Control method of multi-level Buck-Boost converter

Abstract

The invention discloses a control method of a multi-level Buck-Boost converter, which belongs to the technical field of power converters, and can realize soft switching of all switching tubes and minimization of inductive current pulsation and effective value by reasonably utilizing each control degree of freedom of the converter and controlling inductive current into a pentagonal form. And an optimal working mode is adopted, and the rising and falling slopes of the inductive current are adjusted in a pseudo inductive current discontinuous mode, so that the circulation time of the negative current is reduced, and the light load efficiency of the converter is improved.

Description

Technical Field

[0001] This invention relates to the field of power converter technology, and in particular to a control method for a multilevel Buck-Boost converter. Background Technology

[0002] Four-Switch Buck-Boost (FSBB) converters offer advantages such as step-up / step-down conversion, positive output voltage polarity, a small number of passive components, and bidirectional energy flow, and are widely used in photovoltaic power generation systems, electric vehicle charging systems, and energy storage systems. Due to limitations in the voltage ratings of existing switching devices, multi-level technology is typically employed to reduce voltage stress on the switching transistors when the input or output voltage is high, thus forming multi-level Buck-Boost converters.

[0003] To reduce inductor current ripple in multilevel Buck-Boost converters, existing technologies propose a two-mode control method. While this minimizes inductor current ripple, the converter operates in Continuous Current Mode (CCM) under this method, with the switching transistors in a hard-switching state, limiting further increases in switching frequency. In recent years, the rapid development of wide-bandgap semiconductor devices, such as gallium nitride (GaN) and silicon carbide (SiC), has made it possible to increase switching frequency. Although GaN and SiC devices have low turn-off losses, their turn-on losses are still significant. Therefore, achieving zero-voltage switching (ZVS) for wide-bandgap semiconductor devices is crucial for improving converter efficiency. Summary of the Invention

[0004] The present invention aims to provide a control method for a multilevel Buck-Boost converter.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows: A control method for a multilevel Buck-Boost converter is disclosed, applied to a multilevel Buck-Boost converter, wherein the multilevel Buck-Boost converter includes a Buck converter unit, a Boost converter unit, and a filter unit; the Buck converter unit includes... A switching transistor ~ and the body diode of the switching transistor ~ Junction capacitance ~ ,as well as A flying capacitor ~ Composition; In steady-state operation, the Buck converter unit flies across the capacitor. , … The voltages are maintained at respectively , 、 …、 ,composition Each level; the Boost converter unit includes A switching transistor ~ and the body diode of the switching transistor ~ Junction capacitance ~ ,as well as A flying capacitor ~ Composition; During steady-state operation, the Boost converter unit has a flying capacitor. , … The voltages are maintained at respectively , 、 …、 ,composition One level; The first end of the filter inductor in the filter unit is connected to the midpoint of the bridge arm of the Buck converter unit, and the second end of the filter inductor is connected to the midpoint of the bridge arm of the Boost converter unit. The manufacturing method includes, Step S1: By increasing the voltage at the midpoint of the Buck converter arm while keeping the voltage at the midpoint of the Boost converter arm zero, the output filter inductor current increases linearly. In step S1, the Buck transformation unit is turned on. j One upper transistor controls the voltage at the midpoint of the Buck converter bridge arm. And maintain the voltage at the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor increases linearly; Step S2: By decreasing the voltage at the midpoint of the Buck converter unit and increasing the voltage at the midpoint of the bridge arm of the Boost converter unit, the output filter inductor current first increases and then decreases. In step S2, the voltage at the midpoint of the Buck converter bridge arm is transferred from... The voltage gradually decreases to 0, while the voltage at the midpoint of the Boost converter bridge arm gradually increases from 0 to... ,in, The conduction count of the upper transistor in the OP segment Buck converter unit. The conduction count of the upper transistor in the RS segment Boost converter unit; as the inductor voltage decreases continuously, the current of the filter inductor first rises and then falls. Step S3: By turning off all the upper transistors of the Buck converter unit and keeping some of the upper transistors of the Boost converter unit on, the output inductor current decreases linearly. When the inductor current decreases to the negative current reference value for achieving soft switching of the switching transistors... At this time, all lower transistors of the Boost unit are turned off, and the inductor current is maintained at the negative current reference value for achieving soft switching of the switching transistors. : In step S3, when the current of the filter inductor drops to point R and the current at point R... At that time, among them I ZVS To achieve the minimum current for soft switching of the switching transistors, all upper transistors of the Buck converter unit are turned off, making the voltage at the midpoint of the bridge arm of the Buck converter unit zero; the Boost converter unit has k With one upper transistor turned on, the voltage at the midpoint of the Boost converter bridge arm... The current in the filter inductor decreases linearly to the negative current reference value required for soft switching of the switching transistor. ; Step S4, based on the real-time monitoring of the converter's input voltage V in Output voltage V o The relationship between the current and operating modes is used to adaptively switch the current operating mode and output the optimal current control waveform adapted to the current operating condition. In step S4, when V in ≤ V o / n When the inductor current exhibits a quadrilateral shape that monotonically decreases in the middle section; when V in / m > V o At this time, the inductor current exhibits a quadrilateral shape that monotonically increases in the middle section.

[0006] Furthermore, to minimize the voltage difference between the inductors in segments PQ and QR and ensure they are of opposite polarity, one side of the voltage level needs to be fixed while the other side uses an adjacent voltage level. The first approach is that when... V in / m ≤ V o / nAt the time corresponding to point Q, one of the upper transistors of the Buck converter is turned off, causing the voltage at the midpoint of the Buck converter bridge arm to decrease by one level, while the voltage at the midpoint of the Boost converter bridge arm remains unchanged.

[0007] Furthermore, the second option is, when V in / m > V o / n At point Q, one Boost converter transistor is turned on, raising the voltage at the midpoint of the Boost converter arm by one level, while the voltage at the midpoint of the Buck converter arm remains unchanged.

[0008] Furthermore, in step S2, the average power corresponding to the PQ segment... P PQ The expression is: , in, One switching cycle is the total time for all switching transistors to complete one full on / off operation during the switching process. At time P, At point Q, The voltage at point B, the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor is... The conduction number of the upper transistor in the PQ segment Boost converter unit. For output voltage, This represents the total number of upper transistors in the Boost converter unit. Let P be the current. Let Q be the current. This is the inductance value. The conduction number of the upper transistor in the PQ segment Buck converter unit. Input voltage, This represents the total number of upper transistors in the Buck converter unit.

[0009] Furthermore, in step S2, the average power corresponding to the QR segment... P QR The expression is: , in, One switching cycle is the total time for all switching transistors to complete one full on / off operation during the switching process. At point R, At point Q, The voltage at point B, the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor is... The conduction count of the upper transistor in the QR segment Boost converter unit. For output voltage, This represents the total number of upper transistors in the Boost converter unit. Let R be the current. Let Q be the current. This is the inductance value. The conduction count of the upper transistor in the QR segment Buck converter unit. Input voltage, This represents the total number of upper transistors in the Buck converter unit.

[0010] Furthermore, in step S1, at the initial moment of each switching cycle, the voltage at the midpoint of the Buck converter arm is zero, and the voltage at the midpoint of the Boost converter arm is zero.

[0011] Furthermore, the control strategy for the optimal working mode includes: When the load is heavy, the multilevel Buck-Boost converter operates in pseudo-continuous current mode, and the current at point P in this pseudo-continuous current mode... 、 The currents at both point Q and point R are greater than the minimum current required to achieve soft switching of the switching transistor. I ZVS When the current at point P I P and the current at point R I R All currents decreased to the minimum current required to achieve soft switching of the switching transistor. I ZVS At this point, the multilevel Buck-Boost converter reaches the critical operating point of pseudo-current continuous mode; When the load decreases further, the converter will operate in pseudo-discontinuous current mode, in which the currents at point P and point R will be fixed at the minimum current required to achieve soft switching of the switching transistor. I ZVS Furthermore, when the current in the filter inductor drops to the negative current reference value for achieving soft switching of the switching transistor... At this time, all the lower transistors of the Buck converter and Boost converter are turned on simultaneously, so that the current of the filter inductor is maintained at the negative current reference value for achieving soft switching of the switching transistors. ; In order to shorten the current of the filter inductor, it is necessary to maintain the current at the negative current reference value for achieving soft switching of the switching transistor. This reduces the voltage applied to the inductor during the OP and RS segments, thereby shortening the negative current reference value required for soft switching of the switching transistor at a constant frequency. The circulation time.

[0012] Furthermore, the current in the filter inductor is drawn from the negative current reference value used to achieve soft switching of the switching transistor. Rise to the minimum current required to achieve soft switching of the switching transistor. I ZVS Time change Δ T Lj The expression is: , in, This is the inductance value. This represents the total number of upper transistors in the Buck converter unit. The conduction count of the upper transistor in the OP segment Buck converter unit. This is the input voltage.

[0013] Furthermore, the current in the filter inductor is reduced from the minimum current required to achieve soft switching of the switching transistor. I ZVS The current drops to the negative current reference value for achieving soft switching of the switching transistor. Time change Δ T Rk The expression is: , in, This is the inductance value. This represents the total number of upper transistors in the Boost converter unit. The conduction number of the upper transistor in the RS segment Boost converter unit. This is the output voltage.

[0014] In order to maintain at Time T neg The levels of the OP and RS segments are always maintained at the minimum value. j 1 and k 1. The reduction should be gradual as the load decreases; As the load decreases, maintain at Time T neg It will gradually increase; When maintained at Time T neg The current reaching the filter inductor from Rise to I ZVS Time change Δ T Lj and the current from the filter inductor I ZVS Descending to Time change Δ T RkWhen the value is at its minimum, immediately reduce the level of the corresponding segment; The minimum value is the current in the filter inductor from Rise to I ZVS Time change Δ T Lj When, decrease j 1; The minimum value is the current from the filter inductor. I ZVS Descending to − I ZVS Time change Δ T Rk When, decrease k 1, to maintain at Time T neg The load will drop back to 0; as the load continues to decrease, the above process will repeat to ensure that it remains at 0. Time T neg It remains at the minimum value until the converter enters an unloaded state.

[0015] Beneficial effects: This invention provides a control method for a multi-level Buck-Boost converter, which utilizes the filter inductor... L c The current is controlled in a pentagonal form, enabling soft switching of all switching transistors; and it adopts the optimal operating mode, adjusting the filter inductor. L c The rise and fall slopes of the current are used to achieve the filtering inductance. L c The current ripple and RMS value are minimized, and the control degrees of freedom are optimized under light load conditions, thereby significantly improving the overall efficiency of the converter.

[0016] To make the above-mentioned features and advantages of the invention more apparent and understandable, specific embodiments are described below, and detailed descriptions are provided in conjunction with the accompanying drawings. Attached Figure Description

[0017] Figure 1 This is a circuit topology diagram of a multilevel Buck-Boost converter according to the present invention.

[0018] Figure 2 For the filter inductor under the control method of the present invention L c The waveform of the current.

[0019] Figure 3 for V in ≤ V o / n Time filter inductorL c Waveform of the current.

[0020] Figure 4 for V in / m > V o Time filter inductor L c Waveform of the current.

[0021] Figure 5 For Scheme 1 filter inductor L c current and v A , v B Voltage waveform diagram.

[0022] Figure 6 For Scheme 2 filter inductor L c current and v A , v B Voltage waveform diagram.

[0023] Figure 7 Filter inductors for different input voltage pseudo-current continuous modes L c The waveform diagram of the current changing with the load. Figure 7 (a) is Filter inductor in pseudo-current continuous mode L c The waveform of the current as a function of the load. Figure 7 (b) is Filter inductor in pseudo-current continuous mode L c The waveform of the current as a function of the load. Figure 7 (c) is Filter inductor in pseudo-current continuous mode L c The waveform of the current as a function of the load.

[0024] Figure 8 Filter inductors for different input voltage pseudo-current discontinuous modes L c The waveform of the current as a function of the load. Figure 8 (a) is Filter inductor in time-discontinuous current mode L c The waveform of the current as a function of the load. Figure 8 (b) is Filter inductor in time-discontinuous current mode L c The waveform of the current as a function of the load. Figure 8 (c) is Filter inductor in time-discontinuous current mode L c The waveform of the current as a function of the load.

[0025] Figure 9 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 300V. Figure 9 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 300V. Figure 9 (a) shows the steady-state experimental waveform of the converter at half load when the input voltage is 300V. Figure 9 (c) is the steady-state experimental waveform of the converter under no-load when the input voltage is 300V.

[0026] Figure 10 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 500V. Figure 10 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 500V. Figure 10 (a) is the steady-state experimental waveform of the converter at half load when the input voltage is 500V. Figure 10 (c) is the steady-state experimental waveform of the converter under no-load when the input voltage is 500V.

[0027] Figure 11 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 900V. Figure 11 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 900V. Figure 11 (a) shows the steady-state experimental waveform of the converter at half load when the input voltage is 900V. Figure 11 (c) is the steady-state experimental waveform of the converter under no-load when the input voltage is 900V. Detailed Implementation

[0028] To make the objectives and technical solutions of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0029] Figure 1This is a circuit topology diagram of a multilevel Buck-Boost converter according to the present invention. Figure 1 As shown, a multi-level Buck-Boost converter 1 includes a Buck converter unit 11 and a filter unit. L c Boost converter 12; the first terminal of Buck converter 11 is connected to the input voltage. V in The second end of the Buck transform unit 11 is connected to the filter unit. L c The first end, the filter unit L c The second terminal is connected to the first terminal of the Boost converter unit 12, and the second terminal of the Boost converter unit 12 is connected to the output voltage. V o Input voltage V in Through Buck transformation unit 11 and filtering unit L c After buck and boost conversion by the Boost converter unit 12, a stable DC output voltage is output. V o .

[0030] Buck converter 11 includes A switching transistor , ... , A flying capacitor , ... Switching transistor , ... Connect in sequence, switching transistors , ... Connect in sequence, switching transistors The second end is connected to the switching transistor. The first end, flying capacitor The first end is connected to the switching transistor The source, flying capacitor The second end is connected to the switching transistor. The drain electrode.

[0031] Furthermore, the switching transistor With switching transistor Complementary conduction, switching transistor With switching transistor Complementary conduction, and so on, switching transistors With switching transistor Complementary conduction.

[0032] Furthermore, the upper transistor of the Buck converter unit 11 is a switching transistor. , ... The transistors are turned on sequentially; similarly, the lower transistor of Buck converter 11 is switched on by a switch. , ... The circuits are activated sequentially.

[0033] Furthermore, during steady-state operation, due to the symmetrical conduction of the switching transistors, the charge and discharge of each flying capacitor are balanced within one switching cycle, achieving voltage self-balancing. The flying capacitors of the Buck converter unit... , … The voltages are maintained at respectively , 、 …、 This enables multi-level voltage output at the midpoint of the bridge arm and ensures balanced voltage stress across all switches.

[0034] Furthermore, by connecting different numbers of flying capacitors, the output at the midpoint of the bridge arm is made to be 0. , 、 …、 、 ,composition Each level.

[0035] Furthermore, diodes , ... They are switching transistors , ... Body diode; capacitor , ... They are switching transistors , ... Junction capacitance.

[0036] Boost converter 12 includes A switching transistor , ... , ) flying capacitor , ... Switching transistor , ... Connect in sequence, switching transistors , ... Connect in sequence, switching transistors The second end is connected to the switching transistor. The first end, flying capacitor The first end is connected to the switching transistor The source, flying capacitor ) The second end is connected to the switching transistor. The drain electrode.

[0037] Furthermore, the switching transistor With switching transistor Complementary conduction, switching transistor With switching transistor Complementary conduction, and so on, switching transistors With switching transistor Complementary conduction.

[0038] Furthermore, the upper transistor of the Boost converter unit 12 is a switching transistor. , ... The transistors are turned on sequentially; similarly, the lower transistor of the Boost converter unit 12 is switched on by the switching transistor. , ... The circuits are activated sequentially.

[0039] Furthermore, during steady-state operation, due to the symmetrical conduction of the switching transistors, the charge and discharge of each flying capacitor are balanced within one switching cycle, achieving voltage self-balancing. The flying capacitors of the Boost converter unit... , … The voltages are maintained at respectively , 、 …、 This enables multi-level voltage output at the midpoint of the bridge arm and ensures balanced voltage stress across all switches.

[0040] Furthermore, by connecting different numbers of flying capacitors, the output at the midpoint of the bridge arm is made to be 0. , 、 …、 、 ,composition Each level.

[0041] Furthermore, diodes D R1 , D R2 ... D R2m They are switching transistorsQ R1 , Q R2 ... Q R2m Body diode; capacitor C R1 , C R2 ... C R2m They are switching transistors Q R1 , Q R2 ... Q R2m Junction capacitance.

[0042] Furthermore, in Buck transform unit 11 and Boost transform unit 12 m , n These represent the number of all upper transistors in Buck converter 11 and Boost converter 12, respectively, and are all arbitrary positive integers.

[0043] Furthermore, the filter inductor in the filter unit L c The first terminal is connected to the midpoint A of the bridge arm of Buck converter 11, and the filter inductor L c The second end is connected to the midpoint B of the bridge arm of the Boost converter unit 12.

[0044] A multilevel Buck-Boost converter 1 also includes an output filter capacitor. C o and load resistance R L Filter capacitor C o The two ends are connected to the two ends of the Boost converter 12, and the load resistor is... R L The first end is connected to a filter capacitor. C o The first terminal, load resistor R L The second end is connected to a filter capacitor. C o The second terminal, load resistor R L The voltage across the two ends is the output voltage. V o .

[0045] Furthermore, the output filter capacitor C o Used to filter out switching frequency ripple.

[0046] This invention discloses a control method for a multilevel Buck-Boost converter. To achieve soft switching of all switching transistors, the junction capacitance of the switching transistors needs to be charged and discharged within the dead time of each pair of switching transistor drive signals. I ZVS To achieve the minimum current required for soft switching of the switching transistor. To achieve the switching transistor Q L1 ~ Q Lm and Q R(n+1) ~ Q R2n For soft switching, it is necessary to ensure that the filter inductor is in place before the switching transistor is turned on. L c current i Lc Less than or equal to To realize the switching transistor Q L(m+1) ~ Q L2m and Q R1 ~ Q Rn For soft switching, it is necessary to ensure that the filter inductor is in place before the switching transistor is turned on. L c current i Lc Greater than or equal to I ZVS .

[0047] A control method for a multilevel Buck-Boost converter includes steps S1 to S4: Step S1: By increasing the voltage at the midpoint of the Buck converter arm, the voltage at the midpoint of the Boost converter arm is kept zero, and the output filter inductor current increases linearly.

[0048] More specifically, to achieve zero-voltage turn-on for all switches, the voltage at the midpoint A of the Buck converter bridge arm must satisfy the following at the beginning of each switching cycle: And the voltage at the midpoint B of the Boost converter bridge arm Make the filter inductor L c current i Lc Maintain at To transfer energy to the load, the filter inductor... L c current i Lc It needs to be increased to a positive value.

[0049] Figure 2For the filter inductor under the control method of the present invention L c Please refer to the waveform diagram of the current. Figure 2 ,like Figure 2 As shown in the middle OP section, during the dead time before the switching transistor turns on, the control filter inductor is... L c current i Lc The absolute value is not less than I ZVS The Buck converter unit is turned on. j One upper transistor controls the voltage at the midpoint A of the Buck converter bridge arm. And maintain the voltage at the midpoint B of the Boost converter bridge arm. At this time, the filter inductor L c current i Lc Linear increase.

[0050] Step S2: By lowering the voltage at the midpoint of the Buck converter unit and raising the voltage at the midpoint of the bridge arm of the Boost converter unit, the output filter inductor current first rises and then falls.

[0051] More specifically, when the filter inductor L c current i Lc The current rises to point P and the current at point P At this time, the filter inductor L c current i Lc The flow is in the forward direction, from the midpoint of the Buck converter unit through the filter inductor to the midpoint of the Boost converter unit. L c current i Lc Not less than I ZVS This ensures that the junction capacitance of the lower MOSFET in the Buck converter unit and the upper MOSFET in the Boost converter unit is completely discharged within the dead time, reducing the voltage across both MOSFETs to zero and achieving zero-voltage turn-on. While maintaining zero-voltage turn-on, the upper MOSFET is sequentially turned off and the corresponding lower MOSFET is turned on, reducing the voltage at midpoint A of the Buck converter unit bridge arm. from Gradually decreasing to 0, the upper transistor is turned on and the corresponding lower transistor is turned off in turn, thus reducing the voltage at the midpoint B of the Boost converter bridge arm. Starting from 0 and gradually increasing to ,in, The conduction count of the upper transistor in the OP segment Buck converter unit. This represents the conduction state of the upper transistor in the RS-segment Boost converter unit. At this time, the inductor voltage... The filter inductance is continuously decreasing. L c current i Lc It first rises linearly and then falls linearly.

[0052] Furthermore, in the PQ segment, the inductor voltage ,in, The conduction number of the upper transistor in the PQ segment Buck converter unit. Let be the conduction number of the upper transistor in the PQ segment Boost converter unit, and , The average power corresponding to the PQ segment. P PQ The expression is: , in, A switching cycle is the total time it takes for all the switches in the converter to complete one full on / off operation. At time P, At point Q, Let P be the current. Let Q be the current at point Q.

[0053] Furthermore, to minimize the current increment in the PQ segment, the voltage at the midpoint A of the Buck converter arm should be selected during the PQ stage. Voltage higher than the midpoint B of the Boost converter bridge arm And the combination of the two values ​​that is closest, at which point the filter inductor... L c current i Lc A linear increase with the gentlest slope of current change.

[0054] Furthermore, the filter inductor L c current i Lc After reaching the peak point Q, the filter inductor L c current i Lc Linear decrease, such as Figure 2 The QR segment is shown in the diagram. At this time, the inductor voltage... ,in, The conduction count of the upper transistor in the QR segment Buck converter unit. Let be the conduction number of the upper transistor in the QR segment Boost converter unit, and , The average power corresponding to the QR segment. P QR The expression is: , in, At point R, Let R be the current at point R.

[0055] Furthermore, to minimize the current increment in the QR segment, the voltage at the midpoint A of the Buck converter arm should be selected during the QR phase. Voltage below the midpoint B of the Boost converter bridge arm And the combination of the two values ​​that is closest, at which point the filter inductor... L c current i Lc A linear decrease with the gentlest slope of current change.

[0056] Step S3: By turning off all the upper transistors of the Buck converter unit and keeping some of the upper transistors of the Boost converter unit on, the output inductor current decreases linearly. When the inductor current decreases to... At this time, all lower transistors of the Boost unit are turned off, maintaining the inductor current at [value missing]. .

[0057] More specifically, such as Figure 2 As shown in the RS segment, when the filter inductor L c current i Lc When it drops to point R and the current at point R At this time, all the upper transistors of the Buck converter are turned off, so that the voltage at the midpoint A of the Buck converter bridge arm is reduced. ; Boost converter has k With one upper transistor conducting, the voltage at the midpoint B of the Boost converter bridge arm... Filter inductor L c current i Lc linearly decreasing to .

[0058] Furthermore, to avoid filter inductance L c current i Lc Further decrease, turn on all the lower transistors of the Boost converter unit, so that the voltage at the midpoint B of the Boost converter unit bridge arm is reduced. , filter inductor L c current iLc Maintain at This provides zero-voltage turn-on conditions for the next switching cycle.

[0059] Step S4, based on the real-time monitoring of the converter's input voltage V in Output voltage V o The relationship between the current and operating modes is used to adaptively switch the current operating mode and output the optimal current control waveform adapted to the current operating conditions.

[0060] Figure 3 for V in ≤ V o / n Time filter inductor L c The waveform of the current, when V in ≤ V o / n At any time Then the filter inductor L The current of c i Lc It presents a quadrilateral shape with a monotonically decreasing QR segment in the middle.

[0061] Figure 4 for V in / m > V o Time filter inductor L c The waveform of the current, when V in / m > V o At any time Then the filter inductor L c current i Lc It presents a quadrilateral shape with a monotonically increasing PQ segment in the middle.

[0062] In pentagonal current control, to minimize the inductor voltage difference and ensure opposite polarities between segments PQ and QR, one side of the PQ and QR segments must maintain a fixed voltage level, while the other side uses an adjacent voltage level. Two specific implementation schemes exist: Figure 5 For Scheme 1 filter inductor L c current and v A , vB The voltage waveform diagram shows that, in Scheme 1, one of the upper transistors of a Buck converter is turned off at the moment corresponding to point Q, causing the voltage at the midpoint A of the Buck converter bridge arm to... v A Lower one level ( The voltage at point B, the midpoint of the Boost converter bridge arm... v B Remain unchanged ( The minimum voltage difference satisfies .

[0063] Figure 6 For Scheme 2 filter inductor L c current and v A , v B The voltage waveform diagram shows that, in Scheme 2, one of the Boost converter transistors is turned on at the time corresponding to point Q, causing the voltage at the midpoint B of the Boost converter bridge arm to... v B Raise by one level ( The voltage at point A, the midpoint of the Buck converter bridge arm... v A Remain unchanged ( The minimum voltage difference satisfies .

[0064] To achieve a smoother current change, the switching action scheme should be determined based on the ratio of input voltage to output voltage: when V in / m ≤ V o / n When, adopt option 1; when V in / m > V o / n In this case, option 2 will be adopted.

[0065] In practical implementation, the control method of this invention can further employ an optimal operating mode based on the converter's load conditions to improve efficiency across the entire load range. This optimal operating mode optimizes the control method by controlling the voltage across the inductors in the OP and RS segments, thereby adjusting the filter inductors in the OP and RS segments. L c The rise and fall times of the current are shortened; under heavy load, the time for the input to directly transfer energy to the output is extended, and under light load, the time for the negative current to be maintained is shortened, thereby improving the overall efficiency of the converter.

[0066] The pseudo-continuous current mode is characterized by the filter inductor current not dropping to zero throughout the entire switching cycle, remaining in a continuously conducting state, and its absolute value not less than [a certain value]. I ZVS This ensures that the switching transistor is turned on with zero voltage throughout the entire process; The pseudo-current discontinuous mode is when the filter inductor current drops to Afterwards, the current value is maintained for a period of time, exhibiting a discontinuous conduction characteristic, which reduces light load losses while ensuring zero-voltage turn-on.

[0067] More specifically, the control strategy for the optimal working mode includes: Figure 7 Filter inductors for different input voltage pseudo-current continuous modes L c The waveform diagram of the current changing with the load. Figure 7 (a) is Filter inductor in pseudo-current continuous mode L c The waveform of the current as a function of the load. Figure 7 (b) is Filter inductor in pseudo-current continuous mode L c The waveform of the current as a function of the load. Figure 7 (c) is Filter inductor in pseudo-current continuous mode L c The waveform diagram of current variation with load is shown below. Please refer to... Figure 7 When the load is heavy, the multilevel Buck-Boost converter operates in pseudo-critical continuous current mode (PCRM), in which the current at point P is... I P Current at point Q I Q and the current at point R I R All greater than I ZVS To maximize the time for direct energy transfer from input to output in pseudo-current continuous mode, the filter inductance of the OP segment should be... L c The current rises rapidly, and the filter inductor in the RS segment... L c The current drops rapidly. Therefore, take Make the voltage of the OP segment inductor be V in Simultaneously take Make the inductor voltage of RS segment be .

[0068] Furthermore, as the load decreases, the PQ and QR segments will shift downwards in parallel. To achieve zero-voltage turn-on for all switches, the following must be met: and Therefore, when the current at point P... I P and the current at point R I R All decreased to I ZVS At this point, the multilevel Buck-Boost converter reaches the critical operating point of pseudo-current continuous mode.

[0069] Figure 8 Filter inductors for different input voltage pseudo-current discontinuous modes L c The waveform of the current as a function of the load. Figure 8 (a) is Filter inductor in time-discontinuous current mode L c The waveform of the current as a function of the load. Figure 8 (b) is Filter inductor in time-discontinuous current mode L c The waveform of the current as a function of the load. Figure 8 (c) is Filter inductor in time-discontinuous current mode L c The waveform diagram of current variation with load is shown below. Please refer to... Figure 8 If the load decreases further, the converter will operate in pseudo-discontinuous current mode (PDCM). At this time, the current at point P... I P and the current at point R I R will be fixed in I ZVS And when the filter inductor L c current i Lc Descending to At that time, all the lower transistors of the Buck converter and Boost converter are turned on simultaneously, causing the filter inductor to... L c current i Lc Maintain at To shorten the filter inductance L c current i Lc Maintain at TimeT neg Reducing the conduction loss caused by the negative current circulation can lower the voltage applied to the inductor in the OP and RS sections, thereby extending the operating time of the OP and RS sections.

[0070] Furthermore, in the OP segment, the inductor voltage is Filter inductor L c current i Lc from Rise to I ZVS If the level of the OP segment is reduced... j 1. Filter inductor L c current i Lc The upward slope decreases accordingly, and its rising time will be prolonged by Δ. T Lj Thus maintaining at Time T neg Decrease Δ accordingly T Lj Δ T Lj For filter inductors L c current i Lc from Rise to I ZVS The change in time, Δ T Lj The expression is: , Furthermore, in the RS segment, the inductor voltage is Filter inductor L c current i Lc from I ZVS Descending to If the level of the RS segment is reduced... k 1. Filter inductor L c current i Lc The descent slope decreases accordingly, and its descent time will be prolonged by Δ. T Rk Thus maintaining at Time T neg Decrease Δ accordingly T Rk ΔT Rk For filter inductors L c current i Lc from I ZVS Descending to The change in time, Δ T Rk The expression is: , Furthermore, j 1 and k The smaller 1 is, the greater the corresponding Δ T Lj and Δ T Rk The larger. In order to make T neg The levels of the OP and RS segments are always maintained at the minimum value. j 1 and k 1. The value should be gradually reduced as the load decreases. Specifically, as the load decreases, T neg It will gradually increase; when T neg Reaching Δ T Lj and Δ T Rk When the minimum value is reached, immediately reduce the level of the corresponding segment (if the minimum value is Δ). T Lj Then decrease j 1; If it is Δ T Rk Then decrease k 1), to make T neg It will drop back to 0. As the load continues to decrease, the above process will repeat, ensuring... T neg It remains at the minimum value until the converter enters an unloaded state.

[0071] To further illustrate the superiority of the control method of the present invention, an experimental example of the present invention is given below.

[0072] Set the converter parameters as follows: Input voltage V in Output voltage is 300~900V. V o 400V, flying capacitor C fly 10 µ F, switching frequency f sFor 300kHz, filter inductor L c 13 μ H, Output capacitor C o 4 µ F. Selecting a multilevel Buck-Boost converter m =2, n The topology with =1 was established and experimentally verified. Figure 9 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 300V. Figure 9 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 300V. Figure 9 (a) shows the steady-state experimental waveform of the converter at half load when the input voltage is 300V. Figure 9 (c) shows the steady-state experimental waveform of the converter under no-load when the input voltage is 300V; Figure 10 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 500V. Figure 10 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 500V. Figure 10 (a) is the steady-state experimental waveform of the converter at half load when the input voltage is 500V. Figure 10 (c) shows the steady-state experimental waveform of the converter under no-load when the input voltage is 500V; Figure 11 The following are steady-state experimental waveforms of the converter under full load, half load, and no load conditions when the input voltage is 900V. Figure 11 (a) is the steady-state experimental waveform of the converter under full load when the input voltage is 900V. Figure 11 (a) shows the steady-state experimental waveform of the converter at half load when the input voltage is 900V. Figure 11 (c) shows the steady-state experimental waveform of the converter under no-load conditions when the input voltage is 900V. Figures 9-11 It can be seen that all switching transistors can achieve zero-voltage turn-on and the filter inductor L c The current ripple is relatively small.

[0073] This invention discloses a control method for a multi-level Buck-Boost converter. By controlling the filter inductor current into a pentagonal form, soft switching of all switching transistors can be achieved. Furthermore, by adopting an optimal operating mode and adjusting the rise and fall slopes of the filter inductor current, the rise and fall slopes of the filter inductor current are minimized, thereby minimizing the ripple and effective value of the filter inductor current. The method also optimizes the degree of freedom of control under light load conditions, thus significantly improving the overall efficiency of the converter.

[0074] Although the present invention has been disclosed above by way of embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make some modifications and refinements without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A control method for a multilevel Buck-Boost converter, applied to a multilevel Buck-Boost converter, wherein the multilevel Buck-Boost converter includes a Buck converter unit, a Boost converter unit, and a filter unit; the Buck converter unit includes... A switching transistor ~ and the body diode of the switching transistor ~ Junction capacitance ~ ,as well as A flying capacitor ~ Composition; In steady-state operation, the Buck converter unit flies across the capacitor. , … The voltages are maintained at respectively , 、 …、 ,composition Each level; the Boost converter unit includes A switching transistor ~ and the body diode of the switching transistor ~ Junction capacitance ~ ,as well as A flying capacitor ~ Composition; During steady-state operation, the Boost converter unit has a flying capacitor. , … The voltages are maintained at respectively , 、 …、 ,composition One level; The first end of the filter inductor in the filter unit is connected to the midpoint of the bridge arm of the Buck converter unit, and the second end of the filter inductor is connected to the midpoint of the bridge arm of the Boost converter unit. Its features are, The control method includes, Step S1: By increasing the voltage at the midpoint of the Buck converter arm while keeping the voltage at the midpoint of the Boost converter arm zero, the output filter inductor current increases linearly. In step S1, the Buck transformation unit is turned on. j One upper transistor controls the voltage at the midpoint of the Buck converter bridge arm. And maintain the voltage at the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor increases linearly; Step S2: By decreasing the voltage at the midpoint of the Buck converter unit and increasing the voltage at the midpoint of the bridge arm of the Boost converter unit, the output filter inductor current first increases and then decreases. In step S2, the voltage at the midpoint of the Buck converter bridge arm is transferred from... The voltage gradually decreases to 0, while the voltage at the midpoint of the Boost converter bridge arm gradually increases from 0 to... ,in, The conduction count of the upper transistor in the OP segment Buck converter unit. The conduction count of the upper transistor in the RS segment Boost converter unit; as the inductor voltage decreases continuously, the current of the filter inductor first rises and then falls. Step S3: By turning off all the upper transistors of the Buck converter unit and keeping some of the upper transistors of the Boost converter unit on, the output inductor current decreases linearly. When the inductor current decreases to the negative current reference value for achieving soft switching of the switching transistors... At this time, all lower transistors of the Boost unit are turned off, and the inductor current is maintained at the negative current reference value for achieving soft switching of the switching transistors. : In step S3, when the current of the filter inductor drops to point R and the current at point R... At that time, among them I ZVS To achieve the minimum current for soft switching of the switching transistors, all upper transistors of the Buck converter unit are turned off, making the voltage at the midpoint of the bridge arm of the Buck converter unit zero; the Boost converter unit has k With one upper transistor turned on, the voltage at the midpoint of the Boost converter bridge arm... The current in the filter inductor decreases linearly to the negative current reference value required for soft switching of the switching transistor. ; Step S4, based on the real-time monitoring of the converter's input voltage V in Output voltage V o The relationship between the current and operating modes is used to adaptively switch the current operating mode and output the optimal current control waveform adapted to the current operating condition. In step S4, when V in ≤ V o / n When the inductor current exhibits a quadrilateral shape that monotonically decreases in the middle section; when V in / m > V o At this time, the inductor current exhibits a quadrilateral shape that monotonically increases in the middle section.

2. The control method for a multilevel Buck-Boost converter as described in claim 1, characterized in that, To minimize the voltage difference between the inductors in segments PQ and QR and ensure they have opposite polarities, one side of the voltage level needs to be fixed while the other side uses an adjacent voltage level. The first approach is to... V in / m ≤ V o / n At the time corresponding to point Q, one of the upper transistors of the Buck converter is turned off, causing the voltage at the midpoint of the Buck converter bridge arm to decrease by one level, while the voltage at the midpoint of the Boost converter bridge arm remains unchanged.

3. The control method for a multilevel Buck-Boost converter as described in claim 2, characterized in that, The second option is, when V in / m > V o / n At point Q, one Boost converter transistor is turned on, raising the voltage at the midpoint of the Boost converter arm by one level, while the voltage at the midpoint of the Buck converter arm remains unchanged.

4. The control method for a multilevel Buck-Boost converter as described in claim 1, characterized in that, In step S2, the average power corresponding to segment PQ P PQ The expression is: ， in, The total time of one switching cycle. At time P, At point Q, The voltage at point B, the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor is... The conduction number of the upper transistor in the PQ segment Boost converter unit. For output voltage, This represents the total number of upper transistors in the Boost converter unit. Let P be the current. Let Q be the current. This is the inductance value. The conduction number of the upper transistor in the PQ segment Buck converter unit. Input voltage, This represents the total number of upper transistors in the Buck converter unit.

5. The control method for a multilevel Buck-Boost converter as described in claim 1, characterized in that, In step S2, the average power corresponding to the QR segment P QR The expression is: ， in, The total time of one switching cycle. At point R, At point Q, The voltage at point B, the midpoint of the bridge arm of the Boost converter unit. The current in the filter inductor is... The conduction count of the upper transistor in the QR segment Boost converter unit. For output voltage, This represents the total number of upper transistors in the Boost converter unit. Let R be the current. Let Q be the current. This is the inductance value. The conduction count of the upper transistor in the QR segment Buck converter unit. Input voltage, This represents the total number of upper transistors in the Buck converter unit.

6. The control method for a multilevel Buck-Boost converter as described in claim 1, characterized in that, In step S1, at the beginning of each switching cycle, the voltage at the midpoint of the Buck converter arm is zero, and the voltage at the midpoint of the Boost converter arm is zero.

7. The control method for a multilevel Buck-Boost converter as described in claim 1, characterized in that, The control strategies for the optimal working mode include: When the load is heavy, the multilevel Buck-Boost converter operates in a pseudo-continuous current mode, where the current at point P is... 、 The currents at both point Q and point R are greater than the minimum current required to achieve soft switching of the switching transistor. I ZVS When the current at point P I P and the current at point R I R All currents decreased to the minimum current required to achieve soft switching of the switching transistor. I ZVS At this point, the multilevel Buck-Boost converter reaches the critical operating point of pseudo-current continuous mode; As the load decreases further, the converter will operate in a pseudo-current discontinuous mode, where the currents at point P and point R will be fixed at the minimum current required to achieve soft switching of the switching transistor. I ZVS Furthermore, when the current in the filter inductor drops to the negative current reference value for achieving soft switching of the switching transistor... At this time, all the lower transistors of the Buck converter and Boost converter are turned on simultaneously, so that the current of the filter inductor is maintained at the negative current reference value for achieving soft switching of the switching transistors. ; In order to shorten the current of the filter inductor, it is necessary to maintain the current at the negative current reference value for achieving soft switching of the switching transistor. This reduces the voltage applied to the inductor during the OP and RS segments, thereby shortening the negative current reference value required for soft switching of the switching transistor at a constant frequency. The circulation time.

8. The control method for a multilevel Buck-Boost converter as described in claim 7, characterized in that, The current in the filter inductor is from the negative current reference value used to achieve soft switching of the switching transistor. Rise to the minimum current required to achieve soft switching of the switching transistor. I ZVS Time change Δ T Lj The expression is: ， in, This is the inductance value. This represents the total number of upper transistors in the Buck converter unit. The conduction count of the upper transistor in the OP segment Buck converter unit. This is the input voltage.

9. The control method for a multilevel Buck-Boost converter as described in claim 8, characterized in that, The current in the filter inductor is from the minimum current required to achieve soft switching of the switching transistor. I ZVS The current drops to the negative current reference value for achieving soft switching of the switching transistor. Time change Δ T Rk The expression is: ， in, This is the inductance value. This represents the total number of upper transistors in the Boost converter unit. The conduction number of the upper transistor in the RS segment Boost converter unit. This is the output voltage.

10. The control method for a multilevel Buck-Boost converter as described in claim 9, characterized in that, In order to maintain at Time T neg The levels of the OP and RS segments are always maintained at the minimum value. j 1 and k 1. The reduction should be gradual as the load decreases; As the load decreases, maintain at Time T neg It will gradually increase; When maintained at Time T neg The current reaching the filter inductor from Rise to I ZVS Time change Δ T Lj and the current from the filter inductor I ZVS Descending to Time change Δ T Rk When the value is at its minimum, immediately reduce the level of the corresponding segment; The minimum value is the current in the filter inductor from Rise to I ZVS The change in time Δ T Lj , reduce j 1; The minimum value is the current in the filter inductor from I ZVS Descending to The change in time Δ T Rk , reduce k 1, to maintain at Time T neg Fall back to 0; as the load continues to decrease, ensure it remains at Time T neg It remains at the minimum value until the converter enters an unloaded state.

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