JPH02268275A - Detection of power factor - Google Patents

Abstract

PURPOSE:To achieve a detection of a power factor using a specified formula from a power waveform. CONSTITUTION:A current to a load 6 from a power supply source 5 causes a change in magnetic field through a magnetic field generating means 7 to vary resistance values of magnetoresistance elements 8-1 and 8-2. Measuring current is a current flowing through the load 6 and as an element group 8 has diagonal apexes 8a and 8b connected in parallel with the supply source 5, a voltage of the supply source 5 is applied to the apexes 8a and 8b. When a magnetic field generated with the flowing of a load current through the means 7 is applied to the elements 8-1 and 8-2, a corresponding output of the voltage of the supply source 5 is generated at a terminal 9. Since changes in resistance values of the elements 8-1-8-4 cause a change in voltage, an output of the terminal 9 is proportional to a product of a current of the load 6 and a voltage across it to allow measurement of a load power. A microcomputer 29 computes a power factor by a formula I to be shown on a display device 18. Thus, a power factor can be detected simply. In the formula, A is maximum of instantaneous power waveform and B minimum of instantaneous power waveform.

Description

[Detailed Description of the Invention] [Summary] The present invention relates to a method for detecting power information, particularly power factor, and aims to provide a method for easily detecting power factor from a power waveform. From A and minimum value B, power factor =
The power factor is configured to be detected using (A+B)/(A-B).

[Industrial application field]

The present invention relates to a method for detecting power information, particularly power factor, and can be used in all industrial fields that use power and require power factor display.

[Conventional technology]

As far as the inventor is aware, there is currently no power information display device that displays power and power factor at the same time. That is, conventionally, for example, if it was necessary to display instantaneous power (or instantaneous power, integrated power) and power factor on a monitor, it was necessary to use a dedicated power factor display separately in addition to the power display. there were.

[Problem to be solved by the invention]

Some customers have requested that power and power factor be displayed on a monitor at the same time using one device, but it has not been possible to meet this request in the past.

An object of the present invention is to devise a method for easily detecting power factor from power information, and to satisfy the above-mentioned demands.

[Means to solve the problem]

In order to achieve the above object, according to the present invention, from the maximum value A and the minimum value B of the waveform of instantaneous power, the power factor - (A + B)
/ (A B) to detect the power factor.

[Function] Parameters for displaying power include integrated power and instantaneous power. The integrated power (unit: WH) is the integrated value of the power consumed by the device, and is obtained by integrating the instantaneous power. The instantaneous power itself is the instantaneous current i (t) and the instantaneous voltage v (t
).

Here, instantaneous current 1(t) and instantaneous voltage v(t) are expressed by the following equation.

v (t) =v/'TV sin ωt1(t)=j
5in (ωt+φ) However, ■ and ■ are the effective voltage and effective current.

Therefore, the instantaneous power ρ(L) is ρ(t) = 2VI·sln ωt−5in (ω is 10φ). However, φ represents the phase difference between current and voltage.

Also, at this time, effective power P=VI cosφ (unit: W) apparent power
5=VI Power factor expressed as cosφ=P/S.

2VI ・sin (JJ t-5in (ω is 10φ) Therefore, P/S = =2 sin ωt-5in (ω is 10φ) = cosφ-(
cos 2ωt' CO3φsin 2ωt-5in
φ) −cosφ−cos (2ωt+φ)=F(ωL,φ)
Here, in order to evaluate the power factor from the power waveform, θ=2ωt
Then, f(θ) = cosφ−cos (θ+φ) Therefore, θ, − is π−φ (k is an integer) In other words, when θ=θ, f(θ) (power waveform) becomes an extreme value. .

The cases are divided into cases where k is an odd number and cases where k is an even number.

1) k-2n+1 (absolute value is odd) f(θk)
= cosφ−cos ((2n+1)π−φ+φ)”
cosφ−cos (2n + 1) yc= co
sφ+l=A (A≧O)・(1)2) k=2
n (absolute value is even and includes O) f(θk) = co
sφ-cos 12nx-φ10φ)”cosφ-cos
2n π = −10 cosφ=B (B≦0) (2) A is the local maximum value (maximum value), and B is the local minimum value (minimum value).

The following calculation is performed to obtain cosφ using only A and B.

A I +l B I I 1 + cosφl+l
−1+cosφ 1 +cosφ+l cosφ w cosφ ... (3) Thus, the maximum value (local maximum value) A and the minimum value (local minimum value) B of the power waveform
Focusing on the power factor c from IAI-IBI/IAI+IB+
It can be seen that osφ can be calculated.

〔Example〕

FIG. 1 is a diagram showing the basic configuration of an embodiment of the present invention.

In FIG. 1, 5 is a power supply source, 6 is a load, 7 is a means for generating a magnetic field, 8 is a magnetoresistive element group, 8a and 8b are diagonal vertices of the bridge-connected magnetoresistive element group, and 9 is a power source. The value measurement terminal Hex indicates the magnetic field generated by the magnetic field generating means.

In the above-mentioned wattmeter that measures the power supplied from the power supply source 5 to the load 6, the magnetic field generating means 7 is inserted in series with the load 6, and is located at one diagonal vertex 8a.

8a is a power supply source 5 for the bridge-connected magnetoresistive element group 8;
Or connected in parallel with the load 6. Magnetoresistive element group 8
At least one element is arranged so that its resistance value changes depending on the magnetic field generated by the magnetic field generating means 7, and the electric power is determined by the output 9 taken out from the other diagonal vertex 8b, 8b of the magnetoresistive element group. It consists of things.

The current value flowing from the power supply source 5 to the load 6 via the magnetic field generating means 7 generates a magnetic field change and causes the magnetoresistive element 8-1.
Change the resistance value of 8-2. Moreover, the measured current is naturally the current flowing through the load 6. The magnetoresistive element group 8 has one diagonal vertex 8a.

8b is connected in parallel with the power supply source 5 in FIG. 1, so that the voltage of the power supply source 5 is at the diagonal apex 8a.

8b. When no load current flows through the magnetic field generating means 7, the bridge of the magnetoresistive element group is balanced, so no output is generated at the terminal 9. The magnetic field caused by the load current passing through the magnetic field generating means 7 is generated by the magnetic resistance elements 8-1 to 8-1.
When the voltage is applied to, for example, 8-1 and 8-2 among 8-4, the resistance value changes, causing the bridge to become unbalanced, and the output corresponding to the voltage of the aforementioned supply source 5 to be applied to terminal 9. occurs in At this time, it is sufficient to affect one of the elements 8-1 to 8-4. Here, magnetoresistive elements 8-1 to 8-4
The change in the resistance value of is proportional to the current flowing through the load 6, and this change disrupts the balance of the bridge connection and causes a voltage change, so the output of the output terminal 9 is the product of the current flowing through the load 6 and the voltage across it. The load power can be measured proportionally.

The output terminal 9 is connected to a microcomputer 29 via an amplifier 25 and an A/D converter 26. This microcomputer 29 calculates the power factor from the output (power waveform) from the wattmeter and displays it on a display device.

FIG. 2 is a diagram showing an embodiment in which the present invention is implemented as an outlet with a power monitor.

In this embodiment, as shown in FIG. 2, a commercial power plug 15 and an outlet 16 are provided on the side surface of the casing 14, and a keyboard 17 is provided on the surface of the casing 14.
A liquid crystal display device 18 for displaying integrated power (unit: W), integrated power (unit: WH), and power factor (no unit), a key 22 for switching whether the power charge is integrated or instantaneous, a clear key 23, and a key for displaying the power factor. A key 26, a numeric keypad 24 for inputting a fee structure, etc. are provided, and a circuit shown in FIG. 1 is housed inside.

FIG. 3 shows the instantaneous voltage, instantaneous current waveforms, and power waveforms. Only the phases of the voltage (2) and the current (I) are shifted by φ, and the rest are shown at the same level (the same ω). As mentioned above, if the local maximum value A and local minimum value B of the power waveform are found, the power factor c
osφ is determined from equation (3).

Incidentally, the instantaneous power is, for example, 1 to 4 from the power waveform shown in Figure 3.
The integrated power is expressed as the average value of the total sampling value for 1 second by sampling every ms, and the cumulative value of the instantaneous power values is expressed as WH. These calculation processes are processed within the MPU 29.

As described above, one display can display instantaneous power, integrated power,
Three pieces of power information, including the power factor, can be easily obtained from the power waveform.

[Effects of the Invention] As described above, according to the present invention, the power factor can be easily determined from the power waveform, and if necessary, the power factor can be displayed together with the instantaneous power and the integrated power on a single display. can.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a perspective view showing the external appearance of a power display to which the present invention is applied, and FIG. 3 is a diagram showing voltage, current, and power waveforms. 5...Power supply source, 7...Magnetic field generating means, 1
8...Display unit, 29...Microcomputer unit.

Claims (1)

[Claims] A method of detecting from the maximum value A and minimum value B of the instantaneous power waveform using the following formula: power factor = (A + B) / (A - B).