Isolated three-active-bridge converter numeralization parameter optimization design method based on hierarchical constraint

Abstract

The invention relates to an isolation type three-active-bridge converter numerical parameter optimization design method based on hierarchical constraint, and belongs to the field of power electronics. According to the method, the working principle of the isolated three-active bridge converter is analyzed, and a frequency domain steady-state analysis model is established; according to design requirements, working characteristics and a safe working domain of the ITAB converter, voltage gain constraint, inductance range constraint and maximum transmission power constraint are introduced in sequence; all main circuit parameters are constrained step by step, so that the parameter optimization range is greatly reduced; a power loss model of ITAB is established, and a mapping relation between a design space and a performance space is defined; and with the minimum weighted average loss of the whole working domain of the converter as a design target, parameter optimization design of the ITAB is completed, and an optimal circuit parameter combination is determined. According to the optimization design method, the parameter design space can be greatly reduced, the optimization difficulty is remarkably reduced, and the average efficiency of the converter in the whole working domain is improved.

Description

Technical Field

[0001] The invention belongs to the field of power electronics and relates to a numerical parameter optimization design method of an isolated three-active bridge converter based on hierarchical constraints. Background Art

[0002] In independent renewable energy power generation systems such as DC microgrids and aerospace power systems, in order to cope with the intermittent and random nature of renewable energy power generation, it is usually necessary to equip energy storage devices as energy buffer units to ensure the stability and continuity of system power supply. Compared with multiple two-port converters, a single multi-port converter realizes power transmission and control between multiple ports in an integrated manner. It has the advantages of the least power conversion links, the highest integration, and high efficiency. It has been widely used in DC microgrids, electric vehicles, and energy storage. However, with the complexity of application scenarios and the diversification of multi-port converter structures, how to give full play to their performance advantages has become a widely concerned issue. This not only involves the selection of conversion topology, but also involves challenges in parameter design and other aspects.

[0003] When the conversion topology is determined, the parameter design of the main circuit directly affects the steady-state performance limit of the converter, and plays a decisive role in key indicators such as voltage regulation capability, power transmission efficiency, and soft switching characteristics. Therefore, accurate parameter design can not only improve the overall performance of the converter, but also ensure that it achieves the expected effect in practical applications.

[0004] At present, the mainstream idea of ​​parameter optimization design of power electronic converters is the combination of software simulation and engineering verification. Although this design idea is widely used in engineering practice, the accuracy of the design results depends entirely on the calculation accuracy of the power electronic simulation tool. At the same time, the design process relies heavily on the designer's engineering experience to narrow the parameter range; and the repeated verification and iterative optimization of the simulation and hardware platform will make the design process cumbersome and time-consuming. In view of the above reasons, researchers have gradually turned their attention to numerical design methods based on object mathematical models. By determining the design space, performance space and mapping relationship, the parameter optimization design problem is finally converted into a mathematical optimization problem and solved by computer. However, parameter design research is almost concentrated on two-port converters, and there are few reports on the optimization design of the main circuit parameters of multi-port converters. Multi-port converters need to design more parameters, including the high-frequency transformer turns ratio and power inductance value of each port, at least 6 design parameters. The parameters are seriously coupled with each other, and it is difficult to determine the optimal parameter combination based on the maximum transmission power requirement and the law of voltage gain as simply as the two-port dual active full bridge.

[0005] At present, the research on parameter design of multi-port converters only combines the requirements of maximum transmission power, port voltage and current, and roughly selects the turns ratio and power inductance value of the transformer, and hardly considers the influence of hardware parameters on the steady-state performance of multi-port converters. Therefore, it is of great significance to explore a numerical parameter optimization design method for isolated three-active bridge converters based on the hierarchical constraint idea. Summary of the invention

[0006] In view of this, the purpose of the present invention is to provide a numerical parameter optimization design method for an isolated three-active bridge converter based on hierarchical constraints, so as to solve the problems that the isolated multi-port converter has numerous design parameters, strong coupling between parameters and great influence on conversion efficiency.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] The numerical parameter optimization design method of isolated three-active bridge converter based on hierarchical constraints is proposed. The circuit topology of isolated three-active bridge ITAB converter includes three ports connected by three-winding transformer and three H-bridge switch networks; N1: N2: N3 is the turns ratio of the three ports of high-frequency transformer; L1~L3 is the sum of transformer leakage inductance and external inductance; the excitation inductance is assumed to be infinite; S1~S4, Q1~Q4 and J1~J4 represent the switch devices in the three H-bridges respectively, and the active switch T x , parasitic capacitance C ossx And the anti-parallel diode D x Composition; v h1 ~v h3 is the AC square wave voltage generated by the three H bridges; i L1 ~i L3 represents the instantaneous current value flowing through the inductors L1 to L3; V1 to V3 and i1 to i3 represent the terminal voltage and terminal current of the three ports respectively. The design method includes the following steps:

[0009] S1. Based on the electrical characteristics of the converter and the conversion relationship of the inductance, the Y-type circuit is converted into a Δ-type equivalent circuit;

[0010] S2. Based on Fourier series decomposition, the frequency domain expression of the AC square wave voltage output by the full bridge is obtained. Based on the Δ-type equivalent circuit and power coupling relationship, the effective value expression of the inductor current and the transmission power expression of each port are derived.

[0011] S3. Based on the working characteristics, safe working domain and performance requirements of ITAB, voltage gain constraints, inductance range constraints and maximum transmission power constraints are introduced to reduce the parameter design space;

[0012] S4. Determine the performance space of ITAB, establish the mapping relationship between the parameter design space and the performance space, take the minimum loss of ITAB converter as the optimization goal, and find the optimal set of parameter combinations through traversal.

[0013] Further, the Δ equivalent circuit transformation in S1 specifically comprises the following steps:

[0014] Based on the electrical characteristics of the converter, the electrical quantities of ports 2 and 3 are converted to the primary side:

[0015]

[0016] Among them, the transformation ratio of the high-frequency transformer is n 12 =N1 / N2, n 13 =N1 / N3,n 23 =N2 / N3, N1, N2 and N3 represent the number of turns of the three windings of the transformer respectively;

[0017] According to the conversion relationship of inductance, the Y-type circuit is converted into a Δ-type equivalent circuit. The conversion relationship of inductance in the two equivalent models is expressed by the following formula:

[0018]

[0019] According to the fact that the power emitted by each port is equal to the sum of the power transmitted between the port and the two adjacent ports, the expression of the effective value of the inductor current and the expression of the power transmitted by each port are specifically expressed as follows:

[0020]

[0021] Furthermore, in S2, the conversion of the frequency domain steady-state analysis model specifically comprises the following steps:

[0022] The voltage gain of the ITAB converter is expressed as:

[0023]

[0024] The reference current and power of the ITAB converter are expressed as:

[0025]

[0026] Based on Fourier series decomposition, the AC square wave voltage v output by the full bridge is obtained h1 ~v h3 The frequency domain expression of is:

[0027]

[0028] Where, the angular frequency ω s =2πf s , f srepresents the switching frequency of ITAB;

[0029] Based on the Δ-type equivalent circuit, the normalized instantaneous value of the inductor current i is obtained. L1,N ~i L3,N expression:

[0030]

[0031] According to the working characteristics of the ITAB converter, the average value of the inductor current in a steady-state switching cycle is equal to 0, and the following current relationship expression is obtained:

[0032]

[0033] The instantaneous value expression of the inductor current is specifically expressed as:

[0034]

[0035] Where A1 = A 12 -A 13 , B1=B 12 -B 13 , A2=A 23 -A 12 , B2=B 23 -B 12 , A3=A 31 -A 23 , B3=B 31 -B 23 ; A 12 , B 12 , A 13 , B 13 , A 23 , B 23 It is expressed as:

[0036]

[0037] The effective value of the inductor current of the ITAB converter is expressed by the following formula:

[0038]

[0039] The per-unit value of the power transmitted by each port in one switching cycle is expressed by the following formula:

[0040]

[0041] Furthermore, in S3, the parameter design space constraint includes the following specific steps:

[0042] S301: Normalize the six parameters of the parameter design space of the ITAB converter, namely, the power inductance values ​​L1, L2, L3 and the number of transformer turns N1, N2, N3, and convert the parameters in the parameter design space into L1, k 12 , k 13 、n 12、 n 13 The specific steps of these five parameters include:

[0043] Taking N3 as the reference, normalize the turns N1 and N2 of ports 1 and 2 to n 12 and n 13 ;

[0044] Taking L1 as the reference, the inductance L2 and L3 are normalized to k according to the conversion expression of the inductance in the equivalent model. 12 and k 13 , k 12 and k 13 It is expressed by the following formula:

[0045]

[0046] S302: Based on the voltage gain requirement, constrain n 12 and n 13 :

[0047] According to the fact that the closer the voltage gain ratio is to 1 under the same transmission power, the smaller the reactive power of the converter is and the higher the operating efficiency is, the voltage gain range of the ITAB converter is set to M. 12 ∈[0.5, 1.3] and M 13 ∈[0.8, 1.2], to exclude the parameter combination with large reactive power; based on the above voltage gain range and gain expression, solve the turns ratio n 12 and n 13 Design range, parameter n 12 and n 13 The range is successfully narrowed down to n 12 ∈[0.9, 1.3], n 13 ∈[2.7, 3.4];

[0048] S303: Based on the inductance range requirement, constrain k 12 and k 13 :

[0049] Based on the winding leakage inductance limitation of the three ports of the transformer, the voltage of port 3 is relatively small, and the corresponding number of winding turns is relatively small. The power inductance ranges of the three ports are limited to L1 ≥ 4μH, L2 ≥ 4μH and L3 ≥ 2μH respectively;

[0050] L2 and L3 with respect to L1, k 12 and k 13The functional relationship is expressed by the following formula:

[0051]

[0052] Combine the above formula to solve the parameter k 12 and k 13 The effective design space, k 12 and k 13 The range is related to L1;

[0053] S304: Based on the maximum transmission power requirement, further constrain L1, k 12 and k 13 :

[0054] According to the technical parameters of the ITAB converter and considering a certain overload, the maximum transmission power range of the three ports of the ITAB converter should meet |P 1,max |≥5kW, P 2,max ≥4kW,|P 3,max |≥4kW, i.e. P 1,max , P 2,max and P 3,max About k 12 and k 13 The constraint relationship is expressed by the following formula:

[0055]

[0056] According to the above formula, k can be further reduced 12 and k 13 The effective design space of L1 is 12 and k 13 The effective design space of k 12 and k 13 The parameter design space is gradually reduced; when L1=60μH, there is no design space that meets the maximum power requirement; the range of design parameter L1 needs to be constrained to L1∈[4μH, 50μH]; based on the above voltage gain, inductance range and maximum power constraints, the five parameters in the parameter design space of ITAB converter are narrowed down to: n 12 ∈[0.9, 1.3], n 13 ∈[2.7, 3.5], L1∈[4μH, 50μH].

[0057] Further, in S4, a mapping relationship between the parameter design space and the performance space is established, wherein the performance space is determined to be the power transmission loss of the ITAB converter, and the specific steps include:

[0058] The loss model of ITAB converter is established to solve the functional relationship between loss and design parameters; the power loss is mainly composed of four parts: the conduction loss of the switching device Pcon and switching loss P sw , the core loss P of the magnetic component core and copper loss P cu .

[0059] Furthermore, in S4, the target parameter optimization step specifically includes:

[0060] In [L1, k 12 , k 13 、n 12、 n 13 ] parameter in the limited design space Con_para, with the ITAB converter loss minimization as the optimization goal, the optimal set of parameter combinations [L1, k 12 , k 13 、n 12、 n 13 ] opt ;

[0061] According to the working mode, a typical working point is selected, and then the weighted average loss is used as the final indicator to measure the quality of each set of parameters; by traversing and comparing the weighted average losses corresponding to each set of parameters, a set of optimal parameter combinations is finally determined.

[0062] The beneficial effects of the present invention are as follows: the method combines the converter operating characteristics and safe operating domain, introduces constraints such as voltage gain and maximum power in turn, greatly reduces the parameter design space, and significantly reduces the optimization difficulty; the design goal is to minimize the weighted average loss of the converter in the entire operating domain, and the main circuit parameter optimization of the multi-port converter is completed. The present invention takes into account the main circuit parameters and their complex coupling, avoids the problem of efficiency reduction caused by ignoring the coupling effect, and at the same time, the optimization process is based on the entire operating domain to ensure efficient operation under various loads and working conditions, and can effectively improve the average efficiency of the converter in the entire operating domain.

[0063] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0065] Figure 1 Flow chart of the parameter optimization design steps for ITAB converter;

[0066] Figure 2 The topology diagram of the isolated three-active bridge converter based on magnetic integration;

[0067] Figure 3 It is the schematic diagram of the equivalent circuit model of ITAB converter; Figure 3 (a) is a Y-type equivalent circuit; Figure 3 (b) is the Δ-type equivalent circuit;

[0068] Figure 4 It is the fundamental component vector diagram of ITAB converter;

[0069] Figure 5 k is the inductance range constraint 12 and k 13 Schematic diagram of the parameter design space L1 = 30μH;

[0070] Figure 6 Schematic diagram of parameter design space of k12 and k13 under the maximum transmission power constraint; Figure 6 (a) L1 = 10 μH; Figure 6 (b) L1 = 30 μH; Figure 6 (c) L1 = 50 μH; Figure 6 (d) L1 = 60 μH;

[0071] Figure 7 Schematic diagram of inductor current values ​​under three parameter combinations;

[0072] Figure 8 Schematic diagram of loss distribution under three parameter combinations;

[0073] Fig. 9 The typical working waveform diagram of the optimal parameter combination at the working point of V1 = 380V, V2 = 360V, V3 = 132V, P1 = P3 = -300W;

[0074] Fig.10 The typical working waveform diagram of the typical parameter combination 1 at the working point of V1 = 380V, V2 = 360V, V3 = 132V, P1 = P3 = -300W;

[0075] Fig.11 Schematic diagram of the measured efficiency curves of the optimized parameter combination and the typical parameter combination 1. DETAILED DESCRIPTION

[0076] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0077] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0078] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0079] like Figure 1 As shown in the figure, the numerical parameter optimization design method of the isolated three-active bridge converter based on the hierarchical constraint idea is as follows:

[0080] S1. Analyze the working principle of the isolated three-active bridge converter. Based on the electrical characteristics of the converter and the conversion relationship of the inductance, convert the Y-type circuit into a Δ-type equivalent circuit.

[0081] S2. Establish a frequency domain steady-state analysis model, obtain the frequency domain expression of the AC square wave voltage output by the full-bridge based on Fourier series decomposition, and derive the effective value expression of the inductor current and the transmission power expression of each port based on the Δ-type equivalent circuit and power coupling relationship.

[0082] S3. Based on the working characteristics, safe working domain and performance requirements of ITAB, voltage gain constraints, inductance range constraints and maximum transmission power constraints are introduced to reduce the parameter design space.

[0083] S4. Determine the performance space of ITAB, establish the mapping relationship between the parameter design space and the performance space, take the minimum loss of ITAB converter as the optimization goal, and find the optimal set of parameter combinations through traversal.

[0084] In the specific implementation process, Figure 2 As shown, the circuit topology of the isolated three-active bridge ITAB converter includes three ports connected by a three-winding transformer and three H-bridge switch networks. N1:N2:N3 is the turns ratio of the three ports of the high-frequency transformer. L1~L3 is the sum of the transformer leakage inductance and the external inductance. Since the excitation inductance of the transformer is much larger than the leakage inductance, the excitation inductance is assumed to be infinite. S1~S4, Q1~Q4 and J1~J4 represent the switch devices in the three H-bridges, which are composed of active switches T x , parasitic capacitance C ossx And the anti-parallel diode D x Composition. h1 ~v h3 is the AC square wave voltage generated by the three H bridges. L1 ~i L3 Indicates the instantaneous current value flowing through the inductors L1~L3. V1~V3 and i1~i3 respectively represent the terminal voltage and terminal current of the three ports. Figure 2 shown.

[0085] In the specific implementation process, based on the electrical characteristics of the converter and the conversion relationship of the inductance, the Y-type circuit is converted into a Δ-type equivalent circuit, such as Figure 3 shown.

[0086] Specifically, based on the electrical characteristics of the converter, the electrical quantities of ports 2 and 3 can be converted to the primary side:

[0087]

[0088] Among them, the high-frequency transformer n 12 =N1 / N2, n 13 =N1 / N3,n 23 =N2 / N3, N1, N2 and N3 represent the number of turns of the three windings of the transformer respectively.

[0089] like Figure 3 (a) is the Y-type equivalent circuit of the ITAB converter. The Y-type circuit is converted into a Δ-type equivalent circuit according to the conversion relationship of the inductance. The conversion relationship of the inductance in the two equivalent models can be expressed by the following formula:

[0090]

[0091] like Figure 3As shown in (b), the Δ-type equivalent circuit intuitively reflects the power coupling relationship between the three ports, that is, the power emitted by each port is equal to the sum of the power transmitted between the port and the two adjacent ports, which can be specifically expressed as:

[0092]

[0093] During the specific implementation, the frequency domain analysis method is used to establish a unified mathematical model of the ITAB converter.

[0094] Specifically, the voltage gain of the ITAB converter is expressed as:

[0095]

[0096] The reference current and power of the ITAB converter are expressed as:

[0097]

[0098] Based on Fourier series decomposition, the AC square wave voltage v output by the full bridge is obtained h1 ~v h3 The frequency domain expression of is:

[0099]

[0100] Where, the angular frequency ω s =2πf s , f s Represents the switching frequency of ITAB.

[0101] based on Figure 3 (a) shows the Δ-type equivalent circuit, the normalized instantaneous value of the inductor current i L1,N ~i L3,N It can be expressed by the following formula:

[0102]

[0103] According to the working characteristics of the ITAB converter, the average value of the inductor current in a steady-state switching cycle is equal to 0, and the relationship expression can be expressed by the following formula:

[0104]

[0105] Substituting the normalized instantaneous value of the inductor current into the above inductor current relationship expression, the instantaneous value expression of the inductor current can be specifically expressed as:

[0106]

[0107] Where A1 = A 12 -A 13 , B1=B 12 -B13 , A2=A 23 -A 12 , B2=B 23 -B 12 , A3=A 31 -A 23 , B3=B 31 -B 23 . A 12 , B 12 , A 13 , B 13 , A 23 , B 23 It can be expressed as:

[0108]

[0109] Combining the instantaneous value expression of the inductor current and A 12 , B 12 , A 13 , B 13 , A 23 , B 23 The effective value of the inductor current of the ITAB converter can be expressed by the following formula:

[0110]

[0111] Combined with the transmission power coupling relationship expression, the AC square wave voltage v output by the full bridge h1 ~v h3 The expression of the instantaneous value of the inductor current and the per-unit value of the power transmitted by each port during the switching cycle can be expressed by the following formula:

[0112]

[0113] In the specific implementation process, the port voltage, power range and other technical parameters of the ITAB converter are determined in combination with the actual application scenario analysis. Based on the working characteristics, safe working domain and performance requirements of ITAB, voltage gain constraints, inductance range constraints and maximum transmission power constraints are introduced to reduce the parameter design space. The steps are as follows:

[0114] S301: The parameter design space of the ITAB converter includes six parameters: power inductance values ​​L1, L2, L3 and transformer turns N1, N2, N3. These six parameters are normalized to convert the parameters in the parameter design space into L1, L2, L3 and N1, N2, N3. 12 , k 13 、n 12、 n 13 The specific steps of these five parameters include:

[0115] Taking N3 as the reference, normalize the turns N1 and N2 of ports 1 and 2 to n 12 and n 13 .

[0116] Taking L1 as the reference, the inductance L2 and L3 are normalized to k according to the conversion expression of the inductance in the equivalent model. 12 and k 13 , k 12 and k 13 It can be expressed by the following formula:

[0117]

[0118] S302: Based on the voltage gain requirement, constrain n 12 and n 13 :

[0119] Specifically, the fundamental wave vector diagram of the voltage and current of the ITAB converter under the same transmission power is drawn. Figure 4 As shown, according to It can be seen from the position that under the same transmission power (active power), the closer the voltage amplitudes of the three ports are (i.e., the voltage gain M 12 The closer it is to 1), the smaller the component of the inductor current projected onto the imaginary axis Im. In other words, at the same transmission power, the closer the voltage gain ratio is to 1, the smaller the reactive power of the converter is and the higher the operating efficiency is.

[0120] According to the same transmission power, the closer the voltage gain ratio is to 1, the smaller the reactive power of the converter is and the higher the operating efficiency is. The voltage gain range of the ITAB converter can be set to M 12 ∈[0.5, 1.3] and M 13 ∈[0.8, 1.2] to exclude the parameter combination with large reactive power. Based on the above voltage gain range and gain expression, the turns ratio n can be solved 12 and n 13 Design range, parameter n 12 and n 13 Range n 12 ∈[0.9, 1.3], n 13 ∈[2.7,3.4].

[0121] S303: Based on the inductance range requirement, constrain k 12 and k 13 :

[0122] Considering the actual engineering application, due to the limitation of winding process, the windings of the three ports of the transformer have a certain leakage inductance. Considering that the voltage of port 3 is small, the corresponding number of winding turns is relatively small. The power inductance range of the three ports is limited to L1 ≥ 4μH, L2 ≥ 4μH and L3 ≥ 2μH respectively.

[0123] According to the conversion relationship of the inductance and the normalized k 12 and k 13 The expression of L2 and L3 with respect to L1, k 12 and k 13 The functional relationship can be expressed by the following formula:

[0124]

[0125] Combining the above formula, we can solve the parameter k 12 and k 13 The effective design space, k 12 and k 13 The range is related to L1, to show the constrained k 12 and k 13 Design scope, such as Figure 5 As shown, the k value based on the power inductance range constraint is plotted when L1 = 30μH. 12 and k 13 effective design space.

[0126] S304: Based on the maximum transmission power requirement, further constrain L1, k 12 and k 13 .

[0127] According to the technical parameters and considering a certain overload, the maximum transmission power range of the three ports of the ITAB converter should meet |P 1,max |≥5kW, P 2,max ≥4kW,|P 3,max |≥4kW, i.e. P 1,max , P 2,max and P 3,max About k 12 and k 13 The constraint relationship can be expressed by the following formula:

[0128]

[0129] According to the above formula, k can be further reduced 12 and k 13 The effective design space is Figure 6 It shows that k 12 and k 13 effective design space. Figure 6 (a) L1 = 10 μH; Figure 6 (b) L1 = 30 μH; Figure 6 (c) L1 = 50 μH; Figure 6 (d) is L1 = 60μH; observe the effective design space, as L1 increases, k 12 and k 13 The parameter design space is gradually decreasing. When L1=60μH, there is no design space that meets the maximum power requirement. So far, the range of design parameter L1 needs to be constrained to L1∈[4μH, 50μH]. Based on the above voltage gain, inductance range and maximum power constraints, the five parameters in the parameter design space of ITAB converter are narrowed down to: 12 ∈[0.9, 1.3], n 13 ∈[2.7, 3.5], L1∈[4μH, 50μH], k 12 and k 13 Range such as Figure 6 shown.

[0130] Finally, the infinite parameter design space can be reduced to only 205 groups [L1, k 12 , k 13 、n 12、 n 13 ] parameter in the limited design space Con_para. Due to the large number of parameters, only the variable combinations [L1, k 12 , k 13 、n 12、 n 13 ], a total of 17 groups, Table 1 shows the parameter combinations that meet all constraints when L1 = 30μH.

[0131] Table 1

[0132]

[0133] In the specific implementation process, the performance space is determined as the power transmission loss of the ITAB converter. The mapping relationship between the parameter design space and the performance space is established, and the specific steps include:

[0134] The loss model of ITAB converter is established to solve the functional relationship between loss and design parameters. Power loss mainly consists of four parts: conduction loss P con and switching loss P sw , the core loss P of the magnetic component core and copper loss P cu .

[0135] In the specific implementation process, the optimization of target parameters includes the following specific steps:

[0136] In the 205 groups [L1, k12 , k 13 、n 12、 n 13 ] parameter in the limited design space Con_para, with the ITAB converter loss minimization as the optimization goal, the optimal set of parameter combinations [L1, k 12 , k 13 、n 12、 n 13 ] opt .

[0137] According to the working mode, points are evenly taken, typical working points are selected, and then the weighted average loss is used as the final indicator to measure the quality of each group of parameters; a total of 72 typical working points are taken, and then the weighted average loss of the 72 working points is used as the final indicator to measure the quality of each group of parameters; by traversing and comparing the weighted average losses corresponding to each group of parameters, a set of optimal parameter combinations can be determined in the end. This set of parameters not only meets all the above constraints, but also has the minimum power transmission loss.

[0138] To illustrate the effect of parameter optimization, two typical parameter combinations and the optimal parameter combination are selected from the Con_para space for comparative analysis. The specific values ​​of the three groups of parameters are shown in Table 2.

[0139] Table 2

[0140]

[0141] In order to better illustrate the advantages of the comprehensive optimization modulation method in the present invention, this embodiment has performed relevant simulations, and the specific simulation results are as follows:

[0142] like Figure 7 As shown in the figure, the effective value of the inductor current and the stress of the ITAB converter under the three parameter combinations are plotted as the port power P3 changes. It can be seen that no matter how the port power changes, the current size of the optimal parameter combination [40μH, 3.2, 3.0, 1.1, 2.7] is almost maintained at the lowest level, which proves the advantage of the optimal parameter combination [40μH, 3.2, 3.0, 1.1, 2.7] in reducing the converter loop current.

[0143] In order to more intuitively illustrate the optimal parameter combination [L1, k 12 , k 13 、n 12、 n 13 ] opt The impact on system losses, such as Figure 8As shown in Figure 7, the loss distribution of the three groups of parameters is compared, showing the loss distribution of the three groups of parameters when P3 = 1000 W. At this operating point, the converter losses of typical combinations 1 and 2 are 20.4 W and 17.4 W respectively, and the total loss of the optimal parameter combination is 10.2 W, which is almost half of the above two typical combinations.

[0144] According to the comparison results of current and loss, the optimal parameter combination can effectively reduce the loop current level and power transmission loss of the ITAB converter through parameter design, thereby improving the operating efficiency of the converter.

[0145] In order to better illustrate the advantages of the comprehensive optimization modulation method in the present invention, this embodiment has conducted relevant experiments, and the specific experimental results are as follows:

[0146] like Fig. 9 and Fig.10 As shown, the two sets of parameters of typical combination 1 and optimal combination were experimentally tested, showing the typical working waveform of transmission power P1=P3=-300W when port voltage V1=380V, V2=360V, V3=132V. Their steady-state performance was fully analyzed and compared.

[0147] At the current effective value level, the inductor current effective values ​​corresponding to the optimal parameter combination are 1.09A, 2.38A and 3.45A, which are basically consistent with the theoretically calculated 1.11A, 2.31A and 3.22A. Compared with the typical combination 1, under the optimized parameters, the current values ​​of the three ports of ITAB are reduced by about 50%. The above experimental test results illustrate the advantages of the determined optimal parameter combination in reducing the current level.

[0148] like Fig.11 As shown in the figure, the conversion efficiency of the ITAB converter varies with power. Compared with the measured efficiency curve of the typical combination 1, the efficiency curve of the optimal parameter combination has been significantly improved in the entire power range. The weighted average efficiency of the two sets of circuit parameters is 96.08% and 97.48% respectively. Through parameter optimization design, the conversion efficiency of ITAB has been improved by about 1.5% overall.

[0149] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A numerical parameter optimization design method for isolated three-active bridge converter based on hierarchical constraints. The circuit topology of the isolated three-active bridge ITAB converter includes three ports connected by a three-winding transformer and three H-bridge switch networks; N1: N2: N3 is the turns ratio of the three ports of the high-frequency transformer; L1~L3 is the sum of the transformer leakage inductance and the external inductance; the excitation inductance is assumed to be infinite; S1~S4, Q1~Q4 and J1~J4 represent the switch devices in the three H-bridges respectively, and the active switch T x , parasitic capacitance C ossx And the anti-parallel diode D x Composition; v h1 ~v h3 is the AC square wave voltage generated by the three H bridges; i L1 ~i L3 Indicates the instantaneous current value flowing through the inductors L1~L3; V1~V3 and i1~i3 respectively represent the terminal voltage and terminal current of the three ports, which are characterized by: The design method includes the following steps: S1. Based on the electrical characteristics of the converter and the conversion relationship of the inductance, the Y-type circuit is converted into a Δ-type equivalent circuit; S2. Based on Fourier series decomposition, the frequency domain expression of the AC square wave voltage output by the full bridge is obtained. Based on the Δ-type equivalent circuit and power coupling relationship, the effective value expression of the inductor current and the transmission power expression of each port are derived. S3. Based on the working characteristics, safe working domain and performance requirements of ITAB, voltage gain constraints, inductance range constraints and maximum transmission power constraints are introduced to reduce the parameter design space; S4. Determine the performance space of ITAB, establish the mapping relationship between the parameter design space and the performance space, take the minimum loss of ITAB converter as the optimization goal, and find the optimal set of parameter combinations through traversal.

2. The method for numerical parameter optimization design of isolated triple active bridge converter based on hierarchical constraints according to claim 1 is characterized in that: The Δ equivalent circuit conversion in S1 specifically comprises the following steps: Based on the electrical characteristics of the converter, the electrical quantities of ports 2 and 3 are converted to the primary side: Among them, the transformation ratio of the high-frequency transformer is n 12 =N1 / N2, n 13 =N1 / N3,n 23 =N2 / N3, N1, N2 and N3 represent the number of turns of the three windings of the transformer respectively; According to the conversion relationship of inductance, the Y-type circuit is converted into a Δ-type equivalent circuit. The conversion relationship of inductance in the two equivalent models is expressed by the following formula: According to the fact that the power emitted by each port is equal to the sum of the power transmitted between the port and the two adjacent ports, the expression of the effective value of the inductor current and the expression of the power transmitted by each port are specifically expressed as follows:

3. The numerical parameter optimization design method of isolated triple active bridge converter based on hierarchical constraint concept according to claim 1 is characterized in that: In S2, the conversion of the frequency domain steady-state analysis model includes the following specific steps: The voltage gain of the ITAB converter is expressed as: The reference current and power of the ITAB converter are expressed as: Based on Fourier series decomposition, the AC square wave voltage v output by the full bridge is obtained h1 ~v h3 The frequency domain expression of is: Where, the angular frequency ω s =2πf s , f s represents the switching frequency of ITAB; Based on the Δ-type equivalent circuit, the normalized instantaneous value of the inductor current i is obtained. L1,N ~i L3,N expression: According to the working characteristics of the ITAB converter, the average value of the inductor current in a steady-state switching cycle is equal to 0, and the following current relationship expression is obtained: The instantaneous value expression of the inductor current is specifically expressed as: Where A1 = A 12 -A 13 , B1=B 12 -B 13 , A2=A 23 -A 12 , B2=B 23 -B 12 , A3=A 31 -A 23 , B3=B 31 -B 23 ; A 12 , B 12 , A 13 , B 13 , A 23 , B 23 It is expressed as: The effective value of the inductor current of the ITAB converter is expressed by the following formula: The per-unit value of the power transmitted by each port in one switching cycle is expressed by the following formula:

4. The method for numerical parameter optimization design of isolated triple active bridge converter based on hierarchical constraint concept according to claim 1 is characterized in that: In S3, the parameter design space constraint includes the following specific steps: S301: Normalize the six parameters of the parameter design space of the ITAB converter, namely, the power inductance values ​​L1, L2, L3 and the number of transformer turns N1, N2, N3, and convert the parameters in the parameter design space into L1, k 12 , k 13 、n 12、 n 13 The specific steps of these five parameters include: Taking N3 as the reference, normalize the turns N1 and N2 of ports 1 and 2 to n 12 and n 13 ; Taking L1 as the reference, the inductance L2 and L3 are normalized to k according to the conversion expression of the inductance in the equivalent model. 12 and k 13 , k 12 and k 13 It is expressed by the following formula: S302: Based on the voltage gain requirement, constrain n 12 and n 13 : According to the fact that the closer the voltage gain ratio is to 1 under the same transmission power, the smaller the reactive power of the converter is and the higher the operating efficiency is, the voltage gain range of the ITAB converter is set to M. 12 ∈[0.5, 1.3] and M 13 ∈[0.8, 1.2], to exclude the parameter combination with large reactive power; based on the above voltage gain range and gain expression, solve the turns ratio n 12 and n 13 Design range, parameter n 12 and n 13 The range is successfully narrowed down to n 12 ∈[0.9, 1.3], n 13 ∈[2.7, 3.4]; S303: Based on the inductance range requirement, constrain k 12 and k 13 : Based on the winding leakage inductance limitation of the three ports of the transformer, the voltage of port 3 is relatively small, and the corresponding number of winding turns is relatively small. The power inductance ranges of the three ports are limited to L1 ≥ 4μH, L2 ≥ 4μH and L3 ≥ 2μH respectively; L2 and L3 with respect to L1, k 12 and k 13 The functional relationship is expressed by the following formula: Combine the above formula to solve the parameter k 12 and k 13 The effective design space, k 12 and k 13 The range is related to L1; S304: Based on the maximum transmission power requirement, further constrain L1, k 12 and k 13 : According to the technical parameters of the ITAB converter and considering a certain overload, the maximum transmission power range of the three ports of the ITAB converter should meet |P 1,max |≥5kW, P 2,max ≥4kW,|P 3,max |≥4kW, i.e. P 1,max , P 2,max and P 3,max About k 12 and k 13 The constraint relationship is expressed by the following formula: According to the above formula, k can be further reduced 12 and k 13 The effective design space of L1; observe that k 12 and k 13 The effective design space of k 12 and k 13 The parameter design space is gradually reduced; when L1=60μH, there is no design space that meets the maximum power requirement; the range of design parameter L1 needs to be constrained to L1∈[4μH, 50μH]; based on the above voltage gain, inductance range and maximum power constraints, the five parameters in the parameter design space of ITAB converter are narrowed down to: n 12 ∈[0.9, 1.3], n 13 ∈[2.7, 3.5], L1∈[4μH, 50μH].

5. The method for numerical parameter optimization design of isolated triple active bridge converter based on hierarchical constraints according to claim 1, characterized in that: In S4, a mapping relationship between the parameter design space and the performance space is established, wherein the performance space is determined to be the power transmission loss of the ITAB converter. The specific steps include: The loss model of ITAB converter is established to solve the functional relationship between loss and design parameters; the power loss is mainly composed of four parts: the conduction loss of the switching device P con and switching loss P sw , the core loss P of the magnetic component core and copper loss P cu .

6. The method for numerical parameter optimization design of isolated triple active bridge converter based on hierarchical constraints according to claim 1, characterized in that: In S4, the target parameters are optimized, and the specific steps include: In [L1, k 12 , k 13 、n 12、 n 13 ] parameter in the limited design space Con_para, with the ITAB converter loss minimization as the optimization goal, the optimal set of parameter combinations [L1, k 12 , k 13 、n 12、 n 13 ] opt ; According to the working mode, a typical working point is selected, and then the weighted average loss is used as the final indicator to measure the quality of each set of parameters; by traversing and comparing the weighted average losses corresponding to each set of parameters, a set of optimal parameter combinations is finally determined.

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