Ataollah Mokhberdoran

Symmetric and Asymmetric Design and Implementation of New Cascaded Multilevel Inverter Topology

Nowadays, use of multilevel inverters in high-power applications clearly can be seen. High quality and lower distortion of the output voltage and low blocking voltage of semiconductor switches are being presented as the major privileges of the multilevel inverter compared to the traditional voltage source inverter. In this paper, a new topology of multilevel inverter is proposed as fundamental block. The proposed topology is generalized using series connection of the fundamental blocks. The proposed multilevel inverter has been analyzed in both symmetric and asymmetric operation modes. A great perfection in voltage levels number with minimum switching devices has been obtained in both symmetric and asymmetric modes. Thereafter, a detailed study of losses and peak inverse voltage (PIV) of the proposed multilevel inverter is given. Also, in continuation, a comparison between the proposed topology and the traditional one and a recently developed topology is carried out. Finally, a computer simulation using MATLAB/Simulink is presented and a laboratory prototype implementation verifies the results.

A new topology of fast solid-state HVDC circuit breaker for offshore wind integration applications

Emerging new voltage source converter based HVDC applications demand fast short-circuit fault current interruption. Fast dc circuit breakers are identified as the feasible solution to handle the dc fault current. Switching overvoltage across the dc circuit breakers is destructive for the interrupter device and also for the other components of the system. A new topology of fast solid-state circuit breaker for HVDC applications is proposed in this paper. Instead of conventional approaches, a pre-charged capacitor is used for soft switching. Different modes of operation of proposed circuit breaker are analysed and also design process of circuit parameters are described. Finally, simulation results are presented.

A directional protection strategy for multi-terminal VSC-HVDC grids

Protection issue is identified as the main drawback of the emerging multi-terminal HVDC grids. Multi-terminal HVDC grids demand fast short-circuit fault current interruption. The fast DC circuit breakers as a promising solution can be implemented as either bidirectional or unidirectional devices. In additional to less implementation cost, the unidirectional DC circuit breakers have less power losses as compared to the bidirectional ones. A protection strategy for multi-terminal HVDC grids based on unidirectional breaking devices is discussed and assessed in this paper. The performance of unidirectional protection strategy is examined under different fault scenarios in a four-terminal MMC-HVDC grid model. Furthermore, the impacts of unidirectional protection strategy on the power converters and also the current interruption and surge arrester ratings of the DC circuit breakers are discussed.

Current Flow Controlling Hybrid DC Circuit Breaker

This paper proposes a new device by combining features of an interline dual H-bridge current flow controller with the core idea of a hybrid HVdc circuit breaker for meshed HVdc grid application. The proposed device can substitute two dc circuit breakers at a dc bus with at least two adjacent transmission lines. In addition to the current interruption action, the current in one of the adjacent lines can be controlled by the embedded current flow controller. The system-level behavior of the proposed current flow controlling hybrid dc circuit breaker is similar to that of the typical hybrid dc circuit breaker and the interline dual H-bridge current flow controller. The operation principles of the proposed device are introduced and analyzed in this work. The component ratings are compared to the existing solution, and the functionality of the proposed device is verified by simulation.