An electric heating system with cold and hot air prevention function and a control method thereof

Abstract

The application discloses an electric heating system with cold and hot air prevention functions and a control method thereof. The electric heating system comprises a shell, a heating body, a cooling fan, a power supply circuit, a cold air prevention control circuit and a hot air prevention control circuit. The heating body is fixedly installed in the shell, and the cooling fan is installed at an air inlet of the shell. The heating body and the cooling fan are connected in parallel to the power supply circuit. The cold air prevention control circuit and the cooling fan are connected in series to a cooling fan power supply branch, and are used for controlling the cooling fan power supply branch to be disconnected when the temperature of the heating body is less than a set cold air prevention temperature. The hot air prevention control circuit is connected in series to the power supply circuit, and is used for controlling the power supply circuit to be disconnected when the temperature at an air outlet reaches a hot protection temperature. The electric heating system opens the fan through an internal real temperature, solves the defect that the cold air prevention effect of a conventional delay is poor, can prevent the external environment from being affected by the overheating of the air outlet temperature, controls the air outlet temperature of the electric heating system within a set range, improves the user comfort experience, and ensures the safe operation of the electric heating system.

Description

Technical Field

[0001] This invention relates to the field of air conditioning control technology, specifically to an electric heating system with anti-cold and hot air functions and its control method. Background Technology

[0002] When an air conditioning system is turned on in heating mode, if it immediately blows cold air, the low ambient temperature can cause discomfort. Therefore, it is generally designed with an anti-cold air mode. Household air conditioners typically check the coil temperature in the compressor circuit; some use software-delayed fan start. However, for purely electric heating air conditioners, there is no coil to monitor, making this heating method unsuitable. Furthermore, software delay methods are susceptible to errors in control timing due to environmental factors and equipment status, resulting in poor anti-cold air performance.

[0003] In heating mode, conventionally designed household air conditioners typically monitor the coil temperature and the air outlet temperature, sending the temperature data to the processor on the control board for analysis and processing. This is a combination of hardware and software to control the airflow to prevent overheating.

[0004] To address the aforementioned problems and phenomena, a method and device for controlling cold and overheating air using a purely hardware circuit is proposed. Summary of the Invention

[0005] This invention provides an electric heating system and its control method with anti-cold and hot air functions. The electric heating system uses a control circuit to automatically control the start and stop of the heat dissipation fan and turns on the fan based on the actual internal temperature. This solves the problem of poor anti-cold air effect achieved by conventional delay methods and prevents the external environment from being affected by overheating of the air outlet. It keeps the air outlet temperature of the electric heating system within the set range, improves the user's comfort experience, and ensures the safe operation of the electric heating system.

[0006] The present invention adopts the following specific technical solution:

[0007] First, the present invention provides an electric heating system with anti-cold and hot air functions. The electric heating system includes a shell, a heating element, a heat dissipation fan, a power supply circuit, an anti-cold air control circuit, and an anti-hot air control circuit.

[0008] The cooling fan is installed at the air inlet of the housing;

[0009] The heating element is fixedly installed inside the housing;

[0010] The heating element and the cooling fan are connected in parallel in the power supply circuit to form a power supply branch for the heating element and a power supply branch for the cooling fan.

[0011] The anti-cold air control circuit is connected in series with the cooling fan in the power supply branch of the cooling fan. It is used to control the power supply branch of the cooling fan to disconnect when the temperature of the heating element is lower than the set anti-cold air temperature, so that the cooling fan will not start without power.

[0012] The heat protection control circuit is connected in series with the power supply circuit and is used to control the power supply circuit to disconnect when the temperature at the air outlet of the housing reaches the thermal protection temperature, so as to disconnect the power supply to the heating element and the cooling fan.

[0013] Furthermore, the anti-cold air control circuit includes an NTC thermistor (Negative Temperature Coefficient thermistor), a first resistor, a second resistor, a control power supply, a first normally open relay, and a first NMOS transistor (Negative channel-Metal-Oxide-Semiconductor) mounted on the heating element.

[0014] The first normally open relay is connected in series with the cooling fan;

[0015] One end of the NTC thermistor is connected to the gate (G) of the first NMOS transistor, and the other end is connected to the source (S) of the first NMOS transistor to form a first branch and simultaneously connected to the drain (D) of the first NMOS transistor to form a second branch; the first resistor is connected in the first branch; the source (S) of the first NMOS transistor is connected to the negative terminal of the control power supply; the second branch is sequentially connected to the second resistor, the positive terminal of the control power supply, and the control circuit of the first normally open relay; the control circuit of the first normally open relay is connected between the positive terminal of the control power supply and the drain (D) of the first NMOS transistor.

[0016] When the potential difference between the NTC thermistor and the first resistor is greater than 6V, the first NMOS transistor is turned on and the first normally open relay is closed.

[0017] Furthermore, the anti-cold air control circuit includes two NTC thermistors connected in parallel.

[0018] Furthermore, the heat protection control circuit includes a PTC thermistor (Positive Temperature Coefficient thermistor) installed at the air outlet, a third resistor, a fourth resistor, a control power supply, a second normally open relay, and a second NMOS transistor.

[0019] The second normally open relay is connected in series in the power supply circuit;

[0020] One end of the PTC thermistor is connected to the gate (G) of the second NMOS transistor, and the other end is connected to the source (S) of the second NMOS transistor to form a third branch and simultaneously connected to the drain (D) of the second NMOS transistor to form a fourth branch; the third resistor is connected in the third branch; the source (S) of the second NMOS transistor is connected to the negative terminal of the control power supply; the fourth branch is sequentially connected to the fourth resistor, the positive terminal of the control power supply, and the second normally open relay; the second normally open relay is connected between the positive terminal of the control power supply and the drain (D) of the second NMOS transistor.

[0021] During heating operation, when the potential difference between the PTC thermistor and the third resistor is greater than 6V, the second NMOS transistor is turned on and the second normally open relay is closed.

[0022] Furthermore, the heat protection control circuit includes two PTC thermistors connected in parallel.

[0023] Furthermore, a contactor for controlling the on / off state of the power supply circuit is also connected in series in the power supply circuit.

[0024] Furthermore, the heating element is an electric heating element.

[0025] In addition, the present invention also provides a control method for the above-mentioned electric heating system, the control method comprising the following steps:

[0026] The control contactor connects the power supply circuit to activate the heating mode;

[0027] Compare the temperature at the air outlet with the thermal protection temperature. When the temperature at the air outlet is greater than or equal to the thermal protection temperature, disconnect the power supply circuit from the heating element and the cooling fan. When the temperature at the air outlet is less than the thermal protection temperature, connect the power supply circuit to the heating element, and the heating element will start working to heat the air.

[0028] The system compares the temperature of the heating element with the set anti-cold air temperature. When the temperature of the heating element is lower than the set temperature, the cooling fan is kept disconnected from the power supply circuit. When the temperature of the heating element is greater than or equal to the set temperature, the cooling fan is connected to the power supply circuit and the cooling fan starts working.

[0029] Furthermore, a heat protection control circuit is used to compare the temperature at the air outlet with the thermal protection temperature and control the on / off state of the power supply circuits for the heating element and the cooling fan.

[0030] Furthermore, the anti-cold air control circuit compares the temperature of the heating element with the set anti-cold air temperature and controls the on / off state of the power supply branch of the cooling fan.

[0031] Beneficial effects:

[0032] 1. The electric heating system of the present invention includes a cold air prevention control circuit and a hot air prevention control circuit, and the heating element and the cooling fan are connected in parallel in the power supply circuit. The cold air prevention control circuit and the cooling fan are connected in series in the power supply branch of the cooling fan, and are used to control the cooling fan to not start when the temperature of the heating element is lower than the set cold air prevention temperature. The hot air prevention control circuit is connected in series in the power supply circuit, and is used to control the heating element and the cooling fan to disconnect the power when the temperature at the air outlet reaches the thermal protection temperature. Both the cold air prevention control circuit and the hot air prevention control circuit are composed of physical structures. The fan is turned on by the actual internal temperature of the heating element, which solves the defect of the conventional cold air prevention effect achieved by delay control. It can also prevent the air outlet temperature from overheating and affecting the external environment, so that the air outlet temperature of the electric heating system is controlled within the set temperature range, improving the user's comfort experience. At the same time, by monitoring the air outlet temperature, thermal protection of the internal system is achieved, ensuring the safe operation of the electric heating system.

[0033] 2. The electric heating system of the present invention combines the installation and use of PTC thermistors, NTC thermistors, NMOS transistors and normally open relays to form a thermal control circuit. It automatically controls the start and stop of the heat dissipation fan according to the parameters of the thermistors, and has the characteristics of simple, accurate and reliable control circuit structure. Attached Figure Description

[0034] Figure 1 This is a three-dimensional structural diagram of one side of the electric heating system of the present invention;

[0035] Figure 2 This is a three-dimensional structural diagram of the other side of the electric heating system of the present invention;

[0036] Figure 3 This is a circuit control schematic diagram of the electric heating system of the present invention;

[0037] Figure 4 Circuit diagram for the cold air control circuit;

[0038] Figure 5 Circuit diagram for the hot air control circuit;

[0039] Figure 6 This is a flowchart of the control method of the present invention.

[0040] Among them, 1-shell, 2-heating element FH, 3-heat dissipation fan, 4-NTC thermistor, 5-PTC thermistor. Detailed Implementation

[0041] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] Example 1

[0043] like Figure 1 and Figure 2 As shown, this embodiment provides an electric heating system with anti-cold and anti-hot air functions. The electric heating system includes a housing 1, a heating element FH2, a cooling fan M3, a power supply circuit, an anti-cold air control circuit, and an anti-hot air control circuit. The housing 1 can be a cylindrical structure with open structures at both ends and a hollow channel formed inside. The hollow channel is arranged along the axial direction of the housing 1. One end of the housing 1 is an air inlet, the other end is an air outlet, and the middle part forms an air duct.

[0044] The heating element FH2 is fixedly installed inside the housing 1, that is, installed in the hollow channel of the housing 1; the heating element FH2 is an electric heating element, such as flexible electric heating materials such as carbon fiber and graphene; a cooling fan M3 is installed at the air inlet of the housing 1, and the cooling fan M3 accelerates the air flow in the air duct so that the heat generated by the heating element FH2 can be quickly exchanged.

[0045] like Figure 3 As shown, the heating element FH and the cooling fan M are connected in parallel in the power supply circuit, forming a power supply branch for the heating element and a power supply branch for the cooling fan. The power supply circuit supplies power to the heating element FH and the cooling fan M. The power supply circuit is connected between the live wire L and the neutral wire N of the AC power supply. A contactor KM1 for controlling the on / off state of the power supply circuit is installed between the live wire L and the neutral wire N. The contactor KM1 is connected in series with the second normally open relay KV2. When the contacts of the contactor KM1 and the second normally open relay KV2 are all connected, the heating element FH2 can be energized and generate heat. The heating element FH2 is connected in parallel with the cooling fan M3, and a first normally open relay KV1 is connected in series in the cooling fan power supply branch of the cooling fan M3. The cooling fan M3 can only be energized and work when the coils of the contactor KM1, the second normally open relay KV2, and the first normally open relay KV1 are all energized.

[0046] In this embodiment, the control circuits of the first normally open relay KV1 and the second normally open relay KV2 can use the same power supply, which is 24V DC.

[0047] The anti-cold air control circuit is connected in series with the cooling fan M3 in the cooling fan power supply branch. It is used to disconnect the cooling fan power supply branch when the temperature of the heating element FH2 is lower than the set anti-cold air temperature, preventing the cooling fan M3 from starting due to lack of power. Figure 3 and Figure 4 As shown, the anti-cold air control circuit includes an NTC thermistor 4 (Negative Temperature Coefficient thermistor) mounted on the heating element FH2, a first resistor R3, a second resistor R4, a control power supply, a first normally open relay KV1, and a first NMOS transistor (Negative channel-Metal-Oxide-Semiconductor) Q1, wherein:

[0048] The first normally open relay KV1 is connected in series with the cooling fan M3; one end of the NTC thermistor 4 is connected to the gate (G) of the first NMOS transistor Q1, and the other end is connected to the source (S) of the first NMOS transistor Q1 to form a first branch, and simultaneously connected to the drain (D) of the first NMOS transistor Q1 to form a second branch. The resistance of the NTC thermistor 4 decreases as the temperature increases. The source (S) of the first NMOS transistor Q1 is connected to the negative terminal of the control power supply; the first resistor R3 is connected in the first branch; the second branch is connected in sequence to the second resistor R4, the positive terminal of the control power supply, and the control circuit of the first normally open relay KV1; the control circuit of the first normally open relay KV1 is connected between the positive terminal of the control power supply and the drain (D) of the first NMOS transistor Q1; when the potential difference between the NTC thermistor 4 and the first resistor R3 is greater than 6V, the first NMOS transistor Q1 conducts, and the first normally open relay KV1 closes; the contacts of the first normally open relay KV1 are connected in series with the cooling fan M3 and in parallel with the heating element FH2 in the power supply circuit; Figure 4 As shown, the anti-cold air control circuit includes two NTC thermistors 4 connected in parallel; the two NTC thermistors 4 connected in parallel are Figure 4As the temperature rises, the resistance of the NTC thermistor 4 will decrease. Connecting two NTC thermistors 4 in parallel avoids the problem of the circuit never conducting due to resistor failure when using only a single NTC thermistor 4. R1 and R2 are installed at the gate (G) of the first NMOS transistor Q1. The first resistor R3 is a fixed resistor installed between the gate (G) and source (S) of the first NMOS transistor Q1. Through parameter design, when the potential difference between the parallel resistor R1 / / R2 and the first resistor R3 is greater than 6V, the first NMOS transistor Q1 will conduct. Furthermore, even if R1 or R2 fails, the potential difference between R1 or R2 and R3 will still be greater than 6V, ensuring that the first NMOS transistor Q1 can conduct at high temperatures during electric heating. The first normally open relay KV1 is a DC 24V power supply relay installed at the drain (D) of the first NMOS transistor Q1. When the first NMOS transistor Q1 conducts, the contacts of the first normally open relay KV1 close.

[0049] The heat protection control circuit is connected in series with the power supply circuit. It is used to disconnect the power supply circuit when the temperature at the air outlet reaches the thermal protection temperature, thus de-energizing the heating element FH2 and the cooling fan M3. Figure 3 and Figure 5 As shown, the heat protection control circuit includes a PTC thermistor 5 (Positive Temperature Coefficient thermistor) installed at the air outlet, a third resistor R7, a fourth resistor R8, a control power supply, a second normally open relay KV2, and a second NMOS transistor Q2, wherein:

[0050] The second normally open relay KV2 is connected in series in the power supply circuit; one end of the PTC thermistor 5 is connected to the gate (G) of the second NMOS transistor Q2, and the other end is connected to the source (S) of the second NMOS transistor Q2 to form a third branch, and simultaneously connected to the drain (D) of the second NMOS transistor Q2 to form a fourth branch. The resistance of the PTC thermistor 5 increases with increasing temperature; the third resistor R7 is connected in the third branch; the source (S) of the second NMOS transistor Q2 is connected to the negative terminal of the control power supply; the fourth branch is connected in sequence to the fourth resistor R8, the positive terminal of the control power supply, and the control circuit of the second normally open relay KV2; the control circuit of the second normally open relay KV2 is connected between the positive terminal of the control power supply and the drain (D) of the second NMOS transistor Q2; in heating mode, when the potential difference between the PTC thermistor 5 and the third resistor R7 is greater than 6V, the second NMOS transistor Q2 conducts, and the second normally open relay KV2 closes; the contacts of the second normally open relay KV2 are connected in the power supply circuit; the anti-heat control circuit includes two PTC thermistors 5 connected in parallel, and the two... The two PTC thermistors 5 connected in parallel are R5 and R6. As the temperature rises, the resistance of the PTC thermistors 5 will increase. Connecting two PTC thermistors 5 in parallel prevents the circuit from becoming permanently unconductable if one of them fails. R5 and R6 are installed at the gate (G) of the second NMOS transistor Q2. The third resistor R7 is a fixed resistor installed between the gate (G) and source (S) of the second NMOS transistor Q2. Through parameter design, when the set high temperature is not reached, the parallel resistance of R5 and R6 is "R5 / / R6". The potential difference between resistor 6” and the third resistor R7 is greater than 6V, keeping the second NMOS transistor Q2 on. If either R5 or R6 of the two PTC thermistors 5 fails, the potential difference between R5 or R6 and the third resistor R7 will still be greater than 6V, ensuring that the second NMOS transistor Q2 can conduct when the electric heating is not at a high temperature. The second normally open relay KV2 is a 24V power supply relay installed at the drain of the second NMOS transistor Q2. When the second NMOS transistor Q2 is on, the contacts of the second normally open relay KV2 close.

[0051] The two NTC thermistors 4 are mounted on the heating element FH2, and the two PTC thermistors 5 are mounted at the air outlet of the housing 1. The heating element FH2 and the air outlet are structurally designed to accommodate the thermistors and power supply wiring. Figure 1 , 2 The heating element structure, air outlet structure, and the entire air duct structure are shown; the rest... Figure 4 and Figure 5 The electronic components are installed in the control box outside the housing 1.

[0052] The aforementioned electric heating system incorporates a cold air prevention control circuit and a hot air prevention control circuit in its power supply circuit. When the temperature of the heating element FH2 is lower than the set cold air prevention temperature, the cold air prevention control circuit cuts off the power to the cooling fan M3 to prevent it from blowing out cold air and causing discomfort. When the temperature at the air outlet reaches the thermal protection temperature, the hot air prevention control circuit cuts off the power to both the heating element FH2 and the cooling fan M3 to prevent FH2 from continuing to heat up and to prevent excessively hot air from being blown out. Simultaneously, it controls the cooling fan M3 to continue rotating to prevent overheated air from being blown out. Both the cold air prevention control circuit and the hot air prevention control circuit are composed of electronic components and other physical structures. By activating the fan based on the actual internal temperature of the heating element FH2, they overcome the shortcomings of conventional cold air prevention methods that rely on time delays. This also prevents the air outlet temperature from overheating and affecting the external environment, keeping the electric heating system's outlet temperature within the set range and improving user comfort. Furthermore, by monitoring the outlet temperature, they provide thermal protection for the internal system, ensuring the safe operation of the electric heating system.

[0053] The above-mentioned electric heating system, combined with the installation and use of PTC thermistor 5, NTC thermistor 4, NMOS transistor, first normally open relay KV1, second normally open relay KV2 and contactor KM1, constitutes a low-voltage control circuit for high-voltage thermal control. It automatically controls the start and stop of the cooling fan M3 to provide heating based on the parameters of the thermistor, and has the characteristics of simple, accurate and reliable control circuit structure.

[0054] Example 2

[0055] This embodiment provides a control method for the above-mentioned electric heating system, such as... Figure 6 As shown, the control method includes the following steps:

[0056] The control contactor KM1 connects the power supply circuit to start the heating mode; the contactor KM1 controls the on and off of the power supply, thereby controlling whether the heating element FH2 and the cooling fan M3 work.

[0057] The system compares the temperature at the air outlet with the thermal protection temperature. When the temperature at the air outlet is greater than or equal to the thermal protection temperature, the power supply circuit is disconnected from the heating element FH2 and the cooling fan M3. When the temperature at the air outlet is less than the thermal protection temperature, the power supply circuit is connected to the heating element FH2, and the heating element FH2 starts working to heat the air. A heat protection control circuit compares the temperature at the air outlet with the thermal protection temperature and controls the on / off state of the power supply circuit. Specifically, the PTC thermistor 5 at the air outlet determines the air outlet temperature. When the temperature has not reached the overheat protection value, the PTC thermistor 5... When the control circuit containing the PTC thermistor 5 is activated, the second normally open relay KV2 it controls is energized, and its normally open contact closes, thus powering the heating element FH2. When the temperature is too high and reaches the overheat protection value, the low-voltage control circuit containing the PTC thermistor 5 is cut off, the second normally open relay KV2 it controls is de-energized, and its normally open contact opens, de-energizing the heating element FH2. The cooling fan M3 cannot start, preventing hot air from being blown out due to overheating. Because it is de-energized and no longer heats, the PTC thermistor 5 will gradually return to normal temperature. At this time, the temperature is not high, and the power supply control of the circuit with low temperature will be executed again.

[0058] The temperature of the heating element FH2 is compared with the set anti-cold air temperature. When the temperature of the heating element FH2 is lower than the set anti-cold air temperature, the cooling fan M3 remains disconnected from the power supply circuit. When the temperature of the heating element FH2 is greater than or equal to the set anti-cold air temperature, the cooling fan M3 is connected to the power supply circuit and the cooling fan M3 starts working. An anti-cold air control circuit compares the temperature of the heating element FH2 with the set anti-cold air temperature and controls the connection and disconnection of the cooling fan M3 from the power supply circuit. The specific control principle is as follows: when the electric heating is turned on, the NTC thermistor 4 where the heating element FH2 is located will determine... When the temperature of the heating element FH2 is low and has not reached the set anti-cold air temperature, the low-voltage control circuit of the NTC thermistor 4 is not turned on, the first normally open relay KV1 controlled by it is not energized, the normally open contact remains open, and the cooling fan M3 is not powered, thus realizing the anti-cold air function; when the temperature of the heating element FH2 reaches the set anti-cold air temperature, the low-voltage control circuit of the NTC thermistor 4 is turned on, the first normally open relay KV1 controlled by it is energized, the normally open contact closes, and the cooling fan M3 is powered, blowing hot air out from the air outlet.

[0059] Obviously, those skilled in the art can make various modifications and variations to the embodiments of the present invention without departing from the spirit and scope of the invention. Therefore, if these modifications and variations fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations.

Claims

1. An electric heating system with anti-cold and hot air functions, characterized in that, It includes the casing, heating element, cooling fan, power supply circuit, cold air protection control circuit, and hot air protection control circuit; The cooling fan is installed at the air inlet of the housing; The heating element is fixedly installed inside the housing; The heating element and the cooling fan are connected in parallel in the power supply circuit to form a power supply branch for the heating element and a power supply branch for the cooling fan. The anti-cold air control circuit includes an NTC thermistor, a first resistor, a second resistor, a control power supply, a first normally open relay, and a first NMOS transistor, all mounted on the heating element. The first normally open relay is connected in series with the cooling fan in the power supply branch of the cooling fan. One end of the NTC thermistor is connected to the gate (G) of the first NMOS transistor, and the other end is connected to the source (S) of the first NMOS transistor to form a first branch and simultaneously connected to the drain (D) of the first NMOS transistor to form a second branch. The first resistor is connected in the first branch. The source (S) of the first NMOS transistor is connected to the negative terminal of the control power supply. The second branch sequentially connects the second resistor, the positive terminal of the control power supply, and the control circuit of the first normally open relay. The control circuit of the first normally open relay is connected between the positive terminal of the control power supply and the drain (D) of the first NMOS transistor. The heat protection control circuit includes a PTC thermistor, a third resistor, a fourth resistor, a control power supply, a second normally open relay, and a second NMOS transistor, all installed at the air outlet. The second normally open relay is connected in series in the power supply circuit. One end of the PTC thermistor is connected to the gate (G) of the second NMOS transistor, and the other end is connected to the source (S) of the second NMOS transistor to form a third branch and simultaneously connected to the drain (D) of the second NMOS transistor to form a fourth branch. The third resistor is connected in the third branch. The source (S) of the second NMOS transistor is connected to the negative terminal of the control power supply. The fourth branch sequentially connects the fourth resistor, the positive terminal of the control power supply, and the control circuit of the second normally open relay. The control circuit of the second normally open relay is connected between the positive terminal of the control power supply and the drain (D) of the second NMOS transistor. The anti-cold air control circuit is configured such that when the temperature of the heating element is lower than the set anti-cold air temperature, the potential difference between the NTC thermistor and the first resistor is less than the conduction threshold voltage of the first NMOS transistor, the first NMOS transistor is turned off, the first normally open relay remains open, and the power supply branch of the cooling fan is disconnected, so that the cooling fan does not start due to lack of power; when the temperature of the heating element is greater than or equal to the set anti-cold air temperature, the potential difference between the NTC thermistor and the first resistor is greater than or equal to the conduction threshold voltage, the first NMOS transistor is turned on, the first normally open relay is closed, and the power supply branch of the cooling fan is connected. The heat protection control circuit is configured such that when the temperature at the air outlet is lower than the thermal protection temperature, the potential difference between the PTC thermistor and the third resistor is greater than or equal to the conduction threshold voltage of the second NMOS transistor, the second NMOS transistor is turned on, the second normally open relay remains closed, and the power supply circuit is connected; when the temperature at the air outlet reaches the thermal protection temperature, the potential difference between the PTC thermistor and the third resistor is less than the conduction threshold voltage, the second NMOS transistor is turned off, the second normally open relay is turned off, and the power supply circuit is disconnected, thereby de-energizing the heating element and the cooling fan.

2. The electric heating system as described in claim 1, characterized in that, The anti-cold air control circuit includes two NTC thermistors connected in parallel.

3. The electric heating system as described in claim 2, characterized in that, The heat protection control circuit includes two PTC thermistors connected in parallel.

4. The electric heating system as described in claim 3, characterized in that, The power supply circuit also includes a contactor connected in series to control the on / off state of the power supply circuit.

5. The electric heating system according to any one of claims 1-4, characterized in that, The heating element is an electric heating element.

6. A control method for an electric heating system as described in any one of claims 1-5, characterized in that, Includes the following steps: The control contactor connects the power supply circuit to activate the heating mode; The heat protection control circuit compares the temperature at the air outlet with the thermal protection temperature. When the temperature at the air outlet is greater than or equal to the thermal protection temperature, the potential difference between the PTC thermistor and the third resistor is less than the conduction threshold voltage of the second NMOS transistor. The second NMOS transistor is turned off, the second normally open relay is turned off, and the power supply circuit is disconnected from the heating element and the cooling fan. When the temperature at the air outlet is lower than the thermal protection temperature, the potential difference between the PTC thermistor and the third resistor is greater than or equal to the conduction threshold voltage, the second NMOS transistor is turned on, the second normally open relay is closed, the power supply circuit is connected to the heating element, and the heating element starts to work to heat. The anti-cold air control circuit compares the temperature of the heating element with the set anti-cold air temperature. When the temperature of the heating element is lower than the set anti-cold air temperature, the potential difference between the NTC thermistor and the first resistor is less than the conduction threshold voltage of the first NMOS transistor, so the first NMOS transistor is turned off, the first normally open relay remains open, and the cooling fan remains disconnected from the power supply circuit. When the temperature of the heating element is greater than or equal to the set anti-cold air temperature, the potential difference between the NTC thermistor and the first resistor is greater than or equal to the conduction threshold voltage, the first NMOS transistor is turned on, the first normally open relay is closed, the cooling fan is connected to the power supply circuit, and the cooling fan starts working.

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