Calculation method of fault-tolerant current of five-phase permanent magnet motor considering second and fourth order torque fluctuations under open circuit

Abstract

The present invention relates to a method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering the second and fourth order torque fluctuations under an open circuit, which belongs to the field of multi-phase permanent magnet motors. The present invention is to improve the torque performance of a five-phase permanent magnet motor whose back electromotive force includes third and fifth order harmonics under an open circuit fault, so that the motor has the ability to operate smoothly under an open circuit fault. The method of the present invention only adjusts the phase of the non-open circuit phase current when an open circuit fault occurs, suppresses the second and fourth order torque fluctuation components related to the back electromotive force fundamental wave, third harmonic and fifth harmonic in the torque neutralization after the fault, so as to maintain the low torque fluctuation characteristics, and then realize stable fault-tolerant operation. The open circuit fault is divided into two types: a single-phase winding open circuit fault and an inverter switch tube open circuit fault. The limiting condition is that the zero-sequence current is not constrained. Under the premise of ensuring the torque output capacity of the motor, the present invention effectively reduces the torque fluctuation of the fault-tolerant operation of the five-phase motor when a single-phase winding open circuit fault and an inverter switch tube open circuit fault occur.

Description

Technical Field

[0001] The invention belongs to the field of multi-phase permanent magnet motors and relates to a fault-tolerant control technology under an open circuit fault. Background Art

[0002] Permanent magnet synchronous motors are widely used in modern vehicles, aerospace, high-end industrial equipment and other fields due to their significant advantages in efficiency and power density. Currently, three-phase permanent magnet synchronous motors are widely used, and their related supporting technologies are already very mature. However, the fault tolerance of traditional three-phase permanent magnet synchronous motors is poor, especially when the winding is open-circuited or short-circuited, the output torque characteristics of the motor deteriorate, or even fail to work, making it difficult to meet the stringent requirements of pure electric vehicles, aerospace, etc. for motor system reliability and fault tolerance. The phase redundancy characteristics of multi-phase permanent magnet motors give them better fault tolerance than traditional three-phase permanent magnet motors, and can meet the future development of pure electric vehicles and other fields for motor system reliability and fault tolerance.

[0003] Winding open circuit fault is a typical fault type in permanent magnet motors. When a winding open circuit fault occurs, the symmetry of the working winding in the motor is destroyed, and the magnetic field generated by the winding is no longer a circular rotating magnetic field, which makes the torque characteristics of the motor deteriorate, which is typically manifested as a decrease in the average torque and an increase in torque fluctuation. In order to enable multi-phase permanent magnet motors to work reliably under winding open circuit faults, on the one hand, special fault-tolerant designs are required, and on the other hand, corresponding open circuit fault-tolerant control strategies need to be developed to improve their torque output characteristics under faults. The advantages and disadvantages of the open circuit fault-tolerant control strategy are crucial to improving the torque output characteristics of multi-phase permanent magnet motors under winding open circuit faults. Summary of the invention

[0004] The purpose of the present invention is to improve the torque output characteristics of a five-phase permanent magnet motor under an open-circuit fault of a winding, and to provide a fault-tolerant current calculation method for a five-phase permanent magnet motor taking into account second and fourth torque fluctuations under an open circuit.

[0005] The method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering the second and fourth torque fluctuations under open circuit described in the present invention takes the A-phase winding open circuit as an example to illustrate the fault-tolerant control method of the five-phase permanent magnet motor when any one phase winding is open circuit as follows:

[0006] Adjust the input current of the remaining four-phase windings B, C, D, and E according to

[0007]

[0008] Work is performed to improve post-fault torque characteristics;

[0009] In the formula, i B1 、i C1 、i D1 、iE1 are the adjusted B, C, D, and E phase winding currents, I m1 is the amplitude of the B, C, D, and E phase winding current after adjustment, ω is the current angular frequency, θ1, θ2, θ3, and θ4 are the phases of the B, C, D, and E phase winding currents after adjustment, respectively;

[0010] Make the average torque term in the electromagnetic torque as large as possible; at the same time, constrain the quadratic fluctuation torque term and the quartic fluctuation torque term to zero, and then obtain the corresponding objective function P based on the Lagrange multiplier method to obtain θ1, θ2, θ3, θ4:

[0011]

[0012] Where λ1, λ2, λ3 and λ4 are Lagrangian operators; θ j The adjusted phase winding current phases j=1, 2, 3, 4 correspond to θ1, θ2, θ3, θ4 respectively.

[0013] Preferably, the process of obtaining θ1, θ2, θ3, and θ4 is:

[0014] When the third and fifth harmonics in the rotor magnetic field are considered, the expression of the no-load back electromotive force of the four-phase windings B, C, D, and E is:

[0015]

[0016] In the formula, e B 、e C 、e D and e E are the no-load back EMF of the four-phase windings B, C, D and E, respectively; E1, E3 and E5 are the amplitudes of the fundamental wave, third harmonic and fifth harmonic of the no-load back EMF, respectively;

[0017] When an open circuit fault occurs in the A-phase winding, the expression of the electromagnetic torque of the five-phase permanent magnet motor is:

[0018]

[0019] Where, T em is the electromagnetic torque, Ω is the mechanical angular velocity of the motor rotor, T0, T2 and T4 are the average torque term, the second-order fluctuation torque term and the fourth-order fluctuation torque term in the electromagnetic torque of the five-phase permanent magnet motor respectively;

[0020] In order to improve the torque output characteristics of the five-phase permanent magnet motor after a one-phase winding open circuit fault, it is necessary to make the average torque term in the electromagnetic torque as large as possible, while constraining the secondary fluctuation torque term and the fourth fluctuation torque term to zero. The corresponding constraint condition expression is:

[0021]

[0022] Based on the Lagrange multiplier method, the expression of the corresponding objective function P is obtained as follows:

[0023]

[0024] Where λ1, λ2, λ3 and λ4 are Lagrangian operators;

[0025] Then, the adjusted phases of the B, C, D, and E phase winding currents, namely θ1, θ2, θ3, and θ4, can be obtained.

[0026] Preferably, when any switch tube of a bridge arm where any phase winding of the five-phase permanent magnet motor is located is open-circuited, the phase winding is opened by controlling the conduction state of the switch tube of the bridge arm where the open switch tube is located.

[0027] Preferably, the method for converting the switch tube open circuit into the winding open circuit condition is: when a switch tube is open circuited, all the switch tube gate drive signals are blocked.

[0028] Preferably, the five-phase permanent magnet motor is powered by a five-phase full-bridge inverter, a five-phase six-bridge-arm inverter or other five-phase multi-bridge-arm inverter that allows the neutral point current to be non-zero.

[0029] Beneficial effects of the invention: The invention discloses a method for calculating the fault-tolerant current of a five-phase permanent magnet motor taking into account two or four torque fluctuations under open circuit. When an open circuit fault occurs in one phase, two adjacent phases, or two phases apart of the winding of the five-phase permanent magnet motor, the five-phase permanent magnet motor can output a relatively large torque after the fault while ensuring that the torque fluctuation is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 It is a schematic diagram of the five-phase full-bridge inverter topology;

[0031] Figure 2 It is a schematic diagram of the topology of a five-phase six-bridge-arm inverter;

[0032] Figure 3 It is a schematic diagram of closing other switch tubes in the same bridge arm to form a winding open circuit fault when a switch tube open circuit fault occurs in a five-phase full-bridge inverter. DETAILED DESCRIPTION

[0033] The following will describe the implementation methods of the present invention in detail with reference to the accompanying drawings and embodiments, so that the implementation process of how the present invention applies technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly. It should be noted that as long as there is no conflict, the various embodiments of the present invention and the various features in the embodiments can be combined with each other, and the technical solutions formed are all within the protection scope of the present invention.

[0034] The method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering second and fourth torque fluctuations under open circuit described in this embodiment is for the case where an open circuit fault occurs in any phase winding, wherein the open circuit fault includes one or a combination of the following situations: an open circuit of the winding, and an open circuit of the switch tube in the inverter bridge arm where the winding is located.

[0035] The five-phase permanent magnet motor is powered by a five-phase full-bridge inverter, a five-phase six-bridge-arm inverter or other five-phase multi-bridge-arm inverters that allow the neutral point current to be non-zero.

[0036] Specific implementation method: Figure 1 to Figure 2 This embodiment will be described.

[0037] Taking the A-phase winding open circuit as an example, the calculation method of the fault-tolerant current of the remaining normal windings of the five-phase permanent magnet motor when any phase winding is open circuit is as follows:

[0038] When an open-circuit fault occurs in the A-phase winding, the set values ​​of the input currents of the remaining B, C, D, and E four-phase windings are adjusted. The corresponding expression is:

[0039]

[0040] In the formula, i B1 、i C1 、i D1 、i E1 are the adjusted B, C, D, and E phase winding currents, I m1 is the amplitude of the B, C, D, and E phase winding current after adjustment, ω is the current angular frequency, θ1, θ2, θ3, and θ4 are the phases of the B, C, D, and E phase winding currents after adjustment, respectively;

[0041] When the third and fifth harmonics in the rotor magnetic field are considered, the expression of the no-load back electromotive force of the four-phase windings B, C, D, and E is:

[0042]

[0043] In the formula, e B 、e C 、e D and e E are the no-load back EMF of the four-phase windings B, C, D and E, respectively; E1, E3 and E5 are the amplitudes of the fundamental wave, third harmonic and fifth harmonic of the no-load back EMF, respectively;

[0044] When an open circuit fault occurs in the A-phase winding, the expression of the electromagnetic torque of the five-phase permanent magnet motor is:

[0045]

[0046] Where, T emis the electromagnetic torque, Ω is the mechanical angular velocity of the motor rotor, T0, T2 and T4 are the average torque term, the second-order fluctuation torque term and the fourth-order fluctuation torque term in the electromagnetic torque of the five-phase permanent magnet motor respectively;

[0047] In order to improve the torque output characteristics of the five-phase permanent magnet motor after a one-phase winding open circuit fault, it is necessary to make the average torque term in the electromagnetic torque as large as possible, while constraining the secondary fluctuation torque term and the fourth fluctuation torque term to zero. The corresponding constraint condition expression is:

[0048]

[0049] Based on the Lagrange multiplier method, the expression of the corresponding objective function P is obtained as follows:

[0050]

[0051] Where λ1, λ2, λ3 and λ4 are Lagrangian operators;

[0052] Then, the adjusted phases of the B, C, D, and E phase winding currents, namely θ1, θ2, θ3, and θ4, can be obtained.

[0053] Embodiment: A specific embodiment of a five-phase permanent magnet motor with an open-circuit fault in one phase winding is given below.

[0054] Taking a 10-slot 8-pole five-phase permanent magnet motor as an example, the output torque characteristics of the five-phase permanent magnet motor in a normal state, a one-phase winding open-circuit state, and after adopting the method of the present invention are given respectively, as shown in Table 1, to further illustrate the advantages of the method of the present invention.

[0055] Table 1 Comparison of torque characteristics under normal state and phase A open circuit fault state

[0056] Working status Normal state Phase A open circuit (not controlled) Phase A open circuit (fault-tolerant control) Output torque (N·m) 38 30.4 28.5 Torque ripple (%) 0.4 21.4 6.1

[0057] It can be seen that the five-phase permanent magnet motor fault-tolerant current calculation method considering the second and fourth torque fluctuations under open circuit described in the present invention can significantly reduce the torque fluctuation of the five-phase permanent magnet motor under a one-phase winding open circuit fault, thereby better meeting the system application requirements.

[0058] Specific implementation method 2: The following is combined Figure 3 This embodiment is described. This embodiment further describes the first embodiment. The open circuit fault covers one of the two situations, namely, the open circuit of the winding and the open circuit of the switch tube of the inverter bridge arm where the winding is located, or a combination thereof.

[0059] The technical solution provided in the first embodiment is for the case of an open-circuit winding fault. Therefore, when an open-circuit switch fault occurs in the inverter bridge arm where the winding is located, it is only necessary to convert this situation into an open-circuit winding fault type and then perform the control method described in the first embodiment. The specific solution is given below.

[0060] When any switch tube of a bridge arm where any phase winding of a five-phase permanent magnet motor is located is open-circuited, the phase winding is opened by controlling the conduction state of the switch tube of the bridge arm where the open switch tube is located.

[0061] See also Figure 3 , take the case where the switch tube of the inverter bridge arm where the A phase winding is located is open circuit as an example, assuming Figure 3 After the switch tube VT3 in the circuit is open-circuited, the gate drive signals of the switch tubes VT1, VT2 and VT4 are blocked, and the open-circuit fault of the switch tube where the winding is located is converted into a winding open-circuit fault, thereby reducing the difficulty of fault-tolerant control of subsequent open-circuit faults.

[0062] Although the embodiments disclosed in the present invention are as above, the above contents are only embodiments adopted for facilitating the understanding of the present invention and are not intended to limit the present invention. Any technician in the technical field to which the present invention belongs can make any modifications and changes in the form and details of the implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering second and fourth order torque fluctuations under open circuit, characterized in that: The method includes a method for calculating the open-circuit fault-tolerant current of the A-phase winding When an open-circuit fault occurs in the A-phase winding, the set values ​​of the input currents of the remaining B, C, D, and E four-phase windings are adjusted. The corresponding expression is: In the formula, i B1 、i C1 、i D1 、i E1 are the adjusted B, C, D, and E phase winding currents, I m1 is the amplitude of the B, C, D, and E phase winding current after adjustment, ω is the current angular frequency, θ1, θ2, θ3, and θ4 are the phases of the B, C, D, and E phase winding currents after adjustment, respectively; When the third and fifth harmonics in the rotor magnetic field are considered, the expression of the no-load back electromotive force of the four-phase windings B, C, D, and E is: In the formula, e B 、e C 、e D and e E are the no-load back EMF of the four-phase windings B, C, D and E, respectively; E1, E3 and E5 are the amplitudes of the fundamental wave, third harmonic and fifth harmonic of the no-load back EMF, respectively; When an open circuit fault occurs in the A-phase winding, the expression of the electromagnetic torque of the five-phase permanent magnet motor is: Where, T em is the electromagnetic torque, Ω is the mechanical angular velocity of the motor rotor, T0, T2 and T4 are the average torque term, the second-order fluctuation torque term and the fourth-order fluctuation torque term in the electromagnetic torque of the five-phase permanent magnet motor respectively; In order to improve the torque output characteristics of the five-phase permanent magnet motor after a one-phase winding open circuit fault, it is necessary to make the average torque term in the electromagnetic torque as large as possible, while constraining the secondary fluctuation torque term and the fourth fluctuation torque term to zero. The corresponding constraint condition expression is: Based on the Lagrange multiplier method, the expression of the corresponding objective function P is obtained as follows: Where λ1, λ2, λ3 and λ4 are Lagrangian operators; Then, the adjusted phases of the B, C, D, and E phase winding currents, namely θ1, θ2, θ3, and θ4, can be obtained.

2. The method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering second and fourth order torque fluctuations under open circuit according to claim 1 is characterized in that: When the inverter switch tube of the five-phase permanent magnet motor is open-circuited, the switch tube open circuit is converted into a winding open circuit condition by controlling the conduction state of the inverter switch tube.

3. The method for calculating the fault-tolerant current of a five-phase permanent magnet motor considering second and fourth order torque fluctuations under open circuit according to claim 1 or 2, characterized in that: The five-phase permanent magnet motor is powered by a five-phase full-bridge inverter, a five-phase six-bridge-arm inverter or other five-phase multi-bridge-arm inverters that allow the neutral point current to be non-zero.

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