CN217486176U

CN217486176U - Protection circuit of alternating current relay

Info

Publication number: CN217486176U
Application number: CN202221495348.9U
Authority: CN
Inventors: 许金韡; 黄敏; 方刚; 向军; 刘滔
Original assignee: Goodwe Technologies Co Ltd
Current assignee: Goodwe Technologies Co Ltd
Priority date: 2022-06-14
Filing date: 2022-06-14
Publication date: 2022-09-23
Anticipated expiration: 2032-06-14

Abstract

The application relates to power electronic equipment technical field, concretely relates to exchange relay protection circuit includes: the first end and the second end of the voltage-boosting circuit are used for being connected with a second power supply; the third end is used for being connected with a first power supply; one end of the alternating current relay is connected with the fourth end of the buck-boost circuit, and the other end of the alternating current relay is used for being connected with the first power supply; the first end of the first control branch circuit is connected with two ends of a contact of the alternating current relay, and the second end of the first control branch circuit is connected with the control end of a transistor in the buck-boost circuit and used for detecting and switching on and off the buck-boost circuit based on the voltage drop of the two ends of the contact; the pre-charging branch is connected with the alternating current relay in parallel; the transient voltage suppression diode is connected with the switching device in series, and the transient voltage suppression diode and the switching device are connected with the first resistor in parallel. When the voltage at two ends of the contact of the alternating current relay is larger than the clamping voltage value, the current only flows to the first power supply through the transient voltage suppression diode and does not pass through the alternating current relay, and the alternating current relay is guaranteed not to be disconnected with current.

Description

Protection circuit of alternating current relay

Technical Field

The application relates to the technical field of power electronic equipment, in particular to an alternating current relay protection circuit.

Background

The relays include a dc relay and an ac relay, but the dc relay is large in size and high in price, and particularly, the dc relay with high voltage and high current is very high in price, which increases the use cost. When the alternating current relay is abnormal, if the alternating current relay is disconnected with current, direct current arcing ignition can occur, and when the alternating current relay is serious, a Printed Circuit Board (PCB) is burnt, so that insulation is damaged, and even the risk of equipment ignition is caused.

With the development of photovoltaic power generation, the demand for energy storage is increasing. As shown in fig. 1, the first power source P and the second power source (not shown) exchange electric energy through the buck-boost circuit 108 including an inductor, a transistor, a capacitor, and the like, and the current generated during starting is large, so the pre-charging branch 101 is usually added to the circuit, and the ac relay 109 is connected in parallel with the pre-charging branch 101 to bypass the pre-charging branch, so as to reduce the loss.

In order to prevent the alternating current relay from being broken down to cause danger, the on-off of the boost-buck circuit can be controlled by detecting the voltages at two ends of a coil or two ends of a contact in the alternating current relay, and the boost-buck circuit is timely disconnected when the alternating current relay is broken down to avoid the danger caused by current when the contact of the alternating current relay is disconnected. Due to the existence of the inductor in the buck-boost circuit, inductive current still exists after the buck-boost circuit is disconnected and flows through the alternating current relay, and the risk of direct current arcing ignition caused by the disconnection of current still exists.

SUMMERY OF THE UTILITY MODEL

In order to solve one of the technical defects, an embodiment of the present application provides an ac relay protection circuit, including:

the first end and the second end of the voltage-boosting circuit are used for being connected with a second power supply to form a first closed loop; the third end is used for being connected with a first power supply; one end of the alternating current relay is connected with the fourth end of the voltage boosting and reducing circuit, and the other end of the alternating current relay is used for being connected with the first power supply to form a second closed loop; the first end of the first control branch circuit is connected to two ends of a contact of the alternating current relay, and the second end of the first control branch circuit is connected with the control end of a transistor in the buck-boost circuit and used for detecting and switching on and off the buck-boost circuit based on the voltage drop of two ends of the contact; the pre-charging branch is connected with the alternating current relay in parallel; the pre-charging branch circuit comprises a transient voltage suppression diode, a switching device and a first resistor, wherein the transient voltage suppression diode is connected with the switching device in series, and the transient voltage suppression diode and the switching device are connected with the first resistor in parallel.

Preferably, the transient voltage suppressor diode is a bidirectional transient voltage suppressor diode.

Preferably, the transient voltage suppression diode is a unidirectional transient voltage suppression diode.

Preferably, the ac relay protection circuit further comprises a processing unit; the switching device includes:

a grid electrode of the second MOS tube is connected with the processing unit, a drain electrode of the second MOS tube is connected with the transient voltage suppression diode, and a source electrode of the second MOS tube is connected between the first power supply and the first resistor;

or the second IGBT tube, the grid is connected with the processing unit, the emitter is connected with the transient voltage suppression diode, and the collector is connected between the first power supply and the first resistor.

Preferably, the pre-charging branch further comprises: the grid electrode of the first MOS tube is connected with the processing unit, the source electrode of the first MOS tube is connected between the source electrode of the first resistor and the second MOS tube or between the collector electrodes of the first resistor and the second IGBT tube, and the drain electrode of the first MOS tube is connected between the alternating current relay and the first power supply;

or the grid electrode of the first IGBT tube is connected with the processing unit, the emitting electrode of the first IGBT tube is connected between the source electrode of the first resistor and the second MOS tube or between the collector electrodes of the first resistor and the second IGBT tube, and the collector electrode of the first IGBT tube is connected between the alternating current relay and the first power supply.

Preferably, the pre-charging branch further comprises: and the anode of the diode is connected between the first resistor and the source electrode of the second MOS tube or between the first resistor and the collector electrode of the second IGBT tube, and the cathode of the diode is connected between the alternating current relay and the first power supply.

Preferably, the first control branch comprises: the first end of the second resistor is connected with one end of the alternating current relay contact; the first end of the third resistor is connected with the other end of the alternating current relay contact; the non-inverting input end of the first operational amplifier is connected with the second end of the second resistor, and the inverting input end of the first operational amplifier is connected with the second end of the third resistor; the positive input end of the first comparator is connected with a first constant voltage source, the negative input end of the first comparator is connected with the output end of the first operational amplifier, and the output end of the first comparator is connected with the input end of the processing unit; and the input end of the driving unit is connected with the output end of the processing unit, and the output end of the driving unit is connected with the control end of the transistor in the step-up and step-down circuit.

Preferably, the ac relay protection circuit further includes: and the first end of the second control branch circuit is connected to two ends of a coil of the alternating current relay, and the second end of the second control branch circuit is connected with the control end of a transistor in the boost-buck circuit and is used for detecting and switching on and off the boost-buck circuit based on the voltage at two ends of the coil.

Preferably, the second control branch comprises: a first end of the fourth resistor is connected with one end of the coil of the alternating current relay; a first end of the fifth resistor is connected with the other end of the coil of the alternating current relay; the non-inverting input end of the second operational amplifier is connected with the second end of the fourth resistor, and the inverting input end of the second operational amplifier is connected with the second end of the fifth resistor; and the positive input end of the second comparator is connected with a second constant voltage source, the negative input end of the second comparator is connected with the output end of the second operational amplifier, and the output end of the second comparator is connected with the processing unit.

Preferably, the processing unit comprises a complex programmable logic device or a digital signal processor.

Adopt the AC relay protection circuit that provides in this application embodiment, the voltage at diode clamper AC relay both ends is restrained to the transient voltage in the pre-charging branch road, and when the voltage at AC relay contact both ends was greater than the clamping voltage value, the electric current only can be through transient voltage suppression diode flow direction first power, and does not pass through AC relay, guarantees that AC relay can not take the current disconnection to avoid danger.

Drawings

The accompanying drawings, which are included to provide a further understanding of the application and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the application and together with the description serve to explain the application and not to limit the application. In the drawings:

FIG. 1 is a circuit diagram of a prior art AC relay protection circuit;

FIG. 2 is a circuit diagram of an AC relay protection circuit according to the present application;

FIG. 3 is a further circuit diagram of the protection circuit of the AC relay of the present application;

fig. 4 is a further circuit diagram of the ac relay protection circuit of the present application.

Detailed Description

In order to make the technical solutions and advantages in the embodiments of the present application more clearly understood, the following description of the exemplary embodiments of the present application with reference to the accompanying drawings is made in further detail, and it is obvious that the described embodiments are only a part of the embodiments of the present application, and are not exhaustive of all the embodiments. It should be noted that the embodiments and features of the embodiments in the present application may be combined with each other without conflict.

In the description of the present application, it is to be understood that the terms "first", "second" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implying any number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of the present application, "plurality" means at least two, e.g., two, three, etc., unless specifically limited otherwise.

In this application, unless expressly stated or limited otherwise, the terms "connected" and "coupled" are to be construed broadly, as they may be, for example, fixedly coupled, detachably coupled, or integrally formed; can be mechanically connected, electrically connected or can communicate with each other; may be directly connected or indirectly connected through an intermediate. The specific meaning of the above terms in the present application can be understood by those of ordinary skill in the art as appropriate.

As shown in fig. 1, the first power source P and the second power source (not shown) can exchange power through the buck-boost circuit 108 including an inductor, a transistor, a capacitor, and the like, the pre-charging branch 101 is connected between the buck-boost circuit 108 and the first power source P, and the pre-charging branch 101 is bypassed by using the ac relay 109 connected in parallel with the pre-charging branch 101, so as to reduce loss. In the process of implementing the present application, the inventor finds that although the on-off of the buck-boost circuit 108 can be controlled in time based on the voltage across the coil or across the contacts in the ac relay 109, due to the existence of the inductor, after the buck-boost circuit 108 is turned off, current still flows through the ac relay 109, so that the ac relay 109 is disconnected with current, and there is a risk of ignition of the dc arc.

In view of the above problems, an embodiment of the present invention provides an ac relay protection circuit, as shown in fig. 2 to 4, the ac relay protection circuit includes a buck-boost circuit 108, an ac relay 109, a first control branch and a precharge branch, and the second power source can use the ac relay protection circuit to charge the first power source P, or the second power source can use the ac relay protection circuit to receive the electric energy of the first power source P. The buck-boost circuit 108 may include an inductor L, a capacitor (e.g., the first capacitor C1 and the second capacitor C2), and a transistor (e.g., the third NMOS transistor Q3 and the fourth NMOS transistor Q4) to boost or buck, and the precharge branch 101 may be used for precharging during initial charging to prevent damage to the transistor in the buck-boost circuit 108 due to excessive current. For example, the second power source charges the first power source using a tank inverter (including a buck-boost circuit therein). The alternating current relay protection circuit also comprises a fuse F, and the fuse F is connected between the first power supply P and the buck-boost circuit.

The buck-boost circuit 108 has a first terminal, a second terminal, a third terminal and a fourth terminal, and the first terminal and the second terminal of the buck-boost circuit 108 can be connected to the positive pole and the negative pole of a second power source (not shown) to form a first closed loop; the third end of the buck-boost circuit 108 may be connected to the positive electrode or the negative electrode of the first power source P, the fourth end of the buck-boost circuit 108 is connected to one end of the ac relay 109, and the other end of the ac relay 109 may be connected to the negative electrode or the positive electrode of the first power source P, thereby forming a second closed loop. The current of the second power source P can pass through the buck-boost circuit 108, and charge the second power source P through the buck-boost circuit 108. That is, the third terminal of the buck-boost circuit 108 may be connected to the positive pole of the first power source P, and the ac relay 109 may be connected to the negative pole of the first power source P, or the third terminal of the buck-boost circuit 108 may be connected to the negative pole of the first power source P, and the ac relay 109 may be connected to the positive pole of the first power source P. The first end of the buck-boost circuit 108 may be connected to the positive pole of the second power source, and the second end of the buck-boost circuit 108 may be connected to the negative pole of the second power source, or the first end of the buck-boost circuit 108 may be connected to the negative pole of the second power source, and the second end of the buck-boost circuit 108 may be connected to the positive pole of the second power source. The specific connection can be reasonably selected according to actual conditions, and is not limited herein.

The first end of the first control branch is connected to two ends of a contact 1091 of the ac relay 109, and the second end of the first control branch is connected to control ends of transistors (such as a third NMOS transistor Q3 and a fourth NMOS transistor Q4 in fig. 2) in the buck-boost circuit 108. The first control branch detects a voltage drop across the contact 1091 of the ac relay 109 (i.e., a voltage across the contact 1091), and controls the on/off of the buck-boost circuit 108 based on the voltage drop across the contact 1091. When the contact 1091 of the ac relay 109 fails, a voltage drop occurs across the contact 1091. After the first control branch detects the voltage drop values at the two ends of the contact 1091, comparing the detected voltage drop values with a first preset threshold, and if the detected voltage drop values are greater than the first preset threshold, the contact 1091 breaks down; if the detected voltage drop value is less than or equal to the first preset threshold, the contact 1091 is not malfunctioning. When the contact 1091 is determined to have a fault, the first control branch controls the buck-boost circuit to be disconnected, so that the generation of current is cut off in time.

The pre-charge branch is connected in parallel with the ac relay 109. The pre-charging branch comprises a transient voltage suppression diode T, a switching device Q2 and a first resistor R1, wherein the transient voltage suppression diode T is connected with the switching device Q2 in series, and the transient voltage suppression diode T and the switching device Q2 are connected with the first resistor R1 in parallel. When the charging power supply is used for initially charging the first power supply P, the alternating current relay 109 and the switching device Q2 are disconnected, the step-up and step-down voltage circuit 108 is switched on, and the current of the charging power supply charges the first resistor R1 through the first resistor R1; after the preset time, the ac relay 109 and the switching device Q2 are closed, and the current of the charging power supply charges the first power supply P through the ac relay 109. The tvs T may clamp the voltage across the ac relay 109 such that the ac relay 109 has a clamped voltage across it. And when the contact 1091 of the ac relay 109 fails, the transient voltage suppression diode T may generate a certain voltage drop, and the first control branch may detect the voltage drop generated by the transient voltage suppression diode T, so as to further ensure that the first control branch may timely disconnect the buck-boost circuit 108.

When the contact 1091 of the ac relay 109 fails, the voltage across the ac relay 109 increases, and when the voltage across the ac relay 109 is higher than the clamp voltage, even if there is an inductive current in the inductor L in the step-up/step-down circuit 108, the current will only flow to the second power supply P through the transient voltage suppression diode T, and will not pass through the ac relay 109, thereby ensuring that the ac relay 109 will not be disconnected with current. The transient voltage suppression diode may be a bidirectional transient voltage suppression diode or a unidirectional transient voltage suppression diode.

In summary, when the voltage across the contact 1091 of the ac relay 109 is greater than the clamping voltage value, the current only flows to the first power supply P through the transient voltage suppressor diode and does not pass through the ac relay 109, so that the ac relay 109 is not disconnected with current, thereby avoiding danger.

In one or more embodiments, as shown in fig. 2-4, the ac relay protection circuit also includes a processing unit 106. The switching device Q2 may include a second MOS transistor or a second IGBT transistor. When the switching device Q2 includes a second MOS transistor, a gate of the second MOS transistor is connected to the processing unit 106, a drain of the second MOS transistor is connected to the transient voltage suppression diode T, a source of the second MOS transistor is connected between the first power supply P and the first resistor R1, and the processing unit 106 controls on/off of the second MOS transistor by controlling the gate of the second MOS transistor. When the switching device Q2 includes a second IGBT, a gate of the second IGBT is connected to the processing unit 106, an emitter of the second IGBT is connected to the transient voltage suppression diode T, a collector of the second IGBT is connected between the first power supply P and the first resistor R1, and the processing unit 106 controls the gate of the second IGBT to turn on or off the second IGBT. The second MOS transistor may be an NMOS transistor or a PMOS transistor.

In one or more embodiments, as shown in fig. 2 to 4, the pre-charging branch further includes a first MOS transistor Q1 or a first IGBT transistor. When the pre-charging branch includes the first MOS transistor Q1, the gate of the first MOS transistor Q1 is connected to the processing unit 106, the source of the first MOS transistor Q1 is connected between the sources of the first resistor R1 and the second MOS transistor, or the source of the first MOS transistor Q1 is connected between the collector of the first resistor R1 and the collector of the second IGBT, the drain of the first MOS transistor Q1 is connected between the ac relay 109 and the first power supply P, the parasitic diode in the first MOS transistor Q1 can prevent the positive electrode and the negative electrode of the first power supply P from being connected reversely, and the processing unit 106 controls the on-off of the first MOS transistor Q1 by controlling the gate of the first MOS transistor Q1. When the pre-charging branch comprises a first IGBT tube, the grid electrode of the first IGBT tube is connected with the processing unit 106, the emitter electrode of the first IGBT tube is connected between the first resistor R1 and the source electrode of the second MOS tube, or the source electrode of the first IGBT tube is connected between the first resistor R1 and the collector electrode of the second IGBT tube, the collector electrode of the first IGBT tube is connected between the alternating current relay 109 and the first power supply P, the parasitic diode in the first IGBT tube can prevent the positive electrode and the negative electrode of the first power supply P from being reversely connected, and the processing unit 106 controls the on-off of the first IGBT tube by controlling the grid electrode of the first IGBT tube. The first MOS transistor may be an NMOS transistor or a PMOS transistor.

In some embodiments, as shown in fig. 4, the pre-charge branch includes a diode D. The anode of the diode D is connected between the first resistor R1 and the source of the second MOS transistor, or the anode of the diode D is connected between the first resistor R1 and the collector of the second IGBT, and the cathode of the diode D is connected between the ac relay 109 and the first power supply P. The diode D is disposed to prevent the positive and negative electrodes of the first power source P from being connected in reverse.

In one or more embodiments, as shown in fig. 2-4, the first control branch includes a second resistor R2, a third resistor R3, a first operational amplifier 102, a first comparator 103, a processing unit 106, and a driving unit 107. A first end of the second resistor R2 is connected to one end of the contact 1091 of the ac relay 109, a first end of the third resistor R3 is connected to the other end of the contact 1091 of the ac relay 109, a non-inverting input end of the first operational amplifier 102 is connected to a second end of the second resistor R2, an inverting input end of the first operational amplifier 102 is connected to a second end of the third resistor R3, an output end of the first operational amplifier 102 is connected to a negative input end of the first comparator 103, a positive input end of the first comparator 103 is connected to the first constant voltage source U1, an output end of the first comparator 103 is connected to an input end of the processing unit 106, an output end of the processing unit 106 is connected to an input end of the driving unit 107, and an output end of the driving unit 107 is connected to a control end of a transistor in the step-up and step-down circuit. The second resistor R2, the third resistor R3 and the first operational amplifier 102 perform differential sampling operation on the voltage at two ends of the contact 1091 of the ac relay 109, calculate the voltage drop at two ends of the contact 1091 and transmit the detected voltage drop to the negative input end of the first comparator 103, the first constant voltage source U1 connected to the positive input end of the first comparator 103 has a first preset threshold, if the voltage drop at two ends of the contact 1091 is greater than the first preset threshold, the first comparator 103 generates a trigger signal and transmits the trigger signal to the processing unit 106, and the processing unit 106 controls the driving unit 107 to turn off a Pulse modulation (PWM) signal to a transistor in the voltage step-up/step-down circuit 108 according to the trigger signal, so as to prevent the circuit from continuously working at the ac relay 109 to generate continuous dc arcing and burn the ac relay.

In one or more embodiments, as shown in fig. 3 and 4, the ac relay protection circuit further includes a second control branch. The first end of the second control branch is connected to two ends of a coil 1092 of the ac relay 109, and the second end of the second control branch is connected to a control end of a transistor in the buck-boost circuit 108, so as to detect and switch on/off the buck-boost circuit 108 based on the voltage at two ends of the coil. The ac relay 109 may include a third constant voltage source U3, a coil 1092, and a fifth NMOS transistor Q5 connected in series, a gate of the fifth NMOS transistor Q5 is connected to the processing unit 106, and the processing unit 106 controls the gate of the fifth NMOS transistor Q5 to control the on/off of the fifth NMOS transistor Q5, so as to control the operation of the coil 1092. When the coil 1092 fails, the voltage across the coil 1092 may be lower than the operating voltage of the ac relay. The second control branch may detect a voltage across the coil 1092, and disconnect the buck-boost circuit 108 when the voltage across the coil 1092 is less than a second preset threshold.

The second control branch may include a fourth resistor R4, a fifth resistor R5, a second operational amplifier 104, a second comparator 105, a processing unit 106, a second constant voltage source U2, and a driving unit 107. A first end of the fourth resistor R4 is connected to one end of the coil 1092 of the ac relay 109, a first end of the fifth resistor R5 is connected to the other end of the coil 1092 of the ac relay 109, a non-inverting input end of the second operational amplifier 104 is connected to a second end of the fourth resistor R4, an inverting input end of the second operational amplifier 104 is connected to a second end of the fifth resistor R5, an output end of the second operational amplifier 104 is connected to a negative input end of the second comparator 105, a positive input end of the second comparator 105 is connected to the second constant voltage source U2, and an output end of the second comparator 105 is connected to the processing unit 106.

The fourth resistor R4, the fifth resistor R5 and the second operational amplifier 104 perform differential sampling operation on the voltage at two ends of the coil 1092 of the ac relay 109, calculate the voltage at two ends of the coil 1092 and transmit the detected voltage value to the negative input end of the second comparator 105, the second constant voltage source U2 connected to the positive input end of the second comparator 105 has a second preset threshold, if the voltage at two ends of the coil 1092 is smaller than the second preset threshold, the second comparator 105 generates a trigger signal and transmits the trigger signal to the processing unit 106, and the processing unit 106 controls the driving unit 107 to turn off a Pulse modulation signal (Pulse width modulation, short: PWM) to a transistor in the voltage step-up/down circuit 108 according to the trigger signal, so as to avoid that the circuit continuously works in the ac relay 109 to generate continuous dc arcing and burn the ac relay. The Processing unit 106 may include a Complex Programmable Logic Device (CPLD) or a Digital Signal Processor (DSP).

The time length of the disconnection of the alternating current relay contact is generally millisecond level, and the first control branch and the second control branch are adopted to control the connection and disconnection of the boost-buck circuit based on the voltage of the alternating current relay contact and/or the voltage of the two ends of the coil. According to a mathematical model of the current drop in an inductor:

where T represents the inductor current fall time, W represents the inductance of the inductor, I represents the inductance current at the time of turning off the buck-boost circuit, and U represents the voltage difference across the inductor. According to the current reduction mathematical model of the inductor, the reduction time of the inductive current is dozens of microseconds and is far shorter than the disconnection time of the alternating current relay, the current on the inductor can be reduced to zero before the contact of the alternating current relay is disconnected, and the risk of current high-voltage disconnection of the alternating current relay is avoided.

It will be apparent to those skilled in the art that various changes and modifications may be made in the present application without departing from the spirit and scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is intended to include such modifications and variations as well.

Claims

1. An ac relay protection circuit, comprising:

the first end and the second end of the voltage-boosting circuit are used for being connected with a second power supply to form a first closed loop; the third end is used for being connected with a first power supply;

one end of the alternating current relay is connected with the fourth end of the buck-boost circuit, and the other end of the alternating current relay is used for being connected with the first power supply to form a second closed loop;

the first end of the first control branch circuit is connected to two ends of a contact of the alternating current relay, and the second end of the first control branch circuit is connected with the control end of a transistor in the buck-boost circuit and used for detecting and switching on and off the buck-boost circuit based on the voltage drop of two ends of the contact;

the pre-charging branch is connected with the alternating current relay in parallel; the pre-charging branch circuit comprises a transient voltage suppression diode, a switching device and a first resistor, wherein the transient voltage suppression diode is connected with the switching device in series, and the transient voltage suppression diode and the switching device are connected with the first resistor in parallel.

2. An ac relay protection circuit according to claim 1, wherein the transient voltage suppression diode is a bidirectional transient voltage suppression diode.

3. An ac relay protection circuit according to claim 1, wherein the transient voltage suppression diode is a unidirectional transient voltage suppression diode.

4. An ac relay protection circuit according to any of claims 1-3, wherein the ac relay protection circuit further comprises a processing unit; the switching device includes:

or the grid electrode of the second IGBT tube is connected with the processing unit, the emitter electrode of the second IGBT tube is connected with the transient voltage suppression diode, and the collector electrode of the second IGBT tube is connected between the first power supply and the first resistor.

5. The ac relay protection circuit of claim 4, wherein the pre-charge branch further comprises:

the grid electrode of the first MOS tube is connected with the processing unit, the source electrode of the first MOS tube is connected between the source electrode of the first resistor and the second MOS tube or between the collector electrodes of the first resistor and the second IGBT tube, and the drain electrode of the first MOS tube is connected between the alternating current relay and the first power supply;

6. The ac relay protection circuit of claim 4, wherein the pre-charge branch further comprises:

and the anode of the diode is connected between the first resistor and the source electrode of the second MOS tube or between the first resistor and the collector electrode of the second IGBT tube, and the cathode of the diode is connected between the alternating current relay and the first power supply.

7. An ac relay protection circuit according to claim 4, wherein said first control branch comprises:

the first end of the second resistor is connected with one end of the alternating current relay contact;

the first end of the third resistor is connected with the other end of the alternating current relay contact;

the non-inverting input end of the first operational amplifier is connected with the second end of the second resistor, and the inverting input end of the first operational amplifier is connected with the second end of the third resistor;

the positive input end of the first comparator is connected with a first constant voltage source, the negative input end of the first comparator is connected with the output end of the first operational amplifier, and the output end of the first comparator is connected with the input end of the processing unit;

and the input end of the driving unit is connected with the output end of the processing unit, and the output end of the driving unit is connected with the control end of the transistor in the step-up and step-down circuit.

8. The ac relay protection circuit of claim 7, further comprising:

and the first end of the second control branch circuit is connected to two ends of a coil of the alternating current relay, and the second end of the second control branch circuit is connected with the control end of a transistor in the boost-buck circuit and is used for detecting and switching on and off the boost-buck circuit based on the voltage at two ends of the coil.

9. The ac relay protection circuit of claim 8, wherein the second control branch comprises:

a first end of the fourth resistor is connected with one end of the coil of the alternating current relay;

a first end of the fifth resistor is connected with the other end of the coil of the alternating current relay;

the non-inverting input end of the second operational amplifier is connected with the second end of the fourth resistor, and the inverting input end of the second operational amplifier is connected with the second end of the fifth resistor;

and the positive input end of the second comparator is connected with a second constant voltage source, the negative input end of the second comparator is connected with the output end of the second operational amplifier, and the output end of the second comparator is connected with the processing unit.

10. An ac relay protection circuit according to any of claims 5 to 9, wherein the processing unit comprises a complex programmable logic device or a digital signal processor.