Multi-Objective Planning Techniques in Distribution Networks: A Composite Review

Syed Kazmi, Muhammad Shahzad, Dong Shin
2017 Energies  
Distribution networks (DNWs) are facing numerous challenges, notably growing load demands, environmental concerns, operational constraints and expansion limitations with the current infrastructure. These challenges serve as a motivation factor for various distribution network planning (DP) strategies, such as timely addressing load growth aiming at prominent objectives such as reliability, power quality, economic viability, system stability and deferring costly reinforcements. The continuous
more » ... nsformation of passive to active distribution networks (ADN) needs to consider choices, primarily distributed generation (DG), network topology change, installation of new protection devices and key enablers as planning options in addition to traditional grid reinforcements. Since modern DP (MDP) in deregulated market environments includes multiple stakeholders, primarily owners, regulators, operators and consumers, one solution fit for all planning scenarios may not satisfy all these stakeholders. Hence, this paper presents a review of several planning techniques (PTs) based on mult-objective optimizations (MOOs) in DNWs, aiming at better trade-off solutions among conflicting objectives and satisfying multiple stakeholders. The PTs in the paper spread across four distinct planning classifications including DG units as an alternative to costly reinforcements, capacitors and power electronic devices for ensuring power quality aspects, grid reinforcements, expansions, and upgrades as a separate category and network topology alteration and reconfiguration as a viable planning option. Several research works associated with multi-objective planning techniques (MOPT) have been reviewed with relevant models, methods and achieved objectives, abiding with system constraints. The paper also provides a composite review of current research accounts and interdependence of associated components in the respective classifications. The potential future planning areas, aiming at the multi-objective-based frameworks, are also presented in this paper. Keywords: active distribution network (ADN); distributed generation (DG); distributed energy resources (DERs); distribution network planning (DP); multi-objective optimization (MOO); multi-criteria decision analysis (MCDA); distributed generation placement (DGP); volt-ampere reactive power (VAR) compensation and power quality (VPQ); component reinforcement and up gradation (CRU); network (distribution) topology change and reconfiguration (NTR); planning techniques (PT); multiple objective planning (MOP); multi-objective planning techniques (MOPTs); future distribution networks (FDNs) 2 of 44 options, increasingly competitive electricity market scenarios and environmental concerns result in stressed operating conditions for both TNWs and DNWs. In comparison, DNWs gets a higher share of stressed conditions due to their design, planning and operation limitations [1] . Traditionally DNWs were purposely planned to operate in a radial configuration to maintain one-way power flow. Such a setup was preferred largely due to simple protection equipment, reduced short circuit currents (SCCs) of the networks, easy control requirements, a safe and economical operation for the end consumer. However, the rapid growth of DNWs and associated loads over large geographical areas results in technical issues like voltage instability, increased system losses, low network reliability, compromised power quality and capacity enhancement concerns, respectively [2,3]. The factors above are motivating system planners to find alternative methods rather than traditional ones, to meet the increased demand and concerned issues promptly. The possible solution strategy calls for planning modifications on short/medium/long-term basis in the potential areas of generation capacity enhancement, improving power quality, load management, emissions control and ensuring overall system reliability. Energies 2017, 10, 208 3 of 44 Rodriguez et al. [7] regarding MO-based DG/DER planning methods till 2009. Georgilakis and Hatziargyriou [8, 10] presented two notable planning surveys for optimal DG placement and grid reinforcements, respectively. The multi-objective planning (MOP) problem had partially addressed in both works. Kalambe in [9] offered a bibliographic survey regarding single objective techniques focusing on loss minimization for DG, capacitor placement, and network reconfiguration (NTR) respectively. DG as an attractive planning alternative for utilities regarding loss minimization, voltage stability and deferring costly grid reinforcements has advocated in [10] [11] [12] . The integration of RES-based DGs (REG) to achieved clean energy and emission reduction are among the notable motives for researchers. However planning with only high penetration of REG is not very productive due to the limitations in traditional operational (inadequate reactive power support at unity power factor, power quality) and protection capabilities of current DNWs [13] . Hence, volt-amphere reactive (VAR) power compensation and power quality issues have been addressed with planned allocation of capacitors [14] and advanced power electronic devices [15] . The protection issue has addressed with planned allocation of protection and automation devices; to ensure reliability and system stability under both normal and emergency scenarios [16] . Also, a few new MDP strategies are employed to address load management issues by employing coordinated planning of multiple components (DG units, capacitors, protection devices) with NR (and/or topology alteration) [17] [18] [19] . A review of the literature shows that most of the planning techniques address single objectives optimization on a large scale. However, little attention is paid to various planning techniques (PTs) in multi-objective framework [20] , which can be interdependent, integrated and coordinated with traditional planning options from a MDP viewpoint. Hence the potential planning techniques in this paper are distinctly classified into four categories. The first category covers planning components, primarily DG units (of various types and concepts), STs and EVs. The second category comprises capacitors (types) and power electronic devices, to ensure VAR compensation and power quality. The third category contains protection, automation devices, and traditional grid reinforcements to guarantee reliability and system stability under new or expansion planning scenarios [8, 18, 19] . Finally, network topology optimization with alteration and/or NTR (to retain the radial nature of distribution systems) has been considered as a planning option. Energies 2017, 10, 208 4 of 44 It is a well-established fact that real world planning problems are multi-objective (MO) in nature. Also, more investigation is needed to carry out realistic (MO) planning by upgrading conventional to smart DNWs or redesigning them from the beginning. Hence, the core aim of this paper is to provide a background for future distribution network (FDN) planning on the basis of the limitations perceived in available works and from the perspectives of MO achievement. The paper is organized as follows: Section 2 covers classification details of planning techniques, objectives, MO formulations and major considerations for MOP models. A composite review of studied works has presented regarding decision variables, constraints, objectives, test systems, methods and considered models within PT taxonomies in Section 3. Section 4 outlines MO method classification. The contribution of the reviewed work has presented in Section 5. Future research directions have been suggested in Section 6. The paper concludes in Section 7. Classifications of Planning Techniques and Key Enablers The primary objective from the perspective of planning, operation, and upgrading of any DNW is to meet the demands of end consumers in a better, safe, economical, reliable and timely manner (planning horizon). The general DP problem is considered a mixed integer nonlinear programming problem (MINLP) [8, 10] . The TDP problem focuses on minimization of economic cost objectives for traditional reinforcements subject to a set of constraints. The MDP problem focuses on planning techniques (PT) from various aspects, multiple objectives, decision variables, load models while abiding with system constraints. Based on our literature survey, four PTs are presented in Sections 2.1-2.4. Distributed Generation Placement (DGP) The DG is defined as "a small-scale electrical power generation source connected directly to the DNW or on the consumer side of the meter". The DG type by connection and voltage level includes DGs on the DNW side with a medium voltage (MV) or low voltage (LV), whereas usually LV is on the consumer side. The DG units connected directly to DNW (close to load centers) are considered as an attractive planning alternative for utilities worldwide. However, high DG penetration has changed the nature of DNW from passive to an active one with bidirectional power flows. The prominent benefits attributed to DGP-based planning include voltage support, loss minimization, an alternative to costly reinforcements, and reduction of GHG (with REGs). Broader DG concepts by types are covered in [11] [12] [13] as follows: Volt-Ampere Reactive Power Compensation and Power Quality (VPQ) Capacitor (Cap) placement is one of the oldest techniques, still in use today (as shunt capacitor banks). They primarily provide VAR compensation within DNWs (located at SS or distributed in the field) to reduce reactive power losses, power factor correction and voltage stability. Moreover, improvement in power electronics, particularly FACTS devices and power filters, make room for modifications in planning approach, which is meeting load demands ensuring both VAR compensation and power quality during the planning process. The broad VPQ category, comprising of planning components, are arranged as per following types [14, 15] :
doi:10.3390/en10020208 fatcat:7lletw53lvg2jlkwffwsmmscwu