Research Of Control Strategy Of Multi-channel Three-level Wind Power System

This thesis is based on a multi-channel three-level wind power system.A dual-phase permanent magnet synchronous generator system structure with a parallel back-to-back three-level neutral point clamped voltage source converter is constructed.The AC magneto motive force of the dual-phase permanent magnet synchronous motor is analyzed,where the 5th and 7th harmonic magnetomotive force generated by the fundamental current are eliminated.The mathematical model and equivalent circuit of a dual-three permanent magnet synchronous motor are established based on vector space decoupling transformation,which achieves the decoupling of motor components.The motor components are mapped onto three mutually orthogonal sub-planes,?-?,x-y,and o1-o2 sub-planes.The working principle of the three-level converter topology is analyzed,and the equivalent circuit of the parallel converter circulation is established.A space vector pulse width modulation strategy based on the double decoupling vector spaces is proposed for multi-channel three-level systems.It simplifies the voltage vector,selects the voltage vector to synthesize the ?-? sub-plane and the x-y sub-plane reference voltage,and the voltage vectors of the two sub-planes are decoupled from each other.The carrier disposition based pulse width modulation(CDB PWM)strategy,the space vector pulse width modulation strategy based on tranditional six-phase vector space decoupling(T VSD SVM)and double decoupling vector spaces(D VSD SVM)are compared.The utilization ratio of bus voltage of D VSD-SVM is relatively higher and the design is relatively simpler.It can control the x-y sub-plane current caused by load imbalance and zero-sequence plane current,and is applicable to other multi-phase three-level systems.A base control strategy for multi-channel three-level wind power systems is designed in this thesis.The maximum power point tracking fan vector control strategy based on optimal torque control is designed on the motor side.The converter control strategy based on reactive power control and DC capacitor voltage control is designed on the grid side.The d-q sub-plane of the fan vector control strategy adopts a voltage control method based on feedforward compensation to eliminate the coupling term.The closed-loop PR controller of the x-y sub-plane can dynamically compensate the x-y sub-plane voltage caused by motor asymmetry and back-EMF,and can control the harmonic current caused by motor asymmetry and back-EMF harmonics.The dq current of the grid side converter control strategy adopts a feedforward decoupled PI controller.DC voltage can be controlled by PI controller without static difference to achieve the decoupling control of power.Injecting the zero-sequence voltage can suppress the circulating current of the parallel converter.The fault tolerant control of multi-channel wind power systems,the fault tolerant control of dual-three permanent magnet synchronous motor and the fault tolerant control of three-level converter are designed in this thesis.Fault tolerant control is implemented by cutting off the faulty channel.Open circuit fault tolerant control changes the currents of the other phases to makes the resultant rotating magnetomotive force consistent with that before the failure,it can maintain the same torque after fault while achieves different optimization goals.A model of motor with open circuit fault is established based on fault tolerant control of vector space decoupling,and different optimization goals can be achieved by controlling the reconstructed z-plane current.After the open-circuit fault or short-circuit fault occurs in the device,the fault tolerant control of the converter is implemented using redundant vectors.The control strategies of this thesis are vertified by simulations and experiments.