A sensorless control method for switched reluctance motor

Abstract

The application discloses a kind of switched reluctance motor position sensorless control method, belong to switched reluctance motor position sensorless control field.The application utilizes analog circuit to detect idle phase pulse current peak value, when peak value is greater than the threshold value set, rising edge voltage signal is generated, motor speed is calculated according to the time interval and angle interval between two rising edge voltage signals, and then the real-time position angle of rotor is calculated, overcome the difficulty that the sampling frequency of analog-digital conversion module in digital processor is insufficient under higher speed;Motor speed adjusts pulse injection frequency, while ensuring the accuracy of rotor position detection, unnecessary consumption of digital processor resources by high-frequency pulse under relatively low speed is avoided;Without complex algorithm, the digital processor power consumption is reduced.

Description

Technical Field

[0001] This invention belongs to the field of sensorless control of switched reluctance motors, and more specifically, relates to a sensorless control method for switched reluctance motors. Background Technology

[0002] Switched reluctance motors (SRMs) employ a doubly salient pole structure for both the stator and rotor, constructed from laminated silicon steel sheets. The stator has concentrated windings, while the rotor has neither windings nor permanent magnets, resulting in a simple structure, low manufacturing cost, and suitability for high-speed operation. Each phase is controlled relatively independently, enabling single-phase operation, thus ensuring high reliability and suitability for harsh operating environments. These numerous advantages have led to the widespread application of SRMs in textile manufacturing, machine tools, and other fields, while also showing great promise in aerospace power supplies and electric vehicles.

[0003] Switched reluctance motor (SRM) speed control systems are a type of self-controlled variable frequency speed control system. Therefore, accurate rotor position information is crucial for switching between starting and generating modes, as well as for the sequential conduction control of each phase winding, directly affecting the efficient and reliable operation of the SRM. Currently, position detection in SRM speed control systems mainly relies on position sensors mounted on the rotor. However, position sensors not only increase the size and cost of the motor, but their accuracy also decreases significantly or even fails under harsh environments such as high temperatures and strong magnetic fields, and during high-speed operation. Therefore, researching sensorless technology is of great significance for SRMs to fully realize their superior performance.

[0004] In the low-speed operation phase of a motor, sensorless technology mainly relies on idle phase current detection. This method involves injecting high-frequency voltage pulses into the idle phase and comparing the peak value of the response current with a set threshold to calculate the rotor position. However, due to limitations imposed by the digital processor's performance and the complexity of the control algorithm, the sampling frequency of the response current cannot be captured in a timely manner at specific positions, resulting in errors in speed and position calculations. Summary of the Invention

[0005] In view of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a sensorless control method for switched reluctance motors, the purpose of which is to improve the accuracy of position calculation.

[0006] To achieve the above objectives, the present invention provides a sensorless control method for a switched reluctance motor, comprising:

[0007] S1. Fix the rotor at the speed update point, inject an initial voltage pulse, and use the peak value of the current sensor's output voltage as the voltage threshold.

[0008] S2. Inject voltage pulses into the idle phase; wherein, the pulse injection frequency is positively correlated with the current speed of the motor, and the rise time of the response current is the same under different pulse injection frequencies;

[0009] S3. Detect the peak output voltage of the current sensor using a peak detection circuit;

[0010] S4. Compare the obtained peak output voltage with the voltage threshold. If the peak voltage is higher than the voltage threshold, the analog circuit generates a rising edge voltage signal. Calculate the motor speed using the time interval and angle interval between two adjacent rising edge voltage signals, and reset the peak detection circuit.

[0011] S5. Integrate the motor speed over time to obtain the rotor position angle increment, add it to the rotor position angle corresponding to the speed update point to obtain the real-time rotor position angle, and then control the on and off of each phase winding of the motor.

[0012] Furthermore, the number of pulses injected in the pulse injection interval is the same at both high and low speeds.

[0013] Furthermore, the formula for calculating the injected pulse frequency is:

[0014]

[0015] θ1 and θ2 are the starting and ending angles of the pulse injection interval, respectively, and N r Where n is the number of rotor poles, n is the motor speed, and N represents the number of pulses injected in the pulse injection interval.

[0016] Furthermore, the duty cycle of the injected pulse satisfies:

[0017]

[0018] In the formula, f is the pulse injection frequency, D is the duty cycle, f0 represents the pulse injection frequency when the voltage threshold is selected, and D0 represents the duty cycle when the voltage threshold is selected.

[0019] Furthermore, the formula for calculating the motor speed is:

[0020]

[0021] In the formula, Δθ is the angular interval between two adjacent rising edge voltage signals, and T is the time interval between two rising edge voltage signals.

[0022] Furthermore, the formula for calculating the real-time rotor position angle is:

[0023] θ=θ p +6N r nt

[0024] In the formula, θ is the real-time position angle of the motor. p t is the rotor position angle of the motor corresponding to the previous speed update point, and t is the time interval between the moment the rotor reaches the speed update point and the current moment.

[0025] Furthermore, the peak detection circuit includes a diode, a capacitor, a first resistor, and a second resistor.

[0026] Overall, the above-described technical solutions conceived by this invention can achieve the following beneficial effects compared with the prior art.

[0027] This invention utilizes analog circuits to detect the peak value of the idle phase pulse current. When the peak value exceeds a set threshold, a rising edge voltage signal is generated. The motor speed is calculated based on the time interval and angular interval between two rising edge voltage signals, and then the real-time rotor position angle is calculated. This overcomes the difficulty of insufficient sampling frequency of the analog-to-digital conversion module in the digital processor at higher speeds. By adjusting the pulse injection frequency through the motor speed, the accuracy of rotor position detection is ensured while avoiding unnecessary consumption of digital processor resources by high-frequency pulses at relatively low speeds. It does not require complex algorithms, thus reducing the computing power overhead of the digital processor. Attached Figure Description

[0028] Figure 1 This is a hardware structure diagram of the speed regulation system in an embodiment of the present invention;

[0029] Figure 2 This is a schematic diagram of the rotational speed update point in an embodiment of the present invention;

[0030] Figure 3 This is a schematic diagram of the A-phase current waveform in an embodiment of the present invention;

[0031] Figure 4 This is an analog circuit diagram in an embodiment of the present invention;

[0032] Figure 5 This is a flowchart of the rotational speed calculation in an embodiment of the present invention;

[0033] Figure 6 This is a flowchart of the sensorless control process in an embodiment of the present invention. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0035] Using a three-phase 6 / 4-pole switched reluctance motor as a prototype, the digital processor adopted is a TMS320F28335 DSP (hereinafter referred to as DSP28335), and the steady-state speed of the motor is 500 r / min.

[0036] Figure 1 The diagram shows the hardware structure of the speed control system. The dashed box on the left contains the DSP28335 digital processor, which is mainly responsible for implementing the motor control algorithm, generating PWM waves, and interacting with the host computer. The dashed box on the right contains the analog circuitry; its input voltage comes from a current sensor, and its output voltage is the output of a voltage comparator, which serves as the input to the capture unit in the DSP28335.

[0037] Figure 2 The diagram shows the location of the speed update point. As can be seen from the diagram, the speed update point is located within the inductance decrease range, which is 210° in this embodiment. After determining its specific location, the voltage threshold is obtained through offline experiments, i.e., the peak value obtained by the peak detection circuit after a pulse injection experiment is performed at the rotor position of 210°. The specific steps are as follows:

[0038] Step 1.1: Define the rotor position angle when the stator teeth of phase A are aligned with the rotor slots as the reference rotor position angle origin;

[0039] Step 1.2: Fix the motor rotor at the 210° position;

[0040] Step 1.3: Inject a voltage pulse with a frequency of 10kHz and a duty cycle of 30% into phase A winding. At this time, the output of the peak detection circuit in the analog circuit is the voltage threshold U. th .

[0041] During the operation of a switched reluctance motor, the excitation range is characterized by an increase in inductance as the rotor position increases, while the idle range is characterized by a decrease in inductance as the rotor position increases. Therefore, when a voltage pulse is injected into the idle phase, the peak response current increases with the rotor position, meaning the input voltage of the peak detection circuit exhibits a monotonically increasing characteristic. This characteristic ensures that the DSP28335 captures only one rising edge voltage signal during a given phase pulse injection period.

[0042] Figure 3 The diagram shows the current waveform of phase A winding under sensorless control. When the rotor position angle of phase A is at the on-state angle θ... on and the shut-off angle θ off During this period, current hysteresis control is used to excite the A-phase winding. When the rotor position angle of the A-phase is in the pulse injection range, a voltage pulse of a certain frequency and duty cycle is injected into the A-phase.

[0043] Assuming in Figure 3The midpoint 1 is the speed update point. If the DSP's A / D sampling module is used to directly sample the output voltage of the current sensor, the DSP cannot detect the current information at point 1 in time because A / D sampling is discrete sampling. The sampled currents at the two sampling points 2 and 3 near point 1 are both less than the set threshold, so the speed update algorithm cannot be triggered. The sampled current at sampling point 4 will be greater than the set threshold, which leads to speed calculation error.

[0044] To solve the above problems, the following approach is adopted: Figure 4 The analog circuit shown detects the peak value of the pulse response current. The preceding stage of the analog circuit is a peak detection circuit, and the following stage is a voltage comparator circuit. The peak detection circuit detects the peak value of the output voltage of the current sensor. The detection result serves as the input to the voltage comparator circuit, which compares it with a voltage threshold. When the voltage exceeds the threshold, the output of the voltage comparator circuit changes from low to high and remains high until the peak detection circuit is reset. This rising edge voltage signal is captured by the DSP, which then performs corresponding actions such as speed calculation and position update.

[0045] Compared with existing peak detection circuits, Figure 4 The circuit shown includes an added discharge resistor R2. R2 is not connected to the circuit when detecting the peak value, but is connected when the peak detection circuit needs to be reset. Because R2 has a small resistance, it allows for rapid capacitor discharge, thus enabling the peak detection circuit to quickly return to its initial state.

[0046] Figure 5 The diagram shows the speed calculation flowchart. When the DSP captures the rising edge voltage signal, it enters a capture interrupt. Within the interrupt, speed calculation and other operations are performed. The specific steps are as follows:

[0047] Step 2.1: Calculate the motor speed based on the time interval and angular interval between two adjacent rising edge voltage signals. The calculation formula is as follows:

[0048]

[0049] In the formula, Δθ is the angular interval between two adjacent rising edge voltage signals, T is the time interval, and N is the distance between the rising edges of the voltage signals. r This represents the number of rotor poles. In this embodiment, Δθ is taken as 120°, and N... r The value is 4.

[0050] Step 2.2: Determine the rotor position angle θ at the speed update point p If phase A is the pulse injection phase at this time, then θ p It is 210°; if phase B is the pulse injection phase at this time, then θ p It is 330°; if phase C is the pulse injection phase at this time, then θ p It is 90°.

[0051] Step 2.3: Reset the peak detection circuit by discharging the capacitor.

[0052] Figure 6 The diagram shows the sensorless control flowchart. To ensure position calculation accuracy, the DSP executes the main sensorless control program every 50μs. The specific steps are as follows:

[0053] Step 3.1: Calculate the real-time position of the rotor, specifically:

[0054] θ=θ p +6N r nt

[0055] In the formula, θ is the real-time position angle of the motor. p N is the motor rotor position angle corresponding to the previous speed update point. r denoted as the rotor pole number, n as the motor speed, and t as the time interval between the rotor reaching the speed update point and the current time.

[0056] Step 3.2: Calculate the pulse injection frequency and duty cycle. The pulse injection frequency is:

[0057]

[0058] In the formula, θ1 and θ2 are the starting and ending angles of the pulse injection interval, respectively, and N... r denoted by , where n is the number of rotor poles and n is the motor speed.

[0059] The purpose of using this formula to determine the pulse injection frequency is to increase the pulse injection frequency at high speeds and decrease it at low speeds within the applicable speed range of the idle phase current detection method, while always ensuring the same number of voltage pulses within the pulse injection interval. This approach ensures the accuracy of speed and position calculations at different speeds while avoiding the waste of DSP resources at low speeds when using the same pulse injection frequency.

[0060] The pulse injection duty cycle should meet the following requirements:

[0061]

[0062] In the formula, f is the pulse injection frequency and D is the duty cycle.

[0063] This formula is used to determine the voltage pulse duty cycle to ensure that the rise time of the response current is the same under different pulse injection frequencies. In the formula, the left side of the equal sign represents the rise time of the response current during the offline experiment in step 1.3, and the right side represents the rise time of the response current during online control. When the rise times of the two response currents are equal, the peak values ​​of the response current at the same location are also equal, thus enabling the correct detection of the voltage threshold at the speed update point.

[0064] Step 3.3: Determine the excitation phase and perform excitation. Based on the rotor position angle calculated in Step 3.1, determine whether the rotor is within the excitation range. If it is within the excitation range, excitation is performed using the current hysteresis control method.

[0065] Step 3.4: Determine the pulse injection phase and inject voltage pulses. Based on the rotor position angle calculated in Step 3.1, determine whether the rotor is in the pulse injection interval. If it is in the pulse injection interval, perform pulse injection according to the pulse injection frequency and duty cycle calculated in Step 3.2.

[0066] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sensorless control method for a switched reluctance motor, characterized in that, include: S1. Fix the rotor at the speed update point, inject an initial voltage pulse, and use the peak value of the current sensor's output voltage as the voltage threshold. S2. Inject voltage pulses into the idle phase; wherein, the pulse injection frequency is positively correlated with the current speed of the motor, and the rise time of the response current is the same under different pulse injection frequencies; S3. The peak value of the output voltage of the current sensor is detected by a peak detection circuit in an analog circuit; the first stage of the analog circuit is a peak detection circuit, and the second stage is a voltage comparison circuit. S4. The voltage comparison circuit in the analog circuit compares the obtained peak output voltage with the voltage threshold. If the peak voltage is higher than the voltage threshold, the voltage comparison circuit in the analog circuit generates a rising edge voltage signal. The motor speed is calculated using the time interval and angle interval between two adjacent rising edge voltage signals, and the peak detection circuit is reset. The formula for calculating the motor speed is: In the formula, n is the motor speed. The angular interval between two adjacent rising edge voltage signals. For time intervals, The number of rotor poles; S5. Integrate the motor speed over time to obtain the rotor position angle increment, add it to the rotor position angle corresponding to the speed update point to obtain the real-time rotor position angle, and then control the on and off of each phase winding of the motor.

2. The sensorless control method for a switched reluctance motor according to claim 1, characterized in that, The number of pulses injected in the pulse injection interval is the same at both high and low speeds.

3. The sensorless control method for a switched reluctance motor according to claim 2, characterized in that, The formula for calculating the injected pulse frequency is: , These are the start and end angles of the pulse injection interval, respectively. The number of rotor poles, Where N is the motor speed, and N represents the number of pulses injected in the pulse injection interval.

4. The sensorless control method for a switched reluctance motor according to claim 3, characterized in that, The injected pulse duty cycle satisfies: In the formula, For pulse injection frequency, Duty cycle, This indicates the pulse injection frequency when the voltage threshold is selected. This indicates the duty cycle when selecting the voltage threshold.

5. The sensorless control method for a switched reluctance motor according to claim 4, characterized in that, The formula for calculating the real-time position angle of the rotor is: In the formula, This is the real-time position angle of the motor. This is the motor rotor position angle corresponding to the previous speed update point. This is the time interval between the moment the rotor reaches the speed update point and the current moment.

6. A sensorless control method for a switched reluctance motor according to any one of claims 1-5, characterized in that, The peak detection circuit includes a diode, a capacitor, a first resistor, and a second resistor.

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