A three-phase four-bridge-arm permanent magnet synchronous motor system open-circuit fault-tolerant control method considering continuous current

Abstract

The application discloses a three-phase four-bridge-arm permanent magnet synchronous motor system open-circuit fault-tolerant control method considering freewheeling current, comprising the following steps: according to the open-circuit fault position and quantity, establishing the freewheeling current loop of the upper and lower tubes of the same bridge arm and the single tube open circuit, and decomposing the freewheeling current component; under the consideration of the third harmonic back electromotive force, aiming at the torque disturbance caused by the freewheeling current, designing the combined 1 current compensation torque DC component, the combined 2 current compensation torque disturbance caused by the freewheeling current fundamental component, the combined 3 current compensation torque disturbance caused by the freewheeling current third harmonic component, combining the content of each component of the freewheeling current to give a torque compensation scheme, and obtaining a final phase current reconstruction scheme; obtaining the dq0 current given value through coordinate transformation, obtaining the dq0 axis voltage given value by using a proportional integral resonant regulator; obtaining the abc phase voltage given value through coordinate transformation; combining the duty cycle calculation and PWM modulation to obtain the driving signal for controlling the permanent magnet synchronous motor.

Description

Technical Field

[0001] This invention belongs to the field of motor drive and fault-tolerant control technology, and specifically relates to an open-circuit fault-tolerant control method for a three-phase four-bridge permanent magnet synchronous motor system that takes into account freewheeling current. Background Technology

[0002] Permanent magnet synchronous motors (PMSMs), with their advantages of high precision and high dynamic performance, are widely used in key fields such as new energy vehicles, robotics, and aerospace. Their control systems consist of the motor, controller, driver, and sensors. Each component is susceptible to failure during long-term operation, with the switching transistor being a particularly vulnerable point. Under complex loads and extreme environments, it is prone to open-circuit faults due to component breakage, weld detachment, or loss of drive signals. To optimize the air gap magnetic field distribution, reduce harmonic losses, and increase power density, third harmonic flux linkages are typically introduced in the design of three-phase PMSMs. Furthermore, the conduction of the freewheeling diode in a faulty phase generates a freewheeling current, which is affected by motor speed, back EMF characteristics, and changes in the topology after a fault. When considering the third harmonic back EMF, the freewheeling current is deeply coupled with the fundamental and third harmonic back EMFs, leading to increased system torque ripple, aggravated speed fluctuations, and increased current tracking errors. The impact of the freewheeling current is more pronounced at high speeds and when the motor inductance is low, potentially causing motor shutdown in severe cases. Therefore, in critical fields requiring continuous and reliable operation, such as aerospace and transportation, fault-tolerant control is necessary to maintain normal system operation.

[0003] To date, various fault-tolerant control methods have been proposed by scholars both domestically and internationally for open-circuit faults in switching transistors. However, existing methods do not fully consider the influence of freewheeling current, nor can they achieve accurate reconstruction of the fundamental current and harmonic current under the coupling effect of the third harmonic back electromotive force and freewheeling current. Therefore, they do not fundamentally solve the problems of torque ripple and performance degradation. Currently, fault-tolerant control methods for single-transistor open-circuit faults in three-phase permanent magnet synchronous motors are mainly divided into three categories:

[0004] 1. Single-tube open-circuit fault-tolerant control method based on two-phase fault tolerance: This method reduces the system to two-phase operation by isolating the faulty phase and adjusting the amplitude and phase of the current in the remaining two phases to maintain a constant rotating magnetomotive force. This method is simple to implement and has low control complexity, but it does not utilize the normal tube in the faulty phase, resulting in reduced system efficiency.

[0005] 2. Single-tube open-circuit fault-tolerant control method based on DC injection: After a fault, a constant zero-sequence current is injected to ensure that the fault phase current flows continuously during the positive or negative half-cycle, thus ensuring that the system maintains three-phase operation. Its advantage is its simplicity of implementation, but the injected DC component will couple with the third harmonic back EMF, further aggravating the periodic torque pulsation and seriously affecting steady-state performance.

[0006] 3. A single-tube open-circuit fault-tolerant control method based on two-phase to three-phase switching: Zero-sequence current is injected during the half-cycle when the faulty phase current cannot flow normally; during the half-cycle when the current can flow normally, the three-phase currents are kept symmetrical. While this method can improve the speed range and load capacity, it requires precise determination of the mode switching time, resulting in high control complexity. Furthermore, it does not compensate for the time-varying characteristics of the freewheeling current, leading to insufficient current tracking accuracy. Summary of the Invention

[0007] The purpose of this invention is to provide a fault-tolerant control method for open-circuit switching transistors in a three-phase four-bridge permanent magnet synchronous motor system that takes into account freewheeling current. This method can suppress periodic pulsations in speed and torque and improve current control accuracy. It is applicable to surface-mounted permanent magnet synchronous motors.

[0008] To achieve the above objectives, this invention proposes an open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current. This method includes the following steps:

[0009] Step 1, based on the three-phase current i of the permanent magnet synchronous motor a i b i c Determine the number and location of open-circuit faults, establish an equivalent model of the follow current of the fault phase, and decompose the components of the follow current.

[0010] Step 2: When considering the third harmonic back electromotive force, the combined current 1 is used to compensate the DC component of the torque, and the combined currents 2 and 3 are used to cancel the torque disturbance generated by the fundamental wave of the freewheeling current and the third harmonic component, respectively.

[0011] Step 3: Based on the principle that the output torque remains unchanged before and after the fault, the three combined currents described in Step 2 are superimposed in a certain proportion to obtain the reconstructed three-phase currents abc.

[0012] Step 4: Reconstruct the three-phase currents abc described in Step 3, transform them to the dq0 axis to obtain the given value of dq0, and obtain the corresponding harmonic current injection amount.

[0013] Step 5: Based on the error between the given value of the dq0 axis current and the actual value of the dq0 axis current described in Step 4, perform proportional-integral resonance regulation to obtain the given value of the dq0 axis voltage.

[0014] Step 6: Perform coordinate transformation, duty cycle calculation, and PWM modulation on the given dq0 axis voltage value to obtain the drive signal for controlling the permanent magnet synchronous motor.

[0015] Furthermore, in step 1, the specific process of establishing the equivalent model of the fault phase continuous current is as follows:

[0016] Step A, phase a open circuit fault, the phase a voltage equation satisfies:

[0017]

[0018] Among them, i a Let L be the phase current; L be the phase inductance; R be the phase resistance; e be the phase current. a Let U be the opposite electromotive force; AN Let A be the phase voltage relative to the midpoint N of the three-phase winding;

[0019] Step B, ignoring the voltage drop across the resistor and linearizing the differential term of the current, when both the upper and lower transistors of phase a experience an open-circuit fault simultaneously, the peak value i of the fault phase current... a_peak :

[0020]

[0021] Among them, T s D is the switching period; n U represents the proportion of the on-time of the n-phase upper tube to one switching cycle; D For the diode forward voltage drop, e a >U D At that time, the freewheeling diode connected in reverse parallel to the upper transistor of phase a is turned on; e a <-U D At that time, the freewheeling diode connected in reverse parallel to the lower diode of phase a is turned on;

[0022] Step C, since the freewheeling current state is affected by the state of the n-phase switches, the duration t of the freewheeling current within one switching cycle is:

[0023]

[0024] Among them, u dc This is the DC bus voltage;

[0025] Step D: Obtain the average freewheeling current i of the open circuit of the upper and lower tubes of phase a using the area equivalence principle. a_average ,

[0026]

[0027] Step E: When a single-tube open-circuit fault occurs in phase a, since the switching state of the remaining normal tubes in the faulty phase is adjustable, the actual sampled value of the faulty phase current is kept consistent with the peak value of the freewheeling estimation model by adjusting the duty cycle. The peak value of the faulty phase current is i. a_max :

[0028]

[0029] Step F involves checking the fault phase current i for both upper and lower transistors of phase a being open-circuited and for a single transistor being open-circuited. a_FPC Decompose;

[0030]

[0031] The fault follow current contains a fundamental frequency, a third harmonic, and a DC component, with amplitudes I and I, respectively. a1 I a3 and I dc θ e It is an electrical angle;

[0032] With both the upper and lower tubes of phase a open circuit, and e a >U D At that time, the components of the freewheeling current are:

[0033]

[0034] With both the upper and lower tubes of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are:

[0035]

[0036] The tube on phase a is open-circuited, and e a >U D At that time, the components of the freewheeling current are:

[0037]

[0038] With the lower tube of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are:

[0039]

[0040] in, ψ is the electric angular velocity of the motor. f1 and ψ f3 For fundamental flux linkage and third harmonic flux linkage;

[0041] Since the amplitude of the back electromotive force is greater than the diode forward voltage drop when the motor is running, the diode forward voltage drop and the DC component of the freewheeling current are ignored.

[0042] Furthermore, in step 2, the motor back electromotive force model e considering the third harmonic is... a ,e b ,e c for:

[0043]

[0044] Output electromagnetic torque model T e for:

[0045]

[0046] Among them, i a i b i c For the three-phase currents a, b, and c, p n It is the extreme logarithm;

[0047] The DC component of the current-compensated torque in combination 1, and the current i in combination 1. B1 i C1 for:

[0048]

[0049] Where λ is the ratio of the third harmonic flux linkage to the fundamental flux linkage, I m1 Let I be the current amplitude, and when λ=0 and the fault phase follow current is neglected. m1 The phase current amplitude is consistent with that under normal operating conditions;

[0050] The DC component of the torque T generated by the combined current 1 e1 for:

[0051]

[0052] The torque pulsation generated by the coupling of the fundamental component of the fault continuous current and the back electromotive force in combination 2 current compensation fault is expressed as the three-phase symmetrical current i A2 i B2 i C2 :

[0053]

[0054] The DC component T generated by the combined current 2 e2 for:

[0055]

[0056] The third harmonic component of the fault current-compensated continuous current in combination 3 couples with the back electromotive force to generate torque pulsation, the expression of which is i A3 i B3 i C3 :

[0057]

[0058] The DC component T generated by combination 3 e3 for:

[0059]

[0060] The current content of combination 2 and combination 3 depends on the amplitude of the fundamental and third harmonic components of the freewheeling current, while the current content of combination 1 depends on the torque generated by the current of combination 2 and combination 3 and the load torque.

[0061] Furthermore, in step 3, the three combined currents described in step 2 are superimposed, resulting in the superimposed three-phase current iabc. A i B i C for:

[0062]

[0063] The principle that the output torque remains unchanged before and after the fault is:

[0064]

[0065] in, The DC component of the q-axis current under normal operating conditions is given by the given rotational speed ω. * The error between the actual rotational speed ω and the given value of the DC current of the q-axis is obtained through a proportional-integral controller. .

[0066] Furthermore, in step 4, the coordinate transformation matrix T for transforming the three-phase currents abc to the current along the dq0 axis is:

[0067]

[0068] The superimposed current described in step 3 is transformed using the coordinate transformation matrix T to obtain the given current along the dq0 axis:

[0069]

[0070] Based on the principle of unchanged output torque before and after the fault described in step 3, the current I in combination 1 is obtained. m1 for:

[0071]

[0072] In combination 1, current I m1 Substituting the value into the dq0-axis current, we obtain the harmonic injection amounts of the dq0-axis current at each frequency as follows:

[0073]

[0074] Among them, i d_2 i is the d-axis current frequency double-harmonic injection amount; d_4 The fourth-harmonic injection amount of the d-axis current; i q_2 i is the q-axis current frequency double-harmonic injection amount; q_4 The injection amount is the fourth harmonic of the q-axis current; i 0_1 This is the fundamental frequency injection amount for zero-axis current; for both upper and lower transistors of phase a open circuit, harmonic current injection occurs throughout the entire fundamental frequency cycle; for the upper transistor of phase a open circuit, harmonic current injection occurs only at e a >U DHarmonic current injection is performed at that time. For the lower transistor of phase a, it is open-circuited, and only at phase e... a <-U D Harmonic current injection is performed at that time.

[0075] Furthermore, in step 5, the difference between the current setpoint of the dq0 axis of the permanent magnet synchronous motor and the actual dq0 axis current is input into a proportional resonant integrator to obtain the voltage setpoint u of the dq0 axis. d * u q * and u0 * The actual value of the dq0 axis current is obtained by the three-phase sampled currents abc through the coordinate transformation matrix T.

[0076] Furthermore, in step 6, the dq0-axis voltage is transformed to the given value u of the abc three-phase voltage by using the inverse matrix of the coordinate transformation matrix T. a * u b * and u c * :

[0077]

[0078] Furthermore, the duty cycle D of each phase a, b, c, and n under normal operating conditions is obtained. a D b D c D n for:

[0079]

[0080] Among them, D a D b and D c These represent the proportions of the on-time of phases a, b, and c within one switching cycle; u min and u max These are the maximum and minimum values ​​among the given values ​​of the three-phase voltages a, b, and c, respectively.

[0081] The upper pipe of phase a is open-circuited and e a >U D Or phase a's lower tube is open and e's... a <-U D Duty cycle for:

[0082]

[0083] Among them, K ea This is the back electromotive force amplitude correction factor; This is an estimate of the back electromotive force;

[0084] The obtained duty cycles of phases a, b, c, and n are input into the PWM modulation module to obtain the drive signal S for controlling the permanent magnet synchronous motor. a S b S c and S n , of which S a S b S c and S n A value of 1 indicates that the upper pipe is on and the lower pipe is off; a value of 0 indicates that the upper pipe is on and the lower pipe is off.

[0085] Beneficial effects: Compared with the prior art, the technical solution of the present invention has the following beneficial technical effects:

[0086] (1) Compared with the existing single-tube open-circuit fault-tolerant control method based on two-phase fault tolerance, the method of the present invention makes full use of the normal tube of the faulty phase when the single tube is open-circuit faulted, so that the faulty phase can provide the torque component normally; when both tubes are faulted, the disturbance of the freewheeling current of the faulty phase is taken into account.

[0087] (2) Compared with the existing single-tube open-circuit fault-tolerant control method based on DC injection, the method of the present invention fully considers the torque disturbance component generated by the coupling of the fundamental and third harmonic back electromotive force with the current when performing current reconstruction, and realizes the compensation of the torque disturbance component by harmonic current injection.

[0088] (3) Compared with the existing single-tube open-circuit fault-tolerant control method based on two-phase and three-phase switching, the present invention considers the influence of the fault phase freewheeling current in the two-phase state when the single tube is open-circuit faulted. By recalculating the duty cycle of the fault phase, the fault phase current is in a completely continuous state, making the fault phase output voltage controllable and reducing the current tracking error. Attached Figure Description

[0089] Figure 1 This is the three-phase four-bridge-arm fault-tolerant drive topology used in this invention;

[0090] Figure 2 This is a control block diagram of the present invention;

[0091] Figure 3 Block diagram for back electromotive force amplitude correction;

[0092] Figure 4 The experimental results are for a simultaneous open-circuit fault in phase a, where both upper and lower tubes are open. Figure 4 (a1) is the phase current waveform before compensation; Figure 4 (a2) shows the phase current waveform after compensation; Figure 4 (b1) is the dq axis current waveform before compensation; Figure 4 (b2) shows the dq-axis current waveform after compensation; Figure 4(c1) is the zero-axis current waveform before compensation; Figure 4 (c2) is the zero-axis current waveform after compensation.

[0093] Figure 5 The waveforms of torque, back EMF correction coefficient, and speed error before and after freewheeling current compensation.

[0094] Figure 6 The experimental results are for an open-circuit fault in the upper tube of phase a. Figure 6 (a1) is the phase current waveform before compensation; Figure 6 (a2) shows the phase current waveform after compensation; Figure 6 (b1) is the dq axis current waveform before compensation; Figure 6 (b2) shows the dq-axis current waveform after compensation; Figure 6 (c1) is the zero-axis current waveform before compensation; Figure 6 (c2) is the zero-axis current waveform after compensation.

[0095] Figure 7 The waveforms of torque, back EMF correction coefficient, and speed error before and after freewheeling current compensation.

[0096] Figure 8 The experimental results are for an open-circuit fault in the lower tube of phase a. Figure 8 (a1) is the phase current waveform before compensation; Figure 8 (a2) shows the phase current waveform after compensation; Figure 8 (b1) is the dq axis current waveform before compensation; Figure 8 (b2) shows the dq-axis current waveform after compensation; Figure 8 (c1) is the zero-axis current waveform before compensation; Figure 8 (c2) is the zero-axis current waveform after compensation.

[0097] Figure 9 The waveforms of torque, back EMF correction coefficient, and speed error before and after freewheeling current compensation.

[0098] Figure 10 It is the ratio of the torque ripple component to the DC component before and after freewheeling current compensation. Figure 10 (a) is the ratio of torque harmonic component to DC component when both upper and lower tubes of phase a are open at the same time. Figure 10 (b) is the ratio of torque harmonic components to DC components when the upper tube of phase a is open; Figure 10 (c) is the ratio of the torque harmonic component to the DC component when the lower tube of phase a is open. Detailed Implementation

[0099] The technical solution and beneficial effects of the present invention will be described in detail below with reference to the accompanying drawings.

[0100] like Figure 2 As shown, this invention provides an open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current, based on a three-phase four-arm inverter, including the following steps:

[0101] Based on the location and number of open-circuit faults, establish freewheeling current loops for open circuits in both upper and lower tubes and for open circuits in a single tube on the same bridge arm, and decompose the freewheeling current components.

[0102] Considering the third harmonic back EMF, to address the torque disturbance generated by the freewheeling current, we design combination 1 to compensate for the DC component of the torque, combination 2 to compensate for the torque disturbance generated by the fundamental component of the freewheeling current, and combination 3 to compensate for the torque disturbance generated by the third harmonic component of the freewheeling current. Based on the components of the freewheeling current, we give a torque compensation scheme and obtain the final phase current reconstruction scheme.

[0103] The current setpoint for dq0 is obtained through coordinate transformation, and the voltage setpoint for the dq0 axis is obtained using a proportional-integral resonant regulator; the voltage setpoints for phases abc are also obtained through coordinate transformation.

[0104] By combining duty cycle calculation and PWM modulation, the drive signal for controlling the permanent magnet synchronous motor is obtained.

[0105] The drive system of an embodiment of the present invention includes: a DC voltage source, an inverter circuit, a permanent magnet synchronous motor, a drive circuit, a current sampling circuit, and a central processing unit. The DC voltage source provides the DC bus voltage, and the current sampling circuit measures the three-phase current of the motor. Figure 1 As shown, under normal operating conditions, the three-phase four-arm permanent magnet synchronous motor is driven by a standard three-phase inverter, and the system operates in three-phase three-arm mode; when a single-tube open-circuit fault is detected, the redundant fourth arm is activated through the bidirectional thyristor K. n The system is connected to the neutral point N of the three-phase winding and operates in three-phase four-bridge arm mode.

[0106] In this embodiment, the parameters of the surface-mounted permanent magnet synchronous motor are: number of pole pairs p n =4, stator phase resistance R s =1.1Ω, direct-axis inductance L d =1.5mH, quadrature axis inductance L q =1.5mH, permanent magnet fundamental flux linkage ψ f1 =0.137Wb, permanent magnet third harmonic flux linkage ψ f3 =0.006Wb. The specific experimental conditions were: DC bus voltage 160V, switching frequency 10kHz, simulating an open circuit in phase a switch, and data recording using an oscilloscope.

[0107] This invention establishes an equivalent model of the freewheeling current and performs component analysis, designing a corresponding current combination scheme to compensate for the torque disturbance generated by the freewheeling current, suppressing torque and speed fluctuations during steady-state operation, and simultaneously reducing current following error. Figure 1 As shown, the present invention provides an open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current. The method includes the following steps:

[0108] Step 1, based on the three-phase current i of the permanent magnet synchronous motor a i b i c Determine the number and location of open-circuit faults, establish an equivalent model of the follow current of the fault phase, and decompose the components of the follow current.

[0109] Step 2: When considering the third harmonic back electromotive force, the combined current 1 is used to compensate the DC component of the torque, and the combined currents 2 and 3 are used to cancel the torque disturbance generated by the fundamental wave of the freewheeling current and the third harmonic component, respectively.

[0110] Step 3: Based on the principle that the output torque remains unchanged before and after the fault, the three combined currents described in Step 2 are superimposed in a certain proportion to obtain the abc three-phase reconfiguration current.

[0111] Step 4: Transform the three-phase reconstructed currents abc described in Step 3 to the dq0 axis to obtain the given value of dq0, and obtain the corresponding harmonic current injection amount.

[0112] Step 5: Based on the error between the given value of the dq0 axis current and the actual value of the dq0 axis current described in Step 4, perform proportional-integral resonance regulation to obtain the given value of the dq0 axis voltage.

[0113] Step 6: Perform coordinate transformation, duty cycle calculation, and PWM modulation on the given dq0 axis voltage value to obtain the drive signal for controlling the permanent magnet synchronous motor.

[0114] Furthermore, in step 1, the specific process of establishing the equivalent model of the fault phase continuous current is as follows:

[0115] Step A, phase a open circuit fault, the phase a voltage equation satisfies:

[0116]

[0117] Among them, i a Let L be the phase current; L be the phase inductance; R be the phase resistance; e be the phase current. a Let U be the opposite electromotive force; AN Let A be the phase voltage relative to the midpoint N of the three-phase winding;

[0118] Step B, ignoring the voltage drop across the resistor and linearizing the differential term of the current, when both the upper and lower transistors of phase a experience an open-circuit fault simultaneously, the peak value i of the fault phase current... a_peak :

[0119]

[0120] Among them, T s D is the switching period; n U represents the proportion of the on-time of the n-phase upper tube to one switching cycle; D For the diode forward voltage drop, e a >U D At that time, the freewheeling diode connected in reverse parallel to the upper transistor of phase a is turned on; e a <-U D At that time, the freewheeling diode connected in reverse parallel to the lower diode of phase a is turned on;

[0121] Step C, since the freewheeling current state is affected by the state of the n-phase switches, the duration t of the freewheeling current within one switching cycle is:

[0122]

[0123] Among them, u dc This is the DC bus voltage;

[0124] Step D: Obtain the average freewheeling current i of the open circuit of the upper and lower tubes of phase a using the area equivalence principle. a_average ,

[0125]

[0126] Step E: When a single-tube open-circuit fault occurs in phase a, since the switching state of the remaining normal tubes in the faulty phase is adjustable, the actual sampled value of the faulty phase current is kept consistent with the peak value of the freewheeling estimation model by adjusting the duty cycle. The peak value of the faulty phase current is i. a_max :

[0127]

[0128] Step F involves checking the fault phase current i for both upper and lower transistors of phase a being open-circuited and for a single transistor being open-circuited. a_FPC Decompose;

[0129]

[0130] The fault follow current contains a fundamental frequency, a third harmonic, and a DC component, with amplitudes I and I, respectively. a1 I a3 and I dc θ e It is an electrical angle;

[0131] With both the upper and lower tubes of phase a open circuit, and ea >U D At that time, the components of the freewheeling current are:

[0132]

[0133] With both the upper and lower tubes of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are:

[0134]

[0135] The tube on phase a is open-circuited, and e a >U D At that time, the components of the freewheeling current are:

[0136]

[0137] With the lower tube of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are:

[0138]

[0139] in, ψ is the electric angular velocity of the motor. f1 and ψ f3 For fundamental flux linkage and third harmonic flux linkage;

[0140] Since the amplitude of the back electromotive force is greater than the diode forward voltage drop when the motor is running, the diode forward voltage drop and the DC component of the freewheeling current are ignored.

[0141] Furthermore, in step 2, the motor back electromotive force model e considering the third harmonic is... a ,e b ,e c for:

[0142]

[0143] Output electromagnetic torque model T e for:

[0144]

[0145] Among them, i a i b i c For the three-phase currents a, b, and c, p n It is the extreme logarithm;

[0146] The DC component of the current-compensated torque in combination 1, and the current i in combination 1. B1 i C1 for:

[0147]

[0148] Where λ is the ratio of the third harmonic flux linkage to the fundamental flux linkage, I m1 Let I be the current amplitude, and when λ=0 and the fault phase follow current is neglected. m1 The phase current amplitude is consistent with that under normal operating conditions;

[0149] The DC component of the torque T generated by the combined current 1 e1 for:

[0150]

[0151] The torque pulsation generated by the coupling of the fundamental component of the fault continuous current and the back electromotive force in combination 2 current compensation fault is expressed as the three-phase symmetrical current i A2 i B2 i C2 :

[0152]

[0153] The DC component T generated by the combined current 2 e2 for:

[0154]

[0155] The third harmonic component of the fault current-compensated continuous current in combination 3 couples with the back electromotive force to generate torque pulsation, the expression of which is i A3 i B3 i C3 :

[0156]

[0157] The DC component T generated by combination 3 e3 for:

[0158]

[0159] The current content of combination 2 and combination 3 depends on the amplitude of the fundamental and third harmonic components of the freewheeling current, while the current content of combination 1 depends on the torque generated by the current of combination 2 and combination 3 and the load torque.

[0160] Furthermore, in step 3, the three combined currents described in step 2 are superimposed, resulting in the superimposed three-phase current iabc. A i B i C for:

[0161]

[0162] The principle that the output torque remains unchanged before and after the fault is:

[0163]

[0164] in, The DC component of the q-axis current under normal operating conditions is given by the given rotational speed ω. * The error between the actual rotational speed ω and the given value of the DC current of the q-axis is obtained through a proportional-integral controller. .

[0165] Furthermore, in step 4, the coordinate transformation matrix T for transforming the three-phase currents abc to the current along the dq0 axis is:

[0166]

[0167] The superimposed current described in step 3 is transformed using the coordinate transformation matrix T to obtain the given current along the dq0 axis:

[0168]

[0169] Based on the principle of unchanged output torque before and after the fault described in step 3, the current I in combination 1 is obtained. m1 for:

[0170]

[0171] In combination 1, current I m1 Substituting the value into the dq0-axis current, we obtain the harmonic injection amounts of the dq0-axis current at each frequency as follows:

[0172]

[0173] Among them, i d_2 i is the d-axis current frequency double-harmonic injection amount; d_4 The fourth-harmonic injection amount of the d-axis current; i q_2 i is the q-axis current frequency double-harmonic injection amount; q_4 The injection amount is the fourth harmonic of the q-axis current; i 0_1 This is the fundamental frequency injection amount for zero-axis current; for both upper and lower transistors of phase a open circuit, harmonic current injection occurs throughout the entire fundamental frequency cycle; for the upper transistor of phase a open circuit, harmonic current injection occurs only at e a >U D Harmonic current injection is performed at that time. For the lower transistor of phase a, it is open-circuited, and only at phase e... a <-U D Harmonic current injection is performed at that time.

[0174] Furthermore, in step 5, the difference between the current setpoint of the dq0 axis of the permanent magnet synchronous motor and the actual dq0 axis current is input into a proportional resonant integrator to obtain the voltage setpoint u of the dq0 axis. d* u q * and u0 * The actual value of the dq0 axis current is obtained by the three-phase sampled currents abc through the coordinate transformation matrix T.

[0175] Furthermore, in step 6, the dq0-axis voltage is transformed to the given value u of the abc three-phase voltage by using the inverse matrix of the coordinate transformation matrix T. a * u b * and u c * :

[0176]

[0177] Furthermore, the duty cycle D of each phase a, b, c, and n under normal operating conditions is obtained. a D b D c D n for:

[0178]

[0179] Among them, D a D b and D c These represent the proportions of the on-time of phases a, b, and c within one switching cycle; u min and u max These are the maximum and minimum values ​​among the given values ​​of the three-phase voltages a, b, and c, respectively.

[0180] The upper pipe of phase a is open and e a >U D Or phase a's lower tube is open and e's... a <-U D Duty cycle for:

[0181]

[0182] Among them, K ea This is the back electromotive force amplitude correction factor; This is an estimate of the back electromotive force;

[0183] The obtained duty cycles of phases a, b, c, and n are input into the PWM modulation module to obtain the drive signal S for controlling the permanent magnet synchronous motor. a S b S c and S n , of which S a S b S c and Sn A value of 1 indicates that the upper pipe is on and the lower pipe is off; a value of 0 indicates that the upper pipe is on and the lower pipe is off.

[0184] This invention is based on Figure 1 The three-phase four-arm fault-tolerant topology shown adopts Figure 2 The harmonic current injection control block diagram shown compensates for torque disturbances caused by open-circuit faults and freewheeling currents. The back EMF amplitude correction scheme is as follows: Figure 3 As shown in the figure. In the experiment, the bus voltage was 160V, the load torque was 1.8 N·m, and the reference speed was set to 500 r / min. The experimental results are as follows. Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 and Figure 9 As shown, this includes phase current, dq-axis current (given and actual values), zero-axis current (actual and given values), torque, and back EMF correction factor K. ea and rotational speed error. Figure 10 This represents the proportion of torque ripple component relative to DC component before and after freewheeling current compensation. Figure 4 , Figure 5 , Figure 6 , Figure 7 , Figure 8 , Figure 9 and Figure 10 The results show that after adopting the open-circuit fault-tolerant algorithm for switching transistors that considers freewheeling current proposed in this invention, torque and speed fluctuations are reduced, and current following error is reduced, which is consistent with the theory.

[0185] In summary, the technical solution of this invention first establishes equivalent models of the freewheeling current of the fault phase under open-circuit faults of both upper and lower transistors and a single switching transistor, and decomposes the components of the freewheeling current; considering the third harmonic back electromotive force, a current combination scheme is established to compensate for the torque disturbance caused by the open-circuit fault and the freewheeling current; the current reconstruction scheme is combined and converted into harmonic current injection control of the dq0 axis, and a duty cycle calculation method with zero-sequence voltage bias is used to give the duty cycle corresponding to the critical continuous fault phase current under a single switching transistor fault; finally, PWM modulation is performed to obtain the inverter drive signal.

[0186] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0187] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. An open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current, characterized in that, The method includes the following steps: Step 1, based on the three-phase current i of the permanent magnet synchronous motor a i b i c Determine the number and location of open-circuit faults, establish an equivalent model of the follow current of the fault phase, and decompose the components of the follow current. Step 2: When considering the third harmonic back electromotive force, the combined current 1 is used to compensate the DC component of the torque, and the combined currents 2 and 3 are used to cancel the torque disturbance generated by the fundamental wave of the freewheeling current and the third harmonic component, respectively. Step 3: Based on the principle that the output torque remains unchanged before and after the fault, the three combined currents described in Step 2 are superimposed in a certain proportion to obtain the reconstructed three-phase currents abc. Step 4: Reconstruct the three-phase currents abc described in Step 3, transform them to the dq0 axis to obtain the given value of dq0, and obtain the corresponding harmonic current injection amount. Step 5: Based on the error between the given value of the dq0 axis current and the actual value of the dq0 axis current described in Step 4, perform proportional-integral resonance regulation to obtain the given value of the dq0 axis voltage. Step 6: Perform coordinate transformation, duty cycle calculation, and PWM modulation on the given dq0 axis voltage value to obtain the drive signal for controlling the permanent magnet synchronous motor.

2. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 1, characterized in that, In step 1, the specific process of establishing the equivalent model of the fault phase continuous current is as follows: Step A, phase a open circuit fault, the phase a voltage equation satisfies: ； Among them, i a Let L be the phase current; L be the phase inductance; R be the phase resistance; e be the phase current. a Let U be the opposite electromotive force; AN Let A be the phase voltage relative to the midpoint N of the three-phase winding; Step B, ignoring the voltage drop across the resistor and linearizing the differential term of the current, when both the upper and lower transistors of phase a experience an open-circuit fault simultaneously, the peak value i of the fault phase current... a_peak : ； Among them, T s D is the switching period; n U represents the proportion of the on-time of the n-phase upper tube to one switching cycle; D For the diode forward voltage drop, e a >U D At that time, the freewheeling diode connected in reverse parallel to the upper transistor of phase a is turned on; e a <-U D At that time, the freewheeling diode connected in reverse parallel to the lower diode of phase a is turned on; Step C, since the freewheeling current state is affected by the state of the n-phase switches, the duration t of the freewheeling current within one switching cycle is: ； Among them, u dc This is the DC bus voltage; Step D: Obtain the average freewheeling current i of the open circuit of the upper and lower tubes of phase a using the area equivalence principle. a_average , ； Step E: When a single-tube open-circuit fault occurs in phase a, since the switching state of the remaining normal tubes in the faulty phase is adjustable, the actual sampled value of the faulty phase current is kept consistent with the peak value of the freewheeling estimation model by adjusting the duty cycle. The peak value of the faulty phase current is i. a_max : ； Step F involves checking the fault phase current i for both upper and lower transistors of phase a being open-circuited and for a single transistor being open-circuited. a_FPC Decompose; ； The fault follow current contains a fundamental frequency, a third harmonic, and a DC component, with amplitudes I and I, respectively. a1 I a3 and I dc θ e It is an electrical angle; With both the upper and lower tubes of phase a open circuit, and e a >U D At that time, the components of the freewheeling current are: ； With both the upper and lower tubes of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are: ； The tube on phase a is open-circuited, and e a >U D At that time, the components of the freewheeling current are: ； With the lower tube of phase a open circuit, and e a <-U D At that time, the components of the freewheeling current are: ； in, ψ is the electric angular velocity of the motor. f1 and ψ f3 For fundamental flux linkage and third harmonic flux linkage; Since the amplitude of the back electromotive force is greater than the diode forward voltage drop when the motor is running, the diode forward voltage drop and the DC component of the freewheeling current are ignored.

3. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 2, characterized in that, In step 2, the motor back electromotive force model e considering the third harmonic is described. a ,e b ,e c for: ； Output electromagnetic torque model T e for: ； Among them, i a i b i c For the three-phase currents a, b, and c, p n It is the extreme logarithm; The DC component of the current-compensated torque in combination 1, and the current i in combination 1. B1 i C1 for: ； Where λ is the ratio of the third harmonic flux linkage to the fundamental flux linkage, I m1 Let I be the current amplitude, and when λ=0 and the fault phase follow current is neglected. m1 The phase current amplitude is consistent with that under normal operating conditions; The DC component of the torque T generated by the combined current 1 e1 for: ； The torque pulsation generated by the coupling of the fundamental component of the fault continuous current and the back electromotive force in combination 2 current compensation fault is expressed as the three-phase symmetrical current i A2 i B2 i C2 : ； The DC component T generated by the combined current 2 e2 for: ； The third harmonic component of the fault current-compensated continuous current in combination 3 couples with the back electromotive force to generate torque pulsation, the expression of which is i A3 i B3 i C3 : ； The DC component T generated by combination 3 e3 for: ； The current content of combination 2 and combination 3 depends on the amplitude of the fundamental and third harmonic components of the freewheeling current, while the current content of combination 1 depends on the torque generated by the current of combination 2 and combination 3 and the load torque.

4. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 3, characterized in that, In step 3, the three combined currents described in step 2 are superimposed, and the superimposed three-phase current i of phases abc is obtained. A i B i C for: ； The principle that the output torque remains unchanged before and after the fault is: ； in, The DC component of the q-axis current under normal operating conditions is given by the given rotational speed ω. * The error between the actual rotational speed ω and the given value of the DC current of the q-axis is obtained through a proportional-integral controller. .

5. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 4, characterized in that: In step 4, the coordinate transformation matrix T for transforming the three-phase currents abc to the current along the dq0 axis is: ； The superimposed current described in step 3 is transformed using the coordinate transformation matrix T to obtain the given current along the dq0 axis: ； Based on the principle of unchanged output torque before and after the fault described in step 3, the current I in combination 1 is obtained. m1 for: ； In combination 1, current I m1 Substituting the value into the dq0-axis current, we obtain the harmonic injection amounts of the dq0-axis current at each frequency as follows: ； Among them, i d_2 i is the d-axis current frequency double-harmonic injection amount; d_4 The fourth-harmonic injection amount of the d-axis current; i q_2 i is the q-axis current frequency double-harmonic injection amount; q_4 The injection amount is the fourth harmonic of the q-axis current; i 0_1 This is the fundamental frequency injection amount for zero-axis current; for both upper and lower transistors of phase a open circuit, harmonic current injection occurs throughout the entire fundamental frequency cycle; for the upper transistor of phase a open circuit, harmonic current injection occurs only at e a >U D Harmonic current injection is performed at that time. For the lower transistor of phase a, it is open-circuited, and only at phase e... a <-U D Harmonic current injection is performed at that time.

6. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 5, characterized in that: In step 5, the difference between the current setpoint of the permanent magnet synchronous motor's dq0 axis and the actual dq0 axis current is input into a proportional-resonant integrator to obtain the dq0 axis voltage setpoint u. d * u q * and u0 * The actual value of the dq0 axis current is obtained by the three-phase sampled currents abc through the coordinate transformation matrix T.

7. The open-circuit fault-tolerant control method for a three-phase four-arm permanent magnet synchronous motor system considering freewheeling current as described in claim 6, characterized in that: In step 6, the dq0-axis voltage is transformed to the given three-phase voltage u of abc using the inverse of the coordinate transformation matrix T. a * u b * and u c * : ； Furthermore, the duty cycle D of each phase a, b, c, and n under normal operating conditions is obtained. a D b D c D n for: ； Among them, D a D b and D c These represent the proportions of the on-time of phases a, b, and c within one switching cycle; u min and u max These are the maximum and minimum values ​​among the given values ​​of the three-phase voltages a, b, and c, respectively. The upper pipe of phase a is open-circuited and e a >U D Or phase a's lower tube is open and e's... a <-U D Duty cycle for: ； Among them, K ea This is the back electromotive force amplitude correction factor; This is an estimate of the back electromotive force; The obtained duty cycles of phases a, b, c, and n are input into the PWM modulation module to obtain the drive signal S for controlling the permanent magnet synchronous motor. a S b S c and S n , of which S a S b S c and S n A value of 1 indicates that the upper pipe is on and the lower pipe is off; a value of 0 indicates that the upper pipe is on and the lower pipe is off.

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