Provide Voltage Support Research Articles

Smart Operation Control of Power and Heat Demands in Active Distribution Grids Leveraging Energy Flexibility

Demand flexibility plays a crucial role in mitigating the intermittency of renewable power sources. This paper focuses on an active distribution grid that incorporates flexible heat and electric demands, specifically heat pumps (HPs) and electric vehicles (EVs). Additionally, it addresses photovoltaic (PV) power generation facilities and electrical batteries to enhance demand flexibility. To exploit demand flexibility from both heat and electric demand, along with the integration of PVs and batteries, Control and Communication Mechanisms (CCMs) are formulated. These CCMs integrate demand flexibility into the distribution grids to obtain economic benefits for private households and, at the same time, facilitate voltage control. Concerning EVs, the paper discusses voltage-based droop control, scheduled charging, priority charging, and up-/down-power regulation to optimize the charging and discharging operations. For heat demands, the on-off operation of the HPs integrated with phase change material (PCM) storage is optimized to unlock heat-to-power flexibility. The HP controllers aim to ensure as much self-consumption as possible and provide voltage support for the distribution grid while ensuring the thermal comfort of residents. Finally, the developed CCMs are implemented on a small and representative community of an active distribution grid with eight houses using Power Factory software and DIgSILENT simulation language (DSL). This scalable size of the active distribution network facilitates the careful study of symbiotic interaction among the flexible load, generation, and different houses thoroughly. The simulation results confirm that the integration of flexible demands into the grid using the designed CCMs results in the grid benefiting from stabilized voltage control, especially during peak demand hours.

Low Voltage Ride Through Control Strategy for a Two-Stage Grid-Tied Solar Photovoltaic System with Grid Faults

This paper investigates a low voltage ride-through (LVRT) control strategy for a two-stage grid-tied solar photovoltaic (SPV) system with line-to-ground (L-G) and double line-to-ground (L-L-G) faults. A proportional resonant (PR) controller controls the SPV inverter based on classical and reactive power oscillation-based reference current generating techniques. The proposed method injects reactive power as an ancillary service to provide voltage support and prevent power outages, reduces the DC component injection into the grid currents, and finally injects sinusoidal currents into the grid, avoid voltage oscillations in the DC-link and limit the inverter current by operating the boost converter in non-MPPT mode during L-G & L-LG faults. Experimental results for reference current generation using classical method and proposed method are compared to highlight the proposed controller’s ability to maintain power quality during faults.

Cooperative Control Strategy of Multifunctional Inverters For Power Quality Enhancement in Smart Microgrid

This paper deals with a cooperative strategy, based on the conservative power theory decomposition, which can be applied to control the inverters used to connect the distributed energy resources in a three-phase microgrid. In addition to inject/absorb active power at their point of connection, these inverters are operated according to their available power capability so as to enhance the power quality at the point of common coupling to the main network. Simulation results are shown considering, as an example, a three-phase three-wire microgrid equipped with two inverters, together with unbalanced and nonlinear loads. Among the different analyzed situations, the possibility to supply reactive power at the point of common coupling is shown with a view to provide voltage support, which is an asset in the framework of smart distribution networks.

Analysis of equilibrium points and optimal grid support of grid-forming modular multilevel converter for balanced and unbalanced faults

This short-communication presents a steady-state analysis of a grid-forming Modular Multilevel Converter (MMC) providing optimal voltage support to the AC network under normal and constrained conditions. The analysis is performed based on a multi-objective function (OF) optimization problem which prioritizes to maximize the positive-sequence and to minimize the negative- and zero-sequence voltage components at the point of common coupling (PCC) while it also considers the minimization of the arm impedance losses, respectively. If the voltage condition at the PCC is satisfied, the optimization attempts to reduce the arm impedance losses; otherwise, the algorithm prioritizes the PCC’s voltage components in order to minimize the error. Different network voltage and internal fault scenarios are evaluated, where it is shown that the suggested problem formulation can be used to obtain the optimal MMC’s quantities, providing voltage support during the faults.

A Generic Voltage Control for Grid-Forming Converters With Improved Power Loop Dynamics

Grid-forming converters (GFMCs) provide voltage support and other grid services, such as inertia and droop, in more-electronics power systems. The GFMCs with small droop coefficients or connected to the grid through a small impedance may have a fast power loop, which leads to serious conflicts with the inner ac voltage control loop, resulting in power oscillations or even instability. To address this problem, an extremely fast ac voltage loop should be expected for GFMCs. On top of that, GFMCs must operate well in both stand-alone and grid-tied conditions. Through detailed analysis, this article first reveals that the grid-tied operation of a dual-loop controlled GFMC with an <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">LCL</i> output filter features a much slower voltage control loop than that of the stand-alone mode. To improve the dynamics of GFMCs, we propose a generic voltage control scheme with a high-pass filter in the current feedback loop. The generic voltage controller has fast voltage tracking performances under both grid-tied and stand-alone operations, thereby enabling GFMCs to achieve better power regulation and grid service. The improvements in both voltage tracking and power control are verified via experiments.

A Novel Power Injection Priority Optimization Strategy for Voltage Support Control of PMSG-based Wind Farm

This article presents a novel power injection priority optimization-based control strategy for a PMSG-based wind farm. The proposed strategy seeks to provide voltage support while mitigating the frequency excursion resulting from voltage dip during the fault. To achieve this objective, the conventional fixed reactive power injection priority plan is replaced by an adaptive power injection priority plan in the proposed method. The control problem is formulated as a multi-objective function optimization problem, where the power injection priority plan is calculated by minimizing the shortfall of WF active power and maximizing the reactive power injection of WF. During the fault period, the optimized result is directly applied to the outer control of machine-side converter and grid-side converter to regulate the active/reactive power generation. The simulation system model and proposed optimal model are built in EMTDC/PSCAD and MATLAB, respectively, to verify the effectiveness of the proposed strategy. Test results demonstrate that the proposed control strategy is applicable to mitigate frequency excursion while complying with the voltage support requirement during the fault.

REDUCING THE SHOOTING OF HYBRID PHOTOVOLTAIC PLANTS ON SCR AND LI-GRIDS

The main threat by comparable methods lately is the temporary downtime for accurate-current network dispatch errors. Throughout a temporary outage, Power Electronic based power sources stop operating, giving rise to possible security defiance towards the network, in this research, the potentially viable choice to serve continuous work temporarily for the scheme is provided with consideration of identifying upgrades to existing photovoltaic generators (photovoltaic generators discrete) and an upgrade in the separate establishment of existing “photovoltaic” and “Energy Storage Systems” discrete hybrid photovoltaics. This study aims to find a series of power sources with Power Electronic interfaces that are connected to a low “Short Circuit Ratio” network and “Low Inertia” grid to operate without a moment's stoppage.&#x0D; The proposed method was proved by adopting PSS/e on a method where power electronics-occupying assets produce the majority of energy. Inverter models along with temporary shutdown through an equal 3-period fault were advanced in PSS/e. together with increasing infiltration of “Power Electronics” established multitude and resources, progressive completion is needed to improve network stability in low a) areas and low inertia networks. The requirements for progressive solvent arose out of the steady variation in the paradigm of the power grid from the dominant systems of traditional electric machines to the high penetration of systems based on power electronics. A technical comparison was made between distinct categories of resolution (divergent photovoltaic and divergent hybrid photovoltaic) to operate a photovoltaic generator's weak “Short Circuit Ratios” also “Low Inertia” grating (grid).&#x0D; The results of this study indicate that the proposed solution is calculated nether disparate running term and error class adopting the Electromagnetic Transient model. Moreover, to analyze distinct solvents, a specialized proportion is served on discrete hybrid photovoltaic generators. The proposed solution is the development of conventional increase as well as contemporary condensers, deter capacitors, and reducers to advanced photovoltaic generators and hybrid photovoltaic generators to provide voltage support to ensure continuous working through lopsided dispatch streak disturbances, and another solution is photovoltaic-energy generation. Integrated storage system connected to High Voltage dc and high voltage ac transmission network.

Small-Signal Stability Assessment of Multi- Converter-Based-Renewable Systems With STATCOMs Based on Generalized Short-Circuit Ratio

The increasing integration of renewable resources (such as wind and solar) through grid-following converters is shifting the modern power system into a multi-converter-based- renewable (multi-CBR) system. In such a multi-CBR system, the dynamic interaction between CBRs and the power network may cause small-signal stability issues, especially under low short-circuit strength conditions. While static synchronous compensators (STATCOMs) are integrated into the multi-CBR system for providing voltage support, their dynamics also influence the small-signal stability. However, it has not been theoretically revealed how STATCOMs affect the small-signal stability, especially for low short-circuit strength systems. To fill this gap, this paper proposes a method to analyze small-signal stability of a multi-CBR system with STATCOMs based on grid strength analysis, wherein the grid strength is represented by short-circuit ratio (SCR) for a single-CBR system and generalized SCR (gSCR) for a multi-CBR system. Firstly, we analyze the relationship between small-signal stability and SCR in a single-CBR single-STATCOM system. Then, we study the relationship between the small-signal stability and gSCR in a multi-CBR system with STATCOMs. On this basis, a gSCR-based method is proposed for assessing the small-signal stability of a multi-CBR system with STATCOMs. The proposed method is validated through eigenvalue analysis, electromagnetic transient simulations and hardware-in-loop simulations.

Fast DC Fault Current Suppression and Fault Ride-Through in Full-Bridge MMCs via Reverse SM Capacitor Discharge

In the event of a DC side fault in modular multilevel converters (MMCs), the fault current contributions are initially made by submodule (SM) capacitor discharge, which occurs before the fault is detected, followed by the AC side contribution to the DC side fault. While the AC side currents can be regulated using fault blocking SMs, the initial discharge of the SM capacitors results in high DC fault currents, which can take several milliseconds to be brought under control. This paper presents a method to actively control the rate of rise of the DC fault current by regulating the discharge of SM capacitors and accelerating the suppression of fault current oscillations during fault ride-through (FRT) in a full-bridge (FB)-MMC system. In the proposed method, the discharge direction of the FBSM capacitors is reversed following the detection of a DC side fault, which leads to a reversal in the fault current direction and a fast drop-off towards the zero-crossing. Immediately after the zero-crossing of the DC fault current, the DC fault is cleared by adjusting the arm voltage references and operating the MMC as a static synchronous compensator (STATCOM) to provide voltage support to the AC grid. The proposed control scheme provides faster fault current suppression, more effective SM capacitor voltage regulation, low AC side and MMC arm current transient peaks, and an overall superior DC-FRT performance compared to methods in which the conventional fault ride-through operation is initiated immediately upon DC fault detection.

An overview of grid-connected fuel cell system for grid support

Fuel cell (FC) technology has become popular recently for its low-carbon characteristics. Depending on the different structures of the system and controls of the converter, grid-connected FC systems can achieve various goals in supporting the grid. Grid-following (GFL) and grid-forming (GFM) control are normally used for the controller of converters. In this paper, an overview of how the grid-connected FC system can support the grid is presented. The basic grid-connected FC system operation principles are firstly introduced, followed by the comparisons between FC and batteries, which shows the advantages and disadvantages of the FC system. Different functions of the FC system are then reviewed. Renewable sources, particularly wind turbines and photovoltaic farms, have some problems in the integration with the grid during the insufficient wind speed or radians, and FC systems can help renewables achieve better integration with the grid. Moreover, FC cannot only balance the system power as a primary energy source, but provide voltage support during system contingencies as well. Nevertheless, the FC system has some problems with oscillation and harmonics. Finally, the challenges of grid-connected FC systems are presented.

Using PV inverters for voltage support at night can lower grid costs

Areas with sparse transmission lines are common in regions with high solar energy potential and need voltage support. This may require installing expensive voltage compensators, such as static synchronous compensators (STATCOMs). This expense can increase the cost and decrease the acceptance of large-scale adoption of solar power. Unlike current photovoltaic (PV) inverter controllers, which provide voltage support only during the day, commercially available augmented voltage controllers can provide voltage support at night. We examine whether PV inverters improve nighttime voltage on the grid and how much such an operation would cost compared to a STATCOM. We ran grid contingency analyses on a model for West Texas within the Electric Reliability Council of Texas (ERCOT) jurisdiction under spring and summer conditions to determine if PV inverters can support nighttime voltage under varying reactive power demand. The cost of reactive power has not been defined previously, especially in the context of the United States. Our methods and application provide a way to determine the cost of reactive power for both PV project developers and system planners. Allowing PV inverters to provide reactive power can reduce system costs by millions of dollars, or 4–15 times less costly than installing a STATCOM. We determined inverter voltage support costs by calculating the cost of earlier inverter replacements due to increased reactive power output and voltage controllers. The net system savings argue for ERCOT changing their voltage support policies to incentivize PV plants to provide voltage support at night.

Data-Driven Fast Voltage Control in Non-DPMU Distribution Networks With Microgrids

Traditional voltage control methods for distribution networks assume perfect knowledge of the power system model. Nevertheless, the extensive scale of future distribution networks makes it unrealistic to acquire the overall operation state monitoring. Moreover, with the deregulation of distribution networks, partial controllable resources belong to independent systems, such as microgrids, causing distribution system operators unable to force them to provide voltage support directly. To cope with the previously mentioned problems, a data-driven fast voltage control method for distribution networks with MGs is proposed in this article. First, voltage sensitivity matrices are estimated indirectly by identifying line parameters in a regression approach, without using measurement data of distribution phasor measurement units (DPMUs) in distribution networks. Then, an incomplete information game model is proposed to motivate MGs to provide ancillary services of voltage control. To guarantee privacy, only a little key information is shared among MGs and distribution system operators. Moreover, MGs make voltage control strategies autonomously based on the data-driven deep reinforcement learning algorithms, while maximizing their own profits. Finally, we test the method on the modified IEEE 33-node networks and IEEE 123-node networks. The results demonstrate that the proposed method can provide an accurate voltage estimation in electricity markets with non-DPMU measurement data and increase energy and asset utilization.

Soft open points based load restoration for the urban integrated energy system under extreme weather events

With frequent occurrences of extreme natural disasters such as typhoons in urban integrated energy systems (UIES), it is of great significance to cope with different kinds of disturbances. This paper proposes a load restoration method under typhoon weather for urban distribution and natural gas networks based on soft open points (SOP). Firstly, the typhoon wind speed model is introduced and the line fault rates of distribution networks under typhoons are calculated. Secondly, the gas turbine and electric-driven compressor are considered as the coupling units of the integrated electric–gas energy system, and related models are constructed. The fault analysis method of the natural gas network is proposed considering the faults in the distribution network lead by typhoons. Thirdly, SOP installed in the distribution network with the V/f control mode is applied to restore electrical loads and provide voltage support for the loads on the fault side. After that, the loads of the gas network could also be restored because of the restoration of the coupling units. Optimal energy flow is applied to determine the output of the power and gas sources, coupling units and also the loads to be restored. Finally, the fault rate of each line under typhoon disaster is analysed and the correctness and effectiveness of the resilience improving method based on SOP are verified with test systems UIES E33-G14 and UIES E123-G48.

Multi-stage supply restoration of active distribution networks with SOP integration

Supply restoration from outages is essential for improving the reliability of active distribution networks (ADNs) after fault isolation. Soft open point (SOP) can adjust the power flow among feeders and provide voltage support for power outage areas. Considering the sequential coordination of switching operation and SOP control mode selection, a multi-stage supply restoration method with SOPs is proposed for ADNs. First, the sequential energization is formulated, in which the impact of SOP control mode on restoration sequence is analyzed. By providing voltage support, the coordination of SOPs will rapidly energize the outage area and improve the voltage profile. Then, a multi-stage restoration model with SOPs is proposed, in which reconfiguration of switches and control mode selection of SOPs are coordinated in sequence to maximize the load recovery level of ADNs. Through the switching action-time mapping, secure operation is ensured during the entire supply restoration process. Finally, the effectiveness of the proposed method is validated on a modified IEEE 33-node distribution system and practical distribution networks with four-terminal SOP. Results show that the proposed method can fully exploit the potential benefits of SOPs and effectively enhance the load recovery level of ADNs.

A hybrid architecture for volt-var control in active distribution grids

Modern active distribution grids are characterized by the increasing penetration of distributed energy resources (DERs). The proper coordination and scheduling of a large numbers of these small-scale and spatially distributed DERs is necessary, and warrants the use of novel distributed approaches. In this paper, we propose a hybrid volt-var control architecture for the distribution grid, which leverages existing centralized and local approaches to planning, decision making, and control, and augments it with distributed optimization and distributed control for DER management. First, we propose a convex model to describe the power physics of distribution grids of meshed topology and unbalanced structure, based on current injection and McCormick Envelopes. Second, we employ the distributed proximal atomic coordination (PAC) algorithm to coordinate DERs to provide voltage support. We implement volt-var optimization by optimally coordinating DERs including PV smart inverters and demand response. We present results using the IEEE-34 bus network, using real data from a distribution feeder in Hawaii, to model load and PV generation. Different levels of DER penetration and objective functions are simulated. Our results show the need for the coordination of DERs to improve voltage profiles, even in networks with existing voltage control devices. Further, we show the need for flexible reactive power capabilities to achieve desired grid performance.

Power Flow and Power Quality Enhancement by TCSC using five different Novel Methods.

The demand of electricity is continuously increasing due to increase in population and urbanisation. Due to lack of generation and transmission facilities there is over exploitation of present resources. The existing transmission lines are overloaded which make the system prone to stability problems. In the proposed work the power flow is increased in the existing system after using FACTS device using five different methods. They are firing by TCR pulse generator, using control subsystem based on RS Flip Flop, using Synchronised 6 pulse generator, using Thyristor -6 pulse generator with PLL, and pulse generator block of MATLAB.TCSC is used to control the dynamic power flow and also to enhance the power quality of the system. The power quality of the system is polluted due to use of common harmonic loads like computers, motor drives, arc and induction furnaces, battery charges, rectifiers, induction heating equipment. So, power electronics-based device TCSC is used in the proposed work. increases the efficiency of the line and improve the stability and security of the system. The active power at the receiving end is enhanced using the above different methods and the various results of power flow enhancement and THD analysis is shown. The THD analysis of the system is done in the present work using all the different methods. There provide other benefits to the system like damping power system oscillations, mitigating sub synchronous resonance, providing voltage support, improving transient stability.

An Active Voltage Coordinate Control Strategy of DFIG-Based Wind Farm with Hybrid Energy Storage System

In a power system with wind farms, the point of common coupling (PCC) usually suffers from voltage instability under large wind speed variations and the load impact. Using the internal converter of a doubly fed induction generator (DFIG)-based wind turbine to provide voltage support auxiliary service is an effective scheme to suppress the voltage fluctuation at PCC. To satisfy the reactive power demand of the connected grid, an active voltage coordinate control strategy with the hybrid energy storage system of the wind farm is proposed. The dynamic reactive power balance model is established to show the interaction between the reactive power limitation of the wind farm and the reactive power compensation demand of the grid. This indicates the initial conditions of the active voltage coordinate control strategy. According to the critical operating point and the operation state of the DFIG, the active and reactive power coordinate control strategy composed of active ω-β coordinate control and active β control is proposed to enhance the reactive power support capability and stabilize the grid voltage. To compensate the active power shortage, an auxiliary control strategy based on the hybrid energy storage system is introduced. The simulation results show that the proposed strategy can suppress the voltage fluctuation effectively and make full use of primary energy.

Transient Stability Enhancement of a Grid-Connected Large-Scale PV System Using Fuzzy Logic Controller

This paper presents a new intelligent control strategy to augment the low-voltage ride-through (LVRT) potential of photovoltaic (PV) plants, and the transient stability of a complete grid system. Modern grid codes demand that a PV plant should be connected to the main power system during network disturbance, providing voltage support. Therefore, in this paper, a novel fuzzy logic controller (FLC) using the controlled cascaded strategy is proposed for the grid side converter (GSC) of a PV plant to guarantee voltage recovery. The proposed FLC offers variable gains based upon the system requirements, which can inject a useful amount of reactive power after a severe network disturbance. Therefore, the terminal voltage dip will be low, restoring its pre-fault value and resuming its operation quickly. To make it realistic, the PV system is linked to the well-known IEEE nine bus system. Comparative analysis is shown—using power system computer-aided design/electromagnetic transients including DC (PSCAD/EMTDC) software—between the conventional proportional–integral (PI) controller-based cascaded strategy and the proposed control strategy to authenticate the usefulness of the proposed strategy. The comparative simulation results indicate that the transient stability and the LVRT capability of a grid-tied PV system can be augmented against severe fault using the proposed FLC-based cascaded GSC controller.

Study of various indexes for Power loss Reduction in Distributed Systems

In swift growing economy, the forceful factors for intensification of Distributed Generation (DG) integration in power distribution system are the expeditious increasing load demands in distribution systems. This research paper work presents load flow program to find out optimal placement and sizing of DG to provide voltage support for the weak distribution system at base case load. Repeated Load Flow (RLF), PSO and SPSO method are used to determine the candidate buses for DG placement in distribution network. Optimal sizing of DG is carried out using RLF with continuous load flow and PSO with random generation of DG sizes.

Integration of Prosumers with Battery Storage and Electric Vehicles Via Transactive Energy

This paper presents a novel transactive energy approach that uses the utility's distributed energy management system, the home energy management systems in the residential customers and the existing inter-communication infrastructure to: 1) enable the electric utilities to identify the negative impacts of integrating local distributed energy resources (such as rooftop solar photovoltaic) and electric vehicles; 2) provide voltage support, transformer management and phase balancing to mitigate such impacts (utilities’ objectives); and 3) create a day-ahead local energy market whose participants are the homeowners with home battery storage. In this market, the homeowners compete among each other through a dynamic Bertrand game to maximize their payoffs (customer's preferences). The results have demonstrated the capability of the proposed transactive energy approach to resolve the conflicting objectives between the utility and the customers by improving the service voltage, extending the lifetime of the transformers, and reducing the voltage unbalance, while increasing the profits for the homeowners through the energy arbitrage without sacrificing the homeowner's convenience.