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One of the modular multilevel converter (MMC) applications with scalability is renewable energy generation. Nowadays, renewable energy is especially the source of momentum, which stimulates the energy transition and reduction of greenhouse gas emissions. However, its existing control schemes may not precisely reveal the inherent mannerism of MMCs. The aim of this article is to optimize the cell voltage, arm current, and circulating current of converter arms in MMCs based on the Lagrange multiplier of an energy cost function and arm current tracking control law. Meanwhile, determination of the capacitors and switch ratings in each cell still has a big challenge, and it can result in cell-voltage fluctuations under unbalanced grid-connection conditions. This article presents unique approaches to derive cell-voltage expression in terms of arm currents, which reduces cell-voltage fluctuations by injecting zero-mean current, and the duty-ratio control laws. Moreover, tradeoff between cell voltage and circulating current can be also conducted. Experimental and simulated results from a 3-kW single-phase MMC have verified the functionality of the proposed control method, analysis, and comprehensive discussion. [ABSTRACT FROM AUTHOR]

This paper presents a sinusoidal pulsewidth modulation (SPWM) based direct digital control with average-voltage model (AVM) and division–summation process for paralleled three-phase three-wire (3φ3W) grid-connected converters to reduce circulating currents. With the direct digital control, plant of each single-phase converter can be derived directly, and a controller is then designed to cover the variation effects of filter inductance and grid voltage. Based on SPWM and AVM over a switching cycle, each 3φ3W converter can be decomposed into three single-phase converters and each converter is controlled individually to track its sinusoidal reference current tightly, reducing circulating currents significantly. Equal current sharing is therefore also achieved. The control laws for achieving grid connection are derived in detail. In the design and implementation, the inductances corresponding to various inductor currents are measured offline and stored in the controller for scheduling loop gain cycle by cycle. Experimental and simulated results from a three-converter system confirm the analysis and discussion of the proposed control approaches. [ABSTRACT FROM AUTHOR]

The objective of this paper is to propose a feedforward delta modulation (FDM) control for switching-mode power converters. The operation principle and mathematical derivation for both the conventional delta modulation (CDM) and the FDM are presented. The proposed FDM uses the control signal to generate the variable integrating slope to obtain better control ability. By comparing to the CDM, the proposed FDM can improve the performance of the dc–ac inverter. The advantages include the following features: 1) wider switching frequency range with smaller electromagnetic interference; 2) larger fundamental component with less harmonics; 3) higher duty-ratio linearity; and 4) elimination of asymmetrical operation. In addition, the proposed FDM can be applied to the dc–dc converter, which cannot be done by using the CDM. It can achieve the fast transient response with voltage-mode control. The FDM controller design strategy for the dc–dc converter is given in this paper, followed by a design example. Finally, experimental results are shown to verify the performance of the proposed FDM for both the dc–dc inverter and the dc–dc converter. [ABSTRACT FROM PUBLISHER]