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Solar Array Simulation for Testing MPPT Drives
Simulating a solar panel or a solar panel array for MPPT Drive testing
To simulate a solar panel. We need to create an I-V curve for the solar panel. First let’s review how a solar cell works so we can understand what the function generator will define for the solar panel, a set of connected solar cells. A solar cell model consists of a current source which represents the solar light creating current, a p-n junction represented by a diode, and resistances in series with and in parallel with the p-n junction. Photons impinge upon electrons in the p-n junction and provide sufficient energy to enable the electronics to transition to the conduction band. The electric field that builds up turns on the diode, and current flows to the output of the solar cell. Figure 2 shows a simple model for a solar cell.
The series and shunt resistances represent the losses in the solar cell. The series resistance represents the resistance of the solar cell semiconductor material and the resistance of its metal contacts. The shunt resistance represents the insulation resistance defined by the leakage current through the p-n junction. Having a lower series resistance and a higher shunt resistance increases the efficiency of the solar cell.
Based on this model, the solar cell has an I-V characteristic as shown by the red curve in Figure 3. The p-n junction exhibits an inverse diode characteristic. The key parameters that define the curve are the solar cell’s short circuit current, ISC, its open circuit voltage, VOC, and the point where the solar cell’s power output is a maximum, the maximum power point, MPP. The ISC and the VOC are the maximum current and voltage that the solar cell can generate. VMP and IMP, as shown by the blue curve in Figure 3, represent the I-V parameters of the maximum power output that the solar cell can generate. Operating the solar cell at its MPP ensures maximum performance from the solar cell and is the target operating point.
The built-in function generator of the EPS instruments, such as the PSB bidirectional DC power supplies, makes it easy to create the solar cell I-V curve. The function generator requires four parameters: the open circuit voltage, the short circuit current, and the maximum power point current and voltage. Figure 4 shows the setup screen which will create the I-V curve
Test engineers can use the simulated solar cell to test solar cell inverters and how well they can track the maximum power point of the solar cell or solar panel. The function generator enables testing of an inverter’s efficiency in compliance with standard EN 50530 Overall efficiency of grid connected phototovoltaic inverters. The EN50530 test mode allows determination of inverter response to changes in the maximum power point. In addition, the test mode allows inputs to change irradiance on the solar panel and changes in its surface temperature. Both parameters affect solar cell output.
Using a test rack of as many as 64 PSB 30 kW supplies, a test engineer can simulate a 1.92 MW solar farm. This allows complete testing of solar inverters for power distribution applications.
I-V characteristic of a solar cell (red curve) and the power output (blue curve)
Programable DC Supply with PV Panel and PV array simulator as per EN50530 and Sandia
Circuit model for a solar cell
