This paper presents a synchronous current control method for a three-level neutral point clamped inverter. Synchronous reference frame control based on two decoupled proportional-integral (PI) controllers is used to control the current in direct and quadrature axes. A phase disposition pulse width modulation (PDPWM) method in regular symmetrical sampling is used for generating the inverter switching signals. To eliminate the harmonic content with no phase errors, two first-order low pass filters (LPFs) are used for the currents. The simulation of closed-loop control is done in Matlab/Simulink. The Vertex-5 field programmable gate array (FPGA) in Labview/CompactRio is used for the implementation of the control algorithm. The control and switch pulse generation are done in independent parallel loops. The synchronization of both loops is achieved by controlling the length of waiting time for each loop. The simulation results are validated with experiments. The results show that the control action is reliable and efficient for the load current control. 1. Introduction The efficient conversion of renewable energy to electrical energy is still a key area of research. All renewable energy projects require power electronics converters for interfacing with the grid and controlling the energy exchange. Most of the basic conversion strategy of renewable energy follows a two-step procedure. First step is to convert the variable AC to constant DC. Active rectifiers or passive rectifiers with DC/DC converters are the generally used methods to date. However, the main part of the conversion unit is an inverter. It is used not only for connecting to different loads, but also for providing the necessary control actions required for the load. To meet the high energy demand, conversion and integration of renewable energy sources are suggested universally. The majority of the renewable energy plants are geographically far from the load centers. The integration of this power needs a very long transmission cable to reach the point of common connection. High voltage power transmission meets better efficiency by reducing cable losses. Thereby, the use of multilevel converters is also gone up [1]. Different conventional topologies of multilevel inverter structures are proposed in [2]. Neutral point clamped (NPC) inverter is a widely accepted topology amongst these [3–6]. In most of the applications, the performance of the voltage source inverter (VSI) depends on the quality of the applied current control strategy. It enhances the control accuracy of the instantaneous current
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