Aspects of Power Quality in Modern Electricity Distribution Systems with Growing Penetration of Distributed Energy Generation

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Chinese explanation / 中文解读

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Original abstract

Electricity supply systems are undergoing significant transformation, driven by efforts aimed at decarbonising electricity supply. Centralised generation is being disrupted by renewable and distributed energy resources (DER), many of which both cause, and are affected by, power quality (PQ) disturbances. This thesis investigates the impact of this transition on PQ, with a focus on low voltage (LV) networks, and consumer-level effects. The integration of high volumes of DER is central to this investigation, which explores both technical and economic outcomes.The study is situated in the Australian context, where DER penetration, particularly rooftop solar photovoltaic (PV) generation, is world leading. Similar trends are anticipated elsewhere as climate-related electricity reforms accelerate.There is ongoing debate on how recent and future changes to electricity supply affect PQ. DER related voltage regulation challenges have already been witnessed, while DER power electronic interfaces (e.g. solar PV inverters) theoretically have the potential to cause increasing voltage harmonic distortion. Additionally, the displacement of large synchronous generators by DERs may result in greater frequency excursions than previously observed.This thesis presents empirical analysis of PQ disturbances over time, leveraging data from the University of Wollongong’s Power Quality Compliance Audit (PQCA). Operating since 2002, the PQCA collects PQ data from most Australian Distribution Network Service Providers (DNSPs), offering a robust dataset predating the rapid DER uptake beginning around 2010. Findings show clear changes in voltage magnitude profiles in LV networks attributable to solar PV, but little evidence of significant impacts on voltage unbalance or harmonic distortion.Long-term data analysis confirmed that increasing DERs has created voltage regulation challenges. This prompted investigations into how voltage magnitude affects consumer equipment performance (operating characteristics and lifespan) and economics (electricity costs).Extensive laboratory testing was conducted on a wide range of residential appliances to assess their response to varying voltage magnitudes, both within regulatory limits and at levels typical of poor performing sites. While no failures occurred, appliance behaviour varied significantly with voltage.Experimental results were used to develop algorithms to estimate the quantitative impact of supply voltage magnitude on consumers. These algorithms were applied to calculate economic impacts, revealing that the cost of equipment degradation due to voltage variation may exceed increased energy consumption by an order of magnitude, based on Australian case studies.Concerning supply frequency, two mechanisms contribute to larger frequency excursions in modern systems: reduced inertia from replacing synchronous machines with inverter-based generation, and deliberate frequency modulation in microgrids or stand-alone systems to balance load and generation. While frequency variation is effective for microgrid control (through use of inverter frequency-watt responses), its impact on appliance performance remains underexplored. This gap motivated a comprehensive laboratory evaluation of 44 common domestic appliances, spanning new, used, modern and older technologies, tested across frequencies from 50 Hz to 52 Hz.Inverters are known sources of harmonic emissions. Using field measurements, laboratory testing, and power system modelling, this thesis investigates the impact of small-scale solar PV inverters on LV network harmonic distortion. The outcomes, which indicate modest harmonic emissions from solar PV inverters, help explain why widespread inverter deployment has not led to expected increase in voltage harmonic levels.Voltage sags are known to have substantial economic consequences for consumers. Emerging evidence suggests DER integration may be contributing to increased sag events. Despite longstanding awareness of consumer impact, few quantitative tools exist to assess these effects. This thesis introduces generic algorithms to estimate the economic impact of voltage sags and interruptions. These methods are simple to apply, requiring minimal data, and use well-established sag and financial parameters available in most modern networks. The results enable DNSPs, regulators, and customers to estimate costs at individual sites or across entire networks, supporting cost-benefit analyses for remediation projects.Collectively, this thesis provides insight into how evolving electricity supply networks affect PQ disturbances and, in turn, consumer outcomes, both technically and economically. It identifies the most impactful disturbance types and explains why some, such as harmonics, are less impactful than anticipated. The thesis also develops novel, practical algorithms for quantifying the effects of voltage magnitude and sags, equipping DNSPs with tools to justify mitigation strategies.

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