Sensorless control method and apparatus for a three-phase switched reluctance motor

Abstract

A sensorless control method and an apparatus for a three-phase switched reluctance motor. The sensorless control method obtains line inductances of three phases according to real-time phase inductances of the three-phase switched reluctance motor and then determines feature points of the line inductances of the three phases. A position angle of the rotor at any time in the next corresponding region is calculated according to an average rotation speed of the rotor in the region corresponding to two adjacent feature points. A control signal is output to realize a precise sensorless control for the three-phase switched reluctance motor. The control apparatus includes a microcontroller, a power conversion circuit, a drive module for the power conversion circuit, a current detection module, a voltage detection module, an input and output module and a direct current regulated power supply.

Claims

1. A sensorless control method for a three-phase switched reluctance motor, comprising: S1) obtaining phase inductances according to real-time phase inductances of three-phase windings of the three-phase switched reluctance motor; S2) dividing an electrical cycle of the three-phase switched reluctance motor into three conduction regions with a same electrical angle, and obtaining line inductances in a corresponding conduction region according to the phase inductances obtained in step S1 of the three-phase windings; S3) determining feature points of line inductances of three phases according to the line inductances obtained in step S2; calculating a position angle and a time interval of a region corresponding to the feature points of two adjacent line inductances; and calculating an average rotation speed ω.sub.n of a rotor in the region corresponding to the feature points of the two adjacent line inductances according to the position angle and the time interval of the region; S4) calculating a position angle θ.sub.n+1(t) of the rotor at any time t in a next corresponding region according to the average rotation speed ω.sub.n of the rotor obtained in step S3 in the corresponding region; and S5) outputting a control signal to the three-phase switched reluctance motor according to the position angle of the rotor obtained in step S4, so as to realize a precise sensorless control for the three-phase switched reluctance motor.

2. The sensorless control method of claim 1, wherein the real-time phase inductance in step S1 is calculated as follows: operating the three-phase switched reluctance motor in a single-phase sequential cyclic conduction mode; controlling a power conversion circuit to inject a pulse voltage with a certain frequency into each phase winding; and detecting a difference of a slope of a phase current and a direct-current bus voltage of each phase winding in real time; and calculating the inductance of each phase winding according to formula (1): $\begin{array}{cc}L=\frac{2u_{\mathrm{dc}}}{\Delta i}& \left(1\right)\end{array}$ wherein the u.sub.dc is the direct-current bus voltage; and the Δi is the difference of the slope of the phase current between a turn-on and a turn-off of a switch tube.

3. The sensorless control method of claim 2, wherein in step S4, according to the average rotation speed of the rotor ω.sub.n obtained in step S3 in a region n, the position angle θ.sub.n+1(t) of the rotor at any time t in the next corresponding region (n+1) is calculated by the following formula:
θ.sub.n+1(t)=θ.sub.n+1(t.sub.0)+ω.sub.n(t−t.sub.0)  (23) wherein θ.sub.n+1(t) represents the position angle of the rotor at any time t in the region (n+1), and θ.sub.n+1(t.sub.0) represents the position angle of the rotor at a starting time t.sub.0 of the region (n+1).

4. The sensorless control method of claim 1, wherein the step S1 comprises: in an electrical cycle of the rotor of the three-phase switched reluctance motor, detecting a corresponding direct-current bus voltage and a difference of a slope of a phase current at different rotor position angles θ.sub.k selected at a same time interval, respectively; calculating a corresponding inductance L.sub.k according to the formula (1) to obtain n groups of parameters (θ.sub.k, L.sub.k) (k=1, . . . n); and according to the n groups of parameters, obtaining the phase inductions of the three-phase windings:
L.sub.A(θ.sub.e)=B.sub.1(i)+B.sub.2(i)cos θ.sub.e+B.sub.3(i)cos 2θ.sub.e  (2)
L.sub.B(θ.sub.e)=B.sub.1(i)+B.sub.2(i)cos(θ.sub.e−2π/3)+B.sub.3(i)cos 2(θ.sub.e−2π/3)  (3)
L.sub.C(θ.sub.e)=B.sub.1(i)+B.sub.2(i)cos(θ.sub.e+2π/3)+B.sub.3(i)cos 2(θ.sub.e+2π/3)  (4) wherein L.sub.A(θ.sub.e), L.sub.B(θ.sub.e), L.sub.C(θ.sub.e) represent the phase inductances of A, B, and C phase windings of the three-phase switched reluctance motor, respectively; θ.sub.e represents an electrical angle of the rotor; and B.sub.1(i), B.sub.2(i) and B.sub.3(i) represent coefficients of the phase inductances.

5. The sensorless control method of claim 1, wherein the step S2 comprises: defining a difference between the inductances of two adjacent phase windings of the switched reluctance motor as a line inductance of the two adjacent phase windings; in an electrical cycle of the rotor of the three-phase switched reluctance motor, dividing the electrical cycle into a first conduction region, a second conduction region and a third conduction region with the same electrical angle; and the line inductances corresponding to the three-phase switched reluctance motor are represented as follows:
L.sub.AB(θ.sub.e)=L.sub.A(θ.sub.e)−L.sub.B(θ.sub.e)  (6)
L.sub.BC(θ.sub.e)=L.sub.B(θ.sub.e)−L.sub.C(θ.sub.e)  (7)
L.sub.CA(θ.sub.e)=L.sub.C(θ.sub.e)−L.sub.A(θ.sub.e)  (8) wherein L.sub.AB(θ.sub.e) represents the line inductance between the A and B phase windings of the switched reluctance motor; L.sub.BC(θ.sub.e) represents the line inductance between the B and C phase windings; and L.sub.CA(θ.sub.e) represents the line inductance between the C and A phase windings.

6. The sensorless control method of claim 5, wherein in step S2, the line inductances of the three-phase switched reluctance motor in the first conduction region of an electrical cycle are represented as follows: $\begin{array}{cc}{L}_{\mathrm{Ab}}\left({\theta }_e\right)=\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e\right)-B_2\left(i\right)\cos \left({\theta }_e-2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e\right)-B_3\mathrm{cos2}\left({\theta }_e-2\pi /3\right)\right]& \left(9\right)\\ L_{\mathrm{bc}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e-\pi /2\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e+\pi /2\right)& \left(10\right)\\ L_{\mathrm{cA}}\left({\theta }_e\right)=\left[B_1\left(i\right)-B_1\left(I\right)\right]+\left[B_2\left(i\right)\cos \left({\theta }_e+2\pi /3\right)-B_2\left(I\right)\cos \left({\theta }_e\right)\right]+\hspace{1em}\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e\right)\right]& \left(11\right)\end{array}$ wherein the A phase is a conducting phase, and the B and C phases are non-conducting phases.

7. The sensorless control method of claim 5, wherein in step S2, the line inductances of the three-phase switched reluctance motor in the second conduction region of an electrical cycle are represented as follows: $\begin{array}{cc}{L}_{\mathrm{aB}}\left({\theta }_e\right)=\left[B_1\left(i\right)-B_1\left(I\right)\right]+\left[B_2\left(i\right)\cos \left({\theta }_e\right)-B_2\left(I\right)\cos \left({\theta }_e-2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)\right]& \left(12\right)\\ L_{\mathrm{bC}}\left({\theta }_e\right)=\hspace{1em}\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e-2\pi /3\right)-B_2\left(i\right)\cos \left({\theta }_e+2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)-B_3\left(i\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)\right]& \left(13\right)\\ L_{\mathrm{ca}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e+5\pi /6\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e-5\pi /6\right)& \left(14\right)\end{array}$ wherein the B phase is a conducting phase, and the A and C phases are non-conducting phases.

8. The sensorless control method of claim 5, wherein in step S2, the line inductances of the three-phase switched reluctance motor in the third conduction region of an electrical cycle are represented as follows: $\begin{array}{cc}{L}_{\mathrm{ab}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e+\pi /6\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e-\pi /6\right)& \left(15\right)\\ L_{\mathrm{bC}}\left({\theta }_e\right)=\left[B_1\left(i\right)-B_1\left(I\right)\right]+\hspace{1em}\left[B_2\left(i\right)\cos \left({\theta }_e-2\pi /3\right)-B_2\left(I\right)\cos \left({\theta }_e+2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)\right]& \left(16\right)\\ L_{\mathrm{Ca}}\left({\theta }_e\right)=\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e+2\pi /3\right)-B_2\left(i\right){\mathrm{cos\theta }}_e\right]+\hspace{1em}\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)-B_3\left(i\right){\mathrm{cos2\theta }}_e\right]& \left(17\right)\end{array}$ wherein the C phase is a conducting phase, and the A and B phases are non-conducting phases.

9. The sensorless control method of claim 1, wherein in step S3, the position angle of the region corresponding to the feature points of two adjacent line inductances is: $\begin{array}{cc}{\mathrm{\Delta \theta }}_n=\frac{{\mathrm{\Delta \theta }}_e}{N_{r}}& \left(21\right)\end{array}$ wherein Δθ.sub.n represents the position angle of the region corresponding to the feature points of the two adjacent line inductances; Δθ.sub.e represents the electrical angle of a region n corresponding to the feature points of the two adjacent line inductances; N.sub.r represents a number of a rotor pole of the three-phase switched reluctance motor.

10. A control apparatus for the sensorless control method of claim 1, comprising: a microcontroller; a power conversion circuit; a drive module for the power conversion circuit; a current detection module; a voltage detection module; an input and output module; and a direct current regulated power supply; wherein the microcontroller is connected to the drive module, the current detection module, the voltage detection module and the input and output module, respectively; the power conversion circuit is connected to the three-phase switched reluctance motor, the drive module, the current detection module and the voltage detection module; the microcontroller is configured to send a control signal to the power conversion circuit through the drive module, and respectively output a chopping current and a high-frequency pulse to a conducting phase winding and a non-conducting phase winding of the three-phase switched reluctance motor through the power conversion circuit; the microcontroller is also configured to calculate the rotor position angle of the three-phase switched reluctance motor according to a feedback signal of voltage and current detected by the voltage detection module and the current detection module; the drive module is configured to receive the control signal of pulse width modulation (PWM) output by the microcontroller, and output a corresponding control signal to control a switching state of a corresponding power switch in the power conversion circuit; the current detection module is configured for real-time detection of a current of each phase of the three-phase switched reluctance motor in the power conversion circuit; the voltage detection module is configured for real-time detection of a voltage of each phase of the three-phase switched reluctance motor in the power conversion circuit; the power conversion circuit is configured to receive the control signal output by the power conversion circuit drive module, and output a chopping current to the conducting phase winding of the three-phase switched reluctance motor and a high frequency pulse to the non-conducting phase winding, respectively; the input and output module is configured to set control parameters of the three-phase switched reluctance motor and display state parameters such as speed and position angle of the rotor; and the direct current regulated power supply is configured to provide a voltage and a current to a system in normal operation.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a curve diagram of phase inductances and line inductances of a three-phase switched reluctance motor in accordance with the present disclosure;

(2) FIG. 2 is a schematic diagram of intersection points of line inductances of a three-phase switched reluctance motor in accordance with the present disclosure;

(3) FIG. 3 is a schematic diagram of an time interval of a region obtained from intersection points of two adjacent line inductances in accordance with the present disclosure; and

(4) FIG. 4 is a block diagram of a sensorless control apparatus for a three-phase switched reluctance motor in accordance with the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

(5) The embodiments of the present disclosure will be described with reference to the accompanying drawings. It should be noted that the embodiments provided herein are illustrative, and not intended to limit the scope of the present disclosure.

Embodiment 1

(6) FIG. 1 is a curve diagram of phase inductances and line inductances of a three-phase switched reluctance motor of the present disclosure. In FIG. 1, an upper part is a phase inductance curve, and a lower part is a line inductance curve. In the phase inductance curve, a first conduction phase of three-phase switched reluctance motor in a cycle of a rotor is phase A, and a subsequent conduction phase is phase B and a final conduction phase is phase C.

(7) According to a real-time detection of a difference of a slope of a phase current of each phase winding and a direct-current bus voltage, an inductance of each phase winding is calculated according to formula (1). Base on the inductance of each phase winding, a numerical fitting method is used to obtain phase inductances shown in formulas (2)-(4):

(8) $\begin{array}{cc}L=\frac{2u_{\mathrm{dc}}}{\Delta i}& \left(1\right)\\ L_A\left({\theta }_e\right)=B_1\left(i\right)+B_2\left(i\right){\mathrm{cos\theta }}_e+B_3\left(i\right){\mathrm{cos2\theta }}_e& \left(2\right)\\ L_B\left({\theta }_e\right)=B_1\left(i\right)+B_2\left(i\right)\cos \left({\theta }_e-2\pi /3\right)+B_3\left(i\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)& \left(3\right)\\ L_C\left({\theta }_e\right)=B_1\left(i\right)+B_2\left(i\right)\cos \left({\theta }_e+2\pi /3\right)+B_3\left(i\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)& \left(4\right)\end{array}$

(9) in the formulas, L.sub.A(θ.sub.e), L.sub.B(θ.sub.e), L.sub.C(θ.sub.e) represent the phase inductances of A, B, and C phase windings of the three-phase switched reluctance motor, respectively; θ.sub.e represents an electrical angle of the rotor; and B.sub.1(i), B.sub.2(i) and B.sub.3(i) represent coefficients of the phase inductances.

(10) The coefficients B.sub.1(i), B.sub.2(i) and B.sub.3(i) can be uniformly expressed as:
B.sub.j(i)=A.sub.j5i.sup.5+A.sub.j4i.sup.4+A.sub.j3i.sup.3+A.sub.j2i.sup.2+A.sub.j1i+A.sub.j0 (j=1,2,3)  (5)

(11) in the formula, Bj(i) represents the j-th coefficient of the phase inductance; i represents a current of the current phase winding; and A.sub.j0˜A.sub.j5 represent coefficients of the Bj(i).

(12) Then, the line inductances are calculated according to the phase inductances by the following formulas:
L.sub.AB(θ.sub.e)=L.sub.A(θ.sub.e)−L.sub.B(θ.sub.e)  (6)
L.sub.BC(θ.sub.e)=L.sub.B(θ.sub.e)−L.sub.C(θ.sub.e)  (7)
L.sub.CA(θ.sub.e)=L.sub.C(θ.sub.e)−L.sub.A(θ.sub.e)  (8)

(13) in the formulas, L.sub.AB(θ.sub.e) represents the line inductance between the A and B phase windings of the three-phase switched reluctance motor; L.sub.BC(θ.sub.e) represents the line inductance between the B and C phase windings; and L.sub.CA(θ.sub.e) represents the line inductance between the C and A phase windings.

(14) It should be noted that:

(15) the three-phase switched reluctance motor is operated in a single-phase sequential cyclic conduction mode, that is, each phase of the three-phase switched reluctance motor is conducted at a same electrical angle in turns, and thus one electrical cycle can be divided into three conduction regions with the same electrical angle, in which the A phase is a conducting phase, and the B and C phases are non-conducting phases; the B phase is a conducting phase, and the A and C phases are non-conducting phases; and the C phase is a conducting phase, and the A and B phases are non-conducting phases.

(16) Assuming that the three-phase switched reluctance motor runs under a certain load and stable speed, a current of the conducting phase current is I, and a current of the non-conducting phase is i, then the coefficients of the conducting phase inductances are B.sub.1(I), B.sub.2(I) and B.sub.3(I), and the coefficients the non-conducting phase inductances o are B.sub.1(i), B.sub.2(i) and B.sub.3(i). According to formulas (6)-(8), the line inductances shown in formulas (9)-(20) of the three-phase switched reluctance motor corresponding to the three regions in one electrical cycle are obtained. In order to distinguish the conducting phase from the non-conducting phase, the subscripts of the line inductances of the conducting phases are represented by capital letters whereas those of the non-conducting phases are represented by lowercase letters.

(17) (I) In the first conduction region, the A phase is a conducting phase, and the B and C phases are non-conducting phases. The line inductances of the three phases are represented as formulas (9)-(11):

(18) $\begin{array}{cc}{L}_{\mathrm{Ab}}\left({\theta }_e\right)=\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e\right)-B_2\left(i\right)\cos \left({\theta }_e-2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e\right)-B_3\mathrm{cos2}\left({\theta }_e-2\pi /3\right)\right]& \left(9\right)\\ L_{\mathrm{bc}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e-\pi /2\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e+\pi /2\right)& \left(10\right)\\ L_{\mathrm{cA}}\left({\theta }_e\right)=\left[B_1\left(i\right)-B_1\left(I\right)\right]+\left[B_2\left(i\right)\cos \left({\theta }_e+2\pi /3\right)-B_2\left(I\right)\cos \left({\theta }_e\right)\right]+\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e\right)\right].& \left(11\right)\end{array}$

(19) (II) In the second conduction region, the B phase is a conducting phase, and the A and C phases are non-conducting phases. The line inductances of the three phases are represented as formulas (12)-(14).

(20) $\begin{array}{cc}{L}_{\mathrm{aB}}\left({\theta }_e\right)=\left[B_1\left(i\right)-B_1\left(I\right)\right]+\left[B_2\left(i\right)\cos \left({\theta }_e\right)-B_2\left(I\right)\cos \left({\theta }_e-2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)\right]& \left(12\right)\\ L_{\mathrm{bC}}\left({\theta }_e\right)=\hspace{1em}\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e-2\pi /3\right)-B_2\left(i\right)\cos \left({\theta }_e+2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)-B_3\left(i\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)\right]& \left(13\right)\\ L_{\mathrm{ca}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e+5\pi /6\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e-5\pi /6\right)& \left(14\right)\end{array}$

(21) (III) In the third conduction region, the C phase is a conducting phase, and the A and B phases are non-conducting phases. The line inductances of the three phases are represented as formulas (15)-(17):

(22) 0$\begin{array}{cc}{L}_{\mathrm{ab}}\left({\theta }_e\right)=\sqrt{3}{B}_2\left(i\right)\cos \left({\theta }_e+\pi /6\right)+\sqrt{3}{B}_3\left(i\right)\cos \left(2{\theta }_e-\pi /6\right)& \left(15\right)\\ L_{\mathrm{bC}}\left({\theta }_e\right)=\hspace{1em}\left[B_1\left(i\right)-B_1\left(I\right)\right]+\left[B_2\left(i\right)\cos \left({\theta }_e-2\pi /3\right)-B_2\left(I\right)\cos \left({\theta }_e+2\pi /3\right)\right]+\hspace{1em}\left[B_3\left(i\right)\mathrm{cos2}\left({\theta }_e-2\pi /3\right)-B_3\left(I\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)\right]& \left(16\right)\\ L_{\mathrm{Ca}}\left({\theta }_e\right)=\left[B_1\left(I\right)-B_1\left(i\right)\right]+\left[B_2\left(I\right)\cos \left({\theta }_e+2\pi /3\right)-B_2\left(i\right){\mathrm{cos\theta }}_e\right]+\left[B_3\left(I\right)\mathrm{cos2}\left({\theta }_e+2\pi /3\right)-B_3\left(i\right){\mathrm{cos2\theta }}_e\right].& \left(17\right)\end{array}$

(23) According to formulas (2)-(4) and formulas (9)-(17), curves of the phase inductances L.sub.A(θ.sub.e), L.sub.B(θ.sub.e) and L.sub.C(θ.sub.e) and the line inductances L.sub.AB(θ.sub.e), L.sub.BC(θ.sub.e) and L.sub.CA(θ.sub.e) of the three phases are obtained, as shown in FIG. 1.

(24) It is shown that for each region, the corresponding curves of the phase inductance and line inductance are symmetrical. In addition, as shown in formulas (9)-(17), in one electrical cycle, the curve of the line inductance is composed of three segments. Taking L.sub.AB(θ.sub.e) for example, the curve of line inductances in one electrical cycle of L.sub.AB(θ.sub.e) is composed of three curves of the line inductances L.sub.Ab(θ.sub.e), L.sub.aB(θ.sub.e) and L.sub.ab(θ.sub.e) in above-mentioned three regions.

(25) According to the formulas (9)-(17) and FIG. 1, the phase angle difference between two adjacent line inductances is 2π/3, which is shown as follows:
L.sub.AB(θ.sub.e−2π/3)=L.sub.BC(θ.sub.e)  (18)
L.sub.BC(θ.sub.e−2π/3)=L.sub.CA(θ.sub.e)  (19)
L.sub.CA(θ.sub.e−2π/3)=L.sub.AB(θ.sub.e)  (20)

(26) that is, the phase angles that the line inductance L.sub.BC(θ.sub.e) lagged by L.sub.AB (θ.sub.e), L.sub.CA(θ.sub.e) lagged by L.sub.BC(θ.sub.e) and L.sub.AB(θ.sub.e) lagged by L.sub.CA(θ.sub.e) are 2π/3. Therefore, for any two adjacent line inductances, the electrical angle of the region corresponding to any two position points with the same inductance is 2π/3, and the electrical angle is irrelevant to the phase current and the coefficients B.sub.1(i), B.sub.2(i) and B.sub.3(i) of the phase inductances.

(27) Assuming that the main technical parameters of a three-phase 6/4 structure switched reluctance motor are shown in Table 1, n sets of position angle and corresponding inductance parameter (θ.sub.k, L.sub.k) are obtained according to the technical parameters shown in Table 1, and then the corresponding phase inductance and coefficient Bj(i) thereof are obtained by means of least square method (Table 2).

(28) TABLE-US-00001 TABLE 1 Parameters of the three-phase 6/4 structure switched reluctance motor Parameter Value Power rating/kW 4 Rated current/A 16 Rated torque/Nm 32 Resistance of phase winding/Ω 3

(29) TABLE-US-00002 TABLE 2 Coefficients of B.sub.j(i) of the three-phase 6/4 structure switched reluctance motor j A.sub.j5 A.sub.j4 A.sub.j3 A.sub.j2 A.sub.j1 A.sub.j0 1 6.35e−10 −1.23e−7 8.84e−6  −2.8e−4 2.8e−3 3.51e−2 2 6.69e−11  −1.3e−8 9.19e−7 −2.667e−5  1.415e−4   5.2e−3 3 1.24e−10 −3.48e−8 3.28e−6 −1.25e−4 1.2e−3 4.47e−2

(30) As shown in formulas (18)-(20), the phase difference between any two adjacent line inductances is 2π/3, that is, the difference of electrical angle Δθ.sub.e between feature points of any two adjacent line inductances is 2π/3. According to the conversion between the electrical angle and the position angle of the rotor:

(31) $\begin{array}{cc}{\mathrm{\Delta \theta }}_n=\frac{{\mathrm{\Delta \theta }}_e}{N_r}& \left(21\right)\end{array}$
the position angle of the region corresponding to the feature points of any two adjacent line inductances is:

(32) ${\mathrm{\Delta \theta }}_n=\frac{2\pi }{3N_r}.$

(33) According to formula (21), as for the three-phase 12/8 structure switched reluctance motor, N.sub.r=8. Therefore, the position angle of the region corresponding to the feature points of any two adjacent line inductances is Δθ.sub.n=π/12. As for the three-phase 6/4 structure switched reluctance motor, N.sub.r=4. Therefore, the position angle of the region corresponding to the feature points of any two adjacent line inductances is Δθ.sub.n=π/6.

(34) FIG. 2 is a schematic diagram of intersection points of line inductances of a three-phase switched reluctance motor in accordance with the present disclosure. When L.sub.AB(θ)=L.sub.BC(θ)=L.sub.CA(θ), all the position points (θ.sub.k, L(θ.sub.k)) include the position angle θ.sub.k of the rotor and the line inductance L are the feature points of line inductance. For the sake of convenience, the intersection points of line inductances are preferably selected as the feature points. The intersection points of line inductances included positive intersection points and negative intersection points. In the FIG. 2, the intersection points marked X1-2, X1-4, and X1-6 of line inductances are the positive intersection points, the intersection points marked X1-1, X1-3, and X1-5 of line inductances are the negative points. The method for judging the positive intersection points and the negative intersection points is: according to the line inductances obtained in step S2, it is judged whether any two line inductances at the same position angle are equal; if they are equal, then it is judged whether the line inductances are greater than 0; if they are greater than 0, the intersection points of the line inductances are the positive intersection points; otherwise, the intersection points of the line inductances are the intersection points.

(35) FIG. 3 is a schematic diagram of a time interval of a region obtained from intersection points of two adjacent line inductances in accordance with the present disclosure. The obtaining of the time interval of the region n from the positive intersection point X1-2 to X1-4 of the line inductances is taken as an example for description. When the microcontroller captured the positive intersection point X1-2, a timer is reset and then started for timing, and the next adjacent line inductances are detected at the same time. When the positive intersection point X1-4 of the adjacent line inductances occurs, the time interval Δt.sub.n detected by the timer is recorded and saved. The Δt.sub.n is the time interval of the region from the feature point X1-2 to the feature point X1-4 of the two adjacent line inductances. Then the timer is reset and restarted for timing, the next adjacent line inductances are detected until the feature point X1-6 appears, and then the timer records the time interval of the corresponding region. The steps for obtaining the time interval of a region are repeated, and in this way, all time intervals of regions of two adjacent line inductances are obtained.

(36) For the three-phase 6/4 structure switched reluctance motor with N.sub.r=4, the position angle of the intersection point of two adjacent lines is obtained according to formula (21):

(37) ${\mathrm{\Delta \theta }}_n=\frac{{\mathrm{\Delta \theta }}_e}{N_r}=\frac{2\pi }{3N_r}=\frac{2\pi }{3*4}=\frac{\pi }{6}\left(\mathrm{rad}\right)$

(38) Assuming that the time interval Δt.sub.n of the region corresponding to the intersection points of the two adjacent line inductances is 10 ms, an average rotate speed ω of the rotor in the corresponding region is obtained according to formula (22):

(39) $\stackrel{\_}{\omega }=\frac{{\mathrm{\Delta \theta }}_n}{{\Delta t}_n}=\frac{\pi }{6}/{10}^{-2}=16.7\pi \left(\mathrm{rad}/s\right)$

(40) Assuming that the position angle at the start time t.sub.0 of the next corresponding region is π/4, the position angle of the rotor at any time in the next corresponding is calculated according to formula (23):

(41) $\begin{array}{c}{\theta }_{n+1}\left(t\right)={\theta }_{n+1}\left(t_0\right)+\stackrel{\_}{{\omega }_n}\left(t-t_0\right)\\ =\pi /4+16.7\pi *3*{10}^{-3}\\ \approx 0.942\left(\mathrm{rad}\right)\end{array}$

Embodiment 2

(42) FIG. 4 is a block diagram of a sensorless control apparatus of the present disclosure for a three-phase switched reluctance motor. The control apparatus includes: a microcontroller; a power conversion circuit; a drive module for the power conversion circuit; a current detection module; a voltage detection module; an input and output module; and a direct current regulated power supply.

(43) The microcontroller is connected to the drive module, the current detection module, the voltage detection module and the input and output module, respectively. The power conversion circuit is connected to the three-phase switched reluctance motor, the drive module, the current detection module and the voltage detection module.

(44) The microcontroller is configured to send a control signal to the power conversion circuit through the drive module, and respectively output a chopping current and a high-frequency pulse to a conducting phase winding and a non-conducting phase winding of the three-phase switched reluctance motor through the power conversion circuit. The microcontroller is also configured to calculate the rotor position angle of the three-phase switched reluctance motor according to a feedback signal of voltage and current detected by the voltage detection module and the current detection module.

(45) The drive module is configured to receive the control signal of pulse width modulation (PWM) output by the microcontroller, and output a corresponding control signal to control a switching state of a corresponding power switch in the power conversion circuit.

(46) The current detection module is configured for real-time detection of a current of each phase of the three-phase switched reluctance motor in the power conversion circuit.

(47) The voltage detection module is configured for real-time detection of a voltage of each phase of the three-phase switched reluctance motor in the power conversion circuit.

(48) The power conversion circuit is configured to receive the control signal output by the power conversion circuit drive module, and output a chopping current to the conducting phase winding of the three-phase switched reluctance motor and a high frequency pulse to the non-conducting phase winding, respectively.

(49) The input and output module is configured to set control parameters of the three-phase switched reluctance motor and display state parameters such as speed and position angle of the rotor.

(50) The direct current regulated power supply is configured to provide a voltage and a current to a system in normal operation.

(51) The above-mentioned embodiments are preferred embodiments, and not intended to limit the present disclosure. Any variations, alternatives and modifications without departing from the spirit of the present disclosure should fall in the scope of the appended claims.