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| A Single-Phase Voltage-Source High-Frequency-Link Microinverter with Double-Line-Frequency Power Decoupling Ability |
| Li Xuewen1, Liu Jia1, Ji Fangchao1, Cao Xueqian2, Liu Jinjun1 |
1. School of Electrical Engineering Xi’an Jiaotong University Xi’an 710049 China;
2. Chint Power Systems Co. Ltd Shanghai 201600 China |
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Abstract In distributed residential photovoltaic (PV) power generation systems, microinverters have attracted significant attention due to their benefits, including component-level maximum power point tracking (MPPT), plug-and-play flexibility, and high security. However, most existing microinverters are designed for grid-connected applications and are primarily suited for single-phase two-wire systems. Additionally, the intrinsic double-line-frequency power fluctuation problem greatly limits the increase in power density and reliability of microinverters. This paper proposes a novel voltage-source high-frequency-link (HFL) microinverter with double-line-frequency power decoupling capability, which is compatible with various single-phase distribution grids.
On the primary side of the proposed microinverter, a Boost converter is integrated with the full bridge of the HFL microinverter by sharing the switches. The integration has high voltage gain and additional double- line-frequency power decoupling capability. On the secondary side, a novel structure with three-wire output is proposed to be compatible with single-phase two-wire and single-phase three-wire power systems. Due to its voltage-source-inverter (VSI) characteristics, the proposed microinverter is suitable for grid-connected and islanded applications.
This paper introduces the circuit structure of the proposed microinverter. A soft-switching modulation is proposed along with its logic implementation. Operation modes during a switching cycle and the soft-switching characteristics of each switch are analyzed. The proposed microinverter features a three-wire output, and the two phase-to-neutral output voltages are auto-balanced. Therefore, the specific balancing theory is also analyzed. The double-line-frequency power decoupling principle is presented and analyzed. To meet the required input voltage range and ensure acceptable voltage stress on switching devices, design considerations for key circuit parameters are presented, including the turns ratio of the high-frequency transformer (HFT), the average value of the decoupling capacitor voltage, the inductance of Boost inductor, and the capacitance of the decoupling capacitor.
Moreover, grid-connected and islanded closed-loop control strategies are proposed. Finally, a 600 W prototype is built to verify the proposed topology and strategies. Steady-state and dynamic test results for grid-connected and islanded operations are provided.
The following conclusions can be drawn. (1) The proposed microinverter achieves high gain and double-line-frequency power decoupling, resulting in a 22 V to 55 V wide input voltage and an MPPT efficiency above 99% with a 100μF input capacitance. (2) A special three-wire output is proposed for single-phase two-wire and single-phase three-wire distribution grids, with the two phase-to-neutral voltages auto-balanced without dedicated control. (3) The proposed microinverter operates in both grid-tied and islanded applications, and the closed-loop control strategies ensure stable steady-state operation and fast dynamic response.
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Received: 29 May 2024
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2025, Vol. 40 
