TerraSAS System - Programmable Solar Array Simulator
The Elgar TerraSAS System, (TSAS) provides an easily programmable means of simulating the characteristic behavior of a PV array. The system provides a turn-key approach to testing the maximum peak power tracking (MPPT) characteristics for grid-tied inverters and DC charge controllers. The ability to simulate virtually any fill factor or solar cell material allows the customer to validate the MPPT algorithm with a power source. Hardware control is accomplished by an application running on the local controller that communicates directly to the PV simulator using RS422, which operate as a dedicated IV curve generation processor. The local Graphical User Interface (GUI) is accomplished via another application that provides all of the user controls to the TerraSAS system. Imbedded in the application is the Ethernet (LAN) parser for remote communication and control. All of the functions available locally through the controller are also available remotely.
Why power supply is critical for PV simulations
Many solar inverters generate AC ripple on their DC input, which is connected to the photovoltaic array. For single phase inverters, the frequency of this ripple is twice the line frequency (120 Hz for US models). The simulator's power supplies must not supress this ripple as a function of their regulation loop. 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 tracking the MPP at a much higher speed when compared to conventional dithering techniques (also called perturbate-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.
To satisfy this requirement, the PV simulator must be capable of reproducing the voltage / current behavior of a solar array at the ripple frequency. Most standard switching power supplies employ very large output capacitors and inductors in their output circuits and are unable to deliver the required performance - regardless of the response speed of the I/V curve controller.
Elgar’s line of PV simulators are based on high speed versions of our standard products, where output capacitors and other speed-limiting components have been adjusted. This results in a speed improvement of 10 times or better. Proprietary features built into the PV controller hardware and firmware, combined with our high speed power supplies, deliver the required performance. This technology was extensively tested on micro-inverters and is ready to test the next generation of inverters.
Strengths of using DSP signal processing
Our technology avoids using linear amplifiers, which are fast but bulky and inefficient. The required performance is delivered by high speed switching power supplies and advanced DSP signal processing techniques. Competitors data sheets mentions that speed requirements may not be met in some conditions, "...depending also on the type of MPP tracking principles". An additional linear module is required to satisfy the new requirements. Some competitor's power supplies specifications say that it uses "...innovative IGBT and transformer technology". Our power supplies use Power MOSFETs, which typically switch ten times as fast as the most recent IGBTs. Higher switching frequency translates to smaller output capacitors and inductors - which is the key to a successful high speed power supply design.
Features And Benefits
Simulate dynamic irradiance and temperature ranging from a
clear day to cloud cover conditions
Ramp the voltage, temperature or irradiance level over a
programmed time interval
Readback of voltage, current, irradiance level and temperature setting
Tests for inverter Maximum Power Point Tracking (MPPT)
Provides programmable I-V curves for PV Inverter testing
Simulates different types of solar cell material
Multi-Channel, Up to 1MW