KR900008302B1 - Power factor measuring circuit and method of power meter - Google Patents

Abstract

discriminating a point of time(t0) at which the waveform of the voltage and power signals become zerocrossing point; counting the number of sampling signal by the sampling period of the zero-crossing time point (t0) to a next zero-crossing time point (t1) of the power signal to obtain a value of N1 and counting the number of the sampling signal by the sampling period of the time point (t0) to a next zero-crossing time point (t2) of the voltage and power signals to obtain a value of N; obtaining an angle (alpha) of phase difference from the values of N1 and N; and obtaining the wattless or effective power and the power factor.

Description

Power factor measurement circuit and method of digital integrated power meter

1 is a reactive power measurement circuit using a conventional abnormal phase.

2 is a block diagram according to the present invention.

3 is a detailed circuit diagram of FIG. 2 in accordance with the present invention.

4 is a flow chart according to the present invention.

5 is a diagram showing the relationship between active power, reactive power, apparent power, and power factor.

6 is a waveform diagram between power, voltage and current.

* Explanation of symbols for main parts of the drawings

10: zero potential detector 20: micom calculator

30: A / D converter 40: voltage converter

R1-R12: Resistor SW: Function Adjustment Selector Switch

C1-C2: Capacitor OP1-OP4: Operational Amplifier

IC1: A / D Converter IC2: Micom

The present invention relates to a power factor measurement of a digital integrated power meter, and more particularly, a digital integrated power meter that measures a phase difference between two different waveforms (voltage, current, or current x voltage) in a digital integrated power meter and measures power factor and reactive power therefrom. The present invention relates to a power factor measuring circuit and a method thereof.

In the conventional method, in order to measure power factor and reactive power in a digital integrated power meter, a separate power factor meter is used or a phase shifter configured as shown in FIG. 1 is used to delay the phase of π / 2 [rad] to delay the delay. This waveform was used to calculate the required reactive power.

Therefore, the circuit shown in FIG. 1 used in the conventional ideal phase is not only difficult to accurately match the time constant according to the values of the resistors R15 and R16 and the capacitors C1 and C2, which are time constant elements, but also inferior in precision. Assuming that the above circuit is used, a circuit configured to simultaneously measure active power and reactive power becomes complicated, and a power factor must be measured by using a separate power factor meter. There is a drawback to changing the time constant element.

Accordingly, an object of the present invention is to obtain a predetermined phase difference by inputting a zero crossing point of voltage and power in measuring the power factor and reactive power of a digital integrated power meter, and measuring the power factor and reactive power by software processing without any additional device. The present invention provides a measuring circuit and a method thereof.

It is still another object of the present invention to provide a power factor measurement circuit and a method for enabling accurate measurement without changing an additional device or device even when converting a frequency of an input power source into a power factor and reactive power meter.

In order to achieve the above object, the present invention includes a plurality of comparators having non-inverting input terminals respectively grounded through a resistor, and inputs a voltage waveform signal to an inverting input terminal of the comparator while power = voltage × current at an inverting input terminal of another comparator. A zero potential detector for detecting a zero potential point of the input voltage and the power = voltage × current waveform by inputting a signal corresponding to a waveform; and inputting the power = voltage × current signal to the inverting terminal through a resistor and The inverting terminal is composed of the operational amplifier grounded through the resistor and the output of the operational amplifier to the inverting input terminal through the resistor, and the non-inverting terminal is composed of the operational amplifier grounded through the resistor. A voltage converter converting the positive value and outputting it, and an A / D converter converting the analog output of the voltage converter into a digital value A microcomputer operation unit including ventilation, a microcomputer, and a function selection switch to calculate a phase difference from the detected zero potential time point and perform a process for measuring a predetermined power factor and reactive power corresponding to the function selection of the switch. Characterized in that consisting of.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

FIG. 2 is a block diagram of the power factor measurement circuit of the present invention, and FIG. 3 is a detailed circuit diagram showing an embodiment of the configuration of FIG. 2, wherein the resistor R3 is applied to the non-inverting input terminal (+) of the operational amplifiers OP1 and OP2. ) And (R4) are connected to ground, and a voltage V is input to the inverting input terminal (-) of the operational amplifier OP1 while a voltage x current (VXi) is applied to the inverting input terminal (-) of the other operational amplifier OP2. Input the power (P) corresponding to the waveform of) to detect the zero potential time point of the input voltage (V) and the power = voltage × current waveform (P = VXi) to pull up through each resistor (R1, R2) The zero potential detection unit 10, which is full up, and the power = voltage × current signal P = VXi through the resistor R5 to the inverting terminal (-) of the operational amplifier OP3 through the reference voltage compensation voltage terminal Vd. Input by adding the voltage of) and the non-inverting terminal (+) of the operational amplifier (OP3) is grounded through the resistor (R8) and the bin of the inverting terminal (-) and the output terminal of the operational amplifier (OP3) A ring resistor R7 is connected and connected from the output terminal of the operational amplifier OP3 to the inverting terminal (-) of the operational amplifier OP4 through the resistor R9 and the non-inverting terminal (+) of the operational amplifier OP4. Is grounded through a resistor R11 and a feedback resistor R10 is connected between the inverting terminal (-) of the operational amplifier OP4 and the output terminal to increase the level of the voltage × current signal P = VXi by a predetermined amount (+). Of the voltage converter 40 to convert the analog output of the voltage converter 40 into a digital value, and the A / D converter 30 of the A / D converter 30. The output terminals Q0-Q7 are connected to the data buses D0-D7 of the microcomputer IC1, and the output terminals of the operational amplifiers OP1 and OP2 of the zero potential detection unit 10 are connected to the ports P1, MI1 of the microcomputer IC1. P2) and connect the function selector switch SW to the port P3 to calculate the phase difference from the detected zero potential time point of the zero potential detection unit 10. And a miton calculation unit 20 which controls to perform a process for measuring a predetermined power factor and reactive power corresponding to the function selection of the switch.

The resistors R1 and R2 in the circuit diagram of FIG. 3 are pull-up resistors for the operational amplifiers OP1 and OP2 of the open collector configuration, and the resistors R3 and R4 are the operational amplifiers OP1 and ( OP2) is an offset adjustment resistor, resistor R5 is a current limiting resistor, resistor R6 is a resistor for adding voltage Vd, and resistor R7 is an amplifier of OP3. Amplification gain resistance.

In addition, the resistor R8 is for offset adjustment of the operational amplifier OP3, and the resistor R11 is for offset adjustment of the operational amplifier OP4, and the resistors R9 and R10 are for the operational amplifier OP4. An amplification resistor, and the resistor R12 is for limiting the current of the power supply voltage Vcc. IC2 is a conventional micom, and is configured to store a series of control procedures and necessary data for performing power factor measurement of an integrated power meter according to the present invention.

FIG. 4 is a flowchart showing the procedure of the processing performed by the microcomputer operation unit 20. Each processing procedure for measuring active power or reactive power is selected in response to the actual state of the function selection switch SW. Is a time point t0 at which the waveforms of the voltage and the power signal become zero crossing points through the input ports P1 and P2 of the microcomputer IC2 when the first process and the effective power measurement are not measured in the first process. A second step of determining a and accumulate the number of sampling signals by a predetermined live fling period from the zero crossing time point t0 to the next zero crossing point t1 of the power signal at the zero crossing time point from the second process. The number of sampling signals as the sampling period from the zero crossing time t0 to the next zero crossing point t2 at which the voltage signal and the power signal are zero-crossed at the same time as N1. The third process of accumulating s as an N value, the fourth process of obtaining a predetermined phase difference α from the N1 and N values of the third process, and the value of the phase difference α of the fourth process And a fifth step of obtaining a predetermined selected reactive power or active power and power factor from.

FIG. 5 is a relationship diagram showing the relationship between active power (P), reactive power (Q), apparent power (R), and power factor (cosα), and FIG. 6 shows power (P = VXi), voltage (V), and This is a waveform diagram of the current (1) relationship.

Therefore, a specific embodiment of the present invention will be described in detail with reference to FIGS. 1 to 6, when the voltage V is input through the inverting terminal (−) of the operational amplifier OP1, the non-inverting terminal (+) The zero potential Va is detected at the output terminal of the operational amplifier OP1 by comparison with the reference value through the resistor R3 and is input through the input port P1 of the microcomputer IC2, and at the same time, power = voltage × current R = VXi is inputted through the inverting terminal (-) of the operational amplifier OP2 and zero potential Vb is output to the output terminal of the operational amplifier OP2 by comparing the reference value through the resistor R4 of the non-inverting terminal (+). Is detected and input to the other input port P2 of the microcomputer IC1.

On the other hand, since the power P has a positive value and a negative value as shown in FIG. 6, the voltage P and the voltage conversion of the reference voltage compensation voltage terminal Vd input through the resistor R6. When inputted to the unit 40 and added, the potential level is adjusted upward to have a positive value. That is, since the amount (+) of the voltage (Vc) corresponding to the power (P) input to the voltage converter 40 has both negative values, the voltage as shown in FIG. (Vc) extends from -A to + B. Therefore, when the reference voltage compensation voltage is applied to the reference voltage compensation voltage terminal Vd through the resistor R6 connected to the inverting terminal (−) of the operational amplifier OP3 and added by the operational amplifier OP3, the operational amplifier OP3 is added. The output voltage Ve is expressed by the following equation.

Where R5, R6, and R7 are the resistances of the corresponding resistors, respectively, when R5 = R6 = R7, the voltage Ve is determined by the voltage of the reference voltage compensation voltage terminal Vd. Since only the voltage compensation and the amplification factor 6b in FIG. 6b are inverted without the amplification factor in the operational amplifier OP3, the maximum value is 0 and the minimum value is -B. The reason for adding the voltage of the reference voltage compensation voltage terminal Vd to the voltage Vc is that the voltage Vc level is low so that the output voltage Ve of the operational amplifier OP3 cannot obtain the desired output. To compensate for the level in advance.

The addition operation of the operational amplifier OP3 is described in detail on page "606-607" of "Microelectronics", the theory of which is well known. Therefore, if the inverting amplifier composed of the resistors R9 and R10 and the operational amplifier OP4 is inverted again, the output voltage Vg is always present between positive values 0 to + (A + B). The output voltage V9 of the operational amplifier OP4 is input to the A / D converter 30 to be converted into a predetermined digital value and input to the microcomputer IC2 through the data bus D0-D7 of the microcomputer IC2. The same process as in FIG.

In FIG. 6, the effective power amount Pa can be represented by a square wave with the instantaneous values of current and voltage with respect to the time t if the sampling time ts is very small, and the effective value of the square wave is the amplitude at time t (Fig. Im and Vm), the effective power amount Pa is expressed by the following equation (1).

(Where T is the period of the power waveform P)

Referring to FIG. 5, the relationship between active power (P), reactive power (Q), apparent power (R), and power factor (cosα) is as follows.

P = Rcosα... … … Formula (2)

Q = Rsinα... … … Formula (3)

Q = Rtanα... … … Formula (4)

Therefore, in FIG. 6, the zero crossing point at which the voltage V and the strategy P become zero potential is detected by the operational amplifiers OP1 and OP2 of the zero potential detection unit 10, and thus the input port P1 of the microcomputer IC2. When input to P2, the radian display angle from the zero crossing point t0 where the voltage V and the power P become zero simultaneously to the time t1 when the power P becomes zero When α is one cycle T of power P is 2π [rad], and the sampling number at that time is N, the sampling number from the time point t0 to the time point t1 is N1. The relation holds.

Therefore, the power factor (PF) is as follows.

At this time, if the above equations (3) and (4) are applied, the reactive power amount Q can be obtained by the following equation.

When Q = Rsinα and the effective power amount P is obtained, P = Rcosα.

Here, the apparent power R is inputted to the inverting terminal (-) of the operational amplifier OP3 of the voltage converter 40 through the resistor R5 and outputted as an analog value. The microcomputer IC2 receives and outputs a predetermined digital value through the A / D converter 30.

Referring to the flow chart of Figure 4 will be described the power factor or the effective, reactive power measurement process as follows.

The microcomputer IC2 checks whether to perform measurement with active or reactive power in step 4a according to the setting state of the switch SW connected to the port P3. For example, when measuring reactive power instead of active power measurement in the process (4a), the zero crossing points P1 = 0 and P2 = 0 are set to the input ports P1 and P2 of the microcomputer IC2 ( In the process of 4b), the controller detects zero ("0") and counts the sampling number values N1 and N in the processes (4c and 4j) as shown in Equation (5) from the time of detection, and again the input port P2. When the voltage x current (P = VXi) signal becomes 0 and the time point when the voltage V signal of the input port P1 becomes 0 is checked in the processes (4d) and (4k), and when "0", N1 and The count of N is stopped in the process of (4e, 4l), and α value is obtained by the internal arithmetic processing of the microcomputer IC2 in the process (4f) by the above formula (5).

Therefore, reactive power (applied by Eq. (3)) and power factor (applied by Eq. (6)) can be obtained from (4g, 4h), respectively. On the other hand, the active power calculation is carried out by the calculation process of the microcomputer IC2 in the same manner as the electric process, but by applying the above equation (2) after the α value is obtained, it is possible to sufficiently measure the active power P as above.

As described above, the present invention detects and inputs the zero crossing point of the voltage V and the power P without using an abnormal device in the reactive power measurement and the power factor measurement in the digital integrated power meter to input the input port P1 of the microcomputer IC2. By measuring the number of sampling of the voltage and power waveforms according to the input state at), (P2) respectively, a predetermined phase difference can be obtained, and software processing can be performed without additional circuitry when measuring power factor and reactive power by using this. In addition, even if the frequency of input power fluctuates, it can be applied in other regions without any additional hardware or change.

Claims (3)

In a power factor measurement circuit of a digital integrated power meter, a resistor (R3) and (R4) are connected to a non-inverting input terminal (+) of the operational amplifiers OP1 and OP2 to ground, and an inverting input terminal (-) of the operational amplifier OP1. The voltage V is inputted to the inverting input terminal (-) of the operational amplifier OP2, and the power P corresponding to the waveform of voltage x flow VXi is input to the input voltage V and the voltage x current. The zero potential detector 10 detects the zero potential time point of the waveform P = VXi and pulls up through the resistors R1 and R2, and calculates the voltage X current signal P = VXi through the resistor R5. The inverting terminal (-) of the amplifier OP3 is added with the voltage of the reference voltage compensation voltage terminal Vd, and the non-inverting terminal (+) of the operational amplifier OP3 is grounded through the resistor R8 and the inverting terminal A feedback resistor R7 between (-) and the output terminal of the operational amplifier OP3 is connected, and the operational amplifier OP4 through the resistor R9 from the output of the operational amplifier OP3. The non-inverting terminal (+) of the operational amplifier OP4 is grounded through a resistor R11, and a feedback resistor R10 between the inverting terminal (-) and the output terminal of the operational amplifier OP4. And a voltage converter 40 for converting and outputting the level of the voltage = voltage × current signal P = VXi to a predetermined positive value, and an analog output of the voltage converter 40. A / D converter 30 for converting the signal to a digital value, and the output terminal Q0-Q7 of the A / D converter 30 are connected to the data bus D0-D7 of the microcomputer IC1 and the zero potential detector The output terminals of the operational amplifiers OP1 and OP2 of FIG. 10 are connected to the motors P1 and P2 of the microcomputer IC1, the function selection switch SW is connected to the port P3, and the zero potential detection unit 10 is connected. A process for calculating a predetermined power factor and reactive power amount corresponding to the function selection of the switch by calculating a phase difference from the detected zero potential time point Digital integrated power factor measuring circuit of the meter, characterized by consisting of a microprocessor calculating unit 20 for controlling ever performed. A power factor measurement method of a digital integrated power meter, the first process of selecting each process for measuring the active power or the reactive power corresponding to the actual state of the function selection switch SW, and the process at the first process A second process of determining a time point t0 at which both the voltage and power signal waveforms become a zero crossing point after the selection; and a next zero crossing point t1 of the power signal from the zero crossing time point t0 of the second process. By accumulating the number of sampling signals by a predetermined sampling period up to a value N1, the sampling period from the zero crossing time t0 to the next zero crossing point t2 where the voltage signal and the power signal are zero-crossed simultaneously. A third step of accumulating the number of sampling signals and setting it as an N value; a fourth step of obtaining a predetermined phase difference α from N1 and N values in the third step; And a fifth process of obtaining a predetermined selected reactive power or active power and power factor from a value of the phase difference α in 4 steps. The power factor measurement method according to claim 2, wherein the phase difference angle (α) and the power factor are obtained by applying the following equation from the accumulated values N1 and N of the sampling number.

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