μ approach to robust stability domains in the space of parametric uncertainties for a power system with ideal CPL

Power electronic systems are prone to instability. The problem, generally attributed to the constant power load (CPL) behaviour of their power electronic controlled loads, can become more acute when the systems are subject to parametric uncertainties. The structured singular value (SSV) based method has proven to be a reliable approach for assessing the stability robustness of such uncertain systems. Despite its numerous benefits, the method is not often applied to electrical power systems (EPS) with multiple uncertainties. This may be due to the mathematical complexity underlying the theory. This work aims to make the approach more application-friendly by providing clearer insights into the meaning and usefulness of the robust stability measure for EPS with multiple parametric uncertainties. This is achieved by presenting a methodology for translating analysis results from the frequency domain to the more perceivable uncertain parameters domain. The method directly demonstrates dependences of system stability on uncertain system parameters. Further, it clearly identifies robust stability domains as subsets of the much wider stability domains. The work is based on a representative EPS connected to an ideal CPL. analysis predictions are evaluated and validated against analytical results for the example CPL system

Robust stability analysis of a dc/dc buck converter under multiple parametric uncertainties

Stability studies are a crucial part of the design of power electronic systems, especially for safety critical ap¬plications. Standard methods can guarantee stability under nominal conditions but do not take into account the multiple uncertainties that are inherent in the physical system or in the system model. These uncertainties, if unaccounted for, may lead to highly optimistic or even erroneous stability margins. The structured singular value-based method justifiably takes into account all possible uncertainties in the system. However, the application of the method to power electronic systems with multiple uncertainties is not widely discussed in the literature. This work presents practical approaches to applying the method in the robust stability analysis of such uncertain systems. Further, it reveals the significant impact of various types of parametric uncertainties on the reliability of stability assessments of power electronic systems. This is achieved by examining the robust stability margin of the dc/dc buck converter system, when it is subject to variations in system load, line resistance, operating temperature and uncertainties in the system model. The predictions are supported by time domain simulation and experimental results

Dead-time effects on the voltage spectrum of a PWM inverter

An inverter converts a direct-current power supply to an alternating-current power supply. This con- version is achieved by switching the output between the inputs at high frequency. The resulting output voltage may be described by a high-frequency train of variable-width pulses. Pulse widths are slowly modulated so that this output waveform contains a prescribed low-frequency component, which may then be isolated by an appropriate filtering regime. Techniques for determining the full harmonic spec- trum of input and output voltages and currents are well established, at least for an idealised mathematical model of the inverter. However, this model assumes that changes of inverter configuration can be ef- fected instantaneously, which is not quite the case in practice. In fact, a small amount of dead time must be incorporated into switching regimes in order to avoid short circuits of the input. Although dead time is an important feature of real power conversion devices, its effects on output voltage spectra have not previously been fully determined (except by imposing rather restrictive approximations). This situation is remedied in the present paper, in which we present closed-form expressions for the coefficients of the harmonic spectrum, corroborated by simulations

Toward robust stability of aircraft electrical power systems: using a ?-based structural singular value to analyze and ensure network stability

Transport accounts for nearly two-thirds of the global crude oil consumption and about a quarter of carbon dioxide (CO2) emissions (International Energy Agency 2009, Intergovernmental Panel on Climate Change 2014). The energy use and CO2 emissions in this sector are predicted to increase 80% by 2050 (International Energy Agency 2009). The major contributors of greenhouse effects are expected to be light-duty vehicles (43%), trucks (21%), aviation (20%), and shipping (8%) by 2050 (International Energy Agency 2009). Buses and railways are already sustainable modes of transport. To mitigate the impact of the emissions on climate change, the Intergovernmental Panel on Climate Change, which is the leading international body assessing climate change, recommends a reduction of at least 50% in global CO2 emissions by 2050 (International Energy Agency 2009). This target cannot be met unless there is a deep cut in CO2 emissions from the transportation sector. On the other hand, independent of climate policy actions, the projections are that fossil fuel reserves will become exhausted within the next 50 years. If a more sustainable future is to be achieved, the issues of greenhouse emissions and energy security must be addressed. One long-term solution may well lie in both the adoption of current best technologies and in the development of more advanced technologies, in all sectors of transportation (International Energy Agency 2009). A shift toward more efficient modes of transport, including the more electric aircraft (MEA), are not merely needed, but are required

Design considerations for high-power converters interfacing 10 MW superconducting wind power generators

The design of power electronic converters for the integration of wind generated power into the grid is more and more important due to a new class of Superconducting Generators (SG) with power ratings of up to 20 MW. High efficiency of power converters for high power applications is mandatory in order to reduce the overall cost of the system. This paper proposes a design method to minimise the cost of the system by finding the optimal number of power devices and capacitors for different high power converter topologies. The investigation focuses on determining the optimal number of voltage levels for a Back-To-Back (BTB) Neutral Point Clamped (NPC) converter. The design method is demonstrated by estimating the cost of different BTB NPC power converter topologies for the integration of a 10 MW SG to the gri

Comparison of Electromagnetic Performance of 10-MW Superconducting Generators With Different Topologies for Offshore Direct-Drive Wind Turbines

This paper compares the electromagnetic performance of 10MW superconducting (SC) generators with three different topologies, i.e., iron-cored stator and rotor (ISIRT), iron-cored stator and air-cored rotor (ISART), and air-cored stator and rotor (ASART). The objective is to provide a powerful insight into the advantages and disadvantages of the different topologies, and to establish some design guidelines for selecting an appropriate direct drive SC generator for offshore wind turbine applications. Firstly, the structures of the three SC generator topologies are introduced. Then, the influence of the SC coil cross sectional area on torque capability is compared. After that, three SC generators with different topologies are optimized respectively for further comparison, including the active material cost, weight, harmonics in the electromotive force (EMF), torque ripple, field harmonics in the SC coil, and forces on the rotor and stator components, etc. It is found that, with the same SC quantity, the torque capability of the iron-cored stator and rotor topology is much better than that of the other two topologies. However, the advantage becomes less significant when a larger area of the SC coil is employed. The air gap flux density waveform of the ASART is much smoother than those of the ISIRT and ISART. The torque ripples of the ISIRT and the ISART are much higher than that of the ASART. The field harmonics (both amplitude and frequency) in the SC coil of the ASART are the lowest. For the ISIRT, most of the force on the rotor is acting on the rotor iron, and thus, the SC coil is more likely to be safe from a mechanical performance point of view and the design of the corresponding supporting structure is simple. However, for the air-cored rotor topologies, nearly all the force is acting on the SC coil. For the air-cored stator, the force mainly acts on the armature winding, while for the iron-cored stator, it is mainly on the stator teeth. Due to the excellent mechanical performance of iron, the iron-cored stator is therefore more robust