Method for utilizing interference signals in power electronic converters for data transmission

The invention relates to a method for transmitting data by clocking a power electronic converter, with several converters (DC chopper, inverter) to work together in one system and the data to be exchanged between the converters or to / from a control center. The data can be, for example Present information about the current output of a switched-mode power supply, or the desired setpoint value that a specific converter should deliver, or status data such as temperature, voltage level and the like. The converters working together are locally distributed over a small area. You can for example Switching power supplies, which feed the energy from solar panels into a common intermediate circuit, or distributed direct current supply systems in systems for regenerative energy conversion.

In the energy conversion of power electronic systems, disturbances occur with every switching action caused by the rapid current or voltage change rates. For reasons of electromagnetic compatibility, these must be kept small, but they can never be completely eliminated.

In "Wire Communication System Utilizing Ripple-Modulated DC-DC Converter as Signal Transmitter and Power Supply" by A. Katsuki, M. Matsushima and N. Takimoto in Proceedings of lntelec'99, Copenhagen, DK from 6.-9.6.1999, a data transmission method is proposed for switched-mode power supplies, a change in the series resistance in the output circuit leading to a change in the ripple voltage of the converter and this being used as an information carrier. However, this method has the disadvantage that some additional expenditure of a circuit nature is required and that the signal size is dependent on the load current.

EP 0 580 919 A1 shows a switched-mode power supply in which the frequency can be modulated via a separate device. The modulation signal is obtained from the mains voltage and is, for example, proportional to the rms value of the mains voltage. The purpose is to lower the clock frequency at relatively high currents and thus to reduce switching losses. A data transfer is not intended.

US Pat. No. 4,729,125 A describes a method for data transmission via a current loop. A microprocessor, in cooperation with a measuring sensor, controls the output current of a power supply unit in such a way that a current that is proportional to the measured variable flows. It is a modification of the known data transmission with a current loop and does not use the interfering signals that arise in power electronic converters.

US Pat. No. 4,864,589 A presents a communication system for transmitting spread spectrum signals in a power supply network. In spread spectrum technology, the useful signal is multiplied, for example, by a broadband pseudo-random signal and this is then modulated. This broadband signal is therefore less sensitive to interference and, when using the pseudo-random signal, can only be decoded by stations that have the key.

The invention disclosed here overcomes the disadvantages of the prior art set out above in that the switching frequency of the converter is changed in accordance with an information signal and the resulting interference signals are used on lines for information transmission in a restricted network.

According to the invention, to transmit the desired information, the interference signals that inevitably occur due to the switching processes and propagate on the lines are used for the transmission. This is achieved by using frequency modulation of the switching frequency of the individual converters for analog signals and frequency shift keying for digital signals.

Corresponding codes and adapted protocols, which are obtained from adapting existing fieldbus protocols, or ready-made protocols can be used for interference-free transmission. The spread spectrum technique can also be used with a pseudo-random signal. Using different generator polynomials, the individual converters can be assigned an address at the same time, since only data that is encrypted with this key provide meaningful information. If you want to deliver information to several places at the same time, all these stations must have the same key. You can assign a general and a special key (generator polynomial for the pseudo-random signal) to each station in order to send or receive data to all stations as well as only to certain stations.