Low-power Wind Energy Conversion Systems Research Articles

Linear Quadratic Regulator-Based PI Control of a Non-Ideal Quadratic Boost PFC Converter for Low-Power Wind Energy Conversion Systems Supplying Uninterruptible DC Power

DC–DC converters are efficient in providing a regulated power with power factor control in switch-mode power supplies and also in electric vehicle charging stations. The aim of this research work is to design an efficient DC–DC quadratic boost power factor correction converter for Wind Energy Conversion Systems (WECS) to provide uninterruptible DC power in case of one or two modules loss for low-power applications. The state-space model of the converter is derived using a state-space averaging technique through small signal modeling by considering the non-linearities. The reduced-order model is obtained using Routh-Pade's approximation method to reduce the complexity involved in the design of the controller parameters for the outer and inner loops. The outer voltage is regulated using an Internal Mode Control (IMC)-based proportional integral (PI) controller to overcome the effect of right-half plane zero (RHP) and three-phase currents are shaped by using three PI controllers. The three inner PI controllers for each phase are tuned using three methodologies like Zieglar Nichols, Skogestad and Linear Quadratic Regulator (LQR)-based PI control. The transient and steady-state performances of the closed-loop system are analyzed for variations in the load and set point using extensive computer-based simulation studies. The results reveal that the LQR-based PI controller show considerably better performance in terms of less settling time, overshoot, power factor and %THD, including parasitic parameters of the components.

A DCM Single-Controlled Three-Phase SEPIC-Type Rectifier

A discontinuous conduction mode (DCM) three-phase single-ended primary-inductor converter (SEPIC) is presented in this article. The analyzed converter operates as a high-power factor stage in AC–DC conversion systems. As its main features, it presents three controlled switches and a single control signal with simple implementation and low-current harmonic distortion. The converter topology, its design equations, and its operation modes are presented as well as a simulation analysis considering a 3 kW–220 V three-phase input to 400 V DC output converter. The experimental results are included, considering as an application the rectifier stage in low-power wind energy conversion systems (WECS) based on a 1 kW permanent magnet synchronous generator (PMSG) with variable voltage frequencies. From the analysis performed in the paper and the simulation and experimental results revealed, it is concluded that the converter is indicated to be employed in any AC–DC low-power conversion system, such as DC distribution systems, and distributed generation or hybrid systems containing variable-frequency generation.

The Comparison of the Efficiency of Small Wind Turbine Generators with Horizontal and Vertical Axis Under Low Wind Conditions

Abstract The authors perform a comparative analysis of the efficiency of two types of low-power wind energy conversion systems with horizontal and vertical axis in the meteorological conditions of Latvia. The analysis is based on long-term wind speed measurements over the period of two years conducted by a network of 22 observation stations at the height of 10 m above the ground. The study shows that in the conditions of Latvia wind turbines with a horizontal axis are expected to work with greater efficiency than similar installations with a vertical axis. The paper presents the models of the spatial distribution of average wind speed, Weibull wind speed frequency distribution parameters and the values of the expected operational efficiency for small wind turbine generators. The modelling results are presented in the form of colour contour maps. Overall, the results of the study can serve as a tool for forecasting annual energy production and for estimating the feasibility of commercial use of wind energy at the height of 10 m in the territory of Latvia.

Trends and Development of Sliding Mode Control Applications for Renewable Energy Systems

Based on the matured theoretical framework of sliding mode control for varied, nonlinear, and unpredictable systems, practical designs of sliding mode control have been developed to suit the purpose of controlling power converters under various operating conditions. These design guidelines are particularly valuable for emerging technologies with renewable energy sources. This paper presents a discussion on the recent development of sliding mode control applications for renewable energy systems, and further examines the current trends of achieving efficiency improvement of renewable energy systems and load protections against large overshoot/undershoot in transient states, by utilizing the fast-dynamic-tracking capability of the sliding mode control. Three comparative case studies between the sliding mode control and proportional-integral control involving, namely, a low-power wind energy conversion system, a series-series-compensated wireless power transfer system, and a multiple energy storage system in a direct current (DC) microgrid, are provided.

Nonlinear dynamic power tracking of low-power wind energy conversion system

This paper addresses the use of variable structure control (i.e., sliding mode (SM) control) for improving the dynamic performance of a low-power wind energy conversion system (WECS) that is connected to a dc grid. The SM control is applied to simultaneously match 1) the maximum power generation of the wind turbine system from the wind with 2) the maximum power injection of the grid-connected power converter into the grid. The amount of energy extractable from a dynamically changing wind using the WECS with SM control is compared with that of classic PI control. Both the simulation and experimental results show that more energy can be harvested with the SM control as compared to the PI control for any dynamically changing or random wind conditions.

Real-time replication of a stand-alone wind energy conversion system: Error analysis

This paper provides adequate information about the problem of real-time replicating in laboratory conditions. The dynamic behavior of stand-alone low-power wind energy conversion systems (WECS) in response to the wind speed variations and also to the electrical load variations is replicated. The investigated system consists of a variable-speed wind turbine based on a permanent-magnet synchronous generator (PMSG), a diode bridge rectifier, a DC–DC step-down converter and a wide range DC load. Because of reduced noise level and better steady-state accuracy, a speed-driven hardware-in-the-loop physical WECS simulator has been used to accomplish this task. Its significant drawback – that is, a reduced bandwidth – has been significantly alleviated by using an enhanced software simulator structure which uses a feed-forward compensation of the inherent physical disturbance produced by the generator torque variations. Both time-domain experimental results and a thorough frequency-domain error analysis show good replication performance in the frequency range of variation of both wind speed and electrical load.

Output power maximization of low-power wind energy conversion systems revisited: Possible control solutions

This paper discusses the problem of output power maximization for low-power wind energy conversion systems operated in partial load. These systems are generally based on multi-polar permanent-magnet synchronous generators, who exhibit significant efficiency variations over the operating range. Unlike the high-power systems, whose mechanical-to-electrical conversion efficiency is high and practically does not modify the global optimum, the low-power systems global conversion efficiency is affected by the generator behavior and the electrical power optimization is no longer equivalent with the mechanical power optimization. The system efficiency has been analyzed by using both the maxima locus of the mechanical power versus the rotational speed characteristics, and the maxima locus of the electrical power delivered versus the rotational speed characteristics. The experimental investigation has been carried out by using a torque-controlled generator taken from a real-world wind turbine coupled to a physically simulated wind turbine rotor. The experimental results indeed show that the steady-state performance of the conversion system is strongly determined by the generator behavior. Some control solutions aiming at maximizing the energy efficiency are envisaged and thoroughly compared through experimental results.

Wind turbulence used as searching signal for MPPT in variable-speed wind energy conversion systems

The control problem associated to a class of horizontal-axis fixed-pitch variable-speed low-power wind energy conversion systems, working in the partial load region, consisting in the energy conversion maximization, is approached here under the assumption that the wind turbine model and its parameters are poorly known. Using a new approach derived from the optimum seeking methods category, generically called Maximum Power Point Tracking (MPPT), the proposed control solution aims at driving the average position of the operating point near to optimality. Instead of inducing sinusoidal search signals, the wind turbulence is here used as search disturbance. The high-speed shaft's average rotational speed is slowly adjusted using the Fast Fourier Transform processing of some available measures from the system as an estimate of the operating point's position/distance to optimality. Numerical simulations are used for preliminary checking the control law based on this estimation.