CN114113781A - Frequency measuring circuit of power system - Google Patents
Frequency measuring circuit of power system Download PDFInfo
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- CN114113781A CN114113781A CN202111482390.7A CN202111482390A CN114113781A CN 114113781 A CN114113781 A CN 114113781A CN 202111482390 A CN202111482390 A CN 202111482390A CN 114113781 A CN114113781 A CN 114113781A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
- G01R23/00—Arrangements for measuring frequencies; Arrangements for analysing frequency spectra
- G01R23/02—Arrangements for measuring frequency, e.g. pulse repetition rate; Arrangements for measuring period of current or voltage
Abstract
The invention discloses a power system frequency measuring circuit, which comprises a mutual inductor circuit, a signal conditioning and filtering circuit, a two-stage clamping circuit, a two-stage gain circuit, a hysteresis comparison circuit and a biasing circuit which are connected in sequence; the transformer circuit converts a high-voltage signal on the primary side into a low-voltage signal on the secondary side and electrically isolates the signals; the signal conditioning and filtering circuit conditions the output signal of the mutual inductor to a proper amplitude value and performs low-pass filtering on the output signal of the mutual inductor to filter high-frequency interference; the two-stage clamping circuit clamps the preceding-stage large-amplitude signal to a small amplitude; the two-stage gain circuit amplifies the preceding-stage signal; the hysteresis comparison circuit compares the input signal which is finally amplified by the two stages with a reference signal, and outputs a stable square wave signal which has the same frequency as the input signal and is used for the rear-stage CPU to measure the frequency. The invention can ensure high signal frequency measurement resolution, wide dynamic range, high frequency measurement precision and can measure various harmonics and inter-harmonics.
Description
Technical Field
The invention relates to the field of power systems, in particular to a power system frequency measuring circuit.
Background
The frequency measurement of the power system is an indispensable index, is related to the calculation of indexes such as various harmonics, power factors and the like in the power field, and is widely applied in the fields of fault recording, power quality monitoring, distribution network intelligent terminals, relay protection and the like.
At present, frequency measurement methods are numerous, designed frequency measurement circuits are different, and the measurement indexes which can be achieved are different, so that the following problems mainly exist: frequency measurement is unstable under a rated value; the dynamic range of the amplitude of the frequency measurement signal is small, and the frequency measurement precision of the large and small amplitude signals is not high; the frequency measurement accuracy is greatly affected by each harmonic superposed on the measured signal.
Disclosure of Invention
In order to solve the problems of unstable frequency measurement result under a rated value, small dynamic range of amplitude of a frequency measurement signal, influence of each subharmonic and interharmonic on frequency measurement precision and the like of a frequency measurement circuit of an electric power system, the invention provides the frequency measurement circuit, which can accurately measure the rated value, large amplitude, small amplitude and signal frequency superposed with each subharmonic and interharmonic, and has wide dynamic range of frequency measurement and high precision.
The technical scheme adopted by the invention is as follows:
the power system frequency measuring circuit comprises a mutual inductor circuit, a signal conditioning and filtering circuit, a first-stage clamping circuit, a first-stage gain circuit, a second-stage clamping circuit, a second-stage gain circuit and a hysteresis comparison circuit which are connected in sequence, and further comprises a biasing circuit for providing direct-current bias voltage;
the transformer circuit converts a high-voltage signal on the primary side into a low-voltage signal on the secondary side and electrically isolates the signals;
the signal conditioning and filtering circuit is used for conditioning the output signal of the mutual inductor to a proper amplitude value and carrying out low-pass filtering on the output signal of the mutual inductor so as to filter high-frequency interference;
the two-stage clamping circuit is used for clamping the preceding-stage large amplitude signal to a small amplitude;
the two-stage gain circuit amplifies the preceding-stage signal;
the hysteresis comparison circuit compares the input signal which is finally amplified by the two stages with a reference signal, and outputs a stable square wave signal which has the same frequency as the input signal and is used for the rear-stage CPU to measure the frequency.
In the technical scheme, the bias circuit is connected with the signal conditioning and filtering circuit, the first clamping circuit, the first gain circuit, the second clamping circuit, the second gain circuit and the hysteresis comparison circuit, and provides direct current bias for the circuits.
According to the technical scheme, the transformer circuit adopts a voltage transformer to convert a primary side large-amplitude alternating voltage signal into a secondary side small-amplitude alternating voltage signal, and ensures that the primary side and the secondary side are electrically isolated.
According to the technical scheme, the signal conditioning and filtering circuit adopts a differential proportion amplifying circuit, the differential proportion amplifying circuit comprises an operational amplifier, a balance resistor, feedback electronics and a compensation resistor, the balance resistor is connected between the differential output end of the mutual inductor and the input end of the operational amplifier, and nF-level small capacitors are connected in parallel to the feedback resistor and the compensation resistor to form a low-pass filtering circuit and filter external high-frequency interference.
According to the technical scheme, the first-stage gain circuit and the second-stage gain circuit both adopt reverse amplification circuits, and the amplification factor of each stage is ten times.
According to the technical scheme, the first-stage clamping circuit and the second-stage clamping circuit are both clamped to 2.5 +/-0.3V by adopting resistance current limiting and a bidirectional Schottky diode.
According to the technical scheme, the voltage bias circuit divides the voltage of a power supply resistor, generates a reference voltage with low output impedance through the voltage follower circuit, applies the reference voltage to the in-phase end of a single power supply operational amplifier of the signal conditioning and filtering circuit, the first-stage gain circuit and the second-stage gain circuit, and raises the measured alternating current signal to a positive voltage or above;
according to the technical scheme, the voltage bias circuit is applied to the first-stage clamping circuit and the second-stage clamping circuit, and clamps signals to small signals with bias voltage as the center and +/-0.3V as the swing amplitude value.
In connection with the above technical scheme, the hysteresis comparison circuit adopts a high-speed differential comparator, the input end of the hysteresis comparison circuit is connected with a voltage division circuit, a reference voltage is provided through the voltage division circuit, a negative feedback resistor is connected between the reverse input end and the reverse output end of the hysteresis comparison circuit, and a positive feedback resistor is connected between the in-phase input end and the in-phase output end.
According to the technical scheme, a voltage transformer is adopted as a transformer circuit, the primary input side of the voltage transformer is of a lead type, and is connected with an external measured high-voltage signal; the secondary side output is connected to the signal conditioning and filtering circuit of the later stage in a differential mode.
The invention has the following beneficial effects: the invention adopts a mutual inductor circuit and a signal conditioning and filtering circuit to condition and filter a primary side high-voltage signal and then convert the primary side high-voltage signal into a secondary side low-voltage signal. The two-stage clamping and gain circuit is adopted to change the conditioned sinusoidal signal into a square wave signal with steep edge, and the comparator is ensured to output a stable square wave signal with the same frequency as the measured signal through the hysteresis comparison circuit. In addition, the bias circuit provides direct-current voltage bias for the operational amplifier powered by the single power supply, so that the measured alternating-current signal can be amplified without distortion, the dual-power supply is not needed, and the circuit can be simplified. The invention can ensure high signal frequency measurement resolution, wide dynamic range, high frequency measurement precision and simple and flexible circuit structure, can measure various harmonics and inter-harmonics, and is suitable for various frequency measurement application occasions of an electric power system.
Drawings
The invention will be further described with reference to the accompanying drawings and examples, in which:
FIG. 1 is a schematic diagram of a circuit structure for measuring a frequency of a power system according to an embodiment of the present invention;
FIG. 2 is a circuit diagram of a transformer, signal conditioning and filtering circuit in an embodiment of the present invention;
FIG. 3 is a circuit diagram of a first stage clamping, first stage gain circuit in an embodiment of the present invention;
FIG. 4 is a circuit diagram of a second stage clamping, second stage gain circuit in an embodiment of the present invention;
FIG. 5 is a circuit diagram of a hysteresis comparator circuit in an embodiment of the present invention;
fig. 6 is a circuit diagram of a voltage bias circuit in an embodiment of the present invention.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
As shown in fig. 1, the circuit for measuring the frequency of the power system according to the embodiment of the present invention mainly includes a transformer circuit, a signal conditioning and filtering circuit, a first clamping circuit, a first gain circuit, a second clamping circuit, a second gain circuit, a hysteresis comparison circuit, and a voltage bias circuit. The frequency measurement circuit can ensure high frequency measurement resolution, wide signal amplitude dynamic range, high frequency measurement precision and simple and flexible circuit structure, can measure various harmonics and inter-harmonics, and is suitable for application occasions of various frequency measurements of an electric power system.
The transformer circuit converts a primary side signal (high voltage signal) into a secondary side signal (low voltage signal) and electrically isolates the signals; the signal conditioning and filtering circuit is used for conditioning the output signal of the mutual inductor to a proper amplitude value and carrying out low-pass filtering on the output signal of the mutual inductor so as to filter high-frequency interference; and the two-stage clamping circuit is used for clamping the preceding-stage large amplitude signal to a small amplitude. The two-stage gain circuit amplifies the preceding stage signal to be close to the power supply rail of the operational amplifier, ensures that the operational amplifier is not saturated, and steepens the rising and falling edges of the waveform. The hysteresis comparison circuit compares the finally amplified signal with a reference signal, and outputs a stable square wave signal with the same frequency as the input signal, which is used for the subsequent CPU to measure the frequency. The bias circuit supplies direct current bias for the operational amplifier which is powered by a single power supply in the signal conditioning and filtering circuit and the two-stage gain circuit, and ensures that the tested alternating current signal is amplified without distortion.
Fig. 2 shows a transformer circuit and a signal conditioning and filtering circuit, in which the transformer circuit uses a voltage transformer to convert a large-amplitude ac voltage signal measured on the primary side into a small-amplitude ac voltage signal on the secondary side, and ensures electrical isolation between the primary and secondary sides, and the transformer output is connected to the signal conditioning and filtering circuit. In this embodiment, the primary input side is of a pin type and is connected to an external high voltage signal to be measured. If the shielding layer is arranged in the mutual inductor, the 3 pins need to be grounded to shield external electromagnetic interference, and if the shielding layer is not arranged, the 3 pins can be suspended. The secondary side output of the mutual inductor is connected to a post-stage conditioning and filtering circuit in a differential mode.
The signal conditioning circuit in fig. 2 is a differential proportional inverting amplifier circuit, and parameters ensure that R1/R2 is equal to R4/R3, and the amplification factor is the ratio of R1 to R2. R2 and R3 are balance resistors, one end of each balance resistor is connected to a differential output end of the transformer, the other end of each balance resistor is connected with an input end of the operational amplifier, one end of R4 is connected with a non-inverting end (pin 3 of U1A) of the operational amplifier, the other end of each balance resistor is connected with a bias voltage (REF _2V5) generated by the bias circuit in the figure 6, one end of R1 is connected with an inverting end (pin 2 of U1A) of the operational amplifier, and the other end of the R1 is connected with an output (pin 1 of U1A) of the operational amplifier, so that the operational amplifier U1A can amplify signals without distortion under the condition of single power supply.
In the filter circuit shown in fig. 2, a capacitor C1 is connected in parallel with two ends of a feedback resistor R1, and a capacitor C2 is connected in parallel with two ends of a compensation resistor R4, so as to form a low-pass filter for filtering high-frequency interference in the external environment. Wherein, the C1 and the C2 both adopt nF-level small capacitors.
Fig. 3 shows a first stage clamp circuit and a first stage gain circuit. The first stage clamp consists of a resistor R6 and Schottky diodes D1, D2. R6 has current limiting function, one end is connected to the output of the operational amplifier (pin 1 of U1A) of the conditioning and filtering circuit of figure 2, after the diodes D1 and D2 are connected in parallel in reverse, one end is connected to the bias voltage (REF _2V5) generated by the bias circuit of figure 6, and the other end is connected to the resistor R6, the large amplitude signal to be detected is clamped to 2.5V +/-0.3V, and if the small amplitude signal to be detected is lower than the clamping voltage of the diode, the clamping is not carried out.
The first stage of the gain circuit of fig. 3 is a reverse amplifier circuit, R5 is a feedback resistor, the amplification factor is-R5/R7, and R8 is a balance resistor. One end of R7 is connected with the output of the first stage clamp circuit (right end of R6), the other end is connected with the inverting end of the operational amplifier (6 feet of U1B), one end of R8 is connected with the inverting end of the operational amplifier (5 feet of U1B), the other end is connected with the bias voltage (REF _2V5) generated by the bias circuit in figure 6, and the operational amplifier U1B is ensured to amplify the detected signal output after the first stage clamp to be close to the power supply rail without distortion under the condition of single power supply, and the operational amplifier is ensured to be unsaturated, and the rising edge and the falling edge of the amplified waveform are all steep.
Fig. 4 shows a second stage clamp circuit and a second stage gain circuit. The second stage clamp is composed of a resistor R10 and Schottky diodes D3 and D4. R10 has current limiting effect, one end of which is connected to the output of the first-stage gain circuit operational amplifier (pin 7 of U1B) in FIG. 3, and after the diodes D3 and D4 are connected in parallel in the reverse direction, one end is connected to the bias voltage (REF _2V5) generated by the bias circuit in FIG. 6, and the other end is connected to the resistor R10, so that the detected signal close to the power supply rail of the operational amplifier is clamped to 2.5V +/-0.3V.
The second stage of the gain circuit of fig. 4 is a reverse amplifier circuit, R9 is a feedback resistor, the amplification factor is-R9/R11, and R12 is a balance resistor. One end of R11 is connected with the output of the second stage clamp circuit (right end of R10), the other end is connected with the inverting end of the operational amplifier (2 pin of U2A), one end of R12 is connected with the inverting end of the operational amplifier (3 pin of U2A), the other end is connected with the bias voltage (REF _2V5) generated by the bias circuit in figure 6, the operational amplifier U2A is ensured to continue amplifying the detected signal after the second stage clamp to be close to the power rail of the operational amplifier without distortion under the condition of single power supply, the operational amplifier is ensured to be unsaturated, and the rising edge and the falling edge of the amplified waveform are further steeper.
Further, the clamp circuit is designed before the gain circuit in order to prevent the operational amplifier from saturating due to direct high-power amplification. The signal is clamped and amplified, so that the rising edge and the falling edge of the signal can be ensured to be steeper simultaneously under the condition of enough amplification factor, and the improvement of the sensitivity and the precision of frequency measurement is facilitated.
Furthermore, a two-stage clamping circuit and a two-stage gain circuit are designed, so that the circuit still has enough gain on the premise of reducing the performance requirement of the operational amplifier, the design is simplified, and the dynamic range of frequency measurement is improved.
Fig. 5 shows a hysteresis comparator circuit. The comparator U3A is a differential output type high speed comparator, and is very responsive. R13 is a positive feedback resistor of the comparator, one end of the positive feedback resistor is connected with the non-inverting input end (pin 2 of U3A) of the comparator, and the other end of the positive feedback resistor is connected with the non-inverting output end (pin 7 of U3A) of the comparator; and the R16 negative feedback resistor has one end connected to the inverting input end of the comparator (pin 3 of U3A) and the other end connected to the inverting output end of the comparator (pin 8 of U3A). One end of the resistor R14 is connected with a power supply VCC _5V, the other end is connected with the resistor R15, and the other end is connected with the non-inverting input end (pin 2 of U3A) of the comparator. The other end of the resistor R15 is connected with the system ground, and R14 and R15 form a voltage division circuit which provides a reference voltage for the comparator after voltage division. Circuit operational amplifier output (U1B pin 7)
As shown in fig. 4, the output (pin 1 of U2A) of the second stage gain circuit operational amplifier is connected to the inverting input terminal (pin 3 of U3A) of the comparator, and performs hysteresis comparison with the reference voltage divided by R14 and R15, and the inverting output terminal (pin 8 of U3A) of the comparator outputs a square wave signal having the same frequency as the signal to be measured, and is connected to the CPU circuit of the subsequent stage for acquisition and frequency operation.
Furthermore, a high-speed comparator is adopted to quickly respond to a detected signal with steep rising and falling edges output after passing through a two-stage clamping and gain circuit, and meanwhile, R13, R16, R15 and the comparator U3A form a hysteresis comparator, so that the output of the comparator is prevented from being turned over by mistake when an input signal changes near the threshold value of the comparator, and the frequency measurement accuracy is improved.
Fig. 6 shows a voltage bias circuit, which is mainly implemented by a voltage follower circuit. The resistor R17 has one end connected to the power supply VCC _5V and the other end connected to the resistor R18, and is also connected to the non-inverting input terminal (pin 5 of U2B) of the operational amplifier. The other end of the resistor R18 is connected to system ground, R17 and R18 form a voltage division circuit, the voltage division circuit provides a non-inverting input (pin 5 of U2B) for the operational amplifier U2B, and the output end (pin 7 of U2B) of the operational amplifier outputs a 2.5V reference voltage (REF _2V 5).
Further, the voltage (REF _2V5) output by the voltage bias circuit provides a dc voltage bias for the signal conditioning and filtering circuit of fig. 2, the first stage clamping and gain circuit of fig. 3, and the second stage clamping and gain circuit of fig. 4, so as to ensure that the measured signal is amplified without distortion under the condition that the operational amplifier is powered by the single power supply VCC _ 5V.
In conclusion, the invention overcomes the problems that the frequency measurement signal amplitude dynamic range of the existing power system frequency measurement circuit is small, the frequency measurement precision is not high, the frequency measurement precision of the measured signal after superposition of each subharmonic becomes poor and the like, and provides the frequency measurement circuit which can accurately measure the signal frequency of a rated value, a large amplitude, a small amplitude, superposition of each subharmonic and a interharmonic, and has the advantages of wide frequency measurement dynamic range, high precision, simple and flexible circuit.
It will be understood that modifications and variations can be made by persons skilled in the art in light of the above teachings and all such modifications and variations are intended to be included within the scope of the invention as defined in the appended claims.
Claims (10)
1. A power system frequency measuring circuit is characterized by comprising a mutual inductor circuit, a signal conditioning and filtering circuit, a first-stage clamping circuit, a first-stage gain circuit, a second-stage clamping circuit, a second-stage gain circuit and a hysteresis comparison circuit which are sequentially connected, and the power system frequency measuring circuit also comprises a biasing circuit for providing direct-current bias voltage;
the transformer circuit converts a high-voltage signal on the primary side into a low-voltage signal on the secondary side and electrically isolates the signals;
the signal conditioning and filtering circuit is used for conditioning the output signal of the mutual inductor to a proper amplitude value and carrying out low-pass filtering on the output signal of the mutual inductor so as to filter high-frequency interference;
the two-stage clamping circuit is used for clamping the preceding-stage large amplitude signal to a small amplitude;
the two-stage gain circuit amplifies the preceding-stage signal;
the hysteresis comparison circuit compares the input signal which is finally amplified by the two stages with a reference signal, and outputs a stable square wave signal which has the same frequency as the input signal and is used for the rear-stage CPU to measure the frequency.
2. The power system frequency measurement circuit of claim 1, wherein the bias circuit is coupled to the signal conditioning and filtering circuit, the first clamping circuit, the first gain circuit, the second clamping circuit, the second gain circuit, and the hysteresis comparator circuit to provide dc bias to the circuits.
3. The power system frequency measurement circuit of claim 1, wherein the transformer circuit employs a voltage transformer to convert the primary side measured large amplitude ac voltage signal to a secondary side small amplitude ac voltage signal and to ensure electrical isolation of the primary and secondary sides.
4. The power system frequency measurement circuit according to claim 1, wherein the signal conditioning and filtering circuit employs a differential proportional amplifying circuit, the differential proportional amplifying circuit includes an operational amplifier, a balance resistor, a feedback electronic circuit and a compensation resistor, the balance resistor is connected between the differential output terminal of the transformer and the input terminal of the operational amplifier, and the feedback resistor and the compensation resistor are both connected in parallel with a small nF-stage capacitor to form a low-pass filtering circuit for filtering external high-frequency interference.
5. The power system frequency measurement circuit according to claim 1, wherein the first stage gain circuit and the second stage gain circuit both use reverse amplification circuits, and the amplification factor of each stage is ten times.
6. The power system frequency measurement circuit of claim 1, wherein the first stage clamp and the second stage clamp are both clamped to 2.5 ± 0.3V by using a resistive current-limiting bi-directional schottky diode.
7. The power system frequency measurement circuit of claim 1, wherein the voltage bias circuit divides the voltage of the power supply resistor, generates a reference voltage with low output impedance through the voltage follower circuit, and applies the reference voltage to the non-inverting terminal of the single power supply operational amplifier of the signal conditioning and filtering circuit, the first-stage gain circuit and the second-stage gain circuit to raise the measured alternating current signal to a positive voltage or higher.
8. The power system frequency measurement circuit of claim 7, wherein a voltage bias circuit is applied to the first stage clamp circuit and the second stage clamp circuit to clamp the signal to a small signal centered on the bias voltage with a swing amplitude of ± 0.3V.
9. The power system frequency measurement circuit according to any one of claims 1 to 8, wherein the hysteresis comparator circuit is a high-speed differential comparator, an input terminal of the hysteresis comparator circuit is connected to a voltage divider circuit, a reference voltage is provided by the voltage divider circuit, a negative feedback resistor is connected between an inverting input terminal and an inverting output terminal of the hysteresis comparator circuit, and a positive feedback resistor is connected between a non-inverting input terminal and a non-inverting output terminal of the hysteresis comparator circuit.
10. The power system frequency measuring circuit according to claim 9, wherein the transformer circuit is a voltage transformer, a primary input side of the transformer circuit is a lead type, and the transformer circuit is connected with an external measured high voltage signal; the secondary side output is connected to the signal conditioning and filtering circuit of the later stage in a differential mode.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111482390.7A CN114113781A (en) | 2021-12-07 | 2021-12-07 | Frequency measuring circuit of power system |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN202111482390.7A CN114113781A (en) | 2021-12-07 | 2021-12-07 | Frequency measuring circuit of power system |
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| CN114113781A true CN114113781A (en) | 2022-03-01 |
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| CN202111482390.7A Pending CN114113781A (en) | 2021-12-07 | 2021-12-07 | Frequency measuring circuit of power system |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116800212A (en) * | 2023-08-23 | 2023-09-22 | 中北大学 | Gain-adjustable non-contact ultrasonic receiving signal processing circuit with clamping function |
-
2021
- 2021-12-07 CN CN202111482390.7A patent/CN114113781A/en active Pending
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN116800212A (en) * | 2023-08-23 | 2023-09-22 | 中北大学 | Gain-adjustable non-contact ultrasonic receiving signal processing circuit with clamping function |
| CN116800212B (en) * | 2023-08-23 | 2023-11-03 | 中北大学 | Gain-adjustable non-contact ultrasonic receiving signal processing circuit with clamping function |
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