An Overview of DSP based smart Battery Charger
DSP Batery Charger

An Overview of DSP based smart Battery Charger

Surya Kumar (SK) Singh , Chief Scientist, eAge Technologies India Pvt Ltd www.eageit.com

A Battery is a device used to store and deliver the power to the load when needed. In the modern world with portable devices and electrical vehicles becoming the most needed items in our daily life, the battery charging mechanism got a complete new innovation for fast and full charging... Conventionally, a battery charger consists of a thyristor, also known as silicon controlled rectifier (SCR) suitable for high power output in the battery charging mechanism. As the output of the DC-DC converter varies considerably, in battery charging  applications, conventional  converters cannot be optimized for power conversion.

 

Battery chargers require a change to the battery voltage according to the stable battery current and then, chargers are required to change the battery current according to the stable battery voltage. Traditional battery chargers  use analog controllers. These  controllers can adjust  the charge  voltage  and provide  current control. But the compensation parameters are  generated to resistor and  capacitors in the analog controller. For digital control, the compensation parameters are implemented digitally and they can be mitigated.

 

Of late , a very fast Digital  Signal Processor (DSP) has become a preferred device to take feedback on the charging status of the battery in real-time and adaptively provide constant current and constant voltage as per need. The battery current has to stay at the constant value while the battery voltage increases, and then, the battery current has to decrease while the battery voltage stays at the constant value in the battery chargers. The  schematic  circuit diagram  of battery  chargers that  uses Silicon Control  rectifier (SCR) is shown in the figure below.


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 Common issues for long battery charge time include-

a) input current limit too low,

b) input resistance from source to charge  being high causing input voltage to drop.,

c) output resistance from charger to battery being too high causing the charge to enter voltage regulation mode too early,

 

As the battery charging process is nonlinear, different methods have been developed to effectively control battery charging. Control methods commonly used in battery charging are: constant current (CC), constant voltage (CV), two-step charging (i.e., CC–CV), pulse charging (PC), reflex charging or negative pulse charging (NPC), trickle charge or taper-current (TC), and float charge (FC).

 

Because the process of battery charging and discharging is complex, it requires the design of a robust supervisory control over the classic controller and this is where DSP based algorithms and hardware is used for the effective supervisory control of the battery charging system. A DSP based battery charger block diagram  is shown below.


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