A method for suppressing torque fluctuation at the output shaft end of a reducer based on harmonic current injection method

Abstract

The present invention discloses a method for suppressing torque fluctuation at the output shaft end of a reducer based on a harmonic current injection method, the method comprising the following steps: establishing an electromagnetic sub-model that takes into account magnetic flux harmonics and magnetic saturation characteristics, with voltage as input and current as output; establishing an analytical formula for instantaneous torque by decoupling magnetic common energy into three parts: armature magnetic field, armature-magnetic steel coupling magnetic field, and magnetic steel magnetic field according to the principle of electromechanical energy conversion; deriving an analytical formula for motor torque containing harmonic current coupling terms, deriving a reducer output shaft torque containing harmonic current coupling terms according to the motor output shaft torque containing harmonic current coupling terms, and suppressing the torque fluctuation at the output shaft end by actively injecting harmonic currents of specific amplitudes and phases to generate additional torque fluctuations. The present invention comprehensively considers the electromechanical coupling effect of the entire electric drive system, takes the reducer into account, and generates additional torque fluctuations by actively injecting harmonic currents of specific amplitudes and phases to solve the torque fluctuation problem at the output shaft end of the reducer of the electric drive system.

Description

Technical Field

[0001] The present invention belongs to the technical field of electric vehicle control, and relates to a vibration reduction control method for an electric drive system, and specifically to a method for suppressing torque fluctuations at the output shaft end of a reducer based on a harmonic current injection method. Background Art

[0002] As drive motors develop towards wide speed range, high speed and light weight, integrated electric drive systems are also facing new problems and challenges, among which NVH is one of the important issues that need to be solved urgently. In electric drive systems, there are a large number of periodic disturbances in the motor excitation source, which are caused by both the motor structure and electrical components. In PMSM electric drive systems, they mainly exist in the form of harmonics. The reducer excitation sources include gear time-varying meshing stiffness excitation, gear manufacturing processing / assembly error excitation, gear impact excitation, input shaft torque fluctuation, bearing stiffness excitation, friction excitation, etc. The combined effect of the two will lead to torque fluctuations in the electric drive system.

[0003] At present, there are two main elimination ideas from the control perspective. One method is to compensate the control link through a specific control strategy, mainly including proportional resonant controller, iterative learning control, repetitive control and other methods. This method is committed to improving the sinusoidality of the three-phase current by suppressing the current harmonics to zero, thereby reducing the torque fluctuation caused by the current harmonics. However, due to the interaction between the inherent magnetic flux harmonics of the motor body and the three-phase stator winding current, even if the motor is connected to a completely sinusoidal three-phase alternating current, torque fluctuations will occur. Another method does not rely on the actual variables and disturbances when the system is working, but estimates the disturbance value of the system at a certain stage by establishing a system model. In the control of permanent magnet synchronous motors, it is mainly a harmonic injection method. The harmonic current injected into the fundamental wave of the current will appear as additional torque at the output end, offsetting the adverse effects of the harmonics generated in the current by various periodic disturbances in the system. However, the existing harmonic current injection methods only suppress the fluctuation of the motor output torque, without considering the influence of the reducer.

[0004] Therefore, it is necessary to comprehensively consider the electromechanical coupling effect of the entire electric drive system, improve the existing harmonic current injection method, and seek a control scheme that can take the reducer into account and suppress the torque fluctuation at the output shaft end of the reducer. Summary of the invention

[0005] In view of this, the purpose of the present invention is to provide a method for suppressing torque fluctuations at the output shaft end of a reducer based on the harmonic current injection method, which solves the problem of torque fluctuations at the output shaft end of the reducer of the electric drive system by actively injecting harmonic currents of specific amplitude and phase to generate additional torque fluctuations.

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for suppressing torque fluctuations at the output shaft end of a reducer based on a harmonic current injection method, the method comprising the following steps: under the premise that the influence of external factors of the drive control system and nonlinear factors of the motor temperature is not considered, an electromagnetic sub-model is established that takes into account the magnetic flux harmonics and magnetic saturation characteristics, with voltage as input and current as output; according to the principle of electromechanical energy conversion, the electromagnetic torque is the differential of the magnetic common energy with respect to the rotor angle, and an analytical formula for the instantaneous torque is established by decoupling the magnetic common energy into three parts: the armature magnetic field, the armature-magnet coupling magnetic field, and the magnet magnetic field, and further formula derivation; an analytical formula for the motor torque containing a harmonic current coupling term is derived, and the reducer output shaft torque containing a harmonic current coupling term is derived according to the motor output shaft torque containing a harmonic current coupling term, and the torque fluctuation at the output shaft end is suppressed by actively injecting harmonic currents of specific amplitudes and phases to generate additional torque fluctuations.

[0007] Compared with the prior art, the advantages of the present invention are:

[0008] 1. The present invention takes the torque fluctuation at the output shaft end of the reducer as the research object, and derives the relationship between the output shaft torque of the reducer and the injected harmonic current based on the motor output shaft torque containing the harmonic current coupling term. By actively injecting harmonic currents of specific amplitude and phase to generate additional torque fluctuations, the output shaft torque fluctuations are directly suppressed, which can more comprehensively consider the electromechanical coupling effect of the entire electric drive system.

[0009] 2. The present invention uses a quasi-resonant controller, which is an improved form of an ideal resonant controller, in parallel with a PI controller. The resonant controller has the characteristics of zero phase offset and infinite gain for AC signals of specific frequencies, directly integrates the AC input of a specific frequency, suppresses signals of other frequencies, and has good tracking and control performance for the injected AC signals of a specific frequency, thereby achieving tracking control of the 6th and 12th harmonics in the DC signal and the reference harmonic current command. BRIEF DESCRIPTION OF THE DRAWINGS

[0010] Figure 1 Pure torsional dynamics model for the powertrain

[0011] Figure 2 The electromagnetic model structure diagram

[0012] Figure 3 This is the structure diagram of the proportional integral resonance controller (PIR controller). DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further explained below in conjunction with the accompanying drawings, but it should not be understood as a limitation to the technical solution, and adaptive improvements based on this all fall within the protection scope of the present invention.

[0014] like Figure 1-Figure 3 As shown, the motor output shaft outputs a torque T containing harmonic current coupling terms. m The harmonic components reach the output shaft end of the reducer through two-stage gears. The output shaft torque T is derived according to the dynamic equation of the transmission system. s The relationship between the harmonic current and the injected harmonic current is that the additional torque fluctuation is generated by actively injecting harmonic current of specific amplitude and phase to suppress the torque fluctuation at the output shaft end.

[0015] A method for suppressing torque fluctuation at the output shaft end of a reducer based on a harmonic current injection method, the specific steps of the method are as follows:

[0016] 1. Considering the flux harmonics and magnetic saturation characteristics, a permanent magnet synchronous motor torque model is established that accurately reflects the torque response characteristics.

[0017] ① Under the premise of not considering the influence of the external drive control system and the nonlinear factors of the motor temperature, an electromagnetic sub-model is established that takes into account the magnetic flux harmonics and magnetic saturation characteristics, with voltage as input and current as output, such as Figure 2 ; The model input is the dq axis voltage, which is obtained by coordinate transformation of the three-phase voltage output by the inverter; the dq axis flux is calculated, and then the dq axis current is obtained by looking up the table according to the reverse mapping MAP of the dq axis current, the dq axis flux and the rotor position angle, and finally the dq axis current is used as feedback to calculate the dq axis flux;

[0018]

[0019] In the formula, ψ d , ψ q Respectively represent the dq axis magnetic flux; v d , v q Respectively represent dq axis voltage; R s is the stator winding resistance; i d ,i q is the dq axis current; ω e is the electrical angular velocity of the rotor;

[0020] ② According to the principle of electromechanical energy conversion, the electromagnetic torque is the differential of the magnetic common energy to the rotor angle. By decoupling the magnetic common energy into three parts: armature magnetic field, armature-magnet coupling magnetic field, and magnetic steel magnetic field, and further formula derivation, the instantaneous torque analytical formula is established:

[0021]

[0022] Where P nis the number of pole pairs of the permanent magnet synchronous motor; θ e is the rotor position angle expressed in electrical degrees; dq =[λ d ,λ q ] T is the dq-axis permanent magnet flux; T cog is the cogging torque.

[0023] 2. Solve the reference harmonic current command

[0024] ① After the harmonic current is injected, the dq axis current at any electrical angle is the sum of the fundamental wave and the harmonic; the torque analytical formula is further derived into a form containing the harmonic current coupling term:

[0025]

[0026] In the formula, i db ,i qb Represents the fundamental component of dq axis current; i dh ,i qh Indicates dq axis harmonic current; T mb , T mh Respectively represent the fundamental component and harmonic component of the dq axis torque;

[0027]

[0028] ② Establish the dynamic equation from the motor output shaft to the reducer output shaft:

[0029]

[0030] Where, T m represents electromagnetic torque; θ 1 ,θ 2 ,θ 3 ,θ 4 It represents the motor shaft, the driven wheel of the first gear pair, the driven wheel of the second gear pair, and the equivalent rotation angle of the wheel in sequence; represents the equivalent angular velocity of the motor shaft, the driven wheel of the first gear pair, the driven wheel of the second gear pair, and the wheel in turn; i 1 ,i 2 Indicates the first and second gear ratios of the reducer; k 12 , k 23 , k 34 represents the torsional stiffness of the motor shaft, intermediate shaft and output shaft respectively; c 12 , c 23 , c 34 represents the torsional damping of the motor shaft, intermediate shaft and output shaft respectively; T L Indicates the vehicle's driving resistance torque;

[0031] ③Let the state variable Input variable u=[T m T L ], output variable The dynamic equations are further expressed as standard state space equations:

[0032]

[0033] In the formula,

[0034]

[0035] C = [0 1 1 0 0 1 1 0],

[0036] D=[0]

[0037] ④ Design a state observer to realize θ 2 ,θ 3 , Estimates:

[0038]

[0039] Let |λI-(A-LC)|=0 to obtain the observer gain L;

[0040] ⑤According to the motor output shaft torque T containing the harmonic current coupling term m =T mh +T mb Derivation of the reducer output shaft torque T including harmonic current coupling terms s .

[0041] Let the state variable Input variable u=[T mh T mb ], output variable y = [T sh T sb ], then

[0042] y=Ex+Fu

[0043] In the formula,

[0044] F=[i 1 i 2 i 1 i 2 ]

[0045] ⑥ Solve the dq axis reference harmonic current value based on Lagrangian optimization

[0046] min f=i dh 2 +i qh 2

[0047]

[0048] In the formula, i dh ,i qh Indicates dq axis harmonic current; T s Indicates the output shaft torque of the reducer; T sh Indicates the harmonic component of the reducer output shaft torque; T mreq represents the required torque; i 1 ,i 2 Indicates the first and second gear ratios of the reducer;

[0049] 3. Design of harmonic current injection controller

[0050] A quasi-resonant controller is used in parallel with the PI controller, using a modified form of the ideal resonant controller, such as Figure 3 In both the d-axis and q-axis current loops, multiple resonant controllers are connected in parallel with the PI controller to achieve tracking control of the 6th and 12th harmonics in the DC signal and the reference harmonic current command.

Claims

1. A method for suppressing torque fluctuation at the output shaft end of a reducer based on a harmonic current injection method, the method comprising the following steps: Under the premise that the influence of external factors of the drive control system and the nonlinear factors of the motor temperature are not considered, an electromagnetic sub-model is established with voltage as input and current as output, considering the magnetic flux harmonics and magnetic saturation characteristics; according to the principle of electromechanical energy conversion, the electromagnetic torque is the differential of the magnetic common energy with respect to the rotor angle, and the instantaneous torque analytical formula is established by decoupling the magnetic common energy into three parts: the armature magnetic field, the armature-magnet coupling magnetic field, and the magnetic field of the magnet, and further formula derivation; the motor torque analytical formula containing the harmonic current coupling term is derived, and the reducer output shaft torque containing the harmonic current coupling term is derived according to the motor output shaft torque containing the harmonic current coupling term, and the torque fluctuation at the output shaft end is suppressed by actively injecting harmonic currents of specific amplitudes and phases to generate additional torque fluctuations; the method is characterized in that the specific steps are as follows:

1. Considering the flux harmonics and magnetic saturation characteristics, a permanent magnet synchronous motor torque model is established that accurately reflects the torque response characteristics. ① Under the premise that the influence of the external factors of the drive control system and the nonlinear factors of the motor temperature are not considered, an electromagnetic sub-model is established with voltage as input and current as output, considering the magnetic flux harmonics and magnetic saturation characteristics; the model input is the dq axis voltage, which is obtained by coordinate transformation of the three-phase voltage output by the inverter; the dq axis magnetic flux is obtained by calculation, and then the dq axis current is obtained by looking up the table according to the reverse mapping MAP of the dq axis current, the dq axis magnetic flux and the rotor position angle, and finally the dq axis current is used as feedback to calculate the dq axis magnetic flux; In the formula, ψ d , ψ q Respectively represent the dq axis magnetic flux; v d , v q Respectively represent dq axis voltage; R s is the stator winding resistance; i d ,i q is the dq axis current; ω e is the electrical angular velocity of the rotor; ② According to the principle of electromechanical energy conversion, the electromagnetic torque is the differential of the magnetic common energy to the rotor angle. By decoupling the magnetic common energy into three parts: armature magnetic field, armature-magnet coupling magnetic field, and magnetic steel magnetic field, and further formula derivation, the instantaneous torque analytical formula is established: Where P n is the number of pole pairs of the permanent magnet synchronous motor; θ e is the rotor position angle expressed in electrical degrees; dq =[λ d ,λ q ] T is the dq-axis permanent magnet flux; T cog is the cogging torque; 2. Solve the reference harmonic current command ① After the harmonic current is injected, the dq axis current at any electrical angle is the sum of the fundamental wave and the harmonic; the torque analytical formula is further derived into a form containing the harmonic current coupling term: In the formula, i db ,i qb Represents the fundamental component of dq axis current; i dh ,i qh Indicates dq axis harmonic current; T mb , T mh Respectively represent the fundamental component and harmonic component of the dq axis torque; ② Establish the dynamic equation from the motor output shaft to the reducer output shaft: Where, T m represents electromagnetic torque; θ1, θ2, θ3, θ4 represent the equivalent rotation angles of the motor shaft, the driven wheel of the first gear pair, the driven wheel of the second gear pair, and the wheel respectively; represents the equivalent angular velocity of the motor shaft, the driven wheel of the first gear pair, the driven wheel of the second gear pair, and the wheel in turn; i1 and i2 represent the transmission ratio of the first and second gears of the reducer; k 12 , k 23 , k 34 represents the torsional stiffness of the motor shaft, intermediate shaft and output shaft respectively; c 12 , c 23 , c 34 represents the torsional damping of the motor shaft, intermediate shaft and output shaft respectively; T L Indicates the vehicle's driving resistance torque; ③Let the state variable Input variable u=[T m T L ], output variable The dynamic equations are further expressed as standard state space equations: In the formula, ④ Design a state observer to realize θ2, θ3, Estimates: Let |λI-(A-LC)|=0 to obtain the observer gain L; ⑤According to the motor output shaft torque T containing the harmonic current coupling term m =T mh +T mb Derivation of the reducer output shaft torque T including harmonic current coupling terms s； Let the state variable Input variable u=[T mh T mb ], output variable y = [T sh T sb ], then y=Ex+Fu In the formula, ⑥ Solve the dq axis reference harmonic current value based on Lagrangian optimization In the formula, i dh ,i qh Indicates dq axis harmonic current; T s Indicates the output shaft torque of the reducer; T sh Indicates the harmonic component of the reducer output shaft torque; T mreq Indicates the required torque; i1 and i2 indicate the first and second gear ratios of the reducer; 3. Design of harmonic current injection controller A quasi-resonant controller, an improved form of an ideal resonant controller, is connected in parallel with a PI controller. Multiple resonant controllers are used in parallel with the PI controller in both the d-axis and q-axis current loops to achieve tracking control of the 6th and 12th harmonics in the DC signal and the reference harmonic current command.

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