The Research On Novel No-Dead-Zone SVPWM And Rotor Flux Oriented Control System

Rotor flux oriented control, whose method is simple, performs well on dynamic performance and control accuracy. Large torque can be generated at lower speeds. Consequently, rotor flux oriented control is suitable for the application in AC driving control system of electric forklift. In this thesis, induction motor vector control system based on indirect flux oriented control is the research subject. A novel modulation strategy of no-dead-zone SVPWM (NODZ SVPWM) is proposed after thoroughly study of SVPWM and dead zone. Corresponding simulations and experimental analyses have been carried out.Additional dead zone, which is required in the practical practical application of classical SVPWM, reduces the system output voltage capability and leads to the phenomenon of phase deviation and waveform distortion. Electric forklift generally works at low speed condition with intermittence. And its inverter has low voltage with high current. In such application, the problem is much more highlighted, even causing low frequency oscillation of the motor. Studying SVPWM plus dead zone in deep, this thesis draws a conclusion that the separation between switching state and voltage vector is root cause of dead-time effect. By considering the actions of freewheeling diode under different load conditions, NODZ SVPWM based on transitional switching state is proposed. In this thesis, transitional switching states are defined as2π/3type of switching states playing a role actually equivalent to π type of space vectors and transitional vectors are defined as space vectors, which are equivalent to π type of space vectors, corresponding to transitional switching states. Transitional switching states are added during the switching process of π type of switching states. In this way, conventional dead-time settings are replaced. An ideal switching pattern, switching π type of voltage space vectors without dead-time, is achieved. Dead-zone problems are completely avoided. In the modulation strategy of NODZ SVPWM, the output waveform at the AC side of inverter has no distortion, and the current gets a good sine degree. Simulation analyses and experimental investigation demonstrate the correctness of this method, and prove that the speed regulation performance of motor is effectively improved. This thesis introduces rotor flux oriented control system based on indirect flux oriented. Current loop and Speed loop of the control system are designed. In MATLAB/Simulink, simulation results show that the control system has good dynamic response and steady accuracy. Parallel MOSFET on aluminium substrate is designed for main circuit. TMS320F28335is selected as the core for control circuit. Based on these, experimental platform of the forklift inverter is built. Experimental results show that the designed AC driving control system meets the design requirements with good dynamic performance.