System for transmitting and receiving a power line communication signal over the power bus of a power electronic converter

Abstract

The present application is concerned with a system for transmitting and/or receiving the control and sensing signals between the control units and the power electronic components. One system according to the present application comprises: a transceiver adapted to modulate the communication signal on a communication signal frequency band, and a coupler connected to the power conductor and adapted to couple the modulated communication signal to the power conductor. The present application also concerns a method for transmitting and receiving the control and sensing signals.

Claims

1. A system for transmitting and/or receiving a communication signal via a power conductor of a power electronic converter with a plurality of converter modules, wherein the communication signal comprises control signals, including gate signals, and sensing signals between a main controller and a local controller of the power electronic converter, wherein the main controller sends the control signals to the local controller, and wherein the main controller receives the sensing signals from the local controller, the system comprising: a transceiver adapted to modulate the communication signal on a communication signal frequency hand, and a coupler connected to the power conductor and adapted to couple the modulated communication signal to or from the power conductor of the power electronic converter, thereby exchanging said control and sensing signals between said main and local controllers of the power electronic converter.

2. The system according to claim 1, wherein the coupler comprises a capacitive coupler and/or an inductive coupler.

3. The system according to claim 2, wherein the communication signal frequency band is different to the frequency band of the power waveform.

4. The system according to claim 1, wherein the communication signal frequency band is different to the frequency band of the power waveform.

5. The system according to claim 4, further comprises: a high frequency bypass connected in parallel to a power electronic switch of the power electronic converter and adapted to the communication signal frequency band.

6. A power electronic, converter comprising: a power conductor; a main controller; a local controller; a plurality of converter modules; and a plurality of systems connected with the converter modules for transmitting and/or receiving a communication signal via the power conductor, wherein the communication signal comprises control signals, including date signals, and sensing signals between the main controller and the local controller of the power electronic converter, wherein the main controller sends the control signals to the local controller, and wherein the main controller receives the sensing signals from the local controller, and wherein each of the plurality of systems comprises: a transceiver adapted to modulate the communication signal on a communication signal frequency band; and a coupler connected to the power conductor and adapted to couple the modulated communication signal to or from the power conductor of the power electronic converter, thereby exchanging said control and sensing signals between the main controller and the local controller of the power electronic converter.

7. The system according to claim 6, wherein the coupler comprises a capacitive coupler and/or an inductive coupler.

8. The system according to claim 6, wherein the communication signal frequency band is different to the frequency band of the power waveform.

9. The system according to claim 6, further comprises: a high frequency bypass connected in parallel to a power electronic switch of the power elect converter and adapted to the communication signal frequency band.

10. A method for transmitting and/or receiving a communication signal comprising control signals, including gate signals, and sensing signals between a main controller and a local controller of a power electronic converter with a plurality of converter modules, comprising: modulating the communication signal, by a transceiver, on a communication signal frequency band, coupling the modulated communication signal, by coupler, to or from a power conductor of the power electronic converter, sending the control signals from the main controller to the local controller via the power conductor of the power electronic converter, and receiving, t the main controller, the sensing signals from the local controller.

11. The method according to claim 10, wherein the coupler comprises a capacitive coupler and/or an inductive coupler.

12. The method according to claim 11, wherein the communication signal frequency band is different to the frequency band of the power waveform.

13. The method according to claim 10, wherein the communication signal frequency band is different to the frequency band of the power waveform.

14. The method according to the claim 13, further comprises the step of: connecting a high frequency bypass in parallel to a power electronic switch of the power electronic converter, and bypassing the communication signal on the communication signal frequency band.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The subject-matter of the present invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the attached drawings, in which:

(2) FIG. 1 schematically shows a typical topology of an AC-DC-AC modular multilevel electronic power converter;

(3) FIG. 2 schematically shows a typical communication architecture of a medium voltage power electronic converter, where the control and sensor signals are exchanged between the main controller and the local controllers; and

(4) FIG. 3 schematically shows power line communication, PLC, in a PE converter according to the present invention, in which the PLC transceivers, PLC-TRX, capacitive and inductive couplings, and high frequency gate bypass are shown.

(5) The reference symbols used in the drawings, and their primary meanings, are listed in summary form in the list of designations. In principle, identical parts are provided with the same reference symbols in the figures.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

(6) FIG. 1 shows the topology of a typical Power Electronic 1 converter, PE converter. The PE switches, i.e. power semiconductors, control the current flow through the connected power buses. Using appropriate control commands to the switches, the AC power at the input (V.sub.R, V.sub.S, V.sub.T) is converted to another AC power waveform at the output (V.sub.U, V.sub.V, V.sub.W).

(7) The control and communication infrastructure generates and transmits the control signals, e.g. gate signals, to the PE switches. FIG. 2 shows such communication architecture. The control and sensor signals are exchanged between a main controller 100 and local controllers 200 located in different cabinets over the communication network 110. A local controller 200 together with a number of PE switches make up a Power Electronic Building Block, PEBB. The local connections within a PEBB from the local controller to its PE switches use electrical or optical wires 120.

(8) The present invention takes advantage of the fact that the PE switches 50 in a PE converter are connected to electric power buses, which carry the electric currents to be switched, see FIG. 1. The communication to the distributed control units, i.e. local controller, LCs, associated to the PE switches may thus utilize these power buses as the communication medium, using power line communication.

(9) FIG. 3 shows that the power line communication transceivers couple their communication signals to and from the power buses, according to the present invention. The power bus serves as a communication medium carrying the control and sensor signals in the form of PLC signals, as well as the (AC) power. To minimize interference from the power waveform, with strong harmonics at up to several kHz, PLC signals are modulated to a different frequency band, e.g. of tens of kHz to tens of MHz, and can thus be separated from the power waveform by band-pass or high-pass filtering. The PLC signals have much lower power, of mV to several Volts peak, than the power waveform. In other words, the modulated PLC signals will be transmitted by the electronic couplers having band-pass or high-pass filter characteristic.

(10) The power line signal coupling may be either capacitive or inductive. As an example, the main controller, MC PLC-TRX, 21 is shown with capacitive coupling between the power buses of phases R and S. The capacitive coupling has in general better performance than inductive coupling, but requires space for high voltage capacitors and connectors to pairs of cables, i.e. power buses.

(11) With inductive couplers, the PLC signals are coupled transformer-like using wire coils around the power bus. In FIG. 3, a local controller, LC PLC-TRX, 31 is shown with inductive coupling. Inductive couplers may be easier to install, but coupling performance depends on the mechanical arrangements and, if a magnetic transformer core is used, on its ferromagnetic properties, in particular, its non-linearity due to saturation.

(12) The above example describes the case where the master controller uses capacitive coupling and the local controller uses inductive coupling. Any combination of controllers and PLC couplers is possible.

(13) Due to the converter operation, parts of a power branch to which a controller is connected may, in a given period of time determined by the switching states in the converter, be in non-conducting state, i.e. when the switch is temporarily turned off, no current may flow through that section of the bus. This would affect PLC communication. Hence, preferably, depending on the characteristics of the PE switch, a high frequency (HF) bypass 40 for the PLC signals is introduced in parallel to the PE switches, in order to achieve acceptable communication reliability. This is shown in FIG. 3 as capacitors 40. The HF bypass 40 lets the PLC signal bypass the PE switch, irrespective of the state of the PE switch.

(14) In a preferred embodiment, a PLC transceiver may employ more than one coupler connected to different coupling points on the power bus, as shown as an example in FIG. 3 for the LC PLC-TRX 31. This allows multiple redundant transmission and reception of the PLC communication signal. In particular, in what is known as reception diversity, the PLC receiver may select or combine multiple signals received from different couplers for best performance.

(15) To further mitigate interference from the power waveform, the PLC receiver may employ adaptive noise cancelling. That is, if the power waveform is known by the PLC receiver, e.g. from separate measurements or from separate control information, this known interference can be cancelled, i.e. subtracted, from the total received signal. This further improves the quality of the desired received PLC signal.

(16) The high frequency gate bypass may be realized by the inherent stray capacitances of the PE switch, typically flat silicon semiconductor chips or wafers. Thus, no additional circuitry is required. This depends on the high frequency impedance of the PE devices.

(17) Where receive-only nodes suffice, e.g. in the case where local controllers are designed such they only need to receive control information and do not need to transmit any data, PLC receiver coupling may employ the principle of the Fibre Optic Current Sensor, FOCS. Such FOCS coupling may facilitate PLC installation in a PE converter considerably. However, accuracy and high frequency performance of such FOCS couplers should be designed accordingly.

(18) According to a further aspect of the present invention, the PLC couplers should fit the available space and mechanical arrangements. High interference from the PE operation may affect the reliability of PLC transmission. The data rate supported by the PLC communication depends on the impedance properties of the power bus at high frequencies, and on EMC restrictions on emissions.

(19) While the invention has been described in detail in the drawings and foregoing description, such description is to be considered illustrative or exemplary and not restrictive. Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practising the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain elements or steps are recited in distinct claims does not indicate that a combination of these elements or steps cannot be used to advantage, specifically, in addition to the actual claim dependency, any further meaningful claim combination shall be considered disclosed.