Method for Suppressing Commutation Torque Ripple of Brushless DC Motor Based on Multi-Output Converter

Abstract

The present invention discloses a method for suppressing commutation torque ripple of a brushless DC motor based on a multi-output converter. A voltage scalar selection circuit with a multi-output converter is designed, and the voltage scalar selection circuit is arranged at the front end of a voltage source inverter to control the brushless DC motor; different voltage scalars of the voltage scalar selection circuit are set to adjust the input voltage of the voltage source inverter and the brushless DC motor; the operating state of the brushless DC motor is detected, and during different periods of non-commutation and commutation, the voltage scalar selection circuit is controlled to output different voltages to provide energy, effectively reducing the commutation torque ripple within the full speed range. The present invention uses a unified control method to suppress the commutation torque ripple within the full speed range. The voltage source inverter only adopts the PAM modulation method and control, and the MOS tube does not chop waves, which can minimize the voltage spike damage to the motor. The multi-output converter is used by a low-voltage DC power supply to generate multiple output voltages, improving the utilization rate of the power supply voltage.

Description

Technical Field

[0001] The present invention relates to a multi-output converter and a control method thereof, specifically to a multi-output converter for high-precision operation control of a brushless DC motor - a method for suppressing commutation torque ripple of a brushless DC motor. Background Art

[0002] Brushless DC motors have the advantages of small size, high power density, and simple structure, and are widely used in fields such as aerospace, household appliances, and electric vehicles. However, there is commutation torque ripple during the operation of brushless DC motors, which can cause the motor to vibrate and generate noise, restricting their application scenarios.

[0003] Scholars have carried out a series of studies on the commutation torque ripple problem of brushless DC motors and proposed many methods for suppressing commutation torque ripple, mainly PWM modulation methods and the method of adding a front-end converter.

[0004] The PWM modulation method is the main method for suppressing commutation torque ripple. This method mainly chops the MOS transistors in the voltage source inverter to ensure the smoothness of the non-commutating phase current during commutation and achieve the suppression of commutation torque ripple. The PWM modulation method is divided into high and low speed regions according to the speed range of the motor, and different PWM modulation methods are used in different speed intervals; different PWM modulation methods are also used according to whether the motor is operating in the non-commutation and commutation periods. These methods will make the design of the PWM modulator complex, resulting in the switching of different modulation methods reducing the stability of the system operation.

[0005] The method of adding a front-end converter is the mainstream method for suppressing commutation torque ripple in recent years. This method mainly aims at the problem that the commutation torque ripple in the high-speed region cannot be suppressed due to the limitation of the DC side voltage. The front-end converter provides a higher voltage for the motor during commutation, especially for suppressing commutation torque ripple in the high-speed region. The method of adding a front-end converter still needs to adopt the PWM modulation method in actual implementation, and the chopping of the MOS transistors in the voltage source inverter will also generate high-frequency interference, causing voltage spike damage to the motor.

[0006] Compared with traditional two independent converters, the multi-output converter retains its good interleaved control and greatly reduces the number of devices. By adjusting the MOS transistors in the multi-output converter, multiple different voltage values can be output simultaneously within one modulation period, which provides a new idea for suppressing commutation torque ripple.

[0007] In the existing methods, there are still problems such as complex design of the PWM modulator, more high-frequency interferences, and low utilization rate of the DC side power supply voltage by the front-end converter. Summary of the Invention

[0008] The technical problem to be solved by the present invention is to provide a multi-output converter - brushless DC motor commutation torque ripple suppression method that can reduce the voltage spike damage to the motor and improve the utilization rate of the power supply voltage.

[0009] The technical solution adopted by the present invention is as follows:

[0010] 1) Design a voltage scalar selection circuit with a multi-output converter, and the voltage scalar selection circuit is arranged at the front end of the voltage source inverter to control the brushless DC motor;

[0011] 2) Set different voltage scalars of the voltage scalar selection circuit to act on the input voltage of the voltage source inverter and the brushless DC motor;

[0012] 3) Detect the operating state of the brushless DC motor. When it is detected that the brushless DC motor is operating in different periods of non-commutation period and commutation period, control the voltage scalar selection circuit to output different voltages to provide energy for the brushless DC motor, so as to effectively reduce the commutation torque ripple in the full speed range on the premise of ensuring the normal operation of the brushless DC motor.

[0013] In the above 3), specifically:

[0014] When the brushless DC motor is operating in the non-commutation period, control the voltage scalar selection circuit to select and output a low voltage scalar with a lower voltage to ensure the normal operation of the brushless DC motor;

[0015] When the brushless DC motor is operating in the commutation period, control the voltage scalar selection circuit to select and output a high voltage scalar with a higher voltage to effectively suppress the commutation torque ripple of the brushless DC motor.

[0016] The voltage scalar selection circuit includes a DC power supply U dc , a multi-output converter, an MOS transistor T c and a diode D 10 . The two input ends of the DC power supply and the multi-output converter are connected. The drain of the MOS transistor T c is connected to the positive pole of the diode D 10 and is connected to the negative input terminal of the voltage source inverter. The source of the MOS transistor T c is connected to the negative output terminal corresponding to the high voltage scalar in the multi-output converter. The negative pole of the diode D 10 is connected to the negative output terminal corresponding to the low voltage scalar in the multi-output converter. The positive output terminal of the voltage scalar in the multi-output converter is connected to the positive terminal of the voltage source inverter.

[0017] The multi-output converter has three output terminals, including two negative-polarity output terminals and one positive-polarity output terminal. The voltage between the negative-polarity output terminal and the positive-polarity output terminal corresponding to the high voltage scalar is the high voltage scalar, and the voltage between the negative-polarity output terminal and the positive-polarity output terminal corresponding to the low voltage scalar is the low voltage scalar.

[0018] The described multi-output converter includes inductor L1, capacitor C1, switch tube T7, diode D7, switch tube T8, diode D8, inductor L2, diode D9, capacitor C3, and capacitor C2;

[0019] The whole formed by the anti-parallel connection of switch tube T7 and diode D7 is connected in series with inductor L1 between the two ends of DC power supply U dc The whole formed by the anti-parallel connection of switch tube T8 and diode D8, diode D9, inductor L2, and capacitor C2 are connected in series together. At the same time, the whole formed by the anti-parallel connection of switch tube T8 and diode D8 and diode D9 are connected in series between the two ends of switch tube T7 and diode D7. Capacitor C3 and inductor L3 are connected in series and then paralleled at both ends of diode D9.

[0020] A lead is taken out between capacitor C3 and inductor L3 as the negative-polarity output terminal corresponding to the low voltage scalar of the multi-output converter. A lead is taken out between inductor L2 and capacitor C2 as the negative-polarity output terminal corresponding to the high voltage scalar of the multi-output converter. A lead is taken out between capacitor C3 and diode D9 as the positive-polarity terminal of the multi-output converter.

[0021] In the voltage scalar selection circuit with the multi-output converter, two voltage scalars are selected to ensure the normal operation of the brushless DC motor and the suppression of commutation torque ripple.

[0022] The two voltage scalars of the voltage scalar selection circuit are V m1 and V m2 , where V m1 is the low voltage scalar with a lower output voltage, which provides a lower voltage for the brushless DC motor during non-commutation; V m2 is the high voltage scalar with a higher output voltage, which provides a higher voltage for the brushless DC motor during commutation;

[0023] Under the low voltage scalar V m1 , the output loop of the voltage scalar selection circuit is: the positive-polarity output terminal in the multi-output converter is connected to the forward-conducting winding of the brushless DC motor through the MOS tube in the voltage source inverter. The negative-conducting winding of the brushless DC motor is connected to the negative-polarity output terminal corresponding to the low voltage scalar in the multi-output converter through the MOS tube in the voltage source inverter and diode D 10 in the voltage scalar selection circuit.

[0024] Under the high voltage scalar V m2Under this condition, the output loop of the voltage scalar selection circuit is as follows: the positive output terminal in the multi-output converter is connected to the forward-conducting winding of the brushless DC motor through the MOS transistor in the voltage source inverter, and the negative-conducting winding of the brushless DC motor is connected to the negative output terminal corresponding to the high voltage scalar in the multi-output converter through the MOS transistor in the voltage source inverter and the diode D of the voltage scalar selection circuit. 10 Connect to the negative output terminal corresponding to the high voltage scalar in the multi-output converter.

[0025] When the brushless DC motor operates during non-commutation, control the MOS transistor T c to turn off, and the diode D 10 conducts forward. The voltage scalar output by the voltage scalar selection circuit is the low voltage scalar V m1 . At this time, the input voltage U in of the voltage source inverter is obtained according to the following formula:

[0026] U in = U out1 = 2E + 2RI

[0027] In the formula, U out1 is the output voltage corresponding to the low voltage scalar V c when the MOS transistor T 10 is turned off and the diode D m1 conducts forward. E is the trapezoidal back electromotive force amplitude, R is the phase resistance of the brushless DC motor, and I is the steady-state value of the phase current;

[0028] When the brushless DC motor operates during commutation, control the MOS transistor T c to turn on and the diode D 10 to be reversely cut off. The voltage scalar output by the voltage scalar selection circuit is the high voltage scalar V m2 . At this time, the input voltage U in of the voltage source inverter is obtained according to the following formula:

[0029] U in = U out2 = 4E + 3RI

[0030] In the formula, U out2 is the output voltage corresponding to the high voltage scalar V m1 when the MOS transistor is turned on and the diode is reversely cut off;

[0031] Input the input voltage U in into the voltage source inverter for control to achieve suppression of commutation torque ripple.

[0032] When the commutation ends, the brushless DC motor runs in the non-commutation period again.

[0033] The described voltage source inverter is controlled by PAM modulation and serves as the electronic commutation device for the brushless DC motor. All MOS transistors in the voltage source inverter do not perform chopping.

[0034] The present invention designs a voltage scalar selection circuit with a multi-output converter to achieve smooth operation control of the brushless DC motor; determines the effects of different voltage scalars of the voltage scalar selection circuit on the input voltage of the voltage source inverter and the brushless DC motor; during the non-commutation period of motor operation, selects the voltage scalar with a lower output voltage for control to ensure the normal operation of the brushless DC motor; during the commutation period of motor operation, selects the voltage scalar with a higher output voltage for control to effectively suppress the commutation torque ripple of the brushless DC motor.

[0035] The beneficial effects of the present invention are:

[0036] The method for suppressing the commutation torque ripple of the multi-output converter-brushless DC motor of the present invention uses a unified control method to suppress the commutation torque ripple within the full speed range.

[0037] During the non-commutation and commutation periods, the present invention respectively uses the lower voltage and higher voltage outputs of the multi-output converter to supply energy to the motor. The voltage source inverter is only controlled by the PAM modulation method. As the electronic commutation device of the brushless DC motor, all MOS transistors in the voltage source inverter do not perform chopping, which can minimize the voltage spike damage to the motor. For industrial applications with a lower DC power supply voltage, the multi-output converter can utilize multiple output voltages among them to improve the power supply voltage utilization rate. Description of the Drawings

[0038] Figure 1 is the schematic diagram of the embodiment of the method for suppressing the commutation torque ripple of the multi-output converter-brushless DC motor;

[0039] Figure 2 is the schematic diagram of the brushless DC motor system driven by a single-input dual-output Cuk converter in Embodiment 1;

[0040] Figure 3a is the equivalent circuit diagram of the voltage scalar V m1 during the non-commutation period of motor operation in Embodiment 1;

[0041] Figure 3b is the equivalent circuit diagram of the voltage scalar V m2 during the commutation period of motor operation in Embodiment 1;

[0042] Figure 4a is the current flow diagram during the non-commutation period of motor operation in B + A - ;

[0043] Figure 4bIt is when the motor operates at B + A - →C + A - Current flow diagram during commutation;

[0044] Figure 5 It is a modulation schematic diagram of the commutation torque ripple suppression method for a multi-output converter - brushless DC motor. Specific implementation manner

[0045] The following will make a detailed description of the commutation torque ripple suppression method for a multi-output converter - brushless DC motor of the present invention in conjunction with embodiments and drawings.

[0046] The specific embodiments of the present invention and their implementation situations are as follows:

[0047] 1) Design a brushless DC motor control circuit with a voltage scalar selection circuit A of a multi-output converter I, and the voltage scalar selection circuit A is arranged at the front end of a voltage source inverter II;

[0048] As Figure 1 shown, the voltage scalar selection circuit A includes a DC power supply, a multi-output converter I, an MOS transistor T c and a diode D 10 constituted. Among them, the negative output terminal of the high voltage scalar in the multi-output converter I is connected to the source electrode of the MOS transistor T c , the negative electrode of the diode D 10 is connected to the drain electrode of the MOS transistor T c and is connected to the negative input terminal of the voltage source inverter II. The negative output terminal of the low voltage scalar in the multi-output converter I is connected to the positive electrode of D 10 , and the positive input terminal of the voltage source inverter II is connected to the positive output terminal of the voltage scalar selection circuit A.

[0049] 2) Determine different voltage scalars of the voltage scalar selection circuit A and their effects on the input voltages of the voltage source inverter II and the brushless DC motor III;

[0050] As Figure 1 shown, in the voltage scalar selection circuit A, by the switching state of the MOS transistor T c , two voltage scalars are selected to ensure the normal operation of the brushless DC motor III and the suppression of commutation torque ripple. The two voltage scalars are respectively represented as V m1 and V m2 , where V m1 is the voltage scalar with a lower output voltage, which provides a lower voltage for the brushless DC motor III during non-commutation periods; V m2The voltage scalar with a higher output voltage provides a higher voltage to the brushless DC motor III during the commutation period.

[0051] 3) Detecting the operating state of the brushless DC motor III. When it is detected that the brushless DC motor III is operating in the non-commutation period and the commutation period, providing energy to the motor according to different voltage scalars of the voltage scalar selection circuit A, while ensuring the normal operation of the brushless DC motor III, effectively reducing the commutation torque fluctuation within the full speed range.

[0052] like Figure 1 As shown in the figure, when the commutation is detected to be over, the brushless DC motor III is running in the non-commutation period, and the MOS tube T in the voltage scalar selection circuit A c Turn off, diode D 10 Forward conduction, the output voltage scalar is V m1 , at this time, the input voltage U of the voltage source inverter II is in for:

[0053] U in =U out1 =2E+2RI (1)

[0054] Where U out1 For MOS tube T c Turn off, diode D 10 Forward conduction voltage scalar V m1 The output voltage of , E is the trapezoidal back EMF amplitude, R is the phase resistance of brushless DC motor III, and I is the steady-state value of phase current.

[0055] like Figure 1 As shown, H A , H B , H C Respectively represent the Hall sensor signals inside the motor. A , H B , H C When the commutation process starts, the brushless DC motor III runs during the commutation period, and the MOS tube T in the voltage scalar selection circuit A c Open, diode D 10 Reverse cutoff, the output voltage scalar is V m2 At this time, the input voltage U of the voltage source inverter II is in for:

[0056] U in =U out2 =4E+3RI (2)

[0057] Where U out2 V is the voltage scalar when the MOS tube is turned on and the diode is reversely cut off m1The output voltage. When the commutation ends, the brushless DC motor Ⅲ resumes operation during non-commutation periods.

[0058] 4) When it is detected that the brushless DC motor (Ⅲ) operates in different periods of non-commutation and commutation, control the voltage scalar selection circuit (A) to output different voltages to supply energy to the brushless DC motor (Ⅲ).

[0059] During the non-commutation period of the brushless DC motor Ⅲ, select the voltage scalar V with a lower output voltage m1 for control to ensure the normal operation of the brushless DC motor Ⅲ. The voltage scalar V m1 The output loop of the lower voltage scalar selection circuit A is as follows: The positive output terminal of the multi-output converter Ⅰ is sequentially connected to the forward-conducting winding of the brushless DC motor Ⅲ through the MOS tube in the voltage source inverter Ⅱ. The negative-conducting winding of the brushless DC motor Ⅲ is connected to the negative output terminal of the lower voltage scalar in the multi-output converter Ⅰ through the MOS tube and diode D in the voltage source inverter Ⅱ 10 connected to the negative output terminal of the lower voltage scalar in the multi-output converter Ⅰ.

[0060] During the commutation period of the brushless DC motor Ⅲ, select the voltage scalar V with a higher output voltage m2 for control to effectively suppress the commutation torque ripple of the brushless DC motor Ⅲ. The voltage scalar V m2 The output loop of the lower voltage scalar selection circuit A is as follows: The positive output terminal of the multi-output converter Ⅰ is sequentially connected to the forward-conducting winding of the brushless DC motor Ⅲ through the MOS tube in the voltage source inverter Ⅱ. The negative-conducting winding of the brushless DC motor Ⅲ is connected to the negative output terminal of the higher voltage scalar in the multi-output converter Ⅰ through the MOS tube and diode D in the voltage source inverter Ⅱ 10 connected to the negative output terminal of the higher voltage scalar in the multi-output converter Ⅰ.

[0061] In specific implementation, the voltage source inverter Ⅱ only adopts the PAM modulation method for control. As the electronic commutation device of the brushless DC motor Ⅲ, the MOS tubes in the voltage source inverter Ⅱ do not perform chopping.

[0062] The schematic diagram of the embodiment of the present invention is as Figure 1 shown. This system is composed of three parts: a voltage scalar selection circuit A, a voltage source inverter Ⅱ, and a brushless DC motor Ⅲ. The DC power supply, multi-output converter Ⅰ, MOS tube T c and diode D 10 together constitute the voltage scalar selection circuit A, which is arranged at the front end of the voltage source inverter Ⅱ to control the brushless DC motor Ⅲ. The switching state of the MOS tube T c is used to change the output voltage scalar of the voltage scalar selection circuit A.

[0063] Figure 2 Shown is an embodiment that implements the present invention using a single-input dual-output Cuk converter, hereinafter referred to as Embodiment 1.

[0064] In Embodiment 1, a single-input dual-output Cuk converter is selected, which consists of MOS transistors T7 and T8, diode D9, inductors L1 - L3, and capacitors C1 - C3, and is connected to a DC power supply U dc , MOS transistor T c and diode D 10 constitute a voltage scalar selection circuit A. The DC power supply voltage is the input voltage of the single-input dual-output Cuk converter. The drain of MOS transistor T c is connected to the negative pole of diode D 10 and is connected to the negative terminal of the input U in of the voltage source inverter II. The source of MOS transistor T c is connected to the negative output terminal of the voltage across both ends of capacitor C2 in the single-input dual-output Cuk converter. The positive pole of diode D 10 is connected to the negative output terminal of the voltage across both ends of capacitor C3 in the single-input dual-output Cuk converter. The positive output terminals of the voltages across both ends of capacitors C2 and C3 in the single-input dual-output Cuk converter are connected to the positive terminal of the voltage source inverter II. The MOS transistors of the voltage source inverter II are T1 - T6 respectively, D1 - D6 are the anti-parallel diodes corresponding to the MOS transistors, and i A , i B , i C are the three-phase currents of the brushless DC motor III.

[0065] As Figure 1 shown, by designing the voltage scalar selection circuit A, the switching of different output voltage scalars of the single-input dual-output Cuk converter is realized. During the commutation period, the voltage across both ends of capacitor C2 is selected to increase the input voltage U in of the voltage source inverter. During the non-commutation period, the voltage across both ends of capacitor C3 of the single-input dual-output Cuk converter is adjusted through a speed and current PI controller to meet the speed regulation requirements of the motor. Equation 7 is used to control the MOS transistors in the single-input dual-output Cuk converter to adjust the voltage across both ends of capacitor C2 in the single-input dual-output Cuk converter, maintain the stability of the non-commutation phase current, and thus suppress the commutation torque ripple. By collecting the signals of the sensors (i A , i B , i C and H A , H B , H C ), the start and end signals during the commutation period and the non-commutation phase current values are detected and generated, and the switching signal for controlling MOS transistor T c is generated.

[0066] As Figure 1As shown, in the voltage source inverter II, the MOS transistors are controlled by the PAM method. At this time, the duty cycle d of the MOS transistors T1 - T6 is 1, which can minimize the voltage spikes and current ripples generated by PWM modulation.

[0067] Figure 3a and Figure 3b As shown, the voltage scalar V m1 and V m2 are the equivalent circuits constructed in Embodiment 1. The output voltage across the two ends of the capacitor C2 of the single - input dual - output Cuk converter is U o1 , and the output voltage across the two ends of the capacitor C3 is U o2 .

[0068] Figure 3a As shown, the MOS transistor T c conducts, and the diode D 10 is reversely cut off. The output of the voltage scalar selection circuit A is the output voltage across the two ends of the capacitor C3 of the single - input dual - output Cuk converter I. At this time, the capacitor C3 supplies power to the motor alone. At this time, the input voltage of the voltage source inverter II satisfies U in = U out1 = U o2 .

[0069] Figure 3b As shown, the diode D 10 conducts forward, and the MOS transistor T c is turned off. The output of the voltage scalar selection circuit A is the output voltage across the two ends of the capacitor C2 of the single - input dual - output Cuk converter I. At this time, the capacitor C2 supplies power to the motor alone. At this time, the input voltage of the voltage source inverter II satisfies U in = U out2 = U o1 .

[0070] According to Kirchhoff's law, the input voltage U in of the voltage source inverter II under different voltage scalars is

[0071]

[0072] Assuming that the magnetic circuit of the motor is unsaturated and ignoring the voltage drop of the MOS transistor and the influence caused by its own structure, the three - phase winding terminal voltage equation of the brushless DC motor III is:

[0073]

[0074] In the formula, u A , u B , u C are the phase voltages of the three - phase windings of the motor; u N is the neutral - point voltage of the motor.

[0075] Figure 4a As shown, the brushless DC motor Ⅲ operates at B + A - During the non - commutation period, windings of phases B and A are conducting, and phase C is floating. When the DC power supply voltage U dc is constant, the input voltage of the single - input double - output Cuk converter Ⅰ is U dc . Through the first and second equations of Equation (4), B + A - The line voltage between phases B and A during the non - commutation period is

[0076]

[0077] where, R represents the phase resistance of the brushless DC motor Ⅲ, t represents the time of a modulation period, and i A represents the phase current of phase A in the brushless DC motor Ⅲ.

[0078] During the entire modulation period, the phase current of phase A hardly changes. The average value of the line voltage u BA between phases B and A can be obtained as:

[0079]

[0080] where, U BA represents the average value of the line voltage between phases B and A, represents the line voltage between phases B and A;

[0081] Figure 4b As shown, the brushless DC motor Ⅲ operates at B + A - →C + A - During the commutation period. Ignoring the conduction voltage drops of the MOS transistors and free - wheeling diodes, the control mode of the voltage - source inverter Ⅱ adopts the PAM control mode. To suppress the commutation torque ripple of the brushless DC motor Ⅲ, the voltage scalar V m2 is selected as the input voltage of the voltage - source inverter Ⅱ, that is, V m2 satisfies Equation (2).

[0082] The output U o1 of the single - input double - output Cuk converter is the same as that of the traditional Cuk converter, and this output is controlled by the MOS transistor T7. The duty cycle d7 of the MOS transistor T7 can be obtained as

[0083]

[0084] When it is detected that the current of the turned - off phase is zero, the commutation ends, and the MOS transistor T c is turned off, and the control strategy during the non - commutation period is entered.

[0085] During the non - commutation period, the control mode of the voltage - source inverter II still adopts the PAM control mode. To meet the speed - regulation requirements of the brushless DC motor III, the voltage scalar V m1 is selected as the input voltage of the voltage - source inverter II, that is, V m1 satisfies Equation (1).

[0086] The output U of the single - input double - output Cuk converter o2 is controlled by the MOS transistor T8, and the duty cycle d8 of T8 is obtained as

[0087]

[0088] Figure 5 is the modulation schematic diagram of the multi - output converter - brushless DC motor commutation torque ripple suppression method of the present invention. When the motor operates during the non - commutation period, the MOS transistor T c is turned off, and the voltage scalar V m1 is selected as the input voltage of the voltage - source inverter II. The double - closed - loop control is used to regulate the MOS transistor T8 in the single - input double - output Cuk converter to meet the motor speed - regulation requirements. The detailed control method is as Figure 1 . When the motor operates during the commutation period, the MOS transistor T c is turned on, and the voltage scalar V m2 is selected as the input voltage of the voltage - source inverter II. Equation (7) is used to regulate the MOS transistor T7 in the single - input double - output Cuk converter to meet the voltage requirements during the commutation period. The voltage - source inverter II only adopts the PAM control mode and only plays the role of electronic commutation.

[0089] Through the above steps, the multi - output converter - brushless DC motor commutation torque ripple suppression method of the present invention is realized. Compared with the traditional method, the multi - output converter can be extended to the application of low - voltage DC power supplies, which can improve the utilization rate of the DC power supply voltage; there is no need to switch the control strategy according to the speed. Different voltage scalars are selected during the non - commutation period and the commutation period respectively, which can effectively suppress the commutation torque ripple in the full - speed range; the voltage - source inverter II only adopts the PAM control mode, which can minimize the voltage spike damage to the motor and simplify the program design of the controller at the same time.

Claims

1. A method for suppressing commutation torque ripple of a brushless DC motor based on a multi-output converter, characterized in that, The method comprises the following steps: 1) Design a voltage scalar selection circuit (A) with a multi-output converter (Ⅰ), and the voltage scalar selection circuit (A) is arranged at the front end of a voltage source inverter (Ⅱ) to control a brushless DC motor; The described voltage scalar selection circuit (A) includes a DC power supply U dc , a multi-output converter (I), an MOS transistor T c and a diode D 10 . The DC power supply is connected to two input terminals of the multi-output converter (I). The drain of the MOS transistor T c is connected to the positive electrode of the diode D 10 and is connected to the negative input terminal of the voltage source inverter (II). The source of the MOS transistor T c is connected to the negative output terminal corresponding to the high voltage scalar in the multi-output converter (I). The negative electrode of the diode D 10 is connected to the negative output terminal corresponding to the low voltage scalar in the multi-output converter (I). The positive output terminal of the voltage scalar in the multi-output converter (I) is connected to the positive terminal of the voltage source inverter (II); 2) Set different voltage scalars of the voltage scalar selection circuit (A) to act on the input voltages of the voltage source inverter (Ⅱ) and the brushless DC motor (Ⅲ); 3) Detect the operating state of the brushless DC motor (Ⅲ). When it is detected that the brushless DC motor (Ⅲ) operates in different periods of non-commutation period and commutation period, control the voltage scalar selection circuit (A) to output different voltages to supply energy to the brushless DC motor (Ⅲ), so as to effectively reduce the commutation torque ripple in the full speed range on the premise of ensuring the normal operation of the brushless DC motor (Ⅲ); When the brushless DC motor (Ⅲ) operates in the non-commutation period, control the voltage scalar selection circuit (A) to select and output a low voltage scalar with a lower voltage for control to ensure the normal operation of the brushless DC motor (Ⅲ); When the brushless DC motor (Ⅲ) operates in the commutation period, control the voltage scalar selection circuit (A) to select and output a high voltage scalar with a higher voltage for control to effectively suppress the commutation torque ripple of the brushless DC motor (Ⅲ).

2. The commutation torque ripple suppression method for the multi-output converter - brushless DC motor according to claim 1, characterized in that: The two voltage scalars of the voltage scalar selection circuit (A) are V m1 and V m2 , where V m1 is the low voltage scalar with a lower output voltage, which provides a lower voltage for the brushless DC motor (Ⅲ) during non-commutation; V m2 is the high voltage scalar with a higher output voltage, which provides a higher voltage for the brushless DC motor (Ⅲ) during commutation; At the low-voltage scalar V m1 The output loop of the voltage scalar selection circuit (A) is as follows: the positive output terminal of the multi-output converter (I) is connected to the forward-conducting winding of the brushless DC motor (III) through the voltage source inverter (II), and the negative-conducting winding of the brushless DC motor (III) is connected to the negative output terminal corresponding to the low-voltage scalar in the multi-output converter (I) through the voltage source inverter (II) and diode D 10 ; At the high voltage scalar V m2 Below, the output loop of the voltage scalar selection circuit (A) is as follows: The positive output terminal in the multi-output converter (I) is connected to the forward-conducting winding of the brushless DC motor (III) through the voltage source inverter (II), and the negative-conducting winding of the brushless DC motor (III) is connected to the negative output terminal corresponding to the high voltage scalar in the multi-output converter (I) through the voltage source inverter (II) and the diode D 10 Connect.

3. The method for suppressing commutation torque ripple of a multi-output converter - brushless DC motor according to claim 1, characterized in that: The described brushless DC motor (III) operates during non-commutation, controlling the MOS transistor T c to turn off, and the diode D 10 to conduct forward. The voltage scalar selection circuit (A) outputs a low voltage scalar V m1 . At this time, the input voltage U of the voltage source inverter (II) is obtained according to the following formula in as follows: U in = U out1 = 2E + 2RI Where, U out1 is the MOS transistor T c when turned off, and the diode D 10 is the low voltage scalar V when conducting forward, m1 the corresponding output voltage, E is the trapezoidal back electromotive force amplitude, R is the phase resistance of the brushless DC motor (Ⅲ), and I is the steady-state value of the phase current; The described brushless DC motor (III) operates during commutation, controlling the MOS transistor T c to turn on and the diode D 10 to be reverse cutoff. The voltage scalar selection circuit (A) outputs a high voltage scalar V m2 . At this time, the input voltage U of the voltage source inverter (II) is obtained according to the following formula in as follows: U in = U out2 = 4E + 3RI Wherein, U out2 is the high voltage scalar V m1 corresponding to the output voltage when the MOS transistor is turned on and the diode is reversely cut off; Input the input voltage U in into the voltage source inverter (II) for control to achieve commutation torque ripple suppression.

4. The method for suppressing commutation torque ripple of a multi-output converter - brushless DC motor according to claim 1, characterized in that: The voltage source inverter (Ⅱ) is controlled by a PAM modulation method. As an electronic commutation device of the brushless DC motor (Ⅲ), all MOS transistors in the voltage source inverter (Ⅱ) do not perform chopping.

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