Multilevel inverters have created a new wave of interest in industry and research. While the classical topologies have proved to be a viable alternative in a wide range of high-power medium-voltage applications, there has been an active interest in the evolution of newer topologies. Reduction in overall part count as compared to the classical topologies has been an important objective in the recently introduced topologies. In this paper, some of the recently proposed multilevel inverter topologies with reduced power switch count are reviewed and analyzed. The paper will serve as an introduction and an update to these topologies, both in terms of the qualitative and quantitative parameters. Also, it takes into account the challenges which arise when an attempt is made to reduce the device count. Based on a detailed comparison of these topologies as presented in this paper, appropriate multilevel solution can be arrived at for a given application.

Large-scale solar photovoltaic (PV) systems encounter unpredictable partial shaded conditions (PSC). PSC, causing multiple peaks in the power-voltage (P–V) characteristics, potentially downgrades the performance of the PV system. However, the PV system should be operated at global maximum power point (GMPP) for its efficient utilization. For the tracking of GMPP, a scheme based on Flying Squirrel Search Optimization (FSSO) is proposed in this work. For an effective adoption with much reduced convergence time, the original FSSO is modified to update the squirrel position without the presence of predator. An experimental investigation of the proposed scheme is carried out employing a quasi-Z-source converter for the extraction of maximum power under PSC. The proposed scheme yields higher tracking efficiency, non-oscillatory steadystate response, and lower transients. Simulation and experimental investigations under various shading patterns indicate that the proposed strategy outperforms other popular maximum power point tracking (MPPT) strategies based on Perturb & Observe (P&O), Particle Swarm Optimization (PSO), and Grey Wolf Optimization (GWO).

The merit of switched-capacitors-based multilevel inverters (SCMLIs) is generally quantified in terms of a “cost function” (CF) that incorporates parameters such as voltage gain, component count, total standing voltage (TSV), and number of levels. In this article, a 13-level inverter is proposed with the aim of achieving a low value of CF. The proposed single-stage SCMLI uses one input source and three capacitors to attain a voltage gain of 3. It requires 13 power switches, of which the peak inverse voltage (PIV) of nine switches is restricted to the source voltage. The remaining four switches have PIV equal to twice the source voltage and they operate at low frequency. Thus, for all switches, the PIV is less than the amplitude of the output voltage. Moreover, the capacitors are self-balanced at all regions of modulation index values. The proposed inverter is validated through simulation and experimental results. A comparison of the proposed topology with other contemporary SCMLIs shows that it is highly competent in terms of CF, PIV and TSV requirements, waveform resolution, and capability to achieve voltage balancing of capacitors at low values of modulation index.

A novel integrated converter for electric vehicles (EVs) is proposed in this work. For battery charging operation, the proposed converter system enables a complementary deployment of the utility grid and a solar photovoltaic (PV) system. Since both sources (acting one at a time) utilize the same converter, the developed charging system therefore has a smaller number of components. In addition, an inductor voltage detection (IVD) technique has been incorporated to correct the power factor in continuous conduction mode (CCM), which eliminates the need for a current sensor for power factor correction (PFC). The proposed system operates for all the modes required for an EV e.g., charging, propulsion (PRN) and regenerative braking (RBG). In charging mode (with either grid or solar PV), the proposed system operates as an isolated secondary ended primary inductance converter (SEPIC) converter. In PRN and RBG modes, it operates as a boost converter and a buck converter, respectively. Details of all these modes are described in the paper, along with the design of the components. In addition, results of simulation and experimental studies are presented for a 1 kW set-up based on the proposed configuration. A comparison with other topologies shows the techno-economic competence of the proposed system.

AC-to-DC conversion is integral to the two-stage charging interface of electric vehicle (EV) batteries. For such chargers, the use of multilevel rectifiers (MLRs) reduces voltage ratings of power switches, while achieving a high-quality input voltage waveform. Balancing of capacitors in MLRs, however, is an important challenge. In this work, a power factor correction (PFC) five-level rectifier with self-balanced switched capacitors is proposed. Each leg of the presented topology comprises five power switches and one switched capacitor, where the voltage ratings of power switches are equal to the output dc voltage. It does not require an additional filter capacitor on the dc side, as the load appears in parallel always with a switched capacitor of one of the legs. The five-level operation with continuous conduction leads to the elimination of the capacitive filter on the ac-side and inductive filter on the dc-side. This article presents the operating principle, modulation strategy, closed-loop control, and design aspects of the proposed rectifier. The proposed topology is validated through experimental results and a comparison is made with other topologies. Following three features of the proposed topology make it suitable for EV battery charging applications—buck operation with a wide output regulation, the possibility of bidirectional flow of power needed for vehicle-to-grid systems, and easy realization of its three-phase version by simply adding one more leg. These features too have been demonstrated with experimental results.