Los motores de induccion son un componente critico de muchos procesos industriales y estan a menudo integrados en equipos comercialmente disponibles. Estos representan mas del 90% de los motores de la industria, de los cuales este consume alrededor del 50% de la energia global y el 68% de la industria de la energia se convierte en motores. Existen varias normas de clasificacion internacionales, regionales y nacionales, procedimientos de prueba y etiquetado de eficiencia energetica de motores de induccion, como IEEE112, IEC60034, CSA390 entre otros. Cada uno de estos estandares da resultados diferentes, por lo que es dificil determinar la eficiencia real y por lo tanto plantear un modelo de gestion de la energia, esto a su vez dificulta los motores comerciales y no permite una comparacion directa entre estos. Debido a esto se ha hecho una tabla comparativa de las normas IEC60034, IEEE112 y CSA390 para caracterizar cada una de ellas y conocer sus diferencias.
Keywords: medium frequency transformer ; power electronics Reference EPFL-TALK-231022 Record created on 2017-09-10, modified on 2017-09-11
This paper deals with a time-domain homogenization technique for litz-wire bundles embedded in a finite element (FE) model. An elementary FE model is used to determine dimensionless frequency-and time-domain coefficients regarding the skin and proximity effects in litz-wire bundles. Thanks to these coefficients, litz-wire bundles become homogeneous conductors which are easy to integrate into a FE model of a complete device. The method is validated with the reference solution of the 2-D FE transformer model, which is computed by finely discretizing each conductor. The results agree well with the accurate reference solution.
This paper presents an auto-tuning technique for online selection of the cost function weight factors in model predictive control (MPC). The weight factors in the cost function with multiple control objectives directly affect the performance and robustness of the MPC. The proposed method in this paper determines the optimum weight factors of the cost function for each sampling time; the optimization of the weight factors is done based on the prediction of the absolute error of the optimization objective and the corresponding constraints. The application considered is a reactive power compensation technique using MPC of a direct matrix converter. This technique compensates lagging power factor loads using inductive energy storage elements instead of electrolytic capacitors (e-caps). The result demonstrates that the proposed auto-tuning approach of cost function weights makes the control algorithm robust to parameter variation and other uncertainties such as load variation. The proposed capacitor-less reactive power compensator based on auto tuned MPC cost function weight factor is implemented experimentally using dSpace DS1007.
In highly microgrid (MG) integrated distribution systems, problems such as a sudden cut out of the MGs due to grid faults may lead to adverse effects to the grid. As a consequence, ancillary services provided by MGs are preferred since it can make the MG a contributor to ride through the faults. In this paper, a voltage support strategy based on negative sequence droop control, which regulate the positive/negative sequence active and reactive power flow by means of sending proper voltage reference to the inner control loop, is proposed for the grid connected MGs to ride through voltage sags under complex line impedance conditions. In this case, the MGs should inject a certain amount of positive and negative sequence power to the grid so that the voltage quality at load side can be maintained at a satisfied level. A two layer hierarchical control strategy is proposed in this paper. The primary control loop consists of voltage and current inner loops, conventional droop control and virtual impedance loop while the secondary control loop is based on positive/negative sequence droop control which can achieve power injection under voltage sags. Experimental results with asymmetrical voltage sags are conducted to verify the effectiveness of the proposed control strategy.
Leakage current reduction is one of the most important issues for transformerless PV grid-connected inverters. Many interesting single-phase topologies have been reported to reduce the leakage currents. However, three-phase PV inverter topologies with reduced leakage currents are not received much attention. In this paper, a new family of three-phase topology is proposed to reduce the leakage current for transformerless PV systems. It derives from the single-phase dc-bypass topologies, and a new modulation is presented to coordinate the dc-bypass switches and H-bridge switches. Theoretical analysis and performance tests are carried out to verify the effectiveness of the proposed topology.
Film capacitors are widely assumed to have superior reliability performance than Aluminum electrolytic capacitors in DC-link design of power electronic converters. However, the assumption needs to be critically judged especially for applications under high humidity environments. This paper proposes a humidity-dependent lifetime derating factor for a type of plastic-boxed metallized DC film capacitors. It overcomes the limitation that the humidity impact is not considered in the state-of-the-art DC film capacitor lifetime models. The lifetime derating factor is obtained based on a total of 8,700 hours accelerated testing of film capacitors under different humidity conditions, enabling a more justified lifetime prediction of film capacitors for DC-link applications under specific climatic environments. The analysis of the testing results and the detailed discussion on the derating factor with different lifetime definitions and confidence levels are presented.
This paper presents two power generation systems with a two-phase permanent magnet (PM) synchronous machine associated to a rectifier with small number of controlled switches. The topologies have as main purpose converting wind energy into electrical energy for low power applications, providing a great potential to be used in urban areas. They can be used in applications connected to the grid or in the stand-alone mode or feeding a micro grid. Compared with two three-phase generation systems that use reduced number of controlled switches, the proposed topologies permit obtaining sinusoidal machine currents, with low harmonic distortion, using a smaller number of controlled switches. Simulation and experimental results also are presented.
A novel method using gate overdrive is suggested to avoid explosion of IGBT modules in converters. With this method, the gate drive impedance is set to low (~0 Ω), such that the driving capability of the gate drive is not limited by the short-circuit present between the gate and auxiliary emitter terminals of a damaged IGBT. Using the implemented gate driving concept, the fault current can be redirected through good chips in the module and the current concentration in the faulty chip of the IGBT module could be reduced to avoid explosion.
A novel battery state of charge (SOC) estimation method is developed in the paper using sliding mode observer and the Nernst Equation based battery model. The method to design sliding mode observer is presented. The proposed estimator is less computational complex but it can obtain relatively accurate result. The performance of the system was verified by simulations and experiments.
A multilevel boost power factor correction (PFC) rectifier is presented in this paper controlled by cascaded controller and multicarrier pulse width modulation technique. The presented topology has less active semiconductor switches compared to similar ones reducing the number of required gate drives that would shrink the manufactured box significantly. A simple controller has been implemented on the studied converter to generate a constant voltage at the output while generating a five-level voltage waveform at the input without connecting the load to the neutral point of the dc bus capacitors. Multicarrier pulse-width modulation technique has been used to produce switching pulses from control signal at a fixed switching frequency. Multilevel voltage waveform harmonics has been analyzed comprehensively which affects the harmonic contents of input current and the size of required filters directly. Full experimental results confirm the good dynamic performance of the proposed five-level PFC boost rectifier in delivering power from ac grid to the dc loads while correcting the power factor at the ac side as well as reducing the current harmonics remarkably.
Cascaded converters are generally used for medium-voltage (MV) grid-connected applications due to the limitation in the voltage rating of available silicon (Si) power devices. These converters find application in active power filters, STATCOM or as the active front end converters for solid state transformers at the distribution voltage levels. The high voltage wide bandgap semiconductor devices have enabled the grid connected operation of noncascaded converters. This results in high power density, less number of switching devices, and high efficiency for three-phase MV grid interface. This also results in control simplicity without the need for complex dc bus balancing algorithms otherwise needed for cascaded converters. However, such noncascaded, grid-connected converters introduce challenges in maintaining power quality at low currents. This paper investigates the harmonic performance and current distortion of the grid-connected, three-level neutral point clamped converter using 15 kV silicon carbide Insulated Gate Bipolar Transistor (IGBTs). A suitable control scheme for stable harmonic compensation is proposed. The challenges and control performance are explained through frequency domain analysis, simulations, and experimental validation on a developed prototype of the three-phase converter up to 4.16 kV, three-phase MV grid-connected operation.
A coupled field-circuit (CFC) method for thermal modeling of electrical machine is proposed, in which some components of electrical machine are modeled with finite element (FE) method while others are modeled with lumped parameter thermal network (LPTN) method. The FE region and the thermal network are related with heat flow through borders of FE region and the temperature of nodes in thermal network. The coupling principle for static temperature distribution and transient temperature rise is elaborated in detail and 3D FE modeling is implemented to take the end winding into consideration. The proposed method is compared with LPTN method and full-order 3D FE method for the thermal modeling of a permanent magnet vernier machine. Experiment is conducted to verify the proposed method. The transient temperature rise procedure of the hot spot in winding in short time is investigated with the proposed method. The FE analysis is conducted with the software package developed with the help of finite element program generator (FEPG).
Small-signal state-space analysis of power system stability relies on linearized models where steady state operation corresponds to constant values of all state variables. Such models are available and commonly used for analysis of configurations with three-phase 2- or 3-level Voltage Source Converters (VSC). However, the Modular Multilevel Converter (MMC), which is emerging as a preferred topology for VSC-based HVDC transmission, is based on single-phase modules with internal capacitors experiencing double frequency voltage oscillations in steady state. Thus, well-established VSC models applied for small-signal stability studies of MMC-based HVDC systems will ignore the internal energy dynamics of the MMC. This paper presents a simplified model of an MMC HVDC terminal, suitable for small-signal linearization while including the aggregated effect of the internal energy dynamics, the internal circulating currents and the corresponding control loops. This model can be combined with models of ac and dc systems and is intended for including the average energy dynamics of MMC-based HVDC terminals in power system stability studies.
The use of high voltage allows a power processing system to operate with low currents, improving efficiency. Nevertheless, final applications usually require low voltage inlet, which can be provided using modular multilevel converters submodules, for instance. However, every submodule's gate-unit requires energy from an isolated low power auxiliary supply. Generally, this is done by using an external converter since it is not practical to directly step-down the high voltage to required levels. In this context, this paper proposes a multi-cell solution based on stacking of buck-boost converters intended to be the first non-isolated stage of an isolated high step-down voltage ratio converter. Analysis and design are presented together with experimental verification of a 200 W rated power converter with 1.5 kV to 3.0 kV input voltage range and a nominal output voltage of 350 V.
Energy storage technologies such as Lithium-ion (Li-ion) batteries are widely used in the present effort to move towards more ecological solutions in sectors like transportation or renewable-energy integration. However, today's Li-ion batteries are reaching their limits and not all demands of the industry are met yet. Therefore, researchers focus on alternative battery chemistries as Lithium-Sulfur (Li-S), which have a huge potential due to their high theoretical specific capacity (approx. 1675 Ah/kg) and theoretical energy density of almost 2600 Wh/kg. To analyze the suitability of this new emerging technology for various applications, there is a need for Li-S battery performance model; however, developing such models represents a challenging task due to batteries' complex ongoing chemical reactions. Therefore, the literature review was performed to summarize electrical circuit models (ECMs) used for modeling the performance behavior of Li-S batteries. The studied Li-S pouch cell was tested in the laboratory in order to parametrize four basic ECM topologies. These topologies were compared by analyzing their voltage estimation accuracy values, which were obtained for different battery current profiles. Based on these results, the 3 R-C ECM was chosen and the Li-S battery cell discharging performance model with current dependent parameters was derived and validated.
A global permanent magnet synchronous machine (PMSM) loss minimization control method is proposed based on nonlinear optimization in this paper. A look-up table based PMSM flux-linkage model is introduced to account for the saturation and cross-coupling effect, and the iron loss model is also numerically developed to account for the harmonic effect. The loss minimization problem can be programmed as a convex nonlinear optimization problem, which can be solved by an optimizer efficiently and effectively. The accuracy of the torque and iron loss is verified by FEA simulations, which confirm the effectiveness of the proposed method.
This paper presents techniques for high-voltage isolated converters to achieve high power efficiency at high switching frequencies. To minimize the converter switching loss, an isolated quasi-square-wave zero-voltage switching three-level half-bridge architecture is adopted. An integrated synchronous three-level gate driver is proposed to ensure reliability of all eGaN power FETs and provide fast propagation delays for high-frequency converter operation. Thanks to the auto-reconfigurability of the proposed V SW -based dead-time controller in the gate driver, ZVS of all power FETs with minimal body diode conduction loss can be achieved in a wide input range (110V-250V) to guarantee the reliability of the proposed converter. Implemented in a 0.7μm 700V CMOS-LDMOS process, the proposed gate driver achieves ≤ 18ns propagation delays and enables a 250V 45W isolated three-level converter to achieve the peak power efficiencies of 94.2% and 89.1% at 1MHz and 2MHz, respectively.
An adaptive current-sharing control strategy with virtual circulating impedance for single-phase parallel connected UPS is proposed in this paper. The current-sharing scheme of the paralleled system is developed and the theoretical analysis of the virtual circulating impedance is studied. The impact of the virtual circulating impedance on the stability of the paralleled system is also discussed. Moreover, to improve the current sharing accuracy during variable operating conditions, the virtual circulating impedance of inverter is adjusted automatically. Experimental results are provided to validate the feasibility of the proposed control strategy.
In this paper, axial-flux permanent magnet machine is modelled to precisely imitate static eccentricities. From the model, the effect of the non-uniform airgap permeance which arises from static eccentricities on current harmonics and torque is experimentally studied. The influence of two cogging torque minimization techniques on both signatures, in the presence of static eccentricity is also examined and a comparison is made between the single-sided and double-sided rotor topologies. Static eccentricity incited significant increases in the amplitudes of space and sub-harmonics in the single-sided topology. The double-sided topology, unlike the single-sided topology, is found to be tolerant to the presence of static eccentricity due to opposing effect of the resulting asymmetrical properties of the airgap. Also, the cogging torque minimization techniques do not impair on the fault detection technique.
