US20060043944A1 - Detection of the supply state of a load supplied by a variable voltage - Google Patents

Detection of the supply state of a load supplied by a variable voltage Download PDF

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Publication number
US20060043944A1
US20060043944A1 US11/216,919 US21691905A US2006043944A1 US 20060043944 A1 US20060043944 A1 US 20060043944A1 US 21691905 A US21691905 A US 21691905A US 2006043944 A1 US2006043944 A1 US 2006043944A1
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United States
Prior art keywords
voltage
load
circuit
switch
variable
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Abandoned
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US11/216,919
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English (en)
Inventor
Laurent Moindron
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STMicroelectronics SA
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STMicroelectronics SA
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Assigned to STMICROELECTRONICS S.A. reassignment STMICROELECTRONICS S.A. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: MOINDRON, LAURENT
Publication of US20060043944A1 publication Critical patent/US20060043944A1/en
Priority to US11/966,246 priority Critical patent/US8022675B2/en
Abandoned legal-status Critical Current

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/165—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values
    • G01R19/16533—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application
    • G01R19/16538—Indicating that current or voltage is either above or below a predetermined value or within or outside a predetermined range of values characterised by the application in AC or DC supplies
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
    • H02P4/00—Arrangements specially adapted for regulating or controlling the speed or torque of electric motors that can be connected to two or more different electric power supplies
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R19/00—Arrangements for measuring currents or voltages or for indicating presence or sign thereof
    • G01R19/10—Measuring sum, difference or ratio
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01R—MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES
    • G01R31/00—Arrangements for testing electric properties; Arrangements for locating electric faults; Arrangements for electrical testing characterised by what is being tested not provided for elsewhere
    • G01R31/34—Testing dynamo-electric machines
    • G01R31/343—Testing dynamo-electric machines in operation

Definitions

  • the present invention generally relates to the detection of the supply state of a load supplied by a variable voltage (A.C. or unipolar) and more specifically the supervision of the state of this load and of one or several switches controlling it.
  • A.C. or unipolar variable voltage
  • the present invention more specifically applies to the detection of possible failures of the load or of switches in series with this load.
  • FIG. 1 shows a conventional example of an assembly of supervision of the state of a load Q supplied by an A.C. voltage Vac under control of two switches T and SW.
  • This example relates to the control of the motor (load Q) of a washing machine under the action of a first switch formed of a triac T receiving a control signal CT from a programmer (not shown).
  • a second switch SW symbolizes a door-opening detection contact of the machine to interrupt the motor supply in case of an opening (turning-off of switch SW).
  • Triac T is in series with load Q and switch SW between two terminals 1 and 2 of application of A.C. voltage Vac (generally, the electric distribution mains voltage).
  • the supervision of the respective states of the motor and of the switches is performed by analyzing the voltage at point 3 of interconnection of triac T and of motor Q.
  • Two resistors R 1 and R 2 are respectively connected between terminal 2 and node 3 , and between node 3 and a node 4 for sampling an analog measurement voltage Van.
  • Voltage Van is applied to input IN of an analog-to-digital converter 5 (ADC).
  • ADC analog-to-digital converter 5
  • Converter 5 is supplied by a D.C. voltage Vdc, applied between terminals 6 and 7 , which is low as compared with A.C. voltage Vac (typically 5 to 10 volts, to be compared with 110 or 220 volts).
  • node 4 corresponds to the midpoint of a resistive dividing bridge, formed of two resistors RH and RL generally of the same value, in series between terminals 6 and 7 . Accordingly, the quiescent level of the converter approximately corresponds to half voltage Vdc (Vdc/2).
  • Voltage reference input VREF of converter 5 is connected to terminal 6 and its digital inputs are intended to be interpreted, for example, by a microprocessor or microcontroller ⁇ C (not shown). In the example shown, an 8-bit converter is considered.
  • node 3 to supervise the analog voltage across the load enables reading several voltages according to the respective states of switches T and SW.
  • FIG. 2 shows examples of shapes of analog voltage Van along time in a period of A.C. supply voltage Vac.
  • Sinusoidal voltage Van (dotted line SWONLOK in FIG. 2 ) varies between a voltage THH slightly smaller than voltage Vdc and a voltage THL slightly greater than ground. Difference Vdc ⁇ VTH corresponds to the minimum voltage drop in resistor RH. Level THL corresponds to the minimum voltage drop in resistor RL.
  • switch SW is also off, a sinusoid (shape in full line LDEF) of amplitude smaller than that of the preceding operation (shape SWONLOK) is found on input IN of converter 5 .
  • This case also corresponds to the case where switch SW is on, while load Q is defective, that is, it exhibits an impedance greater than that of its normal operation.
  • a problem of conventional circuits for supervising the state of a load and of its switches is linked to the tolerances of the different components and mainly to the possible variations of the voltage reference of converter 5 which is provided by voltage Vdc, likely not to have a perfect stability.
  • FIG. 3 illustrates, in the case of an A.C. voltage of a 50-Hz frequency, the possible ranges of variation of the different shapes.
  • threshold voltage Van is compared with threshold voltages, and more specifically the digital outputs of converter 5 are compared with digital values.
  • intermediary thresholds THIHH and THIHL are set between threshold THH and median value MED, and thresholds THILH and THILL are set between the median value and threshold THL.
  • a disadvantage is that there are significant risks of false detection in case of a loss of synchronism of the measurement or in case of a distortion of voltage Vac (wrong shape factor).
  • Another disadvantage is that the possibility of performing a single measurement per half period slows down the detection.
  • the reliability of the detection thus is sensitive to a possible variation of A.C. voltage Vac.
  • Another disadvantage is that a circuit of supervision of the load state is not transposable without modifications to a mains voltage of different frequency or amplitude.
  • the present invention aims at providing a method for detecting the state of a load supplied by a variable voltage (A.C. or unipolar) or of at least one switch controlling this load, which overcomes at least some disadvantages of known solutions.
  • the present invention especially aims at providing a solution which is freed of the tolerances of the components forming the detector.
  • the present invention also aims at providing a solution which is not sensitive to variations of the D.C. voltage.
  • the present invention also aims at providing a solution which operates for different supply voltage frequencies and amplitudes, with no modification, and which is not sensitive to the shape factor of the non-D.C. supply voltage.
  • the present invention also aims at providing a circuit for supervising the state of a load and of at least one switch controlling it, implementing this detection method.
  • the present invention also aims at providing a solution avoiding use of an analog-to-digital converter.
  • the present invention provides method for detecting the state of supply of a load by a variable voltage, comprising measuring logarithmic values representative of the variable supply voltage and of a voltage across the load, and calculating the difference between said logarithmic values.
  • said values are logarithmic.
  • an analog voltage representing said difference is compared with predetermined characteristic operation thresholds of the circuit.
  • the times when said analog voltage is taken into account are synchronized on the variable supply voltage.
  • an absolute value of an analog voltage representing said difference is compared with predetermined characteristic operation thresholds of the circuit.
  • said absolute value is averaged before being compared with said thresholds.
  • the variable supply voltage is an A.C. voltage.
  • variable supply voltage is a non-D.C. unipolar voltage.
  • the present invention also provides a circuit for supervising the state of supply of a load by a variable voltage in series with at least one first switch, comprising means for measuring values representative of the variable voltage and a voltage across the load and for making logarithmic said values, and an element for calculating the difference between said logarithmic values.
  • a second switch is in series with the load and the first switch.
  • the circuit comprises an element for calculating the absolute value of the output voltage of said element for calculating the difference.
  • said absolute value is averaged.
  • the circuit comprises at least one comparator with at least one characteristic operation threshold of the assembly.
  • FIGS. 1, 2 , and 3 previously described, are intended to show the state of the art and the problem to solve;
  • FIG. 4 schematically and functionally illustrates the detection method according to the present invention
  • FIG. 5 shows an embodiment of a circuit for detecting the supply state of an A.C. load according to the present invention
  • FIG. 6 illustrates, in a timing diagram, the operation of the circuit of FIG. 5 ;
  • FIG. 7 shows an embodiment of a circuit for exploiting the measurement performed by the circuit of FIG. 5 without using an analog-to-digital converter
  • FIG. 8 shows an embodiment of a circuit for detecting the supply state of a load supplied by a variable unipolar voltage according to the present invention.
  • variable is used to designate a non-D.C. voltage, that is, an A.C. or modulated unipolar voltage. As will be seen hereafter, this voltage is not necessarily periodic.
  • FIG. 4 schematically and functionally illustrates an embodiment of the method for detecting the supply state of a load supplied by an A.C. voltage Vac.
  • Detection of the supply voltage of a load is used to designate the detection not only of the load state, but also of one or several switches which control it.
  • Load Q is, as previously, series-connected between switches T and SW between terminals 1 and 2 of application of voltage Vac.
  • control switches T and SW of the load have been shown in dotted lines. Indeed, the method of the present invention may apply even in the absence of switches or in the presence of a single switch in series with the load.
  • two diodes D 1 and D 2 are connected in anti-parallel between an input terminal of element 10 and terminal 2 . Further, two diodes D 3 and D 4 are connected in antiparallel between the other input terminal of element 10 and a terminal of the load.
  • a resistor RREF connects terminal 1 to the non-inverting input of element 10 and a resistor RIN connects the second terminal of load Q to its inverting input.
  • the result provided by element 10 is amplified with a constant gain K to provide an analog signal Vout representative of the load supply state.
  • Diodes D 1 to D 4 are used to make the variation of the voltages at the input of element 10 logarithmic.
  • voltage Vout may be expressed as follows:
  • Vout K.Ln(VQ/Vac).
  • Measured voltage Vout is thus independent from possible variations of the relatively low D.C. measurement element supply voltage Vdc, from variations of the frequency and of the amplitude of A.C. supply voltage Vac, and from the shape factor of this voltage Vac. Further, as will be seen in relation with FIG. 6 , the obtained waveforms are flattened due to diodes D 1 to D 4 .
  • FIG. 5 shows an example of assembly for the implementation of the method of the present invention in an example of application identical to that previously described in relation with FIG. 1 .
  • Triac T, load Q, and switch SW can be found in series between terminals 1 and 2 on which is applied A.C. supply voltage Vac.
  • resistor R 1 between terminals 3 and 2 , and a resistor RIN connected to an input terminal IN of a measurement circuit 20 can be found.
  • resistor R 1 is placed in parallel only with the load and resistor RIN connects load 3 to input terminal IN of measurement circuit 20 .
  • the difference on the detected states will be discussed in relation with FIG. 6 .
  • Resistor R 1 corresponds to the resistor which, for the application of the present invention, conditions the relatively low impedance of the load. In fact, load Q must have, in normal operation, an impedance smaller than resistor R 1 .
  • resistors R 1 and RIN are different from each other.
  • Resistor R 1 preferably is of high value with respect to resistor RIN.
  • resistor RIN preferably is of same value as resistor RREF, which connects terminal 2 to a reference input REF of circuit 20 .
  • the difference calculation element is formed of an operational amplifier 21 supplied by a D.C. voltage Vdc relatively low with respect to voltage Vac.
  • a D.C. voltage equal to Vdc/2 is further applied between terminals 6 and 7 , terminal 6 being directly connected to terminal 1 to form a common voltage node with voltage Vac, and terminal 7 corresponding to ground on the D.C. voltage side.
  • the inverting input of amplifier 21 is connected, by a resistor R 22 , to the cathode of diode D 3 and to the anode of diode D 4 and, by a resistor R 23 , to measurement input IN.
  • the non-inverting input of amplifier 21 is connected by a resistor R 24 to reference input REF of circuit 20 and by a resistor R 25 to the output of amplifier 21 .
  • the anode of diode D 1 and the cathode of diode D 2 are connected to input REF.
  • the cathode of diode D 1 , the anode of diode D 2 , the cathode of diode D 3 , and the anode of diode D 4 are connected to terminal 6 .
  • the output of amplifier 21 is applied to an absolute value calculation circuit 22 providing a rectified voltage RVout.
  • element 22 is omitted.
  • Voltage Vout provided by amplifier 21 is then analyzed by taking into account the periodicity of voltage Vac.
  • An advantage of analyzing absolute value RVout of voltage Vout is that this enables applying the present invention to non-periodic voltages.
  • the input stages of amplifier 21 are replaced with two analog-to-digital converters.
  • this is not a preferred embodiment since that of FIG. 5 is of simpler implementation.
  • FIG. 6 illustrates the shape of voltage RVout provided by element 22 in different cases of operation.
  • Thresholds MED and THH are defined, for example as previously, and thresholds REFIH and REFH are defined between levels MED and THH. Thresholds REFIH and REFH may correspond in value to preceding thresholds THILH and THIHH, respectively. However, their exploitation is different.
  • An advantage of the present invention in the embodiment using diodes D 1 to D 4 is that it considerably flattens the waveforms obtained on voltage Vout. Accordingly, the possible time windows of analysis of the analog shapes are considerably widened.
  • FIG. 6 reproduces an example applied to an A.C. voltage at the 50-Hz frequency and it can be seen that the possible analysis windows of voltage RVout with respect to the threshold voltages are considerably greater. For example, only two milliseconds around the zero crossings are to be excluded from the analysis window. Further, it can be seen hereafter that a permanent detection may even be performed.
  • signal Vout or RVout is converted by an analog-to-digital converter before being exploited by a microcontroller or microprocessor.
  • voltage RVout is compared in parallel with the different thresholds to directly provide digital information about the operating state of the system.
  • voltage RVout is applied to an average value calculation circuit 30 for the case of a periodic voltage Vac.
  • the average value of absolute value RVout of the difference between the voltage across the load and the supply voltage is considered, voltage RVout being provided, for example, by the circuit of FIG. 5 .
  • averager 30 is formed of an RC cell having its time constant selected to approximately correspond to the period of voltage Vac.
  • the output of circuit 30 is sent to first respective inputs of four comparators 31 , 32 , 33 , and 34 having their respective second inputs receiving reference levels MMED, MREFIH, MREFH, and MTHH determined according to thresholds MED, REFIH, REFH, and THH.
  • thresholds MMED, MREFIH, MREFH, and MTHH are considered to respectively correspond to thresholds MED, REFIH, REFH, and THH.
  • thresholds MMED, MREFIH, MREFH, and MTHH will be determined by taking into account the possible level lowering linked to the averager function. It is arbitrarily assumed that each comparator provides an output in the high state when its threshold is exceeded. The opposite is of course possible.
  • comparator 31 If comparator 31 provides a high state, this means that threshold MREFH is exceeded, and thus that the measurement circuit is defective.
  • comparator 32 provides a high state while comparator 31 provides a low state, this means that triac T is on, or that triac T and switch SW are off. According to the level of threshold MREFH, this may also mean a defect of the triac.
  • comparator 33 If comparator 33 provides a high state while comparators 31 and 32 provide low states, this means that the load is defective.
  • comparator 34 If only comparator 34 is in the high state, this means that, the triac being off, switch SW is on and the load is not defective.
  • a fifth comparator of comparison with a threshold ranging between levels MREFIH and MREFH is used to differentiate an on operation of the triac from a diode operation.
  • the binary states provided by the circuit of FIG. 7 enable direct interpretation by a microprocessor or a wired logic without for it to be necessary to use an analog-to-digital converter.
  • An advantage of this embodiment is that it enables a permanent detection, with no synchronization of the detection times with respect to A.C. voltage Vac.
  • a direct exploitation such as that of FIG. 7 is impossible with a conventional circuit due to the waveforms that it provides.
  • Another advantage of the present invention is that the detection is insensitive to the possible tolerances of D.C. voltage Vdc.
  • Another advantage of the present invention is that a same circuit can be used when the A.C. voltage varies in frequency and/or in amplitude.
  • the margin is such in the differences between voltages that it is, in practice, not always necessary to modify the thresholds especially to switch from a voltage Vac of 110 V, 60 Hz to a voltage Vac of 230 V, 50 Hz.
  • Another advantage of the present invention in its preferred embodiment is that it avoids use of an analog-to-digital converter.
  • An advantage of the present invention is that the provided detection circuit is compatible with a detection under a variable power supply, be it A.C. or unipolar, periodic or aperiodic.
  • Another advantage of the present invention is that it enables instantaneous detection of the defects, without it being necessary to wait for the interpretation of synchronized measurements.
  • FIG. 8 shows the diagram of an embodiment of the present invention applied to a load supplied by a variable unipolar voltage.
  • the load is a magnetron Q′ powered by a modulated voltage Vm applied between terminals 1 and 2 , high with respect to a low supply voltage Vdc applied to its cathode 40 via a diode D 6 .
  • a control switch M connects cathode 40 of the magnetron to ground 2 or 7 common to voltages Vm and Vdc, and receives a control signal CT′.
  • a security relay forms a switch SW between terminal 1 and anode 41 of magnetron Q′.
  • Circuit 20 ′ of supervision of the supply state comprises an amplifier 21 examining the difference between the non-D.C. supply voltage Vm and the voltage across load Q′.
  • a resistor R 1 is in parallel with load Q′.
  • a resistor RIN connects cathode 40 to input IN of circuit 20 ′.
  • a resistor RREF connects terminal 1 to input REF of circuit 20 ′.
  • Input IN is connected to the inverting input of comparator 21 by a resistor R 23 and, by a diode D 3 , to ground 7 .
  • the inverting input is connected to the output providing voltage Vout by a resistor R 25 ′.
  • Input REF is connected to the non-inverting input by a resistor R 24 and, by a diode D 1 , to ground 7 .
  • the non-inverting input is connected to ground 7 by a resistor R 22 ′.
  • Operational amplifier 21 forming the comparator is supplied by voltage Vdc.
  • Voltage Vout is compared with thresholds enabling detecting different conditions.
  • the operation of the assembly of FIG. 8 can be deduced from the operations discussed in relation with the previous drawings.
  • the present invention is likely to have various, alterations, improvements, and modifications which will readily occur to those skilled in the art.
  • the practical implementation of the circuit of the present invention is within the abilities of those skilled in the art according to the functional indications given hereabove and by using conventional components.
  • the threshold determination is also within the abilities of those skilled in the art according to the application and especially to the D.C. supply voltage.

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Measurement Of Current Or Voltage (AREA)
  • Emergency Protection Circuit Devices (AREA)
US11/216,919 2004-08-31 2005-08-31 Detection of the supply state of a load supplied by a variable voltage Abandoned US20060043944A1 (en)

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US11/966,246 US8022675B2 (en) 2004-08-31 2007-12-28 Detection of the supply state of a load supplied by a variable voltage

Applications Claiming Priority (2)

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FR0451944A FR2874700B1 (fr) 2004-08-31 2004-08-31 Detection de l'etat d'alimentation d'une charge alimentee par une tension variable
FR04/51944 2004-08-31

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Cited By (1)

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FR2929408A1 (fr) * 2008-03-31 2009-10-02 Stmicroelectronics Tours Sas S Detection de l'etat des elements d'une branche electrique comprenant une charge et un interrupteur

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TWI571029B (zh) * 2015-10-28 2017-02-11 茂達電子股份有限公司 補償電路及使用其的儲能裝置
CN109374999A (zh) * 2018-09-17 2019-02-22 青岛海尔科技有限公司 一种用于洗衣机检测的便携式工装、pcb板及检测方法

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US4585987A (en) * 1983-08-12 1986-04-29 John Fluke Mfg. Co., Inc. Regulated voltage supply with sense current cancellation circuit
US4628397A (en) * 1984-06-04 1986-12-09 General Electric Co. Protected input/output circuitry for a programmable controller
US5329223A (en) * 1992-06-26 1994-07-12 Green Technologies, Inc. Ideal voltage controller for conserving energy in inductive loads
US6081123A (en) * 1996-11-18 2000-06-27 Schneider Electric Sa Device for preventive detection of faults with identification of the type of load
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Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2929408A1 (fr) * 2008-03-31 2009-10-02 Stmicroelectronics Tours Sas S Detection de l'etat des elements d'une branche electrique comprenant une charge et un interrupteur
EP2107382A1 (fr) 2008-03-31 2009-10-07 STMicroelectronics (Tours) SAS Détection de l'état des éléments d'une branche électrique comprenant une charge et un interrupteur
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US8022675B2 (en) 2011-09-20
US20080157784A1 (en) 2008-07-03
FR2874700A1 (fr) 2006-03-03
FR2874700B1 (fr) 2006-11-17

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