Controlling a wind turbine during a grid fault where the grid voltage drops below a nominal grid voltage. After detection of a grid fault, the total current limit for the power converter output is increased to a total maximum overload current limit. Depending on whether active or reactive current generation is prioritized, an active or reactive current reference is determined. The active current reference is determined in a way so that a reduction in active power production due to the grid voltage drop is minimized and based on the condition that the vector-sum of the active output current and the reactive output current is limited according to the total maximum overload current limit, and a maximum period of time is determined in which the power converter can be controlled based on the active/reactive current references. Afterwards the power converter is controlled based on the active and reactive current references.

Provided is a hybrid control device for a static synchronous compensator (STATCOM), the device including: a first arithmetic operation unit calculating the deviation between a reference voltage desired to be controlled by the STATCOM and output voltage to be output so as to output the same; a proportional integral (PI) controller performing PI control on the deviation output from the first arithmetic operation unit within a range between a new inductive reactive current maximum value and a new capacitive reactive current maximum value, so as to output a reactive current output value; and a second arithmetic operation unit adding the preset reactive current set value to the reactive current output value output from the PI control unit so as to output a reactive current reference value.

Distributed grid intelligence enables grid saturation control. A distributed control node can determine that a segment of the power grid exceeds a saturation threshold. A power grid can be saturated by real power when local power sources at customer premises are connected to the grid. The grid saturation threshold can be a point at which real power generation capacity of local energy sources exceeds a threshold percentage of peak real power demand for the power grid segment where the power generation capacity exists. The control node at a consumer node can dynamically adjust a ratio of real power to reactive power for the segment of the power grid as seen from the grid, and reduce grid saturation.

A method and a control system adapted to control a power conversion system connected to an AC power grid, wherein the control system is adapted to receive an externally provided reactive power reference and the control system includes a controller adapted to control the reactive power fed to the AC grid by the power conversion system and to produce a reactive current reference, an active current reference, a total current limiter for producing limited active and reactive current references. The total current limiter operates in reactive current priority limiting the active current reference. Further including means adapted to produce a capacity signal indicating the current capacity of the power conversion system. The control system further includes a minimum reactive power reference tracker adapted to generate an internally generated reactive power reference which is adapted to be fed to the controller adapted to control the reactive power fed by the power conversion system to the AC grid, where the minimum reactive power reference tracker is adapted to control the internally generated reactive power reference to a value with which the active current reference is not limited.

A load apparatus is connected to an AC power source and is supplied with power from the AC power source. An operation state control unit controls, based on a target value about a power-source quality including either a power-source power factor of the AC power source or a power-source harmonic of the AC power source and on a present power-source quality, an operation state of the load apparatus.

A plurality of active filter devices (41, 42, 43) that each have an output connected to a harmonic-generating load device (2) and are capable of generating a compensating current for performing at least one of reduction of a harmonic current of the harmonic-generating load device (2) and improvement of the power factor of the fundamental wave are provided. The plurality of active filter devices (41, 42, 43) provide two or more types of capacities, and the number and combination of operating active filter devices among the active filter devices (41, 42, 43) change in accordance with the magnitude of the compensating current.

Systems and methods for controlling wind turbines providing reactive power are provided. In particular, a method for controlling a power system that includes a controller and one or more wind turbines electrically connected to a power grid through a point of interconnection can be provided. The method can include receiving signals from a sensor associated with the wind turbines. The method can also include determining wind turbines that are operating in low wind or no wind operating conditions based, at least in part, on the one or more of the sensor signals. The method can also include determining a reactive power capability of the wind turbines operating in low wind or no wind conditions and generating control signals based, at least in part, on the reactive power capability of the wind turbines. The method can also include controlling an operational state of the wind turbines based on the control signals.

A wind turbine system (20, 70) is connected to an electrical grid (42) by an inverter (38) that provides turbine terminal voltage (Vt) support to the grid during a grid low voltage fault that is concurrent with a lack of real power production from the generator (30) by providing reactive power to the grid. A processor (46) controls the inverter to preserve a minimum voltage on a local DC bus (34) by stopping the reactive power output when the DC bus voltage drops to a threshold value (59) that is above a low bus voltage trip setpoint (56). An energy storage device (48) such as a battery may be connected to the DC bus to provide power that supports a prolonged ride-through capability during the grid fault.

A reactive power system comprises a plurality of electrical capacitor banks, with each electrical capacitor bank electrically connected in series with an electrical switch. The electrical switches may be electrically connected to a system such as, for example, an electrical induction motor starter system. A controller is coupled with the motor starter system and each of the electrical switches. The controller, in response to receiving a signal from the motor starter system, determines which of the plurality of electrical capacitor banks from which electrical power should be provided for the motor starter system. For the determined or identified electrical capacitor bank(s), the controller identifies the corresponding electrical switch(es) and communicates a signal to close the switch(es). Closing the switches results in the capacitors in the corresponding electrical capacitor banks to be electrically connected to the motor starter system and to provide current to the motor starter system.

A system and a method for locally controlling delivery of electrical power along the distribution feeder by measuring certain electricity parameters of a distribution feeder line using a substation phasor measurement unit (PMU) electrically coupled to a substation distribution bus at a first node on the feeder line, and at least one customer site PMU electrically coupled to a low voltage end of a transformer at a customer site, wherein the transformer is coupled by a drop line to a second node on the distribution feeder line and the customer site is coupled by another drop line to the transformer, and by controlling at least one controllable reactive power resource and optionally a real power resource connected to the second node or at the customer site. Related apparatus, systems, articles, and techniques are also described.