Three-level-four-quadrant frequency converter capable of suppressing direct voltage fluctuation and control method

The invention discloses a three-level-four-quadrant frequency converter capable of suppressing direct voltage fluctuation and a control method, and relate to the field of power electronics. The frequency converter adopts an IGBT power unit as a core; a power main circuit topology adopts an alternating current-direct current-alternating current structure; a three-level form is adopted, wherein thedirect-current side adopts a direct-current capacitor as an energy storage element to provide a direct current voltage for a voltage type inverter; the direct-current capacitor is in a series mode ofan upper capacitor and a lower capacitor, and the two sides of the upper capacitor and the lower capacitor are connected with a resistor in parallel separately, so that the balance control of the direct-current voltage is achieved; the three-phase alternating current power supply is filtered by an electric reactor and then passes through an IGBT rectifier circuit, so that the direct-current circuit is charged; after the en