No abstract

No abstract

No abstract

Abstract-This letter proposes a new control scheme for the neutral-point (NP) balance in single-phase three-level NP-clamped converters. The control is addressed considering the plant under study, a nonlinear time-variant system. A quasi-exact linearization is applied allowing the application of classic control techniques. The described method is simple, general, and suitable for buck and boost topologies, as well as for inverter or rectifier operating modes under either linear or nonlinear loading. Correct operation is verified under simulated and experimental operation.

This paper proposes a new control scheme for its application directly extends to a buck rectifier and to buck the neutral-point balance in single-phase three level neutral-and boost inverters. point clamped converters. The control is addressed, considering Section II of this paper briefly describes the switching the plant under study a Non-Linear Time-Variant system and applying a quasi-exact linearization to it. This way it is possible to scheme and converter operation considered for this study. apply classic control techniques. The method depicted is simple, Section III focuses on performing an accurate mathematigeneral and suitable to back and boost topologies as well as to cal description of the system: starting from the electrical inverter or rectifier operating modes.schematic of the converter, a Non-Linear Time-Varying difCorrect operation is verified under both simulation environ-ferential equation that models the system will be extracted. ment and experimental operation. Experimental operation has been verified with linear and non-linear load.Once the system is properly modelled, section IV will focus on control design. First step has to be a linearization process; I. INTRODUCTION this will be the discussed in IV-A. Once the problem has been PWM converters guarantee harmonic quality on AC signals reduced to a Linear Time Invariant control design problem, IVand DC output voltage regulation. Neutral-point clamped B will propose a simple classic zero-pole network as control multilevel technologies [1] [2] provide an easy way to increase scheme and will describe de final control system, showing output voltage, nominal power and to reduce even more the a block diagram of the whole system and discussing some harmonic distortion. The price paid for the use of these kind final implementation issues. Finally, section V will verify the of topologies is an increasing control complexity in several correct operation of the proposal by means of experimental parts of the system, as for example, the neutral-point capacitor testing. voltage equalisation.The unbalancing of intermediate levels in these topologies II. CONVERTER OPERATION AND SWITCHING SCHEME induces signal quality problems such as output voltage distortion and increases the risk of device destruction due to overDuring normal operation, the converter function is to genvoltage across the capacitors, switching devices and clamping erate an AC voltage (Vab) from a DC voltage (VPN) by diodes.driving IGBTs of figure l.a to a correct state. A more intuitive Multilevel equalisation in three-phase converters has been switching model of the system under study is shown in an active research topic during last years. Several approaches figure l b. such as especial modulations [3], addition of special signals In the model of figure l.b, VPN is the DC side voltage, to PWM signals [4] [5], etc. have been proposed and its which for convenience will be called output voltage, Vab iS effectiveness proved, the AC side voltage which will be called input voltage, iL The challeng...