SU665274A1 - Method of measuring reactive power and energy - Google Patents

Description

one

The invention relates to the field of electrical measurements, in particular to the measurement of reactive power n alternating current energy.

There are known methods for measuring reactive power and energy, according to which the measured voltage or current is shifted in phase by 90 °, using special phase-shifting circuits, and then converted into power (energy), using watt-meter active power converters, i.e. the formation of reactive power or energy is implemented equations

 +)

. (COt + 6,)

t

Ji /, (+ j.-f. „J

Vff - Wp -

.Sin (COt + h) d.

In this case, the reactive power Q and energy are determined by the expressions

Q f // sinf; Wp llHir.,

However, such methods are valid and applicable only at sinusoidal voltages and currents.

With higher harmonics in the voltage and current, the reactive power is determined by

Q - lij sin, -f h / a sin ... +,.,. +. A ftSin; fA + ....

A shift by the phase of the voltage or current by a quarter of a period (e.g., delay lines) causes the active power (for even harmonics) to be included in the reactive power components. The implementation of the phase shift of 90 ° each harmonic is associated with the difficulties of technical implementation.

The purpose of the invention is to increase the accuracy of measuring reactive power and reactive energy at non-sinusoidal periodic voltages and currents.

This is achieved by the method of measuring reactive power and energy, including multiplying two measured values, integrating them over time, before multiplying, the instantaneous values of the measured voltages and currents of each harmonic decrease (increase) by k times, where k is harmonics, one of the quantities, for example voltage, is differentiated (integrated) and the derivative (integral) is multiplied by another value, for example current.

By instantaneous values of non-sinusoidal currents and voltages, you can determine the reactive power and energy from the expressions

Q

"G.

fk cx

Q, dtdt ... (r);

0 TT o k-i

/ 00

, --l (, rf .. (2);

IS

j,) k dt

t) k

0

k-oo

t k-oo

... (2)

s

0 k

A i. ft co 7-ft CO

-is

")

0 ft l 7- (3 fV .... (3);

6 A I

ft 00

ft X5

47,

-fV

(four); J p ... 7 k dt

0 ft I

.f

ikdfdi ... (4).

The validity of these equations can be verified by substituting the values

Uk (,); and

Jft: - / m Sin (A cot +),

where Mft and fft are the instantaneous values of / rx voltage and current harmonics. According to the invention, the inventive method consists in the following:

1. The instantaneous values of each harmonic, for example, of the j and the current are reduced (increased) by a factor of k, where k is the order of the harmonic. This operation is performed using special frequency filters in

as inductive lines, whose input impedance for a sufficiently large length is equal to the characteristic impedance

1 / g ik cot

Jk cot

2.One of the quantities, for example voltage, differentiate (integrate).

3. The derivative (integral) is multiplied by another quantity, for example, current.

4. The product obtained is integrated over time and energy is measured, and averaged over time, power is measured.

The proposed method allows creating devices for measuring reactive power and reactive energy, using all active power converters based on the principle of integrating the product of the instantaneous values of voltage and current over time.

The drawing shows a diagram illustrating the proposed method for generating reactive power and reactive energy.

Non-sinusoidal currents are supplied to the inputs, the amplitudes of the harmonics of which in blocks 1 and 2 are reduced 4 times. It is also possible to build devices using this method with a decrease in voltage only.

or only current k times. Then, voltage or current harmonics are differentiated (block 3).

These signals are fed to a power meter converter - integrator 4 of the product of two analog signals, the output of which forms reactive power or reactive energy. The basic relative error of the converter did not exceed ± 0.5%.

Claims (1)

Invention Formula A method for measuring reactive power and energy, including multiplying two measured quantities, integrating them over time, characterized in that, in order to improve the measurement accuracy at non-sinusoidal periodic voltages and currents, before multiplying, the instantaneous values of the measured voltages and currents of each harmonic reduce (increase) by a factor of k, where k is the order of the harmonic, one of the quantities — for example, voltage, differentiate (integrate) and the derivative (integral) is multiplied by another quantity, for example, current.