• Energy Research

This paper focuses on the distributionally robust dispatch for integrated transmission-distribution (ITD) systems via distributed optimization. Existing distributed algorithms usually require synchronization of all subproblems, which could be hard to scale, resulting in the under-utilization of computation resources due to the subsystem heterogeneity in ITD systems. Moreover, the most commonly used distributionally robust individual chance-constrained dispatch models cannot systematically and robustly ensure simultaneous security constraint satisfaction. To address these limitations, this paper presents a novel distributionally robust joint chance-constrained (DRJCC) dispatch model for ITD systems via asynchronous decentralized optimization. Using the Wasserstein-metric based ambiguity set, we propose data-driven DRJCC models for transmission and distribution systems, respectively. Furthermore, a combined Bonferroni and conditional value-at-risk approximation for the joint chance constraints is adopted to transform the DRJCC model into a tractable conic formulation. Meanwhile, considering the different grid scales and complexity of subsystems, a tailored asynchronous alternating direction method of multipliers (ADMM) algorithm that better adapts to the star topological ITD systems is proposed. This asynchronous scheme only requires local communications and allows each subsystem operator to perform local updates with information from a subset of, but not all, neighbors. Numerical results illustrate the effectiveness and scalability of the proposed model.

This paper discusses the design of the damping control of FACTS with multiple operating points. The problem of such a damping control design is actually the problem of designing optimal output-feedback controllers for a multi-model system, of which control requirements can be described by nonlinear matrix inequalities (NMI). The design approach can transfer the original NMI into linear matrix inequalities (LMI) through suitable parameterization and transformation. This can be applicable to the design of FACTS damping control that can guarantee the satisfactory performance over a wide range of operating conditions rather than one operating condition. There are two control design strategies that can be applied in applying the LMI approach. The first control design strategy is that a single damping controller is determined and used for all operating points. The second control strategy is that instead of using a single damping controller for all operating points, multiple damping controllers are designed and utilized. Each of the multiple damping controllers is corresponding to a few operating points. The advantage of the second control design strategy is that the LMI design problem is relatively small and easy to solve, and the corresponding damping controllers may provide better control performance in comparison to the single damping controller of the first design strategy. The LMI approach along with the two design strategies are demonstrated on a 4-machine 2-area system. Numerical results show that the damping controller designed by the two multiple operating point based approaches can ensure simultaneous stability and adequate damping for the multiple operating points.

The demands for massive renewable energy integration, passive network power supply, and global energy interconnection have all gradually increased, posing new challenges for high voltage direct current (HVDC) power transmission systems, including more complex topology and increased diversity of bipolar HVDC transmission. This study proposes that these two factors have led to new requirements for HVDC control strategies. Moreover, due to the diverse applications of HVDC transmission technology, each station in the system has different requirements. Furthermore, the topology of the AC-DC converter is being continuously developed, revealing a trend towards hybrid converter stations. Keywords: Direct current transmission system, Topology, Control strategy, AC-DC converter

This paper investigates a specific type of converter-based general interface, which can be used for AC microgrids integrating to the active distribution network. The interface, a Back-to-Back (BtB) converter, is used to connect the AC sides of the distribution network and the microgrid. The common DC link of the BtB converter is connected to one terminal of a bidirectional DC-DC converter whilethe other terminal of the DC-DC converter is connected with an energy storage system. By adopting proposed coordinated control within the interface, the distribution network and the microgrid can be decoupled in terms of the AC voltage and current. Furthermore, this interface can provide enhanced voltage stability and high power quality in the case of severe disturbances on the AC side. Hence, the microgrid can be integrated into the distribution network in a safe and flexible way. A testing system is built using RSCAD and the structure and control strategy proposed in this paper are verified through the Real Time Digital Simulator (RTDS).

Abstract The investment cost of renewable energy systems for achieving net-zero energy buildings (ZEB/NZEB) is a vital factor concerned by most building owners, which raises a requirement for a new financial scheme specifically designed considering the level of ZEB. This study thus focuses on the design of reward-penalty mechanism for promoting the target of net-zero energy balance in each building design, enabling that a cost-effective design option for buildings where high integration of renewable energy systems can be expected. The benefits for building owners are formulated into three scenarios (S0, S1, and S2), in which the effectiveness of the proposed three functions were investigated. The results show that a higher cost is required by a lower level of ZEB whilst considerable bonuses can be realized by owners opting for higher levels of ZEB. In addition, the boundary of building energy consumption level as well as zero energy level is identified and provided for the proposed three reward-penalty functions. Based on the case study, the proposed reward-penalty functions were verified to be effective for a building energy consumption level between 0.8 and 2.0, with an error index lower than 7.0%. This study can provide an efficient yet effective approach for developing a financial scheme to further boost zero energy buildings.

Countries around the world are rapidly deploying renewable energy generation to reduce carbon emissions. Countries in the Gulf Cooperation Council (GCC) are investing heavily in PV generation due to their rich solar resources. As PV technology becomes more mature, future PV developments will largely depend on the cost of the PV generation but there is currently very limited published work that shows a detailed design and in particular the economic analysis of large-scale PV farms. Therefore, this paper uses the Qatar’s first PV farm, the 800MWp Alkarsaah PV farm as a case study to explain the design considerations and especially the economic benefits of large-scale PV farms. Economic comparisons will be made with the most efficient CCGT (combined cycle gas turbine) plants in the network to highlight the economic benefits of PV farms. The results show that the Levelized cost of electricity (LCOE) for this PV farm is 14.03$/MWh, much lower than the LCOE of 39.18$/MWh and 24.6$/MWh from the most efficient CCGTs in the network, highlighting the significant economic benefits of developing PV farms in a low carbon power networks in the future.

AbstractA comprehensive process of the control and protection against a DC fault in a voltage source converter (VSC) based high-voltage direct current (HVDC) system typically includes fault detection, fault isolation and system recovery. Regarding an offshore wind farm (OWF) integrated modular multilevel converter (MMC) based multi-terminal HVDC (MTDC) system with two control paradigms, i.e. master-slave control and droop control under DC faults, this paper presents the fault isolation, including the isolation of the faulted line section, with detailed control and protection sequence, which would be useful for practical engineering. The control and protection sequence at the system recovery/reconfiguration phase is comprehensively investigated, which includes: (1) when to start the recovery/reconfiguration control; (2) the sequence between deblocking the MMCs and reclosing the AC circuit breakers (AC CBs); and (3) the recovery sequence of each HVDC terminal. Based on the analysis of the system characteristics, a preferred recovery/reconfiguration scheme is proposed. Simulation results on the real-time digital simulator (RTDS) validate the proposed scheme and demonstrate the advantages through comparison with a different recovery sequence. The impact of transient and permanent DC faults on the system recovery/reconfiguration control is discussed. In addition, the recovery/reconfiguration control of the MTDC in radial and meshed topologies is compared and demonstrated. Based on the analytical and simulation studies, a general guideline on the recovery/reconfiguration control of MMC MTDC systems is proposed.