A method and device for preventing reverse flow of instrument phase sequence adjustment

Abstract

The application discloses a method and device for preventing reverse flow of instrument phase sequence, and belongs to the technical field of household energy storage reverse flow control. In the method, the energy storage inverter outputs three-phase pure reactive current with different amplitudes and equal amplitudes in stages, and the detection and correction of current phase sequence and voltage phase sequence are sequentially completed according to a fixed time sequence, and finally the detection and correction of current polarity are completed based on the positive and negative properties of reactive power. The device comprises an energy storage inverter and a reverse flow detection ammeter connected through an RS485 bidirectional communication bus, and the inverter is internally provided with a reactive output control module, a data reading module, an error determination module and a parameter correction module. The application can accurately locate and correct three types of high-frequency wiring faults without changing the hardware wiring, eliminate detection interference, reduce installation and operation and maintenance costs, and ensure stable and reliable operation of the reverse flow prevention function.

Description

Technical Field

[0001] This invention belongs to the field of backflow prevention control technology for residential energy storage, specifically relating to a method and device for adjusting the phase sequence of instruments for backflow prevention. Background Technology

[0002] With the large-scale promotion of distributed residential photovoltaic energy storage systems, anti-reverse current function has become a mandatory compliance requirement for grid connection of residential energy storage systems. The reverse current detection meter installed at the grid connection point is the data detection unit for anti-reverse current control. However, wiring problems such as incorrect voltage / current phase sequence connection and reversed polarity of current transformers during on-site installation are the core industry pain points that cause meter data distortion and anti-reverse current failure.

[0003] To address the aforementioned wiring errors, existing technologies mainly fall into two categories: manual rectification and automated detection. Manual rectification relies on professional installers using phase sequencers to troubleshoot phase by phase and manually adjust hardware wiring. This approach suffers from high labor and time costs, low maintenance efficiency, and stringent requirements for installers' professional skills, making it unsuitable for the large-scale deployment needs of the residential photovoltaic energy storage grid-connected industry. Existing automated detection solutions have significant technical limitations: some solutions rely on complex algorithms such as Clark coordinate transformation and real-time phase difference calculation, placing high demands on the hardware computing power of inverters and meters, thus increasing system implementation costs; some solutions do not employ a phased detection-correction closed-loop design, failing to eliminate interference from current phase sequence errors on voltage phase sequence detection and phase sequence misalignment on polarity detection, resulting in a high false positive rate. Furthermore, they cannot fully cover the three common field faults: current phase sequence errors, voltage phase sequence errors, and reversed polarity of current transformers, making it difficult to fundamentally solve the problem of reverse current failure.

[0004] In summary, existing technologies cannot simultaneously meet the application requirements of full fault coverage, no hardware modification, low computing power, and high reliability. A more complete automatic phase sequence adjustment scheme is urgently needed for user storage anti-backflow scenarios. Summary of the Invention

[0005] The purpose of this invention is to overcome the deficiencies in the prior art and provide a method and device for adjusting the phase sequence of instruments to prevent backflow. The technical solution is as follows: In a first aspect, this application provides a method for adjusting the phase sequence of an instrument for backflow prevention. The method is applied to a residential energy storage anti-backflow system comprising an energy storage inverter and a backflow detection meter, wherein the energy storage inverter and the backflow detection meter establish a bidirectional communication connection. The method includes the following steps: S1. The energy storage inverter outputs three-phase pure reactive currents with different amplitudes to the three-phase power grid, reads the three-phase current amplitude data collected by the reverse current detection meter, determines the phase with current phase sequence misalignment by amplitude comparison, and writes the correct current phase sequence parameters into the reverse current detection meter to complete the correction. S2. After the current phase sequence correction is completed, the energy storage inverter outputs three-phase pure reactive current with the same amplitude to the three-phase power grid, reads the three-phase reactive power data of the reverse current detection meter, determines the type and phase of the voltage phase sequence error based on the phase characteristics of the reactive power, and writes the correct voltage phase sequence parameters into the reverse current detection meter to complete the correction. S3. After the voltage phase sequence correction is completed, the energy storage inverter reads the three-phase reactive power data of the reverse current detection meter, determines the phase with reversed current polarity based on the positive and negative attributes of the reactive power, and writes the correct current polarity parameters into the reverse current detection meter to complete the correction.

[0006] The steps S1, S2, and S3 are executed sequentially in a fixed time order. The next step of detection and correction can only be performed after the parameter correction of the previous step is completed.

[0007] Furthermore, the energy storage inverter is bidirectionally connected to the reverse current detection meter via an RS485 bus. The energy storage inverter reads the real-time electrical acquisition data of the reverse current detection meter via the RS485 bus and writes phase sequence configuration parameters and polarity configuration parameters to the reverse current detection meter.

[0008] Furthermore, in step S1, the energy storage inverter sorts and marks its own output three-phase reactive current according to its amplitude, and matches the sorting marks with the sorting results of the three-phase current amplitude collected by the reverse current detection meter to determine the phase with current phase sequence misalignment.

[0009] Furthermore, in step S2, the phase characteristic of the reactive power is determined based on the three-phase AC reactive power calculation formula Q=U×I×sinφ; where Q is the single-phase reactive power, U is the effective value of the phase voltage, I is the effective value of the phase current, and φ is the power factor angle of the phase voltage and phase current in the same sampling channel of the meter.

[0010] Furthermore, in step S2, the types of voltage phase sequence errors include two-phase phase sequence reversal and all three-phase phase sequence misalignment; If the reactive power values ​​of any two phases collected by the reverse current detection meter are both within the first preset value range, then it is determined that the phase sequence of the two phase voltages is reversed. If the three-phase reactive power values ​​collected by the reverse current detection meter are all within the first preset value range, then it is determined that the three-phase voltage phase sequence is completely misaligned. The first preset value range is -0.4 times to -0.6 times the rated reactive power of a single phase output by the energy storage inverter.

[0011] The setting of the first preset numerical range is based on the inherent phase characteristics of three-phase alternating current and the actual working conditions at the household-storage grid connection site. Its core principle and numerical derivation process are as follows: This derivation assumes that the current phase sequence has been fully corrected. At this point, the three-phase current sampling channels of the meter correspond perfectly with the inverter output current, with no misalignment or deviation. The only variable present is the voltage sampling wiring phase sequence error. It also adopts the power industry's common phase rule: with the grid A-phase voltage as the 0° reference, the three-phase voltages naturally differ by 120°, i.e., A-phase voltage 0°, B-phase voltage -120°, and C-phase voltage 120°. The power factor angle φ in the reactive power formula is defined as the phase voltage phase minus the phase current phase within the same sampling channel of the meter, i.e., the angle by which the voltage leads the current.

[0012] In the testing phase of this patent, the inverter outputs a purely capacitive reactive current, forcing the active power to be 0 to avoid active power impact on the grid. Under normal conditions without wiring errors, the power factor angle φ of the voltage and current in the same phase circuit needs to be guaranteed to be 90°. Therefore, the phases of the three-phase currents output by the inverter are determined as follows: Phase A current phase: 0°-90°=-90°; Phase B current phase: -120°-90°=-210°, equivalent to 150°; Phase C current phase: 120°-90°=30°. Under this setting, the three-phase currents are still 120° apart, outputting a balanced reactive current, which fully complies with the grid connection specifications.

[0013] The core calculation logic of the reverse current detection meter is to use the voltage and current within the same sampling channel as parameters of the same phase path to calculate the power factor angle and reactive power. It cannot identify the true phase sequence of the power grid, only the input signal from its own terminals. When the voltage sampling phase sequence is incorrect, the voltage phase within the same phase path will shift by a fixed multiple of 120°, resulting in a fixed shift in the power factor angle φ. This can be divided into two scenarios: The first scenario involves a reversed phase sequence of two-phase voltages. Taking the most common case of reversed A and B phase voltage connections at a residential power storage facility as an example, in this case, the A-phase sampling channel of the meter is connected to the B-phase voltage of the power grid, with a phase of -120°. The current within the channel is still the corrected A-phase current, with a phase of -90°. The calculated power factor angle φ = -120° - (-90°) = -30°, equivalent to 330°. Conversely, if the B-phase sampling channel of the meter is connected to the A-phase voltage of the power grid, with a phase of 0°, the current within the channel is still the corrected B-phase current, with a phase of 150°. The calculated power factor angle φ = 0° - 150° = -150°, equivalent to 210°. The second scenario involves a complete misalignment of the three-phase voltage phase sequence. Taking the BCA phase sequence connection as an example, the A, B, and C phase channels of the meter are connected to the B, C, and A phase voltages of the power grid, respectively, with corresponding phases of -120°, 120°, and 0°. The current phases within the corresponding channels remain -90°, 150°, and 30°. Calculations show that the three-phase power factor angle is -150°, equivalent to 210°. Taking the CAB phase sequence connection as an example, calculations show that the three-phase power factor angle is -30°, equivalent to 330°.

[0014] Based on the three-phase AC reactive power calculation formula Q=U×I×sinφ, substituting the derived phase angles of 210° and 330° into the formula, we can obtain that the values ​​of sin210° and sin330° are both -0.5. Under ideal operating conditions, the effective value of the phase voltage U and the effective value of the phase current I in the same phase circuit are both rated values, and their product is the rated reactive power of a single phase. Therefore, when the voltage phase sequence is incorrect, the ideal value of the reactive power of the corresponding phase is -0.5 times the rated reactive power of the single phase.

[0015] Considering factors such as transformer phase angle difference, meter sampling delay, grid harmonics, and inverter control accuracy in engineering sites, which can lead to a normal deviation of ±7° in the actual phase difference, and a deviation of no more than ±10° under extreme conditions, this patent sets the upper range of the judgment interval to -0.6 to -0.4 times the rated reactive power, which can cover the phase deviation of all field conditions. For conventional applications in residential energy storage scenarios, the range of -0.55 to -0.45 times is preferred. This range ensures the accuracy of phase sequence determination, avoids misjudgment in non-phase-out conditions, and fully covers more than 99% of field installation conditions, balancing detection sensitivity and anti-interference capability.

[0016] Furthermore, in step S3, if the reactive power of any phase collected by the reverse current detection meter is negative, it is determined that the polarity of the corresponding current transformer is reversed.

[0017] On the other hand, this application also provides an instrument phase sequence adjustment device for anti-backflow, the device implementing the steps of any of the above methods, the device including an energy storage inverter and a backflow detection meter, the energy storage inverter and the backflow detection meter being connected via an RS485 bidirectional communication bus; The reverse current detection meter is installed at the grid connection point of the household energy storage anti-reverse current system to collect current, voltage and power data on the grid side.

[0018] The energy storage inverter has a built-in reactive power output control module, data reading module, error judgment module and parameter correction module; The control output terminal of the reactive power output control module is electrically connected to the three-phase inverter main circuit of the energy storage inverter. The AC output terminal of the three-phase inverter main circuit is electrically connected to the three-phase power grid and is used to output three-phase pure reactive current with adjustable amplitude to the three-phase power grid. The status feedback terminal of the reactive power output control module is electrically connected to the first input terminal of the error judgment module. The signal input terminal of the data reading module is electrically connected to the RS485 bus receiver of the energy storage inverter, and is used to read the electrical acquisition data of the reverse current detection meter; the signal output terminal of the data reading module is electrically connected to the second input terminal of the error judgment module. The signal output terminal of the error determination module is electrically connected to the signal input terminal of the parameter correction module. It is used to sequentially determine current phase sequence errors, voltage phase sequence errors, and current polarity errors based on the output parameters of the reactive power output control module and the collected data obtained by the data reading module. The command output terminal of the parameter correction module is electrically connected to the RS485 bus transmitter of the energy storage inverter. It is used to write the corresponding correct phase sequence and polarity parameters to the reverse current detection meter via the RS485 bus based on the determination result of the error determination module, thus completing the correction.

[0019] Furthermore, the reactive power output control module has at least two fixed reactive current output levels: the first output level is used to output three-phase pure reactive current with different amplitudes to the three-phase power grid, and the second output level is used to output three-phase pure reactive current with the same amplitude to the three-phase power grid.

[0020] Furthermore, the error determination module includes a current phase sequence determination unit and a voltage phase sequence determination unit; The signal input terminal of the current phase sequence determination unit is electrically connected to the reactive power output control module and the data reading module, respectively, and the signal output terminal is electrically connected to the parameter correction module. It is used to sort the three-phase reactive current of the first output level by amplitude and match it one-to-one with the three-phase current amplitude sorting collected by the reverse current detection meter to determine the misaligned phase of the current phase sequence. The signal input terminal of the voltage phase sequence determination unit is electrically connected to the reactive power output control module and the data reading module, respectively, and the signal output terminal is electrically connected to the parameter correction module.

[0021] Furthermore, the error determination module also includes a current polarity determination unit, the signal input terminal of which is electrically connected to the data reading module, and the signal output terminal of which is electrically connected to the parameter correction module.

[0022] The advantages and beneficial effects of this invention are as follows: 1. Improve the accuracy of detection and judgment, and ensure the stable operation of the anti-reverse current function. This invention adopts a phased time-sequential closed-loop detection and correction design. The next detection stage is started only after the parameters of the previous stage are corrected. This can completely eliminate detection interference between different types of wiring errors, accurately locate and correct three types of wiring faults: current phase sequence misalignment, voltage phase sequence misalignment, and current transformer polarity reversal. This provides accurate electrical acquisition data for the anti-reverse current closed-loop control, and avoids the failure of the anti-reverse current function caused by wiring errors at the root.

[0023] 2. Achieve fully automated calibration, significantly reducing installation and maintenance costs. This invention completes calibration by writing configuration parameters to the meter via a two-way communication link, eliminating the need to modify on-site hardware wiring or conduct manual on-site inspections and rectifications. This significantly reduces the professional skill requirements for on-site installers and substantially improves the on-site construction and subsequent maintenance efficiency of the household energy storage system.

[0024] 3. The solution has a simple logic, is easy to implement, and has strong adaptability to various scenarios. This invention adopts a simplified detection logic of amplitude comparison and reactive power amplitude range determination. It does not require complex coordinate transformation, real-time phase calculation, or other algorithms. It has low hardware computing power requirements for inverters and meters and can be directly adapted to common hardware equipment used in household storage and anti-reverse current scenarios. The solution has low implementation cost and is easy to scale up and apply. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the energy storage anti-backflow system described in this invention; Figure 2 This is a flowchart illustrating the instrument phase sequence adjustment method of the present invention; Figure 3 This is a schematic diagram of the instrument phase sequence adjustment device of the present invention. Detailed Implementation

[0026] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings and examples. The following examples are only used to more clearly illustrate the technical solutions of the present invention and should not be construed as limiting the scope of protection of the present invention.

[0027] In this embodiment, the provided instrument phase sequence adjustment method for backflow prevention is applied to a three-phase four-wire household energy storage anti-backflow grid-connected system. The rated electrical parameters of the system are: rated grid phase voltage of 220V and rated frequency of 50Hz, rated grid-connected capacity of energy storage inverter of 5kW, a 0.5-level precision three-phase multi-function meter for backflow detection, and a 0.2-level precision open-type current transformer.

[0028] like Figure 1 As shown, the hardware architecture of the residential energy storage anti-backflow system is as follows: The grid side consists of a low-voltage public power grid and a legally mandated trade settlement billing meter installed at the grid inlet. The core detection and control unit includes a backflow detection meter installed in series at the grid connection point and an energy storage inverter connected to the AC side of the grid connection point; the voltage sampling terminals of the backflow detection meter are connected to the three phases A, B, and C of the grid and the neutral line N, respectively, and the current sampling circuit is connected to the three phase lines A, B, and C through open-type current transformers, respectively, for real-time acquisition of electrical data at the grid connection point; the DC side of the energy storage inverter is connected to the photovoltaic array and the lithium iron phosphate battery pack, respectively, and its AC output terminal has a built-in three-phase inverter main circuit and DSP control unit, supporting independent closed-loop control of three-phase reactive power.

[0029] Preferably, the energy storage inverter and the reverse current detection meter's RS485 interface are physically connected via shielded twisted-pair cable, and bidirectional data interaction is achieved using the Modbus RTU protocol. The energy storage inverter is configured as the communication master station, and the reverse current detection meter is configured as the communication slave station. The communication parameters are set to a baud rate of 9600bps, 8 data bits, 1 stop bit, and no parity bit. The energy storage inverter reads the real-time electrical acquisition data from the reverse current detection meter via Modbus protocol function code 03H, and writes phase sequence mapping and current polarity reversal parameters to the configurable register of the reverse current detection meter via function code 06H, thereby completing phase sequence and polarity correction without modifying the hardware wiring.

[0030] In this embodiment, the reverse current detection meter has three built-in read / write configuration registers: the current phase sequence mapping register has an address of 0x0010 and a default value of 0x0001 corresponding to the ABC positive phase sequence, which is used to configure the phase sequence mapping relationship of the three-phase current acquisition data; the voltage phase sequence mapping register has an address of 0x0011 and a default value of 0x0001 corresponding to the ABC positive phase sequence, which is used to configure the phase sequence mapping relationship of the three-phase voltage acquisition data; the current polarity configuration register has an address of 0x0012 and a default value of 0x0000, where bit 0 corresponds to phase A, bit 1 corresponds to phase B, and bit 2 corresponds to phase C. When each bit is set to 1, the polarity of the corresponding phase current is reversed, which is used to configure the polarity reversal function of each phase current acquisition.

[0031] Preferably, before executing the phase sequence adjustment method of this embodiment, system initialization and parameter pre-configuration need to be completed to ensure the stable execution of the detection process. The specific steps are as follows: A1. Equipment power-on self-test: The energy storage inverter and the reverse current detection meter complete the power-on start-up, perform internal hardware self-test and program initialization, and confirm that there are no hardware faults and no grid abnormality alarms. A2. Communication Link Verification: The energy storage inverter periodically sends heartbeat query frames to the reverse current detection meter via RS485 bus. If it receives the correct response frame from the meter three times in a row, it confirms that the two-way communication link is stable and normal. A3. Pre-configuration of detection range: Two fixed reactive current output ranges are preset in the DSP control unit of the energy storage inverter. Both ranges control the active power output to 0 to avoid active power impact on the power grid during the detection process. The specific range parameters are as follows: First output setting: Phase A output reactive current Ia=5A, Phase B output reactive current Ib=3A, Phase C output reactive current Ic=1A. The amplitudes of the three-phase reactive currents are different, giving each phase current a unique and identifiable amplitude identifier. Second output setting: Phases A, B, and C all output 5A of reactive current, with the three-phase reactive current amplitudes being completely identical, eliminating the interference of current amplitude differences on reactive power calculation; A4. Threshold Pre-configuration: A first preset value range is preset, the range being based on the single-phase rated reactive power under the second level, and the value is -0.55 to -0.45 times the benchmark value; in this embodiment, the rated phase voltage is 220V, the rated reactive current is 5A, and the single-phase rated reactive power Q e =U×I=220V×5A=1100var, therefore the first preset value range is -605var~-495var, which covers the numerical fluctuations under actual engineering conditions such as power grid harmonics, metering errors, and sampling drift.

[0032] like Figure 2 As shown, preferably, in another embodiment, the instrument phase sequence adjustment method for backflow prevention includes the following steps: S1. Current Phase Sequence Detection and Automatic Correction: The core purpose of this step is to identify and correct phase sequence misalignment faults in open-type current transformers. The specific execution process is as follows: S101, the energy storage inverter controls the three-phase inverter main circuit to switch to the first output position, outputting three-phase pure reactive currents with different amplitudes to the three-phase power grid, i.e., phase A I a =5A, B phase I b =3A, C phase I c =1A, and simultaneously lock the active power output to 0; the inverter synchronously sends the three-phase current amplitude of this output and the tag information sorted from largest to smallest to the internal error judgment unit; in this embodiment, the sorting tag of the output current is as follows: the first digit corresponds to phase A, and the output reactive current is 5A; the second digit corresponds to phase B, and the output reactive current is 3A; the third digit corresponds to phase C, and the output reactive current is 1A.

[0033] S102. After the inverter output current stabilizes, the three-phase current amplitude data collected by the reverse current detection meter is read through the Modbus protocol 03H function code. In this embodiment, the meter data read is 3A for phase A, 5A for phase B, and 1A for phase C. The inverter then synchronously sends the collected three-phase current data to the error judgment unit.

[0034] The S103 error detection unit sorts the three-phase current amplitudes collected by the meter from largest to smallest, resulting in the following sorting order: the first position corresponds to phase B, with a collected current of 5A; the second position corresponds to phase A, with a collected current of 3A; and the third position corresponds to phase C, with a collected current of 1A. The sorting results are then compared one-to-one with the sorting marks output by the inverter to determine the phases with misaligned current phase sequences. The output phase corresponding to the first sorted position is phase A, and the collected phase is phase B; the output phase corresponding to the second sorted position is phase B, and the collected phase is phase A; the output phase corresponding to the third sorted position is phase C, and the collected phase is phase C. Therefore, it is determined that the current transformers for phases A and B have misaligned phase sequences, while the current phase sequence for phase C is correct.

[0035] S104. The error judgment unit generates the correct current phase sequence mapping parameters based on the comparison results. The inverter writes the correct current phase sequence parameters into the current phase sequence mapping register of the reverse current detection meter via Modbus protocol 06H function code. After receiving the configuration parameters, the meter automatically updates the phase sequence mapping relationship of the internal three-phase current acquisition data, completing the automatic correction of the current phase sequence.

[0036] After S105 calibration is completed, the inverter reads the three-phase current amplitude data of the reverse current detection meter again to confirm that the data collected by the meter is completely matched with the output current amplitude of the inverter. It is then determined that the current phase sequence calibration is complete, the current phase sequence configuration is latched, and the next detection step is initiated.

[0037] S2. Voltage Phase Sequence Detection and Automatic Correction: The core purpose of this step is to identify and correct voltage wiring phase sequence errors, provided that the current phase sequence has been fully corrected. The specific execution process is as follows: After the current phase sequence correction verification (S201) is passed, the inverter controls the three-phase inverter main circuit to switch to the second output position, outputting three-phase pure reactive currents with completely consistent amplitudes to the three-phase grid. Specifically, phases A, B, and C all output 5A reactive current, while the active power output remains at 0, completely eliminating the interference of current amplitude differences on reactive power calculation. The inverter synchronously sends the single-phase rated reactive power of 1100var output to the error detection unit.

[0038] S202. After the inverter output stabilizes, the three-phase reactive power data calculated and output by the reverse current detection meter is read via Modbus protocol 03H function code. In this embodiment, the collected data read is A phase -552var, B phase -548var, and C phase 1100var. The inverter synchronously sends the collected reactive power data to the error judgment unit.

[0039] S203. The error detection unit performs voltage phase sequence error detection based on the three-phase AC reactive power calculation formula Q=U×I×sinφ. Where Q is the single-phase reactive power, U is the effective value of the phase voltage, I is the effective value of the phase current, and φ is the power factor angle of the phase voltage and phase current in the same phase.

[0040] The principle behind this step is that, assuming the current phase sequence is fully corrected, the current phase of the same phase path is perfectly matched with the inverter output. Under normal positive phase sequence pure reactive output, the power factor angle φ between the phase voltage and phase current is 90°, and sin90° has a value of 1. Therefore, the reactive power under normal phase sequence is Q=UI, with a value of 1100var. When the voltage phase sequence is misaligned, the power factor angle between the phase voltage and phase current of the same phase path will shift by a fixed amount, as follows: When the phase sequence of any two phase voltages is reversed, the voltage and current power factor angles of the corresponding two phases become 210° or 330°, where the values ​​of sin210° and sin330° are both -0.5. Under ideal operating conditions, the reactive power of the corresponding two phases is -0.5 times the rated reactive power.

[0041] When the three-phase voltage phase sequence is completely misaligned, the voltage and current power factor angles of the three phases become 210° or 330°. Under ideal conditions, the reactive power of the three phases is -0.5 times the rated reactive power.

[0042] S204. Based on the above principle and the pre-configured first preset value range, the error determination unit performs voltage phase sequence error type and phase identification determination, and the determination rules are as follows: If the reactive power of any two phases collected by the reverse current detection meter is within the range of -605var to -495var, and the reactive power of the remaining phase deviates from the rated value of 1100var by no more than ±5%, then it is determined that the phase sequence of the two phases is reversed.

[0043] If the three-phase reactive power collected by the reverse current detection meter is all within the range of -605var to -495var, then it is determined that the three-phase voltage phase sequence is completely misaligned.

[0044] In this embodiment, the collected A-phase -552var and B-phase -548var are both within the first preset value range, and the C-phase 1100var deviates from the rated value by less than ±5%. Therefore, it is determined that the phase sequence of the A-phase and B-phase voltages is reversed, while the phase sequence of the C-phase voltage is correct.

[0045] S205. The error judgment unit generates the correct voltage phase sequence mapping parameters based on the judgment result. The inverter writes the correct voltage phase sequence parameters into the voltage phase sequence mapping register of the reverse current detection meter through Modbus protocol 06H function code. After receiving the configuration parameters, the meter automatically updates the phase sequence mapping relationship of the internal three-phase voltage acquisition data, completing the automatic correction of the voltage phase sequence.

[0046] S206. After the calibration is completed, the inverter reads the three-phase reactive power data of the reverse current detection meter again, confirms that the deviation of the three-phase reactive power from the rated value of 1100var does not exceed ±5%, determines that the voltage phase sequence calibration is complete, latches the current voltage phase sequence configuration, and proceeds to the next detection step.

[0047] S3. Current Polarity Detection and Automatic Correction: The core purpose of this step is to identify and correct the reverse polarity fault of the current transformer, provided that the voltage and current phase sequence have been fully corrected. The specific execution process is as follows: After the voltage phase sequence correction verification (S301) is passed, the inverter maintains stable operation at the second output level, meaning all three phases output 5A of pure reactive current and the active power output is 0. The three-phase reactive power data collected by the reverse current detection meter is read again via Modbus protocol function code 03H. In this embodiment, the collected data read this time is 1100var for phase A, 1100var for phase B, and -1100var for phase C. The inverter synchronously sends the collected reactive power data to the error judgment unit.

[0048] S302. The error judgment unit performs current polarity judgment based on the positive and negative attributes of reactive power. The judgment rule is that, provided that the voltage and current phase sequence have been fully corrected, when the inverter outputs capacitive reactive current, the normal reactive power collected by the meter should be positive. If the reactive power of a certain phase is negative, it is determined that the polarity of the corresponding current transformer is reversed.

[0049] In this embodiment, the collected C-phase -1100var is a negative value, therefore it is determined that the polarity of the C-phase current transformer is reversed, while the polarity of the A-phase and B-phase currents is correct.

[0050] S303. The error judgment unit generates the correct current polarity configuration parameters based on the judgment result. The inverter writes the C-phase polarity reversal parameter into the current polarity configuration register of the reverse current detection meter through Modbus protocol 06H function code. After receiving the configuration parameters, the meter automatically reverses the current acquisition polarity of the C-phase, completing the automatic correction of the current polarity.

[0051] S304. After the calibration is completed, the inverter reads the three-phase reactive power data of the reverse current detection meter again to confirm that the three-phase reactive power is positive and the deviation from the rated value of 1100var does not exceed ±5%. The current polarity calibration is then determined to be complete, and the entire process of detection and calibration is finished.

[0052] After the entire calibration process is completed, the inverter exits the detection mode and resumes normal grid-connected operation. It then reads the active and reactive power data collected by the reverse current detection meter in real time and executes the anti-reverse current closed-loop control logic. Field verification showed that the calibrated meter data perfectly matched the actual electrical state of the grid connection point, demonstrating stable and reliable anti-reverse current function with no data distortion, misjudgment, or failure to operate.

[0053] The steps S1, S2, and S3 are executed sequentially in a fixed time order. The next step of detection and correction can only be performed after the parameter correction of the previous step is completed.

[0054] like Figure 3 As shown, in another embodiment, a meter phase sequence adjustment device for backflow prevention is provided. This device is used to perform the meter phase sequence adjustment method for backflow prevention as described in any of the foregoing embodiments. The device in this embodiment is applied to a three-phase four-wire household energy storage backflow prevention grid-connected system. The system's rated electrical parameters are: rated grid phase voltage 220V, rated frequency 50Hz, rated grid-connected capacity of the energy storage inverter 5kW, a 0.5-class precision three-phase multi-function meter for backflow detection, and a 0.2-class precision open-type current transformer.

[0055] The device described in this embodiment can be adapted to all types of installation conditions in residential energy storage grid connection scenarios. Without modifying the on-site hardware wiring, it can automatically complete the detection and correction of three types of high-frequency faults: current phase sequence misalignment, voltage phase sequence misalignment, and current transformer polarity reversal, thus ensuring the stable and reliable operation of the anti-reverse current function from the root.

[0056] The instrument phase sequence adjustment device for backflow prevention described in this embodiment has core hardware components including an energy storage inverter, a backflow detection meter, and an RS485 bidirectional communication bus.

[0057] The energy storage inverter is the core control unit of the device. Its AC side is electrically connected to the grid connection point via a grid-connected contactor, and its DC side is electrically connected to the photovoltaic array and the lithium iron phosphate battery pack, respectively. The energy storage inverter integrates a three-phase inverter main circuit, a DSP control unit, an RS485 communication interface, signal acquisition circuits, and drive circuits. The three-phase inverter main circuit adopts a three-phase full-bridge IGBT topology, enabling independent closed-loop control of reactive power for each of the three phases. The DSP control unit uses a 32-bit floating-point digital signal processor, providing the computation and control platform for all functional modules of the device. The RS485 communication interface uses an isolated transceiver to resist electromagnetic interference in the field and ensure the stability of the communication link.

[0058] Preferably, the reverse current detection meter is the core data acquisition unit of the device, installed in series at the grid connection point, located between the household billing meter and the energy storage inverter grid connection point. The voltage sampling terminals of the reverse current detection meter are electrically connected to phases A, B, and C of the grid and the neutral line N, respectively. The current sampling circuit is connected to the three phase lines A, B, and C through open-type current transformers, enabling real-time acquisition of three-phase current, three-phase voltage, active power, and reactive power electrical data at the grid connection point. The reverse current detection meter has a built-in readable and writable non-volatile configuration register, supporting modification of phase sequence mapping and polarity configuration parameters via the communication bus, allowing phase sequence and polarity correction of the acquired data to be completed without modifying the hardware wiring.

[0059] Preferably, the RS485 bidirectional communication bus is constructed using shielded twisted-pair cable. The two ends of the bus are connected to the RS485 communication interface of the energy storage inverter and the RS485 communication interface of the reverse current detection meter, respectively, enabling full-duplex bidirectional data interaction between the energy storage inverter and the reverse current detection meter. In this embodiment, the bus adopts the Modbus-RTU communication protocol. The energy storage inverter is configured as the communication master station, with its station address set to 01; the reverse current detection meter is configured as the communication slave station, with its station address set to 02; the communication parameters are set to a baud rate of 9600bps, 8 data bits, 1 stop bit, and no parity bit.

[0060] Preferably, in this embodiment, the DSP control unit of the energy storage inverter integrates a reactive power output control module, a data reading module, an error judgment module, and a parameter correction module. Each module is electrically connected and interacts with data via the DSP's internal bus. The hardware electrical connections and signal flow between modules are fixed, ensuring stable execution of the entire detection and correction process.

[0061] Specifically, the core function of the reactive power output control module is to generate and output a three-phase pure reactive current with a preset amplitude, providing an identifiable excitation signal for phase sequence and polarity detection. The control output terminal of the reactive power output control module is electrically connected to the drive circuit of the three-phase inverter main circuit of the energy storage inverter, and can send PWM control signals to the drive circuit to control the three-phase inverter main circuit to output reactive current with the corresponding amplitude. The status feedback terminal of the reactive power output control module is electrically connected to the first input terminal of the error judgment module, and can send the current output reactive current level, three-phase current amplitude, and sorting mark information to the error judgment module in real time.

[0062] Preferably, the reactive power output control module has two preset fixed reactive current output levels. Both levels control the active power output to 0, avoiding active power impact on the public power grid during the detection process and preventing interference with the normal power consumption of the user-side load. The first output level is the current phase sequence detection level, corresponding to the output of three-phase pure reactive current with different amplitudes.

[0063] In this embodiment, the preset parameters for the first output level are 5A reactive current output for phase A, 3A reactive current output for phase B, and 1A reactive current output for phase C. These differentiated amplitudes assign unique and identifiable identifiers to the three-phase currents, providing a basis for current phase sequence comparison and determination. The second output level is for voltage phase sequence and current polarity detection, corresponding to three-phase pure reactive currents with completely identical output amplitudes. In this embodiment, the preset parameters for the second output level are 5A reactive current output for phases A, B, and C, completely eliminating the interference of current amplitude differences on reactive power calculation and ensuring the accuracy of voltage phase sequence and current polarity determination results.

[0064] In an optional implementation of this embodiment, the reactive power output control module can adaptively adjust the output current amplitude of the two sets of levels according to the on-site power grid conditions and meter accuracy. It is only necessary to keep the three-phase current amplitudes of the first output level different from each other and the three-phase current amplitudes of the second output level completely consistent.

[0065] Preferably, the core function of the data reading module is to acquire real-time data from the reverse current detection meter and distribute the acquired data to the corresponding judgment units. The signal input terminal of the data reading module is electrically connected to the RS485 bus receiver of the energy storage inverter, and can acquire the electrical data uploaded by the reverse current detection meter through the RS485 bidirectional communication bus. The signal output terminal of the data reading module is electrically connected to the second input terminal of the error judgment module, and can synchronously send the preprocessed acquired data to each judgment unit within the error judgment module.

[0066] The data reading module incorporates a Modbus protocol parsing unit and a data preprocessing unit. The protocol parsing unit can parse and verify the communication frames received from the bus, extracting valid three-phase current amplitude and three-phase reactive power acquisition data; the data preprocessing unit can filter and de-jitter the acquired data, eliminating abnormal jump data caused by grid harmonics and on-site electromagnetic interference, ensuring the stability and validity of the data input to the error judgment module.

[0067] Preferably, the core function of the error determination module is to determine and locate the type of three types of faults—current phase sequence misalignment, voltage phase sequence misalignment, and current transformer polarity reversal—based on the output parameters of the reactive power output control module and the data acquired by the data reading module. The signal output terminal of the error determination module is electrically connected to the signal input terminal of the parameter correction module, and can send the fault determination result and the corresponding correction parameters to the parameter correction module.

[0068] The error detection module has built-in current phase sequence detection unit, voltage phase sequence detection unit and current polarity detection unit. The three detection units are started in sequence according to a fixed timing. The detection work of the next unit can only be started after the detection and correction action of the previous unit is completed, so as to completely eliminate the detection interference between different fault types.

[0069] Specifically, the signal input terminal of the current phase sequence determination unit is electrically connected to the reactive power output control module and the data reading module, respectively, and can synchronously acquire the three-phase current amplitude sorting mark output by the inverter and the three-phase current amplitude data collected by the meter. The signal output terminal of the current phase sequence determination unit is electrically connected to the parameter correction module, and can send the phase determination result of the current phase sequence misalignment and the correct current phase sequence parameters to the parameter correction module.

[0070] The current phase sequence determination unit has a built-in amplitude sorting and comparison subunit, which can sort and mark the three-phase reactive current output by the inverter from largest to smallest amplitude, and at the same time sort the three-phase current amplitude collected by the meter from largest to smallest. By comparing the two sets of sorting results one by one, the specific phase with current phase sequence misalignment can be accurately located.

[0071] The signal input terminals of the voltage phase sequence determination unit are electrically connected to the reactive power output control module and the data reading module, respectively, and can synchronously acquire the single-phase rated reactive power output by the inverter and the three-phase reactive power data collected by the meter. The signal output terminal of the voltage phase sequence determination unit is electrically connected to the parameter correction module, and can send the type of voltage phase sequence error, the misaligned phase, and the correct voltage phase sequence parameters to the parameter correction module.

[0072] The voltage phase sequence determination unit performs the determination based on the three-phase AC reactive power calculation formula Q=U×I×sinφ, where Q is the single-phase reactive power, U is the effective value of the phase voltage, I is the effective value of the phase current, and φ is the power factor angle of the phase voltage and phase current in the same phase path. The voltage phase sequence determination unit has a preset first value range, which is based on the single-phase rated reactive power corresponding to the second output level, and the value ranges from -0.55 to -0.45 times the benchmark value. In this embodiment, the single-phase rated reactive power is 1100var, and the first preset value range is from -605var to -495var.

[0073] In this embodiment, the core principle of voltage phase sequence determination is that, under the premise that the current phase sequence has been fully corrected, the current phase of the same phase path has been fully matched with the inverter output. Under normal positive phase sequence pure reactive power output, the power factor angle φ of the phase voltage and phase current is 90°, and the sin90° value is 1. Therefore, the reactive power value under normal phase sequence is 1100var. When the phase sequence of any two phase voltages is reversed, the power factor angles of the corresponding two phases become 210° or 330°, where the sin210° and sin330° values ​​are both -0.5. Under ideal operating conditions, the reactive power of the corresponding two phases is -0.5 times the rated reactive power. When all three phase voltages are misaligned, the power factor angles of the three phases all become 210° or 330°, and under ideal operating conditions, the reactive power of all three phases is -0.5 times the rated reactive power.

[0074] The voltage phase sequence determination unit has the following determination rule: if the reactive power of any two phases collected by the reverse current detection meter is within the first preset value range, and the reactive power of the remaining phase deviates from the rated value of 1100var by no more than ±5%, then the voltage phase sequence of the two phases is determined to be reversed; if the reactive power of all three phases collected by the reverse current detection meter is within the first preset value range, then the voltage phase sequence of all three phases is determined to be misaligned.

[0075] The signal input terminal of the current polarity determination unit is electrically connected to the data reading module, which can acquire the three-phase reactive power data collected by the meter after voltage and current phase sequence correction. The signal output terminal of the current polarity determination unit is electrically connected to the parameter correction module, which can send the phase determination result of the current transformer polarity reversal and the correct polarity configuration parameters to the parameter correction module.

[0076] The current polarity determination unit has the following rules: under the premise that the voltage and current phase sequence have been fully corrected, when the inverter outputs capacitive reactive current, the normal reactive power collected by the meter should be positive; if the reactive power of a certain phase is negative, it is determined that the polarity of the corresponding current transformer is reversed.

[0077] Preferably, the core function of the parameter correction module is to write the corresponding configuration parameters to the reverse current detection meter according to the judgment result of the error judgment module, thereby completing the automatic correction of phase sequence and polarity. The instruction output terminal of the parameter correction module is electrically connected to the RS485 bus transmitter of the energy storage inverter, and the correction parameters can be written into the corresponding configuration register of the reverse current detection meter through the RS485 bidirectional communication bus.

[0078] The parameter correction module has a built-in register mapping subunit with a preset configuration register address mapping relationship for the reverse current detection meter. Based on the correction parameters sent by the error judgment module, it can generate a corresponding Modbus write instruction frame and send it to the reverse current detection meter via the bus to complete the parameter configuration.

[0079] In an optional embodiment of this example, the RS485 bidirectional communication bus can be replaced with a power line carrier communication bus, an Ethernet communication bus, or a wireless LoRa communication bus, as long as stable bidirectional data interaction can be achieved between the energy storage inverter and the reverse current detection meter.

[0080] In another optional embodiment of this example, the two output levels of the reactive power output control module can be adapted and adjusted according to the rated capacity of the system. The three-phase current amplitude of the first output level can be set to an arithmetic sequence distribution, as long as the three-phase amplitudes are different from each other; the three-phase current amplitude of the second output level can be adjusted according to the reactive power carrying capacity of the power grid, as long as the three-phase amplitudes are completely consistent.

[0081] In another optional embodiment of this example, the first preset value range in the error judgment module can be adapted and adjusted according to the accuracy level of the meter and the transformer. The range can be flexibly set between -0.6 times and -0.4 times the rated reactive power to ensure the accuracy of the judgment result and the adaptability to the on-site working conditions.

[0082] Those skilled in the art should understand that the above embodiments are merely exemplary implementations and not limitations on the scope of protection of the present invention. Equivalent substitutions and detailed adjustments to the hardware topology, module integration methods, communication protocols, and preset parameters of the device without departing from the core principles of the present invention are all within the scope of protection of the present invention.

Claims

1. A method for adjusting the phase sequence of an instrument for backflow prevention, comprising an energy storage inverter and a backflow detection meter, characterized in that, Includes the following steps: S1. The energy storage inverter outputs three-phase pure reactive currents with different amplitudes to the three-phase power grid, reads the three-phase current amplitude data collected by the reverse current detection meter, determines the phase with current phase sequence misalignment by amplitude comparison, and writes the correct current phase sequence parameters into the reverse current detection meter to complete the correction. S2. After the current phase sequence correction is completed, the energy storage inverter outputs three-phase pure reactive current with the same amplitude to the three-phase power grid, reads the three-phase reactive power data of the reverse current detection meter, determines the type and phase of the voltage phase sequence error based on the phase characteristics of the reactive power, and writes the correct voltage phase sequence parameters into the reverse current detection meter to complete the correction. S3. After the voltage phase sequence correction is completed, the energy storage inverter reads the three-phase reactive power data of the reverse current detection meter, determines the phase with reversed current polarity based on the positive and negative attributes of the reactive power, and writes the correct current polarity parameters into the reverse current detection meter to complete the correction.

2. The instrument phase sequence adjustment method according to claim 1, characterized in that, The energy storage inverter is bidirectionally connected to the reverse current detection meter via an RS485 bus. The energy storage inverter reads the real-time electrical acquisition data of the reverse current detection meter via the RS485 bus and writes the phase sequence configuration parameters and polarity configuration parameters to the reverse current detection meter.

3. The instrument phase sequence adjustment method according to claim 1, characterized in that, In step S1, the energy storage inverter sorts and marks its own output three-phase reactive current according to its amplitude, and matches the sorting marks with the sorting results of the three-phase current amplitude collected by the reverse current detection meter to determine the phase with misaligned current phase sequence.

4. The instrument phase sequence adjustment method according to claim 1, characterized in that, In step S2, the phase characteristic of the reactive power is determined based on the three-phase AC reactive power calculation formula Q=U×I×sinφ; where Q is the single-phase reactive power, U is the effective value of the phase voltage, I is the effective value of the phase current, and φ is the power factor angle of the phase voltage and phase current in the same sampling channel of the meter.

5. The instrument phase sequence adjustment method according to claim 4, characterized in that, In step S2, the types of voltage phase sequence errors include two-phase phase sequence reversal and all three-phase phase sequence misalignment; If the reactive power values ​​of any two phases collected by the reverse current detection meter are both within the first preset value range, then it is determined that the phase sequence of the two phase voltages is reversed. If the three-phase reactive power values ​​collected by the reverse current detection meter are all within the first preset value range, then it is determined that the three-phase voltage phase sequence is completely misaligned. The first preset value range is -0.4 times to -0.6 times the rated reactive power of a single phase output by the energy storage inverter.

6. The instrument phase sequence adjustment method according to claim 1, characterized in that, In step S3, if the reactive power of any phase collected by the reverse current detection meter is negative, it is determined that the polarity of the corresponding current transformer is reversed.

7. An instrument phase sequence adjustment device for preventing backflow, used to execute the instrument phase sequence adjustment method according to claims 1 to 6, characterized in that, It includes an energy storage inverter and a reverse current detection meter, wherein the energy storage inverter and the reverse current detection meter are connected via an RS485 bidirectional communication bus; The energy storage inverter has a built-in reactive power output control module, data reading module, error judgment module and parameter correction module; The control output terminal of the reactive power output control module is electrically connected to the three-phase inverter main circuit of the energy storage inverter, the AC output terminal of the three-phase inverter main circuit is electrically connected to the three-phase power grid, and the status feedback terminal of the reactive power output control module is electrically connected to the first input terminal of the error judgment module. The signal input terminal of the data reading module is electrically connected to the RS485 bus receiving terminal of the energy storage inverter, and the signal output terminal is electrically connected to the second input terminal of the error judgment module. The signal output terminal of the error determination module is electrically connected to the signal input terminal of the parameter correction module; the command output terminal of the parameter correction module is electrically connected to the RS485 bus transmitter of the energy storage inverter.

8. The instrument phase sequence adjustment device according to claim 7, characterized in that, The reactive power output control module has at least two fixed reactive current output levels: the first output level is used to output three-phase pure reactive current with different amplitudes to the three-phase power grid, and the second output level is used to output three-phase pure reactive current with the same amplitude to the three-phase power grid.

9. The instrument phase sequence adjustment device according to claim 7, characterized in that, The error determination module includes a current phase sequence determination unit and a voltage phase sequence determination unit; The signal input terminal of the current phase sequence determination unit is electrically connected to the reactive power output control module and the data reading module, respectively, and the signal output terminal is electrically connected to the parameter correction module. The signal input terminal of the voltage phase sequence determination unit is electrically connected to the reactive power output control module and the data reading module, respectively, and the signal output terminal is electrically connected to the parameter correction module.

10. The instrument phase sequence adjustment device according to claim 7, characterized in that, The error determination module further includes a current polarity determination unit, the signal input terminal of which is electrically connected to the data reading module, and the signal output terminal of which is electrically connected to the parameter correction module.

Images