Electromagnet power-off magnetic field maintaining device

Abstract

The application discloses a magnet retaining device for electromagnet during power failure, which comprises a main circuit, a control circuit and a communication module, wherein a rectifying unit and a programmable controller are respectively connected with the communication module; a three-phase AC power supply is connected to the primary side of a transformer through a circuit breaker; the secondary side of the transformer is connected to the rectifying unit through a fuse, a fuse and an AC contactor; the rectifying unit outputs a DC voltage; the electromagnet is connected to the rectifying unit through a fuse and a diode module; the electromagnet is forwardly excited to work; the rectifying unit outputs a positive DC voltage; the electromagnet is connected to the rectifying unit through a fuse and three normally open contacts of an AC contactor connected in parallel with the diode module. The magnet retaining device for electromagnet during power failure realizes four-quadrant operation of the electromagnet, energy storage and rapid release of the electromagnet, and magnet retaining operation during power failure. When the rectifying unit cannot feed back operation, the energy storage of the electromagnet can be released through an added freewheeling circuit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of power-off magnetic preservation devices, in particular to a power-off magnetic preservation device for electromagnet. BACKGROUND

[0002] The existing power-off magnetic preservation device for electromagnet adopts three-phase uncontrollable rectification or three-phase full-control bridge rectification, and provides positive excitation and reverse demagnetization power supply for the electromagnet through the DC contactor commutation. The energy storage of the electromagnet cannot be quickly released when the positive excitation and reverse demagnetization power supply stops, and the working efficiency is low.

[0003] PROFIBUS is a fieldbus standard used in automation technology, which was promoted by fourteen companies and five research institutions in Germany in 1987. PROFIBUS is the abbreviation of PROcess FIeld BUS. PROFIBUS and PROFINET used in industrial Ethernet are two different communication protocols. PROFIBUS can be divided into two types, namely PROFIBUS DP used by most people and PROFIBUS PA used in process control. PROFIBUS DP (Decentralized Peripherals) is used in factory automation applications and can be controlled by a central controller to control many sensors and actuators. The status of each module can be known by using standard or optional diagnostic functions. PROFIBUS PA (Process Automation) is used in process automation systems and is monitored by process control systems to control measurement equipment. It is an intrinsically safe communication protocol that can be applied to explosion-proof areas (Ex-zone 0 and Ex-zone 1 in the classification of industrial explosion-proof hazardous areas). The physical layer (cable) matches IEC 61158-2, allowing the communication cable to provide power to the field device. Even in the event of a failure, the amount of current can be limited to avoid situations that may cause an explosion. Because power is supplied by the network, the number of devices that can be connected to a PROFIBUS PA network is limited. The communication rate of PROFIBUS PA is 31.25 kbit / s. The communication protocol used by PROFIBUS PA is the same as that used by PROFIBUS DP. As long as there is a conversion device, it can be connected to the PROFIBUS DP network. The faster PROFIBUS DP is used as the network backbone to deliver signals to the controller. In some applications that require simultaneous automation and process control, PROFIBUS DP and PROFIBUS PA can be used simultaneously. SIMATIC S7-1200 is a compact and modular PLC that can complete simple logic control, advanced logic control, HMI and network communication tasks. It has strong scalability, high flexibility and design, can realize the communication interface of the highest standard industrial communication and a complete set of integrated technology functions, so that the controller becomes an important part of a complete and comprehensive automation solution. SUMMARY

[0004] In order to solve the problem of the existing electromagnet power-off magnetic device, the electromagnet energy storage cannot be quickly released when the forward excitation and reverse demagnetization power supply stops, and the working efficiency is low.

[0005] In order to achieve the above technical purpose, the technical scheme of the present application is as follows:

[0006] The electromagnetic iron power-off magnetism maintaining device is designed, which comprises a main circuit, a control circuit, a communication module and an electromagnet; the main circuit comprises a direct current voltage commutation circuit, a diode module one, a programmable controller and a battery pack, wherein the direct current voltage commutation circuit comprises a rectification unit, the rectification unit is in communication connection with the communication module; the diode module one is in series connection with a fuse three, the diode module one is in parallel connection with an alternating current contactor two, the rectification unit is connected with the electromagnet through the alternating current contactor two and the fuse three, the diode module one is further in parallel connection with a diode module two; the programmable controller is in communication connection with the communication module; the battery pack is connected with an alternating current contactor four; the rectification unit rectifies output current with positive on the top and negative on the bottom, the current of the battery pack passes through the alternating current contactor four and the diode module two, and the electromagnet is powered at the same time, so that the power-off magnetism maintaining function is realized.

[0007] Further, the direct current voltage commutation circuit further comprises:

[0008] a direct current contactor three, the direct current contactor three is in series connection with a resistance one; an emergency stop button, the emergency stop button is connected with the rectification unit;

[0009] Wherein, the direct current contactor three and the resistance one constitute a freewheeling circuit for releasing the energy storage of the electromagnet; when communication problems occur, the rectification unit can be stopped by pressing the emergency stop button to disconnect the normally closed contact.

[0010] Further, the main circuit further comprises:

[0011] a three-phase alternating current power supply, the three-phase alternating current power supply is in series connection with a circuit breaker one, the three-phase alternating current power supply is connected with a transformer through the circuit breaker one, the transformer is in series connection with a circuit breaker three and a filter, and the transformer is connected with the rectification unit through the circuit breaker three and the filter.

[0012] Further, the transformer is further connected with a fuse one and a fuse two, the fuse one and the fuse two are in parallel connection; the fuse one is in series connection with an alternating current contactor one, and the alternating current contactor one is connected with the rectification unit.

[0013] Further, the output end of the rectification unit is connected with a fuse three, and the fuse three is connected with the diode module one.

[0014] Further, the transformer is further connected with a charging module, the charging module is connected with a circuit breaker two, and the circuit breaker two is connected with the battery pack.

[0015] Further, the charging module is further connected with a negative relay four.

[0016] Further, the control circuit further comprises:

[0017] Signal conversion isolator for converting DC voltage signal into 0-10V standard voltage.

[0018] Further, the control circuit further comprises:

[0019] Relay one, relay two, relay three, relay four, the relay one, relay two K, relay three, relay four are in parallel.

[0020] Further, the control circuit further comprises:

[0021] Switching power supply, the specification of the switching power supply is DC 24V power supply;

[0022] Wherein, the control circuit switching power supply is a programmable controller, signal conversion isolator, relay one, relay two, relay three, relay four provides electric energy.

[0023] The beneficial effects of the application: this electromagnet power-off magnetic device, using DC voltage commutation circuit, realize the four quadrant work of electromagnet excitation demagnetization, electromagnet energy storage fast release, power-off magnetic working time, through the increase of freewheeling circuit release electromagnet energy storage when the rectifier unit cannot feedback operation. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical scheme in the embodiments of the present application or prior art, the drawings needed in the embodiments will be briefly introduced below, and obviously, the drawings in the following description are only some embodiments of the present application, and those skilled in the art can obtain other drawings according to these drawings without creative labor.

[0025] Figure 1 It is the main circuit schematic diagram of the electromagnet power-off magnetic device according to the embodiment of the present application;

[0026] Figure 2 It is Figure 1 the partial principle of DC voltage commutation circuit in Figure 1 ;

[0027] Figure 3 It is Figure 1 the partial principle of DC voltage commutation circuit in Figure 2 ;

[0028] Figure 4 It is the control circuit schematic diagram of the electromagnet power-off magnetic device according to the embodiment of the present application;

[0029] Figure 5is a control circuit partial principle of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application Figure 1 ;

[0030] Figure 6 is a control circuit partial principle of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application Figure 2 ;

[0031] Figure 7 is a control circuit partial principle of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application Figure 3 ;

[0032] Figure 8 is a control circuit partial principle of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application Figure 4 ;

[0033] Figure 9 is a control circuit partial principle of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application Figure 5 ;

[0034] Figure 10 is a PROFIBUS DP communication network structure schematic diagram of the electromagnet power-off magnetic field maintaining device according to the embodiment of the present application. DETAILED DESCRIPTION

[0035] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art belong to the scope of protection of the present application.

[0036] As Figure 1As shown, the electromagnet power-off magnetic field protection device according to the embodiment of the application comprises a main circuit, a control circuit and a communication module ED2; the main circuit comprises a direct current voltage commutation circuit, a diode module V1, a programmable controller ED1 and a battery pack GB; wherein the direct current voltage commutation circuit comprises a rectifier unit U1, the rectifier unit U1 is in communication connection with the communication module ED2; the diode module V1 is in series connection with a fuse three FU3, the diode module V1 is in parallel connection with an alternating current contactor two KM2, the rectifier unit U1 is connected with an electromagnet through the alternating current contactor two KM2 and the fuse three FU3; the diode module V1 is further in parallel connection with a diode module two V2; the programmable controller ED1 is in communication connection with the communication module ED2; the battery pack GB is connected with an alternating current contactor four KM4; the rectifier output of the rectifier unit U1 is in positive on and negative off, the current of the battery pack GB is passed through the alternating current contactor four KM4 and the diode module two V2, and the electromagnet is powered at the same time, so as to realize the power-off magnetic field protection function.

[0037] As shown in the figure, Figures 1-3 In the embodiment, the direct current voltage commutation circuit further comprises:

[0038] a direct current contactor three KM3 in series connection with a resistance one R1, and an emergency stop button SE1 connected with the rectifier unit U1;

[0039] Wherein, the direct current contactor three KM3 and the resistance one R1 constitute a freewheeling circuit for releasing the energy storage of the electromagnet; when the communication has a problem, the rectifier unit U1 can be stopped by pressing the emergency stop button SE1 to disconnect the normally closed contact.

[0040] As shown in the figure, Figures 1-3 In the embodiment, the main circuit further comprises:

[0041] a three-phase alternating current power supply in series connection with a circuit breaker one QF1, the three-phase alternating current power supply is connected with a transformer TR1 through the circuit breaker one QF1, the transformer TR1 is in series connection with a circuit breaker three QF3 and a filter ZF, and the transformer TR1 is connected with the rectifier unit U1 through the circuit breaker three QF3 and the filter ZF.

[0042] As shown in the figure, Figures 1-3 In the embodiment, the transformer TR1 is further connected with a fuse one FU1 and a fuse two FU2, and the fuse one FU1 and the fuse two FU2 are in parallel connection; the fuse one FU1 is in series connection with an alternating current contactor one KM1, and the alternating current contactor one KM1 is connected with the rectifier unit U1.

[0043] AsFigures 1-3 As shown in the figure, in this embodiment, the output end of the rectifier unit U1 is connected with a fuse three FU3, and the fuse three FU3 is connected with the diode module one V1.

[0044] As shown in the figure, in this embodiment, the output end of the rectifier unit U1 is connected with a fuse three FU3, and the fuse three FU3 is connected with the diode module one V1. Figures 1-3 As shown in the figure, in this embodiment, the transformer TR1 is also connected with a charging module U2, and the charging module U2 is connected with a breaker two QF2, and the breaker two QF2 is connected with the battery pack GB.

[0045] As shown in the figure, in this embodiment, the output end of the rectifier unit U1 is connected with a fuse three FU3, and the fuse three FU3 is connected with the diode module one V1. Figures 1-3 As shown in the figure, in this embodiment, the charging module U2 is also connected with a negative relay four KA4.

[0046] As shown in the figure, in this embodiment, the output end of the rectifier unit U1 is connected with a fuse three FU3, and the fuse three FU3 is connected with the diode module one V1. Figures 4-8 As shown in the figure, in this embodiment, the control circuit further comprises:

[0047] The signal conversion isolator PD1 is used to convert the direct current voltage signal into a 0-10V standard voltage.

[0048] As shown in the figure, in this embodiment, the control circuit further comprises: Figures 4-8

[0049] The relay one KA1, the relay two KA2, the relay three KA3 and the relay four KA4 are connected in parallel.

[0050] As shown in the figure, in this embodiment, the control circuit further comprises: Figures 4-8 The switching power supply PW1 has a specification of DC24V power supply.

[0051] The control circuit switching power supply PW1 provides power for the programmable controller ED1, the signal conversion isolator PD1, the relay one KA1, the relay two KA2, the relay three KA3 and the relay four KA4.

[0052] As shown in the figure, in this embodiment, the programmable controller ED1 adopts Siemens S7 1200.

[0053] Figures 4-8 As shown in the figure, in this embodiment, the communication module ED2 adopts the communication module CP1243-5 of the PROFIBUS DP master station.

[0054] As shown in the figure, in this embodiment, the rectifier unit U1 adopts the four-quadrant working direct current driving device 6RA80 of Siemens. Figure 9 As shown in the figure, in this embodiment, the rectifier unit U1 adopts the four-quadrant working direct current driving device 6RA80 of Siemens.

[0055] Figures 1-3 As shown in the figure, in this embodiment, the rectifier unit U1 adopts the four-quadrant working direct current driving device 6RA80 of Siemens. ​​​

[0056] For the convenience of further understanding of the above technical solutions, the working principle will be described:

[0057] As shown in Figures 1-3 The three-phase AC power supply of the main circuit is connected to the primary side 1, 2, 3 of the transformer TR1 through the circuit breaker QF1, the secondary side 22, 23 of TR1 provides the electronic board power supply for the rectifier unit U1 through the circuit breaker three QF3 and the filter ZF, U1 adopts the four-quadrant working DC drive device 6RA80 of Siemens. The secondary side 4, 5, 6 of TR1 is connected to U1 through the fuse FU1 and FU2 and the AC contactor KM1, the positive and negative DC voltage output by U1 is connected to the electromagnet through the fuse three FU3 and the diode module V1, and the electromagnet works in positive excitation. The negative and positive DC voltage output by U1 is connected to the electromagnet through FU3 and the three normally open contacts of the AC contactor two KM2 connected in parallel with V1, and the electromagnet works in reverse demagnetization. The normally open contacts of KM2 realize sparkless on-off to achieve four-quadrant operation of the electromagnet. The positive and negative rectified power output by U1 is connected to the electromagnet through V1 and the standby power supply of the battery pack GB through the normally open contacts of KM4 and the diode module V2, so that the electromagnet can be powered at the same time to realize the power-off magnetic preservation function. In the power-off magnetic preservation state, the electromagnet is demagnetized, U1 cannot feedback operation, and the energy stored in the electromagnet is released through the freewheeling circuit composed of the normally open contacts of the DC contactor three KM3 and the resistor R1. The voltage surge is absorbed by the voltage-sensitive resistor RV1. The normally closed contacts of the emergency stop button SE1 are connected to X177.9 and X177.12 of U1, and X177.9 and X177.13, when communication problems occur, U1 can be stopped by pressing SE1 to disconnect the normally closed contacts. The secondary side 22, 23, 24 of TR1 is connected to the charging module U2, and the GB is charged through the circuit breaker two QF2, and the normally open contacts KA4 are connected to the charging module 53, 54, to ensure that the charging module stops working when the power-off magnetic preservation works.

[0058] As shown in Figures 4-8As shown, the switch power supply PW1 of the control circuit provides DC 24V power supply for the programmable controller ED1, the signal conversion isolator PD1, the relay KA1-KA4. When the emergency stop button SE1 is not pressed, the normally closed contact is closed, and when the freewheeling circuit is not working, the KM3 normally closed contact is closed. When both conditions are met, ED1 receives the U1 on signal through PROFIBUS DP communication, and when the on-off switch SA1 normally open contact is closed, KA2 and AC contactor KM1 work, and the AC power supply is connected to U1. When U1 is not running and the SA1 normally closed contact is closed, KA2 and KM1 stop working, and the connection of the AC power supply to U1 is disconnected. When the electromagnet is excited, U1 has been closed, KM1 normally open contact is closed, and the on-off switch SA2 normally open contact is closed, ED1 sends the running control word and the forward given value to U1, and U1 rectifies the output to positive and negative DC voltage. The DC voltage signal is converted to 0-10V standard signal by PD1, and is sent to the analog input of ED1 for voltage detection. When the electromagnet is demagnetized, U1 has been closed, KM1 normally open contact is closed, and SA2 normally closed contact is closed, ED1 sends the stop running control word to U1. When ED1 receives the U1 positive rotation stop signal and the DC contactor KM4 is not working, the normally closed contact is closed, KA3 and AC contactor KM2 are controlled to work. After ED1 receives the feedback signal that KM2 is working and the normally open contact is closed, it sends the running control word and the reverse given value to U1, and U1 rectifies the output to negative and positive DC voltage. During the excitation of the electromagnet, when the power grid is powered off, KM1 stops working. When ED1 detects that the KM1 normally open contact is open or the U1 DC voltage value is lower than the set value, KA4 and KM4 work, and the alarm HA1 sends an audible and visual alarm. When the electromagnet is demagnetized in the power-off magnetism preservation state, KM4 works and the normally closed contact is open, and SA2 normally closed contact is closed. U1 cannot feedback the operation, and KA1 and KM3 work for a period of time and then disconnect KM4. The charging module U2 and GB provide DC power supply for KM3, KM4 and HA1.

[0059] As shown in Figure 9 , the communication network is the communication connection between the PROFIBUS DP master communication module ED2 and the rectifier unit U1. ED1 uses Siemens S7 1200, ED2 is PROFIBUS DP master communication module CP1243-5, and U1 uses Siemens four-quadrant working DC drive device 6RA80.

[0060] As shown in Figures 1-9As shown, the working principle is that the electromagnetic magnet power-off magnetic device contains: a communication network, a control circuit, a main circuit, the communication network is the communication connection between PROFIBUS DP master communication module ED2 and rectifier unit U1, programmable controller ED1 uses Siemens S7 1200, ED2 uses PROFIBUS DP master communication module CP1243-5, and U1 uses Siemens four-quadrant working DC drive device 6RA80. The main circuit further comprises a DC voltage commutation circuit, the positive and negative DC voltage on the U1 rectifier output is connected to the electromagnet through fuse three FU3 and diode module one V1, the electromagnet is excited to work, the negative and positive DC voltage on the U1 rectifier output is connected to the electromagnet through FU3 and the three normally open contacts of AC contactor two KM2 connected in parallel with V1, the electromagnet is demagnetized to work, during the excitation of the electromagnet, when the power grid is powered off, KM1 stops working, when ED1 detects that the normally open contact of KM1 is disconnected or ED1 detects that the DC voltage is lower than the set value, KA4 and KM4 work, V1 and V2 connected in parallel at the two cathodes, so that the U1 rectifier output positive and negative rectified power supply and GB through the standby power supply provided by the normally open contact of KM4 and diode module two V2 can supply power to the electromagnet at the same time, realize the power-off magnetic function, at this time the electromagnet demagnetization U1 cannot feedback operation, the energy storage of the electromagnet is released through the freewheeling circuit composed of DC contactor three KM3 normally open contact and resistance one R1, emergency stop button SE1 normally closed contact connects X177.9 and X177.12 of U1, X177.9 and X177.13, when the communication problem occurs, U1 can be stopped by pressing SE1 to disconnect the normally closed contact.

[0061] In the working process, the control circuit switch power supply PW1 provides DC 24V power supply for ED1, signal conversion isolator PD1, and relays KA1-KA4. When the emergency stop button SE1 is not pressed, the normally closed contact is closed, and when the freewheeling circuit is not working, the normally closed contact of KM3 is closed. In the case that both conditions are met, when ED1 receives the U1 on signal through PROFIBUS DP communication, the closing switch SA1 normally open contact is closed, KA2 and AC contactor KM1 work, the AC power supply is connected to U1. When U1 is not running and the SA1 normally closed contact is closed, KA2 and KM1 stop working, the connection of the AC power supply to U1 is disconnected, the electromagnet is excited, U1 has been closed, KM1 normally open contact is closed, and the conversion switch SA2 normally open contact is closed, ED1 sends the running control word and the forward given value to U1, U1 rectifies the output to positive and negative DC voltage, the DC voltage signal is converted to 0-10V standard signal through PD1, and is sent to the analog input of ED1 for voltage detection. In the normal state, the electromagnet is demagnetized, U1 has been closed, KM1 normally open contact is closed, and SA2 normally closed contact is closed, ED1 sends the stop running control word to U1, U1 stops rectifying the output, and feeds back the running release electromagnet energy storage, ED1 receives the positive rotation stop signal and the DC contactor KM4 is not working, that is, the normally closed contact is closed, and then KA3 and AC contactor KM2 are controlled to work. After ED1 receives the feedback signal that KM2 works, that is, the normally open contact is closed, it sends the running control word and the reverse given value to U1, U1 rectifies the output to negative and positive DC voltage, and sets the time to reach U1 to stop rectifying the output, and feeds back the running release electromagnet energy storage. The three-phase AC power supply of the main circuit is connected to the primary side 1, 2 and 3 of the transformer TR1 through the circuit breaker one QF1, the secondary side 22 and 23 of TR1 provides the electronic board power supply for U1 through the circuit breaker three QF3 and the filter ZF, the secondary side 4, 5 and 6 of TR1 is connected to the rectifier unit U1 through the fuses FU1 and FU2, KM1, the voltage surge absorbing resistor RV1, the secondary side 22, 23 and 24 of TR1 is connected to the charging module U2, and the standby power supply battery pack GB is charged through the circuit breaker two QF2. KA4 normally open contact is connected to the charging module 53 and 54, and the charging module stops working when the power failure magnetic working is ensured.

[0062] In the description of the present application, it should be understood that the indicated orientation or positional relationship is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as a limitation on the present application.

[0063] In the present application, unless otherwise explicitly specified and limited, for example, can be fixedly connected, or can be detachably connected, or integrated; can be mechanically connected, or electrically connected; can be directly connected, or indirectly connected through an intermediate medium, can be the internal communication of two elements or the interaction relationship of two elements, unless otherwise explicitly limited, the specific meaning of the above-mentioned terms in the present application can be understood according to the specific circumstances by those skilled in the art.

[0064] Although the embodiments of the present application have been shown and described, those skilled in the art can understand that various changes, modifications, replacements and variations can be made to the embodiments without departing from the principles and spirits of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A device for maintaining the magnetism of an electromagnet when it is de-energized, characterized in that, Including main circuit, control circuit, communication module and electromagnet, the main circuit includes DC voltage commutation circuit, diode module one, programmable controller and battery pack, wherein, the DC voltage commutation circuit includes rectifier unit, the rectifier unit is connected with communication module, diode module one is connected with fuse three, diode module one is connected with AC contactor two, the rectifier unit is connected with the electromagnet through AC contactor two, fuse three, diode module one is also connected with diode module two, the programmable controller is connected with communication module, the battery pack is connected with AC contactor four, the current of rectifier unit rectification output is positive on the negative side through diode module one, the current of battery pack is through AC contactor four, diode module two, and the electromagnet is powered simultaneously, realizes the function of power failure magnetic preservation; The DC voltage commutation circuit further comprises: DC contactor three, the DC contactor three is connected with resistance one, emergency stop button, the emergency stop button is connected with the rectifier unit; Wherein, the DC contactor three, resistance one constitute freewheeling circuit, for the release of electromagnet energy storage; The main circuit further comprises: Three-phase AC power supply, the three-phase AC power supply is connected with circuit breaker one, the three-phase AC power supply is connected with transformer through the circuit breaker one, the transformer is connected with circuit breaker three and filter, and the transformer is connected with the rectifier unit through the circuit breaker three and filter.

2. The power-off magnetic field maintaining device for an electromagnet according to claim 1, characterized by The transformer is also connected with fuse one and fuse two, and the fuse one and the fuse two are connected in parallel;The fuse one is connected with AC contactor one, and the AC contactor one is connected with the rectifier unit.

3. The power-off magnetic holding device of an electromagnet according to claim 2, characterized by The output end of the rectifier unit is connected with fuse three, and the fuse three is connected with the diode module one.

4. The power-off magnetic holding device of an electromagnet according to claim 3, wherein The transformer is also connected with charging module, and the charging module is connected with circuit breaker two, and the circuit breaker two is connected with the battery pack.

5. The power-off magnetic holding device of an electromagnet according to claim 4, wherein The charging module is also connected with negative relay four.

6. The power-off magnetic holding device of an electromagnet according to claim 5, wherein The control circuit further comprises: Signal conversion isolator, for converting DC voltage signal into 0-10V standard voltage.

7. The power-off magnetic holding device of an electromagnet according to claim 6, wherein The control circuit further comprises: Relay one, relay two, relay three, relay four, the relay one, relay two, relay three and relay four are connected in parallel.

8. The power-off magnetic holding device of an electromagnet according to claim 7, wherein The control circuit further comprises: Switching power supply, the specification of the switching power supply is DC24V power supply; Wherein, the control circuit switching power supply provides power for programmable controller, signal conversion isolator, relay one, relay two, relay three and relay four.

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