Analysis and Design of a High Efficiency Energy Regenerative Snubber Applied to a Tapped Inductor Boost Converter

High boost ratio DC-DC converters are needed for many applications such as photovoltaic inverter systems where a low voltage input is often required to be boosted by a factor of ten or more with high efficiency. To achieve this coupled inductor based converters are often studied. In addition to providing high voltage gain, these converters provide benefits compared to non-coupled designs such as reduced RMS currents and galvanic isolation. However, their use also presents challenges; in practical devices imperfect magnetic coupling between windings gives rise to stored leakage inductance energy that may resonate with stray circuit capacitances resulting in ringing and large voltage transients. This problem is amplified in high step-up converters where the magnetic device typically contains a large number of secondary turns. As secondary leakage inductance scales with n2 this often results in a substantial secondary leakage inductance. A protective snubber circuit is typically required to absorb the leakage energy. Dissipation of the leakage energy results in poor converter efficiency and overheating; a desirable snubber should recycle the absorbed energy and create favorable zero-voltage or zero-current conditions at switching instances. In this thesis, a regenerative snubber universally suitable for coupled inductor converters containing an output inductor rectifier is presented. The snubber has been applied to a tapped-inductor boost converter designed for solar MPPT/inverter applications. The converter is able to achieve a high step-up ratio with high efficiency, limit EMI, and reduce voltage stress on switching devices.