Distribution voltage control considering the impact of PV generation on tap changers and autonomous regulators

The uptake of variable megawatts from photovoltaics (PV) challenges distribution system operation. The primary problem is significant voltage rise in the feeder that forces existing voltage control devices such as on-load tap-changers and line voltage regulators to operate continuously. The consequence is the deterioration of the operating life of the voltage control mechanism. Also, conventional non-coordinated reactive power control can result in the operation of the line regulator at its control limit (runaway condition). This paper proposes an optimal reactive power coordination strategy based on the load and irradiance forecast. The objective is to minimize the number of tap operations so as not to reduce the operating life of the tap control mechanism and avoid runaway. The proposed objective is achieved by coordinating various reactive power control options in the distribution network while satisfying constraints such as maximum power point tracking of PV and voltage limits of the feeder. The option of voltage support from PV plant is also considered. The problem is formulated as constrained optimization and solved through the interior point technique. The effectiveness of the approach is demonstrated in a realistic distribution network model

An alternative Volt-VAR management scheme for active distribution grids: ABB

Larger penetration of distributed generation and active loads is expected in the near future. These new loads have brought up new challenges to the electrical networks as well as new possible opportunities. The possibility of using these new elements to regulate and control the voltage is considered as the future scenario. Therefore this thesis, develops a coordination between the most common elements in the networks (capacitor banks, STATCOMs, OLTCs/VRs and DGs), in order to study their interaction and how they together could manage the voltage level. In addition, EV charging station integration has been also evaluated. Considering this scenario, several simulations varying different parameters such as time delay or bandwidth are carried out. Also the concept line compensation is taken into consideration in the networks analysed. Through all the simulations accomplished it is proved that a coordination is necessary between all the elements. Later on, a discussion about how each configuration affects the network complete this thesis. Besides, the simulated scenarios show that DGs and EVs can contribute to voltage regulation in an effcient way.Ingeniería Industria

Impact of distributed generation on protection and voltage regulation of distribution systems : a review

During recent decades with the power system restructuring process, centralized energy sources are being replaced with decentralized ones. This phenomenon has resulted in a novel concept in electric power systems, particularly in distribution systems, known as Distributed Generation (DG). On one hand, utilizing DG is important for secure power generation and reducing power losses. On the other hand, widespread use of such technologies introduces new challenges to power systems such as their optimal location, protection devices' settings, voltage regulation, and Power Quality (PQ) issues. Another key point which needs to be considered relates to specific DG technologies based on Renewable Energy Sources (RESs), such as wind and solar, due to their uncertain power generation. In this regard, this paper provides a comprehensive review of different types of DG and investigates the newly emerging challenges arising in the presence of DG in electrical grids.fi=vertaisarvioitu|en=peerReviewed

Distributed Voltage Control in Distribution Networks with Electric Vehicle Charging Stations and Photovoltaic Generators

The developments of distributed generators (DGs) and electric vehicles (EVs) are dramatical due to the rapid increase of friendly environment desire. While on another hand, the proliferation of distributed generators (DGs) and electric vehicle charging stations (EVCSs) has brought voltage regulation challenges to distribution systems due to their high generations and heavy loads. In this thesis, a distributed control strategy is proposed which mainly consisted by a reactive compensation algorithm to dispatch surplus reactive power from DGs and EVCSs for proper voltage regulation without violating their converters’ capacity limits or stressing conventional voltage control devices, i.e., on-load tap changers (OLTCs), and an active power curtailment algorithm for DGs to properly integrate OLTC in voltage regulation when the reactive power compensation is deficient. The proposed control algorithms rely on consensus theory and sensitivity analysis, thus, minimizing the active and reactive powers needed for voltage support, and decreasing the net cost of voltage regulation. In the proposed control strategy, three distributed voltage regulation algorithms, as well as a distributed control method for OLTC, are developed and coordinated to realize adequate voltage maintaining effects. Simulation results of a typical distribution system confirm the effectiveness and robustness of the proposed distributed control strategy in continuously maintaining proper voltage regulation for the whole distribution system with minimum power demands from DGs and EVCSs, and reduced tap operation for OLTC, within every 24 hours

Coordinated Voltage Control in Modern Distribution Systems

Modern distribution systems, especially with the presence of distributed generation (DG) and distribution automation are evolving as smart distribution systems. Distribution management systems (DMSs) with communication infrastructure and associated software and hardware developments are integral parts of the smart distribution systems. With such advancement in distribution systems, distribution system voltage and reactive power control are dominant by Volt/VAr (voltage and reactive power) optimisation and utilisation of DG for system Volt/VAr support. It is to be noted that the respective controls and optimisation formulations are typically adopted from primary, secondary and tertiary voltage and reactive power controls at upstream system level. However, the characteristics of modern distribution systems embedded with high penetration of DG are different from transmission systems and the former distribution systems with uni-directional power flow. Also, coordinated control of multiple Volt/VAr support DG units with other voltage control devices such as on-load tap changer (OLTC), line voltage regulators (VRs) and capacitor banks (CBs) is one of the challenging tasks. It is mainly because reverse power flow, caused predominantly by DG units, can influence the operation of conventional voltage control devices. Some of the adverse effects include control interactions, operational conflicts, voltage drop and rise cases at different buses in a network, and oscillatory transients. This research project aimed to carry out in-depth study on coordinated voltage control in modern MV distribution systems utilising DG for system Volt/VAr support. In the initial phase of the research project, an in-depth literature review is conducted and the specific research gaps are identified. The design considerations of the proposed coordinated voltage control, which also uses the concept of virtual time delay, are identified through comprehensive investigations. It emphasises on examining and analysing both steady-state and dynamic phenomena associated with the control interactions among multiple Volt/VAr support DG units and voltage control devices. It would be essential for ensuring effective coordinated voltage control in modern distribution systems. In this thesis, the interactions among multiple DG units and voltage control devices are identified using their simultaneous and non-simultaneous responses for voltage control through time domain simulations. For this task, an analytical technique is proposed and small signal modelling studies have also been conducted. The proposed methodology could be beneficial to distribution network planners and operators to ensure seamless network operation from voltage control perspective with increasing penetration of DG units. Notably, it has been found that the significant interactions among multiple DG units and voltage control devices are possible under conventional standalone, rule-based, and analytics based control strategies as well as with real-time optimal control under certain system conditions. In the second phase of the research project, the proposed coordinated voltage control strategy is elaborated. The control design considerations are fundamentally based on eliminating the adverse effects, which can distinctly be caused by the simultaneous and non-simultaneous responses of multiple Volt/VAr support DG units and voltage control devices. First, the concept of virtual time delay is applied for dynamically managing the control variables of Volt/VAr support DG units and voltage control devices through the proposed control parameter tuning algorithm. Because it has been found that the conventional time-graded operation cannot eliminate the adverse effects of DG-voltage control device interactions under certain system conditions. Secondly, the distinct control strategies are designed and tested for effectively and efficiently coordinating the operation of multiple Volt/VAr support DG units and voltage control devices in real-time. The test results have demonstrated that the proposed coordinated voltage control strategy for modern MV distribution systems can effectively be implemented in real-time using advanced substation centred DMS. The proposed coordinated voltage control strategy presented in this thesis may trigger paradigm shift in the context of voltage control in smart distribution systems. In the final phase of the research project, short-term and/or long-term oscillations which can be possible for a MV distribution system operation embedded with Volt/VAr support DG are discussed. Typically, the short-term oscillations are occurred due to interactions among different DG units and their controllers (i.e., inter-unit electro-mechanical oscillations in synchronous machine based DG units) while the long-term oscillations occurred due to DG-voltage control device interactions. Also, sustained oscillations may occur due to tap changer limit cycle phenomenon. The concept of alert-state voltage control is introduced for mitigating the sustained oscillations subjected to OLTC limit cycles in the presence of high penetration of DG. The investigative studies in this thesis further emphasise the requirements of supplementary control and other mitigating strategies for damping the oscillations in modern active MV distribution systems. The proposed research will pave the way for managing increasing penetration of DG units, with different types, technologies and operational modes, from distribution system voltage control perspective

A coordinated voltage regulation algorithm of a power distribution grid with multiple photovoltaic distributed generators based on active power curtailment and on-line tap changer

The aim of this research is to manage the voltage of an active distribution grid with a low X/R ratio and multiple Photovoltaic Distributed Generators (PVDGs) operating under varying conditions. This is achieved by providing a methodology for coordinating three voltage-based controllers implementing an Adaptive Neuro-Fuzzy Inference System (ANFIS). The first controller is for the On-Line Tap Changer (OLTC), which computes its adequate voltage reference. Whereas the second determines the required Active Power Curtailment (APC) setpoint for PVDG units with the aim of regulating the voltage magnitude and preventing continuous tap operation (the hunting problem) of OLTC. Finally, the last component is an auxiliary controller designed for reactive power adjustment. Its function is to manage voltage at the Common Coupling Point (CCP) within the network. This regulation not only aids in preventing undue stress on the OLTC but also contributes to a modest reduction in active power generated by PVDGs. The algorithm coordinating between these three controllers is simulated in MATLAB/SIMULINK and tested on a modified IEEE 33-bus power distribution grid (PDG). The results revealed the efficacy of the adopted algorithm in regulating voltage magnitudes in all buses compared to the traditional control method.Peer ReviewedPostprint (published version

NOVEL OPTIMAL COORDINATED VOLTAGE CONTROL FOR DISTRIBUTION NETWORKS USING DIFFERENTIAL EVOLUTION TECHNIQUE

This paper investigates a Distributed Generators (DG) connected to distribution networks offer multiple benefits for power networks and environments in the case of renewable sources. Nevertheless, if there is not an appropriate planning and control strategy, several issues, such as voltage rise problems and increased power losses, may happen. In order to overcome such disadvantages, in this paper, a coordinated voltage control method for distribution networks with multiple distributed generators is proposed. This method is based on a differential evolution DE approach to obtain the optimal setting points for each control component. Furthermore this proposed method considers both of time-varying load demand and production, leading to not only an improvement in the voltage profile but also to optimally minimize the active power loss

On Coordinated Control of OLTC and Reactive Power Compensation for Voltage Regulation in Distribution Systems With Wind Power

Active management strategies such as coordinated on load tap changer (OLTC) voltage control and reactive power compensation (RPC) are frequently suggested for voltage regulation in a distribution system with a high level of distributed generation (DG). This paper proposes a control and coordination algorithm for these two active management strategies. Voltage control through OLTC is achieved by using state estimation (SE) to determine the voltage in the network. To lower the implementation cost of the proposed control strategy, pseudo-measurements are used together with real-time measurement data in the SE. Moreover, the deadband of the automatic voltage control (AVC) relay is relaxed so that the AVC relay acts on the network's maximum or minimum voltage obtained through the SE. This is found to be simpler to realize than adjusting the set point of the AVC relay. Voltage control through RPC is actualized by using integral controllers implemented locally at the wind turbine site. Furthermore, RPC from the local wind turbine is also used to mitigate an overvoltage at a remote bus on the same feeder when the remote wind turbine reaches its regulation limit. The applicability of the proposed voltage regulation algorithm is successfully demonstrated using a case study syste

Voltage regulation of unbalanced distribution network with distributed generators through genetic algorithm

Energy demand has rapidly increased since the manufacturing revolution in the 19th century. One of the higher energy demands is electricity. The great majority of devices in the manufacturing field run on electricity. The vertically integrated grid paradigm has to be changed to supply the increase in the electrical demand residentially and commercially. Distributed generators (DG) such as Photovoltic (PV) is used to supply the increase in the electrical demand. Photovoltaic (PV) is one of the fast growing distributed generators (DG) as a renewable energy source. However, installing many PV systems to the distribution system can cause power quality problems such as over voltage. This would be more concern in an unbalanced electrical distribution network where nowadays most of the PV systems are connected. PV system should coordinate with other DGs and already existing voltage regulators such as on load tap changer (OLTC) on voltage regulation so that they can support the electrical grid without adding voltage problems. This dissertation focuses on voltage regulation of unbalanced distribution system through the utilization of PV reactive power feature by minimizing the system losses using genetic algorithm. The proposed method provides a single phase controlled PV system that regulates each phase voltage individually and focuses in maintaining the voltage for each phase within a certain limit. In addition, this study proposes a single-phase OLTC control by changing the tap position individually using loss minimization. The proposed algorithm is implemented in Matlab and Simulink. Results show that the PV reactive power can be utilized to control the system voltage as well as to minimize the traditional voltage regulator operations