Contact protection circuit and method of power relay

Abstract

The invention discloses a contact protection circuit and method of a power relay. The circuit comprises a system control unit, a voltage zero-cross detection unit and a current zero-cross detection unit, the voltage zero-cross detection unit is used for generating a TTL signal with the same phase as the input voltage of the power relay according to the input voltage of the power relay; the current zero-cross detection unit is used for generating a TTL signal with the same phase as the input current of the power relay according to the input current of the power relay; the system control unit is used for controlling the power relay to be closed according to a TTL signal with the same phase as the input voltage of the power relay when receiving the starting signal, and controlling the power relay to be disconnected according to a TTL signal with the same phase as the input current of the power relay when receiving the stopping signal; the power relay can be controlled to be closed near a voltage phase zero crossing point and disconnected near a current phase zero crossing point, and the phenomena of sparking, arc discharge and the like generated in the actual use process of the power relay are weakened.

Description

Technical Field

[0001] The present application relates to the technical field of protection circuits, and in particular to a contact protection circuit and method for a power relay. Background Art

[0002] Electromagnetic relay is an electronic control device, which has a control system (also called input circuit) and a controlled system (also called output circuit). It is usually used in automatic control circuits. Electromagnetic relay is actually an "automatic switch" that uses a smaller current and a lower voltage to control a larger current and a higher voltage. Therefore, it plays the role of voltage isolation, automatic adjustment, safety protection, and circuit conversion in the circuit.

[0003] As a type of electromagnetic relay, the closing and opening of power relays in high-voltage, high-power control systems will cause sparks, arcs, etc. In severe cases, the power relay contacts will be burned, causing the control system to fail or stick. Summary of the invention

[0004] Based on the above-mentioned deficiencies in the prior art, the present application provides a contact protection circuit and method for a power relay to solve the problem that the closing and opening of the power relay in a high-voltage, high-power control system will cause sparks, arcs, etc., and in severe cases, the power relay contacts will be burned, causing the control system to fail or stick.

[0005] In order to achieve the above objectives, this application provides the following technical solutions:

[0006] A first aspect of the present application provides a contact protection circuit for a power relay, comprising: a system control unit, a voltage zero-crossing detection unit, and a current zero-crossing detection unit;

[0007] The voltage zero-crossing detection unit is used to generate a TTL signal in phase with the input voltage of the power relay according to the input voltage of the power relay;

[0008] The current zero-crossing detection unit is used to generate a TTL signal in phase with the input current of the power relay according to the input current of the power relay;

[0009] The system control unit is used to control the power relay to be attracted according to a TTL signal with the same phase as the input voltage of the power relay when a start signal is received, and to control the power relay to be disconnected according to a TTL signal with the same phase as the input current of the power relay when a stop signal is received.

[0010] Optionally, in the above-mentioned contact protection circuit of the power relay, the voltage zero-crossing detection unit comprises at least: a first isolation optocoupler, a second isolation optocoupler and a voltage comparator;

[0011] The first isolation optocoupler and the second isolation optocoupler are used to convert the input voltage of the power relay from a high-voltage analog signal to a low-voltage digital signal;

[0012] The voltage comparator is used to perform pulse shaping on the low-voltage digital signal to obtain a TTL signal with the same phase as the input voltage of the power relay.

[0013] Optionally, in the above-mentioned contact protection circuit of the power relay, the voltage zero-crossing detection unit further comprises: a first current limiting resistor and a second current limiting resistor;

[0014] The first current limiting resistor and the second current limiting resistor are respectively arranged at the front stage of the first isolation optocoupler and the second isolation optocoupler to perform current limiting protection on the first isolation optocoupler and the second isolation optocoupler.

[0015] Optionally, in the above-mentioned contact protection circuit of the power relay, the TTL signal of the same phase as the input voltage of the power relay is a periodic pulse signal with the phase voltage zero-crossing point as the high level and non-zero-crossing point as the low level.

[0016] Optionally, in the above-mentioned contact protection circuit of the power relay, the current zero-crossing detection unit comprises at least: a current sensor and an amplifier;

[0017] The current sensor is connected to the load of the power relay and is used to detect the input current of the power relay;

[0018] The amplifier is used to amplify the input current of the power relay to obtain a TTL signal with the same phase as the input current of the power relay.

[0019] Optionally, in the contact protection circuit of the power relay, the TTL signal of the same phase as the input current of the power relay is a periodic pulse signal with the zero crossing point of the phase current as the high level and the non-zero crossing point as the low level.

[0020] Optionally, in the above-mentioned contact protection circuit of the power relay, the system control unit is further used to obtain the pull-in response time and the disconnection response time of the power relay;

[0021] When the start signal is received, the power relay is controlled to be attracted according to the TTL signal with the same phase as the attraction response time and the input voltage of the power relay; when the stop signal is received, the power relay is controlled to be disconnected according to the TTL signal with the same phase as the disconnect response time and the input current of the power relay.

[0022] A second aspect of the present application provides a contact protection method for a power relay, which is applied to a system control unit in a contact protection circuit of a power relay as disclosed in any one of the first aspects, and the method comprises:

[0023] Receiving a target control signal sent by a user, wherein the target control signal is a start signal or a stop signal;

[0024] According to the target control signal, the power relay is controlled to operate at the corresponding zero point; if the target control signal is the start signal, the power relay is controlled to be attracted at the voltage phase zero point; if the target control signal is the stop signal, the power relay is controlled to be disconnected at the current phase zero point.

[0025] Optionally, in the above-mentioned contact protection method of the power relay, controlling the power relay to be attracted at the voltage phase zero crossing point includes:

[0026] Determining the voltage phase zero crossing point and the pull-in response time of the power relay;

[0027] According to the pull-in response time and the voltage phase zero-crossing point, the power relay is controlled to pull in at the voltage phase zero-crossing point.

[0028] Optionally, in the above-mentioned contact protection method of the power relay, controlling the power relay to disconnect at the current phase zero crossing point includes:

[0029] Determining a current phase zero crossing point and a disconnection response time of the power relay;

[0030] The power relay is controlled to be disconnected at the current phase zero crossing point according to the current phase zero crossing point and the disconnection response time.

[0031] The present application provides a contact protection circuit for a power relay, comprising: a system control unit, a voltage zero-crossing detection unit and a current zero-crossing detection unit; the voltage zero-crossing detection unit is used to generate a TTL signal with the same phase as the input voltage of the power relay according to the input voltage of the power relay; the current zero-crossing detection unit is used to generate a TTL signal with the same phase as the input current of the power relay according to the input current of the power relay; the system control unit is used to control the power relay to be attracted according to the TTL signal with the same phase as the input voltage of the power relay when receiving a start signal, and to control the power relay to be disconnected according to the TTL signal with the same phase as the input current of the power relay when receiving a stop signal, and can control the power relay to be attracted near the voltage phase zero-crossing point and disconnected near the current phase zero-crossing point, thereby reducing the sparking, arcing and other phenomena generated by the power relay during actual use, and solving the problem that the closing and disconnecting of the power relay in a high-voltage, high-power control system will cause sparking, arcing and other phenomena, and in severe cases, the power relay contacts will be burned, causing the control system to fail or stick. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying any creative work.

[0033] Figure 1 A schematic diagram of the structure of a contact protection circuit of a power relay provided in an embodiment of the present application;

[0034] Figure 2 A circuit diagram of a voltage zero-crossing detection unit provided in an embodiment of the present application;

[0035] Figure 3 A schematic diagram of a waveform of a TTL signal with the same phase as the input voltage of a power relay provided in an embodiment of the present application;

[0036] Figure 4 A schematic diagram of the structure of a current zero-crossing detection unit provided in an embodiment of the present application;

[0037] Figure 5 A flow chart of a contact protection method for a power relay provided in an embodiment of the present application. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0039] In this application, relational terms such as first and second, etc. are used only to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0040] The present application provides a contact protection circuit and method for a power relay to solve the problem that the closing and opening of a power relay in a high-voltage, high-power control system may cause sparking, arcing, etc., and in severe cases may even burn the power relay contacts, causing the control system to fail or stick.

[0041] See also Figure 1 The contact protection circuit of the power relay mainly includes: a system control unit 101, a voltage zero-crossing detection unit 102 and a current zero-crossing detection unit 103.

[0042] The voltage zero-crossing detection unit 102 is used to generate a TTL (Transistor-Transistor Logic) signal having the same phase as the input voltage of the power relay according to the input voltage of the power relay.

[0043] In some embodiments, Figure 2 As shown, the voltage zero-crossing detection unit 102 at least includes: a first isolation optocoupler U1, a second isolation optocoupler U2 and a voltage comparator U1A.

[0044] The first isolation optocoupler U1 and the second isolation optocoupler U2 are used to convert the input voltage of the power relay from a high-voltage analog signal to a low-voltage digital signal; the voltage comparator U1A is used to perform pulse shaping on the low-voltage digital signal to obtain a TTL signal with the same phase as the input voltage of the power relay.

[0045] In practical applications, the first isolation optocoupler U1, the second isolation optocoupler U2, and the voltage comparator U1A in the zero-crossing voltage detection unit 102 can be used to obtain a TTL signal in phase with the 220 / 50Hz AC input voltage signal of the power relay, and convert the AC input voltage signal into a TTL signal.

[0046] In some embodiments, such as Figure 2 shown, the zero-crossing voltage detection unit 102 may further include: a first current-limiting resistor R1 and a second current-limiting resistor R2. The first current-limiting resistor R1 and the second current-limiting resistor R2 are respectively arranged at the front stage of the first isolation optocoupler U1 and the second isolation optocoupler U2 to perform current-limiting protection on the first isolation optocoupler U1 and the second isolation optocoupler U2.

[0047] It should be noted that after the input voltage of the relay flows through the first current-limiting resistor R1 and the second current-limiting resistor R2 into the first isolation optocoupler U1 and the second isolation optocoupler U2, the input voltage can be converted from a high-voltage analog signal to a low-voltage digital signal, and then the low-voltage digital signal can be pulse-shaped through the processing of the voltage comparator U1A, and a TTL signal in phase with the input voltage of the power relay can be obtained.

[0048] Specifically, the specific structure of the zero-crossing voltage detection unit 102 can be as Figure 2 shown. The working process of the zero-crossing voltage detection unit 102 is as follows:

[0049] When the input voltage Ua of the power relay is 0, the first isolation optocoupler U1 and the second isolation optocoupler U2 are cut off and output a high level. The voltage at the positive input terminal of the voltage comparator U1A is higher than the voltage at the negative input terminal of the voltage comparator U1A (Ux>Uy), and the voltage comparator U1A outputs a high level; conversely, when the input voltage Ua of the power relay is not equal to 0, the first isolation optocoupler U1 and the second isolation optocoupler U2 are turned on and output a low level. The voltage at the positive input terminal of the voltage comparator U1A is lower than the voltage at the negative input terminal of the voltage comparator U1A (Ux<Uy), and the voltage comparator U1A outputs a low level. That is to say, the zero-crossing voltage detection unit 102 will output a periodic pulse signal with a high level at the zero-crossing point of the phase voltage and a low level at non-zero-crossing points, that is, a TTL signal in phase with the input voltage of the power relay, as Figure 3 shown.

[0050] Combined with Figure 3 shown, the sine wave is an AC voltage signal. When the input voltage is greater than 0, the TTL signal in phase with the input voltage of the power relay outputs a high level. It can be seen that the rising edge of the TTL signal in phase with the input voltage of the power relay is the zero-crossing point of the voltage phase of the power relay.

[0051] The current zero-crossing detection unit 103 is used to generate a TTL signal having the same phase as the input current of the power relay according to the input current of the power relay.

[0052] In some embodiments, Figure 4 As shown, the current zero-crossing detection unit 103 at least includes: a current sensor and an amplifier.

[0053] The current sensor is connected to the load of the power relay and is used to detect the input current of the power relay.

[0054] The amplifier is used to amplify the input current of the power relay to obtain a TTL signal with the same phase as the input current of the power relay.

[0055] In practical applications, the current sensor may be a Hall current sensor, which can detect the input current on the load side of the power relay and convert it into a TTL signal in phase with the input current after being amplified by an amplifier.

[0056] It should be noted that the TTL signal of the same phase as the input current of the power relay is a periodic pulse signal with the phase current zero crossing point as the high level and the non-zero crossing point as the low level; in other words, the rising edge of the TTL signal of the same phase as the input current of the power relay is the current phase zero point.

[0057] The system control unit 101 is used to control the power relay to be attracted according to the TTL signal with the same phase as the input voltage of the power relay when receiving the start signal, and to control the power relay to be disconnected according to the TTL signal with the same phase as the input current of the power relay when receiving the stop signal.

[0058] In actual applications, the system control unit 101 includes at least an MCU, which can control the power relay to be attracted according to a TTL signal with the same phase as the input voltage of the power relay when receiving a start signal, and can control the power relay to be disconnected according to a TTL signal with the same phase as the input current of the power relay when receiving a stop signal.

[0059] It should be noted that the MCU can obtain the TTL signal of the same phase as the input voltage of the power relay through its own INT0 pin, and obtain the TTL signal of the same phase as the input current of the power relay through its own INT1 pin. Among them, the rising edge of the TTL signal of the same phase as the input voltage of the power relay is the voltage phase zero crossing point, and the rising edge of the TTL signal of the same phase as the input current of the power relay is the current phase zero crossing point.

[0060] Since the system control unit 101 has an unknown response time for the power relay to be closed, the power relay can only be closed near the voltage phase zero point according to the TTL signal with the same phase as the input voltage of the power relay, and the power relay cannot be controlled to be closed precisely at the voltage phase zero point. Although the spark intensity can be reduced to a certain extent, there is still a certain risk of sparking; similarly, since the system control unit 101 has an unknown response time for the power relay to be disconnected, the power relay can only be controlled to be disconnected near the current phase zero point according to the TTL signal with the same phase as the input current of the power relay, and the power relay cannot be controlled to be disconnected precisely at the current phase zero point. Although the arcing phenomenon can be weakened to a certain extent, there is still a certain risk of arcing. In this regard, in some embodiments, the power relay can be set to 2 channels, one for closing and disconnecting control, and the other for action time detection, so as to know the closing response time and disconnecting response time of the power relay.

[0061] In some embodiments, the power relay may be a double-pole double-throw relay, which can provide one circuit for closing and opening control and another circuit for action time detection.

[0062] It should be noted that in addition to detecting the action time through one channel of the power relay, in practice it can also be directly obtained based on the known parameters of the power relay. This application does not limit the specific method of action time detection, which is within the protection scope of this application.

[0063] In actual applications, when the system control unit 101 is also used to obtain the closing response time and the disconnecting response time of the power relay, when a start signal is received, the power relay can be controlled to be closed according to a TTL signal with the same phase as the closing response time and the input voltage of the power relay; when a stop signal is received, the power relay can be controlled to be disconnected according to a TTL signal with the same phase as the disconnecting response time and the input current of the power relay.

[0064] It is also assumed that the system control unit 101 includes at least an MCU (Microcontroller Unit). When the MCU implements the above functions, it is specifically used for: when receiving a start signal, first determining the voltage phase zero point of the power relay according to the TTL signal with the same phase as the input voltage of the power relay, and then controlling the drive circuit of the power relay to be attracted at the voltage phase zero point according to the attraction response time, which can accurately control the power relay to be attracted at the voltage phase zero point to avoid sparking; when receiving a stop signal, first determining the current phase zero point of the power relay according to the TTL signal with the same phase as the input current of the power relay, and then controlling the drive circuit of the power relay to be disconnected at the current phase zero point according to the disconnection response time, which can accurately control the power relay to be disconnected at the current phase zero point to avoid arcing.

[0065] It should be noted that in practice, after the system control unit 101 executes each closing control and disconnection control, the phase point error corresponding to the closing control and disconnection control can be obtained, so that the next time the closing control and disconnection control are executed, the phase point error corresponding to the previous closing control and disconnection control can be corrected, thereby ensuring that the power relay achieves the optimal control effect each time the closing control and disconnection control are executed.

[0066] It can be understood that the MCU can monitor and record the action time of the power relay's closure and disconnection, automatically correct the advance amount of the control signal, and effectively avoid control errors caused by action time offset.

[0067] It should be noted that, since the power relay's pull-in response time is T1, in order to ensure that the power relay pulls in at the zero point of the phase, the MCU needs to start the power relay T1 in advance to ensure that the power relay pulls in at the zero point of the next voltage phase. Therefore, when the MCU detects the rising edge of the signal of the INT0 pin, it can start the countdown T (T = 20ms-T1, 50Hz), and start the relay immediately after the countdown is completed, so as to ensure that the power relay pulls in at the zero point of the next voltage phase; similarly, the MCU can calculate the power relay's disconnection response time T2 and the signal countdown of the INT1 pin to ensure that the power relay disconnects at the next current phase zero point. In this way, contact protection of the power relay during pull-in and disconnection can be achieved.

[0068] Based on the above principles, the contact protection circuit of the power relay provided in this embodiment includes: a system control unit 101, a voltage zero-crossing detection unit 102 and a current zero-crossing detection unit 103; the voltage zero-crossing detection unit 102 is used to generate a TTL signal with the same phase as the input voltage of the power relay according to the input voltage of the power relay; the current zero-crossing detection unit 103 is used to generate a TTL signal with the same phase as the input current of the power relay according to the input current of the power relay; the system control unit 101 is used to control the power relay to be attracted according to the TTL signal with the same phase as the input voltage of the power relay when receiving a start signal, and to control the power relay to be disconnected according to the TTL signal with the same phase as the input current of the power relay when receiving a stop signal, and can control the power relay to be attracted near the voltage phase zero-crossing point and disconnected near the current phase zero-crossing point, thereby reducing the sparking, arcing and other phenomena generated by the power relay during actual use, and solving the problem that the closing and disconnecting of the power relay in a high-voltage and high-power control system will cause sparking, arcing and other phenomena, and in severe cases, the power relay contacts will be burned, causing the control system to fail or stick.

[0069] Based on the above, optionally, another embodiment of the present application further provides a contact protection method for a power relay, which is applied to a system control unit in a contact protection circuit of a power relay as described in any of the above embodiments, see Figure 5 , the method mainly includes:

[0070] S101: Receive a target control signal sent by a user.

[0071] The target control signal is a start signal or a stop signal.

[0072] In practical applications, the target control signal sent by the user can be received by the MCU in the system control unit.

[0073] Specifically, corresponding physical buttons can be set for the start signal and the stop signal, and the corresponding control signal can be sent by triggering the corresponding physical buttons; corresponding control buttons can also be set on the MCU control panel, and the corresponding control signal can be sent by triggering the corresponding control buttons; of course, it is not limited to this, and can also be determined according to the application environment and user needs, all within the protection scope of this application.

[0074] S102. According to the target control signal, the power relay is controlled to operate at the corresponding zero point.

[0075] If the target control signal is a start signal, the control power relay is energized at the voltage phase zero point; if the target control signal is a stop signal, the control power relay is disconnected at the current phase zero point.

[0076] In practical applications, the specific process of controlling the power relay to be attracted at the voltage phase zero crossing point is as follows, mainly including steps S201 and S202:

[0077] S201. Determine the voltage phase zero-crossing point and the pull-in response time of the power relay.

[0078] In practical applications, the voltage phase zero crossing point of the power relay can be determined by the TTL signal of the same phase as the input voltage of the power relay generated by the voltage zero crossing detection unit in the contact protection circuit of the power relay. The pull-in response time of the power relay can be determined by monitoring the pull-in response time of the power relay.

[0079] S202. According to the pull-in response time and the voltage phase zero-crossing point, control the power relay to pull in at the voltage phase zero-crossing point.

[0080] In practical applications, after determining the voltage phase zero crossing point and the pull-in response time of the power relay, the power relay can be controlled to be pulled in at a time point corresponding to the pull-in response time before the next voltage phase zero crossing point, thereby achieving the power relay being pulled in at the voltage phase zero crossing point.

[0081] In practical applications, the specific process of controlling the power relay to disconnect at the current phase zero crossing point is as follows, mainly including steps S301 and S302:

[0082] S301. Determine the current phase zero-crossing point and disconnection response time of the power relay.

[0083] In practical applications, the current phase zero crossing point of the power relay can be determined by a TTL signal of the same phase as the input current of the power relay generated by the current zero crossing detection unit in the contact protection circuit of the power relay. The disconnection response time of the power relay can be determined by monitoring the disconnection response time of the power relay.

[0084] S302. Control the power relay to disconnect at the current phase zero-crossing point according to the current phase zero-crossing point and the disconnection response time.

[0085] In practical applications, after determining the current phase zero crossing point and disconnection response time of the power relay, the power relay can be controlled to disconnect at a time point corresponding to the disconnection response time before the next current phase zero crossing point, thereby achieving disconnection of the power relay at the current phase zero crossing point.

[0086] Based on the above principles, the contact protection method of the power relay provided in the present embodiment is applied to the system control unit in the contact protection circuit of the power relay as described in any of the above embodiments, and the method includes: receiving a target control signal sent by a user; according to the target control signal, controlling the power relay to operate at the corresponding zero point; wherein, if the target control signal is a start signal, the power relay is controlled to be attracted at the voltage phase zero point; if the target control signal is the stop signal, the power relay is controlled to be disconnected at the current phase zero point, thereby reducing the sparking, arcing and other phenomena generated by the power relay during actual use, and solving the problem that the closing and opening of the power relay in a high-voltage, high-power control system will cause sparking, arcing and other phenomena, and in severe cases, the power relay contacts will be burned, causing the control system to fail or stick.

[0087] It should be noted that the relevant description about the contact protection circuit of the power relay can be found in the above corresponding embodiments, which will not be described in detail here.

[0088] Professionals may further appreciate that the units and algorithm steps of each example described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of the two. In order to clearly illustrate the interchangeability of hardware and software, the composition and steps of each example have been generally described in the above description according to function. Whether these functions are performed in hardware or software depends on the specific application and design constraints of the technical solution. Professionals and technicians may use different methods to implement the described functions for each specific application, but such implementation should not be considered to be beyond the scope of this application.

[0089] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to the embodiments shown herein, but will conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A contact protection circuit for a power relay, characterized in that: include: A system control unit, a voltage zero-crossing detection unit and a current zero-crossing detection unit; The voltage zero-crossing detection unit is used to generate a TTL signal in phase with the input voltage of the power relay according to the input voltage of the power relay; The current zero-crossing detection unit is used to generate a TTL signal in phase with the input current of the power relay according to the input current of the power relay; The system control unit is used to control the power relay to be attracted according to a TTL signal with the same phase as the input voltage of the power relay when a start signal is received, and to control the power relay to be disconnected according to a TTL signal with the same phase as the input current of the power relay when a stop signal is received.

2. The contact protection circuit of the power relay according to claim 1, characterized in that: The voltage zero-crossing detection unit at least includes: a first isolation optocoupler, a second isolation optocoupler and a voltage comparator; The first isolation optocoupler and the second isolation optocoupler are used to convert the input voltage of the power relay from a high-voltage analog signal to a low-voltage digital signal; The voltage comparator is used to perform pulse shaping on the low-voltage digital signal to obtain a TTL signal with the same phase as the input voltage of the power relay.

3. The contact protection circuit of the power relay according to claim 2, characterized in that: The voltage zero-crossing detection unit further includes: a first current limiting resistor and a second current limiting resistor; The first current limiting resistor and the second current limiting resistor are respectively arranged at the front stage of the first isolation optocoupler and the second isolation optocoupler to perform current limiting protection on the first isolation optocoupler and the second isolation optocoupler.

4. The contact protection circuit of the power relay according to claim 2, characterized in that: The TTL signal of the same phase as the input voltage of the power relay is a periodic pulse signal with the phase voltage zero-crossing point as the high level and the non-zero-crossing point as the low level.

5. The contact protection circuit of the power relay according to claim 1, characterized in that: The current zero-crossing detection unit at least includes: a current sensor and an amplifier; The current sensor is connected to the load of the power relay and is used to detect the input current of the power relay; The amplifier is used to amplify the input current of the power relay to obtain a TTL signal with the same phase as the input current of the power relay.

6. The contact protection circuit of the power relay according to claim 4, characterized in that: The TTL signal of the same phase as the input current of the power relay is a periodic pulse signal with the zero-crossing point of the phase current as the high level and the non-zero-crossing point as the low level.

7. The contact protection circuit of the power relay according to claim 1, characterized in that: The system control unit is also used to obtain the pull-in response time and the disconnection response time of the power relay; When the start signal is received, the power relay is controlled to be attracted according to the TTL signal with the same phase as the attraction response time and the input voltage of the power relay; when the stop signal is received, the power relay is controlled to be disconnected according to the TTL signal with the same phase as the disconnect response time and the input current of the power relay.

8. A contact protection method for a power relay, characterized in that: A system control unit applied to a contact protection circuit of a power relay according to any one of claims 1 to 7, the method comprising: Receiving a target control signal sent by a user, wherein the target control signal is a start signal or a stop signal; According to the target control signal, the power relay is controlled to operate at the corresponding zero point; if the target control signal is the start signal, the power relay is controlled to be attracted at the voltage phase zero point; if the target control signal is the stop signal, the power relay is controlled to be disconnected at the current phase zero point.

9. The contact protection method of a power relay according to claim 8, characterized in that: Controlling the power relay to be attracted at the voltage phase zero crossing point includes: Determining the voltage phase zero crossing point and the pull-in response time of the power relay; According to the pull-in response time and the voltage phase zero-crossing point, the power relay is controlled to pull in at the voltage phase zero-crossing point.

10. The contact protection method of a power relay according to claim 8, characterized in that: Controlling the power relay to disconnect at the current phase zero crossing point includes: Determining a current phase zero crossing point and a disconnection response time of the power relay; The power relay is controlled to be disconnected at the current phase zero crossing point according to the current phase zero crossing point and the disconnection response time.

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