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Distributed frequency and synchronization control system for offshore wind farms with an high voltage direct current

Country of Origin: Spain
Reference Number: TOES20201006003
Publication Date: 6 October 2020

Summary

A Spanish university has developed a distributed system for controlling frequency and synchronization of wind-driven power generators in off-shore wind farms connected to the grid by means of high voltage direct current (HVDC) through a diode rectifier station. It is less complex, less expensive and more flexible than existing solutions. They are looking for manufacturers or companies managing wind/marine turbines and parks to sign a financial, license or technical cooperation agreement.

Description

A Spanish public university has developed a distributed control system for synchronizing and regulating the frequency of a set of wind-driven power generators in an offshore wind farm, allowing DC electric power transmission to the general grid through an HVDC-LCC (high voltage direct current with line commutated converter) link.
The system uses the capacity of wind turbines for voltage-frequency control based on reactive power distribution. It is less complex, less expensive, and more flexible. Furthermore, it eliminates the additional elements used in other current solutions.
It is based on the distribution of reactive power between turbines by means of controlling the quadrature component of the current at the inverter outlet of each wind-driven power generator, which is in turn achieved by acting on the internal voltages of the inverter.
Today, the integration of offshore wind farms in onshore electric power systems is being proposed worldwide as an alternative in order to reduce fossil fuel consumption and greenhouse gas emissions. Largely due to the fact that projected, large offshore farms are located far from the coast, connection with HVDC links (by means of DC) is technically and economically more suitable than an HVAC transmission system (by means of Alternating Current - AC).
The university had already developed a centralized system for controlling voltage and frequency for an offshore wind farm connected to a grid by means of a DC link with a diode rectifier. However, the current development of a system with distributed control has the advantage of using the capacity of wind turbines for voltage-frequency control, without adding any additional element (capacitor bank) like in the centralized solution.
The system is directed at a distributed method for the synchronization and control of frequency in wind-driven power generators of an offshore wind farm. The wind-driven power generators are serially connected through several power lines to a three-phase AC busbar. This busbar is in turn connected to a step-up transformer of the farm which powers the HVDC link through an AC/DC rectifier station formed by diode bridges. Finally, the other end of the HDVC link located on land will be connected to a DC/AC inverter station which will inject the generated power into the general AC grid.
The operation of the distributed system will control frequency using the reactive power channel, with the active power channel decoupled. Each wind-driven power generator is capable of regulating the frequency at its terminals, something unheard today since they are connected to a grid with a given frequency. The wind-driven power generators are synchronized with one another to form the grid frequency by means of inclination control, using the reactive power as a signal for synchronization. The operation of the diode rectifier is possible once the grid frequency has been generated. Furthermore, the reactive power is equally distributed among all the wind-driven power generators making up the wind farm.
The control method is carried out for each of the wind-driven power generators of the wind farm. Active power fluctuations, due to variations in wind speed, will lead to changes in the reactive power, and in the frequency at the outlet of the wind-driven power generator. The variation in frequency will be compensated by acting on the voltage regulator, modifying the reactive power injected by the wind-driven power generator. However, in steady state, the frequencies of all the wind-driven power generators will tend towards a specific frequency of 50 Hz. In order to achieve this, an increase in reference angular speed is integrated in a master wind-driven power generator.
University is looking for manufacturers/operators of wind turbines or parks interested in field trials through financial agreement, further development of the technology through technical cooperation agreement or technology transfer through license agreement.
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Advantages and Innovations

Innovative aspects:
- It uses HVDC-LCC technology which is more mature, cost-effective, efficient, and reliable than HDC-VSC technology
- It entails a novel technique for synchronizing wind-driven power generators based on the reactive power channel.
- It does not require any additional element.
- It is based on distributed control.
- Each wind-driven power generator is capable of regulating the frequency at its terminals.
- It allows the connection of isolated wind farms, particularly offshore wind farms, to the grid.
- It replaces conventional large-sized capacitors with smaller capacitors.
- The wind-driven power generators always work within the acceptable operating limits.
Advantages:
- It synchronizes the frequency of wind-driven power generators without using any additional element or line.
- Easy-to-implement solution.
- Flexible solution.
- Lower cost.
- It replaces conventional large-sized capacitors with smaller capacitors.
- The wind-driven power generators always work within the acceptable operating limits.

Stage Of Development

Concept stage

Stage Of Development Comment

A model is available in the laboratory for the stimulation of the connection in access networks with monitoring technique.

Requested partner

- Type of partner sought: Company
- Specific area of activity of the partner: Manufacturers and managers of wind/marine turbines and parks.
- Task to be performed: Financial agreement for the development of field trials, technical cooperation agreement for the development of the technology towards specific applications in European Union projects or license agreement for the technology transfer in order to integrate the technology in the current portfolio of the partner company.

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