Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1997-01-21
1998-02-10
Krishnan, Aditya
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
H02J 708
Patent
active
057175799
DESCRIPTION:
BRIEF SUMMARY
CROSS-REFERENCE TO RELATED APPLICATIONS
The present application is a National Stage Application under 35 U.S.C. .sctn.371, of PCT International Patent Application Number PCT/DE95/00985, (published as International Publication Number WO 96/03791), filed Jul. 20, 1995, that designated the United States.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a switched-mode power supply unit with single-phase or multi-phase mains connection for the generation of isolated d.c. voltages, and more specifically for charging a single battery or battery strings. The invention in particular relates to a battery charger for electric vehicles or the like.
2. Description of the Related Art
In general, power supply units, especially those of high power ratings, are expected to load the mains with active power only. To keep charging times of high-capacity batteries short it is aimed at fully using the maximum power supplied by the mains, whereby the waveform of the line voltage must not unsuitably be distorted by line current interference. Moreover, batteries that consist of a string of series-connected electrochemical cells shall, in general, have a long service life. Premature damages and early failures of single battery blocks due to, in practice, unavoidable differences in capacities of the battery blocks can be avoided by obtaining, in each charging procedure, identical voltages for the individual battery blocks. During a discharging cycle the differences in capacity between the single battery blocks can be compensated by corresponding permanent charge equalisation performed by the charger.
It is well-known that, because of their excellent efficiency, switched-mode power supply units are used for charging batteries. According to the best known working principle the line voltage is converted into a smoothed d.c. voltage, using diodes and capacitors, from which electronic switches generate voltage pulses of frequencies ranging between 10 kHz and 100 kHz. These voltage pulses are then applied to the primary winding of a suitable transformer and, thereby, generate an impressed a.c. voltage in the secondary winding; said voltage being shaped to the desired output voltage by means of a rectifier and filter circuit. Then, this output voltage is conducted through a control unit in such a way that the desired charging current develops (cp. U. Tietze, Ch. Schenk: "Halbleiterschaltungstechnik", Springer-Verlag, 5th Edition, 1980, pages 395 ff.).
Moreover, it is well-known that, in units with single-phase mains connections, the line current may be conducted in a sinusoidal waveform if the rectified line voltage is further treated by a boost converter installed downstream the rectifier, a combination often called step-up converter (cp. U. Tietze, Ch. Schenk: "Halbleiterschaltungstechnik", Springer-Verlag, 5th Edition, 1980, pages 395, as well as M. Herfurth: "Aktives Oberschwingungs-filter mit konstanter Betriebsfrequenz und 600 W Ausgangsleistung", Semi-Conductor Application Report of SIEMENS, Print Reference PD 22 9002). In such a circuit, the rectified line current either flows through an inductor, which takes on magnetic energy, and an electronic switch, or through the inductor, the isolating diode and a voltage-determining element (capacitor, battery), energy being transmitted from the inductor to the voltage-determining element. The ON/OFF times of the electronic switch are controlled depending on the line voltage waveform so that a line current of an almost sinusoidal shape is developing. Here, the line current amplitude results from the required power to be converted. A corresponding control method is known from the application instructions for special integrated circuits (e.g. Claudio de Sa e Silva: Power Factor Correction with the UC 3854, Application Paper of UNITRODE).
With regard to batteries consisting of a string of series-connected battery blocks it is known that, due to always existing differences in capacity of the single battery blocks, the check for the sum of all block vol
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International Search Report corresponding to PCT/DE95/00985.
"An SMR Topology with Suppressed DC Link Components and Predictive Line Current Waveshaping", IEEE Transactions On Industry Applications, vol. 1A-23, No. 4, Jul./Aug. 1987, 644-653.
"Power Factor Correction With The UC3854", by Claudio de Sa e Silva, Senior Applications Engineer, Unitrode Integrated Circuits.
"Aktives Oberschwingungsfilter Mit Konstanter Betriebsfrequenz Und 600 W Ausgangsleistung", PD 22 9002 Siemens, Auto-/Industrieelektronik.
"Kompakter serienreifer Antrieb fur Elektrofahrzeuge", Brown Boven Technik May 1985, pp. 229-234.
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