Research On The Modulation Strategy Of Dual Three-level Inverter Based On An Open-End Winding Induction Motor With A Single DC

The cascaded topology of dual inverter is a new idea for the development of multilevel inverter topologies.It can be widely applied to medium and high voltage variable frequency speed control technologies in industrial production,transportation and other fields.And it can improve the speed control performance and power density of frequency conversion equipment,thus promoting the development of China's high-voltage and high-power inverter industries,effectively reducing energy consumption and reducing environmental pollution.The multilevel inverter with dual-terminal tandem has many kinds of topologies and flexible combinations.Combining with industrial applications,the open-winding asynchronous motor is used as the control object,and the dual three-level inverter topology with a single DC bus is selected for the system.Aimed at zero-sequence currents,common-mode voltages,and unbalanced DC-capacitor voltages,several modulation strategies have been studied and solutions have been proposed in this paper.The switching state of the dual-level three-level inverter with a single DC bus is analyzed,and a switch model is established at first in this paper.Based on the switch model,the zero-sequence voltage and the common-mode voltage in the double-inverter system is defined.The formula of the space voltage vector of the dual-level three-level inverter is written by the switch variable function,and the space voltage vector diagram of the dual-level three-level inverter is obtained as the research basis.Aiming at the problem of the zero-sequence current in the common three-level dual-level inverter system,a kind of reference voltage vector 180° decoupling modulation strategy is studied in this paper.This modulation strategy can eliminate the zero-sequence current in the system by eliminating the average zero-sequence voltage.However,due to the presence of high-frequency instantaneous zero-sequence voltage in the system by using 180° decoupling modulation method,a kind of reference voltage vector 120° decoupling is proposed in this paper based on the reference voltage vector decoupling.The new modulation method can eliminate the instantaneous zero-sequence voltage,thus eliminating the zero-sequence circulation under the common bus structure.Aiming at the common-mode voltage that may exist in the dual three-level inverter system,a zero common-mode voltage vector modulation strategy is studied in this paper.This modulation strategy can completely eliminate the common-mode voltage in the system,thus eliminating the harm caused by the common-mode voltage.But the utilization of DC bus voltage is low and the modulation algorithm is very complicated.Therefore,in combination with the reference voltage vector 120° decoupling modulation method,a method for suppressing the common-mode voltage based on a virtual space vector is proposed.The method can reduce the amplitude of the common-mode voltage,relatively improve the utilization of the DC bus voltage,and simplify the modulation algorithm.In this paper,Matlab/Simulink simulation and hardware experiment platform are established.The correctness and effectiveness of the proposed modulation strategies are verified by simulation and experiment respectively.