A Loss Optimization Control Method for Low-Speed Dual-Three-Phase Motor Drive System
By using nonlinear optimization and vector control methods, the current limit value is calculated and the current reference value is optimized, which solves the problems of motor heat loss and temperature unevenness under low speed and static conditions, and improves the safety and service life of the system.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- INST OF OPTICS & ELECTRONICS CHINESE ACAD OF SCI
- Filing Date
- 2023-02-14
- Publication Date
- 2026-07-17
AI Technical Summary
Existing loss optimization control methods are mainly aimed at medium and high speed conditions, and lack solutions for motor heat loss and uneven temperature distribution under low speed and stationary conditions, which leads to unsafe system operation and affects service life.
A nonlinear optimization method is adopted, and a loss optimization model is established by calculating the current limit value and solving the problem using the interior point method. Combined with the vector control method, the current reference value is optimized to reduce the motor's heat loss and temperature unevenness.
It effectively reduces motor heat loss at low speeds and under stationary conditions, improves uneven temperature distribution, and enhances system safety and service life.
Smart Images
Figure CN116054649B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of loss optimization technology for motor drive systems, and specifically relates to a loss optimization control method for a low-speed dual three-phase motor drive system. Background Technology
[0002] Multiphase motors have the characteristics of strong fault tolerance, low torque ripple, and lower power per phase. At the same time, dual three-phase motors are easy to manufacture and can be realized by adjusting the windings of traditional three-phase motors. Therefore, dual three-phase motors are of great significance for the research of high-reliability and high-precision drive systems.
[0003] However, in some practical applications, motor drive systems are required to operate at low speeds and in stationary conditions, such as in elevators, electric vehicles, and high-precision CNC machine tools. In these low-speed applications, the motor still needs to output torque to drive the system's operation and maintain its position, resulting in extremely low motor phase current frequencies and large amplitudes. This often leads to continuous heating of single-phase windings, causing overheating and uneven heat distribution, severely impacting system safety. Therefore, optimizing and controlling losses in motor drive systems under low-speed conditions is of great significance.
[0004] In recent years, multiphase motor control has developed rapidly, and loss optimization control of two-phase and three-phase motors has been extensively studied by many scholars. However, existing loss optimization control methods often focus on medium- and high-speed operating conditions, considering the reduction of total and average motor losses, and lack research on loss optimization techniques under low-speed and stationary conditions. Excessive heat loss and uneven temperature distribution in motors under low-speed and stationary conditions can cause irreversible damage to actual systems, severely affecting their service life. Therefore, research on loss optimization techniques for actual systems operating under low-speed and stationary conditions is essential. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing loss optimization methods under low-speed and stationary conditions mentioned in the background art, and to provide a loss optimization control method for low-speed dual three-phase motor drive systems based on nonlinear optimization.
[0006] To solve the above-mentioned technical problems, the present invention proposes the following technical solution:
[0007] A loss optimization control method for a low-speed dual three-phase motor drive system, the method comprising the following steps:
[0008] Step 1: For the mathematical models of motors with different winding topologies, analyze the minimum value that the phase current amplitude can reach without changing the torque output. This minimum value is the current limit value m(θ). This includes: calculating the corresponding current limit value according to the different current constraints of isolated neutral point topology, connected neutral point topology, and open winding topology; where θ is the electrical angle.
[0009] Step 2: Using the current limit value m(θ) and unit torque output as constraints, and the total copper loss as the objective function, establish a nonlinear optimization problem, and use the interior point method to solve it to obtain the optimal six-phase current reference value for each electrical angle.
[0010] Step 3: Convert the optimal six-phase current reference value for each electrical angle into a decoupled current reference value through VSD transformation, and perform curve fitting to obtain the optimal current reference expression;
[0011] Step 4: Use the optimal current expression as the input reference value of the motor control system to drive the dual three-phase motor to achieve loss optimization control.
[0012] Furthermore, in step 1, the current limit value is the minimum phase current amplitude that can be achieved under the condition of constant torque output. The formula for the current constrained by the torque condition is as follows:
[0013]
[0014] Among them, i q It is the q-axis current of the motor in the rotating coordinate system, which is proportional to the motor's output torque, θ e It is the electrical angle of the rotor, i A i B i C i D i E i F It is the six-phase current of the motor; at a certain electrical angle, when the maximum phase current value is reduced and the other phase current values are increased to compensate for the torque until all phase current values are equal, the phase current value at this time is the current limit value m(θ) at that electrical angle.
[0015] Furthermore, the current limit value m(θ) mentioned in step 1 is a function that varies with the electrical angle θ. The function is obtained by combining the current constraint conditions of the winding topology.
[0016] The constraints of the isolated neutral point topology are as follows:
[0017]
[0018] In this case, the current of the phase with the smallest torque contribution in phases ABC and DEF is represented by the currents of the other two phases, so as to satisfy the constraint conditions of the above isolated neutral point topology.
[0019] The constraints for the topology connecting neutral points are as follows:
[0020] i A +i B +i C +i D +i E +i F =0
[0021] Among them, the current of the phase with the smallest torque contribution in phases ABCDEF is represented by the currents of the other five phases to satisfy the constraints of the above-mentioned connection neutral point topology.
[0022] In an open winding topology: the current limit value can be obtained by directly making the six-phase currents equal.
[0023] Furthermore, the constant torque mentioned in step 1 is for a unit q-axis current. In practical applications, the input reference value is multiplied by the actual q-axis current reference value to suit the actual system.
[0024] Furthermore, the purpose of the nonlinear optimization described in step 2 is to minimize the phase current amplitude while keeping the torque output constant, thereby minimizing the maximum instantaneous copper loss of the phase and reducing the total instantaneous copper loss under the above premise, thus meeting the loss optimization requirements for low-speed and stationary operating conditions.
[0025] Furthermore, the curve fitting method described in step 3 is to use a sine sum to fit the current curve within one cycle into a superposition of multiple orders of sines, and the orders of these sines are all set to integers.
[0026] Furthermore, the motor control system described in step 4 adopts a vector control method, wherein, when operating at low speed or in a stationary condition, a PI controller is used to track the current reference value, or a controller with zero deadbeat and repetitive control is used to track the current reference value with higher precision.
[0027] Compared with the prior art, the beneficial effects of the present invention are:
[0028] (1) The loss optimization control method for dual three-phase motors proposed in this invention for low speed and static conditions can reduce the heat loss of motor and drive system to a greater extent and improve the problem of uneven temperature distribution compared with existing loss optimization methods.
[0029] (2) This invention constructs loss optimization as a nonlinear optimization problem. The equations obtained by traditional KKT conditions often do not have solutions. This invention uses the interior point method for numerical calculation, which can directly obtain the optimal reference value for each electrical angle.
[0030] (3) The current limit value calculation and internal point method solution in this invention can also be applied to three-phase open winding motors.
[0031] (4) The optimal current expression for unit output torque obtained in this invention can be multiplied by the actual q-axis current value in the actual application system to be applicable to the actual system and various working conditions. Attached Figure Description
[0032] Figure 1 This is a schematic diagram of the winding topology of the dual three-phase motor used in this invention, wherein (a) is an isolated neutral point topology, (b) is a connected neutral point topology, and (c) is an open winding topology.
[0033] Figure 2 This is a flowchart of a specific implementation method of the present invention;
[0034] Figure 3 The optimal six-phase current within one cycle obtained by the present invention is shown in (a) for an isolated neutral point topology, (b) for a connected neutral point topology, and (c) for an open winding topology. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining this invention and not for limiting it; that is, the described embodiments represent only selected embodiments of this invention and not all embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0036] Figure 1 This is a schematic diagram of the winding topology of the dual three-phase motor used in this invention. This invention calculates the current limit value while maintaining constant output torque, establishes the objective function and constraints, constructs a nonlinear optimization problem, and then solves it using the interior point method to obtain the current reference value. Curve fitting is then performed to obtain the optimal reference current expression, which is finally substituted into the control system, effectively reducing the motor's heat loss and uneven temperature distribution. Furthermore, since this invention calculates the current reference value based on a unit q-axis current, in practical applications, the current reference value can be multiplied by the actual q-axis current reference value, making it applicable to various operating conditions.
[0037] More specifically, the specific implementation steps of the loss optimization control method for a low-speed dual three-phase motor drive system of the present invention are as follows (see...). Figure 2 ):
[0038] Step 1: For the mathematical models of motors with different winding topologies, analyze the minimum value that the phase current amplitude can reach without changing the torque output. This is called the current limit value m(θ). Based on the different current constraints of isolated neutral point, connected neutral point, and open winding topologies, the corresponding current limit values can be calculated.
[0039] The current limit needs to be calculated under the premise of the same torque output, with the following constraints:
[0040]
[0041] Among them, i q It is the q-axis current of the motor in the rotating coordinate system, which is proportional to the motor's output torque, θ e It is the electrical angle of the rotor, i A i B i C i D i E i F This refers to the six-phase current of the motor. At a certain electrical angle, when the maximum phase current value is reduced and the other phase current values are increased to compensate for the torque, until all phase current values are equal, the current limit value at this point is the current limit value for that electrical angle. Based on the constraints of different winding topologies on the current, the formula for calculating the current limit value is as follows:
[0042] A. Isolating the neutral point
[0043]
[0044] B. Connect the neutral point
[0045]
[0046] C. Open winding
[0047]
[0048] Since the current limit is θ e Since the function is a piecewise function with respect to the independent variable, the process of calculating the extrema is quite cumbersome. Therefore, this invention adopts the method of directly plotting the function curve of one period and selecting the maximum current limit value as the constraint condition to meet the requirements of any electrical angle on the current amplitude. Finally, the phase current constraints for isolated neutral point, connected neutral point, and open winding are found to be 0.9283, 0.8966, and 0.8038, respectively.
[0049] Step 2: Using the phase current limit and unit torque output as constraints, and the total copper loss as the objective function, establish a nonlinear optimization problem and use the interior point method to solve it to obtain the optimal six-phase current reference value for each electrical angle.
[0050] Different winding topologies can all be constructed as a nonlinear optimization problem, the only difference being the different phase current constraints. The problem is expressed as follows:
[0051] A. Isolating the neutral point
[0052] min f = i A 2 +i B 2 +i C 2 +i D 2 +i E 2 +i F 2
[0053]
[0054] B. Connect the neutral point
[0055] min f = i A 2 +i B 2 +i C 2 +i D 2 +i E 2 +i F 2
[0056]
[0057] C. Open winding
[0058] min f = i A 2 +i B 2 +i C 2 +i D 2 +i E 2 +i F 2
[0059]
[0060] The optimization problem described above can be simply represented as follows:
[0061] min f(x)
[0062]
[0063] Here, x is the optimization variable of the problem, f(x) is the objective function, g(x) is the inequality expression, and g with subscripts and superscripts represents the upper and lower bounds of the inequality constraints. The interior-point method is a typical approach for solving nonlinear optimization problems with inequality constraints. Its steps can be summarized as follows: τ uses a barrier function to transform the inequality constraints into the objective function, where τ is a very small positive number.
[0064]
[0065] sth(x)=0
[0066] Then, the equality constraints are transformed into unconstrained optimization using the Lagrange multiplier method:
[0067]
[0068]
[0069] Finally, the above equation is solved using an iterative method to obtain the result. Alternatively, other methods that can solve inequality constraints can also be used to calculate the constructed nonlinear optimization problem.
[0070] In practical applications, the nonlinear optimization problem described in step 2 often lacks an algebraic solution due to the complexity of the equations. The interior point method is a typical method for solving nonlinear optimization problems with inequality constraints. It can numerically solve the constructed nonlinear optimization problem and obtain the optimal current reference value for each electrical angle.
[0071] Step 3: Convert the optimal six-phase current reference value for each electrical angle into a decoupled current reference value through VSD transformation, and perform curve fitting to obtain the optimal current reference expression; Figure 3 This invention provides the optimal six-phase current within one cycle.
[0072] Curve fitting uses a sine sum method, which is the superposition of sine functions of different orders, where the order of the sine function is an integer, which facilitates the understanding and design of the controller of the drive system.
[0073] Step 4: Use the optimal current expression as the input reference value of the motor control system to drive the dual three-phase motor to achieve loss optimization control.
[0074] After obtaining the current reference expression, this invention substitutes the reference current into the control system, enabling the controller to track the current reference value. Since the derivation uses unit torque output, in a practical system, the input reference value can be directly multiplied by the actual q-axis current reference value to suit the actual system and various operating conditions. The actual q-axis current reference value is determined by the motor torque.
[0075] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed in the specific embodiments and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be modified within the scope of the concept described in the present invention through the teachings and inspirations above or through technology or knowledge in related fields. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.
Claims
1. A loss optimization control method for a low-speed dual three-phase motor drive system, characterized in that, The method includes the following steps: Step 1: For the mathematical models of motors with different winding topologies, analyze the minimum achievable value of the phase current amplitude without changing the torque output. This minimum value is the current limit value. m(θ) This includes: calculating the corresponding current limit values based on different current constraint conditions for isolated neutral point topologies, connected neutral point topologies, and open winding topologies; among which... θ It is an electrical angle; Step 2: Set the current limit value m(θ) With unit torque output as a constraint and total copper loss as the objective function, a nonlinear optimization problem is established, and the interior point method is used to solve it to obtain the optimal six-phase current reference value for each electrical angle. Step 3: Convert the optimal six-phase current reference value for each electrical angle into a decoupled current reference value through VSD transformation, and perform curve fitting to obtain the optimal current reference expression; Step 4: Use the optimal current expression as the input reference value of the motor control system to drive the dual three-phase motor to achieve loss optimization control; In step 1, the current limit value is the minimum phase current amplitude that can be achieved under the condition of constant torque output. The formula for the current constrained by the torque condition is as follows: in, i q The motor in a rotating coordinate system q The shaft current is directly proportional to the motor's output torque. θ e It is the electrical angle of the rotor. i A , i B , i C , i D , i E , i F This refers to the six-phase current of the motor. At a certain electrical angle, when the maximum phase current value is reduced and the other phase current values are increased to compensate for the torque until all phase current values are equal, the phase current value at this point is the current limit value at that electrical angle. m(θ) ; The current limit value mentioned in step 1 m(θ) It is the angle that varies with electricity. θ The changing function, the functional expression is obtained in combination with the constraints of the winding topology on the current; The constraints of the isolated neutral point topology are as follows: In this case, the current of the phase with the smallest torque contribution in phases ABC and DEF is represented by the currents of the other two phases, so as to satisfy the constraint conditions of the above isolated neutral point topology. The constraints for the topology connecting neutral points are as follows: Among them, the current of the phase with the smallest torque contribution in phases ABCDEF is represented by the currents of the other five phases to satisfy the constraints of the above-mentioned connection neutral point topology. In an open-winding topology: the current limit value can be obtained by directly making the six-phase currents equal; in, i A , i B , i C , i D , i E , i F It is the six-phase current of the motor.
2. The loss optimization control method for a low-speed dual three-phase motor drive system according to claim 1, characterized in that, The constant torque mentioned in step 1 is for a unit q For shaft current, in practical applications, the input reference value is multiplied by the actual value. q The shaft current reference value is adapted for use in actual systems.
3. The loss optimization control method for a low-speed dual three-phase motor drive system according to claim 1, characterized in that, The purpose of the nonlinear optimization described in step 2 is to minimize the phase current amplitude while keeping the torque output constant, thereby minimizing the maximum instantaneous copper loss of the phase and reducing the total instantaneous copper loss under the above premise, thus meeting the loss optimization requirements for low-speed and stationary operating conditions.
4. The loss optimization control method for a low-speed dual three-phase motor drive system according to claim 1, characterized in that, The curve fitting method described in step 3 is to use a sine sum to fit the current curve within one cycle into a superposition of multiple orders of sines, and the orders of these sines are all set to integers.
5. The loss optimization control method for a low-speed dual three-phase motor drive system according to claim 1, characterized in that, The motor control system described in step 4 adopts a vector control method. In low-speed or stationary conditions, a PI controller is used to track the current reference value, or a controller with zero deadbeat and repetitive control is used to track the current reference value with higher precision.