Pulse Width Modulation and SRF Based Closed-Loop Control of Stand-alone Single-phase 5L-ANPC Inverter

Abstract

Multi-level Inverter (MLI) has higher voltage and larger power handling capability along with low Total Harmonic Distortion (THD) compared to a two-level inverter. Neutral Point Clamped (NPC) and Flying Capacitor (FC) based MLIs are the popular ones among the various MLI topologies. Combining the features of NPC and FC based MLIs, an Active NPC Inverter (ANPCI) is proposed in the literature. This paper presents the operation and control of a Single-Phase Five-Level ANPCI (1P-5L-ANPCI) in stand-alone mode. Two different Pulse Width Modulation (PWM) techniques, viz., Alternate Phase Opposite Disposition (APOD) and Phase Disposition and Shifting (PDS) are explained for the IP-5L-ANPCI and their performance is compared. An algorithm for FC voltage balancing and Neutral Point Potential (NPP) balancing is incorporated in the PWM control. The closed-loop control of the inverter is performed in Synchronous Reference Frame. The stationary frame signals are transformed to synchronously rotating dq reference frame using a Modified Second Order Generalized Integrator (MSOGI) that is capable of rejecting DC offset in the measured signals. The performance of the converter is verified using PSCAD/EMTDC both in open-loop and closed-loop. The results are presented for R-load, RL-load and step changes in the DC-link voltage, reference load voltage and load. The results also verify the effectiveness of the FC voltage balancing and NPP balancing algorithm.