A sensorless control method for switched reluctance motor based on phase current monitoring

Abstract

The present invention discloses a position sensorless control method for a switched reluctance motor based on phase current monitoring. When the motor is stationary, a small current is injected into each phase winding simultaneously, the current rise time or chopping frequency is detected, and the relationship between the time or frequency of each phase is compared to perform initial position partitioning; during the startup and normal operation of the motor, the current rise time or chopping frequency under different rotor positions is continuously collected, the time or frequency at the characteristic point is found and the threshold is updated; the current information of the non-conducting phase is monitored in real time and compared with the threshold. When the monitored value reaches the threshold, it is considered that the rotor passes the characteristic point position. The average speed of an interval is calculated with the help of characteristic point detection, and the rotor position at any time in the next interval is reconstructed using the average speed. The present invention can overcome the serious limitations of traditional position sensorless technology, such as high dependence on the motor inductance model, complex control process, and low universality of the solution, and can improve the simplicity and practicality of positionless control technology.

Description

Technical Field

[0001] The present invention relates to the field of switched reluctance motor systems, and in particular to a position sensorless control method for a switched reluctance motor. Background Art

[0002] Real-time rotor position monitoring during the operation of a switched reluctance motor is crucial for ensuring stable operation. Traditional control methods require the addition of position sensors to monitor the motor's current rotor position for speed regulation and phase commutation. However, adding position sensors increases system cost, size, and complexity, reducing system reliability and stability under specific operating conditions. To reduce system cost and enhance system reliability under specific operating conditions, sensorless control methods can be employed. Currently, the most widely studied sensorless control methods include the phase current slope method, pulse injection, and novel intelligent algorithms. These methods rely on offline inductance models, which are complex and prone to errors, resulting in low practicality. Summary of the Invention

[0003] In order to reduce the complexity of the position reconstruction method and enhance the practicality of the method, the present invention proposes a position sensorless control method for a switched reluctance motor based on phase current monitoring. Starting from the mapping relationship between the current rise time and chopping frequency within the hysteresis loop bandwidth and the winding phase inductance, the inductance model is not solved. The current rise time or chopping frequency within the hysteresis loop bandwidth of the non-conducting phase is directly monitored to determine the position of the characteristic point. The position relationship between the characteristic point and the mechanical structure of the motor is used to reconstruct the rotor position, accurately calculate the real-time position of the rotor, and effectively control the motor.

[0004] The object of the present invention is achieved by injecting a small current into the non-conducting phase of the switched reluctance motor, monitoring the current rise time or chopping frequency within the hysteresis loop bandwidth of the non-conducting phase to obtain characteristic point position information for rotor position reconstruction;

[0005] The sensorless control method includes three main stages: initial position detection, motor start-up, rotor position reconstruction and speed regulation;

[0006] In the initial position detection stage, a small current is injected into each phase winding and the hysteresis loop bandwidth is set to i ref ±Δi, by comparing the rise time Δt of each phase current within the hysteresis bandwidth r Or the chopping frequency f completes the initial position partition;

[0007] During the motor startup phase, the starting point where the rotor enters the minimum inductance zone from the inductance decreasing zone is taken as the characteristic point. When the threshold at the characteristic point is unknown, the initial threshold t measured offline is used. a0 , t b0 , tc0 , t d0 Guide the motor to start, collect and analyze the current rise time or chopping frequency of the non-conducting phase when the rotor is in different positions during the motor operation, and update the time threshold t at the characteristic point according to the real-time working conditions rz Or frequency threshold f z And serve as the detection feature of the next interval;

[0008] In the rotor position reconstruction and speed control stage, the current rise time or chopping frequency of the non-conducting phase is first monitored. When the time or frequency reaches the threshold, it is considered that the rotor has passed the characteristic point position. Next, the average speed in the interval is calculated using the time interval between the two characteristic points. The average speed of the interval is then used to reconstruct the rotor position at any time in the next interval. Finally, the reconstructed rotor position information is used to guide the motor commutation and speed regulation.

[0009] The beneficial effects of the present invention are:

[0010] The present invention can overcome the serious limitations of traditional position sensorless control technology, such as high dependence on the motor inductance model, complex control process, and low universality of the solution, and can improve the simplicity and practicality of position sensorless control technology. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 is a flow chart of the control method of the present invention;

[0012] Figure 2 This is the overall control block diagram of the position sensorless control method for the switched reluctance motor;

[0013] Figure 3 This is a schematic diagram of obtaining the current rise time and chopping frequency;

[0014] Figure 4 This is a schematic diagram of the measurement of current rise time and chopping frequency at a special position;

[0015] Figure 5 It is a schematic diagram of the initial position partition;

[0016] Figure 6 It is the motor starting flow chart;

[0017] Figure 7 This is a diagram showing the relationship between current, inductance, current rise time, and chopping frequency;

[0018] Figure 8 It is a schematic diagram of position reconstruction. DETAILED DESCRIPTION

[0019] The embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0020] The present invention provides a position sensorless control method for a switched reluctance motor based on phase current monitoring, such as Figure 1 As shown, the following steps are included:

[0021] Step S1: inject a constant current into the winding to fix the rotor position. After the position is fixed, inject a small current into the corresponding phase to be detected, detect the current rise time or chopping frequency and use it as the initial threshold of the phase;

[0022] Step S2: injecting a small current into the four-phase windings simultaneously, detecting the current rise time or chopping frequency within the hysteresis band of the four-phase windings respectively, and determining the range of the rotor initial position and the initial conduction phase based on the magnitude relationship of the measured values;

[0023] Step S3: Using the initial threshold value measured in step S1 to guide the motor to complete startup and start collecting the current rise time or chopping frequency when the rotor is in different positions. During the motor startup process, if the current rise time or chopping frequency reaches the corresponding threshold value, it is considered that the rotor has passed through a special position, and the switching state is adjusted according to the commutation logic;

[0024] Step S4: The position where the rotor enters the minimum inductance region from the inductance decreasing region is used as a characteristic point. Based on the difference in the motor voltage equation before and after the characteristic point, the change pattern of the current rise time or chopping frequency when the rotor enters the characteristic point is inferred. Combined with the time information collected in real time in step S3, the current rise time or chopping frequency at the characteristic point is found and the threshold is updated;

[0025] Step S5: monitoring the non-conducting phase current information in real time, detecting the characteristic point position according to the threshold value obtained in step S4, and issuing a position index signal when the rotor passes the characteristic point;

[0026] Step S6, calculating the interval between adjacent signals based on the characteristic point position index signal sent in step S5, and estimating the average speed of the rotor in the interval based on the mechanical angle between adjacent characteristic points;

[0027] Step S7, reconstructing the rotor position at any time in the next interval based on the average rotation speed between adjacent feature points obtained in step S6;

[0028] Step S8: realizing position sensorless control of the switched reluctance motor according to the reconstructed rotor position information.

[0029] The main framework of the present invention is as follows Figure 2 As shown, during the operation of the motor, the non-conducting phase current information is monitored in real time, and the rotor position is calculated and reconstructed based on the monitored current information. The position reconstruction result is used to guide the motor to perform commutation and speed control.

[0030] The present invention provides a method for controlling a switched reluctance motor without a position sensor. The method uses small current injection information as a basis to monitor the current rise time or chopping frequency of the non-conducting phase in real time to reconstruct the rotor position. The current rise time and chopping frequency are obtained as follows: Figure 3 shown.

[0031] Set the chopping bandwidth to ±Δi. When the current is lower than the chopping lower limit, the switch is turned on. When the current is higher than the chopping upper limit, the switch is turned off. Ignoring the influence of the winding mutual inductance, the motor voltage equations when the switch is turned on and when the switch is turned off in the static state are as follows:

[0032]

[0033]

[0034] Where: U ph is the phase voltage; R ph is the winding resistance; i ph is the phase current; L ph (θ) is the phase inductance; θ is the rotor position angle.

[0035] According to the voltage equation, the current slope relationship expressions when the switch is turned on and when the switch is turned off are as follows:

[0036]

[0037]

[0038] According to the current slope, the time Δt of each current rise within the hysteresis bandwidth can be obtained. r The expressions for the chopping frequency f are as follows:

[0039]

[0040]

[0041] Where: 2Δi ph is the chopping bandwidth.

[0042] Taking an 8 / 6 switched reluctance motor as an example, the specific control process of the position sensorless control method of the switched reluctance motor based on phase current monitoring proposed in the present invention is described below.

[0043] Before starting the motor, several sets of special position current rise time or chopping frequency are measured offline as initial thresholds. The initial threshold measurement method is as follows: Figure 4 shown.

[0044] The figure takes the measurement of the initial threshold of the special position of phase D as an example. First, a constant current is applied to phase A to rotate the rotor until it is aligned with the stator pole. Then a small current is injected into phase D to measure the current rise time t when the phase is in the special position. d0 Or chopping frequency f d0 As the initial threshold, the initial thresholds of other phases are measured in the same way.

[0045] The position-free control method of the switched reluctance motor of the present invention comprises three stages: initial position partitioning, motor startup and operation, rotor position reconstruction and speed regulation;

[0046] When stationary, a small current is injected into the four-phase windings at the same time, and the following can be obtained by comparing the four-phase current rise time or chopping frequency: Figure 5 The initial rotor position can be divided into four small intervals, which are divided by the intersection of the two-phase current rise time or the chopping frequency, and each small interval occupies 15°.

[0047] The motor startup process is the intermediate process from the rotor being stationary to normal operation. In this process, the initial position partitioning method is used to determine the initial conduction phase, and the special position time threshold measured offline is used to guide the motor commutation. When the time or frequency information reaches the threshold, it is considered that the rotor has passed the special position, and the commutation is performed according to the set commutation logic. The specific control process is as follows: Figure 6 shown.

[0048] During the motor startup process, in the conduction interval, the current chopping control is performed on the phase, and in the non-conduction interval, a small current is injected into the phase, such as Figure 7 The rise time or chopping frequency of the injected current within the hysteresis band is monitored to update the characteristic point threshold information.

[0049] When the rotor is in the inductance rising zone and the inductance falling zone, the winding inductance is greatly affected by the change of the rotor position. At this time, the motor back electromotive force cannot be ignored. When considering the influence of the back electromotive force, the current rise time Δt r The expressions for the chopping frequency f are as follows:

[0050]

[0051]

[0052] Where: ω is the rotor rotation angular velocity.

[0053] After the rotor enters the minimum inductance area, the winding inductance changes little, the motor back electromotive force can be ignored, and the inductance is approximately equal to L min , the time Δt for the current to rise r The expressions for the chopping frequency f are as follows:

[0054]

[0055]

[0056] When the rotor enters the minimum inductance area from the inductance decreasing area, a characteristic point θ appears. x Before the characteristic point, the current rise time t r Continuously decreases, f continues to increase, after the characteristic point, t r It approaches the minimum value and no longer changes significantly. Similarly, f approaches the maximum value and no longer changes significantly. During motor operation, the current rise time or chopping frequency is collected and calculated online, and the current rise time at the characteristic point can be obtained and recorded as t rz Or the chopping frequency is recorded as f z , update the threshold and use it for feature point position detection in the next interval.

[0057] During the operation of the motor, when the current rise time of the corresponding phase reaches the threshold time t rz Or the chopping frequency reaches the threshold frequency f z When , the rotor is considered to have entered the minimum inductance region and generates a position index signal such as Figure 8 As shown, it corresponds to the moment when the inductance enters the minimum region. rr1 , t rr2 Respectively represent the time when the two rising edges occur; Δt rr Represents the time between two rising edges; Δθ represents the angle between two rising edges. The speed is calculated and the timer is reset every time a feature point is detected. The motor speed expression is as follows:

[0058]

[0059] The corresponding rotor position reconstruction result is:

[0060] θ t =nt rr ×360°-θ x

[0061] Where: θ0 is the angle between two adjacent feature points; θ t Reconstruct the angle for the rotor position; t rr is the time difference between the current moment and the last time a feature point appeared; θ x is the angle difference between the feature point and the actual 0° position.

[0062] According to the rotor position reconstruction result, the reconstructed rotor position is used to guide the motor commutation and speed regulation, realizing the motor position sensorless control.

[0063] The above description merely represents the preferred embodiments of the present invention, and while the description is relatively specific and detailed, it should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications, improvements, and substitutions without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A position sensorless control method for a switched reluctance motor based on phase current monitoring, characterized in that: The following steps are involved: Step S1: inject a constant current into the winding to fix the rotor position. After the position is fixed, inject a small current into the corresponding phase to be detected, detect the current rise time or chopping frequency and use it as the initial threshold of the phase; Step S2: injecting a small current into the four-phase windings simultaneously, detecting the current rise time or chopping frequency within the hysteresis band of the four-phase windings respectively, and determining the range of the rotor initial position and the initial conduction phase based on the magnitude relationship of the measured values; Step S3: Using the initial threshold value measured in step S1 to guide the motor to complete startup and start collecting the current rise time or chopping frequency when the rotor is in different positions. During the motor startup process, if the current rise time or chopping frequency reaches the corresponding threshold value, it is considered that the rotor has passed through a special position, and the switching state is adjusted according to the commutation logic; Step S4: The position where the rotor enters the minimum inductance region from the inductance decreasing region is used as a characteristic point. Based on the difference in the motor voltage equation before and after the characteristic point, the change pattern of the current rise time or chopping frequency when the rotor enters the characteristic point is inferred. Combined with the time information collected in real time in step S3, the current rise time or chopping frequency at the characteristic point is found and the threshold is updated; Step S5: monitoring the non-conducting phase current information in real time, detecting the position of a characteristic point according to the threshold value obtained in step S4, and issuing a position index signal when the rotor passes through the characteristic point; Step S6, calculating the interval between adjacent signals based on the characteristic point position index signal sent in step S5, and estimating the average speed of the rotor in the interval based on the mechanical angle between adjacent characteristic points; Step S7, reconstructing the rotor position at any time in the next interval based on the average rotation speed between adjacent feature points obtained in step S6; Step S8: realizing position sensorless control of the switched reluctance motor according to the reconstructed rotor position information.

2. The position sensorless control method for a switched reluctance motor based on phase current monitoring according to claim 1, characterized in that: Before the motor starts, the current rise time or chopping frequency threshold at the characteristic point is unknown, and the special position threshold measured offline is used to guide the motor start.

3. The position sensorless control method for a switched reluctance motor based on phase current monitoring according to claim 1, characterized in that: Update the threshold at the characteristic point online. After the motor starts running, collect and analyze the current rise time or chopping frequency of the rotor at different positions. Combine theoretical derivation with actual data to obtain the current rise time or chopping frequency when the rotor enters the characteristic point, and update the threshold.

4. The position sensorless control method for a switched reluctance motor based on phase current monitoring according to claim 1, characterized in that: The non-conducting phase is used as the detected phase, and the current information of the non-conducting phase is monitored in real time and used as the basis for position detection.

5. The position sensorless control method for a switched reluctance motor based on phase current monitoring according to claim 1, characterized in that: The motor rotor position is reconstructed by detecting the position information of feature points. A position index signal is generated when the rotor passes through a feature point. The speed is calculated based on the time between adjacent index signals, and the real-time position of the rotor in the next interval is reconstructed based on the average speed of the previous interval.

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