AC/DC converter

Details AC/DC converter AC/DC converter

1997-07-29

1999-11-02

Nguyen, Matthew

Electric power conversion systems

Current conversion

With condition responsive means to control the output...

363125, H02M 542, H02M 700

Patent

active

059782420

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

This invention relates to a converter circuit arrangement for transferring power from an electrical two-conductor current loop to a functional unit. The circuit comprises an inductive coupling (transformer) and an AC/DC converter based on the switch mode. More specifically this is here derived from a DC/DC converter of the "Boost Mode" type. The current loop conducts an alternating current of a fixed frequency and amplitude for the power transfer, and signals to and from the functional unit are superimposed on the power transfer current in the current loop.
In the inductive coupling the current loop constitutes a primary winding and a rectifier device is located at the secondary side for DC supply to the functional unit. Moreover there is included a voltage regulator for controlling an electronic switch for operation in switch mode as mentioned, a power coil and at least one capacitor.
The invention has been primarily developed in connection with a so-called fieldbus for interconnecting several functional units, as for example measuring instruments or control units in process control installations, and the like. For example, a current loop bus of the type Current Bus Mode according to IEC 1158-2, can be of interest here. This fieldbus or current loop constitutes a two-conductor line, where functional units connected to it communicate, by means of signals, through this line, at the same time as they are supplied with required power in the form of current supply through the same pair of conductors. In such a current loop bus the functional units are connected in series in the bus. Power for current supply from the bus is tapped over the equivalent impedance introduced by the functional unit concerned, into the two-conductor line. This is fed with a constant alternating current from a central unit. Each of the functional units appears as a series load in the current loop bus, and draws power being proportional to the real part of the series load. In practice the connection of functional units to the current loop is effected inductively by the bus' forming one or more windings at the primary side of a transformer. With such an inductive connection the secondary side of this transformer can be an integrated part of the functional unit concerned.
In addition to the above mentioned power or current supply for the operation of associated functional units, the inductive coupling can also be adapted to provide for signal transfer or communication between the fieldbus and the respective functional units. Such signals are superimposed on the power feed, and in practice will normally have a signal strength lying several decades lower than the current amplitude for power transfer. Accordingly it is very important that the power signal has a sinusoidal shape as closely as possible, so that required filtering at the individual functional units will be simplified. Moreover the load represented by each unit with respect to the current loop bus, should be as linear as possible in order to prevent the functional units from introducing harmonic noise into the fieldbus network. Such noise will be disturbing and detrimental for said signal communication. Harmonic noise components from the power supply part or from non-linearities in the individual functional unit, will be spread into the signal band for communication and thereby reduce the signal-to-noise ratio.
These considerations also apply in the alternative of providing for signal transfer to/from the fieldbus by a separate inductive coupling or transformer.
In fieldbus systems or installations of actual interest to this invention, the feed frequency of the AC supply is substantially higher than the common mains frequency, namely 16 kHz in a specific fieldbus embodiment. The frequencies employed for the above discussed communication or signal transfer, usually are significantly higher than this current supply frequency. As will further appear from the description below, the converter circuits for the functional units comprise an electronic switc

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patent: 5783933 (1998-07-01), Bailly
patent: 5886891 (1999-03-01), Jiang et al.

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