Study On Modulation Strategies Of Four-Level Double-T-type Inverter And Its Speed Regulating System

With the rapid development of power electronic technology and microprocessors technology,AC variable-frequency control technology has also made a breakthrough.However,the application of the AC variable-frequency control system in the occasion of high voltage and high power was restricted to the maximum voltage and current of the power electronic devices.And with the industrial and mining enterprises of the motor-driven equipment,high power factor,low harmonic content requirements continue to increase,A variety of multi-level inverter topology have been proposed,More and more multi-level inverter is used in high-power mining hoist,fans,compressors,conveyors and other occasions.The weakness of traditional NPC four-level inverter and its operation principle is analysed in this paper,and an improved double-T-type four-level inverter is proposed,Then the topology characteristics and the influence of the switch combinations on the neutral point voltage and the voltage of the clamping capacitors of double T-type four-level inverter are analyzed in detail.On this basis,a neighborhood SVPWM modulation strategy and a switch combination selection logic which can forming a charge or discharge loop are proposed.So that the system can be achive the stability of the mid-point voltage and clamping capacitors voltage through choice the corresponding switch state and switch combination in different states.The simulation results show that the voltage vector is not controlled in the dead time of the multi-level inverter.According to the characteristics of the new topology,the dead time PWM signal is processed and the problem of uncontrolled voltage vector in dead time is solved.Finally,the double-T-type four-level inverter and the neighborhood SVPWM modulation strategy is verified by simulation.Finally,the simulation model of vector control system under the PLECS is established.The simulation results show that the control system has good dynamic response and steady-state accuracy.And the hardware and software of the control system based on EP4CE10E22C8 have been designed.No-load and load mutations experimental study has carried on in the experimental platform.The experimental results shows the system has good dynamic and static performance,which proved that system has high practical value.