Electrochemical Cell Loss Minimization in Modular Multilevel Converters Based on Half-Bridge Modules

Abstract

In the developing context of distributed generation and flexible smart grids, in order to realize electrochemical storage systems, Modular Multilevel Converters (MMCs) represent an interesting alternative to the more traditional Voltage Source Inverters (VSIs). This paper presents a novel analytical investigation of electrochemical cell power losses in MMCs and their dependence on the injected common mode voltage. Steady-state cell losses are calculated under Nearest Level Control (NLC) modulation for MMCs equipped with a large number of half-bridge modules, each directly connected to an elementary electrochemical cell. The total cell losses of both a Single Star MMC (SS-MMC) and a Double Star MMC (DS MMC) are derived and compared to the loss of a VSI working under the same conditions. An optimum common mode voltage injection law is developed, leading to the minimum cell losses possible. In the worst case, it achieves a 17.5% reduction in cell losses compared to conventional injection laws. The analysis is experimentally validated using a laboratory prototype set-up based on a two-arm SS-MMC with 12 modules per arm. The experimental results are within 2.5% of the analytical models for all cases considered.

Special Issue on Power Converter of Electric Machines, Renewable Energy Systems, and Transportation

“…Finally, the paper authored by Gianluca Brando, Efstratios Chatzinikolaou, Dan Rogers and Ivan Spina, focuses on an analytical investigation of electrochemical cell power losses in modular multilevel converters and their dependence on the injected common mode voltage. The development of an optimal common mode voltage injection law allows us to minimize cell power losses under balanced operating conditions [10].…”

Seven Level Voltage Source Converter Based Static Synchronous Compensator with a Constant DC-Link Voltage

“…The proposed energy-based multilevel multicell inverter has been implemented to provide negligible total harmonic distortion for power quality issues in microgrid applications [38]. A half-bridge modular multilevel converter with the nearest level control technique is deliberated to minimize the cell losses in balanced power conditions [39]. The over current of a multi-level converter based HVDC (high voltage direct current) transmission system is controlled via fault ride through a control algorithm for smooth system operations [40].…”