Comparative study of the sinusoidal-wave and square-wave circulating current injection methods for low-frequency operation of the modular multilevel converters

An Enhanced $dq$-Based Vector Control System for Modular Multilevel Converters Feeding Variable-Speed Drives

“…7a the results obtained by implementing the conventional control strategy reported in [12], [19] are shown. In this case the mitigation currents are off-line calculated using (15) and the control systems are based on PI controllers implemented in the stationary frame. On the other hand, the results obtained by the mitigation currents regulated using the proposed control strategy are shown in Fig.…”

“…Vector control of the v ∆ Cαβ voltage 1) At low rotational speed (LFM): As discussed in several publications [12]- [16], [22] the most critical operating point of a M 2 C-drive is when the electrical frequency is low and the machine is operating with a relatively high current. Moreover, ifĩ Σ * αβ is off-line calculated using (15), there are several issues which can potentially hinder the correct mitigation of the low frequency voltage pulsation in the M 2 C capacitors. Some of these issues have been discussed at Section I.…”

An Integrated Converter and Machine Control System for MMC-Based High-Power Drives

“…Fig. 3(a) shows the optimal values of i d obtained when the parameters of the MMC-based drive utilised in this work are used to solve the optimisation problem of (20), showing that the magnitude of p ωe is reduced (particularly for low ω e values) when flux weakening operation is applied. To obtain this figure, the electrical torque chracteristic was defined as:…”

“…Two constraints have been defined in (20) to obtain the required electrical torque in the machine, τ e (ω e ), while keeping the stator current magnitude below i max . Fig.…”

“…Therefore, in the so-called "Low-Frequency Mode" (LFM), mitigation is required to reduce the capacitor voltage fluctuations using quantities such as additional circulating currents and common-mode voltages (hereafter called "mitigating variables"). Conversely, when the mitigation is no longer required, the "High-Frequency Mode" (HFM) is usually enabled [10], [11], [15], [20].…”