Exponential soft start method for dual-active full-bridge DC-DC converter

Abstract

The invention discloses an exponential soft start method for a dual-active full-bridge DC-DC converter, which comprises two full bridges, an inductor and an isolation transformer, and comprises the following steps: when a DAB is started, S1, S4, S5 and S8 are in one group, S2, S3, S6 and S7 are in one group, the states of two groups of switch tubes are complementary, and the coordinated output of a system in the starting process is ensured; meanwhile, the control circuit performs exponential control on the effective duty ratio rising curve of the PWM starting voltage of the two groups of switch tubes, so that the voltage of the control signal is smoothly increased in the starting process. Two groups of PWM duty ratios with a large difference value are set at the beginning of starting, so that the difference value between the two groups of PWM duty ratios is exponentially and smoothly reduced along with time, and finally, the two groups of PWM duty ratios are both changed into 0.5. The method is applicable to the control of only one group of PWM or two groups of PWM, has low requirements on a control algorithm and hardware, can quickly establish voltage, and is relatively quick to start.

Description

Technical Field

[0001] The present invention relates to a dual active full bridge (DAB) DC-DC converter, and in particular to an exponential soft starting method for the dual active full bridge DC-DC converter. Background Art

[0002] The Dual Active Bridge (DAB) DC-DC converter is a topology widely used in high power density power conversion systems. It has the advantages of high efficiency, high power density, and bidirectional energy flow. It is usually used in electric vehicles, power systems, and energy storage systems. It consists of two full bridges, an inductor, and an isolation transformer. The specific switch tube number and topology are as follows: Figure 1 shown.

[0003] In a DAB converter, during initial startup, the electronic components are usually subjected to a large current surge due to a sudden change in current, which increases device losses and shortens their service life. In addition, this surge current may also cause problems such as switch damage and magnetic component saturation, affecting system stability. To solve the current overshoot problem, it is usually necessary to introduce a soft start solution to make the current rise smoothly.

[0004] Existing technology and defects:

[0005] The existing DAB soft start methods are mainly phase-shift soft start or high-frequency soft start. Phase-shift soft start gradually increases power transmission by adjusting the phase difference between the two full bridges to control the current during the startup process. However, phase-shift soft start requires the PWM signals of the two full bridges to be controlled separately, which has high requirements for the control algorithm and hardware, and is not applicable to DAB with only one set of PWM control. High-frequency soft start uses a switching frequency higher than the normal working frequency. Although it can effectively suppress the current rise and reduce the impact current, the switching loss of the power device will increase, and the startup process will take a long time, resulting in low startup efficiency.

[0006] In addition, although the existing DAB soft-start solution can control the rise of current, the changes in the startup process are not smooth enough, and there is a risk of exacerbating system instability; although the current can be suppressed, the current response speed and control accuracy cannot be controlled.

[0007] It can be seen that the existing solutions have shortcomings in terms of smoothness and response time during the startup process. A more efficient and smooth soft start solution is needed to meet the strict requirements of complex application scenarios.

[0008] In view of this, the present invention is proposed. Summary of the invention

[0009] The object of the present invention is to provide an exponential soft-start method for a dual-active full-bridge DC-DC converter to solve the above-mentioned technical problems existing in the prior art.

[0010] The objective of the present invention is achieved through the following technical solutions:

[0011] The dual active full-bridge DC-DC converter exponential soft-start method of the present invention comprises two full bridges composed of eight switch tubes S1, S2, S3, S4, S5, S6, S7 and S8, an inductor Lr and an isolation transformer T;

[0012] The switch tubes S1-S4 form a primary full bridge, the switch tubes S5-S8 form a secondary full bridge, and the inductor Lr and the high-frequency transformer T connect the primary full bridge and the secondary full bridge;

[0013] The switch tube S1 is coupled between the input terminal and the primary inductor Lr, the switch tube S2 is coupled between the switch tube S1 and the ground terminal, the switch tube S3 is coupled between the input terminal and the high-frequency transformer T, and the switch tube S4 is coupled between the switch tube S3 and the ground terminal;

[0014] The switch tube S5 is coupled between the secondary full-bridge input terminal and the output voltage, the switch tube S6 is coupled between the switch tube S5 and the ground terminal, the switch tube S7 is coupled between the secondary full-bridge input terminal and the high-frequency transformer T, and the switch tube S8 is coupled between the switch tube S7 and the ground terminal;

[0015] The soft start method of exponentially dynamically adjusting the duty cycle of the dual active full-bridge DC-DC converter includes:

[0016] When DAB starts, the switch tubes S1, S4, S5, and S8 form a group, and the switch tubes S2, S3, S6, and S7 form a group. The states of the two groups of switch tubes complement each other to ensure the coordinated output of the system during the startup process.

[0017] At the same time, the control circuit performs exponential control on the effective duty cycle rising curve of the PWM starting voltage of the two groups of switch tubes, so that the voltage of the control signal increases smoothly during the starting process.

[0018] Compared with the prior art, the dual-active full-bridge DC-DC converter exponential soft-start method provided by the present invention is applicable under the control of only one or two groups of PWM, has low requirements on the control algorithm and hardware, can quickly establish voltage, and starts quickly. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a dual active full-bridge DC-DC converter topology;

[0020] Figure 2The PWM control signal startup process of two groups of switch tubes of DAB in the embodiment of the present invention is shown in the figure: (a) initial startup; (b) startup steady state;

[0021] Figure 3 It is a schematic diagram of exponential increase of effective duty cycle of PWM control signal according to an embodiment of the present invention;

[0022] Figure 4 1 is a comparison diagram of voltage and current waveforms of hard start and soft start of the present invention; in the figure, (a) hard start; (b) soft start of the present invention. DETAILED DESCRIPTION

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the drawings in the embodiments of the present invention; it is obvious that the described embodiments are only part of the embodiments of the present invention, not all of the embodiments, which does not constitute a limitation of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0024] First, the terms that may be used in this article are explained as follows:

[0025] The term “and / or” means that either or both of them can be realized at the same time. For example, X and / or Y means both “X” or “Y” and “X and Y”.

[0026] The terms "include", "comprises", "contains", "has" or other descriptions with similar semantics should be interpreted as non-exclusive inclusion. For example, including certain technical feature elements (such as raw materials, components, ingredients, carriers, dosage forms, materials, dimensions, parts, components, mechanisms, devices, steps, procedures, methods, reaction conditions, processing conditions, parameters, algorithms, signals, data, products or products, etc.) should be interpreted as including not only certain technical feature elements explicitly listed, but also other technical feature elements known in the art that are not explicitly listed.

[0027] The term "consisting of..." means excluding any technical feature elements not explicitly listed. If this term is used in a claim, it will make the claim closed, so that it does not contain technical feature elements other than the technical feature elements explicitly listed, except for the conventional impurities related to them. If this term only appears in a clause of a claim, it only limits the elements explicitly listed in the clause, and the elements recorded in other clauses are not excluded from the overall claim.

[0028] The contents not described in detail in the examples of the present invention belong to the prior art known to professionals in the field. If no specific conditions are specified in the examples of the present invention, the conditions are carried out according to the conventional conditions in the field or the conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used in the examples of the present invention, they are all conventional products that can be purchased commercially.

[0029] The dual active full-bridge DC-DC converter exponential soft-start method of the present invention comprises two full bridges composed of eight switch tubes S1, S2, S3, S4, S5, S6, S7 and S8, an inductor Lr and an isolation transformer T;

[0030] The switch tubes S1-S4 form a primary full bridge, the switch tubes S5-S8 form a secondary full bridge, and the inductor Lr and the high-frequency transformer T connect the primary full bridge and the secondary full bridge;

[0031] The switch tube S1 is coupled between the input terminal and the primary inductor Lr, the switch tube S2 is coupled between the switch tube S1 and the ground terminal, the switch tube S3 is coupled between the input terminal and the high-frequency transformer T, and the switch tube S4 is coupled between the switch tube S3 and the ground terminal;

[0032] The switch tube S5 is coupled between the secondary full-bridge input terminal and the output voltage, the switch tube S6 is coupled between the switch tube S5 and the ground terminal, the switch tube S7 is coupled between the secondary full-bridge input terminal and the high-frequency transformer T, and the switch tube S8 is coupled between the switch tube S7 and the ground terminal;

[0033] The soft start method of exponentially dynamically adjusting the duty cycle of the dual active full-bridge DC-DC converter includes:

[0034] When DAB starts, the switch tubes S1, S4, S5, and S8 form a group, and the switch tubes S2, S3, S6, and S7 form a group. The states of the two groups of switch tubes complement each other to ensure the coordinated output of the system during the startup process.

[0035] At the same time, the control circuit performs exponential control on the effective duty cycle rising curve of the PWM starting voltage of the two groups of switch tubes, so that the voltage of the control signal increases smoothly during the starting process.

[0036] At the beginning of startup, two groups of PWM duty cycles with larger differences are set, so that the difference between the two groups of PWM duty cycles decreases exponentially and smoothly over time, and finally the two groups of PWM duty cycles both become 0.5.

[0037] Assuming that the effective duty cycle of one set of PWM is D, the other set is 1-D, so that the effective duty cycle D increases exponentially to the desired effective duty cycle.

[0038] In summary, the exponential soft-start method for the dual-active full-bridge DC-DC converter of the embodiment of the present invention is applicable regardless of whether there is only one or two PWM control groups, and has low requirements on the control algorithm and hardware, and can quickly establish voltage and start quickly.

[0039] In order to more clearly demonstrate the technical solution and technical effects provided by the present invention, the embodiments of the present invention are described in detail with specific embodiments below.

[0040] Example 1

[0041] like Figures 1 to 4 As shown:

[0042] Dual Active Bridge (DAB) DC-DC converter exponential dynamic duty cycle soft start scheme:

[0043] When DAB starts, S1, S4, S5, and S8 form a group, and S2, S3, S6, and S7 form a group. The states of the two groups of switch tubes are complementary to ensure the coordinated output of the system during the startup process. At the same time, the control circuit exponentially controls the effective duty cycle rising curve of the PWM startup voltage, so that the voltage of the control signal increases smoothly during the startup process.

[0044] At the beginning of startup, set two sets of PWM duty cycles with large differences, such as Figure 2 As shown in (a), the difference between the two sets of PWM duty cycles decreases exponentially over time, and finally the two sets of PWM duty cycles become 0.5, as shown in Figure 2 As shown in (b), limiting the effective duty cycle of one group at the initial startup and limiting the current rise can effectively limit the inrush current. During the voltage establishment process, the effective duty cycle of the group is increased exponentially until the effective duty cycle reaches about 0.5 and enters a steady state.

[0045] like Figure 3 As shown in the figure, assuming that one group of PWM effective duty cycle is D, the other group is 1-D, so that the effective duty cycle D increases exponentially to the desired effective duty cycle. For example, if the initial setting of one group of PWM duty cycle is set to 0.1, and the effective duty cycle needs to be increased from 0.1 to 0.5, it only needs to increase smoothly according to the exponential curve.

[0046] Testing and experimental verification:

[0047] The soft start scheme proposed in the present invention is simulated and tested. Figure 4 As shown:

[0048] First, before the system starts, the exponential function is initialized, and the exponential growth rate, initial control signal duty cycle and other parameters are set according to the system characteristics and startup requirements. After the system starts, the control circuit modulates the duty cycle of the PWM control voltage signal through the exponential function, so that it increases from the initial value to the target value, ensuring the stability of the power circuit output.

[0049] Depend on Figure 4 It can be seen that when soft start protection is not adopted, the impact current can reach 2000A, while the impact current of the exponential soft start scheme is less than 500A, which is less than 40% of the hard start, verifying the effectiveness of the exponential soft start scheme of the present invention in reducing the impact current during DAB startup.

[0050] It can be seen that compared with the traditional soft start solution, the exponential soft start can more smoothly control the voltage change during the startup process, reduce current shock and voltage stress. The fast response characteristics of the exponential function also enable the converter to achieve stable output in a shorter time, which is suitable for scenarios with strict requirements on startup time.

[0051] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by any technician familiar with the technical field within the technical scope disclosed in the present invention should be included in the protection scope of the present invention. Therefore, the protection scope of the present invention should be based on the protection scope of the claims. The information disclosed in the background technology section of this article is only intended to deepen the understanding of the overall background technology of the present invention, and should not be regarded as an admission or in any form that the information constitutes prior art known to those skilled in the art.

Claims

1. A dual active full-bridge DC-DC converter exponential soft-start method, characterized in that: The dual active full bridge includes two full bridges composed of eight switch tubes S1, S2, S3, S4, S5, S6, S7, S8, an inductor Lr and an isolation transformer T; The switch tubes S1-S4 form a primary full bridge, the switch tubes S5-S8 form a secondary full bridge, and the inductor Lr and the high-frequency transformer T connect the primary full bridge and the secondary full bridge; The switch tube S1 is coupled between the input terminal and the primary inductor Lr, the switch tube S2 is coupled between the switch tube S1 and the ground terminal, the switch tube S3 is coupled between the input terminal and the high-frequency transformer T, and the switch tube S4 is coupled between the switch tube S3 and the ground terminal; The switch tube S5 is coupled between the secondary full-bridge input terminal and the output voltage, the switch tube S6 is coupled between the switch tube S5 and the ground terminal, the switch tube S7 is coupled between the secondary full-bridge input terminal and the high-frequency transformer T, and the switch tube S8 is coupled between the switch tube S7 and the ground terminal; The soft start method of exponentially dynamically adjusting the duty cycle of the dual active full-bridge DC-DC converter includes: When DAB starts, the switch tubes S1, S4, S5, and S8 form a group, and the switch tubes S2, S3, S6, and S7 form a group. The states of the two groups of switch tubes complement each other to ensure the coordinated output of the system during the startup process. At the same time, the control circuit performs exponential control on the effective duty cycle rising curve of the PWM starting voltage of the two groups of switch tubes, so that the voltage of the control signal increases smoothly during the starting process.

2. The exponential soft-start method for a dual active full-bridge DC-DC converter according to claim 1, characterized in that: At the beginning of startup, two groups of PWM duty cycles with larger differences are set, so that the difference between the two groups of PWM duty cycles decreases exponentially and smoothly over time, and finally the two groups of PWM duty cycles both become 0.

5.

3. The exponential soft-start method for a dual active full-bridge DC-DC converter according to claim 2, wherein: Assuming that the effective duty cycle of one set of PWM is D, the other set is 1-D, so that the effective duty cycle D increases exponentially to the desired effective duty cycle.

Images