Secondary Control Mechanisms Research Articles

Suppression of low‐frequency oscillations in hybrid/multi microgrid systems with an improved model predictive controller

AbstractGrid‐forming inverters are used for voltage regulation and frequency control in autonomous hybrid microgrids and multi‐microgrid systems by imitating synchronous generators. However, in microgrids with weak grids including low inertia levels and small X/R ratios, these inverters interact with each other, and as a result low‐frequency oscillations (LFO) arise. LFO impacts the frequency stability of multi‐microgrid systems. Nevertheless, LFO can be mitigated by the load‐frequency control system, which serves as a secondary control mechanism. However, the presence of wind turbines and photovoltaic systems in hybrid microgrids adds complexity to the operation of the load‐frequency control due to the uncertainty associated with these renewable energy resources, and various controllers have been employed. This paper proposes a novel approach to enhance the performance of the load‐frequency control system and suppress LFO. The presented technique reduces the complexity of the hybrid microgrid structure by reducing the number of controllers. The model predictive control (MPC) technique is utilized for load‐frequency control and the weight parameters of the MPC are determined using the rain optimization algorithm. The proposed method demonstrates improved dynamic response, reduced overshoot and undershoot responses, decreased controller complexity, and effective LFO suppression. The simulation results verify the effectiveness of the method.

Voltage unbalance and inertia based frequency control framework considering intelligent load management for stand-alone operation of microgrid

The less inertial microgrid with high penetration of Renewable Energy Sources (RES) faces several issues including voltage and frequency unbalance. The intermittent nature of RES-based Distributed Generations (DGs) makes the system unstable in the absence of a control mechanism in a stand-alone microgrid. The integration of single-phase loads and sudden load switching on the distribution side make the system prone to several malicious events. The unbalance in voltage among the phases and the high Rate of Change of Frequency (RoCoF) are the major concern for degrading the system’s performance during peak and off-peak hours. The paper addresses a hierarchical dual loop voltage and frequency control mechanism where the primary control is equipped with droop strategy and Positive-Negative Sequence Control (PNSC) to maintain Voltage Unbalance Factor (VUF) and adhere to IEC-61000-3-13. Further, the inertial loop is also implemented to mitigate frequency deviation and reduce transient overshoot. The secondary control mechanism enables intelligent load management by scheduling Thermostatic Control Loads (TCLs) during peak hours. The utmost care is taken for the Customer’s Thermal Comfort (CTC) while scheduling the loads. The rigorous simulation is done in MATLAB Simulink and Digsilent Power Factory with a modified IEEE 13 bus system considering system dynamics. Further, the real-time simulation is also performed with OPAL-RT to validate the efficacy of the above methodology.

Hierarchical control of networked microgrid with intelligent management of TCLs: A case study approach

Significant integration of Renewable Energy Sources (RES) has led to the evolution of an alternative platform with distributed generation and clustered loads in low or medium-voltage distribution networks. However, a standalone microgrid is susceptible to several inconsistencies that may lead to system failure and disruption due to the inherent uncertainty of RES and its intermittent nature. The paper proposes a coordinated and hierarchical control framework with an inverter-fed primary controller to maintain the nominal voltage and frequency with a regulated exchange of ancillary power in networked microgrids. Further, during peak hours, a secondary control mechanism is incorporated through Demand Side Management (DSM). Intelligent aggregation of TCLs has been done based on decision tree models and further controls to maintain the nominal frequency in networked microgrids adhering to IEC 60929 considering different temperature ranges (16–22) °C. A thorough investigation is carried out considering two separate microgrids of critical and non-critical loads respectively (one a hospital microgrid and another residential microgrid) connected through an interlinking converter. The modeling of the test system and analysis of the proposed control mechanism is simulated in MATLAB SIMULINK and real-time validation in the OPAL-RT platform considering several dynamics.

Power system frequency profile improvement using satin bowerbird optimized tilt fractional cascade controller with reduced data based cost function

The objectives of the automatic generation control (AGC) are attained via secondary control mechanism with optimal controller gains. The best solutions of these gains are identified by population search-based algorithms with the help of performance metrices. The controller design issues of AGC treat these performance metrics as a cost function. This paper introduces a new performance measure implemented with dominated samples information extracted from the frequency and tie line power changes. This new integral square error (NISE) is incorporated in fitness function and tested on isolated and multi area interconnected power system scenarios with satin bowerbird optimizer to tune the controller gains. Additionally, integral-tilt proportional-fractional order derivative controller is proposed in this paper and comparisons are made with popular controllers to show the merits in terms of AGC specifications. Optimal gain parameters of all controllers are achieved with existing integral square error and the proposed NISE cost functions and extensive simulations are carried out to illustrate the merits of the work. Studies are also expanded to nonlinear systems in order to evaluate the adaptability, performance improvement, and effectiveness of the suggested cost function, controller, and tuning method.

IDBD-Based Beamforming Algorithm for Improving the Performance of Phased Array Radar in Nonstationary Environments

Adaptive array processing technology for a phased array radar is usually based on the assumption of a stationary environment; however, in real-world scenarios, nonstationary interference and noise deteriorate the performance of the traditional gradient descent algorithm, in which the learning rate of the tap weights is fixed, leading to errors in the beam pattern and a reduced output signal-to-noise ratio (SNR). In this paper, we use the incremental delta-bar-delta (IDBD) algorithm, which has been widely used for system identification problems in nonstationary environments, to control the time-varying learning rates of the tap weights. The designed iteration formula for the learning rate ensures that the tap weights adaptively track the Wiener solution. The results of numerical simulations show that in a nonstationary environment, the traditional gradient descent algorithm with a fixed learning rate has a distorted beam pattern and reduced output SNR; however, the IDBD-based beamforming algorithm, in which a secondary control mechanism is used to adaptively update the learning rates, showed a similar beam pattern and output SNR to a traditional beamformer in a Gaussian white noise background; that is, the main beam and null satisfied the pointing constraints, and the optimal output SNR was obtained. Although the proposed algorithm contains a matrix inversion operation, which has considerable computational complexity, this operation could be replaced by the Levinson-Durbin iteration due to the Toeplitz characteristic of the matrix; therefore, the computational complexity could be decreased to O(n), so additional computing resources are not required. Moreover, according to some intuitive interpretations, the reliability and stability of the algorithm are guaranteed.

A novel solid state transformer based control topology for interconnected MV and LV hybrid microgrids

Hybrid microgrid continues to be an attraction for researchers as it brings the advantages of both ac and dc systems under one roof. The interlinking converter (ILC) of this system regulates the ac frequency and dc voltage while maintaining bidirectional power. This paper proposes a novel solid-state transformer (SST) based topology for interconnected medium voltage (MV) and low voltage (LV) hybrid microgrids. Based on the topology, various control modes are identified and correspondingly, an autonomous power sharing scheme is presented with dc voltage and ac frequency regulation. A linear voltage-frequency control is discussed for ac/dc and dc/ac converters of SST which provides a secondary control mechanism. The dual active bridge (DAB) of the SST operates at voltage control mode while providing electrical isolation and stable system operation. The proposed topology and control scheme is significant in the sense that it allows integration of ac and dc grids with different voltage and frequency levels. In addition, the secondary dc voltage or ac frequency regulation control at any hybrid microgrid automatically regulates the ac frequency and dc voltage in the system which reduces system cost. Various simulated scenarios in PSCAD with load changes highlight the optimal performance of the proposed scheme.

Mechanical Thrombectomy of Pulmonary Emboli With Use of the Indigo System and Lightning 12 Intelligent Aspiration

Mechanical Thrombectomy of Pulmonary Emboli With Use of the Indigo System and Lightning 12 Intelligent Aspiration

Invasive Weed Optimized Area Centralized 2 Degree of Freedom Combined PID Controller Scheme for Automatic Generation Control

Frequency disturbances caused by load perturbations of multi area interconnected power system are reduced by using proper control schemes provided via secondary control loop along with primary control of generation plants. These secondary controllers provide simultaneous control signal to individual machines of a particular area when the control scheme is area centralized. This area centralized mechanism provides quick control action with less computational burden since control problem dimensions gets reduced even the area consists multiple plants/machines. Such centralized new cascade control scheme is proposed in this paper to supervise the secondary control mechanism and it is implemented with parallel connection of 2-Degree of Freedom Proportional-Integral-Derivative (2-DOF PID) controller combined with regular PID controller. The performance of this new controller is studied on multi area multi machine interconnected power system with participation factor concept and later its relative performance in terms of dynamic and steady state specifications are compared with conventional PID and 2-DOF PID controllers. These control parameters are tuned by Invasive Weed Optimization (IWO) algorithm to achieve better system outputs. Case studies presented in this paper show the advantages of proposed control scheme.

Adaptive control of isolated intersections based on sequential signal-stage optimisation

Fluctuations in traffic flows at isolated intersections throughout the day have a negative impact on the control effects of certain traffic signal control methods. To solve this problem, adaptive signal control of isolated intersections based on sequential signal-stage optimisation is proposed under a multi-stage optimal decision framework to reduce vehicle delays and increase traffic efficiency. In this paper, to maximise the traffic capacity of an intersection during a signal stage, a primary and secondary control mechanism is designed in which the signal-stage phase (SSP) is composed of primary and secondary compatible phases. The SSP can be dynamically obtained and its maximum duration can be determined in a predictable manner. The terminal conditions are also designed to end the current SSP in a timely manner to increase the traffic throughput of an isolated intersection during a signal cycle. For easier understanding, the adaptive signal control algorithm is elaborated in detail. Numerous simulation experiments were performed in the Vissim 5.4 software program and the simulation results demonstrated that, compared with fixed timing control, segmented timing control and fully actuated control, the proposed control method can clearly reduce the average vehicle delay and the impact on average vehicle stops is acceptable.

“Ah lef ma case fo God”: Faith and agency in Sierra Leone's postwar reconciliation.

This article describes a qualitative ethnographic analysis of local experiences of truth-telling performances within Sierra Leone's Truth and Reconciliation Commission. Whereas proponents of truth commissions claim that such processes promote postwar reconciliation, this study found that local religious belief impeded such effects. While belief did enhance the local willingness to reconcile, in tandem with postwar insecurity, it also promoted a reliance on secondary control mechanisms wherein individuals subjugated their own agency in reconciliation to the power of God. Within this context, the man-made processes of truth-telling were experienced by local people as redundant at best and provocative at worst.

Primary, secondary, and emotional control across adulthood

Schulz and Heckhausen (1996) have recently formulated a theory of successful aging that centers on perceptions of control as a major theme in the developmental process. They suggest primary control is a universal phenomenon and that people will strive for primary control over secondary control. Secondary control mechanisms, on the other hand, may serve to mediate losses in primary control. This study evaluates the relationship between primary and secondary control among 327 men and women, by administering a general sense of control scale and an emotion control measure with four sub-scales. Consistent with previous research, both age and gender differences were found in primary and secondary control. The results of this study provide support for the theory of emotional selectivity which postulates that as people age they are more able to regulate their emotions, thereby directing energies at increasing secondary control mechanisms (Carstensen, 1986).

Haem biosynthesis in peripheral blood in erythropoietic protoporphyria.

Summary The enzymes of haem biosynthesis have been measured in the peripheral blood of 10 patients with erythropoietic protoporyphria. The activity of leukocyte φ-aminolaevulinic acid synthase was significantly elevated (P < 0.0001) as was that of erythrocyte porphobilinogen deaminase (P = 0′0023). There was a consistent depression of leukocyte ferrochelatase activity (P < 0.0001). This study provides evidence that this disease is related to a generalized genetically determined deficiency of ferrochelatase activity. Control of the pathway is by end product repression and inhibition of φ–aminolaevulinic acid synthase with possible secondary control mechanism at the level of porphobilinogen deaminase.

Is porphobilinogen deaminase activity a secondary control mechanism in haem biosynthesis in humans? [proceedings

Is porphobilinogen deaminase activity a secondary control mechanism in haem biosynthesis in humans? [proceedings