DC-DC converter-based multi-bus DC microgrids(MGs) in series have received much attention, where the conflict between voltage recovery and current balancing has been a hot topic. The lack of models that accurately por...DC-DC converter-based multi-bus DC microgrids(MGs) in series have received much attention, where the conflict between voltage recovery and current balancing has been a hot topic. The lack of models that accurately portray the electrical characteristics of actual MGs while is controller design-friendly has kept the issue active. To this end, this paper establishes a large-signal model containing the comprehensive dynamical behavior of the DC MGs based on the theory of high-order fully actuated systems, and proposes distributed optimal control based on this. The proposed secondary control method can achieve the two goals of voltage recovery and current sharing for multi-bus DC MGs. Additionally, the simple structure of the proposed approach is similar to one based on droop control, which allows this control technique to be easily implemented in a variety of modern microgrids with different configurations. In contrast to existing studies, the process of controller design in this paper is closely tied to the actual dynamics of the MGs. It is a prominent feature that enables engineers to customize the performance metrics of the system. In addition, the analysis of the stability of the closed-loop DC microgrid system, as well as the optimality and consensus of current sharing are given. Finally, a scaled-down solar and battery-based microgrid prototype with maximum power point tracking controller is developed in the laboratory to experimentally test the efficacy of the proposed control method.展开更多
During the operation of a DC microgrid,the nonlinearity and low damping characteristics of the DC bus make it prone to oscillatory instability.In this paper,we first establish a discrete nonlinear system dynamic model...During the operation of a DC microgrid,the nonlinearity and low damping characteristics of the DC bus make it prone to oscillatory instability.In this paper,we first establish a discrete nonlinear system dynamic model of a DC microgrid,study the effects of the converter sag coefficient,input voltage,and load resistance on the microgrid stability,and reveal the oscillation mechanism of a DC microgrid caused by a single source.Then,a DC microgrid stability analysis method based on the combination of bifurcation and strobe is used to analyze how the aforementioned parameters influence the oscillation characteristics of the system.Finally,the stability region of the system is obtained by the Jacobi matrix eigenvalue method.Grid simulation verifies the feasibility and effectiveness of the proposed method.展开更多
In this paper,an improved sag control strategy based on automatic SOC equalization is proposed to solve the problems of slow SOC equalization and excessive bus voltage fluctuation amplitude and offset caused by load a...In this paper,an improved sag control strategy based on automatic SOC equalization is proposed to solve the problems of slow SOC equalization and excessive bus voltage fluctuation amplitude and offset caused by load and PV power variations in a stand-alone DC microgrid.The strategy includes primary and secondary control.Among them,the primary control suppresses the DC microgrid voltage fluctuation through the I and II section control,and the secondary control aims to correct the P-U curve of the energy storage system and the PV system,thus reducing the steady-state bus voltage excursion.The simulation results demonstrate that the proposed control strategy effectively achieves SOC balancing and enhances the immunity of bus voltage.The proposed strategy improves the voltage fluctuation suppression ability by approximately 39.4%and 43.1%under the PV power and load power fluctuation conditions,respectively.Furthermore,the steady-state deviation of the bus voltage,△U_(dc) is only 0.01–0.1 V,ensuring stable operation of the DC microgrid in fluctuating power environments.展开更多
In light of the growing integration of renewable energy sources in power systems,the adoption of DC microgrids has become increasingly popular,due to its simple structure,having no frequency,power factor concerns.Howe...In light of the growing integration of renewable energy sources in power systems,the adoption of DC microgrids has become increasingly popular,due to its simple structure,having no frequency,power factor concerns.However,the dependence of DC microgrids on cyber-networks also makes them susceptible to cyber-attacks.Potential cyberattacks can disrupt power system facilities and result in significant economic and loss of life.To address this concern,this paper presents an attack-resilient control strategy for microgrids to ensure voltage regulation and power sharing with stable operation under cyber-attack on the actuators.This paper first formulates the cyber-security problem considering a distributed generation based microgrid using the converter model,after which an attack-resilient control is proposed to eliminate the actuator attack impact on the system.Steady state analysis and root locus validation illustrate the feasibility of the proposed method.The effectiveness of the proposed control scheme is demonstrated through simulation results.展开更多
With the penetration of a large number of photovoltaic power generation units and power electronic converters,the DC microgrid shows low inertia characteristics,which might affect the stable operation of the microgrid...With the penetration of a large number of photovoltaic power generation units and power electronic converters,the DC microgrid shows low inertia characteristics,which might affect the stable operation of the microgrid in extreme cases.In order to enhance the“flexible features”of the interface converter connected to the DC bus,a control strategy of DCmicrogrid with photovoltaic and energy storage based on the virtual DC generator(VDCG)is proposed in this paper.The interface converters of the photovoltaic power generation system and the energy storage system simulates the inertia and damping characteristics of the DC generator to improve the stability of the DC bus voltage.The impedance ratio of DC microgrid was obtained by establishing the small-signal model of photovoltaic power generation system and energy storage system,and the Nyquist curves was applied to analyze the small-signal stability of the system.Finally,the simulation results were verified with MATLAB/Simulink.The results show that the proposed control strategy can slow down the fluctuation of bus voltage under the conditions of photovoltaic power fluctuation and load mutation,thus enhancing the system stability.展开更多
This article presents a distributed periodic eventtriggered(PET)optimal control scheme to achieve generation cost minimization and average bus voltage regulation in DC microgrids.In order to accommodate the generation...This article presents a distributed periodic eventtriggered(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.展开更多
A single-bus DC microgrid can represent a wide range of applications. Control objectives of such systems include high-performance bus voltage regulation and proper load sharing among multiple distributed generators(DG...A single-bus DC microgrid can represent a wide range of applications. Control objectives of such systems include high-performance bus voltage regulation and proper load sharing among multiple distributed generators(DGs) under various operating conditions. This paper presents a novel decentralized control algorithm that can guarantee both the transient voltage control performance and realize the predefined load sharing percentages. First, the output-constrained control problem is transformed into an equivalent unconstrained one. Second, a two-step backstepping control algorithm is designed based on the transformed model for bus-voltage regulation. Since the overall control effort can be split proportionally and calculated with locally-measurable signals, decentralized load sharing can be realized. The control design requires neither accurate parameters of the output filters nor load measurement. The stability of the transformed systems under the proposed control algorithm can indirectly guarantee the transient bus voltage performance of the original system. Additionally, the high-performance control design is robust, flexible, and reliable. Switch-level simulations under both normal and fault operating conditions demonstrate the effectiveness of the proposed algorithm.展开更多
In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converte...In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converter.The grid interface current is directly controlled by a battery DC-DC converter within the DC microgrid.Based on a comprehensive analysis of the battery DC-DC converter and interface current control,the control system has been mathematically modelled.This enabled two transfer functions to be derived that reflect the dynamic response of the inductor current to the duty cycle variation(inner loop),and the dynamic response of the grid interface current to the inductor current variation(outer loop).Experimental study has been done to assess the effectiveness of the proposed control strategy.The experimental results indicate that the proposed control strategy has a good performance to control the grid interface current without an interface converter,regardless the variations of both PV and the load conditions.展开更多
针对交直流混合微电网中双向AC/DC换流器在外界扰动下出现的直流母线电压波动问题,设计了一种应用于双向AC/DC换流器的非线性扩张状态观测器(nonlinear extended state observer,NLESO),以实现对分布式电源功率波动和负荷投切变化等不...针对交直流混合微电网中双向AC/DC换流器在外界扰动下出现的直流母线电压波动问题,设计了一种应用于双向AC/DC换流器的非线性扩张状态观测器(nonlinear extended state observer,NLESO),以实现对分布式电源功率波动和负荷投切变化等不确定因素的快速追踪与补偿,保证了在不同扰动下交直流混合微电网的稳定性。进一步提出了基于NLESO的改进积分滑模控制方法,提高了直流母线电压的控制精度。结合非线性光滑函数设计了滑模趋近律,消除了传统滑模控制中的高频抖振现象。通过Lyapunov理论对系统的稳定性进行分析验证,仿真结果表明该控制方法响应速度快、控制精度高、抗扰动能力强并且无抖振现象。展开更多
This paper presents performance analysis on hybrid AC/DC microgrid networks for residential home cluster. The design of the proposed microgrid includes comprehensive types of Distributed Generators (DGs) as hybrid pow...This paper presents performance analysis on hybrid AC/DC microgrid networks for residential home cluster. The design of the proposed microgrid includes comprehensive types of Distributed Generators (DGs) as hybrid power sources (wind, Photovoltaic (PV) solar cell, battery, fuel cell). Details about each DG dynamic modeling are presented and discussed. The customers in home cluster can be connected in both of the operating modes: islanded to the microgrid or connected to utility grid. Each DG has appended control system with its modeling that will be discussed to control DG performance. The wind turbine will be controlled by AC control system within three sub-control systems: 1) speed regulator and pitch control, 2) rotor side converter control, and 3) grid side converter control. The AC control structure is based on PLL, current regulator and voltage booster converter with using of photovoltaic Voltage Source Converter (VSC) and inverters to connect to the grid. The DC control system is mainly based on Maximum Power Point Tracking (MPPT) controller and boost converter connected to the PV array block and in order to control the system. The case study is used to analyze the performance of the proposed microgrid. The buses voltages, active power and reactive power responses are presented in both of grid-connected and islanded modes. In addition, the power factor, Total Harmonic Distortion (THD) and modulation index are calculated.展开更多
基金supported in part by the National Natural Science Foundation of China(62173255, 62188101)Shenzhen Key Laboratory of Control Theory and Intelligent Systems,(ZDSYS20220330161800001)。
文摘DC-DC converter-based multi-bus DC microgrids(MGs) in series have received much attention, where the conflict between voltage recovery and current balancing has been a hot topic. The lack of models that accurately portray the electrical characteristics of actual MGs while is controller design-friendly has kept the issue active. To this end, this paper establishes a large-signal model containing the comprehensive dynamical behavior of the DC MGs based on the theory of high-order fully actuated systems, and proposes distributed optimal control based on this. The proposed secondary control method can achieve the two goals of voltage recovery and current sharing for multi-bus DC MGs. Additionally, the simple structure of the proposed approach is similar to one based on droop control, which allows this control technique to be easily implemented in a variety of modern microgrids with different configurations. In contrast to existing studies, the process of controller design in this paper is closely tied to the actual dynamics of the MGs. It is a prominent feature that enables engineers to customize the performance metrics of the system. In addition, the analysis of the stability of the closed-loop DC microgrid system, as well as the optimality and consensus of current sharing are given. Finally, a scaled-down solar and battery-based microgrid prototype with maximum power point tracking controller is developed in the laboratory to experimentally test the efficacy of the proposed control method.
基金National Natural Science Foundation of China(Nos.51767017,51867015,62063016)Fundamental Research Innovation Group Project of Gansu Province(18JR3RA133)Gansu Provincial Science and Technology Program(20JR5RA048,20JR10RA177).
文摘During the operation of a DC microgrid,the nonlinearity and low damping characteristics of the DC bus make it prone to oscillatory instability.In this paper,we first establish a discrete nonlinear system dynamic model of a DC microgrid,study the effects of the converter sag coefficient,input voltage,and load resistance on the microgrid stability,and reveal the oscillation mechanism of a DC microgrid caused by a single source.Then,a DC microgrid stability analysis method based on the combination of bifurcation and strobe is used to analyze how the aforementioned parameters influence the oscillation characteristics of the system.Finally,the stability region of the system is obtained by the Jacobi matrix eigenvalue method.Grid simulation verifies the feasibility and effectiveness of the proposed method.
基金supported by the NationalNatural Science Foundation of China(No.52067013)the Natural Science Foundation of Gansu Province(No.20JR5RA395)as well as the Tianyou Innovation Team of Lanzhou Jiaotong University(TY202010).
文摘In this paper,an improved sag control strategy based on automatic SOC equalization is proposed to solve the problems of slow SOC equalization and excessive bus voltage fluctuation amplitude and offset caused by load and PV power variations in a stand-alone DC microgrid.The strategy includes primary and secondary control.Among them,the primary control suppresses the DC microgrid voltage fluctuation through the I and II section control,and the secondary control aims to correct the P-U curve of the energy storage system and the PV system,thus reducing the steady-state bus voltage excursion.The simulation results demonstrate that the proposed control strategy effectively achieves SOC balancing and enhances the immunity of bus voltage.The proposed strategy improves the voltage fluctuation suppression ability by approximately 39.4%and 43.1%under the PV power and load power fluctuation conditions,respectively.Furthermore,the steady-state deviation of the bus voltage,△U_(dc) is only 0.01–0.1 V,ensuring stable operation of the DC microgrid in fluctuating power environments.
基金supported by VILLUM FONDEN,Denmark under the VILLUM Investigator Grant(No.25920):Center for Research on Microgrids(CROM)。
文摘In light of the growing integration of renewable energy sources in power systems,the adoption of DC microgrids has become increasingly popular,due to its simple structure,having no frequency,power factor concerns.However,the dependence of DC microgrids on cyber-networks also makes them susceptible to cyber-attacks.Potential cyberattacks can disrupt power system facilities and result in significant economic and loss of life.To address this concern,this paper presents an attack-resilient control strategy for microgrids to ensure voltage regulation and power sharing with stable operation under cyber-attack on the actuators.This paper first formulates the cyber-security problem considering a distributed generation based microgrid using the converter model,after which an attack-resilient control is proposed to eliminate the actuator attack impact on the system.Steady state analysis and root locus validation illustrate the feasibility of the proposed method.The effectiveness of the proposed control scheme is demonstrated through simulation results.
基金funded by the National Natural Science Foundation of China(52067013)the Provincial Natural Science Foundation of Gansu(20JR5RA395).
文摘With the penetration of a large number of photovoltaic power generation units and power electronic converters,the DC microgrid shows low inertia characteristics,which might affect the stable operation of the microgrid in extreme cases.In order to enhance the“flexible features”of the interface converter connected to the DC bus,a control strategy of DCmicrogrid with photovoltaic and energy storage based on the virtual DC generator(VDCG)is proposed in this paper.The interface converters of the photovoltaic power generation system and the energy storage system simulates the inertia and damping characteristics of the DC generator to improve the stability of the DC bus voltage.The impedance ratio of DC microgrid was obtained by establishing the small-signal model of photovoltaic power generation system and energy storage system,and the Nyquist curves was applied to analyze the small-signal stability of the system.Finally,the simulation results were verified with MATLAB/Simulink.The results show that the proposed control strategy can slow down the fluctuation of bus voltage under the conditions of photovoltaic power fluctuation and load mutation,thus enhancing the system stability.
基金supported by the U.S.Office of Naval Research(N00014-21-1-2175)。
文摘This article presents a distributed periodic eventtriggered(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.
基金supported in part by the U.S.Office of Naval Research(N00014-16-1-3121,N00014-18-1-2185)the National Natural Science Foundation of China(61673347,U1609214,61751205)
文摘A single-bus DC microgrid can represent a wide range of applications. Control objectives of such systems include high-performance bus voltage regulation and proper load sharing among multiple distributed generators(DGs) under various operating conditions. This paper presents a novel decentralized control algorithm that can guarantee both the transient voltage control performance and realize the predefined load sharing percentages. First, the output-constrained control problem is transformed into an equivalent unconstrained one. Second, a two-step backstepping control algorithm is designed based on the transformed model for bus-voltage regulation. Since the overall control effort can be split proportionally and calculated with locally-measurable signals, decentralized load sharing can be realized. The control design requires neither accurate parameters of the output filters nor load measurement. The stability of the transformed systems under the proposed control algorithm can indirectly guarantee the transient bus voltage performance of the original system. Additionally, the high-performance control design is robust, flexible, and reliable. Switch-level simulations under both normal and fault operating conditions demonstrate the effectiveness of the proposed algorithm.
基金funding from the U.K.EPSRC UKRI Innovation Fellowship scheme(EP/S001662/2)the European Union’s Horizon 2020 research and innovation programme under grant agreement No.734796.
文摘In this paper,a grid interface current control strategy is presented for a DC microgrid,which aims to reduce the disturbance from PV generation and the load variation to the main grid without a grid interface converter.The grid interface current is directly controlled by a battery DC-DC converter within the DC microgrid.Based on a comprehensive analysis of the battery DC-DC converter and interface current control,the control system has been mathematically modelled.This enabled two transfer functions to be derived that reflect the dynamic response of the inductor current to the duty cycle variation(inner loop),and the dynamic response of the grid interface current to the inductor current variation(outer loop).Experimental study has been done to assess the effectiveness of the proposed control strategy.The experimental results indicate that the proposed control strategy has a good performance to control the grid interface current without an interface converter,regardless the variations of both PV and the load conditions.
文摘针对交直流混合微电网中双向AC/DC换流器在外界扰动下出现的直流母线电压波动问题,设计了一种应用于双向AC/DC换流器的非线性扩张状态观测器(nonlinear extended state observer,NLESO),以实现对分布式电源功率波动和负荷投切变化等不确定因素的快速追踪与补偿,保证了在不同扰动下交直流混合微电网的稳定性。进一步提出了基于NLESO的改进积分滑模控制方法,提高了直流母线电压的控制精度。结合非线性光滑函数设计了滑模趋近律,消除了传统滑模控制中的高频抖振现象。通过Lyapunov理论对系统的稳定性进行分析验证,仿真结果表明该控制方法响应速度快、控制精度高、抗扰动能力强并且无抖振现象。
文摘This paper presents performance analysis on hybrid AC/DC microgrid networks for residential home cluster. The design of the proposed microgrid includes comprehensive types of Distributed Generators (DGs) as hybrid power sources (wind, Photovoltaic (PV) solar cell, battery, fuel cell). Details about each DG dynamic modeling are presented and discussed. The customers in home cluster can be connected in both of the operating modes: islanded to the microgrid or connected to utility grid. Each DG has appended control system with its modeling that will be discussed to control DG performance. The wind turbine will be controlled by AC control system within three sub-control systems: 1) speed regulator and pitch control, 2) rotor side converter control, and 3) grid side converter control. The AC control structure is based on PLL, current regulator and voltage booster converter with using of photovoltaic Voltage Source Converter (VSC) and inverters to connect to the grid. The DC control system is mainly based on Maximum Power Point Tracking (MPPT) controller and boost converter connected to the PV array block and in order to control the system. The case study is used to analyze the performance of the proposed microgrid. The buses voltages, active power and reactive power responses are presented in both of grid-connected and islanded modes. In addition, the power factor, Total Harmonic Distortion (THD) and modulation index are calculated.