Research On Direct Torque Control For PMSG-based Direct-drive Wind Power Converter

In recent years, Direct Torque Control (DTC) has become more and morepopular. With the wind power technology continues to evolve，DTC has alsobeen a growing number of applications to the wind power generation system.This paper presents a direct torque control scheme for a permanent magnetsynchronous generator (PMSG) for direct-drive wind power generation system.Direct control of torque and amplitude of the stator flux vector allows very fasttorque dynamic response of PMSG.This paper provides an overview of the status quo of the development ofwind power at home and abroad. The advantages and disadvantages of differenttypes of wind turbine are drawn to comparisons. Topology, operation principleand control strategy of back-to-back drive converter in the direct-drive windpower generation system are analyzed. Direct-drive wind power generationsystem includes permanent magnet synchronous generator, generation-sideconverter and grid-side converter. The focus of this paper is to study thegeneration-side converter operation principle and its control strategy, and themathematical models of PMSG in three different kinds of coordinate system areestablished.This paper analyzes the basic principle of direct torque control, includingthe analysis of the inverter voltage vector model, the control action of eachvoltage vector to flux and torque. Through analysis we can see, the core ofdirect torque control is to regulate the magnitude and direction of rotation of theflux vector and torque vector by selecting the appropriate voltage vector, so asto achieve the purpose of the direct control of torque. Besides that, this paperdescribes the composition of permanent magnet synchronous generator directtorque control system, including flux and torque observers, flux and torquehysteretic loop controllers, flux vector sector to judge, voltage vector switchingtable. In order to verify the correctness and feasibility of above control program,control system simulation model is given based on Matlab/Simulink.Direct torque control technology analysis shows that the accuracy of thestator flux observer has a direct impact on the control performance of the system. In this paper, after by analyzing the shortcomings of the traditional stator fluxobserver, several improved observers are proposed. Improved observers acertain extant effectively inhibit the DC offset generated by the traditional pureintegral observer due to the non-zero initial value, thereby increasing theaccuracy of the flux observer.On the basis of theoretical analysis, a3kw VSCF direct drive permanentmagnet power system simulation platform is developed. Details of the maincircuit, the detection circuit and drive circuit are introduced. And control systemsoftware design base on DSP is given, including the main program and interruptprogram design, of which interrupt program realizes the algorithm of directtorque control. By experimental debugging, the experimental waveform of apermanent magnet synchronous generator of direct torque control is obtained,basically the same with simulation waveform.Through the simulation and experiment, the program of direct torquecontrol of permanent magnet synchronous generator is correctness andfeasibility, so it’s help to promote application of direct torque control teleologyin wind power.