Le Nhat Hoang Tran, Laurent Gerbaud, Nicolas Retière and Hieu Nguyen Huu
Static converters generate current harmonics in power grids. For numerous studies, analytical frequency modeling is preferred to carry out their harmonic modeling in the context…
Abstract
Purpose
Static converters generate current harmonics in power grids. For numerous studies, analytical frequency modeling is preferred to carry out their harmonic modeling in the context of sizing by optimization. However, a design by optimization has to consider other constraints, e.g. modeling constraints and operating constraints. In this way, this paper aims to focus on applying an analytical frequency modeling on the sizing by optimization of an aircraft electrical power channel.
Design/methodology/approach
The paper aims to size a multiphysical system by optimization. In this way, the sizing of an aircraft electrical power channel by optimization has been carried out. The models of all the channel components are analytical. Specifically, the frequency model of the power electronics is based on Tran et al. (2016) and is made of equalities and inequalities. Due to this modeling choice, the optimization satisfies hundreds of constraints, such as modeling constraints and static converter operating constraints. Furthermore, transient constraints are only verified after optimization.
Findings
The difficulty is the modeling of the system by taking into account nonlinear implicit equations having several solutions. A solution is the addition of inequality constraints to the model to guide the implicit solving. Furthermore, this greatly helps the optimization algorithm to find the good operating mode of the static converter, at steady state. This aspect is indispensable to validate the sizing model.
Research limitations/implications
The number of the configurations per operating period of the static converters is defined a priori and limited.
Originality/value
The analytical model for the sizing is formulated as a constrained optimization problem. Its solving and the sizing by optimization are carried out by the same optimization algorithm.
Details
Keywords
Olivier Bossi, julien pouget, Nicolas Retiere and Laurent Gerbaud
Due to the increase of the traffic, issues are appearing on DC electrified railway feeding systems. One candidate solution to solve these issues and to improve their performances…
Abstract
Purpose
Due to the increase of the traffic, issues are appearing on DC electrified railway feeding systems. One candidate solution to solve these issues and to improve their performances is to add storage systems in the railway DC electrical network. The paper presents a method based on an Optimal Power Flow (OPF) for the analysis and design of DC railway feeding systems with storage.
Design/methodology/approach
The paper describes a new methodology based on optimization to study DC electrified railways, including storage systems. A load flow model of a DC 1500V railway electrification system is presented, including the mobility of the train sets. Then, an Optimal Power Flow model of the DC network, including energy storage systems and feeding substation rectifiers has been developed. Finally, the OPF model has been tested on a real application case showing its benefits while searching solutions in order to improve the network performances.
Findings
An OPF model suitable for analysis of DC networks with storage is presented. It shows its ability to solve large scale problems.
Research limitations/implications
The paper focuses on the physical model of the network. The optimization model will have to be extended with application constraints.
Originality/value
The hypothesis presented in this paper allows to remove the discontinuities of the system in order to use a continuous optimization approach.
Le Nhat Hoang Tran, Laurent Gerbaud, Nicolas Retiere and H. Nguyen Huu
Static converters generate current harmonics in grids. Numerous studies on analytical frequency models of converters are often required to carry out their harmonic modeling in the…
Abstract
Purpose
Static converters generate current harmonics in grids. Numerous studies on analytical frequency models of converters are often required to carry out their harmonic modeling in the context of sizing by optimization. Some formulations are proposed to solve such models. Each formulation has its own advantages and drawbacks. The paper mainly focuses on two formulations: the first to be solved by Sequential Quadratic Programming (SQP) and the second to be solved by Newton-Raphson (NR). In this way, the paper presents the performances of each formulation and compares the results of both formulations for the modeling of a single-phase diode rectifier.
Design/methodology/approach
The paper aims to compare SQP formulation and NR formulation, and to propose the ways to improve their convergence. In the modeling, by using an explicit formulation of the state variables combined to a numerical method, equations are defined to reduce, as far as possible, the number of unknowns.
Findings
The difficulty is to find the good operating mode of the static converter. So, outside the equations and the constraints, the paper proposes to use the eigenvalues of the state space matrixes to initialize the duration of every configuration and to consider the operating symmetries of the static converter that allow to reduce the research area and also the variables calculated.
Research limitations/implications
The number of the conducting phase per half period is a priori, as the operating mode.
Originality/value
The modeling is based on the use of linear components, ideal switches and the static converter operates in steady-state. The main difficulties are to formulate the equations representing the non-controlled switching of semiconductors, and to solve them.
Following the ‘Sarkozy’ era (2007–2012), France has engaged in ‘zero-tolerance’ policies, which have brought an increasing number of people into the criminal justice system (CJS)…
Abstract
Following the ‘Sarkozy’ era (2007–2012), France has engaged in ‘zero-tolerance’ policies, which have brought an increasing number of people into the criminal justice system (CJS). In an already extremely impoverished CJS, these policies have led to serious financial problems and have made an already existing prison overcrowding problem worse. Consequently, the CJS has gradually opted for a McDonald (Ritzer, 2019; Robinson, 2019) type of offender processing, whether in prosecutor-led procedures (representing roughly half of all penal procedures: Ministry of Justice, 2019) or in the sentencing phase (Danet, 2013). A similar trend has been found in probation and in prisoner release (in French: ‘sentences’ management).
The prison and probation services, which merged in 1999, have since then been in a position to benefit from the 1958 French Republic Constitution, which places the executive in a dominant position and notably allows it to draft the bills presented to a rather passive legislative power (Rousseau, 2007) and even to enjoy its own set of normative powers (‘autonomous decrees’ – Hamon & Troper, 2019). By way of law reforming (2009, 2014, and 2019 laws), the prison and probation services have thus embraced the McDonaldisation ethos. Their main obsession has been to early release as many prisoners as possible in order to free space and to accommodate more sentenced people. To do so, the prison services have created a series of so-called ‘simplified’ early release procedures, where prisoners are neither prepared for nor supported through release, where they are deprived of agency and where due process and attorney advice are removed. Behind a pretend rehabilitative discourse, the executive is only interested in efficiently flushing people out of prison; not about re-entry efficacy. As Ritzer (2019) points out, McDonaldisation often leads to counter-productive or absurd consequences. In the case of early release, the stubborn reality is that one cannot bypass actually doing the rehabilitative and re-entry work. I shall additionally argue that not everything truly qualifies as an early release measure (Ostermann, 2013). Only measures which respect prisoners’ agency prepare them for their release, which support them once they are in the community, which address their socio-psychological and criminogenic needs, and which are pronounced in the context of due process and defence rights truly qualify as such. As it is, French ‘simplified’ release procedures amount to McRe-entry and mass nothingness.