CN115296553A - Three-level inverter control system and method for electric propulsion system of electric airplane - Google Patents
Three-level inverter control system and method for electric propulsion system of electric airplane Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P21/00—Arrangements or methods for the control of electric machines by vector control, e.g. by control of field orientation
- H02P21/0003—Control strategies in general, e.g. linear type, e.g. P, PI, PID, using robust control
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0012—Control circuits using digital or numerical techniques
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/0003—Details of control, feedback or regulation circuits
- H02M1/0038—Circuits or arrangements for suppressing, e.g. by masking incorrect turn-on or turn-off signals, e.g. due to current spikes in current mode control
-
- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/483—Converters with outputs that each can have more than two voltages levels
- H02M7/487—Neutral point clamped inverters
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
- H02M7/53873—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current with digital control
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/022—Synchronous motors
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P25/00—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details
- H02P25/02—Arrangements or methods for the control of AC motors characterised by the kind of AC motor or by structural details characterised by the kind of motor
- H02P25/022—Synchronous motors
- H02P25/024—Synchronous motors controlled by supply frequency
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P27/00—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage
- H02P27/04—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage
- H02P27/06—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters
- H02P27/08—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation
- H02P27/14—Arrangements or methods for the control of AC motors characterised by the kind of supply voltage using variable-frequency supply voltage, e.g. inverter or converter supply voltage using dc to ac converters or inverters with pulse width modulation with three or more levels of voltage
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02P—CONTROL OR REGULATION OF ELECTRIC MOTORS, ELECTRIC GENERATORS OR DYNAMO-ELECTRIC CONVERTERS; CONTROLLING TRANSFORMERS, REACTORS OR CHOKE COILS
- H02P2207/00—Indexing scheme relating to controlling arrangements characterised by the type of motor
- H02P2207/05—Synchronous machines, e.g. with permanent magnets or DC excitation
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
- Y02T50/00—Aeronautics or air transport
- Y02T50/60—Efficient propulsion technologies, e.g. for aircraft
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Abstract
The invention belongs to the technical field of topology design and control of inverters for motors of electric propulsion systems of aviation electric airplanes, and particularly relates to a control system and a control method of a three-level inverter of an electric propulsion system of an electric airplane, which comprises the following steps: collecting the phase current of a controlled permanent magnet synchronous motor A, B, and performing PARK conversion, rotating speed loop-current loop PI control, PARK inverse conversion and CLARK inverse transformation is carried out to calculate three-phase voltage; step two: judging a target vector V according to the three-phase voltage ref The position of the three-level sector; step three: target vector V ref A conversion from a three-level sector representation to a two-level sector representation; and outputs a target vector V under a two-level reference ref ', step four: according to a target vector V under a two-level reference ref ' calculating the on-off time of a switch tube; step five: acquiring midpoint voltage from a three-level inverter, and adjusting the on-off time of a switching tube according to the magnitude of the midpoint voltage; step six: and generating 12 paths of PWM waves according to the adjusted on-off time of the switching tube and outputting the PWM waves to the three-level inverter.
Description
Technical Field
The invention belongs to the technical field of topology design and control of inverters for motors of electric propulsion systems of aviation electric airplanes, and particularly relates to a control system and a control method of a three-level inverter of an electric propulsion system of an electric airplane.
Background
In recent years, in order to alleviate and solve the influence of the aircraft on the environment and the dependence on petroleum resources, a new energy electric aircraft has been developed for a long time, the electric aircraft is an aircraft which uses a motor to drive a propeller, a ducted fan or other devices to generate forward power, the performance and the application of the electric aircraft mainly depend on an electric propulsion system, and the electric propulsion system is composed of a motor and related devices which provide thrust for the electric aircraft and is the core of the electric aircraft. The motors currently installed on electric airplanes are mainly brushed and brushless permanent magnet direct current motors. With the increasing requirements on the endurance and efficiency of the electric aircraft, the 270V direct-current bus voltage system widely applied to military and civil aircraft cannot meet the requirements on energy storage and control at present, and the 540V direct-current bus voltage system and even the higher system obtain more attention.
The existing aviation electric aircraft electric propulsion system mostly uses a two-level inverter as a core control unit for power conversion, as shown in table 1, each phase bridge arm of the two-level inverter has only two level states, the structure is simple and reliable, the control is easy to realize, but the two-level inverter cannot meet the requirements of high switching frequency, high rated voltage, low harmonic output and low electromagnetic interference of the aircraft and simultaneously ensures high efficiency and low heating along with the increasing of direct current bus voltage of the aviation electric aircraft electric propulsion system and the increasing of power consumption capacity. Therefore, in order to meet the requirements of the electric propulsion system of the future electric aircraft, the structure and the control method of the inverter need to be improved. In the aspect of structure, a three-level inverter topology is required, the layout of a control structure is optimized, and the power-to-weight ratio of a system is improved. In the aspect of control, the three-level inverter has two problems, namely, the three-level inverter has a midpoint voltage unbalance problem, and the safety of the aviation electric propulsion system is threatened by the overhigh unbalance voltage, which cannot be allowed by the high-safety and high-reliability equipment of the airplane. On the other hand, the current three-level inverter neutral-point voltage balance strategy is often complex in calculation process, complex operation not only causes complex writing logic of digital software and serious occupation of chip resources, but also brings negative influence on the operation stability of the controller. The patent provides a three-level topological structure suitable for an electric propulsion system of an electric airplane, and provides a simple and reliable novel three-level midpoint voltage balance control method which is convenient to realize digital programming.
TABLE 1 two-level inverter single-phase bridge arm level state table
Disclosure of Invention
The purpose of the invention is as follows: a three-level inverter control system and method for an electric propulsion system of an electric airplane are provided.
A three-level inverter control system for an electric aircraft electric propulsion system, comprising: the system comprises a controlled permanent magnet synchronous motor, a PARK conversion module, a rotating speed ring-current ring 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 which are sequentially connected;
the PARK conversion module collects phase current of a controlled permanent magnet synchronous motor A, B and outputs three-phase voltage after passing through a rotating speed loop-current loop PI control module, a PARK inverse conversion module and a CLARK inverse conversion module;
the sector judging and converting module judges a target vector V according to the input three-phase voltage ref In the three-level sector, and the target vector V ref A three-level sector representation is changed into a two-level sector representation; and outputs a target vector V under a two-level reference ref ’；
The switching time calculation module calculates the switching time according to a target vector V ref ' calculating the on-off time of a switching tube;
the midpoint voltage suppression module adjusts the on-off time of the switching tube according to the midpoint voltage acquired from the three-level inverter;
the PWM wave generation module generates 12 paths of PWM waves according to the adjusted on-off time of the switching tube to control the three-level inverter to generate target three-phase voltage so as to control the controlled permanent magnet synchronous motor to operate.
A method of controlling a three-level inverter of an electric propulsion system of an electric aircraft, the method for controlling the system, the method comprising the steps of:
the method comprises the following steps: the method comprises the steps of collecting phase current of a controlled permanent magnet synchronous motor A, B, and calculating three-phase voltage V through PARK conversion, rotating speed loop-current loop PI control, PARK inverse conversion and CLARK inverse conversion a 、V b 、V c ；
Step two: judging a target vector V according to the three-phase voltage ref The position of the three-level sector;
step three: target vector V ref A conversion from a three-level sector representation to a two-level sector representation; and outputs a target vector V under a two-level reference ref ’；
Step four: according to a target vector V under a two-level reference ref ' calculating the on-off time of a switch tube;
step five: acquiring midpoint voltage from a three-level inverter, and adjusting the on-off time of a switching tube according to the midpoint voltage;
step six: and generating 12 paths of PWM waves according to the adjusted on-off time of the switching tube and outputting the PWM waves to the three-level inverter.
Further, in the second step, the three-level sector is formed by dividing each edge of the regular hexagonThe central points of the two main sectors are respectively connected with the central line of the regular hexagon to divide the regular hexagon into six sectors which are respectively defined as a main sector 1-a main sector 6; according to the three-phase voltage V, as shown in the table below a 、V b 、V c Judging the target vector V ref Location within the three-level sector:
| V a | V b | V c | main 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 |
。
Further, in the third step, the target vector V is obtained by the following process ref The transition from three-level sector representation to two-level-like sector representation:
step 31: target vector V ref The main sector is expanded into a hexagon-like two-level vector diagram; the side length of the hexagonal two-level vector diagram is half of that of the three-level sector, and the center of the hexagonal two-level vector diagram is taken as a zero vector V 0 Defined as V 0 As vector starting points, the six vectors respectively taking six vertexes of the two-level vectors of the hexagon as key points are respectively V 1 ～V 6 (ii) a The hexagonal two-level vector diagram is divided into 1-6 regions counterclockwise and defined as sub-sectors 1-6, the three-level inverter vector diagram has 6 main sectors in total and 36 sub-sectors in total;
step 32: target vector V ref The starting point is converted into the center of a hexagonal two-level vector diagram and is converted into V ref ’；
V ref ’＝V ref -V map ；
V map For matching vectors, the matching vectors are determined according to the following table:
wherein, V dc For three-level inverters by inputting DC bus voltage, represented by values of alpha and betaThe projection of the matching vector Vmap on an alpha axis and a beta axis under a CLARK coordinate system; p, O, N represent the states of the three-phase legs of the three-level inverters a, B, C, as shown in the following table:
further, in the fourth step, according to V ref ' calculating the on-off time of the switching tube comprises the following steps:
step 41: in the main sector 1, bridge arm states N and B do not exist in the phase A of the three-level inverter, and a bridge arm state P does not exist in the phase C of the three-level inverter; defining the A-phase P state as 1,O state 0, B, C-phase O state as 1,N state 0, V in the hexagonal two-level vector 1 ～V 6 Denoted as 100 → 110 → 010 → 011 → 001 → 101, zero vector V 0 May be represented as 111 or 000; the remaining 5 main sectors ABC phases are defined as shown in the table below:
step 42: v ref The method is characterized in that two adjacent vectors and a zero vector are represented into a 7-segment SVPWM form, the two adjacent vectors and the zero vector have respective action time, the action time of the two adjacent vectors and the zero vector is obtained as same as that of the traditional two-level 7-segment SVPWM, each segment of action time corresponds to the action time of a PON (passive optical network) of a switching state of each phase of bridge arm according to the definition of the adjacent vectors and the zero vector of different main sectors, the corresponding on-off time of each switching tube of each phase of bridge arm is finally obtained according to the definition of the PON, and the total on-off time of 6 basic switches of 36 sub-sectors is obtained by summarizing the following table:
| on-off time of basic switch | Basic switch on-off time sequence |
| T S -T 0 /2 | 1 |
| T a +T 0 /2 | 2 |
| T 0 /2 | 3 |
| T b +T 0 /2 | 4 |
| 0 | 5 |
| |
6 |
The on-off time of all switch tubes in the three-level inverter is one of the on-off time of the basic switch, and the numerical value of the on-off time of the basic switch given in the table refers to the duration time of the high level of the PWM wave;
step 43: ta and Tb are calculated as follows:
when 3: (Va + Vb)/Vdc > Ts
Ta＝3*Va*Ts/Vdc
Tb＝3*Vb*Ts/Vdc
When 3 x (Va + Vb)/Vdc < Ts
Ta＝3*Va*Ts/(Va+Vb)
Tb＝3*Vb*Ts/(Va+Vb)
T 0 ＝Ts-Ta-Tb；
Wherein, T s For switching period, V a ，V b Is a V ref ' projection on alpha and beta axes under the CLARK coordinate system;
and step 44: according to T a And T b Can obtain V ref ' switching on-off time of 12 switching tubes in 36 sub-sectors is shown in the following table, the on-off time of the third switching tube in each phase is complementary to the first, the on-off time of the fourth switching tube in each phase is complementary to the second, and the sum of the times is T s :
The digital sequence numbers under the on-off time of the switches correspond to the on-off time sequence of the basic switches given in the step 42 one by one, namely the on-off time of the basic switches is the on-off time of the switch tubes.
Further, in the fifth step, if the midpoint voltage is positive, the action time of the positive small vector is increased;
if the midpoint voltage is negative, increasing the action time of the negative small vector;
if the midpoint voltage is zero, no change is made;
in the three-level inverter, specific values corresponding to the output positive small vectors and the output negative small vectors are shown in the following table, and the voltage level of the space vector is unchanged and the direction of the space vector is changed in the operation process of the inverter.
Further, in the fifth step, defining:
T x ＝T 0 /2*(1-f)
T y ＝T 0 /2*(1+f)
f is the midpoint voltage suppression coefficient, range (-1,1);
the corrected on-off time of the basic switch is as follows:
| corrected on-off time of basic switch | Basic switch on-off time sequence |
| T s -T x | 1 |
| T a +T y | 2 |
| T y | 3 |
| T b + |
4 |
| 0 | 5 |
| |
6 |
And replacing the on-off time of the switch in the step 44 from the basic on-off time to the corrected basic on-off time, so as to obtain the on-off time of the switching tube capable of inhibiting the neutral point voltage fluctuation of the three-level inverter.
Further, the 12-way PWM wave generation process is as follows:
defining the on-off time of the switch tube as t, adopting the count-up and count-down of the PWM wave generation chip, defining the maximum value of the digital quantity as D, and defining the current value of the digital quantity as D', when
D’>(T s -t) D/2, pwm wave generating chip output high level;
D’<(T s -t) D/2, the pwm wave generating chip outputs a low level.
The invention provides a three-level inverter control system and a three-level inverter control method for an electric propulsion system of an electric plane.
Drawings
FIG. 1 is a diagram of a three level inverter topology;
FIG. 2 is a block diagram of a three level inverter control system;
FIG. 3 is a three-level inverter sector layout diagram;
FIG. 4 is a diagram of a mechanism for generating a neutral point voltage imbalance;
FIG. 5 is a graph of the effect of neutral point voltage balance control; fig. 5 a) a schematic diagram of three-level inverter output three-phase voltages; FIG. 5 b) a neutral point voltage diagram;
FIG. 6 is a schematic diagram of the three level inverter output voltage THD; FIG. 6 a) is a schematic diagram of three-phase voltage THD output by a three-level inverter adopting a midpoint voltage suppression algorithm; FIG. 6 b) a schematic diagram of a three-level inverter outputting three-phase voltage THD according to a traditional algorithm;
fig. 7 is a block diagram of a novel three-level inverter midpoint voltage control algorithm.
Detailed Description
The topological structure of the three-level inverter adopted by the invention is shown in figure 1, the A, B, C three-phase bridge arm has 12 switching tubes, and each phase of bridge arm has 4 switching tubes. The switch tube is defined to be turned on to be 1 and turned off to be 0, different switch sequences of each phase of switch tube have different phase output levels, 3 levels are provided in total, and the level is defined as P, N, O. Further, the combination of the 3-phase output levels causes the inverter to output different vector voltages, and there are 27 kinds of output voltage vectors. Table 2 shows the level state of each phase of the bridge arm of the three-level inverter, and table 3 shows the vector state of the output voltage of the three-level inverter.
TABLE 2 bridge arm level state of three-level inverter
TABLE 3 space Voltage vector Table
Based on the topology structure and topology analysis, the specific implementation process of the invention is as follows:
as shown in the control block diagram of fig. 2, a three-level SVPWM control algorithm based on a midpoint voltage balance control strategy is shown in a dotted line block diagram, a three-level inverter topological structure diagram is shown in a solid line block diagram, a controlled object is a permanent magnet synchronous motor PMSM, when the motor normally operates, two-phase currents of the motor A, B are sampled, and the three-phase currents of the motor are converted into currents i on a dq axis through vector conversion d ，i q . ASR is a speed loop, ACR is a current loop, and the input is an expected rotating speed w ref Actual rotational speed w e D axis current i d Q-axis current i q The output is the expected motor input vector u after PI regulation d ，u q The above parts and permanent magnet motor i d The control strategies of the two-level SVPWM of =0 are completely consistent and are not described in detail.
Generating a desired motor input vector u d ，u q Then, the conventional sector discrimination method is to determine V by the position sensor as shown in FIG. 3 a) ref (u d ，u q A resultant vector in a three-phase coordinate system), the present patent employs a sector discrimination method described below; u is to be d ，u q Inverse transform to u a 、u b 、u c By comparing the values between the three-phase voltages, V is determined ref The specific implementation of the sector(s) of (c) is shown in table 4. As shown in fig. 3 b), the three-level sector is a regular hexagon, and the middle point of each side is drawn with the connecting line of the center of the regular hexagonDivided into six sectors, defined as main sector 1-main sector 6.
TABLE 4 sector discrimination
| Va | Vb | Vc | Main 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 |
After the sector discrimination is completed, V is paired ref Performing sector conversion, as shown in FIG. 3 c) and FIG. 3 d), taking sector 1 as an example, and converting the target vector V ref The starting point is converted to the sector center and can be converted into V ref1 . The calculation formula is as follows:
V ref1 ＝V ref -V map
V map different matching vectors are corresponding to different main sectors, as shown in table 5:
table 5 matching vector table
The alpha and beta values represent the matching vector V map Projection on an alpha axis and a beta axis under a CLARK coordinate system;
in fig. 3 d), the original vectors are PPP (OOO, NNN), POP (ONO), PNO, PNN, PON, PPO (OON), POO (ONN), respectively. Like a two-level hexagon, define V map ＝V 0 A new hexagonal vector diagram can be obtained, wherein 7 matching vectors V are arranged in the diagram 0 ～V 6 The counter-clockwise ordering constitutes 6 sub-sectors, and 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 composition formula is as follows:
V 1* T a +V 2* T b +V 0* T 0 ＝V ref1* T S
after the main sector is distinguished, the subsequent steps are similar to the two-level SVPWM: firstly, determining the sub-sector where the converted target vector is located, and secondly, calculating the on-off time of each switching tube. The value of the on-off time of the switching tube given in this patent corresponds to the duration of the high level of the PWM wave. In the two-level SVPWM, only 3 pairs of power switches are needed, only three groups of time need to be calculated, and 6 pairs of power switches are needed in three levels, and 6 groups of time need to be calculated. In consideration of simplification of MCU computing resources, taking the main sector 1 as an example, as shown in fig. 3 d), for the target vector, the bridge arm states N, B, and C do not exist in the phase a of the system. A-phase P state is defined as 1,O state 0, B and C-phase O state is defined as 1,N state 0, so that a vector diagram completely consistent with two-level SVPWM can be obtained.
The remaining 5 main sectors ABC phases are defined as shown in the table below:
at the moment, the sector graph and the two-level SVPWM sector graph have the same form, so far, the three-level problem is converted into two levels, the calculation of the on-off time of the switch can completely delay the two-level method, the on-off time of the switch of the two-level inverter is only 3 basic on-off times, the three-level inverter has 6 basic on-off times, the table 6 gives the basic on-off times of the switch tubes, and the on-off time of all the switch tubes in the used three-level inverter is one of the basic on-off times.
TABLE 6 basic ON-OFF TIME OF SWITCH TUBE
| On-off time of basic switch | Basic switch on-off time sequence |
| T S -T 0 /2 | 1 |
| T a +T 0 /2 | 2 |
| T 0 /2 | 3 |
| T b +T 0 /2 | 4 |
| 0 | 5 |
| |
6 |
Wherein, T a ，T b ，T 0 The calculation process is as follows:
when 3 is (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)
T 0 ＝Ts-Ta-Tb；
Wherein, T s For switching period, V a ，V b Is a V ref ' values on the alpha and beta axes under the CLARK coordinate system;
according to T a And T b Can obtain V ref ' switching on-off time of 12 switching tubes in 36 sub-sectors is shown in the following table, the on-off time of the third switching tube in each phase is complementary to that of the first switching tube, and the on-off time of the fourth switching tube in each phase is complementary to that of the second switching tube in each phaseSupplement, time sum is T s :
TABLE 7 ON-OFF TIME TABLE FOR SWITCH
And the on-off time of the basic switch corresponding to the 1-6 digital sequence in the six columns of the on-off time of the switch in the table 7 and the on-off time sequence of the basic switch in the table 6 is the on-off time of the switch tube.
After the on-off time of a switch is calculated by the traditional three-level control, 12 paths of PWM waves are directly generated to control the on-off state of an inverter, so that a motor is controlled. Fig. 4 shows the reason why the midpoint voltage imbalance occurs under the conventional three-level control, and it can be seen that the short vector and the long vector are not connected to the neutral point between the capacitors, and the midpoint voltage is not affected, and the middle vector may cause charging or discharging of the upper capacitor, depending on the current direction of the motor winding, the positive small vector may cause discharging of the upper capacitor, the negative small vector may cause discharging of the lower capacitor, and the combined action of the middle vector and the long vector causes the unbalanced oscillation of the midpoint voltage. The method for restraining the midpoint voltage of the three-level inverter is adopted, and after the on-off time of a switch is calculated, the voltage V is introduced DH And V DL The neutral point voltage balance strategy is based on the characteristic of a redundant small vector when V is detected DH >V DL Suppression coefficient f>0, the inhibition coefficient adopts a fixed value or is given by an optimization algorithm, the action time of the positive small vector is increased in one control period, and conversely, when V is detected DH <V DL Suppression coefficient f<0, in one control period, increasing the action time of the negative small vector. The specific algorithm is as follows:
T x ＝T 0 /2*(1-f)
T y ＝T 0 /2*(1+f)
f is the midpoint voltage suppression coefficient, range (-1,1);
after the above-mentioned midpoint voltage suppression strategy is adopted, the switch on-off basic time is corrected, as shown in table 8:
TABLE 8 corrected basic switch ON-OFF TIME TABLE
Comparing the tables 6 and 8, the sequences in the two tables correspond one by one, and the corrected switch on-off time corresponding to the 1-6 digital sequence in the six columns of the switch on-off time in the table 7 and the basic switch on-off time sequence in the table 8 is the final on-off time of the switch tube. The corresponding values in table 7 are replaced with the values in table 8, and the final on-off time of the 12-way switch after the midpoint voltage suppression algorithm is adopted can be obtained.
Finally, the control system generates 12 paths of PWM waves, and the 12 paths of PWM waves are generated in the following process:
defining the on-off time of the switch tube as t, adopting the count-up and count-down of the PWM wave generation chip, defining the maximum value of the digital quantity as D, and defining the current value of the digital quantity as D', when
D’>(T s -t) D/2, pwm wave generating chip outputs high level;
D’<(T s -t) D/2, the pwm wave generating chip outputs a low level.
12 way PWM controls inverter output voltage, figure 5 shows the result of this patent novel control strategy, wherein, figure 5 a) is inverter output three-phase voltage, two capacitor voltages on figure 5 b), the midpoint voltage under figure 5 b), it can be seen that, on the basis of traditional three-level control (0-0.3 s), after adding novel three-level inverter to restrain midpoint voltage control strategy (0.3-0.6 s), three-phase voltage waveform is more smooth, midpoint voltage fluctuation frequency is smaller, the scope is lower.
The sector is distinguished to 12 paths of PWM waves generated by a control system, the control strategy is the core of a novel three-level inverter restraining midpoint voltage control strategy different from a traditional control algorithm, the output voltage THD of the three-level inverter adopting a midpoint voltage restraining algorithm and a traditional algorithm is shown in fig. 6 a) and fig. 6 b), and it can be seen that after the algorithm is adopted, the voltage harmonic content is obviously reduced, the quality is obviously improved, fig. 7 is a program block diagram of the part, the traditional algorithm is arranged in a dotted line, and the block diagram outside the dotted line is a novel algorithm.
Claims (8)
1. The utility model provides an electric aircraft electric propulsion system three-level inverter control system which characterized in that: the system comprises: the system comprises a controlled permanent magnet synchronous motor, a PARK conversion module, a rotating speed ring-current ring 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 which are sequentially connected;
the PARK conversion module collects phase current of a controlled permanent magnet synchronous motor A, B and outputs three-phase voltage after passing through a rotating speed loop-current loop PI control module, a PARK inverse conversion module and a CLARK inverse conversion module;
the sector judging and converting module judges a target vector V according to the input three-phase voltage ref In the three-level sector, and the target vector V ref A three-level sector representation is changed into a two-level sector representation; and outputs a target vector V under a two-level reference ref ’；
The switching time calculation module calculates the switching time according to a target vector V ref ' calculating the on-off time of a switching tube;
the midpoint voltage suppression module adjusts the on-off time of the switching tube according to the midpoint voltage acquired from the three-level inverter;
the PWM wave generation module generates 12 paths of PWM waves according to the adjusted on-off time of the switching tube to control the three-level inverter to generate target three-phase voltage so as to control the controlled permanent magnet synchronous motor to operate.
2. A method of controlling a three-level inverter of an electric aircraft electric propulsion system, the method for controlling the system of claim 1, characterized in that: the method comprises the following steps:
the method comprises the following steps: the method comprises the steps of collecting phase current of a controlled permanent magnet synchronous motor A, B, and calculating three-phase voltage V through PARK conversion, rotating speed loop-current loop PI control, PARK inverse conversion and CLARK inverse conversion a 、V b 、V c ；
Step two: judging a target vector V according to the three-phase voltage ref The position of the three-level sector;
step three: target vector V ref A conversion from a three-level sector representation to a two-level sector representation; and outputs a target vector V under a two-level reference ref ’；
Step four: according to a target vector V under a two-level reference ref ' calculating the on-off time of a switch tube;
step five: acquiring midpoint voltage from a three-level inverter, and adjusting the on-off time of a switching tube according to the midpoint voltage;
step six: and generating 12 paths of PWM waves according to the adjusted on-off time of the switching tube and outputting the PWM waves to the three-level inverter.
3. The three-level inverter control method according to claim 2, characterized in that: in the second step, the three-level sector is that the middle point of each side of the regular hexagon is respectively connected with the center of the regular hexagon to divide the regular hexagon into six sectors which are respectively defined as a main sector 1-a main sector 6; according to the three-phase voltage V, as shown in the table below a 、V b 、V c Judging the target vector V ref Location within the three-level sector:
。
4. The three-level inverter control method according to claim 3, characterized in that: in the third step, the target vector V is obtained by the following process ref The transition from three-level sector representation to two-level-like sector representation:
step 31: target vector V ref The main sector is expanded into a hexagonal two-level vector diagram; the side length of the hexagonal two-level vector diagram is half of that of the three-level sector, and the center of the hexagonal two-level vector diagram is taken as a zero vector V 0 Defined by V 0 As vector starting points, the six vectors respectively taking six vertexes of the two-level vectors of the hexagon as key points are respectively V 1 ～V 6 (ii) a The hexagonal two-level vector diagram is divided into 1-6 regions counterclockwise and defined as sub-sectors 1-6, the three-level inverter vector diagram has 6 main sectors in total and 36 sub-sectors in total;
step 32: target vector V ref The starting point is converted into the center of a hexagonal two-level vector diagram and is converted into V ref ’；
V ref ’＝V ref -V map ；
V map For the matching vector, the matching vector is determined according to the following table:
wherein, V dc Inputting direct-current bus voltage for the three-level inverter, wherein the alpha and beta values represent the projection of a matching vector Vmap on an alpha axis and a beta axis under a CLARK coordinate system; p, O, N represent the states of the three-phase legs of the three-level inverters a, B, C, as shown in the following table:
5. the three-level inverter control method according to claim 4, characterized in that: in the fourth step, according to V ref ' calculating the on-off time of the switching tube comprises the following steps:
step 41: in the main sector 1, the bridge arm states N, B and C of the A-phase and B-phase bridge arms of the three-level inverter do not exist; defining the A-phase P state as 1,O state 0, B, C-phase O state as 1,N state 0, V in the hexagonal two-level vector 1 ～V 6 Denoted as 100 → 110 → 010 → 011 → 001 → 101, zero vector V 0 May be represented as 111 or 000; the remaining 5 main sector ABC three-phase states are defined as shown in the table below:
step 42: v ref The method is characterized in that two adjacent vectors and a zero vector are represented into a 7-segment SVPWM form, the two adjacent vectors and the zero vector have respective action time, the action time of the two adjacent vectors and the zero vector is obtained as same as that of the traditional two-level 7-segment SVPWM, each segment of action time corresponds to the action time of a PON (passive optical network) of a switching state of each phase of bridge arm according to the definition of the adjacent vectors and the zero vector of different main sectors, the corresponding on-off time of each switching tube of each phase of bridge arm is finally obtained according to the definition of the PON, and the total on-off time of 6 basic switches of 36 sub-sectors is obtained by summarizing the following table:
The on-off time of all switch tubes in the three-level inverter is one of the on-off time of basic switches, and the numerical value of the on-off time of the basic switches given in the table refers to the duration time of the PWM wave high level;
step 43: ta and Tb are calculated as follows:
when 3 is (Va + Vb)/Vdc > Ts
Ta＝3*Va*Ts/Vdc
Tb＝3*Vb*Ts/Vdc
When 3 x (Va + Vb)/Vdc < Ts
Ta＝3*Va*Ts/(Va+Vb)
Tb＝3*Vb*Ts/(Va+Vb)
T 0 ＝Ts-Ta-Tb；
Wherein, T s For switching the tube period, V a ，V b Is a V ref ' projection on alpha and beta axes under the CLARK coordinate system;
and step 44: according to T a And T b Can obtain V ref ' at 36 sub-sectorsThe on-off time of the 12 switching tubes is shown in the following table, the on-off time of the third switching tube of each phase is complementary to that of the first switching tube, the on-off time of the fourth switching tube of each phase is complementary to that of the second switching tube, and the sum of the times is T s :
And the on-off time of the basic switch corresponding to the numerical sequence number in the six columns under the on-off time of the switch and the on-off time sequence of the basic switch given in the step 42 is the on-off time of the switch tube.
6. The three-level inverter control method according to claim 5, characterized in that: in the fifth step, if the midpoint voltage is positive, the action time of the positive small vector is increased;
if the midpoint voltage is negative, increasing the action time of the negative small vector;
if the midpoint voltage is zero, no change is made;
in the three-level inverter, specific values corresponding to the output positive small vectors and the output negative small vectors are shown in the following table, and the voltage level of the space vector is unchanged and the direction of the space vector is changed in the operation process of the inverter.
7. The three-level inverter control method according to claim 6, characterized in that: in the fifth step, defining:
T x ＝T 0 /2*(1-f)
T y ＝T 0 /2*(1+f)
f is the midpoint voltage suppression coefficient, range (-1,1);
the corrected on-off time of the basic switch is as follows:
And the corrected basic switch on-off time corresponding to the digital serial number in the six columns of the switch on-off time and the basic switch on-off time sequence is the final corrected on-off time of the switch tube.
8. The three-level inverter control method according to claim 6, characterized in that: the 12-path PWM wave generation process is as follows:
defining the on-off time of the switch tube as t, adopting the count-up and count-down of the PWM wave generation chip, defining the maximum value of the digital quantity as D, and defining the current value of the digital quantity as D', when
D’>(T s -t) D/2, pwm wave generating chip outputs high level;
D’<(T s -t) D/2, the pwm wave generating chip outputs a low level.
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