Permanent magnet synchronous electric drive system current harmonic suppression method considering control delay

Abstract

The invention relates to a permanent magnet synchronous electric drive system current harmonic suppression method considering control delay, and belongs to the technical field of permanent magnet synchronous motors. According to the current harmonic extraction method provided by the invention, only the storage space of the controller needs to be consumed, the current harmonics of each order can be extracted without the help of a low-pass filter, and the current harmonics of each order do not influence each other. The dynamic response and stability of the harmonic current closed-loop control system under the influence of control delay are analyzed, the harmonic current closed-loop control system is related to the current fundamental frequency and the proportionality coefficient, the dynamic response of the system is reduced along with rising of the fundamental frequency, and the seventh harmonic current closed-loop control system is prone to instability. PI parameters need to be designed by considering the influence of control delay.

Description

Technical Field

[0001] The present invention belongs to the technical field of permanent magnet synchronous motors, and relates to a method for suppressing current harmonics of a permanent magnet synchronous electric drive system taking control delay into consideration. Background Art

[0002] Electric drive systems in aerospace, electric vehicles, rail transit and other fields have high requirements for torque or current control. Current harmonics are superimposed on the fundamental current as multiples of the fundamental frequency. After the system responds, the output torque or speed pulsates significantly, which makes the motor control performance worse. In addition, excessive harmonic content will cause the motor to heat up and reduce efficiency. Taking electric vehicles as an example, it will increase power consumption and seriously affect the endurance. Therefore, it is very important to study the extraction and suppression of current harmonics.

[0003] At present, the methods for suppressing current harmonics are mainly divided into: main body design optimization and software current harmonic suppression strategy. Main body design optimization mainly improves the sinusoidality of the air gap magnetic field by changing the motor structure. Due to the limitations of process processing and inverter nonlinear characteristics, it is impossible to fundamentally eliminate current harmonics. In the research of software current harmonic suppression algorithm, most studies adopt online extraction and suppression of current harmonics. Some scholars have proposed to use the different angular frequencies of each harmonic, and transform the original phase current into each synchronous rotating coordinate system through coordinate transformation. With the help of low-pass filters, the DC value of each current harmonic can be obtained, and harmonic suppression can be completed through the PI harmonic current loop. However, the use of low-pass filters cannot take into account the rapid response of the system and the accurate extraction of current harmonics. Some scholars have also proposed to improve the traditional low-pass filtering link into a closed-loop current harmonic detection method including repeated control. However, this harmonic extraction makes the entire control complicated and parameter-dependent, and the delay effect of the filter in the loop cannot be ignored. Some scholars even proposed that there is no need to extract current harmonics online. Instead, based on the deadbeat control, the current harmonic reference value is adaptively injected according to the gradient descent method in the synchronous rotating coordinate system. There is no need to extract the current harmonic value, which can effectively eliminate the current harmonics caused by non-ideal factors. However, the selection of adaptive gain can easily lead to system instability, and the actual use is greatly affected by parameters. It can be seen that no matter how the structure of the current online extraction of current harmonics is changed, it is inevitable to use a low-pass filter, or there are drawbacks such as large amount of calculation and parameter changes affecting stability. It is urgent to carry out research on current harmonic extraction and suppression methods with both fast response and accurate extraction.

[0004] Based on the above background, the present invention aims at the problems of time delay effect and residual AC quantity in traditional low-pass filtering for extracting current harmonics, and proposes a PI parameter design method for reconstructing a virtual multi-phase motor to extract each current harmonic and suppress harmonic current. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for suppressing current harmonics in a permanent magnet synchronous electric drive system considering control delay, to achieve accurate and delay-free extraction of current harmonics in a permanent magnet synchronous motor, and to complete the suppression of current harmonics at a low switching frequency.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for suppressing current harmonics in a permanent magnet synchronous electric drive system considering control delay, the method comprising the following steps:

[0008] S1: Analyze the ability of the three-phase motor system itself to decompose current harmonics for the space where the fundamental wave and low-order harmonics of the three-phase permanent magnet synchronous motor are mapped after vector space decomposition transformation.

[0009] S2: It is analyzed that the three-phase motor can map the fundamental wave current, 5th current harmonic and 7th current harmonic into mutually independent sub-spaces, and the single-phase permanent magnet synchronous motor is fictitiously regarded as a three-phase permanent magnet synchronous motor to extract each order of current harmonics without using a low-pass filter; the original phase current of the motor is phase-shifted by 20° and 40° respectively to obtain a three-phase motor system, i ABC represents the original phase current of the motor, i AnBnCn represents the phase current of the nth set of windings of the fictitious three-phase motor, n = 1, 2, 3;

[0010] The three-phase motor refers to a three-phase nine-phase motor.

[0011] S3: Record the rotor position angle and the phase current value, and perform phase-shift reconstruction as:

[0012] S31: Record n sets of rotor electrical angles θe and phase currents i A , determine the desired phase current phase θ * = θ e -π / x, j = 1, Δθ min = π, j min = n;

[0013] S32: Δθ = θ * -θ e (j), judge whether j < n; if so, enter S331; if not, enter S332;

[0014] S331: Judge whether Δθ < Δθ min , if so, enter S3311; if not, enter S3312;

[0015] S332: Judge whether θ * = θ e (j min ), if so, enter S3321; if not, enter S3322;

[0016] S3311: Δθ=Δθ min , j min =j, j=j+1; return to S32;

[0017] S3312: Δθ min No change, j=j+1; return to S32;

[0018] S3321:i A1 =i A (j min ),i B1 =i B (j min );Finish;

[0019] S3322: By j min The two points before and after determine the slope k, i A1 =i A (j min )+k(θ * -θ e (j min ));Finish;

[0020] S4: Based on the positive and negative sequence relationship of the 5th harmonic current and the 7th harmonic current, the influence of control delay in the harmonic mathematical model is considered, and the 5th harmonic current loop and the 7th harmonic current loop models are reconstructed; the corresponding Bode diagram is drawn using the system transfer function of the current closed loop to analyze the dynamic response and stability of the system; the analysis shows that the control delay considerations show that with the increase of the fundamental frequency, the response bandwidth decreases and the response becomes slower, and the 7th harmonic current loop is affected by the selection of the proportional parameter kp of the PI regulator, resulting in system instability. The PI parameters are designed considering the influence of control delay;

[0021] S5: Based on the harmonic current loop model, the angle delay is ignored and only the time delay is considered;

[0022] For the suppression of the 5th harmonic current, the delay link G d (s) = e -sTd As a nonlinear link, it is substituted into the system for parameter design and expressed using the second-order Pade as follows:

[0023]

[0024] When only the time delay link and the controlled object are considered, the system open-loop transfer function is expressed as:

[0025]

[0026] By drawing the Bode diagram, we can ensure that the system phase margin is 45°, and increase the system response bandwidth by reducing the phase margin. The proportional coefficient k of the PI controller is selected.p ; Define the proportionality factor k p and the integration coefficient k i The ratio relationship is τ i =k p / k i = 0.01, by drawing the Bode diagram of the PI controller separately, we can select τ with lower influence on the system phase delay. i , determine the PI parameters of the harmonic suppression current loop.

[0027] The beneficial effects of the present invention are:

[0028] (1) The current harmonic extraction method proposed in the present invention only consumes the storage space of the controller and can extract each current harmonic without the aid of a low-pass filter. The current harmonics do not affect each other.

[0029] (2) The present invention analyzes the dynamic response and stability of the harmonic current closed-loop control system under the influence of control delay, and concludes that the harmonic current closed-loop control system is related to the current fundamental frequency and the proportional coefficient. As the fundamental frequency increases, the dynamic response of the system decreases, and the 7th harmonic current closed-loop control system is prone to instability. It is necessary to consider the influence of control delay to design the PI parameters.

[0030] (3) The present invention draws the Bode diagram of the system transfer function after considering the delay effect, and uses the graphical method to improve the response bandwidth while ensuring the phase margin. The proportional coefficient k is defined respectively. p and the integration coefficient k i .

[0031] Other advantages, objectives and features of the present invention will be described in the following description to some extent, and to some extent, will be obvious to those skilled in the art based on the following examination and study, or can be taught from the practice of the present invention. The objectives and other advantages of the present invention can be realized and obtained through the following description. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be described in detail below in conjunction with the accompanying drawings, wherein:

[0033] Figure 1 Mapping space between multi-phase motor winding structure and corresponding harmonics;

[0034] Figure 2 Reconstruct the three-phase motor idea by shifting the original phase current;

[0035] Figure 3 The block diagram of the algorithm for reconstructing three-phase motor by phase shifting the original phase current;

[0036] Figure 4To consider the harmonic current loop model after control delay; Figure 4 (a) is the fifth harmonic current loop; Figure 4 (b) is the seventh harmonic current loop;

[0037] Figure 5 This is the closed-loop suppression block diagram of the 5th harmonic current;

[0038] Figure 6 For current harmonic extraction comparison;

[0039] Figure 7 Comparison of phase current FFT under different harmonic suppression methods; Figure 7 (a) is the phase current FFT without suppression; Figure 7 (b) is the phase current FFT under traditional low-pass filtering harmonic suppression; Figure 7 (c) FFT of phase current extracted from the proposed fictitious multi-phase motor with harmonic suppression. DETAILED DESCRIPTION

[0041] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the illustrations provided in the following embodiments only illustrate the basic concept of the present invention in a schematic manner, and the following embodiments and features in the embodiments can be combined with each other without conflict.

[0042] Among them, the drawings are only used for illustrative explanations, and they only represent schematic diagrams rather than actual pictures, and should not be understood as limitations on the present invention. In order to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of actual products. For those skilled in the art, it is understandable that some well-known structures and their descriptions in the drawings may be omitted.

[0043] The same or similar numbers in the drawings of the embodiments of the present invention correspond to the same or similar parts; in the description of the present invention, it should be understood that if the terms "upper", "lower", "left", "right", "front", "rear", etc. indicate the orientation or position relationship, they are based on the orientation or position relationship shown in the drawings, which is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation. Therefore, the terms describing the position relationship in the drawings are only used for illustrative purposes and cannot be understood as limiting the present invention. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to specific circumstances.

[0044] The present invention is a method for extracting and suppressing current harmonics in a permanent magnet synchronous electric drive system. The method comprises the following steps:

[0045] S1: The space where the fundamental wave and low-order harmonics of the three-phase permanent magnet synchronous motor are mapped after vector space decomposition and transformation is as follows Figure 1 As shown in the figure, the three-phase motor system itself is analyzed for its ability to decompose current harmonics.

[0046] S2: The analysis shows that the three-phase motor can map the fundamental current, the 5th and 7th current harmonics to independent subspaces, so it is considered to fictionalize the single three-phase permanent magnet synchronous motor as a three-phase permanent magnet synchronous motor without the help of a low-pass filter to extract the current harmonics. Figure 2 As shown, the original phase current of the motor is shifted by 20° and 40° to obtain a three-phase motor system, i ABC Represents the original phase current of the motor, i AnBnCn (n=1, 2, 3) represent the phase currents of the nth winding of a fictitious three-phase motor.

[0047] S3: Figure 2 Reconstruction idea, record the rotor position angle and phase current value in Table 1, and the block diagram of the phase shift reconstruction algorithm is as follows Figure 3 shown.

[0048] Table 1

[0049]

[0050]

[0051] S4: Based on the positive and negative sequence relationship between the 5th harmonic current and the 7th harmonic current, considering the influence of control delay in the harmonic mathematical model, the 5th harmonic current loop and the 7th harmonic current loop models are reconstructed as follows: Figure 4 As shown, Figure 4 To consider the harmonic current loop model after control delay; Figure 4 (a) is the fifth harmonic current loop; Figure 4 (b) is the 7th harmonic current loop. The corresponding Bode diagram is drawn using the system transfer function of the current closed loop to analyze the system dynamic response and stability. The analysis shows that the control delay is taken into consideration. With the increase of the fundamental frequency, the response bandwidth decreases, the response becomes slower, and the 7th harmonic current loop is affected by the selection of the proportional parameter kp of the PI regulator, which may cause system instability. It is necessary to consider the influence of control delay to design the PI parameters.

[0052] S5: Figure 4 Harmonic current loop model, ignoring angle delay and only considering time delay, taking the 5th harmonic as an example, the harmonic current suppression block diagram can be expressed as Figure 5 shown.

[0053] Delay Link As a nonlinear link, it is difficult to directly substitute it into the system for parameter design. It can be expressed as follows using the second-order Pade approximation:

[0054]

[0055] When only the time delay link and the controlled object are considered, the system open-loop transfer function is expressed as:

[0056]

[0057] By drawing the Bode diagram, we can ensure that when the system phase margin is 45°, the system response bandwidth can be increased by reducing the phase margin, so as to select the proportional coefficient k of the PI controller. p . Define the proportionality factor k p and the integration coefficient k i The general ratio relationship is τ i =k p / k i = 0.01, by drawing the Bode diagram of the PI controller separately, we can select τ with lower influence on the system phase delay. i , in order to determine the PI parameters of the harmonic suppression current loop, the actual control can be slightly adjusted on this basis.

[0058] Example

[0059] (1) When the motor speed is 450r / min and the load torque is 2N·m, Figure 6 The figure shows the current harmonics obtained by decomposing the 5th and 7th current harmonics using the above-mentioned phase-shifted original phase current reconstruction virtual multi-phase motor algorithm, and the current harmonic DC value i obtained by transforming it to the synchronous rotating coordinate system of each harmonic dq5 and i dq7 , compared with the low-pass filter at the cut-off frequency f c The current harmonics extracted at 1, 5, 10, and 20 Hz are shown in the figure. c =1Hz extraction effect is similar, but the cutoff frequency f in the actual control system c Too low will bring greater signal phase delay and affect the system's dynamic response capability.

[0060] (2) When running at 450r / min with load, Figure 7 Comparison of phase current FFT under different harmonic suppression methods; Figure 7 (a) is the phase current FFT without suppression; Figure 7 (b) is the phase current FFT under traditional low-pass filtering harmonic suppression; Figure 7(c) is the phase current FFT of the proposed fictitious multi-phase motor under harmonic suppression. When the traditional method is used, the amplitudes of the 5th and 7th current harmonics account for 2.43% and 1.25% of the fundamental wave, respectively. The algorithm using low-pass filtering to extract harmonics for suppression can reduce the 5th and 7th current harmonics by 85%. When the proposed method is used, the amplitudes of the 5th and 7th current harmonics account for 1.01% and 0.57% of the fundamental wave, reducing the 5th and 7th current harmonics by 94%.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the purpose and scope of the technical solution, which should be included in the scope of the claims of the present invention.

Claims

1. A method for suppressing current harmonics in a permanent magnet synchronous electric drive system considering control delay, characterized in that: The method comprises the following steps: S1: The fundamental wave and low-order harmonics of the three-phase permanent magnet synchronous motor are mapped to the space after vector space decomposition and transformation, and the decomposition ability of the three-phase motor system itself for current harmonics is analyzed; S2: The analysis shows that the three-phase motor can map the fundamental current, the fifth current harmonic and the seventh current harmonic to independent subspaces. The single three-phase permanent magnet synchronous motor is fictitious as a three-phase permanent magnet synchronous motor without the help of a low-pass filter to extract the current harmonics. The original phase current of the motor is shifted by 20° and 40° to obtain a three-phase motor system. ABC Represents the original phase current of the motor, i AnBnCn represents the phase current of the nth winding of a fictitious three-phase motor, n = 1, 2, 3; S3: Record the rotor position angle and phase current value, and perform phase shift reconstruction as follows: S31: Record n ​​groups of rotor electrical angles θ e and phase current i A , determine the desired phase current phase θ * =θ e -π / x, j = 1, Δθ min =π,j min =n; where θ * Represents the rotor electrical angle corresponding to the desired fictitious phase current, θ e is the actual record of the rotor electrical angle; π / x represents the phase current shift angle of the fictitious multi-phase motor. The fictitious three-phase motor needs to shift the phase by π / 9 and 2π / 9; Δθ min represents the difference between the rotor electrical angle corresponding to the point selected from the n groups of rotor electrical angles that is closest to the expected fictitious phase current and the actual rotor electrical angle, j min is the sequence order of the selected data that is closest to the expected value; S32: Δθ = θ * - θ e (j), determine whether j < n; if so, go to S331; if not, go to S332; S331: Determine whether Δθ<Δθ min If yes, then go to S3311; if no, then go to S3312; S332: Determine whether θ * =θ e (j min ), if yes, go to S3321; if no, go to S3322; S3311: Δθ=Δθ min ,j min =j,j=j+1; return S32; S3312: Δθ min No change, j=j+1; return to S32; S3321:i A1 =i A (j min ),i B1 =i B (j min );Finish; S3322: By j min The two points before and after determine the slope k, i A1 =i A (j min )+k(θ * -θ e (j min ));Finish; S4: Based on the positive and negative sequence relationship of the 5th harmonic current and the 7th harmonic current, the influence of control delay in the harmonic mathematical model is considered, and the 5th harmonic current loop and the 7th harmonic current loop models are reconstructed; the corresponding Bode diagram is drawn using the system transfer function of the current closed loop, and the control delay is analyzed. With the increase of the fundamental frequency, the response bandwidth decreases, the response becomes slower, and the 7th harmonic current loop is affected by the selection of the proportional parameter kp of the PI regulator, resulting in system instability. The traditional proportional integral PI parameters are designed considering the influence of control delay; Ignoring the control delay, the mathematical model of the harmonic current loop is: where u d5th and u q5th Represents the 5th harmonic current loop dq axis output voltage, i d5 and i q5 Represents the actual dq axis current of the 5th harmonic current loop, ψ m5 Represents the 5th flux linkage value generated by the permanent magnet due to the magnetic field distortion of the permanent magnet synchronous motor, and the 7th is the same as above; where u' dq and u" dq They represent the actual output dq axis voltages of the 5th and 7th current harmonic loop output voltages after considering the control delay; Substituting into the above formulas respectively, the 5th harmonic current loop and 7th harmonic current loop models are obtained as follows: where R′ = Rcosθ d +5ω e L s sinθ d ; R″ = Rcosθ d -7ω e L s sinθ d ; L′ = L″ = L s cosθ d ; S5: Based on the harmonic current loop model, the angle delay is ignored and only the time delay is considered; For the suppression of the 5th harmonic current, the delay link G d (s) = e -sTd As a nonlinear link, it is substituted into the system for parameter design and expressed using the second-order Pade as follows: Where T d Represents the delay time of the control system, T d =1.5T s ; When only the time delay link and the controlled object are considered, the system open-loop transfer function is expressed as: Where L represents the phase inductance of the actual controlled motor, and R represents the actual phase resistance; By drawing the Bode diagram, we can ensure that the system phase margin is 45°, and increase the system response bandwidth by reducing the phase margin. The proportional coefficient k of the PI controller is selected. p , as shown below: Where C is the amplitude gain corresponding to a phase margin of 45°; Define the scaling factor k p and the integration coefficient k i The ratio relationship is τ i =k p / k i = 0.01, by drawing the Bode diagram of the PI controller alone, τ i The actual selection range depends on the specific control object and the required control performance. It is necessary to select τ that has an impact on the system phase delay below a certain value. i , determine the PI parameters of the harmonic suppression current loop, k i =k p / τ i .

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