A positive and negative sequence current measuring device and method

Abstract

The application discloses a positive and negative sequence current measuring device and method, comprising a shell. The inside of the shell is fixedly installed with a signal acquisition unit, a signal filtering unit, a measuring unit, a main control unit, an RS485 communication unit and an OLED display unit. The main control unit is connected with the measuring unit, the RS485 communication unit and the OLED display unit respectively. The signal acquisition unit is connected with the signal filtering unit and the measuring unit. The phase current to be measured is connected with the device. The power measurement value formed by the voltage channel, the current channel and the multifunctional measuring channel of the single-phase measurement chip of the measuring unit is calculated to obtain the phase current angle, so that the positive and negative sequence current calculation is realized. The method avoids using the high-performance analog-to-digital converter, avoids the complex algorithm such as the effective value, the frequency tracking and the phase measurement, reduces the algorithm requirement of the MCU main control chip, and reduces the development difficulty and saves the cost.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of electric power measurement, and particularly relates to a positive and negative sequence current measuring device and method. BACKGROUND

[0002] Positive and negative sequence currents play an important role in power quality monitoring and control, and relay protection. The fault characteristics of equipment in a power system often have a certain corresponding relationship with the positive and negative sequence currents, so that the causes of system faults can be diagnosed. For example, the stator current of a generator is stable positive sequence current, i.e. three-phase symmetrical sinusoidal alternating current, in the normal operation mode. When the generator bears an asymmetric load, the armature current and the terminal voltage of the generator will appear asymmetric, and the stator current can be decomposed into a negative sequence component. Since the rotating magnetic field induced by the negative sequence current is opposite to the positive sequence component, it will cause the generator to heat up and have an adverse effect. Therefore, it is particularly important to accurately extract the positive and negative sequence currents for accurate analysis of the operating state of the generator.

[0003] In the above prior art, no matter which detection method is used, a high-performance analog-to-digital converter and a DSP processor are inevitably used, and even a complex phase-locked loop circuit and a frequency tracking circuit are used. The overall circuit is complex, and the hardware cost is high. The positive and negative sequence current extraction method based on a high-performance analog-to-digital converter must be used with a high-performance microprocessor, which also directly increases the hardware cost. Some designers use analog operational amplifiers to build a negative sequence current measurement circuit and use a phase-shifting method to achieve the measurement purpose. However, in actual operation, the anti-electromagnetic interference is poor, and the accuracy is easily affected by factors such as frequency change and temperature. When it is necessary to measure the positive sequence current, an additional positive sequence current measurement circuit needs to be built, which increases the complexity of the circuit and lacks economy. SUMMARY

[0004] The purpose of the present application is to provide a positive and negative sequence current measuring device and method to solve the problems of complex circuit, high hardware cost and difficult calculation in the background art.

[0005] To achieve the above purpose, the application adopts the following technical scheme: a positive and negative sequence current measuring device, comprising a shell. A signal acquisition unit, a signal filtering unit, a measuring unit, a main control unit, an RS485 communication unit and an OLED display unit are fixedly installed inside the shell. The main control unit is connected with the measuring unit, the RS485 communication unit and the OLED display unit respectively. The signal filtering unit is connected with the measuring unit. The signal acquisition unit is connected with the signal filtering unit.

[0006] Preferably, the master control unit comprises an MCU microcontroller, a ferroelectric memory and a decoupling capacitor, the ferroelectric memory and the MCU microcontroller are connected through an I2C bus, and the decoupling capacitor is connected between the power supply pin and the ground of the MCU microcontroller.

[0007] Preferably, the signal acquisition unit comprises A, B and C three-phase current transformers and sampling resistors, and the sampling resistors are connected in parallel with the output terminals of the current transformers.

[0008] Preferably, the signal filtering unit comprises resistors and capacitors.

[0009] Preferably, the measurement unit comprises a single-phase metering chip (model: V9261F, manufacturer: Hangzhou Wanguo Science and Technology Co., Ltd.) and a crystal oscillator, the single-phase metering chip and the crystal oscillator are connected in parallel, the output terminal of the A-phase current transformer is connected with the voltage channel of the single-phase metering chip through the signal filtering unit, the output terminal of the B-phase current transformer is connected with the current channel of the single-phase metering chip through the signal filtering unit, and the output terminal of the C-phase current transformer is connected with the multifunctional measurement channel of the single-phase metering chip through the signal filtering unit.

[0010] Preferably, the RS485 communication unit comprises an RS485 chip and a TVS diode, the input pin of the RS485 chip is connected with the master control unit through an USART bus, and the output pin of the RS485 chip is connected in parallel with the TVS diode.

[0011] Preferably, the OLED display unit comprises an OLED display screen, and the OLED display screen is connected with the master control unit through an SPI bus.

[0012] The application further provides a positive and negative sequence current measurement method, comprising the following steps:

[0013] S1, if it is a large current grounding system, reading the effective value register value of the single-phase metering chip, converting the register value into actual effective values of three-phase currents, calculating the included angle between the three-phase currents, and calculating the positive and negative sequence currents according to the phasor values composed of the effective values and phase values of the A, B and C three-phase currents.

[0014] S2, if it is a small current grounding system, reading the effective value register value of the single-phase metering chip, converting the register value into actual effective values of two-phase currents, calculating the included angle between the two-phase currents, and calculating the positive and negative sequence currents according to the phasor values composed of the effective values and phase values of the A and C two-phase currents.

[0015] Preferably, the method of S1 is further refined as:

[0016] Sa, the calculation formula of the included angle between the current A phase and the B phase is:

[0017]

[0018] wherein, is the A-phase and B-phase current angle value, R P is the metering chip active power register value, R U is the metering chip voltage channel effective value register value, R I1 is the metering chip current channel effective value register value,

[0019] The calculation formula of the current A-phase and C-phase angle is:

[0020]

[0021] wherein, is the A-phase and C-phase current angle value, R PM is the metering chip multifunctional active power register value, R U is the metering chip voltage channel effective value register value, R I2 is the metering chip multifunctional current channel effective value register value.

[0022] Preferably, the method of S1 is further refined as:

[0023] Sa, the forced A-phase current phase is wherein is the A-phase current phase value;

[0024] Sb, the B-phase current phase is calculated by the angle of the A-phase and B-phase currents, and the calculation formula is as follows:

[0025]

[0026] wherein, is the B-phase current phase value, is the A-phase and B-phase current angle value;

[0027] Sc, the C-phase current phase is calculated by the angle of the A-phase and C-phase currents, and the calculation formula is as follows:

[0028]

[0029] wherein, is the C-phase current phase value, is the A-phase and C-phase current angle value;

[0030] Sd, it is judged and whether they are less than 0°, if so, add 360°, judge and If greater than 360°, subtract 360°.

[0031] Preferably, the method of S1 is further refined as:

[0032] Sa, convert the obtained effective value and phase value into the algebraic value form of complex number, the calculation formula is as follows:

[0033]

[0034] In the formula, i=0, 1, 2 represents A, B, C three-phase, I i is the effective value of each phase current, φ i is the phase value of each phase current, R k is the real part of each phase current phasor complex number, M k is the imaginary part of each phase current phasor complex number, where K is directly taken as meaningful A1, B1 and other symbols to clearly express the meaning.

[0035] Sb, rotate the B-phase and C-phase phasors by 120° and 240° respectively, and the calculation formula is:

[0036]

[0037]

[0038] Sc, according to the obtained complex phasor value calculate the negative sequence current phasor, and the calculation formula is as follows:

[0039]

[0040] Sd, according to the negative sequence current phasor obtained by Sc, calculate the effective value of the negative sequence current, and the calculation formula is as follows:

[0041]

[0042] Se, rotate the B-phase and C-phase phasors by 240° and 120° respectively, and the calculation formula is:

[0043]

[0044]

[0045] Sf, again calculate the positive sequence current phasor according to the obtained complex phasor value , and the calculation formula is as follows:

[0046]

[0047] Sg, finally, according to the positive sequence current phasor obtained by Sf, calculate the effective value of the positive sequence current, and the calculation formula is as follows:

[0048]

[0049] Preferably, the method of S2 is further refined as:

[0050] Sa, rotating the A-phase and C-phase phasors by 30° and 90° respectively, and the calculation formula is:

[0051]

[0052]

[0053] Sb, according to the obtained complex phasor value Calculate the negative sequence current phasor, and the calculation formula is as follows:

[0054]

[0055] Sc, according to the negative sequence current phasor obtained by Sb, the effective value of the negative sequence current is calculated, and the calculation formula is as follows:

[0056]

[0057] Sd, rotating the A-phase and C-phase phasors by 330° and 90° respectively, and the calculation formula is:

[0058]

[0059]

[0060] Se, according to the obtained complex phasor value Calculate the positive sequence current phasor, and the calculation formula is as follows:

[0061]

[0062] Sf, according to the positive sequence current phasor obtained by Se, the effective value of the positive sequence current is calculated, and the calculation formula is as follows:

[0063]

[0064] The technical effects and advantages of the present application are as follows:

[0065] 1. The present application is based on single-phase metering chip, compared with analog integrated operational amplifier, the circuit complexity is reduced, since the integrated single-chip scheme is adopted, the anti-interference degree, accuracy and reliability are higher than those of traditional scheme;

[0066] 2、The application calculates the input current angle, indirectly measures the current phase value, avoids using high-performance analog-to-digital converters, saves equipment costs, avoids complex algorithms such as effective value, frequency tracking, phase measurement, reduces the algorithm requirement of the MCU master control chip, and reduces the technical development difficulty and saves the cost of the master control chip according to the characteristics of the single-phase metering chip, the power measurement value formed by the voltage channel, the current channel and the multifunctional measurement channel;

[0067] 3、According to the amplitude and phase results, the symmetrical phasor method is used, and the positive and negative sequence currents can be calculated only by rotating the phase by a certain angle, thereby reducing the calculation difficulty;

[0068] 4、The application utilizes the characteristic that the sum of three-phase current vectors of a small current grounding system is 0, solves the B-phase current according to the A-phase and C-phase currents, and then applies the positive and negative sequence measurement algorithm of a large current grounding system to the small current grounding system to obtain the positive and negative sequence current calculation formula of the small current grounding system, so that the calculation method is simple, the calculation mode can be switched through menu setting, and the problem of device incompatibility caused by inconsistent grounding modes is effectively avoided. BRIEF DESCRIPTION OF DRAWINGS

[0069] Fig. 1 It is an internal structure schematic diagram of the shell of the application;

[0070] Fig. 2 It is a system block diagram of the application;

[0071] Fig. 3 It is a method flowchart of the application.

[0072] In the figure, 1 is a shell, 2 is a master control unit, 3 is a signal acquisition unit, 4 is a signal filtering unit, 5 is a measurement unit, 6 is an RS485 communication unit, and 7 is an OLED display unit. DETAILED DESCRIPTION

[0073] The technical solutions in the embodiments of the application will be clearly and completely described below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments. The specific embodiments described herein are only used to explain the application, and are not used to limit the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor are within the scope of protection of the application.

[0074] The application provides a method for calculating positive and negative sequence currents, comprising the following steps: Figs. 1-3The positive and negative sequence current measuring device shown comprises a shell 1, a signal acquisition unit 3, a signal filtering unit 4, a measuring unit 5, a main control unit 2, an RS485 communication unit 6 and an OLED display unit 7 are fixedly installed in the shell 1, the main control unit 2 is connected with the measuring unit 5, the RS485 communication unit 6 and the OLED display unit 7 respectively, the signal filtering unit 4 is connected with the measuring unit 5, and the signal acquisition unit 3 is connected with the signal filtering unit 4.

[0075] The main control unit 2 comprises an MCU microcontroller, a ferroelectric memory and a decoupling capacitor, the ferroelectric memory and the MCU microcontroller are connected through an I2C bus, and the decoupling capacitor is connected between the power supply pin and the ground of the MCU microcontroller.

[0076] The signal acquisition unit 3 comprises A, B and C three-phase current transformers and a sampling resistor, and the sampling resistor is connected in parallel with the output end of the current transformer.

[0077] The signal filtering unit 4 comprises a resistor and a capacitor, the input end is connected with the aforementioned signal acquisition unit 3, and the output end is connected with the measuring unit 5.

[0078] The measuring unit 5 comprises a single-phase metering chip (model: V9261F) and a crystal oscillator, the single-phase metering chip and the crystal oscillator are connected in parallel, the output end of the A-phase current transformer is connected with the voltage channel of the single-phase metering chip through the signal filtering unit 4, the output end of the B-phase current transformer is connected with the current channel of the single-phase metering chip through the signal filtering unit 4, and the output end of the C-phase current transformer is connected with the multifunctional measurement channel of the single-phase metering chip through the signal filtering unit 4.

[0079] The RS485 communication unit 6 comprises an RS485 chip and a TVS diode, the input pin of the RS485 chip is connected with the main control unit 2 through a USART bus, and the output pin of the RS485 chip is connected with the TVS diode in parallel.

[0080] The OLED display unit 7 comprises an OLED display screen, and the OLED display screen is connected with the main control unit 2 through an SPI bus.

[0081] The application further provides a positive and negative sequence current measuring method, comprising the following steps:

[0082] S1, if it is a large current grounding system, the effective value register value of the single-phase metering chip is read, the register value is converted into the actual effective value of three-phase current, the included angle between the three-phase current is calculated, and the positive and negative sequence current is calculated according to the phase value composed of the effective value and the phase value of A, B and C three-phase current;

[0083] S2, if it is a small current grounding system, read the single-phase metering chip effective value register value, convert the register value to two-phase current actual effective value, calculate the included angle between two-phase current, according to the phase value composed of A, C two-phase current effective value and phase value, calculate positive and negative sequence current.

[0084] The method of S1 is further refined as:

[0085] Sa, the calculation formula of the included angle between current A phase and B phase is:

[0086]

[0087] In the formula, A and B phase current included angle value, R P Active power register value of metering chip, R U Voltage channel effective value register value of metering chip, R I1 Current channel effective value register value of metering chip,

[0088] Sb, the calculation formula of the included angle between current A phase and C phase is:

[0089]

[0090] In the formula, A and C phase current included angle value, R PM Multifunctional active power register value of metering chip, R U Voltage channel effective value register value of metering chip, R I2 Multifunctional current channel effective value register value of metering chip.

[0091] The method of S1 is further refined as:

[0092] Sa, the forced A phase current phase is Among them A phase current phase value;

[0093] Sb, calculate the B phase current phase through the included angle of A and B phase current, the calculation formula is as follows:

[0094]

[0095] In the formula, B phase current phase value, A and B phase current included angle value;

[0096] Sc, calculate the C phase current phase through the included angle of A and C phase current, the calculation formula is as follows:

[0097]

[0098] wherein, is the C-phase current phase value, is the A-phase and C-phase current included angle value;

[0099] Sd, judging and whether it is less than 0°, if less, add 360°, judging and whether it is greater than 360°, if greater, subtract 360°.

[0100] The method of S1 is further refined as:

[0101] Sa, converting the obtained effective value and phase value into the algebraic value form of complex number, the calculation formula is as follows:

[0102]

[0103] wherein, i=0, 1, 2 represents A, B, C three phases, I i is the effective value of each phase current, φ i is the phase value of each phase current, R k is the real part of each phase current phasor complex number, M k is the imaginary part of each phase current phasor complex number, wherein K is directly taken as meaningful A1, B1 and the like symbols to clearly express the meaning.

[0104] Sb, rotating the B-phase and C-phase phasors by 120° and 240° respectively, the calculation formula is:

[0105]

[0106]

[0107] Sc, calculating the negative sequence current phasor according to the obtained complex phasor value , the calculation formula is as follows:

[0108]

[0109] Sd, calculating the effective value of the negative sequence current according to the negative sequence current phasor obtained by Sc, the calculation formula is as follows:

[0110]

[0111] Se, rotating the B-phase and C-phase phasors by 240° and 120° respectively, the calculation formula is:

[0112]

[0113]

[0114] Sf, then based on the obtained complex phasor values The formula for calculating the positive sequence current phasor is as follows:

[0115]

[0116] Finally, based on the positive sequence current phasor obtained from Sf, the effective value of the positive sequence current is calculated using the following formula:

[0117]

[0118] The method in S2 can be further refined as follows:

[0119] Sa, rotate the phasors of phase A and phase C by 30° and 90° respectively, and the calculation formula is:

[0120]

[0121]

[0122] Sb, based on the obtained complex phasor values The formula for calculating the negative sequence current phasor is as follows:

[0123]

[0124] Sc. Calculate the effective value of the negative sequence current based on the negative sequence current phasor obtained from Sb. The calculation formula is as follows:

[0125]

[0126] Sd, rotating the A-phase and C-phase phasors by 330° and 90° respectively, the calculation formula is:

[0127]

[0128]

[0129] Se, based on the obtained complex phasor values The formula for calculating the positive sequence current phasor is as follows:

[0130]

[0131] Sf: Calculate the effective value of the positive sequence current based on the positive sequence current phasor obtained from Se. The calculation formula is as follows:

[0132]

[0133] The application introduces a single-phase metering chip to calculate relevant electrical parameters in a power system in real time, effectively avoids additional frequency tracking circuits such as phase-locked loops, and reduces hardware cost and circuit design complexity. Based on three-channel measurement of the single-phase metering chip, the current phase is indirectly calculated using the power measurement values generated thereby. According to the current effective value and phase value, positive and negative sequence current components are decomposed by a method based on a space vector rotating coordinate system, effectively reducing the complexity of the measurement algorithm. In view of the characteristics of a small current grounding system, the principle that the sum of current vectors in a power system is zero is used to improve the calculation method for extracting positive and negative sequence components based on the space vector rotating coordinate system, ensuring the accuracy of the extraction result.

[0134] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for the purpose of limiting the present application, although the foregoing detailed description of the application is made with reference to the foregoing embodiments, for those skilled in the art, it still can be modified to the technical solutions recorded in the foregoing embodiments, or equivalent replacement of some of the technical features, any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included within the scope of the present application.

Claims

1. A method for measuring positive and negative sequence current, characterized in that: Based on positive and negative sequence current measurement device The positive and negative sequence current measurement method includes the following steps: S1. If it is a high-current grounding system, read the effective value register value of the single-phase metering chip, convert the register value into the actual effective value of the three-phase current, calculate the angle between the three-phase currents, and calculate the positive and negative sequence currents based on the phasor value composed of the effective value and phase value of the three-phase currents A, B, and C. S2. If it is a low-current grounding system, read the effective value register value of the single-phase metering chip, convert the register value into the actual effective value of the two-phase current, calculate the angle between the two-phase current, and calculate the positive and negative sequence currents based on the phasor value composed of the effective value and phase value of the two-phase currents A and C. The method described in S1 is further refined as follows: The formulas for calculating Sa, the angle between current phase A and phase B are: ； In the formula, This represents the angle between the currents in phases A and B. The value is the active power register value of the metering chip. This is the effective value register value of the voltage channel of the metering chip. This is the effective value register value of the current channel of the metering chip. The formulas for calculating Sb, the angle between current phase A and phase C are: ； In the formula, This represents the angle between the currents in phases A and C. The value is for the multi-functional active power register of the metering chip. This is the effective value register value of the voltage channel of the metering chip. This refers to the effective value register value of the multi-functional measurement channel of the metering chip; The method described in S1 is further refined as follows: Sa, convert the obtained effective value and phase value into algebraic form of complex numbers. The calculation formula is as follows: ； In the formula, i = 0, 1, 2 represents the three phases A, B, and C. These are the effective values ​​of the current in each phase. These represent the phase values ​​of the currents in each phase. Let be the real part of the complex phasor of the current in each phase. Let K be the imaginary part of the complex phasor of the current in each phase, where K is directly taken as a meaningful value. A1 , B1 Symbols are used to clearly express meaning; Sb, rotating the B-phase and C-phase phasors by 120° and 240° respectively, the calculation formula is: ； ； Sc, based on the obtained complex phasor values , , The formula for calculating the negative sequence current phasor is as follows: ； Sd, and then the effective value of the negative sequence current is calculated based on the negative sequence current phasor obtained from Sc. The calculation formula is as follows: ； Se, rotate the B-phase and C-phase phasors by 240° and 120° respectively, and the calculation formula is: ； ； Sf, based on the obtained complex phasor value , , The formula for calculating the positive sequence current phasor is as follows: ； Finally, based on the positive sequence current phasor obtained from Sf, the effective value of the positive sequence current is calculated using the following formula: 。 2. The method for measuring positive and negative sequence current according to claim 1, characterized in that: The positive and negative sequence current measuring device includes a housing (1). Inside the housing (1) are fixedly installed a signal acquisition unit (3), a signal filtering unit (4), a measurement unit (5), a main control unit (2), an RS485 communication unit (6), and an OLED display unit (7). The main control unit (2) is connected to the measurement unit (5), the RS485 communication unit (6), and the OLED display unit (7). The signal filtering unit (4) is connected to the measurement unit (5), and the signal acquisition unit (3) is connected to the signal filtering unit (4). The main control unit (2) includes an MCU microcontroller, a ferroelectric memory, and a decoupling capacitor. The ferroelectric memory and the MCU microcontroller are connected via an I2C bus. The power supply pins of the device are connected to the ground via decoupling capacitors. The signal acquisition unit (3) includes three-phase current transformers (A, B, and C) and sampling resistors. The sampling resistors are connected in parallel with the output terminals of the current transformers. The signal filtering unit (4) includes resistors and capacitors. The measurement unit (5) includes a single-phase metering chip and a crystal oscillator. The single-phase metering chip and the crystal oscillator are connected in parallel. The output terminal of the A-phase current transformer is connected to the voltage channel of the single-phase metering chip via the signal filtering unit (4). The output terminal of the B-phase current transformer is connected to the current channel of the single-phase metering chip via the signal filtering unit (4). The output terminal of the C-phase current transformer is connected to the multi-functional measurement channel of the single-phase metering chip via the signal filtering unit (4).

3. The method for measuring positive and negative sequence current according to claim 2, characterized in that: The RS485 communication unit (6) includes an RS485 chip and a TVS diode. The input pin of the RS485 chip is connected to the main control unit (2) via a USART bus, and the output pin of the RS485 chip is connected in parallel with a TVS diode.

4. The method for measuring positive and negative sequence current according to claim 3, characterized in that: The OLED display unit (7) includes an OLED display screen, and the OLED display screen is connected to the main control unit (2) via an SPI bus.

5. The method for measuring positive and negative sequence current according to claim 1, characterized in that: The method described in S1 is further refined as follows: Sa, the phase of the forced A-phase current is =0°, where This represents the phase value of the A-phase current. Sb, calculate the phase of the B-phase current using the angle between the A-phase and B-phase currents. The calculation formula is as follows: ； In the formula, This represents the phase value of the B-phase current. This represents the angle between the currents in phases A and B. Sc. Calculate the phase of the C-phase current using the angle between the A-phase and C-phase currents. The calculation formula is as follows: ； In the formula, This represents the phase value of the C-phase current. This represents the angle between the currents in phases A and C. Sd, Judgment and Check if it's less than 0°. If it is, add 360° to determine the result. and If the angle is greater than 360°, then subtract 360°.

6. The method for measuring positive and negative sequence current according to claim 1, characterized in that: The method in S2 is further refined as follows: Sa, rotate the phasors of phase A and phase C by 30° and 90° respectively, and the calculation formula is: ； ； Sb, based on the obtained complex phasor values , The formula for calculating the negative sequence current phasor is as follows: ； Sc. Calculate the effective value of the negative sequence current based on the negative sequence current phasor obtained from Sb. The calculation formula is as follows: ； Sd, rotating the A-phase and C-phase phasors by 330° and 90° respectively, the calculation formula is: ； ； Se, based on the obtained complex phasor values , The formula for calculating the positive sequence current phasor is as follows: ； Sf: Calculate the effective value of the positive sequence current based on the positive sequence current phasor obtained from Se. The calculation formula is as follows: 。

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