A trapezoidal wave current mode control method for double three-level buck-boost converter

Abstract

The application discloses a trapezoidal wave current mode control method of a double three-level Buck-Boost converter, which comprises the following steps: sampling input and output voltages, flying capacitor voltages and inductor currents; dividing three working intervals, calculating inductor current average, switching frequency and capacitor voltage imbalance; establishing a functional relationship between duty cycle, switching frequency and input / output voltage, inductor average current; performing variable duty cycle control within the duty cycle limit to realize trapezoidal wave current and bidirectional power transmission, and ensure zero-voltage switching of the switch tube; when the duty cycle reaches or exceeds the set limit, automatically switching to a variable duty cycle + variable frequency hybrid control mode, and through synchronous adjustment of the switching frequency and the duty cycle, maintaining the trapezoidal wave current, zero-voltage switching and bidirectional power transmission performance. The method overcomes the problems of large peak current, high switching loss and low efficiency in the traditional hard switching mode.

Description

Technical Field

[0001] This invention belongs to the field of power electronics technology, and in particular relates to a trapezoidal current mode control method for a dual three-level Buck-Boost converter. Background Technology

[0002] Dual three-level Buck-Boost converters have attracted widespread attention in energy storage systems, electric vehicles, and photovoltaic power generation due to their low voltage stress and wide output voltage regulation capability. Current research has yielded control schemes for implementing buck-boost functions in these converters, but these schemes are all based on continuous conduction mode, operating in hard switching, which leads to significant switching losses and electromagnetic interference problems.

[0003] To address these issues, several soft-switching techniques have been proposed for single-level three-level DC-DC converters. For example, zero-voltage switching can be achieved by introducing additional inductors and capacitors to form a resonant circuit, thereby reducing turn-on losses and diode reverse recovery losses. However, these methods also lead to complex circuit structures and increased costs. To eliminate the need for auxiliary components, researchers have further proposed triangular current mode and near-critical conduction mode. By increasing the inductor current ripple, the inductor current has both positive and negative values ​​in each cycle to meet the zero-voltage turn-on condition. However, these two methods cause the peak current to reach more than twice the average current, resulting in large peak current and switching losses. To address this, researchers have proposed a trapezoidal current mode, which can reduce peak current and losses while achieving soft switching and improving efficiency. In addition, the quadrilateral current mode used in four-switch buck-boost converters is not suitable for three-level converters due to problems such as low switching utilization and limited power transmission capability.

[0004] However, the aforementioned soft-switching control schemes are all applicable to single-level three-level DC-DC converters and have not yet been extended to dual-level three-level Buck-Boost converters. Due to differences in their operating characteristics and principles, the soft-switching technology of single-level three-level DC-DC converters cannot be directly applied to dual-level three-level Buck-Boost converters. Therefore, research on soft-switching control schemes for dual-level three-level Buck-Boost converters has significant theoretical and engineering application value. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a trapezoidal current-mode control method for dual three-level Buck-Boost converters. This method effectively overcomes the problems of high switching losses, severe electromagnetic interference, and low efficiency associated with traditional continuous conduction mode hard switching operations. It is applicable to various dual three-level Buck-Boost converter topologies, including stacked, flying capacitor, diode-clamped, and active-clamped types. Furthermore, this invention utilizes automatic switching between variable duty cycle control and a hybrid variable duty cycle + frequency conversion control to further control the dual three-level Buck-Boost converter to operate in trapezoidal current mode. This not only significantly reduces switching losses and improves overall efficiency but also enables bidirectional power transfer.

[0006] To achieve the above objectives, the technical solution adopted by this invention is: a trapezoidal current mode control method for a dual three-level Buck-Boost converter, which switches between variable duty cycle control and mixed control of variable duty cycle and variable switching frequency based on whether the duty cycle of the main switch reaches or exceeds a set limit. Through the automatic switching between variable duty cycle control and mixed control of variable duty cycle and frequency, the converter operates stably in trapezoidal current mode, achieving zero-voltage soft switching and bidirectional power transmission; including the following steps: S10: Samples the input voltage, output voltage, input flyby or cascaded capacitor voltage, output flyby or cascaded capacitor voltage, inductor current, and output current of the dual three-level Buck-Boost converter; S20: Based on input voltage V dc1 With output voltage V dc2 The relationship is divided into three work areas: V dc2 / V dc1 < k 1, k 1< V dc2 / V dc1 < k 2, V dc2 / V dc1 > k 2, of which k 1 and k 2 represents the preset threshold; S30: Calculate the uniform average inductor current, switching frequency, duty cycle, and imbalance of voltage across or cascaded capacitors. S40: Establish the functional relationship between the main switch duty cycle, switching frequency, input voltage, output voltage, and average inductor current; S50: In forward power ILavg >0 and reverse power I Lavg Waveform control is performed for values ​​less than 0. Within the set limit, variable duty cycle control is used to reduce or increase the average inductor current. When the duty cycle reaches or exceeds the set limit, a hybrid control of variable duty cycle and frequency conversion is used, including increasing the switching frequency to reduce the average inductor current and decreasing the switching frequency to increase the average inductor current. Finally, the dual three-level Buck-Boost converter is controlled to operate in trapezoidal current mode to achieve zero-voltage soft switching and bidirectional power transmission.

[0007] Furthermore, the input-side structure of the dual three-level Buck-Boost converter is the same as the output-side structure, which is a stacked three-level, flying capacitor three-level, diode clamped three-level, or active midpoint clamped three-level structure.

[0008] Furthermore, the dual three-level Buck-Boost converter includes four sets of complementary switching pairs: S 1a - S 2a , S 3a - S 4a , S 1b - S 2b and S 3b - S 4b The main switch is S 1a , S 4a , S 2b and S 3b The corresponding duty cycle is D 1a , D 4a , D 2b and D 3b .

[0009] Furthermore, duty cycle D 1a , D 4a , D 2b , D 3b Proportional to the output voltage, in near-critical conduction mode: increase D 1a ,D 4a , D 2b and D 3b Output voltage increases, decreases D 1a , D 4a , D 2b and D 3b Output voltage decreases; duty cycle D 1a and D 2b The duty cycle is proportional to the average inductor current. D 4a and D 3b It is inversely proportional to the average inductor current, increasing D 1a and D 2b , reduce D 4a and D 3b The average inductor current decreases, thus decreasing. D 1a and D 2b Increase D 4a and D 3b The average current of the inductor increases.

[0010] Furthermore, the variable duty cycle control is implemented by fixing the switching frequency while changing the duty cycle of the main switch. D 1a , D 4a , D 2b and D 3b By adjusting the shape and magnitude of the trapezoidal wave current, the average inductor current and output voltage can be further regulated.

[0011] Furthermore, the switching frequency is inversely proportional to the average inductor current. In near-critical conduction mode: increasing the switching frequency decreases the average inductor current; decreasing the switching frequency increases the average inductor current; increasing the switching frequency decreases the average inductor current. The switching frequency is also related to the duty cycle. D 1a and D 2b Proportional D 4a and D3b Inversely proportional, increasing the switching frequency and duty cycle D 1a and D 2b Increase D 4a and D 3b Reduce, lower the switching frequency, and decrease the duty cycle. D 1a and D 2b Decrease D 4a and D 3b Increase.

[0012] Furthermore, the use of a sawtooth wave modulation scheme enables... D 1a and D 4a Alternating action S 1a and S 4a , D 2b and D 3b Alternating action S 2b and S 3b .

[0013] Furthermore, four different trapezoidal modulation schemes are obtained based on different switching sequences of the main switch. An optimized modulation scheme is selected according to the operating conditions to improve the efficiency of the converter.

[0014] Furthermore, based on the relationship between the input voltage and the output voltage, three operating ranges are derived: V dc2 / V dc1 < k 1, D 1a + D 4a <1, D 2b + D 3b <1 indicates Buck mode; k 1< V dc2 / V dc1 < k 2, D 1a + D 4a =1,D 2b + D 3b =1, indicating Buck-Boost mode; V dc2 / V dc1 > k 2, D 1a + D 4a >1, D 2b + D 3b >1 indicates Boost mode.

[0015] Furthermore, the automatic switching control of the converter through variable duty cycle control and variable duty cycle and frequency conversion hybrid control operates in near critical conduction mode. The inductor current has both positive and negative values ​​in each cycle, and all switching transistors can achieve zero-voltage soft switching to improve the converter's operating efficiency. The control method comprises three parts: voltage / current closed-loop control of the converter, equalization control of capacitor voltage, and waveform control of trapezoidal wave. The aforementioned variable duty cycle control and automatic switching of variable duty cycle and frequency conversion hybrid control achieve positive power. I Lavg >0 and reverse power I Lavg Trapezoidal wave bidirectional power control with a value of <0.

[0016] The beneficial effects of adopting this technical solution are: This invention proposes a trapezoidal current-mode control method for dual three-level Buck-Boost converters. By automatically switching between variable duty cycle control and a hybrid variable duty cycle + frequency conversion control, the converter operates stably in trapezoidal current mode, achieving zero-voltage soft switching and bidirectional power transfer. Within a set limit, variable duty cycle control is used. By establishing the relationship between duty cycle and average inductor current, and input / output voltage, the duty cycles of the four main switches and the switching timing are dynamically adjusted to control the converter's operation in trapezoidal current mode. When the duty cycle reaches or exceeds the set limit, a hybrid variable duty cycle + frequency conversion control is employed. By establishing the relationship between switching frequency and average inductor current, and duty cycle, the switching frequency is adjusted in real time to ensure the converter operates in trapezoidal current mode. The advantage of this scheme, which automatically switches between variable duty cycle control and hybrid variable duty cycle + frequency conversion control, is that it can achieve zero-voltage conduction and bidirectional power transfer of all power switches in near-critical conduction mode, significantly reducing switching losses and diode reverse recovery losses, thereby effectively improving the overall system efficiency.

[0017] This invention solves the problems of high peak current, large switching loss and low efficiency in traditional continuous conduction mode hard switching operation, enabling the converter to achieve trapezoidal current waveform across the entire operating range, further suppressing current peak and optimizing loss characteristics.

[0018] The control method proposed in this invention has good topology applicability. Its control logic is based on the general switching states and principles of dual three-level Buck-Boost converters, so it can be widely used in various bidirectional three-level Buck-Boost converter structures such as stacked, flying capacitor, diode midpoint clamping, and active midpoint clamping. Attached Figure Description

[0019] Figure 1 This is a schematic flowchart of a trapezoidal current mode control method for a dual three-level Buck-Boost converter according to the present invention; Figure 2 This invention describes the stacked dual three-level Buck-Boost converter topology and its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control. Figure 3 This invention relates to a flying capacitor dual three-level Buck-Boost converter and its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control. Figure 4 This invention relates to a diode-midpoint clamped dual three-level Buck-Boost converter and its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control. Figure 5 This invention relates to an active midpoint clamped dual three-level Buck-Boost converter and its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control; Figure 6 These are four different modulation schemes for the dual three-level Buck-Boost converter based on trapezoidal wave current mode in this invention. Figure 7 This is a schematic diagram illustrating the functional relationship between the main switch duty cycle and the output voltage and average inductor current in this invention. Figure 8 This is a schematic diagram illustrating the functional relationship between the switching frequency, the average inductor current, and the main switch duty cycle in this invention. Figure 9 This is a block diagram of the variable duty cycle control of the dual three-level Buck-Boost converter based on trapezoidal wave current mode in this invention. Figure 10 This is a block diagram of the variable duty cycle + variable switching frequency hybrid control of the dual three-level Buck-Boost converter based on trapezoidal wave current mode in this invention. Detailed Implementation

[0020] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described below with reference to the accompanying drawings.

[0021] In this embodiment, see Figure 1 As shown, this invention proposes a trapezoidal current mode control method for a dual three-level Buck-Boost converter. Based on whether the duty cycle of the main switch reaches or exceeds a set limit, it switches between variable duty cycle control and a hybrid control combining variable duty cycle and variable switching frequency. Through automatic switching between variable duty cycle control and the hybrid control combining variable duty cycle and frequency, the converter operates stably in trapezoidal current mode, achieving zero-voltage soft switching and bidirectional power transfer. The method includes the following steps: S10: Samples the input voltage, output voltage, input flyby or cascaded capacitor voltage, output flyby or cascaded capacitor voltage, inductor current, and output current of the dual three-level Buck-Boost converter; S20: Based on input voltage V dc1 With output voltage V dc2 The relationship is divided into three work areas: V dc2 / V dc1 < k 1, k 1< V dc2 / V dc1 < k 2, V dc2 / V dc1 > k 2, of which k 1 and k 2 represents the preset threshold; S30: Calculate the uniform average inductor current, switching frequency, duty cycle, and imbalance of voltage across or cascaded capacitors. S40: Establish the functional relationship between the main switch duty cycle, switching frequency, input voltage, output voltage, and average inductor current; S50: In forward power I Lavg >0 and reverse power I LavgWaveform control is performed for values ​​less than 0. Within the set limit, variable duty cycle control is used to reduce or increase the average inductor current. When the duty cycle reaches or exceeds the set limit, a hybrid control of variable duty cycle and frequency conversion is used, including increasing the switching frequency to reduce the average inductor current and decreasing the switching frequency to increase the average inductor current. Finally, the dual three-level Buck-Boost converter is controlled to operate in trapezoidal current mode to achieve zero-voltage soft switching and bidirectional power transmission.

[0022] The trapezoidal current mode control method with automatic switching between variable duty cycle control and variable duty cycle + frequency conversion hybrid control proposed in this invention can be used for, for example... Figure 2 The stacked dual three-level Buck-Boost converter topology shown herein, along with its trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control implementation, are illustrated. Figure 3 The flying capacitor dual three-level Buck-Boost converter topology shown herein, along with its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control, is illustrated. Figure 4 The diode-neutral-clamped dual three-level Buck-Boost converter topology shown, along with its trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control implementation, can also be used for... Figure 5 The active midpoint clamped dual three-level Buck-Boost converter topology shown is illustrated, along with its implementation method of trapezoidal current variable duty cycle and variable duty cycle + variable switching frequency hybrid control. Figure 2 , Figure 3 , Figure 4 and Figure 5 These four converter topologies have the same input and output structure, and can generate three levels: 2, 1, and 0. The four main switches are controlled by different pulse width modulation signals, and the duty cycle is alternated between odd and even periods.

[0023] The dual three-level Buck-Boost converter includes four sets of complementary switching pairs: S 1a - S 2a , S 3a - S 4a , S 1b - S 2b and S 3b - S 4b The main switch is S 1a , S 4a , S 2band S 3b The corresponding duty cycle is D 1a , D 4a , D 2b and D 3b .

[0024] Preferably, three operating ranges are obtained based on the relationship between the input voltage and the output voltage: V dc2 / V dc1 < k 1, D 1a + D 4a <1, D 2b + D 3b <1, Buck mode; k 1< V dc2 / V dc1 < k 2, D 1a + D 4a =1, D 2b + D 3b =1, Buck-Boost mode; V dc2 / V dc1 > k 2, D 1a + D 4a >1, D 2b + D 3b >1, Boost mode.

[0025] Preferably, the variable duty cycle control is implemented by fixing the switching frequency while changing the duty cycle of the main switch. D 1a , D 4a , D 2b , D 3b By adjusting the shape and magnitude of the trapezoidal wave current, the average inductor current and output voltage can be further regulated.

[0026] Preferably, the implementation method of variable duty cycle + variable switching frequency hybrid control is as follows: adjust the switching frequency to ensure that the converter operates in trapezoidal current mode, thereby realizing zero-voltage soft switching, and further realizing the regulation of average inductor current and output voltage.

[0027] like Figure 6 The diagram illustrates four different modulation schemes for a dual three-level Buck-Boost converter based on a trapezoidal current mode. By adjusting the switching sequence of the main switch, the output switching voltage of the converter can be controlled, allowing both the input and output sides to generate three levels (0, 1, and 2), thereby further generating a trapezoidal inductor current. Specifically, if the level sequence of the input-side three-level bridge is fixed at 2-1-0, four different modulation schemes can be obtained by changing the level sequence of the output-side three-level bridge. These schemes all maintain the same trapezoidal current waveform, but each has its own advantages. Therefore, the optimal modulation scheme can be flexibly selected according to the actual operating conditions.

[0028] like Figure 7 The diagram shows the relationship between the main switch duty cycle, output voltage, and average inductor current. Duty Cycle D 1a , D 4a , D 2b , D 3b Proportional to output voltage; duty cycle D 1a , D 2b The duty cycle is proportional to the average inductor current. D 4a , D 3b It is inversely proportional to the average inductor current. The derivation of the relationship between output voltage and duty cycle, and between average inductor current and duty cycle, is as follows: First, combining the volt-second balance principle and the superposition theorem, we obtain the relationship between duty cycle and output voltage / input voltage: ; Based on the formula for duty cycle and output voltage / input voltage, a constraint condition for duty cycle is obtained as follows: ; Then, the current change corresponding to the two peak currents based on the trapezoidal wave current mode is calculated as follows: ; Further solving for the area of ​​the trapezoidal wave current yields the average inductor current: ; Substituting the current change and duty cycle at the two peak currents with the input voltage / output voltage relationship into the above formula for average inductor current, we can obtain the final expression for the average inductor current: ; Based on the expression for the average inductor current, another constraint on the duty cycle can be obtained: ; The duty cycle can be solved by simultaneously solving the two constraint equations for the duty cycle. D 1a , D 4a The final expression: ; In even-numbered periods, the duty cycle D 1a and D 4a Interchange, acting on S 1a and S 4a .

[0029] in V dc1 Input voltage, V dc2 For output voltage, L This is the inductance value. f sw For switching frequency, I p- This is the negative valley current.

[0030] like Figure 8 The diagram illustrates the relationship between switching frequency, average inductor current, and duty cycle. Switching frequency is inversely proportional to the average inductor current; switching frequency is inversely proportional to the duty cycle. D 1a , D 2b Proportional D 4a , D 3b Inversely proportional, based on the final expression for the average inductor current mentioned above, the final expression for the switching frequency can be derived as follows: ; like Figure 9 The diagram shown is a variable duty cycle control block diagram for a dual three-level Buck-Boost converter based on trapezoidal current mode, as follows: Figure 10The diagram shows a hybrid control block diagram of a dual three-level Buck-Boost converter based on trapezoidal wave current mode, employing a variable duty cycle and variable switching frequency control. The variable duty cycle control loop and the hybrid control loop include three parts: output voltage / inductor current closed-loop control, input / output capacitor voltage balancing control, and trapezoidal wave waveform control. The output voltage / inductor current closed-loop control is a constant voltage / constant current source control; the input / output capacitor voltage balancing control is achieved by calculating the voltage imbalance between the series capacitors on the input and output sides; when the duty cycle is within a set limit, waveform control is performed through variable duty cycle control, i.e., by establishing the relationship between the main switch duty cycle, the average inductor current, and the output voltage to further adjust the duty cycle, such as by decreasing the duty cycle. D 1a Increase duty cycle D 4a This can reduce the average inductor current and increase the duty cycle. D 1a , D 4a It can increase the output voltage; when the duty cycle reaches or exceeds the set limit, waveform control is performed by a combination of variable duty cycle and variable switching frequency, that is, the relationship between the switching frequency and the average inductor current and the main switch duty cycle is established to further adjust the switching frequency. For example, increasing the switching frequency can reduce the average inductor current.

[0031] In summary, this invention solves the problems of high peak current, high switching loss, and low efficiency in traditional continuous conduction mode hard switching operation, enabling the converter to achieve bidirectional trapezoidal current wave through mixed control switching of variable duty cycle and variable duty cycle + variable switching frequency, thereby reducing switching loss and improving the overall efficiency of the converter.

[0032] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A trapezoidal current-mode control method for a dual three-level Buck-Boost converter, characterized in that, The switching between variable duty cycle control and mixed control of variable duty cycle and variable switching frequency is performed based on whether the duty cycle of the main switch reaches or exceeds the set limit. This automatic switching ensures the converter operates stably in trapezoidal current mode, achieving zero-voltage soft switching and bidirectional power transfer. The input-side structure of the dual three-level Buck-Boost converter is the same as the output-side structure, which is a stacked three-level, flying capacitor three-level, diode-clamped three-level, or active midpoint-clamped three-level structure. The dual three-level Buck-Boost converter includes four sets of complementary switching pairs: S 1a -S 2a S 3a -S 4a S 1b -S 2b and S 3b -S 4b The main switch is S. 1a ,S 4a ,S 2b With S 3b The corresponding duty cycle is D. 1a D 4a D 2b With D 3b ; include step: S10: Samples the input voltage, output voltage, input flyby or cascaded capacitor voltage, output flyby or cascaded capacitor voltage, inductor current, and output current of the dual three-level Buck-Boost converter; S20: Based on the input voltage V dc1 With output voltage V dc2 The relationship is divided into three working areas: V dc2 / V dc1 <k1,k1<V dc2 / V dc1 <k2,V dc2 / V dc1 >k2, where k1 and k2 are preset thresholds; S30: Calculate the uniform average inductor current, switching frequency, duty cycle, and imbalance of voltage across or cascaded capacitors. S40: Establish the functional relationship between the main switch duty cycle, switching frequency, input voltage, output voltage, and average inductor current; S50: In forward power I Lavg >0 and reverse power I Lavg Waveform control is performed for values ​​less than 0. Within the set limit, variable duty cycle control is used to reduce or increase the average inductor current. When the duty cycle reaches or exceeds the set limit, a hybrid control of variable duty cycle and variable switching frequency is used, including increasing the switching frequency to reduce the average inductor current and decreasing the switching frequency to increase the average inductor current. Finally, the dual three-level Buck-Boost converter is controlled to operate in trapezoidal current mode to achieve zero-voltage soft switching and bidirectional power transmission.

2. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, Duty cycle D 1a D 4a D 2b D 3b Proportional to the output voltage, in near-critical conduction mode: increasing D 1a D 4a D 2b and D 3b As the output voltage increases, D decreases. 1a D 4a D 2b and D 3b The output voltage decreases; the duty cycle D 1a and D 2b The duty cycle D is proportional to the average inductor current. 4a and D 3b It is inversely proportional to the average inductor current; increasing D... 1a and D 2b Decrease D 4a and D 3b The average inductor current increases; D decreases. 1a and D 2b Increase D 4a and D 3b The average inductor current decreases.

3. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, The variable duty cycle control is implemented by fixing the switching frequency while changing the duty cycle D of the main switch. 1a D 4a D 2b and D 3b By adjusting the shape and magnitude of the trapezoidal wave current, the average inductor current and output voltage can be further regulated.

4. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, Switching frequency is inversely proportional to the average inductor current. In near-critical conduction mode: decreasing the switching frequency increases the average inductor current, while increasing the switching frequency decreases the average inductor current. Switching frequency is also inversely proportional to the duty cycle D. 1a and D 2b Proportional, D 4a and D 3b Inversely proportional, increasing the switching frequency increases the duty cycle D. 1a and D 2b Increase, D 4a and D 3b Reduce the switching frequency, decrease the duty cycle D 1a and D 2b Decrease, D 4a and D 3b Increase.

5. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, Using a sawtooth wave modulation scheme enables D 1a With D 4a Alternating action on S 1a With S 4a D 2b With D 3b Alternating action on S 2b With S 3b .

6. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, Four different trapezoidal modulation schemes are obtained based on the different switching sequences of the main switch. An optimized modulation scheme is selected according to the operating conditions to improve the efficiency of the converter.

7. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, Based on the relationship between input voltage and output voltage, three operating ranges are obtained: V dc2 / V dc1 <k1,D 1a +D 4a <1,D 2b +D 3b <1 indicates Buck mode; k1 <V dc2 / V dc1 <k2,D 1a +D 4a =1, D 2b +D 3b =1, indicating Buck-Boost mode; V dc2 / V dc1 >k2,D 1a +D 4a >1, D 2b +D 3b >1 indicates Boost mode.

8. The trapezoidal current mode control method for a dual three-level Buck-Boost converter according to claim 1, characterized in that, The automatic switching control converter operates in near-critical conduction mode through variable duty cycle control and variable duty cycle and variable switching frequency hybrid control. The inductor current has both positive and negative values ​​in each cycle, and all switching transistors can achieve zero-voltage soft switching to improve the converter's operating efficiency. The control method comprises three parts: voltage and current closed-loop control of the converter, equalization control of capacitor voltage, and waveform control of trapezoidal wave. The aforementioned variable duty cycle control and automatic switching of variable duty cycle and variable switching frequency hybrid control achieve positive power I Lavg >0 and reverse power I Lavg Trapezoidal wave bidirectional power control with a value of <0.

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