1. Charge controllers
Charge controllers are used in PV systems to control the charge and discharge process of batteries. Two main types of charge controllers are available in the market. One is the PWM-type and second is the MPPT-type.
(a) The PWM-type charge controller
The PWM-type employs a shunt or series switching topology to control the flow of current between the source and battery while the voltage is maintained at a constant level.
(b) The MPPT charge controller
The MPPT-type charge controller is a PWM controller with maximum power point tracking capability. The latter is achieved through impedance matching of the load through PWM such that maximum current is fed to the load at all times. In such a scenario, the voltage supplied by the controller is not constant.
Mode of operation: Charge controllers have a series float charger which is a trickle charger with automatic on and off switch and this is why this charger type is mostly used in renewable energy systems. A float charger can have three stages:
The bulk stage is the stage during the charging process during which high current is allowed to flow from the source to the battery. Under the PWM mechanism with HIGH time representing the condition of a closed switch allows current flow is long enough to maintain a constant voltage increase.
The absorption stage is the stage during which the battery voltage reaches maximum level and current starts decreasing to maintain constant voltage. This is achieved by modulating ONs and OFFs of the switch; shorter time for OFFs.
The float stage is the stage during which current is pulsed to maintain a charged condition in the battery at a constant voltage. An additional stage known as the equalization stage may be also present in some charge controllers designed to be used in systems where more than one battery are used. Equalisation is the process whereby the battery voltage is overcharged at roughly one volt above the float voltage level to equalize charge in all cells in the battery bank.
Inverters convert dc voltage to an ac voltage. For PV systems, there are several inverter choices based on panel configuration and system size. String inverters are used in systems where individual solar panels are connected in series. Central inverters are used when the PV array consists of several strings of series-connected panels while micro-inverters are equipped with all modules in an array to optimize power output. Central and string-type inverters are the most commonly used inverters by PV installers/companies.
|Power rating||<100 kW||5 kW – 2 MW||<0.5 kW|
|Connection type||Single/Three Phase||Single/Three Phase||Single Phase|