A method for determining a direct current component in an electric device that is connected to a high-voltage supply network. The method includes the following steps: acquiring operating noises of the electric device with the aid of acoustic sensors that are part of a portable unit and that provide acoustic signals at the output; breaking the acoustic signals down into their frequency components by a Fourier transformation, yielding a frequency spectrum; determining odd and even frequency components of the frequency spectrum in dependence upon a basic frequency of the high-voltage supply network and setting them in a ratio to one another; concluding that a direct current component is present if the ratio exceeds a predefined threshold value.

The invention provides a method and system for operating a solar farm inverter as a Flexible AC Transmission System (FACTS) device—a STATCOM—for voltage control. The solar farm inverter can provide voltage regulation, damping enhancement, stability improvement and other benefits provided by FACTS devices. In one embodiment, the solar farm operating as a STATCOM at night is employed to increase the connectivity of neighbouring wind farms that produce peak power at night due to high winds, but are unable to connect due to voltage regulation issues. The present invention can also operate during the day because there remains inverter capacity after real power export by the solar farm. Additional auxiliary controllers are incorporated in the solar farm inverter to enhance damping and stability, and provide other benefits provided by FACTS devices.

Method for determining parameter of a passive impedance adapter applicable to VSC-HVDC, including: S1. obtaining VSC-HVDC impedance and VSC-HVDC impedance curve X(f) based on VSC-HVDC impedance; S2. estimating upper limit value of the main capacitor in the passive impedance adapter; S3. calculating adapter parameter curve X.sub.adapter(f); S4. determining value of the main capacitor and varying value of the main resistor until min[X(f)−X.sub.adapter(f)] is maximized; determining whether min[X(f)−X.sub.adapter(f)]>k holds; S5. If min[X(f)−X.sub.adapter(f)]>k does not hold, increasing the value of the main capacitor and performing steps S2-S4 until min[X(f)−X.sub.adapter(f)]>k holds when the value of the main capacitor is within the range of the value of the main capacitor, storing the parameters in an available parameter set; S6. reducing the value of the main capacitor, and storing the parameters when min[X(f)−X.sub.adapter(f)]>k holds in the available parameter set; S7. selecting the available parameters from the available parameter set.

A control unit for an active filter for reducing resonance in an electric system is provided. The electric system comprises a power source distributing an alternating current to an AC conductor connected to a power consuming unit for distributing the AC to the power consuming unit. The active filter comprises a DC power source and a DC conductor connecting the DC power source to the AC conductor. The control unit comprises: a voltage measurement unit adapter to create a voltage signal on the basis of a measured voltage; a computing unit adapted to compute, using a biquadratic filter, a first compensating current on the basis of the voltage signal for reducing resonance in the electric system and a switching system placed between the DC power source and the DC conductor for creating the calculated first compensating current.

A hybrid inductive device includes a magnetic core and a plurality of coil windings. The magnetic core has a plurality of winding areas. The plurality of coil windings are respectively wound in the plurality of winding areas. A gap is between the coil windings in two adjacent winding areas. A winding direction of the coil winding in each of the plurality of winding areas on the magnetic core is different from winding directions of the coil windings in the adjacent winding areas on the magnetic core. The coil winding in each of the plurality of winding areas is symmetrical to the coil windings in the adjacent winding areas.

The invention provides a method and system for operating an inverter based distributed power generation source with energy storage system, as a Flexible AC Transmission System (FACTS) device—a STATCOM. The inverter based distributed power generation source can provide reactive power compensation, voltage regulation, damping enhancement, stability improvement and other benefits provided by FACTS devices. These STATCOM functions are provided when the said energy storage based distributed power generation source is doing at least one of: i) not exchanging active power with said power grid system, or ii) exchanging active power less than a maximum inverter capacity with said power grid system. The present invention thus provides a technological improvement that opens up a new set of applications and potential revenue earning opportunities for energy storage based distributed power generation sources other than simply from exchanging (injecting or absorbing) active power.

A method for constructing a general probability model of a harmonic emission level for an industrial load is provided. The method establishes, based on harmonic data monitored by a power quality monitoring system, a general probability model by combining a parametric estimation method based on a normal distribution function and a lognormal distribution function with a nonparametric estimation method represented by a kernel density estimation method, taking a degree of approximation between the general probability model and an actual probability distribution of each harmonic current as an objective function based on parameters required by the general probability model, and optimizing and solving the parameters of the proposed general probability model by using a multiplier method to determine parameters of the general probability model to finally obtain a general probability model applicable to different industrial loads.

An inverter includes an inverter circuit; an alternating current filter, where an input port of the alternating current filter is connected to an output port of the inverter circuit; an alternating current electromagnetic interference (EMI) filter; and a first alternating current switch, connected between an output port of the alternating current filter and an input port of the alternating current EMI filter. The first split capacitor is disposed between the first alternating current switch and the input port of the alternating current EMI filter; and when the first alternating current switch is turned off, the first split capacitor is disconnected from the output port of the alternating current filter, and the first split capacitor is connected to a circuit in which an alternating current system connected to the output port of the alternating current EMI filter is located, to suppress harmonic distortion of the alternating current system.

A measurement module uses harmonic compensation factors to minimize the effects of harmonic distortion in measurements of a source current by a current sensor of the module. The module samples at a first sampling rate, measurements of the source current to generate a first current measurement. The module samples at a second sampling rate higher than the first sampling rate, for an interval of time, measurements of the source current to generate a second current measurement. The module determines a harmonic compensation factor based, at least, on a difference between the first current measurement and the second current measurement. The module determines a reported current computed as a function of at least the first current measurement, the difference between the first current measurement and the second current measurement, and the harmonic compensation factor. The reported current represents a magnitude of the source current adjusted by the harmonic compensation factor.

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.