Research On Multilevel Active Neutral Point Clamped Inverter With Switched Capacitors

Multilevel inverters have been widely used in power conversion applications due to small volume,high efficiency and high power quality.Higher output voltage level is a necessary concern that influences output performance of multilevel inverters.However,it is difficult to extend the output voltage levels limited by volume,cost,efficiency and power quality.Only three-level and five-level inverters are usually applied in industrial applications nowadays.Therefore,it is necessary to design a simplified topology to achieve more output voltage levels.As the switched-capacitor part can output more voltage level,a new multilevel inverter topology with switched capacitors is proposed in this thesis,focusing on the following aspects:(1)With the advantage combination of the switched capacitors and ANPC multilevel topolygy,the composition methods of switched-capacitor active neutral-point clamped multilevel topology are studied.The characteristics of the SC-ANPC multilevel inverter and the ANPC multilevel inverter are compared and analyzed.(2)The topologies of SC-ANPC seven-level and nine-level inverter and their basic working principles are analyzed respectively.Based on the former analysis,the one-dimensional SVPWM strategy condersing less switching numbers of SC-ANPC seven-level and nine-level topologies are studied.The MATLAB/Simulink models of seven-level and nine-level inverters are built to verify the effectiveness of the proposed one-dimensional SVPWM strategy.(3)For the switched capacitor voltage equalization of SC-ANPC seven-level inverter,the charging and discharging mechanisms of the switched capacitors in series and parallel are analysed.The effects of the parameters on the steady-state voltage of the switched capacitors are analyzed.Under the specific conditions,the range of power factor is calculated and the power factor angle which will enable the switched capacitors to balance their voltage automatically is also obtained at the same time.Condering the one-dimensional SVPWM strategy with voltage equalization,three kinds of voltage space vector based control strategies are proposed to balance the voltage of switched capacitor when the power factor angle is out of the calculation range.The effect of switched capacitor voltage hysteresis control is compared with the other two control strategies and the results show that the proposed hysteresis control has the great advantage of low switching loss and low capacitor voltage ripple.The effectiveness of the switched capacitor voltage control strategies are validated by the designed single-phase SC-ANPC seven-level inverter simulation model and experimental prototypy separately.(4)The capacitor voltage control strategy for SC-ANPC nine-level inverter are studied to equalize the voltage of switched capacitors and flying capacitor.The charge and discharge modes of the switching capacitor and the flying capacitor under different switching vectors are studied.The proposed one-dimensional SVPWM method with less switching numbers is used to select the inverter switching modes.The hysteresis control principle of switching capacitor and flying capacitor voltage is analyzed.The mutual cooperation of the two proposed voltage hysteresis control is discussed and the capacitor voltage hysteresis control strategy of SC-ANPC nine-level inverter is proposed.The simulation model in MATLAB/Simulink and experimental platform based on dSPACE1005 and Typhoon602 combined real-time simulation system are set up to verifiy the correctness of the capacitor voltage hysteresis control strategy.The simulation and experimental results verifies the effectiveness of the capacitor voltage control strategy.