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WO1999002997A2 - Detecteur de courant continu et alternatif a echantillonnage en discontinu - Google Patents

Detecteur de courant continu et alternatif a echantillonnage en discontinu Download PDF

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Publication number
WO1999002997A2
WO1999002997A2 PCT/IB1998/001034 IB9801034W WO9902997A2 WO 1999002997 A2 WO1999002997 A2 WO 1999002997A2 IB 9801034 W IB9801034 W IB 9801034W WO 9902997 A2 WO9902997 A2 WO 9902997A2
Authority
WO
WIPO (PCT)
Prior art keywords
current
sensing
voltage
transformer
winding
Prior art date
Application number
PCT/IB1998/001034
Other languages
English (en)
Other versions
WO1999002997A3 (fr
Inventor
Wen-Jian Gu
Nai-Chi Lee
Original Assignee
Koninklijke Philips Electronics N.V.
Philips Norden Ab
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Koninklijke Philips Electronics N.V., Philips Norden Ab filed Critical Koninklijke Philips Electronics N.V.
Publication of WO1999002997A2 publication Critical patent/WO1999002997A2/fr
Publication of WO1999002997A3 publication Critical patent/WO1999002997A3/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R15/00—Details of measuring arrangements of the types provided for in groups G01R17/00 - G01R29/00, G01R33/00 - G01R33/26 or G01R35/00
    • G01R15/14—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks
    • G01R15/18—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers
    • G01R15/183—Adaptations providing voltage or current isolation, e.g. for high-voltage or high-current networks using inductive devices, e.g. transformers using transformers with a magnetic core

Definitions

  • the invention relates to devices and circuits for "non-contacting" measurement of current, whose output is an electrical signal which is isolated electrically from the conductor whose current is being sensed; and more particularly to such a sensor which can measure both DC and AC currents.
  • the non-contacting current sensor described in co-pending application Ser. No. 08/366,150 filed Dec. 28. 1994 uses a simple 2-winding current transformer having a magnetizing path like that shown in Fig. 2.
  • One winding is a line current winding, which may simply be a line conductor passing through the core opening, or may be a multi-turn winding.
  • a sensing winding, on the same core is energized by a reversing voltage source, such as a square wave, at a frequency higher than any frequency component of the line current to be measured.
  • the sensing current i s waveform will be a triangular wave whose peaks occur at the switching instants of the square wave. In this zero line current situation, the sensing current i s is symmetrical and insignificant.
  • the flux in the core varies from points a to c within the unsaturated flux range, about its midpoint b.
  • the lower (absolute magnitude) of the two sensing current samples will be an accurate measure of the line current.
  • line current is sensed by a circuit which provides a repetitively reversing voltage to a sensing winding or coil on a current transformer, sufficient to drive the transformer from saturation due to line current into its linear region at least once per reversing cycle.
  • Current in the sensing winding for one polarity of the voltage causes current to flow aiding the flux due to any line current then flowing.
  • the transformer core is already in, or is driven into, saturation.
  • the direction of sensing current is reversed and rises to a value sufficient to bring the transformer flux below the saturation level, thus creating a minor loop. After the sensing current has been sampled while in the minor loop condition, during at least the next cycle the application of voltage to this sensing winding is inhibited.
  • the current through the sensing winding is sampled twice during one cycle of the reversing voltage, at each instant of voltage reversal, thereby assuring that one sample is obtained while the core is unsaturated.
  • the current is sampled initially at the instants of the third and fourth successive reversals of the voltage being applied to the sensing winding, and the sample having the lower absolute value is selected as a sample proportional to the line current.
  • Application of the reversing voltage to that sensing winding is then inhibited for a period of time greater than two or three times the duration between two successive reversals.
  • the delay is selected such that the next applied cycle of reversing voltage starts with a half cycle in the direction which had produced the previous lower absolute value.
  • Use of the invention does not require that the repetitive reversals be equally spaced in time, or that they occur in a predictable pattern, or that the applied voltage be constant between reversals. It is merely necessary that the sampling occur such that one sample is taken while the core is unsaturated However, in order to assure that current components up to a certain frequency are sensed, the samples must be taken at a higher frequency than any of the current components.
  • the reversals occur at a relatively high frequency, for example in synchronization with a digital clock or a regular high frequency waveform, having a frequency at least four times the frequency of the highest frequency current component which is to be measured.
  • the current consumption of the sensor can be reduced in proportion to the duty cycle of application of the high frequency voltage to the sensor. For example, if the highest current component of interest is at 5 kHz, and a current sensing system operating at 40 kHz is available, inhibiting current through the sensing winding every other cycle will reduce sensor power consumption with little loss of accuracy, because current will be driven through the winding only about half the time. To the contrary, if the clock frequency were reduced to 20 kHz, the accuracy of sensing would be the same but the sensor power consumption will nearly double compared to the 50% duty cycle at 40 kHz; alternatively, high frequency accuracy can be reduced and a reduced duty cycle will save power.
  • a plurality of sensing windings are provided, each on a respective transformer core linked by a respective conductor of a multiconductor electrical supply.
  • a control circuit applies the high frequency source and resulting sensing current successively to each of the sensing windings. This enables one high frequency generator and sensing electronics to read the current in each conductor.
  • One application of the invention can be in the field of ground fault detection.
  • the use of two current sensing devices according to the prior art would usually not provide sufficient accuracy of current measurement, because it is necessary to sense a very small difference between two comparatively large currents. Typical calibration inaccuracies of the current sensing devices would introduce errors far greater than the permissible ground fault current.
  • identical sensing windings can be placed around each of the two conductors, and sensing current through a single sensing resistor is applied alternately, in different cycles of voltage reversal, to each of the two sensing windings. The voltage across the single sensing resistor is sampled for each of the flows of sensing current and processed in a single set of electronic circuits.
  • a three-phase circuit is conveniently measured by providing a sensing winding in each of the three line conductors; and if a four- wire wye system is being used, a fourth transformer core and sensing winding is provided. If the multiplexer switches connection every other cycle of the high frequency, a current sample of each respective conductor is obtained once in each eight cycles of the high frequency. A very efficient use of the circuitry is obtained, while current components at high harmonic frequencies in the line can be accurately measured.
  • a three-phase system can operate at a lower clock frequency, and the multiplexer can switch connections for each cycle of the high frequency. This still enables measurement of all three or four currents with the same power consumption as would be used, according to the prior art, to measure one.
  • Fig. 1 is a simplified schematic diagram of a sensor according to the invention
  • Fig. 2 shows the magnetizing path followed along the B-H curve for zero line current
  • Fig. 3 is a graph of voltage and sensing current waveforms for a device with discontinuous sampling
  • Fig. 4 is a more detailed schematic diagram of the sensor of Fig. 1
  • Fig. 5 is a schematic diagram of a multi-pole current sensor
  • Fig. 6 is a schematic diagram of a different embodiment of a multi-pole current sensor.
  • the current sensor 10 has only four elements: a driver 12 which is a square wave or other reversing voltage source responsive to a timing control 20, a sensing resistor R s , a current transformer 15, and a sampler 19 also responsive to the timing control 20 for providing a current signal.
  • the current transformer 15 has a core 16 made of a material suitable for a linear current transformer, a line winding 17 through which line current i B flows, and a sensing winding 18 through which a sensing current i s flows.
  • the voltage source 12, DC blocking capacitor C b , sensing resistor R s and line winding 17 of the current transformer 15 are connected in series.
  • the square wave voltage source is operated at a frequency HF which is at least twice, and preferably four times, that of the highest frequency component of line current which it is desired to measure, and has a peak voltage which, when the line current is zero, causes the core flux to vary over a range ⁇ B as shown in Fig. 2.
  • This range is selected such that the flux values at times a and c are less than the value B s at which the core begins to saturate.
  • H s to produce the saturation flux B s be as small as possible.
  • the core 16 should have a high permeability.
  • High sensitivity also requires that ⁇ B be small.
  • ⁇ B should be larger, for example sufficient to cover a range of + 0.8 B s when line current is zero.
  • the element unique to the instant invention is shown schematically in Fig. 1.
  • the timing control 20 not only controls the instant of sampling by the sampler 19, but also inhibits the reversing voltage source or driver 12 for certain time periods.
  • Fig. 3 is a timing chart including clock, voltage and sensing current waveforms produced by the circuit of Fig. 4.
  • the timing control 20 of Fig. 1 contains circuits, all individually well known, for controlling the timing and inhibition of the repetitively reversing voltage from the driver 12. For simplicity and economy, all switching and sampling is performed under control of the signals from a digital clock 21.
  • the clock signal is provided to a flip-flop 21 whose output signals Q j and Q j are supplied to AND gates 23 and 24, whose output signals are the trigger signals for the driver 12.
  • the output Qi is also provided as an input to a counter 25 whose outputs Q 2 and Q 3 are provided to a delay controller 26 and AND-gate 27, respectively.
  • the output Q 2 of the counter 25 stays high for four clock periods, and provides an enable signal to the delay controller 26, during which the flip-flop 22 goes through two full cycles.
  • the output Q 3 of the counter 25 stays high for two clock periods, and provides an enable signal to an AND-gate 27, whose other input is the clock signal.
  • the signal Q 4 from the gate 27 is thus two successive cycles of the clock signal, which are first inputs to AND-gates 28, 29.
  • the other inputs to the AND-gates 28, 29 respectively, are the signals Q ! and Q j from the clock 21. This produces signals and Q 6 from the gates 28, 29 which will cause sampling of the current signal at two successive clock cycles.
  • the first function of the timing control 20 is triggering of the reversing signal driver 12.
  • the output Q 7 of delay controller 26 turns the driver 12 on for two full clock cycles.
  • the driver 12 includes four power switching transistors Q A - Q D in a full bridge configuration.
  • transistors Q A and Q B alternately connect a node A to the supply voltage V c and to ground
  • transistors Q c and Q D alternately connect a node B to ground and to the supply voltage V c .
  • line winding 17 of the current transformer 15 and sensing resistor R s are connected in series between the nodes A and B. This causes the node voltage A - B to be applied to drive the sensing current i s (curve 35 of Fig. 3) through the winding 17.
  • the voltage across the sensing resistor is a measure of the current, and is applied to the inputs of a differential amplifier 36.
  • sampling hold circuits 37, 38 Each of these samples the current at the instant of the respective signal Qs and Q 6 from the gates 28, 29, and holds the value until the next sampling. These samples are inputs to an analog signal selector 39, which selects the smaller sample signal and provides it as the sensor output.
  • analog signal selector 39 selects the smaller sample signal and provides it as the sensor output.
  • general purpose logic IC's such as those having generalized type numbers 4016 or 4066, from many different sources, may be used. If a positive output is desirable, indicative of the absolute value of the current, then a summing amplifier or analog adder can be used instead of difference amplifier 36. Alternatively, an analog data selector IC such as type 4529 can be used instead of the analog switches and amplifiers shown in Fig. 4, to provide a positive output.
  • the current sensor of Fig. 5 permits measuring three line currents, such as those in a three phase circuit, with far less circuitry and far less power consumption than having three current sensors such as described in the '150 patent application.
  • This embodiment includes four half-bridge drivers, each controlling one pair of power switching transistors.
  • the sensing resistor can be sampled during the second of two cycles of voltage application while still preserving the delay function such that current is sensed during the third and fourth half-cycles of voltage application.
  • two line currents have one polarity (or one is approximately zero) and one has the other.
  • four are used for one phase
  • four are used for a second phase
  • four are used for the third phase
  • four are available as resting periods when little power is consumed, or for transitions from positive to negative (the delay of Q 7 ).
  • each half-bridge driver 133, 233, 333, 433 which are identical, and each drive a transistor pair Q A , Q B connected between a common supply voltage V c and ground.
  • Each half-bridge driver produces three output states: one of the switching transistors on and the other off, the one switching transistor off and the other on, and both transistors off so that the node is floating in a high impedance state.
  • the four transistor pairs define nodes P T - P 4 .
  • a single sensing resistor R s is connected between node P 4 and a node P s .
  • a first sensing winding 117 is connected between nodes P 1 and P s and identical sensing windings 217, 317 are connected between the other nodes and node P s , such that each sensing winding has a respective terminal connected to a terminal of the sensing resistor.
  • Each half-bridge driver has two inputs, which are connected to respective outputs of a logic control and timing circuit 120, which is timed by a clock 21.
  • the half-bridge driver 433 and a selected one of the other half bridge drivers cause a sequence of two cycles of reversing voltage to be established between node P 4 the corresponding other node P j - P 3 , so that a sensing current i ⁇ L is 2 or is 3 flows through the corresponding sensing winding and sensing resistor R s .
  • the control logic circuit 120 also controls a sampling circuit 51, a demultiplexer 52, and three sample holding circuits 155, 255, 355.
  • the circuit 51 performs the amplification function of amplifier 36, the sampling hold functions of circuit elements 37 and 38, and selector function of analog signal selector 39 of Fig. 4, to provide a time division demultiplexed output to the demultiplexer 52, which in turn provides line current signals to the three holding circuits 155 - 355.
  • the driver 433 and its associated power switching transistors are active for sensing current through all the current transformers. Therefore average power dissipation from them will be greater than for the other drivers and power transistors.
  • Fig. 6 is like that of Fig. 5 except that it uses separate sensing resistors for each current transformer, and has balanced dissipation from the power transistors if line currents are balanced.
  • This embodiment could also be advantageous in a situation where it might be desirable to have a different scale factor for one line conductor but use identical current transformers, or where stray coupling in the lines connecting the node P s to the various current transformers interferes with the desired accuracy of measurement.
  • the four half-bridge drivers 133, 233, 333, 433 and their respective transistor pairs Q A , Q B may be identical to those of Fig. 5.
  • the four transistor pairs define nodes P j - P 4 .
  • a sensing winding 117 and a sensing resistor R S1 are connected in series, with identical sensing windings 217, 317 and sensing resistors R S2 and R S3 between the other nodes.
  • Each half-bridge driver has two inputs, which are connected to respective outputs of a logic timing circuit 620, which is timed by a clock 21. For a given sequence of four clock periods, an adjoining pair of half-bridge drivers cause a sequence of two cycles of reversing voltage to be established between the corresponding nodes, so that a sensing current i sl , i S2 or i S3 flows through the corresponding sensing winding and sensing resistor.
  • the control logic circuit 620 also controls a dual channel 3 to 1 selector 650, a sampling circuit 651, a demultiplexer 52, and three sample holding circuits 155, 255, 355.
  • the two terminals of each sensing resistor R S1 , R S2 and R S3 are respectively connected to the inputs of the selector 650 which functions as a demultiplexer, providing current signals successively for the three lines, corresponding to the input for one line to differential amplifier 36 of Fig. 4, to the sampling circuit 651.
  • the circuit 651 performs the amplification function of amplifier 36, the sampling hold functions of circuit elements 37 and 38, and selector function of analog signal selector 39 of Fig. 4, to provide a time division demultiplexed output to the three sample holding circuits 155 - 355.
  • a fourth current transformer and current sensing resistor could be added between nodes P 4 and P, , for example to measure the neutral conductor current in a four wire wye power system. This would allow more measurements with the same number of drivers and power transistors, but might increase the total power consumption undesirably, because a series connection of the three other sensing resistors and sensing windings would be connected in parallel with transformer and resistor which are being used for measurement at any given time. The significance of this last factor would be determined, in part, by the symmetry, or lack thereof, of current flow in the various conductors being measured.
  • Figs. 5 and 6 uses conventional low level multiplexing for logic signals to the half bridge drivers, and for sensed voltage signals to the differential amplifier. It will be clear to those of ordinary skill that, in a modification of the embodiment of Fig. 5, one full bridge driver can be used, with one sensing resistor again connected via a node P s to one terminal of each of the sensing windings. However, rather than being connected to individual half bridge power circuits, the other ends of the sensing windings can be connected through transmission gates (bidirectional switches) formed, for example, by an n- channel MOSFET and a p-channel MOSFET connected in parallel.
  • transmission gates bidirectional switches
  • This variation has the disadvantage that, to measure three line currents, a total of 7 n-channel MOSFET's and 3 p- channel MOSFET's would be required, compared to only 8 n-channel MOSFET's in the embodiment of Fig. 5. Further, because of lower carrier mobility in p-channel MOSFET's, the on resistance is typically 2.5 to 3 times that of n-channel devices having the same channel proportions.
  • the senor has only two current transformers, which measure the currents in the two conductors of a single phase line.
  • the half bridge driver 333 and its associated circuitry are not used, so that the control 120 and demultiplexer 52 process only two measurement situations in which, in the absence of a substantial ground fault, the successive currents will be approximately equal and opposite, differing only by the effect of the small time delay between measurements.
  • current leakage of a turned off MOSFET is very small, typically much less than one microamp.
  • difference in leakage between the turned off power transistors will be well below the current sensitivity usually needed for ground fault detection: e.g., 1 to 10 ma line current divided by 1000: 1 turns ratio.
  • the voltage source need not be a square wave.
  • the voltage source can be asymmetric, so long as it drives the flux once each high frequency cycle into the non-saturated region.
  • sampling need not occur at the voltage reversal (cross-over) instant, so long as it occurs while the flux is in the non-saturated region.
  • the current transformer core need not be linear, so long as there is a sufficient region of high permeability so that the magnetizing current, equivalent to that shown in Fig. 3, is less than the desired resolution in measuring line current after taking the transformer turns ratio into account.
  • a DC blocking capacitor can be included in series with the sensing winding.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Transformers For Measuring Instruments (AREA)
  • Measurement Of Current Or Voltage (AREA)

Abstract

Du courant est détecté par un circuit qui fournit une tension d'inversion haute fréquence à un bobinage détecteur situé sur un transformateur de courant, de manière à amener le transformateur dans sa région linéaire une fois par cycle de tension appliquée. Le courant passant par le bobinage détecteur est échantillonné pendant que le transformateur se trouve dans cette région linéaire. Après la prise d'un échantillon de courant par application de la tension d'inversion, la consommation de puissance du détecteur est réduite par inhibition de l'application de la tension au bobinage détecteur pendant un ou plusieurs des cycles haute fréquence, ou bien le même circuit de commande et de détection est utilisé pour provoquer l'application de tension d'inversion à un bobinage détecteur sur un transformateur différent qui mesure du courant passant par un conducteur différent, comme dans un agencement polyphasé ou pour surveiller du courant de défaut à la terre. De préférence, le courant est échantillonné approximativement aux instants d'inversion de la tension appliquée au bobinage détecteur, et l'échantillon ayant la valeur absolue plus faible est sélectionné en tant qu'échantillon proportionnel au courant de ligne.
PCT/IB1998/001034 1997-07-08 1998-07-06 Detecteur de courant continu et alternatif a echantillonnage en discontinu WO1999002997A2 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US88927997A 1997-07-08 1997-07-08
US08/889,279 1997-07-08

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WO1999002997A2 true WO1999002997A2 (fr) 1999-01-21
WO1999002997A3 WO1999002997A3 (fr) 1999-04-08

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006093724A1 (fr) * 2005-02-25 2006-09-08 Honeywell International Inc. Capteur de courant a tore bobine magnetique
EP2779343A3 (fr) * 2013-03-15 2014-11-05 Rockwell Automation Technologies, Inc. Surcharge à fréquence variable de multi-moteurs
US11682894B2 (en) 2020-04-09 2023-06-20 Hs Elektronik Systeme Gmbh Electric safety circuit

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4314200A (en) * 1977-09-01 1982-02-02 Bbc Brown, Boveri & Company Limited Method and apparatus for detection of magnetization
US5223789A (en) * 1989-06-23 1993-06-29 Fuji Electric Co., Ltd. AC/DC current detecting method
US5811965A (en) * 1994-12-28 1998-09-22 Philips Electronics North America Corporation DC and AC current sensor having a minor-loop operated current transformer

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006093724A1 (fr) * 2005-02-25 2006-09-08 Honeywell International Inc. Capteur de courant a tore bobine magnetique
EP2779343A3 (fr) * 2013-03-15 2014-11-05 Rockwell Automation Technologies, Inc. Surcharge à fréquence variable de multi-moteurs
US9001476B2 (en) 2013-03-15 2015-04-07 Rockwell Automation Technologies, Inc. Multimotor variable frequency overload
US11682894B2 (en) 2020-04-09 2023-06-20 Hs Elektronik Systeme Gmbh Electric safety circuit

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Publication number Publication date
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