Flying capacitor voltage-sharing control method and system in three-level Buck circuit

Abstract

The invention discloses a flying capacitor voltage-sharing control method and system in a three-level Buck circuit, and the method comprises the steps: obtaining a duty ratio signal corresponding to a difference value between an output voltage reference value and an actual value through a first proportional-integral regulator; a compensation duty ratio signal corresponding to the difference value between the flying capacitor voltage natural stability maintenance value and the actual value is obtained through a second proportional-integral regulator; calculating according to the compensation duty ratio signal to obtain a compensation phase shift signal; and based on a PWM modulation principle, according to the duty ratio signal, the compensation duty ratio signal and the compensation phase shift signal, obtaining driving signals of the two upper tubes and the two lower tubes. The flying capacitor type three-level Buck circuit implementing the method disclosed by the invention realizes voltage balance in a full-load range, and particularly can ensure the voltage balance of the flying capacitor under a light load.

Description

Technical Field

[0001] This invention belongs to the field of power exchange, and particularly relates to a method and system for controlling the voltage equalization of flying capacitors in a three-level Buck circuit. Background Technology

[0002] Compared to two-level Buck converters, three-level Buck converters with flying capacitors offer higher efficiency and power density, reduced device voltage stress, and decreased inductor ripple, particularly when the input-output voltage conversion ratio is large. In an ideal circuit, the charging and discharging cycles of the flying capacitor are the same, and the flying capacitor voltage naturally stabilizes at half the input voltage, meaning the natural stability value of the flying capacitor voltage is V. in / 2. However, in practical applications, due to the mismatch of actual drive signals and the different switching characteristics of the switching transistors, the charging and discharging cycles of the flying capacitor cannot be exactly the same. This will cause the flying capacitor voltage to be higher or lower than V. in / 2, at this point the three-level Buck converter cannot function properly. Therefore, for a three-level Buck converter, flying capacitor voltage equalization control is essential.

[0003] The purpose of flying capacitor voltage equalization control is to ensure that the flying capacitor voltage is half of the input voltage. Currently, the mainstream voltage equalization control methods include current source charging / discharging control, phase-shift compensation control, and duty cycle compensation control. Current source charging / discharging control uses an additional current source or auxiliary circuit to charge and discharge the flying capacitor to achieve voltage equalization, such as the methods described in publications CN115955108A and CN110401344A. This method is simple to control but introduces additional losses and has low equalization efficiency. Phase-shift control equalizes the flying capacitor voltage by adjusting the phase relationship of the drive signal, such as the three-level Buck circuit and flying capacitor voltage equalization control method provided in publication CN113541473A. Duty cycle control equalizes the flying capacitor voltage by adjusting the duty cycle difference of the drive signal, such as the three-level Buck circuit and flying capacitor voltage equalization control method provided in CN113541473A. Both of these methods do not introduce additional losses and have the advantages of high efficiency and low heat generation. However, both of these methods ignore the influence of inductor current ripple. When the load current is small (e.g., the load current is less than 5% of the rated current), i.e., under light load conditions, phase shift compensation or duty cycle compensation alone cannot guarantee voltage equalization of the flying capacitor, and may even lead to a more unbalanced voltage of the flying capacitor.

[0004] Therefore, it is necessary to study a method and system for controlling the voltage equalization of the flying capacitor in a three-level Buck circuit, which can ensure high efficiency and good voltage equalization effect under the full load range, thereby improving the reliability of the three-level Buck circuit with flying capacitor. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention proposes a method and system for controlling the voltage equalization of flying capacitors in a three-level Buck circuit.

[0006] The technical solution of the present invention is as follows:

[0007] A method for controlling the voltage equalization of a flying capacitor in a three-level Buck circuit, wherein the two ends of the flying capacitor are respectively connected between the two upper transistors and between the two lower transistors in the three-level Buck circuit, and assist the upper and lower transistors in converting the input voltage into the output voltage. The method includes:

[0008] The output voltage reference value V is obtained through the first proportional-integral regulator. oref Compared with the actual value V o Difference V between o_err The corresponding duty cycle signal d is used to obtain the naturally stable maintenance value V of the flying capacitor voltage through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd;

[0009] The compensation phase shift signal ΔT is obtained based on the compensation duty cycle signal Δd.

[0010] Based on the PWM modulation principle, the drive signals for the two upper transistors and the two lower transistors are obtained according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

[0011] Furthermore, in the three-level Buck circuit, the first upper transistor Q... hs1 Second upper tube Q hs2 Second lower tube Q ls2 and the first tube Q ls1 This forms a three-level Buck bridge arm connected in series, with an input voltage V. in and input capacitor C in Parallel connection, and the upper tube Q hs1 and lower tube Q ls1 Connection; Flying capacitor C fly The upper end and the first upper tube Q hs1 Second upper tube Q hs2 The common point connection, the flying capacitor C fly The lower end and the second lower tube Q ls2 and the first tube Q ls1 The common point is connected; one end of the filter inductor L is connected to the second upper transistor Q. hs2 Second lower tube Q ls2 The common point is connected, and the other end is connected to the output capacitor C. o connect.

[0012] Furthermore, the method for obtaining the drive signals of the two upper transistors and the two lower transistors is as follows:

[0013] Based on the PWM modulation principle, the duty cycle signal d is added to the compensated duty cycle signal Δd, and the first upper transistor Q is obtained through PWM modulation. hs1 The driving signal d hs1 Then, the duty cycle signal d is subtracted from the compensated duty cycle signal Δd, and phase shift compensation is performed using the compensated phase shift signal ΔT. The second upper MOSFET Q is obtained through PWM modulation. hs2 The driving signal d hs2 ; Put the first upper tube Q hs1 The driving signal d hs1 The complementary signal is used as the first lower transistor Q. ls1 The drive signal will drive the second upper transistor's drive signal d. hs2 The complementary signal is used as the second lower transistor Q. ls2 The driving signal.

[0014] Furthermore, the specific method for performing phase shift compensation using the compensated phase shift signal ΔT includes:

[0015] The 180° of the basic phase-shifting unit is added to the compensated phase-shifting signal ΔT.

[0016] Furthermore, the transfer function G(s) of both the first proportional-integral controller and the second proportional-integral controller is:

[0017]

[0018] In the formula, k p k is the proportionality coefficient. i is the integral coefficient.

[0019] Furthermore, the relationship between the compensated phase shift signal ΔT and the compensated duty cycle signal Δd is ΔT>Δd.

[0020] Furthermore, the relationship between the compensated phase shift signal ΔT and the compensated duty cycle signal Δd is ΔT = 1.1·Δd.

[0021] A flying capacitor voltage equalization control system in a three-level Buck circuit, wherein the two ends of the flying capacitor are respectively connected between the two upper transistors and the two lower transistors in the three-level Buck circuit, and assist the upper and lower transistors in converting the input voltage into the output voltage. The system includes a duty cycle signal, a compensation duty cycle signal acquisition module, a compensation phase shift signal calculation module, and a PWM modulation module.

[0022] The duty cycle signal and the compensation duty cycle signal acquisition module are used to obtain the output voltage reference value V through the first proportional-integral regulator. oref Compared with the actual value V oDifference V between o_err The corresponding duty cycle signal d is used to obtain the naturally stable maintenance value V of the flying capacitor voltage through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd;

[0023] The compensation phase-shift signal calculation module is used to calculate the compensation phase-shift signal ΔT based on the compensation duty cycle signal Δd.

[0024] The PWM modulation module is used to obtain the drive signals of the two upper transistors and the two lower transistors based on the PWM modulation principle, according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

[0025] An electronic device includes a memory and a processor, the memory storing a computer program, the processor being configured to invoke and run the computer program stored in the memory to perform the method as described in any of the preceding methods.

[0026] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of the method described in any of the preceding claims.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] This invention proposes a method and system for controlling the voltage equalization of flying capacitors in a three-level Buck circuit. The method obtains the compensation duty cycle signal Δd corresponding to the difference between the naturally stable maintained value and the actual value of the flying capacitor voltage through a proportional-integral regulator, and calculates the compensation phase shift signal ΔT based on the compensation duty cycle signal. Therefore, it can ensure that the flying capacitor type three-level Buck circuit implementing the method of this invention can achieve voltage equalization across the entire load range, especially under light load conditions.

[0029] The method of the present invention only requires adjusting the drive signal of the switching transistor, without the need for an auxiliary current source or equalization circuit. It is simple to implement, low in cost, and does not generate additional losses.

[0030] The three-level Buck converter using the flying capacitor voltage equalization control method and system of the three-level Buck circuit of this invention can achieve voltage equalization across the entire load range, especially ensuring voltage equalization of the flying capacitor under light load. Attached Figure Description

[0031] Figure 1 The circuit diagram for a flying capacitor type three-level Buck circuit;

[0032] Figure 2Schematic diagram of the flying capacitor voltage equalization control method;

[0033] Figure 3 This is a block diagram of the proportional-integral controller used in this invention;

[0034] Figure 4 The waveform diagram for working under light load with conventional duty cycle compensation;

[0035] Figure 5 The waveform diagram shows the working waveform of the voltage equalization control method proposed in this invention under light load.

[0036] Figure 6 The waveform diagram shows the working waveform of the pressure equalization control method proposed in this invention under full load. Detailed Implementation

[0037] The present invention will be further illustrated below with reference to the accompanying drawings and specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. After reading this invention, any modifications of the invention in various equivalent forms by those skilled in the art will fall within the scope defined by the appended claims.

[0038] Example 1:

[0039] This invention provides a method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit, such as... Figure 1 and Figure 2 As shown, the two ends of the flying capacitor are connected between the two upper transistors and the two lower transistors in a three-level Buck circuit, respectively, to reduce the voltage stress on the switching devices and assist the upper and lower transistors in converting the input voltage into the output voltage. This method includes:

[0040] Based on the output voltage loop control principle, the output voltage reference value V is obtained through the first proportional-integral regulator. oref Compared with the actual value V o Difference V between o_err The corresponding duty cycle signal d, and based on the flying capacitor voltage equalization control principle, the natural stable maintenance value V of the flying capacitor voltage is obtained through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd;

[0041] The compensation phase shift signal ΔT is obtained from the compensation duty cycle signal Δd.

[0042] Based on the PWM modulation principle, the drive signals for the two upper transistors and the two lower transistors are obtained according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

[0043] The method of this invention obtains the compensation duty cycle signal Δd corresponding to the difference between the naturally stable maintained value and the actual value of the flying capacitor voltage through a proportional-integral regulator, and calculates the compensation phase shift signal ΔT based on the compensation duty cycle signal. Therefore, it can ensure that the flying capacitor type three-level Buck circuit implementing the method of this invention can achieve voltage balance across the entire load range, especially under light load conditions.

[0044] Example 2:

[0045] This embodiment is further designed based on Embodiment 1, as follows: Figure 1 As shown, in this example, the first upper transistor Q in the three-level Buck circuit... hs1 Second upper tube Q hs2 Second lower tube Q ls2 and the first tube Q ls1 This forms a three-level Buck bridge arm connected in series, with an input voltage V. in and input capacitor C in Parallel connection, and the upper tube Q hs1 and lower tube Q ls1 Connection; Flying capacitor C fly The upper end and the first upper tube Q hs1 Second upper tube Q hs2 The common point connection, the flying capacitor C fly The lower end and the second lower tube Q ls2 and the first tube Q ls1 The common point is connected; one end of the filter inductor L is connected to the second upper transistor Q. hs2 Second lower tube Q ls2 The common point is connected, and the other end is connected to the output capacitor C. o connect.

[0046] Furthermore, in an ideal circuit, Q hs1 and Q hs2 The drive signals have the same duty cycle but are 180° out of phase; Q hs1 and Q ls1 Complementary drive signals, Q hs2 and Q ls2 The drive signals are complementary. The voltage across the flying capacitor naturally remains at the input voltage V. in Half of, i.e., V in / 2.

[0047] Example 3:

[0048] This embodiment, based on Embodiment 2, further designs the following method for obtaining the drive signals of the two upper transistors and two lower transistors:

[0049] Based on the PWM modulation principle, the duty cycle signal d is added to the compensation duty cycle signal Δd, i.e., d + Δd, and the first upper transistor Q is obtained through PWM modulation. hs1 The driving signal d hs1 Then, the duty cycle signal d is subtracted from the compensated duty cycle signal Δd, i.e., d-Δd, and phase shift compensation is performed using the compensated phase shift signal ΔT. The second upper MOSFET Q is obtained through PWM modulation. hs2 The driving signal d hs2 ; Put the first upper tube Q hs1 The driving signal d hs1 The complementary signal is used as the first lower transistor Q. ls1 The drive signal will drive the second upper transistor's drive signal d. hs2 The complementary signal is used as the second lower transistor Q. ls2 The driving signal.

[0050] Furthermore, the drive signal can be applied to the switching transistor through any form of drive circuit to control the switching transistor's on and off, thereby enabling the normal operation of the three-level Buck circuit.

[0051] Furthermore, this invention ensures voltage balance of the flying capacitor under light load by compensating for the phase shift signal ΔT, because the influence of inductor current ripple under light load is not negligible. When the first upper transistor Q... hs1 When the circuit is turned on, the flying capacitor operates in a charging state, and when the second upper transistor Q... hs2 When turned on, the flying capacitor operates in a discharging state. Due to the influence of inductor current ripple, under light load conditions, only the first upper transistor Q is affected. hs1 The duty cycle is d + Δd, and the second upper tube Q hs2 The duty cycle of d-Δd is insufficient to ensure that the charging and discharging charges of the flying capacitor are equal, thus failing to maintain voltage balance. Therefore, this invention adds a compensation phase-shifting signal ΔT to allow the second upper transistor Q to... hs2 The conducting phase also shifts by ΔT, ensuring voltage balance across the flying capacitor.

[0052] Example 4:

[0053] This embodiment, based on Embodiment 1, further incorporates the following design: The specific method for phase shift compensation using the compensation phase shift signal ΔT in this example includes:

[0054] The 180°, which serves as the basic phase-shifting unit, is added to the compensated phase-shifting signal ΔT, resulting in 180° + ΔT.

[0055] Example 5:

[0056] This embodiment is further designed based on Embodiment 1, as follows: Figure 3As shown, in this example, the transfer function G(s) of both the first proportional-integral controller and the second proportional-integral controller is:

[0057]

[0058] In the formula, k p k is the proportionality coefficient. i is the integral coefficient.

[0059] Example 6:

[0060] This embodiment, based on Embodiment 1, further designs the relationship between the compensation phase-shift signal ΔT and the compensation duty cycle signal Δd as follows: ΔT > Δd. The compensation phase-shift signal ΔT is selected by the value of the compensation duty cycle signal Δd, eliminating the need for additional control loops and complex calculation formulas, thus simplifying the implementation.

[0061] Example 7:

[0062] This embodiment is a further design based on embodiment six, in which the relationship between the compensation phase shift signal ΔT and the compensation duty cycle signal Δd is ΔT = 1.1·Δd, thereby ensuring that the phase shift angle ΔT > Δd, which in turn ensures that the voltage equalization effect is effective across the entire load range.

[0063] Example 7:

[0064] The present invention discloses a flying capacitor voltage equalization control system in a three-level Buck circuit. The two ends of the flying capacitor are respectively connected between the two upper transistors and the two lower transistors in the three-level Buck circuit. It is used to reduce the voltage stress of the switching devices and assist the upper and lower transistors in converting the input voltage into the output voltage. The system includes a duty cycle signal and a compensation duty cycle signal acquisition module, a compensation phase shift signal calculation module, and a PWM modulation module.

[0065] The duty cycle signal and compensation duty cycle signal acquisition module is used to obtain the output voltage reference value V through the first proportional-integral regulator according to the output voltage loop control principle. oref Compared with the actual value V o Difference V between o_err The corresponding duty cycle signal d, and based on the flying capacitor voltage equalization control principle, the natural stable maintenance value V of the flying capacitor voltage is obtained through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd;

[0066] The compensation phase-shift signal calculation module is used to calculate the compensation phase-shift signal ΔT based on the compensation duty cycle signal Δd.

[0067] The PWM modulation module is used to obtain the drive signals of the two upper transistors and two lower transistors based on the PWM modulation principle, according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

[0068] Example 9:

[0069] An electronic device includes a memory and a processor. The memory stores a computer program, and the processor is used to invoke and run the computer program stored in the memory to perform the methods of any of the above embodiments.

[0070] A computer-readable storage medium storing a computer program that, when executed by a processor, implements the steps of any of the above embodiments.

[0071] Application Examples:

[0072] This example uses a 240W three-level Buck prototype platform to experimentally verify the effectiveness of the flying capacitor voltage equalization control method of the three-level Buck circuit of this invention. The prototype has a switching frequency of 300kHz, a filter inductor of 1.5μH, and a flying capacitor of 60μF. The experimental steps are as follows:

[0073] 1) Set the DC input to 20V, the three-level Buck converter output voltage to 5V, and the load current to 0.5A. For example... Figure 4 As shown, conventional duty cycle compensation control is used, and the voltage V at the midpoint SW node of the bridge arm is... SW The high-level voltages are different, indicating that the voltage across the flying capacitor is not V. in / 2, under light load, voltage equalization of flying capacitors cannot be achieved solely through duty cycle compensation.

[0074] 2) Set the DC input to 20V, the three-level Buck converter output voltage to 5V, and the load current to 0.5A. Figure 5 As shown, using the method of this invention, the voltage V at the midpoint SW node of the bridge arm is... SW The same high-level voltage indicates that the voltage across the flying capacitor is V at this time. in / 2, Under light load, the method of this invention can achieve voltage equalization of flying capacitors.

[0075] 3) Set the DC input to 48V, the three-level Buck converter output voltage to 14.8V, and the load current to 16A. Figure 6 As shown, using the method of this invention, the voltage V at the midpoint SW node of the bridge arm is... SW The same high-level voltage indicates that the voltage across the flying capacitor is V at this time. in / 2. The method of this invention can also achieve voltage equalization of flying capacitors under full load.

[0076] The experimental results show that the method of the present invention can ensure voltage balance of the flying capacitor across the entire load range, thereby improving the reliability of the converter.

[0077] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for controlling the voltage equalization of a flying capacitor in a three-level Buck circuit, wherein the two ends of the flying capacitor are respectively connected between the two upper transistors and between the two lower transistors in the three-level Buck circuit, and assist the upper and lower transistors in converting the input voltage into the output voltage, characterized in that, The method includes: The output voltage reference value V is obtained through the first proportional-integral regulator. oref Compared with the actual value V o Difference V between o_err The corresponding duty cycle signal d is used to obtain the naturally stable maintenance value V of the flying capacitor voltage through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd; The compensation phase shift signal ΔT is obtained based on the compensation duty cycle signal Δd; Based on the PWM modulation principle, the drive signals for the two upper transistors and the two lower transistors are obtained according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

2. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 1, characterized in that, The first upper transistor Q in the three-level Buck circuit hs1 Second upper tube Q hs2 Second lower tube Q ls2 and the first tube Q ls1 This forms a three-level Buck bridge arm connected in series, with an input voltage V. in and input capacitor C in Parallel connection, and the upper tube Q hs1 and lower tube Q ls1 Connection; Flying capacitor C fly The upper end and the first upper tube Q hs1 Second upper tube Q hs2 The common point connection, the flying capacitor C fly The lower end and the second lower tube Q ls2 and the first tube Q ls1 Public point connection; One end of the filter inductor L is connected to the second upper transistor Q hs2 Second lower tube Q ls2 The common point is connected, and the other end is connected to the output capacitor C. o connect.

3. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 2, characterized in that, The method for obtaining the driving signals of the two upper transistors and the two lower transistors is as follows: Based on the PWM modulation principle, the duty cycle signal d is added to the compensated duty cycle signal Δd, and the first upper transistor Q is obtained through PWM modulation. hs1 The driving signal d hs1 Then, the duty cycle signal d is subtracted from the compensated duty cycle signal Δd, and phase shift compensation is performed using the compensated phase shift signal ΔT. The second upper MOSFET Q is obtained through PWM modulation. hs2 The driving signal d hs2 ; Put the first upper tube Q hs1 The driving signal d hs1 The complementary signal is used as the first lower transistor Q. ls1 The drive signal will drive the second upper transistor's drive signal d. hs2 The complementary signal is used as the second lower transistor Q. ls2 The driving signal.

4. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 1, characterized in that, The specific method for phase compensation using the compensation phase shift signal ΔT includes adding 180°, which serves as the basic phase shift unit, to the compensation phase shift signal ΔT.

5. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 1, characterized in that, The transfer function G(s) of both the first proportional-integral controller and the second proportional-integral controller is: In the formula, k p k is the proportionality coefficient. i is the integral coefficient.

6. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 1, characterized in that, The relationship between the compensated phase shift signal ΔT and the compensated duty cycle signal Δd is that ΔT > Δd.

7. The method for controlling the voltage equalization of flying capacitors in a three-level Buck circuit according to claim 6, characterized in that, The relationship between the compensated phase shift signal ΔT and the compensated duty cycle signal Δd is ΔT = 1.1·Δd.

8. A flying capacitor voltage equalization control system in a three-level Buck circuit, wherein the two ends of the flying capacitor are respectively connected between the two upper transistors and between the two lower transistors in the three-level Buck circuit, and assist the upper and lower transistors in converting the input voltage into the output voltage, characterized in that, The system includes a duty cycle signal and a compensation duty cycle signal acquisition module, a compensation phase shift signal calculation module, and a PWM modulation module; The duty cycle signal and the compensation duty cycle signal acquisition module are used to obtain the output voltage reference value V through the first proportional-integral regulator. oref Compared with the actual value V o Difference V between o_err The corresponding duty cycle signal d is used to obtain the naturally stable maintenance value V of the flying capacitor voltage through the second proportional-integral regulator. in / 2 and the actual value V cfly Difference V between cfly_err The corresponding compensation duty cycle signal Δd; The compensation phase-shift signal calculation module is used to calculate the compensation phase-shift signal ΔT based on the compensation duty cycle signal Δd. The PWM modulation module is used to obtain the drive signals of the two upper transistors and the two lower transistors based on the PWM modulation principle, according to the duty cycle signal d, the compensation duty cycle signal Δd, and the compensation phase shift signal ΔT.

9. An electronic device, characterized in that, The electronic device includes a memory and a processor, the memory storing a computer program, and the processor being configured to invoke and run the computer program stored in the memory to perform the method as described in any one of claims 1 to 7.

10. A computer-readable storage medium storing a computer program, characterized in that, When the computer program is executed by a processor, it implements the steps of the method as described in any one of claims 1 to 7 above.

Images