CN103543319B - The measuring method of the high-precision rapid survey circuit of power system inner width range current - Google Patents

Abstract

The invention discloses a measurement method of a high-precision fast measurement circuit for a wide range of current in a power system, comprising: a current transformer connected in sequence, a signal conditioning circuit, a limiter, an A/D converter and a CPU, and the signal conditioning circuit includes sequentially connected Connected preamplifier, main amplifier, adaptive amplifier, preamplifier connected to current transformer, adaptive amplifier connected to limiter, node between main amplifier and adaptive amplifier connected to three branches, each branch Both are provided with an average value extraction circuit and a voltage comparator connected in sequence, the average value extraction circuit is connected to the input end of the self-adaptive amplifier, and the voltage comparator is connected to the multi-way switch through the first level shifter. The circuit has an automatic level discrimination and encoding circuit of a multi-level voltage comparator, which can automatically select a suitable feedback resistance and amplification factor for the amplifier, and has a faster measurement speed while improving the measurement accuracy of a wide range of current signals.

Description

Measuring method of high-precision and fast measuring circuit for wide-range current in power system

technical field

The invention relates to the field of analog quantity measurement for power systems, in particular to a measurement method for a high-precision fast measurement circuit for wide-range currents in the power system.

Background technique

The current of the power system is an important parameter that reflects the operating state of the power system. During normal operation, the power system needs to obtain the current value for various analysis and calculation of the power system. To protect the safety of systems and equipment, current measuring equipment is one of the necessary equipment for power systems. However, since the current value is affected by the working conditions of the user equipment, the current value varies in a large range during normal operation. Ordinary measuring equipment can only guarantee high measurement accuracy near the rated current value, and the measurement accuracy will decrease when the current value changes in a wide range. The research is of great significance and practical value for devices with high measurement accuracy for currents from zero to rated value and even a wider range.

In order to achieve high current measurement accuracy in a wide range, the current solution in the power field is to use two sets of circuits. One circuit is responsible for providing current values for monitoring and metering. Its accuracy is high, but its adaptable current range is small, usually Zero to rated current; another set of circuits is responsible for providing the current value required for protection. Its accuracy is slightly worse than the former, but the adaptable current range is large, which can be zero to dozens of times the rated current.

In the field of industrial measuring instruments, automatic range technology can be used to improve the measurement accuracy of wide range signals. The main principle is to firstly measure the signal, estimate its approximate value, and then adjust the amplification factor of the amplifier accordingly to make it best match with the range of the A/D converter, thereby improving the measurement accuracy. However, this solution requires the cooperation of software and hardware to measure the signal twice or even multiple times, and it needs to be tried step by step to achieve the best magnification, which affects the measurement speed.

All in all, a technical problem that needs to be urgently solved by those skilled in the art is: how to accurately and quickly realize the measurement of a wide range of current signals.

Contents of the invention

The object of the present invention is to solve the above problems, and provide a measurement method of a high-precision and fast measurement circuit for a wide range of current in a power system. The basic idea of the present invention is also to improve the measurement accuracy of the wide-range current signal by adjusting the magnification of the amplifier, but the improvement is that the judgment of the value range of the current signal is not through A/D conversion and software estimation, but through a hardware voltage comparator It is done automatically, so the present invention can fully rely on the hardware circuit to automatically adjust to the best magnification, and only needs one measurement to obtain the accurate value of the current. This not only meets the precise measurement requirements for a wide range of current, but also greatly improves the measurement speed.

In order to achieve the above object, the present invention adopts the following technical solutions:

A high-precision and fast measurement circuit for a wide range of current in the power system, including: a current transformer, which converts the power current into a small current signal and then transmits it to the signal conditioning circuit. The signal conditioning circuit converts the current signal into a The voltage signal is transmitted to the limiter, and the limiter transmits the signal to the A/D converter, and the A/D converter carries out analog-to-digital conversion on the signal and transmits the data to the CPU (central processing unit);

The signal conditioning circuit includes: a preamplifier, the preamplifier converts the current signal into a voltage signal and sends it to the main amplifier, the main amplifier further amplifies the signal and sends it to the adaptive amplifier, and the signal of the adaptive amplifier will be transmitted to At the same time, the signal further amplified by the main amplifier will pass through three average value extraction circuits, and the average voltage obtained after passing through the three average value extraction circuits will be respectively transmitted to three voltage comparators, and compared by the three voltage comparators Finally, the three voltage comparators output high/low levels respectively, and transmit the high/low levels to two level converters respectively, and the first level converter transmits the converted signal to the multiplexer switch that also receives the output of the adaptive amplifier. The second level converter transmits the converted signal to the CPU.

The average value extraction circuit includes three parallel branches, two diodes in series are arranged on the first branch and the second branch, a capacitor C is arranged on the third branch, and a capacitor C is arranged on the first branch. The positive pole of the first diode D1 is connected to the input terminal Vin1, the positive pole of the first diode D1 is also connected to the negative pole of the third diode, the negative pole of the first diode D1 is connected to the output terminal, and the The anode of the third diode D3 is grounded, the anode of the second diode D2 on the second branch is connected to the input terminal Vin2, and the anode of the second diode D2 is also connected to the fourth diode D4 The cathode of the second diode D2 is connected to the output terminal, the anode of the fourth diode D4 is grounded, and the two ends of the capacitor C are respectively grounded and the output terminal.

Each of the level converters includes three identical level conversion circuits, each level conversion circuit is provided with a triode, the base of the triode is connected to the input terminal through a first resistor, and the emitter of the triode is grounded. The collector of the triode is connected to the power supply (the first level shifter is connected to the power supply VDD, and the second level shifter is connected to the power supply VCC) through the second resistor, and the collector of the triode is connected to the output terminal.

The measurement method adopted by the measurement circuit is mainly divided into the following steps:

Step 1: The current transformer transforms the current signal I1 in the power system into a small current signal I2, and sends it to the signal conditioning circuit;

Step 2: Convert the current signal I2 into a voltage signal Vo1 and send it to the main amplifier. The main amplifier is responsible for further amplifying Vo1 into a voltage signal Vo2 and sending it to the adaptive amplifier; at the same time, the voltage signal Vo2 is processed to obtain the voltage signal Vo2 The corresponding voltage average value |Vo2| is sent to three voltage comparators, and a three-digit digital code is generated after comparison by the three voltage comparators;

Step 3: After the three-digit code is converted into a level suitable for the multiplexer, it is sent to the three strobe terminals of the multiplexer; like this, the output results of the three voltage comparators can be automatically converted into The adaptive amplifier selects the appropriate feedback resistor, and at the same time selects the appropriate voltage amplification factor, so that the adaptive amplifier outputs the voltage signal Vo3;

Step 4: The voltage signal Vo3 output by the adaptive amplifier is sent to the A/D converter through the limiter, and the A/D converter converts the analog quantity into a digital quantity, and the digital quantity is sent to the CPU; at the same time, the three voltage comparators output After the three-digit digital code is converted into a level suitable for the CPU, it is sent to the three digital input terminals of the CPU to obtain the feedback resistance and amplification factor connected to the current adaptive amplifier, so that the CPU can calculate an accurate current value.

In the second step, the specific working steps of the voltage comparators are as follows: the three voltage comparators have different threshold voltages Vd1, Vd2, and Vd3 respectively;

By sending the average voltage |Vo2| into the first voltage comparator for comparison with the threshold voltage Vd1, if |Vo2|>Vd1, the first voltage comparator outputs a high level; otherwise, it outputs a low level;

Send |Vo2| to the second voltage comparator to compare with the threshold voltage Vd2, if |Vo2|>Vd2, the second voltage comparator outputs high level; otherwise, it outputs low level;

Send |Vo2| to the third voltage comparator to compare with the threshold voltage Vd3, if |Vo2|>Vd3, the third voltage comparator outputs high level; otherwise, it outputs low level;

In this way, the three levels output by the three voltage comparators form a three-digit digital code.

The current signal I1 in the first step is transformed into a small current signal I2 through a current transformer.

The pre-operational amplifier in the signal conditioning circuit in the second step converts the current signal I2 into a voltage signal Vo1.

In the second step, the voltage signal Vo2 is processed by an average value extraction circuit to obtain an average voltage value |Vo2| corresponding to the voltage signal Vo2 and then sent to three voltage comparators.

The three-digit digital code in step 3 is converted to a level suitable for the multiplexer through the first level converter.

The three-digit codes output by the three voltage comparators are converted to a level suitable for the CPU through the second level converter. The key point of the present invention is that in order to solve the problem of high-precision measurement of wide-range current, an automatic level discrimination and encoding circuit featuring a multi-level voltage comparator is designed by referring to the principle of the automatic range circuit of the instrument, and the automatic selection of the amplifier is completely through the hardware. Appropriate feedback resistors and amplification factors can quickly output appropriate voltage signals to the A/D converter.

The beneficial effects of the present invention are:

1. When solving the problem of wide-range current measurement, multiple different feedback resistors are configured for the adaptive amplifier, and the appropriate feedback resistor can be automatically selected according to the level of the input voltage signal, and the amplification factor of the amplifier can be adjusted to improve the measurement accuracy.

2. By setting multiple voltage comparators, it is not necessary to perform one or more A/D conversions and software estimations before adjusting the magnification and performing final A/D conversions as in the traditional method. The level discriminant and encoding circuit adjusts the magnification at one time, so that the measurement speed is faster while the measurement accuracy is improved.

3. The present invention is simple and easy to understand when introducing the measurement method, taking three voltage comparators as an example, but it can actually support more voltage comparators, thereby further improving the measurement accuracy, so it has good scalability and application value .

Description of drawings

Fig. 1 schematic diagram of principle of the present invention;

Figure 2 is a diagram of an embodiment of the present invention;

Fig. 3 average value extraction circuit schematic diagram;

Fig. 4 schematic diagram of the first level shifter;

Fig. 5 is a schematic diagram of a second level shifter;

Among them, 1. Current transformer, 2. Preamplifier, 3. Main amplifier, 4. Adaptive amplifier, 5. Limiter, 6. A/D converter, 7. CPU, 8. Average value extraction circuit, 9. A voltage comparator. 10. A first level shifter. 11. A multiplexer. 12. A second level shifter.

detailed description

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

As shown in Figures 1 and 2, the high-precision and fast measurement circuit for a wide range of current in the power system includes: a current transformer 1, a signal conditioning circuit, a limiter 5, an A/D converter 6 and a CPU 7 connected in sequence,

The signal conditioning circuit includes a preamplifier 2, a main amplifier 3, and an adaptive amplifier 4 connected in sequence, the preamplifier 2 is connected with the current transformer 1, and the adaptive amplifier 4 is connected with the limiter 5,

The node between the main amplifier 3 and the adaptive amplifier 4 is connected with three branches, and each branch is provided with an average value extraction circuit 8 and a voltage comparator 9 connected in sequence, wherein the average value extraction circuit 8 is connected to The input end of adaptive amplifier 4, voltage comparator 9 is connected with multiplexer 11 by first level converter 10, multiplexer 11 is connected with the output end of adaptive amplifier 4; Each voltage comparator 9 also It is connected to CPU7 through the second level shifter 12 .

As shown in Figure 3, the average value extraction circuit 8 includes three parallel branches, two diodes in series are arranged on the first branch and the second branch, and a capacitor C is arranged on the third branch. The anode of the first diode D1 on the first branch is connected to the input terminal Vin1, the anode of the first diode D1 is also connected to the cathode of the third diode, and the anode of the first diode D1 The negative pole is connected to the output terminal, the positive pole of the third diode D3 is grounded, the positive pole of the second diode D2 on the second branch is connected to the input terminal Vin2, and the positive pole of the second diode D2 is also connected to The cathode of the fourth diode D4, the cathode of the second diode D2 is connected to the output terminal, the anode of the fourth diode D4 is grounded, and the two ends of the capacitor C are respectively grounded and the output terminal.

As shown in Figures 4 and 5, each of the level shifters includes three identical level shifting circuits, each level shifting circuit is provided with a triode, and the base of the triode is connected to the input terminal through a first resistor , the emitter of the triode is grounded, the collector of the triode is connected to the power supply through the second resistor (wherein the first level shifter is connected to the power supply VDD, and the second level shifter is connected to the power supply VCC), the collector of the triode The electrodes are connected to the output terminals.

The measurement method adopted by the high-precision and fast measurement circuit of wide-range current in the power system is mainly divided into the following steps:

Step 1: Transform the line current signal I1 in the power system into a small current signal I2 (mA level) through the current transformer 1, and send it to the signal conditioning circuit;

Step 2: The signal conditioning circuit mainly includes three operational amplifiers OP07 (preamplifier 2, main amplifier 3 and adaptive amplifier 4 from front to back), three voltage comparators LM311 and a multiplexer CD4051. The pre-operational amplifier converts the current signal I2 into a voltage signal Vo1 and sends it to the main amplifier 3 . The main amplifier 3 is responsible for further amplifying Vo1 into a voltage signal Vo2 and sending it to the adaptive amplifier 4 . At the same time, the voltage signal Vo2 is processed by the average value extraction circuit 8 (see FIG. 3 ), and the average value |Vo2| corresponding to the AC signal Vo2 is obtained and then sent to three voltage comparators 9, which have different Threshold voltages Vd1=5V, Vd2=2V, and Vd3=0.5V. The voltage |Vo2| is sent to the voltage comparator 9 for comparison with the threshold voltage Vd1. If |Vo2|>Vd1, the first voltage comparator U1 outputs a high level; otherwise, it outputs a low level. Similarly, send |Vo2| to the second voltage comparator U2 to compare with Vd2, and to the third voltage comparator U3 to compare with Vd3. U2 and U3 will output high level or low level according to the comparison result, so The 3 levels output by the three voltage comparators 9 form a three-bit code;

Step 3: the three-bit codes output by the three voltage comparators 9 pass through the level conversion circuit 1 (see Figure 4, wherein VDD=+12V), and after being converted into a level suitable for the multiplexer 11, they are sent into the multiplexer Three strobe ends (A, B, C ends) of the transfer switch CD4051. There are eight inputs and one output outside the multiplexer 11, and there are eight switches inside. One switch can be selected from the eight switches to close according to the coding of the three strobe terminals, that is, one of the eight switches can be selected to be connected. For example, when the three codes are 000, turn on the resistance R0, and the R0 resistance value is 10 times of R11, that is, the amplification factor of the adaptive amplifier 4=10; and when the three codes are 111, turn on the resistance R7, and The resistance values of R7 and R11 are equal, that is, the magnification factor=1. In this way, an appropriate feedback resistor can be automatically selected for the adaptive amplifier 4 according to the output results of the three voltage comparators 9 , and an appropriate voltage amplification factor can be selected at the same time, so that the adaptive amplifier 4 outputs the voltage signal Vo3. Since the subsequent A/D converter 6 supports the input voltage signal of plus or minus 10V, the purpose of adjusting the magnification is to make the peak value of Vo3 not exceed plus or minus 10V but close to plus or minus 10V to obtain the best measurement accuracy;

Step 4: The voltage signal Vo3 output by the adaptive amplifier 4 is sent to the analog input terminal of the subsequent A/D converter 6 (AD1674) through the limiter 5 composed of diodes. AD1674 inputs analog quantity through 14 pins, and converts it into corresponding digital quantity, and digital quantity is sent to CPU7 through 12-bit data bus DB0~DB11, where CPU7 is embedded controller 80C196. Simultaneously, the three encoded signals that three voltage comparators 9 output pass through level conversion circuit 2 (seeing Fig. 5, wherein VCC=+5V), after being converted into the 0 to +5V level that is suitable for CPU7, send into the three of CPU7 A digital input terminal to inform CPU7 of the feedback resistance and magnification of the current adjustable amplifier connection, so that CPU7 can calculate the accurate current value based on the obtained A/D conversion digital value multiplied by the magnification.

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 (1)

1. The measurement method of the high-precision and fast measurement circuit of the wide-range current in the power system is characterized in that the measurement circuit includes: A current transformer, the current transformer transforms the power current into a small current signal and transmits it to the signal conditioning circuit, the signal conditioning circuit converts the current signal into a voltage signal and then transmits it to the limiter, and the limiter transmits the signal For the A/D converter, the A/D converter performs analog-to-digital conversion on the current and transmits the data to the CPU; The signal conditioning circuit includes: a preamplifier OP07, the preamplifier OP07 converts the current signal into a voltage signal and sends it to the main amplifier OP07, the main amplifier OP07 further amplifies the signal and sends it to the adaptive amplifier OP07, the adaptive amplifier OP07 The signal of OP07 will be transmitted to the limiter, and the signal further amplified by the main amplifier OP07 will also pass through three average value extraction circuits, and the average voltage obtained after passing through the three average value extraction circuits will be transmitted to three voltage comparators respectively. After being compared by the three voltage comparators, the three voltage comparators output high/low levels respectively, and transmit the high/low levels to the two level shifters respectively, among which the first level shifter will convert the The signal is transmitted to the multiplexer CD4051, and the multiplexer CD4051 also receives the output of the adaptive amplifier OP07, automatically adjusts the amplification factor for the adaptive amplifier OP07, and the second level shifter transmits the converted signal to the CPU ; The average value extraction circuit includes three parallel branches, two diodes in series are arranged on the first branch and the second branch, a capacitor C is arranged on the third branch, and a capacitor C is arranged on the first branch. The positive pole of the first diode D1 is connected to the input terminal Vin1, the positive pole of the first diode D1 is also connected to the negative pole of the third diode D3, and the negative pole of the first diode D1 is connected to the output terminal, so The anode of the third diode D3 is grounded, the anode of the second diode D2 on the second branch is connected to the input terminal Vin2, and the anode of the second diode D2 is also connected to the fourth diode D4 The negative pole of the second diode D2 is connected to the output terminal, the positive pole of the fourth diode D4 is grounded, and the two ends of the capacitor C are grounded and the output terminal respectively; Each of the level converters includes three identical level conversion circuits, each level conversion circuit is provided with a triode, the base of the triode is connected to the input terminal through a first resistor, and the emitter of the triode is grounded. The collector of the triode is connected to the power supply through the second resistor, and the collector of the triode is connected to the output terminal; The method is divided into the following steps: Step 1: Transform the current signal I1 in the power system into a small current signal I2 through a current transformer, and send it to the signal conditioning circuit; Step 2: The preamplifier in the signal conditioning circuit 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 Vo1 into a voltage signal Vo2 and sending it to the adaptive amplifier; at the same time, the voltage signal Vo2 After being processed by the average value extraction circuit, the average voltage |Vo2| corresponding to the voltage signal Vo2 is obtained and then sent to three voltage comparators, and after the comparison of the three voltage comparators, a three-digit digital code is generated; the specific working steps of the voltage comparator As follows: These three voltage comparators have different threshold voltages Vd1, Vd2 and Vd3 respectively; By sending the average voltage |Vo2| into the first voltage comparator for comparison with the threshold voltage Vd1, if |Vo2|>Vd1, the first voltage comparator outputs a high level; otherwise, it outputs a low level; Send |Vo2| to the second voltage comparator to compare with the threshold voltage Vd2, if |Vo2|>Vd2, the second voltage comparator outputs high level; otherwise, it outputs low level; Send |Vo2| to the third voltage comparator to compare with the threshold voltage Vd3, if |Vo2|>Vd3, the third voltage comparator outputs high level; otherwise, it outputs low level; In this way, the three levels output by the three voltage comparators form a three-digit digital code; Step 3: After the three-digit digital code is converted into a level suitable for the multiplexer through the first level converter, it is sent to the three gate terminals of the multiplexer; thus, it can be compared according to the three voltages The output result of the converter automatically selects the appropriate feedback resistor for the adaptive amplifier, and at the same time selects the appropriate voltage amplification factor, so that the adaptive amplifier outputs the voltage signal Vo3; Step 4: The voltage signal Vo3 output by the adaptive amplifier is sent to the A/D converter through the limiter, and the A/D converter converts the analog quantity into a digital quantity, and the digital quantity is sent to the CPU; at the same time, the three voltage comparators output After the three-digit digital code is converted into a level suitable for the CPU by the second level converter, it is sent to the three digital input terminals of the CPU to obtain the feedback resistance and magnification of the current adaptive amplifier connection of the CPU, so that the CPU calculates accurate current value.