Memory motor winding multiplexing control method and system for flux linkage observation

Abstract

A memory motor winding multiplexing control method and system for flux linkage observation. The method comprises the following steps: I: when the magnetization state of a memory motor needs to be adjusted, selecting a flux regulation current reference value according to a rotation speed of the motor; II: by means of current feedback control, driving a direct-current flux regulation winding to generate a flux regulation current so as to adjust the magnetization state of a permanent magnet; III: when the memory motor is operating normally, collecting an induction voltage of the flux regulation winding and extracting an induced electromotive force of the flux regulation winding; and IV: using the induced electromotive force of the flux regulation winding to calculate the flux linkage of the permanent magnet for vector control of the motor.

Claims

1. A memory motor winding multiplexing control method for flux linkage observation, comprising the following steps: step 1: selecting a flux regulation current reference value i*.sub.f in a flux regulation current look-up table according to a rotation speed ω.sub.m of the motor when the magnetization state of the permanent magnet of a memory motor needs to be adjusted; step 2: driving a direct-current flux regulation winding to generate a flux regulation current by means of current chopping control according to the flux regulation current reference value i*.sub.f, which is obtained in the step 1, and the flux regulation current actual value i.sub.f, thereby adjusting the magnetization state of the permanent magnet of the memory motor; step 3: acquiring an induced voltage u.sub.f of the direct-current flux regulation winding when the memory motor operates normally, and extracting an induced electromotive force e.sub.f of the flux regulation winding according to the induced voltage u.sub.f of the direct-current flux regulation winding; step 4: calculating the flux linkage ψ.sub.pm, of the permanent magnet according to the induced electromotive force e.sub.f of the flux regulation winding obtained in the step 3, and performing vector control on the memory motor according to the flux linkage ψ.sub.pm of the permanent magnet; wherein the flux regulation current look-up table in the step 1 is acquired with the following method: S1.1 selecting k magnetization states ψ.sub.MS1, ψ.sub.MS2, . . . , ψ.sub.MSk and corresponding rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk to form a discrete correspondence relationship according to the mechanical features of the memory motor in different magnetization states of the permanent magnet; S1.2 measuring the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk corresponding to the k magnetization states described in the step S1.1 by means of offline experiments; S1.3 storing the discrete correspondence relationship between the rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk described in the step S1.1 and the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk described in the step S1.2 into the flux regulation current look-up table.

2. The control method according to claim 1, wherein the current chopping control in the step 2 is a control method for generating a switching signal by performing hysteresis comparison between the flux regulation current actual value i.sub.f and the selected flux regulation current reference value i*.sub.f.

3. The control method according to claim 1, wherein the induced electromotive force e.sub.f of the flux regulation winding is extracted in the step 3 with following method specifically: S3.1 obtaining observed d-axis current î.sub.d with a formula ${\hat{i}}_d=\frac{2}{3}\int \frac{u_f-{\hat{e}}_f}{M_{\mathrm{sf}}}\mathrm{dt}$ in the current cycle, wherein M.sub.sf is the mutual inductance of the direct-current flux regulation winding to the stator, and ê.sub.f is the observed induced electromotive force of the direct-current flux regulation winding, which is obtained from a delayed feedback of the output from a Proportional Integral (PI) regulator in the previous cycle; S3.2 comparing the observed d-axis current î.sub.d with the actual d-axis current i.sub.d to obtain an error, inputting the error to the PI regulator to obtain an output from the PI regulator, which is the observed induced electromotive force ē.sub.f the direct-current flux regulation winding in the current cycle; S3.3 differentiating the observed induced electromotive force ê.sub.f of the direct-current flux regulation winding obtained in the step S3.2, and taking the obtained differential value as a feedback for participating in the calculation in the next cycle.

4. The control method according to claim 1, wherein the flux linkage ψ.sub.pm of the permanent magnet is calculated in the step 4 with the following method specifically: S4.1 inputting the induced electromotive force e.sub.f of the flux regulation winding into a single-phase PLL, and separating a q-axis component e.sub.f_q of the induced electromotive force of the flux regulation winding, so as to obtain a d-axis component e.sub.f_d of the induced electromotive force of the flux regulation winding; S4.2 calculating the flux linkage ψ.sub.f of the flux regulation winding with a formula ψ.sub.f=K.sub.eω.sub.ee.sub.f_d, wherein K.sub.e and ω.sub.e are electromotive force coefficient and electric angular speed respectively, and the electromotive force coefficient K.sub.e is obtained through offline experiments; S4.3 subtracting the flux linkage ψ.sub.d of the d-axis stator from the flux linkage ψ.sub.f of the flux regulation winding to obtain the flux linkage ψ.sub.pmn of the permanent magnet.

5. A memory motor winding multiplexing control system for flux linkage observation, comprising: a flux regulation current reference value selection circuit configured to select a flux regulation current reference value i*.sub.f in the flux regulation current look-up table according to the rotation speed ω.sub.m of the motor when the magnetization state of the permanent magnet of a memory motor needs to be adjusted; a current chopping control circuit configured to drive a direct-current flux regulation winding by means of current chopping control to generate flux regulation current according to the flux regulation current reference value i*.sub.f outputted from the flux regulation current reference value selection circuit and the flux regulation current actual value i.sub.f, thereby adjusting the magnetization state of the permanent magnet of the memory motor; an induced electromotive force extraction circuit configured to acquire an induced voltage u.sub.f of the direct-current flux regulation winding and extract the induced electromotive force e.sub.f of the flux regulation winding according to the induced voltage u.sub.f when the memory motor operates normally; a permanent magnet flux linkage calculation circuit configured to calculate the flux linkage ψ.sub.pm, of the permanent magnet according to the induced electromotive force e.sub.f of the flux regulation winding outputted from the induced electromotive force extraction circuit, so as to perform vector control on the memory motor according to the flux linkage ψ.sub.pm of the permanent magnet; wherein the flux regulation current look-up table is acquired with the following method: S1.1 selecting k magnetization states ψ.sub.MS1, ψ.sub.MS2, . . . , ψ.sub.MSk and corresponding rotation speed values ω.sub.m1, ω.sub.m1, . . . , ω.sub.mk to form a discrete correspondence relationship according to the mechanical features of the memory motor in different magnetization states of the permanent magnet; S1.2 measuring the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk corresponding to the k magnetization states described in the step S1.1 by means of offline experiments; S1.3 storing the discrete correspondence relationship between the rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk described in the step S1.1 and the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk described in the step S1.2 into the flux regulation current look-up table.

6. The control system according to claim 5, wherein the current chopping control is specifically a control method for generating a switching signal by performing hysteresis comparison between the flux regulation current actual value i.sub.f and the selected flux regulation current reference value i*.sub.f.

7. The control system according to claim 5, wherein the induced electromotive force extraction circuit specifically comprises: an observed d-axis current calculation unit configured to implement a formula ${\hat{i}}_d=\frac{2}{3}\int \frac{u_f-{\hat{e}}_f}{M_{\mathrm{sf}}}\mathrm{dt}$ to calculate the observed d-axis current î.sub.d, wherein M.sub.sf is the mutual inductance of the direct-current flux regulation winding to the stator, and ê.sub.f is the observed induced electromotive force of the direct-current flux regulation winding, which is obtained through a feedback from a time delay unit; a comparator configured to compare the observed d-axis current î.sub.d with the actual d-axis current i.sub.d to obtain an error and then input the error to a PI regulator; a PI regulator configured to perform proportional and integral control to output the observed induced electromotive force ê.sub.f of the direct-current flux regulation winding in the current cycle according to the output from the comparator, wherein the output from the PI regulator is the actual induced electromotive force e.sub.f of the direct-current flux regulation winding when the observed d-axis current î.sub.d is equal to the actual d-axis current i.sub.d; a time delay unit configured to delay the output from the PI regulator and feed the output back to the observed d-axis current calculation unit for participating in the calculation in the next cycle.

8. The control system according to claim 5, wherein the permanent magnet flux linkage calculation circuit specifically comprises: a single-phase PLL configured to separate a q-axis component e.sub.f_q of the induced electromotive force of the flux regulation winding from the induced electromotive force e.sub.f of the flux regulation winding, so as to obtain a d-axis component e.sub.f_d of the induced electromotive force of the flux regulation winding; a direct-current flux regulation winding flux linkage calculation unit configured to implement a formula ψ.sub.f=K.sub.eω.sub.ee.sub.f_d to obtain the flux linkage ψ.sub.f of the direct-current flux regulation winding, wherein K.sub.e and ω.sub.e are electromotive force coefficient and electric angular speed respectively, and the electromotive force coefficient K.sub.e is obtained through offline experiments; an adder configured to subtract the flux linkage ψ.sub.d of the d-axis stator from the flux linkage ψ.sub.f of the direct-current flux regulation winding to obtain the flux linkage ψ.sub.pm of the permanent magnet.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the control system in an embodiment of the present invention.

(2) FIG. 2 is a schematic diagram of the induced electromotive force extraction step in FIG. 1.

(3) FIG. 3 is a schematic diagram of the permanent magnet flux linkage calculation step in FIG. 1.

(4) FIG. 4 is a schematic diagram of the feed-forward decoupling regulation step in FIG. 1.

DESCRIPTION OF THE EMBODIMENTS

(5) In an embodiment of the present invention, the present invention provides a memory motor winding multiplexing control method for flux linkage observation, in which the controlled object is a direct-current flux regulation memory motor, the control process is shown in FIG. 1, and an armature winding and a direct-current flux regulation winding are components installed in the motor; a three-phase inverter is driven in a vector control mode with a space vector PWM (SVPWM) technique, a PI regulator is employed for the outer speed loop, a feed-forward decoupling regulator is employed for the inner current loop, and feed-forward decoupling is realized by utilizing the flux linkage ψ.sub.pm of the permanent magnet obtained through flux linkage observation; the flux regulation power converter employs an H-bridge direct-current power converter structure, and is driven by means of current chopping control in the flux regulation period to generate flux regulation current in the direct-current flux regulation winding, and thereby adjusting the magnetization state of the permanent magnet. The flux regulation power converter is cut off and a voltage sensor is utilized to acquire the voltage of the flux regulation winding to observe the flux linkage of the permanent magnet and thereby realize multiplexing control of the direct-current flux regulation winding during normal operation. Specifically, the method comprises the following steps:

(6) step 1: selecting a flux regulation current reference value i*.sub.f in a flux regulation current look-up table according to a rotation speed ω.sub.m of the motor when the magnetization state of the permanent magnet of a memory motor needs to be adjusted;

(7) Wherein, the flux regulation current look-up table is acquired with the following method:

(8) S1.1 selecting k magnetization states ψ.sub.MS1, ψ.sub.MS2, . . . , ψ.sub.MSk and corresponding rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk to form a discrete correspondence relationship according to the mechanical features of the memory motor in different magnetization states of the permanent magnet;

(9) S1.2 measuring the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk corresponding to the k magnetization states described in the step S1.1 by means of offline experiments;

(10) S1.3 storing the discrete correspondence relationship between the rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk described in the step S1.1 and the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk described in the step S1.2 into the flux regulation current look-up table.

(11) step 2: driving a direct-current flux regulation winding to generate a flux regulation current by means of current chopping control according to the flux regulation current reference value i*.sub.f and the flux regulation current actual value i.sub.f obtained in the step 1, thereby adjusting the magnetization state of the permanent magnet of the memory motor; the current chopping control is specifically a control method for generating a switching signal by performing hysteresis comparison between the flux regulation current actual value i.sub.f and the selected flux regulation current reference value i*.sub.f.

(12) step 3: acquiring an induced voltage u.sub.f of the direct-current flux regulation winding when the memory motor operates normally, and extracting an induced electromotive force e.sub.f of the flux regulation winding according to the induced voltage u.sub.f of the direct-current flux regulation winding;

(13) The voltage equation of the flux regulation winding is analyzed as follows:

(14) $\begin{array}{cc}{u}_f=i_f{R}_f+L_f\frac{{\mathrm{di}}_f}{\mathrm{dt}}+\frac{3}{2}{M}_{\mathrm{sf}}\frac{{\mathrm{di}}_d}{\mathrm{dt}}+e_f& \left(1\right)\end{array}$

(15) wherein, u.sub.f, i.sub.f, i.sub.d and e.sub.f are the induced voltage of the flux regulation winding, the current in the flux regulation winding, the d-axis current, and the induced electromotive force of the flux regulation winding respectively, and R.sub.f, L.sub.f and M.sub.sf are the resistance of the flux regulation winding, the self-inductance of the flux regulation winding, and the mutual inductance of the flux regulation winding to the stator respectively;

(16) in the flux linkage observer, the current i.sub.f in the flux regulation winding is 0; thus, the first two terms at the right side of the equation are omitted, and the formula (1) may be rewritten to:

(17) $\begin{array}{cc}{u}_f=\frac{3}{2}{M}_{\mathrm{sf}}\frac{{\mathrm{di}}_d}{\mathrm{dt}}+e_f& \left(2\right)\\ {\hat{i}}_d=\frac{2}{3}\int \frac{u_f-{\hat{e}}_f}{M_{\mathrm{sf}}}\mathrm{dt}& \left(3\right)\end{array}$

(18) Therefore, as shown in FIG. 2, the specific step of extracting the induced electromotive force e.sub.f of the flux regulation winding comprises:

(19) S3.1 obtaining observed d-axis current î.sub.d with a formula

(20) ${\hat{i}}_d=\frac{2}{3}\int \frac{u_f-{\hat{e}}_f}{M_{\mathrm{sf}}}\mathrm{dt}$
in the current cycle, wherein M.sub.sf is the mutual inductance of the direct-current flux regulation winding to the stator, and ê.sub.f is the observed induced electromotive force of the direct-current flux regulation winding, which is obtained from a delayed feedback of the output from a PI regulator in the previous cycle;

(21) S3.2 comparing the observed d-axis current î.sub.d with the actual d-axis current i.sub.d to obtain an error, inputting the error to the PI regulator to obtain an output from the PI regulator, which is the observed induced electromotive force ê.sub.f of the direct-current flux regulation winding in the current cycle;

(22) S3.3 differentiating the observed induced electromotive force ê.sub.f of the direct-current flux regulation winding obtained in the step S3.2, and taking the obtained differential value as a feedback for participating in the calculation in the next cycle;

(23) step 4: calculating the flux linkage ψ.sub.pm of the permanent magnet according to the induced electromotive force e.sub.f of the flux regulation winding obtained in the step 3, and performing vector control on the memory motor according to the flux linkage ψ.sub.pm of the permanent magnet.

(24) The induced electromotive force e.sub.f of the flux regulation winding consists of a permanent magnet flux linkage induced component, a d-axis flux linkage inducted component, and a q-axis flux linkage inducted component, and may be expressed as:

(25) $\begin{array}{cc}\begin{array}{c}{e}_f=e_{f\_d}+e_{f\_q}\\ =\left(E_{f\mathrm{\_\psi }d}+E_{f\_\mathrm{pm}}\right)\cos {\omega }_{e}t+E_{f\mathrm{\_\psi }q}\sin {\omega }_{e}t\end{array}& \left(4\right)\end{array}$

(26) wherein, e.sub.f_d and e.sub.f_q are the d-axis component and q-axis component of the induced electromotive force of the flux regulation winding, E.sub.f_ψd, E.sub.f_pm and E.sub.f_ψq are the amplitudes of the electromotive force components induced by the d-axis flux linkage, permanent magnet flux linkage, and q-axis flux linkage in the flux regulation winding, wherein the amplitude E.sub.f_pm of the electromotive force component induced by the permanent magnet flux linkage in the flux regulation winding includes the flux linkage ψ.sub.pm of the permanent magnet to be solved, and the relationship may be expressed as follows:

(27) $\begin{array}{cc}\begin{array}{c}{E}_{f\_d}=E_{f\mathrm{\_\psi }d}+E_{f\_\mathrm{pm}}\\ ={\omega }_e{K}_e\left({\psi }_{\mathrm{pm}}+i_d{L}_d\right)\end{array}& \left(5\right)\end{array}$

(28) wherein, E.sub.f_d is the amplitude of the d-axis component of the induced electromotive force of the flux regulation winding, and the flux linkage ψ.sub.pm of the permanent magnet may be calculated according to the formulae (4) and (5) through the following steps, as shown in FIG. 3:

(29) S4.1 inputting the induced electromotive force e.sub.f of the flux regulation winding into a single-phase PLL, and separating a q-axis component e.sub.f_q of the induced electromotive force of the flux regulation winding, so as to obtain a d-axis component e.sub.f_d of the induced electromotive force of the flux regulation winding;

(30) S4.2 calculating the flux linkage ψ.sub.f of the flux regulation winding with a formula ψ.sub.f=K.sub.eω.sub.ee.sub.f_d, wherein K.sub.e and ω.sub.e are electromotive force coefficient and electric angular speed respectively, and the electromotive force coefficient K.sub.e is obtained through offline experiments;

(31) S4.3 subtracting the flux linkage ψ.sub.d of the d-axis stator from the flux linkage ψ.sub.f of the flux regulation winding to obtain the flux linkage ψ.sub.pm of the permanent magnet.

(32) The process of vector control on the memory motor according to the flux linkage ψ.sub.pm of the permanent magnet is shown in FIGS. 1 and 4, wherein a PI regulator is employed for the outer speed loop, a feed-forward decoupling regulator is employed for the inner current loop, and feed-forward decoupling is realized by utilizing the flux linkage ψ.sub.pm of the permanent magnet obtained through flux linkage observation. The voltage equation in the dq coordinate system is as follows:

(33) $\begin{array}{cc}{u}_d=R_s{i}_d+L_d\frac{{\mathrm{di}}_d}{\mathrm{dt}}-{\omega }_e\left({\psi }_{\mathrm{pm}}+i_d{L}_d\right)u_q=R_s{i}_q+L_q\frac{{\mathrm{di}}_q}{\mathrm{dt}}+{\omega }_e{i}_q{L}_q& \left(6\right)\end{array}$

(34) wherein, R.sub.s, L.sub.d and L.sub.q are the resistance of the stator, d-axis self-inductance, and q-axis self-inductance respectively, and u.sub.d, u.sub.q, i.sub.d, i.sub.q, ψ.sub.e and ψ.sub.pm are the d-axis voltage, q-axis voltage, d-axis current, q-axis current, electric angular speed, and flux linkage of the permanent magnet respectively; to realize decoupling control on the d-axis current and q-axis current, the respective current should be set to be i*.sub.d and i*.sub.q and voltage decoupling should be carried out to obtain control variables u*d and u*.sub.q in voltage form, then the formula (6) may be rewritten to:
u.sub.d*=u.sub.d_ref−ω.sub.e(ψ.sub.pm+i.sub.d*L.sub.d)
u.sub.q*=u.sub.q_ref+ω.sub.ei.sub.q*L.sub.q  (7)

(35) wherein, u*.sub.d and u*.sub.q are set values of d-axis voltage and q-axis voltage respectively, u.sub.d_ref and u.sub.q_ref are the outputs of the PI regulators in the d-axis current loop and q-axis current loop respectively, i*.sub.d and i*.sub.q are set values of d-axis current and q-axis current, then the feed-forward decoupling regulator in the current loop may be established according to the formula (7), specifically with the following method: the errors between the set values i*.sub.d and i*.sub.q of d-axis current and q-axis current and the actual feedback values of d-axis current and q-axis current are inputted to two PI regulators respectively, to obtain the outputs u.sub.d_ref and u.sub.q_ref of the PI regulators in d-axis current loop and q-axis current loop; with the flux linkage ψ.sub.pm of the permanent magnet and the electric angular speed ω.sub.e, the set values u*.sub.d and u*.sub.q of d-axis voltage and q-axis voltage are calculated according to the formula (7), and thereby feed-forward decoupling control is realized.

(36) In an embodiment of the present invention, the present invention further provides a memory motor winding multiplexing control system for flux linkage observation, corresponding to the method described above. The system comprises:

(37) a flux regulation current reference value selection module configured to select a flux regulation current reference value i*.sub.f in the flux regulation current look-up table according to the rotation speed ω.sub.m of the motor when the magnetization state of the permanent magnet of a memory motor needs to be adjusted;

(38) a current chopping control module configured to drive a direct-current flux regulation winding by means of current chopping control to generate flux regulation current according to the flux regulation current reference value i*.sub.f outputted from the flux regulation current reference value selection module and the flux regulation current actual value i.sub.f; thereby adjusting the magnetization state of the permanent magnet of the memory motor; the current chopping control is specifically a control method for generating a switching signal by performing hysteresis comparison between the flux regulation current actual value i.sub.f and the selected flux regulation current reference value i*.sub.f.

(39) an induced electromotive force extraction module configured to acquire an induced voltage u.sub.f of the direct-current flux regulation winding and extract the induced electromotive force e.sub.f of the flux regulation winding according to the induced voltage u.sub.f when the memory motor operates normally;

(40) a permanent magnet flux linkage calculation module configured to calculate the flux linkage ψ.sub.pm of the permanent magnet according to the induced electromotive force e.sub.f of the flux regulation winding outputted from the induced electromotive force extraction module, so as to perform vector control on the memory motor according to the flux linkage ψ.sub.pm of the permanent magnet.

(41) Wherein, the flux regulation current look-up table is acquired with the following method:

(42) S1.1 selecting k magnetization states ψ.sub.MS1, ψ.sub.MS2, . . . , ψ.sub.MSk and corresponding rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk to form a discrete correspondence relationship according to the mechanical features of the memory motor in different magnetization states of the permanent magnet;

(43) S1.2 measuring the flux regulation current values i.sub.f1, i.sub.f2, . . . , i.sub.fk corresponding to the k magnetization states described in the step S1.1 by means of offline experiments;

(44) S1.3 storing the discrete correspondence relationship between the rotation speed values ω.sub.m1, ω.sub.m2, . . . , ω.sub.mk described in the step S1.1 and the flux regulation current values i.sub.f1, i.sub.f2, i.sub.fk described in the step S1.2 into the flux regulation current look-up table.

(45) Wherein, the induced electromotive force extraction module specifically comprises:

(46) an observed d-axis current calculation unit configured to implement a formula

(47) ${\hat{i}}_d=\frac{2}{3}\int \frac{u_f-{\hat{e}}_f}{M_{\mathrm{sf}}}\mathrm{dt}$
to calculate the observed d-axis current î.sub.d, wherein M.sub.sf is the mutual inductance of the direct-current flux regulation winding to the stator, and ê.sub.f is the observed induced electromotive force of the direct-current flux regulation winding, which is obtained through a feedback from a time delay unit;

(48) a comparator configured to compare the observed d-axis current î.sub.d with the actual d-axis current i.sub.d to obtain an error and then input the error to a PI regulator;

(49) a PI regulator configured to perform proportional and integral control to output the observed induced electromotive force ê.sub.f of the direct-current flux regulation winding in the current cycle according to the output from the comparator, wherein the output from the PI regulator is the actual induced electromotive force e.sub.f of the direct-current flux regulation winding when the observed d-axis current î.sub.d is equal to the actual d-axis current i.sub.d;

(50) a time delay unit configured to delay the output from the PI regulator and feed the output back to the observed d-axis current calculation unit for participating in the calculation in the next cycle.

(51) Wherein, the permanent magnet flux linkage calculation module specifically comprises:

(52) a single-phase PLL configured to separate a q-axis component e.sub.f_q of the induced electromotive force of the flux regulation winding from the induced electromotive force e.sub.f of the flux regulation winding, so as to obtain a d-axis component e.sub.f_d of the induced electromotive force of the flux regulation winding;

(53) a direct-current flux regulation winding flux linkage calculation unit configured to implement a formula ψ.sub.f=K.sub.eω.sub.ee.sub.f_d to obtain the flux linkage ψ.sub.f of the direct-current flux regulation winding, wherein K.sub.e and ω.sub.e are electromotive force coefficient and electric angular speed respectively, and the electromotive force coefficient K.sub.e is obtained through offline experiments;

(54) an adder configured to subtract the flux linkage ψ.sub.d of the d-axis stator from the flux linkage ψ.sub.f of the direct-current flux regulation winding to obtain the flux linkage ψ.sub.pm of the permanent magnet.

(55) It should be understood that the system and method disclosed in the embodiments of the present application may be implemented in other ways. The embodiment of the system described above is only exemplary. For example, the division of the modules and units is only a division in term of logic function, and may be implemented in other ways in the actual implementation. For example, a plurality of units or components may be combined or integrated into another system, or some features may be omitted or not implemented. Besides, the illustrated or discussed coupling or direct coupling or communication connection between the devices or units may be implemented via some interfaces, and the indirect coupling or communication connection between the devices or units may be electrical, mechanical, or in other forms.

(56) Those skilled in the art can further aware that the exemplary units and algorithm steps described in the embodiments disclosed herein may be implemented by electronic hardware, computer software or a combination thereof, and software modules may reside in random access memory (RAM), memory, read only memory (ROM), electrically programmable ROM, electrically erasable and programmable ROM, registers, hard disk, removable disk, CD-ROM, or any other form of storage media well-known in the art.

(57) The embodiments are disclosed and described above for the purpose of enabling those skilled in the art to implement or use the present invention. It is obvious to those skilled in the art that various modifications can be made to those embodiments. The general principle defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the scope of the present invention should not be limited to those embodiments illustrated herein, but should be comprehended as the broadest scope consistent with the principle and novel features disclosed herein.