literature survey of 3 stage solar mppt charge controller

A charge regulator, a charge regulator, or a battery regulator limit the speed at which electric current is added or withdrawn from the electric batteries. It prevents overcharging and can protect against overvoltage, which can reduce battery performance or service life and can pose a safety risk. It can also prevent total drainage ("deep discharge") from a battery, or perform controlled discharges, depending on battery technology, to protect battery life. The terms "charge controller" or "charge controller" may refer to an autonomous device, or to control the integrated circuits within a battery pack, a battery operated device or a battery charger.

The main function of a load regulator or regulator is to protect your battery from overload and block a reverse current. If a non-self-regulating solar array is connected to lead acid batteries without overload protection, the life of your batteries will be compromised.
The simple controllers contain a transistor that deflects the PV load circuit, ending the load at a pre-set high voltage, and once a preconfigured connection is reached, opens the shunt, allowing the load to resume.
Not always, but generally. Generally, there is no need for a load controller with small maintenance, or drip load panels, such as panels from 1 to 5 watts. A general rule of thumb is that if the panel emits approximately 2 watts or less for every 50 amp-hours of battery life, then you do not need one.

For example, a standard flooded golf car battery is around 210 amp-hours. So to keep a couple of sets of them (12 volts) just for maintenance or storage, you would want a panel that is about 4.2 watts. The popular 5 watt panels are close enough and will not need a controller. If you maintain AGM deep cycle batteries, such as the Concorde Sun Xtender, you can use a smaller 2 to 2 watt panel.