Abstract
Conventional single-cell dual buck inverters present high reliability, however they cannot be directly used in high voltage applications, because of the limited voltage rating of commercial switching devices. Therefore, a novel modular multilevel dual buck inverter (MMDBI), capable of processing voltage and power at higher levels, requiring a single dc input voltage, is proposed in this paper. Non-interleaved phase-shifted discontinuous modulation (NIPSDM) and interleaved phase-shifted discontinuous modulation (IPSDM) schemes are applied to the proposed inverter to reduce the current stress in the switching devices. Despite beneficial to the converter efficiency, the use of these discontinuous modulation approaches results in current zero-crossing distortion, which needs to be appropriately managed. In this work, theoretical values for the common-mode and differential-mode current ripples under NIPSDM and IPSDM modulation strategies are derived, and each switching operating mode is fully analyzed. From that, an adjustable current threshold value, which depends on the theoretical current ripple magnitude, is incorporated into the modulation strategy, producing a minimum switching overlap period between the two buck cells that eliminates the current zero-crossing distortion and produces a high-quality output current. Extensive simulation and experimental investigations are presented to demonstrate the feasibility and effectiveness of proposed topology and adjustable discontinuous modulation strategy.
Highlights
Inverters play a crucial role in renewable power generation systems, uninterruptable power supplies, motor drives, airplane power systems, active filters, among others
ADJUSTABLE DISCONTINUOUS MODULATION Same as for the conventional dual buck converter, when the modular multilevel dual buck inverter (MMDBI) topology operates with discontinuous modulation (NIPSDM OR interleaved phase-shifted discontinuous modulation (IPSDM)), upper and lower arm current ripples at zero-crossings are nonzero, and this causes undesirable current zero-crossing distortion, which needs to be managed
CURRENT ZERO-CROSSING DISTORTION ANALYSIS When operating with a discontinuous modulation scheme (NIPSDM or IPSDM) with zero threshold (under the assumption that the current zero-crossing point is known as illustrated in Fig. 9(a)), the MMDBI topology presents current zero-crossing distortion during changes of the arm current polarity, and this effect is more severe for lower converter switching frequencies
Summary
Inverters play a crucial role in renewable power generation systems, uninterruptable power supplies, motor drives, airplane power systems, active filters, among others. Full-cycle modulation requires all switches operating simultaneously within a fundamental period This approach incorporates a bias into the inductor currents that produces an additional output voltage level [17], at the expense of higher device current stress and reduced converter efficiency. The cascaded dual buck half-bridge topology [20], [21] and the cascaded dual buck full-bridge topology [22]–[24] were proposed as alternatives to increase the converter reliability Within this context, the use of carrier phase-shifted unipolar or bipolar PWM strategies allows increasing the effective converter switching frequency and this potentially eliminates the ripple current at zero crossings, reducing the distortion [20].
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
