Module Level Power Electronics Research Articles

Application of Module Level Power Electronics Technology in Distributed Photovoltaic Power Generation System

Distributed photovoltaic power generation system usually adopts series wiring scheme, which has problems such as high voltage DC electrical safety risk, power mismatch of modules and maintenance management difficulty. Three schemes of module level power electronics technology are proposed, including string inverter with rapid shutdown device, string inverter with module optimizer and micro inverter. The electrical shut-off, power generation data monitoring, power optimization and inverter function characteristics of each scheme are described and compared, and the suggested application scenarios are given. In addition, typical electrical topology schemes of module level power electronic devices including rapid shutdown device, module optimizer and micro inverter are introduced.

DC Series Arc Fault Detection and Self- Extinguishing Method With Power Stage Design of Module Level Power Electronics

DC Series Arc Fault Detection and Self- Extinguishing Method With Power Stage Design of Module Level Power Electronics

Partial shading losses mitigation of a rooftop PV system with DC power optimizers based on operation and simulation-based evaluation

Building-applied photovoltaic (PV) systems improve urban building energy efficiency but are vulnerable to partial shading (PS) from near obstructions. This causes electrical losses owing to mismatch as well as reduction in module surface’s irradiance. Module level power electronics (MLPE) can mitigate these electrical losses caused by PS.The evaluation of the effectiveness of MLPEs in mitigating mismatch losses serves as the primary basis for determining its application during the system-design stage. However, research regarding the effects of applying MLPE is lacking. Further, the studies lack comparisons with various general PV system types, such as inverter types and array configurations.Therefore, the purpose of this study is to evaluate the mismatch losses mitigation effect of the DC power optimizer (DCPO), one of MLPEs. A rooftop PV (RTPV) system with DCPOs is selected for this study, and PS and operational performance are analyzed for RTPV system. Then, comparative analysis for the performance of the mimic RTPV model and seven general PV models, which are modeled for array configurations and different inverter types, is conducted using the simulation software.We developed four PV models with a central inverter and two with a string inverter, each with different shaded module connections. The annual array yields of these models decreased by up to 3.23% than mimic RTPV model, except for the model with micro inverters categorized as MLPE, which only experienced a 0.3% decrease. In the mismatch, it is expected that the PV system with MLPE can improve performance compared to the without MLPE.

Non-Isolated Current-Fed Series Resonant Converter with Hybrid Control Algorithms for DC Microgrid

Module-level power electronics can optimize the power generation of photovoltaic panels, which requires a simple topology structure, high power conversion efficiency, and wide voltage gain, corresponding to irradiance variations. This paper proposes a non-isolated current-fed L-C series resonant converter and its control algorithms. The proposed converter can obtain a buck–boost voltage gain with the hybrid control algorithm utilizing the switching frequency modulation and asymmetric pulse width modulation. The proper power stage design can guarantee the soft-switching capability for the entire operating range. Also, the control strategy is designed to obtain a small rms current. The operational principle of proposed converter is analyzed in order to design the resonant tank and control strategy. The performance of designed converter can be verified with the experimental results with a 500 W prototype converter.

Understanding partial shading effects in shingled PV modules

Shingled solar modules are one of several technologies currently being considered to obtain higher solar module efficiencies. Using equivalent circuit modelling this paper investigates the robustness of shingled modules to partial shading with respect to the power produced and the power dissipated in shaded shingles. The modeling results are experimentally verified. We find that power losses in shingled modules can be larger than in conventional modules for similar shading conditions. The risk of significant local heating resulting from partial shading, potentially leading to catastrophic module failure can also be higher in shingled modules due to the substantially higher reverse biases experienced by shaded shingles. Both risks can effectively be mitigated by operating each shingled module at its own maximum power point, for instance by using module level power electronics on each module or by incorporating a sufficient number of bypass diodes into the module design.

New monitoring method to characterize individual modules in large photovoltaic systems

Photovoltaic (PV) systems power losses are approximately 15–20% of the performance ratio for current PV systems. There are several reasons that explain PV modules failures, and since they are connected in series to the rest of the string, a failure in one module may result in losses in the entire string. In addition, some of these failures, if are not fixed in time may become permanent and may reduce the lifespan of the PV modules. Periodic monitoring is the only way to detect these failures. Monitoring techniques oriented to groups of modules are unable to detect faults in individual modules. I-V curve tracers, which are oriented to module level and use power electronics components and large capacitors, require to disconnect the PV module from the rest of the system and long measurement times. This works proposes a methodology, that is able to take partial measurements of individual PV modules and recompose their characteristics with only small capacitors in the range of tens of microfarads and without power electronics components. The monitoring methodology is able to measure individual PV modules without modifying the electrical interconnection circuit and to deviate the operating point to ±0.3 A and 5 V in less than 5 ms. From this deviation, the system recomposes the PV module I-V characteristics with accuracies that are between 1 and 3% for the region close to maximum power.

A Time-Series Data Analysis Methodology for Effective Monitoring of Partially Shaded Photovoltaic Systems

The majority of photovoltaic (PV) systems in the Netherlands are small scale, and installed on residential and commercial rooftops, where different objects in many cases may lead to the presence of shading and inevitable energy loss. Nevertheless, the energy loss due to expected shadow must be distinguished from the energy loss due to other malfunctions. In this study an algorithmic tool is presented that automates the process of analyzing monitoring data of partially shaded PV systems. The algorithm compares long-term and high-resolution yield data of a partially shaded PV system with the yield data of an unshaded PV system, as reference PV system, and automatically detects the energy loss due to the expected shadow, caused by any surrounding obstacles, and distinguishes it from any additional energy loss due to other malfunctions. This study focuses on PV systems with module-level power electronics (MLPE) since these are mostly used on PV systems on rooftops. Three different cases of shaded MLPE PV systems are presented to illustrate the versatility of the methodology. Furthermore, suggestions for further research are discussed at the end of the paper.

Solar Optiverter—A Novel Hybrid Approach to the Photovoltaic Module Level Power Electronics

In this paper, the concept of an Optiverter is proposed as a novel class of photovoltaic (PV) module level power electronics systems. Functionally, the Optiverter is a hybrid technology that combines the ultrawide maximum power point tracking (MPPT) voltage window of the PV power optimizers with the direct ac connectivity and inherent safety of the PV microinverters. Thanks to the advanced multimode control with variable dc-link and the shade-tolerant MPPT algorithm, the proposed Optiverter ensures efficient energy harvest from the PV module in different shading scenarios. To justify the superiority of the concept, the performance of a 300 W prototype of the PV Optiverter is experimentally compared to that of the industrial microinverters in different operation conditions, including an extreme case with opaque shading of two out of three substrings of the PV module.

Selection Map for PV Module Installation Based on Shading Tolerability and Temperature Coefficient

Power generation from photovoltaic (PV) modules suffers from heat losses that are a function of the temperature coefficient of maximum power ( γ ) of the PV module. Another loss mechanism is shading, where the power output of the module and ultimately the system can be severely compromised. Various approaches such as passive, active, or smart bypasses and module level power electronics have been employed to minimize the effects of shading on a PV module. So far, the performance of a PV module under shading had only been addressed vaguely and was generally described qualitatively. Therefore, a probability-based parameter called shading tolerability (ST) was recently developed to quantify the behavior of PV modules under all kinds of shade. However, the observations pertaining to ST were only carried out at 25 °C ambient temperature. Hence, this paper aims to: 1) investigate whether ST is an innate property of a PV module by formulating a correlation between ST and ambient temperature, 2) classify various PV technologies based on ST and γ, and 3) develop a PV module selection map. Theoretical result shows that thermal features of a PV module (nominal operational cell temperature and γ) can influence the PV module ST by 12.25%. Also, an analytical limit is derived for ST variation with respect to ambient temperature change $(\Delta \text{ST}/ \Delta T_{a})$ . The proposed selection map, which is similar to the Ragone plot for energy-storing devices, is validated using the data of 27 PV systems installed in the Netherlands. The map can be used for optimal selection of PV modules for the design of PV systems simply by knowing the specifications of the module along with the meteorological conditions of the installation location.

Photovoltaic Module and Submodule Level Power Electronics and Control

The nine papers in this special section focus on photovoltaic module and sub-module level power electronics. Grid connected photovoltaic energy systems have experienced an explosive growth over the last decade, with a cumulative installed capacity surpassing the 400 GW milestone as of 2017. Among PV system configurations, distributed module-level converter architectures can lead to a higher energy yield by mitigating partial shading, persistent shading (soiling, snow, bird droppings, and fallen leaves), mismatch, and aging, through a higher maximum power point tracking (MPPT) efficiency. Also, distributed electronics might be the key for implementing diagnostic and prognostic actions at a module level. Among these configurations, microinverters (also known as ac-module inverter), which connect a single PV module to the grid, and PV power optimizers, which are dc–dc converters performing the MPPT function at a module level, have attracted the academic and industrial interest in the last decade. So much so, that both microinverters and dc–dc power optimizers are commercialized by tens of companies around the world, with a great variety of circuit topologies, which comprise combinations of one or more power stages, interleaved converters, resonant converters, topologies with and without isolation, etc.

Simulated potential for enhanced performance of mechanically stacked hybrid III–V/Si tandem photovoltaic modules using DC–DC converters

This work examines a tandem module design with GaInP2 mechanically stacked on top of crystalline Si, using a detailed photovoltaic (PV) system model to simulate four-terminal (4T) unconstrained and two-terminal voltage-matched (2T VM) parallel architectures. Module-level power electronics is proposed for the 2T VM module design to enhance its performance over the breadth of temperatures experienced by a typical PV installation. Annual, hourly simulations of various scenarios indicate that this design can reduce annual energy losses to ∼0.5% relative to the 4T module configuration. Consideration is given to both performance and practical design for building or ground mount installations, emphasizing compatibility with existing standard Si modules.

High-Performance Quasi-Z-Source Series Resonant DC–DC Converter for Photovoltaic Module-Level Power Electronics Applications

This paper presents the high-performance quasi-Z-source series resonant dc-dc converter as a candidate topology for the photovoltaic module-level power electronics applications. The converter features a wide input voltage and load regulation range thanks to the multimode operation, i.e., when the shoot-through pulse width modulation and phase-shift modulation are combined in a single switching stage to realize the boost and buck operating modes, respectively. Our experiments confirmed that the proposed converter is capable of ensuring ripple-free 400 V output voltage within the sixfold variation of the input voltage (from 10 to 60 V). The converter prototype assembled achieved a maximum efficiency of 97.4%, which includes the auxiliary power and control system losses.

Accelerated Testing of Module-Level Power Electronics for Long-Term Reliability

This work has applied a suite of long-term-reliability accelerated tests to a variety of module-level power electronics (MLPE) devices (such as microinverters and optimizers) from five different manufacturers. This dataset is one of the first (only the paper by Parker et al. entitled “Dominant factors affecting reliability of alternating current photovoltaic modules,” in Proc. 42nd IEEE Photovoltaic Spec. Conf. , 2015, is reported for reliability testing in the literature), as well as the largest, experimental sets in public literature, both in the sample size (five manufacturers including both dc/dc and dc/ac units and 20 units for each test) and the number of experiments (six different experimental test conditions) for MLPE devices. The accelerated stress tests (thermal cycling test per IEC 61215 profile, damp heat test per IEC 61215 profile, and static temperature tests at 100 and 125 °C) were performed under powered and unpowered conditions. The first independent long-term experimental data regarding damp heat and grid transient testing, as well as the longest term (>9 month) testing of MLPE units reported in the literature for thermal cycling and high-temperature operating life, are included in these experiments. Additionally, this work is the first to show in situ power measurements, as well as periodic efficiency measurements over a series of experimental tests, demonstrating whether certain tests result in long-term degradation or immediate catastrophic failures. The result of this testing highlights the performance of MLPE units under the application of several accelerated environmental stressors.

Protocolo para comunicación inalámbrica en instalaciones de energías renovables

During the last four years, photovoltaic (PV) has faced its first consolidation phase, due among other factors to the economic crisis. Under these circumstances, the PV industry had the vital need to reduce costs. A new technology, called module level power electronics (MLPE), is since then rapidly expanding and carries the promises to increase not only the efficiency but also the flexibility and safety of PV systems. However, an optimal MLPE solution shall depend on the effectiveness of its data communication management. Unfortunately, today, there is no standard protocol available that encompasses the desired features as listed below. This article proposes a protocol for wireless communications: open, robust, secure, light to implement on a small micro-controller, achieving ultra-low power consumptions and, thanks to being message oriented, avoids information fragmentation and allows for low bandwidth needs even in high noise level environments. Above all, this protocol provides a solution to standardize communication between all components of a PV system (regardless of type and size). Finally, this protocol can be extended to wind and hydro-micro-generation systems and to the remote monitoring of any other application in which DBWP could be interesting.

A comprehensive study on partial shading response of c-Si modules and yield modeling of string inverter and module level power electronics

Building Integrated and Building Attached Photovoltaic (BIPV, BAPV) systems may suffer from lower performance than predicted as a result of not considered partial shading. New system architectures have been proposed to optimize performance. The common approach of these new architectures is to track the Maximum Power Point (MPP) of every solar module individually. A simulation model is developed to quantify the benefits and drawbacks of different PV system architectures. The model includes a shading evaluation of the installation with means of 3D modeling, irradiance calculations, PV cell modeling and finally an empirical power conversion model. The energy yield of three leading architectures is confirmed (string inverter, power optimizer, micro inverter) for clear and partial shading conditions by means of an outdoor field test. Results with the irradiance profile of the Netherlands show that the string inverter system outperforms MLPE in 2 out of 3 partial shading scenarios that were evaluated in this study. It is found that the energy yield benefit of MLPE has a seasonal and latitude variation with the highest contribution during winter months. Additionally a study was performed to evaluate the energy yield at different irradiance profiles. Results show that there is a marginal benefit of the micro inverter system at higher irradiance locations when partial shading is present. The analysis method can be used by PV installers and system designer to determine which is the optimal system architecture for maximum energy yield especially when partial shading is present.

Outdoor characterization and comparison of string and MLPE under clear and partially shaded conditions

AbstractBuilding integrated and building attached photovoltaic (BIPV, BAPV) systems may suffer from lower performance than predicted as a result of unwanted partial shading. New system architectures have been proposed to optimize performance. The common approach of these new architectures is to track the maximum power point of every solar module individually. This paper demonstrates the effect of shading on energy yield by evaluating power level management on the module level compared to string level. Three independent PV systems were installed and extensively monitored in Eindhoven, a reference string inverter system, a power optimizer system and a micro inverter system. The DC and AC performance ratio (PR) of the systems have been analyzed for different weather types based on the clearness index. A pole shading covering 1–2% of the total system surface has been used to evaluate system performance under a specific type of partial shading. Module Level Power Electronics (MLPE) is capable of increasing the PR up to 35% under certain partial shading conditions. However, the string inverter system outperformed MLPE under unshaded operation conditions.