CN118264159A - H-bridge driving-based direct current motor rapid braking method - Google Patents

Abstract

The invention relates to the field of motor driving, in particular to a direct current motor rapid braking method based on H bridge driving, which can rapidly realize braking without a complex system and has low cost, and comprises a load motor and an H bridge with a tail current sensing resistor, and is characterized by comprising a digital control module, wherein the digital control module provides a preset current value and the tail current output by the H bridge, and outputs a comparison result after being compared by an analog comparator, and the digital control module processes according to the comparison result and outputs a control signal to the H bridge; in the braking process, the braking current in attenuation is not required to be detected, only the current at the tail current sensing resistor in the driving stage is detected, and the half-bridge current detection device is omitted.

Description

H-bridge driving-based direct current motor rapid braking method

Technical Field

The invention relates to the field of motor driving, in particular to a direct current motor rapid braking method based on H-bridge driving.

Background

The DC motor has wide application and excellent start-stop and speed regulation performance. When the motor needs to be stopped quickly, common quick braking methods include mechanical braking, resistance braking and inertial damping braking; the mechanical brake is realized by utilizing a brake, the resistor is connected in series with two ends of the motor, when the motor is required to be braked, the resistor is connected into a circuit through a switch, so that the motor is rapidly decelerated and stopped, the inertial damping brake is used for suddenly disconnecting the power supply, and the motor is rapidly stopped by utilizing the inertia of the motor. The first two methods can realize quick braking, but require additional hardware support, while the third method can realize braking, but the braking process has longer time than the first two methods. In addition, there is also a commonly used electronic braking method, that is, braking current generated by braking with back electromotive force is used to generate braking force, when a braking instruction is received, the motor is disconnected from the power voltage, two upper pipes or two lower pipes of the H bridge are conducted, and because larger back electromotive force is applied to the coil winding before braking, larger braking current is generated at the moment, and larger braking current generates larger braking force, so that the motor is stopped rapidly. However, this back emf braking method is not current controllable without detecting the braking current, which requires a detection unit such as a current mirror to monitor each half-bridge current, which is complex and costly.

Disclosure of Invention

In order to solve the problems that a brake current detection system is complex and the cost is high in the H-bridge driving process of the existing direct current motor, the invention provides a direct current motor rapid braking method based on H-bridge driving, which can rapidly realize braking, does not need a complex system and is low in cost.

The technical scheme is as follows: the quick braking method of the direct current motor based on the H bridge driving comprises a load motor and the H bridge with a tail current induction resistor, and is characterized by comprising a digital control module, wherein the digital control module provides a comparison result of a preset current value and the tail current output by the H bridge after being compared by an analog comparator, and the digital control module processes the comparison result and outputs a control signal to the H bridge;

When a system sends a braking instruction, the upper two or the lower two MOS tubes of the H bridge are conducted, current decays under the action of counter electromotive force and increases towards the negative direction, a first period of braking time is entered, the MOS tubes which normally work at two opposite angles originally after the first period of braking time is ended are conducted to enter a driving state, the current rises under the action of a power supply and is compared with a preset current value until the preset current value is reached, an analog comparator feeds back to a digital control module, the upper two or the lower two MOS tubes of the H bridge are controlled to be conducted to enable the current to enter an attenuation stage, a second period of braking time is entered, the MOS tubes which normally work at two opposite angles originally after the second period of braking time are conducted to enter the driving state again, and the driving and attenuation processes are repeated until the rotating speed of a motor is zero.

After the invention is adopted, in the braking process, the braking current in attenuation is not required to be detected, only the current at the tail current sensing resistor in the driving stage is required to be detected, a half-bridge current detection device is omitted, a complex system is not required, the cost is low, and the preset current value are controlled

Drawings

FIG. 1 is a schematic diagram of a system of the present invention;

FIG. 2 is a schematic diagram of the current variation during braking according to the present invention.

Detailed Description

Referring to fig. 1 and 2, a method for quickly braking a dc motor based on H-bridge driving includes a load motor, an H-bridge 110 with a tail current sensing resistor 111, and a digital control module 100, wherein the digital control module 100 provides a comparison result obtained by comparing a preset current value with a tail current output by the H-bridge through an analog comparator 101, the digital control module 101 processes the comparison result and outputs a control signal to the H-bridge 110, and the preset current value given by the digital control module 101 is sent to the analog comparator 101 after passing through the digital-analog converter 102. It should be noted that the digital signal provided to the digital-to-analog converter 102 by the digital control section 100 will vary with the internal state thereof, so that the analog comparator 101 can perform comparison of various level values.

When the motor is just started, the motor rotating speed and the counter electromotive force are 0, the coil current rises rapidly under the action of the power supply voltage, and reaches Itrip after t1 time, so that the inductance L=U _dc·t₁/I_trip,U_dc is the bus voltage; the motor can be regarded as a steady state within a short period of time of normal operation, and the voltage at two ends of the motor is used for overcoming counter electromotive force except overcoming the voltage drop of the coil resistor R, and the expression is as follows: u _dc ·duty=ir+kω, where I is the coil average current, U _dc is the bus voltage, k is the back emf constant, ω is the motor speed; a PWM control signal from an external controller such as an MCU enters the digital control module 100, the Duty ratio of the input signal is duty_in, the digital control module 100 rectifies according to Itrip current limiting requirements, so that the motor current does not exceed Itrip, and the rectified digital control module 100 outputs a Duty ratio of duty_out; PWM decay phase current satisfactionWherein t _off is PWM low-level turn-off time, and V _b is the current ripple obtained by substituting the inductance into the normal working state

When the system sends out a braking instruction, the upper two or the lower two MOS tubes of the H bridge are conducted, at the moment, the current decays under the action of counter electromotive force and increases towards the negative direction, as shown in fig. 2, the first period of braking time is entered, the two opposite angle MOS tubes which normally work originally after the first period of braking time is ended are conducted to enter a driving state, the current rises under the action of a power supply and is compared with a preset current value until reaching the preset current value, an analog comparator feeds back to a digital control module, the upper two or the lower two MOS tubes of the H bridge are controlled to be conducted to enable the current to enter an attenuation stage, the second period of braking time is entered, the conduction of the two opposite angle MOS tubes which normally work originally after the second period of braking time is entered again to enter the driving state, and the driving and attenuation processes are repeated until the motor rotation speed is zero.

When the system sends out a braking instruction, the upper two or the lower two MOS tubes of the H bridge are conducted, the coil current is attenuated under the action of counter electromotive force and increases towards the negative direction, and the braking time is prolongedWherein delta I _brake is brake current ripple, I _trip is a current value obtained after t ₁ time passes by coil current after the motor is started; after the braking time t _dc is over, the two opposite-angle MOS tubes which normally work are conducted to enter a driving state, the coil current rises under the action of a power supply,When the current rises to the digital signal Itrip provided by the digital control module 100 to the digital-to-analog converter 102, the comparator 101 turns over and feeds back to the digital control module 100, the system opens two MOS tubes above or below the H bridge, the current enters the attenuation stage, and the rotation speed of the attenuation stage is reduced relative to the rotation speed of the previous driving stage, and the average current is basically unchanged, so that the braking time t' _dc required by the braking current change DeltaI _brake satisfies the following conditionsIn conclusion, the method comprises the steps of,When the inequality is equal, t' _dc can be calculated according to the timing t _on of the driving phase timer, and the value is conservative, so that the current change cannot exceed delta I _brake to prevent the system from being damaged due to overlarge brake current; obviously, as the rotation speed during the braking process decreases, t _on gradually decreases, and t' _dc gradually increases, and the whole braking process is a feedback type convergence process. In summary, the braking time is determined by preset Itrip and Δi _brake, and the smaller the Itrip is, the larger the Δi _brake is, the larger the braking current is, and the faster the braking is.

Claims (1)

1. The quick braking method of the direct current motor based on the H bridge driving comprises a load motor and the H bridge with a tail current induction resistor, and is characterized by comprising a digital control module, wherein the digital control module provides a comparison result of a preset current value and the tail current output by the H bridge after being compared by an analog comparator, and the digital control module processes the comparison result and outputs a control signal to the H bridge;

When a system sends a braking instruction, the upper two or the lower two MOS tubes of the H bridge are conducted, current decays under the action of counter electromotive force and increases towards the negative direction, a first period of braking time is entered, the MOS tubes which normally work at two opposite angles originally after the first period of braking time is ended are conducted to enter a driving state, the current rises under the action of a power supply and is compared with a preset current value until the preset current value is reached, an analog comparator feeds back to a digital control module, the upper two or the lower two MOS tubes of the H bridge are controlled to be conducted to enable the current to enter an attenuation stage, a second period of braking time is entered, the MOS tubes which normally work at two opposite angles originally after the second period of braking time are conducted to enter the driving state again, and the driving and attenuation processes are repeated until the rotating speed of a motor is zero.