This article proposes a method of management and control of a continuous bus powered by renewable energies for autonomous applications. The DC bus is obtained from two systems of renewable sources (the solar system an...This article proposes a method of management and control of a continuous bus powered by renewable energies for autonomous applications. The DC bus is obtained from two systems of renewable sources (the solar system and the wind system) and storage battery (Lithium Ion). The continuous bus control and management procedure require efficiency in the control of the charge and discharge of the battery according to the load energy demand (DC Motor). The battery charging process is non-linear, varying over time with considerable delay, so it is difficult to achieve the best performance on control with energy management using traditional control approaches. A fuzzy control strategy is used in this article for battery control. To improve battery life, fuzzy control manages the desired state of charge (SOC). The entire system designed is modeled and simulated on MATLAB/Simulink Environment.展开更多
In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To ...In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.展开更多
Three space vector pulse width modulation (SVPWM) schemes, called 7-segment space vector modulation (SVM), 5-segment SVM and 3-segment SVM are studied in this paper. The basic principle of SVPWM is presented. The ...Three space vector pulse width modulation (SVPWM) schemes, called 7-segment space vector modulation (SVM), 5-segment SVM and 3-segment SVM are studied in this paper. The basic principle of SVPWM is presented. The switching sequence of different scheme is described. The modulation signals, DC bus voltage utilization, and output line voltage harmonic of these schemes are analyzed by the MATLAB software with different modulation index M and frequency modulation index N. The simulation results are analyzed and show that discontinuous modulating functions lead a reduction of switching actions. The DC bus voltage utilization of three schemes is almost the same. For all three SVM, the frequency modulation index N will affect the harmonic characteristic, and the modulation index M will affect DC bus voltage utilization and the harmonic content. The experiment is implemented by the DSP of TMS320F2812. The results validate three algorithms and the simulation.展开更多
The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator(PMSG)compensated by external circuits in series with the 3-phase windings is investigated in this paper.The asymmetr...The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator(PMSG)compensated by external circuits in series with the 3-phase windings is investigated in this paper.The asymmetric impedance includes the unbalanced resistances,unbalanced self-inductances,and unbalanced mutual inductances.From the perspective of the second harmonic inductances in dq-frame and from the perspective of the second harmonic power,it is theoretically demonstrated that the original asymmetric 3-phase system with asymmetric impedance can be modified to a balanced system by external circuits consisting of resistances and inductances.Therefore,the second harmonic power and DC bus voltage due to the asymmetries can be suppressed naturally without any software modifications.The feasibility of this compensation method is validated by elaborate experiments at different speeds and under different load condition,although the effectiveness might be slightly affected by the non-linearity of the compensation inductance in practice.展开更多
Impedance analysis is an effective method to analyze the oscillation issue associated with grid-connected photovoltaic systems.However,the existing impedance modeling of a gridconnected photovoltaic inverter usually o...Impedance analysis is an effective method to analyze the oscillation issue associated with grid-connected photovoltaic systems.However,the existing impedance modeling of a gridconnected photovoltaic inverter usually only considers the effect of a single perturbation frequency,ignoring the coupling frequency response between the internal control loops of a grid-connected inverter,which severely affects the accuracy of the stability analysis.Hence,a method of impedance modeling and stability analysis for grid-connected photovoltaic inverters considering cross-coupling frequency is proposed in this paper.First,the generation mechanism of frequency coupling in gridconnected photovoltaic inverters,and the relationship between the coupling frequency and perturbation frequency are analyzed.Secondly,a sequence impedance model of grid-connected photovoltaic systems considering the coupling frequency is established by using the harmonic linearization method.The impact of DC bus voltage control strategy on frequency coupling characteristics of a grid-connected photovoltaic system is evaluated,and the impact of a coupling frequency term on system stability is quantitatively analyzed.Finally,the advantages of the proposed method are verified by several simulations.The results show that the proposed impedance model can accurately predict the potential resonance points of the system,and the coupling frequency characteristics will become much stronger with smaller DC bus capacitance or larger bandwidth of the DC bus controller.展开更多
文摘This article proposes a method of management and control of a continuous bus powered by renewable energies for autonomous applications. The DC bus is obtained from two systems of renewable sources (the solar system and the wind system) and storage battery (Lithium Ion). The continuous bus control and management procedure require efficiency in the control of the charge and discharge of the battery according to the load energy demand (DC Motor). The battery charging process is non-linear, varying over time with considerable delay, so it is difficult to achieve the best performance on control with energy management using traditional control approaches. A fuzzy control strategy is used in this article for battery control. To improve battery life, fuzzy control manages the desired state of charge (SOC). The entire system designed is modeled and simulated on MATLAB/Simulink Environment.
基金funded by the National Natural Science Foundation of China(52067013),and the Provincial Natural Science Foundation of Gansu(20JR5RA395).
文摘In the DC microgrid,the lack of inertia and damping in power electronic converters results in poor stability of DC bus voltage and low inertia of the DC microgrid during fluctuations in load and photovoltaic power.To address this issue,the application of a virtual synchronous generator(VSG)in grid-connected inverters control is referenced and proposes a control strategy called the analogous virtual synchronous generator(AVSG)control strategy for the interface DC/DC converter of the battery in the microgrid.Besides,a flexible parameter adaptive control method is introduced to further enhance the inertial behavior of the AVSG control.Firstly,a theoretical analysis is conducted on the various components of the DC microgrid,the structure of analogous virtual synchronous generator,and the control structure’s main parameters related to the DC microgrid’s inertial behavior.Secondly,the voltage change rate tracking coefficient is introduced to adjust the change of the virtual capacitance and damping coefficient flexibility,which further strengthens the inertia trend of the DC microgrid.Additionally,a small-signal modeling approach is used to analyze the approximate range of the AVSG’s main parameters ensuring system stability.Finally,conduct a simulation analysis by building the model of the DC microgrid system with photovoltaic(PV)and battery energy storage(BES)in MATLAB/Simulink.Simulation results from different scenarios have verified that the AVSG control introduces fixed inertia and damping into the droop control of the battery,resulting in a certain level of inertia enhancement.Furthermore,the additional adaptive control strategy built upon the AVSG control provides better and flexible inertial support for the DC microgrid,further enhances the stability of the DC bus voltage,and has a more positive impact on the battery performance.
基金This work was supported by the Research Fund for the Doctoral Program of Higher Education of China under Grant No. 20050487044.
文摘Three space vector pulse width modulation (SVPWM) schemes, called 7-segment space vector modulation (SVM), 5-segment SVM and 3-segment SVM are studied in this paper. The basic principle of SVPWM is presented. The switching sequence of different scheme is described. The modulation signals, DC bus voltage utilization, and output line voltage harmonic of these schemes are analyzed by the MATLAB software with different modulation index M and frequency modulation index N. The simulation results are analyzed and show that discontinuous modulating functions lead a reduction of switching actions. The DC bus voltage utilization of three schemes is almost the same. For all three SVM, the frequency modulation index N will affect the harmonic characteristic, and the modulation index M will affect DC bus voltage utilization and the harmonic content. The experiment is implemented by the DSP of TMS320F2812. The results validate three algorithms and the simulation.
文摘The unbalanced impedance of the asymmetric 3-phase wind power permanent magnet synchronous generator(PMSG)compensated by external circuits in series with the 3-phase windings is investigated in this paper.The asymmetric impedance includes the unbalanced resistances,unbalanced self-inductances,and unbalanced mutual inductances.From the perspective of the second harmonic inductances in dq-frame and from the perspective of the second harmonic power,it is theoretically demonstrated that the original asymmetric 3-phase system with asymmetric impedance can be modified to a balanced system by external circuits consisting of resistances and inductances.Therefore,the second harmonic power and DC bus voltage due to the asymmetries can be suppressed naturally without any software modifications.The feasibility of this compensation method is validated by elaborate experiments at different speeds and under different load condition,although the effectiveness might be slightly affected by the non-linearity of the compensation inductance in practice.
文摘Impedance analysis is an effective method to analyze the oscillation issue associated with grid-connected photovoltaic systems.However,the existing impedance modeling of a gridconnected photovoltaic inverter usually only considers the effect of a single perturbation frequency,ignoring the coupling frequency response between the internal control loops of a grid-connected inverter,which severely affects the accuracy of the stability analysis.Hence,a method of impedance modeling and stability analysis for grid-connected photovoltaic inverters considering cross-coupling frequency is proposed in this paper.First,the generation mechanism of frequency coupling in gridconnected photovoltaic inverters,and the relationship between the coupling frequency and perturbation frequency are analyzed.Secondly,a sequence impedance model of grid-connected photovoltaic systems considering the coupling frequency is established by using the harmonic linearization method.The impact of DC bus voltage control strategy on frequency coupling characteristics of a grid-connected photovoltaic system is evaluated,and the impact of a coupling frequency term on system stability is quantitatively analyzed.Finally,the advantages of the proposed method are verified by several simulations.The results show that the proposed impedance model can accurately predict the potential resonance points of the system,and the coupling frequency characteristics will become much stronger with smaller DC bus capacitance or larger bandwidth of the DC bus controller.