FI118931B - Apparatus and method for measuring electrical power - Google Patents

Description

1118931

Apparatus and method for measuring electrical power

The invention relates to an apparatus for measuring electrical power according to the preamble of claim 1.

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The invention also relates to a method for measuring electrical power.

An embodiment of the invention is also an electrical energy measuring device and method.

10 Million Watt hour meters are manufactured 100 million a year. Recently, the focus has shifted to the so-called. from inductive to electronic kilowatt hour meters. Furthermore, the importance of telecommuting is increasing. In addition to the actual kilowatt-hour meters, power is measured on a number of machines and devices. There are pressures to bring power measurement to almost all devices, but due to the cost of the power meter and the lack of an inexpensive interface 13, this is not yet the case. With the availability of a generic and affordable interface and power measurement component for machinery and equipment, as well as for factories and at home, the market potential for the components would be several billion pieces each year. The current Kilowatt hour meters are not yet integrated at the component level. This is due to the limitations of high voltages and high currents, and the requirement for 20 precision and high dynamic range.

Nowadays, a company that sells energy meters sells the product to an electric company that installs it in companies or households. If the business changes as a • a ***** component manufacturer sells a power measurement unit to a home appliance manufacturer, for example, * * * 25 power metering would be integrated very quickly into one circuit.

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. At present, the new Kilowatt hour meters used in households will cost the electricity company approximately € 30, if not included with eg a telemetry. The most common technique 1 · * '* is to use current transformers. This solution is expensive because the current transformer itself • aa; '30 is not usable because it is saturated with dc current (current regulations require ia · "* meter to withstand direct current). One solution is the use of two current transformers a ·· V * serial connection, but this adds to the meter cost One solution used is to set a · 2 · 118931 current transformer into a resistive current divider, which reduces both AC and DC power and does not saturate the transformer. This method is inexpensive and works, but multiplication has to be done with an expensive IC circuit, plus 5 inductors must be large enough to have enough voltage from the magnetic field. Resistance shunt is also used in kilowatt hour meters, but the problem is n resistance without overheating at high currents, a common solution, especially for single-phase kWh meters. In all of the above solutions, multiplication is done by the IC.

Hall sensors have long been used in kilowatt hour meters, but their high temperature dependence and poor sensitivity have made the method difficult. In the Hall sensor, multiplication occurs directly in the component because the Hall voltage is the product of the current through the 15 magnetic fields and the Hall component.

From 1978 to 1980, the applicant developed an electronic kilowatt hour meter called watt watch. The purpose of the product was to allow households to monitor the power consumption of various devices with an inexpensive meter. Current measurement • · ·:. * 20 was based on resistor shunts and multiplication was done by pulse width to height converter. 1984 ··· · · 1987 - The applicant developed a microprocessor based kilowatt hour meter. This was the first microprocessor based meter in the world and is now used in power quality * * * · "* meters. From 1996 to 1998, the applicant developed a kilowatt hour hour meter based on gradiometric induction coils. In this context, an integrated circuit was also developed where the multiplication of current and voltage was done by sigma,. delta converters and digital multipliers.

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The object of the invention is to solve the problems of the prior art described above and, for this purpose, to provide an entirely new type of apparatus and method for measuring electrical power.

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The invention is based on the fact that the sensor component is implemented as a silicon micromechanical structure such that the multiplication of the current and the voltage occurs directly in the measuring component.

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In one preferred embodiment of the invention, power is generated as a time integral to determine energy consumption.

More specifically, the apparatus according to the invention is characterized by what is shown in the characterizing part of claim 1.

The method according to the invention, in turn, is characterized by what is stated in the characterizing part of claim 12.

IS The invention provides considerable advantages.

By the method according to the invention, the instantaneous moment can be varied by means of a spring constant and by the current flowing in the winding. Current is measured without galvanic contact. The component measures the actual power directly with one component. The method does not require 20 expensive ICs, but a cheap CMOS chip is enough. The meter has a wide dynamic range.

·· · ί. * The component can be used to develop a power meter for various accuracy classes. The sensor is not sensitive to · · · · · i t ί · * rectilinear and if we use gradiometric reading, it is also not for the external · * »* * ·“ field. The invention enables measurement of reactive power in addition to actual power. If • «***** the current flowing through the MEMS component is supplied from DC voltage, the component will convert to • · * * ·” * 25 magnetometers and can be used to measure current. Further, the device according to the invention e m **** is advantageous in mass production.

The invention will now be described by way of example and with reference to the accompanying drawings.

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Figure 1a is a top plan view of one of the inventive power meters.

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Figure 1b is a sectional side elevation view of the power meter of Figure 1a.

Figure 2 is a schematic view of another energy meter according to the invention.

Figure 3 is a diagrammatic view of a third measuring array according to the invention.

Figure 4a is a schematic top plan view of a fourth measuring stream according to the invention.

Fig. 4b shows a cross-section of the solution of Fig. 4a in the plane Λ-Α.

The present invention provides a new way of making a kilowatt hour meter which is not sensitive to direct current and where the multiplication of current and voltage occurs directly in the component to be measured.

Figures 1a and Ib show a schematic diagram of a micromechanical power meter. The purpose of the solution of Fig. 1 is to measure the power passing through the phase conductor 3. The voltage to be measured, the voltage between phase conductor 3 and neutral conductor 20, is applied between terminals 8 and 9 ·· · ί V of coil 2 from voltage divider 50 and thus converted into coil 2 in wire. A switch 51 and a phase inverter 52 may be used for mechanical stabilization of the sensor component:. *, So that the direction of the current flowing in the winding 2 periodically can be changed. The figure shows a • e * ··· 'flip-flop type moving plate 1, integrated on both sides • · · ***** coils 2 for generating 25 magnetic fields. The current conductor 3 to be measured passes close to the winding, generating. magnetic field gradient sensor component 4. Plate 1 drive for wires 3 * ♦ * • · ·

With reference to H1 and 7, capacitors are measured capacitively by means of the electrodes 6 illustrated in Fig. 1b, and when the spring constant of the flip-flop 1, 5 is known, the effective force, which in turn is directly proportional to the power supplied by the power cord 3 • * ** ·· *. Alternatively, as will be described, the electrodes 6 may alternatively be used for force feedback, whereby the effective force is obtained through a feedback variable (current or voltage).

According to Figure 2, another alternative is to coat the plate 21 with a metal layer 27 and 5 to generate a vortex current therewith by a stationary winding 22 in the component located at a base 26 spaced from the plate 21. The winding 22 is coupled similarly to and component manufacturability. If we place the component near the power conductor 23, the current will generate a magnetic field on the moving plate 10 21. The current flowing through the plate 21 generates a magnetic dipole at the voltage to be measured. The force exerted on the plate is the current iu in the winding 22 and the Btrist input F = iuxBi of the magnetic field. If we consider the end result as a scalar, we find that for sinusoidal signals, the force F = aUI cos φ, where φ is the phase difference between the voltage and the wire, and a is a constant. That is, by measuring the force integral in 15 times we get to measure the electrical energy. It is essential in this invention that the multiplication operation required for power measurement is performed directly in the measuring component. On the other hand, high sensitivity allows the high current not to be galvanically applied to the large component, but it is sufficient that the power cable passes close to the component. There are other fascinating features of this method, ··. ·, 20, but they will come up later when we describe the electronics of the meter.

• · • · • · «*« • · · •. ***. Next, one possible realization of the sensor is described. The force is measured e.g.

·· «• by making a structure of a flip-flop, where on both sides of the flip-flop there is a coil 2 generating a magnetic dipole · * ·: ***: 25, as shown in Figure 1. On both sides there is a plurality of electrodes 6 for capacitively measuring the position of the flip-flop 4 and, on the other hand, for keeping the flip-flop position constant by electrical feedback. The measured power t ·· generates a flip-flop force, but the feedback voltage is adjusted so that the flip-flop · '·' · 4 remains at its equilibrium point on average. When the flip-flop is in equilibrium, the mean value of • ♦ · *** · 30 is equal to the actual power to be measured. The position of the flip-flop ···. ··· is measured capacitively. If the feedback has different electrode sizes, you cannot scale the *, * · · feedback voltage. This means that if the power to be measured is low, • 9 999 118931 6 is fed back to the flip-flop via a low capacitance electrode. A small electrode leads to the need for high voltage to reach equilibrium. For high power, the feedback voltage is applied to a large electrode. For example, different feedback electrodes are illustrated in Fig. 2 by reference numeral 25 and S measuring electrodes are indicated by reference numeral 24. This allows for dynamic range expansion. In other words, by using, for example, a constant voltage and a constant length pulse for compensation, we obtain power directly from the pulse train frequency. In addition, reactive power causes us to drive pulses to the opposite side of the flip-flop. The measurement and feedback is made against ground 28. In the end, the difference represents 10 of the actual power and the number of '' negative 'pulses represents the proportion of reactive power. This means that both actual and reactive power can be measured with the same component. In addition, by using pulses of different lengths or different electrodes, we can extend the dynamic range of the meter.

15 Micromechanical components often exhibit creep due to surface charge and mechanical instabilities. If we reverse the direction of the voltage, the direction of the magnetic dipole, and hence the force exerted on the flip-flop, also turns. If we reverse the direction of the voltage every 20 cycles, for example, we will be able to eliminate creep almost completely. The voltage is reversed, for example, by 20 micromechanical or semiconductor switches. The connection for changing the voltage direction M · • V is also shown in Fig. 1a.

If we consider both creep removal and force feedback, we get a power meter whose accuracy depends solely on the stability of the reference.

a * · · * · "* 25 Also, since the power feedback is done directly digitally, digitizing the signal ** ·· * does not increase the inaccuracy of the meter. If the position of the power cord and the component does not change, we can easily build a low cost meter.

Figure 3 illustrates a stiffener where the current conductor is modified such that the magnetic field gradient at the sensor is small. Due to the symmetry of the power cord, ··· V: the other field of the magnetometer is the same but opposite sign. This rigidity a * a m * • 9 a ·· 118931 7 results in the sum of the two power meters being independent of an external homogeneous 50 Hz magnetic field. The design of the power cable also results in that the power reading does not change in the first order even if the component moves, for example due to thermal expansion, in relation to the power cable.

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Kilowatt-hour meters must be capable of withstanding a very strong 50 Hz (or 60 Hz) external magnetic field without showing a false reading. One way to eliminate the external field is to use the flip-type MEMS component 4 of Figure 1, but placing current windings 2 (as shown) on both sides of the flip bound that only field 10 gradient caused by current line 3 generates flip turning force. The component should be reasonably high in order to obtain a sufficiently high sensitivity and to prevent the component from being sensitive to the position of the power cord and component.

It is also possible to make the arrangement according to Fig. 3. Here, two identical MEMS-kilowatt hour sensors 31 and associated IC circuit 34 are placed in a housing 30 adjacent to the power line 33, and sufficient sensitivity is obtained even if the MEMS component 31 is less than 1 mm x 1 mm. Because the elements of the gradiometric measurement have a different component, we can spread the base 20 up to 5mm to 8mm without significantly increasing component costs. It is also noted that MEMS component 31 does not need to be vacuum packed as we can allow gas damping in this embodiment.

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Figures 4a and 4b illustrate a fourth embodiment of the invention, in which the micromechanical component 41 is disposed inside the current conductor 43. The current conductor is 4 * * * ... · advantageously thinned near the line ΑΆ to increase the magnetic field strength. The coil 45 is located as accurately as possible in the center of the current conductor 43, whereby the total flux of the magnetic field passing through the coil 45 is zero, and the coil 45 can be used as a reference coil to eliminate external interference.

a · · • *. * 30 The coil 46 is again placed at the maximum point of the magnetic field. The element 41 is • aa typically similar to the flip component 4 shown in Figures 1a-1b and also a: * · *: possibly similarly electrically coupled. The measuring and controlling IC circuit 44 is preferably fabricated on the same substrate as the micromechanical circuit 41, for example by SOI (Silicon On Insulator) technology. Figure 4a illustrates in more detail the placement of the enclosed element 40 in the slot 43.

5 If the component is used in an 1-phase watt-hour meter, it is preferable to place the full power measurement in the IC circuit inside the component, but in a 3-phase meter it is preferable to . The cost of producing one gradiometric power meter 10 could be 0.3 to 0.5 € and the selling price would be in the range of 1.5 € to 2 €. In a 1-phase kilowatt-hour meter, the cost is reasonable, since power measurement does not require many external elements, but in a 3-phase meter, the total cost is already significant. However, if we make a remote reading kilowatt hour meter that includes processor and memory, the situation is again favorable overall.

The present invention discloses a method of using a micromechanical component as a power and kilowatt hour meter. In the method, the product of current and voltage becomes a force, which is measured capacitively. The force is most preferably compensated by a pulse train using feedback loops of different magnitudes. The procedure compensates for possible non-linearities and the dynamic range is extremely wide. Any creep associated with the MEMS-mmm *, * m component is compensated for by changing the phase of an AC current proportional to the voltage across the flip-flop at regular intervals. External • m m m # .....

*** The effect of the magnetic field on the meter's operation can be eliminated, for example, by placing * * · two components in the same housing so that a homogeneous field effectively exerts an equal force on both sensors.

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Claims (22)

Apparatus for measuring electrical power flowing in a conductor (3), comprising means for simultaneously measuring voltage (U) and Current (I), characterized in that it comprises - means (2, 22, 27) for converting the voltage (U) to a current in a mechanical element (1, 21), which is in a power-fluence relationship in relation to the conductor (3), and 10. means for determining the power flux between the mechanical element (1, 21) and the conductor (3, 23), the power flux being directly proportional to the product of the voltage (U) and the current (I). Device according to claim 1, characterized in that it comprises means 15 for forming a time integral from the product of the voltage and the current. Device according to claim 1 or 2, characterized in that the force influence is measured from the deviation of the mechanical element (1,21). • · • · · «· • · · • · [./. 20 Device according to Claim 1 or 2, characterized in that it comprises • · · · ··· means for holding the mechanical element (1, 2) in place by means of a power ether, coupling and means. to determine the power influences from the power feedback of the power feedback. «# · · 5. Device according to claim 4, characterized in that it comprises means. for compensating the force by means of a puisko. »· · · · · 6. Device according to claim 4 or 5, characterized in that it has different large feedback electrodes (25) for different power levels. «Φ * * ·” 30 • · 118931 Device according to any of the preceding claims, characterized in that it comprises means (SO, 51, 52) for changing the polarity of the voltage (U) and thus changing the direction of the current in the mechanical element (1, 21) to eliminate in-stabilities. 5 Apparatus according to any of the preceding claims, characterized in that the means (2, 22, 27) for converting the voltage (U) to a current amount is a coil (1). Device according to any one of the preceding claims, characterized in that the means (2, 22, 27) for converting the voltage (U) to a current amount is a conductive tab (27). Device according to any of the preceding claims, characterized in that it comprises means (4, 2) for converting the gradient of the magnetic field of the conductor (3) to a power quantity, which in turn is proportional to the electrical power flowing in the conductor (3). Device according to any of the preceding claims, characterized in that the means (2, 22, 27) for converting the voltage (U) to a current amount ie · The mechanical element (1,21) is arranged inside the conductor (3.43). • · • · ··· • i i A method for measuring electrical power flowing in a conductor (3), at which conductive voltage (U) and Current (I) are simultaneously measured,. . Characterized by the fact that the tt voltage (U) is converted to a current in a mechanical element (1, 21), which is in a power-to-air ratio in relation to the conductor (3), and • · 118931 - the power flux between the mechanical element (1, 21) and the conductor (3, 23) is determined, the power flux being directly proportional to the product of the voltage (U) and the current (I). ). S Method according to claim 12, characterized in that a time integral is formed from the product of the voltage and the current. Method according to claim 12 or 13, characterized in that the force flux is measured from the deviation of the mechanical element (1,21). 10 15. A method according to claim 12 or 13, characterized in that the mechanical element (1, 21) is held in place by means of a force feedback and the power influence is determined from the control quantities of the force feedback. 15 Method according to claim 15, characterized in that the force is compensated by a pulse queue. Method according to claim 15 or 16, characterized in that: · · · | · Different Large Plug Couplers (25) are used for different power levels. 20 • a • · a 18. A method according to any of the preceding claims, characterized in that • the polarity of the voltage (U) is changed and thus the direction of the current changes in the • t | • tl "In the mechanical element (1.21) to eliminate instabilities. • a ·· · ..... 25 A method according to any of the preceding claims, characterized by • · ·, ···. by using as a means (2, 22, 27) for converting the voltage (U) to a current quantity a · a coil (1). • a a a · a · aa · a a a a 7 20. A method according to any of the preceding claims, characterized by # a * · 1ϊ in that, as a means (2, 22, 27) for converting the voltage (U) to a current quantity 1, a conductive piano (27) is used. 118931 Method according to any of the preceding claims, characterized in that the gradient of the magnetic field generated by the conductor (3) is converted into a power quantity, which in turn is proportional to the electric power flowing in the conductor (3). 5 Method according to any of the preceding claims, characterized in that the means (2, 22, 27) for converting the voltage (U) to a current in the mechanical element (1,21) are arranged inside the conductor (3). 43). «· · · · · · · · · · · · · 1 · · · · · · · · · · t · • · ··· · · · · · · · · · · · · · · · · · 1 · «· · * · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · # ·· 1 • 9 1 • 9 · * · 1