Third harmonic suppression method suitable for twelve-phase open-winding permanent magnet motor

Abstract

The invention discloses a third harmonic suppression method suitable for a twelve-phase open-winding permanent magnet motor, and the method comprises the steps: collecting the three-phase current of four channels, summing the three-phase current of each channel, dividing the sum by 3, and calculating the third harmonic current of each channel as four AC quantities; the third harmonic currents of the four channels are negated and combined with the third harmonic currents to obtain eight symmetrical alternating quantities; the eight phases of alternating current quantities with the difference of 45 degrees are converted into eight direct current quantities in a rotating coordinate system through an eight-phase park transformation matrix, and dq-axis currents are adjusted to zero through a PI controller; the output quantity of the PI controller is calculated by using an eight-phase park inverse transformation matrix to obtain eight alternating-current quantities, the first four alternating-current quantities are respectively added with corresponding modulation waves of four channels, the modulation waves are output for SPWM modulation, accurate suppression of a third harmonic direct-current plane is realized, and the method is simple and easy to implement, high in universality and easy to popularize to harmonic suppression of any-phase motors.

Description

Technical Field

[0001] The invention belongs to the technical field of multi-phase motor harmonic control, and in particular relates to a third harmonic suppression method applicable to a twelve-phase open-winding permanent magnet motor. Background Art

[0002] The electric propulsion system composed of medium-voltage multi-phase open-winding motor and its matching midpoint clamped three-level 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 system. Compared with the traditional three-phase star motor system, the open-winding motor topology has a natural low-order harmonic path. The open-winding motor system is greatly affected by low-order harmonics, and the third harmonic has the most significant impact due to its small zero-sequence impedance and low harmonic frequency.

[0003] The zero-sequence equivalent circuit of an open-winding permanent magnet motor powered by a multi-phase H-bridge inverter is as follows: Figure 1 As shown, it can be seen that in the zero-sequence circuit, the zero-sequence voltage originates from the common-mode voltage generated by the inverter modulation and the harmonic back EMF caused by the permanent magnet flux harmonics inside the motor, among which the third harmonic back EMF is dominant. Considering the zero-sequence circuit, only the third harmonic back EMF generated by the permanent magnet is taken into account, and the mathematical model of the open-winding permanent magnet synchronous motor in the synchronous rotating coordinate system is:

[0004]

[0005] in,

[0006]

[0007] Where, e0 is the third harmonic back EMF; ψ f , 3f Respectively represent the fundamental and third harmonic flux linkage of the permanent magnet, ω e is the rotor electrical angular velocity; θ e is the rotor electrical angle.

[0008] Considering the interaction between zero-sequence current and third harmonic back EMF, the electromagnetic torque of the permanent magnet motor can be derived as shown in the following formula, where n p is the number of motor pole pairs.

[0009] T e =1.5n p [ψ f i q +(L d -L q )i d i q -6ψ 3f sin(3θ e )i0]

[0010] It can be seen from the above formula that since the zero-sequence current i0 has the third harmonic property, when the two triple frequency quantities sin(3θ) and i0 are multiplied, this term will become a six-frequency torque fluctuation component, and the magnitude of the torque fluctuation is proportional to the magnitude of the zero-sequence current and the third harmonic flux. Its existence will affect the performance of torque control, causing speed fluctuation and noise to increase.

[0011] In addition, according to the injected zero-sequence voltage U Z The midpoint potential control principle, the expression of the average value of the neutral current in a single carrier cycle after the existence of the third harmonic current is:

[0012]

[0013] In the above formula, sgn(·) is a sign function. It can be seen from the formula that the third zero-sequence current harmonic will form a neutral line current of the corresponding frequency, which will cause low-frequency fluctuations in the midpoint potential of the inverter. Therefore, it is necessary to effectively suppress the zero-sequence and other third harmonic currents.

[0014] On the one hand, due to the same phase of the third zero-sequence current harmonic, it cannot be converted to the DC plane like the 5th / 7th harmonics and suppressed by the proportional integral regulator (PI); on the other hand, the third zero-sequence current frequency is 3 times the fundamental frequency. If the rated frequency of the main motor is 50Hz, the corresponding third zero-sequence current harmonic is 150Hz, which has exceeded the current loop bandwidth limit of the large-capacity inverter (due to the junction temperature limit of the device, the switching frequency cannot be higher than 1kHz). The conventional quasi-proportional resonant (PR) controller is not effective and may even cause system instability. Conventional methods also fail to give full play to the multi-phase freedom characteristics of the motor system. Summary of the invention

[0015] The purpose of the present invention is to solve the above technical problems and provide a third harmonic suppression method suitable for a twelve-phase open-winding permanent magnet motor, which avoids the current loop bandwidth limitation of a large-capacity motor system and the instability problem caused by the phase mutation of the resonance point of the conventional quasi-proportional resonant PR controller.

[0016] To achieve the above object, the present invention provides a third harmonic suppression method applicable to a twelve-phase open-winding permanent magnet motor as follows:

[0017] 1) For the three-phase current i of the four channels abc1 ~i abc4 Collect the three-phase currents of each channel separately, sum them up and divide them by 3, and calculate the third harmonic current i of each channel. 01 、i 02 、i 03 、i 04 As four exchange quantities;

[0018] 2) Invert the third harmonic current of the four channels to obtain -i 01 、-i 02 、-i 03 、-i 04 , with i 01 、i 02 、i 03 、i 04 The third harmonic current combination results in eight symmetrical alternating currents, each with a phase difference of 45°;

[0019] 3) Eight alternating currents i with a phase difference of 45° 01 、i 02 、i 03 、i 04 、-i 01 、-i 02 、-i 03 、-i 04 The eight-phase park transformation matrix T8 is used to convert the eight DC quantities i in the rotating coordinate system d8 、i q8 andi z1 ~i z6 , the dq axis current is adjusted to zero using a PI controller;

[0020] 4) The output of the PI controller is transformed using the eight-phase park inverse transformation matrix Calculate and get eight alternating quantities u 01 ~u 08 , take the first four alternating quantities u 01 ~u 04 , respectively corresponding to the four channels of modulation wave u abc1 ~u abc4 Each corresponding addition outputs a modulated wave Perform SPWM modulation.

[0021] Furthermore, the eight-phase park transformation matrix T8 is:

[0022]

[0023] θ is the phase angle of the corresponding state quantity in the natural coordinate system.

[0024] Furthermore, the eight-phase park inverse transformation matrix for:

[0025]

[0026] θ is the phase angle of the corresponding state quantity in the natural coordinate system.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] 1) Simple control: The third harmonics of the four channels of the twelve-phase motor only need to be inverted to meet the 8 input quantities of the matrix, and after park transformation, the third harmonics can be suppressed by inverse transformation according to the output of the PI controller and compensation in the modulation wave;

[0029] 2) Strong versatility: The eight-dimensional park transformation and inverse transformation matrices are both expanded from the three-phase circuit coordinate transformation theory. By simply adjusting the transformation matrix accordingly, it can be easily applied to any phase motor harmonic suppression, which has strong versatility.

[0030] 3) Good suppression effect: Since the third harmonic is converted into DC after park transformation, the regulation effect of PI current controller is strong, and accurate suppression of the third harmonic can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The zero-sequence equivalent circuit diagram of an open-winding permanent magnet motor powered by a multi-phase H-bridge inverter;

[0032] Figure 2 It is the main circuit of the twelve-phase propulsion inverter of the present invention;

[0033] Figure 3 It is the main circuit of the twelve-phase open-winding motor winding of the present invention;

[0034] Figure 4 This is a block diagram of the third harmonic suppression closed-loop control of the twelve-phase permanent magnet motor of the present invention;

[0035] Figure 5 The present invention is a comparison diagram of the third harmonic suppression effect of the twelve-phase open-winding permanent magnet motor at a speed of 30r / min (Figures (a), (c), (e) and (g) are third harmonic suppression diagrams before optimization, and Figures (b), (d), (f) and (h) are third harmonic suppression diagrams after optimization);

[0036] Figure 6 The third harmonic suppression effect diagram of the twelve-phase open-winding permanent magnet motor of the present invention at a rotation speed of 150r / min (Figures (a), (c), (e) and (g) are the third harmonic suppression diagrams before optimization, and Figures (b), (d), (f) and (h) are the third harmonic suppression diagrams after optimization). DETAILED DESCRIPTION

[0037] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0038] The research object of the present invention is a twelve-phase open-winding permanent magnet motor, in which the twelve-phase inverter is defined as four channels, and each channel is composed of three three-level H-bridge inverter units with a common DC bus. Figure 2 The schematic diagram of the winding arrangement of the twelve-phase four-channel propulsion motor is shown in Figure 3As shown, the twelve-phase permanent magnet motor is composed of four three-phase open windings. The internal difference of each three-phase is 120° electrical angle, and the difference of each two three-phase windings is 15° spatial electrical angle. Taking the first channel as an example, a set of symmetrical three-phase current expressions is as follows:

[0039]

[0040] In the formula, i a1 、i b1 、i c1 Indicates the three-phase current of the first channel, I M Represents the three-phase fundamental current amplitude, and ω represents the angular velocity. Sum the three-phase currents of each channel and divide by 3 to calculate the third harmonic current i of each channel. 01 、i 02 、i 03 、i 04 As four AC quantities, the expressions of the third harmonic currents of the four channels are as follows:

[0041]

[0042] In the formula, I m is the third harmonic current amplitude, and ω represents the angular velocity.

[0043] Let θ = 3ωt, and simplify equation (2) to:

[0044]

[0045] The difference between the two three-phase windings of the twelve-phase open-winding permanent magnet motor is 15°, corresponding to the third harmonic current i 01 、i 02 、i 03 、i 04 The third harmonic currents of the four channels are reversed with a 45° electrical angle difference, and combined with the original third harmonic current to obtain eight symmetrical AC quantities i 01 、i 02 、i 03 、i 04 、-i 01 、-i 02 、-i 03 、-i 04 , the phase difference is 45°.

[0046] It can be seen from the above formula that the phase difference of the third harmonic current of each channel is only 45 degrees, which is three times the 15° difference between every two three-phase windings.

[0047] In order to suppress the third harmonic, the present invention performs park transformation on the third harmonic of each channel to obtain the DC value, and then accurately controls it. For multi-phase or even arbitrary phase park transformation, the derivation principle is generalized from the three-phase park transformation, and the coordinate transformation matrix of the generalized park transformation can be expressed as (instantaneous power remains unchanged):

[0048]

[0049] In the formula, n represents the number of phases in the multiphase system, C is the coordinate transformation matrix, and θ is the phase angle of the corresponding state quantity in the natural coordinate system. The matrix theory is explained as:

[0050] 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=1,2Kn-1. When n is an odd number, m=(n-1) / 2, and the last row is removed; when n is an even number, m=n / 2-1, and the last row is retained.

[0051] Obviously, the third harmonic of four channels alone does not meet the condition of n-phase current. 01 ~i 04 Negate the original i 01 ~i 04 and the inverted -i 01 ~-i 04 When the phases of the two signals differ by 45°, the multi-phase symmetrical sinusoidal signal condition can be met. Therefore, based on equation (4), the eight-phase park transformation matrix is ​​expressed as:

[0052]

[0053] For a sinusoidally symmetric time-varying signal, after it is converted from the natural coordinate system to the rotating coordinate system, only two components are not zero, and the general expression is:

[0054]

[0055] In the formula, p1 and p2 represent the non-zero components of the rotating coordinate system. Similarly, after the eight-phase Park transformation, only the dq axis output value is a DC quantity, and the rest are zero. At this time, the dq axis current is adjusted to zero using the PI controller, which can suppress the third harmonic. Then, the AC quantity obtained by the eight-phase park inverse transformation is taken and then compensated to each phase modulation wave. The eight-phase park inverse transformation matrix is ​​as follows:

[0056]

[0057] The eight alternating current quantities u are obtained by calculation 01 ~u08 , take the first four alternating quantities u 01 ~u 04 , compensated to the four channels corresponding modulation wave u abc1 ~u abc4 Let's take the first channel as an example:

[0058]

[0059] In the formula, The third harmonic of the current is suppressed by changing the third harmonic content in the modulation wave, and the same is true for the second, third and fourth channels. The closed-loop control block diagram of the third harmonic suppression of the twelve-phase permanent magnet motor of the present invention is shown in FIG. Figure 4 shown.

[0060] The present invention is applied to a twelve-phase open-winding permanent magnet synchronous motor. Figure 5 and Figure 6 The third harmonic and FFT analysis of the first channel current of the twelve-phase open-winding permanent magnet motor of the present invention at speeds of 30r / min and 150r / min are shown respectively. Through simulation comparison results, it can be found that after adding the third harmonic suppression algorithm, the third harmonic content of the current is significantly reduced regardless of whether the motor is running steadily at low speed or high speed, which proves that the effective value of the fundamental current of the motor under rated conditions can be increased. The algorithm can greatly improve the operating conditions of the permanent magnet motor.

[0061] The present invention is a third harmonic suppression method applicable to a twelve-phase open-winding permanent magnet motor. The control strategy can suppress the third harmonic of the current by controlling the third harmonic component of the modulation wave. The adjustment amount is calculated by the eight-phase park transformation matrix and the PI controller, and the versatility is strong. The present invention can meet the third harmonic suppression of the twelve-phase open-winding permanent magnet motor, and can be extended to any phase motor system by the same logic.

Claims

1. A third harmonic suppression method applicable to a twelve-phase open-winding permanent magnet motor, characterized in that: The inhibition method is as follows: 1) For the three-phase current i of the four channels abc1 ~i abc4 Collect the three-phase currents of each channel separately, sum them up and divide them by 3, and calculate the third harmonic current i of each channel. 01 、i 02 、i 03 、i 04 As four exchange quantities; 2) Invert the third harmonic current of the four channels to obtain -i 01 、-i 02 、-i 03 、-i 04 , with i 01 、i 02 、i 03 、i 04 The third harmonic current combination results in eight symmetrical alternating currents, each with a phase difference of 45°; 3) Eight alternating currents i with a phase difference of 45° 01 、i 02 、i 03 、i 04 、-i 01 、-i 02 、-i 03 、-i 04 The eight-phase park transformation matrix T8 is used to convert the eight DC quantities i in the rotating coordinate system d8 、i q8 andi z1 ~i z6 , the dq axis current is adjusted to zero using a PI controller; 4) The output of the PI controller is transformed using the eight-phase park inverse transformation matrix Calculate and get eight alternating quantities u 01 ~u 08 , take the first four alternating quantities u 01 ~u 04 , respectively corresponding to the four channels of modulation wave u abc1 ~u abc4 Each corresponding addition outputs a modulated wave Perform SPWM modulation.

2. The third harmonic suppression method for a twelve-phase open-winding permanent magnet motor according to claim 1 is characterized in that: The eight-phase park transformation matrix T8 is: θ is the phase angle of the corresponding state quantity in the natural coordinate system.

3. The third harmonic suppression method for a twelve-phase open-winding permanent magnet motor according to claim 1 is characterized in that: The eight-phase park inverse transformation matrix for: θ is the phase angle of the corresponding state quantity in the natural coordinate system.

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