Battery charging using a transformer with a single primary winding and plural secondary windings
First Claim
1. A charge equalizer for equalizing the charge on two or more energy storage cells connected in series, comprising:
- (a) a transformer having a single primary winding and plural secondary windings, wherein each secondary winding is adapted to be connected to a one of the energy storage cells;
(b) power converter means for applying an equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells; and
(c) means for increasing a magnitude of the qualization voltage signal as the charge on the energy storage cells becomes equalized.
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Accused Products
Abstract
A simple, low-cost technique for charge equalization of a series connected string of battery cells is provided. The secondary windings of a transformer having a single primary winding and multiple secondary windings are connected across each battery cell to be equalized. A single power converter applies a charging signal to the primary of the transformer, inducing a charging current in each secondary which is inversely related to the charge on the battery cells to be equalized. The transformer is preferably implemented as a coaxial winding transformer having low secondary-to-secondary winding coupling. The power converter is preferably implemented as a forward converter supplied with DC power from an adjustable DC power source. A source voltage provided by the DC source may preferably be adjusted during the course of charge equalization to preferentially direct charge to weaker cells. The charge equalization system may be used in combination with a bulk charging system to provide for both rapid charging of a battery string as well as equalization of the battery cells within the string.
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Citations
35 Claims
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1. A charge equalizer for equalizing the charge on two or more energy storage cells connected in series, comprising:
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(a) a transformer having a single primary winding and plural secondary windings, wherein each secondary winding is adapted to be connected to a one of the energy storage cells; (b) power converter means for applying an equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells; and (c) means for increasing a magnitude of the qualization voltage signal as the charge on the energy storage cells becomes equalized.
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2. A charge equalizer for equalizing the charge on two or more energy storage cells connected in series, comprising:
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(a) a transformer having a single primary winding and plural secondary windings, wherein each secondary winding is adapted to be connected to a one of the energy storage cells; (b) a secondary rectifier connected to each secondary winding and adapted to be connected in series with the corresponding energy storage cell to half-wave rectify a charging voltage appearing on the secondary winding; (c) a controllable DC voltage source for providing a DC source voltage; (d) a DC-to-AC power converter having an input connected to the DC voltage source and an output connected to the primary of the transformer to apply an AC voltage signal to the primary of the transformer which causes the charging voltage to appear on the secondary windings and which induces a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells; and (e) source voltage control means for gradually raising the DC source voltage level as the charge on the energy storage cells becomes equalized. - View Dependent Claims (3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A charging system for charging a string of two or more energy storage cells connected in series, and for equalizing the charge on the energy storage cells, comprising:
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(a) a bulk charging system having an input adapted to be connected to a source of AC power and an output adapted to be connected across the string of energy storage cells for applying a bulk DC charge voltage across the string of energy storage cells; and (b) a charge equalizer circuit including a transformer having a single primary winding and plural secondary windings wherein each secondary winding is adapted to be connected to a one of the energy storage cells, a power conversion means for applying a charge equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells, and means for increasing a magnitude of the charge equalization voltage signal as the charge on the energy storage cells becomes equalized. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. A method of equalizing the charge on two or more energy storage cells connected in series, comprising the steps of:
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(a) connecting each secondary winding of a transformer having plural secondary windings and a single primary winding to a one of the energy storage cells to be charged; (b) applying a voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells; and (c) increasing a magnitude of the voltage signal as the charge on the energy storage cells becomes equalized. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34)
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35. A charge equalizer for equalizing the charge on two or more energy storage cells connected in series, comprising:
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(a) a coaxial winding transformer having a single primary winding and plural secondary windings, wherein each secondary winding is adapted to be connected to a one of the energy storage cells, and wherein the coaxial winding transformer includes plural coaxial cables corresponding to the number of secondary windings and which are wound around a transformer core, wherein each coaxial cable includes an outer conductor and an inner conductor completely enclosed in the outer conductor, and wherein the outer conductors are connected in parallel to form the transformer primary winding and each inner conductor forms a transformer secondary winding; and (b) power converter means for applying an equalization voltage signal to the primary of the transformer to induce a charging current in each secondary winding whose average magnitude is inversely related to a charge voltage level of the corresponding energy storage cell to equalize the charge on the energy storage cells.
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Specification