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Compared with the conventional flying capacitor (FC) multicell converters, the simplified FCMC converter family has a significantly reduced number of FCs with a much higher power density. However, such simplification results in a limited number of redundant switching states, which makes the balancing of FC voltages a very challenging task that confines their valid operation range. In this article, a modified carrier-overlapped PWM is proposed for simplified FC three-cell (SFC3C) converters with five to eight output voltage levels to achieve full modulation index and power factor range operation. For SFC3C converters operating under five to seven-level cases, where one or more degrees of switching state redundancy exist, the FC voltages are regulated by adjusting the correspondence between carriers and switches for optimal state selections. For SFC3C converters operating as a eight-level case with no redundancy, the FC voltages can be balanced naturally with the fixed relationship between the carriers and switches. An active control by dwell time adjustment is used for better regulating the FCs. Experimental results verify the validity of the proposed method.

In the future, electric vehicle (EV) charging dc–dc converter systems are usually required for realizing bidirectional operation, electric isolation, and large voltage range, which can be realized at the dc stage. However, because of unavoidable reactive power, the typical bidirectional and isolated dc–dc converters, such as dual-active-bridge (DAB) dc–dc converters and LC-based resonant dc–dc converters, usually generate large current stress at wide-range voltage. Thus, the design cost for high-power applications will inevitably be expensive. Consequently, this article, combining a three-level buck–boost stage, adopts a DAB-based two-stage dc–dc converter with a low current stress. Then, the simple control schemes, including the soft start-up method, the linear current-control-based inner loop technique, and the soft shutdown method, are proposed for the charging of EV. Especially, based on the naturally transient behavior, the linear current-control-based inner loop technique is presented with low computational burden and without instability concern. The proposed linear technique can easily and steadily realize the charging requirements such as constant current, power, and voltage charging. Besides, the presented method has no current and voltage shoots during transient process, which can significantly enhance charging reliability. Moreover, the changing rate of a charging current can be consistent and controllable to fulfill batteries’ charging requirement. Finally, experiment results are provided to verify the effectiveness of the proposed techniques.

Ice storms can cause serious damage to power distribution systems, thus the development of effective anti-icing and de-icing strategies is of great significance. In this article, an optimal anti-icing and de-icing coordinated operation scheme is proposed to enhance the resilience of distribution systems against ice storms, which is based on the ice-melting capacity of distribution lines. Firstly, a comprehensive risk analysis for anti-icing and de-icing in ice storms is provided. Then, a novel critical condition for anti-icing initiation is proposed based on the weather forecast deviation and potential load loss in distribution systems. On this basis, the coordinated optimization model for anti-icing and de-icing in distribution networks with intelligent soft open point and energy storage systems is established, aims at minimizing the overall load loss. Considering the double risk of overloading anti-icing and de-icing methods, the power flow limit violation function is used in the optimization model to reasonably allocate the proportion of various risks. Finally, the proposed method is verified in the IEEE 33-node distribution network.

Common-mode voltage (CMV) is harmful to high-power converter-fed drive systems, thus actively suppressing the CMV that is of great significance. Compared with CMV reduction, CMV elimination is a better choice as it can totally avoid the influence of CMV. In this letter, a discrete selective harmonic elimination (SHE) formulation with CMV elimination ability is proposed, which uses output voltage levels as variables to be optimized instead of switching angles as in conventional SHE models. In this formulation, the optimization objective is low-order harmonic elimination, while CMV elimination is used as a constraint. The output result is the complete full SHE- pulsewidth modulated waveform over one fundamental period, where selected low-order harmonics and CMV have both been eliminated. Experimental results verify the effectiveness of the proposed formulation, and some comparison results are also provided.

Common-mode voltage (CMV) can greatly reduce the reliability and performance of back-to-back two-level converter-fed motor drive systems. To address this issue, a novel CMV elimination scheme based on reference voltage decomposition is proposed in this article. First, the reference voltage of each phase is decomposed into two virtual reference voltages, resulting in six virtual reference voltages that are inter-related for back-to-back two-level converters. Then, by comparing each virtual reference voltage with a triangle carrier based on the two-level pulsewidth modulation (PWM), the final PWM voltage of each phase can be obtained from the differences between the corresponding two virtual PWM outputs. With the proposed method, both the amplitude and RMS value of CMV can be eliminated theoretically with satisfactory output waveform qualities. Simulations and experimental results are presented to verify the proposed method.

Combining buck, boost, or buck-boost stages, the dual-active-bridge (DAB)-based two-stage dc–dc converter is regarded as a promising solution for high-power electric vehicle (EV) charging, where wide voltage range is required. However, the design of the control system becomes more complicated because of the power coupling between the two stages. Therefore, a natural transient-behavior-based control theory is proposed for simplifying the control system of the DAB-based two-stage dc–dc converter. Expect for the EV charging, this control theory can also be used for this two-stage converter connected to other high inertia loads, where the terminal voltage is changed slowly. Under the proposed method, the DAB stage is controlled as a step-change current source. Besides, the duty ratio of the buck, boost, or buck-boost stages, which can be directly calculated by the input and output voltage, is employed to match the middle dc-link voltage and the input voltage for DAB stage. Then the dynamic response for the input current of the buck, boost, or buck-boost stages is relied on their own natural transient behavior. Crucially, based on the transient analysis, the settling time of the buck, boost, or buck-boost stage can be determined for the step change, and the control period only needs to be larger than this settling time. Moreover, since the steady state can be obtained for each control period, a reliable control performance can be obtained without general stability analysis. Finally, experiment results are provided to verify the effectiveness of the proposed theory.

High frequency and high amplitude common-mode voltage (CMV) can induce a number of problems on the reliable operations of back-to-back two-level converters, such as shaft voltages and bearing currents. To restrain the CMV for back-to-back two-level converters, a simple and effective CMV reduction method based on zero-sequence voltage (ZSV) injection is proposed in this article. By injecting the optimal amount of ZSV on either the rectifier-side or the inverter-side, the corresponding pulse overlapping areas that result in high CMV amplitudes can be eliminated with the proposed method, then the amplitude of CMV can be reduced by half, and the pulse edges of CMV can be reduced by one-third. Simulation and experimental results are presented to verify the effectiveness of the proposed method in CMV reduction, while some comparisons are also conducted to demonstrate the superiority of the proposed method.