WO2021249770A1 - Method and control unit for zero cross relay switching - Google Patents

Method and control unit for zero cross relay switching Download PDF

Info

Publication number
WO2021249770A1
WO2021249770A1 PCT/EP2021/063962 EP2021063962W WO2021249770A1 WO 2021249770 A1 WO2021249770 A1 WO 2021249770A1 EP 2021063962 W EP2021063962 W EP 2021063962W WO 2021249770 A1 WO2021249770 A1 WO 2021249770A1
Authority
WO
WIPO (PCT)
Prior art keywords
relay
switch
event
arc
control
Prior art date
Application number
PCT/EP2021/063962
Other languages
French (fr)
Inventor
Peter SPISÁK
Original Assignee
BSH Hausgeräte GmbH
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 BSH Hausgeräte GmbH filed Critical BSH Hausgeräte GmbH
Priority to EP21729463.6A priority Critical patent/EP4165674A1/en
Publication of WO2021249770A1 publication Critical patent/WO2021249770A1/en

Links

Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/02—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current for modifying the operation of the relay
    • H01H47/18—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current for modifying the operation of the relay for introducing delay in the operation of the relay
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/002—Monitoring or fail-safe circuits
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H47/00—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current
    • H01H47/22—Circuit arrangements not adapted to a particular application of the relay and designed to obtain desired operating characteristics or to provide energising current for supplying energising current for relay coil
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H50/00—Details of electromagnetic relays
    • H01H50/16—Magnetic circuit arrangements
    • H01H50/18—Movable parts of magnetic circuits, e.g. armature
    • H01H50/24—Parts rotatable or rockable outside coil
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H9/00—Details of switching devices, not covered by groups H01H1/00 - H01H7/00
    • H01H9/50—Means for detecting the presence of an arc or discharge

Definitions

  • the present document is directed at a method and a control unit for controlling the state of an (electro-) mechanical relay, notably for setting the control time instant for switching on or off the relay.
  • Mechanical relays are widely used e.g. in home appliances.
  • the relay contacts and/or its mechanical components may be subjected to degradation resulting from plasmatic arcs which form between the relay contacts during switching events of the relay.
  • the phenomenon of plasmatic arcs may cause degradation of the relay mechanics by damaging the relay contact material, by damaging the relay return springs and/or by damaging other relay mechanical parts.
  • extensive electromagnetic emission noise may be caused by the arc current between the contacts, wherein the arc noise may disturb operation of an appliance.
  • a plasmatic arc may cause contact material to be evaporated and/or scattered within a relay, thereby affecting the overall reliability of the relay.
  • a damaged relay may affect the reliability of the home appliance which comprises the relay.
  • zero cross detection for detecting the zero crossing of the AC mains voltage sine wave may be used.
  • the switching times of a relay may then be set based on the detected zero crossing time instants, such that the relay is switched on or off at time instants when the AC mains voltage sine wave exhibits a zero crossing.
  • a relay typically exhibits a control delay between the control time instant of a control signal for switching on or off the relay and the connect or disconnect time instant at which the relay is actually switched on or off, thereby allowing or disabling the AC mains current to flow.
  • the control time instant needs to be advanced with regards to the zero crossing time instant by the control delay.
  • the present document is directed at the technical problem of setting the control time instant for switching on or off a relay in a precise and reliable manner, notably in order to reduce the degradation of a relay during operation of the relay in conjunction with an AC power supply. This technical problem is solved by the subject-matter of each of the independent claims. Preferred examples are described in the dependent claims, in the following description and in the attached drawing.
  • the relay may comprise a movable anchor or armature and a coil.
  • the coil may be configured to exert a (magnetic) force onto the anchor subject to a coil current (notably a DC (direct current) current) at a control port, in order to connect contacts of the relay.
  • the contacts of the relay may be configured to enable or to disable an electrical connection between load ports of the relay.
  • the load ports may be coupled to an AC voltage (e.g. a 230V mains voltage at an AC frequency of 50Hz or an 110V mains voltage at an AC frequency of 60Hz).
  • the contacts of the relay may be connected, i.e. brought into contact with one another, subject to a coil current creating a magnetic field which attracts the movable anchor.
  • the coil current may be generated by applying a control voltage to the control port of the relay.
  • the contacts may be disconnected, i.e. separated from one another, subject to the coil current dropping to zero, such that the magnetic field is interrupted.
  • the coil current may be interrupted by coupling the control port to ground.
  • the method may comprise applying, at a control time instant, a control signal to the control port for initiating a switch-off event or a switch-on event of the relay.
  • the control time instant may depend on a previously determined control delay of the relay.
  • the control signal may be a step-up function increasing the control voltage from zero to a constant control voltage level (for initiating a switch-on event).
  • the control signal may be a step-down function decreasing the control voltage from the constant control voltage level to zero (for initiating a switch-off event).
  • the method may comprise determining an upcoming or future zero crossing time instant of the AC voltage which is applied to the load ports of the relay.
  • the zero crossing time instant may be the time instant at which the AC voltage changes polarity.
  • the control time instant may be determined based on the previously determined control delay and based on the zero crossing time instant. In particular, the control time instant may be moved forward or advanced with respect to the (upcoming or future) zero crossing time instant by the control delay. By moving forward the control signal in dependence of the control delay of the relay, the disconnect time instant (at which the contacts of the relay disconnect) or the connect time instant (at which the contacts connect) may be moved closer to the zero crossing time instant (compared to an arbitrary selection of the control time instant). As a result of this, the generation of arcs between the contacts during a switch-off event or during a switch-on event may be reduced or avoided, thereby reducing degradation of the relay.
  • the method may comprise determining phase shift information regarding a phase shift between the AC voltage and the load current at the load ports of the relay.
  • the phase shift may be caused by a (non-resistive, notably an inductive) load which is coupled to the load ports.
  • the control delay may be determined based on the phase shift information, thereby enabling the use of the method for non-resistive (e.g. inductive) loads (such as an electrical motor).
  • the disconnect time instant at which the contacts of the relay disconnect
  • the connect time instant at which the contacts connect
  • the method comprises determining arc information regarding the formation of a plasmatic arc between the contacts of the relay during the switch-off event or the switch-on event of the relay.
  • the arc information may be indicative of whether or not an arc is generated during the switch-off event or the switch-on event.
  • the arc information may be indicative of the start time instant and/or the end time instant and/or the duration of the arc.
  • the arc information may be determined based on arc noise that is generated by the arc.
  • the method further comprises updating (e.g. shifting) the control delay based on the arc information, notably based on the start time instant and/or the end time instant and/or the duration of the arc.
  • the control delay may be updated and/or shifted by an offset corresponding to or depending on the temporal duration of the detected arc noise.
  • the control delay may be updated such that the arc would not have been generated during the current switch-off event or switch-on event of the relay, if the updated control delay had been used to determine the control time instant for the current switch-off event or switch-on event of the relay.
  • the method may comprise detecting arc noise caused by an arc between the contacts of the relay.
  • the arc information may be determined in a precise manner based on the detected arc noise.
  • a relay signal may be measured during the switch-off event or the switch-on event of the relay.
  • the relay signal may indicate a signal value as a function of time, during the switch-off event or the switch-on event of the relay.
  • the relay signal may correspond to or may be indicative of the course of the coil current through the coil of the relay during the switch-off event or the switch-on event of the relay.
  • the method may then comprise determining arc information regarding the arc noise comprised within the relay signal.
  • the method may comprise determining the start time instant of the beginning of the arc noise and/or the end time instant of the end of the arc noise.
  • the arc information may then be indicative of the start time instant and/or the end time instant and/or the duration of the arc (i.e. the temporal difference between the start time instant and the end time instant).
  • the control delay may be updated in a precise manner.
  • a control unit for controlling a relay may comprise analog and/or digital circuitry.
  • the control unit is configured to apply, at a control time instant, a control signal to the control port for initiating a switch-off event or a switch-on event of the relay, wherein the control time instant depends on a previously determined control delay of the relay.
  • the control unit may comprise a (analog) detection circuit which is configured to determine arc information regarding the formation of an arc between the contacts of the relay during the switch-off event or the switch-on event of the relay. Furthermore, the control unit is configured to update the control delay based on the arc information.
  • the detection circuit may be configured to sense a relay signal during the switch-off event or the switch-on event of the relay. Furthermore, the detection circuit may comprise a power detector (notably a radio frequency (RF) power detector) which is configured to determine a power level of the relay signal within a pre-determined frequency band. In other words, the power level of a subband of the relay signal, which corresponds to a pre determined frequency band, may be determined.
  • a power detector notably a radio frequency (RF) power detector
  • the pre-determined frequency band comprises frequencies of the arc noise which is generated by an arc between the contacts of the relay.
  • the pre-determined frequency band may exhibit a lower bound of 1 MHz or higher.
  • the detection circuit may be configured to determine the arc information based on the power level of the relay signal within the pre-determined frequency band.
  • the detection circuit may be configured to detect an increased power level (compared to a reference power level), thereby detecting the presence of arc noise within the relay signal.
  • the arc information may be determined in a precise manner.
  • the detection circuit may be configured to determine a reference power level of the relay signal within the pre-determined frequency band prior to a time instant at which the contacts of the relay are disconnected or connected (notably prior to the formation of an arc).
  • the reference power level may be determined using the power detector.
  • the reference power level may be indicative of the background noise within the relay signal.
  • the detection circuit may be configured to compare the power level of the relay signal within the pre-determined frequency band, which is determined during the switch-off event or the switch-on event of the relay, with the reference power level, to determine the arc information.
  • the detection circuit may comprise a comparator which is configured to compare the power level with the reference power level.
  • the comparator may be configured to generate a deviation signal which indicates time instants at which the power level exceeds the reference power level (and by consequence, time instants at which the relay signal comprises arc noise).
  • the arc information may then be determined in a precise manner based on the deviation signal.
  • an appliance notably a home appliance (such as a dish washer, an oven, a washing machine, a dryer, a refrigerator, a cooking machine, etc.) is described.
  • the appliance may comprise the control unit described in the present document.
  • the appliance may comprise a plurality of relays. Furthermore, the appliance may comprise a joint detection circuit for the plurality of relays.
  • the detection circuit may be designed as outlined in the present document.
  • the detection circuit may be configured to determine arc information regarding the formation of an arc between contacts of any one of the plurality of relays during a switch-off event or a switch-on event of the respective relay.
  • the appliance may comprise a control unit which is configured to determine that a (arbitrary) first relay from the plurality of relays is to be switched-on or switched-off.
  • the control unit may be configured to apply, at a control time instant, a control signal to the control port of the first relay for initiating a switch-off event or a switch- on event of the first relay, wherein the control time instant depends on a previously determined control delay of the first relay.
  • the control unit may be configured to update the control delay of the first relay based on the arc information determined by the detection unit during the switch-off event or the switch-on event of the first relay.
  • a joint detection circuit may be used for adjusting the control delay of multiple relays, thereby providing a cost efficient appliance.
  • the appliance may comprise a measurement point which is affected by arc noise that is generated by a switch-off event or a switch-on event of any one of the plurality of relays.
  • the detection circuit may be configured to sense a relay signal at the measurement point, and to determine the arc information based on the relay signal.
  • the control delays of the relays may be adjusted in a precise and reliable manner.
  • the measurement point may be such that it allows detection of arc information and/or arc noise in a wireless manner.
  • the measurement point may comprise and/or may be implemented as an antenna.
  • the antenna may be placed at a central point between the plurality of relays. By making use of an antenna for measuring the arc information, arc detection may be performed in a particularly efficient and reliable manner.
  • Fig. 1 shows an example electromechanical relay
  • Fig. 2a shows the temporal course or curve of the coil current during a switch-on event
  • Fig. 2b shows the temporal course or curve of the coil current during a switch-off event
  • Fig. 3a illustrates arc noise within the coil current during a switch-off event
  • Fig. 3b illustrates the time interval of arc noise in relation to the AC mains voltage
  • Fig. 4 shows an example detection circuit for detecting arc noise
  • Fig. 5 illustrates an example envelope signal for the arc noise
  • Fig. 6 shows a flow chart of an example method for controlling a switch-on event or a switch-off event of a relay.
  • Fig. 1 shows an example relay 1.
  • the relay 1 comprises a coil 2 which is configured to generate a magnetic field, subject to a coil current l(t) which is applied to the control port 4.
  • the coil 2 may comprise a coil core 8, which is configured to direct the magnetic field towards an armature or anchor 3 of the relay 1.
  • the armature or anchor 3 is configured to be attracted by the magnetic field generated by the coil 2.
  • the armature 3 is typically moved away from the coil 2 and the coil core 8 using a spring 10.
  • the magnetic field which is generated by the coil 2 may cause a sufficiently high attracting force onto the armature 3, such that spring force for the spring 10 is overcome and such that the armature 3 is pulled towards the coil core 8 to switch on the relay 1.
  • the armature 3 is coupled to a contact 5, wherein the contact 5 of the armature 3 touches the contact 5 of the base of the relay 1 , when the armature 3 is pulled towards the coil core 8.
  • the load ports 6 of the relay 1 are electrically coupled with one another, thereby allowing a current to flow between the load ports 6 and notably between the contacts 5.
  • the contacts 5 By interrupting the coil current l(t), the magnetic field is interrupted and the armature 3 is pulled away from the coil core 8 due to the spring force caused by the spring 10. Eventually, the contacts 5 are disconnected from one another, thereby switching off the relay 1. In a relaxed or inactive state, the contacts 5 form a contact gap S having a certain gap width.
  • the armature 3 is pulled towards the coil core 8, as soon as a coil current l(t) is applied to the control port 4.
  • the coil current l(t) may be applied at a control time instant.
  • the contacts 5 start touching each other, thereby switching on the relay 1 and thereby allowing a load current to flow via the load ports 6.
  • the armature 3 typically does not yet touch the coil core 8.
  • the time instant, at which the armature 3 touches the coil core 8 may be referred to at the close time instant, as the relay 1 is now fully closed.
  • the (flexible) connecting plate between the armature 3 and the contact 5 of the armature 3 forms a flat spring 11 in a flexed condition, wherein the force of the flat spring 11 pulls the armature 3 away from the coil core 8.
  • the magnetic field need to overcome the forces of the return spring 10 of the armature 3 and of the flat spring 11 of the contact 5.
  • the control port 4 is disconnected from a control voltage (at a control time instant).
  • the coil current l(t) decreases gradually such that the magnetic force decreases causing the flat spring 11 to return to a relaxed state and subsequently causing the return spring 10 to pull the contact 5 of the armature 3 away from the contact 5 of the base of the relay 1.
  • the time instant, at which the contacts 5 are disconnected may be referred to as the disconnect time instant.
  • a switch-on event or a switch-off event may lead to plasmatic arcs between the contacts 5, if the contacts 5 are connected or disconnected at a time instant, when the voltage across the load ports 6 is relatively high (e.g. 24V or higher) and/or when there is a load current through the load ports 6. This may lead to a degradation of the contacts 5 and of the mechanical components of the relay 1. In order to avoid such degradations, it is preferable to place the (dis)connect time instant of a switch- on event or a switch-off event at a zero crossing of the AC voltage which is applied to the load ports 6 and/or at a zero crossing of the load current at the load ports 6. In view of this, the control delay between the control time instant, at which the control voltage is applied to or disconnected from the control port 4, and the (dis)connect time instant, at which the contact gap S is closed or opened, needs to be determined in a precise manner.
  • Fig. 2a shows an example curve or course 201 of the coil current 200 during a switch-on event. It can be seen that the coil current 200 increases gradually, but exhibits an intermediate drop.
  • Fig. 2b shows an example curve or course 202 of the coil current 200 during a switch-off event. It can be seen that the coil current 200 decreases gradually, but exhibits an intermediate peak.
  • Fig. 3a illustrates arc noise 302 within the course 202 of the coil current 200, which originates from the relay contact arc that is generated, in case the relay contacts 5 open just after the A/C mains voltage at the contacts 5 crossed the zero voltage, such that the A/C mains voltage lies above the critical voltage level (of e.g. 24V). Once the arc has built up, the arc lasts almost until the next zero cross of the mains voltage. Furthermore, Fig. 3a shows the course 301 of the first derivative of the course 202 of the coil current 200. The first derivative, notably the maximum of the first derivative, may be used for detecting the actual (dis)connect time instant.
  • Fig. 3b illustrates the time interval 312 during which arc noise 302 is present within the coil current 200. Furthermore, Fig. 3b shows the A/C mains voltage wave 310, which exhibits a zero crossing at zero crossing time instant 311. It can be seen that the arc noise 302 is generated, as long as the A/C mains voltage exceeds a certain threshold voltage (e.g. 24V). In addition, Fig. 3b shows the control time instant 313 (at the point, where the curve 202 of the coil current 200 starts to drop) at which a control signal is to be applied to the control port 4 of the relay 1 to initiate a switch-on event or a switch-off event of the relay 1. The control time instant 313 precedes the zero crossing time instant 311 by a control delay 315.
  • a control delay 315 at the point, where the curve 202 of the coil current 200 starts to drop
  • the curve 202 of the coil current 200 is shifted relative to the A/C mains voltage wave 310.
  • the curve 202 may be shifted such that the beginning of the interval
  • an arc detection zero cross relay control (ADRC) scheme is described.
  • the scheme makes use of circuitry for detecting the occurrence of electromagnetic arc noise.
  • the circuitry may be used for determining arc information regarding arc noise 302. Timing information regarding the control time instant
  • the control delay 315 for switching on or off the relay 1 may be determined based on the arc information.
  • the timing information may be compared to the A/C mains zero cross timing 311 to determine the control time instant 313.
  • the arc information may be used for enabling a precise relay switching control to avoid the creation of arcs. Switching the relay contacts 5 may therefore be performed within the time interval, during which the A/C mains voltage is below the critical voltage threshold.
  • the ADRC scheme may be used in various different electro mechanic relay switching circuits which are equipped with a A/C mains zero detect circuit and/or with processor controlled relay switching. Typically, no relay control (hardware) changes are required.
  • the ADRC scheme is suitable for circuits switching a resistive load (e.g. heating elements) and/or a non-resistive (e.g. inductive) load.
  • Fig. 4 shows an example detection circuit 400 for detecting arc noise 302 which is caused by an arc during a switch-on or switch-off event of a relay 1.
  • the detection circuit 400 is configured to analyze a relay signal 401 which is captured during the switch-on or switch- off event of the relay 1.
  • the relay signal 401 may correspond to the course 202 of the coil current 200.
  • the detection circuit 400 may be configured to determine arc information 406 based on the relay signal 401 , wherein the arc information 406 indicates
  • the detection circuit 400 of Fig. 4 is operated with a supply voltage VCC 413 (e.g. at 5V).
  • the detection circuit 400 comprises a pre-amplifier 410 with an amplification transistor 411, which is configured to amplify the relay signal 401 to provide an amplified relay signal 402.
  • a (radio frequency, RF) power detector 412 may be used to detect the power of the (amplified) relay signal 401, 402 within a particular (RF) frequency band, wherein the frequency band should be different from one or more operating frequencies of the appliance within which the detection circuit 400 is used.
  • the particular frequency band should comprise frequencies of the arc noise 302 which is to be detected.
  • the power detector 412 may be switched on or off using an on/off signal 422.
  • the power detector 412 provides as output a power signal 403 (notably a power level) which is indicative of the power of the (amplified) relay signal 401 , 402 within the particular frequency band at a particular time instant.
  • the detection circuit 400 may comprise a sample-and-hold circuit 418 which is configured to store the power signal 403 for a time instant at which the relay signal 401 does not comprise any arc noise 302. This power signal or power level 403 may be considered to be a reference level of the background noise which is comprised within the relay signal 401.
  • the sample-and-hold circuit 418 comprises a transistor 413 which is controlled using the sample-and-hold control signal 421 and which allows the power signal 403 to be stored in the capacitor 414.
  • the stored power signal 403 may be provided as a reference signal (or reference level) 404 to a comparator 416 via a voltage follower 415.
  • the power signal 403 at different time instants during a switch-on or switch-off event of the relay 1 may be compared to the reference signal 404 using the comparator 416, wherein the comparator 416 provides a deviation signal 405 which indicates whether or not the power signal 403 deviates from the reference signal 404.
  • a signal conditioner 417 may be used to transform the deviation signal 405 into a rectangular or binary signal which indicates whether arc noise 302 is present or is not present within the relay signal 401.
  • the arc information 406 may comprise or may correspond to the rectangular or binary signal.
  • a detection circuit 400 which comprises a power detector 412 (such as Linear Technology LTC5507 RF power detector).
  • the power detector 412 and the radio frequency (RF) pre-amplifier stage 410 form a RF frequency power detector which may be tuned to a frequency range or frequency band of about 1 MHz to 100 MHz.
  • Amplification of the pre-amplifier 410 may be set up according to the detected noise level of arc noise 302 in the particular appliance within which the detection circuit 400 is used.
  • the power detector 412 may convert the detected electromagnetic noise 302 into a voltage (i.e. the power level 403) which is proportional to the noise power within the relay signal 401 (in dBm).
  • the sample-and-hold control signal 421 of the sample-and-hold circuit 418 may be operated by a control processor to store general RF noise level information (i.e. a reference power level 404) just before the expected time instant of the occurrence of arc noise 302.
  • the reference power level 404 may be stored a few microseconds after the control time instant 313, i.e. after the relay switch operating action (relay closing or opening) has been issued by the relay control processor 100.
  • the operational amplifier 416 compares two different RF noise levels, i.e. the reference noise level 404 stored in the sample-and-hold circuit 418 just before operation of the relay contacts 5 with the instantaneous noise level 403. If the instantaneous noise level 403 is higher than the stored reference noise level 404, the difference is amplified by the operational amplifier 416, providing a deviation signal 405 which indicates that arc noise 302 has occurred due to an arc between the relay contacts 5.
  • a signal conditioner 417 may be used for producing a rectangular pulse envelope 406 framing the duration of the arc noise 302.
  • the rectangular pulse envelope 406 provides exact time information regarding the beginning and the end of the arc between the relay contacts 5.
  • the rectangular pulse envelope 406 may be used for recalculating the control delay 315 relatively to the A/C mains zero cross time instant 311, in order to avoid the generation of an arc during a subsequent switch-on or switch-off event.
  • Fig. 5 shows an example rectangular pulse envelope 406.
  • the envelope 406 indicates a start time instant 501 for the beginning of the arc noise 302 and/or an end time instant 502 for the end of the arc noise 302.
  • the detection circuit 400 may be controlled using a control processor or control unit 100.
  • the control unit 100 may be configured to enable the detection circuit 400 by switching on the power detector 412 using the on/off signal 422, and by controlling the sample-and- hold circuit 418 using the sample-and-hold control signal 421. Furthermore, the control unit 100 may be configured to control operation of the relay 1.
  • the control unit 100 may issue a command to switch off (or switch on) the relay 1 at a control time instant T 0ff 313.
  • the control time instant 313 may be determined by applying a (negative) time delay 315 to the A/C mains voltage zero cross time instant 311.
  • the time delay (referred to as the control delay) 315 may have been determined and stored at a previous switching event of the relay 1.
  • the control unit 100 closes the transistor 413 (using the control signal 421), in order to store the (reference) noise level 404, possibly just before the expected relay contact opening time.
  • the capacitor 414 stores the voltage level 404 indicating the electromagnetic (background) noise (in dBm power), measured just before relay contact opening. This voltage is provided to the (-) input of the comparator 416 via the voltage follower 415.
  • a voltage 403 corresponding to the dBm power of the consequent electromagnetic arc noise 302 is provided to the (+) input of the comparator 416.
  • the comparator 416 amplifies the difference of both voltages and outputs a deviation signal 405 to the signal conditioner 417 which provides the rectangular pulse 406 indicative of the arc noise 302.
  • the rectangular pulse 406 indicates the beginning of the arc T ai 501 (when opening the relay contacts 5) and the end of the arc T a 2 502 (which may correspond to the A/C mains voltage falling below the critical voltage threshold).
  • the ADRC scheme allows determining the actual time instant 501 of the relay contact opening and the actual time instant 502 of the end of the arc, regardless the type of load, i.e. also for non-resistive loads (e.g. inductive loads).
  • the ADRC scheme may therefore monitor the actual arcing status between the relay contacts 5 for different types of loads.
  • the control unit 100 may use the information about T ai 501 and/or T a 2 502 to recalculate the control time instant T 0f r 313 for switching off the relay 1 in the future, such that no arc is generated during the future switching event.
  • the time delay 315 which is to be applied to the zero crossing time instant 311 to determine the control time instant 313 may be adjusted based on T ai 501 and/or T a 2502.
  • Fig. 5 shows the example of a non-resistive, notably inductive, load.
  • the are noise 302 follows the load current 510 which is phase shifted with respect to the A/C mains voltage wave 310.
  • the relay 1 should be switched on or off at a zero crossing time instant 511 at which the load current 510 exhibits a zero crossing.
  • typically only the zero crossing time instant 311 of the A/C mains voltage wave 310 can be detected.
  • the time delay 315 between the zero crossing time instant 311 of the A/C mains voltage wave 310 and the control time instant 313 for controlling the relay 1 may take into account the phase shift which is caused by the non-resistive load, thereby enabling arc free switching in conjunction with a non-resistive load.
  • the relay control process and relay operating time corrections which are performed by the control unit 100 may take into account phase shift corrections for a non- resistive load. This may involve a constant phase shift correction or a more complex process calculating a worst-case scenario, if the phase shift is not constant during the appliance operation. While the above-mentioned T ai time 501 refers to relay contact opening, the T a 2 time 502 indicates the end of the respective electric arc due to electric current in a non-resistive load.
  • the electromagnetic noise 302 which is caused by an arc, is typically radiant white wideband noise, which may propagate throughout the entire circuity of an appliance.
  • the relay signal 401 may be captured at various different measurement points within an appliance.
  • the measurement point may be an antenna which is placed within the vicinity of the one or more relays 1.
  • the measurement point may be such that is allows for a wireless detection of arc noise 302.
  • noise detection may be performed using a single detection circuit 400 at a single, properly selected, measurement point for multiple, notably for all, relays 1 of an appliance.
  • the arc information 406 provided by the detection circuit 400 may be used by a control unit 100 of the appliance to control multiple (notably all) relays 1 of the appliance.
  • the proposed ADRC technology can be used as a standalone relay switching technology to avoid arcing or as a supplemental safety technology to confirm the absence of arcs when switching the relays 1 using another zero cross switching technique.
  • Fig. 6 shows a flow chart of an example method 600 for controlling a relay 1.
  • the relay 1 may comprise a movable anchor 3 and a coil 2 which is configured to exert a force onto the anchor 3 subject to a coil current 200 at a control port 4, in order to connect the contacts 5 of the relay 1.
  • the method 600 comprises applying 601, at a control time instant 313, a control signal to the control port 4 of the relay 1 for initiating a switch-off event or a switch-on event of the relay 1.
  • the control signal may lead to a coil current 200 or the control signal may lead to an interruption of the coil current 200.
  • the control time instant 313 depends on a previously determined control delay 315 of the relay 1. Furthermore, the control time instant 313 typically depends on a zero crossing time instant 311 of the AC voltage 310 (which is applied to the load ports 6 of the relay 1), at which the AC voltage 311 changes polarity and/or crosses zero.
  • the method 600 further comprises determining 602 arc information 406 regarding the formation of an arc between the contacts 5 of the relay 1 during the switch-off event or the switch-on event of the relay 1.
  • the arc information 406 may be indicative of a start time instant 501 at which the arc starts to exist, and/or of an end time instant 502 at which the arc ceases to exist.
  • the existence of an arc may be detected via arc noise 302 generated by the arc.
  • the method 600 comprises updating 603 the control delay 315 based on the arc information 406.
  • the control delay 315 may be updated or shifted in dependence of the start time instant 501 , the end time instant 502 and/or the duration 312 of the arc or the arc noise 302.
  • the control delay 315 may be updated with the goal to avoid the generation of an arc during a subsequent switch-off event or switch-on event of the relay 1.
  • the control delay 315 may be updated such that the arc would not have been generated at the current switch-off event or switch-on event, if the updated control delay 315 had been used to determine the control time instant 313 for the current switch-off event or switch-on event.
  • the arc detection zero cross relay control (ADRC) scheme may be used for zero cross switching of electromechanical relays 1 in a standalone manner or as a supplemental scheme to another zero cross relay control scheme (e.g., for increasing safety of the scheme). Furthermore, the ADRC scheme may be used for safety and/or predictive maintenance of an appliance.
  • ADRC arc detection zero cross relay control
  • the aspects which are outlined in the present document enable a reliable and efficient control of a relay 1.
  • the control scheme allows reducing the deteriorations of a relay 1, which are caused by switch-on or switch-off events of the relay 1.

Landscapes

  • Relay Circuits (AREA)

Abstract

A method (600) for controlling a relay (1) is described. The method (600) comprises applying (601), at a control time instant (313), a control signal to a control port (4) of the relay (1) for initiating a switch-off event or a switch-on event of the relay (1), wherein the control time instant (313) depends on a previously determined control delay (315) of the relay (1). The method (600) further comprises determining (602) arc information (406) regarding the formation of an arc between contacts (5) of the relay (1) during the switch- off event or the switch-on event of the relay (1), and updating (603) the control delay (315) based on the arc information (406).

Description

Method and Control Unit for Zero Cross Relay Switching
The present document is directed at a method and a control unit for controlling the state of an (electro-) mechanical relay, notably for setting the control time instant for switching on or off the relay.
Mechanical relays are widely used e.g. in home appliances. When switching a relay at a random time instant relatively to the AC mains power sine wave, the relay contacts and/or its mechanical components may be subjected to degradation resulting from plasmatic arcs which form between the relay contacts during switching events of the relay. The phenomenon of plasmatic arcs may cause degradation of the relay mechanics by damaging the relay contact material, by damaging the relay return springs and/or by damaging other relay mechanical parts. Furthermore, extensive electromagnetic emission noise may be caused by the arc current between the contacts, wherein the arc noise may disturb operation of an appliance. In addition, a plasmatic arc may cause contact material to be evaporated and/or scattered within a relay, thereby affecting the overall reliability of the relay. Eventually, a damaged relay may affect the reliability of the home appliance which comprises the relay.
In order to avoid the phenomenon of plasmatic arcs, zero cross detection for detecting the zero crossing of the AC mains voltage sine wave may be used. The switching times of a relay may then be set based on the detected zero crossing time instants, such that the relay is switched on or off at time instants when the AC mains voltage sine wave exhibits a zero crossing.
A relay typically exhibits a control delay between the control time instant of a control signal for switching on or off the relay and the connect or disconnect time instant at which the relay is actually switched on or off, thereby allowing or disabling the AC mains current to flow. In order to perform the switch-on or switch-off of the relay at a zero crossing time instant, the control time instant needs to be advanced with regards to the zero crossing time instant by the control delay. The present document is directed at the technical problem of setting the control time instant for switching on or off a relay in a precise and reliable manner, notably in order to reduce the degradation of a relay during operation of the relay in conjunction with an AC power supply. This technical problem is solved by the subject-matter of each of the independent claims. Preferred examples are described in the dependent claims, in the following description and in the attached drawing.
According to an aspect, a method for controlling a relay is described. The relay may comprise a movable anchor or armature and a coil. The coil may be configured to exert a (magnetic) force onto the anchor subject to a coil current (notably a DC (direct current) current) at a control port, in order to connect contacts of the relay. The contacts of the relay may be configured to enable or to disable an electrical connection between load ports of the relay. The load ports may be coupled to an AC voltage (e.g. a 230V mains voltage at an AC frequency of 50Hz or an 110V mains voltage at an AC frequency of 60Hz).
During a switch-on event, the contacts of the relay may be connected, i.e. brought into contact with one another, subject to a coil current creating a magnetic field which attracts the movable anchor. The coil current may be generated by applying a control voltage to the control port of the relay. On the other hand, during a switch-off event, the contacts may be disconnected, i.e. separated from one another, subject to the coil current dropping to zero, such that the magnetic field is interrupted. The coil current may be interrupted by coupling the control port to ground.
The method may comprise applying, at a control time instant, a control signal to the control port for initiating a switch-off event or a switch-on event of the relay. The control time instant may depend on a previously determined control delay of the relay. The control signal may be a step-up function increasing the control voltage from zero to a constant control voltage level (for initiating a switch-on event). Alternatively, the control signal may be a step-down function decreasing the control voltage from the constant control voltage level to zero (for initiating a switch-off event).
The method may comprise determining an upcoming or future zero crossing time instant of the AC voltage which is applied to the load ports of the relay. The zero crossing time instant may be the time instant at which the AC voltage changes polarity. The control time instant may be determined based on the previously determined control delay and based on the zero crossing time instant. In particular, the control time instant may be moved forward or advanced with respect to the (upcoming or future) zero crossing time instant by the control delay. By moving forward the control signal in dependence of the control delay of the relay, the disconnect time instant (at which the contacts of the relay disconnect) or the connect time instant (at which the contacts connect) may be moved closer to the zero crossing time instant (compared to an arbitrary selection of the control time instant). As a result of this, the generation of arcs between the contacts during a switch-off event or during a switch-on event may be reduced or avoided, thereby reducing degradation of the relay.
The method may comprise determining phase shift information regarding a phase shift between the AC voltage and the load current at the load ports of the relay. The phase shift may be caused by a (non-resistive, notably an inductive) load which is coupled to the load ports. The control delay may be determined based on the phase shift information, thereby enabling the use of the method for non-resistive (e.g. inductive) loads (such as an electrical motor). In particular, by taking into account the phase shift information, the disconnect time instant (at which the contacts of the relay disconnect) or the connect time instant (at which the contacts connect) may be moved closer to the time instant at which the load current exhibits a zero crossing (which is the time instant relevant for the creation of a plasmatic arc between the contacts of the relay).
The method comprises determining arc information regarding the formation of a plasmatic arc between the contacts of the relay during the switch-off event or the switch-on event of the relay. The arc information may be indicative of whether or not an arc is generated during the switch-off event or the switch-on event. Furthermore, the arc information may be indicative of the start time instant and/or the end time instant and/or the duration of the arc. The arc information may be determined based on arc noise that is generated by the arc.
The method further comprises updating (e.g. shifting) the control delay based on the arc information, notably based on the start time instant and/or the end time instant and/or the duration of the arc. In particular, the control delay may be updated and/or shifted by an offset corresponding to or depending on the temporal duration of the detected arc noise. The control delay may be updated such that the arc would not have been generated during the current switch-off event or switch-on event of the relay, if the updated control delay had been used to determine the control time instant for the current switch-off event or switch-on event of the relay.
By taking into account arc information regarding the formation of arcs during switch-off events or switch-on events, a precise zero cross control of a relay is enabled, thereby reducing degradation of the relay.
The method may comprise detecting arc noise caused by an arc between the contacts of the relay. The arc information may be determined in a precise manner based on the detected arc noise. For detecting arc noise, a relay signal may be measured during the switch-off event or the switch-on event of the relay. The relay signal may indicate a signal value as a function of time, during the switch-off event or the switch-on event of the relay. The relay signal may correspond to or may be indicative of the course of the coil current through the coil of the relay during the switch-off event or the switch-on event of the relay. The method may then comprise determining arc information regarding the arc noise comprised within the relay signal.
The method may comprise determining the start time instant of the beginning of the arc noise and/or the end time instant of the end of the arc noise. The arc information may then be indicative of the start time instant and/or the end time instant and/or the duration of the arc (i.e. the temporal difference between the start time instant and the end time instant). By making use of this temporal information of the arc noise, the control delay may be updated in a precise manner.
According to a further aspect, a control unit for controlling a relay is described. The control unit may comprise analog and/or digital circuitry. The control unit is configured to apply, at a control time instant, a control signal to the control port for initiating a switch-off event or a switch-on event of the relay, wherein the control time instant depends on a previously determined control delay of the relay. The control unit may comprise a (analog) detection circuit which is configured to determine arc information regarding the formation of an arc between the contacts of the relay during the switch-off event or the switch-on event of the relay. Furthermore, the control unit is configured to update the control delay based on the arc information.
The detection circuit may be configured to sense a relay signal during the switch-off event or the switch-on event of the relay. Furthermore, the detection circuit may comprise a power detector (notably a radio frequency (RF) power detector) which is configured to determine a power level of the relay signal within a pre-determined frequency band. In other words, the power level of a subband of the relay signal, which corresponds to a pre determined frequency band, may be determined.
The pre-determined frequency band comprises frequencies of the arc noise which is generated by an arc between the contacts of the relay. In particular, the pre-determined frequency band may exhibit a lower bound of 1 MHz or higher.
The detection circuit may be configured to determine the arc information based on the power level of the relay signal within the pre-determined frequency band. In particular, the detection circuit may be configured to detect an increased power level (compared to a reference power level), thereby detecting the presence of arc noise within the relay signal. By determining the (RF) power level of a subband of the relay signal, the arc information may be determined in a precise manner.
The detection circuit may be configured to determine a reference power level of the relay signal within the pre-determined frequency band prior to a time instant at which the contacts of the relay are disconnected or connected (notably prior to the formation of an arc). The reference power level may be determined using the power detector. The reference power level may be indicative of the background noise within the relay signal.
Furthermore, the detection circuit may be configured to compare the power level of the relay signal within the pre-determined frequency band, which is determined during the switch-off event or the switch-on event of the relay, with the reference power level, to determine the arc information. In particular, the detection circuit may comprise a comparator which is configured to compare the power level with the reference power level. The comparator may be configured to generate a deviation signal which indicates time instants at which the power level exceeds the reference power level (and by consequence, time instants at which the relay signal comprises arc noise). The arc information may then be determined in a precise manner based on the deviation signal.
According to a further aspect, an appliance, notably a home appliance (such as a dish washer, an oven, a washing machine, a dryer, a refrigerator, a cooking machine, etc.) is described. The appliance may comprise the control unit described in the present document.
The appliance may comprise a plurality of relays. Furthermore, the appliance may comprise a joint detection circuit for the plurality of relays. The detection circuit may be designed as outlined in the present document. In particular, the detection circuit may be configured to determine arc information regarding the formation of an arc between contacts of any one of the plurality of relays during a switch-off event or a switch-on event of the respective relay.
In addition, the appliance may comprise a control unit which is configured to determine that a (arbitrary) first relay from the plurality of relays is to be switched-on or switched-off. Furthermore, the control unit may be configured to apply, at a control time instant, a control signal to the control port of the first relay for initiating a switch-off event or a switch- on event of the first relay, wherein the control time instant depends on a previously determined control delay of the first relay. In addition, the control unit may be configured to update the control delay of the first relay based on the arc information determined by the detection unit during the switch-off event or the switch-on event of the first relay.
Hence, a joint detection circuit may be used for adjusting the control delay of multiple relays, thereby providing a cost efficient appliance.
The appliance may comprise a measurement point which is affected by arc noise that is generated by a switch-off event or a switch-on event of any one of the plurality of relays. The detection circuit may be configured to sense a relay signal at the measurement point, and to determine the arc information based on the relay signal. By making use of a joint measurement point for the plurality of relays, the control delays of the relays may be adjusted in a precise and reliable manner. The measurement point may be such that it allows detection of arc information and/or arc noise in a wireless manner. In particular, the measurement point may comprise and/or may be implemented as an antenna. The antenna may be placed at a central point between the plurality of relays. By making use of an antenna for measuring the arc information, arc detection may be performed in a particularly efficient and reliable manner.
It should be noted that the methods and systems including its preferred embodiments as outlined in the present document may be used stand-alone or in combination with the other methods and systems disclosed in this document. In addition, the features outlined in the context of a system are also applicable to a corresponding method. Furthermore, all aspects of the methods and systems outlined in the present document may be arbitrarily combined. In particular, the features of the claims may be combined with one another in an arbitrary manner.
The invention is explained below in an exemplary manner with reference to the accompanying drawing, wherein
Fig. 1 shows an example electromechanical relay;
Fig. 2a shows the temporal course or curve of the coil current during a switch-on event;
Fig. 2b shows the temporal course or curve of the coil current during a switch-off event;
Fig. 3a illustrates arc noise within the coil current during a switch-off event;
Fig. 3b illustrates the time interval of arc noise in relation to the AC mains voltage;
Fig. 4 shows an example detection circuit for detecting arc noise;
Fig. 5 illustrates an example envelope signal for the arc noise; and Fig. 6 shows a flow chart of an example method for controlling a switch-on event or a switch-off event of a relay.
As indicated above, the present document is directed at reducing the degradation of an electromechanical relay, which is used for switching on or off an AC power supply (e.g. an AC mains supply at 230V with an AC frequency of 50Hz). In this context Fig. 1 shows an example relay 1. The relay 1 comprises a coil 2 which is configured to generate a magnetic field, subject to a coil current l(t) which is applied to the control port 4. The coil 2 may comprise a coil core 8, which is configured to direct the magnetic field towards an armature or anchor 3 of the relay 1. The armature or anchor 3 is configured to be attracted by the magnetic field generated by the coil 2. The armature 3 is typically moved away from the coil 2 and the coil core 8 using a spring 10. The magnetic field which is generated by the coil 2 may cause a sufficiently high attracting force onto the armature 3, such that spring force for the spring 10 is overcome and such that the armature 3 is pulled towards the coil core 8 to switch on the relay 1.
The armature 3 is coupled to a contact 5, wherein the contact 5 of the armature 3 touches the contact 5 of the base of the relay 1 , when the armature 3 is pulled towards the coil core 8. As a result of this, the load ports 6 of the relay 1 are electrically coupled with one another, thereby allowing a current to flow between the load ports 6 and notably between the contacts 5.
By interrupting the coil current l(t), the magnetic field is interrupted and the armature 3 is pulled away from the coil core 8 due to the spring force caused by the spring 10. Eventually, the contacts 5 are disconnected from one another, thereby switching off the relay 1. In a relaxed or inactive state, the contacts 5 form a contact gap S having a certain gap width.
In the course of a switch-on event, the armature 3 is pulled towards the coil core 8, as soon as a coil current l(t) is applied to the control port 4. The coil current l(t) may be applied at a control time instant. At a subsequent connect time instant, the contacts 5 start touching each other, thereby switching on the relay 1 and thereby allowing a load current to flow via the load ports 6. At the connect time instant, the armature 3 typically does not yet touch the coil core 8. The time instant, at which the armature 3 touches the coil core 8 may be referred to at the close time instant, as the relay 1 is now fully closed. Once the relay 1 is fully closed, the (flexible) connecting plate between the armature 3 and the contact 5 of the armature 3 forms a flat spring 11 in a flexed condition, wherein the force of the flat spring 11 pulls the armature 3 away from the coil core 8. Hence, the magnetic field need to overcome the forces of the return spring 10 of the armature 3 and of the flat spring 11 of the contact 5.
In the course of a switch-off event, the control port 4 is disconnected from a control voltage (at a control time instant). As a result of this, the coil current l(t) decreases gradually such that the magnetic force decreases causing the flat spring 11 to return to a relaxed state and subsequently causing the return spring 10 to pull the contact 5 of the armature 3 away from the contact 5 of the base of the relay 1. The time instant, at which the contacts 5 are disconnected may be referred to as the disconnect time instant.
As outlined in the introductory section, a switch-on event or a switch-off event may lead to plasmatic arcs between the contacts 5, if the contacts 5 are connected or disconnected at a time instant, when the voltage across the load ports 6 is relatively high (e.g. 24V or higher) and/or when there is a load current through the load ports 6. This may lead to a degradation of the contacts 5 and of the mechanical components of the relay 1. In order to avoid such degradations, it is preferable to place the (dis)connect time instant of a switch- on event or a switch-off event at a zero crossing of the AC voltage which is applied to the load ports 6 and/or at a zero crossing of the load current at the load ports 6. In view of this, the control delay between the control time instant, at which the control voltage is applied to or disconnected from the control port 4, and the (dis)connect time instant, at which the contact gap S is closed or opened, needs to be determined in a precise manner.
Fig. 2a shows an example curve or course 201 of the coil current 200 during a switch-on event. It can be seen that the coil current 200 increases gradually, but exhibits an intermediate drop. Fig. 2b shows an example curve or course 202 of the coil current 200 during a switch-off event. It can be seen that the coil current 200 decreases gradually, but exhibits an intermediate peak.
Fig. 3a illustrates arc noise 302 within the course 202 of the coil current 200, which originates from the relay contact arc that is generated, in case the relay contacts 5 open just after the A/C mains voltage at the contacts 5 crossed the zero voltage, such that the A/C mains voltage lies above the critical voltage level (of e.g. 24V). Once the arc has built up, the arc lasts almost until the next zero cross of the mains voltage. Furthermore, Fig. 3a shows the course 301 of the first derivative of the course 202 of the coil current 200. The first derivative, notably the maximum of the first derivative, may be used for detecting the actual (dis)connect time instant.
Fig. 3b illustrates the time interval 312 during which arc noise 302 is present within the coil current 200. Furthermore, Fig. 3b shows the A/C mains voltage wave 310, which exhibits a zero crossing at zero crossing time instant 311. It can be seen that the arc noise 302 is generated, as long as the A/C mains voltage exceeds a certain threshold voltage (e.g. 24V). In addition, Fig. 3b shows the control time instant 313 (at the point, where the curve 202 of the coil current 200 starts to drop) at which a control signal is to be applied to the control port 4 of the relay 1 to initiate a switch-on event or a switch-off event of the relay 1. The control time instant 313 precedes the zero crossing time instant 311 by a control delay 315.
By changing the control delay 315 and by changing the control time instant 313 accordingly, the curve 202 of the coil current 200 is shifted relative to the A/C mains voltage wave 310. The curve 202 may be shifted such that the beginning of the interval
312 coincides with the zero crossing time instant 311. In this case the arc disappears, because the relay contacts 5 are opened exactly at the zero crossing time instant 311.
In the present document an arc detection zero cross relay control (ADRC) scheme is described. The scheme makes use of circuitry for detecting the occurrence of electromagnetic arc noise. In particular, the circuitry may be used for determining arc information regarding arc noise 302. Timing information regarding the control time instant
313 and/or the control delay 315 for switching on or off the relay 1 may be determined based on the arc information. The timing information may be compared to the A/C mains zero cross timing 311 to determine the control time instant 313. In particular, the arc information may be used for enabling a precise relay switching control to avoid the creation of arcs. Switching the relay contacts 5 may therefore be performed within the time interval, during which the A/C mains voltage is below the critical voltage threshold.
The ADRC scheme may be used in various different electro mechanic relay switching circuits which are equipped with a A/C mains zero detect circuit and/or with processor controlled relay switching. Typically, no relay control (hardware) changes are required. The ADRC scheme is suitable for circuits switching a resistive load (e.g. heating elements) and/or a non-resistive (e.g. inductive) load.
Fig. 4 shows an example detection circuit 400 for detecting arc noise 302 which is caused by an arc during a switch-on or switch-off event of a relay 1. The detection circuit 400 is configured to analyze a relay signal 401 which is captured during the switch-on or switch- off event of the relay 1. The relay signal 401 may correspond to the course 202 of the coil current 200. The detection circuit 400 may be configured to determine arc information 406 based on the relay signal 401 , wherein the arc information 406 indicates
• whether the relay signal 401 comprises arc noise 302 or not; and/or
• the start time instant and/or the end time instant of the arc noise 302.
The detection circuit 400 of Fig. 4 is operated with a supply voltage VCC 413 (e.g. at 5V). The detection circuit 400 comprises a pre-amplifier 410 with an amplification transistor 411, which is configured to amplify the relay signal 401 to provide an amplified relay signal 402. A (radio frequency, RF) power detector 412 may be used to detect the power of the (amplified) relay signal 401, 402 within a particular (RF) frequency band, wherein the frequency band should be different from one or more operating frequencies of the appliance within which the detection circuit 400 is used. Furthermore, the particular frequency band should comprise frequencies of the arc noise 302 which is to be detected. The power detector 412 may be switched on or off using an on/off signal 422.
The power detector 412 provides as output a power signal 403 (notably a power level) which is indicative of the power of the (amplified) relay signal 401 , 402 within the particular frequency band at a particular time instant. The detection circuit 400 may comprise a sample-and-hold circuit 418 which is configured to store the power signal 403 for a time instant at which the relay signal 401 does not comprise any arc noise 302. This power signal or power level 403 may be considered to be a reference level of the background noise which is comprised within the relay signal 401. The sample-and-hold circuit 418 comprises a transistor 413 which is controlled using the sample-and-hold control signal 421 and which allows the power signal 403 to be stored in the capacitor 414. The stored power signal 403 may be provided as a reference signal (or reference level) 404 to a comparator 416 via a voltage follower 415.
The power signal 403 at different time instants during a switch-on or switch-off event of the relay 1 may be compared to the reference signal 404 using the comparator 416, wherein the comparator 416 provides a deviation signal 405 which indicates whether or not the power signal 403 deviates from the reference signal 404. A signal conditioner 417 may be used to transform the deviation signal 405 into a rectangular or binary signal which indicates whether arc noise 302 is present or is not present within the relay signal 401. The arc information 406 may comprise or may correspond to the rectangular or binary signal.
Hence, a detection circuit 400 is described, which comprises a power detector 412 (such as Linear Technology LTC5507 RF power detector). The power detector 412 and the radio frequency (RF) pre-amplifier stage 410 form a RF frequency power detector which may be tuned to a frequency range or frequency band of about 1 MHz to 100 MHz. Amplification of the pre-amplifier 410 may be set up according to the detected noise level of arc noise 302 in the particular appliance within which the detection circuit 400 is used.
As the expected (detected) arc noise 302 is white wideband noise, the choice of the detection frequency band is typically not critical. Its lower limit should be above any of the working frequencies of the appliance, in order to ensure that the detection of arc noise 302 is not disturbed by the operation of the appliance. The power detector 412 may convert the detected electromagnetic noise 302 into a voltage (i.e. the power level 403) which is proportional to the noise power within the relay signal 401 (in dBm).
The sample-and-hold control signal 421 of the sample-and-hold circuit 418 may be operated by a control processor to store general RF noise level information (i.e. a reference power level 404) just before the expected time instant of the occurrence of arc noise 302. The reference power level 404 may be stored a few microseconds after the control time instant 313, i.e. after the relay switch operating action (relay closing or opening) has been issued by the relay control processor 100.
The operational amplifier 416 compares two different RF noise levels, i.e. the reference noise level 404 stored in the sample-and-hold circuit 418 just before operation of the relay contacts 5 with the instantaneous noise level 403. If the instantaneous noise level 403 is higher than the stored reference noise level 404, the difference is amplified by the operational amplifier 416, providing a deviation signal 405 which indicates that arc noise 302 has occurred due to an arc between the relay contacts 5.
A signal conditioner 417 may be used for producing a rectangular pulse envelope 406 framing the duration of the arc noise 302. The rectangular pulse envelope 406 provides exact time information regarding the beginning and the end of the arc between the relay contacts 5. The rectangular pulse envelope 406 may be used for recalculating the control delay 315 relatively to the A/C mains zero cross time instant 311, in order to avoid the generation of an arc during a subsequent switch-on or switch-off event.
Fig. 5 shows an example rectangular pulse envelope 406. The envelope 406 indicates a start time instant 501 for the beginning of the arc noise 302 and/or an end time instant 502 for the end of the arc noise 302.
The detection circuit 400 may be controlled using a control processor or control unit 100. The control unit 100 may be configured to enable the detection circuit 400 by switching on the power detector 412 using the on/off signal 422, and by controlling the sample-and- hold circuit 418 using the sample-and-hold control signal 421. Furthermore, the control unit 100 may be configured to control operation of the relay 1. The control unit 100 may issue a command to switch off (or switch on) the relay 1 at a control time instant T0ff 313. The control time instant 313 may be determined by applying a (negative) time delay 315 to the A/C mains voltage zero cross time instant 311. The time delay (referred to as the control delay) 315 may have been determined and stored at a previous switching event of the relay 1.
After issuing the switch off command at the control time instant T0ff 313, the control unit 100 closes the transistor 413 (using the control signal 421), in order to store the (reference) noise level 404, possibly just before the expected relay contact opening time. The capacitor 414 stores the voltage level 404 indicating the electromagnetic (background) noise (in dBm power), measured just before relay contact opening. This voltage is provided to the (-) input of the comparator 416 via the voltage follower 415.
If an arc between relay contacts 5 occurs, a voltage 403 corresponding to the dBm power of the consequent electromagnetic arc noise 302 is provided to the (+) input of the comparator 416. The comparator 416 amplifies the difference of both voltages and outputs a deviation signal 405 to the signal conditioner 417 which provides the rectangular pulse 406 indicative of the arc noise 302. The rectangular pulse 406 indicates the beginning of the arc Tai 501 (when opening the relay contacts 5) and the end of the arc Ta2 502 (which may correspond to the A/C mains voltage falling below the critical voltage threshold). Hence, the ADRC scheme allows determining the actual time instant 501 of the relay contact opening and the actual time instant 502 of the end of the arc, regardless the type of load, i.e. also for non-resistive loads (e.g. inductive loads). The ADRC scheme may therefore monitor the actual arcing status between the relay contacts 5 for different types of loads.
The control unit 100 may use the information about Tai 501 and/or Ta2 502 to recalculate the control time instant T0fr 313 for switching off the relay 1 in the future, such that no arc is generated during the future switching event. In particular, the time delay 315 which is to be applied to the zero crossing time instant 311 to determine the control time instant 313 may be adjusted based on Tai 501 and/or Ta2502.
Fig. 5 shows the example of a non-resistive, notably inductive, load. As can be seen in Fig. 5, the are noise 302 follows the load current 510 which is phase shifted with respect to the A/C mains voltage wave 310. The relay 1 should be switched on or off at a zero crossing time instant 511 at which the load current 510 exhibits a zero crossing. On the other hand, typically only the zero crossing time instant 311 of the A/C mains voltage wave 310 can be detected. The time delay 315 between the zero crossing time instant 311 of the A/C mains voltage wave 310 and the control time instant 313 for controlling the relay 1 may take into account the phase shift which is caused by the non-resistive load, thereby enabling arc free switching in conjunction with a non-resistive load.
Hence, the relay control process and relay operating time corrections, which are performed by the control unit 100 may take into account phase shift corrections for a non- resistive load. This may involve a constant phase shift correction or a more complex process calculating a worst-case scenario, if the phase shift is not constant during the appliance operation. While the above-mentioned Tai time 501 refers to relay contact opening, the Ta2 time 502 indicates the end of the respective electric arc due to electric current in a non-resistive load.
As already indicated above, the electromagnetic noise 302, which is caused by an arc, is typically radiant white wideband noise, which may propagate throughout the entire circuity of an appliance. Hence, the relay signal 401 may be captured at various different measurement points within an appliance. By way of example, the measurement point may be an antenna which is placed within the vicinity of the one or more relays 1. Hence, the measurement point may be such that is allows for a wireless detection of arc noise 302. In particular, noise detection may be performed using a single detection circuit 400 at a single, properly selected, measurement point for multiple, notably for all, relays 1 of an appliance. The arc information 406 provided by the detection circuit 400 may be used by a control unit 100 of the appliance to control multiple (notably all) relays 1 of the appliance.
The proposed ADRC technology can be used as a standalone relay switching technology to avoid arcing or as a supplemental safety technology to confirm the absence of arcs when switching the relays 1 using another zero cross switching technique.
Fig. 6 shows a flow chart of an example method 600 for controlling a relay 1. The relay 1 may comprise a movable anchor 3 and a coil 2 which is configured to exert a force onto the anchor 3 subject to a coil current 200 at a control port 4, in order to connect the contacts 5 of the relay 1.
The method 600 comprises applying 601, at a control time instant 313, a control signal to the control port 4 of the relay 1 for initiating a switch-off event or a switch-on event of the relay 1. The control signal may lead to a coil current 200 or the control signal may lead to an interruption of the coil current 200. The control time instant 313 depends on a previously determined control delay 315 of the relay 1. Furthermore, the control time instant 313 typically depends on a zero crossing time instant 311 of the AC voltage 310 (which is applied to the load ports 6 of the relay 1), at which the AC voltage 311 changes polarity and/or crosses zero.
The method 600 further comprises determining 602 arc information 406 regarding the formation of an arc between the contacts 5 of the relay 1 during the switch-off event or the switch-on event of the relay 1. In particular, the arc information 406 may be indicative of a start time instant 501 at which the arc starts to exist, and/or of an end time instant 502 at which the arc ceases to exist. The existence of an arc may be detected via arc noise 302 generated by the arc.
In addition the method 600 comprises updating 603 the control delay 315 based on the arc information 406. In particular, the control delay 315 may be updated or shifted in dependence of the start time instant 501 , the end time instant 502 and/or the duration 312 of the arc or the arc noise 302. The control delay 315 may be updated with the goal to avoid the generation of an arc during a subsequent switch-off event or switch-on event of the relay 1. For this purpose, the control delay 315 may be updated such that the arc would not have been generated at the current switch-off event or switch-on event, if the updated control delay 315 had been used to determine the control time instant 313 for the current switch-off event or switch-on event.
The arc detection zero cross relay control (ADRC) scheme may be used for zero cross switching of electromechanical relays 1 in a standalone manner or as a supplemental scheme to another zero cross relay control scheme (e.g., for increasing safety of the scheme). Furthermore, the ADRC scheme may be used for safety and/or predictive maintenance of an appliance.
The aspects which are outlined in the present document enable a reliable and efficient control of a relay 1. The control scheme allows reducing the deteriorations of a relay 1, which are caused by switch-on or switch-off events of the relay 1.
It should be noted that the description and drawings merely illustrate the principles of the proposed methods and systems. Those skilled in the art will be able to implement various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and embodiment outlined in the present document are principally intended expressly to be only for explanatory purposes to help the reader in understanding the principles of the proposed methods and systems. Furthermore, all statements herein providing principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass equivalents thereof.

Claims

1. A method (600) for controlling a relay (1); wherein the method (600) comprises
- applying (601), at a control time instant (313), a control signal to a control port (4) of the relay (1) for initiating a switch-off event or a switch-on event of the relay (1); wherein the control time instant (313) depends on a previously determined control delay (315) of the relay (1);
- determining (602) arc information (406) regarding the formation of an arc between contacts (5) of the relay (1) during the switch-off event or the switch-on event of the relay (1); and
- updating (603) the control delay (315) based on the arc information (406).
2. The method (600) of claim 1, wherein the method (600) comprises
- detecting arc noise (302) caused by an arc between the contacts (5) of the relay (1); and
- determining (602) the arc information (406) based on the detected arc noise (302).
3. The method (600) of claim 2, wherein the method (600) comprises
- measuring a relay signal (401) during the switch-off event or the switch-on event of the relay (1); and
- determining arc information (406) regarding the arc noise (302) comprised within the relay signal (401).
4. The method (600) of claim 3, wherein the relay signal (401) corresponds to or is indicative of a course (202) of a coil current (200) through a coil (2) of the relay (1) during the switch-off event or the switch-on event of the relay (1).
5. The method (600) of any of claims 2 to 4, wherein
- the method (600) comprises determining a start time instant (501) of a beginning of the arc noise (302) and/or an end time instant (502) of an end of the arc noise (302); and - the arc information (406) is indicative of the start time instant (501) and/or the end time instant (502).
6. The method (600) of any of claims 2 to 5, wherein the method (600) comprises adjusting, notably shifting, the control delay (315) by an offset corresponding to or depending on a temporal duration (312) of the arc noise (302).
7. The method (600) of any previous claims, wherein
- contacts (5) of the relay (1) are configured to enable or to disable an electrical connection between load ports (6) of the relay (1);
- an AC voltage (310) is applied to the load ports (6);
- the method (600) comprises, determining a zero crossing time instant (311) of the AC voltage (311), at which the AC voltage (311) changes polarity; and
- the method (600) comprises, determining the control time instant (313) based on the previously determined control delay (315) and based on the zero crossing time instant (311).
8. The method (600) of claim 7, wherein determining the control time instant (313) comprises advancing the zero crossing time instant (311) by the previously determined control delay (315).
9. The method (600) of any of claims 7 to 8, wherein the method (600) comprises
- determining phase shift information regarding a phase shift between the AC voltage (310) and a load current (510) at load ports (6) of the relay (1) caused by a load; and
- determining the control delay (315) based on the phase shift information.
10. A control unit (100) for controlling a relay (1); wherein
- the control unit (100) is configured to apply, at a control time instant (313), a control signal to a control port (4) for initiating a switch-off event or a switch-on event of the relay (1); wherein the control time instant (313) depends on a previously determined control delay (315) of the relay (1); - the control unit (100) comprises a detection circuit (400) configured to determine arc information (406) regarding the formation of an arc between contacts (5) of the relay (1) during the switch-off event or the switch-on event of the relay (1); and
- the control unit (100) is configured to update the control delay (315) based on the arc information (406).
11. The control unit (100) of claim 10; wherein
- the detection circuit (400) is configured to sense a relay signal (401) during the switch-off event or the switch-on event of the relay (1);
- the detection circuit (400) comprises a power detector (412) configured to determine a power level (403) of the relay signal (401) within a pre-determined frequency band; wherein the pre-determined frequency band comprises frequencies of arc noise (302) generated by an arc between the contacts (5) of the relay (1); wherein the pre-determined frequency band notably exhibits a lower bound of 1MHz or higher; and
- the detection circuit (400) is configured to determine the arc information (406) based on the power level (403) of the relay signal (401) within the pre-determined frequency band.
12. The control unit (100) of claim 11; wherein the detection circuit (400) is configured to
- determine a reference power level (404) of the relay signal (401) within the pre determined frequency band prior to a time instant at which the contacts (5) of the relay (1) are disconnected or connected, using the power detector (412); and
- compare the power level (403) of the relay signal (401) within the pre-determined frequency band, which is determined during the switch-off event or the switch-on event of the relay (1) using the power detector (412), with the reference power level (404), to determine the arc information (406).
13. The control unit (100) of claim 12; wherein
- the detection circuit (400) comprises a comparator (416) configured to compare the power level (403) with the reference power level (404); - the comparator (416) is configured to generate a deviation signal (405) which indicates time instants at which the power level (403) exceeds the reference power level (404); and
- the detection circuit (400) is configured to determine the arc information (406) based on the deviation signal (405).
14. An appliance which comprises
- a plurality of relays (1);
- a joint detection circuit (400) for the plurality of relays (1); wherein the detection circuit (400) is configured to determine arc information (406) regarding the formation of an arc between contacts (5) of each one of the plurality of relays (1) during a switch-off event or a switch-on event of the respective relay (1); and
- a control unit (100) which is configured to
- determine that a first relay (1) from the plurality of relays (1) is to be switched-on or switched-off;
- apply, at a control time instant (313), a control signal to a control port (4) of the first relay (1) for initiating a switch-off event or a switch-on event of the first relay (1); wherein the control time instant (313) depends on a previously determined control delay (315) of the first relay (1); and
- update the control delay (315) of the first relay (1) based on the arc information (406) determined by the detection unit (400) during the switch- off event or the switch-on event of the first relay (1).
15. The appliance of claim 14; wherein
- the appliance comprises a measurement point which is affected by arc noise (302) that is generated by a switch-off event or a switch-on event of any one of the plurality of relays (1); wherein the measurement point notably comprises an antenna; and
- the detection circuit (400) is configured to
- sense a relay signal (401) at the measurement point; and
- determine the arc information (406) based on the relay signal (401).
PCT/EP2021/063962 2020-06-10 2021-05-26 Method and control unit for zero cross relay switching WO2021249770A1 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
EP21729463.6A EP4165674A1 (en) 2020-06-10 2021-05-26 Method and control unit for zero cross relay switching

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE102020207276.0A DE102020207276A1 (en) 2020-06-10 2020-06-10 Method and control unit for switching a relay at zero crossing
DE102020207276.0 2020-06-10

Publications (1)

Publication Number Publication Date
WO2021249770A1 true WO2021249770A1 (en) 2021-12-16

Family

ID=76250318

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/EP2021/063962 WO2021249770A1 (en) 2020-06-10 2021-05-26 Method and control unit for zero cross relay switching

Country Status (3)

Country Link
EP (1) EP4165674A1 (en)
DE (1) DE102020207276A1 (en)
WO (1) WO2021249770A1 (en)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP4227974A1 (en) * 2022-02-09 2023-08-16 BSH Hausgeräte GmbH Method and electronic circuit for relay stock detection

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0353986A2 (en) * 1988-08-04 1990-02-07 Whirlpool Corporation Relay control method and apparatus for a domestic appliance
US6088205A (en) * 1997-12-19 2000-07-11 Leviton Manufacturing Co., Inc. Arc fault detector with circuit interrupter
EP2226820A2 (en) * 2009-03-05 2010-09-08 Rockwell Automation Technologies, Inc. Switching phase offset for contactor optimization
US20130154774A1 (en) * 2011-12-14 2013-06-20 Vijay Bhavaraju Hybrid bi-directional dc contactor and method of controlling thereof
WO2020020555A1 (en) * 2018-07-24 2020-01-30 BSH Hausgeräte GmbH Method and control unit for switching on or off a relay

Family Cites Families (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE102016117273B4 (en) 2016-09-14 2018-03-29 Phoenix Contact Gmbh & Co. Kg Relay with a controller and method for controlling a relay
DE102018118329B3 (en) 2018-07-30 2020-01-30 Insta Gmbh Procedure for switching a relay to zero and relay switching

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0353986A2 (en) * 1988-08-04 1990-02-07 Whirlpool Corporation Relay control method and apparatus for a domestic appliance
US6088205A (en) * 1997-12-19 2000-07-11 Leviton Manufacturing Co., Inc. Arc fault detector with circuit interrupter
EP2226820A2 (en) * 2009-03-05 2010-09-08 Rockwell Automation Technologies, Inc. Switching phase offset for contactor optimization
US20130154774A1 (en) * 2011-12-14 2013-06-20 Vijay Bhavaraju Hybrid bi-directional dc contactor and method of controlling thereof
WO2020020555A1 (en) * 2018-07-24 2020-01-30 BSH Hausgeräte GmbH Method and control unit for switching on or off a relay

Also Published As

Publication number Publication date
EP4165674A1 (en) 2023-04-19
DE102020207276A1 (en) 2021-12-16

Similar Documents

Publication Publication Date Title
CN110506318B (en) Relay control method, control circuit and processor
US6768615B2 (en) Spark elimination circuit for controlling relay contacts
US5267120A (en) Relay control apparatus
US9608432B2 (en) Electric leakage determination circuit for electric leakage circuit breaker
US5055962A (en) Relay actuation circuitry
EP3827453B1 (en) Method and control unit for switching on or off a relay
US20180259582A1 (en) Household appliance
KR20060064649A (en) Control of plasma transitions in sputter processing systems
EP4165674A1 (en) Method and control unit for zero cross relay switching
US7593211B2 (en) Automatically configuring vacuum contactor
JP2004503903A (en) Actuation method of electromagnetic switchgear and electromagnetic switchgear
WO1990010942A1 (en) Method and apparatus for connecting or disconnecting an electrical load circuit
EP0736888B1 (en) Controlled switching
CA2752576C (en) Electric cooking appliance with relay driver
US7737762B2 (en) Solid-state switch
CN107818886B (en) Relay with controller
EP2885804B1 (en) Regulated power supply assembly for use in electrical switch
CN111092545B (en) Impulse current suppression device
JP6821676B2 (en) Auxiliary circuit of micro electromechanical system relay circuit
CN210120061U (en) Switch structure for controlling short-time on-off of single-phase line
RU2715393C1 (en) Drive mechanism for medium-voltage automatic circuit breaker
CN109994341B (en) Relay zero switch self-calibration method and system
KR20020026736A (en) Relay Protection Method used Triac
CN113451076A (en) Voltage suppression device and method based on zero-crossing detection and storage medium
KR20120058376A (en) Switch for prevention of inrush current shock and cut-off standby power

Legal Events

Date Code Title Description
121 Ep: the epo has been informed by wipo that ep was designated in this application

Ref document number: 21729463

Country of ref document: EP

Kind code of ref document: A1

NENP Non-entry into the national phase

Ref country code: DE

ENP Entry into the national phase

Ref document number: 2021729463

Country of ref document: EP

Effective date: 20230110