed two-dimensional compensation calibration surface and output the reference action delay τ_base(T,V) of the switch under the corresponding operating conditions; (2-4) Aging characteristic correction: Based on the cumulative number of switch actions N, the aging correction function f(N) obtained by fitting based on accelerated aging test is called to calculate the aging correction amount, and the characteristic compensation of the reference action time delay is performed throughout the entire life cycle to offset the time delay drift caused by switch mechanical fatigue. (2-5) Total action delay calculation: The total action delay τ of the switch is calculated by superimposing the fixed delay τ_drive of the drive circuit. The calculation formula is: τ=τ_base+f(N)+τ_drive; (2-6) Historical correction amount superposition: Read the previous switching self-learning output of the switching correction amount δ_prev, and calculate the final advance amount Δt in combination with the total action delay τ. The calculation formula is: Δt=τ+δ_prev; (2-7) Calculation of drive command timing: Based on the reference zero-crossing time T0 and the final advance issuance amount Δt, calculate the issuance time t_send of the drive control signal. The calculation formula is: t_send=T0-Δt; When the system reaches the t_send time, it outputs a closing or opening drive command to the switching switch. (2-8) Actual action moment capture: After the drive command is issued, the status of the auxiliary contact of the switch or the sudden change signal of the circuit current is detected in real time, and the actual action moment T_act of the switch contact is captured with high precision and the timestamp is recorded; (2-9) Zero crossing deviation calculation: Based on the actual action time T_act and the reference zero crossing time T0, calculate the zero crossing deviation e of this switching. The calculation formula is: e=T_act-T0, where a positive value of e indicates that the switch operates after zero crossing, and a negative value of e indicates that the switch operates before zero crossing. (2-10) Deviation tolerance judgment: Compare the zero-crossing deviation e with the preset tolerance deviation threshold: If the zero-crossing deviation e is within the allowable range, the current model parameters remain unchanged, the current switching process ends, and the system waits for the next switching instruction. If the zero-crossing deviation e exceeds the allowable range, the self-learning correction process will be initiated, and the following steps will be performed: (2-10.1) Sliding window sample update: Store the sample data (e,T,V,N) of this cut into a sliding window of a preset length; the sliding window adopts a first-in-first-out mechanism and stores the most recent M groups of valid cut samples. (2-10.2) Calculation of recursive correction: The weighted least squares recursive algorithm is used to fit the sample data in the sliding window to obtain the new correction δ_new; (2-10.3) Filtering and smoothing: The new correction amount δ_new is smoothed by a first-order low-pass filter algorithm to obtain the updated cutting correction amount δ. The calculation formula is: δ=α・δ_new+(1-α)・δ_prev, where α is the filtering and smoothing coefficient, which is used to suppress parameter fluctuations caused by single abnormal samples. (2-10.4) Parameter Iteration Storage: The updated switching correction δ is stored in the parameter storage area and used as the historical correction δ_prev for the next round of switching. The current switching process ends and waits for the next switching instruction.

[0016] In the above steps (2-10), if the zero-crossing deviation e is less than the preset allowable deviation threshold (e.g., ±50μs) for multiple consecutive times, the model is considered to have converged, which can reduce the learning intensity and reduce the computational cost.

[0017] In step (2-10.1) above, the most recent M sample data (e.g., M=20) are stored in a sliding window of a preset length to remove outliers; In step (2-10.3) above, to avoid oscillation, a first-order low-pass filter algorithm is used to smooth the new correction amount δ_new.

[0018] In the above steps (2-3), by measuring the distribution of the action time of the switching switch under different ambient temperatures, different bus voltages, and different aging degrees, a two-dimensional compensation calibration surface of "action signal issuance time - actual contact action time" is constructed, forming an initial compensation parameter library covering the entire life cycle of the switching switch.

[0019] The above step (2) incorporates all the core factors (temperature, voltage, mechanical aging) that affect the action delay of the switching switch into the calibrated action time compensation model. The full-condition parameter fitting is completed at the factory, and the compensation value of the corresponding condition can be directly called during operation. The initial accuracy is much higher than that of a single fixed parameter, which improves the environmental adaptability and life-cycle consistency of the switching accuracy from the source and reduces the number of iteration corrections in the early stage of operation.

[0020] In the further optimized scheme, in step (2-3), the underlying logic of the two-dimensional compensation calibration surface is defined by two sets of core formulas, and the meaning and mapping relationship of each physical quantity are as follows: (2-3.1) Basic formula for action timing: t_actual = t_trigger + t_delay(W), where: t_actual refers to the moment when the switch contacts actually complete the closing / opening action, and is the output dependent variable of the model; t_trigger refers to the moment when the control system issues a drive command to the switching switch, and is the first input independent variable of the model; t_delay(W) refers to the action delay function of the switch, which represents the time difference from the issuance of the drive command to the actual action of the contact. Its value is determined by the comprehensive operating condition index W, and is the function output corresponding to the second input independent variable of the model. (2-3.2) Optimal trigger time formula: t_trigger=t_zero-t_delay(W)-t_guard, where: t_zero refers to the time when the target voltage crosses zero, that is, the preset target action time for zero-crossing switching; t_guard refers to a preset safety margin used to offset random fluctuations and ensure that the throwing and cutting actions fall within the allowable accuracy range; t_trigger refers to the optimal timing for issuing the drive command to achieve precise zero-crossing switching.

[0021] The basic formula for the action timing in step (2-3.1) above is the core mapping rule of the surface: given the drive triggering time and the operating condition, the actual action time of the switch can be uniquely determined, forming a quantitative correspondence between "drive input and action output". Using the action signal emission time t_trigger as the first-dimensional independent variable, the comprehensive operating condition index W as the second-dimensional independent variable, and the actual contact action time t_actual as the output dependent variable, based on the core formula t_actual = t_trigger + t_delay(W), a continuous two-dimensional compensation calibration surface can be constructed by fitting test data from discrete operating condition points. Any coordinate point (t_trigger, W) on the surface corresponds to a unique actual action time t_actual, which can intuitively present the time delay variation law between drive commands and actual actions under different operating conditions. In practical applications, the optimal drive triggering time for achieving target zero-crossing switching under any operating condition can be quickly obtained through reverse lookup of the surface.

[0022] The optimal triggering time formula in step (2-3.2) above is the application goal of the compensation model: based on the target zero-crossing time, combined with the action delay of the corresponding operating condition, the advance issuance amount of the drive command is derived in reverse, so as to achieve precise alignment between the switching action time and the voltage zero-crossing point. The comprehensive operating condition index W is a coupled quantification of the two core influencing factors, ambient temperature and switch aging degree, with a value range of 0-1; W=0 corresponds to the baseline operating condition of 25℃ normal temperature and brand-new equipment; W=1 corresponds to the extreme operating condition of 70℃ high temperature and end of life. The operating condition parameters determine the spatial shape of the surface by changing the magnitude of the action delay, and the specific influence law is as follows: (1) Effect of temperature deviation from the reference: When the ambient temperature deviates from the reference value of 25℃, the resistance effect of the switch electromagnetic circuit and the cold welding effect of mechanical parts are aggravated, resulting in an increase in the switching action delay; (2) Effects of aging accumulation: As the number of cumulative operation of the switch increases, aging phenomena such as internal spring fatigue and contact erosion gradually accumulate, increasing mechanical resistance and operation time delay. (3) Coupling effect of high temperature and high aging: When high temperature environment and aging accumulation work together, the rate of degradation of switching performance is significantly accelerated, and the action delay shows a nonlinear increase, rather than a linear superposition of the two factors.

[0023] The aforementioned pattern dictates that action delay cannot be represented by a single fixed value, and fixed parameter compensation cannot meet the switching accuracy requirements of all working conditions and the entire life cycle. Therefore, it is necessary to construct a two-dimensional compensation calibration surface that covers all working conditions.

[0024] In a further optimized scheme, in step (2-3), the two-dimensional compensation calibration surface adopts a construction mechanism of "factory initial calibration + recursive correction during operation" to ensure that the model continuously matches the real-time characteristics of the switch. Initial calibration before leaving the factory: Before leaving the factory, multiple sets of switching action time delay data under temperature and aging conditions are measured through a full-condition test matrix to obtain discrete mapping sample points; an initial two-dimensional compensation calibration surface is constructed through data fitting to form a benchmark compensation parameter library that covers typical operating conditions throughout the entire life cycle of the equipment. Recursive correction during operation: After the equipment is put into operation, the surface nodes are dynamically and recursively corrected through a self-learning mechanism: After each switching is completed, the actual operating parameters and the actual action deviation are collected, and the time delay mapping parameters of the corresponding operating points are updated; the surface shape is gradually corrected through iteration, so that the compensation model continuously matches the real-time action characteristics of the switch, offsets the characteristic drift caused by aging and temperature change, and ensures the zero-crossing switching accuracy throughout the entire life cycle.

[0025] In the preferred embodiment, in step (2), the closing and opening control parameters are obtained through a large number of switching tests during the factory stage: the difference between each switching point and the zero crossing point is recorded in the switching test, the advance parameter is adjusted in reverse, and the initial closing and opening control parameter calibration is completed.

[0026] In the preferred embodiment, in step (3), the "trial and error-learning" mechanism dynamically corrects the advance of the cut: it records the time deviation sequence between the actual contact point action time and the predicted zero crossing point for each cut in real time, and uses the sliding window weighted least squares algorithm to recursively optimize the advance compensation value to achieve dynamic online calibration of time delay drift within the life cycle.

[0027] In the preferred embodiment, the low-voltage switchgear is an AC low-voltage integrated distribution box. Also known as a JP cabinet, the AC low-voltage integrated distribution box is an outdoor power distribution device that integrates power distribution, metering, reactive power compensation, and protection functions. It is mainly used in rural power grids, residential area terminals, and small factory power distribution systems.

[0028] In the preferred embodiment, the intelligent capacitor is of the ZC868 series. The ZC868 series low-voltage intelligent capacitor is based on two or more sets (Δ type) or one or more sets (Y type) of low-voltage power capacitors, integrating modern measurement and control, power electronics, network communication, and automation control technologies. It replaces the traditional reactive power compensation device, which consists of separate components such as controllers, fuses, composite switches or mechanical contactors, thermal relays, low-voltage capacitors, and indicator lights connected by wires within a cabinet. It features flexible compensation methods, good compensation effect, small device size, low power consumption, convenient installation and maintenance, long service life, strong protection functions, and high reliability.

[0029] Compared with the prior art, the present invention has the following advantages: This invention enables the switching action of the switching switch to automatically track changes in voltage and current, and combines these changes with the switching characteristics to perfectly match the optimal closing and opening drive parameters, achieving precise zero crossing. This suppresses inrush current impacts and arcing during capacitor switching, avoids damage to the capacitor dielectric from instantaneous large currents, improves the overall equipment operating stability, and significantly extends the service life of the capacitor equipment. Attached Figure Description

[0030] Figure 1 This is a flowchart illustrating the construction of an action time compensation model according to a specific embodiment of the present invention; Figure 2 This is a schematic diagram of a two-dimensional compensation calibration surface according to a specific embodiment of the present invention; Figure 3 This is a 2D engineering reference drawing of the compensation calibration surface according to a specific embodiment of the present invention; Figure 4This is a flowchart illustrating how the zero-crossing capture unit acquires the voltage zero-crossing moment in a specific embodiment of the present invention. Detailed Implementation

[0031] The following description, in conjunction with the accompanying drawings and preferred embodiments of the present invention, will provide further details.

[0032] like Figure 1-4 As shown, the precise zero-crossing switching method for low-voltage switchgear in this embodiment includes the following steps: (1) Real-time sampling and zero-crossing capture: The intelligent capacitor of the low-voltage switch cabinet has a built-in sampling front-end, a zero-crossing capture unit and a main control chip; each time the intelligent capacitor switches the capacitor bank, the voltage at both ends of the switching switch is quantized and collected in real time through the sampling front-end, the zero-crossing capture unit latches the zero-crossing moment of the voltage, and the main control chip synchronously senses the voltage waveform and driving voltage status at both ends of the switching switch. (2) Characteristic matching and switching calculation: Combine the voltage zero crossing time, voltage waveform, driving voltage state in step (1) with the electromagnetic-mechanical action time delay characteristics of the switching switch itself. Based on the pre-built action time compensation model, calculate the advance issuance amount of the switching control signal to obtain the accurate switching time after compensation. Then match the optimized closing and opening driving parameters to control the switching switch to perform zero crossing switching. (3) Dynamic Iterative Correction: After each switching is completed, the actual action time of this switching, the deviation between the actual switching point and the zero crossing point, and the current / voltage change characteristics when the switch is closed are collected. The action time compensation model is iteratively updated through the "trial and error-learning" mechanism, and the optimal closing and opening driving parameters for the next switching are fitted and generated for the next round of zero crossing switching control.

[0033] In step (1) above, the sampling front end refers to the part of the circuit closest to the signal source being measured in the signal acquisition link. In the smart capacitor, the voltage across the relay is not directly converted into a weak signal type and transmitted to the chip. Instead, the circuit directly analyzes the voltage and only transmits high / low levels as signals indicating whether the signal has crossed zero.

[0034] In step (1) above, the circuit of the zero-crossing capture unit achieves precise latching of the voltage zero-crossing point at the microsecond level, providing a reliable time reference.

[0035] In step (2) above, the electromagnetic-mechanical action delay characteristics of the switching switch itself are combined with the pre-calibrated time compensation curve / two-dimensional compensation calibration surface to calculate the advance issuance amount of the switching control signal, so as to ensure that the contact of the switching switch completes the action at the voltage zero crossing point, thereby offsetting the switching deviation caused by the action delay of the switching switch in principle.

[0036] In step (3) above, after each switching is completed, the actual action time of this switching, the deviation between the actual switching point and the zero crossing point, and the current and voltage change characteristics are collected. The closing and opening drive parameters of the next time are iteratively corrected through the self-learning mechanism, and the characteristic drift caused by switch aging, temperature change and voltage fluctuation is automatically adapted to achieve self-maintaining zero crossing accuracy throughout the entire life cycle.

[0037] In step (1), the zero-crossing capture unit accurately obtains the time of voltage zero-crossing through the comparison circuit: (1-1) Raw signal input: The power frequency AC voltage at both ends of the switching switch is used as the raw input signal and sent to the detection link to provide the raw sampling object for subsequent zero-crossing detection; (1-2) Voltage divider / current limiting conditioning circuit processing: The high-voltage AC signal is linearly attenuated by a resistor voltage divider and current limiting network, reducing the grid-level high-voltage signal to the safe input range allowed by the operational amplifier device; (1-3) Voltage follower buffer isolation: A voltage follower composed of operational amplifiers is used as an intermediate buffer stage, and impedance isolation is achieved by utilizing its high input impedance and low output impedance characteristics. (1-4) Zero-crossing comparator core shaping: The zero-crossing comparator circuit is used as the core unit. The comparator reference terminal is connected to the 0V ground reference. The input sinusoidal AC signal is compared with the 0V reference in real time. The output is high level during the positive half-cycle of AC and low level during the negative half-cycle. The continuous sine wave is directly converted into a square wave signal synchronized with the power frequency, thus completing the zero-crossing shaping of the analog sine wave signal into a digital jumping signal. (1-5) RC filtering + Schmitt shaping debouncing: First, the high-frequency noise, glitches and power grid interference superimposed on the square wave signal are filtered out by the RC filter network. Then, the square wave is shaped twice by the Schmitt trigger to eliminate the output oscillation and multiple jumps caused by noise jitter of the comparator, and the output is a clean square wave with steep edges and no noise. (1-6) Level conversion: The shaped square wave signal is passed through a level conversion circuit to match the signal amplitude to the rated operating level of the main control chip's IO port, so as to achieve level compatibility between the detection circuit and the main control chip and obtain a standard square wave; (1-7) MCU hardware capture: The obtained standard square wave is sent to the MCU timer capture unit of the main control chip. The hardware capture channel captures the rising edge and falling edge of the square wave in real time and records the zero-crossing time register value. The moment of the transition edge is the precise zero-crossing time of the voltage.

[0038] The above steps (1-3) include voltage follower buffer isolation: a voltage follower composed of operational amplifiers is used as an intermediate buffer stage. Its high input impedance and low output impedance characteristics are used to achieve impedance isolation, completely avoiding the interference of the load effect of the subsequent circuit on the voltage division accuracy of the preceding stage, ensuring the amplitude accuracy and phase authenticity of the sampled signal, and preventing the introduction of zero-crossing phase error due to load bias.

[0039] The RC filtering and Schmitt shaping debouncing steps (1-5) above can ensure that each zero-crossing point corresponds to a unique transition edge, thus eliminating false triggering at the hardware level.

[0040] The above step (1) completes zero-crossing shaping through hardware comparison circuit, avoiding the calculation delay and quantization error of software sampling; the main control chip only needs to capture the square wave transition edge, and the time resolution can reach the microsecond level, improving the accuracy of the zero-crossing reference from the source.

[0041] In step (2), the motion time compensation model is constructed using the full-condition test matrix and accelerated aging type test before leaving the factory, according to the following steps: (2-1) Initial operating condition acquisition: After receiving the switching trigger command, the current real-time operating condition parameters are first read, including ambient temperature T, bus voltage V and cumulative number of switch actions N; at the same time, the zero-crossing capture unit is started to monitor the voltage waveform in real time. (2-2) Reference zero-crossing time locking: The zero-crossing capture unit determines whether the next zero-crossing time T0 of the voltage has been latched: if not latched, it waits for the interrupt trigger signal of the hardware comparator; if latched, it acquires and latches the reference zero-crossing time T0. (2-3) Reference action delay query: Using ambient temperature T and bus voltage V as input variables, query the pre-constructed two-dimensional compensation calibration surface and output the reference action delay τ_base(T,V) of the switch under the corresponding operating conditions; (2-4) Aging characteristic correction: Based on the cumulative number of switch actions N, the aging correction function f(N) obtained by fitting based on accelerated aging test is called to calculate the aging correction amount, and the characteristic compensation of the reference action time delay is performed throughout the entire life cycle to offset the time delay drift caused by switch mechanical fatigue. (2-5) Total action delay calculation: The total action delay τ of the switch is calculated by superimposing the fixed delay τ_drive of the drive circuit. The calculation formula is: τ=τ_base+f(N)+τ_drive; (2-6) Historical correction amount superposition: Read the previous switching self-learning output of the switching correction amount δ_prev, and calculate the final advance amount Δt in combination with the total action delay τ. The calculation formula is: Δt=τ+δ_prev; (2-7) Calculation of drive command timing: Based on the reference zero-crossing time T0 and the final advance issuance amount Δt, calculate the issuance time t_send of the drive control signal. The calculation formula is: t_send=T0-Δt; When the system reaches the t_send time, it outputs a closing or opening drive command to the switching switch. (2-8) Actual action moment capture: After the drive command is issued, the status of the auxiliary contact of the switch or the sudden change signal of the circuit current is detected in real time, and the actual action moment T_act of the switch contact is captured with high precision and the timestamp is recorded; (2-9) Zero crossing deviation calculation: Based on the actual action time T_act and the reference zero crossing time T0, calculate the zero crossing deviation e of this switching. The calculation formula is: e=T_act-T0, where a positive value of e indicates that the switch operates after zero crossing, and a negative value of e indicates that the switch operates before zero crossing. (2-10) Deviation tolerance judgment: Compare the zero-crossing deviation e with the preset tolerance deviation threshold: If the zero-crossing deviation e is within the allowable range, the current model parameters remain unchanged, the current switching process ends, and the system waits for the next switching instruction. If the zero-crossing deviation e exceeds the allowable range, the self-learning correction process will be initiated, and the following steps will be performed: (2-10.1) Sliding window sample update: Store the sample data (e,T,V,N) of this cut into a sliding window of a preset length; the sliding window adopts a first-in-first-out mechanism and stores the most recent M groups of valid cut samples. (2-10.2) Calculation of recursive correction: The weighted least squares recursive algorithm is used to fit the sample data in the sliding window to obtain the new correction δ_new; (2-10.3) Filtering and smoothing: The new correction amount δ_new is smoothed by a first-order low-pass filter algorithm to obtain the updated cutting correction amount δ. The calculation formula is: δ=α・δ_new+(1-α)・δ_prev, where α is the filtering and smoothing coefficient, which is used to suppress parameter fluctuations caused by single abnormal samples. (2-10.4) Parameter Iteration Storage: The updated switching correction δ is stored in the parameter storage area and used as the historical correction δ_prev for the next round of switching. The current switching process ends and waits for the next switching instruction.

[0042] In the above steps (2-10), if the zero-crossing deviation e is less than the preset allowable deviation threshold (e.g., ±50μs) for multiple consecutive times, the model is considered to have converged, which can reduce the learning intensity and reduce the computational cost.

[0043] In step (2-10.1) above, the most recent M sample data (e.g., M=20) are stored in a sliding window of a preset length to remove outliers; In step (2-10.3) above, to avoid oscillation, a first-order low-pass filter algorithm is used to smooth the new correction amount δ_new.

[0044] In the above steps (2-3), by measuring the distribution of the action time of the switching switch under different ambient temperatures, different bus voltages, and different aging degrees, a two-dimensional compensation calibration surface of "action signal issuance time - actual contact action time" is constructed, forming an initial compensation parameter library covering the entire life cycle of the switching switch.

[0045] The above step (2) incorporates all the core factors (temperature, voltage, mechanical aging) that affect the action delay of the switching switch into the calibrated action time compensation model. The full-condition parameter fitting is completed at the factory, and the compensation value of the corresponding condition can be directly called during operation. The initial accuracy is much higher than that of a single fixed parameter, which improves the environmental adaptability and life-cycle consistency of the switching accuracy from the source and reduces the number of iteration corrections in the early stage of operation.

[0046] In steps (2-3), the underlying logic of the two-dimensional compensation calibration surface is defined by two sets of core formulas, and the meaning and mapping relationship of each physical quantity are as follows: (2-3.1) Basic formula for action timing: t_actual = t_trigger + t_delay(W), where: t_actual refers to the moment when the switch contacts actually complete the closing / opening action, and is the output dependent variable of the model; t_trigger refers to the moment when the control system issues a drive command to the switching switch, and is the first input independent variable of the model; t_delay(W) refers to the action delay function of the switch, which represents the time difference from the issuance of the drive command to the actual action of the contact. Its value is determined by the comprehensive operating condition index W, and is the function output corresponding to the second input independent variable of the model. (2-3.2) Optimal trigger time formula: t_trigger=t_zero-t_delay(W)-t_guard, where: t_zero refers to the time when the target voltage crosses zero, that is, the preset target action time for zero-crossing switching; t_guard refers to a preset safety margin used to offset random fluctuations and ensure that the throwing and cutting actions fall within the allowable accuracy range; t_trigger refers to the optimal timing for issuing the drive command to achieve precise zero-crossing switching.

[0047] The basic formula for the action timing in step (2-3.1) above is the core mapping rule of the surface: given the drive triggering time and the operating condition, the actual action time of the switch can be uniquely determined, forming a quantitative correspondence between "drive input and action output". Using the action signal emission time t_trigger as the first-dimensional independent variable, the comprehensive operating condition index W as the second-dimensional independent variable, and the actual contact action time t_actual as the output dependent variable, based on the core formula t_actual = t_trigger + t_delay(W), a continuous two-dimensional compensation calibration surface can be constructed by fitting test data from discrete operating condition points. Any coordinate point (t_trigger, W) on the surface corresponds to a unique actual action time t_actual, which can intuitively present the time delay variation law between drive commands and actual actions under different operating conditions. In practical applications, the optimal drive triggering time for achieving target zero-crossing switching under any operating condition can be quickly obtained through reverse lookup of the surface.

[0048] The optimal triggering time formula in step (2-3.2) above is the application goal of the compensation model: based on the target zero-crossing time, combined with the action delay of the corresponding operating condition, the advance issuance amount of the drive command is derived in reverse, achieving precise alignment between the switching action time and the voltage zero-crossing point. The comprehensive operating condition index W is a coupled quantification of the two core influencing factors: ambient temperature and switch aging degree, with a value range of 0-1; W=0 corresponds to the baseline operating condition of 25℃ normal temperature and brand-new equipment; W=1 corresponds to the extreme operating condition of 70℃ high temperature and end of life. Figure 3 As shown in the 2D engineering reference diagram of the compensation calibration surface, the working parameters determine the spatial shape of the surface by changing the magnitude of the action delay. The specific influence laws are as follows: (1) Effect of temperature deviation from the reference: When the ambient temperature deviates from the reference value of 25℃, the resistance effect of the switch electromagnetic circuit and the cold welding effect of mechanical parts are aggravated, resulting in an increase in the switching action delay; (2) Effects of aging accumulation: As the number of cumulative operation of the switch increases, aging phenomena such as internal spring fatigue and contact erosion gradually accumulate, increasing mechanical resistance and operation time delay. (3) Coupling effect of high temperature and high aging: When high temperature environment and aging accumulation work together, the rate of degradation of switching performance is significantly accelerated, and the action delay shows a nonlinear increase, rather than a linear superposition of the two factors.

[0049] The aforementioned pattern dictates that action delay cannot be represented by a single fixed value, and fixed parameter compensation cannot meet the switching accuracy requirements of all working conditions and the entire life cycle. Therefore, it is necessary to construct a two-dimensional compensation calibration surface that covers all working conditions.

[0050] In steps (2-3), the two-dimensional compensation calibration surface adopts a construction mechanism of "factory initial calibration + runtime recursive correction" to ensure that the model continuously matches the real-time characteristics of the switch. Initial calibration before leaving the factory: Before leaving the factory, multiple sets of switching action time delay data under temperature and aging conditions are measured through a full-condition test matrix to obtain discrete mapping sample points; an initial two-dimensional compensation calibration surface is constructed through data fitting to form a benchmark compensation parameter library that covers typical operating conditions throughout the entire life cycle of the equipment. Recursive correction during operation: After the equipment is put into operation, the surface nodes are dynamically and recursively corrected through a self-learning mechanism: After each switching is completed, the actual operating parameters and the actual action deviation are collected, and the time delay mapping parameters of the corresponding operating points are updated; the surface shape is gradually corrected through iteration, so that the compensation model continuously matches the real-time action characteristics of the switch, offsets the characteristic drift caused by aging and temperature change, and ensures the zero-crossing switching accuracy throughout the entire life cycle.

[0051] In step (2), the closing and opening control parameters are obtained through a large number of switching tests during the factory stage: the difference between each switching point and the zero crossing point is recorded in the switching test, the advance parameter is adjusted in reverse, and the initial closing and opening control parameter calibration is completed.

[0052] In step (3), the "trial and error-learning" mechanism dynamically corrects the lead time of the cut: the time deviation sequence between the actual contact point action time and the predicted zero crossing point is recorded in real time, and the lead compensation value is recursively optimized by the sliding window weighted least squares algorithm to realize the dynamic online calibration of the time delay drift within the life cycle.

[0053] The low-voltage switchgear is an AC low-voltage integrated distribution box. Also known as a JP cabinet, it is an outdoor power distribution device that integrates power distribution, metering, reactive power compensation, and protection functions. It is mainly used in rural power grids, residential area terminals, and small factory power distribution systems.

[0054] The intelligent capacitor is model ZC868 series. The ZC868 series low-voltage intelligent capacitor is based on two or more sets (Δ type) or one or more sets (Y type) of low-voltage power capacitors, integrating modern measurement and control, power electronics, network communication, and automation control technologies. It replaces the traditional reactive power compensation device, which consists of separate components such as controllers, fuses, composite switches or mechanical contactors, thermal relays, low-voltage capacitors, and indicator lights connected by wires in a cabinet. It features flexible compensation methods, good compensation effect, small device size, low power consumption, convenient installation and maintenance, long service life, strong protection functions, and high reliability.

[0055] Furthermore, it should be noted that the names of the various parts of the specific embodiments described in this specification may differ. All equivalent or simple variations made to the structure, features, and principles described in this invention are included within the scope of protection of this invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the structure of this invention or exceed the scope defined in these claims, all of which should fall within the scope of protection of this invention.

Claims

1. A precise zero-crossing switching method for low-voltage switchgear, characterized in that... Includes the following steps: (1) Real-time sampling and zero-crossing capture: The intelligent capacitor of the low-voltage switch cabinet has a built-in sampling front-end, a zero-crossing capture unit and a main control chip; each time the intelligent capacitor switches the capacitor bank, the voltage at both ends of the switching switch is quantized and collected in real time through the sampling front-end, the zero-crossing capture unit latches the zero-crossing moment of the voltage, and the main control chip synchronously senses the voltage waveform and driving voltage status at both ends of the switching switch. (2) Characteristic matching and switching calculation: Combine the voltage zero crossing time, voltage waveform, driving voltage state in step (1) with the electromagnetic-mechanical action time delay characteristics of the switching switch itself. Based on the pre-built action time compensation model, calculate the advance issuance amount of the switching control signal to obtain the accurate switching time after compensation. Then match the optimized closing and opening driving parameters to control the switching switch to perform zero crossing switching. (3) Dynamic Iterative Correction: After each switching is completed, the actual action time of this switching, the deviation between the actual switching point and the zero crossing point, and the current / voltage change characteristics when the switch is closed are collected. The action time compensation model is iteratively updated through the "trial and error-learning" mechanism, and the optimal closing and opening driving parameters for the next switching are fitted and generated for the next round of zero crossing switching control.

2. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: In step (1), the zero-crossing capture unit accurately obtains the time of voltage zero crossing through a comparison circuit: (1-1) Raw signal input: The power frequency AC voltage at both ends of the switching switch is used as the raw input signal and sent to the detection link to provide the raw sampling object for subsequent zero-crossing detection; (1-2) Voltage divider / current limiting conditioning circuit processing: The high-voltage AC signal is linearly attenuated by a resistor voltage divider and current limiting network, reducing the grid-level high-voltage signal to the safe input range allowed by the operational amplifier device; (1-3) Voltage follower buffer isolation: A voltage follower composed of operational amplifiers is used as an intermediate buffer stage, and impedance isolation is achieved by utilizing its high input impedance and low output impedance characteristics. (1-4) Zero-crossing comparator core shaping: The zero-crossing comparator circuit is used as the core unit. The comparator reference terminal is connected to the 0V ground reference. The input sinusoidal AC signal is compared with the 0V reference in real time. The output is high level during the positive half-cycle of AC and low level during the negative half-cycle. The continuous sine wave is directly converted into a square wave signal synchronized with the power frequency, thus completing the zero-crossing shaping of the analog sine wave signal into a digital jumping signal. (1-5) RC filtering + Schmitt shaping debouncing: First, the high-frequency noise, glitches and power grid interference superimposed on the square wave signal are filtered out by the RC filter network. Then, the square wave is shaped twice by the Schmitt trigger to eliminate the output oscillation and multiple jumps caused by noise jitter of the comparator, and the output is a clean square wave with steep edges and no noise. (1-6) Level conversion: The shaped square wave signal is passed through a level conversion circuit to match the signal amplitude to the rated operating level of the main control chip's IO port, so as to achieve level compatibility between the detection circuit and the main control chip and obtain a standard square wave; (1-7) MCU hardware capture: The obtained standard square wave is sent to the MCU timer capture unit of the main control chip. The hardware capture channel captures the rising edge and falling edge of the square wave in real time and records the zero-crossing time register value. The moment of the transition edge is the precise zero-crossing time of the voltage.

3. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: In step (2), the action time compensation model is constructed using the full-condition test matrix and accelerated aging type test before leaving the factory, according to the following steps: (2-1) Initial operating condition acquisition: After receiving the switching trigger command, the current real-time operating condition parameters are first read, including ambient temperature T, bus voltage V and cumulative number of switch actions N; at the same time, the zero-crossing capture unit is started to monitor the voltage waveform in real time. (2-2) Reference zero-crossing time locking: The zero-crossing capture unit determines whether the next zero-crossing time T0 of the voltage has been latched: if not latched, it waits for the interrupt trigger signal of the hardware comparator; if latched, it acquires and latches the reference zero-crossing time T0. (2-3) Reference action delay query: Using ambient temperature T and bus voltage V as input variables, query the pre-constructed two-dimensional compensation calibration surface and output the reference action delay τ_base(T,V) of the switch under the corresponding operating conditions; (2-4) Aging characteristic correction: Based on the cumulative number of switch actions N, the aging correction function f(N) obtained by fitting based on accelerated aging test is called to calculate the aging correction amount, and the characteristic compensation of the reference action time delay is performed throughout the entire life cycle to offset the time delay drift caused by switch mechanical fatigue. (2-5) Total action delay calculation: The total action delay τ of the switch is calculated by superimposing the fixed delay τ_drive of the drive circuit. The calculation formula is: τ=τ_base+f(N)+τ_drive; (2-6) Historical correction amount superposition: Read the previous switching self-learning output of the switching correction amount δ_prev, and calculate the final advance amount Δt in combination with the total action delay τ. The calculation formula is: Δt=τ+δ_prev; (2-7) Calculation of drive command timing: Based on the reference zero-crossing time T0 and the final advance issuance amount Δt, calculate the issuance time t_send of the drive control signal. The calculation formula is: t_send=T0-Δt; When the system reaches the t_send time, it outputs a closing or opening drive command to the switching switch. (2-8) Actual action moment capture: After the drive command is issued, the status of the auxiliary contact of the switch or the sudden change signal of the circuit current is detected in real time, and the actual action moment T_act of the switch contact is captured with high precision and the timestamp is recorded; (2-9) Zero crossing deviation calculation: Based on the actual action time T_act and the reference zero crossing time T0, calculate the zero crossing deviation e of this switching. The calculation formula is: e=T_act-T0, where a positive value of e indicates that the switch operates after zero crossing, and a negative value of e indicates that the switch operates before zero crossing. (2-10) Deviation tolerance judgment: Compare the zero-crossing deviation e with the preset tolerance deviation threshold: If the zero-crossing deviation e is within the allowable range, the current model parameters remain unchanged, the current switching process ends, and the system waits for the next switching instruction. If the zero-crossing deviation e exceeds the allowable range, the self-learning correction process will be initiated, and the following steps will be performed: (2-10.1) Sliding window sample update: Store the sample data (e,T,V,N) of this cut into a sliding window of a preset length; the sliding window adopts a first-in-first-out mechanism and stores the most recent M groups of valid cut samples. (2-10.2) Calculation of recursive correction: The weighted least squares recursive algorithm is used to fit the sample data in the sliding window to obtain the new correction δ_new; (2-10.3) Filtering and smoothing: The new correction amount δ_new is smoothed by a first-order low-pass filter algorithm to obtain the updated cutting correction amount δ. The calculation formula is: δ=α・δ_new+(1-α)・δ_prev, where α is the filtering and smoothing coefficient, which is used to suppress parameter fluctuations caused by single abnormal samples. (2-10.4) Parameter Iteration Storage: The updated switching correction δ is stored in the parameter storage area and used as the historical correction δ_prev for the next round of switching. The current switching process ends and waits for the next switching instruction.

4. The precise zero-crossing switching method for low-voltage switchgear as described in claim 3, characterized in that: In steps (2-3), the underlying logic of the two-dimensional compensation calibration surface is defined by two sets of core formulas, and the meaning and mapping relationship of each physical quantity are as follows: (2-3.1) Basic formula for action timing: t_actual = t_trigger + t_delay(W), where: t_actual refers to the moment when the switch contacts actually complete the closing / opening action, and is the output dependent variable of the model; t_trigger refers to the moment when the control system issues a drive command to the switching switch, and is the first input independent variable of the model; t_delay(W) refers to the action delay function of the switch, which represents the time difference from the issuance of the drive command to the actual action of the contact. Its value is determined by the comprehensive operating condition index W, and is the function output corresponding to the second input independent variable of the model. (2-3.2) Optimal trigger time formula: t_trigger=t_zero-t_delay(W)-t_guard, where: t_zero refers to the time when the target voltage crosses zero, that is, the preset target action time for zero-crossing switching; t_guard refers to a preset safety margin used to offset random fluctuations and ensure that the throwing and cutting actions fall within the allowable accuracy range; t_trigger refers to the optimal timing for issuing the drive command to achieve precise zero-crossing switching.

5. The precise zero-crossing switching method for low-voltage switchgear as described in claim 4, characterized in that: In steps (2-3), the two-dimensional compensation calibration surface adopts a construction mechanism of "factory initial calibration and recursive operation correction" to ensure that the model continuously matches the real-time characteristics of the switch. Initial calibration before leaving the factory: Before leaving the factory, multiple sets of switching action time delay data under temperature and aging conditions are measured through a full-condition test matrix to obtain discrete mapping sample points; an initial two-dimensional compensation calibration surface is constructed through data fitting to form a benchmark compensation parameter library that covers typical operating conditions throughout the entire life cycle of the equipment. Recursive correction during operation: After the equipment is put into operation, the surface nodes are dynamically and recursively corrected through a self-learning mechanism: After each switching is completed, the actual operating parameters and the actual action deviation are collected, and the time delay mapping parameters of the corresponding operating points are updated; the surface shape is gradually corrected through iteration, so that the compensation model continuously matches the real-time action characteristics of the switch, offsets the characteristic drift caused by aging and temperature change, and ensures the zero-crossing switching accuracy throughout the entire life cycle.

6. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: In step (2), the closing and opening control parameters are obtained through a large number of switching tests during the factory stage: the difference between each switching point and the zero crossing point is recorded in the switching test, the advance parameter is adjusted in the opposite direction, and the initial closing and opening control parameter calibration is completed.

7. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: In step (3), the "trial and error-learning" mechanism dynamically corrects the advance of the cut: it records the time deviation sequence between the actual contact point action time and the predicted zero crossing point for each cut in real time, and uses the sliding window weighted least squares algorithm to recursively optimize the advance compensation value to achieve dynamic online calibration of time delay drift within the life cycle.

8. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: The low-voltage switchgear is an AC low-voltage integrated distribution box.

9. The precise zero-crossing switching method for low-voltage switchgear as described in claim 1, characterized in that: The smart capacitor is a ZC868 series model.

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