1. Technical Field
The present invention relates to grid connection technology, and more particularly, to a power conversion circuit for use in a grid-connected renewable power system.
2. Description of Related Art
In theory, renewable energy is energy which comes from natural resources and is inexhaustible, such as solar power, wind power, geothermal energy, hydropower, tidal power, or biomass energy, which are derived from energy that originates in the nature. It is an important industrial development policy of technologically advanced countries to strike a balance between power generation and environmental protection, so as for human beings to achieve sustainable development on the Earth, by converting renewable energy into daily electric power efficiently and economically.
Grid connection technology plays an important role in a green renewable power system. With grid connection technology, once the power generated by a renewable power supply is not sufficient for a load, or in case of a failure of the renewable power supply, a utility power supply will start to supply power to the load. If the power generated by the renewable power supply is not sufficient for the load and thus the utility power supply has to supply power to supplement the required power, the frequency and phase of the output voltage of a converter between the renewable power supply and the utility power supply will be necessarily consistent with that of the grid power. Also, any surplus power supplied by the renewable power supply when the power requirement of the load is met will be fed back to the power plant.
Referring to FIG. 1, there is shown a rough structural schematic view of a conventional grid-connected renewable power system.
Referring to FIG. 1, a conventional grid-connected renewable power system comprises a renewable power supply 10, a power conversion circuit 20, a utility power supply 30, and a load 40.
The power conversion circuit 20 comprises a controller 24, a DC-DC converter 210, a DC-AC inverter 220, and an output circuit 230.
The DC-DC converter 210 receives renewable power generated by the renewable power supply 10 and converts the received renewable power into stable and constant direct current (DC) power. The DC-AC inverter 220 converts the DC power from the DC-DC converter 210 into alternating current (AC) power. The controller 24 controls the operation of the renewable power supply 10, the DC-DC converter 210, the DC-AC inverter 220, and the output circuit 230. Under the control of the controller 24, the output circuit 230 supplies the AC power and/or the grid power to the load 40.
With grid connection technology, the detected angular position of the AC power from the DC-AC inverter 220 and the detected angular position of a grid power serve as a key index to the efficiency thereof. Conventional angular position detection technology is based on a zero-detection circuit and a digital phase-locked loop. However, the zero-detection circuit incurs costs and is susceptible to interference to the detriment of the accuracy in angular position measurement. Although the digital phase-locked loop is advantageously characterized by short response time and high precision, it is difficult to design a controller for use with a digital phase-locked loop.