This study proposes a high efficient bi-directional inverter for a photovoltaic (PV) system integrated with an energy storage system. The proposed bi-directional inverter controls the bi-directional power flow and satisfies the power requirement between the grid and the dc sources. The proposed bi-directional inverter achieves high efficiency by employing a transformerless structure and by minimising the power losses. The inverter structure can suppress the leakage current, which is considered to be one of the most important design parameters in a transformerless PV system. The efficiency and leakage current of the proposed bi-directional inverter are analysed. Furthermore, its bi-directional operation principles and control method are described. Finally, a 3-kW prototype is implemented to confirm the theoretical analysis and the validity of the proposed bi-directional inverter.

In this study, a single-stage half-bridge flyback converter using a synchronous rectifier (SR) is proposed to achieve unity power factor and higher efficiency. The proposed power factor correction can achieve almost a unity power factor and low input ripple current. The asymmetrical pulse-width modulation (APWM) half-bridge flyback converter operates under zero-voltage switching to reduce switching losses. The conduction loss of the system can be reduced by replacing the diode rectifier with an SR using a low on-resistance metal oxide semiconductor field effect transistor and the SR switch operates under zero-current switching. Detailed analysis is presented on the proposed converter. Experimental results for a 24 V/200 W converter at a constant switching frequency of 100 kHz were obtained to prove the analysis.

In this study, parallel operation of photovoltaic (PV) power conditioning system (PCS) modules for large-scale PV power generation is proposed. This system consists of PCS modules that are connected in parallel and share the dc-link voltage. PCS modules can be easily connected in parallel for high-power extension and independent control of the PCS module is achieved. Since this system does not use communication lines among the PCS modules, sensing signal noise and the mutual interference can be neglected. In addition, the number of PCS modules operating simultaneously can be controlled in accordance with the irradiance. Thus, system efficiency can be maximised and PCS module life time is extended. Further, the system has high availability since it has N + 1 redundancy that is achieved by increasing the power capacity of PCS modules through the use of an additional PCS module. A prototype of the proposed system is implemented at a rated power of 500 kW. Experimental results for parallel operation of PCS modules show the feasibility of the proposed control.

This study proposes a high efficient series resonant ac-dc converter. The proposed series resonant converter has a structure integrated with an ac chopper. The proposed converter provides turn-on with zero-voltage switching of all switches and performs direct power conversion without several power conversion processes. Therefore the proposed converter can achieve high efficiency by minimising losses during ac-dc power conversion. In addition, it achieves high power factor without an additional circuit. The concept and operation principle of the converter are analysed and verified. A 300 W prototype is implemented to show the performance of the proposed converter.

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