Buck-boost dc converter and hybrid power system

Abstract

Disclose a kind of Buck-Boost DC converter and composite power supply system, Buck-Boost DC converter includes inductance L, N-MOSFET switch SW2, diode D2, diode D3, diode D4, diode D5, wherein, the anode of diode D2, the cathode of diode D3 and the source of N-MOSFET switch and the one end of inductance L are connected, the cathode of diode D2 is connected with the drain of N-MOSFET switch and constitutes the positive pole of input end of Buck-Boost DC converter, the anode of diode D3 and the anode of diode D4 constitute the negative pole of output end of Buck-Boost DC converter, the other end of inductance L is connected with by the cathode of diode D4 and the anode of D5 and constitutes the negative pole of input end, the cathode of diode D5 is as the positive pole of output end of Buck-Boost DC converter.

Description

Technical Field

[0001] This invention belongs to the field of DC-DC converter technology, specifically a Buck-Boost DC-DC converter and a composite power supply system. Background Technology

[0002] In lithium-ion battery power systems, the charging and discharging capabilities of the battery pack play a crucial role. On one hand, the lithium-ion battery power system needs to ensure the peak power demand of the electric motor during start-up and acceleration; on the other hand, it needs to provide power smoothly during the constant speed motion of the electric motor. The lithium-ion battery power system acts like an energy "reservoir," fluctuating with the power demand of the electric motor, which places high demands on the output performance of the lithium-ion battery pack. Generally, it is difficult for lithium-ion batteries to simultaneously meet both high energy density and high power density. Therefore, high-energy-density lithium-ion battery packs are selected in new energy power systems to meet the long-range requirements of electric vehicles, but high-power output can cause irreversible damage to lithium-ion batteries, reducing their lifespan. To meet the high power demands during start-up, acceleration, and hill climbing, supercapacitors are introduced to form a composite power system to meet the power requirements under various driving conditions. To match the voltage, the lithium-ion battery pack is generally powered in parallel with the supercapacitor via a DC-DC converter. When the output voltage of the lithium battery pack and the supercapacitor are mismatched, the lithium battery pack supplies power through a DC-DC converter to boost or buck the voltage. However, when the output voltages of the lithium battery and the supercapacitor are matched, passing the lithium battery pack through a DC-DC converter would actually reduce efficiency. To address this issue, the circuit structure of the hybrid power supply system can be optimized so that the lithium battery pack can supply power directly without a DC-DC converter. Furthermore, in the Buck-Boost DC-DC converter structure, the positive and negative terminals of the converter's input are opposite to those of the output, and correspondingly, the positive and negative terminals of the load correspond to those of the output. This complicates the circuitry that directly connects the lithium battery pack and the load. By appropriately designing the connection between the positive output terminal of the lithium battery pack, the positive output terminal of the DC-DC converter, and the positive terminal of the load, the structure of the hybrid power supply system can be simplified, and the efficiency of the power supply and the Buck-Boost DC-DC converter can be improved.

[0003] The information disclosed in the background section is only intended to enhance the understanding of the background of the present invention, and therefore may contain information that does not constitute prior art known to those skilled in the art. Summary of the Invention

[0004] To address the problems existing in the prior art, this invention proposes a Buck-Boost DC-DC converter and a composite power supply system, which can not only meet the high power requirements of the power system, but also rationally allocate the output of each power source during normal operation, realizing direct power supply from the lithium battery pack and power supply after transformation.

[0005] The objective of this invention is achieved through the following technical solution: A Buck-Boost DC-DC converter includes an inductor L, an N-MOSFET switch SW2, diodes D2, D3, D4, and D5. The anode of diode D2 and the cathode of diode D3 are connected to the source of the N-MOSFET switch and one end of the inductor L. The cathode of diode D2 is connected to the drain of the N-MOSFET switch, forming the positive input terminal of the Buck-Boost DC-DC converter. The anodes of diodes D3 and D4 form the negative output terminal of the Buck-Boost DC-DC converter. The other end of the inductor L is connected to the negative input terminal formed by the cathode of diode D4 and the anode of diode D5. The cathode of diode D5 serves as the positive output terminal of the Buck-Boost DC-DC converter.

[0006] In the Buck-Boost DC-DC converter, diodes D3, D4, and D5 form a rectifier bridge circuit.

[0007] A composite power supply system includes a lithium battery pack, an N-MOSFET switch SW1, a diode D1, a Buck-Boost DC-DC converter, and a supercapacitor. The positive terminal of the lithium battery pack is connected to the positive input terminal of the Buck-Boost DC-DC converter, the drain of the N-MOSFET switch SW1, and the negative terminal of the diode D1. The negative terminal of the lithium battery is connected to the negative input terminal of the Buck-Boost DC-DC converter. The source of the N-MOSFET switch SW1 and the positive terminal of the diode D1 are connected to the positive output terminal of the Buck-Boost DC-DC converter. The positive terminal of the supercapacitor is connected to the source of the N-MOSFET switch SW1, the positive terminal of the diode D1, and the positive output terminal of the Buck-Boost DC-DC converter. The negative terminal of the supercapacitor is connected to the negative output terminal of the Buck-Boost DC-DC converter. By controlling the opening and closing of the N-MOSFET switches SW1 and SW2, the lithium battery pack can directly supply power or supply power after passing through the Buck-Boost DC-DC converter.

[0008] In the aforementioned composite power system, the lithium battery pack is transformed by the Buck-Boost DC-DC converter to power the supercapacitor by controlling the opening and closing of the N-MOSFET switch SW2.

[0009] In the aforementioned composite power system, the load is connected in parallel across the supercapacitor.

[0010] In the aforementioned composite power system, the load includes an inverter motor.

[0011] In the aforementioned composite power system, the operating modes of the composite power system include direct power supply from the lithium battery pack to the supercapacitor, power supply from the lithium battery pack alone, power supply from the supercapacitor alone, power supply from the lithium battery after being transformed by a Buck-Boost DC-DC converter, and power supply from the supercapacitor alone for the recovery of braking energy.

[0012] In the aforementioned composite power supply system, when the lithium battery pack is directly powered by the N-MOSFET switch SW1, the N-MOSFET switch SW1 is turned on and the N-MOSFET switch SW2 is turned off. The current flowing out from the load returns to the negative terminal of the lithium battery pack after passing through the diode D4, forming a circuit.

[0013] In the aforementioned composite power system, when the lithium battery pack is powered by the Buck-Boost DC-DC converter, the N-MOSFET switch SW1 remains off. By controlling the duty cycle of the N-MOSFET switch SW2, the lithium battery pack can be boosted or bucked for output. In the transformer output, when the N-MOSFET switch SW2 is on, the lithium battery pack, the N-MOSFET switch SW2, and the inductor L form a circuit, and the supercapacitor supplies power to the load alone. When the N-MOSFET switch SW2 is off, the direction of the induced electromotive force on the inductor L changes, and the current flows out from under the inductor L, passes through diode D5, and then supplies power. The current then flows back to the other end of the inductor L through diode D3 to form a circuit.

[0014] In the aforementioned composite power supply system, the duty cycle of the N-MOSFET switch SW2 is controlled to be greater than or less than 0.5, so that the lithium battery pack can achieve boost or buck output after passing through the Buck-Boost DC-DC converter.

[0015] Compared with existing technologies, this invention has the following advantages: The output terminal of the Buck-Boost DC-DC converter described in this invention consists of a semi-rectifier circuit; the supercapacitor and the negative terminal of the load are connected to the semi-rectifier circuit. The lithium battery pack charges the supercapacitor and powers the load through the Buck-Boost DC-DC converter; it can also directly power the load by adjusting the state of the N-MOSFET switch. When the lithium battery pack directly powers the load and the supercapacitor, the current forms a complete loop through the semi-rectifier circuit. By controlling the on / off state of the NMOSFET switches WS1 and SW2, direct output from the lithium battery, direct output from the supercapacitor, and buck-boost coordinated output are achieved, meeting the power requirements of different loads, enabling the composite power supply to operate in the optimal output state, and extending its service life. The composite power system controls the output of the lithium battery pack through the N-MOSFET switch, realizing real-time switching of multiple operating modes. It can meet the various power requirements of the electric power system while rationally allocating the operating modes of the lithium battery and supercapacitor, improving the efficiency of the DC-DC converter and the entire power system. Attached Figure Description

[0016] Various other advantages and benefits of the present invention will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. It is obvious that the drawings described below are merely some embodiments of the invention, and those skilled in the art can obtain other drawings based on these drawings without any inventive effort. Furthermore, the same reference numerals denote the same parts throughout the drawings.

[0017] In the attached diagram:

[0018] Figure 1 This is a schematic diagram of the structure of a Buck-Boost DC-DC converter and a hybrid power supply system according to an embodiment of the present invention;

[0019] Figure 2 This is a schematic diagram of the supercapacitor-only power supply mode of a Buck-Boost DC-DC converter and composite power system according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the direct power supply mode of the Buck-Boost DC-DC converter and composite power system according to an embodiment of the present invention, using a lithium battery and a supercapacitor.

[0021] Figure 4 This is a schematic diagram of the lithium battery-powered operation mode of the Buck-Boost DC-DC converter and composite power system according to an embodiment of the present invention.

[0022] Figures 5(a) and 5(b) are schematic diagrams of the working mode of the Buck-Boost DC-DC converter and the composite power supply system after lithium battery transformation according to an embodiment of the present invention. Figure 5(a) is a schematic diagram of the working state when SW2 is turned on, and Figure 5(b) is a schematic diagram of the working state when SW2 is turned off.

[0023] Figure 6 This is a schematic diagram of the supercapacitor energy recovery operation mode of a Buck-Boost DC-DC converter and hybrid power system according to an embodiment of the present invention.

[0024] In all the attached diagrams, the gray areas represent circuits that are not in operation under the corresponding conditions.

[0025] The present invention will be further explained below with reference to the accompanying drawings and embodiments. Detailed Implementation

[0026] The following will refer to the appendix. Figures 1 to 6Specific embodiments of the invention will be described in more detail below. While specific embodiments of the invention are shown in the accompanying drawings, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art.

[0027] It should be noted that certain terms are used in the specification and claims to refer to specific components. Those skilled in the art will understand that different terms may be used to refer to the same component. This specification and claims do not distinguish components based on differences in terminology, but rather on differences in function. The terms "comprising" or "including" used throughout the specification and claims are open-ended and should be interpreted as "comprising but not limited to." The following descriptions are preferred embodiments for carrying out the invention; however, these descriptions are for the purpose of understanding the general principles of the specification and are not intended to limit the scope of the invention. The scope of protection of this invention is determined by the appended claims.

[0028] To facilitate understanding of the embodiments of the present invention, further explanations and descriptions will be provided below with reference to the accompanying drawings and specific embodiments. The accompanying drawings do not constitute a limitation on the embodiments of the present invention.

[0029] To better understand, such as Figure 1 As shown, the Buck-Boost DC-DC converter includes an inductor L, an N-MOSFET switch SW2, diodes D2, D3, D4, and D5. The anode of diode D2 and the cathode of diode D3 are connected to the source of the N-MOSFET switch and one end of the inductor L. The cathode of diode D2 is connected to the drain of the N-MOSFET switch and forms the positive input terminal of the Buck-Boost DC-DC converter. The anodes of diodes D3 and D4 form the negative output terminal of the Buck-Boost DC-DC converter. The other end of the inductor L is connected to the negative input terminal formed by the cathode of diode D4 and the anode of diode D5. The cathode of diode D5 serves as the positive output terminal of the Buck-Boost DC-DC converter.

[0030] In a preferred embodiment of the Buck-Boost DC-DC converter, diodes D3, D4, and D5 form a rectifier bridge circuit.

[0031] A composite power supply system includes a lithium battery pack, an N-MOSFET switch SW1, a diode D1, a Buck-Boost DC-DC converter, and a supercapacitor. The positive terminal of the lithium battery pack is connected to the positive input terminal of the Buck-Boost DC-DC converter, the drain of the N-MOSFET switch SW1, and the negative terminal of the diode D1. The negative terminal of the lithium battery is connected to the negative input terminal of the Buck-Boost DC-DC converter. The source of the N-MOSFET switch SW1 and the positive terminal of the diode D1 are connected to the positive output terminal of the Buck-Boost DC-DC converter. The positive terminal of the supercapacitor is connected to the source of the N-MOSFET switch SW1, the positive terminal of the diode D1, and the positive output terminal of the Buck-Boost DC-DC converter. The negative terminal of the supercapacitor is connected to the negative output terminal of the Buck-Boost DC-DC converter. By controlling the opening and closing of the N-MOSFET switches SW1 and SW2, the lithium battery pack can directly supply power or supply power after passing through the Buck-Boost DC-DC converter.

[0032] In a preferred embodiment of the composite power system, the lithium battery pack is transformed by the Buck-Boost DC-DC converter to power the supercapacitor by controlling the opening and closing of the N-MOSFET switch SW2.

[0033] In a preferred embodiment of the composite power system, the load is connected in parallel across the supercapacitor.

[0034] In a preferred embodiment of the composite power system, the load includes an inverter motor.

[0035] In a preferred embodiment of the composite power system, the operating modes of the composite power system include direct power supply from the lithium battery pack to the supercapacitor, power supply from the lithium battery pack alone, power supply from the supercapacitor alone, power supply from the lithium battery after being transformed by a Buck-Boost DC-DC converter, and power supply from the supercapacitor alone for regenerative braking.

[0036] In a preferred embodiment of the composite power supply system, when the lithium battery pack is directly powered by the N-MOSFET switch SW1, the N-MOSFET switch SW1 is turned on and the N-MOSFET switch SW2 is turned off. The current flowing out from the load returns to the negative terminal of the lithium battery pack after passing through the diode D4, forming a circuit.

[0037] In a preferred embodiment of the composite power supply system, when the lithium battery pack is powered by the Buck-Boost DC-DC converter, the N-MOSFET switch SW1 remains off. The duty cycle of the N-MOSFET switch SW2 is controlled to achieve boost or buck output of the lithium battery pack. In the transformer output, when the N-MOSFET switch SW2 is turned on, the lithium battery pack, the N-MOSFET switch SW2, and the inductor L form a circuit, and the supercapacitor supplies power to the load alone. When the N-MOSFET switch SW2 is turned off, the direction of the induced electromotive force on the inductor L changes, and the current flows out from under the inductor L, passes through diode D5, and then outputs power. The current then flows back to the other end of the inductor L through diode D3 to form a circuit.

[0038] In a preferred embodiment of the composite power supply system, the duty cycle of the N-MOSFET switch SW2 is controlled to be greater than or less than 0.5, so that the lithium battery pack can achieve boost or buck output after passing through the Buck-Boost DC-DC converter.

[0039] In one embodiment, the composite power system includes a lithium battery pack, an inductor L, a supercapacitor, N-MOSFET switches SW1 and SW2, and diodes D1, D2, D3, D4, and D5; wherein the anode of diode D2 and the cathode of diode D3 are connected to the source of the N-MOSFET switch and one end of the inductor L, the cathode of diode D2 is connected to the drain of the N-MOSFET switch, and the anodes of diodes D3 and D4 form the negative output terminal of the Buck-Boost DC-DC converter, which is connected to the supercapacitor L. The supercapacitor and the negative terminal of the load are connected. The other end of the inductor L is connected to the negative terminal of the DC-DC boost converter, which consists of the negative terminal of diode D4 and the positive terminal of diode D5. The negative terminal of diode D5 is the positive terminal of the Buck-Boost DC-DC converter output, and is connected to the positive terminal of the supercapacitor and the load. The positive terminal of the lithium battery is connected to the drain of N-MOSFET switch SW1 and the negative terminal of diode D1. The negative terminal of the lithium battery is connected to the lower end of inductor L. The source of N-MOSFET switch SW1 and the positive terminal of diode D1 are connected to the negative terminal of diode D5.

[0040] The required power is determined by acquiring the bus voltage through the voltage acquisition module and the bus current through the current acquisition module; the state of charge (SOC) of the supercapacitor and the lithium battery pack is calculated by acquiring the supercapacitor voltage through the voltage acquisition module and the lithium battery pack output current change through the current acquisition module.

[0041] When the power demand is greater than zero, the system assesses the required power level and the state of charge (SOC) of the supercapacitor and lithium battery pack. If the supercapacitor's SOC exceeds 90% or the required power reaches a high-power level, the supercapacitor will provide power independently. Figure 2 As shown; at this time, both the N-MOSFET switch SW1 and the Buck-Boost DC-DC converter are in the off state.

[0042] As the supercapacitor discharges for a period of time and its SOC drops below 90%, the hybrid power system switches to a combined output power mode of the lithium battery pack and the supercapacitor. If the terminal voltage of the lithium battery pack matches the output voltage of the supercapacitor, the N-MOSFET switch SW1 turns on, and the lithium battery pack and the supercapacitor jointly output power. Figure 3 As shown.

[0043] Because the voltage of a supercapacitor decays rapidly during discharge, it needs to be recharged when its state of charge (SOC) drops below 30%. At this point, the hybrid power system supplies power to the load from the lithium battery pack while simultaneously charging the supercapacitor. Figure 4 As shown. When the lithium battery pack outputs power during this period, the current returns to the negative terminal of the battery through diode D4 in the rectifier circuit within the Buck-Boost DC-DC converter.

[0044] When the lithium battery pack continuously supplies power to the supercapacitor and the load output, if the terminal voltage of the supercapacitor continues to recover to a higher level while the terminal voltage of the lithium battery pack decreases, the lithium battery pack will then supply power to the load after being boosted by the Buck-Boost DC-DC converter. The operating states of the Buck-Boost DC-DC converter are shown in Figures 5(a) and 5(b). When the N-MOSFET switch SW2 is on, the lithium battery pack and inductor L form a circuit; when the N-MOSFET switch SW2 is off, the induced current in inductor L flows out from below, passes through diode D5 in the rectifier circuit to supply power to the supercapacitor and the load, and then returns to the other end of the inductor after passing through diode D3 in the rectifier circuit. By controlling the duty cycle of the N-MOSFET switch SW2 to be greater than or less than 0.5, the lithium battery pack can achieve boost or buck output after passing through the Buck-Boost DC-DC converter.

[0045] When the power demand is less than zero during the braking phase, the supercapacitor recovers the braking energy. At this time, both N-MOSFET switches SW1 and SW2 are turned off, and neither the lithium battery nor the Buck-Boost DC-DC converter works.

[0046] like Figure 6As shown, in one embodiment, the operating modes of the hybrid power system can be divided into: direct power supply from the lithium battery to the supercapacitor, power supply from the lithium battery alone, power supply from the supercapacitor alone, power supply from the lithium battery after being transformed by a Buck-Boost DC-DC converter, and power supply from the supercapacitor alone to recover braking energy. When the power demand is greater than zero, voltage matching between the lithium battery pack and the supercapacitor is detected. At this time, N-MOSFET switch SW1 is turned on and N-MOSFET switch SW2 is turned off, and the lithium battery pack directly supplies power to the load through the supercapacitor. When discharging, the output voltage of the lithium battery pack and the supercapacitor are mismatched. The lithium battery pack is transformed by the Buck-Boost DC-DC converter and then jointly supplies power to the supercapacitor. At this time, N-MOSFET switch SW1 is turned off. After the supercapacitor discharges, its output voltage drops, and the lithium battery pack supplies power to both the supercapacitor and the load simultaneously. When a higher power demand is reached, the supercapacitor supplies power alone according to its characteristics. At this time, both N-MOSFET switches SW1 and SW2 are turned off. When the power demand is less than zero, the supercapacitor recovers braking energy. At this time, both N-MOSFET switches SW1 and SW2 are turned off.

[0047] Although embodiments of the present invention have been described above in conjunction with the accompanying drawings, the present invention is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, and not restrictive. Those skilled in the art can make many other forms based on the guidance of this specification and without departing from the scope of protection of the claims of the present invention, and all of these are within the scope of protection of the present invention.

Claims

1. A composite power supply system, characterized in that, It includes a lithium battery pack, an N-MOSFET switch SW1, a diode D1, a Buck-Boost DC-DC converter, and a supercapacitor. The positive terminal of the lithium battery pack is connected to the positive input terminal of the Buck-Boost DC-DC converter, the drain of the N-MOSFET switch SW1, and the negative terminal of the diode D1. The negative terminal of the lithium battery is connected to the negative input terminal of the Buck-Boost DC-DC converter. The source of the N-MOSFET switch SW1 and the positive terminal of the diode D1 are connected to the positive output terminal of the Buck-Boost DC-DC converter. The positive terminal of the supercapacitor is connected to the source of the N-MOSFET switch SW1, the positive terminal of the diode D1, and the positive output terminal of the Buck-Boost DC-DC converter. The negative terminal of the supercapacitor is connected to the negative output terminal of the Buck-Boost DC-DC converter. By controlling the opening and closing of the N-MOSFET switches SW1 and SW2, the lithium battery pack can directly output power or supply power after passing through the Buck-Boost DC-DC converter. The Buck-Boost DC-DC converter includes an inductor L, an N-MOSFET switch SW2, diodes D2, D3, D4, and D5. The anode of diode D2 and the cathode of diode D3 are connected to the source of the N-MOSFET switch and one end of the inductor L. The cathode of diode D2 is connected to the drain of the N-MOSFET switch and forms the positive input terminal of the Buck-Boost DC-DC converter. The anodes of diodes D3 and D4 form the negative output terminal of the Buck-Boost DC-DC converter. The other end of the inductor L is connected to the negative input terminal formed by the cathode of diode D4 and the anode of diode D5. The cathode of diode D5 serves as the positive output terminal of the Buck-Boost DC-DC converter.

2. The composite power supply system according to claim 1, characterized in that, Diodes D3, D4, and D5 form a rectifier bridge circuit.

3. The composite power supply system according to claim 1, characterized in that, By controlling the turn-on and turn-off of the N-MOSFET switch SW2, the lithium battery pack is transformed by the Buck-Boost DC-DC converter to power the supercapacitor.

4. The composite power supply system according to claim 1, characterized in that, The load is connected in parallel across the supercapacitor.

5. The composite power supply system according to claim 4, characterized in that, The load includes an inverter motor.

6. The composite power supply system according to claim 1, characterized in that, The operating modes of the hybrid power system include direct power supply from the lithium battery pack to the supercapacitor, power supply from the lithium battery pack alone, power supply from the supercapacitor alone, power supply from the lithium battery after being transformed by the Buck-Boost DC-DC converter, and power supply from the supercapacitor alone to recover braking energy.

7. The composite power supply system according to claim 1, characterized in that, When the lithium battery pack is directly powered by the N-MOSFET switch SW1, the N-MOSFET switch SW1 is turned on and the N-MOSFET switch SW2 is turned off. The current flowing out of the load returns to the negative terminal of the lithium battery pack after passing through the diode D4, forming a circuit.

8. The composite power supply system according to claim 1, characterized in that, When the lithium battery pack is powered by the Buck-Boost DC-DC converter, the N-MOSFET switch SW1 remains off. The duty cycle of the N-MOSFET switch SW2 is controlled to achieve boost or buck output of the lithium battery pack. In the transformer output, when the N-MOSFET switch SW2 is turned on, the lithium battery pack, the N-MOSFET switch SW2, and the inductor L form a circuit, and the supercapacitor supplies power to the load alone. When the N-MOSFET switch SW2 is turned off, the direction of the induced electromotive force on the inductor L changes, and the current flows out from under the inductor L, passes through diode D5, and then supplies power. The current then flows back to the other end of the inductor L through diode D3 to form a circuit.

9. The composite power supply system according to claim 1, characterized in that, The duty cycle of the N-MOSFET switch SW2 is controlled to be greater than or less than 0.5, enabling the lithium battery pack to achieve boost or buck output after passing through the Buck-Boost DC-DC converter.

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