Henry Guldner

The active NPC converter and its loss-balancing control

The three-level neutral-point-clamped voltage-source converter (NPC VSC) is widely used in high-power medium-voltage applications. The unequal loss distribution among the semiconductors is one major disadvantage of this popular topology. This paper studies the loss distribution problem of the NPC VSC and proposes the active NPC VSC to overcome this drawback. The switch states and commutations of the converter are analyzed. A loss-balancing scheme is introduced, enabling a substantially increased output power and an improved performance at zero speed, compared to the conventional NPC VSC.

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

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.

Bifurcation and statistical analysis of DC-DC converters

The paper presents a design-oriented analysis of dc-dc converters valid for both periodic and aperiodic operation. Bifurcation and statistical analysis are applied to a peak current mode controlled boost converter. The main benefit of aperiodic (chaotic) converter operation - reduction of electromagnetic interference - is discussed. Periodic and aperiodic behavior are compared. Periodic converter operation exhibits the smallest ripple waveform but the worst (purely discrete) spectrum. Aperiodic converter operation yields a broader spectrum but a larger ripple. Tradeoffs between ripple and spectrum for the practical use of chaotic dc-dc converters are suggested. The paper discusses the choice of the converters bifurcation parameter from the ripple and spectrum points of view.

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.

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

Principles of electronic ballasts for fluorescent lamps-an overview

In the lower power range, electronic ballasts represent an interesting application of power electronics. While the usable power semiconductors are relatively easy to understand, the diversity of circuit topologies, discussed in the literature, is considerably more difficult to evaluate. What further complicates the situation, is the fact that in addition to technical requirements (crest factor, power factor, EMC), cost plays the major role in this application. In this paper we present a classification for known circuit topologies and add some new ones. The classification allows one to compare different circuit topologies with respect to component count and technical performance.

Closed analytical model of a 20 kV output voltage, 800 W output power series-parallel-resonant converter with Walton Cockroft multiplier

A closed analytical model of an asymmetrically switched class D converter with series-parallel-resonant (LCC) tank and three-stage Walton Cockroft multiplier featuring output voltage adjustable from zero to 20 kV and a maximum output power of 800 W is presented. The converter circuit is briefly described. A model for the dynamic behaviour of the Walton Cockroft multiplier is developed via state space modelling in the discrete time domain, which then allows itself to be approximated as a low-pass filter with parameters that are a function of the converter operating point. The analytical model of the converter is based on the extended describing function and the generalised averaging technique. It is simulated using MATLAB and the results are compared to both simulation results using a switched model with SIMPLORER and measurements on the converter in operation. Agreements of simulated and experimental data support the models validity. The converter is controlled digitally with a Xilinx Spartan-3E FPGA.

High output voltage DC/DC converter based on parallel connection of piezoelectric transformers

In recent years, piezoelectric transformer (PT) has attracted attention in many practical applications in power electronics field. But the fact that, PT still has some drawbacks and the most issue is the limitation of transferred power. The parallel connection of PTs is introduced in this paper as a solution to the problem that mentioned above. In the experiment part, a high output voltage DC/DC converter based on parallel connection of two market-available Rosen-type PTs are built in order to verify the capable of improving the output power of PT in parallel operating