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Project deliverable Open Access

Control Layer Based Control Algorithms

Karsten, Tim; Hu, Jingxin

The operation of a hybrid Alternating Current - Direct Current (AC/DC) grid relies on power electronic converters interfacing different sections of the grid. Each converter controls primarily voltage, current or transferred power. Together they achieve stable operation of the grid. Within this Work Package (WP) a layer based control approach for the converters in a hybrid grid has
been proposed. As a reference system the HYPERRIDE demo site in Aachen was considered since the developed control algorithms are to be implemented there. Furthermore, it is important that the system can be operated under no communication, with the converter level control alone.

With these specifications in mind, control algorithms for different converter topologies were developed and implemented on hardware test setups.The existing GE 3L-NPC DAB and downscaled 3L-NPC AFE testbenches at the demo site in Aachen, together with the for their operation already developed converter control algorithms, served as basis for the contributions of this deliverable. Those contributions include:

  • Dead-time compensation of Dual Active Bridge (DAB);
  • Active thermal balancing of DAB;
  • Hardware implementation and verification of Three Level Neutral Point Clamped (3L-NPC)
  • DAB modulation;
  • Hardware implementation and verification of Instantaneous Current Control (ICC) of DAB;
  • Hardware implementation and verification of 3L-NPC Active Front End (AFE) control;
  • Down-scaled two-level DAB testbench.

The DAB topology is addressed because it couples Direct Current (DC) parts of the system and provides galvanic isolation. Moreover, it can reach high efficiencies with the proposed control algorithms. Basic operation characteristics of the DAB are covered with Single Phase-Shift (SPS)
mode. Different modes of operation are presented to allow interfacing of energy storage systems and other types of loads and sources to the grid while maintaining soft-switching operation. A dead-time compensation is proposed to mitigate the effects of dead-times on operation of the DAB. In order to balance the thermal stress on the devices of the DAB, a balancing
strategy is implemented. The control algorithms were tested and verified on a down-scaled hardware setup. An advanced three level modulation scheme and ICC for dynamic operation of the DAB were implemented and tested on the full-scale GE 3L-NPC DAB converter which is part of the demo site.

The coupling of Alternating Current (AC) and DC parts of the grid is achieved with AFE converters. The required control algorithms for current, voltage and power control are reviewed. They were implemented on a down-scaled 3L-NPC converter. Additionally, the balancing control of the split DC link of the 3L-NPC was experimentally verified.

An overview of the different proposed control layers is given. The features of each layer are discussed. Simulations were conducted to verify overall system stability under operation with converter level control since the HYPERRIDE demo site is currently under commissioning.

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