Circuit arrangement for current measurement

Abstract

Circuit arrangement for current measurement, wherein a current transformer is arranged to generate an input voltage from a current in a conductor, which is delivered to an input, and a first output is located at the connection of two identical first electrodes of a diode, a measuring resistor is inserted between two identical second electrodes of the diode, a second output is located at the connection of one of the diodes with the second electrodes and the measuring resistor, an extension bridge node is located at the connection of the other of the diodes and the measuring resistor, the diode at the second output is formed by the source-drain diode of a first self-blocking field effect transistor, the diode at the extension bridge node is formed by the source-drain diode of a second self-blocking field effect transistor, a control device drives the gate of the first field effect transistor and the gate of the second field effect transistor by identical control voltages, respectively, and a measuring device measures a measuring voltage across the measuring resistor, which is proportional to the current in the conductor.

Description

Technical Field

[0001] The present invention relates to a circuit arrangement for measuring current in a conductor through which current flows, wherein a current transformer is configured to generate an input voltage from the current in the conductor, the input voltage being supplied to the input of a diode bridge circuit. Background Technology

[0002] In power distribution infrastructure, such as smart DC and AC distribution networks (so-called "smart grids"), information about grid conditions, such as voltage levels, current loads, power flows, and load distribution, is typically determined by multiple distributed sensor units.

[0003] In order to monitor and potentially control the power grid, sensor data is transmitted and centrally evaluated in a central unit.

[0004] Importantly, the current / voltage measurement data acquired in the sensor unit can be used to calculate active and reactive power.

[0005] In many applications of sensor units used for current measurement in AC power distribution networks, it is advantageous that the sensor unit obtains energy from the conductor in which it is mounted for power supply.

[0006] Typically, an inductive current measuring transformer is used for this purpose, which has a fixed magnetic core made of magnetic material.

[0007] Here, the secondary winding of the current transformer is connected to a rectifier circuit, such as a diode bridge circuit, which provides rectified current to the sensor unit.

[0008] To perform current measurement, a shunt resistor or measuring resistor is typically connected in parallel with the secondary winding of the current transformer by an electronic switch. A voltage proportional to the primary current of the current transformer is measured across the shunt resistor or measuring resistor, as described in publication EP4125180A1.

[0009] The challenge for these electronic switches and the circuitry following them is that the current measurement signal, i.e., the voltage across the shunt resistor, cannot be directly referenced to the power supply voltage ground, which is tapped before the rectifier.

[0010] Therefore, an additional differential amplifier is required, which increases system complexity or incurs additional hardware costs.

[0011] To solve the previous problem, known circuit arrangements for sensor units connect a measuring resistor in the form of a shunt resistor after the rectifier circuit, thereby eliminating the need to directly acquire AC voltage measurement signals, where only the effective value of the current needs to be measured once.

[0012] However, if the sensor unit is to be used for (distributed) AC current measurement synchronized with a reference AC voltage to monitor the load flow direction in a power distribution network, then such a circuit arrangement has significant drawbacks. Summary of the Invention

[0013] Therefore, the object of the present invention is to provide a current measurement solution with reduced workload that does not require an additional external power supply.

[0014] The object of the invention is achieved by a circuit arrangement for measuring current in a conductor through which current flows, wherein a current transformer is configured to generate an input voltage from the current in the conductor, the input voltage being supplied to the input terminal of a diode bridge circuit, and the first output terminal of the diode bridge circuit is located at the connection of the same first electrodes of the diodes in the diode bridge circuit, wherein a measuring resistor for measuring current is inserted between two identical second electrodes of the diodes in the diode bridge circuit, wherein the type of the second electrode is different from the type of the first electrode, the second output terminal of the diode bridge circuit is located at the connection of one of the diodes having the second electrode with the measuring resistor, and an extended bridge node is located in the diode having the second electrode. Another connection to the measuring resistor, and the diode at the second output terminal of the diode bridge circuit is composed of the source-drain diode of the first self-blocking field-effect transistor, and the diode at the extended bridge node of the diode bridge circuit is composed of the source-drain diode of the second self-blocking field-effect transistor, and the control device is configured to drive the gate of the first field-effect transistor and the gate of the second field-effect transistor by the same control voltage respectively, and thereby switch the circuit device between the charging mode and the measurement mode for the capacitor connecting the first output terminal to the extended bridge node, and the measuring device is configured to measure the measuring voltage across the measuring resistor in the switched measurement mode, the measuring voltage being proportional to the current in the conductor.

[0015] This enables the application of both rectifier and analog switch functions, allowing current measurement using shunt resistors without the need for an additional differential amplifier as specified in the prior art.

[0016] This allows for selective switching of the shunt resistor for interference-free current measurement.

[0017] This circuit device can extract energy from a combination of conductor current and alternating current measurements, and reduces implementation costs.

[0018] Thus, sensor units can be implemented to acquire AC current or AC voltage pointers, which are then transmitted from multiple sensor units to a central unit in a distributed measurement system.

[0019] This allows for sufficiently accurate calculation of the average active and reactive power values ​​for load flow monitoring in AC distribution networks.

[0020] This also enables the use of energy-efficient wireless communication technologies, which is particularly advantageous for solutions that recover local energy from the current in the current of each phase conductor of the energy supply network.

[0021] In this respect, the same control voltage for the voltages on the gates of two field-effect transistors is understood to be: reaching or exceeding a voltage threshold, i.e., the field-effect transistor is in an active or conducting state or in a low-impedance saturation state.

[0022] In other words, applying the same gate voltage to both transistors corresponds to switching the field-effect transistor from charging mode to measurement mode, i.e., a logic switch between the two field-effect transistors.

[0023] The second output terminal and the expansion bridge node are obviously not at the same connection point.

[0024] In other words, the second output terminal and the expansion bridge node are located on different sides of the measured resistance.

[0025] Therefore, a diode bridge circuit is formed between two input terminals and two output terminals by a bridge circuit with diodes and field-effect transistors, wherein the diodes of the field-effect transistors can be switched by corresponding control voltages.

[0026] In an extended embodiment of the invention, it is specified that the first input terminal of the diode bridge circuit is connected to the extended bridge node via another diode, and the electrode type of the other diode corresponds to the electrode type of the diode at the extended bridge node.

[0027] In an extended embodiment of the invention, the measuring device is further configured to periodically switch between a charging mode and a measuring mode.

[0028] Therefore, the capacitor can be charged mainly through the other diode in the diode bridge circuit.

[0029] This allows for faster charging of the capacitor, or more precisely, reduces the time required for charging.

[0030] Additionally, this other diode can protect the measuring resistor from high transient pulse currents.

[0031] In charging mode, the capacitor is charged.

[0032] In measurement mode, the measuring device evaluates the voltage across the measuring resistor.

[0033] Therefore, the current flowing through the conductors of the energy supply network can be monitored periodically.

[0034] Clearly, this invention can be applied individually to all conductors in an energy supply network. Attached Figure Description

[0035] The invention will be described in more detail with reference to embodiments in the following accompanying drawings. In the drawings: Figure 1 A current sensor according to the prior art is shown; Figures 2-5 Various embodiments of the present invention are shown. Detailed Implementation

[0036] Figure 1 A current sensor according to the prior art is shown, wherein, in a circuit arrangement, a current-carrying grid conductor L is surrounded by the magnetic core CO of an inductive current transformer CT.

[0037] The secondary winding of the current transformer CT is connected to the AC voltage input terminal of the rectifier, which is in the form of a diode bridge circuit B with bridge nodes B1-B4 and a measuring resistor R at the extended bridge node B5.

[0038] The diode bridge circuit B includes diodes D1, D2, D3, and D4, which will also be referenced in the following figures.

[0039] Zener diode ZD is used as a protection element for the circuit, and capacitor C is used for smoothing after rectifier B.

[0040] Correspondingly, using this circuit device, current measurement can be performed in the conductor L through which current I flows by measuring resistor R, amplifier AMP, and control circuit CU.

[0041] The current transformer CT is configured to generate an input voltage U from the current I in the conductor L, which is supplied to the input terminals B1 and B2 of the diode bridge circuit B, and the first output terminal B3 of the diode bridge circuit B is located at the connection of the same first electrodes E1 and E2 of the diodes D1 and D2 of the diode bridge circuit B.

[0042] The first electrodes E1 and E2 of diodes D1 and D2 are the cathodes K1 and K2 of these diodes.

[0043] exist Figure 2 The image shows a first embodiment of a circuit device with a diode bridge circuit according to the present invention, which is based on the aforementioned prior art.

[0044] The first electrodes E1 and E2 of diodes D1 and D2, which are in the form of corresponding cathodes K1 and K2, are located at the first output terminal B3 of diode bridge circuit B.

[0045] In this circuit arrangement, the current-carrying grid conductor L is surrounded by the magnetic core CO of the inductive current transformer CT.

[0046] The secondary winding of the current transformer CT is connected to the AC voltage input terminal, which has input terminals B1 and B2 of a rectifier in the form of a diode bridge circuit B.

[0047] The diode bridge circuit B includes diodes D1 and D2, as well as a first n-channel field-effect transistor T1 and a second n-channel field-effect transistor T2. These field-effect transistors perform the function of diodes in the off state.

[0048] The diode bridge circuit B also includes a measuring resistor R between the two electrodes E3 and E4. This measuring resistor is small enough that it does not significantly affect the rectification function of the bridge circuit B, or more precisely, it does not significantly affect the charging of the capacitor C.

[0049] The gate connections of the first and second n-channel field-effect transistors T1 and T2 constitute circuit nodes G1 and G2, and these circuit nodes can be driven together, for example.

[0050] The first and second field-effect transistors, T1 and T2, are n-channel FETs, which behave like diodes in the off state.

[0051] The sensor unit with measuring resistor R can be powered via rectifier B and can charge capacitor C.

[0052] Once capacitor C has stored enough charge, the circuit is switched from the charging state to the measuring state.

[0053] Therefore, the same voltage is applied to the two gate connection terminals G1 and G2 of FETs T1 and T2 relative to ground, i.e., the extended bridge node B5.

[0054] Therefore, the two FETs T1 and T2 are in a low impedance state between their source and drain terminals, and the shunt resistor or measuring resistor R is connected to the two terminals of the secondary winding of the current transformer CT, namely the input terminals B1 and B2.

[0055] Diodes D1 and D2 remain off, and thus capacitor C1 is not discharged because these diodes, in this state, are biased relative to ground B5 due to the voltage on the charged capacitor C1, and are also connected in reverse between circuit nodes B1 and B2.

[0056] The second electrodes E3 and E4 of the diodes D3 and D4, which are composed of transistors T1 and T2, are their anodes A3 and A4, and are located at the second output terminal B4.

[0057] The diode D4 located at the second output terminal B4 of the diode bridge circuit B is composed of the source and drain diodes of the first self-blocking field-effect transistor T1.

[0058] The control device CU is configured to drive the gate of the first field-effect transistor T1 and the gate of the second field-effect transistor T2 by the same control voltage at nodes G1 and G2, and thereby switch the circuit device between the charging mode and the measurement mode for the capacitor C that connects the first output terminal B3 to the measurement resistor R at the extended bridge node B5.

[0059] Therefore, the series circuit for measuring resistor R and capacitor C exists between the third output terminal B3 and the second output terminal B4.

[0060] A Zener diode (ZD) can be connected in parallel with a capacitor (C) for circuit protection.

[0061] Nodes G1 and G2 are represented only as "logic" because the control voltage can be provided, for example, by a corresponding voltage divider, and therefore are represented by dashed lines.

[0062] The measuring device MU is configured to measure the voltage across the measuring resistor R, i.e., between node B4 and extension bridge node B5, in the switched measuring mode. This voltage is proportional to the current I in conductor K.

[0063] The measuring device MU is also configured to periodically switch between charging mode and measuring mode.

[0064] exist Figure 3 The image shows a second embodiment of the circuit device according to the present invention.

[0065] The statements in the previous attached figure also apply here.

[0066] As shown in the previous figure, another diode D5 is inserted between the first input terminal B1 of the diode bridge circuit B and the extended bridge node B5, wherein the electrode type of the diode D4, which is composed of transistor T1, is the same as the electrode type of the other diode D5 at the connection point.

[0067] In this embodiment, the electrode E5 of another diode D5 located at the extended bridge node B5 is the anode.

[0068] The sum of the measuring resistor R and the source-drain resistance of the first self-blocking field-effect transistor T1 is designed such that the measured voltage is lower than the threshold voltage of another diode D5 in the diode bridge circuit B, which is connected to the source terminal of the second self-blocking field-effect transistor T2.

[0069] Accordingly, the parameters of the measuring resistor R can be determined.

[0070] The capacitor C is charged mainly by diodes D1-D3 and another diode D5 in the diode bridge circuit B.

[0071] However, partial charging is also achieved through diode D4 connected in parallel with the other diode D5 and the measuring resistor R.

[0072] This enables faster charging of capacitor C, or more precisely, reduces the time required for charging.

[0073] exist Figure 4 The image shows a third embodiment of the circuit device according to the present invention.

[0074] Here, the first and second self-blocking field-effect transistors T1 and T2 are p-channel transistors, respectively.

[0075] This implementation plan is functionally equivalent to, according to Figure 2 The circuit employs n-channel transistors T1 and T2; however, the polarity of the current transformer CT and the driving of transistors T1 and T2 can be considered accordingly.

[0076] Diodes D1 and D2 are connected in common via their anodes A1 and A2, which correspond to electrodes E1 and E2.

[0077] Diodes D3 and D4, which are composed of transistors T1 and T2, are connected in common through their cathodes K1 and K2, which correspond to electrodes E3 and E4.

[0078] The current transformer (CT) may include windings L1 and L2, wherein winding L1 may be composed of a conductor L, which is surrounded by a magnetic core CO as shown in the foregoing figures.

[0079] for Figure 2 and Figure 3 In some embodiments, it can also be specified that the current transformer has multiple windings on both sides.

[0080] exist Figure 5 The fourth embodiment of the circuit device according to the present invention is shown in the figure.

[0081] Here, the first and second self-blocking field-effect transistors T1 and T2 are p-channel transistors, respectively.

[0082] This implementation plan is functionally equivalent to, according to Figure 3 The circuit employs n-channel transistors T1 and T2; however, the polarity of the current transformer CT and the driving of transistors T1 and T2 can be considered accordingly.

[0083] Diodes D1 and D2 are connected in common via their anodes A1 and A2, which correspond to electrodes E1 and E2.

[0084] Diodes D3 and D4, which are composed of transistors T1 and T2, are connected in common through their cathodes K1 and K2, which correspond to electrodes E3 and E4.

[0085] In addition, the first input terminal B1 of the diode bridge circuit B is connected to the extended bridge node B5 via another diode D5.

[0086] The cathode K5 of another diode D5 is connected to the cathode K3 of the diode formed by the second transistor T2.

[0087] List of reference numerals AMP amplifier Anodes of diodes A1-A4 B1-B5 nodes B. Diode bridge circuit C capacitor CO magnetic core CT current transformer CU control device Diodes D1-D5 The electrodes of diodes E1-E5 are either the anode or the cathode. Gates of G1 and G2 field-effect transistors I Current Cathode of diodes K1-K5 L-shaped conductor The windings of current transformers L1 and L2 MU measuring device R measures resistance T1 and T2 transistors U Input voltage ZD Zener diode.

Claims

1. A circuit apparatus for measuring current in a conductor (L) through which current (I) flows, wherein, The current transformer (CT) is configured to generate an input voltage (U) from the current (I) in the conductor (L), which is supplied to the input terminals (B1, B2) of a diode bridge circuit (B), and the first output terminal (B3) of the diode bridge circuit (B) is located at the connection point of the two identical first electrodes (E1, E2) of the diodes (D1, D2) of the diode bridge circuit (B). Its features are, The measuring resistor (R) used for the current measurement is inserted between the two identical second electrodes (E3, E4) of the diodes (D3, D4) in the diode bridge circuit (B), wherein the type of the second electrodes (E3, E4) is different from the type of the first electrodes (E1, E2). The second output terminal (B4) of the diode bridge circuit (B) is located at the connection point between one of the diodes (D3, D4) having the second electrodes (E3, E4) and the measuring resistor (R), and The extended bridge node (B5) is located at the connection point of another diode (D3, D4) with the second electrode (E3, E4) to the measuring resistor (R), and The diode (D4) located at the second output terminal (B4) of the diode bridge circuit (B) is composed of the source-drain diode of the first self-blocking field-effect transistor (T1), and The diode (D3) in the diode bridge circuit (B) located at the extended bridge node (B5) is composed of the source-drain diode of the second self-blocking field-effect transistor (T2), and The control unit (CU) is configured to drive the gates (G1) of the first field-effect transistor (T1) and the second field-effect transistor (T2) with the same control voltage, thereby switching the circuitry between a charging mode and a measurement mode for the capacitor (C) connecting the first output terminal (B3) to the extended bridge node (B5). The measuring device (MU) is configured to measure the voltage across the measuring resistor (R) in the switched measuring mode, the voltage being proportional to the current (I) in the conductor (L).

2. The circuit arrangement according to the preceding claim, wherein, The first input terminal (B1) of the diode bridge circuit (B) is connected to the extended bridge node (B5) via another diode (D5), and the type of the electrode (E5) of the other diode (D5) corresponds to the type of the electrode (E3, E4) of the diode (D3, D4) at the extended bridge node (B5).

3. The circuit arrangement according to any one of the preceding claims, wherein, The measuring device (MU) is also configured to periodically switch between the charging mode and the measuring mode.

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