Ratio Setpoint Research Articles

Wind Turbine Fatigue Load Analysis for Derating Control Strategies Aimed at Grid Balancing

With the exponential growth of wind energy worldwide, wind power plant owners are eager to participate in grid balancing, in order to compete with traditional power plant owners. In this way, they take part in frequency control which notably amounts to reacting to grid faults by an adequate injection of power. The latter calls for power reserve. For wind farms, this is achieved by derating methods which consist in extracting from the wind less power than the available power, in order to be able to increase the produced power when needed. The objective of this paper is to compare two wind turbine (WT) derating methods in terms of lifetime damage equivalent load (DEL). The first strategy is based on a modification of the generator torque set point to achieve derating, while keeping the standard pitch angle control. The second strategy achieves derating by pitch control while keeping the standard tip speed ratio set point. Both strategies were simulated in OpenFAST under various wind conditions covering all the WT operating regions. Focusing on having a constant power reserve, the simulation results on a single WT show that the pitch-based strategy is the best, among the two considered ones, when it comes to derating while reducing lifetime DEL.

A Performance analysis of the Claridge-Culp-Liu dehumidification process: A novel approach for drying moist air based on membrane separation, vacuum compression and sub-atmospheric condensation

Abstract This paper covers a basic model for analyzing the performance of the Claridge-Culp-Liu dehumidification process. The fundamental process efficiency limit for dehumidification is close to COPCarnot, but for the eight dehumidification cases examined, the limiting or ideal energy use required is 26% to 56% that of a Carnot condensing system as shown in an earlier paper. The model presented in this paper is used to show the membrane system performance reduction caused by finite membrane area, finite water vapor permeance, non-zero air permeance, non-zero system air pressure drop, non-ideal compressors, vacuum pumps, and condensers. The performance of a “conservative” membrane system based on the use of existing components is computed for eight specific conditions along with that of a “target” system that assumes expected component performance after additional future component development. The “conservative” membrane system would use 36% to 66% as much energy as a system with a COP=7 chiller to produce the same dehumidification for the eight cases examined while the “target” system would use 15% to 40% the energy of a system with a COP=7 chiller. In addition to the significant energy reduction over conventional technology, the membrane system offers the advantages of: 1) no HFC refrigerant use; 2) direct isothermal control over humidity ratio setpoint; 3) maximum capacity occurs at design conditions; and 4) system generates pure water extracted from air as a by-product.

Optimization of a liquid desiccant based dedicated outdoor air-chilled ceiling system serving multi-zone spaces

A liquid desiccant based dedicated outdoor air-chilled ceiling (DOAS-CC) system is proposed to serve a multi-zone space. The outdoor airflow rate and the supply air humidity ratio are two crucial variables in such a system, which significantly influence indoor thermal comfort, indoor air quality and energy consumption. Two strategies are presented to optimize these two variables in the study. They are the demand-controlled ventilation (DCV) strategy and the supply air humidity ratio set-point reset strategy. To evaluate the performances of these two strategies, a basic control strategy, i.e., the strategy adopting constant ventilation flow rate and constant supply air humidity ratio, is selected as the benchmark. Performances of the two strategies in terms of indoor air temperature, relative humidity and CO2 concentration as well as energy consumption are analyzed using simulation tests. The results show that the supply air humidity ratio set-point reset strategy is effective for the indoor air humidity control. It can save about 19.4% of total energy consumption during the whole year. The DCV-based ventilation strategy can further reduce about 10.0% of energy consumption.

Control of a hydraulically actuated continuously variable transmission

Vehicular drivelines with hierarchical powertrain control require good component controller tracking, enabling the main controller to reach the desired goals. This paper focuses on the development of a transmission ratio controller for a hydraulically actuated metal push-belt continuously variable transmission (CVT), using models for the mechanical and the hydraulic part of the CVT. The controller consists of an anti-windup PID feedback part with linearizing weighting and a setpoint feedforward. Physical constraints on the system, especially with respect to the hydraulic pressures, are accounted for using a feedforward part to eliminate their undesired effects on the ratio. The total ratio controller guarantees that one clamping pressure setpoint is minimal, avoiding belt slip, while the other is raised above the minimum level to enable shifting. This approach has potential for improving the efficiency of the CVT, compared to non-model based ratio controllers. Vehicle experiments show that adequate tracking is obtained together with good robustness against actuator saturation. The largest deviations from the ratio setpoint are caused by actuator pressure saturation. It is further revealed that all feedforward and compensator terms in the controller have a beneficial effect on minimizing the tracking error.

Control of a Continuously Variable Transmission in an Experimental Vehicle

This paper focusses on the development of a component controller for a hydraulically actuated metal push-belt Continuously Variable Transmission (CVT), using models for the mechanical and the hydraulic part of the CVT. The ratio controller guarantees that one clamping pressure setpoint is minimal, while the other is raised above the minimum level to enable shifting. This approach is beneficial with respect to efficiency and wear. Vehicle experiments show that good tracking is obtained. The largest deviations from the ratio setpoint are caused by hardware limitations.

Coordinated control of a mechanical hybrid driveline with a continuously variable transmission

Requirements for a driveline with respect to fuel economy and driveability can generally not be met simultaneously even with a continuously variable transmission (CVT). A new driveline concept with an additional flywheel makes it possible to compensate for the engine inertia in transient situations. This allows the driveline to be operated for optimal fuel economy without losing driveability. However, to realize this objective it is inevitable to control the driveline in a coordinated way. In light of the system uncertainties and the unknown load as well as nonlinearities a nonlinear robust controller is proposed to generate the setpoints for engine torque and CVT ratio. The focus is on the control law for the CVT ratio setpoint. The controlled CVT regulates the power flow from the engine and flywheel to the wheels while compensating for the internal inertias.

Power plant air/fuel ratio optimisation

It is argued that power plant air/fuel ratio is one of the more important parameters in achieving improved combus tion efficiency and reducing pollutant emissions. However, for most power plant the air/fuel ratio is fixed. This paper presents a feasibility study, based on operational data, which demonstrates how these gains may be realised by changing the air/fuel ratio set-point value. This is achieved by using a neural network to model an optimisation process satisfying pre-defined efficiency and emission require ments. The initial results are encouraging.