Identifying Circulating Currents and Zero-Sequence Voltages for Reduction in Stored Capacitor Energy in Modular Multilevel Converters

Optimization Methods to Reduce Capacitor Stress in Modular Multilevel Converters

“…Tellegen's theorem is used to derive a model for the stored capacitor energy in an arm as a function of the arm voltage and arm current. Similar stored capacitor energy relationships have been reported in [9], [12], [18], [20], [22], however alternative assumptions are used and it is not clear how these models are related to the one proposed in this paper. Experimental validation of the model is presented in Section III-C.…”

“…The authors of [18], [19] consider optimisation problems that minimise objective functions that contain a linear combination of variables that influence capacitor stress and MMC power losses. A two-step linear programming method is considered in [18] that uses auxiliary optimisation parameters that provide upper and lower bounds to stored capacitor energy, an upper bound on average current, and upper bounds on harmonic zero-sequence voltage magnitudes. A linear combination of these auxiliary variables form the objective functions considered in [18] for each linear program step.…”

“…A two-step linear programming method is considered in [18] that uses auxiliary optimisation parameters that provide upper and lower bounds to stored capacitor energy, an upper bound on average current, and upper bounds on harmonic zero-sequence voltage magnitudes. A linear combination of these auxiliary variables form the objective functions considered in [18] for each linear program step. The primary purpose of the technique studied in [18] is to reduce capacitor voltage ripple subject to constraints on peak arm voltage, peak arm current and average arm current.…”

“…A linear combination of these auxiliary variables form the objective functions considered in [18] for each linear program step. The primary purpose of the technique studied in [18] is to reduce capacitor voltage ripple subject to constraints on peak arm voltage, peak arm current and average arm current. However, there was no method to minimise the peak capacitor voltage, which is a key metric in determining overall capacitor and semiconductor stress.…”

Multi-Objective Genetic Algorithm Based Coordinated Second- and Third-Order Harmonic Voltage Injection in Modular Multilevel Converter

“…However, the third-order harmonic voltage is fixed without taking the second-order harmonic into consideration, and the RMS of arm current may increase [23]. There is a linear programming optimization approach has been taken to analyze the third-order harmonic injection combined with the second-order circulating current injection method [21].…”