EP1454424A1

EP1454424A1 - Coupler arrangement

Info

Publication number: EP1454424A1
Application number: EP02789082A
Authority: EP
Inventors: Ake Hansen
Original assignee: Schneider Electric Powerline Communications AB
Current assignee: Schneider Electric Powerline Communications AB
Priority date: 2001-11-21
Filing date: 2002-11-21
Publication date: 2004-09-08
Also published as: WO2003044982A1; AU2002353710A1

Abstract

The present invention relates to a signal coupling arrangement (140, 150) comprising a first transformer side having a first winding (142, 152) connected to a signal input and a second transformer side having a second winding (143, 153) having first and second terminals and connected to a signal output. To reduce the noise, the second winding (143, 153) is provided with additional terminals (144, 154) connected to a ground for reducing noise and preferably reducing losses through the M factor and/or enhancing Q factor provides for a dynamic and high bandwidth.

Description

Coupler Arrangement

Technical Field

The present invention relates to a signal coupling arrangement, specially a so-called power-line coupler for transforming signals on to the power grid. More specially, the invention relates to a signal coupling arrangement comprising a first coil connected to a signal input and a second coil connected to a signal output.

Background of the invention

The applicant is developing a solution for transforming the power line network into a high-class information infrastructure capable of handling the high demands that users and network operators have on the next generation IP-based multimedia services. The technology is in a suite of products ranging from plug & play end-user modems to reliable and robust network infrastructure. The benefits of using the power line network for communication is that the network is already in place and that it is omni-present, a normal house has power sockets in almost every corner. To the user, this means, for example convenient and cost effective Internet access.

Thus, a new method f transmitting digital information over the mains network and/or distribution network is provided. The schematic view of fig.l illustrates an example of a solution provided by the applicant. In a first step, shown in block A, information, such as digital, voice and/or image data is modulated and transformed onto the mains distribution network in a medium voltage transformer. Before supplying the power to household, it is transformed into low voltage electricity, i.e. block B, in a low voltage transformer. At the user premises, e.g. a house, the information on the power line is transformed to suitable data by means of modems connected directly to the power line, block C. Function of a so-called air coupler, by its physical parameters, is to convert nominal impedance, such as 50 ohm (from the amplifier, to the front end) to the line impedance (220 V). A schematic view of an air coupler and its electrical equivalence is illustrated in Figs. 2a and 2b. The coupler comprises of first coil, L2, arranged inside a first coil LI and each connected to a power line.

One can simply calculate the reactance to be the same as the network's impedance, that means that X_c = ωL₂ = 100 ohm and ωL = 50 ohm.

In a more scientific and analytic approach, when designing a coupler it can be translated into an schematic equivalent, as shown in the diagram of fig. 3.

The line impedanceZ₀ can be calculated as:

2π Q Z_n =

RsRg

Where

M = K JL_l *L₂ Q = ωL₂ IR_s

The factor K is dependent on the physical distance between the two coils and their orientation relative each other. Optimum energy transfer is obtained when

(2.7rfM)² IR_S is equal to Rg. The disadvantage with this coupler is: 1. Losses through the M factor that will give efficiency at 25-40 %.

2. The Q factor provides a limited bandwidth of some 6- 8 MHz.

3. Manufacturing problems, which will force to trimming of every unit.

4. Screening to reduce EMC will affect performance of the coupler.

To improve the performance of the coupler, it is possible to increase the K factor and eliminate the Q parameter; preferably, by using a coupler with a ferrite core. This solution is very common in wideband power amplifiers within the Radio Frequency (RF) bands. To achieve the wideband solution, the wires are wired in a bifilar mode on a core. This design works as a transmission line and wiring on a representative toroid, the signal is coupled in a magnetic mode at lower frequencies and capacitively at higher frequencies. A coupler wired in transmission mode has the transfer function expressed mathematically as:

PowerOutput _ 4(1 + cos/?/)²

PowerAvailable 3(1 + cos/?/)² + 4 sin² /?/

where β is phase constant and / is the length of the wire

This means that the response is down 1 dB at / = λl and zero level occurs at

/ = λl2 . For a good wideband response this transformer must be small. The K factor is close to 1. For example, a possible bandwidth is 1 MHz to 50 MHz.

An alternative is the broadband binocular transformer, as illustrated in Figs. 4a and 4b. As the wires are surrounded by more core volume of ferrite material, it is less sensitive to the mutual dependency of the wires. That means that the wires can be coiled in a more straight way and the function is more like an ordinary transformer, i.e.:

»ι)² ₌ Z, , (κ₂)² Z₂ '

wherein n_x and n₂ are number of coils and Z and Z₂, the impedance of the first and the second coil.

The equivalent schematic for the binocular is illustrated in Fig. 5 looks as follows:

Following formulas can be used for this circuit:

£ - 1

L = z_c

2ω_L

where Z_c corresponds to the representative transformer impedance. ω_H high cut off angular frequency ω_L low cut off angular frequency L_L is the leakage inductance

C_d capacitance, mainly between the wires L_e equivalent magnetizing inductance.

The formulas shows that the bandwidth is wide at minimum C_D and L_L which is dependent of a few number of wire turns. The L_e value is maintained by a high A_L value, which also yields a small number of turns. The disadvantages with the ferrite coupler are, due to its high coupling factor, it is also sensitive to longitudinal noise and transients.

There are number documents related to the field, which do not solve the problems sat out in a satisfying way.

EP 961 415 Al relates to data transmission method, which has a signal to be transmitted fed to the electrical supply lines of a LV, MV, or HV installation and extracted simultaneously via at least 2 output couplers. Their signals are combined via a selection and combination stage, to provide a single output signal.

In WO 93/25011 a switching arrangement is provided for coupling a transmitting unit to a transmission line. According to the application, a transformer is provided, whose secondary winding is a portion of the transmission line and whose primary winding is .connected with the transmitting unit and integrated into a parallel resonance circuit, whose resonant frequency is tuned, each time, to the carrier frequency of the transmitted signal. In addition, a tuning unit may be provided for the automatic tuning of the parallel resonance circuit.

A communications apparatus is disclosed in EP 913 955 A2, which is adapted for use with a mains electricity transmission and/or distribution network, and includes signal transmission and/or reception means, and frequency conversion means for converting the frequency of a signal transmitted or received by signal transmission and/or reception means to a frequency which facilitates improved propagation of the signal on the network. Preferably the signal transmission and/or reception means is adapted to operate according to a telephony standard which uses a relatively high carrier frequency (e.g. CT2), and the frequency conversion means is usable to convert a signal having a relatively high carrier frequency to a signal having a lower carrier frequency.

In US 4,142,178, a high voltage signal coupler couples carrier communication signals between a distribution network primary conductor and communication elements located at spaced intervals on the distribution network. A single bushing, high frequency, coupling capacitor communicates the carrier communication signals between one of the distribution network primary conductors and a conductor which is at ground or real earth potential with respect to power current frequencies. A parallel resonant circuit, formed by a tuning capacitor and a hollow core of magnetic material inductively surrounding the power frequency ground conductor, couples the carrier communication signals to the communication elements connected thereto at a predetermined frequency without interfering with the operation of the ground conductor at the frequency of the power current.

In US 5,406,249, an apparatus and a method for communicating data among transceivers in an electrical utility distribution system where a signal path between the transceivers includes multiple power distribution transformers is described. A first transceiver, common-mode coupled to a secondary of a first power distribution transformer transmits a carrier signal modulated by a data stream to the secondary. The modulated signal is transferred to the primary of the first power distribution transformer which is coupled to the primary of a second power distribution transformer. A second transceiver, common-mode coupled to a secondary of the second power distribution transformer, receives the modulated signal from the secondary. Both transceivers are protected from the high power delivered at the line frequency by filtering capacitors which attenuate signals at the line frequency and pass signals at the carrier signal frequency. In one embodiment A first secondary distribution means and a second secondary distribution means are single phase distribution lines, respectively, and a center tap of a secondary winding of each of said first and second distribution transformers is connected to a earth ground. Because the PLC (Power Line Carrier) signal is a common-mode signal relative to earth ground, and the center node of the secondary windings of distribution transformer is coupled to earth ground, the PLC signal is imposed on the three secondary windings.

Summery of the invention

The main object if the invention is to provide a signal coupler that reduces and eliminates the drawbacks corresponded with the known couplers. Advantages, with the coupler according to the invention include: less losses through the M factor, better Q factor provides for a dynamic and high bandwidth, simple manufacturing, with less trimming and adjustment work and better screening providing better performance of the coupler. Moreover, the invention provides a more compact coupler.

For this reasons, in the initially mentioned arrangement, the second winding is provided with additional terminals connected to a ground. Most preferably, the additional terminals are arranged (substantially) in same distance to said first and second terminals. Preferably, the transformer comprises a Radio Frequency coil. According to one embodiment transformer comprises a toroid coil or a cylindrical coil.

In a main system connected to transmission data system, the invention also relates to an arrangement for coupling/decoupling a data signal comprising a first transformer side having a first winding connected to a power and signal input and a second transformer side having a second winding having first and second terminals and connected to a power and signal output. The second winding is provided with additional terminals connected to a ground.

The invention also relates to a method of reducing noise in a signal coupling arrangement comprising a first winding connected to a signal input and a second winding connected to a signal output, wherein the method comprises grounding longitudinal component in said wiring of at least one of said wirings substantially via a center position. Short description of the figures

In the following the invention will be described in more detail with reference to exemplary embodiments illustrated in the attached drawings, in which:

Fig. 1 is a schematic illustration of information transmission system over mains network,

Fig. 2a and 2b are schematic layout of an air coupler and its electrical equitant,

Fig. 3 is an electrical equivalent of a coupler,

Figs. 4a and 4b show in a schematic way a binocular shaped transformer, in frontal and side views, respectively, Fig. 5 is an equivalent diagram of a ferrite coupler.

Fig. 6 is an equivalent diagram illustrating a coupler according to a first aspect of the invention, Figs. 7a and 7b illustrate suppressing of the common mode noise currents, Fig. 8 is Fig. 9 illustrates a measurement set for measuring noise in a coupler according to prior art, Fig. lOillustrates the result of the measurement according to the set in Fig. 9, Fig. 11 illustrates a measurement set for measuring noise in a coupler according to the present invention, Fig. 12illustrates the result of the measurement according to the set in Fig. 11, Fig. 13 illustrates a measurement set for measuring noise in another coupler according to the present invention, Fig. 14 illustrates a first embodiment of the invention applied on toriod coil, Fig. 15 illustrates a first embodiment of the invention applied on P9 coil, Fig. 16illustrates an equivalent diagram illustrating a coupler according to Figs. 15 and 16, Fig. 17illustrates the result of the measurement according to the set in Fig. 13, and Fig. 18 illustrates the result of the measurement according to the set in Fig. 17

Detailed description of the embodiments

The coupler according to the present invention solves the problems by changing it from an unbalanced configuration to a balanced one.

The solution is schematically illustrated in Fig. 6, which is an exemplary coupling to verify the suppressed noise. The signal on the output is measured with a high impedance input oscilloscope. Compared to an unbalanced coupler the noise floor is lowered approximately 10-20 dB. The invention comprises arranging a grounded center tap on the coil of the coupler.

When using an unbalanced coupler the longitudinal noise is superimposed on the signal on the secondary side of the coupler, i.e. the unshielded wire in the core and the connection wiring peaks the longitudinal noise and the transient components as in wire antenna. The balanced coupler will maneuver the noise to a center tap on the coupler and cancel-out the noise, i.e. the longitudinal components are earthed neutral via the center of the coupler. One result is that the noise floor is reduced for benefit of the signal dynamic. It is illustrated in a schematic way in Figs. 7a and 7b, comparing the noise current i_c in an unbalanced (Fig. 7a) and balanced (Fig 7b) according to the invention. In the unbalanced coupler common mode noise currents, i_c, is coupled directly to the output of the coupler as a noise modulated on the output signal. This is because of the coupling capacitance, C_{s ar}y_/ between the first and secondary sides.

In the balanced coupler, the capacitance, C_{s ar}y_/ between the first and secondary sides is focused to the center tap region and transform the common mode noise currents to the center tap; thus, eliminating the noise on the output signal.

The Fig. 8 shows a proposal of a front-end receiver including a balanced coupler according to the present invention. To improve the suppression of the noise and EMC (also on TX side) a filter inductor is inserted on the 220 V line. The amplifier operates with high input impedance and transforms the signal into a low impedance mode.

To better illustrate the advantageous of the invention, a number measurements where conducted which are illustrated in Figs. 9 to 14.

Fig. 9 is a measurement set comprising an unbalanced coupler. For measurement one AMIDON transformer (N=3:4) was used, which was connected to the power line of 220 V through two filtering capacitors of 10 nF. A TEKTRONIX 3032 oscilloscope was used to measure the signal over a coaxial cable. The result is illustrated in the diagram of Fig. 10. At 30 MHz the noise was measured to -90 dB, which corresponds to -120 dBm.

Fig. 11 is a measurement set comprising a balanced coupler. For measurement, one AMIDON transformer (N=3:4) and TOKO 1026 (N = l : l*l) transformer were used. The AMIDON transformer was connected to the power line of 220 V through two filtering capacitors. In the first measurement 10 nF capacitors where used and in a second measurement 470 pF capacitors. The center of the coils was grounded. A TEKTRONIX 3032 oscilloscope was used to measure the signal over a coaxial cable. The result is illustrated in the diagram of Fig. 12 for 10 nF. At 30 MHz the noise was measured to -100 dB, which corresponds to -130 dBm. For 470 pF capacitors, the change was marginal : -99 dB.

Fig. 13 is a measurement set comprising a balanced coupler. For measurement, two TOKO 1026 (N = l: l*l) transformers were used, which where connected to the power line of 220 V through two filtering capacitors of 470 pF. A TEKTRONIX 3032 oscilloscope was used to measure the signal over a coaxial cable. The result is illustrated in the diagrams of Figs. 17 and 18. The diagram of Fig. 18 illustrates the coupler not connected to the power line. The diagram of Fig. 18 illustrates the coupler connected to the power line. At 30 MHz the noise was measured to -90 dB, which corresponds to -120 dBm.

Figs. 14 and 15 illustrate the physical appearances of two embodiments of couplers according to the invention. In Fig. 14, the coupler 140 comprises a ring toroid 141 having primary windings 142 and secondary windings 143. The primary winding comprises the center tap 144. The equivalent electrical diagram is illustrated in Fig. 16. The terminals are designated with roman characters / to vl, wherein /^' and v are the terminals of the secondary winding, /^'/^' and /^'/^'/^' the center tap terminals, and v and vi the primary winding terminals.

In Fig. 15, illustrating the (P9) core of a transformer 150 comprises a cylindrical core 151 having primary windings 152 and secondary windings 153. The center tap 154 is arranged at the secondary winding 153. The equivalent electrical diagram of Fig. 16 also considers this embodiment. Thus, the terminals, as in aforementioned embodiment, are designated with roman characters / to vi, wherein / and v are the terminals of the secondary winding, /^'/^' and /^'/^'/^' the center tap terminals, and v and vi the primary winding terminals.

Clearly, the invention is not limited to above illustrated transformers, and other transformers being able to

It should be noted that above measurements are given as non-limiting examples, and the result of the measurements may vary due to the parameters involved in the measurement devices, etc.

The invention is not limited to the shown embodiments but can be varied in a number of ways, e.g. through combination of two or more embodiments shown, without departing from the scope of the appended claims and the arrangement and the method can be implemented in various ways depending on application, functional units, needs and requirements etc.

Claims

1. A signal coupling arrangement (140, 150) comprising a first transformer side having a first winding (142, 152) connected to a signal input and a second transformer side having a second winding (143, 153) having first and second terminals and connected to a signal output, characterized in that said second winding (143, 153) is provided with additional terminals (144, 154) connected to a ground for reducing noise and preferably reducing losses through the M factor and/or enhancing Q factor provides for a dynamic and high bandwidth.

2. The coupling arrangement of claim 1, characterized in that said additional terminals are (144, 154) arranged substantially in same distance to said first and second terminals.

3. The coupling arrangement of claim 1, characterized in that said additional terminals are (144, 154) arranged in same distance to said first and second terminals.

4. The coupling arrangement of claim 1, characterized in that said transformer comprises a Radio Frequency coil.

5. The coupling arrangement according to any of claims 1-4, characterized in that said transformer comprises a toroid coil (141).

6. The coupling arrangement according to any of claims 1-4, characterized in that said transformer comprises a cylindrical coil (151).

7. The coupling arrangement according to any of claims 1-6, characterized in that said first windings is a primary winding and said second winding is a secondary winding.

8. In a main system connected to transmission data system, an arrangement (140, 150) for coupling/decoupling a data signal comprising a first transformer side having a first winding (142, 152) connected to a power and signal input and a second transformer side having a second winding (143, 153) having first and second terminals and connected to a power and signal output, characterized in that said second winding (143, 153) is provided with additional terminals (144,

154) connected to a ground.

9. A method of reducing noise in a signal coupling arrangement (140, 150) comprising a first winding (142) connected to a signal input and a second winding (152) connected to a signal output, wherein the method comprises grounding longitudinal component in said wiring of at least one of said wirings substantially via a center position.