A voltage drop Vz.sub.s is calculated based on an output current detection value Iac and a virtual synchronous impedance Zs or a corrected virtual synchronous impedance Zs′, and a value obtained by subtracting the voltage drop Vz.sub.s from an internal induced voltage Ef is output as a grid voltage command value Vac*. Zs calculation unit 7 limits an output current phase θ so that the output current phase θ is within an effective range by a phase limiter 12a, and calculates the corrected virtual synchronous impedance Zs′ based on a limited output current phase θ, the internal induced voltage Ef, a grid voltage detection value Vac and a current limit value Ilim. Accordingly, in grid interconnection power conversion device that controls a virtual synchronous generator, it is possible to continue operation while suppressing an overcurrent and possess a synchronizing power generated by action or working of a virtual synchronous impedance.

A method for evaluating resonance stability of a flexible direct current (DC) transmission system in an offshore wind farm includes: establishing an s-domain equivalent circuit of a flexible DC transmission system in an offshore wind farm, constructing an s-domain node admittance matrix of the flexible DC transmission system in the offshore wind farm, determining a resonant mode of the system based on a zero root of a determinant of the node admittance matrix, and determining stability of the system. In the method, an s-domain impedance model is used to describe dynamic characteristics of a wind turbine, a flexible DC converter, and other power devices, avoiding coupling between device modeling and an operation mode of the system. In addition, the node admittance matrix is used for analysis so as to fully consider a plurality of power electronic devices and a grid structure of the offshore wind farm, realizing comprehensive analysis.

A method for evaluating resonance stability of a flexible direct current (DC) transmission system in an offshore wind farm includes: establishing an s-domain equivalent circuit of a flexible DC transmission system in an offshore wind farm, constructing an s-domain node admittance matrix of the flexible DC transmission system in the offshore wind farm, determining a resonant mode of the system based on a zero root of a determinant of the node admittance matrix, and determining stability of the system. In the method, an s-domain impedance model is used to describe dynamic characteristics of a wind turbine, a flexible DC converter, and other power devices, avoiding coupling between device modeling and an operation mode of the system. In addition, the node admittance matrix is used for analysis so as to fully consider a plurality of power electronic devices and a grid structure of the offshore wind farm, realizing comprehensive analysis.

The application relates to an oscillation active damping control method and system for grid-tied type-4 wind turbine generator. The method comprises: based on an interconnection model of multiple subsystems, constructing a stored energy function and a dissipated energy function of a current inner loop control subsystem, and interaction energy functions between the current inner loop control subsystem and other subsystems are constructed, then establishing an energy feedback model of Type-4 wind turbine generator; when the oscillation occurs, obtaining instantaneous angular frequency of the PLL, and then based on the energy feedback model, adjusting the current reference value of the q-axis current inner loop generated by the reactive power outer loop control subsystem, to make the stored energy function decrease with time, so as to suppress the oscillation.

Methods include, in response to a line frequency variation of a power grid, adjusting a voltage setpoint of a voltage regulator coupled to the power grid at a grid edge to maintain a voltage at the grid edge, wherein the adjusting the regulated voltage setpoint is configured to reduce the line frequency variation to stabilize the line frequency of the power grid. Apparatus include a voltage regulator configured to couple to a power grid at a grid edge and to maintain a voltage at the grid edge, wherein the voltage regulator is further configured to adjust a voltage setpoint of a voltage regulator in response to a line frequency variation of the power grid to reduce the line frequency variation and stabilize the line frequency of the power grid.

Protection system for limiting the impact of disruptions of an external urban or industrial electrical network on a local electrical network of a site which is connected to the external network and which includes at least one local electric power source, referred to as “local source” connected to the local network and capable of injecting the surplus electric power into the external network, with the protection system including a synchronous machine connected to the local network which is itself connected to the external network by way of a choke, referred to as “network choke.” The protection system includes at least a local choke which is associated with the local source and which is connected to the local network between this local source and the synchronous machine.

Protection system for limiting the impact of disruptions of an external urban or industrial electrical network on a local electrical network of a site which is connected to the external network and which includes at least one local electric power source, referred to as “local source” connected to the local network and capable of injecting the surplus electric power into the external network, with the protection system including a synchronous machine connected to the local network which is itself connected to the external network by way of a choke, referred to as “network choke.” The protection system includes at least a local choke which is associated with the local source and which is connected to the local network between this local source and the synchronous machine.

A method identifies asymmetrical vibrations during the operation of an electric device which is connected to a high-voltage grid. Vibrations of the electric device are detected using vibration sensors which provide measured values on the output side. The measured values and/or values derived from the measured values are transmitted to a communication unit via a close-range communication connection. The measured values and/or the values are transmitted by the communication unit to a data processing cloud via a far-range communication connection. The measured values are separated into frequency components by the data processing cloud using a Fourier transformation, thereby obtaining a frequency spectrum. Odd and even frequency components of the frequency spectrum are ascertained based on a base frequency of the high-voltage supply grid and put into a ratio R relative to one another. The presence of asymmetrical vibrations is indicated if the ratio R exceeds a specified threshold.

A method identifies asymmetrical vibrations during the operation of an electric device which is connected to a high-voltage grid. Vibrations of the electric device are detected using vibration sensors which provide measured values on the output side. The measured values and/or values derived from the measured values are transmitted to a communication unit via a close-range communication connection. The measured values and/or the values are transmitted by the communication unit to a data processing cloud via a far-range communication connection. The measured values are separated into frequency components by the data processing cloud using a Fourier transformation, thereby obtaining a frequency spectrum. Odd and even frequency components of the frequency spectrum are ascertained based on a base frequency of the high-voltage supply grid and put into a ratio R relative to one another. The presence of asymmetrical vibrations is indicated if the ratio R exceeds a specified threshold.

A method and a system for evaluating inertia of a power system and a storage medium. The method includes: injecting a cosine active power disturbance into the power system by small-disturbance injection, and obtaining frequency response at a node where the disturbance is injected, where the active power disturbance can be an energy storage, wind power, or photovoltaic power; acquiring an evaluation framework of inertia and frequency regulation capability of the power system according to relative characteristics of a frequency response function; and constructing a mathematical relationship between the impedance and frequency response characteristics according to a relationship among active power disturbance, frequency fluctuation and impedance.