Fronius International Gmbh

Stefan Wieser

Harald Josef Kreuzer

Roland Pieler

Michael Rothböck

Christian Fasthuber

Bernhard Doppelbauer

Dietmar Striegl

Richard Grasboeck

Richard Grasböck

Wolfgang Metzner

Gerald Ritzberger

Roland Jungreithmair

Martin Wolf

Martin Mörtenhuber

Roland Lecher

Johannes Graf

Richard GRASBÖCK

Method for optimizing a maximum power point of a solar cell stack having modules, each including an MLSD unit, and an inverter. The MLSD unit shuts down the module when module voltage falls below a first voltage threshold, and switches it on, when a predefined second voltage threshold is exceeded. For optimal performance, the solar cell stack carries out: Defining, changing an electrical control parameter to a first wait value so that the second voltage threshold is exceeded exceeded; maintaining first wait value for a first time period so the modules are switched on by the MLSD units; changing electrical control parameter to a threshold value in a variation range and determining current-voltage curves for the modules in variation range; determining maximum stack power from current-voltage curves of the modules in the variation range; and predefining the determined maximum stack power as the maximum performance point.

Controlling a solar power plant

To determine an AC insulation resistance between the AC connections of an inverter and a ground potential, the AC connections are connected to an AC energy sink in an emergency standby operation in order to transmit energy from a DC energy source to an AC energy sink and an insulation test is performed in emergency standby operation. An AC fault current flowing between an AC connection and the ground potential is determined, and the AC insulation resistance is calculated from the AC fault current.

Monitoring device for emergency standby operation

In order to achieve improved single-phase operation of an inverter having a first input pole and a second input pole and including at least three phase branches, each having at least one upper power switch and at least one lower power switch connected in series to the at least one upper power switch via an output pole, a switching unit is provided. The switching unit is designed to switch the inverter from multi-phase operation to single-phase operation by closing a center point connection switch in order to connect the third output pole to the DC link center point. The switching unit is further designed, in single-phase operation, to effect a control of the upper and lower power switch of the third phase branch for symmetrizing the DC link voltages at the first and second DC link capacitors.

Inverter capable of switching between single- phase operation and three-phase operation

A switching arrangement of an inverter with a filter circuit and a grid relay. For the filter circuit use is made of an equivalent circuit consisting of effective filter inductance, from filter inductance and topology of the filter circuit and effective filter capacitance, from the filter capacitance and topology of the filter circuit. The effective filter inductance and the effective filter capacitance are system parameters. To determine system parameters, a voltage pulse is applied between a first conductor output and a second conductor output when the grid relay is open; the first conductor output and the second conductor output are connected via the switching arrangement to form a closed oscillating circuit a current value of the effective filter inductance and the effective filter capacitance is determined from a current curve and/or voltage curve in the resonant circuit as system parameters for controlling the switching arrangement.

Determination of filter parameters in an inverter

A method for operating an inverter includes applying, via a switching unit of the inverter, an AC voltage to a phase line in which a filter inductor is arranged, determining a coil current (i) of the filter inductor and determining a coil voltage (u) of the filter inductor, determining a first value (L(I)) of the filter inductor for a first value of the coil current (I), determining an inductance profile of the filter inductor with respect to the coil current, using the determined first value of the filter inductance and optionally using the at least one determined further value of the filter inductance, and controlling the switching unit of the inverter, via a control unit, to generate an alternating current in the phase line. At least one parameter of the control process is continuously adapted to the momentary coil current according to the determined current-dependent inductance profile.

Method for identifying the filter inductor of a grid inverter

In a method for operating an inverter for converting DC voltage into AC voltage, having at least one DC/DC step-up converter for converting a DC input voltage applied at the step-up converter DC input into an output voltage higher by a voltage stroke, an intermediate circuit, a DC/AC converter and an AC output for connection to a supply network and/or consumers, a voltage ripple is superimposed on the intermediate circuit voltage and in each step-up converter a switch is switched on/off with a specific switching frequency and a specific duty cycle, for measuring the output voltage of each step-up converter and the intermediate circuit voltage including the voltage ripple. A minimum voltage stroke of each step-up converter is dynamically calculated as a function of the respective measured step-up converter input voltage and the measured intermediate circuit voltage ripple, which minimizes the intermediate circuit voltage setpoint.

Method for operating an inverter and inverter for carrying out the method

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Pettenbach, Austria

Stefan Wieser