CN113315440A - Permanent magnet synchronous motor model-free prediction current control method based on current difference full update - Google Patents

Abstract

The invention relates to a permanent magnet synchronous motor model-free predictive current control method based on current difference full update, which comprises the steps of firstly obtaining three-phase current at the moment k, the electrical angle of a rotor, given rotating speed, three-phase current at the moment k-1 and the switching state; then, calculating the dq-axis current difference of the action vector in the kth sampling period, calculating the dq-axis current difference corresponding to all basic voltage vectors according to the relation of the corresponding current differences of the projection of different basic voltage vectors to a rotating coordinate system, 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 does not need the parameters of resistance, flux linkage and inductance to participate in the operation, can effectively reduce the influence of model mismatch on the system performance, and can fully calculate the current difference in one sampling period, thereby effectively improving the updating frequency of the current difference.

Description

Permanent magnet synchronous motor model-free prediction current control method based on current difference full update

Technical Field

The invention relates to a permanent magnet synchronous motor model-free prediction current control method based on current difference full update, and belongs to the field of motor driving and control.

Background

The Model Predictive Current Control (MPCC) directly selects the optimal switching state by minimizing the cost function, thereby ensuring good current tracking performance and having the advantages of high response speed, multi-objective optimization, simple principle and the like. However, the current tracking accuracy of the MPCC strategy mainly depends on accurate motor parameters including stator resistance, dq-axis inductance and permanent magnet flux linkage, however, in practical application, the motor parameters are difficult to accurately obtain, and can also change along with the change of an 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 model-based current prediction by adopting current differences and current states at different switching states, which are stored in a current difference lookup table at past moments, and does not need any motor parameter to participate in operation, so that the MFPCC algorithm has strong parameter robustness. However, stable operation of the MFPCC algorithm relies on high precision current differences, and therefore requires a higher current difference update frequency.

Disclosure of Invention

The technical problem is as follows: aiming at the problems, the model-free prediction current control method of the permanent magnet synchronous motor based on the current difference full update is provided, the full update of the current difference in a period can be realized on the premise of ensuring the optimal output of the cost function, and the update frequency of the current difference is effectively improved.

The technical scheme is as follows: a permanent magnet synchronous motor model-free prediction current control method based on current difference full update comprises the following steps:

step 1: will give a rotation speed N_r ^refAnd the actual rotational speed N_rObtaining a q-axis reference current i at the moment of (k +1) through a rotating speed outer ring PI controller_q ^ref(k +1) and giving a d-axis reference current i_d ^ref(k+1)＝0；

Step 2: obtaining the electrical angle theta of the permanent magnet synchronous motor through an encoder, and obtaining three-phase stator current i at the (k-1) moment and the k moment_s(k-1) and i_s(k) And c, performing Clark conversion and Park conversion on the three-phase stator current to obtain the stator electricity at the time (k-1) and the time kComponent i of the flow in dq axis_d(k-1)、i_q(k-1) and i_d(k)、i_q(k)；

And step 3: obtaining the dq axis current difference delta i under the action of the (k-1) moment basic voltage vector by using a current difference calculation module_d|S_k-1、Δi_q|S_k-1Calculating the dq axis current differences corresponding to all basic voltage vectors according to the relation of the corresponding current differences projected onto the dq coordinate system, and updating a current difference lookup table;

and 4, step 4: 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 i_d(k+1)|S_j、i_q(k+1)|S_j；

And 5: the base voltage vector that minimizes the cost function is output by rolling optimization.

Has the advantages that: the method is based on the permanent magnet synchronous motor, constructs a current prediction model based on a current difference lookup table, avoids motor parameters from participating in operation, improves the robustness of the parameters, simultaneously realizes the full update of the current difference in a period, effectively improves the update frequency of the current difference and avoids the influence caused by the update stagnation of the current difference.

Drawings

FIG. 1 is a schematic diagram of model-free predictive current control for a PMSM according to the present invention;

FIG. 2 is a space voltage vector projection diagram of the inverter provided by the present invention;

FIG. 3 is a q-axis current tracking performance simulation diagram of the MFPCC algorithm provided by the present invention, (a) is a current tracking simulation under the condition of accurate parameters, and (b) is a current tracking simulation under the condition of increasing the resistance by 50%;

fig. 4 shows a phase a current waveform 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.

A permanent magnet synchronous motor model-free prediction current control method based on current difference full update is shown in a schematic diagram of fig. 1 and comprises a rotating speed outer ring PI controller module 1, a minimum cost function module 2, an inverter module 3, a permanent magnet synchronous motor module 4, an encoder module 5, a current difference calculation module 6, a current difference lookup table module 7 and a current prediction module 8.

As shown in fig. 2, the method comprises the following steps:

step 1: obtaining a q-axis reference current i at the moment of (k +1) according to a rotating speed outer ring PI controller_q ^ref(k+1)：

Will give a rotation speed N_r ^refAnd the actual rotational speed N_rDifference e of_nSending the reference current to a rotating speed outer ring PI controller, and obtaining a q-axis reference current i at the moment of (k +1) according to a formula (1)_q ^ref(k+1)：

Wherein k is_pAnd k_iRespectively, 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 through an 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 sensor_s(k-1) and i_s(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)、i_β(k-1) and i_α(k)、i_β(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)、i_q(k-1) and i_d(k)、i_q(k)；

And step 3: obtaining the dq axis current difference delta i under the action of the (k-1) moment basic voltage vector by using a current difference calculation module_d|S_k-1、Δi_q|S_k-1And calculating the dq axis current difference corresponding to all the basic voltage vectors according to the relation of the corresponding current difference projected onto the dq coordinate system, and updating the current difference lookup table.

Wherein, the dq axis current difference delta i under the action of the (k-1) moment basic voltage vector_d|S_k-1、Δi_q|S_k-1Is obtained by calculation of formula (4), S_k-1Indicating the switch state at time (k-1). The method for calculating the dq-axis current difference corresponding to all the basic voltage vectors according to the relation of the corresponding current difference projected onto the dq coordinate system is as follows:

step A: the switch states corresponding to the zero vector are respectively S₇、S₈Judgment S_k-1Whether the corresponding basic voltage vector is a zero vector or not is judged, if yes, the dq-axis current difference corresponding to other basic voltage vectors is not calculated, and if not, the next step is executed;

and B: the action effect of the basic voltage vector is divided into two parts according to the formula (5), namely the natural attenuation delta i of the dq axis current under the action of the zero vector_d0、δi_q0Forced response delta i of dq axis current under action of active vector_d|S_j、δi_q|S_jWhen S is_j＝S₇，S₈Time delta i_d|S_j＝0、δi_q|S_j＝0；

And C: v_jJ-0, 1,2 … 7 corresponds to the voltage vector under 8 switches, as shown in fig. 2, and then 6 non-zero basic voltage vectors are divided into voltage set 1: v₁,V₂,V₃And voltage set 2: v₄,V₅,V₆(ii) a When S is_k-1When the corresponding basic voltage vector belongs to the voltage collection 1, calculating and synthesizing the dq-axis current difference corresponding to the basic voltage vector on the static coordinate system according to the formula (6); delta i can be obtained by the formula (5)_x|V_jAnd u_x|V_jBetweenThe voltage set 1 satisfies the formula (7), so S is the time when S is equal to S_k-1The corresponding basic voltage vector is V₁Then, the current difference corresponding to other basic voltages in the voltage collection 1 can be calculated according to the formula (8); all right of the way to S_k-1The corresponding basic voltage vector is V₂、V₃Then, the current difference corresponding to other basic voltages in the voltage collection 1 can be calculated according to the formulas (9-1) and (9-2); meanwhile, the current difference corresponding to the basic voltage in the voltage collection 2 can be calculated according to the formula (10);

step D: when S is_k-1When the corresponding basic voltage vector belongs to the voltage set 2, calculating and synthesizing the dq-axis current difference corresponding to the basic voltage vector on the static coordinate system according to the formula (11); when S is_k-1The corresponding basic voltage vectors are respectively V₆、V₅、V₄Then, the current difference corresponding to other basic voltages in the voltage collection 2 can be calculated according to the formulas (12-1), (12-2) and (12-3); meanwhile, the current difference corresponding to the basic voltage in the voltage collection 1 can be calculated according to the formula (13);

Δi|V_1-1＝Δi|V_1-2＝Δi|V_1-3 (7)

wherein, Δ i_d|S_j、Δi_q|S_jAre respectively in the on-off state S_j(ii) a dq-axis current difference under influence; i.e. i_d、i_qThe components of the stator current in the dq axis respectively; l is_d、L_qThe inductance components of the dq axes, respectively; psi_fIs a permanent magnet flux linkage; r represents a stator resistance; t is_sRepresents a sampling period; omega_eRepresenting the electrical angular velocity, ω_e＝dθ/dt；u_d|S_jAnd u_q|S_jRespectively representing the switch states S_jAn applied dq axis stator voltage component; s_jRepresents the switch state, j ═ 1,2, …, 8; Δ i_d|V_j、Δi_q|V_jIndicating the switching state V_jApplied dq-axis current difference, j ═ 1,2, …, 8; theta is an electrical angle; Δ i | V_n-jRepresenting vector V in collection of voltages n_jThe corresponding current difference.

Step E: and storing the calculated dq-axis current difference under different switch states into a current difference lookup table containing 8 different switch states, replacing the original data of the same switch state in the lookup table, and finishing updating the current difference lookup table.

And 4, step 4: 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 i_d(k+1)|S_j、i_q(k+1)|S_j；

And 5: outputting a base voltage vector u that minimizes a cost function by rolling optimization of the cost function_minThe specific method comprises the following steps: firstly, i is_d ^ref(k+1)、i_q ^ref(k+1)、i_d(k+1)|S_jAnd i_q(k+1)|S_jInto a cost function (14) to obtain different S_jValue function output g of_j＝{g₁,g₂,…,g₈}; then, the minimized cost function output g is obtained by equation (15)_minThen u is_minI.e. satisfy g_minThe basic voltage vector of (2).

g_min＝min{g₁,g₂,...,g₂₇} (15)

Firstly, obtaining three-phase stator current i at (k-1) time and k time_s(k-1) and i_s(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 controller_q ^ref(k +1) and given a d-axis current reference i_d ^refStep 2, when (k +1) ═ 0, component i of stator current on dq axis at time (k-1) and time k is obtained_d(k-1)、i_q(k-1) and i_d(k)、i_q(k) (ii) a Then updated through step 3A current difference look-up table; calculating a predicted value of the dq axis current at the (k +1) moment by combining the current difference lookup table updated in the step (3) through the step (4), substituting the predicted value into the cost function in the step (5), performing rolling optimization, and outputting a basic voltage vector u which minimizes the cost function_min。

The simulation results of the model-free prediction current control of the permanent magnet synchronous motor based on the total current difference updating are shown in fig. 3 and 4. From (a) of fig. 3, 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. 3, 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. 4 shows the waveform of the a-phase current, 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 (2)

1. A permanent magnet synchronous motor model-free prediction current control method based on current difference full update is characterized by comprising the following steps:

step 1: will give a rotation speed N_r ^refAnd the actual rotational speed N_rObtaining a q-axis reference current i at the moment of (k +1) through a rotating speed outer ring PI controller_q ^ref(k +1) and giving a d-axis reference current i_d ^ref(k+1)＝0；

Step 2: obtaining the electrical angle theta of the permanent magnet synchronous motor through an encoder, and obtaining three-phase stator current i at the (k-1) moment and the k moment_s(k-1) and i_s(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 moment (k-1) and the moment k on the dq axis_d(k-1)、i_q(k-1) and i_d(k)、i_q(k)；

And step 3: obtaining a basic voltage vector at the moment (k-1) by using a current difference calculation moduleDq-axis current difference Δ i by quantity_d|S_k-1、Δi_q|S_k-1Calculating the dq axis current differences corresponding to all basic voltage vectors according to the relation of the corresponding current differences projected onto the dq coordinate system, and updating a current difference lookup table;

and 4, step 4: 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 i_d(k+1)|S_j、i_q(k+1)|S_j；

And 5: the base voltage vector that minimizes the cost function is output by rolling optimization.

2. The method for model-free predictive current control of the PMSM based on current difference full update as claimed in claim 1, wherein in step 3, the dq-axis current difference Δ i under the action of the (k-1) time basic voltage vector_d|S_k-1、Δi_q|S_k-1Is obtained by calculation of formula (1), S_k-1Represents the switch state at the time (k-1);

the method for calculating the dq-axis current difference corresponding to all the basic voltage vectors according to the relation of the corresponding current difference projected onto the dq coordinate system comprises the following steps:

step A: the switch states corresponding to the zero vector are respectively S₇、S₈Judgment S_k-1Whether the corresponding basic voltage vector is a zero vector or not is judged, if yes, the dq-axis current difference corresponding to other basic voltage vectors is not calculated, and if not, the next step is executed;

and B: the action effect of the basic voltage vector is divided into two parts according to the formula (2), namely the natural attenuation delta i of the dq axis current under the action of the zero vector_d0、δi_q0Forced response delta i of dq axis current under action of active vector_d|S_j、δi_q|S_jWhen S is_j＝S₇，S₈Time delta i_d|S_j＝0、δi_q|S_j＝0；

Wherein, Δ i_d|S_j、Δi_q|S_jAre respectively in the on-off state S_j(ii) a dq-axis current difference under influence; s_jRepresents the switch state, j ═ 1,2, …, 8; r represents a stator resistance; omega_eRepresenting the electrical angular velocity, ω_eD θ/dt; theta is an electrical angle; i.e. i_d、i_qThe components of the stator current in the dq axis respectively; l is_d、L_qThe inductance components of the dq axes, respectively; psi_fIs a permanent magnet flux linkage; t is_sRepresents a sampling period; u. of_d|S_j、u_q|S_jRespectively representing the switch states S_jAn applied dq axis stator voltage component;

and C: divide 6 non-zero basis voltage vectors into a collection of voltages 1: v₁,V₂,V₃And voltage set 2: v₄,V₅,V₆(ii) a When S is_k-1When the corresponding basic voltage vector belongs to the voltage collection 1, calculating and synthesizing the dq-axis current difference corresponding to the basic voltage vector on the static coordinate system according to the formula (3);

wherein, Δ i | V_1-1、Δi|V_1-2、Δi|V_1-3Respectively representing the vector V in the voltage set 1₁,V₂,V₃A corresponding current difference;

obtaining δ i by the formula (2)_x|V_jAnd u_x|V_jThe current difference corresponding to the voltage set 1 satisfies the formula (4), δ i_x|V_jAnd u_x|V_jRespectively represent a vector V_jCorresponding dq-axis forced response and dq-axis determinationA sub-voltage, x ═ d, q;

Δi|V_1-1＝Δi|V_1-2＝Δi|V_1-3 (4)

so when S_k-1The corresponding basic voltage vector is V₁Then, the current difference corresponding to other basic voltages in the voltage collection 1 is calculated according to the formula (5);

all right of the way to S_k-1The corresponding basic voltage vector is V₂、V₃Then, the current difference corresponding to other basic voltages in the voltage collection 1 is calculated according to the formulas (6-1) and (6-2);

meanwhile, the current difference corresponding to the basic voltage in the voltage collection 2 is calculated according to the formula (7);

wherein, Δ i_d|V_j、Δi_q|V_jIndicating the switching state V_jApplied dq-axis current difference, j ═ 1,2, …, 8;

step D: when S is_k-1When the corresponding basic voltage vector belongs to the voltage collection 2, calculating and synthesizing the dq-axis current difference corresponding to the basic voltage vector on the static coordinate system according to the formula (8);

wherein, Δ i | V_2-6、Δi|V_2-5、Δi|V_2-4Respectively representing vector V in voltage set 2₆,V₅,V₄A corresponding current difference; (ii) a

When S is_k-1The corresponding basic voltage vectors are respectively V₆、V₅、V₄Then, the current difference corresponding to other basic voltages in the voltage collection 2 is calculated according to the formulas (9-1), (9-2) and (9-3);

meanwhile, the current difference corresponding to the basic voltage in the voltage collection 1 is calculated according to the formula (10);

step E: and storing the calculated dq-axis current difference under different switch states into a current difference lookup table containing 8 different switch states, replacing the original data of the same switch state in the lookup table, and finishing updating the current difference lookup table.

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