The electric braking of a DC motor is of three types, (i) Rheostatic or dynamic braking, (ii) Plugging or reverse current braking and (iii) Regenerative beaking. (ii) Plugging or Reverse current braking: In this method, armature connections are reversed and hence motor tends to run in opposite direction.
As the coils are energized, the magnetic field they produce between them induces an electric current in the rotor. This current produces its own magnetic field that tries to oppose the thing that caused it (the magnetic field from the outer coils). The interaction between the two fields causes the rotor to turn.
DC injection braking can be used as the primary braking system or as a part of a multi-brake system for a single motor or a piece of machinery. In emergency situations, DC current braking systems stops the motor much faster and more efficiently than friction braking systems.
A variable frequency drive (VFD) is a type of motor controller that drives an electric motor by varying the frequency and voltage of its power supply.
The low network impedance of an AC network means that a small DC voltage from the grid connected inverters creates a large DC current injection. This DC current is not a fault current, but is caused by asymmetry between the positive and negative half-wave of the current fed into the grid.
Motor brakes generally use friction between mating surfaces to stop or hold a load. The same brake can be used for both of these functions, but if stopping time is important, the brake must have sufficient torque to stop within the allotted time. Actuation is either through electrical, mechanical, or pneumatic methods.
Braking a small, high-speed DC motor
- You can briefly reverse power them.
- A DC motor can be stopped by shorting the motor terminals.
- I have performed the experiment above with the L293D controller, and the results are basically the same as shorting the motor terminals with a piece of wire.
A DC motor consists of an stator, an armature, a rotor and a commutator with brushes. Opposite polarity between the two magnetic fields inside the motor cause it to turn. DC motors are the simplest type of motor and are used in household appliances, such as electric razors, and in electric windows in cars.
In practical DC machines, armature resistance is basically very low, generally about 0.5 Ω. Therefore, a large current flows through the armature during starting.
Arduino Motor Control Setup
- Connect 5V and ground of the IC to 5V and ground of Arduino.
- Connect the motor to pins 2 and 3 of the IC.
- Connect IN1 of the IC to pin 8 of Arduino.
- Connect IN2 of the IC to pin 9 of Arduino.
- Connect EN1 of IC to pin 2 of Arduino.
- Connect SENS A pin of IC to the ground.
In series motor back emf cannot exceed the supply voltage. So regenerative braking is not possible.
Explanation: Plugging is the best braking method among all braking techniques. In plugging the value of the armature current reverses and the mechanical energy is extracted. A very high braking torque is produced in case of plugging.
Dynamic brakes use the kinetic energy of a train's turning wheels to create electrical energy, which causes the train to decelerate. The dynamic brake grids consume electricity that make the traction motor less able to turn and thus slow down.
DC cumulative compound motor
Another drawback to plugging is that it can induce high mechanical shock loads on the motor and connected equipment, due to the abrupt stop that it causes. Plugging is also a very inefficient method of stopping and, therefore, generates significant heat.
Thus, the speed of a DC motor can control in three ways: By varying the flux, and by varying the current through field winding. By varying the armature voltage, and the armature resistance. Through the supply voltage.
â€But if you want more braking plus energy, use a generator G or DC motor and, by creating a resistor between the two ends of the coil, you can control the braking force and use its energy to generate and store electricity. Switched Reluctance Motor is the best in terms of regenerative braking.
There are three types of electric braking, all of which are applicable to the usual types of electric motors, viz. plugging (or counter-current braking), dynamic (or rheostatic) braking and regenerative braking.
Dynamic braking is the use of the electric motors as generators when slowing the machine speed. It is termed rheostatic if the generated electrical power is dissipated as heat in brake grid resistors, and regenerative if the power is returned to the supply line.
DC machines are also used in applications where high starting torque and accurate speed control over a wide range are important. Major applications for DC motors are: elevators, steel mills, rolling mills, locomotives, and excavators. Like other rotating machines, DC motors result from the interaction of two magnets.
Also DC is typically preferred for easier RPM control (like in trains, tramcars, etc) but this is not a problem for elevators - they typically use two-speed three-phase AC motors and speeds are changed by switching the number of poles.
In case of DC Series motor, as the speed of Motor increases, the armature current and hence the field flux will decrease and therefore Back emf E can never be greater than the supply voltage V. Therefore, Regenerative Braking is not possible in DC Series Motor.
Dc motor (Ma) and induction motor (Mc) are currently manufactured and used in 105 N tram drive, their parameters are available. Dc motor (Mb), brushless motor (Me) and slip-ring motor (Md) pa- rameters have been determined by analysis.
Due to the simplicity of the AC induction motor's single moving part, the Tesla Roadster does not experience the engine compression braking of a traditional internal combustion engine (ICE). When the torque serves to slow the vehicle then energy is returned to the battery and presto - we have regenerative braking!
Efficiency of the regenerative braking process varies across many vehicles, motors, batteries and controllers, but is often somewhere in the neighborhood of 60-70% efficient. This simply means that 70% of the kinetic energy lost during the act of braking can be turned back into acceleration later.
The advantages of the regenerative system are the reduced energy consumption and the reduced wear of brake shoes and wheel tyres, and the consequent lowering of maintenance costs. The disadvantages are that the motors are larger and more costly.
