Proper Reactive Power Research Articles

Voltage Sag Mitigation by using SVC

This paper deals with modeling and simulation of SVC in IEEE 14 bus System with Induction Motor load for avoiding voltage sag. Single phase to ground fault is applied in predominant Induction motor load bus for voltage sag analysis. The effect of reactive power compensation to prevent sag has been analyzed with and without SVC. Simulations of the SVC were carried out by using Power System Computer Aided Design (PSCAD) software. Simulation results prove that the SVC is capable of mitigating voltage sag with proper reactive Power support.

Enhancing Small Signal Stability and Reactive Power-sharing Accuracy in Autonomous Microgrids by a New Decentralized Reactive Power Controller

Load sharing without communication between voltage source converters is most important for reliable operation of microgrids. The common approach to achieve this is using the conventional droop technique. Although this method shares a common active load, reactive power sharing is strongly affected by system parameters. In addition, there is an inherent trade-off between the reactive power-sharing accuracy, voltage regulation, and small signal stability margin. This article presents a novel decentralized reactive power controller for parallel operation of voltage source converters in an autonomous microgrid, which leads to the proper reactive power sharing, voltage regulation, and small signal stability margin in microgrids. The proposed methodology and other reactive power-sharing controllers are simulated in IEEE 37-bus test system, and the multi-objective optimization method is used to optimum tuning of each controller and comparison against each other. Simulation results show better performance of the proposed technique in comparison to other reactive power controllers. Furthermore, since the frequency and magnitude of voltage source converters is changed when the demand is altered in the droop method, the conventional load flow cannot be employed to calculate the operation point; a novel method to calculate the operation point in a voltage source converter based microgrid is proposed in this article.

Multiple distribution static synchronous compensators for distribution feeder voltage support

The potential of multiple distribution static synchronous compensators (DSTATCOMs) to improve the voltage profile of radial distribution networks has been reported in the literature by few authors. However, the operation of multiple DSTATCOMs across a distribution feeder may introduce control interactions and/or voltage instability. This study proposes a control scheme that alleviates interactions among controllers and enhances proper reactive power sharing among DSTATCOMs. A generalised mathematical model is presented to analyse the interactions among any number of DSTATCOMs in the network. The criterion for controller design is developed by conducting eigenvalue analysis on this mathematical model. The proposed control scheme is tested in time domain on a sample radial distribution feeder installed with multiple DSTATCOMs and test results are presented.

Reactive Power Control Design in Doubly Fed Induction Generators for Wind Turbines

The high penetration level of wind power generation in an interconnected electrical network carries new technical challenges regarding system stability. Despite the stochastic nature of the wind, grid reliability has to be guaranteed. In compliance with power companies' new requirements on wind turbines as regards contribution to voltage regulation, this paper proposes a reactive power controller design for doubly fed induction generator drives. This drive topology enables the control of reactive power independently of the active power flow using both rotor and mains-side inverters. This degree of freedom is used in order to share the reactive powers circulating in the drive system and resulting from the reactive power required in the network. The controllers are designed using well-known linear control techniques in order to present the same dynamics. Furthermore, the proper reactive power share can be used to enhance the drive efficiency. Experimental results show the performance of the proposed reactive power control.

An Expert System Approach for Multi-Year Short-Term Transmission System Expansion Planning: An Indian Experience

This paper proposes an expert system approach to short-term expansion planning (STEP). The rules which drive STEP can be classified into MW, MVAR, and ampacity management rules. MW and ampacity management rules are for alleviating transmission line congestion. Reactive power management is required for voltage control at load busses, conformity to the capacity curve of the generators, and containing the MW losses within acceptable limits. Embedding reactive power management in STEP is a challenging task since ac load flow may not converge in absence of proper reactive power planning and load modeling. Therefore, we also propose enhancements to the fast decoupled load flow algorithm for on-the-fly reactive power management. The enhanced algorithm not only can detect divergent load flow scenarios but also self-correct it by restarting the whole process with greater degree of freedom in reactive power controls. The proposed approach leads to development of an automated tool for STEP which has the capability to work, even with incomplete information. A simple method for evaluating location and requirement of shunt reactor is also proposed. By analysis and comparative evaluation, we show that the proposed system can arrive at a solution which is close to optimal. Results on the Western Regional Grid of India with an approximate load of 28 000 MW and 1200 nodes are presented to demonstrate effectiveness of the proposed approach.

Wireless-Control Strategy for Parallel Operation of Distributed-Generation Inverters

In this paper, a method for the parallel operation of inverters in an ac-distributed system is proposed. This paper explores the control of active and reactive power flow through the analysis of the output impedance of the inverters and its impact on the power sharing. As a result, adaptive virtual output impedance is proposed in order to achieve a proper reactive power sharing, regardless of the line-impedance unbalances. A soft-start operation is also included, avoiding the initial current peak, which results in a seamless hot-swap operation. Active power sharing is achieved by adjusting the frequency in load transient situations only, owing to which the proposed method obtains a constant steady-state frequency and amplitude. As opposed to the conventional droop method, the transient response can be modified by acting on the main control parameters. Linear and nonlinear loads can be properly shared due to the addition of a current harmonic loop in the control strategy. Experimental results are presented from a two-6-kVA parallel-connected inverter system, showing the feasibility of the proposed approach