Publications
12 results found
Chengwei L, Rodriguez-Bernuz JM, Junyent-Ferre A, 2021, A low-cost and efficient fault detection and location algorithm for LVDC microgrid, IEEE Workshop on Control and Modeling for Power Electronics (COMPEL), Publisher: IEEE, Pages: 1-7
Low voltage DC (LVDC) microgrids have many potential advantages for the electrification of rural developing areas. In the long term, these micro-grids could be interconnected to create local mini-grids, which would enhance resilience and power supply stability. Despite their advantages, effective protection of these networks remains a challenge that is holding back their adoption. Thus, this paper presents a low-cost and efficient fault detection and location algorithm for the interconnection of LVDC microgrids. This algorithm is specially tailored for rural areas of difficult access in developing countries since it relies on inexpensive auxiliary devices. To be specific, the algorithm locates the fault by coordinating power converters and relays. It only uses relays and does not require extra high sampling rate sensors, which simplifies implementation and costeffectiveness. The communication bandwidth is also very low. The algorithm can be effective for both low impedance and high impedance faults. In addition, it could be easily adaptive to different topologies. A DC network with ring structure is set up in Simulink to test the proposed algorithm. The simulation results shows the effectiveness of the proposed algorithm for low and high impedance faults.
Westermanspier D, Rodriguez-Bernuz JM, Prieto-Araujo E, et al., 2021, Real-time optimization-based reference calculation integrated control for MMCs considering converter limitations, IEEE Transactions on Power Delivery, Vol: 37, Pages: 2886-2901, ISSN: 0885-8977
The paper addresses a real-time optimization-based reference calculation integrated with a control structure for Modular Multilevel Converters (MMC) operating under normal and constrained situations (where it has reached current and/or voltage limitations, e.g. during system faults). The algorithm prioritizes to satisfy the Transmission System Operators (TSO) AC grid current demanded set-points. The constrained optimization problem is formulated based on the steady-state model of the MMC, whereby the prioritization is achieved through distinct weights defined in the Objective Function’s (OF) terms. The resultant optimization problem, however, is highly nonlinear requiring high computation burden to be solved in real-time. To overcome this issue, this paper applies a Linear Time-Varying (LTV) approximation, where the nonlinear dynamics of the system are represented as constant parameters, while a Linear Time-Invariant (LTI) system is used to formulate the optimization constraints. The converter's current references are determined in real-time by solving a constrained linearized optimization problem at each control time step, considering the TSO's demands, the current MMC operating point and its physical limitations. Finally, the linearized-optimization problem is integrated with the MMC controllers and evaluated under different network conditions, where the results indicated that method can be potentially employed to obtain the MMCs current references.
Rodriguez Bernuz JM, McInerney I, Junyent Ferre A, et al., 2021, Design of a linear time-varying Model Predictive Control energy regulator for grid-tied VSCs, IEEE Transactions on Energy Conversion, Vol: 36, Pages: 1425-1434, ISSN: 0885-8969
This paper presents an energy regulator based on a Model Predictive Control (MPC) algorithm for a Voltage Source Converter (VSC). The MPC is formulated to optimise the converter performance according to the weights defined in an objective function that trades off additional features, such as current harmonic distortion, reactive power tracking and DC bus voltage oscillation. Differently from most approaches found in the research literature, the MPC proposed here considers the coupling dynamics between the AC and DC sides of the VSC. This study is focused on the example case of a single-phase VSC, which presents a nonlinear relationship between its AC and DC sides and a sustained double-line frequency power disturbance in its DC bus. To reduce the burden of the MPC, the controller is formulated to benefit from the slow energy dynamics of the system. Thus, the cascaded structure typically used in the control of VSCs is kept and the MPC is set as an energy regulator at a reduced sampling frequency while the current control relies on a fast inner controller. The computational burden of the algorithm is further reduced by using a linear time-varying approximation. The controller is presented in detail and experimental validation showing the performance of the algorithm is provided.
Rodriguez Bernuz JM, Junyent Ferre A, Xiang X, 2021, Optimal droop offset adjustments for accurate energy trading in rural DC mini-grid clusters, 2020 International Conference on Smart Grids and Energy Systems (SGES 2020), Publisher: IEEE, Pages: 453-458
Off-grid micro-grids and solar home systems have become an enabler for the electrification of rural areas in developing countries. Their future integration into full-scale grids poses multiple technical challenges. This paper presents a concept of local DC mini-grid formed by the interconnection of nearby micro-grids. This is envisioned as a step towards the bottom-up development of a larger grid. The paper places special emphasis on the analysis of the controller structure, which is based on a variation of the common droop controller. Generally, decentralised droop schemes present inherent limitations to achieve, simultaneously, DC voltage regulation and accurate energy tracking. The decentralised controller proposed here improves conventional approaches by optimally adjusting the droop controller setpoints based on an Optimal Power Flow (OPF) algorithm that takes into account the characteristics of individual converters and the energy trading commands. This approach can benefit from the communication layer required by the energy trading system. The control design of the mini-grid is customised for its deployment on a variation of the dual active bridge (DAB) power electronic converter. Despite the use of a centralised OPF, the system stability is guaranteed by the decentralised low-level controller. The performance of the control approach and its sensitivity to unknown system parameters is measured and validated through detailed simulation studies.
Hategekimana P, Junyent Ferre A, Ntagwirumugara E, et al., 2020, Assessment of feasible DC microgrid network topologies for rural electrification in Rwanda: studying the Kagoma Village, 2020 International Conference on Smart Grids and Energy Systems (SGES 2020), Publisher: IEEE
This paper investigates the network topology fordistributing electricity in the remote village using solar PVwith DC microgrid. The expansion of the national gridelectricity into rural villages remains a challenge due to theincreased costs of distribution and transmission systems.The optimum selection of the network topology isimportant, relative to the density of the population, villagesize, and the group arrangement of a particular village.The modified Newton–Raphson’s algorithm (N-R) hasbeen programmed in MATLAB to evaluate the voltagedrop and system efficiency, obtained with different typesof the distribution system and the nominal voltages to beused. In this paper, the methodology to decide the bestdistribution topology, nominal operating voltage level, andthe conductor size (based on voltage drop and total cost)was addressed for a specific remote village in Rwanda.
Rodriguez-Bernuz JM, Junyent Ferre A, 2020, Operating region extension of a modular multilevel converter using model predictive control: a single phase analysis, IEEE Transactions on Power Delivery, Vol: 35, Pages: 171-182, ISSN: 0885-8977
The modular multilevel converter is the state-of-the-art topology for voltage source converter HVDC. Despite its advantages, this converter handles large internal low-frequency energy ripples, and the capacitance that supports these dynamics is a key design parameter that affects the operating region of the converter. Different strategies can be found in the literature to increase the feasible region of operation of the converter. Nevertheless, they are typically open loop in nature and use precalculated control references. This paper presents an alternative based on model predictive control that steers the system through optimal control trajectories that are calculated online. This provides feedback and corrective control action in real time. The predictive controller used for this purpose is presented and a linear time-varying approximation is used to reduce the computational burden of the algorithm. The feasible boundaries of the converter are sought and the final performance of the control algorithm is evaluated through detailed simulations using a switching model of the converter.
Rodriguez-Bernuz J-M, Junyent-Ferre A, 2018, Model predictive circulating current regulator for single-phase modular multilevel converter, 10th IEEE Annual Energy Conversion Congress and Exposition (ECCE), Publisher: IEEE, Pages: 4824-4830, ISSN: 2329-3721
This paper describes a model predictive strategy to reduce the sub-module voltage oscillation in a single-phase modular multi-level converter. This task is accomplished by a predictive controller which solves an optimal control problem sequentially. By choosing the objective function weights appropriately, this controller can naturally trade-off sub-modules voltage ripple and recirculating current. It is shown that the sub-module voltage oscillation can be reduced without degrading the efficiency excessively, enhancing the performance of the overall converter. Additionally, it is guaranteed that the recirculating current can be regulated without exceeding the physical limitations of the device.
Junyent Ferre A, Li Y, RodrÃguez-Bernuz JM, 2018, A three-phase active rectifier topology for bipolar DC distribution, IEEE Transactions on Power Electronics, Vol: 33, Pages: 1063-1074, ISSN: 0885-8993
A new three-phase active rectifier topology is proposed for bipolar dc distribution, which can achieve the independent dc-pole control, with only one two-level voltage source converter and an ac-side grounding inductor. The averaged large-signal model and linearized small-signal model of the rectifier are derived in the stationary reference frame. Moreover, a control system is proposed with proper controller parameters. Besides, the rectifier is tested on an experiment platform. Comprehensive experiment results are given and analyzed to validate the function of the proposed rectifier under different operation conditions, including the rectifier start-up performance, rectifier dynamics with unbalanced dc loads for two poles, and rectifier dynamics with asymmetrical dc voltages for two poles. Finally, the proposed rectifier is compared with other two existing ac-dc conversion approaches, in terms of required number and rating of components as well as power losses with different load imbalance levels, which further highlight some potential benefits of the proposed topology.
Rodriguez-Bernuz J-M, Junyent-Ferre A, 2017, Model predictive DC bus voltage regulator with active power curtailment capability for single-phase inverters, 19th European Conference on Power Electronics and Applications (EPE ECCE Europe), Publisher: IEEE, ISSN: 2325-0313
rodriguez-bernuz JM, Junyent Ferre A, 2016, Model predictive current reference calculation for single-phase VSCs, 2016 18TH EUROPEAN CONFERENCE ON POWER ELECTRONICS AND APPLICATIONS (EPE'16-ECCE EUROPE)
Rodriguez-Bernuz J-M, Prieto-Araujo E, Girbau-Llistuella F, et al., 2015, Experimental validation of a single phase Intelligent Power Router, Sustainable Energy, Grids and Networks, Vol: 4, Pages: 1-15, ISSN: 2352-4677
Girbau-Llistuella F, Rodriguez-Bernuz JM, Prieto-Araujo E, et al., 2014, Experimental validation of a single phase intelligent power router, 2014 IEEE PES Innovative Smart Grid Technologies Conference Europe (ISGT-Europe), Publisher: IEEE
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