Main circuit: "rectifier" for converting power supply into DC power, "smoothing loop" for absorbing voltage ripple generated by converter and inverter, and "inverter" for converting      DC power into AC power.  2. Rectifier: The power frequency power supply is converted into a DC power supply.  3. Smoothing loop: Suppress voltage fluctuation.  4. Inverter: Contrary to a rectifier, the inverter converts DC power into AC power of the required frequency.  5. Control circuit: The loop where the main circuit provides control signals.