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

Abstract

The invention discloses a single-sensor analog control method for a three-level flying capacitor buck converter, which comprises the following steps of: analyzing the on-off logic of each switching device when a three-level flying capacitor buck converter circuit normally operates, and calculating a coordinate sequence (Q1, Q2) formed by a first switching device and a second switching device; q2) is used as the standard to describe the working state of the circuit; taking one working mode point (1, 0) as an example to analyze the influence of flying capacitor voltage balance on the normal operation of the circuit and the voltage sharing of the device; a single-sensor analog control method is provided to control the three-level flying capacitor buck converter; then, the static stability characteristic of the technology applied to the three-level flying capacitor buck converter is studied; for the situation that subharmonic oscillation is generated within a certain range, subharmonic oscillation is eliminated in a slope compensation mode, and the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated is verified; a compensation slope strategy is applied to the analog control circuit.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a single-sensor analog control method for a three-level flying capacitor buck converter. Background Art

[0002] In recent years, multi-level flying capacitor buck converters have attracted much attention in automotive level conversion systems due to their high efficiency and compactness. Typically, a three-level flying capacitor buck converter is used as an exemplary embodiment. Compared with the traditional two-level buck circuit, this topology inherits the advantages of the multi-level converter topology, 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, reducing the volume and cost of the entire system; at the same time, smaller magnetic components are conducive to system thermal management and improve the efficiency and stability of the converter.

[0003] During the operation of the multi-level flying capacitor buck converter, the above advantages can only be fully realized when the flying capacitor voltage reaches a balance. In an exemplary embodiment of the present invention, for the three-level flying capacitor buck converter, the flying capacitor voltage reaches a balance, which means that when the circuit reaches a steady state, the power transmission of the flying capacitor is equal to the discharge amount and the flying capacitor voltage value is equal to half of the input voltage. In practical applications, due to the parasitic parameters in the circuit and the differences between the power switching elements, it is difficult to always keep the flying capacitor voltage balanced. The problem of controlling the flying capacitor voltage balance has become a major challenge in the topological application of multi-level flying capacitor buck converters.

[0004] There have been some studies on the flying capacitor voltage imbalance problem, but most methods focus on the use of active balancing strategies and rely on multiple sensors for control. Although these methods can solve the voltage imbalance problem to a certain extent, they also bring some new challenges. First, increasing the number of sensors will not only increase the cost of the system, but also increase the size of the controller, which runs counter to the development trend of miniaturization and lightweight of modern power electronic equipment. Secondly, 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. This is particularly critical in high-speed and high-precision application scenarios, because any delay or error may have a negative impact on system performance. In addition, the reliability and maintenance difficulty of multi-sensor systems are also relatively high. Sensor failure or signal transmission problems may cause the control system to fail, which in turn affects the normal operation of the entire system. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the deficiency of too many sensors required for the existing flying capacitor voltage balance, and to provide a single sensor analog control method for a three-level flying capacitor buck converter, thereby providing a more convenient solution to the flying capacitor voltage balance problem in a three-level flying capacitor buck circuit.

[0006] The embodiment of the present disclosure provides a single sensor analog control method for a three-level flying capacitor buck converter, comprising the following steps:

[0007] The on-off logic of each switch device in the normal operation of the three-level flying capacitor buck converter circuit is analyzed, and the working state of the circuit is described based on the coordinate sequence (Q1, Q2) composed of the first switch device and the second switch device. There are four working modes, namely (0,0), (0,1), (1,0), and (1,1). The circuit working dynamic switching process is divided into two working modes according to the range of the voltage conversion ratio G. The voltage conversion ratio G is the output voltage V o With input voltage V g The ratio is: mode 1, i.e., when G<0.5, the working modal points are switched in the order of (0,1)→(0,0)→(1,0)→(0,0) in a cycle; mode 2, i.e., when G>0.5, the working modal points are switched in the order of (0,1)→(1,1)→(1,0)→(1,1) in a cycle;

[0008] 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 balancing of the device is analyzed; then a structure of controlling the three-level flying capacitor buck converter using a single sensor analog control method is proposed, in which the analog control circuit is implemented by using RS trigger and D trigger; then the static stability characteristics of the three-level flying capacitor buck converter are studied by applying this technology. 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 will produce subharmonic oscillations;

[0009] In the case of subharmonic oscillation within a certain range, slope compensation is used to eliminate subharmonic oscillation and the compensation slope value for eliminating subharmonic oscillation is derived to meet the condition And verify the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated;

[0010] Apply the compensation ramp strategy to the analog control circuit.

[0011] In a possible implementation manner, the three-level flying capacitor buck converter circuit includes a DC input voltage V g 、Flying capacitor C fly , the bridge arm composed of the switching device, the filter inductor Lo , output capacitor C o and DC output; where the DC input voltage V g The bridge arm formed by the switching device is connected in parallel; the bridge arm formed by the switching device includes a first switching device Q1, a second switching device Q2, a third switching device Q3 and a fourth switching device Q4 connected in series in sequence, wherein the first switching device Q1 and the fourth switching device Q4 present complementary conduction characteristics, and the second switching device Q2 and the third switching device Q3 present complementary conduction characteristics; the flying capacitor C fly connected in parallel with the series branch formed by the second switch device Q2 and the third switch device Q3; the filter inductor L o and output capacitor C o The series branch formed by the third switch device Q3 and the fourth switch device Q4 is connected in parallel with the series branch formed by the third switch device Q3 and the fourth switch device Q4; the output capacitor C o Connect in parallel with the DC output. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0013] Figure 2 for Figure 1 Four operating modes of the three-level flying capacitor buck converter circuit and its equivalent circuit diagram shown;

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

[0015] Figure 4 for Figure 3 A specific implementation method of the analog control circuit described in (without adding 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;

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

[0018] Figure 7 When G is less than 0.5, consider the flying capacitor C fly With small perturbation V fly Switching waveform and circuit waveform when ;

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

[0020] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the 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.

[0021] The embodiment of 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 switch device in the normal operation of the three-level flying capacitor buck converter circuit is analyzed, and the working state of the circuit is described based on the coordinate sequence (Q1, Q2) composed of the first switch device and the second switch device. There are four working modes, namely (0,0), (0,1), (1,0), and (1,1). The circuit working dynamic switching process is divided into two working modes according to the range of the voltage conversion ratio G. The voltage conversion ratio G is the output voltage V o With input voltage V g The ratio is: mode 1, i.e., when G<0.5, the working modal points are switched in the order of (0,1)→(0,0)→(1,0)→(0,0) in a cycle; mode 2, i.e., when G>0.5, the working modal points are switched in the order of (0,1)→(1,1)→(1,0)→(1,1) in a cycle;

[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 balancing of the device is analyzed; then a structure of controlling the three-level flying capacitor buck converter using a single sensor analog control method is proposed, in which the analog control circuit is implemented by using RS trigger and D trigger; then the static stability characteristics of the three-level flying capacitor buck converter are studied by applying this technology. 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 will produce subharmonic oscillations;

[0024] Then, for the situation where subharmonic oscillation occurs within a certain range, slope compensation is used to eliminate subharmonic oscillation and the compensation slope value for eliminating subharmonic oscillation is derived to meet the condition And verify the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated;

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

[0026] like Figure 1 , a basic circuit structure of a three-level flying capacitor buck converter circuit used in a specific application example of the present invention is given. The three-level flying capacitor buck converter circuit includes a DC input voltage V g 、Flying capacitor C fly , the bridge arm composed of the switching device, the filter inductor L o , output capacitor C o And DC output. Among them, the DC input voltage V g The bridge arm formed by the switching device is connected in parallel. The bridge arm formed by the switching device includes a first switching device Q1, a second switching device Q2, a third switching device Q3 and a fourth switching device Q4 connected in series in sequence, wherein the first switching device Q1 and the fourth switching device Q4 present complementary conduction characteristics, and the second switching device Q2 and the third switching device Q3 present complementary conduction characteristics. The flying capacitor C fly The filter inductor L is connected in parallel with the series branch formed by the second switch device Q2 and the third switch device Q3. o and output capacitor C o The series branch formed by the third switch device Q3 and the fourth switch device Q4 is connected in parallel with the series branch formed by the third switch device Q3 and the fourth switch device Q4. o In the exemplary embodiment of the present invention, the DC output is connected in parallel with a pure resistive load R as an example, and the voltage across the pure resistive load R is recorded as the output voltage V o . At the same time, to help with subsequent explanations, Figure 1 In the three-level flying capacitor buck converter circuit, the voltage across the series connection of the third switch device Q3 and the fourth switch device Q4 is denoted as the switch node voltage V sw , and assuming that the flying capacitor C fly and filter inductor L o The reference current direction is Figure 1 shown.

[0027] Furthermore, for Figure 1 The three-level flying capacitor step-down converter circuit, the input voltage V g With the first switch device Q1, the flying capacitor C fly The fourth switch device Q4 forms a first switch loop; at the same time, the flying capacitor C flyThe first switching device Q1 and the fourth switching device Q4 form a second switching loop together with the second switching device Q2 and the third switching device Q3. The driving signals of the first switching device Q1 and the fourth switching device Q4 are complementary, while the driving signals of the second switching device Q2 and the third switching 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 switching device Q1 and the second switching device Q2 are equal and the phase difference is 180°.

[0028] Furthermore, for the above three-level flying capacitor buck converter circuit, if the driving signal of a certain switch device is at a high level, the switch device is turned on, which is recorded as Q n =1 (where n=1, 2, 3, 4); if the driving signal of a switch device is low, the switch device is closed, recorded as Q n =0 (where n=1, 2, 3, 4). As the driving signals of the four switching devices have complementary logic, only the driving signals of the first switching device Q1 and the second switching device Q2 are used as examples to illustrate the possible working conditions of the circuit under the control of the driving signals. Figure 2 , with the on-state of the first switch device Q1 as the horizontal axis and the on-state of the second switch device Q2 as the vertical axis. Since the switch device has only two states, on and off, the on-state of the first switch device Q1 and the second switch device Q2 is used to describe Figure 1 There are four possible working conditions of the three-level flying capacitor buck converter circuit, namely (0,0), (0,1), (1,0), and (1,1).

[0029] In a specific application example, a possible circuit operating state is taken as an example to be described in detail, but the embodiment of the present invention is not limited thereto. Figure 2 In the working state of the coordinate point (1,0), when the first switch device Q1 is turned on and the second switch device Q2 is turned off, then correspondingly under the complementary logic driving signal, the fourth switch device Q4 is turned off and the third switch device Q3 is turned on, wherein the turned-on switch device is equivalent to a wire, and the turned-off device is not drawn. The equivalent circuit working mode is as follows: Figure 2 At the same time, in the first switch loop, the voltage relationship exists in the following equation, where the flying capacitor C fly The voltage across the two ends is v fly , the voltage across the fourth switch device Q4 is

[0030]

[0031] In the second switch loop, the voltage relationship exists in the following equation: the voltage across the second switch device Q2 is

[0032]

[0033] As can be seen from Equation (2) and Equation (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 does not reach the steady-state value, the charge and discharge are unbalanced, and finally it will lead to the imbalance of the three-level flying capacitor buck converter system and the loss of its circuit function. Therefore, for the three-level flying capacitor buck converter circuit shown in or , controlling the voltage v across the flying capacitor C Figure 1 to reach balance is particularly crucial for the normal operation of this circuit. fly fly fly fly

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

[0035] In a specific application example, the proposed single-sensor-based analog leading-edge type V 2 control technology is applied to the three-level flying capacitor buck converter shown in 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 o of the three-level flying capacitor converter accurately reaches the preset target value, but also can simultaneously achieve the automatic balance of the flying capacitor voltage C fly . The control structure refers to Figure 3 . The control idea is based on the control of the ripple of the output voltage V o . Figure 3 As shown in Figure 1 , on the basis of the basic circuit of the three-level flying capacitor buck converter shown in o , 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 on the inductor LThe current flows completely through the output capacitor C o and through a series resistor R e Give the output capacitor C o discharge, thus R e A voltage drop Δi with the same slope as the inductor current is generated on the L R e When C o When the capacity is large, its voltage V cap It can be considered constant, and the output voltage detected by the output voltage sensor consists of a constant amount and a ripple amount, that is, V o =V cap +Di L R e . Output voltage V o The changing trend of the inductor current ripple Δi L The single sensor-based simulation of the leading edge type V 2 The control technology senses the change of output voltage ripple through the output voltage sensor, and responds accordingly to generate a corresponding drive signal.

[0036] The control process is as follows: At a certain moment, the output voltage of the three-level flying capacitor buck converter is sampled by the output voltage sensor, and the obtained value is recorded as v s Then, the output voltage sampling value v s is transmitted to perform the simulation of the leading edge type V 2 In the analog control circuit of control technology. When the analog control circuit receives the output voltage sampling value at that moment, it goes through a series of analog leading edge type V 2 The processing steps of the control technology design eventually generate corresponding drive signals S1, S2, S3, and S4. These drive signals are respectively connected to and drive the first switch device Q1, the second switch device Q2, the third switch device Q3, and the fourth switch device Q4. Among them, the drive signals S1 and S4 are complementary outputs, and the drive signals S2 and S3 are complementary outputs. The different conduction states of the four switch devices determine the working mode of the three-level flying capacitor buck converter, which in turn affects the formation of the output voltage. The newly generated output voltage is detected by the output voltage sensor and then transmitted to the analog control circuit for analysis and processing. Based on the feedback information, the analog control circuit will generate a new drive signal to control the operation of each switch device respectively. This process is iterated continuously, so that the analog leading edge type V based on a single sensor is 2 The control technology can continuously and accurately implement dynamic regulation of the three-level flying capacitor buck converter to ensure that its operating status meets the expected target.

[0037] In the specific application example, the three-level flying capacitor buck converter has two operating modes, defining the output voltage V o With input voltage Vg The ratio is the voltage conversion ratio G, that is, According to the range of voltage conversion ratio G, the actual working circuit switching of the three-level flying capacitor buck converter is divided into two modes, namely, mode 1: when G < 0.5, the circuit working mode is Figure 2 The equivalent circuit operating points are switched in the order of (0,1)→(0,0)→(1,0)→(0,0) in a cycle; Mode 2: When G>0.5, the circuit works in the mode Figure 2 The operating points of the equivalent circuit are switched in the order of (0,1)→(1,1)→(1,0)→(1,1)→(0,1).

[0038] In a specific application example, the analog leading edge type V based on a single sensor proposed in the present invention is described in detail by taking one of the working modes of the three-level flying capacitor buck converter, namely mode 1, when G < 0.5 as an example. 2 The control principle of the control technology, but the embodiments of the present invention are not limited thereto.

[0039] Since the driving signal S1 of the first switch device of the three-level flying capacitor buck converter is 180° out of phase with the driving signal S2 of the second switch device, assuming that the switching period is T s , the switching frequency is f s , Then the difference between S1 and S2 In the embodiment of the present disclosure, it is defined as is the switching node change period, the switching node change frequency,

[0040] refer to Figure 4 , Figure 3 The specific implementation and control principle of the analog control circuit described in the embodiment are as follows: a dual-loop control is adopted and an RS trigger and a D trigger are used in the inner loop of the control to realize the simulation of the leading edge type V 2 Control technology strategy, simulating the leading edge type V 2 The control strategy controls the output voltage v collected by the output voltage sensor in the outer loop. s The output voltage reference V ref The difference is amplified by the error amplifier to generate the control voltage v pi The external clock signal is connected to the reset terminal of the RS flip-flop, that is, the R terminal. The frequency of the external clock signal is Clk = 2f s =f sw . Then in each switching node cycle At the beginning, the clock signal inputs a reset signal to the RS trigger, resets the RS trigger, and the Q output of the RS trigger outputs a low level and enters two AND gates respectively. The two AND gates simultaneously output a low level, generating a drive signal S1=0, S2=0. Then the drive signals S1 and S2 are output through two NOT gates respectively, generating drive signals S3=1, S4=1 for the corresponding complementary switch devices. The drive signals drive the on and off of the four switch devices respectively, that is, the first switch device Q1 is turned off, the second switch device Q2 is turned off, the third switch device Q3 is turned on, and the fourth switch device Q4 is turned on. At this time, the three-level flying capacitor converter is in Figure 2 The (0,0) operating mode point, the output voltage V o The output voltage sensor collects the output voltage V o The change of v s It decreases linearly from the initial value. s Reduced to the control voltage v generated by the control outer loop pi When the three-level flying capacitor buck converter works in mode 1, that is, the voltage conversion ratio G is less than 0.5, the switch trigger signal is sent to the set end of the RS trigger, that is, the S end. The switch trigger signal sets the RS trigger, and the Q output end of the RS trigger outputs a high level to enter the two AND gates, and at the same time transmits the high level signal to the clock input end DClk of the D trigger. For the D trigger, the input end D is connected to the reverse output end When the clock input DClk signal comes, the output of the D flip-flop will be "flipped", so the drive signals S1 and S2 will be different. The high level is outputted periodically and alternately to drive the first switch device Q1 and the second switch device Q2 to turn on, thereby realizing the normal operation of the three-level flying capacitor buck converter.

[0041] Since this control technology directly regulates the output voltage V o , so by analyzing the output voltage V o The effectiveness of the proposed technology is evaluated by the static stability of the proposed technology. Taking one of the working modes of the three-level flying capacitor buck converter, namely mode 1, when G < 0.5, as an example, the single-sensor analog leading-edge V 2 The static stability of the control technology, but the present disclosure is not limited to this. The output voltage sampling value v s The output voltage V of the three-level flying capacitor buck converter o The actual value of the static stability characteristics is the same, so by analyzing the output voltage sampling value v s The static stability of the proposed technology is used to evaluate the effectiveness of the proposed technology. The analysis process is as follows:

[0042] First, we assume that the flying capacitor voltage v fly A balance has been reached, that is refer to Figure 5 , the three-level flying capacitor buck converter is given in the CCM mode (continuous conduction mode, that is, in one switching cycle, the inductor current never reaches 0, that is, the output voltage is in a stable output state), and when the voltage conversion ratio satisfies G<0.5, the simulated leading edge type V 2 Under control, the control waveform after positive and negative disturbances occur. The solid line is the output voltage sampling value v s The steady-state waveform of the dotted line is v after the disturbance occurs. s Transient waveform, m1, m2 are the slopes of output voltage rise and fall, v pi is the control voltage output by the error amplifier, T s is the switching period, 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 cycle, Δv s [k+1] is the value of Δv s [k] caused by the voltage deviation. According to the working principle of the three-level flying capacitor buck converter, we have:

[0043]

[0044] For a three-level flying capacitor buck converter in CCM mode, V o =GV g ,Depend on Figure 5 In both positive and negative disturbance cases, we can obtain:

[0045]

[0046] It can be seen from formula (4) that when 0.25<G<0.5, Δv s [k+1] <Dv s [k], the voltage deviation will gradually decay to zero, indicating that the simulated leading edge type V 2 control Figure 1 The three-level flying capacitor buck converter is stable; when 0<G<0.25, Δv s [k+1]>Dv s [k], the voltage deviation will gradually increase, indicating that the simulated leading edge type V 2 control Figure 1 The three-level flying capacitor buck converter is unstable and will generate subharmonic oscillations.

[0047] In a specific application example, in the case of subharmonic oscillation within the range, a slope compensation method is used to eliminate the subharmonic oscillation, and the minimum slope value of the required compensation slope that can eliminate the subharmonic oscillation is derived. When 0<G<0.25, in order to make the leading edge type V 2 The three-level flying capacitor buck converter can still work stably, and the control voltage v formed in the outer loop can be pi The superimposed slope is k comp The ramp signal forms a new control voltage, which is input to one end of the comparator and compared with the output voltage.

[0048] In a specific application example, the leading edge type V 2 Taking the slope compensation method used when the output voltage of the three-level flying capacitor buck converter is positively disturbed as an example, the process of deriving the minimum slope value of the compensation slope is described in detail, but the embodiment of the present invention is not limited to this. The process of deriving the minimum slope value of the compensation slope is as follows: Figure 6 , is a schematic diagram of the principle of using the slope compensation method when the output voltage has a positive disturbance. Figure 6 We can get:

[0049]

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

[0051]

[0052] From formula (6), we know that in the range of 0<G<0.5, if When established, we get:

[0053]

[0054] Based on this, the following conclusions can be drawn: In CCM mode, in order to ensure the simulated leading edge type V 2 Control the stable operation of the three-level flying capacitor buck converter. pi By superimposing a slope compensation voltage whose slope satisfies equation (7), the analog leading edge type V 2 Controlling subharmonic oscillations in a three-level flying capacitor buck converter.

[0055] For the time being, we assume that the flying capacitor voltage v fly A balance has been reached. Further analysis of the simulated leading edge type V based on a single sensor proposed in the present invention 2 The control technique is applied to the static stability of the three-level flying capacitor buck converter. The following conclusions are obtained: In CCM mode, the three-level flying capacitor buck converter is controlled by the proposed simulated leading edge type V2 During control, in operating mode 1 where G < 0.5, the stable operating range of the circuit is 0.25 < G < 0.5. However, in the range 0 < G < 0.25, the circuit operates unstably and sub - harmonic oscillations occur. Further, by superimposing a ramp voltage with a slope satisfying pi on the original voltage control signal v generated by the outer - loop control, the sub - harmonic oscillations can be eliminated, enabling the circuit to operate stably within the entire range of operating mode 1 where G < 0.5. However, even if the assumption that "the flying - capacitor voltage v fly has reached equilibrium" does not hold, the above conclusion still holds, and when the sub - harmonic oscillations are eliminated, the flying - capacitor voltage can reach equilibrium autonomously.

[0056] Furthermore, to verify the conclusion that "after eliminating sub - harmonic oscillations, the flying - capacitor voltage can reach equilibrium autonomously", the verification process is as follows: Assume that there is a perturbation on the flying capacitor, that is, the flying - capacitor voltage such as Figure 7 . Due to the existence of the perturbation on the flying capacitor, the resulting effect will surely be reflected in the unbalanced charge - discharge of the flying capacitor, and at the same time, it will cause different duty cycles of the two driving signals S1 and S2, which are set as D1 and D2 respectively. From the geometric relationship of the waveforms, we can obtain respectively:

[0057]

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

[0059]

[0060] where A pos and A neg are the positive and negative areas of the flying - capacitor current curve respectively. Solving from the geometric relationship and substituting equations (8) and (9) into equation (10), we obtain the formula for the average current of the flying capacitor in the range 0 < G < 0.5:

[0061]

[0062] From equation (11), it can be seen that in the range 0 < G < 0.5, when the compensation ramp slope satisfies , it will make the positive and negative of the average current I fly of the flying capacitor have opposite signs to the positive and negative of the flying - voltage perturbation V fly . Therefore, the conclusion can be drawn that the analog leading - edge type V 2 control technology is applied to Figure 1For the three-level flying capacitor buck converter described above, once the sub-harmonic oscillation of the converter output voltage is suppressed, this technique will inherently stabilize the flying capacitor voltage and make it finally reach the equilibrium state.

[0063] Those skilled in the art can understand that although the flying capacitor buck converter circuits are analyzed within the range of operating mode 0 < G < 0.5, when 0.5 < G < 1, there are similar derivation processes and conclusions. In summary, the following conclusions can be obtained:

[0064] (1) Simulate the leading-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 oscillations will occur;

[0065] (2) For sub-harmonic oscillations, when the slope satisfies The ramp of is superimposed on the voltage control signal v generated by the outer loop pi To eliminate sub-harmonic oscillations;

[0066] (3) Once the sub-harmonic oscillation of the output voltage is suppressed, the simulated leading-edge type V 2 The control method inherently stabilizes the flying capacitor voltage in the three-level flying capacitor buck converter and makes it finally reach the equilibrium state.

[0067] In the embodiments of the present disclosure, for the case of sub-harmonic oscillations occurring within a certain range, the Figure 3 Specific implementation manner of the described analog control circuit after superimposing the ramp compensation signal is proposed. Refer to Figure 8 , In a specific application example, based on the Figure 4 Described implementation scheme, a compensation ramp with a slope satisfying pi Is superimposed on the voltage control signal v generated by the control outer loop. It not only suppresses sub-harmonic oscillations but also ensures that the flying capacitor voltage reaches equilibrium.

[0068] It should be understood that the exemplary embodiments described herein are illustrative and not restrictive. Although one or more embodiments of the present invention are described in conjunction with the accompanying drawings, those of ordinary skill in the art should understand that various changes in form and detail can be made without departing from the spirit and scope of the present invention 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: The following steps are involved: The on-off logic of each switch device in the normal operation of the three-level flying capacitor buck converter circuit is analyzed, and the working state of the circuit is described based on the coordinate sequence (Q1, Q2) composed of the first switch device and the second switch device. There are four working modes, namely (0,0), (0,1), (1,0), and (1,1). The circuit working dynamic switching process is divided into two working modes according to the range of the voltage conversion ratio G. The voltage conversion ratio G is the output voltage V o With input voltage V g The ratio is: mode 1, i.e., when G<0.5, the working modal points are switched in the order of (0,1)→(0,0)→(1,0)→(0,0) in a cycle; mode 2, i.e., when G>0.5, the working modal points are switched in the order of (0,1)→(1,1)→(1,0)→(1,1) in a cycle; 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 balancing of the device is analyzed; then a structure of controlling the three-level flying capacitor buck converter using a single sensor analog control method is proposed, in which the analog control circuit is implemented by using RS trigger and D trigger; then the static stability characteristics of the three-level flying capacitor buck converter are studied by applying this technology. 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 will produce subharmonic oscillations; In the case of subharmonic oscillation within a certain range, slope compensation is used to eliminate subharmonic oscillation and the compensation slope value for eliminating subharmonic oscillation is derived to meet the condition And verify the characteristic that the flying capacitor voltage is naturally balanced when the subharmonic oscillation is eliminated; Apply the compensation ramp strategy to the analog control circuit.

2. The single sensor analog control method for a three-level flying capacitor buck converter according to claim 1, characterized in that: The three-level flying capacitor buck converter circuit includes a DC input voltage V g 、Flying capacitor C fly , the bridge arm composed of the switching device, the filter inductor L o , output capacitor C o and DC output; where the DC input voltage V g The bridge arm formed by the switching device is connected in parallel; the bridge arm formed by the switching device includes a first switching device Q1, a second switching device Q2, a third switching device Q3 and a fourth switching device Q4 connected in series in sequence, wherein the first switching device Q1 and the fourth switching device Q4 present complementary conduction characteristics, and the second switching device Q2 and the third switching device Q3 present complementary conduction characteristics; the flying capacitor C fly connected in parallel with the series branch formed by the second switch device Q2 and the third switch device Q3; the filter inductor L o and output capacitor C o The series branch formed by the third switch device Q3 and the fourth switch device Q4 is connected in parallel with the series branch formed by the third switch device Q3 and the fourth switch device Q4; the output capacitor C o Connect in parallel with the DC output.

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