A three-level inverter control system and method for electric aircraft electric propulsion system

Abstract

The present invention belongs to the field of inverter topology design and control technology for electric propulsion system of electric aircraft, and in particular to a three-level inverter control system and method for electric propulsion system of electric aircraft. Step 1: collect the A and B phase currents of the controlled permanent magnet synchronous motor, and calculate the three-phase voltage through PARK transformation, speed loop-current loop PI control, PARK inverse transformation, and CLARK inverse transformation; Step 2: determine the target vector V according to the three-phase voltage ref The position in the three-level sector; Step 3: Set the target vector V ref The three-level sector representation is transformed into a two-level sector representation; and the target vector V under the two-level reference is output ref ', Step 4: According to the target vector V under the two-level reference ref 'Calculate the on-off time of the switch tube; Step 5: Collect the midpoint voltage from the three-level inverter and adjust the on-off time of the switch tube according to the midpoint voltage; Step 6: Generate 12 PWM waves according to the adjusted on-off time of the switch tube and output them to the three-level inverter.

Description

Technical Field

[0001] The present invention belongs to the technical field of inverter topology design and control for electric motors of electric propulsion systems of electric aircraft, and in particular to a three-level inverter control system and method for electric propulsion systems of electric aircraft. Background Art

[0002] In recent years, in order to alleviate and solve the impact of aircraft on the environment and dependence on oil resources, new energy electric aircraft have achieved long-term development. Electric aircraft refers to an aircraft that uses electric motors to drive propellers, ducted fans or other devices to generate forward power. Its performance and use mainly depend on the electric propulsion system. The electric propulsion system consists of motors and related devices that provide thrust for electric aircraft and is the core of electric aircraft. The motors currently installed on electric aircraft are mainly brushed and brushless permanent magnet DC motors. With the increasing requirements for the endurance and efficiency of electric aircraft, the 270V DC bus voltage system currently widely used in military and civil aircraft can no longer meet the energy storage and control requirements, and the DC bus voltage of 540V or even higher systems has received more attention.

[0003] The existing electric propulsion systems of electric aircraft mostly use two-level inverters as the core control unit for power conversion. As shown in Table 1, the two-level inverter has only two level states per phase bridge arm. Its structure is simple and reliable, and the control is easy to implement. However, with the increase of DC bus voltage of electric propulsion systems of electric aircraft, the increasing capacity of electric power consumption, the two-level inverter cannot meet the requirements of high switching frequency, high rated voltage, low harmonic output, low electromagnetic interference, and high efficiency and low heat generation of aircraft. Therefore, in order to meet the needs of electric propulsion systems of electric aircraft in the future, it is necessary to improve the structure and control method of the inverter. In terms of structure, it is necessary to adopt a three-level inverter topology, optimize the layout of the control structure, and improve the power-to-weight ratio of the system. In terms of control, there are two problems with the three-level inverter at present. First, the three-level inverter has a problem of unbalanced midpoint voltage. Excessive unbalanced voltage will threaten the safety of the electric propulsion system of the aircraft, which is not allowed for high-safety and high-reliability equipment such as aircraft. On the other hand, the current three-level inverter midpoint voltage balance strategy often has a complicated calculation process. The complex calculation not only makes the digital software programming logic complicated and occupies a lot of chip resources, but also has a negative impact on the stability of the controller. This patent provides a three-level topology suitable for the electric propulsion system of electric aircraft, and provides a matching new three-level midpoint voltage balance control method that is easy to implement with digital programming, simple and reliable.

[0004] Table 1 Two-level inverter single-phase bridge arm level status table

[0005] Summary of the invention

[0006] The purpose of this invention is to propose a three-level inverter control system and method for an electric aircraft electric propulsion system.

[0007] A three-level inverter control system for an electric aircraft electric propulsion system, comprising: a controlled permanent magnet synchronous motor, a PARK conversion module, a speed loop-current loop PI control module, a PARK inverse conversion module, a CLARK inverse conversion module, a sector judgment conversion module, a switching time calculation module, a midpoint voltage suppression module, a PWM wave generation module, and a three-level inverter connected in sequence;

[0008] The PARK conversion module collects the A and B phase currents of the controlled permanent magnet synchronous motor, and outputs the three-phase voltage after passing through the speed loop-current loop PI control module, the PARK inverse conversion module, and the CLARK inverse conversion module;

[0009] The sector identification conversion module determines the target vector V according to the input three-phase voltage ref The location in the three-level sector and the target vector V ref The three-level sector representation is transformed into a two-level sector representation; and the target vector V under the two-level reference is output ref ';

[0010] The switching time calculation module calculates the target vector V ref 'Calculate the on-off time of the switch tube;

[0011] The midpoint voltage suppression module adjusts the on-off time of the switch tube according to the midpoint voltage collected from the three-level inverter;

[0012] The PWM wave generation module generates 12 PWM waves according to the adjusted on-off time of the switch tube to control the three-level inverter to generate the target three-phase voltage to control the operation of the controlled permanent magnet synchronous motor.

[0013] A method for controlling a three-level inverter of an electric aircraft electric propulsion system, the method being used to control the system, the method comprising the following steps:

[0014] Step 1: Collect the A and B phase currents of the controlled permanent magnet synchronous motor, and calculate the three-phase voltage V through PARK transformation, speed loop-current loop PI control, PARK inverse transformation, and CLARK inverse transformation. a 、V b 、V c ;

[0015] Step 2: Determine the target vector V based on the three-phase voltage ref Location within the three-level sector;

[0016] Step 3: Set the target vector V refThe three-level sector representation is transformed into a two-level sector representation; and the target vector V under the two-level reference is output ref ';

[0017] Step 4: According to the target vector V under the two-level reference ref 'Calculate the on-off time of the switch tube;

[0018] Step 5: Collect the midpoint voltage from the three-level inverter and adjust the on-off time of the switch tube according to the midpoint voltage;

[0019] Step 6: Generate 12 PWM waves according to the adjusted switch on-off time and output them to the three-level inverter.

[0020] Further, in step 2, the three-level sector is to divide the regular hexagon into six sectors by connecting the midpoint of each side of the regular hexagon with the center of the regular hexagon, which are defined as main sectors 1 to main sectors 6 respectively; according to the following table, according to the three-phase voltage V a 、V b 、V c Determine the target vector V ref Location in the three-level sector:

[0021] <![CDATA[V a ]]> <![CDATA[V b ]]> <![CDATA[V c ]]> Primary sector >0 <0 <0 1 >0 >0 <0 2 <0 >0 <0 3 <0 >0 >0 4 <0 <0 >0 5 >0 <0 >0 6 .

[0022] Further, in step 3, the target vector V is converted into ref Transformed from a three-level sector representation to a quasi-two-level sector representation:

[0023] Step 31: Set the target vector V ref The main sector is extended to a hexagonal two-level vector diagram; the side length of the hexagonal two-level vector diagram is half of the side length of the three-level sector, the center of the hexagonal two-level vector diagram is the zero vector V0, and the six vectors with V0 as the vector starting point and the six vertices of the hexagonal two-level vector as the focus are defined as V1 to V6; the hexagonal two-level vector diagram is divided into 1 to 6 areas counterclockwise, which are defined as sub-sectors 1 to 6. The three-level inverter vector diagram has a total of 6 main sectors and a total of 36 sub-sectors;

[0024] Step 32: Set the target vector V ref The starting point is converted to the center of the hexagonal two-level vector diagram and becomes V ref ';

[0025] V ref '=V ref -V map ;

[0026] V map is the matching vector, which is determined according to the following table:

[0027]

[0028] Among them, V dc is the DC bus voltage input to the three-level inverter. The α and β values ​​represent the projection of the matching vector Vmap on the α and β axes in the CLARK coordinate system. P, O, and N represent the states of the three-phase bridge arms A, B, and C of the three-level inverter, as shown in the following table:

[0029]

[0030] Further, in step 4, according to V ref 'The calculation process of the switch tube on-off time is as follows:

[0031] Step 41: In the main sector 1, the three-level inverter A phase does not have the bridge arm state N, and the B and C phase bridge arms do not have the bridge arm state P; define the A phase P state as 1, the O state as 0, the B and C phase O state as 1, the N state as 0, V1 to V6 in the hexagonal two-level vector are expressed as 100→110→010→011→001→101, and the zero vector V0 can be expressed as 111 or 000; the remaining five main sectors ABC three-phase definitions are shown in the following table:

[0032]

[0033]

[0034] Step 42: V ref 'Two adjacent vectors and zero vector are expressed as a 7-segment SVPWM form, which is the same as the traditional two-level 7-segment SVPWM. The action time of two adjacent vectors and zero vector is obtained. The three vectors have their own action time. According to the definition of adjacent vectors and zero vectors of different main sectors, each action time corresponds to the action time of the switch state PON of each phase bridge arm. According to the definition of PON, the corresponding on-off time of each switch tube of each phase bridge arm is finally obtained. The summary of 36 sub-sectors has a total of 6 basic switch on-off times as shown in the following table:

[0035] Basic switch on / off time Basic switch on and off time series <![CDATA[T S -T0 / 2]]> 1 <![CDATA[T a +T0 / 2]]> 2 <![CDATA[T0 / 2]]> 3 <![CDATA[T b +T0 / 2]]> 4 0 5 <![CDATA[T S ]]> 6

[0036] The on-off time of all the switches in the three-level inverter is one of the basic on-off time. The value of the basic on-off time given in the table refers to the high-level duration of the PWM wave.

[0037] Step 43: Calculate Ta and Tb. The calculation process is as follows:

[0038] When 3*(Va+Vb) / Vdc>Ts

[0039] Ta = 3 * Va * Ts / Vdc

[0040] Tb = 3 * Vb * Ts / Vdc

[0041] When 3 * (Va + Vb) / Vdc < Ts

[0042] Ta = 3 * Va * Ts / (Va + Vb)

[0043] Tb = 3 * Vb * Ts / (Va + Vb)

[0044] T0 = Ts - Ta - Tb;

[0045] Wherein, T s is the switching tube period, V a , V b is the projection of V ref ' on the α-axis and β-axis in the CLARK coordinate system;

[0046] Step 44: According to the values of T a and T b , the switching on and off times of the 12 switching tubes in the 36 sub-sectors of V ref ' are as follows in the table. The switching on and off time of the third switching tube in each phase is complementary to the first one, and the switching on and off time of the fourth switching tube in each phase is complementary to the second one. The sum of the times is T s :

[0047]

[0048] Wherein, the digital serial numbers under the switching on and off times correspond one-to-one with the basic switching on and off time sequence given in Step 42, that is, the basic switching on and off time is the switching on and off time of this switching tube.

[0049] Furthermore, in the fifth step, if the midpoint voltage is positive, the action time of the positive small vector is increased;

[0050] if the midpoint voltage is negative, the action time of the negative small vector is increased;

[0051] if the midpoint voltage is zero, no change is made;

[0052] In a three-level inverter, the corresponding specific values of the output positive small vector and negative small vector are shown in the following table. During the operation of the inverter, its space vector voltage level remains unchanged while the direction changes.

[0053]

[0054] Furthermore, in the fifth step, it is defined that:

[0055] T x = T0 / 2 * (1 - f)

[0056] T y =T0 / 2*(1+f)

[0057] f is the midpoint voltage suppression coefficient, range (-1,1);

[0058] The corrected basic switch on-off time is as follows:

[0059] Corrected basic switch on / off time Basic switch on and off time series <![CDATA[T s -T x ]]> 1 <![CDATA[T a +T y ]]> 2 <![CDATA[T y ]]> 3 <![CDATA[T b +T y ]]> 4 0 5 <![CDATA[T S ]]> 6

[0060] By replacing the switch on-off time in step 44 with the basic switch on-off time and the corrected basic switch on-off time, the switch on-off time that can suppress the fluctuation of the midpoint voltage of the three-level inverter can be obtained.

[0061] Furthermore, the 12-channel PWM wave generation process is as follows:

[0062] Define the switch on and off time as t, the PWM wave generation chip uses up and down counting, the maximum value of the digital quantity is defined as D, the current value of the digital quantity is D', when

[0063] D'>(T s -t)*D / 2, the PWM wave generating chip outputs a high level;

[0064] D'<(T s -t)*D / 2, the PWM wave generating chip outputs a low level.

[0065] The present invention provides a three-level inverter control system and method for an electric aircraft electric propulsion system. When the motor is running, the three-level inverter outputs a voltage vector fed back by a control loop and suppresses the unbalanced voltage at the midpoint. BRIEF DESCRIPTION OF THE DRAWINGS

[0066] Figure 1 Three-level inverter topology diagram;

[0067] Figure 2 Block diagram of three-level inverter control system;

[0068] Figure 3 It is the sector planning diagram of the three-level inverter;

[0069] Figure 4 This is a diagram of the mechanism of neutral point voltage imbalance;

[0070] Figure 5 This is the effect diagram of neutral point voltage balance control; Figure 5 a) Schematic diagram of three-phase voltage output of three-level inverter; Figure 5 b) Neutral point voltage schematic diagram;

[0071] Figure 6Schematic diagram of output voltage THD of three-level inverter; Figure 6 a) Schematic diagram of the output three-phase voltage THD of a three-level inverter using the midpoint voltage suppression algorithm; Figure 6 b) Schematic diagram of the output three-phase voltage THD of the three-level inverter using the traditional algorithm;

[0072] Figure 7 Program block diagram of the new three-level inverter midpoint voltage control algorithm. DETAILED DESCRIPTION

[0073] The topological structure of the three-level inverter used in the present invention is as follows: Figure 1 As shown, there are 12 switches in the three-phase bridge arm A, B, and C, with 4 switches in each phase bridge arm. Define the switch tube to be on as 1 and off as 0. Different switching sequences of each phase switch tube will have different phase output levels, with a total of 3 levels, defined as P, N, and O. Furthermore, the combination of the three-phase output levels will cause the inverter to output different vector voltages, with a total of 27 output voltage vectors. Table 2 gives the level state of each phase bridge arm of the three-level inverter, and Table 3 gives the output voltage vector state of the three-level inverter.

[0074] Table 2 Three-level inverter bridge arm level status

[0075]

[0076] Table 3 Space voltage vector table

[0077]

[0078]

[0079] Based on the above topological structure and topological analysis, the specific implementation process of the present invention is as follows:

[0080] like Figure 2 As shown in the control block diagram, the dashed box diagram is a three-level SVPWM control algorithm based on the midpoint voltage balance control strategy, and the solid box diagram is a simplified diagram of the three-level inverter topology structure. The controlled object is a permanent magnet synchronous motor PMSM. When the motor is operating normally, the motor A and B two-phase currents are sampled, and after vector transformation, the motor three-phase current is converted into the dq axis current i d ,i q ASR is the speed loop, ACR is the current loop, and the input is the desired speed w ref , actual speed w e , d-axis current i d , q-axis current i q , the output is the desired motor input vector u after PI adjustment d ,u q , the above parts are related to permanent magnet motor id =0 The two-level SVPWM control strategy is exactly the same and will not be repeated here.

[0081] Generate the desired motor input vector u d ,u q After that, the traditional sector identification method is as follows Figure 3 a) As shown, the position sensor determines V ref (u d ,u q The sector of the synthetic vector in the three-phase coordinate system) is determined by the following sector discrimination method; u d ,u q The inverse transform is u a 、u b 、u c , by comparing the values ​​between the three-phase voltages, determine V ref The specific implementation method is shown in Table 4. Figure 3 As shown in b), the three-level sector is a regular hexagon, and the line connecting the midpoint of each side and the center of the regular hexagon is divided into six sectors, which are defined as main sector 1 to main sector 6.

[0082] Table 4 Sector identification

[0083] V Vb Vc Primary sector >0 <0 <0 1 >0 >0 <0 2 <0 >0 <0 3 <0 >0 >0 4 <0 <0 >0 5 >0 <0 >0 6

[0084] After the sector identification is completed, V ref Perform sector conversion, such as Figure 3 c) and Figure 3 d), taking sector 1 as an example, the target vector V ref The starting point is converted to the center of the sector and can be converted to V ref1 The calculation formula is as follows:

[0085] V ref1 =V ref -V map

[0086] V map Different matching vectors correspond to different main sectors, as shown in Table 5:

[0087] Table 5 Matching vector table

[0088]

[0089] The α and β values ​​represent the matching vector V map Projection on the α-axis and β-axis in the CLARK coordinate system;

[0090] exist Figure 3In d), the original vectors are PPP(OOO,NNN), POP(ONO), PNO, PNN, PON, PPO(OON), POO(ONN). Similar to the two-level hexagon, define V map = V0, a ​​new hexagonal vector diagram can be obtained. There are 7 matching vectors V0~V6 in the figure, which are arranged counterclockwise to form 6 sub-sectors. The three-level inverter can be divided into 36 sub-sectors in total. It can be seen that the target vector has been converted to V in sub-sector 1. ref1 , at this time, the vector synthesis formula is as follows:

[0091] V 1* T a +V 2* T b +V 0* T0=V ref1* T S

[0092] After the main sector is identified, the subsequent steps are similar to the two-level SVPWM: first, determine the sub-sector where the converted target vector is located, and second, calculate the on-off time of each switch tube. The on-off time of the switch tube given in this patent corresponds to the high-level duration of the PWM wave. In the two-level SVPWM, there are only 3 pairs of power switches, and only three groups of time need to be calculated. There are 6 pairs of power switches in the three-level, and 6 groups of time need to be calculated. Considering the simplification of MCU computing resources, taking the main sector 1 as an example, Figure 3 d) For the target vector, in the system's phase A, there is no bridge arm state N, and there is no P state in the bridge arms of phases B and C. Define the A phase P state as 1, the O state as 0, the B and C phase O state as 1, and the N state as 0, so that a vector diagram that is completely consistent with the two-level SVPWM can be obtained.

[0093] The remaining five main sectors ABC three-phase definitions are shown in the following table:

[0094]

[0095]

[0096] At this time, the sector diagram is the same as the two-level SVPWM sector diagram. So far, the three-level problem is converted to a two-level problem. The two-level method can be used to calculate the switch on-off time. The two-level inverter has only three basic on-off times, and the three-level inverter has a total of six basic on-off times. Table 6 gives the basic on-off time of the switch tube. The on-off time of all the switch tubes in the three-level inverter is one of the basic on-off times.

[0097] Table 6 Basic on-off time of switch tube

[0098] Basic switch on / off time Basic switch on and off time series <![CDATA[T S -T0 / 2]]> 1 <![CDATA[T a +T0 / 2]]> 2 <![CDATA[T0 / 2]]> 3 <![CDATA[T b +T0 / 2]]> 4 0 5 <![CDATA[T S ]]> 6

[0099] Among them, T a , T b , the calculation process of T0 is as follows:

[0100] When 3*(Va + Vb) / Vdc > Ts

[0101] Ta = 3*Va*Ts / Vdc

[0102] Tb = 3*Vb*Ts / Vdc

[0103] When 3*(Va + Vb) / Vdc < Ts

[0104] Ta = 3*Va*Ts / (Va + Vb)

[0105] Tb = 3*Vb*Ts / (Va + Vb)

[0106] T0 = Ts - Ta - Tb;

[0107] Among them, T s is the switching period of the switch tube, V a , V b is the value of V ref ' on the α-axis and β-axis in the CLARK coordinate system;

[0108] According to the values of T a and T b , the switching on and off times of the 12 switch tubes in the 36 sub-sectors of V ref ' are as follows in the table. The switching on and off time of the third switch tube in each phase is complementary to the first one, and the switching on and off time of the fourth switch tube in each phase is complementary to the second one. The sum of the times is T s :

[0109] Table 7 Switching On and Off Time Table

[0110]

[0111]

[0112] Among them, the basic switching on and off time corresponding to the 1-6 digital sequence in the six columns where the switching on and off times in Table 7 belong is the switching on and off time of the switch tube.

[0113] After calculating the switching on and off times by the traditional three-level control, 12 PWM waves are directly generated to control the switching state of the inverter, thereby controlling the motor. Figure 4The reasons for the unbalanced midpoint voltage under traditional three-level control are given. It can be seen that the short vector and the long vector are not connected to the neutral point between the capacitors, and will not affect the midpoint voltage. The midpoint vector may cause the upper capacitor to charge or discharge, depending on the direction of the motor winding current. The positive small vector will cause the upper capacitor to discharge, and the negative small vector will cause the lower capacitor to discharge. The combined action of the midpoint vector and the long vector causes the unbalanced oscillation of the midpoint voltage. This patent adopts a method that can suppress the midpoint voltage of the three-level inverter. After calculating the switch on and off time, the voltage V is introduced DH and V DL The midpoint voltage balance strategy is based on the characteristics of redundant small vectors. When V DH >V DL When the suppression coefficient f>0, the suppression coefficient adopts a fixed value or is given by the optimization algorithm. In one control cycle, the positive small vector action time is increased. On the contrary, when V is detected DH <V DL When the suppression coefficient f<0, the negative small vector action time is increased within a control cycle. The specific algorithm is as follows:

[0114] T x =T0 / 2*(1-f)

[0115] T y =T0 / 2*(1+f)

[0116] f is the midpoint voltage suppression coefficient, range (-1,1);

[0117] After adopting the above midpoint voltage suppression strategy, the switch on-off basic time is corrected, as shown in Table 8:

[0118] Table 8 Corrected basic switch on-off schedule

[0119]

[0120]

[0121] Comparing Table 6 and Table 8, the sequences in the two tables correspond one to one. The 1-6 digital sequence in the six columns of the switch on-off time in Table 7 corresponds to the basic switch on-off time sequence in Table 8. The corrected switch on-off time is the final on-off time of the switch tube. Replacing the corresponding values ​​in Table 7 with the values ​​in Table 8 can obtain the final 12-way switch on-off time after adopting the midpoint voltage suppression algorithm.

[0122] Finally, the control system generates 12 PWM waves. The generation process of 12 PWM waves is as follows:

[0123] Define the switch on and off time as t, the PWM wave generation chip uses up and down counting, the maximum value of the digital quantity is defined as D, the current value of the digital quantity is D', when

[0124] D'>(T s -t)*D / 2, the PWM wave generating chip outputs a high level;

[0125] D'<(T s -t)*D / 2, the PWM wave generating chip outputs a low level.

[0126] 12-way PWM controls the inverter output voltage, Figure 5 The results of the patented new control strategy are given, among which, Figure 5 a) The inverter outputs three-phase voltage, Figure 5 b) are two capacitor voltages, Figure 5 b) is the midpoint voltage. It can be seen that on the basis of the traditional three-level control (0-0.3s), after adding the new three-level inverter midpoint voltage suppression control strategy (0.3-0.6s), the three-phase voltage waveform is smoother, the midpoint voltage fluctuation frequency is smaller, and the range is lower.

[0127] The core of the new three-level inverter neutral point voltage suppression control strategy is different from the traditional control algorithm, which generates 12 PWM waves from sector identification to control system. Figure 6 a) and Figure 6 b) The output voltage THD of the three-level inverter using the midpoint voltage suppression algorithm and the traditional algorithm respectively. It can be seen that after adopting the patented algorithm, the voltage harmonic content is significantly reduced and the quality is significantly improved. Figure 7 This is the flowchart of this part. The part inside the dotted line is the traditional algorithm, and the part outside the dotted line is the new algorithm.

Claims

1. A three-level inverter control system for an electric aircraft electric propulsion system, characterized in that: The system includes: a controlled permanent magnet synchronous motor, a PARK transformation module, a speed loop-current loop PI control module, a PARK inverse transformation module, a CLARK inverse transformation module, a sector judgment transformation module, a switching time calculation module, a midpoint voltage suppression module, a PWM wave generation module, and a three-level inverter, which are connected in sequence. The PARK transformation module collects the A and B phase currents of the controlled permanent magnet synchronous motor, and outputs three-phase voltages after passing through the speed loop-current loop PI control module, the PARK inverse transformation module, and the CLARK inverse transformation module. The sector identification conversion module determines the target vector V according to the input three-phase voltage ref The location in the three-level sector and the target vector V ref The three-level sector representation is transformed into a two-level sector representation; and the target vector V under the two-level reference is output ref '; The switching time calculation module calculates the target vector V ref 'Calculate the on-off time of the switch tube, the process is as follows: Step 41: In main sector 1, there is no bridge arm state N in the A phase of the three-level inverter, and there is no bridge arm state P in the B and C phase bridge arms; define the P state of the A phase as 1, the O state as 0, the O state of the B and C phases as 1, the N state as 0, and the V1 to V6 in the hexagon-like two-level vectors are represented as 100→110→010→011→001→101, and the zero vector V0 can be represented as 111 or 000; the ABC three-phase states of the remaining 5 main sectors are defined as shown in the following table: Step 42: V ref 'Two adjacent vectors and zero vector are expressed as a 7-segment SVPWM form, which is the same as the traditional two-level 7-segment SVPWM. The action time of two adjacent vectors and zero vector is obtained. The three vectors have their own action time. According to the definition of adjacent vectors and zero vectors of different main sectors, each action time corresponds to the action time of the switch state PON of each phase bridge arm. According to the definition of PON, the corresponding on-off time of each switch tube of each phase bridge arm is finally obtained. The summary of 36 sub-sectors has a total of 6 basic switch on-off times as shown in the following table: The on-off time of all switching tubes in the used three-level inverter is one of the basic switching on-off times, and the values of the basic switching on-off times given in the table refer to the high-level duration of the PWM wave. Step 43: Calculate Ta and Tb, and the calculation process is as follows: When 3*(Va + Vb) / Vdc > Ts Ta = 3*Va*Ts / Vdc Tb = 3*Vb*Ts / Vdc When 3*(Va + Vb) / Vdc < Ts Ta = 3*Va*Ts / (Va + Vb) Tb = 3*Vb*Ts / (Va + Vb) T0 = Ts - Ta - Tb; Among them, T s is the switching cycle, V a , V b V ref 'Projection on the α-axis and β-axis in the CLARK coordinate system; Step 44: According to T a and T b The value of V ref The on-off time of the 12 switch tubes in the 36 sub-sectors is as follows: the on-off time of the third switch tube in each phase is complementary to the first, and the on-off time of the fourth switch tube in each phase is complementary to the second. The time is T s : Among them, the digital serial numbers in the following six columns of the switching on-off time correspond to the basic switching on-off time sequence given in Step 42, and the basic switching on-off time is the on-off time of the switching tube. The midpoint voltage suppression module adjusts the on-off time of the switching tube according to the magnitude of the midpoint voltage collected from the three-level inverter. Specifically, if the midpoint voltage is positive, the action time of the positive small vector is increased; if the midpoint voltage is negative, the action time of the negative small vector is increased; if the midpoint voltage is zero, no change is made. The PWM wave generation module generates 12 PWM waves according to the adjusted on-off time of the switching tube to control the three-level inverter to generate the target three-phase voltage, thereby controlling the operation of the controlled permanent magnet synchronous motor.

2. A three-level inverter control method for an electric aircraft electric propulsion system, the method being used to control the system of claim 1, characterized in that: The method includes the following steps: Step 1: Collect the A and B phase currents of the controlled permanent magnet synchronous motor, and calculate the three-phase voltage V through PARK transformation, speed loop-current loop PI control, PARK inverse transformation, and CLARK inverse transformation. a 、V b 、V c ; Step 2: Determine the target vector V based on the three-phase voltage ref Location within the three-level sector; Step 3: Set the target vector V ref The three-level sector representation is transformed into a two-level sector representation; and the target vector V under the two-level reference is output ref '; Step 4: According to the target vector V under the two-level reference ref 'Calculate the on-off time of the switch tube, the process is as follows: Step 41: In main sector 1, there is no bridge arm state N in the A phase of the three-level inverter, and there is no bridge arm state P in the B and C phase bridge arms; define the P state of the A phase as 1, the O state as 0, the O state of the B and C phases as 1, the N state as 0, and the V1 to V6 in the hexagon-like two-level vectors are represented as 100→110→010→011→001→101, and the zero vector V0 can be represented as 111 or 000; the ABC three-phase states of the remaining 5 main sectors are defined as shown in the following table: Step 42: V ref 'Two adjacent vectors and zero vector are expressed as a 7-segment SVPWM form, which is the same as the traditional two-level 7-segment SVPWM. The action time of two adjacent vectors and zero vector is obtained. The three vectors have their own action time. According to the definition of adjacent vectors and zero vectors of different main sectors, each action time corresponds to the action time of the switch state PON of each phase bridge arm. According to the definition of PON, the corresponding on-off time of each switch tube of each phase bridge arm is finally obtained. The summary of 36 sub-sectors has a total of 6 basic switch on-off times as shown in the following table: The on-off time of all switching tubes in the used three-level inverter is one of the basic switching on-off times, and the values of the basic switching on-off times given in the table refer to the high-level duration of the PWM wave. Step 43: Calculate Ta and Tb, and the calculation process is as follows: When 3*(Va + Vb) / Vdc > Ts Ta = 3*Va*Ts / Vdc Tb = 3*Vb*Ts / Vdc When 3*(Va + Vb) / Vdc < Ts Ta = 3*Va*Ts / (Va + Vb) Tb = 3*Vb*Ts / (Va + Vb) T0 = Ts - Ta - Tb; Among them, T s is the switching cycle, V a , V b V ref 'Projection on the α-axis and β-axis in the CLARK coordinate system; Step 44: According to T a and T b The value of V ref The on-off time of the 12 switch tubes in the 36 sub-sectors is as follows: the on-off time of the third switch tube in each phase is complementary to the first, and the on-off time of the fourth switch tube in each phase is complementary to the second. The time is T s : Among them, the digital serial numbers in the following six columns of the switch on - off time correspond to the basic switch on - off time in the basic switch on - off time sequence given in step 42, and the on - off time of the switch tube is the on - off time of the switch tube; Step Five: Collect the mid - point voltage of the three - level inverter, and adjust the on - off time of the switch tubes according to the magnitude of the mid - point voltage; if the mid - point voltage is positive, increase the action time of the positive small vector; if the mid - point voltage is negative, increase the action time of the negative small vector; if the mid - point voltage is zero, make no change; In the three - level inverter, the specific values of the output positive small vector and negative small vector are shown in the following table. During the operation of the inverter, its space vector voltage level remains unchanged while the direction changes; Step Six: Generate 12 - way PWM waves according to the adjusted on - off time of the switch tubes and output them to the three - level inverter.

3. The three-level inverter control method according to claim 2, characterized in that: In step 2, the three-level sector is to divide the regular hexagon into six sectors by connecting the midpoint of each side of the regular hexagon with the center of the regular hexagon, which are defined as main sectors 1 to main sectors 6 respectively; according to the following table, according to the three-phase voltage V a 、V b 、V c Determine the target vector V ref Location in the three-level sector: 。 4. The three-level inverter control method according to claim 3, characterized in that: In step 3, the target vector V is converted into ref Transformed from a three-level sector representation to a quasi-two-level sector representation: Step 31: Set the target vector V ref The main sector is extended to a hexagonal two-level vector diagram; the side length of the hexagonal two-level vector diagram is half of the side length of the three-level sector, the center of the hexagonal two-level vector diagram is the zero vector V0, and the six vectors with V0 as the vector starting point and the six vertices of the hexagonal two-level vector as the focus are defined as V1 to V6; the hexagonal two-level vector diagram is divided into 1 to 6 areas counterclockwise, which are defined as sub-sectors 1 to 6. The three-level inverter vector diagram has a total of 6 main sectors and a total of 36 sub-sectors; Step 32: Set the target vector V ref The starting point is converted to the center of the hexagonal two-level vector diagram and becomes V ref '; V ref '=V ref -V map ; V map is the matching vector, which is determined according to the following table: Among them, V dc is the DC bus voltage input to the three-level inverter. The α and β values ​​represent the projection of the matching vector Vmap on the α and β axes in the CLARK coordinate system. P, O, and N represent the states of the three-phase bridge arms A, B, and C of the three-level inverter, as shown in the following table: 。 5. The three-level inverter control method according to claim 4, characterized in that: In the said Step Five, it is defined that: T x =T0 / 2*(1-f) T y =T0 / 2*(1+f) f is the mid - point voltage suppression coefficient, and its range is (-1, 1); The corrected basic switch on - off time is as follows in the table: The digital serial numbers in the following six columns of the switch on - off time correspond to the corrected basic switch on - off time in the basic switch on - off time sequence, and the corrected final on - off time of the switch tube is the corrected on - off time of the switch tube.

6. The three-level inverter control method according to claim 5, characterized in that: The generation process of the 12 - way PWM waves is as follows: Define the on - off time of the switch tube as t, the PWM wave generating chip uses up - down counting, the maximum digital value is defined as D, and the current digital value is D'. When D'>(T s -t)*D / 2, the PWM wave generating chip outputs a high level; D'<(T s -t)*D / 2, the PWM wave generating chip outputs a low level.

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