TRANSIENT CURRENT PLANNING METHOD FOR ULTRA-HIGH-SPEED PERMANENT MAGNET SYNCHRONOUS MOTOR FOR IMPROVING SPEED REGULATION RESPONSE CAPABILITIES

Abstract

A transient current planning method for an ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities is provided. A transient current planning module uses a voltage model considering transient current changes to calculate current instruction values of an ultra-high-speed permanent magnet synchronous motor under MTPA control, general flux-weakening control, and MTPV control; a mode switching condition judgment subsystem judges whether a control mode is MTPA control or general flux-weakening control, or MTPV control, and sends d- and q-axis current instruction values in the corresponding control mode to a voltage decoupling control module; and the voltage decoupling control module calculates d- and q-axis voltage instruction values for controlling the motor, so as to realize control over the ultra-high-speed permanent magnet synchronous motor.

Claims

1. A transient current planning method for an ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities, wherein the transient current planning method is based on a transient current planning system comprising a transient current planning module, and the transient current planning module comprises a MTPA control subsystem, a general flux-weakening control subsystem, a MTPV control subsystem, and a mode switching condition judgment subsystem; the MTPA control subsystem calculates d- and q-axis current instruction values under a MTPA control, the general flux-weakening control subsystem calculates d- and q-axis current instruction values in a general flux-weakening control stage, the MTPV control subsystem calculates d- and q-axis current instruction values in a MTPV control stage, the mode switching condition judgment subsystem judges whether a control mode is the MTPA control or a general flux-weakening control or an MTPV control, and sends the d- and q-axis current instruction values in a corresponding control mode to a voltage decoupling control module, and the voltage decoupling control module calculates d- and q-axis voltage instruction values for controlling the ultra-high-speed permanent magnet synchronous motor; the transient current planning method comprises the following steps: step (1): judging, by the mode switching condition judgment subsystem, whether to switch to the general flux-weakening control or the MTPV control, and if yes, entering step (2); otherwise, entering step (5), wherein switching or not is determined by judging whether d- and q-axis voltage values reach limit values as a switching point, and a judgment formula is:
√{square root over (U.sub.d.sup.2+U.sub.q.sup.2)}<U.sub.max if the judgment formula is established, switching to the MTPA control is performed; otherwise, the transient current planning method turns to step (2); step (2): judging, by the mode switching condition judgment subsystem, whether a rotational speed sampling value ω.sub.r is greater than a MTPV control starting point rotational speed ω.sub.Vs, and if not, entering step (3); if yes, entering step (4); step (3): receiving, by the general flux-weakening control subsystem, d- and q-axis current instruction values I*.sub.d and I*.sub.q in a MTPA control stage and the rotational speed sampling value, and calculating the d- and q-axis current instruction values in the general flux-weakening control stage, wherein a d-axis current instruction value in the general flux-weakening control stage is:
a.sub.1.sup.2I*.sub.d.sup.2+2a.sub.1a.sub.2I*.sub.d+a.sub.2.sup.2+b.sub.1.sup.2(I.sub.max.sup.2−I*.sub.d.sup.2)+b.sub.2.sup.2+2b.sub.1b.sub.2√{square root over (I.sub.max.sup.2−I*.sub.d.sup.2)}=U.sub.max.sup.2 wherein, a.sub.1, a.sub.2, b.sub.1, b.sub.2, A, and B are all variables, and a.sub.1=ω.sub.r L.sub.d, a.sub.2=ω.sub.r λ.sub.PM+L.sub.qB, B=dI.sub.q/dt, b.sub.1=ω.sub.r L.sub.q, b.sub.2=L.sub.dA, A=dI.sub.d/dt; I.sub.max is a maximum stator current, λ.sub.PM is a permanent magnet flux linkage, L.sub.d is a d-axis inductance, L.sub.q is a q-axis inductance, I.sub.q is a q-axis current instruction initial value, and I.sub.d is a d-axis current instruction initial value; a q-axis current instruction value in the general flux-weakening control stage is:
I*.sub.q=√{square root over (I.sub.max.sup.2−I*.sub.d.sup.2)} step (4): receiving, by the MTPV control subsystem, the rotational speed sampling value ω.sub.r and d- and q-axis current sampling values i.sub.d and i.sub.q, and calculating the d- and q-axis current instruction values in the MTPV control stage, wherein a calculation formula of a d-axis current instruction value in the MTPV control stage is: $\frac{\left(\rho -\text{?}\right)L\text{?}A-\sqrt{{\left(\rho -\text{?}\right)}^{2}L\text{?}{A}^2+4\left(\rho -\text{?}\right)\omega \text{?}L\text{?}C}}{2\omega \text{?}L\text{?}}-\frac{C}{\sqrt{U\text{?}-\left(\omega \text{?}L\text{?}I\text{?}+\lambda \text{?}\omega \text{?}+L\text{?}B\right)\text{?}}}=0$ $\text{?}\text{indicates text missing or illegible when filed}$ a calculation formula of a q-axis current instruction value in the MTPV control stage is: $I_q^{*}=\frac{C}{\left(\rho -1\right)\sqrt{U\text{?}-{\left({\omega }_r{L}_d{I}_d^2+\lambda \text{?}{\omega }_r+L_{q}B\right)}^2}}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein, ρ and C are both variables, and ρ=L.sub.d/L.sub.q, C=ρω.sub.r[λ.sub.PM/L.sub.q+(ρ−1)I*.sub.d][L.sub.dI*.sub.d+λ.sub.PM+BL.sub.q/ω.sub.r]; and step (5): receiving, by the voltage decoupling control module, the d- and q-axis current instruction values sent by the transient current planning module and calculating d- and q-axis voltage instructions, so as to implement a control over the ultra-high-speed permanent magnet synchronous motor.

2. The transient current planning method of the transient current planning system for the ultra-high-speed permanent magnet synchronous motor according to claim 1, wherein a process of obtaining the d- and q-axis current instruction values in the MTPA control stage is: judging whether I.sub.q is greater than a maximum q-axis current I.sub.qmax1, wherein if yes, a first calculation formula of the d- and q-axis current instruction values is: $\{\begin{array}{c}{I}_d^{*}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+\frac{I_{\max }^2}{2}}\\ I_q^{*}=\mathrm{sign}\left(n^{*}\right)\sqrt{I_{\max }^2-I_{\mathrm{dmax}1}^2}\end{array};$ if not, a second calculation formula of the d- and q-axis current instruction values is: $\{\begin{array}{c}{I}_d^{*}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+I_q^2}\\ I_q^{*}=I_q\end{array},$ wherein sign(n*) is a sign function.

3. The transient current planning method of the transient current planning system for the ultra-high-speed permanent magnet synchronous motor according to claim 2, wherein a calculation formula of the maximum q-axis current I.sub.qmax1 is: $\{\begin{array}{c}{I}_{\mathrm{dmax}1}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+\frac{I_{\max }^2}{2}}\\ I_{\mathrm{qmax}1}=\sqrt{I_{\max }^2-I_{\mathrm{dmax}1}^2}\end{array},$ wherein I.sub.dmax1 is a maximum d-axis current under the MTPA control.

4. The transient current planning method of the transient current planning system for the ultra-high-speed permanent magnet synchronous motor according to claim 1, wherein the q-axis current instruction initial value is obtained from $T_e=\frac{{\omega }_{\mathrm{ref}}-{\omega }_r}{\Delta t}J\mathrm{and}{T}_e=\frac{1}{2}{n}_p[{\lambda }_{\mathrm{PM}}+\sqrt{{\lambda }_{\mathrm{PM}}^2+4{I_q^2\left(L_d-L_q\right)}^2]I_q},$ wherein T.sub.e is an electromagnetic torque, ω.sub.ref is a target rotational speed, Δt is a sampling interval, J is a shaft moment of inertia, and n.sub.p is a number of pole-pairs.

5. The transient current planning method of the transient current planning system for the ultra-high-speed permanent magnet synchronous motor according to claim 1, wherein the MTPV control starting point rotational speed is calculated by combining the d- and q-axis current instruction values in the MTPV control stage and a current limit circle equation, specifically as follows: $\{\begin{array}{c}\frac{\left(\rho -\text{?}\right)L_{d}A-\sqrt{{\left(\rho -\text{?}\right)}^{2}L\text{?}{A}^2+4\left(\rho -\text{?}\right)\omega \text{?}L\text{?}C}}{2\omega \text{?}L\text{?}}-\frac{C}{\sqrt{U\text{?}-\left(\omega \text{?}L\text{?}I\text{?}+\lambda \text{?}\omega \text{?}+L\text{?}B\right)\text{?}}}=0\\ I\text{?}=\frac{C}{\left(\text{?}-\text{?}\right)\sqrt{U\text{?}-\left(\omega \text{?}L\text{?}I\text{?}+\lambda \text{?}\omega \text{?}+L\text{?}B\right)\text{?}}}\\ I\text{?}+I\text{?}=I\text{?}\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$

6. The transient current planning method of the transient current planning system for the ultra-high-speed permanent magnet synchronous motor according to claim 1, wherein values of A and B in the general flux-weakening control stage are: $\{\begin{array}{c}A=\frac{I_{d1}-I_{dr}}{\Delta t}\\ B=\frac{I\text{?}-I\text{?}}{\Delta t}\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein I.sub.dr and I.sub.qr are respectively d- and q-axis current sampling values; I.sub.d1 and I.sub.q1 are respectively the d- and q-axis current instruction values in the general flux-weakening control stage, specifically as follows: $\{\begin{array}{c}I\text{?}=\frac{L_d{\lambda }_{\mathrm{PM}}-L_q\sqrt{{\lambda }_{\mathrm{PM}}^2+\left(L_q^2-L_d^2\right)\left(I_{\max }^2-\frac{U_{\max }^2}{\omega \text{?}{L}_q^2}\right)}}{L_q^2-K_d^2}\\ I\text{?}=\sqrt{I_{\max }^2-I_d^2\text{?}}\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$

7. The transient current planning method of the transient current planning system for ultra-high-speed permanent magnet synchronous motor according to claim 1, wherein values of A and B in the MTPV control stage are: $\{\begin{array}{c}A=\frac{I_{d2}-I\text{?}}{\Delta t}\\ B=\frac{I_{q2}-I\text{?}}{\Delta t}\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein I.sub.d2 and I.sub.q2 are respectively the d- and q-axis current instruction values in the MTPV control stage, specifically as follows: $\{\begin{array}{c}{I}_{d2}=-\frac{{\lambda }_{\mathrm{PM}}}{L_d}+E\\ I_{q2}=\frac{\sqrt{{\left(U\text{?}/{\omega }_r\right)}^2-{\left(L_{d}E\right)}^2}}{L_q}\\ E=\frac{{\mathrm{\rho \lambda }}_{\mathrm{PM}}-\sqrt{{\left({\mathrm{\rho \lambda }}_{\mathrm{PM}}\right)}^2+8{\left(\rho -1\right)}^2{\left(U\text{?}/{\omega }_r\right)}^2}}{4\left(\rho -1\right)L_d}\end{array}$ $\text{?}\text{indicates text missing or illegible when filed}$ wherein, E is a variable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 is an architecture diagram illustrating control over an ultra-high-speed permanent magnet synchronous motor in the present invention;

[0034] FIG. 2 is a flowchart illustrating transient current trajectory planning for the ultra-high-speed permanent magnet synchronous motor in the present invention; and

[0035] FIG. 3 is a diagram illustrating a changing trend of a current trajectory before and after transient current changes are considered.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The present invention is further illustrated below with reference to the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited thereto.

[0037] FIG. 1 shows a transient current planning system for an ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities. A transient current planning module is established. The module receives a target rotational speed ω.sub.ref, an electrical angular velocity sampling value ω.sub.r, and d- and q-axis current sampling values i.sub.d, i.sub.q, and uses a voltage model considering transient current changes to calculate current instruction values of the ultra-high-speed permanent magnet synchronous motor under MTPA control, general flux-weakening control, and MTPV control to obtain a current trajectory; meanwhile, the transient current planning module uses given switching rules to judge a control mode (MTPA control or general flux-weakening control or MTPV control) that should be adopted by the ultra-high-speed permanent magnet synchronous motor, and outputs d- and q-axis current instructions I*.sub.d, I*.sub.q in the control mode to a voltage decoupling control module; and the voltage decoupling control module calculates d- and q-axis voltage instruction values U*.sub.d and U*.sub.q, so as to realize control over the ultra-high-speed permanent magnet synchronous motor.

[0038] The transient current planning module includes a MTPA control subsystem, a general flux-weakening control subsystem, a MTPV control subsystem, and a mode switching condition judgment subsystem.

[0039] As shown in FIG. 2, a transient current planning method for an ultra-high-speed permanent magnet synchronous motor for improving speed regulation response capabilities specifically includes the following steps:

[0040] Step (1); a rotational speed command is input.

[0041] Step (2): a transient current planning module receives a target rotational speed ω.sub.ref, an electrical angular velocity sampling value ω.sub.r, and d- and q-axis current sampling values i.sub.d and i.sub.q.

[0042] Step (3): a q-axis current instruction initial value I.sub.q is obtained by a rotational speed regulator and a PI regulator, and I.sub.q is input to a MTPA control subsystem.

[0043] The q-axis current instruction initial value I.sub.q is obtained through the following method:

[0044] 1) a required electromagnetic torque is calculated by the rotational speed regulator and the PI regulator, where a calculation formula is:

[00012]$\begin{array}{cc}{T}_e=\frac{{\omega }_{\mathrm{ref}}-{\omega }_r}{\Delta t}J& \left(1\right)\end{array}$

[0045] where in the formula, Δt is a sampling interval, and J is a shaft moment of inertia.

[0046] 2) A relation between the torque and the q-axis current initial value I.sub.q is calculated according to an electromagnetic torque equation and a current limit equation:

T.sub.e=½n.sub.p[λ.sub.PM+√{square root over (λ.sub.MP.sup.2+4I.sub.q.sup.2(L.sub.d−L.sub.q).sup.2)}]I.sub.q  (2)

[0047] where in the formula, n.sub.p is a number of pole-pairs, λ.sub.PM is a permanent magnet flux linkage, L.sub.d is a d-axis inductance, and L.sub.q is a q-axis inductance.

[0048] The current instruction initial value I.sub.q is obtained from formulas (1) and (2).

[0049] Step (4): the MTPA control subsystem calculates d- and q-axis current instruction values in a MTPA control stage.

[0050] 1) A maximum q-axis current I.sub.qmax1 under MTPA control is calculated, where a calculation formula is:

[00013]$\begin{array}{cc}\{\begin{array}{c}{I}_{d\max 1}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+\frac{I_{\max }^2}{2}}\\ I_{q\max 1}=\sqrt{I_{\max }^2-I_{d\max 1}^2}\end{array}& \left(3\right)\end{array}$

[0051] wherein the formula, I.sub.d max1 is a maximum d-axis current under MTPA control, and I.sub.max is a maximum stator current.

[0052] 2) It is judged whether I.sub.q is greater than I.sub.qmax1, and if yes, a calculation formula of the d- and q-axis current instruction values is:

[00014]$\begin{array}{cc}\{\begin{array}{c}{I}_d^{*}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+\frac{I_{\max }^2}{2}}\\ I_q^{*}=\mathrm{sign}\left(n^{*}\right)\sqrt{I_{\max }^2-I_{d\max 1}^2}\end{array}& \left(4\right)\end{array}$

[0053] if not, a calculation formula of the d- and q-axis current instruction values is:

[00015]$\begin{array}{cc}\{\begin{array}{c}{I}_d^{*}=\frac{{\lambda }_{\mathrm{PM}}}{4\left(L_q-L_d\right)}-\sqrt{\frac{{\lambda }_{\mathrm{PM}}^2}{16{\left(L_q-L_d\right)}^2}+I_q^2}\\ I_q^{*}=I_q\end{array}& \left(5\right)\end{array}$

[0054] where in the formula, sign(n*) is a sign function.

[0055] Step (5): a mode switching condition judgment subsystem judges whether to switch to general flux-weakening control or MTPV control, and if yes, the method enters step (6); otherwise, the method enters step (9).

[0056] The judging whether to switch to general flux-weakening control or MTPV control is achieved by judging whether d- and q-axis voltage values reach limit values as a switching point, and a judgment formula is:

√{square root over (U.sub.d.sup.2+U.sub.q.sup.2)}<U.sub.max  (6)

[0057] where in the formula, U.sub.max is a terminal voltage limit value.

[0058] If formula (6) is established, switching to MTPA control is performed; if the condition is not established, the method turns to step (6) to further judge the control mode.

[0059] Step (6): the mode switching condition judgment subsystem judges whether the electrical angular velocity sampling value is greater than a MTPV control starting point rotational speed, namely, ω.sub.r≥ω.sub.Vk, and if not, the method enters (7); if yes, the method enters step (8).

[0060] Step (7): a general flux-weakening control subsystem receives the d- and q-axis current instruction values calculated in step (4) and the electrical angular velocity sampling value, and calculates d- and q-axis current instruction values in the general flux-weakening control stage, and the method enters step (9).

[0061] The derivation process of the d- and q-axis current instruction values under general flux-weakening control considers transient current changes to improve precise response of a torque in the general flux-weakening control stage, enlarge the torque output range of the motor, and achieve the purpose of enhancing speed regulation response capabilities.

[0062] A voltage model considering transient current changes is:

[00016]$\begin{array}{cc}\{\begin{array}{c}{U}_d={\mathrm{RI}}_d+L_d\frac{{\mathrm{dI}}_d}{\mathrm{dt}}-{\omega }_r{L}_q{I}_q\\ U_q={\mathrm{RI}}_q+L_q\frac{{\mathrm{dI}}_q}{\mathrm{dt}}+{\omega }_r\left(L_d{I}_d+{\lambda }_{\mathrm{PM}}\right)\end{array}& \left(7\right)\end{array}$

[0063] wherein the formula, R is a stator resistance, and I.sub.d is a d-axis current instruction initial value.

[0064] In current applications, in order to derive a current trajectory instruction more conveniently, transient current voltage drop terms

[00017]$L_d\frac{{\mathrm{dI}}_d}{dt}\mathrm{and}{L}_q\frac{{\mathrm{dI}}_q}{dt}$

in formula (7) are usually omitted, while the control system provided in the present invention considers transient current voltage drop terms.

[0065] After transient current changes are considered, a calculation formula of the d-axis current instruction value in the general flux-weakening control stage is:

a.sub.1.sup.2I*.sub.d.sup.2+2a.sub.1a.sub.2I*.sub.d+a.sub.2.sup.2+b.sub.1.sup.2(I.sub.max.sup.2−I*.sub.d.sup.2)+b.sub.2.sup.2+2b.sub.1b.sub.2√{square root over (I.sub.max.sup.2−I*.sub.d.sup.2)}=U.sub.max.sup.2  (8)

[0066] wherein the formula, a.sub.1, a.sub.2, b.sub.1, b.sub.2, A, and B are all variables, and a.sub.1=ω.sub.r L.sub.d, a.sub.2=ω.sub.r λ.sub.PM+L.sub.qB, B=dI.sub.q/dt, b.sub.1=ω.sub.r L.sub.q, b.sub.2=L.sub.dA, A=dI.sub.d/dt.

[0067] A calculation formula of the q-axis current instruction value in the general flux-weakening control stage is:

I*.sub.q=√{square root over (I.sub.max.sup.2−I*.sub.d.sup.2)}  (9)

[0068] When a Simulink control model is built, formulas (8) and (9) are written as an m-file to facilitate calculation of d- and q-axis current instruction values in the case of any electrical angular velocity sampling value in the general flux-weakening control stage.

[0069] Step (8): the MTPV control subsystem receives the electrical angular velocity sampling value ω.sub.r and the d- and q-axis current sampling values i.sub.d, i.sub.q, and calculates d- and q-axis current instruction values in the MTPV control stage.

[0070] The derivation process of the d- and q-axis current instruction values in the MTPV control stage considers transient current changes to improve precise response of a torque in the MTPV control stage, enlarge the torque output range of the motor, and achieve the purpose of enhancing speed regulation response capabilities. After transient current changes are considered, a calculation formula of the d-axis current instruction value in the MTPV control stage is:

[00018]$\begin{array}{cc}\frac{\left(\rho -1\right)L_{d}A-\sqrt{{\left(\rho -1\right)}^2{L}_d^2{A}^2+4\left(\rho -1\right){\omega }_r{L}_{q}C}}{2{\omega }_r{L}_q}-\frac{C}{\sqrt{U_{\max }^2-{\left({\omega }_r{L}_d{I}_d^{*}+{\lambda }_{\mathrm{PM}}{\omega }_r+L_{q}B\right)}^2}}=0& \left(10\right)\end{array}$

[0071] a calculation formula of the q-axis current instruction value in the MTPV control stage is:

[00019]$\begin{array}{cc}{I}_q^{*}=\frac{C}{\left(\rho -1\right)\sqrt{U_{\max }^2-{\left({\omega }_r{L}_d{I}_d^{*}+{\lambda }_{\mathrm{PM}}{\omega }_r+L_{q}B\right)}^2}}& \left(11\right)\end{array}$

[0072] where in the formulas, ρ and C are both variables, and ρ=L.sub.d/L.sub.q, C=ρω.sub.r[λ.sub.PM/L.sub.q+(ρ−1)I*.sub.d][L.sub.dI*.sub.d=λ.sub.PM+BL.sub.q/ω.sub.r].

[0073] When a Simulink control model is built, formulas (10) and (11) are written as an in-file to facilitate calculation of d- and q-axis current instruction values in the case of any electrical angular velocity sampling value in the MTPV control stage.

[0074] In addition, the MTPV control starting point rotational speed is calculated by combining the d and q current instruction values in the MTPV control stage and a current limit circle equation; a calculation formula is:

[00020]$\begin{array}{cc}\{\begin{array}{c}\begin{array}{c}\frac{\left(\rho -1\right)L_{d}A-\sqrt{{\left(\rho -1\right)}^2{L}_d^2{A}^2+4\left(\rho -1\right){\omega }_{\mathrm{Vs}}{L}_{q}C}}{2{\omega }_{\mathrm{Vs}}{L}_q}-\\ \frac{C}{\sqrt{U_{\max }^2-{\left({\omega }_{\mathrm{Vs}}{L}_d{I}_d^{*}+{\lambda }_{\mathrm{PM}}{\omega }_{\mathrm{Vs}}+L_{q}B\right)}^2}}=0\end{array}\\ I_q^{*}=\frac{C}{\left(\rho -1\right)\sqrt{U_{\max }^2-{\left({\omega }_{\mathrm{Vs}}{L}_d{I}_d^{*}+{\lambda }_{\mathrm{PM}}{\omega }_{\mathrm{Vs}}+L_{q}B\right)}^2}}\\ I_d^{*2}+I_q^{*2}=I_{\max }^2\end{array}.& \left(12\right)\end{array}$

[0075] In the above process, a transient current change value needs to be calculated while considering transient current changes, and a calculation method is as follows:

[0076] For the general flux-weakening control stage, while not considering transient current changes, a voltage limit elliptic equation and a current limit circle equation may be combined to obtain d- and q-axis current instruction values as follows:

[00021]$\begin{array}{cc}\{\begin{array}{c}I\text{?}=\frac{L\text{?}\lambda \text{?}-L\text{?}\sqrt{\lambda \text{?}+\left(L\text{?}-L\text{?}\right)\left(I\text{?}-\frac{U\text{?}}{\omega \text{?}L\text{?}}\right)}}{L\text{?}-L\text{?}}\\ I\text{?}=\sqrt{I\text{?}-I\text{?}}\end{array}.& \left(13\right)\end{array}$$\text{?}\text{indicates text missing or illegible when filed}$

[0077] Differences between I.sub.d1 and I.sub.q1 and d- and q-axis current sampling values I.sub.dr, I.sub.qr are respectively calculated, and a PID regulator may be used to calculate values of A and B in the general flux-weakening control stage, where a calculation formula is:

[00022]$\begin{array}{cc}\{\begin{array}{c}A=\frac{I\text{?}-I\text{?}}{\Delta t}\\ B=\frac{I\text{?}-I\text{?}}{\Delta t}\end{array}.& \left(14\right)\end{array}$$\text{?}\text{indicates text missing or illegible when filed}$

[0078] For the MTPV control stage, while not considering transient current changes, a voltage limit elliptic equation and an electromagnetic torque equation may be combined to obtain d- and q-axis current instruction values as follows:

[00023]$\begin{array}{cc}\{\begin{array}{c}{I}_{d2}=-\frac{{\lambda }_{\mathrm{PM}}}{L_d}+E\\ I_{q2}=\frac{\sqrt{{\left(U_{\max }/{\omega }_r\right)}^2-{\left(L_{d}E\right)}^2}}{L_q}\\ E=\frac{{\mathrm{\rho \lambda }}_{\mathrm{PM}}-\sqrt{{\left({\mathrm{\rho \lambda }}_{\mathrm{PM}}\right)}^2+8{\left(\rho -1\right)}^2{\left(U_{\max }/{\omega }_r\right)}^2}}{4\left(\rho -1\right)L_d}\end{array}& \left(15\right)\end{array}$

[0079] where E is a variable.

[0080] Differences between I.sub.d2 and I.sub.q2 and d- and q-axis current sampling values I.sub.dr, I.sub.qr are respectively calculated, and the PID regulator may be used to calculate values of A and B in the MTPV control stage, where a calculation formula is:

[00024]$\begin{array}{cc}\{\begin{array}{c}A=\frac{I_{d2}-I_{\mathrm{dr}}}{\Delta t}\\ B=\frac{I_{q2}-I_{\mathrm{qr}}}{\Delta t}\end{array}.& \left(16\right)\end{array}$

[0081] Step (9): the voltage decoupling control module receives the d- and q-axis current instruction values I*.sub.d, I*.sub.q sent from the transient current planning module, and calculates d- and q-axis voltage instructions U*.sub.d, U*.sub.q.

[0082] Step (10): a coordinate transform module converts the d- and q-axis voltage instructions U*.sub.d, U*.sub.q into U.sub.a and U.sub.b, and a SVPWM module outputs a six-pulse IGBT control signal, meanwhile, an angular velocity calculation module and a position detection module detect a rotor position and an electrical angular velocity sampling value in real time for use in the calculation of the above steps to complete motor control.

[0083] As shown in FIG. 3, the current trajectory used in the current ultra-high-speed permanent magnet synchronous motor is obtained from steady-state voltage and current models, and the trajectory is OA.fwdarw.AB.sub.1.fwdarw.B.sub.1C.sub.1, where the section OA is a MTPA (maximum torque per ampere) control stage, the section AB.sub.1 is a general flux-weakening control stage, and the section B.sub.1C.sub.1 is a MTPV (maximum torque per volt) control stage. Since the derivation of the trajectory does not consider the influence of transient current, higher torque output capability cannot be achieved. After the influence of transient current is considered, a voltage limit ellipse will move to the upper right (the moved voltage limit ellipse is denoted by dashed lines). At this time, the section AB.sub.1 turns into shorter AB.sub.2, and the section B.sub.1C.sub.1 will also move to the upper right to become B.sub.2C.sub.2. At this time, the torque of the section B.sub.2C.sub.2 will be larger than that of the section B.sub.1C.sub.1, thereby achieving a larger torque output range in the MTPV control stage.

[0084] The described embodiment is a preferred embodiment of the present invention, but the present invention is not limited to the aforementioned embodiment. Any obvious improvements, substitutions or modifications that can be made by those skilled in the art without departing from the essential content of the present invention shall fall within the protection scope of the present invention.