阅读说明：本技术 一种开绕组电机变母线电压工况下直接转矩控制优化方法 (Direct torque control optimization method for open-winding motor under variable bus voltage working condition ) 是由 孔祥浩 陶文杰 魏佳丹 张卓然 于 2019-09-25 设计创作，主要内容包括：本发明公开一种开绕组电机变母线电压工况下直接转矩控制优化方法,以降低单位控制周期内的转矩变化的增加量和减小量的差值为目标,优化选择开关表控制策略中的空间电压矢量,降低基于开关表的直接转矩控制下的的开绕组电机输出转矩脉动,并以双电源母线电压的比值作为控制变量,结合定子磁链在十八扇区中所处的位置和滞环控制器输出信号在线选择开关表,实现变母线电压工况下开绕组永磁电机的优化控制。该控制方法能够有效提升蓄电池供电条件下开绕组电机的驱动输出性能。(The invention discloses a direct torque control optimization method for an open-winding motor under a variable bus voltage working condition, which aims to reduce the difference value between the increment and the decrement of torque change in a unit control period, optimizes and selects a space voltage vector in a switch table control strategy, reduces the output torque ripple of the open-winding motor under the direct torque control based on the switch table, takes the ratio of the voltage of a double-power bus as a control variable, and combines the position of a stator flux linkage in eighteen sectors and an on-line selection switch table of output signals of a hysteresis controller to realize the optimal control of the open-winding permanent magnet motor under the variable bus voltage working condition. The control method can effectively improve the driving output performance of the open winding motor under the condition of power supply of the storage battery.)

1. A direct torque control optimization method under the condition of variable bus voltage of an open winding motor is disclosed, wherein the open winding motor comprises two inverters, and the bus voltages of the two inverters are respectively U_dc1And U_dc2The control optimization method is characterized by comprising the following steps:

step one, collecting three-phase current i_a、i_b、i_cThree phase voltage u_a、u_b、u_cBus voltage U of double inverter_dc1，U_dc2And motor position angle theta_r；

Step two, collecting current signals i_a、i_b、i_cSum voltage signal u_a、u_b、u_c3/2 transformation is carried out to obtain stator current i_sα、i_sβAnd the voltage alpha, beta axis components u_sα、u_sβ；

Step three, utilizingTransformed i_sα、i_sβ、u_sα、u_sβObserving the stator flux linkage to obtain stator flux linkage psi_sαAnd psi_sβ(ii) a Using stator flux linkage psi_sαAnd psi_sβObtaining stator flux linkage amplitude psi_s；

Using the obtained psi_sα、ψ_sβ、i_sα、i_sβCalculating the electromagnetic torque T of an electric machine_e；

Step four, calculating a rotating speed actual value omega by utilizing the collected position angle signal_rSetting the motor rotation speed to a given value omega_rSum of actual values of speed ω_rSubtracting to obtain a rotation speed error epsilon_ωError of rotation speed epsilon_ωObtaining a torque set value T through a PI control module_e*；

Step five, obtaining the electromagnetic torque T according to calculation_eWith a given value of torque T_eComparing to obtain torque control signal tau, and calculating flux linkage amplitude and flux linkage given value psi_sComparing to obtain a magnetic linkage control signal phi, wherein the calculation formula is as follows:

step six, equally dividing the whole 360-degree vector space of the open-winding motor into eighteen sectors through nine boundary straight lines, and defining a sector positive and negative judgment function as follows:

when the independent variable z is negative or zero, the function value is 0, when the independent variable z is positive, the function value is 1; defining results of nine boundary straight lines after passing through a positive and negative judgment function as a-i, and determining the positive and negative of a-i according to the boundary position of the stator flux linkage relative to the sector in an alpha beta coordinate system;

and obtaining a sector number N according to the variables a-i, wherein the corresponding formula is as follows:

N＝2a+3b+2c+2d+2e+2f+2g+3h+i；

step seven, obtaining U according to sampling_dc1，U_dc2Calculating the ratio x of bus voltage to U_dc2/U_dc1If x is within the interval of 0.8-1, selecting a switch table control scheme 1;

scheme 1

If x is within the interval of 0.655-0.8, selecting a switch table control scheme 2;

scheme 2

If x is within the interval 0.5-655, selecting a switch table control scheme 3.

Scheme 3

2. The open-winding motor direct torque control optimization method under the variable bus voltage working condition according to claim 1, characterized by comprising the following steps: in the second step, a transformation matrix for 3/2 transformation of the current and voltage signals is:

3. the direct torque control optimization method for the open-winding motor under the working condition of variable bus voltage according to claim 1, wherein the direct torque control optimization method is characterized in thatThe method comprises the following steps: in the third step, the stator flux linkage psi_sαAnd psi_sβThe calculation formula of (2) is as follows:

in the formula, R represents a one-phase stator armature winding resistor of the open-winding permanent magnet synchronous motor.

4. The open-winding motor direct torque control optimization method under the variable bus voltage working condition according to claim 1, characterized by comprising the following steps: in the third step, the stator flux linkage amplitude calculation formula is as follows:

5. the open-winding motor direct torque control optimization method under the variable bus voltage working condition according to claim 1, characterized by comprising the following steps: in the third step, the calculation formula of the electromagnetic torque is as follows:

in the formula P_nThe number of pole pairs of the motor is shown.

6. The open-winding motor direct torque control optimization method under the variable bus voltage working condition according to claim 1, characterized by comprising the following steps: in the sixth step, the positive and negative calculation formulas of a to i are determined according to the position of the stator flux linkage relative to the boundary of the sector in the α β coordinate system as follows:

Technical Field

The invention relates to a direct torque control optimization method for a permanent magnet motor with a lower winding under the working condition of variable bus voltage, belonging to the field of motor systems and control.

Background

The open-winding motor is an alternating current motor which opens a neutral point of an armature winding of the motor and controls two ends of the armature winding through a three-phase converter on the premise of not changing a magnetic circuit and a structure of a traditional three-phase alternating current motor. Compared with the traditional three-phase alternating current motor, the basic performance of the open winding motor is not influenced, the windings of the open winding motor are relatively independent, and the reliability of the motor body is improved to a certain extent; the open-winding motor can be equivalent to a three-level or four-level system under a double-inverter control system, the inherent neutral point voltage balance problem of a multi-level converter does not exist, and the current harmonic content can be reduced more conveniently; from the power perspective, under the same current harmonic requirement, the switching frequency of the double-converter system is obviously lower than that of the single-inverter system, and through reasonable configuration of the converter power, the single-converter power in the double-converter system can be greatly reduced, so that the open-winding motor has obvious advantages in a wide rotating speed range and a high-power occasion.

The existing open-winding motor can be divided into two topological structures of a series type and a parallel type according to the direct current bus connection mode of a double converter, the converters at two sides of the parallel type topological structure only need one direct current source, although the form of the power supply is simple, the structure can provide a path for zero sequence current in the system, and Direct Torque Control (DTC) based on a switching table is difficult to suppress the zero-sequence current in the open-winding motor in the parallel topology well, therefore, the open-winding motor driving system usually directly adopts the series topology of the open-winding motor, compared with the parallel topology, two mutually isolated direct current sources are needed in the system, the cost of the power supply is increased, however, because no zero-sequence current path exists, the problem of zero-sequence current suppression does not need to be considered, and therefore zero-sequence current in the control process of the open-winding motor system is structurally avoided. And the double-power converter can synthesize more voltage vectors through reasonable configuration of bus voltages on two sides, and can be equivalent to a four-level system particularly when the bus voltages on the two sides are unequal, so that a larger space is provided for optimization of a switch table in a DTC (digital control time series) switch table.

However, in the series open-winding motor system, the working process of the battery supplying power to the inverter is a complex electrochemical process, and is affected by various aspects such as temperature, current, power, residual capacity and the like, the voltage of the battery is not necessarily fixed in the whole working process, and taking a power battery pack as an example, the output voltage of the battery can change along with the operation condition:

1) under the same charge state, the voltage of the battery pack is inversely proportional to the magnitude of the discharge current;

2) under the same capacity, the voltage of the battery pack is inversely proportional to the temperature;

3) as the charging and discharging process continues to cycle, the degradation of the battery pack performance also results in a decrease in voltage output capability.

The distribution of voltage space vectors in the system is closely related to the amplitude values of bus voltages at two sides, except for the problem that the voltage of the power battery pack changes in the actual charging and discharging process, under the influence of power characteristics, the situation that the amplitude values of a plurality of bus voltages change in the open-winding motor driving system can cause the amplitude values of the space voltage vectors and the angle relation among the space voltage vectors to change, under the situation, DTC controls various preset off-line switching tables to possibly not adapt to the voltage vector synthesized by the current bus voltage any more, the situation that the control performance is deteriorated and even the system is unstable can be caused inevitably, and therefore the switch table under the variable voltage working condition needs to be improved in a targeted mode, and the performance of the open-winding motor DTC system is improved.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a switching table scheme under the working condition of variable bus voltage by using a vector optimization principle of reducing the difference value between the torque increment and the torque decrement in the torque control process, so that the output performance of the motor under the working condition of the variable bus is ensured, and the torque pulsation of the motor with a winding under the direct torque control is reduced.

In order to achieve the purpose, the technical scheme provided by the invention is as follows: a direct torque control optimization method under the condition of variable bus voltage of an open winding motor is disclosed, wherein the open winding motor comprises two inverters, and the bus voltages of the two inverters are respectively U_dc1And U_dc2The control optimization method comprises the following steps:

step one, collecting three-phase current i_a、i_b、i_cThree phase voltage u_a、u_b、u_cBus voltage U of double inverter_dc1，U_dc2And motor position angle theta_r；

Step two, collecting current signals i_a、i_b、i_cSum voltage signal u_a、u_b、u_c3/2 transformation is carried out to obtain stator current i_sα、i_sβAnd the voltage alpha, beta axis components u_sα、u_sβ；

Step three, utilizing the transformed i_sα、i_sβ、u_sα、u_sβObserving the stator flux linkage to obtain stator flux linkage psi_sαAnd psi_sβ(ii) a Using stator flux linkage psi_sαAnd psi_sβObtaining stator flux linkage amplitude psi_s；

Using the obtained psi_sα、ψ_sβ、i_sα、i_sβCalculating the electromagnetic torque T of an electric machine_e；

Step four, calculating a rotating speed actual value omega by utilizing the collected position angle signal_rSetting the motor rotation speed to a given value omega_rSum of actual values of speed ω_rSubtracting to obtain a rotation speed error epsilon_ωError of rotation speed epsilon_ωObtaining a torque set value T through a PI control module_e*

Step five, obtaining a torque control signal tau according to the comparison of the electromagnetic torque obtained by calculation and a torque set value, and obtaining a flux linkage amplitude psi according to calculation_sGiven value psi of flux linkage_sComparing to obtain a magnetic linkage control signal phi, wherein the calculation formula is as follows:

step six, equally dividing the whole 360-degree vector space of the open-winding motor into eighteen sectors through nine boundary straight lines, and defining a sector positive and negative judgment function as follows:

when the independent variable z is negative or zero, the function value is 0, when the independent variable z is positive, the function value is 1; defining results of nine boundary straight lines after passing through a positive and negative judgment function as a-i, and determining the positive and negative of a-i according to the boundary position of the stator flux linkage relative to the sector in an alpha beta coordinate system;

the pattern variables a-i obtain the sector number N, and the corresponding formula is as follows:

N＝2a+3b+2c+2d+2e+2f+2g+3h+i；

step seven, obtaining U according to sampling_dc1，U_dc2Calculating the ratio x of bus voltage to U_dc2/U_dc1If x is within the interval of 0.8-1, selecting a switch table control scheme 1;

scheme 1

If x is within the interval of 0.655-0.8, selecting a switch table control scheme 2;

scheme 2

If x is within the interval 0.5-655, selecting a switch table control scheme 3.

Scheme 3

The technical scheme is further designed as follows: in the second step, a transformation matrix for 3/2 transformation of the current and voltage signals is:

in the third step, the stator flux linkage psi_sαAnd psi_sβThe calculation formula of (2) is as follows:

in the formula, R represents a one-phase stator armature winding resistor of the open-winding permanent magnet synchronous motor.

In the third step, the stator flux linkage amplitude calculation formula is as follows:

in the third step, the calculation formula of the electromagnetic torque is as follows:

in the formula P_nThe number of pole pairs of the motor is shown.

In the sixth step, the positive and negative calculation formulas of a to i are determined according to the position of the stator flux linkage relative to the boundary of the sector in the α β coordinate system as follows:

compared with the prior art, the invention has the following beneficial effects:

compared with the traditional offline switch meter control mode, the online selection switch meter control strategy provided by the invention has smaller torque ripple and higher torque stability in a wide bus voltage change range.

The optimized direct torque control strategy of the variable bus voltage working condition switch table provided by the invention can enable the motor to be normally driven in a wide bus voltage change range, and compared with a motor system adopting a traditional off-line switch table control strategy, the motor system adopting the control strategy of the invention has more stable output performance.

Drawings

FIG. 1 is an open winding motor topology with dual power supplies;

FIG. 2 is a schematic diagram of space vector synthesis and eighteen sector division of an open-winding motor;

FIG. 3 is a schematic diagram of the effect of voltage space vectors on stator flux linkage per unit period;

FIG. 4 is a schematic diagram of a synthetic voltage vector under a variable bus voltage condition;

FIG. 5 is a schematic diagram of voltage vector selection for increasing torque;

FIG. 6 is a schematic diagram of three reduced torque voltage vector selection schemes for a sector with large vectors;

FIG. 7 is a schematic diagram of three reduced torque voltage vector selection schemes for a sector in which a non-large vector is located;

FIG. 8 shows a sector Δ T where a large vector is located_e+And Δ T_e-A schematic diagram of the difference between the two;

FIG. 9 shows a sector Δ T where a non-large vector is located_e+And Δ T_e-A schematic diagram of the difference between the two;

FIG. 10 is a block diagram of direct torque control of an open-close motor switch meter under a variable bus voltage condition;

FIG. 11 is a schematic view of sector calculation;

FIG. 12 shows waveforms of output torque before and after optimization of the switching table under variable bus voltage conditions.

Detailed Description

The invention is described in detail below with reference to the figures and the specific embodiments.

The invention discloses a direct torque control optimization method for an open-winding motor under a bus voltage changing working condition, and aims to obtain a unit period expression of a torque increment and a torque decrement by analyzing the asymmetry of motor torque, and provide a direct torque control method for a switching table based on the principle of minimizing the difference of the torque increment and the torque decrement.

The open winding motor topological structure powered by double power supplies is shown in figure 1, and the bus voltages of an inverter 1 and an inverter 2 are respectively U_dc1And U_dc2When the bus voltages of the inverters on the two sides are unequal, the equivalent three-level topology of the open-winding double-inverter under the condition that the bus voltages are equal originally is changed into a four-level topology, the voltage vector synthesized by the double-inverter and the corresponding switch state thereof and the 18 space voltage vectors contained in the outermost periphery hexagon are shown in fig. 2, wherein, the parts (a) and (b) are the voltage vector synthesized by the double-inverter and the corresponding switch state thereof respectively, and the vector V in fig. 2(c) is the vector V_xyThe spatial voltage vector synthesis in accordance with fig. 2(a) (b): namely, the x vector of the 6 basic voltage vectors generated by the inverter 1 is selected, and the y vector of the 6 basic voltage vectors generated by the inverter 2 is selected. Taking the division of the sectors under the condition that the bus voltage ratio is 1:0.5 as an example, the space is divided into 18 sectors, each sector occupies 20 degrees, as shown in fig. 2(d), the sectors corresponding to the voltage vectors with the larger amplitudes in 6 of the 18 sectors are defined as the sectors where the voltage vectors with the larger amplitudes are located, and the sectors corresponding to the voltage vectors with the smaller amplitudes in 12 are defined as the sectors where the voltage vectors with the smaller amplitudes are not located. Defining bus voltage amplitude U_dc2/U_dc1Is x.

By analyzing the torque variation, the asymmetry of the torque increment and the torque decrement variation in the torque control process is researched, the reduction of the difference value of the torque increment and the torque decrement variation is taken as a vector optimization principle, and a switch table scheme under the working condition of variable bus voltage is optimized.

The present invention analyzes the torque asymmetry as follows:

the electromagnetic torque equation of the surface-mounted permanent magnet synchronous motor can be expressed asWherein p is the number of pole pairs of the motor, psi_fIs a permanent magnet flux linkage, delta is a torque angle of the motor, L_sIs the armature inductance. In the running of the motorIn the process, the electromagnetic torque full differential equation of the motor can be expressed asWherein delta psi_sΔ δ is the amount of change in the stator flux linkage per unit control period, and Δ δ is the amount of change in the torque angle. FIG. 3 is a schematic diagram showing the effect of voltage space vector on stator flux linkage in a unit period, and the expression of flux linkage amplitude in a unit period is Δ ψ from FIG. 3_s(n)＝|u_s(n-1)|T_s cosθ_uψ(n-1)Wherein T is_sTo control the period, u_sFor the selected voltage vector, θ_uψAngle θ for the voltage vector to lead the stator flux linkage_ψuIs the angle at which the voltage vector lags the stator flux linkage. The amount of torque angle change can be expressed as the difference between the amounts of stator and rotor flux chain angle change, i.e.A detailed expression of the torque variation amount can thus be obtained:

the expression is a detailed expression of the torque variation under the action of the selected voltage vector in a unit period, and the expression can be divided into three parts, namely delta T_e1、△T_e2And Δ T_e3Represents:

if the selected voltage vector in the switch table control is an increasing torque, the three terms are all positive values, and if the selected voltage vector is used to decrease the torque, Δ T_e1And Δ T_e2Is a negative value, and Δ T_e3Still positive. The expression for the torque increase and decrease per unit control period can therefore be expressed as:

it can be seen that the torque increase amount is smaller than the torque decrease amount by 2 Δ T_e1I.e. the effect of the voltage vector on the torque variation is asymmetric. The switching table optimization strategy provided by the invention is to reduce the torque asymmetry and optimize the output torque ripple of the open-winding motor system.

The voltage vector selection principle of the invention is as follows:

from the equation (3), it is found that the torque decrease amount is larger than the torque increase amount by 2 Δ T under the same other conditions_e3This value is proportional to the motor speed and the torque angle cosine value, i.e. the higher the speed, the smaller the load, the greater the difference between the torque reduction and the torque increase, and the more pronounced the asymmetry of the torque control. Therefore, the asymmetry of the torque control is analyzed under the worst light load condition, and equations (2) and (3) are substituted with the load angle δ of 0o to obtain an expression of the torque increase amount and the torque decrease amount in the unit control period when the asymmetry of the torque control is most significant. The optimization analysis of the switch table under the working condition of variable bus voltage is based on the principle of minimizing the difference between the two.

The derivation analysis of the proportional relation between the synthesized voltage vector and the voltage under the condition of unequal bus voltages is as follows:

the synthetic voltage vector diagram under the variable bus voltage working condition is shown in FIG. 4, and the amplitude of the synthetic voltage vector u and the expression of the relation between theta x and x can be calculated according to the geometrical relationship and are respectively as follows:

in the sector where the large vector is located, the magnitude of the voltage vector can be expressed as | U | ═ U |_a|(x+1)。

The voltage vector selection method for increasing the torque in the invention is as follows:

the invention takes the sector 10 of a large voltage vector and the sector 8 of a non-large voltage vector in eighteen sectors as an example for the analysis of the switch table optimization strategy under the working condition of variable bus voltage, and because of the spatial symmetry of the divided eighteen sectors, the analysis of other sectors is the same as that of the two typical sectors in principle. Firstly, aiming at the selection of the voltage vector for increasing the torque, the selection schematic diagram is shown in fig. 5, because the voltage vector which causes the maximum torque increase in the unit control period in each sector can be changed along with the change of the bus voltage, in order to simplify and analyze the corresponding relation between the asymmetry of the torque control and the amplitude ratio of the bus voltage, the voltage vector corresponding to the third sector which is ahead of the sector where the stator flux linkage is located is always selected as the voltage vector u of the torque increase flux linkage₁Selecting a voltage vector corresponding to a sixth sector leading the sector in which the stator flux linkage is located as a voltage vector u for increasing the torque reducing flux linkage₂。

The voltage vector selection method for reducing the torque in the invention is as follows:

through the torque asymmetry analysis of equation (4), the switching table optimization method proposed by the present invention is based on minimizing the torque increment and the torque reduction difference. It is therefore necessary to calculate the expression for the torque increment and the torque reduction amount first. From the formula (4), the torque increase per unit control period and | u₊|sinθ_uψProportional, u for typical sectors 10 and 8₊|sinθ_uψCalculated from table 1:

table 1: | u₊|sinθ_uψFormula for calculation

Two typical sector calculation formulas are respectively taken into formula (4), and delta T can be calculated_e+ range, the values of the parameters used in the calculation are as follows: p is 2, L_s＝8.17mH，ψ_f＝ψ_s＝0.432Wb，T_s＝5e-5s，|U_aThe torque increment range of a sector where a large vector is located is within 0.169-0.255 and the torque increment range of a sector where a non-large vector is located is within 0.132-0.2 in the process of changing the bus voltage ratio from 0.5 to 1, and the reduction amount of the torque in a unit control period is set to meet the requirement of 0 to 0 under the premise of keeping a certain margin in order to reduce the asymmetric characteristic of torque control as far as possible<ΔT_e-<0.3. The torque reduction amount range is brought into formula (4) to obtain | u_-|sinθ_ψuFurther finding θ_ψuIs as shown in formula (6):

the calculation method of | u- | and | u + | is the same, and in order to avoid error and leakage, theta needs to be enabled on the premise of reserving a certain margin_ψuIs as large as possible, so that here all are made ofAs the magnitude of the voltage vector u-. Therefore, the range of theta psi u is calculated to be within the range of-27 to 30 degrees in the process of changing the bus voltage ratio from 0.5 to 1. Therefore, taking a voltage vector diagram under the condition that the amplitude ratio of bus voltage is 1:0.5 as an example, 10 sectors are used for representing the sector where a large vector is located, 8 sectors are used for representing the sector where a non-large vector is located, and the voltage vector u for reducing the torque is discussed in two categories₃(Torque reduction, flux linkage reduction) and u₄Three combinations of (torque reduction, flux linkage increase). Three reduced torque voltage vector selection schemes for the sector in which the large vector is located are shown in fig. 6. Three reduced torque voltage vector selection schemes for sectors other than the large vector are shown in fig. 7.

| u of exemplary sectors 10 and 8_-|sinθ_ψuCalculated from table 2:

table 2: | u_-|sinθ_ψuFormula for calculation

The delta T can be calculated by taking the strain into formula (4)_e-a span curve of the value of (a) and the previously calculated Δ T_eThe comparison of the value range curves of + can conclude that: in the sector where the large vector is located, the vector is combined with the vectors (a) and (b) to obtain the delta T_eAnd Δ T_eThe + is closest, so that the problem of torque pulsation under variable bus working conditions can be reduced. In the sector where the non-large vector is located, the vector combination (b) and (c) are adopted to obtain delta T_eAnd Δ T_e+ is closest. FIG. 8 shows the Δ T in the sector where the large vector is located_e+ and Δ T_e-a curve comparing the difference with 0, wherein the action effect of the vector combinations (a) and (b) is the same when the bus voltage ratio is 0.655, the control effect of the vector combination (a) is better when the bus voltage ratio x is in the range of 0.5-0.655, and the control effect of the vector combination (b) is better when the bus voltage ratio x is in the range of 0.655-1; FIG. 9 shows the Δ T in the sector where the non-large vector is located_e+ and Δ T_eThe effect of the vector combinations (b) and (c) is the same when the bus voltage ratio is 0.8, the control effect of the vector combination (b) is better when the bus voltage ratio x is in the range of 0.5-0.8, and the control effect of the vector combination (c) is better when the bus voltage ratio x is in the range of 0.8-1. Based on the method, an optimized switching table scheme can be obtained according to the bus voltage proportion:

table 3: switch meter scheme 1 (suitable for bus voltage ratio x in 0.8 ~ 1 interval)

Table 4: switching table scheme 2 (applicable to bus voltage ratio x within the interval of 0.655-0.8):

table 5: switching table scheme 3 (applicable to the bus voltage ratio x within the interval of 0.5-0.655):

the structure of the open-winding permanent magnet motor control system adopted by the invention is shown in figure 1. The control system comprises a double-inverter module, a motor body module, a current signal acquisition module, a rotating speed signal acquisition module and a controller module.

As shown in fig. 10, the present invention controls the motor system shown in fig. 1 by optimizing the switching table in the conventional direct torque control, and specifically includes the following steps:

step one, signal acquisition;

three-phase current i is collected by utilizing current and voltage sampling link_a、i_b、i_cThree phase voltage u_a、u_b、u_cBus voltage U of double inverter_dc1，U_dc2And motor position angle theta_r。

Step two, signal conversion;

the current signal i acquired in the step one is processed_a、i_b、i_cVoltage signal u_a、u_b、u_c3/2 transformation is carried out to obtain stator current and voltage alpha beta axis component i_sα、i_sβ、u_sα、u_sβThe transformation matrix is:

step three, calculating a correlation quantity;

using transformed i_sα、i_sβ、u_sα、u_sβAnd (3) observing stator flux linkage, wherein a voltage observation model is adopted, and the calculation formula is as follows:

in the formula, R represents a one-phase stator armature winding resistor of the open-winding permanent magnet synchronous motor.

The stator flux linkage amplitude calculation method comprises the following steps:

using the obtained psi_sα、ψ_sβ、i_sα、i_sβCalculating the electromagnetic torque of the motor, wherein the torque calculation formula is as follows:

wherein P is_nThe number of pole pairs of the motor is shown.

Step four, calculating a torque set value;

for a given torque value T_eCalculating actual value omega of rotation speed by using collected position angle signals_rSetting the given value omega of the motor rotation speed according to the requirement_rAnd setting the motor speed to a given value omega_rSum of actual values of speed ω_rSubtracting to obtain a rotation speed error epsilon_ωError of rotation speed epsilon_ωObtaining a torque set value T through a PI control module_e*

Step five, calculating a torque flux linkage control signal;

setting flux linkage given value psi according to requirement_sObtaining a torque control signal tau according to the comparison between the calculated electromagnetic torque and a torque given value, obtaining a flux linkage control signal phi according to the comparison between the calculated flux linkage amplitude and a flux linkage given value, wherein the calculation formula is as follows:

judging a sector;

according to the eighteen sector divisions of fig. 2, it can be seen that there are eighteen sector boundaries in total under the eighteen sector divisions, where two of them share a straight line, so there should be a total of nine straight lines corresponding to the boundaries. The invention defines a sector judgment function as follows:

when the independent variable z is negative or zero, the function value is 0, and when the independent variable z is positive, the function value is 1. The result of nine boundary straight lines passing through the positive and negative judgment function is defined as a-i, the positive and negative of a-i are determined according to the relative sector boundary position of the stator flux linkage in the alpha beta coordinate system, and the specific calculation formula is as follows:

fig. 11 is a schematic diagram illustrating sector calculation. The corresponding relationship between the sector number N and the variables a to i is as follows:

N＝2a+3b+2c+2d+2e+2f+2g+3h+i

selecting a switch table scheme;

according to the U obtained by sampling in the step (1)_dc1，U_dc2Calculating the ratio x of bus voltage to U_dc2/U_dc1If x is within the interval of 0.8-1, selecting scheme 1; if x is within the interval of 0.655-0.8, selecting scheme 2; if x is within the interval 0.5-655, option 3 is selected.