Four-phase excitation control method for inter-phase mutual inductance seven-phase switched reluctance motor capable of suppressing output of negative torque

Abstract

The invention discloses an inter-phase mutual inductance seven-phase switched reluctance motor four-phase excitation control method for suppressing output of negative torque, and the method comprises the steps: designing a conduction phase sequence control method in which the conduction directions of two-phase current of middle output negative torque are the same for a seven-phase switched reluctance motor; aiming at a control method that the conduction directions of current of two middle phases are the same, a full-bridge driving circuit is adopted, non-dotted terminals of windings of all phases are connected together, and each same dotted terminal is connected to the midpoint of an upper bridge arm and the midpoint of a lower bridge arm of a full-bridge arm; a linkage conduction strategy of each bridge arm switching device during four-phase coincidence excitation is designed aiming at the adoption of a full bridge type driving circuit, and the switch reluctance motor driving system is driven to operate. Based on the working principle of inter-phase series excitation of a motor body, a phase current conduction circulation control scheme capable of enabling each phase current to be in positive and negative bidirectional conduction is provided, the directions of the middle two phases of current are the same, the directions of generated magnetic fields are the same, and a magnetic flux loop cannot be formed, so that the negative torque output by the middle two phases is inhibited.

Description

Technical Field

[0001] The present invention relates to a four-phase excitation control method for a seven-phase switched reluctance motor, specifically a four-phase excitation control method for a seven-phase switched reluctance motor that suppresses inter-phase mutual inductance for outputting negative torque, and belongs to the technical field of motor phase winding current control. Background Art

[0002] As one of the entire switched reluctance motor family, the seven-phase switched reluctance motor (SRM) offers many advantages, including reduced torque ripple, higher power density, and improved fault tolerance. However, research on phase winding current control methods for seven-phase SRMs is limited. Traditional SRM control methods based on half-bridge drive circuits mainly include the following:

[0003] 1) Two-phase windings are turned on by coincidence: Figure 10 As shown, taking the A-phase winding as an example, the conduction state of the A-phase winding is defined as A+ when current flows from the same-name terminal, and A- otherwise. The motor conduction sequence is: B+C-, D+E-, F+G-, A-B+, C-D+, E-F+, G-A+. During non-commutation, two phases are simultaneously conducting and outputting torque. During commutation, at most two phases are conducting simultaneously, and it is possible for no winding to be conducting.

[0004] 2) Four-phase winding coincidence conduction: Figure 11 As shown in the figure, the motor conduction sequence is: B+C-, D+E-, F+G-, A-B+, C-D+, E-F+, G-A+. In the non-commutated state, four phases are always conducting simultaneously and generating positive torque. During commutation, at most four phases are conducting simultaneously, and at least two phases are conducting simultaneously.

[0005] The existing SRM conduction phase control methods based on half-bridge drive circuits are limited in terms of output torque, and the electromagnetic utilization rate of two-phase excitation is low; for example, a short-end short-magnetic-circuit split-type switched reluctance motor and its control circuit (CN201510916866.1) proposes a control method and drive circuit suitable for odd-phase switched reluctance motors. The drive circuit is as follows: Figure 12 As shown in the figure, the motor conduction sequence under this drive circuit is: B+C-, D+E-, F+G-, A-B+, C-D+, E-F+, G-A+. When four-phase excitation is used, taking B+C-D+E- as an example, since the current conduction directions of adjacent phase windings B+C- are opposite at the time of commutation, the magnetic circuit will be closed through the air gap between the two rotor blocks, and the leakage magnetic flux during motor operation will be greatly increased. The motor output torque formula is: When the currents in the middle two phases are conducted in opposite directions The negative value superimposed magnetic field generates negative torque. The torque curve under this control method is as follows Figure 13As shown, since only phase A can conduct in both directions, the other phases cannot. This is detrimental to the output torque of a seven-phase series-connected reluctance motor. If the conduction polarity of the two middle phases BC is opposite, a superimposed magnetic field is generated, which in turn produces a negative torque, as indicated by BC in the figure. The torque finally output by the motor will produce large fluctuations due to the superposition of negative torque and affect the final average torque output. Therefore, when the four-phase coincident excitation is performed, the current directions of the middle two phases must be opposite, resulting in a significant drop in torque at the commutation moment and the problem of uneven torque troughs. The existing SRM conduction phase control method based on the half-bridge drive circuit is limited in terms of output torque. The electromagnetic utilization rate of the two-phase excitation is low. During four-phase excitation, the current conduction directions of adjacent phase windings are opposite at the commutation moment. When A+B- and C+D- are turned on at the same time, since B-C+ is in the reverse conduction state, the position of the U-shaped rotor block at this time cannot meet the control state of B-C+ to form a closed magnetic circuit in reverse series on the same rotor block. Therefore, the magnetic circuit will be closed through the air gap between the two rotor blocks, and the leakage flux during motor operation will be greatly increased. Summary of the Invention

[0006] The purpose of the present invention is to provide a four-phase excitation control method for a seven-phase switched reluctance motor that suppresses the inter-phase mutual inductance of the output negative torque in order to solve at least one of the above-mentioned technical problems, fully utilize the structural advantages of the inter-phase coupled seven-phase switched reluctance motor, use four-phase excitation to improve the output torque, and at the same time suppress the mutual inductance of the output negative torque and the torque drop at the phase change moment, and design a bridge arm switching device linkage conduction strategy based on a modular full-bridge drive circuit for the new control method to improve the drive versatility.

[0007] The present invention achieves the above-mentioned object through the following technical solution: a four-phase excitation control method for a seven-phase switched reluctance motor for suppressing the inter-phase mutual inductance that outputs negative torque, including a seven-phase switched reluctance motor, and the four-phase excitation control method for the seven-phase switched reluctance motor includes the following steps:

[0008] S1. For a seven-phase switched reluctance motor, design a phase sequence control method to ensure that the currents in the middle two phases have the same conduction direction.

[0009] S2. For the control method in which the conduction directions of the middle two phase currents are the same, a full-bridge drive circuit is used. The non-identical ends of the windings of each phase are connected together, and each identical end is connected to the midpoint of the upper and lower arms of a full-bridge arm respectively.

[0010] S3. For a full-bridge drive circuit, a linkage conduction strategy for the switching devices of each bridge arm during four-phase coincident excitation is designed to drive the switched reluctance motor drive system.

[0011] As a further solution of the present invention: the seven-phase switched reluctance motor includes a stator core and rotor teeth, the rotor teeth are movably arranged on the inner side of the stator core, the rotor teeth are a U-shaped block structure, the tooth stages of the stator core are wound with excitation windings, and the magnetic circuit generated by the power supply of the excitation winding is closed along the tooth poles of adjacent stator cores and the U-shaped rotor salient poles of the rotor teeth.

[0012] As a further solution of the present invention: in S1, the conduction phase sequence control method of the seven-phase switched reluctance motor is composed of 14 conduction stages, the middle two phases of each conduction stage have the same conduction polarity, and the windings in the conduction stage are A-phase winding, B-phase winding, C-phase winding, D-phase winding, E-phase winding, F-phase winding, and G-phase winding in sequence; the conduction state of the A-phase winding when the current flows into the same end is defined as A+, and vice versa as A-, and the conduction stages are: A-B+C+D-, C+DE-F+, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, F+GA-B+.

[0013] As a further solution of the present invention: In S2, the full-bridge drive circuit adopted includes a seven-phase full-bridge power converter. The seven-phase full-bridge power converter topology is composed of seven bridge arms, two bridge arms are respectively connected to the positive and negative busbars, each bridge arm is composed of two upper and lower switching tubes connected in series, the same-name ends of each phase winding are connected to the connection point between the two switching tubes of the bridge arm, and the non-same-name ends of each phase winding are connected to each other.

[0014] As a further solution of the present invention: in S3, the linkage conduction strategy of the switch devices of each bridge arm specifically includes:

[0015] When the motor is running, the energized phase winding and the required current direction are determined by detecting the rotor position, and the corresponding phase is controlled by the corresponding relationship between the conducting phase and the switching device;

[0016] Since two sets of two-phase windings are connected in series in each conduction stage, two switching devices are required to be turned on in the upper and lower bridge arms, and the linkage control of each bridge arm is achieved by the combined conduction of two switching devices in the upper and lower bridge arms.

[0017] The beneficial effects of the present invention are:

[0018] 1) The present invention starts from the working principle of interphase series excitation of the motor body and proposes a phase current conduction circulation control scheme that allows the current of each phase to be bidirectionally conductive, positive and negative. The current directions of the middle two phases are the same, and the directions of the generated magnetic fields will also be the same, so no flux loop will be formed, thereby suppressing the negative torque output by the middle two phases. Since the traditional asymmetric half-bridge circuit cannot control the bidirectional conduction of each phase current, a new full-bridge drive circuit is designed to realize the phase winding current circulation control of A-B+C+D-, C+DE-F+, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, F+GA-B+;

[0019] 2) The present invention suppresses the negative torque caused by the two middle phases conducting in opposite directions during four-phase coincident excitation, thereby significantly optimizing the average output torque and torque ripple of the motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the winding distribution structure of the B and C phase magnetic flux paths of the present invention;

[0021] Figure 2 This is a schematic diagram of the phase sequence of the low torque ripple control for the seven-phase switched reluctance motor proposed in the present invention;

[0022] Figure 3 Schematic diagram of the topological structure of the driving circuit applicable to the present invention;

[0023] Figure 4 This is a magnetic flux circuit diagram of the control method proposed by the present invention;

[0024] Figure 5 This is a schematic diagram of the current loop of the control method proposed in the present invention when A+BC-D+ four-phase excitation is used;

[0025] Figure 6 Schematic diagram of the current loop of the control method A+BC-D+ during four-phase demagnetization proposed by the present invention;

[0026] Figure 7 A comparison diagram of the output torque waveforms of the control method proposed in the present invention and the control method in the literature;

[0027] Figure 8 The current waveforms of the seven-phase currents according to the control method proposed in the present invention are as follows;

[0028] Figure 9 This is a schematic diagram of the static torque of the generator during commutation;

[0029] Figure 10This is a schematic diagram of the conventional SRM conduction phase control method with two-phase winding coincidence conduction;

[0030] Figure 11 This is the second schematic diagram of the SRM conduction phase control method for the traditional four-phase winding coincidence conduction;

[0031] Figure 12 Schematic diagram of the driving circuit of the traditional SRM conduction phase control method;

[0032] Figure 13 Schematic diagram of the torque curve of the traditional SRM conduction phase control method;

[0033] In the figure: 1. Stator core; 2. Rotor teeth; 3. Excitation winding. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] Example 1, as Figures 1 to 8 As shown, a four-phase excitation control method for a seven-phase switched reluctance motor for suppressing inter-phase mutual inductance to output negative torque includes a seven-phase switched reluctance motor. The four-phase excitation control method for the seven-phase switched reluctance motor includes the following steps:

[0036] S1. For a seven-phase switched reluctance motor, design a phase sequence control method to ensure that the currents in the middle two phases have the same conduction direction.

[0037] S2. For the control method in which the conduction directions of the middle two phase currents are the same, a full-bridge drive circuit is used. The non-identical ends of the windings of each phase are connected together, and each identical end is connected to the midpoint of the upper and lower arms of a full-bridge arm respectively.

[0038] S3. For a full-bridge drive circuit, a linkage conduction strategy for the switching devices of each bridge arm during four-phase coincident excitation is designed to drive the switched reluctance motor drive system.

[0039] Embodiment 2. In addition to all the technical features of embodiment 1, this embodiment also includes: a seven-phase switched reluctance motor includes a stator core 1 and rotor teeth 2, the rotor teeth 2 are movably arranged on the inner side of the stator core 1, and the rotor teeth 2 are of a U-shaped block structure. The tooth stage of the stator core 1 is wound with an excitation winding 3. The magnetic circuit generated by the energization of the excitation winding 3 is closed along the tooth poles of the adjacent stator core 1 and the U-shaped rotor salient poles of the rotor teeth 2. Therefore, the currents of the adjacent two-phase excitation windings 3 need to be conducted in series, and the magnetic fields generated by the adjacent two-phase excitation windings are connected in series to form a closed loop. It should be noted that the winding on the counterclockwise side of each phase stator tooth is marked with an "*" with the same-name end, and the current is stipulated to flow from the same-name end in a positive direction. If Figure 1 As shown, the winding currents of phases B and C need to be in opposite directions to form a closed magnetic flux circuit. Therefore, the basic requirement for the phase winding current of the drive motor is that the excitation currents of the adjacent two phase windings are in opposite directions.

[0040] In S1, the conduction phase sequence control method of the seven-phase switched reluctance motor consists of 14 conduction stages. The conduction polarity of the middle two phases in each conduction stage is the same. The windings in the conduction stage are A-phase winding, B-phase winding, C-phase winding, D-phase winding, E-phase winding, F-phase winding, and G-phase winding. Taking the A-phase winding as an example, the conduction state of the A-phase winding when the current flows into the same-name terminal is defined as A+, otherwise it is A-. The conduction stages are: A-B+C+D-, C+DE-F +, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, F+GA-B+, the magnetic fields generated by the middle two phases weaken each other and suppress the generation of negative torque, thereby reducing torque fluctuations and helping to improve the average output torque and operating stability of the motor.

[0041] In S2, the full-bridge drive circuit used includes a seven-phase full-bridge power converter. The seven-phase full-bridge power converter topology consists of seven bridge arms, two of which are connected to the positive and negative busbars, respectively. Each bridge arm consists of two upper and lower switching transistors connected in series. The same-name end of each phase winding is connected to the connection point between the two switching transistors in the bridge arm, and the non-like-name end of each phase winding is connected to each other. The conduction phase is controlled by controlling the combined conduction mode of the upper and lower switching transistors of two adjacent phase bridge arms. This control method suppresses the negative torque output by the two intermediate phases of the four-phase excitation, significantly reduces air gap leakage, and helps improve the motor's torque performance.

[0042] In S3, the linkage conduction strategy of the switch devices in each bridge arm specifically includes:

[0043] When the motor is running, the energized phase winding and the required current direction are determined by detecting the rotor position, and the corresponding phase is controlled by the corresponding relationship between the conducting phase and the switching device;

[0044] Since two sets of two-phase windings are connected in series in each conduction stage, two switching devices are required to be turned on in the upper and lower bridge arms, and the linkage control of each bridge arm is achieved by the combined conduction of two switching devices in the upper and lower bridge arms.

[0045] The bridge arm linkage strategy of the full power converter is shown in the following table:

[0046] Conducting phase Conductive devices Conducting phase Conductive devices A+ S1 A- S2 B+ S3 B- S4 C+ S5 C- S6 D+ S7 D- S8 E+ S9 E- S10 F+ S11 F- S12 G+ S13 G- S14

[0047] When current flows through the excitation winding, the current flows as follows: positive bus → S1 → A → B → S4 → negative bus; positive bus → S5 → C → D → S8 → negative bus, achieving A-B + C + D excitation. The output torque is generated by the sum of each phase's self-inductance and the mutual inductance of the adjacent two phases. When the four phases ABCD are demagnetized, the next conduction phase, C + DE - F + excitation, is initiated. S5, S8, S9, and S12 form the conducting bridge arm switch combination, and the current flows as follows: positive bus → S5 → C → D → S8 → negative bus; positive bus → S9 → E → F → S12 → negative bus. Subsequently, the interphase-magnetized switched reluctance motor rotates continuously by continuously controlling the bridge arm switches according to the conduction strategy. Compared to the traditional asymmetric half-bridge topology, the DC bus voltage is divided by the two phase windings in series, reducing the voltage applied to the switching devices to half the bus voltage, thus reducing component selection costs. Furthermore, the reversible phase current direction ensures that the two middle phases have the same conduction polarity during four-phase excitation. Their magnetic fields weaken each other, effectively reducing the generation of negative torque and thus torque ripple. When all four phases are simultaneously conducting, the magnetic circuit forms multiple closed paths through adjacent stator poles and the U-shaped rotor, improving magnetic energy utilization and power density.

[0048] Advantages of this technical solution: The previous drive circuit is based on an asymmetric half-bridge drive circuit in which current can only flow in one direction. The conduction direction of each phase winding is A+, A-, B+, C-, D+, E-, F+, G-. Except for phase A, the other six phases can only conduct in one direction. Therefore, the four-phase conduction of the motor has seven states: A-B+C-D+, C-D+E-F+, E-F+G-A+, D-A+B+C-, B+C-D+E-, D+E-F+G-, F+GA-B+. As can be seen from the above, except for the two states of F+GA-B+ and D-A+B+C-, the conduction polarities of the middle two phases in the other five conduction states are opposite, and the magnetic fields generated by the currents of the two middle phases will be superimposed on each other. This is not conducive to the output torque of the seven-phase interphase series flux-type reluctance motor. For example Figure 9 The static torque diagram of the motor during phase commutation is given. At angle θ0, the FG phase is aligned. At angle θ onAt the commutation moment, FG should be turned off and CD should be turned on, while AB remains on during this process. If the conduction polarity of the two middle phases BC is opposite, a superimposed magnetic field will be generated, resulting in a negative torque as indicated by BC in the figure. The resulting torque of the motor will fluctuate significantly due to the superposition of negative torques, affecting the final average torque output.

[0049] The key issue is that when the four phases are conducting, the currents in the middle two phases conduct in opposite directions, creating a magnetic flux loop. This part of the magnetic flux loop outputs a negative torque. Therefore, it is necessary to suppress the negative torque output by the middle two phases when the four phases are conducting simultaneously.

[0050] This technical solution, based on the operating principle of interphase series excitation in a motor, proposes a phase current conduction cycle control scheme that enables bidirectional conduction in each phase, both positive and negative. The following motor phase winding conduction control cycle is designed: A-B+C+D-, C+DE-F+, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, F+GA-B+. The currents in the middle two phases are in the same direction, and the magnetic fields they generate are also in the same direction, preventing the formation of a magnetic flux loop and suppressing the negative torque output by the middle two phases. Since the traditional asymmetric half-bridge circuit cannot control the bidirectional conduction of each phase current, a new full-bridge drive circuit is designed to realize the phase winding current circulation control of A-B+C+D-, C+DE-F+, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, F+GA-B+.

[0051] The advantage of this technical solution is that it suppresses the negative torque of the two middle phases conducting in opposite directions during four-phase coincident excitation, thereby greatly optimizing the average output torque and torque ripple of the motor. The results of the motor working characteristic optimization of this solution are as follows: Figure 7 shown.

[0052] By designing a current conduction scheme for the phase windings with the same current direction in the middle two phases such as A-B+C+D-, and designing a full-bridge drive circuit based on this scheme, the switching device linkage conduction strategy of the full-bridge drive circuit is designed to realize the current conduction scheme of the phases A-B+C+D-, etc., and drive the seven-phase switched reluctance motor to operate.

[0053] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

[0054] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A method for controlling four-phase excitation of a seven-phase switched reluctance motor to suppress inter-phase mutual inductance that produces negative torque, comprising a seven-phase switched reluctance motor, characterized in that: The four-phase excitation control method of the seven-phase switched reluctance motor comprises the following steps: S1. For a seven-phase switched reluctance motor, a method is designed to control the phase sequence of the middle two phases when the current conduction directions are the same when the four-phase excitation is applied. S2. For the control method in which the conduction directions of the middle two phase currents are the same, a full-bridge drive circuit is used. The non-identical ends of the windings of each phase are connected together, and each identical end is connected to the midpoint of the upper and lower arms of a full-bridge arm respectively. S3. For a full-bridge drive circuit, a linkage conduction strategy for the switching devices of each bridge arm during four-phase coincident excitation is designed to drive the operation of the switched reluctance motor drive system.

2. The four-phase excitation control method of a seven-phase switched reluctance motor according to claim 1, characterized in that: The seven-phase switched reluctance motor comprises a stator core (1) and rotor teeth (2), wherein the rotor teeth (2) are movably arranged inside the stator core (1), and the rotor teeth (2) are of a U-shaped block structure. The tooth stages of the stator core (1) are wound with excitation windings (3), and the magnetic circuit generated by energizing the excitation windings (3) is closed along the tooth poles of adjacent stator cores (1) and the U-shaped rotor salient poles of the rotor teeth (2).

3. The four-phase excitation control method of a seven-phase switched reluctance motor according to claim 1, characterized in that: In S1, the conduction phase sequence control method of the seven-phase switched reluctance motor consists of 14 conduction stages, the middle two phases of each conduction stage have the same conduction polarity, and the windings in the conduction stages are A-phase winding, B-phase winding, C-phase winding, D-phase winding, E-phase winding, F-phase winding, and G-phase winding in sequence; the conduction state of the A-phase winding when the current flows into the same-name end is defined as A+, and vice versa as A-, and the conduction stages are: A-B+C+D-, C+DE-F+, E-F+G+A-, G+AB-C+, B-C+D+E-, D+EF-G+, F-G+A+B-, A+BC-D+, C-D+E+F-, E+FG-A+, G-A+B+C-, B+CD-E+, D-E+F+G-, and F+GA-B+.

4. The four-phase excitation control method of a seven-phase switched reluctance motor according to claim 1, characterized in that: In S2, the full-bridge drive circuit used includes a seven-phase full-bridge power converter. The seven-phase full-bridge power converter topology is composed of seven bridge arms, two bridge arms are connected to the positive and negative busbars respectively, each bridge arm is composed of two upper and lower switching tubes connected in series, the same-name end of each phase winding is connected to the connection point between the two switching tubes of the bridge arm, and the non-same-name ends of each phase winding are connected to each other.

5. The four-phase excitation control method of a seven-phase switched reluctance motor according to claim 1, characterized in that: In S3, the linkage conduction strategy of the switch devices of each bridge arm specifically includes: When the motor is running, the energized phase winding and the required current direction are determined by detecting the rotor position, and the corresponding phase is controlled by the corresponding relationship between the conducting phase and the switching device; Since two sets of two-phase windings are connected in series in each conduction stage, two switching devices are required to be turned on in the upper and lower bridge arms, and the linkage control of each bridge arm is achieved by the combined conduction of two switching devices in the upper and lower bridge arms.

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