Concerns for global warming caused by human activity, the increasing cost and potential eventual lack of availability of oil and natural gas, even the shortage of water for hydroelectric power, have resulted in interest in cost-effective methods and materials for providing energy. Renewable energy sources, especially electricity generated by photovoltaic panels, have been of keen interest. At the present time the widespread use and installation of photovoltaic or solar panels and other solar equipment is hampered by many factors, including poor efficiency, short product life, and significant cost.
Photovoltaic panels may be expected by their makers to last at least twenty five years. However, the inverters used in today's installations require very large, high capacitance electrolytic capacitors. Existing photovoltaic panel inverter topologies use capacitance to convert photovoltaic panel diode arrays from current sources to voltage sources and for moving energy from valleys to peaks in the alternating current (“AC”) waveform. The capacitance density of existing photovoltaic panel inverter topologies requires electrolytic capacitors. Practical electrolytic capacitors are fundamentally not suitable for long life applications at high temperatures. The electrolytic capacitors in photovoltaic panels may be subjected to large temperature extremes, such as the high temperatures experienced on a building roof. These temperature extremes may shorten the effective life of the electrolytic capacitors. Additionally, the liquid in the electrolytic capacitors will eventually leak out of the canisters. Both of these short comings of electrolytic capacitors may cause the electrolytic capacitors or the entire photovoltaic panel to be replaced in as little as five years after installation. This leads to an increased lifetime total cost of ownership for a photovoltaic panel system.
Conventional Boost-Buck inverter systems used with photovoltaic panels may require substantial capacitance at the intermediate node to hold a high direct current (“DC”) voltage for the inverter to then step down to create a lower AC voltage output. A typical inverter system may consist of a boost stage, which creates a high intermediate voltage, then a buck stage that may convert that voltage back down to a regulated output. As an example, a conventional Boost-Buck inverter may boost a 30V DC voltage input from a photovoltaic panel to a 400V DC voltage, which may in turn be stepped down to create a 208V AC voltage output. The voltage boost in the example Boost-Buck inverter may require a large capacitance, such as 100-1000 microfarad (100 μF-1000 μF). This large capacitance is typically electrolytic and may present the problems discussed above in relation to electrolytic capacitors. Also, stepping the voltage up to a fixed high voltage DC bus, which may typically be higher than an output (i.e., line) peak voltage, may result in additional losses in the boost stage. Additionally, conventional inverter systems may require high speed switching of all of the phase outputs to convert the DC input to a two or three phase AC output. This switching of all the phase outputs may result in switching losses at the output.