Battery energy storage systems,fuel cells,and photovoltaic generators are being adopted in distribution networks to achieve CO;emission reduction.These power sources require inverters to connect to AC networks.However...Battery energy storage systems,fuel cells,and photovoltaic generators are being adopted in distribution networks to achieve CO;emission reduction.These power sources require inverters to connect to AC networks.However,sub-networks,such as a microgrids containing inverter power sources,may be disconnected from the utility network and operated in a standalone mode during extended blackouts.This study focuses on a standalone microgrid supplied by inverter power sources without a synchronous generator and proposes a new microgrid inverter control.In this inverter control,a single grid forming inverter is operated as a master power source to determine frequency and voltage,and other inverters,called grid following inverters,are operated as subordinate power sources with active and reactive power control.The necessary functions in the energy management system are examined,and the coordinated operation of all inverters in the microgrid is demonstrated via simulation.展开更多
Nonlinear loads in the power distribution system cause non-sinusoidal currents and voltages with harmonic components.Shunt active filters(SAF) with current controlled voltage source inverters(CCVSI) are usually used t...Nonlinear loads in the power distribution system cause non-sinusoidal currents and voltages with harmonic components.Shunt active filters(SAF) with current controlled voltage source inverters(CCVSI) are usually used to obtain balanced and sinusoidal source currents by injecting compensation currents.However,CCVSI with traditional controllers have a limited transient and steady state performance.In this paper,we propose an adaptive dynamic programming(ADP) controller with online learning capability to improve transient response and harmonics.The proposed controller works alongside existing proportional integral(PI) controllers to efficiently track the reference currents in the d-q domain.It can generate adaptive control actions to compensate the PI controller.The proposed system was simulated under different nonlinear(three-phase full wave rectifier) load conditions.The performance of the proposed approach was compared with the traditional approach.We have also included the simulation results without connecting the traditional PI control based power inverter for reference comparison.The online learning based ADP controller not only reduced average total harmonic distortion by 18.41%,but also outperformed traditional PI controllers during transients.展开更多
This paper studies the design and sizing of a filter (<em>L-C</em>) for an inverter with 180<span style="white-space:nowrap;"><span style="white-space:nowrap;">°<...This paper studies the design and sizing of a filter (<em>L-C</em>) for an inverter with 180<span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span> control in Medium voltage (MV), based on formulas of the capacitance of the capacitor <em>C</em> and the inductance <em>L</em> of the filter (<em>L-C</em>) of an SPWM inverter. These formulas were obtained by minimizing two parameters: the reactive power of the capacitor (capped at 5% of the apparent power of the load) and the ripple of the current flowing through inductance <em>L</em> (capped at 10% of the current supplying the load). The application of these formulas for the calculation of the filter (<em>L-C</em>) of the 180<span style="white-space:nowrap;">°</span> control inverter in MV is not conclusive. Studies have been carried out to make them applicable. The results show that limiting the current ripple in the inductor to 10% of the load current is a valid assumption and that limiting the reactive power of the capacitor to 5% of the apparent power of the load presents shortcomings. The results also show that setting the inductance <em>L</em> of the filter to <em>L<sub>maxi </sub></em>and the capacitor <em>C </em>from 35 × <em>C<sub>maxi</sub></em> to 400 × <em>C</em><em><sub>maxi </sub></em>gives voltage and current THDs that meet the 519 IEEE-2014 standards.展开更多
This study proposes a two-stage photovoltaic(PV)voltage control strategy for centralized control that ignores short-term load fluctuations.In the first stage,a deterministic power flow model optimizes the 15-minute ac...This study proposes a two-stage photovoltaic(PV)voltage control strategy for centralized control that ignores short-term load fluctuations.In the first stage,a deterministic power flow model optimizes the 15-minute active cycle of the inverter and reactive outputs to reduce network loss and light rejection.In the second stage,the local control stabilizes the fluctuations and tracks the system state of the first stage.The uncertain interval model establishes a chance constraint model for the inverter voltage-reactive power local control.Second-order cone optimization and sensitivity theories were employed to solve the models.The effectiveness of the model was confirmed using a modified IEEE 33 bus example.The intraday control outcome for distributed power generation considering the effects of fluctuation uncertainty,PV penetration rate,and inverter capacity is analyzed.展开更多
In this article,the LCL filter used for the three-phase two-level inverter with six-pulse control is designed from the components of the LC filter by means of a coefficient k varying between 0 and 1.The coefficient k ...In this article,the LCL filter used for the three-phase two-level inverter with six-pulse control is designed from the components of the LC filter by means of a coefficient k varying between 0 and 1.The coefficient k is used to determine the values of the inductances of the LCL filter in relation to the inductance of the LC filter.The capacitor capacity of the LCL filter is identical to that of the LC filter.To obtain the RMS voltage and current of the load,a method based on measuring the error of the RMS voltage and current of the load is proposed.This approach,applied to the three-phase,two-level inverter with 180˚full-wave control,enables us to reduce the value of the LCL filter inductance.Satisfactory results are obtained by simulation on MATLAB-Simulink software and compared with the LCL filter results.展开更多
The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage ...The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage DC(LCC-HVDC).The negative-sequence voltage affects the phase-locked loop(PLL)and the inverter control,thus the inverter is vulnerable to the subsequent commutation failure(SCF).In this paper,the analytical expression of the negative-sequence voltage resulting from the symmetrical fault with the commutation voltage is derived using the switching function and Fourier decomposition.The analytical expressions of the outputs of the PLL and inverter control with respect to time are derived to quantify the contribution of the negative-sequence voltage to the SCF.To deal with the AC component of the input signals in the PLL and the inverter control due to the negative-sequence voltage,the existing proportional-integral controls of the PLL,constant current control,and constant extinction angle control are replaced by the linear active disturbance rejection control against the SCF.Simulation results verify the contributing factors to the SCF.The proposed control reduces the risk of SCF and improves the recovery speed of the system under different fault conditions.展开更多
This rapid communication provides the author’s viewpoints on the need to develop grid stability functions for inverter-based resources,in particular,controls to enhance system stability.This discussion will be focuse...This rapid communication provides the author’s viewpoints on the need to develop grid stability functions for inverter-based resources,in particular,controls to enhance system stability.This discussion will be focused on transient stability and frequency regulation.Some future research directions are also presented.展开更多
Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance...Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance operating point are derived.Then,the post-disturbance equilibrium points are found and their stability properties are characterized.Furthermore,the attraction regions of the stable equilibrium points are accurately depicted by calculating the stable and unstable manifolds of the surrounding unstable equilibrium points,which presents an explanation to system transient stability.Finally,the transient control considerations are provided to help the inverter ridethrough the disturbance and maintain its stability characteristics.It is shown that the transient angle stability is not a serious problem for droop controlled inverters with proper control settings.展开更多
High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,wh...High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.展开更多
Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This st...Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid.PQ control and droop control techniques are established to control the microgrid operation.P-f and Q-E droop control is used to attain real and reactive power sharing.The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge.To address these issues,two DGs are interfaced with two parallel inverters in an islanded AC microgrid.PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references.The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics.A dual control strategy is proposed for the AC microgrid under islanded operation without communication link.Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.展开更多
文摘Battery energy storage systems,fuel cells,and photovoltaic generators are being adopted in distribution networks to achieve CO;emission reduction.These power sources require inverters to connect to AC networks.However,sub-networks,such as a microgrids containing inverter power sources,may be disconnected from the utility network and operated in a standalone mode during extended blackouts.This study focuses on a standalone microgrid supplied by inverter power sources without a synchronous generator and proposes a new microgrid inverter control.In this inverter control,a single grid forming inverter is operated as a master power source to determine frequency and voltage,and other inverters,called grid following inverters,are operated as subordinate power sources with active and reactive power control.The necessary functions in the energy management system are examined,and the coordinated operation of all inverters in the microgrid is demonstrated via simulation.
文摘Nonlinear loads in the power distribution system cause non-sinusoidal currents and voltages with harmonic components.Shunt active filters(SAF) with current controlled voltage source inverters(CCVSI) are usually used to obtain balanced and sinusoidal source currents by injecting compensation currents.However,CCVSI with traditional controllers have a limited transient and steady state performance.In this paper,we propose an adaptive dynamic programming(ADP) controller with online learning capability to improve transient response and harmonics.The proposed controller works alongside existing proportional integral(PI) controllers to efficiently track the reference currents in the d-q domain.It can generate adaptive control actions to compensate the PI controller.The proposed system was simulated under different nonlinear(three-phase full wave rectifier) load conditions.The performance of the proposed approach was compared with the traditional approach.We have also included the simulation results without connecting the traditional PI control based power inverter for reference comparison.The online learning based ADP controller not only reduced average total harmonic distortion by 18.41%,but also outperformed traditional PI controllers during transients.
文摘This paper studies the design and sizing of a filter (<em>L-C</em>) for an inverter with 180<span style="white-space:nowrap;"><span style="white-space:nowrap;">°</span></span> control in Medium voltage (MV), based on formulas of the capacitance of the capacitor <em>C</em> and the inductance <em>L</em> of the filter (<em>L-C</em>) of an SPWM inverter. These formulas were obtained by minimizing two parameters: the reactive power of the capacitor (capped at 5% of the apparent power of the load) and the ripple of the current flowing through inductance <em>L</em> (capped at 10% of the current supplying the load). The application of these formulas for the calculation of the filter (<em>L-C</em>) of the 180<span style="white-space:nowrap;">°</span> control inverter in MV is not conclusive. Studies have been carried out to make them applicable. The results show that limiting the current ripple in the inductor to 10% of the load current is a valid assumption and that limiting the reactive power of the capacitor to 5% of the apparent power of the load presents shortcomings. The results also show that setting the inductance <em>L</em> of the filter to <em>L<sub>maxi </sub></em>and the capacitor <em>C </em>from 35 × <em>C<sub>maxi</sub></em> to 400 × <em>C</em><em><sub>maxi </sub></em>gives voltage and current THDs that meet the 519 IEEE-2014 standards.
基金supported by the China National Natural Science Foundation(52177082)China National Key R&D Program(2020YFC0827001)Science and Technology Project of Jilin Electric Power Co.,Ltd(2020JBGS-03).
文摘This study proposes a two-stage photovoltaic(PV)voltage control strategy for centralized control that ignores short-term load fluctuations.In the first stage,a deterministic power flow model optimizes the 15-minute active cycle of the inverter and reactive outputs to reduce network loss and light rejection.In the second stage,the local control stabilizes the fluctuations and tracks the system state of the first stage.The uncertain interval model establishes a chance constraint model for the inverter voltage-reactive power local control.Second-order cone optimization and sensitivity theories were employed to solve the models.The effectiveness of the model was confirmed using a modified IEEE 33 bus example.The intraday control outcome for distributed power generation considering the effects of fluctuation uncertainty,PV penetration rate,and inverter capacity is analyzed.
文摘In this article,the LCL filter used for the three-phase two-level inverter with six-pulse control is designed from the components of the LC filter by means of a coefficient k varying between 0 and 1.The coefficient k is used to determine the values of the inductances of the LCL filter in relation to the inductance of the LC filter.The capacitor capacity of the LCL filter is identical to that of the LC filter.To obtain the RMS voltage and current of the load,a method based on measuring the error of the RMS voltage and current of the load is proposed.This approach,applied to the three-phase,two-level inverter with 180˚full-wave control,enables us to reduce the value of the LCL filter inductance.Satisfactory results are obtained by simulation on MATLAB-Simulink software and compared with the LCL filter results.
基金supported by National Natural Science Foundation of China(No.51877061).
文摘The negative-sequence voltage is often caused by the asymmetrical fault in the AC system,as well as the harmonics after the symmetrical fault at the AC side of inverter in line commutated converter based high-voltage DC(LCC-HVDC).The negative-sequence voltage affects the phase-locked loop(PLL)and the inverter control,thus the inverter is vulnerable to the subsequent commutation failure(SCF).In this paper,the analytical expression of the negative-sequence voltage resulting from the symmetrical fault with the commutation voltage is derived using the switching function and Fourier decomposition.The analytical expressions of the outputs of the PLL and inverter control with respect to time are derived to quantify the contribution of the negative-sequence voltage to the SCF.To deal with the AC component of the input signals in the PLL and the inverter control due to the negative-sequence voltage,the existing proportional-integral controls of the PLL,constant current control,and constant extinction angle control are replaced by the linear active disturbance rejection control against the SCF.Simulation results verify the contributing factors to the SCF.The proposed control reduces the risk of SCF and improves the recovery speed of the system under different fault conditions.
基金supported in part by the Engineering Research Center Program of the NSF and US DOE under the NSF Award Number EEC-1041877the CURENT Industry Partnership Program.
文摘This rapid communication provides the author’s viewpoints on the need to develop grid stability functions for inverter-based resources,in particular,controls to enhance system stability.This discussion will be focused on transient stability and frequency regulation.Some future research directions are also presented.
基金supported in part by National Natural Science Foundation of China (No.51877133)China Scholarship Council,and National Science Foundation (Award No.1810105)。
文摘Transient angle stability of inverters equipped with the robust droop controller is investigated in this work.At first,the conditions on the control references to guarantee the existence of a feasible post-disturbance operating point are derived.Then,the post-disturbance equilibrium points are found and their stability properties are characterized.Furthermore,the attraction regions of the stable equilibrium points are accurately depicted by calculating the stable and unstable manifolds of the surrounding unstable equilibrium points,which presents an explanation to system transient stability.Finally,the transient control considerations are provided to help the inverter ridethrough the disturbance and maintain its stability characteristics.It is shown that the transient angle stability is not a serious problem for droop controlled inverters with proper control settings.
基金supported in part by the German academic exchange service (DAAD)and CONICET.
文摘High penetration of renewable energy sources(RES)leads to new challenges for protection devices.Protection schemes are typically designed according to the dynamic behavior of rotating machines as generation sources,while the RES dynamic response,mainly governed by inverters,is not considered.Consequently,some relevant algorithms of transmission line protection are experiencing challenges because of the fact that magnitude and phase angle com-parison,amount of negative-sequence,and short-circuit current level are affected by the RES.Therefore,an in-depth study of this issue is necessary,one which considers the main causes and new methodological criteria solutions.This work presents an extensive literature review of the evaluation of electrical protection performance and the effects of RES connected to a power grid through inverters.Bibliographic data on many representative publications related to this topic are obtained to show the current research lines and their proposed solutions.In addition,this work identi-fies the main protection functions affected and describes the new protection schemes that consider RES.Finally,an analysis and discussion of the selected bibliography are presented.
基金This work was supported in part by the National Natural Science Foundation of China under Grant 51477098National Key R&D Program of China(2016YFB0900504).
文摘Parallel operation of inverter modules is the solution to increase the reliability,efficiency,and redundancy of inverters in microgrids.Load sharing among inverters in distributed generators(DGs)is a key issue.This study investigates the feasibility of power-sharing among parallel DGs using a dual control strategy in islanded mode of a microgrid.PQ control and droop control techniques are established to control the microgrid operation.P-f and Q-E droop control is used to attain real and reactive power sharing.The frequency variation caused by load change is an issue in droop control strategy whereas the tracking error of inverter power in PQ control is also a challenge.To address these issues,two DGs are interfaced with two parallel inverters in an islanded AC microgrid.PQ control is investigated for controlling the output real and reactive power of the DGs by assigning their references.The inverter under enhanced droop control implements power reallocation to restore the frequency among the distributed generators with predefined droop characteristics.A dual control strategy is proposed for the AC microgrid under islanded operation without communication link.Simulation studies are carried out using MATLAB/SIMULINK and the results show the validity and effective power-sharing performance of the system while maintaining a stable operation when the microgrid is in islanding mode.
