Five-level inverter control system and method for eVTOL aircraft

Abstract

The invention discloses a five-level inverter control system and method for an eVTOL aircraft, and belongs to the field of five-level inverters, and the system comprises a three-phase resistance-inductance load which is used for simulating resistance-inductance characteristics; the ANPC-5L inverter system is used for driving a three-phase resistance-inductance load; the current sampling module is used for collecting three-phase output current of the ANPC-5L inverter system in real time; the reference three-phase current generation module is used for generating a reference three-phase output current as a target value of the three-phase output current of the ANPC-5L inverter system; and the control module is used for realizing multi-target cooperative control of the ANPC-5L inverter system. By adopting the five-level inverter control system and method for the eVTOL aircraft, the dynamic stability of the flying capacitor voltage can be realized, the waveform quality of the output current can be ensured, and the amplitude of the maximum common-mode voltage can be limited not to exceed one sixth of the direct-current bus voltage, so that the reliability of the inverter is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of five-level inverters, and in particular to a five-level inverter control system and method for an eVTOL aircraft. Background Art

[0002] As the core vehicle for next-generation urban air mobility, electric vertical take-off and landing (eVTOL) aircraft require power systems that meet stringent requirements such as high power density, high reliability, and lightweight design. The performance of the DC-AC power converter, a core unit of the power system, directly impacts the eVTOL aircraft's flight range, electromagnetic compatibility, and the lifespan of key components.

[0003] In recent years, multilevel inverters have gradually become the preferred solution for high-voltage, high-power aviation electric propulsion systems due to their advantages such as low output voltage harmonic content and reduced voltage stress on power devices. The active neutral-point-clamped five-level (ANPC-5L) inverter combines the advantages of both the active neutral-point-clamped inverter and the flying capacitor inverter. It eliminates the need for clamping diodes and uses only a small number of capacitors, offering advantages such as flexible output levels and high reliability.

[0004] However, the existing ANPC-5L inverter faces three major technical bottlenecks in the application scenario of eVTOL aircraft. First, the problem of voltage stability control of the flying capacitor is prominent. The power of the eVTOL aircraft changes frequently during the takeoff / landing phase. The capacitor voltage balancing strategy based on proportional-integral controller feedback regulation is difficult to adapt to dynamic load changes, which can easily lead to flying capacitor voltage oscillation, thereby causing overvoltage of power devices and even the risk of failure. Secondly, the problem of excessive common-mode voltage amplitude is significant. The conventional ANPC-5L inverter modulation strategy fails to effectively suppress the common-mode voltage. Its high-frequency component will aggravate the electromagnetic interference between the motor bearing current and the inverter. In severe cases, it will interfere with the normal operation of the eVTOL aircraft flight control computer system, posing a threat to flight safety. Finally, the quality of the inverter output current waveform is a difficult problem. The traditional finite set model predictive control scheme has the advantages of fast dynamic response and easy addition of nonlinear constraints. However, its operating mechanism of ergodic optimization to obtain the switching state makes the inverter switching frequency unstable, the current ripple large, and the current spectrum irregular, which is not conducive to the design of electromagnetic interference filter parameters. Especially in the eVTOL aircraft application scenario, the additional electromagnetic interference filter installed due to the irregular current spectrum will hinder the improvement of the system power-to-weight ratio. Summary of the Invention

[0005] The purpose of the present invention is to provide a five-level inverter control system and method for eVTOL aircraft to solve the above technical problems.

[0006] To achieve the above objectives, the present invention provides a five-level inverter control system for an eVTOL aircraft, comprising: Three-phase resistive-inductive load, used to simulate the resistive-inductive characteristics of the eVTOL motor; ANPC-5L inverter system is used to convert the electrical energy of the DC power supply into three-phase AC power to drive three-phase resistive and inductive loads; Current sampling module, used to collect the three-phase output current of the ANPC-5L inverter system in real time; A reference three-phase current generation module is used to generate a reference three-phase output current as a target value of the three-phase output current of the ANPC-5L inverter system; The control module is used to achieve multi-objective coordinated control of the ANPC-5L inverter system by integrating model prediction ideas and space vector modulation. Through a closed-loop control strategy, it uses the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module to optimize the switching state of the ANPC-5L inverter system and achieve tracking control of the three-phase output current with respect to the reference three-phase output current.

[0007] Preferably, the ANPC-5L inverter system includes a DC power supply, a DC bus capacitor, a flying capacitor, an A-phase power conversion unit, a B-phase power conversion unit, and a C-phase power conversion unit, wherein the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit all include a low-frequency bridge arm and a high-frequency bridge arm, the low-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected in parallel with the DC power supply, and the high-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected to the ANPC-5L inverter system.

[0008] Preferably, the low-frequency bridge arm includes a first low-frequency switching tube, a second low-frequency switching tube, a third low-frequency switching tube and a fourth low-frequency switching tube, wherein the collector of the first low-frequency switching tube is connected to a DC power supply, the emitter of the first low-frequency switching tube is connected to the collector of the second low-frequency switching tube, the emitter of the second low-frequency switching tube is connected to the collector of the third low-frequency switching tube, and the emitter of the third low-frequency switching tube is connected to the collector of the fourth low-frequency switching tube, and the first low-frequency switching tube and the second low-frequency switching tube form a complementary switch pair, and the third low-frequency switching tube and the fourth low-frequency switching tube form a complementary switch pair; The high-frequency bridge arm includes a first high-frequency switching tube, a second high-frequency switching tube, a third high-frequency switching tube and a fourth high-frequency switching tube, wherein the first high-frequency switching tube is connected between the emitter of the first low-frequency switching tube and the collector of the second low-frequency switching tube, the emitter of the first high-frequency switching tube is connected to the collector of the third high-frequency switching tube, the emitter of the third high-frequency switching tube is connected to the collector of the fourth high-frequency switching tube, the emitter of the fourth high-frequency switching tube is connected to the collector of the second high-frequency switching tube, and the emitter of the second high-frequency switching tube is connected between the emitter of the third low-frequency switching tube and the collector of the fourth low-frequency switching tube.

[0009] Preferably, the three-phase resistive-inductive load includes an a-phase branch load, a b-phase branch load and a c-phase branch load respectively connected to the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit, and the a-phase branch load, the b-phase branch load and the c-phase branch load all include a resistor and an inductor connected in series, one end of the inductor is connected to the resistor, and the other end is connected between the emitter of the third high-frequency switching tube and the collector of the fourth high-frequency switching tube.

[0010] Preferably, the DC bus capacitor includes a first DC bus capacitor and a second DC bus capacitor connected in series between the positive and negative electrodes of the DC power supply, the midpoint between the first DC bus capacitor and the second DC bus capacitor is connected to one end of a lead, and the other end of the lead is connected between the emitter of the second low-frequency switching tube and the collector of the third low-frequency switching tube; One plate of the flying capacitor is connected between the emitter of the first high-frequency switch tube and the collector of the third high-frequency switch tube, and the other plate is connected between the emitter of the fourth high-frequency switch tube and the collector of the second high-frequency switch tube.

[0011] Preferably, the sampling point of the current sampling module is located between the inductor and the high-frequency bridge arm.

[0012] A method for controlling a five-level inverter system for an eVTOL aircraft includes the following steps: S1, collect the three-phase output current of the ANPC-5L inverter system and generate the reference three-phase output current: Assume that the sampling period of the system is , in At the beginning of the sampling cycle, the current sampling module is used to collect the three-phase output current of the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit in the ANPC-5L inverter system in real time. , 、 and Represent the output current of phase a, phase b and phase c respectively; In the At the beginning of the sampling period, the reference three-phase output current can be obtained by referring to the three-phase current generation module. , 、 and Represent the reference current of phase a, phase b and phase c respectively; S2. Establish a discrete mathematical model for the ANPC-5L inverter system to obtain the constraint relationship between voltage and current; S3, based on the space vector modulation strategy, combined with the cost function rolling, determine the vector triangle where the reference voltage vector is located and the driving signal of the low-frequency switch tube; S4. Calculate the action duration of each reference voltage vector based on the vector triangle, synthesize the reference voltage vector, achieve voltage balance between the DC bus capacitor and the flying capacitor by adjusting the duty cycle, and generate a drive signal for the high-frequency switch tube; S5. Distribute the generated driving signals of the low-frequency switching tube and the high-frequency switching tube to the low-frequency switching tube and the high-frequency switching tube respectively.

[0013] Preferably, step S2 specifically includes the following steps: S21, the midpoint between the first DC bus capacitor and the second DC bus capacitor is the zero potential reference point, then the three-phase output voltage of the ANPC-5L inverter system is and the midpoint of the three-phase resistive-inductive load Voltage at The relationship between them is: (1); Where, 、 and They represent the output voltages of phase a, phase b, and phase c of the ANPC-5L inverter system respectively; Indicates the load inductance value; represents the load resistance; At the same time, the switching states of the a-phase power conversion unit, b-phase power conversion unit, and c-phase power conversion unit of the ANPC-5L inverter system are determined by the low-frequency bridge arm and the high-frequency bridge arm, which are recorded as a quaternion At this time, the three-phase output voltage of the ANPC-5L inverter system is changed by using the switch state. Mapped into 5 discrete levels to achieve multi-level output: (2); Where, Indicates the three-phase switch status, 、 and Respectively represent the switching states of the a-phase power conversion unit, the b-phase power conversion unit, and the c-phase power conversion unit; Indicates the DC bus voltage; Combining formula (1) and formula (2) we get: (3); Where, 、 and Respectively represent the ANPC-5L inverter system Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads Output voltage; S22. Discretize formula (1) and get The expected reference three-phase output voltage of the sampling period for: (4); Where, 、 and Respectively represent The expected phase a, phase b, and phase c reference output voltages for the sampling period; 、 and Respectively represent Output current of phase a, phase b and phase c in the sampling period; 、 and Respectively represent The reference output current of phase a, phase b and phase c of the sampling period; S23. Based on formula (4), while tracking the expected reference three-phase output voltage, considering the computational burden, the cost function defined is and common-mode voltage : (5); (6); Where, 、 and Represent the reference output voltages of phase a, phase b, and phase c respectively; 、 and Respectively represent Sub-sampling cycle of ANPC-5L inverter system a Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads output voltage.

[0014] Preferably, step S3 specifically includes the following steps: S31, convert the three-phase switch state to The voltage vector in the coordinate system is used to obtain the voltage vector diagram; S32. Based on the low-frequency bridge arm switch state, select six evenly distributed characteristic vectors as sector boundaries to obtain six sectors. Each sector corresponds to a set of low-frequency switch tube state combinations. Use formula (5) to perform rolling optimization on the six characteristic vectors to determine the target sector where the reference voltage vector is located. S33, determining three hexagonal areas and one diamond area with the characteristic vector in the target sector as the center, substituting the voltage vectors corresponding to the three hexagonal areas and the one diamond area into formula (5) and performing rolling optimization to determine the target center area; S34. When the target area is a hexagonal area, extract the six vertex voltage vectors of the hexagonal area, select the two vertex voltage vectors with the minimum cost by formula (5), and introduce the characteristic vector corresponding to the hexagonal area to form a three-element vector group; When the target area is a diamond area, the four vertex voltage vectors of the diamond area are extracted, and the three vertex vectors with the minimum cost are selected by formula (5) to form a three-element vector group; A vector triangle where the reference voltage vector is located is formed using a three-element vector group.

[0015] Preferably, step S4 specifically includes the following steps: S41, set the three reference voltage vectors constituting the vector triangle to be 、 and ,and , Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components of the 、 and ,get: (7); Where, represents the reference voltage vector, and ; Solving formula (7) yields: (8); (9); (10); in, (11); (12); (13); (14); (15); Where, Represents the reference voltage vector and the square of the distance in space; Represents the reference voltage vector and Relative to the reference voltage vector relevance; Represents the reference voltage vector and the square of the distance in space; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; represents the reference output voltage, and, , ; S42, by adjusting the duty cycle to achieve DC bus capacitor and flying capacitor voltage balance, and the DC bus capacitor voltage balance vector action duration adjustment for: (16); Where, represents the DC bus capacitor voltage balance tracking target, and ; represents the proportionality coefficient; represents the DC bus capacitor voltage difference, and , and represent the first DC bus capacitor voltage and the second DC bus capacitor voltage respectively; S43, introduce the duration adjustment of vector action , the duration of action of a pair of central vectors Reassign to and : (17); (18); S44, action duration based on three reference voltage vectors 、 and And the duration of action of the redistributed pair of central vectors and , according to the volt-second balance principle, the conduction duty cycle of the high-frequency switch tube is determined , realize the synthesis of reference voltage vector; S45, determining the initial state duty cycle according to the switching state of the initial voltage vector ; S46, dynamically adjusting the duty cycle of the complementary switch pair of the high-frequency switch tubes based on the three-phase output current direction and the flying capacitor voltage deviation to achieve flying capacitor voltage balance; S47 , comparing the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate a PWM drive signal for the high-frequency switch tube.

[0016] Therefore, the present invention adopts the above-mentioned five-level inverter control system and method for eVTOL aircraft, which has the following beneficial effects: 1. Reduce the number of candidate voltage vectors and lower the computational burden: The space vector is divided into six sectors, each of which is subdivided into three hexagonal sub-regions and one diamond sub-region. Through hierarchical optimization, candidate voltage vectors are screened. The number of candidate voltage vectors required for cost function optimization is reduced from the full traversal of traditional methods (e.g., 81 vectors) to 16, significantly reducing the computational burden of the control algorithm and improving real-time performance. 2. Eliminate dependence on weight factors and simplify parameter adjustment: Discard traditional weight factors in the model predictive control scheme, achieve DC bus capacitor voltage balance through duty cycle adjustment, and use redundant switch state selection to achieve flying capacitor voltage balance, avoiding system performance fluctuations caused by inaccurate weight factor adjustment, reducing parameter optimization complexity, and improving control robustness.

[0017] 3. Efficiently suppress common-mode voltage and improve electromagnetic compatibility: Voltage vectors with high common-mode voltage are discarded, and the common-mode voltage amplitudes of the remaining 79 voltage vectors are suppressed to within one-sixth of the DC bus voltage. This significantly reduces motor bearing current and inverter electromagnetic interference, avoids interference with the eVTOL flight control system, and improves flight safety. 4. Dynamically stabilize capacitor voltage and enhance system reliability: By adjusting the duty cycle distribution of a pair of center vectors in the triangular sector, the voltage difference is dynamically adjusted using the proportional coefficient. The duty cycle of the complementary switch pair is dynamically switched according to the output current direction and capacitor voltage deviation, forcing the capacitor to charge and discharge. This solves the voltage oscillation problem of traditional PI control under dynamic loads, avoids power device failures caused by overvoltage, and improves the long-term operational reliability of the inverter. 5. Improve the quality of the output current waveform and optimize system performance: Use a fixed switching sequence (such as seven-segment or five-segment) and carrier comparison to generate the drive signal to ensure stable switching frequency; synthesize the reference voltage through model prediction and space vector modulation to reduce current ripple, regularize the output current spectrum, reduce the ripple amplitude, and facilitate the design of electromagnetic interference filter parameters. At the same time, avoid the decrease in system power-to-weight ratio caused by additional filters, and meet the high power density requirements of eVTOL.

[0018] In summary, the present invention improves the quality of the output current waveform while ensuring the dynamic stability of the flying capacitor voltage and suppressing the common-mode voltage, thereby systematically improving the performance and reliability of the eVTOL aircraft power conversion device.

[0019] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a topology diagram of a five-level inverter control system for an eVTOL aircraft according to the present invention; Figure 2 The voltage vector and sector division diagram described in the simulation experiment of the present invention; Figure 3 The simulation experiment of the present invention is described Figure 2 The division diagram of the middle area (including 3 hexagonal areas and 1 diamond area) corresponding to sector I in ; Figure 4 Schematic diagram of the vector triangle corresponding to sector 1 described in the simulation experiment of the present invention; Figure 5 1 is a timing diagram of the switching sequence of the vector triangles S2 and S20 in sector I described in the simulation experiment of the present invention, wherein (a) is the timing diagram of the switching sequence of S2, and (b) is the timing diagram of the switching sequence of S20; Figure 6 This is a schematic diagram of the comparison of duty cycle and carrier described in the simulation experiment of the present invention; Figure 7 This is a schematic diagram of the driving signal of the high-frequency switch tube described in the simulation experiment of the present invention; Figure 8The simulation waveforms of the ANPC-5L inverter system described in the simulation experiment of the present invention, wherein (a) is the three-phase output current waveform, (b) is the flying capacitor voltage waveform, (c) is the DC bus capacitor voltage waveform, and (d) is the common-mode voltage waveform; Figure 9 The experimental results of the ANPC-5L inverter system described in the present invention are simulated and verified, where (a) is the output current waveform of phase a, and (b) is the first flying capacitor Voltage waveform, (c) is the first DC bus capacitor Voltage waveform, (d) is the second DC bus capacitor Voltage waveform, (e) is the common mode voltage waveform. DETAILED DESCRIPTION

[0021] In order to make the purposes, technical solutions and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention are further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, where the same or similar numbers throughout represent the same or similar elements or elements with the same or similar functions.

[0022] It should be noted that the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or server that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or are inherent to these processes, methods, products or devices.

[0023] The embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0024] like Figure 1 As shown, a five-level inverter control system for an eVTOL aircraft includes: Three-phase resistive-inductive load, used to simulate the resistive-inductive characteristics of the eVTOL motor; ANPC-5L inverter system is used to convert the electrical energy of the DC power supply into three-phase AC power to drive three-phase resistive and inductive loads; Current sampling module, used to collect the three-phase output current of the ANPC-5L inverter system in real time; A reference three-phase current generation module is used to generate a reference three-phase output current as a target value of the three-phase output current of the ANPC-5L inverter system; The control module is used to achieve multi-objective coordinated control of the ANPC-5L inverter system by integrating model prediction ideas and space vector modulation. Through a closed-loop control strategy, it uses the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module to optimize the switching state of the ANPC-5L inverter system and achieve tracking control of the three-phase output current with respect to the reference three-phase output current.

[0025] Specifically, the ANPC-5L inverter system includes a DC power supply, a DC bus capacitor, a flying capacitor, an A-phase power conversion unit, a B-phase power conversion unit, and a C-phase power conversion unit, wherein the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit each include a low-frequency bridge arm and a high-frequency bridge arm, the low-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected in parallel with the DC power supply, and the high-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected to the ANPC-5L inverter system.

[0026] The low-frequency bridge arm includes a first low-frequency switching tube, a second low-frequency switching tube, a third low-frequency switching tube and a fourth low-frequency switching tube, wherein the collector of the first low-frequency switching tube is connected to a DC power supply, the emitter of the first low-frequency switching tube is connected to the collector of the second low-frequency switching tube, the emitter of the second low-frequency switching tube is connected to the collector of the third low-frequency switching tube, the emitter of the third low-frequency switching tube is connected to the collector of the fourth low-frequency switching tube, and the first low-frequency switching tube and the second low-frequency switching tube are a complementary switch pair, and the third low-frequency switching tube and the fourth low-frequency switching tube are a complementary switch pair; the high-frequency bridge arm includes The invention comprises a first high-frequency switching tube, a second high-frequency switching tube, a third high-frequency switching tube and a fourth high-frequency switching tube, wherein the first high-frequency switching tube is connected between the emitter of the first low-frequency switching tube and the collector of the second low-frequency switching tube, the emitter of the first high-frequency switching tube is connected to the collector of the third high-frequency switching tube, the emitter of the third high-frequency switching tube is connected to the collector of the fourth high-frequency switching tube, the emitter of the fourth high-frequency switching tube is connected to the collector of the second high-frequency switching tube, and the emitter of the second high-frequency switching tube is connected between the emitter of the third low-frequency switching tube and the collector of the fourth low-frequency switching tube.

[0027] Combine Figure 1 It can be seen that in this embodiment, the low-frequency bridge arm of the a-phase power conversion unit is provided with a first low-frequency switching tube Ta1, a second low-frequency switching tube Ta2, a third low-frequency switching tube Ta3, and a fourth low-frequency switching tube Ta4, and its high-frequency bridge arm is provided with a first high-frequency switching tube Ta5, a second high-frequency switching tube Ta6, a third high-frequency switching tube Ta7, and a fourth high-frequency switching tube Ta8. Similarly, the switch tube arrangements of the b-phase power conversion unit and the c-phase power conversion unit are obtained.

[0028] The three-phase resistance-inductive load includes an a-phase branch load, a b-phase branch load, and a c-phase branch load, which are respectively connected to the a-phase power conversion unit, the b-phase power conversion unit, and the c-phase power conversion unit, and the a-phase branch load, the b-phase branch load, and the c-phase branch load each include a resistor and an inductor connected in series, one end of the inductor is connected to the resistor, and the other end is connected between the emitter of the third high-frequency switching tube and the collector of the fourth high-frequency switching tube.

[0029] The DC bus capacitor includes a first DC bus capacitor and a second DC bus capacitor connected in series between the positive and negative poles of the DC power supply. The midpoint between the first DC bus capacitor and the second DC bus capacitor is set to be connected to one end of the lead, and the other end of the lead is connected between the emitter of the second low-frequency switching tube and the collector of the third low-frequency switching tube; one plate of the flying capacitor is connected between the emitter of the first high-frequency switching tube and the collector of the third high-frequency switching tube, and the other plate is connected between the emitter of the fourth high-frequency switching tube and the collector of the second high-frequency switching tube.

[0030] The sampling point of the current sampling module is located between the inductor and the high-frequency bridge arm.

[0031] A method for controlling a five-level inverter system for an eVTOL aircraft includes the following steps: S1, collect the three-phase output current of the ANPC-5L inverter system and generate the reference three-phase output current: Assume that the sampling period of the system is , in At the beginning of the sampling cycle, the current sampling module is used to collect the three-phase output current of the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit in the ANPC-5L inverter system in real time. , 、 and Represent the output current of phase a, phase b and phase c respectively; In the At the beginning of the sampling period, the reference three-phase output current can be obtained by referring to the three-phase current generation module. , 、 and Represent the reference current of phase a, phase b and phase c respectively; S2. Establish a discrete mathematical model for the ANPC-5L inverter system to obtain the constraint relationship between voltage and current; Step S2 specifically includes the following steps: S21, the midpoint between the first DC bus capacitor and the second DC bus capacitor is the zero potential reference point, then the three-phase output voltage of the ANPC-5L inverter system is and the midpoint of the three-phase resistive-inductive load Voltage at The relationship between them is: (1); Where, 、 and They represent the output voltages of phase a, phase b, and phase c of the ANPC-5L inverter system respectively; Indicates the load inductance value; represents the load resistance; At the same time, the switching states of the a-phase power conversion unit, b-phase power conversion unit, and c-phase power conversion unit of the ANPC-5L inverter system are determined by the low-frequency bridge arm and the high-frequency bridge arm, which are recorded as a quaternion At this time, the three-phase output voltage of the ANPC-5L inverter system is changed by using the switch state. Mapped into 5 discrete levels to achieve multi-level output: (2); Where, Indicates the three-phase switch status, 、 and Respectively represent the switching states of the a-phase power conversion unit, the b-phase power conversion unit, and the c-phase power conversion unit; Indicates the DC bus voltage; Combining formula (1) and formula (2) we get: (3); Where, 、 and Respectively represent the ANPC-5L inverter system a Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads Output voltage; S22. Discretize formula (1) and get The expected reference three-phase output voltage of the sampling period for: (4); Where, 、 and Respectively represent The expected phase a, phase b, and phase c reference output voltages for the sampling period; 、 and Respectively represent Output current of phase a, phase b and phase c in the sampling period; 、 and Respectively represent The reference output current of phase a, phase b and phase c of the sampling period; S23. Based on formula (4), while tracking the expected reference three-phase output voltage, considering the computational burden, the cost function defined is and common-mode voltage : (5); (6); Where, 、 and Represent the reference output voltages of phase a, phase b, and phase c respectively; 、 and Respectively represent Sub-sampling cycle of ANPC-5L inverter system a Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads output voltage.

[0032] S3, based on the space vector modulation strategy, combined with the cost function rolling, determine the vector triangle where the reference voltage vector is located and the driving signal of the low-frequency switch tube; Step S3 specifically includes the following steps: S31, convert the three-phase switch state to The voltage vector in the coordinate system is used to obtain the voltage vector diagram; S32. Based on the low-frequency bridge arm switch state, select six evenly distributed characteristic vectors as sector boundaries to obtain six sectors. Each sector corresponds to a set of low-frequency switch tube state combinations. Use formula (5) to perform rolling optimization on the six characteristic vectors to determine the target sector where the reference voltage vector is located. S33, determining three hexagonal areas and one diamond area with the characteristic vector in the target sector as the center, substituting the voltage vectors corresponding to the three hexagonal areas and the one diamond area into formula (5) and performing rolling optimization to determine the target center area; S34. When the target area is a hexagonal area, extract the six vertex voltage vectors of the hexagonal area, select the two vertex voltage vectors with the minimum cost by formula (5), and introduce the characteristic vector corresponding to the hexagonal area to form a three-element vector group; When the target area is a diamond area, the four vertex voltage vectors of the diamond area are extracted, and the three vertex vectors with the minimum cost are selected by formula (5) to form a three-element vector group; A vector triangle where the reference voltage vector is located is formed using a three-element vector group.

[0033] S4. Calculate the action duration of each reference voltage vector based on the vector triangle, synthesize the reference voltage vector, achieve voltage balance between the DC bus capacitor and the flying capacitor by adjusting the duty cycle, and generate a drive signal for the high-frequency switch tube; Step S4 specifically includes the following steps: S41, set the three reference voltage vectors constituting the vector triangle to be 、 and ,and , Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components of the 、 and ,get: (7); Where, represents the reference voltage vector, and ; Solving formula (7) yields: (8); (9); (10); in, (11); (12); (13); (14); (15); Where, Represents the reference voltage vector and the square of the distance in space; Represents the reference voltage vector and Relative to the reference voltage vector relevance; Represents the reference voltage vector and the square of the distance in space; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; represents the reference output voltage, and, , ; S42, by adjusting the duty cycle to achieve DC bus capacitor and flying capacitor voltage balance, and the DC bus capacitor voltage balance vector action duration adjustment for: (16); Where, represents the DC bus capacitor voltage balance tracking target, and ; represents the proportionality coefficient, is a non-zero value; represents the DC bus capacitor voltage difference, and , and represent the first DC bus capacitor voltage and the second DC bus capacitor voltage respectively; S43, introduce the duration adjustment of vector action , the duration of action of a pair of center vectors (a pair of vectors with the same phase and amplitude but opposite effects on the neutral point voltage) is Reassign to and : (17); (18); S44, action duration based on three reference voltage vectors 、 and And the duration of action of the redistributed pair of central vectors and , according to the volt-second balance principle, the conduction duty cycle of the high-frequency switch tube is determined , realize the synthesis of reference voltage vector; S45, determining the initial state duty cycle according to the switching state of the initial voltage vector ; S46, dynamically adjusting the duty cycle of the complementary switch pair of the high-frequency switch tubes based on the three-phase output current direction and the flying capacitor voltage deviation to achieve flying capacitor voltage balance; S47 , comparing the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate a PWM drive signal for the high-frequency switch tube.

[0034] S5. Distribute the generated driving signals of the low-frequency switching tube and the high-frequency switching tube to the low-frequency switching tube and the high-frequency switching tube respectively.

[0035] Simulation experiment Build in Matlab / Simulink Figure 1 The eVTOL aircraft is controlled by a five-level inverter. The experimental parameters are set as follows: DC bus voltage ; The first DC bus capacitor voltage ; Second DC bus capacitor voltage ;Three-phase flying capacitor ; Load inductance ; Load resistance ; Sampling period .

[0036] Use a three-digit number to represent the voltage vector (three-phase switch state), which means "SSa SSb SSc". For example, "400" means SSa=4, SSb=0, SSc=0, and the following is obtained: Figure 2 The voltage vector diagram shown in Figure 2 The vectors "311," "331," "131," "133," "113," and "313" in the cost function are used to perform rolling optimization to select the sector regions. The switching states of the low-frequency switches Tx1, Tx2, Tx3, and Tx4 are also determined. Since Tx1 and Tx2 are complementary switch pairs, Tx3 and Tx4 are complementary switch pairs, and Tx1 and Tx3 have the same control signal, only one control signal is required for each phase. This results in the control signals corresponding to different sectors, as shown in Table 1.

[0037] Table 1 Voltage vectors corresponding to the six sectors and the switch states corresponding to Tx1~Tx4 ;

[0038] like Figure 3 As shown in FIG, the sector is further divided into three hexagonal middle regions and one diamond middle region. The specific middle region where the reference voltage is located is determined by rolling optimization of the cost function using the voltage vectors corresponding to different middle regions.

[0039] Table 2 Candidate voltage vectors of target regions corresponding to sectors ;

[0040] like Figure 4 As shown by Figure 4 Combined with Table 2, it can be seen that (in Table 2, 1, 2, and 3 correspond to hexagonal areas; 4 corresponds to diamond areas). Taking the middle area corresponding to sector I as an example, the voltage vectors corresponding to the three hexagonal areas and diamond areas of sector I are "310 (421)", "211 (322)", "301 (412)", and "400", respectively; the corresponding four voltage vectors (for the hexagonal area, the corresponding two voltage vectors have the same result, and any one of them can be selected) are substituted into the cost function to calculate the four corresponding cost function values, and the middle area corresponding to the minimum cost function value is selected. Then, the vector triangle is obtained using step S34 of the present invention, that is, the triangular area where the reference voltage vector is located. The duration of action of the three reference voltage vectors obtained by the present invention is further calculated. 、 and And the duration of action of the redistributed pair of central vectors and Determine the on-duty cycle of the high-frequency switch In this simulation experiment, Figure 4 Taking the triangle vector S2 in sector I as an example, its corresponding voltage vectors are "310" ("421"), "410", and "420", so its switching sequence is defined as "310-410-420-421-420-410-310".

[0041] like Figure 5 As shown, the duration of action of "310" and "421" are respectively and The duration of the "410" action is The duration of the effect of "420" is .pass 、 and And the sequence switching can determine the duty cycle of the switch For the diamond area, the situation is slightly different. Taking the vector triangle S20 in sector I as an example, its corresponding voltage vectors are "400", "401", and "411", and its switching sequence is "400-401-411-401-400". The sequence switching and action duration are as follows: Figure 5 As shown in (b), the duration of the effect of "411" is The duration of the effect of "401" is The duration of the effect of "400" is .

[0042] Table 3 Switching sequence of vector triangles S1 to S20 corresponding to sector I ;

[0043] Assuming that the vector triangles in each hexagonal area and the rhombus area have the same initial voltage vector, the initial state duty cycle is determined by the initial voltage vector (SSa, SSb, SSc) If SSx=0 or 2, then set ; If SSx = 1, 3 or 4, set By analogy, assuming the initial voltage vector of the vector triangle is "310", the duty cycle can be determined to be 、 and .

[0044] like Figure 6 As shown, in order to achieve flying capacitor voltage balance, it is necessary to allocate different duty cycles to the complementary switch pairs Tx5 and Tx6, Tx7 and Tx8 according to the difference in output current and flying capacitor voltage, where , is the duty cycle of the complementary switch pair Tx5 and Tx6, is the duty cycle of the complementary switch pair Tx7 and Tx8.

[0045] Table 4 Duty cycle distribution method for balancing flying capacitor voltage ;

[0046] For example, when the output current If the flying capacitor voltage exceeds its reference value, the capacitor needs to be properly discharged to restore the balance. For example, it regulates the voltage in the following way: , then set , ;if , then set , . Get Figure 7 The driving signal of the high-frequency switch tube is shown in FIG. The simulation results are as follows Figure 8 As shown, we can see that 1. The three-phase output current: the sine waveform is smooth, the ripple is small, and the spectrum is regular (no random ripple of traditional model predictive control). 2. The flying capacitor voltage: stable around 100V, and the fluctuation amplitude is less than 5V during the dynamic process. 3. The DC bus capacitor voltage remains balanced (the difference is less than 2V), verifying the duty cycle adjustment effect. 4. The common mode voltage is all 5. Only 16 voltage vectors need to be optimized in each sampling period, and the computational burden is small.

[0047] Physical prototype verification: Build the experimental platform of ANPC-5L inverter system and set the experimental parameters as follows: input voltage ; First DC bus capacitor ; Second DC bus capacitor Flying capacitor ; Load inductance ; Load resistance ; Sampling period The result is as follows Figure 9 As shown in the figure, 1. Dynamic Performance: Under step load, current overshoot is less than 5%, and recovery time is short, demonstrating the fast response advantage of the proposed model predictive control. 2. Steady-State Accuracy: The capacitor-voltage balance error is within the engineering tolerance (<1%), meeting the stringent reliability requirements of eVTOL. 3. Engineering Applicability: The hardware experimental results are highly consistent with the simulation, verifying the portability of the control algorithm from simulation to actual deployment.

[0048] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A five-level inverter control system for an eVTOL aircraft, characterized by: include: Three-phase resistive-inductive load, used to simulate the resistive-inductive characteristics of the eVTOL motor; ANPC-5L inverter system is used to convert the electrical energy of the DC power supply into three-phase AC power to drive three-phase resistive and inductive loads; Current sampling module, used to collect the three-phase output current of the ANPC-5L inverter system in real time; A reference three-phase current generation module is used to generate a reference three-phase output current as a target value of the three-phase output current of the ANPC-5L inverter system; The control module is used to achieve multi-objective coordinated control of the ANPC-5L inverter system by integrating model prediction ideas and space vector modulation. Through a closed-loop control strategy, it uses the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module to optimize the switching state of the ANPC-5L inverter system and achieve tracking control of the three-phase output current with respect to the reference three-phase output current.

2. The five-level inverter control system for an eVTOL aircraft according to claim 1, characterized in that: The ANPC-5L inverter system includes a DC power supply, a DC bus capacitor, a flying capacitor, an A-phase power conversion unit, a B-phase power conversion unit, and a C-phase power conversion unit. The A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit each include a low-frequency bridge arm and a high-frequency bridge arm. The low-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected in parallel with the DC power supply, and the high-frequency bridge arms of the A-phase power conversion unit, the B-phase power conversion unit, and the C-phase power conversion unit are all connected to the ANPC-5L inverter system.

3. The five-level inverter control system for an eVTOL aircraft according to claim 2, characterized in that: The low-frequency bridge arm includes a first low-frequency switching tube, a second low-frequency switching tube, a third low-frequency switching tube, and a fourth low-frequency switching tube, wherein the collector of the first low-frequency switching tube is connected to a DC power supply, the emitter of the first low-frequency switching tube is connected to the collector of the second low-frequency switching tube, the emitter of the second low-frequency switching tube is connected to the collector of the third low-frequency switching tube, and the emitter of the third low-frequency switching tube is connected to the collector of the fourth low-frequency switching tube, and the first low-frequency switching tube and the second low-frequency switching tube form a complementary switch pair, and the third low-frequency switching tube and the fourth low-frequency switching tube form a complementary switch pair; The high-frequency bridge arm includes a first high-frequency switching tube, a second high-frequency switching tube, a third high-frequency switching tube and a fourth high-frequency switching tube, wherein the first high-frequency switching tube is connected between the emitter of the first low-frequency switching tube and the collector of the second low-frequency switching tube, the emitter of the first high-frequency switching tube is connected to the collector of the third high-frequency switching tube, the emitter of the third high-frequency switching tube is connected to the collector of the fourth high-frequency switching tube, the emitter of the fourth high-frequency switching tube is connected to the collector of the second high-frequency switching tube, and the emitter of the second high-frequency switching tube is connected between the emitter of the third low-frequency switching tube and the collector of the fourth low-frequency switching tube.

4. The five-level inverter control system for an eVTOL aircraft according to claim 3, characterized in that: The three-phase resistance-inductive load includes an a-phase branch load, a b-phase branch load, and a c-phase branch load, which are respectively connected to the a-phase power conversion unit, the b-phase power conversion unit, and the c-phase power conversion unit, and the a-phase branch load, the b-phase branch load, and the c-phase branch load each include a resistor and an inductor connected in series, one end of the inductor is connected to the resistor, and the other end is connected between the emitter of the third high-frequency switching tube and the collector of the fourth high-frequency switching tube.

5. The five-level inverter control system for an eVTOL aircraft according to claim 4, characterized in that: The DC bus capacitor includes a first DC bus capacitor and a second DC bus capacitor connected in series between the positive and negative electrodes of the DC power supply. The midpoint between the first DC bus capacitor and the second DC bus capacitor is connected to one end of a lead, and the other end of the lead is connected between the emitter of the second low-frequency switching tube and the collector of the third low-frequency switching tube. One plate of the flying capacitor is connected between the emitter of the first high-frequency switch tube and the collector of the third high-frequency switch tube, and the other plate is connected between the emitter of the fourth high-frequency switch tube and the collector of the second high-frequency switch tube.

6. The five-level inverter control system for an eVTOL aircraft according to claim 5, characterized in that: The sampling point of the current sampling module is located between the inductor and the high-frequency bridge arm.

7. A method for controlling a five-level inverter system for an eVTOL aircraft according to claim 6, characterized in that: The following steps are involved: S1, collect the three-phase output current of the ANPC-5L inverter system and generate the reference three-phase output current: Assume that the sampling period of the system is , in At the beginning of the sampling cycle, the current sampling module is used to collect the three-phase output current of the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit in the ANPC-5L inverter system in real time. , 、 and Represent the output current of phase a, phase b and phase c respectively; In the At the beginning of the sampling period, the reference three-phase output current can be obtained by referring to the three-phase current generation module. , 、 and Represent the reference current of phase a, phase b and phase c respectively; S2. Establish a discrete mathematical model for the ANPC-5L inverter system to obtain the constraint relationship between voltage and current; S3, based on the space vector modulation strategy, combined with the cost function rolling, determine the vector triangle where the reference voltage vector is located and the driving signal of the low-frequency switch tube; S4. Calculate the action duration of each reference voltage vector based on the vector triangle, synthesize the reference voltage vector, achieve voltage balance between the DC bus capacitor and the flying capacitor by adjusting the duty cycle, and generate a drive signal for the high-frequency switch tube; S5. Distribute the generated driving signals of the low-frequency switching tube and the high-frequency switching tube to the low-frequency switching tube and the high-frequency switching tube respectively.

8. The five-level inverter control system for an eVTOL aircraft according to claim 7, characterized in that: Step S2 specifically includes the following steps: S21, the midpoint between the first DC bus capacitor and the second DC bus capacitor is the zero potential reference point, then the three-phase output voltage of the ANPC-5L inverter system is and the midpoint of the three-phase resistive-inductive load Voltage at The relationship between them is: （1）； Where, 、 and They represent the output voltages of phase a, phase b, and phase c of the ANPC-5L inverter system respectively; Indicates the load inductance value; represents the load resistance; At the same time, the switching states of the a-phase power conversion unit, b-phase power conversion unit, and c-phase power conversion unit of the ANPC-5L inverter system are determined by the low-frequency bridge arm and the high-frequency bridge arm, which are recorded as a quaternion At this time, the three-phase output voltage of the ANPC-5L inverter system is changed by using the switch state. Mapped into 5 discrete levels to achieve multi-level output: （2）； Where, Indicates the three-phase switch status, 、 and Respectively represent the switching states of the a-phase power conversion unit, the b-phase power conversion unit, and the c-phase power conversion unit; Indicates the DC bus voltage; Combining formula (1) and formula (2) we get: （3）； Where, 、 and Respectively represent the ANPC-5L inverter system a Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads Output voltage; S22. Discretize formula (1) and get The expected reference three-phase output voltage of the sampling period for: （4）； Where, 、 and Respectively represent The expected phase a, phase b, and phase c reference output voltages for the sampling period; 、 and Respectively represent Output current of phase a, phase b and phase c in the sampling period; 、 and Respectively represent The reference output current of phase a, phase b and phase c of the sampling period; S23. Based on formula (4), while tracking the expected reference three-phase output voltage, considering the computational burden, the cost function defined is and common-mode voltage : （5）； （6）； Where, 、 and Represent the reference output voltages of phase a, phase b, and phase c respectively; 、 and Respectively represent Sub-sampling cycle of ANPC-5L inverter system a Mutually, b Mutually, c Phases are relative to the midpoint of the three-phase resistive and inductive loads output voltage.

9. The five-level inverter control system for an eVTOL aircraft according to claim 8, characterized in that: Step S3 specifically includes the following steps: S31, convert the three-phase switch state to The voltage vector in the coordinate system is used to obtain the voltage vector diagram; S32. Based on the low-frequency bridge arm switch state, select six evenly distributed characteristic vectors as sector boundaries to obtain six sectors. Each sector corresponds to a set of low-frequency switch tube state combinations. Use formula (5) to perform rolling optimization on the six characteristic vectors to determine the target sector where the reference voltage vector is located. S33, determining three hexagonal areas and one diamond area with the characteristic vector in the target sector as the center, substituting the voltage vectors corresponding to the three hexagonal areas and the one diamond area into formula (5) and performing rolling optimization to determine the target center area; S34. When the target area is a hexagonal area, extract the six vertex voltage vectors of the hexagonal area, select the two vertex voltage vectors with the minimum cost by formula (5), and introduce the characteristic vector corresponding to the hexagonal area to form a three-element vector group; When the target area is a diamond area, the four vertex voltage vectors of the diamond area are extracted, and the three vertex vectors with the minimum cost are selected by formula (5) to form a three-element vector group; A vector triangle where the reference voltage vector is located is formed using a three-element vector group.

10. The five-level inverter control system for an eVTOL aircraft according to claim 9, characterized in that: Step S4 The specific steps include: S41, set the three reference voltage vectors constituting the vector triangle to be 、 and ,and , Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components, Represent the reference voltage vector The a-phase, b-phase, and c-phase components of the 、 and ,get: （7）； Where, represents the reference voltage vector, and ; Solving formula (7) yields: （8）； （9）； （10）； in, （11）； （12）； （13）； （14）； （15）； Where, Represents the reference voltage vector and the square of the distance in space; Represents the reference voltage vector and Relative to the reference voltage vector relevance; Represents the reference voltage vector and the square of the distance in space; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; Indicates the reference output voltage With reference voltage vector The deviation in the reference voltage vector projection; represents the reference output voltage, and, , ; S42, by adjusting the duty cycle to achieve DC bus capacitor and flying capacitor voltage balance, and the DC bus capacitor voltage balance vector action duration adjustment for: （16）； Where, represents the DC bus capacitor voltage balance tracking target, and ; represents the proportionality coefficient; represents the DC bus capacitor voltage difference, and , and represent the first DC bus capacitor voltage and the second DC bus capacitor voltage respectively; S43, introduce the duration adjustment of vector action , the duration of action of a pair of central vectors Reassign to and : （17）； （18）； S44, action duration based on three reference voltage vectors 、 and And the duration of action of the redistributed pair of central vectors and , according to the volt-second balance principle, the conduction duty cycle of the high-frequency switch tube is determined , realize the synthesis of reference voltage vector; S45, determining the initial state duty cycle according to the switching state of the initial voltage vector ; S46, dynamically adjusting the duty cycle of the complementary switch pair of the high-frequency switch tubes based on the three-phase output current direction and the flying capacitor voltage deviation to achieve flying capacitor voltage balance; S47 , comparing the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate a PWM drive signal for the high-frequency switch tube.

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