Abstract: A multilevel converter for performing a DC to AC or an AC to DC voltage conversion as provided. The multilevel converter has a first DC terminal and a second DC terminal, a first converter arm and a second converter arm, wherein each converter arm comprises at least one converter cell, at least one AC terminal and an electric component. The first converter arm, the electric component and the second converter arm are connected in series between the first DC terminal and the second DC terminal. The electric component is connected between the first converter arm and the second converter arm.

Abstract: A method for controlling operation of a power converter is provided. The method includes determining, in a rotating dq-reference frame, a direct current error signal and a quadrature current error signal, performing a first control procedure, and performing a second control procedure. The method also includes obtaining a direct voltage control signal by subtracting a signal resulting from the second control procedure from a signal resulting from first control procedure, and obtaining a quadrature voltage control signal by adding a signal resulting from the second control procedure to a signal resulting from the first control procedure. The method includes executing a transformation from the rotating dq-reference frame to a stationary abc-reference frame based on the obtained signals, and controlling switching states of the plurality of semiconductor switches based on the signals resulting from the executed transformation from the rotating dq-reference frame to the stationary abc-reference frame.

Abstract: A multilevel converter for converting between an AC voltage and a DC voltage and a method of starting up such multilevel converter are provided. The multilevel converter has an AC terminal and a DC terminal for connecting the multilevel converter to either an AC power source or a DC power source, respectively, which supplies the voltage to be converted. The multilevel converter further comprises at least one converter leg, the DC terminal comprising a first and a second DC terminal, the converter leg comprising plural converter cells connected in series between the first and second DC terminals. The AC terminal of the multilevel converter is electrically coupled to an electrical link between two of said converter cells of said converter leg.