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This study proposes a design procedure and experimental validation for a robust H2 state feedback controller applied to a DC-DC boost converter modelled as a linear system affected by time-varying parameters lying in known intervals. The parameters considered as time-varying are the input voltage, the load resistance and the operating point duty cycle. A polytopic representation of the system is derived and the controller is designed by means of a convex optimisation problem based on linear matrix inequalities. The conventional H2 controller is extended to cope with alpha-stability and robust linear quadratic regulator design, providing different strategies to trade-off the magnitude of the control gains and the response of the closed-loop system. Tight correspondences between numerical simulations and the experimental results prove the viability of the application of this technique for this kind of plant. Finally, a robust performance analysis illustrates the capacity of the closed-loop system to reject energy bounded disturbances, with interpretation for the cases of time-varying and time-invariant parameters. [ABSTRACT FROM AUTHOR]

This study develops a generalised pulse width modulation (PWM) approach to eliminate both the low-frequency oscillations and imbalances in the dc-link capacitor voltages, which are the main drawbacks of diode clamped converters. The algorithm has been developed within the carrier-based PWM framework to facilitate its implementation in diode clamped converters with four or more levels. In addition, a generalised control strategy for dc voltage control is proposed and its stability is demonstrated. The good performance of the proposed modulation technique is demonstrated from simulation and experimental results for a four-level diode-clamped inverter. [ABSTRACT FROM AUTHOR]

This study presents an efficient method for estimating transient stability indices of electric power systems. It is based on equivalent network reduction techniques. The electromechanical equivalent system has been accomplished by considering clusters of coherent generators. The angular speed deviations of synchronous generators have been used as a criterion to perform the groups. The reduced order is obtained by replacing two groups of coherent generators by a single machine equivalent. With these equivalents, critical fault clearing times and security margins are calculated by using the well-known equal-area criterion. The method was compared with others, especially those based on the concepts of transient energy function. The critical fault clearing times are in agreement with and very close to those obtained by using Liapunov's direct method or the time-domain solution of the n-machine original system. Some numerical results are presented for a 3- and 10-generator power systems. The method is an excellent tool that can be applied as a filter to identify potentially harmful contingencies and to select these to perform detailed transient stability analysis. [ABSTRACT FROM AUTHOR]

Single- and three-phase synchronisation methods based on optimum filtering theory are proposed. These methods are based mainly on the Kalman filter and are therefore termed Kalman filter-phase locked loop. They explicitly include in the problem formulation the presence of harmonics, voltage unbalance, measurement noise, transients and frequency deviation. Such perturbations degrade the performance of many synchronisation structures presented in literature. The formulation presented here makes the synchronisation signals less sensitive to these perturbations. It is also shown that the proposed methods can be helpful by also providing the amplitude, instantaneous phase and frequency of grid voltages that can be useful for the analysis of power quality. Furthermore, the Kalman filter provides a way of obtaining the best compromise between transient response and measurement noise rejection for the synchronisation signals. The paper sets out the development of the proposed methods together with the choice of tuning parameters and their physical meaning. Simulations and experimental results using a DSP TMS320F2812 are presented to show the effectiveness of the proposed schemes. [ABSTRACT FROM AUTHOR]

A new open-loop synchronisation method for three-phase PWM converters connected to the utility grid is proposed, which gives good performance under distorted and highly unbalanced grid voltages. Moreover, it has a better performance in terms of distortion in the synchronisation signals when compared with other open-loop methods. It has a good transient performance for frequency, phase and amplitude disturbances when compared with closed-loop methods. In addition, a frequency adaptation algorithm is proposed for applications where large frequency variations are expected, such as in weak grids. Experimental results using a DSP TMS320F2812 are given to demonstrate the good performance of the proposed synchronisation method. [ABSTRACT FROM AUTHOR]

The paper presents a systematised and generalised methodology of second-order output filter for inverters that synthetise sinusoidal voltage waveforms through space-vector pulse-width modulation (PWM). The objective of this methodology is to determine the largest natural frequency of the filter that ensures specification of the maximum total harmonic distortion (THD) admissible in the output voltages of the PWM inverter. The proposed methodology is discussed in detail, including the description of the steps needed to derive the design procedure for different topologies of voltage inverters, and the procedure for obtaining the design curves. To illustrate the use of the proposed methodology, detailed design procedures are given for single-phase, three-phase three-wire and three-phase four-wire filter topologies. Finally, examples are presented which include experimental results demonstrating the validity of the proposed design methodology. [ABSTRACT FROM AUTHOR]

A new digital voltage controller is proposed, derived in agreement with the internal model principle for three-phase inverters with ΔY transformer at the output. A dynamic model of the inverter, transformer, filter and load in stationary α–β co-ordinates is derived and a decoupling method is proposed. The proposed digital controller is not prone to amplify DC components, which can lead to output transformer saturation. Additionally, this digital controller results in a simple form and is well suited for fixed-point implementation. Experimental results, implemented in a 16-bit DSP controller, validate the theoretical developments and demonstrate the good steady-state performance of the proposed controller under both nonlinear balanced and unbalanced loads. [ABSTRACT FROM AUTHOR]

Operation modes of zero-voltage transition (ZVT) PWM converters with resonant auxiliary circuit (RAC) are identified and analysed by means of a common topology. A novel stateplane approach is used to determine the soft-switching boundary for this sort of converter. A unified design criterion, based on the analytical definition of the soft-switching boundary, is described in detail. By means of the proposed criterion the time spent on repetitive numerical simulation of a given topology to define its design guidelines based on a set of particular features can be significantly reduced. The theoretical analysis is confirmed by means of experimental results obtained from ZVT-PWM boost converters, which operate at 1 kW, 100 kHz. [ABSTRACT FROM AUTHOR]

Presents a family of zero voltage transition (ZVT) DC-DC PWM converters which uses a series resonant L-C network connected in series with the auxilliary switch, called a self-cummulated auxilliary network. Simple and reliable means of achieving ZCS conditions to auxilliary switch commutations for wide line and load ranges; Analysis of the improved ZVT PWM boost converter.

Proposes two novel limiting algorithms for three-phase four-leg voltage source inverters to constrain the command vector inside the polyhedron defined by the boundaries of the inverter linear operating range. Use of an inscribed ellipsoid on the polyhedron; Development of the algorithm based on the polyhedron boundary planes.