CN116959919A - Method for operating a contactor and associated device - Google Patents

Abstract

The present disclosure relates to a method and apparatus for operating a contactor. A switch assembly is disposed on at least one phase leg of a contactor, the switch assembly comprising a thyristor and an electromagnetic relay connected in parallel with the thyristor, the method comprising: providing a trigger signal to a control electrode of the thyristor to enable the thyristor to be conducted in response to a turn-on instruction of the contactor; detecting the current of the phase leg; determining the closing time of the electromagnetic relay based on the current; and providing a trigger signal to the electromagnetic relay based on the actuation timing to cause the electromagnetic relay to close. By controlling the closing timing of the electromagnetic relay, arc-free closing of the relay can be achieved in a low cost manner to increase the life of the contactor.

Description

Method for operating a contactor and associated device

Technical Field

Embodiments of the present disclosure generally include control of contactors, and more particularly, to methods and apparatus for operating electrical devices.

Background

Loads such as motors typically include inductive loads. Contactors are conventionally used to control the motor start-up. Due to the inductance of the inductive load, when the current flowing through the inductive load changes transiently, an induced electromotive force is generated at two ends of the inductive load, and the value of the induced electromotive force is proportional to the inductance and the change rate of the current. The performance of the switching devices within the contactor, and thus the life of the contactor, will be severely affected due to the inductive nature of the inductive load of the motor. It is desirable to be able to improve the method for operating the contactor to increase the useful life and/or performance of the contactor.

Disclosure of Invention

Embodiments of the present disclosure provide a method and apparatus for operating a contactor that aims to address one or more of the above problems, as well as other potential problems.

According to a first aspect of the present disclosure, a method for operating a contactor is provided. A switch assembly is disposed on at least one phase leg of the contactor, the switch assembly including a thyristor and an electromagnetic relay connected in parallel with the thyristor, the method comprising: providing a trigger signal to a control electrode of the thyristor to enable the thyristor to be conducted in response to a turn-on instruction of a contactor; detecting a current of the phase leg; determining a closing timing of the electromagnetic relay based on the current; and providing a trigger signal to the electromagnetic relay based on the actuation timing to cause the electromagnetic relay to close.

In some embodiments, determining a pull-in time of the electromagnetic relay based on the current comprises: determining a period of the current; determining a current zero crossing in the phase leg based on the period; and determining the actuation timing of the electromagnetic relay based on the current zero-crossing point such that the current in the phase leg is zero when the electromagnetic relay is actuated.

In some embodiments, determining the pull-in timing of the electromagnetic relay based on the current zero crossing comprises: acquiring an actuation curve of the electromagnetic relay; determining the actuation timing of the electromagnetic relay based on the actuation curve; and determining the actuation timing of the electromagnetic relay based on the actuation timing and the current zero crossing point.

In some embodiments, determining the pull-in timing of the electromagnetic relay based on the pull-in timing and the current zero crossing comprises: determining a time difference between the cycle and the pull-in timing; based on the time difference, the actuation timing of the electromagnetic relay is determined.

In some embodiments, determining the pull-in timing of the electromagnetic relay based on the time difference comprises: in the next cycle immediately following the cycle of detecting the current, after the time difference has elapsed from the start of the next cycle, a pull-in instruction is sent to the electromagnetic relay.

In some embodiments, each phase leg of the contactor includes a switch assembly, each switch assembly including a respective thyristor and a respective electromagnetic relay connected in parallel with the respective thyristor, wherein each phase leg is controlled independently of each other.

In some embodiments, the contactor is configured to close the phase leg to start the motor.

In some embodiments, the contactor is configured to close the phase leg to enable an inductive load.

According to a second aspect of the present disclosure, there is provided an apparatus for operating a contactor having a switch assembly disposed on at least one phase leg of the contactor, the switch assembly comprising a thyristor and an electromagnetic relay connected in parallel with the thyristor, the apparatus comprising: current sampling means for sampling the current in the phase leg; and a controller communicatively connected with the current sampling apparatus and configured to perform the method of the first aspect.

According to a third aspect of the present disclosure there is provided a motor starter comprising an apparatus according to the second aspect.

According to a fourth aspect of the present disclosure, there is provided a computer readable medium having stored thereon computer executable instructions which, when executed on a processor, perform the method according to the first aspect.

According to the method and the device for operating the contactor, by controlling the closing timing of the electromagnetic relay, the arc-free closing of the relay can be realized in a low-cost manner, and the service life of the contactor is further prolonged.

Drawings

The above, as well as additional purposes, features, and advantages of embodiments of the present disclosure will become readily apparent from the following detailed description when read in conjunction with the accompanying drawings. In the accompanying drawings, several embodiments of the present disclosure are shown by way of example, and not by way of limitation.

Fig. 1 shows a schematic diagram of a system for controlling a load according to one embodiment of the present disclosure.

Fig. 2 shows a flow diagram of a method for operating a contactor according to one embodiment of the present disclosure.

Fig. 3 shows a flow diagram of a method for operating a contactor according to one embodiment of the present disclosure.

Fig. 4 shows a flow diagram of a method for operating a contactor according to one embodiment of the present disclosure.

Fig. 5 illustrates a schematic diagram for determining actuation timing of an electromagnetic relay according to one embodiment of the present disclosure.

Fig. 6 illustrates a block diagram of an apparatus capable of implementing various embodiments of the present disclosure.

Like or corresponding reference characters indicate like or corresponding parts throughout the several views.

Detailed Description

Preferred embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While the preferred embodiments of the present disclosure are illustrated in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.

The term "comprising" and variations thereof as used herein means open ended, i.e., "including but not limited to. The term "or" means "and/or" unless specifically stated otherwise. The term "based on" means "based at least in part on". The terms "one example embodiment" and "one embodiment" mean "at least one example embodiment. The term "another embodiment" means "at least one additional embodiment". The terms "upper," "lower," "front," "rear," and the like, as used herein, refer to a place or position relationship based on the orientation or position relationship shown in the drawings, and are merely for convenience in describing the principles of the present disclosure, and do not refer to or imply that the elements referred to must have a particular orientation, be configured or operated in a particular orientation, and thus should not be construed as limiting the present disclosure.

Fig. 1 shows a schematic diagram of a system 100 for controlling a load according to an embodiment of the present disclosure. The load 50 may comprise a device that is an inductive load. In some embodiments, the load 50 may be, for example, an electric motor. The system 100 may be, for example, a contactor or motor starter for controlling the starting and stopping of the load 50. A contactor or motor starter is a device for assisting in the starting of a motor. It should be noted that although the operation principle for controlling the start-up of the inductive load according to the embodiment of the present disclosure is described with the contactor as an example in the illustrated embodiment; this is merely exemplary and the load 50 may comprise any other suitable device including an inductive load. Furthermore, although the operation process is described by taking a contactor as an example, the method according to the embodiment of the present disclosure may be applied to other similar devices.

As shown in fig. 1, the system 100 may include three-phase power La, lb, lc, respectively, with an inductive load 50 (shown only schematically overall in the figure). A plurality of switch assemblies may be provided for each phase line for controlling the operation of the load, each switch assembly may include a thyristor and an electromagnetic relay. It should be noted that although in the illustrated embodiment a three-phase electric motor is taken as an example to illustrate the principle of operation of the method and apparatus according to embodiments of the present disclosure; this is merely exemplary; the apparatus and method according to embodiments of the present disclosure may be applied to single-phase electricity or two-phase electricity.

In the illustrated embodiment, at least the thyristor G1 and the electromagnetic relay U1 connected in parallel to each other are provided in the power supply circuit for the La phase. Similarly, for the Lb phase, a thyristor G2 and an electromagnetic relay U2 connected in parallel to each other are provided in the power supply circuit; for the Lc phase, a thyristor G3 and an electromagnetic relay U31 connected in parallel to each other are provided in the power supply circuit.

The system 100 may also include a controller 20, an input interface 40, and a driver 30. An input interface 40 may be connected to the controller 20 to provide for control instructions. The controller 20 may be configured to generate control instructions, which may be converted via the driver 30 to be suitable for driving the switch assemblies G1, U1; g2, U2; g3, U3. Although in the illustrated embodiment, the driver 30 is shown as a separate component, in other embodiments, the driver 30 may be integrated into the controller 20.

The operation of the system 100 is as follows. After the input interface 40 receives an instruction to start the load 50, the controller 20 sends an instruction to the driver 30 to first close the thyristors G1, G2, G3, after which the power on the respective phases La, lb, lc is supplied to the load 50 through the branch of the switching device where the thyristors G1, G2, G3 are set. After closing the thyristors G1, G2, G3, the controller 20 then sends instructions to the driver 30 to close the electromagnetic relays U1, U2, U3. After the electromagnetic relays U1, U2, U3 receive the instruction from the driver 30, the electromagnetic relays U1, U2, U3 are closed to short-circuit the thyristors G1, G2, G3. The controller 20 then sends instructions to the thyristors to turn off G1, G2, G3. The power in each phase La, lb, lc is thereby supplied to the load 50 via the branches of the electromagnetic relays U1, U2, U3.

The above system has the following advantages. Taking the operation of the La phase leg as an example, the other phase legs are similar. Since the thyristor G1 and the electromagnetic relay U1 are connected in parallel with each other and sequentially turned on, particularly when the thyristor G1 is first turned on and then the electromagnetic relay U1 is turned on again, the electromagnetic relay U1 is subjected to only a voltage drop across the thyristor G1 when turned on, the voltage drop being, for example, around 1 to 2V; this avoids the influence on the performance of the electromagnetic relay U1 due to an excessive voltage drop.

The inventors of the present disclosure have discovered that the above-described operational sequences may continue to be optimized to further improve the performance of the system 100. The inventors found that when the electromagnetic relay U1 is operated at an arbitrary closing timing, the electromagnetic relay may be closed under a condition that a large current flows through the La phase leg, and the large current may generate an arc at the contact of the electromagnetic relay, and the continuously generated arc may abrade the contact to affect the life of the electromagnetic relay.

The system 100 according to embodiments of the present disclosure may further include current sensing devices 10a, 10b, 10c. The current sensing means 10a, 10b, 10c are arranged to sense the current flowing through the respective phase current La, lb, lc loop. The current sensing means may be implemented in various ways as long as current sensing can be implemented. In some embodiments, the current sensing device may be implemented as a voltage divider resistor, a hall sensor, a CT transformer, a magnetic sensor (TMR), or the like.

The system 100 according to the embodiment of the present disclosure can achieve arc-free closing of the relay in a low-cost manner based on the current acquired by the current sensing devices 10a, 10b, 10c and by controlling the closing timing of the electromagnetic relay, thereby improving the lifetime of the system 100.

Fig. 2 shows a flow diagram of a method 200 for operating a contactor according to one embodiment of the present disclosure. The method 200 may include the following acts. At block 202, a trigger signal is provided to a gate of the thyristor to cause the thyristor to conduct in response to a turn-on command of the contactor. At block 204, the current of the phase leg is detected. At block 206, a firing opportunity for the electromagnetic relay is determined based on the current. At block 208, a trigger signal is provided to the electromagnetic relay to cause the electromagnetic relay to close based on the actuation opportunity.

Also referring to fig. 1, taking the La phase leg as an example, after the input interface 40 inputs an instruction to the controller 20 for controlling the start of the load 50, the controller 20 may generate a corresponding control instruction and send the instruction to the driver 30. The driver 30 in turn drives the thyristor G1 closed. The controller 20 may sample the current of the La phase leg through the current sensing device 10a and determine the actuation timing of the electromagnetic relay based on the sampled current. Based on the actuation timing, the controller 20 sends an instruction to the driver 30 to cause the driver 30 to drive the electromagnetic relay to close at the actuation timing. After the electromagnetic relay is closed, the controller 20 then sends instructions to the thyristors to turn off G1, G2, G3.

It is worth noting that although the method 200 for operating a contactor is described by taking the La phase leg as an example, the other phase legs Lb, lc may be performed independently and in a similar manner with respect to La, and detailed description thereof will be omitted.

The term "attracting timing" herein refers to timing at which contacts of the electromagnetic relay are closed, which is determined in such a manner as to reduce an arc generated when the contacts of the electromagnetic relay are closed. The attraction time machine is determined such that the current flowing through the electromagnetic relay is equal to or smaller than a predetermined threshold value in consideration of the fact that the arc generation is related to the magnitude of the current flowing through the electromagnetic relay, wherein the predetermined threshold value may be related to the current of the arc at the time of generation of the electromagnetic relay. In some embodiments, the pull-in motor is determined such that the current of the phase leg in which the electromagnetic relay is located is zero. Thus, according to the method of the embodiment of the present disclosure, the risk of arc generation when the contacts of the electromagnetic relay are closed can be reduced by controlling the contact closing timing of the electromagnetic relay.

Determining the actuation timing of the electromagnetic relay based on the sampled current may include a variety of implementations. Fig. 3 shows a flow diagram of a method 300 for operating a contactor according to one embodiment of the present disclosure. Fig. 3 illustrates one embodiment of determining the actuation timing of an electromagnetic relay based on a sampled current. As shown in fig. 3, method 300 may include the following acts. At block 302, a period of current is determined based on the sampled current. For example, a plurality of points (e.g., 3 points) may be sampled for the phase leg to determine the period of the current based on the sampled points. At block 304, based on the period, a current zero crossing in the phase leg is determined. At block 306, a pull-in timing of the electromagnetic relay is determined based on the current zero-crossing point such that the electromagnetic relay is at the current zero point in the phase line at the pull-in timing.

An embodiment of determining the actuation timing of the electromagnetic relay based on the period of the current of the phase leg is exemplarily shown in the embodiment of fig. 3. This has the advantage that the accuracy of the zero crossing determination can be ensured by determining the period of the current and determining the pull-in time based on the period of the current, taking into account the presence of an inductive load in the load 50, and thus the possible fluctuation in the period of the current of the phase leg.

In other embodiments, the actuation timing of the electromagnetic relay may be operated at a predetermined actuation timing. This applies, for example, to the case where the phase leg is relatively stable, and the case where the current zero crossing or near zero crossing of the phase leg can be accurately determined.

Fig. 4 shows a flow diagram of a method for operating a contactor 400 according to one embodiment of the present disclosure. Fig. 4 illustrates one embodiment of determining the actuation timing of an electromagnetic relay based on the current zero-crossing point. As shown in fig. 4, method 400 may include the following acts. At block 402, a pull-in curve of an electromagnetic relay is acquired. At 404, a pull-in timing of the electromagnetic relay is determined based on the pull-in curve. At 405, a pull-in timing of the electromagnetic relay is determined based on the pull-in timing and the current zero crossing.

In the embodiment shown in fig. 4, the switching-on characteristic of the moving contact of the electromagnetic relay is taken into account in the switching-on of the electromagnetic relay, so that the zero-crossing or the proximity of the zero-crossing of the current of the phase leg can be determined more precisely.

In some embodiments, determining a pull-in timing of an electromagnetic relay based on a pull-in timing and a current zero crossing includes: determining the time difference between the period and the suction time; and transmitting an actuation instruction to the electromagnetic relay based on the time difference. In this case, the closing of the zero crossing of the current of the electromagnetic relay can be conveniently achieved based on the time difference as a control parameter.

Fig. 5 illustrates a schematic diagram for determining actuation timing of an electromagnetic relay according to one embodiment of the present disclosure. As shown in fig. 5, the upper graph shows the current curve 52 on the phase leg; the lower graph 54 shows a current curve 54 at the coil of the electromagnetic relay. Wherein at point C1 (corresponding to time t 3), the electromagnetic relay starts to perform a closing action; and at point C2 (corresponding to time t 4), the electromagnetic relay is reliably switched on. In some embodiments, the closing time t of the electromagnetic relay is selected such that the closing point C2 of the electromagnetic relay coincides with the zero crossing of the current on the phase leg (time t4 in the figure) or is close to the zero crossing of the current on the phase leg (in this case, the current value is small although the current on the phase leg is not zero).

The process diagram shown in fig. 5 is explained taking as an example that the switching-on timing of the electromagnetic relay is selected so that the switching-on point C2 of the electromagnetic relay coincides with the zero-crossing point of the current on the phase leg. As shown in fig. 5, the symbol T represents a period of current, and T1-T2 represent a first period, i.e., a period in which the controller 20 receives a load start instruction from the input interface 40, during which the controller 20 can determine the period T of the phase current by sampling the phase current; t2-t4 represent a second period immediately following the first period; .

The known actuation timing of the electromagnetic relay, shown in fig. 5 as the time corresponding to the time between C1-C2, can be obtained, and the time difference Δt can be calculated by subtracting the time period from the period T. After the end of the first period and when the zero-crossing point of the current is determined, a drive signal of the electromagnetic relay is emitted after a time of Δt, i.e. at time t. By such an operation, the contact sucking point C2 of the electromagnetic relay corresponds to the zero crossing point t4 of the current of the next cycle.

By issuing an electromagnetic relay closing instruction at time t, the electromagnetic relay is attracted at the current zero-crossing point t4 of the next cycle immediately after the first cycle. The advantage of this is that the electromagnetic relay can be closed as early as possible, avoiding a long duration of the on-time of the thyristor G1. In addition, the accuracy of control can also be improved in consideration of the fluctuation of the frequency in the phase legs. It is worth noting that this is merely exemplary, and the closing timing may be determined in any other suitable manner taking into account the known timing of the electromagnetic relay.

According to an embodiment of the present disclosure, each phase leg of the contactor comprises a switch assembly, each switch assembly comprising a respective thyristor and a respective electromagnetic relay connected in parallel with the respective thyristor, wherein each phase leg is controlled independently of each other. Therefore, the electromagnetic relay on each phase branch can be ensured to realize zero-crossing starting.

According to a second aspect of the present disclosure there is provided an apparatus for operating a contactor having a switch assembly disposed on at least one phase leg of the contactor, the switch assembly comprising a thyristor and an electromagnetic relay connected in parallel with the thyristor, the apparatus comprising: the current sampling device is used for sampling the current in the phase branch; and a controller communicatively connected to the current sampling apparatus and configured to perform the method of the above aspect.

Fig. 6 illustrates a block diagram of a computing device 600 capable of implementing various embodiments of the disclosure. As shown, the device 600 includes a Central Processing Unit (CPU) 601 that can perform various suitable actions and processes in accordance with computer program instructions stored in a Read Only Memory (ROM) 602 or loaded from a storage unit 608 into a Random Access Memory (RAM) 603. In the RAM 603, various programs and data required for the operation of the device 600 may also be stored. The CPU 601, ROM 602, and RAM 603 are connected to each other through a bus 604. An input/output (I/O) interface 605 is also connected to bus 604.

Various components in the device 600 are connected to the I/O interface 605, including: an input unit 606 such as a keyboard, mouse, etc.; an output unit 607 such as various types of displays, speakers, and the like; a storage unit 608, such as a magnetic disk, optical disk, or the like; and a communication unit 609 such as a network card, modem, wireless communication transceiver, etc. The communication unit 609 allows the device 600 to exchange information/data with other devices via a computer network, such as the internet, and/or various telecommunication networks.

The processing unit 601 performs the various methods and processes described above, such as methods 200, 300, 500, 600. For example, in some embodiments, the methods 200, 300, 400 may be implemented as a computer software program tangibly embodied on a machine-readable medium, such as the storage unit 608. In some embodiments, part or all of the computer program may be loaded and/or installed onto the device 600 via the ROM 602 and/or the communication unit 609. When the computer program is loaded into RAM 603 and executed by CPU 601, one or more steps of process 200 described above may be performed. Alternatively, in other embodiments, the CPU 601 may be configured to perform the methods 200, 300, 400 by any other suitable means (e.g., by means of firmware).

The functions described above herein may be performed, at least in part, by one or more hardware logic components. For example, without limitation, exemplary types of hardware logic components that may be used include: a Field Programmable Gate Array (FPGA), an Application Specific Integrated Circuit (ASIC), an Application Specific Standard Product (ASSP), a system on a chip (SOC), a load programmable logic device (CPLD), etc.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program code may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus such that the program code, when executed by the processor or controller, causes the functions/operations specified in the flowchart and/or block diagram to be implemented. The program code may execute entirely on the machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of this disclosure, a machine-readable medium may be a tangible medium that can contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of a machine-readable storage medium would include an electrical connection based on one or more wires, a portable computer diskette, a hard disk, a Random Access Memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

To provide for interaction with a user, the systems and techniques described here can be implemented on a computer having: a display device (e.g., a CRT (cathode ray tube) or LCD (liquid crystal display) monitor) for displaying information to a user; and a keyboard and pointing device (e.g., a mouse or trackball) by which a user can provide input to the computer. Other kinds of devices may also be used to provide for interaction with a user; for example, feedback provided to the user may be any form of sensory feedback (e.g., visual feedback, auditory feedback, or tactile feedback); and input from the user may be received in any form, including acoustic input, speech input, or tactile input.

The systems and techniques described here can be implemented in a computing system that includes a background component (e.g., as a data server), or that includes a middleware component (e.g., an application server), or that includes a front-end component (e.g., a user computer having a graphical user interface or a web browser through which a user can interact with an implementation of the systems and techniques described here), or any combination of such background, middleware, or front-end components. The components of the system can be interconnected by any form or medium of digital data communication (e.g., a communication network). Examples of communication networks include: local Area Networks (LANs), wide Area Networks (WANs), and the internet.

Moreover, although operations are depicted in a particular order, this should be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are included in the above discussion, these should not be construed as limiting the scope of the present disclosure. Certain features that are described in the context of separate embodiments can also be implemented in combination in a single implementation. Conversely, various features that are described in the context of a single implementation can also be implemented in multiple implementations separately or in any suitable subcombination.

Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are example forms of implementing the claims.

The foregoing description of the embodiments of the present disclosure has been presented for purposes of illustration and description, and is not intended to be exhaustive or limited to the embodiments disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the various embodiments described. The terminology used herein was chosen in order to best explain the principles of the embodiments, the practical application, or the technical improvements in the marketplace, or to enable others of ordinary skill in the art to understand the embodiments disclosed herein.

Claims (11)

1. A method for operating a contactor having a switch assembly disposed on at least one phase leg of the contactor, the switch assembly comprising a thyristor and an electromagnetic relay connected in parallel with the thyristor, the method comprising:

providing a trigger signal to a control electrode of the thyristor to enable the thyristor to be conducted in response to a turn-on instruction of a contactor;

detecting a current of the phase leg;

determining a closing timing of the electromagnetic relay based on the current; and

and providing a trigger signal to the electromagnetic relay based on the actuation timing to cause the electromagnetic relay to close.

2. The method of claim 1, wherein determining a pull-in time of the electromagnetic relay based on the current comprises:

determining a period of the current;

determining a current zero crossing in the phase leg based on the period; and

and determining the closing timing of the electromagnetic relay based on the current zero crossing point so that the current in the phase branch is zero when the electromagnetic relay is closed.

3. The method of claim 2, wherein determining the on-time of the electromagnetic relay based on the current zero crossing comprises:

acquiring an actuation curve of the electromagnetic relay;

determining the actuation timing of the electromagnetic relay based on the actuation curve; and

the actuation timing of the electromagnetic relay is determined based on the actuation timing and the current zero crossing.

4. The method of claim 3, wherein determining the pull-in timing of the electromagnetic relay based on the pull-in timing and the current zero crossing comprises:

determining a time difference between the cycle and the pull-in timing;

based on the time difference, the actuation timing of the electromagnetic relay is determined.

5. The method of claim 4, wherein determining the on-time of the electromagnetic relay based on the time difference comprises:

in the next cycle immediately following the cycle of detecting the current, after the time difference has elapsed from the start of the next cycle, a pull-in instruction is sent to the electromagnetic relay.

6. The method of any of claims 1-5, wherein each phase leg of the contactor comprises a switch assembly, each switch assembly comprising a respective thyristor and a respective electromagnetic relay in parallel with the respective thyristor, wherein each phase leg is controlled independently of each other.

7. The method of any of claims 1-5, wherein the contactor is configured to close the phase leg to start a motor.

8. The method of any of claims 1-5, wherein the contactor is configured to close the phase leg to initiate an inductive load.

9. An apparatus for operating a contactor having a switch assembly disposed on at least one phase leg of the contactor, the switch assembly comprising a thyristor and an electromagnetic relay connected in parallel with the thyristor, the apparatus comprising:

current sampling means for sampling the current in the phase leg; and

a controller communicatively connected with the current sampling apparatus and configured to perform the method of any of claims 1-8.

10. A motor starter comprising the apparatus of claim 9.

11. A computer readable medium having stored thereon computer executable instructions which, when executed on a processor, perform the method according to any of claims 1-8.