Suzan Eren

Neutral Point Clamped (NPC) converters are widely adopted in high-power wind energy conversion systems due to their ability to handle high voltages with reduced device stress. However, one of the main challenges of NPC topology is the unequal distribution of switching losses, which leads to thermal imbalances and reliability concerns. This paper proposes a modulation scheme for NPC converter in wind power applications, aiming to achieve active thermal control, loss balancing, and capacitor voltage regulation. The key idea is to reconstruct the middle voltage level of each phase through a linear combination of the three available levels, ensuring volt-second balance while reducing neutral-point current. This approach not only equalizes the switching losses among devices but also decreases the RMS current stress on DC-link capacitors, enabling the use of smaller and more cost-effective capacitors. Unlike conventional methods, the proposed scheme maintains its effectiveness across the entire range of modulation indexes, including those typical of low-voltage ride-through (LVRT) conditions in wind turbines. Importantly, all semiconductor devices operate at the same switching frequency, without a significant increase, ensuring equalized loss distribution. Experimental results validate that the applicability of the proposed method over the entire range of modulation indexes.

In this article, a new controller for a dc/dc buck converter is introduced, with a key feature that it does not rely on a current sensor, which minimizes sensitivity to sensor errors, including sensor noise and offsets. This is made possible by using a delayed, positive feedback term of the output voltage. The controller achieves stabilization without the need for current feedback during challenging situations of powering constant power loads and/or reverse power flow, i.e., the boost mode, operation. This article includes theoretical analyses using both approximate and precise methods, a step-by-step algorithm for designing controller parameters, and comprehensive performance evaluations through simulations and laboratory experiments, demonstrating its efficacy. This article concludes that the proposed method has robust stability and high noise immunity and is a suitable choice to be employed in extreme practical conditions.

Parallel operation of inverters is one method to increase power ratings of motor drives for high power applications. This paper proposes a novel variation of Field-Oriented Control for parallel inverters driving AC machines. The proposed strategy is implemented directly in the natural (abc) reference frame and overcomes many issues faced by conventional controllers for parallel motor drives. At the core of this control strategy is a proposed Resonant Proportional Integral (RPI) controller, which uses integrated plant dynamics to achieve the functionality of a second-order Proportional Resonant (PR) controller using only a first-order Proportional Integral (PI) controller. Hence the proposed control strategy is very simple, requiring only an inner first-order RPI controller for the the stator currents, and an outer PI controller for motor speed and maximum torque per ampere (MTPA) operation. A theoretical analysis of the RPI controller is given, which is supported by simulation and experimental results.

Three-phase four-level three-capacitor converter (3P4L3C) employs a single flying capacitor per phase, eliminating redundant switching states. However, this topology presents a significant challenge in capacitor voltage regulation, as conventional modulation techniques, including carrier-based SPWM and SVM, fail to maintain voltage balance. This article proposes a supervised voltage regulation method that dynamically adjusts duty ratios to compensate for capacitor voltage deviations, ensuring stable operation. Beyond regulation, a unified electrothermal lifetime evaluation framework is introduced to quantify how improved regulation impacts capacitor reliability. The framework integrates ripple-spectrum-based ESR loss calculation, hotspot temperature estimation, nonlinear damage accumulation, and Monte Carlo simulation under realistic mission profiles. Simulation and experimental results confirm that the proposed supervised voltage regulation achieves stable capacitor voltage regulation while reducing ripple current and thermal stress. As a result, the 3P4L3C converter demonstrates approximately 20% longer capacitor lifetime compared to the conventional 3P4L6C topology, highlighting the benefit of integrating control and reliability assessment within a single design framework.

Having single stage conversion and combining different energy sources, hybrid source inverters (HSIs) are recognized as a viable solution for driving electric vehicles (EV). With only one path between each source and motor, efficiency and power density increase in these inverters. For modulation, in the literature, the classic space vector modulation (SVM) technique is employed. Although this modulation is simple, it suffers from high switching frequency, high switching loss, high and uneven thermal distribution between switches. In this article, a new reconstructed vector-based modulation technique for enhanced operation of HSIs is proposed and verified with simulation and experimental prototype. This modulation takes advantage of using reconstructed space vectors, and instead of using only one dc voltage level for each mode, it uses different dc voltage sources to construct the reference voltage, which leads to switching frequency distribution, better thermal junction profile and improved efficiency. These two modulation techniques are compared across various metrics, including junction temperature profile, efficiency, output total harmonic distortion (THD), and switching and conduction losses and significant improvements are demonstrated.

Hybrid energy sources in electric vehicles are a well-established approach to mitigating pollution caused by fossil fuels, thanks to their integration of batteries and ultra-capacitors. While various hybrid source inverters (HSIs) have been introduced in the literature to enable single-stage conversion, further advancements in topology and operation are still achievable. This article proposes a novel HSI structure that utilizes four shared IGBTs across three phases, complemented by a secondary two-level voltage source inverter. Compared to conventional HSIs, the proposed topology reduces the number of switches and eliminates the need for diodes. The shared-switch configuration leads to lower switching and conduction losses, enhancing overall efficiency. In addition to the new topology, a modified space vector modulation technique tailored for HSIs is introduced. This modulation strategy is applied to the proposed topology, and its performance is evaluated across multiple metrics, including junction temperature profile, efficiency, output total harmonic distortion, and switching and conduction losses. The results demonstrate significant performance improvements. Furthermore, both simulation and experimental results are presented to validate the functionality of the proposed topology and modulation scheme.

Multilevel dual-active-bridge (DAB) converters utilize low-voltage-rating power switches with reduced channel resistance, provide additional degrees of freedoms for control, and exhibit improved efficiency. This article proposes a four-level modulation strategy for a neutral-point-clamped (NPC) DAB converter to address the performance limitations of NPC-DAB topologies operating under conventional modulation schemes—particularly in applications with wide voltage gain variations, such as renewable energy and battery energy storage systems. The proposed modulation scheme preserves compatibility with passive flying capacitor voltage balancing, while extending the zero-voltage switching (ZVS) range and mitigating over-voltage stress across NPC switches through adjusting two independent control parameters: duty-cycle and phase shift, without the need for complicated calculations or prestored lookup table of optimized control trajectories. The four-level voltage waveform significantly reduces inductor peak and rms currents under extreme voltage gain conditions, alleviating current stress and conduction losses in both the inductor and the switches. Unlike conventional modulation strategies where unequal voltage distribution is observed across the switches under varying voltage gains, the converter ensures safe operation by maintaining voltage balancing across switches and split-capacitors even under high voltage gains without requiring any additional active switches or complicated control methods. Theoretical analysis, validated through experimental results, demonstrates reduced turn-off and conduction losses, reduced transformer turns-ratio, and enhanced efficiency compared to conventional modulation techniques, particularly with significant voltage gain deviations.

This paper presents a detailed analysis and design of a coupled inductor high step-down converter for 48V-bus data centers. The proposed converter maintains the simplicity and low component count of conventional converters while extending the duty cycle and enabling soft-switching conditions for the MOSFETs. The proposed adaptive frequency control method adjusts the switching frequency proportionally to the output current to achieve Zero Current Switching (ZCS) at light loads, where VRMs operate the majority of the time. This frequency control method is compatible with state-of-the-art VRM controllers with adaptive on-time features. Furthermore, this converter is adaptable to interleaved structures with phase-shedding capability, enhancing transient performance and power density. Finally, this paper presents the steady-state analysis and experimental results of a 24W prototype.

Current-fed isolated DC-DC converters are widely studied and adopted in low-voltage high-current applications, such as photovoltaic (PV) systems, fuel cells, and energy storage systems. This is due to the advantages they provide, including low input current ripple and high step-up ratio. In high-voltage DC-DC applications or thin-film PV modules with higher maximum power point (MPP) voltage ranges, high-voltage switches are required as switches in conventional two-level dual active bridge (DAB) DC-DC converters must withstand the whole port voltage. In this paper, a three-level current-fed neutral-point-clamped (3L-CF NPC) DC-DC converter is designed and implemented, utilizing low-voltage rating MOSFETs and offering high control flexibility and low electromagnetic interference (EMI) due to the limited dv/dt. First, the operation principle, power characteristics, and current characteristics in different modes under the dual-phase shift (DPS) modulation scheme are discussed. It has been discovered that certain operating regions impose voltage stress on the primary switches under this modulation strategy. A detailed circuit analysis is presented to identify the coordinates of the safe operation region with reduced voltage stress, demonstrating the expansion of the safe operation region for 3L-CF NPC compared to 3L-voltage-fed (VF) NPC. An extensive analysis of zero-voltage switching (ZVS) conditions is performed for both primary and secondary switches to determine the soft-switching areas under various operating and design conditions. Moreover, the trajectories of control parameters, aimed at optimizing the turn-off current and RMS values of switches under different source and load conditions, are identified for the purposes of efficiency improvement. Finally, the performance of the proposed converter is verified with experimental results from a laboratory prototype, exhibiting high efficiency, voltage balancing, no voltage stress, and ZVS across various load conditions.