Analysis and evaluation of harmonic distortion in industrial networks caused by HVAC air-conditioning systems

The topic of this research, conducted at Mitsubishi Electric Hydronics, in the form of an internship, it is the development of a simulation program for the calculation of the harmonic distortion of conditioning machines. The environment in which the simulation program will be implemented is the Neplan software. Well'study the machines in use and their electrical characteristics, focusing on the harmonic distortion that these generate when they are connected to the proprietary network.ope

Efficacy of Smart PV Inverter as a Strategic Mitigator of Network Harmonic Resonance and a Suppressor of Temporary Overvoltage Phenomenon in Distribution Systems

The research work explores the design of Smart PV inverters in terms of modelling and investigates the efficacy of a Smart PV inverter as a strategic mitigator of network harmonic resonance phenomenon and a suppressor of Temporary Overvoltage (TOV) in distribution systems. The new application and the control strategy of Smart PV inverters can also be extended to SmartPark-Plug in Electric Vehicles as the grid becomes smarter. As the grid is becoming smarter, more challenges are encountered with the integration of PV plants in distribution systems. Smart PV inverters nowadays are equipped with specialized controllers for exchanging reactive power with the grid based on the available capacity of the inverter, after the real power generation. Although present investigators are researching on several applications of Smart PV inverters, none of the research-work in real time and in documentation have addressed the benefits of employing Smart PV inverters to mitigate network resonances. U.S based standard IEEE 519 for power quality describes the network resonance as a major contributor that has an impact on the harmonic levels. This dissertation proposes a new application for the first time in utilizing a Smart PV inverter to act as a virtual detuner in mitigating network resonance. As a part of the Smart PV inverter design, the LCL filter plays a vital role on network harmonic resonance and further has a direct impact on the stability of the controller and rest of the distribution system. Temporary Overvoltage (TOV) phenomenon is more pronounced especially during unbalanced faults like single line to ground faults (SLGF) in the presence of PV. Such an abnormal incident can damage the customer loads. IEEE 142-“Effective grounding” technique is employed to design the grounding scheme for synchronous based generators. The utilities have been trying to make a PV system comply with IEEE 142 standard as well. Several utilities are still employing the same grounding schemes even now. The attempt has resulted in diminishing the efficacy of protection schemes. Further, millions of dollars and power has been wasted by the utilities. As a result, the concept of effective grounding for PV system has become a challenge when utilities try to mitigate TOV. With an intention of economical aspects in distribution systems planning, this dissertation also proposes a new application and a novel control scheme for utilizing Smart PV/Smart Park inverters to mitigate TOV in distribution systems for the first time. In other words, this novel application can serve as an effective and supporting schema towards ineffective grounding systems. PSCAD/EMTDC has been used throughout the course of research. The idea of Smart inverters serving as a virtual detuner in mitigating network harmonic resonance and as a TOV suppressor in distribution systems has been devised based on the basic principle of VAR injection and absorption with a new control strategy respectively. This research would further serve as a pioneering approach for researchers and planning engineers working in distribution systems

Towards the Development of High-Fidelity Models for Large Scale Solar Energy Generating Systems

Small and large scale solar photovoltaic energy generating systems have been observed to take a leading place in power systems around the world which are aiming to move away from the use of fossil fuels. Technical and other challenges associated with such systems have become the focus areas of discussion and investigation in recent years. Among a range of technical challenges, power quality issues associated with the power electronic converters, especially the harmonics, are an important aspect in order to ensure that their stipulated limits are maintained. While harmonics caused by small-scale inverters, for example, those used in rooftop systems, are managed through their harmonic current emission compliance requirements, the harmonics caused by large scale inverters used in solar farms need to be managed at network levels which is essentially the responsibility of the network owners and operators. To be successful in this management process, the relevant generator connection requirements and system standards, relevant data provided by inverter manufacturers, pre-connection and post-connection studies and procedures require attention. With regard to limits associated with harmonic voltage levels at medium, high and extra high voltage (MV, HV and EHV) levels, well-established international standards exist, whereas the pre-connection study procedures which have existed for many years are now being challenged, noting the increase in the number and capacity of inverter based resources (IBRs). With regard to pre-connection harmonic compliance studies associated with power electronic based grid integrated resources or devices, the most well-known approach is the use of equivalent frequency domain models of the systems on either side of the point of connection or the grid interface. The grid is often represented by an equivalent harmonic impedance together with a corresponding background harmonic voltage. The power electronic based resources or the devices are represented by Thevenin or Norton models at the harmonic frequencies of interest, which are provided by their vendors where the approaches or the conditions under which these models are determined are not comprehensively known. It is however understood that the parameters of such equivalent circuits are mostly determined based on site tests and represent worst case harmonic performance, which do not necessarily correspond to rated power output. There is also the anecdotal understanding that such models are determined based on mathematical or simulation modelling. The most significant concern associated with such frequency domain models is their suitability for representation of the actual harmonic behaviour at a given point in time, thus posing the question of their fidelity which forms the backbone of the work presented in this thesis