The application of cascaded multilevel converters in large-scale photovoltaic plants connected to the utility grid has many advantages, such as the absence of sinusoidal filters and line-frequency transformers. Improved overall performance under partial shading conditions is possible due to the distribution of arrays among a large number of maximum power point trackers. In this situation, although the cells operate at different power levels, the three-phase currents injected into the point of common coupling must be balanced. A suitable control technique is required to achieve this goal. This paper presents a complete algorithm to handle three-phase power balance and single-phase power harvesting simultaneously. Simulation results assuming a medium-voltage system connected to a typical utility grid illustrate the dynamic and steady-state performance capability of the proposed strategy. Experimental results of a low-voltage, solid-state transformer-based, three-cell prototype are also included.

Central inverters based on conventional topologies are the current preferred solution in solar farms because of their low cost and simplicity. However, such topologies have some disadvantages such as poor maximum power tracking, use of bulky filters, and low-frequency transformers. An interesting alternative in this case is the SiC-based cascaded multilevel converter (CMC), which provides a distributed maximum power point tracking control with reduced footprint and high flexibility. Each cell of a CMC usually has, as an intermediate stage, a solid-state transformer based on a dual-active-bridge dc-dc converter. Due to the unidirectional power flow characteristic of the photovoltaic application and aiming at further reduction in the converter volume, this work proposes a forward dual-active-bridge (F-DAB) topology, which reduces the number of active switches. This paper shows through analytical, simulation, and experimental results that the cell using an F-DAB is superior to other unidirectional topologies in three aspects: higher power density with commercially available power modules, reduced part count, and simplicity of control.

Belt conveyors in mining industry constitute an efficient and economical way for minerals and heavy-load transportation from mines to their destination. The ongoing desire to further extend the length, speed, and capacity of the conveyors has led to the increasing size of the conveyor-drive systems. More and more frequently, high-capacity belt conveyors are efficiently driven employing medium-voltage power converters connected with large induction motors. Power converters in the megawatt (MW) range are often used, increasing the power-quality issues in the grid system. This work proposes a new true unit power factor active front end for regenerative multimotor conveyor-drive systems. The proposed solution eliminates all the current harmonics in the range considered by the international standards without using sinusoidal filters. Three-winding conventional transformer and well-established medium-voltage power converters are considered to ensure the robustness and simplicity requirements.

Mining process requires different types of pumps to transfer fluids from one point to another. In the majority of applications, those pumps are driven by variable speed motor drives in order to improve the energy efficiency of the overall system. Large pumps, ranging from hundreds of kW to a few MW, usually demand medium voltage converters. Transformerless converters reduce the footprint required for the installation, but give rise to additional concerns related to the common-mode voltages applied to the system and motor. The absence of an isolation transformer along with the use of PWM rectifiers are the root causes of this issue. This concern increases when long cables are needed to connect the converter to the motor. This paper presents an application where 3L NPC transformerless medium voltage converters were applied to drive motor pumps in a mining plant. The passive filtering techniques used to address the common-mode voltage issues were analyzed through simulations. The proposed solutions were field tested with successful results.

Steel production worldwide continues to grow and, consequently, also the energy consumption of the steel sector. With the applications of the electric arc furnace route in the steelmaking process, the concern with aspects of power quality and overload of the transmission grid lines increases. This work presents the zero harmonic distortion (ZHD) converter static synchronous compensator (STATCOM), which makes it possible to increase the displacement power factor of an electric arc furnace (EAF) application from 0.88 to 0.98 with total demand distortion in the grid around 1.44% with the ZHD prototype operation, this being accomplished without using high-order sinusoidal filters and with consolidated components in the industry.

Large charging cranes are used to introduce hot metal into the basic oxygen furnace through the use of induction motor drives for the main and auxiliary hoist. These motor drives shall have the capability of dealing with bidirectional power flow due to the action of lifting (motoring) or lowering (regenerating) the load. The use of the active rectifier increases the energy efficiency since the braking energy is not lost in heat. This article proposes a true unit power factor converter with a common dc bus and compares it to an existent solution. Theoretical analysis, simulation results, and losses calculation show the advantages of the proposal in terms of power quality, energy efficiency, and reliability. Hardware-in-the-loop results show the proper work of the developed control system.