Variable-step-size predictive torque control method for AC motor based on synchronous space vector modulation

Abstract

The present invention discloses a variable step size predictive torque control method for an AC motor based on synchronous space vector modulation, comprising the following steps: measuring the stator current of phases A and B to obtain the stator current vector at the current control beat k; obtaining the phase reference value of the stator flux vector based on the excitation current command and the torque current command; obtaining the phase reference value of the stator flux vector at the k+2 control beat based on the phase reference value of the stator flux vector; obtaining the sampling position closest to the stator flux vector at the k+2 control beat, and then correcting the stator flux vector at the k+2 control beat; obtaining the reference voltage command based on the corrected stator flux vector in combination with the sampling step size of the k+1 to k+2 control beats; obtaining the duty cycle of the basic output voltage based on the reference voltage command to realize motor control. The method disclosed by the present invention has a faster torque dynamic response speed and can realize smooth pulse mode switching.

Description

Technical Field

[0001] The invention relates to an AC motor variable step-size prediction torque control method based on synchronous space vector modulation, belonging to the technical field of motor control. Background Art

[0002] Synchronous space vector modulation is very suitable for inverter control under low carrier ratio operating conditions because of its low output voltage harmonics and no current ripple when sampling at the carrier starting point. However, synchronous space vector modulation has specific requirements for the phase sampling point of the controller output voltage command, which makes it difficult to achieve high dynamic closed-loop control based on synchronous space vector modulation.

[0003] Traditional vector control uses a linear current regulator, which is limited by the limited bandwidth gain upper limit under low carrier ratio operating conditions, and the dynamic response speed of the system is slow. In addition, in order to ensure the symmetry of the output voltage pulse to maintain the low harmonic characteristics of synchronous space vector modulation, the control system needs to compare the phase angle of the reference voltage with the phase difference of the preset sampling point in real time, and then adjust the control cycle according to the phase-locked loop, feedforward compensation and other methods to eliminate the steady-state error of the sampling point. However, in order to ensure stability, its dynamic response speed is slow, and it is difficult to ensure the symmetry of the output pulse in the transient process.

[0004] Therefore, it is necessary to conduct a more in-depth study on the existing torque control to solve the above problems. Summary of the invention

[0005] In order to overcome the above problems, the inventors have conducted in-depth research and proposed a variable step size predictive torque control method for an AC motor based on synchronous space vector modulation, comprising the following steps:

[0006] S1. Measure the stator current of phases A and B to obtain the stator current vector at the current control beat k;

[0007] S2, obtaining a phase reference value of a stator flux vector based on an excitation current command and a torque current command;

[0008] S3, obtaining a phase reference value of the stator flux vector at k+2 control beats based on the phase reference value of the stator flux vector;

[0009] S4, obtaining the sampling position closest to the stator flux vector at the k+2 control beat, and then correcting the stator flux vector at the k+2 control beat;

[0010] S5. Based on the corrected stator flux vector and the sampling step length of the control cycle from k+1 to k+2, a reference voltage command is obtained;

[0011] S6. Obtain the duty cycle of the basic output voltage based on the reference voltage command to achieve motor control.

[0012] In a preferred embodiment, in S1, the stator current vector i s (k) is expressed as:

[0013]

[0014] Among them, i a Represents the stator current of phase A, i b represents the B-phase stator current, j represents an imaginary number

[0015] In a preferred embodiment, in S2, for a synchronous motor, the phase reference value of the stator flux vector can be expressed as:

[0016]

[0017] For an induction motor, the phase reference value of the stator flux vector can be expressed as:

[0018]

[0019] in, Represents the phase reference value of the stator flux vector, Indicates the excitation current command, Represents the torque current command, ψ f is the permanent magnet flux, ∠ represents the phase angle calculation symbol, θ r is the phase of the rotor flux vector, L d represents the d-axis stator inductance, L q represents the q-axis stator inductance, L s Represents stator inductance, L σ Represents the leakage inductance of the induction motor.

[0020] In a preferred embodiment, the phase reference value of the stator flux vector during the k+2 control cycle is It is expressed as:

[0021]

[0022] Among them, ω e is the synchronous electrical speed of the rotor flux vector, T sc (k+1) is the time from the current k control beat to the k+1 control beat, T s ′ c is the preset sampling time.

[0023] In a preferred embodiment, the sampling position r closest to the stator flux vector at k+2 control cycles is expressed as:

[0024]

[0025] Wherein, θ0 represents the starting value of the flux phase reference value.

[0026] In a preferred embodiment, the modified k+2 control beat stator flux vector is expressed as:

[0027]

[0028] In a preferred embodiment, the sampling step length of the k+1 to k+2 control beats is expressed as:

[0029]

[0030] In a preferred embodiment, the reference voltage instruction It is expressed as:

[0031]

[0032] in, represents the stator flux vector of k+1 control cycle, is the amplitude command of the stator flux, R s is the stator resistance, is the stator current of k+1 control cycle.

[0033] In a preferred embodiment, the duty cycle of the basic output voltage is expressed as:

[0034]

[0035] Where M represents the modulation ratio, d x d y is the duty cycle of the two basic effective voltage vectors, and d0 represents the duty cycle of the zero vector.

[0036] In a preferred embodiment, the modulation ratio is set to

[0037] Among them, U dc is the measured value of DC bus voltage.

[0038] The beneficial effects of the present invention include:

[0039] (1) The phase of the output voltage can be automatically aligned to the preset sampling point without feedforward compensation or auxiliary controllers such as phase-locked loops, thereby inheriting the excellent harmonic characteristics of synchronous optimized spatial modulation during quasi-steady-state operation;

[0040] (2) Compared with the conventional vector control strategy using a linear current regulator, it has a faster torque dynamic response speed;

[0041] (3) Able to achieve smooth pulse mode switching. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 A schematic flow chart of a method for controlling an AC motor with variable step-size predictive torque based on synchronous space vector modulation according to a preferred embodiment of the present invention is shown;

[0043] Figure 2 The test waveform of the five-frequency synchronous space vector modulation in the embodiment 1 at full load steady state is shown;

[0044] Figure 3 The test waveforms when switching between different modulation modes in Example 1 are shown;

[0045] Figure 4 The performance comparison between Example 1 and Comparative Example 1 in the seven-frequency synchronous space vector modulation mode is shown. DETAILED DESCRIPTION

[0046] The present invention will be further described in detail below through the accompanying drawings and embodiments. Through these descriptions, the characteristics and advantages of the present invention will become more clear and distinct.

[0047] The word "exemplary" is used exclusively herein to mean "serving as an example, embodiment, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments. Although various aspects of the embodiments are shown in the drawings, the drawings are not necessarily drawn to scale unless otherwise noted.

[0048] According to a method for controlling an AC motor with variable step-size predictive torque based on synchronous space vector modulation provided by the present invention, Figure 1 As shown, the following steps are included:

[0049] S1. Measure the stator current of phases A and B to obtain the stator current vector at the current control beat k;

[0050] S2, obtaining a phase reference value of a stator flux vector based on an excitation current command and a torque current command;

[0051] S3, obtaining a phase reference value of the stator flux vector at k+2 control beats based on the phase reference value of the stator flux vector;

[0052] S4, obtaining the sampling position closest to the stator flux vector at the k+2 control beat, and then correcting the stator flux vector at the k+2 control beat;

[0053] S5. Based on the corrected stator flux vector and the sampling step length of the control cycle from k+1 to k+2, a reference voltage command is obtained;

[0054] S6. Obtain the duty cycle of the basic output voltage based on the reference voltage command to achieve motor control.

[0055] In the present invention, the phase of the output voltage can be automatically aligned to the preset sampling point without feedforward compensation or auxiliary controllers such as a phase-locked loop, so that the excellent harmonic characteristics of synchronous optimized spatial modulation can be inherited during quasi-steady-state operation.

[0056] Specifically,

[0057] In S1, the stator current vector i is s (k) is expressed as:

[0058]

[0059] Among them, i a Represents the stator current of phase A, i b represents the B-phase stator current, and j represents an imaginary number.

[0060] According to the present invention, both the A-phase stator current and the B-phase stator current can be obtained by directly measuring the motor power supply circuit through sensors.

[0061] In S2, preferably, for a synchronous motor, the phase reference value of the stator flux vector can be expressed as:

[0062]

[0063] Preferably, for an induction motor, the phase reference value of the stator flux vector can be expressed as:

[0064]

[0065] in, Represents the phase reference value of the stator flux vector, Indicates the excitation current command, Represents the torque current command, ψ f is the permanent magnet flux, ∠ represents the phase angle calculation symbol, θ r is the phase of the rotor flux vector, L d represents the d-axis stator inductance, L q represents the q-axis stator inductance, L s Represents stator inductance, L σ Represents the leakage inductance of the induction motor.

[0066] According to the present invention, for a synchronous motor, the phase θ of the rotor flux vector r It can be directly measured by the encoder; for induction motors, the phase of the rotor flux vector θ r According to the measured speed ω r Calculation, expressed as:

[0067]

[0068] Among them, T r is the rotor time constant.

[0069] In S3, the phase reference value of the stator flux vector at the k+2 control beat It is expressed as:

[0070]

[0071] Among them, ω e is the synchronous electrical speed of the rotor flux vector, T sc (j+1) is the time from the current k control beat to the k+1 control beat, T s ′ c is the preset sampling time.

[0072] Preferably, T′ sc =1 / (6Nf e )

[0073] Among them, f e =ω e / 2π is the fundamental frequency, and N is the number of sampling points in each 60° sector of the synchronous space vector modulation strategy.

[0074] In S4, the sampling position r closest to the stator flux vector at k+2 control beats is expressed as:

[0075]

[0076] Among them, θ0 represents the starting value of the flux phase reference value, and round() represents the rounding function in a rounding manner.

[0077] The corrected k+2 control beat stator flux vector is expressed as:

[0078]

[0079] In S5, the sampling step length of the control beat from k+1 to k+2 is expressed as:

[0080]

[0081] The reference voltage command It is expressed as:

[0082]

[0083] in, represents the stator flux vector of k+1 control cycle, is the amplitude command of the stator flux, R s is the stator resistance, is the stator current of k+1 control cycle.

[0084] In a preferred embodiment, It can be estimated by the flux observer, According to the stator current vector at time k Obtained, expressed as

[0085] In S6, the duty cycle of the basic output voltage is expressed as:

[0086]

[0087] Where M represents the modulation ratio, d x d y is the duty cycle of the two basic effective voltage vectors, and d0 represents the duty cycle of the zero vector.

[0088] Preferably, the modulation ratio is set to

[0089] Among them, U dc is the measured value of DC bus voltage.

[0090] It should be understood that the various forms of processes shown above can be used to reorder, add or delete steps. For example, the steps described in the disclosure of the present invention can be performed in parallel, sequentially or in different orders, as long as the desired results of the technical solution disclosed in the present invention can be achieved, and this document does not limit this.

[0091] Example

[0092] Example 1

[0093] Conducting a motor control test experiment includes the following steps:

[0094] S1. Measure the stator current of phases A and B to obtain the stator current vector at the current control beat k;

[0095] S2, obtaining a phase reference value of a stator flux vector based on an excitation current command and a torque current command;

[0096] S3, obtaining a phase reference value of the stator flux vector at k+2 control beats based on the phase reference value of the stator flux vector;

[0097] S4, obtaining the sampling position closest to the stator flux vector at the k+2 control beat, and then correcting the stator flux vector at the k+2 control beat;

[0098] S5. Based on the corrected stator flux vector and the sampling step length of the control cycle from k+1 to k+2, a reference voltage command is obtained;

[0099] S6. Obtain the duty cycle of the basic output voltage based on the reference voltage command to achieve motor control.

[0100] In S1, the stator current vector i is s (k) is expressed as:

[0101]

[0102] In S2, the phase reference value of the stator flux vector can be expressed as:

[0103]

[0104] The phase reference value of the stator flux vector during the k+2 control cycle It is expressed as:

[0105]

[0106] The sampling position r closest to the stator flux vector at k+2 control beats is expressed as:

[0107]

[0108] The corrected k+2 control beat stator flux vector is expressed as:

[0109]

[0110] The sampling step length of the k+1 to k+2 control beat is expressed as:

[0111]

[0112] The reference voltage command It is expressed as:

[0113]

[0114] The duty cycle of the basic output voltage is expressed as:

[0115]

[0116] The modulation ratio is set to

[0117] Among them, U dc is the measured value of DC bus voltage.

[0118] In the experiment, the motor was switched in turn between five-frequency synchronous space vector modulation mode, seven-frequency synchronous space vector modulation mode, eleven-frequency synchronous space vector modulation mode, thirteen-frequency synchronous space vector modulation mode, fifteen-frequency synchronous space vector modulation mode and SVM modulation mode. The test waveform results are shown in the figure. Figure 2-3 shown.

[0119] in, Figure 2 This is the test waveform of the five-frequency synchronous space vector modulation at full load steady state. It can be seen from the figure that the output line voltage waveform and the three-phase stator current waveform are symmetrical, and the output torque is stable, that is, the output steady-state property is strong.

[0120] Figure 3 This is the test waveform when switching between different modulation modes. It can be seen from the figure that the switching between different modulation modes is smooth and fast, without current or torque shock.

[0121] Comparative Example 1

[0122] The same motor as in Example 1 was used, and a conventional vector control method was used to perform a test in a seven-frequency synchronous space vector modulation mode, and compared with the method in Example 1 in a seven-frequency synchronous space vector modulation mode. The results are as follows: Figure 4 shown.

[0123] As can be seen from the figure, the torque command step setting time of the method in Example 1 is about 2.5ms, while the method in Comparative Example 1 under the same test conditions requires 7ms, indicating that the method in Example 1 has a dynamic response speed of oil volume.

[0124] The present invention has been described above in conjunction with preferred embodiments, but these embodiments are only exemplary and serve only as an illustration. On this basis, the present invention may be subjected to a variety of substitutions and improvements, all of which fall within the scope of protection of the present invention.

Claims

1. A variable step size predictive torque control method for an AC motor based on synchronous space vector modulation, characterized in that: The following steps are involved: S1. Measure the stator current of phases A and B to obtain the stator current vector at the current control beat k; S2, obtaining a phase reference value of a stator flux vector based on an excitation current command and a torque current command; S3, obtaining a phase reference value of the stator flux vector at k+2 control beats based on the phase reference value of the stator flux vector; S4, obtaining the sampling position closest to the stator flux vector at the k+2 control beat, and then correcting the stator flux vector at the k+2 control beat; S5. Based on the corrected stator flux vector and the sampling step length of the control cycle from k+1 to k+2, a reference voltage command is obtained; S6, obtaining a duty cycle of a basic output voltage based on a reference voltage command to achieve motor control; Among them, the sampling position r closest to the stator flux vector at k+2 control beats is expressed as: θ0 represents the starting value of the flux phase reference value, is the phase reference value of the stator flux vector at k+2 control beats, N is the number of sampling points in each 60° sector of the synchronous space vector modulation strategy, and round() represents the rounding function; The corrected k+2 control beat stator flux vector is expressed as:

2. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 1, characterized in that: In S1, the stator current vector i is s (k) is expressed as: Among them, i a Represents the stator current of phase A, i b represents the B-phase stator current, and j represents an imaginary number.

3. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 1, characterized in that: In S2, for synchronous motors, the phase reference value of the stator flux vector is expressed as: For induction motors, the phase reference value of the stator flux vector is expressed as: in, Represents the phase reference value of the stator flux vector, Indicates the excitation current command, Represents the torque current command, ψ f is the permanent magnet flux, ∠ represents the phase angle calculation symbol, θ r is the phase of the rotor flux vector, L d represents the d-axis stator inductance, L q represents the q-axis stator inductance, L s Represents stator inductance, L σ Represents the leakage inductance of the induction motor.

4. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 3 is characterized in that: The phase reference value of the stator flux vector during the k+2 control cycle It is expressed as: Among them, ω e is the synchronous electrical speed of the rotor flux vector, T sc (k+1) is the time from the current k control beat to the k+1 control beat, T s ′ c is the preset sampling time.

5. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 4, characterized in that: The sampling step length of the k+1 to k+2 control beat is expressed as:

6. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 5, characterized in that: The reference voltage command It is expressed as: in, represents the stator flux vector of k+1 control cycle, is the amplitude command of the stator flux, R s is the stator resistance, is the stator current of k+1 control cycle.

7. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 6, characterized in that: The duty cycle of the basic output voltage is expressed as: Where M represents the modulation ratio, d x ,d y is the duty cycle of the two basic effective voltage vectors, and d0 represents the duty cycle of the zero vector.

8. The variable step size predictive torque control method for an AC motor based on synchronous space vector modulation according to claim 7, characterized in that: The modulation ratio is set to Among them, U dc is the measured value of DC bus voltage.

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