Converters
Objectives
While braking, electric vehicles are able to recapture a portion of the energy that is normally lost to friction.
This is possible because electric motors can function as electric generators as they slow down.
But those generators are creating an alternating current which is not compatible with the vehicles batteries which function using direct current.
In order to resolve this problem a converter is used. At its most basic, a converter is a device used to condition an electric current.
In this lesson, we will look at how a converter works on a battery electric vehicle to convert alternating current to direct current.
Converters
There two different basic categories of electrical devices that are each known as a converter.
There are the DC to DC converters, which use transformers or regulators, to either step up, or step down, voltage.
Then there are the AC to DC converters, which will be the focus for our vehicles.
AC to DC converters, use diodes to set the direction of current flow across the load.
The key is to remove the polarity switching that is a fundamental aspect of alternating current. This is what a rectifier does.
By passing the AC current through a single diode, only half of the AC wave is able to flow. This gives us a sort of stuttering DC-like current.
This is known as half wave rectification.
It can be useful for some applications, such as DC circuits that need to be triggered at regular intervals, but most electronics require a steady current.
We're wasting half our current here!
This is where full bridge rectification comes in.
By passing the alternating current through this diamond arrangement of diodes, both the positive and negative halves of the AC waveform will output as a single polarity.
The layout of the diodes ensures that the current flow is always going across the load in the same direction.
The output becomes a pulsing current with only a single polarity.
Adding a capacitor to the output side of the circuit smooths out these pulses.
But recharging a battery requires a very steady DC voltage supply. Even these relatively small fluctuations are an issue.
This calls for a voltage regulator!
Voltage regulators are integrated circuits which take in an input voltage of a given range and, by limiting the current, they ensure a constant voltage output.
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