Optimized Dispatch of Energy Storage Systems in Unbalanced Distribution Networks

© 2010-2012 IEEE. This paper presents a method to achieve optimal active and reactive power contributions from each energy storage system in an unbalanced distribution network to minimize power loss, while ensuring network current and voltage constraints are satisfied. By modeling loads as either constant current or constant impedance, the ac optimal power flow is transformed into a noniterative convex optimization problem. The application of capacity constraints, voltage constraints, and energy storage constraints in an unbalanced three-phase four-wire system is considered, addressing specific issues pertaining to unbalanced networks such as voltage unbalance and neutral voltage displacement. The proposed method is then used to demonstrate optimized dispatch of energy storage systems in a suitable four-wire unbalanced distribution test network. The contribution of losses in the neutral wire to the total losses is also determined for a test system under a range of operating conditions and various neutral earthing systems, highlighting the importance of considering this in a typical unbalanced distribution network

Distributed Algorithm for Optimal Power Flow on an Unbalanced Radial Network

The optimal power flow (OPF) problem is fundamental in power systems operation and planning. Large-scale renewable penetration calls for real-time feedback control, and hence the need for distributed solutions for the OPF problem. In this paper we propose a solution for an unbalanced radial distribution network. Our distributed algorithm is based on alternating direction method of multiplier (ADMM). The main idea is to exploit the tree topology of distribution networks and decompose the OPF problem in such a way that the subproblems in each ADMM macro-iteration either have closed-form solutions or reduce to eigenvalue problems whose size remains constant as the network size scales up. We present simulations on IEEE 13, 34, 37 and 123 bus unbalanced distribution network to illustrate the scalability and optimality of the proposed algorithm

Distribution power markets: detailed modeling and tractable algorithms

The increasing integration of renewable generation presents power systems with economic and reliability challenges, mostly due to renewables' volatility, which cannot be effectively addressed with business-as-usual practices. Fortunately, this is concurrent with rising levels of Distributed Energy Resources (DERs), including photovoltaics, microgeneration and flexible loads like HVAC loads and electric vehicles. DERs are capable of attractive time-shiftable behavior and of transacting reactive power and reserves in addition to real power. If DER capacity is optimally allocated among these three products, distribution network and economic benefits can be realized and renewable-related challenges can be mitigated, enabling increased renewable integration safety limits. In order to achieve optimal DER scheduling, this thesis proposes the formulation of a spatiotemporal marginal-cost based distribution power market and develops and implements tractable clearing algorithms. First, we formulate a centralized market clearing algorithm whose result is the optimal DER real power, reactive power and reserves schedules and the optimal nodal marginal costs. Our market formulation develops for the first time detailed and realistic models of the salient distribution network variable costs (transformer degradation, voltage sensitive loads) together with distribution network constraints (voltage bound constraints, that reflect distribution network congestion and AC load flow), and intertemporal DER dynamics and capabilities. However, the centralized algorithm does not scale, motivating the use of distributed algorithms. We propose two distributed algorithms: • A fully distributed algorithm that relies on massively parallel DER and distribution line specific sub-problem solutions, iteratively coordinated by nodal price estimates which promote and eventually enforce nodal balances. Upon convergence, nodal balances hold and optimal marginal costs are discovered. We further existing practices by using local penalty updates and stopping criteria that significantly reduce communication requirements. • A novel, partially distributed formulation in which DERs self-schedule in parallel based on centrally calculated price estimates, resulting from a load flow calculation. Nodal balances hold during all iterations. Finally, we are, to the best of our knowledge, the first to study voltage-constrained distribution market instances cleared with distributed methods. We decrease the deviation of marginal costs from their optimal values using first order optimality conditions and use voltage barrier functions for speedier convergence.2020-03-31T00:00:00

Peningkatan Kualitas Daya pada Perencanaan Terkoordinasi Jaringan Sistem Distribusi Radial Melalui Penyelesaian Advanced-Optimal Power Flow (Advanced-OPF) Berbasis Metode Hierarchical Clustering Technique

Pada umumnya sistem distribusi adalah radial. Sifat radial memiliki kesederhanaan dalam operasionalnya. Sistem distribusi radial (radial distribution system-RDS) hanya memiliki sebuah gardu induk sebagai satu-satunya sumber tenaga listrik. Gardu induk menerima tenaga listrik dari stasiun pembangkit terpusat melalui interkoneksi jaringan transmisi. Pelanggan listrik menerima daya listrik dari gardu induk melalui jaringan RDS dimana jaringan RDS tersebut merupakan jaringan pasif dan banyak diterapkan di lapangan. Oleh karena itu, aliran daya listrik di jaringan RDS adalah searah. Rasio X / R yang tinggi pada saluran-saluran distribusi menghasilkan drop tegangan yang besar, stabilitas tegangan rendah dan rugi-rugi daya saluran. Itu semuanya menyebabkan penurunan kualitas daya pada operasional jaringan RDS. Dalam dekade terakhir, beberapa upaya dilakukan untuk peningkatan profil tegangan dan sekaligus pengurangan/penurunan rugi-rugi daya saluran melalui penempatan sumber-sumber daya reaktif secara terdistribusi. Salah satunya adalah penempatan lokasi dan ukuran kapasitor bank yang optimal pada jaringan RDS. Meskipun teknik penempatan lokasi dan ukuran kapasitor bank yang optimal cukup menjanjikan, tetapi perbaikan-perbaikan yang diperoleh pada profil tegangan jaringan RDS masih berada di bawah tegangan rata-rata atau tegangan steady state yang diinginkan (1,0 p.u.). Selain itu, jaringan RDS belum sepenuhnya dapat diandalkan karena sifatnya masih pasif. Baru-baru ini, solusi yang telah direkomendasikan untuk mengatasi kepasifan jaringan RDS dengan mengintegrasikan sumber daya dengan kapasitas kecil sampai sedang berbasis teknologi energi baru terbarukan untuk peningkatan kualitas daya listrik. Sumber-sumber listrik tersebar dengan kapasitas kecil sampai sedang berbasis teknologi energi baru terbarukan pada jaringan RDS disebut sebagai pembangkit-pembangkit tersebar/terdistribusi (dispersed generations or distributed generations - DG). Aliran daya sistem distribusi merupakan komponen utama dari perencanaan dan operasi jaringan RDS. Hasil simulasi aliran daya biasanya digunakan untuk perencanaan dan perancangan ekspansi sistem distribusi, mengetahui rugi-rugi daya ditiap-tiap saluran dan mengevaluasi kondisi jaringan RDS yang ada. Oleh sebab itu dibutuhkan strategi perencanaan dan operasi dalam jaringan RDS tersebut. Keberagaman strategi perencanaan dan operasi dalam jaringan RDS telah banyak dilakukan dan salah satunya perencanaan terkoordinasi (coordinated planning). Perencanaan terkoordinasi adalah suatu kegiatan perencanaan untuk mengkoordinasikan kegiatan rekonfigurasi jaringan (network reconfiguration, penempatan dan penetapan ukuran kapasitor (placement and sizing of capacitor) serta penempatan dan penetapan ukuran pembangkit-pembangkit terdistribusi (placement and sizing of distributed generations - DGs) pada jaringan RDS. Setiap kegiatan perencanaan terkoordinasi tersebut merupakan persoalan optimasi dimana setiap optimasi memiliki fungsi obyektif tunggal (single) maupun jamak (multi) dan memenuhi kendala-kendala (constraints) yang ditetapkan. Perencanaan terkoordinasi menghasilkan strategi terbaik melalui sejumlah kombinasi alternatif yang mungkin baik secara berurutan (sequensial) maupun bersamaan (simultaneous) yang dipecahkan melalui penyelesaian aliran daya optimal lanjut (Advanced-Optimal Power Flow –Advanced - OPF) berbasis Hierarchical Clustering Technique-HCT. Penelitian disertasi ini telah dihasilkan pengembangan formulasi algoritma aliran daya optimal lanjut (Advanced - OPF) berbasis HCT yang memiliki performansi terbaik untuk tujuan meminimumkan rugi-rugi daya saluran (PLOSS), meminimumkan level deviasi tegangan (VOLT) dan memaksimumkan daya aktif keluaran DGs (PDGs) untuk peningkatan kualitas daya pada kegiatan perencanaan terkoordinasi pada jaringan RDS. Selain itu, penelitian disertasi ini telah dihasilkan simulator sistem pengambil keputusan perencanaan terkoordinasi (Decision Support System Coordinated Planning – DSS - CP) untuk menunjang perencanaan, operasi dan optimasi jaringan RDS pada jaringan standar-Sistem IEEE-33 BUS dan jaringan riil-Penyulang Basuki Rahmat-51 BUS. Performansi terbaik telah ditunjukkan melalui serangkaian perencanaan, operasi dan optimasi melalui simulasi Advanced-OPF-Coordinated Planning berbasis HCT pada jaringan RDS baik jaringan standar – Sistem IEEE-33 BUS maupun jaringan riil – Penyulang Basuki Rahmat-51BUS. Sistem IEEE-33 BUS memberikan performansi terbaik pada kegiatan perencanaan terkoordinasi secara serempak melalui rekonfiguransi jaringan, penempatan & penetapan ukuran unit-unit DG, dan penempatan & penetapan ukuran kapasitor bank Sedangkan Penyulang Basuki Rahmat-51BUS memberikan performansi terbaik pada kegiatan perencanaan terkoordinasi melalui penempatan & penetapan ukuran unit-unit DG dibandingkan dengan rekonfiguransi jaringan dan penempatan & penetapan ukuran kapasitor bank Selain itu, penelitian disertasi ini telah dihasilkan simulator sistem pengambil keputusan perencanaan terkoordinasi (Decision Support System Coordinated Planning – DSS - CP) berbasis HCT untuk menunjang perencanaan, operasi dan optimasi jaringan RDS pada umumnya serta khususnya pada Sistem IEEE-33 BUS dan Penyulang Basuki Rahmat-51BUS. Simulator DSS-CP berbasis HCT mampu memetakan strategi kegiatan perencanaan terkoordinasi berdasarkan prioritas nilai fitness fungsi obyektif (baik tunggal maupun banyak) Advanced-OPF secara hierarki dari terkecil sampai terbesar. ============== Generally the distribution system is radial. The radial property has it’s simply operational. The radial distribution system (RDS) only has a substation as is the electric source. Substation gains the electric source from center generation via transmission network interconnection. The customer gets the electric power from substation across RDS network. The RDS network is passive network and it ‘s application is more. Therefore, electric power flow on RDS network is unidirectional. The high X/R ratio of distribution lines causes a great voltage drop, low voltage stability and line power losses. All them effect power quality decreasing on RDS network operational. In the last decade, many efforts had been done to improve voltage profile and to decrease line power losses by placement distributed active/reactive power sorurces. One of them is optimal bank capacitor placement and sizing on RDS network. Although the optimal capacitor bank placement and sizing technique are promising, the voltage profile improvements are obtained in the RDS network. They are still below the voltage average on desired steady state voltage (1.0 p.u.). In addition, the RDS network is still less reliable because it is still a passive network. Recently, the solution has been recommended to overcome the passivity of RDS networks by integrating resources with small to medium capacity based on renewable energy technologies. Overall are to improve the electric power quality. Distributed electric sources which have small to medium-sized capacity based on new renewable energy technologies in RDS networks are referred to as dispersed generations or distributed generations (DGs). The distribution system power flow is a major component of RDS network planning and operations. The power flow simulation results are usually used for planning and designing the expansion of the distribution system, knowing the power losses in each line and evaluating the conditions of the existing RDS network. Therefore, they are required planning and operating strategies in the RDS network. The diversity of planning and operating strategies in RDS networks has been widely implemented and one of them is the coordinated planning.The coordinated planning is a planning activity to coordinate network reconfiguration, placement & sizing of the capacitor bank, and placement & sizing of distributed generations (DGs) unit in RDS networks. Each the coordinated planning activity is an optimization problem in which each optimization has a single or multi objective function and meets the constraints set. The coordinated planning produces the best strategy through a combination of alternatives that may be sequential or simultaneous solved by completion of an Advanced-Optimal Power Flow (Advanced-OPF) based on Hierarchical Clustering Technique (HCT). This dissertation research has gained an optimal power flow algorithms formulation development of Advanced-OPF-CP based on HCT. It has the best performance for the purpose of line power loss (PLOSS) minimizing , voltage deviation (VOLT) minimizing and the active power output of DGs maximizing ( PDGs) for enhanced power quality in the coordinated planning activities on RDS networks. In addition, this dissertation research has resulted in a simulator of the coordinated planning decision making system (Decision Support System Coordinated Planning (DSS - CP) based on HCT. The DSS-CP Based on HCT Simulator has supported planning, operation and optimization of RDS network on a standard network-the IEEE-33 BUS system and a real network - the Basuki Rahmat -51 BUS feeder. The best performance has been demonstrated through a series of planning, operation and optimization using the Advanced-OPF-CP based on HCT Simulator on RDS networks which are both a standard network - the IEEE-33 BUS system and a real network - the Basuki Rahmat-51BUS feeder. The IEEE-33 BUS system provides the best performance in the coordinated planning activities simultaneously through network reconfiguration, placement & sizing of DGs unit, and the placement & sizing of bank capacitor. While the Basuki Rahmat-51BUS feeder gives the best performance in coordinated planning activities through placement & sizing of the DG units if it is compared to the network reconfiguration and the placement and sizing of the bank capacitor. Finally, this dissertation research had resulted in the DSS-CP Based on HCT-simulator to support generally planning, operation and optimization of RDS network in general and especially on the IEEE-33 BUS system and the Basuki Rahmat-51BUS feeder. The DSS-CP based on HCT simulator is capable of mapping the coordinated planning strategy based on the priority of the objective functional (either single/multi) fitness values (either single or multiple) hierarchically from the smallest to the largest values