Fractional dc-dc conversion topology based on partial power processing and its power control method

Abstract

The application discloses a fractional DC-DC conversion topology based on partial power processing and a power control method thereof. The power control method comprises the following steps: determining the output voltage of a front-stage semi-DAB converter according to the first difference value of the system input voltage and the DC bus voltage; obtaining the system output voltage, comparing the system output voltage with the preset output voltage to obtain the second difference value, inputting the second difference value into a preset proportional-integral controller to obtain the output power standard value; obtaining the voltage conversion ratio according to the input voltage and the output voltage, processing the output power standard value and the voltage conversion ratio by using the KKT algorithm to obtain the optimal phase shift ratio combination of the front-stage semi-DAB converter, so that the rear-stage LLC resonant circuit works at the preset resonant point. In this case, under the premise of keeping the system complexity relatively low, the technical effects of high system efficiency, strong adaptability to a wide input voltage range and wide-range voltage gain capability can be realized.

Description

Technical Field

[0001] This application relates to the field of power electronic converter technology, and in particular to a fractional-stage DC-DC converter topology based on partial power processing and its power control method. Background Technology

[0002] With the continuous development of new energy technologies, power electronics technologies, and high-performance power devices, DC power distribution and DC power conversion technologies have been widely applied in aerospace, new energy power generation, electric transportation, and data centers. Compared with traditional AC power supply systems, DC systems have advantages such as fewer energy conversion stages, simplified control structures, and higher system efficiency, and have gradually become an important development direction for high-performance power supply systems. In DC systems, different power sources and loads often have characteristics such as voltage level differences, power flow changes, and wide range of operating conditions. Therefore, high-performance and highly adaptable DC-DC converters have become key core units in DC power distribution systems.

[0003] Among existing DC-DC converter topologies, the Dual Active Bridge (DAB) converter has been widely studied and applied in medium-to-high power DC-DC conversion scenarios due to its advantages such as symmetrical primary and secondary structure, ease of achieving high-frequency electrical isolation, and inherent support for bidirectional power transfer. A DAB converter typically consists of two sets of full-bridge circuits connected by a high-frequency isolation transformer on the primary and secondary sides. Its power transfer mainly relies on the phase shift between the voltages of the two bridge arms for adjustment, featuring flexible power regulation and fast dynamic response. It is suitable for applications requiring bidirectional energy flow, such as energy storage systems, electric propulsion systems, and multi-terminal DC distribution networks.

[0004] With the continuous improvement of electrification levels in aerospace systems, airborne and spaceborne platforms are increasingly adopting high-voltage DC bus structures, placing higher demands on DC-DC converters in terms of power rating, efficiency, and reliability. In such applications, DAB converters can operate in the power range of several kilowatts to tens of kilowatts and can achieve soft switching through phase-shift control, thereby reducing switching losses. However, under light load conditions or high voltage conversion ratios, DAB converters using traditional single-phase shift control (SPS) tend to generate large circulating currents and reactive power, leading to increased current stress and decreased system efficiency, thus limiting their application performance over a wide operating range.

[0005] Compared to DAB converters, LLC resonant converters, as a typical unidirectional power transfer topology, have been widely used in server power supplies, electric vehicle on-board chargers, and avionics secondary power supplies. Through the proper configuration of resonant inductors and capacitors, LLC resonant converters can achieve zero-voltage turn-on over a wide load range, offering advantages such as high conversion efficiency and low electromagnetic interference; their efficiency near rated operating conditions typically reaches over 95%. However, the operating performance of LLC resonant converters is highly sensitive to the matching relationship between the operating frequency and resonant parameters. When the input voltage or load varies significantly, large-amplitude frequency modulation is required to maintain output stability, which can easily lead to problems such as complex magnetic component design and increased control difficulty. Furthermore, the LLC topology lacks bidirectional power transfer capability, making it difficult to meet the application requirements of energy storage interfaces or multi-terminal DC systems.

[0006] In recent years, Partial Power Processing (PPP) has gained increasing attention to further improve overall system efficiency and reduce stress on power devices. This concept processes only the portion of power in the system that requires regulation, while the remaining power is passed through direct flow or bypass, effectively reducing the power processing ratio of the converter and improving system efficiency. Although PPP structures have shown promising application prospects in photovoltaic systems, DC microgrids, and energy storage interfaces, their topologies and control methods are typically complex, leading to increased system coupling and higher difficulties in stability analysis and engineering implementation. They also face numerous challenges, especially in aerospace applications where reliability requirements are stringent.

[0007] In summary, there is an urgent need to propose a DC-DC conversion technology that can adapt to a wide input voltage range and multiple operating conditions, while ensuring high efficiency and effectively reducing device current stress, so as to meet the application requirements of high-performance DC power supply systems. Summary of the Invention

[0008] The purpose of this application is to provide a fractional-stage DC-DC converter topology based on partial power processing and its power control method, so as to solve the above-mentioned technical problems existing in the prior art. The various technical effects of the preferred technical solutions among the many technical solutions provided in this application are described in detail below.

[0009] To achieve the above objectives, this application provides the following technical solutions: The first aspect of this application discloses a fractional-stage DC-DC converter topology based on partial power processing. The fractional-stage DC-DC converter topology includes a front-stage semi-DAB converter and a rear-stage LLC resonant circuit. The front-stage semi-DAB converter includes a full-bridge circuit on the primary side, an isolation transformer between the primary and secondary sides, and rectifier and power regulation devices on the secondary side. The full-bridge circuit includes power switches S1 and S3 in the upper bridge arm and power switches S2 and S4 in the lower bridge arm. The rectifier and power regulation devices include two parallel power branches. The power branch includes a diode D1 and a power switch S5 connected in series, and the other power branch includes a diode D2 and a power switch S6 connected in series. The subsequent LLC resonant circuit includes a first LLC circuit unit and a second LLC circuit unit arranged symmetrically. Both the first LLC circuit unit and the second LLC circuit unit include a half-bridge inverter circuit, an LLC resonant network, a high-frequency isolation transformer, and a rectifier output circuit connected in sequence. The input side of the first LLC circuit unit is connected in series with the input side of the second LLC circuit unit, and the output side of the first LLC circuit unit is connected in parallel with the second LLC circuit unit.

[0010] In some embodiments, the half-bridge inverter circuit includes two power switching devices, the LLC resonant network includes a resonant inductor, a resonant capacitor, and a magnetizing inductor, and the rectifier output circuit includes four of the power switching devices.

[0011] In some embodiments, the output voltage of the front-stage semi-DAB converter and the system input voltage of the fractional-stage DC-DC converter topology based on partial power processing together constitute the input voltage of the rear-stage LLC resonant circuit.

[0012] The second aspect of this application discloses a power control method applied to a fractional-stage DC-DC converter topology based on partial power processing as described above. The power control method includes: acquiring the system input voltage of the system based on partial power processing of the fractional-stage DC-DC converter topology; determining the output voltage of the preceding semi-DAB converter based on a first difference between the system input voltage and the DC bus voltage; acquiring the system output voltage of the fractional-stage DC-DC converter topology based on partial power processing; comparing the system output voltage with a preset output voltage to obtain a second difference; inputting the second difference into a preset proportional-integral controller to obtain a per-unit output power value; obtaining a voltage conversion ratio based on the input voltage and the output voltage; processing the per-unit output power value and the voltage conversion ratio using a KKT algorithm to obtain an optimal shift ratio combination for the preceding semi-DAB converter; and generating drive signals for each power switch in the preceding semi-DAB converter based on the optimal shift ratio combination to make the subsequent LLC resonant circuit operate at a preset resonant point.

[0013] In some embodiments, the shift ratio combination of the front-end semi-DAB converter includes the shift ratio D1 inside the primary side of the front-end semi-DAB converter, the shift ratio D2 between power switch S1 and power switch S6, and the shift ratio D3 between the rising edge of the switching signal of power switch S1 and power switch S5.

[0014] In some embodiments, the step of processing the per-unit output power and the voltage conversion ratio using the KKT algorithm to obtain the optimal phase shift combination of the front-end semi-DAB converter includes: calculating the corresponding normalized power constraint parameters based on the per-unit output power and the voltage conversion ratio; establishing a normalized peak inductor current objective function based on the normalized power constraint parameters, and constructing a Lagrangian function by combining the operating mode constraints that satisfy the phase shift ratio D3 ≥ the phase shift ratio D2 ≥ the phase shift ratio D1 ≥ 0; processing the Lagrangian function using KKT conditions to solve for the optimal phase shift variables that satisfy the constraints; and obtaining the optimal phase shift combination of the front-end semi-DAB converter based on the optimal phase shift variables.

[0015] In some embodiments, the Lagrange function and the KKT condition are shown in the following equations: Where M is the voltage conversion ratio of the preceding semi-DAB converter. M = N 1 V 2 / V1 ,in N 1 = N p :N s N P and N S , respectively, are the primary and secondary turns of the preceding semi-DAB converter, and p is the normalized output power of the preceding semi-DAB converter.

[0016] In some embodiments, the normalized peak inductor current objective function i c This can be expressed by the following formula: Among them, I peak I is the peak value of the inductor current during a single operating cycle. N This represents the inductor current at the maximum transmittable power under single-phase-shift control.

[0017] In some embodiments, the constraint condition is expressed as: .

[0018] In some embodiments, the expression for the optimal shift ratio combination is: .

[0019] Implementing one of the technical solutions described above in this application has the following advantages or beneficial effects: In this application, the voltage conversion ratio of the front-stage semi-DAB converter is first obtained, then the per-unit output power value is obtained based on the system output voltage. Next, the KKT algorithm is used to process the voltage conversion ratio and the per-unit output power value to obtain the optimal shift ratio combination and drive signal, so that the subsequent LLC resonant circuit operates at a preset resonant point. In other words, by adjusting the operating state of the front-stage semi-DAB converter, this application can effectively regulate the input voltage of the subsequent LLC resonant circuit, enabling the system to adapt to a wider range of input voltage variations and obtain the required voltage gain.

[0020] In this context, while maintaining relatively low system complexity, it can achieve high system efficiency, strong adaptability to a wide input voltage range, and wide-range voltage gain capability. It is particularly suitable for high-performance DC power supply systems with high requirements for efficiency, power density, and power supply performance, such as aerospace, EV charging systems, and renewable energy grid connection, and has high engineering application value. Attached Figure Description

[0021] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings: Figure 1 This is a schematic diagram of the circuit topology of the fractional-stage DC-DC converter topology based on partial power processing according to an embodiment of this application; Figure 2 This is a schematic flowchart of the power control method according to an embodiment of this application; Figure 3 This is another schematic flowchart of the power control method according to an embodiment of this application; Figure 4 This is a schematic diagram of phase-shift control optimized using KKT conditions according to an embodiment of this application.

[0022] In the figure: 1. Fractional DC-DC converter topology based on partial power processing; 10. Front-end semi-DAB converter; 20. Rear-end LLC resonant circuit; 11. Full-bridge circuit on the primary side; 12. Isolation transformer; 13. Rectifier and power regulation device; 21. First LLC circuit unit; 22. Second LLC circuit unit. Detailed Implementation

[0023] To make the objectives, technical solutions, and advantages of this application clearer, various exemplary embodiments described below will be referenced to the accompanying drawings, which form part of the exemplary embodiments and depict various exemplary embodiments that may be adopted to implement this application. Unless otherwise indicated, the same numbers in different drawings represent the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this disclosure. It should be understood that they are merely examples of processes, methods, and apparatuses consistent with some aspects of this application disclosed as detailed in the appended claims, and other embodiments may be used, or structural and functional modifications may be made to the embodiments listed herein without departing from the scope and spirit of this application.

[0024] In the description of this application, it should be understood that the terms "center," "longitudinal," "lateral," etc., indicate the orientation or positional relationship based on the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the referred element must have a specific orientation, or be constructed and operated in a specific orientation. 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. The term "multiple" means two or more. The terms "connected" and "linked" should be interpreted broadly, for example, they can be fixed connections, detachable connections, integral connections, mechanical connections, electrical connections, communication connections, direct connections, indirect connections through an intermediate medium, and can be the internal connection of two elements or the interaction relationship between two elements. The term "and / or" includes any and all combinations of one or more of the related listed items. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.

[0025] To illustrate the technical solutions described in this application, specific embodiments are provided below, showing only the parts related to the embodiments of this application.

[0026] This application relates to a fractional-stage DC-DC converter topology 1 based on partial power processing and its power control method. The fractional-stage DC-DC converter topology 1 based on partial power processing of this application reasonably allocates the system power processing path through the corresponding power control method. Even if the front-end DAB converter is operating in a low-efficiency state, it can still ensure that the overall system maintains a high energy conversion efficiency, thereby meeting the requirements of high-performance DC power supply systems to operate stably and efficiently over a wide input voltage range.

[0027] like Figures 1 to 4 As shown, this application provides a fractional-stage DC-DC converter topology 1 based on partial power processing. The fractional-stage DC-DC converter topology 1 based on partial power processing may include a front-stage semi-DAB converter 10 and a rear-stage LLC resonant circuit 20.

[0028] In some embodiments, the front-end semi-DAB converter 10 may include a full-bridge circuit 11 on the primary side, an isolation transformer 12 between the primary and secondary sides, and a rectifier and power regulation device 13 on the secondary side for realizing unidirectional power transmission.

[0029] The full-bridge circuit 11 may include power switches S1 and S3 in the upper bridge arm, and power switches S2 and S4 in the lower bridge arm.

[0030] The rectifier and power regulation device 13 may include two power branches connected in parallel. One power branch includes a diode D1 and a power switch S5 connected in series, and the other power branch includes a diode D2 and a power switch S6 connected in series.

[0031] Specifically, one end of the isolation transformer 12 is connected to power switch S2 and power switch S4, and the other end of the isolation transformer 12 is connected to diode D1 and power switch S5.

[0032] In some embodiments, the downstream LLC resonant circuit 20 is an isolated structure, which may include a symmetrically arranged first LLC circuit unit 21 and second LLC circuit unit 22. Both the first LLC circuit unit 21 and the second LLC circuit unit 22 may include a half-bridge inverter circuit, an LLC resonant network, a high-frequency isolation transformer, and a rectifier output circuit connected in sequence. The input side of the first LLC circuit unit 21 and the input side of the second LLC circuit unit 22 are connected in series, and the output side of the first LLC circuit unit 21 and the second LLC circuit unit 22 are connected in parallel, for transforming the DC bus voltage and outputting a stable DC voltage to the load.

[0033] In some embodiments, the half-bridge inverter circuit may include two power switching devices, the LLC resonant network may include a resonant inductor, a resonant capacitor and a magnetizing inductor, and the rectifier output circuit may include four power switching devices.

[0034] The output voltage of the front-stage semi-DAB converter 10 can be combined with the system input voltage of the fractional-stage DC-DC converter topology 1 based on partial power processing to form the input voltage of the rear-stage LLC resonant circuit 20.

[0035] This application relates to a power control method that can be applied to the fractional DC-DC converter topology 1 based on partial power processing described above, and includes the following steps (steps S1 to S3): S1. Obtain the system input voltage of the fractional-stage DC-DC converter topology 1 based on partial power processing, and determine the output voltage of the front-stage semi-DAB converter 10 based on the first difference between the system input voltage and the DC bus voltage.

[0036] In some embodiments, the fractional-stage DC-DC converter topology 1 based on partial power processing may include a front-stage semi-DAB converter 10, an intermediate DC bus, and a rear-stage LLC resonant circuit 20.

[0037] The front-end semi-DAB converter 10 can be used as a partial power processing stage to regulate part of the power in the input system; the rear-end LLC resonant circuit 20 can be used as a full power processing stage to convert all the output power of the system and supply power to the load.

[0038] Specifically, the system input voltage is directly fed into the input terminal of the subsequent LLC resonant circuit 20 through a direct power path. Simultaneously, the preceding semi-DAB converter 10 processes a portion of the input power. The output voltage of the preceding semi-DAB converter 10 and the system input voltage are superimposed or synthesized at the input side of the subsequent LLC resonant circuit 20 to obtain its input voltage. By adjusting the operating state of the preceding semi-DAB converter 10, the input voltage of the subsequent LLC resonant circuit 20 can be effectively regulated, enabling the system to adapt to a wide range of input voltage variations and obtain the required voltage gain.

[0039] In this embodiment of the application, the output power of the front-end semi-DAB converter 10 satisfies a preset proportional relationship with the total system output power, and its processing power accounts for only a portion of the total system power. The preset proportional relationship can be expressed as follows: Where P2 is the output power of the front-end semi-DAB converter 10, P0 is the total system output power, U2 is the output voltage of the two power branches on the secondary side of the front-end semi-DAB converter 10, that is, the output voltage of the secondary H-bridge H2, and U... bus η is the DC bus voltage, and η2 is the efficiency of the subsequent LLC resonant circuit 20. The preceding semi-DAB converter 10 operates as a partial power processing stage, and its output voltage is superimposed on the system input voltage in series to form the input voltage of the subsequent LLC resonant circuit 20.

[0040] By combining partial power processing of the front-stage semi-DAB converter 10 with full power processing of the rear-stage LLC resonant circuit 20, the overall system efficiency is significantly improved while achieving matching for a wide input voltage range. It is particularly suitable for medium-to-high power DC power supply applications with high performance requirements, such as aerospace and renewable energy grid connection, and therefore has good engineering application prospects.

[0041] S2. Obtain the system output voltage of fractional DC-DC converter topology 1 based on partial power processing, compare the system output voltage with the preset output voltage to obtain the second difference, input the second difference into the preset proportional-integral controller to obtain the per-unit value of output power.

[0042] The total output power of the system is determined by the system input voltage, the pre-stage regulation power of the semi-DAB converter 10, and the conversion characteristics of the LLC resonant circuit 20. The total output power can be expressed as: Wherein, N1 is the turns ratio of the primary and secondary sides of the front-end semi-DAB converter 10, satisfying N1=Np:Ns, D1 is the shift ratio inside the primary side of the front-end semi-DAB converter 10, D2 is the shift ratio between power switches S1 and S6, D3 is the shift ratio between power switches S1 and S5, U1 is the input voltage of the H-bridge H1 on the primary side of the front-end semi-DAB converter 10, f1 is the switching frequency of the front-end semi-DAB converter 10, and L is the leakage inductance of the front-end semi-DAB converter 10.

[0043] The total output power of the system in this application is mainly borne by the subsequent LLC resonant circuit 20, while the preceding semi-DAB converter 10 only plays the role of power regulation and voltage compensation, thereby avoiding the efficiency superposition loss caused by the step-by-step power transfer in the traditional multi-stage series structure.

[0044] In some embodiments, the total voltage gain of the system can be expressed as: Where M is the voltage conversion ratio of the preceding semi-DAB converter 10, Ln is the inductance coefficient, and f n Q is the normalized switching frequency of the preamplifier stage. e This is the quality factor.

[0045] S3. Obtain the voltage conversion ratio based on the input voltage and output voltage. Use the KKT algorithm to process the per-unit value of the output power and the voltage conversion ratio to obtain the optimal shift ratio combination of the front-stage semi-DAB converter 10. Generate the drive signal of each power switch in the front-stage semi-DAB converter 10 based on the optimal shift ratio combination so that the rear-stage LLC resonant circuit 20 operates at the preset resonant point.

[0046] By adjusting the output voltage of the front-stage semi-DAB converter 10, the DC bus voltage of the system can be kept stable. When the system input voltage changes, the shift ratio combination of the front-stage semi-DAB converter 10 is adjusted according to the current stress optimization condition, thereby controlling the output voltage of the front-stage semi-DAB converter 10 to change accordingly, compensating for the fluctuation of the input voltage, and thus ensuring that the input voltage of the rear-stage LLC resonant circuit 20 is constant. Therefore, the rear-stage LLC resonant circuit 20 always operates under rated input voltage conditions, responsible for handling all the power of the system and outputting energy to the load. Due to the proposed composite structure, even with the relatively low efficiency of the front-stage semi-DAB converter 10, the overall system can still achieve high-efficiency operation.

[0047] In some embodiments, the shift ratio combination of the front-end semi-DAB converter 10 includes the internal shift ratio D1 of the primary side of the front-end semi-DAB converter 10, the shift ratio D2 between power switch S1 and power switch S6, and the shift ratio D3 between the rising edge of the switching signal of power switch S1 and power switch S5.

[0048] The system input voltage range of this application can be from 360V to 720V, and the DC bus voltage can be set to 800V. This enables high-efficiency full-power energy transfer.

[0049] In some embodiments, the voltage conversion ratio can be calculated using the following formula: Where N1 is the turns ratio of the primary and secondary sides of the front-end semi-DAB converter 10, U1 is the input voltage of the primary side H-bridge H1 of the front-end semi-DAB converter 10, and U2 is the output voltage of the two power branches on the secondary side of the front-end semi-DAB converter 10, that is, the output voltage of the secondary side H-bridge H2.

[0050] In some embodiments, the inductance coefficient can be calculated using the following formula: Among them, L m It is the magnetizing inductor of the subsequent LLC resonant circuit 20, L r This is the resonant inductor of the subsequent LLC resonant circuit 20.

[0051] In some embodiments, the per-unit switching frequency of the front-end stage can be calculated using the following formula: Among them, f sw Let f0 be the switching frequency of the subsequent LLC resonant circuit 20, and f0 be the series resonant frequency of the subsequent LLC resonant circuit 20, which is expressed as: Among them, C r This is the resonant capacitor for the subsequent LLC resonant circuit 20.

[0052] In some embodiments, the quality factor can be defined as: Among them, R e The equivalent resistance of the subsequent LLC resonant circuit 20 is expressed as: Where N2 is the transformer turns ratio in the subsequent LLC resonant circuit 20, R L This is the load resistance of the system.

[0053] The system input voltage and the output voltage of the preceding semi-DAB converter 10 are synthesized on the input side of the subsequent LLC resonant circuit 20. This allows the overall system voltage gain to be not only related to the LLC resonant parameters, but also to be flexibly extended by adjusting the operating state of the preceding semi-DAB converter 10. This enables stable operation over a wide input voltage range and high voltage gain capability.

[0054] For Partial Power Processing (PPP) converters, given input voltage, output voltage, and output power, multiple phase shift combinations typically exist to meet the same power transfer requirements. However, the internal power flow distribution and current transfer paths differ among different phase shifts, leading to significantly different internal current stresses within the converter. Larger current peaks not only increase the conduction losses of power devices and the copper losses in transformer windings but also enhance device current and thermal stresses, thereby affecting system efficiency, power density, and operational reliability. Therefore, minimizing converter current stress by obtaining the optimal phase shift combination while meeting the target power transfer requirements is crucial for improving overall system performance.

[0055] In some embodiments, the KKT algorithm is used to process the per-unit output power and voltage conversion ratio to obtain the optimal phase shift combination of the front-end semi-DAB converter 10. This may include: calculating the corresponding normalized power constraint parameters based on the per-unit output power and voltage conversion ratio; establishing a normalized peak inductor current objective function based on the normalized power constraint parameters, and constructing a Lagrangian function by combining the operating mode constraint that the phase shift variables satisfy phase shift ratio D3 ≥ phase shift ratio D2 ≥ phase shift ratio D1 ≥ 0; processing the Lagrangian function using KKT conditions to solve for the optimal phase shift variables that satisfy the constraints; and obtaining the optimal phase shift combination of the front-end semi-DAB converter 10 based on the optimal phase shift variables.

[0056] To further reduce the internal current stress of the converter while meeting power transmission requirements, this application normalizes the peak inductor current i c As the optimization objective, a phase shift optimization model based on minimizing current stress is constructed. The peak current is chosen as the optimization index because it not only directly reflects the maximum current stress borne by the power device and magnetic device, but is also closely related to conduction loss, magnetic device loss, and device thermal stress.

[0057] By reducing the peak current, the device RMS current can be effectively reduced, the system operating efficiency can be improved, and favorable conditions can be created for achieving better soft-switching conditions.

[0058] Compared with the traditional parameter scanning method, the KKT method can obtain the analytical relationship between optimization variables without traversing the entire parameter space. This not only significantly reduces the solution complexity, but also helps to reveal the intrinsic connection and variation law between the optimal shift ratios.

[0059] In some embodiments, when the current-stage semi-DAB converter 10 operates under the condition D3≥D2≥D1≥0, the final established Lagrangian function and its corresponding KKT condition are as follows: Where M is the voltage conversion ratio of the preceding semi-DAB converter 10. M = N 1 V 2 / V 1 ,in N 1 = N p :N s N P and N S Let be the number of primary and secondary turns of the preceding semi-DAB converter 10, respectively, and p be the normalized output power of the preceding semi-DAB converter 10, expressed as: Where P2 is the output power of the front-end semi-DAB converter 10, P N The maximum transmission power under single-phase-shift control is expressed as: In some embodiments, the normalized peak inductor current objective function i c This can be expressed by the following formula: Among them, I peak I is the peak value of the inductor current during a single operating cycle. N This represents the inductor current at the maximum transmittable power under single-phase shift (SPS) control.

[0060] In some embodiments, the constraints can be derived from the self-constraint of the shift ratio and the requirement for the zero-crossing point of the resonant inductor current to achieve ZVS turn-on, and can be specifically expressed as follows: .

[0061] After simplification, we can obtain the boundary conditions that the three shifts D1, D2, and D3 need to satisfy. Specifically, the boundary conditions, i.e., the constraints, can be further expressed as: .

[0062] By solving the Lagrange function and its corresponding KKT conditions, the optimal shift ratio combination is obtained, and its expression is as follows: .

[0063] Substituting the constraints into the normalized peak inductor current objective function, the minimum current stress is obtained, as shown in the following expression: .

[0064] Compared with existing technologies, this application introduces the concept of partial power processing, achieving high system efficiency, strong adaptability to a wide input voltage range, and wide-range voltage gain capability while maintaining relatively low system complexity. It is particularly suitable for high-performance DC power supply systems with high requirements for efficiency, power density, and power supply performance, such as aerospace, EV charging systems, and renewable energy grid connection, and has high engineering application value.

[0065] Figure 3 This is a schematic flowchart of the power control method of this application, as shown below. Figure 3 As shown, S100, Collect the input voltage U1, which is the system input voltage of this application; S200, based on U1 and DC bus voltage U bus The difference, namely the first difference in this application, determines the output voltage U2 of the DAB converter and the proportion of power it processes; S300, output voltage U0 sampling; S310. Calculate the error signal based on the output voltage U0 and the preset output voltage. This error signal is the second difference value. S320. Input the error signal e into the PI controller, i.e., the preset proportional-integral controller, and calculate the per-unit value P0 of the system output power; S400, Calculate the DAB voltage gain, which is also the voltage conversion ratio; S500, the optimal shift ratio combination of DAB is calculated using the KKT algorithm; S600: Generates MOSFET drive signals based on the optimal shift ratio combination; When the S700 and LLC converters are operating near the resonant point, the system output voltage can be fed back to step S300.

[0066] like Figure 4 As shown, the waveform diagram of the front-end semi-DAB converter 10 under the condition D3≥D2≥D1≥0 is given. The inductor current stress formula of the front-end semi-DAB converter 10 in this application is based on... Figure 4 The derivation is shown in the figure.

[0067] When the current stage semi-DAB converter 10 operates under the condition D3≥D2≥D1≥0, the per-unit peak current is selected as the objective function ic of the normalized peak inductor current, and the optimal shift ratio combination that minimizes the peak current is solved using the Karush–Kuhn–Tucker (KKT) conditions. The objective function ic of the normalized peak inductor current is determined by the peak value I of the inductor current within a single operating cycle. peak And the per-unit representation of the inductor current IN corresponding to the maximum transmittable power under single-phase shift (SPS) control. By solving the above optimization conditions, the optimal phase shift combination can be obtained, thereby achieving current stress optimization.

[0068] In this application, the voltage conversion ratio of the front-end semi-DAB converter 10 is first obtained. Then, the per-unit value of the output power is obtained based on the system output voltage. Next, the KKT algorithm is used to process the voltage conversion ratio and the per-unit value of the output power to obtain the optimal shift ratio combination and drive signal, so that the subsequent LLC resonant circuit 20 operates at a preset resonant point. In other words, by adjusting the operating state of the front-end semi-DAB converter 10, this application can effectively regulate the input voltage of the subsequent LLC resonant circuit 20, enabling the system to adapt to a wider range of input voltage changes and obtain the required voltage gain.

[0069] In this context, while maintaining relatively low system complexity, it can achieve high system efficiency, strong adaptability to a wide input voltage range, and wide-range voltage gain capability. It is particularly suitable for high-performance DC power supply systems with high requirements for efficiency, power density, and power supply performance, such as aerospace, EV charging systems, and renewable energy grid connection, and has high engineering application value.

[0070] The above description is merely a preferred embodiment of this application. Those skilled in the art will understand that various changes or equivalent substitutions can be made to these features and embodiments without departing from the spirit and scope of this application. Furthermore, under the teachings of this application, these features and embodiments can be modified to adapt to specific situations and materials without departing from the spirit and scope of this application. Therefore, this application is not limited to the specific embodiments disclosed herein, and all embodiments falling within the scope of the claims of this application are within the protection scope of this application.

Claims

1. A fractional-stage DC-DC converter topology based on partial power processing, characterized in that, The fractional-stage DC-DC converter topology based on partial power processing includes a front-stage semi-DAB converter and a rear-stage LLC resonant circuit. The front-end semi-DAB converter includes a full-bridge circuit on the primary side, an isolation transformer between the primary and secondary sides, and rectifiers and power regulators on the secondary side. The full-bridge circuit includes power switches S1 and S3 in the upper bridge arm, and power switches S2 and S4 in the lower bridge arm. The rectifiers and power regulators include two power branches connected in parallel. One power branch includes a diode D1 and a power switch S5 connected in series, and the other power branch includes a diode D2 and a power switch S6 connected in series. The subsequent LLC resonant circuit includes a first LLC circuit unit and a second LLC circuit unit arranged symmetrically. Both the first LLC circuit unit and the second LLC circuit unit include a half-bridge inverter circuit, an LLC resonant network, a high-frequency isolation transformer, and a rectifier output circuit connected in sequence. The input side of the first LLC circuit unit is connected in series with the input side of the second LLC circuit unit, and the output side of the first LLC circuit unit is connected in parallel with the second LLC circuit unit.

2. The fractional-stage DC-DC converter topology based on partial power processing according to claim 1, characterized in that, The half-bridge inverter circuit includes two power switching devices, the LLC resonant network includes a resonant inductor, a resonant capacitor, and a magnetizing inductor, and the rectifier output circuit includes four of the power switching devices.

3. The fractional-stage DC-DC converter topology based on partial power processing according to claim 1, characterized in that, The output voltage of the front-stage semi-DAB converter and the system input voltage of the fractional-stage DC-DC converter topology based on partial power processing together constitute the input voltage of the rear-stage LLC resonant circuit.

4. A power control method, characterized in that, The power control method is applied to the fractional-stage DC-DC converter topology based on partial power processing as described in any one of claims 1 to 3, and the power control method includes: Obtain the system input voltage of the fractional-stage DC-DC converter topology based on partial power processing, and determine the output voltage of the preceding semi-DAB converter based on the first difference between the system input voltage and the DC bus voltage; The system output voltage of the fractional-stage DC-DC converter topology based on partial power processing is obtained, the system output voltage is compared with a preset output voltage to obtain a second difference, and the second difference is input into a preset proportional-integral controller to obtain the per-unit value of output power. The voltage conversion ratio is obtained based on the input voltage and the output voltage. The KKT algorithm is used to process the per-unit value of the output power and the voltage conversion ratio to obtain the optimal shift ratio combination of the front-stage semi-DAB converter. The drive signals of each power switch in the front-stage semi-DAB converter are generated based on the optimal shift ratio combination so that the subsequent LLC resonant circuit operates at a preset resonant point.

5. The power control method according to claim 4, characterized in that, The shift ratio combination of the front-end semi-DAB converter includes the shift ratio D1 inside the primary side of the front-end semi-DAB converter, the shift ratio D2 between power switch S1 and power switch S6, and the shift ratio D3 between the rising edge of the switching signal of power switch S1 and power switch S5.

6. The power control method according to claim 5, characterized in that, The process of using the KKT algorithm to process the per-unit output power and the voltage conversion ratio to obtain the optimal phase shift combination of the front-end semi-DAB converter includes: calculating the corresponding normalized power constraint parameters based on the per-unit output power and the voltage conversion ratio; establishing a normalized peak inductor current objective function based on the normalized power constraint parameters, and constructing a Lagrangian function by combining the operating mode constraints that satisfy the phase shift ratio D3 ≥ the phase shift ratio D2 ≥ the phase shift ratio D1 ≥ 0; processing the Lagrangian function using KKT conditions to solve for the optimal phase shift variables that satisfy the constraints; and obtaining the optimal phase shift combination of the front-end semi-DAB converter based on the optimal phase shift variables.

7. The power control method according to claim 6, characterized in that, The Lagrange function and the KKT condition are shown in the following equations: Where M is the voltage conversion ratio of the preceding semi-DAB converter. M = N 1 V 2 / V 1 ,in N 1 = N p :N s N P and N S , respectively, are the primary and secondary turns of the preceding semi-DAB converter, and p is the normalized output power of the preceding semi-DAB converter.

8. The power control method according to claim 7, characterized in that, The normalized peak inductor current objective function i c This can be expressed by the following formula: Among them, I peak I is the peak value of the inductor current during a single operating cycle. N This represents the inductor current at the maximum transmittable power under single-phase-shift control.

9. The power control method according to claim 7, characterized in that, The constraint condition is expressed as follows: 。 10. The power control method according to claim 7, characterized in that, The expression for the optimal shift ratio combination is: 。

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