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Braking resistor (pulse resistor)
Feb 19, 2018

Braking resistor (pulse resistor)


        The so-called "DC braking", generally refers to when the inverter output frequency is close to zero, the motor speed reduced to a certain value, the inverter to the induction motor stator winding into the DC, the formation of static magnetic field, this time in the motor can Consumption braking state, the rotating rotor cutting the static magnetic field generated braking torque, the motor stopped quickly. In the process of motor braking, because the output frequency of the inverter gradually decreases, the synchronous magnetic field speed in the stator winding is lower than the rotor speed, and the motor is in regenerative braking. At this time, the kinetic energy stored in the rotating system is converted into the form of electric energy heat loss In the asynchronous motor rotor circuit, in order to prevent the regenerative braking and the energy feedback during DC braking caused by the deceleration of the motor, the inverter and the motor are damaged, and a special braking unit / braking resistor Inverter inverter circuit generally uses 6 IGBT, each IGBT and are connected with a diode. When the motor is stopped, the inertia of the motor causes the energy to pass through a full-bridge circuit consisting of the six diodes, rectified into DC, and fed back to the grid. If you do not add braking unit, will make the DC part of the capacitor voltage increases, will burn out the inverter. Add the brake unit, the feedback energy will be consumed in the automatic resistance. Without brake unit, the motor will continue to run by inertia for a long time, coupled with the brake unit, according to the conservation of energy, the feedback energy is consumed, that is, the motor inertia energy is consumed, so the motor brake speed It is obviously accelerated. Faster stop is more block of energy consumption sake. Energy conservation law! Kinetic energy consumption will stop moving. Working process: synchronous speed is lower than the actual speed of the motor when the motor is decelerating, the motor is in the state of generating power, the mechanical energy is converted into electric energy, feedbacked to the DC bus of the inverter through the freewheeling diode inside the IGBT, the brake unit works when the DC bus voltage is higher than a certain value Brake resistance power is converted to heat consumption. Actually drag the load magnetic field to stop the movement, and the motor starting process is a reason, but the starting magnetic field speed faster than the actual speed, stop the process of magnetic field speed slower than the actual speed. When the motor is powered off, only the mechanical energy is lost. At this moment, a series of resistors are connected in series to generate heat consumption, which converts the mechanical energy into heat energy to stop the energy consumption faster. Braking principle: After the motor cuts off the AC power, the rotor continues to rotate due to inertia, Immediately in the two-phase stator windings into the DC, the stator that is to produce a static magnetic field. The guide bar in the rotor cuts off this stationary magnetic field to produce induced current, which is subjected to the electromagnetic force in the static magnetic field. The torque generated by this force is in the opposite direction of rotor inertia rotation, called the braking torque, which forces the rotor speed to drop. When the rotor speed drops to 0, the rotor no longer cuts the magnetic field, the motor stops and the brake is over. This method is to use the energy of rotor rotation cutting magnetic flux generated braking torque, in essence, the rotor kinetic energy consumed in the rotor circuit resistance, it is called energy braking. The law of conservation of mechanical energy. Energy can not disappear, mechanical energy can be converted to other energy. When not adding the resistance and stator DC, the motor stops only after stopping by inertia, but the inertia of the rotor is very large, the normal motor without braking motor will turn many more laps, because its energy can not be consumed, but Consumption in the rotor resistance, in fact, only produce some weak heat loss. In addition to say some plus braking situation, coupled with braking, to see the above principle, including energy consumption brake both ends of the stator into the DC (in fact, plus DC itself is a brake), the rotor is kinetic energy, the stator When adding DC, itself produces an opposite torque, which is the motor brake, braking energy is definitely converted. The rotor is the induction current, without external resistance, in fact, the kinetic energy will be converted into copper consumption and loss of iron loss, if the additional resistance, the rotor circuit resistance is large, the motor power is fixed when the power off, I converted into heat loss square RT, R increases, the time T decreases, so the kinetic energy becomes less time, braking fast.