Multiport dc-dc converters have been intensively concerned and studied in power electronics-based systems. However, the instability issue and its suppression method are rarely discussed. This article investigates the stability of the triple active bridge (TAB) converter with two constant power loads by impedance-based method, where the output impedance of the TAB converter is derived by the extra element theorem. Then, a virtual impedance-based active damping (AD) control is proposed, where the virtual impedance has four different positions at the output capacitor of the dc port. The effect of the proposed AD control on output impedance and system dynamic response is analyzed. Meanwhile, the range of the virtual impedance is specified. Simulation is performed in PLECS and experimental tests are conducted on a scale-down TAB prototype to verify the effectiveness of the proposed AD control.

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This article investigates the stability of triple active bridge (TAB) converter with different types of loads. In this paper, port2 of TAB converter adopts voltage control to supply a constant power load (CPL), and port3 uses voltage control to supply a resistor or uses current control to supply a battery. Then, an extra element theorem-based (EET) modelling method based on the small signal model of the TAB converter is developed to derive the output impedance of different cases. The AC sweeping is implemented to validate the effectiveness of derivation. Furthermore, the impedance-based analysis method is applied to analyze the system stability. The analysis result shows that the instability issue caused by CPL at port2 can be suppressed by reducing the resistance load value at port3 or output current of port3. Simulation and experimental results are given to validate the stability analysis.@en

With the increasing penetration of converter-interfaced generators, the frequency containment reserve (FCR) from conventional generators keeps going down, leading to a potential risk of frequency instability under contingencies. Consequently, Converter-interfaced generators are required to provide FCR and participate in the corrective rescheduling. Nevertheless, how to assess the FCR and quantify the adequacy of FCR under contingencies is a big challenge in modern new power system. To address this challenge, a cross-entropy-based frequency-constrained contingency-state-analysis (FC-CSA) model is proposed in this paper. Notably, both frequency control (FC) of units (i.e., conventional synchronous generators and converter-interfaced generators), and under frequency load shedding (UFLS) are incorporated in the primary frequency response. Then a unified system frequency response (SFR) function representing frequency dynamic is derived. This SFR function is extracted and reformulated as a group of mixed-integer linear constraints and participates in the traditional CSA model. Moreover, a set of frequency dynamic indexes, i.e., Expectation of UFLS risk, Expectation of FCR from conventional and converter-interfaced generators, is extended to depict the FCR that the power system requires. These indexes are calculated by the FC-CSA in a cross-entropy-based monte carlo simulation (CE-MCs). Case studies on a modified IEEE 6-bus test system and IEEE 118-bus test system are carried out to demonstrate the effectiveness of the proposed FC-CSA model.

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The traditional fault control strategy of converter-interfaced renewable energy sources (CIRESs) may bring about a lower sensitivity level or misoperation of fault component-based directional elements. To overcome this problem, a new control scheme is proposed to adjust sequence impedance angles of CIRESs by computing suitable current references of the CIRES controller. Meanwhile, these current references are maximized by an iterative algorithm to make full use of the short-circuit capacity of CIRESs. The proposed control scheme is applicable to various faulty conditions such as different fault types, power factors, weak grids, and larger fault resistances. Compared with the new directional elements that need to update protection algorithms, the proposed control strategies can make CIRESs compatible with the existing directional elements whilst the necessary fault ride-through (FRT) requirements can still be satisfied. Furthermore, all the controller parameters are not required to be revised based on the detected fault type, even with only local measured data collected. The associated PSCAD simulations, real-time digital simulator (RTDS) testing and the downscale hardware experiment verify the proposed method.

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Supplementary control (SC) technology is widely leveraged by power supply companies in active distribution networks (ADNs) to improve their stability and dynamic characteristics. Yet, the existed SCs are generally implemented from inside the converter controllers of distributed generators (DGs) or active loads, so there is a need to redesign the internal physical structure of the existing controller, resulting in the increasing work amount of assembling and workability. This paper studies the specific R & D process of a novel external coupling type SC (ECSC), which is based upon current source injection (CSI-ECSC) for improving the dynamic characteristics of ADN. The SC current signals are coupled to the current sampling loop from outside the converter controller. And the employment of the existing current sample makes it unnecessary to redesign the internal physical structure of the existing controller. As a result, the SC assembling is simplified and its workability is improved. In this paper, a detailed exemplary ADN with direct-drive permanent magnet synchronous generator (PMSG) is firstly set up in math for full eigenvalue analysis. Then, the CSI-ECSC is designed with its control loop, interface circuit, and parameter setting. Furthermore, by using PSCAD/EMTDC, groups of case studies are conducted in ADNs where photovoltaics (PVs) and energy storage (ES) are included. Finally, the real-time hardware-in-the-loop (HIL) testing validates the functionality of the realized CSI-ECSC in RTDS.

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To promote the integration of renewable energy resources into modern energy systems, high-voltage dc (HVdc) and circuit breaker (CB) technologies have become critical to achieving secure and efficient energy transmission. This article reviews the technical development of the related areas, compares diverse breaker concepts and topologies, investigates possible coordination and testing solutions, and points out the remaining challenges as well as future needs. The time-domain simulation and comparative analysis are adopted in this article to analyze and compare the performances of different HVdc CBs. By making use of different selectivity levels of multiterminal HVdc (MTdc) grids, the suitable planning and placement of HVdc CBs can be conducted. Furthermore, by providing insights into the performance of HVdc CBs, the work presented in this article can serve as a useful asset for the upcoming standardization and industrial application process of HVdc grid and CB design and testing.

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Multi-agent Pickup and Delivery (MAPD) is a challenging industrial problem where a team of robots is tasked with transporting a set of tasks, each from an initial location and each to a specified target location. Appearing in the context of automated warehouse logistics and automated mail sortation, MAPD requires first deciding which robot is assigned what task (i.e., Task Assignment or TA) followed by a subsequent coordination problem where each robot must be assigned collision-free paths so as to successfully complete its assignment (i.e., Multi-Agent Path Finding or MAPF). Leading methods in this area solve MAPD sequentially: first assigning tasks, then assigning paths. In this work we propose a new coupled method where task assignment choices are informed by actual delivery costs instead of by lower-bound estimates. The main ingredients of our approach are a marginal-cost assignment heuristic and a meta-heuristic improvement strategy based on Large Neighbourhood Search. As a further contribution, we also consider a variant of the MAPD problem where each robot can carry multiple tasks instead of just one. Numerical simulations show that our approach yields efficient and timely solutions and we report significant improvement compared with other recent methods from the literature.

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eAssessment The application of multiterminal (MT), high-voltage dc (HVdc) (MTdc) grid technology requires test procedures for the operation and implementation of the protection solutions. The test procedures are usually derived from experience and from extensive measurement data, which, at present, are still not widely available. Based on a hardware-inthe- loop (HIL) method, advanced dc protection testing strategies, utilizing existing experience for ac grids and requirements for MTdc grids, may overcome this gap.@en

A method for comparing the levelized cost of energy (LCoE) of different superconducting drive trains is introduced. The properties of a 10-MW MgB₂ superconducting direct-drive generator and the cost break down of the nacelle components are presented and scaled up to a turbine with a rotor diameter of up to 280 m. The partial load efficiency of the generator is evaluated for a constant cooling power of 0, 50, and 100 kW, and the annual energy production is used to determine the impact on the LCoE.

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