DC/DC converter with reduced ripple

Abstract

A DC/DC converter is provided which can be produce easily and inexpensively with an alternating current component with which a superimposed direct current is reduced in an output voltage (ripple). A C+DC/DC converter includes an input and output, a series arm which is arranged between the input and the output and in which at least one first inductor and first capacitor are arranged, and a capacitor arranged in a first shunt arm at the output. A second shunt arm arranged parallel to the first shunt arm is equipped with a first switch and a second switch arranged in series and a second inductor such that the first connection of the inductor is connected to a point between the first inductor and the first capacitor and the second connection of the inductor is connected to a point between the first and the second switch.

Claims

1. A DC/DC converter comprising: an input and an output, a longitudinal arm arranged between the input and the output and having at least a first inductor and a first capacitor, a first shunt arm connected across the output, a second shunt arm connected in parallel with the first shunt arm and having a second inductor and a second active semiconductor switch connected in series, wherein a terminal of the second inductor facing away from the second active semiconductor switch is directly connected to the output, and a first active semiconductor switch having a first terminal connected to a point between the second inductor and the second active semiconductor switch and a second terminal connected to a point between the first inductor and the first capacitor.

2. The DC-to-DC converter according to claim 1, wherein the first and second active semiconductor switches are a BJT (Bipolar Junction Transistor), a MOSFET (Metal-Oxide-Semiconductor Field-Effect-Transistor) or an IGBT (Insulated Gate Bipolar Transistor).

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) Further details, features and advantages of embodiments of the invention will become apparent from the following description of exemplary embodiments with reference to the appended drawings:

(2) FIG. 1: a prior art DC/DC converter (SEPIC-Converter),

(3) FIG. 2 a first implementation of the DC/DC converter according to the invention,

(4) FIG. 3: a second implementation of the DC/DC converter according to the invention,

(5) FIG. 4 a third implementation of the DC/DC converter according to the invention,

(6) FIG. 5 an application of the DC/DC converter according to the invention in an AC bridge, and

(7) FIG. 6 a graphical representation of detected ripple in comparison between the prior art and the present invention.

(8) FIG. 1 shows a prior art DC/DC converter 1. The illustrated DC/DC converter 1 is a so-called SEPIC-Converter (SEPICSingle Ended Primary Inductor Converter), which was selected as a representative example of the group of non-galvanically separating converters which are constructed with passive 4 storage devices, for example two capacitors and two inductors. The characteristic of this DC/DC converter enables operation in such a way that the output voltage can be smaller or greater than the input voltage.

(9) The DC/DC converter 1 has an input 2 to which an input voltage Ue can be applied, and an output 3 at which an output voltage Ua is supplied that has been converted by the DC/DC converter 1. The DC/DC converter 1 may supply an output voltage Ua which may be larger or smaller than the input voltage Ue.

(10) The DC/DC converter 1 has in a longitudinal arm a first inductor 4, a first capacitor 5 and a diode 6. In an output-side shunt arm, a second capacitor 8 is arranged in parallel with a load resistor connected to the output 3, which is not shown in FIG. 2. In a further shunt arm, a second inductor 7 is arranged between the first capacitor 5 and the diode 6. A first switch 9 is also arranged in a third shunt arm between the first inductor 4 and the first capacitor 5.

(11) When the switch 9 in the DC/DC converter 1 shown in FIG. 1 is closed, the input voltage is present at the first inductor 4. Simultaneously, a voltage having a value corresponding of the input voltage at the input 2 is present at the first capacitor 5. The current flowing through the first and second inductor 4 and 7 increases, with energy being stored in the inductors 4 and 7.

(12) At this time, the second capacitor 8 arranged at the output side supplies the output current for a connected load or a consumer, since the diode 6 is blocking. When the switch 9 is opened, the polarity of the voltages at the first and second inductors 4 and 7 is reversed. The diode 6 turns on and supplies the stored energy to the second capacitor 8 and thus also to the connected load,

(13) FIG. 2 shows a first implementation of the DC/DC converter 1 according to the invention. The DC/DC converter 1 has in its longitudinal arm, i.e. between its input 2 and its output 3, at least a first inductor 4 and a first capacitor 5. A second capacitor 8, which is connected in parallel to an unillustrated load at the output 3, is arranged in an output-side shunt arm.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(14) A first switch 9 and a second switch 10 connected in series are also arranged parallel to the output 3 and the second capacitor 8. A second inductor 7 is disposed between the first inductor 4 and the first capacitor 5 and a terminal disposed between the series-connected switches 9 and 10.

(15) Preferably, the switches 9 and 10 are implemented as active semiconductor switches. For example, BJT (Bipolar Junction Transistor), MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor), IGBT (Insulated-Gate Bipolar Transistor) or others switches may be used.

(16) It is contemplated to control the switches with a control signal generated by a central controller, which is not shown in FIG. 2. The central controller provides the control signals for the mechanical or electronic switches 9 and 10 such that the switches 9 and 10 are activated alternately. Thus, the switch 9 is closed when the switch 10 is opened and vice versa.

(17) In the circuit arrangement according to the invention shown in FIG. 2, the direction of the current flow is dependent on a selected duty cycle of the control signals of the switches 9 and 10 as well as on the voltages Ue and Ua present at the input 2 and at the output 3.

(18) The switches 9 and 10 can be controlled using the method of state-space averaging and a special form of zero-voltage switching, wherein the oscillating circuit is arranged parallel to the switch and is actively excited to oscillate by an additional switching pulse.

(19) The DC/DC converter 1 in FIG. 2 is able to generate from an input voltage Ue applied to the input 2 a larger output voltage Ua at the output 3. In such a DC/DC converter 1, ripple is reduced in accordance with the invention, i.e. the pulsating direct current at the input 2 is smaller. The input can be interchanged with the output, thus reversing the operation. When an input voltage Ue is applied to the output 3 and the DC/DC converter 1 is controlled accordingly, an output voltage Ua is supplied at the input 2 which is, for example, less than Ue.

(20) In the event that the operation of the DC/DC converter is reversed, the reduced ripple is no longer present at the input side of the converter, but rather at the output side.

(21) FIG. 3 shows a second implementation of the DC/DC converter 1 according to the invention. The DC/DC converter 1 has in its longitudinal arm, between its input 2 and its output 3, at least a first inductor 4 and a first capacitor 5. A second capacitor 8, which is connected in parallel to an unillustrated load at output 3, is arranged in an output-side shunt arm.

(22) Moreover, a second inductor 7 and a second switch 10 connected in series are arranged in parallel with the output 3 and the second capacitor 8. A first switch 9 is arranged between the first inductor 4 and the first capacitor 5 and a terminal disposed between the second inductor 7 and the first switch 9.

(23) FIG. 4 shows a third implementation of the DC/DC converter 1 according to the invention. The DC/DC converter 1 has in its longitudinal arm between its input 2 and its output 3 at least a first inductor 4 and a first capacitor 5. A second capacitor 8, which is connected in parallel to an unillustrated load at the output 3, is arranged in an output-side shunt arm.

(24) Likewise, a second switch 10 and a second inductor 7 connected in series are arranged parallel to the output 3 and the second capacitor 8. A second switch 9 is connected between the first inductor 4 and the first capacitor 5 and a terminal disposed between the series-connected elements switch 10 and second inductor 7.

(25) In the DC/DC converter 1 shown in FIG. 4, the polarity of the voltage at the output 3 is inverted.

(26) The switches 9 and 10 can be controlled by the method of state-space averaging as well as a special form of zero-voltage switching, wherein the oscillating circuit is parallel to the switch and is actively excited to oscillate by an additional switching pulse.

(27) In the event that an active semiconductor switch, such as an IGBT or a MOSFET, is used for the switches 9 and/or 10, these switches 9 and/or 10 form a diode in a state in which the switch 9 and/or 10 is/are not activated. This diode allows a directed current flow. In the case where one or both switches 9 and/or 10 is/are activated, the semiconductor switches have a very low transfer resistance and enable current flow in any direction.

(28) FIG. 5 shows an application of the DC/DC converter 1 in an AC bridge. In order to generate, for example, a sinusoidal AC voltage required for a load, such as a motor, two DC/DC converters 1 are used. A voltage source is connected on the input side to the inputs of both DC/DC converters 1. The DC/DC converter 1 shown in the upper part of FIG. 5 generates a positive half-wave in response to corresponding control signals for the switches 9 and 10 in the DC/DC converters 1. This is shown in FIG. 5 in a small diagram with a current-time profile of the current 11. The negative half-wave is generated by the lower DC/DC converter 1. The corresponding profile of the current 12 is also shown in a small diagram.

(29) It has been demonstrated, when comparing a DC/DC converter 1 according to the invention of FIG. 2 with a prior art SEPIC-Converter that the disturbing ripple could be greatly reduced. As shown in part in FIG. 6, comparative measurements have shown that the SEPIC-Converter, shown in the upper part of the current-time profile, exhibits ripple currents in the range of about 4 A, whereas the converter according to the invention shown in the lower part of the current-time profile, had a ripple current in the range of about 4 mA. Thus, the ripple could be greatly minimized by virtue of the invention.

(30) The invention can be used in many areas for the conversion of electrical energy, such as in the Unidirectional or bidirectional DC/DC conversion, Extension of DC version to an AC bridge, Impedance spectroscopy of energy sources (low ripple), Control of electric motors or Battery charging in battery management systems.

(31) An exemplary application of the invention in impedance spectroscopy will be described below.

(32) The characteristic impedance of an electrochemical energy source, such as an accumulator or a fuel cell, provides information about the internal states of the source. In order to measure the impedance, the source is either supplied with a targeted disturbing current and the voltage response is measured, or a disturbance voltage is superposed on the source, and the reaction of the current is detected. In both cases, the ripple current or the ripple voltage is superposed on this targeted interference signal. The effect of the ripple current can be significantly reduced with the illustrated invention, thus allowing a significantly improved impedance measurement, which is hardly affected by disturbances.

(33) The DC/DC converter according to the invention advantageously reduces ripple without the need to resort to additional, larger or different components in the DC/DC converter circuit. Another advantage is that the components used in the DC/DC converter have no specific dimensioning requirements.