Improved four-mode control method for four-switch Buck-Boost converter

Abstract

The invention relates to an improved four-mode control method for a four-switch Buck-Boost converter, and the method comprises the steps: adding two expansion modes on the basis of a conventional Buck mode and a conventional Boost mode when an input voltage is close to an output voltage, and adding a gain hysteresis loop during mode switching in order to prevent frequent mode switching. In the extended Buck mode, the gain of the Buck circuit is fed back and adjusted, a rectifier tube of the Boost circuit works at the minimum conduction time meeting soft switching, and a follow current tube is in complementary conduction; in the extended Boost mode, the gain of the Boost circuit is fed back and adjusted, a rectifier tube of the Buck circuit works at the maximum conduction time meeting soft switching, and a follow current tube is in complementary conduction; and under the extended Buck and extended Boost modes, working frequency required by soft switching is calculated and adjusted in real time so as to ensure soft switching. According to the invention, soft switching can be realized, the input voltage range is wide, the mode switching is stable, the inductive current ripples can be effectively reduced by controlling the frequency and the switching tube conduction time sequence, the loss is reduced, and the operation efficiency of the converter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of four-switch Buck-Boost converter control, and particularly relates to an improved four-mode control method for a four-switch Buck-Boost converter with a wide input voltage range, high frequency, small volume and high operating efficiency requirements. Background Art

[0002] As a small power conversion device, the switching power supply is widely used in fields such as precision equipment, battery systems, data centers, vehicle charging products, aerospace, etc. With the rapid development of semiconductor device technology and the improvement of requirements for various application scenarios, high frequency, high efficiency, high power density, etc. have become the main development directions of switching power supplies. The traditional single-pole isolated DC-DC topology is simple and has stable and reliable performance. However, due to the limitations of magnetic components, its performance is difficult to meet the requirements under a wide range of input voltages. The two-stage circuit scheme of pre-stage voltage regulation cascaded with post-stage isolation can achieve a wider input voltage range and higher operating efficiency, and has received more attention.

[0003] However, the control difficulty of the two-stage circuit scheme lies more in the pre-stage pre-regulation link, which is a non-isolated DC-DC circuit topology. Due to being not restricted by transformers, it has a relatively high operating efficiency. Among common topologies, the four-switch Buck-Boost has a wide voltage regulation range, small stress on switching tubes, and few passive components, and can achieve a higher power density, with significant advantages. However, the traditional two-mode control method of the four-switch Buck-Boost has deficiencies such as large inductor current ripple, failure to achieve soft switching, and low efficiency. Currently, some scholars have proposed a three-mode variable-frequency soft-switching control method. By restricting the duty cycle of the Buck circuit link, adjusting the duty cycle of the Boost circuit link to regulate the circuit gain, and then achieving soft switching through variable frequency. However, the gain adjustment range of this method conflicts with the inductor current ripple, resulting in the intermediate mode not being able to operate at the optimal point. Some scholars have also proposed a low-ripple control strategy. By adding more modes, the voltage regulation range of the intermediate mode is increased, the duty cycle of the Buck or Boost circuit link is restricted to the maximum value, and combined with the control of the bridge arm phase-shifting time, the inductor current ripple is effectively reduced. However, this method cannot achieve soft switching of all switching tubes, and the switching losses seriously affect the operating efficiency.

[0004] Therefore, for a four-switch Buck-Boost converter with a wide input voltage range, high frequency, small volume and high operating efficiency requirements, the present invention proposes an improved four-mode control method for a four-switch Buck-Boost converter. Summary of the Invention

[0005] The object of the present invention is to provide an improved four-mode control method for a four-switch Buck-Boost converter, which can solve the deficiencies in the prior art, can achieve soft switching and has small inductor current ripple, effectively improving the operating efficiency of the four-switch Buck-Boost converter.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An improved four-mode control method for a four-switch Buck-Boost converter, the method comprising the following steps:

[0008] S1. Obtain the input voltage V in and output voltage V o .

[0009] S2. According to the relationship between the input voltage V in and output voltage V o of the four-switch Buck-Boost converter, select the operating mode of the converter; the operating modes include Buck mode, Boost mode, extended Buck mode and extended Boost mode.

[0010] S3. Set the switching conditions of the converter operating mode, and set a hysteresis region at the critical point of mode switching. Determine the current operating mode of the converter according to the switching conditions of the converter operating mode and the hysteresis region.

[0011] S4. According to the operating mode of the converter, perform corresponding control on the four-switch Buck-Boost converter:

[0012] S41. In Buck mode, feedback-regulate the gain of the Buck circuit to control the output voltage of the converter. The rectifier diode in the Boost circuit is turned off and the freewheeling diode is turned on.

[0013] S42. In Boost mode, feedback-regulate the gain of the Boost circuit to control the output voltage of the converter. The rectifier diode in the Buck circuit is turned on and the freewheeling diode is turned off.

[0014] S43. In extended Buck mode, feedback-regulate the gain of the Buck circuit to control the output voltage of the converter. The rectifier diode in the Boost circuit works at the minimum conduction time that satisfies the soft-switching condition, and the freewheeling diodes conduct complementarily.

[0015] S44. In extended Boost mode, feedback-regulate the gain of the Boost circuit to control the output voltage of the transformer. The rectifier diode in the Buck circuit works at the maximum conduction time that satisfies the soft-switching condition, and the freewheeling diodes conduct complementarily.

[0016] In the S45, extended Buck mode and extended Boost mode, calculate the operating frequency required for soft switching based on the operating state of the converter, and adjust the switching frequency of the converter in real time to achieve soft switching.

[0017] As a further improvement of the above technical solution, in the Buck mode, the rectifier diode of the Boost circuit remains off, the freewheeling diode remains on, and the Buck circuit operates normally. In the Buck mode, the rectifier diode in the Boost circuit is the switching transistor Q4, and the freewheeling diode is the switching transistor Q3.

[0018] As a further improvement of the above technical solution, in the Boost mode, the rectifier diode of the Buck circuit remains on, the freewheeling diode remains off, and the Boost circuit operates normally. In the Boost mode, the rectifier diode in the Buck circuit is the switching transistor Q1, and the freewheeling diode is the switching transistor Q2.

[0019] As a further improvement of the above technical solution, in the extended Buck mode and extended Boost mode, the switching transistors Q1 and Q4 are turned on simultaneously, and within the target gain range, extend the conduction time of the switching transistors Q1 and Q3, and make the conduction time of the switching transistors Q1 and Q3 not greater than the maximum conduction time to ensure the soft switching condition.

[0020] As a further improvement of the above technical solution, the switching conditions of the converter operating mode are:

[0021] (1) Buck mode, V o <0.95×V in .

[0022] (2) Extended Buck mode, 0.95×V in <V o <V in .

[0023] (3) Extended Boost mode, V in <V o <1.05×V in .

[0024] (4) Boost mode, V o >1.05×V in .

[0025] Among them, V in is the input voltage of the four-switch Buck-Boost converter, and V bus is the output voltage of the four-switch Buck-Boost converter.

[0026] As a further improvement of the above technical solution, extending the conduction time of the switch tube Q1 and the switch tube Q3, and making the conduction time of the switch tube Q1 and the switch tube Q3 not greater than the maximum conduction time to ensure the soft-switching condition, includes:

[0027] Using Equation (1) and Equation (2) to obtain the critical values of the duty cycles of the switch tube Q1 and the switch tube Q3 that satisfy the soft-switching condition, and then determining the maximum conduction time of the switch tube Q1 and the switch tube Q3:

[0028]

[0029] In Equation (1) and Equation (2), D Buck_max and D Boost_min are respectively the maximum duty cycle of the Buck circuit and the minimum duty cycle of the Boost circuit that satisfy the soft-switching condition; T is the switching period; T dead is the dead time; L is the energy storage inductor; I ZVS_Vin , I ZVS_Vo are respectively the sum of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors of the switch tube Q1 and the switch tube Q3, and the critical values of the inductor current that satisfy the soft-switching condition when the input voltage and the output voltage are respectively applied.

[0030] As a further improvement of the above technical solution, in step S45, in the extended Buck mode and the extended Boost mode, calculating the operating frequency required for soft switching through the operating state of the converter, and adjusting the switching frequency of the converter in real time to achieve soft switching, includes:

[0031] S451. In the extended Buck mode and the extended Boost mode, use Equation (3) to respectively obtain the duty cycles D' Buck , D′ Boost of the Buck circuit and the Boost circuit in the four-switch Buck-Boost converter considering the dead time:

[0032]

[0033] In Equation (3), D' Buck is the duty cycle of the Buck circuit considering the dead time, D' Boost is the duty cycle of the Boost circuit considering the dead time, T is the switching period; T dead is the dead time; D buck is the duty cycle of the Buck circuit, D boost is the duty cycle of the Boost circuit;

[0034] S452. Through the change process of the inductor current, combined with the conduction time of the switch tube, use Equation (4) to calculate the required reference switching frequency f ref, by controlling the change of the switching frequency to ensure the realization of soft switching:

[0035]

[0036] In Equation (4), f ref is the reference switching frequency, D' Buck is the duty cycle of the Buck circuit considering the dead time, D' Boost is the duty cycle of the Boost circuit considering the dead time, V in is the input voltage, V o is the output voltage, L is the energy storage inductor, I o is the output current, I ZVS_Vin 、I ZVS_Vo are respectively the sum of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors Q1 and Q3 of the switching tubes, and are the critical values of the inductor current that satisfy the soft switching condition when they are the input voltage and the output voltage respectively.

[0037] Compared with the prior art, the advantages of the present invention are:

[0038] (1) The improved four-mode control method of the four-switch Buck-Boost converter described in the present invention can not only overcome the deficiencies of the existing control methods, solve the problems of large inductor current ripple, large loss and low operating efficiency of the traditional control methods, but also realize soft switching with small inductor current ripple and wide input voltage range, effectively improving the operating efficiency of the converter, and having the characteristics of strong practicability and easy implementation.

[0039] (2) The present invention significantly improves the efficiency, stability, and reliability of the four-switch Buck-Boost converter through an improved four-mode control method, gain hysteresis setting, soft-switching implementation, and optimized conduction time. Specifically, traditional Buck-Boost converters usually only use the Buck mode and the Boost mode and cannot effectively handle the situation where the input voltage is close to the output voltage. The present invention introduces an extended Buck mode and an extended Boost mode, which can more effectively handle the situation where the input voltage is close to the output voltage, improving the efficiency and adaptability of the converter. Traditional mode switching methods usually do not consider the hysteresis region, resulting in frequent switching near the critical point, affecting the stability and reliability of the system. The present invention effectively reduces the frequent mode switching caused by small fluctuations in the input voltage by setting the hysteresis region, improving the stability and reliability of the system. Traditional Buck-Boost converters usually do not implement soft-switching, resulting in large switching losses and low efficiency. The present invention ensures the implementation of soft-switching in the extended Buck mode and the extended Boost mode by calculating and adjusting the switching frequency of the switching tubes, significantly reducing the switching losses and electromagnetic interference (EMI), and improving the efficiency and reliability of the converter. Traditional Buck-Boost converters usually do not adjust the conduction timing of the switching tubes, and the freewheeling time is relatively long, increasing the losses. In the present invention, switching tubes Q1 and Q4 are turned on simultaneously, reducing the freewheeling time to the minimum and improving the working efficiency. Traditional Buck-Boost converters usually do not optimize the conduction time, resulting in large inductor current ripple. The present invention reduces the current ripple of inductor L and the inductor loss and improves the energy transfer efficiency by adjusting the conduction time of Q1 and Q3 to the maximum, while ensuring the realization of the soft-switching condition. Description of the Drawings

[0040] Figure 1 is the working principle diagram of the improved four-mode control method of the four-switch Buck-Boost converter in the present invention;

[0041] Figure 2 is the schematic diagram of the gain hysteresis method adopted by the present invention;

[0042] Figure 3 is the switching timing and inductor current waveform diagram in the extended Buck mode and the extended Boost mode. In Figure 3 , the abscissa is time, and the ordinate is the PWM signal of the switching tube. PWM1, PWM2, PWM3, and PWM4 are the PWM signals of switching tubes Q1, Q2, Q3, and Q4 respectively. Detailed Embodiment

[0043] The following further describes the present invention with reference to the drawings:

[0044] When the control method of the present invention is implemented, the initialization of the PWM module and the switching tubes and the detection of the converter voltage parameters are first performed. Initialize the PWM (Pulse Width Modulation) module of the microcontroller, set the initial switching frequency and duty cycle. At the same time, initialize the switching tubes Q1, Q2, Q3, and Q4 to ensure that they are in a safe off state in the initial state. Use a voltage sensor to detect the current input voltage and output voltage of the converter, and send the detected voltage values to the controller (such as a microcontroller or a dedicated power management chip).

[0045] As Figure 1 shown, the improved four-mode control method of the four-switch Buck-Boost converter according to the present invention includes the following steps:

[0046] S1. Obtain the input voltage V in of the four-switch Buck-Boost converter and the output voltage V o .

[0047] S2. According to the relationship between the input voltage V in and the output voltage V o of the four-switch Buck-Boost converter, select the working mode of the converter; the working modes include Buck mode, Boost mode, extended Buck mode, and extended Boost mode.

[0048] S3. Set the switching conditions of the converter working mode, and set a hysteresis region at the critical point of mode switching. Determine the current working mode of the converter according to the switching conditions and the hysteresis region of the converter working mode. To prevent frequent mode switching, add a gain hysteresis at the switching conditions to increase the stability of the system.

[0049] S4. According to the working mode of the converter, perform corresponding control on the four-switch Buck-Boost converter:

[0050] S41. In Buck mode, the rectifier tube of the Boost circuit remains off, the freewheeling diode remains on, and the Buck circuit works normally. In Buck mode, feedback adjusts the gain of the Buck circuit to control the output voltage of the converter, the rectifier tube in the Boost circuit is off, and the freewheeling diode is on.

[0051] S42. In Boost mode, the rectifier tube of the Buck circuit remains on, the freewheeling diode remains off, and the Boost circuit works normally. In Boost mode, feedback adjusts the gain of the Boost circuit to control the output voltage of the converter, the rectifier tube in the Buck circuit is on, and the freewheeling diode is off.

[0052] S43. In the extended Buck mode, the feedback adjusts the gain of the Buck circuit to control the output voltage of the converter. The rectifier diode in the Boost circuit is fixed to operate at the minimum conduction time that satisfies the soft-switching condition, and the freewheeling diodes conduct complementarily.

[0053] S44. In the extended Boost mode, the feedback adjusts the gain of the Boost circuit to control the output voltage of the converter. The rectifier diode in the Buck circuit is fixed to operate at the maximum conduction time that satisfies the soft-switching condition, and the freewheeling diodes conduct complementarily.

[0054] S45. In the extended Buck mode and the extended Boost mode, the operating frequency required for soft-switching is calculated based on the operating state of the converter, and the switching frequency of the converter is adjusted in real time to achieve soft-switching, thereby reducing the switching loss and improving the efficiency.

[0055] In the extended Buck mode and the extended Boost mode, in order to reduce the freewheeling time and improve the efficiency, the switching transistors Q1 and Q4 are turned on simultaneously. Within the required gain range, the conduction times of the switching transistors Q1 and Q3 are made as long as possible without exceeding the maximum conduction time that ensures the soft-switching condition. In the extended Buck mode and the extended Boost mode, when the load increases, the energy transferred by the conduction times of the switching transistors Q1 and Q3 is insufficient, resulting in the failure of soft-switching. Therefore, it is necessary to reduce the frequency and increase their conduction times to increase the energy transferred to the load. The present invention calculates the switching frequency required for achieving soft-switching through the change process of the inductor current in combination with the conduction times of the switching transistors. By controlling the change of the switching frequency, the realization of soft-switching is ensured.

[0056] As a further improvement of the above technical solution, the switching conditions of the converter operating mode are:

[0057] (1) Buck mode, V o <0.95×V in .

[0058] (2) Extended Buck mode, 0.95×V in <V o <V in .

[0059] (3) Extended Boost mode, V in <V o <1.05×V in .

[0060] (4) Boost mode, V o >1.05×V in .

[0061] Wherein, V inis the input voltage of the four-switch Buck-Boost converter, V o is the output voltage of the four-switch Buck-Boost converter.

[0062] As a further improvement of the above technical solution, in order to prevent frequent mode switching at the critical selection conditions, a hysteresis needs to be added. The implementation method is as Figure 2 shown. Hysteresis is a control strategy used to prevent frequent switching near the critical point of mode switching. By setting a hysteresis region, it can be ensured that when the circuit gain changes within a certain range, the operating mode of the converter remains unchanged until the circuit gain exceeds the hysteresis region. A hysteresis region is set near the critical point of the converter's operating mode switching. For example, when the output voltage remains within the range of V o -ΔV to V o +ΔV, continuously detect the change of the input voltage V in to determine whether it enters the hysteresis region. If V in enters the hysteresis region, keep the current mode unchanged until V in exceeds the hysteresis region. When V in exceeds the hysteresis region, reselect the operating mode according to the relationship between the new input voltage and the output voltage, and perform mode switching. By setting the hysteresis region, it can effectively prevent frequent switching near the critical point of mode switching and ensure the stable operation of the converter.

[0063] In Figure 2 , the ordinate D buck is the duty cycle of the Buck circuit, and the abscissa D boost is the duty cycle of the Boost circuit. The angle represents the circuit gain. D Buck_max and D Boost_min are the critical duty cycle values for the Buck circuit and the Boost circuit to meet the soft-switching conditions respectively, and their calculation methods are shown in formulas (1) and (2). Figure 2 The virtual path in

[0064] As a further improvement of the above technical solution, in the extended Buck mode and the extended Boost mode, in order to reduce the freewheeling time and improve the efficiency, the switching transistors Q1 and Q4 are turned on simultaneously. Within the required gain range, the conduction times of the switching transistors Q1 and Q3 are made as long as possible, while not exceeding the maximum conduction time that satisfies the soft-switching condition. The purpose of this strategy is to maximize the energy transfer efficiency while maintaining the soft-switching condition. In the four-switch Buck-Boost converter, the extended Buck mode and the extended Boost mode are special operating modes designed to improve the efficiency of the converter when the input voltage is close to the output voltage. These modes optimize the conduction and turn-off times of the switching transistors, reduce the freewheeling time, and thus improve the efficiency.

[0065] Soft-switching technology significantly reduces switching losses and electromagnetic interference (EMI) by achieving zero-voltage (ZVS) or zero-current (ZCS) conditions during the conduction and turn-off of the switching transistors. To achieve soft-switching, it is necessary to ensure that the voltage and current conditions of the switching transistors during conduction and turn-off meet specific requirements. By calculating and setting the conduction times of the switching transistors Q1 and Q3, the energy transfer efficiency is maximized while satisfying the soft-switching condition.

[0066] Specifically, first, use Equation (1) and Equation (2) to find the critical duty cycle values of the Buck circuit and the Boost circuit that satisfy the soft-switching condition, and then determine the maximum conduction times of the switching transistors Q1 and Q3 according to the relationship between the maximum conduction time and the critical duty cycle value. The maximum conduction time is the product of the corresponding critical duty cycle value and the switching period T:

[0067]

[0068] In Equation (1) and Equation (2), D Buck_max and D Boost_min are respectively the maximum duty cycle of the Buck circuit and the minimum duty cycle of the Boost circuit that satisfy the soft-switching condition; T is the switching period; T dead is the dead time; L is the energy storage inductor; I ZVS_Vin , I ZVS_Vo are respectively the sum of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors Q1 and Q3, and the critical inductor current values that satisfy the soft-switching condition when the input voltage and the output voltage are applied respectively.

[0069] As a further improvement of the above technical solution, in the Buck mode, the gain of the converter is G Buck =D Buck =V o / V i . In the Boost mode, the gain of the converter is G Boost =1 / (1 - D Boost), where D Boost = 1 - V in / V o , D Buck is the duty cycle of the Buck circuit, and D Boost is the duty cycle of the Boost circuit.

[0070] By adjusting the gains of the Buck circuit and the Boost circuit through feedback, the output voltage of the converter can be controlled more precisely under different operating modes, ensuring efficient energy conversion and improving the efficiency and stability of the system.

[0071] As a further improvement of the above technical solution, ignoring the change in inductor current during the dead time, the switching timings and inductor current waveforms in the extended Buck mode and the extended Boost mode are as Figure 3 shown. Figure 3 The switching timings and inductor current waveforms in the extended Buck mode and the extended Boost mode are shown. By Figure 3 , the on and off times of the switching transistors and the change in inductor current under different modes can be visually observed. The inductor current waveform shows the current change of the inductor L at different stages, and these changes depend on the on and off states of the switching transistors. In Figure 3 , I0 represents the current condition required to satisfy the soft switching of Q1 and Q4, I1 represents the current condition required to satisfy the soft switching of Q3, I2 represents the current condition required to satisfy the soft switching of Q2, and I3 represents the current condition required to satisfy the soft switching of Q1 and Q4.

[0072] Ignoring the charge and discharge time of the switching transistor C oss , the inflection point current at each stage is obtained using Equation (5):

[0073]

[0074] In Equation (5), I0 is the critical current value to satisfy the soft switching condition of Q1 and Q4, I1, I2, and I3 are the current values at the inflection points of the inductor current waveform, L is the value of the energy storage inductor, V in and V o are the input voltage and output voltage of the converter respectively, and the meanings of T1, T2, and T3 are as Figure 3 shown, where T1 represents the simultaneous conduction time of Q1 and Q4, T2 represents the simultaneous conduction time of Q1 and Q3, and T3 represents the simultaneous conduction time of Q2 and Q3.

[0075] Ensure that the inductor currents I0, I1, and I2 satisfy the soft switching conditions of the switching transistors Q1, Q2, Q3, and Q4, thereby achieving efficient energy transfer and reducing switching losses.

[0076] The soft switching conditions that each inflection point current needs to satisfy are shown in Equation (6):

[0077]

[0078] In Equation (6), C oss is the parasitic capacitance value between the drain and source of MOS transistors Q1 to Q4, and L is the energy storage inductor.

[0079] Use Equation (7) to determine the current condition for soft switching:

[0080]

[0081] In Equation (7), I ZVS_Vin , I ZVS_Vo are the critical values of the inductor current that satisfy the soft-switching condition when the sum of the voltages across the parasitic capacitances between the drain and source of two soft-switching MOS transistors is the input voltage and the output voltage, respectively.

[0082] As a further improvement of the above technical solution, in step S45, in the extended Buck mode and the extended Boost mode, calculate the operating frequency required for soft switching through the operating state of the converter, and adjust the switching frequency of the converter in real time to achieve soft switching, including:

[0083] S451. In the extended Buck mode and the extended Boost mode, use Equation (3) to obtain the duty cycles D' Buck , D′ Boost :

[0084]

[0085] In Equation (3), D' Buck is the duty cycle of the Buck circuit considering the dead time, D' Boost is the duty cycle of the Boost circuit considering the dead time, T is the switching period; T dead is the dead time; D buck is the duty cycle of the Buck circuit, D boost is the duty cycle of the Boost circuit;

[0086] S452. Through the change process of the inductor current, combined with the conduction time of the switching transistor, use Equation (4) to calculate the required reference switching frequency f ref , and by controlling the change of the switching frequency, ensure the realization of soft switching:

[0087]

[0088] In Equation (4), f ref is the reference switching frequency, D' BuckFor the Buck circuit, considering the dead-time duty cycle, D' Boost For the Boost circuit, considering the dead-time duty cycle, V in is the input voltage, V o is the output voltage, L is the energy storage inductor, I o is the output current, I ZVS_Vin 、I ZVS_Vo are the sums of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors Q1 and Q3 of the switching transistors, respectively. When they are the input voltage and the output voltage respectively, they are the critical values of the inductor current that satisfy the soft-switching condition. The expression of the switching frequency shown in Equation (4) is obtained from Equations (3), (8), (9) and (10).

[0089] When the load increases, the energy transferred during the conduction time of the switching transistors Q1 and Q3 is insufficient, resulting in the failure of soft switching. Therefore, it is necessary to reduce the frequency, increase the conduction time of the switching transistors, and increase the energy transferred to the load. Through the change process of the inductor current, combined with the conduction time of the switching transistors, the switching frequency required to achieve soft switching is calculated. By controlling the change of the switching frequency, the realization of soft switching is ensured.

[0090] The following introduces the derivation process of the reference switching frequency f ref :

[0091] First, the output current I o of the converter is calculated using Equation (8):

[0092]

[0093] In Equation (8), T1, T2, T3, I1, I2 are obtained from the switching timing and inductor current waveform diagrams in the extended Buck mode and extended Boost mode shown Figure 3 by.

[0094] Secondly, the relational expression satisfied by the frequency that meets the soft-switching condition is obtained using Equation (9):

[0095]

[0096] In Equation (9), f ref is the reference switching frequency.

[0097] Then, from Figure 3 the switching timing and inductor current waveform diagrams in the extended Buck mode and extended Boost mode shown, T1, T2 and T3 are obtained:

[0098] T1 = D Boost ·T - T dead , T2 = (DBuck -D Boost )·T - T dead ,T3 = (1 - D Buck )·T - T dead (10)

[0099] In formula (10), D Buck is the duty cycle of the Buck circuit, and D Boost is the duty cycle of the Boost circuit.

[0100] In summary, the present invention can reduce the control difficulty of the four-switch Buck-Boost converter, and improve the disadvantages of the traditional control method, such as large inductor current ripple, large loss, and low operating efficiency. The present invention has a wide input voltage range, can achieve soft switching, and has small inductor current ripple, effectively improving the operating efficiency of the converter. It is a practical control method for the four-switch Buck-Boost converter. Specifically, the present invention relates to an improved four-mode control method for the four-switch Buck-Boost converter, including: when the input voltage is close to the output voltage, on the basis of the traditional Buck and Boost modes, two extended modes are added. To prevent frequent mode switching, a gain hysteresis is added during mode switching. In the extended Buck mode, the gain of the Buck circuit is regulated by feedback, and the rectifier diode of the Boost circuit operates at the minimum conduction time to satisfy soft switching, and the freewheeling diodes conduct complementarily; in the extended Boost mode, the gain of the Boost circuit is regulated by feedback, and the rectifier diode of the Buck circuit operates at the maximum conduction time to satisfy soft switching, and the freewheeling diodes conduct complementarily; in the extended Buck and extended Boost modes, the operating frequency required for soft switching is calculated and adjusted in real time to ensure soft switching. The present invention can achieve soft switching, has a wide input voltage range, and stable mode switching. By controlling the frequency and the conduction timing of the switching tubes, the inductor current ripple can be effectively reduced, the loss can be decreased, and the operating efficiency of the converter is improved.

[0101] The above-described embodiments are merely descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. An improved four-mode control method for a four-switch Buck-Boost converter, characterized in that, The method includes the following steps: S1. Obtain the input voltage V of the four-switch Buck-Boost converter in and the output voltage V o ; S2. Select the operating mode of the converter according to the relationship between the input voltage V of the four-switch Buck-Boost converter in and the output voltage V o . The operating modes include Buck mode, Boost mode, extended Buck mode, and extended Boost mode; S3. Set the switching conditions for the converter operating mode, and set a hysteresis region at the critical point of mode switching. Determine the current operating mode of the converter according to the switching conditions of the converter operating mode and the hysteresis region; S4. Perform corresponding control on the four-switch Buck-Boost converter according to the operating mode of the converter: S41. In Buck mode, feedback regulates the gain of the Buck circuit to control the output voltage of the converter. The rectifier diode in the Boost circuit is turned off, and the freewheeling diode is turned on; S42. In Boost mode, feedback regulates the gain of the Boost circuit to control the output voltage of the converter. The rectifier diode in the Buck circuit is turned on, and the freewheeling diode is turned off; S43. In extended Buck mode, feedback regulates the gain of the Buck circuit to control the output voltage of the converter. The rectifier diode in the Boost circuit works at the minimum conduction time that satisfies the soft-switching condition, and the freewheeling diode conducts complementarily; S44. In extended Boost mode, feedback regulates the gain of the Boost circuit to control the output voltage of the converter. The rectifier diode in the Buck circuit works at the maximum conduction time that satisfies the soft-switching condition, and the freewheeling diode conducts complementarily; S45. In extended Buck mode and extended Boost mode, calculate the operating frequency required for soft switching according to the operating state of the converter, and adjust the switching frequency of the converter in real time to achieve soft switching.

2. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 1, wherein in the Buck mode, the rectifier diode of the Boost circuit remains in the off state, the freewheeling diode remains in the on state, and the Buck circuit operates normally. In the Buck mode, the rectifier diode in the Boost circuit is the switching tube Q4, and the freewheeling diode is the switching tube Q3.

3. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 1, wherein in the Boost mode, the rectifier diode of the Buck circuit remains in the on state, the freewheeling diode remains in the off state, and the Boost circuit operates normally. In the Buck mode, the rectifier diode in the Buck circuit is the switching tube Q1, and the freewheeling diode is the switching tube Q2.

4. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 1, wherein in the extended Buck mode and extended Boost mode, the switching tubes Q1 and Q4 are turned on simultaneously, and within the target gain range, the conduction time of the switching tubes Q1 and Q3 is extended, and the conduction time of the switching tubes Q1 and Q3 is not greater than the maximum conduction time that ensures the soft-switching condition.

5. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 1, wherein the switching conditions for the converter operating mode are: (1) Buck mode, V o <0.95×V in ; (2) Extended Buck mode, 0.95×V in <V o <V in ; (3) Extended Boost mode, V in <V o <1.05×V in ; (4) Boost mode, V o > 1.05 × V in ; Among them, V in is the input voltage of the four-switch Buck-Boost converter, and V o is the output voltage of the four-switch Buck-Boost converter.

6. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 4, wherein Extending the conduction time of the switching transistor Q1 and the switching transistor Q3, and making the conduction time of the switching transistor Q1 and the switching transistor Q3 not greater than the maximum conduction time to ensure the soft-switching condition, includes: Using Equation (1) and Equation (2) to obtain the critical values of the duty cycles of the switching transistor Q1 and the switching transistor Q3 that satisfy the soft-switching condition, and further determining the maximum conduction time of the switching transistor Q1 and the switching transistor Q3: In Formula (1) and Formula (2), D Buck_max and D Boost_min are respectively the maximum duty cycle of the Buck circuit and the minimum duty cycle of the Boost circuit that satisfy the soft-switching condition; T is the switching period; T dead is the dead time; L is the energy storage inductor; I ZVS_Vin , I ZVS_Vo are respectively the sum of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors Q1 and Q3. They are the critical values of the inductor current that satisfy the soft-switching condition when the input voltage and the output voltage are applied respectively.

7. The improved four-mode control method for a four-switch Buck-Boost converter according to claim 1, wherein In the step S45, in the extended Buck mode and the extended Boost mode, calculating the operating frequency required for soft switching through the operating state of the converter, and adjusting the switching frequency of the converter in real time to achieve soft switching, includes: S451. In the extended Buck mode and the extended Boost mode, the duty cycles D' and D' of the Buck circuit and the Boost circuit in the four-switch Buck-Boost converter considering dead time are respectively obtained by using Equation (3). Buck , D′ Boost : In Equation (3), D' Buck is the duty cycle of the Buck circuit considering dead time, D' Boost is the duty cycle of the Boost circuit considering dead time, T is the switching period; T dead is the dead time; D buck is the duty cycle of the Buck circuit, D boost is the duty cycle of the Boost circuit; S452. Through the change process of the inductor current and in combination with the conduction time of the switching transistor, the reference switching frequency f required for realizing soft switching is calculated using Equation (4): ref , and by controlling the change of the switching frequency, the realization of soft switching is ensured: In Equation (4), f ref is the reference switching frequency, D' Buck is the duty cycle of the Buck circuit considering the dead time, D' Boost is the duty cycle of the Boost circuit considering the dead time, V in is the input voltage, V o is the output voltage, L is the energy storage inductor, I o is the output current, I ZVS_Vin and I ZVS_Vo are respectively the sum of the voltages across the parasitic capacitances between the drain and source of the two MOS transistors Q1 and Q3 of the switching transistors, and are the critical values of the inductor current that satisfy the soft-switching condition when they are the input voltage and the output voltage respectively.

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