Current Control Strategies for a Star Connected Cascaded H-Bridge Converter Operating as MV-AC to MV-DC Stage of a Solid State Transformer

Abstract

Nowadays, the increasing number of nonlinear loads and renewable energy resources pose new challenges for the standard electrical grid. Conventional solutions cannot handle most of them. The weakest component in the whole system is a conventional distribution (converting medium to low AC voltage) transformer. It should not operate with unbalanced, heavily distorted voltage and cannot control power flow or compensate current harmonics. One of the promising solutions to replace the conventional transformer and thus minimize power flow and grid distortions is a power electronics device called a solid state transformer (SST). Depending on the SST topology, it can have different functionalities, and, with the proper control algorithm, it is able to compensate any power imbalances in both low voltage (LV) and medium voltage (MV) grid sides. In the case of a three energy conversion stage SST, the LV and the MV stages can be treated separately. This paper focuses on the MV-AC to the MV-DC stage only based on a star-connected cascaded H-bridge converter. In this paper, a simple control solution for such a converter enabling different current control strategies to distribute power among the phases in an MV grid in the case of voltage imbalances is proposed. Simulation and experimental results proved good performance and verified the validity of the proposed control algorithm.

Battery Energy Storage Systems for the New Electricity Market Landscape: Modeling, State Diagnostics, Management, and Viability—A Review

“…Variants using bridge inverter cells are shown in [200], as this topology requires six branches instead of three, like the Cascade H-Bridge topology [205]. One advantage of this design is its flexibility in connecting energy storage elements, whether directly to the DC link, parallel to the double star branches as a large battery cluster, or distributed across the double star branches, similarly to the Cascade H-Bridge connection [193,205,206].…”

“…parallel to the double star branches as a large battery cluster, or distributed across the double star branches, similarly to the Cascade H-Bridge connection [193,205,206].…”

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“…As a result, the use of multi-level converters has more advantages in the MV side such as modularity, a smaller passive filter, higher reliability, and fault-tolerant capability. Examples of multi-level converters used in the MV side of SST are NPC [134], FC [135], CHB [136], and MMC [137,138]. Figure 8 shows the different possible topologies of SST according to the input/output connection of power electronic converters.…”

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“…Several research papers considered the design and the control of modular and cascaded configurations instead of the conventional back-to-back converter in different RESs including PV and WTs [68][69][70][71][72][73][74][75][76][77][78][79][80]. Taking the large-scale PV (LSPV) systems, for example, modular converters emerged as a promising candidate where the power conversion stage is formed from several submodules (SMs) instead of one bulky centralized power converter.…”