For the high-power Li-Ion battery (LIB) Formation and Grading System using multi-stage conversion structure, bidirectional isolated DC-DC converter with high input voltage and large output current is needed to achieve isolation and relatively fixed voltage conversion gain. This paper proposes a modulation strategy and modifies the topology to achieve naturally bidirectional power transfer, automatic power sharing and power limitation for an Input-series-output-parallel (ISOP) LLC-DCX converter. Firstly, an active Pulse Width Modulation (PWM) strategy is proposed to avoid synchronous rectifier (SR) sensing and to achieve the nature bidirectional power flow for each sub-module. The resonant current always keeps discontinuous, and the conversion gain can keep constant if ignoring the conduction resistance. Secondly, clamping diodes are added in the conventional LLC converter to limit the inrush current during start-up, and to achieve constant power limitation under over load condition. Thirdly, with the proposed modulation, the power sharing of two-module ISOP LLC converter is analyzed and compared with the conventional ISOP LLC converter. Finally, experiments based on an 8kW (output:15V/533A) prototype composed of two-module ISOP LLC converter are conducted to verify the effectiveness of the proposed solution.

This letter presents a transformerless single-phase PV inverter, which combines with common-ground and active power decoupling techniques. The leakage current is eliminated and bulky electrolytic capacitors are removed, thus improving the system safety and reliability. In addition, it needs only four switches and can be implemented conveniently by a commercial H-bridge module. The validity of the inverter is verified with a 2-kW prototype.

Leakage current and Electro-Magnetic Interference (EMI) are closely related to the common-mode (CM) circuit in transformer-less photovoltaic (PV) inverter systems. However, the correlation between them is elusive, as they are always studied independently because of the different frequency bands involved. This paper establishes the CM circuit models of the current source inverter (CSI), and the inherent relationship and the affecting factors between leakage current and CM EMI are revealed. Based on the established models, the leakage current and conducted EMI are accurately predicted with reduced computational burden. In addition, some suppression measures for leakage current and CM EMI are derived, including the effectiveness of connecting neutral wire. Finally, by simulations and experiments, the correctness of the theoretical analysis is verified.

The brushless doubly fed induction machine (BDFM) has great potential in the wind energy generation system because it offers the advantages of higher reliability and maintenance-free operation. In this paper, a mathematical model in the power windings stator flux orientation frame is discussed by taking the rotor flux as the disturbance. Consequently, the control of the BDFM system is implemented by generating suitable control winding currents. Moreover, in order to eliminate the speed error and compensate the system uncertainties caused by the rotor flux and parameter perturbations, an integral sliding mode variable structure controller for the rotor speed is developed, and the reactive power is adjusted by a proportional-integral (PI) controller in the outer-loop. Furthermore, the control winding currents are regulated by the PI control scheme in the inner-loop. The proposed control frame achieves a good static and satisfactory dynamic control performance. Finally, simulation and experimental results are used to verify the correctness and feasibility of the proposed method.

Photovoltaic (PV) micro-inverter converts the DC from a PV panel to AC directly, which has the advantages of improved energy harvesting, friendly “plug-and-play” operation, enhanced flexibility/expandability, excellent system redundancy and no DC cabling/safety issue, therefore it is an attractive solution for grid-connected PV system. In AC PV module applications, the features like power density, reliability, efficiency and reactive power capability are essential for the micro-inverters. In order to overcome the drawbacks of the conventional micro-inverters including the power density/reliability issues caused by the bulky input capacitors and the limited output reactive power capability, a three-phase micro-inverter without energy storage capacitors is proposed in this paper. The proposed micro-inverter consists of a flyback stage, a third-harmonic injection circuit and a line-commutated current-source type inverter. The flyback stage realizes maximum power point tracking, while the third-harmonic injection circuit is responsible for output power factor correction. In addition to having the potential of achieving compact structure, long lifetime and high efficiency, the developed micro-inverter provides extended output reactive power control range and three-phase balanced output. Finally, the proposed topology and method are verified by simulations and experimental results.