An efficient method for speed control of induction wind turbine generator with dual AC-DC-AC converter

One of the key issues in the efficient conversion of wind kinetic energy into electricity is the regulation of turbine speed to achieve maximum electrical power generation. The asynchronous generator with full load double AC-DC-AC power converter has not been widely used due to its poor performance in low wind speed. In this paper a method for turbine speed control of induction generator with full-scale double AC-DC-AC power converter to maximize absorbed wind power in the wide wind speed range, using the calculated maximum turbine power as a reference, is proposed. The configuration of an AC-DC-AC converter for connecting an asynchronous generator to the grid, as well as modeling of Pulse Width Modulation converter is presented in detail. Performance of the proposed control concept to maximize the absorbed wind power is verified through the simulation in MATLAB®. Finally, the advantages and disadvantages of the proposed control concept are discussed.

An Optimal Speed Control Method of Multiple Turboshaft Engines Based On Sequence Shifting Control Algorithm

In order to overcome the problem of significant drop in operational efficiency remarkably while power turbine speed varies among a large range, an optimal speed control method of multiple turboshaft engines based on sequential shifting control (SSC) algorithm is proposed. Firstly, combined with multi-speed gearboxes, a sequential shifting control algorithm of multiple turboshaft engines is proposed and designed to accomplish continuously variable speed control. Then, selecting the minimum engine fuel flow as the optimization objective, an integrated optimization method of optimal speed based on multiple engines and multi-speed gearboxes is proposed to promote the operational economy. Finally, the simulation tests of the optimal speed control method of twin and triple turboshaft engines is conducted separately. The results demonstrate that the optimal speed control method of multiple turboshaft engines based on SSC algorithm can change the power turbine speeds by no more than 7% and main rotor speed by over 8% simultaneously. In addition, compared with the fixed-ratio transmission (FRT), engine fuel flows decrease by more than 2% under different cruise states. It proves that the optimal speed control method is beneficial to obtain more superior overall performances of the integrated helicopter/multi-engine system without considerable loss of compressor surge margin.

Investigation on rotor jet interference in a hydraulic reaction turbine for low head low flow water conditions

The focus of this paper is to investigate the issue of water jet interference, which is a common flaw in simple reaction turbines. When the turbine’s wall crosses the water jet coming from another nozzle, this is known as jet interference. The governing equations are also used to analyse the Z-Blade simple water reaction turbine for an ideal and practical example, based on the principles of mass-, impulses and energy conservation. Various evaluations of real and potential operating losses for low-head (3–5 m) and low-flow (3 L/s and below) water resources have been conducted. According to experimental data, the Z-Blade turbine Type B achieves the maximum rotational speeds at 450 rpm, followed by Type A at 400 rpm and Type C at 300 rpm. By performing parametric analysis via governing equations, the calculated non-interference speed is approximately twice that of the turbine’s maximum speed. Furthermore, as the turbine reaches its maximum rotational speed at the optimal length diameter, the turbine speed decreases without interference from the jet nozzle rotor. This resembles a phenomenon of non-interference rotor jet on Z-Blade turbine.

THE EFFECT OF NUMBER OF BLADES EXPERIMENTALLY ON THE HORIZONTAL WIND TURBINE SPEED

The aim of this research is to find the effect of the number of blades on the wind turbine speed and to find which number of blades is suitable for low wind areas and high wind areas. In wind turbine design; the number of blades, tip speed ratio, and the rotational speed of the rotor are the most important factors. At first, the tip speed ratio and the number of blades must be selected. The power of a wind turbine generator depends on the rotational speed of the rotor. The increase in wind velocity leads to an increase in the rotor speed. At wind velocity 2.36m/s, the rotational speed of 6 blades, 4 blades and 3 blades was 288, 54, and 34 rpm respectively. And, at wind velocity 13.85m/s, the rotational speed of 6 blades, 4 blades, and 3 blades are 1856, 2220, and 2103 rpm respectively. So, when the number of blades decreases, the rotational speed will increase at high wind velocity. But, at low wind velocity, the rotational speed is more effective when the number of blades increases. So, 6 rotor blades were found as suitable for low wind velocity areas as in Iraq.

Modeling and Control of Flywheel-Integrated Generators in Split-Shaft Wind Turbines

This paper introduces the modeling and control of split-shaft drivetrains where the system's inertia is adjusted to store the energy. Accordingly, a flywheel is mechanically coupled with the rotor of a doubly-fed induction generator. The generator is driven by a split-shaft drivetrain that decouples the turbine's shaft from the shaft of the generator to provide independent control of their angular velocities. Hence, the turbine controller can track the point of maximum power (MPPT) while the generator controller can adjust the generator speed. Accordingly, The flywheel, which is directly connected to the shaft of the generator, is charged and discharged by controlling the generator speed. In this process, the flywheel can modify the electric power generation of the generator on-demand. Since the drivetrain is a split-shaft, the turbine speed is not affected by this energy storing process. This improves the quality of injected power to the grid. The structure of the flywheel energy storage can be simplified by removing its dedicated motor/generator and the power electronics driver. This significant modification can only occur in the split-shaft drivetrain. Two separate supervisory controllers are developed in the form of fuzzy logic regulators to generate a real-time output power reference. Furthermore, small-signal models are developed to analyze and improve the MPPT controller. Extensive simulation results demonstrate the feasibility of such a system and its improved quality of power generation.

Uncertain Gain and Time-Delay Control of 300-kW SOFC-GT

This paper presents a Proportional Integral Derivative (PID) controller design with the presence of an uncertain internal gain and additional time delay in the forward path of a 300 kW Solid Oxide Fuel Cell-Gas Turbine (SOFC-GT). The outputs of the system are turbine speed and the fuel cell mass flow rate. A fixed set of proportional controller coefficients are determined to graphically develop an area of selection for the integral and derivative coefficients of the PID controller. The inputs to the power plant are the electric load and cold air valve. The decentralized controllers are applied to four sub-systems as a Single Input Single Output (SISO). The PID controller coefficients are selected from a singular matrix solution that stabilizes the system and satisfies the internal gain and time delay uncertainties. Two sub-systems are the transfer functions of the turbine speed over the electric load and the cold air valve. The other two sub-systems are the transfer functions of the fuel cell mass flow rate over the electric load and the cold air bypass valve. Multiple options for selecting PID controller coefficients are beneficial to the SOFC-GT plant due to the wide range of operations and internal uncertainty interactions. The specific internal time delay and gain margins increase the reliability and robustness of the SOFC-GT with multiple uncertain parameters.

Double Fed Induction Generator Control Design Based on a Fuzzy Logic Controller for an Oscillating Water Column System

Oscillating water column (OWC) systems are water power generation plants that transform wave kinetic energy into electrical energy by a surrounded air column in a chamber that changes its pressure through the waves motion. The chamber pressure output spins a Wells turbine that is linked to a doubly fed induction generator (DFIG), flexible devices that adjust the turbine speed to increase the efficiency. However, there are different nonlinearities associated with these systems such as weather conditions, uncertainties, and turbine stalling phenomenon. In this research, a fuzzy logic controller (FLC) combined with an airflow reference generator (ARG) was designed and validated in a simulation environment to display the efficiency enhancement of an OWC system by the regulation of the turbine speed. Results show that the proposed framework not only increased the system output power, but the stalling is also avoided under different pressure profiles.