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176 results on '"Cha, Hanju"'

32. A three-phase current-fed dc/dc converter with active clamp for low-dc renewable energy sources

Author

Cha, Hanju, Choi, Jungwan, and Enjeti, Prasad N.

Subjects
Alternative energy sources -- Research, Electric current converters -- Design and construction, Clamping circuits -- Design and construction, Power electronics -- Research, Pulse-duration modulation -- Methods, Electric current converter, Business, Electronics, Electronics and electrical industries
Abstract

This paper focuses on a new three-phase high power current-fed dc/dc converter with an active clamp. A three-phase dc/dc converter with high efficiency and voltage boosting capability is designed for use in the interface between a low-voltage fuel-cell source and a high-voltage dc bus for inverters. Zero-voltage switching in all active switches is achieved through using a common active clamp branch, and zero current switching in the rectifier diodes is achieved through discontinuous current Conduction in the secondary side. Further, the converter is capable of increased power transfer due to its three-phase power configuration, and it reduces the rms current per phase, thus reducing conduction losses. Moreover, a delta-delta connection on the three-phase transformer provides parallel current paths and reduces conduction losses in the transformer windings. An efficiency of above 93% is achieved through both improvements in the switching and through reducing conduction losses. A high voltage ratio is achieved by combining inherent voltage boost characteristics of the current-fed converter and the transformer turns ratio. The proposed converter and three-phase PWM strategy is analyzed, simulated, and implemented in hardware. Experimental results are obtained on a 500-W prototype unit, with all of the design verified and analyzed. Index Terms--Active clamp, leakage inductance, three-phase dc-dc converter, three-phase pulsewidth modulation (PWM) strategy, voltage transfer ratio, zero-voltage switching (ZVS).

Published
2008

39. A Study of 10MW Load Commutated Inverter for Gas-Turbine Start-up

Author

An Hyunsung and Cha Hanju

Subjects
Phase-locked loop, Control theory, Computer science, Rotor (electric), law, Position (vector), Mode (statistics), Inverter, Estimator, Commutation, Synchronous motor, law.invention
Abstract

This paper proposes a stable sensorless start-up method of the actual 10MW LCI system and analyzed the characteristic of the existing system for the simulation modeling. The 10MW LCI system is modeled to verify the performance of the proposed sensorless methods, controllers, operating modes and so on. The simulation model is designed by applying the operating conditions of the 10MW actual system and parameters of the 200MVA synchronous machine. The proposed sensorless methods for initial start-up of the gas-turbine is composed of the initial rotor position detector and methods for the low speed and high speed range. The operation mode of the LCI system is divided into the forced commutation mode and natural commutation mode according to the rotor speed, and the sensorless methods are applied differently by the operation mode. The sensorless methods are referred to as closed loop current control and flux estimator. The initial rotor position detector is applied to detect rotor position at the standstill of the machine using an induced back-emf by the injection of a field current, and the estimated error is less than 1%. After estimation of the initial rotor position, the LCI system is operated by the closed loop current control at the forced commutation mode, and it operates at less than 10% of the rated speed. The LCI system is operated from 10% to 90% of the rated speed through the flux estimator for the natural commutation mode, and the rotor speed/position is estimated by the phase locked loop. The performance of proposed sensorless start-up and the operation modes of LCI system is verified by the proposed simulation modeling.

Published
2018
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