In general, the integral sliding mode control (ISMC) with an integral sliding surface would lead to tracking errors under unbalanced and harmonic grid voltage conditions. In order to eliminate tracking errors under these conditions, multi-resonant items are added to the conventional integral sliding surface in the proposed strategy, which can be called multi-resonant-based sliding mode control (MRSMC). A comparison of tracking precision on the ISMC and MRSMC is analyzed. In order to regulate the system powers directly, the errors of instantaneous active and reactive powers are selected as the state variables. Finally, the output current harmonics and a majority of the doubly-fed induction generator’s (DFIG) electromagnetic torque pulsations can be removed under unbalanced and harmonic grid voltage conditions. Simulation and experimental results are presented to verify the correctness and effectiveness of the proposed strategy.

An active grid impedance cancellator using the concept of series active filter to suppress the effect of the grid disturbance and stabilize the single-phase grid-connected inverters with an LCL filter operating under variable grid conditions is presented. Harmonic interaction between the inverter and the grid is thereby avoided owing to the cancellation of equivalent grid impedance. More importantly, the impedance cancellator offers an active damping function to ease the heavy burden of the inverter control, such as power control, phase locked loop, current regulation, impedance shaping, etc. The impedance cancellator is a full-bridge dc-ac converter having no passive inductive-capacitive (LC) filter. It is connected in series with the inverter output and is operated as a negative virtual grid impedance. As the VA rating of the impedance cancellator is low, the efficiency of the entire system is not sacrificed. Starting with the impedance-based analytical modeling method, the basic principle of equivalent grid impedance cancellator is derived and studied. Then, the digital control strategy and the modeling of equivalent grid impedance cancellator are examined. The experimental results of a prototype cancellator for a single-phase inverter is favorably compared with theoretical predictions.

Dual active bridge (DAB) converter is one of the most popular bidirectional isolated dc/dc converters. Comparing with the two-level DAB converter, the multilevel DAB topologies take advantages of providing more control degrees of freedom to enhance the control flexibility. Therefore, these topologies are promising alternatives for wide voltage range applications. This article proposed an optimizing modulation strategy for neutral-point-clamped hybrid three-level dual active bridge (NH3L-DAB) converter to minimize the rms value of inductor current and the conduction losses. First, the basic operating principle of NH3L-DAB is analyzed comprehensively in the article. Afterward, the concept of global optimal condition is employed to derive the optimal modulation, and the corresponding analytical expressions of the control coordinates for rms current minimization are derived. By applying the optimal modulation strategy, NH3L-DAB facilitates to break the performance barriers of the prior-of-art of two-level DAB converter when the voltage transmission ratio has large variation. Finally, a bidirectional prototype with 200–450 V input and 20–28.8 V output is built to demonstrate the superior performance of the proposed optimal modulation strategy, and the detailed explanation of the experimental results is given as well.

Due to the quick development of wide bandgap power devices, the power density of the converters is expected to be much higher. In order to increase the power density and efficiency of the DAB converter, especially the efficiency under light load, a quasi-optimal current root-mean-square (RMS) control strategy to achieve All-ZVS is proposed by taking the inductor RMS current optimization algorithm into account in this paper. First the constraint conditions for realizing ZVS of all switching devices under different operating modes are concluded by analyzing the switching mode and the working principle of the DAB converter under the triple phase shift (TPS) modulation. The ZVS domain for All-ZVS operation in each operating mode is further obtained. Then, the GOC strategy is combined with the ZVS condition to derive the novel modulation for all operating modes. Based on this scheme, the switching conditions of all switches can be improved, and the efficiency of the DAB system under the light load is optimized. With ZVS operation, the switching frequency can be raised. Finally, a GaN HEMT based prototype of DAB converter was built and the switching frequency is 200kHz, the effectiveness of the proposed modulation scheme was verified by the experimental results.

Interleaved parallel cascaded multilevel technology is an attractive approach for converters to achieve high efficiency, high-power density, and high modularity. In this letter, a novel single-phase interleaved parallel cascaded three-level (IPC-TL) power factor correction (PFC) converter is proposed. It is formed by cascading two interleaved parallel totem-pole PFC cells. The proposed topology exhibits the merits of lower inductance volt-second and inductor current ripples, lower common-mode noise, and lower control cost, compared with the traditional IPC-TL topology. A laboratory-scale experimental prototype is developed to verify the effectiveness of the proposed topology.

In this paper, the primary-side regulation (PSR) technique to achieve accurate output current in LLC resonant converter has been studied. A novel PSR control scheme for LLC LED driver based on “magnetizing current cancellation method” is proposed. The proposed “magnetizing current cancellation method” can effectively eliminate the effect of magnetizing current in the sampled primary resonant current under both continuous conduction mode (CCM) and discontinuous conduction mode (DCM). Thus, the accurate output current can be estimated on the primary side of LLC resonant converter. The magnetizing current cancellation method for the LLC LED driver with symmetric primary resonant current and asymmetric primary resonant current has been analyzed in detail. Some design considerations have also been presented. After that, a LLC PSR control circuit has been designed out based on the theoretic analysis. Finally, a 48V-78V/1.3A laboratory prototype for LED driver has been built up and experimental results show that good output current regulation has been obtained.