DC-DC converter based on coupled inductors and control method

Abstract

This invention discloses a DC-DC converter and control method based on coupled inductors, comprising a capacitor connected in parallel across the low-voltage side; the capacitor is also connected in parallel across the high-voltage side; the coupled inductor module includes a first winding and a second winding mounted on the same magnetic core, one end of the first winding being connected to the midpoint of a first switch and a second switch, and one end of the second winding being connected to the midpoint of a third switch and a fourth switch; the other ends of the first winding and the second winding are connected to form a common connection point, which is connected to a reference potential terminal on the high-voltage side; the high-voltage side transmits electrical energy to the high-voltage side through the first bridge arm, the second bridge arm, and the coupled inductor module; this invention winds two inductors on the same magnetic core to form mutual inductance, replacing two independent filter inductors or energy storage inductors in traditional circuits with coupled inductors, significantly reducing the size and weight of magnetic devices and increasing power density.

Description

Technical Field

[0001] This invention relates to a DC-DC converter and control method based on coupled inductors, belonging to the field of converter technology. Background Technology

[0002] In high-power renewable energy applications such as new energy vehicles and energy storage systems, the demand for high-power-density, bidirectional DC-DC converters is becoming increasingly urgent. These converters need to achieve efficient, rapid, and customized charging and discharging of the power battery within the limited space of the vehicle, thereby maximizing the benefits of precious battery energy. Therefore, the industry's core requirements for converters can be summarized as: high power, small size, light weight, and low cost.

[0003] In existing technologies, the use of a four-switch Buck-Boost topology to achieve bidirectional buck-boost functionality has become mainstream. To further improve power ratings and reduce current ripple, two-phase interleaved parallel connection technology is widely used. However, this approach has a fundamental bottleneck: the size and weight of the magnetic components.

[0004] Traditional two-phase interleaved inductors typically employ two independent filter inductors. This leads to the following prominent problems: 1. Size and weight disadvantages: The two completely independent inductors and their magnetic cores occupy a considerable amount of space and weight in the converter, which directly restricts the further improvement of the system power density.

[0005] 2. Cost and Consistency Challenges: Two independent magnetic components are required, resulting in higher material and assembly costs. Furthermore, even slight deviations in the two inductor parameters (such as inductance and saturation point) can affect the precise balance of the two-phase current, leading to unsatisfactory ripple cancellation. This necessitates more sophisticated devices or complex control systems for compensation, increasing system complexity and cost.

[0006] 3. Optimize the ceiling: Existing interleaved parallel schemes focus their optimization on switching devices and control algorithms, but lack fundamental structural optimization of the inductive devices that occupy the majority of the volume.

[0007] Therefore, how to revolutionize the size and weight of magnetic components while inheriting the advantages of high power and low ripple of interleaved parallel technology has become a key challenge to promote the development of high-power DC-DC technology in vehicles. Summary of the Invention

[0008] The purpose of this invention is to overcome the problem of low power per unit volume in existing DC-DC converters and to provide a DC-DC converter and control method based on coupled inductors. To achieve the above objectives / to solve the above technical problems, the present invention is implemented using the following technical solution:

[0009] First aspect: A DC-DC converter based on a coupled inductor, comprising a low-voltage side, a high-voltage side, a first bridge arm, a second bridge arm, a first capacitor, a second capacitor, and a coupled inductor module, wherein the first capacitor is connected in parallel across the low-voltage side; and the second capacitor is connected in parallel across the high-voltage side. The first bridge arm is composed of a first switch and a second switch connected in series, and the second bridge arm is composed of a third switch and a fourth switch connected in series; The coupled inductor module includes a first winding and a second winding disposed on the same magnetic core. One end of the first winding is connected to the midpoint of the first and second switching transistors, and one end of the second winding is connected to the midpoint of the third and fourth switching transistors. The other end of the first winding is connected to the other end of the second winding to form a common connection point, which is connected to the reference potential terminal on the high voltage side; The high-voltage side transmits electrical energy to the high-voltage side through the first bridge arm, the second bridge arm, and the coupling inductor module.

[0010] Optionally, the common connection point is formed by connecting the same-named end of the first winding and the opposite-named end of the second winding, or the common connection point is formed by connecting the opposite-named end of the first winding and the same-named end of the second winding.

[0011] Optionally, a current detection unit is also included, which is connected in series between the low-voltage side and the coupling inductor module to detect the current flowing through the coupling inductor module.

[0012] Optionally, the first, second, third, and fourth switching transistors can all be any one of power MOSFETs, IGBTs, or GaN devices.

[0013] Optionally, the first and third switching transistors are used as upper bridge arm switching transistors and connected to the positive potential on the high voltage side. The second and fourth switching transistors serve as lower bridge arm switching transistors and are connected to the negative potential on the high-voltage side.

[0014] Optionally, the drive signals of the first bridge arm and the second bridge arm have a fixed phase difference.

[0015] Optionally, the phase difference is 180 degrees.

[0016] Second aspect: A control method for a DC-DC converter based on coupled inductors, the method comprising: Step S1: The controller generates the first PWM drive signal and the second PWM drive signal; Step S2: Use the first PWM drive signal to control the operation of the switching transistor in the first bridge arm, and use the second PWM drive signal to control the operation of the switching transistor in the second bridge arm; Step S3: Set the first PWM drive signal and the second PWM drive signal to have the same switching period and the same duty cycle; Step S4: In phase control, the second PWM drive signal is delayed by T / 2 switching cycles relative to the first PWM drive signal; Step S5: Under the 180° phase-interleaved drive, the current ripple component flowing through the first winding in the coupled inductor module is out of phase with the current ripple component flowing through the second winding. Step S6: Use the current ripple components with opposite phases to generate alternating magnetic flux in opposite directions in the common magnetic core, so that the alternating magnetic flux cancels each other out inside the magnetic core.

[0017] Optionally, in step S4, when the duty cycle varies within the range of 0 to 1, the controller always maintains a phase difference of 180° between the first PWM drive signal and the second PWM drive signal to achieve the cancellation effect of AC magnetic flux within the magnetic core.

[0018] Optionally, a current balancing step is also included: using the mutual inductance coupling characteristics between the first winding and the second winding in the coupled inductor module to suppress the current imbalance between the two bridge arms caused by differences in device parameters.

[0019] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: This invention winds two inductors around the same magnetic core to form mutual inductance, replacing the two independent filter inductors or energy storage inductors in traditional circuits with coupled inductors. This significantly reduces the size and weight of magnetic devices and increases power density. Because the AC magnetic flux in the magnetic core is largely canceled out, the magnetic core is less prone to saturation. Smaller magnetic cores can be used for the same power, or greater power can be carried without increasing the size. This reduces the size and weight by about 20%-40% compared to the two independent inductor solutions, directly overcoming the space and weight bottlenecks in automotive applications.

[0020] This invention retains the advantage of two-phase interleaved parallel connection, which is easy to expand to more phases. At the same time, the integration of magnetic components reduces the number of parts, simplifies the production and assembly process, and reduces material and management costs.

[0021] The two windings of the coupled inductor in this invention have strong magnetic coupling, which means that changes in the current of one phase will affect the other phase through mutual inductance. This physical characteristic generates a natural current balancing trend. Combined with peak current mode control, the system can achieve excellent current sharing performance without additional complex current sharing circuits, reducing the stringent requirements for the consistency of switching transistor and inductor parameters, and improving the overall reliability and production yield.

[0022] With the combined effect of magnetic flux cancellation and self-current equalization, the input and output current ripple of this invention are further suppressed, the demand for filter capacitors is reduced, and the system efficiency and electromagnetic compatibility are improved simultaneously. Attached Figure Description

[0023] Figure 1 The diagram shown is a schematic of the DC-DC converter circuit structure of the present invention. Figure 2 The diagram shown is a schematic of the drive signals for the two bridge arms of the DC-DC converter of the present invention. Detailed Implementation

[0024] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0025] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0026] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] like Figure 1 As shown, this invention discloses a DC-DC converter based on coupled inductors. Through an integrated solution of "coupled inductors + specific timing control," it fundamentally optimizes magnetic components while maintaining the advantages of a two-phase interleaved parallel architecture. The core of this invention lies in integrating two filter inductors into a single magnetic core via magnetic circuit coupling, and applying 180° interleaved, current-mode-based specific timing control to create a synergistic effect between the hardware structure and the control strategy, specifically on both the low-voltage and high-voltage sides. The first capacitor C1 is connected in parallel across the two ends of the low-voltage side; The second capacitor C2 is connected in parallel across the high-voltage side. The first bridge arm is composed of a first switch S1 and a second switch S2 connected in series. The common connection point of the first switch S1 and the second switch S2 is defined as the first midpoint M1. The second bridge arm is composed of a third switch S3 and a fourth switch S4 connected in series, and the common connection point of the third switch S3 and the fourth switch S4 is defined as the second midpoint M2. A coupled inductor module, comprising a first winding La and a second winding Lb disposed on the same magnetic core; Wherein, one end of the first winding La is connected to the first midpoint M1, and one end of the second winding Lb is connected to the second midpoint M2; The other end of the first winding La and the other end of the second winding Lb are connected to each other to form a common connection point M3, which is connected to the reference potential terminal on the low voltage side. The low-voltage side transmits electrical energy to the high-voltage side through the first bridge arm, the second bridge arm, and the coupling inductor module.

[0028] In this embodiment, the first winding La and the second winding Lb have a defined polarity of the same terminal when wound on the magnetic core; the common connection point is formed by connecting the same terminal (or opposite terminal) of the first winding La and the opposite terminal (or same terminal) of the second winding Lb, so that the two windings generate magnetic flux mutual assistance or mutual cancellation effect when the circuit is working to suppress current ripple; the black dot (•) in the figure represents the same terminal.

[0029] In this embodiment, a current detection unit is also included. The current detection unit is connected in series between the input terminal and the coupling inductor module, or in series between the first winding La and / or the second winding Lb and the midpoint of the corresponding bridge arm, for detecting the current flowing through the coupling inductor module.

[0030] In this embodiment, the first switch S1, the second switch S2, the third switch S3, and the fourth switch S4 are all any one of power MOSFETs, IGBTs, or GaN devices.

[0031] In this embodiment, the first bridge arm and the second bridge arm are connected in parallel across the input first capacitor C1; the first switch S1 and the third switch S3 serve as upper bridge arm switches and are connected to the input positive potential; the second switch S2 and the fourth switch S4 serve as lower bridge arm switches and are connected to the input negative potential or ground.

[0032] In this embodiment, the coupled inductor module replaces the two discrete inductors that are connected in series on the output paths of the first and second bridge arms respectively in the traditional circuit, and achieves a reduction in size and an increase in power density through a single magnetic core integrated structure.

[0033] In this embodiment, the converter is configured in an interleaved parallel control mode, and the drive signals of the first bridge arm and the second bridge arm have a fixed phase difference. The mutual inductance characteristics of the coupled inductor module are used to achieve automatic balancing of the two currents and cancellation of the output current ripple.

[0034] Example 2, as Figure 2 As shown, a control method for a DC-DC converter based on coupled inductors is disclosed, including the following steps: Step S1: The controller generates a first PWM drive signal (PWM1) and a second PWM drive signal (PWM2). Step S2: Use the first PWM drive signal (PWM1) to control the operation of the switching transistor in the first bridge arm, and use the second PWM drive signal (PWM2) to control the operation of the switching transistor in the second bridge arm; Step S3: Set the first PWM drive signal (PWM1) and the second PWM drive signal (PWM2) to have the same switching period T and the same duty cycle D (D=Ton / T). Step S4: In phase control, the second PWM drive signal (PWM2) is strictly delayed by half a switching cycle (T / 2) relative to the first PWM drive signal (PWM1), that is, a 180° phase interleaving is maintained; Step S5: Under the 180° phase-interleaved drive, the current ripple component flowing through the first winding La in the coupled inductor module is out of phase with the current ripple component flowing through the second winding Lb. Step S6: Using current ripple components with opposite phases to generate AC magnetic flux in opposite directions in the common magnetic core, the AC magnetic flux cancels each other out inside the magnetic core, thereby reducing the physical volume requirement of the coupled inductor module while maintaining the same output current ripple index, or increasing the equivalent inductance and dynamic response speed of the converter with the same physical volume.

[0035] In step S4, when the duty cycle D varies within the range of 0 to 1, the controller always maintains a phase difference of 180° between the first PWM drive signal (PWM1) and the second PWM drive signal (PWM2) to ensure that the cancellation effect of AC magnetic flux in the core can be achieved throughout the entire operating range.

[0036] The control method in this embodiment also includes a current balancing step: by utilizing the mutual inductance coupling characteristics between the first winding La and the second winding Lb in the coupled inductor module, the current imbalance between the two bridge arms caused by the difference in device parameters is automatically suppressed, without the need for an additional independent current sharing control loop.

[0037] Through the aforementioned hardware and software co-design, this invention achieves the following significant benefits: 1. Significantly reduced size and weight of magnetic devices, and increased power density: Because the AC magnetic flux in the core is largely canceled out, the core is less prone to saturation, allowing for the use of smaller cores for the same power output, or enabling the carrying of greater power without increasing size. The size and weight of inductive devices can be reduced by approximately 20%-40% compared to two independent inductor solutions, directly overcoming the space and weight bottlenecks in automotive applications.

[0038] 2. Easy to expand power capacity and save system costs: This invention retains the advantage of easily expanding to more phases by using two-phase interleaved parallel connection. At the same time, the integration of magnetic components reduces the number of parts, simplifies the production and assembly process, and reduces material and management costs.

[0039] 3. Achieving "Self-Current Sharing" and Enhancing Reliability: The strong magnetic coupling between the two windings of the coupled inductor means that changes in the current of one phase will affect the other phase through mutual inductance. This physical characteristic creates a natural current balancing tendency. Combined with peak current mode control, the system can achieve excellent current sharing performance without the need for additional complex current sharing circuits. This reduces the stringent requirements for the consistency of switching transistor and inductor parameters, improving overall system reliability and production yield.

[0040] 4. Superior electrical performance: With the combined effect of magnetic flux cancellation and self-current equalization, input and output current ripple is further suppressed, the demand for filter capacitors is reduced, and system efficiency and electromagnetic compatibility (EMI) performance are improved simultaneously.

[0041] This invention deeply integrates "coupled inductors" with "180° staggered peak current control," representing not only an improvement in circuit topology but also a systematic solution addressing the size and weight limitations of high-power automotive DC-DC converters. It achieves miniaturization of magnetic components, simplification of the system, and optimization of performance, possessing significant industrial application value.

[0042] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A DC-DC converter based on coupled inductors, characterized in that, It includes a low-voltage side, a high-voltage side, a first bridge arm, a second bridge arm, a first capacitor (C1), a second capacitor (C2), and a coupling inductor module. The first capacitor (C1) is connected in parallel across the low-voltage side; the second capacitor (C2) is connected in parallel across the high-voltage side. The first bridge arm is composed of a first switch (S1) and a second switch (S2) connected in series, and the second bridge arm is composed of a third switch (S3) and a fourth switch (S4) connected in series. The coupled inductor module includes a first winding (La) and a second winding (Lb) disposed on the same magnetic core. One end of the first winding (La) is connected to the midpoint (M1) of the first switch (S1) and the second switch (S2), and one end of the second winding (Lb) is connected to the midpoint (M2) of the third switch (S3) and the fourth switch (S4). The other end of the first winding (La) is connected to the other end of the second winding (Lb) to form a common connection point (M3), which is connected to the reference potential terminal on the high voltage side. The high-voltage side transmits electrical energy to the high-voltage side through the first bridge arm, the second bridge arm, and the coupling inductor module.

2. The DC-DC converter based on coupled inductors according to claim 1, characterized in that, The common connection point (M3) is formed by connecting the same-named end of the first winding (La) and the opposite-named end of the second winding (Lb), or the common connection point (M3) is formed by connecting the opposite-named end of the first winding (La) and the same-named end of the second winding (Lb).

3. The DC-DC converter based on coupled inductors according to claim 1, characterized in that, It also includes a current detection unit, which is connected in series between the low-voltage side and the coupling inductor module to detect the current flowing through the coupling inductor module.

4. The DC-DC converter based on coupled inductors according to claim 1, characterized in that, The first switch (S1), the second switch (S2), the third switch (S3), and the fourth switch (S4) are all any one of power MOSFET, IGBT, or GaN devices.

5. The DC-DC converter based on coupled inductors according to claim 1, characterized in that, The first switch (S1) and the third switch (S3) serve as upper bridge arm switches and are connected to the positive potential on the high voltage side. The second switch (S2) and the fourth switch (S4) are used as lower bridge arm switches and are connected to the negative potential on the high voltage side.

6. The DC-DC converter based on coupled inductors according to claim 1, characterized in that, The drive signals of the first bridge arm and the second bridge arm have a fixed phase difference.

7. The DC-DC converter based on coupled inductors according to claim 6, characterized in that, The phase difference is 180 degrees.

8. A control method for a DC-DC converter based on a coupled inductor as described in any one of claims 1-7, characterized in that, The method includes: Step S1: The controller generates the first PWM drive signal and the second PWM drive signal; Step S2: Use the first PWM drive signal to control the operation of the switching transistor in the first bridge arm, and use the second PWM drive signal to control the operation of the switching transistor in the second bridge arm; Step S3: Set the first PWM drive signal and the second PWM drive signal to have the same switching period and the same duty cycle; Step S4: In phase control, the second PWM drive signal is delayed by T / 2 switching cycles relative to the first PWM drive signal; Step S5: Under the 180° phase-interleaved drive, the current ripple component flowing through the first winding (La) in the coupled inductor module is out of phase with the current ripple component flowing through the second winding (Lb). Step S6: Use the current ripple components with opposite phases to generate alternating magnetic flux in opposite directions in the common magnetic core, so that the alternating magnetic flux cancels each other out inside the magnetic core.

9. The control method according to claim 8, characterized in that, In step S4, when the duty cycle varies within the range of 0 to 1, the controller always maintains a phase difference of 180° between the first PWM drive signal and the second PWM drive signal, thereby achieving the cancellation effect of AC magnetic flux within the magnetic core.

10. The control method according to claim 8, characterized in that, It also includes a current balancing step: using the mutual inductance coupling characteristics between the first winding (La) and the second winding (Lb) in the coupled inductor module to suppress the current imbalance between the two bridge arms caused by differences in device parameters.

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