AC relay control circuit and control method

Abstract

The present invention provides an AC relay control circuit and a control method, which are applied to a high-voltage DC line. The control circuit includes a pre-charging module and a low-voltage control module. The pre-charging module is respectively connected to an external power supply module, a low-voltage control module and a power conversion module. The pre-charging module includes at least a first AC relay, a second AC relay and a capacitor charging unit. The first AC relay and the second AC relay are connected in series in the high-voltage DC line. The first AC relay and the second AC relay are used to pre-charge the capacitor charging unit, and the capacitor charging unit is used to store electric energy. The low-voltage control module is used to set the action sequence of the first AC relay and the second AC relay, and control the shut-off of the first AC relay and the second AC relay. The present invention effectively reduces the volume and cost of the power conversion system by using a small AC relay, and improves the power density, safety and flexibility of the system.

Description

Technical Field

[0001] The present invention relates to the technical field of power conversion, and in particular to an AC relay control circuit and a control method. Background Art

[0002] The power conversion system converts input electrical energy (such as AC or DC) into the voltage, current and frequency required at the output end through a series of circuits and control strategies. Power conversion systems are widely used in fields such as household appliances, industrial control, electric vehicles and communication systems, providing stable and efficient power support for various devices. Among them, the DCDC conversion system converts one DC voltage into another DC voltage. In the high-voltage (1000-2000V DC) DC / DC conversion system, directly charging the large-capacity input capacitor may generate a large surge current, which will not only damage the power supply and capacitor, but also may cause impact on other parts of the system. Therefore, it is necessary to pre-charge the input capacitor, and at the same time, it is also necessary to safely isolate the input capacitor from the subsequent circuit when the system is powered off to prevent the risk of electric shock caused by residual charge of the capacitor and protect the subsequent circuit from the influence of power supply fluctuations.

[0003] In view of the above problems, a 3300V high-voltage insulated gate bipolar transistor IGBT is usually connected in parallel to the input main circuit, and the IGBT needs to be timed to achieve the pre-charging solution. The 3300V high-voltage IGBT module has a relatively large package volume because it needs to withstand high voltage and high current. At the same time, when multiple IGBTs are used in parallel, the overall occupied space will be significantly increased. Since the IGBT works in a high-voltage environment, the drive circuit needs to be electrically isolated from the main circuit to prevent the high voltage from damaging the control circuit. This usually requires the design of a complex drive circuit, which increases the complexity of the circuit. When the IGBT is used as a pre-charging switch and the main power is cut off, the IGBT itself cannot directly cut off the input circuit of the module. In order to ensure that the system achieves a safe isolation effect when the main power is cut off, additional measures need to be taken to cut off the input circuit. Therefore, the solution of using a 3300V high-voltage IGBT in parallel with the input main circuit to achieve pre-charging has significant disadvantages such as large volume, complex drive circuit and safety isolation problems. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides an AC relay control circuit and control method, which effectively solve the problems of large volume, complex driving circuit and safety isolation in the existing pre-charging solutions.

[0005] In a first aspect, the present invention provides an AC relay control circuit, which is applied to a high-voltage DC line formed by an external power supply module and a power conversion module. The control circuit includes: a pre-charging module and a low-voltage control module, wherein:

[0006] The pre-charging module is respectively connected to the external power supply module, the low voltage control module and the power conversion module, and the pre-charging module at least includes a first AC relay, a second AC relay and a capacitor charging unit, the first AC relay and the second AC relay are connected in series in the high voltage DC line, the first AC relay and the second AC relay are used to perform pre-charging adjustment on the capacitor charging unit, and the capacitor charging unit is used to store electric energy;

[0007] The low voltage control module is used to set the action sequence of the first AC relay and the second AC relay, and control the shut-off of the first AC relay and the second AC relay.

[0008] Further, the pre-charging module includes a first delay capacitor, a freewheeling capacitor, a first AC relay, a second AC relay, a first resistor, a power supply and a capacitor charging unit, wherein:

[0009] One end of the first delay capacitor is respectively connected to one end of the coil of the first AC relay, the first switch contact of the first AC relay, one end of the coil of the second AC relay and the first switch contact of the second AC relay, and is commonly connected to the positive electrode of the power supply;

[0010] The first switch contact of the first AC relay is connected to one end of the freewheeling capacitor, the other end of the freewheeling capacitor is connected to the second switch contact of the first AC relay and is connected to one end of the first resistor, the other end of the first resistor is connected to the second switch contact of the second AC relay, and one end of the first resistor is also connected to the capacitor charging unit and the power conversion module;

[0011] The other end of the coil of the first AC relay is connected to the second switch contact of the second AC relay and connected to the low-voltage control module together. The other end of the coil of the second AC relay is respectively connected to the low-voltage control module. The other end of the first delay capacitor is connected to the negative pole of the power supply and grounded.

[0012] Furthermore, the capacitor charging unit includes a plurality of bus capacitors, the plurality of bus capacitors are connected in series, one end of the capacitor charging unit is connected to a connection line between the first resistor and the power conversion module, and the other end of the capacitor charging unit is grounded.

[0013] Further, the low voltage control module includes a control unit, a diode, a second resistor, a third resistor, a second delay capacitor, a first coupler and a second coupler, wherein:

[0014] The control unit is connected to one end of the second resistor, the other end of the second resistor is connected to the first end of the first coupler, the second end of the first coupler is grounded, the third end of the first coupler is connected to the other end of the coil of the second AC relay, and the fourth end of the first coupler is grounded;

[0015] The control unit is connected to the positive electrode of the diode, the negative electrode of the diode is connected to one end of the third resistor and jointly connected to one end of the second delay capacitor, the other end of the third resistor is connected to the first end of the second coupler, the second end of the second coupler is connected to the other end of the second delay capacitor and grounded, the third end of the second coupler is connected to the other end of the coil of the first AC relay, and the fourth end of the second coupler is grounded.

[0016] Furthermore, the freewheeling capacitor is used for freewheeling when the first AC relay is disconnected, and the capacity range of the freewheeling capacitor is 100-300NF.

[0017] Furthermore, the capacity calculation formula of the first delay capacitor is:

[0018]

[0019] In the above formula, C 1 is the capacity of the first delay capacitor, t 1 is the delay time of shutting off the AC relay coil when it is powered on. R 1 is the coil impedance of the AC relay, V t is the release voltage of the switch contacts of the AC relay, E 1 is the power supply voltage.

[0020] Furthermore, the capacity calculation formula of the second delay capacitor is:

[0021]

[0022] In the above formula, C 2 is the capacity of the second delay capacitor, t 2 is the delay time of shutting down after the AC relay receives the driving signal, R 2 is the resistance value of the third resistor, V u is the voltage drop when the second coupler is turned on, E 2 is the driving voltage.

[0023] Furthermore, the control unit is one or more of a digital signal processor, a single-chip microcomputer, a system on chip and a microcontroller chip, and the first coupler and the second coupler are photoelectric couplers and / or magnetic isolators.

[0024] In a second aspect, the present invention provides an AC relay control method, the control method is applied to the AC relay control circuit described in the first aspect of the present invention, the control method comprising:

[0025] The external power supply module supplies power to the control circuit, the low voltage control module sends a first pulse signal to drive the second AC relay to close, and the capacitor charging unit performs pre-charging;

[0026] When the capacitor charging unit is charged to a set voltage, the low voltage control module sends a second pulse signal to drive the first AC relay to close and disconnect the second AC relay;

[0027] If the control circuit receives a shutdown instruction, the low-voltage control module first turns off the power conversion module, and then sends a third pulse signal to drive the first AC relay to disconnect.

[0028] Furthermore, the control method further includes:

[0029] The power supplies of the first AC relay and the second AC relay are isolated so that the circuit between the power supply and the low-voltage control module meets the set withstand voltage level.

[0030] The AC relay control circuit and control method provided by the present invention, by applying the AC relay in the high-voltage DC circuit, redefines the voltage level of the peripheral circuit of the AC relay, and then optimizes the software control logic and the corresponding hardware isolation circuit, and designs the delay circuit to ensure that the AC relay can be safely and reliably used in the high-voltage DC circuit. By using a small AC relay, the overall volume of the drive circuit is significantly reduced, which is easier to integrate the system and effectively improves the power density of the system; there are many types of AC relays, which are easy to select during design, and the cost of AC relays is low, which is conducive to project implementation; the peripheral control circuit and control logic of the AC relay are simple, and only the power conversion circuit of the capacitor rear stage needs to be strictly controlled to stop working first, and then the AC relay can be controlled to switch; after the external power supply module is powered off, the AC relay is also in a disconnected state, which can realize the removal of the system input power, and improve the safety and flexibility of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 is a schematic diagram of the structure of an AC relay control circuit provided by an embodiment of the present invention;

[0033] Figure 2 is a schematic diagram of an AC relay control circuit provided by an embodiment of the present invention;

[0034] Figure 3 is a schematic diagram of a first flow chart of an AC relay control method provided by an embodiment of the present invention;

[0035] Figure 4 It is a second flow chart of the AC relay control method provided in an embodiment of the present invention.

[0036] Description of main component symbols:

[0037] 100, AC relay control circuit; 110, pre-charging module; 120, low voltage control module; 200, external power supply module; 300, power conversion module. DETAILED DESCRIPTION

[0038] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be further clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. It should be noted that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0039] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the related listed items.

[0041] In high voltage (1000-2000V DC) DC / DC conversion systems, directly charging large-capacity input capacitors may generate large surge currents, which will not only damage the power supply and capacitors, but may also cause impacts on other parts of the system. Therefore, it is necessary to pre-charge the input capacitor. At present, 3300V high-voltage insulated gate bipolar transistors IGBTs are usually connected in parallel to the input main circuit, and the IGBTs need to be timed to achieve the pre-charging solution. The 3300V high-voltage IGBT module has a relatively large package volume because it needs to withstand high voltage and high current. At the same time, when multiple IGBTs are used in parallel, the overall occupied space will be significantly increased. Since the IGBT works in a high-voltage environment, the drive circuit needs to be electrically isolated from the main circuit to prevent the high voltage from damaging the control circuit. This usually requires the design of a complex drive circuit, which increases the complexity of the circuit. When the IGBT is used as a pre-charging switch and the main power is cut off, the IGBT itself cannot directly cut off the input circuit of the module. In order to ensure that the system achieves a safe isolation effect when the main power is cut off, additional measures need to be taken to cut off the input circuit. Therefore, the solution of using 3300V high-voltage IGBT in parallel with the input main circuit to achieve pre-charging has significant disadvantages such as large size, complex drive circuit and safety isolation problems.

[0042] Example 1

[0043] In view of the above-mentioned deficiencies in the prior art, an embodiment of the present invention provides an AC relay control circuit, which effectively solves the problems of large volume, complex driving circuit and safety isolation in the existing pre-charging solution. Figure 1 : is a schematic diagram of the structure of an AC relay control circuit provided by an embodiment of the present invention, such as Figure 1 As shown, the AC relay control circuit 100 is applied to a high-voltage DC line formed by an external power supply module 200 and a power conversion module 300. In an embodiment of the present invention, the voltage of the high-voltage DC line is above 1000V. The AC relay control circuit 100 includes a pre-charging module 110 and a low-voltage control module 120, wherein:

[0044] The pre-charging module 110 is respectively connected to the external power supply module 200, the low voltage control module 120 and the power conversion module 300. Figure 2 is a schematic diagram of an AC relay control circuit provided by an embodiment of the present invention, such as Figure 2 As shown, the pre-charging module 110 includes at least a first AC relay K1, a second AC relay K2 and a capacitor charging unit. The first AC relay K1 and the second AC relay K2 are connected in series in the high-voltage DC line. The first AC relay K1 and the second AC relay K2 are used to perform pre-charging adjustment on the capacitor charging unit, and the capacitor charging unit is used to store electrical energy.

[0045] The pre-charging module 110 includes a first delay capacitor C1, a freewheeling capacitor C2, a first AC relay K1, a second AC relay K2, a first resistor R1, a power supply and a capacitor charging unit, wherein:

[0046] One end of the first delay capacitor C1 is respectively connected to one end of the coil of the first AC relay K1, the first switch contact of the first AC relay K1, one end of the coil of the second AC relay K2 and the first switch contact of the second AC relay K2, and the first switch contact of the first AC relay K1 is connected to one end of the freewheeling capacitor C2.

[0047] The other end of the freewheeling capacitor C2 is connected to the second switch contact of the first AC relay K1 and is commonly connected to one end of the first resistor R1. The other end of the first resistor R1 is connected to the second switch contact of the second AC relay K2. One end of the first resistor R1 is also connected to the capacitor charging unit and the power conversion module. The other end of the coil of the first AC relay K1 is connected to the second switch contact of the second AC relay K2 and is commonly connected to the low-voltage control module 120. The other end of the coil of the second AC relay K2 is respectively connected to the low-voltage control module 120. The other end of the first delay capacitor C1 is connected to the negative pole of the power supply and is grounded. The voltage range of the power supply is 12-24V.

[0048] The capacitor charging unit includes multiple large-capacity bus capacitors, and the multiple bus capacitors are connected in series. In an embodiment of the present invention, the capacitor charging unit includes three large-capacity bus capacitors, namely a first charging capacitor C3, a second charging capacitor C4 and a third charging capacitor C5. One end of the first charging capacitor C3 is connected to the connection line between the first resistor R1 and the power conversion module, the other end of the first charging capacitor C3 is connected to one end of the second charging capacitor C4, the other end of the second charging capacitor C4 is connected to one end of the third charging capacitor C5, and the other end of the third charging capacitor C5 is grounded.

[0049] In an embodiment of the present invention, when the control circuit loses power, due to the different undervoltage points of various components in the control circuit, the AC relay may act first and then stop after the power conversion module, resulting in the risk of the AC relay operating under load. In order to ensure that the AC relay can be disconnected with a delay after the control power is lost to ensure no-load operation, the circuit needs to be specially designed. Specifically, in order to ensure that the coil power supply of the AC relay is delayed, it is necessary to select the delay capacitor C1. The capacity of the first delay capacitor can be calculated according to the capacitor discharge formula, which is:

[0050]

[0051] In the above formula, C 1 is the capacity of the first delay capacitor C1, t 1 is the delay time of shutting off when the AC relay coil is powered.R 1 is the coil impedance of the AC relay, V t is the release voltage of the switch contacts of the AC relay, E 1 is the power supply voltage.

[0052] The capacitance range of the freewheeling capacitor C2 is generally set to 100-300NF. The freewheeling capacitor C2 is used for short-term freewheeling when the first AC relay K1 is disconnected, so as to reduce the damage caused by voltage shock to the first AC relay K1.

[0053] The low voltage control module 120 is used to set the action sequence of the first AC relay K1 and the second AC relay K2, and control the shut-off of the first AC relay K1 and the second AC relay K2. The low voltage control module 120 includes a control unit, a diode D1, a second resistor R2, a third resistor R3, a second delay capacitor C6, a first coupler U1 and a second coupler U2, wherein:

[0054] The control unit is connected to one end of the second resistor R2, the other end of the second resistor R2 is connected to the first end of the first coupler U1, the second end of the first coupler U1 is grounded, the third end of the first coupler U1 is connected to the other end of the coil of the second AC relay K2, and the fourth end of the first coupler U1 is grounded; the control unit is connected to the positive electrode of the diode D1, the negative electrode of the diode D1 is connected to one end of the third resistor R3 and are jointly connected to one end of the second delay capacitor C6, the other end of the third resistor R3 is connected to the first end of the second coupler U2, the second end of the second coupler U2 is connected to the other end of the second delay capacitor C6 and is grounded, the third end of the second coupler U2 is connected to the other end of the coil of the first AC relay K1, and the fourth end of the second coupler U2 is grounded.

[0055] In the embodiment of the present invention, in order to ensure that the driving signal of the AC relay has the same delay, the second delay capacitor C6 and the third resistor R3 need to be specially selected. The capacity calculation formula of the second delay capacitor C6 is:

[0056]

[0057] In the above formula, C 2 is the capacity of the second delay capacitor C6, t 2 is the delay time for the AC relay to shut down after receiving the drive signal. Generally, the delay is set to 5-10ms. R 2 is the resistance value of the third resistor R3, V u is the voltage drop when the second coupler U2 is turned on, E 2 is the driving voltage.

[0058] Optionally, while the signal is being held, a diode D1 is provided in the control loop to prevent current backflow from causing uncertainty in the holding time.

[0059] In an embodiment of the present invention, the control unit includes but is not limited to one or more of a digital signal processor, a single chip microcomputer, a system on chip and a microcontroller chip, and the first coupler U1 and the second coupler U2 are photoelectric couplers and / or magnetic isolators.

[0060] The AC relay control circuit provided by the embodiment of the present invention, by applying the AC relay in the high-voltage DC circuit, redefines the voltage level of the peripheral circuit of the AC relay, and then optimizes the software control logic and the corresponding hardware isolation circuit, and designs the delay circuit to ensure that the AC relay can be safely and reliably used in the high-voltage DC circuit. By using a small AC relay, the overall volume of the drive circuit is significantly reduced, making it easier to integrate the system, and effectively improving the power density of the system; there are many types of AC relays, which are easy to select during design, and the cost of AC relays is low, which is conducive to the implementation of the project.

[0061] Example 2

[0062] Based on the same technical concept, an embodiment of the present invention provides an AC relay control circuit method, which is applied to the AC relay control circuit in the above-mentioned embodiment 1. Figure 3 is a first flow chart of the AC relay control method provided by an embodiment of the present invention, such as Figure 3 As shown, the control method includes the following steps:

[0063] S100, the external power supply module supplies power to the control circuit, the low-voltage control module sends a first pulse signal to drive the second AC relay to close, and the capacitor charging unit performs pre-charging.

[0064] When high voltage is input, the AC relay's on-load disconnection and on-load closing will cause the contacts to arc, and the AC relay has no arc extinguishing device, which may burn the AC relay in severe cases. Therefore, in order to avoid the AC relay's on-load closing and on-load disconnection and to ensure that the AC relay works under absolute no-load conditions, a specific action sequence needs to be designed for the AC relay.

[0065] In the embodiment of the present invention, when the contactor K0 of the external power supply module 200 is closed, the control circuit is powered, the control unit sends a first pulse signal to drive the second AC relay K2 to close, and the strong current passes through the first resistor R1 to pre-charge the three large-capacity bus capacitors.

[0066] S200: When the capacitor charging unit is charged to a set voltage, the low voltage control module sends a second pulse signal to drive the first AC relay to close and disconnect the second AC relay.

[0067] In the embodiment of the present invention, when the electric charge of the capacitor charging unit reaches 90% of the input voltage, the control unit sends a second pulse signal again to drive the first AC relay K1 to close and disconnect the second AC relay K2. When it is detected that the control circuit is normal, the power conversion module is started by the control unit to ensure that the AC relay is closed under no-load conditions.

[0068] S300: If the control circuit receives a shutdown instruction, the low-voltage control module first turns off the power conversion module, and then sends a third pulse signal to drive the first AC relay to disconnect.

[0069] The second AC relay K2 is disconnected after pre-charging is completed, while the first AC relay K1 is in a closed state. When the control circuit receives a shutdown signal or a system failure occurs and needs to disconnect the AC relay, the control unit first turns off the power conversion module and then executes the command to disconnect the first AC relay K1 to ensure that the AC relay works under no-load conditions.

[0070] Optionally, the first AC relay K1 is turned off under no-load conditions. However, since the voltage across the switch contacts of the AC relay is too high, the action duration of the switch contacts of the AC relay is relatively long, usually between 10-30ms, which will also cause a certain amount of arcing. Therefore, it is necessary to directly connect a smaller freewheeling capacitor C2 in series between the two switch contacts of the first AC relay K1. The capacity range of the freewheeling capacitor C2 is set to 100-300NF, which is mainly used for short-term freewheeling when disconnected to reduce the damage to the AC relay caused by voltage shock.

[0071] The voltage resistance level between the coil winding of the AC relay and the switch contacts is insufficient, which can easily cause the circuit of the pre-charging module to be connected to the circuit of the low-voltage control module, causing the circuit of the low-voltage control module to burn out. Therefore, the power supply of the AC relay coil needs to be isolated, and the drive signal also needs to be isolated. Figure 4 is a second flow chart of the AC relay control method provided by an embodiment of the present invention, such as Figure 4 As shown, the control method also includes:

[0072] S400: Isolate the power supplies of the first AC relay and the second AC relay so that the circuits of the power supplies and the low-voltage control module meet the set withstand voltage level.

[0073] Due to the small size of the AC relay, the safety withstand voltage of the switch contacts and the coil cannot meet the 1000-2000V high-voltage system. In the embodiment of the present invention, it is necessary to isolate the power supply (12-24V DC / GND2) of the AC relay so that the power supply and the control circuit (GND1) of the low-voltage control module meet the specified maximum withstand voltage level. In the embodiment of the present invention, the maximum withstand voltage level is set to 5600VAC. The control signal output by the low-voltage control module also needs to be isolated. In the embodiment of the present invention, the first coupler U1 and the second coupler U2 are used for isolation, wherein the first coupler U1 and the second coupler U2 use photoelectric couplers, and the isolation voltage is greater than 5600VAC.

[0074] The AC relay control method provided by the embodiment of the present invention applies an AC relay in a high-voltage DC circuit. The peripheral control circuit and control logic of the AC relay are simple. It only needs to strictly control the power conversion circuit after the capacitor to stop working first, and then control the AC relay to switch. After the external power supply module is powered off, the AC relay is also in a disconnected state, which can realize the cutting off of the system input power, thereby improving the safety and flexibility of the system.

[0075] In summary, the AC relay control circuit and control method provided by the present invention, by applying AC relays in high-voltage DC circuits, redefines the voltage level of the peripheral circuit of the AC relay, and then optimizes the software control logic and the corresponding hardware isolation circuit, and designs a delay circuit to ensure that the AC relay can be safely and reliably used in high-voltage DC circuits. By using small AC relays, the overall volume of the drive circuit is significantly reduced, which makes it easier to integrate the system and effectively improves the power density of the system; there are many types of AC relays, which are easy to select during design, and the cost of AC relays is low, which is conducive to project implementation; the peripheral control circuit and control logic of the AC relay are simple, and only the power conversion circuit of the capacitor rear stage needs to be strictly controlled to stop working first, and then the AC relay can be controlled to switch; after the external power supply module is powered off, the AC relay is also in a disconnected state, which can realize the removal of the system input power, and improve the safety and flexibility of the system.

[0076] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0077] The above-mentioned embodiments only express several implementation methods of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

[0078] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An AC relay control circuit, characterized in that: The control circuit is applied to a high-voltage DC line formed by an external power supply module and a power conversion module. The control circuit includes: a pre-charging module and a low-voltage control module, wherein: The pre-charging module is respectively connected to the external power supply module, the low voltage control module and the power conversion module, and the pre-charging module at least includes a first AC relay, a second AC relay and a capacitor charging unit, the first AC relay and the second AC relay are connected in series in the high voltage DC line, the first AC relay and the second AC relay are used to perform pre-charging adjustment on the capacitor charging unit, and the capacitor charging unit is used to store electric energy; The low voltage control module is used to set the action timing of the first AC relay and the second AC relay, and control the shut-off of the first AC relay and the second AC relay; The pre-charging module includes a first delay capacitor, a freewheeling capacitor, a first AC relay, a second AC relay, a first resistor, a power supply and a capacitor charging unit, wherein: One end of the first delay capacitor is respectively connected to one end of the coil of the first AC relay, the first switch contact of the first AC relay, one end of the coil of the second AC relay and the first switch contact of the second AC relay, and is commonly connected to the positive electrode of the power supply; The first switch contact of the first AC relay is connected to one end of the freewheeling capacitor, the other end of the freewheeling capacitor is connected to the second switch contact of the first AC relay and is connected to one end of the first resistor, the other end of the first resistor is connected to the second switch contact of the second AC relay, and one end of the first resistor is also connected to the capacitor charging unit and the power conversion module; The other end of the coil of the first AC relay is connected to the second switch contact of the second AC relay and connected to the low-voltage control module, the other end of the coil of the second AC relay is connected to the low-voltage control module, and the other end of the first delay capacitor is connected to the negative electrode of the power supply and grounded; The capacitor charging unit includes a plurality of bus capacitors, the plurality of bus capacitors are connected in series, one end of the capacitor charging unit is connected to the connection line between the first resistor and the power conversion module, and the other end of the capacitor charging unit is grounded; The low voltage control module includes a control unit, a diode, a second resistor, a third resistor, a second delay capacitor, a first coupler and a second coupler, wherein the first coupler and the second coupler are photoelectric couplers, wherein: The control unit is connected to one end of the second resistor, the other end of the second resistor is connected to the first end of the first coupler, the second end of the first coupler is grounded, the third end of the first coupler is connected to the other end of the coil of the second AC relay, and the fourth end of the first coupler is grounded; The control unit is connected to the positive electrode of the diode, the negative electrode of the diode is connected to one end of the third resistor and jointly connected to one end of the second delay capacitor, the other end of the third resistor is connected to the first end of the second coupler, the second end of the second coupler is connected to the other end of the second delay capacitor and grounded, the third end of the second coupler is connected to the other end of the coil of the first AC relay, and the fourth end of the second coupler is grounded.

2. The AC relay control circuit according to claim 1, characterized in that: The freewheeling capacitor is used for freewheeling when the first AC relay is disconnected, and the capacity range of the freewheeling capacitor is 100-300NF.

3. The AC relay control circuit according to claim 1, characterized in that: The capacity calculation formula of the first delay capacitor is: In the above formula, C 1 is the capacity of the first delay capacitor, t 1 is the delay time for shutting off the power supply to the coil of the AC relay, R 1 is the coil impedance of the AC relay, V t is the release voltage of the switch contacts of the AC relay, E 1 is the power supply voltage.

4. The AC relay control circuit according to claim 1, characterized in that: The capacity calculation formula of the second delay capacitor is: In the above formula, C 2 is the capacity of the second delay capacitor, t 2 is the delay time of shutting down after the AC relay receives the driving signal, R 2 is the resistance value of the third resistor, V u is the voltage drop when the second coupler is turned on, E 2 is the driving voltage.

5. The AC relay control circuit according to claim 1, characterized in that: The control unit is one or more of a digital signal processor, a single chip microcomputer, a system on chip and a microcontroller chip.

6. An AC relay control method, characterized in that: The control method is applied to the AC relay control circuit according to any one of claims 1 to 5, and the control method comprises: The external power supply module supplies power to the control circuit, the low voltage control module sends a first pulse signal to drive the second AC relay to close, and the capacitor charging unit performs pre-charging; When the capacitor charging unit is charged to a set voltage, the low voltage control module sends a second pulse signal to drive the first AC relay to close and disconnect the second AC relay; If the control circuit receives a shutdown instruction, the low-voltage control module first turns off the power conversion module, and then sends a third pulse signal to drive the first AC relay to disconnect; The power supplies of the first AC relay and the second AC relay are isolated so that the circuit between the power supply and the low-voltage control module meets the set withstand voltage level.

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