Abb Schweiz Ag

Abb Research Ltd.

Eidgenossische Technische Hochschule Zurich

Abb Power Grids Switzerland Ag

Tobias Geyer

Peter Muszynski

Georgios Papafotiou

Ioannis Tsoumas

Frederick Kieferndorf

Nikolaos Oikonomou

Mario Schweizer

Peter Al-Hokayem

Vedrana Spudic

Eduardo Rohr

Michail Vasiladiotis

Alexandre Christe

Hendrik Du Toit Mouton

Wim Van-Der-Merwe

Christof Gutscher

Silvia Mastellone

Manuel Vetterli

Georgios Darivianakis

Daniel Quevedo

Wim Van-der-Merwe

Annika Birth

Martinus David Dorfling

Christian Meier

Ralph Mario Burkart

Andrea Rueetschi

Manfred Morari

Petros Karamanakos

Wim Van Der Merwe

Baljit Singh Riar

Described herein is a method of operating a power electronic converter device for an electrical power conversion system. The power electronic converter device includes a converter circuit including an input side, an output side, a first converter, and at least one second converter. The second converter includes at least one floating cell with a DC intermediate circuit and semiconductor devices. The method includes: switching the semiconductor devices of the floating cell at switching instants determined with optimized pulse patterns or carrier-based pulse width modulation; determining a fundamental voltage component for the floating cell; and generating the fundamental voltage component in the actual voltage of the floating cell by modifying the switching instants, such that a voltage Vof the DC intermediate circuit is lying in a given reference voltage range for balancing the DC intermediate circuit of the floating cell.

Method for operating a power electronic converter device with floating cells

Described herein is method for controlling an electrical converter, the electrical converter converting an input voltage (v) into a multi-level output voltage (v), the method incudes: determining an optimized pule pattern (u(x)); and determining switching states from the optimized pulse pattern (u(x)) and applying the switching states to semiconductor switches of the electrical converter, such that the multi-level output voltage (v) is generated, where the optimized pulse pattern (u(x)) includes a plurality of switching transitions (Δu), each switching transition (Δu) encoding a transition between two different levels of the multi-level output voltage (v), at a switching angle (x), where the optimized pulse pattern (u(x)) is determined by optimizing a cost function, where the cost function J(x)=ΔuA(x)Δu is a cost matrix A(x), and where each entry of the cost matrix A(x) depends on polynomials into which the switching angles (x) are input.

Optimizing pulse patterns with Bernoulli polynomials

A method for controlling an electrical converter system is provided herein. The method includes determining a switching signal and a reference trajectory of at least one electrical quantity of the electrical converter system over a horizon of future sampling instants; generating a sequence of averaged switch positions from the switching signal over the horizon; determining a sequence of optimized averaged switch positions with optimized averaged switch positions by optimizing a cost function based on the sequence of averaged switch positions; determining an optimized switching signal for the current sampling interval by moving switching transitions in the switching signal, such that the average of the switching signal with the modified switching transitions equals the optimized averaged switch position; and applying at least the next switching transition of the optimized switching signal for the current sampling interval to the electrical converter system.

Model predictive pulse pattern control based on optimizing a sequence of averaged switch positions

In one embodiment, a method of operating a power electronic converter device for an electrical power converter system is provided. The power electronic converter device includes a converter circuit, a first converter, and a second converter. The first converter and the second converter are switch with a switching pattern such that the first converter and the second converter generate voltages with stepwise voltages changes and an output voltage of the power electronic converter device results from a superposition of the voltages of the first converter and the second converter. The switching pattern includes switching instants for the second converter such that the voltage of the second converter leaves the fundamental voltage component of the voltage of the first converter unchanged, such that the second converter does not generate a fundamental component of the output voltage.

Disclosed herein is a method for controlling an electrical converter system that includes: determining a nominal pulse pattern (t*, Δu*) and a reference trajectory (x*) of at least one electrical quantity of the electrical converter system over a horizon of future sampling instants, the nominal pulse pattern (t*, Δu*) comprises switching transitions (Δu*) between output voltages of an electrical converter of the electrical converter system and the reference trajectory (x*) indicates a desired future development of an electrical quantity of the converter system; determining a small-signal pulse pattern (ũ(t, λ)) by minimizing a cost function; determining a modified pulse pattern (t, Δu) by moving the switching transitions of the nominal pulse pattern (t*, Δu*) to generate modified switching transitions; and applying at least the next switching transition of the modified pulse pattern (t, Δu) to the electrical converter system.

Model predictive pulse pattern control based on small-signal pulse pattern optimization

An electrical converter includes a main converter for generating a first output voltage and a converter cell for converting the first output voltage into a second output voltage. A method for operating an electrical converter includes: receiving a reference voltage for the electrical converter; pulse width modulating the reference voltage with a first modulation frequency for generating a first switching signal for the main converter; switching the main converter with the first switching signal to generate the first output voltage; estimating the first output voltage from the first switching signal; determining a voltage error by subtracting the estimated first output voltage from the reference voltage; pulse width modulating the voltage error with a second modulation frequency, which is higher than the first modulation frequency, for generating a further switching signal for the converter cell; and switching the converter cell with the further switching signal to generate the second output voltage.

Cascaded pulse width modulation converter control

A method for controlling a three-phase electrical converter includes selecting a three-phase optimized pulse pattern from a table of pre-computed optimized pulse patterns based on a reference flux. The method includes determining a two-component optimal flux from the optimized pulse pattern and a one-component optimal third variable. The method includes determining a two-component flux error from a difference of the optimal flux and an estimated flux estimated based on measurements in the electrical converter. A one-component third variable error is determined from a difference of the optimal third variable and an estimated third variable. The optimized pulse pattern is modified by time-shifting switching instants of the optimized pulse pattern such that a cost function depending on the time-shifts is minimized. The method includes applying the modified optimized pulse pattern to the electrical converter.

Model predictive control of a converter based on pulse width modulated switching patterns

Systems, methods, techniques and apparatuses of power converters are disclosed. One exemplary embodiment is a method of controlling and modulating a converter with a controller including forming a mathematical representation of the electrical system including the converter, providing reference values for controlled variables, calculating gradients of controlled variables based on the mathematical representation of the electrical system, determining possible switching sequences in the modulation period, the switching sequence defining the order in which the switches are switched, for each possible switching sequence, minimizing the error between the provided references and the corresponding controlled variables based on the calculated gradients by optimizing the switching time instants of the switching sequence, selecting the switching sequence with the smallest error, and applying the switching sequence with the corresponding switching times in the modulation period to modulate the controllable switches.

Power converter operation using a model predictive controller

A method for controlling a converter system includes: determining, with a first controller stage, an output voltage reference for the converter system; generating, with the first controller stage, switching commands for a main converter based on the output voltage reference, such that the main converter converts an input voltage into an intermediate voltage provided at an output of the main converter and following the output voltage reference; and generating, with a second controller stage, switching commands for a floating converter cell connected to the output of the main converter, such that the floating converter cell converts the intermediate voltage into an output voltage provided at an output of the floating converter cell, wherein the floating converter cell comprises a cell capacitor and a semiconductor switch arrangement for connecting and disconnecting the cell capacitor between the output of the main converter and the output of the floating converter cell.

Two stage control of converter system with floating cells

A method of decoupled modulation of a direct AC/AC MMC between a first AC network L having a first waveform and a second AC network R having a second waveform includes performing first and second modulations based on respective reference signals of the first and second AC networks to generate, for each phase leg, first and second integer command signals corresponding to first and second combinations of cell states in the branches of the phase leg needed for generating the first and second waveforms. The method also includes, based on the first and second integer command signals, mapping to each branch a number of cell states to be used for concurrently generating both the first and second waveforms.

Modulation of AC/AC MMC

In a method of controlling a DC-to-AC Modular Multilevel Converter (MMC) having a three-phase AC side connected to a three-phase AC network and having a DC side connected to a DC network, the MMC has a double-star topology with a plurality of phase-legs. Each phase-leg has a first branch and a second branch. Each of the first and second branches includes a plurality of series connected converter cells. The method includes obtaining an Optimized Pulse Pattern (OPP) for the MMC. The method also includes adapting the OPP to the MMC by means of closed-loop pulse pattern control. The method also includes, based on the adapted OPP, sending firing signals to the plurality of cells of each branch.

Control of DC-to-AC modular multilevel converter

A method for controlling a three-phase electrical converter comprises: selecting a three-phase optimized pulse pattern from a table of pre-computed optimized pulse patterns based on a reference flux; determining a two-component optimal flux from the optimized pulse pattern and determine a one-component optimal third variable; determining a two-component flux error from a difference of the optimal flux and an estimated flux estimated based on measurements in the electrical converter; determining a one-component third variable error from a difference of the optimal third variable and an estimated third variable; modifying the optimized pulse pattern by time-shifting switching instants of the optimized pulse pattern such that a cost function depending on the time-shifts is minimized, wherein the cost function comprises a flux error term and a third variable error term, wherein the flux error term is based on a difference of the flux error and a flux correction function providing a flux correction based on the time-shifts and the third variable error term is based on a difference of the third variable error and a third variable correction function providing a third variable correction based on the time-shifts; and applying the modified optimized pulse pattern to the electrical converter.

Controlling a three-phase electrical converter

A method for operating an electrical converter including: determining an optimized pulse pattern from a fundamental voltage reference for the electrical converter, wherein the optimized pulse pattern is determined from a first lookup table and includes discrete voltage amplitude values changing at predefined switching instants; determining a harmonic content reference from the fundamental voltage reference based on a second lookup table, wherein the harmonic content reference is a harmonic current reference determined from the frequency spectrum of a current of the electrical converter or the harmonic content reference is a filtered voltage reference determined by applying a first order frequency filter to a voltage, which current or voltage is generated, when the optimized pulse pattern is applied to the electrical converter; determining a harmonic content error from the harmonic content reference by subtracting an estimated output voltage and/or estimated output current of the electrical converter from the harmonic content reference; modifying the optimized pulse pattern by timeshifting switching instants such that the fundamental voltage reference is tracked and the harmonic content error is corrected by the timeshifted switching instants; applying the modified optimized pulse pattern to semiconductor switches of the electrical converter.

Control of electrical converter based on optimized pulse patterns

A method for controlling a modular converter connected to an electrical grid for active power filtering the electrical grid to compensate for a load connected to the electrical grid, comprises: receiving an actual load current and an actual converter state of the modular converter; determining, from the actual load current and a history of previous load currents, a sequence of future load currents over a prediction horizon; predicting a sequence of future converter states of the modular converter and a sequence of manipulated variables for the modular converter over the prediction horizon by solving an optimization problem based on the actual converter state and the future load currents by minimizing an objective function mapping control objectives to a scalar performance index subject to the dynamical evolution of a prediction model of the modular converter and subject to constraints; and applying a next switching state, which is determined from a first element of the sequence of manipulated variables, to the modular converter.

Model predictive control of a modular multilevel converter

An electrical converter is interconnected via a filter with an electrical load or an electrical power source. A method for controlling the converter comprises the steps of: receiving a reference flux (&#x3c8;*) for the electrical converter; determining output signals (y) comprising currents and/or voltages measured in the filter; determining an estimated flux (&#x3c8;) from the output signals (y); determining a corrective flux (&#x3c8;) from the output signals (y) based on a mathematical model of the filter and a quadratic cost function; determining control input signals (u) for the electrical converter based on a sum of the estimated flux (&#x3c8;) and the corrective flux (&#x3c8;); controlling the converter with the control input signals (u); and algorithmic filtering of at least one of the output signals (y) by applying a signal filter to the at least one output signal, which is designed for amplifying the at least one output signal at a resonance frequency of the filter, whereby the corrective flux (&#x3c8;) is determined from the filtered output signals.

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Zurich, Switzerland

Tobias Geyer