SU1613966A1 - Digital meter of a.c.power - Google Patents

Abstract

The invention relates to electrical measuring technology and can be used in digital meters of active and reactive power with analog signal multiplication. The aim of the invention is to improve the accuracy of measuring active and reactive power in circuits with an asymmetrical current oscillation with respect to time. This goal is achieved by introducing a differential amplifier 14, the first 12 and second 13 sampling-storage units (BVH), switch 2, controlled by a pulse generator 16, a counter 17, a decoder 18. The meter also contains a source 1 of reference voltages, an input converter 3 voltage, input converter 6 characters, first 4 and second 7 adders, first 5 and second 8 phase shifters, two-pole switch 9, analog multiplier 10, integrator 11, analog-to-digital converter 15. Error compensation, about according to the asymmetry of current oscillations (NCT), is performed in two cycles. In the first cycle, the output voltage of the integrator (I) 11, containing the additive component of the error due to the tubing, is fixed by the first BVH 12. In the second cycle, the voltage And 11 is fixed by the second BVH 13, and this voltage also contains as an additive error due to tubing. Differential amplifier 14 generates a differential signal proportional to the active or reactive power, free from the named error. The measurement accuracy of active and reactive power is significantly increased due to the independence of the measurement result on the value of the transfer factors of the phase shifters and on the asymmetry of current oscillations relative to the time axis. 1 il.

Description

The invention relates to digital measurement technology and can be used in digital active and reactive power meters with analog signal multiplication.

The purpose of the invention is to improve the accuracy of measuring active and reactive power in circuits with asymmetrical current oscillations with respect to time.

The drawing shows the functional diagram of the proposed digital ac power meter o The device contains a source 115

reference voltage, switch 2, input voltage converter 3, first adder 4, first phase shifter 5, current input converter 6, second adder 7, second 20

phase shifter 8, two-pole switch 9, analog multiplier 10, integrator 11, first 12, second 13 sampling-storage units, differential amplifier 14, analog-digital converter 15, pulse generator 16, counter 17, decoder 18 .

The input voltage is connected to the input of the input converter 3 of the voltage source, the output of which is connected to the summing input of the first adder 4, the subtracting input of which is connected to the output of switch 2, the first and second inputs of which are connected to the corresponding the outputs of the source 1 of the reference voltages The current input is connected to the input of the current input converter 6, the output of which is connected to the first summing input of the second adder, the second summing world input 1 is connected to the output of the integrator 11 and to the information input first rows 12 and 13 of the second sample and hold blocks vhody45

the controls of which are respectively connected to the first and second outputs of the decoder 18, the third output of which is connected to the control input of the switch 2. The output of the pulse generator 16 is connected to the counting input of the counter 17, whose information outputs are connected to the information inputs of the decoder 18. The output of the first unit 12 sample-storage is connected to the non-inverting input of the differential amplifier 14, the inverting input of which is connected to the output of the second unit 13

sample storage, and the output of the differential amplifier 14 is connected to the input of the analog-to-digital converter 15.

The transceiver of the first adder 4 is connected to the first input of the bipolar switch 9 and to the input of the first phase shifter 5, the output of which is connected to the second input of the two-pole switch 9, the third input of which is connected to the output of the second adder 8, the output of which is connected to the fourth the input of the bipolar switch 9, the outputs of which are connected to the corresponding inputs of the analog multiplier 10, the output of which is connected to the input of the integrator 11.0

When the active power is measured by an operator's signal, the bipolar switch 9 is transferred to the upper position I. The voltage U (t) and current i (t) are converted into voltage converters 3 and current 6 with coe (1 k conversion factor K and V. respectively. At their exit receive

and, (t) K; U (t); U ,, / t) K-i (t).

(one)

According to the signal from the output of the generator of 16 pulses, the counter 17, consisting of two flip-flops, changes its state. During the first two pulses, the signal from the third output of the deflector 18, switch 2 is in the upper position, and at the time of the third and fourth pulses - reader 2 is in the lower position. In the upper position of the switch 2, the voltage U from the output of the source 1 of the reference voltages is supplied to the subtraction input of the first adder 4 ". For the duration of the second period, the recording permission signal is fed from the first output of the decoder 18 to the control input of the first sampling-storage unit 12. For the fourth period, the signal from the second output of the decoder 18 is fed to the control input of the second sampling-storage unit 13.

Voltage at the output of the first 4 and second 7 adders, when it finds 5I (S 13966

SRI switch 2 in BOpxjroM position are equal

U, (t) K; U (t) - U,; U, j (t) K -Kt) - Z,

(2)

where Z. is the voltage at the output of the integrator 11 in the steady state voltage U, (t) and UjiCt) through

the bipolar switch 9 is fed to the corresponding inputs of the analog multiplier 10, and at its output the voltage is in steady state

the mode is zero

with

, Un (t) KpU, (t) UjjCt), U (t) -Uo, {K2i. (T) + Z, l. (T) i (t) +, Z, U (t) -) -, ; Z,

 0

where Kp is the transmission coefficient of the analog multipliers,

In this case, the voltage at the output of the integrator 11 is equal to Z.O

Up to the moment of equilibrium, the voltage Up (t) is integrated in the integrator 11 which has a time constant J. During the integration time t, the voltage at the output of the integrator 11 becomes

equal

t

ing || Un (t) dt

%

 (t) i (t) dt. ° t

.K, K, z, j% (,, i (t) dtKnUo, t,

 J Z, dt.

0

The time constant of the integrator 11 is chosen such that it is much longer than the period of the studied voltage fluctuations U (t) and current i (t). In order to forgive the presentation of the material, the transfer coefficients of the first 4 and second 7 adders are equal to one. Since, by the condition of the problem, the voltage U (t) has a symmetrical shape with respect to the time axis, the integral component t

U (t) dt O in steady state

one

,, KpKg

with component mode

t

M &

0 (

i (t) dt is denoted by Z

Since the voltage at the output of the analog re-live 10 becomes zero, the voltage Z at the output of the integrator 11 stops changing j Enter the following (and denoted by 1:

CR, K2

U (t) .i (t) P is the averaged value of the product U (t) i (t), J J is the active power R.

i (t) is the averaged value of the current i (t). If the current i (t) oscillates with respect to the time axis, the expression i (t) Z is not equal to zero Taking into account that the expression U (t) is averaged during integration in integrator 11 and is equal to zero in the steady state, have

CRP -, -, Z, O Since K, K, then

one

Ll to Z UQI

(BUT)

The component K Z is numerically equal to the Q error of measurement of the active power due to the asymmetry of the current oscillations i (t) with respect to the time axis (impulse load mode). Voltage (4) during the duration of the second period of the pulse generator 16 is recorded in the first block 12 of the sample-storage.

After the end of the second period, the switch 2 according to the signal from the third

The output of the decoder 18 is shifted to the lower position. To subtract the input of the adder 4, the voltage U is applied (j2 from the output of the reference voltage source).

By analogy with the above operation in the steady state, the voltage at the output of the analog multiplier 10 is equal to

Un4 (t), U (t) - (t) +

+ Z К „K., K, and (t) i (t) - ,, (t) - +, z, Uu), p

55 - KnK2Uo2 i (t) - K „yog 2 0

since U (t) 0,

Hence, the value of the voltage at the output of the integrator 11 is determined.

7 Kg.K, R

and

og

.

(five)

duration time of the fourth

period The voltage Zg on the signal from the second output of the decoder 18 is recorded in the second block 13 sample-storage. The output of the differential amplifier 14 receive voltage

and (z.) to

where K K «K, K.; P

G-1 l

 WozJ

(6)

the gain of the differential amplifier 14,

By the choice of KKK G-i- - 10,

 JoгJ where m Oh, 1, 2, .. o expression (6)

proportional to the value of the measured active power P. At the output of the analog-to-digital converter, 15 have a code

N

ADC

G-1- - -IJ.,

Luo

- (7)

not dependent on asymmetry of current imbalances i (t) with respect to the time axis, which leads to an increase in the measurement accuracy of active power in circuits with asymmetry of current oscillations relative to the time axis o In the future, the device operates similarly to that described above, with each pair of pulses generator 16 updates the voltage in the corresponding blocks 12 and 13 of the sample-storage

When measuring reactive power Q according to the operator's signal, the bipolar switch 9 is moved to the lower position. In this case, the voltages from the outputs of the first 4 and second 7 adders through phase shifters 5 and 8 and the bipolar switch 9 are fed to the inputs of the analog multiplier 10

Since phase shifters 5 and 8 provide a phase shift of 90 between their output voltages in a wide frequency range, the product of the voltage at the output of the phase shifter 5 and the output voltage of the phase shifter 8 produces a voltage proportional to the reactive power Q, Denote the transfer coefficients of the phase shifters 5 and 8, respectively, through K e-and Kg. Then the voltages at the output of phase shifters 5 and 8, respectively, are equal with (2)

0

five

0

five

0

five

0

.

0

U (t) KjD UjCt) - Uo,, - (8) U (t) .ig (t) - Z Z / j,

Moreover, the oscillations of harmonic components in U (t) and Uj (t) are shifted relative to each other by 90, Indices Ut- (t) and igCt) denote the voltages U. (t) and (t), but shifted by 90 one relative to the other. Therefore, the averaged values of the product y (t) i (t) Q are proportional to the value of reactive power Q. Similarly to the case described above, when measuring active power to measure reactive power, it can be shown that in this case, a code proportional to reactive power is generated at the output of the analog-digital converter 15

N, W.

When K, - K, K, -1 - -1 -1 is a multiple of 10, the measurement result is directly proportional to the value of the reaction. the power Q,

Thus, a digital AC power meter improves the accuracy of measuring active and reactive power in circuits with an asymmetrical current oscillation relative to the time axis by ensuring the independence of the measurement result from the value of the transfer ratios of phase shifters and from the current oscillation relative to the time axis.

Claims (1)

Invention Formula Digital measure of ac power, containing input voltage converter, input current converter, analog multiplier, integrator, first and second adders, analog-to-digital converter, source of reference voltages, the output of the input voltage converter connected to the summing input of the first sum torus, the output of the input current converter is connected to the first summing input of the second adder, the second summing input of which is connected to the output of the integrator, the input of which is li ne to the output of analog multiplier, characterized in that for the purpose of measuring accuracy povsh1eni active and reactive power in chains with asymmetrical current waveform relative to the time axis, it introduced a pulse generator sch.etchik; depyfrator, switch, two-pole switch, first and second phase shifters, Q first and second sampling-storage units, differential amplifier,  the output of the pulse generator is connected to the counting input of the counter, the information outputs of which are connected to the information inputs of the decoder, the first and second outputs of which are connected to the control inputs of the first and second blocks, respectively, the third 20 the output is connected to the control input of the switch, the first and second inputs of which are connected respectively with the first and second outputs of the reference voltage source, and the output is connected to the subtracting input of the first adder, the output of which is connected to the first input of a two-pole switch and to the input of the first phase shifter connected to the second input of a two-pole switch, the third input of which is connected to the output of the second the adder and the input of the second phase shifter, the output of which is connected to the fourth input of a two-pole switch connected to the outputs of the analogue multiplier, the integrator output is connected to the inputs of the first and second sampling-storage units, the outputs of which are connected respectively to the non-inverting and inverting inputs of a differential amplifier, the output of which is connected to the input of an analog-digital converter.