1,322 research outputs found
Decentralized and Coordinated Vf Control for Islanded Microgrids Considering DER Inadequacy and Demand Control
This paper proposes a decentralized and coordinated voltage and frequency
(Vf) control framework for islanded microgrids, with full consideration of the
limited capacity of distributed energy resources (DERs) and Vf dependent load.
First, the concept of DER inadequacy is illustrated with the challenges it
poses. Then, a decentralized and coordinated control framework is proposed to
regulate the output of inverter based generations and reallocate limited DER
capacity for Vf control. The control framework is composed of a power regulator
and a Vf regulator, which generates the supplementary signals for the primary
controller. The power regulator regulates the output of grid forming inverters
according to the real time capacity constraints of DERs, while the Vf regulator
improves the Vf deviation by leveraging the load sensitivity to Vf. Next, the
static feasibility and small signal stability of the proposed method are
rigorously proven through mathematical formulation and eigenvalue analysis.
Finally, a MATLAB Simulink simulation demonstrates the functionalities of the
control framework. A few goals are fulfilled within the decentralized and
coordinated framework, such as making the best use of limited DERs capacity,
enhancing the DC side stability of inverter based generations, and reducing
involuntary load shedding
Zero-inertia Offshore Grids: N-1 Security and Active Power Sharing
With Denmark dedicated to maintaining its leading position in the integration
of massive shares of wind energy, the construction of new offshore energy
islands has been recently approved by the Danish government. These new islands
will be zero-inertia systems, meaning that no synchronous generation will be
installed in the island and that power imbalances will be shared only among
converters. To this end, this paper proposes a methodology to calculate and
update the frequency droops gains of the offshore converters in compliance with
the N-1 security criterion in case of converter outage. The frequency droop
gains are calculated solving an optimization problem which takes into
consideration the power limitations of the converters as well as the stability
of the system. As a consequence, the proposed controller ensures safe operation
of off-shore systems in the event of any power imbalance and allows for greater
loadability at pre-fault state, as confirmed by the simulation results.Comment: Submitted to "IEEE Transactions on Power Systems" on February 19,
202
Optimal Protection Coordination of Active Distribution Networks Powered by Synchronverters
The integration of distributed generators (DGs) into distribution networks leads to the emergence of active distribution networks (ADNs). These networks have advantages, such as deferring the network upgrade, lower power losses, reduced power generation cost, and lower greenhouse gas emission, DGs are classified due to their interface with the network as inverter-interfaced or synchronous-interfaced. However, DGs integration results in bidirectional power flow, higher fault current levels, deterioration of the protection coordination of the directional overcurrent relays (DOCRs) which are used in ADNs, reduced system stability due to the invertersâ lack of damping. The stability can be enhanced by controlling the inverters to behave as synchronous generators, which are known as synchronverters. In this thesis, a two-stage optimal protection coordination (OPC) scheme is proposed to guarantee reliable protection of ADNs while protecting synchronverters from overcurrent using virtual impedance fault current limiters (VI-FCLs). VI-FCLs provide a cost-effective way to protect synchronverters from overcurrent. The first stage integrates the fault current calculations of synchronverters in the fault analysis to find the parameters of VI-FCLs used to limit the synchronverterâs fault current. In the second stage, the fault current calculations, along with the designed VI-FCLs from the first stage, are employed to determine the optimal relaysâ settings to minimize the total operating times for all the DOCR. It is found that fixed VI-FCLs can limit synchronvertersâ fault currents but may make the OPC problem infeasible to solve. Thus, an adaptive VI-FCL is proposed to ensure a feasible OPC under various fault conditions, i.e., locations and resistances
Adaptive fuzzy sliding mode command-filtered backstepping control for islanded PV microgrid with energy storage system
This study focuses on the control of islanded photovoltaic (PV) microgrid and design of a controller for PV system. Because the system operates in islanded mode, the reference voltage and frequency of AC bus are provided by the energy storage system. We mainly designed the controller for PV system in this study, and the control objective is to control the DC bus voltage and output current of PV system. First, a mathematical model of the PV system was set up. In the design of PV system controller, command-filtered backstepping control method was used to construct the virtual controller, and the final controller was designed by using sliding mode control. Considering the uncertainty of circuit parameters in the mathematical model and the unmodeled part of PV system, we have integrated adaptive control in the
controller to achieve the on-line identification of component parameters of PV system. Moreover, fuzzy control was used to approximate the unmodeled part of the system. In addition, the projection operator guarantees the boundedness of adaptive estimation. Finally, the control effect of designed controller was verified by MATLAB/Simulink software. By comparing with the control results of proportion-integral (PI) and other controllers, the advanced design of controller was verified
Utilization of Differential Thrust for Lateral/Directional Stability of a Commercial Aircraft with a Damaged Vertical Stabilizer
This thesis investigates the utilization of differential thrust to help a
commercial aircraft with a damaged vertical stabilizer regain its lateral/directional
stability. In the event of an aircraft losing its vertical stabilizer, the consequential
loss of the lateral/directional stability is likely to cause a fatal crash. In this thesis,
the damaged aircraft model is constructed, and the lateral/directional dynamic
stability and frequency domain analyses are conducted. The propulsion dynamics of
the aircraft are modeled as a system of differential equations with engine time
constant and time delay terms to study the engine response time with respect to a
differential thrust input. The novel differential thrust control module is presented to
map the rudder input to differential thrust input. Then, the differential thrust
based control strategies such as linear quadratic regulator (LQR), model reference
adaptive system (MRAS), and Hâ loop-shaping based robust control system are
proposed to be utilized to help maintain stability and control of the damaged
aircraft. For each type of control system design, robustness and sensitivity analysis
is also conducted to test the performance of each control system in the presence of
noise and uncertainty. Results demonstrate successful applications of such control
methodologies as the damaged aircraft can achieve stability under feasible control
efforts and without any actuator saturation. Finally, a comparison study of three
control systems is conducted to investigate the merits and limits of each control
system. Overall, the Hâ loop-shaping based robust control system was found to
have the most remarkable results for stabilizing and saving the damaged aircraft
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