阅读说明：本技术 一种直流电机软启动控制方法及系统 (Direct current motor soft start control method and system ) 是由 韩永杰 刘钧 刘骥 余意 于 2021-01-07 设计创作，主要内容包括：本发明公开了一种直流电机软启动控制方法及系统,所述方法包括：将电机启动过程分为电容充电阶段和位于电容充电阶段后的电机启动阶段,在电容充电阶段,驱动波形为PWM脉冲,在电机启动阶段,驱动波形为高电平直流电压。采用本发明的技术方案,无需采用软启动电阻就可以实现电机软启动,实现方式简单。(The invention discloses a method and a system for controlling soft start of a direct current motor, wherein the method comprises the following steps: the motor starting process is divided into a capacitor charging stage and a motor starting stage positioned after the capacitor charging stage, wherein in the capacitor charging stage, the driving waveform is PWM pulse, and in the motor starting stage, the driving waveform is high-level direct-current voltage. By adopting the technical scheme of the invention, the soft start of the motor can be realized without adopting a soft start resistor, and the realization mode is simple.)

1. A soft start control method of a direct current motor is characterized by comprising the following steps:

the motor starting process is divided into a capacitor charging stage and a motor starting stage positioned after the capacitor charging stage, wherein in the capacitor charging stage, the driving waveform is PWM pulse, and in the motor starting stage, the driving waveform is high-level direct-current voltage.

2. The soft-start control method of a dc motor according to claim 1, wherein the PWM pulse has an on time and an off time t_on、t_offCalculated by the following formula:

wherein, V_DRFor outputting voltage, V, to motor drive circuits_CFor the voltage across the equivalent capacitor of the filter circuit at the motor port, R_DRIs an equivalent resistance of the motor drive circuit, L_DRIs equivalent inductance of motor drive circuit, C is equivalent capacitance of filter circuit arranged between motor and drive circuit, R is equivalent capacitance of motor drive circuit_mIs the internal resistance of the DC motor, L_mIs a coil inductance of a direct current motor, I_DRTo drive the current, I_CIs a capacitance current, I_mIs the motor current.

3. The soft-start control method of a direct current motor according to claim 2, wherein the frequency of the PWM pulse is obtained by:

setting the PWM pulse as a fixed duty ratio, setting an initial frequency, then doubling the initial frequency and judging whether overcurrent protection can be triggered to quickly find f_xAnd f_yWherein f is_xFrequency value of not triggering over-current protection, f_yTo trigger the frequency value of the overcurrent protection, the initial frequency is then set to (f)_x+f_y) And/2, continuously judging whether overcurrent protection is triggered or not, and obtaining final f through multiple iterations_xAs the frequency of the PWM pulses.

4. The soft-start control method of a dc motor according to claim 2, wherein a driving current peak feedback value and a driving peak current command value are used for loop regulation to obtain the frequency of the PWM pulse.

5. A soft start control system of a direct current motor is characterized by comprising: the control unit is used for controlling the driving circuit to send out driving signals to drive the motor to work, the control unit divides the starting process of the motor into a capacitor charging stage and a motor starting stage located behind the capacitor charging stage, the waveform of the driving signals is PWM pulses in the capacitor charging stage, and the waveform of the driving signals is high-level direct-current voltage in the motor starting stage.

6. The system for controlling the soft start of the direct current motor according to claim 5, wherein a filter circuit is further arranged between the driving circuit and the motor, and a current detection and protection circuit is further arranged between the control unit and the motor driving circuit.

7. The soft-start control system of a dc motor of claim 6, wherein the PWM pulse has an on-time and an off-time t_on、t_offCalculated by the following formula:

wherein, V_DRFor outputting voltage, V, to motor drive circuits_CFor the voltage across the equivalent capacitor of the filter circuit at the motor port, R_DRIs an equivalent resistance of the motor drive circuit, L_DRIs equivalent inductance of motor drive circuit, and C is equivalent inductance arranged between the motor andequivalent capacitance of filter circuit between drive circuits, R_mIs the internal resistance of the DC motor, L_mIs a coil inductance of a direct current motor, I_DRTo drive the current, I_CIs a capacitance current, I_mIs the motor current.

8. The soft-start control system of a dc motor of claim 6, wherein the control unit obtains the frequency of the PWM pulses by:

setting the PWM pulse as a fixed duty ratio, setting an initial frequency, then doubling the initial frequency and judging whether overcurrent protection can be triggered to quickly find f_xAnd f_yWherein f is_xFrequency value of not triggering over-current protection, f_yTo trigger the frequency value of the overcurrent protection, the initial frequency is then set to (f)_x+f_y) And/2, continuously judging whether overcurrent protection is triggered or not, and obtaining final f through multiple iterations_xAs the frequency of the PWM pulses.

9. The soft-start control system of a dc motor of claim 6, wherein the control unit performs loop regulation using a driving current peak feedback value and a driving peak current command value to obtain the frequency of the PWM pulse.

Technical Field

The invention relates to the field of direct current motor control, in particular to a direct current motor soft start control method and system.

Background

The direct current motor is widely applied to the fields of aerospace, metallurgy, new energy, textile manufacturing and the like, and has the advantages of simple structure, low cost and convenience in control. The small direct current motor is simple to control, can be started only by providing a direct current power supply, but has the problems of large starting current, difficult starting and the like under partial conditions. Although the method can solve the problem of starting the motor to a certain extent, the power consumption required by the soft starting resistor is large, the heat dissipation problem exists, the system efficiency is reduced, and the system cost and the volume are increased.

Disclosure of Invention

The invention aims to solve the technical problem that the direct current motor in the prior art is large in power consumption and difficult in heat dissipation due to the adoption of a soft start resistor during starting, and provides a solution of a direct current motor soft start control method and a system.

The embodiment of the invention provides a soft start control method of a direct current motor, which comprises the following steps:

the motor starting process is divided into a capacitor charging stage and a motor starting stage positioned after the capacitor charging stage, wherein in the capacitor charging stage, the driving waveform is PWM pulse, and in the motor starting stage, the driving waveform is high-level direct-current voltage.

In the embodiment of the invention, in the PWM pulse, the on time and the off time t_on、t_offCalculated by the following formula:

wherein, V_DRFor outputting voltage, V, to motor drive circuits_CFor the voltage across the equivalent capacitor of the filter circuit at the motor port, R_DRIs an equivalent resistance of the motor drive circuit, L_DRIs equivalent inductance of motor drive circuit, C is equivalent capacitance of filter circuit arranged between motor and drive circuit, R is equivalent capacitance of motor drive circuit_mIs the internal resistance of the DC motor, L_mIs a coil inductance of a direct current motor, I_DRTo drive the current, I_CIs a capacitance current, I_mIs the motor current.

In the embodiment of the present invention, the frequency of the PWM pulse is obtained as follows:

setting the PWM pulse as a fixed duty ratio, setting an initial frequency, then doubling the initial frequency and judging whether overcurrent protection can be triggered to quickly find f_xAnd f_yWherein f is_xFrequency value of not triggering over-current protection, f_yTo trigger the frequency value of the overcurrent protection, the initial frequency is then set to (f)_x+f_y) And/2, continuously judging whether overcurrent protection is triggered or not, and obtaining final f through multiple iterations_xAs the frequency of the PWM pulses.

In the embodiment of the invention, the frequency of the PWM pulse is obtained by performing loop regulation by using the peak value feedback value of the driving current and the command value of the driving peak value current.

In an embodiment of the present invention, a system for controlling soft start of a dc motor is further provided, including: the control unit is used for controlling the driving circuit to send out driving signals to drive the motor to work, the control unit divides the starting process of the motor into a capacitor charging stage and a motor starting stage located behind the capacitor charging stage, the waveform of the driving signals is PWM pulses in the capacitor charging stage, and the waveform of the driving signals is high-level direct-current voltage in the motor starting stage.

In the embodiment of the invention, a motor port filter circuit is also arranged between the drive circuit and the motor, and a current detection and protection circuit is also arranged between the control unit and the motor drive circuit.

In the embodiment of the invention, in the PWM pulse, the on time and the off time t_on、t_offCalculated by the following formula:

wherein, V_DRFor outputting voltage, V, to motor drive circuits_CFor the voltage across the equivalent capacitor of the filter circuit at the motor port, R_DRIs an equivalent resistance of the motor drive circuit, L_DRFor motor drive circuit equivalent electricityThe inductance C is a filter circuit equivalent capacitance arranged between the motor and the drive circuit, and R is_mIs the internal resistance of the DC motor, L_mIs a coil inductance of a direct current motor, I_DRTo drive the current, I_CIs a capacitance current, I_mIs the motor current.

In the embodiment of the present invention, the control unit obtains the frequency of the PWM pulse by:

setting the PWM pulse as a fixed duty ratio, setting an initial frequency, then doubling the initial frequency and judging whether overcurrent protection can be triggered to quickly find f_xAnd f_yWherein f is_xFrequency value of not triggering over-current protection, f_yTo trigger the frequency value of the overcurrent protection, the initial frequency is then set to (f)_x+f_y) And/2, continuously judging whether overcurrent protection is triggered or not, and obtaining final f through multiple iterations_xAs the frequency of the PWM pulses.

In the embodiment of the present invention, the control unit performs loop regulation using a driving current peak value feedback value and a driving peak value current command value to obtain the frequency of the PWM pulse.

Compared with the prior art, the method and the system for controlling the soft start of the direct current motor divide the starting process of the motor into a capacitor charging stage and a motor starting stage positioned after the capacitor charging stage, the waveform of the driving signal is PWM pulse in the capacitor charging stage, and the waveform of the driving signal is high-level direct current voltage in the motor starting stage, so that the soft start of the motor can be realized without adopting a soft start resistor, the realization mode is simple, extra devices and cost are not required to be added, the cost and the volume can be effectively saved, and the product adaptability is strong; in addition, aiming at the characteristics of different motors, the dichotomy mode can be adopted for open-loop adjustment, parameters can be matched quickly, and the stability of driving peak current can be ensured and the soft start of the motor can be realized through a closed-loop adjustment mode.

Drawings

Fig. 1 is a diagram of a typical dc motor control system architecture.

Fig. 2 is a block diagram of a typical dc motor and its control system.

Fig. 3 is a simplified circuit diagram of a dc motor driving circuit.

Fig. 4 is a motor starting portion voltage current waveform without the addition of a soft start strategy.

Fig. 5 is a voltage and current waveform of a starting portion of a dc motor in the soft start control method of the dc motor according to the embodiment of the present invention.

Fig. 6 is a flowchart of calculating the PWM pulse frequency using the bisection method according to an embodiment of the present invention.

Fig. 7 is a block diagram of a control loop that can dynamically adjust the PWM frequency using a drive current peak feedback loop, according to an embodiment of the present invention.

Detailed Description

Fig. 1 is a diagram of a typical dc motor control system architecture. The direct current motor control system comprises a motor driving unit, a control unit and a direct current motor unit. The control unit is used for detecting the working state of the motor and controlling the action of the driving unit according to the system requirement and the algorithm. The motor driving unit is used for receiving the control signal of the control unit and driving the motor to work.

Fig. 2 is a block diagram of a typical dc motor control system, further exploded from fig. 1. Wherein, the control unit comprises a control chip and a position detection circuit. The control chip is used for realizing a motor control algorithm and providing a driving logic signal. The position detection circuit is used for detecting the running state of the motor. The motor driving unit comprises a driving circuit and a current detection and protection circuit, wherein the driving circuit can be a driving chip with current protection or a switching circuit built by a discrete switching device. The current detection and protection circuit is used for detecting the driving current of the driving circuit and transmitting the detected current signal to the control chip, and overcurrent protection is realized through the control chip. The direct current motor unit comprises a direct current motor, a position detection switch device and a filter circuit. The position detection switch device is used for feeding back the running state of the motor. The filter circuit is arranged between the drive circuit and the direct current motor and is used for enhancing the anti-electromagnetic interference capability of the system.

Fig. 3 is a simplified circuit diagram of the dc motor driving circuit of fig. 2. Wherein, V_DRFor outputting voltage, V, to motor drive circuits_CFor the voltage across the equivalent capacitor of the filter circuit at the motor port, R_DRIs an equivalent resistance of the motor drive circuit, L_DRIs equivalent inductance of motor drive circuit, C is equivalent capacitance of filter circuit arranged between motor and drive circuit, R is equivalent capacitance of motor drive circuit_mIs the internal resistance of the DC motor, L_mIs a coil inductance of a direct current motor, I_DRTo drive the current, I_CIs a capacitance current, I_mIs the motor current.

Fig. 4 is a motor starting portion voltage current waveform without the addition of a soft start strategy. Wherein V_DRFor outputting a voltage waveform to the drive circuit, direct high-level driving, V_CIs the voltage waveform at two ends of an equivalent capacitor of a filter circuit at a motor port I_DROutputting a current waveform for the drive circuit. The soft start of the motor is divided into a capacitor charging stage and a motor starting stage, the capacitor charging stage, V_DRThe port capacitor is charged through the impedance of the driving circuit, and the impact current is large due to the small impedance of the driving circuit, and the maximum impact current is assumed to be I_pk1，I_pk1The capacitance magnitude and line impedance are related; in the starting stage of the motor, after the capacitor is fully charged, V_DRThe drive motor is soft-started, and the maximum starting current is I_pkm，I_pkmDependent on the characteristics of the motor itself, generally I_pk1Will be much larger than I_pkmIs of_pkm5 to 10 times of the total weight of the composition. When designing motor drive circuits, it is customary to design them only according to I_pkmConsidering its maximum drive current capability and protection threshold I_pro，I_proIs usually set to I_pkm1.5 to 2 times of that of the compound I_pk1Will be greater than I_proAnd the driving unit can report an overcurrent fault in the capacitor charging stage, the direct current power supply is closed, and the motor cannot be started successfully. If the maximum driving current capability considered in designing the driving is larger than I_pk1The cost of the driving circuit rises linearly, and different direct current motors have larger parameter difference of filter circuits under different application scenes, namely I_pk1The difference is large, and the drive electricity is increased through hardwareAnd the system has poor adaptability.

Fig. 5 is a voltage and current waveform of a starting part of a motor by using a soft starting method of a direct current motor according to an embodiment of the invention. Wherein V_DROutput voltage waveform V for driving circuit_CIs the voltage waveform at two ends of an equivalent capacitor of a filter circuit at a motor port I_DROutputting a current waveform for the drive circuit. In the embodiment of the invention, the motor soft start control method comprises the following steps: the motor starting process is divided into a capacitor charging stage and a motor starting stage positioned after the capacitor charging stage, wherein in the capacitor charging stage, the driving waveform is PWM pulse, and in the motor starting stage, the driving waveform is high-level direct-current voltage.

By adopting the motor soft start control method provided by the embodiment of the invention, the capacitor is precharged by adding a control mode of soft start pulse driving, so that the overcurrent caused by capacitor charging can be reduced, and the specific working waveform is shown in fig. 5. The soft start is carried out by adding PWM pulse, so that the driving current I can be effectively reduced_DRPeak value of (1), peak current I_pk2Can be realized by increasing the PWM wave-generating frequency or reducing the PWM on-duty ratio. However, the PWM on duty ratio cannot be infinitely reduced because the voltage across the capacitor is in a discharging state during the PWM off period, and it is necessary to ensure that the charging voltage of the capacitor is greater than the discharging voltage within one PWM period. The frequency and the on-duty ratio of the PWM are matched with the impedance R of the driving loop_DRInternal resistance R of DC motor_mAnd a filter circuit capacitor C, and the like, and a specific PWM frequency and duty ratio design concept will be given according to a simplified circuit diagram of the motor driving system shown in fig. 3.

For the on-time t_onInternal:

for the off-time t_offInternal:

due to the equivalent resistance R of the driving circuit_DRMuch smaller than the internal resistance R of the motor_mWhile, at the same time, the inductance L of the motor winding_mIs relatively large and at start-up I_mStarting substantially from zero current. Therefore, in the PWM wave generation soft start stage, the capacitance C of the filter circuit can be approximately charged and discharged actually, and the equivalent resistance R of the drive circuit can be approximately_DRAs charging resistor, internal resistance R of DC motor_mIs a discharge resistor. Thus, equation (3.1) can be simplified to:

equation (3.2) can be simplified to:

for motors of a determined manufacturer type, R_m、L_mC, R can be obtained by actual test_DR、L_DRThe theoretical calculation can be carried out through the diameter and the length of the driving wire, and under the condition that the parameters are known, the parameter range of the proper PWM pulse can be easily determined through the formula (3.3) and the formula (3.4).

As shown in fig. 6, in the embodiment of the present invention, under the mode of initially setting the PWM pulse frequency and the duty ratio, the dichotomy is used to try to change the PWM pulse frequency continuously, and whether the driving circuit will report the overcurrent protection is tested, so as to obtain the PWM pulse frequency of the matching system quickly. The method specifically comprises the following steps: setting the PWM pulse as a fixed duty ratio, setting an initial frequency, then doubling the initial frequency and judging whether overcurrent protection can be triggered to quickly find f_xAnd f_yWherein f is_xFrequency value of not triggering over-current protection, f_yTo trigger the frequency value of the overcurrent protection, the initial frequency is then set to (f)_x+f_y) And/2, continuously judging whether overcurrent protection is triggered or not, and obtaining final f through multiple iterations_xAs a stationThe frequency of the PWM pulses.

As shown in fig. 7, in the embodiment of the present invention, the frequency of the PWM pulse can be obtained by performing loop regulation using the driving current peak feedback value and the driving peak current command value. Wherein, I_{pro_set}To drive the peak current command, I_{pro_set}Need to be less than the driving peak current threshold I_proAnd a certain margin is left, I_{DR_pk}For drive current peak feedback, G_i(s) is a loop regulator, typically a PI regulator. And in the soft start stage, peak current closed-loop control is adopted, PWM driving frequency is adjusted, the peak value of driving current is stabilized, and the motor can be started normally to work.

In summary, by using the method and system for controlling soft start of a dc motor of the present invention, the starting process of the motor is divided into a capacitor charging stage and a motor starting stage after the capacitor charging stage, in the capacitor charging stage, the waveform of the driving signal is a PWM pulse, in the motor starting stage, the waveform of the driving signal is a high level dc voltage, and the soft start of the motor can be realized without using a soft start resistor, so that the implementation manner is simple, additional devices and costs are not required to be added, the cost and volume can be effectively saved, and the product adaptability is strong; in addition, aiming at the characteristics of different motors, the dichotomy mode can be adopted for open-loop adjustment, parameters can be matched quickly, and the stability of driving peak current can be ensured and the soft start of the motor can be realized through a closed-loop adjustment mode.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.