Three-level Buck-Boost converter modulation method and system

Abstract

The invention discloses a three-level Buck-Boost converter modulation system, which comprises a three-level half-bridge unit, a DC-DC conversion half-bridge unit and a modulation unit, and is characterized in that the three-level half-bridge unit comprises a first switch tube, a second switch tube, a third switch tube, a fourth switch tube and a flying capacitor, and when an input voltage is twice greater than an output voltage, the first switch tube is switched on, and the second switch tube is switched off; the modulation unit alternately outputs a first switch time sequence and a second switch time sequence, so that flying capacitor voltage is balanced, charges of parasitic capacitors in the switches are consumed through reverse current before all the switches are turned on, switching tubes are turned on in a zero-voltage mode, and multi-section inductive current is generated. According to the modulation system disclosed by the invention, the optimal effective value of the inductive current and the self-balance of the flying capacitor voltage are realized through the alternate control of the switch sequence, and the hardware design is simplified.

Description

Technical Field

[0001] The present invention belongs to the technical field of power electronics, and particularly relates to a modulation method and system for a three-level Buck-Boost converter. Background Art

[0002] In a common DC bus photovoltaic energy storage system, the DC bus voltage is affected by both the fluctuations of photovoltaic power output and the dynamic characteristics of the load, showing significant non-linear fluctuation characteristics. To maintain the stability of the system voltage, the energy storage unit needs to achieve dynamic energy interaction between the battery device and the DC grid through a bidirectional DC converter. Currently, the four-switch Buck-Boost converter has become a key technical solution for photovoltaic energy storage systems due to its advantages such as bidirectional power transmission ability, buck-boost characteristics, and the same polarity of input and output. However, with the evolution of the photovoltaic system voltage level towards a 1500V high-voltage architecture, the traditional four-switch Buck-Boost converter faces problems such as an increase in the voltage stress of switching devices and a decrease in reliability.

[0003] Under this background, the three-level Buck-Boost converter has the advantages of halving the stress of switching tubes and having a small volume of magnetic components and filtering components, and has excellent application prospects in the field of photovoltaic energy storage.

[0004] The existing modulation methods for three-level Buck-Boost converters generally follow the quadrilateral modulation of four-switch Buck-Boost converters, requiring the switching frequency of the Boost arm to be twice that of the Buck arm, which brings potential electromagnetic interference problems, and the potential of the three-level structure to expand the voltage range has not been fully utilized. Summary of the Invention

[0005] Aiming at the above technical bottleneck, the present invention provides a modulation method and system for a three-level Buck-Boost converter. By reconstructing the inductor current waveform within a unit cycle, while achieving the same frequency operation of all switching tubes, the effective value of the current is reduced, making the effective value of the inductor current the smallest, avoiding the electromagnetic interference problems caused by multi-frequency modulation, and also realizing the soft-switching operation of all switching tubes.

[0006] The present invention discloses a three-level Buck-Boost converter modulation system, comprising: an input filter capacitor connected to an input voltage, and an output filter capacitor, a three-level half-bridge unit, a DC-DC conversion half-bridge unit, and a modulation unit connected to an output voltage. The three-level half-bridge unit includes a first switching tube, a second switching tube, a third switching tube, a fourth switching tube, and a flying capacitor. The flying capacitor is connected between the connection point of the first switching tube and the second switching tube and the connection point of the third switching tube and the fourth switching tube. The DC-DC conversion half-bridge unit includes a fifth switching tube and a sixth switching tube. The midpoint of the three-level half-bridge unit is the connection point of the second switching tube and the third switching tube; the midpoint of the DC-DC conversion half-bridge unit is the connection point of the fifth switching tube and the sixth switching tube. The midpoint of the three-level half-bridge unit is connected to the midpoint of the DC-DC conversion half-bridge unit through an inductor. The first switching tube and the fourth switching tube conduct complementarily; the second switching tube and the third switching tube conduct complementarily; the fifth switching tube and the sixth switching tube conduct complementarily. When the input voltage is greater than twice the output voltage, the modulation unit alternately outputs a first switching timing and a second switching timing to balance the voltage of the flying capacitor, and consumes the charge of the parasitic capacitance in the switch using a reverse current before all switches are turned on, enabling the switching tubes to turn on with zero voltage, and generating multiple segments of inductor current. The first switching timing is such that the switching tubes are turned on in the order of: the second, fourth, and sixth switching tubes conduct; the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct; the second switching timing is such that the switching tubes are turned on in the order of: the first, third, and sixth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct.

[0007] The present invention also discloses a modulation method based on the above three-level Buck-Boost converter modulation system. Through the alternating modulation of two different switching timings, the charge of the parasitic capacitance in the switches is consumed by the reverse current before all switches are turned on, enabling all switch tubes to turn on with zero voltage and generating multiple segments of inductor current. Among them, the first switch tube and the fourth switch tube conduct complementarily; the second switch tube and the third switch tube conduct complementarily; the fifth switch tube and the sixth switch tube conduct complementarily; the first switching timing is such that the turn-on sequence of the switch tubes is: the second, fourth, and sixth switch tubes conduct, the second, fourth, and fifth switch tubes conduct, the third, fourth, and fifth switch tubes conduct, the first, third, and fifth switch tubes conduct, the third, fourth, and fifth switch tubes conduct, and the third, fourth, and sixth switch tubes conduct; the second switching timing is such that the turn-on sequence of the switch tubes is: the first, third, and sixth switch tubes conduct, the first, third, and fifth switch tubes conduct, the third, fourth, and fifth switch tubes conduct, the second, fourth, and fifth switch tubes conduct, the third, fourth, and fifth switch tubes conduct, and the third, fourth, and sixth switch tubes conduct.

[0008] The Buck-Boost converter modulation method and system in the present invention effectively improve the efficiency performance of the three-level Buck-Boost converter under the condition that the input voltage is greater than twice the output voltage, expand the high-efficiency operation range of the converter in a wide voltage range, and provide an innovative solution for the energy conversion requirements of bidirectional wide-gain voltage regulation in the photovoltaic energy storage system.

[0009] Generally speaking, through the above technical solutions conceived by the present invention, the following beneficial effects can be achieved:

[0010] By reconstructing the inductor current waveform within a unit period, compared with traditional modulation, the effective value of the inductor current is reduced, the efficiency performance of the three-level Buck-Boost converter under the condition that the input voltage is greater than twice the output voltage is improved, and the high-efficiency operation range of the converter in a wide voltage range is expanded.

[0011] All switch tubes are enabled to operate at the same frequency, and soft switching of all switch tubes is achieved within a wide voltage range, reducing the switching loss.

[0012] By controlling the alternating modulation of two switching timings, the self-balancing of the flying capacitor voltage is achieved, avoiding the complex algorithms and hardware sampling circuits required for active control of the flying capacitor voltage, and simplifying the software and hardware design solutions. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 It is a topology diagram of a three-level Buck-Boost converter according to an embodiment of the present invention;

[0014] Figure 2Waveform diagram of the three-level Buck-Boost converter modulation method according to Embodiment 3 of the present invention;

[0015] Figure 3a Schematic diagram of the first mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0016] Figure 3b Schematic diagram of the second mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0017] Figure 3c Schematic diagram of the third mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0018] Figure 3d Schematic diagram of the fourth mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0019] Figure 3e Schematic diagram of the fifth mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0020] Figure 3f Schematic diagram of the sixth mode of the three-level Buck-Boost converter provided according to an embodiment of the present invention;

[0021] Figure 4a Simulation result diagram of the switch tube drive waveform and the inductor current waveform provided according to an embodiment of the present invention;

[0022] Figure 4b Simulation result diagram of the flying capacitor voltage, output voltage, output current, and output power provided according to an embodiment of the present invention;

[0023] Figure 4c Simulation result diagram of the soft switching of switches S1-S4 provided according to an embodiment of the present invention. Detailed implementation manners

[0024] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] In the present invention, terms such as "first", "second", etc. (if any) in the present invention and the accompanying drawings are used to distinguish similar objects, and do not necessarily describe a specific order or sequence.

[0026] Embodiment 1:

[0027] The present invention discloses a three-level Buck-Boost converter modulation system, including a three-level Buck-Boost converter and a modulation unit ( Figure 1 not shown) as Figure 1 shown, Figure 1 which includes an input filter capacitor C in , where the input voltage V in is connected to both ends of C in , an output filter capacitor C o , C o is connected to the output voltage V o at both ends, a three-level half-bridge unit, a DC-DC conversion half-bridge unit. The three-level half-bridge unit includes a first switching tube S1, a second switching tube S2, a third switching tube S3, a fourth switching tube S4 and a flying capacitor C f , C f is connected between the connection point of S1 and S2 and the connection point of S3 and S4. The DC-DC conversion half-bridge unit includes a fifth switching tube Q1 and a sixth switching tube Q2. The midpoint a of the three-level half-bridge unit is the connection point of S2 and S3; the midpoint b of the DC-DC conversion half-bridge unit is the connection point of Q1 and Q2. The midpoint a of the three-level half-bridge unit is connected to the midpoint b of the DC-DC conversion half-bridge unit through an inductor L. S1 and S4 conduct complementarily; S2 and S3 conduct complementarily; Q1 and Q2 conduct complementarily. The modulation unit is an electronic or digital signal processing module for adjusting the output waveform. In the embodiment of the present invention, when the input voltage V in is greater than twice the output voltage V o , the modulation unit alternately outputs a first switching timing and a second switching timing, so that the voltage of the flying capacitor C f is balanced, and the charge of the parasitic capacitance in the switch is consumed by the reverse current before all switches are turned on, all switching tubes are turned on with zero voltage, and multiple segments of inductor current are generated. When the inductor current flows from the midpoint a of the three-level half-bridge unit to the midpoint b of the DC-DC conversion half-bridge unit, it means that the inductor current is positive. When the inductor current flows from the midpoint b of the DC-DC conversion half-bridge unit to the midpoint a of the three-level half-bridge unit, it means that the inductor current is negative.

[0028] It should be noted that the first switching sequence makes the switching tubes turn on in the following order: the second, fourth, and sixth switching tubes conduct, the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct; the second switching sequence makes the switching tubes turn on in the following order: the first, third, and sixth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct. As Figure 2 shown is the switching sequence diagram of the modulated three-level Buck-Boost converter output by the modulation unit and the inductor current i L 's output waveform, and the voltage V ab between nodes a and b.

[0029] As Figure 2 shown, the first switching sequence includes twelve working stages within one switching period, which are respectively:

[0030] At the starting moment of the first stage, turn off the third switching tube S3. In the first stage, the second switching tube S2 and the third switching tube S3 are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the second switching tube S2;

[0031] At the starting moment of the second stage, the second switching tube S2 turns on with zero voltage. In the second stage, the second switching tube S2, the fourth switching tube S4, and the sixth switching tube Q2 conduct, and the voltage V ab across the inductor L is 0.5V in ;

[0032] At the starting moment of the third stage, turn off the sixth switching tube Q2. In the third stage, the fifth switching tube Q1 and the sixth switching tube Q2 are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fifth switching tube S1;

[0033] At the starting moment of the fourth stage, the fifth switching tube Q1 turns on with zero voltage. In the fourth stage, the second switching tube S2, the fourth switching tube S4, and the fifth switching tube Q1 conduct, and the voltage V ab across the inductor L is 0.5V in -V o ;

[0034] At the starting moment of the fifth stage, turn off the second switching tube S2. In the fifth stage, the second switching tube S2 and the third switching tube S3 are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the third switching tube S3;

[0035] At the start of the sixth stage, the third switching transistor S3 turns on with zero voltage. In the sixth stage, the third switching transistor S3, the fourth switching transistor S4, and the fifth switching transistor Q1 conduct, and the voltage V across the inductor ab is -V o ;

[0036] At the start of the seventh stage, the fourth switching transistor S4 is turned off. In the seventh stage, the first switching transistor S1 and the fourth switching transistor S4 are in the dead time, and the inductor current flows negatively to discharge the junction capacitance of the first switching transistor S1;

[0037] At the start of the eighth stage, the first switching transistor S1 turns on with zero voltage. In the eighth stage, the first switching transistor S1, the third switching transistor S3, and the fifth switching transistor Q1 conduct, and the voltage V across the inductor ab is 0.5V in -V o ;

[0038] At the start of the ninth stage, the first switching transistor S1 is turned off. In the ninth stage, the first switching transistor S1 and the fourth switching transistor S4 are in the dead time, and the inductor current flows positively to discharge the junction capacitance of the fourth switching transistor S4;

[0039] At the start of the tenth stage, the fourth switching transistor S4 turns on with zero voltage. In the tenth stage, the third switching transistor S3, the fourth switching transistor S4, and the fifth switching transistor Q1 conduct, and the voltage V across the inductor ab is -V o ;

[0040] At the start of the eleventh stage, the fifth switching transistor Q1 is turned off. In the eleventh stage, the fifth switching transistor Q1 and the sixth switching transistor Q2 are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the sixth switching transistor Q2;

[0041] At the start of the twelfth stage, the sixth switching transistor Q2 turns on with zero voltage. In the twelfth stage, the third switching transistor S3, the fourth switching transistor S4, and the sixth switching transistor Q2 conduct, and the voltage V across the inductor ab is 0.

[0042] Furthermore, the second switching timing has twelve working stages within one switching cycle, which are respectively:

[0043] At the start of the first stage, the fourth switching transistor S4 is turned off. In the first stage, the first switching transistor S1 and the fourth switching transistor S4 are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the first switching transistor S1;

[0044] At the start of the second stage, the first switching transistor S1 turns on with zero voltage. In the second stage, the first switching transistor S1, the third switching transistor S3, and the sixth switching transistor Q2 conduct, and the voltage V across the inductorab is 0.5V in ;

[0045] At the start of the third stage, turn off the sixth switching transistor Q2. During the third stage, the fifth switching transistor Q1 and the sixth switching transistor Q2 are in the dead time, and the inductor current flows in the positive direction to discharge the junction capacitance of the fifth switching transistor Q1;

[0046] At the start of the fourth stage, the fifth switching transistor Q1 turns on with zero voltage. During the fourth stage, the first switching transistor S1, the third switching transistor S3, and the fifth switching transistor Q1 conduct, and the voltage across the inductor V ab is 0.5V in -V o ;

[0047] At the start of the fifth stage, turn off the first switching transistor S1. During the fifth stage, the first switching transistor S1 and the fourth switching transistor S4 are in the dead time, and the inductor current flows in the positive direction to discharge the junction capacitance of the fourth switching transistor S4;

[0048] At the start of the sixth stage, the fourth switching transistor S4 turns on with zero voltage. During the sixth stage, the third switching transistor S3, the fourth switching transistor S4, and the fifth switching transistor Q1 conduct, and the voltage across the inductor V ab is -V o ;

[0049] At the start of the seventh stage, turn off the third switching transistor S3. During the seventh stage, the second switching transistor S2 and the third switching transistor S3 are in the dead time, and the inductor current flows in the negative direction to discharge the junction capacitance of the second switching transistor S2;

[0050] At the start of the eighth stage, the second switching transistor S2 turns on with zero voltage. During the eighth stage, the second switching transistor S2, the fourth switching transistor S4, and the fifth switching transistor Q1 conduct, and the voltage across the inductor V ab is 0.5V in -V o ;

[0051] At the start of the ninth stage, turn off the second switching transistor S2. During the ninth stage, the second switching transistor S2 and the third switching transistor S3 are in the dead time, and the inductor current flows in the positive direction to discharge the junction capacitance of the third switching transistor S3;

[0052] At the start of the tenth stage, the third switching transistor S3 turns on with zero voltage. During the tenth stage, the third switching transistor S3, the fourth switching transistor S4, and the fifth switching transistor Q1 conduct, and the voltage across the inductor V ab is -V o ;

[0053] Turn off the fifth switching transistor Q1 at the start of the eleventh stage. In the eleventh stage, the fifth switching transistor Q1 and the sixth switching transistor Q2 are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the sixth switching transistor Q2.

[0054] At the start of the twelfth stage, the sixth switching transistor Q2 is turned on with zero voltage. In the twelfth stage, the third switching transistor S3, the fourth switching transistor S4, and the sixth switching transistor Q2 are conducting, and the voltage V across the inductor ab is 0.

[0055] It should be noted that in Embodiment 1 of the present invention, the operating modes of the three-level Buck - Boost converter are as Figures 3a - 3f shown. In the first switching timing, the sequence of circuit mode transformation is the first mode - the second mode - the third mode - the fourth mode - the fifth mode - the sixth mode; in the second switching timing, the sequence of circuit mode transformation is the sixth mode - the fourth mode - the third mode - the second mode - the third mode - the fifth mode, Figures 3a - 3f which reflects the states of switch turn - on and turn - off. When the converter operates in the first mode, the second mode, the fourth mode, and the sixth mode, the flying capacitor C f is charged and discharged; when the two operating timings are alternately modulated, the flying capacitor C f discharges in the first mode and the second mode, and charges in the fourth mode and the sixth mode, and the charge - discharge current waveforms in the first mode and the sixth mode are the same, and the charge - discharge current waveforms in the second mode and the fourth mode are the same. Therefore, the modulation system disclosed in Embodiment 1 can achieve the self - balancing of the voltage of the flying capacitor C f voltage.

[0056] Furthermore, the magnitudes of the inductor current i L in different time periods are corresponding as follows:

[0057]

[0058] Among them, V in is the input voltage of the three - level Buck - Boost converter; V o is the output voltage of the three - level Buck - Boost converter; T1 = t1 - t0; T2 = t2 - t1; T3 = t3 - t2; T4 = t4 - t3; T5 = t5 - t4; T6 = t6 - t5; L is the inductance value; I d is the initial value of the inductor current to achieve unit - cycle, and its value is the current required for all switching transistors to be turned on with zero voltage. When the magnitude of the inductor current at time t3 is set as I d ; and the magnitude of the inductor current in the T6 time period is set to remain I d unchanged, at this time, the effective value of the inductor current is minimized, and the calculation method of I d is:

[0059]

[0060] Among them, t d is the dead time of the three-level Buck-Boost converter, and C OSS is the parasitic capacitance of the switch.

[0061] The inductor current calculated and solved by the above formula satisfies the minimum effective value of the inductor current. The derivation process of T1 - T6 is as follows:

[0062] First, according to the balance of the voltage-second product of the inductor, the equation can be listed:

[0063] 0.5V in (T1 + T2 + T4) = V o (T2 + T3 + T4 + T5)

[0064] According to the output power, the equation can be listed:

[0065]

[0066] Since the three-level Buck-Boost converter adopts constant-frequency control and the switching period is T s , so it satisfies:

[0067] T1 + T2 + T3 + T4 + T5 + T6 = T s

[0068] When the inductor current magnitude at the end of the T1 segment is set to be I d , the inductor current magnitude of the T6 segment is -I d , and the feasible solution with the minimum length of the T6 segment is limited. The full switch tubes achieve soft switching and the effective value of the inductor current is optimal, that is, the minimum. Specifically, after limiting T1 and T6 in the above manner, the reason for the optimal effective value of the inductor current belongs to the well-known knowledge in the art and will not be elaborated further. Then:

[0069]

[0070] Combining the above five constraint equations and six independent variables, when the number of solutions is not unique, among the numerical solutions of all equation groups that meet the conditions, select a group of solutions with the smallest T6, and the values of T1 - T6 can be obtained. Furthermore, the conduction time of each switch tube can also be determined. The modulation unit controls the switch tubes according to the switch turn-on time determined in the above manner, and the zero-voltage turn-on of the switch tubes and the minimum effective value of the inductor current can be achieved. Here, T1 - T6 is called the degree of freedom. The modulation unit obtains the target switch timing and switch turn-on time by controlling the degree of freedom T1 - T6, that is, the above first switch timing and second switch timing.

[0071] Embodiment 2:

[0072] The present invention also discloses a method for modulating a converter in a three-level Buck-Boost converter modulation system. Through the alternating modulation of two different switching timings, namely the first switching timing and the second switching timing, the charge of the parasitic capacitance in the switch is consumed by the reverse current before all switches are turned on, so that all switch tubes are turned on with zero voltage, generating multiple segments of inductor current. Among them, the first switch tube and the fourth switch tube in the three-level Buck-Boost converter are complementary conduction; the second switch tube and the third switch tube are complementary conduction; the fifth switch tube and the sixth switch tube are complementary conduction. Specifically, the topological structure diagram of the three-level Buck-Boost converter is as Figure 1 shown.

[0073] It should be noted that the method of modulating the switch tubes in the three-level Buck-Boost converter in Embodiment 2 is the same as that in Embodiment 1, and will not be described again to avoid redundancy.

[0074] In order to verify the three-level Buck-Boost converter modulation method disclosed by the present invention, a simulation model of a three-level Buck-Boost converter based on an input voltage of 400V, an output voltage of 100V and a rated power of 300W is built, satisfying that the input voltage is greater than twice the output voltage, and the operating frequency is set to 100kHz. The simulation waveform is as Figures 4a - 4c shown.

[0075] As Figure 4a shown are the driving waveforms of switch tubes S1, S2, S3, S4, as well as Q1 and Q2, and the effective value waveform diagram of the inductor current. The driving waveforms of the switch tubes are consistent with the theoretical derivation, that is, consistent with Figure 2 and all switch tubes can achieve soft switching. The effective value of the inductor current is 4.633A and the peak value is 11.390A, which are respectively reduced by 14.1% and 19.3% compared with the traditional modulation, proving the efficiency advantage of the modulation method.

[0076] Figure 4b The steady-state characteristics of the flying capacitor voltage, output voltage, output current, and output power are recorded from top to bottom. The simulation results show that the output voltage is stable at 100V, the output current is 3A, the output power accurately matches the 300W design target, and the fluctuation range of the flying capacitor voltage is less than 1%, indicating that the alternating modulation of the two switching timings has successfully achieved the self-balancing of the flying capacitor voltage without external active control.

[0077] Figure 4c Shown are the driving signals of the first switch tube S1 to the fourth switch tube S4 and the waveforms of their drain-source voltages Vds at a certain moment. It can be seen that before the driving rising edge arrives, that is, before the switch tube is turned on, its Vds voltage has dropped to zero, fully proving the reliability of the soft-switching mechanism under all working conditions.

[0078] The simulation experiment results show that the above results fully verify the technical advantages of the present invention in aspects such as a wide voltage range (for example, when the input voltage is greater than twice the output voltage, but not limited to this), flying capacitor voltage self-balancing, and low electromagnetic interference characteristics, expand the high-efficiency operation range of the converter in a wide voltage range, and meet the stringent requirements of the photovoltaic energy storage system for bidirectional energy conversion.

[0079] In summary, for the three-level Buck-Boost converter modulation method and system disclosed in the present invention, by reconstructing the inductor current waveform within a unit period, while achieving the same-frequency operation of all switching tubes, the effective current value is reduced, making the effective value of the inductor current the smallest, avoiding the electromagnetic interference problem caused by multi-frequency modulation electromagnetic interference, and also realizing the soft-switching operation of all switching tubes. Secondly, the Buck-Boost converter modulation system and method in the present invention effectively improve the efficiency performance of the three-level Buck-Boost converter under the condition that the input voltage is greater than twice the output voltage, expand the high-efficiency operation range of the converter in a wide voltage range, and provide an innovative solution for the energy conversion requirements of bidirectional wide-gain voltage regulation in the photovoltaic energy storage system.

[0080] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A three-level Buck-Boost converter modulation system, comprising: An input filter capacitor connected to the input voltage, an output filter capacitor connected to the output voltage, a three-level half-bridge unit, a DC-DC conversion half-bridge unit, and a modulation unit, wherein the three-level half-bridge unit includes a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, and a flying capacitor, the flying capacitor is connected between the connection point of the first switch tube and the second switch tube and the connection point of the third switch tube and the fourth switch tube, the DC-DC conversion half-bridge unit includes a fifth switch tube and a sixth switch tube, the midpoint of the three-level half-bridge unit is the connection point of the second switch tube and the third switch tube; the midpoint of the DC-DC conversion half-bridge unit is the connection point of the fifth switch tube and the sixth switch tube, the midpoint of the three-level half-bridge unit is connected to the midpoint of the DC-DC conversion half-bridge unit through an inductor, the first switch tube and the fourth switch tube conduct complementarily; the second switch tube and the third switch tube conduct complementarily; the fifth switch tube and the sixth switch tube conduct complementarily, and it is characterized in that: When the input voltage is greater than twice the output voltage, the modulation unit alternately outputs a first switch timing and a second switch timing, so that the voltage of the flying capacitor is balanced, and the charge of the parasitic capacitance in the switch is consumed by the reverse current before all switches are turned on, the switch tubes are turned on with zero voltage, and multiple segments of inductor current are generated, wherein the first switch timing is such that the turn-on sequence of the switch tubes is: the second, fourth, and sixth switch tubes are conducting, the second, fourth, and fifth switch tubes are conducting, the third, fourth, and fifth switch tubes are conducting, the first, third, and fifth switch tubes are conducting, the third, fourth, and fifth switch tubes are conducting, the third, fourth, and sixth switch tubes are conducting; the second switch timing is such that the turn-on sequence of the switch tubes is: the first, third, and sixth switch tubes are conducting, the first, third, and fifth switch tubes are conducting, the third, fourth, and fifth switch tubes are conducting, the second, fourth, and fifth switch tubes are conducting, the third, fourth, and fifth switch tubes are conducting, the third, fourth, and sixth switch tubes are conducting.

2. The three-level Buck-Boost converter modulation system according to claim 1, wherein The first switch timing includes twelve working stages within one switch cycle, which are respectively: At the starting moment of the first stage, the third switch tube is turned off. In the first stage, the second switch tube and the third switch tube are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the second switch tube; At the starting moment of the second stage, the second switch tube is turned on with zero voltage. In the second stage, the second switch tube, the fourth switch tube, and the sixth switch tube are conducting; At the starting moment of the third stage, the sixth switch tube is turned off. In the third stage, the fifth switch tube and the sixth switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fifth switch tube; At the starting moment of the fourth stage, the fifth switch tube is turned on with zero voltage. In the fourth stage, the second switch tube, the fourth switch tube, and the fifth switch tube are conducting; At the starting moment of the fifth stage, the second switch tube is turned off. In the fifth stage, the second switch tube and the third switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the third switch tube; At the starting moment of the sixth stage, the third switch tube is turned on with zero voltage. In the sixth stage, the third switch tube, the fourth switch tube, and the fifth switch tube are conducting; Turn off the fourth switching tube at the starting moment of the seventh stage. In the seventh stage, the first switching tube and the fourth switching tube are in the dead time, and the inductor current flows negatively to discharge the junction capacitance of the first switching tube; At the starting moment of the eighth stage, the first switching tube is turned on with zero voltage. In the eighth stage, the first switching tube, the third switching tube, and the fifth switching tube are conducting; Turn off the first switching tube at the starting moment of the ninth stage. In the ninth stage, the first switching tube and the fourth switching tube are in the dead time, and the inductor current flows positively to discharge the junction capacitance of the fourth switching tube; At the starting moment of the tenth stage, the fourth switching tube is turned on with zero voltage. In the tenth stage, the third switching tube, the fourth switching tube, and the fifth switching tube are conducting; Turn off the fifth switching tube at the starting moment of the eleventh stage. In the eleventh stage, the fifth switching tube and the sixth switching tube are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the sixth switching tube; At the starting moment of the twelfth stage, the sixth switching tube is turned on with zero voltage. In the twelfth stage, the third switching tube, the fourth switching tube, and the sixth switching tube are conducting.

3. The three-level Buck-Boost converter modulation system according to claim 1, wherein The second switching timing has twelve working stages within one switching cycle, which are respectively: Turn off the fourth switching tube at the starting moment of the first stage. In the first stage, the first switching tube and the fourth switching tube are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the first switching tube; At the starting moment of the second stage, the first switching tube is turned on with zero voltage. In the second stage, the first switching tube, the third switching tube, and the sixth switching tube are conducting; Turn off the sixth switching tube at the starting moment of the third stage. In the third stage, the fifth switching tube and the sixth switching tube are in the dead time, and the inductor current flows positively to discharge the junction capacitance of the fifth switching tube; At the starting moment of the fourth stage, the fifth switching tube is turned on with zero voltage. In the fourth stage, the first switching tube, the third switching tube, and the fifth switching tube are conducting; Turn off the first switching tube at the starting moment of the fifth stage. In the fifth stage, the first switching tube and the fourth switching tube are in the dead time, and the inductor current flows positively to discharge the junction capacitance of the fourth switching tube; At the starting moment of the sixth stage, the fourth switching tube is turned on with zero voltage. In the sixth stage, the third switching tube, the fourth switching tube, and the fifth switching tube are conducting; Turn off the third switching tube at the starting moment of the seventh stage. In the seventh stage, the second switching tube and the third switching tube are in the dead time, and the inductor current flows negatively to discharge the junction capacitance of the second switching tube; At the starting moment of the eighth stage, the second switching tube is turned on with zero voltage. In the eighth stage, the second switching tube, the fourth switching tube, and the fifth switching tube are conducting; Turn off the second switching tube at the starting moment of the ninth stage. In the ninth stage, the second switching tube and the third switching tube are in the dead time, and the inductor current flows positively to discharge the junction capacitance of the third switching tube; At the starting moment of the tenth stage, the third switching tube is turned on with zero voltage. In the tenth stage, the third switching tube, the fourth switching tube, and the fifth switching tube are conducting; Turn off the fifth switching tube at the starting moment of the eleventh stage. In the eleventh stage, the fifth switching tube and the sixth switching tube are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the sixth switching tube; At the starting moment of the twelfth stage, the sixth switching tube is turned on with zero voltage, and in the twelfth stage, the third, fourth, and sixth switching tubes are conducting.

4. The three-level Buck-Boost converter modulation system according to claim 1, wherein When the inductor current flows from the midpoint of the three-level half-bridge unit to the midpoint of the DC-DC conversion half-bridge unit, the inductor current is positive, and when the inductor current flows from the midpoint of the DC-DC conversion half-bridge unit to the midpoint of the three-level half-bridge unit, the inductor current is negative.

5. The three-level Buck-Boost converter modulation system according to claim 4, characterized in that, The calculation formula for the inductor current is as follows: Among them, V in is the input voltage of the three-level Buck-Boost converter; V o is the output voltage of the three-level Buck-Boost converter; T1 = t1 - t0; T2 = t2 - t1; T3 = t3 - t2; T4 = t4 - t3; T5 = t5 - t4; T6 = t6 - t5; L is the inductance value; I d is the initial value of the inductor current per unit cycle, and its value is the minimum current required to turn on all the switching tubes with zero voltage.

6. The three-level Buck-Boost converter modulation system according to claim 5, characterized in that, The inductance current is set to I at time t3 d ; and the value of the inductance current is I during the time period T6 d , and its calculation method is as follows: Among them, t d is the dead time of the three-level Buck-Boost converter, and C OSS is the switch parasitic capacitance.

7. A modulation method for a three-level Buck-Boost converter modulation system according to claim 1, characterized in that, Through two different switching sequences for alternative modulation, before all switches are turned on, the reverse current is used to consume the charge of the parasitic capacitance in the switches, enabling all switching tubes to be turned on with zero voltage and generating multiple segments of inductor current. Among them, the first and fourth switching tubes conduct complementarily; the second and third switching tubes conduct complementarily; the fifth and sixth switching tubes conduct complementarily. The first switching sequence makes the switching tube turn-on sequence as follows: the second, fourth, and sixth switching tubes conduct, the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct; the second switching sequence makes the switching tube turn-on sequence as follows: the first, third, and sixth switching tubes conduct, the first, third, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the second, fourth, and fifth switching tubes conduct, the third, fourth, and fifth switching tubes conduct, the third, fourth, and sixth switching tubes conduct.

8. The modulation method of the three-level Buck-Boost converter modulation system according to claim 7, characterized in that The first switching sequence includes twelve working stages within one switching cycle, which are respectively: At the starting moment of the first stage, the third switching tube is turned off. In the first stage, the second and third switching tubes are in the dead time, and the inductor current flows reversely to discharge the junction capacitance of the second switching tube. At the starting moment of the second stage, the second switching tube is turned on with zero voltage. In the second stage, the second, fourth, and sixth switching tubes are conducting. At the starting moment of the third stage, the sixth switching tube is turned off. In the third stage, the fifth and sixth switching tubes are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fifth switching tube. At the starting moment of the fourth stage, the fifth switching tube is turned on with zero voltage. In the fourth stage, the second, fourth, and fifth switching tubes are conducting. At the starting moment of the fifth stage, the second switching tube is turned off. In the fifth stage, the second and third switching tubes are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the third switching tube. At the starting moment of the sixth stage, the third switching tube is turned on with zero voltage. In the sixth stage, the third, fourth, and fifth switching tubes are conducting. At the starting moment of the seventh stage, the fourth switching tube is turned off. In the seventh stage, the first and fourth switching tubes are in the dead time, and the inductor current flows negatively to discharge the junction capacitance of the first switching tube. At the starting moment of the eighth stage, the first switching tube is turned on with zero voltage. In the eighth stage, the first, third, and fifth switching tubes are conducting. Turn off the first switch tube at the start of the ninth stage. In the ninth stage, the first switch tube and the fourth switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fourth switch tube. At the start of the tenth stage, the fourth switch tube turns on with zero voltage. In the tenth stage, the third switch tube, the fourth switch tube, and the fifth switch tube are conducting. Turn off the fifth switch tube at the start of the eleventh stage. In the eleventh stage, the fifth switch tube and the sixth switch tube are in the dead time, and the inductor current flows backward to discharge the junction capacitance of the sixth switch tube. At the start of the twelfth stage, the sixth switch tube turns on with zero voltage. In the twelfth stage, the third switch tube, the fourth switch tube, and the sixth switch tube are conducting.

9. The modulation method of the three-level Buck-Boost converter modulation system according to claim 7, characterized in that, The second switching sequence has twelve working stages within one switching period, which are: Turn off the fourth switch tube at the start of the first stage. In the first stage, the first switch tube and the fourth switch tube are in the dead time, and the inductor current flows backward to discharge the junction capacitance of the first switch tube. At the start of the second stage, the first switch tube turns on with zero voltage. In the second stage, the first switch tube, the third switch tube, and the sixth switch tube are conducting. Turn off the sixth switch tube at the start of the third stage. In the third stage, the fifth switch tube and the sixth switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fifth switch tube. At the start of the fourth stage, the fifth switch tube turns on with zero voltage. In the fourth stage, the first switch tube, the third switch tube, and the fifth switch tube are conducting. Turn off the first switch tube at the start of the fifth stage. In the fifth stage, the first switch tube and the fourth switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the fourth switch tube. At the start of the sixth stage, the fourth switch tube turns on with zero voltage. In the sixth stage, the third switch tube, the fourth switch tube, and the fifth switch tube are conducting. Turn off the third switch tube at the start of the seventh stage. In the seventh stage, the second switch tube and the third switch tube are in the dead time, and the inductor current flows negatively to discharge the junction capacitance of the second switch tube. At the start of the eighth stage, the second switch tube turns on with zero voltage. In the eighth stage, the second switch tube, the fourth switch tube, and the fifth switch tube are conducting. Turn off the second switch tube at the start of the ninth stage. In the ninth stage, the second switch tube and the third switch tube are in the dead time, and the inductor current flows forward to discharge the junction capacitance of the third switch tube. At the start of the tenth stage, the third switch tube turns on with zero voltage. In the tenth stage, the third switch tube, the fourth switch tube, and the fifth switch tube are conducting. Turn off the fifth switch tube at the start of the eleventh stage. In the eleventh stage, the fifth switch tube and the sixth switch tube are in the dead time, and the inductor current flows backward to discharge the junction capacitance of the sixth switch tube. At the start of the twelfth stage, the sixth switch tube turns on with zero voltage. In the twelfth stage, the third switch tube, the fourth switch tube, and the sixth switch tube are conducting.

10. The modulation method of the three-level Buck-Boost converter modulation system according to claim 7, characterized in that, When the inductor current flows from the midpoint of the three-level half-bridge unit to the midpoint of the DC-DC conversion half-bridge unit, the inductor current is positive. When the inductor current flows from the midpoint of the DC-DC conversion half-bridge unit to the midpoint of the three-level half-bridge unit, the inductor current is negative. Among them, the calculation formula for the inductor current is as follows: Among them, V in is the input voltage of the three-level Buck-Boost converter; V o is the output voltage of the three-level Buck-Boost converter; T1 = t1 - t0; T2 = t2 - t1; T3 = t3 - t2; T4 = t4 - t3; T5 = t5 - t4; T6 = t6 - t5; L is the inductance value; I d is the initial value of the inductor current per unit period, and its value is the current required for all switching transistors to turn on with zero voltage. where t d is the dead time of the three-level Buck-Boost converter, and C OSS is the switch parasitic capacitance.

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