Modulated Model Predictive Control for Current Ripples Reduction and Neutral-Point Voltage Balance in Three-Level Inverter

Model predictive control (MPC) method has been widely used in the current control of three-phase voltage source inverters due to the parameters are easy to design, the fast dynamic response and it is convenient to apply nonlinear systems. However, the MPC has the problem that the switching frequency can change arbitrarily that results in high requirements for switching devices. What's more, the inherent characteristics of the performance optimization function module can cause tracking errors. On the other hand, the Space vector pulse width modulation (SVPWM) control method has a high DC side voltage utilization rate and a fixed and adjustable switching frequency, which can achieve fast and accurate conversion of the voltage command signal to the switching signal. However, it cannot control current separately. Based on this, in this article, a Modulated Model Predictive control which combines SVPWM control method with MPC method is mentioned for decreasing current ripples and balancing the neutral-point voltage in NPC inverter. A three-phase three-level NPC grid-connected system was built to verify the mentioned control method. According to the simulation results, the control method mentioned in this article is able to decrease the ripples of inverter output current effectively, and has excellent performance to keep the neutral-point voltage balanced.