Torque control method for three-phase switched reluctance motor based on aligned position detection

Abstract

The application discloses a three-phase switched reluctance motor torque control method based on aligned position detection and relates to the technical field of motor control. In each position sector with two adjacent aligned positions as end points, a high-frequency current pulse is injected into a non-conducting phase with monotonous position change of inductance, and no trailing current is ensured before injection; the inductance of the non-conducting phase is estimated according to the rising slope of the high-frequency current pulse or the falling slope of the trailing current; if the inductance is less than a preset threshold, the instantaneous torque control based on a torque distribution function is adopted according to the inductance estimation position; otherwise, the position is not estimated, the change of the conducting phase torque with the position is ignored, and the given current of the conducting phase is determined according to the current-torque characteristics at the 60-degree electric angle position. Compared with the technology of adopting the instantaneous torque control only in the two-phase conducting area, the application can reduce the cost of the position sensor and inhibit the torque pulsation since only the aligned position needs to be detected and the instantaneous torque control area is expanded.

Description

Technical Field

[0001] This invention discloses a torque control method for a three-phase switched reluctance motor based on alignment position detection, which relates to the field of motor control technology. Background Technology

[0002] Switched reluctance motors (SRMs) offer advantages such as high starting torque, wide speed range, and high reliability, making them promising candidates for applications in fields like electric vehicles. However, a complex nonlinear relationship exists between the electromagnetic torque and rotor position of a SRM. The effectiveness of torque ripple suppression in SRMs heavily relies on high-precision absolute position information. Currently, high-precision absolute position information is primarily obtained through high-resolution absolute position sensors, which increase the cost and decrease the reliability of the motor system.

[0003] Therefore, sensorless position estimation has become a research hotspot in recent years. These methods typically rely on the relationship between electromagnetic properties (magnetic flux, inductance, and incremental inductance) and position, estimating position by identifying these electromagnetic characteristics. However, under low-speed, heavy-load conditions, the electromagnetic properties of the conducting phase are insensitive to position changes, and the position accuracy when using voltage integration to estimate the magnetic flux or inductance is easily affected by accumulated errors. Furthermore, if position estimation is based solely on the non-conducting phase, it is difficult to accurately select the position estimation phase during startup and low-speed conditions. In summary, sensorless position estimation still struggles to achieve high-precision position estimation under various operating conditions.

[0004] To address this, some researchers have combined the two methods mentioned above, utilizing position sector signals provided by low-resolution switching Hall effect position sensors. In sectors where torque is sensitive to position changes, high-frequency current pulses are injected into the non-conducting phase windings. Position is estimated based on the pulse peak value, thereby achieving instantaneous torque control and suppressing torque ripple. This method is simple and easy to implement, achieving a good balance in terms of cost, reliability, and torque ripple suppression effectiveness. However, the torque ripple suppression effect of this method still lags significantly behind that of full-cycle instantaneous torque control; furthermore, this method requires an induction magnetic ring with the same number of pole pairs as the motor rotor poles, resulting in high manufacturing costs for the induction magnetic ring.

[0005] Patent 202411897857.8 provides a current partitioning planning method for a three-phase switched reluctance motor based on a switch-type Hall position sensor. The method includes: if the rotor is in a Hall sector where only one phase torque is in the same direction as the given total motor output torque, then only this phase is turned on, and the given current of the turned phase does not change with the rotor position. The given current of the turned phase is determined with the average torque of the sector being the same as the given total torque as the target. If the rotor is in a Hall sector where only one phase torque is in the opposite direction to the given total motor output torque, then a high-frequency pulse current is injected into the winding of this phase. The rotor position is estimated based on the pulse peak value, thereby determining the given torque of the other two phases, and subsequently determining the given current of the other two phases. By estimating the rotor position in sectors where the turned phase torque is sensitive to the rotor position and planning the turned phase current curve in real time, torque pulsation is suppressed.

[0006] This method has the following technical drawbacks:

[0007] 1. Instantaneous torque control is only implemented in half of the sectors, so the torque ripple suppression effect is still significantly worse than that of full-cycle instantaneous torque control;

[0008] 2. An induction magnetic ring with the same number of pole pairs as the motor rotor is required to divide the instantaneous torque control zone and the average torque control zone according to the alignment and misalignment positions detected by the Hall position sensor. Therefore, the cost of the induction magnetic ring is relatively high. Summary of the Invention

[0009] This invention provides a torque control method for a three-phase switched reluctance motor based on alignment position detection, to solve the following technical problems:

[0010] 1. In view of the shortcomings of the existing technology in terms of poor torque ripple suppression effect, the present invention performs continuous position estimation in a part of the position region where only one phase torque is in the same direction as the given total output torque of the motor, thereby expanding the instantaneous torque control region and thus improving the torque ripple suppression effect.

[0011] 2. To address the high cost of existing induction magnetic rings, this invention selects a non-conducting phase with monotonically changing inductance as the position estimation phase within each position sector, with two adjacent aligned positions as endpoints. High-frequency current pulses are injected into the non-conducting phase when there is no tailing current. The instantaneous torque control region and the average torque control region are directly divided based on the rising slope of the high-frequency current pulse injected into the non-conducting phase or the falling slope of the tailing current. This reduces the cost of the induction magnetic ring, requiring only an induction magnetic ring with half the number of pole pairs as the motor rotor poles.

[0012] The technical solution adopted in this invention is:

[0013] A torque control method for a three-phase switched reluctance motor based on alignment position detection includes: injecting high-frequency current pulses into the non-conducting phase whose inductance varies monotonically with position in each position sector with adjacent alignment positions as endpoints; estimating the unsaturated inductance of the non-conducting phase based on the rising slope of the high-frequency current pulse injected into the non-conducting phase or the falling slope of the tail current; if the inductance is less than a preset threshold, estimating the position based on the inductance, thereby determining the given torque of the conducting phase based on the given total torque, the estimated position, and the torque distribution function, and further determining the given current of the conducting phase based on the given torque of the conducting phase, the estimated position, and the current-torque-position characteristic; otherwise, not estimating the position, ignoring the change of the conducting phase torque with position, and determining the given current of the conducting phase based on the current-torque characteristic at a 60° electrical angle position.

[0014] Furthermore, the alignment position, i.e. the position where the stator poles and rotor poles are completely aligned, can be detected by a switch-type Hall position sensor, and the number of pole pairs of the matching induction magnetic ring can be only half the number of rotor poles.

[0015] Furthermore, if a Hall sensor with only half the number of pole pairs of the induction magnetic ring is used, then when installing the sensor, the output signal of the Hall element corresponding to the non-conducting state should be either all high level or all low level when the motor is in different alignment positions of one phase.

[0016] Furthermore, the pulse injection is achieved by applying a rectangular wave voltage with a certain frequency and duty cycle to both ends of the winding of the non-conducting phase.

[0017] Furthermore, the high and low levels of the rectangular wave voltage are the positive and negative bus voltages, respectively.

[0018] Furthermore, the frequency and duty cycle of the rectangular wave voltage should meet the following conditions:

[0019] 1) The peak value of the pulse is not greater than the critical saturation current;

[0020] 2) The pulse peak value is accurately detected;

[0021] 3) The current is zero before the rectangular wave voltage changes from low level to high level.

[0022] Furthermore, the pulse injection should be performed under the premise that there is no tail current in the non-conducting phase.

[0023] Furthermore, to avoid pulse injection when there is still tail current in the non-conducting phase, the method is as follows: before applying a positive bus voltage to the non-conducting phase, check whether the current of the non-conducting phase is zero; if it is zero, turn on the power switch of the non-conducting phase and apply the positive bus voltage; otherwise, continue to apply the negative bus voltage.

[0024] Furthermore, the tail current descent slope specifically refers to the descent slope of the tail current that is not greater than the critical saturation current.

[0025] Furthermore, the formula for estimating the unsaturated inductance based on the pulse rise slope or the tail current fall slope is as follows:

[0026]

[0027] In the formula, For the estimated unsaturated inductance of phase j, This is the DC bus voltage. This refers to the time it takes for the pulse current to rise from zero to its peak value, or the time it takes for the tail current to fall. For the j-phase current in time The change within, It is the reciprocal of the current slope.

[0028] Furthermore, in time Within the current, the current should remain continuously changing; otherwise, the inductance should not be estimated to avoid an overestimation of the inductance.

[0029] Furthermore, the threshold is the value of the unsaturated inductance when one edge of the stator pole of the non-conducting phase is aligned with one edge of the rotor pole.

[0030] Furthermore, the steps for obtaining the current-torque-position characteristics are as follows:

[0031] 1) Obtain the curve data of the monotonic change of torque with current at multiple different positions between the minimum and maximum inductance positions through electromagnetic simulation or experimental measurement, and find the maximum torque value T. max ;

[0032] 2) Based on the curve data obtained in the previous step, respectively, derive the curve data of the monotonic change of current with torque: Using the torque value in the curve data of the monotonic change of torque with current as the known independent variable value, and the current value as the known function value, use interpolation to calculate the independent variables as 0 and T. max / N、2T max / N、……、(N-1)T max / N and T max The current value at that time is obtained, which gives the curve data of the current changing monotonically with the torque.

[0033] 3) Summarize the curve data obtained in the previous step to obtain the required current-torque-position characteristics.

[0034] Furthermore, the 60° electrical angle position specifically refers to a position that is 60° electrical angle away from the misaligned position of the corresponding conducting phase and 120° electrical angle away from the aligned position of the corresponding conducting phase. Attached Figure Description

[0035] Figure 1 This is a schematic diagram illustrating the principle of the present invention;

[0036] Figure 2 The waveform diagram of Hall signal and phase inductance in an embodiment of the present invention is shown.

[0037] Figure 3 This is a diagram showing the inductance characteristics of phase A of the motor in an embodiment of the present invention;

[0038] Figure 4 This is a torque characteristic diagram of phase A of the motor in an embodiment of the present invention;

[0039] Figure 5 This is a current-torque-position characteristic diagram of phase A of the motor in an embodiment of the present invention;

[0040] Figure 6 This is a current-torque characteristic diagram of phase A at a 60° electrical angle position in an embodiment of the present invention;

[0041] Figure 7 This is a general flowchart of an embodiment of the present invention;

[0042] Figure 8 This is a flowchart of the pulse injection sub-process of an embodiment of the present invention;

[0043] Figure 9 This is a flowchart of the position estimation sub-process of an embodiment of the present invention;

[0044] Figure 10 This is a flowchart of the A-phase torque control sub-process of an embodiment of the present invention;

[0045] Figure 11 The above are the Hall signal and phase inductance waveforms when using the prior art in the embodiments of the present invention;

[0046] Figure 12 The above is a simulation waveform diagram using the prior art when the rotational speed is 100 rpm and the given total torque is 15 Nm in an embodiment of the present invention.

[0047] Figure 13 The simulation waveform diagram is shown in the embodiment of the present invention when the rotational speed is 100 rpm and the given total torque is 15 Nm.

[0048] Figure 14 The above is a simulation waveform diagram using the prior art when the rotational speed is 500 rpm and the given total torque is 10 Nm in an embodiment of the present invention.

[0049] Figure 15 The simulation waveform of the proposed method is shown in the embodiment of the present invention when the rotational speed is 500 rpm and the given total torque is 10 Nm. Detailed Implementation

[0050] The embodiments of the present invention will now be described with reference to the accompanying drawings.

[0051] Adopting such Figure 1 The method shown in this embodiment controls a three-phase 12 / 8-pole switched reluctance motor. The power converter is an asymmetrical half-bridge structure, and the position sensor is a switching Hall sensor with only 4 pairs of magnetic poles in the inductive magnetic ring. The waveforms of the Hall signal and the phase inductance, and their relative positional relationship, are as follows: Figure 2 As shown in the figure. θ a,A θ a,B and θ a,C These represent the alignment positions of phases A, B, and C, respectively; N s The position sector number is related to the logic level H1 of Hall signal 1, the logic level H2 of Hall signal 2, and the logic level H3 of Hall signal 3 by N. s =4H3+2H2+H1.

[0052] In this embodiment, the rated voltage of the motor is 72 V, the stator pole arc and rotor pole arc are 120° electrical angle and 128.16° electrical angle, respectively, and the inductance characteristics are as follows: Figure 3 As shown. By Figure 3 It can be seen that the inductance curve at a current of 20 A coincides with the inductance curve at a current of 10 A, but differs significantly from the inductance curve at a current of 30 A; therefore, in this embodiment, a current pulse peak value not exceeding 20 A will not lead to magnetic circuit saturation. Figure 3 It can be seen that within the stator-rotor polar overlap region of phase A, the phase A inductance is not sensitive to position changes; therefore, the position is not estimated based on the phase A inductance in this region. Figure 3 In this embodiment, the 184.08° electrical angle position is the position where the rear edge of the stator pole of phase A is aligned with the rear edge of the rotor pole. At this position, the unsaturated inductance of phase A is 2.71 mH. Therefore, in this embodiment, if the estimated inductance value is greater than or equal to 2.71 mH, the position is not estimated based on the inductance.

[0053] In this embodiment, the torque characteristics are as follows: Figure 4 As shown. Figure 4 Using the torque value from the torque-current variation data at a certain location as a known independent variable and the current value as a known function value, interpolation is used to calculate the current value when the independent variables are 0, 32 / 16, 2×32 / 16, ..., 15×32 / 16, and 32 Nm, thus obtaining the data on the monotonic variation of current with torque at that location. Figure 4 The torque-current variation data at each position is processed as described above to obtain the data on the monotonic variation of current with torque at each position. Summarizing these data yields the current-torque-position characteristic data, such as... Figure 5 As shown.

[0054] Figure 4 In this embodiment, when the rotor is between 60° and 64.08° electrical angle, the C-phase stator poles and rotor poles completely coincide, and the C-phase is not used for position estimation. However, the A-phase torque is not sensitive to position changes. Therefore, when the rotor is between 60° and 64.08° electrical angle, the change of A-phase torque with position is ignored, and it is assumed that the relationship between A-phase torque and current at any position is consistent with the relationship between A-phase torque and current at the 60° electrical angle position. In this embodiment, the relationship between A-phase torque and current at the 60° electrical angle position is as follows: Figure 6 As shown.

[0055] The overall process adopted in this embodiment is as follows: Figure 7 As shown, it is executed every 5 μs. The graph shows that when the timing variable N... c Torque control is executed when N is an integer multiple of 5, therefore the torque control cycle is 5 × 5 μs = 25 μs; when N c When N equals 0, a positive bus voltage is applied to the non-conducting phase to inject a pulse. c When the voltage is equal to 16, a negative bus voltage is applied to the non-conducting phase and inductance and position estimation are performed. Therefore, the pulse period and position estimation period are both 40×5 μs = 200 μs, and the pulse rise time in each pulse period is 16×5 μs = 80 μs.

[0056] The pulse injection sub-process used in this embodiment is as follows: Figure 8 As shown in the figure. It can be seen from the figure that when sector number N... s When N equals 2 or 5, phase A is selected as the position estimation phase, and a current pulse is injected into phase A when there is no tail current in phase A; when N s When N equals 1 or 6, phase B is selected as the position estimation phase, and a current pulse is injected into phase B when there is no tail current in phase B; when N s When the value is 3 or 4, phase C is selected as the position estimation phase. A current pulse is injected into phase C when there is no tail current. This is determined by judging the current phase current value (i...). A0 i B0 and i C0 The presence of a tail current in the position estimation phase is determined by whether the value is greater than zero. If it is greater than zero, a tail current exists, and the upper and lower bridge arm switches of the position estimation phase are turned off. Otherwise, no tail current exists, and the upper and lower bridge arm switches of the position estimation phase are turned on to inject a current pulse.

[0057] The location estimation sub-process used in this embodiment is as follows: Figure 9 As shown in the figure. F A,int F B,int and F C,intThese are flag variables used to indicate whether the pulse injection process of phases A, B, and C has been interrupted; if the flag variable is 1, the pulse injection process is interrupted, and position estimation is not performed. The position is determined by judging the current phase current value (i...). A i B and i C The system checks whether the current value (i) recorded in the pulse injection sub-process is greater than zero to determine if the tailing current has decreased to zero before the current moment, thus avoiding an overestimation of the inductance. A0 i B0 and i C0 Whether the value is less than 20 A is used to ensure that the inductance and position estimates based on the tail current are not affected by magnetic saturation. Inductance estimate L A,est L B,est and L C,est The unit is mH, and the coefficient k1 in the inductance estimation formula is 72 × (200 × 10⁻⁶). -6 (×16 / 40)×10 3 =5.76. F A,rdy F B,rdy and F C,rdy These are the flag variables used to indicate whether the position estimation based on phases A, B, and C was successful; if the flag variable is 1, the position estimation was successful.

[0058] Taking phase A as an example, the torque control sub-process used in this embodiment is as follows: Figure 10 As shown in the figure. T ref For a given total torque, T A,ref Given the torque for phase A, i A,ref Given a current in phase A, θ est To estimate the obtained position angle, f u (θ est ) is the torque distribution function near the misaligned position, f a (θ est The torque distribution function is close to the alignment position. The judgment on whether the state of the upper and lower bridge arm switches of phase A has changed is achieved by judging whether the state of the switch at the current moment is the same as the state recorded in the pulse injection sub-process. The current control method is hard chopper control (control frequency is 40 kHz).

[0059] f u (θ est The expression for ) is as follows:

[0060]

[0061] f a (θ est The expression for ) is as follows:

[0062]

[0063] The method of this invention was compared with an existing method that performs instantaneous torque control only in the two-phase conduction region through simulation using MATLAB / Simulink software. In the simulation model using the existing method, the position sensor is a switch-type Hall sensor with eight pairs of magnetic poles in the inductive magnetic ring. The aligned and misaligned positions of each phase can be detected by this sensor. The waveforms of the Hall signal and the phase inductance and their relative positions are shown below. Figure 11 As shown in the figure, θ u,A θ u,B and θ u,C These represent the misalignment positions of phases A, B, and C, respectively. The simulation waveforms at a speed of 100 rpm and a given total torque of 15 Nm are shown below. Figure 12 and Figure 13 As shown, the simulation waveform at a rotational speed of 500 rpm and a given total torque of 10 Nm is as follows. Figure 14 and Figure 15 As shown, when the rotational speed is 100 rpm and the given total torque is 15 Nm, the torque ripple obtained by the method of this invention is significantly smaller; when the rotational speed is 500 rpm and the given total torque is 10 Nm, the torque control effects of the two methods are comparable, but the existing method requires a higher resolution position sensor.

Claims

1. A torque control method for a three-phase switched reluctance motor based on alignment position detection, characterized in that, The process includes the following: In each position sector with adjacent alignment positions as endpoints, a high-frequency current pulse is injected into the non-conducting phase where the inductance changes monotonically with position; Estimate the unsaturated inductance of the non-conducting phase based on the rising slope of the high-frequency current pulse injected into the non-conducting phase or the falling slope of the tail current. If the inductance is less than a preset threshold, the position is estimated based on the inductance, and the given torque of the conducting phase is determined based on the given total torque, the estimated position, and the torque distribution function. Then, the given current of the conducting phase is determined based on the given torque of the conducting phase, the estimated position, and the current-torque-position characteristic. Otherwise, the position is not estimated, the change of the conducting phase torque with position is ignored, and the given current of the conducting phase is determined based on the current-torque characteristic at the 60° electrical angle position.

2. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The alignment position, which is the position where the stator poles and rotor poles are completely aligned, is detected by a switch-type Hall position sensor. The number of pole pairs of the matching induction magnetic ring is only half that of the rotor poles.

3. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, If a Hall sensor with only half the number of pole pairs of the induction magnetic ring is used, then when installing the sensor, the output signal of the Hall element corresponding to the non-conducting state should be either all high level or all low level when the motor is in different alignment positions of one phase.

4. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The pulse injection is achieved by applying a rectangular wave voltage with a certain frequency and duty cycle to both ends of the winding of the non-conducting phase; The high and low levels of the rectangular wave voltage are the positive and negative bus voltages, respectively. The frequency and duty cycle of the rectangular wave voltage should meet the following conditions: 1) The peak value of the pulse is not greater than the critical saturation current; 2) The pulse peak value is accurately detected; 3) The current is zero before the rectangular wave voltage changes from low level to high level.

5. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The pulse injection should be performed under the premise that there is no tail current in the non-conducting phase; To avoid pulse injection when tail current still exists in the non-conducting phase, the following method is used: before applying a positive bus voltage to the non-conducting phase, check whether the current of the non-conducting phase is zero; if it is zero, turn on the power switch of the non-conducting phase and apply the positive bus voltage; otherwise, continue to apply the negative bus voltage.

6. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The tail current descent slope specifically refers to the descent slope of the tail current that is not greater than the critical saturation current.

7. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The formula for estimating unsaturated inductance based on the pulse rise slope or the tail current fall slope is: ， In the formula, For the estimated unsaturated inductance of phase j, This is the DC bus voltage. This refers to the time it takes for the pulse current to rise from zero to its peak value, or the time it takes for the tail current to fall. For the j-phase current in time The change within, It is the reciprocal of the slope of the current. In time Within the inductance, the current should remain continuously changing; otherwise, the inductance should not be estimated.

8. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The threshold is the value of the unsaturated inductance when one edge of the stator pole of the non-conducting phase is aligned with one edge of the rotor pole.

9. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The steps for obtaining the current-torque-position characteristics are as follows: 1) Obtain the curve data of the monotonic change of torque with current at multiple different positions between the minimum and maximum inductance positions through electromagnetic simulation or experimental measurement, and find the maximum torque value T. max ; 2) Based on the curve data obtained in the previous step, respectively, derive the curve data of the monotonic change of current with torque: Using the torque value in the curve data of the monotonic change of torque with current as the known independent variable value, and the current value as the known function value, use interpolation to calculate the independent variables as 0 and T. max / N、2T max / N、……、(N-1)T max / N and T max The current value at that time is obtained, which is the curve data of the current changing monotonically with the torque; 3) Summarize the curve data obtained in the previous step to obtain the required current-torque-position characteristics.

10. The torque control method for a three-phase switched reluctance motor based on alignment position detection according to claim 1, characterized in that, The 60° electrical angle position specifically refers to a position that is 60° electrical angle away from the misaligned position of the corresponding conducting phase and 120° electrical angle away from the aligned position of the corresponding conducting phase.

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