Auto-ranging supplies provide flexible power to test residential inverters

One of the most crucial components of a solar power system is the solar inverter. Solar inverters generate AC power from the DC energy output by solar arrays. A single channel DC/AC inverter may connect to multiple solar panels, all connected in parallel. The output of this solar array may range from 100 VDC to 600 VDC.

Inverters designed for residential applications take this DC input and typically produce 3 – 12 kW of single-phase, two-phase, or three-phase AC power connected to the power grid. These inverters use a technique called maximum power point tracking, or MPPT, to extract the maximum power from the solar arrays. Using this technique, they can supply as much as 8000 W of power, depending on the amount of sunlight available.

To properly test these inverters, you can use the EA-PSI 9750-20 3U auto-ranging power supply to simulate the solar array. It can provide up to 5 kW at voltages up to 750 VDC and currents up to 20 ADC. To get this wide range of voltages and currents from a traditional supply, you would have to purchase a more expensive 15 kW unit.

Multiple Supplies Simulate Multiple Solar Arrays

Commercial solar inverters typically operate in the range of 30-1MW , with a solar array DC input voltage of up to 1500 VDC and produce three-phase AC power. At these power levels, it’s not practical to use a single array input. Instead, commercial inverters have multiple maximum power point tracking (MPPT) inputs that are summed at the DC/DC level before feeding into the DC/AC inverter. To test this type of inverter, you would use several autoranging power supplies, one for each input, as shown in the figure below.

EA Elektro-Automatik’s programmable supplies are rated as low as 1 kW per channel to as high as 2 MW per supply. The maximum output voltage is 2,000 VDC, and there no limit on how many supplies that you can use for this application. In addition, you can program each DC supply independently to simulate different irradiance profiles. For instance, on one inverter input, you can simulate a solar array in full sun, while on another input, you can simulate a solar panel that is partially or completely shaded.

Solar simulation software provides Sandia, EN50530, or custom test profiles

To wring the maximum amount of power from a solar array, MPPT inverters must accurately track the solar array outputs as the amount of sunlight hitting the array changes. Simply connecting a static DC voltage to an inverter does not test how well it can do this. Solar-array simulation is required, and both static and dynamic tests are required.

The EA PSI Series has a built-in function generator that allows you to simulate the dynamic performance of a solar array under a variety of conditions. In essence, you control the sun! The built-in function generator allows you to program up to 4096 data points in order to simulate simple solar array curves based on Isc, Voc, Vmpp and Impp. For more advanced solar simulation, you can use Elektro-Automatik’s EA Power Control (EAPC) software to easily set up Sandia, EN50530, or custom test profiles.

Test battery storage systems with a battery simulator

Another important component of both residential and commercial solar installations is the battery storage system. These systems allow users to generate and store power while the sun is shining or the wind is blowing and to use that power when it’s dark or when it’s calm. Solar inverters used in these applications must not only feed power back to the grid, but also charge batteries when generating power and draw current from the batteries when they’re not.

To test this type of inverter, you need to simulate both a system’s solar array and batteries; to simulate charge and discharge cycles, the battery simulator must be bi-directional. To perform the necessary tests, you can use an EA PSI Series power supply as a solar array simulator and an EA PSB Series supply as the battery simulator. The PSB Series is a bi-directional, programmable DC battery simulator that includes the ability to both source and sink power (2-quadrant). The PSB sources power to the inverter when power is demanded from the batteries and sinks power during the charge cycle. Using the PSI and PSB Series to simulate solar arrays and batteries, allows you to maintain full control and perform effective and repeatable tests.