Investigating the Effects of Non-Linear Loads on Generator Sets

Biogas is a renewable fuel that can be used for many applications, such as fuel for kitchen stove, heating and drying system, electricity generation engine, and fuel to run farm tractor. The biogas used in this research was produced from tapioca wastewater treatment equipped with covered lagoon digester. Gasoline generator set having rated capacity 2500-W was modified in such a way that is able to run with 100% biogas. The experiment was performed by running generator set at different loads with incremental of 100-W. Three replications were conducted to get the average values. Performance parameters to be evaluated include biogas consumption, speed of engine (RPM), output power, and thermal efficiency. Results showed that generator set is able to work with raw biogas with methane content of 53%. The generator set reached a maximum load of 1300 W (52% of rated capacity). Biogas consumption increased with load from 1.40 kg·h−1 (no load) to 2.56 kg·h−1 at a load of 1300-W. Biogas specific consumption decreased with load from 16.4 g·W−1·h−1 at load 100 W to 2.2 g·W−1·h−1 at load 1300 W. Output power also increased with load from 0.04 to 0.49 ampere, respectively at a load od 100-W and 1300-W. Engine speed, on the other hand, decreased with load from 3686 RPM (no load) to 2413 RPM (load 1300-W). With biogas methane content of 53%, the maximum thermal efficiency of the generator set was calculated to be 11%.

The dynamic evolution of renewable energy sources (RESs) with utilization of power electronics converters (PECs) caused the situation, where many energy generation units works parallel in local systems named microgrids (MGs). This distributed generation systems with many few kW micro-sources have to provide energy for linear and non-linear loads in grid connected mode of operation, but also in islanded mode of operation, which requires more advanced monitoring and energy management algorithms to ensure power balance and good voltage quality. The issues of power management in islanded AC microgrids are studied by many research centres and novel solutions are necessary to improve the reliability of MGs. In literature, there is still a gap for development of harmonic power sharing method in MG with most often used non-linear loads. Together with active and reactive power management algorithms the harmonic power sharing algorithm need to be implemented in control system to obtain complete solutions. The most often used approach in MG is hierarchical control structure, which includes the basic control loops at primary level, independent for each of PECs and outer control loops at secondary level, which allow to improve voltage amplitude and frequency in point of common coupling, as well as power sharing between PECs. Moreover, the hierarchical control structure is a great opportunity to implement a distributed control algorithm, which is able to execute many operations in the same time. Based on this idea, the novel proportional harmonic power sharing algorithm has been developed. It causes the harmonic power sharing between PECs proportionally to active powers, improving the output current waveforms of converters by decreasing the amplitude of selected current harmonics. The principles of hierarchical droop control and reactive power management has been presented in this paper. The developed solution has been implemented in simulation research together with proportional reactive power sharing algorithm. In order to present the advantage of harmonic power sharing, the results have been compared with non-controlled harmonic power.

Introduction. The implementation of renewable energy resources into the electrical grid has increased significantly in recent years. Wind power is one of the existing resources. Presently, power electronics has become an indispensable tool in wind power plants. Problem. However the associated control usually has an impact on increasing the harmonic distortion, especially on the output voltage. Goal. This paper proposes a new sliding mode control strategy, applied on a rotor-side of a doubly-fed induction generator. The main goal is to meet the electrical power requirements, while responding to the power quality issues. Methodology. The wind energy conversion system must be able to not only track the maximum power point of the wind energy, but also to mitigate the harmonic currents caused by the non-linear loads. To achieve this goal, the power converters are driven by the proposed sliding mode control strategy. The corresponding two gains of the sliding surface are well selected using a particle swarm optimization algorithm. The particle swarm optimization algorithm solves a constrained optimization problem whose fitness function is a prior formulated as the sum of two mean square error criterions. The first criterion presents the tracking dynamic of the reference active power while the second one presents the tracking dynamic of the reference reactive power. The novelty lies in the implementation of the particle swarm optimization algorithm in conventional sliding mode control strategy, in which the proposed-improved sliding mode control strategy is developed. The wind energy conversion system control uses the principal of the vector oriented control to decouple the control of the active power from that of the reactive power. Results. The improved sliding mode control strategy is applied to control separately theses powers in the presence of non-linear loads. The energy assessment of this strategy is analysed using the wind energy conversion system model based on SimPower software. Originality. The obtained simulation results confirm the superiority of the proposed-improved sliding mode control strategy in terms of reference tracking dynamics and suppression of harmonic currents.

: Current heavy-fuel military tactical generator sets in the 10 to 15 kw class use Diesel engines which drive low speed (3600 rpm) electrical generators. These gen sets have weight-to-power ratios that range from about 100 to 150 lbs/kw and volume-to-power ratios from about 4.0 to 5.3 ft3 per kw. In this program a preliminary design was completed for a 15 kw class dual-use, compact, light-weight portable turboelectric power gen system (designated the LTS22) with efficiency equal to the best current Army generators, a weight of approximately 100 lb (weight-to-power ratio of less than 7 lbkw) and a volume of approximately 6.2 cubic feet (volume-to-power ratio of 0.4 ft3/kw) Thus the weight and size of the LTS22 turboelectric gen set would be approximately 1/10 of today's US Army gen sets. The LTS22 generator preliminary design uses a high speed microturbine engine with an integral permanent magnet generator and electronic power controller to achieve a very light weight system. A high effectiveness, compact laminar flow (CLF) recuperator together with a low pressure-ratio turbine cycle will achieve an overall system efficiency equal to the current small diesel powered gen sets.

DC power systems connecting to single-phase DC/AC inverters with nonlinear loads will have their DC sources being injected with AC ripple currents containing a low-frequency component at twice the output voltage frequency of the inverter and also other current harmonics. Such a current may create instability in the DC power system, lower its efficiency, and shorten the lifetime of the DC source. This paper presents a general waveform control method that can mitigate the injection of the low-frequency ripple current by the single-phase DC/AC inverter into the DC source. It also discusses the inhibiting ability of the waveform control method on other coexisting harmonics, while the DC source delivers AC power to a nonlinear load. With the application of the waveform control, the average DC output power is supplied by the DC source, while the other harmonics pulsation power can be confined to the AC side (between the capacitors and the AC load). Theoretical analyses and experiment results are provided to explain the operation and the inhibiting ability, and to showcase the performance of the approach in tackling the harmonics. Results validate that the proposed solution can achieve significant mitigation of harmonic component at DC side with nonlinear load as well as a high quality output voltage without the need for extra large capacitive energy storage element implementation.

With the wide use of power conversion devices - 'nonlinear loads' - many harmonic currents are being injected into the power grid. Shunt Active Power Filters SAPF are the power electronic equipment to compensate the harmonic currents caused by nonlinear loads. As the foundation of the harmonics recognition and compensation, harmonic extraction is the key technology in SAPF. Artificial Neural Networks ANN method has the features of parallel computation and satisfactory results for distorted source voltages over traditional extraction methods. This paper proposes a new harmonic extraction method based on ANN. To test the feasibility of different types of neural networks in this application, this paper compares the performances of three types of ANN: Echo State Networks ESN, Recurrent Neural Networks RNN and Multilayer Perceptron Networks MLP.

In a distribution system, to compensate for the effect of voltage sag/swell and mitigate harmonic currents, a unified power quality conditioner (UPQC) is used. Conventionally, the power rating of UPQC is determined based on the expected sag/swell, linear and nonlinear loads. However, with the shift towards usage of electronic loads and electrical drives, the composition of nonlinear loads is increasing. Hence, the UPQC deployed earlier may not be capable of handling increased harmonic currents due to its limited current rating. While trying to compensate for both harmonic currents and voltage sag/swell, the shunt converter (of UPQC) may reach its current limit and would result in undesirable behaviour. To address this issue, a technique to prioritise sag/swell compensation over active filtering is proposed in this study. The remaining power capacity of UPQC (after sag/swell compensation) is utilised for harmonic filtering. Adaptive determination of harmonic compensation current also allows prioritising the various harmonics to be compensated. This helps in case passive tuned filters are installed for some harmonic frequencies for which UPQC need not respond. Detailed simulation studies are performed on MATLAB/SIMULINK platform and results are included in this study. A laboratory prototype of single phase UPQC is developed to validate the performance of the proposed scheme.

Harmonic distortion in electric distribution system is increasingly growing due to the widespread use of nonlinear loads. Large concentrations of these loads have the potential to raise harmonic voltages and currents in an electrical distribution system to unacceptable high levels that can adversely affect the system. Hence there is need to study the impact of nonlinear loads in the system. This paper presents a method based on bispectrum analysis to characterize typical single phase nonlinear loads by analyzing the harmonic currents produced by these loads. Measurements are conducted using a power quality monitor to record the harmonic current waveforms, individual harmonic distortion levels and total harmonic distortion. To investigate the harmonic characteristics of these loads, the fast Fourier transform technique and the advance signal processing technique such as the bispectrum analysis are used. The results of harmonic characteristics obtained from these loads are compared so as to investigate the effectiveness of the bispectrum analysis in characterizing the various nonlinear loads.

41 - Active Filters

This paper will discuss the monitoring and data analysis of nonlinear load power quality by analyzing electrical railway, which is a typical nonlinear load in Beijing. Firstly, this paper will introduce a method of designing the software and hardware of a kind of highly accurate and large-capacity energy quality data recorder, which is capable of accurately recording voltage, electric current wave, etc., data on site for a long standing and can restore the original data with upper computer in lab. Secondly, this paper will analyze the data collected by the energy quality data recorder from Beijing Xiazhuang transformer substation, which is responsible for supplying electricity to Daqin railway and is a typical nonlinear electrical railway load. On the one hand this paper presents the complete data of fundamental current and harmonic current in a typical working day (as shown in graphs) and analyzes the correlation between fundamental current and main harmonic current. On the other hand, this paper also analyzes the amplitude of main harmonic current distribution with statistical methods and establishes an autoregressive (AR) model to illustrate the distribution of main harmonic current. From the above analysis we can get the key data for evaluating the impact generated by this transformer substation on the grid's electrical energy quality.

Introduction. To improve the power quality of a supply system, the total harmonic distortion (THD) is the most important parameter in the quantification of harmonics caused by nonlinear loads. In practice, it must be less than 5 %. The novelty of the proposed work consists in the use of a cascaded five level active filter, when the converter consisting of six H-bridge pairs, each one includes four transistors. Purpose. To increase the efficiency of this filter, two techniques for quantification of harmonic currents are proposed, first the PQ-theory which is simple but can only be used in case of a balanced grid, and second the synchronous reference frame theory (SFR-theory), which is capable of creating harmonic current not only in an unbalanced grid, but also in an unbalanced and distorted beam. Methods. Using the control techniques, the harmonic current is extracted from load current and considered as a reference. The constructed current should follow this reference. Results. The estimation of the active and reactive powers is based on the measurement of the currents crossing the load and the network voltages, these powers are used to determine the shape of the harmonic (reference) current. Using the PI regulator, the output current of the five-level inverter follows the reference current perfectly. The inverters output current is injected into the grid to eliminate harmonic currents. Practical value. In practice, the harmonic distortion rate THD is the most widely used criterion for criticizing the waveform of the currents and judging the quality of the energy involved. For currents on the source side, the THD is considered acceptable if it is less than 5 %, in our proposal the THD is 0.85 % with the PQ-theory and 2.34 % with SFR-theory, so it is optimal.

Energy and research on energy systems places a focus on all facets of electrical energy, as well as innovation in energy production and delivery, alternative resources, and efficient devices. Systems and equipment for converting, providing, and utilising energy as a kind of electricity are the subject of research initiatives. Power electronics are now a more integral part of power systems, enhancing quality and efficiency and fostering the gradual materialization of intelligent, efficient energy. Many different types of power electronics exist in power systems. The architectural study of changing electrical transformed from one medium to another is known as power electronics. Fields such as electronics reprocess or recover more than 80percent of the entire of the electricity produced at a world average rate of 3.4 billion kilowatts per hour each year. Power electronics converters, sometimes referred to as power converters or switching converters, are used to process or convert electrical energy. Electricity comes in two flavours: AC power and DC power. The distribution system is divided into AC distribution systems and DC distribution systems based on the type of power it uses. Power system analysis is an essential part of electrical power system design. Calculations and simulations are performed to verify that the electrical system, including the system components, is properly specified to perform as planned, withstand the expected stress, and be protected from failures. Advantages of Power Electronics: High power density electricity. Improved efficiency up to 99% in energy conversion. Because to its efficiency and dependability, switching power supply are also being used in medical devices with acoustically sensitive applications. Power system reliability, in general, relates to problems like service interruption and power outages. This is frequently described as a goal to try relying on codes specifically relevant to the consumer. SAIFI, SAIDI, and CAIDI are common dependability index values for US applications. DEMATEL (Decision Making Trial and Evaluation Laboratory) They are divided into analysis using the Nonmetal mineral product industry, General equipment manufacturing, Mining and washing of coal, Textile industry, Food manufacturing industry It is the interaction between the factors Visualized and assesses dependent relationships Through the structural model Also deals with identifying important. Power Electronics in Power Systems, Power Electronics in Transportation Systems, Energy Conservation, Heating & Lighting Control and Renewable Energy Integration Power Systems and Power Electronics in Power Electronics in Power Systems is got the first rank whereas is the Energy Conservation is having the Lowest rank. Power Systems and Power Electronics in Power Electronics in Power Systems is got the first rank whereas is the Energy Conservation is having the Lowest rank.

As a continuation of the work done by the QSE (Electrical Supply Quality) research group at the UPC (Polytechnic University of Catalonia) on non-linear load modelling to determine harmonic distortion in electrical power systems, this thesis consists of the carrying out of a series of studies of the most usual non-linear loads in the said systems (single-phase and three-phase rectifiers with capacitive filter, three-phase 6-pulse rectifiers and discharge lamps), basically aiming to characterize their behaviour and assess their influence on electrical power systems. The thesis was prepared in cooperation with the GNOM (Group of Numerical Optimization and Modelling) research group at the UPC in order to be able to analyse the numerical problem raised by the system of non-linear equations which characterizes each of the non-linear loads, as well as being able to approach optimization issues with some certainty of success. In summary, the aims of this thesis are as follows: -To analyse modelling of the most usual four non-linear loads in electrical power systems in order to incorporate the invariant concept in a justified way and establish ranges of values for the said invariants depending on their usual operating conditions. -To exploit the possibilities offered by invariants and, on the basis of the ranges of values obtained for each of them, to proceed to characterize the deterministic behaviour of the non-linear loads which are the object of the study and also to analyse the phenomena of harmonic cancellation and interaction. -To describe and study experimentally, also on the basis of invariants, the fundamental and harmonic currents (magnitude and angle) consumed by the non-linear loads considered in this thesis, whether by obtaining experimental models (databases) validated both experimentally and numerically, by validating the studied analytical models experimentally or by fitting the parameters of any of the previous models (parameter estimation) on the basis of experimental acquisitions. -To study the neutral conductor current in three-phase systems to which single-phase non-linear loads are connected (in particular, single-phase rectifiers with capacitive filter), by using invariants and validating the results of this experimentally. Como continuación de los trabajos realizados por el grupo de investigación QSE (Calidad del Suministro Eléctrico) de la UPC (Universidad Politécnica de Cataluña) sobre modelización de cargas no lineales para la determinación de la distorsión armónica en los sistemas eléctricos de potencia, se ha realizado como tesis una serie de estudios sobre las cargas no lineales más habituales en dichos sistemas (rectificadores monofásicos y trifásicos con filtro capacitivo, rectificadores trifásicos de 6 pulsos y lámparas de descarga) encaminados básicamente a la caracterización de su comportamiento y al análisis de su influencia en los sistemas eléctricos de potencia. La tesis se ha desarrollado en colaboración con el grupo de investigación GNOM (Grupo de Optimización Numérica y Modelización) de la UPC para poder analizar el problema numérico planteado por el sistema de ecuaciones no lineales que caracteriza cada una de las cargas no lineales, así como poder abordar con garantías problemas de optimización. Resumidamente, los objetivos de esta tesis son: -Analizar la modelización de las cuatro cargas no lineales más habituales en los sistemas eléctricos de potencia con el objetivo de introducir de forma justificada el concepto de invariante y establecer rangos de valores para dichos invariantes de acuerdo a sus condiciones habituales de funcionamiento. -Aprovechar las posibilidades que ofrecen los invariantes y, a partir de los rangos de valores obtenidos para cada uno de ellos, proceder a caracterizar el comportamiento determinístico de las cargas no lineales objeto de estudio y también a analizar los fenómenos de la cancelación y la interacción armónica. -Caracterizar y estudiar experimentalmente, también a partir de los invariantes, las intensidades fundamental y armónicas (módulo y ángulo) que consumen las cargas no lineales consideradas en esta tesis, ya sea mediante la obtención de modelos experimentales (bases de datos) validados tanto experimental como numéricamente, la validación experimental de los modelos analíticos estudiados o bien el ajuste de los parámetros de cualquiera de los anteriores modelos (estimación de parámetros) a partir de adquisiciones experimentales. -Estudiar la intensidad del neutro en sistemas trifásicos en los que hay conectadas cargas no lineales monofásicas (en particular, rectificadores monofásicos con filtro capacitivo), utilizando los invariantes y validando experimentalmente los resultados que se obtengan.

The connection of nonlinear loads such as thyristor drive systems to the power system creates waveform distortion due to the harmonic currents which are injected. The propagation of the harmonic currents throughout the power system is governed by a number of factors including resistance, inductance and capacitance of circuit elements and the system load. The harmonic current at the nonlinear load may be substantially balanced, but due to asymmetry in overhead line and transformer configurations, in particular, residual harmonic currents are produced, which circulate through line capacitance-to-ground and transformer grounded star points. These currents, being of zero sequence order, may cause noise interference in neighbouring telephone circuits. Since the harmonic currents in the power system may become amplified as they progress to the power frequency source, the interference could be considerably increased. The paper addresses the basic theory involved and studies particular systems with a view to using simplified manual calculations. From a knowledge of the residual current magnitude produced by a nonlinear load, noise interference could be determined.

Circularity assessment of power electronic converters: manual disassembly, bill of material, circularity indicators and actionable guidelines