Application Of Voltage Control Research Articles

Improved high voltage operation of amorphous In–Ga–Zn–O thin film transistor by carrier density enhancement

We report on improved high voltage operation of amorphous-In–Ga–Zn–O (a-IGZO) thin film transistors (TFTs) by increasing carrier density and distributing the high bias field over the length of the device which utilizes an off-set drain structure. By decreasing the O2 partial pressure during sputter deposition of IGZO, the channel carrier density of the high voltage a-IGZO TFT (HiVIT) was increased to ∼1018 cm−3. Which reduced channel resistance and therefore the voltage drop in the ungated offset region during the on-state. To further decrease the electric field in the offset region, we applied Ta capping and subsequent oxidation to locally increase the oxygen vacancy levels in the offset region thereby increasing local carrier density. The reduction of the drain field in the offset region from 1.90 V μm−1 to 1.46 V μm−1 at 200 V drain voltage, significantly improved the operational stability of the device by reducing high field degradation. At an extreme drain voltage of 500 V, the device showed an off-state current of ∼10−11 A and on-state current of ∼1.59 mA demonstrating that with further enhancements the HiVIT may be applicable to thin-film form, low leakage, high voltage control applications.

Artificial Jellyfish Search Algorithm-Based Selective Harmonic Elimination in a Cascaded H-Bridge Multilevel Inverter

This paper used an artificial jellyfish search (AJFS) optimizer suitable for selective harmonic elimination-based modulation for multilevel inverter (MLI) voltage control application. The main objective was to remove the undesired lower-order harmonics in the output voltage waveform of an MLI. This algorithm was motivated by the behavior of jellyfish in the ocean. Jellyfish have the ability to find the global best position where a large quantity of nutritious food is available. The paper applied AJFS algorithm on five, seven, and nine levels of CHB-MLI. The optimum switching angle was calculated for the entire modulation range for the desired lower-order harmonics elimination. The problem formulated to achieve the objective was solved in a MATLAB environment. The total harmonic distortion (THD) values of five-, seven-, and nine-level inverters for various modulation indexes were computed using AJFS and compared with the powerful differential evolution (DE) algorithm. The comparison of THD results clearly demonstrated superior THD in the output of CHB-MLI of the AJFS algorithm over DE and GA algorithm for low and medium values of modulation index. The experimental results further validated the better performance of the AJFS algorithm.

Secondary Voltage Control Application in a Smart Grid with 100% Renewables

This paper presents secondary voltage control by extracting reactive power from renewable power technologies to control load buses voltage in a power system at different operating conditions. The study is performed on a 100% renewable 14-bus system. Active and reactive powers controls are considered based on grid codes of countries with high penetration levels of renewable energy technologies. A pilot bus is selected in order to implement the secondary voltage control. The selection is based on short-circuit calculation and sensitivity analysis. An optimal Proportional Integral Derivative (PID) voltage controller is designed using genetic algorithm. A comparison between system with and without secondary voltage control is presented in terms of voltage profile and total power losses. The optimal voltage magnitudes at busbars are calculated to achieve minimum power losses using optimal power flow. The optimal placement of Phasor Measurement Units (PMUs) is performed in order to measure the voltage magnitude of buses with minimum cost. Optimization and simulation processes are performed using DIgSILENT and MATLAB software applications.

Impedance sensitivity-based corrective method for online voltage control in smart distribution grids

With the rapid increase in hosting large penetration levels of Distributed Generation (DG), voltage stability problem has raised a main concern for distribution networks. This study proposes a new centralized voltage control method following a security purpose for active distribution grids. The method is based on a sensitivity analysis to optimally dispatch the control variables. The sensitivity analysis uses a Thevenin-based load impedance margin (TLIM) derived from the nodal measurements to take into the consideration the changes in the system operation, especially those caused by the rapid-response devices of DGs. Sensitivity of load and equivalent impedances to control variables is investigated via the derivation of nodal voltage and current with respect to control variables. Accordingly, the contribution of each control variable in change TLIM and, hence, in voltage control can accurately be obtained. The changes of the impedances of pilot bus, which has the smallest value among all the TLIMs, are formulated in a multi-step optimization problem in terms of impedance sensitivities for the optimal dispatch of controls. The proposed sensitivities and their application in voltage control are successfully validated by a 11-kV distribution grid including 77 bus and hosting 22 DG units. Simulation results show the validity and the accuracy of the proposed sensitivity method in voltage control during different scenarios.

Nonlinear Tracking Controller for DC/DC Boost Converter Voltage Control Applications via Energy-Shaping and Invariant Dynamic Surface Approach

In this brief, a novel nonlinear tracking control law is presented for dc/dc boost converter voltage control applications through the energy-shaping approach. The first feature is to devise a self-tuner to update the invariant surface according to the output voltage-tracking error. The second is to prove that the exponential convergence and performance recovery properties without steady-state errors under the use of the nominal parameter information of converters. A 3-kW prototype dc/dc boost converter is adopted for experimental verifications of the proposed controller.

Wide-area measurement-based voltage stability sensitivity and its application in voltage control

This work proposes a measurement-based voltage stability index, namely wide-area measurement-based voltage stability sensitivity based on L index. The sensitivities of L index with respect to nodal reactive power (Q) and real power (P) injections are first derived. The derived L-Q and L-P sensitivities analyze the impact of nodal injection to nodal voltage stability and can help determine the reactive power compensation and emergency load shedding amount for voltage stability control. To improve the computational efficiency, a simplified L index, L′, along with its sensitivities with respect to nodal reactive and real power injection (L′-Q and L′-P sensitivities) are derived which makes the proposed approach suitable for the practical large-scale systems. Moreover, a control strategy for voltage stability is proposed based on the L-Q, L-P, L′-Q, and L′-P sensitivities. The proposed sensitivities and control strategy are tested on the New England 39 bus system and the IEEE 118 system. Test results on both systems verify the proposed sensitivities and the control strategy by demonstrating their accuracy and robustness in voltage stability assessment and control. In conclusion, the proposed measurement-based sensitivities can be applied to voltage stability assessment and control by using the wide-area measurements.

An integrated lookahead control-based adaptive supervisory framework for autonomic power system applications

Management of the power system infrastructure is a challenge due to its complex dynamics, size, deregulated operation, quality of service demands, and stability concerns. Autonomic computing has recently gained interest on power systems arena for self-healing, self-configuration, self-optimization, and self-protection schemes. Robustness and reliability of the power system can be enhanced with appropriate autonomic control action following the disturbances. Predictive optimal tuning of real time control parameters from the finite set of control actions is considered in this paper to prevent from impending system deterioration. We present the formulation of a generic, higher layer model-based Limited Lookahead Control (LLC) approach that can be applied to a variety of power system applications. The system model, including the lower level controller, load dynamics, and a network assists the controller action. Discrete time control decisions are made based on the optimization of the predicted response to a limited horizon from the developed model. Heuristics based A* algorithm is integrated into the framework to reduce the control overhead for real-time operation. Finally, we present a case studies on Matlab, and RTDS® to demonstrate the applicability of the proposed framework. A nine bus multi-machine power system benchmark is considered for voltage control application with the finite set of capacitor tuning.

Data Traffic Scheduling for Cyber Physical Systems With Application in Voltage Control of Distributed Generations: A Hybrid System Framework

The design of the communication infrastructure in cyber physical systems (CPSs) is of key importance since it conveys information from sensors to controllers. Scheduling in the medium access control layer, i.e., the selection of active communication links, plays an important role in improving efficiency of communication in CPS. Different from traditional scheduling algorithms designed for pure data communication networks, the scheduling in CPS is for the purpose of optimizing the physical dynamics and needs to be designed with awareness of the dynamics. In this paper, the scheduling problem in CPS is fitted into the framework of the hybrid systems, in which different selections of links correspond to different dynamic modes. Both centralized and distributed scheduling algorithms are designed. The proposed algorithms are also applied in the background of voltage control of distributed generations (DGs). Numerical simulations show that the proposed framework and algorithms achieve good performances.

Performance improvement of indirect vector controlled induction motor drive using multi-level inverter

Multi-level inverter has emerged as an important topology in the area of high power-medium voltage control applications due to its several advantages such as a better output voltage with reduced total harmonic distortion (THD), reduction of voltage ratings of the power semiconductor switching devices and also the reduced electro-magnetic interference problems etc. This paper presents the performance of an indirect vector controlled induction motor drive fed from five-level, three-level and two-level inverters under different operating conditions (dynamic and steady state). The control scheme uses space vector modulation (SVM) technique for five-level, three-level and two-level inverter circuits. For two-level inverter control, an SVM algorithm in which the calculation of switching times proportional to the instantaneous values of the reference phase voltage. It eliminates the calculation of sector and angle information. For three-level and five-level inverter control, a simplified SVM technique is implemented, which reduces the coordinate transformations complications in the algorithms. In this, the space vector diagram of the three-level and five-level inverter is decomposed into six space vector diagrams of two-level inverters. The torque ripple and the performance of induction motor drive with three-level, five-level and two-level inverters are compared under different operating conditions.

Particle Swarm Optimization Solving Nonlinear Programming Problems in Power System

In order to improve the control capability of the power system voltage stability and to enhance spatial and temporal coordination of voltage control means, it is essential to establish the model of emergency voltage control that can globally mobilize reactive power support and voltage control potential. Focus on the long-term voltage stability of power system, the paper introduce nonlinear programming into emergency voltage control, settle the problem that how to establish the model of emergency voltage control. Based on detailed models of power system, the receding optimization model of long-term voltage stability control is established under framework of model predictive control. In order to improve the computational efficiency and reduce feedback delays, nonlinear programming sensitivity algorithm is proposed to solve receding optimization model. The proposed method can improve computational efficiency significantly which creates the condition for the emergency voltage control application to large-scale systems.

Harmonic State-Space Model of a Controlled TCR

This paper presents a harmonic state-space (HSS) model of a three-phase thyristor-controlled reactor (TCR) in a voltage-control application. In using the HSS description, the importance of incorporating the effect of harmonic interaction on the dynamics of a power system containing a TCR or other flexible ac transmission system controllers is illustrated. Although nonlinear in nature, the significant effect of switching instant variation is included in the linearized model. The model size is minimized with the selection of the minimum necessary set of harmonic frequencies. To validate the HSS models, the steady-state harmonics and the step response were validated with a PSCAD/EMTDC simulation.

Reactive power control of wind farms for voltage control applications

In the last few years, there is a strong trend towards decentralised production and supply, leading to a situation where a growing number of small and medium size producers will be connected to energy networks. But at the same time, the power quality of the generation must be ensured and this means that the electrical parameters of the distribution network have to be maintained within their upper and lower limits. Therefore, new problems related to the management and operation of energy transfer and distribution and to the efficient distribution of renewable energy in the grids are actually arising. Hence, it is reasonable to think that dispersed generation (wind energy generation in this paper) should start to take part in the control of electric variables, and in particular, in reactive power control which is directly related to the voltage level control of distribution networks. This paper presents a control strategy developed for the reactive power regulation of wind farms made up with double fed induction generators, in order to contribute to the voltage regulation of the electrical grid to which farms are connected.

STATCOM control for power system voltage control applications

A static compensator (STATCOM) is a device that can provide reactive support to a bus. It consists of voltage sourced converters connected to an energy storage device on one side and to the power system on the other. In this paper the conventional method of PI control is compared and contrasted with various feedback control strategies. A linear optimal control based on LQR control is shown to be superior in terms of response profile and control effort required. These methodologies are applied to an example power system.