Study On Direct Torque Control Of Permanent Magnet Synchronous Motor Fed By Three-level Inverter

Along with the rapid development of new permanent magnetic materials, modern power electronics and motion control technology, permanent magnet synchronous motor has attracted extensive attention for its advantages such as simple structure, high power density and efficiency in the field of high performance AC speed regulation. Direct torque control, as an excellent strategy of AC drive, is developing in the direction of high-voltage large-capacity. Multi-level inverter possesses obvious advantages in the large-capacity AC drive system due to its small switching stress, low output harmonic content and so on, diode-clamped three-level inverter is used most widely. In this paper, theoretical analysis, simulation study and experimental verification are made to prove the validity of direct torque control of permanent magnet synchronous motor fed by three-level inverter.Based on the theories of multi-level inverter and direct torque control, the mathematical models of permanent magnet synchronous motor and diode-clamped three-level inverter are established, the problems in direct torque control system fed by three-level inverter are analyzed in detail.Based on the traditional single-vector method and virtual-vector method, two novel schemes of direct torque control fed by three-level inverter are studied. Scheme 1 is direct torque fuzzy control based on virtual vector fed by three-level inverter, 12 virtual voltage vectors with equivalent amplitude are designed, torque and flux errors are fuzzily graded, sector numbers are mapped to reduce the fuzzy rules, output of fuzzy controller is virtual vector number, neutral-point voltage is realized by time control; the other is three-level direct torque control based on virtual vector modulation, the predictive voltage vector is derived by space vector equations and synthesized by 12 designed virtual voltage vectors, neutral-point voltage is also controlled by time control. Virtual voltage vectors are both introduced in two schemes, to control the output voltage amplitude bounding of three-level inverter and neutral-point voltage balancing of DC side, based on good steady and dynamic performances.In the end, the validities of the proposed two schemes of direct torque control fed by three-level inverter are verified on Matlab/Simulink. Experiment platform of diode-clamped three-level inverter for AC speed regulation is built, software control procedures are written according to the hardware platform on TMS320F2812, the traditional SVPWM algorithm for three-level inverter are partly verified by experiment.