Research On Three-level Inverters Based On DSP

Recently, multi-level inverter has been widely applied in power electronics, and its control strategies and topologies of power circuits are become the research focuses. Comparing with the two-level inverter, it has many advantages, such as high efficiency and good dynamic performance, making less harmonic waves and suiting for high voltage large capacity applications. However, its basic control strategies are much more complicated than that of a two-level inverter, and the unbalance problem of the neutral-point may appear with the increase of the level order. If DSP digital control technique is applied to multi-level inverter, its control strategy can be optimized and system performance is advanced, while the control circuits are simplified.The topology of diode-clamped three-level inverter is studied in this paper. Firstly, the topology and principle of three-level inverter are introduced, its circuit equations are deeply analyzed, and the mathematical model of three-level inverter are established based on the switch function. On this basis, mathematical formula for the improved SVPWM is deduced in detail. To make simulation and realization much easier, the operating order of switching vector is determined by controlling the midpoint voltage. Then, the reason for unbalance of the capacitor voltage in three-level inverter is analyzed. A SVPWM method is also proposed, which can balance the midpoint voltage of the DC capacitor. Finally, simulation is carried out on the SVPWM method and control strategy of neutral point balance for three-level inverters with MATLAB. Simulation results prove the feasibility of the proposed method.