Comparison of New Multilevel Inverter Topology with Conventional Topologies Used for Induction Heating System

In this article, a comparison of innovative multilevel inverter topology with standard topologies has been conducted. The proposed single phase five level inverter topology has been used for induction heating system. This suggested design generates five voltage levels with a fewer number of power switches. This reduction in number of switches decreases the switching losses and the number of driving circuits and reduce the complexity of control circuit. It also reduces the cost and size for the filter used. Analysis and comparison has been done among the conventional topologies (neutral clamped and cascade H-bridge multilevel inverters) with the proposed inverter topology. The analysis includes the total harmonic distortion THD, efficiency and overall performance of the inverter systems. The simulation and analysis have been done using MATLAB/ SIMULINK. The results show good performance for the proposed topology in comparison with the conventional topologies.

An Intelligent Control Strategy for a Highly Reliable Microgrid in Island Mode

An intelligent control strategy based on a membership cloud model in a high reliable off-grid microgrid with a reconfigurable inverter is proposed in this paper. The operating principle of the off-grid microgrid with the reconfigurable inverter is provided, which contains four operating modes. An open-circuit fault diagnosis for the inverter is presented first. The polarities of the midpoint voltages defined in the paper are used to recognize the faulty power switch. The reconfigurable inverter allows the power switches of different bridges to be reconfigured, when there are power switches faulty, to let the inverter operate in faulty state. The working principle of the reconfigurable inverter is given. The membership cloud model with two output channels is built to obtain the virtual impedance to suppress the circulating currents between inverters when the reconfigurable inverter is in faulty state. A pulse resetting method is presented. The general intelligent control strategy for the reconfigurable inverter is formed as the droop-virtual impedance-voltage-current-pulses resetting control. The validity of the intelligent control strategy of the system is verified by simulation.

The Time-Varying Relation between Stock Returns and Monetary Variables

The nature of the relation between stock returns and the three monetary variables of interest rates (bond yields), inflation and money supply growth, while oft studied, is one that remains unclear. We argue that the nature of the relation changes over time, and this variation is largely driven by shocks, with a change in risk associated with each variable shifting the pattern of behaviour. We show a change in the correlation between each of the three variables with stock returns. Notably, a predominantly negative correlation with bond yields and inflation becomes positive, while the opposite is true for money supply growth. The shift begins with the bursting of the dotcom bubble but is exacerbated by the financial crisis. Results of predictive regressions for stock returns also indicate a switch in behaviour. Predominantly negative predictive power switches temporarily to positive around economic shocks. This suggests that higher yields, inflation and money growth typically depress returns but support the market during periods of stress. However, after the financial crisis, higher inflation and money growth exhibit persistent positive predictive power and suggest a change in the risk perception of higher values.

Improved Cascaded H-Bridge Multilevel Inverters with Voltage-Boosting Capability

This paper proposes two improved cascaded H-bridge (ICHB) multilevel inverters that feature voltage-boosting capability. The conventional H-bridge with a front-end dc–dc boost converter was restructured for single-stage operation. The developed three-level topology not only saves one power switch but also exhibits lower voltage stress across its capacitor. Extension to five-level generation was also introduced by merely adding two power switches and one capacitor. The final five-level topology outperforms the classical cascaded H-bridge (CHB) multilevel inverter with a significant reduction in the power switch count, with a 42% and 50% reduction in both the isolated dc source and inductor counts. The power efficiency was also improved without compromising the modularity feature of the classical CHB multilevel inverter. The operation and theoretical analysis of the proposed topologies were validated via simulations and experimental tests.

Gain Compression of n-MESFET for High Power Applications in MIMO

In this paper, a new n-type recessed Metal semiconductor field effect transistor (MESFET) with GaAs/ SiC materials is designed for high power applications in Multi Input Multi Output (MIMO) systems. Based on electrical characteristics of MESFET, a SPICE model of the proposed device is developed. For power switches, the power MESFETs are used. The feasibility of the technology is validated by the electrical measurements of the device. The operational technology has been shown by the characterizations done on the proposed device. To optimize the electrical performance, the contact resistance technique has to be enhanced. In this work, the output power and Gain compression of proposed n-channel MESFET at 100 MHz and 1 GHz for high input power is obtained. The output power at fundamental frequency of operation for high input power is also obtained.

Improving the Quality of the Underwater Robot’s Contactless Battery Charging System

A special feature of the contactless battery charging system of an autonomous underwater robot is the use of a transformer with separating primary and secondary windings. As a result, a non-magnetic gap arises, which leads to the need to increase the primary current and the output current of the autonomous inverter. One of the ways to improve the quality of the system is the use of a resonant circuit at the inverter output in combination with the "soft switching" mode of its power switches. The use of resonance on the transformer secondary side also allows you to equalize the current loads of the primary and secondary windings. In this way, a minimum of losses in the inverter is achieved and the power transformer of the system is optimized. This allows you to reduce the size of the system while maintaining the transmitted power, or increase the transmitted power while maintaining the dimensions. The problem solved by using mathematical modelling with verification of the solution adequacy in a full-scale experiment.