This article presents a hybrid modulation scheme for a single-phase transformerless inverter based on H6 topology. This inverter uses Gallium-Nitride (GaN) devices to improve the efficiency and power density of the inverter. A comparative analysis is conducted on two existing modulation schemes. The impact of GaN devices on leakage current and power loss of the H6 inverter is evaluated. Among these schemes, one demonstrates a lower leakage current but higher power loss compared to the other. In this context, the proposed modulation scheme has better performance than the first scheme in terms of efficiency while also exhibiting lower leakage current than the second scheme. The operation modes of the proposed modulation scheme are described and analyzed in detail. The scheme is validated and verified using simulation studies. Furthermore, the scheme is compared with the existing literature to validate the performance of the inverter. A 3 kW PV inverter with the proposed scheme achieves an efficiency improvement of 0.35 % compared to the first scheme and a leakage reduction of 87.89 % towards the second scheme.

Reliability of inverters in electric vehicles (EV) is one of the limiting factors for increased penetration of EVs. The power semiconductor devices (PSDs) are more prone to failure than the other components in EV inverters, due to frequent thermal cycling. For reliability oriented design of an EV inverter, it is essential to study the impact of different EV operational conditions on PSD lifetime. In this paper, an integrated model based study of lifetime of PSDs in EV inverter is presented. The study is carried out for light weight passenger electric car with single speed transmission (SST). The study assimilates the effect of various operational factors on the lifetime of PSD. These factors include transient driving cycles, transmission gear ratio value and extent of energy recuperation. It is found that the lifetime of PSD is severely affected due to aggressive driving patterns, random gear ratio selection of SST and high energy recuperation. The detailed simulation results and their analysis are included in the paper.

Medium-frequency (MF) transformer is employed in several DC-DC converters, where its leakage inductance plays a crucial role in the converter operation, such as creating resonance in soft switching converter, limiting current in dual active bridge converter, etc. Therefore, it is paramount to accurately estimate the leakage inductance during the design stage. In the literature, leakage inductance calculation at medium frequency is analyzed considering the effects of eddy currents, winding arrangement, etc., but the effect of winding material remains unexplored. This is analyzed by calculating the magnetomotive force (MMF) distribution in the winding volume for different conductor materials. This helps deduce the energy stored in the winding and thereby formulate the effective leakage inductance analytically. Moreover, conductor materials with different resistivities exhibit different temperature coefficients. Therefore, this study also investigates the effect of temperature rise in the windings on the effective leakage inductance due to the change in the wire resistivity. Finally, a comparative analysis between Al and Cu foil designs of a 16 kVA, 1.5/20 kV, 20 kHz transformer is presented to summarize the relative benefits of using Al foils for high power MF transformer designs. The analytical model is verified using 2D FEM analysis. This study shows that higher resistivity material leads to higher leakage energy stored in the conductor volume; consequently this helps achieving higher leakage inductance. As the material resistivity increases with temperature, this also leads to higher leakage inductance.

This paper presents the challenges and solutions in implementing the voltage regulation loop of the distributed secondary controller for dc microgrid in a digital signal processor (DSP). Secondary controllers are generally used to keep the average dc microgrid voltage at the nominal value. However, some unforeseen issues may hamper the operation of the secondary controller. One of such issues is the saturation of controllers due to the lower resolution of the variables in DSP. This, in turn, results in the average terminal voltage deviating from the desired value. This work focuses on addressing this particular problem. Different variables related to the secondary controllers are observed from the DSP. The buildup of these variables is correlated with theory to arrive at a solution. Although there are multiple publications on secondary controllers, practical challenges and issues are not discussed in sufficient detail in the literature. The efficacy of the proposed solution is validated in a scaled-down DC microgrid prototype.

DC system for solar photovoltaic (PV) application is gaining popularity due to high efficiency and reliability. This system could be interconnected to ac and dc grids. For high availability of power supply to loads, energy storage elements are interconnected using dc-dc converters. Power management control for this system is necessary to ensure high utilization of renewable sources and stable operation of system. DC bus signaling technique, suggested in literature, does not consider extreme system operation, for instance battery fully charged or battery deep discharge conditions. A modified technique based on dc bus voltage signaling considers the above mentioned conditions only for one battery storage unit. Moreover, power sharing among multiple battery units is not discussed. To address these limitations, this paper presents a distributed power management scheme based on dc bus signaling controller. The proposed scheme is capable of controlling multiple storage, solar PV and grid converters. Detailed simulation studies are carried out to verify the effectiveness of the scheme and results are included.

Demand for high power direct grid feeding solar photovoltaic (PV) inverters in increasing. To reduce stress on semiconductor devices and harmonic distortion of current waveform, multilevel topology based solar inverters are suggested in literature. Use of Neural Point Clamped (NPC) topology is limited due to complex layout of switches and diodes as compared to 2-level Voltage Source Converter (VSC). Moreover, both NPC and VSC offer only one MPPT tracker for each inverter. Therefore, these inverters may not be effective in extracting maximum power from large PV array under partial shading condition. To address these limitations, a 3-level solar inverter integrating two 2-Level VSCs, supplying real power to the grid is proposed in this paper. Simple layout of the switches and two MPPT trackers are the attractive features of the proposed topology over the 3-level NPC based solar inverter. Mathematical model of the system is derived based on which a controller for the scheme is designed. Effect of partially shaded PV array on current harmonic distortion is analyzed. Effectiveness of the scheme is verified through detailed simulation study.