A modular direct converter for transformerless rail interties

Modular Multilevel Converter Control Methods Performance Benchmark for Medium Voltage Applications

“…9. Second harmonic circulating current injection (negative sequence) for capacitor voltage ripple reduction: (a) implementation that only considers the αβ components, where φ = atan(Q /P ), and (b) instantaneous power mode in [27] where the zero sequence component is discarded (usually the active power feed-forward is faster). Note that there shouldn't be any phase advance in the feed-forward term, hence…”

Virtual Submodule Concept for Fast Semi-Numerical Modular Multilevel Converter Loss Estimation

“…The analytical averaged model accounts for all parasitic elements in the circuit, especially the branch inductance L br , which was the main motivation of [12] compared to the simplified models of [13], [14], as well as the circulating current in steady state, where no large branch energy imbalances occur. The derivation starts from the expressions of the branch voltage (e p/n ) and current (i p/n ).…”

“…Two scenarios for the branch voltage have to be accounted for in (1), depending on the presence or not of a common mode (CM) voltage term made from a combination of one or more triplen harmonics, which can be used to extend the linear modulation range up to k AC = 2/ √ 3. In addition, two scenarios can be analyzed regarding the shaping of the circulating current in (2): 1) no second harmonic circulating current, which corresponds to a circulating current suppression controller alike behavior and 2) second harmonic circulating current injection, which was initially proposed in [13] to reduce the capacitor voltage ripple. Consequently, the branch current contains three terms:…”

On the integration of low frequency transformer into modular multilevel converter

“…The choice of the harmonic content of the circulating current (also called partial bus current or differential current) is free to select, as long as the harmonic spectrum of the grid current comprises only of a fundamental component. In particular, a second harmonic component may be intentionally injected in the arm currents in order to reduce the capacitive storage requirements [13], [14] or [15]. The modulation functions for each arm are complementary since each arm has to block the full input DC link voltage, and are given as:…”