Average Bus Voltage Research Articles

Distributed Cooperative Control Strategy for Stable Voltage Restoration and Optimal Power Sharing in Islanded DC Microgrids

Conventionally, voltage regulation and economic dispatch in DC microgrid are performed at different time scales, which cannot keep the distributed generators (DGs) at the optimal operating point in real time. In this paper, a novel distributed cooperative control strategy is proposed to synchronously achieve stable bus voltage restoration and optimal power sharing in islanded DC microgrids. The proposed strategy breaks the constraints of hierarchical control strategies, and incorporates the objectives of voltage regulation and economic dispatch into a distributed cooperative control framework to eliminate average bus voltage deviation and minimize total power generation costs in real time. The stability of the proposed strategy is verified by eigenvalue analysis and steady-state analysis. Furthermore, the concept of “incremental cost (IC) margin” is introduced in cooperative control considering capacity constraints to avoid the converter output power violation and performance degradation. Finally, the MATLAB/Simulink simulation and StarSim HIL experimental results verify the effectiveness and robustness of the proposed strategy in an islanded DC microgrid under various testing scenarios.

Distributed Unified Controller Design for Parallel Battery Storage System in DC Shipboard Microgrid

In this paper, a novel distributed unified controller is designed to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable DC bus voltage for parallel battery storage systems (BSSs) in DC shipboard microgrid (DC-SMG). Different from the droop-based secondary controller, the designed distributed unified controller is a droop-free primary controller, which can incorporate SoC balancing, current sharing, and voltage regulation functions in the primary control layer. On this basis, each BSS uses an improved dynamic diffusion algorithm (DDA) to iteratively estimate the average information, and completes information exchange by a neighbor-to-neighbor communication network. Furthermore, the small-signal stability, large-signal stability, and global steady-state performance of the system is investigated using eigenvalue analysis, mixed potential theory (MPT), and matrix theory, respectively. Finally, the Matlab/Simulink simulation model and the StarSim HIL experimental platform for DC-SMG are built. The results show that the designed distributed unified controller can simultaneously achieve dynamic SoC balancing, proportional load current sharing, and smooth average bus voltage regulation, and has a faster SoC convergence speed and more stable control effect than the state-of-the-art methods.

Optimal-Consensus-Based Event-Triggered Control Strategy for Island AC Microgrids

This article proposed an optimal-consensus-based even t-triggered control strategy to coordinate multiple distributed generators (DGs) in an alternative current (ac) microgrid. The proposed control strategy integrated the average bus voltage recovery and the proportional reactive power sharing by turning the coordinated control problem into a convex optimization problem, which realized the bus voltage control and proportional reactive power sharing of the DGs in one controller so that the controller structure is significantly simplified. Accordingly, the controller provided an asynchronous event-triggered mechanism considering the finite availability of communication resources, which reduces communication burdens and avoids Zeno behaviors. The sufficient conditions are demonstrated using the Lyapunov function for maintaining the stability of the proposed control strategy. Several simulations are exhibited using the MATLAB/Simulink platform and the results are reviewed to validate the effectiveness of the proposed control strategy for enhancing the ac microgrid robustness and reducing communication burdens.

Mitigation of Power Losses and Enhancement in Voltage Profile by Optimal Placement of Capacitor Banks With Particle Swarm Optimization in Radial Distribution Networks

The prime purpose of placing a capacitor bank in a power system is to provide reactive power, reduce power losses, and enhances voltage profile. The main challenge is to determine the optimum capacitor position and size that reduces both system power losses and the overall cost of the system with rigid constraints. For this purpose, different optimization techniques are used, for example Particle Swarm Optimization (PSO) which converges the complex non-linear problem in a systematic and methodological way to find the best optimal solution. In this paper, the standard IEEE 33-bus and 69-bus systems are used to find the optimum location and size of the capacitors bank. These power networks are simulated in Siemens PSS®E software. For the optimum solution of capacitor banks, the PSO algorithm is used. The PSO fitness function is modelled in such a way which contains the high average bus voltage, the small size of capacitor banks, and low power losses. The fitness function used is a weighted type to reduce the computation time and multi-objective function complexity.

Optimal Placement and Sizing of Distributed Generation (DG) Units in Electrical Power Distribution Networks

Researchers' attention has recently been on the best ways to integrate Distributed Generation (DG) into the conventional centralized electrical power distribution systems, particularly in the context of the smart grid idea due to its reputation as a viable remedy for the lack of electric power supply. To optimize the environmental, financial, and technological advantages of DG units’ integration for distribution network operators, it is crucial to determine their ideal position and size. The main objective of this study was to develop and simulate an optimization system for the placement and sizing of distributed generation units in electrical power distribution networks for power losses reduction and voltage profile improvement. The specific objectives were to model and develop the load flow algorithm and codes; develop a meta-heuristic optimization algorithm and codes that selects the best location and size of the DG unit; simulate the nested load flow and optimization algorithms and codes on MATLAB and analyze the effectiveness of the developed algorithm via testing on the standard IEEE 33-bus radial electrical power distribution benchmark network. The Backward-Forward Sweep (BFS) technique was employed in the load flow modelling owing to its maximization of the radial structure of distribution systems. The optimization algorithm was developed based on the Multi-objective Particle swamp optimization (PSO) meta-heuristic technique due to its effective global searching characteristic. The line and load data for the IEEE 33-bus test network being a cutting-edge benchmark for contemporary power distribution networks; were obtained from the Power Systems Test Case Archive- a secondary data source. For this network fed by a synchronous generator, the chosen base MVA (Mega Volt Amp) was 10MVA and the base voltage was 12.66kV. The total active and reactive power demand were 3.715MW and 2.3Mvar respectively. The simulation was done on R2021a version of MATLAB/Simulink. The total real and reactive power losses obtained from base case simulation without the placement of any DG unit in the network were obtained as 201.8925kW and 134.6413kvar respectively while the per unit (p.u) average bus voltage was 0.948594 p.u. After the optimal allocation of one, two, three and four DG units, the total real power loss (in kW) in the network reduced by 140.89, 173.89, 189.89 and 195.89 respectively while the total reactive power loss (in kvar) reduced by 86.64, 114.64, 124,64 and 128.64 respectively. Likewise, the per unit average bus voltage improved by 0.0376p. u, 0.0458p.u, 0.0480p.u and 0.0498p.u respectively. Also, the decrease in the total real and reactive power losses and the improvement in bus voltage profiles varies proportionally with the number of DG units optimally placed. In conclusion, the results shows that the total real power loss and the total reactive power loss of the network, were significantly decreased; and the voltage profile of the system was drastically enhanced by incorporating DG units at predetermined buses. The developed algorithm is recommended for application in a real electrical power distribution network for more efficient integration of new distributed generation units in the current electrical power distribution networks.

Security Enhancement of Power Systems through Interline Power Flow Controller (IPFC) under Contingency Condition: A Case Study and Analysis‐EEP 400 kV System

Increasing contingency issues result in inevitable bus voltage violations and force the system to operate around its limit. This situation creates strains that are faced by the security of the Ethiopian Electric Power (EEP) 400 kV system. In this paper, the static security assessment (SSA) of the system under the base and N-1 contingency scenarios was examined by using Newton-Raphson (NR) method. The Bus and line loading-based composite severity indices (CSI) were utilized to determine the state of the system and to get an optimal location for interline power flow controller (IPFC) placement. In this research, the optimal sizing of IPFC was done by using Grey Wolf Optimization (GWO) algorithm. From N-1 contingency analysis, Gelan to Sebeta and Gelan to Holeta branches were found as optimal places for IPFC placement. The IPFC optimal parameters were the series voltage and angle injection found as Vse1 = 0.1101pu, Vse2=0.1096pu, δse1=-0.1848rad, and δse2=2.7682rad with the optimal size of 50 MVA for each IPFC. The average bus voltage severity index (BVSI) without and with IPFC cases was found as 217.243% and 2.641% respectively. The average line severity index (LSI) without and with IPFC cases were found as 39.448% and 15.283% respectively. Moreover, the total line loss under severe N-1 contingency scenarios without and with IPFC integration was 437.783 MW and 63.136 MW respectively. From analysis, it was observed and concluded that the static security of the EEP 400 kV system under N-1 contingency conditions is effectively improved by the integration of IPFC.

Dynamic Pricing Strategy of Charging Station Based on Traffic Assignment Simulation

The number of electric vehicles is increasing rapidly worldwide, leading to increasing demand for charging. This will negatively impact the grid. Therefore, it is essential to relieve the power grid operation pressure by changing the charging behaviour of users. In this paper, the charging behaviour of electric vehicles was guided by price instruments to maintain grid balance This paper uses travel simulation to establish the relationship between travel demand and electricity prices. The results were evaluated through the amount of grid voltage drop and network loss. Furthermore, we used the differential evolutionary algorithm to calculate the optimal operation status of the grid, which contains the minimal network loss and maximal voltage drop at different charging stations and the charging price. Finally, the effectiveness of the mechanism proposed in this paper was compared with other simulation examples. The results showed that the pricing strategy could guide users’ charging choices and maintain the grid load balancing. The simulation results show that the average bus voltage increases by 1.26% and 6.59%, respectively, under different requirements.

Droop-Free Distributed Cooperative Control Framework for Multisource Parallel in Seaport DC Microgrid

In this article, a novel distributed cooperative control framework is proposed to solve the problems of unbalanced load current sharing and bus voltage deviation in seaport DC microgrid. This framework without droop control, and a novel droop-free cooperative controller is constructed to achieve current sharing and voltage regulation goals. Each distributed generator (DG) transmits information based on a sparse communication network, and uses a discrete dynamic consensus algorithm (DCA) to complete the accurate estimation of a virtual average state variable containing voltage and current information. In addition, a current limiting function adapted to DCA is designed to avoid control failure and prevent the converter output currents from exceeding the rated value. Finally, the influence of boundary weight, communication delays, and calculation delays on the system stability is analyzed, and a seaport DC microgrid simulation model and StarSim HIL experimental platform are built. The results show that the proposed control scheme can achieve average bus voltage restoration and proportional load current sharing within the allowable range of communication delays and calculation delays, and has prominent plug-and-play capabilities.

Distributed Aperiodic Control of Multibus DC Microgrids With DoS-Attack Resilience

In this article, we present a distributed aperiodic control algorithm for multibus DC microgrids to realize proper current sharing and voltage regulation under denial-of-service (DoS) attacks. To deal with the DoS attacks, an estimation mechanism using only local information is designed when the communication channels are jammed, which avoids persistent load fluctuations or instability of bus voltages caused by malicious attacks. Moreover, an aperiodic communication mechanism is employed using the local and neighbors’ current states stored in the zero-order holder to determine the communication instants. The proposed resilient aperiodic control achieves proportional load current sharing and maintains the weighted average bus voltage invariant simultaneously. Voltage drift under DoS attacks can be avoided. Furthermore, sufficient stability conditions are established for control gains concerning the attack parameters. The Lyapunov synthesis shows that the current sharing error can exponentially converge towards an adjustable set, and the weighted average bus voltage can be maintained at its nominal value. The advantages of the proposed control are illustrated by switch-level simulations and a hardware-in-the-loop experiments.

Hierarchical Cooperative Control Strategy for Battery Storage System in Islanded DC Microgrid

This paper presents a novel hierarchical cooperative control strategy to solve the problems of unbalanced State of Charge (SoC), unreasonable load current sharing, and unstable bus voltage for battery storage system (BSS) in islanded DC microgrid. In the communication layer, a neighbor-to-neighbor communication network architecture is constructed in which each battery storage unit (BSU) only communicates information with neighboring nodes, and a multi-agent consensus algorithm is used to iteratively estimate the relevant average global variables. In the main control layer, the droop coefficient is dynamically adjusted by constructing a fast SoC convergence function to ensure that the load current is reasonably distributed based on the rated capacity of each BSU. In the secondary control layer, a virtual voltage drop equalization controller and an average bus voltage compensation controller are designed to eliminate the impact of line impedance mismatch and compensate the average bus voltage. Furthermore, an optimized factor is designed to accelerate the later stage of SoC convergence. Finally, a DC microgrid experimental platform based on StarSim HIL is built, and the results demonstrate that the proposed strategy can achieve the control objectives of fast SoC balance, proportional load current sharing, and bus voltage stability.

Distributed Event-Triggered Hierarchical Control to Improve Economic Operation of Hybrid AC/DC Microgrids

A Hybrid AC/DC microgrid (MG) can integrate distributed generation sources and distributed loads on the AC and DC side of the MG by eliminating many unnecessary power conversion devices, which is more flexible and efficient. However, to achieve reliable and economic operation of a hybrid AC/DC MG is challenging due to its complex structure. In this paper, a novel distributed event-triggered hierarchical control strategy is proposed to improve the economic operation of a hybrid AC/DC MG. For the primary control, distributed local controls of AC DGs, DC DGs, and interlinking converters (ICs) are realized by adopting the droop control method. For the secondary control, the distributed economic dispatch, distributed average bus voltage discovery, and distributed proportional power-sharing algorithms are first proposed; then, control objectives of voltage and frequency restoration and economic operation of the hybrid AC/DC MG are realized based upon the developed algorithms. Furthermore, the distributed secondary control is built upon an event-triggered mechanism developed in this paper, which can reduce the communication burden. The simulation results demonstrate the effectiveness of the proposed control strategy.

Investigation of Distribution System Stability with Incorporation of Capacitor Switching: A Case Study of Monatan 11 Kv Distribution System

Effectiveness of an electrical distribution system depends on the stability of its voltage profile. Several methods such as Static Compensator (SC), Thyristor Controlled Series Compensation (TCSC) and Series Capacitor have been applied for the stability of the system. However, these methods have been characterized by harmonic variation and low efficiency. Therefore, this research paper applied Shunt Switching Capacitor (SSC) on 11 kV distribution system located at Monatan, Ibadan, Oyo State in order to investigate the stability of the system during outages. Hourly data on bus voltage of the system were collected to determine the average bus voltage and voltage drop of the distribution system for stability evaluation using IEEE statutory limits method. Load Flow Model (LFM) of the distribution system was developed with incorporation of Capacitor Switching Compensation (CSC). This was solved using Kirchoff’s Current Law( KCL) analysis to improve the average bus voltage and voltage drop of the distribution system while simulation was done using MATLAB R2015a. The results of the average bus voltage and voltage drop of the distribution system were 10.5 and 4.2 , respectively. The CSC model improved the average bus voltage and voltage drop by 6 % and 33 % respectively. The research showed that incorporating capacitor switching as a compensation technique enhanced the stability of the distribution systems. The research is useful in the planning and optimization of electrical distribution systems. Keywords: Electrical Distribution System, Voltage, Capacitor Switching Compensation, Load Flow Models, Monatan 11 kV Distribution System, Voltage Drop, MATLAB. DOI: 10.7176/NCS/14-02 Publication date: August 31 st 2022

An Improved Distributed Secondary Control Strategy for Battery Storage System in DC Shipboard Microgrid

In this article, an improved distributed secondary control strategy is proposed to achieve state of charge (SoC) balance, accurate load current sharing, and bus voltage recovery for battery storage system in dc shipboard microgrid. First, each battery storage unit (BSU) is regarded as a multiagent, and a neighbor-to-neighbor communication network is constructed to reduce the system communication burden. Each BSU is based on distributed consensus protocol, and global consensus can be achieved only by communication between adjacent BSUs. On this basis, a novel consensus-based SoC balancing algorithm is proposed to achieve accurate load current sharing, and a dc bus voltage controller is designed to achieve secondary regulation of the bus voltage. Furthermore, the SoC convergence characteristics, systems stability analysis, global dynamic model, and steady-state analysis of the proposed control strategy are studied. Finally, the simulation and StarSim HIL experimental results show that the proposed control strategy can achieve SoC dynamic balance, accurate load current sharing, and average bus voltage recovery under various complex conditions, and has a faster SoC convergence speed than advanced methods.

Distributed Periodic Event-Triggered Optimal Control of DC Microgrids Based on Virtual Incremental Cost

This article presents a distributed periodic event-triggered (PET) optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids. In order to accommodate the generation constraints of the distributed generators (DGs), a virtual incremental cost is firstly designed, based on which an optimality condition is derived to facilitate the control design. To meet the discrete-time (DT) nature of modern control systems, the optimal controller is directly developed in the DT domain. Afterward, to reduce the communication requirement among the controllers, a distributed event-triggered mechanism is introduced for the DT optimal controller. The event-triggered condition is detected periodically and therefore naturally avoids the Zeno phenomenon. The closed-loop system stability is proved by the Lyapunov synthesis for switched systems. The generation cost minimization and average bus voltage regulation are obtained at the equilibrium point. Finally, switch-level microgrid simulations validate the performance of the proposed optimal controller.

Multi-Objective Hierarchically-Coordinated Volt/Var Control for Active Distribution Networks With Droop-Controlled PV Inverters

Due to increasing installation of photovoltaic (PV) units, reactive power compensation from PV inverters contributes significantly to Volt/Var control (VVC) for active distribution networks. While PV inverters support VVC functions, lack of systematic coordination and heavily varying PV power generation lead to low control efficiency. To maximize benefits of the inverter-based VVC, this paper proposes a multi-objective hierarchically-coordinated VVC method with droop-controlled PV inverters. This method aims to minimize both average bus voltage deviation and network power loss, by simultaneously optimizing PV inverter reactive power setpoints for central control and droop control functions for local control. The droop control characteristics of PV inverters are fully modeled, including voltage ranges of the dead band and control zones, as well as droop slope gradients. In addition, this paper applies a Taguchi’s orthogonal array testing technique to handle random variations of PV power generation in the optimization problem. Moreover, to efficiently solve this optimization problem with integer variables, this paper proposes a solution algorithm based on model relaxation and a feasibility pump method. The proposed method is tested on two distribution systems, and simulation results verify highly efficient control performance in comparison with existing methods.

Distributed Optimal Control of DC Microgrid Considering Balance of Charge State

State-of-charge (SoC) imbalance and bus voltage deviation are two of the main problems in autonomous dc microgrids. Based on this concern, this paper presents an improved dual-quadrant SoC weighted control strategy and a distributed optimization control method to achieve SoC balance, ensuring accurate power-sharing and bus voltage recovery. Firstly, this paper couples the injected/released power with the current SoC and observed average SoC value to weight the droop coefficient, which is based on the charge/discharge mode for the energy storage system. Then a secondary controller is designed based on distributed optimal control to eliminate the bus voltage deviation caused by the line impedance difference. The proposed optimal control method optimizes the average bus voltage to the nominal value and achieve accurate power-sharing by constructing the correlated variables and voltage independent intermediate variables exchanged among bulk energy storage units (ESUs). Since the voltage observer cannot accurately observe the true average bus voltage under the communication delay, the proposed distributed optimal control method without the voltage observer can ensure that the average bus voltage is optimized to the nominal value, thus improving the robustness of the control system. Finally, the correctness and effectiveness of the proposed method are verified in Simulink/MATLAB.

Distributed Event-triggered Secondary Control for Average Bus Voltage Regulation and Proportional Load Sharing of DC Microgrid

This paper proposes a novel distributed event-triggered secondary control method to overcome the drawbacks of primary control for direct current (DC) microgrids. With event-triggered distributed communication, the proposed control method can achieve system-wide control of parallel distrubted generators (DGs) with two main control objectives: ① estimate the average bus voltage and regulate it at the nominal value; ② achieve accurate current sharing among the DGs in proportion to their power output ratings. Furthermore, the proposed control strategy can be implemented in a distributed way that shares the required tasks among the DGs. Thus, it shows the advantages of being flexible and scalable. Furthermore, this paper proposes a simple event-triggered condition that does not need extra state estimator. Thus, limited communication among neighbors is required only when the event-triggered condition is satisfied, which significantly reduces the communication burden at the cyber layer.

A Fully Distributed Economic Dispatch Method in DC Microgrid Based on Consensus Algorithm

Uncertainties of intermittent renewables and complexities of load demands bring challenges to the optimal operation of the microgrid. This paper proposes a fully distributed method based on consensus algorithm for solving the economic dispatch problem (EDP) of DC microgrid. The proposed distributed method is performed using multiagent system. It only needs information from neighboring agents and does not need a central controller. A two-level control structure is adopted to realize the economic dispatch and voltage regulation simultaneously. The upper level obtains the optimal power reference of dispatchable agents and maintains the power balance of the system. The lower level performs an improved droop control to track the power reference and regulate the average bus voltage for the microgrid. The proposed method’s properties and convergence are analyzed using eigenvalue perturbation theory to obtain a faster convergence speed. By designing the adjacency matrix appropriately, the proposed method can ensure the system stable when the communication topology changes. Finally, several simulations are designed to verify the effectiveness of this novel control method.

A Unified Distributed Cooperative Control of DC Microgrids Using Consensus Protocol

In this work, we propose an effective and simple control approach for islanded DC microgrids that allows each distributed generator (DG) to achieve accurate voltage regulation and power-sharing. An improved dynamic consensus protocol, which is robust to measurement noise and states initialization, is employed to enable each agent to locally calculate the average bus voltage with a sparse cyber network. On this basis, we propose a cooperative controller that merges the voltage regulation and power-sharing objectives in a unified fashion. The proposed approach only uses neighbors’ voltage information to regulates the average bus voltage to its nominal value while maintaining proportional power-sharing or optimal power dispatch. This significantly simplifies its implementation and reduces the communication bandwidth requirement. A global model of the DC microgrid considering the cyber network is established in the form of a state-space-model, where the reference voltage vector corresponds to the input and the average bus voltage vector denotes the state. Then, the input-to-state stability analysis is carried out. To the end, comprehensive hardware-in-the-loop (HiL) tests are conducted to validate the effectiveness of the proposed control strategy. The proposed control strategy exhibits plug-and-play capability, and it is resilient to message update rate and communication failure.

Fully Distributed Discrete-Time Control of DC Microgrids With ZIP Loads

In a multibus dc microgrid, both the constant power loads (CPLs) and the discrete-time (DT) sampling of digital controllers tend to destabilize the system. To address these issues, a novel distributed DT control scheme is presented in this article to achieve proportional load current sharing and weighted average bus voltage regulation in dc microgrids with constant impedance loads, constant current loads, and CPLs (ZIP loads). First, a dc microgrid model with ZIP loads is established in the DT domain, based on which the distributed DT controller is developed. A sparse communication network is then exploited to achieve the proportional load current sharing by exchanging sampled current information between neighbors. Specifically, a distributed voltage observer utilizing the neighbors’ current information and local voltage information is designed to estimate and regulate the weighted average bus voltage. To alleviate the destabilizing effect induced by the DT sampling of digital controllers, a constrained condition on control gains is established. Additionally, a sufficient condition on CPLs that guarantees their negative impact on stability being locally counteracted is proposed. Through Lyapunov synthesis, the objectives of current sharing and voltage regulation are proved to be achieved simultaneously. Simulation studies on a detailed switch-level model validate the control scheme and demonstrate its robustness against communication network imperfections and the capability of accommodating plug-and-play operations.