CONTROL METHOD FOR SEMI-CENTRALIZED OPEN WINDING MULTI-MOTOR DRIVE SYSTEM

Abstract

A control method for a semi-centralized open winding multi-motor drive system includes: first, measuring current, voltage and position signal, computing system thrust by a velocity loop; then, distributing the thrust to each motor, converting the thrust into q axis current, computing dq axis voltages required for each motor by a current loop, and transforming the voltage demand to abc coordinate system through coordinate transformation; subsequently, modulating the voltage of each motor into a duty ratio instruction to judge whether the motor is in an over-modulated operating area, and performing over-modulation processing on the voltage in the over-modulated area; and finally, distributing the duty ratio instructions to independent and shared inverters. The control method of the present disclosure can reduce the hardware cost and improve the safety and reliability of the system.

Claims

1. A control method for a semi-centralized open winding multi-motor drive system, wherein the drive system is composed of N motors (N>0), one side of each rotor winding is respectively connected to an independent inverter, the other sides of all rotor windings are connected to a shared inverter together, and all rotors are rigidly connected; the control method comprises the following steps: step 1: distributing a q axis current instruction i*.sub.q_x to a motor according to a thrust demand F*.sub.e: $i_{q\_x}^{*}=\frac{{?}_s{F}_e^{*}}{3N?{?}_{f1}}$ wherein ?.sub.?1 represents a permanent flux linkage of the motor, ?.sub.s represents a polar distance of the same polarity between linear motors, and N represents the number of motors; step 2: computing a dq0 axis voltage required for each motor: first, computing a dq axis voltage using a proportional integral (PI) regulator: $\{\begin{array}{c}{u}_{d\_x}=k_{p\_d\mathrm{\_x}}\left(i_{d\_x}^{*}-i_{d\_x}\right)+k_{\mathrm{i\_d}\_x}?\left(i_{d\_x}^{*}-i_{d\_x}\right)\mathrm{dt}\\ u_{d\_x}=k_{p\_q\mathrm{\_x}}\left(i_{q\_x}^{*}-i_{q\_x}\right)+k_{\mathrm{i\_q}\_x}?\left(i_{q\_x}^{*}-i_{q\_x}\right)\mathrm{dt}\end{array}$ wherein i.sub.d_x, i*.sub.d_x, i.sub.q_x and i*.sub.q_x respectively represent actual dq axis currents and reference dq axis currents of the motor x, u*.sub.d_x and u*.sub.q_x represent voltage demands of the motor x, k.sub.p_d_v, k.sub.i_d_v, k.sub.p_q_v and k.sub.i_q_v respectively represent proportional coefficients and integral coefficients of a dq axis current regulator of the motor x, and x is the motor x, taking I, II, . . . , N; then, computing a zero sequence voltage by a proportional resonant (PR) regulator, as shown in the form of discretization: $u_k=K_{p\_\mathrm{PI}}*e_k+b_0*e_k+b_2*e_{k-2}-a_1{u}_{k-1}-a_2{u}_{k-2}$ $\{\begin{array}{c}{a}_0=-a_2=\frac{4K_s{?}_c{T}_s}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2}\\ a_1=0,b_1=1\\ b_1=\frac{2{?}_0^2{T}_s^2-8}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2},b_2=\frac{4-4{?}_c{T}_s+{?}_0^2{T}_s^2}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2}\end{array}$ wherein u.sub.k represents a zero sequence voltage reference value u*.sub.0_x computed by the PR regulator at the time k, e.sub.k represents a difference value between 0 and a zero sequence current at the time k, subscripts k, k-1 and k-2 represent values at the time k, time k-1 and time k-2, T.sub.s represents a counting period of a real-time processor, ?.sub.c represents a proportional resonant frequency, ?.sub.0 represents an electrical angular frequency of the motor, and K.sub.p_PI and K.sub.s represent proportional resonant coefficients of the motor; step 3: converting a dq axis reference voltage of each motor to the abc coordinate system: $\left[\begin{array}{c}{u}_{a\_x}^{*}\\ u_{b\_x}^{*}\\ u_{c\_x}^{*}\end{array}\right]=\left[\begin{array}{ccc}\cos \left({?}_x\right)& -s\mathrm{in}\left({?}_x\right)& 1\\ \cos \left({?}_x-\frac{2}{3}?\right)& -\sin \left({?}_x-\frac{2}{3}?\right)& 1\\ \cos \left({?}_x+\frac{2}{3}?\right)& -\sin \left({?}_x-\frac{2}{3}?\right)& 1\end{array}\right]\left[\begin{array}{c}{u}_{d\_x}^{*}\\ u_{q\_x}^{*}\\ u_{0\_x}^{*}\end{array}\right]$ step 4: computing a voltage modulation coefficient of each phase of each motor:
m.sub.y_x=u*.sub.y_x/u.sub.dc wherein u*.sub.y_x represents a phase voltage of the motor x, a subscript y represents a y phase, taking a, b or c, u.sub.dc represents a direct current voltage of the motor, and m.sub.y_x represents a y-phase voltage modulation coefficient of the motor x; computing limit values of the voltage modulation coefficient: $\{\begin{array}{c}{m}_{y\_\max }=\max \left\{m_{y\_I},m_{y\_\mathrm{II}},.Math.,m_{y\_N}\right\}\\ m_{y\_\min }=\min \left\{m_{y\_I},m_{y\_\mathrm{II}},.Math.,m_{y\_N}\right\}\end{array}$ wherein m.sub.y_max represents a maximum voltage modulation coefficient of the y phase, and m.sub.y_min represents a minimum voltage modulation coefficient of the y phase; judging an operating area of the motor:
k=max {m.sub.a_max?m.sub.a_min, m.sub.b_max?m.sub.b_min, m.sub.c_max?m.sub.c_min} wherein in a case that k>1, the motor is located in an over-modulated area, otherwise, the motor is located in a linear modulation area; step 5: processing the over-modulated area: computing limit values of a corrected voltage modulation coefficient: $\{\begin{array}{c}{m}_{y\_\max }^k=\frac{m_{y\_\max }}{\max \left\{1,m_{y\_\max }-m_{y\_\min }\right\}}\\ m_{y\_\min }^k=\frac{m_{y\_\min }}{\max \left\{1,m_{y\_\max }-m_{y\_\min }\right\}}\end{array}$ wherein m.sub.y_max.sup.k represents an improved maximum voltage modulation coefficient of the y phase, and m.sub.y_min.sup.k represents an improved minimum voltage modulation coefficient of the y phase; computing corrected limit coefficients (k.sub.y_x.sup.max, k.sub.y_x.sup.min) of the voltage modulation coefficient: $\{\begin{array}{c}{k}_{y\_x}^{\max }=\frac{\min \left\{m_{y\_x},m_{y\_\max }^k\right\}}{m_{y\_x}}\\ k_{y\_x}^{\min }=\frac{\max \left\{m_{y\_x},m_{y\_\min }^k\right\}}{m_{y\_x}}\end{array}$ computing a phase correction coefficient k.sub.y_x of the voltage modulation coefficient of each phase:
k.sub.y_x=min {k.sub.y_x.sup.max, k.sub.y_x.sup.min} computing a correction coefficient k.sub.x of the motor of the voltage modulation coefficient:
k.sub.x=min {k.sub.a_x, k.sub.b_x, k.sub.c_x} computing a voltage modulation coefficient corrected value m.sub.y.sup.k by the corrected value and the voltage modulation coefficient:
m.sub.y_x.sup.k=k.sub.xm.sub.y_x step 6: computing limit duty ratios (?.sub.y_s_max, ?.sub.y_s_max) of a shared bridge arm: $\{\begin{array}{c}{?}_{y\_s\_\max }=\min \left\{1-m_{y\_\max }^k,1\right\}\\ {?}_{y\_s\_\min }=\max \left\{-m_{y\_\min }^k,0\right\}\end{array}$ computing an optimal duty ratio ?.sub.y_s of the shared bridge arm by the limit duty ratios: ${?}_{y\_s}=\frac{{?}_{y\_s\_\max }+{?}_{y\_s\_\min }}{2}$ computing a duty ratio of an independent bridge arm based on the optimal duty ratio of the shared bridge arm and the voltage modulation coefficient:
?.sub.y_x=m.sub.y_x.sup.k+?.sub.y_P

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] To describe the technical solutions in the embodiments of the present disclosure or in existing technologies more clearly, the accompanying drawings required for describing the embodiments or existing technologies are briefly introduced below. Apparently, a person of ordinary skill in the art may still derive other drawings from these accompanying drawings without creative efforts.

[0031] FIG. 1 is a multi-motor topological diagram of a semi-centralized open winding drive system in the present disclosure.

[0032] FIG. 2 is a velocity diagram of a drive system during steady state operation in the present disclosure.

[0033] FIG. 3 is a three-phase current diagram of a motor I during steady state operation in the present disclosure.

[0034] FIG. 4 is a q axis current diagram of a motor I during steady state operation in the present disclosure.

[0035] FIG. 5 shows a duty ratio of an A phase during steady state operation in the present disclosure.

DETAILED DESCRIPTION

[0036] The following clearly and completely describes the technical solutions in the embodiments of the present disclosure with reference to the accompanying drawings in the embodiments of the present disclosure. Apparently, the described embodiments are some of the embodiments of the present disclosure rather than all of the embodiments. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present disclosure without creative efforts shall fall within the protection scope of the present disclosure.

[0037] As shown in FIG. 1 to FIG. 5, the present disclosure provides a control method for a semi-centralized open winding multi-motor drive system. To verify the effect of the present disclosure, a permanent magnet linear motor is selected. Parameters of the linear motor are as follows: the stator phase resistance is 3?, the stator phase inductance is L.sub.d=L.sub.q=L.sub.s=33.5 mH, and the permanent magnet flux linkage is 0.125 Wb. The conditions of three drive motors during steady state operation are verified through experiments.

[0038] The drive system is composed of N motors (N>0), one side of each rotor winding is respectively connected to an independent inverter, the other sides of all rotor windings are connected to a shared inverter together, and all rotors are rigidly connected.

[0039] The control method includes the following steps:

[0040] (1) In the semi-centralized open winding multi-motor drive system, a distribution mode of a thrust current is as follows: [0041] a q axis current instruction i*.sub.q_x is distributed to a motor according to a thrust demand F*.sub.e:

[00010]$i_{q\_x}^{*}=\frac{{?}_s{F}_e^{*}}{3N?{?}_{f1}}$ [0042] where ?.sub.?1 represents a permanent flux linkage of the motor, ?.sub.s represents a polar distance of the same polarity between linear motors, and N represents the number of motors.

[0043] (2) A dq0 axis voltage required for each motor is computed: [0044] a dq axis voltage is computed using a PI regulator:

[00011]$\{\begin{array}{c}{u}_{d\_x}=k_{p\_d\mathrm{\_x}}\left(i_{d\_x}^{*}-i_{d\_x}\right)+k_{\mathrm{i\_d}\_x}?\left(i_{d\_x}^{*}-i_{d\_x}\right)\mathrm{dt}\\ u_{d\_x}=k_{p\_q\mathrm{\_x}}\left(i_{q\_x}^{*}-i_{q\_x}\right)+k_{\mathrm{i\_q}\_x}?\left(i_{q\_x}^{*}-i_{q\_x}\right)\mathrm{dt}\end{array}$ [0045] where i.sub.d_x, i*.sub.d_x, i.sub.q_x and i*.sub.q_x respectively represent actual dq axis currents and reference dq axis currents of the motor x, u*.sub.d_x and u*.sub.q_x represent voltage demands of the motor x, k.sub.p_d_v, k.sub.i_d_v, k.sub.p_q_v and k.sub.i_q_v respectively represent proportional coefficients and integral coefficients of a dq axis current regulator of the motor x, and x is the motor x, taking I, II, . . . , N.

[0046] A zero sequence voltage is computed by a PR regulator, as shown in the form of discretization:

[00012]$u_k=K_{p\_\mathrm{PI}}*e_k+b_0*e_k+b_2*e_{k-2}-a_1{u}_{k-1}-a_2{u}_{k-2}$$\{\begin{array}{c}{a}_0=-a_2=\frac{4K_s{?}_c{T}_s}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2}\\ a_1=0,b_1=1\\ b_1=\frac{2{?}_0^2{T}_s^2-8}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2},b_2=\frac{4-4{?}_c{T}_s+{?}_0^2{T}_s^2}{4+4{?}_c{T}_s+{?}_0^2{T}_s^2}\end{array}$ [0047] where u.sub.k represents a zero sequence voltage reference value u*.sub.0_x computed by the PR regulator at the time k, e.sub.k represents a difference value between 0 and a zero sequence current at the time k, subscripts k, k-1 and k-2 represent values at the time k, time k-1 and time k-2, T.sub.s represents a counting period of a real-time processor, ?.sub.c represents a proportional resonant frequency, ?.sub.0 represents an electrical angular frequency of the motor, and K.sub.p_PI and K.sub.s represent proportional resonant coefficients of the motor.

[0048] (3) A dq axis reference voltage of each motor is converted to the abc coordinate system:

[00013]$\left[\begin{array}{c}{u}_{a\_x}^{*}\\ u_{b\_x}^{*}\\ u_{c\_x}^{*}\end{array}\right]=\left[\begin{array}{ccc}\cos \left({?}_x\right)& -s\mathrm{in}\left({?}_x\right)& 1\\ \cos \left({?}_x-\frac{2}{3}?\right)& -\sin \left({?}_x-\frac{2}{3}?\right)& 1\\ \cos \left({?}_x+\frac{2}{3}?\right)& -\sin \left({?}_x-\frac{2}{3}?\right)& 1\end{array}\right]\left[\begin{array}{c}{u}_{d\_x}^{*}\\ u_{q\_x}^{*}\\ u_{0\_x}^{*}\end{array}\right]$

[0049] (4) A voltage modulation coefficient of each phase of each motor is computed:

m.sub.y_x=u*.sub.y_x/u.sub.dc [0050] where u*.sub.y_x represents a phase voltage of the motor x, a subscript y represents a y phase, taking a, b or c, u.sub.dc represents a direct current voltage of the motor, and m.sub.y_x represents a y-phase voltage modulation coefficient of the motor x.

[0051] Limit values of the voltage modulation coefficient are computed:

[00014]$\{\begin{array}{c}{m}_{y\_\max }=\max \left\{m_{y\_I},m_{y\_\mathrm{II}},.Math.,m_{y\_N}\right\}\\ m_{y\_\min }=\min \left\{m_{y\_I},m_{y\_\mathrm{II}},.Math.,m_{y\_N}\right\}\end{array}$ [0052] where m.sub.y_max represents a maximum voltage modulation coefficient of the y phase, and m.sub.y_min represents a minimum voltage modulation coefficient of the y phase.

[0053] An operating area of the motor is judged:

k=max {m.sub.a_max?m.sub.a_min, m.sub.b_max?m.sub.b_min, m.sub.c_max?m.sub.c_min} [0054] in a case that k>1, the motor is located in an over-modulated area; otherwise, the motor is located in a linear modulation area.

[0055] (5) The over-modulated area is processed: [0056] limit values of a corrected voltage modulation coefficient are computed:

[00015]$\{\begin{array}{c}{m}_{y\_\max }^k=\frac{m_{y\_\max }}{\max \left\{1,m_{y\_\max }-m_{y\_\min }\right\}}\\ m_{y\_\min }^k=\frac{m_{y\_\min }}{\max \left\{1,m_{y\_\max }-m_{y\_\min }\right\}}\end{array}$ [0057] where m.sub.y_max.sup.k represents an improved maximum voltage modulation coefficient of the y phase, and m.sub.y_min.sup.k represents an improved minimum voltage modulation coefficient of the y phase; [0058] corrected limit coefficients (k.sub.y_x.sup.max, k.sub.y_x.sup.min) of the voltage modulation coefficient are computed:

[00016]$\{\begin{array}{c}{k}_{y\_x}^{\max }=\frac{\min \left\{m_{y\_x},m_{y\_\max }^k\right\}}{m_{y\_x}}\\ k_{y\_x}^{\min }=\frac{\max \left\{m_{y\_x},m_{y\_\min }^k\right\}}{m_{y\_x}}\end{array}$ [0059] a phase correction coefficient k.sub.y_x of the voltage modulation coefficient of each phase is computed:

k.sub.y_x=min {k.sub.y_x.sup.max, k.sub.y_x.sup.min} [0060] a correction coefficient k.sub.x of the motor of the voltage modulation coefficient is computed:

k.sub.x=min {k.sub.a_x, k.sub.b_x, k.sub.c_x} [0061] a voltage modulation coefficient corrected value m.sub.y.sup.k is computed by the corrected value and the voltage modulation coefficient:

m.sub.y_x.sup.k=k.sub.xm.sub.y_x

[0062] (6) Limit duty ratios (?.sub.y_s_max, ?.sub.y_s_max) of a shared bridge arm are computed:

[00017]$\{\begin{array}{c}{?}_{y\_s\_\max }=\min \left\{1-m_{y\_\max }^k,1\right\}\\ {?}_{y\_s\_\min }=\max \left\{-m_{y\_\min }^k,0\right\}\end{array}$ [0063] an optimal duty ratio ?.sub.y_s of the shared bridge arm is computed by the limit duty ratios:

[00018]${?}_{y\_s}=\frac{{?}_{y\_s\_\max }+{?}_{y\_s\_\min }}{2}$ [0064] a duty ratio of an independent bridge arm is computed based on the optimal duty ratio of the shared bridge arm and the voltage modulation coefficient:

?.sub.y_x=m.sub.y_x.sup.k+?.sub.y_P

[0065] FIG. 2 is a velocity diagram of a drive system during steady state operation, which can be seen that the velocity control in the present disclosure is relatively accurate and stable. FIG. 3 is a three-phase current diagram of a motor I during steady state operation, which can be seen that the present disclosure can achieve relatively stable control and better performance for a multi-motor system. FIG. 4 is a q axis current diagram of a motor I during steady state operation, which can be seen that the present disclosure is capable of following a torque instruction. FIG. 5 shows a duty ratio of an A phase during steady state operation, which can be seen that the duty ratio distribution mode of each inverter of the A phase is basically consistent with the proposed strategy. In the descriptions of this specification, a description of a reference term such as an embodiment, an example, or a specific example means that a specific feature, structure, material, or characteristic that is described with reference to the embodiment or the example is included in at least one embodiment or example of the present disclosure. In this specification, exemplary descriptions of the foregoing terms do not necessarily refer to the same embodiment or example. In addition, the described specific features, structures, materials, or characteristics may be combined in a proper manner in any one or more of the embodiments or examples.

[0066] The foregoing displays and describes basic principles, main features of the present disclosure and advantages of the present disclosure. A person skilled in the art may understand that the present disclosure is not limited to the foregoing embodiments. Descriptions in the embodiments and this specification only illustrate the principles of the present disclosure. Various modifications and improvements are made in the present disclosure without departing from the spirit and the scope of the present disclosure, and these modifications and improvements shall fall within the protection scope of the present disclosure.