Design and implementation of the low computational burden phase‐shifted modulation for DC–DC modular multilevel converter

Abstract

DC-DC modular multilevel converter (DC-DC MMC) with the medium-frequency or high-frequency interlinked transformer is an attractive candidate for high-voltage-direct-current system and DC grid. This study proposes the phase-shifted modulation for DC-DC MMC, aiming to reduce the switching losses, minimise the computational burdens and obtain the satisfactory performance. According to the features of DC-DC MMC, the least but necessary control parameters are extracted, and their control cycles are also properly designed to adapt to the digital implementation. Then, the modulation algorithm is designed and the parameter mapping is realised by the simplest algorithm. Finally, the voltage fluctuations of the submodules (SMs) under such a modulation are predicted off-line, and the adapted sortand-selection strategy is designed for voltage balance of the SMs. With the proposed modulation, the switching frequencies of all SMs are strictly equivalent to the fundamental frequency; the sampling, parameter mapping and sortand-selection frequencies are also the fundamental frequency. These features alleviate not only the switching loss in the power stage, but also the computational burden in the modulation and control systems. The analysis and design of the proposed modulation will be given in this study, and verified by the experiments.

Recent contributions and future prospects of the modular multilevel converters: A comprehensive review

“…The primary contribution of Chen et al is to develop phase‐shifted modulation in order to reduce switching losses and computational burdens for DC/DC MMC. Switching losses and computational burden is improved through proposed modulation and control scheme.…”

“…The primary contribution of Chen et al 106 NLM technique is known as noncarrier method, which is easy to implement and directly controls the output voltage. [111][112][113] Basic principle of NLM is shown in Figure 9F.…”

Dual Channel Control With DC Fault Ride Through for MMC-Based, Isolated DC/DC Converter

“…The requirement to minimize M q1 and M q2 and considering a given d-current in (12) implies that lower X E will give lower losses.…”

“…However with DC/DC converters, the fundamental frequency of inner circuit (f) is much higher, and therefore the speedterms ( 2 ) are much larger making decoupling more difficult. Equations (12) and (13) suggest cross-coupling for inner current control: M d controls I q while M q controls I d .…”

“…The design of high-power isolated DAB DC/DC converters has attracted lot of research in recent years [10]- [16]. Many advances have been made in design of inner MMC, such as loss reduction using softswitching techniques in quasi-square-wave modulation [10], improved cell voltage balancing control [11], or reducing computation burden caused by balancing and modulation of large number of cells [12]. A medium frequency (1kHz), 1kW prototype, with 4 cells in an arm and stepping ratio of 3, isolated DC/DC is demonstrated in [13].…”