PFC control method and control device

Abstract

The embodiment of the present invention provides a PFC control method and a control device. The PFC control method is applicable to a PFC circuit. When the PFC operates in a continuous mode, the control method includes the following steps: controlling the main switch tube of the PFC circuit to turn off; processing the theoretical off time of the main switch tube to obtain a first processing signal, and the opening information of the main switch tube includes the first processing signal; and controlling the opening state of the main switch tube at least according to the opening information. The control method can improve the control stability of the PFC circuit in the continuous mode.

Description

Technical Field

[0001] The present invention relates to the field of switching power supply control, and in particular to a PFC control method and a control device. Background Art

[0002] Due to the widespread use of switching power supplies, in order to reduce the harmonic current pollution and reactive power increase caused by the non-sinusoidal current waveform distortion generated by the switching power supply; power factor correction (PFC) technology is a method used to improve the power factor of electrical equipment, ensuring that the current waveform and the voltage waveform are as in phase as possible, thereby reducing energy loss and grid harmonic pollution. PFC technology is mainly aimed at capacitive loads, especially equipment with a power greater than 75W. PFC can make the system behave more like a pure resistive load and improve the efficiency of electric energy utilization. In addition to completing the correction of the current waveform, PFC technology also solves the problem of voltage and current in phase.

[0003] There are many PFC technologies, and the most commonly used one is BOOST PFC technology. When BOOST PFC works in high-power applications, the CCM (Continuous Conduction Mode: continuous conduction mode for short) mode is often used. In this mode, unstable operation may occur. Summary of the invention

[0004] In view of this, an embodiment of the present invention provides a PFC circuit control method and a control device, which can suppress current oscillation in CCM mode and improve operation stability.

[0005] In order to solve the above technical problems, this application adopts the following technical solutions:

[0006] A PFC control method is applicable to a PFC circuit, and when the PFC circuit operates in a continuous mode, the method comprises the following steps:

[0007] Controlling the main switch tube of the PFC circuit to turn off;

[0008] Processing the theoretical off-time of the PFC circuit to obtain a first processing signal, wherein the on-time information of the main switch tube includes the first processing signal;

[0009] The switching state of the main switch tube is controlled at least according to the switching information.

[0010] In the scenario where the PFC circuit works in the continuous mode, the control method processes the theoretical off-time of the PFC circuit to obtain a first processing signal, and then controls the on-state of the main switch tube according to the on-time information including the first processing signal, thereby adjusting the state of the main switch tube, which is equivalent to adjusting the on-time and off-time of the main switch tube, so that at a specific phase point of the power frequency, the on-time of the main switch tube can be stabilized at a on-time value, that is, the on-time of the main switch tube converges to a certain on-time value, and finally remains consistent with the on-time value through the adjustment of several switching cycles, so as to achieve the purpose of improving the control stability of the system.

[0011] A PFC control device, suitable for controlling a PFC circuit in a continuous mode, comprises a switch tube control unit and a processing unit;

[0012] The processing unit is used for processing the theoretical off-time of the PFC circuit to obtain a first processing signal, and sending the first processing signal to the switch tube control unit;

[0013] The switch tube control unit is at least used to control the shutdown of the main switch tube of the PFC circuit according to the main switch activation information including the first processing signal.

[0014] The PFC control device is provided with a processing unit, which can process the theoretical off-time of the PFC circuit to obtain a first processing signal. The switch tube control unit then controls the state of the main switch tube according to the main switch tube opening information containing the first processing signal, thereby realizing the adjustment of the state of the main switch tube, which is equivalent to adjusting the on-time and off-time of the main switch tube, so that the on-time of the main switch tube can be stabilized at a on-time value, that is, at a specific phase point of the power frequency, the on-time of the main switch tube converges to a certain on-time value, and through the adjustment of several switching cycles, it is finally kept consistent with the on-time value under the control of the switch tube control unit, so as to achieve the purpose of improving the control stability of the system. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work, but they should fall within the scope of protection of this application.

[0016] Figure 1 It is a principle schematic diagram of a PFC control circuit with peak current control;

[0017] Figure 2Schematic diagram of the main signal waveform of PFC control with peak current control;

[0018] Figure 3 The schematic diagram of the PFC control circuit for 0.5Ton control;

[0019] Figure 4 Schematic diagram of the main signal waveform of PFC control with 0.5Ton control;

[0020] Figure 5 This is a schematic diagram of the unstable operation waveform of the PFC control circuit with peak current control;

[0021] Figure 6 This is a schematic diagram of the unstable operation waveform of the PFC control circuit controlled at 0.5Ton;

[0022] Figure 7 A schematic diagram of main signal waveforms of a PFC control provided by an embodiment of the present application;

[0023] Figure 8 A schematic diagram of main signal waveforms of a PFC control provided by another embodiment of the present application;

[0024] Fig. 9 A schematic block diagram of a PFC control device. DETAILED DESCRIPTION

[0025] In order to better understand the technical solution of the present invention, the embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0026] It should be clear that the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0027] The terms used in the embodiments of the present invention are only for the purpose of describing specific embodiments and are not intended to limit the present invention. The singular forms "a", "the" and "the" used in the embodiments of the present invention and the appended claims are also intended to include plural forms unless the context clearly indicates other meanings. Electrical connections include direct electrical connections and indirect electrical connections.

[0028] It should be understood that the term "and / or" used in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0029] Generally, the PFC circuit includes an inductor, a main switch tube (also referred to as the main tube) and a freewheeling tube; the freewheeling tube can be a diode or a controllable synchronous tube (referred to as an SR tube); in CCM mode, during the switching cycle, the main switch tube and the freewheeling tube are mutually exclusive; when the main switch tube is turned on, the freewheeling tube is turned off and the inductor is excited; when the main switch tube is turned off, the freewheeling tube is turned on and the inductor is demagnetized. Specifically, the PFC circuit can be a boost PFC circuit, or a bridgeless totem pole PFC circuit, a dual boost bridgeless PFC circuit, etc. In order to save power and improve efficiency, a controllable switch tube can be used as a synchronous tube. In CCM mode, the synchronous tube and the main switch tube are mutually exclusive, the conduction control of the main switch tube is equivalent to the shutdown control of the synchronous tube, and the shutdown control of the main switch tube is equivalent to the conduction control of the synchronous tube. When the PFC circuit works in high-power applications, it often works in CCM mode, which may face the problem of unstable operation.

[0030] PFC control methods include peak current control and 0.5Ton control.

[0031] The schematic diagram of the peak current control system is as follows: Figure 1 As shown, the peak current control signal logic diagram is as follows Figure 2 shown; combined Figure 1 and Figure 2 The peak current control principle is explained as follows:

[0032] The conduction control strategy of the main switch is as follows:

[0033] The main switch tube adopts peak current control, and the peak reference current setting is shown in formula (1):

[0034] ……(1)

[0035] Among them, I peak Indicates the peak reference current; I ref Represents the average reference current, which is determined by the control loop based on the input voltage and output voltage of the PFC circuit. Figure 1 and Figure 3 In, T main The conduction time of the main switch.

[0036] When the main switch is turned on, the inductor current I L When the inductor current I L Reach I peak When the peak current comparator output flips, the main switch tube is turned off.

[0037] The conduction control strategy of the synchronous tube: because the synchronous tube and the main switch tube are mutually exclusive, the conduction control of the synchronous tube is equivalent to the shutdown control of the main switch tube.

[0038] The synchronous tube adopts a timed conduction control strategy, and its conduction time is determined by formula (2)

[0039] ……(2)

[0040] in:

[0041] T SR is the theoretical conduction time of the synchronous tube;

[0042] T offs The theoretical off time of the main switch tube;

[0043] V in is the sampled value of the input voltage of the PFC circuit;

[0044] V bulk is the sampled value of the output voltage (also the output bus voltage) of the PFC circuit;

[0045] T sw is the expected switching period when operating in CCM mode.

[0046] 0.5Ton control system schematic diagram Figure 3 As shown, the 0.5Ton control signal logic diagram is as follows Figure 4 shown; combined Figure 3 and Figure 4 Explain the 0.5Ton control principle:

[0047] The conduction control strategy of the main switch tube:

[0048] When the main switch is turned on, the inductor current I L When the inductor current is greater than the average reference current I ref When the average current comparator output signal flips, the counter stops increasing and starts counting down. When the counter value is equal to 0, the main switch is turned off. This control method ensures that the average value of the inductor current is equal to the average reference current I ref .

[0049] The on-control strategy of the SR tube (that is, the off-control strategy of the main switch tube) can also adopt a timed on-control strategy, and its on-time can also be determined by formula (2).

[0050] However, no matter which control method is used, the output current control instability phenomenon will occur. Among them, the peak current control instability phenomenon is as follows Figure 5 As shown:

[0051] Assume that Ts_n period I peak The disturbance causes an upward fluctuation of ΔI peak, which results in an increase in the conduction time of the main tube in this cycle, and the increase is recorded as ΔT on , then the SR tube is turned on for the theoretical time T SR Conducting, we can see:

[0052] The main conduction time of the Ts_n+1 cycle is reduced by 2*ΔT on ;

[0053] The main conduction time of Ts_n+2 period increases by 2*ΔT on ;

[0054] The main conduction time of the Ts_n+3 period is reduced by 2*ΔT on ;

[0055] The main conduction time of Ts_n+4 period increases by 2*ΔT on ;

[0056] The main conduction time of the Ts_n+5 cycle is reduced by 2*ΔT on ;

[0057] …

[0058] The above fluctuations repeat over and over again, and the main switch tube cannot converge to a stable conduction time.

[0059] 0.5Ton control instability phenomenon such as Figure 6 As shown:

[0060] Assume that the average reference current I during Ts_n period ref The disturbance causes an upward fluctuation of ΔI ref , which results in an increase in the conduction time of the main tube in this cycle, and the increase is recorded as ΔT on , then the SR tube is turned on for the theoretical time T SR Conducting, we can see:

[0061] The main conduction time of the Ts_n+1 cycle is reduced by 2*ΔT on ;

[0062] The main conduction time of Ts_n+2 period increases by 2*ΔT on ;

[0063] The main conduction time of the Ts_n+3 period is reduced by 2*ΔT on ;

[0064] The main conduction time of Ts_n+4 period increases by 2*ΔT on ;

[0065] The main conduction time of the Ts_n+5 cycle is reduced by 2*ΔT on ;

[0066] …

[0067] The above fluctuations repeat over and over again, and the main switch tube cannot converge to a stable conduction time.

[0068] Based on this, an embodiment of the present application provides a PFC control method, which adjusts the on-time or off-time of the main switch tube so that the on-time of the main switch tube can converge at a specific phase point of the power frequency, so as to solve the instability problem of the PFC circuit in the CCM mode (continuous mode) and prevent current disturbances from causing abnormal operation or even damage to the system.

[0069] Specifically, when the PFC circuit operates in the continuous mode, the control method includes the following steps:

[0070] Control the main switch of the PFC circuit to turn off;

[0071] The theoretical off time of the main switch is processed to obtain a first processing signal, and the first processing signal is used as one of the main switch opening information; the opening information includes opening starting point information, opening time information, opening end point information, conduction time timing starting point information, conduction time timing end point information, etc. That is, the main switch opening information includes the first processing signal;

[0072] The switching state of the main switch tube is controlled at least according to the switching information including the first processing signal.

[0073] In different control methods, different turn-on information is required to control the turn-on state of the main switch tube. For example, in peak current control, it is often necessary to know the turn-on starting point information, and the turn-on starting point information is generally determined by the turn-on time of the freewheeling tube. When the turn-on time of the freewheeling tube reaches the expected turn-on time, the freewheeling tube is turned off, and the turn-on starting point of the main switch tube arrives. The expected turn-on time of the freewheeling tube can be obtained from the theoretical turn-off time of the main switch tube. The present application compensates the expected turn-on time of the freewheeling tube by the theoretical turn-off time, thereby realizing the turn-on control of the main switch tube; the turn-on end point information is determined by the moment when the inductor current of the PFC circuit reaches the peak reference current, and the turn-on time information is naturally determined by the turn-on starting point information and the turn-on end point information.

[0074] In 0.5Ton control, it is often necessary to know the half-on time, that is, the time for the inductor current to increase from the valley current to the average reference current; then, after the inductor current reaches the average reference current, the main switch tube continues to be turned on for half the on time; therefore, it is necessary to know the on-time timing starting point information, which generally starts from 0. However, the present application compensates the on-time timing starting point information so that it is no longer 0, thereby realizing compensation for the on-time length of the main switch tube.

[0075] In summary, after processing the theoretical off-time, the on-time or off-time of the main switch tube is compensated, and the on-time T of the main switch tube is adjusted. main Or adjust the off time of the main switch tube (that is, the on time of the synchronous tube T SR ). Through this compensation, the on-time of the main switch tube can be converged to avoid system instability. The compensation signal can be directly given or calculated based on other system parameters.

[0076] Specifically, when the peak current control is used to control the PFC circuit, the opening information includes the opening starting point information of the main switch tube, and the first processing signal is obtained by compensating the theoretical off-time by the on-time of the main switch tube; in this embodiment, the first processing signal is equivalent to the off-time of the main switch tube, and the theoretical off-time calculated by formula (2) is compensated, so that the actual off-time of the main switch tube becomes longer in the current switching cycle, thereby delaying the opening starting point of the main switch tube, and under the actual off-time lengthening and average current control, the on-time of the main switch tube tends to be stable. It should be noted that one of the control purposes of both peak current control and 0.5Ton control is to make the inductor current reach the average reference current to meet the output requirements.

[0077] When the PFC circuit is controlled by 0.5Ton control, the opening information includes the timing starting point information of the main switch on time, and the first processing signal is determined by the theoretical off time and the volt-second balance time; the volt-second balance time is the off time required for the inductance of the PFC circuit to reach the volt-second balance when the main switch is turned off. In this way, the on time of the main switch is adjusted, and under the adjustment of the on time and the average current control, the on time of the main switch tends to be stable.

[0078] In one embodiment, the PFC circuit is controlled by using peak current control or 0.5Ton control, and the turn-on information is the turn-on starting point information of the main switch tube; the first processing signal is obtained by the following steps:

[0079] Get the on-time T of the main switch tube in the previous switching cycle main ; On time T main is the time for the inductor current of the PFC circuit to increase from the valley current to the peak current;

[0080] The first processing signal is obtained by adding (1 / N) times the on-time to the theoretical off-time of the main switch tube; wherein N>1;

[0081] Controlling the switching state of the main switch tube at least according to the switching information comprises the following steps:

[0082] When the actual off-time of the main switch tube reaches the first processing signal, the main switch tube is controlled to be turned on.

[0083] refer to Figure 7 , compensation signal T comp The conduction time T of the main switch tube main Get, where: ; Superimpose the compensation signal on the theoretical off time T of the main switch tube offs The actual off time of the main switch after compensation (T offs +T comp ), which is also the first processed signal. Its principle refers to Figure 7 , when the Ts_n period is affected by ΔI peak After the disturbance, the conduction time due to the disturbance is T main becomes longer, even if the actual off time of the main switch tube (T offs +T comp ) than the theoretical off time T offs The valley current still increases, and after Ts_n period, ΔI peak The disturbance disappears, the reference current of the Ts_n+1 cycle returns to normal, and the conduction time T main Get smaller, in T comp Under the compensation effect, the valley current will be reduced to a certain extent, and in order to maintain the average current, the conduction time T of the Ts_n+2 cycle is main It will increase again, at T comp Under the compensation effect, the valley current is adjusted to be smaller. Compared with the valley current at the end of the Ts_n cycle, the valley current at the end of the Ts_n+2 cycle is corrected to a certain extent. After several cycles of adjustment, the on-time of the main switch tube can converge, thereby eliminating the peak current I peak The disturbance causes an upward fluctuation of ΔI peak The impact caused by this makes the system gradually stable. The theoretical off-time is determined by the input voltage, output bus voltage and switching cycle of the PFC circuit, and can be calculated by formula (2). It should be noted that, ignoring the dead time, when the synchronous tube is used for freewheeling, the on-time of the synchronous tube is the off-time of the main switch tube.

[0084] In this embodiment, the conduction time of the synchronous tube is T SR With T comp The sum of T SR The calculation remains unchanged, 1 / N is the compensation coefficient, given by Figure 7It can be seen that in order to keep the average inductor current consistent with the average reference current, the disturbance is attenuated cycle by cycle, and finally stable operation is achieved. This compensation method only needs to obtain the on-time of the main switch tube, the system cost is low, and no additional static error is introduced to the target average current. It can effectively suppress the current oscillation in the CCM mode of peak current control or 0.5Ton control, and because there is no additional average current static error, the system can also switch stably when switching modes.

[0085] The compensation method of this embodiment is applicable to both peak current control and 0.5Ton control. When applied to peak current control, the on-time of the main switch tube can be obtained by the following steps:

[0086] The timing starts when the main switch is turned on and stops when the inductor current of the PFC circuit reaches the peak reference current. The on-time T is obtained. main .

[0087] When used in 0.5Ton control, the on-time of the main switch can be obtained by the following steps:

[0088] The timing starts when the main switch is turned on, and stops when the inductor current of the PFC circuit reaches the average reference current. The half-on time is obtained, and twice the half-on time is the on time T. main .

[0089] In another embodiment, the off time error ΔT of the main switch tube in the previous switching cycle can also be off _(n-1) 1 / N times the main switch conduction time T of the next open tube cycle main In this embodiment, the PFC circuit is controlled by 0.5Ton control, and the opening information is the timing starting point of the main switch tube conduction time;

[0090] The first processed signal is obtained by the following steps:

[0091] Obtain a second time length t2, where the second time length t2 is the time length for the inductor current from the main switch tube to the PFC circuit to drop to the average reference current after the main switch tube is turned off; wherein the volt-second balance time of the inductor in this cycle is twice the second time length; that is, the off time of the main switch tube needs to reach 2*t2, so that the average value of the inductor current can reach the average reference current;

[0092] The first processing signal is obtained by adding (1 / N) times the difference between the volt-second balance time 2*t2 and the theoretical off time to the initial timing starting point of the first timer of the next switching cycle; the first timer is used to time the on time of the main switch tube; wherein N>1;

[0093] The controlling the switching state of the main switch tube at least according to the switching information comprises the following steps:

[0094] When the off time of the main switch tube reaches the theoretical off time, the main switch tube is controlled to be turned on, and the first timer starts timing from the first processing signal.

[0095] Specifically, refer to Figure 8 In this embodiment, when the main switch tube is turned off, the second timer Slop_Cnt is controlled to start timing; in order to prevent the second timer from reaching a negative value, the timing starting point is set to Tbias greater than 0.

[0096] When the inductor current I L Drop to the average reference current I ref After that, the second timer stops timing to obtain the second time length t2;

[0097] The compensation signal is the turn-off time error △T off _1 / N times (n-1), △T off _(n-1) is the difference between twice the second time length and the theoretical off time; wherein, N>1.

[0098] In this embodiment, (1 / N) times the difference between the second duration and the theoretical off time is added to the timing starting point of the first timer Main_Cnt to compensate for the on time of the main switch tube and shorten it. At a specific phase point of the power frequency, the on time of the main switch tube can be converged to ensure control stability. The first timer is used to time and control the on time of the main switch tube.

[0099] Theoretical off time T offs It is determined by the input voltage, output bus voltage and switching period of the PFC circuit and can be calculated by formula (2).

[0100] In this embodiment, ΔT off _(n-1) / N vs. T main _n time compensation. Compare the sampling signal of the inductor current with the average current reference to obtain the off-time for achieving volt-second balance when the main switch is turned off. The off-time is 2*t2. Subtract the off-time for achieving volt-second balance from the theoretical off-time, and add the time deviation in proportion to the on-time of the main switch in the next cycle to obtain stable control. This compensation method is particularly suitable for the control strategy of 0.5Ton control and is suitable for the application scenario of direct inductor current sampling. Figure 8 It can be seen that when a switching cycle is affected by ΔI peak After the disturbance, the on-time T mainIn order to achieve volt-second balance, a longer off-time is required. However, the main switch is still turned off using the theoretical off-time control, which results in a larger inductor current when the main switch is turned on in the next cycle. By reducing (2*t2-T offs ) / N is compensated to the timing starting point of the next cycle (that is, the initial timing starting point of the first timer), so that the conduction time of the next cycle is extended, and correspondingly, the conduction time of the next cycle is shortened... and so on, to achieve the convergence control of the conduction time, the disturbance is attenuated cycle by cycle, and finally achieve stable operation.

[0101] Based on the above PFC control method, the embodiment of the present application further provides a PFC control device 1, such as Fig. 9 As shown, it includes a switch tube control unit 11 and a processing unit 12;

[0102] The processing unit is used for processing the theoretical off-time of the main switch tube of the PFC circuit to obtain a first processing signal, and sending the first processing signal to the switch tube control unit;

[0103] The switch control unit is at least used to control the state of the main switch of the PFC circuit according to the main switch turn-on information including the first processing signal, so as to adjust the on time or off time of the main switch to maintain stable control.

[0104] The switch tube control unit can execute peak current control or 0.5Ton control strategy. The processing unit 12 is used to generate the first processing signal in the above embodiment and input it to the switch tube control unit 11; the switch tube control unit 11 and the processing unit 12 work together to execute the above PFC control method to solve the control instability problem. Of course, different control strategies also need to cooperate with corresponding modules to execute corresponding control strategies, such as peak current control requires a valley sampling unit.

[0105] Specifically, the opening information includes the opening starting point information of the main switch tube, and the first processing signal is obtained by compensating the theoretical off-time by the on-time of the main switch tube; this method is applicable to peak current control and 0.5Ton control.

[0106] When the PFC circuit is controlled by 0.5Ton control, the turn-on information may also be set to include timing starting point information of the main switch tube conduction time, and the first processing signal is determined by the theoretical turn-off time and the volt-second balance time; the volt-second balance time is the turn-off time required for the inductance of the PFC circuit to reach the volt-second balance when the main switch tube is turned off.

[0107] It should be noted that the processing unit and the control unit are only used for functional division. In practice, the two can share hardware resources, such as sharing the first timer, the second timer, the peak current comparator, the average current comparator, etc. The control device can be an integrated circuit, or it can be built by discrete devices, or it can be implemented by discrete devices with a simple control chip. Other technical features and principles of the control device can refer to the control method, which will not be repeated here.

[0108] The above disclosure is only the preferred embodiment of the present application, and cannot be used to limit the scope of rights of the present application. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of this specification are still within the scope covered by the present application.

Claims

1. A PFC control method, applicable to a PFC circuit, characterized in that: When the PFC circuit operates in a continuous mode, the control method comprises the following steps: Controlling the main switch tube of the PFC circuit to turn off; Processing the theoretical off-time of the main switch tube to obtain a first processing signal, wherein the on-time information of the main switch tube includes the first processing signal; Controlling the switching state of the main switch tube at least according to the switching information; The opening information includes the opening starting point information of the main switch tube, and the first processing signal is the actual turning-off time of the main switch tube obtained by compensating the theoretical turning-off time according to the turning-on time of the main switch tube; and the first processing signal is obtained by the following steps: Obtaining the on-time of the main switch tube in the previous switching cycle; the on-time is the time it takes for the inductor current of the PFC circuit to increase from the valley current to the peak current; The first processing signal is obtained by adding 1 / N times of the on-time to the theoretical off-time of the main switch tube; wherein N>1; The controlling the switching state of the main switch tube at least according to the switching information comprises the following steps: When the actual off-time of the main switch tube reaches the first processing signal, controlling the main switch tube to turn on; Alternatively, the turn-on information includes timing starting point information of the conduction time of the main switch tube, and the first processing signal is determined by the theoretical turn-off time and the volt-second balance time; the volt-second balance time is the turn-off time required for the inductance of the PFC circuit to reach the volt-second balance when the main switch tube is turned off; and the PFC circuit is controlled by 0.5Ton control, and the first processing signal is obtained by the following steps: Acquire a second time duration, where the second time duration is the time duration from when the main switch tube is turned off until the inductor current of the PFC circuit drops to the average reference current; The volt-second balance time is twice the second time length; The first processing signal is obtained by adding 1 / N times the difference between the volt-second balance time and the theoretical off time to the initial timing starting point of the first timer; the first timer is used to time the on time of the main switch tube; wherein N>1; The controlling the switching state of the main switch tube at least according to the switching information comprises the following steps: When the off time of the main switch tube reaches the theoretical off time, the main switch tube is controlled to be turned on, and the first timer starts timing from the first processing signal.

2. The PFC control method according to claim 1, characterized in that: Also includes the steps: When the inductor current reaches the average reference current, the first timer is controlled to count backwards; when the reverse timing of the first timer reaches the initial timing starting point, the main switch tube is controlled to be turned off.

3. The PFC control method according to claim 2, characterized in that: The second duration is obtained by following the steps below: When the main switch is turned off, the second timer is controlled to start timing; When the inductor current of the PFC circuit drops to the average reference current, the second timer stops timing to obtain a second duration.

4. The PFC control method according to any one of claims 1 to 3, characterized in that: The initial timing starting point is greater than 0.

5. The PFC control method according to any one of claims 1 to 3, characterized in that: The theoretical off time is calculated by the following formula: in: T offs is the theoretical off time of the main switch tube; V in is a sampled value of the input voltage of the PFC circuit; V bulk is a sampled value of the output voltage of the PFC circuit; T sw is the expected switching period in CCM operation.

6. A PFC control device, suitable for controlling a PFC circuit in a continuous mode, characterized in that: It includes a switch tube control unit and a processing unit; The processing unit is used for processing the theoretical off-time of the main switch tube of the PFC circuit to obtain a first processing signal, and sending the first processing signal to the switch tube control unit; The switch control unit is at least used to control the state of the main switch of the PFC circuit according to the main switch turn-on information including the first processed signal; The opening information includes the opening starting point information of the main switch tube, and the first processing signal is the actual off time of the main switch tube obtained by compensating the theoretical off time according to the on time of the main switch tube; the first processing signal is obtained by the following steps: Obtaining the on-time of the main switch tube in the previous switching cycle; the on-time is the time it takes for the inductor current of the PFC circuit to increase from the valley current to the peak current; The first processing signal is obtained by adding 1 / N times of the on-time to the theoretical off-time of the main switch tube; wherein N>1; The switch control unit is at least used to control the switching state of the main switch according to the following steps: When the actual off-time of the main switch tube reaches the first processing signal, controlling the main switch tube to turn on; Alternatively, the opening information is the timing starting point of the conduction time of the main switch tube, and the first processing signal is determined by the theoretical turn-off time and the volt-second balance time; the volt-second balance time is the turn-off time required for the inductance of the PFC circuit to reach the volt-second balance when the main switch tube is turned off; The first processed signal is obtained by the following steps: Acquire a second time duration, where the second time duration is the time duration from when the main switch tube is turned off until the inductor current of the PFC circuit drops to the average reference current; The volt-second balance time is twice the second time length; The first processing signal is obtained by adding 1 / N times the difference between the volt-second balance time and the theoretical off time to the initial timing starting point of the first timer; the first timer is used to time the on time of the main switch tube; wherein N>1; The switch control unit controls the PFC circuit using 0.5Ton control, and is at least used to control the on-state of the main switch according to the following steps: When the off time of the main switch tube reaches the theoretical off time, the main switch tube is controlled to be turned on, and the first timer starts timing from the first processing signal.

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