German farmers are using CC-Link (Control and Communication Link) fieldbus control system to produce power from biogas through slurry extraction. The biogas is transferred to fuel cogeneration plants and is used to heat power machinery, buildings or export it to the grid.

Dreyer & Bosse (D&B) , a German power plant specialist, provides autonomous cogeneration units using CC-Link open fieldbus network technology for monitoring functions and data communications.

Biogas-fuelled power plants convert special fuel crops, plant waste and liquid manure into energy. Its main component is a power and heat cogeneration unit that produces heat and power from biogas, which is the biomass fermentation unit’s primary output.

German operators of plants which produce electricity from renewable energy sources are being paid guaranteed rates for the green electricity they feed to the public. They can also give the produced heat to a local district heating network.

D&B builds cogeneration units derived from individual selection of standard components. The generators are usually driven by biogas with dual-fuel biogas/diesel engines as backup to ensure availability and reliability.

The CC-Link fieldbus network and modern control technology are made to ensure that the power plants are both economical to operate and reliable.

A D&B system, for example, consists of a 500-kilowatt cogeneration unit installed on a farm with 12.5 acres (five hectares) of pastures and 173 acres (70 hectares). The slurry will be a mixture of manure and straw.

The entire D&B system is being controlled by a powerful compact controller of Mitsubishi Electric, supported by two smaller controllers. The main controller, MELSEC FX3U, is a programmable logic controller (PLC) that communicates with various automation components in the system through standard serial ports and a CC-Link master module. Integrated drivers and instructions for Mitsubishi Electric automation components eliminate time-consuming and complex controller programming.

Automation components include a control panel for clear visualization of all processes, which makes the operation easier for the farmers. An industrial modem will serve as a backup to provide remote access so that the service engineers can interrogate the plant without actually visiting remote farms.

A number of important system monitoring and safety functions are executed through advanced switchgear components with CC-Link interfaces. These air circuit breakers protect the generators against power failure, short circuits and overloads and it also handle the automatic network synchronization with the public power grid. The Mitsubishi Electric Super AE series’ fast-switching circuit breakers serve as a link between the generator set and the gas engine of the public power grid and the cogeneration unit.

The circuit breakers’ electronic trip relay is linked to the central controller through the CC-Link network. The trip relay’s measurement circuits integrated can monitor and analyze all the relevant generator parameters. The circuit breaker can be switched on/off remotely using the CC-Link network through the peripheral I/O module with digital outputs and inputs. The digital inputs are dimensioned to handle the electric currents of the circuit breaker’s drive motor, shunt trip device and closing coil, and are configured as relay contacts.

The simple installation of the system components and the CC-Link fieldbus network enabled the D&B engineers reduce both wiring overheads and material costs. The major factor for choosing this technology is its resistance against electromagnetic interference. Unlike other fieldbus network systems, its CC-Link compatible devices’ conformity tests include comprehensive electromagnetic compatibility tests (EMC), plus other standard tests such as resistance to damp, aging performance and proper functioning.