Single-stage buck-boost DC / DC converter and hybrid modulation method

Abstract

The invention belongs to the technical field of DC / DC converters in the power electronic technology, and discloses a single-stage buck-boost DC / DC converter and a hybrid modulation method. The on-off of the first switch Q1 and the second switch Q2 is controlled through the switch control circuit, so that the converter can be switched between a partial power processing (PSM) mode and a full power processing (Buck-Boost) mode. When the input and output voltage ratio is far away from 1, the system works in a PSM mode, and efficient partial power processing is achieved; when the input and output voltage ratio is close to 1, the system is automatically switched to a Buck-Boost mode, and a Buck-Boost topology is formed by multiplexing part of switching tubes, so that phase shift saturation and transformer magnetic saturation are avoided, and stable work of the system is ensured. According to the invention, single-stage wide-range buck-boost output is realized, and the technical problem that the existing partial power converter cannot work normally at an extreme transformation ratio is effectively solved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of DC / DC converter in power electronics, and particularly relates to a single-stage step-up / down DC / DC converter and a full power / partial power hybrid modulation method. BACKGROUND

[0002] With the increasing demand for high-power electricity in direct current terminals such as electric vehicles, data centers, lighting systems and the like, and the rapid increase in the number of photovoltaic energy storage and direct current ports and direct current microgrids, higher requirements and challenges are put forward for the efficiency, power density, heat dissipation and cost of traditional direct current converters. To solve the above problems, partial power processing (PPP) technology emerges as the times require. PPP establishes an electrical connection between the source and the load, and most of the power is transmitted directly between them, while the internal DC / DC converter only transmits and processes the remaining small part of the power.

[0003] In the existing scheme, the PPP topology is generally parallel (or series) connection of the power supply side and the input of the internal DC / DC converter, and series (or parallel) connection of the load side and the output of the internal DC / DC converter. The internal DC / DC converter of PPP usually adopts a bipolar single-stage DC / DC converter topology or a unipolar single-stage DC / DC converter topology, and a cascaded H-bridge circuit topology in the latter stage. The DC / DC converter part is usually realized based on a dual active bridge (DAB) converter, and energy is transmitted internally through a high-frequency transformer.

[0004] For the existing partial power converter, the internal DC / DC converter cannot realize single-stage step-up / down output, and the ability to cope with a wide input voltage range is insufficient (single-stage step-up / down output has been realized, but there is a slight difference in topology); at the same time, when the input-output ratio is close to 1, the internal DC / DC converter ratio is much larger than the design rated ratio, which leads to moving towards saturation, the maximum power transmission does not meet the port output demand, and the load cannot be stabilized to the rated voltage, which also causes the high-frequency transformer to be saturated, the primary current to be too large, and the converter to be unable to work normally.

[0005] Through the above analysis, the problems and defects of the prior art are that the fundamental contradiction of the existing partial power converter lies in the contradiction between its fixed topology structure and the wide range of operation requirements. The internal DC / DC converter of the existing partial power converter can exert the efficiency advantage of PPP in the conventional working condition, but in the "critical zone" where the input-output ratio is close to 1, it will expose a series of chain technical problems such as control saturation, power limitation, magnetic element saturation and system instability, which seriously limits its reliability and practicality in wide voltage range application scenarios. SUMMARY

[0006] To overcome the problems of some power converters being unable to achieve single-stage buck-boost and failing to operate normally when the input-output ratio is close, this invention discloses a single-stage buck-boost DC / DC converter and a hybrid modulation method to achieve efficient and stable energy transfer when the load voltage fluctuates. The technical solution is as follows: This invention is implemented as follows: a single-stage buck-boost DC / DC converter, including an input port, an output port, a bipolar half-bridge circuit, a unipolar half-bridge circuit, an energy storage inductor, a high-frequency transformer, and a first switch. Second switch and switch control circuit; the bipolar half-bridge circuit and the unipolar half-bridge circuit are isolated and connected through the energy storage inductor and the high-frequency transformer, and connected through the first switch. Connect the terminals of the high-frequency transformer with the same name; The switch control circuit is configured to control the first switch. Second switch The switching on and off selectively enables the converter to operate in partial power processing (PSM) mode or full power processing (Buck-Boost) mode to achieve single-stage buck-boost output and efficient energy transfer. This avoids phase shift saturation and transformer saturation when the input-output voltage ratio is close to 1, ensuring normal converter operation.

[0007] Furthermore, the unipolar half-bridge circuit includes multiple switching transistors and capacitors, while the bipolar half-bridge circuit uses a top-down MOSFET and clamping capacitor connection; the turns ratio of the high-frequency transformer is... Through the first switch Connect the terminals of the high-frequency transformer with the same name, where... It is a real number greater than 0.

[0008] Furthermore, in the converter, under the Buck-Boost operating mode, The freewheeling diode provides a freewheeling path for the inductor current. , Provide a capacitor to support the port. For clamping capacitors, load With capacitor in parallel.

[0009] Furthermore, in PSM mode, the switch control circuit controls the first switch. Off and second switch When the circuit is turned on, the high-frequency transformer operates, energy is transmitted through the transformer, and the converter realizes partial power processing. In Buck-Boost mode, the switch control circuit controls the first switch. On and second switch When shut down, the high-frequency transformer is bypassed, and by reusing some of the switching transistors of the bipolar half-bridge and unipolar half-bridge with the energy storage inductor to form a Buck-Boost topology, the converter achieves full power processing.

[0010] Furthermore, the Buck-Boost topology utilizes multiplexed switching transistors... , , and Implementation, in which the switching transistor Keep open, switching transistor Switching transistor and switching transistor With switching frequency The converter output voltage is adjusted using a duty cycle modulation mode.

[0011] Another object of the present invention is to provide a full-power / partial-power hybrid modulation method for the aforementioned single-stage buck-boost DC / DC converter, the method comprising the following steps: S1, Set the reference phase and output voltage reference value The input voltage and output voltage are sampled to obtain the input voltage. and output voltage ; S2, output voltage reference value With output voltage The difference is used as the input of the PI controller, and then the output of the PI controller is used to obtain the pi ratio D or the duty cycle d, which are then input to the phase shift modulator and the duty cycle modulator respectively to obtain two sets of semiconductor device driving waveforms. S3, via output voltage reference value and input voltage Calculate working status reference value ,Will and interval Compare the values ​​at both ends to determine Whether it falls Within the interval, the operating modes of the converter are determined; S4. If the converter is operating in PSM mode, then select the drive waveform. The actual driving waveform is output; if the converter operates in Buck-Boost mode, then the driving waveform is selected. As the actual driving waveform Out; S5, apply the actual drive waveform Out to , To achieve efficient and stable energy transmission.

[0012] Furthermore, when the converter operates in PSM mode, single-phase-shift modulation is employed, by adjusting the phase shift ratio between the primary and secondary half-bridges. Control power transmission, output voltage and power processed by the internal DC / DC converter Represented as: ; In the formula, The transformer turns ratio For capacitor voltage, For load resistance, Compared to the displacement between the original side half-bridge and the secondary side half-bridge, For switching frequency, , The switching cycle in PSM mode. It is the sum of leakage inductance and external inductance.

[0013] Furthermore, when the converter operates in Buck-Boost mode, a duty cycle modulation mode is adopted, which is achieved by adjusting the duty cycle. The output voltage is controlled, and the relationship between the output voltage, input voltage, and duty cycle is as follows: .

[0014] Furthermore, the converter operating status reference value The calculation formula is: ; PSM working mode and Buck-Boost working mode working limits The settings are as follows: ; Furthermore, the selection of the drive signal is achieved through a multiplexer, which selects either a phase-shift modulation signal or a duty cycle modulation signal according to the mode and applies them to the switching transistor.

[0015] Combining all the above technical solutions, the beneficial effects of this invention are as follows: First, this invention proposes a single-stage buck-boost DC / DC converter and a full-power / partial-power hybrid modulation method, which solves the problem that the partial-power converter cannot work properly when the input-output voltage ratio is close to 1. At the same time, it realizes the single-stage buck-boost output of the internal DC / DC converter, thereby realizing the wide-range buck-boost output of the entire converter and ensuring efficient and stable energy transmission.

[0016] Secondly, this invention constructs a single-stage buck-boost DC / DC converter and a full-power / partial-power hybrid modulation method. By proposing a new topology and switch multiplexing based on the new topology, a Buck-Boost operating mode is introduced to solve problems such as shift ratio saturation, limited power transmission, high-frequency transformer magnetic saturation, and excessive primary-side current under extreme turns ratio conditions. This compensates for the inability of some existing power converters to operate under extreme turns ratio conditions, thereby achieving single-stage full-range buck-boost output. In PSM operating mode, a dual half-bridge structure is adopted on both sides, significantly reducing the current and voltage stress on the switching transistors.

[0017] Third, this invention is applicable to the high-efficiency power supply market, such as fast charging for electric vehicles and data centers. By achieving efficient and stable energy conversion over a wide voltage range, it helps terminal equipment manufacturers reduce system heat dissipation requirements, decrease size, save material costs, and improve system reliability. Its core value lies in breaking through the operating range limitations of partial power converters. Through innovative topology and hybrid modulation methods, this invention achieves for the first time the switching between full-power and partial-power modes for partial power converters when the input-output voltage ratio is close to 1. Since partial power converters cannot operate stably over a wide voltage range (especially when the input-output ratio is close to 1), this invention successfully solves this problem through a mode-switching mechanism, enabling the converter to have both high efficiency and wide operating range capabilities. Attached Figure Description

[0018] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this disclosure and, together with the description, serve to explain the principles of this disclosure; Figure 1 This is a flowchart of the full-power / partial-power hybrid modulation method for a single-stage buck-boost DC / DC converter provided in an embodiment of the present invention; Figure 2 This is a topology diagram of a hybrid power converter provided in an embodiment of the present invention; Figure 3 This is the equivalent circuit diagram of the PSM operating mode provided in the embodiment of the present invention; Figure 4 This is a schematic diagram of the Buck-Boost operating modes provided in an embodiment of the present invention; Figure 5 These are the working mode waveform diagrams of PSM and Buck-Boost provided in the embodiments of the present invention; wherein, (a) is the working mode waveform diagram of PSM, and (b) is the working mode waveform diagram of Buck-Boost; Figure 6 This is a power flow path diagram of the PSM operating mode provided in an embodiment of the present invention; Figure 7 This is a schematic diagram of the operating mode division of the hybrid power converter provided in an embodiment of the present invention; Figure 8 This is a control block diagram of a single-stage buck-boost DC / DC converter provided in an embodiment of the present invention. Detailed Implementation

[0019] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0020] This invention innovatively proposes a single-stage buck-boost DC / DC converter and a hybrid modulation method, employing bipolar half-bridge and unipolar half-bridge circuits and introducing switches. and Mode switching is achieved: Operating in PSM mode at normal input-output ratios to maximize efficiency; when the input-output ratio approaches 1, a multiplexed switch bypasses the high-frequency transformer, switching the circuit to Buck-Boost mode to avoid phase shift saturation and transformer saturation issues. The hybrid modulation method automatically selects the mode based on the voltage ratio, achieving a wide-range buck-boost output. This addresses issues in some existing power converters, such as phase shift saturation, limited power transfer, high-frequency transformer magnetic saturation, and excessive primary-side current when the input-output ratio is close, thus improving reliability and practicality.

[0021] Example 1, such as Figure 1 As shown, the hybrid modulation method for a single-stage buck-boost DC / DC converter provided in this embodiment of the invention includes the following steps: S1, Set the reference phase and output voltage reference value The input voltage and output voltage are sampled to obtain the input voltage. and output voltage ; S2, output voltage reference value With output voltage The difference is used as the input of the PI controller, and then the output of the PI controller is used to obtain the pi ratio D or the duty cycle d, which are then input to the phase shift modulator and the duty cycle modulator respectively to obtain two sets of semiconductor device driving waveforms. S3, via output voltage reference value and input voltage Calculate working status reference value ,Will and interval Compare the values ​​at both ends to determine Whether it falls Within the interval, the operating modes of the converter are determined; S4. If the converter is operating in PSM mode, then select the drive waveform. The actual driving waveform is output; if the converter operates in Buck-Boost mode, then the driving waveform is selected. As the actual driving waveform Out; S5, apply the actual drive waveform Out to , To achieve efficient and stable energy transmission.

[0022] Example 2, Figure 2 The hybrid power converter topology provided in this embodiment of the invention consists of a bipolar half-bridge and a unipolar half-bridge. The bipolar half-bridge is connected using top-paired MOSFETs and clamping capacitors. The two half-bridges are isolated by an energy storage inductor and a high-frequency transformer. The turns ratio is... ,pass Connect the transformer terminals with the same name. In the converter, under Buck-Boost operating mode, As a freewheeling diode, it provides a freewheeling path for the inductor current. , Provide a capacitor to support the port. For clamping capacitors, load With capacitor in parallel.

[0023] In PSM operating mode, a switch is introduced. Turn off, introduce switch With the circuit open, the high-frequency transformer is operating normally, and the power supply... With capacitor ,load Series connection, by KVL constraints: (1) To achieve boost output It must be greater than 0; similarly, for buck output, then... The voltage must be less than 0; therefore, this invention uses a bipolar half-bridge on the primary side to achieve buck-boost output. For example... Figure 6 As shown, the converter performs partial power processing at this time, and the remaining power is directly transmitted to the load through the feedforward channel. The converter achieves partial power processing, and the efficiency is significantly improved.

[0024] Compared to existing partial power converters, when the input-output ratio approaches 1, the shift ratio saturates and the primary-side current becomes too large, preventing the converter from operating normally. Therefore, this invention uses switch multiplexing to change the topology of the converter under extreme operating conditions, enabling the circuit to operate in a new mode, namely the Buck-Boost operating mode.

[0025] Buck-Boost operating mode Conductivity When switched off, the high-frequency transformer ceases operation. At this point, a Buck-Boost topology is formed by reusing MOSFETs and IGBTs. Therefore, this invention enables the circuit to operate stably and efficiently in Buck-Boost mode when the input-output ratio is close to 1, changing the topology under extreme conditions. In this state, the converter performs full-power processing.

[0026] like Figure 7 As shown, for ;like Figure 8 As shown, ; This represents the boundary between the PSM and Buck-Boost operating modes, set by... The value is used to divide the converter's working range. This value serves as a reference for the converter's operating state, determining the appropriate operating mode for the converter. It enables efficient switching between operating states, achieving single-stage buck-boost output.

[0027] PSM operating mode principle; under this operating mode Turn off When the circuit is turned on, the converter uses single-phase-shift modulation, and the operating mode waveform is as follows: Figure 5 As shown in Figure (a) above. The basic idea is to change the equivalent topology of the circuit by controlling the switching transistors on both sides of the half-bridge arm, so as to generate a square wave AC current with adjustable phase on both sides of the energy storage inductor. By utilizing the energy storage effect of the inductor, the direction and magnitude of energy transfer can be controlled. The equivalent circuit diagram is shown below. Figure 3 As shown. By Figure 3 As can be seen, there is only one equivalent inductance between any two square wave voltage sources. Therefore, the calculation method for output voltage and transmission power is the same as that for DAB converters. Thus, output voltage and transmission power can be expressed as: (2) In the formula, The transformer turns ratio For capacitor voltage, For load resistance, Compared to the displacement between the original side half-bridge and the secondary side half-bridge, For switching frequency, , The switching cycle in PSM mode. It is the sum of leakage inductance and external inductance. This refers to the power processed by the internal DC / DC converter.

[0028] The output port current of the internal DC / DC converter is The power feedforward channel current is Therefore, the converter output power can be expressed as: (3) From equation (3), we can see that the ratio of partial processing power to direct transmission power is: Assuming the efficiency of the DC / DC converter is Then the efficiency of the converter in the PSM operating mode is: (4) Therefore, the converter in PSM mode has a much higher efficiency for partial power processing than the converter with the same structure that processes full power.

[0029] Buck-Boost operating mode principle: In this operating mode... Conductivity Turning off, forming a Buck-Boost topology, such as Figure 4 As shown. For the switching transistor , , , Reuse, switching transistor Keep it open for a long time. , , With switching frequency Operation. The converter employs a duty cycle modulation mode, and the operating mode waveform is as follows: Figure 5 As shown in Figure (b).

[0030] Taking one cycle as an example, the operating state of the Buck-Boost converter can be divided into two types based on the conduction state of the switching transistor.

[0031] Working status 1 ( ):when , Conduction, When the circuit is turned off, the voltage across the inductor is equal to the input voltage, the inductor stores energy, and the current increases linearly.

[0032] (5) In the formula, Input voltage, The current is the inductor current, and the inductor voltage and inductor current have the same reference direction.

[0033] Working status 2 ( ):when , Turn off, When the circuit is turned on, the inductor voltage equals the negative output voltage, the inductor releases energy, and the current decreases linearly.

[0034] (6) When the converter is operating in a steady state, the voltage ripple is small. Based on the small ripple approximation and the inductor volt-second balance, it can be obtained that within one cycle... The following formula is satisfied: (7) In the formula, For this mode, the duty cycle The duration of working state 1, The duration of working state 2, The final expression for the output voltage is as follows: (8) In Buck-Boost mode, the converter operates at full power. By using switches and inductors for multiplexing, the converter is able to escape extreme operating environments and enter Buck-Boost mode, achieving efficient and stable energy transfer.

[0035] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A single-stage buck-boost DC / DC converter, characterized in that, Includes input ports, output ports, bipolar half-bridge circuit, unipolar half-bridge circuit, energy storage inductor, high-frequency transformer, and first switch. Second switch and switch control circuit; the bipolar half-bridge circuit and the unipolar half-bridge circuit are isolated and connected through the energy storage inductor and the high-frequency transformer, and connected through the first switch. Connect the terminals of the high-frequency transformer with the same name; The switch control circuit is configured to control the first switch. Second switch The switching on and off selectively enables the converter to operate in partial power processing (PSM) mode or full power processing (Buck-Boost) mode to achieve single-stage buck-boost output and efficient energy transfer. This avoids phase shift saturation and transformer saturation when the input-output voltage ratio is close to 1, ensuring normal converter operation.

2. The single-stage buck-boost DC / DC converter according to claim 1, characterized in that, The unipolar half-bridge circuit includes multiple switching transistors and capacitors, while the bipolar half-bridge circuit uses a top-down MOSFET and clamping capacitor connection; the turns ratio of the high-frequency transformer is... Through the first switch Connect the terminals of the high-frequency transformer with the same name, where... It is a real number greater than 0.

3. The single-stage buck-boost DC / DC converter according to claim 1, characterized in that, In the converter, under Buck-Boost operating mode, The freewheeling diode provides a freewheeling path for the inductor current. , Provide a capacitor to support the port; For clamping capacitors, load With capacitor in parallel.

4. The single-stage buck-boost DC / DC converter according to claim 1, characterized in that, In PSM mode, the switch control circuit controls the first switch. Off and second switch When the circuit is turned on, the high-frequency transformer operates, energy is transmitted through the transformer, and the converter realizes partial power processing. In Buck-Boost mode, the switch control circuit controls the first switch. On and second switch When shut down, the high-frequency transformer is bypassed, and by reusing some of the switching transistors of the bipolar half-bridge and unipolar half-bridge with the energy storage inductor to form a Buck-Boost topology, the converter achieves full power processing.

5. The single-stage buck-boost DC / DC converter according to claim 4, characterized in that, The Buck-Boost topology uses multiplexed switching transistors. , , and Implementation, in which the switching transistor Keep open, switching transistor Switching transistor and switching transistor With switching frequency The converter output voltage is adjusted using a duty cycle modulation mode.

6. A hybrid modulation method for a single-stage buck-boost DC / DC converter, wherein the method is implemented using the single-stage buck-boost DC / DC converter described in any one of claims 1-5, characterized in that, The method includes the following steps: S1, Set the reference phase and output voltage reference value The input voltage and output voltage are sampled to obtain the input voltage. and output voltage ; S2, output voltage reference value With output voltage The difference is used as the input to the PI controller, and then the output of the PI controller is used to obtain the shift ratio. or duty cycle The waveforms are then input to the phase-shift modulator and the duty cycle modulator, respectively, to obtain two sets of semiconductor device driving waveforms. S3, via output voltage reference value and input voltage Calculate working status reference values ,Will and interval Compare the values ​​at both ends to determine Whether it falls Within the interval, the operating modes of the converter are determined; S4. If the converter is operating in PSM mode, then select the drive waveform. The actual driving waveform is output; if the converter operates in Buck-Boost mode, then the driving waveform is selected. As the actual driving waveform Out; S5, apply the actual drive waveform Out to , To achieve efficient and stable energy transmission.

7. The hybrid modulation method for a single-stage buck-boost DC / DC converter according to claim 6, characterized in that, When the converter operates in PSM mode, single-phase-shift modulation is used, and the phase shift ratio between the primary and secondary half-bridges is adjusted. Control power transmission, output voltage and power processed by the internal DC / DC converter Represented as: ； In the formula, The transformer turns ratio For capacitor voltage, For load resistance, Compared to the displacement between the original side half-bridge and the secondary side half-bridge, For switching frequency, , The switching period in PSM mode. It is the sum of leakage inductance and external inductance.

8. The hybrid modulation method for a single-stage buck-boost DC / DC converter according to claim 6, characterized in that, When the converter operates in Buck-Boost mode, a duty cycle modulation mode is used, which is achieved by adjusting the duty cycle. The output voltage is controlled, and the relationship between the output voltage, input voltage, and duty cycle is as follows: 。 9. The hybrid modulation method for a single-stage buck-boost DC / DC converter according to claim 8, characterized in that, Converter operating status reference value The calculation formula is: ； PSM working mode and Buck-Boost working mode working limits The settings are as follows: 。 10. The hybrid modulation method for a single-stage buck-boost DC / DC converter according to claim 6, characterized in that, The selection of the drive signal is achieved through a multiplexer, which selects either a phase-shift modulation signal or a duty cycle modulation signal according to the mode and applies them to the switching transistor.

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