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The cascaded dc–dc converter is a popular topology for large-scale medium-voltage photovoltaic (PV) system with the advantages of high voltage conversion ratio, high efficiency, great flexibility, and independent control capability. However, the absence of optimal string maximum power point tracking (MPPT) operation under power mismatch is a big issue in common centralized control. Furthermore, the cost and time delay are unacceptable resulting from the distance among PV strings in the large-scale PV station and the cascaded dc–dc converter needs to adopt the distributed control method without real-time communication. To this end, by introducing other necessary constraints including voltage constraints, power constraints, and gain constraints on the basis of the distributed MPPT control strategy, a distributed multimode control scheme is proposed in this article. Each submodule (SM) can be switched flexibly between multiple operation modes to maximize the extracted solar energy. Individual string MPPT and autonomous distribution of output voltage are achieved without communication under the proposed distributed control strategy. In this way, optimal operation range is wider, mode switching is simpler, and applicability and robustness are improved. A downscaled prototype and a 35-kV/6-MW simulation system are constructed to verify the effectiveness of the proposed control strategy. [ABSTRACT FROM AUTHOR]

This article presents a nonlinear passivity-based control for a grid-connected cascaded H-bridge (CHB) photovoltaic (PV) system. The proposed control system is based on a port-controlled Hamiltonian model extracted from the synchronous reference frame system. Grid current dynamics is included in this model. Compared to existing solutions, the proposed control method has a robust performance and enhances the stability of the CHB-based PV system in the case of disturbances such as unequal irradiance over distinct PV arrays or a sudden sag or swell in the grid voltage. This controller also provides the independent control of each dc-link voltage. Therefore, the individual maximum power point tracking algorithms can be realized in each PV array, and the harvested energy can be maximized. Finally, simulation results and experimental investigations are conducted to verify the effectiveness of the proposed strategy. [ABSTRACT FROM AUTHOR]

In photovoltaic systems, common-mode voltage (CMV) generates leakage current, which shortens the insulation lifespan and causes safety problems. As for neutral-point-clamped (NPC) inverters, zero CMV PWM (ZCMV PWM) can be implemented to eliminate leakage current, but unable to balance neutral-point (NP) voltage in dc side. This article presents a novel modulation technique for NPC PV inverter. The strategy contains ZCMV PWM and another two modulation modes which keeps CMV constant in one switching period, so as to eliminate leakage current. In order to balance NP voltage, NP current is adjusted by selection of optimal modulation mode and the leakage current is still well eliminated during the process of balancing NP voltage. Compared with conventional ZCMV PWM, the proposed scheme can remove both leakage current and NP voltage deviation. The output performance and limitations of the proposed method are also introduced in the paper. Experiments are provided to verify the validity of the proposed method. [ABSTRACT FROM AUTHOR]

The multiport dc/dc converter with input independent output series structure is simple and efficient for photovoltaic (PV) applications. Through the cascade of sub-modules (SM), the converter has a high step-up ratio to connect MVdc bus. However, it has many ports which increase the risk of short-circuit faults. Therefore, this article proposes a fault ride-through (FRT) topology for multiport converter. When low-voltage ports are short-circuited, they can be isolated by blocking the switches of their own. The FRT topology can support the output voltage of faulty SMs to avoid the disconnection from MVdc bus. Other healthy ports can still generate power to MVdc bus. When the medium-voltage port is short-circuited, the FRT topology can quickly clear the fault current to prevent devices from being damaged. Due to the zero voltage switching, the proposed topology has higher efficiency. For medium-voltage fault, the FRT topology has faster fault clearing speed because more capacitors are reused. Finally, the proposed topology is verified by simulation and experiment. [ABSTRACT FROM AUTHOR]

This article introduces a nonisolated, high step-up voltage multiplier cell (VMC)-based dc–dc converter for applications such as module-integrated converter and power optimizers. The VMC combines switched capacitor with autotransformer techniques and active clamp circuit. The autotransformer tertiary winding is employed to increase voltage gain without operating the main switch under extreme duty cycle condition, to reduce the current through the main switch before it turns offand to ensure its zero-voltage switching (ZVS) operation on a wide operation range. The auxiliary switch in the clamp circuit provides ZVS for the main switch and vice-versa. Thus, both switches are turned on with zero voltage and there is no switching loss. Hence, high switching frequency is used to reduce the passive components’ volume and weight. Besides, the low dc-bias and bidirectional magnetizing current allows a smaller magnetizing inductance in the autotransformer to further minimizing the dimensions of the magnetic core. The leakage inductances are used to provide zero-current switching condition for the diodes, eliminating their reverse-recovery losses. The operation principle, steady-state analysis, and design guidelines are depicted and validated through experimental results obtained from a 350-W prototype of the proposed converter. Efficiency of 96.5% at full load is also reported. [ABSTRACT FROM AUTHOR]

In this article, the Wiener variable step size with variance smoothening (WVSSV) technique is introduced for the utility supportive solar photovoltaic (PV) system. This system performs the function of power factor correction, compensation of nonactive component, and reduction of total harmonics distortion (THD) from the utility grid. The dc–ac converter is used in between the PV array and the common connection point and it is controlled through the WVSSV technique to produce the switching signals. The WVSSV technique presents impressive robustness and good adaptation in highly adverse nonlinear load conditions by estimating the clean and harmonic less fundamental component. The presented technique has a good convergence rate even at the starting of adapting and the step size is adjusted to eliminate the variety of noise and harmonics of nonlinear loads. The efficacy of the WVSSV control technique is presented through simulated and test results and depicts the improved steady-state as well as dynamic performances of the PV system. The THDs of grid parameters are found under the IEEE-519 standard in different working conditions. [ABSTRACT FROM AUTHOR]

This article proposes a novel maximum power point tracking (MPPT) method based on the variant of the pigeon-inspired optimization (PIO) algorithm for photovoltaic systems under partial shading conditions (PSCs). The proposed method integrates the hierarchical network behavior of pigeon flock and revises the map and compass operator of the original PIO algorithm to improve optimization efficiency. In addition, the landmark operator is used to perform a small-scale search to achieve fast tracking. Based on the combination of these mechanisms and dual-mode dynamic tracking scheme, the proposed hierarchical pigeon-inspired optimization (HPIO) MPPT method has a powerful search ability to deal with PSCs. To verify the superiority of the proposed HPIO MPPT method, it is compared with other existing advanced MPPT methods in simulation and experiments. Compared with traditional MPPT techniques based on artificial intelligence, the proposed HPIO MPPT method has a higher success rate in tracking GMPP and excellent tracking speed under PSCs. And the HPIO method also shows excellent performance under complex PSC with multiple clusters and load-variation conditions. [ABSTRACT FROM AUTHOR]

Flexure-based bonding system driven by piezoelectric actuator is quite appealing for fulfilling the nanoscale-accuracy and high-efficiency interconnection tasks. However, it turns obstreperous to implement it for high-efficiency and nanoscale-accuracy interconnection during the soft-landing operation, largely because of a large amount of noise in force sensor and low efficiency of traditional controller. To this end, this article presents a novel hybrid position/force fully (HPFF) closed-loop control strategy to enable the developed flip-chip bonding system to run in the manner of nanoscale-accuracy and high-efficiency interconnection. The integrator composed of inertial filter (ICIF) method is proposed to improve the operation efficiency and reduce the time used in the soft-landing process. Besides, the stability of HPFF strategy is demonstrated in theory and numerical calculation. Finally, a series of validation experiments including ICIF comparing experiments, closed-loop trajectory tracking experiments, robustness experiments under different loads and HPFF closed-loop control experiments are successfully implemented. All the results uniformly confirm that the developed flip-chip bonding system has achieved satisfactory soft-landing interconnection performance by taking advantage of the proposed HPFF closed-loop control strategy. [ABSTRACT FROM AUTHOR]

A virtual synchronous generator (VSG) is one of the promising solutions today for integration of renewable energy sources to the grid. Photovoltaic (PV) power generation is dominating most of the generation in renewable energy. In this scenario, it is imperative to study the combined dynamics of the PV source and the VSG in the grid connection mode. This article presents a study of such a PV power system, which is connected to a grid. The dc-link capacitor is considered as an energy storage (ES) element, which is generally the case in most of the practical systems. The synchronverter control scheme is taken as a VSG model. The small-signal model is obtained for the system under study, which mainly includes PV source and dc-link voltage controller dynamics. From the eigenvalues, which are obtained by using the small-signal model, analysis is carried out to find the effect on system dynamics due to the variation in different system parameters. Furthermore, the effect of maximum power point (MPP) and non-MPP modes on system dynamics is studied. The proposed model is validated through simulation in PSCAD/EMTDC and Controller Hardware In Loop (CHIL) in a Real Time Digital Simulator (RTDS). [ABSTRACT FROM AUTHOR]

Photovoltaic (PV) arrays exhibit multiple local maximum power points (MPPs) in their I-V and P-V characteristic curves when different modules are subjected to different radiations at the same time, known as a partial shading condition (PSC). Hence, tracking the global MPP is crucial to increase the PV system efficiency. Conventional global MPP tracking (GMPPT) algorithms suffer from slow convergence, while some can fail to track the global MPP during PSCs. This article proposes a totally new approach to finding the global MPP during PSC using a single current sensor: the parabolic assumption GMPPT algorithm uses a fixed number of current scans (steps) equal to the number of solar modules connected in series to directly and immediately calculate the global MPP. The proposed algorithm uses simple parabolic equations to calculate the global MPP near-exactly during PSCs. The performance of the proposed algorithm is first evaluated by simulation in MATLAB/Simulink, and then by experimental verification. The results show very fast global MPP tracking and negligible tracking energy loss with an experimental tracking efficiency over 99.6% for the four PSC patterns tested. [ABSTRACT FROM AUTHOR]

This article proposed a simplified flying capacitor voltage (FCV) control strategy based on hybrid clamped three-level boost converter. Compared with the traditional control method, the proposed method does not need the sampling of the FCV and the extra FCV control loop. Hence, the software and hardware resources, like sampling circuits and control algorithm, can all be saved significantly especially in high voltage photovoltaic system with multiple dc inputs. In this article, the balancing mechanism and control parameter design of the proposed method are presented in detail. With the proposed strategy, the FCV can be controlled around half of the bus voltage with error less than 2%. Besides, a precharge strategy for flying capacitor is also provided in this article. The performance and analysis of the proposed strategy are verified by the experiments at last. [ABSTRACT FROM AUTHOR]

Series arc faults (SAFs) are the most common faults in photovoltaic systems. If a SAF is not detected in time, it may lead to some catastrophic damages to the system. This article presents a new method for detecting SAFs in photovoltaic systems based on determinism in the voltage signal. The determinism of the signal is derived using the recurrence plots method. The recurrence plots provide a two-dimensional plot of the signal, from which the degree of determinism in the signal is derived as a criterion for detection of SAFs. The performance of the method is evaluated using plenty of experiments carried out in different SAF and normal conditions. The results confirm the high accuracy, high speed, and low computational burden of the proposed method. [ABSTRACT FROM AUTHOR]

In partially shaded photovoltaic (PV) arrays, the power-voltage curve displays multiple maxima, one of which is the global maximum power point (GMPP). One of the major concerns related to PV systems is to locate and track the GMPP in all circumstances to boost efficiency. Combining conventional hill climbing (HC) algorithm and artificial neural networks (ANNs), a new two-stage GMPP tracking method is introduced in this article that aims to be fast and accurate. Moreover, it does not require irradiance or temperature sensors. In the first stage, the current-voltage (I-V) curve is sampled at specific points determined based on the array I-V curve analysis with the objective to be the minimum samples possible that can reflect the changes of irradiance and temperature. Then a simple feedforward ANN is employed to estimate the neighborhood of the GMPP using these samples. In the second stage, the HC algorithm is adopted to ensure the GMPP is tracked precisely. The proposed method is validated by simulations in MATLAB/Simulink environment and experimental tests under uniform irradiance condition, partial shading conditions, and a wide range of temperatures. [ABSTRACT FROM AUTHOR]

This article presents an enhanced power quality solar photovoltaic (PV) inverter enabling common-mode leakage current elimination. A three-phase transformerless solar energy conversion system is considered here, which, along with peak active-power production from PV array, ensures different power quality improvement capabilities such as grid current harmonics mitigation, grid currents balancing while also offering the grid reactive power support. Unlike conventional power quality inverters, this strategy is robust with respect to abnormalities in grid voltages at far radial ends, and does not compromise with the leakage currents caused by parasitic capacitance of PV array with ground. Common practice in the PV inverter power quality control is to neglect the PV leakage currents; however, they considerably affect the system performance by deteriorating the power quality and causing the safety issues of operating personnel. The standards VDE-00126 and NB/T-32004, therefore, compel the transformerless PV systems to operate with leakage current under 300 mA range. Various simulation and test results show the satisfactory performance of the presented strategy, even under various grid-side abnormalities. The comparative analysis with the state-of-the-art techniques shows the effectiveness of the strategy. Under all test conditions, the harmonics in grid currents are observed within limits as per the IEEE-519 and IEC-61727 standards, whereas the PV leakage currents are maintained well within the range recommended by VDE-00126 standard. [ABSTRACT FROM AUTHOR]

Due to the complex structure of flexible dc distribution systems with distributed photovoltaic power, single-ended measurement based protection cannot work well. The dc line-to-line faults are also difficult to locate due to a short time span with fault characteristics that is affected by various converter structures and control algorithms. To resolve these issues, a new fault detection and location method based on active converter injection is presented. The proposed method modifies the converter to become a frequency-controllable injection source by actively utilizing the coordinated control between local protection and the converters, which can build a clear protection boundary. Moreover, this method can locate the faulted area accurately by selecting the appropriate injected harmonic frequency, which is affected by the outlet capacitance of the dc/dc converter and the cable-distributed capacitance. Compared with current dc protection techniques, this method does not require additional injection equipment and high data sampling frequency. Hardware tests and simulation results are carried out, illustrating that the proposed mechanism is effective to achieve both control and protection through the controllability of power electronics. [ABSTRACT FROM AUTHOR]

Due to the unpredictable and fluctuating nature of solar photovoltaic (PV), energy storage systems (ESS), such as batteries, are always integrated with PV systems to smooth the power supply. In this article, a multiport dc–ac converter (MPC) with differential power processing dc–dc converter (DPPC) is proposed for battery ESS integrated PV systems. The MPC is capable of regulating most of active power among PV, battery and ac grid, and only the differential power (partial power) needs to be handled by the dc-dc converter. Hence, the major merits of higher integration, higher efficiency, and lower cost can be achieved by the proposed configuration. A new cooperative control scheme for the MPC and DPPC is investigated, aiming at realizing flexible active power flow. Besides, a modified space vector pulsewidth modulation is developed for the MPC, taking into the consideration of the voltage variation of both PV and battery. The active power controllability of the MPC and the power rating of the DPPC are quantitatively analyzed. The effectiveness of the proposed configuration, control and modulation schemes is validated by experimental results. [ABSTRACT FROM AUTHOR]

Input parallel output parallel (IPOP) modular power converters have been used to supply high power and high current in various applications. In general, the IPOP modular power converter uses an output power balancing method to equally distribute the amount of output power to each converter. In this article, a hybrid input power balancing method is proposed to obtain high power conversion efficiency, high reliability, and enhanced dynamic performance of the IPOP modular power converters. In the steady state, the proposed method controls input power to be balanced in each converter. A power loss distribution capability of the input power balancing method can improve the entire power conversion efficiency and can reduce the overall operating temperature of the IPOP converters, which can increase lifetime and can improve reliability. During the transient operation, the proposed method makes the IPOP converters under an interleaving mode to tightly regulate the output voltage and to obtain fast dynamic performance. Experimental results with 200-W prototype modular synchronous buck converters verify the performance improvements of the proposed method such as high power conversion efficiency, the power loss distribution capability in the steady-state operation, and the enhanced dynamic performance in the transient operation. [ABSTRACT FROM AUTHOR]

The multiscale defect detection for photovoltaic (PV) cell electroluminescence (EL) images is a challenging task, due to the feature vanishing as network deepens. To address this problem, an attention-based top-down and bottom-up architecture is developed to accomplish multiscale feature fusion. This architecture, called bidirectional attention feature pyramid network (BAFPN), can make all layers of the pyramid share similar semantic features. In BAFPN, cosine similarity is employed to measure the importance of each pixel in the fused features. Furthermore, a novel object detector is proposed, called BAF-Detector, which embeds BAFPN into region proposal network in Faster RCNN+FPN. BAFPN improves the robustness of the network to scales, thus the proposed detector achieves a good performance in multiscale defects detection task. Finally, the experimental results on a large-scale EL dataset, including 3629 images, 2129 of which are defective, show that the proposed method achieves 98.70% (F-measure), 88.07% (mAP), and 73.29% (IoU) in terms of multiscale defects classification and detection results in raw PV cell EL images. [ABSTRACT FROM AUTHOR]

A current sensor based global maximum power point tracking (GMPPT) algorithm of photovoltaic system is proposed in this article to increase the tracking speed during partial shading condition. For the proposed algorithm, the tracking range of duty cycle is reduced by calculating both the upper limit and lower limit of duty cycle and skipping the duty cycle section without global maximum power point. Compared with maximum power trapezium (MPT) algorithm and the combination algorithm of MPT and search-skip-judge, the proposed algorithm reduces the tracking range of duty cycle during both tracking directions and only needs one current sensor to realize control. As a result, the proposed algorithm shows advantages of fast tracking speed, small energy loss, and low hardware cost. Followed by theoretical analysis, the simulation and experimental evaluation validate the claimed advantages of the proposed GMPPT algorithm. [ABSTRACT FROM AUTHOR]

This article proposes a bidirectional battery charger for grid to vehicle and vehicle to grid operations of electric vehicles (EV). The dc stage of the proposed converter offers a quadratic buck–boost voltage gain ratio, which makes it suitable for interconnecting the battery pack unit of EVs with both dc and ac grids as a home EV charger. A high-voltage gain ratio, low voltage, and current stress of switches, high values of utilization factors (UF) for both directions are achieved. Continuous input current and common electrical ground are preserved at the dc–dc stage and also, the continuous output current of the proposed converter makes the realization of the pseudo dc-link method possible for connecting to an ac grid. Consequently, the switching power loss in the dc–ac stage of the EV charger is reduced, and as a result, it allows the proposed charger to run more efficiently and cooler. The operating principle, steady-state characteristics including the current, voltage stress, and UF of the switches, and comparison with other state-of-the-art dc–dc bidirectional converters are carried out in detail. Finally, to verify the theoretical achievements, a 500-W laboratory prototype of the proposed EV charger is implemented. The EV charger exhibits the capability for ac and dc regulation and demonstrates peak efficiency of 97.8% in the forward and 97.5% in the backward direction modes of operation. [ABSTRACT FROM AUTHOR]

The grid-connected quasi-single-stage converter (QSSC) provides a direct power flow path from low-voltage (LV) energy storage systems (ESS) to ac–dc converters, resulting in reduced power conversion stage for high-efficiency ESS integration. However, due to the dc-link voltage ratio between the two ports varies with the ESS state of charge, the voltage vectors in the ac side are unevenly distributed in the QSSC. This nonlinearity brings some challenges in control and modulation design for the ac–dc part of QSSC. In this article, a virtual two-level converter model considering the two ports as a single dc source is proposed, and model predictive power control (MPPC) based on the virtual two-level model is proposed to enhance the grid current performance. The duty cycle of each phase is calculated based on the active and reactive power tracking error minimization in the two-level converter frame, and the duty cycle for each switching pair is obtained by minimizing the power processed by the dc–dc converter. In this way, the complicated implementation of MPPC for a three-level converter is avoided, and the controller design of the QSSC can be simplified. The effectiveness of the proposed virtual two-level converter model and MPPC method are verified with experimental results. [ABSTRACT FROM AUTHOR]

A split dc-link dual-active-bridge (SDLDAB)-based multiport converter (MPC) is proposed in this article. The intended application of the SDLDAB converter is to interface two solar photovoltaic (PV) modules and a battery bank with a dc microgrid. Depending upon the prevailing atmospheric condition, these two solar PV modules can be operated at their maximum power points. This is achieved by maintaining appropriate voltages at the input terminals of the two PV modules. A high-frequency transformer is employed to provide high voltage gain between the dc microgrid and PV as well as battery ports. A direct power flow path is established between the solar PV modules and the battery without involving the transformer. The transformer current is minimized by appropriately modulating the switching sequence of the SDLDAB. Detailed simulation studies are carried out to predict the performance of the system. A laboratory prototype of the SDLDAB having 1-kW power rating is fabricated. The performance of the MPC is validated by carrying out detailed experimental studies on the developed prototype. [ABSTRACT FROM AUTHOR]

In this article, we deal with the development of a fractional-order notch filter (FONF) for a grid-connected solar photovoltaic (PV) system. The developed FONF control approach is used to estimate fundamental active constituents from the distorted load currents, and hence, gating pulses for operating voltage source converter (VSC) are used in the PV system. This control approach for the grid-connected solar PV system is designed to achieve several purposes, such as feeding active power demand of the load/grid and countercurrent-related power quality issues at the common connecting point. The power quality issues taken into consideration are harmonics distortion, reactive power burden on the system, and unbalancing of connected loads. The FONF-based control proposes a modified structure of an integer-order notch filter. The integer-order filters have a limitation due to the fixed integrator and differentiator terms. In FONF, the power of integrator used in a notch filter can be modified according to the application required for obtaining the accurate response of the system. A prototype of the grid-connected solar PV system is developed in the laboratory using IGBTs based VSC and dSPACE MicroLabBox (DS-1202) to demonstrate the behavior of the FONF-based control. Simulation and experimental results are obtained for steady-state and unbalanced loads with variation in the solar irradiance. The harmonic distortions in the system are observed as per the IEEE-519 standard. [ABSTRACT FROM AUTHOR]

Line–line (LL) and line-ground (LG) faults may not be detected by common protection devices in Photovoltaic (PV) arrays as these faults are not detectable under high fault impedance and low mismatch level. In recent years, many efforts have been devoted to overcome these challenges using intelligent methods. However, these methods could not classify the type of faults and diagnose their severity. In this article, we propose a novel and intelligent fault monitoring method to detect and classify LL and LG faults at the dc side of PV systems. For this purpose, the main features of current–voltage curves under different fault events and normal conditions are extracted. The faults are categorized using the hierarchical classification platform. Later, the LL and LG faults are detected and classified by machine learning methods. The proposed method aims to reduce the amount of dataset, which is required for the learning process, and also obtains a higher accuracy in detecting and classifying the fault events at low mismatch levels and high fault impedance compared with other fault diagnostic methods. The experimental results verify that the proposed method precisely detects and classifies LL and LG faults on PV systems under different conditions and severity with the accuracy of 96.66% and 91.66%, respectively. [ABSTRACT FROM AUTHOR]

Centralized photovoltaic (PV) grid-connected inverters (GCIs) based on double-split transformers have been widely used in large-scale desert PV plants. However, due to the large fluctuation of short circuit ratio (SCR) under high-penetration PV power plants, the stability of GCIs controlled in current source mode (CSM) is seriously affected. Reducing the bandwidth of the phase-locked loop (PLL) will improve the stability of CSM-controlled GCI, but the dynamic response performance will be degraded. Even if the PLL bandwidth is designed to be very low, the CSM-controlled GCI still cannot operate stably in very weak grids. The voltage source mode (VSM) controlled GCI can operate stably in very weak grids, but is not suitable for strong grids. Therefore, this article proposes a dual-mode combined control strategy: When SCR gradually decreases, the GCIs operate in full CSM (FCSM), hybrid mode (HM), and full VSM (FVSM) in turn, which effectively improves the stability of GCIs when SCR fluctuates greatly. The stability region of GCIs under the constraints of multiperformance-index is obtained, and the switching boundaries between the above three modes are also quantitatively analyzed in this article. Finally, the correctness of the proposed control strategy is verified by experiments. [ABSTRACT FROM AUTHOR]

Arriving at an accurate and fast amplitude estimation of the sine-wave distorted by harmonics and noise is important for the control of voltage source inverters in grid-connected photovoltaic system. In this article, the three-point interpolation discrete Fourier transform method based on the maximum sidelobe decay windows is proposed for accurate amplitude estimation. The proposed amplitude estimator is speeded-up by using the guaranteed stable recursive method. The influence of noise on the proposed amplitude estimator is investigated, and the amplitude estimation error caused by the spectral interference is also analyzed. The accuracy and effectiveness of the proposed method are verified through simulation and experiments, where the state-of-art amplitude estimation methods and the boundaries specified in the Standard IEEE C37.118.1-2011 are considered. [ABSTRACT FROM AUTHOR]

This article describes the design of an energy management system for a stand-alone cellular-connected outdoor trail camera that can operate without a power grid connection for a long duration. The primary focus of the study is to increase the operational lifetime of the system while decreasing human interference and the demand for maintenance, thereby enhancing the user experience. This is achieved by actively hybridizing three different battery types and a charging circuit supplied by a solar photovoltaic (PV) panel to harvest additional energy. This article investigates different user types and energy requirements for a hunting application. Considering the heterogeneous energy demand and cost requirements of the different user types, the battery energy storage, and PV system size are flexibly adjusted to satisfy the demand of the different types of users. While the proposed energy management circuit comes with an incremental cost increase to the trail camera, it provides essential functionality that will sustain stand-alone operation for a total five years with at most eight maintenance visits, decreasing the maintenance demand of the camera considerably. [ABSTRACT FROM AUTHOR]

In this article, a modified reduced order generalized integrator-based frequency-locked loop (MROGI-FLL) is proposed for controlling the interfacing inverter of the grid-tied photovoltaic system to mitigate the harmonics. Additionally, a fuzzy tuned PID controller is integrated in the proposed scheme to minimize the steady-state error, which results the voltage level is maintained constant at the common dc-link bus terminals. The MROGI-FLL is designed to evaluate the three-phase reference currents by extracting the fundamental constituents from the load currents and grid voltages. The proposed MROGI-FLL has several advantages such as better harmonic mitigation capability, control adaptivity, adaptive frequency and phase, grid synchronization, and low computation burden. The proposed reference current generator is simulated on MATLAB/Simulink platform under steady state and various transient conditions.The comparative study of proposed scheme is compared with the existing and adaptive control techniques, which assures the potency of the proposed control algorithm in-terms of harmonic mitigation, dc-offset rejection, frequency variation, and computation burden. Finally, the experimental results are verified through an experimental platform by using the dSPACE evaluation kit and both the simulation and hardware characteristics are well justified to the IEEE-519 standard limits. [ABSTRACT FROM AUTHOR]

The leakage inductance in flyback converters can induce high-voltage spikes in power switches as well as power losses. Although conventional resistor–capacitor-diode (RCD) snubbers and active clamp circuits can be used to suppress these voltage spikes, the clamping operation of RCD snubbers increases power consumption, while the active clamps require additional power switches. To address these issues, a quasi-resonant flyback converter featuring a divided resonant capacitor is proposed in this article, in order to suppress voltage spikes in power switches and improve the power conversion efficiency. The operational principle of a divided resonant capacitor is analyzed to obtain the design methodology of the divided resonant capacitor. Furthermore, the validity of the proposed design method is verified via experiments, using 15-W prototype quasi-resonant flyback converter. The results indicate that the proposed design effectively reduces voltage spikes and improves power conversion efficiency. [ABSTRACT FROM AUTHOR]

The single-phase five-level transformerless inverters have been gradually applied in photovoltaic grid-connected systems due to low voltage stress and excellent waveform quality. However, they also suffer from serious leakage current as conventional three-level inverters. In order to reduce the leakage current, a single-phase five-level transformerless inverter is proposed in this article. The proposed inverter guarantees that the common-mode (CM) voltage is clamped to a half of the dc-link voltage when outputting ±Vdc/2 and zero voltage levels. Consequently, the high-frequency CM voltage is avoided and the leakage current is suppressed. The voltage stresses of eight switches and two flying capacitors are only Vdc/4, thus the system investment cost and total losses are reduced. The conduction and switching losses are analyzed in detail and a comparison with some existing topologies is also made. Finally, simulations and experiment are carried out based on a 1-kW prototype. The results show that the proposed single-phase five-level inverter can obtain both excellent differential-mode and CM performance. [ABSTRACT FROM AUTHOR]

This article presents a hybrid modular multilevel converter (HMMC) for large-scale photo voltaic (PV) integration to grid. PV panels are directly connected to each submodule of the converter without using any dc–dc converter. A distributed maximum power point tracking (D-MPPT) method is used to extract maximum power from each PV-string under normal, as well as, shading (uniform/nonuniform) condition. Power unbalance among the phases during partial shading is a major issue of such type of converter, which needs to be properly handled for satisfactory operation. To address this issue in a cascaded H-bridge converter, zero sequence voltage (ZSV) injection based methods have been utilized. In this work, ZSV injection is integrated with D-MPPT and the combined method is applied on HMMC to address both interphase and intraphase partial shading satisfying MPPT operation in each submodule. The feasibility of the proposed control method is first verified through PSCAD/EMTDC simulation. Thereafter, a dSPACE Micro-Lab-Box-based experimental prototype is developed to check the performance at 10 kW power level under the presence of real PV panels. A comparative assessment of the proposed system with available topologies has been performed to highlight the notable features. The capability of ZSV controlled HMMC is evaluated under various shading conditions to explore its usefulness to deal with power unbalance conditions. It may be predicted that an HMMC-based PV system with the aforesaid control methods has sufficient merits to become a potential candidate for high power PV integration. [ABSTRACT FROM AUTHOR]

The prime facets for the control of grid integrated voltage source converters (VSC) during abnormal grid variations are the control of voltage as well as power quality. In this article, a unique control strategy is presented for the control of solar photovoltaic (PV) system interfaced to the grid utilizing an interweaved generalized integrator. A single-stage three-phase topology is considered. The primary purpose of control is to deliver the PV power to the grid even during various abnormal grid variations. During normal operation, the system delivers power at unity power factor. However, during variations in the grid voltage, the profile of the PCC voltage is maintained within prescribed limits by reactive power injection. Moreover, LVRT operation is undertaken during severe voltage sags. The utilization of the system is increased in the absence of PV generation during night, the VSC and dc link capacitor act as a distribution static compensator. Contrary to traditional control techniques, power quality of the system is not compromised. The achievements of the control are demonstrated through simulation as well as with hardware implementation. Furthermore, a comparative analysis, with the state-of-the-art techniques, is highlighted, which shows the efficacy of the presented control. [ABSTRACT FROM AUTHOR]

A multilevel topology for photovoltaic (PV) systems with integrated energy storage (ES) is presented in this article. Both PV and ES power cells are connected in series to form a dc link, which is then connected to an H-bridge to convert the dc voltage to an ac one. The main advantage of the proposed converter compared to the cascaded-H-bridge (CHB) converter, as well as compared to the available multilevel topologies, is that fewer semiconductor devices are needed here. As the output voltage levels increase, more switches are saved, which results in a more efficient, cheaper, and smaller converter. So far, there is still no modulation strategy that is designed particularly for PV-fed multilevel converters with built-in ES. The standard modulations are impractical for such an application since they suffer from deficiencies, such as polluted output signals—thus, requiring larger output filter—and overmodulation. A modified modulation strategy for PV+ES multilevel inverters is, therefore, introduced in this article. The proposal has been simulated and experimentally validated to evaluate its effectiveness, where it has been shown that the proposed topology is not exclusively feasible, but also suffers from less conduction and switching loss, achieving higher efficiency with respect to its counterpart CHB. [ABSTRACT FROM AUTHOR]

Globally, the installed capacity of photovoltaic (PV) power plants is undergoing rapid growth. However, the random output power fluctuation of PV plants has brought great challenge to power system stable operation. One of the most effective approaches to counteract the impact of power fluctuation is to carry out power forecasting under ultra-short-term scales, among which the second-level power forecasting technique is still absent since the pure historical data analysis of PV plant output power cannot deal with the sudden output power change induced by moving cloud and the traditional cloud image detection methods actually fail to achieve accurate PV power forecasting in high temporal and spatial resolutions. This article proposes an inverter-data-driven method to achieve the second-level PV power forecasting. In specific, multilayer feed-forward artificial neural network based on the error back propagation algorithm is applied to first establish the mapping relations from shading conditions of PV array to its corresponding output power. Combining with output power of neighboring PV arrays as well as their geographical location information, the shading conditions of those shaded PV array can be reversely deduced. And then, the deduced shading conditions of all PV arrays will be converted into one virtual cloud image to identify the instant cloud characteristics. In consequence, the consecutively generated virtual cloud images can depict the moving direction, speed, and shape of shading cloud and then help easily realize the second-level power forecasting of PV plant. Case study and experimental results verified the performance of the proposed method. [ABSTRACT FROM AUTHOR]

The application of the dual-mode time-sharing technique in novel transformerless photovoltaic (PV) inverters is proposed and investigated. The simultaneous high step-down or high step-up conversion with 97.6% peak efficiency and injected current with total harmonic distortion < 2% are achieved. The leakage current problem, which is a main concern with the transformerless PV inverters, is around 20 mA. The indirect current control, especially at transition of modes of operation is highly improved by utilizing a fast dead-beat control scheme. The working principles of the proposed converter show that the step-down and the step-up voltage gains are (D/(1-D))2 and D/(1-D)2, respectively. Furthermore, a 1 kW, 220 VAC and 200 VDC experimental prototype is implemented to confirm the theoretical achievements. [ABSTRACT FROM AUTHOR]

This article proposed a multiport converter (MPC) configuration for a photovoltaic (PV) battery system. In the proposed design, the battery charging and discharging circuits are integrated with the PV power optimizer through high-frequency ac link. The proposed converter system is capable of regulating the output voltage, following battery charging profile and tracking the maximum power point (MPP) of each PV module. Variable switching frequency is used to achieve maximum power point tracking in this design. All the switches of the converter are able to achieve soft-switching turn-on and turn-off at different operating conditions. The operating principles and the control strategy of the proposed converter are presented. Simulation results and experimental results on a 175-W system are presented to validate the features of the proposed converter. [ABSTRACT FROM AUTHOR]

Power hardware-in-the-loop (PHIL) simulations have been rapidly growing in recent times due to the flexibility it offers in conducting various system-level studies as well as individual device evaluation. Evaluating a power converter has been one of the major applications of PHIL at recent times in the industry. Following this trend, this article proposes a way to evaluate a photovoltaic (PV) microinverter in PHIL arrangement. The mathematical background to quantify the stability criteria for a PHIL network is presented along with theoretical and experimental verifications. The methodology in this article is based on the model of interface devices and accurate delay model to analyze the stability of a PHIL system employing Routh–Hurwitz's formulation. An extensive analysis on stability along with the compensator design to enhance the stability limit of a PHIL system is presented. The workflow developed is applied to evaluate a 250-W PV microinverter, which showed a stable performance with more than 97% efficiency during steady state and transients. [ABSTRACT FROM AUTHOR]

Distribution lines are generally protected by overcurrent relays. With the integration of an inverter-interfaced solar photovoltaic (PV) plant having a current-limiting feature, the fault current seen by the relay on the PV side of that feeder becomes comparable to the load current. The conventional overcurrent relaying principle is not suitable for distribution line protection. Distance relay may be a viable option for protection of distribution lines connecting the solar PV plant. However, positive- and negative-sequence source impedances of the PV plant depend on an inverter controller, which results in limited performance of fixed setting distance relay. This article proposes an adaptive distance relay setting to protect distribution line connecting the PV plant, using prefault voltage and current data at the relaying point. The method calculates positive- and negative-sequence PV source impedances for boundary setting of distance relay at the PV side. The proposed trip boundary is modified adaptively with the change in prefault conditions of the PV plant. Performance of the proposed method is tested for different control strategies and operating capacities of the PV plant and variation in the grid source impedance on a 34-bus distribution system. Real-time application of the proposed method is validated in hardware-in-the-loop using OPAL-RT simulators with IEC 61850 as the communication protocol and found to be accurate. [ABSTRACT FROM AUTHOR]

To improve the power conversion efficiency of a three-phase dual-active-bridge (3P-DAB) converter for low-voltage direct current distribution systems, a practical design methodology is proposed. Commonly, the 3P-DAB converter is designed by only specification, such as the rated power, input/output voltage, and frequency. However, using the conventional design method, the efficiency is low under heavy load conditions due to the high conduction loss. In this article, based on the practical power loss analysis, the effective design methodology of the coupling inductance in the 3P-DAB converter is proposed, focusing on power conversion efficiency. It can mitigate the drawbacks of the common design by reducing the peak and rms phase current and the insulated-gate bipolar transistors turn-off current. Experimental results verify the validity of the proposed design methodology and controller using a 25-kW prototype 3P-DAB converter. [ABSTRACT FROM AUTHOR]

Tunability in magnetoelectric (ME) gyrators is of importance for realizing controllable energy-efficient electronics. Here, we investigated a novel passive control method that exhibits a high frequency tunability of up to 370 Hz using a non-power-consuming (passive) capacitor approach. The method requires zero external controllable power as the frequency is changed. This tuning does not decrease the power conversion efficiency (86%) of the gyrator. Our results indicate that the internal mechanical reactive components need to be changed by passive external capacitors, which proves to be an effective way by which gyrators can achieve high tunability and retain high power conversion efficiency. This article opens an approach toward the design of new tunable circuit components. [ABSTRACT FROM AUTHOR]

Two-stage power conversion of class-D amplifier with front-end switching mode power supply affects the power conversion efficiency of audio amplifier system. Single-stage inverter (SSI) developed from cycloconverter can be used as audio amplifier to improve efficiency. However, current commutation of cycloconverter switches challenges for high efficiency and low total harmonic distortion (THD). In this article, a bipolar phase shift modulation (BPSM) SSI is proposed for high efficiency low distortion audio amplification. Full bridge active clamp (FBAC) circuit is used to clamp the voltage across cycloconverter switches and recycle the energy of filter inductor and leakage inductance. By using active clamp, utilization of magnetizing inductance current and optimization of driving sequence of clamp switches, zero voltage switching of the proposed BPSM FBAC-SSI is achieved over wide range. With BPSM and voltage clamp across cycloconverter switches, low THD of output voltage is also achieved. A 200 kHz prototype with 250 W output power is presented to verify the analysis results of the proposed BPSM FBAC-SSI. [ABSTRACT FROM AUTHOR]

In this article, we have carried out a comprehensive study on the wireless power transfer (WPT) concept from the rectifier circuit construction and state-of-art GaN Schottky barrier diode (SBD) device technology to the WPT system demonstration. Benefited from the wide bandgap, high mobility, and saturation velocity of the gallium nitride (GaN) two-dimensional electron gas, engineered lateral GaN SBD with low turn-on voltage (Von) of 0.47 V, on-resistance (Ron) of 4 Ω, breakdown voltage of 170 V, and junction capacitance $(C_{j})$ of 0.32 pF at 0 V bias are achieved, which satisfy the fundamental requirements for microwave power rectification. After incorporating the high-performance GaN SBD into the optimized rectifier circuit, high radio frequency (RF)/dc conversion efficiency of 79% is achieved, and the input power of per single GaN SBD is increased by 10X when compared with that of a commercially available silicon (Si) SBD at the same efficiency of 50% and frequency of 2.45 GHz. Based on the rectifier circuit, a microwave power transfer system is constructed with 400 light emitting diodes lighted up, verifying the great promise of adopting high-power GaN SBD for the wireless high-power transfer as an alternative energy-harvesting technique for future WPT application. [ABSTRACT FROM AUTHOR]

As the “brain” of the modern photovoltaic power systems, dc solid-state transformers (SSTs) are playing an increasing important role in integrating different photovoltaic modules, batteries, and supercapacitors. This paper aims at improving the conversion efficiency of dc SST for a wide operating range by minimizing the backflow power of the dc SST system. First, the mathematical model of the backflow power from both input and output sides of dc SST is obtained. Then, the penalty function is derived and an enhanced triple phase shift control (ETPS) strategy is proposed to minimize the backflow power for various transmission power and voltage conversion conditions. A comprehensive comparison of the proposed ETPS with other advanced control strategies was carried out through theoretical analysis and experimental tests. Main experimental results are illustrated to verify the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Energy imbalance market (EIM) provides an opportunity that allows larger shares of variable renewable energy sources in the grid. Under highly volatile weather conditions, an accurate forecasting of photovoltaic (PV) power is necessary for grid stability and market operation. Most of existing forecasting methods strongly rely on the accuracy of measurements, and the adaptability of these methods to complex weather conditions is rarely discussed. In this paper, a weather classification multivariate adaptive regression spline (MARS) forecasting model is introduced for complex weather conditions in all seasons. It can be updated incrementally and its high computational efficiency satisfies EIM operations. A data set that consists of the historical power and meteorological parameters produced by a small-scale PV platform is classified and used to train MARS models with forecast horizons ranging from 15 min to 24 h in different seasons. The tests and analyses results indicate higher accuracy, adaptability, and efficiency of the novel model. [ABSTRACT FROM AUTHOR]

This paper proposes an improved maximum power point tracker (MPPT) for photovoltaic (PV) system. The scheme is a hybrid between the adaptive perturb and observe and particle swarm optimization (PSO). The algorithm incorporates the search-skip-judge (SSJ) mechanism to minimize the region within the P−V curve to be searched by the PSO. Furthermore, the PSO performance is enhanced by ensuring that the regions that have been previously explored (by other particle) will not be searched again by (another particle). Thus, the unnecessary movement of particles is minimized—leading to faster convergence. The proposed method is evaluated against four well-known MPPT techniques, namely the modified incremental conductance, the original version of SSJ, the modified cuckoo search, and the hybrid PSO. In addition, an experimental prototype, which is based on PV array simulator is used to verify the simulation. The competing algorithms are tested with a buck-boost converter, driven by the TMS320F240 DSP on the dSPACE DS1104 platform. It was found that the proposed scheme converges to the global maximum power point (GMPP) most rapidly and the GMPP tracking is guaranteed even under complex partial shading conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The employment of solar microconverter allows a more detailed monitoring of the photovoltaic (PV) output power at the single module level; thus, machine learning techniques are capable to track the peculiarities of modules in the PV plants, such as regular shadings. In this way, it is possible to compare in real time the day-ahead forecast power with the actual one in order to better evaluate faults or anomalous trends that might have occurred in the PV plant. This paper presents a method for an effective fault diagnosis; this method is based on the day-ahead forecast of the output power from an existing PV module, linked to a microconverter, and on the outcome of the neighbor PV modules. Finally, this paper also proposes the analysis of the most common error definitions with new mathematical formulations, by comparing their effectiveness and immediate comprehension, in view of increasing power forecasting accuracy and performing both real-time and offline analysis of PV modules performance and possible faults. [ABSTRACT FROM AUTHOR]

The development of a photovoltaic ac module composed of a high static gain nonisolated dc–dc converter with current source output characteristic followed by an unfolding low-frequency inverter is presented in this paper. The operation of the dc–dc converter with high static gain and with reduced switch voltage is obtained using the Cuk converter integrated with the switched-inductor technique. The nonisolated structure allows the elimination of the volume and losses of the power transformer and leakage inductance, and an output filter configuration is proposed to reduce the high-frequency ground leakage current. The grid-tied inverter operating in a discontinuous conduction mode (DCM) allows a sinusoidal output current with low harmonic distortion (THD = 3.72%) to be obtained without current control loop and without the use of a current sensor at the output. The maximum power point tracking operation is obtained without the use of the current sensor. The DCM operation increases the current stress, but the proposed converter presents two switches and two input inductors sharing the input current in these components. The theoretical analysis, design procedure, and experimental results are presented for a prototype with a dc input voltage Vi = 30 V, an ac output voltage Vo = 127 V, and output power Po = 180 W. [ABSTRACT FROM AUTHOR]

This paper explores a power-conversion system for single-phase transformerless ac module application. A nonisolated high-gain dc–dc stage is coupled with a doubly grounded dynamic dc-link inverter to implement the microinverter topology. The front-end boost stage steps up the single-module voltage to a higher dc voltage, typically to 200 or 400 V as required for the following inverter stage. It is a hybrid of an interleaved boost and switched capacitor concept capable of achieving high gain while simultaneously maintaining reduced voltage and current stress, and thus lowering switching and conduction loss for most of the switches. By directly connecting the grid neutral to the photovoltaic (PV) negative, the doubly grounded voltage swing inverter has the advantage of zero capacitive-coupled common-mode ground currents, critical for transformerless PV inverters. The two dc links of the inverter stage share the double-line frequency power decoupling with a combination of higher value of mean voltage and relatively large 120-Hz ripple component–the dynamic dc-link approach. Through an optimization algorithm, the decoupling capacitance is minimized enabling an all-film capacitor implementation while satisfying the converter's operating constraints over a wide range of power factors. The simulation as well as experimental results from a GaN-based hardware prototype validate the converter's performance. [ABSTRACT FROM AUTHOR]

Due to the nonlinear characteristics of a photovoltaic (PV) array, its regulation is highly dependent on the operating point. Focusing on a dc–dc boost converter, this paper first shows how the PV voltage and inductor current controls are affected by the PV array. It then proposes to emulate an impedance virtually connected to the PV array, making it possible to greatly improve the control robustness. Thanks to the proposed strategy, the crossover frequency variation for the whole operating range is reduced from 42 times for the traditional control to 3.5 times when emulating parallel resistance or to 1.4 times when emulating series and parallel resistances, all with simple implementation. Experimental results with a commercial PV inverter and a 4-kWp PV array validate the theoretical analysis and demonstrate the superior performance of the proposed control. [ABSTRACT FROM AUTHOR]