A drive system includes a three-phase motor having a shaft, a first three-phase stator winding which is to be connected to a three-phase AC voltage grid, a second three-phase stator winding which is to be connected to the three-phase AC voltage grid in such a way that a second stator rotating field rotating in opposition results with respect to a first stator rotating field which is generated by means of the first stator winding, and a rotor winding system which is mechanically coupled in a rotationally fixed manner to the shaft. The drive system further includes at least one inverter which is mechanically coupled in a rotationally fixed manner to the shaft and which is electrically coupled to the rotor winding system, wherein the at least one inverter is configured to generate actuation signals for the rotor winding system such that a first rotor rotating field and a second rotor rotating field rotating in opposition to the first rotor rotating field are generated. The at least one inverter is configured to generate the actuation signals for the rotor winding system solely depending on signals detected on the rotor side.

A power generation system is disclosed. The power generation system includes a doubly-fed induction generator (DFIG) coupled to a variable speed engine and a photo-voltaic (PV) power source. The DFIG includes a generator to generate a first electrical power based at least partially on an operating speed of the variable speed engine. The PV power source may supply a second electrical power to a Direct Current (DC) link between a rotor side converter and a line side converter of the DFIG. The generator and the line side converter are coupled to an electric grid and/or a local electrical load to supply the first electrical power and at least a portion of the second electrical power to the local electrical load.

Systems and methods for operating a power system having a doubly fed induction generator are provided. In example implementations, a power system can include a power converter. The power converter can include a line-side converter, a DC link, and a rotor-side converter. The rotor-side converter is configured to convert a DC power on the DC link to an AC signal for a rotor bus. The system can include a control system having one or more control devices. The one or more control devices are configured to operate the rotor-side converter in an overmodulation regime to provide the AC signal for the rotor bus

The present application provides a method of controlling an electrical power system and an apparatus using the same. The electrical power system includes a DC bus and a DC bus capacitor connected to the DC bus. The method includes: receiving a virtual DC bus capacitance value of the DC bus capacitor; detecting a DC bus voltage; calculating an expected value of a DC bus current based on the virtual DC bus capacitance value and the DC bus voltage; and adjusting the DC bus current, so that the DC bus current reaches the expected value and thus the DC bus capacitor is equivalent to the virtual DC bus capacitance value.

A method for computer-implemented controlling a doubly-fed electric machine, where stator windings are directly connected to an electrical grid and where rotor windings of a rotor are connected to the electrical grid via a power conversion system, includes an AC-to-DC converter and a DC-to-AC converter and being adapted to control a rotor current, the method including obtaining a rotational speed of the machine; determining, whether the obtained rotational speed is within a predetermined operational speed range around the synchronous speed; and if it is determined that the obtained rotational speed is within the predetermined operational speed range, controlling the AC-to-DC converter of the power conversion system to force injection of a stator reactive power to create a harmonic at a frequency different than a rated frequency of the machine; and controlling the DC-to-AC converter of the power conversion system to compensate the created stator reactive power and the harmonic.

It is described a method of determining at least one high-level limitation of a system including a doubly fed induction machine, the method comprising: receiving at least one system operation condition parameter related to the actual operation condition; calculating the high-level limitation based on at least one low-level limitation at least one component of the system and the system operation condition parameter, wherein the method is particular performed, while the system is in operation.

Methods for controlling a converter and corresponding apparatus and system are provided. The converter is configured to be connected to a rotor of a doubly-fed induction generator for feeding electrical power into an electrical grid, the converter having a machine-side inverter, a grid-side inverter, and a DC voltage intermediate circuit including a protection element for dissipating power from the DC voltage intermediate circuit. The method includes obtaining information representative of power supplied by the generator to the electrical grid exceeding a target power value beyond a predetermined threshold; and controlling the converter, in response to obtaining the information, such that the grid-side inverter supplies power to the protection element so as to dissipate power from the DC voltage intermediate circuit.

A power generation system is disclosed. The power generation system includes a doubly-fed induction generator (DFIG) coupled to a variable speed engine and a photo-voltaic (PV) power source. The DFIG includes a generator to generate a first electrical power based at least partially on an operating speed of the variable speed engine. The PV power source may supply a second electrical power to a Direct Current (DC) link between a rotor side converter and a line side converter of the DFIG. The generator and the line side converter are coupled to an electric grid and/or a local electrical load to supply the first electrical power and at least a portion of the second electrical power to the local electrical load.