Active impedance-injection module enabled for distributed power flow control of high-voltage (HV) transmission lines is disclosed. The module uses transformers with multi-turn primary windings, series-connected to high-voltage power lines, to dynamically control power flow on those power lines. The insertion of the transformer multi-turn primary is by cutting the line and splicing the two ends of the winding to the ends of the cut high-voltage transmission line. The secondary winding of the transformer is connected to a control circuit and a converter/inverter circuit that is able to generate inductive and capacitive impedance based on the status of the transmission line. The module operates by extracting power from the HV transmission line with the module floating at the HV transmission-line potential. High-voltage insulators are typically used to suspend the module from transmission towers, or intermediate support structures. It may also be directly suspended from the HV transmission line.

A series compensation device suitable to double-circuit lines is disclosed. The device includes one series transformer and one converter. One converter and dual-circuit transmission lines are respectively connected to three windings of one series transformer. In the solution provided in the present application, the device can be independently installed in a power transmission system to be used as a static synchronous series compensator, and can also be used as a component of a unified power flow controller, a convertible static compensator, an interline power flow controller and a unified power quality conditioner to be connected to a power transmission system device in series. The device can save the capacity of a converter, improve the application efficiency of the series compensation device, and reduce the cost and area occupation.

A containerized power flow control system is described, for attachment to a power transmission line or substation. The system includes at least one container that is transportable by road, rail, sea or air. A plurality of identical impedance injection modules is operable while mounted in the container, wherein each of the modules is configurable to inject a pre-determined power control waveform into the power line.

A containerized power flow control system is described, for attachment to a power transmission line or substation. The system includes at least one container that is transportable by road, rail, sea or air. A plurality of identical impedance injection modules is operable while mounted in the container, wherein each of the modules is configurable to inject a pre-determined power control waveform into the power line.

Systems and methods for providing generated power to a power grid subject to active power, reactive power and voltage requirements during varying conditions. An expanded reactive follower for distributed generation including but not limited to wind power plant and solar power plants and loads of other reactive controllers; that includes at least one reactive power generator coupled to an electric power system with a distributed power plant. The reactive power generator (e.g. a rapidly switched capacitor bank with fast reinsertion resistors, or inverter based reactive power generator) is located on either side of the point of interconnection of the power plant. A reactive follower controller controls the reactive power generator on the basis of an estimated reactive power commanded by a reactive power management system for distributed generation plant (e.g. Solar, Wind, Battery, etc. . . . ).

A method can be used to control a flexible interconnection device that includes a number of converters. The method includes receiving a plurality of voltage signals indicating respective voltages of a plurality of load branches and a plurality of current signals indicating respective currents of the plurality of load branches, determining reference active power values for each of the plurality of converters based on the plurality of voltage signals and a plurality of reference voltage signals, determining reference reactive power values for each of the plurality of converters based on the plurality of voltage signals, the plurality of reference voltage signals and the plurality of current signals, and controlling the plurality of converters based on the determined reference active power values and the determined reference reactive power values.

A device for extinction angle control of a high voltage direct current (HVDC) system, includes: a converter reactive power calculator calculating a reactive power variation amount of a converter included in the HVDC system, depending on firing angle control of the converter; an alternating current (AC) system short circuit level calculator calculating a short circuit level of an AC system by applying the reactive power variation amount to a short circuit level formula of the AC system connected to the HVDC system; an extinction angle variation value calculator calculating an extinction angle variation value of the converter, corresponding to the short circuit level; and an extinction angle controller controlling an extinction angle of the converter, depending on an extinction angle control value reflecting the extinction angle variation value.

A modular power flow control system is described for optimizing power flow control in a multi-phase power transmission system. Identical impedance injection modules are arranged in an m?n matrix, where m is the number of series-connected modules inserted into each phase (forming a leg of the installed bank of modules), and n is the number of parallel-connected legs per phase. Each impedance injection module in a phase is configurable to collectively insert a pre-determined (controllable) power control waveform into the phase to which it is attached. The modular flow control system is agile with respect to configurability, reconfigurability, maintenance, size, weight, and cost.

A cascaded multi-level inverter system, a modulation method and a controller for the same are provided. The method includes performing a maximum power point tracking control based on a voltage signal and a current signal of each DC source and a voltage signal and a current signal of the power grid obtained by sampling, calculating a first modulation signal for suppressing power imbalance, and outputting the first modulation signal to each inverter unit; and calculating, based on the calculated reactive current instruction value, the calculated active current instruction value, and a current signal of the reactive compensation device obtained by sampling, a second modulation signal for causing an output power factor of the cascaded multi-level inverter system to be 1, and outputting the second modulation signal to the reactive compensation device.

A wind turbine that includes a housing, an asynchronous generator disposed in the housing and configured to be electrically connected to a power grid connection; a power converter circuit disposed in the housing and configured to be electrically connected to the asynchronous generator; and a variable impedance device disposed in the housing, connected to the generator and configured to limit current by varying impedance in response to a transient current. The wind turbine delivers reactive power to the power grid when the variable impedance device varies impedance in response to the transient current. The variable impedance device can be arranged in series between the asynchronous generator and the power grid connection, or can be in a shunt arrangement between the asynchronous generator and a neural point.