A Generalized Phase-Shift PWM Extension for Improved Natural and Active Balancing of Flying Capacitor Multilevel Inverters

Abstract

The emergence of wide bandgap power devices has brought the attention back to the flying capacitor (FC) multilevel inverters with a large number of stages, in an effort to increase the power density by minimizing the passive components. The main challenge that such systems face, particularly the ones based on high-frequency Gallium-Nitride devices and small-value ceramic capacitors, relate to the stringent requirements for precise and fast capacitor balancing. Conventional natural balancing techniques exhibit poor settling times, while most improved natural balancing methods are not easily scalable to more than five levels. The alternative of active balancing normally requires one isolated sensor per FC which increases the overall system cost and footprint, or a single ac-side sensor that is more compact but calls for sophisticated PWMs that again are not available for multiple levels. In this paper we introduce a generalized pulse width modulation (PWM) strategy based on the phase-shift and carrier swapping principles for an arbitrary number of levels. We provide an easy and intuitive method for the extraction of the PWM pattern, the switching states, and their sequence. Simulations were carried out in Matlab/Simulink and experimental tests were conducted on a single-phase 7-level GaN inverter prototype. Not only is the extended PWM advantageous in natural balancing, but it also provides the right zero switching states for ac-side FC sensing in active balancing.

Modelagem e Controle Das Tensões Dos Capacitores Flutuantes do Inversor com Grampeamento Através de Capacitores Flutuantes

“…Nota-se ainda na Figura 5, que o sistema compensado cruza por zero na frequência desejada, com margem de fase de aproximadamente 81, 5 • e inclinação de -20 dB/dec no gráfico de magnitude, de acordo com os requisitos especificados. A função de transferência do controlador da tensão nos capacitores é representada pela Equação (23).…”

“…Diversas técnicas com o objetivo de controlar a tensão dos capacitores flutuantes de diferentes maneiras vêm sendo relatadas na literatura. Uma estratégia geral de modulação por largura de pulso (PWM) para inversores multiníveis FC é proposta por [23], com uma técnica que visa equilibrar naturalmente e ativamente o sistema, usando a troca de portadoras em diferentes momentos. De acordo com os autores, essa metodologia envolve a troca de portadoras vizinhas em ciclos de comutação consecutivos e, é aplicável para qualquer número de níveis.…”

An improved modulation technique suitable for a three level flying capacitor multilevel inverter

“…The N level FCMLI requires (N − 1) DC link capacitors, 2(N − 1) switches and (N − 1)(N − 2)/2 auxiliary capacitors in each phase leg [12]. Therefore, a single phase 3-level FCMLI comprises of 2 DC link capacitors, 4 switches, and a single auxiliary capacitor Many researches presented different control schemes of FCMLIs for example: in [13] authors proposed a generalized approach to pulse width modulation (PWM) for an infinite number of levels, based on the ideas of carrier swapping and phase shift. It offers a simple and straightforward technique for obtaining the switching states, their order, and the PWM pattern.…”

Extension of Operating Range in Hybrid Cascaded H-Bridge Inverters with Capacitor Voltage Balancing Capability

“…Multilevel converters have emerged as the preferred choice in systems spanning medium to high voltage ratings due to the inherent advantages, such as lower voltage stress at switch devices, reduced harmonic distortion, higher power quality, improved scalability, fault tolerability, and diminished electro-magnetic interference (EMI) compared to two-level counterparts [2,9]. Nevertheless, the number of components in the classical multilevel topologies, such as diode-clamped inverters, flying capacitor inverters, cascaded H-bridge inverters, T-type inverters, generalized P2 inverters, and multilevel active-clamped inverters, increases in proportion to the number of levels [4,[10][11][12][13][14][15][16][17][18][19][20][21][22][23].…”