Albrecht Gensior

On Some Nonlinear Current Controllers for Three-Phase Boost Rectifiers

Several flatness-based current controllers for three-phase three-wire boost rectifiers are compared. For this purpose, the flatness of a rectifier model is shown, and a trajectory planning algorithm that nominally achieves voltage regulation in finite time is given. The main focus lies on the inner loop current controllers. On one hand, linearization-based controllers using exact feedback linearization, exact feedforward linearization, and input-output linearization are discussed. On the other hand, two passivity-based approaches are compared. The first one is the energy shaping and damping injection method, and the other one uses exact tracking error dynamics passive output feedback. Furthermore, a reduced-order load observer is given, and a method that allows the prevention of invalid switching patterns is presented. The presented control algorithms are tested by simulations on a switched model.

On Differential Flatness, Trajectory Planning, Observers, and Stabilization for DC–DC Converters

Differential flatness of buck, buck-boost, and boost converter models is shown. Its benefits if used for controlling the output voltage of these converters are revealed by comparing the flatness-based control with passivity-based and linear control. Two observers for the boost converter are suggested one of which requires only the measurement of the converters output voltage. Both observers can be used with minor changes for the buck-boost converter. Two flatness-based online trajectory planning algorithms are suggested. They exploit the parametrization of the trajectories in the energy. One of them is designed to achieve fast setpoint transitions during converter start-up or despite sudden load steps while simultaneously respecting the converters physical constraints. The other one is considered for applications in power factor correction. Different stabilization strategies are compared. The viability of the observers, the algorithm, and the stabilization strategies are verified by simulations of switched nonideal converter models

A Model-Based Control Scheme for Modular Multilevel Converters

This paper deals with the modeling and nonlinear control of modular multilevel converters. Two nonlinear coordinate transformations are introduced, which lead to a compact and clear representation of the differential equations. Two candidate outputs are discussed, which lead to an internal dynamics of second or third order, respectively. Only the second candidate output is analyzed further. For the corresponding internal dynamics, the conditions which ensure boundedness are examined. A quasi-static feedback leads to a linear input-output behavior. Simulations show the usefulness of the results.

Flatness-Based Loss Optimization and Control of a Doubly Fed Induction Generator System

An electrical power circuit consisting of a doubly fed induction generator and two power-electronic converters is considered. A mathematical model is given, and the flatness of the model is shown. The freedom in the choice of one component of the flat output chosen is used in order to minimize the power losses in the system. Trajectory tracking controllers for the machine and the grid side converter are developed using a backstepping approach. The results are supported by numerical simulations.

Algebraic Parameter Identification and Asymptotic Estimation of the Load of a Boost Converter

A comparison between an algebraic parameter identification algorithm for the load of a boost converter and classical asymptotic observers for the same purpose is provided. Two asymptotic observers are presented, and an algebraic identification algorithm is derived. For the latter, two implementations in the software for a digital signal processor are discussed, and experimental results are given which highlight the properties of both approaches.

Submodule Capacitor Dimensioning for Modular Multilevel Converters

This paper deals with the dimensioning of the capacitors in modular multilevel converters based on analytical equations. Considered design parameters are the (periodic) energy fluctuation, the admissible ripple voltage, and the demand in control reserve. Design examples complete this paper.

Flatness based control of three-phase boost rectifiers

The flatness of the mathematical models of the three-phase three-wire and four-wire boost rectifiers is shown. Two trajectory planning algorithms are developed that enable fast voltage restoration after load steps by considering a load estimate. A load observer is suggested. Two tracking controllers are given. Simulations with a switched model show the value of the results

Derivation of an equivalent submodule per arm for modular multilevel converters

Modular multilevel converters (M2Cs) consist of a high number of cells per phase complicating system analysis and simulation. The present paper introduces a suitable two-terminal network for the series connection of the submodules in an arm. Furthermore, an averaged model for an M2C intended for the use with three-phase AC-loads is derived.

Analysis and Trajectory Tracking Control of a Modular Multilevel Converter

The paper presents a control scheme for modular multilevel converters (M2Cs) where the property of differential flatness of the model of the load connected to the converter is exploited. This is done by encapsulating the subsystem of the load such that it appears in the model of the converter as a current source. The controller comprises a trajectory planning algorithm and a tracking controller. This way of modeling leads to a decoupling of the controller for the load and the controller for the converter, especially for the design of the tracking controller. All developments rely on a single-phase model of an M2C, and it is shown that it shares the properties relevant for control design with the original three-phase model. All results are verified experimentally.

Feed-Forward Control of an HVDC Power Transmission Network

An efficient and well-established technology for power transmission across long distances is high voltage direct current transmission (HVDC). However, HVDC is up to now almost completely limited to peer-to-peer connections or networks with peers situated closely to each other. This contribution introduces the flatness-based design of a feedforward control of tree-like, i.e. cycle-free, HVDC transmission networks comprising two or more converter stations. The resulting control concept allows a flexible determination of the power distribution within the network. Furthermore, effects like power losses and delays due to wave propagation, which are related especially to long transmission lines, can be easily taken into account. Numerical simulations for an example network are included to prove the value of the results.