Browsing by Author "Liang, Gaowen"
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Item Analytical Derivation of Intersubmodule Active Power Disparity Limits in Modular Multilevel Converter-Based Battery Energy Storage Systems(2021-03) Liang, Gaowen; Tafti, Hossein Dehghani; Farivar, Glen G.; Pou, Josep; Townsend, Christopher D.; Konstantinou, Georgios; Ceballos, Salvador; POWER ELECTRONICS AND SYSTEM EQUIPMENTDue to a dramatic increase in grid-connected renewable energy resources, energy storage systems are interesting and important for future power systems, among which the modular multilevel converter (MMC)-based battery energy storage systems (BESSs) are one of the most modular, efficient, and flexible topologies. Uneven active power distribution among submodules (SMs) in the arms of an MMC-based BESS is necessary for certain applications. The main contribution of this article is to present a general analysis of the inter-SM active power disparity problem which incorporates the inherent operational constraints of the MMC converter. An analytical method to derive inter-SM active power disparity limits is introduced. The proposed analysis can help facilitate the design of MMC-based BESS for applications such as recycled batteries and hybrid battery chemistries, which can both require significant inter-SM active power disparity. The analysis formulates a criteria vector and criterion value that describes whether an MMC-based BESS is capable of supplying demanded output powers while subject to inter-SM active power disparity. Simulation and experimental results are obtained on a single-phase system with varying numbers of SMs per arm, which verifies the feasibility and generality of the proposed analytical method.Item Effect of Capacitor Voltage Ripples on Submodule Active Power Control Limits of Cascaded Multilevel Converters(2022-06-01) Liang, Gaowen; Tafti, Hossein Dehghani; Farivar, Glen G.; Pou, Josep; Townsend, Christopher D.; Konstantinou, Georgios; Ceballos, Salvador; POWER ELECTRONICS AND SYSTEM EQUIPMENTIn the operation of cascaded H-bridge converters and modular multilevel converters with energy storage or renewable power resources, unbalanced active power distribution among the submodules (SMs) is unavoidable. Depending on the operating conditions, there are certain upper and lower limits on the active power that can be processed by a single SM or a subset of SMs. The control system needs to restrict the SM power references to these limits, hence, accurate knowledge of the power limits is important. In existing methods to derive the power limits, the SM capacitor voltages are assumed to have negligible ripples, whereas in practice the ripples can be considerable. This article analyzes the effect of capacitor voltage ripples on the SM active power control limits and highlights the importance of considering the ripple effect. A methodology is proposed to accurately incorporate capacitor voltage ripples in the derivation of SM active power control limits. Simulation and experimental results are provided to evaluate the effectiveness of the proposed methodology.