Single-sensor analog control method for three-level flying capacitor buck converter

Abstract

The application discloses a single-sensor analog control method of a three-level flying capacitor step-down converter, and comprises the following steps: analyzing the on-off logic of each switch device when the three-level flying capacitor step-down converter circuit normally operates, and describing the circuit working state according to the coordinate sequence (Q1, Q2) formed by the first switch device and the second switch device; taking one of the working mode points (1, 0) as an example to analyze the influence of the flying capacitor voltage balance on the normal operation of the circuit and the voltage balance of the device; then, a single-sensor analog control method is proposed to control the three-level flying capacitor step-down converter; then, the static stability characteristics of the technology applied to the three-level flying capacitor step-down converter are studied; in view of the situation that the subharmonic oscillation is generated within a certain range, the subharmonic oscillation is eliminated by using a slope compensation mode, and the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated is verified; and the compensation slope strategy is applied to the analog control circuit.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of power electronics, and particularly relates to a single-sensor analog control method for a three-level flying capacitor buck converter. BACKGROUND

[0002] In recent years, multi-level flying capacitor buck converters have attracted much attention in automotive power conversion systems due to their high efficiency and compactness. Typically, taking a three-level flying capacitor buck converter as an exemplary embodiment, this topology inherits the advantages of multi-level converter topology compared to the traditional two-level buck circuit, not only reducing the voltage stress on the switching device by half, but also reducing the voltage ripple of the filter inductor, thereby reducing the size and weight of the filter and the volume and cost of the entire system. Meanwhile, smaller magnetic components are conducive to system thermal management, improving the efficiency and stability of the converter.

[0003] During the operation of a multi-level flying capacitor buck converter, the above advantages can only be fully realized when the flying capacitor voltage reaches equilibrium. In the exemplary embodiment of the present application, for the three-level flying capacitor buck converter, the meaning of the flying capacitor voltage reaching equilibrium is that when the circuit reaches steady state, the flying capacitor's power transmission equals the discharge capacity and the flying capacitor voltage value equals half of the input voltage. In practical applications, due to the existence of parasitic parameters in the circuit and the differences between power switching elements, it is difficult for the flying capacitor voltage to remain balanced at all times, and controlling the flying capacitor voltage balance has become a major challenge in the application of multi-level flying capacitor buck converter topology.

[0004] For the problem of flying capacitor voltage imbalance, there have been some researches, but most of the methods focus on using active balancing strategies and relying on multiple sensors for control. Although these methods can solve the voltage imbalance problem to some extent, they also bring some new challenges. First, increasing the number of sensors not only increases the cost of the system, but also leads to an increase in the size of the controller, which is contrary to the trend of miniaturization and lightweight of modern power electronic devices. Second, the complexity of multi-sensor data processing will bring additional computational burden to the control system, which may affect the response speed and control accuracy of the system. In high-speed and high-precision application scenarios, this is particularly critical, because any delay or error can negatively affect system performance. In addition, the reliability and maintenance difficulty of a multi-sensor system are relatively high. Sensor failure or signal transmission problems can cause the control system to fail, thereby affecting the normal operation of the entire system. SUMMARY

[0005] The technical problem to be solved by the present application is to overcome the problem of excessive number of sensors required for balancing the flying capacitor voltage in the prior art, and to provide a single-sensor analog control method for a three-level flying capacitor step-down converter, thereby providing a more convenient solution to the problem of balancing the flying capacitor voltage in the three-level flying capacitor step-down circuit.

[0006] The single-sensor analog control method for a three-level flying capacitor step-down converter provided by the embodiments of the present disclosure comprises the following steps:

[0007] The on-off logic of each switching device in the three-level flying capacitor step-down converter circuit during normal operation is analyzed, and the circuit operating state is described based on the coordinate sequence (Q1, Q2) formed by the first switching device and the second switching device. There are four operating modes, namely (0, 0), (0, 1), (1, 0), and (1, 1). According to the range of the voltage conversion ratio G, the circuit operating dynamic switching process is divided into two operating modes. The voltage conversion ratio G is the ratio of the output voltage V o to the input voltage V g , and the two operating modes are as follows: mode one, i.e., G < 0.5, the operating mode points are sequentially switched in the order of (0, 1) → (0, 0) → (1, 0) → (0, 0); mode two, i.e., G > 0.5, the operating mode points are sequentially switched in the order of (0, 1) → (1, 1) → (1, 0) → (1, 1).

[0008] The influence of flying capacitor voltage balancing on the normal operation of the circuit and the voltage balancing of the devices is analyzed by taking one of the operating mode points (1, 0) as an example. Then, a single-sensor analog control method for controlling the three-level flying capacitor step-down converter is proposed, wherein the analog control circuit is specifically implemented by using RS flip-flops and D flip-flops. Then, the static stability characteristics of the technology applied to the three-level flying capacitor step-down converter are studied. When 0.25 < G < 0.5 or 0.75 < G < 1, the system is stable. When 0 < G < 0.25 or 0.5 < G < 0.75, the system is unstable and produces subharmonic oscillation.

[0009] For the case of producing subharmonic oscillation within a certain range, a slope compensation method is used to eliminate the subharmonic oscillation, and the compensation slope slope value that satisfies the condition for eliminating the subharmonic oscillation is derived, and the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated is verified.

[0010] The compensation slope strategy is applied to the analog control circuit.

[0011] In one possible implementation, the three-level flying capacitor step-down converter circuit comprises a direct current input voltage V g , a flying capacitor C fly , a bridge arm composed of switching devices, and a filter inductor Lo Output capacitor C o and DC output; wherein, DC input voltage V g The bridge arm, composed of switching devices, is connected in parallel. The bridge arm comprises a first switching device Q1, a second switching device Q2, a third switching device Q3, and a fourth switching device Q4 connected in series. The first switching device Q1 and the fourth switching device Q4 exhibit complementary conduction characteristics, as do the second switching device Q2 and the third switching device Q3. A flying capacitor C... fly It is connected in parallel with the series branch formed by the second switching device Q2 and the third switching device Q3; the filter inductor L o and output capacitor C o The series branch formed by the third switch Q3 and the fourth switch Q4 is connected in parallel with the series branch formed by the third switch Q3 and the fourth switch Q4; the output capacitor C o Connected in parallel with the DC output. Attached Figure Description

[0012] Figure 1 This is the basic circuit structure of a three-level flying capacitor buck converter.

[0013] Figure 2 for Figure 1 The diagram shows the four operating modes of the three-level flying capacitor buck converter circuit and their equivalent circuit diagrams.

[0014] Figure 3 The proposed analog leading-edge voltage dual-loop feedback V based on a single sensor 2 Control technology is applied Figure 1 The diagram shows the control structure of a three-level flying capacitor buck converter.

[0015] Figure 4 for Figure 3 The specific implementation method of the analog control circuit described in the document (without slope compensation);

[0016] Figure 5 Simulated leading edge V in CCM mode when G < 0.5 2 Control waveforms of a three-level flying capacitor buck converter after positive and negative disturbances occur;

[0017] Figure 6 Simulated leading edge V in CCM mode when G < 0.5 2 The control waveform after introducing a compensation ramp when a positive disturbance occurs in the control three-level flying capacitor buck converter;

[0018] Figure 7 When G < 0.5, consider the flying capacitance C. fly With small perturbation V fly Switching waveforms and circuit waveforms at the time;

[0019] Figure 8 For Figure 3 The specific implementation method of the analog control circuit (after adding the slope compensation) is described. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of the present application.

[0021] The present disclosure provides a single-sensor analog control method for a three-level flying capacitor buck converter, comprising the following steps:

[0022] The on-off logic of each switching device of the three-level flying capacitor buck converter circuit during normal operation is analyzed, and the circuit operating state is described according to the coordinate sequence (Q1, Q2) formed by the first switching device and the second switching device. There are four working modes, namely (0, 0), (0, 1), (1, 0) and (1, 1). According to the range of the voltage conversion ratio G, the circuit working dynamic switching process is divided into two working modes. The voltage conversion ratio G is the ratio of the output voltage V o to the input voltage V g , which are mode one, i.e., G < 0.5, and the working mode point is sequentially switched in the order of (0, 1) → (0, 0) → (1, 0) → (0, 0); and mode two, i.e., G > 0.5, and the working mode point is sequentially switched in the order of (0, 1) → (1, 1) → (1, 0) → (1, 1);

[0023] Taking one of the working mode points (1, 0) as an example, the influence of flying capacitor voltage balance on the normal operation of the circuit and the voltage balance of the device is analyzed. Then, a single-sensor analog control method for controlling the three-level flying capacitor buck converter is proposed, in which the analog control circuit is specifically implemented by using RS flip-flops and D flip-flops. Then, the static stability characteristics of the technology applied to the three-level flying capacitor buck converter are studied. When 0.25 < G < 0.5 or 0.75 < G < 1, the system is stable; when 0 < G < 0.25 or 0.5 < G < 0.75, the system is unstable and produces subharmonic oscillation;

[0024] Further, for the case of subharmonic oscillation within a certain range, a slope compensation method is used to eliminate the subharmonic oscillation, and the compensation slope slope value that satisfies the condition for eliminating the subharmonic oscillation is derived, and the characteristic of natural balance of the flying capacitor voltage when the subharmonic oscillation is eliminated is verified;

[0025] Finally, the compensation ramp strategy was applied to the analog control circuit.

[0026] like Figure 1 This paper presents the basic circuit structure of a three-level flying capacitor buck converter circuit used in a specific application example of the present invention. The three-level flying capacitor buck converter circuit includes a DC input voltage V g Flying capacitor C fly Bridge arms composed of switching devices, and filter inductor L o Output capacitor C o And DC output. Wherein, the DC input voltage V g The bridge arm, composed of switching devices, is connected in parallel. The bridge arm comprises four switching devices connected in series: Q1, Q2, Q3, and Q4. Q1 and Q4 exhibit complementary conduction characteristics, as do Q2 and Q3. Flying capacitor C fly It is connected in parallel with the series branch formed by the second switching device Q2 and the third switching device Q3. Filter inductor L o and output capacitor C o The series branch formed by these two switches is connected in parallel with the series branch formed by the third switch Q3 and the fourth switch Q4. Output capacitor C o It is connected in parallel with the DC output. In an exemplary embodiment of the present invention, the DC output is taken as an example of a purely resistive load R connected in parallel, and the voltage across the purely resistive load R is denoted as the output voltage V. o Meanwhile, to aid in subsequent explanations, Figure 1 In a three-level flying capacitor buck converter circuit, the voltage across the series branch of the third switching device Q3 and the fourth switching device Q4 is denoted as the switching node voltage V. sw And assume the flying capacitor C fly and filter inductor L o The direction of the reference current is as follows Figure 1 As shown.

[0027] Furthermore, for Figure 1 The three-level flying capacitor buck converter circuit has an input voltage V. g With the first switching device Q1 and the flying capacitor C fly The first switching circuit is formed by the fourth switching device Q4; simultaneously, the flying capacitor C... flyThe second switch device Q2 and the third switch device Q3 form a second switch loop. The driving signals of the first switch device Q1 and the fourth switch device Q4 are complementary, and the driving signals of the second switch device Q2 and the third switch device Q3 are complementary. When the three-level flying capacitor buck converter circuit reaches a steady state, the duty cycles of the driving signals of the first switch device Q1 and the second switch device Q2 are equal and the phases are 180 degrees apart.

[0028] Further, for the three-level flying capacitor buck converter circuit, if the driving signal of a certain switch device is high, the switch device is turned on, denoted as Q n =1 (wherein n=1, 2, 3, 4); if the driving signal of a certain switch device is low, the switch device is turned off, denoted as Q n =0 (wherein n=1, 2, 3, 4). For the driving signals of the four switch devices, because there are complementary logics between any two, only the driving signals of the first switch device Q1 and the second switch device Q2 are taken as examples to illustrate possible working conditions of the circuit under the control of the driving signals. Referring to Figure 2 , the on state of the first switch device Q1 is taken as the horizontal coordinate, and the on state of the second switch device Q2 is taken as the vertical coordinate. Because the switch device only has two states of being turned on and turned off, the on states of the first switch device Q1 and the second switch device Q2 are taken to describe Figure 1 the working conditions of the three-level flying capacitor buck converter circuit. There are four possibilities, (0, 0), (0, 1), (1, 0), and (1, 1).

[0029] In a specific application example, one of the possible circuit working conditions is taken as an example to be described in detail, but the embodiments of the present application are not limited thereto. Referring to Figure 2 In the working condition of the (1, 0) coordinate point, when the first switch device Q1 is turned on and the second switch device Q2 is turned off, the fourth switch device Q4 is turned off and the third switch device Q3 is turned on under the driving signals of the complementary logics accordingly, wherein the switch device that is turned on is equivalent to a wire, and the switch device that is turned off is not drawn, and the equivalent circuit working mode is as shown in Figure 2 . At the same time, in the first switch loop, the voltage relationship exists in the following equation, and the flying capacitor C fly has a voltage v fly across the two ends, and the fourth switch device Q4 has a voltage

[0030]

[0031] In the second switch loop, the voltage relationship exists in the following equation, and the second switch device Q2 has a voltage

[0032]

[0033] As can be seen from Equations (2) and (3), if the voltage v across the flying capacitor C fly can reach the steady-state value, that is fly then the voltage drops of the second switching device Q2 and the fourth switching device Q4 are equal and only half of the input voltage V . Conversely, if the voltage v across the flying capacitor C g cannot reach the steady-state value, that is, the situation of fly or fly occurs, it will cause the voltage drops of the second switching device Q2 and the fourth switching device Q4 to be unequal, the flying capacitor voltage not to reach the steady-state value, the charge and discharge to be unbalanced, and ultimately the three-level flying capacitor buck converter system shown will be unbalanced and lose its circuit function. Therefore, for the three-level flying capacitor buck converter circuit shown Figure 1 controlling the voltage v across the flying capacitor C fly to reach balance is particularly crucial for the normal operation of this circuit. fly

[0034] In a specific application example, for the problem of balancing the voltage v across the flying capacitor C of the three-level flying capacitor buck converter circuit shown Figure 1 a single-sensor analog control strategy is proposed, that is, the analog leading-edge type voltage double-loop feedback (V fly fly ) control technology based on a single sensor. [[ID=�2]]

[0035] In a specific application example, the proposed analog leading-edge type V 2 control technology based on a single sensor is applied to the three-level flying capacitor buck converter shown Figure 1 . This technology only needs to use a single voltage sensor to monitor and regulate the output voltage, which can not only ensure that the output voltage V of the three-level flying capacitor converter 2 accurately reaches the preset target value, but also can simultaneously achieve the automatic balance of the voltage of the flying capacitor C o . The control structure is shown in fly [[ID=4ģ]]<00Ͳ00245> o . The control idea is based on the control of the ripple of the output voltage V[[ID=4ģ]] o . As shown Figure 3 , on the basis of the basic circuit of the three-level flying capacitor buck converter shown Figure 1 , the equivalent series resistance R e of the branch of the output capacitor C e is reflected. Compared with the load resistance R, R L <<R, then the high-frequency changing inductor current ripple Δi o on the inductor e <<R, then the high-frequency changing inductor current ripple Δi oo e o e L e o cap o cap L e o L 2

[0036] s s 2 2 2

[0037] o ​​​​​​​​​​​​​​​​​​​​​​​​g The ratio of the voltage conversion ratio G, i.e. According to the range of the voltage conversion ratio G, the actual working circuit switching of the three-level flying capacitor buck converter is divided into two modes, which are mode one: when G < 0.5, the circuit working mode is in Figure 2 The equivalent circuit working point is switched in the order of (0, 1)→(0, 0)→(1, 0)→(0, 0) in turn; mode two: when G > 0.5, the circuit working mode is in Figure 2 The equivalent circuit working point is switched in the order of (0, 1)→(1, 1)→(1, 0)→(1, 1)→(0, 1) in turn.

[0038] In a specific application example, one of the working modes of the three-level flying capacitor buck converter, i.e., mode one, G < 0.5, is taken as an example to expand the detailed description of the analog front edge type V 2 The control principle of the control technology, but the embodiments of the present application are not limited thereto.

[0039] Since the driving signal S1 of the first switch device of the three-level flying capacitor buck converter and the driving signal S2 of the second switch device are different by 180°, assuming that the switching period is T s , the switching frequency is f s , Then S1 and S2 are different by time staggered driving. In the embodiments of the present disclosure, the switching node change period is defined as T , and the switching node change frequency is f

[0040] The specific implementation and control principle of the analog control circuit are as follows: Figure 4 , Figure 3 The analog front edge type V 2 control technology strategy, the analog front edge type V 2 control strategy in the outer control loop compares the output voltage v s collected by the output voltage sensor with the output voltage reference V ref set in advance, and the difference is amplified by an error amplifier to generate a control voltage v pi . The external clock signal is connected to the reset end, i.e., the R end, of the RS flip-flop, and the frequency of the external clock signal is C s = 2f sw . Then in each switching node period Initially, a clock signal input provides a reset signal to the RS flip-flop, resetting it. The Q output of the RS flip-flop then goes low and enters two AND gates. Both AND gates simultaneously output low, generating drive signals S1 = 0 and S2 = 0. The outputs of drive signals S1 and S2 then pass through two NOT gates, generating drive signals S3 = 1 and S4 = 1 for the corresponding complementary switching devices. These drive signals control the on / off state of the four switching devices: Q1 is off, Q2 is off, Q3 is on, and Q4 is on. At this point, the three-level flying capacitor converter is in operation. Figure 2 The (0,0) working mode point has an output voltage V. o As the initial value decreases linearly, the output voltage sensor acquires the output voltage V. o Changes, v s It decreases linearly from the initial value. When v... s Reduced to the control voltage v generated by the outer control loop pi When the comparator outputs a switch trigger signal, and the three-level flying capacitor buck converter is operating in mode one (i.e., voltage conversion ratio G < 0.5), the switch trigger signal is sent to the set input (S terminal) of the RS flip-flop. The switch trigger signal sets the RS flip-flop, and the Q output of the RS flip-flop outputs a high level, which enters two AND gates. Simultaneously, the high-level signal is transmitted to the clock input DClk of the D flip-flop. For the D flip-flop, the input D is ANDed with the inverting output... The connection is such that each time the DClk clock input signal arrives, the output of the D flip-flop will "flip" once, thus causing the drive signals S1 and S2 to differ in phase. The alternating high-level outputs periodically drive the first switching device Q1 and the second switching device Q2 to turn on, thereby enabling the normal operation of the three-level flying capacitor buck converter.

[0041] Because this control technology directly regulates the converter's output voltage V o Therefore, by analyzing the output voltage V o The effectiveness of the proposed technology is evaluated by its static stability. Taking one of the operating modes of the three-level flying capacitor buck converter, i.e., mode one, when G < 0.5, as an example, the following detailed explanation is provided: the proposed single-sensor-based analog leading-edge V-type converter... 2 The static stability of the control technology is considered, but this disclosure is not limited thereto. Output voltage sample value v s The output voltage V of the three-level flying capacitor buck converter o The actual value has the same static stability characteristic, therefore, the output voltage sampling value v can be analyzed. s The effectiveness of the proposed technology is evaluated by assessing its static stability. The analysis process is as follows:

[0042] First, temporarily assume the flying capacitor voltage v fly has reached equilibrium, that is Referring to Figure 5 , it is given that the three-level flying capacitor buck converter in CCM mode (continuous conduction mode, that is, the inductor current never reaches 0 in a switching period, that is, the output voltage is in a steady output state) and when the voltage conversion ratio satisfies G < 0.5, the analog front edge type V 2 control waveform after the occurrence of positive and negative disturbances. The solid line is the steady-state waveform of the output voltage sampling value v s , and the dashed line is the transient waveform of v s after the occurrence of disturbances. m1 and m2 are the slopes of the output voltage rising and falling, respectively, v pi is the control voltage output by the error amplifier, T s is the switching period, and T sw is the switching node change period. Δv s [k] is the voltage deviation caused by positive (negative) disturbance in a certain output voltage change period, and Δv s [k+1] is the voltage deviation caused by Δv s [k]. According to the working principle of the three-level flying capacitor buck converter, we have:

[0043]

[0044] For the three-level flying capacitor buck converter in CCM mode, V o = GV g , and Figure 5 Under the conditions of positive and negative disturbances, we have:

[0045]

[0046] As can be seen from equation (4), when 0.25 < G < 0.5, Δv s [k+1] < Δv s [k], the voltage deviation will gradually decay to zero, indicating that the analog front edge type V 2 control Figure 1 proposed in the present application is stable; when 0 < G < 0.25, Δv s [k+1] > Δv s [k], the voltage deviation will gradually amplify, indicating that the analog front edge type V 2 control Figure 1 proposed in the present application is unstable, and subharmonic oscillation will occur.

[0047] In a specific application example, for the case of sub-harmonic oscillation in the range, the slope compensation method is used to eliminate the sub-harmonic oscillation, and the minimum slope value of the required compensation slope that can eliminate the sub-harmonic oscillation is derived. When 0 < G < 0.25, in order to make the analog front edge type V 2 The control three-level flying capacitor buck converter can still work stably, and a new control voltage can be formed by superimposing a slope signal with a slope k comp on the basis of the control voltage v pi , and input to one end of the comparator for comparison with the output voltage.

[0048] In a specific application example, the slope compensation method is used when the output voltage of the analog front edge type V 2 controlled three-level flying capacitor buck converter appears positive disturbance, and the process of deriving the minimum slope value of the compensation slope is described in detail, but the embodiments of the present application are not limited thereto. The process of deriving the minimum slope value of the compensation slope is as follows: reference Figure 6 is a schematic diagram of the principle of the slope compensation method when the output voltage appears positive disturbance. From Figure 6 , we can get:

[0049]

[0050] Substituting equation (3) into equation (5), we can get:

[0051]

[0052] From equation (6), if holds in the range of 0 < G < 0.5, we get:

[0053]

[0054] Based on this, the following conclusions can be drawn: in CCM mode, in order to ensure the stable operation of the analog front edge type V 2 controlled three-level flying capacitor buck converter, superimposing a slope compensation voltage with a slope satisfying equation (7) on the control voltage v pi can eliminate the sub-harmonic oscillation problem of the analog front edge type V 2 controlled three-level flying capacitor buck converter when 0 < G < 0.25.

[0055] It is temporarily assumed that the flying capacitor voltage v fly has reached equilibrium, and the application of the analog front edge type V 2 control technology based on a single sensor proposed in the present application to the static stability of the three-level flying capacitor buck converter is further analyzed. The following conclusions are drawn: in CCM mode, the three-level flying capacitor buck converter is controlled by the analog front edge type V2 Control, in the working mode one, namely G <0.5, the circuit stable working range is 0.25 <G <0.5, and in the range of 0 <G <0.25, the circuit works unstable, and the sub-harmonic oscillation is generated. Further, through the voltage control signal v pi The superimposed slope satisfies The slope voltage, which can eliminate the sub-harmonic oscillation, realizes the stable operation of the circuit in the working mode one, namely G <0.5. However, even if the assumption that the flying capacitor voltage v fly has reached the balance” is not established, the above conclusion is still established, and when the sub-harmonic oscillation is eliminated, the flying capacitor voltage can reach the balance autonomously.

[0056] Further, the conclusion that the flying capacitor voltage can reach the balance autonomously after the sub-harmonic oscillation is eliminated is verified, and the verification process is as follows: it is assumed that there is a disturbance on the flying capacitor, namely the flying capacitor voltage As Figure 7 , due to the existence of the disturbance on the flying capacitor, the influence is bound to be reflected in the charge and discharge imbalance of the flying capacitor, and simultaneously causes the duty cycles of the two driving signals S1 and S2 to be different, which are respectively set as D1 and D2. According to the geometric relationship of the waveform, the following is obtained:

[0057]

[0058] The average current formula flowing through the flying capacitor is:

[0059]

[0060] Wherein, A pos and A neg are the positive and negative areas of the flying capacitor current curve, which are solved according to the geometric relationship and substituted into formula (10), and the average current formula of the flying capacitor in the range of 0 <G <0.5 is obtained:

[0061]

[0062] According to formula (11), in the range of 0 <G <0.5, when the compensation slope satisfies , the positive and negative of the flying capacitor average current I fly and the positive and negative of the flying capacitor voltage disturbance V fly are different. Therefore, the conclusion that the analog front-end type V 2 control technology is applied to Figure 1The three-level flying capacitor buck converter inherently stabilizes the flying capacitor voltage to reach a steady state once the sub-harmonic oscillation of the converter output voltage is suppressed.

[0063] It can be appreciated by those skilled in the art that although the three-level flying capacitor buck converter circuit is analyzed in the range of 0 < G < 0.5, similar derivation and conclusion can be obtained when 0.5 < G < 1. In summary, the following conclusions can be obtained:

[0064] (1) The analog front edge type V 2 When controlling the three-level flying capacitor buck converter, for the voltage conversion ratio When 0.25 < G < 0.5 or 0.75 < G < 1, the system is stable; when 0 < G < 0.25 or 0.5 < G < 0.75, the system is unstable and sub-harmonic oscillation occurs;

[0065] (2) For sub-harmonic oscillation, when the slope satisfies The slope is superimposed on the voltage control signal v pi generated by the outer loop, the sub-harmonic oscillation can be eliminated;

[0066] (3) Once the output voltage sub-harmonic oscillation is suppressed, the analog front edge type V 2 control method inherently stabilizes the flying capacitor voltage in the three-level flying capacitor buck converter to reach a steady state.

[0067] In the embodiments of the present disclosure, for the case of sub-harmonic oscillation occurring in a certain range, the Figure 3 The specific implementation of the analog control circuit after superimposing the slope compensation signal is described. Referring to Figure 8 , in a specific application example, on the basis of the implementation scheme Figure 4 , a compensation slope with a slope satisfying is superimposed on the voltage control signal v pi generated by the control outer loop. Not only can the sub-harmonic oscillation be suppressed, but also the flying capacitor voltage can be ensured to reach a balance.

[0068] It should be understood that the example embodiments described herein are illustrative and non-limiting. Although one or more embodiments of the present application are described in conjunction with the attached figures, it should be understood that various changes in form and detail can be made without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. A single-sensor analog control method for a three-level flying capacitor buck converter, characterized in that, Includes the following steps: The three-level flying capacitor buck converter includes a bridge arm composed of switching devices, and the bridge arm composed of switching devices further includes a first switching device connected in series. Q 1. Second switching device Q 2. Third switching device Q 3 and the fourth switching device Q 4; This paper analyzes the on / off logic of each switching device during normal operation of a three-level flying capacitor buck converter circuit, and uses the coordinate sequence formed by the first and second switching devices as an example. Q 1, Q 2) To accurately describe the circuit's operating state, there are four operating modes: (0,0), (0,1), (1,0), and (1,1). Based on the voltage conversion ratio... G The range divides the dynamic switching process of the circuit into two operating modes, the voltage conversion ratio... G Output voltage V o With input voltage V g The ratios are respectively for Mode 1, i.e. G When <0.5, the working mode points switch sequentially in the order of (0,1)→(0,0)→(1,0)→(0,0); mode two is... G When the value is greater than 0.5, the working mode points switch sequentially in the order of (0,1)→(1,1)→(1,0)→(1,1); The impact of flying capacitor voltage balance on normal circuit operation and device voltage equalization is analyzed using one of the operating mode points (1,0). Then, a structure for controlling a three-level flying capacitor buck converter using a single-sensor analog control method is proposed. The analog control circuit is implemented using RS flip-flops and D flip-flops. The RS flip-flop receives an external clock signal as reset information and a switch trigger signal output from a comparator as a set signal, thereby generating a drive signal. The D flip-flop, triggered by a high-level signal output from the RS flip-flop, flips the drive signal to achieve the desired setting. S 1 and S 2 Alternating outputs thus achieve the first switching device Q 1 Second switching device Q 2 The alternating conduction; then the static stability characteristics of the three-level flying capacitor buck converter were studied by applying the single-sensor analog control method, when 0.25 < G <0.5 or 0.75< G When <1, the system is stable; when 0 < G <0.25 or 0.5< G When the value is less than 0.75, the system is unstable and will produce subharmonic oscillations. To address the issue of subharmonic oscillations occurring within a certain range, a slope compensation method is employed to eliminate these oscillations, and the slope value of the compensation slope for eliminating subharmonic oscillations is derived to satisfy the following conditions. And to verify the characteristic that the voltage of the flying capacitor naturally balances while the harmonic oscillation is eliminated. For output capacitor C o The equivalent series resistance of the branch, L o For filtering inductors; The compensation ramp strategy is applied to the analog control circuit.

2. The single-sensor analog control method for a three-level flying capacitor buck converter as described in claim 1, characterized in that, The three-level flying capacitor buck converter further includes a DC input voltage. V g Flying capacitor Filter inductor L o Output capacitor C o and DC output; wherein, DC input voltage V g The first switching device is connected in parallel with the bridge arm formed by the switching device. Q 1 and the fourth switching device Q 4. Exhibiting complementary conduction characteristics, the second switching device Q 2 and the third switching device Q 3 exhibits complementary conduction characteristics; flying capacitor With the second switching device Q 2 and the third switching device Q The three series branches are connected in parallel; the filter inductor L o and output capacitor C o The series branch formed with the third switching device Q 3 and the fourth switching device Q The four series branches are connected in parallel; the output capacitor C o Connected in parallel with the DC output.

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