This paper proposes a robust design for the ac/ac chopper-based voltage sag/swell compensation systems. This includes the design of a new buck-boost topology and the application of a robust switching scheme for a voltage compensator. The proposed circuit can operate in the buck or boost mode for both the sag and the swell compensations. A control scheme for a fast compensation is also proposed which is suitable for the ac/ac chopper-based compensation system. Detailed analysis and verification through a simulation in the MATLAB are presented highlighting the advantages of the proposed technique. An experimental verification has also been performed by using a laboratory prototype system.
A medium-voltage high-power electric traction system, due to its non-linear nature results in serious power quality issues in power system such as low-power factor and high-harmonic distortion. To mitigate the aforementioned problems, this study presents a seven-level asymmetrical hybrid multilevel converter that can be implemented using a single dc source and two capacitors. The proposed converter is a series connection of a five-level cascaded module (CM) converter with an H-bridge cell to meet the demand of medium-voltage high-power traction applications with improved power factor at minimum harmonic distortion. A modulation scheme presented will operate an H-bridge cell and a CM with a fundamental frequency and highfrequency switching, respectively. The unbalancing of dc-link capacitors voltages due to active power transfer requires corrective control action including current control, voltage control and voltage balancing that has been proposed to keep the dclink capacitor voltage balanced. Working principle of the proposed topology and its mathematical analysis is presented in this work. The effectiveness of the controlled pulse-width modulation strategy and stability of the proposed control method have been validated through simulation and experimental results.
In this study, a single phase thyristor-controlled susceptance (TCS) with integrated reduced power voltage source inverter (VSI) acting as a switching compensator (also known as active power filter) has been proposed to mitigate the harmonics generated by thyristor-controlled reactor (TCR). The proposed scheme has the capability to fully attenuate all harmonics generated by TCR. The proposed technique can perform efficiently even at lower switching frequency of VSIs, which is a desirable feature for higher power rating systems. This results in a more feasible implementation for comparative dynamic control characteristics. This scheme has been described in detail and has been verified through simulation and experimental results.
The design feasibility of a micro unidirectional DC transmission system based on an input-parallel output-parallel (IPOP) converter is analyzed in this paper. The system consists of two subsystems: an input-parallel output-series (IPOS) subsystem to step up the DC link voltage, and an input-series output-parallel (ISOP) subsystem to step down the output voltage. The two systems are connected through a transmission line. The challenge of the delay caused by the communication in the control system is addressed by introducing a ring communication structure, and its influence on the control system is analyzed to ensure the feasibility and required performance of the converter system under practical circumstances. Simulation and experiment results are presented to verify the effectiveness of the proposed design.
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