| This paper focuses on the research on the output voltage constraints and parallel current sharing control of multi suspension converters,wind turbine nacelle suspension air gap tracking,interference suppression,and suspension air gap current synchronization of the suspension system.In essence,the nacelle suspension system has nonlinear,strong interference,and instability.In particularly,suspension starting overshoot,suspension landing,and air gap drop caused by interference can easily lead to engine room suspension failure.However,large current surges can seriously affect the service life of the converter and damage the suspension stability of the nacelle suspension system.Due to inherent control parameters,traditional linear controllers cannot adapt to multiple varying operating conditions,while adaptive control has a certain degree of control delay.Therefore,Barrier Lyapunov Function(BLF)is used to generate a large control force when approaching the constraint boundary,combining finite time observers and adaptive control algorithms,The focus is on solving the output voltage constraints of the converters,steady-state of the nacelle suspension system,and multi-state constraint control under interference.Aiming at the module diversity problems of multiple converters,such as load temperature rise and disturbances,line impedance,and drive response,which seriously affect the current unbalanced distribution,service life,and reliability of multiple converters,firstly,based on the power flow analysis theory of the power system,the power distribution and cycle power generation mechanisms of parallel systems are studied,and a parallel Buck converters system model with load uncertainty interference and module diversity interference is constructed.To solve the problems of difficult measurement of voltage change rate and difficult acquisition of uncertain disturbances in converters system,a finite time observer with state and uncertain disturbance observations is designed,and a finite time differentiator is used to acquire the differential disturbances of the module online.By analyzing the characteristics of converters output voltage startup and load disturbance,a time-varying constrained trajectory is designed considering the startup process and steady-state performance.A finite time controller with output voltage constraints is designed based on BLF to solve the output voltage constraints and current sharing control problems.Based on the construction of Lyapunov functions,the stability of closed loop parallel system is studied,and it is verified that the system states can converge to their stable regions in finite time.An experimental platform for parallel Buck converters based on d SPACE was built,and load switching and voltage sinusoidal tracking experiments were conducted.The experimental results show that the control strategy proposed in this paper achieves effective constraints on the output voltage and large module differential parallel current sharing control under heavy load switching.Compared with the classical finite time control strategy,the maximum voltage sag,maximum voltage rise,sag recovery time,and maximum voltage fluctuation of sinusoidal tracking under load disturbance are increased by 33.3%/26.2%/50%～60%/42.8% in both load disturbance and voltage sinusoidal tracking experiments.Considering the strong interference in the suspension system and the differences in converter modules,the impact of matching interference caused by external interference and converter structure differences on the suspension stability of the engine room is deeply analyzed,and a model of the engine room suspension system with converters is constructed.Using input-output feedback linearization,the constructed suspension kinematics model is transformed into a multi-state suspension control model suitable for Backstepping with matching interference based on position,velocity,and acceleration.To solve the problem of difficult measurement and accurate acquisition of air gap velocity,acceleration,and multi-channel matching interference terms,a finite time observer with interference and state observation capabilities is designed.By analyzing the characteristics of levitation start overshoot,levitation landing,and steady state interference drop,the output air gap time-varying constraint trajectory and levitation speed time-varying constraint trajectory are designed respectively.BLF and Backstepping technology are used to design constrained virtual control laws for air gap error channels and levitation velocity channels,and adaptive laws are designed for air gap error channels to achieve output air gap and velocity constraints while improving air gap tracking accuracy.Aiming at the aforementioned differential interference of multiple converter modules that affects the steady state current sharing,an ideal parallel current model is constructed to design a finite time differentiator for online acquisition.In addition,constant value constraint boundaries are designed to further ensure the transient current synchronization performance of the converters,solve the output and multi states constraint control problem of the nacelle suspension system,and improve the reliability of the multi converter suspension system.Based on the construction of Lyapunov functions,the stability of closed-loop parallel systems is studied,and it is verified that the system states can converge to their stable regions in a finite time.A multi converters wind turbine suspension system experimental platform was built,and axial interference and sinusoidal suspension reference tracking experiments were conducted separately.The performance comparisons with traditional PID and robust adaptive control strategies were conducted.The implementation results showed that the control strategy proposed in this paper has the ability to achieve suspension air gap constraints,air gap speed constraints,and current synchronizaton constraints within a limited time,and the maximum drop in axial disturbance,the maximum rise and return times increased by 76%/79% and 76%respectively.The current synchronization error during the entire suspension process is guaranteed to be within 1.5A,indicating that the proposed control strategy can improve the reliability of the suspension converter while ensuring the anti disturbance performance and air gap sinusoidal tracking performance of the suspension system. |
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