RU2039357C1 - Electricity meter - Google Patents

Abstract

FIELD: electric measurement technology. SUBSTANCE: meter has current and voltage changers 1 and 2, selector switch 3, transformerless power supply 4, multiplier 5 with differential inputs, switch 8, reference voltage source 9, integrator 12, reference-frequency oscillator 13, feedback pulse shaper 14, and pulse counter 15. Newly introduced are selector switch 6, storage capacitor 7, pulse shaper 11, diode bridge in transformless power supply 4, and differential inputs in multiplier 5, as well as switch 10. EFFECT: provision for compensation of additive error of multiplier 5, reduced power requirement. 3 cl, 2 dwg

Description

 The invention relates to electrical engineering and can be used to measure, control and account for electrical power and energy.

Known electricity meters containing a multiplier and a circuit for converting voltage to pulse repetition rate, in which increasing the accuracy of the measurement is achieved by eliminating the influence of additive error by switching the polarity of the input signal and changing the direction of the count in a reversible counter [1] to use a double integration circuit with switched capacitors [2 ]
A disadvantage of the known counters is the complexity of the circuit, due to the need to synchronize the operation of the switches, which reduces the reliability or compensation of the values of the switched capacitors of the double integration circuit.

 The prototype of the invention is an electronic counter with automatic compensation of the offset [3] containing a multiplier, the output of which is connected to the input of the integrator and the analog output of the compensation device, the control output of which is connected to the switches, which, at certain intervals, close the input of the multiplier to the reference potential and bypass the capacitor of the integrator for the time during which the zero voltage comparator connected to the integrator output so acts on the device compensation, consisting of a reversible counter, the outputs of which are connected to a matrix of resistors, the output of which is the analog output of the compensation device, that the output voltage of the integrator becomes equal to zero.

 The disadvantage of this counter is the dependence of the duration and frequency of repetition of compensation cycles on the magnitude of the bias and the measured power, respectively, which introduces an additional error in the measurement result and limits the ability to compensate for the residual voltage of the multiplier when measuring AC power. The need to provide a small time constant for offset compensation reduces the noise immunity of the compensation device.

 The purpose of the invention is improving accuracy and reducing power consumption.

 This goal is achieved in that the additive error is compensated by applying an error voltage to the non-inverting input of the integrator, which is stored by the capacitor connected by the second switch to the output of the multiplier for a period of time determined by the duration of the pulse from the output of the pulse shaper, while one of the inputs of the multiplier is closed to a common wire first switch. The application of the invention allows to simplify the circuit of the electricity meter. The power consumption from the input voltage circuit is reduced due to the use of a diode bridge in a transformerless power supply, and the in-phase voltage between the voltage input and the circuits of the energy meter is suppressed by a differential cascade at the input of the multiplier. The power consumption also decreases when the supply voltage is supplied to the reference voltage source through a switch controlled by a feedback pulse.

 In FIG. 1 shows a diagram of a single-phase electricity meter; in FIG. 2 same, multiphase.

 The electric meter contains input current and voltage converters 1 and 2, a first switch 3, a transformerless power supply 4, a multiplier 5 with differential inputs, a second switch 6, a storage capacitor 7, a first switch 8, a voltage reference 9, a second switch 10, a driver 11 pulses, an integrator 12, a reference frequency generator 13, a feedback pulse shaper 14, and a pulse counter 15.

 The current input is connected through a current converter 1 to the first input of switch 3, the second input of which is connected to a common wire, and the output to input V of multiplier 5. Inputs X of multiplier 5, which are differential, are connected through voltage converter 2 with voltage input and zero point and with the corresponding inputs of the transformerless source 4 power meter electricity. The output of the multiplier 5 is connected to the input of the switch 6, the first output of which is connected to the storage capacitor 7 and the non-inverting input of the integrator 12, and the second to the first inverting input of the integrator 12, the second inverting input of which is connected through the first key 8 to the output of the reference voltage source 9, whose input connected through a second switch 10 to the negative voltage output of the transformerless power source 4. The output of the integrator 12 is connected to the second input of the feedback pulse shaper 14, the first input of which is connected to the output of the reference frequency generator 13 and the input of the pulse shaper 11, the output of which is connected to the control inputs of the switches 3 and 6. The output of the feedback pulse shaper 14 is connected to the control inputs keys 8 and 10 and the counter input 15 pulses.

Input current I and voltage U, converted by current and voltage converters 1 and 2 with coefficients K ₁ and K _u , respectively, are supplied to inputs Y and X of multiplier 5
U _y K _i ˙ IU _x K _u ˙ U (1)
At the indicated positions of the switch 3 and 6, the voltage from the output of the multiplier 5, proportional to the measured power, has the form
U ₅ K ₅ ˙ U _x ˙ U _y ± (U _cm + U _{ost x} +
+ U _{ost y} ), (2) where K _{5 is the} scale factor of the multiplier 5;
U _cm bias voltage of the multiplier 5;
U _ost , U _ost residual voltage at the inputs X and Y of the multiplier 5, respectively, and is fed to the first inverting input of the integrator. If there is a pulse at the output of the shaper 7 pulses, the switches 3 and 6 are translated into the opposite position and the voltage from the output of the multiplier 5
U ₅ '± (U _cm + U _oxt ) (3) is stored on the capacitor 8 and fed to the non-inverting input of the integrator 12. Given that
U _voltage K ₅ ˙ U _y ˙ U _cmx , (4) where U _cmx is the bias voltage at the input X of the multiplier 5, and that the voltage U, and therefore the voltage U _x at the input X of the multiplier 5, varies within small limits, then by choosing the coefficient K _u see (1), it is possible to satisfy the condition
U _x >> U _cmx (5)
Hence
K ₅ ˙ U _x ˙ U _y >> U _ost (6) and the value of U _ost can be neglected.

 Switching switches 3 and 6 occurs with a certain duty cycle Q, the value of which is determined by the shaper 7 pulses, and the stability of the stability of the generator 13 of the reference frequency.

K₁·K_U·K₅·I·U·

(7)
Использование в качестве накопительного элемента конденсатора 7 и достаточно высокая частота повторения выборок позволяют обеспечить высокую помехоустойчивость схемы коррекции аддитивной погрешности, а также при выполнении условия
f_п ≥ 2f₅, (8) где f_п частота повторения выборок;
f₅ наибольшая частота сигнала на выходе перемножителя 5, в счетчике электроэнергии происходит подавление не только напряжения смещения перемножителя 5, а и остаточного напряжения при измерении энергии переменного тока.Thus, the input voltage of the integrator 12 has the final form
U ₁₂ = K ₅ · U _x U _y

K ₁ · K _U · K ₅ · I · U ·

(7)
The use of a capacitor 7 as a storage element and a sufficiently high sampling repetition rate allow for high noise immunity of the additive error correction circuit, as well as when the condition
f _p ≥ 2f ₅ , (8) where f _{p the} sample repetition rate;
f _{5 the} highest frequency of the signal at the output of the multiplier 5, in the electricity meter, not only the bias voltage of the multiplier 5 is suppressed, but also the residual voltage when measuring AC energy.

(9)
Импульсы с выхода преобразователя напряжение-частота (с выхода формирователя 14 импульсов обратной связи), частота следования которых пропорциональна измеряемой мощности, а их количество за единицу времени энергии электрического тока, накапливаются в счетчике 15 импульсов. Применение в бестрансформаторном источнике 4 питания диодного моста (диоды 4В, 4С, 4Д, 4Е), один вход которого соединен через гасящий конденсатор 4А с входом напряжения, другой вход с нулевой точкой, а выходы с входами стабилизатора, состоящего из стабилитронов 4F, 4G и фильтрующих конденсаторов 4I, 4J позволяет получить высокий КПД бестрансформаторного источника 4 питания и соответственно малую мощность, потребляемую счетчиком электроэнергии от входной цепи. Возникающее при этом синфазное напряжение между входом напряжения и цепями счетчика электроэнергии
U_синф U₊ + U_- + 2U_д, (10) где U₊ падение напряжения на стабилитроне 4F;
U_- падение напряжения на стабилитроне 4G;
U_д падение напряжения на выпрямительном диоде, ослабляется входным преобразователем 2 напряжения и дифферен- циальным каскадом по входу Х перемножителя 5.The voltage (7) is converted into frequency by a converter consisting of an integrator 12, a key 9, a reference voltage source 10, a reference frequency generator 13 and a feedback pulse shaper 14 with a coefficient of _Kpn
f _out. = K ₁ · K _U · K ₅ · K _pnch · U · I ·

(nine)
Pulses from the output of the voltage-frequency converter (from the output of the shaper 14 feedback pulses), the repetition rate of which is proportional to the measured power, and their number per unit time of the electric current energy, is accumulated in the counter 15 pulses. The use in a transformerless power supply 4 of a diode bridge power supply (diodes 4V, 4C, 4D, 4E), one input of which is connected through a quenching capacitor 4A with a voltage input, another input with a zero point, and outputs with stabilizer inputs consisting of 4F, 4G and Zener diodes filtering capacitors 4I, 4J allows you to get high efficiency transformerless power source 4 and, accordingly, low power consumed by the electricity meter from the input circuit. The resulting common-mode voltage between the voltage input and the electric meter circuits
U _synf U ₊ + U _- + 2U _d , (10) where U ₊ the voltage drop at the zener diode 4F;
U _is the voltage drop at the zener diode 4G;
U _d the voltage drop across the rectifier diode is attenuated by the input voltage transformer 2 and the differential cascade along the input X of the multiplier 5.

 The introduction of the key 11 between the negative voltage output of the power source 4 and the input of the reference voltage source 10 controlled by the feedback pulse allows to reduce the current consumed from the transformerless power source 4, and therefore the power consumption of the entire electricity meter.

 Figure 2 shows a diagram of an electric meter for measuring power and energy of electric current in multiphase systems (in this case, a three-phase system). The difference from the single-phase version is the use of the corresponding number of multiplication channels 16 and a summing integrator 12.

 Differential voltage inputs attenuate common-mode voltage, which arises between voltage inputs and circuits of the energy meter due to possible asymmetry of the loads in the meter in different phases, making it possible to use a reliable, transformerless power supply that requires fewer elements.

 The use of a transformerless power supply associated with a zero point does not provide the same operating modes of the power supply for various meter switching circuits.

 Electricity meters with differential inputs can be used to measure reactive energy using wattmeter methods.

 Thus, the electricity meter allows to obtain high measurement accuracy due to compensation not only of the bias voltage, but also of the residual voltage of the multiplier, to have a compensation circuit with high noise immunity, provided by the use of a storage capacitor and a sufficiently high sampling frequency, and low power consumption due to the use of a rectification circuit with high efficiency and a switched source of reference voltage, as well as great functionality due to name of the multiplier with differential inputs.

Claims (3)

 1. ELECTRIC POWER METER containing current and voltage converters, a switch, a multiplier with differential inputs, an integrator, a reference frequency generator, a key, a reference voltage source, a feedback pulse shaper, a pulse counter and a transformerless power supply, characterized in that a second a switch, a storage capacitor and a pulse shaper, the input of which is connected to the output and the first input of the feedback pulse shaper, and the output with the control inputs st and second switches, the first output of the second switch is connected with the storage capacitor and the non-inverting input of the integrator, the second output of the first inverting input of the integrator and the input with the output of multiplier with differential inputs.  2. The counter according to claim 1, characterized in that a diode bridge is introduced into it, one output of which is connected through a quenching capacitor to a voltage input, the other to a zero point, and the outputs to the voltage stabilizer inputs of a transformerless power source, a multiplier with differential inputs connected through voltage converter with voltage input and zero point.  3. The counter according to claim 1, characterized in that a second key is inserted into it between the output of the transformerless power source and the input of the reference voltage source, the control input of the second key is connected to the control input of the first key, the input of the pulse counter and the output of the feedback pulse shaper.

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