Electromagnetic valve open circuit and short circuit detection system for energy storage

Abstract

The invention discloses an electromagnetic valve open and short circuit detection system for energy storage, and the system comprises an input voltage detection module which is used for detecting the power supply voltage of an electromagnetic valve; the current detection module is used for detecting the current when the electromagnetic valve works; the voltage detection module is responsible for detecting post-stage voltage of the resettable fuse; the differential voltage detection module is used for detecting a voltage difference value when the electromagnetic valve is used; the output control module can control the on-off of the electromagnetic valve; and the single-chip microcomputer micro-control module can collect detection values of the input voltage detection module, the current detection module, the voltage detection module and the differential voltage detection module and regulate and control the output control module according to the detection values. According to the system, the open circuit state and the short circuit state of the electromagnetic valve can be detected at the same time, the whole scene where 24V voltage is not provided and 24V driving voltage is provided is covered, the problem that a traditional detection circuit is single in function is solved, and comprehensive monitoring of the working state of the electromagnetic valve is achieved by accurately collecting voltage signals of all modules.

Description

Technical Field

[0001] This invention relates to the field of open / short circuit detection technology for solenoid valves, and more particularly to an open / short circuit detection system for energy storage solenoid valves. Background Technology

[0002] In the operation system of energy storage power stations, solenoid valves, as key actuators, are widely used in core aspects such as fluid control and loop switching. The stability of their working state directly determines the operating efficiency and safety level of the energy storage system. As energy storage technology develops towards larger capacity and higher integration, more stringent requirements are placed on the reliability and fault early warning capabilities of solenoid valves. Among them, open circuit and short circuit are the two most common types of faults of solenoid valves. If they are not detected and dealt with in a timely manner, they can easily lead to equipment damage, system shutdown, or even safety accidents. Therefore, achieving accurate and rapid detection of open and short circuit states of solenoid valves has important engineering significance.

[0003] Currently, existing solenoid valve fault detection solutions in the industry have significant limitations and are difficult to meet the actual application needs of energy storage systems. On the one hand, traditional detection circuits often adopt a design mode where open-circuit detection and short-circuit detection are independent, that is, using two separate circuits to achieve detection of a single fault type. This type of solution not only increases the hardware complexity and installation and maintenance difficulty of the system, but also suffers from problems such as detection response delay and incomplete fault diagnosis. It cannot achieve simultaneous monitoring of two types of faults and is difficult to meet the real-time and comprehensive detection requirements of energy storage systems. On the other hand, some solutions that can simultaneously perform open-circuit and short-circuit detection functions often rely on complex circuit topologies and high-precision dedicated chips, leading to a significant increase in hardware costs. At the same time, it increases the difficulty of circuit debugging and the power consumption of system operation, reducing the economic efficiency and practicality of the solution, and making it difficult to promote its application in large-scale energy storage power stations.

[0004] Furthermore, existing detection solutions generally lack effective dual protection mechanisms. When a fault is detected, they cannot quickly disconnect the power supply circuit or take emergency measures, leading to a high risk of the fault escalating. At the same time, existing solutions can only detect faults when the solenoid valve is operating under normal power supply. They struggle to determine the connection status when the valve is not powered, failing to provide fault warnings under all operating conditions, further reducing the operational safety of the energy storage system.

[0005] Therefore, the need for a detection technology that is simple in structure, low in cost, fast in response, can simultaneously detect open and short circuits of solenoid valves, and has full-condition adaptability and dual protection functions has become an urgent technical problem to be solved in the current energy storage field. Summary of the Invention

[0006] To address the aforementioned problems, the present invention aims to provide an open / short circuit detection system for solenoid valves used in energy storage, thereby solving the technical challenges of existing open / short circuit detection schemes for solenoid valves in energy storage systems, such as complex structure, high cost, difficult debugging, high power consumption, lack of dual protection mechanisms, and inability to achieve full-condition fault early warning.

[0007] The objective of this invention can be achieved through the following technical solution: a solenoid valve open / short circuit detection system for energy storage, comprising:

[0008] The input voltage detection module is used to detect the power supply voltage of the solenoid valve.

[0009] The current detection module is used to detect the current when the solenoid valve is working.

[0010] The voltage detection module is used to detect the voltage after the self-resetting fuse;

[0011] The differential voltage detection module is used to detect the voltage difference when the solenoid valve is in use;

[0012] The output control module controls the on / off state of the solenoid valve;

[0013] The microcontroller module collects the detection values ​​from the input voltage detection module, current detection module, voltage detection module, and differential voltage detection module, and adjusts the output control module based on the detection values.

[0014] As a further aspect of the present invention, it also includes:

[0015] A 5V weak pull-up module is used to detect the open / short circuit state of the solenoid valve when it is not in operation.

[0016] As a further embodiment of the present invention, the input voltage detection module includes high-precision resistors R8 and R11 to provide the acquired voltage. , is represented as:

[0017]

[0018] 24V is the power supply voltage.

[0019] As a further embodiment of the present invention, the voltage detection module includes high-precision resistors R19 and R20 to provide the acquired voltage. , is represented as:

[0020]

[0021] 24V is the power supply voltage.

[0022] As a further embodiment of the present invention, the current detection module includes a current transformer U2 and a high-precision current sampling resistor R13, wherein U2 measures the current in R13 and converts it into a voltage for acquisition. , is represented as:

[0023]

[0024] Among them, Gm current transformer amplification gain, I Load R13 represents the detection current, and R5 represents the amplification resistor.

[0025] As a further embodiment of the present invention, the differential voltage detection module employs a dual-channel operational amplifier to provide the acquired voltage. , is represented as:

[0026]

[0027]

[0028] Wherein, FIRE+ is the positive voltage of the solenoid valve, and FIRE- is the negative voltage of the solenoid valve. This is the output of the first stage of the operational amplifier. This is the output of the second stage of the operational amplifier, and R2, R3, R6, and R9 are resistors.

[0029] As a further embodiment of the present invention, a 5V weak pull-up module detects the open / short circuit state of the solenoid valve when it is not in operation, including:

[0030] The output voltage of the second stage of the operational amplifier is:

[0031]

[0032] Where RL is the internal resistance of the solenoid valve, and R4 and R14 are resistors.

[0033] The beneficial effects of this invention are:

[0034] 1. The system of the present invention can simultaneously detect the open circuit and short circuit states of the solenoid valve, covering the entire scenario of "no 24V voltage" and "24V drive voltage provided", solving the problem of the single function of traditional detection circuits. By accurately collecting the voltage signals of each module, it can achieve comprehensive monitoring of the working status of the solenoid valve.

[0035] 2. The system of this invention adopts a dual protection mechanism of current detection and self-resetting fuse, and is equipped with a single-chip microcontroller module to quickly respond to commands. In case of abnormality, the power supply can be cut off immediately, which can effectively prevent the equipment from being damaged by overcurrent and short circuit, reduce the risk of safety accidents, and ensure the stable operation of the system.

[0036] 3. The system circuit structure of this invention is simple, using conventional high-precision resistors, operational amplifiers and other components, requiring no complex design and resulting in low cost; moreover, it supports the replacement of sliding rheostats to adapt to solenoid valves with different internal resistances, making debugging convenient and highly practical. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the circuit structure of the energy storage solenoid valve open / short circuit detection system of the present invention;

[0038] Figure 2 This is a schematic diagram of the open / short circuit detection system for the solenoid valve used in energy storage according to the present invention. Detailed Implementation

[0039] Embodiments of the present invention are described in detail below. Examples of these embodiments are illustrated in the accompanying drawings, wherein the same or similar symbols denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0040] This invention discloses an open / short circuit detection system for an energy storage solenoid valve, the circuit structure upon which the system relies is as follows: Figure 1 As shown, it includes:

[0041] Diode D2 is connected to a 24V power supply at one end. The other end of D2 is connected to a weak pull-up power supply module, an input voltage detection module, and one end of a resettable fuse F1. The other end of the resettable fuse F1 is connected to a voltage detection module, a current detection module, and one end of resistor R13. The other end of R13 is connected to one end of the anti-reverse diode D3, the differential voltage detection module, and the positive voltage output FIRE+ of the solenoid valve. The other end of D3 is connected to one end of resistor R14 and one end of D4 and grounded. The other end of R14 is connected to the other end of D4, the differential voltage detection module, the output control module, and the negative voltage output FIRE- of the solenoid valve.

[0042] The input voltage detection module includes a resistor R11. One end of R11 is connected to one end of capacitor C2, one end of diode ZD3 and one end of resistor R8. The other end of R11 is connected to the other end of capacitor C2 and the other end of diode ZD3 and grounded. The other end of R8 is connected between D2 and F1.

[0043] The weak pull-up power supply module includes diode D1. One end of D1 is connected between D2 and F1, and the other end of D1 is connected to one end of R4. The other end of R4 is connected to a 5V power supply.

[0044] The current detection module includes diode ZD1. One end of ZD1 is connected to one end of capacitor C3, one end of capacitor C1, and one end of resistor R5 and grounded. The other end of ZD1 is connected to the other end of capacitor C3 and one end of resistor R7. The other end of resistor R7 is connected to the other end of capacitor C1, the other end of resistor R5, and one end of diode ZD2. The other end of ZD2 is connected to port 3 of U2. Ports 1 and 2 of U2 are connected in parallel across F1.

[0045] The differential voltage detection module includes operational amplifiers U1B and U1A. Port 2 of U1B is connected to one end of R9 and one end of R2. The other end of R9 is connected to the negative voltage output FIRE- of the solenoid valve. Port 3 of U1B is connected to one end of R10 and one end of R12. The other end of R10 is connected to the positive voltage output FIRE+ of the solenoid valve. The other end of R12 is grounded. The other end of R2 is connected to port 1 of U1B, one end of ZD5, and port 5 of U1A. The other end of ZD5 is grounded. Port 4 of U1B is grounded. Port 8 of U1B is connected to the 3V3 power supply and one end of C4. The other end of C4 is grounded. Port 6 of U1A is connected to one end of R6, one end of R3, and one end of R1. The other end of R6 is grounded. The other end of R3 is connected to the other end of R1. Port 7 of U1A is connected to one end of ZD4. The other end of ZD4 is grounded.

[0046] The output control module includes transistor Q1. The emitter of Q1 is grounded, the base of Q1 is connected to one end of R18 and one end of R15, the other end of R18 is grounded, the other end of R15 is connected to port 3 of U3, the collector of Q1 is connected to the negative voltage output FIRE- of the solenoid valve, port 4 of U3 is connected to a 24V power supply, port 1 of U3 is connected to one end of R16, port 2 of U3 is connected to one end of R17, and the other end of R16 is connected to the other end of R17 and grounded.

[0047] The voltage detection module includes a resistor R20. One end of R20 is connected to one end of C5 and one end of ZD6 and grounded. The other end of R20 is connected to the other end of C5, the other end of ZD6 and one end of R19. The other end of R19 is connected between F1 and R13.

[0048] Example 1:

[0049] Based on the above circuit structure, this embodiment discloses an open / short circuit detection system for an energy storage solenoid valve, such as... Figure 2 As shown, the system includes an input voltage detection module, a current detection module, a voltage detection module, a differential voltage detection module, an output control module, and a microcontroller module.

[0050] The system includes: an input voltage detection module to detect the power supply voltage of the solenoid valve; a current detection module to detect the current when the solenoid valve is operating; a voltage detection module to detect the voltage after the self-resetting fuse; a differential voltage detection module to detect the voltage difference when the solenoid valve is in use; an output control module to control the on / off state of the solenoid valve; and a microcontroller module to collect the detection values ​​from the input voltage detection module, current detection module, voltage detection module, and differential voltage detection module, and adjust the output control module based on the detection values ​​to achieve real-time monitoring and precise control of the solenoid valve's operating status.

[0051] Specifically, the microcontroller module receives power supply voltage information from the input voltage detection module to ensure the system operates in a stable power environment; the current detection module obtains operating current data to determine whether the solenoid valve is within its normal operating load range; the voltage detection module monitors the voltage after the resettable fuse to promptly reflect whether there is overcurrent in the circuit causing the resettable fuse to trip; and the differential voltage detection module collects and processes the voltage difference between the positive and negative terminals of the solenoid valve to provide key information for analyzing the solenoid valve's conduction state and internal resistance changes.

[0052] When the system detects abnormal data, the microcontroller module can quickly drive the output control module to cut off the power supply circuit of the solenoid valve to prevent the fault from escalating.

[0053] The detection system in this embodiment can simultaneously detect the open-circuit and short-circuit states of the solenoid valve. By actively and quickly detecting these states and promptly shutting off the power supply to the equipment, it can effectively prevent equipment damage and safety accidents, ensuring the stable operation of the entire system. The detection circuit has advantages such as simple structure, rapid response, and low cost.

[0054] The input voltage detection module is used to detect the power supply voltage of the solenoid valve. The power supply voltage of the solenoid valve is 24VDC, which is input to the ADC acquisition port of the microcontroller after being divided by high-precision resistors R8 and R11.

[0055] The voltage acquisition range of the microcontroller's ADC is 0-3.3V; simply select a voltage divider resistor with an appropriate resistance value. The voltage acquired by the microcontroller's ADC is:

[0056]

[0057] When R11 = 10KΩ and R8 = 100KΩ, substituting these values ​​into the above formula yields U. GPIO1 =2.18V. When power is supplied to the solenoid valve, the microcontroller's GPIO1 can detect a voltage of 2.18V.

[0058] The current detection module is used to detect the current value when the solenoid valve is working. It is implemented through the current transformer U2, with an amplification gain of Gm=10000uA / V.

[0059] R13 is a high-precision current sampling resistor. The current transformer converts the current into voltage by measuring the voltage difference across the sampling resistor R13, and amplifies it to an appropriate factor for acquisition by the microcontroller's ADC. When the ADC value acquired by the microcontroller exceeds the normal range, the microcontroller can quickly shut off the power supply voltage to the solenoid valve.

[0060] For example, when R13 = 10mΩ, the voltage difference V across R13 is... SENSE =R13*I Load , where I Load This represents the current flowing through R13, and also the current when the load is operating. Since the current transformer's amplification gain is Gm = 10000uA / V, the output current I of the current transformer is... OUT =Gm*V SENSE。 When the amplification resistor R5 = 10kΩ, and assuming the current flowing through the load is 1.5A, the voltage U collected by the microcontroller's voltage acquisition pin GPIO3 will be... GPIO3 =I OUT *R5=1.5V.

[0061] The voltage detection module detects the voltage downstream of the resettable fuse F1. The voltage is divided by high-precision resistors R19 and R20 and then input to the microcontroller's ADC acquisition port. The microcontroller's ADC has a voltage acquisition range of 0-3.3V; therefore, appropriately sized voltage divider resistors should be selected.

[0062] The voltage acquired by the microcontroller's ADC is:

[0063]

[0064] When R19 = 10KΩ and R20 = 100KΩ, substituting these values ​​yields U. GPIO2 =2.18V. When a short circuit fault occurs in the circuit, the self-resetting fuse triggers the overcurrent / overvoltage protection mechanism. The internal polymer PTC material rapidly heats up and expands, and the resistance increases sharply to a near-open circuit state, cutting off the circuit current (i.e., "tripping"), thus achieving overload / short circuit protection. This function can be used in conjunction with a current detection module to provide a dual protection mechanism. When the microcontroller detects an abnormal state, it promptly shuts off the input power to the solenoid valve or shuts off the output of the solenoid valve through the control output module, preventing the solenoid valve from being damaged due to overcurrent.

[0065] The output control module controls the on / off state of the solenoid valve. When the solenoid valve is powered normally and all detection branches are functioning correctly, the output control module is in the open state. When the microcontroller detects a short circuit in the solenoid valve, it can promptly shut off the solenoid valve's output by controlling GPIO5. This effectively prevents equipment damage and safety accidents, ensuring the stable operation of the entire system.

[0066] The differential voltage detection module detects the voltage difference between the positive voltage FIRE+ and the negative voltage FIRE- of the solenoid valve, determining the open / short circuit state of the solenoid valve during operation. The dual operational amplifier used in this design is powered by 3.3V, with a maximum output voltage of 3.3V. With R9=R10=10kΩ and R2=R12=51kΩ, the first-stage output voltage can be calculated using the virtual short and virtual open circuit characteristics of the operational amplifier:

[0067]

[0068] When R6 = 10kΩ and R3 = 110kΩ, the output voltage of the second stage of the operational amplifier is:

[0069]

[0070] To facilitate the use of this circuit for open / short circuit detection of solenoid valves with different internal resistances, the feedback resistor R3 can be replaced with a 10MΩ sliding resistor for easier debugging.

[0071] Example 2:

[0072] Based on Embodiment 1, this embodiment discloses an open / short circuit detection system for an energy storage solenoid valve. The system also includes a 5V weak pull-up module, which is used to detect the open / short circuit state of the solenoid valve when it is not in operation.

[0073] The 5V weak pull-up module uses a 5V power supply, which is insufficient to drive the solenoid valve. However, it can detect the open or short circuit status of the solenoid valve even when no 24V voltage is supplied. When the solenoid valve is not in operation, the 5V weak pull-up module can accurately identify the open or short circuit fault of the solenoid valve through specific circuit design and calculation of the operational amplifier output voltage. This ensures that the basic status of the solenoid valve can be reliably detected before system startup or during standby, improving the comprehensiveness and safety of the entire detection system.

[0074] A 5V weak pull-up module is used, assuming the internal resistance of the solenoid valve is R. L =12Ω, when the solenoid valve is not supplied with 24V voltage, the following situations may occur:

[0075] Scenario 1: The solenoid valve is connected normally. At this time, the output voltage value of the second stage of the operational amplifier acquired by the microcontroller's ADC is:

[0076]

[0077] When R4 = R14 = 1kΩ, then U 02 =1.67V.

[0078] Case 2: Solenoid valve short-circuited, in this case: R L =0Ω, U FIRE+ =U FIRE- Through calculation, it can be concluded that: U 02 =0V;

[0079] Case 3: Solenoid valve is open-circuited. In this case: R L =infinity, U FIRE+ The value is 5V minus the forward voltage drop of the switching diode D1, the measured value is 4.4V, U FIRE- The voltage is 0V. Since the operational amplifier is powered by 3.3V, calculations show that: U 02 =3.3V;

[0080] Furthermore, when supplying a 24V drive voltage to the solenoid valve, the following situations may occur:

[0081] Scenario 4: The solenoid valve is connected normally, at this time U FIRE+ =24V, U FIRE- =0V, since the operational amplifier uses a 3.3V power supply, it can be calculated that: U 02 =3.3V; The rated current of the solenoid valve used in this embodiment is 1.53A when it is working normally. Calculations show that the acquisition voltage U of the current detection module's microcontroller is... GPIO3 =1.53V, at this time the output voltage detection module and the voltage U of the voltage detection module are... GPIO1 =U GPIO2 =2.18V. The microcontroller can determine the normal connection status of the solenoid valve by using the above detection value.

[0082] Case 5: Solenoid valve short-circuited, at this time: R L =0Ω, U FIRE+ =U FIRE- Through calculation, it can be concluded that: U 02 =0V, because the internal resistance of the resettable fuse increases sharply to a near-open circuit state, cutting off the circuit current. At this time, the microcontroller of the current detection module collects the voltage U. GPIO3 =0V, voltage U of the voltage detection module GPIO2 =0V;

[0083] Case 6: Solenoid valve is open-circuited. In this case: R L =infinity, U FIRE+ =24V, UFIRE- =0V, since the operational amplifier uses a 3.3V power supply, it can be calculated that: U 02 =3.3V, at this time the output voltage detection module and the voltage U of the voltage detection module are... GPIO1 =U GPIO2 =2.18V, the acquisition voltage U of the microcontroller in the current detection module. GPIO3 ≈0V;

[0084] By collecting the voltage values ​​of each port in the above six states, the microcontroller can determine the normal, open circuit, and short circuit states of the solenoid valve when it is powered normally; and the normal, open circuit, and short circuit states of the solenoid valve when it is not powered normally.

[0085] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0086] It should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention.

[0087] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0088] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection, an electrical connection, or a connection that allows communication between them; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0089] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

Claims

1. An electromagnetic valve open short detection system for energy storage, characterized by, Comprise: Input voltage detection module for detecting the power supply voltage of the electromagnetic valve; Current detection module for detecting the current when the electromagnetic valve is working; Voltage detection module for detecting the voltage of the post-stage of the self-restoring fuse; Differential voltage detection module for detecting the voltage difference when the electromagnetic valve is in use; Output control module for controlling the on-off of the electromagnetic valve; Single-chip microcomputer micro-control module for collecting the detection values of the input voltage detection module, current detection module, voltage detection module and differential voltage detection module, and for regulating and controlling the output control module according to the detection values.

2. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 1, characterized by Also comprise: 5V weak pull-up module for detecting the open short circuit state of the electromagnetic valve when it is not working.

3. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 1, characterized by The input voltage detection module includes high-precision resistors R8 and R11, which provide the collected voltage , is expressed as: Wherein, 24V is the power supply voltage.

4. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 1, characterized by The voltage detection module comprises high-precision resistors R19 and R20, and provides collected voltage is represented as: Wherein, 24V is the power supply voltage.

5. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 1, characterized by The current detection module includes a current transformer U2 and a high-precision current sampling resistor R13, wherein U2 measures the current of R13 and converts it into a voltage for collection , which is expressed as: Where Gm is the current transformer amplification gain, I Load is the detection current, and R5 is the amplification resistance.

6. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 1, characterized by The differential voltage detection module adopts a double-channel operational amplifier, and provides the collected voltage is expressed as: wherein FIRE+ is a positive voltage of the solenoid valve, and FIRE- is a negative voltage of the solenoid valve, is a first stage output of the operational amplifier, is a second stage output of the operational amplifier, and R2, R3, R6 and R9 are resistors.

7. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 6, characterized by The R3 adopts a 0-10MΩ sliding rheostat.

8. The short-circuit detection system for an electromagnetic valve for energy storage according to claim 2, characterized by 5V weak pull-up module for detecting the open short circuit state of the electromagnetic valve when it is not working, comprising: The second-stage output voltage value of the operational amplifier is: Wherein, RL is the internal resistance of the electromagnetic valve, and R4 and R14 are resistors.

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