Basics of Kinetic Energy Recovery System (KERS)

In this post, I’m going to briefly explain Kinetic Energy Recovery System also know as KERS. The system is used in many areas. As an example of these; Racing Cars (Formula 1), commercial vehicles (Train), construction machines (Digger), automotive (Car) … But before start explaining KERS we need to have basic understanding on Kinetic Energy and Conservation of Energy concepts.

I am going to start explaining with kinetic energy concept. Kinetic energy can be explained as the energy of an object in motion. Kinetic energy of a rigid object in formula form:

where m is the mass and v is the speed of the rigid body. As an example if you driving a car on straight road, with a mass of 1000 kg and constant speed of 20 m/s. The kinetic energy of the car can be calculated as;

So your car has a kinetic energy of 200,000 Joule. What does it mean ?. If you stop pressing the gas pedal and don’t apply brakes, car will eventually stopped by friction factors. But this will take time and length of time heavily depended to kinetic energy of the car. We have learned the concept of kinetic energy, now let’s move on to the conservation of energy concept.

Within the same control volume, the amount of energy remains constant and energy can neither be created nor destroyed. Energy can be converted from one form to another but the total energy within our control volume stay same. As an example; if a moving car use brakes in order to stop, kinetic energy of car will be converted to heat energy in the brakes (remember, brakes work by friction and friction causes heat).

Now that we understand what kinetic energy and conservation of energy is we can move on to our main subject. KERS’ main goal is to convert kinetic energy into a different kind of energy that can be used or stored for later use. Remember braking car example in that case kinetic energy is converted to heat energy but if we put KERS in that car we can convert kinetic energy to electrical energy and store it for later use. Maybe the best example for this is the Formula 1 cars. In a normal Formula 1 race, cars brake almost the entire duration of the race in order to make low-mid speed turns. By braking, the kinetic energy of the car is converted to electrical energy and stored either in supercapacitors or in battery. After that utilized by driver to gain tremendous amount acceleration by electric motor.

How does it work ?

KERS consists of several main components (battery and motor). Significant two main components are MGU and PCU.

MGU unit converts kinetic energy to electrical energy as it can be seened on the top (Image credit Magnetti Marelli). We can think of it as a electric motor but generates electricity instead of using electricity (same principle as wind turbines).

Second one is the PCU (Power Control Unit) as can be seen on the top (Image credit DENSO). This unit consists of three sub components a invertor to convert AC to DC, a boost converter to increase voltage and a DC to DC convertor for low voltage.

Here is the simple visual explanation for KERS (Image credit DensityDesign Research Lab);

In conclusion KERS is a concept that can be used in very different areas where kinetic or mechanic potential energy needs to be utilized some kind of useful energy.