Wednesday, 28 November 2012

Load issues (starting current & harmonics ) with PV systems

Start up current:
Generally high powered equipments consume very high current more than two times its rated value during start. This will greatly affect the PV system when connect to such loads. Usually refrigerators, heaters, water pump and air conditioners consume such high current during start. Given below is the starting current of a refrigerator versus time. It is clearly visible that the current gets stabilized only after t=4.5.

Similarly, when a 2000W water pump is switched on its instantaneous power during start up increase more than two time its rated power i.e. 5000W. This is clearly shown in the image below, the top channel is the current and below is the voltage.






Solution:
Soft starter: The loads affected should have a starter, which could “soften” the start-up.
Use permanent magnets in pumping systems to assist start-up.

Harmonic distortion
Connecting non lineal loads to the inverter cause voltage deformation. These non linear loads cause over heating of appliance which may result in burning insulation material and also leads to short lifetime of equipments.

When a non linear load is connected to the inverter the voltage deformation happens due to the irregular current consumption by the load. This is clearly shown in the image below,
Solution:
Use high switching frequency inverter or using harmonic filters.

Reference: PROBLEMS RELATED TO APPLIANCES IN AUTONOMOUS PV APPLICATIONS. Task 3 experts of the IEA. Website: www.task3.pvps.iea.org.

2 comments:

  1. Excellent blog..this will increase as people begin to understand the benefits offered by solar energy.... solar panels

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  2. Dear Mr.Giridar,

    this is santhosh... i work as an embedded engineer with a bangalore based company, i wish to know the worst case duration for fridge load inrush current and the worst case magnitude for the same. I need this information to rate and impose limits on our Inverter, Kindly share any info u have.

    thanks

    ReplyDelete