Opposition-Based Improved PSO for Optimal Reactive Power Dispatch and Voltage Control

In order to solve the voltage problem of power grid after a high proportion of renewable energy is connected in the new type power system, a reactive power optimization and voltage control method considering gravity energy storage is proposed. This paper analyzes the power model and the reactive power compensation principle of gravity energy storage theoretically, establishes the mathematical models of reactive power optimization and voltage control with the minimum total deviation of node voltage as the objective function. Taking power flow, system operation conditions and energy storage power as constraints, the particle swarm optimization algorithm based on competition theory is used to solve the equation, and the effectiveness and practicability of the proposed method are verified by simulation examples.

A novel multi-agent particle swarm optimization algorithm (MAPS) is proposed for optimal reactive power dispatch and voltage control of power system. The method integrates multi-agent system and particle swarm optimization algorithm. An agent in MAPS represents a particle to particle swarm optimization and a candidate solution to the optimization problem. All agents live in a lattice-like environment, with each agent fixed on a lattice-point. In order to decrease fitness value, quickly, agents compete and cooperate with their neighbors. and they can also use knowledge. Making use of these agent interactions and evolution mechanism of particle swarm optimization. MAPS realizes the purpose or minimizing the value or objective function. MAPS applied for optimal reactive power is evaluated on an IEEE 30-bus power system. It is shown that the proposed approach converges to better solutions much faster than the earlier reported approaches.

Voltage and Frequency control are the two fundamental control problems in power systems. Unlike frequency control, voltage control is complicated by the fact that reactive power can't travel far distances from its source of generation. Due to this distributed nature of reactive power, voltage control is usually performed in decentralized manner. Typically, voltage control problem is divided into a three-level hierarchical structure namely primary, secondary and tertiary voltage control.;The aim of this thesis is to present an optimal secondary voltage control by decomposing a large power system into small subsystems called voltage control areas (VCAs) using the fast community detection algorithm. Each VCA is self-sufficient in satisfying its reactive power demand. A load bus, called pilot point/bus, is selected in each VCA as a representative of the voltage profile of the whole area. Singular value decomposition of Fast Decoupled Load Flow (FDLF) Jacobian is used to optimally control the voltages of these pilot buses.;The presented approach is tested on two standard IEEE test power systems i.e. 9-Bus and 39-Bus systems. The computational time comparison of the fast community detection algorithm with another algorithm called original-GN algorithm is also presented. Through simulation results, it is shown that the presented optimal voltage control (Opt-VC) is a better approach compared to sensitivity based voltage control (Sen-VC).

This paper presents ancillary voltage control for a distribution feeder by using energy storage system (ESS) in microgrid. The microgrid consists of photovoltaic, wind power, and distribution generator. The active and reactive power control, voltage and frequency droop control for the power converter of ESS are proposed to reduce microgrid impact on the distribution feeder. The voltage variation along the feeder due to change of renewable power generation is derived by executing power flow analysis. The actual voltage fluctuation on the microgrid is measured, which is used to control active and reactive power output of the power converter via energy management system in the microgrid SCADA platform. Three operation scenarios of the microgrid with ESS are tested to verify the effectiveness of the proposed control method. It is found that the power output of ESS can be well regulated to reduce voltage fluctuation on the microgid, which is complied with grid connect code to achieve better voltage control performance for the distribution feeder.

Conventional fossil fuels such as coal, oil and natural gas are being reduced and become more and more a source of serious undesirable effects on the environment. Wind power is playing a major role in the effort to augment the share of renewable energy sources in the world energy mix with a continuously increasing penetration into the grid. Wind turbine generators can be divided into two basic categories: fixed speed and variable speed. Variable-speed wind energy systems are presently favored than fixed-speed wind turbines thanks to their higher wind power extraction, improved efficiency, reactive power support and voltage control. This study addresses the problem of control of Wind Energy Conversion System (WECS) in variable speed. To this end, two simultaneous control objectives, namely the maximization of the energy conversion efficiency based on Squirrel Cage Induction Generator (SCIG) wind turbine and the regulation of the active and reactive power feed to the grid, to guarantee Unit Power Factor (UPF), have been established. To deal with the complexity and nonlinearity of the system, the sliding mode control is adopted. Indeed, this technique provides an efficient tool for controller design and presents attractive features such as robustness to parametric uncertainties of the different components of the system. In this way, sliding-mode control laws are developed using Lyapunov stability analysis, to guarantee the reaching and sustaining of sliding mode and stability of the system control. Evaluation of the reliability and performance of the proposed sliding mode control approach has been established on a 3MW three-blade wind turbine. Simulation results demonstrate that the proposed control strategy is effective in terms of MPPT control strategy, active and reactive power tracking trajectories and robustness against system parameter variations.

Reactive power supports by generators are essential for energy and reactive power delivery in the open access grid system. However, so far no fair scheme has been proposed that will enforce capital investment on the needed services, which may jeopardize the cause on power system deregulation. To devise such a scheme, the authors divide reactive support of generators into two functions-reactive power delivery and voltage control-and devise a payment framework to allocate reactive support cost of generators to the bidding loads and bilateral trades on the real-time operating point basis. In their method, the reactive sensitivity matrix derived from the fast decoupled power flow algorithm is used to determine the reactive delivery allocation pattern; meanwhile, efficient reactive loss formulae are developed to charge voltage control costs of generators. The authors demonstrate the potential of their method in a PoolCo. electricity market (EM) by numerical examples.

The increasing integration of renewable energy sources into modern electric grids has led to a rise in uncertain factors that must be managed to maintain voltage security during reactive power optimization (RPO). Traditional deterministic RPO methods fail to account for these uncertainties, which can result in power grid security issues such as voltage violations. To address these challenges, this paper proposes a data-driven interval-based reactive power optimization method (IRPOM). The IRPOM represents the uncertainties associated with renewable power generation and load demands as intervals within the RPO problem formulation. The proposed method uses an improved particle swarm optimization algorithm to solve the RPO problem. In each iteration, the uncertain power flow is solved using the optimizing-scenarios method- (OSM-) based interval power flow (IPF) algorithm. This approach calculates the real power losses and checks whether state quantities, including voltage, power flow, and generator output, exceed their limits. Furthermore, a data-driven modeling approach is introduced to reduce the conservativeness of the IRPOM solutions. The effectiveness of the proposed method is demonstrated through detailed computational analysis on a modified IEEE 30-bus system. The results show that the proposed approach ensures economic efficiency while maintaining a low bus voltage threshold crossing probability close to zero.

Although there are many methods or models widely applied to evaluate water resources carrying capacity, the evaluation result is qualitative not quantitative. In order to quantificationally evaluate groundwater carrying capacity in irrigation district, multi-objective evaluation model of groundwater carrying capacity was established, which includes four objectives, i.e., GDP, grain yield, population and COD emissions. The multi-objectives model can factually describe groundwater carrying capacity for social economy subsystem and ecological environment subsystem in irrigation district. The improved Particle Swarm Optimization (PSO) algorithm was built and adopted to solving the groundwater carrying capacity multi-objective model. In the improve PSO algorithm, linear inertia weight and chaos variation operator are employed to improve basic algorithm global searching capacity. The model was applied to quantificationally evaluate groundwater carrying capacity of People's Victory Canal irrigation district in current year and in 2010 level year.

In order to fit in with the demands of the development of electricity market in China, a multi-objective optimization mathematical model is presented to dispatch load within the units, taking economy, environmental protection and quick responsiveness to dispatching commands into consideration at the same time. And take the minimal whole plants power-supply coal cost rate, the minimal pollutant emissions and the minimal load adjusting time as these three objective functions respectively. The four constraint conditions are unit power balance constraint, load bound constraint, ramping constraint and pollution discharge standards constraint. An improved particle swarm optimization algorithm is used to get the Pareto solution set. The optimal solution was obtained by using the method of multi-attribute decision making, through sequencing the solution set by comprehensive evaluation. A case study based on a power plant with 4×600MW units was carried out. The result shows that the method can solve the multi-objective optimal load distribution problem accurately and quickly, and get the good effect in energy conservation and emissions reduction.

A new approach to optimal reactive power and voltage control problem in a radial distribution system is proposed in this paper. The optimal control problem is to find a proper dispatch schedule for shunt capacitor banks and on-load tap changer at substation and shunt capacitor banks on feeders such that the power loss is minimized and the voltage profile is improved. To reduce computation burden, the whole problem is decomposed into two sub-problems, namely sub-problem on substation level and sub-problem on feeder level. A simplified dynamic programming and a fuzzy logic control algorithm are used to deal with the two sub-problems respectively. Coordination of the two algorithms provides an appropriate solution to the whole control problem. The numerical results demonstrate that the proposed approach is effective and feasible.

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In this paper, a novel intelligent controller for grid connection of DC microgrids is presented. The proposed controller allows the bi-directional AC/DC converter, linking the DC microgrid to the main utility grid, to provide the main functionalities of an inverter. Such functions include bi-directional power flow control and independent control of both active power (P) and reactive power (Q). In addition, the developed controller acts as an intelligent active power filter (APF) to the main grid. This is because it autonomously detects any power quality problems, filters out load-created harmonics and compensates unbalances and/or DC offsets resulting from the local AC load connected at the point of common coupling (PCC). The objective of the controller is to force the AC grid currents at the PCC to be balanced three-phase currents with minor harmonics while maintaining its controllability of power flow regardless of the characteristics of the local AC load. The performance of the developed controller was examined under several extreme cases including: non-linear loads, distorted load currents, unbalanced and offset conditions. The results show that the developed controller succeeds to maintain bi-directional P/Q flow controllability, allows the inverter to provide ancillary services such as reactive power compensation or voltage control to the grid while simultaneously acting as an active power filter to assure improved power quality at the PCC under various loading conditions.

Among the existing power quality problems, the reactive power compensation plays a key role once it helps to maintain the system stability and increases the efficiency. Currently, there are many solutions for reactive power compensation, which unfortunately present a wide variety of problems as large inrush currents, non-continuous compensation and harmonics injection in the system. The application of devices like static VAr compensator, static synchronous compensator or unified power flow controller has demonstrated to be an effective solution for reactive power compensation. However, it is important to note that these options are rarely used in distribution systems by companies that prefer to assimilate the drawbacks of switched capacitor banks instead of investing in more expensive, sophisticated and complex solutions. Despite the large number of proposed devices in distribution systems, there is a lack of solutions with emphasis on cost reduction. Therefore, this paper presents a new topology for reactive power compensation and voltage control in distribution systems. The proposed topology has several interesting features as reduced switching losses, small capacitors and simple control scheme. In addition, the proposed solution uses already existing capacitor banks which makes possible its usage in distribution companies with minimum modifications. Experimental results have been obtained on a 6-kVA prototype to demonstrate the feasibility of the proposed solution.

MVDC is starting to be considered as an option for enhancing transfer capacity and providing increased power quality at distribution networks. There is a term starting to be used of “soft open-point” which can provide controlled power transfer between two 11kV or 33kV distribution groups, without affecting short-circuit levels, voltage differences, loop flows or limitations due to phase-angle differences. The 4-quadrant converters can provide reactive power support and voltage control at each end of the link and multi-terminal is also feasible. There are future technology opportunities including enhancement of existing corridors through the conversion of existing AC lines to DC. This paper provides a technology overview as well as information on recently deployed projects ranging from linking of oil and gas platforms, through to an urban infeed. It will summarise the benefits of MVDC and the applications where it may provide a competitive or preferential alternative solution to conventional technology.

<p>Electricity market activities and a growing demand for electricity have led to heavily stressed power systems. This requires operation of the networks closer to their stability limits. Power system operation is affected by stability related problems, leading to unpredictable system behavior. Voltage stability refers to the ability of a power system to sustain appropriate voltage levels through large and small disturbances. Steady-state voltage stability is concerned with limits on the existence of steady-state operating points for the network. FACTS devices can be utilized to increase the transmission capacity, the stability margin and dynamic behavior or serve to ensure improved power quality. Their main capabilities are reactive power compensation, voltage control and power flow control. Among the FACTS controllers, Static Var Compensator (SVC) provides fast acting dynamic reactive compensation for voltage support during contingency events. In this paper, voltage stability assessment with appropriate representations of tap-changer transformers and SVC is investigated. Integrating both of these devices is the main topic of this paper. Effect of the presence of tap-changing transformers on static VAR compensator controller parameters and ratings necessary to stabilize load voltages at certain values are highlighted. The interrelation between transformer off nominal tap ratios and the SVC controller gains and droop slopes and the SVC rating are found. P-V curves are constructed to calculate loadability margins.</p>