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Sparse code multiple access (SCMA) is a non-orthogonal multiple access (NOMA) uplink solution that overloads resource elements (RE's) with more than one user. Given the success of orthogonal frequency division multiplexing (OFDM) systems, SCMA will likely be deployed as a multiple access scheme over OFDM, called an SCMA-OFDM system. One of the major challenges with OFDM systems is the high peak-to-average power ratio (PAPR) problem, which is typically studied through the PAPR statistics for a system with a large number of independently modulated sub-carriers (SCs). In the context of SCMA systems, the PAPR problem has been studied before through the SCMA codebook design for certain narrowband scenarios, applicable more for low-rate users. However, we show that for high-rate users in wideband systems, it is more meaningful to study the PAPR statistics. In this paper, we highlight some novel aspects to the PAPR statistics for SCMA-OFDM systems that is different from the vast body of existing PAPR literature in the context of traditional OFDM systems. The main difference lies in the fact that the SCs are not independently modulated in SCMA-OFDM systems. Instead, the SCMA codebook uses multi-dimensional constellations, leading to a statistical dependency between the data carrying SCs. Further, the SCMA codebook dictates that an UL user can only transmit on a subset of the available SCs. We highlight the joint effect of the two major factors that influence the PAPR statistics - the phase bias in the multi-dimensional constellation design along with the resource allocation strategy. The choice of modulation scheme and SC allocation strategy are static configuration options, thus allowing for PAPR reduction opportunities in SCMA-OFDM systems through the setting of static configuration parameters. Compared to the class of PAPR reduction techniques in the OFDM literature that rely on multiple signalling and probabilistic techniques, these gains come with no computational overhead. In this paper, we also examine these PAPR reduction techniques and their applicability to SCMA-OFDM systems.

High-gain DC-DC converters have become very important devices in the operation of renewable energy methods such as wind and solar power to provide the required voltage and current levels. This work describes a new common ground ultra-high step-up DC-DC converter constructed with coupled inductors that has a high voltage conversion ratio, minimal voltage stress over semiconductor parts, and high performance. To improve the voltage gain, approaches using a linked inductor and voltage multiplier circuit were employed. The blocking voltages of power MOSFETs are clamped at low levels by voltage multiplier cells and can be regulated by the turn ratio of the coupled inductor, reducing the voltage rating of semiconductors and the cost of the conversion device. The proposed topology and corresponding functionalities are described by delineating the operating modes, steady-state analysis, and a comparative analysis. Experimental results are provided with a 425 W output power at a 100 kHz switching frequency of operation to validate the voltage enhancement achieved by the proposed architecture.

High-gain DC/DC converters play critical roles in most renewable-energy applications such as wind and solar power. A significant number of the high-gain converters are utilized to boost voltage gain by employing an excessive duty cycle and low turn ratio. However, the operation in high duty cycle raises losses and costs, lowers system effectiveness, and results in a low efficiency. This paper proposes a novel solution for a high-gain DC/DC boost converter. The proposed converter can be utilized in low input voltage scenarios that require a large voltage gain, such as solar photovoltaic panels and fuel cells. The novel topology is characterized by a simple operation, high voltage gain, improved efficiency by utilizing two resonance circuits, and continuous input current. An experimental high-gain boost converter with a power output of 300 watts and a voltage ranging from 20 volts to 160 volts is utilized to demonstrate the efficiency of the proposed converter topology.

The need for high gain DC-DC converters has lately increased in tandem with the utilization of renewable energy supplies. Particularly appealing are high gain converters that do not require the inclusion of extra power switches and/or other passive elements to the system. As a result, this study proposes a non-isolated single switch converter with ultra-high voltage gain (UHG) that is appropriate for most renewable energy conversion systems, like solar installations. With only a single MOSFET working within a suitable duty cycle region, the proposed converter provides significant voltage gain and around 95% efficiency. Moreover, the MOSFET in this UHG converter is turned on in zero current switching (ZCS) mode, resolving the diode recovery issue. The recommended UHG converter’s working modes, steady-state parametric study, circuit variables like voltage stress on switching devices, and converter gain are all thoroughly explained. Comparisons have been done with comparable topologies presented in the literature, and lastly, experimental results depending on 200W (20V input, 320V output voltage) are given to validate the operation of the proposed UHG design.

An ultra-high gain DC-DC converter with single-switch structure is introduced in this paper. Full soft-witching is provided by simultaneous use of quasi-resonant performance of one resonant tank and leakage inductance of a three-winding coupled inductor (CI). Adopting the secondary and tertiary windings of the CI in separated voltage multiplier cells enables the converter to provide ultra-high voltage gain. The reverse recovery problem is resolved thanks to the quasi zero current switching performance of nearly all diodes, especially output diode because of the second resonant tank, so the total electromagnetic interference is significantly reduced. Continuous input current with low ripple expands the application of the proposed converter, especially in renewable energy applications. Steady-state performance and design considerations of the introduced converter are analyzed thoroughly and compared with recently introduced converters to establish its merits. Experimental results of a 200 W prototype are given to validate its analysis and performance.