Abstract: An energy storage system and a method for controlling such a system is disclosed. The energy storage system comprises a plurality of interconnected energy storage cells forming an energy storage module, a power converter connected to the energy storage module, a resistor circuit connected in parallel to the energy storage module, a switch connected in series with the resistor circuit and configured to disconnect the resistor circuit from the energy storage module, and a control unit operably connected to the switch. The control unit is configured to receive information pertaining to a transmission of energy in the energy storage system and to control the switch based on said information.

Abstract: A method can be used to control a voltage source converter of a power supporting arrangement to act as a virtual synchronous machine. The method includes obtaining a measured power level of the converter, processing the measured power level using a differential equation of an angular velocity of the virtual synchronous machine in order to obtain a control contribution, providing a phase angle of a physical quantity used to control the converter based on the control contribution, monitoring the ability of the converter to act as a virtual synchronous machine, determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient, and adjusting the control contribution by increasing the damping term and/or decreasing the moment of inertia term in response to determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient.

Abstract: A power supporting arrangement includes a DC network having a first DC line with a first DC potential, a second DC line with a second DC potential, and an energy storage system that includes a first energy storage unit connected in a branch between the first and the second DC lines. A first group of phase arms is connected in a wye-configuration between the power grid and the first DC line and a second group of phase arms connected in a wye-configuration between the power grid and the second DC line. The first and second groups of phase arms are controllable as a voltage source converter. A third group of phase arms is connected to the power grid in a wye-configuration. The third group of phase arms have a neutral point and being controllable to support the power grid with reactive power.

Abstract: A method can be used to control a voltage source converter of a power supporting arrangement to act as a virtual synchronous machine. The method includes obtaining a measured power level of the converter, processing the measured power level using a differential equation of an angular velocity of the virtual synchronous machine in order to obtain a control contribution, providing a phase angle of a physical quantity used to control the converter based on the control contribution, monitoring the ability of the converter to act as a virtual synchronous machine, determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient, and adjusting the control contribution by increasing the damping term and/or decreasing the moment of inertia term in response to determining that the ability of the converter to act as a virtual synchronous machine is deemed insufficient.

Abstract: A power supporting arrangement for a power grid includes a first and a second voltage source converter with an AC side and a DC side. A DC link interconnects the DC sides of the voltage source converters. A first switching arrangement includes a number of settable positions. The AC side of the second voltage source converter is connected to the power grid and the first switching arrangement is connected between a first synchronous machine. The AC side of the first voltage source converter and the power grid and operable to selectively connect the first synchronous machine to the power grid or to the AC side of the first voltage source converter.

Abstract: A method of providing power support to an electrical power grid is provided. The power support is provided by an arrangement including a synchronous machine connected to a converter, the converter in turn being connected to the electrical power grid. The method is performed in a control device controlling the arrangement and includes: receiving feedback from one or both of the electrical power grid and the synchronous machine, and controlling the converter such that power support is provided to or absorbed from the electrical power grid by means of the synchronous machine based on the received feedback. A control device, arrangement, computer program and computer program products are also provided.

Abstract: A method for voltage control of a static synchronous compensator, STATCOM, or a static var compensator, SVC, is presented. The method is performed in a control device. The method includes obtaining a synchronous condenser, SC, error, obtaining a STATCOM or SVC voltage setpoint, adjusting the obtained STATCOM or SVC voltage setpoint with the obtained SC error to a total STATCOM or SVC voltage reference, and providing the total STATCOM or SVC voltage reference for voltage control of the STATCOM or SVC. A control device and a computer program for voltage control of a STATCOM or an SVC are also presented.

Abstract: A method of providing power support to an electrical power grid is provided. The power support is provided by an arrangement including a synchronous machine connected to a converter, the converter in turn being connected to the electrical power grid. The method is performed in a control device controlling the arrangement and includes: receiving feedback from one or both of the electrical power grid and the synchronous machine, and controlling the converter such that power support is provided to or absorbed from the electrical power grid by means of the synchronous machine based on the received feedback. A control device, arrangement, computer program and computer program products are also provided.

Abstract: An electrical chain-link converter system includes a converter phase leg for converting a plurality of DC electrical currents from a plurality of DC power sources to an AC current of an electrical power distribution network. The phase leg includes a plurality of serially connected converter cells each of which is connected to a respective power source of the plurality of DC power sources. The system also includes a control unit associated with the phase leg, the control unit including a processor; and a storage unit storing instructions that, when executed by the processor, cause the control unit to, for each of the converter cells: obtain a dedicated voltage reference for the converter cell; and transmit the voltage reference to the converter cell.

Abstract: A method for controlling a modular multilevel converter to reduce the lower order harmonics generated by the converter is provided. The method may also reduce the overall switching loss of the converter by switching the switches close to fundamental switching frequencies while still reducing the lower order harmonics that are generated.

Abstract: A method for reducing lower order harmonics of a power converter includes, for each phase leg of the converter: obtaining a voltage reference for the phase leg; for a present sample, obtaining a flux error of the output voltage of the leg; dividing the first sample flux error by a time period to obtain an average voltage error over said time period; subtracting an obtained processed average voltage error, based on the average voltage error, from the voltage reference to obtain a modified voltage reference for the phase leg; and providing the modified voltage reference to a modulation unit of the converter for controlling the phase leg.

Abstract: A method for reducing lower order harmonics of a multi-level power converter includes at least one phase leg including a plurality of chain-link connected cells each including a capacitor.

Abstract: A method for reducing lower order harmonics of a power converter includes, for each phase leg of the converter: obtaining a voltage reference for the phase leg; for a present sample, obtaining a flux error of the output voltage of the leg; dividing the first sample flux error by a time period to obtain an average voltage error over said time period; subtracting an obtained processed average voltage error, based on the average voltage error, from the voltage reference to obtain a modified voltage reference for the phase leg; and providing the modified voltage reference to a modulation unit of the converter for controlling the phase leg.

Abstract: A method is performed in a control device for controlling a power compensation arrangement including a voltage source converter and one or more power compensation branches, each power compensation branch including a thyristor controlled reactor, a thyristor switched reactor or a thyristor controlled capacitor. The voltage source converter and the one or more power compensation branches are connected to a same busbar. The method includes: detecting a request in an electrical power system to which the power compensation arrangement is connected; determining, based on the request, a need for reactive power supply to the electrical power system; providing reactive power by means of the voltage source converter and/or by one or more of the power compensation branches; and compensating, by means of the voltage source converter, any disturbances caused by the power compensation branches when providing the reactive power to the electrical power system. Corresponding devices are also disclosed.

Abstract: A method for controlling a chain-link power converter including three phase legs, each of which phase legs includes a plurality of series-connected converter cells, each of the cells including a DC capacitor, the phase legs being connected in a delta configuration. The method includes detecting an unsymmetrical voltage condition at a terminal of the converter; determining a ratio between a zero sequence and a negative sequence component of a compound current to be injected into the converter, based on the detected unsymmetrical voltage condition; calculating the compound current comprising the zero sequence component and the negative sequence component in accordance with the determined ratio; and injecting the compound current into the converter to control the converter in view of the detected unsymmetrical voltage condition.

Abstract: An apparatus and a method for filtering harmonics in a power transmission contact line of a railway system includes a multilevel converter multilevel converter having one single phase leg, which phase leg comprises switching cells, each switching cell comprises semi-conductor switches arranged to selectively provide a connection to a corresponding energy storage element. The multilevel converter also includes a controller provided to control the switching of each switching cell, and wherein the phase leg is configured in two parallel branches of cascaded switching cells, which branches is interconnected in a closed circuit. The controller is provided to monitor the content of harmonics in the contact line, and is adapted to filter the monitored harmonics by means of adapting the switching of the switching cells to absorb the harmonics.

Abstract: A method is performed in a control device for controlling a power compensation arrangement including a voltage source converter and one or more power compensation branches, each power compensation branch including a thyristor controlled reactor, a thyristor switched reactor or a thyristor controlled capacitor. The voltage source converter and the one or more power compensation branches are connected to a same busbar. The method includes: detecting a request in an electrical power system to which the power compensation arrangement is connected; determining, based on the request, a need for reactive power supply to the electrical power system; providing reactive power by means of the voltage source converter and/or by one or more of the power compensation branches; and compensating, by means of the voltage source converter, any disturbances caused by the power compensation branches when providing the reactive power to the electrical power system. Corresponding devices are also disclosed.

Abstract: A method for controlling a chain-link power converter including three phase legs, each of which phase legs includes a plurality of series-connected converter cells, each of the cells including a DC capacitor, the phase legs being connected in a delta configuration. The method includes detecting an unsymmetrical voltage condition at a terminal of the converter; determining a ratio between a zero sequence and a negative sequence component of a compound current to be injected into the converter, based on the detected unsymmetrical voltage condition; calculating the compound current comprising the zero sequence component and the negative sequence component in accordance with the determined ratio; and injecting the compound current into the converter to control the converter in view of the detected unsymmetrical voltage condition.

Abstract: The invention relates to methods and devices for controlling unbalanced active power flow in a three-phase modular multilevel converter 20. The converter 20 comprises a first and second converter 4, 5 both comprising three phase legs arranged in a wye-connection. The first and second converters 4, 5 are interconnected in a double-wye connection, and their neutral paths are independently floating.

Abstract: A method in a controller for protection of a voltage source converter including one or more phases, each phase including one or more series-connected converter cells. Each converter cell has a by-pass switch for enabling by-pass thereof. The method includes the steps of detecting an over-voltage condition, and controlling simultaneously the by-pass switches of each converter cell, so as to bypass the converter cells upon detection of such over-voltage condition. The invention also encompasses a controller, computer programs and computer program products.