typical renewable energy system has multiple parts operating in diff erent voltage domains. At one end of the system are the power sources, such as solar panels, wind turbine generators, and batteries. The primary power sources – solar panels and wind generators – typically include some form of power conditioning. In the case of solar panels, this conditioning includes a DC-DC converter to smooth out the illumination-dependent raw DC voltage from the panels as well as maximum power point tracking circuitry to match the load on the panels to their output level. For wind turbines a rectifier and DC-DC converter combination turns the generator’s variable AC into a stable DC voltage.
Because the battery pack is a secondary power source, capable of storing and delivering energy, its connection to the DC Link is more complex than that of the primary sources. The battery charge controller must control the voltage and current it delivers when charging the battery as well as condition the power the system draws from the battery. Current sensing of both the AC power the inverter is delivering as well as the DC power the primary sources are delivering determines which way and how much energy flows through the battery charge controller.
The conditioning allows the power sources share a common connection called the DC Link to drive the inverter that supplies standard AC power to the household. The inverter may also feed energy back into the power grid when system’s energy generation exceeds the local demand. To maximize efficiency in generating grid-compatible AC voltages, home alternative energy systems typically utilize a DC Link voltage of 600 V to 1200 V.
Inverters in a home alternative energy system typically handle from 1 kW to 30 kW and create 1 or 3-phase AC power. They operate by switching the DC Link voltage at a frequency around 50 kHz under pulse-width modulation control. To handle this switching frequency as well as the high currents and voltages involved in AC power, inverters typically use insulated gate bipolar transistor switches.
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