Sma Solar Technology Ag

Vitali Sakschewski

Stijn Stevens

Daniel Premm

Yehia Tarek Fawzy

Christian Hardt

Thorsten Buelo

Christian Tschendel

Karel De Brabandere

Lars Cramer

Florian Rauscher

Premm Daniel

The disclosure relates to a method and related device for approximately determining voltages at a high-voltage side of a transformer on the basis of measured voltages at a low-voltage side of the transformer. The method includes measuring delta voltages and phase voltages and phase angles at the low-voltage side of the transformer, transforming the phase voltages and phase angles into positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the low-voltage side, determining positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the high-voltage side from the positive and negative phase sequence system voltages and phase angles of the positive and negative phase sequence systems, respectively, at the low-voltage side, determining estimated values of a zero phase sequence system voltage and of a phase angle of a zero phase sequence system at the high-voltage side from the measured delta voltages and phase voltages and phase angles at the low-voltage side, and transforming the positive, negative and zero phase sequence system voltages and the phase angles into phase voltages and/or delta voltages at the high-voltage side of the transformer.

Method and device for approximately determining voltages at a high-voltage side of a transformer

A method and associated apparatus for feeding electric power from a photovoltaic system via a grid connection point into an AC grid having a low short-circuit power is disclosed. The method includes connecting a DC voltage side of at least one first inverter of the photovoltaic system to a photovoltaic generator and an AC voltage side of the at least one first inverter to the grid connection point, wherein the at least one first inverter is operated as a current source, and connecting an AC voltage side of a second inverter of the photovoltaic system to the grid connection point, wherein the second inverter is operated as a voltage source based on measurement values of an AC voltage measured in the region of the photovoltaic system and a predefined characteristic curve. For a first total short-circuit power of all first inverters operated as a current source, and a second total short-circuit power of the AC grid and of the second inverter operated as a voltage source, a ratio of the second total short-circuit power to the first total short-circuit power is greater than or equal to 2.

Feeding electric power from a photovoltaic system into an AC system having a low short-circuit capacity

In order to control a plurality of inverters, which are connected on their input side to a current source each and on their output side to a common grid connection point, electrical variables are measured at the individual inverters and are used for controlling the individual inverters, currents being output by the individual inverters depending on the electrical variables measured at the location of the individual inverters Effects of the connection equipment between the individual inverters and the common grid connection point on currents are determined, electrical variables being measured at the grid connection point and are set in relation to the electrical variables measured at the same time at the individual inverters. The connection equipment between the individual inverters and the common grid connection point is taken into consideration in controlling the individual inverters.

Control of a plurality of inverters connected to a common grid connection point

The disclosure relates to a detection method for an inverter for detecting a grid fault in a power supply grid, includes determining a grid impedance (Z) and/or the rate of change thereof with respect to time (dZ/dt) and/or a rate of change of an absolute value of the grid impedance (Z) with respect to time (d|Z|/dt), comparing the absolute value and/or a real part and/or an imaginary part of the grid impedance (Z) and/or the rate of change thereof with respect to time (dZ/dt) and/or the rate of change of the absolute value of the grid impedance (Z) with respect to time (d|Z|/dt) with respective predetermined limit values. The method also includes detecting a grid fault state based on the comparison, wherein a distinction is drawn between an islanding situation (AID) and a fault ride through (FRT) situation, and signaling an existing islanding situation (AID) or a fault ride through (FRT) situation as a grid fault state. The disclosure additionally relates to an inverter that is arranged to perform the method.

Inverter and detection method for an inverter for detecting a network fault

A method for operating an inverter which is connected to an energy supply grid via a transformer for feeding in electrical energy into the energy supply grid, includes measuring output currents and output voltages of the inverter, and actuating power switches of the inverter using actuation signals that are generated as a function of the measured output currents and the measured output voltages at a fundamental frequency of the energy supply grid. The actuation signals are further generated as a function of a harmonic component of the measured output voltages of the inverter at a multiple of the fundamental frequency using a control loop with positive feedback.

Inverter and operating method for an inverter

A method for grid support by means of an inverter is disclosed, wherein the grid is supported by feeding in compensation currents. The method includes measuring a prevailing grid state, and breaking down voltages measured for measuring the prevailing grid state into symmetrical components of the grid state including positive sequence system components and negative sequence system components. The method further includes determining symmetrical components of a compensation current including positive sequence system components and negative sequence system components of the compensation current as functions of deviations of the positive sequence system components and negative sequence system components of the grid state from reference values, and feeding-in a compensation current as the vector sum of the determined symmetrical components of the compensation current.

Growing community of inventors

Fuldabrueck, Germany

Vitali Sakschewski