An Overview of Solar Emulator Design

Solar emulators simulate the current-voltage curve under varying environmental conditions. This is accomplished without using an actual photovoltaic (PV) panel or external setup for data monitoring and data acquisition [1].

The user can input the desired specifications to simulate the characteristics of a solar panel and use the actual electrical output. This enables the simulation of several environmental conditions, including partial shading conditions. These emulators also serve as an essential tool for research and development (R&D) activities when actual photovoltaic panels cannot be used. Read on to learn more about what a solar emulator is and how it works.

An Overview of Solar Emulators

The energy demand in different forms is constantly growing, particularly renewable energies like wind, solar and geothermal. The harnessing of solar energy has been an active research topic since 1860. Due to the increasing importance of distributed generation and smart grid, solar systems are gaining traction. Several research and development works are based on the efficient utilization of PV energy. The solar arrays produce DC output with non-linear characteristics that vary as a function of temperature and irradiance. For the efficient design of solar systems, a solar emulator that mimics the actual PV characteristics is essential.

Even after a solar PV system is installed and functional, several ongoing issues need to be investigated and solved, such as the reliability of the PV system, analysis of its power generation, and the electricity network efficiencies due to partial shading [2]. To overcome these issues, a repeatable, scalable, and stable PV source is necessary for validation. This highlights the necessity of implementing a PV emulator that mimics the current-voltage (I-V) output characteristics of a functional PV module under various climatic conditions.

Solar energy has secured a large part of the market due to the continued development of PV system technology and lower prices. A solar emulator is a useful tool to estimate power losses due to a daylight period while the photovoltaic panel has a fixed position. Several methods are used to implement solar PV emulators, including various power converter topologies such as DC-DC buck converter and DC-DC boost converter. Other methods are based on modifying a programmable DC power supply so that the internal resistance of the DC source varies exponentially with the output current [3].

 

Design and Working of Solar Emulator

Extensive research has been carried out on various methodologies of solar PV emulators over the last couple of decades. This includes studies related to PV cell, module, and array emulators for over three decades [4]. The first PV emulator prototype was developed based on the analog circuit. In the following years, many studies revolved around technologies related to the electric field but projected studies on solar PV emulators evolved as well. Typically, a solar PV emulator comprises three parts known as the PV model, the control strategy, and the power stage, as illustrated in Figure 1.

Figure 1. Components of a solar PV emulator [4]

These solar PV emulators are classified based on their power range and PV model representation. It is also evident that the PV cell and its modeling are the crucial aspects of any PV emulation structure. Regardless of how complex the model is,, the aim is to obtain data in all operating conditions from the PV emulator that essentially mimics the behavior of the real solar cells very closely.

The modeling has evolved over the years from rudimentary ISDM models to resistance-based and two or three diode-based models. In general, as the model complexity increases, more parameters are required to emulate the necessary system behavior and thus demands higher computing time and complex algorithms to generate the required output.

Similarly, several control strategies have been investigated, starting from a direct referencing method that employs a proportional-integral (PI) regulator and power converter dynamic characteristics to determine the operating point. Although this commonly used method is simple, incorrect sizing of external factors led to significant oscillations at the output of the emulator. To overcome this issue, a fixed step duty cycle method was chosen.

Further, hybrid control modes were explored to enhance the dynamic performance of the solar PV emulator. This led to reduced oscillations and improved performance but suffered from increased expenses and complexity associated with the control algorithm. Other methods include the resistance comparison method, analog-based method, and curve fitting-based method. On the other hand, the power stage can be interfaced with switching or linear components. However, in general, there is always a compromise among the rapidity, efficiency, robustness, and complexity of the choice of solar PV emulator design.

 

Key references:

1. Solar PV Emulator
2. Messaoudi et. al., Design and implementation of a solar PV emulator, 2016.
3. Chalh et. al., A low-cost PV Emulator for testing MPPT algorithm, 2018.
4. Intissar et. al., Design of a Low-Cost PV Emulator Applied for PVECS, 2019.

 

Featured Image used courtesy of Ecosense