A current-optimization-based low-frequency ride-through method for speed-sensorless induction motors

Abstract

The application relates to the field of power electronics and power transmission, and particularly provides a current-optimization-based low-frequency ride-through method for a speed-sensorless induction motor, which specifically comprises a speed observation method based on a full-order observer, a basic principle and method for low-frequency ride-through stability of the speed-sensorless induction motor, and an active zero-frequency ride-through boundary point selection method based on current optimization. The actual effect of the application is that the purpose of controlling the slip speed of the induction motor is achieved by controlling the given excitation current command value, and the control of the synchronous speed of the induction motor can be indirectly realized. In view of the problem of active zero-frequency ride-through boundary point selection in the low-frequency ride-through, the boundary point selection criterion is given in the application in view of the problem of current optimization selection in the ride-through process.

Description

Technical Field

[0001] This invention relates to the field of power electronics and electric drives, and more specifically, to a low-frequency ride-through method for a sensorless induction motor based on current optimization. Background Technology

[0002] Methods for observing the rotor speed of induction motors can be divided into two main categories: one is signal injection, which extracts the rotor position information by sampling the response caused by the injected signal. This method allows the control system to operate stably under load for extended periods when the stator current frequency is extremely low. However, due to the poor anisotropy of the induction motor rotor, it is difficult to extract the true rotor position information in practical applications. The other method is the model method, which calculates the rotor speed using a motor model. Compared to the signal injection method, this method has been widely used in industrial fields. However, at extremely low stator current frequencies, the rotor speed cannot be estimated due to the extremely weak observability of the speed, leading to unstable operation of sensorless induction motor systems. As a type of model method, the full-order observer is unobservable under low-frequency operating conditions (typically when the stator current is at zero frequency). Summary of the Invention

[0003] The main objective of this invention is to provide a current-optimized low-frequency ride-through method for sensorless induction motors to solve problems in related technologies.

[0004] To achieve the above objectives, according to one aspect of the present invention, a sensorless induction motor low-frequency ride-through method based on current optimization is provided, comprising the following steps:

[0005] Reference two-phase static α-β A T-type equivalent model of an induction motor in a coordinate system is constructed by selecting stator current and rotor flux linkage as state variables and building a full-order state observer.

[0006] Based on the T-type equivalent model of the induction motor, the rotor speed is selected as the observed variable, and the state equation of the induction motor full-order observer is made.

[0007] The observer error equation is obtained based on the T-type equivalent model of the induction motor and the state equation of the full-order observer of the induction motor.

[0008] Based on the observer error equation, the adaptive rate of speed identification is derived using Popov's stability theorem.

[0009] At rest in two phases α-β The electromagnetic torque relationship is calculated based on synchronous speed and slip speed in the coordinate system;

[0010] Calculate the stator current amplitude using the electromagnetic torque relationship;

[0011] Based on the stator current amplitude, a schematic diagram showing the variation of the stator current amplitude under different excitation current and electromagnetic torque conditions is drawn.

[0012] The diagram showing the change in current amplitude determines the critical torque value, and active zero-frequency crossover is triggered by dual conditions based on the critical torque value.

[0013] The T-type equivalent model of the induction motor is represented as follows: In the formula, , , These are the stator current, rotor flux linkage, and stator voltage in the two-phase stationary α-β coordinate system, respectively. , , , , ; , , , , , ; , Rs is the stator resistance of the induction motor, Rr is the rotor resistance of the induction motor, Ls is the stator inductance of the induction motor, Lr is the rotor inductance of the induction motor, Lm is the mutual inductance of the induction motor, Tr is the rotor time constant of the induction motor, δ is the leakage inductance coefficient, ωe is the synchronous frequency of the induction motor, ωr is the rotor frequency of the induction motor, and ωs is the slip frequency of the induction motor.

[0014] Furthermore, the state equation of the full-order observer of the induction motor is: In the formula, and It is a coefficient matrix, where the angular velocity of the induction motor rotor is... Replace with observed rotational speed .

[0015] Furthermore, the observer error equation is as follows: In the formula, , , ; , .

[0016] Furthermore, the adaptive rate of the speed identification is expressed as: ,in, , is the adjustable PI parameter of the stator resistance observer; p is the differential operator.

[0017] Furthermore, the electromagnetic torque is expressed as: In the formula, .

[0018] Furthermore, the stator current amplitude is expressed as: .

[0019] Furthermore, the critical torque value is: In the formula, IMmax is the maximum excitation current. .

[0020] Furthermore, the active zero-frequency crossover process triggered by dual conditions is as follows:

[0021] Select the active zero-frequency crossing boundary point based on the current during the zero-frequency crossing process:

[0022] When the load torque is less than the critical torque value, the two boundary points are made to have the same ordinate, and the coordinates of boundary points E1 and E2 are obtained as follows:

[0023] ;

[0024] When the load torque exceeds the critical torque, the excitation current value at boundary point E2 is chosen to be the maximum excitation current IMmax. At this point, the coordinates of boundary points E1 and E2 are obtained as follows:

[0025] , ;

[0026] in, ; ;

[0027] Te represents electromagnetic torque;

[0028] np represents the number of pole pairs in an induction motor;

[0029] Lm represents the mutual inductance of the induction motor;

[0030] Lr represents the rotor inductance of the induction motor;

[0031] Tr represents the rotor time constant of the induction motor;

[0032] This indicates that the synchronous speed limit value is set.

[0033] Compared with existing technologies, the present invention has the following beneficial effects: The practical effect of the present invention is to control the slip speed of the induction motor by controlling the given excitation current command value, thereby indirectly achieving control of the synchronous speed of the induction motor. Regarding the problem of selecting the boundary point for active zero-frequency crossing in low-frequency crossing, the present invention provides a boundary point selection criterion for optimizing the current selection during the crossing process. Attached Figure Description

[0034] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0035] The structures, proportions, sizes, etc., shown in the accompanying drawings of this specification are only for the purpose of assisting those skilled in the art in understanding and reading the content disclosed in the specification, and are not intended to limit the conditions under which the present invention can be implemented. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in the proportions, or adjustments to the size, without affecting the effects and objectives that the present invention can produce, should still fall within the scope of the technical content disclosed in the present invention.

[0036] Figure 1 A schematic diagram showing the variation of stator current amplitude with excitation current and electromagnetic torque;

[0037] Figure 2 There is no current-optimized zero-frequency ride-through test when the load is less than the critical torque;

[0038] Figure 3 When the load exceeds the critical torque, there is a current-optimized zero-frequency ride-through experiment;

[0039] Figure 4 There is no current-optimized zero-frequency ride-through test when the load is less than the critical torque;

[0040] Figure 5 When the load exceeds the critical torque, there is a current-optimized zero-frequency ride-through experiment. Detailed Implementation

[0041] To make the objectives, features, and advantages of this invention more apparent and understandable, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0042] In the description of this invention, it should be understood that the terms "upper," "lower," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of the invention. It should be noted that when a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be a component positioned centrally in the connection.

[0043] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0044] Step 1: Induction Motor Speed ​​Observation Method Based on Full-Order Observer Model

[0045] Reference two-phase static α-β In the T-type equivalent model of the induction motor in the coordinate system, with stator current and rotor flux linkage as state variables, the mathematical model of the induction motor can be expressed as follows:

[0046] (7)

[0047] In the formula, , , They are two-phase stationary phases. α-β Stator current, rotor flux linkage, and stator voltage in a coordinate system. , , , , ; , , , , , ; , ,

[0048] R s It is the stator resistance of the induction motor.

[0049] R r It is the rotor resistance of the induction motor.

[0050] L s It is the stator inductance of an induction motor.

[0051] L r It is the rotor inductance of the induction motor.

[0052] L m It is mutual inductance in induction motors.

[0053] T r It is the rotor time constant of the induction motor.

[0054] δ It is the leakage inductance coefficient.

[0055] ω e It is the synchronous frequency of the induction motor.

[0056] ω r It is the rotor frequency of the induction motor.

[0057] ω s It is the slip frequency of the induction motor.

[0058] Based on the mathematical model of the motor (7), and selecting the rotor speed as the observed variable, the state equation of the full-order observer of the induction motor is:

[0059] (8)

[0060] In the formula, and It is a coefficient matrix, where the rotor speed is... ω r Replace with observed rotational speed .

[0061] Based on the mathematical model equation (7) and the observer equation (8), the observer error equation can be obtained as follows:

[0062] (9)

[0063] In the formula, , , ; , .

[0064] Based on the observer error equation, the adaptive rate of speed identification can be derived using Popov's stability theorem. First

[0065] (10)

[0066] In the formula,

[0067] .

[0068] Substituting, we can get

[0069] (11)

[0070] To satisfy the above equation, the speed adaptive rate can be obtained, and the speed tracking performance can be adjusted by selecting appropriate PI parameters. Therefore, the observer speed adaptive rate can be expressed as:

[0071] (12)

[0072] in, K pω , K iω It is an adjustable PI parameter of the stator resistance observer; p It is a differential operator.

[0073] Step Two: Principle of Sensorless Induction Motor Low-Frequency Cross-Traffic Technology

[0074] In a two-phase synchronous coordinate system, the synchronous speed and the slip speed can be expressed as:

[0075] (13)

[0076] Electromagnetic torque can be expressed as:

[0077] (14)

[0078] In the formula, .

[0079] From equation (13), it can be seen that when the excitation current i sd When the slip speed is constant, the torque current is related to the slip speed. i sq Linear correlation. Conversely, the slip speed can be changed while maintaining constant torque (14) by adjusting the excitation current command value. This maintains a minimum synchronous speed and improves speed observability. The excitation current command value is expressed as:

[0080] (15)

[0081] In the formula, the change in the excitation current command value is expressed as:

[0082] (16)

[0083] Step 3: Current Optimization Methods in Low-Frequency Ride-Through Technology

[0084] Combining the electromagnetic torque relationship (14), the stator current amplitude can be expressed as:

[0085] (17)

[0086] According to equation (17), a schematic diagram of the stator current amplitude variation can be drawn under different excitation current and electromagnetic torque conditions, such as... Figure 1 As shown in the figure. Points E1 and E2 are active boundary crossing points. To complete active zero-frequency crossing, the difference in slip between points E1 and E2 needs to satisfy a minimum slip constraint, i.e.

[0087] (18)

[0088] In the formula, , These are the slips at points E1 and E2, respectively. It is the minimum synchronous speed limit.

[0089] To satisfy the requirements of slip difference (18) and minimum current at the boundary points, the optimal solution is to have the same ordinate at the boundary points. In this case, the stator current at the boundary points will increase with the increase of torque. However, as the torque continues to increase, the abscissa of point E2 will exceed the maximum excitation current limit. At this point, to satisfy the slip difference requirement at the boundary points, boundary point E1 needs to be moved to the left. The critical torque values ​​for the above two cases are:

[0090] (19)

[0091] In the formula, I Mmax It is the maximum excitation current. .

[0092] When the load torque is less than the critical torque value, the two boundary points are made to have the same ordinate, and the coordinates of boundary points E1 and E2 are obtained as follows:

[0093] (20)

[0094] When the load torque exceeds the critical torque, the excitation current value at boundary point E2 is chosen to be the maximum excitation current IMmax. At this point, the coordinates of boundary points E1 and E2 are obtained as follows:

[0095] (twenty one)

[0096] In the formula, .

[0097] Therefore, the active zero-frequency crossing boundary point can be selected according to the motor load condition. When the load is less than the critical torque, the active zero-frequency crossing is triggered by condition (20). When the load is greater than the critical torque, the active zero-frequency crossing is triggered by condition (21). The operating condition point of the induction motor switches instantaneously between E1 and E2.

[0098] Step 4: Experimental Verification

[0099] To verify the effectiveness of the above implementation scheme, a 2.2kW induction motor was used to conduct an experimental demonstration on the towing platform. The motor parameters are shown in Table 1. In the comparative experiment, the rotational speed switching from 100rpm to -100rpm (rated speed 1435rpm) was set to 80s. The rotor speed acceleration was -0.04r / s². 2 In the experiment, the calculated critical load torque was 5.3 Nm. (Symbol) I 2 Represents the square of the effective value of the current, its value is given by ( i 2 sd + i 2 sq The result is calculated as ) / 2.

[0100] Table 1 Parameters of 2.2kW Induction Motor

[0101]

[0102] experiment Figures 2-5 The experiments were conducted under load conditions below and above the critical speed. In all experiments, the entire zero-frequency ride-through process was successfully completed. Before and after the active zero-frequency ride-through, the excitation current gradually decreased, causing the synchronous speed to converge to the synchronous speed limit. During the active zero-frequency ride-through, a step increase in the excitation current caused the motor's operating point to instantaneously switch between different boundary points, simultaneously crossing the stator zero-frequency line.

[0103] In experiments with current optimization Figure 3 and Figure 5 In this process, the square of the effective value of the stator current can be observed. I 2 Both phase current and phase current are compared to experiments without current optimization. Figure 2 and Figure 4 The results show that the proposed method achieves current optimization, as evidenced by the small to medium current values. Comparative experiments are also conducted. Figure 2 and Figure 3 Without current optimization, the motor operating point experiences a significant increase in current after zero-frequency crossover. This indicates that the boundary point selection is unreasonable without current optimization, and the active zero-frequency crossover boundary point needs to be moved to the left. Similarly, comparative experiments... Figure 4 and Figure 5 It can be observed that when optimizing the current, the square of the effective value of the current is... I 2 The phase current is relatively small before zero-frequency ride-through is complete. This indicates that without current optimization, the active zero-frequency ride-through boundary point needs to be shifted to the right, and the excitation current at point E2 needs to be set to... I MmaxComparative experiments verified that the proposed current optimization method can effectively select the optimal active zero-frequency crossing boundary point, thereby achieving optimal current control during the zero-frequency crossing process.

[0104] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0105] It should be noted that the terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments of this application described herein can be implemented, for example, in orders other than those illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or apparatus.

Claims

1. A sensorless induction motor low-frequency ride-through method based on current optimization, characterized in that, Includes the following steps: Reference two-phase static A T-type equivalent model of an induction motor in a coordinate system is constructed, with stator current and rotor flux linkage selected as state variables, and a full-order state observer is built. Based on the T-type equivalent model of the induction motor, the rotor speed is selected as the observed variable, and the state equation of the induction motor full-order observer is made. The observer error equation is obtained based on the T-type equivalent model of the induction motor and the state equation of the full-order observer of the induction motor. Based on the observer error equation, the adaptive rate of speed identification is derived using Popov's stability theorem. At rest in two phases The electromagnetic torque relationship is calculated based on synchronous speed and slip speed in the coordinate system; Calculate the stator current amplitude using the electromagnetic torque relationship; Based on the stator current amplitude, a schematic diagram showing the variation of the stator current amplitude under different excitation current and electromagnetic torque conditions is drawn. The critical torque value is determined based on the current amplitude variation diagram, and active zero-frequency ride-through is triggered by dual conditions based on the critical torque value; The active zero-frequency crossover process triggered by dual conditions is as follows: Select the active zero-frequency crossing boundary point based on the current during the zero-frequency crossing process: When the load torque is less than the critical torque value, the two boundary points are made to have the same ordinate, and the boundary points are determined. and The coordinates are as follows: ； When the load torque exceeds the critical torque, select the boundary point. The excitation current value is the maximum excitation current. At this point, the boundary points are obtained. and The coordinates are as follows: ； in, ; ， ； Indicates electromagnetic torque; Indicates the number of pole pairs of an induction motor; Indicates mutual inductance between induction motors; Indicates the rotor inductance of the induction motor; This represents the rotor time constant of the induction motor; This indicates that the synchronous speed limit value is set.

2. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 1, characterized in that, The state equation of the T-type equivalent model of the induction motor is expressed as follows: ； In the formula, , , They are two-phase stationary phases. Stator current vector, rotor flux linkage vector, and stator voltage vector in the coordinate system; The coefficient matrix is ​​defined as follows: ， ， ， ， ； in, , ; The parameter is defined as follows: , , , , , ; It is the stator resistance of the induction motor. It is the rotor resistance of the induction motor. It is the stator inductance of an induction motor. It is the angular velocity of the induction motor rotor.

3. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 2, characterized in that, The state equation of the full-order observer of the induction motor is: ； In the formula, To observe the quantum current, To observe the rotor flux linkage; and It is a coefficient matrix, and its expression is the same as described above. and The same applies, except for the angular velocity of the induction motor rotor. Replace with observed rotational speed .

4. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 3, characterized in that, The observer error equation is: ； In the formula, For current observation error, This is the magnetic flux observation error; ， ， 。 5. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 4, characterized in that, The adaptive rate of the speed identification is expressed as: ； in, , It is an adjustable PI parameter for the adaptive rate of speed identification; It is a differential operator; superscript This indicates the matrix transpose.

6. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 1, characterized in that, The electromagnetic torque is expressed as: ； In the formula, These are the excitation current component and torque current component in the synchronous rotating coordinate system, respectively.

7. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 6, characterized in that, The stator current amplitude is expressed as: 。 8. The sensorless induction motor low-frequency ride-through method based on current optimization according to claim 1, characterized in that, The critical torque value is: ； In the formula, It is the maximum excitation current. .

Images