A method for unified zero-sequence signal injection into PWM in dual three-phase motor drive system

Abstract

The present invention discloses a method for unified zero-sequence signal injection PWM in a dual three-phase motor drive system. First, a mathematical model of the unified zero-sequence injection signal is established through a six-phase reference voltage. Then, the unified zero-sequence injection signal of two sets of three-phase inverters is determined using the undetermined coefficient method, and a modulation wave signal is generated in combination with the six-phase reference voltage. Finally, based on the carrier comparison PWM principle, a switching signal for controlling the action of the switching tube of the six-phase inverter is generated through the modulation wave signal.

Description

Technical Field

[0001] The present invention belongs to the technical field of motor control, and more particularly, relates to a method for uniformly injecting zero-sequence signals into PWM of a dual three-phase motor drive system. Background Art

[0002] Compared to traditional three-phase motor drive systems, multi-phase motor drive systems offer smoother output torque, high power output at low voltage, and improved fault tolerance. They are widely used in aerospace, ship propulsion, locomotive traction, and other fields. Compared to six-phase motors, dual three-phase motors offer a greater advantage due to their reduced torque ripple, making them particularly suitable for applications with limited supply voltage and high reliability requirements.

[0003] The most widely used PWM (pulse width modulation) algorithms for dual three-phase motors include space vector PWM (SVP) and carrier comparison PWM. SVP has become the most widely used modulation algorithm due to its greater control freedom. Four-dimensional SVPWM (space vector PWM) is a typical SVP algorithm. Four-dimensional SVPWM considers both the α-β subspace and the z1-z2 subspace when synthesizing the reference voltage, effectively suppressing low-frequency harmonic currents.

[0004] However, as the number of dual inverter bridge legs increases, the number of space vectors increases exponentially, significantly increasing the computational complexity of the four-dimensional SVPWM algorithm and requiring significant computational resources. In comparison, carrier comparison PWM is more intuitive and simple. Current research on carrier comparison PWM for dual three-phase motors with multiple inverters primarily focuses on single zero-sequence signal injection and dual zero-sequence signal injection. These methods fail to consider the coupling relationship between the two inverter voltage vectors, severely impacting modulation performance. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the existing technology and provide a method for unified zero-sequence signal injection into PWM of a dual three-phase motor drive system. For an asymmetric six-phase motor drive system driven by dual inverters, the method can effectively suppress the harmonic currents generated during the operation of the motor and improve the system reliability and performance.

[0006] To achieve the above-mentioned object of the invention, the present invention provides a method for uniformly injecting zero-sequence signals into PWM in a dual three-phase motor drive system, characterized by comprising the following steps:

[0007] (1) The voltage of the dual three-phase motor in the stationary coordinate system is transformed into the voltage in the natural coordinate system by the following coordinate transformation formula;

[0008]

[0009] Among them, ux is the six-phase reference voltage in the natural coordinate system, x=a,b,c,u,v,w; u α 、u β is the voltage of the α-β sub-plane in the stationary coordinate system; u z1 、u z2 is the voltage of the z1-z2 subplane in the stationary coordinate system;

[0010] The six-phase reference voltage in the natural coordinate system obtained according to formula (1) is expressed as:

[0011]

[0012] Where m is the modulation ratio, ω is the synchronous electrical angular frequency, and t represents time;

[0013] (2) Establish a unified mathematical model of zero-sequence injection signal:

[0014]

[0015] Among them, e i_inj is the unified zero-sequence injection signal of the two three-phase inverters, i = 1, 2, when i = 1, it represents the unified zero-sequence injection signal of the first three-phase inverter, when i = 2, it represents the unified zero-sequence injection signal of the second three-phase inverter; k is the amplitude correction coefficient; θ i is the phase angle offset coefficient of the two three-phase inverters, u max1 ,u min1 ,u max2 and u min2 Indicates the maximum and minimum reference voltages of the two three-phase inverters, specifically expressed as:

[0016]

[0017] (3) Determine the unified zero-sequence injection signal of the two three-phase inverters in the dual three-phase motor drive system;

[0018] (3.1) Determine the maximum and minimum reference voltages of the two three-phase inverters;

[0019]

[0020] (3.2) Given the four-dimensional SVPWM equivalent zero-sequence injection signal of the dual three-phase motor drive system:

[0021]

[0022] Among them, e 1_SVM ,e 2_SVM They are the equivalent zero-sequence injection signals of two sets of three-phase inverters in the four-dimensional SVPWM of the dual three-phase motor drive system;

[0023] (3.3), let:

[0024]

[0025] (3.4), calculate the amplitude correction coefficient k through equations (3), (5), (6), and (7):

[0026]

[0027] (3.5) is obtained from the phase angle relationship between the two sets of stator windings in the dual three-phase motor drive system:

[0028] θ1=θ2-π / 6 (9)

[0029] (3.6), the phase angle offset coefficients of the two three-phase inverters are calculated by equations (3), (5), (8), and (9):

[0030]

[0031] (3.7), Substituting equations (8) and (10) into equation (3), we can obtain the unified zero-sequence injection signal of the two three-phase inverters;

[0032]

[0033] (4) Generate a modulated wave signal;

[0034]

[0035] Among them, u x_inj (x=a,b,c,u,v,w) represents the generated six-phase modulated wave signal, e 1_inj ,e 2_inj They are the zero-sequence injection signals of the two sets of three-phase inverters respectively;

[0036] (5) Based on the carrier comparison PWM principle, a switching signal for controlling the operation of the three-phase inverter switch tube is generated according to the modulation wave signal generated in step (4).

[0037] The object of the invention of the present invention is achieved like this:

[0038] The present invention discloses a method for unified zero-sequence signal injection PWM for a dual three-phase motor drive system. The method first establishes a mathematical model of the unified zero-sequence injection signal using a six-phase reference voltage. The method of undetermined coefficients is then used to determine the unified zero-sequence injection signal for two sets of three-phase inverters. The signal is then combined with the six-phase reference voltage to generate a modulation wave signal. Finally, based on the carrier comparison PWM principle, the modulation wave signal is used to generate a switching signal for controlling the operation of the switching tubes of the six-phase inverter.

[0039] At the same time, the method for uniformly injecting zero-sequence signals into PWM in a dual three-phase motor drive system of the present invention also has the following beneficial effects:

[0040] (1) The unified zero-sequence signal injection method adopted by the present invention can avoid the tedious and complicated voltage vector selection and vector action time calculation process of four-dimensional SVPWM, effectively improve the calculation efficiency and avoid the waste of computing resources;

[0041] (2) On the basis of ensuring the modulation performance of the dual three-phase motor drive system, the present invention does not require sector division calculations and multiple sector partition calculations, which reduces the requirements of the dual three-phase motor drive system for hardware devices such as control chips and effectively improves the system operation performance;

[0042] (3) The code in the implementation process of the present invention is effectively simplified, which reduces the requirements for hardware devices such as control chips and can effectively reduce errors that occur during program execution. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a topological diagram of a dual three-phase AC motor system powered by a single DC power supply;

[0044] Figure 2 This is a flow chart of a method for uniformly injecting zero-sequence signals into PWM in a dual three-phase motor drive system according to the present invention;

[0045] Figure 3 This is a flow chart of realizing the six-phase switch signal action based on the present invention;

[0046] Figure 4 These are the experimental results of the phase current in the time domain and frequency domain at a stable speed achieved by the four-dimensional SVPWM of the dual three-phase motor drive system;

[0047] Figure 5 These are the experimental results of the phase current in the time domain and frequency domain at a stable speed achieved by the present invention under the same conditions;

[0048] Figure 6 The figure shows the THD comparison of the phase current under different speed conditions achieved by the present invention and the four-dimensional SVPWM. DETAILED DESCRIPTION

[0049] The following describes the specific embodiments of the present invention in conjunction with the accompanying drawings so that those skilled in the art can better understand the present invention. It should be noted that in the following description, when detailed descriptions of known functions and designs may dilute the main content of the present invention, such descriptions will be omitted here.

[0050] Example

[0051] In this embodiment, if Figure 1As shown, the DC power supply U dc The dual three-phase motor drive system includes two three-phase inverters, VSI1 and VSI2. Each inverter has three bridge arms, ABC and UVW, intersecting at midpoints N1 and N2, respectively. Point O is the DC neutral point. The phase angles of each winding in each set differ by 120°, and the phase angles between the two windings differ by 30°.

[0052] Next, we will describe in detail a method for uniformly injecting zero-sequence signals into PWM in a dual three-phase motor drive system according to the present invention. Figure 2 As shown, the specific steps include:

[0053] S1. Convert the voltage of the dual three-phase motor in the stationary coordinate system to the voltage in the natural coordinate system using the following coordinate transformation formula;

[0054]

[0055] Among them, u x is the six-phase reference voltage in the natural coordinate system, x=a,b,c,u,v,w; u α 、u β is the voltage of the α-β sub-plane in the stationary coordinate system; u z1 、u z2 is the voltage of the z1-z2 sub-plane in the stationary coordinate system; in this embodiment, u α 、u β 、u z1 、u z2 The phase currents of the dual three-phase motors obtained by sampling are transformed through four-dimensional current control.

[0056] The six-phase reference voltage in the natural coordinate system obtained according to formula (1) is expressed as:

[0057]

[0058] Wherein, m is the modulation ratio, which in this embodiment is defined as the ratio of the reference phase voltage amplitude to half of the DC bus voltage; ω is the synchronous electrical angular frequency, which is obtained by sampling the dual three-phase motor encoder; t represents time;

[0059] S2. Establish a unified mathematical model of zero-sequence injection signal:

[0060]

[0061] Among them, e i_inj is the unified zero-sequence injection signal of the two three-phase inverters, i = 1, 2, when i = 1, it represents the unified zero-sequence injection signal of the first three-phase inverter, when i = 2, it represents the unified zero-sequence injection signal of the second three-phase inverter; k is the amplitude correction coefficient; θi is the phase angle offset coefficient of the two three-phase inverters, u max1 ,u min1 ,u max2 and u min2 Indicates the maximum and minimum reference voltages of the two three-phase inverters, specifically expressed as:

[0062]

[0063] S3, determining a unified zero-sequence injection signal for two sets of three-phase inverters in a dual three-phase motor drive system;

[0064] S3.1. Determine the maximum and minimum reference voltages of the two three-phase inverters.

[0065]

[0066] S3.2, given the maximum four-vector modulation equivalent zero-sequence injection signal of the dual three-phase motor drive system:

[0067]

[0068] Among them, e 1_SVM ,e 2_SVM They are the equivalent zero-sequence injection signals of two sets of three-phase inverters when the dual three-phase motor drive system is modulated with maximum four-vector modulation;

[0069] S3.3. Order:

[0070]

[0071] S3.4. Calculate the amplitude correction coefficient k using equations (3), (5), (6), and (7):

[0072]

[0073] S3.5. From the phase angle relationship between the two sets of stator windings in the dual three-phase motor drive system, we can obtain:

[0074] θ1=θ2-π / 6 (9)

[0075] S3.6. Calculate the phase angle offset coefficients of the two three-phase inverters using equations (3), (5), (8), and (9):

[0076]

[0077] S3.7, Substitute equations (8) and (10) into equation (3) to obtain the unified zero-sequence injection signal of the two three-phase inverters;

[0078]

[0079] S4, generating a modulated wave signal;

[0080]

[0081] Among them, u x_inj (x=a,b,c,u,v,w) represents the generated six-phase modulated wave signal, e 1_inj ,e 2_inj They are the zero-sequence injection signals of the two sets of three-phase inverters respectively;

[0082] S5. Based on the carrier comparison PWM principle, a switching signal for controlling the operation of the switching tube of the three-phase inverter is generated according to the modulation wave signal generated in step S4.

[0083] Figure 3 The process of generating a modulation wave by a unified zero-sequence signal and then obtaining a switching action signal through CBPWM (carrier comparison PWM) is described. The phase current of the dual three-phase motor obtained by current sampling is transformed by four-dimensional current control to obtain the voltage u in the stationary coordinate system. α 、u β 、u z1 、u z2 After coordinate transformation, the six-phase reference voltage u in the natural coordinate system is obtained x (x=a,b,c,u,v,w), the zero-sequence injection signal e of the two three-phase inverters is obtained by unifying the zero-sequence signal calculation 1_inj ,e 2_inj , ABC three-phase reference voltage and zero sequence injection signal e 1_inj Take the sum to get the modulation wave signal u of the first three-phase winding a_inj 、u b_inj 、u c_inj , UVW three-phase reference voltage and zero sequence injection signal e 2_inj Take the sum to get the modulation wave signal u of the second set of three-phase windings u_inj 、u v_inj 、u w_inj , six-phase modulation wave signal u x_inj (x=a,b,c,u,v,w) and the carrier signal generate a six-phase switching signal S after CBPWM. x (x=a,b,c,u,v,w).

[0084] like Figure 4 As shown in the figure, the traditional four-dimensional SVPWM method is experimentally obtained when the speed n=1200 in steady state. Figure 4 The first figure shows the phase current i of phases A and U. a 、i u The waveform diagram in the time domain, A, U two-phase current i a 、i u The difference is 30°. Figure 4The second figure is the frequency spectrum of phase A current in the frequency domain when the traditional four-dimensional SVPWM method is in steady state and the speed n = 1200. It can be seen that the traditional four-dimensional SVPWM method can effectively suppress harmonic currents.

[0085] like Figure 5 As shown in the figure, the proposed zero-sequence signal injection CBPWM method is experimentally obtained when the speed n=1200 in the steady state. Figure 5 The first figure shows the phase current i of phases A and U. a 、i u The waveform diagram in the time domain, A, U two-phase current i a 、i u The difference is 30°. Figure 5 The second figure is the frequency spectrum of phase A current in the frequency domain when the speed n=1200 is used under the steady-state condition using the proposed zero-sequence signal injection CBPWM method. It can be seen that the proposed zero-sequence signal injection CBPWM method can also effectively suppress harmonic currents.

[0086] like Figure 6 As shown in the figure, the current data obtained from the experiment were calculated to obtain the total harmonic current distortion (THD) values ​​of the phase current of the traditional four-dimensional SVPWM method and the proposed zero-sequence signal injection CBPWM method in the speed range of 200rpm to 1200rpm. The experimental results show that the phase current THD values ​​of the traditional four-dimensional SVPWM method and the proposed zero-sequence signal injection CBPWM method are basically consistent in the full speed range.

[0087] The above results show that the derived unified zero-sequence signal injection carrier comparison PWM and the four-dimensional SVPWM method have consistent good performance, but the unified zero-sequence signal injection carrier comparison PWM has significant advantages in simplifying the computational complexity, and the implementation principle is simpler and more direct. The implementation process code is effectively streamlined, avoiding more errors and reducing the experimental requirements for hardware equipment such as control chips. At the same time, it has good scalability.

[0088] Although the above describes the illustrative specific embodiments of the present invention to facilitate understanding of the present invention by those skilled in the art, it should be clear that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, as long as various changes are within the spirit and scope of the present invention as defined and determined by the appended claims, these changes are obvious, and all inventions and creations using the concepts of the present invention are protected.

Claims

1. A method for uniformly injecting zero-sequence signals into PWM in a dual three-phase motor drive system, characterized in that: The following steps are involved: (1) The voltage of the dual three-phase motor in the stationary coordinate system is transformed into the voltage in the natural coordinate system by the following coordinate transformation formula; Among them, u x is the six-phase reference voltage in the natural coordinate system, x=a,b,c,u,v,w; u α 、u β is the voltage of the α-β sub-plane in the stationary coordinate system; u z1 、u z2 is the voltage of the z1-z2 subplane in the stationary coordinate system; The six-phase reference voltage in the natural coordinate system obtained according to formula (1) is expressed as: Where m is the modulation ratio, ω is the synchronous electrical angular frequency, and t represents time; (2) Establish a unified mathematical model of zero-sequence injection signal: Among them, e i_inj is the unified zero-sequence injection signal of the two three-phase inverters, i = 1, 2, when i = 1, it represents the unified zero-sequence injection signal of the first three-phase inverter, when i = 2, it represents the unified zero-sequence injection signal of the second three-phase inverter; k is the amplitude correction coefficient; θ i is the phase angle offset coefficient of the two three-phase inverters, u max1 ,u min1 ,u max2 and u min2 Indicates the maximum and minimum reference voltages of the two three-phase inverters, specifically expressed as: (3) Determine the unified zero-sequence injection signal of the two three-phase inverters in the dual three-phase motor drive system; (3.1) Determine the maximum and minimum reference voltages of the two three-phase inverters; (3.2) Given the four-dimensional SVPWM equivalent zero-sequence injection signal of the dual three-phase motor drive system: Among them, e 1_SVM ,e 2_SVM They are the equivalent zero-sequence injection signals of two sets of three-phase inverters in the four-dimensional SVPWM of the dual three-phase motor drive system; (3.3), let: (3.4), calculate the amplitude correction coefficient k through equations (3), (5), (6), and (7): (3.5) is obtained from the phase angle relationship between the two sets of stator windings in the dual three-phase motor drive system: (3.6), the phase angle offset coefficients of the two three-phase inverters are calculated by equations (3), (5), (8), and (9): (3.7), Substituting equations (8) and (10) into equation (3), we can obtain the unified zero-sequence injection signal of the two three-phase inverters; (4) Generate a modulated wave signal; Among them, u x_inj (x=a,b,c,u,v,w) represents the generated six-phase modulated wave signal, e 1_inj ,e 2_inj They are the zero-sequence injection signals of the two sets of three-phase inverters respectively; (5) Based on the carrier comparison PWM principle, a switching signal for controlling the operation of the three-phase inverter switch tube is generated according to the modulation wave signal generated in step (4).

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