access icon free Performance optimisation of the grid-connected flyback inverter under improved hybrid conduction mode

© The Institution of Engineering and Technology
Received 09/11/2019, Accepted 16/06/2020, Revised 08/03/2020, Published 19/06/2020

In the unfolding-type interleaved two-switch flyback inverter (ILTFI) operating in discontinuous conduction mode (DCM), the hybrid control strategy combining the one-phase DCM and the two-phase DCM has a significant impact on improving the efficiency under all load conditions. In the situation where the marginal power of this control strategy is increased, the converter may enter CCM. Consequently, the converter cannot track the reference current and the output current quality is notably decreased. To tackle this issue, a novel hybrid control method is proposed which varies the switching frequency based on the output power. The proposed approach is immune to the loss analysis and power losses of the components. Hence, it is independent of components selection and their characteristics. In this case, the smooth transition between the one-phase and the two-phase operation modes is guaranteed without affecting the output power quality and the stability of the converter in DCM. The control complexity of the proposed scheme is low and the converter can be easily controlled in DCM. The performance of the flyback microinverter with the proposed hybrid control scheme is verified by the simulation and the experimental results together with the loss analysis.

Inspec keywords: invertors; photovoltaic power systems; electric current control; power grids; power supply quality; switching convertors

Other keywords: two-switch flyback converter topology; novel hybrid control method; marginal power; stable operation; performance optimisation; load conditions; wide load ranges; reference current; switching frequency; discontinuous conduction mode; improved hybrid conduction mode; low-voltage stress; continuous conduction mode; hybrid control scheme; output current quality; hybrid control strategy; one-phase DCM; power losses; control complexity; output power quality; unfolding-type interleaved two-switch flyback inverter; loss analysis; DCM mode; main switches; two-phase DCM; grid-connected flyback inverter; components selection; flyback microinverter; low-output powers; two-phase operation modes

Subjects: Current control; Solar power stations and photovoltaic power systems; DC-AC power convertors (invertors); Control of electric power systems; Power supply quality and harmonics; Power electronics, supply and supervisory circuits

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