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Report RSE 17000226

Logical coordination between LV compensation devices, series and shunt, to provide different PQ levels in the distribution network. Evaluation of the real controller through Control Hardware In the Loop simulation

The report is about a series compensator to compensate voltage variations and voltage dips. It can act as a fault current limiter, for downstream grid faults. The study, mainly theoretical, has addressed the issue of coordination of the compensators under different operating conditions.

The increasing use of grid connected power electronic systems generates a set of interference phenomena among those devices and distribution grids. Power electronic systems are both sensitive to voltage disturbances and sources of disturbances, such as current harmonic distortion, voltages unbalance and flicker.

Such phenomena motivated the study of a system named Open Unified Power Quality Conditioner, based on power electronic converters and used for the improvement of the Power Quality level in low voltage distribution grids. The system is composed of a voltage compensator, connected in series to a distribution line, and one or more current compensators, shunt connected close to disturbing/sensitive loads. The series compensator is devoted to the compensation of voltage variations and of voltage dips. It can also act as a fault current limiter, for downstream grid faults. Shunt compensators act to cancel load harmonic currents, in addition, they can supply privileged loads in case of grid disturbances, in combination with a static switch located upstream of the compensator/load system and an energy source connected to the DC side of the converter.

The study, mainly theoretical, has addressed the issue of coordination of the compensators under different operating conditions. The behavior of the compensators against various types of failure in the grid were analyzed by means of digital simulation. The ability of the system to cope with all types of faults on the basis of "local" control of the machines only was verified. Also, the possibility of introducing logical coordination between compensators, by the exchange of messages and set points in order to increase the overall system performances, was successfully implemented. By-pass strategies of possible faulted compensators, which leaves in operations the other devices were designed and tested.

Finally, the possibility of implementing those algorithms in a (off the shelf) general purpose microcontroller was verified. The control system, implemented on processor ARM CORTEX M4, was tested by means of real-time Control Hardware In the Loop (RT-CHIL) simulations.

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