Enhanced mathematical modelling of interior permanent magnet synchronous machines for loss minimization control

Energy management is a fundamental facility for humanity. At present, the awareness that renewable energy cannot satisfy the entire energy needs of the community and that traditional energy sources have a limited duration makes it imperative to address the problem of their careful and responsible use. Therefore, the need for an intelligent and functional use of energy has led the technical-scientific community to concentrate its efforts on the issues of sustainable development and energy savings. The electric drives industrial sector has suffered this influence in a visceral way. This sector plays a leading role in the industrial frame as it is one of the main consumers of electricity. Moreover, the topic of electrical drives design and optimization has become of considerable importance especially for the automotive sector and for hybrid and electric traction applications. In particular, in the last two decade, this sector has undergone a considerable technological development thanks to the exponential evolution of power electronics, the use of increasingly performing electric machines and new control techniques. In this scenario, the design and optimization of control algorithms for interior permanent magnet synchronous machines (IPMSM) has became of considerable interest in the scientific and technological community. In detail, the IPMSM is one of the most used electrical machine typologies in the electric traction applications due to the high efficiency and flux-weakening capability. The purpose of the research project “Realization of innovative algorithms for the minimization of the losses in synchronous brushless motors for automotive application” consists in the design and development of innovative Loss Model Algorithm (LMA) for interior permanent magnet synchronous machines (PMSM). The LMAs goal is the identification of the working points of the machine at minimum losses through the optimal determination of the control variables values. Therefore, the use of LMAs in electric drives can be of considerable utility in terms of energy savings especially for automotive application where energy autonomy is a crucial parameter. In detail, a LMA is a control algorithm based on the knowledge of the dynamic mathematical model of the IPMSM. Therefore, the performances of LMA are strictly dependent on the accuracy of the mathematical model and of its electrical and magnetic parameters. In this regard, the research carried out during the PhD course focused on the four macro topics, reported as chapters of the PhD thesis: 1. loss minimization control techniques for PMSM: state of art; 2. performances analysis of the power loss mathematical models; 3. efficiency measurement of electric drives equipped with interior permanent magnets synchronous machine (IPMSM); 4. enhanced mathematical modelling of IPMSM. The first chapter describes the state of art of main Loss Minimization control Algorithms (LMA) for electric drives equipped with PMSM. The LMAs can be classified into two general approaches named Search control and Loss Model Control, respectively. The main features of each approach are presented and discussed. Particular attention is devoted to the conventional IPMSM modelling approach employed in the LMC. Finally, the LMA chosen as a case of study is illustrated. The second chapter describes the performances analysis of the power loss mathematical models for LMC. In detail, the conventional IPMSM modelling approach and the IPMSM modelling approach that take into account the magnetic self-saturation effects and the variability the iron loss with the supply frequency are studied and discussed. In order to evaluate the performances of each modelling approach, several experimental investigations have been carried out on an electric drive equipped with an IPMSM. The third chapter is focused on the design and validation of accurate efficiency measurement approach for electrical drives equipped with IPMSMs. In particular, the efficiency measurement approaches for electrical drives described by the international standards and by the scientific literature are described and discussed. Particular attention was paid to the new standard IEC61800 and their prescriptions have been employed for the efficiency estimation of the electric drive under test. Finally, a new measurement approach for the comparison of the electrical drive efficiency, when it is controlled with several control algorithms, is presented and experimentally validate. The last chapter describes the enhanced mathematical modelling of IPMSM that take into account the magnetic saturation, cross-coupling, spatial harmonics and iron loss effects. This activity was carried out in collaboration with the Institute of Power Electronics System (ELSYS) of the ―Technische Hochschule Nürnberg Georg-Simon Ohm‖ during the PhD visiting period. In particular, the research activity was focused on the finite element modelization and analysis of IPMSMs and the Ansys Maxwell simulation environment (FE software) has been used for the simulation of the IPMSM under test. In detail, in order to define a high-fidelity IPMSM mathematical model, a large number of FEA investigations have been carried out. In this regard, the enhanced IPMSM mathematical model is described, implemented in Matlab®/Simulink environment and, for validation purpose, its performances have been compared with those of the IPMSM implemented in Ansys Maxwell environment

Algorithmic Approach for Slot Filling Factors Determination in Electrical Machines

In several industrial sectors, such as electric and hybrid traction, the demand for increasingly efficient and high power density electrical machines has grown considerably over the last few years. The improvement of slot filling factor of the electrical machines is an useful provision to satisfy this request. In particular, this topic has been the subject of interest for the industrial sector in recent years, since the technology of winding processes have evolved and allow an economically sustainable realization of windings with an ordered structure rather than randomly. The winding phase must be supported by an accurate design process in which it is possible to evaluate the maximum slot filling factor obtainable for a given wire shape and for given dimensions. In this sense, this paper presents an algorithm approach for the calculation of maximum slot filling factors in electrical machines. In particular, the slot filling factor evaluation was carried out both for standard and non-standard slots and with the use of round and rectangular wires. The algorithm proposed can be considered as an additional useful tool for fast design of electrical machines windings

State of art and economic evaluation of wave energy converters. A case study

The even increasing energy demand in the world is a relevant problem for the modern society. The energy supply from fossil fuels has become a critical aspect due to the progressive reduction of reserves and political instability among the Countries. For these reasons, the exploitation of renewable energy sources is looked with a great interest. In this context, solar, wind, geothermal, hydropower, and biomass can be successfully used through commercial technologies. Other potential renewable energy sources could have potential applications in the next future. Among these, sea wave is considered a very promising energy source, especially for small islands. In this context, the paper propones a new configuration of wave energy converter, analyzing the economic aspects for a potential realization in the Mediterranean Sea

Characterization of interior permanent magnet synchronous motors for loss model algorithm identification

The paper provides the results of a detailed experimental study on the variations of the characteristics of an interior permanent magnet synchronous motor, when load, speed and/or magnetization conditions vary. In particular, the characterization is carried out by assessing, for several working conditions, the motor parameters that influence its efficiency. From the knowledge of the variability of these parameters, it is possible to develop a dynamic model of the motor, which accurately describes its behaviour and allows estimating the power losses for whatever speed and load. In order to validate the model, the values of the power losses obtained by using the model are compared with the values measured with experimental tests. The study shows that it is possible to maximize the motor efficiency just acting on the direct axis current component, and therefore, it can be considered a first step towards the definition of a loss model algorithm for a control drive system able to minimize in real-time the power losses of the moto

An Experimental Comparison between an Ironless and a Traditional Permanent Magnet Linear Generator for Wave Energy Conversion

Permanent Magnet Linear Generators (PMLGs) are currently being studied for sea wave energy harvesting. Typically, a PMLG consists of an iron-made armature and a moving translator. The permanent magnets adoption produces parasitic effects, such as cogging force, and the machine weight increment. A solution could be the adoption of an ironless configuration, accepting a power density reduction. This paper investigates the use of ironless PMLGs in sea wave energy conversion systems by an experimental comparative analysis between an iron PMLG prototype and an ironless PMLG prototype, which share the same geometry. The main electrical and mechanical parameters (resistance, mass, and magnetic fields) were preliminarily measured. Subsequently, open-circuit and load tests were carried out to compare the induced voltages, the energy transferred to a resistive load, efficiency and the load average power. The reported comparison shows that iron PMLG performances are significantly superior to the ironless ones during the open-circuit tests, as expected. However, the analysis carried out through the load tests shows that the cogging force significantly limits the energy production, obtaining similar values in both machines. Therefore, the experimental tests justify the use of ironless machines in sea wave energy harvesting, where the maximization of energy production is a relevant target

Reduction of cogging force in linear generators for wave energy harvesting

Due to huge energy potential of sea waves, many technologies have been proposed in the last few years. Some concepts have been developed and sometimes also tested in the open sea. Some prototypes use linear generators to directly convert the vertical motion of buoys into electrical energy. This solution minimizes the numbers of energy conversion steps, increasing the energy efficiency. At the same time, the limited numbers of components could also increase the reliability of the wave energy converter. For this reason, the development of linear generators is considered with great interest. This paper investigated the cogging force, a magnetic force due to the interaction between the magnets and the iron stator. To limit the cogging force, a modified shape of the stator is investigated. Simulations on a specific FEM software are performed, obtaining interesting results

Switching Frequency Effects on the Efficiency and Harmonic Distortion in a Three-Phase Five-Level CHBMI Prototype with Multicarrier PWM Schemes: Experimental Analysis

The current climatic scenario requires the use of innovative solutions to increase the production of electricity from renewable energy sources. Multilevel Power Inverters are a promising solution to improve the penetration of renewable energy sources into the electrical grid. Moreover, the performance of MPIs is a function of the modulation strategy employed and of its features (modulation index and switching frequency). This paper presents an extended and experimental analysis of three-phase five-level Cascaded H-Bridges Multilevel Inverter performance in terms of efficiency and harmonic content considering several MC PWM modulation strategies. In detail, the CHBMI performance is analyzed by varying the modulation index and the switching frequency. For control purposes, the NI System On Module sbRIO-9651 control board, a dedicated FPGA-based control board for power electronics and drive applications programmable in the LabVIEW environment, is used. The paper describes the modulation strategies implementation, the test bench set-up, and the experimental investigations carried out. The results obtained in terms of Total Harmonic Distorsion (THD) and efficiency are analyzed, compared, and discussed

High-Speed Machines: Typologies, Standards, and Operation under PWM Supply

This paper presents an overview of the most recent state of the art in the field of high-speed electric machines fed through high-frequency converters. This type of systems is rapidly wide spreading in aeronautical and automotive applications, as well as microturbines. Each typology has its own advantages and downsides, which are analytically presented in this paper. Some types of high-speed electric machines require high-frequency voltage supply, highly stressing the dielectric materials of the winding insulation system. For this reason, in high-speed electric drives, premature failure may occur and a reduction of the total system reliability has been observed in the past years. Such issues are comprehensively investigated in this paper