A first voltage source converter and converter station including such a first voltage source converter, as well as a method and computer program product for controlling the first voltage source converter are disclosed. The first voltage source converter has a DC side for connection to a DC system, has an AC side for connection to an AC system and is interconnected with an AC side of a second voltage source converter, which has a DC side connected to the DC system. The first voltage source converter includes a number of converter valve pairs, each being connected to a corresponding AC phase of the AC system and a control unit controlling the converter valves to generate at least one AC waveform and to reduce oscillations between the converters.

An active two-terminal inductor device with a controllable inducitance based on an inductance value input L_I. A processor system PRS executes an algorithm which controls a power converter PCV with controllable electric switches connected to the two external terminals A, B along with a fixed value inductor component L1. Based on sampling of at least a voltage or a current in connection with the inductor component L1, the algorithm controls the power converter PCV to provide a resulting inductance across the external terminals A, B which serves to match the inductance value input L_I.

The present disclosure relates to a method and system for evaluating a grid condition of an AC power grid. A time series of voltage and current signals of the AC power grid is captured and a local frequency of the AC power grid is identified. The time series of the voltage and current signals is transformed at the identified local frequency of the AC power grid into transformed signals. Equivalent circuit parameters are estimated from the transformed signals based on a description of an equivalent circuit of the AC power grid. A value of a grid condition indicator is determined based on the calculated equivalent circuit parameters and the identified local frequency of the AC power grid and processed in a grid monitoring system for evaluating the grid condition of the AC power grid.

A method for operating a power system connected to a power grid includes providing an active filter in the converter power path. Further, the method includes determining a change in attenuation of harmonics of the power system over a predetermined frequency spectrum that is needed to comply with one or more grid code requirements of the power grid. Thus, the method includes actively controlling, via a controller, the active filter to provide the change to the attenuation of the harmonics of the power system so as to mitigate the harmonics of the power system.

Disclosed is a method for calculating a transient overvoltage at a direct current (DC) sending end by taking into account a dynamic process of a control system. First, a first reactive power consumed by a converter station is calculated based on system operation parameters and a DC closed-loop transfer function. Then, a transient voltage change rate is calculated based on the first reactive power and a second reactive power on an alternating current (AC) side. Finally, the transient voltage change rate is iterated to obtain the transient overvoltage. According to the technical solution provided by the embodiments of the present disclosure, the transient overvoltage is determined based on the system operation parameters and the closed-loop transfer function of a DC line, the dynamic process of control parameter change caused by a control action of the control system after a fault occurs can be determined by the closed-loop transfer function of the DC line, whereby the transient overvoltage can be determined.

A device for generating electrical energy, in particular a wind turbine, having at least one generator is disclosed. The generator provides electrical energy by means of multi-phase, machine-side connection means and is connected to at least one converter having a DC link via the multi-phase, machine-side connection means. A method for operating a device for generating electrical energy, in particular a wind turbine, is also disclosed. The object of providing a device for generating electrical energy, in particular a wind turbine, which reliably avoids the development of surges despite parasitic inductances and capacitances by means of the machine-side multi-phase connection means is achieved in that means for attenuating at least one series resonance in the zero sequence of the machine-side connection means are provided between generator and converter.

This disclosure describes systems, methods, and devices related to alternating current (AC) mitigation. An AC mitigation system may comprise a conductive portion of the pipeline, wherein the conductive portion of the pipeline is adjacent to a high voltage AC power transmission line. The AC mitigation system may comprise a ground wire connected to the conductive portion of the pipeline. The AC mitigation system may comprise a circuit electrically connected to the ground wire. The AC mitigation system may comprise a means for the conductive portion of the pipeline to route AC power through the circuit.

A suppression method of high-frequency resonance for VSC-HVDC (Voltage Source Converter-High Voltage Direct Current Transmission) system based on nonlinear filter in voltage feed-forward control. It includes that the nonlinear filter is used for the voltage feed-forward link in the current inner loop control. The specific method is to extract each sequence component of the AC (Alternating Current) voltage, calculate the average value of the sequence component at N sample points, compare the current average value with the output result of nonlinear filter in the previous period, and output the result of nonlinear filter in the current period. After corrected, the result is a fixed value varying according to gradient which acts on the voltage feed-forward link of the inner loop. The invention can effectively suppress the high frequency resonance caused by impedance matching between VSC-HVDC system and grid system without losing the rapidity, and at the same time, it can adjust with AC voltage when voltage disturbance such as AC fault occurs, so as to reduce the risk of over-current of the converter valve. At present, the invention only needs to be realized in the secondary control software link without adding a new equipment, which is also low cost, no occupancy of land and convenient for engineering practice.

A method and apparatus for controlling a fault blocking voltage source converter apparatus which is, in use, connected to an AC system and a DC system for power transmission, in the event of a DC side interruption operating the voltage source converter apparatus after identification of a need for a DC side interruption based on a voltage order, so as to extract at least some electrical energy stored in the connected DC system to the voltage source converter apparatus.

A dynamic stability analysis and control method for a voltage sourced converter based high voltage direct current (VSC-HVDC) transmission system. The method includes the following steps: unlocking a converter station of the VSC-HVDC transmission system to make the VSC-HVDC transmission system run in a non-island control mode; extracting corresponding parameters of the VSC-HVDC transmission system, wherein the parameters include an effective voltage value U.sub.t0 of an AC system, an outgoing reactive power Q.sub.vsc0 of the VSC-HVDC transmission system, a gain k.sub.p of a phase-locked loop (PLL), and a proportional integral time constant k.sub.i of the PLL; calculating a short-circuit ratio (SCR), an unit value of U.sub.t0 and an unit value of Q.sub.vsc0; calculating a key stable component; checking the sign of the key stable component to determine the stability of the VSC-HVDC transmission system.