An objective of the invention to provide a hybrid converter station for HVDC system and the method operating the same. The hybrid rectifier station for high voltage direct current system includes: at least one AC bus; at least one line commutated converter configured to convert a portion of AC power supplied from the at least one AC bus to DC power transmitted on HVDC transmission line of the high voltage direct current system thereby generating reactive power demand; and at least one voltage source converter; wherein: the at least one line commutated converter and the at least one voltage source converter are coupled in parallel to the HVDC transmission line; and the at least one voltage source converter is configured to compensate the reactive power demand via the parallel coupling while converting another portion of the AC power supplied from the at least one AC bus to DC power transmitted on the HVDC transmission line. By reusing the VSC supplying both of the active power for power transmission and reactive power for LCC reactive power compensation, it is helpful for raising the total active AC power rating of the HVDC transmission system without incorporating extra power conversion device or changing the design of LCC. Besides, the nominal DC voltage of LCC and VSC is the same and the power flow shifting process is not needed.

The present invention provides a bidirectional high frequency speed drive configured to connect to a utility grid and an electrical machine. The bidirectional high frequency variable speed drive comprises a plurality of inductors each configured to connect to respective phase outputs of the electrical machine, a first plurality of power switches connected to the plurality of inductors, a second plurality of power switches connected to the plurality of inductors, and a controller connected to the first and second plurality of power switches. The controller can generate control signals based on an operating status and a predetermined operating status of the electrical machine. The first output of the first plurality of power switches can be interleaved to a second output of the second plurality of power switches. The present invention also provides methods for the bidirectional high frequency speed drive and apparatuses used to perform the methods of the present invention.