An efficient method for ripple analysis of networks with synchronized switching power converters

In present scenario, reliable operation of power converters must be ensured to enable continuous operation of large rated generating units. With respect to this aim, this paper adopts shared-leg fault tolerant operation for a 5-channel three level neutral point clamped back-to-back power converters (3L- NPC) serving to a typical 250 MW doubly-fed induction machine (DFIM) unit. Under open switch fault condition, faulty leg is identified and isolated with the help of normalized phase current average fault diagnosis method. Thereafter, grid side converter (GSC) and rotor side converter (RSC) share a common leg to deliver the required power to the rotor circuit of DFIM. For this effective operation, double zero-sequence signal is computed and injected into vector control strategy for independent control of GSC and RSC. Furthermore, shared-leg current capability, converter output voltage capability, dc-link voltage oscillations and its thermal performance are analyzed during fault tolerant operation. From the observed test results, two operating conditions are proposed: (i) reduced real power delivery by adjusting speed of hydraulic turbine and (ii) rated real power delivery by absorbing reactive power from the grid. To examine and demonstrate the proposed methodology MATLAB/Simulink2014A tool is used for a 250 MW DFIM unit. An experimental demonstration is performed with 2.2 kW DFIM unit.

A new unequal-weighted sampling method for efficient reliability analysis

Chapter 14 - Power converter solutions and controls for green energy

Under-resonant operation of an ideal multi-resonant series-parallel power converter (MRSPC) with a capacitive output filter is modeled in this paper. This operation allows zero current switching (ZCS), which is convenient for bipolar devices. The capacitive output filtering reduces the recovery effect of the rectifier diodes and is suitable for high output voltage applications. A closed-form solution is found for this power converter, based on state space analysis using energy concepts. This approach simplifies the mathematical operations and gives better physical insight of the system variables. Based on the model, the steady-state characteristics of this power converter are derived by a simulation program, which are discussed and compared with the series resonant half-bridge power converter (SRHC). The optimum power converter parameters are found for given design requirements using computerized optimization routines. Several design examples are presented and compared with SRHC. The validity of the model is verified by SPICE simulations.

An efficient contingency evaluation method for power system security analysis

In order to study the effects of large HVDC power converters on the feeding AC networks, it is of importance to explain and to calculate harmonic phenomena which are a result of power converter operation. During commissioning of real HVDC power converters, it could be seen that harmonics resulting from asymmetry in the system voltages or from asymmetry in power converter operation led to significant difficulties concerning the system design. For this reason, not only the effects of characteristics but also the effects of noncharacteristic converter harmonics must be taken into account. The aim is to describe the steady state harmonic behavior of the converter. The harmonic spectra are not determined by time domain analysis but instead the solution is found by frequency domain calculations. This can result in reduced calculation time in comparison to conventional Fourier analysis of the time functions. The power converter is interpreted as an amplitude modulator with voltage and current converter functions which describe the coupling of the DC circuit and the AC network through the power converter. To verify the theory, comparisons of frequency domain with time domain calculations were carried out. >

Deadtimes are required to avoid simultaneous conduction of high-side and low-side power transistors in half-bridge power converters. During these secure times, free-wheeling current flow generates extra power losses. Very short deadtimes are desired but they cannot be safely set in conventional isolated power converters because of a digital input propagation delay mismatch. A specific deadtime management is introduced in this paper to ensure proper operation of a high-voltage synchronous power converter. A controller integrated in each isolated gate driver secures synchronous switching by detecting the opposite switch turn-off before turn-on. With such a selfswitching technique, very short but safe nonoverlap times can be set. A gate driver has been implemented in a 0.35 μm 20-V CMOS process. The monolithically integrated controller consumes only 140 μA and 0.22 mm2 of silicon area. The proposed local deadtime management has been validated in two synchronous buck converters without external free-wheeling diodes: a 500-W 250-V to 55-V converter based on SiC JFETs and a 30-W 45-V to 10-V converter based on eGaN FETs. In either case, the proposed controller allows a higher efficiency from 10% of the rated load with resulting deadtimes as short as 15 ns.

Sleep Apnea Syndrome (SAS) has attracted considerable attention in recent years because it is known to cause catastrophes when people suffering from it fall asleep while driving. In addition, approximately 70% of SAS patients have other lifestyle-related diseases, which are further complicated owing to SAS; therefore, its early detection is important. Moreover, the detection of pre-SAS, which is likely to turn into SAS in the future, may help in the early detection of SAS. In this study, a method to identify SAS and pre-SAS using only sound data has been proposed. In the proposed method, peculiar breathing sound patterns in SAS are analyzed using the k-means clustering method and perform discriminant analysis using quantification theory based on the results. Because respiratory sound data is extensive and non-uniform during sleep, an efficient analysis method is required. The presented analysis method focuses on the features of SAS sounds, and performs the analysis almost automatically; therefore, the time required for analysis is reduced and the uniformity of the analysis results is guaranteed. Using this method, it is possible to distinguish between non-SAS and SAS symptoms including pre-SAS symptoms, which is difficult to perform using the Apnea-Hypopnea Index, which is a measure of SAS that employs breathing sound data only. Thus, this method, which also analyzes pre-SAS, is convenient for the early detection and treatment of SAS and can also be expected to contribute toward the early detection of preliminary lifestyle-related diseases.

The objective of this paper is to develop a simple method for analyzing the parameter uncertainty of the Japanese life cycle inventory database (LCI DB), termed the inventory database for environmental analysis (IDEA). The IDEA has a weakness of poor data quality because over 60% of datasets in IDEA were compiled based on secondary data (non-site-specific data sources). Three different approaches were used to estimate the uncertainty of the brown rice production dataset, including the stochastic modeling approach, the semi-quantitative DQI (Data Quality Indicator) approach, and a modification of the semi-quantitative DQI approach (including two alternative approaches for modification). The stochastic modeling approach provided the best estimate of the true mean of the sample space and its results were used as the reference for comparison with the other approaches. A simple method for the parameter uncertainty analysis of the agriculture industry DB was proposed by modifying the beta distribution parameters (endpoint range, shape parameter) in the semi-quantitative DQI approach using the results from the stochastic modeling approach. The effect of changing the beta distribution parameters in the semi-quantitative DQI approach indicated that the proposed method is an efficient method for the quantitative parameter uncertainty analysis of the brown rice production dataset in the IDEA.

The paper describes the operation of an AC-DC power converter in which the harmonic distortion in the input current is reduced using a second harmonic-injected PWM scheme. The boost power converter uses a constant switching discontinuous current mode. Expressions for the harmonic components are derived. Simulated and experimental waveforms of an AC-DC power converter are presented and the total harmonic distortion computed. >

A new bivariate dimension reduction method for efficient structural reliability analysis

The purpose of the paper is to consider the main provisions of methods of analysis of the effectiveness of public sector projects. A number of issues remain controversial in the methodology of analysing costs and benefits. So, in addition to determining the costs and benefits to be included in the analysis, one should outline the problem of assessing in the monetary equivalent of the social effects that society receives from the project implementation. Methodology. The social nature and scale of tasks that are solved in the public sector deepen the issue of identification of social effects. Discounting costs and benefits and assessing the social effect in the cost-benefit analysis involves the application of the rate of time preference. The parameters of this rate are analysed and substantiated in the study. In addition to the CBA method, an attention is paid to other methods of efficiency analysis, in particular, the method of cost-effectiveness analysis, method of weighted cost-effectiveness analysis, method of cost-utility analysis. Each method has its own specific features and limitations that determine the direction of their application. Results. It is concluded that finding solutions in the direction of studying the relationship between the social rate of intergovernmental preferences and other methods of discounting will allow us to get an idea, in which range may be the value of social discount rate. The ability to determine the range will allow taking into account the specificity of the project being implemented.

In this paper, a novel technique for current density distribution analysis of solidly modeled filamentary coil is proposed. The proposed method can totally solve the disadvantages of the conventional methods based on current vector potential formulation. The method is verified by the applications to a simple test problem and a coil of deflection yoke model.

A model is presented in this work which is capable to calculate the magnetic behavior and iron losses of a ferromagnetic lamination in a wide frequency range. It is based on an energetic hysteresis model and extends its static approach with eddy-currents in a finite-difference simulation of a lamination sheet. This will also consider the field displacement or skin-effect which cannot be ignored in the lamination sheets of electric machines especially if they are supplied from fast switching power converters. As there is no restriction with respect to the time-dependence of the exciting voltage, the presented approach can be used in machine models to predict the losses for such power converter operation and its pulse-width modulated voltages.

In this paper, an efficient method for the reliability analysis of systems with nonlinear limit states is described. It combines optimization-based and simulation-based approaches and is particularly applicable for problems with highly nonlinear and implicit limit state functions, which are difficult to solve by conventional reliability methods. The proposed method consists of two major parts. In the first part, an optimization-based method is used to search for the most probable point (MPP) on the limit state. This is achieved by using adaptive response surface approximations. In the second part, a multi-modal adaptive importance sampling method is proposed using the MPP information from the first part as the starting point. The proposed method is applied to the reliability estimation of a vehicle body-door subsystem with respect to one of the important quality issues -- the door closing effort. The superiority of the proposed method, in terms of efficiency and accuracy, is demonstrated with a numerical example of highly nonlinear limit state problem, as well as an automotive door closing effort application. A generalized framework for reliability estimation is also proposed for problems with large numbers of random variables and complicated limit states.