Renewable Energy Sources (RES) showed enormous growth in the last few years. In comparison with the other RES, solar power has become the most feasible source because of its unique properties such as clean, noiseless, eco-friendly nature, etc. During the extraction of electric power, the DC–DC converters were given the prominent interest because of their extensive use in various applications. Photovoltaic (PV) systems generally suffer from less energy conversion efficiency along with improper stability and intermittent properties. Hence, there is a necessity of the Maximum power point tracking (MPPT) algorithm to ensure the maximum power available that can be harnessed from the solar PV. In this paper, the most important features of the DC/DC converters along with the MPPT techniques are reviewed and analyzed. A detailed comprehensive analysis is made on different converter topologies of both non-isolated and isolated DC/DC converters. Then, the modulation strategies, comparative performance evaluation are addressed systematically. At the end, recent advances and future trends are described briefly and considered for the next-generation converter’s design and applications. This review work will provide a useful structure and reference point on the DC/DC converters for researchers and designers working in the field of solar PV applications.

https://www.mdpi.com/2079-9292/9/1/31/pdf

A Comprehensive Review of DC–DC Converter Topologies and Modulation Strategies with Recent Advances in Solar Photovoltaic Systems

Single-phase inverters and rectifiers in 230 V $_{\text{rms}}$ applications, with a dc-side voltage of 400 V, achieve ultrahigh efficiency with a simple two-level topology. These single-phase designs typically utilize a line-frequency unfolder stage, which has very low losses and essentially doubles the peak-to-peak voltage that can be generated on the ac side for a given dc-link voltage. For certain applications, however, such as higher power grid-connected photovoltaic inverters, electric vehicle chargers, and machine drives, three-phase converters are needed. Because of the three-phase characteristic of the system, unfolders cannot be similarly used, leading to a higher minimum dc-link voltage of the three-phase line-to-line voltage amplitude, which is typically set to 800 V for 230 V $_{\text{rms}}$ phase voltage systems. Previous demonstrations indicate that significantly more levels—and the associated higher cost and complexity—are required for ultrahigh-efficiency three-phase converters relative to their single-phase counterparts. In this article, we seek to determine the fundamental reason for the performance difference between three-phase 800 V dc-link converters and single-phase 400 V converters. First, we build a 2.2 kW dc/ac hardware demonstrator to confirm the necessity of higher complexity converters, showing a simultaneous reduction in efficiency and power density between a two-level 400 V benchmark (99.2% peak efficiency at 18.0 kW/L) and a three-level 800 V inverter phase-leg (98.8%, 9.1 kW/L). With the motivation confirmed, we derive general scaling laws for bridge-leg losses across the number of levels and dc-link voltage, finding the efficiency-optimal chip area and the minimum semiconductor losses. With commercially available Si or GaN power semiconductors, the scaling laws indicate that six or more levels would be required for an 800 V three-phase ac/dc converter to meet or exceed the bridge-leg efficiency of a two-level 400 V GaN benchmark for a fixed output filter. With a complete Pareto optimization, we find that at least seven levels are necessary to recover the efficiency of the two-level 400 V benchmark, and we validate this theory with a seven-level 800 V 2.2 kW hardware prototype with a power density of 15.8 kW/L and a peak efficiency of 99.03%. Finally, two practical solutions that make use of the benefits of unfolder bridges familiar in single-phase systems are identified for three-phase systems.

Three Levels Are Not Enough: Scaling Laws for Multilevel Converters in AC/DC Applications

A bidirectional three-phase dc–ac converter with embedded dc–dc converter for bidirectional storage interface is proposed in this paper. With the help of the embedded dc–dc converter, the voltage of the storage battery can vary in a wide range. To minimize the power rating and power losses of the embedded dc–dc converter, a simple carrier-based pulsewidth modulation (PWM) strategy with zero-sequence injection is proposed. By adopting the proposed PWM strategy, only a small ratio of total power needs to be processed by the embedded dc–dc converter, while most of the power is only processed by the three-phase dc–ac stage within a single conversion stage. As a result, quasi single-stage power conversion is achieved to improve the conversion efficiency of the overall dc–ac power system. Principles, characteristics, and implementations of the proposed three-phase dc–ac converter and its PWM strategy are analyzed in detail. The feasibility and effectiveness of the proposed solutions are verified with experimental results.

Bidirectional Three-Phase DC–AC Converter With Embedded DC–DC Converter and Carrier-Based PWM Strategy for Wide Voltage Range Applications

Microinverters for grid-connected photovoltaic (PV) power conversion systems often require voltage boost due to the low dc voltage of the PV panels. A high-frequency (HF) transformer-isolated differential-mode Cuk inverter (DMCI) is an attractive topology due to its inherent voltage boost capability and high power density. One of the significant operational issue of the DMCI addressed in this paper is the presence of lower order harmonic distortion in the injected grid current. It is shown that lower order odd and even harmonic voltages are generated with this topology. This problem is accentuated due to the low damping offered by the grid to harmonic voltages. A systematic low-complexity control design is proposed to address this issue. It is shown experimentally that the DMCI operates stably with effective attenuation of the lower order harmonics using the proposed design. Practical operational issues of the DMCI with fast switching GaN field-effect transistor (FET) devices are analyzed and solutions are proposed. It is shown that there can be significant HF noise generation in the DMCI with a frequency range higher than the switching frequency. Practical solutions for resolving HF issues using a combination of circuit layout design and additional passive components are proposed and validated. All of the experimental results are demonstrated on a 500-W GaN-FET-based microinverter prototype.

Resolving Practical Design Issues in a Single-Phase Grid-Connected GaN-FET-Based Differential-Mode Inverter

Wake-up radio is a promising approach to mitigate the problem of idle listening, which incurs additional power consumption for the Internet of Things (IoT) wireless transmission. Radio frequency (RF) energy harvesting technique allows the wake-up radio to remain in a deep sleep and only become active after receiving an external RF signal to ‘wake-up’ the radio, thus eliminating necessary hardware and signal processing to perform idle listening, resulting in higher energy efficiency. This review paper focuses on cross-layer; physical and media access control (PHY and MAC) approaches on passive wake-up radio based on the previous works from the literature. First, an explanation of the circuit design and system architecture of the passive wake-up radios is presented. Afterward, the previous works on RF energy harvesting techniques and the existing passive wake-up radio hardware architectures available in the literature are surveyed and classified. An evaluation of the various MAC protocols utilized for the novel passive wake-up radio technologies is presented. Finally, the paper highlights the potential research opportunities and practical challenges related to the practical implementation of wake-up technology for future IoT applications.

https://www.mdpi.com/1424-8220/19/14/3078/pdf

Advances and Opportunities in Passive Wake-Up Radios with Wireless Energy Harvesting for the Internet of Things Applications.

Three-phase differential-mode inverters are single-stage inverters, which have the potential to reduce the number of devices and cost with higher power density Among such inverter topologies, differential-mode three-phase Cuk inverter (DTCI) has some advantage over other topologies, including modularity, lower number of switches, bidirectional power flow capability, and galvanic isolation DTCI is a promising configuration for renewable-/alternative-energy applications with isolated and nonisolated structures The continuous modulation scheme (CMS), which was introduced originally for the DTCI, activates all of three modules of the inverter CMS increases the circulating power in modules and hence increases inverter power loss This paper describes a discontinuous modulation scheme (DMS) for the DTCI which deactivates one module at a time resulting in a discontinuous operation of the inverter modules The experimental open- and closed-loop results of DMS- and CMS-based DTCI are provided and compared DMS reduces the circulating power, device voltage ratings, and mitigates the DTCI losses The DTCI exhibits a nonlinear voltage gain with both DMS and CMS It has been demonstrated that by feed-forwarding the input voltage and incorporating a static linearization method, the harmonic distortion of the output voltage is considerably reduced

Modulation Scheme for Three-Phase Differential-Mode Ćuk Inverter

In this paper, a modular control approach has been proposed for a single- and three-phase differential-mode Cuk inverter (DMCI) operating with a recently proposed discontinuous-modulation scheme that offers tangible performance benefits over conventional continuous modulation scheme. The modular control scheme uses a combination of a transformation and adaptive control law to meet tracking requirements in the presence of converter nonlinearity. Experimental results for the single- and three-phase DMCI are provided for startup, steady state, load transition, and total harmonic distortion using different types of loads, which validate the efficacy of the implemented modular tracking controller. Further, detailed stability of the closed-loop DMCI module is provided.

Control of Isolated Differential-Mode Single- and Three-Phase Ćuk Inverters at Module Level

A single-stage differential-mode current-fed zero-current-switching inverter has been designed. This inverter has two modules of dc/dc converters that are connected differentially to the input source. This inverter does not require 60-Hz transformer, front-end dc/dc converter, and can boost a low-voltage input to ac output using a compact low-turns-ratio transformer because of the added voltage gain of the topology. Main switches of the inverter are soft switched. The inverter requires a smaller high-frequency transformer because of high-frequency switching, bipolar transformer current, and voltage in every switching cycle, and because the transformer sees only half of the input current. The modularity of the inverter extends the scope of the topology to be used as a dc/dc converter, single-phase inverter, and also the possibility of extending the topology to both split phase and three phase. A harmonic-compensation control is designed and implemented to reduce the total harmonic distortion of the output waveform using a proportional-resonant controller. The design and the analysis of the inverter have been validated using simulation results in the Saber simulator.

A DC/DC Modular Current-Source Differential-Mode Inverter

This study presents numerical simulation of a novel gallium nitride buffered trench gate (GaN-BTG) metal oxide semiconductor field effect transistor (MOSFET) for high-speed and low-power applications. The electrical characteristics of GaN-BTG-MOSFET are compared with BTG MOSFET and conventional trench gate MOSFET. A comparative study of different performance factors such as electric field, electron velocity, threshold voltage (V th), electron mobility, and sub-threshold swing (SS) of these devices has been performed. Results reveal a 43.85% improvement in SS and 9.83% decrement in V th for GaN-BTG-MOSFET. Furthermore, the frequency analysis has been performed in terms of scattering (S) parameters, cut-off frequency (f T) and maximum oscillator frequency (f MAX) to show how the device is also suitable for radio frequency applications. Furthermore, the study of parametric variation of GaN-BTG-MOSFET with the change in channel length, oxide thickness (t ox), and doping concentration has also been presented. Results show that GaN-BTG-MOSFET can act as a promising structure for further scaling down of the trenched MOSFET and assures better performance for sub-20 nm trenched MOSFET.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-cds.2020.0041

Numerical simulation and parametric assessment of GaN buffered trench gate MOSFET for low power applications

Background: Pelvic floor muscle exercises are used since 1948 as first-line treatment for management of genuine stress incontinence in women. This pelvic floor muscle exercises can be delivered simultaneously to a group of women or individually on a one to one basis. Objective: The purpose of this study was to compare the effects of group physiotherapy and individual physiotherapy sessions on the severity of incontinence & quality of life in patients with genuine stress incontinence. Materials and Methods: 40 women with chronic genuine stress incontinence were randomized into Group A - where women were delivered the pelvic floor muscle exercises in a group of 10 (n=20) & Group B - where pelvic floor muscle exercise on a conventional one to one basis, the individual approach (n=20) were administered. Outcome measures which included VAS for measuring severity of incontinence & King's health questionnaire for assessing quality of life were taken at baseline & at the end of 3 months intervention program. Results: Both the group A and group B showed improvement in severity of incontinence and quality of life postintervention when compared with preintervention measurement and 't'calculated value for pre-postintervention measures was statistically significant as it was above the 't' tabulated value. Moreover, Mean±SD of pre-post change in VAS for group A was 2.02±0.46 and for group B was 1.94±0.43 and King's Health Questionnaire scores for group A was 30.09±5.3 and for group B was 21.51±6.73. 't'calculated value for pre-post changes was statistically not significant as it was below the 't' tabulated value of 2.576. Conclusion: Both group and individual physiotherapy pelvic floor muscle exercises for women with genuine stress incontinence are equally effective. One may choose anyone of it to gain benefits.

Harshit Soni

Papers

Modulation Scheme for Three-Phase Differential-Mode Ćuk Inverter

Control of Isolated Differential-Mode Single- and Three-Phase Ćuk Inverters at Module Level

A DC/DC Modular Current-Source Differential-Mode Inverter

Numerical simulation and parametric assessment of GaN buffered trench gate MOSFET for low power applications

Randomized Controlled trial of Group Versus Individual Physiotherapy Sessions for Genuine Stress Incontinence in Women