The embodiments herein relate to a system (100) for controlling a 3-phase transformer device (101, T1, T2, T3). The system (100) comprises the 3-phase transformer device (101, T1, T2, T3) which comprises a primary side and an adjustable secondary side. The system (100) comprises at least one voltage sensor (S1, S2, S3) adapted to sense voltage at the primary side. The system (100) comprises a current sensor (S4) adapted to sense current through the adjustable secondary side, and a resistor (R1) connected in series with the current sensor (S4) at the adjustable secondary side. The system comprises a controller (103) adapted to obtain sensor data indicating the sensed voltage and the sensed current, and to control a parameter associated with the adjustable secondary side of the 3-phase transformer device (101, T1, T2, T3) based on the obtained sensor data.

The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

An apparatus having a first set of windings disposed about a first main leg of a transformer core, and a second set of windings disposed about a second main leg of the transformer core. The first set of windings are electrically coupled to the second set of windings to selectively provide a parallel connection and a series connection between the first set of windings and the second set of windings. Additionally, at least two windings of the first set of windings are electrically coupled to each other to selectively provide a parallel connection and a serial connection between the at least two windings of the first set of windings. Similarly, two windings of the second set of windings are electrically coupled to each other to selectively provide a parallel connection and a serial connection between the at least two windings of the second set of windings.

The present disclosure relates to a voltage regulation circuit (100). The voltage regulation circuit (100) comprises a transformer (130) having a primary winding (132) having a first end (132A) and a second end (132B), and a first secondary winding (134) having a first end (134A) and a second end (134B), wherein the first end (132A) of the primary winding (132) is configured to receive an input voltage and the second end (132B) of the primary winding (132) is configured to produce an output voltage, wherein the first end (134A) of the first secondary winding (134) is connected to a neutral node (180), wherein the primary winding (132) produces a primary voltage based on the input voltage, and wherein a secondary voltage of the first secondary winding (134) is out-of-phase to the primary voltage of the primary winding (132); and a first switch (160) configured to connect the second end (134B) of the first secondary winding (134) with the second end (132B) of the primary winding (132), wherein, when the first switch (160) is connected, the output voltage is the secondary voltage.

An electronic apparatus includes: an operator; and a power circuit configured to supply power to the operator, wherein the power circuit includes a first voltage converter configured to output a first voltage based on input power, and a power factor corrector (PFC) configured to output a second voltage by performing power factor correction for the first voltage, and supplies power based on the first voltage or the second voltage to the operator, wherein the power circuit stops an operation of the PFC, lowers the first voltage to have a level corresponding to the second voltage, and supplies power based on the lowered first voltage to the operator, based on power consumption of the operator lower than or equal to a predetermined value.

Disclosed are a grid-connected power conversion system and a control method thereof. The grid-connected power conversion system includes a fuel cell stack generating a DC voltage, a power conversion system (PCS) converting the DC voltage supplied from the stack into an AC voltage, a multi-input transformer including a primary coil having a plurality of voltage input terminals and a secondary coil transforming a magnitude of the voltage applied to the primary coil and outputting the transformed voltage, the plurality of voltage input terminals determining the number of turns of the primary coil differently from each other, one of the plurality of voltage input terminals receiving the AC voltage converted in the PCS, and a controller selecting the one of the plurality of voltage input terminals of the multi-input transformer based on the magnitude of the DC voltage generated from the stack and determining whether to replace the stack.

The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

The invention relates to a method for controlling a wind turbine which comprises a transformer has a variable turns ratio such as an on load tap changer transformer. The adjustment of the turns ratio is possible when a primary side current or a secondary side current of the transformer is less than a switching current threshold. The method comprises operating the wind turbine so that the primary or secondary side current is above the switching current threshold. In response to obtaining a condition for changing the turns ratio of the transformer, the wind turbine is operated so that the primary or secondary side current is reduced below the switching current threshold so that the turns ratio can be changed during the temporary current reduction.

A method for providing frequency response for a plant coupled to an electric power grid, the plant having an intermittent energy source, comprising: measuring frequency of the power output from the plant and determining a first difference between the measured frequency and a frequency reference; measuring power output from the plant and storing the measured power output as a stored value; while the first difference is within a deadband, determining a second difference as a difference between a power reference and the measured power output; while the first difference indicates over-frequency, determining the second difference as a difference between the stored value and the measured power output; while the first difference indicates under-frequency, setting the second difference equal to the power reference; generating an error by limiting a sum of the first and second differences between error limits; generating a control signal; and, applying the control signal to the source.