Patent US8441231 Z-ARCHIVE-Energy Storage: Bidirectional Direct Current Converters

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Patent US8441231

Issued 2013-05-14

Bidirectional Hysteretic Power Converter

A novel switching hysteretic bidirectional power converter is presented. The converter includes the generation of a synthetic ripple signal and feedback networks to hysteretically control the power converter both when the converter operates as a boost converter with the flow of power in one direction, and when the converter operates as a buck power converter with the flow of power in the opposite direction.

The presented approach provides a switching converter with a much simpler control method with respect to conventional inductive bidirectional power converters. The hysteretic control provides stable operation in all conditions with excellent load and line transient response. Furthermore this allows the operation of the bidirectional power converter with much higher switching frequencies with respect to state of the art conventional approaches, thus reducing the cost and size of the passive components storing energy during the conversion.

Since bidirectional switching power converters are used mainly when the flow of power is bidirectional, the typical application involves the charging and discharging of batteries, and as part of this novel approach, an hysteretic battery charger including hysteretic constant current and constant voltage control is introduced as part of a larger bidirectional switching power converter.

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3 Independent Claims

1. A switching bidirectional power converter to efficiently convert power comprising: an inductor coupled between a first main terminal of said power converter and a switching node; a first power device coupled between said switching node and the negative terminal of said power converter; a second power device coupled between said switching node and a second main terminal of said power converter; wherein the flow of power flows in a first direction from said first main terminal of said power converter to said second main terminal of said power converter when said power converter operates as a step up converter, and flows in a second direction from said second main terminal of said power converter to said first main terminal of said power converter when it operates as a step down converter; a first feedback network to generate a first synthetic ripple signal when said power converter operates as a step up converter; a second feedback network to generate a second synthetic ripple signal when said power converter operates as a step down converter; a comparator providing hysteretic control of said power converter in response to said first and second synthetic ripple signals, to a reference signal, and to a mode selection signal; wherein said mode selection signal determines whether said power converter operates as a step up converter or as a step down converter, and a control logic circuit and a pre-driver circuit for generating the signals to drive said first and second power devices in response to the output signal of said comparator.
8. A method to efficiently convert power from a first power source, coupled to a first main terminal of a power converter, to a second main terminal of said power converter or from a second power source, coupled to said second main terminal of said power converter, to said first main terminal of said power converter comprising: switching a first power device and a second power device; charging and discharging with a modulated duty cycle an inductor; whereby the flow of power in said inductor can be in a first direction or in a second direction in response to a mode selection signal; generating a first synthetic ripple signal when the flow of power is in said first direction and a second synthetic ripple signal when the flow of power is in said second direction opposite to said first direction; comparing said first or said second synthetic ripple signal to a reference signal by means of a comparator in response to said mode selection signal; modulating the duty cycle of said first and second power devices in response to the output of said comparator, whereby the voltage appearing at said first main terminal when the flow of power is in said first direction or the voltage appearing at said second main terminal when the flow of power is in said second direction is regulated to be at a desired value, and whereby the modulation of the duty cycle occurs by means of an hysteretic control.
15. A switching power converter to efficiently convert power from a power source to charge a battery comprising: an inductor coupled between a first main terminal of said power converter and a switching node; a first power device coupled between said switching node and the negative terminal of said power converter; a second power device coupled between said switching node and a second main terminal of said power converter; wherein said battery is coupled to said first main terminal when said power source is coupled to said second main terminal, and wherein said battery is coupled to said second main terminal when said power source is coupled to said first main terminal; a first feedback network to generate a first synthetic ripple signal when said power converter operates in constant voltage mode; a second feedback network to generate a second synthetic ripple signal when said power converter operates in constant current mode; a first comparator providing hysteretic control of said switching power converter in response to said first synthetic ripple signal and to a first reference signal; a second comparator providing hysteretic control of said switching power converter in response to said second synthetic ripple signal and to a second reference signal; a control logic circuit and a pre-driver circuit for generating the signals to drive said first and second power devices in response to the output signals of said first and second comparator, and whereby the modulation of the duty cycle of said switching power converter occurs by means of an hysteretic control in constant current mode of operation and in constant voltage mode of operation.