CN113890382A - Adjustable CT transformation ratio digital controller based on secondary current sampling - Google Patents
Adjustable CT transformation ratio digital controller based on secondary current sampling Download PDFInfo
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- H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
- H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
- H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
- H02M5/12—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers for conversion of voltage or current amplitude only
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- G05F—SYSTEMS FOR REGULATING ELECTRIC OR MAGNETIC VARIABLES
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Abstract
The application discloses adjustable CT transformation ratio digital controller based on secondary current sampling, including three phase current transformer, three group CT secondary current sampling units, three group second grade operational amplifier and output unit, two groups current sampling reference power supply unit, algorithm DSP digital control and communication unit, smart machine terminal. This application combines three-phase current transformer's secondary actual current sampling, current sampling reference power supply unit, obtain secondary current sampling instantaneous value, effective value and peak value etc. through algorithm DSP digital control and communication unit filtration, and through the mathematical model of protection calculation and protection recheck calculation, automated inspection transformation ratio adjustment link etc. obtain automatic/manual regulation's CT transformation ratio parameter, and then obtain the secondary current value after adjusting the CT transformation ratio, and finally with data transmission and the communication through the smart machine terminal, realize each item protection control function, this application CT transformation ratio parameter sets up conveniently, communication control is nimble simple, dynamic response is fast.
Description
Technical Field
The application relates to the technical field of power electronic equipment, in particular to an adjustable CT (computed tomography) transformation ratio digital controller based on secondary current sampling.
Background
A current transformer (CT for short) is a current sensing and transmitting device widely used in an electric power system, which converts a large current on a primary side in the electric power system into a small current on a standard side, and transmits the small current to a secondary device for measurement, control and protection. The precision and reliability of the method are directly closely related to the safety, reliability and the like of the power system. The current in the power generation, transformation, transmission, distribution and utilization lines is very different, even if the current of the main line is in the normal working current range, the main transformer or the current transformer of the main equipment can also cause serious out-of-tolerance or saturation, and various problems of refusal or misoperation of comprehensive protection, large measurement and metering error, inaccurate instrument display and the like are caused.
In addition, as the short-circuit capacity of the power system increases, it often happens that the capacity of the main device is much smaller than the short-circuit capacity of the system, for example: the current transformer parameter selection of the hydraulic generator set becomes a prominent problem which troubles relay protection workers due to seasonal load, high-voltage starting, standby transformers, high-voltage station transformer and the like. If the maximum short-circuit current of the current transformer is selected according to the fact that the maximum short-circuit current of the current transformer does not exceed the accurate limit current of the current transformer during fault, not only is the equipment investment cost too high, but also more importantly, the problems that relay protection setting is difficult, the sensitivity of internal fault protection of main equipment is insufficient, the input threshold of a comprehensive protection device is limited and the like are caused, if the maximum short-circuit current is selected according to the rated capacity of the main equipment, the current transformer is seriously saturated during internal outlet fault, and the protection performance at the moment needs to be analyzed in detail.
In the actual work, in order to prevent the 220kV bus differential protection from causing misoperation caused by errors when a ride-through fault occurs in the case of a certain hydropower project, the 220kV bus differential protection needs to be changed from original 600/5 to 1200/5, and at the moment, a current transformer needs to be replaced to solve the problem of misoperation caused by the fact that the errors exceed the allowable value when the 220kV bus differential protection is in the ride-through fault.
In another case of meeting a certain avionics project in actual work, due to the fact that the short-circuit protection current transformation ratio of the 220kV main transformer is 1700/1, in order to enable the differential protection of the 220kV main transformer to operate reliably, the current transformation ratio needs to be changed from 1700/1 to 600/1, and otherwise, the problem of limitation of a starting constant value input threshold of the differential protection of a main differential protection device is solved.
In the cases, the high-voltage current is changed on site, the 220kVGIS assembly and disassembly are influenced by site environment conditions, the assembly and disassembly are troublesome, a plurality of high-voltage tests are required after the assembly and disassembly, the cost is high, the coordination work is more, the construction period is long, and the condition of struggling with the important progress node on the project site in minutes is violated.
As can be seen in the case, the current transformer is commonly used for both the secondary currents of 5A and 1A, and the primary current is often as small as a few amperes to several thousand amperes. Because different protection devices and measuring instruments have different requirements on the rheological transformation ratio, different transformation ratios can be obtained for different protection devices and measuring instruments, and therefore the performance of various protection devices and the precision of the measuring instruments are not affected.
Disclosure of Invention
The embodiment of the application provides an adjustable CT transformation ratio digital controller based on secondary current sampling, and aims to solve the technical problems that an existing current transformer is poor in applicability, troublesome in fixed disassembly and assembly due to transformation ratio and low in intelligent degree.
The technical scheme adopted by the application is as follows:
an adjustable CT transformation ratio digital controller based on secondary current sampling comprises:
the three-phase current transformer is used for converting large primary side currents of three phases in the power system into three sets of set secondary side rated currents as secondary current sampling signals;
the three groups of CT secondary current sampling units are respectively used for receiving three groups of secondary current sampling signals of the three-phase current transformer and conditioning the three groups of secondary current sampling signals to meet the set requirements;
the three groups of second-stage operational amplifiers and the output unit are respectively electrically connected with the current sampling reference power supply unit and the output ends of the three groups of CT secondary current sampling units, and are used for superposing and operational amplifying the three groups of secondary current sampling signals output by the three groups of CT secondary current sampling units and the power supply reference signals output by the current sampling reference power supply unit to conform to the amplitude processing range of the algorithm DSP digital control and communication unit;
two groups of current sampling reference power supply units are used for respectively providing corresponding power supply reference signals for the second-stage operational amplifier and output unit and the algorithm DSP digital control and communication unit;
the algorithm DSP digital control and communication unit is respectively electrically connected with the output ends of the three groups of second-stage operational amplifiers, the output unit and the current sampling reference power supply unit, is used for calculating a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word and giving an internal protection control word, then obtains a protection fixed value and a transformation ratio by combining a protection calculation and protection recheck calculation mathematical model with an intelligent equipment terminal, continuously and normally works and outputs secondary current data if the transformation ratio meets the requirement, otherwise, calls an automatic correction link to automatically match/manually set transformation ratio parameters to meet the requirement, and obtains a secondary current value after the transformation ratio is adjusted;
and the intelligent equipment terminal is in signal connection with the output end of the algorithm DSP digital control and communication unit and is used for performing communication transmission and data interaction with the algorithm DSP digital control and communication unit to realize a corresponding protection control function.
In a preferred embodiment of the present application, the CT secondary current sampling unit includes:
the input end of the current sampling input unit is electrically connected with the output end of the secondary side winding of the corresponding phase of the three-phase current transformer through a terminal and is used for inputting a secondary current sampling signal;
the sampling resistance unit is electrically connected with the output end of the current sampling input unit and is used for changing the resistance value through a jumper to realize the configuration of two specifications of 1A and 5A of secondary side rated current and converting a secondary current sampling signal into a voltage signal;
the input signal capacitor filtering unit is electrically connected with the output end of the sampling resistor unit and is used for removing the high-frequency pulse signal from the secondary current sampling signal converted into the voltage signal;
the current-limiting voltage-limiting and amplitude-limiting protection unit is electrically connected with the output end of the input signal capacitor filtering unit, is used for limiting the filtered secondary current sampling signal within an input signal range allowed by the operational amplifier, and plays a role in protecting the operational amplifier;
and the first-stage operational amplifier voltage boosting and filtering circuit is electrically connected with the output end of the current-limiting and voltage-limiting and amplitude-limiting protection unit and is used for carrying out operational amplifier, isolation and filtering processing on the secondary current sampling signal.
In a preferred embodiment of the present application, the current sampling reference power supply unit includes:
the algorithm DSP reference power supply unit is used for providing a +3.3V current sampling reference power supply signal and transmitting the signal to the algorithm DSP digital control and communication unit;
and the second-stage operational amplifier current sampling reference power supply unit is electrically connected with the output end of the algorithm DSP reference power supply unit and is used for converting the +3.3V current sampling reference power supply signal into-3.3V reference power supply circuit operational amplifier output voltage and transmitting the output voltage to the input ends of the second-stage operational amplifier and the output unit.
In the preferred embodiment of the present application, the algorithm DSP reference power supply unit includes:
a voltage source for providing a voltage source;
the shunt voltage-dividing resistor is electrically connected with the voltage source and is used for shunting and dividing the voltage of the voltage source;
the filtering, voltage stabilizing and current limiting circuit is connected with the output end circuit of the shunt divider resistor and is used for carrying out capacitance filtering and voltage stabilizing and resistance current limiting on a voltage source after shunt voltage division to obtain a current sampling reference power supply signal of +3.3V and transmitting the current sampling reference power supply signal to the algorithm DSP digital control and communication unit;
the high-low frequency two-stage capacitor filtering unit is used for carrying out high-low frequency two-stage filtering on a +3.3V current sampling reference power supply signal and transmitting the signal to the second-stage operational amplifier current sampling reference power supply unit;
and the 3.3V reference voltage terminal is used for transmitting the +3.3V current sampling reference power supply signal to the algorithm DSP digital control and communication unit.
In a preferred embodiment of the present application, the second-stage operational amplifier current sampling reference power supply unit includes:
one end of the resistor R32 is connected with the high-frequency and low-frequency two-stage capacitor filtering unit;
the operational amplifier U2A is characterized in that the non-inverting input end of the operational amplifier U2A is grounded through a resistor R33, the inverting input end is electrically connected with the other end of the resistor R32, and the output end is electrically connected with the inverting input end through a capacitor C23A;
one end of the resistor R35 is electrically connected with the output end of the operational amplifier U2A, the other end of the resistor R35 is electrically connected with the inverting input end of the operational amplifier U2A through the feedback resistor R34, and is electrically connected with one ends of capacitors C14, C15 and C16 which are arranged in parallel, and the other ends of the capacitors C14, C15 and C16 are grounded;
and a reference voltage terminal, which is led out from one end of a resistor R35 connected with capacitors C14, C15 and C16 which are arranged in parallel, and is used for transmitting the output voltage of the operational amplifier of the reference power supply circuit of-3.3V to the input end of the second-stage operational amplifier and the output unit.
In a preferred embodiment of the present application, the second stage operational amplifier and output unit includes:
the input end of the second-stage operational amplifier conditioning circuit is electrically connected with the output ends of the CT secondary current sampling unit and the current sampling reference power supply unit respectively, and the second-stage operational amplifier conditioning circuit is used for superposing and operational amplifying a secondary current sampling signal output by the CT secondary current sampling unit and a power supply reference signal output by the current sampling reference power supply unit so as to convert the amplitude range of the secondary current sampling signal converted into a voltage signal from-1.65V- +1.65V into 0-3.3V and conform to the amplitude processing range of the DSP digital control and communication unit of the algorithm;
and the voltage amplitude limiting protection and output circuit is electrically connected with the output end of the second-stage operational amplifier conditioning circuit and is used for limiting the signal input to the algorithm DSP digital control and communication unit not to exceed 3.3V.
In a preferred embodiment of the present application, the second stage operational amplifier conditioning circuit includes:
the operational amplifier U1A, the non-inverting input end of the operational amplifier U1A is grounded through a resistor R9, and a resistor R14 and a capacitor C4 are arranged between the inverting input end and the output end in parallel;
one end of the resistor R7 is electrically connected with the output end of the first-stage operational amplifier voltage boosting filter circuit, and the other end of the resistor R7 is electrically connected with the inverting input end of the operational amplifier U1A, and is used for converting the secondary current sampling signal into a current signal;
resistors R11A and R10 connected in series, one end of each resistor being electrically connected to the reference voltage terminal, and the other end of each resistor being electrically connected to the inverting input terminal of the operational amplifier U1A, for converting the output voltage of the operational amplifier of the reference power supply circuit outputted from the reference voltage terminal into a current signal;
one end of the resistor R12 is electrically connected with the output end of the operational amplifier U1A, and the other end of the resistor R12 is electrically connected with the input end of the voltage amplitude limiting protection and output circuit;
the voltage amplitude limiting protection and output circuit comprises:
the resistor R15, one end of the resistor R15 is electrically connected with the resistor R12, and the other end is electrically connected with the I _ R terminal;
the voltage amplitude limiting unit D2 is arranged on a circuit between the resistor R15 and the resistor R12 in parallel and comprises a first voltage stabilizing diode and a second voltage stabilizing diode which are arranged in parallel in a reverse direction, the anode of the first voltage stabilizing diode is connected with +3.3V voltage, the cathode of the first voltage stabilizing diode is connected on the circuit between the resistor R15 and the resistor R12 after being converged with the anode of the second voltage stabilizing diode, and the cathode of the second voltage stabilizing diode is grounded.
In the preferred embodiment of the present application, the algorithm DSP digital control and communication unit includes:
the ADC analog-to-digital conversion unit is respectively electrically connected with the output ends of the two sets of algorithm DSP reference power supply units and the output ends of the three sets of second-stage operational amplifiers and the output unit and is used for acquiring analog-to-digital conversion digital values of the two sets of current sampling reference power supply signals and analog-to-digital conversion digital values of the three sets of secondary current sampling signals;
the control algorithm unit is electrically connected with the output end of the ADC analog-to-digital conversion unit and used for calculating a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word and give an internal protection control word, then a protection constant value and a transformation ratio are obtained by combining a protection calculation and protection rechecking calculation mathematical model with an intelligent equipment terminal, if the transformation ratio meets the requirement, the control algorithm unit continuously and normally works and outputs secondary current data, otherwise, an automatic correction link is called to automatically match/manually set transformation ratio parameters to meet the requirement, and a secondary current value after the transformation ratio is adjusted is obtained;
and the data communication unit is electrically connected with the output end of the control algorithm unit and is used for selecting a communication protocol according to requirements to realize data communication with the intelligent equipment terminal.
Furthermore, the intelligent device terminal comprises a microcomputer protection device, a measuring instrument and a human-computer interface, and the data communication unit comprises: the system comprises an RS485 communication module for realizing communication with a human-computer interface, an RS232 communication module for realizing communication with the measuring instrument and a CAN communication module for realizing communication with the microcomputer protection device.
In a preferred embodiment of the present application, the control algorithm unit is specifically configured to perform the following steps:
s1, initializing an algorithm DSP digital controller;
s2, obtaining an analog-to-digital conversion digital value of the current sampling reference power supply signal, and obtaining a reference calibration value of the analog-to-digital conversion through software filtering and storing the reference calibration value in a register;
s3, acquiring an analog-to-digital conversion digital value of the secondary current sampling signal, filtering by software to obtain a secondary current sampling instantaneous value, and storing the secondary current sampling instantaneous value in a register;
s4, calculating to obtain the effective value and peak value of the secondary current sampling signal, and thus obtaining the data and fault alarm control word of the secondary current sampling signal;
s5, performing communication data interaction according to a communication protocol to obtain an input threshold value, a maximum limit value, a range, precision and a transformation ratio of the intelligent equipment terminal, and storing the input threshold value, the maximum limit value, the range, the precision and the transformation ratio in a register;
s6, according to the mathematical model of protection calculation and protection recheck calculation, obtaining the automatic/manual adjustment CT transformation ratio parameter through the control algorithm;
s7, judging whether the CT transformation ratio meets the requirement by detecting whether the parameters of the input current or the adjusted secondary current sampling signal meet the specified threshold value or the precision requirement;
s8, if the requirements are met, the normal work is continued, and then secondary current sampling signals after the CT transformation ratio is adjusted are obtained and output data are transmitted in a communication mode;
s9, if the requirement is not satisfied, calling an automatic checking and detecting link, and manually setting or automatically adjusting the CT transformation ratio to achieve the requirement, wherein the automatically adjusting the CT transformation ratio specifically comprises the following steps: the value detected by the measuring instrument is set through the HMI interface of the machine or is input into the automatic correction detection link of the control algorithm unit through background debugging software, and the CT transformation ratio parameter is automatically matched, so that the detection parameter or precision reaches the specification requirement; the manual setting is to manually set CT transformation ratio parameters through a human-computer interface, so that the detection parameters or the precision meet the specification requirements.
Compared with the prior art, the method has the following beneficial effects:
the application provides an adjustable CT transformation ratio digital controller based on secondary current sampling, which comprises a three-phase current transformer, three groups of CT secondary current sampling units, three groups of second-stage operational amplifiers and output units, two groups of current sampling reference power supply units, an algorithm DSP digital control and communication unit and an intelligent equipment terminal, wherein the current transformer is not required to be replaced, according to an intelligent digital sampling technology, a DSP microprocessor is taken as a core, an advanced digital signal processing method is adopted, different transformation ratios can be obtained for different protection devices and measuring instruments, so that replacement, disassembly and assembly work is reduced, multiple high-voltage tests after disassembly and assembly are avoided, the construction period is greatly shortened, and the cost is reduced; in addition, the CT transformation ratio can be automatically adjusted and manually set, the setting is convenient, the communication control is flexible and simple, the control precision is high, and the dynamic response is fast.
In addition to the objects, features and advantages described above, other objects, features and advantages will be apparent from the present application. The present application will now be described in further detail with reference to the accompanying drawings.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate embodiments of the application and, together with the description, serve to explain the application and are not intended to limit the application. In the drawings:
fig. 1 is a general block diagram of an adjustable CT ratio digital controller based on secondary current sampling according to a preferred embodiment of the present application.
Fig. 2 is a circuit diagram illustration (phase a) of the CT sub-current sampling unit of the preferred embodiment of the present application.
FIG. 3 is a circuit diagram of the second stage operational amplifier and the output unit according to the preferred embodiment of the present application.
Fig. 4 is a circuit schematic diagram of a current sampling reference power supply unit according to a preferred embodiment of the present application.
FIG. 5 is a schematic diagram of the interface circuit of the DSP digital control and communication unit of the algorithm of the preferred embodiment of the present application.
FIG. 6 is a software algorithm control flow diagram of the control algorithm unit of the preferred embodiment of the present application.
In the figure:
1. a three-phase current transformer; 2. a CT secondary current sampling unit; 3. a second stage operational amplifier and output unit; 4. a current sampling reference power supply unit; 5. an algorithm DSP digital control and communication unit; 6. a current sampling input unit; 7. a sampling resistance unit; 8. an input signal capacitance filtering unit; 9. a current-limiting voltage-limiting and amplitude-limiting protection unit; 10. a first-stage operational amplifier voltage boosting filter circuit; 11. a second stage operational amplifier conditioning circuit; 12. a voltage amplitude limiting protection and output circuit; 13. an ADC analog-to-digital conversion unit; 14. a control algorithm unit; 15. a data communication unit; 16. an RS485 communication module; 17. an RS232 communication module; 18. a CAN communication module; 19. an algorithm DSP reference power supply unit; 20. a second-stage operational amplifier current sampling reference power supply unit; 21. an intelligent device terminal; 210. a microcomputer protection device; 211. a measuring instrument; 212. a human-machine interface; 22. an I-A1 terminal; 23. an I _ R terminal; 24. a voltage source; 25. shunting divider resistance; 26. a 3.3V reference voltage terminal; 27. a filtering, voltage stabilizing and current limiting circuit; 28. a high-frequency and low-frequency two-stage capacitor filtering unit; 29. a reference voltage terminal.
Detailed Description
It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict. The present application will be described in detail below with reference to the embodiments with reference to the attached drawings.
Referring to fig. 1, a preferred embodiment of the present application provides an adjustable CT transformation ratio digital controller based on secondary current sampling, including:
the three-phase current transformer 1 is used for converting large primary side currents of three phases in a power system into three sets of set secondary side rated currents as secondary current sampling signals;
the three groups of CT secondary current sampling units 2 are respectively used for receiving three groups of secondary current sampling signals of the three-phase current transformer 1 and conditioning the three groups of secondary current sampling signals to meet the set requirements;
the three groups of second-stage operational amplifiers and the output unit 3 are respectively and electrically connected with the current sampling reference power supply unit 4 and the output ends of the three groups of CT secondary current sampling units 2, and are used for superposing and operational amplifying the three groups of secondary current sampling signals output by the three groups of CT secondary current sampling units 2 and the power supply reference signals output by the current sampling reference power supply unit 4 so as to conform to the amplitude processing range of the algorithm DSP digital control and communication unit 5;
two groups of current sampling reference power supply units 4 are used for respectively providing corresponding power supply reference signals for the second-stage operational amplifier and output unit 3 and the algorithm DSP digital control and communication unit 5;
an algorithm DSP digital control and communication unit 5 which is respectively electrically connected with the output ends of the three groups of second-stage operational amplifiers and the output unit 3 and the current sampling reference power supply unit 4, is used for calculating a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word and an internal protection control word, then obtains a protection fixed value and a transformation ratio by combining a protection calculation and protection recheck calculation mathematical model with the intelligent equipment terminal 21, if the transformation ratio meets the requirement, the secondary current data are continuously and normally worked and output, otherwise, an automatic correction link is called, the transformation ratio parameters are automatically matched/manually set to meet the requirement, and a secondary current value after the transformation ratio is adjusted is obtained;
and the intelligent equipment terminal 21 is in signal connection with the output end of the algorithm DSP digital control and communication unit 5 and is used for performing communication transmission and data interaction with the algorithm DSP digital control and communication unit 5 to realize a corresponding protection control function.
The embodiment provides an adjustable CT (computed tomography) transformation ratio digital controller based on secondary current sampling, which comprises a three-phase current transformer, three groups of CT secondary current sampling units, three groups of second-stage operational amplifiers and output units, two groups of current sampling reference power supply units, an algorithm DSP (digital signal processor) digital control and communication unit and an intelligent equipment terminal, wherein the current transformer is not required to be replaced, according to an intelligent digital sampling technology, a DSP (digital signal processor) is taken as a core, an advanced digital signal processing method is adopted, different transformation ratios can be obtained for different protection devices and measuring instruments, so that the replacement, disassembly and assembly work is reduced, multiple high-voltage tests after disassembly and assembly are avoided, the construction period is greatly shortened, and the cost is reduced; in addition, the embodiment can automatically adjust and manually set and adjust the transformation ratio of the CT, and has the advantages of convenient setting, flexible and simple communication control, high control precision and quick dynamic response.
As shown in fig. 2, in the preferred embodiment of the present application, the CT secondary current sampling unit 2 includes:
the input end of the current sampling input unit 6 is electrically connected with the output end of the secondary side winding of the corresponding phase of the three-phase current transformer 1 through a terminal and is used for inputting a secondary current sampling signal;
the sampling resistance unit 7 is electrically connected with the output end of the current sampling input unit 6 and is used for changing the resistance value through a jumper to realize the configuration of two specifications of 1A and 5A of secondary side rated current and converting a secondary current sampling signal into a voltage signal;
the input signal capacitor filtering unit 8 is electrically connected with the output end of the sampling resistor unit 7 and is used for removing the high-frequency pulse signal from the secondary current sampling signal converted into the voltage signal;
the current-limiting voltage-limiting and amplitude-limiting protection unit 9 is electrically connected with the output end of the input signal capacitor filtering unit 8, and is used for limiting the filtered secondary current sampling signal within an input signal range allowed by the operational amplifier and playing a role in protecting the operational amplifier;
and the first-stage operational amplifier voltage boosting and filtering circuit 10 is electrically connected with the output end of the current-limiting and voltage-limiting and amplitude-limiting protection unit 9 and is used for carrying out operational amplifier, isolation and filtering processing on the secondary current sampling signal.
In the embodiment, a phase a in a three-phase current transformer 1 is taken as an example, a CT secondary current sampling unit 2 is used for sampling a secondary side winding current of the phase a of the three-phase current transformer 1, that is, a secondary current sampling signal is input from a homonymous terminal S2, a common terminal M2 is in short circuit, the secondary current sampling signal of the phase a is connected to the CT secondary current sampling unit 2 through a current sampling input unit 6, and the three groups of CT secondary current sampling units 2 correspondingly comprise connecting terminals I-R1, I-S1 and I-T1. In fig. 2, the connection terminal I-R1 is a phase a current sampling input terminal, the terminals I-S1 and I-T1 are phase B and phase C input terminals, respectively, and the CT secondary current sampling unit 2 connected to the phase B and the phase C is the same as the CT secondary current sampling unit 2 connected to the phase a in this embodiment, and therefore, the description thereof is omitted.
In this embodiment, the sampling resistance unit 7 converts the secondary current sampling signal into a voltage signal; the secondary side of the three-phase current transformer 1 is rated as 1A and 5A, so the present embodiment sets the resistance value of the sampling resistance unit 7 by arranging a jumper, and the secondary side rated current of the CT is respectively corresponding to two specification current sampling circuits of 1A and 5A. The short circuit state of the default jumper S1 is 1A, and the short circuit state is 5A after the jumper is pulled out. The short-circuit state of the default jumper is set to be 1A, and the voltage magnitude calculation formula at two ends of the sampling resistance unit 7 is as follows:
VR1＝iI-R1×R1A
in the formula, VR1The voltage at two ends of the resistance unit 7 is sampled; i.e. iI-R1As secondary current instantaneous value, R1AThe resistance value of the resistance unit 7 is sampled.
In general, iI-R1Obtaining the current sampling actual voltage V when the secondary side current is rated at 1AR1Is 2V.
Furthermore, the secondary current sampling signal converted into the voltage signal is subjected to removal of a high-frequency pulse signal by the input signal capacitor filtering unit 8, and is limited within an input signal range allowed by the operational amplifier by the current-limiting and voltage-limiting and amplitude-limiting protection unit 9, and plays a role in protecting the operational amplifier, and then is transmitted to the first-stage operational amplifier voltage boosting filtering circuit 10.
In particular, the first-stage operational amplifier voltage boosting filter circuit 10 plays key roles of boosting voltage, isolating, filtering and the like for the secondary current sampling signal. The output voltage of the first stage operational amplifier is boosted by the voltage boost filter circuit 10 and then coupled to the inverting input terminal of the operational amplifier U1A of the second stage operational amplifier conditioning circuit 11 through the I-A1 terminal 22.
The current-limiting, voltage-limiting and amplitude-limiting protection unit 9 of the present embodiment includes a resistor R2 and a voltage amplitude-limiting unit D1, the first-stage operational amplifier voltage boosting filter circuit 10 includes an operational amplifier U1B, a resistor R3, a resistor R4A, a resistor R5A, a capacitor C3, a resistor R6, and a capacitor C2,
one end of the resistor R2 is electrically connected with the output end of the input signal capacitor filtering unit 8, the other end of the resistor R2 is electrically connected with the resistor R4A, the voltage amplitude limiting unit D1 is arranged on a circuit between the resistor R2 and the resistor R4A in parallel, the voltage amplitude limiting unit comprises a first voltage stabilizing diode and a second voltage stabilizing diode which are arranged in parallel in a reverse direction, the positive electrode of the first voltage stabilizing diode is connected with a positive voltage, the negative electrode of the first voltage stabilizing diode is connected with the circuit between the resistor R2 and the resistor R4A after being converged with the positive electrode of the second voltage stabilizing diode, and the negative electrode of the second voltage stabilizing diode is connected with a negative voltage.
The other end of the resistor R4A is electrically connected with the non-inverting input end of the operational amplifier U1B, the resistor R5A and the capacitor C2 are arranged in parallel, one end of the resistor R5 is electrically connected with the non-inverting input end of the operational amplifier U1B, and the other end of the resistor R5 is grounded; the capacitor C3 is arranged between the inverting input end and the output end of the operational amplifier U1B in parallel; one end of the resistor R6 is electrically connected to the output end of the operational amplifier U1B, and the other end of the resistor R6 is electrically connected to the resistor R3 and the inverting input end of the operational amplifier U1B in sequence, and to the I-a1 terminal 22.
Generally, the resistor R2 of this embodiment is in the hundred-ohm level, the resistor R4A is in the kilo-ohm level, the resistor R5A is in the mega-ohm level, the resistance of the R3 of the first stage operational amplifier boosting filter circuit 10 is selected to be in the kilo-ohm level with the resistance of the resistor R4A, and the output voltage of the operational amplifier U1B is:
in the formula, VI-A1The output voltage of the filter circuit 10 is boosted for the first-stage operational amplifier; vR1The voltage at two ends of the resistance unit 7 is sampled; after matching, the first stage operational amplifier boosts the output voltage V of the filter circuit 10I-A1The voltage of the output voltage is approximately equal to the voltage of the two ends of the sampling resistance unit 7, which is equivalent to that the output voltage is boosted and filtered by the first-stage operational amplifier boosting and filtering circuit 10 and then follows the input sampling voltage.
In this embodiment, the megohm-level resistor R5A is configured at the positive-phase input terminal of the operational amplifier U1B of the first-stage operational amplifier boosting filter circuit 10 to raise the voltage of the positive-phase input terminal of the operational amplifier U1B, so that the first-stage operational amplifier boosting filter circuit 10 plays key roles of boosting the voltage, filtering, improving the anti-interference capability, and the like.
When the secondary side rated current of the current is sampled, the output voltage signal of the operational amplifier U1B is about 2V.
As shown in fig. 3, in the preferred embodiment of the present application, the second stage operational amplifier and output unit 3 includes:
the input end of the second-stage operational amplifier conditioning circuit 11 is electrically connected with the output ends of the CT secondary current sampling unit 2 and the current sampling reference power supply unit 4 respectively, and is used for performing superposition and operational amplification on a secondary current sampling signal output by the CT secondary current sampling unit 2 and a power supply reference signal output by the current sampling reference power supply unit 4, so that the amplitude range of the secondary current sampling signal converted into a voltage signal is converted from-1.65V- +1.65V to 0-3.3V, and the amplitude processing range of the algorithm DSP digital control and communication unit 5 is met;
and the voltage amplitude limiting protection and output circuit 12 is electrically connected with the output end of the second-stage operational amplifier conditioning circuit 11 and is used for limiting the signal input to the algorithm DSP digital control and communication unit 5 not to exceed 3.3V.
Wherein, the second stage operational amplifier conditioning circuit 11 includes:
the operational amplifier U1A, the non-inverting input end of the operational amplifier U1A is grounded through a resistor R9, and a resistor R14 and a capacitor C4 are arranged between the inverting input end and the output end in parallel;
one end of the resistor R7 is electrically connected to the output end of the first-stage operational amplifier voltage boosting filter circuit 10, and the other end of the resistor R7 is electrically connected to the inverting input end of the operational amplifier U1A, so as to convert the secondary current sampling signal into a current signal;
resistors R11A and R10 connected in series, one end of each resistor being electrically connected to the reference voltage terminal 29, and the other end of each resistor being electrically connected to the inverting input terminal of the operational amplifier U1A, for converting the reference power supply circuit operational amplifier output voltage outputted from the reference voltage terminal 29 into a current signal;
one end of the resistor R12 is electrically connected with the output end of the operational amplifier U1A, and the other end is electrically connected with the input end of the voltage amplitude limiting protection and output circuit 12;
wherein, the voltage slice protection and output circuit 12 includes:
the resistor R15, one end of the resistor R15 is electrically connected with the resistor R12, and the other end is electrically connected with the I _ R terminal 23;
the voltage amplitude limiting unit D2 is arranged on a circuit between the resistor R15 and the resistor R12 in parallel and comprises a first voltage stabilizing diode and a second voltage stabilizing diode which are arranged in parallel in a reverse direction, the anode of the first voltage stabilizing diode is connected with +3.3V voltage, the cathode of the first voltage stabilizing diode is connected on the circuit between the resistor R15 and the resistor R12 after being converged with the anode of the second voltage stabilizing diode, and the cathode of the second voltage stabilizing diode is grounded.
In this embodiment, the second stage operational amplifier and output unit 3 mainly includes a second stage operational amplifier conditioning circuit 11 and a voltage amplitude limiting protection and output circuit 12.
The reference voltage of the second-stage operational amplifier conditioning circuit 11 is a 3.3V voltage outputted from a 3.3V reference voltage terminal, and is converted into a current signal by the input resistors R11A and R10 after being conditioned by the operational amplifier U2A of the second-stage operational amplifier current sampling reference power supply unit 20 of the current sampling reference power supply unit 4 through the high-low frequency two-stage capacitive filtering unit 28 and the three-stage capacitive filtering, and then inputted to the inverting input terminal of the operational amplifier U1A.
When the secondary current sampling signal is sent to the second stage operational amplifier conditioning circuit 11, the current signal is first converted into a current signal from the I-a1 terminal 22 of the first stage operational amplifier voltage boosting filter circuit 10 through the resistor R7, and then flows into the inverting input terminal of the operational amplifier U1A. After matching and testing, in this embodiment, the reference power supply circuit operational amplifier output voltage V input to the inverting input terminal of the operational amplifier U1AEF1The formula is as follows:
in the formula, VEF1Outputting voltage for the operational amplifier of the reference power supply circuit; v3.3VREF1Converting the reference voltage value for DSP analog-to-digital; - (R34/R32) is the amplification factor of the operational amplifier U2A, and generally, after matching, V is allowedEF1＝-3.3V。
In this embodiment, the sampling reference power supply of the second-stage operational amplifier conditioning circuit 11 has high precision. Wherein, the output voltage of the reference power supply circuit operational amplifier is converted into a current signal by resistors R11A and R10Then to the inverting input of operational amplifier U1A; the secondary current sampling signal is converted into a current signal through the resistor R7 and then transmitted to the inverting input terminal of the operational amplifier U1A, and the secondary current sampling signal is superposed with the output voltage of the operational amplifier of the reference power circuit, so that the output voltage V of the I _ R terminal 23I-RAs actual values of the secondary current sampling signal:
in the formula, VI-ROutputting voltage for the second-stage operational amplifier; vEF1The operational amplifier output voltage of the reference power supply circuit; vI-A1The output voltage of the first-stage operational amplifier is obtained, and the rest are the resistance values of the corresponding resistors.
Generally, after the secondary current sampling signal is processed by the second-stage operational amplifier conditioning circuit 11 and the voltage limiting protection and output circuit 12, when the secondary side current is rated as 1A, the I _ R terminal 23 outputs a voltage signal normally ranging from 2.2V to 2.4V.
In this embodiment, two paths of signals are superimposed on the second-stage operational amplifier conditioning circuit 11 for the purpose of increasing the output voltage, so that the amplitude range of the actual secondary current sine wave sampling signal is converted from-1.65V- +1.65V to 0-3.3V, otherwise, the arithmetic DSP digital control and communication unit 5 treats the-1.65 to 0 negative half-axis signal in the sine wave of the secondary current sampling signal as a zero voltage for processing, and after the superposition and operational amplification processing, the actual value of the secondary current sampling signal is in accordance with the processing range of the arithmetic DSP digital control and communication unit 5, thereby improving the reliability and stability of data sampling and processing.
Meanwhile, in the voltage amplitude limiting protection and output circuit 12 of the present embodiment, the second-stage operational amplifier and output unit 3 outputs the actual current sampling signal to the ADC analog-to-digital conversion unit 13 in the algorithm DSP digital control and communication unit 5 in a voltage signal manner; the voltage amplitude limiting protection is a special case, if the output signal of the second-stage operational amplifier conditioning circuit 11 is larger than the positive/negative 3.3V range of the signal that can be processed by the algorithm DSP digital control and communication unit 5, the amplitude limiting protection is performed, so that the signal input to the algorithm DSP digital control and communication unit 5 does not exceed 3.3V to protect the algorithm DSP digital control and communication unit 5.
As shown in fig. 4, in the preferred embodiment of the present application, the current sampling reference power supply unit 4 includes:
the algorithm DSP reference power supply unit 19 is used for providing a +3.3V current sampling reference power supply signal and transmitting the signal to the algorithm DSP digital control and communication unit 5;
and the second-stage operational amplifier current sampling reference power supply unit 20 is electrically connected with the output end of the algorithm DSP reference power supply unit 19 and is used for converting the +3.3V current sampling reference power supply signal into-3.3V reference power supply circuit operational amplifier output voltage and transmitting the output voltage to the input ends of the second-stage operational amplifier and the output unit 3.
Specifically, the algorithm DSP reference power supply unit 19 includes:
a voltage source 24 for providing a voltage source;
the shunt voltage-dividing resistor 25 is electrically connected with the voltage source 24 and is used for shunting and dividing the voltage of the voltage source;
the filtering, voltage stabilizing and current limiting circuit 27 is connected with the output end circuit of the shunt divider resistor 25 and is used for carrying out capacitance filtering and voltage stabilizing and resistance current limiting on a voltage source after shunt voltage division to obtain a current sampling reference power supply signal of +3.3V and transmitting the current sampling reference power supply signal to the algorithm DSP digital control and communication unit 5;
the high-low frequency two-stage capacitor filtering unit 28 is used for carrying out high-low frequency two-stage filtering on the +3.3V current sampling reference power supply signal and transmitting the signal to the second-stage operational amplifier current sampling reference power supply unit 20;
and the 3.3V reference voltage terminal 26 is used for transmitting a +3.3V current sampling reference power supply signal to the algorithm DSP digital control and communication unit 5.
Specifically, the second-stage operational amplifier current sampling reference power supply unit 20 includes:
one end of the resistor R32 is connected with the high-frequency and low-frequency two-stage capacitor filtering unit 28;
the operational amplifier U2A is characterized in that the non-inverting input end of the operational amplifier U2A is grounded through a resistor R33, the inverting input end is electrically connected with the other end of the resistor R32, and the output end is electrically connected with the inverting input end through a capacitor C23A;
one end of the resistor R35 is electrically connected with the output end of the operational amplifier U2A, the other end of the resistor R35 is electrically connected with the inverting input end of the operational amplifier U2A through the feedback resistor R34, and is electrically connected with one ends of capacitors C14, C15 and C16 which are arranged in parallel, and the other ends of the capacitors C14, C15 and C16 are grounded;
and a reference voltage terminal 29, which is led out from one end of a resistor R35 connected with capacitors C14, C15 and C16 arranged in parallel, and is used for transmitting the output voltage of the operational amplifier of the reference power supply circuit of-3.3V to the input end of the second-stage operational amplifier and output unit 3.
The current sampling reference power supply unit 4 in this embodiment is a two-way current sampling reference power supply, each way includes an algorithm DSP reference power supply unit 19 and a second-stage operational amplifier current sampling reference power supply unit 20, and fig. 4 shows a specific circuit diagram of one way, where a reference voltage output by a 3.3V reference voltage terminal 26 of the algorithm DSP reference power supply unit 19 is +3.3V _ REF1, and a reference voltage output by a reference voltage terminal 29 of the second-stage operational amplifier current sampling reference power supply unit 20 is-VEF 1.
Similarly, the reference voltages respectively output by the other current sampling reference power supply are +3.3V _ REF2 and-VEF 2, and are used as the reference signals of the second analog-to-digital conversion power supply of the algorithm DSP digital control and communication unit 5. The circuits of the two current sampling reference power supplies are the same, and therefore the description is omitted.
The reference voltage output by the 3.3V reference voltage terminal 26 is divided and divided by a voltage source 24 with a voltage of + V1 through a dividing and dividing resistor 25, and then is output with +3.3V after being subjected to the capacitor filtering of the filtering, voltage stabilizing and current limiting circuit 27 and the voltage stabilizing and current limiting of the voltage stabilizing tube, and then is directly input to the ADC analog-to-digital conversion unit 13 of the algorithm DSP digital control and communication unit 5 to be used as a first power reference signal for sampling a secondary current sampling signal for the algorithm DSP digital control and communication unit 5.
In addition, the reference voltage-VEF 1 supplied to the second-stage operational amplifier conditioning circuit 11 has high power supply accuracy. It is obtained by processing the reference voltage +3.3V _ REF1 output by the 3.3V reference voltage terminal 26 by the second stage operational amplifier current sampling reference power supply unit 20.
As shown in fig. 5, in the preferred embodiment of the present application, the algorithm DSP digital control and communication unit 5 includes:
the ADC analog-to-digital conversion unit 13 is electrically connected to the output ends of the two sets of algorithm DSP reference power supply units 19 and the output ends of the three sets of second-stage operational amplifiers and output unit 3, respectively, and is configured to obtain analog-to-digital conversion digital values of the two sets of current sampling reference power supply signals and analog-to-digital conversion digital values of the three sets of secondary current sampling signals;
a control algorithm unit 14, electrically connected to the output end of the ADC analog-to-digital conversion unit 13, configured to calculate a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word, and give an internal protection control word, and then obtain a protection fixed value and a transformation ratio by combining a protection calculation and protection rechecking calculation mathematical model with the intelligent device terminal 21, if the transformation ratio meets the requirement, continuously and normally work and output secondary current data, otherwise, invoke an automatic correction link, perform automatic matching/manually set transformation ratio parameters to meet the requirement, and obtain a secondary current value after the transformation ratio is adjusted;
and the data communication unit 15 is electrically connected with the output end of the control algorithm unit 14 and is used for selecting a communication protocol according to requirements to realize data communication with the intelligent device terminal 21.
Specifically, the intelligent device terminal 21 includes a microcomputer protection device 210, a measuring instrument 211, and a human-computer interface 212, and the data communication unit 15 includes: an RS485 communication module 16 which realizes communication with the human-computer interface 212, an RS232 communication module 17 which realizes communication with the measuring instrument 211, and a CAN communication module 18 which realizes communication with the microcomputer protection device 210.
The data communication unit 15 of this embodiment includes an RS485 communication module 16, an RS232 communication module 17, and a CAN communication module 18, and sets a communication protocol through software to complete a communication function, and CAN select the communication protocol according to external requirements, thereby realizing friendly and harmonious communication with the external microcomputer protection device 210, the measurement instrument 211, and the human-computer interface 212.
The algorithm DSP digital control and communication unit 5 of this embodiment includes an ADC analog-to-digital conversion unit 13, a control algorithm unit 14, and a data communication unit 15, wherein:
if the ADC unit 13 has a high precision requirement, a dedicated 16-bit ADC chip may be used, and in this embodiment, a 12-bit ADC unit provided in the 2812 chip of the DSP is used to perform the ADC conversion of the secondary current sampling signal with a precision of 1/4095.
In the present embodiment, five analog input signals are input to the ADC analog-to-digital conversion unit 13, wherein three analog input signals are three-phase analog input signals based on the secondary current of the three-phase current transformer 1, and two analog input signals are current sampling reference power signals.
The three-phase analog input signals based on the secondary current of the three-phase current transformer 1 are signals from the CT secondary current sampling unit 2 to the second-stage operational amplifier and output unit 3, and are actual secondary current sampling signals of the three-phase current transformer 1, the three-phase analog input signals based on the secondary current of the three-phase current transformer 1 are input to analog-to-digital conversion pins corresponding to the ADC analog-to-digital conversion unit 13 through the I _ R terminal 23 and the I _ S terminal, and the I _ T terminal.
Here, the terminal number of the secondary current sampling signal of the a phase input to the ADC analog-to-digital conversion unit 13 is I-R, and since the second stage operational amplifier of the B phase and the C phase is the same as the output unit 3 in the a phase, and the output terminals corresponding to B and C are I-S and I-T, the description of the present application is omitted.
The two paths of current sampling reference power signals are used as ADC sampling reference power calibration signals and comprise a first path of power reference signal +3.3V-REF1 and a second path of power reference signal +3.3V-REF2, and the two paths of current sampling reference power signals obtained by V1 through resistance conversion shunting, capacitance filtering and voltage stabilization of a voltage stabilizing tube are used as current sampling reference power analog input signals and are connected to analog-to-digital conversion pins corresponding to an ADC analog-to-digital conversion unit 13 of the algorithm DSP.
As shown in fig. 6, in the preferred embodiment of the present application, the control algorithm unit 14 is specifically configured to perform the following steps:
s1, initializing an algorithm DSP digital controller;
s2, obtaining an analog-to-digital conversion digital value of the current sampling reference power signal, and obtaining a reference calibration value of the analog-to-digital conversion by software filtering and storing the reference calibration value in a register, specifically, in this embodiment, obtaining an analog-to-digital conversion digital value of the current sampling reference power signal, and obtaining calibration value data of the analog-to-digital conversion of 3.3V by software filtering, and storing the calibration value data in the register;
s3, obtaining an analog-to-digital conversion digital value of the secondary current sampling signal, filtering the obtained secondary current sampling instantaneous value by software, and storing the obtained secondary current sampling instantaneous value in a register, specifically, in this embodiment, obtaining the analog-to-digital conversion digital value of the secondary current sampling signal by using a 12-bit analog-to-digital conversion unit provided in the 2812 chip, filtering the obtained secondary current sampling instantaneous value by software, and storing the obtained secondary current sampling instantaneous value in the register;
s4, calculating to obtain an effective value and a peak value of the secondary current sampling signal, and thereby obtain data of the secondary current sampling signal and a fault alarm control word, specifically, in this embodiment, by a calculation formula and a protection requirement of an internal controller, data such as the effective value and the peak value of the secondary current sampling signal and the internal fault alarm control word are obtained, so as to provide an internal protection function of the variable ratio digital controller, and the data such as the effective value and the peak value of the secondary current sampling signal and the internal fault alarm control word may be transmitted to the external smart device terminal 21 for use through the data communication unit 15;
s5, performing communication data interaction according to a communication protocol to obtain internal parameters such as an input threshold value, a maximum limit value, a measuring range and precision, a transformation ratio and the like of the intelligent equipment terminal 21 including the microcomputer protection device 210, the measuring instrument 211 and the human-computer interface 212, and storing the internal parameters into a register;
s6, according to the mathematical model of protection calculation and protection recheck calculation, obtaining the automatic/manual adjustment CT transformation ratio parameter through the control algorithm;
s7, judging whether the CT transformation ratio meets the requirement by detecting whether the parameters of the input current or the adjusted secondary current sampling signal meet the specified threshold value or the precision requirement;
s8, if the requirements are met, the normal work is continued, and then secondary current sampling signals after the CT transformation ratio is adjusted are obtained and output data are transmitted through communication;
s9, if the requirement is not satisfied, calling an automatic checking and detecting link, and manually setting or automatically adjusting the CT transformation ratio to achieve the requirement, wherein the automatically adjusting the CT transformation ratio specifically comprises the following steps: the value detected by the measuring instrument is input into an automatic correction detection link of the control algorithm unit 14 through the HMI interface of the machine or through background debugging software, and the CT transformation ratio parameter is automatically matched, so that the detection parameter or precision reaches the specification requirement; the manual setting is to manually set the CT transformation ratio parameter through the human-computer interface 212, so that the detection parameter or accuracy meets the specification requirement.
To sum up, the adjustable CT transformation ratio digital controller based on secondary current sampling comprises an external current transformer input, an internal hardware circuit, software control, intelligent equipment terminal communication and the like. The three-phase current transformer comprises a three-phase current transformer 1, three groups of CT secondary current sampling units 2, three groups of second-stage operational amplifiers and output units 3, two groups of current sampling reference power supply units 4, an algorithm DSP digital control and communication unit 5 and an intelligent device terminal 21.
The software control is based on the secondary current sampling signal of the three-phase current transformer 1 and the current sampling reference power supply unit 4 as input, the ADC analog-to-digital conversion unit 13, the control algorithm unit 14 and the data communication unit 15 in the algorithm DSP digital control and communication unit 5 are used for filtering the current acquisition value by the control algorithm software of the algorithm DSP digital control and communication unit 5 to obtain the secondary current sampling instantaneous value and calculate the secondary current parameters such as an effective value, a peak value and the like. Meanwhile, the algorithm DSP digital control and communication unit 5 can obtain parameters such as threshold value, upper and lower limit range parameters, precision control and the like from the intelligent device terminal 21, and also comprises a comprehensive protection device for obtaining current and voltage parameters and the like. The algorithm DSP digital control and communication unit 5 can calculate and obtain an adjustable CT transformation ratio according to the requirements of the intelligent device terminal 21 and current sampling parameters and the requirements of protection, measurement and display function parameters of the intelligent device terminal 21 and a mathematical model of protection calculation and protection recheck calculation, and set the required CT transformation ratio parameters through an automatic detection and adjustment link of the CT transformation ratio and a human-computer interface so as to obtain an adjusted secondary current value. The regulated secondary current is subjected to data transmission interaction with the intelligent equipment terminal 21 through a communication protocol, and then the microcomputer protection device 210 and the measuring instrument 211 are used for data acquisition, display on a human-computer interface 212 and the like to realize various protection control functions. Therefore, the replacement, disassembly and assembly work is reduced, the multiple high-voltage tests after disassembly and assembly are avoided, the construction period is shortened, and the cost is reduced. The CT transformation ratio can be adjusted through automatic adjustment and manual setting, the setting is convenient, the communication control is flexible and simple, the control precision is high, and the dynamic response is fast.
The above description is only for the purpose of illustrating the preferred embodiments of the present application and is not to be construed as limiting the present application, and any modifications, equivalents, improvements, etc. made within the spirit and principle of the present application should be included in the scope of the present application.
Claims (10)
1. An adjustable CT ratio-changing digital controller based on secondary current sampling is characterized by comprising:
the three-phase current transformer (1) is used for converting large primary side currents of three phases in a power system into three sets of set secondary side rated currents as secondary current sampling signals;
the three groups of CT secondary current sampling units (2) are respectively used for receiving three groups of secondary current sampling signals of the three-phase current transformer (1) and conditioning the three groups of secondary current sampling signals respectively to meet the set requirements;
the three groups of second-stage operational amplifiers and the output unit (3) are respectively and electrically connected with the current sampling reference power supply unit (4) and the output ends of the three groups of CT secondary current sampling units (2) and are used for superposing and operational amplifying the three groups of secondary current sampling signals output by the three groups of CT secondary current sampling units (2) and the power supply reference signals output by the current sampling reference power supply unit (4) and then conforming to the amplitude processing range of the algorithm DSP digital control and communication unit (5);
two groups of current sampling reference power supply units (4) are used for respectively providing corresponding power supply reference signals for the second-stage operational amplifier and output unit (3) and the algorithm DSP digital control and communication unit (5);
the algorithm DSP digital control and communication unit (5) is respectively electrically connected with the three groups of second-stage operational amplifiers and the output unit (3) and the output end of the current sampling reference power supply unit (4), is used for calculating a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word and an internal protection control word, then obtains a protection fixed value and a transformation ratio by combining a protection calculation and protection recheck calculation mathematical model with an intelligent equipment terminal (21), continuously and normally works and outputs secondary current data if the transformation ratio meets the requirement, otherwise, calls an automatic correction link to automatically match/manually set transformation ratio parameters to meet the requirement to obtain a secondary current value after the transformation ratio is adjusted;
and the intelligent equipment terminal (21) is in signal connection with the output end of the algorithm DSP digital control and communication unit (5) and is used for carrying out communication transmission and data interaction with the algorithm DSP digital control and communication unit (5) so as to realize a corresponding protection control function.
2. The adjustable CT scaling digital controller based on sub-current sampling according to claim 1, wherein the CT sub-current sampling unit (2) comprises:
the input end of the current sampling input unit (6) is electrically connected with the output end of the secondary side winding of the corresponding phase of the three-phase current transformer (1) through a terminal and is used for inputting a secondary current sampling signal;
the sampling resistance unit (7) is electrically connected with the output end of the current sampling input unit (6) and is used for changing the resistance value through a jumper to realize the configuration of two specifications of 1A and 5A of secondary side rated current and converting a secondary current sampling signal into a voltage signal;
the input signal capacitor filtering unit (8) is electrically connected with the output end of the sampling resistor unit (7) and is used for removing the high-frequency pulse signal from the secondary current sampling signal converted into the voltage signal;
the current-limiting voltage-limiting and amplitude-limiting protection unit (9) is electrically connected with the output end of the input signal capacitor filtering unit (8), is used for limiting the filtered secondary current sampling signal within an input signal range allowed by the operational amplifier, and plays a role in protecting the operational amplifier;
and the first-stage operational amplifier voltage boosting and filtering circuit (10) is electrically connected with the output end of the current-limiting and voltage-limiting and amplitude-limiting protection unit (9) and is used for carrying out operational amplifier, isolation and filtering processing on the secondary current sampling signal.
3. The adjustable CT ratio-change digital controller based on secondary current sampling according to claim 1, wherein the current sampling reference power supply unit (4) comprises:
the algorithm DSP reference power supply unit (19) is used for providing a +3.3V current sampling reference power supply signal and transmitting the signal to the algorithm DSP digital control and communication unit (5);
and the second-stage operational amplifier current sampling reference power supply unit (20) is electrically connected with the output end of the algorithm DSP reference power supply unit (19) and is used for transmitting the +3.3V current sampling reference power supply signal to the input end of the second-stage operational amplifier and the output unit (3) through the operational amplifier output voltage of the reference power supply circuit which is converted into-3.3V.
4. The adjustable CT scaling digital controller based on secondary current sampling according to claim 3, characterized in that the algorithm DSP reference power supply unit (19) comprises:
a voltage source (24) for providing a voltage source;
the shunt voltage division resistor (25) is electrically connected with the voltage source (24) and is used for shunting and dividing the voltage of the voltage source;
the filtering, voltage stabilizing and current limiting circuit (27) is connected with the output end circuit of the shunt divider resistor (25) and is used for carrying out capacitance filtering and voltage stabilizing and resistance current limiting on a voltage source after shunt division to obtain a current sampling reference power supply signal of +3.3V and transmitting the current sampling reference power supply signal to the algorithm DSP digital control and communication unit (5);
the high-low frequency two-stage capacitor filtering unit (28) is used for carrying out high-low frequency two-stage filtering on a +3.3V current sampling reference power supply signal and transmitting the signal to the second-stage operational amplifier current sampling reference power supply unit (20);
and the 3.3V reference voltage terminal (26) is used for transmitting a +3.3V current sampling reference power supply signal to the algorithm DSP digital control and communication unit (5).
5. The adjustable CT ratio digital controller based on sub-current sampling according to claim 3, wherein the second stage operational amplifier current sampling reference power supply unit (20) comprises:
one end of the resistor R32 is connected with a high-frequency and low-frequency two-stage capacitor filtering unit (28);
the operational amplifier U2A is characterized in that the non-inverting input end of the operational amplifier U2A is grounded through a resistor R33, the inverting input end is electrically connected with the other end of the resistor R32, and the output end is electrically connected with the inverting input end through a capacitor C23A;
one end of the resistor R35 is electrically connected with the output end of the operational amplifier U2A, the other end of the resistor R35 is electrically connected with the inverting input end of the operational amplifier U2A through the feedback resistor R34, and is electrically connected with one ends of capacitors C14, C15 and C16 which are arranged in parallel, and the other ends of the capacitors C14, C15 and C16 are grounded;
and a reference voltage terminal (29) which is led out from one end of a resistor R35 connected with capacitors C14, C15 and C16 which are arranged in parallel and is used for transmitting the output voltage of the operational amplifier of the reference power supply circuit of-3.3V to the input end of the operational amplifier and output unit (3) of the second stage.
6. The adjustable CT ratio-conversion digital controller based on secondary current sampling as claimed in claim 5, wherein the second-stage operational amplifier and output unit (3) comprises:
the input end of the second-stage operational amplifier conditioning circuit (11) is electrically connected with the output ends of the CT secondary current sampling unit (2) and the current sampling reference power supply unit (4) respectively, and is used for superposing and operational amplifying a secondary current sampling signal output by the CT secondary current sampling unit (2) and a power supply reference signal output by the current sampling reference power supply unit (4) so that the amplitude range of the secondary current sampling signal converted into a voltage signal is converted from-1.65V- +1.65V into 0-3.3V to accord with the amplitude processing range of the algorithm DSP digital control and communication unit (5);
and the voltage amplitude limiting protection and output circuit (12) is electrically connected with the output end of the second-stage operational amplifier conditioning circuit (11) and is used for limiting the signal input to the algorithm DSP digital control and communication unit (5) to be not more than 3.3V.
7. The adjustable CT scaling digital controller based on sub-current sampling according to claim 6, characterized in that the second stage operational amplifier conditioning circuit (11) comprises:
the operational amplifier U1A, the non-inverting input end of the operational amplifier U1A is grounded through a resistor R9, and a resistor R14 and a capacitor C4 are arranged between the inverting input end and the output end in parallel;
one end of the resistor R7 is electrically connected with the output end of the first-stage operational amplifier voltage boosting filter circuit (10), and the other end of the resistor R7 is electrically connected with the inverting input end of the operational amplifier U1A, and is used for converting the secondary current sampling signal into a current signal;
resistors R11A and R10 connected in series, one end of each resistor being electrically connected to the reference voltage terminal (29), and the other end of each resistor being electrically connected to the inverting input terminal of the operational amplifier U1A, for converting the reference power supply circuit operational amplifier output voltage outputted from the reference voltage terminal (29) into a current signal;
one end of the resistor R12 is electrically connected with the output end of the operational amplifier U1A, and the other end of the resistor R12 is electrically connected with the input end of the voltage amplitude limiting protection and output circuit (12);
the voltage slice protection and output circuit (12) comprises:
the resistor R15, one end of the resistor R15 is electrically connected with the resistor R12, and the other end is electrically connected with the I _ R terminal (23);
the voltage amplitude limiting unit D2 is arranged on a circuit between the resistor R15 and the resistor R12 in parallel and comprises a first voltage stabilizing diode and a second voltage stabilizing diode which are arranged in parallel in a reverse direction, the anode of the first voltage stabilizing diode is connected with +3.3V voltage, the cathode of the first voltage stabilizing diode is connected on the circuit between the resistor R15 and the resistor R12 after being converged with the anode of the second voltage stabilizing diode, and the cathode of the second voltage stabilizing diode is grounded.
8. The adjustable CT ratio-change digital controller based on secondary current sampling according to claim 1, wherein the algorithm DSP digital control and communication unit (5) comprises:
the ADC analog-to-digital conversion unit (13) is respectively and electrically connected with the output ends of the two sets of algorithm DSP reference power supply units (19) and the output ends of the three sets of second-stage operational amplifiers and the output unit (3) and is used for acquiring analog-to-digital conversion digital values of the two sets of current sampling reference power supply signals and analog-to-digital conversion digital values of the three sets of secondary current sampling signals;
the control algorithm unit (14) is electrically connected with the output end of the ADC analog-to-digital conversion unit (13) and is used for calculating a secondary current effective value and a peak value according to a reference calibration value of analog-to-digital conversion and a secondary current sampling signal instantaneous value to give a data control word and give an internal protection control word, then a protection calculation and protection recheck calculation mathematical model is combined with an intelligent equipment terminal (21) to obtain a protection fixed value and a transformation ratio, if the transformation ratio meets the requirement, the control algorithm unit continuously and normally works and outputs secondary current data, otherwise, an automatic correction link is called to automatically match/manually set transformation ratio parameters to meet the requirement, and a secondary current value after the transformation ratio is adjusted is obtained;
and the data communication unit (15) is electrically connected with the output end of the control algorithm unit (14) and is used for selecting a communication protocol according to requirements to realize data communication with the intelligent equipment terminal (21).
9. The adjustable CT (computed tomography) transformation ratio digital controller based on secondary current sampling as claimed in claim 8, wherein the intelligent device terminal (21) comprises a microcomputer protection device (210), a measuring instrument (211) and a human-computer interface (212), and the data communication unit (15) comprises: the system comprises an RS485 communication module (16) which is communicated with a human-computer interface (212), an RS232 communication module (17) which is communicated with the measuring instrument (211), and a CAN communication module (18) which is communicated with the microcomputer protection device (210).
10. The adjustable CT ratio digital controller based on secondary current sampling according to claim 8, wherein the control algorithm unit (14) is specifically configured to perform the following steps:
s1, initializing an algorithm DSP digital controller;
s2, obtaining an analog-to-digital conversion digital value of the current sampling reference power supply signal, and obtaining a reference calibration value of the analog-to-digital conversion through software filtering and storing the reference calibration value in a register;
s3, acquiring an analog-to-digital conversion digital value of the secondary current sampling signal, filtering by software to obtain a secondary current sampling instantaneous value, and storing the secondary current sampling instantaneous value in a register;
s4, calculating to obtain the effective value and peak value of the secondary current sampling signal, and thus obtaining the data and fault alarm control word of the secondary current sampling signal;
s5, performing communication data interaction according to a communication protocol to obtain an input threshold value, a maximum limit value, a range, precision and a transformation ratio of the intelligent equipment terminal (21) and storing the input threshold value, the maximum limit value, the range, the precision and the transformation ratio in a register;
s6, according to the mathematical model of protection calculation and protection recheck calculation, obtaining the automatic/manual adjustment CT transformation ratio parameter through the control algorithm;
s7, judging whether the CT transformation ratio meets the requirement by detecting whether the parameters of the input current or the adjusted secondary current sampling signal meet the specified threshold value or the precision requirement;
s8, if the requirements are met, the normal work is continued, and then secondary current sampling signals after the CT transformation ratio is adjusted are obtained and output data are transmitted in a communication mode;
s9, if the requirement is not met, calling an automatic checking and detecting link, and manually setting or automatically adjusting the CT transformation ratio to meet the requirement, wherein the automatically adjusting the CT transformation ratio specifically comprises the following steps: the value detected by the measuring instrument is set through a local HMI interface or is input into an automatic correction detection link of a control algorithm unit (14) through background debugging software, and CT transformation ratio parameters are automatically matched, so that the detection parameters or precision meet the specification requirement; the manual setting is to manually set CT transformation ratio parameters through a human-computer interface (212) so that the detection parameters or the precision can meet the specification requirements.
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