Research on Reactive Power Optimization and Voltage Control of Power Grid based on Gravity Energy Storage Technology

In order to meet the high permeability and the access of large scale distributed generation, at present and in the future, active distribution network becomes the trend of smart grid research. This paper introduces the influence of distribution network voltage distribution and stability of distributed energy access based on active distribution network; The reactive power and voltage optimization control method of active power distribution network is summarized from the aspects of optimal voltage regulation measure, voltage regulation measure of power network equipment, reactive power optimal dispatch of power system, and so on. Analysis of the current status of the research, and summarized the existing active distribution network with a distributed power pickup distribution network reactive power and voltage control of the existence of some problems and the insufficiency still some problems that must be solved in the study of reactive power and voltage optimization control of active distribution network are pointed out.

This paper reviews the nature and salient characteristics of reactive power support provision and voltage control issues in electricity markets. The major challenges in the provision of such services from the generation units under both normal and emergency conditions are highlighted. The key issue of assessing the value of the reactive support is addressed. Some key problems and challenges in the adoption of market mechanisms for reactive power support services are discussed. This paper serves as an overview of the challenges that need to be resolved in effectively managing and pricing reactive support and voltage control services.

Reactive power optimization control is an important part of power grid connection. With the construction of New Power System, a large number of distributed new energy will be built and connected to the Grid. In order to deal with the randomness and volatility of new energy and hidden dangers of high proportion of new energy in Grid, reactive power optimization control of grid connected power supply is an important measure to stabilize the power system. Photovoltaic(PV) inverters have independent reactive power control and output capabilities through decoupling. Based on this, this paper proposes a reactive power and voltage equalization(RVE) control algorithm for inverter groups. Aiming at the phenomenon of poor power quality at the source-load point of common coupling(SLPCC) and large voltage drop difference in PV station, a RVE algorithm based on reactive power and voltage vector relationship of inverter generation nodes and array iteration is proposed, and the operation simulation is performed. The results show that the control strategy can carry out effective reactive power control and voltage equalization to inverter groups.

A new and efficient methodology for optimal reactive power and voltage control of distribution networks with distributed generators based on fuzzy adaptive hybrid particle swarm optimisation (PSO) is proposed. The objective is to minimise comprehensive cost, consisting of power loss and operation cost of transformers and capacitors, and subject to constraints such as minimum and maximum reactive power limits of distributed generators, maximum deviation of bus voltages and maximum allowable daily switching operation number. PSO is used to solve the corresponding mixed integer non‐linear programming problem and the hybrid PSO (HPSO) method, consisting of three PSO variants, is presented. In order to mitigate the local convergence problem, fuzzy adaptive inference is used to improve the searching process and the final fuzzy adaptive inference‐based HPSO is proposed. The proposed algorithm is implemented in VC++ 6.0 program language and the corresponding numerical experiments are finished on the modified version of the IEEE 33‐node distribution system with two newly installed distributed generators and eight newly installed capacitors banks. The numerical results prove that the proposed method can search a more promising control schedule of all transformers, all capacitors and all distributed generators with less time consumption, compared with other listed artificial intelligent methods.

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.

An opposition-based improved particle swarm optimization algorithm (OIPSO) is presented for solving multiobjective reactive power optimization problem. OIPSO uses the opposition learning to improve search efficiency, adopts inertia weight factors to balance global and local exploration, and takes crossover and mutation and neighborhood model strategy to enhance population diversity. Then, a new multiobjective model is built, which includes system network loss, voltage dissatisfaction, and switching operation. Based on the market cost prices, objective functions are converted to least-cost model. In modeling process, switching operation cost is described according to the life cycle cost of transformer, and voltage dissatisfaction penalty is developed considering different voltage quality requirements of customers. The experiment is done on the new mathematical model. Through the simulation of IEEE 30-, 118-bus power systems, the results prove that OIPSO is more efficient to solve reactive power optimization problems and the model is more accurate to reflect the real power system operation.

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.

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.

The large-scale integration of distributed renewable generation (DRG) reduces carbon emissions in power systems, but its intermittency and volatility introduce new challenges for voltage and frequency control. This paper proposes a multi-time-scale reactive power optimization approach that incorporates demand-side response. Firstly, based on the interaction characteristics between sources and loads in the distribution network, a demand-side response mechanism using dynamic time-of-use pricing is designed to explore the source-load matching and tracking capabilities. Secondly, a multi-scale day-ahead reactive power optimization control model is constructed, which comprehensively considers the dynamic response mechanism on the demand side. The objective function of this model aims to minimize network losses and voltage deviations while accounting for the day-ahead price response characteristics of loads. The multi-scale reactive power optimization model is then transformed into a Markov decision process and solved via a locally-observed multi-agent deep deterministic policy gradient algorithm to obtain real-time intraday reactive power and voltage control strategies. Finally, the effectiveness of the proposed method is verified through experiments on the IEEE 33-bus system and an actual power grid. Experimental results show that this method can effectively coordinate various reactive power compensation devices and flexible resources, and improve the efficiency and real-time performance of reactive power and voltage control.

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.

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.

<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>

Owing to the characteristics of nonlinearity, asymmetry and stochastic volatility, electrified railway traction loads have arose some hazardous effects to security and stability, reactive power compensation and voltage control, power supply quality of power system. It has practical significance to research on the influence of traction loads to power system for ensuring security and stability of power system. By using Power System Analysis Software Package/User Program Interface (PSASP/UPI) function, the electrified railway traction measurement-based load model (traction load model, TLM) for transient stability simulation are established, and then the TLM is applied to Hunan Electrical Power Network. The dynamic characteristics of TLM and the difference characteristics between TLM and the traditional load model are analyzed through setting different faults. The paper provides a convenient reference for further research on the relay protection setting calculation of power system and safety controlling strategies of traction power supply system.

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.

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.