Photovoltaic Microconverter Research Articles

Self-Healing Photovoltaic Microconverter With Zero Redundancy and Accurate Low-Cost Fault Detection

This paper studies a zero-redundancy fault-tolerant dc-dc series resonant converter (ZR-SRC) for residential photovoltaic (PV) applications. This converter can handle faulty conditions on-the-fly using topology morphing control without increasing the number of components. Furthermore, it can withstand a single fault in both input and output bridge semiconductors, i. e., up to two semiconductor faults. The proposed dc-dc converter could increase the availability of residential photovoltaic-powered dc microgrids. Comprehensive fault diagnosis and localization algorithms are proposed for MOSFETs on both sides of the ZR-SRC. The paper proposes а short-circuit fault (SCF) detection in the input-side MOSFETs using the existing PV voltage measurements, decreasing the converter cost and size. The open-circuit fault (OCF) in the output-side MOSFETs is detected by sensing the voltage of the bottom two switches sharing the same ground with the dc bus. In addition, the post-fault operation of the converter is thoroughly analyzed. Recommendations for the PV power clipping are given to ensure the safe operation of the converter after a fault. A 300 W experimental setup is built to demonstrate the feasibility and performance of the proposed fault-tolerant converter.

Implementation of Global Maximum Power Point Tracking in Photovoltaic Microconverters: A Survey of Challenges and Opportunities

This survey focuses on photovoltaic (PV) module-level power electronic systems. The survey demonstrates that dc-dc converters with a wide input voltage range can enable global maximum power point tracking (GMPPT). It discusses the requirements and challenges in the design and implementation of these converters. A wide input voltage range allows for implementing different algorithms of the GMPPT, among which the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> curve scanning or sweeping is the most robust one. Special attention is paid to buck–boost high step-up dc-dc converter topologies as the most promising solution for residential applications suffering from shading issues. An example of such a converter is presented along with the corresponding implementation of the GMPPT by <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$I$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$V$ </tex-math></inline-formula> curve sweeping. Several case studies of partial shading conditions are synthesized to compare the performance of the local and GMPPT algorithms. The obtained results demonstrate that the GMPPT shows superior performance under partial shading, while its performance is comparable to the conventional local maximum power point tracking (MPPT) under regular operation. The case studies are compared in terms of harvested energy, MPPT efficiency, and converter efficiency. The latter allows for better comparison as the partial shading could result in operation at a reduced input voltage with a measurable efficiency drop.

Application of Cycle Skipping Modulation in Buck–Boost Photovoltaic Microconverters

Cycle skipping modulation (CSM) was previously demonstrated for efficiency improvement in different converters intended for photovoltaic module-level applications. Currently, galvanically isolated buck–boost converters (IBBCs) have attracted increased attention in these applications due to the uptake of dc microgrids. This article revisits the topic of CSM and applies it to a quasi-Z-source-based IBBC. Two new CSM schemes are proposed for the given converter. Power losses in components are estimated for different CSM schemes to predict efficiency improvement that could be attained. A 300-W prototype was built to verify the efficiency estimation results. The efficiency trends are the same between the theoretical estimations and experimental measurements. Converter operation was studied for two bell-shaped solar irradiance daily profiles using a solar array simulator. The converter demonstrates efficiency improvement during morning and evening hours for a sunny day and during the whole day for overcast sky conditions.

Dual‐mode magnetically integrated photovoltaic microconverter with adaptive mode change and global maximum power point tracking

Dual‐mode magnetically integrated photovoltaic microconverter with adaptive mode change and global maximum power point tracking

Impact of Transformer Turns Ratio on the Power Losses and Efficiency of the Wide Range Isolated Buck–Boost Converter for Photovoltaic Applications

In this paper, the impact of transformer turns ratio on the performance of the quasi-Z-source galvanically isolated DC-DC converters is studied. Embedded buck–boost functionality enables these converters to regulate the input voltage and load in a wide range, which makes them suitable for such demanding application as photovoltaic microconverters. The isolation transformer here plays a central role as its turns ratio defines the point of transition between the boost and buck modes and overall capability of the converter to regulate the input voltage in a wide range at high efficiency. The studied quasi-Z-source galvanically isolated DC-DC converter is benchmarked in terms of power loss of components and weighted power conversion efficiency for three different turns ratios of isolation transformer to achieve the best and optimized turns ratio lead to the efficient operation. Operation in a wide range of input voltage at high efficiency is the main criterion for assessing the effect of turns ratio on the efficiency of the converter. The proposed loss model and theoretical predictions of the efficiency were validated with the help of a 300 W experimental prototype of the photovoltaic microconverter based on the quasi-Z-source galvanically isolated DC-DC converter topology.

Topology-Morphing Photovoltaic Microconverter With Wide MPPT Voltage Window and Post-Fault Operation Capability

In this paper the concept of wide input voltage range photovoltaic microconverter with post-fault operation capability is presented. This microconverter could remain operational in the case of short- or open-circuit failure of any switch of its front-end inverter. When the fault occurs, the control system automatically identifies the fault and applies the special post-fault modulation sequence thus keeping the functionality of the microconverter unchanged. The research findings are validated by the help of a 350 W experimental prototype specially developed for integration of silicon PV modules into the residential DC nanogrids with the nominal voltage of 350 V. Paper explains the multi-mode operation principle and fault identification routine. It presents the experimental efficiencies and evaluates the maximum power point tracking performance of the microconverter prior and after the short-circuit fault of an upper switch of the inverter. The daily energy yield test conducted for both cases has confirmed that the proposed approach can extend the service life of PV microconverters with a moderate impact on their performance.

MPPT performance enhancement of low-cost PV microconverters

This paper presents a performance enhancement method for the high-gain isolated dc-dc converters intended for module level photovoltaic applications. DC voltage gain of a microconverter should change in a wide range, which requires use of undesirably high or low values of the switch duty cycle that result in high losses in the front-end stage. A reconfigurable rectifier at the output stage of the photovoltaic microconverter enables dc gain control and, consequently, limits variation of the duty cycle to more favourable range. This work proposes use of a reconfigurable rectifier capable of reconfiguring its topology from a voltage doubler to a voltage quadrupler. The paper explains the derivation, operation and the control principle of a reconfigurable rectifier. A single-switch quasi-Z-source front-end stage was used as an application example of the wide input voltage range photovoltaic microconverter in the experimental study. It is demonstrated that by the application of the proposed approach the lower boundary of the input voltage could be shifted from 20 V down to 8 V, which has enabled for the microconverter a unique possibility of shade-tolerant operation with the implementation of a global MPPT.

Digitally Controlled Current Sensorless Photovoltaic Micro-Converter for DC Distribution

In this paper, a digitally controlled photovoltaic (PV) micro-converter for dc distribution with sensing no current is presented. Current information for maximum power point tracking (MPPT) is estimated from system parameters, which leads to reducing power losses caused in sensing current and the number of components. Operation analysis of boundary conduction, quasiresonant, and discontinuous conduction modes is presented for its implementation. The high current estimation accuracy not only allows adaptive operation mode changes for efficiency optimization, but also guarantees achievement of high MPPT efficiency. Loss analysis of each operation mode is also presented to determine optimal transition points for mode change. A prototype PV micro-converter for a 120-W PV module is implemented by utilizing a digital signal processor. Experimental results verify that the proposed method is stable in both static and dynamic operations. European efficiency and MPPT efficiency are measured higher than 97.5% and 99.5%, respectively.