Frequency-PWM hybrid controller of single-switch forward-flyback converter for DC-link regulation of 27-level cascaded H-bridge inverter

Abstract

Among multilevel inverter topologies, asymmetric Cascaded H-Bridge (CHB) inverters have higher output-voltage levels than symmetrical ones. However, asymmetric multilevel inverters need pre-stage isolated and floating DC power sources, which make the system complicated and bulky. This paper is focused on solving the problem by using a single-core (magnetically-coupled) multiple-output forward-flyback converter as the prestage of trinary 27-level asymmetric Multi-Level Inverters (MLI). The forward and flyback converter is driven by a single switch with a controller employing both a PWM duty control and frequency control for continuous conduction mode (CCM) forward output and discontinuous conduction mode (DCM) flyback output respectively. Each output, then, can be regulated independently even though the single switch is used. The proposed system and control method are validated using a 1-kW hardware prototype for the experimental verification.

Improved Watkins-Johnson topology-based inverter with dual low-side switch and synchronous control strategy

“…The full-bridge topology is generally used in the post stage of high-frequency isolated inverter for dc-ac voltage conversion, which possesses shortcomings of high-side switch driver necessity, shoot-through issue and high conduction loss [1,2,3,4]. In order to solve these problems, the Watkins-Johnson (WJ) topology provides an alternative approach to realizing inverter.…”

Single stage high-frequency non-isolated step-up sinusoidal inverter with three ground-side power switches

“…The voltage step-up stage generally adopts topologies including the boost [7] and the Z-source circuit [8,9]. The voltage inversion stage adopts the half-bridge [10], the full-bridge [11] and its derivative circuits such as H5, H6 [12,13,14], multi-level H-bridge [15] and HERIC [16].…”