Permanent magnet synchronous motor system based on fractional harmonic magnetic field pole-changing weak magnetic speed expansion and driving method thereof

Abstract

The invention provides a permanent magnet synchronous motor system based on fractional harmonic magnetic field pole-changing flux-weakening speed expansion and a driving method thereof, and aims to solve the problem of poor flux-weakening speed expansion performance of a surface-mounted permanent magnet synchronous motor. The motor system is composed of a permanent magnet synchronous motor and a frequency converter, and an inverter driving loop of the frequency converter comprises eight parallel bridge arms. In the mode I, the rotating speed of the motor does not exceed the base speed, an armature winding is connected to be a two-phase winding, and a 2p-pole magnetic field is used for operation; in the mode II, the rotating speed is higher than the base speed, a two-phase winding is connected, a 2p-pole magnetic field is used for operation, and the speed is expanded by adopting an existing flux weakening method; and in the mode III, the rotating speed is continuously increased, the armature winding is connected to be a double-three-phase winding, and a 2p / 3 pole number magnetic field is used for operation. The pole-changing type flux-weakening speed expansion is realized by utilizing 1 / 3 magnetic field harmonic waves and changing the switching-on and switching-off modes of a switching tube of an inverter loop, the problem of difficulty in flux weakening is solved, and the pole-changing type flux-weakening speed expansion device has the advantages of small harmonic circulating current amplitude, large maximum power after pole changing and high utilization rate of the switching tube of the inverter.

Description

Technical Field

[0001] The invention discloses a permanent magnet synchronous motor system with fractional harmonic magnetic field-changing pole-weakening speed expansion and a driving method thereof, belonging to the field of motor design and manufacturing. Background Art

[0002] Surface-mounted permanent magnet synchronous motors (SPMSMs) are widely used in modern high-performance drive systems due to their high torque density and excellent dynamic response characteristics resulting from low magnetic leakage. Existing magnetic field weakening and speed-expanding technologies achieve speed-expanding operation of permanent magnet synchronous motors by injecting a demagnetizing current to generate a demagnetizing armature magnetomotive force, thereby weakening the air gap magnetic field of the motor. However, compared to embedded permanent magnet synchronous motors, SPMSMs are limited by their small direct-axis inductance, resulting in poor magnetic field weakening and speed-expanding performance. Forcibly increasing the direct-axis inductance of the motor will result in slower dynamic response speed, lower torque density, lower power factor, and lower overload capacity. Reducing the magnetic properties of the motor's permanent magnets will sacrifice the motor's torque density.

[0003] In order to solve the above problems, the present invention proposes a surface-mounted permanent magnet synchronous motor system that utilizes the fractional harmonic magnetic field of the motor to achieve pole-changing magnetic field weakening speed expansion. Summary of the Invention

[0004] (1) Technical problems solved

[0005] The problem to be solved by the present invention is the problem described in the technical background.

[0006] (2) Technical solution

[0007] The permanent magnet synchronous motor system based on fractional harmonic magnetic field pole-changing weak magnetic field speed expansion proposed by the present invention is composed of a permanent magnet synchronous motor and a frequency converter. The shape of the permanent magnet of the motor is designed by the existing method, so that the air gap magnetic field of the permanent magnet of the motor (that is, the no-load air gap magnetic field of the motor) contains both a 2p pole number magnetic field and a 2p / 3 pole number magnetic field, where p is an integer greater than or equal to 3; from the perspective of the 2p / 3 pole number magnetic field of the motor, the armature winding is arranged as a double three-phase winding with a shift of 30 degrees, each set of three-phase windings is a 120-degree symmetrical winding, each set of three-phase windings is star-connected, and two neutral points are led out; the inverter drive circuit of the frequency converter contains eight parallel bridge arms, and each bridge arm contains two forward series switching tubes; the six output terminals and two neutral point lead-out lines of the two sets of three-phase windings are respectively connected to the eight bridge arms, such as Figure 2As shown; the driving method proposed in the present invention includes three modes, namely mode I, mode II and mode III; when the mode I driving method is adopted, the rotational speed of the motor does not exceed the base speed, so the winding terminal voltage of the motor has not yet reached the power supply voltage limit of the inverter, so in mode I, when the motor increases its speed, there is no need for weak magnetic field, and the armature winding of the motor is connected as a two-phase winding with a phase difference of 90 degrees by the inverter drive circuit of the inverter, and the motor operates using a 2p pole magnetic field. When the rotational speed of the motor exceeds the base speed, it is divided into two driving modes, mode II and mode III; in mode II, the armature winding of the motor is connected as a two-phase winding with a phase difference of 90 degrees by the inverter drive circuit of the inverter (the spatial electrical angle distribution of the winding axis is as shown Figure 5 As shown), the motor operates with a 2p pole magnetic field, the motor adopts the existing weak magnetic method to increase the speed, and the armature winding current of the motor contains a weak magnetic component; in mode III, the armature winding of the motor is connected by the inverter drive circuit of the inverter to a double Y-connected winding with a shift of 30 degrees (the spatial electrical angle distribution of the winding axis is as shown in FIG. Figure 6 As shown), the motor operates using a 2p / 3 pole magnetic field; the permanent magnet air gap magnetic field of the motor satisfies Among them B 1 / 3 is the magnetic flux density amplitude of the 2p / 3 pole magnetic field in the air gap magnetic field of the permanent magnet, B 1 / 3 is the magnetic flux density amplitude of the 2p-pole magnetic field in the air gap magnetic field of the permanent magnet, k w1 / 3 k is the winding coefficient when the armature winding is connected as a two-phase winding with a phase difference of 90 degrees and its value is greater than zero, w1 It is the winding coefficient when the armature winding is connected as a double three-phase winding with a phase difference of 30 degrees and its value is greater than zero.

[0008] In order to facilitate the understanding of the driving method proposed by the present invention, Figure 1 、 Figure 2 The embodiment shown is introduced as an example.

[0009] Mode I: When the motor system is in this driving mode, the motor speed does not exceed the base speed; the eight bridge arms of the inverter drive circuit of the inverter and the armature winding of the motor are connected as follows: Figure 2As shown, the three upper bridge arm switching tubes in the first bridge arm, the second bridge arm, and the third bridge arm of the inverter drive circuit of the inverter are fed with the same conduction control signal, and the three lower bridge arm switching tubes are also fed with the same conduction control signal. The first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm together constitute a group of H-bridge drive circuits including three parallel branches; the three upper bridge arm switching tubes in the fifth bridge arm, the sixth bridge arm, and the seventh bridge arm of the inverter drive circuit of the inverter are fed with the same conduction control signal, and the three lower bridge arm switching tubes are also fed with the same conduction control signal. The fifth bridge arm, the sixth bridge arm, the seventh bridge arm, and the eighth bridge arm together constitute another group of H-bridge drive circuits including three parallel branches; the two groups of H-bridges drive and supply power to the armature winding of the motor in a power supply mode of two-phase windings with a phase difference of 90 degrees, and the fundamental frequency f of the power supply voltage output by the two groups of H-bridges is consistent with the mechanical speed ω of the motor rotor. r The relationship between them is:

[0010]

[0011] where ω r The unit is rad / s.

[0012] Mode II: When the motor system is in this driving mode, the motor speed does not exceed the base speed; the eight bridge arms of the inverter drive circuit of the inverter and the armature winding of the motor are connected as follows: Figure 2 As shown, the three upper bridge arm switching tubes in the first bridge arm, the second bridge arm, and the third bridge arm of the inverter drive circuit of the inverter are fed with the same conduction control signal, and the three lower bridge arm switching tubes are also fed with the same conduction control signal. The first bridge arm, the second bridge arm, the third bridge arm, and the fourth bridge arm together constitute a group of H-bridge drive circuits including three parallel branches; the three upper bridge arm switching tubes in the fifth bridge arm, the sixth bridge arm, and the seventh bridge arm of the inverter drive circuit of the inverter are fed with the same conduction control signal, and the three lower bridge arm switching tubes are also fed with the same conduction control signal. The fifth bridge arm The sixth bridge arm, the seventh bridge arm and the eighth bridge arm together constitute another group of H-bridge drive circuits including three parallel branches; the two groups of H-bridges drive and supply power to the armature winding of the motor in a power supply mode of two-phase windings with a phase difference of 90 degrees, that is, the fundamental frequency of the power supply voltage of the two groups of H-bridges is the same, the phases are 90 degrees apart from each other, and the relationship between the frequency and the mechanical speed of the motor rotor satisfies formula (1); the inverter introduces a demagnetizing current component into the armature winding of the motor according to the existing weak magnetic speed expansion method, so that the terminal voltage of the armature winding of the motor is within the inverter limit power supply voltage range.

[0013] Mode III: When the motor system is in this driving mode, the motor speed is higher than the base speed; the eight bridge arms of the inverter drive circuit of the inverter and the motor armature winding are connected as follows: Figure 2As shown; all the switch tubes in the fourth bridge arm and the eighth bridge arm of the inverter drive circuit of the inverter are fully closed; the first bridge arm, the second bridge arm, and the third bridge arm constitute a group of three-phase drive circuits, which drive and supply power to the motor windings in a symmetrical three-phase power supply mode; the fifth bridge arm, the sixth bridge arm, and the seventh bridge arm constitute another group of three-phase drive circuits, which drive and supply power to the motor windings in a symmetrical three-phase power supply mode; the inverter drive circuit of the inverter drives and supplies power to the armature winding of the motor in a 30-degree shifted dual three-phase winding power supply mode, and the relationship between the fundamental frequency of the power supply voltage output by the inverter and the mechanical speed of the motor rotor is:

[0014]

[0015] The principle of the invention is explained below through formula deduction.

[0016] When the motor system is in mode I and mode II driving modes, the 2p-pole magnetic field in the air gap magnetic field of the motor is the main magnetic field. The inverter connects the armature winding of the motor into two-phase windings with a phase difference of 90 degrees. According to electromechanics, the no-load phase electromotive force of the motor induced by the 2p-pole magnetic field is:

[0017]

[0018] Where E1 is the amplitude of the no-load phase electromotive force, and θ is the initial phase of the no-load electromotive force of phase D. When loaded, the current supplied by the inverter to the two-phase winding is as follows:

[0019]

[0020] Where I1 is the amplitude of the current flowing through, is the initial phase of the D-phase current; when loaded, the winding terminal voltage of the motor is equal to the sum of the no-load phase electromotive force and the armature impedance voltage drop.

[0021] When in mode III driving mode, the 2p / 3 pole magnetic field in the air gap magnetic field of the motor is the main magnetic field. The inverter connects the armature winding of the motor into dual three-phase windings with a 30-degree phase difference. The no-load electromotive force of each phase is jointly induced by the 2p pole magnetic field and the 2p / 3 pole magnetic field, and its expression is:

[0022]

[0023] Among them E 1 / 3is the amplitude of the no-load phase electromotive force induced by the 2p / 3 pole magnetic field, α is its initial phase, and β is the initial phase of the no-load phase electromotive force induced by the 2p pole magnetic field. Because the motor speed in mode III is higher than the base speed, E1 in equation (5) exceeds the inverter's voltage limit. However, in mode III, the inverter reconnects the motor's armature winding to a dual three-phase winding shifted 30 degrees, so the inverter's output voltage is the line voltage of the winding. Therefore, the motor's no-load line electromotive force can be expressed as:

[0024]

[0025] It can be seen that when in mode III, the part of the no-load line electromotive force of the armature winding of the motor generated by the 2p pole magnetic field induction is offset, and only the part generated by the 2p / 3 pole magnetic field induction remains, and due to Then we can know Therefore, pole-changing weak magnetic speed expansion is realized. When loaded, the current supplied by the inverter to the dual three-phase windings is as follows:

[0026]

[0027] Among them I 1 / 3 The amplitude of the input current, γ is the initial phase of the A phase current.

[0028] As can be seen from the above, the technical solution provided by the present invention utilizes the one-third harmonic magnetic field of the motor, and realizes pole-changing weak magnetic speed expansion by changing the on and off mode of the switch tube in the inverter circuit. The technical solution proposed by the present invention retains the advantages of the surface-mounted permanent magnet synchronous motor, while solving the stubborn problem of weak magnetic field of the traditional surface-mounted permanent magnet synchronous motor. Compared with the prior art, when the motor speed does not exceed the base speed (that is, in mode I), the amplitude of the harmonic circulating current induced in the parallel branch of the armature winding by the one-third harmonic magnetic field adopted by the solution of the present invention is smaller, and the maximum power of the motor after the pole is changed (that is, in mode III) is greater; in addition, the present invention also has the advantage of higher utilization rate of the inverter switch tube. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a front cross-sectional view of the stator and rotor cores of a motor in a specific embodiment;

[0030] Figure 2This is a wiring diagram of an inverter drive circuit of a frequency converter in a specific embodiment, wherein the bridge arm connected to the positive end of the winding labeled 1 is marked as the first bridge arm, the bridge arm connected to the positive end of the winding labeled 2 is marked as the second bridge arm, the bridge arm connected to the positive end of the winding labeled 3 is marked as the third bridge arm, and the bridge arm connected to the neutral point of windings 1, 2, and 3 (from the perspective of a two-pole magnetic field in an air gap magnetic field) is marked as the fourth bridge arm; the bridge arm connected to the positive end of the winding labeled 4 is marked as the fifth bridge arm, the bridge arm connected to the positive end of the winding labeled 5 is marked as the sixth bridge arm, the bridge arm connected to the positive end of the winding labeled 6 is marked as the seventh bridge arm, and the bridge arm connected to the neutral point of windings 4, 5, and 6 (from the perspective of a two-pole magnetic field in an air gap magnetic field) is marked as the eighth bridge arm;

[0031] Figure 3 Schematic diagram of two-phase connection of stator armature winding;

[0032] Figure 4 This is a schematic diagram of the double three-phase connection method of the stator armature winding;

[0033] Figure 5 Schematic diagram of the spatial electrical angle distribution of the winding axis when the stator armature winding adopts the two-phase connection method;

[0034] Figure 6 The figure is a schematic diagram of the spatial electrical angle distribution of the winding axis when the stator armature adopts the double three-phase connection method;

[0035] Figure 7 is the motor operation mode block diagram, where ω r1 is the base speed, ω r2 is the conversion speed from mode II to mode III. In this example, ω r1 <ω r2 And ω r2 =1.95ω r1 . DETAILED DESCRIPTION

[0036] In order to make the technical solutions and advantages of the present invention clearer and more complete, the present invention will be described in detail below with reference to the accompanying drawings and a specific embodiment. The specific embodiment described here is only used to illustrate the present invention and is not used to limit the present invention.

[0037] Specific embodiment 1 is a typical example of the surface-mounted permanent magnet synchronous motor system and driving method based on permanent magnet fractional harmonic pole-changing weak magnetic speed expansion according to the present invention. The motor system in the example includes a surface-mounted permanent magnet synchronous motor based on permanent magnet fractional harmonic pole-changing weak magnetic speed expansion and a frequency converter. The forward cross-sectional view of the stator and rotor cores of the motor in the example is shown in FIG. Figure 1As shown; the motor is a radial flux, circular rotating motor, and its structure includes a stator, a rotor and an air gap between the stator and the rotor. The stator includes a stator core 7 and a stator winding 9, and the rotor includes a rotor core 8, a permanent magnet 10 and a rotating shaft. The stator core of the motor is axially slotted on one side close to the rotor to form 36 stator slots and 36 stator teeth. The coil edges of the stator armature winding are placed in the stator slots. Six permanent magnets are distributed on the outer surface of the rotor core. The permanent magnet shape is designed by the existing method. The shape of the magnet is designed so that the permanent magnet air gap flux density generated by the permanent magnet contains a 6-pole magnetic field component and a 2-pole magnetic field component; from the perspective of the 2-pole magnetic field, the stator winding is arranged as a double three-phase winding with a 30-degree shift, and each set of three-phase windings is a symmetrical three-phase winding and two neutral points are led out; the inverter drive circuit in the inverter in the example includes eight parallel bridge arms, each bridge arm includes two forward series-connected switching tubes, and the six output terminals and two neutral point lead-out wires of the two sets of three-phase windings are respectively connected to the eight bridge arms, such as Figure 2 As shown; the driving method of the motor system in the example is to use the driving method of mode I in the speed range where the speed does not exceed the base speed, and the driving method of mode II in the speed range where the speed is higher than the base speed, and r2 The speed range adopts the driving method of mode III, such as Figure 7 As shown; when in mode III, the motor can further increase its speed by using the existing weak magnetic speed expansion method.

Claims

1. A permanent magnet synchronous motor system based on fractional harmonic magnetic field changing pole weakening speed expansion, characterized in that: The motor system is composed of a permanent magnet synchronous motor and a frequency converter; the motor includes a stator, a rotor and an air gap between the stators; the stator includes a stator core 7 and a stator armature winding 9; the rotor includes a rotor core 8, a permanent magnet 10 and a rotating shaft; the air gap magnetic field of the motor contains both a 2p pole number magnetic field and a 2p / 3 pole number magnetic field, where p is an integer greater than or equal to 3; from the perspective of the 2p / 3 pole number magnetic field of the motor air gap magnetic field, the stator armature winding is arranged as a double three-phase winding with a 30-degree shift, each set of three-phase windings is a 120-degree symmetrical winding, each set of three-phase windings is star-connected, and two neutral points are led out; the inverter drive circuit of the frequency converter includes eight parallel bridge arms, each bridge arm includes two forward series switching tubes, and the six output terminals of the two sets of three-phase windings and the lead-out wires of the two neutral points are respectively connected to the eight bridge arms.

2. The driving method of the permanent magnet synchronous motor system based on fractional harmonic magnetic field changing pole weakening speed expansion according to claim 1 is characterized in that: The driving method is divided into three modes, namely mode I, mode II and mode III. When the mode I driving method is adopted, the rotation speed of the motor does not exceed the base speed, the armature winding of the motor is connected as a two-phase winding with a 90-degree phase difference by the inverter drive circuit of the inverter, and the inverter drives and supplies power to the armature winding of the motor in a power supply mode of the two-phase winding with a 90-degree phase difference, and the fundamental frequency f of the power supply voltage is consistent with the mechanical speed ω of the motor rotor. r The relationship between r =2πf / p; When the mode II driving method is used, the speed of the motor is higher than the base speed, the armature winding of the motor is connected to a two-phase winding with a 90-degree phase difference by the inverter drive circuit of the inverter, and the inverter drives and supplies power to the motor winding in a 90-degree phase difference two-phase winding power supply mode. The fundamental frequency f of the supply voltage is related to the mechanical speed ω of the motor rotor. r The relationship between r =2πf / p, the motor adopts the existing field weakening method to increase the speed, and the armature winding current of the motor contains a field weakening component; when the mode III driving method is adopted, the speed of the motor is higher than the base speed, and the armature winding of the motor is connected by the inverter drive circuit of the inverter to form a dual three-phase winding with a 30-degree shift. The inverter drives and supplies power to the motor winding in a power supply mode of the dual three-phase winding with a 30-degree shift. The fundamental frequency f of the supply voltage is related to the mechanical speed ω of the motor rotor. r The relationship between r =6πf / p.

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