1,721,020 research outputs found
Improved constant-frequency hysteresis current control of VSI inverters with simple feed-forward bandwidth predictionIAS '95. Conference Record of the 1995 IEEE Industry Applications Conference Thirtieth IAS Annual Meeting
No full textHigh-performance hysteresis modulation technique for active filtersProceedings of Applied Power Electronics Conference. APEC '96
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Ac/dc/ac PWM converter with reduced energy storage in the dc link
No full textThe family of quasi-direct power converters, i.e. forced-commutated AC/DC/AC power converters including small energy storage devices in the DC link, is introduced. In particular, the case of a three-phase to three-phase quasi-direct converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. A simple and effective control technique suitable for this purpose, which also provides high power factor and small distortion of the supply currents, is described. The general properties of quasi-direct power converters are discussed, design criteria of both power and control sections are given, and experimental results of a 2 kVA prototype are reported
Power Supply System for Liquid Crystal Monitors
No full textA power supply system for liquid crystal monitors includes a first DC/AC converter (FBS, HBS) operating at predetermined frequency and duty-cycles and being fed by a second DC/DC converter (FC) which regulates the circuit voltage. The feeding system can feed all the fluorescent lamps (L, L1, LN) in the monitor through a bus connection which transmits the output sinusoidal voltage (SG1, SG2, SG3) from the first DC/AC converter (FBS, HBS) to the primary windings of a plurality of parallel connected piezoelectric transformers (PT, PT1, PT2, PTN, PT2N) which are connected with the fluorescent lamps (L, L1, LN)
AC/DC/AC PWM Converter with reduced energy storage in the dc link
No full textThe paper introduces the family of quasi-direct converters, i.e., forced-commutated AC/DC/AC power converters including small energy storage devices in the DC link. In particular, the case of the three-phase to three-phase quasi-direct power converter is considered. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. The paper describes a simple and effective control technique which also provides high-power factor and small distortion of the supply currents. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2-kVA prototype are reporte
Performance optimization of quasi-direct converters
No full textThe paper describes a three-phase to three-phase quasi-direct power converter, i.e. a forced commutated AC/DC/AC power converter with small energy storage devices in the DC link. Since energy storage minimization calls for instantaneous input/output power balance, a proper control strategy is needed. In the paper, an effective digital control of the line current waveforms capable to work with unbalanced line and/or load voltages and providing also high power factor, is presented. After a discussion of the general properties of quasi-direct power converters, design criteria of both power and control sections are given, and experimental results of a 2 kVa prototype are reported
Performance Improvement of Soft-Switched PWM Rectifiers with Inductive Load
No full textA new soft-switched AC/DC PWM power converter structure is presented. It is useful for current-fed inverters and PWM rectifiers. Typical applications are magnet power supplies, high-power AC motor drives and active power filters with magnetic energy storage. Soft switching is provided at the expense of a limited increase of the circuit complexity as compared to usual hard switching solutions. A discussion of the soft commutation process is presented. By a proper switching sequence, overvoltages across the power converter switches can fully be eliminated. Moreover, light-load operation can be achieved. Both typical limitations of soft-switched current-fed topologies are therefore overcome. Simulation and experimental results demonstrate the actual power converter capabilities
Digital Adaptive Hysteresis Current Control With Clocked Commutations and Wide Operating Range
No full textA new hysteresis current control technique of voltage source inverters is proposed, which uses digital calculation to predict the proper band amplitude in order to minimize the error and give a switching frequency synchronized with a clock. The technique is self-adapting to supply and load parameters, and is easily extended to three-phase systems using the decoupling approach already proposed by the same authors. The proposed technique exhibits both the advantages typical of the hysteresis methods, and those of the digital controls. The implementation of the control is done by means of a standard microcontroller and simple additional circuitry. Simulations and experimental tests confirmed the advantages and the excellent performance of the new modulation metho
Cold Cathod Fluorescent Lamp Power Supply Based on Piezoelectric Transformers
No full textThis work discusses design and implementation of a switching power supply for low power cold cathode fluorescent lamps (CCFLs), used in high brightness, back-lighted, liquid crystal displays (LCDs). The power supply design is based on piezoelectric transformers. The use of piezoelectric transformers (PZTs), instead of conventional magnetic ones, allows a significant reduction of the converter's size and component count. The particular features of the piezoelectric transformer allow the designer to directly connect the lamp to the secondary side of the device without the need for the typical ballast capacitor. Besides, the start up over-voltage is automatically generated with no need for input voltage amplitude or frequency modulation. On the other hand, the peculiar PZT secondary side arrangement and its high voltage, low current operation, call for particular care in the implementation of the LCD dimming circuit. The paper describes the different power supply components, particularly focusing on the PZT characteristics, outlines the design procedure for the output stage of the power supply (i.e. a resonant half-bridge inverter) and discusses the LCD brightness control strategy. Experimental results coming from a preindustrialised prototype of the converter are presented
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