Position sensorless control method of BLDCM based on improved fault-tolerant topology of Z-source inverter

Abstract

The present invention discloses a method for controlling a brushless DC motor without position sensor based on an improved fault-tolerant topology of a Z-source inverter, which proposes a new method for detecting the back electromotive force zero-crossing point of a unified fault phase and a healthy phase of a brushless DC motor, so that the terminal voltage of the fault phase can provide the motor back electromotive force information, realizes the position sensorless control of the motor under rated working conditions and non-rated working conditions, and enriches the coping strategies of the brushless DC motor control under special circumstances. In addition, the present invention designs an improved Z-source inverter fault-tolerant reconstruction topology, which can meet the conditions for the brushless DC motor without position sensor control under the action of a through vector, and the terminal voltage of the fault phase can provide the brushless DC motor back electromotive force information, realizing the position sensorless control of the motor under the condition of a drive device failure.

Description

Technical Field

[0001] The invention belongs to the technical field of motor control, and in particular relates to a position sensorless control method of a brushless DC motor (BLDCM) based on a Z-source inverter improved fault-tolerant topology. Background Art

[0002] Z-source inverters have been applied to various types of motor systems, such as induction motors, permanent magnet synchronous motors, and brushless DC motors, because they allow direct pass-through and have good boost capability. In order to adjust the bus voltage, existing technologies have pointed out that the application of Z-source inverters to permanent magnet synchronous motor drive systems can take advantage of their wide output voltage range and meet the motor's operating requirements above the base speed by boosting the voltage, thus avoiding the motor from entering the weak magnetic field region to a certain extent.

[0003] In the Z-source inverter driven brushless DC motor position sensorless control, the most commonly used method is the direct back-EMF method. In the brushless DC motor driven by the voltage source inverter, the voltage at the suspended phase terminal is compared with the reference level to obtain the back-EMF zero crossing point. The zero crossing point signal is delayed by 30° electrical angle to obtain the commutation signal. In the brushless DC motor driven by the Z-source inverter, the literature [Li Xinmin, Xia Changliang, Chen Wei, et al. Z-source inverter driven position sensorless brushless DC motor back-EMF zero crossing point detection method [J]. Proceedings of the CSEE, 2017, 37(17): 5153-5161] proposed a method for detecting the back-EMF zero crossing point when the direct vector is applied. The above back-EMF methods all require the brushless DC motor to operate in a two-phase conduction mode, that is, only two phases of the motor winding are energized, the third phase winding has no continuous current, and is in a suspended state.

[0004] In harsh working conditions, the inverter drive circuit is a weak link prone to failure. When a drive failure occurs in the power device of the six-switch inverter, the bidirectional thyristor is turned on, and the motor winding of the faulty phase is cut to the midpoint of the DC capacitor, and a four-switch inverter can be reconstructed; when a drive failure occurs in the power device of the Z-source inverter, the motor winding of this phase is also cut to the midpoint of the DC capacitor or the Z-source capacitor by the bidirectional thyristor. Around the reconstruction topology, hysteresis current control method, direct torque control method and PWM duty cycle modulation method are proposed to suppress the continuous current of the non-disconnected phase, and the third phase winding without continuous current can generally be well satisfied.

[0005] However, since the on-off action of the switch tube cannot make the fault phase terminal voltage at a floating level relative to the reference voltage, the fault phase terminal voltage is always clamped by the capacitor voltage, and the third phase is generally not in a suspended state. Therefore, the position sensorless control method based on the traditional reconstruction topology can only detect the back EMF zero crossing point in the healthy two phases, but cannot realize the back EMF zero crossing point detection in the fault phase, making the direct back EMF method unable to achieve control. Summary of the invention

[0006] In view of the above, the present invention provides a position sensorless control method for a brushless DC motor based on an improved fault-tolerant topology of a Z-source inverter. The method designs an improved Z-source inverter reconstruction topology. Based on the detection window provided by the improved reconstructed topology direct-through vector, the zero crossing point of the three-phase (two healthy phases and one faulty phase) back EMF can be detected after a drive circuit failure, so that the terminal voltage of the faulty phase can provide the motor back EMF information, thereby realizing position sensorless control of the motor under rated and non-rated conditions.

[0007] A position sensorless control method for a brushless DC motor based on an improved fault-tolerant topology of a Z-source inverter comprises the following steps:

[0008] (1) Improve the fault-tolerant reconstruction topology of the Z-source inverter when a phase switch drive circuit fails;

[0009] (2) Collect the DC bus voltage, the three-phase stator current and three-phase stator terminal voltage of the brushless DC motor, and the average value of the capacitor voltage of the Z source network;

[0010] (3) The through vector duty cycle of the Z-source inverter is calculated and generated by the Z-source boost controller according to the average value of the DC bus voltage and the capacitor voltage;

[0011] (4) Generate the commutation signal of the Z-source inverter through the rotor position detection link according to the three-phase stator terminal voltage, and use the commutation signal to directly calculate the actual speed of the brushless DC motor;

[0012] (5) Generate the compensation vector duty cycle and effective vector duty cycle of the Z-source inverter through the motor current control unit according to the actual speed and the stator current of the fault phase;

[0013] (6) Generate drive signals for all power switching devices in the Z-source inverter through pulse width modulation according to the commutation signal, the direct vector duty cycle, the compensation vector duty cycle and the effective vector duty cycle, and apply switching control.

[0014] Furthermore, the fault-tolerant reconstruction topology of the improved Z-source inverter in step (1) includes a three-phase inverter circuit, a Z-source network, two capacitors C 3 and C 4. Two power switch tubes S with anti-parallel diode structure w1 and S w2 The AC side of the three-phase inverter circuit is connected to the three-phase winding of the brushless DC motor, and the DC side of the three-phase inverter circuit is connected to the Z source network. The positive and negative terminals on the other side of the Z source network are connected through S w1 and S w2 Connected to the positive and negative poles of the DC bus. C 3 and C4 are connected in series between the positive and negative poles of the DC bus. The Z source network is composed of a cross-connected capacitor and inductor. C 3 and C The connection point of 4 is connected to the midpoint of the fault phase bridge arm.

[0015] Furthermore, in step (3), the Z-source boost controller generates the through-vector duty cycle of the Z-source inverter by calculating the following formula:

[0016]

[0017] in: d s is the through vector duty cycle of the Z-source inverter, U dc is the DC bus voltage, U C is the average value of the capacitor voltage of the Z source network. Under the action of the through-vector, the input voltage of the Z source network is obviously higher than the DC power supply voltage, and the diode does not meet the conduction condition. Therefore, under the action of the through-vector, the power switch tube is controlled to be turned off, and the fault phase connected to the midpoint of the DC power supply is no longer clamped by the DC end capacitor. At this time, the fault phase has no continuous current and is in a suspended state, which meets the condition of no position control of the brushless DC motor back-EMF method.

[0018] Preferably, the Z-source boost controller calculates the duty cycle of the direct vector generated d s After constraint adjustment, output d s <1 / 3, then let d s =1 / 3 and output; if d s ≥1 / 3, then output directly d s This technical feature ensures that the improved Z-source inverter fault-tolerant reconfiguration topology can enable the motor to operate under rated conditions.

[0019] Furthermore, the rotor position detection step in step (4) includes:

[0020] A comparator, used to compare the three-phase stator terminal voltages with the reference potentials respectively, and output the three-phase voltage comparison results;

[0021] The back-electromotive force zero-crossing detection module is used to screen and control the three-phase voltage comparison results at the end of the direct vector duty cycle and output a zero-crossing signal;

[0022] Delay and commutation control module, used to delay the zero-crossing signal by 30 ° The output commutation signal is generated after the electrical angle is changed.

[0023] Preferably, the reference potential is selected as the voltage of the negative terminal of the DC side of the three-phase inverter circuit.

[0024] Furthermore, the motor current control unit in step (5) includes:

[0025] PI controller, used to subtract i x The result is PI control adjustment to generate the compensation vector duty cycle of the Z source inverter. i x is the stator current of the fault phase;

[0026] Speed ​​controller for n *minus n The result is adjusted by PI control to generate the stator current reference value i *, n * is the given motor speed reference value, n is the actual speed of the brushless DC motor;

[0027] Current controller for i *minus i The result is PI control adjustment to generate the effective vector duty cycle of the Z source inverter. i It is the absolute value of the feedback current, i.e. the non-commutation phase current (which can be determined by the three-phase stator current).

[0028] A computer device comprises a memory and a processor, wherein the memory stores a computer program, and the processor is used to execute the computer program to implement the above-mentioned brushless DC motor position sensorless control method based on the improved fault-tolerant topology of the Z-source inverter.

[0029] A computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the method for controlling a brushless DC motor without a position sensor based on a Z-source inverter improved fault-tolerant topology is implemented.

[0030] The creativity of the brushless DC motor position sensorless control method of the present invention is mainly reflected in the following key technical points:

[0031] 1. The present invention adopts power switch tube, capacitor, inductor, power MOS tube and diode to design a Z-source inverter fault-tolerant reconstruction topology, wherein a pair of capacitors are first connected in parallel at the DC bus end, and then the positive and negative electrodes of the DC end are connected to the anti-parallel structure of the power switch tube and the diode, and then connected to the Z-source network formed by the cross connection of the capacitor and the inductor, and finally connected to the three-phase inverter circuit composed of the power MOS tube and the diode, and the output end of the three-phase bridge inverter circuit is connected to the three-phase winding of the brushless DC motor.

[0032] 2. When the brushless DC motor of the present invention adopts the back-electromotive force method to detect the rotor position, if a fault occurs in phase C, the designed improved fault-tolerant topology structure can disconnect the two switch tubes of the upper and lower bridge arms of the healthy phase, so that no current passes through the healthy two phases (phase A or phase B) in a 60-degree sector; on the other hand, by controlling the chopping of the healthy two-phase switch tubes, the faulty phase (phase C) can be free of continuous current.

[0033] 3. In the six commutation cycles I to VI of the brushless DC motor of the present invention, there is no current flowing through one phase winding in each commutation cycle, and the corresponding phase terminal voltage is a suspended phase under the action of the through vector. Regardless of whether the suspended phase is a healthy phase or a faulty phase, the back electromotive force of the motor can be extracted; the suspended phase terminal voltage is compared with the reference zero level under the action of the through vector to determine the zero crossing point of the suspended back electromotive force; after the zero crossing point of the suspended back electromotive force is detected, a delay of 30 ° The electrical angle can be used to obtain the commutation signal, thereby realizing position sensorless control of the brushless DC motor, solving the problem that the traditional fault-tolerant reconstruction topology of the Z-source inverter cannot extract the suspended opposite potential.

[0034] 4. The motor control structure of the present invention is composed of three parts: rotor position detection link, motor current control unit, and Z-source boost controller, which work together to realize position sensorless control of brushless DC motor based on Z-source inverter fault-tolerant reconstruction topology. The rotor position detection link uses three voltage comparators to compare the three-phase terminal voltage with the reference zero level after limiting, and the comparison result is recorded by the controller at the end of the direct vector; the motor current control unit adjusts the effective vector duty cycle to adjust the motor phase current of the Z-source four-switch inverter, thereby realizing the regulation of the motor output torque.

[0035] In summary, based on the above technical solution, the present invention designs a brushless DC motor position sensorless control method based on the Z-source inverter fault-tolerant reconstruction topology, and proposes a new method for detecting the back-electromotive force zero-crossing point of the unified fault phase and healthy phase of the brushless DC motor, so that the terminal voltage of the fault phase can provide the motor back-electromotive force information, and realize the position sensorless control of the motor under rated and non-rated conditions, enriching the response strategy of the brushless DC motor control under special circumstances. In addition, the improved Z-source inverter fault-tolerant reconstruction topology designed by the present invention can meet the conditions of brushless DC motor position sensorless control under the action of the through vector, and the terminal voltage of the fault phase can provide the brushless DC motor back-electromotive force information, realizing the position sensorless control of the motor under the condition of drive device failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 This is a block diagram of the improved Z-source inverter fault-tolerant reconstruction topology and its control structure according to the present invention.

[0037] Figure 2Circuit structure diagram of the Z-source inverter with improved fault-tolerant reconfigurable topology for driving a brushless DC motor.

[0038] Figure 3 Schematic diagram of the equivalent circuit of the improved fault-tolerant reconstruction topology under different vector effects, where (a) corresponds to non-direct vector effect and (b) corresponds to direct vector effect.

[0039] Figure 4 Schematic diagram of the equivalent circuit of the motor and fault-tolerant reconstruction topology under the action of the through vector, where (a) the healthy phase a is a suspended phase, and (b) the faulty phase c is a suspended phase.

[0040] Figure 5 Schematic diagram of the relationship between the zero-crossing point of the opposite electromotive force of a brushless DC motor and the commutation signal. DETAILED DESCRIPTION

[0041] In order to describe the present invention more specifically, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0042] This embodiment takes the failure of the C-phase switch drive circuit as an example. Since the back-EMF information provided by the suspended phase terminal voltage is used to implement position sensorless control, the back-EMF method requires the brushless DC motor to operate in a two-phase conduction mode, that is, only two phases of the motor winding are energized, the third phase winding has no continuous current (hereinafter referred to as the I constraint condition), and is in a suspended state (hereinafter referred to as the II constraint condition). Therefore, based on the detection window provided by the through vector of the improved reconstructed topology, the present invention proposes a position sensorless control method that can detect the zero crossing of the three-phase (two-phase healthy, one-phase fault) back-EMF after the drive circuit fails, so that the terminal voltage of the faulty phase can provide the motor back-EMF information, and realize the position sensorless control of the motor under rated and non-rated conditions. The specific implementation is as follows:

[0043] (1) Improved fault-tolerant reconfiguration topology of Z-source inverter.

[0044] by Figure 2 Based on the fault-tolerant reconstruction topology shown in C 4 and L Add switch tube S between 2 w2 And anti-parallel diode D w2 , the present invention proposes an improved fault-tolerant reconstruction topology, wherein R s and L s are the phase resistance and phase inductance of the motor respectively, e j , i j ( j= a, b, c) are opposite potentials and phase currents respectively, and point N is the neutral point of the motor.

[0045] For the improved fault-tolerant topology structure proposed in the present invention, by disconnecting the two switches of the upper and lower bridge arms of the healthy phase, it can be achieved that the healthy two phases (phase a or phase b) have no current passing through a 60-degree sector; on the other hand, by controlling the healthy two-phase switch tube chopping, the fault phase (phase c) can have no continuous current. At this time, the current of each phase of the motor satisfies:

[0046] (1)

[0047] Therefore, constraint condition I can be realized in the proposed improved fault-tolerant topology. In addition, if the two switches of the upper and lower bridge arms of the healthy phase are disconnected, the healthy phase becomes a suspended phase, and constraint condition II can obviously be satisfied on the healthy phase.

[0048] For the fault phase, the present invention will analyze whether the fault phase (phase c) meets the constraint condition II under the action of non-through vector (zero vector, effective vector) and through vector respectively; assuming that the through vector duty cycle is d s , then the non-through vector duty cycle is 1− d s .

[0049] Under the non-through vector action of the Z-source inverter, such as Figure 3 As shown in (a), the three-phase winding of the brushless DC motor is equivalent to three current sources, and the healthy positive current, healthy negative current and fault phase current are respectively i u , i d and i m , the source capacitance and inductor current are i C and i L According to the working principle of the Z-source inverter, the current flowing into the Z-source network under the action of the non-through vector is:

[0050] (2)

[0051] The Z source inductor current is generally a continuous quantity, so the current flowing into the Z source network is not zero. w1 , S w2 The fault phase c cannot be suspended all the time, and the constraint condition II is not satisfied. The terminal voltage of the fault phase c is C 1. C 3Clamp to:

[0052] u c = u C1 - u C3 (3)

[0053] Under the action of the direct vector of the Z source inverter, such as Figure 3 As shown in (b), according to the working principle of the Z-source inverter, the input voltage of the Z-source network under the action of the direct vector is:

[0054] (4)

[0055] From equation (4), it can be seen that the input voltage of the Z source network under the action of the direct vector is obviously higher than the DC power supply voltage, and the diode D w1 , D w2 The conduction condition is not met. Therefore, under the action of the direct vector, S is controlled w1 , S w2 The fault phase c connected to the midpoint of the DC power supply is no longer connected to the capacitor C 1. C 3 clamped, the faulty phase c is now in a suspended state, and the constraint condition II is satisfied.

[0056] (2) Improve the floating phase terminal voltage of the fault-tolerant reconstruction topology.

[0057] The brushless DC motor adopts a three-phase six-step commutation drive mode with two-phase conduction. The three-phase terminal voltage of the motor can be expressed as:

[0058] (5)

[0059] Where: u a , u b and u c is the three-phase terminal voltage, u N is the neutral point voltage; assuming that the healthy phase a is a suspended phase, and the healthy phase b and the faulty phase c have current flowing through them, then under the action of the direct vector, the equivalent circuit of the brushless DC motor and the fault-tolerant reconstruction topology is as follows: Figure 4 As shown in (a) in .

[0060] like Figure 4 As shown in (a), the direct-through vector is realized by turning on the two switches of phase b at the same time. Ignoring the diode conduction voltage drop, the terminal voltage of phases b and c is u b = u c =0. In addition, the current and back EMF of phases b and c satisfy ib =‒ i c , e b =‒ e c Adding equation 1 and equation 2 in equation (5), we can get the neutral point voltage:

[0061] u N =0 (6)

[0062] Substituting equation (6) into equation (5), the floating phase current i a =0, then the floating phase terminal voltage is:

[0063] u a = u N + e a = e a (7)

[0064] Similarly, when the healthy b phase is a suspended phase, the voltage at the suspended phase terminal under the action of the direct vector is:

[0065] u b = e b (8)

[0066] Assume that the faulty phase c is a suspended phase, and the healthy phases a and b have current flowing through them. Based on the above assumptions, under the action of the through vector, the equivalent circuit of the motor and the fault-tolerant reconstruction topology is as follows: Figure 4 As shown in (b) in Figure 4 In (b), the direct-through vector is realized by turning on the four switches of phases a and b at the same time; ignoring the diode conduction voltage drop, the terminal voltage of phases a and b is u a = u b =0. Similar to the derivation process of the voltage at the floating terminal of the healthy phase, when the faulty phase c is a floating phase, the voltage at the floating phase terminal under the action of the direct vector is:

[0067] u c = e c (9)

[0068] The relationship between the zero crossing point and the commutation point of the opposite potential of the brushless DC motor is as follows Figure 5 As shown by Figure 5It can be seen that in the six commutation cycles I to VI, there is one phase winding without current in each commutation cycle, and the corresponding phase terminal voltage is a suspended phase under the action of the direct vector. From equations (7) to (9), it can be seen that no matter whether the suspended phase is a healthy phase or a faulty phase, the suspended phase terminal voltage is compared with the reference zero level under the action of the direct vector to determine the zero crossing point of the suspended phase potential.

[0069] Figure 5 In the diagram, each edge of the curve ZCP (zero-crossing signal) corresponds to a zero-crossing point of the opposite potential of the suspended conductor, and each edge of the curve CP (commutation signal) corresponds to a commutation point. Figure 5 It can be seen that after detecting the zero crossing of the opposite potential in the suspended state, a delay of 30 ° The electrical angle can be used to obtain the commutation signal, thereby realizing position sensorless control of the brushless DC motor.

[0070] (3) Improve the fault-tolerant reconfiguration topology controller.

[0071] like Figure 1 The controller structure of the improved fault-tolerant reconfiguration topology of the Z-source inverter of the present invention is shown in the figure. The controller consists of three parts: rotor position detection link, motor current control unit, and Z-source boost controller. n* is the given speed reference value, n is the actual speed, i* is the current reference value, i is the feedback current, U C is the average voltage across the capacitors of the Z source network.

[0072] Figure 1 In the rotor position detection link, three voltage comparators are used to limit the three-phase terminal voltage and compare it with the reference potential g. The comparison result is recorded by the controller at the end of the through vector. When the result changes relative to the previous modulation cycle, the zero-crossing signal is triggered, and its delay is 30 ° The commutation signal can be obtained by measuring the electrical angle.

[0073] The motor current control unit adjusts the effective vector duty cycle to adjust the motor phase current of the Z-source four-switch inverter, thereby achieving the control of the motor output torque. Figure 5 In the commutation cycles II, III, V and VI shown in the figure, the faulty phase c is a non-suspended phase. At this time, the switch tube of phase a or phase b is turned on. Under the action of the effective vector, zero vector and direct vector, the instantaneous values ​​of the two-phase line voltage are:

[0074] (10)

[0075] Assume that the duty ratios of the effective vector and the through vector are d 1 and ds , then the average voltage of the two-phase line is U for:

[0076] (11)

[0077] From equation (11), it can be deduced that the effective vector duty cycle of the II, III, V and VI commutation cycles is:

[0078] (12)

[0079] In formula (12), the direct vector d s The effective vector is output by the Z-source boost controller, and the effective vector is output by the current PI controller. The outer loop of the current PI controller is the speed PI controller.

[0080] exist Figure 5 In the I and IV commutation cycles shown, the faulty phase c is a suspended phase. At this time, the switches of phases a and b are turned on. Under the action of the effective vector, zero vector and direct vector, the instantaneous values ​​of the two-phase line voltage are:

[0081] (13)

[0082] Then the average voltage of the two-phase line is:

[0083] (14)

[0084] From equation (14), it can be deduced that the effective vector duty cycle of the I and IV commutation cycles is:

[0085] (15)

[0086] Comparing equation (12) with equation (15), in the I and IV commutation cycles, the current PI controller output of the II, III, V and VI commutation cycles needs to be transformed as follows:

[0087] (16)

[0088] In the I and IV commutation cycles, if the effective vector duty cycle derived from equation (16) is directly used, the faulty c phase will generate additional current because the faulty c phase is always connected to the midpoint of the capacitor. In order to avoid the c phase generating current, the current compensation PI controller outputs the compensation duty cycle d c , the given value of the controller is 0, and the feedback value is the c-phase current i c , the effective vector duty cycle after compensation is:

[0089] (17)

[0090] Figure 1 In the Z-source boost controller, the output vector duty cycle is d s , the relationship between the direct vector duty cycle and the inverter input voltage and the Z source capacitor voltage is:

[0091] (18)

[0092] set up U N is the rated voltage of the brushless DC motor. The control objective of the Z-source boost controller is to increase the inverter input voltage so that equation (12) has a feasible solution under rated operating conditions (rated supply voltage and rated load conditions), that is, U = U dc = U N The following constraints should be met:

[0093] (19)

[0094] Combining equations (12), (18) and (19), we can obtain:

[0095] (20)

[0096] The improved fault-tolerant reconstruction topology of the Z-source inverter proposed in the present invention aims to achieve short-term operation after a power device drive failure, so that the electrical equipment can run to the maintenance site in a limp state. In order to simplify the implementation process of the controller, the through-vector duty cycle under fault conditions is set to a fixed value that satisfies equation (20) without dynamic adjustment.

[0097] The above description of the embodiments is to facilitate the understanding and application of the present invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to the above embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments. Improvements and modifications made by those skilled in the art to the present invention based on the disclosure of the present invention should be within the protection scope of the present invention.

Claims

1. A method for controlling a brushless DC motor without position sensor based on a Z-source inverter with improved fault-tolerant topology, comprising the following steps: (1) In the scenario where a certain phase switch drive circuit fails, the fault-tolerant reconstruction topology of the Z-source inverter is improved. The improved fault-tolerant reconstruction topology of the Z-source inverter includes a three-phase inverter circuit, a Z-source network, two capacitors C3 and C4, and two power switch tubes S with anti-parallel diode structures. w1 and S w2 The AC side of the three-phase inverter circuit is connected to the three-phase winding of the brushless DC motor, and the DC side of the three-phase inverter circuit is connected to the Z source network. The positive and negative terminals on the other side of the Z source network are connected through S w1 and S w2 Connected to the positive and negative poles of the DC bus, C3 and C4 are connected in series and connected between the positive and negative poles of the DC bus, the Z source network is composed of a cross-connected capacitor and inductor, and the connection point of C3 and C4 is connected to the midpoint of the fault phase bridge arm; (2) Collect the DC bus voltage, the three-phase stator current and three-phase stator terminal voltage of the brushless DC motor, and the average value of the capacitor voltage of the Z source network; (3) calculating and generating a through vector duty cycle of the Z-source inverter through a Z-source boost controller according to the average value of the DC bus voltage and the capacitor voltage; (4) Generate a commutation signal for the Z-source inverter through the rotor position detection link according to the three-phase stator terminal voltage, and use the commutation signal to directly calculate the actual speed of the brushless DC motor; (5) generating a compensation vector duty cycle and an effective vector duty cycle of the Z-source inverter through a motor current control unit according to the actual speed and the stator current of the fault phase; (6) Generate drive signals for all power switching devices in the Z-source inverter through pulse width modulation according to the commutation signal, the direct vector duty cycle, the compensation vector duty cycle and the effective vector duty cycle, and apply switching control.

2. The method for controlling a brushless DC motor without position sensor based on a Z-source inverter with improved fault-tolerant topology according to claim 1 is characterized in that: In step (3), the Z-source boost controller calculates and generates the through vector duty cycle of the Z-source inverter by the following formula: Where: d s is the through vector duty cycle of the Z-source inverter, U dc is the DC bus voltage, U C is the average value of the capacitor voltage of the Z source network.

3. The method for controlling a brushless DC motor without position sensor based on a Z-source inverter with improved fault-tolerant topology according to claim 2 is characterized in that: The Z-source boost controller calculates the pass vector duty cycle d s After constraint adjustment, output, that is, if d s <1 / 3, then let d s =1 / 3 and output; if d s ≥1 / 3, then directly output d s .

4. The method for controlling a brushless DC motor without position sensor based on a Z-source inverter with improved fault-tolerant topology according to claim 1 is characterized in that: The rotor position detection step in step (4) includes: A comparator, used to compare the three-phase stator terminal voltages with the reference potentials respectively, and output the three-phase voltage comparison results; The back-electromotive force zero-crossing detection module is used to screen and control the three-phase voltage comparison results at the end of the direct vector duty cycle and output a zero-crossing signal; The delay and commutation control module is used to generate an output commutation signal after delaying the zero-crossing signal by 30° electrical angle.

5. The method for controlling a brushless DC motor without position sensor based on a Z-source inverter improved fault-tolerant topology according to claim 4 is characterized in that: The reference potential is selected as the voltage of the negative terminal of the DC side of the three-phase inverter circuit.

6. The method for controlling a brushless DC motor without position sensor based on a Z-source inverter with improved fault-tolerant topology according to claim 1 is characterized in that: The motor current control unit in step (5) comprises: PI controller, used to subtract i from 0 x The result is PI control adjustment to generate the compensation vector duty cycle of the Z source inverter, i x is the stator current of the fault phase; The speed controller is used to perform PI control on the result of subtracting n from n* to generate a stator current reference value i*, where n* is a given motor speed reference value and n is the actual speed of the brushless DC motor; The current controller is used to perform PI control on the result obtained by subtracting i from i* to generate an effective vector duty cycle of the Z source inverter, where i is the absolute value of the feedback current, i.e., the non-commutation phase current.

7. A computer device comprising a memory and a processor, characterized in that: The memory stores a computer program, and the processor is used to execute the computer program to implement a position sensorless control method for a brushless DC motor based on an improved fault-tolerant topology of a Z-source inverter as described in any one of claims 1 to 6.

8. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by a processor, the method for controlling a brushless DC motor without a position sensor based on an improved fault-tolerant topology of a Z-source inverter is implemented as claimed in any one of claims 1 to 6.

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