April 20, 2010

Electrical braking theory, reason of DC injection

 Electrical braking is needed in many applications and used instead of mechanical braking. The advantage of electrical braking is virtually no wear and tear is experienced.

 Electrical braking may be seen in modern cars, traction motor control, train services, alternators and in automotive industries.

 Here I will discuss the basic principle, I will not elaborate in this post because I believe feeding everything in one pack will result in vomiting. So, for deeper understanding, read my blog time to time. Also, you may search my blog to find the later post. I will post them under the label "electrical braking". also, it is a good idea to subscribe via mail, if you want to get my articles in your inbox.

  We understand if we can dissipate motors' kinetic energy quickly, we can implement a braking. So, all we need is to devise a way to dissipate kinetic energy rapidly.

   The main theory of electrical braking is to use a DC (direct current) injection to provide magneto motive resistance to the running rotor. If a DC flux is provided to the rotor and rotor cuts through it, it eventually slows down because DC injection effectively produces a electrical (or more accurately, magnetic) resistance as described below.

   During braking it is obvious that we will remove AC supply from the stator. Rotor will be rotating due to its inertia. The larger the angular momentum, the larger time it takes to stop rotation. Now, after removing the AC supply from the stator, if we apply a DC voltage to the stator, a large DC current will be induced in the rotor. This induction happens because the rotor still rotates in a DC field. This large DC current will heat up the rotor coil(resistance of rotor coil, truly) and energy is dissipated in form of heat. So ,we see, applying a DC voltage to the stator makes a good method of braking. This method is used in dynamic braking. In regenerative braking, rotors kinetic energy is converted to electrical energy and fed back to main supply or other loads.

Here I present a circuit for DC injection.
Fig: DC injection

Here, D1 is a rectifier and C1 is a capacitor bank. When stator is disconnected from main supply, rectifier is supplied from mains and after capacitor we get a DC voltage. This is now supplied to the stator to create a DC flux.
   You may wonder, if current in stator is such a problem, won't it be a problem for AC too? The answer is, of course, no. Because inductance of rotor coil will limit current through it in AC. In this case, this limited current actually helps to rotate by creating Rotors' magnetic field.
      I have posted an article for Dynamic Braking. You can also get related post under the label electrical braking.

You may feel interest about the following:
1. Simple explanations about principle of induction machine
2. Energy saving lamp, curse or blessing !! Working principle reveals it.
3. Regenerative braking of electrical machine
4. Computing N-th Fibonacci number and its sum using Assembly languages,emu8086
5. Maximum and minimum number in an array, using Assembly
6. Slip in Induction Machine : The Hidden Power

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