The Operational Performance Optimization Of The Parallel Converter-fed PMSG Wind Power System With The Optimal Space Vector Modulation Strategy For System Target Indicators

With the advantage of simple structure,high efficiency,high power density,and low maintenance cost,the low-speed permanent magnet synchronous generator(PMSG)has been implemented in aerospace,ship drive,wind power,and other low-speed large torque drive applications.Those critical applications typically require a large current and thus make the parallel converter an ideal and popular topology.But,on the other hand,those critical applications have more stringent requirements on the performance of the parallel converter-fed PM drive system.Since the two-parallel converter is the crucial component of the system,and its crucial indicator optimization dominants the performance improvement of the overall equipment.However,the issues have not been investigated comprehensively in academic circles.Given it,this thesis focuses on the comprehensive performance optimization of the parallel converter-fed PM wind power system by the optimal space vector sequences.The comprehensive optimization in this paper consists of critical indicators optimization and high-reliability optimization.Given the performance improvement of the parallel converter-fed PM drive system with the regular operation and fault-tolerant operation,this paper builds the high-frequency mathematical models describing the coupling among the vector sequences and AC current quality,circulating current,torque ripple,switching device loss,and stator loss,and based on this,this paper proposes some optimal voltage vector sequences for objective parameter optimization.Finally,the contributions of this thesis are summarized:1.This paper investigates the available vector sequences' effects on crucial indicators,including AC-current ripple and zero-sequence circulating current(ZSCC),and given the reference's amplitudes and angles,this thesis proposes the corresponding optimal vector sequences to minimize the current ripple and ZSCC,improving two parallel grid-connected converters' efficiency.Based on this,this paper proposes a space vector modulation method(comprehensive optimization DPWM,CODPWM)with simultaneous current ripple and circulating current minimization.Compared with the existing algorithms,CODPWM achieves the minimum current ripple and ZSCC with the matched equivalent switching frequency.2.The optimization of the crucial indicators,such as switching loss,ZSCC,and torque ripple fundamentally affects the overall performance of the drive system.Therefore,the optimization of the crucial indicators is essential to the high-performance operation of the parallel converter-fed PM drive system.This thesis is the first academic paper that proposes optimal space voltage vector sequences for the comprehensive performance optimization of the converter-fed PM wind power system.This thesis constructs a high-frequency model and reveals the quantitative relationship between vector sequences and circulating current,switching loss,and torque ripple.With it,the optimal vector sequences are developed for comprehensive optimization of key parameters under different speed and rotor position conditions.Based on this,a novel PWM algorithm is proposed to optimize the torque ripple,switching loss,and ZSCC over the entire speed range.The experimental results verify the effectiveness of the proposed algorithm.3.It is imperative to enhance the reliability of post-fault operation to avoid a secondary fault,and this thesis takes the generator side converter as an example.This thesis proposes a comprehensive optimization to improve the reliability of post-fault operation,which includes detailed modeling,reliable control strategy,and optimized modulation strategy.First,this thesis establishes the mathematical models of two paralleled three-phase four-switch.It reveals the relationships between vector sequences and stator loss,torque ripple,and circulating current.Second,a neutral point voltage control method based on state observer is proposed to eliminate the neutral point voltage bias,avoiding a secondary fault.Finally,this thesis proposes various optimal vector sequences for different speed and rotor positions for different target indicators,realizing the high-performance fault-tolerant operation.