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This paper studies the coordinated use of smart inverters with legacy voltage regulating devices to help increase the energy savings from conservation voltage reduction (CVR) in distribution systems with high photovoltaic penetration. Two voltage optimization algorithms are developed to evaluate the CVR benefit by considering two types of smart inverter functions: aggregated reactive power control and autonomous volt/VAR control. In each algorithm, smart inverters are coordinately controlled with the operation of legacy voltage regulating devices including load tap changers and capacitor banks. Both algorithms are tested on representative utility distribution system models. Simulation results demonstrate that the proposed algorithms can achieve around 1.8-3.6% energy savings when only using legacy voltage regulating devices and an additional 0.3-0.9% when adding smart inverters.

There are many photovoltaic (PV) applications where lighter weight and/or bendable PV power would be beneficial. This includes the curved surfaces of buildings, buildings with weight limitations, boats, automobiles, or other portable applications. In many of these cases, the bending will be only a single occurrence at installation or the amount of bending, even if repeated, is not dramatic. This allows for crystalline silicon modules to be used. For flexible applications, the dominant material for the frontsheet is polyethylene tetrafluoroethylene (PETFE). As a fluoropolymer it resists soiling, is UV stable, and PETFE is a more mechanically durable fluoropolymer. However, in the interests of keeping costs down, less expensive alternative polymers are desirable. In this study, highly accelerated ultraviolet light and heat stresses are applied to candidate materials and the degradation kinetics are determined to provide information to evaluate their suitability for use in a PV application.

This paper presents a reliable microgrid for residential society with control methods to design grid forming inverter (GFI) to emulate the seamless-synchronization features to deal with the dynamic concerns of the grid. In this microgrid a photovoltaic (PV)-based GFI with a control scheme in parallel with a PV-battery supported inverter with an enhanced current control is considered to operate under non-ideal grid voltage conditions. The PV-GFI is adaptable to operate either in islanded mode (IAM) or grid integrated mode (GIM) depending under the grid conditions. An adapted power control technique is implemented such that power demand of local loads and harmonic currents are compensated by respective distributed generation. Moreover, the active power demand of all local loads is shared between the main grid and respective local DG. The adapted power controller achieves transient free operation even under the load disturbances. The proposed control methods of microgrid are validated in simulation under various operating conditions.

In a power system with a high-share of photovoltaic systems, the frequency response can be improved by the participation of photovoltaics in frequency control. If the photovoltaic system operates at reduced power, in a so-called de- loaded mode, and maintains a specific amount of power reserve, then participation in system frequency control is usually realized by a droop control method. The implementation of this method is very simple, but it does not provide the recovery of PV power reserve before the secondary frequency control reacts. This means the PV system cannot provide additional support to the grid if a new disturbance occurs in a short time following the first one. This paper presents a novel approach for PV system control in providing support to system frequency. The novel control algorithm aims to enable rapid recovery of PV power reserve which makes the PV system capable of providing support to the cascading disturbance events. The development of such PV system control model is based on a detailed mathematical analysis of the dynamic frequency response. The effectiveness of the proposed method was tested on a two-area multi-machine power system model and through 4 different study cases.

After booming from 2009 to 2012, the German photovoltaic (PV) industry suffered from drastically reduced feed-in tariffs (FITs). With around 3 GWp of newly installed nominal PV capacity in 2013 and a predicted drop to around 2 GWp of additional nominal capacity in 2014 (there had only been 1.03 GWp added by July), the growth of the German PV market has reached 2008 levels (see Figure 1). But with more than 1.5 million PV plants and a total of approximately 38 GWp of nominal capacity, Germany is still the country with the largest amount of installed PV capacity in the world. The political aim is to reach 52 GWp by 2020. In 2013, PV systems provided 6.5% of nationwide electricity consumption (see Figure 2) (RES in total 24%) and covers regularly with up to 20?23 GW on sunny summer days around one-third of the noon peak of around 50?75 GW. As of today, PV systems are already the major source of electricity in Germany when installed capacity is viewed broken down by specific electricity source (see Figure 3).

This paper presents the internal energy balance of a modular multilevel cascade converter with photovoltaic arrays as distributed energy resources. This converter is characterized by a modular arm structure composed of bidirectional cascaded chopper cells with floating DC capacitors, where each cell is connected to a photovoltaic array through a DC/DC converter. A continuous model and a control method are proposed to maintain the internal energy balance and achieve independent voltage control of all the floating DC capacitors, allowing the tracking of the maximum power point for each photovoltaic array. The operation with asymmetric energy generation at different levels of irradiance is discussed to maintain the internal energy balance without distortions in the DC link and AC output currents, focusing on the operation with individual cells with zero energy generated from PV array. This topology and control method is suitable for hybrid multi-terminal high voltage DC systems and hybrid generation systems, such as wind-solar energy systems. Experiments are presented to validate the proposed model and control method.

For microgrid with high photovoltaic penetration, the optimized energy management strategy can not only improve the microgrid benefits effectively, but also ensure the safety and stability of island microgrid. This paper establishes a multi-objective energy optimization model of the microgrid with high photovoltaic penetration based on the photovoltaic operation and maintenance costs, the energy storage system operating life loss, the thermal power environmental pollution and governance costs, the electricity trading from grid, and the fine for controllable load shedding. Then obtain energy optimal management strategy by particle swarm algorithm with inertial weight factor. Finally, the proposed energy optimal management system is verified on a typical microgrid by simulation.

This paper introduces a new active-neutral-point clamped (ANPC) seven-level inverter with a switched-capacitor technique. The introduced inverter generates a seven-level ac output voltage with a maximum voltage-boosting gain of 1.5. Also, a simple modulation technique was proposed, where the capacitors voltages are naturally balanced by the series-parallel connection of the input voltage source. Compared with seven-level inverter topologies, the proposed topology is simpler and its control system does not requires sensors or balancing circuits to stabilize the dc-link voltages. Additionally, the dc-link voltage requirement is reduced by 33.33%, eliminating the need for an intermediate dc-boosting stage and making the introduced inverter a good candidate for applications such as photovoltaic panels and full-cells systems, both characterized by a low input voltage. The operation and performance of the proposed topology is validated through simulation and experimental results.

The solar micro-inverters are becoming popular due to their modularity and capability of extracting maximum available power from each of the solar photovoltaic (PV) modules. The single stage transformer-less micro-inverters are being preferred because, their power conversion efficiency is high. A new single stage transformer-less micro-inverter topology is proposed in this paper which can generate an ac output of 220 V from 35 V PV module. In this topology, it has been achieved that, the voltage across the PV terminals are not polluted by 100 Hz ripple, which is generally the limitation encountered by the converter interfacing single phase ac with the dc system. In this topology, the PV ground is shorted with the neutral of the grid, and hence the magnitude of the leakage current is negligible. The viability of the proposed converter is verified by performing detailed simulation studies on MATLAB/Simulink platform.

In this paper, the generic analysis and design of Zero-Voltage-Switching (ZVS) multi-phase AC/DC converters are proposed. With the Edge Aligned PWM (EA-PWM) scheme, all switches of ZVS multi-phase AC/DC converters can realize ZVS operation. Besides, the switching frequency is fixed and the auxiliary switch only operates once in each switching period. Its operation stages in a switching cycle are analyzed and a generic ZVS condition is derived. Based on the proposed theory, a ZVS two-stage three-phase photovoltaic (PV) inverter is investigated, which is regarded as a 5-phase converter. Its ZVS condition under different working conditions is discussed. Finally, a 10kW prototype with 150kHz switching frequency of the ZVS two-stage three-phase PV inverter is built and the experiment results are given to verify the analysis. In addition, the extension of the ZVS multi-phase converter in different applications is introduced.

This paper presents a coupled-dc power module based cascaded multilevel converter integrating utility-scale photovoltaic generations (CDPM-PV). CDPM-PV inherits merits like modular structure, distributed maximum power point tracking (MPPT), direct distribution grid access, from cascaded H-bridge based PV system (CHB-PV). But, it supplies more flexible power routes than CHB-PV, through coupling different dc-links. Power routes are intended for enlarging the entire operating range including conditions of active power mismatch arising from non-ideal elements like partial shading and parameter variations. The system construction with its self-balancing principle is firstly introduced. Switching states for different operating regions are then derived based on the principle of easing implementation. Based on these, a modulation strategy including initial switching pattern selection and coordinated power routing is proposed to allow module-mismatches. Operating ranges are also analyzed and compared with conventional CHB-PV. Simulation results of a 3MW/13.8kV system developed in Matlab/Simulink platform, and experiment results based on a 2.4kW/311V setup are presented and have demonstrated that the CDPM-PV topology with proposed modulation strategy can not only ride through a larger range of module mismatches, but also improve solar power utilization and system efficiency owing to non-compromised MPPT.

This paper proposes an improved hybrid parallel compen-sator (IHPC) for enhancing the power transfer capability of a photovoltaic (PV) grid-connected inverter. A thyristor switched capacitor (TSC) module is used in series with a conventional inductive-coupling voltage source inverter (IVSI) to reduce the DC-link voltage. Under a low DC-link voltage, the voltage across the insulated gate bipolar tran-sistor (IGBT) will also be low, which will reduce the voltage stress of the IGBT, thereby improving the reliability and reducing the loss of the VSI. First, the mechanism of reac-tive compensation for improving the PV inverter power transmission capability is analyzed. Then, the circuit con-figuration and operating principle of the IHPC are intro-duced. After that, an optimal control strategy for the IHPC is proposed to address the resonance problem caused by the TSC connected in series with the L filter and to improve the compensation performance of the IHPC. Finally, the effec-tiveness of the proposed IHPC and the control method is validated by the simulation and experiments. The results show that the IHPC with optimal control strategy can achieve continuous reactive power compensation under a low DC-link voltage, thereby enhance PV power transfer capability.

The control of a microgrid is quite challenging thus this work implements a robust and fast control technique based on circular limited cycle oscillator frequency locked loop with inner loop filter (CLO-FLL-WIF) for switching operation between an islanded and the grid-connected modes. This microgrid combing solar PV (Photovoltaic) generation, SyRG (Synchronous Reluctance Generator) for pico-hydro generation, and the battery, which works in both standalone and grid-connected modes while feeding local loads uninterruptedly. The output power conversion of a PV array is influenced by irradiation of solar PV array and has low efficiency, therefore, a MPPT (Maximum Power Point Tracking) namely an INC (Incremental Conductance) method is used. In the implemented system, the interfaced power converter is gated in the grid-connected mode and islanded mode using same enhanced second order generalized integrator with a modified frequency locked loop (ESOGI-MFLL) control method. The comparative results validate that the response of ESOGI-MFLL in comparison to the existing control algorithm, is faster under load and generation perturbations. The implemented control techniques are used for fundamental extraction of load component of voltage and current for assessment of reference currents with their respective phases of synchronization while maintaining the required IEEE power quality standard-519. Simulated results of a microgrid for grid-tied PV-BES-SyRG are obtained in MATLAB/Simulink platform to demonstrate its performance.

The reduction in the cost of PV energy is still required to be competitive as an alternative energy source. The efficiency and reliability of PV inverters are important aspects to be enhanced to reduce the cost of PV energy since it is closely related not only to the annual energy production but also to the reduction of operational and maintenance costs of PV systems. In this paper, a single-phase IT-type NPC inverter with one-leg clamping pulse width modulation (OLC-PWM) is proposed for efficiency and reliability improvements. The proposed IT-type NPC inverter with OLC-PWM can improve the efficiency by taking the advantages of I-type and T-type NPC inverters regarding the power loss. Furthermore, its reliability has been improved compared with conventional I-type and T-type NPC inverters. The IT-type NPC inverter also has an ability to balance the neutral-point voltage. The superiorities of the proposed IT-type NPC inverter in terms of reliability and efficiency are validated through the simulations and experiments by comparing the reliabilities and efficiencies of the conventional I-type and T-type, asymmetric I-type and T-type and IT-type NPC inverters.

This article proposes a supervised learning approach for centralized localization of faults in microgrids with radial configuration that can operate in grid-connected or islanded mode. The key concept is to identify faults by learning and analyzing the features of voltage and current disturbances detected by a microgrid central protection unit. Two algorithms are developed that determine fault indices and transient features for simulation-based training, classification, and backup protection purposes. The proposed data-driven approach is effective under high penetration of distributed energy resources (DERs), and is robust under microgrid topology variations. Moreover, it requires few sensors (two for radial structure) and is easy to implement, yet provides high degree of reliability. The performance and accuracy of the developed approach are verified through extensive simulations of low-voltage microgrids that incorporate different types of DERs, including wind and solar photovoltaic systems.

In this paper, a physics-data-based detection method is proposed to detect a variety of cyber-attacks in Photovoltaic (PV) farms using the power electronics-enabled harmonic state space (HSS) models, which, to our knowledge, is original. At the device level, HSS-based detection is developed to monitor harmonic vectors of individual PV converter with minimum sensor measurements, thus improving accuracy and robustness compared to Kalman Filter-based detection. At the system level that involves multiple PV converters, a clustering approach is developed to investigate attack propagation and accurately locate attack sources within a PV farm. The proposed approach is one of the first attempts to address PV security through interaction between the device and system, maximizing the accuracy and robustness at different levels. To verify the feasibility, a comprehensive attacks model is built, including single attack, coordinated attacks, and replay attacks. Besides, the impacts of irradiance changes are taken into consideration in the test scenarios. With the real-time data acquisition and hardware-in-the-loop testbed, comprehensive test results are provided to verify the feasibility of the proposed detection methodology.

This article presents a dual-stage coordinated control approach for voltage regulation and congestion management of active distribution networks (ADN) in the presence of photovoltaic (PV) generators and electric vehicle stations (EVS). The proposed scheme operates on rule-based model predictive control (RBMPC) to optimally manage the settings of the regulating devices, i.e., on-load tap changer (OLTC), distribution static synchronous compensator (DSTATCOM), PV generators, and EV inverters that possess different temporal characteristics. The first (hourly time-scale) and the second (one-minute time-scale) stages of the dual-stage coordinated control mechanism are designed to correct the long-term and short-term voltage fluctuations, respectively. The objectives of the proposed approach are to minimize the number of OLTC operations (first stage) and changes in set-points of PV and EV inverters, and DSTATCOM (second stage) in addition to minimization of slack variables, energy loss, and voltage error at EV stations. In both the stages, predefined rules are set for MPC to optimize different objectives on the basis of the magnitudes of bus voltages. Simulations are performed on 33-bus and 38-bus distribution networks to test the efficacy of the control approach. It is observed that the proposed approach could mitigate the voltage variations as well as line congestion for different scenarios.

Photovoltaic (PV) power generation plant with integrated battery energy storage (BES) is becoming increasingly attractive and necessary as the PV penetration increases. Traditional solutions involve two paralleled inverter systems at the same site. This increases the balance of the system cost as well as the control complexity. Furthermore, high-power step-up transformers are needed to connect to the distribution grid, further increasing the capital cost, land use and installation cost. Combining PV and BES into a single inverter system without the 60Hz step-up transformer is therefore very attractive as the next generation technology for utility scale solar. This effectively calls for the development of a PV+BES Solid State Transformer (PVS-SST). This paper proposes a 13.8kV/3MVA PVS-SST targeting 13.8 kV grid connection on the AC side and 1500V PV farm on the DC side. The PVS-SST utilizes a modular SST concept with total 27 SiC submodules. Each submodule is based on 1700V SiC power MOSFET devices and single stage DAB-based DC/AC power conversion technology. In order to utilize the inevitable parasitic capacitances in the actual hardware, a novel turn-off loss model is proposed and experimentally verified. A comprehensive optimization strategy including the proposed novel turn-off loss model, ZVS range, deadtime calculation, and minimum circulation current is proposed. Medium frequency transformer (MFT) design to achieve very high efficiency and isolation voltage is a grand challenge in the proposed PVS-SST and is discussed in detail. The power-density of the SiC power submodule is 1.6MW/m3 (26W/inch3). The PVS-SST control architecture is discussed with a focus on voltage balancing and real and reactive power controls.

In this work, a reverse saliency (RS) spoke-type permanent magnet (PM) synchronous motor (PMSM) besides its hybrid adaptive notch filter (HANF) based self-sensing for driving a solar photovoltaic water pump system (WPS) is presented. The conventional spoke-PMSM driven WPS experiences two types of problems. Firstly, the motor is operated with a flux-weakening current to produce positive reluctance torque, thereby increasing the PM demagnetization risk. Secondly, an encoder is used to sense the rotor angle, which in turn affects the cost and reliability. To solve the first problem, the RS-PMSM is presented, which operates with a flux-intensifying current to produce positive reluctance torque. While second issue is resolved by using the HANF based rotor angle estimation. Although conventional methods give an estimate of rotor angle, they do not eliminate both the DC-offset and dominant harmonics. The superiority of both the RS-PMSM and HANF over existing solutions, is shown respectively by using finite-element methods and MATLAB/ Simulink based performances. Besides, a prototype motor is also manufactured. The performance of RS-PMSM prototype along with its HANF based self-sensing is obtained in the laboratory and various test results are reported. Meanwhile, a comparison of the HANF with available self-sensing techniques, is also performed.

A novel single-switch coupled-inductor switched-capacitor (CISC) high step-up converter is proposed which has a boost-type input structure allowing an improved input current ripple compared to other leading CISC converters. This is important for sustainable energy applications such as photovoltaic (PV) cells and fuel cells where high current ripple can degrade performance or lifetime. Though large input filters can be added between the energy source and the boost converter to smooth a pulsed converter input current, the proposed converter naturally has a more moderate current ripple, reducing the need for additional filtering. With regards to the coupled inductor, the leakage inductor energy is recycled without using an extra clamped circuit, and core utilization is high. The detailed theoretical operation is presented and an experimental prototype (200 W, 36 V to 48 V input, 400 V output) achieves a maximum efficiency of 97.1%.

The aim of this article is to select the optimum green energy sources for sustainable planning for a region. This research presents an integrated model based on theoretical base of benefit, opportunities, costs, risks and a well-known multicriteria decision-making technique, i.e., the analytical hierarchy process, to evaluate the green energy sources from northeast India along with 16 local factors. The analyzed result shows that solar photovoltaic is the optimum green energy source having the highest score value followed by other sources, appraised by the integrated model. Based on the results this article, we suggest some policies for the energy managers, policymaker, and decision makers. This article has both theoretical and practical implications. Theoretically, it contributes holistic measures for designing and managing the green energy sources selection framework for sustainability, and, practically, it helps various organizations operating in the green energy sources selection sector to improve their sustainability dimension for the cleaner future. The proposed article considers not only various cost criteria, but also all other criteria, such as power generation, implementation period, and useful life, that are considered to select the optimum green energy sources for the better future. The findings of this article can provide useful information to energy decision makers and serve as a reference for Tripura's energy policy.

Different harmonic mitigation techniques have been utilized in grid-connected inverters to suppress the effect of grid voltage distortion on the output current of these inverters. In practice, to scale up the injected current into the grid, a set of parallel grid-connected inverters are often utilized rather than a single high-power inverter in solar Photovoltaic or motor drive systems. Conventional Point of Common Coupling (PCC) feedforward approaches have been used for harmonic rejection of multi-parallel grid-connected inverters. However, these methods need to implement a separate feedforward scheme for each individual inverter. In this paper, a novel full PCC voltage feedforward strategy is proposed to reduce the cost investment, which is implemented only in one of the grid-connected inverters. The proposed strategy is based on cancelling the total parallel admittance of the system by adding a virtual negative admittance to the target inverter. It is shown that the proposed scheme causes no instability issue on the system since it does not affect the system phase margin. To verify the efficiency of the proposed strategy against emitted harmonics from the grid, simulations and experiments on a system with two parallel single-phase grid-tied inverters are performed.

This paper proposed a simplified flying capacitor voltage (FCV) control strategy based on hybrid clamped three-level boost converter (HC-TLBC). 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 (HVPS) with multiple dc inputs. In this paper, 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 pre-charge strategy for flying capacitor is also provided in this paper. The performance and analysis of the proposed strategy are verified by the experiments at last.

In the existing solar photovoltaic modules, cells are connected in series. The performance of the series-connected module degrades severely during partial shading condition. Further, the use of bypass diode causes multiple peak (local and global peaks) problem. Therefore, total cross tied (TCT) connection has been proposed in this paper to connect the cells in a module (TCT connected module) that gives a better performance during partial shading without multiple peak problem. A novel analytical algorithm is presented in this paper, which will help the photovoltaic installers to estimate the output power of a TCT connected module without using any sophisticated measuring instruments except irradiance and temperature measurement. The proposed analytical algorithm is simple, robust and user friendly, which can be widely used in multidisciplinary research. The output of the proposed model is verified with the simulation and laboratory scale experimental results, which shows less than 4.58% error. Moreover, the proposed algorithm is implemented in 10MW solar plant, which shows around 174.44% performance improvement compared to the existing TCT connected array. Further, the current value of the TCT connected module is very high, which can be effectively used in high current applications such as welding even in partial shading condition.

Every network contains different characteristics. In particular, microgrids have unique features compared to utility grids such as high resistance to reactance ratio(R/X). Consequently, both active and reactive current injection is likely to improve the dynamic voltage stability (DVS) of the islanded microgrids. Therefore, instead of injecting only reactive current, both active and reactive current is injected in the proposed voltage support(VS) strategy. Contrarily, without considering the distinctive characteristics of the network, other strategies with both active and reactive current injection provide fixed and uniform active and reactive current for all networks. To convey the distinctive features of network, voltage sensitivity subject to active and reactive current injection is used in the proposed VS strategy. As a consequence, unlike other strategies, the proposed strategy provides unique combination of active and reactive current for every network. The concept and derivation of the proposed strategy is described. Voltage sensitivity analysis is carried out to determine the sensitivity coefficients. The effectiveness of the proposed strategy is theoretically demonstrated and compared with other strategies. Case studies and result analysis on two islanded microgrids show that the proposed VS strategy for photovoltaic system is capable of enhancing the DVS of islanded microgrids compared to other strategies.

Recently, inverters with a common ac and dc ground are gaining significant interest due to their zero common-mode voltage that made them particularly attractive for the solar photovoltaic application. However, the dc source current of the existing topologies is discontinuous, and their voltage gains are limited. This article proposes a novel common-ground-type boost inverter that achieves continuous dc source current with significantly enhanced dynamic voltage gain. It consists of one boost inductor, four capacitors, nine power MOSFETs, and two power diodes. Voltage boosting and generation of nine-level ac voltage are achieved concurrently within a single-stage operation. The operation of the proposed CGT-9L-BI inverter is analyzed. Simulation and experimental results are presented for validation.

The conventional maximum power point tracking (MPPT) controllers are unable to track the global maximum power point (GMPP) during partial shading conditions (PSCs). As a result, many optimization strategies have been used to track the GMPP. Optimization approaches, on the other hand, are iterative methods that cannot distinguish uniform shading conditions (USCs) from PSCs. In this paper, a new partial shading detection approach has been hybridized with the new modified rat swarm optimization algorithm (MRSO). It successfully distinguishes USCs from PSCs in two samples and triggers the MRSO only when the PSC is detected. Consequently, it avoids the excessive global peak search during the USCs, which improves the tracking time for USCs without an unnecessary scan of the entire P–V curve. Furthermore, the proposed MRSO, is simple to implement with simple tuning parameters and fast tracking speed for PSCs. The proposed method has been experimentally validated on a boost converter with a sampling time of 0.05 s. The experimental results showed the successful implementation of the proposed method with an average tracking time for uniform and PSCs of 0.42 s with an average steady-state efficiency of 99.8%. Subsequently, a comparison with state-of-the-art methods in this domain has been provided to assess the efficacy of the proposed method.

Solar-plus-storage systems could effectively mitigate uncertainties of the photovoltaic (PV) generation and improve system reliability by adding an integrated battery energy storage system. As a three-port bidirectional isolated dc-dc converter with soft-switching capability, the triple-active-bridge (TAB) converter inherently match the requirements of the solar-plus-storage system. However, challenges still remain in the TAB converter design to further improve the system efficiency. In this paper, the detailed design, implementation, and demonstration for a silicon carbide (SiC) 150-kW TAB converter are presented. Starting from a brief review of the TAB converter, the modulation scheme, power characteristics, and soft-switching region are analyzed. Then, the detailed design of the H-bridge converter building block is given. To improve the system efficiency, a comprehensive characterization of the SiC gate driver with various external gate resistances is performed to address tradeoffs between switching loss and voltage overshoot during transients, as well as the thermal performance of the H-bridge building block. In addition, the design and characterization for the 20-kHz three-port transformer are also given. Comprehensive experimental studies are conducted on a full-power prototype to verify the proposed design. With a measured 99.1% peak efficiency, the proposed TAB converter can fulfill the requirements for solar-plus-storage applications.

Summarization: Nonisolated photovoltaic (PV) inverters based on a single high-frequency MOSFET power switch have become more and more popular recently. Among these topologies, the conventional buck–boost inverter is fairly achievable but has low efficiency, whereas the buck with boost inverter has the main drawback that its circuit includes too many devices. In order to outperform these topologies, a new MOSFET-switch-based transformerless inverter topology sharing one common ground between the PV source and the grid is presented in this article. The inverter experiences zero leakage current and only one energy-regulating inductor is equipped. The basic principle of operation is studied based on an equivalent circuit analysis. Moreover, the control strategy adopting dead-beat controller for the proposed inverter is designed and introduced in detail. Finally, a 110-V/50-Hz/500-W prototype is built up to test the correctness of the theoretical analysis. According to the measurement results, the efficiency of the prototype is 98.81% and 95.89% in light- and full-load situations, respectively. According to the experimental results, it can be verified that the proposed dc/ac inverter exhibits satisfactory steady-state and transient performance. Παρουσιάστηκε στο: IEEE Journal of Emerging and Selected Topics in Power Electronics

This paper proposes a comprehensive method for optimal coordination of ultrafast solid-state circuit breakers (SSCBs) in radial dc microgrids. The proposed method consists of two consecutive steps. In the first step, SSCBs are optimally coordinated for overload, short circuit, and instantaneous protections. Inverse time-current characteristics (ITCC) curves are formulated to systematically coordinate SSCBs. The trip-curve of each SSCB includes overload, short-circuit, and instantaneous profiles. In determining overload protection, thermal capability of SSCBs is considered; while, the short-circuit and instantaneous tripping profiles are realized based on short circuit thermal capability and ultrafast response time of SSCBs. Coordination time interval (CTI) is included between upstream and downstream SSCBs to achieve selectivity. To avoid miscoordination in practice, CTI is chosen by incorporating the SSCBs’ metal-oxide varistor (MOV) conduction time interval during turn-off process and dc current measurement error. In the second step, the operating speed of the protective scheme is optimized by applying a distance-based secondary protection (DBSP). The DBSP is used to minimize the tripping time when short circuit faults occur close to upstream SSCBs. This significantly reduces the consumed energy by faults, prevents damage, reduces absorbed energy by SSCBs, and enhances safety of operators. The proposed coordination removes the need of communication links between SSCBs and presents high reliability. A 400 V dc microgrid benchmark with photovoltaic (PV) and energy storage systems (ESSs) is examined as a case study in simulation. Besides, experiments are conducted in a 400 V dc system to evaluate effectiveness and accuracy of the DBSP.

The high penetration level of single-phase solar PVs in low voltage distribution systems has raised concern about the Voltage Unbalance (VU) level. Real-time phase reconfiguration using Dynamic Switching Devices (DSD) has been proposed as a cost-effective solution to mitigate the excessive level of Voltage Unbalance.DSDs are fast power electronics devices that could change the phase connection of a solar PV with minimum disturbances. Most of the proposed methodologies for controlling DSDs are based on a central controller and the assumption of availability of Advanced Metering Infrastructure (AMI) and a communication system. In this paper, we propose a distributed control methodology to control DSDs based on the measurement from the local node only and using the sensitivity of nodal voltage to power injection. Each DSD decides on phase swapping if it rectifies the unbalance index of the local node. We show that decreasing the Voltage Unbalance Factor (VUF) of individual nodes will improve the unbalance situation of the whole feeder. The proposed scheme does not require a communication system nor a central controller. The result of simulations confirms the efficacy of the proposed methodology.

The design of electromagnetic interference (EMI) filter with smaller size and lightweight for a high efficiency and high power density 100 kW SiC five-level T-type (5LT2) photovoltaic (PV) inverter becomes more challenging due to the increased EMI noise resulted by high switching frequency, fast switching transients, and the removal of LCL filter. This paper proposes an unbalanced Wheatstone bridge and a two-stage notch filter to attenuate the increased common mode (CM) and differential mode (DM) noise respectively. The conventional Wheatstone bridge will suffer size and weight penalty for 100 kW PV converter due to the high parasitic capacitance of the 100 kW PV panel. An unbalanced Wheatstone bridge with a one-stage LC filter is therefore developed to address this issue and reduce the total CM inductance. The proposed two-stage notch filter is designed to achieve high attenuation, solve its parameter variation issue and help reduce the size and weight of DM filter. The total weight of the designed EMI filter for this 100 kW PV inverter is 3.54 kg. The measured conducted EMI spectrum of the 100 kW SiC PV inverter with and without proposed EMI filter are provided to validate the effectiveness of the EMI filter design.

As residential photovoltaic (PV) system installations continue to increase rapidly, utilities need to identify the locations of these new components to manage the unconventional two-way power flow and maintain sustainable management of distribution grids. But historical records are unreliable and constant re-assessment of active residential PV locations is resource intensive. To resolve these issues, we propose to model the solar detection problem in a machine learning set up based on labeled data, e.g., supervised learning. However, the challenge for most utilities is limited labels or labels on only one type of users. Therefore, we design new semi-supervised learning and one-class classification methods based on autoencoders, which greatly improve the nonlinear data representation of human behavior and solar behavior. The proposed methods have been tested and validated not only on synthetic data based on a publicly available dataset, but also on real-world data from utility partners. The numerical results show robust detection accuracy, laying down the foundation for managing distributed energy resources in distribution grids.

This article discusses optimum designs of photovoltaic (PV) systems with battery energy storage system (BESS) by using real-world data. Specifically, we identify the optimum size of PV panels, the optimum capacity of BESS, and the optimum scheduling of BESS charging/discharging, such that the long-term overall cost, including both utility bills and the PV system, is minimized. The optimization is performed by considering a plethora of parameters, such as energy usage, energy cost, weather, geographic location, inflation, and the cost, efficiency, and aging effects of solar panels and BESS. To capture the impacts of long-term factors such as aging effects, inflation, and discounted economic returns, the problem is formulated as a mixed integer nonlinear programming (MINLP) problem over the time horizon covering the entire life cycles of solar panels and BESS of the order of ten years or longer, whereas almost all existing works on PV system designs consider much shorter time horizons of the order of days or weeks. The MINLP is transformed into mixed integer linear programming (MILP) and solved by branch-and-bound (B&B) algorithm. The complexity of MILP is high due to the long time horizon. A new low-complexity algorithm is then proposed by using dynamic programming, where it is shown that the MINLP problem can be transformed into one that satisfies Bellman’s principal of optimality. Applying the newly developed algorithms on real-world data from a commercial user in San Francisco reveals that the system achieves the break-even point at the 66th month and achieves a 29.3% reduction in total system cost.

In this article, various converters integrated with renewable sources to the utility grid along with its control strategies are proposed. The proposed system uses a buck–boost converter to extract maximum power from photovoltaic (PV) and maintain power balance between the system and utility grid through a voltage source converter (VSC) employing bidirectional power flow. The main feature of the buck–boost converter presented here is to boost the dc voltage of the load by integrating the PV and dc output of the VSC in series. Moreover, the boost converter is utilized to extract the maximum power from a wind source. Additionally, a voltage management scheme is proposed to achieve a regulated constant voltage magnitude higher than that of a conventional voltage source converter integrated with the utility grid. Besides, it can be realized using a conventional voltage source converter along with the existing renewable sources in the system. Finally, the proposed system is validated through simulation and experimental results under various operating conditions.

Due to the complex muti-branch structure of photovoltaic DC distribution systems, 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 are affected by various converter structures and control algorithms. To resolve these issues, a new DC line protection based on active converter injection is proposed. This method uses communication cooperation to realize the coordination of protection and converter control, then the converter becomes a characteristic signal injection source, that can build a clear protection boundary. The proposed method can complete fast fault detection and precise fault location. Moreover, compared with current DC protection techniques, it does not require additional injection equipment and high sampling frequency. Hardware tests are carried out, illustrating that the proposed approach is effective to achieve line protection through active control of power electronics.

In transformerless photovoltaic (PV) generation system, the neutral-point (NP) voltage balancing and the ground current reduction of three-level inverter are carefully regulated using space vector modulation (SVM) scheme. Nevertheless, in low-voltage ride-through (LVRT) operation, the simultaneous reduction of NP voltage oscillation and common mode voltage (CMV) has not been researched yet. To overcome these issues, a selective SVM (SSVM) strategy is proposed in this paper. First, the NP voltage oscillation of three-level inverter in LVRT operation is analyzed in detail, which reveals that the NP voltage is affected by phase currents and duty cycles. Based on the location of output voltage and the direction of grid currents, the correct small vectors are selected under different power factor angles. Then, the small vector force (SVF) including the grid currents and duty cycle on NP voltage is proposed for the first time. According to the value of SVF, the optimal small vector having the most effective impact on NP voltage among the correct vectors and switching sequence are determined. With the proposed method, the NP voltage oscillation and CMV are reduced simultaneously in LVRT operation. Finally, the effectiveness of the proposed method is verified with experimental results.

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 (ANN), a new two-stage global maximum power point tracking (GMPPT) method is introduced in this paper 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.

Co-phase traction power supply system provides the insights for solving the existing power quality and electrical sectioning issues in high-speed railways, and the flexible control of co-phase traction substation (CTSS) with the integration of photovoltaic (PV) and hybrid energy storage system (HESS) attracts widespread attention. However, the strong volatilities and uncertainties of PV and traction load introduce challenges to the reliable and economic operation of CTSS. In this study, the energy management of CTSS aims at minimizing the operating cost of CTSS by coordinating PV, HESS, power flow controller (PFC) and the energy transactions with the power grid, where the three-phase voltage unbalance constraint is taken into account in particular. Furthermore, to handle the uncertainties of PV and traction load, a two-stage robust optimization model is proposed. The first stage determines the operating status of HESS and energy transaction status with grid, and the second stage aims at finding the optimal scheduling power of CTSS and the worst-case scenario with maximized operating cost of CTSS. A column-and-constraint generation algorithm is employed to solve this robust optimization model, along with efficient linearization approaches for the formulation of mixed-integer linear programming. The proposed methodology is tested with a real high-speed railway line case in China.

Most of the existing research focuses on electricity theft cyberattacks in the consumption domain. On the contrary, a high penetration level of distributed generators (DGs) may result in increased electricity theft cyberattacks in the distributed generation domain, which is the focus of this article. In these attacks, malicious customers can hack into the smart meters monitoring their DG units, which are usually photovoltaic, and manipulate their readings to report higher injected energy to the grid and claim more profit under feed-in tariff programs. This article proposes a data-driven approach based on machine learning to detect such thefts. We adopt an anomaly detection approach where a theft detection unit (TDU) based on a regression tree model is designed to detect suspicious data. Historical records of solar irradiance, temperature, and smart meter readings are utilized in the training stage of the detector. The probability density function of the error between the actual readings from DG meters and the predicted generation by the regression model is utilized as a metric to detect suspicious data. Several theft scenarios are used to assess the performance of the TDU. Furthermore, a comparison study with other detectors is presented to demonstrate the superiority of the proposed TDU.

Satisfying fault ride-through requirements, solar photovoltaic (PV) plant remains connected to the grid even during a fault. With current limiting feature, the plant current during a fault becomes comparable to its rated current. This imposes challenges to conventional local data-based protection methods employed in the relay on PV-side. In such a situation, the selectivity of a protection scheme is crucial for maintaining an uninterrupted supply to customers. In this article, a q-axis component-based protection scheme is proposed for the distribution system with a PV plant. The method extracts the second-order harmonic components of q-axis voltage and current at relaying point for fault detection and direction identification. Using this direction information at both ends of a line segment to be protected, internal and external faults are discriminated. The performance of the proposed method is tested on 14-bus distribution system for various fault cases. A comparative analysis with existing techniques shows the strength of the proposed method. Hardware-in-loop testing using OPAL-RT simulator as system and Arduino NANO microcontroller as relay validates the performance of the proposed method in real-time.

Mismatch losses (ML) problem can directly reduce the power generation of a photovoltaic (PV) array as well as complicate maximum power point tracking (MPPT) algorithms by causing multiple peaks to appear in the P-V characteristic. Hence, PV array reconfiguration techniques have become highly popular to minimize the ML of PV arrays. In this article, an optimal dynamic topology reconfiguration method based on a switching matrix is presented for series–parallel (SP) interconnected PV array to mitigate the ML, thereby maximizing the power generation of the PV array. The design of the switching matrix is presented that enables each string of the PV array to be divided into two sections to carry out the efficient dynamic topology reconfiguration with improved flexibility and scalability. The proposed reconfiguration method is assessed and compared with the SP scheme and the recently developed cross diagonal view method. The effectiveness of the proposed solution for the TCT scheme is also confirmed through simulation experiments. The numerical results indicate that the multiple peaks on P-V curves can be reduced and MPPT can be implemented with a simple control algorithm. Additionally, the maximum power generation improved by 20.13% and 14.39% on average compared to the SP scheme and TCT scheme, respectively, for different mismatch conditions of partial shading and random PV module failures.

A novel amplitude-domain pulse-width modulation (AD-PWM) technique for three-phase energy stored quasi-Z-source (ES-qZSI) photovoltaic (PV) power system is proposed in this paper. The proposed modulation technique performs switching states and shoot-through behavior based on the relationship of size among three-phase voltages, showing the attractiveness of extreme simplicity and low computation. This paper further investigates the AD-PWM based three-phase PV power system. An active power control method integrated with reactive power compensation for the system in natural coordinate to avoid complicated calculation of trigonometric function. As a result, active power regulation integrated with reactive power compensation is fast and reliable. Compare with the state-of-arts of control schemes for ES-qZSI system utilizing techniques, the proposed control strategy has advantages: 1) The computation is low because there is no shoot-through reference and avoiding complexity vector calculation; 2) there is a reliable capability of ensuring the grid-injected current tracking the grid voltage in phase, owing to the reactive power generated by reactive power equipment is taken into account to control the ES-qZSI’s output current. Simulation and experimental results verify the outstanding features of the proposed AD-PWM and active power control strategy integrated with the reactive power compensation technique for three-phase ES-qZSI PV power system.