CN217085091U - Multi-mode power factor measuring device - Google Patents
Multi-mode power factor measuring device Download PDFInfo
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- CN217085091U CN217085091U CN202220408502.8U CN202220408502U CN217085091U CN 217085091 U CN217085091 U CN 217085091U CN 202220408502 U CN202220408502 U CN 202220408502U CN 217085091 U CN217085091 U CN 217085091U
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Abstract
The utility model relates to a multi-mode power factor measuring device. The device comprises a signal conditioning module, a zero-crossing detection module, a data processing module, a display module and a power supply unit; the utility model discloses there is a multi-mode power factor measuring device, the device not only can demonstrate the alternating current power factor that measures under three kinds of different modes, can measure power factor more accurately and judge that the circuit is perception or capacitive, the device can regard as the power factor detector of high accuracy to use in daily electric power parameter measurement, can also regard as a teaching experimental apparatus to be used in power factor measuring experiment teaching, three kinds of measuring modes that multi-mode power factor measuring device used can let the student carry out measurement and analysis to the electric wire netting power factor after the different loads of income in the experiment, let the student know the nature of power factor and the relevant knowledge of reactive compensation more directly perceivedly, have better teaching practical value and good economic benefits.
Description
Technical Field
The utility model relates to an electric power parameter measurement device especially relates to a multi-mode power factor measuring device.
Background
The power factor is a factor that measures the efficiency of an electrical device, and its magnitude is related to the nature of the load in the ac circuit. The electric equipment used in daily production and life mostly belongs to inductive loads with low power factors, and the low power factors indicate that the reactive power for alternating magnetic field conversion is high, so that the utilization rate of the equipment is reduced, the power supply loss of a line is increased, and adverse effects are generated on a power grid. The power factor is improved, the power supply quality can be improved, the electric charge expenditure of enterprises is reduced, and the economic benefit is high. Therefore, the accurate measurement of the power factor has important significance for normal operation and reactive power compensation of the power grid, so that the power factor is improved, the power supply quality is improved, and the electric charge expenditure of enterprises is reduced.
The existing power factor measuring method comprises the steps of carrying out zero-crossing detection on alternating-current voltage and current so as to calculate the time difference corresponding to the phase difference between the voltage and the current, and further calculating the phase angle cosine cos phi between the voltage and the current, wherein the phase angle cosine cos phi is the measured power factor; and a power measuring method for calculating the power factor by measuring the active power P and the apparent power S of the load and then using a trigonometric function. Both measurement methods have some disadvantages: the first method for calculating the phase time difference by performing zero-crossing detection on voltage and current generally has low precision, because many nonlinear loads exist on a power grid in real life, interference harmonics generated by the nonlinear loads have great influence on a zero-crossing detection result, and finally, a measured power factor measurement result is inaccurate. Although the second method can measure the result of the power factor value more accurately, the magnitude of the power factor value cannot directly reflect whether the circuit is inductive or capacitive.
Disclosure of Invention
An object of the utility model is to provide a simple structure, measurement accuracy is high, is convenient for popularize to the multi-mode power factor measuring device in daily electric power parameter measurement and the teaching experiment.
The utility model discloses a solve above-mentioned purpose, the concrete technical scheme who adopts is: the multi-mode power factor measuring device comprises a signal conditioning module, a zero-crossing detection module, a data processing module and a display module; the signal conditioning module is used for converting input voltage and current signals into analog signals and respectively outputting the analog signals to the zero-crossing detection module and the data processing module; the zero-crossing detection module is used for respectively carrying out zero-crossing detection on the analog signals of the voltage and the current and transmitting a zero-crossing detection result to the data processing module; the data processing module is used for converting the analog signals into digital signals, carrying out power factor parameter measurement and transmitting the measurement results to the display module; and the display module is connected with the data processing module and is used for displaying the power factor measurement result.
In the present invention, the signal conditioning module includes a current transformer, a current detection circuit, a current type voltage transformer and a voltage detection circuit; the current transformer is used for acquiring current information and outputting current signals to the zero-crossing detection module and the data processing module through the current detection circuit respectively; the current type voltage transformer is used for collecting voltage signals and respectively outputting the voltage signals to the zero-crossing detection module and the data processing module through the voltage detection circuit.
In the utility model discloses an in, Current Transformer (CT) adopts DL-CT10CL, current mode voltage transformer (PT) adopts DL-PT202H 1.
The utility model discloses an in, zero cross detection module adopts voltage comparator LM393 to realize the zero cross detection of signal.
The utility model discloses an in, data processing module adopts domestic MCU.
The utility model discloses an in, the display module adopts the LCD screen for show under three kinds of methods measured power factor value.
Compared with the prior art, multi-mode power factor measuring device improve traditional power factor measuring method, provide one set and can measure power factor more accurately and judge that the circuit is perceptual or capacitive device. The device can be used for accurately measuring the power factor, students can observe the power factors after different loads are connected into the power grid measured by three different methods in experimental teaching, and the results measured by the three methods are displayed on the device, so that the students can more visually know the properties of the power factors and knowledge related to reactive compensation.
Drawings
Fig. 1 is a system block diagram of the multi-mode power factor measuring device of the present invention.
Fig. 2 is a structure diagram of a voltage detection circuit in the multi-mode power factor measuring device of the present invention.
Fig. 3 is a structure diagram of the current detection circuit in the multi-mode power factor measuring device of the present invention.
Fig. 4 is a circuit structure diagram of the ac voltage signal zero-crossing detection after the voltage detection circuit in the multi-mode power factor measuring device of the present invention.
Fig. 5 is a circuit structure diagram of the multi-mode power factor measuring device for detecting the zero-crossing of the ac current signal after passing through the current detection circuit.
Detailed Description
In order to make the technical solution of the present invention better understood, the technical solution of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.
As shown in figure 1, the multifunctional power factor measurement teaching instrument comprises a signal conditioning module, a zero-crossing detection module, a data processing module, a display module and a power supply unit.
The utility model discloses in, signal conditioning module includes current transformer, current detection circuit, current mode voltage transformer and voltage detection circuit. The voltage detection circuit is shown in fig. 2, when voltage is input at the input end of the current type voltage transformer, four current limiting resistors are respectively connected in series behind the measured voltage to convert the measured voltage into working current of about 2mA to be input to the transformer, the four resistors are connected in series to increase power, so that the heat productivity of the resistors is reduced to achieve the purpose of higher precision, then the transformer outputs two paths of currents with the same size and opposite phases in an equal proportion of 1:1, a circuit behind the output end adopts a differential form, the resistors are connected in parallel behind the output end to achieve voltage acquisition of the output end, and finally processed signals are output to the zero-crossing detection module and the data processing module. Similarly, as shown in fig. 3, the current transformer reduces the current signal passing through the load to a processable alternating voltage weak signal in the same scale, and the processed alternating voltage weak signal is respectively output to the zero-crossing detection module and the data processing module through the differential current detection circuit.
The differential circuit can effectively eliminate interference signals existing in the signal transmission process and improve the precision of output signals. Because the two signals generate the same interference, the effective input of the interference signal is zero through the difference of the two signals, and the aim of resisting common-mode interference is achieved. The output ends of the current detection circuit and the voltage detection circuit are connected with a plurality of resistors in parallel, so that the voltage and current signal acquisition is realized, the power can be increased, the heating of the resistors is reduced, and the measurement precision is higher. The capacitors in the detection circuit are used as filter capacitors to filter out interference harmonics.
Under the first kind of measurement mode, the utility model discloses use zero cross detection to measure in the method of power factor, the voltage after anti-interference processing will be passed through to signal conditioning module, current signal exports respectively as figure 4, the zero cross detection module shown in figure 5, zero cross detection module is through fortune LM393 constitution zero crossing comparator, the analog alternating current signal who will gather by signal conditioning module turns into the rectangular wave signal, the rectangular wave signal cycle after the conversion is unanimous with former signal cycle, the positive and negative value of rectangular wave signal represents sinusoidal signal's positive half cycle and negative semi-axis promptly, the rising edge and the falling edge of rectangular wave signal have represented sinusoidal signal's positive and negative zero crossing point respectively. And respectively sending the two converted rectangular wave signals to two external interrupt ports INT0 and INT1 of the MCU, starting timing by a timer of the microprocessor when a falling edge of the rectangular wave voltage signal arrives, stopping timing by the timer of the microprocessor when a falling edge of the rectangular wave current signal arrives, and corresponding to the time difference of the voltage signal and the current signal by the time difference T measured by the timer of the microprocessor. Because the frequency of the grid voltage and the current specified in China are both 50HZ, and the corresponding period is 0.02S, when the T value is determined, the power factor angle phi can be obtained according to the formula phi =0.02/360 multiplied by T, and then the power factor cos phi can be obtained through the calculation of the MCU.
Under the second kind measurement mode, the utility model discloses in the method that uses the power measurement method to measure power factor, the differential voltage signal after the signal conditioning module will be handled spreads into the two way ADC ports of ADC1 and ADC2 of MCU respectively into, and the differential current signal after will handling spreads into two way ADC ports of ADC3 and ADC4 of MCU respectively into, then MCU samples simultaneously to the four way signal that spreads into. Voltage data sampled at each time by two ports of an ADC1 and an ADC2 of the MCU are set as A1 and A2, a voltage value at the current time is set as A, the A value at the current time can be calculated by a formula A = (A1-A2)/2, an array u (N) with the size of 100 is set, sampling is carried out for one hundred times every period, and the voltage value A calculated at each time is sequentially put into the array u (N). Voltage data sampled at each time by two ports of an ADC3 and an ADC4 of the MCU are set as B1 and B2, a current value at the current moment is set as B, the B value at the current moment can be calculated through a formula B = (B1-B2)/2, similarly, an array i (N) with the size of 100 is set, sampling is carried out for one hundred times at each period, and the current value B calculated each time is sequentially placed into the array i (N). The method of subtracting the two paths of differential signals is adopted in the process of sampling the voltage signals and the current signals respectively, so that the interference existing in the circuit can be effectively eliminated, and a more accurate value can be obtained. The MCU samples to obtain a voltage value U (N) and a current value i (N), and the effective voltage value U can use a formula
Calculating to obtain the effective value I of the current by using a formula
Calculating to obtain apparent power S by formula P = UI, and calculating active power P by formula
Calculated, so that the power factor is formulated
Can be calculated out。
Under the third kind measurement mode, the utility model discloses utilize the cross-correlation method to measure power factor and judge the circuit nature, MCU will sample the voltage signal u (N) and the electric current signal i (N) that obtain as two relevant signals, wherein u (N) and i (N) set to two functions, then the cross-correlation function is defined to be two functions
The cross-correlation function describes the degree of mutual match between signals u (n) and i (n) at any two different times. Because the measured voltage and current signals have the same frequency, the phase difference of the voltage and current signals can be obtained by analyzing the time difference between the two signal peaks through cross correlation. The MCU carries out cross-correlation operation through the FFT to find out a point with the maximum amplitude, the correlation of the two signals is the best at the moment, and the subscript difference of the time delay can be obtained through the array subscript corresponding to the point with the best correlation, so that after the time delay difference T is measured, the power factor angle phi can be obtained according to the formula phi =0.02/360 multiplied by T, and the power factor cos phi can be calculated. The current measured power factor can be judged to be in advance or in retard by calculating the positive and negative of the time delay difference T, namely when the time delay difference T is positive, the voltage signal leads the current signal, the circuit property is an inductive circuit, when the time delay difference is negative, the voltage signal lags the current signal, and the circuit property is a capacitive circuit.
The utility model discloses in, display module's LCD display screen will demonstrate the power factor numerical value of surveying under three kinds of modes and the nature of current circuit simultaneously, and the person of facilitating the use observes measuring result more directly perceivedly.
Claims (7)
1. A multi-mode power factor measurement device, characterized by: the device comprises a signal conditioning module, a zero-crossing detection module, a data processing module, a display module, a power supply unit and a communication port; the signal conditioning module is used for converting input alternating voltage and current signals into analog signals which can be collected by the MCU and respectively outputting the analog signals to the zero-crossing detection module and the data processing module; the zero-crossing detection module is used for respectively carrying out zero-crossing detection on the analog signals of the voltage and the current and transmitting a zero-crossing detection result to the data processing module; the display module is used for displaying the power factor measurement result; the power supply unit is used for supplying power to the multi-mode power factor measuring device.
2. A multi-mode power factor measurement device according to claim 1, wherein: the signal conditioning module comprises a current transformer, a current detection circuit, a current type voltage transformer and a voltage detection circuit; the current transformer is used for acquiring current information and outputting current signals to the zero-crossing detection module and the data processing module through the current detection circuit respectively; the current type voltage transformer is used for collecting voltage signals and respectively outputting the voltage signals to the zero-crossing detection module and the data processing module through the voltage detection circuit.
3. The multi-mode power factor measurement device of claim 2, wherein: the Current Transformer (CT) adopts DL-CT10CL, and the current type voltage transformer (PT) adopts DL-PT202H 1.
4. The multi-mode power factor measurement device of claim 1, wherein: the zero-crossing detection module adopts a voltage comparator LM 393.
5. The multi-mode power factor measurement device of claim 1, wherein: the data processing module adopts a domestic MCU.
6. The multi-mode power factor measurement device of claim 1, wherein: the display module adopts an LCD display screen for displaying the measurement result.
7. The multi-mode power factor measurement device of claim 1, wherein: and the communication port communicates with an upper computer in an RS485 communication mode.
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| Application Number | Priority Date | Filing Date | Title |
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| CN202220408502.8U CN217085091U (en) | 2022-02-28 | 2022-02-28 | Multi-mode power factor measuring device |
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| CN202220408502.8U CN217085091U (en) | 2022-02-28 | 2022-02-28 | Multi-mode power factor measuring device |
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Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117723792A (en) * | 2024-02-07 | 2024-03-19 | 国网辽宁省电力有限公司 | Real-time reactive compensation detection device based on high-voltage SVG |
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2022
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN117723792A (en) * | 2024-02-07 | 2024-03-19 | 国网辽宁省电力有限公司 | Real-time reactive compensation detection device based on high-voltage SVG |
| CN117723792B (en) * | 2024-02-07 | 2024-04-19 | 国网辽宁省电力有限公司 | Real-time reactive compensation detection device based on high-voltage SVG |
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