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Photovoltaic Array Simulator Simplifies Evaluation of Solar-Cell Interface Circuit, Algorithms, Performance

09 September 2015

Extracting the maximum power from a photovoltaic array is a challenging task. To extract the output from the bank of solar cells with maximum A photovoltaic array's interface circuitry must be implemented with custom-tailored MPPT algorithms to ensure maximum efficiency in developing output power regardless of operating point.A photovoltaic array's interface circuitry must be implemented with custom-tailored MPPT algorithms to ensure maximum efficiency in developing output power regardless of operating point.efficiency regardless of impinging light intensity, the interface circuitry and array charger/controller must implement an algorithm called maximum power-point tracking (MPPT), which must be carefully tuned to the specific array and its current-voltage (I-V) characteristics.

This difficulty highlights the design engineer's problem of how to test the circuitry and controller under a variety of conditions. It is not practical to use an actual solar array, for several reasons: obviously, the Sun may not be available, consistent, or repeatable; the actual array may be the size of a rooftop or larger; and these arrays often involve high voltage, current and power levels, with many associated safety issues. Improvised solutions are possible, but these take time to construct and usually produce sub-standard, questionable results.

To address the problem, Keysight Technologies (formerly Agilent) has introduced a pair of Photovoltaic Array Simulators—rack-mountable boxes that appear to the electronic circuitry like an actual solar array—and can be programmed to simulate an array of sizes and types, and also provide key data on performance.

The N8937APV (208-VAC input) and N8957APV (400-VAC input) array simulators are autoranging, single-output, programmable DC power sources that can quickly simulate the cell's I-V curve characteristics under different environmental conditions (temperature, irradiance, age, cell technology and more). This enables engineers to quickly and comprehensively test their electronics and algorithms and designers to verify the ability of the inverter to produce grid-level power from low-to-high voltage extremes.

Keysight's photovoltaic array simulators (208-VAC input N8937APV and 400-VAC input N8957AP) are user-programmable DC power sources that simulate the I-V curve characteristics of a photovoltaic array under a variety of temperature, irradiance, age, cell technology and other performance-related factors. Source: Keysight TechnologiesKeysight's photovoltaic array simulators (208-VAC input N8937APV and 400-VAC input N8957AP) are user-programmable DC power sources that simulate the I-V curve characteristics of a photovoltaic array under a variety of temperature, irradiance, age, cell technology and other performance-related factors. Source: Keysight TechnologiesThe instruments provide stable output power plus built-in voltage and current measurements from 500 to 1,500V and 10 to 30A. Despite their high output voltage, they offer 1000 VDC isolation for safety. For simulating larger arrays than a single N8937/57APV can support, multiple units can be connected in parallel for up to 90 kW of power, commensurate with the requirements of interface circuitry of roof-top and larger arrays. This parallel configuration creates looks like one big unit, as the built-in master/slave control enables single-point control with no need to program each simulator individually.

A full range of connectivity options is also included, with GPIB (ancient yet still in widespread legacy use), Ethernet/LAN, USB 2.0, and even analog interfaces so users can select the interface that is compatible with the rest of their test station. There is also a built-in Web server for full remote access, including set up, monitoring and control of the instrument via a stan­dard browser. This is necessary since the size of the array charger/controllers under test often mandates their physical placement outside or away from the test lab.

The array simulator instruments are closely related to Keysight's battery simulators, which address similar problems that occur when testing chargers/controllers for rechargeable batteries ranging from small (a few watts) to the large battery configurations used in building-backup systems, and even EV/HEV power subsystems.

Both the 208-VAC N8937APV and the 400-VAC N8957APV are prices at $15,660 and are available immediately.



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