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In order to realize high-quality control for turboshaft engine with variable rotor speed, a cascade control method based on the acceleration estimator of gas turbine speed (Ngdot) through Complementary filtering – incremental nonlinear dynamic inversion (CF-INDI)with Newton's prediction is proposed. Firstly, an adaptive torsional suppression method based on the Recursive Least Square (RLS) algorithm and combined with the control index of power turbine speed is proposed and designed to solve the torsional instability of control system in turboshaft engine with variable rotor speed. Then, an online Ngdot estimated method based on CF-INDI with Newton's prediction is developed, and the complementary filtering method is applied to compensate for the inaccuracy of the state variable model available at a single working point, and Newton prediction is used to alleviate the problem of lagging acceleration estimate, which is accessible to realize the cascade control for turboshaft engine based on Ngdot. The simulation results show that the RLS adaptive torsional filter can effectively suppress the low-order torsional components with frequencies of 1.2 Hz and 2.0 Hz mixing in power turbine speed, and the torsional suppression effect is remarkable. In addition, under different flight conditions, CF-INDI with Newton prediction is faster and more accurate than INDI Ngdot estimate, and smoother than central difference method, which proves the feasibility of INDI Ngdot estimator. Meanwhile, after the application of CF-INDI with Newton prediction Ngdot estimator in cascade control, the anti-interference capacity of power turbine speed is stronger, and the dynamic control effect is superior, which has satisfactory robustness performance. [ABSTRACT FROM AUTHOR]

A passively adaptive variable rotor diameter is proposed to improve the flight performance of variable-speed rotors. A validated helicopter model to predict rotor performance is utilized. The analyses focus on three typical flight states (i.e., hover, cruise, high speed) to explore the potential of the passively adaptive variable rotor diameter in reducing rotor power. During hover, the variable rotor diameter can optimize the distribution of lift and then reduce the rotor power, especially at lower rotor speeds. At a cruise speed of 150 km/h, the variable rotor diameter can delay stalling and reduce the rotor power, especially at lower rotor speeds. At a high speed of 300km/h, the rotor speed needs to be increased, and the reduced rotor diameter is beneficial reducing power. The reduced power comes from decreasing the parasitic power of the fuselage due to decreasing its longitudinal tilt, and the rotor profile power and induced power increase with relatively small magnitudes. The passively adaptive variable rotor diameter is more suitable for larger take-off weights, and can effectively delay stalling at lower rotor speeds. The strategy of varying the rotor diameter can be designed according to the performance improvement requirements. [ABSTRACT FROM AUTHOR]

The concept of variable rotor speed (VRS) has been recognized as an efficient means to improve rotorcraft operational performance and environmental impact, with electrification being a potential technology to further contribute to that. This paper explores the impact of optimal implementation and scheduling of VRS and power management strategy for conventional and hybrid-electric rotorcraft on energy, fuel, and emissions footprint. A multidisciplinary simulation framework for rotorcraft performance combined with models for engine performance and gaseous emissions estimation is deployed. A holistic optimization approach is developed for the derivation of globally optimal schedules for combined rotor speed and power split targeting minimum energy consumption. Application of the derived optimal schedules at mission level resulted to a 6% improvement in range capability for the VRS tilt-rotor relative to its conventional counterpart. For the hybrid-electric tilt-rotor, combined optimization of VRS and power management leads to an increase in range to 18.4% at 40% and 25% reduced payload for current (250 Wh/kg) and future (450 Wh/kg) battery technology, respectively. For representative urban air mobility (UAM) scenarios, it is demonstrated that the VRS concept resulted in up to 10% and 14% reductions in fuel burn and NOx relative to the nominal rotor speed case, respectively. The utilization of the combined optimum VRS and power split schedules can boost performance with reductions of the order of 20% and 25% in mission fuel/CO2 and NOx at a reduced payload relative to the conventional tilt-rotor. [ABSTRACT FROM AUTHOR]

In order to realize the fast response control for turboshaft engine with variable rotor speed, a dynamic inversion (DI) control method based on state variable model of turboshaft engine is proposed. Meanwhile, in order to expand the application of dynamic inversion controller, the linear parameter varying (LPV) model of turboshaft engine is applied, which constitutes the LPV/DI controller together. The simulation results shows that compared with the conventional PID controller, the LPV/DI controller can effectively reduce the overshoot/droop of the power turbine speed to less than 1% under different flight conditions. The control effect is remarkable and the robust performance is superior. [ABSTRACT FROM AUTHOR]

In order to solve the problem of torsional vibration instability of the control system for turboshaft engine caused by low-order torsional vibration modal drift under variable rotor speed effectively, an adaptive torsional vibration suppression method based on the least mean square algorithm is proposed and designed. First, based on Lagrange equation and state space method, the structural dynamic model of torque transmission chain system is established, which takes into account fixed and variable gear ratio. It is beneficial to express the dynamic characteristics of torsional vibration in real time, so that the variation laws of low-order torsional vibration modal under variable rotor speed and gear ratio are revealed. Then, an adaptive torsional vibration filter based on least mean square algorithm is proposed and designed combined with the active control objective of helicopter power system. Finally, the effectiveness of adaptive torsional vibration suppression method is validated based on numerical simulation and hardware-in-loop simulation separately. The results show that compared with the conventional constant-coefficient notch filter, the adaptive torsional vibration filter can decrease the peaks of all low-order torsional vibration frequency by more than 50%. It proves better robustness, more remarkable effectiveness and superior adaptive ability of the adaptive torsional vibration suppression method. [ABSTRACT FROM AUTHOR]

A novel control method combining nonlinear model predictive control (NMPC) with linear kalman filter (LKF) and adaptive notch filter (ANF) for an integrated helicopter/engine system with variable rotor speed is proposed to enhance the response ability of turboshaft engine. Firstly, based on the integrated helicopter/engine model with variable rotor speed, an ANF combined with frequency estimation is introduced. Then, in order to estimate the significant and unmeasurable performance parameters utilized in model predictive control, such as temperature before turbine, a nonlinear model predictive controller based on LKF is presented. The simulation verifications demonstrate that the fundamental frequency of torsional vibration changes from 1.30 Hz to 2.70 Hz when the rotor speed varies continuously by 50 %. In this case, compared with the notch filter, all torsional vibration amplitudes are damped below 0.1 % by ANF. Meanwhile, in comparison with the PID controller, the NMPC can reduce the overshoot and droop of the power turbine speed to less than 1 % with steady-state error no more than 0.5 % at the off-design point of NMPC based on adaptive torsional vibration suppression. The applications of LKF and similar transformation improve the control accuracy and robustness performance of the NMPC designed at a single operating point. [ABSTRACT FROM AUTHOR]

• A multidisciplinary simulation framework integrating the CCH and turboshaft engine is constructed. • A multi-objective optimization problem is designed to evaluate and quantify the flight performance and environmental impact of the CCH. • The NSGA-II multi-objective optimization method based on entropy weight evaluation is adopted. • The goal of low-emission for CCH is achieved through variable rotor speed and variable geometry adjustment. To address compatibility issues of the operational performance and environmental impact of Coaxial Compound Helicopters (CCH), a low-emission optimization control method for coaxial compound helicopter/engine based on variable geometry adjustment is proposed. Firstly, a multidisciplinary simulation framework for CCH and turboshaft engine is deployed by integrating the power characteristics of CCH, the performance of a variable geometry turbine engine, and the emission characteristics of nitrogen oxides (NO x). Subsequently, a multivariable and multi-objective optimization problem is formulated to assess and quantify the flight performance and environmental impact of CCH through a holistic optimization strategy. On this basis, a Non-dominated Sorting Genetic Algorithm II (NSGA-II) multi-objective optimization method based on entropy weight assessment is employed to obtain the optimal control plan for variable rotor speed and adjustable mechanisms within the operation envelope, by balancing the thermodynamic losses of the engine and the aerodynamic efficiency of the CCH. Finally, the optimization control method for CCH is validated based on flight missions. The simulation results demonstrate that the combination of variable rotor speed and variable geometry adjustment of engine effectively reduces the engine NO x emission index by more than 10.7 % within the full envelope, relative to the original rotor speed plan. In the actual flight mission profile, the total NO x emissions can be reduced by 11.78 %, improving the environmental impact of CCH. [ABSTRACT FROM AUTHOR]

In order to obtain the high‐quality fast response control for helicopter/turboshaft engine with variable rotor speed, a nonlinear model predictive control (NMPC) method based on piecewise objective function is proposed. The piecewise objective function takes into account both the control index of power turbine speed and the rotor dynamics of engine output shaft, which optimizes the transient overshoot and sag of the power turbine speed caused by torques mismatch during variable rotor speed from the root. The results show that compared with conventional MPC method with single objective function only involving the control index of power turbine speed, the novel NMPC method proposed can reduce the overshoot or sag of the power turbine speed by more than 30% during variable rotor speed, which possesses superior control effect of turboshaft engine without losing real‐time performance. [ABSTRACT FROM AUTHOR]

In order to solve the problem that the low‐order torsional model of the integrated helicopter/turboshaft engine system varies significantly under variable rotor speed, research on adaptive torsional vibration suppression methods is conducted. Meanwhile, two adaptive torsional vibration suppression methods, respectively based on fast Fourier transform (FFT) and the least mean square (LMS), are proposed to suppress the low‐order torsional vibration mixing in power turbine speed. Moreover, these two torsional vibration suppression methods are compared in real‐time performance, suppression effect and robustness of performance. The simulation results show that when and only when the designed frequency of the notch filter is away from the low‐order torsional model, the suppression effect of adaptive torsional vibration filter based on FFT is better than that of constant‐coefficient notch filter, but the real‐time performance is worse. On the contrary, no matter how the low‐order torsional model varies, the adaptive filters based on LMS can suppress the low‐order torsion vibration by more than 82.0% and have more superior real‐time and robustness performance, which can overcome torsional vibration instability of turboshaft engine control system under variable rotor speed effectively with more remarkable adaptive ability. [ABSTRACT FROM AUTHOR]

The process of rotor speed variation under tiltrotor cruise state has been studied, and the integrated variable speed control method of tiltrotor based on two-speed gearbox is proposed. Firstly, a nonlinear model predictive controller (NMPC) based on state variable model of the component-level model of the turboshaft engine is designed. Then based on the integrated engine model, the two-speed dual path tiltrotor driveline comprehensive simulation model was developed by utilizing gear kinematics theory, blade element analysis and the theory of classical mechanics. Finally, both a Parallel Shift Control (PSC) strategy and a Sequential Shift Control (SSC) strategy in tiltrotor cruise state were analyzed and compared with conventional PID controller. It is shown that the rotors' speed can synchronously vary by 50 percent under the PSC strategy in tiltrotor cruise state. Meanwhile, disengaging the engine in turn by freewheel clutches can reduce the rotors' speed from 190 rpm to 102.5 rpm along the specified path under the SSC strategy. The overshoot and droop amount of the power turbine speed can be reduced to less than 1.5 % with the steady error no more than 0.2 % through NMPC, which realizes the fast response control of the turboshaft engine. [ABSTRACT FROM AUTHOR]

In order to realize the rapid response control for turboshaft engine during the process of variable rotor speed, the linear quadratic Gaussian with loop transfer recovery (LQG/LTR) control method for turboshaft engine based on torsional vibration suppression is proposed. Firstly, the two-speed dual clutch transmission model is applied to realize the variable rotor speed of helicopter. Then, based on the state variable model of turboshaft engine, the proper LQG/LTR controller is available. In order to eliminate the limitation of low-order torsional vibration on the bandwidth of LQG/LTR controller, a frequency-domain analysis method for the effect of torsional vibration suppression on LQG/LTR controller performance is developed. Finally, the numerical simulation is conducted to verify the LQG/LTR control for turboshaft engine with variable rotor speed based on torsional vibration suppression. The results show that the bandwidth of the LQG/LTR control loop can increase by 2–3 times under torsional vibration suppression. Meanwhile, when the rotor speed varies continuously by 40%, the overshoot and sag of the power turbine speed can decrease to less than 2% through LQG/LTR controller based on torsional vibration suppression, which achieves the rapid response control of the turboshaft engine. [ABSTRACT FROM AUTHOR]

Variable rotor speed and variable blade twist are combined to reduce rotor power and improve helicopter performance. Two modeling methods are respectively utilized. One is based on an empirical aerodynamic model and the other is based on CFD (computational fluid dynamics). The flight data of the UH-60A helicopter is used to validate the methods. The predictions of the rotor power by the empirical method are in good agreement with the test data and the CFD method, which verifies the application of present methods in analyzing helicopter performance. The analyses indicate that significant rotor power reduction can be achieved by decreasing rotor speed. It is not appropriate to decrease the rotor speed too much in high forward flight. More power reduction can be attained by varying rotor speed than by variable blade twist. The individual variation of rotor speed or blade twist can reduce the rotor power by 17.8% or 10.4%, at a forward speed of 250 km/h and weight coefficient of 0.0065. A combination of rotor speed reduction and blade twist can save 20.9%. The maximum power reduction increases with forward speed and then decreases. The optimal performance improvement occurs at the medium to high forward speed. With increasing takeoff weight, the benefit in power saving decreases. Variable blade twist has the potential in reducing blade loads introduced by variable rotor speed. [ABSTRACT FROM AUTHOR]

In this study, a control scheme for the stand‐alone generation system based on brushless doubly‐fed machine (BDFM) is presented. The output voltage amplitude and frequency are kept constant under variable rotor speed and load by regulating the amplitude and frequency of the control winding (CW) current of BDFM appropriately. The control scheme utilises a CW current vector controller as the inner loop, and a power winding voltage amplitude controller and a frequency controller as the outer loop. The proposed control scheme has been implemented on a prototype BDFM designed for the variable‐speed stand‐alone ship shaft generation application. Moreover, the satisfactory dynamic performance and low total harmonic distortion of the output voltage in the proposed stand‐alone generation system is verified by experiments with two kinds of typical loads: three‐phase induction motor load and three‐phase RL inductive load. [ABSTRACT FROM AUTHOR]

A modified sequential shifting control algorithm is proposed for changing the helicopter rotor’s speed in a large variation and providing continuous output power to the rotor. Two turbo-shaft engines and two multi-speed gearboxes, coordinating with the rotor, facilitate a wide rotor speed variation and provide continuous torque to the rotor. In the process of shifting, a new control scheme is proposed to design turbo-shaft engines’ power turbine speed controller which is robust linear matrix inequality control, combined with active disturbance rejection control torque feed-forward compensation, so as to weaken engines’ torque disturbance in rotor speed variation process. In the end, some numerical simulations are carried out to verify the feasibility of the shifting algorithm, based on the integrated helicopter/engine system model which can simulate auto-flight tasks of the real system. The simulation results show that the turbo-shaft engine’s torque disturbance has little influence on engine power turbine speed in the process of torque shifting, and the rotor speed can perform large and rapid speed changes smoothly. [ABSTRACT FROM AUTHOR]

Highlights: [•] Model for wind turbine dynamics with variable rotor speed developed. [•] Mass, stiffness and damping matrices of the system are time dependent. [•] Effect of electrical grid faults on structural vibrations investigated. [•] Proposed active controller suppresses edgewise vibrations due to speed variation. [Copyright &y& Elsevier]