Control circuit, control method and variable frequency controller

Abstract

The embodiment of the invention provides a control circuit, a control method and a variable frequency controller. The control circuit comprises a rectifying unit, a filtering unit, a filtering control unit, a boosting unit, an energy storage unit, a discharging control unit and a main control unit. At least part of filtering devices of the filtering unit are connected in series with the filtering control unit; the filtering branch at least comprises at least part of filtering devices and a filtering control unit; the first end of the discharge control unit is electrically connected with the first end of the boost unit. The second end of the discharge control unit is electrically connected with the first end of the energy storage unit. The second end of the energy storage unit is electrically connected with the second end of the boost unit. The main control unit is at least provided with a first control end, a second control end and a third control end, the first control end is electrically connected with the boosting unit, the second control end is electrically connected with the filtering control unit, and the third control end is electrically connected with the discharging control unit. The control circuit has low requirements on the energy storage capability of the energy storage unit.

Description

Technical Field

[0001] This application relates to the field of circuit control technologies, and more specifically, to a control circuit, a control method, and a variable frequency controller. Background Art

[0002] In variable frequency air conditioner control, as Figure 1 shown, the AC-DC-AC control mode is often adopted. In such controllers, for a controller of about 6 kilowatts, usually several thousand microfarads of DC support capacitors (such as the first capacitor C1) are required as energy storage elements to absorb ripple current and at the same time to keep the DC link voltage (the input voltage of the inverter circuit) stable. Since electrolytic capacitors have a large capacitance value per unit volume and high-density energy storage capabilities, they are widely used as DC support capacitors. Summary of the Invention

[0003] In view of this, embodiments of this application provide a control circuit, a control method, and a variable frequency controller, which can reduce the demand for the energy storage capacity of the energy storage unit.

[0004] To solve the above technical problems, this application adopts the following technical solutions:

[0005] A control circuit includes a rectification unit, a filtering unit, a filtering control unit, a boosting unit, an energy storage unit, a discharge control unit, and a main control unit;

[0006] At least part of the filtering devices of the filtering unit and the filtering control unit are connected in series; the filtering branch at least includes the at least part of the filtering devices and the filtering control unit; the first end of the filtering branch is electrically connected to the first output end of the rectification unit, and the second end of the filtering branch is electrically connected to the second output end of the rectification unit; the first end of the boosting unit is electrically connected to the first end of the filtering branch, the second end of the boosting unit is electrically connected to the second end of the filtering branch, the third end of the boosting unit is electrically connected to the common end of the energy storage unit and the discharge control unit, and the first end of the discharge control unit is electrically connected to the first end of the boosting unit; the second end of the discharge control unit is electrically connected to the first end of the energy storage unit, and the second end of the energy storage unit is electrically connected to the second end of the boosting unit; the main control unit has at least a first control end, a second control end, and a third control end, the first control end is electrically connected to the boosting unit, the second control end is electrically connected to the filtering control unit, and the third control end is electrically connected to the discharge control unit.

[0007] This control circuit is provided with a filtering control unit for controlling the filtering unit, a boosting unit for charging the energy storage unit, and a discharge control unit for controlling the discharge of the energy storage unit, which can reduce the demand for the energy storage capacity of the energy storage unit.

[0008] A variable frequency controller includes the above control circuit and inverter circuit; a first end of the discharge control unit of the control circuit is electrically connected to a positive input end of the inverter circuit; a second end of the energy storage unit is electrically connected to a negative input end of the inverter circuit; the main control unit further has a fourth control end, and the fourth control end is electrically connected to the inverter circuit.

[0009] This variable frequency controller includes the above control circuit. When controlling motors of the same level, the demand for the energy storage capacity of the energy storage unit is relatively low.

[0010] A control method is applicable to the above control circuit. The main control unit of the control circuit presets a reference voltage. The control method includes the following steps:

[0011] Judge whether the output voltage of the rectification unit of the control circuit is greater than or equal to the reference voltage;

[0012] If the output voltage of the rectification unit is greater than or equal to the reference voltage, the main control unit controls the filter control unit to conduct, so that the filter unit filters; the main control unit controls the discharge control unit to disconnect and controls the boost unit to work, so that the boost unit stores energy in the energy storage unit.

[0013] When the output voltage of the rectification unit is greater than or equal to the reference voltage, this control method enables the filter unit to filter by controlling the filter control unit, stores energy in the energy storage unit by controlling the boost unit, and enables the energy storage unit not to discharge by controlling the discharge control unit, which is beneficial to reducing the demand for the energy storage capacity of the energy storage unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained according to the provided drawings.

[0015] Figure 1 It is a schematic diagram of the principle of a variable frequency control circuit;

[0016] Figure 2 It is a schematic diagram of the principle of the control circuit provided by the embodiment of the present application;

[0017] Figure 3 It is a schematic diagram of the principle of the control circuit provided by another embodiment of the present application;

[0018] Figure 4 It is a schematic diagram of the principle of a variable frequency controller provided by the embodiment of the present application;

[0019] Figure 5 Schematic diagrams of the operating ranges of the first, second, and third switching tubes provided by the embodiments of the present application;

[0020] Figure 6 is Figure 5 An enlarged schematic diagram of window A;

[0021] Figure 7 is a Figure 2 Flowchart of the control method for the shown control circuit. Detailed implementation manners

[0022] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0023] In order to reduce the storage capacity required in the controller, such as the capacitance of the electrolytic capacitor, the embodiments of the present application provide a control circuit, and a storage unit with a smaller storage capacity can be used to achieve Figure 1 the same power level as the shown circuit. Specifically, as Figure 2 shown, the control circuit includes a rectification unit 1, a filtering unit 2, a filtering control unit 3, a boosting unit 4, a storage unit 5, a discharge control unit 6, and a main control unit 7. The rectification unit 1 can be electrically connected to the input alternating current Vac. At least some of the filtering devices of the filtering unit 2 and the filtering control unit 3 are connected in series. The filtering branch R includes the filtering control unit 3 and the filtering device connected in series with the filtering control unit 3; the first end of the filtering branch is electrically connected to the first output end of the rectification unit 1, and the second end is electrically connected to the second output end of the rectification unit 2. The first end of the boosting unit 4 is electrically connected to the first end of the filtering branch, the second end of the boosting unit 4 is electrically connected to the second end of the filtering branch, the third end of the boosting unit 4 is electrically connected to the common end of the storage unit 5 and the discharge control unit 6, and the first end of the discharge control unit 6 is electrically connected to the first end of the boosting unit 4; the second end of the discharge control unit 6 is electrically connected to the first end of the storage unit 5, the second end of the storage unit 5 is electrically connected to the second end of the boosting unit 4, and the second end of the discharge control unit 6 and the first end of the storage unit 5 are their common end. The main control unit 7 has at least three output terminals: a first control terminal, a second control terminal, and a third control terminal. The first control terminal is electrically connected to the boosting unit 4, the second control terminal is electrically connected to the filtering control unit 3, and the third control terminal is electrically connected to the discharge control unit 6. The main control unit is used to control the boosting unit 4, the filtering control unit 3, and the discharge control unit 6, and control the output voltage of the entire circuit output to the load 10. The specific control method will be introduced in the following control method.

[0024] In this embodiment, the current of the load 10 can come from the rectifying unit 1 and the energy storage unit 5. Since not all of the energy of the load comes from the energy storage unit 5, the requirement for the energy storage capacity of the energy storage unit 5 is relatively low. That is, when the energy storage unit 5 includes a capacitor, the requirement for the capacitance value of this capacitor is relatively low. Namely, this control circuit can meet the Figure 1 ripple absorption requirements of the same power level of the circuit by using a capacitor with a lower capacitance value, so that low-capacity devices can be used when selecting devices for the energy storage unit; and general electrolytic capacitors are commonly used as the energy storage unit, so it is beneficial to reduce the capacitance of the electrolytic capacitor in the circuit, which is further beneficial to improving the lifespan or reducing the cost; and because there is a boosting unit 4 that can boost the voltage of the energy storage unit 5, it can meet the higher voltage input requirements of the load and achieve the same Figure 1 power level as the circuit.

[0025] Furthermore, as Figure 3 shown, the filtering unit 2 includes a second capacitor C2, and the filtering control unit 3 includes a second diode D2 and a second switching tube K2; the cathode of the second diode D2 is electrically connected to the first end of the second switching tube K2, and the anode of the second diode D2 is electrically connected to the second end of the second switching tube K2; the first end of the second capacitor C2 is electrically connected to the filtering control unit 3 (the first end of the second switching tube K2), and the second end of the second capacitor C2 is electrically connected to the first output terminal of the rectifying unit 1, and the first output terminal is the high-potential terminal of the rectifying unit 1; the second end of the second switching tube K2 is electrically connected to the second output terminal of the rectifying unit 1, and the second output terminal is the low-potential terminal of the rectifying unit 1. The second control terminal of the main control unit is electrically connected to the control terminal of the second switching tube K2. Among them, the second switching tube K2 can be a bidirectional controllable switching tube, such as a MOS tube; the second switching tube K2 can also be a unidirectional controllable switching tube, such as an IGBT.

[0026] In this embodiment, when K2 is turned on, C2 filters the input current for the filtering circuit; when K2 is turned off, and when the discharge control unit controls the energy storage unit to provide electrical energy for the load 10, the discharge loop between the energy storage unit 5 and the second capacitor C2 is cut off to prevent damage to the energy storage unit 5 and the second capacitor C2. It should be noted that when the second switching tube K2 is a unidirectional controllable switching tube, the second diode D2 is a necessary device to form a bidirectional filtering loop during filtering (during filtering, the current may flow into C2 or flow out of C2). And when the second switching tube K2 is a bidirectional controllable switching tube, the second diode D2 is not a necessary device, and the bidirectional controllable switching tube itself can obtain a bidirectional filtering loop. In other words, in one embodiment, the filtering control unit includes a bidirectional controllable switching tube and does not include a diode anti-parallel to the bidirectional controllable switching tube.

[0027] Reference Figure 4 In a specific embodiment, the energy storage unit 5 includes a third capacitor C3, and the third capacitor C3 can be an electrolytic capacitor, a thin film capacitor, etc. The boost unit 4 includes a boost circuit, and the boost circuit includes a first inductor L1, a first switching tube K1, and a first diode D1; the first end of the first inductor L1 is the first end of the boost unit 4, the second end of the first inductor L1 is electrically connected to the first end of the first switching tube K1, the second end of the first switching tube K1 is the second end of the boost unit 4, and the cathode of the first diode D1 is the third end of the boost unit 4. Specifically, the first end of the first inductor L1 is electrically connected to the second end of the second capacitor C2, the second end of the first inductor L1 is electrically connected to the first end of the first switching tube K1, the second end of the first switching tube K1 is electrically connected to the anode of the second diode D2, the first end of the first switching tube K1 is electrically connected to the anode of the first diode D1, the cathode of the first diode D1 is electrically connected to the first end of the third capacitor C3, and the second end of the third capacitor C3 is electrically connected to the second end of the first switching tube K1. The discharge control unit 6 includes a third switching tube K3. The first end of the third capacitor C3 serves as the first end of the energy storage unit and is electrically connected to the high potential end of the load through the third switching tube K3. The second end of the third capacitor C3 serves as the second end of the energy storage unit and is electrically connected to the second end of the first switching tube K1 and the low potential end of the load. The control ends of the first switching tube K1, the second switching tube K2, and the third switching tube K3 are all electrically connected to the main control unit 7. By controlling K1, the boost circuit can charge the third capacitor C3, increasing the voltage value of the third capacitor C3, which is beneficial to meeting the higher voltage input requirements of the load. By controlling K3, the supply / cut-off of electric energy from the third capacitor C3 to the load can be controlled. When K2 and K3 are alternately turned on, the load is alternately powered by the rectification unit 1 and the third capacitor C3, and at the same time, the boost circuit does not work. K2 and K3 are mutually exclusive in conduction.

[0028] Furthermore, as Figure 4As shown, the filtering unit 2 further includes a second inductor L2. The second end of the second capacitor C2 is electrically connected to the high-potential end of the rectifying unit 1 at least through the second inductor L2. The second inductor L2 can also be arranged at the front end of the rectifying unit 1, that is, one end of the second inductor L2 can be electrically connected to the input Vac, and the other end is electrically connected to the input end of the rectifying unit 1. In this embodiment, the filtering unit at least includes an LC filtering circuit composed of the second inductor L2 and the second capacitor C2. In this embodiment, by adding D2 and K2, and making K2 and K3 mutually exclusive and conducting when the input voltage is low, it is possible to avoid the direct parallel connection of the relatively high-voltage C3 and the relatively low-voltage C2 when K3 conducts, and to generate a huge impact current due to the different voltages. Compared with adding a current blocking part (such as a diode or a controllable switch tube) between C3 and C2 to block the current flowing from C3 to C2 when K3 conducts, it is possible to avoid the electrical loss caused by the voltage drop of the current blocking part and improve the circuit efficiency; and compared with the scheme of placing the entire LC filtering circuit at the front end of the rectifying unit, when the input sine wave voltage is relatively high and K2 conducts, the capacitor C2 and the capacitor C3 (separated by an inverted diode of K3) together form a bus surge peak absorption capacitor of the inverter bridge, which is beneficial to reducing surges. Especially, C2 is mostly a non-inductive capacitor (such as a thin-film capacitor), and its peak voltage absorption effect is much better than that of C3.

[0029] The above control circuit can be applied to an inductive controllable load and adopts Figure 1 the circuit topology shown. For a power rating of 6 kW, an electrolytic capacitor (C1) with a capacitance of more than 3000 μF is required for filtering; while using the circuit topology provided by the embodiment of the present application, the capacitance value of the electrolytic capacitor (C3) required for a power rating of 6 kW is less than or equal to 1200 μF. Further, referring to Figure 4 In one embodiment, the control circuit is specifically used to control a motor. Based on this, the embodiment of the present application provides a variable-frequency controller, which includes the above control circuit and an inverter circuit 8. The first end of the discharge control unit 6 of the control circuit is electrically connected to the positive input end of the inverter circuit 8; the second end of the energy storage unit 5 is electrically connected to the negative input end of the inverter circuit 8; the main control unit 7 further has a fourth control end, and the fourth control end 7 is electrically connected to the inverter circuit 8; since the inverter circuit 8 at least includes 6 controllable switch tubes, the fourth control end is used to represent the signal for outputting and controlling these 6 controllable switch tubes, and does not represent a control signal output port, and it can have multiple signal output ports.

[0030] In a specific embodiment, the first end of the third capacitor C3 is electrically connected to the high-potential input terminal of the inverter circuit 8 through the third switching tube K3, the second end of the third capacitor C3 is electrically connected to the low-potential input terminal of the inverter circuit 8, and the output terminal of the inverter circuit 8 is electrically connected to the motor. To reduce harmonics, a second inductor L2 is also provided; the second inductor L2 can be provided on the input side or the output side of the rectifying unit 1. When L2 is provided on the output side of the rectifying unit 1, the second end of the second capacitor C2 is electrically connected to the first output terminal of the rectifying unit 1 through the second inductor L2. This circuit can be applied to a variable-frequency controller.

[0031] In this embodiment, the inverter circuit 8 and the motor M are equivalent to loads, and their input current can come from the rectifying unit 1 and the third capacitor C3. Since not all of the energy of the load comes from C3, the energy storage capacity requirement for C3 is relatively low; and because there is a boosting unit 4 that can boost the voltage of C3, the higher voltage input requirement of the load can be met, and the motor speed can be increased.

[0032] Reference Figure 5 and Figure 6 , the working principle of this variable-frequency controller is as follows:

[0033] Set the reference voltage Vref; when the output voltage Vin of the rectifying unit through the control circuit is ≥Vref, it indicates that the power that can be provided by the input side is relatively high, and the load can be powered by the input-side voltage. At this time, K2 is turned on and K3 is turned off, and the L2 / C2 forms a filter circuit to filter the input current; at the same time, the boosting circuit works to store energy in the energy storage unit. And the voltage of the energy storage unit is greater than the input voltage, which is beneficial to meeting the high-voltage requirement of the load and achieving Figure 1 the same power level.

[0034] When the output voltage Vin < Vref, it indicates that the power that can be provided by the input side is relatively low, and the load needs to be powered by the rectifying unit 1 and the energy storage unit 5 together, and the boosting circuit does not work; in this stage, within a carrier cycle, K2 / K3 are alternately turned on or off according to the duty ratio, that is, as Figure 6 shown, their switching states are in antiphase, that is, mutually exclusive control; during the period when K2 is turned on, the load is powered by the input voltage through L2, and the L2 / C2 forms a filter circuit to filter the input current; during the period when K3 is turned on, the load is powered by the energy storage unit, and at the same time, since the current of the input-side inductor L2 may be greater than 0, the L2 / C3 can also form a filter circuit to filter the input current.

[0035] During the period when K2 is turned on, there are two cases: one is that the voltage of C2 is higher than the input voltage (such as during the period of input voltage drop). Regardless of whether K2 is turned on or not, the inverter bridge is powered by C2 through D2 during the period when K3 is turned off. At this moment, the bus voltage is relatively low and the input is blocked. The inductance of L2 is large enough and in continuous current mode, and L2 will supply the input electrical energy for freewheeling to the inverter bridge and charge C2; the other is that the voltage of C2 is lower than the input voltage (such as during the period of input voltage rise), then the input voltage supplies power to charge C2 and supply power to the inverter through L2 respectively, but at this time the input voltage is very low.

[0036] The above output voltage can be characterized by the output voltage Vin of the rectifying unit. When Vin is greater than or equal to the reference voltage Vref, K1 starts to work, and at this time K3 is completely turned off, thus avoiding the circulating current problem among K3, L1, and D1. The switching frequency of K3 is the same as the IPM carrier frequency. The load power Po = the power Pdb provided by the rectifying unit + the power Pc provided by the boost circuit, that is, Po = Vin * duty2 * Io + Vc3 * duty3 * Io; where duty2 is the duty cycle of the second switching tube, duty3 is the duty cycle of the third switching tube, Vc3 is the voltage of the third capacitor, and Io is the average load output current.

[0037] The embodiment of the present application also provides a control method, which is applicable to the above control circuit. The main control unit of the control circuit presets a reference voltage Vref; as Figure 7 shown, the control method includes the following steps:

[0038] Step S1: Determine whether the output voltage Vin of the rectifying unit of the control circuit is greater than or equal to the reference voltage Vref; a higher output voltage Vin indicates a larger input voltage Vac, and the input alternating current can provide more power. The specific determination method can be to sample the output voltage of the rectifying unit to obtain a sampling signal, and compare the sampling signal with the reference voltage Vref of the corresponding reference voltage, so as to determine the magnitude of Vin and Vref.

[0039] Step S2: If the output voltage Vin of the rectifying unit is greater than or equal to the reference voltage Vref, the main control unit controls the filter control unit to conduct, so as to at least enable the filter unit to perform filtering. At this time, the load energy directly comes from the rectifying unit; the main control unit controls the discharge control unit to disconnect and controls the boost unit to work, so that the boost unit boosts and stores energy in the energy storage unit. That is, at this time, a part of the input power provides power for the load, and a part is stored in the energy storage unit through the boost unit.

[0040] Further, determine whether the output voltage Vin of the rectifying unit is less than the reference voltage Vref;

[0041] If the output voltage Vin is less than the reference voltage Vref, within a carrier cycle, the main control unit controls the mutual exclusive conduction of the filtering control unit and the discharge control unit. That is, when the input voltage Vin is low, the load power comes from the rectifying unit or the energy storage unit. By controlling the mutual exclusive conduction of K2 / K3, it is possible to prevent the current from flowing back from the energy storage unit to the filtering unit and causing damage.

[0042] Referring to the description of the above embodiment of the control circuit, when the boosting unit includes a boosting circuit (i.e., a boost circuit), the discharge control unit includes a third switching tube, and the filtering control unit includes a second switching tube, the main control unit controls at least the duty cycle of the first switching tube of the boosting circuit to control the output voltage of the boosting circuit; the main control unit controls at least the conduction or disconnection of the third switching tube to control the conduction or disconnection of the discharge control unit; the main control unit controls at least the conduction or disconnection of the second switching tube to control the conduction or disconnection of the filtering control unit.

[0043] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A control circuit, characterized in that: It includes a rectifying unit, a filtering unit, a filtering control unit, a boosting unit, an energy storage unit, a discharge control unit and a main control unit; At least part of the filter devices of the filter unit and the filter control unit are connected in series; the filter branch at least includes at least part of the filter devices and the filter control unit; the first end of the filter branch is electrically connected to the first output end of the rectifier unit, and the second end of the filter branch is electrically connected to the second output end of the rectifier unit; the first end of the boost unit is electrically connected to the first end of the filter branch, the second end of the boost unit is electrically connected to the second end of the filter branch, the third end of the boost unit is electrically connected to the common end of the energy storage unit and the discharge control unit, and the first end of the discharge control unit is electrically connected to the first end of the boost unit; the second end of the discharge control unit is electrically connected to the first end of the energy storage unit, and the second end of the energy storage unit is electrically connected to the second end of the boost unit; the main control unit at least has a first control end, a second control end and a third control end, the first control end is electrically connected to the boost unit, the second control end is electrically connected to the filter control unit, and the third control end is electrically connected to the discharge control unit.

2. The control circuit according to claim 1, characterized in that: The boost unit includes a boost circuit, which includes a first inductor, a first switch tube and a first diode; the first end of the first inductor is the first end of the boost unit, the second end of the first inductor is electrically connected to the first end of the first switch tube, the second end of the first switch tube is the second end of the boost unit, the first end of the first switch tube is electrically connected to the anode of the first diode, and the cathode of the first diode is the third end of the boost unit; the first control end is electrically connected to the control end of the first switch tube.

3. The control circuit according to claim 2, characterized in that: The filtering unit includes a second capacitor, a first end of the second capacitor is electrically connected to the filtering control unit, and a second end of the second capacitor is the first end of the filtering branch and is electrically connected to the high potential end of the rectifying unit; the filtering control unit includes a bidirectionally conductive controllable switch tube, or the filtering control unit includes a second switch tube and a second diode; The cathode of the second diode is electrically connected to the first end of the second switch tube, and the anode of the second diode is electrically connected to the second end of the second switch tube; the second end of the second switch tube is the second end of the filter branch and is electrically connected to the low potential end of the rectifier unit; the second control end is electrically connected to the control end of the second switch tube.

4. The control circuit according to claim 3, characterized in that: The filtering unit further includes a second inductor; The second end of the second capacitor is electrically connected to the high potential end of the rectifier unit at least through the second inductor; or, one end of the second inductor can be electrically connected to the input alternating current and the other end is electrically connected to the input end of the rectifier unit.

5. The control circuit according to claim 3 or 4, characterized in that: The energy storage unit includes a third capacitor; the discharge control unit includes a third switch tube; the first end of the discharge control unit is the first end of the third switch tube, the second end of the discharge control unit is the second end of the third switch tube, the first end of the third capacitor is the first end of the energy storage unit, and the second end of the third capacitor is the second end of the energy storage unit.

6. The control circuit according to claim 5, characterized in that: The second capacitor is a film capacitor, and the third capacitor is an electrolytic capacitor; when the power of the control circuit is less than 6 kilowatts, the capacitance of the electrolytic capacitor is less than 1200 microfarads.

7. A frequency conversion controller, characterized in that: It comprises a control circuit and an inverter circuit as described in any one of claims 1 to 6; the first end of the discharge control unit of the control circuit is electrically connected to the positive input end of the inverter circuit; the second end of the energy storage unit is electrically connected to the negative input end of the inverter circuit; the main control unit also has a fourth control end, and the fourth control end is electrically connected to the inverter circuit.

8. A control method, characterized in that: Applicable to the control circuit according to any one of claims 1 to 6, wherein a main control unit of the control circuit is preset with a reference voltage; and the control method comprises the following steps: Determining whether the output voltage of the rectifying unit of the control circuit is greater than or equal to the reference voltage; If the output voltage of the rectifier unit is greater than or equal to the reference voltage, the main control unit controls the filter control unit to be turned on so that at least the filter unit performs filtering; the main control unit controls the discharge control unit to be turned off and controls the boost unit to work so that at least the boost unit stores energy in the energy storage unit.

9. The control method according to claim 8, characterized in that: The following steps are also included: Determining whether the output voltage of the rectifying unit is less than the reference voltage; If the output voltage of the rectifying unit is less than the reference voltage, within a carrier cycle, the main control unit controls the filtering control unit and the discharging control unit to be mutually exclusive, so as to at least discharge the energy storage unit.

10. The control method according to claim 9, characterized in that: When the boost unit includes a boost circuit, the discharge control unit includes a third switch tube, and the filter control unit includes a second switch tube, the main control unit controls the output voltage of the boost circuit at least by controlling the duty cycle of the first switch tube of the boost circuit; the main control unit controls the conduction or disconnection of the discharge control unit at least by controlling the conduction or disconnection of the third switch tube; the main control unit controls the conduction or disconnection of the filter control unit at least by controlling the conduction or disconnection of the second switch tube.

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