Stability of microgrids and weak grids with high penetration of variable renewable energy

Autonomous microgrids and weak grids with high penetrations of variable renewable energy (VRE) generation tend to share several common characteristics: i) low synchronous inertia, ii) sensitivity to active power imbalances, and iii) low system strength (as defined by the nodal short circuit ratio). As a result of these characteristics, there is a greater risk of system instability relative to larger grids, especially as the share of VRE is increased. This thesis focuses on the development of techniques and strategies to assess and improve the stability of microgrids and weak grids. In the first part of this thesis, the small-signal stability of inertia-less converter dominated microgrids is analysed, wherein a load flow based method for small-signal model initialisation is proposed and used to examine the effects of topology and network parameters on the stability of the microgrid. The use of a back-to-back dc link to interconnect neighbouring microgrids and provide dynamic frequency support is then proposed to improve frequency stability by helping to alleviate active power imbalances. In the third part of this thesis, a new technique to determine the optimal sizing of smoothing batteries in microgrids is proposed. The technique is based on the temporal variability of the solar irradiance at the specific site location in order to maximise PV penetration without causing grid instability. A technical framework for integrating solar PV plants into weak grids is then proposed, addressing the weaknesses in conventional Grid Codes that fail to consider the unique characteristics of weak grids. Finally, a new technique is proposed for estimating system load relief factors that are used in aggregate single frequency stability models

Optimal Capacity of a Battery Energy Storage System based on Solar Variability Index to Smooth out Power Fluctuations in PV-Diesel Microgrids

Battery energy storage systems can be integrated with photovoltaic (PV)-diesel microgrids, as an enabling technology to increase the penetration of PV systems and aid microgrid stability by smoothing out the power fluctuations of the PV systems. The aim of this paper is to derive correlations between the optimal capacity of the smoothing batteries and variabilities in daily solar irradiance. Two commonly used smoothing techniques of moving average and ramp rate control are applied on a real solar irradiance dataset with a 1-minute resolution for a full calendar year across 11 sites in Australia. The paper then presents the developed empirical model, based on linear regressions, to estimate the optimal capacity of the batteries without requiring the use of detailed simulation studies. The performance of the developed technique is validated by numerical simulation studies in MATLAB. The study demonstrates that the empirical model provided reasonably accurate estimates when using the moving average smoothing technique, but had limited accuracy under the ramp rate control technique

Interconnected Microgrids via Back-to-Back Converters for Dynamic Frequency Support

This paper presents the back-to-back interconnection of two autonomous microgrids. A back-to-back converter topology, referred to as an interchange converter, is used to provide dynamic frequency support for each autonomous microgrid. The proposed interchange converter facilitates active power exchange between the two microgrids when one cluster does not have sufficient generation capacity to supply its local load demand.During an overloading in the first microgrid, the output power of the energy resources within the other microgrid increases to supply the loads in the first microgrid. Hence, the frequency in both microgrids is kept within the acceptable range. Several study cases are simulated in DIgSILENT PowerFactory software to investigate and verify the successful dynamic frequency support by the help of the interchange converter

Monitoring Posisi Operasi Tim SAR - SRU (Search And Rescue Unit) Pada Daerah Bencana Dengan Memanfaatkan GPS (Global Positioning System)

Dalam kegiatan SAR, komunikasi mempunyai peranan yang sangat penting, salah satunya sebagai sarana komando dan pengendalian yang dimaksudkan agar pada saat terjadi musibah, tim SAR - SRU di lapangan dapat dikendalikan dan dikoordinasikan secara terpadu oleh tim SAR pemantau yaitu OSC (On Scene Commender) atau SMC (SAR Mission Coordinator). Komunikasi selama operasi SAR menjadi faktor pendukung dalam pelaksanaan operasi SAR. Komunikasi yang digunakan biasanya adalah komunikasi suara (voice) yang dalam hal ini radio komunikasi VHF, HF, UHF atau telepon satelit. Oleh sebab itu sangat dituntut keandalan seluruh peralatan komunikasi SAR sebagai pendukung dalam pelaksanaan operasi SAR. Penggunaan alat komunikasi berupa tampilan visual yang efisien dalam monitoring posisi operasi tim SAR - SRU oleh tim SAR pemantau (SMC/OSC) sangat diperlukan, selain komunikasi suara (voice) yang telah biasa digunakan oleh tim SAR saat ini. Pada monitoring posisi operasi tim SAR - SRU ini memanfaatkan GPS receiver dan SMS. Dalam  sistem  ini,  digunakan ATmega162  sebagai  pusat  pengolah data dan  modem GSM wavecom untuk komunikasi via SMS. Komputer dengan akses internet dapat menampilkan posisi tim SAR - SRU melaui Google Map. Selain itu, tim SAR - SRU juga bisa memberikan informasi tentang jumlah korban yang telah ditemukan di daerah bencana. Kata Kunci— GPS receiver, SMS, modem GSM wavecom, ATmega162,  microsoft visual C# 200

Impact of forest plantation on methane emissions from tropical peatland

Tropical peatlands are a known source of methane (CH4) to the atmosphere, but their contribution to atmospheric CH4 is poorly constrained. Since the 1980s, extensive areas of the peatlands in Southeast Asia have experienced land‐cover change to smallholder agriculture and forest plantations. This land‐cover change generally involves lowering of groundwater level (GWL), as well as modification of vegetation type, both of which potentially influence CH4 emissions. We measured CH4 exchanges at the landscape scale using eddy covariance towers over two land‐cover types in tropical peatland in Sumatra, Indonesia: (a) a natural forest and (b) an Acacia crassicarpa plantation. Annual CH4 exchanges over the natural forest (9.1 ± 0.9 g CH4 m−2 year−1) were around twice as high as those of the Acacia plantation (4.7 ± 1.5 g CH4 m−2 year−1). Results highlight that tropical peatlands are significant CH4 sources, and probably have a greater impact on global atmospheric CH4 concentrations than previously thought. Observations showed a clear diurnal variation in CH4 exchange over the natural forest where the GWL was higher than 40 cm below the ground surface. The diurnal variation in CH4 exchanges was strongly correlated with associated changes in the canopy conductance to water vapor, photosynthetic photon flux density, vapor pressure deficit, and air temperature. The absence of a comparable diurnal pattern in CH4 exchange over the Acacia plantation may be the result of the GWL being consistently below the root zone. Our results, which are among the first eddy covariance CH4 exchange data reported for any tropical peatland, should help to reduce the uncertainty in the estimation of CH4 emissions from a globally important ecosystem, provide a more complete estimate of the impact of land‐cover change on tropical peat, and develop science‐based peatland management practices that help to minimize greenhouse gas emissions

Estimation of Induction Motor Parameters Using Hybrid Algorithms for Power System Dynamic Studies

This paper proposes a hybrid Newton-Raphson and genetic algorithm for the estimation of double cage induction motor parameters from commonly available manufacturer data. The hybrid algorithm was tested on a large data set of 6,380 IEC and NEMA motors and then compared with a baseline Newton-Raphson algorithm. The simulation results show that while the proposed hybrid algorithm is more computationally intensive, it does make significant improvements to convergence and error rates