A method for phase sequence switching control of energy meters to ensure the safety of CT / PT secondary circuits

Abstract

This invention relates to the field of power metering technology, specifically disclosing a phase sequence switching control method for energy meters that ensures the safety of the secondary circuit of a current transformer (CT) / potential transformer (PT). The method synchronously acquires and converts three-phase voltage and current signals, constructs a multi-dimensional spatial vector of phase angles, calculates the spatial angle between the vector and the positive-sequence reference vector, and combines this with phase dispersion to generate accurate phase sequence status values ​​to determine reverse phase sequence. When reverse phase sequence is determined, a phased safety switching command sequence is generated based on real-time electrical status verification: first, a disconnect command is issued after verifying voltage stability; then, a current short-circuit command is issued only after verifying a valid voltage drop. The action units are sequentially driven to perform voltage disconnection and current short-circuit operations, driving the dual-contact unit to synchronously switch the three-phase wiring. After switching, the circuit is restored and the phase sequence is re-verified. If multiple failures occur, an adjustment and safety locking mechanism is activated. This invention solves the problems of open circuit on the CT secondary side and short circuit on the PT secondary side during switching.

Description

Technical Field

[0001] This invention relates to the field of power metering technology, specifically to a method for phase sequence switching control of energy meters to ensure the safety of the secondary circuit of a CT / PT. Background Technology

[0002] With the advancement of smart grid construction, although some research has explored automatic phase sequence identification and switching technologies, most remain at the theoretical or simulation stage. The few practical applications often focus on phase sequence judgment itself, failing to fully address the core safety issues of ensuring the secondary side of the current transformer (CT) is not open-circuited and the secondary side of the voltage transformer (PT) is not short-circuited during the switching process. Existing solutions either still require manual intervention for confirmation during the switching process or lack sufficiently robust safety logic, making it difficult to ensure foolproof operation in complex field environments.

[0003] Therefore, designing an intelligent phase sequence switching method that can absolutely guarantee the safe operation of the CT / PT secondary circuit under the premise of full automation and no power interruption has become a key technical requirement for improving the safety, reliability and intelligence level of metering operations. Summary of the Invention

[0004] The purpose of this invention is to provide a method for controlling the phase sequence switching of an energy meter to ensure the safety of the secondary circuit of a CT / PT, so as to solve the above-mentioned technical problems.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for phase sequence switching control of an energy meter to ensure the safety of the secondary circuit of a CT / PT includes the following steps:

[0007] S1: Real-time acquisition of three-phase voltage analog quantities and three-phase current analog quantities from the energy meter, and conversion into corresponding voltage digital signals and current digital signals respectively;

[0008] S2: Analyze the digital voltage and digital current signals to extract the real-time phase angle between each phase voltage and current; construct coordinates on the unit circle using each phase angle to form a multi-dimensional space vector; calculate the angle between the multi-dimensional space vector and the preset positive sequence reference vector in the multi-dimensional space, and normalize the results by combining the dispersion of each phase angle, mapping the normalization result to a unique phase sequence state value; if the phase sequence state value exceeds the preset threshold, it is determined to be a reverse phase sequence state.

[0009] S3: When the reverse phase sequence is determined, a safety switching instruction sequence containing multi-stage instructions is generated. The safety switching instruction sequence includes: voltage loop disconnection instruction and current loop short-circuit instruction.

[0010] S4: Execute the safety switching instruction sequence in sequence: First, drive the first group of action units to perform the voltage loop disconnection operation. After confirming that the effective value of the voltage digital signal meets the drop condition, drive the second group of action units to perform the current loop short-circuit operation. After the current loop short-circuit is confirmed, drive the third group of double-contact action units to simultaneously switch the connection relationship between the three-phase voltage and current, and complete the phase sequence exchange.

[0011] S5: After the phase sequence exchange is completed, the voltage circuit is connected and the current circuit short-circuit operation is released. The three-phase voltage and current digital signals are collected again. The phase sequence status value is recalculated. If the phase sequence status value falls within the normal phase sequence threshold range, the switching is completed. If it is still in the reverse phase sequence state and the switching attempts have not been successful after reaching the preset number of attempts, a safety alarm is triggered and the current state is locked.

[0012] As a further aspect of the present invention: the formation process of the multidimensional spatial vector is as follows:

[0013] Extract the real-time phase angles corresponding to the digital voltage and current signals of each phase;

[0014] For each real-time phase angle, calculate the cosine and sine coordinates of the real-time phase angle on the unit circle;

[0015] The cosine and sine coordinates of the three phases are arranged in the order of the first phase, the second phase, and the third phase to form a multidimensional spatial vector.

[0016] As a further aspect of the present invention: the calculation process of the phase sequence state value is as follows:

[0017] Calculate the cosine of the spatial angle between a multidimensional spatial vector and a preset orthogonal reference vector;

[0018] Calculate the dispersion index of the real-time phase angle of each phase. The dispersion index is the sum of the absolute values ​​of the differences between each phase angle and the average phase angle.

[0019] The weighted sum is obtained by weighting the cosine value of the spatial angle with the dispersion index.

[0020] The phase sequence state values ​​are obtained by performing an inverse cotangent function transformation on the weighted sum.

[0021] As a further aspect of the present invention: the process for determining the trigger condition of the voltage circuit disconnection command is as follows:

[0022] Obtain the effective values ​​of the current phase voltage digital signals within a complete power frequency cycle;

[0023] The effective value of each phase voltage is compared with the preset effective value threshold to determine whether the effective value of the power supply of all phases exceeds the effective value threshold for a first preset time.

[0024] Calculate the fluctuation rate of the effective value of each phase voltage within a first preset time period;

[0025] If the volatility is lower than the preset volatility threshold, a voltage loop disconnection command will be generated.

[0026] As a further aspect of the present invention: the triggering condition determination process for the current loop short-circuit command is as follows:

[0027] After executing the voltage loop disconnection command, delay for a second preset time, re-acquire the digital voltage signals of each phase and calculate the effective value of each phase voltage digital signal;

[0028] The effective values ​​of each phase voltage that are re-acquired are compared with the original effective values ​​recorded before the disconnection command is executed, and the effective value decrease rate of each phase voltage is calculated.

[0029] Determine whether the effective value drop rate of the voltage of all phases has reached or exceeded the preset drop rate threshold, and maintain it for a third preset duration, and confirm the generation of the current loop short-circuit command.

[0030] As a further aspect of the present invention: S4 specifically includes:

[0031] After confirming that the current loop short-circuiting operation is completed, a synchronous switching command is sent to the third group of double-contact action units;

[0032] The three independent units in the third group of double-contact action units control the three phases respectively. After receiving the instruction, each unit synchronously disconnects the moving contact from the first stationary contact and connects to the second stationary contact.

[0033] After the connection switch is completed, check again whether the analog quantities of voltage and current in each phase have established a valid path;

[0034] Once all phases have been confirmed to have established a valid path, the phase sequence exchange is completed, and the connection relationship between voltage and current is simultaneously and synchronously swapped.

[0035] As a further aspect of the present invention: after the connection switching is completed, the analog quantities of voltage and current in each phase are checked again to see if a valid path has been established, specifically including:

[0036] After the connection switch is completed, the analog quantities of voltage and current of each phase are reacquired and converted into corresponding voltage verification digital signals and current verification digital signals respectively.

[0037] The validity of the voltage verification digital signal and the current verification digital signal is verified, including determining whether the signal amplitude is within the preset valid amplitude range, and whether the signal waveform is continuous and uninterrupted within a complete power frequency cycle.

[0038] Based on the verification results of the digital signals of each phase voltage and current, a comprehensive path effectiveness index is calculated and generated.

[0039] When the overall pathway effectiveness index is greater than or equal to the effectiveness threshold, all phases are considered to have established effective pathways.

[0040] As a further aspect of the present invention: the calculation process of the comprehensive pathway effectiveness index is as follows:

[0041] The amplitude verification result is obtained by judging whether the effective value of the digital signal is within the preset effective amplitude range by judging the voltage and current of each phase.

[0042] The waveform continuity verification results are obtained by analyzing whether the sampling point sequence of the phase voltage verification digital signal and the current verification digital signal is continuous and uninterrupted within a complete power frequency cycle.

[0043] The amplitude verification results and waveform continuity verification results of the phase voltage verification digital signal and the current verification digital signal are respectively quantized into the first quantization value and the second quantization value;

[0044] The first quantization value and the second quantization value of each phase are multiplied to obtain the single-phase path reliability coefficient of each phase.

[0045] The reliability coefficients of the single-phase circuits of the three-phase system are sorted, and different weights are assigned to the sorted coefficients.

[0046] The reliability coefficients of all weighted single-phase pathways are summed, and the summation result is mapped to a preset interval through a preset normalization function to obtain the comprehensive pathway effectiveness index.

[0047] As a further aspect of the present invention: the triggering of the security alarm and locking of the current state specifically includes:

[0048] When the number of consecutive switching attempts reaches the preset number and the phase sequence status value is still in reverse phase sequence state, record the phase sequence status values ​​corresponding to the current and historical failed attempts.

[0049] Analyze the distribution characteristics of each phase sequence state value in the historical failure records, and adjust the offset of the reverse phase sequence determination threshold based on the distribution characteristics;

[0050] If the phase sequence status value still falls within the reverse phase sequence range after being re-evaluated according to the dynamically adjusted threshold, a safety alarm command will be generated and a status lock command will be sent to all action units at the same time.

[0051] The state lock command keeps all action units in the immediate state at the time of executing the safety alarm command and blocks the reception and execution of any subsequent external switching commands.

[0052] As a further aspect of the present invention: the offset of adjusting the inverse phase sequence determination threshold based on distribution characteristics specifically includes:

[0053] Extract all phase sequence state values ​​from the historical failure records and form a state value sequence according to the order in which the attempts occurred;

[0054] Analyze the numerical distribution of the state value sequence and calculate the degree of clustering and the location of the cluster center near the inverse phase sequence determination threshold;

[0055] Based on the offset direction and offset distance of the aggregation center position relative to the original reverse phase sequence threshold, the threshold offset is calculated according to a preset ratio.

[0056] The threshold offset is algebraically added to the original reverse phase sequence determination threshold to obtain the adjusted reverse phase sequence determination threshold.

[0057] The beneficial effects of this invention are:

[0058] (1) Traditional methods for handling reverse phase sequence require live operation by personnel or power outage of equipment, posing risks of electric shock and accidental contact. This invention, through a strict "verify before acting" logic, performs real-time verification of the voltage and current circuit status under multiple conditions and for a long duration before issuing any physical switching command (e.g., issuing a disconnect command only after verifying that the voltage is stable and meets the standard, and issuing a short-circuit command only after verifying that the voltage has effectively decreased), ensuring that the secondary side of the current transformer is reliably short-circuited and the secondary side of the voltage transformer is reliably disconnected before switching. This series of interlocking logics based on real-time electrical quantity verification completely replaces traditional manual judgment and operation, thereby eliminating secondary circuit open circuit or short circuit accidents caused by human operation errors or judgment deviations, and reducing the safety risks of on-site operations.

[0059] (2) Traditional methods of correcting reverse phase sequence can lead to power outages for user equipment. This invention, controlled by a microcontroller, automatically completes the entire process from phase sequence status detection and safety condition judgment to physical switching within seconds, all while the system is energized, thus avoiding unplanned power outages. Simultaneously, its innovative phase sequence determination algorithm (integrating spatial vector angle and phase dispersion) can more accurately identify the true reverse phase sequence state, reducing misjudgments; immediately after switching, it verifies the validity of the electrical path and recalculates the phase sequence state to ensure successful switching. This not only reduces equipment downtime and improves power supply reliability but also ensures the accuracy of reactive power metering and power factor calculation through closed-loop correction, which is beneficial to the economic operation of the power grid. Attached Figure Description

[0060] The invention will now be further described with reference to the accompanying drawings.

[0061] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0062] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0063] Please see Figure 1 As shown, this invention provides a method for phase sequence switching control of energy meters to ensure the safety of the secondary circuit of a CT / PT, comprising the following steps:

[0064] S1: Real-time acquisition of three-phase voltage analog quantities and three-phase current analog quantities from the energy meter, and conversion into corresponding voltage digital signals and current digital signals respectively;

[0065] S2: Analyze the digital voltage and digital current signals to extract the real-time phase angle between each phase voltage and current; construct coordinates on the unit circle using each phase angle to form a multi-dimensional space vector; calculate the angle between the multi-dimensional space vector and the preset positive sequence reference vector in the multi-dimensional space, and normalize it by combining the dispersion of each phase phase angle, mapping the normalization result to a unique phase sequence state value; if the phase sequence state value exceeds the preset threshold, it is determined to be a reverse phase sequence state.

[0066] S3: When the reverse phase sequence is determined, a safety switching instruction sequence containing multi-stage instructions is generated. The safety switching instruction sequence includes: voltage loop disconnection instruction and current loop short-circuit instruction.

[0067] S4: Execute the safety switching instruction sequence in sequence: First, drive the first group of action units to perform the voltage loop disconnection operation. After confirming that the effective value of the voltage digital signal meets the drop condition, drive the second group of action units to perform the current loop short-circuit operation. After the current loop short-circuit is confirmed, drive the third group of double-contact action units to simultaneously switch the connection relationship between the three-phase voltage and current, and complete the phase sequence exchange.

[0068] S5: After the phase sequence exchange is completed, the voltage circuit is restored and the current circuit is de-circuited, and the three-phase voltage and current digital signals are collected again; the phase sequence status value is recalculated. If the phase sequence status value falls within the normal phase sequence threshold range, the switching is completed; if it is still in the reverse phase sequence state, and the switching attempts have not been successful after reaching the preset number of times, a safety alarm is triggered and the current state is locked.

[0069] In S1, the analog three-phase voltage and analog three-phase current of the electricity meter are acquired in real time and converted into corresponding digital voltage and digital current signals, respectively. Specifically, this includes:

[0070] The analog voltage and analog current signals of phases A, B, and C of the energy meter are obtained through the measuring terminals of the secondary circuits of the voltage transformer and the current transformer, respectively. The analog voltage signal is the voltage signal to ground, and the analog current signal is the current signal flowing through the metering coil.

[0071] A multi-channel synchronous sampling analog-to-digital converter is used to synchronously sample the acquired three-phase voltage and three-phase current analog quantities. The sampling process is performed at a fixed sampling rate that is an integer multiple of the power frequency signal frequency to ensure that a sufficient number of sampling points are obtained in each power frequency cycle to completely capture the waveform information of voltage and current.

[0072] The sampled discrete instantaneous voltage and current value sequences are converted into binary digital voltage and current signal sequences by the quantization and encoding circuitry within the analog-to-digital converter (ADC). During the conversion process, the reference voltage of the ADC is adjusted to match the dynamic range of the input analog quantity with the full-scale range of the ADC, thus fully utilizing the conversion resolution.

[0073] To maintain a strict synchronous correspondence between voltage and current signals in subsequent analysis, the voltage and current digital signal sequences after conversion are aligned and buffered according to their sampling time timestamps to form a three-phase voltage digital signal group and a three-phase current digital signal group that are strictly synchronized in time, serving as the basis for subsequent analysis steps.

[0074] In S2, the digital voltage and current signals are analyzed to extract the real-time phase angles between each phase voltage and current. Coordinates on a unit circle are constructed using each phase angle to form a multi-dimensional spatial vector. The angle between this multi-dimensional spatial vector and a preset positive-sequence reference vector in the multi-dimensional space is calculated, and normalization is performed based on the dispersion of each phase phase angle. The normalization result is then mapped to a unique phase sequence state value. If the phase sequence state value exceeds a preset threshold, it is determined to be a reverse phase sequence state, specifically including:

[0075] First, the time-aligned three-phase voltage and current digital signal groups are analyzed. For each phase (e.g., phase A), the zero-crossing point within the current power frequency cycle is located from the voltage and current digital signal sequences of that phase. The time difference between the zero-crossing points of the voltage and current signals of the same phase is calculated, and then, based on the rated power frequency angular frequency of the power grid, this time difference is converted into a phase angle in radians, denoted as . Using this method, the phase angle of phase B can be obtained simultaneously. Phase angle with phase C This phase angle This reflects the impedance characteristics of the phase load, and its relative relationship in a three-phase system is the basis for determining the phase sequence.

[0076] To integrate the phase information of the three phases into a unified mathematical structure for analysis, each phase angle is mapped onto a unit circle (a circle with a radius of 1). For any given phase angle... Its position on the unit circle is determined by the x-coordinate. (Cosine coordinates) and ordinate The (sine coordinates) are uniquely determined. The phase angles of the three phases are processed sequentially. , , We get six numbers: , , , , , Arrange these six values ​​in the order of A-phase cosine, A-phase sine, B-phase cosine, B-phase sine, C-phase cosine, and C-phase sine to form a six-dimensional spatial vector, denoted as [missing information]. This vector That is, it contains all the geometric information about the phase relationship between the three-phase voltage and current.

[0077] A positive sequence reference vector representing the standard positive phase sequence wiring state is preset and denoted as: This vector Construction methods and vectors The phase angles are the same, but they are based on the theoretical phase angle under standard positive phase sequence, where the phase voltage leads the phase current (e.g., 0 for purely resistive loads). Vector G is a fixed six-dimensional constant vector. To quantify the currently measured vector... The cosine of the spatial angle between the standard orthogonal vector G and the vector G in six-dimensional space is calculated based on the directional difference between them. This calculation is based on the vector dot product and its magnitude, and the specific formula is as follows: ;

[0078] In this formula, θ represents a vector. The spatial angle between vector G and vector G. The symbol "·" represents the dot product operation of vectors, that is, the sum of the corresponding dimensions of two vectors. Representing vectors The modulus is the square root of the sum of the squares of its components; Similarly, this is the magnitude of vector G. The calculated... It is a real number between -1 and 1. The closer its value is to 1, the closer the current phase sequence state is to the standard positive phase sequence.

[0079] Relying solely on the vector angle is insufficient to fully address complex operating conditions such as three-phase load imbalance. Therefore, a dispersion index reflecting the consistency of the three-phase phase angles is introduced. As an auxiliary criterion, firstly, calculate the real-time phase angles of the three phases. , , arithmetic mean Then, calculate the absolute difference between each phase angle and the average value, i.e. , , Finally, the sum of these three absolute differences is the dispersion index. . The smaller the value, the more concentrated the three-phase phase angle distribution and the better the consistency; in case of reverse phase sequence or wiring error, The value usually increases significantly.

[0080] Cosine value of the spatial angle With dispersion index The two phase sequence states are fused to generate a final, single numerical value P. First, a weighted sum S is calculated from the two values, given by the following formula: ;

[0081] In this formula, and The weighting coefficients are preset and satisfy the following conditions: Its specific value is determined through training and optimization using a large amount of forward and reverse phase sequence sample data; for example, it can be taken as 0.7 and 0.3 respectively. In the formula... Its function is to measure the dispersion index Normalize and convert to the same Contribution in the same direction ( The larger the value, the smaller this term becomes. After calculating the weighted sum S, a mapping transformation is performed using the inverse cotangent function to obtain the phase sequence state value. The inverse cotangent function is used here. The reason for this is that its domain is all real numbers, and it can map the input S to a finite, monotonic range of radian values, making it easy to set a uniform judgment threshold. The final value of P is a radian value with a defined range.

[0082] A threshold for determining the reverse phase sequence is set in advance through experiments and analysis. When the calculated phase sequence state values Greater than this threshold At that time, that is If so, the current energy meter is determined to be in reverse phase sequence. Conversely, if... If the threshold is reached, it is determined to be a normal phase sequence state. The determination of the parameters took into account the positive sequence reference, measurement error tolerance, and safety margin.

[0083] In S3, when a reverse phase sequence is detected, a safety switching instruction sequence containing multi-stage instructions is generated. This sequence includes: a voltage loop disconnect instruction and a current loop short-circuit instruction, specifically:

[0084] After determining the current phase sequence as reversed in step S2, a multi-stage safety switching command sequence executed in a strict order must be generated to ensure the safety and reliability of subsequent switching operations. The core of this sequence lies in the step-by-step, verification-based generation of voltage loop disconnection and current loop short-circuiting commands. Each command must meet specific electrical state conditions to prevent potential secondary circuit hazards caused by direct operation under energized conditions. This step details the trigger condition determination process for these two key commands.

[0085] First, the conditions for generating the voltage circuit disconnection command are determined. The goal of this command is to safely disconnect the voltage signal connected to the energy meter, and its generation must be based on the current voltage circuit being in a stable and effective energized state. The specific determination process consists of four steps. Step 1, Signal validity confirmation: Obtain the latest three-phase voltage digital signal sequence from the buffer, which is continuous for at least one complete power frequency cycle. Perform root mean square operation on these discrete sequence points to calculate the effective voltage values ​​of phases A, B, and C respectively. Step 2, Threshold value and stability duration judgment: Compare the calculated effective voltage values ​​of each phase with a preset "effective voltage value threshold". This threshold value is usually set at 90% of the rated operating voltage of the energy meter to confirm that the voltage circuit is properly connected and the signal strength is sufficient. Only when the effective voltage values ​​of all three phases continuously exceed this threshold value and are maintained for a "first preset duration" (in this embodiment, it is set to no less than 5 consecutive power frequency cycles) is it initially considered that the energized condition is met. Step 3, Signal fluctuation assessment: To eliminate interference from instantaneous voltage drops or severe fluctuations, the voltage stability needs to be further evaluated. The deviation between the effective value of each phase voltage calculated for each power frequency cycle within the first preset time period and its average effective value within that time period is calculated. Then, the absolute value of these deviations is taken and their average value is calculated. This average value is divided by the average effective value to obtain the "fluctuation rate" of the effective value of each phase voltage. Fourth step, final determination: Only when the fluctuation rate of all three phases is lower than a preset "fluctuation threshold" (set to 5% in this embodiment) is the current voltage circuit finally confirmed to be in a stable energized state, and a "voltage circuit disconnection command" is generated. This step-by-step verification mechanism ensures that the disconnection operation is only initiated when the voltage is stable and reliable, avoiding the risk of malfunction when the voltage is abnormal.

[0086] After the voltage loop disconnect command is generated and issued, the current loop short-circuiting operation cannot be performed immediately; it is necessary to verify that the voltage disconnection operation has indeed taken effect. The generation of the current loop short-circuiting command strictly depends on the confirmation of the voltage disconnection effect. The specific determination process is also divided into four steps. Step 1, Effect Verification Delay and Re-acquisition: After issuing the voltage loop disconnect command, the program delays for a "second preset duration" (set to 2 power frequency cycles in this embodiment) to wait for the operation to be executed and the loop state to stabilize. After the delay ends, the digital voltage signals of each phase are immediately re-acquired, and the new effective values ​​of each phase voltage are calculated using the same method as described above. Step 2, Quantitative Calculation of Disconnection Effect: The new effective values ​​of each phase voltage obtained from the re-acquisition are compared with the original effective values ​​of each phase voltage recorded and saved before the disconnection command was executed. For each phase, its "effective value decrease ratio" is calculated. The calculation method for this ratio is: subtract the new effective value from the original effective value, and then divide the difference by the original effective value. The third step is to determine the sustainability and compliance of the voltage drop effect: Check whether the calculated effective value drop ratios of all three phases have reached or exceeded a preset "drop ratio threshold" (70% in this embodiment). This threshold means that the voltage has dropped to a very small portion of its original value, essentially indicating that the voltage loop has been effectively disconnected. Simultaneously, this compliance state needs to be maintained for a "third preset duration" (three consecutive power frequency cycles in this embodiment) to confirm a stable disconnection state, rather than a momentary disturbance. The fourth step is final determination: When the effective value drop ratios of all phases continuously meet the threshold requirement within the third preset duration, it is confirmed that the voltage loop has been reliably disconnected, and a "current loop short-circuit command" is generated. This process ensures that the current short-circuit operation is only performed under the safe premise that the voltage loop has been substantially disconnected, fundamentally preventing the risk of a short circuit in the secondary circuit of the voltage transformer during switching.

[0087] In S4, the safety switching command sequence is executed sequentially: first, the first set of action units is driven to perform a voltage loop disconnection operation; after confirming that the effective value of the voltage digital signal meets the descent condition, the second set of action units is driven to perform a current loop short-circuit operation; after the current loop short-circuit is confirmed, the third set of double-contact action units is driven to simultaneously switch the connection relationship of the three-phase voltage and current, completing the phase sequence exchange, specifically including:

[0088] Once the judgment logic in step S3 confirms that the current loop short-circuit operation has been completed and this state has been stably maintained for more than the preset short-circuit confirmation time, the control logic will generate a "synchronous switching command". This command is a digital command containing specific encoding and timing information, which is simultaneously sent to the control terminals of the three independent physical units corresponding to phases A, B, and C in the "third group of dual-contact action units" through the isolation optocoupler and drive circuit. The prerequisite for sending this command is that a "short-circuit confirmation completed" feedback signal has been received from the current short-circuit status monitoring circuit, ensuring that the secondary side of the current transformer is in a reliable short-circuit protection state.

[0089] Each independent unit of the third group of dual-contact actuation units includes one movable contact (referred to as the movable contact) and two fixed contacts (referred to as the first stationary contact and the second stationary contact, respectively). Before receiving the synchronous switching command, the movable contact of each unit maintains a reliable connection with the first stationary contact, forming the original path before switching. After receiving the command, the miniature drive mechanisms (such as magnetic latching relays or motor drive mechanisms) inside the three units operate simultaneously under the control of the synchronous clock signal. The operation process is as follows: First, the drive mechanism quickly and reliably separates the movable contact from the first stationary contact; then, under mechanical interlocking or electronic synchronization control, the movable contact is driven to move to and establish a reliable electrical connection with the second stationary contact. This process is completed within milliseconds, realizing the synchronous and simultaneous swapping of the physical connection of the three-phase voltage and current terminals. In this embodiment, the A-phase voltage input terminal is swapped with the C-phase voltage input terminal, and the A-phase current input terminal is swapped with the C-phase current input terminal, while the B-phase remains unchanged or participates in the rotation according to a predetermined rule.

[0090] After completing the physical connection switch, it is crucial to immediately verify that the new wiring has correctly established a valid electrical path. This is key to confirming the success of the phase sequence exchange. The testing process consists of four sub-steps. Step 1: Data Reacquisition and Conversion: After the switching action is completed and a short stabilization period is allowed, the analog voltage and current values ​​of each phase are immediately reacquired through the measurement terminals. Using independent analog-to-digital converters, these analog values ​​are converted into new "voltage verification digital signals" and "current verification digital signals," respectively. Step 2: Signal Validity Verification: The converted digital signals are analyzed in two aspects. First, amplitude verification: The effective value of each verification signal within a complete power frequency cycle is calculated, and it is determined whether the effective value falls within a preset "effective amplitude range." This range has a lower limit of 85% of the rated value and an upper limit of 115% of the rated value, used to confirm that the signal strength has returned to normal and is not open-circuited or severely attenuated. Second, waveform continuity verification: Analyze and verify the waveform of the digital signal, checking whether the sequence of sampling points is continuous and without gaps within a complete power frequency cycle, and whether there are instantaneous zeroing or distortions caused by poor contact. This is usually judged by detecting the number of zero-crossing points and the waveform sine. Third, calculate the comprehensive path effectiveness index: In order to use a comprehensive quantitative index to characterize the effectiveness of the entire three-phase circuit reconstruction, an index calculation method based on single-phase reliability and three-phase balance is designed. First, the amplitude verification result (pass / fail) and waveform continuity verification result (pass / fail) of each phase are quantized into values. In this embodiment, "pass" is quantized as a value of 1, and "fail" is quantized as a value of 0, obtaining the "first quantized value" and "second quantized value" respectively. Multiply the two quantized values ​​of the same phase to obtain the "single-phase path reliability coefficient" of that phase, which is 1 or 0. Then, the single-phase path reliability coefficients of phases A, B, and C are sorted from largest to smallest. For the three sorted coefficients, assign weights in descending order of magnitude. For example, the first coefficient has a weight of 0.5, the second has a weight of 0.3, and the third has a weight of 0.2. Multiply each coefficient by its corresponding weight, and then add the three products together to obtain a weighted sum. Finally, input this weighted sum into a preset "normalization function" (in this embodiment, the weighted sum is directly multiplied by 100) to map it to the integer range of 0 to 100. The final value obtained is the "comprehensive path effectiveness index". Fourth step, effectiveness determination: compare the index with a preset "effectiveness threshold" (in this embodiment, it is set to 85). If the calculated index is greater than or equal to the threshold, it is determined that all phases have established stable and effective electrical paths; otherwise, it is determined that the path establishment has failed.

[0091] Once step 3 determines that all phases have established valid pathways, the physical switching operation is confirmed as successful, and the three-phase voltage and current connections of the energy meter have been simultaneously and synchronously swapped according to predetermined rules. The control logic records the status "Successful phase sequence exchange" and updates the internal status flag of the device to "Normal phase sequence." At this point, the core operation of step S4 is complete, and the process enters the final verification and completion stage (step S5). If the pathway validity detection fails, the exchange will not be confirmed as complete, and the process will proceed to the exception handling procedure according to a preset strategy.

[0092] In S5, after the phase sequence exchange is completed, the voltage loop is restored and the current loop is de-circuited, and the three-phase voltage and current digital signals are acquired again; the phase sequence status value is recalculated. If the phase sequence status value falls within the normal phase sequence threshold range, the switching is completed; if it is still in the reverse phase sequence state, and the switching attempt fails after reaching the preset number of attempts, a safety alarm is triggered and the current state is locked, specifically including:

[0093] After the phase sequence exchange operation is completed, the measurement state of the device needs to be restored first. The control logic drives the first set of action units to restore the voltage circuit connection and drives the second set of action units to release the short circuit of the current circuit, so that the energy meter can resume normal metering wiring. Then, immediately following the method in step S1, the analog quantities of three-phase voltage and current are collected again and converted into the latest digital voltage and current signals. Based on these newly collected signals, a completely new "phase sequence state value" is recalculated strictly according to the complete process described in step S2: "real-time phase angle extraction", "multi-dimensional spatial vector construction", "spatial angle cosine value calculation", "phase angle dispersion index calculation" and "phase sequence state numerical synthesis and mapping". The newly calculated phase sequence state value is compared with the preset "normal phase sequence threshold range". If the value falls within this range, the phase sequence switch is considered successful, the entire process ends, and the device enters normal operation monitoring state.

[0094] If the recalculated phase sequence state value still falls within the reverse phase sequence range defined by the "reverse phase sequence determination threshold", then the current switching attempt is deemed a failure. An internal attempt counter will increment once. When the number of consecutive failed attempts reaches a preset maximum value (set to 3 times in this embodiment), it indicates that the fixed threshold determination logic may fail under the current operating conditions, and an intelligent safety handling mechanism needs to be activated. This mechanism first performs data recording and analysis: the device stores all the "phase sequence state values" calculated during the current and previous failed attempts in chronological order, forming a set of historical failure data sequences.

[0095] Next, the system analyzes the distribution characteristics of historical failure data sequences to dynamically adjust the judgment threshold and attempt to make a more accurate final decision. The adjustment process is as follows: First, the numerical distribution of the data sequence is analyzed, focusing on the density of these failed phase sequence state values ​​clustering around the original reverse phase sequence judgment threshold. The method for calculating the degree of clustering is to count the proportion of data points whose values ​​fall within a fixed-width interval centered on the original threshold to the total number of failures. The higher the proportion, the stronger the clustering. At the same time, the "cluster center position" of these clustered data is calculated, which is obtained by taking the arithmetic mean of these clustered values. Then, the adjustment amount is calculated based on the deviation of the cluster center position from the original reverse phase sequence judgment threshold. The "offset distance" is calculated, which is the value of the cluster center position minus the absolute value of the original threshold. The "offset direction" is determined: if the cluster center position is greater than the original threshold, it is a positive offset; otherwise, it is a negative offset. Finally, the calculated offset distance is multiplied by a preset proportional coefficient less than 1 (set to 0.8 in this embodiment) to obtain the final "threshold offset". Adding this directional threshold offset (adding for positive offset and subtracting for negative offset) to the original inverse phase sequence determination threshold yields a "dynamically adjusted inverse phase sequence determination threshold".

[0096] After obtaining the dynamically adjusted new threshold, this new threshold is used to re-evaluate the last calculated phase sequence state value. If the phase sequence state value is still greater than or equal to the new threshold, i.e., still judged as a reverse phase sequence state, it is confirmed as an unrecoverable abnormal condition. At this time, the control logic immediately executes two final safety instructions: First, it generates and issues a "safety alarm instruction," which triggers the device's audible and visual alarm to issue a continuous alarm and sends an abnormal state code to the remote monitoring terminal. Second, it synchronously sends a "state lock instruction" to all action units in the first, second, and third groups. This instruction has the highest priority, and its function is to force the drive circuits of all action units into a locked state, keeping each relay or contact in its immediate physical position at the moment the instruction is issued, and no longer responding to any subsequent switching, disconnecting, or closing instructions issued by external buttons, remote control signals, or automatic programs. This locked state will continue until maintenance personnel physically unlock it using a dedicated reset tool. This mechanism solves the cumulative safety risk that may arise from repeated device operation under unknown fault causes, forcing the system to remain in a defined safe state.

[0097] The working principle of this invention is as follows: First, the three-phase voltage and current signals of the energy meter are simultaneously acquired and digitized. Second, by extracting the real-time phase angle between each phase voltage and current, a multi-dimensional spatial vector representing the three-phase phase relationship is constructed. The cosine value of the spatial angle between this multi-dimensional spatial vector and the standard positive sequence vector is calculated. Combined with the dispersion index of the three-phase phase angle, a unique phase sequence state value is generated through weighted summation and function mapping to accurately determine the reverse phase sequence state. When a reverse phase sequence is determined, the switching does not occur immediately. Instead, a phased safety switching command sequence is first generated. The generation of this safety switching command sequence depends on strict trigger condition verification: the voltage loop disconnection command is only generated after confirming that the three-phase voltage has stably reached a preset threshold and remained so for a certain period of time; subsequently, the current loop short-circuit command is only generated after verifying that the voltage has been reliably disconnected to a preset ratio. Next, the corresponding action units are driven to perform operations in sequence: first, the voltage loop is disconnected; after confirming that the voltage has effectively decreased, the current loop is short-circuited; finally, the dual-contact unit is driven to synchronously switch the three-phase wiring. After the switching is completed, the voltage and current loops are immediately restored, and the signal is reacquired to verify the switching result and calculate a new phase sequence state value. If verification is successful, the process ends; if multiple attempts fail, an intelligent safety mechanism incorporating historical data analysis and dynamic threshold adjustment is activated, ultimately triggering an alarm and locking the state of all action units to ensure system safety. This method, through a progressive safety logic of "verify first, then act, then confirm" and a multi-state feedback closed loop, achieves automatic and accurate phase sequence switching while fundamentally eliminating the risks of open circuits on the secondary side of current transformers and short circuits on the secondary side of voltage transformers.

[0098] The foregoing has provided a detailed description of one embodiment of the present invention, but this description is merely a preferred embodiment and should not be construed as limiting the scope of the invention. All equivalent variations and modifications made within the scope of the claims of this invention should still fall within the patent coverage of this invention.

Claims

1. A method for phase sequence switching control of an energy meter to ensure the safety of the secondary circuit of a CT / PT, characterized in that, Includes the following steps: S1: Real-time acquisition of three-phase voltage analog quantities and three-phase current analog quantities from the energy meter, and conversion into corresponding voltage digital signals and current digital signals respectively; S2: Analyze the digital voltage and digital current signals to extract the real-time phase angle between each phase voltage and current; construct coordinates on the unit circle using each phase angle to form a multi-dimensional space vector; calculate the angle between the multi-dimensional space vector and the preset positive sequence reference vector in the multi-dimensional space, and normalize the results by combining the dispersion of each phase angle, mapping the normalization result to a unique phase sequence state value; if the phase sequence state value exceeds the preset threshold, it is determined to be a reverse phase sequence state. S3: When the reverse phase sequence is determined, a safety switching instruction sequence containing multi-stage instructions is generated. The safety switching instruction sequence includes: voltage loop disconnection instruction and current loop short-circuit instruction. S4: Execute the safety switching instruction sequence in sequence: First, drive the first group of action units to perform the voltage loop disconnection operation. After confirming that the effective value of the voltage digital signal meets the drop condition, drive the second group of action units to perform the current loop short-circuit operation. After the current loop short-circuit is confirmed, drive the third group of double-contact action units to simultaneously switch the connection relationship between the three-phase voltage and current, and complete the phase sequence exchange. S5: After the phase sequence exchange is completed, the voltage circuit is connected and the current circuit short-circuit operation is released. The three-phase voltage and current digital signals are collected again. The phase sequence status value is recalculated. If the phase sequence status value falls within the normal phase sequence threshold range, the switching is completed. If it is still in the reverse phase sequence state and the switching attempts have not been successful after reaching the preset number of attempts, a safety alarm is triggered and the current state is locked.

2. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 1, characterized in that, The formation process of the multidimensional space vector is as follows: Extract the real-time phase angles corresponding to the digital voltage and current signals of each phase; For each real-time phase angle, calculate the cosine and sine coordinates of the real-time phase angle on the unit circle; The cosine and sine coordinates of the three phases are arranged in the order of the first phase, the second phase, and the third phase to form a multidimensional spatial vector.

3. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 1, characterized in that, The calculation process for the phase sequence state value is as follows: Calculate the cosine of the spatial angle between a multidimensional spatial vector and a preset orthogonal reference vector; Calculate the dispersion index of the real-time phase angle of each phase. The dispersion index is the sum of the absolute values ​​of the differences between each phase angle and the average phase angle. The weighted sum is obtained by weighting the cosine value of the spatial angle with the dispersion index. The phase sequence state values ​​are obtained by performing an inverse cotangent function transformation on the weighted sum.

4. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 1, characterized in that, The process for determining the trigger condition of the voltage circuit disconnection command is as follows: Obtain the effective values ​​of the current phase voltage digital signals within a complete power frequency cycle; The effective value of each phase voltage is compared with the preset effective value threshold to determine whether the effective value of the power supply of all phases exceeds the effective value threshold for a first preset time. Calculate the fluctuation rate of the effective value of each phase voltage within a first preset time period; If the volatility is lower than the preset volatility threshold, a voltage loop disconnection command will be generated.

5. The method for phase sequence switching control of an energy meter to ensure the safety of the secondary circuit of a CT / PT as described in claim 1, characterized in that, The trigger condition determination process for the current loop short-circuit command is as follows: After executing the voltage loop disconnection command, delay for a second preset time, re-acquire the digital voltage signals of each phase and calculate the effective value of each phase voltage digital signal; The effective values ​​of each phase voltage that are re-acquired are compared with the original effective values ​​recorded before the disconnection command is executed, and the effective value decrease rate of each phase voltage is calculated. Determine whether the effective value drop rate of the voltage of all phases has reached or exceeded the preset drop rate threshold, and maintain it for a third preset duration, and confirm the generation of the current loop short-circuit command.

6. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 1, characterized in that, S4 specifically includes: After confirming that the current loop short-circuiting operation is completed, a synchronous switching command is sent to the third group of double-contact action units; The three independent units in the third group of double-contact action units control the three phases respectively. After receiving the instruction, each unit synchronously disconnects the moving contact from the first stationary contact and connects to the second stationary contact. After the connection switch is completed, check again whether the analog quantities of voltage and current in each phase have established a valid path; Once all phases have been confirmed to have established a valid path, the phase sequence exchange is completed, and the connection relationship between voltage and current is simultaneously and synchronously swapped.

7. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 6, characterized in that, After the connection switching is completed, the analog quantities of voltage and current in each phase are checked again to see if a valid path has been established. This includes: After the connection switch is completed, the analog quantities of voltage and current of each phase are reacquired and converted into corresponding voltage verification digital signals and current verification digital signals respectively. The validity of the voltage verification digital signal and the current verification digital signal is verified, including determining whether the signal amplitude is within the preset valid amplitude range, and whether the signal waveform is continuous and uninterrupted within a complete power frequency cycle. Based on the verification results of the digital signals of each phase voltage and current, a comprehensive path effectiveness index is calculated and generated. When the overall pathway effectiveness index is greater than or equal to the effectiveness threshold, all phases are considered to have established effective pathways.

8. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 7, characterized in that, The calculation process for the comprehensive pathway effectiveness index is as follows: The amplitude verification result is obtained by judging whether the effective value of the digital signal is within the preset effective amplitude range by judging the voltage and current of each phase. The waveform continuity verification results are obtained by analyzing whether the sampling point sequence of the phase voltage verification digital signal and the current verification digital signal is continuous and uninterrupted within a complete power frequency cycle. The amplitude verification results and waveform continuity verification results of the phase voltage verification digital signal and the current verification digital signal are respectively quantized into the first quantization value and the second quantization value; The first quantization value and the second quantization value of each phase are multiplied to obtain the single-phase path reliability coefficient of each phase. The reliability coefficients of the single-phase circuits of the three-phase system are sorted, and different weights are assigned to the sorted coefficients. The reliability coefficients of all weighted single-phase pathways are summed, and the summation result is mapped to a preset interval through a preset normalization function to obtain the comprehensive pathway effectiveness index.

9. The energy meter phase sequence switching control method for ensuring the safety of the CT / PT secondary circuit according to claim 1, characterized in that, The triggering of the security alarm and locking of the current state specifically includes: When the number of consecutive switching attempts reaches the preset number and the phase sequence status value is still in reverse phase sequence state, record the phase sequence status values ​​corresponding to the current and historical failed attempts. Analyze the distribution characteristics of each phase sequence state value in the historical failure records, and adjust the offset of the reverse phase sequence determination threshold based on the distribution characteristics; If the phase sequence status value still falls within the reverse phase sequence range after being re-evaluated according to the dynamically adjusted threshold, a safety alarm command will be generated and a status lock command will be sent to all action units at the same time. The state lock command keeps all action units in the immediate state at the time of executing the safety alarm command and blocks the reception and execution of any subsequent external switching commands.

10. A method for phase sequence switching control of an energy meter to ensure the safety of the secondary circuit of a CT / PT as described in claim 9, characterized in that, The offset of adjusting the inverse phase sequence determination threshold based on distribution characteristics specifically includes: Extract all phase sequence state values ​​from the historical failure records and form a state value sequence according to the order in which the attempts occurred; Analyze the numerical distribution of the state value sequence and calculate the degree of clustering and the location of the cluster center near the inverse phase sequence determination threshold; Based on the offset direction and offset distance of the aggregation center position relative to the original reverse phase sequence threshold, the threshold offset is calculated according to a preset ratio. The threshold offset is algebraically added to the original reverse phase sequence determination threshold to obtain the adjusted reverse phase sequence determination threshold.

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