| In order to solve global problems such as energy shortage and environmental pollution,people begin to develop and utilize wind energy on a large scale in recent years.Because of its high efficiency and low mechanical failure rate,direct-driven permanent magnet wind power technology has become one of the essential development directions in the field of wind power,especially for large-scale land and offshore wind energy systems with great potential for development.As a critical link of motor control and energy conversion,Power conversion system mainly includes the motor,converter and its auxiliary unit.Its structure and control performance are significant to the overall performance of the unit.The Power conversion system of the wind power system is affected by the multiple operating conditions of wind load fluctuation,power network fluctuation and harmonics,and is subject to the multiple physical constraints of electrical structure and device performance.And the system topology increases significantly with the increase of power level complexity.However,due to the application and development of AC-DC full-power converter technology,the converter structures and controls of direct-drive permanent magnet wind power systems can be separated and decoupled in motor side and network side,making Power conversion system innovation possible in different angles and dimensions.With the trend of wind power toward more complex application scenarios,larger power unit capacity,and more efficient and reliable control performance,the research on Power conversion system structure layer,modulation layer,control layer and application layer will be an essential direction for the development of wind energy toward higher quality.Therefore,this paper takes the Power conversion system of directdrive permanent magnet wind power system as the research object,and takes the traditional three-phase permanent magnet power generation system to the multi-phase permanent magnet power generation system as the span,studies the influence of motor parameter mismatch and the optimal control under unknown load disturbance,the utilization of residual capacity under low operating conditions of the network-side converter,system analysis design,multi-sector switch vector simplification,etc.The following results have been achieved:(1)A robust non-linear predictive current control(RNPCC)method for generators is presented to optimize the current control loop performance of the traditional three-phase power generation system with parameter perturbation of the generator model.Firstly,a model of permanent magnet synchronous generator with parameter perturbation is established.Based on this model,the influence of parameter perturbation on traditional predictive current control is analyzed.A composite integral terminal sliding mode observer is designed to estimate disturbances caused by parameter perturbations in real-time.Finally,an RPNC method,which does not depend on the mathematical model of PMSM,is presented.By injecting estimated disturbance values,the effect of parameter perturbation is effectively eliminated.And it is verified by the experiment.(2)To achieve high power quality parallel connection of the network side converter in traditional three-phase power generation system,the influence of sampling circuit on PI or Deadbeat(DB)based control circuit is studied,and resistance and capacitance(RC)filter is designed in the sampling circuit to reduce the inherent resonance peak.A composite control strategy based on an improved repetitive controller(IRC)and PI controller is designed.By reconstructing the internal model of the classical repetitive controller(CRC),the bandwidth of the PI loop is limited to a lower level,and the harmonic and reactive power compensation performance of the system is improved.The parameters of IRC+PI control are designed to improve the stability of the system.In addition,a fractional compensator is inserted to solve the non-integer delay problem.The feasibility and validity of this control method are verified by experiments.(3)A variable-medium vector space vector modulation method is proposed around the DC unbalanced operation of a large capacity unit with a two-phase side converter in series.When DC voltage is inconsistent,this method divides the medium vector into two categories: 1)dividing the space vector with non-uniform distribution of alpha-beta into 12 fixed sectors with30 degree,2)synthesizing the reference voltage in each sector with three large vectors and variable medium vectors.This method can switch the vector automatically in a certain range of DC voltage fluctuations to avoid DC side voltage inconsistency.Complex sector judgment.Finally,the vector of continuous space vector modulation is simulated on the principle of the minimum number of switches,and the correctness of the proposed method is validated by the simulation results.(4)A cascade predictive torque control method(CPTC)considering unknown load torque disturbance is presented for the stability control of multi-module three-phase permanent magnet synchronous motor under unknown load torque disturbance.Firstly,the mathematical model and electrical characteristics of the three-module three-phase permanent magnet synchronous motor are analyzed by the finite element method.The cascade control structure of the threephase permanent magnet synchronous motor is established.And the CPTC method is used instead of the traditional PI controller to improve the dynamic and static response and tracking performance of the three-phase modular permanent magnet synchronous motor.A speed prediction controller based on an unknown load torque disturbance observer is designed to reduce the speed response time and obtain the reference value of the torque.The results of simulation and experiment verify the superiority of the proposed three-phase modular permanent magnet synchronous motor in stator flux tracking performance and load torque disturbance suppression.At the same time,compared with the traditional three-phase permanent magnet synchronous motor,the proposed three-phase modular permanent magnet synchronous motor has the advantages of small stator current and fast response to unknown load.Based on the Power conversion system optimization of direct-drive permanent magnet wind power system,the effects of parameter mismatch on the motor and the optimal control under unknown load disturbance,the utilization of residual capacity under low operating conditions of the network-side converter,system analysis and design,and the simplification of multi-sector switch vectors are studied in this paper.The analysis and control method in this paper not only improves the Power conversion system performance of direct-drive permanent magnet wind power system,but also can be applied to other types of motor control systems with back-to-back converter,which provides reference for promoting high-performance motor control. |
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