FI110964B - Method and apparatus for measuring power in an AC system - Google Patents

Description

110964

The present invention relates to a method for measuring power in an AC system according to the preamble of claim 1, and to a method for measuring power in an AC system.

The invention also relates to an apparatus according to the preamble of claim 5.

10 For purposes of this application, the term "consumable" refers to equipment connected to a mains power source that either draws electrical power from the grid or supplies electric power to the grid.

KWh meter. wherein the method of the invention can be used to measure power normally by first generating a signal proportional to the current of the wearer and a signal proportional to the voltage of the wearer. The instantaneous effective power is then calculated by multiplying, at a given moment, the value of a signal proportional to said current and the value of said signal proportional to voltage. In turn, the energy consumed in a consumable object is calculated by integrating power over a desired time period.

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The current measurement of a consumable object is usually based on a resistance that converts the current into a voltage, an iron or ferrite core current transformer. induction phenomenon. where the primary current induces a voltage in the secondary windings, to magnetic sensors (e.g., a Hall sensor or a magnetoresistive sensor) or, in some cases, to a light-25 fiber sensing a magnetic field. In all but a resistance-based converter, the measurement is based in one way or another on the utilization of the magnetic field generated by the primary current.

In the induction phenomenon, the alternating current passing through the primary circuit of the current converter produces a magnetic flux that changes with respect to the current. This magnetic flux, in turn, induces a voltage in the secondary circuit of the current converter. This voltage of the secondary converter secondary circuit 'is proportional to the time derivative of the alternating current of the primary circuit of the current converter.

In order to determine the value of the alternating current flowing in the primary converter circuit, the voltage of the secondary converter secondary circuit must be integrated over time.

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Prior art solutions integrate the current measurement signal from the secondary circuit of the current converter. whereupon the integrated current measurement signal is multiplied by the voltage measurement signal to determine the power. Such solutions typically employ active integrators, i.e. amplifiers. This is because the output signal of the inductive current converter is generally low. While the passive RC filter still attenuates the signal to about one-hundredth of the frequency at the fundamental frequency, the passive integrator has generally not been used in prior art solutions.

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Applicant's FI patent 98865 discloses an inductive method for measuring AC, a measuring sensor for measuring AC and its use in a kWh meter. In the method, at least a first-order gradiometer is fitted inside or in the immediate vicinity of the current conductor system, whereby the current flowing through the current system induces a voltage in the gradiometer. The shape of the conductor system and the shape of the coil gradiometer are matched such that the output signal is substantially independent of minor changes in the position of the conductor system and the gradiometer.

Applicant FI Patent Application 20001048 discloses an inductive current converter for measuring alternating current. The current converter comprises a primary current conductor. having two substantially circular current loops connected in parallel. The current loops are concentric overlapping in parallel planes spaced apart. Between the current loops, there is at least one 25 gradiometer in a plane or planes parallel to the levels of the current loops. The primary current passing through the current loops of the primary current conductor is coupled via said magnetic field to said at least one gradiometer and generates a voltage proportional thereto to the primary current.

The main features of the method according to the invention are set forth in the characterizing part of claim 1.

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The main features of the apparatus according to the invention are, in turn, shown in the characterizing part of claim 5.

The solution according to the invention is based on the realization that when it comes to measuring, the electrical power of the 5 consumables does not necessarily need information about the actual value of the consumable current. If the current converter provides a current measurement signal from its secondary circuit. which is proportional to the time derivative of the current of the consumable, the integration may be applied instead of the current measurement signal of the secondary converter secondary circuit to the voltage measurement signal of the voltage converter. Electrical power is obtained by multiplying a current measurement signal proportional to the time derivative of the current by an integrated voltage measurement signal.

The signal can be integrated over time in many different ways. The methods may be analogue, either based solely on passive RC or LR circuits or based on active, i.e., amplified, circuits. In digital kWh meters, integration can be accomplished numerically by various time or frequency domain algorithms. The integration functions satisfactorily when it approximates the transfer function Hi (jo>) = (jcö) 'of the ideal integrator sufficiently well in the respective frequency range. For example, in the kWh measurement, the important frequency range is generally about 10 H / - 1 kHz. Also, the integration must not produce interference signals in other frequency bands. Integration is 20 operations that emphasize low-frequency signals and DC amplification is infinite.

The practical integrators are intended to be implemented in such a way that their output signal contains mainly the integral of the useful part of the input signal. The intention here is thus that the integrator approximates the ideal integrator with sufficient accuracy in the desired frequency range and that it dampens components outside this frequency range. Also, it should not generate any new signal in the output signal, such as, for example, an IX, component or low frequency noise. The integrator must be sufficiently linear so that it does not produce too many harmonic components.

Regardless of the method by which the integration is performed, it is advantageous if the signal to be integrated is of a suitable size or easily convertible, does not contain a flat part and is narrow band. Therefore, integration is more advantageous to apply to the consumed voltage signal than to the consumable current derivative because: the consumable voltage signal (e.g. 230V) does not usually need to be amplified, thus avoiding a harmful DC component due to the offset voltage of the amplifier is so it is a very small consumer target voltage signal is much narrower than the consumer 10 target current signal. thus simplifying the integration task.

Thus, in the method according to the invention, the actual current of the consumable cannot be determined, but the electric power and energy consumed by the consumable can still be calculated.

The solution according to the invention will now be described with reference to the circuits shown in the figures of the accompanying drawings, which, however, are not intended to be limited thereto.

Fig. 1 is a schematic diagram of a measuring circuit of one of the known single-phase k 1 Ym-miUs 20.

Figure 2 illustrates an active, i.e. amplified, per se known integration with which the invention can be implemented.

Figure 3 shows a passive integration known per se by which the invention can be implemented.

Figure 1 is a schematic diagram of a measuring circuit for a single-phase kWh mill known per se. The voltage branch measuring circuit comprises a protection circuit 11. The function of which is 30 to protect the kWh meter from overvoltage peaks from the mains. The protection circuit 1 1 is followed by a voltage circuit 12. which is coupled to the voltage of the consumable to be measured between the phase conductor and the neutral conductor. In the voltage circuit, a voltage level suitable for the multiplier 15 ≤ 5 110964 is formed from the mains voltage. The current branch measuring circuit comprises a current converter 13 followed by a preamplifier 14 for amplifying the voltage signal from the secondary circuit of the current converter 13 to a suitable level for the multiplier 15. The multiplier 15 multiplies the signals proportional to the voltage and current of the consumable to be measured, thereby obtaining a value of 5 for the respective power of the consumable. The power is integrated over time to produce the electrical energy consumed by the consumer. The measuring circuit calculator 16 can be a mechanical tumbler counter or a digital LCD display. The measuring circuit further includes standard pulse outputs 17 with a pulse rate proportional to electrical energy consumption, pulses per kWh.

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In prior art solutions, the signal to be supplied to the current branch multiplier 15 is integrated before the value of the current measurement signal is multiplied by the value of the voltage measurement signal to determine power. It is, therefore, an inductive power converter 13, the secondary-side voltage of the integration, wherein an integrator is placed in the power branch of the connection 15 of the multiplier 15 input port.

In the solution of the invention, the signal to be applied to the voltage branch multiplier is integrated before the value of the voltage measurement signal is multiplied by the value of the current measurement signal to determine the power. Instead, the input signal multiplier 15 does not integrate 20. The integrator is positioned in a voltage branch at the input port 15 of the multiplier.

Referring now to Figures 2 and 3, two integrators known per se will be described. which are suitable for the solution according to the invention.

Fig. 2 shows an active integrator 20, i.e. an amplifier with an amplifier. : ,,, & > 1 // (/ cy) = - - -, R, jcoCR2 +1 The circuit must be dimensioned such that the term comiC-R2 is sufficiently large, preferably> 100.

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The switching transfer function Η (] ω) approaches' at high frequencies (ω> (Omin) function: JOJCR, which can be written as: 5 which is a constant times the transfer function of the ideal integrator. At low frequencies the transfer function approaches -R2 / R1, which is DC Also, the amplifier's own offset voltage is summed to the integrated signal by a factor of -R2 / R !.

In a situation where the phase voltage Uin = 230 V of the 10 consumables connected directly to the integrator, e.g. Thus, the phase error of the integrator at 50 Hz is already relatively small, the signal size at the integrator output is suitable for further processing and the DC gain is about 1.

In a situation where a small signal of a few volts is applied to the integrator, the ratio R 2 / R 1 should be high, preferably> 100. This will increase the DC gain to at least 100. which may be detrimental.

The active integrator shown in Figure 2 is better suited for integrating a large signal, e.g., 230 V phase voltage, than for a small signal proportional to a current derivative.

Figure 3 shows one simple passive RC integrator 30. The transfer function of the circuit is: ,: / <z> RC +1

The circuit must be dimensioned such that the term comin-R-C is sufficiently large, preferably> 100.

110964 This circuit functions in the same way as the circuit shown in Figure 2 if R2 = R1 is selected in the circuit shown in Figure 2. However, this passive circuit does not require an amplifier, which also avoids the harmful offset voltage of the amplifier.

, 5 The circuit can be dimensioned such that R = 1 ΜΩ and C = 300 nF. In this case, the circuit suppresses the phase voltage of the consumable to a voltage of 230 V, which is a suitable value for further processing of the signal.

Only a few examples of the application of the solution of the invention are given above and it will be apparent to those skilled in the art that they may be subject to numerous modifications within the scope of the inventive idea set forth in the appended claims.

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Claims (8)

8 110964 1. A method of measuring power in an AC system. wherein the current of the wearer is led through a first converter based on the induction phenomenon to the measuring circuit. Wherein the measuring circuit has a current measurement signal proportional to the time derivative of the current of the wearer, and wherein the voltage of the wearer is applied directly or through another converter to the measuring circuit, wherein the measuring circuit provides a voltage measurement signal characterized in that the integration is applied to the voltage measurement signal instead of the current measurement signal and that the instantaneous power of the wear object is calculated by multiplying at each calculation moment the value of the current measurement signal by the value of the integrated voltage measurement signal. Method according to Claim 1, characterized in that the integration of the voltage measurement signal is performed by an active RC circuit based on the operational amplifier. 15 Method according to Claim 1, characterized in that the integration of the voltage measurement signal is performed by a passive RC circuit. Method according to claim 1, characterized in that the integration of the voltage measurement signal is performed numerically by a time or frequency domain algorithm. Apparatus for implementing the method of claim 1, comprising a first converter (13) based on an induction phenomenon. converting the consumable current into a current measurement signal proportional to the time derivative of the consumable current. and the narrator (15). wherein the voltage measurement signal proportional to the voltage of the wearer is multiplied with the current measurement signal, characterized in that the apparatus further comprises an integrator (20.30). whereby the voltage measurement signal is integrated, after which the instantaneous power of the wear object is calculated by multiplying, at each calculation moment, the value of the current measurement signal by the value of the integrated voltage measurement signal. 30 Apparatus according to claim 5, characterized in that the integrator (20) is an active RC circuit with an operational amplifier. 9 110964 Apparatus according to claim 5, characterized in that the integration (30) is a passive RC circuit. 8. Apparatus according to claim 5, characterized in that the integration is a numerical method based on a time or frequency domain algorithm. J 110964