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UBC Theses and Dissertations

A novel step-up/step-down full-bridge DC-DC converter for distributed solar power applications Cao, Yu


Among the many renewable energy sources, solar power is becoming one of the quickest to be adopted due to continuous technological progress and reductions in cost. Today's typical photovoltaic modules that are connected together in series and parallel to form strings and sub-arrays. Various distributed photovoltaic architectures are introduced in this thesis and DC-DC converters with maximum power point tracking are also introduced. Partial power processing is a technique to allow only a fraction of the power to be processed by the DC-DC converter, thereby reducing losses and improving efficiency. A new partial power isolated DC-DC converter is proposed in this thesis. The converter features maximum power point tracking and its controller selectively engages the buck portion or the boost portion or both in response to the maximum power point tracking input signal to achieve the desired output voltage and maximum power. With series connected DC-DC converters, each DC-DC converter carries an equal string current and adjusts its output voltage proportional to the available power of the connected photovoltaic module. The proposed topology allows each photovoltaic module to operate at its own maximum power point under varying or mismatched solar irradiance conditions, yet keep the total DC string voltage constant. The proposed circuit is verified using PLECS simulation software. In comparison to the existing circuit with partial power processing method, the proposed circuit overcomes the disadvantage that the output voltage can only be greater than the input voltage. With the two metal oxide semi-conductor field effect transistors added in series with the diodes in the secondary side of the transformer, the new circuit operates at a 100kHZ switching frequency and is able to perform both step up and step down modes with a properly designed control block. As a result, the circuit can convert a voltage from a PV panel that is higher or lower than the output to a regulated DC output voltage.

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Attribution-NonCommercial-NoDerivs 2.5 Canada