Modeling method, system and terminal for electric propulsion aircraft power conversion system

Abstract

The application belongs to the technical field of hybrid electric propulsion aircraft, and discloses a modeling method, system and terminal for an electric propulsion aircraft power conversion system, four working modes of parallel power converters are determined; the circuit is discretely linearized by using a binary resistance method, and a discrete linearization model of boost and bidirectional DC / DC converters is constructed; node voltage transient equations are listed and written, and the electrical coupling characteristics of the parallel circuit are expressed by state variable coupling; the node voltage transient equation and the electrical coupling characteristic expression are solved by using a numerical method, a matrix equation is obtained, and iterative calculation is completed, and then the mathematical model of the electric propulsion aircraft power conversion system is obtained, and the working state simulation of the converter is realized. The application is based on linear discretization of the circuit and electrical state decoupling, and uses an implicit Euler method to solve the rigid differential equation, so that the accuracy and stability of the solution are obviously improved, and the application has good applicability. The application is supported by a master's postgraduate practice and innovation ability cultivation fund of Northwest Polytechnic University.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of hybrid electric propulsion aircraft, and particularly relates to a modeling method, system and terminal for an electric propulsion aircraft power conversion system. BACKGROUND

[0002] At present, a common electric propulsion aircraft power system takes fuel cells as a main power source, lithium batteries as auxiliary energy to improve dynamic response capability, and is connected to a 270V DC bus after being connected to a boost converter and a bidirectional DC / DC converter, respectively. The power conversion system plays an important role in maintaining bus voltage, controlling lithium battery charging and discharging, and adjusting energy distribution. Since the system is a multi-converter system (MCS), there is coupling at the bus voltage, and therefore, establishing an accurate electric propulsion aircraft power conversion system model is one of the key works for electric system simulation.

[0003] At present, the modeling methods for power converters at home and abroad mainly include state space averaging method, description function method and generalized averaging method. These modeling methods have complete mathematical structures and have been widely used in single-converter modeling. However, for the multi-converter system contained in the electric propulsion aircraft, if each converter is modeled independently using the above methods, the influence of the electrical coupling characteristics of the converter output end is ignored, which will obviously reduce the accuracy of the model. People propose an impedance modeling method based on harmonic linearization to realize multi-grid-connected DC / AC converter modeling. The model obtained by this technology can study the interaction between inverters due to the grid impedance of the common coupling point, and can also quantify the influence of the coupling relationship on the impedance characteristics, but this technology cannot be applied to DC / DC converters.

[0004] Through the above analysis, the problems and defects of the prior art are:

[0005] (1) For the multi-converter system contained in the electric propulsion aircraft, modeling each converter independently ignores the influence of the electrical coupling characteristics of the converter output end, which will obviously reduce the accuracy of the model.

[0006] (2) The existing characterization methods for electrical coupling characteristics are mostly limited to impedance analysis, and their applicable objects are only DC / AC or AC / AC converters.

[0007] (3) The modeling specification of MCS has not been unified, and excessive reliance is placed on computer simulation tools to handle complex circuit coupling relationships. SUMMARY

[0008] In view of the problems in the prior art, the present application provides a modeling method, system and terminal for an electric propulsion aircraft power conversion system.

[0009] The application is implemented by a modeling method for an electric propulsion aircraft power conversion system, which comprises the following steps:

[0010] Step one, determine the parallel power converter operating mode;

[0011] Step two, convert the circuit into a discretized linear model;

[0012] Step three, build a node voltage transient equation;

[0013] Step four, represent the parallel state at the DC bus through state variable coupling;

[0014] Step five, solve and complete iterative calculation using numerical methods.

[0015] Further, the determination of the parallel power converter operating mode in step one comprises:

[0016] The hybrid electric propulsion aircraft power conversion system includes a boost converter and a bidirectional DC / DC converter, and uses fuel cells and lithium batteries as voltage sources, respectively. The boost converter connected to the output end of the fuel cell is responsible for lifting the output voltage of the fuel cell to the DC bus voltage of the aircraft; the bidirectional DC / DC converter connected to the lithium battery has two operating modes, and the current flow direction is switched for charging or discharging scenarios. Ignoring the boost converter operating mode, the parallel converter includes four operating modes:

[0017] Mode 1: Q2 is on, Q3 is off, the voltage of L2 linearly rises, the inductance energy storage increases, and the capacitor releases energy to the load;

[0018] Mode 2: Q2 and Q3 are off, the output voltage of the fuel cell V in1 and L2 together provide energy to the load, and achieve the effect of voltage rise;

[0019] Mode 3: Q3 is on, Q2 is off, the DC bus of the aircraft charges the lithium battery, and the bidirectional DC / DC converter is in step-down mode;

[0020] Mode 4: Q2 and Q3 are off, the charging current flows through the anti-parallel D4, the current size decreases exponentially, L2 is large and the switching frequency is high, the converter is in current continuous mode and the ripple is small;

[0021] Wherein, Q2 and Q3 represent the converter switching devices, D4 represents the anti-parallel diode, L1 and L2 represent the boost converter input inductance and bidirectional DC / DC converter input inductance, respectively.

[0022] Further, the circuit transformation in step two into a discrete linear model includes:

[0023] Using the binary resistance method, based on the switching judgment logic of a single switching device, the switching characteristics of the switching device are equivalent to a large resistance. For a controlled power switching device, when the switching tube is added to the forward voltage drop and the driving signal, the switching tube is in the on low resistance state, and vice versa. The on-state switching tube is equivalent to a small resistance, and the off-state switching tube is equivalent to a large resistance. The diode is represented as a discrete linear function of the current voltage, and the discrete linearization model of the boost and bidirectional DC / DC converter is obtained.

[0024] Further, the construction of the node voltage transient equation in step three is:

[0025] ,

[0026] Wherein, and represent the current of inductors L1 and L2 respectively; R1, R3, R4 are the equivalent resistances of the switching tubes; R2 is the equivalent resistance of the diode; L1 and L2 represent the input inductance of the boost converter and the input inductance of the bidirectional DC / DC converter respectively; is the DC bus voltage; V in1 and V in2 represent the output voltages of the fuel cell and the lithium battery respectively.

[0027] Further, the parallel state at the DC bus in step four is represented by the state variable coupling:

[0028] After establishing the fuel cell post-stage boost converter and lithium battery post-stage bidirectional DC / DC converter, the electrical characteristics at the parallel connection of the two converters are expressed in the form of state variable coupling, and the mathematical model of the parallel converter is obtained, which is used to reflect the changes of each state variable and the electrical coupling relationship when the parallel converter is running;

[0029] ,

[0030] Wherein, and represent the current of inductors L1 and L2 respectively; i dc is the current at the DC bus; R1, R3, R4 are the equivalent resistances of the switching tubes; R2 is the equivalent resistance of the diode; C1 and C2 are the output capacitance of the boost converter and the input capacitance of the bidirectional DC / DC converter; V dc is the DC bus voltage; V in1 andV in2 V1 and V2 represent output voltage of fuel cell and lithium battery respectively.

[0031] Further, the solving and completing iterative calculation in step five include:

[0032] The node voltage transient equation and the state variable coupling expression are solved into a matrix equation form to obtain the mathematical model of the electric propulsion aircraft power conversion system; after setting the system parameters and on-off state resistance, the matrix equation is repeatedly solved to realize the working state simulation of the converter;

[0033] The expression of the matrix equation is:

[0034] ,

[0035] Wherein, I1 and I2 represent the current of inductance L1 and L2 respectively; and Wherein, I1 and I2 represent the current of inductance L1 and L2 respectively; i dc I is the current at the DC bus; R1, R3 and R4 are the equivalent resistances of the switch tube; R2 is the equivalent resistance of the diode; V dc V is the DC bus voltage; V in1 and V in2 V1 and V2 represent output voltage of fuel cell and lithium battery respectively.

[0036] Another purpose of the application is to provide a modeling system for the electric propulsion aircraft power conversion system, which applies the modeling method for the electric propulsion aircraft power conversion system, and the modeling system for the electric propulsion aircraft power conversion system comprises:

[0037] A working mode determination module is used to determine the working modes 1-4 of the parallel power converter;

[0038] A circuit discrete linearization module is used to convert the circuit into a discrete linear model;

[0039] A coupling expression module is used to construct the node voltage transient equation, and the electrical coupling characteristics of the parallel circuit are expressed by using the state variable coupling method to obtain the mathematical model of the parallel converter;

[0040] A model construction module is used to solve the node voltage transient equation and the electrical coupling characteristic expression by using a numerical method to obtain the mathematical model of the electric propulsion aircraft power conversion system, and realize the working state simulation of the converter.

[0041] Another object of the present application is to provide a computer device comprising a memory and a processor, the memory storing a computer program, the computer program being executed by the processor to cause the processor to perform the steps of the modeling method for an electric propulsion aircraft power conversion system.

[0042] Another object of the present application is to provide an information data processing terminal for implementing the modeling system for an electric propulsion aircraft power conversion system.

[0043] In combination with the above technical solutions and the technical problems solved, the technical solutions to be protected by the present application have the following advantages and positive effects:

[0044] First, in view of the technical problems existing in the prior art and the difficulty in solving the problems, the technical solutions to be protected by the present application and the results and data obtained during the research and development process are combined in detail and deeply to analyze how the technical solutions solve the technical problems and bring some creative technical effects after solving the problems. The specific description is as follows:

[0045] The modeling method for an electric propulsion aircraft power conversion system of the present application accurately expresses the electrical coupling characteristics at the parallel connection of the power converter and the 270V DC bus and the changes of each state variable using a mathematical model, realizes linear discretization of the circuit and decoupling of the electrical state, and at the same time ensures that the circuit topology is not switched, thereby optimizing the modeling difficulty. The present application can be well applied to the modeling of similar hybrid power systems such as electric propulsion aircraft, and has good portability and expandability, which can provide good support for studying the transient characteristics of the electric propulsion aircraft power system;

[0046] Based on the linear discretization of the circuit and the decoupling of the electrical state, the present application uses the implicit Euler method to solve the rigid differential equation, which can significantly improve the accuracy and stability of the solution. The mathematical model proposed by the present application can be compared and verified with a parallel converter with the same structure and parameters built on the Simulink simulation platform, and the results show that the simulation error is within 1%, which fully verifies the accuracy of the present application for modeling the electric propulsion aircraft power converter. The technical key of the present application is to provide a method for describing the electrical coupling characteristics at the bus by a mathematical model, which has good applicability for modeling the power converter of the electric propulsion aircraft hybrid power system;

[0047] Compared with the prior art, the power converter modeling method for the electric propulsion aircraft of the application has the following advantages: ① The essence of the electrical coupling characteristics is expressed by a mathematical model, the electrical characteristics are retained, and the accuracy of the power conversion model is ensured; ② In the discretization process, compared with the ideal switch method, the application retains the dynamic characteristics of the converter without changing the circuit mode, thereby providing good support for analyzing the transient characteristics of the electric propulsion aircraft in the working state; ③ The application provides a good model basis for the design and stability analysis of the next control system; ④ The dependence on electrical simulation tools is reduced, and the mathematical model has good portability and expansibility;

[0048] Secondly, from the perspective of the product as a whole or the technical solution, the technical solution to be protected by the application has the following technical effects and advantages, which are described as follows:

[0049] In order to realize accurate modeling in the case of multiple converter parallel connection, the application provides a modeling method for multiple converter parallel connection of an electric propulsion aircraft, which accurately expresses the electrical coupling characteristics of the converter output end, and is especially suitable for a multi-converter system (MCS) of an electric propulsion aircraft; from the perspective of the product, the application starts from the bottom modeling scheme of the multiple converter, solves the disadvantage that the conventional modeling method is difficult to express the coupling characteristics of the complex circuit, realizes accurate modeling in the case of multiple converter parallel connection, retains the switching characteristics of the circuit, and supports the dynamic performance research of the circuit; then the whole technical solution is packaged, and the setting interfaces of the circuit parameters and the simulation parameters are reserved, so as to facilitate the user to directly adjust and modify; the user does not need to pay attention to the circuit simulation technology of the system bottom layer, the learning cost can be reduced, and the product practicability and convenience are improved. In addition, the product has strong portability, the core technology can be directly summarized in pseudo code, and does not depend on any operating system or software simulation environment; therefore, the product can also be well applied to other hardware simulation platforms.

[0050] Thirdly, as the auxiliary evidence of the creativity of the application, it is also embodied in the following important aspects:

[0051] The system and the terminal of the application provide a targeted, convenient and reliable research test platform in the research field of the electric propulsion aircraft power system, so that the relevant researchers do not need to purchase commercial simulation software in the full physical domain. The product obtained by the technical solution better grasps the needs of the target users, the product positioning is clear, the target customer group is clear, and the pain points of the researchers on the simulation accuracy requirement and the expensive price of the mainstream simulation tool are well solved;

[0052] The technical scheme of the present application overcomes the technical problem of excessive dependence on mainstream computer simulation tools and poor accuracy of equivalent mathematical models of circuits in complex circuit simulation work. The present application proves that the modeling technology has almost consistent calculation accuracy, calculation speed and reliability with mainstream simulation tools, and its characteristics of not depending on operating systems and integrated development environments (IDE) enable researchers to further get rid of the limitations of IDE, improve the flexibility of development, improve the portability of models, and reduce the environmental constraints when used by users. The above facts fully prove the superiority of the technical scheme, which can effectively overcome the technical problems of researchers on the accuracy and reliability of equivalent mathematical models of circuits. BRIEF DESCRIPTION OF DRAWINGS

[0053] In order to more clearly illustrate the technical scheme of the embodiments of the present application, the drawings needed in the embodiments of the present application will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0054] Figure 1 is a flow chart of a modeling method for an electric propulsion aircraft power conversion system provided by the embodiments of the present application;

[0055] Figure 2 is a schematic diagram of a power conversion system circuit composed of a three-level boost converter and a bidirectional DC / DC converter in parallel provided by the embodiments of the present application;

[0056] Figure 3 is a working schematic diagram of a parallel converter mode 1 provided by the embodiments of the present application;

[0057] Figure 4 is a working schematic diagram of a parallel converter mode 2 provided by the embodiments of the present application;

[0058] Figure 5 is a working schematic diagram of a parallel converter mode 3 provided by the embodiments of the present application;

[0059] Figure 6 is a working schematic diagram of a parallel converter mode 4 provided by the embodiments of the present application;

[0060] Figure 7 is a schematic diagram of a discrete linearization model of a boost and bidirectional DC / DC converter provided by the embodiments of the present application;

[0061] Figure 8 is a working state simulation modeling flow chart of a converter provided by the embodiments of the present application;

[0062] Figure 9A hybrid electric propulsion aircraft power conversion system implementation scheme provided by an embodiment of the application;

[0063] Figure 10 A discrete linearization model schematic diagram of a three-level boost converter and a bidirectional DC / DC converter provided by an embodiment of the application;

[0064] Figure 11 A working schematic diagram of mode 1 of a three-level boost converter provided by an embodiment of the application;

[0065] Figure 12 A working schematic diagram of mode 2 of a three-level boost converter provided by an embodiment of the application;

[0066] Figure 13 A working schematic diagram of mode 3 of a three-level boost converter provided by an embodiment of the application;

[0067] Figure 14 A working schematic diagram of mode 4 of a three-level boost converter provided by an embodiment of the application;

[0068] Figure 15 A simulation curve diagram of inductance current L1 for comparing mathematical model calculation results with Simulink simulation results provided by an embodiment of the application;

[0069] Figure 16 A simulation curve diagram of bus voltage for comparing mathematical model calculation results with Simulink simulation results provided by an embodiment of the application. Embodiment

[0070] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and do not limit the application.

[0071] In view of the problems in the prior art, the application provides a modeling method, system and terminal for an electric propulsion aircraft power conversion system, which are described in detail below in combination with the drawings.

[0072] I. Explanation of embodiments. In order for those skilled in the art to fully understand how the application is specifically implemented, this part is an explanation of the embodiments for expanding the description of the technical scheme.

[0073] As shown in Figure 1 The modeling method for an electric propulsion aircraft power conversion system provided by an embodiment of the application includes the following steps:

[0074] S101, determine the working mode of the parallel power converter;

[0075] S102, converting the circuit into a discretized linear model;

[0076] S103, constructing a node voltage transient equation;

[0077] S104, representing the parallel state at the DC bus through state variable coupling;

[0078] S105, solving and completing iterative calculation by using a numerical method, obtaining a mathematical model of the electric propulsion aircraft power conversion system, and realizing converter working state simulation.

[0079] The power conversion system circuit schematic diagram provided by the embodiment of the application is shown in Figure 2 .

[0080] As a preferred embodiment, the modeling method for the electric propulsion aircraft power conversion system provided by the embodiment of the application specifically comprises the following steps:

[0081] (1) determining the parallel power converter working mode;

[0082] The application is oriented to a hybrid electric propulsion aircraft power conversion system implementation scheme, containing a boost converter and a bidirectional DC / DC converter, and taking a fuel cell and a lithium battery as voltage sources respectively. The boost converter connected with the fuel cell output end is responsible for lifting the fuel cell output voltage to the aircraft DC bus voltage; the bidirectional DC / DC converter connected with the lithium battery has two working modes, and the current flow direction can be switched, which is used for the scenarios of charging or discharging the lithium battery. Ignoring the boost converter working mode, the parallel converter has four working modes, which are specifically shown in Figure 3 , 4 , 5, 6.

[0083] Mode 1: Q2 is turned on, Q3 is turned off, the voltage of inductor L2 linearly rises, the inductor energy storage increases, and the capacitor C3 releases energy to the load.

[0084] Mode 2: Q2 and Q3 are turned off, the fuel cell output voltage V in1 and the inductor L2 together provide energy to the load, and realize the boosting effect.

[0085] Mode 3: Q3 is turned on, Q2 is turned off, the aircraft DC bus charges the lithium battery, and the bidirectional DC / DC converter is in the step-down working mode.

[0086] Mode 4: Q2, Q3 off, the charging current flows through the anti-parallel diode D4, the current size presents exponential curve, the inductance L2 value is larger and the switching frequency is higher, the converter is in current continuous mode and the pulse is smaller.

[0087] (2) Circuit discrete linearization;

[0088] When the computer is simulated, the circuit must be converted into a discrete linear model. However, diodes and controlled power switching devices are nonlinear elements, so they need to be discretely linearized. With the binary resistance method, the switching characteristics of the switching device are equivalent to the size of the resistance based on the switching judgment logic of a single switching device, which can ensure that the circuit topology is unchanged and is a constant topology modeling method. For controlled power switching devices, when the switching tube is added with a forward voltage drop and a driving signal, the switching tube is in a low resistance state, and vice versa. Therefore, the switching tube in the on state can be equivalent to a small resistance, and the switching tube in the off state can be equivalent to a large resistance, as shown in the discrete iterative model. Similarly, the diode can also be represented as a discrete linear function of the current voltage. The discrete linearization model of the boost and bidirectional DC / DC converter is shown in Figure 7 . Figure 7 .

[0089] This modeling method ensures that when the switching mode of the actual circuit changes, only the switching judgment logic design and correction of a single switching device need to be considered, and only the conductance value of some branches needs to be changed, without changing the circuit topology structure, thereby reducing the modeling difficulty.

[0090] (3) Column write node voltage transient equation;

[0091] ,

[0092] wherein, and represent the current of inductors L1 and L2, respectively; R1, R3, and R4 are the equivalent resistances of the switching tube; R2 is the equivalent resistance of the diode; V dc is the DC bus voltage; V in1 and V in2 represent the output voltages of the fuel cell and the lithium battery, respectively.

[0093] (4) Parallel state at the DC bus is represented by state variable coupling;

[0094] The difficulty of modeling parallel converter mainly lies in expressing the electrical coupling characteristics at the parallel position. Taking the power conversion system of the electric propulsion aircraft as an example, the macroscopic performance of the electrical coupling characteristics is that, as long as the bus voltage is stable, the power system can achieve power balance, thereby maintaining stable operation of the system.

[0095] There are two common modeling methods for parallel converters. One is based on equivalent impedance to express the interaction between modules, but it cannot accurately represent the change of coupling amount of the parallel system. The other is to regard the parallel converter as a whole system, and a mathematical model is established by analyzing the principle of the system. The model obtained by this method is relatively accurate, but the modeling is difficult due to the complexity of the model.

[0096] The present application combines the advantages of the first two technologies, and on the basis of completing independent modeling of two converters, a state variable coupling method is proposed to express the electrical coupling characteristics of the parallel circuit. Compared with the first two methods, the modeling difficulty is smaller, and the interaction of the parallel circuit is considered to ensure the accuracy of the model.

[0097] Specifically, after the fuel cell post-stage boost converter and the lithium battery post-stage bidirectional DC / DC converter are established, the electrical characteristics at the parallel position of the two converters are expressed in the form of state variable coupling, and a complete mathematical model of the parallel converter can be obtained. The mathematical model can reflect the change of each state variable and the electrical coupling relationship of the parallel converter during operation, greatly reduces the dependence on simulation tools such as Simulink, improves the flexibility and portability of the model, and provides important guidance for the analysis of the working characteristics of the electric propulsion aircraft power conversion system and the design of the controller.

[0098] ,

[0099] Among them, and respectively represent the currents of inductors L1 and L2; i dc is the current at the DC bus; R1, R3 and R4 are the equivalent resistances of the switching tubes; R2 is the equivalent resistance of the diode; C1 and C2 are respectively the output capacitor of the boost converter and the input capacitor of the bidirectional DC / DC converter; V dc is the DC bus voltage; V in1 and V in2 respectively represent the output voltages of the fuel cell and the lithium battery.

[0100] (5) Numerical method is used to solve and complete iterative calculation.

[0101] The three equations in the foregoing are expressed in the form of the following matrix equation, and thus the mathematical model of the electric propulsion aircraft power conversion system is obtained, and the working state simulation of the converter is realized.

[0102] ,

[0103] Wherein, and represent the currents of the inductors L1 and L2 respectively; i dc is the current at the DC bus; R1, R3 and R4 are the equivalent resistances of the switching tubes; R2 is the equivalent resistance of the diode; C1 and C2 are the output capacitor of the boost converter and the input capacitor of the bidirectional DC / DC converter respectively; V dc is the DC bus voltage; V in1 and V in2 represent the output voltages of the fuel cell and the lithium battery respectively.

[0104] After the system parameters and the on-off state resistances are set, the working state simulation of the converter can be realized by repeatedly solving the matrix equation, and the modeling flowchart under the technology is as shown in Figure 8 .

[0105] In the selection of the numerical solution algorithm, considering that the system is a rigid system, when the explicit Euler method is used to solve the differential equation, although the fast-changing component only exists in a small part of the integral interval, it determines the time step in the entire solving process, therefore, the result obtained by the explicit Euler method will have error accumulation, and the error with the actual result is relatively large, and at the same time, in order to maintain stability, the step must be smaller than a certain value, if an accurate solution is wanted, a smaller step is needed, which will increase the calculation burden of the solver. Based on the above facts, the implicit Euler method is used to solve the rigid differential equation, and the accuracy and stability of the solution can be obviously improved.

[0106] The modeling system for the electric propulsion aircraft power conversion system provided in the embodiment of the application comprises:

[0107] A working mode determination module is configured to determine the working modes 1 to 4 of the parallel power converters;

[0108] A circuit discrete linearization module is configured to convert the circuit into a discrete linear model;

[0109] A coupling representation module is configured to construct a node voltage transient equation, and express the electrical coupling characteristics of the parallel circuit by using the state variable coupling, so as to obtain the mathematical model of the parallel converter;

[0110] The model construction module is used for solving the node voltage transient equation and the electrical coupling characteristic expression by using a numerical method to obtain a mathematical model of the electric propulsion aircraft power conversion system, and realizes the simulation of the working state of the converter.

[0111] The mathematical model provided by the application can be compared and verified with the parallel converter with the same structure and parameters built on the Simulink simulation platform, and the simulation error is less than 1%, which can be seen in the third part of the embodiment.

[0112] The technical key of the application is to provide a method for describing the electrical coupling characteristics at the bus by a mathematical model, which has good applicability for modeling the power converter of the hybrid power system of the electric propulsion aircraft.

[0113] Compared with the prior art, the modeling method for the electric propulsion aircraft power conversion system has the following beneficial effects: ① the essence of the electrical coupling characteristics is expressed by the mathematical model, the electrical characteristics are retained, and the accuracy of the power conversion model is ensured; ② in the discretization process, compared with the ideal switch method, the application retains the dynamic characteristics of the converter without changing the circuit mode, which provides good support for analyzing the transient characteristics of the electric propulsion aircraft in the working state; ③ the application provides a good model basis for the design and stability analysis of the next control system; ④ the application reduces the dependence on electrical simulation tools and plays the good portability and expansibility of the mathematical model.

[0114] II. Application Examples In order to prove the creativity and technical value of the technical solution of the application, this part is an application example of the technical solution on a specific product or related technology.

[0115] The technical solution of the application is applicable to various topological schemes of electric propulsion aircraft power systems, and is a general modeling technical solution in this application scenario. The applicable power system topologies include three-level boost converter+bidirectional buck / boost converter, three-level boost converter+bidirectional cuk converter, two-stage boost converter+bidirectional buck / boost converter, etc. Although there are differences in topology, the technical solution of the application can be referred to by determining the switching mode of the circuit, discretely linearizing the circuit, writing the node voltage transient equation, decoupling the bus voltage, and solving by a numerical method to realize accurate modeling of various topologies.

[0116] Evidence of the effects of the embodiments. The embodiments of the application have achieved some positive effects during research and development or use, and indeed have great advantages compared with the prior art. The following content is described in combination with data, charts, etc. during the test process.

[0117] Figures 2-7 , Figures 9-14 In V in1Vf represents fuel cell output voltage, V in2 Vl represents lithium battery output voltage, Vbus represents DC bus voltage; D2, D3, D4, D7, D8, D9, D 10 D1 represents switch tube anti-parallel diode; C1 represents boost converter output capacitor, C2 represents bidirectional DC / DC converter input capacitor, C3 represents bidirectional DC / DC converter output capacitor, C4 and C5 represent three-level boost converter output capacitor, C6 represents bidirectional DC / DC converter output capacitor in the embodiment, C7 represents bidirectional DC / DC converter input capacitor in the embodiment; L1 represents boost converter input inductor, L2 represents bidirectional DC / DC converter input inductor, L3 represents three-level boost converter input inductor in the embodiment, L4 represents bidirectional DC / DC converter input inductor in the embodiment; R1, R3, R4, R7, R8, R9, R 10 R2, R5, R6 represent diode equivalent resistance. i 1 represents boost converter output current, i 2 represents bidirectional DC / DC converter output current, i 3 represents three-level boost converter output current, i 4 represents bidirectional DC / DC converter output current in the embodiment topology, i dc Ibus represents bus current; i L1, i L2, i L3, i L4 I1, I2, I3, I4 represent current flowing through inductors L1, L2, L3, L4, V dc Vbus represents DC bus voltage; Q1, Q2, Q3 represent switch tubes of boost converter and bidirectional DC / DC converter formed parallel circuit, Q4, Q5, Q6, Q7 represent switch tubes of three-level boost converter and bidirectional DC / DC converter formed parallel circuit; the gray part in circuit device and line represents that the line is off.

[0118] According to the embodiment of the present application principle, as Figure 9 shown, it can be realized as a hybrid electric propulsion aircraft power conversion system solution. The system contains a three-level boost converter and a bidirectional DC / DC converter, and respectively takes fuel cell and lithium battery as voltage source.

[0119] (1) Determine the circuit switch mode;

[0120] The switching actions of the three-level boost converter are analyzed below, which consists of four operating modes, as shown in Figs. Figure 11 , 12 , 13, 14, respectively.

[0121] Mode 1: Q4, Q5 are on, D5, D6 are off, the inductor voltage linearly rises, the inductor energy storage increases, C4, C5 release energy.

[0122] Mode 2: Q4 is on, Q5 is off, D5 is off, D6 is on, the fuel cell output voltage V in1 The circuit composed of L3, Q4 and D6 provides energy for the load.

[0123] Mode 3: Q4 is off, Q5 is on, D5 is on, D6 is off, the fuel cell output voltage V in1 The circuit composed of L3, D5 and Q5 provides energy for the load.

[0124] Mode 4: Q4, Q5 are off, D5, D6 are on, the fuel cell output voltage V in1 The circuit composed of L3, D5 and D6 provides energy for the load.

[0125] (2) Convert the circuit into a discrete linear model;

[0126] Since the controlled power switching devices Q4, Q5, Q6, Q7 and diodes D5, D6 in the circuit are nonlinear elements, the circuit needs to be linearly discretized first to obtain a discrete iterative model of the parallel circuit. Similarly, according to the switching logic of the switching devices, the switching devices and diodes are equivalent to resistors of different sizes, and thus the discrete linear model of the three-level boost converter and the bidirectional DC / DC converter can be obtained as shown in Fig. Figure 10 , which has a constant circuit topology and prevents the problem of non-convergence caused by rapid topology switching.

[0127] (3) Build the node voltage transient equation;

[0128] ,

[0129] ,

[0130] where R7, R8 are the equivalent resistances of the switching tubes in the three-level boost converter, R 5， R6 is the equivalent resistance of the diode in the three-level boost converter, R9, R 10 are the equivalent resistances of the switching tubes in the bidirectional DC / DC converter; and These represent the currents in inductors L3 and L4, respectively. V dc This is the DC bus voltage; V in1 and V in2 These represent the output voltages of the fuel cell and the lithium battery, respectively.

[0131] (4) The parallel state at the DC bus is represented by state variable coupling;

[0132] ,

[0133] Where R7 and R8 are the equivalent resistances of the switching transistors in the three-level boost converter, R 5， The equivalent resistance of the diodes in the three-level boost converter is R6, R9, R 10 C1 is the equivalent resistance of the switching transistor in the bidirectional DC / DC converter; C4 and C5 are the two capacitors at the output of the boost converter; C7 is the capacitor at the input of the bidirectional DC / DC converter. and These represent the currents flowing through inductors L3 and L4, respectively. i dc This refers to the current at the DC bus. V dc This is the DC bus voltage; V in1 and V in2 These represent the output voltages of the fuel cell and the lithium battery, respectively.

[0134] (5) Solve the model numerically and verify its accuracy;

[0135] Thus obtained Figure 8 The mathematical model of the electric propulsion aircraft power conversion system shown below can be expressed in the form of the following matrix equations;

[0136] ,

[0137] Where R7 and R8 are the equivalent resistances of the switching transistors in the three-level boost converter, R 5， The equivalent resistance of the diode in the three-level boost converter is R6, R9, R 10 This is the equivalent resistance of the switching transistor in a bidirectional DC / DC converter. and These represent the currents in inductors L3 and L4, respectively. i dc This refers to the current at the DC bus. V dc This is the DC bus voltage; Vin1 and V in2 Vfuel and Vlithium represent the output voltage of fuel cell and lithium battery respectively.

[0138] The input voltage range of boost circuit is set as 100-130V, the output current range is 100-130V, the switching frequency is 20kHz, the rated output voltage is 270V, the ripple is less than 5%, and the inductance current is not zero when the circuit is loaded with minimum load. The parameters of boost converter are designed based on the above requirements.

[0139] The inductance current equation is:

[0140] ,

[0141] wherein, V is the inductance voltage peak value; D is the duty cycle of switch tube; f s is the switching frequency; I is the average value of inductance current.

[0142] The expression of inductance L is obtained from the above equation as:

[0143] ,

[0144] Take r i 5%, the duty cycle of switch tube in steady state is D =0.55, and the value of inductance L is obtained according to the following equation as:

[0145] ,

[0146] The calculation formula of output capacitor is:

[0147] ,

[0148] wherein, R is the load resistance; is the capacitor voltage ripple size;

[0149] The calculation result is: .

[0150] The simulation parameters of boost circuit can be set as according to the above requirements, C4 and C5 are taken as , the on-state resistance in the binary resistance model of switch tube is taken as 1e-5Ω, the off-state resistance is taken as 0.1MΩ, and the switching frequency is 20kHz. The parameter design principle of bidirectional DC / DC converter is the same as above, and the calculation result is , The total simulation time is 0.1s, and the simulation step is 1e-6s.

[0151] Based on the above system parameters, the model parameters are assigned values, the bus voltage is solved according to the bus voltage decoupling method, then the implicit Euler method is used to solve the matrix equation, the state variables are solved and output, and finally the variable initial value is updated, the solution value of the state variable is assigned to the initial parameter as the initial value, and the state matrix equation is repeatedly solved to realize the iterative calculation simulation of the power electronic circuit.

[0152] The actual effect provided by the embodiment of the application is as follows:

[0153] The transformer model of the same topology and the same parameter is built on the Simulink simulation platform, the calculation results of the mathematical model are compared with the Simulink simulation results, and the comparison results are as shown in Figure 15 and Figure 16 The black line is the simulation result under the modeling method proposed in the application, and the red line is the simulation result under the Power System library module of Simulink. After calculation, the error of the simulation result is only 0.05%, which fully verifies the accuracy of the application for the modeling of the electric propulsion aircraft power converter.

[0154] In summary, the modeling method for the electric propulsion aircraft power converter has the following advantages: ① the essence of the electrical coupling characteristic is expressed by the mathematical model, the electrical characteristic is retained, and the accuracy of the power conversion model is ensured; ② compared with the ideal switch method, the application retains the dynamic characteristics of the converter under the premise of not changing the circuit mode, which provides good support for analyzing the transient characteristics of the electric propulsion aircraft under the working state; ③ it provides a good model basis for the design and stability analysis of the next step control system; ④ it reduces the dependence on the electrical simulation tool, and the mathematical model has good portability and expansibility.

[0155] It should be noted that embodiments of the present application can be realized by hardware, software, or a combination of software and hardware. The hardware portion can be realized by a special logic; the software portion can be stored in a memory and executed by a proper instruction execution system, such as a microprocessor or a specially designed hardware. A person of ordinary skill in the art can understand that the above-mentioned apparatus and method can be realized by computer executable instructions and / or included in processor control codes, such as a carrier medium, such as a magnetic disk, CD or DVD-ROM, a programmable memory, such as a read-only memory (firmware), or a data carrier, such as an optical or electronic signal carrier. The apparatus of the present application and its modules can be realized by a hardware circuit, such as a very large scale integrated circuit or a gate array, a semiconductor, such as a logic chip, a transistor, or a programmable hardware device, such as a field programmable gate array, a programmable logic device, or the like, by software executed by various types of processors, or by a combination of the above-mentioned hardware circuit and software, such as firmware.

[0156] The above description is merely a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any modification, equivalent replacement, and improvement within the technical range disclosed by the present application, and within the spirit and principle of the present application, should be covered within the protection scope of the present application.

Claims

1. A modeling method for power conversion systems of electric propulsion aircraft, characterized in that, The modeling method for power conversion systems of electric propulsion aircraft includes the following steps: Step 1: Determine the operating mode of the parallel power converter; Step two: Transform the circuit into a discrete linear model; Step 3: Construct the transient equations for node voltages; Step 4: Represent the parallel state at the DC bus through state variable coupling; Step 5: Solve using numerical methods and complete iterative calculations; Step one, determining the operating mode of the parallel power converter, includes: The power conversion system for hybrid-electric propulsion aircraft includes a boost converter and a bidirectional DC / DC converter, using a fuel cell and a lithium battery as voltage sources, respectively. The boost converter, connected to the fuel cell output, is responsible for raising the fuel cell output voltage to the aircraft's DC bus voltage. The bidirectional DC / DC converter connected to the lithium battery has two operating modes, switching the current flow direction, for scenarios involving charging or discharging the lithium battery. Ignoring the boost converter's operating modes, the parallel power converter includes four operating modes: Mode 1: Q2 is on, Q3 is off, the voltage of L2 rises linearly, the energy stored in the inductor increases, and the capacitor releases energy to the load; Mode 2: Q2 and Q3 are off, fuel cell output voltage V in1 Together with L2, it provides energy to the load and achieves a boost effect; Mode 3: Q3 is on, Q2 is off, the aircraft DC bus charges the lithium battery, and the bidirectional DC / DC converter is in buck mode. Mode 4: Q2 and Q3 are off, the charging current freewheels through the anti-parallel diode D4, and the current magnitude decreases exponentially, the converter is in continuous current mode; Where Q2 and Q3 represent the converter switching devices, and L1 and L2 represent the input inductance of the boost converter and the input inductance of the bidirectional DC / DC converter, respectively. The transient equations for constructing the node voltages in step three are as follows: Where iL1 and iL2 represent the currents in inductors L1 and L2, respectively; R1, R3, and R4 are the equivalent resistances of the switching transistors; R2 is the equivalent resistance of the diode; L1 and L2 are the input inductances of the boost converter and the bidirectional DC / DC input inductance, respectively; V dc This is the DC bus voltage; V in1 and V in2 These represent the output voltages of the fuel cell and the lithium battery, respectively.

2. The modeling method for power conversion systems of electric propulsion aircraft as described in claim 1, characterized in that, Step two, transforming the circuit into a discretized linear model, includes: Using the binary resistor method, based on the switching judgment logic of a single switching device, the switching characteristics of the switching device are equivalent to large and small resistors. For controlled power switching devices, when a forward voltage drop and a drive signal are applied across the switching transistor, the switching transistor is in a low-resistance conducting state, and vice versa. The switching transistor in the conducting state is equivalent to a small resistor, and the switching transistor in the cut-off state is equivalent to a large resistor. The diode is represented as a discrete linear function of the current terminal voltage, thus obtaining the discrete linearized model of the boost converter and the bidirectional DC / DC converter.

3. The modeling method for power conversion systems of electric propulsion aircraft as described in claim 1, characterized in that, Step four, representing the parallel state at the DC bus through state variable coupling, includes: After establishing the fuel cell post-stage boost converter and the lithium battery post-stage bidirectional DC / DC converter, the electrical characteristics of the two converters at the parallel connection point are expressed in a state variable coupling manner to obtain the mathematical model of the parallel power converter, which is used to reflect the changes of various state variables and electrical coupling relationships during the operation of the parallel converter. Where iL1 and iL2 represent the currents in inductors L1 and L2, respectively; i dc R1 represents the current at the DC bus; R1, R3, and R4 are the equivalent resistances of the switching transistors; R2 is the equivalent resistance of the diode; C1 and C2 are the boost converter capacitor and the bidirectional DC / DC capacitor, respectively; V dc This is the DC bus voltage; V in1 and V in2 These represent the output voltages of the fuel cell and the lithium battery, respectively.

4. The modeling method for power conversion systems of electric propulsion aircraft as described in claim 1, characterized in that, Step five, which involves solving the problem numerically and completing the iterative calculation, includes: The transient equations of node voltages and the coupled expressions of state variables are solved into matrix equations to obtain the mathematical model of the power conversion system of the electric propulsion aircraft. After setting the system parameters and on- and off-state resistances, the matrix equations are solved repeatedly to simulate the working state of the converter. The expression for the matrix equation is: Where iL1 and iL2 represent the currents in inductors L1 and L2, respectively; i dc R1 represents the current at the DC bus; R1, R3, and R4 are the equivalent resistances of the switching transistors; R2 is the equivalent resistance of the diode; V dc This is the DC bus voltage; V in1 and V in2 These represent the output voltages of the fuel cell and lithium battery, respectively; C1 and C2 are the boost converter capacitor and the bidirectional DC / DC capacitor, respectively.

5. A modeling system for a power conversion system of an electric propulsion aircraft, employing the modeling method for a power conversion system of an electric propulsion aircraft as described in any one of claims 1 to 4, characterized in that, The modeling system for power conversion systems in electric propulsion aircraft includes: The operating mode determination module is used to determine the operating modes 1 to 4 of the parallel power converter; The circuit discretization and linearization module is used to transform a circuit into a discretized linear model. The coupling representation module is used to construct the node voltage transient equations and express the electrical coupling characteristics of the parallel circuit by using the state variable coupling method, so as to obtain the mathematical model of the parallel converter. The model building module is used to solve the transient equations of node voltages and the expressions of electrical coupling characteristics using numerical methods, thereby obtaining the mathematical model of the power conversion system of the electric propulsion aircraft and realizing the simulation of the converter's working state.

6. A computer device, characterized in that, The computer device includes a memory and a processor. The memory stores a computer program, which, when executed by the processor, causes the processor to perform the steps of the modeling method for a power conversion system of an electric propulsion aircraft as described in any one of claims 1 to 4.

7. An information data processing terminal, characterized in that, The information data processing terminal is used to implement the modeling system for the power conversion system of an electric propulsion aircraft as described in claim 5.

Images