A position sensorless control method and system for a field-oriented synchronous machine

Abstract

The application discloses a kind of electrically excited synchronous motor position sensorless control method and system, belong to synchronous motor control technical field.The application combines the complete current model considering the damping winding of common voltage model, and introduces effective flux linkage, the difference of stator flux linkage and stator current quadrature axis induced flux linkage is introduced as the effective flux linkage, the output of current model is effective flux linkage instruction by observing stator flux linkage and effective flux linkage, the output of voltage model is effective flux linkage feedback, the difference of the effective flux linkage output of two is PI controller as the compensation item of voltage model, to eliminate the adverse effects of stator resistance and integrator generated by voltage model, reduce the estimation error of effective flux linkage.Compared with the traditional control strategy can only be estimated accurately in steady state, the position sensorless control method proposed by the application can accurately track position and speed in the whole dynamic process of motor.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of synchronous motor control, and more particularly relates to a field-oriented synchronous motor sensorless control method and system. BACKGROUND

[0002] In a megawatt power level full-power rectifier type variable speed pumped storage system, the field-oriented synchronous motor has the advantages of high voltage economy, adjustable power factor, and strong short-circuit current handling capability, and therefore becomes the first choice for full-power variable speed pumped storage systems. In addition, the field-oriented synchronous motor is also suitable for other high-power variable frequency driving occasions such as wind tunnel fans.

[0003] Generally, to achieve high-performance variable frequency control of the synchronous motor, a rotor position sensor is indispensable. However, the position sensor not only increases the system cost, but its accuracy is also affected by the environment. The failure of the position sensor directly leads to shutdown, so the sensorless control technology becomes an alternative to the position sensor.

[0004] Compared with the permanent magnet synchronous motor, the field-oriented synchronous motor has an additional set of field winding and two sets of damping winding. Due to the complex mathematical model of the field-oriented synchronous motor with damping winding, the current common sensorless model based on the field-oriented synchronous motor directly ignores the damping winding or simplifies the damping winding as much as possible to reduce the calculation amount. The impact of this simplification is that the rotor position and speed estimation deviation is large during the dynamic process of the motor, and in severe cases, it may even lead to step-out, which has a devastating impact in high-power applications.

[0005] Generally, position and speed information need to be obtained from the flux linkage, so the flux linkage of the motor needs to be observed. Common flux linkage observers are divided into voltage models and current models. For common fans, pumps and other loads 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 estimation accuracy of the voltage model; while at high speed, the load increases with the increase of the speed, the magnetic circuit of the motor is saturated, and the estimation accuracy of the current model also decreases. Both models have their own speed application range, and cannot achieve sensorless control in the full speed range.

[0006] In summary, a sensorless control technology for the field-oriented synchronous motor that is suitable for the full speed range and can accurately track the position and speed in both dynamic and steady states is needed. SUMMARY

[0007] In view of the defects of the prior art, the purpose of the present application is to provide a field-oriented synchronous motor sensorless control method and system, which aims to solve the problem of inaccurate position and speed estimation in the dynamic process of the traditional field-oriented synchronous motor sensorless control method.

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

[0009] An effective flux command is obtained by sampling the stator current, the rotor excitation current and the introduced effective flux, the introduced effective flux being the difference between the stator flux and the stator current quadrature axis induced flux; the back electromotive force of the motor is obtained by subtracting the stator voltage from the stator resistance voltage drop, the back electromotive force is integrated to obtain the estimated value of the stator flux, and 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 and the effective flux feedback are subtracted, and the difference is PI controlled to be used as a voltage compensation term and compensated into the stator voltage to form a closed loop;

[0010] The effective flux command is input into an arctangent function to obtain the rotor position for speed estimation, so as to realize speed closed loop control.

[0011] Further, the introduced effective flux is:

[0012]

[0013] wherein 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 Q-axis damper winding time constant, and s is a differential operator.

[0014] Further, the effective flux command is:

[0015]

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

[0017] Further, the effective flux command is input into an arctangent function to estimate the rotor position, and the estimated value of the rotor position is:

[0018]

[0019] wherein, is the beta axis component of the effective flux command, is the alpha axis component of the effective flux command.

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

[0021]

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

[0023] The application also provides a position sensorless control system of an electrically excited synchronous motor, comprising:

[0024] a closed-loop effective flux observer, configured to obtain an effective flux command by sampling a stator current, a rotor excitation current and an introduced effective flux, the introduced effective flux being a difference between a stator flux and a cross-axis induced flux of the stator current; subtracting a sampled stator voltage from a stator resistance voltage drop to obtain an induced electromotive force of the motor, integrating the induced electromotive force to obtain an estimated value of the stator flux, and subtracting the estimated value of the stator flux from the cross-axis induced flux of the stator current to obtain an effective flux feedback; and subtracting the effective flux command from the effective flux feedback, and taking a difference value as a voltage compensation item after PI control, and compensating into the stator voltage to form a closed loop;

[0025] a rotor speed estimation module, configured to input the effective flux command into an arctangent function to obtain a rotor position for rotor speed estimation, and to realize rotor speed closed-loop control.

[0026] Compared with the prior art, the above technical scheme conceived by the application can achieve the following

[0027] Advantages:

[0028] (1) The application provides a position sensorless control method and system of an electrically excited synchronous motor, a complete mathematical model of a damping winding of the electrically excited synchronous motor is built, a common voltage model and a complete current model considering the damping winding are combined, and an effective flux is introduced, the introduced effective flux is a difference value of a stator flux and a stator current cross-axis induced flux, the stator flux and the effective flux are observed, the output of the current model is used as an effective flux instruction, the output of the voltage model is used as an effective flux feedback, and a difference value of the effective flux output of the two is taken as a compensation item of the voltage model through a PI controller, so that the adverse effects of the stator resistance and the integrator of the voltage model are eliminated, and the estimation error of the effective flux is reduced.

[0029] (2) The position and speed estimation method provided by the application is relatively simple to realize, and only the effective flux needs to be calculated through an arctangent function and a backward difference method to obtain the rotor position and speed, and the calculation method has good calculation accuracy. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A space vector diagram of a motor stator flux and an effective flux provided by the application;

[0031] Figure 2 A closed-loop effective flux observer control block diagram provided by the application. DETAILED DESCRIPTION

[0032] In order to make the purpose, technical scheme and advantages of the application clearer, the application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the application, and are not used to limit the application. In addition, the technical features involved in each embodiment of the application described below can be combined with each other as long as they do not conflict with each other.

[0033] The application provides a position sensorless control method of an electrically excited synchronous motor, comprising:

[0034] An effective flux instruction is obtained through the sampled stator current, the rotor excitation current and the introduced effective flux, the introduced effective flux is a difference value of the stator flux and the stator current cross-axis induced flux; a back electromotive force of the motor is obtained by subtracting the sampled stator voltage and the stator resistance voltage drop, the estimation value of the stator flux is obtained by integrating the back electromotive force, and the effective flux feedback is obtained by subtracting the estimation value of the stator flux and the stator current cross-axis induced flux; the effective flux instruction and the effective flux feedback are subtracted, and the difference value is taken as a voltage compensation item after PI control, and the compensation is formed into a closed loop in the stator voltage.

[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 will appreciate that existing methods may be used to estimate the rotational speed, such as a backward difference method, a forward difference method, etc., and the embodiments of the present invention do not impose any exclusive limitation on this.

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

[0038]

[0039] Wherein, the d-axis and the q-axis are two orthogonal coordinate axes of the rotating coordinate system of the stator winding, the D-axis and the Q-axis are two orthogonal coordinate axes of the rotating coordinate system of the damper winding, and 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 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 as 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 linkage equation, the obtained expression is

[0047]

[0048] wherein the new leakage reactance coefficient σ dD , σ dQ , σ fD and the damping winding time constant T D , T Q are introduced.

[0049]

[0050] Further simplifying the flux linkage expression, the following expression can be obtained

[0051] wherein the following intermediate variables are introduced again:

[0052]

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

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

[0055]

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

[0057]

[0058] wherein ψ r is the effective flux linkage, ψ s is the stator flux linkage, and the bold indicates a vector. That is, the stator current quadrature axis induced flux linkage.

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

[0060]

[0061] As can be seen from the expression of the effective flux linkage, since the effective flux linkage equation only contains the d-axis component of the stator and the excitation component, the vector direction of the effective flux linkage is always completely coincident with the d-axis direction, whether in the steady state or dynamic process of the motor, and the space vector diagram is as shown in Figure 1 Therefore, the position of the effective flux linkage is determined to calculate the rotor position.

[0062] Generally, the stator (or effective) flux linkage can be obtained by a voltage model and a current model. The voltage model estimates the flux linkage through the stator voltage and the stator current, while the current model estimates the flux linkage through the stator current and the rotor position. Both models have problems when running independently: the voltage model will cause a large flux linkage 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 a large deviation in the estimated flux linkage due to the increase in the load and the saturation of the reactance. Therefore, the present application proposes a closed-loop flux linkage observer, as shown in Figure 2 The output of the current model is the effective flux linkage command, the output of the voltage model is the effective flux linkage feedback, and the difference between the two is output as a compensation item v comp of the voltage regulator through a PI regulator to compensate for the effects of the stator resistance and the integrator, and the calculation expression is:

[0063]

[0064] The expression for estimating the rotor position through the effective flux linkage command is:

[0065]

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

[0067] The expression for estimating the rotor speed through the estimated rotor position is:

[0068]

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

[0070] In summary, the application proposes a new type of position sensorless control method based on the traditional position sensorless control method of the conventional electrically excited synchronous motor. By building a complete mathematical model of the electrically excited synchronous motor including the damping winding, and introducing the effective flux linkage to estimate the rotor position and speed, the dynamic process is more accurate compared to the traditional position sensorless control method which ignores the damping winding. In addition, the closed-loop flux linkage observer has smaller estimation error and higher robustness compared to the traditional open-loop flux linkage observer which uses voltage or current model. Therefore, the control method is suitable for scenarios where position sensors cannot be installed and high control accuracy and dynamic response are required.

[0071] Those skilled in the art will easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application. Any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

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, rotor excitation current and the introduced effective flux. 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 motor's back electromotive force. The back electromotive force is integrated to obtain an estimated value of the stator flux. The estimated value of the stator flux is then subtracted from the stator current quadrature-axis induced flux to obtain an effective flux feedback. The effective flux command is subtracted from the effective flux feedback, and the difference is used as a voltage compensation term after PI control and compensated to the stator voltage to form a closed loop. The introduced effective flux is: Among them, the d-axis and the q-axis are two orthogonal coordinate axes of the rotating coordinate system of the stator winding, and the D-axis and the Q-axis are two orthogonal coordinate axes of the rotating coordinate system of the damper winding. is the stator flux, is the stator current, , is the q-axis leakage reactance coefficient, is the Q-axis leakage reactance coefficient, is the q-axis reactance, , x mq is the q-axis synchronous reactance, is the time constant of the Q-axis damping winding, s is the differential operator; The effective magnetic linkage instructions are: in, , is the d-axis leakage reactance coefficient, is the D-axis leakage reactance coefficient, is the time constant of the D-axis damping winding, is the d-axis reactance, , x md is the d-axis synchronous reactance, is the rotor excitation current; 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 flux linkage instruction is input into the inverse tangent function to estimate the rotor position. The estimated value of the rotor position is: in, is the β-axis component of the effective flux command, is the α-axis component of the effective flux command.

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

4. A position sensorless control system for an electrically excited synchronous motor, characterized in that: include: The closed-loop effective flux observer is used to obtain an effective flux command based on the sampled stator current, rotor excitation current, and introduced effective flux, where the introduced effective flux is the difference between the stator flux and the stator current quadrature-axis induced flux. The sampled stator voltage is subtracted from the stator resistance voltage drop to obtain the motor's back electromotive force, which is integrated to obtain an estimated stator flux. The estimated stator flux is then subtracted from the stator current quadrature-axis induced flux to obtain an effective flux feedback. The effective flux command is subtracted from the effective flux feedback, and the difference is used as a voltage compensation term after PI control and compensated to the stator voltage to form a closed loop. The introduced effective flux is: Among them, the d-axis and the q-axis are two orthogonal coordinate axes of the rotating coordinate system of the stator winding, and the D-axis and the Q-axis are two orthogonal coordinate axes of the rotating coordinate system of the damper winding. is the stator flux, is the stator current, , is the q-axis leakage reactance coefficient, is the Q-axis leakage reactance coefficient, is the q-axis reactance, , x mq is the q-axis synchronous reactance, is the time constant of the Q-axis damping winding, s is the differential operator; The effective magnetic linkage instructions are: in, , is the d-axis leakage reactance coefficient, is the D-axis leakage reactance coefficient, is the time constant of the D-axis damping winding, is the d-axis reactance, , x md is the d-axis synchronous reactance, is the rotor excitation current; The speed estimation module is used to input the effective flux linkage instruction into the arc tangent function to obtain the rotor position for speed estimation and realize speed closed-loop control.

5. The system according to claim 4, characterized in that The effective flux linkage instruction is input into the inverse tangent function to estimate the rotor position. The estimated value of the rotor position is: in, is the β-axis component of the effective flux command, is the α-axis component of the effective flux command.

6. The system according to claim 4, characterized in that The rotational speed is estimated by the backward difference method based on the estimated rotor position, and the expression of the obtained rotational speed is: in, for k The α-axis component of the effective flux command at the moment, for k The α-axis component of the effective flux command at the moment, T s is the sampling frequency, k is the current moment, and k-1 is the previous moment.

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