Electric excitation synchronous motor sensorless control method and system

Abstract

The invention discloses an electro-magnetic synchronous motor sensorless control method and system, and belongs to the technical field of synchronous motor control. A common voltage model and a complete current model considering a damping winding are combined, an effective flux linkage is introduced, the introduced effective flux linkage is a difference value between a stator flux linkage and a stator current quadrature-axis induced flux linkage, the stator flux linkage and the effective flux linkage are observed, the output of the current model is taken as an effective flux linkage instruction, and the stator current quadrature-axis induced flux linkage is calculated. The output of the voltage model is effective flux linkage feedback, and the effective flux linkage output difference value of the two serves as the compensation item of the voltage model through the PI controller, so that the adverse effects generated by the stator resistance of the voltage model and the integrator are eliminated, and the estimation error of the effective flux linkage is reduced. Compared with a traditional control strategy which can only estimate accurately in a steady state, the position sensorless control method provided by the invention can accurately track the position and the speed in the whole dynamic process of the motor.

Description

Technical Field

[0001] The present invention belongs to the technical field of synchronous motor control, and more specifically, relates to a position sensorless control method and system for an electrically excited synchronous motor. Background Art

[0002] In the full-power rectifier variable-speed pumped storage system at the megawatt power level, the electrically excited synchronous motor has the advantages of high-voltage economy, adjustable power factor and strong short-circuit current handling capability, so it has become the first choice for the full-power variable-speed pumped storage system. In addition, the electrically excited synchronous motor is also suitable for other high-power variable-frequency drive occasions such as wind tunnel fans.

[0003] Generally, rotor position sensors are indispensable for high-performance variable frequency control of synchronous motors. However, position sensors not only increase system costs, but their accuracy is also affected by the environment in which they are located. Failure of the position sensor directly leads to downtime, so position sensorless control technology has become an alternative to position sensors.

[0004] Compared with permanent magnet synchronous motors, electrically excited synchronous motors have one more set of excitation windings and two sets of damping windings. Since the mathematical model of electrically excited synchronous motors with damping windings is relatively complex, the common position sensorless models based on electrically excited synchronous motors directly ignore the damping windings or simplify the damping windings as much as possible to reduce the amount of calculation. The impact of this simplification is that the rotor position and speed estimation deviations are large during the dynamic operation of the motor, and in severe cases, it may even cause loss of step, which has a devastating impact in high-power situations.

[0005] Generally, position and speed information needs to be obtained from the magnetic flux, so the magnetic flux of the motor needs to be observed. Common magnetic flux observers are divided into voltage models and current models. For fans and pumps that are common in high-power applications, the load is small at low speed, the signal-to-noise ratio is low, and the stator resistance voltage drop accounts for a large proportion, resulting in poor voltage model estimation accuracy; at high speeds, the load increases with the speed, the motor magnetic circuit is saturated, and the current model estimation accuracy also decreases. Both models have their own speed application ranges, and cannot achieve position sensorless control in the full speed range.

[0006] In summary, it is necessary to propose a position sensorless control technology for an electrically excited synchronous motor that is applicable to the full speed range and can accurately track the position and speed in both dynamic and steady states. Summary of the invention

[0007] In view of the defects of the prior art, the purpose of the present invention is to provide a position sensorless control method and system for an electrically excited synchronous motor, aiming to solve the problem of inaccurate position and speed estimation in the dynamic process of the traditional position sensorless control method for an electrically excited synchronous motor.

[0008] To achieve the above object, the present invention provides a position sensorless control method for an electrically excited synchronous motor, comprising the following steps:

[0009] The effective flux command is obtained by sampling the stator current, the rotor excitation current and the introduced effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux; the sampled stator voltage and the stator resistance voltage drop are subtracted to obtain the back electromotive force of the motor, the back electromotive force is integrated to obtain the estimated value of the stator flux, and then the estimated value of the stator flux is subtracted from the stator current quadrature-axis induced flux to obtain the effective flux feedback; the effective flux command is subtracted from the effective flux feedback, and the difference is used as a voltage compensation item after PI control, and is compensated to the stator voltage to form a closed loop;

[0010] The effective flux linkage command is input into the inverse tangent function to obtain the rotor position for speed estimation and realize speed closed-loop control.

[0011] Furthermore, the introduced effective magnetic flux is:

[0012]

[0013] Among them, ψ s is the stator flux, i s is the stator current, σ q is the q-axis leakage reactance coefficient, σ Q is the Q-axis leakage reactance coefficient, x q is the q-axis reactance, x mq is the q-axis synchronous reactance, T Q is the time constant of Q-axis damping winding, and s is the differential operator.

[0014] Furthermore, the effective magnetic link instruction is:

[0015]

[0016] in, σ d is the d-axis leakage reactance coefficient, σ D is the leakage reactance coefficient of the D axis, which is x d is the d-axis reactance, x md is the d-axis synchronous reactance, i f is the rotor excitation current.

[0017] Furthermore, the effective flux linkage instruction is input into the inverse tangent function to estimate the rotor position, and the estimated value of the rotor position is obtained as follows:

[0018]

[0019] in, is the β-axis component of the effective flux command, It is the α-axis component of the effective flux command.

[0020] Furthermore, the rotational speed is estimated by the backward difference method according to the estimated rotor position, and the expression of the obtained rotational speed is:

[0021]

[0022] in, is the α-axis component of the effective flux command at time k, is the α-axis component of the effective flux command at time k, T s is the sampling frequency, k is the current moment, and k-1 is the previous moment.

[0023] The present invention also provides a position sensorless control system for an electrically excited synchronous motor, comprising:

[0024] A closed-loop effective flux observer is used to obtain an effective flux instruction through the sampled stator current, rotor excitation current and introduced effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux; the sampled stator voltage and the stator resistance voltage drop are subtracted to obtain the back electromotive force of the motor, the back electromotive force is integrated to obtain the estimated value of the stator flux, and then the estimated value of the stator flux is subtracted from the stator current quadrature-axis induced flux to obtain an effective flux feedback; the effective flux instruction is subtracted from the effective flux feedback, and the difference is used as a voltage compensation term after PI control, and is compensated to the stator voltage to form a closed loop;

[0025] The speed estimation module is used to input the effective flux linkage command into the inverse tangent function to obtain the rotor position for speed estimation and realize speed closed-loop control.

[0026] Compared with the prior art, the above technical solutions conceived by the present invention can achieve the following

[0027] Beneficial effects:

[0028] (1) The present invention provides a position sensorless control method and system for an electrically excited synchronous motor, which constructs a complete mathematical model of the electrically excited synchronous motor including a damping winding, combines a common voltage model with a complete current model that takes into account the damping winding, and introduces an effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current cross-axis induced flux. By observing the stator flux and the effective flux, the output of the current model is used as the effective flux instruction, and the output of the voltage model is used as the effective flux feedback. The difference between the effective flux outputs of the two is used as a compensation item of the voltage model through a PI controller, thereby eliminating the adverse effects of the stator resistance and integrator of the voltage model and reducing the estimation error of the effective flux. Compared with the traditional control strategy that can only accurately estimate in steady state, the position sensorless control method proposed in the present invention can accurately track the position and speed of the motor during the entire dynamic process.

[0029] (2) The position and speed estimation method proposed in the present invention is relatively simple to implement. The rotor position and speed can be calculated by simply using the effective magnetic flux through the inverse tangent function and the backward difference method. At the same time, this calculation method also has good calculation accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 A spatial vector diagram of the stator flux and effective flux of the motor provided by the present invention;

[0031] Figure 2 This is a control block diagram of the closed-loop effective flux observer provided by the present invention. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0033] The present invention provides a position sensorless control method for an electrically excited synchronous motor, comprising:

[0034] The effective flux command is obtained by sampling the stator current, the rotor excitation current and the introduced effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux; the sampled stator voltage and the stator resistance voltage drop are subtracted to obtain the back electromotive force of the motor, the back electromotive force is integrated to obtain the estimated value of the stator flux, and then the estimated value of the stator flux is subtracted from the stator current quadrature-axis induced flux to obtain the effective flux feedback; the effective flux command is subtracted from the effective flux feedback, and the difference is used as a voltage compensation item after PI control, and is compensated to the stator voltage to form a closed loop;

[0035] The effective flux in the two-phase stationary coordinate system αβ is input into the inverse tangent function to obtain the rotor position for speed estimation and realize speed closed-loop control.

[0036] Those skilled in the art know that existing methods may be used to estimate the rotation speed, such as a backward difference method, a forward difference method, etc., and the embodiments of the present invention do not limit this method to a unique method.

[0037] For an electrically excited synchronous motor, the flux equation satisfies:

[0038]

[0039] Wherein, the d-axis and q-axis are two orthogonal coordinate axes of the rotating coordinate system of the stator winding, the D-axis and Q-axis are two orthogonal coordinate axes of the rotating coordinate system of the damping winding, ψ d is the d-axis magnetic flux, ψ q is the q-axis magnetic flux, ψ f is the excitation flux, ψ D is the D-axis magnetic flux, ψ Q is the Q-axis magnetic flux, i d is the d-axis current, i q is the q-axis current, i f is the excitation current, i D is the D-axis current, i Q is the Q-axis current, x d is the d-axis reactance, x q is the q-axis reactance, x f is the magnetizing reactance, x D is the D-axis reactance, x Q is the Q-axis reactance, x md is the d-axis synchronous reactance, x mq is the q-axis synchronous reactance. All physical quantities involved in the present invention are expressed in per unit.

[0040] Since the D and Q damping windings are short-circuited, the voltage across the windings is 0, and the voltage equation is:

[0041]

[0042] Among them, r D is the D-axis damping resistance, r Q is the Q-axis damping resistance, ω n is the rated speed.

[0043] Rewrite all synchronous reactances into armature reaction reactances, and the equation is

[0044]

[0045] Among them, σ dis the d-axis leakage reactance coefficient, σ q is the q-axis leakage reactance coefficient, σ f is the excitation leakage reactance coefficient, σ D is the D-axis leakage reactance coefficient, σ Q is the Q-axis leakage reactance coefficient.

[0046] Substituting the rewritten armature reaction reactance equation into the flux equation, the resulting expression is

[0047]

[0048] Among them, the new leakage impedance coefficient σ introduced dD , σ dQ , σ fD and the damping winding time constant T D 、T Q The expression is

[0049]

[0050] Further simplifying the magnetic linkage expression, we can get the following expression:

[0051] Among them, the following intermediate variables are introduced:

[0052]

[0053] It can be seen that the damping flux linkage is a differential equation, and its frequency domain expression is obtained by solving it:

[0054] Finally, the dynamic equation of the stator flux is obtained as follows:

[0055]

[0056] In order to obtain position and speed information, the concept of effective magnetic flux is introduced here. The expression of effective magnetic flux is:

[0057]

[0058] Among them, ψ r is the effective magnetic flux, ψ s is the stator flux, and is shown in bold as a vector. That is the stator current cross-axis induced magnetic flux.

[0059] The scalar expression for the effective flux linkage is:

[0060]

[0061] From the expression of effective flux, it can be seen that since the effective flux equation only contains the d-axis component and the excitation component of the stator, the vector direction of the effective flux always completely coincides with the d-axis direction, whether it is the steady state or dynamic process of the motor. Its space vector diagram is as follows: Figure 1 Therefore, the rotor position can be calculated by determining the position of the effective flux.

[0062] Generally, the stator (or effective) flux can be obtained through a voltage model and a current model. The voltage model estimates the flux through the stator voltage and the stator current, while the current model estimates the flux through the stator current and the rotor position. Both models have problems when running independently: the voltage model will cause a large flux estimation error due to the temperature rise effect of the stator resistance and the zero drift of the integrator; and the current model will cause reactance saturation as the load increases, ultimately resulting in a large deviation in the estimated flux. Therefore, the present invention proposes a closed-loop flux observer, such as Figure 2 The output of the current model is the effective flux command, and the output of the voltage model is the effective flux feedback. The difference between the two is output by the PI regulator as the compensation term v of the voltage regulator. comp , to compensate for the influence of stator resistance and integrator, the calculation expression is:

[0063]

[0064] The expression for estimating the rotor position obtained by the effective flux command is:

[0065]

[0066] in, is the β-axis component of the effective flux command, is the α-axis component of the effective flux command,

[0067] The estimated speed expression obtained by the estimated rotor position is:

[0068]

[0069] in, is the α-axis component of the effective flux command at time k, is the α-axis component of the effective flux command at time k, T s is the sampling frequency, k is the current moment, and k-1 is the previous moment.

[0070] In summary, the present invention proposes a new position sensorless control method based on the traditional electrically excited synchronous motor position sensorless control method. By building a complete mathematical model of the electrically excited synchronous motor including the damping winding, and introducing the effective flux to estimate the rotor position and speed, its dynamic process is more accurate than the traditional position sensorless control method that ignores the damping winding. In addition, the closed-loop flux observer has a smaller estimation error and higher robustness than the traditional open-loop flux observer using a voltage or current model. Therefore, this control method is suitable for scenarios where it is impossible to install a position sensor and where high control accuracy and dynamic response requirements are required.

[0071] It will be easily understood by those skilled in the art that the above description is only 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 in the protection scope of the present invention.

Claims

1. A position sensorless control method for an electrically excited synchronous motor, characterized in that: The following steps are involved: The effective flux command is obtained by sampling the stator current, the rotor excitation current and the introduced effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux; the sampled stator voltage and the stator resistance voltage drop are subtracted to obtain the back electromotive force of the motor, the back electromotive force is integrated to obtain the estimated value of the stator flux, and then the estimated value of the stator flux is subtracted from the stator current quadrature-axis induced flux to obtain the effective flux feedback; the effective flux command is subtracted from the effective flux feedback, and the difference is used as a voltage compensation item after PI control, and is compensated to the stator voltage to form a closed loop; The effective flux linkage command is input into the inverse tangent function to obtain the rotor position for speed estimation and speed closed-loop control.

2. The method according to claim 1, characterized in that The effective magnetic flux introduced is: Among them, ψ s is the stator flux, i s is the stator current, σ q is the q-axis leakage reactance coefficient, σ Q is the Q-axis leakage reactance coefficient, x q is the q-axis reactance, x mq is the q-axis synchronous reactance, T Q is the time constant of Q-axis damping winding, and s is the differential operator.

3. The method according to claim 2, characterized in that The effective magnetic link instructions are: in, σ d is the d-axis leakage reactance coefficient, σ D is the leakage reactance coefficient of the D axis, which is, x d is the d-axis reactance, x md is the d-axis synchronous reactance, i f is the rotor excitation current.

4. The method according to claim 1, characterized in that: The effective flux linkage instruction is input into the inverse tangent function to estimate the rotor position, and the estimated value of the rotor position is obtained as follows: in, is the β-axis component of the effective flux command, It is the α-axis component of the effective flux command.

5. The method according to claim 1, characterized in that The rotation speed is estimated by the backward difference method according to the estimated rotor position, and the expression of the obtained rotation speed is: in, is the α-axis component of the effective flux command at time k, is the α-axis component of the effective flux command at time k, T s is the sampling frequency, k is the current moment, and k-1 is the previous moment.

6. A position sensorless control system for an electrically excited synchronous motor, characterized in that: include: A closed-loop effective flux observer is used to obtain an effective flux instruction through the sampled stator current, rotor excitation current and introduced effective flux, wherein the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux; the sampled stator voltage and the stator resistance voltage drop are subtracted to obtain the back electromotive force of the motor, the back electromotive force is integrated to obtain the estimated value of the stator flux, and then the estimated value of the stator flux is subtracted from the stator current quadrature-axis induced flux to obtain an effective flux feedback; the effective flux instruction is subtracted from the effective flux feedback, and the difference is used as a voltage compensation term after PI control, and is compensated to the stator voltage to form a closed loop; The speed estimation module is used to input the effective flux linkage command into the inverse tangent function to obtain the rotor position for speed estimation and to realize speed closed-loop control.

7. The system according to claim 6, characterized in that The effective magnetic flux introduced is: Among them, ψ s is the stator flux, i s is the stator current, σ q is the q-axis leakage reactance coefficient, σ Q is the Q-axis leakage reactance coefficient, x q is the q-axis reactance, x mq is the q-axis synchronous reactance, T Q is the time constant of Q-axis damping winding, and s is the differential operator.

8. The system according to claim 7, characterized in that The effective magnetic link instructions are: in, σ d is the d-axis leakage reactance coefficient, σ D is the leakage reactance coefficient of the D axis, which is, x d is the d-axis reactance, x md is the d-axis synchronous reactance, i f is the rotor excitation current.

9. The system according to claim 6, characterized in that The effective flux linkage instruction is input into the inverse tangent function to estimate the rotor position, and the estimated value of the rotor position is obtained as follows: in, is the β-axis component of the effective flux command, It is the α-axis component of the effective flux command.

10. The system according to claim 6, characterized in that The rotation speed is estimated by the backward difference method according to the estimated rotor position, and the expression of the obtained rotation speed is: in, is the α-axis component of the effective flux command at time k, is the α-axis component of the effective flux command at time k, T s is the sampling frequency, k is the current moment, and k-1 is the previous moment.

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