Variable Speed Control Research Articles

Impact of Dual Variable Speed and Inlet Valve Control on the Efficiency and Operating Range of Low-Head Contra-Rotating Pump-Turbines

Impact of Dual Variable Speed and Inlet Valve Control on the Efficiency and Operating Range of Low-Head Contra-Rotating Pump-Turbines

A Proposed Controller for Pitch Angle of Wind Turbine

Wind turbines are complicated non-linear systems with certain random disruptions. The pitch control system is a commonly employed method for regulating the electricity generated by a wind turbine. Many researchers have observed developments in the pitch control field during the last few decades. Traditional PID controllers have the drawback of being slow or imprecise when wind and pitch angles suddenly change. These drawbacks can be solved with artificial intelligent algorithms. However, the algorithms' design and implementation are highly complex. A new pitch-regulated variable-speed control strategy for wind turbines to address their nonlinear properties is presented. To manage the pitch system's control mechanisms with disturbances, this research evolved a mathematical model that illustrates HAWT's pitch angle control system and applied a proposed Simple Optimal Intelligent PID Controller (SOI-PID). Under various operating conditions, the proposed SOI-PID controller was tested with the Traditional PID, Fuzzy Logic Controller (FLC), and Fuzzy-Adaptive-PID controller. For system simulation, the MATLAB/Simulink software was used. According to simulation results, compared to PID, FLC, and Fuzzy-Adaptive-PID controllers, the proposed SOI-PID controller responds faster and has a better rise and settling time. Other benefits of the SOI-PID controller are its simplicity of implementation and design, distinguishing it from other intelligent algorithms.

Variable-Speed Operation of Micro-Hydropower Plants in Irrigation Infrastructure: An Energy and Cost Analysis

Micro-hydropower plants have now become a way to decarbonise the power generation system. Older micro-hydropower plants generally operate at a fixed speed. When there is a lack of rainfall, these plants operate outside their design flow causing various problems (such as the occurrence of the phenomenon of cavitation, decreased turbine performance, and decreased operating hours), especially in micro-hydropower plants installed in irrigation infrastructure, where the priority for water use is crops. This study aims to carry out a comparative evaluation of several indicators (cavitation, investment costs, electricity production and economic benefit) of two types of control system on an asynchronous electric generator (a fixed speed control system (scenario 1) and a variable-speed control system (scenario 2)) at the same micro-hydropower plant. The Rebolluelo micro-hydropower plant (Spain) is used for this purpose as a case study. This micro-hydropower plant uses a semi-Kaplan turbine coupled to an asynchronous electric generator through a gearbox. The results show the advantages of using a variable-speed control system. The use of variable-speed technology: (i) eliminates the possibility of cavitation, (ii) increases the power output ratio (from 35.87% to 93.03%), and (iii) increases the economic benefit (from 29.31% to 108.72%). There are also, of course, disadvantages, such as an 11.96% increase in cost. This work demonstrated the superiority of variable speed technology at micro-hydropower plants for three of the four indicators evaluated. This work could be of assistance when making decisions regarding future micro-hydropower plant installations.

Maximising the benefit of variable speed heat-pump water heater with rooftop PV and intelligent battery charging

Domestic applications of thermal energy storage, interacting with rooftop PV and batteries can substantially reduce consumer electricity costs, whilst assisting grid stability. Air source heat pump water heaters (HPs) with inherent thermal storage offer significant purchased energy savings, however, their typical control only considers stored water temperature. We demonstrate that further energy and cost reductions are possible using variable compressor speed controls that optimise thermal performance in real-time, whilst coordinating energy consumption to match available PV or shifting consumption to off-peak hours. The incremental complexity of variable-speed HP water heaters can reduce HP electricity consumption from the grid by up to 28% without PV or battery, 88% with PV, and 99% using PV and battery storage. By integrating the HP and all other domestic electrical loads, we exploit the combination of thermal and battery energy storage using rules-based and machine-learnt hierarchical controls to reduce the net household energy cost. Machine-learnt grid battery charging is shown to reduce annual grid energy consumption by 84%, delivering 99% of the potential energy cost savings. We conclude that a HP with inherent thermal storage, interacting with rooftop PV offers the most cost-effective home energy storage solution, lowering net lifetime costs by up to 27%.

Variable speed limit control strategy at the entrance and exit of freeway tunnel

In order to effectively reduce the accident rate of freeway tunnel section and improve the safety factor of tunnel section, variable speed limit control scheme at the entrance and exit of tunnel is presented from the perspective of safety. First, by considering the influence of tunnel section characteristics on vehicle operation, variable speed limit cells and variable length cells are added to improve the cell transmission model and establish a dynamic traffic flow model; Second, aimed at the minimum speed dispersion and the minimum change rate of tunnel illumination, and taken the fixed speed limit and the maximum speed difference as constraints, the variable speed limit control optimization model at the entrance and exit of the tunnel is established; Third, the genetic algorithm is employed to solve the control function with meeting the safety requirement of traffic operation. The results show that compared with the fixed speed limit mode, the implementation of variable speed control in tunnel group sections can significantly reduce the dispersion of running speed, which is conducive to traffic safety and operation efficiency.

Effectiveness of a Variable-Speed Control Based on Auditory Feedback: Is It Possible?

Variable-speed control in the field is challenging for motion science. Tests were performed to evaluate speed, Froude number, and oxygen consumption if these varied when using the same frequency of steps. The objective of this study was to evaluate the use of auditory feedback to control variable speed on the treadmill and track during acceleration cycles around the transition speed. Twenty-four trained men participated. The protocol was based on 5 ramps of 50seconds each around 80%, 90%, 100%, 110%, and 120% of the walking-running transition speed, recording the frequency of steps with a mobile phone during the treadmill test. The tests were replicated on the track using auditory feedback. When evaluating each speed of the protocols separately for the same frequency of steps, the average speed on the track was always higher on average at 54.7% compared to the laboratory (P < .050), and on the track, it was 16.2% higher than in the laboratory (P > .050). It cannot be considered that the same frequency of steps is equivalent to the same speed in the laboratory and on the track. These results point to the importance of reliable speed control during open field tests.

Comparative performance analysis of variable speed controllers in a wind energy system using NARMA L2 neuro-controller and Super- twisting sliding mode controller

Comparative performance analysis of variable speed controllers in a wind energy system using NARMA L2 neuro-controller and Super- twisting sliding mode controller

An accurate power control strategy for electromagnetic rotary power controllers

AbstractWith the rapid development of active distribution networks, the “petal”‐type distribution network has become the mainstream power supply structure. Power control methods for active distribution networks should be further studied to ensure the safe and reliable power supply of a distribution system. An electromagnetic rotary power flow controller (RPFC) is a feasible solution for controlling power in active distribution networks. However, when testing the effectiveness of the PQ decoupled control method for RPFC based on instantaneous reactive power theory, difficulties were encountered with the synchronous control of the rotor position angle of two rotating‐phase transformers, and the accuracy of power control was unsatisfactory. Given this condition, PQ control is improved in three ways. First, the system's periodic oscillation problem is solved via variable speed control. Second, the servo motor‐rotary phase‐shifting transformer synchronous rotation scheme, which reduces power control error and improves stability, is designed. Third, the overshoot phenomenon in power control is improved using the variable‐domain fuzzy proportional‐integral adaptive method. Experimental results show that the proposed advanced control scheme exhibits good dynamic and static performance in power control scenarios and achieves effective improvement in RPFC.

An improved approach to model compressors, condenser/gas cooler and their control system in refrigeration systems with R404A and R744 based on physical principles

This study introduces an improved methodology to evaluate with accuracy the performance of a conventional system with R404A and a Booster system with R744. Reciprocating and scroll compressors are modeled with improved semi-empirical approaches, and their operation is ideally controlled to maintain the required refrigerant mass flow rate with an On/Off and variable speed control system. The R744 gas cooler is modeled with a four-zones model and the R404A condenser with a three-zones model. The R744 condenser is modeled with the superheated zone discretized into eight zones to avoid unrealistic results due to the variation of its thermophysical properties and the two-phase and subcooled zones with one zone respectively. In line with the design, the Booster condenser enters into the pseudo-critical zone at an ambient temperature of 23 °C, while the gas cooler is activated after 31 °C. The compressor models present errors lower than 10%, while the Booster model presents mean deviations lower than 2.3%. The Booster system presents better COPs than the conventional at ambient temperatures lower than 15ºC. At higher ambient temperatures, the COPs of both systems are similar: the conventional system overperforms the Booster up to 6%, being in disagree with the literature results where these differences increase up to 30%. The proposed methodology allows to reduce the overall model error by 3% with respect to a thermodynamic cycle-based model; allowing to improve the comparison between the Booster system with R744 and the conventional one with R404A, which leads to more transparent results than the reported common comparisons.

Dynamic performance simulation of combined gas electric and steam power plants for cruise-ferry ships

This work aims at investigating the feasibility of COmbined Gas Electric and Steam (COGES) plants onboard Liquefied Natural Gas (LNG) fueled ships, by means of a novel, flexible tool. Firstly, the nominal operating conditions of 6 commercially available gas turbines (GTs) as well as their dynamic performance are simulated. Secondly, 6 different integrated COGES-reciprocating engine power plants are assembled and compared in terms of cogeneration efficiency within an optimized repowering study for the cruise-ferry ship GNV La Suprema. The optimization accounts for variable ship speed, season and GT control strategy for an overall number of 264 operating conditions considered. Thirdly, the time-dependent performance of the best COGES plant is assessed under actual navigation conditions for La Suprema. Overall, the results show the great potential of combining COGES plants with reciprocating engines for the marine sector. In particular, in the ship speed range centered around the actual cruise speed for La Suprema (i.e. 22 knots), all the COGES plants are able to cover the propulsion and hotel power demands more efficiently than reciprocating engines, with a 1–5 % benefit on cogeneration efficiency. Overall, a 51 % maximum cogeneration efficiency is found to be provided by COGES plants based on LM2500 and TITAN250 gas turbines.

Variable Speed Control in PATs: Theoretical, Experimental and Numerical Modelling

The selection of pumps as turbines (PATs) for their respective use in energy optimisation systems is a complicated task, because manufacturers do not provide the characteristic curves. For this reason, some research has been carried out to predict them with computational fluid dynamics (CFD) and mathematical models. The purpose of this study is to validate these two prediction methodologies of flow (Q) vs. head (H) curves through numerical modelling using the computational package OpenFOAM, together with a comparison with the experimental data obtained from a PAT for the case in which the nominal rotation speed of the machine varies. Depending on the configuration and working conditions of the PAT, the simulation performed with OpenFOAM was validated by calibrating it with the nominal curve of the pump and with another simulation performed with CFD workbench SOLIDWORKS FloEFD. Subsequently, the second methodology related to the analyses and mathematical models proposed to predict the Q vs. H curves were also validated with new models in OpenFOAM and the experimental data. The results show that these prediction methods are effective when a machine’s operating point is close to the BEP (best efficient point). The absolute error ranges obtained with these two prediction methodologies for rotation speeds of 880 rpm, 1020 rpm, 1200 rpm, and 1500 rpm are between 5 and 24%, 2 and 17%, 0 and 12%, and 1 and 24%, respectively.

Energy Management For Renewable Hybrid System Based On Artificial Neural Networks (ANN)

Abstract: It has become necessary in recent years to use renewable energy sources, such as wind and solar energy, to meet the load demand. Because of their endless existence and environmentally friendly nature, they are useful for power generation. The management of energy in hybrid wind-solar power sources is the topic of this article. Using a common current source interface multiple-input DC-DC converter, the photovoltaic (PV) array, wind turbine, and battery storage are all connected. The power control between intermittent renewable energy generation, energy storage, and the grid is maintained by the artificial neural network (ANN) controller. For wind turbines to produce the most electricity, variable speed control can be used. For solar systems, the Maximum Power Point Tracking (MPPT) algorithm is used. By keeping the common DC voltage constant, the grid interface inverter sends the energy drawn from the PV array and wind turbine into the grid. Using MATLAB Simulink, the complete control strategy is subjected to a simulation study. The results of the simulation show the photovoltaic/wind hybrid system's dynamic behavior and control effectiveness

Study on fast prediction method of hydrodynamic load of floating horizontal axis tidal current turbine with pitching motion under free surface

The floating horizontal-axis tidal current turbine (HATCT) moves with the floating carrier while rotating, resulting in a change in its relative inflow velocity at any time. If the rotating speed of the HATCT is fixed, the HATCT cannot work at the optimum tip speed ratio, resulting in the failure to achieve the optimum power generation efficiency. Therefore, this paper proposes a control strategy for the rotating speed of the HATCT, and obtains the hydrodynamic loads of the HATCT with variable speed rotation and pitching motion under free surface conditions based on the CFD method. Compared with the hydrodynamic load of the HATCT under the same situation but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATCT, but the load fluctuation in terms of the inflow direction load, power, and pitch moment coefficients are more significant than those with fixed speed control. On this basis, according to the variation law of the damping coefficient with pitch period, pitch amplitude, and tip speed ratio, the hydrodynamic load prediction method of the HATCT with pitching motion is established. The validity of this prediction method is verified by comparing the results with those of CFD calculation.

Fast prediction of hydrodynamic load of floating horizontal axis tidal turbine with variable speed control under surging motion with free surface

For floating HATT11HATT: horizontal axis tidal turbine with variable speed control, a numerical model based on CFD22CFD: Computational fluid dynamics method is proposed to predict the surge force. Compared with the hydrodynamic load of the HATT under the same condition but with fixed speed control, the variable speed control can effectively improve the power coefficient of the HATT. When the surge period is 1.5 s and the surge amplitude is D/8, the average power coefficient increases by 36.36%. But the load fluctuation in terms of the axial load and power coefficients are significantly larger than those with fixed speed control. Based on the hydrodynamic load decomposition model of the HATT with fixed speed rotation and surging motion and the variation law of damping coefficient, the hydrodynamic load prediction method of the HATT with variable speed rotation and surging motion is established. By comparing with the CFD results, it is evidenced that this prediction method can effectively predict the axial load and power coefficients of the HATT. The research findings can provide a reference for the rapid prediction of the hydrodynamic load of the HATT during the actual operation of the floating tidal power station.

Hover Dynamics and Flight Control of a UAM-Scale Quadcopter With Hybrid RPM and Collective Pitch Control

Hover analysis is performed on a 1200-lb gross weight UAM-scale quadcopter with both variable rotor speed and collective pitch control. With these redundant controls, the hover performance and flight dynamics are considered at three trim points, where power consumption can be increased to improve authority of the pitch inputs for changes in rotor thrust. An explicit model following control laws is optimized using CONDUITR to meet ADS-33E-PRF handling qualities specifications, with design margin optimization on each axis. The responses of the linearized system are examined with either control type, and pitch control is shown to outperform RPM-control in heave, while the opposite is true for yaw. Trim in axial climb is simulated, where the collective pitch can be scheduled with the climb rate to maintain effective stall margin. Hybrid control mixing is implemented using a complementary filter, allowing the aircraft to use pitch control for short-term responses and RPM control for trim. The benefits of this hybrid control scheme are demonstrated through simulation of hot/high/heavy conditions, where trimming with RPM control allows the pitch actuators to maintain margin for maneuvers. It is concluded that hybrid control allows the aircraft to reap the benefits of pitch control for maneuverability while maintaining stall margin by using RPM control for trim.

Modeling and Control of Variable Speed Drive Based Loads for Grid Primary Frequency Support

The amount of electricity generation from renewable energy resources (RES) has been increasing significantly all over the globe. However, traditional power grid management is challenged when a large amount of intermittent and unpredictable RES-based generation units are integrated into the power network. This can lead to more severe grid frequency fluctuation events. In this paper, a variable speed drive (VSD) based motor load is utilized as a frequency responsive load to support grid frequency stability. A primary frequency control scheme is proposed and applied to the VSD-based motor load, which incorporates the sophisticated rotating speed feedback controller. Additionally, the proposed frequency responsive VSD-based load is modeled and simplified. As a result, a droop-like response can be achieved with multiple VSD load units. The effectiveness of the proposed model and control scheme is evaluated by experimental studies performed in a multi-converter-based hardware testbed (HTB).

Satellite Attitude Control Using Double-Gimbal Variable-Speed Control Moment Gyroscope: Single-Loop Control Formulation

A single-loop control architecture is proposed to achieve singularity-free attitude control of satellites actuated using a double-gimbal variable-speed control moment gyroscope (DGVSCMG). Satellite and DGVSCMG combined rotational dynamics is modeled in the framework of geometric mechanics. It is shown that the combined attitude dynamics is in control-affine form when the motor torques of the DGVSCMG are taken as control inputs. A single-loop hybrid robust nonsingular fast finite-time sliding mode control (NFFTSMC) is designed to ensure an unwinding-free attitude maneuver. In the proposed single-loop formulation, the respective motor torques of the DGVSCMG are computed directly using only one NFFTSMC without requiring the steering law, resulting in mathematical singularity-free attitude control. A novel sliding surface is also proposed to ensure that the rotor angular speed converges to its nominal value after the maneuver. This eliminates the need of repeated desaturation of the rotor spin rate, unlike all the steering-law-based control architecture. Unwinding-free global stability of the system using the proposed hybrid NFFTSMC is proved for the sliding and reaching phases. Simulation results are presented to substantiate the claim made, assuming the rigid satellite to be equipped with only one DGVSCMG.

Control Moment Gyro Actuator for a Guided Projectile

This paper investigates the suitability of using a gimbaled rotor actuator for trajectory control of a projectile. In this novel concept, a single-gimbal variable-speed control moment gyro is used as the sole control actuation system, allowing actuation in two orthogonal directions and two-dimensional control over the projectile’s flight path without any moving aerodynamic surfaces. A complete nonlinear model of the eight-degree-of-freedom rotational and translational flight mechanics is developed, as well as an accurate aerodynamic model for short-range trajectories. Linear models are derived for control design, and controllers are synthesized along with a steering logic to achieve control of the projectile’s roll and sideslip angles. Successful tracking of both angles is demonstrated, and a large course deviation is achieved, showing significant maneuverability and proving the viability of the concept.

Novel Mechanical Flux-Weakening Design of a Spoke-Type Permanent Magnet Generator for Stand-Alone Power Supply

In this paper, a novel mechanical flux-weakening design of a spoke-type permanent magnet generator for a stand-alone power supply is proposed. By controlling the position of the adjustable modulator ring mechanically, the total induced voltage, i.e., the amplitude of the back EMF vector sum can be effectively adjusted accordingly by the modulation effect. Consequently, the variable-speed constant-amplitude voltage control (VSCAVC) with a large speed range can be achieved. Compared to the electrical flux-weakening method, the mechanical flux-weakening method is easier to operate without the risk of PM demagnetization. The analytical model is presented, and the operation principles are illustrated. To analyze the performance of different combinations of stator/rotor pole pairs, four cases are optimized and analyzed using the finite element method for comparison. The characteristics of VSCAVC are analyzed.

Development and Validation of Control Algorithm for Variable Speed Fixed Pitch Small Wind Turbine

In this study, a power control algorithm of a variable-speed fixed-pitch horizontal-axis lift-type 20 kW small wind turbine (SWT) was proposed and verified through dynamic simulations. The power control algorithm proposed in this study consists of algorithms for Region II to track the maximum power coefficient, for Region II-1/2 to maintain the rated rotor speed, and for Region III to maintain the rated power. To verify the proposed power control algorithm, simulations were performed at the rated wind speed and above the rated wind speed, to which turbulence intensity based on the IEC regulation’s normal turbulence model was applied. As a result, it was confirmed that the proposed controller operates properly in the whole three regions including Regions II, II-1/2, and III. The controller performance was then compared with the variable-speed variable-pitch power controller. Although the performance of the proposed controller was considered good for the target VSVP wind turbine, it was lower than that of the conventional controller applied to the same wind turbine. Compared to the VSVP wind turbine, the VSFP wind turbine with the proposed controller was found to have higher mean loads on the blade and the tower but the fatigue loads in terms of Damage Equivalent Load (DEL) were found to be reduced.