Initial magnetic pole identification method based on lower bridge sampling

Abstract

The invention relates to the technical field of motor control, and particularly discloses an initial magnetic pole identification method based on lower bridge sampling, and the method comprises the steps: monitoring the periodic change of a PWM (Pulse Width Modulation) driving signal, obtaining the starting time t of the PWM driving signal, and setting the t as the current sampling time; obtaining a sector where the motor rotor is located at the current sampling time, and determining a to-be-sampled two-phase current according to the relationship between the sector and the three-phase voltage; acquiring a first phase current and a second phase current; according to the mathematical relationship of the three-phase current of the motor, reconstructing to obtain a third-phase current, and outputting the three-phase current of the motor; repeating the steps S1 to S4 in different sectors until sampling of all the sectors is completed; the forward direction and the reverse direction of the UV phase are conducted respectively; the VW phase is forward and reverse; the WU phase is forward and reverse; a current signal coordinate system is converted through Clarke conversion and Park conversion, and an initial magnetic pole angle is calculated. A Hall sensor or complex shunt resistor configuration is not needed, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of motor control, and more particularly to an initial magnetic pole identification method based on lower bridge sampling. Background Art

[0002] In existing synchronous motor control technologies, efficient and precise motor control often requires sampling the motor current to obtain critical information about its operating status. However, traditional current sampling methods primarily rely on Hall effect sensors or shunt resistors. While these methods can provide sufficient current data, they suffer from numerous drawbacks in practical applications. Hall effect sensors, while offering the advantages of fast response and non-contact measurement, are expensive and can easily degrade in high temperatures or strong magnetic fields, impacting system stability. Furthermore, the traditional shunt resistor configuration requires complex circuit design to ensure accurate current signal sampling, which not only increases circuit complexity but also places high demands on hardware layout. Furthermore, current signal processing often requires additional filtering and amplification circuits to eliminate noise and interference, further increasing cost and design complexity. More importantly, starting a synchronous motor without initial magnetic pole identification can easily lead to reverse rotation or loss of step due to initial position detection errors, compromising the reliability and safety of the device. Therefore, designing a high-precision, low-cost, and simple current sampling method to meet the practical needs of synchronous motor control in dynamic environments has become an urgent challenge in the existing technology. Summary of the Invention

[0003] In order to overcome the above-mentioned defects of the prior art, the present invention provides an initial magnetic pole identification method based on lower bridge sampling, which calculates the rotor position through the motor motion equation and the voltage-current relationship to determine the two-phase current to be sampled; adopts two-phase current sampling and reconstructs the third-phase current, simplifies the sampling process and reduces the complexity of the system; conducts the forward and reverse currents of each phase respectively, collects the current signal, and optimizes the magnetic pole identification effect; uses Clarke transformation and Park transformation to convert the current signal coordinate system, and calculates the magnetic pole angle to solve the problems raised in the above background technology.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] An initial magnetic pole identification method based on lower bridge sampling includes the following steps:

[0006] Step S1 , monitoring the periodic change of a pulse width modulation (PWM) driving signal, obtaining the starting time t of the PWM driving signal, and setting t as the current sampling time.

[0007] Step S2: obtaining the sector where the motor rotor is located at the current sampling time, and determining the two-phase current to be sampled based on the relationship between the sector and the three-phase voltage.

[0008] Step S3: collecting and obtaining the first phase current and the second phase current.

[0009] Step S4: reconstruct the third-phase current according to the mathematical relationship of the three-phase current of the motor, and output the three-phase current of the motor.

[0010] Step S5: Repeat steps S1 to S4 in different sectors until sampling of all sectors is completed.

[0011] Step S6, respectively turning on the UV phase in the forward and reverse directions; the VW phase in the forward and reverse directions; and the WU phase in the forward and reverse directions.

[0012] Step S7: Convert the current signal coordinate system through Clarke transformation and Park transformation to calculate the initial magnetic pole angle.

[0013] The Clarke transformation converts the three-phase current from the three-phase coordinate system to the α-β coordinate system, and the calculation formula is: Among them, i a (t) is the first phase current of the motor in the three-phase coordinate system, i b (t) is the second phase current of the motor in the three-phase coordinate system, i α (t) is the first component converted to the α-β coordinate system, i β (t) is the second component converted to the α-β coordinate system; the Park transformation converts the current in the α-β coordinate system to obtain the current component in the dq coordinate system: i d (t) = i α (t)cos(θ m )+i β (t)sin(θ m ),i q (t)=-i α (t)sin(θ m )+i β (t)cos(θ m ), where i d (t) is the component of the stator current on the d-axis at time t, i q (t) is the component of the stator current on the q-axis at time t, θ m is the magnetic pole angle of the motor; get i d (t) and i q After (t), the initial magnetic pole angle θ is estimated by the following calculation formula m :

[0014] As a further solution of the present invention, in step S1, the periodic change of the PWM signal is used to determine the exact time of current sampling. The PWM drive signal periodically alternates between positive and negative, and the starting time of each cycle can be used as the sampling opportunity. In order to ensure the accuracy of sampling, the starting time t of the PWM signal is strictly synchronized with the current sampling time of the motor. The rotor of the motor will experience different current load states at different angular positions, and these states usually change periodically. If the current sampling time does not accurately match the PWM signal, it may cause sampling errors, thereby affecting the accuracy of magnetic pole identification; in order to solve this problem, a synchronization method is used to ensure that the starting time t of each PWM cycle can accurately correspond to the sampling time of the motor current.

[0015] The timing of current sampling is related to the motion state of the motor rotor. There is a timing relationship between the motor's rotor angle and the input PWM signal. By monitoring the periodic changes in the PWM drive signal, the angular position of the motor rotor can be calculated.

[0016] As a further embodiment of the present invention, in step S2, the motor rotor position is divided into multiple sectors, each sector corresponding to a certain angular range of the motor rotor. The sector in which the motor rotor is located is determined by the current angular position of the motor rotor, and the rotor position is estimated based on the motor's motion equation combined with feedback of current and voltage signals. The specific steps are as follows:

[0017] Step Z1, the motion equation of the motor is: Where J is the moment of inertia of the motor rotor, w is the electrical angular velocity of the motor, is the rate of change of speed, T e is the electromagnetic torque of the motor, T L is the load torque; the electromagnetic torque T of the motor e The electromagnetic torque of the motor is calculated based on the stator current, rotor magnetic field, and motor geometry: Where p is the number of pole pairs of the motor, ψ m is the magnetic flux of the rotor flux, i q is the component of the stator current in the q-axis direction, that is, the current component perpendicular to the rotor magnetic field.

[0018] In step Z2, based on the state equation of the motor, the relationship between the voltage and current of the motor is given by the following equation: Among them, v d is the component of the stator voltage on the d-axis, which is the axis aligned with the rotor magnetic field; v q is the component of the stator voltage on the q-axis, which is perpendicular to the d-axis; i d is the component of the stator current on the d-axis; i qis the component of the stator current on the q-axis; R is the stator resistance; L is the stator inductance.

[0019] Step Z3, by d and i q Sampling and v d and v q The rotor position θ is measured and the rotor current i is calculated. q The relationship is: θ = ∫wdt, where w is obtained from the voltage and current equations of the motor; the rotor position is calculated by numerical integration: θ(t) is the rotor position at time t, θ0 is the rotor position at the initial time, and τ represents the time variable.

[0020] Within each sector, the motor's three-phase voltage exhibits a different phase difference. A control algorithm is used to calculate the duty cycle of the three-phase voltage in each sector. The control algorithm uses space vector PWM (SVPWM) to calculate the duty cycle of the three-phase voltage in each sector. SVPWM calculates the voltage vector at each moment based on the motor's three-phase voltage and current signals to control the motor's output torque and speed. The specific steps are as follows:

[0021] Step Y1, the three-phase voltage signal of the motor is: v a (t),v b (t),v c (t), the v a (t),v b (t),v c (t), are the instantaneous voltage values ​​of the three-phase voltage at time t. According to the electrical angle θ of the motor rotor r ,The voltage vector of the motor is divided into six equally divided sectors. Each sector has a specific voltage vector corresponding to it, and the magnitude and direction of the voltage vector in each sector is determined by the rotor position.

[0022] Step Y2, the three-phase voltage v a (t),v b (t),v c (t) is converted into an equivalent space vector V(t) by mapping the three-phase voltage onto a two-dimensional plane. The conversion uses the following transformation formula: in, is the first rotation matrix, is the second rotation matrix. The first rotation matrix and the second rotation matrix are used to convert the three-phase voltage into a space vector represented by a complex number.

[0023] In step Y3, let T1 and T2 be the duration of two adjacent voltage vectors, and calculate the duty cycle of each voltage vector using the following formula: Among them, V m is the required voltage amplitude, V s is the magnitude of the two adjacent voltage vectors selected, V r is the amplitude of the preset reference voltage vector, T total is the total time of the PWM cycle.

[0024] The motor control system selects two-phase currents with a small duty cycle as the objects to be sampled. The voltage corresponding to the two-phase currents with a small duty cycle is relatively small, which can reduce interference in current sampling.

[0025] As a further aspect of the present invention, step S3 is intended to collect the first-phase current and the second-phase current of the motor. During the control process of a synchronous motor, the motor's three-phase current continuously changes based on factors such as the motor's speed, load, and voltage. Any two of these three-phase currents can reflect the motor's current state. To simplify the sampling process and reduce system complexity, two-phase current sampling is employed. The motor control system obtains motor operating information by directly measuring the current signals of the two phases.

[0026] As a further solution of the present invention, in step S4, the first phase current i is obtained by current sampling. a (t) and the second phase current i b (t), the three-phase currents satisfy the linear phase relationship, and the sum of the three-phase currents is zero: i a (t)+i b (t)+i c (t), i c (t) is the third phase current, i c (t) satisfies i c (t)=-i a (t)-i b (t).

[0027] As a further aspect of the present invention, in step S5, the motor's rotor passes through multiple sectors during each cycle, and the current signal in each sector is different. Therefore, to obtain complete data on the motor's three-phase current, multiple sampling must be performed at different rotor positions (i.e., sectors). This repeated sampling effectively reduces the uncertainty caused by single-sampling errors, ensuring the accuracy of magnetic pole identification and subsequent motor control.

[0028] As a further solution of the present invention, in step S6, the forward and reverse currents of each phase (U, V, W) are respectively turned on, so as to collect more current signals under different current directions and further optimize the accuracy of magnetic pole identification. In the three-phase system of the motor, each phase (U, V, W) can have two working states: forward and reverse. Switching between the U phase and the V phase includes: 1. U phase forward, in this state, the U phase will be forward-conducted, and the current will flow out of the U phase, driving the motor stator to generate a magnetic field; 2. U phase reverse, at this time the U phase current flows in the reverse direction, changing the direction of the magnetic field, and generating a current distribution opposite to the forward U phase. Switching between the V phase and the W phase includes: 1. V phase forward, when the V phase conducts forward current, the current flows to the V phase, generating a specific magnetic field direction, affecting the operation of the motor; 2. V phase reverse, by conducting the reverse V phase current, the direction of the magnetic field is changed, and the current data under different magnetic field states is further collected; the W phase and the U phase are also switched forward and reverse: 1. W phase forward, through the W phase forward current, the motor is driven to generate a magnetic field, affecting the state of the motor; 2. W phase reverse, in this state, the W phase reverse current will flow in the reverse direction, generating a magnetic field opposite to the forward direction, helping the system to collect current data more comprehensively.

[0029] The technical effects and advantages of the initial magnetic pole identification method based on lower bridge sampling of the present invention are as follows: the present invention uses PWM drive signals to determine the current sampling time, ensuring sampling accuracy and avoiding the influence of sampling errors on magnetic pole identification; the rotor position is calculated through the motor motion equation, voltage-current relationship, etc., and the two-phase current to be sampled is determined, reducing sampling interference; two-phase current sampling and reconstruction of the third-phase current simplify the sampling process and reduce system complexity; multiple sampling of different sectors reduces the uncertainty caused by single sampling errors and improves magnetic pole identification accuracy; forward and reverse currents of each phase are respectively conducted to collect current signals and optimize magnetic pole identification effect; the current signal coordinate system is converted by Clarke transformation and Park transformation to accurately calculate the magnetic pole angle. Compared with traditional methods, the present invention does not require Hall sensors or complex shunt resistor configurations, reducing costs, reducing the need for additional filtering and amplification circuits, and simplifying circuit design and hardware layout; at the same time, it avoids the reversal or loss of step problems that may occur when the synchronous motor is started without initial magnetic pole identification, improving the reliability and safety of equipment operation, and meeting the actual requirements of synchronous motor control in dynamic environments for high precision, low cost and simple circuits. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is a flow chart of an initial magnetic pole identification method based on lower bridge sampling of the present invention.

[0031] Figure 2 This is a schematic diagram of hardware topology of the present invention. DETAILED DESCRIPTION

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0033] Example 1

[0034] See Figure 1 As shown in the flowchart, an embodiment of the present invention provides an initial magnetic pole identification method based on lower bridge sampling, which includes the following steps:

[0035] Step S1 , monitoring the periodic change of a pulse width modulation (PWM) driving signal, obtaining the starting time t of the PWM driving signal, and setting t as the current sampling time.

[0036] Step S2: obtaining the sector where the motor rotor is located at the current sampling time, and determining the two-phase current to be sampled based on the relationship between the sector and the three-phase voltage.

[0037] Step S3: collecting and obtaining the first-phase current and the second-phase current.

[0038] Step S4: reconstruct the third-phase current according to the mathematical relationship of the three-phase current of the motor, and output the three-phase current of the motor.

[0039] Step S5: Repeat steps S1 to S4 in different sectors until sampling of all sectors is completed.

[0040] Step S6, respectively turning on the UV phase in the forward and reverse directions; the VW phase in the forward and reverse directions; and the WU phase in the forward and reverse directions.

[0041] Step S7: Convert the current signal coordinate system through Clarke transformation and Park transformation to calculate the initial magnetic pole angle.

[0042] Furthermore, in step S1, the periodic change of the PWM signal is used to determine the exact time of current sampling. The PWM drive signal periodically alternates between positive and negative, and the starting time of each cycle can be used as the sampling time. In order to ensure the accuracy of sampling, the starting time t of the PWM signal is strictly synchronized with the current sampling time of the motor. The rotor of the motor will experience different current load states at different angular positions, and these states usually change periodically. If the current sampling time does not accurately match the PWM signal, it may cause sampling errors, thereby affecting the accuracy of magnetic pole identification; in order to solve this problem, a synchronization method is used to ensure that the starting time t of each PWM cycle can accurately correspond to the sampling time of the motor current.

[0043] The timing of current sampling is related to the motion state of the motor rotor. There is a timing relationship between the motor's rotor angle and the input PWM signal. By monitoring the periodic changes in the PWM drive signal, the angular position of the motor rotor can be calculated.

[0044] Furthermore, in step S2, the motor rotor position is divided into multiple sectors, each sector corresponding to a certain angular range of the motor rotor. The sector in which the motor rotor is located is determined by the current angular position of the motor rotor, and the rotor position is estimated based on the motor's motion equation combined with the feedback of the current and voltage signals. The specific steps are as follows:

[0045] Step Z1, the motion equation of the motor is: Where J is the moment of inertia of the motor rotor, w is the electrical angular velocity of the motor, is the rate of change of speed, T e is the electromagnetic torque of the motor, T L is the load torque; the electromagnetic torque T of the motor e The electromagnetic torque of the motor is calculated based on the stator current, rotor magnetic field, and motor geometry: Where p is the number of pole pairs of the motor, ψ m is the magnetic flux of the rotor flux, i q is the component of the stator current in the q-axis direction, that is, the current component perpendicular to the rotor magnetic field.

[0046] In step Z2, based on the state equation of the motor, the relationship between the voltage and current of the motor is given by the following equation: Among them, v d is the component of the stator voltage on the d-axis, which is the axis aligned with the rotor magnetic field; v q is the component of the stator voltage on the q-axis, which is perpendicular to the d-axis; i d is the component of the stator current on the d-axis; i q is the component of the stator current on the q-axis; R is the stator resistance; L is the stator inductance.

[0047] Step Z3, by d and i q Sampling and v d and v q The rotor position θ is measured and the rotor current i is calculated. q The relationship is: θ = ∫wdt, where w is obtained from the voltage and current equations of the motor; the rotor position is calculated by numerical integration: θ(t) is the rotor position at time t, θ0 is the rotor position at the initial time, and τ represents the time variable.

[0048] Within each sector, the motor's three-phase voltage exhibits a different phase difference. A control algorithm is used to calculate the duty cycle of the three-phase voltage in each sector. The control algorithm uses space vector PWM (SVPWM) to calculate the duty cycle of the three-phase voltage in each sector. SVPWM calculates the voltage vector at each moment based on the motor's three-phase voltage and current signals to control the motor's output torque and speed. The specific steps are as follows:

[0049] Step Y1, the three-phase voltage signal of the motor is: v a (t),v b (t),v c (t), the v a (t),v b (t),v c (t), are the instantaneous voltage values ​​of the three-phase voltage at time t. According to the electrical angle θ of the motor rotor r ,The voltage vector of the motor is divided into six equally divided sectors. Each sector has a specific voltage vector corresponding to it, and the magnitude and direction of the voltage vector in each sector is determined by the rotor position.

[0050] Step Y2, the three-phase voltage v a (t),v b (t),v c (t) is converted into an equivalent space vector V(t) by mapping the three-phase voltage onto a two-dimensional plane. The conversion uses the following transformation formula: in, is the first rotation matrix, is the second rotation matrix. The first rotation matrix and the second rotation matrix are used to convert the three-phase voltage into a space vector represented by a complex number.

[0051] In step Y3, let T1 and T2 be the duration of two adjacent voltage vectors, and calculate the duty cycle of each voltage vector using the following formula: Among them, V m is the required voltage amplitude, V s is the magnitude of the two adjacent voltage vectors selected, V r is the amplitude of the preset reference voltage vector, T total is the total time of the PWM cycle.

[0052] The motor control system selects two-phase currents with a small duty cycle as the objects to be sampled. The voltage corresponding to the two-phase currents with a small duty cycle is relatively small, which can reduce interference in current sampling.

[0053] Furthermore, the purpose of step S3 is to collect the first-phase current and the second-phase current of the motor. During the control process of a synchronous motor, the motor's three-phase current continuously changes based on factors such as the motor's speed, load, and voltage. Any two of these three-phase currents can reflect the motor's current state. To simplify the sampling process and reduce system complexity, a two-phase current sampling method is adopted. The motor control system obtains motor operating information by directly measuring the current signals of the two phases.

[0054] Furthermore, in step S4, the first phase current i is obtained by current sampling. a (t) and the second phase current i b (t), the three-phase currents satisfy the linear phase relationship, and the sum of the three-phase currents is zero: i a (t)+i b (t)+i c (t), i c (t) is the third phase current, i c (t) satisfies i c (t)=-i a (t)-i b (t).

[0055] Furthermore, in step S5, the motor's rotor passes through multiple sectors during each cycle, and the current signal in each sector is different. Therefore, to obtain complete data on the motor's three-phase current, multiple sampling must be performed at different rotor positions (i.e., sectors). This repeated sampling effectively reduces the uncertainty caused by single-sampling errors, ensuring the accuracy of magnetic pole identification and subsequent motor control.

[0056] Furthermore, in step S6, the forward and reverse currents of each phase (U, V, W) are respectively turned on so as to collect more current signals under different current directions and further optimize the accuracy of magnetic pole identification. In the three-phase system of the motor, each phase (U, V, W) can have two working states: forward and reverse. Switching between the U phase and the V phase includes: 1. U phase forward, in this state, the U phase will be forward-conducted, and the current will flow out of the U phase, driving the motor stator to generate a magnetic field; 2. U phase reverse, at this time the U phase current flows in the reverse direction, changing the direction of the magnetic field, and generating a current distribution opposite to the forward U phase. Switching between the V phase and the W phase includes: 1. V phase forward, when the V phase conducts forward current, the current flows to the V phase, generating a specific magnetic field direction, affecting the operation of the motor; 2. V phase reverse, by conducting the reverse V phase current, the direction of the magnetic field is changed, and the current data under different magnetic field states is further collected; the W phase and the U phase are also switched forward and reverse: 1. W phase forward, through the W phase forward current, the motor is driven to generate a magnetic field, affecting the state of the motor; 2. W phase reverse, in this state, the W phase reverse current will flow in the reverse direction, generating a magnetic field opposite to the forward direction, helping the system to collect current data more comprehensively.

[0057] Furthermore, in step S7, the three-phase current signal is converted into a dq coordinate system through Clarke transformation and Park transformation, and then the magnetic pole angle of the motor is calculated.

[0058] The Clarke transformation converts the three-phase current from the three-phase coordinate system to the two-phase coordinate system (α-β coordinate system), and the calculation formula is: α (t) = i a (t), Among them, i a (t) is the first phase current of the motor in the three-phase coordinate system, i b (t) is the second phase current of the motor in the three-phase coordinate system, i α (t) is the first component converted to the α-β coordinate system, i β (t) is the second component transformed into the α-β coordinate system.

[0059] The Park transformation converts the current signal in the α-β coordinate system to the synchronous rotating coordinate system dq coordinate system, so as to combine it with the magnetic pole angle of the motor. By converting the current in the α-β coordinate system, the current component in the dq coordinate system is obtained: d (t) = i α (t)cos(θ m )+i β (t)sin(θ m ),i q (t)=-i α (t)sin(θ m)+i β (t)cos(θ m ), where i d (t) is the component of the stator current on the d-axis at time t, i q (t) is the component of the stator current on the q-axis at time t, θ m is the magnetic pole angle of the motor.

[0060] Get i d (t) and i q After (t), the initial magnetic pole angle θ is estimated by the following calculation formula m :

[0061] Example 2

[0062] See Figure 2 As shown in the schematic diagram, the hardware design of the present invention uses a three-phase resistor configuration of R1, R2, and R3. These three-phase resistors R1, R2, and R3 are installed in the lower bridge arm of the motor drive bridge to achieve current sampling. Each resistor generates a voltage signal proportional to the current passing through the resistor. To obtain accurate data from these signals, a voltage signal acquisition module is designed. This voltage signal acquisition module uses a high-precision analog-to-digital converter (ADC) to convert the analog voltage signals into digital signals.

[0063] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in this application should be included in the scope of protection of this application. Therefore, the scope of protection of this application should be based on the scope of protection of the claims.

[0064] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. An initial magnetic pole identification method based on lower bridge sampling, characterized in that: The steps include: Step S1, monitoring the periodic change of the pulse width modulation drive signal, obtaining the starting time t of the pulse width modulation drive signal, and setting t as the current sampling time; Step S2, obtaining the sector where the motor rotor is located at the current sampling time, and determining the two-phase current to be sampled based on the relationship between the sector and the three-phase voltage; Step S3, collecting and obtaining the first phase current and the second phase current; Step S4, reconstructing the third-phase current according to the mathematical relationship of the three-phase current of the motor, and outputting the three-phase current of the motor; Step S5, repeating steps S1 to S4 in different sectors until sampling of all sectors is completed; Step S6, respectively conduct the UV phase forward and reverse; VW phase forward and reverse; WU phase forward and reverse; Step S7, converting the current signal coordinate system through Clarke transformation and Park transformation to calculate the initial magnetic pole angle; The Clarke transformation converts the three-phase current from the three-phase coordinate system to the α-β coordinate system, and the calculation formula is: α (t) = i a (t), Among them, i a (t) is the first phase current of the motor in the three-phase coordinate system, i b (t) is the second phase current of the motor in the three-phase coordinate system, i α (t) is the first component converted to the α-β coordinate system, i β (t) is the second component converted to the α-β coordinate system; the Park transformation converts the current in the α-β coordinate system to obtain the current component in the dq coordinate system: i d (t) = i α (t)cos(θ m )+i β (t)sin(θ m ),i q (t)=-i α (t)sin(θ m )+i β (t)cos(θ m ), where i d (t) is the component of the stator current on the d-axis at time t, i q (t) is the component of the stator current on the q-axis at time t, θ m is the magnetic pole angle of the motor; get i d (t) and i q After (t), the initial magnetic pole angle θ is estimated by the following calculation formula m :

2. The initial magnetic pole identification method based on lower bridge sampling according to claim 1 is characterized in that In step S2, the sector in which the motor rotor is located is determined by the current angular position of the motor rotor, and the rotor position is estimated based on the motor's motion equation combined with the feedback of the current and voltage signals. The specific steps are as follows: Step Z1, the motion equation of the motor is: Where J is the moment of inertia of the motor rotor, w is the electrical angular velocity of the motor, is the rate of change of speed, T e is the electromagnetic torque of the motor, T L is the load torque; the electromagnetic torque T of the motor e The electromagnetic torque of the motor is calculated based on the stator current, rotor magnetic field, and motor geometry: Where p is the number of pole pairs of the motor, ψ m is the magnetic flux of the rotor flux, i q is the component of the stator current in the q-axis direction, that is, the current component perpendicular to the rotor magnetic field; In step Z2, based on the state equation of the motor, the relationship between the voltage and current of the motor is given by the following equation: Among them, v d is the component of the stator voltage on the d-axis, which is the axis aligned with the rotor magnetic field; v q is the component of the stator voltage on the q-axis, which is perpendicular to the d-axis; i d is the component of the stator current on the d-axis; i q is the component of the stator current on the q-axis; R is the stator resistance; L is the stator inductance; Step Z3, by d and i q Sampling and v d and v q The rotor position θ is measured and the rotor current i is calculated. q The relationship is: θ = ∫wdt, where w is obtained from the voltage and current equations of the motor; the rotor position is calculated by numerical integration: θ(t) is the rotor position at time t, θ0 is the rotor position at the initial time, and τ represents the time variable.

3. The initial magnetic pole identification method based on lower bridge sampling according to claim 1 is characterized in that In step S2, in each sector, the three-phase voltage of the motor will present a different phase difference, and the duty cycle of the three-phase voltage in each sector is calculated through the control algorithm.

4. The initial magnetic pole identification method based on lower bridge sampling according to claim 3 is characterized in that The control algorithm uses space vector modulation technology to calculate the duty cycle of the three-phase voltage in each sector. Space vector modulation technology calculates the voltage vector at each moment based on the three-phase voltage and current signals of the motor to control the output torque and speed of the motor. The specific steps are as follows: Step Y1, the three-phase voltage signal of the motor is: v a (t),v b (t),v c (t), the v a (t),v b (t),v c (t), are the instantaneous voltage values ​​of the three-phase voltage at time t; according to the electrical angle θ of the motor rotor r ,The voltage vector of the motor is divided into six equally divided sectors; each sector has a specific voltage vector corresponding to it, and the magnitude and direction of the voltage vector in each sector is determined by the rotor position; Step Y2, the three-phase voltage v a (t),v b (t),v c (t) is converted into an equivalent space vector V(t) by mapping the three-phase voltage onto a two-dimensional plane. The conversion uses the following transformation formula: in, is the first rotation matrix, is a second rotation matrix, and the first rotation matrix and the second rotation matrix are used to convert the three-phase voltage into a space vector represented by a complex number; In step Y3, let T1 and T2 be the duration of two adjacent voltage vectors, and calculate the duty cycle of each voltage vector using the following formula: Among them, V m is the required voltage amplitude, V s is the magnitude of the two adjacent voltage vectors selected, V r is the amplitude of the preset reference voltage vector, T total is the total time of the PWM cycle.

5. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: In step S4, the first phase current i is obtained by current sampling. a (t) and the second phase current i b (t), the three-phase currents satisfy the linear phase relationship, and the sum of the three-phase currents is zero: i a (t)+i b (t)+i c (t), i c (t) is the third phase current, i c (t) satisfies i c (t)=-i a (t)-i b (t).

6. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: In step S1 , the starting time t of the pulse width modulation signal is strictly synchronized with the current sampling time of the motor, and the angular position of the motor rotor is calculated by monitoring the periodic changes of the pulse width modulation drive signal.

7. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: In step S2, the control system of the motor selects two-phase currents with small duty cycles as objects to be sampled.

8. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: In step S6, the forward and reverse currents of the U phase, V phase, and W phase are respectively conducted, and current signals under different current directions are collected to optimize the accuracy of magnetic pole identification.

9. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: In step S3, a two-phase current sampling method is adopted to obtain the working information of the motor by directly measuring the current signals of the two phases.

10. The method for initial magnetic pole identification based on lower bridge sampling according to claim 1, characterized in that: The sampling frequency of the motor's three-phase voltage and current signals, which is used by space vector modulation technology to calculate the duty cycle, meets the real-time requirements of the control algorithm.

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