Photovoltaic Emulator Research Articles

An Artificial Neural Network-Based Comprehensive Solar Photovoltaic Emulator

With increasing solar photovoltaic-based power generation, a photovoltaic emulator (PVE) is necessary to experimentally validate new control strategies without the influence of external factors such as irradiance and temperature. However, two significant challenges with PVEs are (i) solving the nonlinear equation of photovoltaic (PV) panel and (ii) oscillations in constant current (voltage) region with voltage (current) control. Thus, in this paper, a PVE with the ability to mimic both uniformly irradiated and partially shaded PV panels is proposed by employing artificial neural network (ANN) and piecewise-linearization technique. Based on the input operating conditions (irradiance, temperature, and partial shading), the ANN breaks the nonlinear I-V curve into piecewise-linear segments and outputs their boundary points. Then, with these boundary points, piecewise-linear equations of the segments relating PVE’s voltage and current are formed. Subsequently, using these piecewise-linear equations, the reference PVE voltage corresponding to PVE’s output current is calculated and given to the PI controller of a synchronous buck converter to mimic a PV panel. Thus, the proposed PVE overcomes the problem of solving nonlinear I-V equation by piecewise linearization which in turn aids an impedance-matching technique to mitigate the aforementioned oscillations. The generation of training data and development of ANN were carried out in MATLAB. Finally, the simulation studies performed in MATLAB/Simulink and hardware experiments validated the steady-state accuracy and the transient response which settled within 10 ms endorsing the real-time application of the proposed PVE.

Development of a PV emulator using SMPS converter and a model selection mechanism for characteristic generation

The increasing interest in the testing of photovoltaic systems and conversion components, resulted in the growth of PV emulators development, especially the power converter based ones. These emulators allow the characteristics reproduction of PV modules and panels in a well-controlled environment, by using different PV modeling methods. In this paper, three modeling techniques are investigated for three PV technologies (Amorphous, CdTe and Mono-Si). The investigation of the models is done using experimental data from Green Energy Park in Morocco according to proposed evaluation criteria. The criteria themselves are based on the coefficient of determination, the Root Mean Square Error and the required computational time. The analysis results in a mechanism allowing the selection of the best modeling approach for each PV module technology. Afterwards, simulation work is carried out in order to design the control scheme of the PV emulator power supply. Then, the control and modeling method selection mechanism based on module technologies is implemented experimentally on the designed PV emulator system. Hence, the PV emulator along with its control and modeling method is validated for an example of Amorphous technology module.

A New Photovoltaic Emulator Designed for Testing Low-Power Inverters Connected to the LV Grid

Assessing the performance of photovoltaic systems, particularly dedicated DC/AC inverter devices, requires the use of photovoltaic panels operating under natural environmental conditions, such as variations in solar radiation intensity, temperature and wind speed. Environmental testing is obviously very troublesome, inconvenient and limited. An alternative solution is to use a device that emulates the output photovoltaic panel curves in variable weather conditions, which allows the carrying out of all necessary tests at the laboratory. This paper presents a new photovoltaic emulator (PVE), mimicking the output characteristics of the photovoltaic panels. The proposed PVE is designed and constructed at the renewable energy laboratory for testing low-power PV inverters connected to the LV grid. A novelty of this solution is the method for shaping emulated current–voltage characteristics I–V. The concept of this method assumes autonomous regulation of slopes and shapes of emulated curve fragments. This allows us to obtain the desired shapes of the output characteristics for a wide range of both voltages and currents. The proposed PVE is not a pulse device; it belongs to linear analogue circuits. In order to confirm the assumed concept, a prototype is designed and constructed, and laboratory tests are conducted. Satisfactory results are obtained, confirming the correctness of the adopted concept. High compliance of the emulated characteristics is found in comparison to the characteristics of the selected commercial photovoltaic module. Very good results of dynamic tests and energy efficiency measurements are achieved.

External Current Source–Based Unilluminated PV Partial Shading Emulation System Verified Through the Hybrid Global Search Adaptive Perturb and Observe MPPT Algorithm

In this study, a novel PV emulator and the state-of-art learning–based real-time hybrid global search adaptive perturb and observe (P&O) maximum power point tracking (MPPT) algorithm have been presented. The prime objective of the constructed emulator based on integration of unilluminated solar panels with an external current source to overcome the constraints such as the need for wide surrounding space, high installation cost, and lack of control over the environmental conditions. Moreover, the developed algorithm resolved the drawbacks of the conventional P&O MPPT method associated with the use of a constant perturbation size that leads to poor transient response, high continuous steady-state oscillation, and inefficient tracking performance of maximum power point voltage in the presence of partial shading. The intended algorithm has been verified using MATLAB/Simulink by applying comparative analysis with the conventional P&O MPPT. In addition, the performance of the proposed control scheme is validated experimentally with the implementation of MATLAB/Simulink/Stateflow a on dSPACE Real-Time-Interface (RTI) 1007 processor board and DS2004 A/D and CP4002 Digital I/O boards. The results indicate that the algorithm is effective in reducing power losses and faster in tracking the speed of the maximum power point with less oscillation. In addition, excellent dynamic characteristics of the proposed emulator have been proven to be an ideal tool for testing PV inverters and various maximum power point tracking (MPPT) algorithms for commercial applications and university studies.

The performances of partial shading adjuster for improving photovoltaic emulator

A photovoltaic (PV) emulator (PVE) is essential equipment for the research and diagnostic of PV generation. It is a convenient, highly efficient, and low-cost approach when compared to controllable light sources. Nonetheless, the implementation of the partial shading capability in a PVE is highly limited in terms of efficiency, computation burned, number of power converters, and flexibility to change in the ambient condition. This paper proposes a partial shading adjuster for a PVE that can overcome the aforementioned limitations. The adjuster is applicable to the conventional PVE since it is based on an algorithm that can be added to the controller of the PVE. By adding the adjuster, the conventional PVE can emulate partial shading. The partial shading adjuster is added into a PVE that uses the direct referencing control strategy with the buck controller regulated by the proportional-integral controller. The results show that the PVE maintains its accuracy and produces a stable output voltage and current during the load changes when the adjuster is added. In conclusion, the proposed partial shading adjuster able to improve th

Design and Implementation of a Flexible Photovoltaic Emulator Using a GaN-Based Synchronous Buck Converter.

In order to efficiently facilitate various research works related to power converter design and testing for solar photovoltaic (PV) generation systems, it is a great merit to use advanced power-converter-based and digitally controlled PV emulators in place of actual PV modules to reduce the space, cost, and time to obtain the required scenarios of solar irradiances for various functional tests. This paper presents a flexible PV emulator based on gallium nitride (GaN), a wide-bandgap (WBG) semiconductor, and a based synchronous buck converter and controlled with a digital signal processor (DSP). With the help of GaN-based switching devices, the proposed emulator can accurately mimic the dynamic voltage-current characteristics of any PV module under normal irradiance and partial shading conditions. With the proposed PV emulator, it is possible to closely emulate any PV module characteristic both theoretically, based on manufacturer’s datasheets, and experimentally, based on measured data from practical PV modules. A curve fitting algorithm is used to handle the real-time generation of control signals for the digital controller. Both simulation with computer software and implementation on 1 kW GaN-based experimental hardware using Texas Instruments DSP as the controller have been carried out. Results show that the proposed emulator achieves efficiency as high as 99.05% and exhibits multifaceted application features in tracking various PV voltage and current parameters, demonstrating the feasibility and excellent performance of the proposed PV emulator.

A new generalized cross-connected switched capacitor multilevel inverter topology with high output voltage gain for single phase solar PV unit

Switched capacitor multilevel inverters are gaining much attention these days due to their merits like voltage boosting and voltage balancing characteristics. A Cross Connected Switched Capacitor Multilevel Inverter (C2SC-MLI) topology is proposed in this work. It can synthesize thirteen levels in the terminal voltage waveform and with a voltage boost ratio of 1:3. The topology is extendable by adding additional “n” modules in series. The number of levels (NLevel) and the voltage gain can be increased up to 4i+9 and 1:(i+2) respectively by connecting ‘i’ such ‘n’ modules. The topology also has inherent voltage balancing ability. To prove the advantage of proposed topology it is compared with recent switched capacitor multilevel inverter topologies and conventional multilevel inverter topologies in terms of number of power electronic components required, cost and voltage gain. The performance of proposed topology is validated using simulation in MATLAB and with an experimental prototype rated 0.1 kW fed by a solar PV emulator under steady state and dynamic loading conditions.

Fast‐converging robust PR‐P controller designed by using symmetrical pole placement method for current control of interleaved buck converter‐based PV emulator

AbstractIn this study, the interleaved buck converter‐based photovoltaic (PV) emulator current control is presented. A proportional‐resonant‐proportional (PR‐P) controller is designed to resolve the drawbacks of conventional PI controllers in terms of phase management, which means balancing currents evenly between active phases to avoid thermally stressing and provide optimal ripple cancelation in the presence of parameter uncertainties. The resonant path of the controller (PR) with a constant proportional unity gain is designed considering the changing dynamics of a notch filter by pole placement method (adding mutually complementary poles to the notch transfer function) at PWM switching frequency. The proportional gain path (P) of the controller is used to determine the compatibility of the controller with parameter uncertainty of the phases and designed by utilizing loop‐shaping method. The proposed controller shows superior performance in terms of 10 times faster‐converging transient response, zero steady‐state error with significant reduction in current ripple. Equal load sharing that constitutes the primary concern in multiphase converters is achieved with the proposed controller. Implementing of robust control theory involving comprehensive time and frequency domain analysis reveals 13% improvement in the robust stability margin and 12‐degree bigger phase toleration with the PR‐P controller. In addition to these, the proposed unconventional design process of the controller reduces the computational complexity and provides cost‐effectiveness and simple implementation. Moreover, implementing of auxiliary resistor‐capacitor (RC) circuits parallel with the inductors to sense the current in each phase removes the need for current measurement sensors that contribute to overall cost of the system.

Solar module emulator based on a low-cost microcontroller

The aim of this paper is to present an experimental analysis of a solar module emulator based on a low-cost microcontroller. An Arduino low-cost microcontroller is used to mimic several solar module technologies with high accuracy. The estimation and extraction of the single-diode photovoltaic model parameters is performed by a developed software. Two control strategies are applied to the photovoltaic emulation, one based on the digital proportional integral controller and the second one based on fuzzy logic controller. The emulator is able to follow the module I-V curves for fast and simultaneous real-time change of solar radiation, cell temperature and load, based on an online resolution of the single-diode mathematical model of the photovoltaic module. Finally, the experimental and modeled I-V curves of four different photovoltaic module technologies are compared and assessed the efficiency of the proposed fuzzy logic control strategy compared to the proportional integral control strategy.

Design of novel universal converter for integration of solar and wind energy for AC and DC load

AbstractPower generation through renewable sources using a multistage power conversion process was plagued with efficiency and reliability issues. It led to the evolvement of a novel universal converter for the simultaneous interfacing of solar and wind energy. Solar energy is extracted using a multiphase boost converter, while a 2n converter with a switch reluctance generator has been used for wind energy extraction. In this paper, a novel universal converter is used to integrate both solar and wind energies, which will reduce multiple stages of the power conversion process. This converter generates an output voltage of the sino‐square waveform, which is a combination of a sinusoidal and square waveform. Enhanced efficiency and competency of this sino‐square waveform in domestic and industrial applications have been validated with a systematic comparison with conventional square waveform. These two waveforms have been compared based on various harmonics generation, total harmonic distortion (THD), and switching losses. The proposed topology has been validated with an experimental setup using a PV emulator for solar energy. Wind energy has been implemented using an induction motor with switch reluctance generator.

Design and Implementation of a Simple and Efficient Control Strategy for PVEs

Photovoltaic Emulators (PVEs) has become more a fundamental tool in the study of PV systems. Besides their many operating principles, the design and the implementation of a PVE are still in progress. In this paper, we propose a simple and efficient PVE based on the dsPIC30F4011, which is equipped with a DSP engine dedicated to high-performance control applications. The control algorithm consists of an adaptive PI controller and a Perturb and Observe (P&O) algorithm for reference generation. This innovative and straightforward combination gives an efficient algorithm easy to be loaded and programmed on low-cost digital platforms, such as microcontrollers. The implementation under the dsPIC device makes the prototype inexpensive compared with the existing commercial PVEs, but not at the expense of simplicity and accuracy. The prototype is well optimized and described to be reproducible in laboratories. The effectiveness of the proposed method was validated using a platform that consists of a dsPIC30F4011, a current-controlled buck converter, a current sensor, and voltage one. The results show that the designed emulator prototype accurately behaves as the studied PV panel under different load and weather conditions.

Design and development of realistic PV emulator adaptable to the maximum power point tracking algorithm and battery charging controller

In this paper, PV emulator is developed using double loop PI controlled DC-DC buck converter. Ambient environmental conditions such as irradiance, temperature and wind speed are considered for creating PV reference model in the PV emulator. The simulation model of the proposed PV emulator is created and tested using MATLAB Simulink package. To validate the effectiveness of the proposed PV emulator, it is tested with different operating conditions such as varying irradiance, temperature and wind speed. The current–voltage and power-voltage characteristic of the PV emulator is compared with PV reference model. The suitability of the PV emulator is tested with MPPT algorithm and battery charging controller in addition to number of objectives. Real time testing of the proposed PV emulator is done experimentally and also corresponding results are discussed. The proposed Solar PV emulator has the following properties: (1) higher bandwidth DC-DC buck converter, (2) extremely reliable performance with lower response time, and (3) lower output voltage and current ripple.

Simple and Fast Dynamic Photovoltaic Emulator based on a Physical Equivalent PV‐cell Model

Photovoltaic emulators are a specific type of power electronics system to mimic the behaviour of a photovoltaic (PV) panel or array and facilitate the testing of energy systems. Existing solutions usually require sophisticated hardware design and fast computing. This paper presents a simple, reliable, and effective circuit-based photovoltaic (PV) emulator based on the equivalent PV stacked cells. The PV emulator can be used for solar system testing and analysis, such as maximum power point tracking (MPPT) and partial shading effect. The I– V and P– V characteristic curves of the emulator have been generated by using an LTspice simulator. It is experimentally investigated and compared with a real PV panel and existing emulator products. The experiment results show good agreement with the mimicked actual PV panel. The proposed PV emulator shows a better dynamic response and shorter settling time than several benchmarked commercial products. The enhancement in the time response is due to the simplicity of the emulator, where a few power diodes and some resisters are used. In addition to simplicity, the PV emulator is very cost-effective.

Efficiency Improvement Scheme for PV Emulator Based on a Physical Equivalent PV-Cell Model

Recently, a photovoltaic (PV) emulator is proposed which is based on a combination of a constant current source and a one-diode photovoltaic model. Its superior dynamic performance is compatible with that of a real PV system. Although it is power efficient at the maximum power point (MPP), it suffers from high power loss around and at the open-circuit voltage (OCV) operation condition. The PV emulator can be used for PV system analysis and testing, such as maximum power point tracking (MPPT). This paper presents a new switching circuit which is placed in parallel with the diode string to minimize the power loss. The switching circuit consists of a two-switch non-inverting buck-boost DC/DC converter. When the operating point of the PV emulator moves from the current source region to the voltage source region, the converter, which is more efficient, switches in to replace the diode string seamlessly to maintain the circuit operation of the emulator. Experimental results show that in the worst case scenario, i.e. OCV condition, the efficiency and temperature of the proposed solution reach 81.47% and 30.1 °C respectively, as compared with 2.8% and 94.2 °C respectively for the diode string only case. In terms of dynamic response, the proposed PV emulator lags the real PV panel by only 3.5 ms as compared with 120 ms by a commercial emulator under the 30% to 60% insolation change test.

Symmetrical Pole Placement Method-Based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller With Harmonic Compensator for Single Phase Grid-Connected PV Inverters

In this paper, a symmetrical pole placement Method-based Unity Proportional Gain Resonant and Gain Scheduled Proportional (PR-P) Controller is presented. The proposed PR-P controller resolved the issues that are tracking repeating control input signal with zero steady-state and mitigating of 3rd order harmonic component injected into the grid associated with the use of PI controller for single-phase PV systems. Additionally, the PR-P controller has overcome the drawbacks of frequency detuning in the grid and increase in the magnitude of odd number harmonics in the system that constitute the common concerns in the implementation of conventional PR controller developed as an alternative to PI controller. Moreover, the application of an unprecedented design process based on changing notch filter dynamics with symmetrical pole placement around resonant frequency overcomes the limitations that are essentially complexity and dependency on the precisely modelled system associated with the use of various controllers such as Adaptive, Predictive and Hysteresis in grid connected PV power generation systems. The proposed PR-P controller was validated employing Photovoltaic emulator (PVE) consisting of a DC-DC Buck power converter, a maximum power point tracking (MPPT) algorithm and a full-bridge grid connected inverter designed using MATLAB/Simulink system platform. Details of the proposed controller, Photovoltaic emulator (PVE) simulations, analysis and test results were presented in the paper.

Reconfigurable Photovoltaic Emulator for Differential Diffusion Charge Redistribution Solar Modules

Evaluating, validating, testing, and performing research on hardware components that are connected to actual solar photovoltaic systems can be challenging; photovoltaic emulators are a common practical approach. In particular, addressing emulation for the crucial research topics of partial shading and cell mismatch is important. Differential diffusion charge redistribution is a switched-capacitor architecture using differential power processing for performing maximum power point tracking with cell-level granularity using only a single module-level converter. Among the prohibitive challenges is preventing damage to the module-embedded integrated circuits for the corner cases during fault and failure testing of connected hardware components including power converters. Emulators not only benefit research, but also product development and manufacturing of hardware components and power converters. This paper investigates a reconfigurable linear emulator with an analog controller for photovoltaic modules configured for differential diffusion charge redistribution. Cell mismatch and partial shading are shown to be equivalent and that the averaged behavior of these switched-capacitor solar photovoltaic modules can be represented by two separate continuous-time circuits that are coupled by feedback and constraints leading to an emulator design that is demonstrated through a hardware prototype.

Battery Energy Storage to Mitigate Rapid Voltage/Power Fluctuations in Power Grids Due to Fast Variations of Solar/Wind Outputs

Passing clouds and wind gusts can create unacceptable rapid voltage/power variations in power networks. Simulation results using a real Australian distribution feeder with real load demand and PV output profile show that with a high penetration of PV the voltage variations can increase beyond the allowable limit given by the standards. Similarly, wind gusts can create wind power output variations. This paper addresses the rapid voltage/power variations caused by solar or wind power outputs and presents a control strategy using the energy buffer in energy storage for their impact mitigation. By controlling the discharging/charging operation of the energy storage based on the available energy buffer in the storage unit, not only the rate of power output variations can be maintained at the desired level, but also the voltage variations can be controlled within acceptable limits. An experimental setup, consisting of a PV emulator, inverter, and grid simulator, demonstrates the potential threat of unacceptable voltage variations. The proposed mitigation strategy using energy buffer in the storage for smoothing the power outputs of solar/wind is tested and validated through simulation. Simulation results show that with the proposed control, the fast variations of the voltage/power variations instigated by solar/wind can be maintained within the acceptable limits.

A Fast-Dynamic Control Scheme for a Power-Electronics-Based PV Emulator

The dynamic performance of a photovoltaic (PV) emulator is critical for testing applications with fast maximum power point tracking (MPPT) algorithms. In this article, a power-electronics-based PV emulator (PVE) is proposed to achieve fast-dynamic response, as well as, to emulate accurately in all regions of the current-voltage (I-V) characteristic curve. The control scheme of the proposed PVE consists of an instantaneous output impedance matching (IOIM) controller based on load resistance feedback to generate the voltage reference signal and an inner boundary control (BC) scheme to regulate the converter at a given reference within a short period of time. The IOIM controller overcomes the drawback of conventional PVEs that suffer from oscillating reference signal in a certain region of the I-V characteristic curve. Moreover, use of load resistance feedback in the reference generation algorithm allows the decoupling of the reference signal generator from the inner control loop. The BC scheme adapts a corrected second-order switching surface to achieve a faster response time and robust operation with switching converter loads. Detailed small signal model of the PVE is derived to design the IOIM control loop and to ensure a stable and fast convergent emulation in the entire I-V characteristic curve. Experimental results of a 130 W (VMPP = 35.2 V, IMPP = 3.69 A) prototype are presented with both resistive loads and an MPPT converter to verify its performance under fast varying irradiance and load conditions.

Development of a photovoltaic characteristics generator based on mathematical models for four PV panel technologies

A good study of photovoltaic system requests to have very precise 
 current-voltage characteristic curves of photovoltaic modules for different technologies. The photovoltaic emulator provides an efficient solution to maintain the same current-voltage output of photovoltaic module. It includes three parts: the PV model, the control strategy, and the power converter. This paper provides three classes of modeling and simulation of photovoltaic arrays and presents the synthesis results of the current-voltage characteristic performances obtained by the modeling approaches. The models of the first class are based on electrical circuit model, those of the second class are based on multiple straight lines model, and for the third class, it is based on the look up table. The mathematical model is built using MATLAB/ Simulink, and an experimental bench was carried out to acquire an up-to-date and representative experimental database of four PV panels. This database is used for the validation of these models for the different PV panel technologies under Moroccan meteorological conditions. Following this comparative study, we came to a high agreement between the experimental and simulated current-voltage characteristics for the emulator under study.

Fast Power Emulation Approach to the Operation of Photovoltaic Power Plants Made of Different Module Technologies

This paper gives a comprehensive approach to the emulation of photovoltaic (PV) plants made of different module technologies as well as varying peak power through the advanced fast PV power emulation technique. Even though PVs are recognized as a technology for CO2 emissions mitigation, the proposed emulation technique provides the opportunity to replicate PV plant operation without a carbon footprint because of its working principle. The process of PV power plant emulation consists of several stages which are described in detail. An algorithm for determining PV power plant configuration based on the technical characteristics of the PV emulation system equipment is developed and presented, as well as an algorithm for preparing data on the current–voltage (i–v) characteristics used as input data into programmable sources that mimic the power plant PV array. A case study of a single day operation of PV power plants made of two different topologies and technologies was carried out with the fast PV power emulation approach and the results are evaluated and presented.