Supervisor:
Zhe Chen

Co-Supervisor:
Yanbo Wang

Assessment Committee:
Sanjay Kumar Chaudhary(Chair)

 Professor Jose Ramon Rodriguez Perez, Universidad San Sebastian in Santiago, Chile

Associate Professor Sergio Vázguez Pérez, Universidad de Sevilla

Moderator:
Sanjay Kumar Chaudhary

Abstract:

The increase in wind energy utilization, particularly emerging offshore wind power generation, promotes the revolution of wind turbine toward high-power application. To exploit the offshore wind energy in an efficient and cost-effective way, the application of high-power wind turbine is being paid the increasing concerns. The development of high-power wind turbine undoubtedly poses new technical challenges. More complex power conversion architectures and advanced control strategies are then essential to ensure the secure and stable integration of high-power wind turbine into power system. The three-level Neutral Point Clamped (3L-NPC) converter has been developed as an attractive solution for high-power Wind Energy Conversion Systems (WECS). The 3L-NPC enables high-voltage operation and generates voltage waveforms of three levels, which increases the power rating and leads to reduced cabling and harmonic filter requirements. Meanwhile, Finite Control Set Model Predictive Control (FCS-MPC) has gained attention as an advanced control strategy appropriate for high-power converters. For instance, MPC exhibits fast dynamic response compared with classical linear controllers. Further, it is characterized by a straightforward design to address non-linear characteristics and to realize multiple control objectives within a single control loop. However, the technology readiness assessment of predictive control techniques in high-power wind power converter has not been fully reached.

The goal of this Industrial PhD Project is to develop a new FCS-MPC strategy, address the technical challenges for high-power operation, and investigate its implementation into Ingeteam commercialized power converter solution. This Industrial PhD Project investigates the application of FCS-MPC in 3L-NPC converter, and further analyzes its merits and design intricacies. The main work of this thesis is as follows. Chapter 1 introduces the background and motivation. Chapter 2 presents the proposed FCS-MPC strategy for grid-side control of 3L-NPC. The online tuning method for switching frequency control is proposed, and its capability to effectively regulate switching frequency during different grid conditions and transient operation is demonstrated. Furthermore, fault ride-through capability of 3L-NPC operated with FCS-MPC is developed, and compliance with most recent grid codes requirements in terms of reactive current provision during grid faults is validated. The robustness analysis of FCS-MPC is also performed, where MPC exhibits sensitivity to filter parameter mismatch. The robust FCS-MPC scheme is then proposed, where the MPC is augmented with state observer to identify grid filter parameters and enhance controller performance against parametric uncertainties or variations. Chapter 3 analyzes stability of grid-connected 3L-NPC inverter with MPC. The frequency-scan technique is proposed to obtain impedance characteristic under different controller design and operating conditions. The FCS-MPC shows an inherent capability to operate at low switching frequency with minimum control delay, which is advantageous for stability enhancement. Further, the offshore wind farm simulation model is developed, and the capability of proposed MPC strategy to mitigate instability phenomena is revealed. Chapter 4 implements the proposed control strategy into Ingeteam power converter solution. The implementation of FCS-MPC framework into software package and converter control unit (CCU) is performed. Inherent intricacies of real-time implementation are addressed. An efficient implementation of FCS-MPC algorithm which reduces the number of candidate vectors is employed to optimize computational burden. Finally, the suitable performance of entire power converter solution of two paralleled active NPC (ANPC) conversion lines is verified by means of software-in-the-loop (SiL) and hardware-in-the-loop (HiL) validation. Main conclusions of this PhD Project are drawn, and future research topics are discussed in Chapter 5.

The main contributions of this PhD Thesis are summarized as follows. (1) An advanced FCS-MPC strategy is developed for high-power 3L-NPC converter, which ensures compliance with grid code specifications and demonstrates robustness, (2) The stability of 3L-NPC inverter with FCS-MPC is investigated, showcasing benefits of reduced sampling time for stability enhancement, (3) The proposed FCS-MPC strategy is implemented into Ingeteam commercialized power converter solution, which addresses the real-time implementation challenges in terms of industrial application. This PhD Project improves the operation performance of high-power wind power converters, enhances stability of offshore power system, and achieves a significant step forward in FCS-MPC industrial assessment.