This paper presents a review of advanced control techniques for microgrids. This paper covers decentralized, distributed, and hierarchical control of grid-connected and islanded microgrids. At first, decentralized control techniques for microgrids are reviewed. Then, the recent developments in the stability analysis of decentralized controlled microgrids are discussed. Finally, hierarchical control for microgrids that mimic the behavior of the mains grid is reviewed.

/pdf/advanced-control-architectures-for-intelligent-microgrids-5goubszp15.pdf

Advanced Control Architectures for Intelligent Microgrids—Part I: Decentralized and Hierarchical Control

Due to the stochastic nature of wind, electric power generated by wind turbines is highly erratic and may affect both the power quality and the planning of power systems. Energy Storage Systems (ESSs) may play an important role in wind power applications by controlling wind power plant output and providing ancillary services to the power system and therefore, enabling an increased penetration of wind power in the system. This article deals with the review of several energy storage technologies for wind power applications. The main objectives of the article are the introduction of the operating principles, as well as the presentation of the main characteristics of energy storage technologies suitable for stationary applications, and the definition and discussion of potential ESS applications in wind power, according to an extensive literature review.

A review of energy storage technologies for wind power applications

The paper reviews different approaches, technologies, and strategies to manage large-scale schemes of variable renewable electricity such as solar and wind power. We consider both supply and demand side measures. In addition to presenting energy system flexibility measures, their importance to renewable electricity is discussed. The flexibility measures available range from traditional ones such as grid extension or pumped hydro storage to more advanced strategies such as demand side management and demand side linked approaches, e.g. the use of electric vehicles for storing excess electricity, but also providing grid support services. Advanced batteries may offer new solutions in the future, though the high costs associated with batteries may restrict their use to smaller scale applications. Different “P2Y”-type of strategies, where P stands for surplus renewable power and Y for the energy form or energy service to which this excess in converted to, e.g. thermal energy, hydrogen, gas or mobility are receiving much attention as potential flexibility solutions, making use of the energy system as a whole. To “functionalize” or to assess the value of the various energy system flexibility measures, these need often be put into an electricity/energy market or utility service context. Summarizing, the outlook for managing large amounts of RE power in terms of options available seems to be promising.

https://research.aalto.fi/files/6557604/lund_et_al_review.pdf

Review of energy system flexibility measures to enable high levels of variable renewable electricity

Energy storage for mitigating the variability of renewable electricity sources: An updated review

This paper summarizes the main problems and solutions of power quality in microgrids, distributed-energy-storage systems, and ac/dc hybrid microgrids. First, the power quality enhancement of grid-interactive microgrids is presented. Then, the cooperative control for enhance voltage harmonics and unbalances in microgrids is reviewed. Afterward, the use of static synchronous compensator (STATCOM) in grid-connected microgrids is introduced in order to improve voltage sags/swells and unbalances. Finally, the coordinated control of distributed storage systems and ac/dc hybrid microgrids is explained.

/pdf/advanced-control-architectures-for-intelligent-microgrids-2x95thk2q5.pdf

Advanced Control Architectures for Intelligent Microgrids—Part II: Power Quality, Energy Storage, and AC/DC Microgrids

Wind energy is not constant and windmill output is proportional to the cube of wind speed, which causes the generated power of wind turbine generators (WTGs) to fluctuate. In order to reduce fluctuation, different methods are available to control the pitch angle of blades of windmill. In a previous work, we proposed the pitch angle control using minimum variance control, and output power leveling was achieved. However, it is a controlled output power for only rated wind speed region. This paper presents a control strategy based on average wind speed and standard deviation of wind speed and pitch angle control using a generalized predictive control in all operating regions for a WTG. The simulation results by using actual detailed model for wind power system show the effectiveness of the proposed method.

Output power leveling of wind turbine Generator for all operating regions by pitch angle control

Utilization of renewable energy are coming up from view points of environmental conservation and depletion of fossil fuel. However, the generated power from renewable energies is always fluctuating due to environmental status. Energy storage system is indispensable to compensate these fluctuating components. Energy capacitor system (ECaSS) connected an electric double-layer capacitor (EDLC) with power-electronics devices is useful for the compensation of fluctuating power since one is capable of controlling both active and reactive power simultaneously. This paper proposes the current-source ECaSS (CS-ECS), which consists of EDLC, bi-directional DC-DC converter, and current-source inverter. We have presented the control system for the active/reactive power control of CS-ECS, and have shown the effectiveness of CS-ECS through computer simulations for case of wind power generation system.

Output levelling of renewable energy by electric double-layer capacitor applied for energy storage system

Effective utilization of renewable energies such as wind energy is expected instead of the fossil fuel. Wind energy is not constant and windmill output is proportional to the cube of wind speed, which cause the generated power of wind turbine generators to fluctuate. In order to reduce fluctuating components, there is a method to control pitch angle of blades of windmill. We have proposed the pitch angle control using minimum variance control in a previous work. However, it is a controlled output power for only rated wind speed region. This paper presents a control strategy based on average wind speed and standard deviation of wind speed, and pitch angle control using a generalized predictive control in all operating regions for wind turbine generator. The simulation results with using actual detailed model for wind power system show effectiveness of the proposed method.

Output power leveling of wind turbine generator for all operating regions by pitch angle control

Utilisation of renewable energy is becoming increasingly important from the viewpoints of environmental conservation and depletion of fossil fuel. However, the generating power always fluctuates owing to its environmental status. Therefore, an energy-storage system is indispensable to compensate for these fluctuations. Superconducting magnetic energy storage (SMES) is useful for compensation of fluctuating power, since it is capable of controlling both the active and reactive power simultaneously and quickly. Control systems for active and reactive power control of the series and parallel compensation using SMES are proposed. The effectiveness of the proposed system is demonstrated through the instantaneous-value-analysis-based computer simulations in which various cases (system interconnection, wind turbulence, three-phase-to-earth fault in the power system interconnecting large-capacity wind turbine generators) are studied.

Terminal-voltage and output-power regulation of wind-turbine generator by series and parallel compensation using SMES

In order to perform maximum power point tracking control of wind power generation system, it is necessary to drive windmill at an optimal rotor speed. For that purpose, a rotor position and a wind velocity sensors become indispensable. However, from the aspect of reliability and increase in cost, rotor position sensor and wind velocity sensor are not usually preferred. Hence, wind velocity and position sensorless operating method for wind power generation system using observer is proposed in this paper. Moreover, improving the efficiency of the permanent magnet synchronous generator is also performed by optimizing d-axis current using the Powell method.

H. Fujita

Papers

Output power leveling of wind turbine Generator for all operating regions by pitch angle control

Output levelling of renewable energy by electric double-layer capacitor applied for energy storage system

Output power leveling of wind turbine generator for all operating regions by pitch angle control

Terminal-voltage and output-power regulation of wind-turbine generator by series and parallel compensation using SMES

Wind velocity and rotor position sensorless maximum power point tracking control for wind generation system