Fifth and seventh harmonic suppression method suitable for twelve-phase motor

Abstract

The invention discloses a fifth and seventh harmonic suppression method suitable for a twelve-phase motor, and the method comprises the steps: respectively collecting four sets of three-phase currents of a twelve-phase propulsion system, and obtaining twelve AC quantities; two sets of three-phase windings with the phase difference of 30 degrees of the twelve-phase motor are used as a whole, and the five-order harmonic quantity and the seventh-order harmonic quantity with the phase difference of 30 degrees of the two sets of three-phase currents are converted through a six-phase park conversion matrix to obtain direct current quantity; and combining the output quantity obtained by the direct current quantity through the PI regulator with the direct current quantity of the fundamental wave plane, and using the six-phase park inverse transformation matrix to calculate the obtained alternating current quantity as the corresponding modulation wave of each channel. The method is simple and easy to implement, high in universality, good in fifth and seventh harmonic suppression effect and easy to popularize to other multi-phase motor system harmonic suppression occasions.

Description

Technical Field

[0001] The invention belongs to the technical field of multi-phase motor harmonic suppression, and in particular relates to a fifth and seventh harmonic suppression method applicable to a twelve-phase motor. Background Art

[0002] Compared with the traditional three-phase motor system, the multi-phase motor has more prominent advantages in high-power and high-reliability occasions. The electric propulsion system composed of the multi-phase open-winding propulsion motor and its matching multi-phase H-bridge inverter has the characteristics of simple main circuit topology, strong fault tolerance, small torque pulsation, and easy expansion of power capacity. It is the preferred solution for large-tonnage ship propulsion systems.

[0003] Whether it is a traditional three-phase motor or a multi-phase motor system, the motor winding current has abundant fifth and seventh harmonics due to the inverter PWM modulation dead zone, minimum pulse width limitation or non-ideal magnetic flux. On the one hand, current harmonics affect motor control and easily cause fundamental and harmonic control aliasing. For the three-level converter midpoint potential control or dead zone compensation that depends on the current direction, harmonics will cause control errors or failures; on the other hand, serious distortion of the motor winding current will directly affect the efficiency of the motor system, cause increased vibration, and even deteriorate the system electromagnetic capacitance. Therefore, it is necessary to optimize and suppress harmonics.

[0004] Compared with the traditional three-phase motor system, the redundancy of the phase number of the multi-phase motor system adds a new degree of freedom for the harmonic control of the multi-phase motor system. Due to the high frequency of the fifth and seventh harmonics, the rated frequency of the large-capacity permanent magnet motor promoted by the ship is 50Hz, and the corresponding fifth and seventh current harmonics are 250Hz or 350Hz, which has exceeded the current loop control bandwidth limit of the large-capacity inverter (the large-capacity inverter is limited by the junction temperature of the device, and the switching frequency is ≤1kHz), resulting in poor results of conventional harmonic suppression methods, and conventional methods have not fully utilized the multi-phase degree of freedom characteristics of the motor system. Summary of the invention

[0005] The purpose of the present invention is to solve the above technical problems and provide a fifth and seventh harmonic suppression method suitable for a twelve-phase motor to achieve motor harmonic current optimization control and improve the motor operation control performance.

[0006] To achieve the above object, the present invention provides a method for suppressing fifth and seventh harmonics of a twelve-phase motor:

[0007] 1) The four sets of three-phase currents of the twelve-phase propulsion system are collected separately to obtain twelve alternating current quantities;

[0008] 2) The two sets of three-phase windings of the twelve-phase motor with a phase difference of 30° are taken as a whole, and the fifth and seventh harmonic quantities of the two sets of three-phase currents with a phase difference of 30° are transformed by a six-phase park transformation matrix to obtain DC quantities;

[0009] 3) The output of the DC quantity obtained by the PI regulator is combined with the DC quantity of the fundamental wave plane, and the AC quantity calculated by the six-phase park inverse transformation matrix is ​​used as the corresponding modulation wave of each channel.

[0010] Furthermore, the six-phase park transformation matrix T j for:

[0011]

[0012] The values ​​of j are 5 and 7, corresponding to the transformation matrices of the fifth and seventh harmonic currents respectively.

[0013] Furthermore, the six-phase park inverse transformation matrix T j -1 for:

[0014]

[0015] The j values ​​are 5 and 7, corresponding to the transformation matrices of the fifth and seventh harmonic currents, respectively.

[0016] Furthermore, in step 2), the coordinate transformation of the two sets of three-phase winding currents with a 30° difference is performed using the transformation matrix of formula (4) to obtain:

[0017]

[0018] Furthermore, in step 2), the three-phase currents of the windings of the first and third channels are substituted into the formula (5) and the DC quantity of the three-channel harmonic plane is i dj ( _s i u ( 5m , _ i d ), s5 i u_ ( m 1. d i3) s );

[0019] Substituting the three-phase current of the winding of the second and fourth channels into the formula (5'), the DC value of the harmonic plane of the second and fourth channels is i qj_sum (i q5_sum (i q5_sum13 、i q5_sum24 ),i q7_sum (i q7_sum13 、i q7_sum24 )).

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] 1) Simple control. This method does not require any additional hardware circuits or offline testing. It is simple and easy to implement. After the two sets of three-phase currents of the multi-phase motor with a 30° difference are park transformed, the modulation waves of each channel are obtained by inverse transformation according to the output of the PI controller to suppress the fifth and seventh harmonics.

[0022] 2) Strong versatility. Considering the 30° phase difference between the two sets of motor windings, the proposed park transformation and inverse transformation matrices based on the fifth and seventh harmonic planes are both extended from the three-phase circuit coordinate transformation theory. It only needs to adjust the transformation matrix accordingly. The relevant conclusions can be extended to multiple sets of multi-phase motor systems and have certain universality.

[0023] 3) Good suppression effect. Since the fifth and seventh harmonics are converted into DC quantities (the fundamental wave with a phase difference of 30° is completely offset) after the proposed new six-dimensional park transformation, and the PI current controller has an obvious adjustment effect, the fifth and seventh harmonics of two sets of three-phase currents with a phase difference of 30° can be accurately suppressed, avoiding the problem that conventional control methods need to consider the difficulty in separating and accurately eliminating the harmonic components caused by the harmonic plane transformation of the current fundamental wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the main circuit of the multi-phase motor winding of the present invention;

[0025] Figure 2 It is a closed-loop control block diagram of fifth and seventh harmonic suppression of a multi-phase motor of the present invention;

[0026] Figure 3 1. It is a simulation effect diagram of the fifth and seventh harmonic suppression of the multi-phase motor of the present invention at a speed of 200 r / min (Figures (a), (c), (e) and (g) are diagrams of the fifth and seventh harmonic suppression before, and Figures (b), (d), (f) and (h) are diagrams of the fifth and seventh harmonic suppression after).

[0027] Figure 4 These are experimental effect diagrams of suppressing the fifth and seventh harmonics of the current of the multi-phase motor of the present invention at a rotation speed of 200 r / min (Figures (a), (c), (e) and (g) are diagrams of suppressing the fifth and seventh harmonics before, and Figures (b), (d), (f) and (h) are diagrams of suppressing the fifth and seventh harmonics after). DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0029] The multiphase propulsion system consisting of a twelve-phase inverter and a propulsion motor is taken as the research object. The schematic diagram of the matching twelve-phase motor winding is shown in Figure 1 As shown, it consists of four sets of three-phase windings with a phase difference of 15°.

[0030] The four sets of three-phase currents i of the twelve-phase propulsion system are respectively collected to obtain twelve alternating quantities. When h takes a, b, and c, it represents a set of three-phase currents, and when m takes 1, 2, 3, and 4, it represents the currents of channels one to four respectively; taking the first and third channels of two sets of three-phase currents with a 30° phase difference as an example, when the twelve-phase motor contains fifth and seventh harmonics, the three-phase winding currents of the first and third channels are shown in equations (1) and (2): hm The four sets of three-phase currents i of the twelve-phase propulsion system are respectively collected to obtain twelve alternating quantities. When h takes a, b, and c, it represents a set of three-phase currents, and when m takes 1, 2, 3, and 4, it represents the currents of channels one to four respectively; taking the first and third channels of two sets of three-phase currents with a 30° phase difference as an example, when the twelve-phase motor contains fifth and seventh harmonics, the three-phase winding currents of the first and third channels are shown in equations (1) and (2):

[0031]

[0032] I1 is the amplitude of the fundamental wave, I5 is the amplitude of the fifth harmonic, I7 is the amplitude of the seventh harmonic, ω is the electrical angular velocity, and t is the time.

[0033] In order to suppress the fifth and seventh harmonics, the first and third sets of three-phase windings with a 30° phase difference are taken as a whole, and the second and fourth sets of three-phase windings with a 30° phase difference are taken as a whole. The fifth and seventh harmonic quantities of the two sets of three-phase currents with a 30° phase difference are subjected to a six-phase park transformation matrix transformation to obtain direct current quantities, and then a proportional-integral PI regulator is used for control.

[0034] For the park transformation of multiple phases and even arbitrary phases, its derivation principle is extended from the three-phase park transformation, and the coordinate transformation matrix of its generalized park transformation can be expressed as:

[0035]

[0036] The theoretical explanation of this matrix is as follows:

[0037] If the state signal quantity of an n (n≥3)-phase circuit is expressed in the natural coordinate system as and it can be expressed in the rotating coordinate system as then y = C(θ)x, k = 1, 2…n - 1, u, w are positive integers, and u < w. Among them, α = 2π / n, which is the electrical angle difference between every two sets of windings, C(θ) is the coordinate transformation matrix, and θ is the phase angle of the corresponding state quantity in the natural coordinate system. The value of w is related to the number of phases of the motor. When n is odd, w = (n - 1) / 2, and the last row is removed; when n is even, w = n / 2 - 1, and the last row is retained. The last two rows correspond to the zero-sequence components. In addition, the coefficients in equation (3) are obtained with the power invariance as the constraint condition. When the amplitude invariance is used as the constraint condition, only the coefficients in equation (3) need to be modified to 2 / n.

[0038] Obviously, only for the fifth and seventh harmonic currents of a single-channel three-phase winding, it does not meet the conditions of n-phase currents. However, if the currents i of two sets of three-phase windings with a 30° phase difference abc1 and iabc3 Therefore, the present invention adopts a six-phase park transformation matrix based on the fifth and seventh harmonic planes, and performs synchronous coordinate transformation on the fifth and seventh planes for two sets of three-phase windings with a 30° difference to achieve the decoupling of the fifth and seventh harmonics, so that they are projected as DC quantities in their respective dq planes, and then controlled by a PI regulator. j As shown in formula (4):

[0039]

[0040] θ is the electrical angle of the dq rotation coordinate system.

[0041] The coordinate transformation of the two sets of three-phase winding currents with a 30° difference is carried out using the transformation matrix of formula (4):

[0042]

[0043]

[0044] The values ​​of j in equations (4) and (5) are 5 and 7, which correspond to the transformation matrices of the fifth and seventh harmonic currents, respectively. Substituting the currents in equations (1) and (2) into equations (5) and (5'), respectively, and calculating according to the matrix multiplication principle, we can obtain:

[0045]

[0046] In the above formula, i d_sum13 、i q_sum13 It refers to the fundamental wave plane d-axis and q-axis currents obtained by the six-phase park transformation matrix formula (4) of the winding phase currents of the first and third channels of the twelve-phase open-winding motor, i d5_sum13 、i q5_sum13 Refers to the fifth harmonic plane d, q axis current, i d7_sum13 、i q7_sum13 Refers to the seventh harmonic plane d and q axis current. d5_1 Refers to the d-axis current of the first set of winding current in the fifth harmonic plane, i q5_1 Refers to the q-axis current of the first set of winding current in the fifth harmonic plane, i d5_3 Refers to the d-axis current of the third winding current in the fifth harmonic plane, i q5_3 Refers to the q-axis current of the third winding current in the fifth harmonic plane; i d7_1 Refers to the d-axis current of the first set of winding current in the seventh harmonic plane, i q7_1 Refers to the q-axis current of the first set of winding current in the seventh harmonic plane, i d7_3 Refers to the d-axis current of the third winding current in the seventh harmonic plane, iq7_3 Refers to the q-axis current of the third winding current in the seventh harmonic plane; i d1_1 Refers to the d-axis current of the first set of winding current in the fundamental plane, i q1_1 Refers to the q-axis current of the first set of winding current in the fundamental plane, i d1_3 Refers to the d-axis current of the third winding current in the fundamental plane, i q1_3 It refers to the q-axis current of the third set of winding current on the fundamental plane; the 12-fold frequency component generated by the projection of the 5th (7th) harmonic current on the 7th (5th) harmonic plane can be suppressed by a low-pass filter and can be ignored here. Therefore, the above formula can be further simplified to obtain:

[0047]

[0048] From equations (6) to (8), it can be found that when the six-phase park transformation matrix T is used k After that, the fundamental component, fifth and seventh harmonic components and zero-sequence components in the winding are converted into DC quantities in their respective planes and then suppressed by the PI regulator.

[0049] The output of the PI controller is calculated by the six-phase park inverse transformation matrix to obtain the AC quantity as the corresponding modulation wave of each channel. Therefore, the fifth and seventh harmonics of the winding current can be suppressed by changing the fifth and seventh harmonic content in the modulation wave. Taking the first and third channels of two sets of three-phase windings with a mutual difference of 30° as an example, the six-phase park inverse transformation matrix T based on the fifth and seventh harmonic plane is given. j -1 As shown in formula (9):

[0050]

[0051] According to the above control strategy, since the twelve-phase motor can be regarded as four sets of three-phase windings shifted by 15°, the six-phase park transformation and inverse transformation matrices corresponding to the second and fourth channels only need to replace the above T j and T j -1 The phase angle θ in the matrix can be obtained by subtracting the phase difference of 15° between the sets. Therefore, the three-phase windings of the first and third channels (phase difference of 30°) can be regarded as a whole, and the three-phase windings of the second and fourth channels (phase difference of 30°) can be regarded as a whole, and the above strategies can be used to control them respectively. In theory, the fifth and seventh harmonic currents of the motor can be effectively suppressed. The closed-loop control block diagram of the fifth and seventh harmonic suppression of the multi-phase motor of the present invention is designed as shown in the figure. Figure 2 As shown in the figure, the winding current of the twelve-phase open-winding motor is divided into two groups: one with three channels and two with four channels, each with a difference of 30°. After the six-phase park transformation matrix (4), the DC quantity of each harmonic plane can be obtained as i dk_sum (i d5_sum (id5_sum13 、i d5_sum24 ),i d7_sum (i d7_sum13 、i d7_sum24 )) and i qk_sum (i q5_sum (i q5_sum13 、i q5_sum24 ),i q7_sum (i q7_sum13 、i q7_sum24 )). Then, the PI regulator is used to suppress the output of the regulator, which is u dj * and u qj * (j is 5 or 7), and then combined with the DC quantity u on the fundamental wave plane d * and u q * The modulation wave u can be obtained by inverse transformation matrix (9): abc1 、u abc2 、u abc3 、u abc4 , thereby achieving precise suppression of the fifth and seventh harmonics of the twelve-phase motor's two groups of four three-phase windings with a 30° difference.

[0052] The method proposed in the present invention is now applied to a twelve-phase motor system. Figure 3 and Figure 4 The simulation and experimental results of the fifth and seventh harmonic suppression of the multi-phase motor at a speed of 200r / min are shown respectively. Through the comparison of simulation and experimental results, it can be found that after adding the fifth and seventh harmonic suppression algorithm, the fifth and seventh harmonic contents of the current under the steady-state operation condition of the motor are significantly reduced, which proves that the effective value of the fundamental current of the motor under rated conditions can be improved. The algorithm can greatly improve the operating conditions of the multi-phase induction motor.

[0053] The present invention is a method for suppressing the fifth and seventh harmonics of a multi-phase motor. The control strategy can suppress the fifth and seventh harmonics of the current by changing the fifth and seventh harmonic components of the modulation wave. The adjustment amount is calculated by a six-phase park transformation matrix and a PI controller. The proposed method is simple to program and has strong versatility. The present invention can satisfy the fifth and seventh harmonic suppression of a multi-phase motor, and can be similarly extended to other multi-phase electrical equipment harmonic suppression occasions.

Claims

1. A method for suppressing fifth and seventh harmonics of a twelve-phase motor, characterized in that: The inhibition method is: 1) The four sets of three-phase currents of the twelve-phase propulsion system are collected separately to obtain twelve alternating current quantities; 2) The two sets of three-phase windings of the twelve-phase motor with a phase difference of 30° are taken as a whole, and the fifth and seventh harmonic quantities of the two sets of three-phase currents with a phase difference of 30° are transformed by a six-phase park transformation matrix to obtain DC quantities; 3) The output of the DC quantity obtained by the PI regulator is combined with the DC quantity of the fundamental wave plane, and the AC quantity calculated by the six-phase park inverse transformation matrix is ​​used as the corresponding modulation wave of each channel.

2. The fifth and seventh harmonic suppression method for a twelve-phase motor according to claim 1, characterized in that: The six-phase park transformation matrix T j for: The values ​​of j are 5 and 7, corresponding to the transformation matrices of the fifth and seventh harmonic currents respectively.

3. The fifth and seventh harmonic suppression method for a twelve-phase motor according to claim 1, characterized in that: The six-phase park inverse transformation matrix T j -1 for: The j values ​​are 5 and 7, corresponding to the transformation matrices of the fifth and seventh harmonic currents, respectively.

4. The fifth and seventh harmonic suppression method for a twelve-phase motor according to claim 2 is characterized in that: In step 2), the coordinate transformation of the two sets of three-phase winding currents with a 30° difference is performed using the transformation matrix of formula (4) to obtain:

5. The fifth and seventh harmonic suppression method for a twelve-phase motor according to claim 4 is characterized in that: In step 2), the three-phase currents of the windings of the first and third channels are substituted into the formula (5) and the DC quantity of the three-channel harmonic plane is i dj_sum (i d5_sum (i d5_sum13 、i d5_sum24 ),i d7_sum (i d7_sum13 、i d7_sum24 )); Substituting the three-phase current of the winding of the second and fourth channels into the formula (5'), the DC value of the harmonic plane of the second and fourth channels is i qj_sum (i q5_sum (i q5_sum13 、i q5_sum24 ),i q7_sum (i q7_sum13 、i q7_sum24 )).

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