A speed sensorless zero-frequency ride-through torque current prediction and compensation method

Abstract

The present application discloses a speed sensorless zero-frequency ride-through torque current prediction and compensation method, including: given the initial value of the induction motor excitation current command value, changing the induction motor slip speed by adjusting the change in the induction motor excitation current command value, thereby controlling the motor synchronous speed; the speed sensorless zero-frequency ride-through process can be divided into two parts: the synchronous speed loop control process and the active zero-frequency ride-through process, in which the change value of the induction motor torque current following the change in the excitation current is predicted respectively, and the change value is used as the feedforward compensation value of the induction motor torque current command for the next cycle. The present invention can solve the torque current, electromagnetic torque pulsation and oscillation phenomenon caused by the adaptive change of the zero-frequency ride-through excitation current, and improve the control stability and dynamic performance of the motor under low-frequency working conditions.

Description

Technical Field

[0001] The present application relates to the field of power electronics and electric drive technology, and more specifically, to a speed sensorless zero-frequency ride-through torque current prediction and compensation method. Background Art

[0002] The speed observation methods of induction motors can be divided into two categories: one is based on the anisotropy of the motor, which is typically represented by the high-frequency signal injection method, which extracts the speed information by injecting the high-frequency current response caused by the high-frequency voltage signal. The other is the model method, which uses the motor model to calculate the speed. However, the speed observation method based on the motor mathematical model cannot observe and track the actual speed under zero-frequency conditions.

[0003] In response to this problem, existing literature has proposed a low-frequency ride-through strategy based on excitation current or rotor flux control. However, the control of excitation current or rotor flux under low-frequency conditions requires real-time dynamic adaptive change of excitation current, which causes pulsation and oscillation of motor torque and current, affecting the control performance of the motor under low frequency. Summary of the invention

[0004] In response to at least one defect or improvement need in the prior art, the present invention provides a speed sensorless zero-frequency cross-over torque current prediction and compensation method, which can solve the torque current, electromagnetic torque pulsation and oscillation phenomena caused by the adaptive change of zero-frequency cross-over excitation current, and improve the control stability and dynamic performance of the motor under low-frequency working conditions.

[0005] To achieve the above object, the present invention provides a speed sensorless zero-frequency ride-through torque current prediction and compensation method, comprising:

[0006] Given an initial value of the induction motor excitation current command value, the slip speed of the induction motor is changed by adjusting the change amount of the induction motor excitation current command value;

[0007] In the synchronous speed loop control process, based on the change of the electromagnetic torque of the induction motor and the change of the excitation current in one cycle, the change value of the induction motor torque current following the change of the excitation current is predicted, and the change value is used as the feedforward compensation value of the induction motor torque current command in the next cycle;

[0008] During the active zero-frequency crossing process, based on the change of the induction motor excitation current within one cycle and the slope of the two boundary points, the change value of the induction motor torque current following the change of the excitation current is predicted, and the change value is used as the feedforward compensation value of the induction motor torque current command in the next cycle.

[0009] Furthermore, the change in the excitation current command value Expressed as

[0010]

[0011] Among them, μ is the change amplitude of the excitation current within a cycle, ω e is the synchronous frequency of the induction motor, i sq is the induction motor torque current, sign() is the sign function,

[0012] Furthermore, in the synchronous speed loop control process, the predicting of the change value of the induction motor torque current following the change amount of the excitation current comprises the steps of:

[0013] Determine the calculation formula of the induction motor torque current according to the calculation formula of the induction motor electromagnetic torque;

[0014] The induction motor torque current is derived to obtain the calculation formula for the change of the induction motor torque current following the change of the excitation current. The change of the electromagnetic torque of the induction motor in one cycle is recorded as ΔT e , the change in the induction motor excitation current is recorded as Δi sd The calculation formula for the change in the induction motor torque current following the change in the excitation current is about ΔT e and Δi sd function.

[0015] Furthermore, the coordinates of the two boundary points are expressed as:

[0016]

[0017] Where I is the current amplitude, T e is the electromagnetic torque of the induction motor, n p is the number of pole pairs of the induction motor, L r is the induction motor rotor inductance, L m is the mutual inductance of the induction motor.

[0018] Furthermore, during the synchronous speed loop control process, the induction motor torque current follows the change value Δi of the excitation current change sq The calculation formula is:

[0019]

[0020] In the formula, i sd is the induction motor excitation current, i sq is the induction motor torque current, n p is the number of pole pairs of the induction motor, L r is the induction motor rotor inductance, L mis the mutual inductance of the induction motor.

[0021] Furthermore, ΔT e The calculation formula is:

[0022]

[0023] In the formula, J i represents the moment of inertia, K i is the proportional coefficient of the proportional-integral regulator in the speed observer, e iq represents the Q-axis component of the current error, Δe iq Indicates e iq The amount of change, is i sd The observed quantity, yes The amount of change.

[0024] Furthermore, in the active zero frequency ride-through process, the predicting of the change value of the induction motor torque current following the change amount of the excitation current comprises the steps of:

[0025] The change in the induction motor excitation current is recorded as Δi sd , the slope of the two boundary points is recorded as m, and the change value of the induction motor torque current following the change of the excitation current is recorded as Δi sq , Δi sq =mΔi sd .

[0026] In general, compared with the prior art, the above technical scheme conceived by the present invention can achieve the following beneficial effects: by injecting the change in the excitation current command value, the excitation current of the motor is adaptively changed, thereby changing the motor slip speed, and achieving the purpose of controlling the synchronous speed of the motor under low-frequency conditions, and at the same time, in the process of dynamic change of the excitation current, by solving the change of the torque current following the change in the excitation current, a feedforward compensation of the torque current command is constructed, which solves the torque current, electromagnetic torque pulsation and oscillation caused by the adaptive change of the zero-frequency crossing excitation current, and improves the control stability and dynamic performance of the motor under low-frequency conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1A schematic flow chart of a speed sensorless zero-frequency ride-through torque current prediction and compensation method provided in an embodiment of the present application;

[0029] Figure 2 A schematic diagram of a synchronous speed loop control process is provided for an embodiment of the present application;

[0030] Figure 3 A schematic diagram of an active zero-frequency crossing process is provided for an embodiment of the present application. DETAILED DESCRIPTION

[0031] 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.

[0032] The terms "including" and "having" and any variations thereof in the specification and claims of the present application and the above drawings are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device comprising a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units that are not listed, or may optionally include other steps or units that are inherent to these processes, methods, products or devices.

[0033] like Figure 1 As shown, a speed sensorless zero-frequency ride-through torque current prediction and compensation method of an embodiment of the present invention includes: given an initial value of an induction motor excitation current command value, changing the induction motor slip speed by adjusting the change in the induction motor excitation current command value; in a synchronous speed loop control process, based on the change in the electromagnetic torque of the induction motor and the change in the excitation current of the induction motor within one cycle, predicting the change value of the induction motor torque current following the change in the excitation current, and using the change value as a feedforward compensation value for the induction motor torque current command of the next cycle; in an active zero-frequency ride-through process, based on the change in the excitation current of the induction motor within one cycle and the slopes of two boundary points, predicting the change value of the induction motor torque current following the change in the excitation current, and using the change value as a feedforward compensation value for the induction motor torque current command of the next cycle.

[0034] (1) Derivation of zero-frequency ride-through control strategy:

[0035] In the two-phase synchronous rotating coordinate system, the synchronous speed and slip speed of the induction motor can be expressed as:

[0036]

[0037] Among them, ω e is the synchronous frequency of the induction motor,

[0038] ω r is the induction motor rotor frequency,

[0039] ω s is the induction motor slip frequency,

[0040] T r is the induction motor rotor time constant,

[0041] “^” indicates the observed value corresponding to the physical quantity.

[0042] The electromagnetic torque can be expressed as:

[0043] T e =K e i sd i sq (2)

[0044] In the formula,

[0045] n p is the number of pole pairs of the induction motor,

[0046] T e is the electromagnetic torque of the induction motor,

[0047] i sd is the induction motor field current,

[0048] i sq is the induction motor torque current,

[0049] L r is the induction motor rotor inductance,

[0050] L m is the mutual inductance of the induction motor.

[0051] From formula (1), we can see that if the excitation current i sd The excitation current command value remains unchanged, and the slip speed can be changed under the condition of maintaining constant torque (2) by adjusting the excitation current given value. In this way, a minimum synchronous speed is maintained, and the speed observability is improved. The motor excitation current command value can be expressed as:

[0052]

[0053] In the formula, They respectively represent the field current command value, the initial value of the field current command value, and the amount of change in the field current command value.

[0054] Therefore, the excitation current of the motor can be adaptively changed by injecting the change in the excitation current command value, thereby changing the motor slip speed and achieving the purpose of controlling the motor synchronous speed under low-frequency conditions.

[0055] Among them, the change of the excitation current command value Expressed as

[0056]

[0057] Wherein, μ is the amplitude of the excitation current change within a cycle, and the value is small, generally less than 1% of the per-unit value. sign() is the sign function,

[0058] (2) Torque current prediction compensation method:

[0059] In the process of dynamic change of excitation current, the tracking of torque current will lag behind the change of magnetic current, which will lead to pulsation of torque current and torque, affecting the dynamic control effect of the motor. To this end, the present invention considers solving the change of torque current following the change of excitation current within a cycle, thereby constructing feedforward compensation of torque current command to ensure the dynamic tracking effect of torque. Figure 2 During the synchronous speed loop control process, the current vector rotates counterclockwise. Therefore, the slope of the torque curve at this point and the change in excitation current can be used to predict the change in torque current within a cycle. The specific derivation process is shown in formulas (4)-(7). Figure 3 In the process of active zero-frequency crossing, there are two boundary points A 3 and A 5 , which are the two intersection points of the current limit circle and the torque curve in the figure. The current vector moves from the boundary point A in a short time. 3 Rotate clockwise to A 5 point, therefore, we can use A 3 and A 5 The slope of the line connecting the points and the change in the excitation current are used to predict the change in the torque current within a cycle. The specific derivation process is shown in formulas (8)-(9).

[0060] In the synchronous speed loop control process, the predicted change value of the induction motor torque current following the change amount of the excitation current includes the steps of: determining the calculation formula of the induction motor torque current according to the calculation formula of the induction motor electromagnetic torque; derivatizing the induction motor torque current to obtain the calculation formula of the change value of the induction motor torque current following the change amount of the excitation current, and recording the change amount of the induction motor electromagnetic torque within one cycle as ΔT e , the change in the induction motor excitation current is recorded as Δi sdThe calculation formula for the change in the induction motor torque current following the change in the excitation current is about ΔT e and Δi sd function.

[0061] According to formula (2), the torque current can be expressed as

[0062]

[0063] Figure 2 The slope of the torque curve can be expressed as

[0064]

[0065] According to the slope expression of formula (5), the change of torque current in one cycle can be obtained as

[0066]

[0067] In the formula,

[0068] Δi sd Indicates the change in excitation current,

[0069] Δi sq Indicates the torque current change,

[0070] ΔT e Indicates the change in electromagnetic torque.

[0071] Combining equation (6) and equation (2), the change of torque current can be further simplified to obtain

[0072]

[0073] During the active zero-frequency ride-through process, the process of predicting the change in the induction motor torque current following the change in the excitation current is as follows.

[0074] exist Figure 3 Middle boundary point A 3 and A 5 The slope of the line connecting the points can be expressed as

[0075]

[0076] Where m represents the boundary point A 3 and A 5 The slope of the line connecting the points,

[0077] i sdA3 ,i sdA5 Respectively represent A 3 Dot and A 5 The excitation current at point

[0078] isqA3 ,i sqA5 Respectively represent A 3 Dot and A 5 The torque current at this point.

[0079] A 3 Dot and A 5 Point Figure 2 ,The two intersection points of the current limit circle and the torque curve in 3 can be expressed as

[0080] A 3 :

[0081] A 5 : Where I is the current amplitude.

[0082] Therefore, during the active zero-frequency ride-through process, the change in torque current can be expressed as

[0083] Δi sq =mΔi sd (9)

[0084] (3) Estimation of electromagnetic torque variation:

[0085] The change in electromagnetic torque in equation (6) is unknown, so it is necessary to further estimate the change in electromagnetic torque.

[0086] The mechanical equation of the induction motor can be expressed as

[0087]

[0088] In the formula,

[0089] T l represents the load torque,

[0090] J i Represents the moment of inertia.

[0091] In the speed observer, the observed speed can be expressed as

[0092]

[0093] Among them, K i , K p are the proportional and integral coefficients of the proportional-integral regulator in the speed observer,

[0094] e i represents the current error,

[0095] The superscript "T" indicates the transpose of the matrix.

[0096] Represents the observed magnetic flux.

[0097] Further according to equation (11), the transfer function from the observed speed of the induction motor to the speed error can be expressed as

[0098]

[0099] In the formula, n 2 =m 2 +m 3 ω e , m 3 =2ω e -ω r ,

[0100] R s is the stator resistance of the induction motor,

[0101] R r is the induction motor rotor resistance,

[0102] L s is the stator inductance of the induction motor,

[0103] σ is the leakage inductance coefficient,

[0104] Δω r Indicates the speed error.

[0105] Assume K p The value is zero, and the electromagnetic torque can be expressed as

[0106]

[0107] Combined with formula (11), formula (13) can be simplified to

[0108]

[0109] For low-speed conditions, the synchronous speed can be considered to be zero. Therefore, the above formula can be further simplified to

[0110]

[0111] In one cycle, the load torque is considered constant, so the change of electromagnetic torque can be expressed as

[0112]

[0113] In the formula, e iq represents the Q-axis component of the current error,

[0114] Δe iq Represents the change in the Q-axis component of the current error,

[0115] represents the observed value of the excitation current,

[0116] Indicates the change in the observed value of the excitation current.

[0117] Therefore, in the synchronous speed loop control process, the change of torque current can be predicted by combining equations (7) and (16); in the active zero-frequency crossing process, the change of torque current can be predicted by equation (9). Therefore, for the command value of the current loop torque current, a feedforward compensation is constructed, that is, the predicted change of torque current is superimposed on the torque current command of the induction motor in the next cycle, so as to realize the fast tracking of torque current and suppress the pulsation of torque current and electromagnetic torque in the zero-frequency crossing process.

[0118] The above is only an exemplary embodiment of the present disclosure, and the scope of the present disclosure cannot be limited thereto. That is, any equivalent changes and modifications made according to the teachings of the present disclosure are still within the scope of the present disclosure. After considering the specification and practicing the disclosure here, those skilled in the art will easily think of the implementation scheme of the present disclosure. This application is intended to cover any modification, use or adaptation of the present disclosure, which follows the general principles of the present disclosure and includes common knowledge or customary technical means in the art that are not recorded in the present disclosure. The description and examples are only regarded as exemplary, and the scope and spirit of the present disclosure are defined by the claims.

[0119] The technical features of the above embodiments may be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0120] 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 speed sensorless zero-frequency ride-through torque current prediction and compensation method, characterized in that: include: Given an initial value of the induction motor excitation current command value, the slip speed of the induction motor is changed by adjusting the change amount of the induction motor excitation current command value; In the synchronous speed loop control process, based on the change of the electromagnetic torque of the induction motor and the change of the excitation current in one cycle, the change value of the induction motor torque current following the change of the excitation current is predicted, and the change value is used as the feedforward compensation value of the induction motor torque current command in the next cycle; In the process of active zero-frequency crossing, based on the variation of the excitation current of the induction motor in one cycle and the slopes of the two boundary points, the variation value of the torque current of the induction motor following the variation of the excitation current is predicted, and the variation value is used as the feedforward compensation value of the torque current command of the induction motor in the next cycle; Wherein, in the synchronous speed loop control process, the predicted change value of the induction motor torque current following the change amount of the excitation current comprises the steps of: Determine the calculation formula of the induction motor torque current according to the calculation formula of the induction motor electromagnetic torque; The induction motor torque current is derived to obtain a calculation formula for the change value of the induction motor torque current following the change amount of the excitation current. The change amount of the electromagnetic torque of the induction motor in one cycle is recorded as ΔTe, and the change amount of the excitation current of the induction motor is recorded as Δisd. The calculation formula for the change value of the induction motor torque current following the change amount of the excitation current is a function of ΔTe and Δisd. Among them, during the synchronous speed loop control process, the calculation formula for the change value Δisq of the induction motor torque current following the change in the excitation current is: Where isd is the excitation current of the induction motor, isq is the torque current of the induction motor, , np is the number of pole pairs of the induction motor, Lr is the rotor inductance of the induction motor, and Lm is the mutual inductance of the induction motor; The calculation formula of ΔTe is: Where Ji represents the moment of inertia, Ki is the proportional coefficient of the proportional integral regulator in the speed observer, eiq represents the Q-axis component of the current error, and Δeiq represents the change in eiq. is the observed value of isd, yes The amount of change.

2. The speed sensorless zero-frequency ride-through torque current prediction and compensation method according to claim 1, characterized in that: The change in the excitation current command value Expressed as in, is the variation amplitude of the excitation current within a cycle, ωe is the synchronous frequency of the induction motor, isq is the torque current of the induction motor, sign() is the sign function, .

3. The speed sensorless zero-frequency ride-through torque current prediction and compensation method according to claim 1, characterized in that: The coordinates of the two boundary points are expressed as: Where I is the current amplitude, Te is the electromagnetic torque of the induction motor, , np is the number of pole pairs of the induction motor, Lr is the rotor inductance of the induction motor, and Lm is the mutual inductance of the induction motor.

4. The speed sensorless zero-frequency ride-through torque current prediction and compensation method according to claim 1, characterized in that: In the process of active zero frequency ride-through, the step of predicting the change value of the induction motor torque current following the change amount of the excitation current comprises the following steps: The change of the induction motor excitation current is recorded as Δisd, the slope of the two boundary points is recorded as m, and the change value of the induction motor torque current following the change of the excitation current is recorded as Δisq. .

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