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Saturday, 12 December 2015

Power Conditioning Unit: A key element of Solar PV System

Power Conditioning Unit (PCU) is a very vital piece of equipment in any solar PV system and is also called solar power conditioning unit. The main components of any solar PV system are PV panels, charge controller, battery bank, inverters, cables, switches and the protection.

"Power Conditioning Unit (PCU) is a combined unit consisting of a solar charge controller, an inverter and a grid charger integrated in a single unit." 

Role of Power Conditioning Unit (PCU)

Power Conditioning Unit (PCU) is usually a DSP based PWM technology using IGBT and MOSFET. It facilitates the charging of battery bank through either solar PV panels or the grid/DG system. All the solar PCU has the ability to continuously monitor the state of battery, solar power output and the load. They not only monitors the state of affairs but even displays vital parameters such as PV voltage and current, load percentage, overload percentage, charging current etc.  

The solar energy is intermittent in nature and therefore a balance has to be made between the solar generation and the demand. When excess energy is generated the extra kWh is to be either fed into the grid, which is possible only in case of grid tied system, or to be stored into the battery bank. Due to over usage of power, if the battery voltage goes below a pre-defined level, the PCU will automatically transfer the load to the utility grid and simultaneously charges the batteries through the grid supply. 

Once the batteries attain a given voltage, the PCU cuts off the grid power to the system and returns back the load on to the solar system. The rest of the battery charging is now done by the solar PV system. In this way the PCU gives priority to the solar power over the grid, and uses the grid power only when the solar power and the battery power of required level is not available.

Fig.1: Back view of an off-grid Solar PCU

Significant advantages of PCU

The significant advantages of PCU are pure sine wave output with low Total Harmonic Distortion (a measure of power quality), higher efficiency, data logging monitoring etc. The commercially available PCU have efficiency more than 85% and nearly 5% Total Harmonic Distortion (THD) for linear loads. These units come with the deep discharge protection and thus ensure the health of batteries. PCUs have nearly 300% overload facility for a few milliseconds which helps during the starting of heavy loads. Thus these units have the inbuilt overload and short-circuit protection and therefore no need to worry about overloads and short circuits. Remote monitoring of the unit can be done with the help of RS232, Ethernet, GSM and GPRS.

Ratings of commercially available single phase PCU

The usual ratings of commercially available single phase off-grid PCU in India are 600 VA/24 V, 1kVA/24 V, 2kVA or 3kVA/48 V, 3/4/ 5/6 kVA/96 V, 7.5 kVA/120 V