Harmonic Suppression Method of Brushless Doubly-Fed Motor

Abstract

The invention discloses a method for suppressing harmonics of a brushless doubly-fed motor, which belongs to the technical field of brushless doubly-fed motors and comprises the following steps: S1: three sets of windings with pole pairs of P1, P2 and P3 are used to form a motor stator winding, and a composite span arrangement is used between each set of windings; S2: the positive directions of magnetic flux, current and voltage are selected; S3: the rotor winding is transformed to the stator side through a turns ratio, the number of turns of the stator and the rotor windings are equal, and the mutual inductance magnetic flux between each winding passes through an air gap; S4: the air gap magnetic field characteristics are analyzed to obtain an air gap magnetic field waveform; S5: a four-quadrant frequency converter is used to adjust the speed of the three sets of stator windings to obtain the harmonic magnetomotive force fluctuation amplitude; three sets of windings with adjustable spans are used to form the stator winding, and the spans between the power winding, the control winding and the pitch-adjusting winding and the spans between the coils of each winding are gradually shortened within a certain range so that the harmonic magnetic fields overlap with each other, the short-distance effect is increased, and the harmonic magnetomotive force intensity is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of brushless doubly-fed motors, and in particular to a method for suppressing harmonics of brushless doubly-fed motors. Background Art

[0002] Doubly-fed motor is also called AC excitation motor, which includes the motor itself and AC excitation automatic control system. The motor itself is a wound rotor induction motor or a specially designed brushless motor. Doubly-fed motor is the product of the combination of motor with power electronics technology and CNC technology, and is a high-tech product of mechatronics.

[0003] The two sets of stator windings of the brushless double-fed AC motor can be connected to the industrial frequency grid and the variable frequency power supply at the same time. It has the operating characteristics of synchronous motors and asynchronous motors. The required inverter capacity is small and the operation is reliable. Especially in the case of higher voltage levels, the low voltage of the variable frequency power supply can control the high voltage, and the energy saving effect is significant. Compared with the brushless double-fed motor, the advantages are: simpler structure, no brushes make the reliability stronger, and the control end can adjust the power factor. Under the corresponding control end power supply mode, the corresponding operation modes include: asynchronous operation mode, synchronous operation mode, subsynchronous mode and supersynchronous mode. Among them, subsynchronous and supersynchronous are collectively referred to as double-fed operation modes. The control end can control the operation mode of the motor, and its power only accounts for a part of the total power of the motor. It can absorb energy from the grid and return energy to the grid at the same time, which can effectively reduce the capacity of the speed control system. This makes the brushless double-fed motor have great application prospects in the speed control system. It also has excellent potential in other fields, including wind power, hydropower generation and variable speed constant frequency power generation.

[0004] However, the research process of high-voltage brushless doubly-fed motors is still limited by some technical problems. In the research of high-voltage brushless doubly-fed motors, high harmonic content and low conductor utilization are key factors affecting motor efficiency. The existing method of suppressing harmonics is to combine magnetic resistance with short-circuit cage bars and establish a mathematical model of BDFM in a rotating coordinate system to obtain the electromagnetic torque equation under this model. By collecting three-phase power current, designing a power harmonic torque current detection circuit, a power harmonic torque current tracking circuit, and a power harmonic torque current compensation circuit, the method of suppressing the torque pulsation existing in the operation of BDFM is obtained. The above method is difficult to suppress harmonics and is not a direct suppression. Summary of the invention

[0005] The object of the present invention is to provide a method for harmonic suppression of a brushless doubly-fed motor, which adopts three groups of windings with adjustable spans to form a stator winding, gradually shortens the spans between the power winding, the control winding and the adjustable span winding, and the spans between the coils of each winding within a certain range so that the harmonic magnetic fields overlap with each other, adds a short-distance effect caused by the change in relative position, reduces the intensity of the harmonic magnetomotive force, and solves the problems raised in the above-mentioned background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for suppressing harmonics of a brushless doubly-fed motor, comprising the following steps:

[0007] S1: The motor stator winding is composed of three sets of windings with pole pairs of P1, P2 and P3, where the pole pair of P1 corresponds to the power winding, the pole pair of P2 corresponds to the control winding, and the pole pair of P3 corresponds to the pitch-adjusting winding. A composite span arrangement is used between each set of windings;

[0008] S2: Select the positive direction of flux, current and voltage. The positive direction of stator voltage and current follows the convention of generator. Positive current produces positive flux. The position of the axis of the stator three-phase winding is fixed in space. The positive direction of rotor voltage and current follows the convention of generator. Positive current produces positive flux. The rotor axis is offset as the rotor rotates.

[0009] S3: The rotor winding is transformed to the stator side through the turns ratio, the number of turns of the stator and rotor windings are equal, and the mutual induction flux between each winding passes through the air gap;

[0010] S4: Analyze the air gap magnetic field characteristics of the brushless doubly-fed motor in the asynchronous operation mode, and use finite element calculation software to simulate and obtain the air gap magnetic field waveform;

[0011] S5: The power winding with a pole pair number of P1 is directly connected to the low-voltage power grid, and the control winding is connected to the four-quadrant inverter. The four-quadrant inverter is connected to the stator winding, power winding and pitch-adjusting winding through the industrial frequency power supply. According to the air gap magnetic field waveform in S4, the four-quadrant inverter is used to adjust the speed of the three sets of stator windings;

[0012] S6: According to the air gap magnetic field waveform in S4, the spacing between the three sets of stator windings is adjusted until the fluctuation amplitude of the harmonic magnetomotive force is less than 1 ampere / pole.

[0013] Furthermore, in S4, the air gap magnetic field characteristics of the cage rotor, wound rotor, and hybrid rotor brushless doubly-fed motors in the asynchronous operation mode are analyzed.

[0014] Furthermore, in S4, the air gap magnetic field characteristics of the reluctance rotor brushless doubly-fed motor in the asynchronous operation mode are analyzed.

[0015] Furthermore, the reluctance rotor brushless double-fed motor uses silicon steel sheet material to make the motor rotor.

[0016] Furthermore, the power winding coil is placed at the top of the stator slot, the control winding coil is placed at the bottom of the stator slot, the pitch-adjusting winding coil is between the power winding coil and the control winding coil, and the three stator winding coils are arranged separately.

[0017] Furthermore, the number of stator slots Z=72, the number of rotor slots Z=48, the number of power winding pole pairs P1=3, the number of control winding pole pairs P2=1, and the number of adjustable pitch winding pole pairs P3 is 1, 3 or 5.

[0018] Furthermore, the number of slots per phase in the power winding is 2, the span of the even slots is 10, and the span of the odd slots is 8; the number of slots per phase in the control winding is 6, the span of the even slots is 30, and the span of the odd slots is 28; the number of slots per phase in the pitch-adjustable winding is 2, the span of the even slots is 10, and the span of the odd slots is 8.

[0019] Furthermore, the number of slots per phase in the power winding is 2, the span of the even slots is 10, and the span of the odd slots is 8; the number of slots per phase in the control winding is 6, the span of the even slots is 30, and the span of the odd slots is 28; the number of slots per phase in the pitch-adjustable winding is 4, the span of the even slots is 20, and the span of the odd slots is 18.

[0020] Furthermore, the number of slots per phase in the power winding is 2, the span of the even slots is 10, and the span of the odd slots is 8; the number of slots per phase in the control winding is 6, the span of the even slots is 30, and the span of the odd slots is 28; the number of slots per phase in the pitch-adjustable winding is 6, the span of the even slots is 30, and the span of the odd slots is 28.

[0021] Furthermore, S1 includes the following specific steps:

[0022] S101: the pitch regulating winding corresponding to the pole pair number P3 is located between the power winding corresponding to the pole pair number P1 and the control winding corresponding to the pole pair number P2;

[0023] S102: The composite span portion of each set of windings uses the connection mode of forward series connection and reverse series connection;

[0024] S103: Two adjacent sets of stator windings with different pole pairs are indirectly coupled via the rotor.

[0025] Compared with the prior art, the beneficial effects of the present invention are as follows: the brushless doubly-fed motor harmonic suppression method proposed in the present invention adopts three groups of windings with adjustable spans to form the stator winding, wherein the adjustable span winding is located between the power winding and the control winding, and the spans between each set of windings with different or relative pole pairs are adjusted, and harmonics of different intensities are generated in the air gap between adjacent windings within different distances. The harmonic state of the brushless doubly-fed motor is intuitively observed based on the air gap magnetic field waveform, and the spans between the power winding, the control winding and the adjustable span winding and the spans between the coils of each winding are gradually shortened within a certain range so that the harmonic magnetic fields overlap with each other, thereby adding a short-distance effect caused by the change in relative position, reducing the intensity of the harmonic magnetomotive force, and thus suppressing the harmonics of the brushless doubly-fed motor. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 The stator winding and rotor winding connection diagram of the present invention;

[0027] Figure 2 The stator winding structure diagram of the present invention;

[0028] Figure 3 The stator winding and four-quadrant frequency converter connection diagram of the present invention;

[0029] Figure 4 A magnetic potential distribution diagram generated by a single coil current of the present invention;

[0030] Figure 5 is the air gap magnetic field waveform of the power winding in the first embodiment of the present invention;

[0031] Figure 6 is the air gap magnetic field waveform of the control winding in the first embodiment of the present invention;

[0032] Figure 7 is the air gap magnetic field waveform of the pitch regulating winding in the first embodiment of the present invention;

[0033] Figure 8 is the air gap magnetic field waveform of the control winding in the second embodiment of the present invention;

[0034] Fig. 9 is the air gap magnetic field waveform of the power winding in the third embodiment of the present invention;

[0035] Fig.10 is the air gap magnetic field waveform of the control winding in the third embodiment of the present invention;

[0036] Fig.11 The present invention is a flow chart of the method for harmonic suppression of a brushless doubly-fed motor.

[0037] In the figure: 1. stator winding; 11. power winding; 12. control winding; 13. pitch-adjustable winding; 2. rotor winding; 3. four-quadrant inverter. DETAILED DESCRIPTION

[0038] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. 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 creative work are within the scope of protection of the present invention. Embodiment 1

[0039] See also Figure 1-7 , a method for suppressing harmonics of a brushless doubly-fed motor comprises the following steps:

[0040] S1: Three sets of windings with pole pairs of P1, P2 and P3 are used to form the stator winding 1 of the motor, wherein the pole pair P1 corresponds to the power winding 11, the pole pair P2 corresponds to the control winding 12, and the pole pair P3 corresponds to the pitch-adjusting winding 13. A composite span arrangement is adopted between each set of windings; the power winding 11 coil is placed at the top of the stator slot, the control winding 12 coil is placed at the bottom of the stator slot, the pitch-adjusting winding 13 coil is between the power winding 11 coil and the control winding 12 coil, and the three stator winding 1 coils are arranged separately; the specific implementation steps of this step are as follows:

[0041] S101: the pitch regulating winding 13 corresponding to the pole pair number P3 is located between the power winding 11 corresponding to the pole pair number P1 and the control winding 12 corresponding to the pole pair number P2;

[0042] S102: The composite span portion of each set of windings uses the connection mode of forward series connection and reverse series connection;

[0043] S103: two adjacent sets of stator windings 1 with different pole pairs are indirectly coupled via the rotor;

[0044] S2: Select the positive direction of flux, current and voltage. The positive direction of stator voltage and current follows the convention of generator. Positive current produces positive flux. The position of the axis of the stator three-phase winding is fixed in space. The positive direction of rotor voltage and current follows the convention of generator. Positive current produces positive flux. The rotor axis is offset as the rotor rotates.

[0045] S3: The rotor winding 2 is transformed to the stator side through the turns ratio, the number of turns of the stator and rotor windings are equal, and the mutual induction flux between each winding passes through the air gap;

[0046] S4: Analyze the air gap magnetic field characteristics of the brushless doubly fed motor in the asynchronous operation mode, and use finite element calculation software to simulate and obtain the air gap magnetic field waveform; analyze the air gap magnetic field characteristics of the cage rotor, wound rotor, and hybrid rotor brushless doubly fed motor in the asynchronous operation mode, and analyze the air gap magnetic field characteristics of the reluctance rotor brushless doubly fed motor in the asynchronous operation mode. The reluctance rotor brushless doubly fed motor uses silicon steel sheet material to make the motor rotor;

[0047] S5: The power winding 11 with a pole pair number of P1 is directly connected to the low-voltage power grid, and the control winding 12 is connected to the four-quadrant inverter 3. According to the air gap magnetic field waveform in S4, the four-quadrant inverter 3 is used to adjust the speed of the three sets of stator windings 1;

[0048] S6: According to the air gap magnetic field waveform in S4, the spacing between the three sets of stator windings 1 is adjusted until the fluctuation amplitude of the harmonic magnetomotive force is less than 1 ampere / pole.

[0049] A brushless doubly-fed motor with stator slot number Z=72, rotor slot number Z=48, pole pair number P1=3 of power winding 11, pole pair number P2=1 of control winding 12, and pole pair number P3=3 of pitch-adjustable winding 13 is selected. The number of slots per phase of power winding 11 is 2, the span of even slots is 10, and the span of odd slots is 8. The number of slots per phase of control winding 12 is 6, the span of even slots is 30, and the span of odd slots is 28. The number of slots per phase of pitch-adjustable winding 13 is 2, the span of even slots is 10, and the span of odd slots is 8.

[0050] The distribution of the magnetic potential generated by a coil current along the circumference of the air gap, where 2θ p is the span of the coil (expressed in mechanical angle), the number of turns of each coil is N, the current passing through is ix, and for simplicity, the coordinate θ of the stator space is s (Mechanical angle) The origin is set on the axis of the coil. Among them, τ is the pole pitch, f x (θ s ) is the magnetic potential distribution function generated by a winding, then the magnetic potential generated by a phase winding current is:

[0051]

[0052] For the stator power winding 11, the harmonic order of the three-phase synthetic magnetic potential is:

[0053] ν p =(1±6k)p p (k=0, 1, 2, ...)

[0054] Among them, p p is the number of pole pairs of the power winding 11, k is the winding coefficient of the fundamental wave of the power winding 11, when k=0, ν p is the fundamental magnetic potential of the power winding 11, when ν pWhen ν is positive, the harmonic and fundamental wave have the same direction. p When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the power winding 11 is:

[0055]

[0056] where k wpν is the ν of the stator power winding 11 p Winding coefficients of subharmonics;

[0057] Similarly, for the stator control winding 12, the harmonic order of the three-phase synthetic magnetic potential is

[0058] ν c =(1±6k)p c (k=0, 1, 2, ...)

[0059] p c is the number of pole pairs of the control winding 12, k is the winding coefficient of the fundamental wave of the control winding 12, when k=0, ν c To control the fundamental magnetic potential of winding 12, when ν c When ν is positive, the harmonic and fundamental wave have the same direction. c When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the control winding 12 is:

[0060]

[0061] Where: k wcv is the ν of the stator control winding 12 c Winding coefficients of subharmonics;

[0062] For the stator pitch-adjustable winding 13, the harmonic order of the three-phase synthetic magnetic potential is

[0063] ν r =(1±6k)p i (k=0, 1, 2, ...)

[0064] p i is the number of pole pairs of the pitch-adjustable winding 13, k is the winding coefficient of the fundamental wave of the pitch-adjustable winding 13, when k=0, ν r is the fundamental magnetic potential of the pitch-adjusting winding 13, when ν r When ν is positive, the harmonic and fundamental wave have the same direction. r When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the pitch-adjusting winding 13 is:

[0065]

[0066] Where: k wrvis the ν of the stator pitch winding 13 r Winding factor of subharmonics. Embodiment 2

[0067] See also Figure 8 , a method for suppressing harmonics of a brushless doubly-fed motor comprises the following steps:

[0068] S1: Three sets of windings with pole pairs of P1, P2 and P3 are used to form the stator winding 1 of the motor, wherein the pole pair P1 corresponds to the power winding 11, the pole pair P2 corresponds to the control winding 12, and the pole pair P3 corresponds to the pitch-adjusting winding 13. A composite span arrangement is adopted between each set of windings; the power winding 11 coil is placed at the top of the stator slot, the control winding 12 coil is placed at the bottom of the stator slot, the pitch-adjusting winding 13 coil is between the power winding 11 coil and the control winding 12 coil, and the three stator winding 1 coils are arranged separately; the specific implementation steps of this step are as follows:

[0069] S101: the pitch regulating winding 13 corresponding to the pole pair number P3 is located between the power winding 11 corresponding to the pole pair number P1 and the control winding 12 corresponding to the pole pair number P2;

[0070] S102: The composite span portion of each set of windings uses the connection mode of forward series connection and reverse series connection;

[0071] S103: two adjacent sets of stator windings 1 with different pole pairs are indirectly coupled via the rotor;

[0072] S2: Select the positive direction of flux, current and voltage. The positive direction of stator voltage and current follows the convention of generator. Positive current produces positive flux. The position of the axis of the stator three-phase winding is fixed in space. The positive direction of rotor voltage and current follows the convention of generator. Positive current produces positive flux. The rotor axis is offset as the rotor rotates.

[0073] S3: The rotor winding 2 is transformed to the stator side through the turns ratio, the number of turns of the stator and rotor windings are equal, and the mutual induction flux between each winding passes through the air gap;

[0074] S4: Analyze the air gap magnetic field characteristics of the brushless doubly fed motor in the asynchronous operation mode, and use finite element calculation software to simulate and obtain the air gap magnetic field waveform; analyze the air gap magnetic field characteristics of the cage rotor, wound rotor, and hybrid rotor brushless doubly fed motor in the asynchronous operation mode, and analyze the air gap magnetic field characteristics of the reluctance rotor brushless doubly fed motor in the asynchronous operation mode. The reluctance rotor brushless doubly fed motor uses silicon steel sheet material to make the motor rotor;

[0075] S5: The power winding 11 with a pole pair number of P1 is directly connected to the low-voltage power grid, and the control winding 12 is connected to the four-quadrant inverter 3. According to the air gap magnetic field waveform in S4, the four-quadrant inverter 3 is used to adjust the speed of the three sets of stator windings 1;

[0076] S6: According to the air gap magnetic field waveform in S4, the spacing between the three sets of stator windings 1 is adjusted until the fluctuation amplitude of the harmonic magnetomotive force is less than 1 ampere / pole.

[0077] A brushless doubly-fed motor with stator slot number Z=72, rotor slot number Z=48, pole pair number P1=3 of power winding 11, pole pair number P2=1 of control winding 12, and pole pair number P3=3 of adjustable pitch winding 13 is selected. The number of slots per phase of power winding 11 is 2, the span of even slots is 10, and the span of odd slots is 8. The number of slots per phase of control winding 12 is 6, the span of even slots is 30, and the span of odd slots is 28. The number of slots per phase of adjustable pitch winding 13 is 4, the span of even slots is 20, and the span of odd slots is 18.

[0078] The distribution of the magnetic potential generated by a coil current along the circumference of the air gap, where 2θ p is the span of the coil (expressed in mechanical angle), the number of turns of each coil is N, the current passing through is ix, and for simplicity, the coordinate θ of the stator space is s (Mechanical angle) The origin is set on the axis of the coil. Among them, τ is the pole pitch, f x (θ s ) is the magnetic potential distribution function generated by a winding, then the magnetic potential generated by a phase winding current is:

[0079]

[0080] For the stator power winding 11, the harmonic order of the three-phase synthetic magnetic potential is:

[0081] ν p =(1±6k)p p (k=0, 1, 2, ...)

[0082] Among them, p p is the number of pole pairs of the power winding 11, k is the winding coefficient of the fundamental wave of the power winding 11, when k=0, ν p is the fundamental magnetic potential of the power winding 11, when ν p When ν is positive, the harmonic and fundamental wave have the same direction. p When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the power winding 11 is:

[0083]

[0084] where k wpν is the ν of the stator power winding 11 p Winding coefficients of subharmonics;

[0085] Similarly, for the stator control winding 12, the harmonic order of the three-phase synthetic magnetic potential is

[0086] ν c =(1±6k)p c (k=0, 1, 2, ...)

[0087] p c is the number of pole pairs of the control winding 12, k is the winding coefficient of the fundamental wave of the control winding 12, when k=0, ν c To control the fundamental magnetic potential of winding 12, when ν c When ν is positive, the harmonic and fundamental wave have the same direction. c When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the control winding 12 is:

[0088]

[0089] Where: k wcv is the ν of the stator control winding 12 c Winding coefficients of subharmonics;

[0090] For the stator pitch-adjustable winding 13, the harmonic order of the three-phase synthetic magnetic potential is

[0091] ν r =(1±6k)p i (k=0, 1, 2, ...)

[0092] p i is the number of pole pairs of the pitch-adjustable winding 13, k is the winding coefficient of the fundamental wave of the pitch-adjustable winding 13, when k=0, ν r is the fundamental magnetic potential of the pitch-adjusting winding 13, when ν r When ν is positive, the harmonic and fundamental wave have the same direction. r When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the pitch-adjusting winding 13 is:

[0093]

[0094] Where: k wrv is the ν of the stator pitch winding 13 r Winding factor of subharmonics. Embodiment 3

[0095] See also Figure 9-11 , a method for suppressing harmonics of a brushless doubly-fed motor comprises the following steps:

[0096] S1: Three sets of windings with pole pairs of P1, P2 and P3 are used to form the stator winding 1 of the motor, wherein the pole pair P1 corresponds to the power winding 11, the pole pair P2 corresponds to the control winding 12, and the pole pair P3 corresponds to the pitch-adjusting winding 13. A composite span arrangement is adopted between each set of windings; the power winding 11 coil is placed at the top of the stator slot, the control winding 12 coil is placed at the bottom of the stator slot, the pitch-adjusting winding 13 coil is between the power winding 11 coil and the control winding 12 coil, and the three stator winding 1 coils are arranged separately; the specific implementation steps of this step are as follows:

[0097] S101: the pitch regulating winding 13 corresponding to the pole pair number P3 is located between the power winding 11 corresponding to the pole pair number P1 and the control winding 12 corresponding to the pole pair number P2;

[0098] S102: The composite span portion of each set of windings uses the connection mode of forward series connection and reverse series connection;

[0099] S103: two adjacent sets of stator windings 1 with different pole pairs are indirectly coupled via the rotor;

[0100] S2: Select the positive direction of flux, current and voltage. The positive direction of stator voltage and current follows the convention of generator. Positive current produces positive flux. The position of the axis of the stator three-phase winding is fixed in space. The positive direction of rotor voltage and current follows the convention of generator. Positive current produces positive flux. The rotor axis is offset as the rotor rotates.

[0101] S3: The rotor winding 2 is transformed to the stator side through the turns ratio, the number of turns of the stator and rotor windings are equal, and the mutual induction flux between each winding passes through the air gap;

[0102] S4: Analyze the air gap magnetic field characteristics of the brushless doubly fed motor in the asynchronous operation mode, and use finite element calculation software to simulate and obtain the air gap magnetic field waveform; analyze the air gap magnetic field characteristics of the cage rotor, wound rotor, and hybrid rotor brushless doubly fed motor in the asynchronous operation mode, and analyze the air gap magnetic field characteristics of the reluctance rotor brushless doubly fed motor in the asynchronous operation mode. The reluctance rotor brushless doubly fed motor uses silicon steel sheet material to make the motor rotor;

[0103] S5: The power winding 11 with a pole pair number of P1 is directly connected to the low-voltage power grid, and the control winding 12 is connected to the four-quadrant inverter 3. According to the air gap magnetic field waveform in S4, the four-quadrant inverter 3 is used to adjust the speed of the three sets of stator windings 1;

[0104] S6: According to the air gap magnetic field waveform in S4, the spacing between the three sets of stator windings 1 is adjusted until the fluctuation amplitude of the harmonic magnetomotive force is less than 1 ampere / pole.

[0105] A brushless doubly-fed motor with stator slot number Z=72, rotor slot number Z=48, pole pair number P1=3 of power winding 11, pole pair number P2=1 of control winding 12, and pole pair number P3=3 of adjustable pitch winding 13 is selected. The number of slots per phase of power winding 11 is 2, the span of even slots is 10, and the span of odd slots is 8. The number of slots per phase of control winding 12 is 6, the span of even slots is 30, and the span of odd slots is 28. The number of slots per phase of adjustable pitch winding 13 is 6, the span of even slots is 30, and the span of odd slots is 28.

[0106] The distribution of the magnetic potential generated by a coil current along the circumference of the air gap, where 2θ p is the span of the coil (expressed in mechanical angle), the number of turns of each coil is N, the current passing through is ix, and for simplicity, the coordinate θ of the stator space is s (Mechanical angle) The origin is set on the axis of the coil. Among them, τ is the pole pitch, f x (θ s ) is the magnetic potential distribution function generated by a winding, then the magnetic potential generated by a phase winding current is:

[0107]

[0108] For the stator power winding 11, the harmonic order of the three-phase synthetic magnetic potential is:

[0109] ν p =(1±6k)p p (k=0, 1, 2, ...)

[0110] Among them, p p is the number of pole pairs of the power winding 11, k is the winding coefficient of the fundamental wave of the power winding 11, when k=0, ν p is the fundamental magnetic potential of the power winding 11, when ν p When ν is positive, the harmonic and fundamental wave have the same direction. p When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the power winding 11 is:

[0111]

[0112] where k wpν is the ν of the stator power winding 11 p Winding coefficients of subharmonics;

[0113] Similarly, for the stator control winding 12, the harmonic order of the three-phase synthetic magnetic potential is

[0114] ν c =(1±6k)p c (k=0, 1, 2, ...)

[0115] pc is the number of pole pairs of the control winding 12, k is the winding coefficient of the fundamental wave of the control winding 12, when k=0, ν c To control the fundamental magnetic potential of winding 12, when ν c When ν is positive, the harmonic and fundamental wave have the same direction. c When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the control winding 12 is:

[0116]

[0117] Where: k wcv is the ν of the stator control winding 12 c Winding coefficients of subharmonics;

[0118] For the stator pitch-adjustable winding 13, the harmonic order of the three-phase synthetic magnetic potential is

[0119] ν r =(1±6k)p i (k=0, 1, 2, ...)

[0120] p i is the number of pole pairs of the pitch-adjusting winding 13, k is the winding coefficient of the fundamental wave of the pitch-adjusting winding 13, when k=0, ν r is the fundamental magnetic potential of the pitch-adjusting winding 13, when ν r When ν is positive, the harmonic and fundamental wave have the same direction. r When it is negative, the harmonic and the fundamental wave are in opposite directions, so the amplitude of the harmonic magnetic potential generated by the current of the pitch-adjusting winding 13 is:

[0121]

[0122] Where: k wrv is the ν of the stator pitch winding 13 r Winding factor of subharmonics.

[0123] In the above-mentioned Embodiment 1, Embodiment 2 and Embodiment 3, the air gap magnetic field waveform is obtained by simulation using finite element calculation software, and the data is substituted into the above formula to calculate that the amplitude of the harmonic magnetic potential generated by the current of stator winding 1 and the amplitude of the harmonic magnetic potential generated by the current of power winding 11 are both less than 1, as shown in Table 1.

[0124] Table 1 Statistics of the amplitude of harmonic magnetic potential

[0125] In summary, the brushless doubly-fed motor harmonic suppression method proposed in the present invention adopts three groups of windings with adjustable spans to form the stator winding 1, wherein the adjustable span winding 13 is located between the power winding 11 and the control winding 12, and the spans between each set of windings with different or relative pole pairs are adjusted, and harmonics of different intensities are generated in the air gap between adjacent windings within different distances. The harmonic state of the brushless doubly-fed motor is intuitively observed based on the air gap magnetic field waveform, and the spans between the power winding 11, the control winding 12 and the adjustable span winding 13 and the spans between the coils of each winding are gradually shortened within a certain range so that the harmonic magnetic fields overlap with each other, thereby adding a short-distance effect caused by the change in relative position, reducing the intensity of the harmonic magnetomotive force, and thus suppressing the harmonics of the brushless doubly-fed motor.

[0126] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical scheme and inventive concept of the present invention within the technical scope disclosed by the present invention, which should be covered by the protection scope of the present invention.

Claims

1. A method for suppressing harmonics in a brushless doubly-fed motor, characterized in that: The following steps are involved: S1: Three sets of windings with pole pairs P1, P2 and P3 are used to form the stator winding (1) of the motor, wherein the pole pair P1 corresponds to the power winding (11), the pole pair P2 corresponds to the control winding (12), and the pole pair P3 corresponds to the pitch-adjusting winding (13), and a composite span arrangement is used between each set of windings; S2: Select the positive direction of flux, current and voltage. Positive current generates positive flux. The position of the stator three-phase winding axis in space is fixed. Positive current generates positive flux. The rotor axis is offset as the rotor rotates. S3: The rotor winding (2) is transformed to the stator side through the turns ratio, the number of turns of the stator and rotor windings is equal, and the mutual induction flux between each winding passes through the air gap; S4: Analyze the air gap magnetic field characteristics of the brushless doubly-fed motor in the asynchronous operation mode, and use finite element calculation software to simulate and obtain the air gap magnetic field waveform; S5: The power winding (11) with a pole pair number of P1 is directly connected to the low-voltage power grid, and the control winding (12) is connected to the four-quadrant inverter (3). According to the air gap magnetic field waveform in S4, the four-quadrant inverter (3) is used to adjust the speed of the three sets of stator windings (1); S6: According to the air gap magnetic field waveform in S4, the spacing between the three sets of stator windings (1) is adjusted until the harmonic magnetomotive force fluctuation amplitude is less than 1 ampere / pole.

2. A method for suppressing harmonics of a brushless doubly-fed motor as claimed in claim 1, characterized in that: In S4, the air gap magnetic field characteristics of cage rotor, wound rotor and hybrid rotor brushless doubly-fed machines in asynchronous operation mode are analyzed.

3. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: In S4, the air gap magnetic field characteristics of the reluctance rotor brushless doubly fed machine in the asynchronous operation mode are analyzed.

4. A method for suppressing harmonics of a brushless doubly-fed motor as claimed in claim 3, characterized in that: The reluctance rotor brushless doubly-fed motor uses silicon steel sheet material to make the motor rotor.

5. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: The power winding (11) coil is placed at the top of the stator slot, the control winding (12) coil is placed at the bottom of the stator slot, the pitch-adjusting winding (13) coil is between the power winding (11) coil and the control winding (12) coil, and the three stator winding (1) coils are arranged separately.

6. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: The number of stator slots Z=72, the number of rotor slots Z=48, the number of pole pairs of the power winding (11) P1=3, the number of pole pairs of the control winding (12) P2=1, and the number of pole pairs P3 of the pitch-adjustable winding (13) is 1, 3 or 5.

7. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: The number of slots per phase of the power winding (11) is 2, the span of the even slots is 10, and the span of the odd slots is 8. The number of slots per phase of the control winding (12) is 6, the span of the even slots is 30, and the span of the odd slots is 28. The number of slots per phase of the pitch-adjusting winding (13) is 2, the span of the even slots is 10, and the span of the odd slots is 8.

8. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: The number of slots per phase of the power winding (11) is 2, the span of the even slots is 10, and the span of the odd slots is 8. The number of slots per phase of the control winding (12) is 6, the span of the even slots is 30, and the span of the odd slots is 28. The number of slots per phase of the pitch-adjusting winding (13) is 4, the span of the even slots is 20, and the span of the odd slots is 18.

9. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: The power winding (11) has 2 slots per phase, the span of the even slots is 10, and the span of the odd slots is 8. The control winding (12) has 6 slots per phase, the span of the even slots is 30, and the span of the odd slots is 28. The adjustable pitch winding (13) has 6 slots per phase, the span of the even slots is 30, and the span of the odd slots is 28.

10. A method for suppressing harmonics in a brushless doubly-fed motor as claimed in claim 1, characterized in that: S1 includes the following specific steps: S101: The pitch regulating winding (13) corresponding to the pole pair number P3 is located between the power winding (11) corresponding to the pole pair number P1 and the control winding (12) corresponding to the pole pair number P2; S102: The composite span portion of each set of windings uses the connection mode of forward series connection and reverse series connection; S103: Two adjacent sets of stator windings (1) with different pole pairs are indirectly coupled via the rotor.

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