Parallel Connected Voltage Source Converters using Coupled Inductors
Creators: Takongmo, Marius
Publisher: name: University of Alberta Library
Year: 2023

<p>Multi-level coupled inductor voltage source converter topologies using two level inverters and advanced pulse width modulation (PWM) schemes are presented to reduce<br>
the footprint of high-power non isolated converters by lowering the size/weight of the magnetics.<br>
Interleaved PWM switching of two-level inverter legs connected to coupled inductors (CIs) having cross-coupled windings is a topic examined for low voltage high<br>
power converters. The winding arrangement significantly reduces the series output inductance as seen at the output of each phase of the voltage source converter. Balanced ac<br>
currents flowing through the inductor low series output inductance produce a small fundamental voltage drop across the coupled inductor windings and insignificant lowers<br>
the fundamental flux in the inductor magnetic core. In consequence, the peak flux and hence, the size/weight of the interface inductors required to average the outputs of the<br>
parallel connected two-level inverter legs can be reduced. The low series output inductance equally favors rapid transient response and makes it feasible to generate high-frequency<br>
fundamental multi-level PWM output voltages in the kilohertz range.<br>
A common mode (CM) dc-choke and a differential mode (DM) ac coupled inductor are investigated to separately filter the common mode and differential mode PWM voltages experienced between two parallel connected voltage source converters using to the same dc-link. The dc choke presents a high inductance to common mode PWM, and the ac<br>
inductor presents a high inductance to differential mode PWM voltages. The size and weight of the two coupled inductor types is smaller than using three conventional coupled <br>
inductors, which can cope with both common mode and differential mode PWM voltages across their windings. The system described is useful to reduce common mode to ground<br>
noise in uninterrupted power supplies and motor drives, reduce cable interactions, and increase the power density of interleaved PWM switching converters by reducing the size/<br>
weight of the converter’s magnetics. </p>

<p>Neutral point clamped (NPC) coupled inductor topologies having inner high-frequency PWM modules are presented for high voltage high current applications such as <br>
ultra fast electric vehicle chargers and electric drives. The neutral point clamped converters reduce the voltage stress across all the switching devices to Vdc/2 and lowers switching<br>
losses. The first NPC converter examined, unidirectional converter, has a reduced switch count and produce more voltage levels at the coupled inductor outputs when compared<br>
with VSCs having the same number of switching devices. Such multi-level PWM output voltages can easily be filtered with a small ac inductance, thereby reducing the size/weight<br>
of the overall converter. The second neutral point clamped converter, bidirectional converter, has two high-frequency modules at the output stage of each phase and connected<br>
together using a 3-limb interface coupled inductor. This inductor is smaller than using three conventional C-shaped coupled inductors. A PWM scheme that produces no common<br>
mode voltage across the 3-limb inductor windings is used to control the bidirectional NPC converter.</p>

<p>A discontinuous PWM, DPWM, control for neutral point clamped converters having inner high-frequency PWM modules is presented to reduce the peak flux, size, and<br>
weight of the magnetics in high voltage high current voltage source converters. The DPWM control ensures that the flux patterns remain centered at zero with no jumps;<br>
thereby reducing the peak flux and the required size/weight of interface coupled inductors.</p>