Charging circuit and control method thereof, and electrical appliance

Abstract

This invention discloses a charging circuit and its control method and electrical appliance. The charging circuit includes a rectifier bridge, with its input terminal connected to an AC power supply and its output terminal connected to both sides of a bus capacitor. It also includes a protection circuit connected in series between the input terminal of the rectifier bridge and the AC power supply. The protection circuit includes at least one current-limiting element, which limits the negative half-cycle input of the AC power supply to achieve current limiting. Compared with the prior art, this invention uses a PTC resistor and a diode connected in series in the charging circuit, halving the current through the PTC resistor, reducing heat generation in the PTC resistor, and avoiding the problem of the PTC resistor exploding due to inrush current. Furthermore, this invention can determine the moment when the AC power supply reaches its peak voltage and can shut off the relay at that moment, preventing damage to the circuit caused by a large reverse current.

Description

Technical Field

[0001] This invention relates to a charging circuit for a frequency converter driver, and more particularly to a charging circuit and its control method and electrical components. Background Technology

[0002] Currently, most inverter drives use cement resistors in their charging protection circuits to prevent excessive inrush current. However, cement resistors can crack at high temperatures. PTC resistors, on the other hand, exhibit a very slow resistance change with temperature before reaching a certain threshold, but their resistance rises sharply above that temperature. In the event of a large short-circuit current, the PTC resistor's temperature rises rapidly, disconnecting the circuit and providing protection. Once the circuit returns to normal, the PTC resistor's impedance recovers, allowing it to be used again. Therefore, PTC resistors are used to replace cement resistors. However, when a PTC resistor is connected in series in the charging circuit, the continuous current flow causes it to heat up quickly, resulting in a sudden change in resistance that breaks the charging circuit, rendering the inverter drive malfunction.

[0003] Therefore, how to design a charging circuit and its control method and electrical appliances that can reduce the heat generation of PTC resistors is a technical problem that the industry urgently needs to solve. Summary of the Invention

[0004] In view of the problem that in the prior art, when a PTC resistor is connected in series in the charging circuit, the resistance value may suddenly change and disconnect the charging circuit, the present invention proposes a charging circuit and its control method and electrical appliances.

[0005] The technical solution of the present invention is to propose a charging circuit, including a rectifier bridge, wherein the input terminal of the rectifier bridge is connected to an AC power supply and the output terminal is connected to both sides of a bus capacitor. The circuit also includes a protection circuit connected in series between the input terminal of the rectifier bridge and the AC power supply. The protection circuit includes at least one current limiting element, and the current limiting element can limit the negative half-cycle input of the AC power supply to achieve the current limiting effect.

[0006] Furthermore, it also includes a peak detection circuit connected to the bus capacitor, a control circuit for controlling the on / off state of the protection circuit, and a main control unit connecting the peak detection circuit and the control circuit. The peak detection circuit can be used to detect when the AC power supply is at its peak voltage and feed it back to the main control unit. When the AC power supply is at its peak voltage, the main control unit controls the protection circuit to turn off through the control circuit.

[0007] Furthermore, the current limiting element includes at least one PTC resistor and a diode D1 connected in series with the PTC resistor, wherein the positive terminal of the diode D1 is arranged facing the live wire of the AC power supply and the negative terminal is arranged facing the input terminal of the rectifier bridge.

[0008] Furthermore, the control circuit includes a relay K1, the control terminal of which is connected to the main control unit, and the controlled terminal of which is connected in parallel to both sides of the protection circuit.

[0009] Furthermore, the charging circuit also includes a sampling circuit connected to both ends of the bus capacitor, the sampling circuit including resistor R1 and resistor R2; The resistors R1 and R2 are connected in series and then in parallel to the two ends of the bus capacitor. The input terminal of the peak detection circuit is connected between the resistors R1 and R2.

[0010] Furthermore, the peak detection circuit includes: voltage follower U1, voltage follower U2, resistor R3, resistor R4, resistor R5, resistor R6, capacitor C1, transistor Q1, and diode D2; The non-inverting input of the voltage follower U1 is connected between resistors R1 and R2 as the input of the peak detection circuit. The inverting input is connected to the output of the voltage follower U1. The output is connected to the positive terminal of diode D2 after series with resistor R4. The negative terminal of diode D2 is connected to the non-inverting input of voltage follower U2. The output of voltage follower U2 is connected to the main control unit. The inverting input is connected to the output of voltage follower U2. One end of capacitor C1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2, and the other end is grounded. The collector of transistor Q1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2 after series with resistor R5. The base is connected to the main control unit after series with resistor R6, and the emitter is grounded. One end of resistor R3 is connected to the non-inverting input of comparator U2, and the other end is grounded.

[0011] This invention also proposes a control method for a charging circuit, comprising: During the power-on phase, the input voltage of the AC power supply is detected, and it is determined whether the input voltage is greater than the charging threshold voltage. If so, the peak detection circuit determines the moment when the AC power supply is at its peak voltage, and the protection circuit is turned off when the AC power supply is at its peak voltage. Otherwise, the protection circuit will be activated to suppress the input current of the AC power supply.

[0012] Furthermore, before determining the moment when the AC power supply reaches its peak voltage through the peak detection circuit, it is also necessary to determine the maximum voltage corresponding to the peak voltage in the peak detection circuit, including: Set a peak voltage threshold and detect the voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit; Determine whether the voltage magnitude of the feedback signal is greater than the peak voltage threshold. If so, set the peak voltage threshold to equal the voltage of the feedback signal, re-detect the voltage magnitude of the feedback signal, and reset the detection count to zero. If not, record the number of detections, and stop detection when the number of detections reaches a preset number, setting the current peak voltage threshold to the maximum voltage of the AC power supply.

[0013] Furthermore, after determining the maximum voltage of the peak detection circuit, the method further includes: The main control unit sends a high-level signal to transistor Q1 to discharge capacitor C1; Determine whether the magnitude of the feedback voltage is equal to zero. If so, start detecting the moment when the AC power supply is at its peak voltage. If not, the main control unit continues to send a high-level signal to transistor Q1 and re-detects the magnitude of the feedback voltage.

[0014] Furthermore, the peak voltage moment of the AC power supply is determined by the peak detection circuit, and the protection circuit is shut off when the AC power supply reaches the peak voltage, including: The voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit is detected; When the voltage of the feedback signal reaches the current peak voltage threshold, the main control unit sends a high-level signal to the control terminal of relay K1 to shut down the protection circuit.

[0015] The present invention also proposes an electrical appliance having a frequency converter driver, wherein the frequency converter driver employs the above-described charging circuit.

[0016] Furthermore, the electrical appliance is an air conditioner.

[0017] Compared with the prior art, the present invention has at least the following beneficial effects: This invention connects a PTC resistor and a diode in series in the charging circuit, which halves the current through the PTC resistor, reduces the heat generated by the PTC resistor, and avoids the problem of the PTC resistor exploding due to surge current. In addition, this invention can also determine the moment when the AC power supply is at its peak voltage and can turn off the relay at the moment of peak voltage to avoid damage to the circuit caused by large reverse current. Attached Figure Description

[0018] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the overall connection of the charging circuit of the present invention; Figure 2 This is a flowchart illustrating the overall control process of the charging circuit of the present invention. Detailed Implementation

[0020] To make the technical problems, solutions, and beneficial effects of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0021] Therefore, a feature pointed out in this specification is used to describe one feature of one embodiment of the invention, and does not imply that every embodiment of the invention must have the described feature. Furthermore, it should be noted that this specification describes many features. Although certain features may be combined to illustrate possible system designs, these features may also be used in other combinations not explicitly stated. Therefore, unless otherwise stated, the described combinations are not intended to be limiting.

[0022] The principles and structure of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0023] PTC resistors (positive temperature coefficient thermistors) can replace cement resistors due to their temperature characteristics. However, when a PTC resistor is connected in series in a charging circuit, the current continuously flows through it, causing its temperature to rise rapidly. This sudden change in resistance can break the charging circuit, preventing the inverter driver from functioning properly. The solution of this invention is to connect the PTC resistor in series with a diode, thereby avoiding the negative half-cycle current input of the AC power supply, reducing the current by half, and thus preventing the problem of excessive current on the PTC causing the charging circuit to break.

[0024] Specifically, the charging circuit proposed in this invention includes a rectifier bridge, whose input terminal is connected to an AC power source and whose output terminal is connected to both sides of a bus capacitor. This rectifier bridge rectifies the AC power output from the AC power source, converting it into DC power to supply the bus capacitor. A protection circuit is provided between the input terminal of the rectifier bridge and the AC power source. This protection circuit includes at least one current-limiting element, which limits the negative half-cycle input of the AC power source, thereby reducing the current by at least half to achieve the current-limiting effect.

[0025] The current-limiting element includes at least one PTC resistor for current limiting and a diode D1 connected in series with the PTC resistor. The anode of the diode D1 is positioned towards the live wire of the AC power supply, and the cathode is positioned towards the input terminal of the rectifier bridge. The protection circuit consists of at least one of these current-limiting elements. Please refer to [link to relevant documentation]. Figure 1The protection circuit consists of a set of current-limiting components, specifically including two PTC resistors connected in series (resistors PTC1 and PTC2, respectively), and a diode D1 connected in series with the two PTC resistors. Due to the reverse cutoff characteristic of the diode, when the AC power supply is in the positive half-cycle current input, the current output by the AC power supply enters from the positive terminal of diode D1 and exits from the negative terminal of diode D1, which allows it to work normally. When the AC power supply is in the negative half-cycle current input, the current output by the AC power supply enters from the negative terminal of diode D1 and exits from the positive terminal of diode D1. At this time, diode D1 acts as a reverse cutoff, thereby suppressing the current input in this part and achieving the current-limiting effect.

[0026] By employing the above-described configuration, this invention can convert AC power input into AC power with only a positive half-cycle, thereby reducing the current flowing through the PTC resistor by half and reducing the heat generated by the PTC resistor. In other embodiments of this invention, multiple current-limiting elements can be connected in series, or the diode D1 can be replaced with other switching elements with reverse cutoff to achieve the same control effect.

[0027] Since the charging circuit suppresses the current input of the AC power supply, it will waste the electrical energy under normal operation of the charging circuit. Therefore, a control circuit is required to control the shutdown of the protection circuit to avoid the waste of electrical energy. The protection circuit is shut down by short-circuiting the protection circuit (if the protection circuit is open-circuited, the current input of the AC power supply will not be able to be output, and the circuit will not work).

[0028] In this invention, an X capacitor is connected across the two ends of the AC power supply for filtering. This X capacitor stores voltage during the charging circuit's operation. If the control circuit closes during the negative half-cycle of the AC power supply, the voltage stored in the X capacitor will create a voltage drop with the live wire, generating a large reverse current that can damage the circuit. Since the voltage stored in the X capacitor is necessarily less than the peak voltage of the AC power supply, the control and protection circuit of this invention shuts off when the AC power supply reaches its peak voltage, effectively preventing the generation of reverse current. Therefore, this invention also includes at least a peak voltage detection circuit and a main control unit connecting the peak voltage detection circuit and the control circuit. The peak voltage detection circuit can detect when the AC power supply reaches its peak voltage and feed this information back to the main control unit. The main control unit can then control the protection circuit to shut off when the AC power supply reaches its peak voltage to prevent the generation of a large reverse current.

[0029] Please see Figure 1The control circuit includes relay K1, whose control terminal is connected to the main control unit, and its controlled terminal is connected in parallel across the protection circuit. When the controlled terminal of relay K1 is closed, the current output from the AC power supply is transmitted to the rectifier bridge through the controlled terminal of relay K1, causing a short circuit in the protection circuit. The operation of relay K1 is controlled by the main control unit. When the main control unit sends a high-level signal, the control terminal of relay K1 is energized, thereby controlling the controlled terminal to close.

[0030] Please see Figure 1 In order to obtain the voltage signal output by the AC power supply, the present invention also provides a sampling circuit, which includes resistor R1 and resistor R2. Among them, resistors R1 and R2 are connected in series and then in parallel to the two ends of the bus capacitor. The input terminal of the peak detection circuit is connected between resistors R1 and R2 for power supply.

[0031] Due to the series voltage division, this invention, through this design, can obtain a voltage input proportional to the input voltage of the AC power supply, and can make the maximum output voltage of the peak detection circuit correspond to the peak voltage, which can be used to detect when the AC power supply is at its peak voltage. In addition, the voltage input to the peak detection circuit can be adjusted by setting an appropriate ratio of resistors R1 and R2 to adapt to the operating voltage of the peak detection circuit.

[0032] Furthermore, the peak detection circuit includes: voltage follower U1, voltage follower U2, resistor R3, resistor R4, resistor R5, resistor R6, capacitor C1, transistor Q1, and diode D2. The non-inverting input of voltage follower U1 is connected between resistors R1 and R2 as the input of the peak detection circuit. The inverting input is connected to the output of voltage follower U1. The output is connected to the positive terminal of diode D2 after series with resistor R4. The negative terminal of diode D2 is connected to the non-inverting input of voltage follower U2. The output of voltage follower U2 is connected to the main control unit. The inverting input is connected to the output of voltage follower U2. One end of capacitor C1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2, and the other end is grounded. The collector of transistor Q1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2 after series with resistor R5. The base is connected to the main control unit after series with resistor R6. The emitter is grounded. One end of resistor R3 is connected to the non-inverting input of comparator U2, and the other end is grounded.

[0033] The peak detection principle is as follows: Voltage follower U1 is connected between resistors R1 and R2 to obtain voltage input and outputs a voltage signal proportional to the output voltage of the AC power supply to capacitor C1 (this proportion is determined by resistors R1 and R2). Capacitor C1 begins charging. When the voltage on capacitor C1 reaches a value proportional to the peak voltage of the AC power supply, capacitor C1 stops charging and stores this voltage value. At this time, the voltage at the non-inverting input of voltage follower U2 is equal to the voltage on capacitor C1, that is, the voltage V1 output to the main control unit is equal to the voltage on capacitor C1, which is the maximum voltage proportional to the peak voltage. In this way, the maximum voltage of the peak detection circuit can be determined. Then, the main control unit sends a high-level signal to transistor Q1, causing transistor Q1 to conduct and discharge capacitor C1. After capacitor C1 has discharged completely, transistor Q1 is disconnected again and the output voltage of the voltage follower is detected. When the voltage V1 output by the peak detection circuit to the main control unit reaches the maximum voltage again, the input voltage of the AC power supply is also at the peak voltage. The moment when the AC power supply is at the peak voltage can be determined. At this moment, the main control unit can send a high-level signal to the control terminal of relay K1 to shut down the protection circuit and avoid the generation of reverse current.

[0034] The present invention also proposes a control method for a charging circuit, which includes: During the power-on phase, the input voltage of the AC power supply is detected to determine whether the charging voltage is greater than the charging threshold voltage. If so, the peak detection circuit determines the moment when the AC power supply is at its peak voltage, and the protection circuit is turned off when the AC power supply is at its peak voltage. Otherwise, the protection circuit will be activated to suppress the input current of the AC power supply.

[0035] Before determining the moment when the AC power supply reaches its peak voltage using the peak detection circuit, it is also necessary to determine the maximum voltage corresponding to the peak voltage in the peak detection circuit, which includes: Set the peak voltage threshold and detect the voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit; Determine whether the voltage magnitude of the feedback signal is greater than the peak voltage threshold. If so, set the peak voltage threshold to equal the voltage of the feedback signal, re-detect the voltage magnitude of the feedback signal, and reset the detection count to zero. If not, record the number of detections, and stop detection when the number of detections reaches the preset number, and record the current peak voltage threshold.

[0036] Please see Figure 1 and Figure 2 The feedback signal of the peak detection circuit is Figure 1The voltage V1 in the circuit increases as capacitor C1 charges. If the initial peak voltage threshold is set to zero, the peak voltage threshold can be continuously updated through the above control. When the peak voltage threshold reaches the maximum voltage of the peak detection circuit, the update stops and the current peak voltage threshold is recorded. At this time, the peak voltage threshold is the maximum voltage corresponding to the peak voltage of the peak detection circuit and the peak voltage of the AC power supply.

[0037] Because multiple detections and comparisons were used to record the peak voltage threshold, although the voltage V1 of the feedback signal has reached its maximum, it cannot be used to determine when the AC power supply is at its peak voltage. Therefore, after recording the peak voltage threshold, it is necessary to re-detect when the AC power supply is at its peak voltage. At this time, capacitor C1 needs to be discharged first, which specifically includes: The main control unit sends a high-level signal to transistor Q1 to discharge capacitor C1; Determine if the voltage of the feedback signal is equal to zero. If so, start detecting when the AC power supply is at its peak voltage. If not, the main control unit continues to send a high-level signal to transistor Q1 and re-detects the voltage magnitude of the feedback signal.

[0038] After capacitor C1 has discharged, the feedback signal voltage V1 is zero. Since transistor Q1 is conducting, the voltage V1 increases as the input voltage of the AC power supply increases. When the voltage V1 reaches the currently set peak voltage threshold, the input voltage of the AC power supply also reaches its peak voltage. This can be used to determine when the AC power supply is at its peak voltage, so as to shut down the protection circuit. The specific steps include: The voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit; When the voltage of the feedback signal reaches the current peak voltage threshold, the main control unit sends a high-level signal to the control terminal of relay K1 to shut down the protection circuit.

[0039] Please see Figure 2 Vcharge represents the charging threshold voltage. During the power-on phase, if the bus voltage is greater than this voltage, it indicates that the bus capacitor has completed charging. Relay K1 needs to be closed to turn off the protection circuit to avoid wasting electrical energy. Conversely, if the bus capacitor voltage is less than the charging voltage threshold, it indicates that the bus capacitor is in the charging phase. Relay K1 needs to be opened to turn on the protection circuit and suppress the charging current.

[0040] The bus voltage is the voltage on the bus capacitor. Once this voltage is determined to be greater than the charging voltage threshold, it is also necessary to determine whether relay K1 has been closed. If relay K1 is not closed, it is necessary to determine the moment when the AC power supply is at its peak voltage and close relay K1 at that moment to avoid the generation of reverse current. Figure 2 The `Stage` parameter determines whether it's the first or second detection stage. The first detection stage determines the peak voltage threshold, while the second detection stage determines when the AC power supply reaches its peak voltage. Initially, if `Stage` is set to 0, it will first perform the peak voltage threshold determination. Figure 1 Vmax represents the charging voltage threshold, and Cnt represents the number of detections. By detecting the magnitude of voltage V1 and continuously updating the peak voltage threshold, the peak voltage threshold can be determined and recorded as the maximum voltage of the peak detection circuit. After completing this step, capacitor C1 is discharged and Stage=1 is set to enter the second detection stage.

[0041] In the second detection stage, by detecting the magnitude of voltage V1, and when voltage V1 reaches the currently recorded peak voltage threshold, it can be determined that the AC power supply is at its peak voltage. At this time, relay K1 is turned off to shut down the protection circuit, and the peak voltage threshold is set to 0, Stage=0, to restore the initial state.

[0042] The present invention employs the above-mentioned control method, which can determine the moment when the AC power supply is at its peak voltage and can turn off the relay at the moment when the AC power supply is at its peak voltage, thereby avoiding damage to the circuit caused by the generation of large reverse current.

[0043] The present invention also proposes an electrical appliance having a frequency converter driver, wherein the frequency converter driver employs the above-described charging circuit.

[0044] Furthermore, the aforementioned appliance is an air conditioner.

[0045] Compared with the prior art, the present invention connects the charging circuit by connecting the PTC resistor and the diode in series, which halves the current through the PTC resistor, reduces the heat generation of the PTC resistor, and avoids the problem of the PTC resistor exploding due to surge current. In addition, the present invention can also determine the moment when the AC power supply is at its peak voltage and can turn off the relay at the moment when the peak voltage is reached, avoiding damage to the circuit caused by the large reverse current.

[0046] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A charging circuit, comprising a rectifier bridge, wherein the input terminal of the rectifier bridge is connected to an AC power source and the output terminal is connected to both sides of a bus capacitor, characterized in that, It also includes a protection circuit connected in series between the input terminal of the rectifier bridge and the AC power supply. The protection circuit includes at least one current limiting element, and the current limiting element can limit the negative half-cycle input of the AC power supply to achieve the current limiting effect. It also includes a peak detection circuit connected to the bus capacitor, a control circuit for controlling the on / off state of the protection circuit, and a main control unit connecting the peak detection circuit and the control circuit. The peak detection circuit can be used to detect when the AC power supply is at its peak voltage and feed it back to the main control unit. When the AC power supply is at its peak voltage, the main control unit controls the protection circuit to turn off through the control circuit. The charging circuit also includes a sampling circuit connected to both ends of the bus capacitor, and the sampling circuit includes resistors R1 and R2. The resistors R1 and R2 are connected in series and then in parallel to the two ends of the bus capacitor. The input terminal of the peak detection circuit is connected between the resistors R1 and R2. The peak detection circuit includes: voltage follower U1, voltage follower U2, resistor R3, resistor R4, resistor R5, resistor R6, capacitor C1, transistor Q1, and diode D2. The non-inverting input of voltage follower U1 is connected between resistors R1 and R2 as the input of the peak detection circuit. The inverting input is connected to the output of voltage follower U1. The output is connected to the positive terminal of diode D2 after series with resistor R4. The negative terminal of diode D2 is connected to the non-inverting input of voltage follower U2. The output of voltage follower U2 is connected to the main control unit. The inverting input is connected to the output of voltage follower U2. One end of capacitor C1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2, and the other end is grounded. The collector of transistor Q1 is connected between the negative terminal of diode D2 and the non-inverting input of voltage follower U2 after series with resistor R5. The base is connected to the main control unit after series with resistor R6, and the emitter is grounded. One end of resistor R3 is connected to the non-inverting input of voltage follower U1, and the other end is grounded.

2. The charging circuit according to claim 1, characterized in that, The current limiting element includes at least one PTC resistor and a diode D1 connected in series with the PTC resistor, wherein the positive terminal of the diode D1 is arranged facing the live wire of the AC power supply and the negative terminal is arranged facing the input terminal of the rectifier bridge.

3. The charging circuit according to claim 1, characterized in that, The control circuit includes a relay K1, the control terminal of which is connected to the main control unit, and the controlled terminal of which is connected in parallel to both sides of the protection circuit.

4. A control method employing the charging circuit as described in claim 3, characterized in that, include: During the power-on phase, the input voltage of the AC power supply is detected, and it is determined whether the input voltage is greater than the charging threshold voltage. If so, the peak detection circuit determines the moment when the AC power supply is at its peak voltage, and the protection circuit is turned off when the AC power supply is at its peak voltage. Otherwise, the protection circuit will be activated to suppress the input current of the AC power supply.

5. The control method according to claim 4, characterized in that, Before determining the moment when the AC power supply is at its peak voltage using the peak detection circuit, it is also necessary to determine the maximum voltage corresponding to the peak voltage in the peak detection circuit, including: Set a peak voltage threshold and detect the voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit; Determine whether the voltage magnitude of the feedback signal is greater than the peak voltage threshold. If so, set the peak voltage threshold to equal the voltage of the feedback signal, re-detect the voltage magnitude of the feedback signal, and reset the detection count to zero. If not, record the number of detections, and stop detection when the number of detections reaches a preset number, setting the current peak voltage threshold to the maximum voltage of the AC power supply.

6. The control method according to claim 5, characterized in that, After determining the maximum voltage of the peak detection circuit, the method further includes: The main control unit sends a high-level signal to transistor Q1 to discharge capacitor C1; Determine whether the voltage magnitude of the feedback signal is equal to zero. If so, start detecting the moment when the AC power supply is at its peak voltage. If not, the main control unit continues to send a high-level signal to transistor Q1 and re-detects the voltage magnitude of the feedback signal.

7. The control method according to claim 5, characterized in that, Determining the moment when the AC power supply reaches its peak voltage using a peak detection circuit, and shutting off the protection circuit when the AC power supply reaches its peak voltage, includes: The voltage magnitude of the feedback signal transmitted from the peak detection circuit to the main control unit is detected; When the voltage of the feedback signal reaches the current peak voltage threshold, the main control unit sends a high-level signal to the control terminal of relay K1 to shut down the protection circuit.

8. An electrical appliance, said electrical appliance having a frequency converter driver, characterized in that, The frequency converter driver has a charging circuit as described in any one of claims 1 to 3.

9. The electrical appliance according to claim 8, characterized in that, The appliance in question is an air conditioner.

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