A method for feeding electric power into an electrical supply grid by means of a local feed unit. The feed unit is connected to a grid link point connected to a transformer point directly or via a supply connection. The transformer point is connected to a grid section via a transformer. The method includes feeding electrical real power into the electrical supply grid at the grid link point, feeding electrical reactive power into the electrical supply grid at the grid link point, detecting a change to be made in the real power to be fed in, and changing the fed-in real power in accordance with the detected change to be made. The method includes limiting a change in the fed-in reactive power over time when changing the fed-in real power and/or immediately thereafter or temporarily activating voltage control on the basis of the change in the fed-in real power.

An apparatus for a load tap changer includes a first primary winding electrically connected to a first contact, the first contact configured to connect to one of a plurality of taps in a load tap changer; a second contact, the second contact configured to connect to one of the plurality of taps in the load tap changer; a magnetic core; and a control circuit including: a secondary winding configured to magnetically couple to the first primary winding and the magnetic core; and an electrical network electrically connected to the secondary winding, the electrical network being configured to prevent magnetic saturation of the magnetic core during switching of the first or second contact.

A method and apparatus for minimizing circulating currents on a power distribution line. In one embodiment, the method comprises dynamically adjusting a turns ratio of a tap changing transformer, the tap changing transformer coupled to a power grid distribution line that is also coupled to a plurality of microgrid branches wherein at least one microgrid branch of the plurality of microgrid branches comprises a distributed energy resource (DER), based on a reactive power measured locally to the tap changing transformer, to minimize current circulating on the power grid distribution line.

Embodiments of the present disclosure can include a hybrid transformer system comprising an electrical voltage transformer comprising: a high-voltage winding, the high-voltage winding comprising a first end and a second end, the first end having a lower voltage than the second end; a plurality of taps disposed proximate the first end of the high-voltage winding; a multi-level converter coupleable to the plurality of taps of the electrical voltage transformer, the multi-level converter configured to simultaneously control voltage injection and VAR injection to the high-voltage winding of the electrical voltage transformer; and a controller electrically coupleable to the multi-level converter, such that when the multi-level converter is coupled to the plurality of taps of the electrical voltage transformer, the controller is configured to selectively inject at least one of VARs or voltage to the high-voltage winding of the electrical voltage transformer.

A system may include a transformer that converts a first voltage to a second voltage, such that the second voltage is output via a conductor. The system may also include a wireless current sensor that may detect current data associated with current conducting via the conductor. The system may also include a processor that may receive the current data, determine a voltage at a location on the conductor based on the current data and an impedance associated with the conductor, and send a signal to a load tap changer in response to the voltage being different from an expected voltage at the location.

The invention relates to a method for controlling a wind turbine configured with an on load tap changer transformer which enables adjustment of a current ratio of a primary side current of the transformer and a secondary side current of the transformer. The method comprises detecting that a network voltage on the primary side or secondary side of the transformer is outside a pre-determined voltage range, and in response determining a current reference for the primary side current based on the detected network voltage. The power converter of the wind turbine is controlled to generate an increase of the primary side current towards the current reference, and the current ratio of the transformer is adjusted towards a higher ratio of the current ratio.

System for providing electrical power to wind turbine components comprising a busbar, an electrical grid, and an auxiliary power source for selectively providing electrical power to the busbar with an auxiliary power voltage, wherein the main voltage is different from the auxiliary power voltage. The system includes one or more wind turbines comprising a wind turbine generator, a main transformer for connecting the wind turbine generator to the busbar, one or more wind turbine components, and an auxiliary wind turbine transformer. The wind turbine components are arranged to be selectively connected to the main transformer and the busbar through a first path or a second path. The system is configured to select the first path if the voltage at the busbar is the main voltage and to select the second path if the voltage at the busbar is the auxiliary power voltage.

In a three-phase, four-wire electrical distribution system, a zig-zag transformer and at least one Cascade Multilevel Modular Inverter (CMMI) is coupled between the distribution system and the neutral. A controller modulates the states of the H-bridges in the CMMI to build an AC waveform. The voltage is chosen by the controller in order to control an equivalent impedance that draws an appropriate neutral current through the zig-zag transformer. This neutral current is generally chosen to cancel the neutral current sensed in the line. In other embodiments, the chosen neutral current may be based on a remotely sensed imbalance, rather than on a local value, determined by the power utility as a critical load point in the system. The desired injection current is then translated by the controller into a desired zero-sequence reactive impedance, based on measurement of the local terminal voltage, allowing the controller to regulate the current without generating or consuming real power. In some embodiments, the zig-zag transformer is omitted.

A method and apparatus for minimizing circulating currents on a power distribution line. In one embodiment, the method comprises dynamically adjusting a turns ratio of a tap changing transformer, the tap changing transformer coupled to a power grid distribution line that is also coupled to a plurality of microgrid branches wherein at least one microgrid branch of the plurality of microgrid branches comprises a distributed energy resource (DER), based on a reactive power measured locally to the tap changing transformer, to minimize current circulating on the power grid distribution line.

An apparatus for a load tap changer includes a first primary winding electrically connected to a first contact, the first contact configured to connect to one of a plurality of taps in a load tap changer; a second contact, the second contact configured to connect to one of the plurality of taps in the load tap changer; a magnetic core; and a control circuit including: a secondary winding configured to magnetically couple to the first primary winding and the magnetic core; and an electrical network electrically connected to the secondary winding, the electrical network being configured to prevent magnetic saturation of the magnetic core during switching of the first or second contact.