An optimized design method of hybrid bidirectional LLC-DAB converter

Abstract

The application discloses an optimization design method of a hybrid bidirectional LLC-DAB converter, and relates to the technical field of switching power supplies, and comprises the following steps: determining the structure of the hybrid bidirectional LLC-DAB converter; determining the parameter boundary condition of switch realization zero-voltage turn-on in the hybrid bidirectional LLC-DAB converter, and calculating the expression of total loss and dynamic performance of the hybrid bidirectional LLC-DAB converter; determining the parameters affecting the expression of total loss and the parameters affecting the expression of dynamic performance; and adopting a multi-objective particle swarm optimization algorithm to optimize each parameter, so as to realize the optimization of the hybrid bidirectional LLC-DAB converter. The application can quantitatively select the power capacity distribution parameters in the hybrid bidirectional LLC-DAB converter and the passive element parameters in the circuit, improve the converter efficiency as much as possible under the premise of meeting the dynamic performance, and maximize the utilization of the LLC resonant converter circuit with high efficient power transmission.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, specifically to an optimized design method for a hybrid bidirectional LLC-DAB converter. Background Technology

[0002] Currently widely used bidirectional isolated DC-DC converter modules, such as bidirectional LLC resonant converters and dual active bridge (DAB) converters, each have their own drawbacks: the former introduces high circulating current over a wide voltage regulation range, reducing efficiency; the latter is prone to losing soft switching under light loads and has high turn-off losses under heavy loads.

[0003] With the increasing voltage and power levels in practical applications, multi-bidirectional isolated DC-DC converter module combination systems have become a research hotspot for scholars worldwide. Common combination structures mainly include combinations of multiple DAB converters and multiple LLC converters. To overcome the shortcomings of individual converter modules and improve the performance of combined bidirectional isolated DC-DC converters, many studies combine DAB converter modules and bidirectional LLC resonant converter modules in a Sigma structure. This leverages the high efficiency of the bidirectional LLC resonant converter module in DC transformer (DCX) mode power transfer and the flexibility of bidirectional power flow control of the DAB converter module. It not only achieves efficient power transfer over a wide load range but also improves dynamic performance under bidirectional power flow. However, existing LLC-DAB converter combination schemes introduce a large number of switches.

[0004] To address the aforementioned problems and complex circuit structure of LLC-DAB hybrid converters, an improved LLC-DAB hybrid bidirectional converter has been proposed in the prior art. This converter multiplexes the secondary-side rectifier bridge circuit, eliminating four switching devices and achieving full-load range soft switching ZVS for all switching devices in the LLC circuit, thereby improving the converter's efficiency.

[0005] However, in the aforementioned studies of hybrid bidirectional LLC-DAB converters, they simply stated that the main power is handled by the LLC resonant converter, with the DAB converter processing a portion of the power. The specific power distribution principle was not discussed in detail. Furthermore, some studies suggest that the DAB converter is more efficient than the LLC resonant converter, while previous studies mostly considered the LLC resonant converter more efficient; however, these were all qualitative analyses without quantitative comparisons. Most designs rely on engineering experience to determine power distribution and then design the corresponding circuit component parameters, lacking universality and practicality. Simultaneously, while employing complex model calculation methods can improve accuracy, it cannot fully reflect the system characteristics and introduces computational complexity.

[0006] Based on the current research, hybrid LLC-DAB bidirectional converters have promising application prospects, but there is still no clear method for parameter optimization design. To better utilize the LLC-DAB hybrid bidirectional converter, its power distribution relationship needs to be optimized, which directly determines the system's efficiency and dynamic performance. However, since these two performance indicators are difficult to consider simultaneously, direct design is challenging. Therefore, advanced optimization algorithms can be considered during the design process. In recent years, to obtain optimal results, optimization algorithms such as Bee Colony Optimization (BCO), Particle Swarm Optimization (PSO), and Genetic Algorithm (GA) have been frequently used in the field of power electronics. In this invention, there are more than two objectives to optimize, requiring the introduction of a multi-objective optimization algorithm, which has been less studied in the design of DC-DC converters. Summary of the Invention

[0007] This invention proposes an optimized design method for a hybrid bidirectional LLC-DAB converter to solve the problems mentioned in the background art.

[0008] This invention provides an optimized design method for a hybrid bidirectional LLC-DAB converter, comprising the following steps:

[0009] By connecting the secondary side of the auxiliary DAB circuit transformer in parallel with the secondary side of the LLC primary circuit transformer, a hybrid bidirectional LLC-DAB converter structure is obtained.

[0010] The transfer function between the input and output voltages of the hybrid bidirectional LLC-DAB converter is established by using a reduced-order modeling method. The dynamic performance of the input and output voltages of the hybrid bidirectional LLC-DAB converter is characterized by the crossover angular frequency of the LLC primary circuit and the single-phase phase shift of the auxiliary DAB circuit, respectively, thus obtaining the overall dynamic performance expression of the hybrid bidirectional LLC-DAB converter.

[0011] Calculate the total loss expression for the hybrid bidirectional LLC-DAB converter;

[0012] The parameters affecting the total loss expression of the hybrid bidirectional LLC-DAB converter and the parameters affecting the dynamic performance of the hybrid bidirectional LLC-DAB converter are determined. These parameters include the turns ratio of the transformer in the primary circuit of the LLC, as well as the magnetic component and reaction component of the hybrid bidirectional LLC-DAB converter.

[0013] The parameter boundary conditions for achieving zero-voltage turn-on of the switches in the hybrid bidirectional LLC-DAB converter are used as parameter design constraints. A multi-objective particle swarm optimization algorithm is used to optimize each parameter, thereby optimizing the hybrid bidirectional LLC-DAB converter.

[0014] Furthermore, the parameter boundary conditions for the switches in the hybrid bidirectional LLC-DAB converter to achieve zero-voltage turn-on are as follows:

[0015]

[0016] Among them, C P_DAB To assist the junction capacitance of the switching devices in the DAB circuit;

[0017] f s T is the switching frequency; dead R is the dead time; R is the load resistance.

[0018] C P_LLC The junction capacitance of the primary side circuit of the LLC;

[0019] C S L is the junction capacitance of the secondary-side switch; k The leakage inductance is used to assist the DAB circuit;

[0020] V in This refers to the total input voltage of the hybrid bidirectional LLC-DAB converter;

[0021] V o The output voltage of the hybrid bidirectional LLC-DAB converter;

[0022] V C2 The input voltage for the auxiliary DAB circuit;

[0023] K1 is the turns ratio of transformer T1 in the primary circuit of LLC;

[0024] K2 is the turns ratio of transformer T2 in the auxiliary DAB circuit;

[0025] D φ The steady-state phase angle; L m For magnetizing inductance;

[0026] n is the ratio of the maximum to the minimum steady-state phase shift angle, and its calculation formula is:

[0027]

[0028] Among them, D φmax This represents the maximum power margin.

[0029] D φmin It is the ratio of reactive power to active power.

[0030] Furthermore, the switching conduction loss P of the hybrid bidirectional LLC-DAB converter sw_c The calculation formula is:

[0031] P sw_c =2IRMS_LLC 2 R LLC +2I RMS_DAB 2 R DAB +2I RMS_s 2 R s (3)

[0032] Among them, I RMS_LLC This represents the on-state current of all switches in the primary circuit of the LLC;

[0033] R LLC The on-resistance of all switches in the primary circuit of the LLC;

[0034] I RMS_DAB To provide the conduction current for all switches in the DAB circuit;

[0035] R DAB The on-resistance of all switches in the auxiliary DAB circuit;

[0036] I RMS_s This is the conduction current of the secondary side switch;

[0037] R s The on-resistance of the secondary side switch;

[0038] Among them, I RMS_LLC I RMS_DAB I RMS_S The calculation formulas are as follows:

[0039]

[0040]

[0041] I RMS_s =K1I RMS_LLC +K2I RMS_DAB (6)

[0042] Among them, T s For the switching period; i Lr (t) represents the resonant inductor current.

[0043] Furthermore, the switching turn-off loss P of the hybrid bidirectional LLC-DAB converter sw_off The calculation formula is:

[0044] P sw_off =2P sw_off_LLC +2P sw_off_DAB +2P sw_off_s (7)

[0045] Among them, P sw_off_LLCFor the switching turn-off loss of the primary side circuit of LLC;

[0046] P sw_off_DAB To assist in reducing the switching turn-off losses of the DAB circuit;

[0047] P sw_off_s For the switching and turning-off losses of the secondary side switch;

[0048] Among them, P sw_off_LLC P sw_off_DAB P sw_off_s The calculation formulas are as follows:

[0049]

[0050] Among them, V C1 This is the input voltage for the primary side circuit of the LLC;

[0051] t off_LLC t off_DAB t off_s These are the turn-off times of the switches in the primary side circuit of LLC, the auxiliary DAB circuit, and the secondary side circuit, respectively.

[0052] I sw_off_LLC I sw_off__DAB I sw_off__s The turn-off currents for the primary circuit of the LLC, the auxiliary DAB circuit, and the secondary circuit are respectively calculated using the following formulas:

[0053]

[0054] Among them, f r It is the resonant frequency.

[0055] Furthermore, the inductor copper loss P of the hybrid bidirectional LLC-DAB converter C_L_loss The calculation formula is:

[0056] P C_L_loss =I 2 RMS_LLC R C_L_LLC +I 2 RMS_DAB R C_L_DAB (10)

[0057] Among them, R C_L_LLC Consider the skin effect on the inductor of the primary side circuit of LLC;

[0058] R C_L_DAB The equivalent resistance of the inductor in the DAB circuit is considered to account for the skin effect;

[0059] Among them, R C_LThe formula for calculating the equivalent resistance of an inductor, considering the skin effect, is as follows:

[0060]

[0061] Among them, R dc_C_L The DC resistance on the inductor;

[0062] N n N represents the number of shares in the Litz parameters. L Number of bundle layers;

[0063] The formula for calculating Δ is:

[0064]

[0065] Where d w δ is the diameter of the Litz line and δ is the skin depth.

[0066] Furthermore, the transformer copper loss P of the hybrid bidirectional LLC-DAB converter C_T_loss The calculation formula is:

[0067]

[0068] Among them, R C_T_LLC Considering the skin effect, the equivalent resistance on the transformer of the primary side circuit of LLC;

[0069] R C_T_DAB The equivalent resistance of the inductor transformer in the DAB circuit is considered to account for the skin effect;

[0070] Among them, R C_T Considering the skin effect, the equivalent resistance of the transformer.

[0071] Furthermore, the inductor iron loss P of the hybrid bidirectional LLC-DAB converter I_L_loss The calculation formula is:

[0072] P I_L_loss =P I_L_LLC +P I_L_DAB (14)

[0073] Among them, P I_L_LLC For the inductor iron loss of the primary side circuit of LLC;

[0074] P I_L_DAB To reduce the inductor iron loss in the auxiliary DAB circuit;

[0075] The inductor iron loss P is calculated using the Steinmetz equation. iron_loss The calculation formula is as follows:

[0076]

[0077] Among them B max V is the peak magnetic flux density; L The volume of the selected magnetic core;

[0078] K, α, and β are Steinmetz parameters, respectively.

[0079] Furthermore, the transformer iron loss P of the hybrid bidirectional LLC-DAB converter I_T_loss The calculation formula is:

[0080] P I_T_loss =P I_T_LLC +P I_T_DAB (16)

[0081] Among them, P I_T_LLC For the transformer iron loss of the primary circuit of LLC;

[0082] P I_T_DAB To reduce transformer iron losses in the DAB circuit;

[0083] Among them, in calculating the transformer iron loss P I_T At that time, the peak flux density expressions for the LLC primary circuit and the auxiliary DAB circuit are:

[0084]

[0085] Where N T D represents the number of turns in the transformer. d For duty cycle, A e This represents the cross-sectional area of ​​the magnetic core.

[0086] A e2 To assist in determining the core cross-sectional area of ​​the transformer in the DAB circuit;

[0087] The total loss of the hybrid bidirectional LLC-DAB converter is obtained by adding the switching turn-on loss, switching turn-off loss, inductor copper loss, transformer copper loss, inductor iron loss, and transformer iron loss together.

[0088] Furthermore, a model of the output voltage of the hybrid bidirectional LLC-DAB converter is established using a reduced-order modeling method, resulting in:

[0089]

[0090] Among them G d (s) is the transfer function from the control variable to the output voltage;

[0091] G in (s) is the transfer function from input voltage to output voltage;

[0092] Where A, B, C, D1, and E are the corresponding variables in equation (18), and their expressions are as follows:

[0093]

[0094] The auxiliary DAB circuit uses single-phase phase-shift modulation to regulate the output voltage, where the steady-state phase angle D φ The calculation formula is:

[0095]

[0096] Using the crossing angular frequency ω c1 To analyze the dynamic performance of the hybrid bidirectional LLC-DAB converter, the calculation formula is as follows:

[0097]

[0098] C1 is the input capacitor of the primary side circuit of LLC; C2 is the input capacitor of the auxiliary DAB circuit.

[0099] Furthermore, the optimization of various parameters using a multi-objective particle swarm optimization algorithm to optimize the hybrid bidirectional LLC-DAB converter includes the following steps:

[0100] Initialize the acceleration constant, external archive EXA, and target weight ω;

[0101] The turns ratio K1 of transformer T1 in the primary circuit of LLC is increased in fixed steps and set to λ. min *V in / V0, where λ min Minimum power capacity allocation factor;

[0102] Initialize the LLC primary circuit resonant cavity parameter boundaries, particle velocity, position, and optimal archive PBA. The LLC primary circuit resonant cavity parameter boundaries are calculated based on the excitation inductance value, as follows:

[0103]

[0104] Where L r The resonant inductance of the primary side circuit of the LLC; L m Magnetizing inductor for the primary side circuit of LLC;

[0105] C r This is the resonant capacitor for the primary side circuit of the LLC;

[0106] Update the particle velocity and position, and calculate the objective function value. The update equations for particle velocity and position are as follows:

[0107]

[0108] Where v i and pos i Let Rand be the velocity and position of the i-th particle; Rand is a random function.

[0109] Pbest i and gbest i These represent the individual best result for the i-th particle and the global best result for all particles, respectively.

[0110] K and N are the current iteration number and the dimension of the parameters, respectively; c1 and c2 are acceleration factors.

[0111] Calculate the non-dominated solutions for all particles at the current iteration time, and update the best archive PBA based on the non-dominated solutions;

[0112] Save all the best archives PBA and determine the non-dominant solutions, saving them in the external archive EXA. The optimal result corresponding to the current K1 is also saved in the external archive EXA.

[0113] Increase the fixed step size of K1 when K1 is greater than λ. max *V in / V0, where λ max If the minimum power capacity allocation factor is used, then all optimal results for K1 are obtained and stored in the external archive EXA;

[0114] All optimal results in the external archive EXA contain parameters of the hybrid bidirectional LLC-DAB converter;

[0115] The parameters include:

[0116] The turns ratio K1 of transformer T1 in the primary circuit of LLC, the resonant inductance of the primary circuit of LLC, the resonant capacitance of the primary circuit of LLC, the magnetizing inductance of the primary circuit of LLC, the turns ratio K2 of transformer T2 in the auxiliary DAB circuit, and the leakage inductance of the auxiliary DAB circuit.

[0117] The formula for calculating the turns ratio K2 of transformer T2 in the auxiliary DAB circuit is as follows:

[0118] K2=(V in -K1*V0) / V0 (24).

[0119] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0120] This invention optimizes the total loss, dynamic performance, and zero-voltage switching (ZVS) of a hybrid bidirectional LLC-DAB converter in bidirectional power transmission. Using the multi-objective particle swarm optimization (MO-PSO) algorithm, it optimizes the design of a hybrid bidirectional LLC-DAB converter constructed with a Sigma structure, providing the optimal power capacity allocation relationship between the two converter circuits and verifying the advantages of the LLC resonant converter as the main power processing unit. This invention can quantitatively select power capacity allocation parameters and passive component parameters in the hybrid bidirectional LLC-DAB converter, namely the transformer turns ratio and inductor / capacitor parameters in different sub-converter circuits. This allows for maximizing converter efficiency while meeting dynamic performance requirements, maximizing the utilization of the LLC resonant converter circuit with high-efficiency power transmission. Furthermore, the use of the MO-PSO algorithm leverages the advantages of artificial intelligence algorithms to overcome the computational difficulties of complex circuit models. Attached Figure Description

[0121] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0122] Figure 1 A schematic diagram of the structural flow of an optimized design method for a hybrid bidirectional LLC-DAB converter provided by the present invention;

[0123] Figure 2 The topology of the hybrid bidirectional LLC-DAB converter in the optimization design method of the hybrid bidirectional LLC-DAB converter provided by the present invention is shown in the figure.

[0124] Figure 3 This is a flowchart illustrating the optimization design using the Multi-Objective Particle Swarm Optimization (MO-PSO) algorithm in the optimization design method for a hybrid bidirectional LLC-DAB converter provided by this invention. Detailed Implementation

[0125] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. However, it should be understood that the scope of protection of the present invention is not limited to the specific implementation.

[0126] Example 1

[0127] like Figure 1 As shown, this invention provides an optimized design method for a hybrid bidirectional LLC-DAB converter, comprising the following steps:

[0128] Step S1: Connect the secondary side of the auxiliary DAB circuit transformer in parallel with the secondary side of the LLC primary circuit transformer to obtain a hybrid bidirectional LLC-DAB converter structure.

[0129] Step S2: The transfer function between the input voltage and output voltage of the hybrid bidirectional LLC-DAB converter is established by using the reduced-order modeling method. The dynamic performance of the input voltage and output voltage of the hybrid bidirectional LLC-DAB converter is characterized by the crossover angular frequency of the LLC primary circuit and the single-phase phase shift of the auxiliary DAB circuit, respectively, and the overall dynamic performance expression of the hybrid bidirectional LLC-DAB converter is obtained.

[0130] Step S3: Calculate the total loss expression for the hybrid bidirectional LLC-DAB converter;

[0131] Step S4: Determine the parameters that affect the total loss expression of the hybrid bidirectional LLC-DAB converter, and the parameters that affect the dynamic performance of the hybrid bidirectional LLC-DAB converter. The parameters include the turns ratio of the transformer in the primary circuit of the LLC, and the magnetic component and reaction component of the hybrid bidirectional LLC-DAB converter.

[0132] Step S5: The parameter boundary conditions for achieving zero-voltage turn-on of the switches in the hybrid bidirectional LLC-DAB converter are used as parameter design constraints. The multi-objective particle swarm optimization algorithm is used to optimize each parameter to achieve optimization of the hybrid bidirectional LLC-DAB converter.

[0133] like Figure 2 The topology of the hybrid bidirectional LLC-DAB converter in this invention is shown in the figure. By directly connecting the secondary side of the auxiliary DAB circuit transformer in parallel with the secondary side of the LLC primary circuit transformer, only four switches are needed on the secondary side, thus reducing the number of switches in the hybrid bidirectional LLC-DAB converter structure.

[0134] exist Figure 2 In the middle, L r L m L k These are resonant inductance, magnetizing inductance, and leakage inductance, respectively.

[0135] C o C1, C2, C r These are the output filter capacitor, the input capacitor of the LLC primary circuit, the input capacitor of the auxiliary DAB circuit, and the resonant capacitor, respectively.

[0136] Cp_LLC, Cp_DAB and C s These are the junction capacitances of the primary side circuit of the LLC, the auxiliary DAB circuit, and the secondary side switch, respectively.

[0137] Vin V o V C1 V C2 v Cr These represent the total input voltage, output voltage, LLC primary circuit input voltage, DAB auxiliary circuit input voltage, and resonant capacitor voltage, respectively.

[0138] K1 and K2 are the turns ratios of transformers T1 and T2, respectively.

[0139] This hybrid bidirectional LLC-DAB converter operates at a fixed resonant switching frequency with a duty cycle of 50%.

[0140] Q i The driving signals (i = 1, 2, 3, and 4) and S i (i = 1, 2, 3 and 4) have the same driving signal on the secondary side.

[0141] For the auxiliary DAB circuit, Q5 and Q8 are simultaneously turned on and off, and there is a phase shift angle φ for the drive signals of Q1 and S1. Voltage regulation and power flow control can be achieved by controlling φ.

[0142] It is worth noting that from V in Side to V o Power transfer on the side is called forward power transfer.

[0143] Since the primary circuit of the LLC operates in DCX mode (DC transformer), it is assumed that V in steady state... C1 / K1=V2.

[0144] The main power achieves high conversion efficiency through the LLC primary-side circuit, while the auxiliary DAB circuit utilizes a portion of the power for voltage regulation and bidirectional power flow control. The power distribution between the LLC primary-side circuit and the auxiliary DAB circuit is related to their input voltage. In other words, it is directly related to K1. Therefore, the design of K1 is critical, as it determines the power flowing through each circuit, thus affecting the design of the circuit parameters.

[0145] To ensure that the hybrid bidirectional LLC-DAB converter achieves both high efficiency and good dynamic performance, this invention will analyze the following optimization objectives to better guide the design of system parameters.

[0146] In step S1, in order to improve the efficiency of the converter, it is necessary to achieve ZVS for the converter LLC circuit and secondary circuit over the full load range, and ZVS for the auxiliary DAB circuit over a wide range.

[0147] Analysis shows that achieving zero voltage on the secondary side is difficult. The discharge / charge time of the primary circuit in the LLC converter needs to be designed to be shorter than that of the secondary circuit to expand the operating range of the zero-voltage switch (ZVS). Additionally, the minimum leakage inductance corresponding to the minimum turn-off current can be obtained, ensuring the operation of the ZVS under light load conditions. Therefore, the parameter boundary conditions for achieving zero-voltage turn-on in the hybrid bidirectional LLC-DAB converter are:

[0148]

[0149] Among them, C P_DAB To assist the junction capacitance of the switching devices in the DAB circuit;

[0150] f s For the switchable frequency; T dead R is the dead time; R is the load resistance.

[0151] C P_LLC The junction capacitance of the primary side circuit of the LLC;

[0152] C S L is the junction capacitance of the secondary-side switch; k The leakage inductance is used to assist the DAB circuit;

[0153] V in This refers to the total input voltage of the hybrid bidirectional LLC-DAB converter;

[0154] V o The output voltage of the hybrid bidirectional LLC-DAB converter;

[0155] V C2 The input voltage for the auxiliary DAB circuit;

[0156] K1 is the turns ratio of transformer T1 in the primary circuit of LLC;

[0157] K2 is the turns ratio of transformer T2 in the auxiliary DAB circuit; D φ This is the steady-state phase angle;

[0158] L m For magnetizing inductance; L k To assist the leakage inductance of the DAB circuit;

[0159] n is the ratio of the maximum to the minimum steady-state phase shift angle, and its calculation formula is:

[0160]

[0161] Among them, D φmax For maximum power margin; D φmin It is the ratio of reactive power to active power.

[0162] The losses of zero-voltage switching (ZVS) not only affect overall power loss but also introduce electromagnetic interference, thus impacting converter performance. Therefore, when considering both efficiency and dynamic performance optimization objectives, the implementation of ZVS turn-on needs to be treated as a constraint in the parameter design.

[0163] In step S2, the total loss of the converter consists of seven parts: switch turn-on loss, switch conduction loss, switch turn-off loss, inductor copper loss, transformer copper loss, inductor iron loss, and transformer iron loss. The loss decomposition analysis of each part is as follows:

[0164] Step S2.1: Switching loss

[0165] Because this converter can achieve zero voltage for all switches, the switching losses are zero.

[0166] Step S2.2: Switch conduction loss

[0167] The total switching conduction loss can be calculated using the root mean square (RMS) current flowing through the switch. Therefore, the switching conduction loss P of the hybrid bidirectional LLC-DAB converter... sw_c The calculation formula is:

[0168] P sw_c =2I RMS_LLC 2 R LLC +2I RMS_DAB 2 R DAB +2I RMS_s 2 R s (3)

[0169] Among them, I RMS_LLC This represents the on-state current of all switches in the primary circuit of the LLC;

[0170] R LLC The on-resistance of all switches in the primary circuit of the LLC;

[0171] I RMS_DAB To provide the conduction current for all switches in the DAB circuit;

[0172] R DAB The on-resistance of all switches in the auxiliary DAB circuit;

[0173] I RMS_s This is the conduction current of the secondary side switch;

[0174] R s The on-resistance of the secondary side switch;

[0175] Among them, I RMS_LLC IRMS_DAB I RMS_S The calculation formulas are as follows:

[0176]

[0177]

[0178] I RMS_s =K1I RMS_LLC +K2I RMS_DAB (6)

[0179] Among them, T s For the switching period; i Lr (t) represents the resonant inductor current.

[0180] Step S2.3: Since the switching turn-off loss is related to the turn-off current and the switching turn-off time, the switching turn-off loss P of the hybrid bidirectional LLC-DAB converter... sw_off The calculation formula is:

[0181] P sw_off =2P sw_off_LLC +2P sw_off_DAB +2P sw_off_s (7)

[0182] Among them, P sw_off_LLC For the switching turn-off loss of the primary side circuit of LLC;

[0183] P sw_off_DAB To assist in reducing the switching turn-off losses of the DAB circuit;

[0184] P sw_off_s For the switching and turning-off losses of the secondary side switch;

[0185] Among them, P sw_off_LLC P sw_off_DAB P sw_off_s The calculation formulas are as follows:

[0186]

[0187] Among them, V C1 This is the input voltage for the primary side circuit of the LLC;

[0188] t off_LLC t off_DAB t off_s These are the turn-off times of the switches in the primary side circuit of LLC, the auxiliary DAB circuit, and the secondary side circuit, respectively.

[0189] I sw_off_LLC I sw_off__DAB I sw_off__sThe turn-off currents for the primary circuit of the LLC, the auxiliary DAB circuit, and the secondary circuit are respectively calculated using the following formulas:

[0190]

[0191] Among them, f r It is the resonant frequency.

[0192] Step S2.4: Since the copper loss of the inductor is mainly caused by the resistance of the Litz wire in the winding of the inductor, the copper loss P of the inductor in the hybrid bidirectional LLC-DAB converter is... C_L_loss The calculation formula is:

[0193] P C_L_loss =I 2 RMS_LLC R C_L_LLC +I 2 RMS_DAB R C_L_DAB (10)

[0194] Among them, R C_L_LLC Consider the skin effect on the inductor of the primary side circuit of LLC;

[0195] R C_L_DAB The equivalent resistance of the inductor in the DAB circuit is considered to account for the skin effect;

[0196] Among them, R C_L The formula for calculating the equivalent resistance of an inductor, considering the skin effect, is as follows:

[0197]

[0198] Among them, R dc_C_L The DC resistance on the inductor;

[0199] N n N represents the number of shares in the Litz parameters. L Number of bundle layers;

[0200] The formula for calculating Δ is:

[0201]

[0202] Where d w δ is the diameter of the Litz line and δ is the skin depth.

[0203] Step S2.5: Since the transformer copper loss is similar to the inductor copper loss, the transformer copper loss P of the hybrid bidirectional LLC-DAB converter is... C_T_loss The calculation formula is:

[0204]

[0205] Among them, R C_T_LLC Considering the skin effect, the equivalent resistance on the transformer of the primary side circuit of LLC;

[0206] R C_T_DAB The equivalent resistance of the inductor transformer in the DAB circuit is considered to account for the skin effect;

[0207] Among them, R C_T Considering the skin effect, the equivalent resistance of the transformer.

[0208] Step S2.6: Inductor iron loss is mainly caused by the hysteresis and eddy currents of the material. Therefore, the inductor iron loss P of the hybrid bidirectional LLC-DAB converter... I_L_loss The calculation formula is:

[0209] P I_L_loss =P I_L_LLC +P I_L_DAB (14)

[0210] Among them, P I_L_LLC For the inductor iron loss of the primary side circuit of LLC;

[0211] P I_L_DAB To reduce the inductor iron loss in the auxiliary DAB circuit;

[0212] The inductor iron loss P is calculated using the Steinmetz equation. iron_loss The calculation formula is as follows:

[0213]

[0214] Among them B max V is the peak magnetic flux density; L The volume of the selected magnetic core;

[0215] K, α, and β are Steinmetz parameters, respectively.

[0216] Step S2.7: Transformer iron loss P of the hybrid bidirectional LLC-DAB converter I_T_loss The calculation formula is:

[0217] P I_T_loss =P I_T_LLC +P I_T_DAB (16)

[0218] Among them, P I_T_LLC For the transformer iron loss of the primary circuit of LLC;

[0219] P I_T_DAB To reduce transformer iron losses in the DAB circuit;

[0220] Among them, in calculating the transformer iron loss P I_TAt that time, the peak flux density expressions for the LLC primary circuit and the auxiliary DAB circuit are:

[0221]

[0222] Where N T D represents the number of turns in the transformer. d For duty cycle, A e This represents the cross-sectional area of ​​the magnetic core.

[0223] A e2 The cross-sectional area of ​​the transformer core in the auxiliary DAB circuit.

[0224] Step S2.8: Add up the losses of the first seven parts to obtain the total loss of the converter.

[0225] P total_loss =P sw_on +P sw_c +P sw_off +P C_L_loss +P C_T_loss +P I_L_loss +P I_T_loss (18)

[0226] In step S3, the dynamic performance of the hybrid bidirectional LLC-DAB converter is determined, including:

[0227] A model of the output voltage of the hybrid bidirectional LLC-DAB converter is established using a reduced-order modeling method, yielding:

[0228]

[0229] Among them G d (s) is the transfer function from the control variable to the output voltage;

[0230] G in (s) is the transfer function from input voltage to output voltage;

[0231] Where A, B, C, and D are the corresponding variables in equation (18), and their expressions are as follows:

[0232]

[0233] The auxiliary DAB circuit uses single-phase phase-shift modulation to regulate the output voltage, so the steady-state phase angle D φ The calculation formula is:

[0234]

[0235] Using the crossing angular frequency ω c1 To analyze the dynamic performance of the hybrid bidirectional LLC-DAB converter, the calculation formula is as follows:

[0236]

[0237] C1 is the input capacitor of the primary side circuit of LLC; C2 is the input capacitor of the auxiliary DAB circuit.

[0238] In summary, designing a hybrid LLC-DAB bidirectional converter requires consideration of multiple objectives, including losses and dynamic performance. Each optimization objective relates to the turns ratio K1 of the transformer T1 in the LLC primary circuit, the magnetic components (the resonant inductance Lr of the LLC primary circuit, and the leakage inductance L of the auxiliary DAB circuit). k Magnetizing inductance L in the primary side circuit of LLC m ) is the resonant capacitance C of the primary side circuit of LLC and the reaction component. r These parameters are directly related to the input / output capacitance. The choices of these parameters also influence each other. Therefore, traditional single-objective parameter optimization algorithms are no longer applicable.

[0239] In step S4, since the LLC primary-side circuit is used as the DC transformer DCX in this converter to ensure high efficiency, and the auxiliary DAB circuit ensures dynamic performance, these two objectives need to be considered and compromised. These two objectives will affect the design of system parameters. Therefore, this invention will use a multi-objective optimization algorithm to solve this problem. Because this algorithm has a fast convergence speed and is easy to implement, the multi-objective particle swarm optimization algorithm MO-PSO is selected to optimize the hybrid LLC-DAB bidirectional converter. The flowchart of its optimization design is as follows: Figure 3 As shown.

[0240] The multi-objective particle swarm optimization algorithm is used to optimize various parameters to achieve optimization of the hybrid bidirectional LLC-DAB converter, including the following steps:

[0241] When the multi-objective particle swarm optimization algorithm MO-PSO is started, the acceleration constant, external archive EXA and target weight ω are first initialized;

[0242] Since the selection of magnetic components is related to the turns ratio K1 of transformer T1 in the primary circuit of LLC, it is increased in fixed steps and set to λ. min *V in / V0, where λ min Minimum power capacity allocation factor;

[0243] Step 4.1: Initialize the LLC primary-side circuit resonant cavity parameter boundaries, particle velocity, position, and optimal archive PBA. The LLC primary-side circuit resonant cavity parameter boundaries are calculated based on the excitation inductance value, as follows:

[0244]

[0245] Where L r The resonant inductance of the primary side circuit of the LLC; L m Magnetizing inductor for the primary side circuit of LLC;

[0246] C r This is the resonant capacitor for the primary side circuit of the LLC;

[0247] Step 4.2: Update particle velocity and position, and calculate the objective function value. The update equations for particle velocity and position are as follows:

[0248]

[0249] Where v i and pos i Let Rand be the velocity and position of the i-th particle; Rand is a random function.

[0250] Pbest i and gbest i These represent the individual best result for the i-th particle and the global best result for all particles, respectively.

[0251] K and N are the current iteration number and the dimension of the parameters, respectively; c1 and c2 are acceleration factors.

[0252] Step 4.3: Calculate the non-dominated solutions for all particles at the current iteration time, and update the best archive PBA based on the non-dominated solutions. If there are still iterations, return to step 5.2.

[0253] Step 4.4: Save all optimal archived PBAs in a temporary file, and identify non-dominant solutions, saving them in the external archive EXA, to continue the calculation for the next generation. If this is not the last generation, return to step 5.2. At this point, the optimal result corresponding to the current K1 is saved in the external archive EXA;

[0254] Step 4.5: Increase the fixed step size of K1 when K1 is less than or equal to λ. max *V in If / V0, then return to step 5.2; where λ max This is the maximum power allocation factor;

[0255] When K1 is greater than λ max *V in / V0, the multi-objective particle swarm optimization algorithm MO-PSO stops, then all the optimal results of K1 are obtained and saved in the external archive EXA;

[0256] All optimal results in the external archive EXA contain parameters of the hybrid bidirectional LLC-DAB converter; the parameters include: the turns ratio K1 of transformer T1 in the LLC primary circuit, the resonant inductance of the LLC primary circuit, the resonant capacitance of the LLC primary circuit, the magnetizing inductance of the LLC primary circuit, the turns ratio K2 of transformer T2 in the auxiliary DAB circuit, and the leakage inductance of the auxiliary DAB circuit.

[0257] The formula for calculating the turns ratio K2 of transformer T2 in the auxiliary DAB circuit is as follows:

[0258] K2=(V in -K1*V0) / V0 (25).

[0259] Finally, it should be noted that the above-disclosed embodiment is only one specific embodiment of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for optimal design of a hybrid bidirectional LLC-DAB converter, characterized in that, Includes the following steps: By connecting the secondary side of the auxiliary DAB circuit transformer in parallel with the secondary side of the LLC primary circuit transformer, a hybrid bidirectional LLC-DAB converter structure is obtained. The transfer function between the input and output voltages of the hybrid bidirectional LLC-DAB converter is established by using a reduced-order modeling method. The dynamic performance of the input and output voltages of the hybrid bidirectional LLC-DAB converter is characterized by the crossover angular frequency of the LLC primary circuit and the single-phase phase shift of the auxiliary DAB circuit, respectively, thus obtaining the overall dynamic performance expression of the hybrid bidirectional LLC-DAB converter. Calculate the total loss expression for the hybrid bidirectional LLC-DAB converter; The parameters that affect the total loss expression of the hybrid bidirectional LLC-DAB converter and the parameters that affect the dynamic performance of the hybrid bidirectional LLC-DAB converter are determined. The above two types of parameters are collectively referred to as the parameters to be optimized. The parameters to be optimized include the turns ratio of the transformer in the primary circuit of the LLC, as well as the magnetic component and reaction component of the hybrid bidirectional LLC-DAB converter. The parameter boundary conditions for achieving zero-voltage turn-on of the switches in the hybrid bidirectional LLC-DAB converter are used as parameter design constraints. A multi-objective particle swarm optimization algorithm is used to optimize each parameter to achieve the optimization of the hybrid bidirectional LLC-DAB converter.

2. The method of claim 1, wherein: The parameter boundary conditions for the switches in the hybrid bidirectional LLC-DAB converter to achieve zero-voltage turn-on are as follows: （1） wherein, C P_DAB to assist the junction capacitance of the switching devices in the DAB circuit; f s for a switching frequency; T dead for a dead time; R for a load resistance; C P_LLC a junction capacitor for the LLC primary side circuit; C S a junction capacitance for the secondary side switch; L k a leakage inductance for the auxiliary DAB circuit V in is the total input voltage of the hybrid bidirectional LLC-DAB converter; V o for the output voltage of the hybrid bidirectional LLC-DAB converter; V C2 To assist the input voltage of the DAB circuit; K 1 is a transformer in the LLC primary side circuit T 1 is the turns ratio of 1 K 2 is the turns ratio of the transformer in the auxiliary DAB circuit T 2 D φ is the steady state phase angle; L m is the excitation inductance; n The ratio of the maximum and minimum steady-state phase shift angle is calculated as follows: （2） wherein D ϕmax is the maximum power margin; D ϕmin is the ratio of reactive power to active power.

3. The method of claim 2, wherein: Switching conduction loss of the hybrid bidirectional LLC-DAB converter P sw_c The calculation formula is: （3） wherein, I RMS_LLC the on current for all switches in the LLC primary side circuit; R LLC the on-resistance of all switches in the LLC primary side circuit; I RMS_DAB To assist the on current of all switches in the DAB circuit; R DAB To assist the on-resistance of all switches in the DAB circuit; I RMS_s for the on current of the secondary side switch; R s the on-resistance of the secondary side switch; wherein I RMS_LLC , I RMS_DAB , I RMS_S The calculation formulas of the above are respectively: （4） （5） （6） in, T s For switching cycles; i Lr ( t ) represents the resonant inductor current.

4. The method of claim 3, wherein: Switching loss of the hybrid bidirectional LLC-DAB converter P sw_off The calculation formula is: （7） wherein, P sw_off_LLC is the switching turn-off loss of the LLC primary side circuit; P sw_off_DAB To assist the switching off loss of DAB circuit; P sw_off_s switching losses of the secondary side switches; wherein P sw_off_LLC , P sw_off_DAB , P sw_off_s The calculation formulas are respectively: （8） wherein, V C1 Vin is the input voltage to the LLC primary side circuit; t off_LLC , t off_DAB , t off_s respectively the turn-off time of the switches of the LLC primary side circuit, the auxiliary DAB circuit, the secondary side circuit. I sw_off_LLC , I sw_off__DAB , I sw_off__s The off currents of the LLC primary side circuit, the auxiliary DAB circuit, and the secondary side circuit are respectively IoffLLC, IoffDAB, and Ioffsec, and the calculation formulas are respectively: （9） wherein, f r is the resonant frequency.

5. The method of claim 4, wherein: Inductor copper loss of the hybrid bidirectional LLC-DAB converter P C_L_loss The calculation formula is: （10） wherein, R C_L_LLC Rskin is the equivalent resistance considering the skin effect on the inductor of the LLC primary side circuit; R C_L_DAB Rcs is the equivalent resistance of the DAB circuit inductor taking into account the skin effect; wherein, R C_L Rskin is the equivalent resistance of the skin effect on the inductor, which is calculated by the formula: （11） wherein R dc_C_L Rdc is the direct current resistance on the inductor; N n is the number of strands in the Litz parameter; N L is the number of bundles; The formula for calculating Δ is: （12） wherein d w is the wire diameter of the litz wire, δ is the skin depth.

6. The method of claim 5, wherein: Transformer copper loss of the hybrid bidirectional LLC-DAB converter P C_T_loss The calculation formula is: （13） wherein, R C_T_LLC Rskin is the equivalent resistance taking into account the skin effect on the transformer of the LLC primary side circuit; R C_T_DAB To assist the DAB circuit inductor transformer on the equivalent resistance considering the skin effect; RC_T_s is the equivalent resistance of the transformer on the secondary side circuit considering the skin effect; IRMS_s is the on-state current of the secondary-side switch; wherein R C_T Equivalent resistance of transformer taking into account skin effect 。 7. The method of claim 6, wherein: Inductor core loss of the hybrid bidirectional LLC-DAB converter P I_L_loss The calculation formula is: （14） wherein, P I_L_LLC is the inductance iron loss of the LLC primary side circuit; P I_L_DAB To assist the inductance iron loss of DAB circuit; The inductance iron loss is calculated by using Steinmetz equation P iron_loss The calculation formula is: （15） wherein B max Bpkis the peak magnetic flux density; V L V is the volume of the selected magnetic core; K , α , β are Steinmetz parameters, respectively.

8. The method of claim 7, wherein: Transformer iron loss of the hybrid bidirectional LLC-DAB converter P I_T_loss The calculation formula is: （16） wherein, P I_T_LLC is the transformer core loss of the LLC primary side circuit; P I_T_DAB To assist the transformer core loss of DAB circuit; Wherein in the calculation of transformer iron loss P I_T The peak magnetic flux density expression of the LLC primary side circuit and the auxiliary DAB circuit is: （17） wherein N T is the number of turns of the transformer, D d is the duty cycle, A e is the cross-sectional area of the magnetic core; A e2 NT1 is the number of turns of the transformer in the main DAB circuit; NT2 is the number of turns of the transformer in the auxiliary DAB circuit; The total loss of the hybrid bidirectional LLC-DAB converter is obtained by adding the switching turn-on loss, switching turn-off loss, inductor copper loss, transformer copper loss, inductor iron loss, and transformer iron loss.

9. The method of claim 2, wherein: A model of the output voltage of the hybrid bidirectional LLC-DAB converter is established using a reduced-order modeling method, yielding: （18） wherein G d ( s ) is the transfer function of the control variable to the output voltage; A, B, C, D1, and E are the variables corresponding to the transfer function model, respectively. is a small perturbation of the duty cycle; m is the voltage matching ratio; Co is the output filter capacitance; G in ( s ) is the transfer function from input voltage to output voltage; wherein A , B , C , D 1、 E are the corresponding variables in formula (18), respectively, whose expressions are: （19） where the auxiliary DAB circuit uses single phase-shift modulation to regulate the output voltage, where the steady-state phase angle D φ The calculation formula is as follows: （20） Using the crossover frequency ω c1 The dynamic performance of the hybrid bidirectional LLC-DAB converter is analyzed using the crossover frequency, which is calculated as （21） wherein C 1 is an input capacitance for the primary side circuit of the LLC; C 2 is an input capacitance for the auxiliary DAB circuit.

10. The method of claim 9, wherein: The optimization of the hybrid bidirectional LLC-DAB converter by employing a multi-objective particle swarm optimization algorithm to optimize various parameters includes the following steps: Initializing acceleration constants, external archive EXA and target weight ω ; The turns ratio of transformer T1 in the primary side circuit of LLC is set to be K 1. Increase by a fixed step size and set it to λ min V in / V 0 wherein λ min is a minimum power capacity allocation factor;​ Initialize the LLC primary circuit resonant cavity parameter boundaries, particle velocity, position, and optimal archive PBA. The LLC primary circuit resonant cavity parameter boundaries are calculated based on the excitation inductance value, as follows: （22） wherein L r is a resonant inductance of the primary side circuit of the LLC; L m is a magnetizing inductance of the primary side circuit of the LLC; C r a resonant capacitor for the LLC primary side circuit; Update the particle velocity and position, and calculate the objective function value. The update equations for particle velocity and position are as follows: （23） wherein v i and pos i is the velocity and position of the i th particle; Rand is a random function; pbest i and gbest i are the individual best result of the i th particle, the global best result of all particles, respectively; k、 N is the current iteration number, and c 1 and c 2 are acceleration factors. Calculate the non-dominated solutions for all particles at the current iteration time, and update the best archive PBA based on the non-dominated solutions; All the best archive PBA are saved and the non-dominant solutions are determined, saved in the external archive EXA, currently K 1 The corresponding best result is saved in the external archive EXA; Increase K A fixed step size of 1, when K 1 greater than λ max * V in / V 0 ,in λ max If the minimum power capacity allocation factor is used, then we get... K 1. All optimal results are stored in an external archive EXA. All optimal results in the external archive EXA contain parameters of the hybrid bidirectional LLC-DAB converter; The parameters include: Turns ratio of transformer T1 in the primary side LLC circuit K 1. Resonant inductance of the primary side LLC circuit, resonant capacitance of the primary side LLC circuit, magnetizing inductance of the primary side LLC circuit, turns ratio of transformer T2 in the auxiliary DAB circuit K 2. Leakage inductance of the auxiliary DAB circuit Wherein the transformer in the auxiliary DAB circuit T 2 of the turns ratio K The solution formula of 2 is: （24）。

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