scholarly journals Comparative Study of Control Strategies for Stabilization and Performance Improvement of DC Microgrids with a CPL Connected

Energies ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2663
Author(s):  
Isaías V. de Bessa ◽  
Renan L. P. de Medeiros ◽  
Iury Bessa ◽  
Florindo A. C. Ayres Junior ◽  
Alessandra R. de Menezes ◽  
...  
Keyword(s):  
Control Strategies ◽  
Output Feedback Control ◽  
Stability Margin ◽  
Performance Indices ◽  
Dc Microgrid ◽  
Stability Margins ◽  
Dc Microgrids ◽  
Constant Power Loads ◽  
And Performance ◽  
The Stability

The DC microgrid system is composed by converters that operate like feeders and loads. Among these loads, we highlight the constant power loads (CPLs) that may cause instability in the microgrid, observed in the form of undesired oscillations due to its negative impedance behavior. Therefore, this work proposes to use performance indices and stability margins to evaluate state and output feedback control strategies for stabilization of DC microgrids. In particular, it is proposed to evaluate the stability margin of the proposed methodologies by means of the impedance relations in the microgrid based on the Middlebrook criterion. Our simulations and tests showed the relation between the performance and stability degradation and the microgrid impedances variation.

Walking Stability Analysis of Multi-Legged Crablike Robot over Slope

2013 ◽  
Vol 572 ◽  
pp. 636-639
Author(s):  
Xi Chen ◽  
Gang Wang
Keyword(s):  
Mathematical Model ◽  
Stability Analysis ◽  
Stability Criterion ◽  
Stability Margin ◽  
Static Stability ◽  
Matlab Simulation ◽  
And Performance ◽  
The Stability ◽  
The Mathematical Model ◽  
The Relationship

This paper deals with the walking stability analysis of a multi-legged crablike robot over slope using normalized energy stability margin (NESM) method in order to develop a common stabilization description method and achieve robust locomotion for the robot over rough terrains. The robot is simplified with its static stability being described by NESM. The mathematical model of static stability margin is built so as to carry out the simulation of walking stability over slope for the crablike robot that walks in double tetrapod gait. As a consequence, the relationship between stability margin and the height of the robots centroid, as well as its inclination relative to the ground is calculated by the stability criterion. The success and performance of the stability criterion proposed is verified through MATLAB simulation and real-world experiments using multi-legged crablike robot.

scholarly journals Investigations on Vehicle Rollover Prevention Using LQG Regulator

2014 ◽  
Vol 2014 ◽  
pp. 1-11
Author(s):  
Binda Mridula Balakrishnan ◽  
Marimuthu Rajaram
Keyword(s):  
Control Strategies ◽  
Stability Margin ◽  
Initial Investigation ◽  
Rollover Prevention ◽  
Contact Information ◽  
Vehicle Rollover ◽  
The Stability ◽  
And Control

This paper presents results of an initial investigation into vehicle roll model and control strategies suitable for preventing vehicle untripped rollovers. For vehicles that are deemed to be susceptible to wheel-liftoff, various control strategies are implemented in simulation. In this study, the authors propose a method for rollover prevention that does not require such accurate contact information. The validity of the stability margin is shown, and it is used to realize rollover prevention in the direction of the roll. The primary assumption in their implementation is that the vehicle in question is equipped with a conventional controller system.

A Study of the Effect of Mixed Cores on the Stability of BWRs

2010 ◽  
Author(s):  
Jose March-Leuba ◽  
Weidong Wang ◽  
Tai L. Huang
Keyword(s):  
Pressure Drop ◽  
Natural Circulation ◽  
Strong Dependence ◽  
Stability Margin ◽  
Fuel Type ◽  
Stability Margins ◽  
Full Power ◽  
Set Up ◽  
The Stability ◽  
Fuel Elements

Cores loaded with a mixture of fuel types are known to reduce stability margins. Mixed fuel cores have become more common as utilities change fuel suppliers, or when fuel vendors upgrade their fuel designs to take advantage of improved thermal and mechanical margins. This paper studies some of the physical processes that reduce the stability of mixed cores. A number of runs have been performed using the LAPUR6 stability code to evaluate the effect on mixed cores on the stability of a typical BWR. To this end, two fuel types have been set up with two different single-phase to two-phase pressure drop ratios by artificially adjusting the spacer and inlet orifice friction coefficients. The flow and pressure drop characteristics of both fuels have been matched at full flow, full power conditions. All manufacturers match the pressure drop of new fuels so that the flow distributions among the new and old fuel elements operating at the same power are approximately constant. The critical power ratio and thermo-mechanical criteria are typically limiting at full power; therefore matching the flow performance at full power maximizes the margin to these criteria. Stability is of concern at low flows, especially at natural circulation, where the thermal-hydraulic conditions are significantly different from full flow and power. Our simulations show that even if two fuel elements are perfectly matched at full flow, the axial void fraction distribution changes significantly when the flow is reduced to natural circulation conditions and the two fuel elements are not fully thermal-hydraulically compatible at the reduced flows. Basically, the two fuel types set up two separate natural circulation lines, and one of the fuel types essentially starves the other from flow. Since stability has such a strong dependence with channel flow, the reactor stability is controlled by the fuel type that has the smaller flow at natural circulation. A counterintuitive result of this study shows that, in general, loading a more stable fuel type into a mixed core has the opposite effect, and the stability margin of that mixed core is lower until the new, more stable fuel becomes dominant. Because of the burnable Gadolinium in most modern BWR fuels, the highest reactivity fuel elements are the once-burned. Loading a more stable fuel type starves the flow of the high-reactivity older fuel, reducing the stability margin.

scholarly journals Practical Design Considerations for Performance and Robustness in the Face of Uncertain Flexible Dynamics in Space Manipulators

2021 ◽  
Vol 8 ◽  
Author(s):  
Connor Holmes
Keyword(s):  
Control Strategies ◽  
Low Frequency ◽  
Open Loop ◽  
Unmodeled Dynamics ◽  
Loop Control ◽  
Stability Margins ◽  
Flexible Mode ◽  
Space Manipulators ◽  
The Face ◽  
And Performance

Low frequency dynamics introduced by structural flexibility can result in considerable performance degradation and even instability in on-orbit, robotic manipulators. Although there is a wealth of literature that addresses this problem, the author has found that many advanced solutions are often precluded by practical considerations. On the other hand, classical, robust control methods are tractable for these systems if the design problem is properly constrained. This paper investigates a pragmatic engineering approach that evaluates the system’s stability margins in the face of uncertain, flexible perturbation dynamics with frequencies that lie close to or within the bandwidth of the nominal closed-loop system. The robustness of classical control strategies is studied in the context of both collocated (joint rate) and non-collocated (force/torque and vision-based) feedback. It is shown that robust stability and performance depend on the open-loop control bandwidth of the nominal control law (as designed for a simplified, rigid plant). Namely, the designed bandwidth must be constrained to be lower than the minimum flexible mode frequency of the unmodeled dynamics by a given factor. This strategy gives credence to popular heuristic methods commonly used to reduce the effect of unmodeled dynamics in complex manipulator systems.

scholarly journals Equivalent Sliding Mode Controller for Stability of DC Microgrid

2021 ◽  
Vol 12 (1) ◽  
pp. 23
Author(s):  
Muhammad Rashad ◽  
Uzair Raoof ◽  
Nazam Siddique ◽  
Bilal Ashfaq Ahmed
Keyword(s):  
Reactive Power ◽  
Sliding Mode ◽  
Voltage Regulation ◽  
Pi Controller ◽  
Operating Conditions ◽  
Dc Microgrid ◽  
Dc Microgrids ◽  
Central Controller ◽  
The Stability ◽  
Decentralized Architecture

DC microgrids are gaining popularity due to their lack of reactive power compensation, frequency synchronization, and skin effect problems. However, DC microgrids are not exempted from stability issues. The stability of DC microgrids based on decentralized architecture is presented in this paper. Centralized architecture can degrade system performance and reliability due to the failure of a single central controller. Droop with proportional integral (PI) controller based on decentralized architecture is being used for DC microgrid stability. However, droop control requires a tradeoff between voltage regulation and droop gain. Further, global stability through PI controller cannot be verified and controller parameters cannot be optimized with different operating conditions. To address limitations, an equivalent sliding mode (SM) controller is proposed for a DC microgrid system in this paper. Detailed simulations are carried out, and results are presented, which show the effectiveness of an equivalent SM controller.

scholarly journals Research on Virtual Inductive Control Strategy for Direct Current Microgrid with Constant Power Loads

2019 ◽  
Vol 9 (20) ◽  
pp. 4449 ◽  
Author(s):  
Zhiping Cheng ◽  
Meng Gong ◽  
Jinfeng Gao ◽  
Zhongwen Li ◽  
Jikai Si
Keyword(s):  
Transmission Line ◽  
Direct Current ◽  
Control Strategy ◽  
Control Method ◽  
Control Strategies ◽  
Performance Comparison ◽  
Distributed Resources ◽  
Constant Power ◽  
Dc Microgrid ◽  
Constant Power Loads

In order to improve the stability of direct current (DC) microgrid with constant power loads, a novel virtual inductive approach is proposed in this paper. It is known that the negative impedance characteristic of constant power loads will lead to DC bus voltage fluctuation, which will be more serious when they integrate into the DC microgrid though a large transmission line inductive. For the convenience of analysis, a simplified circuit model of the system is obtained by modeling the distributed resources. Unlike the existing control strategies, the proposed control strategy constructs a negative inductance link, which helps to counteract the negative effects of the line inductive between the power source and the transmission line. Detailed performance comparison of the proposed control and virtual capacitance are implemented through MATLAB/simulink simulation. Moreover, the improved performance of the proposed control method has been further validated with several detailed studies. The results demonstrate the feasibility and superiority of the proposed strategy.

Study of Casing Treatment Effects in Axial Flow Compressors

1975 ◽  
Vol 97 (4) ◽  
pp. 477-483 ◽  
Author(s):  
M. P. Boyce ◽  
R. N. Schiller ◽  
A. R. Desai
Keyword(s):  
Axial Flow ◽  
Stability Margin ◽  
Stable Operation ◽  
Stability Margins ◽  
Casing Treatment ◽  
Blade Tip ◽  
Flow Compressor ◽  
The Stability ◽  
Casing Treatments ◽  
Axial Flow Compressors

The phenomenon of surge in an axial flow compressor has long eluded the analytical fluid dynamist. In the recent years, a growing degree of improvement and sophistication in the design of axial flow compressors to achieve higher pressure ratios has resulted in increasingly narrow domains of stable operation. A search for improving stability margins revealed the importance of the blade tip region and casing treatments. The authors have approached the problem by both experimental and analytical methods. The results are mutually confirming. Important new inroads have been made in understanding the flow in the blade tip region, operation of casing treatments and the mechanism of the onset of surge. Some significant conclusions in the selection and design of casing treatments and their effects on the stability margin are presented and explained on the basis of experimental and theoretical results.

Stabilization of a Translating Tensioned Beam Through a Pointwise Control Force

1998 ◽  
Vol 122 (2) ◽  
pp. 322-331 ◽  
Author(s):  
W. D. Zhu ◽  
B. Z. Guo ◽  
C. D. Mote,
Keyword(s):  
Stability Margin ◽  
Numerical Approach ◽  
Distributed Model ◽  
Control Force ◽  
Stability Margins ◽  
Distribution Of Eigenvalues ◽  
Modes Of Vibration ◽  
The Subject ◽  
The Stability ◽  
Necessary And Sufficient

A spectral analysis determining asymptotically the distribution of eigenvalues of a constrained, translating, tensioned beam in closed form is the subject of this paper. The constraint is modeled by a spring-mass-dashpot subsystem that is located at any position within the span of the beam. It can represent a feedback controller with a collocated sensor and actuator. The necessary and sufficient condition that ensures a uniform stability margin for all the modes of vibration is determined. Influences of system parameters on the distribution of eigenvalues are identified. The analytical predictions are validated by numerical analyses. The constraint location maximizing the stability margin of the distributed model is predicted through a combined analytical and numerical approach. The implications and utility of the results are illustrated. The methodology developed can be extended to predict stability margins and optimize control parameters for controlled translating beams with other types of boundary conditions and controller structures. [S0022-0434(00)00702-4]

Analytic Modeling and Integral Control of Heterogeneous Thermostatically Controlled Load Populations

2014 ◽  
Author(s):  
Azad Ghaffari ◽  
Scott Moura ◽  
Miroslav Krstić
Keyword(s):  
Power Control ◽  
Output Feedback ◽  
Electricity Consumption ◽  
Output Feedback Control ◽  
Stability Margin ◽  
Control Technique ◽  
Seasonal Temperature ◽  
Integral Control ◽  
Modeling And Control ◽  
The Stability

Thermostatically controlled loads (TCLs) account for approximately 50% of U.S. electricity consumption. Various techniques have been developed to model TCL populations. A High-fidelity analytical model of heterogeneous TCL populations facilitates the aggregate synthesis of power control in power networks. Such a model assists the utility manager to increase the stability margin of the network. The model, also, assists the customer to schedule his/her tasks in order to reduce his/her energy cost. We present a deterministic hybrid partial differential equation (PDE) model which accounts for heterogeneous populations of TCLs, and facilitates analysis of common scenarios like cold load pick up, cycling, and daily and/or seasonal temperature changes to estimate the aggregate performance of the system. The proposed technique is flexible in terms of parameter selection and ease of changing the set-point temperature and deadband width all over the TCL units. We provide guidelines to maintain the numerical stability of the discretized model during computer simulations. Moreover, the proposed model is a close fit to design output feedback algorithms for power control purposes. Our integral output feedback control, designed using the comparison principle, guarantees fast and efficient power tracking for various real-world scenarios. We present simulation results to verify the effectiveness of the proposed modeling and control technique.

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