CN107677870A - A kind of quick measuring circuit of power distribution network zero-sequence current - Google Patents

Abstract

The invention discloses a kind of quick measuring circuit of power distribution network zero-sequence current.It is directed to the problem of widely different zero sequence current signal detection speed of current numerical value is slow, there is provided a kind of quick accurate measurement method of power system zero-sequence current.This method improves the measurement accuracy of zero sequence current signal by adjusting the multiplication factor of amplifier, and signal number range judges what is be automatically performed by hardware comparator.The present invention can fully rely on hardware and be automatically adjusted to best magnification, it is only necessary to which one-shot measurement just obtains the exact value of electric current.So not only possess to zero-sequence current accurate measurement capabilities of all sizes, and substantially increase measuring speed.

Description

A Fast Measurement Circuit of Zero-sequence Current in Distribution Network

technical field

The invention relates to the field of measurement of analog quantities used in power systems, in particular to an amplification measurement method for zero-sequence currents in power systems.

Background technique

The zero-sequence current of the power system is an important parameter that reflects the operating state of the power system. The zero-sequence current of the power system is very small during normal operation, but it will appear larger when a ground fault (including single-phase grounding and two-phase grounding) occurs. zero sequence current. Therefore, by measuring the size of the zero-sequence current, it is possible to quickly and accurately detect whether a ground fault occurs in the power system. However, due to the great difference in the magnitude of the zero-sequence current under different conditions such as normal operation and faults of the power system, and the general current measurement equipment can only guarantee high measurement accuracy when the current rating changes near the current rating, it is necessary to study how to measure the current from a small current It is a device with high measurement accuracy to high current.

At present, automatic range technology is generally used to improve the measurement accuracy of various signals. The main principle is to firstly measure the signal, estimate its approximate value, and then adjust the magnification of the amplifier accordingly, so as to achieve the best match with the range of the AD converter, thereby improving the measurement progress. However, this solution requires two or more measurements of the signal with the cooperation of software and hardware, and tries step by step to achieve the best magnification, thus affecting the measurement speed.

All in all, a technical problem that needs to be solved urgently by those skilled in the art is: how to quickly and accurately measure various zero-sequence current signals with great differences in values.

Contents of the invention

The purpose of the present invention is to solve the above problems and provide a fast and accurate measurement method for the zero-sequence current of the power system. The basic idea of the present invention is to improve the measurement accuracy of the zero-sequence current signal by adjusting the magnification of the amplifier, but the improvement is that the judgment of the signal value range is not through A/D conversion and software estimation, but is automatically completed by a hardware comparator Therefore, the present invention can fully rely on hardware to automatically adjust to the best magnification, and only needs one measurement to obtain the accurate value of the current. This not only has the ability to accurately measure zero-sequence currents of different sizes, but also greatly improves the measurement speed.

In order to achieve the above purpose, the present invention adopts the following technical solutions (see accompanying drawing 1).

A rapid measurement circuit for zero-sequence current in a distribution network, the main principle and working process are as follows.

Step 1: Transform the line current signal I1 in the power system into a small current signal I2 through a zero-sequence current transformer (CT), and send it to the signal conditioning circuit.

Step 2: The signal conditioning circuit mainly includes three operational amplifiers (preamplifier, main amplifier and adjustable amplifier from front to back), three voltage comparators and a multiplexer (eight select one type). The preamplifier converts the current signal I2 into a voltage signal Vo1 and sends it to the main amplifier, and the main amplifier is responsible for further amplifying the voltage signal into a voltage signal Vo2 to drive the three post-position voltage comparators and adjustable amplifiers. The three voltage comparators have different threshold voltages Vd1, Vd2, and Vd3. By comparing Vo2 with the three threshold voltages, the three voltage comparators will output high or low levels according to the relationship between them. signal, thus forming a three-bit code.

Step 3: The three-bit codes output by the three voltage comparators are sent to the three gates of the multiplexer, so that one switch is selected and closed from the eight-way switch, and at the same time, a suitable feedback is connected to the adjustable amplifier. Resistor, choose the appropriate voltage magnification, so that the adjustable amplifier output voltage signal Vo3.

Step 4: The voltage signal Vo3 output by the adjustable amplifier is sent to the A/D converter at the back to convert the analog quantity into a digital quantity, and the digital quantity is sent to the CPU and enters the memory of the CPU. The three-digit codes output by the three voltage comparators are sent to the three digital input terminals of the CPU at the same time to inform the CPU of the current feedback resistance connected to the adjustable amplifier, so that the CPU can calculate the accurate current value.

The second step specifically includes: the signal conditioning circuit includes two operational amplifiers, three voltage comparators, and a multiplexer (one of eight types). Among them, the pre-operational amplifier (U0) converts the current signal I2 into a voltage signal Vo1, which is simultaneously sent to the post-main amplifier (U4) and three voltage comparators (U1, U2 and U3). The three voltage comparators have different threshold voltages Vd1, Vd2, and Vd3 respectively. By sending the voltage Vo1 into the voltage comparator U1 for comparison with the threshold voltage Vd1. If Vo1>Vd1, U1 outputs high level; otherwise, it outputs low level. Similarly, send Vo1 to U2 to compare with Vd2, send Vo1 to U3 to compare with Vd3, U2 and U3 will output high level or low level according to the comparison result, so that the three voltage comparators output Ping forms a three-digit code.

The step three specifically includes: the three-bit codes output by the three voltage comparators are sent to the three gate terminals of the multiplexer. There are eight inputs and one output on the outside of the multiplexer, and eight switches inside, one of the eight switches can be selected to be closed, and one of the eight channels can be selected to be connected according to the codes of the three strobe terminals. For example, when the three-digit code is 000, turn on the resistor R0; and when the three-digit code is 111, turn on the resistor R7. In this way, an appropriate feedback resistor can be automatically selected for the main amplifier, that is, an appropriate voltage amplification factor can be selected, so that the main amplifier outputs the amplified voltage signal Vo2.

The step four is specifically: the voltage signal Vo2 output by the main amplifier is sent to the A/D converter behind, so that the analog quantity is converted into a digital quantity, and the digital quantity is sent to the CPU through the data bus DBus to collect and enter the memory of the CPU. The three-bit codes output by the three voltage comparators pass through the level conversion circuit and are converted to a level suitable for the CPU, and then sent to the three digital input terminals of the CPU to inform the CPU of the current feedback resistor connected to the main amplifier, so that the CPU can calculate Get an accurate current value.

The key point of the present invention is that in order to solve the problem of high-precision measurement of zero-sequence current, on the basis of the existing automatic range circuit, an automatic level discrimination coding circuit featuring multi-level voltage comparators is designed to automatically select the appropriate one for the main amplifier. Feedback resistance and magnification can quickly output a suitable voltage signal.

The beneficial effects of the present invention are: when solving the problem of zero-sequence current measurement with different amplitudes, it is not necessary to perform a measurement first and then adjust the magnification as in the traditional method, but to use the automatic level discrimination encoding circuit to adjust it once. magnification for faster measurement speed while improving measurement accuracy.

Description of drawings

Fig. 1 is a structural schematic diagram of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, a zero-sequence current measurement circuit includes the following steps.

Step 1: Transform the zero-sequence current signal I1 in the power system into a small current signal I2 through a zero-sequence transformer (CT), and send it to the signal conditioning circuit.

The second step specifically includes: the signal conditioning circuit includes two operational amplifiers, three voltage comparators, and a multiplexer (one of eight types). Among them, the pre-operational amplifier (U0) converts the current signal I2 into a voltage signal Vo1, which is simultaneously sent to the post-main amplifier (U4) and three voltage comparators (U1, U2 and U3). The three voltage comparators have different threshold voltages Vd1, Vd2, and Vd3 respectively. By sending the voltage Vo1 into the voltage comparator U1 for comparison with the threshold voltage Vd1. If Vo1>Vd1, U1 outputs high level; otherwise, it outputs low level. Similarly, send Vo1 to U2 to compare with Vd2, send Vo1 to U3 to compare with Vd3, U2 and U3 will output high level or low level according to the comparison result, so that the three voltage comparators output Ping forms a three-digit code.

The step three specifically includes: the three-bit codes output by the three voltage comparators are sent to the three gate terminals of the multiplexer. There are eight inputs and one output on the outside of the multiplexer, and eight switches inside, one of the eight switches can be selected to be closed, and one of the eight channels can be selected to be connected according to the codes of the three strobe terminals. For example, when the three-digit code is 000, turn on the resistor R0; and when the three-digit code is 111, turn on the resistor R7. In this way, an appropriate feedback resistor can be automatically selected for the main amplifier, that is, an appropriate voltage amplification factor can be selected, so that the main amplifier outputs the amplified voltage signal Vo2.

The step four is specifically: the voltage signal Vo2 output by the main amplifier is sent to the A/D converter behind, so that the analog quantity is converted into a digital quantity, and the digital quantity is sent to the CPU through the data bus DBus to collect and enter the memory of the CPU. The three-bit codes output by the three voltage comparators pass through the level conversion circuit and are converted to a level suitable for the CPU, and then sent to the three digital input terminals of the CPU to inform the CPU of the current feedback resistor connected to the main amplifier, so that the CPU can calculate Get an accurate current value.

Although the specific implementation of the present invention has been described above in conjunction with the accompanying drawings, it does not limit the protection scope of the present invention. Those skilled in the art should understand that on the basis of the technical solution of the present invention, those skilled in the art do not need to pay creative work Various modifications or variations that can be made are still within the protection scope of the present invention.

Claims (4)

1. a kind of quick measuring circuit of power distribution network zero-sequence current, its cardinal principle and workflow are as follows：

Step 1：Line current signal I1 in power system is passed through into zero sequence current mutual inductor（CT）It is transformed to low current signal I2, it is sent into signal conditioning circuit；

Step 2：Mainly include three operational amplifiers in signal conditioning circuit（Preamplifier is followed successively by from front to back, master is put Big device and adjustable amplifier）, three voltage comparator and a multicircuit switches（Eight select a type）；Wherein preamplifier will Current signal I2 is converted to voltage signal Vo1 and is sent into main amplifier, and main amplifier is responsible for voltage signal being further enlarged into Voltage signal Vo2 is to drive rearmounted three voltage comparators and adjustable amplifier；Three voltage comparators have different thresholds Threshold voltage Vd1, Vd2, and Vd3, by by Vo2 and three threshold voltages respectively compared with, it is different according to its magnitude relationship, Three voltage comparators export high level or low level signal by corresponding, so as to form tri-bit encoding；

Step 3：The tri-bit encoding of three voltage comparator outputs is admitted to three gating ends of multicircuit switch, so as to right It should select to close a way switch from eight way switch, while also just be connected to suitable feedback resistance for adjustable amplifier, select Suitable voltage amplification factor, makes adjustable amplifier output voltage signal Vo3；

Step 4：The voltage signal Vo3 of adjustable amplifier output is admitted to A/D converter below, and analog quantity is converted into number Word amount, digital quantity are admitted to the memory that CPU enters CPU；The tri-bit encoding of three voltage comparator outputs is admitted to CPU simultaneously Three digital quantity inputs, inform the feedback resistance of CPU current adjustable amplifiers connection, CPU is calculated accurately Current value.

2. a kind of quick measuring circuit of power distribution network zero-sequence current according to claim 1, it is characterized in that：The step 2 tool Body is that signal conditioning circuit includes two operational amplifiers, three voltage comparators and a multicircuit switch（Eight select one Type）；Wherein preamplifier（U0）Current signal I2 is converted into voltage signal Vo1, the voltage signal is admitted to simultaneously Rearmounted main amplifier（U4）With three voltage comparators（U1, U2 and U3）, three voltage comparators have different threshold values respectively Voltage Vd1, Vd2, and Vd3, by the way that voltage Vo1 is sent into voltage comparator U1 compared with threshold voltage Vd1, if Vo1 >Vd1, then U1 outputs high level, otherwise exports low level；Similarly, Vo1 is respectively fed to U2 compared with Vd2, Vo1 is sent into For U3 compared with Vd3, U2 and U3 can correspondingly export high level or low level, such three voltage comparators output according to comparative result 3 level formed tri-bit encoding.

3. a kind of quick measuring circuit of power distribution network zero-sequence current according to claim 1, it is characterized in that：The step 3 tool Body is that the tri-bit encoding of three voltage comparators output is admitted to three gating ends of multicircuit switch, outside multicircuit switch The tunnels of Bu You eight input and exported all the way, and there are eight switches inside, can be opened according to the coding difference at three gating ends from eight The Central Shanxi Plain selects a switch closure, selects to connect all the way from eight tunnels；Such as when tri-bit encoding is 000, connect resistance R0；And When tri-bit encoding is 111, resistance R7 is connected；Thus suitable feedback resistance can be selected for main amplifier automatically, also It is the suitable voltage amplification factor of selection, makes the voltage signal Vo2 after main amplifier output amplification.

4. a kind of quick measuring circuit of power distribution network zero-sequence current according to claim 1, it is characterized in that：The step 4 tool Body is admitted to A/D converter below for the voltage signal Vo2 of main amplifier output, analog quantity is converted to digital quantity, numeral Amount is admitted to memories of the CPU by data/address bus DBus collections into CPU；The tri-bit encoding warp of three voltage comparator output Over level change-over circuit, after the level for being converted to suitable CPU, CPU three digital quantity inputs are sent into, inform that CPU is currently led The feedback resistance of amplifier connection, allows CPU to calculate accurate current value.