A novel algorithm for increased power balance in cascaded H-bridge multilevel cells in a hybrid power amplifier
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ORIGINAL PAPER
A novel algorithm for increased power balance in cascaded H-bridge multilevel cells in a hybrid power amplifier Luccas M. Kunzler1
· Luiz A. C. Lopes1
Received: 19 August 2019 / Accepted: 27 August 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract This paper concerns the issue of unbalanced output power among cells in cascaded H-bridge multilevel (CHBM) converters with conventional staircase modulation techniques under low modulation signals. This is a common condition in highvoltage/frequency hybrid power amplifiers (HPAs) consisting of a CHBM converter in series with a linear power amplifier (LPA). The online implementation of a modulation technique called split-voltage first-in first-out (SV-FIFO) that mitigates this issue is presented in this study. Differently from conventional techniques, it needs to take into consideration the magnitude and frequency of the reference voltage to generate the gating signals of the CHBM converter. This paper also introduces a design procedure for a series-type HPA and a means for generating online the gating signals of the CHBM converter, with SV-FIFO, and the reference signal for the LPA in closed loop with a mixed signal controller. Experimental results for a series-type HPA with a six-cell CHBM converter and a commercial LPA are provided to validate the design procedure of the HPA and demonstrate the enhanced (active) power balance of SV-FIFO and the effectiveness of the proposed control scheme for the HPA under transient and steady-state conditions. Keywords Power amplifiers · Power conversion · Modular multilevel converters · Cascaded H-bridge multilevel (CHBM) converters
1 Introduction Power amplifiers (PA) are an essential equipment for powerhardware-in-the-loop (PHIL) simulations. They are required in the emulation of rotating machines, loads and even power grids to create all sorts of testing conditions. It is a common equipment used in the automotive, aerospace and drive/relay industries [1, 2]. Linear power amplifiers (LPAs) provide an overall great performance but are expensive, mostly at increased power ratings. For high power amplifiers with fast dynamic response and reduced waveform distortion, the hybrid power amplifier (HPA) configuration can provide a good cost-performance compromise. HPAs are built with the association of a low-cost switch-mode power amplifier (SMPA) and a LPA. The SMPA brings the ability to process a large amount of power, while the LPA, due to its high bandwidth and fast response, is responsible for improving the
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Luccas M. Kunzler [email protected] Electrical and Computer Engineering Department, Concordia University, 1515 St. Catherine W, EV Building 5.139, Montreal, Canada
quality of the output waveform, in a similar way to an active power filter. SMPAs realized with a cascaded H-bridge multilevel (CHBM) converter, bring an increased modularity to the system and allow the HPA to be used for high-voltage applications [3–5]. This paper concerns a HPA where the SMPA and LPA are connected in
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