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This paper deals with the time-domain simulation of electric machine drives in Python. Python offers a full-featured numerical computing environment, comparable to leading commercially available alternatives, whilst being fully open-source. Adopting the open-source ecosystem allows electric drives researchers to utilize new methods from other fields, easily share their findings, and improve collaboration with other researchers both in academia and industry. For this purpose, we have launched the Python-based time-domain simulation platform motulator for electric drives. To learn more, the reader is encouraged to visit the GitHub page of the project: https: //github.com/Aalto-Electric-Drives/motulator., Part of ISBN 9798350398991QC 20231013

A multiphase induction machine model using vector space decomposition or harmonic plane decomposition provides insights into many space harmonics through decoupled reference frames, each hosting specific space vectors related to particular harmonics. The dynamics of each voltage and current space vector are described by an equivalent circuit, whose parameters must be obtained either by finite-element analysis or laboratory measurements. This paper presents and experimentally verifies a methodology for calculating these parameters from a single configuration, with minimal knowledge of the geometrical dimensions of the machine., Part of ISBN 979-8-3503-9899-1QC 20230925

The share of photovoltaic systems has greatly increased in electricity generation in recent years. As the prices of solar power plant components have decreased lately, companies need to find ways to achieve savings. By connecting central inverters in parallel to a same winding of a transformer, a cheaper regular transformer can be used instead of a transformer having two separate windings on the inverter side. However, this parallel connection creates a path for circulating current to flow in the system which produces additional losses and stresses vulnerable system components. In this thesis, the circulating current in the parallel-connected system is analyzed. A simulation model is used to obtain the common-mode voltage produced by the two inverters and the equivalent circuit of the system is used to calculate the circulating current from the voltage. Laboratory measurements are conducted to verify the accuracy of the calculations and define if the parallel connection is feasible to use with the existing system components. The inverters used in this thesis are large modular 1500 V 5 MW central inverters both having four identical power sections. These inverters are connected to the same MV transformer so that they share a galvanic connection thus allowing circulating current to flow in the system. It was found that the calculated circulating current reaches high magnitude from less than 10 A rms to above 100 A rms depending on the system DC voltage level and number of power sections in the inverters. The laboratory measurements showed that the circulating current in the system is higher than the calculated circulating current. The calculated circulating current is lower as the simulation model and the equivalent circuit do not take account the non-idealities and resonance behaviour of the system components. It can be concluded that it is not feasible to use the parallel connection with the components currently in the system due to the high circulating current, and, Aurinkosähköjärjestelmien osuus on merkittävästi kasvanut sähköntuotannossa lähivuosina. Kun aurinkosähköjärjestelmien komponenttien hinnat ovat lähiaikoina laskeneet, yritysten tulee löytää tapoja saavuttaa säästöjä. Kytkemällä aurinkosähkövaihtosuuntaajat rinnan samaan muuntajan käämitykseen, voidaan halvempia tavallisia muuntajia käyttää. Tämä rinnankytkentä kuitenkin luo kiertovirralle tien järjestelmässä, mikä lisää häviöitä ja rasittaa järjestelmän herkkiä komponentteja. Tässä diplomityössä analysoitiin kiertovirtaa rinnankytketyssä järjestelmässä. Simulaatiomallin avulla saatiin kahden invertterin välinen yhteismuotoinen jännite, jota käytettiin yhdessä ekvivalentin piirin kanssa kiertovirran laskemiseen. Laboratoriomittauksilla määritettiin laskelmien tarkkuutta ja tarkasteltiin, onko rinnankytkennän käyttö mahdollista järjestelmässä olevilla nykyisillä komponenteilla. Diplomityössä käytetyt vaihtosuuntaajat olivat modulaarisia 1500 V 5 MW keskusvaihtosuuntaajia, joissa molemmissa oli neljä identtistä tehokenttää. Nämä vaihtosuuntaajat kytkettiin rinnan samaan muuntajaan, jotta ne ovat galvaanisessa yhteydessä keskenään ja mahdollistavat kiertovirran kulun järjestelmässä. Työssä havaittiin, että lasketut kiertovirrat vaihtelivat alle 10 A rms ja yli 100 A rms välillä riippuen järjestelmän DC jännitetasosta ja tehokenttien määrästä vaihtosuuntaajissa. Laboratoriomittauksista nähtiin, että kiertovirta järjestelmässä on suurempi kuin mitattu kiertovirta. Laskettu kiertovirta oli pienempi, sillä simulaatiomalli ja ekvivalentti piiri eivät ottaneet huomioon järjestelmän komponenttien epäideaalisuuksia sekä resonanssia. Tämän työn pohjalta voidaan päätellä, että rinnankytketyn järjestelmän käyttö nykyisillä komponenteilla ei ole mahdollinen suuren kiertovirran takia ja että tätä ilmiötä tulisi tutkia pidemmälle.

This article deals with standstill identification of an induction motor drive for sensorless self-commissioning purposes. The proposed identification method is based on an advanced model of a squirrel-cage induction motor. The model includes the deep-bar effect and the magnetic saturation characteristics. The excitation signals are fed to the stator using a standard inverter without compensating for its nonlinearities. The saturable stator inductance is first identified by means of a robust flux-integration test, where unknown voltage disturbances are canceled with suitably selected current pulses. Then, the deep-bar characteristics are identified by means of a dc-biased sinusoidal excitation using different frequencies. Finally, the cross-saturation characteristics of the rotor leakage inductance are identified by altering the dc bias of the excitation signal. The identified characteristics are transformed to the parameters of the advanced motor model taking into account the interrelations of the aforementioned phenomena. Since the physical phenomena affecting the standstill identification process are properly included in the identified model, fewer approximations are needed and more accurate parameter estimates are obtained. The identification procedure is validated by means of experiments using two different induction motors (5.6 and 45 kW)., QC 20210916

The stability of the converter-grid interconnection can be studied by analyzing the product of the converter output admittance and the grid impedance. For reliable stability analysis, it has been of interest to obtain accurate converter output admittance models for a wide range of frequencies, ideally also around and above the Nyquist frequency of the converter system. This article presents a modeling method for the output admittance of power converters defined in the Laplace domain that takes into account the discrete nature of the control system. The modeling method is based on analyzing the intersample behavior of sampled-data systems, a class of systems that includes the modern digitally controlled power converters. The proposed method is compared to conventional admittance modeling methods, and its accuracy is validated by means of simulations and experiments., QC 20210825