A brushless DC motor sliding mode control system based on auxiliary boost and control method thereof

Abstract

The present invention discloses a brushless DC motor sliding mode control system based on auxiliary boost and a control method thereof, belonging to the field of brushless DC motor control. In the present invention, when the motor body operates under high-speed commutation conditions, the auxiliary boost converter is connected to the three-phase inverter through a switch selection circuit, and the converter control module adjusts the duty cycle of the auxiliary boost converter and the output voltage of the auxiliary boost converter; when the motor body operates under low-speed commutation conditions or non-commutation interval conditions, the auxiliary boost converter is disconnected from the three-phase inverter, and the sliding mode control module generates a current reference value, generates a modulation signal through PI regulation, and drives the switch tube in the three-phase inverter. The present invention overcomes the serious commutation torque pulsation problem of the brushless DC motor and improves the excellent performance of the sliding mode control method in speed regulation.

Description

Technical Field

[0001] The invention relates to the field of brushless DC motor control, and in particular to a brushless DC motor sliding mode control system and a control method based on auxiliary boost. Background Art

[0002] At present, brushless DC motors (BLDCM) have been widely used in aerospace, household smart appliances, green energy electric vehicles, medical equipment and other fields. In high-end precision applications such as aerospace, there are extremely high requirements for the accuracy and performance of BLDCM, but BLDCM generally has a relatively serious torque pulsation problem. The output condition of electromagnetic torque directly determines the performance of the motor control system. Large torque pulsation will naturally cause noise and vibration problems to the motor, seriously reducing the reliability and service life of the motor control system, and limiting its application in high-precision fields. In the prior art, DC-DC converters are used to suppress torque pulsation, but traditional DC-DC converters have problems such as low voltage gain at the same duty cycle and high stress on the device under the same voltage output.

[0003] The brushless DC motor is a nonlinear multi-parameter variable system with strong coupling characteristics and a certain variable structure mode. Sliding Mode Control (SMC) is often used in the field of motor control and speed regulation. It can effectively improve the dynamic response speed of the motor. However, when the traditional reaching law SMC method is applied in the BLDCM control system, it has high requirements on the accuracy of the controlled model and relatively few adjustable sliding mode control parameters. It is impossible to make local precise and subtle adjustments to the main controller, and the stability cannot meet the requirements.

[0004] Therefore, technicians in this field are committed to developing a brushless DC motor control system and control method that can take into account both torque pulsation suppression and motor speed regulation. Summary of the invention

[0005] The present invention provides a brushless DC motor sliding mode control system and control method based on auxiliary boost, which applies an auxiliary boost conversion topology to the front end of the inverter, so that the DC bus voltage of the motor is stably increased during high-speed commutation, ensuring the consistency of the current change rate in the commutation area, overcoming the serious commutation torque pulsation problem of the brushless DC motor, and further improving the excellent performance of the sliding mode control method in BLDCM speed regulation.

[0006] On one hand, the present invention provides a brushless DC motor sliding mode control system based on auxiliary boost, comprising a motor body, an inverter circuit, a main controller and a rotor position detection circuit, wherein the inverter circuit comprises an auxiliary boost converter, a switch selection circuit and a three-phase inverter connected in sequence, and the main controller comprises a converter control module and a sliding mode control module;

[0007] When the motor body operates under high-speed commutation conditions, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter;

[0008] When the motor body operates under low-speed commutation conditions or non-commutation interval conditions, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, and the sliding mode control module generates a current reference value, which is used to generate a modulation signal through PI regulation to drive the switch tube in the three-phase inverter to chop and regulate the DC power supply input voltage.

[0009] Further, the auxiliary boost converter includes a power switch tube Q1, a power switch tube Q2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, an inductor L, a capacitor C1, a capacitor C2, a capacitor C3 and a capacitor C4;

[0010] The source of the power switch tube Q2 is connected to the negative electrode of the DC power supply, the drain of the power switch tube Q2 is connected to the positive electrode of the DC power supply via the inductor L, the anode of the diode D1 is connected to the positive electrode of the DC power supply, and its cathode is connected to the inductor L, the negative end of the capacitor C1 is connected to the positive end of the DC power supply, and its positive end is connected to the drain of the power switch tube Q1, the source of the power switch tube Q1 is connected to the cathode of the diode D1, the cathode of the diode D2 is connected to the drain of the power switch tube Q1, and its cathode is connected to the drain of the power switch tube Q2; the diode D3, the diode D4, the diode D5, the capacitor C3 and the capacitor C4 are connected in series and connected to the drain and source of the power switch tube Q2, the two ends of the capacitor C2 are respectively connected to the anode of the diode D3 and the cathode of the diode D4, and the cathode of the diode D3 is connected to the midpoint of the capacitor C3 and the capacitor C4.

[0011] Furthermore, the conduction ratio α is:

[0012]

[0013] Among them, k e is the reverse electromotive force constant, Ω is the rotor mechanical angular velocity, U in is the input voltage.

[0014] Furthermore, the switch selection circuit includes a switch tube K1 and a switch tube K2 connected in parallel, and the switch tube K1 is connected in series with a diode D6.

[0015] Furthermore, the current reference value i output by the sliding mode control module ref for:

[0016]

[0017] in, is the reaching law, which is:

[0018]

[0019] s is the sliding mode function; tanh(·) is the hyperbolic tangent function; ε>0, k>0.

[0020] It can be seen that when |s|>δ, due to α∈(0,1), |s| in the fal function α Compared with the general exponential approach law, the term can achieve a faster approach speed, that is, |s| α >s, and the smaller s is, the smaller the relative speed difference is; when |s| α ≤δ, (1-α) still belongs to the interval (0, 1), so s / δ (1-α) Greater than s, increasing the sliding mode approach speed.

[0021] Another aspect of the present invention provides a brushless DC motor sliding mode control method based on auxiliary boost, which is implemented based on the brushless DC motor sliding mode control system based on auxiliary boost, and includes the following steps:

[0022] S1, determine whether the motor body is running under high-speed commutation conditions, if yes, execute step S2, if no, execute step S3;

[0023] S2, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter;

[0024] S3, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, the sliding mode control module generates a current reference value, and generates a modulation signal through PI regulation to drive the switch tube in the three-phase inverter.

[0025] Furthermore, the method for determining whether the motor body is operating under high-speed commutation conditions includes:

[0026] A speed threshold is set. When the speed of the motor body is greater than the speed threshold, it is determined whether it is in the commutation interval. If so, the motor body is operating under high-speed commutation conditions.

[0027] The start of the commutation zone is determined by the change in the Hall sensor signal in the motor body. The Hall sensor signal is input into the controller. The motor speed can be calculated and the commutation time can be determined by capturing the rising and falling edges of the three Hall signals and combining logic. After each commutation moment begins, the magnitude of the off-phase current is detected. When the off-phase current drops to zero, it indicates that the commutation is over.

[0028] Compared with the prior art, the present invention has the following technical effects:

[0029] 1. The control system of the present invention selects to connect the auxiliary boost converter to power the motor or generate a current reference value through the sliding mode control module according to the current working condition of the motor through the switch selection circuit to generate a modulation signal to control the speed of the motor body, which can not only keep the motor commutation torque pulsation, but also effectively improve the speed regulation performance of the motor.

[0030] 2. The auxiliary boost converter adopted in the present invention has the advantages of high gain, low device stress and stable voltage output characteristics, which broadens its application in motors, makes device selection easy to implement, reduces system cost and volume, and can simultaneously complete phase switching of the off-phase and on-phase currents, improves the waveform quality of the non-phase switching current, and effectively reduces the torque pulsation of the motor during high-speed phase switching.

[0031] 3. The sliding mode control method with improved reaching law adopted in the present invention has the advantages of small overshoot, fast dynamic response speed, and strong robustness to external interference and internal parameter perturbation compared with the traditional PI control and constant speed reaching law SMC speed control method.

[0032] The concept, specific structure and technical effects of the present invention will be further described below in conjunction with the accompanying drawings to fully understand the purpose, characteristics and effects of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is a schematic diagram of the overall structure of a control system according to a specific embodiment of the present invention;

[0034] Figure 2 is a circuit structure schematic diagram of an inverter circuit of a specific embodiment of the present invention;

[0035] Figure 3 is a flow chart of a control method according to a specific embodiment of the present invention;

[0036] Figure 4 It is a comparative simulation waveform diagram of the speed response time under three different control modes of PI control, traditional sliding mode control and improved sliding mode control in a specific embodiment of the present invention;

[0037] Figure 5 1 is a phase current waveform and a DC bus voltage waveform with and without an auxiliary boost converter in a specific embodiment of the present invention, Figure 5 a is the phase current waveform and DC bus voltage waveform without auxiliary boost converter, 5b is the phase current waveform and DC bus voltage waveform with auxiliary boost converter;

[0038] Figure 6is an enlarged diagram of the phase current waveform and the DC bus voltage waveform with and without the auxiliary boost converter in a specific embodiment of the present invention, Figure 6 a is an enlarged diagram of the phase current waveform and DC bus voltage waveform without an auxiliary boost converter, and 6b is an enlarged diagram of the phase current waveform and DC bus voltage waveform with an auxiliary boost converter;

[0039] Figure 7 The phase current switching waveforms when there is a phase current switching with or without an auxiliary boost converter in a specific embodiment of the present invention are as follows: Figure 7 As shown, Figure 7 a is the phase current switching waveform without auxiliary boost method. Figure 7 b is the phase current switching waveform with auxiliary boost method.

[0040] Figure 8 8a is a waveform diagram of the motor no-load starting speed when the speed loop adopts the traditional PI control and the improved sliding mode control in a specific embodiment of the present invention, and 8b is a waveform diagram of the motor no-load starting speed when the speed loop adopts the traditional PI. Figure 8 b is the no-load starting speed waveform of the motor when the improved reaching law SMC is adopted.

[0041] Fig. 9 9a is a motor deceleration waveform diagram when the speed loop adopts traditional PI control and improved sliding mode control in a specific embodiment of the present invention, and 9b is a motor deceleration waveform diagram when the speed loop adopts traditional PI. Fig. 9 b is the motor deceleration waveform when the improved reaching law SMC is adopted;

[0042] Fig.10 10a is a waveform diagram of the speed response of the motor to a sudden load when the speed loop adopts the traditional PI control and the improved sliding mode control in a specific embodiment of the present invention, and 10b is a waveform diagram of the speed response of the motor to a sudden load when the speed loop adopts the traditional PI control. Fig.10 b is the speed response waveform of the motor when the load is suddenly added when the improved reaching law SMC is used. DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention by specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that the following embodiments and features in the embodiments can be combined with each other without conflict.

[0044] It should be noted that the illustrations provided in the following embodiments are only used to illustrate the basic concept of the present invention in a schematic manner, and thus the illustrations only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0045] While some exemplary embodiments of the present invention have been described for the purpose of illustration, it should be understood that the present invention may be implemented in other ways not specifically shown in the drawings.

[0046] like Figure 1 As shown, in a specific embodiment, a brushless DC motor sliding mode control system based on auxiliary boost is provided, including a motor body, an inverter circuit, a main controller and a rotor position detection circuit. The control principle of the control system is to output the DC power supply voltage as alternating current through the inverter circuit. The alternating current acts on the stator winding to form a stator magnetic field, and the rotor magnetic field is generated by the rotor permanent magnet. The interaction of the two magnetic fields will form a force effect. The above control process converts electrical energy into mechanical energy, and finally realizes the rotation of the rotor. Subsequently, the control circuit receives the real-time rotor position information provided by the rotor position detection circuit, and controls the on and off of the power switch tube in the inverter circuit according to the signal and the set commutation logic signal, and turns on the corresponding motor winding, thereby realizing electronic commutation. The three-phase winding voltage equation of the motor body is:

[0047]

[0048] In the formula, u a 、u b 、u c is the phase voltage, e a 、e b 、e c is the reverse electromotive force, i a 、i b 、i c is the phase current, L is the phase inductance, r is the phase resistance, and M is the winding mutual inductance.

[0049] The amplitude E of the induced potential of the stator winding is:

[0050]

[0051] Among them, k e is the reverse electromotive force constant.

[0052] The electromagnetic torque of the motor is T e for:

[0053]

[0054] Where I is the phase current amplitude.

[0055] The mechanical rotor equation of the motor body is

[0056]

[0057] Where B is the damping coefficient, J is the moment of inertia, T L is the load torque.

[0058] like Figure 2 As shown, in a specific embodiment, the inverter circuit includes an auxiliary boost converter, a switch selection circuit and a three-phase inverter connected in sequence, and the main controller includes a converter control module and a sliding mode control module.

[0059] As shown in the figure, the auxiliary boost converter includes a power switch tube Q1, a power switch tube Q2, a diode D1, a diode D2, a diode D3, a diode D4, a diode D5, an inductor L, a capacitor C1, a capacitor C2, a capacitor C3 and a capacitor C4;

[0060] The source of the power switch tube Q2 is connected to the negative electrode of the DC power supply, the drain of the power switch tube Q2 is connected to the positive electrode of the DC power supply via the inductor L, the anode of the diode D1 is connected to the positive electrode of the DC power supply, and its cathode is connected to the inductor L, the negative end of the capacitor C1 is connected to the positive end of the DC power supply, and its positive end is connected to the drain of the power switch tube Q1, the source of the power switch tube Q1 is connected to the cathode of the diode D1, the cathode of the diode D2 is connected to the drain of the power switch tube Q1, and its cathode is connected to the drain of the power switch tube Q2; the diode D3, the diode D4, the diode D5, the capacitor C3 and the capacitor C4 are connected in series and connected to the drain and source of the power switch tube Q2, the two ends of the capacitor C2 are respectively connected to the anode of the diode D3 and the cathode of the diode D4, and the cathode of the diode D3 is connected to the midpoint of the capacitor C3 and the capacitor C4.

[0061] L and Q1, Q2, D1, D2 form a switch inductor network, C1 and Q1, D2 form the first switch capacitor network, and C2-D4-C3-D5-C4-D3 form the second switch capacitor network, which can increase the output voltage on the one hand and clamp the voltage stress of the device on the other hand. Q1 and Q2 are turned on and off at the same time when working, and the same PWM drive signal is used to control and adjust the conduction ratio α, which can meet the boost demand for the DC bus voltage during high-speed commutation of the motor and reduce the complexity of the control system.

[0062] The adjustment process of the auxiliary boost (SC-SL-Boost) converter in this embodiment is about tens of milliseconds, but the BLDCM switching time interval is generally tens to hundreds of microseconds, which is much shorter than the converter adjustment time. In order to achieve the rapid increase of the DC bus voltage when the motor is switching, a switch selection circuit is used in this embodiment to switch different adjustment strategies according to the current operating conditions of the motor body. The switch selection circuit includes a switch tube K1 and a switch tube K2 in parallel, and the switch tube K1 is connected in series with a diode D6. The main controller determines the interval to which the motor operates based on the real-time rotor position information provided by the Hall position sensor. When the BLDCM operates in the non-switching interval, K1 is turned on and K2 is turned off, and the DC power supply voltage is selected to directly power the BLDCM; in order to prevent the current from flowing from the inverter to the DC power supply, causing the body diode of K1 to be forward-conducted, the switch selection circuit needs to add a diode D6.

[0063] In a specific embodiment, when the motor body operates under high-speed commutation conditions, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter;

[0064] When the motor is running in the high-speed range and switching, the DC bus voltage U dc Satisfaction: U dc <4E, that is, the duty cycle of the switch tube in the three-phase inverter needs to satisfy D>1, but the maximum limit of the duty cycle is 1, and the maximum DC bus voltage is the input DC power supply voltage, so it is necessary to use the auxiliary boost topology circuit for boosting, that is, select the auxiliary boost converter to directly power BLDCM. At this time, K1 is turned off and K2 is turned on. When switching, the output voltage U O >U in At this time, the input-output relationship of the auxiliary boost converter is:

[0065]

[0066] From the above formula, we can see that when the fixed power supply voltage is known, the output voltage U O The size of is determined by the conduction ratio α of the switch tubes Q1 and Q2. In order to suppress the BLDCM commutation torque pulsation, it is required that the motor commutates to meet U dc =4E, the corresponding conduction ratio α calculation formula of the SC-SL-Boost converter can be derived as follows:

[0067]

[0068] Combining the motor torque equation and the amplitude E of the stator winding induced electromotive force, the conduction ratio α of the auxiliary boost converter can be derived as:

[0069]

[0070] Where, Ω is the rotor mechanical angular velocity, U in Input voltage

[0071] As can be seen from the above formula, when the rated power supply voltage of the motor is known, during the high-speed commutation process of the motor body, it is only necessary to detect the motor speed in real time to calculate the conduction ratio α of the switch tubes Q1 and Q2, and drive the switch tubes Q1 and Q2 to conduct, so that the motor DC bus voltage meets four times the back electromotive force, and the open phase and closed phase currents will complete the commutation at the same time, thereby suppressing the motor commutation torque pulsation.

[0072] When the motor body operates under low-speed commutation conditions or non-commutation interval conditions, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, and the sliding mode control module generates a current reference value, which is used to generate a modulation signal through PI regulation to drive the switch tube in the three-phase inverter to chop and regulate the DC power supply input voltage.

[0073] When the motor is working in the low speed range and switching phases: U dc >4E, that is, the duty cycle of the inverter switch tube satisfies 0<D<1. In this case, the switch tube K1 is turned on, K2 is turned off, and the switch selection circuit cuts the power supply voltage to the main circuit to directly power the motor. At this time, the improved reaching law sliding mode control strategy is only applied to the speed loop, and the current loop still uses PI control to adjust the inverter switch tube duty cycle D to adjust the speed and current of the motor control system, maintain the non-commutation phase current stable, and there is no need to increase the DC bus voltage in the commutation interval.

[0074] In this embodiment, the sliding surface used by the sliding mode control module is an integral sliding surface, which can effectively eliminate the steady-state error in the system following process and can play the effect of smoothing the motor torque. The sliding surface s is:

[0075]

[0076] Here, c is a constant greater than 0.

[0077] In order to make the improved speed feedback controller follow more accurately, the speed error is used as a state variable to design it in this embodiment, that is:

[0078]

[0079] Where: r is the reference speed, and ω is the actual speed.

[0080] The sliding mode reaching law in this embodiment for:

[0081]

[0082] Where tanh(·) is the hyperbolic tangent function; ε>0, k>0;

[0083] According to the above sliding surface s, state variables and sliding reaching law get:

[0084]

[0085] Then the output current reference value i is obtained ref for:

[0086]

[0087] like Figure 3 As shown, in a specific embodiment, a brushless DC motor sliding mode control method based on auxiliary boost is implemented based on a brushless DC motor sliding mode control system based on auxiliary boost of the above embodiment, and includes the following steps:

[0088] S1, determine whether the motor body is running under high-speed commutation conditions, if yes, execute step S2, if no, execute step S3;

[0089] A speed threshold is set. When the speed of the motor body is greater than the speed threshold, it is determined whether it is in the commutation interval. If so, the motor body is operating under high-speed commutation conditions.

[0090] The start of the commutation zone is determined by the change in the Hall sensor signal in the motor body. The Hall sensor signal is input into the controller. The motor speed can be calculated and the commutation time can be determined by capturing the rising and falling edges of the three Hall signals and combining logic. After each commutation moment begins, the magnitude of the off-phase current is detected. When the off-phase current drops to zero, it indicates that the commutation is over.

[0091] S2, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter;

[0092] S3, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, the sliding mode control module generates a current reference value, and generates a modulation signal through PI regulation to drive the switch tube in the three-phase inverter to chop and regulate the DC power supply input voltage.

[0093] The sliding surface, state variable selection and output current reference value of the sliding mode control module of this embodiment can be referred to the above embodiment, and will not be repeated here. In the sliding mode control method of this embodiment, the speed loop adopts an improved sliding mode control method, and the current loop still adopts the traditional PI control. The method of the speed loop and the current loop cooperating to generate a PWM modulation signal to drive the duty cycle D of the switch tube in the three-phase inverter is already very mature in the prior art, and the method of adjusting the duty cycle D of the switch tube in the three-phase inverter is not the innovation point of the present invention, so it will not be repeated here.

[0094] In order to further verify the present invention, in a specific embodiment, a brushless DC motor control system experimental platform was built, which consists of a BLDCM, a magnetic powder brake, a control driver, an SC-SL-Boost converter, a logic analyzer, a host computer, an oscilloscope, and a power supply. Due to limited laboratory conditions, only a motor with a relatively small power is used as the control object to verify the implementation effect of the control system. The parameters of the experimental platform are shown in Table 1:

[0095] Table 1 Experimental platform parameters

[0096]

[0097] The parameters of the SC-SL-Boost converter are shown in Table 2:

[0098] Table 2 SC-SL-Boost converter parameters

[0099]

[0100] Figure 4 The comparative simulation waveform diagram of the speed response time under three different control methods: traditional PI control, traditional sliding mode control, and improved sliding mode control. It can be seen that by adopting the improved sliding mode control method of this application, the system response time is shorter and the response speed is faster.

[0101] In order to verify the effectiveness of the BLDCM commutation torque pulsation suppression method based on auxiliary boost, a control system without an auxiliary boost converter and the auxiliary boost converter of the present invention are used in a comparative experiment. When the motor body is commutated at high speed, the boost situation of the SC-SL-Boost converter and the phase current with and without the auxiliary boost method are compared and analyzed. In the experiment, the given speed n = 1800r / min, the load torque T L =2.5N·m, the phase current waveform and DC bus voltage waveform are as follows Figure 5 As shown, Figure 5 a is the phase current and bus voltage waveform using the non-auxiliary boost method. Figure 5 b is the waveform of phase current and bus voltage with auxiliary boost method. Figure 5 It can be seen from a that when the non-assisted boost commutation torque pulsation suppression method is used, the commutation torque pulsation can only be suppressed by adjusting the inverter duty cycle D, but the upper limit of the duty cycle D is 1, which cannot meet the condition that the bus voltage is equal to 4 times the back electromotive force amplitude during high-speed operation. Figure 5 b It can be seen that when the auxiliary boost commutation torque pulsation suppression method is used, the DC bus voltage relies on the SC-SL-Boost converter to boost the motor to approximately meet 4 times the back EMF amplitude during high-speed commutation, thereby suppressing the commutation torque pulsation. In addition, the motor speed n = 1800r / min, the DC bus voltage should be 144V in theory, but the actual experimental DC bus average voltage is 150V, and the voltage error is 6V. The voltage error may be caused by measurement errors and fluctuations in the output voltage of the converter capacitor, but the experiment generally meets the boost requirements and does not cause negative effects, thus verifying the feasibility of the designed SC-SL-Boost converter boost scheme.

[0102] In order to further compare the stability of the phase current of the two commutation torque ripple suppression methods, the phase current waveform and bus voltage waveform obtained by the control system without and with auxiliary boost converter are shown in the figure below. Figure 6 As shown, Figure 6 a is the enlarged waveform obtained by the non-assisted boost method. In the figure, it can be seen that the non-commutation phase current presents a sawtooth shape at each commutation moment, and the current has a large drop. Figure 6 b is an enlarged waveform diagram using the auxiliary boost method of the present invention. When the phase current stability of the auxiliary boost commutation torque pulsation suppression method proposed in this article is used, the non-commutation current drops by about 14% of the steady-state current during motor commutation, and its current shape is close to an ideal square wave, proving the effectiveness of the BDLCM commutation torque pulsation suppression method based on auxiliary boost.

[0103] In order to further analyze the current slope change of the two commutation torque ripple suppression methods with and without auxiliary boost method when the phase current is switched, the phase current switching waveform is as follows: Figure 7 As shown, Figure 6 a is the phase current switching waveform without auxiliary boost method. Figure 7 b is the phase current switching waveform with auxiliary boost method.

[0104] Comparing the effects of the two torque pulsation suppression methods on the current of the off phase A and the on phase B during motor commutation, the current drop rate of the off phase A is greater than the current rise rate of the on phase B when the non-assisted boost method is used. In order to maintain the stability of the non-commutation current during high-speed motor commutation, this method saturates the inverter power switch tube, and the maximum duty cycle of the switch tube is 1. At this time, the maximum DC bus voltage is the power supply voltage, and the off phase and the on phase current still cannot reach a stable state at the same time. However, using the auxiliary boost commutation torque pulsation suppression method proposed in this paper, the current drop rate of the off phase A is equal to the current rise rate of the on phase B, which makes the commutation torque pulsation suppression effect significant.

[0105] Under high-speed commutation conditions, when the brushless DC motor applies the improved reaching law SMC strategy, the improved reaching law SMC method is only used in the speed loop, and the current loop still uses traditional PI control. Figure 8 a and Figure 8 b are the no-load starting speed waveforms of the motor when the speed loop adopts the traditional PI and the improved reaching law SMC, respectively, and the given speed is 1000r / min.

[0106] By comparison, it is found that when the speed loop adopts traditional PI control, the speed overshoot is obvious, and the transition time when the speed rises is greater than 1.6s; when the speed loop adopts the improved reaching law SMC, the motor can achieve stable operation after the speed reaches the target setting value, without obvious overshoot, and the transition time when rising is short, which is about 0.85s. The above comparative experimental results show that when the improved reaching law SMC is used for adjustment, the motor has better dynamic response performance at no-load starting and smaller overshoot.

[0107] Fig. 9 a and 9b are the deceleration waveforms under two speed control strategies, observing the dynamic response of the motor speed when it decelerates from 1000r / min to 500r / min. By comparison, it is found that when the speed loop adopts traditional PI control, when the motor decelerates to the steady-state value, the total time is about 80ms, and the speed overshoot is large. Fig. 9 When the speed loop shown in b is using the improved reaching law SMC, when the motor decelerates to the steady-state value, it only takes about 48ms in total and the speed overshoot is smaller. This once again verifies that when the speed loop is adjusted using the improved reaching law SMC, the motor has a faster dynamic response speed and a smaller overshoot.

[0108] Fig.10 Figures a and b show the dynamic response of the motor speed when a load is suddenly added while the motor is running at a constant speed of 1000 r / min. By comparison, it is found that when the traditional PI control is used in the speed loop, when the motor is suddenly loaded with a load of 5 N·m, the speed drops to 800 r / min. Fig.10 a; Fig.10The speed loop shown in b is under the improved reaching law SMC. When the motor is suddenly loaded with 5N·m, the speed drops to about 890r / min and quickly recovers to the steady-state value of the speed before loading. The experimental results show that when the speed loop is adjusted using the improved reaching law SMC, it has better dynamic response performance and is more robust when external disturbances occur.

[0109] The above comparative experimental results show that the phase current waveform quality of the BLDCM commutation torque pulsation method based on the auxiliary boost topology of this embodiment is significantly improved compared with the non-auxiliary boost torque pulsation suppression method, which is helpful for suppressing high-speed commutation torque pulsation. The SC-SL-Boost converter can take into account the advantages of high gain, low device stress and stable voltage output characteristics, broadens its application in motors, makes device selection easy to implement, and reduces system cost and volume. Compared with the non-auxiliary boost method, the simulation results show that the commutation torque pulsation suppression method proposed in this paper can make the off-phase and on-phase currents complete commutation at the same time, improve the waveform quality of the non-commutation current, and effectively reduce the torque pulsation of the motor during high-speed commutation.

[0110] By observing the speed response under motor starting, deceleration, sudden load and other conditions, it is verified that when the speed loop is adjusted using the improved reaching law SMC strategy, the entire system responds faster, has a smaller overshoot and better robustness than traditional PI control.

[0111] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A brushless DC motor sliding mode control system based on auxiliary boost, comprising a motor body, an inverter circuit, a main controller and a rotor position detection circuit, characterized in that: The inverter circuit includes an auxiliary boost converter, a switch selection circuit and a three-phase inverter connected in sequence, and the main controller includes a converter control module and a sliding mode control module; When the motor body operates under high-speed commutation conditions, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter; The conduction ratio α is: ;in, is the back electromotive force constant, is the rotor mechanical angular velocity, is the DC power supply input voltage; The switch selection circuit includes a first path and a second path. The first path includes a switch tube K1 and a diode D6. The drain of the switch tube K1 is connected to the positive electrode of the power supply, the source of the switch tube K1 is connected to the anode of the diode D6, and the cathode of the diode D6 is connected to the three-phase inverter. The second path includes a switch tube K2. The drain of the switch tube K2 is connected to the auxiliary boost converter, and the source of the switch tube K2 is connected to the cathode of the diode D6. When the motor body operates under low-speed commutation conditions or non-commutation interval conditions, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, and the sliding mode control module generates a current reference value. , a modulation signal is generated through PI regulation to drive the switch tube in the three-phase inverter; The current reference value of the output of the sliding mode control module for: ； in, is the reaching law, which is: ； is the sliding mode function; is the hyperbolic tangent function; , .

2. According to claim 1, a brushless DC motor sliding mode control system based on auxiliary boost, characterized in that: The auxiliary boost converter includes a power switch tube , power switch tube ,diode ,diode ,diode ,diode ,diode , inductance L, capacitance ,capacitance ,capacitance and capacitor ; Power switch tube The source of the power switch is connected to the negative pole of the DC power supply. The drain of the diode is connected to the positive pole of the DC power supply through the inductor L. The anode is connected to the positive pole of the DC power supply, and the cathode is connected to the inductor L and the capacitor The negative end is connected to the positive end of the DC power supply, and the positive end is connected to the power switch tube The drain of the power switch tube The source-connected diode The cathode of the diode The cathode of the power switch tube is connected The drain of the power switch is connected to the anode of the power switch. The drain of the diode ,diode ,diode ,capacitance and capacitor Connect in series and then in parallel with the power switch tube The drain and source, the capacitance Connect diodes at both ends Anode and diode The cathode of the diode Cathode connection capacitance and capacitor The midpoint of .

3. A brushless DC motor sliding mode control method based on auxiliary boost, characterized in that: A brushless DC motor sliding mode control system based on auxiliary boost according to any one of claims 1 to 2 is implemented, comprising the following steps: S1, determine whether the motor body is running under high-speed commutation conditions, if yes, execute step S2, if no, execute step S3; S2, the auxiliary boost converter is connected to the three-phase inverter through the switch selection circuit, and the converter control module adjusts the conduction ratio α of the auxiliary boost converter to adjust the output voltage of the auxiliary boost converter; S3, the auxiliary boost converter is disconnected from the three-phase inverter through the switch selection circuit, and the sliding mode control module generates a current reference value, which is then adjusted by PI to generate a modulation signal to drive the switch tube in the three-phase inverter.

4. The brushless DC motor sliding mode control method based on auxiliary boost according to claim 3 is characterized in that: Methods for determining whether the motor body is operating under high-speed commutation conditions include: A speed threshold is set. When the speed of the motor body is greater than the speed threshold, it is determined whether it is in the commutation interval. If so, the motor body is operating under high-speed commutation conditions.

Images