Energy efficiency optimization method for permanent magnet shielded motor vector control

Abstract

The present application relates to a kind of permanent magnet shielding motor vector control energy efficiency optimization method considering magnetic field lagging phase angle, belong to permanent magnet shielding motor control field.It is characterized by: by analyzing shield sleeve eddy current effect, the analytical expression of magnetic field lagging phase angle is derived using electromagnetic field theory;The lagging phase angle is introduced into permanent magnet flux linkage term to be corrected, and the eddy current loss of shield sleeve and stator iron loss are combined into equivalent iron loss component, and a system controllable loss model is constructed;Under the constraint of constant torque, the analytical expression of total controllable loss about direct-axis current is derived and the optimal direct-axis current given value is solved.The actual application introduces angle compensation in the coordinate transformation link of vector control system, and the optimal direct-axis current given value is sent into current regulator, the accurate decoupling of dq axis current is realized, the total loss of motor is reduced, so as to improve the overall efficiency of motor control system.

Description

Technical Field

[0001] This invention relates to the field of permanent magnet shielded motor technology, and in particular to a method for optimizing the energy efficiency of vector control of a permanent magnet shielded motor. Background Technology

[0002] Canned motor pumps, with their leak-free integrated sealing structure, are widely used in the petrochemical, pharmaceutical, and nuclear power industries for transporting flammable, explosive, and highly corrosive hazardous media. As the core drive component of the canned motor pump, its operating efficiency and control precision directly determine the safety and energy efficiency of the entire pumping system. Compared to traditional induction motors, permanent magnet synchronous motors offer significant advantages such as high power density, high efficiency, and excellent speed regulation performance, better meeting the modern industrial demands for efficient, energy-saving, and highly reliable operation of canned motor pumps.

[0003] However, to achieve complete isolation between the transported medium and the internal electrical components of the motor, a metal shielding sleeve is typically installed between the stator windings and the rotor permanent magnets of a permanent magnet shielded motor. While the introduction of the shielding sleeve solves the problem of medium leakage, it also significantly increases the electromagnetic complexity of the motor. During motor operation, the alternating magnetic field in the air gap induces eddy currents in the conductive shielding sleeve. This eddy current effect has two main adverse effects: firstly, the eddy currents generate additional losses on the shielding sleeve, directly reducing the overall operating efficiency of the motor; secondly, the reaction magnetic field generated by the eddy currents causes a phase lag in the main magnetic field passing through the shielding sleeve. This magnetic field lag effect directly affects the electromagnetic torque output characteristics and power factor of the motor, and causes deviations in the coordinate transformation based on the ideal rotor position angle in traditional vector control systems, thereby compromising the decoupling accuracy of the dq-axis current.

[0004] For the energy efficiency optimization problem of motor systems, commonly used control strategies in existing technologies mainly include maximum torque-to-current ratio control, online search-based optimization methods, and efficiency optimization control methods based on motor loss models. Among them, the loss model-based method directly solves for the optimal current command by establishing analytical relationships between various motor losses and operating parameters. It has the advantages of low computational load and fast dynamic response, and has achieved certain application results in conventional permanent magnet synchronous motors or induction motors. However, due to the complex characteristics of the shielding sleeve of shielded motors, the above-mentioned traditional efficiency optimization control strategies have not yet been applied to permanent magnet shielded motors.

[0005] Therefore, how to establish an accurate loss model that takes into account the eddy current effect and magnetic field hysteresis characteristics of the shielding sleeve, and on this basis design an efficiency optimization control strategy that can solve the optimal direct-axis current in real time and compensate for the magnetic field hysteresis phase angle, so as to break through the bottleneck of existing technology in improving the energy efficiency and control accuracy of permanent magnet shielded motors, has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] content To address the aforementioned problems, this application provides an improved energy efficiency optimization method for vector control of permanent magnet shielded motors. The aim is to solve the problem of combining the controllable losses of the motor and the lag phase angle of the magnetic field in the mathematical model of permanent magnet shielded motors, so as to reduce the total loss and improve the overall efficiency of the control system.

[0007] The technical solution adopted in this invention is: An energy efficiency optimization method for vector control of a permanent magnet shielded motor, characterized by the following steps: Step 1: Based on the analytical expression of the magnetic field lag phase angle caused by the eddy current effect of the shielding sleeve, the flux linkage term of the permanent magnet is modified, and the dq axis voltage equation considering the magnetic field lag effect is established. Step 2: Combine the eddy current loss of the shielding sleeve and the iron loss of the stator into an equivalent iron loss component, and construct a system total controllable loss model that takes into account the eddy current loss of the shielding sleeve and the iron loss of the motor. Step 3: Combining the decomposition relationship between the torque component and the iron loss component of the dq axis current, with the goal of minimizing the total controllable loss of the system, derive the analytical expression of the total controllable loss with respect to the direct axis current, and solve for the optimal direct axis current setpoint under constant torque constraints. Step 4: In the vector control coordinate transformation stage, the rotor position angle is compensated by the real-time calculated magnetic field lag phase angle, and the optimal direct-axis current setpoint is sent to the current regulator to realize the energy efficiency optimization control of the permanent magnet shielded motor.

[0008] In the first step, the analytical expression for the magnetic field lag phase angle is: (1) in, Indicates the phase lag angle of the magnetic field. Electric angular velocity, For the magnetic permeability of the shielding sleeve, The conductivity of the shielding sleeve material, This refers to the thickness of the shielding sleeve.

[0009] In the first step, the component of the corrected permanent magnet flux linkage on the dq axis is expressed as: (2) Where j represents the imaginary unit, Indicates permanent magnet flux linkage. This indicates the modified permanent magnet flux linkage.

[0010] The dq-axis voltage equation considering the magnetic field hysteresis effect is as follows: (3) Where d and q are the direct and quadrature axes of the motor's coordinate system, respectively, and t is time. This refers to the dq-axis stator voltage. For dq axis current, For dq axis inductance, For stator resistance, It represents the electric angular velocity.

[0011] The relationship between the stator current decomposed into torque component and iron loss component is as follows: (4) in, For torque components, This represents the iron loss amount.

[0012] Based on the aforementioned decomposition relationship, the dq-axis voltage equation and electromagnetic torque equation are rewritten in a form containing only torque components: (5) (6) in This represents the number of pole pairs of the motor.

[0013] Furthermore, the eddy current loss of the shielding sleeve and the stator iron loss are combined into an equivalent iron loss component, and a total controllable loss model of the system considering the eddy current loss of the shielding sleeve and the iron loss of the motor is constructed.

[0014] The total controllable loss of the system is expressed as the sum of copper loss and iron loss, and its analytical expression is: (7) in, This represents the total controllable loss of the system. and These represent the motor's copper loss and the motor's equivalent iron loss, respectively. This is the equivalent iron loss resistance.

[0015] Under constant torque constraints and steady-state motor operation conditions, setting the partial derivative of the total controllable losses of the system with respect to the direct-axis current to zero, the steady-state optimal direct-axis current is obtained as follows: (8) in, (9) The specific technical effects of this invention are as follows: The magnetic field orientation accuracy of the vector control system for permanent magnet shielded motors has been improved. By quantitatively deriving the analytical expression of the magnetic field lag angle caused by the eddy current of the shielding sleeve, and correcting it into the magnetic flux terms of the permanent magnet and the dq-axis voltage equation, the current decoupling deviation caused by neglecting the phase lag in the traditional model has been effectively overcome.

[0016] Real-time optimization of the energy efficiency of permanent magnet shielded motors was achieved. By establishing an equivalent iron loss model that takes into account the eddy current loss of the shielding sleeve, the optimal direct-axis current was analytically solved under constant torque constraints. This avoids the shortcomings of traditional online search methods, such as large computational load and slow dynamic response, and significantly reduces the total electrical loss of the system and improves the overall efficiency of the control system.

[0017] Overall, compared with the traditional constant flux linkage control strategy, the energy efficiency optimization strategy proposed in this invention closely revolves around the loss distribution characteristics of the permanent magnet shielded motor. By constructing an accurate loss model that takes into account the magnetic field lag phase angle, the optimal direct-axis current is solved in real time, which significantly reduces the total electrical loss of the system and provides a direct and effective approach for the efficient and energy-saving operation of the shielded pump system. Attached Figure Description

[0018] Figure 1 This is the equivalent circuit of the dq axis of a permanent magnet shielded motor that takes into account iron loss and magnetic field phase angle lag; Figure 2 This is a schematic diagram of the vector control energy efficiency optimization control system for permanent magnet shielded motors. Figure 3 It is a permanent magnet shielded motor energy efficiency optimization control strategy and traditional Comparison chart of electrical loss results for different strategies; Figure 4 It is a permanent magnet shielded motor energy efficiency optimization control strategy and traditional Comparison chart of overall strategy efficiency results. Detailed Implementation

[0019] To more clearly demonstrate the purpose, technical solution, and effects of this invention, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and do not limit the scope of the invention. Furthermore, in the various embodiments of the invention described below, the technical features involved can be combined with each other as long as they do not conflict with each other.

[0020] To reduce losses and improve efficiency in the vector control system of permanent magnet shielded motors, this invention proposes an energy efficiency optimization method for vector control of permanent magnet shielded motors.

[0021] Step 1: Based on the analytical expression of the magnetic field hysteresis phase angle, the flux linkage term of the permanent magnet is corrected, and the dq-axis voltage equation considering the magnetic field hysteresis effect is established; Step 2: Combine the eddy current loss of the shielding sleeve and the stator iron loss into an equivalent iron loss component, and construct a system loss model that takes into account the eddy current loss of the shielding sleeve and the iron loss of the motor.

[0022] Step 3: Combining the decomposition relationship between the torque component and the iron loss component of the dq axis current, with the goal of minimizing the total controllable loss of the system, derive the analytical expression of the total controllable loss of the system with respect to the direct axis current and solve for the optimal direct axis current setpoint.

[0023] Step 4: In the vector control coordinate transformation stage, the rotor position angle is compensated by the real-time calculated hysteresis angle, and the optimal direct-axis current setpoint is sent to the current regulator to realize the energy efficiency optimization control of the permanent magnet shielded motor.

[0024] The eddy current effect generated by the shielding sleeve under the action of an alternating magnetic field causes a phase lag in the magnetic field. This lag angle is closely related to the electric angular frequency, the material parameters of the shielding sleeve, and its thickness. Based on electromagnetic field diffusion theory and the thin-plate approximation, the phase lag angle of the transmitted magnetic field relative to the incident magnetic field is... (degree) can be expressed as: (1) in, Indicates the phase lag angle of the magnetic field. Electric angular velocity, To ensure the permeability of the shielding sleeve, The conductivity of the shielding sleeve material, The thickness of the shielding sleeve is given. This formula shows that the hysteresis angle is linearly related to the rotational speed and proportional to the square of the shielding sleeve thickness. In this invention, this hysteresis angle is used to correct the permanent magnet flux linkage component in the dq-axis coordinate system to accurately reflect the influence of the shielding sleeve's eddy current effect on the motor's magnetic field.

[0025] Based on the above magnetic field hysteresis angle The hysteresis effect is incorporated into the permanent magnet flux linkage term, and the corrected component of the permanent magnet flux linkage on the dq axis is expressed as: (2)

[0026] Where j represents the imaginary unit, Indicates permanent magnet flux linkage. This indicates the modified permanent magnet flux linkage.

[0027] The dq-axis voltage equation considering the hysteresis angle is: (3) Where d and q represent the direct axis and quadrature axis of the motor coordinate system, respectively, and t is time. This refers to the dq-axis stator voltage. For dq axis current, For dq axis inductance, This is the stator resistance.

[0028] The losses in a permanent magnet shielded motor include copper loss, iron loss, shielding sleeve loss, mechanical loss, and stray loss. The first three are controllable losses. Iron loss and shielding sleeve eddy current loss are both generated by alternating magnetic field excitation and have highly coupled frequency domain characteristics; therefore, this paper focuses on shielding sleeve loss. Combined with iron loss into an equivalent iron loss component Unified modeling. The shielding sleeve loss is modeled using an empirical formula: (4) In the formula This indicates the shielding sleeve loss (W). The shielding sleeve loss coefficient; is the average air gap magnetic flux density (T); n is the synchronous speed of the motor (r / min); The length of the iron core is in cm. The inner diameter of the shielding sleeve stator (cm); The thickness of the shielding sleeve is in cm. The resistivity of the shielding sleeve material ( ).

[0029] The equivalent circuit of a permanent magnet shielded motor, considering the equivalent iron loss of the motor and the lag phase angle of the magnetic field, is as follows: Figure 1 As shown. Using iron loss resistors. The amount consumed is used to characterize the equivalent iron loss. According to Figure 1 ,stator Shaft current can be divided into two parts: torque component and iron loss component, i.e. (5) in, For torque components, This represents the iron loss amount.

[0030] Therefore, the voltage equation and torque equation can be rewritten as (6)~(7).

[0031] (6) (7)

[0032] In the formula, For electromagnetic torque, This represents the number of pole pairs of the motor.

[0033] Depend on Figure 1 Permanent magnet shielded motors can be obtained The iron loss components of the shaft stator current are shown in equations (8) and (9): (8) (9) in, This represents the equivalent iron loss resistance.

[0034] In the permanent magnet shielded motor model that considers iron losses, copper losses... and iron consumption They can be respectively equivalent to stator resistance. The power consumed and the back electromotive force act on the iron loss resistance The heat loss on the surface is shown in equations (16) and (17): (10) (11) in, and These represent the motor's copper loss and equivalent iron loss, respectively.

[0035] Therefore, the controllable losses of a permanent magnet shielded motor can be expressed as the sum of copper losses and iron losses: (12) in, Represents the total controllable loss of the system. Substituting the electromagnetic torque equation into equation (12): (13) Under constant torque constraints, a given negative direct-axis current can weaken the air gap composite flux, thereby reducing iron loss and shielding sleeve eddy current loss. To maintain constant output torque, the quadrature-axis current needs to be increased accordingly, resulting in a slight increase in copper loss. The total system loss curve shows a characteristic of first decreasing and then increasing with the change of direct-axis current, and there is a unique minimum point. Based on this, the optimal direct-axis current can be solved to achieve energy efficiency optimization.

[0036] As can be seen from equation (13), when the motor is running in steady state, the motor's electric angular velocity is... electromagnetic torque As a constant, the electromagnetic loss of the motor is a function of... The equation, as long as it satisfies The optimal stator current active component of the motor during steady-state operation can then be obtained. for: (14) Therefore, the optimal direct-axis current for the permanent magnet shielded motor during steady-state operation is:

[0037] Figure 2This is a schematic diagram of the vector control energy efficiency optimization control system for a permanent magnet shielded motor. The control system includes a speed PI regulator 1, an optimal direct-axis current calculation module 2, a torque PI regulator 3, an excitation current regulator 4, an inverse Park transform module 5, a space vector SVPWM module 6, a three-phase voltage source inverter 7, a Clark transform module 8, a Park transform module 9, a position and speed sensor 10, and the permanent magnet shielded motor body 11.

[0038] Figure 3 This image shows a comparison curve of electrical losses between the energy efficiency optimization control strategy for the permanent magnet shielded motor described in this invention and the traditional constant flux linkage control strategy. A surface-mounted permanent magnet shielded motor with a rated power of 3 kW, used to drive a shielded vortex vacuum pump, was used as the research object, and a simulation model was built on the MATLAB / Simulink platform. The simulation conditions were set as follows: the load torque was constant. The rotational speed was set to the rated value, and the curves of the total electrical loss of the system over time under the two strategies were compared. The results show that, under the same load and rotational speed conditions, the total electrical loss during steady-state operation is reduced by approximately 16.7% compared to the traditional constant flux linkage strategy, verifying the effectiveness of the loss model and the optimal current solution method.

[0039] Figure 4 The figures show a comparison of the overall system efficiency of the energy efficiency optimization strategy described in this invention and the traditional constant flux linkage control strategy under different speed conditions. The simulation is set with a constant load torque. The rotational speed was varied from 1500 r / min to 3000 r / min. The comparison results show that the strategy of this invention, by solving for the optimal direct-axis current in real time, can effectively improve system efficiency across the entire rotational speed range, with a maximum improvement of approximately 3%.

[0040] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and 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 energy efficiency optimization method for vector control of a permanent magnet shielded motor, characterized in that, The method steps are as follows: Step 1: Based on the analytical expression of the magnetic field lag phase angle caused by the eddy current effect of the shielding sleeve, the flux linkage term of the permanent magnet is modified, and the dq axis voltage equation considering the magnetic field lag effect is established. Step 2: Combine the eddy current loss of the shielding sleeve and the iron loss of the stator into an equivalent iron loss component, and construct a system total controllable loss model that takes into account the eddy current loss of the shielding sleeve and the iron loss of the motor. Step 3: Combining the decomposition relationship between the torque component and the iron loss component of the dq axis current, with the goal of minimizing the total controllable loss of the system, derive the analytical expression of the total controllable loss with respect to the direct axis current, and solve for the optimal direct axis current setpoint under constant torque constraints. Step 4: In the vector control coordinate transformation stage, the rotor position angle is compensated by the real-time calculated magnetic field lag phase angle, and the optimal direct-axis current setpoint is sent to the current regulator to realize the energy efficiency optimization control of the permanent magnet shielded motor.

2. The energy efficiency optimization method for vector control of a permanent magnet shielded motor according to claim 1, characterized in that, In the first step, the analytical expression for the magnetic field lag phase angle is: （1） in, Indicates the phase lag angle of the magnetic field. Electric angular velocity, For the magnetic permeability of the shielding sleeve, The conductivity of the shielding sleeve material, This refers to the thickness of the shielding sleeve.

3. The energy efficiency optimization method for vector control of a permanent magnet shielded motor according to claim 1, characterized in that, In the first step, the component of the corrected permanent magnet flux linkage on the dq axis is expressed as: （2） Where j represents the imaginary unit, Indicates permanent magnet flux linkage. This indicates the corrected permanent magnet flux linkage; The dq-axis voltage equation considering the magnetic field hysteresis effect is as follows: （3） Where d and q represent the direct axis and quadrature axis of the motor coordinate system, respectively, and t is time. This refers to the dq-axis stator voltage. For dq axis current, For dq axis inductance, This is the stator resistance.

4. The energy efficiency optimization method for vector control of a permanent magnet shielded motor according to claim 1, characterized in that, In the second step, the relationship between the stator current decomposed into torque component and iron loss component is as follows: （4） in, For torque components, Iron loss amount; Based on the aforementioned decomposition relationship, the dq-axis voltage equation and electromagnetic torque equation are rewritten in a form containing only torque components: （5） （6） in For electromagnetic torque, This represents the number of pole pairs of the motor. Furthermore, the eddy current loss of the shielding sleeve and the stator iron loss are combined into an equivalent iron loss component, and a total controllable loss model of the system considering the eddy current loss of the shielding sleeve and the iron loss of the motor is constructed.

5. The energy efficiency optimization method for vector control of a permanent magnet shielded motor according to claim 4, characterized in that, In the third step, the total controllable loss of the system is expressed as the sum of copper loss and iron loss, and its analytical expression is: （7） in, This represents the total controllable loss of the system. and These represent the motor's copper loss and equivalent iron loss, respectively. This is the equivalent iron loss resistance; Under constant torque constraints and steady-state motor operation conditions, setting the partial derivative of the total controllable losses of the system with respect to the direct-axis current to zero, the steady-state optimal direct-axis current is obtained as follows: （8） in （9）。

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