Non-inductive control method for brushless direct current motor of circuit breaker

Abstract

The invention discloses a non-inductive control method for a brushless direct current motor of a circuit breaker, and the method comprises the steps: obtaining a relation between a moment corresponding to a first rising edge in each period of a PWM signal of any one of three phases of the brushless direct current motor and a moment corresponding to a first rising edge in each period of a commutation signal of the phase; the commutation signal of the phase is constructed based on the relation and the commutation signal high level duration time, the brushless direct current motor is controlled according to the constructed three-phase commutation signals, and compared with the prior art, the method has the technical effects that the phase delay problem caused by a filter does not exist; the full-speed-domain performance is excellent, and the low-speed loading capacity is similar to that of a scheme formed by position sensors such as HALL; wiring is simple and reliable, and position detection precision is high.

Description

Technical Field

[0001] This invention relates to a sensorless control method for a brushless DC motor in a circuit breaker, applicable to the control of a three-phase brushless DC motor. Background Technology

[0002] Currently, most electrical mechanisms in switchgear and circuit breakers utilize brushless DC motors powered by 48V / 24V DC, employing sensor-based control methods such as Hall position sensors. However, due to installation deviations of Hall position sensors, the often exposed environments of switchgear and circuit breakers, and the influence of harsh environments (such as saline-alkali land, acidic or alkaline conditions), Hall position sensors become unreliable, leading to inaccurate rotor position detection in the brushless DC motor. This can easily result in commutation failure and motor mechanism malfunction. Therefore, in these application scenarios, sensorless control technology is crucial for brushless DC motors. The key to sensorless control of brushless DC motors is how to accurately acquire rotor position signals without the need for position sensors.

[0003] In existing technologies, such as the design and research of a controller for a brushless DC motor operating mechanism for a high-voltage vacuum circuit breaker (2014, 50(07):63-69.DOI:10.13296 / j.1001-1609.hva.2014.07.011) and the research and optimization of an intelligent operating mechanism for an SF6 high-voltage circuit breaker (2013, 17(07):94-98+104.DOI:10.15938 / j.emc.2013.07.017), if a sensorless control strategy is adopted, the back EMF method is the mainstream solution for detecting rotor position. However, at low speeds, the back EMF waveform is distorted, and the zero-crossing point is inaccurate, leading to inaccurate rotor position detection. Moreover, the back EMF method usually uses a filter to filter out high-frequency interference, which brings about phase compensation problems and makes the wiring more complex. At the same time, the low-speed load-carrying capacity is poor, and the position detection accuracy is related to the speed. In the existing technology, there is also a method for controlling brushless DC motors using the extended Kalman filter algorithm. For example, a sensorless vector control method for induction motors based on adaptive extended Kalman filtering is disclosed on the China Patent Network, with application number 202210344270.9. The method involved in this patent has good control performance in medium and high-speed sensorless control using the extended Kalman filter algorithm, but the control effect is poor at low speeds. In addition, the method involved in this patent also has problems such as too many parameters and difficulty in debugging. Summary of the Invention

[0004] The purpose of this invention is to provide a sensorless control method for a brushless DC motor in a circuit breaker. By constructing commutation signals for different phases using PWM signals, this method solves the problems of back EMF waveform distortion and inaccurate zero-crossing point in existing technologies during low-speed control, which leads to inaccurate rotor position detection.

[0005] Another objective of this invention is to provide a sensorless control method for a brushless DC motor in a circuit breaker, which solves the problem of phase compensation caused by using filters to filter out high-frequency interference in the prior art, and simplifies the wiring of the brushless DC motor.

[0006] To achieve the above objectives, the present invention provides a sensorless control method for a brushless DC motor in a circuit breaker. The method includes: acquiring a first relevant information of the brushless DC motor; acquiring the high-level duration of a commutation signal based on the first relevant information; and acquiring a second relevant information of a PWM signal of a certain phase of the brushless DC motor, wherein the second relevant information includes at least the time corresponding to the first rising edge of the PWM signal in each cycle. Based on the first relevant information and the second relevant information, the commutation signal of one phase of the brushless DC motor is obtained, and then the commutation signals of the other two phases are obtained. The brushless DC motor is controlled by the commutation signals of the three phases.

[0007] Preferably, for a certain phase of a brushless DC motor, the time corresponding to the first rising edge of the commutation signal in each cycle of that phase is the same as the time corresponding to the first rising edge of the PWM signal in each cycle of that phase.

[0008] Preferably, the first relevant information includes at least: the speed signal of the brushless DC motor, which is obtained through digital filtering.

[0009] Preferably, the first relevant information includes at least: the number of pole pairs of the brushless DC motor, wherein the number of pole pairs is the number of magnetic pole pairs on the rotor of the brushless DC motor.

[0010] Preferably, the high-level duration of the commutation signal includes: the high-level duration of the commutation signal is obtained based on the rotational speed signal and the number of pole pairs.

[0011] Preferably, the commutation signal acquisition process for each phase includes: selecting a phase among the three phases and acquiring the commutation signal of that phase; and acquiring the commutation signals of the three phases based on the time delay relationship between the commutation signal of that phase and the other two phases.

[0012] Preferably, for a certain phase of a brushless DC motor, the period corresponding to the commutation signal of that phase is the same as the difference between the time corresponding to the first rising edge of the PWM signal in two adjacent periods of that phase.

[0013] Preferably, the second relevant information includes: the time corresponding to the first rising edge of the PWM signal in a certain cycle, and the time difference between the first rising edge in the adjacent cycle.

[0014] Preferably, the control process of the brushless DC motor based on the commutation signals of each phase includes: obtaining the position of the motor rotor of the brushless DC motor based on the level corresponding to the commutation signals of each phase at each time; and controlling the current conduction and current direction between each phase based on the position of the motor rotor.

[0015] Preferably, the brushless DC motor is started at a preset speed until the period of the constructed commutation signal matches the period of the calculated PWM signal, and the brushless DC motor is controlled based on the constructed commutation signal.

[0016] The beneficial effects of this invention are that, based on the relationship between a given rotational speed and the PWM waveform and the commutation signal, it has the following advantages compared with the prior art.

[0017] 1. The phase delay problem caused by the lack of a filter.

[0018] 2. It has excellent performance across the entire speed range, and its low-speed load capacity is similar to that of solutions composed of position sensors such as HALL.

[0019] 3. The wiring is simple and reliable, and the position detection accuracy is high. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method that relates to the present invention.

[0021] Figure 2 This is a schematic diagram of a brushless DC motor.

[0022] Figure 3 This is a timing diagram of the first output speed and the output torque of a brushless DC motor.

[0023] Figure 4 This is a timing diagram showing the relationship between the commutation signal and the PWM signal of a first-order brushless DC motor.

[0024] Figure 5 This is a timing diagram of the second output speed and the output torque of a brushless DC motor.

[0025] Figure 6 This is a timing diagram showing the relationship between the second commutation signal and the PWM signal of a brushless DC motor.

[0026] Figure 7 This is a timing diagram of the third output speed and the output torque of a brushless DC motor.

[0027] Figure 8 This is a timing diagram showing the relationship between the third commutation signal and the PWM signal of a brushless DC motor.

[0028] Figure 9 This is a timing diagram of the fourth output speed and the output torque of a brushless DC motor.

[0029] Figure 10 This is a timing diagram showing the relationship between the fourth commutation signal and the PWM signal of a brushless DC motor.

[0030] Figure 11 This is a timing diagram of the fifth output speed and the output torque of a brushless DC motor.

[0031] Figure 12 This is a timing diagram showing the relationship between the fifth commutation signal and the PWM signal of a brushless DC motor.

[0032] Figure 13 This is a timing diagram showing the relationship between the sixth commutation signal and the PWM signal of a brushless DC motor.

[0033] Figure 14 This is a timing diagram showing the relationship between the seventh commutation signal and the PWM signal of a brushless DC motor.

[0034] Figure 15 This is a timing diagram showing the relationship between the eighth commutation signal and the PWM signal of a brushless DC motor.

[0035] Figure 16 This is a timing diagram of the sixth output speed and the output torque of a brushless DC motor.

[0036] Figure 17 This is a timing diagram of the seventh output speed and the output torque of a brushless DC motor.

[0037] Figure 18 This is a timing diagram showing the relationship between the ninth commutation signal and the PWM signal of a brushless DC motor. Detailed Implementation

[0038] Example 1 This embodiment discloses an implementation process of the method involved in the present invention, for details please refer to [link / reference]. Figure 1 The method includes: Start the brushless DC motor so that it outputs at a preset speed.

[0039] The PWM signal of a certain phase is monitored in real time. If it is stable (a unique first rising edge can be captured in each cycle) and the time of the first rising edge of the PWM signal in each cycle of the phase is accurately obtained, the commutation signal period is calculated based on the time difference between the first rising edges of the PWM signal in two adjacent cycles of the phase or the reference speed. The commutation signal is constructed using the time corresponding to the first rising edge of the PWM signal in each cycle and the high-level duration (half of the commutation period). Otherwise, the PWM signal of the certain phase is monitored. The rotor speed of the brushless DC motor is measured to obtain the measured speed, and the period of the commutation signal is calculated based on the obtained measured speed.

[0040] The period of the constructed commutation signal is compared with the period of the calculated PWM signal. If the comparison results are consistent, sensorless control is switched, and the brushless DC motor is controlled in real time according to the constructed commutation signal to make the motor control smooth. If the comparison results are inconsistent, the output of the motor speed is controlled again.

[0041] The first relevant information includes: the speed signal of the brushless DC motor, wherein the speed signal of the brushless DC motor is obtained through digital filtering, including but not limited to Gaussian filtering, median filtering, amplitude limiting filtering, and wavelet filtering.

[0042] The first relevant information also includes: the number of pole pairs of the brushless DC motor, which specifically refers to the number of magnetic pole pairs on the rotor of the brushless DC motor.

[0043] The high-level duration of the commutation signal of each phase of the brushless DC motor is obtained based on the relationship between the high-level duration and the first relevant information. The first relevant information is input into the relationship model between the high-level duration and the first relevant information. The relationship model responds to the first relevant information and outputs the high-level duration of the commutation signal of each phase of the brushless DC motor.

[0044] The specific relationship model is as follows: the duration of the commutation signal high level is obtained by dividing the PWM signal period time by 2 and multiplying by 3. Alternatively, it can be obtained based on the relationship model between rotational speed and the duration of the commutation signal high level: the duration of the commutation signal high level for each phase is equal to the constant 30 divided by the product of the number of pole pairs of the brushless DC motor and the rotational speed of the brushless DC motor. It should be noted that the constant 30 has a corresponding dimension, specifically r, where r represents the number of revolutions of the brushless DC motor rotor; the number of pole pairs of the brushless DC motor does not have a corresponding dimension.

[0045] For example, if the rotor speed of a brushless DC motor is 400 r / min and the number of poles is 1, then the high-level duration of the commutation signal for each phase of the brushless DC motor is 4.5 s; if the rotor speed of a brushless DC motor is 1000 r / min and the number of poles is 2, then the high-level duration is 0.9 s; if the rotor speed of a brushless DC motor is 2000 r / min and the number of pole pairs is 6, then the high-level duration of the commutation signal for each phase of the brushless DC motor is 0.15 s.

[0046] Obtain the second relevant information of the PWM signal of a certain phase of the brushless DC motor.

[0047] The relevant information of the PWM signal includes, but is not limited to, the time of the first rising edge of the PWM signal in each cycle of a certain phase.

[0048] The relevant information of the PWM signal includes, but is not limited to, the period of the PWM signal of a certain phase.

[0049] The process for obtaining the second relevant information includes, but is not limited to, capturing the moment corresponding to the first rising edge of the PWM signal of a certain phase within each cycle and maintaining a high level for 180° electrical angle to obtain the commutation signal of that phase. Furthermore, in this embodiment, the process for obtaining the 180° electrical angle of the second relevant information is based on the reference rotational speed or the time difference between the first rising edges of two adjacent cycles of the PWM signal of a certain phase.

[0050] The process for obtaining the second relevant information includes, but is not limited to, capturing in real time the moment corresponding to the first rising edge of the PWM signal of a certain phase within a certain cycle, as well as the moment corresponding to the first rising edge within the adjacent cycle.

[0051] Taking the phase of the brushless DC motor involved in this embodiment as an example. For example, the phases of the brushless DC motor include: phase A, phase B, and phase C. Any one of phases A, B, and C is selected, and the second related information of the PWM signal of that phase is obtained. If phase A of the brushless DC motor is selected, the second related information of the PWM signal of phase A is obtained; if phase B of the brushless DC motor is selected, the second related information of the PWM signal of phase B is obtained; if phase C of the brushless DC motor is selected, the second related information of the PWM signal of phase C is obtained.

[0052] For a certain phase of a brushless DC motor, after obtaining the second relevant information of the PWM signal of that phase, the commutation signal of that phase is constructed based on the second relevant information of the PWM signal of that phase and the high-level duration of the commutation signal of each phase.

[0053] The process for constructing the commutation signal of this phase is as follows: based on the second relevant information of this phase, the period of the commutation signal of this phase is determined.

[0054] Based on the relationship between the time corresponding to the first rising edge of the commutation signal in each cycle of the phase and the time corresponding to the first rising edge of the PWM signal in each cycle of the phase, and the high-level duration of the commutation signal of each phase, the high-level duration interval of the commutation signal of the phase in its corresponding cycle is determined. The relationship between the time corresponding to the first rising edge of the commutation signal in each cycle of the phase and the time corresponding to the first rising edge of the PWM signal in each cycle of the phase is as follows: the time corresponding to the first rising edge of the commutation signal in the Nth cycle of the phase is the same as the time corresponding to the first rising edge of the PWM signal in the Nth cycle of the phase, where N is a positive integer.

[0055] In the period of the commutation signal of this phase, the start time of the high-level duration interval is: the time corresponding to the first rising edge of the commutation signal in its corresponding period; the end time of the high-level duration interval is: the time of the rising edge of the commutation signal in its corresponding period plus the high-level duration of each phase commutation signal.

[0056] After determining the commutation signal of any one of the three phases of the brushless DC motor, the commutation signals of the three phases are obtained based on the time delay relationship between the three phases. Based on the commutation signals of the three phases, the real-time position of the rotor of the brushless DC motor is obtained. Based on the real-time position of the rotor of the brushless DC motor, the corresponding PWM control signal is obtained. The obtained PWM control signal is input into the control circuit to control the rotation of the rotor of the brushless DC motor.

[0057] See Figure 2 ,exist Figure 2 In a brushless DC motor, there are three phases, namely phase A, phase B and phase C. The method involved in this embodiment is to obtain the PWM signal of phase A, phase B or phase C, and obtain a commutation signal equivalent to the commutation signal of the Hall sensor at the position of phase A, phase B or phase C based on the PWM signal of phase A, phase B or phase C.

[0058] For example, if the PWM signal of phase A is obtained, the commutation signal of phase A is obtained based on the PWM signal of phase A; if the PWM signal of phase B is obtained, the commutation signal of phase B is obtained based on the PWM signal of phase B; if the PWM signal of phase C is obtained, the commutation signal of phase C is obtained based on the PWM signal of phase C.

[0059] After obtaining the commutation signals of phases A, B, and C, based on the time delay relationship between phases A, B, and C, for example, still using... Figure 2Taking a brushless DC motor as an example, if the motor rotates counterclockwise at a certain speed v (the dimension of speed v is r / min) (starting from the position where the rotor points to phase A), then phase B lags phase A by 120° and phase C lags phase B by 120°. The phase of the commutation signal of phase B lags behind the phase of the commutation signal of phase A by T1. Therefore, the commutation signal of phase B is specifically equivalent to the commutation signal of phase A shifted by +T1 in the time axis direction. The phase of the commutation signal of phase C lags behind the phase of the commutation signal of phase B by T2. Therefore, the commutation signal of phase C is specifically equivalent to the commutation signal of phase B shifted by +T2 in the time axis direction. The specific values ​​of T1 and T2 are: the high-level duration of the commutation signal multiplied by 2 and divided by 3.

[0060] After obtaining the commutation signals of phases A, B, and C, to obtain the position of the brushless DC motor rotor at a certain moment, the level correlation values ​​of the commutation signals of phases A, B, and C at that moment must be obtained. It should be noted that if the level of the commutation signal of phase A, B, or C at that moment is high, the level correlation value at that moment is 1; if the level of the commutation signal of phase A, B, or C at that moment is low, the level correlation value at that moment is 0.

[0061] by Figure 2 Taking the rotor in the image as an example, it should be noted that the direction indicated by the arrow represents the rotor's position in a certain phase, in which case the commutation signal for that phase is high. If the rotor is in... Figure 2 If the positions are specified, then the level correlation values ​​of the commutation signals of phases A, B, and C are 0, 0, and 1, respectively.

[0062] After obtaining the voltage levels of phases A, B, and C, the voltages of phases A, B, and C are controlled based on these values, thereby controlling the brushless DC motor. Figure 2 Taking the rotor as an example, when the rotor is in this position, the control circuit controls the voltage of phase A and phase C so that phase A and phase C are the same, and the direction of current flow changes according to the winding method of the coils of phase A and phase C.

[0063] If C is the positive terminal and A is the negative terminal, the magnetic field generated by phase A is directed from the center of the circle to the endpoint of phase A, and the magnetic field generated by phase C is directed in the opposite direction from the center of the circle to the endpoint of phase C. In this case, the control circuit controls the current to flow into phase C and out of phase A.

[0064] The system first stores the preset PWM control signal in the control circuit, which then controls the brushless DC motor based on the preset PWM control signal. During the control process, the system generates commutation signals for each phase in real time to determine the position of the brushless DC motor rotor. Based on the rotor position of the brushless DC motor, the system generates corresponding control commands for the circuit to control the rotation of the rotor.

[0065] Using the method described in this embodiment, the position of the rotor in a brushless DC motor can be accurately obtained through a PWM signal without adding any additional adjustment parameters, thereby achieving control of the brushless DC motor.

[0066] Example 2 This embodiment discloses the specific process of controlling a motor using a method according to the present invention.

[0067] The parameters for controlling the brushless DC motor are shown in Table 1.

[0068] Table 1 parameter Parameter value Voltage V 48 Rotational speed (r / min) 3000 Phase resistance Ω 0.06 Phase inductance mH 0.1 Back electromotive force coefficient V / (r / min) 0.0158 Rated power W 700 Extreme logarithm 5 <![CDATA[ Moment of inertia kg·mm 2 ]]> 4 Test scenario 1: The brushless DC motor is controlled by a PWM signal to output at a certain speed. The duty cycle of the PWM signal is 1, and the motor speed is 3000 r / min.

[0069] After the brushless DC motor has been running for 0.1 seconds, the control mode of the motor is switched to the sensorless control state. That is, the time corresponding to the first rising edge of the PWM signal of the brushless DC motor in each cycle is obtained by the method involved in Example 1, and the period of the PWM signal is obtained.

[0070] The commutation signal period and the high-level duration of the commutation signal are obtained.

[0071] The commutation signal of phase A is obtained based on the time corresponding to the first rising edge in each cycle of the PWM signal, the commutation signal period, and the high-level duration of the commutation signal.

[0072] After the brushless DC motor outputs a speed of 3000 r / min for 0.25 s, a torque of 1 Nm is applied to the brushless DC motor. Refer to the speed output timing diagram and torque output timing diagram of the brushless DC motor. Figure 3 .

[0073] See Figure 4 ,exist Figure 4 There are timing diagrams for three signals, including the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1, the timing diagram of the actual commutation signal of the brushless DC motor in phase A, and the timing diagram of the PWM signal of phase A.

[0074] As can be seen from the signal timing diagram in the figure, the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1 is small in difference from the timing diagram of the actual commutation signal of the brushless DC motor in phase A. Moreover, after applying a torque of 1 Nm to the brushless DC motor, the load error is only 1.73°.

[0075] Test scenario 2: The brushless DC motor is controlled by a PWM signal to output speed, where the duty cycle of the PWM signal is 0.5 and the speed of the brushless DC motor is 1500 r / min.

[0076] After the brushless DC motor has been running for 0.1 seconds, the control mode of the motor is switched to the sensorless control state. That is, the time corresponding to the first rising edge of the PWM signal in each cycle of the brushless DC motor is obtained by the method involved in Example 1, and the cycle of the PWM signal is obtained.

[0077] The commutation signal period and the high-level duration of the commutation signal are obtained.

[0078] The commutation signal of phase A is obtained based on the time corresponding to the first rising edge in each cycle of the PWM signal, the commutation signal period, and the high-level duration of the commutation signal.

[0079] After the brushless DC motor outputs a speed of 1500 r / min for 0.25 s, a torque of 0.2 Nm is applied to the brushless DC motor. Refer to the speed output timing diagram and torque output timing diagram of the brushless DC motor. Figure 5 .

[0080] See Figure 6 ,exist Figure 6 There are timing diagrams for three signals, including the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1, the timing diagram of the actual commutation signal of the brushless DC motor in phase A, and the timing diagram of the PWM signal of phase A.

[0081] As can be seen from the signal timing diagram in the figure, the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1 is small in difference from the timing diagram of the actual commutation signal of the brushless DC motor in phase A. Moreover, after applying a torque of 0.2 Nm to the brushless DC motor, the load error is only 4.1°.

[0082] Test scenario 3: The brushless DC motor is controlled by a PWM signal to output at a certain speed. The duty cycle of the PWM signal is 0.1, and the speed of the brushless DC motor is 227 r / min.

[0083] After the brushless DC motor has been running for 0.1 seconds, the control mode of the motor is switched to the sensorless control state. That is, the first rising edge of the PWM signal of the brushless DC motor in each cycle is obtained by the method involved in Example 1, and the period of the PWM signal is obtained.

[0084] The commutation signal period and the high-level duration of the commutation signal are obtained.

[0085] The commutation signal of phase A is obtained based on the time corresponding to the first rising edge in each cycle of the PWM signal, the commutation signal period, and the high-level duration of the commutation signal.

[0086] After the brushless DC motor outputs a speed of 227 r / min for 0.25 s, a torque of 0.2 Nm is applied to the brushless DC motor. Refer to the speed output timing diagram and torque output timing diagram of the brushless DC motor. Figure 7 .

[0087] See Figure 8 ,exist Figure 8 There are timing diagrams for three signals, including the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1, the timing diagram of the actual commutation signal of the brushless DC motor in phase A, and the timing diagram of the PWM signal of phase A.

[0088] As shown in the signal timing diagram, the difference between the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method described in Example 1 and the timing diagram of the actual commutation signal of the brushless DC motor in phase A is small. The commutation error before applying 0.2 Nm of torque to the brushless DC motor is only 1.55°, and the commutation error under load after applying 0.2 Nm of torque to the brushless DC motor is only 1.77°.

[0089] Test scenario 4: A brushless DC motor is controlled by a PWM signal to output at a certain speed, wherein the speed of the brushless DC motor is 70 r / min.

[0090] After the brushless DC motor outputs at a speed of 70 r / min for 0.25 s, the sensorless control method involved in Example 1 is switched to apply 0.2 Nm of torque to the brushless DC motor.

[0091] At this point, refer to the speed output timing diagram and torque output timing diagram of the brushless DC motor. Figure 9 ...

[0092] At this point, the timing diagrams of the commutation signal of phase A, the actual commutation signal timing diagram of phase A, and the PWM signal timing diagram of phase A obtained through the sensorless control method described in Example 1 are referred to. Figure 10 .

[0093] Depend on Figure 10 It can be seen that before the brushless DC motor is loaded with 0.2 Nm of torque, the commutation error between the timing diagram of the commutation signal obtained by the sensorless control method involved in Example 1 and the timing diagram of the actual commutation signal of phase A is only 3.84°.

[0094] See Figure 11 ,Depend on Figure 11 It can be seen that the speed of the brushless DC motor is slightly lower than 3000 r / min, and the speed and torque fluctuate slightly when under load. Therefore, the speed of the brushless DC motor should be reduced by 400 r / min.

[0095] After the brushless DC motor outputs at the speed set above for 0.2s, the sensorless control method involved in Example 1 is switched to apply. After the brushless DC motor outputs at the speed set above for 0.3s, a torque of 2Nm is applied to the brushless DC motor.

[0096] See Figure 12 ,exist Figure 12 There are timing diagrams for three signals, including the timing diagram of the commutation signal of the brushless DC motor in phase A obtained by the method involved in Example 1, the timing diagram of the actual commutation signal of the brushless DC motor in phase A, and the timing diagram of the PWM signal of phase A.

[0097] Before applying 2 Nm of torque to the brushless DC motor, the error between the timing diagram of the commutation signal of phase A obtained by the sensorless control method described in Example 1 and the timing diagram of the actual commutation signal of phase A is only 0.25°. After applying 2 Nm of torque to the brushless DC motor, the error between the timing diagram of the commutation signal of phase A obtained by the sensorless control method described in Example 1 and the timing diagram of the actual commutation signal of phase A is only 1.45°. The small error indicates that the obtained commutation signal is relatively accurate.

[0098] The above open-loop test results fully demonstrate the scientific nature and accuracy of the sensorless control method involved in this invention, and because it does not require additional hardware circuitry, it balances low cost and reliability.

[0099] Under open-loop testing conditions, the speed of low-speed sensorless control can even reach below 70 r / min, which is 2% of the rated speed, thus widening the speed range of sensorless control.

[0100] If only the PWM signal is used as a reference, then there is no need to refer to the rotational speed. Only the frequency of the PWM signal and the rise time need to be captured to construct the corresponding commutation signal. Then, the three-phase commutation signal can be obtained by delaying the single-phase commutation signal. Table 2 shows the open-loop test results.

[0101] Table 2 Serial Number Duty cycle D Loading time t / s Load size F / Nm Switching time t / s No-load speed n / r / min Loaded speed n / r / min No-load commutation error θ / ° On-load commutation error θ / ° (a) 1 0.25 1 0.1 3000 2896 0.09 0.021 (b) 0.5 0.25 0.2 0.1 1500 1467 0.045 0.267 (c) 0.5 0.25 2 0.1 1500 1263 0.045 0.193 (d) 0.1 0.25 0.2 0.1 291 233 0.053 0.124 See Figure 13 , Figure 13 The figure shows a comparison of commutation signals obtained under a dual-closed-loop test with a given speed of 1500 r / min, switching to the sensorless control described in Example 1 at 0.1 s, and applying a 2 Nm load at 0.3 s. The commutation error is only 0.0045° under no-load conditions and only 0.226° under load conditions.

[0102] See Figure 14 , Figure 14 The following is a comparison chart of commutation signals obtained by switching to the sensorless control described in Example 1 at a given speed of 70 r / min, switching to the sensorless control described in Example 1 at 0.35s, applying 0.2 Nm at 1.2s, and testing for a total duration of 2s. The commutation accuracy is 0.701° under no-load conditions and 0.448° under load.

[0103] See Figure 15 , Figure 15 The test was conducted at a given speed of 50 r / min. The system switched to sensorless control at 0.35 s, applied 0.2 Nm at 0.8 s, 0.4 Nm at 1.2 s, and 0.6 Nm at 1.6 s, for a total test duration of 2 s. The commutation signal comparison chart shows the following: No-load error: 279 μs; Commutation error under 0.2 Nm load: 235 μs; Commutation error under 0.4 Nm load: only 137 μs; Commutation error under 0.6 Nm load: only 178 μs. See the speed and torque timing diagrams for reference. Figure 16 .

[0104] The closed-loop tests described above fully demonstrate the scientific validity and accuracy of the contactless control method involved in this invention. Furthermore, because it requires no additional hardware circuitry, it balances low cost and reliability. In the closed-loop test, the speed of the low-speed contactless control can even reach 50 r / min, which is 1.67% of the rated speed, thus broadening the speed range of the contactless control.

[0105] At a speed of 30 r / min under Hall signal control: 0.2 Nm is applied at 0.8 s, 0.4 Nm at 1.2 s, and 0.6 Nm at 1.6 s. (See the speed and torque timing diagrams.) Figure 17 .

[0106] Example 1 involves a rotational speed of 30 r / min under sensorless control: the sensorless control is switched at 0.8 s, and 0.2 Nm is applied at 1.5 s. At this time, the no-load error is 0.62° and the load error is 0.356°. Figure 18 The following diagram shows a comparison of commutation signals. Figure 18It can be seen that under the control of the HALL position sensor, the speed fluctuation and torque pulsation are also quite obvious, and the control effect is not good. Even after optimizing the current loop, the effect is still the same. Therefore, it is meaningless to discuss sensorless control at a speed of 30r / min.

Claims

1. A sensorless control method for a brushless DC motor in a circuit breaker, characterized in that, The method includes: Obtain the first relevant information of the brushless DC motor, and based on the first relevant information, obtain the high-level duration of the commutation signal; obtain the second relevant information of the PWM signal of a certain phase of the brushless DC motor, wherein the second relevant information includes at least the time corresponding to the first rising edge in each cycle of the PWM signal; Based on the first relevant information and the second relevant information, the commutation signal of one phase of the brushless DC motor is constructed, and then the commutation signals of the other two phases are constructed. The brushless DC motor is controlled by the commutation signals of the three phases.

2. The sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, characterized in that, For a certain phase of a brushless DC motor, the time corresponding to the first rising edge of the commutation signal in each cycle of that phase is the same as the time corresponding to the first rising edge of the PWM signal in each cycle of that phase.

3. The sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, characterized in that, The first relevant information includes at least: The speed signal of the brushless DC motor is obtained through digital filtering.

4. A sensorless control method for a brushless DC motor in a circuit breaker according to claim 1 or 3, characterized in that, The first relevant information includes at least: The number of pole pairs in a brushless DC motor, where the number of pole pairs is the number of magnetic pole pairs on the rotor of the brushless DC motor.

5. The sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, characterized in that, The high-level duration of the commutation signal includes: The duration of the high level of the commutation signal is obtained based on the rotational speed signal and the number of pole pairs.

6. A sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, 2, or 5, characterized in that, The method includes: Select one phase from the three phases and obtain the commutation signal of that phase; based on the time delay relationship between the commutation signal of that phase and the other two phases, obtain the commutation signals of the three phases.

7. The sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, characterized in that, For a certain phase of a brushless DC motor, the period corresponding to the commutation signal of that phase is the same as the time difference between the first rising edge of the PWM signal in two adjacent periods of that phase.

8. The sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, characterized in that, The second relevant information includes: the period of the PWM signal; The high-level duration of the commutation signal includes: the high-level duration of the commutation signal can also be obtained based on the period of the PWM signal of the second relevant information.

9. A sensorless control method for a brushless DC motor in a circuit breaker according to any one of claims 1 to 3, characterized in that, The control process for a brushless DC motor based on three-phase commutation signals includes: Based on the commutation signals of the three phases, the position of the motor rotor of the brushless DC motor is obtained at the corresponding level at each moment. Based on the location of the motor rotor, the current conduction and direction between the three phases are controlled.

10. A sensorless control method for a brushless DC motor in a circuit breaker according to claim 1, 2, 3, 5, or 7, characterized in that, The method starts the brushless DC motor at a preset speed until the period of the constructed commutation signal matches the period calculated based on the rotational speed. Then, the brushless DC motor is controlled based on the constructed commutation signal.

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