A Space Vector Pulse Width Modulation Method for Multi-phase Motor Faults

Abstract

The present invention discloses a space vector pulse width modulation method for multi-phase motor faults, and belongs to the field of motor control technology. The present invention is to solve the problem that the existing fault-tolerant control method for motor phase failure cannot suppress the common mode voltage. The present invention adopts the principle of conservation of magnetic motive force before and after phase failure and takes the maximum torque output as a constraint to obtain a new space voltage vector diagram, selects ten non-zero voltage vectors with the largest amplitude and the smallest common mode voltage amplitude, and divides the space voltage vector diagram into ten sectors, performs sector judgment on the reference voltage vector, and determines the action order of each basic voltage vector with the minimum number of switch tubes for each action as the optimization goal, and calculates the action order and action time of the basic voltage vector; the present invention improves the operating performance of the multi-phase motor under fault conditions and effectively improves the reliability of the speed regulation system.

Description

Technical Field

[0001] The invention relates to the field of motor control, and in particular to a space vector pulse width modulation method for multi-phase motor faults. Background Art

[0002] Multiphase permanent magnet synchronous motor (PMSM) has been widely used in various industries in recent years due to its low voltage and high power, high efficiency, fault tolerance, low noise and other performance advantages. At the same time, with the development of microelectronics and modern power electronics technology, fault-tolerant technology has been widely used in many application fields with high reliability requirements. At present, for the fault-tolerant control strategy of multiphase PMSM, traditional fault-tolerant control methods are mostly hysteresis control and direct torque control (DTC), but these two methods do not consider the problem of common mode voltage, which will induce high-amplitude shaft voltage on the motor shaft and form shaft current, causing the motor bearing to be damaged quickly and shortening the service life of the motor. Therefore, it is very necessary to study the suppression of common mode voltage while operating multiphase PMSM in fault-tolerant state. Summary of the invention

[0003] In order to solve the above problems, the present invention provides a space vector pulse width modulation method for multi-phase motor faults, which effectively suppresses the adverse effects of common mode voltage on motor bearings during system fault-tolerant operation.

[0004] A space vector pulse width modulation method for multi-phase motor faults comprises the following steps:

[0005] S1. When a phase failure occurs in a multi-phase motor, a motor model after the phase failure is established, and a new type of space voltage vector vector diagram is established based on the conservation of magnetomotive force and the maximum output torque;

[0006] S2, selecting ten voltage vectors in the space voltage vector diagram as basic voltage vectors according to the fact that the voltage vector is large and the common mode voltage is small;

[0007] S3. Determine the sector where the reference voltage vector is located, determine the action sequence of each basic voltage vector and calculate the action time of the basic voltage vector based on the optimization target of the least number of switches per action.

[0008] Preferably, step S1 comprises:

[0009] Establish the current of the six-phase motor during normal operation;

[0010] Taking the maximum amplitude of each phase current as the objective function, the corrected remaining five-phase current is obtained;

[0011] A new type of space vector diagram after a one-phase open-phase fault occurs in the multi-phase motor is obtained according to the corrected current phase and amplitude.

[0012] Preferably, the following steps are included: the objective function is:

[0013]

[0014] Among them, a X and b X It represents the projection of the remaining five-phase current on the α-axis and β-axis.

[0015] Preferably, step S2 specifically includes:

[0016] In the space voltage vector diagram, ten voltage vectors with the largest amplitudes are selected as basic voltage vectors, and the ten basic voltage vectors constitute ten sectors.

[0017] Preferably, step S3 comprises:

[0018] Determine the sector where the reference voltage vector is located according to the polar coordinate angle value of the reference voltage;

[0019] Selecting two basic voltage vectors and a zero vector adjacent to the reference voltage vector to synthesize a reference vector;

[0020] Determine the action order of each basic voltage vector based on the optimization target of having the least number of switches per action;

[0021] Calculate the action time of each basic voltage vector.

[0022] As described above, the space vector pulse width modulation method for multi-phase motor fault provided by the present invention has the following effects:

[0023] 1. After the phase is cut off, the present invention uses the mathematical model of the phase-cut motor to change the current phase according to the conservation of magnetomotive force and the maximum torque constraint conditions. The principle of conservation of magnetomotive force before and after the phase is cut off is adopted and the maximum torque output is used as the constraint condition to obtain a new type of space voltage vector vector diagram. The magnetic field oriented control of the system is completed through sector allocation and selection of basic voltage vectors, and calculation of vector action time. While ensuring the torque, the torque pulsation caused by the open circuit fault of the stator winding can be greatly reduced.

[0024] 2. In the basic voltage vector selection link of the present invention, the basic voltage vector is selected based on the consideration condition of minimum common mode voltage, and the selected vectors are all common mode voltages of only U dc It effectively reduces the damage to the motor bearings caused by the shaft current generated by the common mode voltage, and can significantly improve the service life of the motor.

[0025] 3. The vector action sequence and time of this scheme are determined based on the optimization target after selecting the basic vector for the symmetrical six-phase motor in this article. It is aimed at calculating the new basic voltage vector after the six-phase motor is out of phase.

[0026] 4. The present invention adopts a vector pulse width modulation method to effectively solve the contradiction between dynamic response and switching frequency caused by traditional fault-tolerant control strategies, which are mostly hysteresis control or direct torque control. Under the premise of ensuring dynamic response, each power tube can operate once in each switching cycle to reduce switching losses.

[0027] 5. The present invention is suitable for rail transportation, wind power generation, aerospace, and other occasions with high reliability requirements, from daily life to national defense technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a topological diagram of a six-phase motor inverter with common neutral point symmetry according to the present invention;

[0029] Figure 2 This is a structural diagram of the stator winding of a six-phase permanent magnet synchronous motor with a common neutral point symmetry according to the present invention;

[0030] Figure 3 It is a spatial vector comparison diagram of the common neutral point symmetrical six-phase permanent magnet synchronous motor before and after one phase is disconnected;

[0031] Figure 4 It is a basic equivalent circuit diagram of the windings of the common neutral point symmetrical six-phase permanent magnet synchronous motor of the present invention after one phase is disconnected;

[0032] Figure 5 It is a new type of space voltage vector diagram of the common neutral point symmetrical six-phase permanent magnet synchronous motor after one phase is disconnected;

[0033] Figure 6 It is a sector division diagram of the space vector pulse width modulation method of the present invention;

[0034] Figure 7 It is a space vector sequence diagram of the space vector pulse width modulation method of the present invention;

[0035] Figure 8 It is a vector action time diagram of the space vector pulse width modulation method of the present invention;

[0036] Fig. 9 It is the simulation model block diagram of the space vector pulse width modulation method;

[0037] Fig.10 It is the modulation wave waveform diagram of the system in steady-state operation;

[0038] Fig.11 It is the starting speed waveform of the system in the fault-tolerant operation state;

[0039] Fig.12 It is a partial enlarged diagram of the starting speed waveform of the system in the fault-tolerant operating state;

[0040] Fig.13 This is the motor speed waveform when the load changes suddenly at a constant speed;

[0041] Fig.14 This is the motor torque waveform when the load changes suddenly at a constant speed; DETAILED DESCRIPTION

[0042] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0043] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0044] like Figure 1 As shown, a space vector pulse width modulation method for multi-phase motor fault includes the following steps:

[0045] S1. When a phase failure occurs in a multi-phase motor, a motor model after the phase failure is established, and a new type of space voltage vector vector diagram is established based on the conservation of magnetomotive force and the maximum output torque;

[0046] S11, establishing the current of the six-phase motor during normal operation;

[0047] When a single-phase fault occurs in a six-phase motor, this embodiment takes the E-phase fault as an example. Figure 2 As shown in the figure, it is a symmetrical six-phase PMSM stator winding structure diagram. In order to meet the principle that the motor running state remains unchanged before and after the phase is cut off, it is necessary to ensure that the motor synthetic magnetomotive force remains unchanged. The synthetic magnetomotive force of the six-phase PMSM can be expressed as:

[0048]

[0049] In the formula, is the electrical angle, and N is the number of turns of each phase winding. Taking phase B as an example, the winding function is The winding current of a six-phase motor during normal operation is:

[0050]

[0051] S12, taking the maximum amplitude of each phase current as the objective function, obtaining the corrected remaining five-phase current;

[0052] The maximum amplitude of each phase current is taken as the objective function:

[0053]

[0054] The optimization goal of the current is to make f 1 The conventional analytical method is difficult to solve it. We can use the minimum value calculation function fmincon provided by the MATLAB optimal toolbox to solve it. According to the principle that the synthetic magnetic potential before and after the circuit is unchanged, we can get:

[0055]

[0056] According to the trigonometric formula, the residual phase current can be expressed as:

[0057]

[0058] In the formula, a X and b X It represents the projection of the remaining five-phase current on the α-axis and the β-axis. Substituting the remaining five-phase current in the form of trigonometric functions and separating the sine term and cosine term, we can get:

[0059]

[0060] In addition to equation (6), considering that the six-phase motor windings use a common neutral point, the current of each phase must also meet the following constraints:

[0061]

[0062] f 1 As the objective function, the above formula is the constraint condition. When phase E is disconnected, the expression of the remaining five-phase current can be solved:

[0063]

[0064] Where: I m is the phase current amplitude when the motor is operating normally.

[0065] S13, obtaining a space vector diagram after a one-phase open-phase fault occurs in the multi-phase motor according to the corrected current phase and amplitude.

[0066] According to the corrected current phase and amplitude, the post-fault space vector diagram can be obtained. Figure 3The figure shows the space vector diagram before and after the fault. X (x=A,D,B,C,F) is the switching state of a bridge arm of the inverter. X =1, indicating that the upper tube is turned on and the lower tube is turned off; when S X = 0, indicating that the upper tube is turned off and the lower tube is turned on. Due to the open circuit of phase E, S E and is abandoned, and the six-phase inverter becomes a five-phase inverter. In this system, Figure 4 As shown, there are two basic equivalent circuits Figure 4 (a) and 4(b). 4(a) is to open the upper tubes of two bridge arms and the lower tubes of three bridge arms, or in the opposite way, the upper tubes of three bridge arms are opened and the lower tubes of two bridge arms are opened. 4(b) is to open the upper tube of one bridge arm and the lower tubes of four bridge arms, or in the opposite way. For a five-phase inverter, there are 2 5 = 32 different switch states, each of which is represented in binary format. For example, switch state V21 (10101) represents that the upper tubes of the three bridge arms A, B, and F are turned on, and the lower tubes of the two bridge arms D and C are turned on. Its equivalent circuit diagram belongs to one of the cases in 4 (a). The voltage vectors V corresponding to these 32 switch states s The value of can be derived as:

[0067]

[0068] Substituting the 32 switch states into equation (9) respectively, we can obtain the values ​​of each voltage vector as shown in Table 1. Plotting the voltage vector amplitude and phase on the vector diagram can yield the following: Figure 5 The space voltage vector vector diagram is shown.

[0069] Table 1: Voltage vector amplitude data table of each basic voltage;

[0070]

[0071]

[0072] S2, selecting ten voltage vectors in the space voltage vector diagram as basic voltage vectors according to the fact that the voltage vector is large and the common mode voltage is small;

[0073] Basic voltage vector selection and sector division such as Figure 6 As shown, the basic equivalent circuit diagrams of the ten basic voltage vectors selected all belong to the two cases in type 4 (a), that is, three bridge arm upper tubes are turned on or two bridge arm upper tubes are turned on. When three bridge arm upper tubes are turned on, the common mode voltage U NO It can be obtained from the first line of formula (10) that when the upper tubes of the two bridge arms are turned on, the common mode voltage U NOIt can be obtained from the second line of formula (10):

[0074]

[0075] Among them, N is the neutral point of the motor, O is the midpoint of the DC bus, so the common mode voltage U of the ten basic voltage vectors is NO for

[0076] S3. Determine the sector where the reference voltage vector is located, determine the action sequence of each basic voltage vector and calculate the action time of the basic voltage vector based on the optimization target of the least number of switches per action.

[0077] According to the reference voltage vector V ref The polar coordinate angle value of Judge V ref The sector where the When the reference voltage vector V ref When located in the Kth sector, two adjacent basic voltage vectors and the zero vector are selected to synthesize the reference vector. And with the goal of reducing device losses, a suitable switching sequence is selected in each sector to synthesize the target vector. Taking the first sector as an example, the sequence of the basic voltage vectors is: V31 (11111) - V25 (11001) - V24 (11000) - V0 (00000) - V24 (1100 0) - V25 (11001) - V31 (11111). The sequence of selecting the space vectors in each sector is as follows: Figure 7 As shown. When V ref When in the first sector, the basic voltage vector selects two adjacent non-zero voltage vectors, namely V25 and V24. Assume that the action time of vectors V25 and V24 is T 1 and T 2 , the system sampling time is T S , synthetic reference voltage vector V ref The specific action time is as follows Figure 8 As shown. According to the equilibrium equivalence principle, the following formula can be obtained:

[0078] V ref T s =V 25 T 1 +V 24 T 2 +T 0 (V 31 or V 0 ) (11)

[0079] T 1 +T 2 +T 0 =T S (12)

[0080] According to the triangle sine theorem, we can get:

[0081]

[0082] To synthesize the required reference voltage space vector, it is necessary to calculate the action time T of each vector 1 、T 2 、T 0 Substituting equations (11) and (12) into (13), we can obtain the action time of each vector:

[0083]

[0084] When V ref When located in other sectors, the action time of each vector is shown in Table 2.

[0085] Table 2: Data table of corresponding basic voltage vector action time in each sector;

[0086]

[0087] By looking up Table 1, we can know that: V 25 =0.6045·U dc , V 24 =0.5591·U dc Substituting it into equation (14), we get:

[0088]

[0089] In order to further illustrate the space vector pulse width modulation method applicable to multi-phase motor faults of the present application, this embodiment is verified in the following manner:

[0090] The parameters of the six-phase permanent magnet synchronous motor in this embodiment are: each phase winding resistance R = 1.4Ω, pole pair number P = 3, d-axis inductance L d =4.85mH, q-axis inductance L q =4.85mH, moment of inertia J = 15e -3 kg / m 2 In the simulation, the symmetrical six-phase PMSM fault operation is performed at speeds of 500 rpm and 1000 rpm, and at load torques of 10 N·M and 20 N·M.

[0091] Fig. 9 The figure shows a simulation model block diagram of a space vector pulse width modulation method suitable for multi-phase motor faults, including a reference voltage vector V ref As the input of the sector judgment module, vector action time calculation module, basic voltage vector selection module, and carrier comparison and generation module.

[0092] Fig.10 It is the modulation wave waveform of the system under steady-state operation, in which phase B is symmetrical with phase C, and phase D is symmetrical with phase F, so the figure takes the three waveforms of A, D, and B as an example. It can be seen from the picture that each phase is approximately a saddle wave, which verifies the feasibility and effectiveness of the design method described in the present invention, and at the same time illustrates that the present invention can improve the voltage utilization rate compared with the traditional SVPWM.

[0093] Fig.11 This is the waveform of the system's startup speed in the fault-tolerant operating state. The speed is first set to 500rpm and then to 1000rpm at 0.25s. According to the simulation waveform, it can be seen that the system reaches a steady state of 500rpm after 0.016s during the startup process, the maximum overshoot is 6rpm, and the system fluctuation after steady state is within 1rpm. Fig.12 The partial enlarged view of this part is shown. When the given speed is set to 1000rpm at 0.25s, the system dynamic response is also 0.016s, and then reaches a steady state of 1000rpm. It shows that the design method of the present invention has a small overshoot and an extremely fast response speed when the system is fault-tolerant.

[0094] Fig.13 The figure shows the motor speed waveform when the load changes suddenly at a constant speed. Fig.13 The figure shows the motor speed waveform when the load changes suddenly at a constant speed. When the motor is running stably at a constant speed of 1000rpm and a load torque of 10N·M, the load torque increases to 20N·M in 0.2s and decreases to 10N·M in 0.4s. Fig.13 It can be seen that when loaded, the system response time is 0.005s. Fig.14 It can be seen that when loading, the torque suddenly rises to 25N·M and stabilizes to 20N·M after 0.005s, and the torque response is fast. This shows that the space vector pulse width modulation method of the present invention has good robustness and can significantly reduce the torque pulsation caused by the stator winding open circuit fault while ensuring the torque.

[0095] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A space vector pulse width modulation method for multi-phase motor fault, characterized in that: The steps include: S1. When a phase failure occurs in a multi-phase motor, a motor model after the phase failure is established, and a new type of space voltage vector vector diagram is established based on the conservation of magnetomotive force and the maximum output torque, including the following steps: Establish the current of the six-phase motor during normal operation; The maximum amplitude of each phase current is used as the objective function to obtain the corrected remaining five-phase current; the objective function is: ； Among them, a X and b X It represents the projection of the remaining five-phase current on the α-axis and β-axis; A new type of space vector diagram after a phase failure of one phase of the multi-phase motor occurs is obtained according to the corrected current phase and amplitude; S2. According to the principle that the voltage vector is large while the common mode voltage is small, ten voltage vectors with the largest amplitudes in the space voltage vector vector diagram are selected as basic voltage vectors, and the ten basic voltage vectors constitute ten sectors; S3, determining the sector where the reference voltage vector is located, determining the action order of each basic voltage vector according to the optimization target of the least switch tubes in each action, and calculating the action time of the basic voltage vector, including the following steps: Determine the sector where the reference voltage vector is located according to the polar coordinate angle value of the reference voltage; Selecting two basic voltage vectors and a zero vector adjacent to the reference voltage vector to synthesize a reference vector; Determine the action order of each basic voltage vector based on the optimization target of having the least number of switches per action; Calculate the action time of each basic voltage vector.

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