Dual active bridge with distributed inductance

Abstract

A dual active bridge includes a first converter arranged on a primary side of the dual active bridge, a second converter arranged on a secondary side of the dual active bridge, a high frequency transformer that has two windings and that operatively connects the first converter to the second converter, and a plurality of inductors, which are arranged along the legs on one of the two windings of the high frequency transformer, and which are split between the legs of that winding. In one embodiment, the plurality of inductors are split between the legs of the winding disposed on the secondary side of the dual active bridge. The plurality of inductors may consist of two inductors, of which a first one is arranged of the first leg of the winding and a second one is arranged on the second leg of the winding.

Claims

1. A dual active bridge comprising: a first converter arranged on a primary side of the dual active bridge; a second converter arranged on a secondary side of the dual active bridge; a high frequency transformer having two windings and operatively connecting the first converter to the second converter; and a plurality of inductors arranged along legs on one of the two windings of the high frequency transformer, the plurality of inductors being split between the legs of the one of the two windings, wherein the plurality of inductors are split between the legs of the one of the two windings disposed on the secondary side of the dual active bridge, wherein the plurality of inductors consists of a first inductor and a second inductor, and wherein the first inductor is arranged on a first leg of the one of the windings, and the second inductor is arranged on a second leg of the one of the windings, and wherein each of the first and the second converter comprises four switch cells, and wherein a voltage across the first and the second inductor is:
V.sub.lk=½.Math.(V.sub.in+V.sub.out)−ΣV.sub.CESAT-S1 . . . CESAT-S8−(I.Math.R) wherein: V.sub.lk=voltage across the first and the second inductor, V.sub.in=primary DC-link voltage, V.sub.out=secondary DC-link voltage, V.sub.CESAT-S1 . . . CESAT-S8=saturation voltage of switch cells S.sub.1 . . . S.sub.8, I=current, R=resistance of the first and the second inductor.

2. The dual active bridge according to claim 1, wherein the first converter receives a primary DC-link voltage from a voltage source via an AC-DC Power Factor Correction stage, and wherein the second converter provides a secondary DC-link voltage to a load.

3. The dual active bridge according to claim 2, wherein the AC-DC Power Factor Correction stage is connected to a grid, and wherein the load is a battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings constitute a part of this specification and include exemplary embodiments of the invention, which may be embodied in various forms. It is to be understood that in some instances various aspects of the invention may be shown exaggerated or enlarged to facilitate an understanding of the invention.

(2) FIG. 1 illustrates a dual active bridge according to the prior art.

(3) FIG. 2 is a chart illustrating the operation of a dual active bridge as depicted in FIG. 1.

(4) FIG. 3 illustrates, in schematic form, a dual active bridge according to the invention.

(5) FIG. 4 is a chart illustrating the operation of a dual active bridge as depicted in FIG. 3.

(6) FIG. 5 illustrated an application of a dual active bridge as depicted in FIG. 3.

(7) FIGS. 6 and 7 illustrate applications of a dual active bridge as depicted in FIG. 3.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(8) Detailed descriptions of embodiments of the invention are provided herein. It is to be understood, however, that the present invention may be embodied in various forms. Therefore, the specific details disclosed herein are not to be interpreted as limiting, but rather as a representative basis for teaching one skilled in the art how to employ the present invention in virtually any detailed system, structure, or manner.

(9) Turning first to FIG. 3, a dual active bridge 30 according to the invention includes a first converter 31, arranged on a primary side of dual active bridge 30; a second converter 32, arranged on a secondary side of the dual active bridge; and a high frequency transformer 33, which has a first winding 34 and a second winding 35, and which is disposed between first converter 31 and second converter 32, so as to operatively connect first converter 31 to second converter 32, and vice versa.

(10) Each of first converter 31 and second converter 32 includes four bidirectional switch cells S.sub.1 . . . S.sub.4 and S.sub.5 . . . S.sub.8 according to an architecture which is known in the art and which, accordingly, will not be described further.

(11) First converter 31 receives a primary DC-link voltage V.sub.in from a voltage source 39, for example, from the grid 40 via a PFC (Power Factor Correction) power stage 38 or a Full Bridge (FB) AC-DC stage, and operates as a DC-DC converter. Second converter 32 operates as a DC-DC converter to provide a DC-link voltage to a load 41, such as a battery 42. Examples of this configuration are depicted in FIGS. 6 and 7. Therefore, the combination of a PFC or FB stage and of a DAB according to the invention provides for isolated and bi-directional power conversion and is particularly suitable, among many possible applications, for On-Board Chargers (OBC) of electric vehicles for deployment in charging, vehicle-to-grid, vehicle-to-load, and grid ancillary services. Other applications of dual active bridge 30 are however possible.

(12) In a dual active bridge according to the invention, a plurality of inductors is arranged along the legs of one of the two windings of the high frequency transformer and are split between the legs of that winding. In the embodiment illustrated in FIG. 3, there are two inductors 36 and 37, one of which is disposed on a first leg of winding 35 and the other one of which is disposed on the second leg of winding 35.

(13) It can be seen that, in the present embodiment, inductors 36 and 37 are arranged on the legs of winding 35 on the secondary side of dual active bridge 30, but in different embodiments, more than two inductors may be present and be split between the legs of winding 35. In still other embodiments, the inductors may be split between the legs of winding 34 on the primary side of the dual active bridge.

(14) A dual active bridge with distributed inductance according to the invention, such as dual active bridge 30, provides the advantage of reducing the Volt-microsecond (V-μs) product substantially due to the sum of the voltage applied over each of the phases.

(15) Turning now to FIG. 4, it can be seen that, by placing the inductance across a common-core inductor on the two output leads of the DAB transformer, a substantial reduction in inductor V-μs product takes place and, consequently, there is a reduction in peak currents. This leads to a reduction in peak flux requirements (that is, less core material) and a reduction in copper and active switch losses due to a slight reduction in peak current.

(16) Still with reference to FIG. 4, the voltage across the indictor can be expressed as:
V.sub.lk=½.Math.(V.sub.in+V.sub.out)−ΣV.sub.CESAT-S1 . . . CESAT-S8−(I.Math.R)  (1)
where:
V.sub.lk=voltage across the first and the second inductor,
V.sub.in=DC-link voltage from a voltage source,
V.sub.out=DC-link voltage to a load,
V.sub.CESAT-S1 . . . CESAT-S8=saturation voltage of bidirectional switch cells S.sub.1 . . . S.sub.8,
I=current,
R=resistance of the first and the second inductor.

(17) Therefore, when there are eight bidirectional switch cells, equation (1) reads as:

(18) $\begin{array}{cc}{V}_{\mathrm{lk}}=\frac{1}{2}.Math.\left(V_{\mathrm{in}}+V_{\mathrm{out}}\right)-\left(V_{\mathrm{CESAT}-S1}+V_{\mathrm{CESAT}-S2}+V_{\mathrm{CESAT}-S3}+V_{\mathrm{CESAT}-S4}+V_{\mathrm{CESAT}-S5}+V_{\mathrm{CESAT}-S6}+V_{\mathrm{CESAT}-S7}+V_{\mathrm{CESAT}-S8}\right)-\left(I.Math.R\right)& \left(2\right)\end{array}$

(19) In a high voltage application, such as that depicted in FIG. 4, equation (2) may be written as:
V.sub.lk=½.Math.(375+350)−(2.Math.8)−(20.Math.1.5)=316  (3)

(20) In this application, a person of skill in the art will notice voltages nearing 300 VDC for only a modestly higher T.sub.on period. Therefore, the V-μs product is 300/48000.Math.T.sub.on/T.sub.period=1,625 V-μs assuming a 26% duty cycle. This corresponds to a core flux reduction of 26%.

(21) FIG. 5 illustrates an actual implementation of a DAB with distributed inductance according to the invention in a real-life application.

(22) While the invention has been described in connection with the above-described embodiments, it is not intended to limit the scope of the invention to the particular forms set forth, but on the contrary, it is intended to cover such alternatives, modifications, and equivalents as may be included within the scope of the invention. Further, the scope of the present invention fully encompasses other embodiments that may become obvious to those skilled in the art and the scope of the present invention is limited only by the appended claims.