CN113992100A - Improved three-level model-free prediction current control method for permanent magnet synchronous motor - Google Patents

Improved three-level model-free prediction current control method for permanent magnet synchronous motor Download PDF

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CN113992100A
CN113992100A CN202111496483.5A CN202111496483A CN113992100A CN 113992100 A CN113992100 A CN 113992100A CN 202111496483 A CN202111496483 A CN 202111496483A CN 113992100 A CN113992100 A CN 113992100A
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於锋
周陈辉
王子诺
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Nantong University
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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
    • H02P21/22—Current control, e.g. using a current control loop
    • 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
    • H02P21/14—Estimation or adaptation of machine parameters, e.g. flux, current or voltage
    • 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
    • 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
    • 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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Abstract

The invention relates to an improved three-level model-free prediction current control method of a permanent magnet synchronous motor, which comprises the following steps of firstly determining a related current reference value through a given rotating speed; then judging the type of the current applied voltage vector and the serial number of the voltage collection, and calculating the current difference corresponding to the basic voltage in each voltage collection on the basis of the current dq-axis current difference through corresponding rules, thereby realizing the calculation of the dq-axis current difference used by all voltage vectors and updating a current difference lookup table; then, a predicted value of the dq-axis current at the time k +1 is calculated, and a basic voltage vector which minimizes the cost function is output through rolling optimization. The method and the device are fully suitable for the market trend of the application of the three-level inverter, meanwhile, the corresponding control does not need specific motor parameters to participate in operation, the influence of model adaptation on the control performance of the system is effectively relieved, and the problem of current difference update stagnation in the traditional model-free prediction current control is effectively solved.

Description

Improved three-level model-free prediction current control method for permanent magnet synchronous motor
Technical Field
The invention relates to an improved three-level model-free prediction current control method for a permanent magnet synchronous motor, and belongs to the field of motor driving and control.
Background
Nowadays, a three-level inverter represented by a three-level neutral point clamped (3L-NPC) inverter has attracted considerable attention in the fields of high-power electronics and motor driving, and compared with a traditional two-level inverter, the three-level inverter has certain advantages in the aspects of alleviating voltage distortion, reducing semiconductor stress and switching frequency, so that the topological structure becomes an attractive research subject for the industry and academia. Meanwhile, in practical application, motor parameters are difficult to accurately learn, and can also change along with the change of the operating environment, the problem of model mismatch cannot be avoided, and the application range of the MPCC is greatly limited. Based on this, in order to reduce the influence of the uncertainty of the parameters on the system control performance, a Model-free predictive current control (MFPCC) algorithm based on current difference detection has been proposed.
The MFPCC algorithm replaces the model-based current prediction by employing the current state and the current difference at different switch states, which are stored in the current difference look-up table at the past time, without any motor parameters participating in the operation. However, the current forced updating method has the problem that the updating of the current difference lookup table is not neglected, and the existing forced updating method is to force and output one (or more) voltage vector(s) as the final vector of the driving motor when the voltage vector(s) is (are) detected not to be applied in a plurality of continuous sampling periods, but simultaneously sacrifice the optimal output of the cost function.
Disclosure of Invention
The technical problem is as follows: aiming at the problems, an improved permanent magnet synchronous motor three-level model-free prediction current control method is provided, full update of current difference in a sampling period is achieved, update frequency of the current difference can be effectively improved, and meanwhile calculation burden of a system is reduced by setting a vector candidate rule.
The technical scheme is as follows: an improved three-level model-free prediction current control method for a permanent magnet synchronous motor is characterized by comprising the following steps:
step 1: the electrical angle theta of the permanent magnet synchronous motor is obtained through an encoder, and the (k-1) time and the three-phase time at the k time are obtained through a current sensorStator current is(k-1) and is(k) And s is a, b and c, and then Clark conversion and Park conversion are carried out on the three-phase stator current to obtain a component i of the stator current at the (k-1) moment and the moment k on the dq axisd(k-1)、iq(k-1) and id(k)、iq(k)；
Step 2: determining the voltage vector V applied at time (k-1)kThe kind of (1) and the voltage collection number, thereby calculating the dq-axis current difference delta i corresponding to the basic voltage vector in each voltage collectiond|ViAnd Δ iq|ViThen, according to the relation among the current differences in each voltage collection set, the calculation of the dq axis current differences corresponding to all the voltage vectors is completed, and the updating of a current difference lookup table is realized;
and step 3: predicting dq axis currents in different switching states at (k +1) moment by combining a current prediction module and a current difference lookup table to obtain a predicted value id(k+1)|VjAnd iq(k+1)|Vj；
And 4, step 4: after the candidate vectors are set, different voltage vectors V are obtainedjValue function output g ofj＝{g1,g2,…,g27}; and finally, outputting the optimal switching state to drive the inverter through a midpoint potential balance module.
Further, in step 2, the dq-axis current difference Δ i corresponding to the basic voltage vector of each voltage combination setd|ViAnd Δ iq|ViThe calculation method comprises the following steps: first, the voltage vector V applied at the time of (k-1) is determined from Table 1kAnd determining its vector type:
TABLE 1
Category Voltage vectors
0 V25,V26,V27
1 V1,V2,V3,V13,V14,V15
2 V4,V16
3 V5,V6,V7,V17,V18,V19
4 V8,V20
5 V9,V10,V11,V21,V22,V23
6 V12,V24
If VkBelonging to the zero vector, then there is Δ id|V25、26、27＝δid0＝Δid|Sk-1，Δiq|V25、26、27＝δiq0＝Δiq|Sk-1(ii) a Wherein, δ id0、δiq0Represents the natural decay of the dq-axis current; Δ id|Sk-1And Δ iq|Sk-1Represents the dq-axis current difference under the action of the voltage vector at the time (k-1),
Figure BDA0003400906610000021
if VkIf the difference is small, the dq-axis current difference Δ i of the base voltage vector in the sum of all the voltage vectors is calculated according to equation (1)d|ViAnd Δ iq|ViIn which V isiIn particular V1、V4、V5、V8、V9、V12、V25；
Figure BDA0003400906610000022
Wherein, betadi、βqiRespectively representing a voltage vector ViThe included angle between the d axis and the q axis; beta is adk、βqkRespectively representing a voltage vector VkThe included angle between the d axis and the q axis; delta id|Vk、δiq|VkRepresenting a voltage vector VkThe forced response of the applied dq-axis current,
Figure BDA0003400906610000023
the parameter values are shown in table 2;
TABLE 2
Figure BDA0003400906610000031
In the table, VxRepresenting the amplitude coefficient between the characteristic voltage vectors;
if VkIf the voltage belongs to a large vector, the basic voltage vector V in the voltage combination set is calculated according to the formula (2)mCorresponding dq-axis current difference Δ id|VmAnd Δ iq|VmThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to the formula (3)d|ViAnd Δ iq|Vi；
Figure BDA0003400906610000032
Figure BDA0003400906610000033
Wherein, δ id|VmAnd δ iq|VmAre respectively a voltage vector VmForced response of the applied dq axis current;
if VkBelongs to the middle vector and is a basic vector, the dq-axis current difference delta i corresponding to the basic voltage vector in the sum of all the voltage vectors is directly calculated according to the formula (1)d|ViAnd Δ iq|Vi(ii) a If VkIf the voltage vector belongs to the middle vector but not to the basic vector, the basic voltage vector V in the voltage combination set is calculated according to the formula (4)nCorresponding dq-axis current difference Δ id|VnAnd Δ iq|VnThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to the equation (5)d|ViAnd Δ iq|Vi；
Figure BDA0003400906610000034
Figure BDA0003400906610000035
Wherein, δ id|VnAnd δ iq|VnAre respectively a voltage vector VnForced response of the applied dq-axis current.
Further, in step 2, the method for updating the current difference lookup table includes: after the dq-axis current differences corresponding to the basic voltage vectors of the voltage sets 1, 3 and 5 are obtained, the dq-axis current differences corresponding to other voltage vectors in the same set are calculated through a formula (6); the dq-axis current differences corresponding to all the other voltage vectors of the voltage sets 2, 4 and 6 are calculated by an equation (7); storing the calculated dq-axis current difference under different switch states into a current difference lookup table containing 27 different switch states, replacing original data in the table under the same switch state, and finishing updating the current difference lookup table;
Figure BDA0003400906610000041
Figure BDA0003400906610000042
wherein, the parameter a takes 1, 3 and 5, and the parameter b takes 2, 4 and 6, corresponding to the voltage vector serial number.
Further, the step 3 specifically includes: firstly, the dq axis current difference delta i under different switch states is obtained from a current difference lookup tabled|VjAnd Δ iq | Vj(ii) a Then, according to the formula (8), a predicted value i of the current of the dq axis in different switching states at the moment of (k +1) is calculatedd(k+1)|VjAnd iq(k+1)|Vj；
Figure BDA0003400906610000043
Further, in step 4, the vector candidate rule is: taking basic vectors in adjacent sectors of action vectors at the last sampling moment as alternative vectors, taking continuous jumping of only one-phase switch state in one sampling period as a second principle, screening small vectors, medium vectors and large vectors, and then completely supplementing the types of the small, medium, large and zero vectors of the screened vectors, wherein the number of the final alternative vectors is 6-9;
TABLE 3
Figure BDA0003400906610000044
Figure BDA0003400906610000051
Table 3 is the final candidate rule.
Has the advantages that: the permanent magnet synchronous motor based on the three-level inverter power supply has the advantages that the current prediction model based on the current difference lookup table is constructed, the motor parameters are prevented from participating in operation, the robustness of the parameters is improved, the method realizes the full update of the current difference in a period, and the update frequency of the current difference is effectively improved. Meanwhile, the adopted vector candidate method reduces the number of the candidate vectors to 6-9, thereby reducing the calculation burden of the system.
Drawings
FIG. 1 is a schematic diagram of three-level model-free predictive current control for a permanent magnet synchronous motor according to the present invention;
fig. 2 is a simulation diagram of q-axis current tracking performance of the MFPCC algorithm proposed in the present invention, where (a) of fig. 3 is a current tracking simulation under the condition of an accurate parameter (R ═ 5.25 ohms), and (b) of fig. 3 is a current tracking simulation under the condition of a resistance increase of 50% (R ═ 7.875 ohms);
fig. 3 shows three-phase current waveforms of the MFPCC algorithm proposed by the present invention.
Detailed Description
The present invention will be described in further detail below by way of examples with reference to the accompanying drawings, which are illustrative of the present invention and are not to be construed as limiting the present invention.
An improved three-level model-free prediction current control schematic diagram of a permanent magnet synchronous motor is shown in fig. 1 and comprises a rotating speed outer ring PI controller module 1, a minimum cost function module 2, a midpoint potential balance module 3, an inverter module 4, a permanent magnet synchronous motor module 5, an encoder module 6, a current difference calculation module 7, a current difference lookup table module 8 and a current prediction module 9.
As shown in fig. 2, the method comprises the following steps:
step 1: obtaining a reference q-axis current i at the moment of (k +1) according to a rotating speed outer ring PI controllerq ref(k+1)：
Will give a rotation speed Nr refAnd the actual rotational speed NrDifference e ofnSent to an outer ring PI controller of the rotating speedObtaining a reference q-axis current i at the time of (k +1) according to equation (1)q ref(k+1)：
Figure BDA0003400906610000061
Wherein k ispAnd kiRespectively, proportional gain and integral gain of the rotating speed PI controller, and s is a complex variable.
Step 2: acquiring an electrical angle theta of the permanent magnet synchronous motor from the encoder; and then measuring three-phase stator current i of the permanent magnet synchronous motor at the (k-1) moment and the k moment respectively by using a current sensors(k-1) and is(k) And s is a, b and c, and the alpha and beta axis components i of the stator current at the time (k-1) and the time k are obtained after Clark conversion of the formula (2)α(k-1)、iβ(k-1) and iα(k)、iβ(k) And then obtaining dq axis component i of stator current at the time of (k-1) and the time of k through Park conversion of formula (3)d(k-1)、iq(k-1) and id(k)、iq(k)；
Figure BDA0003400906610000062
Figure BDA0003400906610000063
And step 3: determining the voltage vector V applied at time (k-1) from Table 1kAnd determining its vector type:
TABLE 1
Category Voltage vectors
0 V25,V26,V27
1 V1,V2,V3,V13,V14,V15
2 V4,V16
3 V5,V6,V7,V17,V18,V19
4 V8,V20
5 V9,V10,V11,V21,V22,V23
6 V12,V24
If VkBelonging to the zero vector, the corresponding dq axis current difference is respectively delta id|V25、26、27＝δid0＝Δid|Sk-1，Δiq|V25、26、27＝δiq0＝Δiq|Sk-1(ii) a Wherein, δ id0、δiq0Represents the natural decay of the dq-axis current; Δ id|Sk-1And Δ iq|Sk-1Represents the dq-axis current difference under the action of the voltage vector at the time (k-1),
Figure BDA0003400906610000064
if VkIf the difference is small, the dq-axis current difference Δ i of the base voltage vector in the sum of all the voltage vectors is calculated according to equation (4)d|ViAnd Δ iq|ViIn which V isiIn particular V1、V4、V5、V8、V9、V12、V25；
Figure BDA0003400906610000071
Wherein, betadi、βqiRespectively representing a voltage vector ViThe included angle between the d axis and the q axis; beta is adk、βqkRespectively representing a voltage vector VkThe included angle between the d axis and the q axis; in the formula Vi、VkRespectively represent a vector ViAnd VkThe amplitude coefficient of (d), δ id|Vk、δiq|VkRepresenting a voltage vector VkThe forced response of the applied dq-axis current,
Figure BDA0003400906610000072
the parameter values are shown in table 2;
TABLE 2
Figure BDA0003400906610000073
In the table, VxRepresenting the amplitude coefficient between the characteristic voltage vectors;
if VkIf the voltage vector belongs to a large vector, the dq axis current difference delta i corresponding to the basic voltage vector in the voltage combination set is calculated according to the formula (5)d|VmAnd Δ iq|VmThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to the equation (6)d|ViAnd Δ iq|Vi；
Figure BDA0003400906610000074
Figure BDA0003400906610000075
Wherein, δ id|VmAnd δ iq|VmAre respectively a voltage vector VmForced response of the applied dq axis current;
if VkBelongs to the middle vector and is a basic vector, the dq-axis current difference delta i corresponding to the basic voltage vector in the sum of all the voltage vectors is directly calculated according to the formula (4)d|ViAnd Δ iq|Vi(ii) a If VkIf the voltage vector belongs to the middle vector but not to the basic vector, the basic voltage vector V in the voltage combination set is calculated according to the formula (7)nCorresponding dq-axis current difference Δ id|VnAnd Δ iq|VnThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to equation (8)d|ViAnd Δ iq|Vi；
Figure BDA0003400906610000081
Figure BDA0003400906610000082
Wherein, δ id|VnAnd δ iq|VnAre respectively a voltage vector VnForced response of the applied dq-axis current.
And 4, step 4: after the dq-axis current differences corresponding to the basic voltage vectors of the voltage sets 1, 3 and 5 are obtained, the dq-axis current differences corresponding to other voltage vectors in the same set are calculated through a formula (9); the dq-axis current differences corresponding to all the other voltage vectors of the voltage sets 2, 4 and 6 are calculated by an equation (10); and storing the calculated dq-axis current difference under different switch states into a current difference lookup table containing 27 different switch states, replacing the original data of the same switch state in the lookup table, and finishing updating the current difference lookup table.
Figure BDA0003400906610000083
Figure BDA0003400906610000084
Wherein, the parameter a takes 1, 3 and 5, and the parameter b takes 2, 4 and 6, corresponding to the voltage vector serial number.
And 5: obtaining dq axis current difference delta i under different switch states from a current difference lookup tabled|VjAnd Δ id|Vj(ii) a Then, a predicted value i of the current of the dq axis in different switching states at the moment (k +1) is calculated according to the formula (11)d(k+1)|VjAnd iq(k+1)|Vj。
Figure BDA0003400906610000085
Step 6: considering the basic vector in the adjacent sector of the action vector at the previous sampling moment as the candidate vector, and taking the continuous jump of only one-phase switch state in one sampling period as the second principle, screening small, medium and large vectors, and then supplementing the types of the small, medium, large and zero vectors of the screened vector completely to improve the accuracy of the optimal vector selection, wherein the number of the final candidate vectors is 6-9, and Table 3 shows that
Vector Pre-selection Vector Pre-selection
V1 V1 V3 V4 V5 V21 V24 V26 V15 V11 V12 V14 V15 V16 V19 V26
V2 V2 V3 V4 V6 V7 V22 V23 V24 V26 V16 V12 V13 V15 V16 V18 V19 V20 V26
V3 V1 V3 V4 V7 V23 V24 V26 V17 V13 V16 V17 V19 V20 V21 V26
V4 V1 V3 V4 V5 V7 V8 V24 V26 V18 V14 V15 V16 V18 V19 V20 V22 V23 V26
V5 V1 V3 V4 V5 V7 V8 V9 V11 V26 V19 V15 V16 V17 V19 V20 V23 V26
V6 V2 V4 V6 V7 V8 V10 V26 V20 V16 V18 V19 V20 V21 V23 V24 V26
V7 V3 V4 V6 V7 V8 V11 V26 V21 V1 V3 V17 V19 V20 V21 V23 V24 V26
V8 V4 V5 V7 V8 V10 V11 V12 V26 V22 V2 V18 V20 V22 V23 V24 V26
V9 V5 V8 V9 V11 V12 V13 V26 V23 V3 V19 V20 V22 V23 V24 V26
V10 V6 V7 V8 V10 V11 V12 V14 V15 V26 V24 V2 V3 V4 V20 V21 V23 V24 V26
V11 V7 V8 V9 V11 V12 V15 V26 V25 V1 V3 V9 V17 V25
V12 V8 V10 V11 V12 V13 V15 V16 V26 V26 V2 V4 V5 V10 V13 V18 V21 V26
V13 V9 V11 V12 V13 V15 V16 V17 V19 V26 V27 V6 V14 V15 V22 V25
V14 V10 V12 V14 V15 V16 V18 V26
The method firstly obtains three-phase stator current i at (k-1) time and k times(k-1) and is(k) S ═ a, b, c, rotor electrical angle θ; then obtaining a reference q-axis current i at the moment (k +1) through a PI controllerq ref(k +1) and given a d-axis current reference id refStep 2, when (k +1) ═ 0, component i of stator current on dq axis at time (k-1) and time k is obtainedd(k-1)、iq(k-1) and id(k)、iq(k) (ii) a Calculating the dq-axis current difference corresponding to the basic voltage of each voltage vector set through the step 3; then updating the current difference lookup table through the step 4; calculating a predicted value of the dq axis current at the time of k +1 by combining the current difference lookup table updated in the step 4 in the step 5, and outputting a basic voltage vector u which minimizes the cost function by performing rolling optimization in the step 6min；
An improved three-level model-free prediction current control simulation result of the permanent magnet synchronous motor is shown in fig. 2 and fig. 3. From (a) of fig. 2, it can be seen that the actual current can well track the reference current under the condition of accurate motor parameters, and from (b) of fig. 2, the MFPCC method provided by the invention can keep good q-axis current tracking performance all the time because no motor parameter is needed to participate in the operation. Fig. 3 shows three-phase current waveforms, and it can be seen that the current positive limit is good.
The foregoing is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, various modifications and decorations can be made without departing from the principle of the present invention, and these modifications and decorations should also be regarded as the protection scope of the present invention.

Claims (5)

1. An improved three-level model-free prediction current control method for a permanent magnet synchronous motor is characterized by comprising the following steps:
step 1: the electrical angle theta of the permanent magnet synchronous motor is obtained through an encoder, and the three-phase stator current i at the (k-1) moment and the k moment is obtained through a current sensors(k-1) and is(k) And s is a, b and c, and then Clark conversion and Park conversion are carried out on the three-phase stator current to obtain a component i of the stator current at the (k-1) moment and the moment k on the dq axisd(k-1)、iq(k-1) and id(k)、iq(k)；
Step 2: determining the voltage vector V applied at time (k-1)kThe kind of (1) and the voltage collection number, thereby calculating the dq-axis current difference delta i corresponding to the basic voltage vector in each voltage collectiond|ViAnd Δ iq|ViThen, according to the relation among the current differences in each voltage collection set, the calculation of the dq axis current differences corresponding to all the voltage vectors is completed, and the updating of a current difference lookup table is realized;
and step 3: predicting dq axis currents in different switching states at (k +1) moment by combining a current prediction module and a current difference lookup table to obtain a predicted value id(k+1)|VjAnd iq(k+1)|Vj；
And 4, step 4: after the candidate vectors are set, different voltage vectors V are obtainedjValue function output g ofj＝{g1,g2,…,g27}; and finally, outputting the optimal switching state to drive the inverter through a midpoint potential balance module.
2. The improved PMSM three-level model-free predictive current control method as claimed in claim 1, wherein in step 2, the dq-axis current difference Δ i corresponding to the base voltage vector in each voltage combination setd|ViAnd Δ iq|ViThe calculation method comprises the following steps: first, the voltage vector V applied at the time of (k-1) is determined from Table 1kAnd determining its vector type:
TABLE 1
Category Voltage vectors 0 V25,V26,V27 1 V1,V2,V3,V13,V14,V15 2 V4,V16 3 V5,V6,V7,V17,V18,V19 4 V8,V20 5 V9,V10,V11,V21,V22,V23 6 V12,V24
If VkBelonging to the zero vector, then there is Δ id|V25、26、27＝δid0＝Δid|Sk-1，Δiq|V25、26、27＝δiq0＝Δiq|Sk-1(ii) a Wherein, δ id0、δiq0Represents the natural decay of the dq-axis current; Δ id|Sk-1And Δ iq|Sk-1Represents the dq-axis current difference under the action of the voltage vector at the time (k-1),
Figure FDA0003400906600000011
if VkIf the difference is small, the dq-axis current difference Δ i of the base voltage vector in the sum of all the voltage vectors is calculated according to equation (1)d|ViAnd Δ iq|ViIn which V isiIn particular V1、V4、V5、V8、V9、V12、V25；
Figure FDA0003400906600000021
Wherein, betadi、βqiRespectively representing a voltage vector ViThe included angle between the d axis and the q axis; beta is adk、βqkRespectively representing a voltage vector VkThe included angle between the d axis and the q axis; delta id|Vk、δiq|VkRepresenting a voltage vector VkThe forced response of the applied dq-axis current,
Figure FDA0003400906600000022
the parameter values are shown in table 2;
TABLE 2
Figure FDA0003400906600000023
In the table, VxRepresenting the amplitude coefficient between the characteristic voltage vectors;
if VkIf the voltage belongs to a large vector, the basic voltage vector V in the voltage combination set is calculated according to the formula (2)mCorresponding dq-axis current difference Δ id|VmAnd Δ iq|VmThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to the formula (3)d|ViAnd Δ iq|Vi；
Figure FDA0003400906600000024
Figure FDA0003400906600000025
Wherein, δ id|VmAnd δ iq|VmAre respectively a voltage vector VmForced response of the applied dq axis current;
if VkBelongs to the middle vector and is a basic vector, the dq-axis current difference delta i corresponding to the basic voltage vector in the sum of all the voltage vectors is directly calculated according to the formula (1)d|ViAnd Δ iq|Vi(ii) a If VkIf the vector belongs to the middle vector but not to the basic vector, the formula is firstly shown(4) Calculating the basic voltage vector V of the voltage combination setnCorresponding dq-axis current difference Δ id|VnAnd Δ iq|VnThen, the dq-axis current difference Δ i corresponding to the base voltage vector in the total set of all the voltage vectors is calculated according to the equation (5)d|ViAnd Δ iq|Vi；
Figure FDA0003400906600000031
Figure FDA0003400906600000032
Wherein, δ id|VnAnd δ iq|VnAre respectively a voltage vector VnForced response of the applied dq-axis current.
3. The improved three-level model-free predictive current control method for the permanent magnet synchronous motor according to claim 2, wherein in the step 2, the method for updating the current difference lookup table is as follows: after the dq-axis current differences corresponding to the basic voltage vectors of the voltage sets 1, 3 and 5 are obtained, the dq-axis current differences corresponding to other voltage vectors in the same set are calculated through a formula (6); the dq-axis current differences corresponding to all the other voltage vectors of the voltage sets 2, 4 and 6 are calculated by an equation (7); storing the calculated dq-axis current difference under different switch states into a current difference lookup table containing 27 different switch states, replacing original data in the table under the same switch state, and finishing updating the current difference lookup table;
Figure FDA0003400906600000033
Figure FDA0003400906600000034
wherein, the parameter a takes 1, 3 and 5, and the parameter b takes 2, 4 and 6, corresponding to the voltage vector serial number.
4. The improved three-level model-free predictive current control method for the permanent magnet synchronous motor according to claim 2, wherein the step 3 specifically comprises: firstly, the dq axis current difference delta i under different switch states is obtained from a current difference lookup tabled|VjAnd Δ iq | Vj(ii) a Then, according to the formula (8), a predicted value i of the current of the dq axis in different switching states at the moment of (k +1) is calculatedd(k+1)|VjAnd iq(k+1)|Vj；
Figure FDA0003400906600000041
5. The improved three-level model-free predictive current control method for the permanent magnet synchronous motor according to claim 1, wherein in step 4, the vector candidate rule is as follows: taking basic vectors in adjacent sectors of action vectors at the last sampling moment as alternative vectors, taking continuous jumping of only one-phase switch state in one sampling period as a second principle, screening small vectors, medium vectors and large vectors, and then completely supplementing the types of the small, medium, large and zero vectors of the screened vectors, wherein the number of the final alternative vectors is 6-9;
TABLE 3
Vector Pre-selection Vector Pre-selection V1 V1 V3 V4 V5 V21 V24 V26 V15 V11 V12 V14 V15 V16 V19 V26 V2 V2 V3 V4 V6 V7 V22 V23 V24 V26 V16 V12 V13 V15 V16 V18 V19 V20 V26 V3 V1 V3 V4 V7 V23 V24 V26 V17 V13 V16 V17 V19 V20 V21 V26 V4 V1 V3 V4 V5 V7 V8 V24 V26 V18 V14 V15 V16 V18 V19 V20 V22 V23 V26 V5 V1 V3 V4 V5 V7 V8 V9 V11 V26 V19 V15 V16 V17 V19 V20 V23 V26 V6 V2 V4 V6 V7 V8 V10 V26 V20 V16 V18 V19 V20 V21 V23 V24 V26 V7 V3 V4 V6 V7 V8 V11 V26 V21 V1 V3 V17 V19 V20 V21 V23 V24 V26 V8 V4 V5 V7 V8 V10 V11 V12 V26 V22 V2 V18 V20 V22 V23 V24 V26 V9 V5 V8 V9 V11 V12 V13 V26 V23 V3 V19 V20 V22 V23 V24 V26 V10 V6 V7 V8 V10 V11 V12 V14 V15 V26 V24 V2 V3 V4 V20 V21 V23 V24 V26 V11 V7 V8 V9 V11 V12 V15 V26 V25 V1 V3 V9 V17 V25 V12 V8 V10 V11 V12 V13 V15 V16 V26 V26 V2 V4 V5 V10 V13 V18 V21 V26 V13 V9 V11 V12 V13 V15 V16 V17 V19 V26 V27 V6 V14 V15 V22 V25 V14 V10 V12 V14 V15 V16 V18 V26
Table 3 is the final candidate rule.
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