Bistable electromagnetic switching device

Abstract

A bistable electrical switching device (1) is provided. The bistable electrical switching device (1) comprises a controller and an electromagnetic drive unit (2), wherein the electromagnetic drive unit comprises a moveable armature (3) that can move between a first stable position and a second stable position. The controller is configured to provide a first actuation signal (800,900) to cause the moveable armature (3) to move from the first stable position to the second stable position, wherein the first actuation signal comprises at least two first pulses (801) having a first polarity, wherein the controller and the electromagnetic drive unit are configured such that a pulse having the first polarity causes the armature to accelerate in the direction of the second stable position from the first stable position.

Description

[0001] Bistable electromagnetic switching device

[0002] The present disclosure relates to a bistable electromagnetic switching device and an actuation mechanism for a bistable electromagnetic relay.

[0003] Electromagnetic relays are used switching devices including hybrid circuit breakers (HCB). A hybrid circuit breaker generally includes a semiconductor switching unit, which is shunted by a bypass relay. In normal operation the contacts of the bypassrelay are closed and the semiconductor switching unit is typically in a non-conductive mode. The current passing the hybrid circuit breaker flows through the low resistance bypass relay.

[0004] Bistable electromagnetic relays remain stably latched in both the off-position and the on-position and require actuation to move between the two stable states. Opening and closing of a bistable electromagnetic relay is achieved through the operation of an electromagnetic drive mechanism, which causes an actuator of the relay to move between open and closed positions. In the case of a detected electrical fault, such as a short circuit condition, the bistable relay is actuated to separate electric contacts of the relay as quickly as possible. The faster the contact separation operation, the faster the current commutates to the semiconductor switching unit. In order to close the bypass relay after a fault condition has cleared, the bistable relay is actuated to close the electric contacts of the relay. The electromechanical forces on the actuator during closing of the bistable relay are normally similar in magnitude to the forces used during opening of the bistable relay but in the opposite direction.

[0005] Due to the importance of achieving a quick separation of contacts during opening of the such under fault conditions, large forces are used in the actuation of the relay. The kinetic energy imparted into the moveable parts of the relay is dissipated in collisions of the relay contacts, which can result in deformation of the electrical contacts over time, and high levels of mechanical stress are generated in moveable armature elements used to actuate the device. As a result of the deformation of the electrical contacts, the resistance between electrical contacts can increase over repeated switching operations, resulting in increased heating of the relay and dissipative energy losses. Mechanical stresses in the moveable armature can lead to deterioration of the device over repeated switching operations and reduce the lifespan of the device. It is an object of the present invention to overcome the drawbacks of the state of the art by providing a bistable electromagnetic relay with a simple structure that avoids deformation of electrical contacts and deterioration of device performance due to mechanical stresses over repeated switching operations.

[0006] Summary of Invention

[0007] In one aspect of the disclosure, a bistable electrical switching device is provided. The bistable electrical switching device comprises a controller and an electromagnetic drive unit, wherein the electromagnetic drive unit comprises a moveable armature that can move between a first stable position and a second stable position, wherein the controller is configured to provide a first actuation signal to cause the moveable armature to move from the first stable position to the second stable position, wherein the first actuation signal comprises at least two first pulses having a first polarity, wherein the controller and the electromagnetic drive unit are configured such that a pulse having the first polarity causes the armature to accelerate in the direction of the second stable position from the first stable position.

[0008] In some examples, the duration of the final first pulse of the at least two first pulses is longer than that of any preceding first pulse.

[0009] In some examples, the durations of the first pulses of the at least two first pulses increase with time such that, after the initial first pulse, each subsequent first pulse has a longer duration than the first pulse that preceded it.

[0010] In some examples, at least two first pulses of the at least two first pulses are separated by at least one rest period.

[0011] In some examples, the at least one rest period has a duration between Ips and 5 seconds and, more preferably, a duration between lOOOps and 5000ps.

[0012] In some examples, the at least one rest period has a duration between lOOOps and 5000ps.

[0013] In some examples, the first actuation signal comprises at least one second pulse having a second polarity opposite to the first polarity and occurring between successive first pulses of the at least two first pulses, wherein the controller and the electromagnetic drive unit are configured such that a pulse of the second polarity causes the armature to accelerate in the direction of the first stable position from the second stable position.

[0014] In some examples, the at least one second pulse and each of the at least two first pulses have the same magnitude.

[0015] In some examples, the durations of the first pulses of the at least two first pulses increase with time such that, after the initial first pulse, each subsequent first pulse has a longer duration than the first pulse that preceded it.

[0016] In some examples, the controller comprises an H-bridge arrangement for controlling the polarity of actuation signals output by the controller.

[0017] In some examples, at least one first pulse of the at least two first pulses has a duration between Ips and 5 seconds

[0018] In some examples, at least one first pulse of the at least two first pulses has a duration between 300ps and 500ps.

[0019] In some examples, the electromagnetic drive unit further comprises: a yoke; at least one permanent magnet; and at least one coil; wherein the moveable armature is a rotatable armature configured to rotate between the first stable position and the second stable position, wherein the at least one coil is configured to generate a magnetic field that causes a torque on the rotatable armature upon receiving an actuation signal, and wherein first pulses of an actuation signal having a first polarity cause a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the second stable position from the first stable position, and wherein second pulses of an actuation signal having a second polarity opposite the first polarity cause a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the first stable position from the second stable position.

[0020] In some examples, the yoke, the rotatable armature and the at least one permanent magnet are arranged such that a magnetic field produced by the at least one permanent magnet passes through the yoke and the armature in both the first and second stable positions and causes a magnetic holding force that biases the armature to remain in the respective stable position.

[0021] In some examples, the moveable armature is coupled to a moveable contact arm that forms part of an electric circuit, wherein the moveable contact arm is in an OFF state when the rotatable armature is in the first stable position and an ON state when the rotatable armature is in the second stable position.

[0022] In some examples, the controller is further configured to provide, upon receiving a trigger signal, a second actuation signal to cause the moveable armature to move from the second stable position to the first stable position, wherein the second actuation signal comprises a single continuous second pulse having the second polarity.

[0023] In another aspect of the disclosure, a method of controlling a bistable electrical switching device is provided. The method comprising generating a first actuation signal to cause a moveable armature of the bistable electrical switching device to move from a first stable position to a second stable position, wherein the first actuation signal comprises at least two first pulses (801) having a first polarity.

[0024] In some examples, the duration of the final first pulse of the at least two first pulses is longer than that of any preceding first pulse.

[0025] In some examples, the first pulses of the at least two first pulses are separated by at least one rest period 802 and / or the first actuation signal 900 comprises a second pulse 901 of a second polarity opposite the first polarity and occurring between any two successive first pulses of the at least two first pulses.

[0026] In one aspect of the disclosure, a bistable electrical switching device is provided. The bistable electrical switching device comprises a controller and an electromagnetic drive unit, wherein the electromagnetic drive unit comprises a moveable armature that can move between a first stable position and a second stable position, wherein the controller is configured to provide a first actuation signal to cause the moveable armature to move from the first stable position to the second stable position and a second actuation signal to cause the moveable armature to move from the second stable position to the first stable position, and wherein the electromagnetic drive unit and controller are configured such that the magnitude of the maximum velocity of the armature when moving in response to the first actuation signal is less than the magnitude of the maximum velocity of the armature when moving in response to the second actuation signal.

[0027] In some examples, the first actuation signal comprises a series of first pulses having a first polarity, wherein the controller and the electromagnetic drive unit are configured such that a pulse having the first polarity causes the armature to accelerate in the direction of the second stable position from the first stable position.

[0028] In some examples, at least two first pulses of the series of first pulses are separated by at least one rest period.

[0029] In some examples, the at least one rest period has a duration between Ips and 5 seconds and, more preferably, a duration between lOOOps and 5000ps.

[0030] In some examples, the first actuation signal comprises at least one second pulse having a second polarity opposite to the first polarity and occurring between successive first pulses of the series of first pulses, wherein the controller and the electromagnetic drive unit are configured such that a pulse of the second polarity causes the armature to accelerate in the direction of the first stable position from the second stable position.

[0031] In some examples, the durations of the first pulses of the series of first pulses increase with time such that, after the initial first pulse, each subsequent first pulse has a longer duration than the first pulse that preceded it.

[0032] In some examples, the controller comprises an H-bridge arrangement for controlling the polarity of actuation signals output by the controller.

[0033] In some examples, at least one first pulse of the series of first pulses has a duration between Ips and 5 seconds and, preferably, between lOOps and 700ps and, more preferably, between 300ps and 500ps.

[0034] In some examples, the electromagnetic drive unit further comprises: a yoke; at least one permanent magnet; and at least one coil; wherein the moveable armature is a rotatable armature configured to rotate between the first stable position and the second stable position, wherein the at least one coil is configured to generate a magnetic field that causes a torque on the rotatable armature upon receiving an actuation signal, and wherein an actuation signal having a first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the second stable position from the first stable position, and wherein an actuation signal having a second polarity opposite the first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the first stable position from the second stable position. In some examples, the yoke, the rotatable armature and the at least one permanent magnet are arranged such that a magnetic field produced by the at least one permanent magnet passes through the yoke and the armature in both the first and second stable positions and causes a magnetic holding force that biases the armature to remain in the respective stable position.

[0035] In some examples, the moveable armature is coupled to a moveable contact arm that forms part of an electric circuit, wherein the moveable contact arm is in an OFF state when the rotatable armature is in the first stable position and an ON state when the rotatable armature is in the second stable position.

[0036] In some examples, the moveable armature is a rotatable armature that is coupled to the moveable contact arm via a shaft.

[0037] In some examples, the controller is further configured to provide, upon receiving a trigger signal, the second actuation signal to cause the moveable armature to move from the second stable position to the first stable position, wherein the second actuation signal comprises a single second pulse having the second polarity.

[0038] In some examples, the first stable position corresponds to an ON state of a circuit and the second stable position corresponds to an OFF state of the circuit.

[0039] In another aspect of the disclosure, a method of controlling a bistable electrical switching device is provided. The method comprises: generating a first actuation signal to cause a moveable armature to move from a first stable position to a second stable position, and generating a second actuation signal to cause a moveable armature to move from the second stable position to the first stable position, wherein the magnitude of the maximum velocity of the armature when moving in response to the first actuation signal is less than the magnitude of the maximum velocity of the armature when moving in response to the second actuation signal.

[0040] In some examples, the first actuation signal comprises a series of first pulses having a first polarity.

[0041] In some examples, the series of first pulses are separated by respective rest periods and / or the first actuation signal comprises a second pulse of a second polarity opposite the first polarity and occurring between successive pulses of the series of first pulses.

[0042] In another aspect of the disclosure, a bistable electrical switching device is provided. The bistable electrical switching device comprises a controller and an electromagnetic drive unit, wherein the electromagnetic drive unit comprises: a yoke; a rotatable armature that can rotate between a first stable position and a second stable position; at least one permanent magnet; and at least one coil, wherein the at least one coil is configured to generate a magnetic field that causes a torque on the rotatable armature upon receiving an actuation signal, and wherein an actuation signal having a first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the second stable position from the first stable position, and wherein an actuation signal having a second polarity opposite the first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the first stable position from the second stable position, and wherein the controller is configured to provide a first actuation signal to the at least one coil to cause the rotatable armature to move from the first stable position to the second stable position, wherein the first actuation signal comprises a series of first pulses having the first polarity.

[0043] In some examples, the series of first pulses are separated by respective rest periods.

[0044] In some examples, each rest period has a duration between Ips and 5 seconds and, more preferably, a duration between lOOOps and 5000ps.

[0045] In some examples, the first actuation signal comprises at least one second pulse having the second polarity and occurring between successive first pulses of the series of first pulses.

[0046] In some examples, the second pulse has the has same magnitude as the first pulses of the series of first pulses and, preferably, wherein the second pulse and the first pulses of the series of first pulses have the same magnitude.

[0047] In some examples, the durations of the first pulses of the series of first pulses increase with time such that, after the initial first pulse, each subsequent first pulse has a longer duration than the first pulse that preceded it. In some examples, the second pulse has a duration that is less than the duration of each first pulse of the series of first pulses and, preferably, has a duration between 50ps and 500ps.

[0048] In some examples, the controller comprises an H-bridge arrangement for controlling the polarity of actuation signals output by the controller.

[0049] In some examples, the duration of the final first pulse of the series of first pulses has a longer duration than the preceding first pulses of the series of first pulses and, preferably, the final first pulse of the series of first pulses has a duration between Ips and 5 seconds and, more preferably, between 500ps and 2500ps.

[0050] In some examples, at least one first pulse of the series of first pulses has a duration between Ips and 5 seconds and, preferably, between lOOps and 700ps and, more preferably, between 300ps and 500ps.

[0051] In some examples, the yoke, the rotatable armature and the at least one permanent magnet are arranged such that a magnetic field produced by the at least one permanent magnet passes through the yoke and the armature in both the first and second stable positions and causes a magnetic holding force that biases the armature to remain in the respective stable position.

[0052] In some examples, the rotatable armature is coupled via a shaft to a moveable contact arm that forms part of an electric circuit, wherein the moveable contact arm is in an OFF state when the rotatable armature is in the first stable position and an ON state when the rotatable armature is in the second stable position.

[0053] In some examples, the controller is further configured to provide, upon receiving a trigger signal, a second actuation signal to the at least one coil to cause the rotatable armature to move from the second stable position to the first stable position, wherein the second actuation signal comprises a single second pulse having the second polarity.

[0054] In another aspect of the invention, a method of controlling a bistable electrical switching device comprising a rotatable armature that has a first stable position and a second stable position, the bistable electrical switching device being configured such that an actuation signal having a first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the second stable position from the first stable position, and wherein an actuation signal having a second polarity opposite the first polarity causes a torque on the rotatable armature biasing the rotatable armature to accelerate in the direction of the first stable position from the second stable position is provided. The method comprises: generating a first actuation signal to cause a rotatable armature to move from a first stable position to a second stable position, the first actuation signal comprising a series of first pulses having the first polarity.

[0055] In some examples, the series of first pulses are separated by respective rest periods.

[0056] In some examples, the first actuation signal comprises a second pulse of the second polarity and occurring between successive pulses of the series of first pulses.

[0057] Brief Description of the Figures

[0058] Fig. 1 shows an open front side of part of a bistable electrical switching device suitable for use in embodiments of the disclosure in the first stable position;

[0059] Fig. 2 shows an open back side of the part of the bistable electrical switching device according to Fig. 1;

[0060] Fig. 3 shows an open front side of the relay according to Fig. 1 in the second stable position;

[0061] Fig. 4 shows an open back side of the relay according to Fig. 3;

[0062] Fig. 5 shows a sectional view according to the cutting plane A - A according to Fig. 3;

[0063] Fig. 6 illustrates the effect of changing the polarity of an actuation signal on the magnetic field in electromagnetic drive unit suitable for use in embodiments of the invention;

[0064] Fig. 7 schematically depicts an H-bridge suitable for use in embodiments of the disclosure;

[0065] Fig. 8 illustrates an actuation signal according to an example of the disclosure;

[0066] Fig. 9 illustrates an actuation signal according to another example of the disclosure. Detailed Description of Embodiments

[0067] The present disclosure provides a bistable electromagnetic switching device, such as a bistable relay, and a method for controlling a bistable electromagnetic switching device. In accordance with embodiments of the disclosure, the bistable electromagnetic switching device is controlled to provide a "soft" switching operation. During the soft switching operation, an armature of the bistable electromagnetic switching device is controlled using a pulsed actuation signal that causes the armature to move from a first stable position to a second stable position with less kinetic energy than would be imparted if using a continuous actuation signal. The soft switching operation may be used to turn on the device to connect a power source of circuit to a load. A "hard" switching operation may, in contrast, use a continuous actuation signal (without pulses) in order, for example, to achieve rapid disconnection of a power source under fault conditions. The soft switching operation allows the kinetic energy of an electrical contact arm to be reduced during actuation of the switching device in comparison to the hard switching operation, thereby avoiding deformation of electrical contacts of the electrical contact arm during switching operations that are not time sensitive. Because the soft switching operations and the hard switching operations differ only in the duration / timing of the actuation pulses and not the magnitude of the actuation pulses, the two switching operations can be provided with simple hardware and control structures.

[0068] In the embodiments described in detail, the soft switching operation is a turn-on operation (for connecting a power source to a load) and the hard switching operation is a turn-off operation (for disconnecting a power source). The disclosure also provides a soft turn-off operation for use when turning off the bistable electromagnetic switching device in the absence of an electrical fault. In the soft turn-off operation, a pulsed actuation signal may be used to turn off a device. Both the soft turn-on operation and soft turn-off operation reduce the mechanical stress on an armature of the bistable electromagnetic switching device.

[0069] In embodiments of the disclosure, the bistable electromagnetic switching device 1 comprises an electromagnetic drive unit 2 and a controller. The electromagnetic drive unit comprises a moveable armature, and the controller provides actuation signals that cause the armature between a first stable position and a second stable position, the electromagnetic drive unit and controller are configured such that the magnitude of the maximum velocity of the armature when moving in response to the first actuation signal is less than the magnitude of the maximum velocity of the armature when moving in response to the second actuation signal.

[0070] The bistable electromagnetic switching device 1 may be embodied as a magnetically latched relay in which the moveable armature 3 rotates between the first and second stable positions in which the armature 3 contacts a yoke 4. The electromagnetic drive unit 2 may be coupled to a conductive moveable contact arm 8, which completes or disconnects a circuit depending on its position. A magnetic field that passes between permanent magnets 23 and 24 via the armature 3 and the yoke 4 generates a holding force biasing the armature to remain in the first and second stable positions. Coils 21 and 22 are wound around parts of the yoke 4 and receive actuation signals from a controller, which generates magnetic fields causing the armature 3 of the electromagnetic drive unit 2 to move between first and second stable positions. When the armature of the electromagnetic drive unit 2 is in a first stable position, the moveable contact arm may be in a switched-off state such that the moveable contact arm 8 is separated from at least one stationary electrical contact of the electrical switching device 1 and current cannot flow through the circuit. When the armature of the electromagnetic drive unit 2 is in a second stable position, the moveable contact arm 8 may be in a switched-on state such that the moveable contact arm 8 is in contact with a stationary electrical contact of the electrical switching device and current can flow through the circuit. As such, the electromagnetic drive unit 2 may be controlled to connect and disconnect a circuit via the moveable contact arm. Switching on the electromagnetic switching device 1 causes the moveable contact arm 8 to be brought into contact with a stationary electrical contact through a collision, which can lead to deformation of the moveable contact arm 8 or the stationary electrical contact if the collision energy is sufficiently high.

[0071] Figs. 1 to 5 show an example of a bistable electromagnetic switching device 1 suitable for use in embodiments of the disclosure when combined with a controller or controlled according to a suitable method, as described in more detail below. The skilled person will understand that the controller and the control mechanisms described herein can be applied to bistable switching devices having structures that differ from those shown in Figs. 1 to 5, which are provided to illustrate examples of the use of actuation signals of the controller.

[0072] The electromagnetic switching device 1 comprises an electromagnetic drive unit 2 with a rotatable armature 3 and a yoke 4. The armature 3 comprises a first magnetic contact region 5 and the yoke 4 comprises a second magnetic contact region 6. The first magnetic contact region 5 is in contact with the second magnetic contact region 6 in a second stable position of the armature, corresponding to a second state of the electromagnetic switching device 1 in which corresponds the electromagnetic switching device 1 is switched on. The electromagnetic switching device 1 further comprises a stationary first electric contact 7 and a moveable contact arm 8 with at least a second electric contact 9, the first electric contact 7 contacts the second electric contact 9 in the second state, with the armature 3 and the contact arm 8 are arranged together on a shaft 10.

[0073] In the second state, the electromagnetic switching device 1 has a high contact pressure between the moveable contact arm 8 and the first stationary electrical contact 7, resulting in a low electrical resistance through the electromagnetic switching device 1. The electromagnetic switching device 1 preferably has no air gap between the yoke 4 and the armature 3, causing low power requirements for the coils 21, 22 of the electromagnetic drive unit 2 in the event of switching.

[0074] The arrangement of the armature 3 and the contact arm 8 on the same shaft 10 provides a system with low inert mass and a low moment of inertia. As a reason the armature 3 and the contact arm 8 can be accelerated very fast.

[0075] The electromagnetic switching device 1 comprises an electromagnetic drive unit 2 and an electric switching mechanism.

[0076] The electromagnetic drive unit 2 comprises a rotatable armature 3 and a yoke 4. The electromagnetic drive unit 2 further comprises at least a first coil 21, wound at least in part around an area of the yoke 4. In the illustrated embodiments, the electromagnetic drive unit 2 further comprises a second coil 22, wound at least in part around an area of the yoke 4. The electromagnetic drive unit 2 especially further comprises at least a first permanent magnet 23, which is arranged between two parts of the yoke 4.

[0077] In the illustrated embodiment the electromagnetic drive unit 2 further comprises a second permanent magnet 24, which is also arranged between two parts of the yoke 4. In the illustrated embodiment, as shown in Fig. 1 to 5, the arrangement comprising the yoke 4, the first and second coil 21, 22 and the first and second permanent magnet 23, 24 is essentially symmetrical. The electromagnetic switching device 1 can be switched between two different stable states. The first state is defined as a switched-off state. In this state the moveable contact arm 8 is opened to separate at least one electric contact 7, 14 of the moveable contact arm 8 from stationary electric contacts 15 and 9, and an electric current flow through the electromagnetic switching device 1 is disabled. The second state is defined as a switched-on state. In this state the electric contacts 7 and 14 of the moveable contact arm 8 and the stationary electric contacts 15 and 9 are in contact with each other, and an electric current flow through the electromagnetic switching device 1 is enabled.

[0078] The armature 3 is rotatably mounted. The armature 3 comprises at least a first arm, with a first magnetic contact region 5 for contacting a second magnetic contact region 6 of the yoke 4. In the second stable position of the armature 3, the first magnetic contact region 5 is in contact with the second magnetic contact region 6.

[0079] In the illustrated embodiment, the yoke 4 comprises a further magnetic contact region on an opposite side of the second magnetic contact region 6, which is described herein as a fifth magnetic contact region 27. The armature 3 is arranged such that the first magnetic contact region 5 is in touch with the fifth magnetic contact region 27 in the first stable position.

[0080] In the illustrated embodiment, as shown in Fig. 1 to 5, the armature 3 comprises a second arm, with the second arm is embodied as third magnetic contact region 16. Preferably, the armature 3 is substantially symmetrical. In the illustrated embodiment, the yoke 4 further comprises a fourth magnetic contact region 17 and a sixth magnetic contact region 28. In the second stable position the third magnetic contact region 16 is in contact with the fourth magnetic contact region 17. In the first stable position, the third magnetic contact region 16 is in touch with the sixth magnetic contact region 28.

[0081] The electric switching mechanism comprises a stationary first electric contact 7, which is arranged on a first contact piece 25, which may comprise an opening or a soldering log for external connecting. The electric contact mechanism further comprises a moveable contact arm 8. The moveable contact arm 8 comprises a second electric contact 9.

[0082] In the second state (i.e. when the armature is in the second stable position) the first electric contact 7 contacts the second electric contact 9. In the embodiment illustrated in Fig. 1 to 5, the contact arm 8 is substantially symmetric and comprises a third electric contact 14 to contact a stationary fourth electric contact 15 of the electromagnetic switching device 1. The stationary fourth electric contact 15 is arranged on a second contact piece 26, which may comprise an opening or a soldering log for external connecting.

[0083] The contact arm 8 in the illustrated embodiment provides a double contact that can be separated or closed. In other embodiments, the contact arm may include only one electrical contact that is separated from a stationary electrical contact.

[0084] The contact arm 8 is coupled to the armature 3 by the shaft 10. Both, the armature 3 and the contact arm 8 are arranged together on the same shaft 10. The shaft 10 may be embodied as torsional element or may be rigid.

[0085] The electromagnetic switching device 1 comprises a relay housing 18, which is only shown in Fig. 5. The relay- housing 18 comprises two bushings for supporting the shaft 10. The shaft 10 is floating mounted in the relay housing 18 with a definite tolerance of movement in directions perpendicular to an axle of the shaft 10. This enables the shaft 10 to compensate further changes in the geometry of the electromagnetic drive unit 2 and / or the electric contact system.

[0086] In the illustrated embodiment, the electromagnetic switching device 1 comprises at least one auxiliary spring 19, 20, which is also an electric contact element. The auxiliary spring 19, 20 biases the contact arm 8 in direction to the first electric contact 7 in the first state.

[0087] Figs. 6a and 6b illustrate magnetic field paths in an electromagnetic drive unit 2 that would be suitable for use in the present invention. Fig. 6a illustrates a situation where neither of coils 21 and 22 are energised and magnetic field lines are generated between the poles of permanent magnetic elements 23 and 24 via the yoke 4 and the actuator 3. The magnetic fields between the permanent magnetic elements 23 and 24 generates a holding force between the armature 3 and the surfaces of the yoke 4 that the actuator is in contact with. As such, when the armature 3 is in a first stable position, the magnetic holding force biases the actuator to remain in the first stable position against external forces. Similarly, when the armature 3 is in the second stable position, the magnetic holding force biases the armature 3 to remain in the second stable position. Fig. 6b illustrates the change in magnetic field paths in the example of Fig. 6a when coils 21 and 22 are energised. In particular, the coils are arranged such that when energized in a first current direction, as shown in Fig. 6b, only one of the first and second positions of the armature 3 remains stable, and the armature 3 is biased towards the stable position and away from the unstable position. In the situation illustrated in Fig. 6b, the second position armature 3 is no longer stable and a torque is generated to cause rotational acceleration of the actuator towards the first position. After the armature 3 has rotated to the first position, removing current from the coils 21 and 22 causes both the first and second positions to become stable, and the armature will remain in the first position. By introducing a current in the coils in a second direction opposite the first direction, magnetic fields in the yoke 4 and armature 3 can generated causing only the first position to remain stable, in which case the armature 3 will accelerate towards the first position. As such, the electromagnetic drive unit 2 can be controlled to move the armature 3 from the second position to the first position by introducing current of a first direction into the coils, and the electromagnetic drive unit 2 can be controlled to move the armature from the second position to the first position by introducing current in a second direction into the coils (i.e. reversing the current of the first direction).

[0088] In embodiments of the present disclosure, the current provided to coils 21 and 22 can be controlled using an H-bridge 700 as shown in Fig. 7. In these embodiments, coils 21 and 22 can be disposed between contacts 702 and 703. Contacts 702 and 703 are connected to voltage sources via the four semiconductor switches 701a-d. When first 701a and fourth 701d switches are turned on and second 701b and third 701c switches are turned off, current flows through coils 21 and 22 in a first direction. The direction of current is reversed when first 701a and fourth 701d switches are turned off and second 701b and third 701c switches are turned on. Current can be removed from the coils 21 and 22 by turning all four switches 701a-d off. Actuation of the electromagnetic drive unit 2 is controlled by selecting a direction of current through the coils 21 and 22 by controlling switches 701a-d of the H-bridge 700. The switches of the H-bridge may be controlled by a processor. The processor or the processor in combination with the H-bridge may be considered to correspond to the controller as described in the present disclosure.

[0089] It is desirable for the electromagnetic drive unit 2 to achieve rapid actuation under fault conditions to move from the second stable position, in which the electromagnetic switching device 1 is switched on, to a first stable position, in which the electromagnetic switching device 1 is switched off. Such rapid actuation can be achieved by providing a single continuous current signal to coils 21 and 22 until the armature of the electromagnetic switching device 1 has completed its rotation into the first stable condition. A suitable actuation signal could be achieved by switching the second 701b and third 701c switches of the H-bridge 700 on for a suitable period of time while first 701a and 701d switches remain off, before turning all four switches 701a-d off when the electromagnetic switching device 1 is fully opened. Actuation of the electrical switching device 1 from the second stable position to the first stable position may be performed upon receiving a trigger signal indicating detection of an electrical fault.

[0090] Switching on of the electromagnetic switching device 1 by actuating the electromagnetic drive unit 2 from the first stable position to the second stable condition may be performed based on a user input or on receiving a signal indicating that an electrical fault condition has cleared. Switching on of the electromagnetic switching device 1 occurs in the absence of an electrical fault condition and is therefore not time-sensitive. As such, a high velocity of the armature 3 and moveable contact arm 8 is not necessary. Furthermore, switching on of the electromagnetic switching device 1 causes the moveable contact arm of the electromagnetic switching device 1 to collide with a stationary electric contact 7, 15 of the electromagnetic switching device 1, which can result in deformation of the electric contacts if the collision velocity is large. Figs. 8 and 9 illustrate control signals that can be used to control the actuation of the electromagnetic drive unit 2 from the first stable position to the second stable position to reduce a collision velocity of the moveable contact arm 8 with a stationary electric contact.

[0091] Fig. 8 illustrates a control signal for actuation of an electromagnetic drive unit 2 in order to switch on the electromagnetic switching device 1. In the present disclosure, a control signal that causes the armature of the electromagnetic switching device 1 to move from the first stable position to the second stable position is referred to as a "first actuation signal". A control signal that causes the armature of the electromagnetic switching device 1 to move from the second stable position to the first stable position is referred to as a "second actuation signal". In the embodiments described in detail in the description, the first stable position corresponds to a turned- off state of the switch, and the second stable position corresponds to a turned-on state of the switch.

[0092] According to the example control signal in Fig. 8, a first actuation signal comprises a series of pulses are provided to coils 21 and 22 in order to cause the armature 3 to rotate from the first stable position to the second stable position. The pulses may correspond to either a voltage applied across the coils 21 and 22 or current generated in the coils 21 and 22. In the present disclosure, a pulse that causes the armature 3 to accelerate in the direction of the second stable position from the first stable position is hereinafter referred to as a "first pulse 801" (which includes an "acceleration pulse" and a "closing pulse"). A pulse that causes the armature 3 to accelerate in the direction of the first stable position from the second stable position is hereinafter referred to as a "second pulse 802" (or a "break pulse"). A first actuation signal may comprise only first pulses 801, or may comprise a combination of first pulses 801 and second pulses 802 (where the second pulses 802 act to reduce the velocity of the armature 103 imparted by the first pulses 801).

[0093] According to the embodiment of Fig. 8, the first actuation signal 800 comprises a series of first pulses 801, which are successively provided to the electromagnetic drive unit 2 in order to switch on the electromagnetic switching device 1. In the example described in detail, three first pulses 801 are provided. In variations of this embodiment, fewer or more than three first pulses 801 may be provided in the series of first pulses. In the example described in detail, all of the first pulses 801 have different durations. However, in other examples, one or more of the first pulses 801 may have equal durations.

[0094] In the example described in detail, the durations of the first pulses 801 increase with time as the actuation signal 800 is provided. As such, the initial first pulse 801a of the series has the shortest duration, the second first pulse 801b has a longer duration, and the final first pulse 801n has the longest duration. In examples in which the series of first pulses 800 includes a different number of first pulses 801 (e.g. more than three first pulses), each first pulse 801 of the series of first pulses has a longer duration than the first pulses that preceded it. The first pulses 801 are separated by rest periods 802 in which the signal is paused (i.e. no voltage is applied across coils 21 and 22 and no current flows in the coils.) The duration of the rest periods 802 is chosen such that the rotatable armature 3 settles with approximately zero rotational velocity in either the first stable position or the second stable position by the end of the rest period 802.

[0095] The initial first pulse 801a causes the rotatable armature 3 to accelerate away from the first position in the direction of the second position. If the initial first pulse 801 is sufficient to cause the armature to reach the second position, it will remain in the stable second position after the first pulse 801a has ceased. If the duration of the initial first pulse 801a is not sufficient to cause the rotatable armature 3 to reach the second stable position, the rotatable armature 3 will return to the first stable position during the first rest period.

[0096] The second first pulse 801b has a longer duration than the initial first pulse 801a. The duration of successive first pulses 801 of the series of first pulses increases at least until a pulse of sufficient duration to bring the armature from the first position to the second position is achieved. The final first pulse 801n of the series may be a closing pulse having a substantially longer duration than the preceding first pulses 801 and serves to ensure that the second position of the rotatable armature 3 is reached.

[0097] Because the first actuation signal comprises a series of first pulses 801 having increasing duration, the particular first pulse that successfully causes movement of the armature 3 from the first to the second position will have a duration that is close to the minimum duration required to achieve this movement. As such, the armature 3 is not provided with kinetic energy that substantially exceeds the minimum kinetic energy needed to accomplish the switching operation. Further subsequent first pulses

[0098] 801 provided to the armature 3 after it has reached the second stable position will not result in acceleration of the armature 3 as the armature 3 will be constrained from further motion due to the pressure of the electrical contacts. Therefore, providing a series of first pulses of increasing duration can achieve reliable actuation of the switch while minimizing the kinetic energy of the armature 3 during actuation. Furthermore, the use of a series of first pulses of increasing duration does not require an optimal pulse duration to be determined prior to operation and is not sensitive to changes in the performance characteristics over the lifecycle of the electrical switching device.

[0099] Preferably, the initial first pulse 801 has a duration between 300ps and 500ps and, most preferably, has a duration of 370ps. Preferably, both rest periods 802 have a duration of between Ips and 1 second, more preferably have a duration between lOOOps and 5000ps and, most preferably, have a duration of 4000ps. Preferably the second first pulse has a duration between 300ps and 500ps and, most preferably, has a duration of 410ps. Preferably, the final first pulse has a duration between 500ps and 2500ps and, most preferably, has a duration of 2000ps.

[0100] In a further variation of the embodiment of Fig. 8, the durations of the rest periods

[0101] 802 between the first pulses 801 is chosen such that the armature 3 does not reach a stable position between subsequent first pulses. In this example, two initial first pulses 801a, 801b briefly accelerate the armature 3 from the first position towards the second position. The initial first pulses may have equal or different durations from each other. The two initial first pulses 801a, 801b are followed by a final first pulse 801n (or "closing pulse") that has a longer duration than the initial first pulses and ensures that the armature 3 has reached the second stable position. Because no current flows in the coils 21 and 22 during the rest periods 802, the first position becomes a stable position during the rest periods. As such, the armature 3 is decelerated (i.e. accelerated towards the first position) during the first rest period 802 until the armature 3 reaches almost zero velocity (while being located at an intermediate position between the first stable position and the second stable position). The second first pulse 801 causes the armature 3 to begin rotating again towards to second position before the final ("closing") first pulse 801 ensures complete closure of the electromagnetic switching device 1. The rest periods 802 between the first pulses result in a reduced velocity of the armature 3 at the point in which it reaches the second stable position in comparison to switching devices in which a continuous closing pulse is provided.

[0102] The reduced impact velocity between the moveable contact arm 8 and a stationary electrical contact in the above-described examples results in reduced deformation of the electrical contacts. This leads to reduced resistance, heating and dissipative power losses. As only the duration and direction of voltage / current pulses is varied in opening and closing actuation control signals with the magnitude of the voltage / current control signal remaining unchanged, the provision of asymmetric opening and closing of the electromagnetic switching device 1 can be achieved with a simple structure requiring only control of the first to fourth switches 701a-d of the Id- bridge 700.

[0103] The number and duration of first pulses and rest periods can be chosen to achieve reliable switching on of the electromagnetic switching device 1 and to reduce the collision velocity of the moveable contact arm during switching on. In some embodiments, the first actuation signal may include fewer or more than three first pulses.

[0104] Fig. 9 illustrates another embodiment of an actuation signal 900 in which two first pulses 801 are provided and in which a second pulse 901 in the reverse direction to the first pulses 801 is provided between the two first pulses instead of a rest period. In this embodiment, the first pulses 801 can be provided to the coils 21 and 22 by turning on switches 701a and 701d of the H-bridge while switches 701b and 701c are turned off. The second pulse 901 can be provided to the coils 21 and 22 by turning off switches 701a and 701d of the H-bridge and turning on switches 701b and 701c. In the embodiment of Fig. 9, the second pulse 901 decelerates the armature 3 during turning on of the electromagnetic switching device 1 in order to reduce the collision velocity of the moveable contact arm 8 during switching on.

[0105] Preferably, the initial first pulse 801a has a duration between 350ps and 700ps and, most preferably, has a duration of 400ps. Preferably, the second pulse 901 has a duration of between 50ps and 500ps and, most preferably, has a duration of lOOps. Preferably, the final first pulse 801n has a duration between 500ps and 2500ps and, most preferably, has a duration of lOOOps.

[0106] The number and duration of first pulses 801 and second pulses 901 can be chosen to achieve reliable switching on of the electromagnetic switching device 1 and to reduce the collision velocity of the moveable contact arm during switching on. In some embodiments, the first actuation signal 900 may include fewer or more than three first pulses 801 and may include more than one second pulse 901.

[0107] In the above-described embodiments, the movement of the armature 3 from a first stable position to a second stable position corresponds to a switch-on operation of the bistable electrical switching device. In other embodiments, it is also advantageous to provide a soft switch-off operation for circumstances in which a fast switch-off is not required. For example, it is advantageous to reduce the mechanical stress on the armature 3 during a switch-off operation in the absence of a short circuit condition. As such, a soft-switch off operation is provided in accordance with the above embodiments in which the first stable position of the armature corresponds to a switched-on state of the electrical switching device and the second stable position corresponds to a switched-off state. Preferably, the electrical switching device is configured such that the switch-on operation is always a soft switch-on operation including an actuation signal comprising a series of first pulses 801. Preferably, the electrical switching device is configured such that, in the absence of a detected electrical fault condition, the switch-off operation is a soft-switch off operation including an actuation signal comprising a series of first pulses 801 and, when an electrical fault is detected, the switch-off operation is a fast switch-off comprises a single extended first pulse 801.

Claims

Claims1. A bistable electrical switching device (1) comprising a controller and an electromagnetic drive unit (2), wherein the electromagnetic drive unit comprises a moveable armature (3) that can move between a first stable position and a second stable position, wherein the controller is configured to provide a first actuation signal (800,900) to cause the moveable armature (3) to move from the first stable position to the second stable position, wherein the first actuation signal comprises at least two first pulses (801) having a first polarity, wherein the controller and the electromagnetic drive unit are configured such that a pulse having the first polarity causes the armature to accelerate in the direction of the second stable position from the first stable position.

2. The bistable electrical switching device of claim 1, wherein the duration of the final first pulse (801n) of the at least two first pulses (801) is longer than that of any preceding first pulse, and, preferably, wherein the durations of the first pulses of the at least two first pulses increase with time such that, after the initial first pulse (801a), each subsequent first pulse has a longer duration than the first pulse that preceded it.

3. The bistable electrical switching device of any preceding claim, wherein at least two first pulses of the at least two first pulses (801) are separated by at least one rest period (802).

4. The bistable electrical switching device of claim 3, wherein the at least one rest period (802) has a duration between Ips and 5 seconds and, more preferably, a duration between lOOOps and 5000ps.

5. The bistable electrical switching device of any preceding claim, wherein the first actuation signal (900) comprises at least one second pulse (901) having a second polarity opposite to the first polarity and occurring between successive first pulses (801) of the at least two first pulses, wherein the controller and the electromagnetic drive unit are configured such that a pulse of the second polarity causes the armature to accelerate in the direction of the first stable position from the second stable position.

6. The bistable electrical switching device of claim 5, wherein the at least one second pulse and each of the at least two first pulses have the same magnitude.

7. The bistable electrical switching device of any preceding claim, wherein the durations of the first pulses of the at least two first pulses increase with time such that, after the initial first pulse, each subsequent first pulse has a longer duration than the first pulse that preceded it.

8. The bistable electrical switching device of any preceding claim, wherein the controller comprises an H-bridge (700) arrangement for controlling the polarity of actuation signals output by the controller.

9. The bistable electrical switching device of any preceding claim, wherein at least one first pulse (801) of the at least two first pulses has a duration between Ips and 5 seconds and, preferably, between lOOps and 700ps and, more preferably, between 300ps and 500ps.

10. The bistable electrical switching device of any preceding claim, wherein the electromagnetic drive unit further comprises: a yoke (2); at least one permanent magnet (23,24); and at least one coil (21,22); wherein the moveable armature is a rotatable armature configured to rotate between the first stable position and the second stable position, wherein the at least one coil (21,22) is configured to generate a magnetic field that causes a torque on the rotatable armature (3) upon receiving an actuation signal, and wherein first pulses of an actuation signal having a first polarity cause a torque on the rotatable armature (3) biasing the rotatable armature (3) to accelerate in the direction of the second stable position from the first stable position, and wherein second pulses of an actuation signal having a second polarity opposite the first polarity cause a torque on the rotatable armature (3) biasing the rotatable armature to accelerate in the direction of the first stable position from the second stable position.

11. The bistable electrical switching device of any preceding claim, wherein the moveable armature is coupled to a moveable contact arm (8) that forms part ofan electric circuit, wherein the moveable contact arm (9) is in an OFF state when the rotatable armature (3) is in the first stable position and an ON state when the rotatable armature is in the second stable position.

12. The bistable electrical switching device of any preceding claim, wherein the controller is further configured to provide, upon receiving a trigger signal, a second actuation signal to cause the moveable armature (3) to move from the second stable position to the first stable position, wherein the second actuation signal comprises a single continuous second pulse having the second polarity.

13. A method of controlling a bistable electrical switching device (1) comprising generating a first actuation signal (800,900) to cause a moveable armature (3) of the bistable electrical switching device to move from a first stable position to a second stable position, wherein the first actuation signal comprises at least two first pulses (801) having a first polarity.

14. The method of claim 13, wherein the final first pulse of the at least two first pulses has a longer duration than that of any preceding first pulse.

15. The method of claim 13 or claim 14, wherein : first pulses of the at least two first pulses are separated by at least one rest period (802) and / or the first actuation signal (900) comprises a second pulse (901) of a second polarity opposite the first polarity and occurring between any two successive first pulses of the at least two first pulses.

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