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Solar Array Simulation Enables Inverter Manfacturers to Meet Test Challenges

Solar Array Simulation Enables Inverter Manfacturers to Meet Test Challenges

As a result of improvements in solar array technology and initiatives for implementing green technologies, solar systems are becoming an increasingly cost‐effective solution for residential and commercial applications.

The onus is now on solar inverter manufacturers to keep up with the market’s rapidly accelerating requirements, especially the development in solar array technology and evolving performance parameters.

Historically, inverter manufactures have used the actual solar arrays when testing their products. This method seems logical but it is proving to be non-optimal. The reason is that when applied in the real world, solar arrays have to operate in an uncontrolled, often unpredictable environment. Their output is dependent on a range of variables including the intensity of the sunlight (full sun vs. cloudy conditions), ambient temperature, external shading effects (from tree branches or chimneys), bird droppings, dust and many other factors.

 

 




To ensure that an inverter design will transfer the maximum amount of power from a solar array to the grid, that is to say that it’s operating at or near the Maximum Power Point (MPP), it must be tested under a wide variety of conditions, just like it would encounter in a natural environment.

However, it’s not only important to not only create a wide variety of input power conditions, but these conditions must also be repeatable for design and production testing. This is virtually impossible to achieve using solar arrays.

To properly test photovoltaic (PV) inverters (both in development as well and production) you need a power source, such as the Elgar TerraSAS, that can reliably and repeatedly simulate actual solar array performance. TerraSAS uses the National Renewable Energy Laboratory’s (NREL) Solar Advisor Model (SAM) database, which includes key parameters such as Voc, Isc, Vmpp at 24C and standard 1000 W/m2 isolation, to simulate hundreds of commercially available PV products.

The SAM provides powerful tools to help designers predict system performance for virtually any fill factor or solar material. As a result, you can use the TerraSAS solar array simulator to perform realistic, dynamic,
interactive tests of your PV inverter.
 





Realistic Simulation

Whatever solar array simulator you use, the simulation must be as realistic as possible. For example, many PV inverters generate AC ripple on the DC connected to the photovoltaic array. For single‐phase inverters, the frequency of this ripple is twice the line frequency (100Hz). An increasing number of inverters (and virtually all micro‐inverters) accurately measure amplitude and phase of the ripple voltage and current to quickly track the MPP of the array.

This approach allows the inverter to track the MPP at a much higher speed when compared to conventional dithering techniques (also called perturb and observe). Faster tracking of the MPP results in a much higher overall efficiency in cloudy conditions, where the irradiance is constantly changing. It is likely that all solar inverters will use this approach in the near future, since end-users are very sensitive to the overall efficiency of their solar energy installations.

The simulator’s power supplies must not suppress this ripple as a function of their regulation loop. To perform the most effective test, the solar array simulator must be capable of reproducing the voltage / current behaviour of a solar array even in the presence of this ripple.

This is just one of the parameters that you must consider when selecting a solar array simulator. For more information on solar array simulators and what to look for when choosing them, contact Fuseco, your trusted partner in programmable power solutions.
 

More about the Elgar TerraSAS
 

The TerraSAS consists of programmable DC power supplies, a rack mounted controller, keyboard and LCD display with control software and GUI interface, output isolation, polarity reversing relays and a unique PV simulation engine that controls the power supply. This combination of hardware allows the TerraSAS to simulate most test protocols or combination of events that a solar installation will be subjected to. Power supplies are available in 1-15KW increments to simulate arrays up to 1MW.

 

Features:

  • Simulate dynamic irradiance & temperature across a variety of weather conditions              
  • Ramp voltage, temperature or irradiance levels over programmed intervals
  • Test for inverter Maximum Power Point Tracking (MPPT)
  • Provide programmable I-V curves for PV Inverter testing
  • Simulate different types of solar cell materials
  • Multi-Channel, up to 1MW


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