Abstract:In this paper, a two-stage three-port isolated bidirectional DC-DC converter (BDC) for hybrid energy storage system (HESS) applications in DC microgrids is proposed. It has an enlarged zero-voltage-switching (ZVS) region and reduced power circulation loss. A front-end three-phase interleaved BDC is introduced to the supercapacitor (SC) channel to compensate voltage variations of SC. Consequently, wide ZVS range and reduced circulation power loss for SC and DC bus ports are achieved under large-scale fluctuating SC voltage. Furthermore, a novel modified pulse-width-modulation (PWM) and phase-shift (PHS) hybrid control method with two phase-shift angles is proposed for BA port. And it contributes to an increasing number of switches operating in ZVS mode with varying battery (BA) voltage. Phase shift control with fixed driving frequency is applied to manage power flow. The ZVS range as well as the current stress of resonant tanks under varying port voltages is analyzed in detail. Finally, a 1 kW prototype with peak efficiency of 94.9% is built, and the theoretical analysis and control method are verified by experiments.
A two-mode resonant DC-DC converter with auxiliary switch (named as sLLC-C) has been presented. Two simple structural circuits (namely LLC and LLCC) are integrated into one topology with only two magnetic cores, through the topological transformation method. The proposed converter successfully inherits the advantages of the above two circuits, while avoiding their drawbacks as well. At the rating condition, it functions as an LLC circuit, and thus high conversion efficiency is easily obtained. The LLCC working mode is called automatically once the input voltage increases. In such a way, within a limited frequency range, the voltage gain range is effectively extended. A detailed parameter design is given to help achieve desirable performances. Finally, experiments are carried out to validate the feasibility and correctness of the proposed sLLC-C converter. The output voltage is maintained at 400 V, even if the input voltage varies in the range of 150-400 V. Besides, the preferable soft-switching characteristics are ensured for both the power switches and secondary-side diodes. The maximum efficiency of 97.3% is achieved. Thus, wide voltage gain range and high conversion efficiency are acquired simultaneously. These performances make the proposed converter well appropriate for the fuel cell generation applications.
Abstract:A high frequency dual-buck full-bridge inverter for small power renewable energy applications is proposed in this paper. The implementation of the wide band gap SiC (Silicon Carbide) power device contributes to the high switching frequency of 400 kHz. This high frequency contributes to reduced converter volume as well as improved power density, which greatly strengthens its portability and application range. For the control strategy, a voltage-current dual loop controller is employed. A three-pole-three-zero (3P3Z) compensator is applied in the current loop in order to track the current reference without static error. A voltage loop two-pole two-zero (2P2Z) compensator is used to generate the current reference for stabilizing the DC bus voltage. Not only is the inner current loop analyzed in detail, which includes the modeling of the equivalent inductor-capacitor-inductor (LCL)-type inverter and the design of the 3P3Z compensator, but also the outer voltage loop is discussed, the model of which is established based on the energy balance. Furthermore, a feedback linearization method is adopted to simplify the duty cycle calculation and helps to accelerate the control speed. A second-order generalized integrator software phase lock loop (SOGI-SPLL) is employed to obtain the phase angle and to synchronize the inverter output current with the grid voltage. A parallel structure algorithm is conducted based on a dual-core microcontroller unit (MCU) for the first time to control the high frequency inverter. This approach avoids the contradiction between the high frequency operation and the limited computing capacity of the conventional single-core MCUs. The software structure, time-consuming distribution, and interactive communication method are analyzed in detailed. Finally, this paper verifies the feasibility of the theoretical analyses through simulation and experiments based on a 1 kW prototype.
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