Improved dual vector model predictive permanent magnet synchronous motor flux linkage control method

Abstract

The application discloses an improved double-vector model prediction permanent magnet synchronous motor flux linkage control method. Firstly, the first optimal voltage vector, two adjacent effective voltage vectors and a zero voltage vector are taken as the candidate voltage vectors of the second optimal voltage vector, the global optimal voltage vector combination is obtained through the second optimal voltage vector selection table and the selection rule, instead of only selecting the first optimal voltage vector and the second optimal voltage vector as the local optimal voltage vector combination of the zero voltage vector, so as to reduce the stator flux linkage ripple; then, a new duty cycle calculation method is proposed by defining the stator flux linkage deviation factor, and the calculation burden of the system is reduced. Compared with the traditional duty cycle model prediction flux linkage control algorithm, the application improves the local optimality of the optimal voltage vector combination obtained in the control method, the larger stator flux linkage ripple and other defects.

Description

Technical Field

[0001] This invention relates to the field of control technology for permanent magnet synchronous motors, and in particular to an improved dual-vector model predictive method for flux linkage control of permanent magnet synchronous motors. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs) possess advantages such as simple structure, high power density, and strong control performance, making them widely applicable. Different control algorithms for PMSMs, including vector control, direct torque control, sliding mode control, nonlinear control, and model predictive control, have been studied to address various control objectives. Currently, model predictive flux linkage control, as a control method based on a motor model, offers advantages such as fast dynamic response and ease of adding constraints to the cost function, and has been successfully applied in the field of PMSM drives.

[0003] Traditional single-vector model predictive flux control uses only one voltage vector per control cycle, making it difficult to achieve error-free prediction. This is especially true at low motor speeds, where the voltage vector amplitude is small, causing the optimal voltage vector evaluated through the cost function to frequently switch between the effective and zero voltage vectors. This leads to large stator flux and electromagnetic torque ripples, as well as high phase current harmonic distortion, thus reducing the system's predictive flux accuracy. While increasing the sampling frequency can improve the steady-state performance of the control system, the improvement is limited by the computational capabilities of microcontrollers such as DSPs.

[0004] To further improve the steady-state performance of model predictive flux control, duty cycle control is introduced. Duty cycle control first selects the voltage vector that minimizes the cost function as the optimal voltage vector, and then calculates the duration of this voltage vector based on the deadbeat principle. The remaining time of the control cycle is the zero voltage vector. This strategy can improve the motor's control performance and reduce stator flux pulsation during steady-state operation. However, most existing algorithms use a cascade method to select the effective voltage vector and calculate its duration. The resulting optimal voltage vector combination is only locally optimal, not globally optimal, and the improvement in control performance is not ideal. Furthermore, generalized two-vector and three-vector control methods are introduced. Although these methods significantly improve performance, they increase the computational burden of the system.

[0005] To address the aforementioned issues, this invention proposes an improved dual-vector model predictive flux linkage control method for permanent magnet synchronous motors, based on the traditional duty cycle model predictive flux linkage control algorithm. By rationally selecting the two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector as candidate voltage vectors for the second optimal voltage vector, a globally optimal voltage vector combination is determined. This method can more effectively reduce stator flux linkage pulsation while simultaneously reducing the computational burden of the system. Summary of the Invention

[0006] The purpose of this invention is to determine the globally optimal voltage vector combination to reduce stator flux pulsation, and to propose an improved dual-vector model predictive method for flux control of permanent magnet synchronous motors, thereby improving the steady-state performance of permanent magnet synchronous motor systems.

[0007] An improved dual-vector model predictive flux linkage control method for permanent magnet synchronous motors is characterized by using the two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector as candidate voltage vectors for the second optimal voltage vector. The global optimal voltage vector combination is obtained through the second optimal voltage vector selection table and its selection rules, rather than only selecting the local optimal voltage vector combination of the first and second optimal voltage vectors as the zero voltage vector, in order to reduce stator flux linkage pulsation.

[0008] Its specific characteristics are as follows:

[0009] The two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector are used as candidate voltage vectors for the second optimal voltage vector. The stator flux deviation factor δ is defined. i for

[0010]

[0011] In the formula, ψ s (k+2) is (k+2)T s The predicted value of the stator flux linkage at time t. It is the stator flux reference value, and the subscript i corresponds to the stator flux deviation factor of the i-th (i = 0, 1, ..., 7) voltage vector acting on the motor;

[0012] Define δ opt , δ0, δ opt+1 and δ opt-1 The first optimal voltage vector u is respectively opt The zero voltage vector u0 and the two adjacent effective voltage vectors u of the first optimal voltage vector. opt+1 and u opt-1 The stator flux deviation factor is defined by the following three stator flux determination coefficients:

[0013]

[0014] Based on the positive and negative relationships of the three stator flux linkage determination coefficients, a second optimal voltage vector selection table is established as shown in the table below.

[0015] Table 1. Second Optimal Voltage Vector Selection Table

[0016]

[0017] The selection rule for the second optimal voltage vector is as follows:

[0018] (1) When the stator flux linkage determination coefficient λ ψ1 , λ ψ2 and λ ψ0 When both values ​​are greater than 0, there is no voltage vector among the candidate voltage vectors for the second optimal voltage vector that satisfies the requirement of reducing stator flux pulsation. Therefore, the first optimal voltage vector is still selected as the second optimal voltage vector, meaning that only the first optimal voltage vector u is used within this control cycle. opt ;

[0019] (2) When the stator flux linkage determination coefficient λ ψ1 or λ ψ2 When the value is less than 0, the two adjacent effective voltage vectors u of the first optimal voltage vector can be directly determined. opt+1 or u opt-1 To satisfy the second optimal voltage vector for reducing stator flux linkage pulsation;

[0020] (3) When the stator flux linkage determination coefficient λ ψ1 and λ ψ2 When both are less than 0, it is necessary to compare the two stator flux deviation factors δ. opt+1 and δ opt-1 The absolute value of the stator flux deviation factor is selected, and the voltage vector u corresponding to the smaller absolute value is chosen. opt+1 or u opt-1 As the second optimal voltage vector;

[0021] (4) When the stator flux linkage determination coefficient λ ψ0 If the value is less than 0, then the zero voltage vector u0 is selected as the second optimal voltage vector.

[0022] Therefore, a second optimal voltage vector that meets the stator flux linkage control requirements of the permanent magnet synchronous motor control system can be selected, thereby determining the globally optimal voltage vector combination at this moment.

[0023] Compared with the traditional duty cycle model predictive flux control algorithm, this invention improves upon the shortcomings of the traditional control algorithm, such as the optimal voltage vector combination where the first and second optimal voltage vectors are zero voltage vectors being only locally optimal rather than globally optimal, and the stator flux pulsation being large. Attached Figure Description

[0024] Figure 1 This is a block diagram of an improved dual-vector model for predicting the flux linkage control system of a permanent magnet synchronous motor.

[0025] Figure 2 This is a schematic diagram showing the global optimal voltage vector combination corresponding to the relationship between different magnetic flux reference values ​​and predicted values.

[0026] Figure 3This is a schematic diagram showing the relationship between different reference and predicted flux linkage values, corresponding to the global optimal voltage vector combination. Detailed Implementation

[0027] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0028] The improved dual-vector model predictive flux linkage control method for permanent magnet synchronous motors proposed in this invention is implemented based on the hardware of a typical surface-mount permanent magnet synchronous motor digital control drive system. The most basic hardware includes a permanent magnet synchronous motor, a digital signal processor, an absolute position encoder, a contactless Hall current sensor, an inverter, and a DC power supply. The system control algorithm is implemented in the digital signal processor. The overall system block diagram of this invention is shown below. Figure 1 As shown. This invention relies on discrete algorithms and is implemented using a digital signal processor.

[0029] The relationship between the axes in the control system is defined as follows: the axis of the A-phase winding in the ABC three-phase stator coordinate system coincides with the α-axis in the αβ two-phase stationary coordinate system. The rotor position electrical angle θ is defined as the direct axis (d-axis) in the dq synchronous rotating coordinate system oriented by the permanent magnet magnetic field of the permanent magnet rotor coincides with the axis of the A-phase winding. e The starting point.

[0030] First, assume that the three-phase windings of the permanent magnet synchronous motor are perfectly symmetrical, and neglect eddy current losses and hysteresis losses. Then, use a non-contact Hall current sensor to monitor the three-phase stator current i of the permanent magnet synchronous motor. A i B and i C Measurements are performed on the three-phase stator current i by a digital signal processor. A i B and i C Sampling. Then, the sampled three-phase stator current i... A i B and i C The α-axis current i in the αβ two-phase stationary coordinate system is obtained by Clark transformation. α and β-axis current i β Its coordinate transformation expression is:

[0031]

[0032] Then, consider the α-axis current i in the αβ two-phase stationary coordinate system. α and β-axis current i β The direct-axis current i in the dq synchronous rotating coordinate system oriented by the permanent magnet magnetic field of the permanent magnet rotor is obtained by the Park transformation. d and cross-axis current i q Its coordinate transformation expression is:

[0033]

[0034] The voltage equation and flux linkage equation for a surface-mounted permanent magnet synchronous motor are as follows:

[0035]

[0036]

[0037] In the formula, u d and u q These are the d-axis and q-axis components of the stator voltage, respectively; i d and i q These are the d-axis and q-axis components of the stator current, respectively; ψ d and ψ q ψ represents the d-axis and q-axis components of the stator flux linkage, respectively; R is the stator resistance; L is the motor synchronous inductance; ψ f For rotor permanent magnet flux linkage; ω e θ is the electric angular velocity; e denoted as the rotor position electrical angle; p is the differential operator.

[0038] The corresponding state equations are obtained from equations (5) and (6).

[0039]

[0040] Using sampling period T s Applying a first-order forward Euler approximation to equation (7), and considering system delay compensation, the predicted flux linkage model for the permanent magnet synchronous motor is:

[0041]

[0042] The substitution valence function is

[0043]

[0044] In the formula, ψ d (k+2) and ψ q (k+2) is (k+2)T s Predicted stator flux linkage values ​​along the d-axis and q-axis at time ψ d (k+1) and ψ q (k+1) is (k+1)T s Calculated values ​​of stator flux linkage on the d-axis and q-axis, taking delay compensation into account at all times; u d (k+1) and u q (k+1) is the value applied to (k+1)T s The d-axis and q-axis components of the voltage vector at time u d (k+1) and u q (k+1) in kT sObtained within a certain timeframe; This is the stator flux linkage reference value.

[0045] Using the principle of no difference in beats, let (k+2)T s The stator flux linkage at time [time] reaches the reference value, i.e.

[0046]

[0047] We can obtain (k+1)T s The reference voltage vector at time t is

[0048]

[0049] in

[0050]

[0051]

[0052]

[0053]

[0054]

[0055]

[0056] In the formula, and The d-axis and q-axis components of the reference voltage vector; ψ d (k) and ψ q (k) is kT s Calculated values ​​of stator flux linkage along the d-axis and q-axis at time u; d (k) and u q (k) is the value applied to kT s The d-axis and q-axis components of the voltage vector at time u d (k) and u q (k) in (k-1)T s Obtained within a certain timeframe; and These are the d-axis and q-axis components of the stator flux linkage reference value.

[0057] Will and The components in the dq synchronous rotating coordinate system are transformed into components in the αβ two-phase stationary coordinate system.

[0058]

[0059] Therefore, the phase of the reference voltage vector can be obtained as follows:

[0060]

[0061] By determining the sector where the reference voltage vector is located, the first optimal voltage vector to be selected can be determined.

[0062] The two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector are used as candidate voltage vectors for the second optimal voltage vector. According to equation (9), the stator flux deviation factor δ is defined. i for

[0063]

[0064] In the formula, the subscript i corresponds to the stator flux deviation factor of the i-th (i = 0, 1...7) voltage vector acting on the motor.

[0065] The diagram illustrating the relationship between different reference and predicted flux linkage values ​​and the corresponding global optimal voltage vector combinations is shown below. Figure 2 and Figure 3 As shown.

[0066] Assuming the first optimal voltage vector is u1, then the candidate voltage vectors for the second optimal voltage vector include u0, u2, and u6. Figure 2 In the middle, the stator flux linkage reference value The stator flux deviation factor δ1 corresponding to the first optimal voltage vector is negative. Therefore, the second optimal voltage vector could be u0, u2, or u6. As shown in the figure, the stator flux deviation factors corresponding to u0 and u6 are also negative, while only the stator flux deviation factor corresponding to u2 is positive. This indicates that in the next control cycle, only the voltage vector combination of u1 and u2 can reach the stator flux reference value, meaning the product of δ1 and δ2 is less than 0. Figure 3 In the middle, the stator flux linkage reference value When δ1 and δ2 are positive, only δ0 and δ6 are negative, so the second optimal voltage vector can be selected from u0 and u6. Therefore, by analyzing the positive and negative relationships between the stator flux deviation factors of the candidate voltage vectors of the first and second optimal voltage vectors acting on the motor, a voltage vector that reduces stator flux pulsation can be selected from the candidate voltage vectors of the second optimal voltage vector as the second optimal voltage vector. If the control performance of one of the effective voltage vectors is better than that of the zero voltage vector, then that effective voltage vector is selected as the second optimal voltage vector, instead of using the zero voltage vector as the second optimal voltage vector of the optimal vector combination.

[0067] To more intuitively select the second optimal voltage vector and improve the system's computational efficiency, δ is defined. opt , δ0, δ opt+1 and δ opt-1 The first optimal voltage vector u is respectively optThe zero voltage vector u0 and the two adjacent effective voltage vectors u of the first optimal voltage vector. opt+1 and u opt-1 The stator flux linkage deviation factor. The subscript opt+1 represents the adjacent effective voltage vector spatially leading the first optimal voltage vector, and opt-1 represents the adjacent effective voltage vector spatially lagging behind the first optimal voltage vector. Three stator flux linkage determination coefficients are defined as follows:

[0068]

[0069] For example: when λ ψ1 Less than 0, λ ψ2 and λ ψ0 If it is greater than 0, it means that δ opt and δ opt+1 If the sign is reversed, then u opt and u opt+1 The voltage vector combination can meet the stator flux linkage control requirements of the permanent magnet synchronous motor control system.

[0070] Based on the positive and negative relationships of the three stator flux linkage determination coefficients, a second optimal voltage vector selection table is established as shown in the table below.

[0071] Table 1. Second Optimal Voltage Vector Selection Table

[0072]

[0073] The selection rule for the second optimal voltage vector is as follows:

[0074] (1) When the stator flux linkage determination coefficient λ ψ1 , λ ψ2 and λ ψ0 When both values ​​are greater than 0, there is no voltage vector among the candidate voltage vectors for the second optimal voltage vector that satisfies the requirement of reducing stator flux pulsation. Therefore, the first optimal voltage vector is still selected as the second optimal voltage vector, meaning that only the first optimal voltage vector u is used within this control cycle. opt ;

[0075] (2) When the stator flux linkage determination coefficient λ ψ1 or λ ψ2 When the value is less than 0, the two adjacent effective voltage vectors u of the first optimal voltage vector can be directly determined. opt+1 or u opt-1 To satisfy the second optimal voltage vector for reducing stator flux linkage pulsation;

[0076] (3) When the stator flux linkage determination coefficient λ ψ1 and λ ψ2 When both are less than 0, it is necessary to compare the two stator flux deviation factors δ. opt+1 and δ opt-1The absolute value of the stator flux deviation factor is selected, and the voltage vector u corresponding to the smaller absolute value is chosen. opt+1 or u opt-1 As the second optimal voltage vector;

[0077] (4) When the stator flux linkage determination coefficient λ ψ0 If the value is less than 0, then the zero voltage vector u0 is selected as the second optimal voltage vector.

[0078] Therefore, a second optimal voltage vector that reduces the stator flux pulsation of the permanent magnet synchronous motor control system can be selected, thereby determining the globally optimal voltage vector combination at this moment.

[0079] Traditional duty cycle model predictive flux linkage control algorithms, after obtaining the first optimal voltage vector through cost function evaluation, need to calculate the duty cycle of the first optimal voltage vector to obtain its action time T1 within the current control cycle. qj and s q0 and are the slopes of the stator quadrature-axis flux linkage change under the action of the effective voltage vector and the zero voltage vector, respectively, and are calculated using the following formula:

[0080] s qj =u qj (k)-R / Lψ q (k)-ω e ψ d (k) (16)

[0081] s q0 =-R / Lψ q (k)-ω e ψ d (k) (17)

[0082] In the formula, u dj and u qj It is the candidate voltage vector u of the second optimal voltage vector. j The d-axis and q-axis components, where u j It should start from the first optimal voltage vector u opt and the two adjacent effective voltage vectors u of the first optimal voltage vector opt+1 and u opt Choose from -1.

[0083] Using the principle of no difference in beats, let (k+2)T s The stator flux linkage at time [time] reaches the reference value, i.e. The duty cycle γ of the first optimal voltage vector can be calculated as follows:

[0084]

[0085] Then the duration of the first optimal voltage vector is T1 = γT sThe duration of the second optimal voltage vector is T2 = T s -T1. However, calculating the duty cycle using the above formula is quite complex. Therefore, this invention proposes a duty cycle calculation method based on the stator flux deviation factor. Combining the duty cycle γ and the stator flux deviation factor with equation (9), a new cost function expression is obtained, which can be expressed as follows:

[0086] g=|γδ opt +(1-γ)δ j | (19)

[0087] In the formula, δ opt It is the stator flux deviation factor corresponding to the first optimal voltage vector; δ j It is the stator flux deviation factor corresponding to the second optimal voltage vector.

[0088] Differentiate the function

[0089]

[0090] The duty cycle of the first optimal voltage vector can be obtained.

[0091]

[0092] Equation (21) uses the stator flux deviation factor obtained by the newly defined cost function to calculate the duty cycle, which reduces the computational burden of the algorithm. Secondly, compared with the traditional duty cycle model prediction flux control algorithm, the calculation takes into account the stator flux pulsation of the motor, which can better suppress and reduce flux pulsation.

[0093] This invention proposes an improved dual-vector model predictive flux linkage control method. The method uses the two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector as candidate voltage vectors for the second optimal voltage vector. By using a second optimal voltage vector selection table and its selection rules, a globally optimal voltage vector combination is obtained, rather than simply selecting the first and second optimal voltage vectors as locally optimal combinations with zero voltage vectors. Compared to the traditional duty cycle model predictive flux linkage control algorithm, this method effectively reduces stator flux linkage pulsation and lowers the computational burden of the system, thereby improving the steady-state performance of the permanent magnet synchronous motor control system.

[0094] The above embodiments illustrate and describe the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the above embodiments are merely illustrative. Therefore, any omissions, modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An improved dual-vector model predictive method for flux linkage control of a permanent magnet synchronous motor, characterized in that, The two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector are used as candidate voltage vectors for the second optimal voltage vector. A globally optimal voltage vector combination is obtained through a second optimal voltage vector selection table and its selection rules, rather than simply selecting the first and second optimal voltage vectors as locally optimal combinations with zero voltage vectors. This reduces stator flux linkage pulsation. Its specific characteristics are as follows: The two adjacent effective voltage vectors and the zero voltage vector of the first optimal voltage vector are used as candidate voltage vectors for the second optimal voltage vector. The stator flux deviation factor δ is defined. i for In the formula, ψ s (k+2) is (k+2)T s Stator flux linkage prediction at time 10:00 It is the stator flux reference value, and the subscript i corresponds to the stator flux deviation factor of the i-th (i = 0, 1, ..., 7) voltage vector acting on the motor; Define δ opt , δ0, δ opt+1 and δ opt-1 The first optimal voltage vector u is respectively opt The zero voltage vector u0 and the two adjacent effective voltage vectors u of the first optimal voltage vector. opt+1 and u opt-1 The stator flux deviation factor is defined by the following three stator flux determination coefficients: Based on the sign relationship of the three stator flux linkage determination coefficients, a second optimal voltage vector selection table is established as shown in the table below. Table 1. Second Optimal Voltage Vector Selection Table The selection rule for the second optimal voltage vector is as follows: (1) When the stator flux linkage determination coefficient λ ψ1 , λ ψ2 and λ ψ0 When both values ​​are greater than 0, there is no voltage vector among the candidate voltage vectors for the second optimal voltage vector that satisfies the requirement of reducing stator flux pulsation. Therefore, the first optimal voltage vector is still selected as the second optimal voltage vector, meaning that only the first optimal voltage vector u is used within this control cycle. opt ; (2) When the stator flux linkage determination coefficient λ ψ1 or λ ψ2 When the value is less than 0, the two adjacent effective voltage vectors u of the first optimal voltage vector can be directly determined. opt+1 or u opt-1 To satisfy the second optimal voltage vector for reducing stator flux linkage pulsation; (3) When the stator flux linkage determination coefficient λ ψ1 and λ ψ2 When both are less than 0, it is necessary to compare the two stator flux deviation factors δ. opt+1 and δ opt-1 The absolute value of the stator flux deviation factor is selected, and the voltage vector u corresponding to the smaller absolute value is chosen. opt+1 or u opt-1 As the second optimal voltage vector; (4) When the stator flux linkage determination coefficient λ ψ0 When the value is less than 0, the zero voltage vector u0 is selected as the second optimal voltage vector; Therefore, a second optimal voltage vector that meets the stator flux linkage control requirements of the permanent magnet synchronous motor control system can be selected, thereby determining the globally optimal voltage vector combination at this moment.

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