Experimental experiences of the summation of flicker contribution from individual wind turbines in a wind park

This paper presents flicker emission measurements from a wind park consisting of seven variable speed wind turbines. The grid flicker level is compared with the calculated contribution from the wind turbines, and in addition, the individual flicker contribution is compared with the summed contribution of all the seven turbines. It is found that the total flicker content produced by the wind park is higher than the value found by using the summation equation given in IEC-61400-21. For the investigated wind park the underestimation is 20 \% which is lower compared to a previously reported case when using a smaller wind park equipped with fixed-speed wind turbines. Moreover it is found that on this low flicker level grid, the prediction of grid flicker impact by the wind energy installations match the measured grid flicker content very well

An analysis of inverter switching loss minimization based on discontinuous PWM for a salient-pole PMSM

This article presents the result of an inverter switching loss minimization technique based on discontinuous PWM patterns for a salient-pole PMSM with a two-level voltage source inverter for an automotive application. The suggested PWM patterns are evaluated using the resulting electromagnetic torque considering peak-to-peak ripple as well as the DC-current harmonic spectra. The study focuses on high rotational speeds, from 0.6-2.5 ωbase considering both current and voltage limitations. The analysis focuses on electromagnetic torque characteristics evaluated at steady state operation. The results show that the electromagnetic torque ripple is increased by up to 73 % and 78 % whereas the inverter switching losses is decreased by up to -17%and -41%for the EUDC driving cycle using DPWM30 and DPWM60, respectively

Modeling of Wind Turbines for Power System Studies

In this paper the modelling of wind turbines for power system studies is investigated. Complexities of various parts of a wind turbine model, such as aerodynamic conversion, drive train, and generator representation, are analyzed. The results are verified by field measurements made on a stall-regulated fixed-speed wind turbine. The modelling focuses on deriving a representation that is suitable for use in grid simulation program

Inverter losses minimization using variable switching frequency based on multi-objective optimization

This article presents the result of an VSI-losses minimization technique based on multi-objective convex optimization for a salient-pole PMSM with a two-level VSI for an automotive application. The optimization, using the switching frequency as control variable, is based on a multi-objective cost function defined by the combination of VSI-losses and electromagnetic torque peak-peak ripple, analytically expressed using time-domain current predictions. The optimization target is to keep an optimum balance between VSI-losses and electromagnetic torque ripple, using variable switching frequency (VSF). The primary objective with this article is the presented design methodology. Simulations are used to verify functionality as well as influence of different scaling factors. In addition, the NEDC driving cycle is used to further quantify the results for two different cost function setups

Power Quality Issues of a Battery Fast Charging Station for a Fully-Electric Public Transport System in Gothenburg City

An automatic fast charger station with a power level of 120 kW is developed for city Bus Line 60 in Gothenburg, Sweden. There are some power quality issues towards the utility grid during the charger operation. The aim of this paper is to explain the project and to present the measurement results with respect to power quality issues. The main specifications of the battery, charger, charging infrastructure and bus route are explained. The measurement results show that the harmonic emission is within the prescribed limit despite the high amount of low-frequency harmonics because of a passive diode rectification. It is suggested to replace the passive diode rectifier with an active front-end converter to eliminate low order current harmonics and to obtain a unity power factor operation. The main contribution of this work is to demonstrate a practical example of an electric charging system for an electric public transport system in Gothenburg

On Dynamic Diode Characteristics and EMI Performance of an Inverter with Undeland Snubber

In this paper, two different power diodes were modeled in SPICE and implemented in a 100kW inverter. The reverse and forward recovery characteristics of the diodes were simulated and compared with hardware measurement to verify the validity of the SPICE diode models. The diodes showed different dynamic and static performance and simulations were performed to investigate which parameters that influence the losses and EMI-performance most. The simulations showed that the conducted emissions were reduced with approximately 3dB by selecting a diode with softer dynamic characteristics on expense of increased losses. Furthermore, an Undeland snubber was implemented which resulted in a reduction of the conducted emissions, recovery of the snubber energy and reduction of the losses in the switching elements. However, the forward and reverse recovery characteristics of the snubber diodes must be considered when designing the circuit since they also have an impact on the conducted emissions and the losses in the circuit

Performance Analysis of Current BEVs - Based on a Comprehensive Review of Specifications

This paper aims to provide an analysis of BEV performance that is based on a comprehensive collection of specifications of over 40 currently globally available battery electric vehicles (BEVs). The analysis comprise dimensional, powertrain and performance data. The collected data is provided in the paper to facilitate further academic studies. There is a wide variety of BEVs from small to large as well as high performing sedans and sport cars. It was found that all BEVs are using Li-ion batteries with specific energy of 55-170 Wh/kg, and that battery weights are representing 13%-37% of the vehicle weight. Furthermore, the majority of the BEVs are using permanent magnet motors, where some indicate power densities of 1.5-3.1 kW/kg. The specified NEDC driving range varies between 85- 528 km, and the energy consumption between 117-268 Wh/km. A rough estimation indicates that the powertrain’s share of the net energy consumption during NEDC may be up to around 40%-54%