Injection Of Higher Harmonics Research Articles

VSI LC filter optimized by a genetic algorithm from connected to island microgrid operation

In microgrids (MG) with a high penetration of renewable energy sources (RES) power converters are used to regulate the produced energy to a single voltage and frequency reference value across the MG. Adequate incorporation of an LC filter at the output of power electronic devices allows the attenuation of harmful harmonics that can be introduced to the MGs energy bus. By traditional methods, LC filter values can be calculated by means of the power rating, switching frequency, cutoff frequency, and using the bode frequency domain. Nonetheless, in the transition from a connected to an autonomous MG operation, the calculated LC filter can lead to high harmonic injection. As a result, a tuning methodology capable of obtaining the right set of parameters for the LC filter for a transition event can improve the performance of the MG. This work optimizes the LC output parameters with respect to the size of the filter components, the IEEE Std 519-2014, and bandwidth of the filter, within a bounded region of values subjected to performance conditions such as voltage output, and the produced total harmonic distortion (THD) measurements during the transition from a connected to an autonomous operation. In a case study, genetic algorithm optimization is used to obtain the LC filter parameters and compared to a conventional arithmetic methodology to obtain the values of the filter. The optimization results in a set of values that lead to a higher harmonic attenuation after the transition rather than a conventional method using the switching frequency as the main design factor.

Uticaj solarne elektrane na kvalitet električne energije u niskonaponskoj distributivnoj mreži

The electric power system, as an integrated system for transmission, distribution and consumption of electricity, is one of the most complex technical and economic systems today. Customers affect on the voltage quality of power network, but the network also has an impact on customers. All disturbances in the network can disrupt operation of the network and affect on operation of the customers, as well as reduce the level of efficiency and operation life or even seriously damage network. Number of customers is increasing every day, as well as proportion of customers who generate disturbances in the network and, at the same time, are sensitive to them. These circumstances impose the need for frequent monitoring of the network, so the analysis of power quality is not unjustified cost but extremely important and profitable investment. The quality of electricity, as part of the overall quality supply of electricity customers in deregulated conditions of liberal electricity market becomes significant regulatory parameter for network operators and a significant contracting parameter on the electricity market. Network operators are obliged to establish a system of individual measurements and a system of permanent monitoring of power quality parameters to determine the state and improve the parameters to the standardized level. Technical parameters are determined by the recommendations made at the international level and may, but do not need, be legally binding. Maintaining a certain level of voltage quality at some point of the network is the responsibility of electricity distributor. This task distributor executes by limiting of negative effects of producer/customer to the network. Therefore, each electricity producer/customer is obliged to reduce own negative feedback effects (injection of higher harmonics, taking of reactive power, emissions of flickers and loads unbalances) to a prescribed, prearranged, limited values. There are many norms that describe the quality of electricity, but in Europe the best known is EN50160 (issued by CENLEC). This paper presents the approach to measuring the voltage quality at the point of electricity delivery from distributed source into distribution network from the aspect of limiting the negative feedback of distributed source on the voltage quality.

Marine Duty Harmonic Mitigation on DC Propulsion Saves Oil Service Vessel Program

An offshore oil and gas service vessel equipped with dc propulsion drives retrofitted with revenue generating equipment, such as remote operated vehicles (ROV) and cranes, could not pass sea trials due to multiple failures (including loss of navigation) caused by harmonic distortion. Marine propulsion systems represent a dominant load on most vessels and dynamically positioned (DP) offshore installations. These propulsion systems are typically nonlinear in nature with very high harmonic injection, which can have a significant impact on vessel wide systems and subsystems. AC adjustable speed drive (ASD) propulsion systems characteristically inject current harmonics into the generator system impedance creating voltage distortion. DC ASDs produce even higher voltage distortion levels due to voltage notching caused by the thyristor firing which makes their harmonic mitigation requirement much more challenging. In order to eliminate the numerous harmonic problems, the dc propulsion system of the oil service vessel was retrofitted with harmonic mitigation equipment. The case study discusses: 1) operational issues including component failures in crane controls and ROV equipment while operating in DP mode; 2) field testing to document the harmonic distortion conditions created by the propulsion and thruster dc ASDs prior to treatment; 3) computer simulation of the dc drive propulsion system to determine a harmonic mitigation strategy; and 4) extensive sea trial testing of the power system with harmonic mitigation to demonstrate compliance with ABS harmonic limits, compatibility of the harmonic mitigation with the ASD equipment, and resolution of all connected equipment failures and operational problems.