Sensorless control method for switched reluctance motor

Abstract

The invention discloses a position sensorless control method for a switched reluctance motor, and belongs to the technical field of motor control. According to the method, current chopping control is carried out in a conduction interval, low-threshold chopping control is carried out in a non-conduction interval, and the current hysteresis width changes along with the rotation speed, so that the rotor position estimation precision when the rotation speed is increased is ensured. According to the method, current information of each phase is collected, a current slope difference value is calculated, three-phase inductance is obtained through calculation according to the current slope difference value, the inductance obtained through calculation is compared with a preset inductance threshold value, and on-off signals of each phase and pulse signals of special position points can be obtained. According to the time interval between the rising edges of the adjacent position pulse signals and the corresponding rotor position angle difference value, the real-time rotating speed of the motor is obtained through calculation, and the motor rotor position at any moment is estimated. The method is simple in structure and convenient to implement, is not affected by inductance saturation, and is high in position estimation reliability and universality.

Description

Technical Field

[0001] This invention relates to a sensorless control method for a switched reluctance motor, belonging to the technical field of switched reluctance motor control. Background Technology

[0002] Switched reluctance motors (SRMs) have attracted significant attention in industrial and new energy vehicle sectors due to their simple structure, high fault tolerance, and flexible control parameters. SRMs rely on precise rotor position information for commutation; however, installing mechanical position sensors not only increases system size and installation costs but also makes the sensors susceptible to harsh environments. Therefore, to integrate SRM control systems and enhance system stability, it is necessary to research sensorless control methods.

[0003] Current sensorless control methods for switched reluctance motors mainly fall into four categories: phase current waveform method, flux linkage method, and state observer based on conducting phase detection; pulse injection method, modulation method, and additional element method based on non-conducting phase detection; and intelligent control detection method based on neural networks. For the start-up and low-speed operation phases, the most commonly used method is the non-conducting phase pulse injection method. This method estimates the rotor position angle by injecting pulses into the non-conducting phase and utilizing information such as voltage and response current. Patents with publication numbers CN110829938A and CN110247606A both estimate rotor position information and perform commutation operation by detecting the current amplitude at a certain position. However, this method directly ignores the influence of the motion back EMF and the equivalent voltage drop of the windings. As the motor speed increases, the proportion of the freewheeling region in the non-conducting region increases, and the time of one electrical cycle decreases, leading to a reduction in the number of pulse injections in the non-conducting region. This reduces the accuracy of rotor position estimation and may even affect sensorless control. Summary of the Invention

[0004] To overcome the problems existing in related technologies, the technical problem to be solved by the present invention is to provide a sensorless control method for switched reluctance motors. This method can update the pulse injection mode of the current hysteresis width in the non-conducting interval in real time according to the rotational speed, so as to ensure that the number of pulses in the pulse injection interval remains basically unchanged when the rotational speed increases, thereby ensuring the rotor position detection accuracy when the rotational speed increases. By improving the pulse injection mode, the rotor position can also achieve detection accuracy when the rotational speed increases. The technical solution adopted by the present invention to solve the aforementioned technical problem is as follows: A sensorless control method for a switched reluctance motor involves injecting pulses into the non-conducting phase of the switched reluctance motor and performing current chopping control on the conducting phase. The control method includes the following: Let the number of pulse injections in the non-conducting region be... The current hysteresis width of the low-threshold hysteresis pulse injection is calculated according to the following formula. for: in, L 0 represents the average inductance value over the entire non-conducting range; The voltage across the winding is For winding resistance, For rotational speed, The angle is within the non-conducting range; During pulse injection, the number of pulse injections A in the non-conducting region remains constant. As the rotational speed increases, the current hysteresis width decreases. The current hysteresis width, calculated in real time according to the rotational speed using the above formula, is used as the upper limit of the pulse injection current. Then, phase current information is collected, and phase inductance is calculated using the phase current slope difference method, thereby enabling positionless control.

[0005] Furthermore, the phase inductance is calculated using the phase current slope difference method, wherein the phase inductance... The expression is:

[0006] in, This represents the difference in phase current slope. This represents the rotor position angle.

[0007] Furthermore, the specific process for setting the inductance threshold is as follows: when single phases are turned on alternately, the intersection point of the phase inductance characteristic curves of two adjacent phases in the upper half is taken as the inductance threshold. When single-phase and dual-phase conduction alternately, two inductance thresholds need to be set, one high and one low. The inductance thresholds mentioned above should be used. As a high inductance threshold When the preceding phase of the currently conducting phase is in the off position, the inductance value of the following phase is the low inductance threshold. .

[0008] Furthermore, by comparing the estimated inductance value of the non-conducting region with the set inductance threshold, the turn-on and turn-off signals for each phase are obtained. Specifically, when single phases are turned on in turn, if the estimated phase inductance value of the current phase is less than the inductance threshold... If the current conducting phase is turned off, the next phase is turned on according to the phase sequence. When single and dual phases are turned on alternately, if the phase inductance value of the currently estimated phase is less than the high inductance threshold... If the phase inductance value of the currently estimated phase is less than the low inductance threshold, then the next phase will be turned on. Then the currently conducting phase will be turned off.

[0009] At the same time, utilizing the inductance threshold The intersection of the inductance calculated in the non-conducting region and the point where a special position point pulse signal is triggered, for any number of phases... The stator pole number is The number of rotor poles is of Mutually In a switched reluctance motor with this structure, there is a [missing information - likely a rotor cycle or component]. The above intersection points are detected. There are three special position points, corresponding to rotor position angles of 0°, 0°, and 0° respectively. , ... .

[0010] Further, the rotor position angle is calculated. Specifically, based on the time interval between the rising edges of pulse signals at adjacent special position points and the corresponding rotor position angle difference, the average angular velocity is calculated using the following formula: (10) In the formula, , and Calculate the average angular velocity, angle difference, and time interval of the pulse signal for adjacent positions respectively; Then, calculate the rotor position angle at any given time according to formula (11). (11) In the formula, and These are the rotor position angles at the current moment and the previous moment, respectively. Sampling time; The rotor position angle is obtained by using the special position point pulse signal correction formula (11).

[0011] Furthermore, the current rises from zero to its peak value in each pulse cycle. The time required The fall time of the current from its peak to zero The ratio of the sum of the pulses to the time in the non-conducting interval is used as the number of pulse injections in the non-conducting interval, thus obtaining the time lag loop width that varies with the rotational speed while ensuring that the number of pulses remains basically constant.

[0012] Compared with the prior art, the present invention has the following beneficial effects: The control method of this invention allows the hysteresis width of the pulse-injected current to change in real time with the rotational speed in the non-conducting interval, ensuring that the number of pulses in the pulse injection interval remains basically unchanged as the rotational speed increases, thereby ensuring the accuracy of rotor position detection when the rotational speed increases.

[0013] The method of this invention calculates phase inductance based on the phase current slope difference method and uses the inductance threshold method for positionless control. The inductance calculation equation does not contain back EMF and winding voltage drop, which is beneficial to improving the motor's working performance and expanding the working range of SRM.

[0014] The method of this invention only requires the detection of current signals, making it simple to implement, computationally simple, and with low hardware requirements. Attached Figure Description

[0015] Figure 1 This is a schematic flowchart of the sensorless control method for switched reluctance motors in this invention. Figure 2 This is an equivalent diagram of the switched reluctance motor winding in this invention; Figure 3 This is a simulation diagram showing the variation of the current hysteresis width during pulse injection in the non-conducting region as a function of rotational speed in this invention. Figure 4 This is a schematic diagram of the full-cycle inductance calculation principle in this invention; Figure 5 These are schematic diagrams illustrating different operating modes of the switched reluctance motor drive circuit in this invention; Figure 6 This is a schematic diagram of the commutation operation logic in this invention; Figure 7 This is a schematic diagram of the rotor position estimation principle in this invention. Detailed Implementation

[0016] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but this is not intended to limit the scope of protection of this application.

[0017] The present invention provides a sensorless control method for switched reluctance motors (see [link]). Figure 1 ), including the following steps: Step 1: Let the number of pulse injections in the non-conducting region be... The current hysteresis width of the pulse injection in the non-conducting range is set according to the rotation speed. The current chopping control is used in the conducting range, and the low threshold chopping control is used in the non-conducting range. Pulses are injected in the non-conducting range. During pulse injection, the number of pulses injected into the non-conducting region The current hysteresis width remains constant. As the rotational speed increases, the current hysteresis width decreases. The current hysteresis width, calculated in real time based on the rotational speed according to the following formula, is used as the upper limit of the pulse injection current. The actual current, i.e., the upper and lower limits of the pulse injection current, is considered to vary between 0 and the current hysteresis width.

[0018]

[0019] in, L 0 represents the average inductance value over the entire non-conducting range; The voltage across the winding is For winding resistance, For rotational speed, The angle is within the non-conducting range; The current hysteresis width injected for low-threshold hysteresis pulses.

[0020] Current chopper control is generally used in low-speed operation conditions. In this embodiment, the motor speed range is 0-1500 r / min.

[0021] Step 2: Collect phase current information and calculate the phase current slope difference to obtain the full-cycle inductance; Step 3: Compare the estimated inductance value of the non-conducting region with the set inductance threshold to obtain the turn-on and turn-off signals of each phase and trigger a pulse signal at a special position point. This method can effectively detect the non-freewheeling region even at high speeds under low-speed operating conditions.

[0022] Step 4: Calculate the average angular velocity based on the time interval between the rising edges of the pulse signals at adjacent special position points and the corresponding rotor position angle difference. Then, calculate the real-time rotational speed and the rotor position angle at any time based on the average angular velocity. At the same time, use the pulse signals at special position points to correct the rotor position angle.

[0023] In step 1, since the high-frequency pulse period is extremely short, the inductance can be considered to remain unchanged within the period. Each pulse period is a process of the current rising from zero and falling back to zero. Therefore, the energizing process of a single pulse can be equivalent to the energizing process of an inductor with zero initial stored energy. The current response can be expressed by the zero-state equation as: (1) In the formula, In response to current, This is the power supply voltage. For winding resistance, For inductance, The rise time of the response current within a single cycle of the pulse injection.

[0024] The peak response current can be calculated. The time required for: (2) When the winding is turned off, the voltage across the winding is The current flows from The current begins to decay until it reaches zero; the current decreases over time. Calculate according to the following formula: (3) Let the time of the non-conducting region be... ,but Obtained from rotational speed (4) In the formula, The angle of the non-conducting region. The value is the rotational speed.

[0025] Let the number of pulse injections in the non-conducting region be... This is achieved by making the following equation hold (the current rises from zero to its peak value in each pulse cycle). The time required The fall time of the current from its peak to zero The ratio of the sum of the pulses in the non-conducting interval to the time in the non-conducting interval (represented by the number of pulse injections in the non-conducting interval) yields the formula for the lag loop width as a function of rotational speed, ensuring that the number of pulses remains essentially constant. (5) By simultaneously deriving equations (2)-(5), the peak current, i.e. the current hysteresis width of the low-threshold hysteresis pulse injection, can be obtained. for: (6) The above analysis assumes that the high-frequency pulse period is extremely short, and the inductance within the period can be considered as not changing. However, the inductance changes throughout the non-conducting range. The hysteresis width mentioned above is a monotonically decreasing function of the inductance. Therefore, to ensure the required number of pulse injections, the average inductance value can be substituted. The final pulse injection current hysteresis width is calculated, where The calculation formula is as follows: (7) In the formula, and These are the minimum and maximum inductances in the non-conducting region, respectively.

[0026] In step 2, phase current information is collected, and the phase current slope difference is calculated to obtain the full-cycle inductance. The calculation method is as follows: For an asymmetric half-bridge topology, its phase voltage equation is: (8) In the formula, This is the power supply voltage. For winding resistance, For current, For phase inductance, The angular velocity of the motor. This represents the rotor position angle.

[0027] When the switching transistor operates in negative voltage demagnetization mode, ignoring the switching time, the expression for the phase inductance (estimated inductance) can be obtained from the difference between the voltage and current slopes: (9) In the formula, For phase inductance, This is the power supply voltage. The slope of the current rise, The slope of the current decrease, This represents the difference in phase current slope.

[0028] As can be seen from the above equation, there is no back EMF or winding voltage drop in the phase inductance equation, which is beneficial to improving the motor's working performance and expanding the operating range of the SRM.

[0029] In step 3, the estimated inductance value of the non-conducting region is compared with the set inductance threshold to obtain the turn-on and turn-off signals of each phase and trigger a pulse signal at a special position point. The specific process of setting the inductance threshold is as follows: when single phases are turned on alternately, the intersection point of the phase inductance characteristic curves of two adjacent phases in the upper half is taken as the inductance threshold. When single-phase and dual-phase conduction alternately, two inductance thresholds need to be set, one high and one low. The inductance thresholds mentioned above should be used. As a high inductance threshold When the preceding phase of the currently conducting phase is in the off position, the inductance value of the following phase is the low inductance threshold. .

[0030] Furthermore, by comparing the estimated inductance value of the non-conducting region with the set inductance threshold, the turn-on and turn-off signals for each phase are obtained. Specifically, when single phases are turned on in turn, if the estimated phase inductance value of the current phase is less than the inductance threshold... If the current conducting phase is turned off, the next phase is turned on according to the phase sequence. When single and dual phases are turned on alternately, if the phase inductance value of the currently estimated phase is less than the high inductance threshold... If the phase inductance value of the currently estimated phase is less than the low inductance threshold, then the next phase will be turned on. Then the currently conducting phase will be turned off.

[0031] At the same time, utilizing the inductance threshold The intersection of the inductance calculated in the non-conducting region and the point where a special position point pulse signal is triggered, for any number of phases... The stator pole number is The number of rotor poles is of Mutually In a switched reluctance motor with this structure, there is a [missing information - likely a rotor cycle or component]. The above intersection points are detected. There are three special position points, corresponding to rotor position angles of 0°, 0°, and 0° respectively. , ... .

[0032] In step 4, the average angular velocity is calculated according to (10). (10) In the formula, , and Calculate the average angular velocity, angle difference, and time interval of the pulse signal for adjacent positions.

[0033] Then, the rotor position angle at any given time is calculated according to formula (11). (11) In the formula, and These are the rotor position angles at the current moment and the previous moment, respectively. Sampling time.

[0034] The following explanation uses a 12 / 10 three-phase switched reluctance motor as an example.

[0035] Figure 2 This is the equivalent circuit diagram of the switched reluctance motor winding in this invention, where U is the power supply voltage, R is the winding resistance, and L is the equivalent winding inductance. The winding equivalent circuit can be viewed as a series closed-loop circuit of the winding resistance and equivalent winding inductance, the switching element S, and the power supply voltage. Let the rise time of the response current within a single pulse injection cycle be... The current fall time is High-frequency pulses have extremely short periods, and the inductance can be considered to remain unchanged during the period. Each pulse cycle is a process in which the current rises from zero and then falls back to zero. Figure 3 This is a simulation diagram of the hysteresis width of the pulse injection current in the non-conducting region as a function of rotational speed, according to an embodiment of the present invention (the rated voltage of this motor is 60V, the base speed is 1500r / min, and the rated torque is...). ), in the picture and These represent the rotational speed and the hysteresis width of the pulsed current, respectively. As can be seen from the graph, as the rotational speed increases... Rise to During the process, in order to ensure that the number of pulse injections in the non-conducting region remains basically constant at different speeds, the current hysteresis width is adjusted from... Reduced to This ensures the accuracy of rotor position detection, expands the speed range applicable to sensorless control methods at low and medium speeds, and reduces the increased switching losses of switching transistors and the waste of digital processor resources caused by excessive pulse counts at relatively low speeds.

[0036] Figure 4 This is a schematic diagram of the full-cycle inductance calculation in this invention. , , , and The figures represent the current of phase A, the current hysteresis width in the non-conducting region, the current slope difference of phase A, the phase inductance of phase A, and the rotor position angle. As can be seen from the figure, by chopping control in the conducting region and injecting pulses into the non-conducting region, the current information of each phase is collected, the current slope difference is calculated, and then the three-phase inductance is calculated based on the current slope difference. For an asymmetrical half-bridge topology, taking phase A as an example, as follows... Figure 5 As shown in the figure and The transistor and the freewheeling diode are respectively the switching transistor and the freewheeling diode, and their phase voltage equations are as follows: (8) In the formula, This is the power supply voltage. For resistance, For current, For phase inductance, The angular velocity of the motor. This represents the rotor position angle. The first term on the right-hand side of the equation is the phase winding voltage drop, the second term is the electromotive force (EMF), and the third term is the back EMF. The switching transistor operates in three modes: positive voltage excitation, zero-voltage freewheeling, and negative voltage demagnetization. When a phase is switched on, the operating mode is positive voltage excitation, such as... Figure 5 As shown in (a), when switching transistors SA1 and SA2 are simultaneously turned on, a positive voltage is applied across the winding, and the voltage equation is: (12) In the formula, The slope of the current rise.

[0037] When a certain related circuit is interrupted, there are two freewheeling modes: one is the zero-voltage freewheeling mode, such as... Figure 5 As shown in (b), SA1 is disconnected, no voltage is applied across the winding, and the current freewheels through DA2 and SA2. The voltage equation is: (13) In the formula, The slope of the current decrease Another type is the negative voltage demagnetization mode, such as Figure 5 As shown in (c), with switches SA1 and SA2 disconnected, a negative voltage is applied across the winding, and current flows through D. A1 D A2 When power is fed to a source, the voltage equation is: (14) Compared to the positive voltage excitation mode, the negative voltage demagnetization mode results in a faster current drop and stronger control capability, thus the negative voltage demagnetization mode is more effective. Ignoring the switching time of the switching transistor, by combining equations (12) and (14), and dividing the difference between the voltage and current slopes, we can obtain the expression for the phase inductance: (9) In the formula, For phase inductance, This is the power supply voltage. The slope of the current rise, The slope of the current decrease, This represents the difference in phase current slope.

[0038] Figure 6 This is a schematic diagram of the commutation operation logic in this invention. , , , and These are the phase inductance, inductance threshold, turn-on / turn-off signals, position pulse signals, and rotor position angles for each phase. The diagram shows that the turn-on / turn-off signals for the other two phases are obtained by comparing the estimated inductance value of the non-conducting region with the set inductance threshold. For example, when the inductance value of phase A in the non-conducting region drops to the inductance threshold, phase B is turned off, phase C is turned on, and phase B is selected as the estimated phase. Simultaneously, the inductance threshold is used... (High inductance threshold when single-phase and dual-phase conduction alternately) The intersection of the inductance calculation value in the non-conducting region triggers a special position point pulse signal. For a three-phase 12 / 10 switched reluctance motor, three special positions will be detected in one rotor cycle, with corresponding rotor position angles of 0°, 12° and 24°.

[0039] Figure 7 This is a schematic diagram of the rotor position estimation principle in this invention. and These are the pulse signal and the rotor position angle, respectively. , and The pulse signals for rotor position angles of 0°, 12°, and 24° are the special position point pulse signals. Based on the time interval between the rising edges of adjacent special position point pulse signals and the corresponding rotor position angle difference, the average angular velocity is calculated using formula (10), and then the real-time rotational speed and rotor position angle at any time are calculated: (10) In the formula, , and Calculate the average angular velocity, angle difference, and time interval of the pulse signal for adjacent positions.

[0040] The rotor position in the current interval is calculated from the average angular velocity of the previous interval. The formula for calculating the rotor position angle at any given time is formula (11): (11) In the formula, and These are the rotor position angles at the current moment and the previous moment, respectively. Sampling time.

[0041] Meanwhile, the rotor position angle at any given time is corrected using pulse signals at specific position points. One rotor cycle is divided into three position estimation intervals, namely intervals I, II, and III, and there are three position correction points in one rotor cycle, namely 0°, 12°, and 24°.

[0042] Any aspects not covered in this invention are applicable to existing technologies.

Claims

1. A sensorless control method for a switched reluctance motor, comprising injecting pulses into the non-conducting phase of the switched reluctance motor and performing current chopping control on the conducting phase, characterized in that... The control method Includes the following: Let the number of pulse injections in the non-conducting region be... The current hysteresis width of the low-threshold hysteresis pulse injection is calculated according to the following formula. for: ， in, L 0 represents the average inductance value over the entire non-conducting range; The voltage across the winding is For winding resistance, For rotational speed, The angle is within the non-conducting range; During pulse injection, the number of pulse injections A in the non-conducting region remains constant. As the rotational speed increases, the current hysteresis width decreases. The current hysteresis width, calculated in real time according to the rotational speed using the above formula, is used as the upper limit of the pulse injection current. Then, phase current information is collected, and phase inductance is calculated using the phase current slope difference method, thereby enabling positionless control.

2. The control method according to claim 1, characterized in that, The phase inductance is calculated using the phase current slope difference method. The expression is: ， in, This represents the difference in phase current slope. This represents the rotor position angle.

3. The control method according to claim 1, characterized in that, An inductance threshold is set, and the turn-on / off signals for each phase are obtained by comparing the estimated inductance value of the non-conducting region with the set inductance threshold. Specifically, when single phases are turned on in turn, if the estimated phase inductance value of the current phase is less than the inductance threshold... If the current conducting phase is turned off, the next phase will be turned on according to the conducting phase sequence. When single and dual phases are turned on alternately, if the estimated phase inductance value of the currently active phase is less than the high inductance threshold... If the phase inductance value of the currently estimated phase is less than the low inductance threshold, then the next phase will be turned on. Then the currently conducting phase will be turned off.

4. The control method according to claim 3, characterized in that, The specific process for setting the inductance threshold is as follows: when single phases are turned on alternately, the intersection point of the phase inductance characteristic curves of two adjacent phases in the upper half is taken as the inductance threshold. When single-phase and dual-phase circuits are alternately conducting, two inductance thresholds need to be set, one high and one low. As a high inductance threshold When the preceding phase of the currently conducting phase is in the off position, the inductance value of the following phase is the low inductance threshold. .

5. The control method according to claim 3, characterized in that, Using inductor threshold The intersection of the inductance calculated in the non-conducting region and the point where a special position point pulse signal is triggered, for any number of phases... The stator pole number is The number of rotor poles is of Mutually In a switched reluctance motor with this structure, there is a [missing information - likely a rotor cycle or component]. The above intersection points are detected. There are three special position points, corresponding to rotor position angles of 0°, 0°, and 0° respectively. , ... .

6. The control method according to claim 5, characterized in that, The calculation of the rotor position angle involves the following process: based on the time interval between the rising edges of pulse signals at adjacent special position points and the corresponding rotor position angle difference, the average angular velocity is calculated using the following formula. （10） In the formula, , and Calculate the average angular velocity, angle difference, and time interval of the pulse signal for adjacent positions respectively; Then, calculate the rotor position angle at any given time according to formula (11). （11） In the formula, and These are the rotor position angles at the current moment and the previous moment, respectively. Sampling time; The rotor position angle is obtained by using the special position point pulse signal correction formula (11).

7. The control method according to claim 1, characterized in that, The current rises from zero to its peak value in each pulse cycle. The time required The fall time of the current from its peak to zero The ratio of the sum of the pulses to the time in the non-conducting interval is used as the number of pulse injections in the non-conducting interval, thus obtaining the time lag loop width that varies with the rotational speed while ensuring that the number of pulses remains basically constant.

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