Vpliv magnetnega nasičenja na stacionarne obratovalne lastnosti reguliranega asinhronskega motorja

The paper presents a method for determination of the steady-state torque characteristics of the induction motor in the case of rotor field-oriented control (RFOC) with nonlinear magnetizing characteristic of the iron core included. The torque characteristics are determined for the constant stator current and the constant d-axis stator current. The characteristics obtained at a constant stator current are used to maximize the torque capability of the RFOC induction motor. The aim of the presented work is to obtain required steady-state torque with minimal stator current. Experiments show that the proposed selection of a magnetizing reference is promising.V članku je predstavljen postopek za določanje navornih karakteristik pri stacionarnem obratovanju asinhronskega stroja v orientaciji rotorskega polja z upoštevanjem magnetnega nasičenja železa. Določene so navorne karakteristike pri konstantnem statorskem toku ▫$I_{sd}$▫ v d- osi (enačba (6) in sliki 1 in 2), izpostavljena pa je potreba upoštevanja nasičenja pri določitvi navornih karakteristik pri konstantnem statorskem toku Is z enačbo(7) (sliki 3 in 4). Določeni sta tudi krivulji maksimalnega navora v primeru vodenja asinhronskega stroja brez (9) in z (10) upoštevanjem nasičenja. Predlagan je algoritem za primeren izbor referenčne vrednosti toka ▫$I_{sd}$▫, ki naj bi omogočal tvorjenje zahtevanega navora z najmanjšim statorskim tokom (enačbi (13) in (14)). Krivulja maksimalnega navora reguliranega asinhronskega stroja z upoštevanjem nasičenja je bila potrjena tudi eksperimentalno (sliki 6 in 7). Podani rezultati kažejo, da je smiselno spreminjati referenčno vrednost toka ▫$I_{sd,ref}$▫ na predlagani način, saj s tem zagotovimo manjši statorski tok in manjše izgube

Intra-minute cloud passing forecasting based on a low cost iot sensor - a solution for smoothing the output power of PV power plants

Clouds moving at a high speed in front of the Sun can cause step changes in the output power of photovoltaic (PV) power plants, which can lead to voltage fluctuations and stability problems in the connected electricity networks. These effects can be reduced effectively by proper short-term cloud passing forecasting and suitable PV power plant output power control. This paper proposes a low-cost Internet of Things (IoT)-based solution for intra-minute cloud passing forecasting. The hardware consists of a Raspberry PI Model B 3 with a WiFi connection and an OmniVision OV5647 sensor with a mounted wide-angle lens, a circular polarizing (CPL) filter and a natural density (ND) filter. The completely new algorithm for cloud passing forecasting uses the green and blue colors in the photo to determine the position of the Sun, to recognize the clouds, and to predict their movement. The image processing is performed in several stages, considering selectively only a small part of the photo relevant to the movement of the clouds in the vicinity of the Sun in the next minute. The proposed algorithm is compact, fast and suitable for implementation on low cost processors with low computation power. The speed of the cloud parts closest to the Sun is used to predict when the clouds will cover the Sun. WiFi communication is used to transmit this data to the PV power plant control system in order to decrease the output power slowly and smoothly

Simulations of Transformer Inrush Current by Using BDF-Based Numerical Methods

This paper describes three different ways of transformer modeling for inrush current simulations. The developed transformer models are not dependent on an integration step, thus they can be incorporated in a state-space form of stiff differential equation systems. The eigenvalue propagations during simulation time cause very stiff equation systems. The state-space equation systems are solved by using A- and L-stable numerical differentiation formulas (NDF2) method. This method suppresses spurious numerical oscillations in the transient simulations. The comparisons between measured and simulated inrush and steady-state transformer currents are done for all three of the proposed models. The realized nonlinear inductor, nonlinear resistor, and hysteresis model can be incorporated in the EMTP-type programs by using a combination of existing trapezoidal and proposed NDF2 methods

Evaluation of Different Methods for Voltage Sag Source Detection

This paper compares and evaluates three different methods for voltage sag source detection. First method (method I) is based on the assumption, that the energy flow at the monitoring point increases during downstream events and decreases during upstream events. Second and third method (methods II and III) are both based on the assumption that currents measured at the monitoring point increase during downstream events and decrease during upstream events. The slope of a current-voltage trajectory is investigated in method II, while a real current component is observed within method III. Both current-based methods (II and III) require fundamental harmonic components of sampled voltages and currents, which are extracted using discrete orthogonal series expansion, such as Fourier or Walsh. Algorithms of this type are especially appropriate for studying steady-state and periodically repeating conditions. Voltage sags are, on the contrary, transient disturbance events. Thus, usage of the discussed algorithms may not be appropriate. Furthermore, criteria within methods II and III are checked for each phase individually. In the cases of asymmetrical voltage sags exact interpretation of the obtained results, therefore, might not be possible. Method I is, on the contrary, based on instantaneous values of line voltages and currents, while three-phase criterion is used. An exact interpretation of the results obtained by this method is, therefore, also possible in cases of asymmetrical voltage sags. All the discussed methods for voltage sag source detection have been tested by applying extensive simulations and field tests. The results for ground faults, asymmetrical voltage sags, upstream events and motor starting have been analyzed in order to evaluate all the discussed methods. The obtained results show that all discussed methods are very successful in cases of heavy motor starting and other symmetrical voltage sags. In cases of asymmetrical voltage sags the methods II and III do not work well, especially for those originating from the upstream side, while the method I is not successful only in particular cases of voltage sags due to upstream ground faults. Based on the performed evaluation it can be concluded, that further development is still needed to increase the degree of confidence in the discussed methods

The impact of events in the Slovene high – voltage network on the power quality in the distribution networks

This work analyses the impact of different events in Slovene high-voltage network on power quality in the 20 kV and 0.4 kV distribution networks. In order to perform the analysis a simplified dynamic model of the Slovene power system was build in the program package Matlab/Simulink, using toolbox PowerSys. The obtained model is appropriate for simulation of electromagnetic transients in duration up to a few seconds. It contains simplified dynamic models of all main generators and power transformers installed in the Slovene power system, detailed models of 400 kV, 220 kV and 110 kV networks, simplified models of the neighboring power systems and models of important consumers. The 20 kV and 0.4 kV distribution networks are modeled in the details only in the area of interests. Everywhere else, they are represented as constant loads connected to the 110 kV network. The aforementioned dynamic model was applied to analyze the impact of different events in the Slovene power system on power quality in the 0.4 kV distribution network during transients and in steady states. The power quality in distribution network was analyzed on 0.4 kV busbars in five substations (Cerkno, Škofja Loka, Vevče, Šentjur, Rače) for the following set of events: a switch-off of a 300 MVA (400 kV/110 kV) power transformer in the substation Okroglo; a three-phase short circuit on 110 kV busbars in the substation Kleče; a three-phase short circuit on 20 kV busbars in the substation Rogaška Slatina and a switch-on in a pumping regime of pump-turbine plants Avče and Kozjak which are currently at the design stage. The results obtained show that aforementioned events in some points of Slovene distribution network can cause power quality distortion over that allowed by the power quality standards

Разработка и исследование конструкции привода управляемого задерживающего устройства шароструйно-эжекторного бурового снаряда

В работе рассмотрены принципы шароструйного бурения, а так же устройство шаростуйно-эжекторного снаряда. Предложены варианты модернизации данного снаряда.In this paper, the principles of pellet impact drilling, as well as the construction of a pellet-ejector projectile, are considered. Variants of modernization of this projectile are offered