A 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, the PFC circuit adopts 0.5Ton control, the control method comprises the following steps: when the main switch tube of the PFC circuit is turned on, a first timer starts to count forward from a first timing point until the inductor current of the PFC circuit reaches an average reference current; when the inductor current reaches the average reference current, the first timer counts backward; during the period when the main switch tube is turned on, a first compensation curve is obtained, the first compensation curve represents the timing curve of the second timer. The control method can improve the control stability of the PFC circuit in the continuous working 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, wherein the PFC circuit adopts 0.5Ton control, and the control method comprises the following steps:

[0007] When the main switch tube of the PFC circuit is turned on, the first timer starts counting forward from a first timing point until the inductor current of the PFC circuit reaches an average reference current;

[0008] When the inductor current reaches the average reference current, the first timer counts backwards;

[0009] During the conduction period of the main switch tube, a first compensation curve is obtained, wherein the first compensation curve represents a timing curve of the second timer;

[0010] When the reverse timing curve of the first timer intersects the first compensation curve, the main switch tube is controlled to be turned off.

[0011] In the scenario where the PFC circuit operates in the continuous mode, the control method constructs a first compensation curve during the conduction period of the main switch tube, uses a first timer to time and control the conduction time of the main switch tube, and controls the main switch tube to be turned off when the first compensation curve and the reverse timing curve of the first timer intersect. In this way, the conduction time of the main switch tube can be compensated and controlled to prevent the conduction time from cyclically fluctuating and failing to converge due to disturbances, which is beneficial to improving the stability of control.

[0012] A PFC control device is applicable to a PFC circuit, wherein the PFC circuit adopts 0.5Ton control, and the control device is used to execute the above-mentioned PFC control method. The control device can improve control stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] 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.

[0014] Figure 1 The schematic diagram of the PFC control circuit for 0.5Ton control;

[0015] Figure 2 Schematic diagram of the main signal waveform of PFC control with 0.5Ton control;

[0016] Figure 3 The waveform diagram of the unstable operation of the PFC control circuit under 0.5Ton control is shown;

[0017] Figure 4 A schematic diagram of the main signal waveform for adding the first compensation curve for control;

[0018] Figure 5 To add a schematic diagram of the main signal waveform of the first compensation curve control;

[0019] Figure 6 Another main signal waveform diagram for adding a first compensation signal control;

[0020] Figure 7 A schematic block diagram of a PFC control device. DETAILED DESCRIPTION

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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 (also recorded 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 on-control of the main switch tube is equivalent to the off-control of the synchronous tube, and the off-control of the main switch tube is equivalent to the on-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.

[0026] The PFC control method includes peak current control and 0.5Ton control. The technical solution provided in this application aims to solve the problem of unstable operation of the PFC circuit using 0.5Ton control in CCM mode.

[0027] In order to better understand this solution, let's first introduce the control principle of 0.5Ton:

[0028] 0.5Ton control system schematic diagram Figure 1 As shown, the schematic diagram of the main signal waveform of 0.5Ton control is as follows Figure 2 shown; combined Figure 1 and Figure 2Explain the 0.5Ton control principle:

[0029] The conduction control strategy of the main switch tube:

[0030] When the main switch is turned on, the inductor current I L Rising, the internal counter is driven to start timing, generating a counting curve as shown in the curve Main_Cnt. When the inductor current I L Greater than the average reference current I ref When the average current comparator flips, the counter stops increasing and starts counting down. When the counter count 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 .

[0031] 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.

[0032] The conduction control strategy of the synchronous tube (that is, the shut-down control strategy of the main tube) can adopt a timed conduction control strategy, and its conduction time can also be determined by formula (1).

[0033] …… (1)

[0034] in:

[0035] T SR is the theoretical conduction time of the synchronous tube;

[0036] T offs The theoretical off time of the main switch tube;

[0037] V in is the sampled value of the input voltage of the PFC circuit;

[0038] V bulk is the sampled value of the output voltage (also the output bus voltage) of the PFC circuit;

[0039] T sw is the expected switching period when operating in CCM mode.

[0040] refer to Figure 3 The reasons why the PFC circuit under the above 0.5Ton control may operate unstably are as follows:

[0041] 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 synchronous tube is turned on for the theoretical time T SRConducting, we can see:

[0042] The main conduction time of the Ts_n+1 cycle is reduced by 2*ΔT on ;

[0043] The main conduction time of Ts_n+2 period increases by 2*ΔT on ;

[0044] The main conduction time of the Ts_n+3 period is reduced by 2*ΔT on ;

[0045] The main conduction time of Ts_n+4 period increases by 2*ΔT on ;

[0046] The main conduction time of the Ts_n+5 cycle is reduced by 2*ΔT on ;

[0047] …

[0048] The above fluctuations repeat over and over again, and the main switch tube cannot converge to a stable conduction time.

[0049] Based on this, the present application provides a PFC control method, using the above-mentioned PFC circuit using 0.5Ton control, referring to Figure 4 Waveform diagram, the control method comprises the following steps:

[0050] When the main switch of the PFC circuit is turned on, the first timer starts counting forward from the first timing point until the inductor current I L Reach the average reference current I ref ;

[0051] When the inductor current reaches the average reference current, the first timer starts counting backwards; wherein a timing curve of the first timer is shown as curve Main_Cnt.

[0052] During the conduction period of the main switch tube, a first compensation curve is obtained, and the first compensation curve represents the timing curve of the second timer; the timing curve of the second timer is shown in the curve Slop_Cnt. The conduction time of the main switch tube can be slope compensated by the first compensation curve.

[0053] When the reverse timing curve of the first timer (ie, the descending portion of the curve Main_Cnt) intersects the first compensation curve, the main switch tube is controlled to be turned off.

[0054] The first compensation curve is not limited to a certain form, and can be Figure 4As shown in the middle curves ①②③, the first compensation curve and the reverse timing curve of the first timer can intersect, thereby changing the on-time of the main switch tube so that its switching cycle will not be affected by the on-time error cycle caused by the interference signal, so that the on-time of the main switch tube can converge, providing system control stability.

[0055] Further, refer to Figure 4 In one embodiment, the first compensation curve is shown as curve ①, and the first compensation curve is obtained by at least the following steps:

[0056] When the main switch is turned on, the second timer starts counting forward from 0 with a first preset slope to obtain a first compensation curve (as shown in curve ①); wherein the first preset slope is less than the forward timing slope of the first timer (i.e., the rising slope of the rising portion of the curve Main_Cnt), so that the first compensation curve can intersect with the falling portion of the curve Main_Cnt. When the two curves intersect, the main switch is controlled to be turned off.

[0057] In another embodiment, the first compensation curve is shown as curve ②, and the first compensation curve is obtained by the following steps:

[0058] When the main switch is turned on, the second timer starts from 0 and starts counting forward at the second preset slope until the inductor current of the PFC circuit reaches the average reference current and stops counting, and keeps the timing duration to obtain the first compensation curve (as shown in curve ②); wherein, the second preset slope is less than the forward timing slope of the first timer (i.e., the rising slope of the rising part of the curve Main_Cnt). In this way, the timing holding part of the first compensation curve and the falling part of the curve Main_Cnt can intersect, and the main switch is controlled to be turned off at the moment when the two curves intersect.

[0059] In another embodiment, the first compensation curve is shown as curve ③, and the first compensation curve is obtained by the following steps:

[0060] When the inductor current I L Reach the average reference current I ref When , the second timer starts counting forward from 0 with a third preset slope to obtain a first compensation curve (as shown in curve ③). The rising first compensation curve can intersect with the falling part of the curve Main_Cnt, and the main switch tube is controlled to be turned off when the two curves intersect.

[0061] Furthermore, in the above embodiment, the first timing point may be 0. However, if the first timing point is 0, slope compensation through the first compensation curve will cause a static error in the average current. In order to eliminate the static error of the target average current, Figure 5 As shown, the first timing point can be controlled to be the ideal opening time Ton_ideal 1 / N times, that is, the first timer starts from T on_ideal / N starts timing to obtain the Main_Cnt curve. Static error compensation is achieved through the following steps:

[0062] The ideal on-time T of the main switch is calculated based on the switching frequency, duty cycle and / or off-time of the main switch of the PFC circuit. on_ideal The ideal on-time is determined by the switching frequency and duty cycle, and the off-time is determined by the input voltage and output voltage of the PFC circuit; and the first timing point is set to the ideal on-time T on_ideal 1 / N times of , where N>1 and N is an integer.

[0063] refer to Figure 6 In another embodiment, in order to eliminate the static error of the target average current caused by the slope compensation, the first timing point can be controlled to be the main switch tube conduction time T of the previous switching cycle. main_ 1 / N times of (n-1), that is, the first timer starts from T main_ (n-1) / N starts timing to obtain the Main_Cnt curve. The static error compensation is implemented through the following steps:

[0064] Get the on-time T of the last switching cycle of the main switch tube main (n-1); setting the first timing point to 1 / N times the conduction time of the main switch tube in the previous switching cycle, where N>1 and N is an integer.

[0065] Figure 5 and Figure 6 By raising the first timing point and not setting it to 0, it is also possible to prevent the first timing curve and the reverse timing curve of the first timer from intersecting at a negative time value during the dynamic adjustment process, which cannot be achieved in engineering applications and makes the adjustment process slow, that is, the time from the interference time to the interference time elimination is longer.

[0066] Combine the following Figure 5 The compensation principle is explained in detail:

[0067] The first timer starts from T on_ideal / N starts timing, the inductor current I L Reach the average reference current I ref The forward timing is stopped and the reverse timing is started, until the reverse timing curve drops to intersect with the first compensation curve Slop_Cnt, and then the main switch tube is turned off.

[0068] In this embodiment, when the main switch is turned on, the first timer starts from the first timing point T on_ideal / N starts forward timing; the second timer starts forward timing from 0 with a slope of 1 / N (that is, the first preset slope k), where N>1. The first timer is mainly used to time and control the on-time of the main switch tube; the second timer is mainly used to generate a first compensation curve. In this embodiment, the first compensation curve is the timing curve of the second timer. Figure 5 and attached Figure 6 In the example, the forward timing slope of the first timer is recorded as k1, and the first preset slope is k, k=1 / N <k1。

[0069] When the inductor current I L Reach the average reference current I ref After that, the first timer counts in reverse direction, and the second timer continues to count in forward direction;

[0070] When the reverse timing curve of the first timer intersects with the first compensation curve, it means that the reverse timing of the first timer drops to the timing of the second timer. At this time, the main switch tube is turned off. In this embodiment, the main switch tube is not turned off when the inductor current drops to 0 or the first timing point, but when it drops to the timing of the second timer Slop_Cnt, which shortens the conduction time and allows the conduction time of the main switch tube to converge. Figure 5 As shown, after several switching cycles are adjusted, the main conduction time can be stabilized at a certain value at a specific phase point of the power frequency.

[0071] The compensation method provided in this embodiment is the on-time slope compensation, and can be T on_ideal / N is used to compensate for the static error of the average current. The system cost is low, and the additional static error of the target average current can be eliminated by setting the first timing point, so that no jitter occurs during mode switching. The inductor current can be obtained by sampling the switch current or directly by sampling the inductor current. In other words, the compensation method is applicable to both the switch current sampling and the inductor current sampling methods.

[0072] In addition, when the PFC control adopts digital control, the first timer and the second timer can be obtained by counting and clock signals. At this time, in this embodiment, the first timer is the first counter and the second timer is the second counter. Figure 5 When the main switch is turned on, the second counter will also count forward, and its slope is greater than 0 and less than or equal to 1 / 2 of the forward counting slope of the first counter. Specifically, the counting period of the first counter can be set to 0.5 times the counting period of the second counter; for example, the first counter counts once for each clock signal, and the second counter counts once for every 2 clock signals. When the first counter counts downward and is less than the count of the second counter, the main switch is turned off to play the role of slope compensation.

[0073] like Figure 5 As shown, assuming that the average reference current I ref The disturbance causes an upward fluctuation of ΔI ref , which results in an increase in the on-time of the main switch tube in this cycle, and the increase is recorded as ΔT on After that, the synchronous tube is turned off for the theoretical time T off The theoretical off time is determined by the input voltage, output bus voltage and switching period of the PFC circuit, which can be calculated by formula (1). In order to maintain the suppression of the average value of the inductor current and the average reference current, it can be deduced that:

[0074] The main conduction time of the Ts_n+1 cycle is reduced by 2*ΔT on / (1+k);

[0075] The main conduction time of Ts_n+2 period increases by 2*ΔT on / (1+k)^2;

[0076] The main conduction time of the Ts_n+3 period is reduced by 2*ΔT on / (1+k)^3;

[0077] The main conduction time of Ts_n+4 period increases by 2*ΔT on / (1+k)^4;

[0078] The main conduction time of the Ts_n+5 cycle is reduced by 2*ΔT on / (1+k)^5;

[0079] …

[0080] As shown above, the fluctuation decays cycle by cycle, and the main switch tube finally converges to a stable on-time value to operate, making the system control stable. Wherein, k is the slope of the first compensation curve.

[0081] See also Figure 6 In another slope compensation embodiment, the control method is as follows:

[0082] Get the on-time T of the last switching cycle of the main switch tube main_ (n-1);

[0083] When the main switch is turned on, the first timer starts from the first timing point T main_ (n-1) / N starts counting forward, the second timer starts counting forward from 0 with a slope of 1 / N (ie, the first preset slope) to obtain the first compensation curve Slop_Cnt; wherein, N>1, and N is an integer.

[0084] When the inductor current of the PFC circuit reaches the average reference current, the first timer starts counting backwards and the second timer starts counting forwards. The first timer is mainly used to time and control the on-time of the main switch tube. The second timer is mainly used to generate a first compensation curve. In this embodiment, the first compensation curve is the timing curve of the second timer.

[0085] The first compensation curve intersects with the reverse timing curve of the first timer, indicating that the reverse timing of the first timer drops to the forward timing of the second timer, at which time the main switch is turned off; in this embodiment, the main switch is not turned off when the inductor current drops to 0 or the first timing point, but when it drops to the timing of the second timer, shortening the conduction time so that the conduction time of the main switch can converge. Figure 5 As shown, after several switching cycles are adjusted, the main conduction time can be stabilized at a certain value at a specific phase point of the power frequency.

[0086] The compensation method provided in this embodiment is the on-time slope compensation, and can be T main_ (n-1) / N is used to compensate for the static error of the average current. The system cost is low, and the additional static error of the target average current can be eliminated by setting the first timing point, so that no jitter occurs during mode switching. This compensation method is applicable to both the inductor current sampling method and the switch tube current sampling method.

[0087] Based on the above PFC control method, the embodiment of the present application further provides a PFC control device 1, such as Figure 7 As shown, it is used to execute the PFC control method described in any of the above embodiments to reduce the instability caused by disturbances and improve the system control stability.

[0088] It should be noted that the control device can be an integrated circuit, or can be built with discrete devices, or can be implemented with discrete devices and a simple control chip. The PFC control method and control device proposed in this application are particularly suitable for digital control PFC control chips.

[0089] 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: The PFC circuit adopts 0.5Ton control, and the control method includes the following steps: When the main switch tube of the PFC circuit is turned on, the first timer starts counting forward from the first timing point until the inductor current of the PFC circuit reaches the average reference current; When the inductor current reaches the average reference current, the first timer counts backwards; During the conduction period of the main switch tube, a first compensation curve is obtained, wherein the first compensation curve represents a timing curve of the second timer; When the reverse timing curve of the first timer intersects the first compensation curve, the main switch tube is controlled to be turned off.

2. The PFC control method according to claim 1, characterized in that: The first compensation curve is obtained by at least the following steps: When the main switch tube is turned on, the second timer starts from 0 and starts forward timing with a first preset slope to obtain the first compensation curve; wherein the first preset slope is smaller than the forward timing slope of the first timer.

3. The PFC control method according to claim 1, characterized in that: The first compensation curve is obtained by the following steps: When the main switch tube is turned on, the second timer starts from 0 and starts to count forward with a second preset slope until the inductor current of the PFC circuit reaches the average reference current and stops counting, and keeps the timing time to obtain the first compensation curve; wherein the second preset slope is less than the forward timing slope of the first timer.

4. The PFC control method according to claim 1, characterized in that: The first compensation curve is obtained by the following steps: When the inductor current of the PFC circuit reaches the average reference current, the second timer starts counting forward from 0 at a third preset slope to obtain the first compensation curve.

5. The PFC control method according to any one of claims 1 to 4, characterized in that: The following steps are also included: The ideal on-time of the main switch is calculated according to the switching frequency, duty cycle and / or off-time of the main switch of the PFC circuit; the first timing point is set to 1 / N times of the ideal on-time, where N>1 and N is an integer.

6. The PFC control method according to any one of claims 1 to 4, characterized in that: The first timing point is 0.

7. The PFC control method according to any one of claims 1 to 4, characterized in that: The following steps are also included: Obtain the on-time of the main switch tube in the previous switching cycle; set the first timing point to 1 / N times the on-time of the main switch tube in the previous switching cycle, where N>1 and N is an integer.

8. The PFC control method according to claim 2, characterized in that: The first timer is a first counter, and the second timer is a second counter; a counting period of the first counter is 0.5 times of a counting period of the second counter.

9. The PFC control method according to any one of claims 1 to 4, characterized in that: The off time of the main switch is the theoretical off time; 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 when operating in CCM mode.

10. A PFC control device, suitable for a PFC circuit, characterized in that: The PFC circuit adopts 0.5Ton control, and the control device is used to execute the PFC control method according to any one of claims 1 to 9.

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