Excitation loss fault-tolerant control method and system for doubly salient electro-magnetic motor

Abstract

The invention discloses an excitation loss fault-tolerant control method and system of an electro-magnetic doubly salient motor, and belongs to the field of motor control. On the basis of rotating speed current double closed-loop control, the control mode of a current loop is improved, two electric cycles are divided into six current conduction states, the conduction state of a power tube is obtained in combination with a converter topological structure after motor excitation loss, the direction of three-phase current is changed, and therefore the commutation process of the current is optimized, and the current conversion efficiency is improved. The amplitude of current change is reduced, the torque pulsation of the motor after excitation loss is reduced, and the torque current ratio is improved. According to the invention, the problem that the torque pulsation is large and the torque current ratio is low when the electro-magnetic doubly salient motor adopts a traditional field loss fault-tolerant control strategy is solved. By changing the conduction sequence of the power tubes, the purposes of suppressing the torque ripple of excitation loss operation of the electro-magnetic doubly salient pole and reducing copper consumption are achieved, the algorithm control is simple, and the portability is high.

Description

Technical Field

[0001] The invention specifically discloses a demagnetization fault-tolerant control method and system for an electrically excited double-salient-pole motor, belonging to the field of motor control. Background Art

[0002] The electrically excited doubly salient motor is a new type of special motor. When the excitation winding and converter of the electrically excited doubly salient motor fail, it will cause demagnetization. At this time, if the control method when the excitation is normal is still used, the electrically excited doubly salient motor drive system will not be able to operate normally, affecting its reliability.

[0003] At present, the research on the control strategy of demagnetization fault-tolerant operation of electrically excited doubly salient pole motors includes:

[0004] The Chinese invention patent document CN108123646A discloses an "electrically excited double-pole motor excitation fault-tolerant power generation system and control method thereof". This method proposes the use of a bridge converter before demagnetization to conduct research on demagnetization fault-tolerant power generation, and realizes the motor's demagnetization fault-tolerant power generation without changing the converter.

[0005] The Chinese invention patent document CN109450340A discloses an "electrically excited double-salient-pole motor demagnetization fault-tolerant power generation system and control method thereof". This method achieves demagnetization fault-tolerant power generation by using an H-bridge converter and a single-cycle angle position control strategy, but has the problems of a large number of switching tubes and large torque pulsation, large copper loss during demagnetization operation, and a low torque-to-current ratio.

[0006] Shi Hongjun et al. published "A fault-tolerant electric operation method for an electrically excited double-pole motor under demagnetization fault" (China, publication date: September 30, 2022, publication number: CN115133844A), which introduces a demagnetization fault-tolerant electric control strategy using a standard dual-cycle current given function. This strategy designs three-phase current given functions for different position intervals, but the control algorithm is relatively complex to implement. When the speed increases, the current tracking performance decreases, the torque pulsation increases, and the torque-to-current ratio decreases.

[0007] The "Demagnetization Fault-Tolerant Control Method for an Electromagnetic Doubly Salient Motor with Asymmetric Current Dual-Cycle" (China, Publication Date: September 8, 2023, Publication Number: CN116722790A) disclosed by Shi Hongjun et al. introduces a demagnetization fault-tolerant electric control strategy using asymmetric current dual-cycle control. The strategy designs an asymmetric distribution of three-phase current to reduce copper loss under demagnetization and improve the torque-to-current ratio. However, the control algorithm is also complex to implement, and the torque pulsation increases and the torque-to-current ratio decreases when the speed increases.

[0008] The above-mentioned electromagnetic double-salient-pole motor demagnetization fault-tolerant electric operation control strategies all adopt a control method in which the three-phase currents are given separately. The algorithm is relatively complex to implement and the applicable speed range is narrow. When the speed increases, the torque pulsation increases and the torque-to-current ratio decreases.

[0009] Yang Lan proposed the "DSEM System Design for Fault-Tolerant Operation under Demagnetization State" (Master's thesis in 2018). This design divides an electrical cycle into three current conduction states based on the bridge converter, and proposes a speed and current closed-loop demagnetization fault-tolerant control based on three-phase and three-states. However, this control strategy adopts a single-cycle current control method, and the torque pulsation is large.

[0010] In summary, the prior art still has the following problems:

[0011] 1. The algorithm is not portable and depends on specific motor parameters. When the parameters of the electrically excited double-salient-pole motor change, the algorithm needs to be redesigned.

[0012] 2. When hysteresis control is used, the switching frequency is not fixed, which will generate a large amount of current harmonics. Summary of the invention

[0013] The technical problem to be solved by the present invention is to reduce the torque pulsation of the electrically excited double-pole motor during demagnetization fault-tolerant operation without increasing the power tube, and to improve the torque-to-current ratio; the algorithm is easy to implement and has strong portability and is independent of specific motor parameters. In response to the above problems, the present invention proposes a demagnetization fault-tolerant control method and system for an electrically excited double-pole motor. Two electrical cycles are divided into six current conduction states, so that one of the phases can always provide a positive torque output during the commutation stage, thereby reducing the torque pulsation and improving the torque-to-current ratio. The proposed strategy avoids complex calculations, is simple to control, and has strong portability.

[0014] In order to achieve the purpose of the present invention, the present invention provides a demagnetization fault-tolerant control method for an electrically excited double-saliency motor. The circuit topology of the suppression method includes: dc , capacitor C, three-phase bridge converter, electrically excited doubly salient motor, asymmetric half-bridge converter and DC power supply U f ; The electrically excited double-pole motor comprises a three-phase armature winding and a single-phase excitation winding, and the three-phase armature winding and the single-phase excitation winding are coupled by mutual inductance;

[0015] The three-phase bridge converter includes three bridge arms, including a total of six power tubes with anti-connected diodes, any one of which is denoted as power tube Q ij , i is the phase sequence, i = a, b, c; j is the serial number, j = 1, 2; power tube Q i1 The collector and DC power supply U dcThe DC positive bus is connected to the emitter of the power tube Q i2 The collector and the corresponding phase of the three-phase armature winding, the power tube Q i2 The emitter is connected to the DC power supply U dc The capacitor is connected in parallel to the self-flowing power supply U dc and between the three-phase bridge converter;

[0016] The asymmetric half-bridge converter includes a power tube Q7, a power tube Q8, a diode D7 and a diode D8, wherein the collector of the power tube Q7 is connected to the DC power supply U f The positive electrode of the diode D7 is connected to the cathode of the diode D7, the emitter is connected to one end of the one-phase excitation winding and the cathode of the diode D8, and the anode of the diode D8 is connected to the DC power supply U f The cathode of the diode D7 is connected to the emitter of the power tube Q8, and the anode of the diode D7 is connected to the other end of the one-phase excitation winding and the collector of the power tube Q8;

[0017] The control method comprises: dividing two electrical cycles of the electromagnetic double-pole motor after demagnetization into six states according to the electrical angle θ of the electromagnetic double-pole motor, and realizing demagnetization fault-tolerant electric operation of the electromagnetic double-pole motor by controlling the conduction state of each power tube and the direction of the three-phase current in the six states;

[0018] The conduction state of each power tube and the direction of the three-phase current in the six states are as follows:

[0019] State 1: When θ∈[0°,120°), the A phase current i a is positive, the B phase current i b is negative, the C phase current i c is zero, the power tube Q a1 And power tube Q b2 Turn on, other power tubes are turned off;

[0020] State 2: When θ∈[120°,240°), the C phase current i c is positive, the B phase current i b is negative, the A phase current i a is zero, the power tube Q c1 And power tube Q b2 Turn on, other power tubes are turned off;

[0021] State 3: When θ∈[240°,360°), the C phase current i c is positive, the A phase current i a is negative, the B phase current i b is zero, the power tube Q c1 And power tube Q a2 Turn on, other power tubes are turned off;

[0022] State 4: When θ∈[360°,480°), the B phase current i b is positive, the A phase current i a is negative, the C phase current i c is zero, the power tube Q b1 And power tube Q a2 Turn on, other power tubes are turned off;

[0023] State 5: When θ∈[480°,600°), the B phase current i b is positive, the C phase current i c is negative, the A phase current i a is zero, the power tube Q b1 And power tube Q c2 Turn on, other power tubes are turned off;

[0024] State 6: When θ∈[600°,720°), the A phase current i a is positive, the C phase current i c is negative, the B phase current i b is zero, the power tube Q a1 And power tube Q c2 Turn on, other power tubes are turned off;

[0025] The electrical cycle is 360°. In each electrical cycle, the changes in the three-phase self-inductance of the three-phase armature winding are as follows:

[0026] When θ∈[0°,120°), the self-inductance of phase A is L a In the rising state, the self-inductance of phase B L b Remain unchanged, the self-inductance of phase C L c In a declining state;

[0027] When θ∈[120°,240°), the self-inductance of phase A is L a In a decreasing state, the self-inductance of phase B L b In the rising state, the self-inductance of phase C L c remain unchanged;

[0028] When θ∈[240°,360°), the self-inductance of phase A is L a Remain unchanged, the self-inductance of phase B L b In a decreasing state, the self-inductance of phase C L c In rising state.

[0029] Preferably, the direction of the three-phase current is determined as follows:

[0030] The formula of reluctance torque after demagnetization of the electrically excited double-pole motor is introduced as follows:

[0031]

[0032] Where, T r is the reluctance torque, θ m is the rotational mechanical angle;

[0033] The A phase current i a 、B phase current i b and C phase current i c Denoted as p-phase current i p , the A phase self-inductance L a 、B phase self-inductance L b and C phase self-inductance L c Denoted as p-phase self-inductance L p , p is the phase sequence, p = a, b, c; the three-phase windings of the electrically excited double-pole motor are connected at a common neutral point N, and its three-phase current satisfies the constraint condition i a +i b +i c =0; the direction of the three-phase current changes as follows:

[0034] When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from positive to negative, p From positive to zero;

[0035] When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from zero to positive p The direction remains unchanged;

[0036] When the p-phase self-inductance change rate dL p / dθ m When it is zero, the direction of the p-phase current is determined by the current directions of the other two phases according to the constraint that the sum of the three-phase currents is zero.

[0037] The present invention also provides a demagnetization fault-tolerant control system for an electrically excited double-salient-pole motor, the control system comprising a circuit topology, a drive signal module, a switch state selection module, a photoelectric encoder, a controller, a speed loop PI regulator, and a current loop PI regulator;

[0038] The photoelectric encoder is used to measure the rotor position signal of the electrically excited double-salient-pole motor, and the controller is used to calculate the motor speed according to the rotor position signal as the feedback speed n;

[0039] The speed loop PI regulator is used to adjust the speed according to the feedback speed n and the given motor speed n * The difference between the three-phase reference current amplitude signal I p ;

[0040] The current loop PI regulator is used to convert the three-phase reference current amplitude signal I pRespectively with the three-phase current amplitude signal i p Compare and output PWM signals to the drive signal module to adjust the amplitude of the three-phase current;

[0041] The switch state selection module is used to obtain the power tube on and off signal according to the rotor position signal;

[0042] The driving signal module is used to adjust the amplitude of the three-phase current according to the PWM signal; the driving signal module is also used to control the on and off of each power tube according to the power tube on and off signal.

[0043] Preferably, the control process is as follows:

[0044] Step 1: The electro-magnetic double-salient-pole motor measures the rotor position signal through a photoelectric encoder, and calculates the motor speed through a controller as the feedback speed n; the motor speed n is given * The difference between the speed n and the feedback speed n is output by the speed loop PI regulator as the three-phase reference current amplitude signal I p ; Three-phase reference current amplitude signal I p Respectively with the three-phase current amplitude signal i p In comparison, the PWM signal is output to the drive signal module through the current loop PI regulator;

[0045] Step 2: When the electrically excited double-salient-pole motor has a demagnetization fault, the motor is switched to the switch state selection module after demagnetization. The switch state selection module obtains a power tube on-off signal through a rotor position signal and outputs the signal to the drive signal module.

[0046] Step 3: The drive signal module performs a logic operation on the power tube on / off signal obtained by the switch state selection module and the PWM signal output by the current loop PI regulator, and finally determines the on / off of each power tube.

[0047] The beneficial effects of the present invention are as follows:

[0048] (1) The two electrical cycles are divided into six current conduction states, which optimizes the current commutation process. This allows one of the three-phase currents to always provide positive torque output during the commutation process, thus avoiding the generation of large negative torque, reducing torque pulsation, and improving the torque-to-current ratio.

[0049] (2) By changing the conduction state of the switch tube, the motor can achieve demagnetization fault-tolerant operation, avoiding the complex mathematical calculation process that exists when using the current given function. The algorithm control is simple and has strong portability.

[0050] (3) The on and off of the power tube is controlled by a PWM signal, and the switching frequency of the power tube is fixed, thereby reducing the harmonics caused by current chopping.

[0051] (4) The output of the speed loop PI regulator is used as the amplitude of the reference current, eliminating the intermediate torque closed loop and the need for a torque observer, which reduces the complexity of the algorithm and makes the algorithm easy to apply in practice. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 A control diagram for applying the control method of the present invention.

[0053] Figure 2 The current, each phase torque and total torque simulation waveforms obtained in the simulation of the present invention. DETAILED DESCRIPTION

[0054] The present invention is further described in detail below in conjunction with the accompanying drawings.

[0055] Figure 1 For the control diagram of the control method of the present invention, Figure 1 It can be seen that the circuit topology applying this suppression method includes giving the DC power supply U dc , capacitor C, three-phase bridge converter, electrically excited doubly salient motor, asymmetric half-bridge converter and DC power supply U f The electrically excited double-salient-pole motor comprises a three-phase armature winding and a single-phase excitation winding, and the three-phase armature winding and the single-phase excitation winding are coupled by mutual inductance.

[0056] The three-phase bridge converter includes three bridge arms, including a total of six power tubes with anti-connected diodes, any one of which is denoted as power tube Q ij , i is the phase sequence, i = a, b, c; j is the serial number, j = 1, 2. Power tube Q i1 The collector of the DC power supply U dc The DC positive bus is connected to the emitter of the power tube Q i2 The collector and the i-phase of the three-phase armature winding, the power tube Q i2 The emitter is connected to the DC power supply U dc The capacitor is connected in parallel to the self-flowing power supply U dc and between the three-phase bridge converter.

[0057] The asymmetric half-bridge converter includes a power tube Q7, a power tube Q8, a diode D7 and a diode D8, wherein the collector of the power tube Q7 is connected to the DC power supply U f The positive electrode of the diode D7 is connected to the cathode of the diode D7, the emitter is connected to one end of the one-phase excitation winding and the cathode of the diode D8, and the anode of the diode D8 is connected to the DC power supply U f The cathode of the diode D7 is connected to the emitter of the power tube Q8, and the anode of the diode D7 is connected to the other end of the one-phase excitation winding and the collector of the power tube Q8.

[0058] exist Figure 1 Up, Da1 , D a2 , D b1 , D b2 , Q c1 and Q c2 The six power tubes Q ij Anti-parallel diodes.

[0059] Depend on Figure 1 It can be seen that the present invention provides a demagnetization fault-tolerant control method for an electromagnetic double-pole motor. According to the electrical angle θ of the electromagnetic double-pole motor, the two electrical cycles of the electromagnetic double-pole motor after demagnetization are divided into six states. By controlling the conduction state of each power tube and the direction of the three-phase current in the six states, the demagnetization fault-tolerant electric operation of the electromagnetic double-pole motor is realized.

[0060] The conduction state of each power tube and the direction of the three-phase current in the six states are as follows:

[0061] State 1: When θ∈[0°,120°), the A phase current i a is positive, the B phase current i b is negative, the C phase current i c is zero, the power tube Q a1 And power tube Q b1 Turn on, other power tubes are turned off;

[0062] State 2: When θ∈[120°,240°), the C phase current i c is positive, the B phase current i b is negative, the A phase current i a is zero, the power tube Q c1 And power tube Q b1 Turn on, other power tubes are turned off;

[0063] State 3: When θ∈[240°,360°), the C phase current i c is positive, the A phase current i a is negative, the B phase current i b is zero, the power tube Q c1 And power tube Q a2 Turn on, other power tubes are turned off;

[0064] State 4: When θ∈[360°,480°), the B phase current i b is positive, the A phase current i a is negative, the C phase current i c is zero, the power tube Q b1 And power tube Q a2 Turn on, other power tubes are turned off;

[0065] State 5: When θ∈[480°,600°), the B phase current ib is positive, the C phase current i c is negative, the A phase current i a is zero, the power tube Q b1 And power tube Q c2 Turn on, other power tubes are turned off;

[0066] State 6: When θ∈[600°,720°), the A phase current i a is positive, the C phase current i c is negative, the B phase current i b is zero, the power tube Q a1 And power tube Q c2 Turn on, other power tubes are turned off;

[0067] The electrical cycle is 360°. In each electrical cycle, the changes in the three-phase self-inductance of the three-phase armature winding are as follows:

[0068] When θ∈[0°,120°), the self-inductance of phase A is L a In the rising state, the self-inductance of phase B L b remains unchanged, and the self-inductance Lc of phase C is decreasing;

[0069] When θ∈[120°,240°), the self-inductance of phase A is L a In a decreasing state, the self-inductance of phase B L b It is in an ascending state, and the self-inductance Lc of phase C remains unchanged;

[0070] When θ∈[240°,360°), the self-inductance of phase A is L a Remain unchanged, the self-inductance of phase B L b It is in a decreasing state, and the self-inductance Lc of phase C is in an increasing state.

[0071] In this embodiment, the direction of the three-phase current is determined as follows:

[0072] The formula of reluctance torque after demagnetization of the electrically excited double-pole motor is introduced as follows:

[0073]

[0074] Where, T r is the reluctance torque, θ m is the mechanical angle of rotation.

[0075] The A phase current i a 、B phase current i b and C phase current i c Denoted as p-phase current i p , the A phase self-inductance L a 、B phase self-inductance L b and C phase self-inductance Lc is recorded as p phase self-inductance L p, p is the phase sequence, p = a, b, c; the three-phase windings of the electrically excited double-pole motor are connected at a common neutral point N, and its three-phase current satisfies the constraint condition i a +i b +i c =0; the direction of the three-phase current changes as follows:

[0076] When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from positive to negative, p From positive to zero;

[0077] When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from zero to positive p The direction remains unchanged;

[0078] When the p-phase self-inductance change rate dL p / dθ m When it is zero, the direction of the p-phase current is determined by the current directions of the other two phases according to the constraint that the sum of the three-phase currents is zero.

[0079] The present invention also provides a demagnetization fault-tolerant control system for an electrically excited double-pole motor, the control system comprising a circuit topology, a drive signal module, a switch state selection module, a photoelectric encoder, a controller, a speed loop PI regulator and a current loop PI regulator.

[0080] The photoelectric encoder is used to measure the rotor position signal of the electrically excited double-salient-pole motor, and the controller is used to calculate the motor speed according to the rotor position signal as the feedback speed n.

[0081] The speed loop PI regulator is used to adjust the speed according to the feedback speed n and the given motor speed n * The difference between the three-phase reference current amplitude signal I p .

[0082] The current loop PI regulator is used to convert the three-phase reference current amplitude signal I p Respectively with the three-phase current amplitude signal i p After comparison, the PWM signal is output to the drive signal module to adjust the amplitude of the three-phase current.

[0083] The switch state selection module is used to obtain the power tube on and off signal according to the rotor position signal.

[0084] The driving signal module is used to adjust the amplitude of the three-phase current according to the PWM signal; the driving signal module is also used to control the on and off of each power tube according to the power tube on and off signal.

[0085] In this embodiment, the control process is as follows:

[0086] Step 1: The electro-magnetic double-salient-pole motor measures the rotor position signal through a photoelectric encoder, and calculates the motor speed through a controller as the feedback speed n; the motor speed n is given * The difference between the speed n and the feedback speed n is output by the speed loop PI regulator as the three-phase reference current amplitude signal I p ; Three-phase reference current amplitude signal I p Respectively with the three-phase current amplitude signal i p In comparison, the PWM signal is output to the drive signal module through the current loop PI regulator.

[0087] Step 2: When the electrically excited double-pole motor has a demagnetization fault, it switches to the switch state selection module after demagnetization. The switch state selection module obtains the power tube on-off signal through the rotor position signal and outputs it to the drive signal module.

[0088] Step 3: The drive signal module performs a logical AND operation on the power tube on / off signal obtained by the switch state selection module and the PWM signal output by the current loop PI regulator, and finally determines the on / off of each power tube.

[0089] In order to verify the effectiveness of the method for reducing the torque pulsation of an electrically excited double-pole motor, a Matlab / Simulink simulation is performed on an electrically excited double-pole motor. In this embodiment, the rated voltage of the electrically excited double-pole motor is 270V and the rated power is 500W. The simulated speed is given as 200rpm and the load torque is 3N·m.

[0090] Figure 2 The figure shows the simulated waveforms of the total torque, each phase torque and three-phase current when the speed is stable. Figure 2 It can be seen that during the commutation stage, the direction of one phase current does not change, providing a stable positive torque output, and the other two phase currents are commutated, and their negative torque is small, thereby reducing the pulsation of the total torque and improving the performance of the electromagnetic double-pole motor's demagnetization fault-tolerant operation.

Claims

1. A method for controlling the demagnetization fault tolerance of an electrically excited double-pole motor, wherein the circuit topology of the control method includes: providing a DC power supply U dc , capacitor C, three-phase bridge converter, electrically excited doubly salient motor, asymmetric half-bridge converter and DC power supply U f ; The electrically excited double-pole motor comprises a three-phase armature winding and a single-phase excitation winding, and the three-phase armature winding and the single-phase excitation winding are coupled by mutual inductance; The three-phase bridge converter includes three bridge arms, including a total of six power tubes with anti-connected diodes, any one of which is denoted as power tube Q ij , i is the phase sequence, i = a, b, c; j is the serial number, j = 1, 2; power tube Q i1 The collector and DC power supply U dc The DC positive bus is connected to the emitter of the power tube Q i2 The collector and the corresponding phase of the three-phase armature winding, the power tube Q i2 The emitter is connected to the DC power supply U dc The capacitor is connected in parallel to the self-flowing power supply U dc and between the three-phase bridge converter; The asymmetric half-bridge converter includes a power tube Q7, a power tube Q8, a diode D7 and a diode D8, wherein: The collector of power tube Q7 and DC power supply U f The positive electrode of the diode D7 is connected to the cathode of the diode D7, the emitter is connected to one end of the one-phase excitation winding and the cathode of the diode D8, and the anode of the diode D8 is connected to the DC power supply U f The cathode of the diode D7 is connected to the emitter of the power tube Q8, and the anode of the diode D7 is connected to the other end of the one-phase excitation winding and the collector of the power tube Q8; The control method is characterized in that: according to the electrical angle θ of the electromagnetic double-pole motor, two electrical cycles after the electromagnetic double-pole motor loses magnetism are divided into six states, and the conduction state of each power tube and the direction of the three-phase current in the six states are controlled to realize the demagnetization fault-tolerant electric operation of the electromagnetic double-pole motor; The conduction state of each power tube and the direction of the three-phase current in the six states are as follows: State 1: When θ∈[0°,120°), the A phase current i a is positive, the B phase current i b is negative, the C phase current i c is zero, the power tube Q a1 And power tube Q b2 Turn on, other power tubes are turned off; State 2: When θ∈[120°,240°), the C phase current i c is positive, the B phase current i b is negative, the A phase current i a is zero, the power tube Q c1 And power tube Q b2 Turn on, other power tubes are turned off; State 3: When θ∈[240°,360°), the C phase current i c is positive, the A phase current i a is negative, the B phase current i b is zero, the power tube Q c1 And power tube Q a2 Turn on, other power tubes are turned off; State 4: When θ∈[360°,480°), the B phase current i b is positive, the A phase current i a is negative, the C phase current i c is zero, the power tube Q b1 And power tube Q a2 Turn on, other power tubes are turned off; State 5: When θ∈[480°,600°), the B phase current i b is positive, the C phase current i c is negative, the A phase current i a is zero, the power tube Q b1 And power tube Q c2 Turn on, other power tubes are turned off; State 6: When θ∈[600°,720°), the A phase current i a is positive, the C phase current i c is negative, the B phase current i b is zero, the power tube Q a1 And power tube Q c2 Turn on, other power tubes are turned off; The electrical cycle is 360°. In each electrical cycle, the changes in the three-phase self-inductance of the three-phase armature winding are as follows: When θ∈[0°,120°), the self-inductance of phase A is L a In the rising state, the self-inductance of phase B L b Remain unchanged, the self-inductance of phase C L c In a declining state; When θ∈[120°,240°), the self-inductance of phase A is L a In a decreasing state, the self-inductance of phase B L b In the rising state, the self-inductance of phase C L c remain unchanged; When θ∈[240°,360°), the self-inductance of phase A is L a Remain unchanged, the self-inductance of phase B L b In a decreasing state, the self-inductance of phase C L c In rising state.

2. The method for controlling the loss of excitation of an electrically excited double-salient-pole motor according to claim 1, characterized in that: The directions of the three-phase currents are determined as follows: The formula of reluctance torque after demagnetization of the electrically excited double-pole motor is introduced as follows: Where, T r is the reluctance torque, θ m is the rotational mechanical angle; The A phase current i a 、B phase current i b and C phase current i c Denoted as p-phase current i p , the A phase self-inductance L a 、B phase self-inductance L b and C phase self-inductance L c Denoted as p-phase self-inductance L p , p is the phase sequence, p = a, b, c; the three-phase windings of the electrically excited double-pole motor are connected at a common neutral point N, and its three-phase current satisfies the constraint condition i a +i b +i c =0; the direction of the three-phase current changes as follows: When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from positive to negative, p From positive to zero; When the p-phase self-inductance change rate dL p / dθ m When the p-phase current i changes from zero to positive p The direction remains unchanged; When the p-phase self-inductance change rate dL p / dθ m When it is zero, the direction of the p-phase current is determined by the current directions of the other two phases according to the constraint that the sum of the three-phase currents is zero.

3. A demagnetization fault-tolerant control system for an electrically excited double-salient-pole motor, characterized in that: A demagnetization fault-tolerant control method for an electrically excited double-salient-pole motor according to any one of claims 1 to 2 is adopted, wherein the control system comprises a circuit topology, a drive signal module, a switch state selection module, a photoelectric encoder, a controller, a speed loop PI regulator and a current loop PI regulator; The photoelectric encoder is used to measure the rotor position signal of the electrically excited double-salient-pole motor, and the controller is used to calculate the motor speed according to the rotor position signal as the feedback speed n; The speed loop PI regulator is used to adjust the speed according to the feedback speed n and the given motor speed n * The difference between the three-phase reference current amplitude signal I p ; The current loop PI regulator is used to convert the three-phase reference current amplitude signal I p Respectively with the three-phase current amplitude signal i p Compare and output PWM signals to the drive signal module to adjust the amplitude of the three-phase current; The switch state selection module is used to obtain the power tube on and off signal according to the rotor position signal; The driving signal module is used to adjust the amplitude of the three-phase current according to the PWM signal; the driving signal module is also used to control the on and off of each power tube according to the power tube on and off signal.

4. The demagnetization fault-tolerant control system of an electrically excited double-salient-pole motor according to claim 3, characterized in that: The control process is as follows: Step 1: The electro-magnetic double-salient-pole motor measures the rotor position signal through a photoelectric encoder, and calculates the motor speed through a controller as the feedback speed n; the motor speed n is given * The difference between the speed n and the feedback speed n is output by the speed loop PI regulator as the three-phase reference current amplitude signal I p ; Three-phase reference current amplitude signal I p Respectively with the three-phase current amplitude signal i p In comparison, the PWM signal is output to the drive signal module through the current loop PI regulator; Step 2: When the electrically excited double-salient-pole motor has a demagnetization fault, the motor is switched to the switch state selection module after demagnetization. The switch state selection module obtains a power tube on-off signal through a rotor position signal and outputs the signal to the drive signal module. Step 3: The drive signal module performs a logic operation on the power tube on / off signal obtained by the switch state selection module and the PWM signal output by the current loop PI regulator, and finally determines the on / off of each power tube.

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