Photovoltaic Emulator Applications

A solar photovoltaic (PV) emulator is a programmable power supply designed to emulate solar panels. With a fast transient response, the emulator responds to change in load conditions and maintains the output on voltage-current characteristics [1].

The solar panel configuration can be defined by the user based on the system specifications, along with choosing the proper environmental conditions for emulation through selecting the ambient conditions. The desired specifications of solar panels that can be input by the user include open-circuit voltage, short circuit current, temperature coefficient, irradiation, area, and series resistance.

The solar arrays produce a DC output with non-linear characteristics varying as a function of temperature and irradiance. The power electronic systems connected to the solar arrays, such as solar inverters, account for variations to characterize the array’s output and maximize the power converted [2]. The solar array output characteristics vary significantly from the standard DC power supply, thus requiring additional control requirements for the DC power supply to satisfy the necessary system specifications.

The devices connected to the solar array intend to maximize the power output by locating the maximum operating point. They also adjust the operating point to account for the fluctuations in sunlight and temperature. This translates to fluctuations in the voltage and current characteristics of the solar arrays, mostly due to change in temperature, irradiance, and other environmental conditions. Typically, it is observed that the change in irradiance affects the output current while the variation in temperature influences the output voltage.

To reproduce the current and voltage characteristics of a PV system in the laboratory for a reliable, efficient, and rapid PV energy conversion systems analysis and improvement, implementation methods for solar PV emulators are considered. The conventional setup consists of an experimental platform using a light-emitting diode or halogen lamp as controllable artificial light for the PV module [3]. But it suffers from the drawbacks of requiring large amounts of power and wide space for setting up the equipment, complicated test bench configuration, and lack of possibility to manipulate the temperature.

The PV emulator systems with reconfigurable DC power source and convenient, ambient condition control for both steady-state and transient responses serve as the tool to reproduce the output electrical characteristics of different PV modules regardless of external atmospheric conditions.

 

Solar Emulator Implementation

The typical implementation considers a solar emulator to a controlled DC power supply that can reproduce the PV panel characteristics regardless of the environmental conditions. This stems from the general architecture of the PV emulator, as shown in Figure 1. It comprises three key elements; PV model implementation, control strategy, and power stage control [4].

The PV model replicates the characteristic of the PV panel that needs to be emulated. It receives temperature, irradiance, and measured values of PV voltage or current as inputs. Depending on the control type of the power converter, PV voltage or current input is chosen. The control strategy is the stage between the PV model and the converter, and it determines the intersection point between the PV emulator characteristic and the load characteristic. The power converter could be a linear regulator, programmable DC power supply with closed-loop control, or a switching mode power supply.

Figure 1. The generic architecture of a solar photovoltaic emulator [4]

The detailed implementation of solar PV emulators involves the typical power and control circuits. The power circuit incorporates a DC source, a four-quadrant chopper in current control mode, an inductive filter L, and an adjustable resistive load. This is illustrated in Figure 2 [5]. Here, the output current and voltage of the chopper circuit must replicate the same behavior as that of a real PV module.

Figure 2. Solar PV emulator implementation [5]

The values of solar irradiance, temperature, output voltage, and current of the chopper serve as inputs to the digital control circuit. Two main loops are utilized to achieve the necessary control of the circuit:  an external voltage loop and an internal current loop. The current loop includes a proportional-integral (PI) controller that regulates the emulated PV current based on the reference signal and feeds it to the voltage loop. The voltage loop requires the Temperature (T)/Irradiance (G) impact algorithm and the I-V curve linearization algorithm to control the emulated PV voltage and estimate the current reference signal.

 

Key references:

1. Solar PV Emulator
2. Solar Emulation and Inverter Testing | Magna-Power
3. Intissar et. al., Design of a Low-Cost PV Emulator Applied for PVECS, 2019.
4. Youssef et. al., High-Performance Emulator for Fixed Photovoltaic Panels, 2019.
5. Messaoudi et. al., Design and implementation of a solar PV emulator, 2016.