Fault-tolerant current reconstruction method after open circuit of any two phases of slice motor

Abstract

The invention discloses a fault-tolerant current reconstruction method for eliminating reversal magnetic potential after disconnection of any two phases of a slice motor. A motor structure with six teeth and one pair of poles is adopted. The method comprises the following steps: firstly, according to a magnetic potential calculation formula, writing a magnetic potential expression of residual-phase current in an air gap after two phases are disconnected; according to the obtained magnetic potential expression, extracting a reverse magnetic potential expression in the magnetic potential expression; the expression of the reverse magnetic potential is equivalent to a magnetic vector, and the magnetic vector is divided into two groups of eight vectors after equivalence; the phase of the current of the residual phase is reconstructed so that the four vectors about one pair of poles form a rectangle, meanwhile, the phase and amplitude proportion of the current of the residual phase is reconstructed so that the sum of the four vectors about two pairs of poles is zero, the suspension force is kept consistent with the suspension force without fault tolerance, and suspension force pulsation does not exist. According to the invention, the defect that the reconstruction current after the traditional two-phase open circuit is applied to the slice motor is overcome, the stable suspension after any two-phase open circuit is realized, the suspension performance of the slice motor after fault tolerance is improved, and the practicability is enhanced.

Description

Technical Field

[0001] The invention relates to the technical field of bearingless motor control, and mainly to a fault-tolerant current reconstruction method after any two phases of a thin-film motor are disconnected based on magnetic field modulation theory and eliminate reverse magnetic potential. Background Art

[0002] During the operation of the thin-film motor, once the suspension winding has a short circuit fault, the suspension performance will be greatly reduced, causing unnecessary losses. The existing fault-tolerant methods for bearing motors are not fully applicable to the short circuit fault tolerance of the suspension winding of thin-film motors. The existing short circuit fault-tolerant methods for thin-film motors do not start from the perspective of eliminating suspension pulsation and maintaining stable suspension of thin-film motors. Instead, they solve the equations for the residual current based on the power optimal constraint. In the solution process, the influence of the reverse magnetic potential on the suspension force is ignored. Although the reconstructed current can make the motor continue to suspend, the radial displacement of the rotor becomes larger and the suspension performance is reduced.

[0003] The document "A method for reconstructing single-phase circuit-breaking fault-tolerant current of thin-film motors (202411260114.X)" publishes a method for reconstructing single-phase circuit-breaking fault-tolerant current. The core idea is to divide the five vectors into two groups. The three vectors in a group form a triangle. The two vectors in a group have opposite phases, and the amplitudes of the five-phase currents are equal.

[0004] When the motor is disconnected by two phases, the above control concept is no longer applicable. First, the grouping condition is not met. When a group consists of three vectors, the remaining vector cannot be offset. Second, even if a pair of poles is eliminated, the five-phase current amplitude is equal and it is difficult to eliminate the two pairs of poles.

[0005] At the same time, the existing technology is also unable to perform fault-tolerant control on two-phase circuit breaks that are one phase apart, which limits the application of two-phase circuit break fault-tolerant control. Summary of the invention

[0006] Purpose of the invention: In view of the problems existing in the above-mentioned background technology, the present invention provides a method for controlling any two-phase circuit break fault-tolerantly based on magnetic field modulation theory to offset the reverse magnetic potential during the current reconstruction process. Compared with the traditional circuit break reconstruction current, the current reconstructed by the present invention realizes that a pair of pole magnetic potentials constitute a rectangle under the premise that vector grouping cannot be realized and the two-pole magnetic potentials are difficult to offset. The two-pole magnetic potentials are offset by the design of unequal current amplitudes, the reverse magnetic potential is offset, the suspension force pulsation is eliminated, and it is suitable for any two-phase circuit break, and is more suitable for circuit break fault-tolerant control of thin-film motors.

[0007] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is:

[0008] A fault-tolerant current reconstruction method after any two phases of a thin-film motor are disconnected, wherein the motor adopts a six-tooth one-pole motor structure, and the method comprises the following steps: firstly, according to the calculation formula of the magnetic potential, a magnetic potential expression of the residual phase current in the air gap after the two phases are disconnected is given; according to the magnetic potential expression, a reverse magnetic potential expression is extracted; according to the reverse magnetic potential expression, the reverse magnetic potential of one pair of poles and two pairs of poles is equivalent to two groups of eight vectors about one pair of poles and two pairs of poles; the phase of the current of the residual phase is reconstructed so that four vectors about one pair of poles form a rectangle, and at the same time, the phase and amplitude ratio of the current of the residual phase are reconstructed so that the sum of the four vectors about the two pairs of poles is zero; and the residual phase current is constructed so that the phases of the two vectors differ by 180 degrees and then cancel each other out.

[0009] Preferably, the motor structure includes 6 L-shaped stators, each L-shaped stator includes an axial stator yoke and radial stator teeth, which are surrounded by a thin-film rotor, and the radial stator teeth are flush with the rotor. Each axial stator yoke is respectively wound with a suspension winding and a torque winding, the torque winding is a pair of poles, and the suspension winding is two pairs of poles, thereby realizing suspension control and rotation control at the same time; the bottom of the L-shaped stator is connected through an iron core magnetic ring; a pair of permanent magnets are attached to the outside of the thin-film rotor.

[0010] Preferably, taking the two-phase circuit breaking separated by one phase as an example, the method comprises the following steps: the mechanical angles of the circuit breaking phases are 0° and 120° respectively, and the synthetic magnetic potential of one pair of poles and two pairs of poles is considered. The specific synthetic magnetic potential expression of one pair of poles and two pairs of poles is shown in formula (1):

[0011]

[0012] In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F are the magnetic potentials of one pole and two pole pairs of the four-phase winding, respectively; B, D, E, and F are the phases of the four-phase currents, respectively; is the magnitude of the magnetic potential of a pair of poles, is the amplitude of the two-pole magnetic potential, θ is the rotor position angle, ωt is the synchronous electrical angular frequency of the motor;

[0013] According to the composite magnetic potential expression of one pair of poles and two pairs of poles in formula (1), the extracted reversal magnetic potential expression is expressed in the form of formula (2):

[0014]

[0015] In the formula, F 1Bf 、F 1Df 、F1Ef 、F 1Ff 、F 2Bf 、F 2Df 、F 2Ef 、F 2Ff They are the reverse magnetic potentials of one pole and two poles of the four-phase winding respectively;

[0016] According to the reversal magnetic potential expression of formula (2), the reversal magnetic potential of one pair of poles and two pairs of poles is equivalent to two groups of eight vectors about one pair of poles and two pairs of poles, as shown in formula (3):

[0017]

[0018] In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F They are the vectors equivalent to the reverse magnetic potentials of one pole and two poles of the four-phase winding;

[0019] Let B=E=D-30°=F+30°, then F 1B 、F 1D 、F 1E 、F 1F The phases of the four vectors differ by 90°, and the four vectors are connected end to end to form a rectangle, and the sum of the vectors is zero; let B = E = D-30° = F + 30°, F 2B and F 2E The resultant vector and F 2D and F 2F The synthesized vector phase difference is 180°, and the ratio of the initial length is The ratio of the B(E) phase current to the D(F) phase current amplitude is Make F 2B and F 2E The resultant vector and F 2D and F 2F The sum of the resulting vectors is zero;

[0020] Make F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F The four vectors are superimposed on each other and then canceled out. After the current is constructed according to the cancellation process, the new four-phase current is shown in formula (4):

[0021]

[0022] Preferably, according to the principle of vector superposition, in order to make the four vectors cancel each other out after being superimposed, there are two superposition methods: one is that the four vectors are paired with each other, with a difference of 180° to cancel each other out, and the other is that the four vectors are paired with a difference of 90° to cancel each other out. The specific scheme is as follows: Figure 1 shown.

[0023] Preferably, when open-circuit faults occur in phases A and C of the motor, the current in equation (4) is injected to eliminate the related magnetic potential and suspension force pulsation; when open-circuit faults occur in the remaining two phases, the remaining phase currents are reconstructed.

[0024] The fault-tolerant current reconstruction method for eliminating reverse magnetic potential after any two phases of a thin-film motor are disconnected based on magnetic field modulation theory provided by the present invention has the following beneficial effects compared with the existing methods:

[0025] (1) When the remaining four vectors cannot be grouped into 3 or 2 vectors, a rectangular cancellation method without grouping vectors is proposed. A rectangle formed by four vectors of a pair of poles is cancelled out. The aspect ratio of the rectangle is further limited, so that the sum of the two pairs of poles vectors is zero.

[0026] (2) During the current reconstruction process, the reverse magnetic potentials of one pair of poles and two pairs of poles are offset, the pulsation of the suspension force is eliminated, and a stable suspension force is obtained.

[0027] (3) The air gap magnetic potential remains unchanged before and after fault tolerance, the suspension force remains stable and unchanged, and the entire control system remains unchanged.

[0028] (4) The current reconstruction process is simple, and the reconstructed current form is simple, which is convenient for fault-tolerant current input and motor control.

[0029] (5) The suspension performance before and after fault tolerance remains unchanged. Compared with the existing fault-tolerant current reconstruction method, the motor performance after fault tolerance is greatly improved.

[0030] (6) Fault-tolerant control of any two-phase circuit breaker can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 Schematic diagram of a method for superimposing four vectors to obtain a zero vector sum provided by the present invention, wherein (a) the four vectors are mutually offset by 90° each other and connected end to end to cancel each other out; (b) the four vectors are mutually offset by 180° each other in pairs;

[0032] Figure 2 It is a schematic diagram of a superposition process in which the sum of four vectors provided by the present invention is zero;

[0033] Figure 3 This is an axial cross-sectional view of a six-tooth one-pole bearingless permanent magnet thin-film motor provided by the present invention;

[0034] Figure 4 This is a simulation diagram of the suspension force when six-phase normal suspension current is passed;

[0035] Figure 5 This is the simulation diagram of the suspension force when four-phase fault-tolerant current is passed through the simulation;

[0036] Figure 6 It is the suspension force fitting diagram before and after the fault-tolerant current is introduced in the simulation. DETAILED DESCRIPTION

[0037] The present invention is further described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] The present invention adopts Figure 3 The bearingless permanent magnet thin-film motor shown adopts a six-teeth-one-pole motor structure, including six L-shaped stators 2. Each L-shaped stator 2 includes an axial stator yoke and radial stator teeth, which surround the thin-film rotor. The radial stator teeth are flush with the rotor. Each axial stator yoke is respectively wound with a suspension winding 4 and a torque winding 5. The torque winding is a pair of poles, and the suspension winding is two pairs of poles, so that suspension control and rotation control are realized at the same time. The bottom of the L-shaped stator is connected through an iron core magnetic ring 3. A pair of permanent magnets with poles are attached to the outside of the thin-film rotor 1.

[0039] Specifically, taking the case of two-phase disconnection separated by one phase as an example, the mechanical angles of the disconnected phases are 0° and 120° respectively. Considering the synthetic magnetic potential of one pole and two poles, the specific synthetic magnetic potential expression of one pole and two poles is shown in formula (1):

[0040]

[0041] In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F are the magnetic potentials of one pole and two pole pairs of the four-phase winding, and B, D, E, and F are the phases of the four-phase current.

[0042] According to the composite magnetic potential expression of one pair of poles and two pairs of poles in formula (1), the extracted reversal magnetic potential expression can be expressed in the form of formula (2):

[0043]

[0044] In the formula, F1Bf 、F 1Df 、F 1Ef 、F 1Ff 、F 2Bf 、F 2Df 、F 2Ef 、F 2Ff They are the reverse magnetic potentials of one pole pair and two pole pairs of the four-phase winding respectively.

[0045] According to the reversal magnetic potential expression of formula (2), the reversal magnetic potential of one pair of poles and two pairs of poles is equivalent to two groups of eight vectors about one pair of poles and two pairs of poles, as shown in formula (3):

[0046]

[0047] In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F They are the vectors equivalent to the reverse magnetic potentials of one pair of poles and two pairs of poles of the four-phase winding.

[0048] After 2 phases are open circuited, 4 vectors remain. The 3-vector and 2-vector grouping method in the document "A method for reconstructing single-phase circuit-breaking fault-tolerant current of a thin-film motor (202411260114.X)" cannot be used. Therefore, the present invention first proposes a rectangular cancellation method, that is, let B = E = D-30° = F+30°, then F 1B 、F 1D 、F 1E 、F 1F If the phases of the four vectors differ by 90°, then these four vectors can be connected end to end to form a rectangle, and the sum of the vectors is zero.

[0049] Let B = E = D-30° = F + 30°, F 2B and F 2E The resultant vector phase angle is 120°, F 2D and F 2F The resultant vector phase angle is 300°, and the phases are opposite, but the ratio of their initial lengths is Furthermore, the ratio of the B (E) phase current to the D (F) phase current amplitude is designed to be Even if Figure 1 The aspect ratio of the middle rectangle is Make F 2B and F 2E The resultant vector and F 2D and F 2F The sum of the resulting vectors is zero, such as Figure 2 shown.

[0050] Based on the above principles, Figure 2 After the current is constructed by the offset process, the new four-phase current is shown in formula (4):

[0051]

[0052] In order to verify whether the derivation is correct, the suspension force before and after the fault-tolerant current is passed into the motor is simulated in the MAXWELL simulation, and the results are compared to verify whether the theoretical derivation is correct.

[0053] Figure 4 This is the simulation diagram of the suspension force when six-phase normal suspension current is passed through the simulation. Figure 5 This is the simulation diagram of the suspension force when four-phase fault-tolerant current is passed through the simulation. Figure 6 It is a fitting diagram of the suspension force before and after the fault-tolerant current is introduced in the simulation. From the comparison of several pictures, it can be seen that the fault-tolerant current reconstruction method of the thin-film motor after any two phases are disconnected based on the magnetic field modulation theory to eliminate the reverse magnetic potential provided by the present invention is

[0054] (1) After eliminating the reverse magnetic potential, a stable suspension force can be obtained.

[0055] (2) The motor suspension force is stable after fault tolerance.

[0056] (3) Compared with the suspension force before fault tolerance, the suspension force after fault tolerance remains consistent in the x and y directions.

[0057] (4) It can perform fault-tolerant operation on a two-phase circuit breaker fault separated by one phase, which cannot be performed by the existing method.

[0058] In summary, compared with the existing fault-tolerant reconstruction current, the fault-tolerant current reconstruction method of the thin-film motor after any two phases are disconnected based on the magnetic field modulation theory to eliminate the reverse magnetic potential provided by the present invention makes the suspension force before and after fault tolerance remain unchanged, greatly improves the suspension performance after fault tolerance, and realizes fault-tolerant operation after any two phases are disconnected.

[0059] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A fault-tolerant current reconstruction method for a thin-film motor after any two phases are disconnected, wherein the motor adopts a six-teeth-one-pole motor structure, characterized in that: The method comprises the following steps: firstly, according to the calculation formula of magnetic potential, a magnetic potential expression of the residual phase current in the air gap after two-phase circuit breaking is given; according to the magnetic potential expression, a reverse magnetic potential expression is extracted; according to the reverse magnetic potential expression, the reverse magnetic potential of one pair of poles and two pairs of poles is equivalent to two groups of eight vectors about one pair of poles and two pairs of poles; the phase of the current of the residual phase is reconstructed so that four vectors about one pair of poles form a rectangle, and at the same time, the phase and amplitude ratio of the current of the residual phase are reconstructed so that the sum of the four vectors about the two pairs of poles is zero; and the residual phase current is constructed so that the phases of the two vectors differ by 180 degrees and then cancel each other out.

2. According to claim 1, a fault-tolerant current reconstruction method after any two phases of a thin-film motor are disconnected, the motor structure includes 6 L-shaped stators, each L-shaped stator includes an axial stator yoke and radial stator teeth, which surround the thin-film rotor, and the radial stator teeth are flush with the rotor. Each axial stator yoke is respectively wound with a suspension winding and a torque winding, the torque winding is a pair of poles, and the suspension winding is two pairs of poles, and suspension control and rotation control are realized at the same time; the bottom of the L-shaped stator is connected by an iron core magnetic ring; a pair of poles of permanent magnets are attached to the outside of the thin-film rotor.

3. The fault-tolerant current reconstruction method of a thin-film motor after any two phases are disconnected according to claim 1, characterized in that: Taking two phases separated by one phase as an example, the method comprises the following steps: the mechanical angles of the disconnected phases are 0° and 120° respectively, and the synthetic magnetic potential of one pair of poles and two pairs of poles is considered. The specific synthetic magnetic potential expression of one pair of poles and two pairs of poles is shown in formula (1): In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F are the magnetic potentials of one pole and two pole pairs of the four-phase winding, respectively; B, D, E, and F are the phases of the four-phase currents, respectively; is the magnitude of the magnetic potential of a pair of poles, is the amplitude of the two-pole magnetic potential, θ is the rotor position angle, ωt is the synchronous electrical angular frequency of the motor; According to the composite magnetic potential expression of one pair of poles and two pairs of poles in formula (1), the extracted reversal magnetic potential expression is expressed in the form of formula (2): In the formula, F 1Bf 、F 1Df 、F 1Ef 、F 1Ff 、F 2Bf 、F 2Df 、F 2Ef 、F 2Ff They are the reverse magnetic potentials of one pole and two poles of the four-phase winding respectively; According to the reversal magnetic potential expression of formula (2), the reversal magnetic potential of one pair of poles and two pairs of poles is equivalent to two groups of eight vectors about one pair of poles and two pairs of poles, as shown in formula (3): In the formula, F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F They are the vectors equivalent to the reverse magnetic potentials of one pole and two poles of the four-phase winding; Let B=E=D-30°=F+30°, then F 1B 、F 1D 、F 1E 、F 1F The phases of the four vectors differ by 90°, and the four vectors are connected end to end to form a rectangle, and the sum of the vectors is zero; let B = E = D-30° = F + 30°, F 2B and F 2E The resultant vector and F 2D and F 2F The synthesized vector phase difference is 180°, and the ratio of the initial length is The ratio of the B(E) phase current to the D(F) phase current amplitude is Make F 2B and F 2E The resultant vector and F 2D and F 2F The sum of the resulting vectors is zero; Make F 1B 、F 1D 、F 1E 、F 1F 、F 2B 、F 2D 、F 2E 、F 2F The four vectors are superimposed on each other and then canceled out. After the current is constructed according to the cancellation process, the new four-phase current is shown in formula (4):

4. The fault-tolerant current reconstruction method of a thin-film motor after two-phase circuit breaking according to claim 3 is characterized in that: According to the principle of vector superposition, in order to make four vectors cancel each other out after superposition, there are two superposition methods. One is that the four vectors are paired with each other, with a difference of 180° between them and cancel each other out. The other is that the four vectors are paired with a difference of 90° between them and connected end to end and cancel each other out.

5. The fault-tolerant current reconstruction method of a thin-film motor after two-phase circuit breaking according to claim 3 is characterized in that: When open-circuit faults occur in phases A and C of the motor, the current in equation (4) is injected to eliminate the related magnetic potential and suspension force pulsations; when open-circuit faults occur in the remaining two phases, the remaining phase currents are reconstructed.

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