Heigo Mõlder

A review of the harmonic and unbalance effects in electrical distribution networks due to EV charging

For wide use of electric vehicles (EVs), there are different aspects of the electric power system to consider for making it ready for the increased load by battery charging. The topics include power production, peak load management, distribution transmission capacity but also distribution network power quality and many more. This paper presents an overview on the likely power quality impacts in the distribution networks associated with EV charging. Based on a literature review, focus is especially put on harmonics and load unbalance in the network. Most relevant papers observing these topics are presented summarizing their contribution. The power quality aspects in distribution networks discussed here are not often presented within analysis of permissible EV penetration levels. Harmonics or voltage unbalance and effects associated with these could introduce additional limits to the EV charging capacity for the distribution networks. Therefore the analysis on the EV charging influence on these power quality topics requires also high-priority discussions before drawing conclusions on the distribution networks capabilities.

Harmonic load of residential distribution network — Case study monitoring results

The non-linear loads in domestic applications are becoming more common as the power electronic converters are being implemented more widely. This can lead to more significant load current distortions. This paper is presenting a case study results to describe the expected harmonic distortions and to provide models to estimate their magnitudes during day for different times of year. The results presented are from a residential area low-voltage network, which is also providing the heating power for the households. The discussion is presented about the daily harmonic current profiles, which are presented to vary to great extent, harmonic to harmonic and for the different times of the year. The daily profiles of the harmonics with more stable characteristics are described using daily patters trend models.

Current harmonics of EV chargers and effects of diversity to charging load current distortions in distribution networks

Charging of electric vehicles (EVs) is expected to bring a healthy addition of load for the distribution networks. The residential networks where the EV owners would charge their vehicles after returning from daily activities would especially be subjected to high load increase. As EV charger is a powerful nonlinear load rather large harmonic currents can be present during the EV charging. This means a significant increase also to the current harmonics. Analysis of the quantities of the harmonic currents is necessary for guaranteeing the distribution network operation that would meet the power supply standards. In this paper, the EV charging measurement results are presented and analyzed with focus on the current waveform distortions. Different EVs are analyzed for the current harmonics present during the slow rate home charging. For the modeling of the EV charging loads in the networks, discussion is presented on the harmonic currents summing and cancellation effects. The results presented in the paper can be further used for modeling of the actual harmonic loads of the EVs in the distribution networks.

Multi-electrode arc furnace technology with improved metal processing capability using current driven mixing

This paper presents a finite element solution for three-dimensional isothermal flow for DC arc furnace where low frequency AC component is added. Electrodes of the furnace are connected with independent supply sources. Current densities, magnetic flux densities, force densities and flow of molten metal are investigated in the case of two different furnace constructions. Methodology for supply source control described in this paper can be used in industrial applications for mixing molten metals or other conductive liquids.

Estimating the harmonic distortions in a distribution network supplying EV charging load using practical source data — Case example

This paper presents a case example of simulations of the total harmonic load currents when the electric vehicle charging is added to the residential area distribution network workday harmonic current load profiles. For the distribution network harmonic current data, actual recorded harmonic daily load patterns of a residential area low-voltage network are used. Vehicle behavior and daily utilization estimates are based on a traffic statistic study results. The electric vehicles harmonic current loads were measured for 4 different commercially available vehicles. Based on the traffic survey, the total EV charging demand has been simulated with Monte Carlo methods used and total distribution network harmonic currents presented. Results of the simulation are focusing on the 3rd and 5th harmonic currents. It will be presented that it is highly likely that there will be significant harmonic cancellation of the harmonic currents also for the lower order of harmonics present. Results of the study indicate rather minor increase in the harmonic currents due to EV charging.

Electric vehicle charger load current harmonics variations due to supply voltage level differences — Case examples

Modern switching power converters responsible for AC to DC conversion use advanced control methods that guarantee close to unity power factor and sine-like current waveforms. The level of harmonic distortions of such converters that employ power factor correction (PFC) can be rather low and remain in ranges of few percent. Such converters are employed also as chargers as electric vehicles (EVs). When EVs are connected to the low-voltage grid for slow charging, the AC supply voltage levels of the different charging locations are likely to vary. This can also provide effect to the load current waveform distortions, affecting the magnitude and phase shift angles of the individual harmonics. In this paper a discussion is presented on the effects of the AC supply voltage variations to the load current harmonic patterns and summation of harmonic currents when the chargers are used at different AC voltage levels.

Air-Core Sensors Operation Modes for Partial Discharge Detection and On-line Diagnostics in Medium Voltage Networks

Abstract In this paper, sensors for the application of high voltage networks insulation diagnostics are focused on. For detection and localization of the components with insulation deterioration, observing the partial discharge transients is one of the main methods. However, as the partial discharge traces are transients of extremely short duration, monitoring of such transients is also a challenging task. This paper presents the inductive sensors that would be suitable for the on-line partial discharge monitoring and the selection of operating mode and characteristics are discussed. The issues of resonance and signal processing are analyzed for the targets of reaching highest accuracy of the measurements. Operation criteria and performance limits such as sensitivity and upper bandwidth are particularly discussed. It is presented that in order to reach highest accuracy and sensitivity the sensor should be used in damped mode. Applying the accurate air-core inductive sensors would allow the condition monitoring systems to be cheaper and thus mounted for permanent and continuous condition monitoring in various locations in the power distribution networks.

Harmonic distortions of multiple power factor compensated EV chargers

Electric vehicle chargers are mostly power converters with power factor correction and waveform shaping features included. Different vehicle makes and models will likely have different charger control and topology. While the charger charging currents have generally low AC waveform distortions, including variety of chargers at the same time can provide even further lower harmonic currents. This is due to harmonic cancellation brought by different harmonic patterns of different chargers. The present paper analyzes the sine distortions and the sum of the harmonic currents of multiple harmonic sources of such type. The inputs for the analysis are the measurements of the commercial EVs harmonic charging current patterns. It will be shown that remarkable harmonic cancellation will be likely if different vehicle types are included in the pool of vehicles charging at the same time. The results presented here for the EV chargers would be valid also for other similar mains interface converters.

Magnetic current sensor stray components in high frequency operation and their effects

Some of the most severe faults in electrical power networks are caused by faulty insulation or short-circuits. These events are accompanied by traces of partial discharges and traveling waves and recording such pulsed signals accurately is the key for providing effective on-line status monitoring of power lines. Capturing the high-frequency transients is very essential to protection means of local power systems employing power converters and smart-grids [1]. In this paper, operation of an inductive current sensor for on-line measurements is analyzed at high frequencies. Analysis focuses on the aspects of external components used with the sensor but also the connecting components linking the sensor to the measurement circuitry. Some practical aspects are discussed that can help to improve measurement accuracy and effectiveness.

Investigation of molten metal mixing in a DC electric arc furnace with added AC component on different frequencies

This paper describes flowing of molten metal in a novel electric arc furnace. Combined AC and DC components are used in the supply system for the furnace. Finite element method is used to investigate the impact of AC component frequency on the flowing of molten metal.