A power frequency load removal circuit and method for a power quality analyzer

Abstract

The application relates to the technical field of power distribution network automation, and discloses a de-power-frequency load circuit for low-voltage topology relation identification, which comprises a phase-shifting circuit, an inverting circuit, a differential amplification circuit and an ADC sampling circuit. The de-power-frequency load circuit is used for subtracting a 50Hz component, which accounts for a major part of a current signal collected by a current transformer or a flexible coil, from an original signal after the 50Hz component is phase-shifted by 90 degrees, obtaining a characteristic signal after de-power-frequency load, and amplifying the characteristic signal to an optimal dynamic range of an ADC, so that the success rate of software identification is improved. The power-frequency signal is almost completely removed, and the de-power-frequency load circuit has fewer peripheral devices and is lower in cost compared with a high-order active high-pass filtering scheme under the condition of the same effect.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power distribution network automation, and in particular to a power frequency load removing circuit and method for a power consumption inspection instrument. BACKGROUND

[0002] In a power system, low-voltage topology relations include "house-transformer relations" and "house-meter and transformer branch relations". A "district" refers to a power supply area of a transformer, "house-transformer relations" refer to the power supply attribution relations between each power consumer in the district and the district power supply transformer, and "house-meter and transformer branch relations" refer to the power supply attribution relations between each power consumer and the branch under the district power supply transformer. Accurate topology relations are particularly important in power system operation optimization, low-voltage power distribution monitoring and fault analysis, line loss calculation and other applications.

[0003] The prior art mainly injects a characteristic current signal into the power grid at the end of the power frequency 50Hz by switching control of fixed resistance or fixed capacitance, and detects the characteristic current signal on the secondary side of the current transformer of the transformer bus of the district transformer to be identified or on the branch line of the transformer bus by using a flexible coil. After signal conditioning and analysis, the topology relations are obtained.

[0004] Among them, in the characteristic signal identification part, the existing scheme generally enters the ADC for frequency domain analysis after hardware conditioning. In the signal conditioning part: since the power frequency (50Hz) current signal in the bus is much larger than the injected characteristic current signal, the existing scheme mainly has two kinds: one is to convert the current signal collected by the transformer into a voltage signal and then directly send it to the ADC for analysis; this way, the characteristic signal collected by the ADC is very weak, and the recognition success rate is low. The other is to do active filtering on the hardware, compress the power frequency current signal size to prevent it from exceeding the ADC range, and further amplify the characteristic signal, and then perform noise processing and signal enhancement through the adjacent cycle subtraction method, i.e., the power frequency load removal mentioned in this paper. However, the active filtering scheme often needs multiple active filters to compress the power frequency current signal amplitude, which is built by a large number of analog components, has a high cost, and cannot completely eliminate the power frequency current signal. The characteristic signal component entering the ADC is still limited by the size of the power frequency signal amplitude, and still needs to be processed by the power frequency load removal in the software processing part. SUMMARY

[0005] The present application aims at the deficiencies and defects of the prior art, and provides a power frequency load removing circuit and method for a power consumption inspection instrument, which realizes the process of removing power frequency load of the current signal collected by a current transformer or a flexible coil before an ADC through a hardware mode, and sends the amplified characteristic current signal into the ADC, so as to reduce the hardware cost caused by the load processing step of software and the active filter conditioning mode, and also correspondingly improve the detection capability of weak signals.

[0006] The object of the present application can be realized by the following technical solutions.

[0007] A power frequency load removing circuit for a power consumption inspection instrument, comprising a phase-shifting circuit, an inverting amplification circuit, a differential amplification circuit and an ADC sampling circuit.

[0008] The phase-shifting circuit comprises a first operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor and a capacitor, and performs-180° phase-shifting on the collected signal.

[0009] R3=R4

[0010]

[0011] R2=4R1

[0012] ω=2πf

[0013] f=50Hz

[0014] wherein R1, R2, R3 and R4 are the resistance values of the first resistor, the second resistor, the third resistor and the fourth resistor respectively, C is the capacitance value, ω is the angular frequency, and f is the frequency.

[0015] The inverting amplification circuit comprises a second operational amplifier, a fifth resistor, a sixth resistor and a seventh resistor, and is used for inverting and gain of the collected signal, and the signal gain is 1 / 2.

[0016] R6=2R5=2R7

[0017] wherein R5, R6 and R7 are the resistance values of the fifth resistor, the sixth resistor and the seventh resistor respectively.

[0018] The differential amplification circuit comprises a third operational amplifier, an eighth resistor, a ninth resistor and a tenth resistor, and is used for differentially amplifying the signals processed by the phase-shifting circuit and the inverting gain circuit.

[0019] R8=R9

[0020] R 10 =R 11

[0021] Gain=R 11 / R9

[0022] wherein R8, R9, R 10 , R 11 are the resistance values of the eighth resistor, the ninth resistor, the tenth resistor and the eleventh resistor respectively; Gain is a signal gain;

[0023] The ADC sampling circuit is used for frequency domain analysis of the signal after differential amplification.

[0024] Further, the frequency domain analysis is to analyze whether the signal collected by the mutual inductor contains a characteristic frequency, if yes, it indicates that the power consumer belongs to the current transformer area, otherwise, it indicates that it does not belong to the transformer area.

[0025] A method for identifying low-voltage topology relationship, comprising the following steps:

[0026] S1: connecting a current signal collecting device at the transformer bus or the secondary side of the bus mutual inductor to collect the current signal and converting it into a voltage signal through a sampling resistor, and dividing the voltage signal into two paths;

[0027] S2: one path of the signal is phase-shifted by-180°, and the other path of the signal is inverted;

[0028] S3: the two output signals are sent to an ADC after differential amplification processing;

[0029] S4: the software performs frequency domain analysis on the signal collected by the ADC: further judges whether the signal contains a characteristic frequency;

[0030] S5: if yes, it indicates that the power consumer belongs to the current transformer, otherwise, it does not belong to.

[0031] The beneficial technical effects of the present application are:

[0032] 1. Compared with the software load frequency removal method in the low-voltage topology relationship identification, the load frequency removal method proposed by the present application is in the form of an analog circuit, which removes the largest proportion of the power frequency signal in the current signal containing the characteristic signal before the current signal enters the ADC, and amplifies the characteristic signal to the best dynamic range of the ADC, thereby improving the success rate of software identification.

[0033] 2. Compared with the high-order active high-pass filtering method, the high-order active filtering method can only reduce the power frequency signal by a certain multiple, but cannot completely remove the power frequency signal. The load frequency removal method proposed by the present application can almost completely remove the power frequency signal in the current signal containing the characteristic signal by phase-shifting and subtracting, and has fewer peripheral devices. Compared with the high-order active high-pass filtering scheme, the cost of the present application is lower under the same effect.

[0034] 3、The method for removing the power frequency load is suitable for any scene needing to remove periodic sinusoidal signals, and can remove periodic signals of different frequencies under the cooperation of peripheral circuits and the allowable bandwidth of operational amplifiers. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 Circuit diagram of the present application.

[0036] Figure 2 Original power frequency current signal waveform with characteristic current of the present application.

[0037] Figure 3 Current signal waveform after removing the power frequency load. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application.

[0039] Example:

[0040] The present circuit and method are mainly used to remove the power frequency load of the current signal collected by the current transformer or flexible coil before the ADC through the hardware mode, and amplify the characteristic current signal and then send it to the ADC, so as to reduce the hardware cost caused by the software load processing steps and active filter conditioning mode, and also improve the detection ability of weak signals. The present application provides the following technical method:

[0041] The power frequency load removal circuit is shown in Figure 1 , wherein D1 / D2 / D3 is an operational amplifier, D1 and its peripheral circuit shift the initial signal by-180°, and the signal gain is 1 / 2, D2 and its peripheral circuit invert the initial signal, and the signal gain is 1 / 2, and D3 and its peripheral circuit differentially amplify the output of D1 and D2 to complete the hardware removal of the power frequency load, and further amplify the characteristic signal and then enter the ADC sampling.

[0042] D1, a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4 and a capacitor C constitute a phase shifter to realize-180° phase shift of the 50Hz power frequency signal, and need to satisfy:

[0043] R3=R4

[0044]

[0045] R2=4R1

[0046] ω=2πf

[0047] f=50Hz

[0048] Wherein R1, R2, R3, R4 are resistance values of the first resistance, the second resistance, the third resistance, the fourth resistance respectively; C is a capacitance value; ω is an angular frequency; f is a frequency;

[0049] D2, the fifth resistance R5, the sixth resistance R6, the seventh resistance R7 constitute an inverter and a 1 / 2 signal gain, which need to satisfy:

[0050] R6=2R5=2R7

[0051] Wherein R5, R6, R7 are resistance values of the fifth resistance, the sixth resistance, the seventh resistance respectively;

[0052] D3, the eighth resistance R8, the ninth resistance R9, the tenth resistance R10, the eleventh resistance R11 constitute a differential amplifier, which need to satisfy:

[0053] R8=R9

[0054] R 10 =R 11

[0055] Gain=R 11 / R9

[0056] Wherein R8, R9, R 10 , R 11 are resistance values of the eighth resistance, the ninth resistance, the tenth resistance, the eleventh resistance respectively; Gain is a signal gain;

[0057] In combination with the above conditions, the original power frequency current signal waveform with a characteristic current is as shown in Figure 2 , and the current signal waveform after removing the power frequency load is as shown in Figure 3 It can be seen that the method can remove the power frequency current signal in the original signal, retain the characteristic current signal and further amplify it, and send it into an ADC for further frequency domain analysis and decoding.

[0058] The above embodiments are descriptions of specific implementation manners of the present application, rather than limitations of the present application. Those skilled in the art can make various transformations and changes without departing from the spirit and scope of the present application to obtain corresponding equivalent technical solutions, therefore all equivalent technical solutions shall be included in the patent protection scope of the present application.

Claims

1. A circuit for removing power frequency loads in an electrical testing instrument, characterized in that, This includes phase-shifting circuits, inverting amplifier circuits, differential amplifier circuits, and ADC sampling circuits; The phase-shifting circuit includes a first operational amplifier, a first resistor, a second resistor, a third resistor, a fourth resistor, and a capacitor, which shifts the phase of the acquired signal by -180°. R3 = R4 R2 = 4R1 ω=2πf f = 50Hz Where R1, R2, R3, and R4 are the resistance values ​​of the first, second, third, and fourth resistors, respectively; C is the capacitance value; ω is the angular frequency; and f is the frequency. The inverting amplifier circuit includes a second operational amplifier, a fifth resistor, a sixth resistor, and a seventh resistor, used to invert and increase the gain of the acquired signal, with a signal gain of 1 / 2; R6 = 2R5 = 2R7 R5, R6, and R7 are the resistance values ​​of the fifth, sixth, and seventh resistors, respectively. The differential amplifier circuit includes a third operational amplifier, an eighth resistor, a ninth resistor, a tenth resistor, and an eleventh resistor, which differentially amplifies the signal processed by the phase shift circuit and the inverting gain circuit. R8 = R9 R 10 =R 11 Gain=R 11 / R9 Among them, R8, R9, R 10 R 11 These are the resistance values ​​of the eighth, ninth, tenth, and eleventh resistors, respectively; Gain is the signal gain. The ADC sampling circuit is used for frequency domain analysis of the differentially amplified signal.

2. The power frequency load removal circuit for an electrical testing instrument according to claim 1, characterized in that, The frequency domain analysis involves analyzing whether the signal collected by the transformer contains characteristic frequencies. If it does, it indicates that the electricity customer belongs to the current transformer area; otherwise, it indicates that the customer does not belong to this transformer area.

3. A method for removing power frequency loads for low-voltage topology identification, comprising the following steps: S1: Connect a data acquisition device to the transformer bus or the secondary side of the bus transformer to acquire the current signal and convert it into a voltage signal through a sampling resistor, then split this voltage signal into two paths; S2: One signal is phase-shifted by -180°, and the other signal is phase-inverted; S3: The two output signals are differentially amplified and then sent to the ADC; S4: The software performs frequency domain analysis on the signal acquired by the ADC to further determine whether the signal contains characteristic frequencies; S5: If it includes information indicating that the electricity customer belongs to the current transformer, otherwise it does not.

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