Bus Regulation Research Articles

Delay-tolerant hierarchical distributed control for DC microgrid clusters considering microgrid autonomy

A microgrid cluster (MGC) is formed by interconnected geographically adjacent microgrids (MGs), which can effectively improve power supply reliability. To fulfill the requirements of coordination between MGs while exerting the autonomy ability of each MG, this paper proposes a hierarchical distributed control method for DC MGCs with MG autonomous-cooperative mode switching. The proposed method can not only realize the proportional current sharing between the MGs and the voltage regulation of the common bus but also allow MGs to operate in autonomous or cooperative mode by establishing and disconnecting the inter-MG communication links. In addition, considering that the delay of inter-MG communication links affects multiple control links of the proposed control method, a delay-dependent stability analysis method based on Padé approximation and eigenvalue spectrum comparison is proposed. By stability analysis, the time delay margin (TDM) is determined, and the key link that determines the TDM is identified as the observer based on the proportional-integral (PI) consensus algorithm. On this basis, the scattering transformation (ST) is introduced to improve the stability of the observer under delay and thus enhance the TDM of DC MGCs, which is confirmed by stability analysis based on a new system model integrating node variables and edge variables. Finally, the performance of the proposed control method and stability analysis results are verified by hardware-in-loop (HIL) tests and MATLAB/Simulink simulations

Enabling High-Power Conditioning and High-Voltage Bus Integration Using Series-Connected DC Transformers in Spacecrafts

This article proposes a photovoltaic power processor for high-voltage and high-power distribution bus, between 300 V and 900 V, to be used in future space platforms like large space stations or lunar bases. Solar arrays with voltages higher than 100 V are not available for space application, being necessary to apply power conversion techniques. The idea behind this is to use series-connected zero-voltage and zero-current unregulated and isolated DC converters to achieve high bus voltage from the existing solar arrays. Bus regulation is then achieved through low-frequency hysteretic control. Topology description, semiconductor selection, design procedure, simulation and experimental validation, including tests in vacuum and partial pressures, are presented.

Secondary Control Strategies in the DC Microgrids

Now, DC microgrids have become more popular for several reasons, including the lack of issues related to reactive power and frequency control, the direct integration of energy storage devices and solar photovoltaic, and the higher utilization of DC loads. A DC microgrid using several sources (distributed generation) is a popular research area. The main issue in such a DC microgrid is to provide good voltage regulation and proportional power sharing among all sources. Control strategy is very important to solve the above issue in order to maintain the reliability and stability of DC microgrids. Hence, a comprehensive review of DC microgrid control techniques is essential. Compared to other methods, hierarchical control is widely used to solve the aforementioned issue. It consists of three layers of control: primary control, secondary control, and tertiary control. At the primary level, to improve current sharing performance, droop control is usually applied. Secondary control is used for voltage regulation of the DC bus. A tertiary control is a higher-level control to achieve Optimization and economical grid operation. In traditional primary control, it is not possible to attain accurate power sharing and voltage regulation simultaneously. Thus, secondary control is required. So, this paper reviews the secondary level control techniques in the hierarchical control strategy for DC microgrids. Precisely, Centralized, distributed, and decentralized approach-based secondary control are reviewed. Several secondary control techniques have been thoroughly examined in terms of their advantages and disadvantages making this an excellent resource for both academics and business executives.

Retracted

Retracted

Sustainable power management in light electric vehicles with hybrid energy storage and machine learning control

This paper presents a cutting-edge Sustainable Power Management System for Light Electric Vehicles (LEVs) using a Hybrid Energy Storage Solution (HESS) integrated with Machine Learning (ML)-enhanced control. The system's central feature is its ability to harness renewable energy sources, such as Photovoltaic (PV) panels and supercapacitors, which overcome traditional battery-dependent constraints. The proposed control algorithm orchestrates power sharing among the battery, supercapacitor, and PV sources, optimizing the utilization of available renewable energy and ensuring stringent voltage regulation of the DC bus. Notably, the ML-based control ensures precise torque and speed regulation, resulting in significantly reduced torque ripple and transient response times. In practical terms, the system maintains the DC bus voltage within a mere 2.7% deviation from the nominal value under various operating conditions, a substantial improvement over existing systems. Furthermore, the supercapacitor excels at managing rapid variations in load power, while the battery adjusts smoothly to meet the demands. Simulation results confirm the system's robust performance. The HESS effectively maintains voltage stability, even under the most challenging conditions. Additionally, its torque response is exceptionally robust, with negligible steady-state torque ripple and fast transient response times. The system also handles speed reversal commands efficiently, a vital feature for real-world applications. By showcasing these capabilities, the paper lays the groundwork for a more sustainable and efficient future for LEVs, suggesting pathways for scalable and advanced electric mobility solutions.

Efficient power management and control of DC microgrid with supercapacitor-battery storage systems

This paper introduces a novel power management strategy (PMS) that aims to facilitate power-sharing between battery and supercapacitor (SC) energy storage systems. The proposed technique is employed to resolve the discrepancy between power demand and generation, as well as to regulate the voltage of the dc bus. The implementation of a hybrid adaptive fuzzy integrated fractional order PD-PI controller (HAFI FPD-PI controller), in the hybrid energy storage system (HESS) results in enhanced regulation of the dc bus, while simultaneously minimising the levels of stress imposed on the battery. Moreover, the proposed PMS improves the lifespan of batteries by redirecting unwaged battery currents to SCs for rapid compensations. In addition, the stability study of dc microgrid is performed. The efficacy of the proposed PMS is evaluated by the utilisation of varying solar irradiation, wind speed, and load. The effectiveness of the proposed PMS was examined by simulations, which involved a comparison of peak deviations in the dc bus voltage with conventional PMS techniques used in literature. The real-time verification of the results has been conducted using OPAL-RT real-time simulator.

Optimized nonlinear controller for fuel cell, supercapacitor, battery, hybrid photoelectrochemical and photovoltaic cells based hybrid electric vehicles

Hybrid electric vehicles are getting popular due to the depletion of fossil fuel and natural gas reserves. It is important to utilize renewable energy sources to avoid the horrific effects of global warming and greenhouse gas emissions. This study presents an optimized nonlinear controller for a hybrid energy storage system (HESS) of fuel cell, battery, supercapacitor, and hybrid photoelectrochemical and photovoltaic cells (HPEV) based hybrid electric vehicles. All these energy sources are connected to a DC-DC power converter followed by a DC-AC inverter and a motor. Lyapunov based nonlinear controller is proposed to achieve tight DC bus regulation, good tracking of sources current, and global asymptotic stability of the closed loop system. The gain parameters of the proposed nonlinear controller are optimized using the grey wolf optimization (GWO) algorithm for performance improvement. Maximum power point tracking of HPEV is performed using an artificial neural network. Experimental data from the extra-urban driving cycle is used to demonstrate the performance of the proposed optimized HESS using Matlab/Simulink. To validate the performance of the proposed system the simulation results are compared with hardware in the loop experimental results. It can be observed from the simulation results that the proposed GWO optimized nonlinear controller decreases errors, and enhances the performance of the dynamical system.

New Sizing Methodology and Efficiency Analysis of Satellite’s Electrical Power Subsystem

This paper describes a novel methodology to improve the preliminary design and efficiency analysis of the satellite’s electrical power subsystem. Several studies have addressed this issue by proposing a solar array sizing method based on the use of fixed efficiency paths during sunlight and eclipse periods. Indeed, these studies restrict the use of the battery for eclipse periods, and thus the solar array is sized to support the peak power loads on its own. To the authors’ knowledge, no one has so far deeply and jointly analyzed the influence of the power profile demand, the use of the battery during sunlight periods, and the architecture on the efficiency paths to size the electrical power subsystem. This work offers a methodology that takes into account these variables to better estimate the global efficiency of the electrical power subsystem and, consequently, to refine the first design iterations of a satellite. This methodology is particularized for the most common architectures based on power and voltage bus regulation, although it can be implemented in more complex architectures. A case study involving a real space mission, the UPMSat-2 (a 50 kg satellite launched in September 2020), is conducted to test this methodology.

Prescribed Performance-Based Secondary Control for DC Microgrid

In this article, based on the prescribed performance control approach, a distributed secondary control scheme is developed for an islanded DC microgrid, to achieve current sharing among the converters and voltage regulation of the DC bus while guaranteeing the prescribed transient performance of the system. With the proposed controller, the evolution of both the bus voltage error and the current sharing error can be constrained within a predefined imposed bound. In this way, the safety of the electrical devices can be ensured and the dynamic performance of the microgrid can be improved. In addition, the controller is quite simple for implementation without sampling and delivering the information of the DC bus voltage. Simulation studies and experiment tests are carried out to demonstrate the effectiveness of the proposed secondary control scheme.

Cooperative Primary Control of a Hybrid AC/DC Microgrid Based on AC/DC Virtual Generators

This article presents a dynamic control strategy for a hybrid AC/DC Microgrid (MG). To allow a high penetration of renewable energies, provide an increased system reliability during islanding and reduce the dependency on the mains, Energy Storage Systems (ESSs) are included in both the DC and AC grids. The MG is composed by DC grid, with connection to the mains and a central battery ESS, and a flexible number of AC subgrids coupled to the DC bus through AC/DC 3-phase Interlinking Converters. The paper presents three main contributions: 1) A DC bus regulation scheme is proposed based on DC virtual generators and P/V DC droop that allows to adapt the participation in the power sharing for DC bus regulation and provides with an automatic transition between grid-connected and islanding modes; 2) In order to provide a cooperative operation between the different AC subgrids, allowing the automatic power sharing between them through the DC bus, a Hybrid AC/DC Virtual Generator control scheme is proposed based on the Virtual Synchronous Generator concept, for its implementation in the interlinking converters; 3) an AC voltage and frequency compensator suitable for systems with high resistive line impedance. The discussion is supported with small signal analysis, simulations and Hardware-in-the-loop.

Voltage regulation of a remote microgrid bus with a modular multilevel STATCOM

This paper presents a strategy to control the voltage at a remote bus of a distribution network by using a modular multilevel static synchronous compensator. The mathematical models presented in this paper are based on the transfer impedance of the nodal admittance matrix of the system. They allow building a voltage control loop in the dq-reference frame to regulate the voltage of a remote bus of the power system. As the mains’ impedance may vary during the system operation, the ac voltage control loop is designed considering the worst case to ensure the correct operation of the voltage control loop. It is also shown how the variation of the mains’ inductance impacts the voltage control of the remote bus. Moreover, it is shown that the use of a PI controller provides a better margin phase for the remote bus voltage control loop. A static synchronous compensator based on the modular multilevel converter, with 28 submodules per leg, is modelled in an electromagnetic transient program and connected to a medium-voltage distribution network based on the IEEE 14 bus system. Lastly, an heuristic algorithm is used to regulate the reference signal of the ac voltage control loop so that the PCC voltage does not exceed its voltage limit. It is shown that this algorithm can reconcile the regulation of the remote bus voltage and the PCC voltage limit.

Design and verification of the energy system of the China space station core module

<p indent="0mm">After its successful launch on April 29, 2021, the China space station core module has been operating stably in orbit. The energy system is an important part of the core module, converting solar energy into electricity and then controlling and regulating the electric energy to provide a continuous, stable, and reliable power supply to all electrical equipment. This paper introduces the structure of the energy system used in the module, analyzes the design of independent energy health management, high voltage bus regulation, and large flexible solar cell wing, and introduces on-orbit flight verification.

A study of a solar PV and wind-based residential DC NanoGrid with dual energy storage system under islanded/ interconnected/grid-tied modes

Progress in Direct Current (DC) power technologies has paved way for the emergence of DC Nano Grid (NG) as a new research area drawing international attention. This paper aims to design a simple and cohesive control algorithm for a solar PV and wind generator coupled low power residential DC NG with electrical and thermal energy storage systems. The envisaged NG control architecture extracts maximum power from solar PV, effects maximum active power transfer from wind generator with voltage regulation of the DC bus, draws/delivers balanced sinusoidal currents at Unity Power Factor (UPF) from/to the grid and monitors power scheduling to DC and thermal loads. The maximum solar PV power is extracted through incremental conductance algorithm and maximum wind power is tracked using a polynomial curve fit equation derived from the wind power curves without implementation of any speed/torque control loops. The maximum active power transfer from wind and UPF operation of the grid is achieved using a reference current generation method based on symmetrical components theory of equal current strategy with no complex transformations. A power factor of 0.99 with generation of balanced sinusoidal currents during both grid power import and export is achieved. Further, the operation of the proposed DC NG in all possible modes such as islanded/grid-tied/interconnected modes are monitored through a supervisory controller implemented in OPAL-4510 Real Time Digital Simulator (RTDS) under varying solar irradiation, wind velocity and load conditions, which projects the suitability of the system to be implemented in any geographical location (hilly terrain/rural/urban) either with limited availability of renewable sources or grid supply. The successful operation of the system is validated through experimentation on a 120 W scaled-down hardware prototype.

State-of-Charge Balancing Control for Modular Battery System With Output DC Bus Regulation

State-of-charge (SOC) balancing of battery cells is very crucial for the battery management system (BMS) to prolong the operational lifetime of the battery system. In this article, an adaptive control algorithm is proposed to balance the SOCs for a series-connected battery system. The control strategy achieves power balancing using the current-SOC droop concept while maintaining a stable dc bus voltage regulation at the battery pack. The proposed control algorithm achieves the control objectives without any communication necessity among the batteries. Moreover, the control design and the stability analysis are shown in detail using small-signal modeling. Furthermore, the simulation and experimental validation are provided to verify the effectiveness of the proposed control algorithm. In addition, the conventional centralized control method is compared with the proposed distributed control concept. The proposed approach shows higher reliability, flexibility, and scalability compared to the conventional centralized cell balancing structures.

Stability of DC Boost converter Feeding Constant Power Load using Fuzzy Controller Based Lyapunov

ABSTRACT Tight voltage regulation of the DC microgrid bus may lead to instability issue which leads to microgrid system collapse. Constant power load (CPL) is a serious problem that exists in cascaded power electronic converters which must have a robust controller to mitigate instability issue. The controller based on mathematical model is vulnerable to model mismatch which could lead to instability especially with highly nonlinear plant. Boost converter feeding CPL is a highly nonlinear non-minimum phase system which is difficult to control based on mathematical model. In this paper a supervisory stable Fuzzy Logic Controller (SFC) based on Lyapunov theory is designed to mitigate the instability issue that is caused by the negative incremental impedance which behaves as CPL of dc boost converter. The proposed SFC is able to stabilise the output voltage of the boost converter under nominal and uncertain conditions. The proposed controller is validated through simulation using Matlab/Simulink. To the best of the authors’ knowledge this method hasn’t been introduced before.

Distributed Fixed-Time Secondary Control for DC Microgrid Via Dynamic Average Consensus

In this paper, a dynamic average consensus-based distributed fixed-time secondary control scheme is proposed for an islanded DC microgrid, to achieve both current sharing among the converters and voltage regulation of the DC bus within a fixed settling time. The secondary controller is designed using sign functions and fraction-based feedback signals for accelerating the convergence. To release the requirement on the piror knowledge of the communication topology of DC microgrid, an adaptive law is proposed to update the control gain autonomously. The proposed secondary controllers do not need to deliver the output current data to the neighbors and sample the voltage of the DC bus, making them easier to be implemented in practice. To demonstrate the effectiveness of the proposed secondary controllers, five simulation cases and three experiment tests are carried out. It can be illustrated that the proposed secondary control schemes are resilient to the constant power loads and sources, the failure of communication links, and the scenario of plug-and-play.

Robust optimal predictive control for real-time bus regulation strategy with passenger demand uncertainties in urban rapid transit

The bus is inevitably affected by various factors during the trip, which causes that the phenomenon of bus bunching often occurs. This paper proposed a nonlinear optimal control model with passenger demand and disturbance uncertainties for the real-time bus regulation in urban rapid transit. The aim of this model is to assure the stability of bus headway in the line, reduce passengers’ waiting time and improve bus service level. Considering the system uncertainties and the real-time control requirement of bus regulation, a robust optimal predictive control algorithm is put forward to generate the real-time optimal bus regulation strategy based on updated delay feedback of buses by a rolling horizon strategy. Simultaneously, by using continuous interval number to describe the uncertain parameters, the robust counterpart of the formulated robust optimization model is obtained using the duality theory, which is further converted to a mixed integer convex quadratic programming problem by a linearization method, which can be easily solved to obtain the robust solution with a good performance for any value of uncertain parameters. Finally, some numerical experiments are conducted to verify the validity of the presented optimization model in improving the stability of the bus headway.

A Sliding Surface for Controlling a Semi-Bridgeless Boost Converter with Power Factor Correction and Adaptive Hysteresis Band

This paper proposes a new sliding surface for controlling a Semi-Bridgeless Boost Converter (SBBC) which simultaneously performs Power Factor Correction (PFC) and DC bus regulation. The proposed sliding surface is composed of three terms: First, a normalized DC voltage error term controls the DC bus and rejects DC voltage disturbances. In this case, the normalization was performed for increasing system robustness during start-up and large disturbances. Second, an AC current error term implements a PFC scheme and guarantees fast current stabilization during disturbances. Third, an integral of the AC current error term increases stability of the overall system. In addition, an Adaptive Hysteresis Band (AHB) is implemented for keeping the switching frequency constant and reducing the distortion in zero crossings. Previous papers usually include the first and/or the second terms of the proposed sliding surface, and none consider the AHB. To be best of the author’s knowledge, the proposed Sliding Mode Control (SMC) is the first control strategy for SBBCs that does not require a cascade PI or a hybrid PI-Sliding Mode Control (PI-SMC) for simultaneously controlling AC voltage and DC current, which gives the best dynamic behavior removing DC overvoltages and responding fast to DC voltage changes or DC load current perturbations. Several simulations were carried out to compare the performance of the proposed surface with a cascade PI control, a hybrid PI-SMC and the proposed SMC. Furthermore, a stability analysis of the proposed surface in start-up and under large perturbations was performed. Experimental results for PI-SMC and SMC implemented in a SBBC prototype are also presented.

Power management and control of a grid-independent DC microgrid with hybrid energy storage system

In this paper, a novel power management strategy (PMS) for power-sharing among battery and supercapacitor (SC) energy storage systems has been proposed and applied to resolve the demand-generation difference and DC bus voltage regulation. The proposed compensation for PI controller managed hybrid energy storage systems (HESSs) provides for improved DC bus regulation with minimal battery stress levels. Further, redirections of unwaged battery currents to SCs for fast compensations in the proposed PMS enhances battery life span. Moreover, the stability analysis of DC microgrid is also evaluated. The proposed PMS effectiveness was investigated by simulations, including a comparison of peak deviations in dc bus voltage with a traditional control strategy. The results have been experimentally verified by hardware-in-loop (HIL) on an FPGA-based real-time simulator.

Limits control and energy saturation management for DC bus regulation in photovoltaic systems with battery storage

Because of the considerable fluctuations of the power generation and load in Photovoltaic (PV) - Battery (BAT) systems, power management strategies become indispensable since BAT is needed to maintain the generation/load balance, and to regulate the DC bus. Indeed, energy management strategies must take into account the limits of the system, i.e. the nominal PV/BAT power rating and the state of charge (SOC) of BAT. However, the actual use might be different from the intended one, forcing the system to attain its limits. This paper is mainly focused on the limits control and energy saturation management applying to a sample standalone DC micro grid. It consists to share accurately the variable power loads among sources according to their ratings, including the regenerative breaking in minimum SOC'BAT case and the full supply of power load demand in maximum SOC'BAT case. Furthermore, the DC bus voltage is regulated to its predefined level, as a design parameter.The proposed control algorithms are detailed, and the system design during overstress and nominal conditions is given. The main advantage of this algorithm is its simplicity. The efficiency of the control strategy for energy saturation management is verified and analyzed through simulation/experimental system using Matlab/Simulink and DSpace. The results obtained show that the proposed technique can intelligently manage the energy flows and thus ensure that the system operates correctly and safely in the different modes: normal mode and saturated mode.