Five-level inverter control system and method for an eVTOL aircraft

Abstract

The application discloses a kind of five-level inverter control systems and methods for eVTOL aircraft, belong to five-level inverter field, including: three-phase resistance-inductance load, for simulating resistance-inductance characteristic;ANPC-5L inverter system, for driving three-phase resistance-inductance load;Current sampling module, for real-time acquisition ANPC-5L inverter system three-phase output current;Reference three-phase current generation module, for generating reference three-phase output current, as ANPC-5L inverter system three-phase output current target value;Control module, for realizing the multi-target collaborative control of ANPC-5L inverter system.Using the above-mentioned five-level inverter control system and method for eVTOL aircraft, not only can realize the dynamic stability of flying capacitor voltage, but also can ensure the waveform quality of output current, and can limit the amplitude of maximum common-mode voltage to not more than one sixth of DC bus voltage, so as to improve the reliability of inverter.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of five-level inverter, and particularly relates to a five-level inverter control system and method for an eVTOL aircraft. BACKGROUND

[0002] An electric vertical take-off and landing (eVTOL) aircraft is a core carrier of next-generation urban air transportation, and its power system needs to meet strict requirements such as high power density, high reliability and light weight. A direct current-alternating current (DC-AC) power conversion device is a core unit of the power system, and its performance directly affects the endurance, electromagnetic compatibility and service life of key components of the eVTOL aircraft.

[0003] In recent years, a multi-level inverter gradually becomes an optimal solution for a high-voltage and high-power aviation electric propulsion system due to low output voltage harmonic content, small voltage stress of a power device and other advantages. An active neutral-point-clamped five-level (ANPC-5L) inverter combines the advantages of an active neutral-point-clamped inverter and a flying capacitor inverter, does not need to configure a clamping diode, only uses a small number of capacitors, and has the advantages of flexible output level and high reliability.

[0004] However, the existing ANPC-5L inverter faces three technical bottlenecks in the application scenario of the eVTOL aircraft. First, the voltage stability control problem of the flying capacitor is prominent. The power of the eVTOL aircraft frequently changes suddenly during the take-off / landing stage, and the capacitor voltage balancing strategy based on the feedback adjustment of a proportional-integral controller is difficult to adapt to the dynamic load change, which easily leads to oscillation of the flying capacitor voltage, thereby causing the risk of overvoltage of the power device and even failure. Second, the problem of high amplitude of common-mode voltage is significant. The conventional ANPC-5L inverter modulation strategy cannot effectively suppress the common-mode voltage, and the high-frequency component of the common-mode voltage can aggravate the motor bearing current and the electromagnetic interference of the inverter, which seriously interferes with the normal work of the flight control computer system of the eVTOL aircraft and poses a threat to flight safety. Finally, the problem of output current waveform quality of the inverter is difficult. The traditional limited set model predictive control scheme has the advantages of fast dynamic response and easy addition of nonlinear constraints, but the running mechanism of obtaining the switching state through traversal optimization makes the switching frequency of the inverter not fixed, the current ripple is large, and the current spectrum is irregular, which is not conducive to the design of electromagnetic interference filter parameters, especially in the application scenario of the eVTOL aircraft, the additional electromagnetic interference filter caused by the irregular current spectrum will hinder the improvement of the power-to-weight ratio of the system. SUMMARY

[0005] The application aims to provide a five-level inverter control system and method for eVTOL aircraft, and solve the above technical problems.

[0006] To achieve the above-mentioned purpose, the application provides a five-level inverter control system for eVTOL aircraft, comprising:

[0007] A three-phase resistive-inductive load is used to simulate the resistive-inductive characteristics of eVTOL motors.

[0008] An ANPC-5L inverter system is used to convert the power of a DC power supply into three-phase alternating current to drive the three-phase resistive-inductive load.

[0009] A current sampling module is used to collect the three-phase output current of the ANPC-5L inverter system in real time.

[0010] A reference three-phase current generation module is used to generate a reference three-phase output current as the target value of the three-phase output current of the ANPC-5L inverter system.

[0011] A control module is used to realize multi-objective collaborative control of the ANPC-5L inverter system by integrating the model prediction idea and the space vector modulation, and to realize the tracking control of the three-phase output current on the reference three-phase output current by optimizing and adjusting the switching state of the ANPC-5L inverter system through the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module, and through the closed-loop control strategy.

[0012] Preferably, the ANPC-5L inverter system comprises 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 comprise 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 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 connected with the ANPC-5L inverter system.

[0013] Preferably, the low-frequency bridge arm comprises 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 with the DC power supply, the emitter of the first low-frequency switching tube is connected with the collector of the second low-frequency switching tube, the emitter of the second low-frequency switching tube is connected with the collector of the third low-frequency switching tube, the emitter of the third low-frequency switching tube is connected with 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 switching pair, and the third low-frequency switching tube and the fourth low-frequency switching tube are a complementary switching pair.

[0014] The high-frequency bridge arm comprises a first high-frequency switch tube, a second high-frequency switch tube, a third high-frequency switch tube and a fourth high-frequency switch tube, wherein the first high-frequency switch tube is connected between the emitter of the first low-frequency switch tube and the collector of the second low-frequency switch tube, the emitter of the first high-frequency switch tube is connected to the collector of the third high-frequency switch tube, the emitter of the third high-frequency switch tube is connected to the collector of the fourth high-frequency switch tube, the emitter of the fourth high-frequency switch tube is connected to the collector of the second high-frequency switch tube, and the emitter of the second high-frequency switch tube is connected between the emitter of the third low-frequency switch tube and the collector of the fourth low-frequency switch tube.

[0015] Preferably, the three-phase resistive and inductive load comprises a-phase branch load, b-phase branch load and c-phase branch load connected to the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit respectively, and the a-phase branch load, the b-phase branch load and the c-phase branch load each comprise a resistor and an inductor connected in series, one end of the inductor being connected to the resistor, and the other end being connected between the emitter of the third high-frequency switch tube and the collector of the fourth high-frequency switch tube.

[0016] Preferably, the DC bus capacitor comprises 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, and a midpoint between the first DC bus capacitor and the second DC bus capacitor is connected to one end of a lead wire, and the other end of the lead wire is connected between the emitter of the second low-frequency switch tube and the collector of the third low-frequency switch tube.

[0017] One pole 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 pole plate is connected between the emitter of the fourth high-frequency switch tube and the collector of the second high-frequency switch tube.

[0018] Preferably, the sampling point of the current sampling module is located between the inductor and the high-frequency bridge arm.

[0019] The method of the five-level inverter control system for eVTOL aircraft comprises the following steps:

[0020] S1, collecting three-phase output currents of the ANPC-5L inverter system, and generating reference three-phase output currents: assuming that the sampling period of the system is , at the beginning of the first sampling period, the three-phase output currents 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 are collected in real time by using the current sampling module , , and represent the a-phase, b-phase and c-phase output currents respectively;

[0021] , at the beginning of the second At the beginning of the next sampling period, the reference three-phase output current can be obtained through the reference three-phase current generation module. , , and These represent the reference currents for phases a, b, and c, respectively.

[0022] S2. Establish a discretized mathematical model for the ANPC-5L inverter system to obtain the constraint relationship between voltage and current;

[0023] S3. Based on the space vector modulation strategy, the vector triangle where the reference voltage vector is located and the driving signal of the low-frequency switching transistor are determined by the cost function rolling.

[0024] S4. Calculate the duration of each reference voltage vector based on the vector triangle, synthesize the reference voltage vector, and achieve voltage balance between the DC bus capacitor and the flying capacitor by adjusting the duty cycle to generate the drive signal for the high-frequency switching transistor.

[0025] S5. Distribute the generated drive signals for the low-frequency switch and the high-frequency switch to the low-frequency switch and the high-frequency switch, respectively.

[0026] Preferably, step S2 specifically includes the following steps:

[0027] S21, using the midpoint between the first DC bus capacitor and the second DC bus capacitor as an example. Taking zero potential as the reference point, the three-phase output voltage of the ANPC-5L inverter system Midpoint of three-phase resistive-inductive load voltage at The relationship between them is:

[0028] (1);

[0029] In the formula, , and These represent the output voltages of phase a, phase b, and phase c of the ANPC-5L inverter system, respectively. Indicates the load inductance value; Indicates the load resistance;

[0030] Meanwhile, 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 defined as being jointly determined by the low-frequency bridge arm and the high-frequency bridge arm, denoted as a quadruple. At this time, the three-phase output voltage of the ANPC-5L inverter system is controlled by the switching state. Mapped to 5 discrete levels to achieve multi-level output:

[0031] (2);

[0032] wherein, denotes the three-phase switching states, , and denote the switching states of the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit, respectively; denotes the DC bus voltage;

[0033] By combining formula (1) and formula (2), we get:

[0034] (3);

[0035] wherein, , and denote the output voltages of the ANPC-5L inverter system with respect to the midpoint of the three-phase resistive-inductive load, the a-phase, b the b-phase, c the c-phase, respectively;

[0036] S22, discretize formula (1) to get the expected reference three-phase output voltage of the nth sampling period:

[0037] (4);

[0038] wherein, , and denote the expected a-phase, b-phase and c-phase reference output voltages of the nth sampling period, respectively; , and denote the a-phase, b-phase and c-phase output currents of the nth sampling period, respectively; , and denote the a-phase, b-phase and c-phase reference output currents of the nth sampling period, respectively; S23, based on formula (4), while tracking the expected reference three-phase output voltage, considering the calculation burden, the cost function and the common-mode voltage are defined as:

[0039] (5);

[0040] (6);

[0041] (6); ​​​​

[0042] wherein, , and represent the reference output voltages of the a-phase, b-phase and c-phase respectively; , and represent the output voltages of the a-phase, b-phase and c-phase respectively of the ANPC-5L inverter system in the nth sampling period relative to the midpoint of the three-phase resistive-inductive load; a b c

[0043] Preferably, the step S3 specifically comprises the following steps:

[0044] S31, converting the three-phase switching state into a voltage vector in the stationary reference frame to obtain a voltage vector diagram;

[0045] S32, taking the low-frequency bridge arm switching state as a reference, selecting six evenly distributed characteristic vectors as sector boundaries to obtain six sectors, each sector corresponding to a group of low-frequency switching tube state combinations, and using formula (5) to perform rolling optimization on the six characteristic vectors to determine the target sector where the reference voltage vector is located;

[0046] S33, determining three hexagonal regions and one rhombic region with the characteristic vectors within the target sector as the center, substituting the voltage vectors corresponding to the three hexagonal regions and one rhombic region into formula (5) to perform rolling optimization to determine the target middle region;

[0047] S34, when the target middle region is a hexagonal region, extracting six vertex voltage vectors of the hexagonal region, screening out two vertex voltage vectors with the smallest cost through formula (5), and introducing the characteristic vectors corresponding to the hexagonal region to form a three-element vector group;

[0048] When the target middle region is a rhombic region, extracting four vertex voltage vectors of the rhombic region, screening out three vertex vectors with the smallest cost through formula (5) to form a three-element vector group;

[0049] Using the three-element vector group to form a vector triangle where the reference voltage vector is located.

[0050] Preferably, the step S4 specifically comprises the following steps:

[0051] S41, setting the three reference voltage vectors constituting the vector triangle as , and , and , represent the reference voltage vectors​​​​​​ a-phase, b-phase, c-phase components of the reference voltage vector a-phase, b-phase, c-phase components of the reference voltage vector a-phase, b-phase, c-phase components of the reference voltage vector

[0052] (7);

[0053] wherein, represents the reference voltage vector, and

[0054] solving formula (7) obtains:

[0055] (8);

[0056] (9);

[0057] (10);

[0058] wherein,

[0059] (11);

[0060] (12);

[0061] (13);

[0062] (14);

[0063] (15);

[0064] wherein, represents the square of the distance in space between the reference voltage vector and represents the correlation of the reference voltage vector and with respect to the reference voltage vector represents the square of the distance in space between the reference voltage vector and represents the deviation of the reference output voltage from the reference voltage vector ​​​​​​​​​​a projection of the reference voltage vector represents the reference output voltage a deviation of the reference voltage vector a projection of the reference voltage vector ; represents the reference output voltage, and , ;

[0065] S42, the DC bus capacitor and flying capacitor voltage balance is realized by adjusting the duty ratio, and the vector action duration adjustment amount of the DC bus capacitor voltage balance is:

[0066] (16);

[0067] wherein, represents the DC bus capacitor voltage balance tracking target, and ; represents a proportional coefficient; represents the DC bus capacitor voltage difference, and , and respectively represent the first DC bus capacitor voltage and the second DC bus capacitor voltage;

[0068] S43, the vector action duration adjustment amount is introduced, and the action duration of a pair of center vectors is re-allocated as and :

[0069] (17);

[0070] (18);

[0071] S44, based on the action duration , and of three reference voltage vectors and the action duration and of a pair of center vectors after re-allocation, the conduction duty ratio of the high-frequency switch tube is determined according to the volt-second balance principle to realize the synthesis of the reference voltage vector;

[0072] S45, the initial state duty ratio is determined according to the switching state of the initial voltage vector;

[0073] S46, the duty ratio of the complementary switching pair of the high-frequency switch tube is dynamically adjusted in combination with the direction of the three-phase output current and the flying capacitor voltage deviation to realize the flying capacitor voltage balance;

[0074] S47, compare the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate a PWM driving signal of the high-frequency switch tube.

[0075] Therefore, the five-level inverter control system and method for the eVTOL aircraft have the beneficial effects that:

[0076] 1. Reducing the number of candidate voltage vectors and the calculation burden: dividing the space vector into 6 sectors, each sector being subdivided into 3 hexagonal sub-regions and 1 rhombic sub-region, and screening the candidate voltage vectors through hierarchical optimization, the number of candidate voltage vectors required for cost function optimization being reduced from full traversal (e.g. 81 vectors) to 16, significantly reducing the calculation amount of the control algorithm and improving real-time performance;

[0077] 2. Eliminating the dependence on weight factors and simplifying parameter adjustment: discarding the traditional weight factor in the model predictive control scheme, achieving DC bus capacitor voltage balance through duty cycle adjustment, and achieving flying capacitor voltage balance through redundant switch state selection, avoiding system performance fluctuations caused by inaccurate weight factor parameter adjustment, reducing parameter optimization complexity, and improving control robustness.

[0078] 3. Efficiently suppressing common-mode voltage and improving electromagnetic compatibility: discarding voltage vectors with high common-mode voltage, and suppressing the common-mode voltage amplitude of the remaining 79 voltage vectors to within one-sixth of the DC bus voltage, significantly reducing motor bearing current and inverter electromagnetic interference, avoiding interference with the eVTOL flight control system, and improving flight safety;

[0079] 4. Dynamically stabilizing capacitor voltage and enhancing system reliability: adjusting the duty cycle distribution of a pair of center vectors in the triangular sector, dynamically adjusting the voltage difference using a proportional coefficient, and dynamically switching the duty cycle of complementary switch pairs according to the output current direction and capacitor voltage deviation, forcing capacitor charging and discharging, solving the voltage oscillation problem of traditional PI control under dynamic load, avoiding faults caused by overvoltage of power devices, and improving the long-term operation reliability of the inverter;

[0080] 5. Improving output current waveform quality and optimizing system performance: using fixed switching sequences (e.g. seven-segment, five-segment) and carrier comparison to generate driving signals, ensuring stable switching frequency; synthesizing reference voltage through model prediction and space vector modulation, reducing current ripple, regularizing the output current spectrum, reducing ripple amplitude, facilitating electromagnetic interference filter parameter design, while avoiding the decline in system power-to-weight ratio caused by additional filters, meeting the high power density requirements of eVTOL.

[0081] In summary, this invention improves the output current waveform quality while ensuring dynamic stability of the flyover capacitor voltage and suppressing common-mode voltage, thereby systematically enhancing the performance and reliability of the eVTOL aircraft power conversion device.

[0082] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0083] Figure 1 This is a topology diagram of a five-level inverter control system for an eVTOL aircraft according to the present invention;

[0084] Figure 2 This is the voltage vector and sector division diagram described in the simulation experiment of this invention;

[0085] Figure 3 The simulation experiment described in this invention Figure 2 The partition diagram of the central region (including 3 hexagonal regions and 1 rhombus region) corresponding to sector I in the diagram;

[0086] Figure 4 This is a schematic diagram of the vector triangle corresponding to sector I in the simulation experiment of this invention;

[0087] Figure 5 The following is a timing diagram of the switching sequence of vector triangles S2 and S20 in sector I of 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.

[0088] Figure 6 This is a schematic diagram of duty cycle and carrier comparison in the simulation experiment of this invention;

[0089] Figure 7 This is a schematic diagram of the driving signal of the high-frequency switching transistor described in the simulation experiment of this invention;

[0090] Figure 8 The simulation waveforms of the ANPC-5L inverter system described in the simulation experiment of this invention are shown in (a) for the three-phase output current waveform, (b) for the flying capacitor voltage waveform, (c) for the DC bus capacitor voltage waveform, and (d) for the common-mode voltage waveform.

[0091] Figure 9 The following diagram shows the experimental results of the ANPC-5L inverter system described in the simulation verification of this invention. (a) is the output current waveform of phase a, and (b) is the waveform of the first flying capacitor. Voltage waveform diagram, (c) is the first DC bus capacitor Voltage waveform diagram, (d) is the second DC bus capacitor Voltage waveform diagram, (e) is the common-mode voltage waveform diagram. DETAILED DESCRIPTION

[0092] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the embodiments of the present application are further described in detail below with reference to the drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present application and should not be used to limit the embodiments of the present application. Based on the embodiments of the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of the present application. Examples of the embodiments are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout.

[0093] It should be noted that the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or server comprising a series of steps or units does not have to be limited to only those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to the process, method, product or device.

[0094] The embodiments of the present application are described in detail below with reference to the drawings.

[0095] As shown in Figure 1 A five-level inverter control system for eVTOL aircraft includes:

[0096] A three-phase inductive load for simulating the inductive characteristics of eVTOL motors;

[0097] An ANPC-5L inverter system for converting the power of a DC power supply into three-phase AC power to drive the three-phase inductive load;

[0098] A current sampling module for real-time acquisition of three-phase output current of the ANPC-5L inverter system;

[0099] A reference three-phase current generation module for generating a reference three-phase output current as a target value of the three-phase output current of the ANPC-5L inverter system;

[0100] A control module for realizing multi-objective collaborative control of the ANPC-5L inverter system by integrating model predictive thinking and space vector modulation, and for realizing tracking control of the three-phase output current on the reference three-phase output current by optimizing and adjusting the switching state of the ANPC-5L inverter system through a closed-loop control strategy using the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module.

[0101] Specifically, the ANPC-5L inverter system comprises 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 comprise 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 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 connected with the ANPC-5L inverter system.

[0102] The low-frequency bridge arm comprises a first low-frequency switch tube, a second low-frequency switch tube, a third low-frequency switch tube and a fourth low-frequency switch tube, wherein the collector of the first low-frequency switch tube is connected with the DC power supply, the emitter of the first low-frequency switch tube is connected with the collector of the second low-frequency switch tube, the emitter of the second low-frequency switch tube is connected with the collector of the third low-frequency switch tube, the emitter of the third low-frequency switch tube is connected with the collector of the fourth low-frequency switch tube, the first low-frequency switch tube and the second low-frequency switch tube form a complementary switch pair, and the third low-frequency switch tube and the fourth low-frequency switch tube form a complementary switch pair; the high-frequency bridge arm comprises a first high-frequency switch tube, a second high-frequency switch tube, a third high-frequency switch tube and a fourth high-frequency switch tube, wherein the first high-frequency switch tube is connected between the emitter of the first low-frequency switch tube and the collector of the second low-frequency switch tube, the emitter of the first high-frequency switch tube is connected with the collector of the third high-frequency switch tube, the emitter of the third high-frequency switch tube is connected with the collector of the fourth high-frequency switch tube, the emitter of the fourth high-frequency switch tube is connected with the collector of the second high-frequency switch tube, and the emitter of the second high-frequency switch tube is connected between the emitter of the third low-frequency switch tube and the collector of the fourth low-frequency switch tube.

[0103] In combination Figure 1 It can be known that, in the embodiment, the low-frequency bridge arm of the a-phase power conversion unit is provided with the first low-frequency switch tube Ta1, the second low-frequency switch tube Ta2, the third low-frequency switch tube Ta3 and the fourth low-frequency switch tube Ta4, and the high-frequency bridge arm of the a-phase power conversion unit is provided with the first high-frequency switch tube Ta5, the second high-frequency switch tube Ta6, the third high-frequency switch tube Ta7 and the fourth high-frequency switch tube Ta8, and the switch tube arrangement of the b-phase power conversion unit and the c-phase power conversion unit is obtained in the same way.

[0104] The three-phase resistive-inductive load comprises a-phase branch load, b-phase branch load and c-phase branch load connected with the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit respectively, and the a-phase branch load, the b-phase branch load and the c-phase branch load each comprise a resistance and an inductance connected in series, one end of the inductance is connected with the resistance, and the other end is connected between the emitter of the third high-frequency switch tube and the collector of the fourth high-frequency switch tube.

[0105] The direct current bus capacitor comprises a first direct current bus capacitor and a second direct current bus capacitor connected in series between the positive and negative poles of the direct current power supply, the midpoint between the first direct current bus capacitor and the second direct current bus capacitor is connected to one end of a lead wire, and the other end of the lead wire is connected between the emitter of the second low-frequency switch tube and the collector of the third low-frequency switch tube; one pole 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 pole plate is connected between the emitter of the fourth high-frequency switch tube and the collector of the second high-frequency switch tube.

[0106] The sampling point of the current sampling module is located between the inductor and the high-frequency bridge arm.

[0107] The method of the five-level inverter control system for eVTOL aircraft comprises the following steps:

[0108] S1, collecting three-phase output currents of the ANPC-5L inverter system, and generating reference three-phase output currents: assuming that the sampling period of the system is , at the beginning of the first sampling period, the three-phase output currents 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 are collected in real time by a current sampling module , , , and represent the a-phase, b-phase and c-phase output currents respectively;

[0109] At the beginning of the first sampling period, the reference three-phase output currents , , , and represent the a-phase, b-phase and c-phase reference currents respectively;

[0110] S2, establishing a discrete mathematical modeling for the ANPC-5L inverter system, and obtaining a constraint relationship between the voltage and the current;

[0111] Step S2 specifically comprises the following steps:

[0112] S21, taking the midpoint between the first direct current bus capacitor and the second direct current bus capacitor as a zero potential reference point, then the relationship between the three-phase output voltage of the ANPC-5L inverter system and the voltage at the midpoint of the three-phase inductive load is:

[0113] (1)

[0114] ​In the formula, , and These represent the output voltages of phase a, phase b, and phase c of the ANPC-5L inverter system, respectively. Indicates the load inductance value; Indicates the load resistance;

[0115] Meanwhile, 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 defined as being jointly determined by the low-frequency bridge arm and the high-frequency bridge arm, denoted as a quadruple. At this time, the three-phase output voltage of the ANPC-5L inverter system is controlled by the switching state. Mapped to 5 discrete levels to achieve multi-level output:

[0116] (2);

[0117] In the formula, Indicates the status of the three-phase switch. , and These represent the switching states of phase a power conversion unit, phase b power conversion unit, and phase c power conversion unit, respectively. Indicates the DC bus voltage;

[0118] Combining equations (1) and (2), we get:

[0119] (3);

[0120] In the formula, , and These represent the ANPC-5L inverter system. a Mutually, b Mutually, c The phases are respectively relative to the midpoint of the three-phase resistive-inductive load. ; output voltage;

[0121] S22. Discretize formula (1) to obtain the first... The expected reference three-phase output voltage for the next sampling period for:

[0122] (4);

[0123] In the formula, , and They represent the first The expected reference output voltages of phases a, b, and c in the next sampling period; , and a-phase, b-phase and c-phase output currents of the i-th sampling period, respectively; a-phase, b-phase and c-phase output currents of the i-th sampling period, respectively; , a-phase, b-phase and c-phase output currents of the i-th sampling period, respectively; a-phase, b-phase and c-phase output currents of the i-th sampling period, respectively; a-phase, b-phase and c-phase output currents of the i-th sampling period, respectively;

[0124] S23, based on formula (4), while tracking the expected reference three-phase output voltage, considering the calculation burden, the cost function defined and common-mode voltage :

[0125] (5);

[0126] (6);

[0127] In the formula, , and respectively represent the reference output voltages of a-phase, b-phase and c-phase; , and respectively represent the output voltages of a-phase, b-phase and c-phase of the ANPC-5L inverter system of the i-th sampling period relative to the midpoint of the three-phase inductive load . a b c

[0128] 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 switching tube;

[0129] Step S3 specifically includes the following steps:

[0130] S31, convert the three-phase switching state into a voltage vector in the coordinate system, and obtain a voltage vector diagram;

[0131] S32, take the low-frequency bridge arm switching state as the benchmark, select six evenly distributed characteristic vectors as the sector boundary, obtain six sectors, each sector corresponds to a group of low-frequency switching tube state combination, and use formula (5) to perform rolling optimization on the six characteristic vectors, and determine the target sector where the reference voltage vector is located;

[0132] S33, determine three hexagonal regions and one rhombic region with the characteristic vectors in the target sector as the center, substitute the voltage vectors corresponding to the three hexagonal regions and one rhombic region into formula (5) and perform rolling optimization, and determine the target region;

[0133] ​​​​S34. When the target region is a hexagonal region, extract the voltage vectors of the six vertices of the hexagonal region, select the two vertices with the lowest cost through formula (5), and introduce the feature vectors corresponding to the hexagonal region to form a ternary vector group.

[0134] When the target region is a rhombus region, extract the voltage vectors of the four vertices of the rhombus region, and select the three vertices with the lowest cost through formula (5) to form a three-element vector group;

[0135] The vector triangle containing the reference voltage vector is constructed using a set of three vectors.

[0136] S4. Calculate the duration of each reference voltage vector based on the vector triangle, synthesize the reference voltage vector, and achieve voltage balance between the DC bus capacitor and the flying capacitor by adjusting the duty cycle to generate the drive signal for the high-frequency switching transistor.

[0137] Step S4 specifically includes the following steps:

[0138] S41. Set the three reference voltage vectors that constitute the vector triangle as follows: , and ,and , Representing the reference voltage vector respectively The a-phase, b-phase, and c-phase components, Representing the reference voltage vector respectively The a-phase, b-phase, and c-phase components, Representing the reference voltage vector respectively The a-phase, b-phase, and c-phase components, and their corresponding durations of action are respectively , and ,get:

[0139] (7);

[0140] In the formula, Represents the reference voltage vector, and ;

[0141] Solving formula (7) yields:

[0142] (8);

[0143] (9);

[0144] (10);

[0145] in,

[0146] (11);

[0147] (12);

[0148] (13);

[0149] (14);

[0150] (15);

[0151] wherein, represents a reference voltage vector and a square of a distance in space; represents a reference voltage vector and a correlation with respect to a reference voltage vector ; represents a reference voltage vector and a square of a distance in space; represents a reference output voltage and a deviation from a reference voltage vector in a projection of a reference voltage vector ; represents a reference output voltage and a deviation from a reference voltage vector in a projection of a reference voltage vector ; represents a reference output voltage, and, , ;

[0152] S42, a DC bus capacitor and a flying capacitor voltage balance is achieved by adjusting the duty ratio, and the vector action duration adjustment amount of the DC bus capacitor voltage balance is:

[0153] (16);

[0154] wherein, represents a DC bus capacitor voltage balance tracking target, and ; represents a proportional coefficient, is a non-zero value; represents a DC bus capacitor voltage difference, and , and respectively represent the first DC bus capacitor voltage and the second DC bus capacitor voltage;

[0155] S43, introduce the vector action duration adjustment amount , the action duration 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 redistributed as and :

[0156] (17);

[0157] (18);

[0158] S44, based on the action duration of three reference voltage vectors , and and the action duration of a pair of center vectors after redistribution and , according to the volt-second balance principle to determine the conduction duty cycle of the high-frequency switch tube , realize the synthesis of reference voltage vector;

[0159] S45, determine the initial state duty cycle according to the switching state of the initial voltage vector ;

[0160] S46, dynamically adjust the duty cycle of the complementary switching pair of high-frequency switch tubes in combination with the direction of three-phase output current and the deviation of flying capacitor voltage, and realize the balance of flying capacitor voltage;

[0161] S47, compare the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate the PWM drive signal of the high-frequency switch tube.

[0162] S5, respectively distribute the generated drive signals of the low-frequency switch tube and the high-frequency switch tube to the low-frequency switch tube and the high-frequency switch tube.

[0163] Simulation experiment

[0164] The five-level inverter control system experimental platform for eVTOL aircraft is built in Matlab / Simulink as shown in Figure 1 , and the following experimental parameters are set: DC bus voltage ; first DC bus capacitor voltage ; second DC bus capacitor voltage ; three-phase flying capacitor ; load inductance ; load resistance ; sampling period .

[0165] A three-digit number is used to represent the voltage vector (three-phase switching state), which means "SSa SSb SSc", for example, "400" represents SSa=4, SSb=0, SSc=0, to obtain the voltage vector diagram as shown in Figure 2 , and the vector "311", "331", "131", "133", "113", "313" in Figure 2 Rolling optimization of the cost function is used to select the sector. At the same time, the switching states of the low-frequency switching tubes Tx1, Tx2, Tx3 and Tx4 are determined, and since Tx1 and Tx2 are complementary switching pairs, Tx3 and Tx4 are complementary switching pairs, and Tx1 and Tx3 have the same control signal, therefore, only one control signal needs to be determined for each phase, thereby obtaining the control signals corresponding to different sectors as shown in Table 1.

[0166] Table 1 Voltage vectors corresponding to six sectors and switching states of Tx1-Tx4

[0167] ;

[0168] As shown in Figure 3 , the sector is further divided into three hexagonal sub-regions and one diamond sub-region. The specific sub-region where the reference voltage is located is determined by rolling optimization of the cost function through the voltage vectors corresponding to different sub-regions.

[0169] Table 2 Candidate voltage vectors of target sub-regions corresponding to sectors

[0170] ;

[0171] As shown in Figure 4 , from Figure 4 In combination with Table 2 (in Table 2, 1, 2, and 3 correspond to hexagonal regions; 4 corresponds to a diamond region), the sub-region corresponding to sector I is taken as an example. The voltage vectors corresponding to the three hexagonal regions and the diamond region of sector I are "310(421)", "211(322)", "301(412)", and "400", respectively. Four corresponding cost function values are calculated by substituting the corresponding four voltage vectors (for hexagonal regions, the corresponding two voltage vectors have the same result, and one of them can be selected) into the cost function, and the sub-region corresponding to the smallest cost function value is selected. Further, the vector triangle, i.e., the triangular region where the reference voltage vector is located, is obtained by using the step S34 of the present application. Further, the action duration , and of the three reference voltage vectors obtained by using the present application and the action duration and of the center vector pair after reassignment are used to determine the conduction duty cycle of the high-frequency switching tube In the simulation experiment, take the triangular vector S2 in sector I in Figure 4 as an example, the corresponding voltage vector is "310" ("421"), "410", "420", so the switching sequence is defined as "310-410-420-421-420-410-310".

[0172] As shown in Figure 5 , the duration of "310" and "421" is and , respectively, the duration of "410" is , and the duration of "420" is . The duty cycle of the switch can be determined by , and and sequence switching. For the rhombus region, the situation is slightly different, take the vector triangle S20 in sector I as an example, the corresponding voltage vector is "400", "401", "411", and the switching sequence is "400-401-411-401-400", sequence switching and duration are shown in Figure 5 (b), the duration of "411" is , the duration of "401" is , and the duration of "400" is .

[0173] Table 3 Switching sequence of vector triangle S1-S20 corresponding to sector I

[0174] ;

[0175] Assume that the vector triangle in each hexagon region and rhombus region has the same initial voltage vector, so the initial state duty cycle is determined by the initial voltage vector (SSa, SSb, SSc) . If SSx=0 or 2, set ; if SSx=1, 3 or 4, set . By analogy, assuming the initial voltage vector of the vector triangle is "310", the duty cycles of , and can be determined.

[0176] As shown in Figure 6 , in order to realize the flying capacitor voltage balance, different duty cycles need to be allocated to the complementary switch pairs Tx5 and Tx6, Tx7 and Tx8 according to the output current and the flying capacitor voltage, where , duty cycle of the complementary switch pair Tx5 and Tx6, duty cycle of the complementary switch pair Tx7 and Tx8.

[0177] Table 4 Duty cycle allocation method for balancing flying capacitor voltage

[0178]

[0179] For example, when the output current exceeds its reference value, the capacitor needs to be properly discharged to restore balance. Take the flying capacitor as an example, which regulates its voltage by the following method: if , set , ; if , set , . The drive signal of the high-frequency switch tube is obtained as shown in Figure 7 . The simulation verification result is shown in Figure 8 . It can be seen that 1, the three-phase output current: the sine waveform is smooth, the ripple is small, and the frequency spectrum is regular (without the random ripple of traditional model predictive control). 2, the flying capacitor voltage: stable at about 100V, the fluctuation amplitude is less than 5V in the dynamic process. 3, the DC bus capacitor voltage is balanced (the difference is less than 2V), verifying the duty cycle adjustment effect. 4, the common-mode voltage is between ; 5, only 16 optimal voltage vectors are needed in each sampling period, and the calculation burden is small.

[0180] Physical prototype verification:

[0181] An experimental platform of ANPC-5L inverter system is built, and the experimental parameters are set as follows: input voltage ; first DC bus capacitor ; second DC bus capacitor ; flying capacitor ; load inductance ; load resistance ; sampling period . The result is shown in Figure 9 . It can be seen that 1, dynamic performance: under step load, the current overshoot is less than 5%, and the recovery time is short, proving the fast response advantage of the model predictive control of the invention. 2, steady-state accuracy: the capacitor voltage balance error is within the engineering allowable range (<1%), meeting the stringent requirements of eVTOL on reliability. 3, engineering applicability: the hardware experimental result is highly consistent with the simulation, verifying the portability of the control algorithm from simulation to actual deployment.

[0182] ​It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method of a five-level inverter control system for an eVTOL aircraft, characterized by: The five-level inverter control system for eVTOL aircraft comprises: a three-phase resistive-inductive load for simulating the resistive-inductive characteristics of eVTOL motors; an ANPC-5L inverter system for converting the power of a direct-current power supply into three-phase alternating current to drive the three-phase resistive-inductive load; a current sampling module for collecting the three-phase output current of the ANPC-5L inverter system in real time; a reference three-phase current generation module for generating reference three-phase output current as the target value of the three-phase output current of the ANPC-5L inverter system; a control module for realizing multi-objective collaborative control of the ANPC-5L inverter system by integrating model prediction and space vector modulation, and for realizing tracking control of the three-phase output current on the reference three-phase output current by optimizing and adjusting the switching state of the ANPC-5L inverter system through a closed-loop control strategy and using the feedback current of the current sampling module and the reference three-phase output current of the reference three-phase current generation module; The method comprises the following steps: S1, collect the three-phase output currents of the ANPC-5L inverter system, and generate a reference three-phase output current: assuming that the sampling period of the system is , at the beginning of the first sampling period, the current sampling module collects the three-phase output currents of the a-phase, b-phase and c-phase power conversion units in the ANPC-5L inverter system in real time , , , , respectively represent the a-phase, b-phase and c-phase output currents At the beginning of the first sampling period, the reference three-phase output current is obtained by the reference three-phase current generation module , , and represent the a-phase, b-phase and c-phase reference currents, respectively. S2, a discrete mathematical modeling is established for the ANPC-5L inverter system to obtain the constraint relationship between voltage and current; Step S2 specifically comprises the following steps: S21, using the midpoint between the first DC bus capacitor and the second DC bus capacitor as an example. Taking zero potential as the reference point, the three-phase output voltage of the ANPC-5L inverter system Midpoint of three-phase resistive-inductive load voltage at The relationship between them is: （1）； wherein, , and represent the a-phase, b-phase and c-phase output voltages of the ANPC-5L inverter system, respectively; represents the load inductance value; represents the load resistance; Meanwhile, the switch states of the a-phase power conversion unit, the b-phase power conversion unit and the 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, and are recorded as a four-tuple At this time, the three-phase output voltage of the ANPC-5L inverter system is mapped to five discrete levels by using the switch states , and multi-level output is achieved. （2）； wherein denotes the three-phase switching state, , and denote the switching states of the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit, respectively; denotes the DC link voltage; The simultaneous equations (1) and (2) are obtained: （3）； In the formula, , and These represent the ANPC-5L inverter system. Mutually, Mutually, The phases are respectively relative to the midpoint of the three-phase resistive-inductive load. ; output voltage; S22, discretize equation (1) to obtain the expected reference three-phase output voltage for the n-th sampling period is: is: （4）； In the formula, , and They represent the first The expected reference output voltages of phases a, b, and c in the next sampling period; , and They represent the first The output currents of phases a, b, and c in each sampling period; , and They represent the first Reference output currents of phases a, b, and c in the next sampling period; S23、Based on formula (4), while tracking the expected reference three-phase output voltage, considering the calculation burden, the defined cost function and common-mode voltage : （5）； （6）； In the formula, , and These represent the reference output voltages for phases a, b, and c, respectively. , and They represent the first ANPC-5L inverter system in the next sampling period a Mutually, b Mutually, c The phases are respectively relative to the midpoint of the three-phase resistive-inductive load. ; output voltage; S3, based on the space vector modulation strategy, the vector triangle in which the reference voltage vector is located and the drive signal of the low-frequency switching tube are determined in combination with the rolling cost function; Step S3 specifically comprises the following steps: S31, converting the three-phase switching state into a voltage vector in the coordinate system, to obtain a voltage vector diagram; S32, taking the low-frequency bridge arm switching state as the benchmark, six evenly distributed characteristic vectors are selected as sector boundaries to obtain six sectors, each sector corresponds to a group of low-frequency switching tube state combinations, and the six characteristic vectors are rolled and optimized by formula (5) to determine the target sector in which the reference voltage vector is located; S33, taking the characteristic vectors within the target sector as the center to determine three hexagonal regions and one rhombic region, the voltage vectors corresponding to the three hexagonal regions and one rhombic region are substituted into formula (5) for rolling optimization to determine the target region; S34, when the target region is a hexagonal region, the six vertex voltage vectors of the hexagonal region are extracted, the two vertex voltage vectors with the smallest cost are selected by formula (5), and the characteristic vectors corresponding to the hexagonal region are introduced to form a three-element vector group; When the target region is a rhombic region, the four vertex voltage vectors of the rhombic region are extracted, the three vertex vectors with the smallest cost are selected by formula (5) to form a three-element vector group; The three-element vector group is used to form a vector triangle in which the reference voltage vector is located; S4, based on the vector triangle, the duration of each reference voltage vector is calculated, and the reference voltage vector is synthesized to realize voltage balance of the direct-current bus capacitor and the flying capacitor by adjusting the duty cycle, and the drive signal of the high-frequency switching tube is generated; S5, the generated drive signals of the low-frequency switching tube and the high-frequency switching tube are respectively distributed to the low-frequency switching tube and the high-frequency switching tube.

2. The method of five-level inverter control system for eVTOL aircraft according to claim 1, characterized in that: The ANPC-5L inverter system comprises a direct-current power supply, a direct-current 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 comprise 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 connected in parallel with the direct-current 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 connected with the ANPC-5L inverter system.

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

4. The method of a five-level inverter control system for an eVTOL aircraft according to claim 3, wherein: The three-phase resistive-inductive load comprises a-phase branch load, b-phase branch load and c-phase branch load connected with the a-phase power conversion unit, the b-phase power conversion unit and the c-phase power conversion unit respectively, and the a-phase branch load, the b-phase branch load and the c-phase branch load each comprise a resistance and an inductance connected in series, one end of the inductance is connected with the resistance, and the other end is connected between the emitter of the third high-frequency switch tube and the collector of the fourth high-frequency switch tube.

5. The method of five-level inverter control system for eVTOL aircraft according to claim 4, characterized in that: The direct-current bus capacitor comprises a first direct-current bus capacitor and a second direct-current bus capacitor connected in series between the positive and negative poles of the direct-current power supply, the midpoint between the first direct-current bus capacitor and the second direct-current bus capacitor is connected with one end of a lead wire, and the other end of the lead wire is connected between the emitter of the second low-frequency switch tube and the collector of the third low-frequency switch tube; One pole 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 pole 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 method of a five-level inverter control system for an eVTOL aircraft according to claim 5, wherein: The sampling point of the current sampling module is located between the inductance and the high-frequency bridge arm.

7. The method of a five-level inverter control system for an eVTOL aircraft according to claim 6, characterized in that: Step S4 Specifically comprises the following steps: S41, set three reference voltage vectors constituting a vector triangle as , , and , respectively represent the a-phase, b-phase and c-phase components of the reference voltage vector , respectively represent the a-phase, b-phase and c-phase components of the reference voltage vector , respectively represent the a-phase, b-phase and c-phase components of the reference voltage vector , and the corresponding action durations are , , respectively, to obtain:​​ （7）； wherein represents a reference voltage vector, and ; Solving formula (7) obtains: （8）； （9）； （10）； Wherein, （11）； （12）； （13）； （14）； （15）； wherein represents a reference voltage vector and a square of a distance in space; represents a reference voltage vector and a correlation with respect to a reference voltage vector ; represents a reference voltage vector and a square of a distance in space; represents a reference output voltage and a deviation from a reference voltage vector is a projection of the deviation on a reference voltage vector ; represents a reference output voltage and a deviation from a reference voltage vector is a projection of the deviation on a reference voltage vector ; represents a reference output voltage, and, , ; In S42, the DC bus capacitor and flying capacitor voltage balance is achieved by adjusting the duty cycle, and the vector action duration adjustment amount of the DC bus capacitor voltage balance is is: （16）； In the formula, represents a direct current bus capacitor voltage balance tracking target, and ; represents a proportional coefficient; represents a direct current bus capacitor voltage difference, and , and respectively represent a first direct current bus capacitor voltage and a second direct current bus capacitor voltage; S43, introducing a vector action duration adjustment amount the action duration of a pair of center vectors is reassigned as and : （17）； （18）； S44, duration of action of the three reference voltage vectors , and and the duration of action of a pair of center vectors after redistribution and determine the conduction duty cycle of the high-frequency switch tube according to the volt-second balance principle , realize the synthesis of reference voltage vectors; S45, determine an initial state duty cycle from the switching state of the initial voltage vector ; S46, in combination with the three-phase output current direction and the flying capacitor voltage deviation, dynamically adjusting the duty cycle of the complementary switch pair of the high-frequency switch tube, realizing the flying capacitor voltage balance; S47, compare the duty cycle of the high-frequency switch tube adjusted in step S46 with the carrier signal to generate a PWM driving signal of the high-frequency switch tube.

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