This paper proposes a novel high-efficiency generation technique for photovoltaic(PV) system,named maximum power point capturing(MPPC) technique. This is an aperiodic perturbation MPPC technique compared to the conven...This paper proposes a novel high-efficiency generation technique for photovoltaic(PV) system,named maximum power point capturing(MPPC) technique. This is an aperiodic perturbation MPPC technique compared to the conventional periodic perturbation maximum power point tracking technique. Firstly, under a closed-loop circuit and an open-loop circuit,the complete I-V curves and P-V curves are defined. Secondly, the proposed MPPC technique is based on the complete I-V curves and a practical model of solar PV systems.The proposed method realizes that maximum power point(MPP) is captured online, and its control strategy is designed to set a steady operating area around MPP. The duty cycle keeps constant when the operating point is within the steady operating area, i.e., aperiodic perturbation, and when the operating point is outside the steady operating area, MPPC is triggered to capture a new MPP with an updated steady operating area. Simulation results demonstrate that no oscillations exist in steady-state;dynamic performances are improved;and only two perturbations are required to capture the new MPP. Using the proposed MPPC method,low voltage ride through and high voltage ride through can be prevented.展开更多
When the power grid suffers from grid faults that cause phase disturbances,the grid-connected converter becomes destabilized by the interaction between the phase-locked loop(PLL)and the control loop.In this paper,the ...When the power grid suffers from grid faults that cause phase disturbances,the grid-connected converter becomes destabilized by the interaction between the phase-locked loop(PLL)and the control loop.In this paper,the stability of the PLL affected by the control loop under transient grid faults is studied.First,the equivalent model of the PLL under the influence of the control loop is established.Then,different response processes of PLLs under the ground fault with various control parameters are qualitatively analyzed.Furthermore,a small-signal model is proposed to assess the stability of the PLL under different control loop parameters.The system poles can be calculated to show the physical origin of the instability.Finally,simulations of a three-phase 21-level modular multilevel converter(MMC)built in PSCAD and a down-scale experiment is performed to verify the parameter influence of the control loop on the PLL.展开更多
In this paper,a computation framework for addressing combined economic and emission dispatch(CEED)problem with valve-point effects as well as stochastic wind power considering unit commitment(UC)using a hybrid approac...In this paper,a computation framework for addressing combined economic and emission dispatch(CEED)problem with valve-point effects as well as stochastic wind power considering unit commitment(UC)using a hybrid approach connecting sequential quadratic programming(SQP)and particle swarm optimization(PSO)is proposed.The CEED problem aims to minimize the scheduling cost and greenhouse gases(GHGs)emission cost.Here the GHGs include carbon dioxide(CO_(2)),nitrogen dioxide(NO_(2)),and sulphur oxides(SO_(x)).A dispatch model including both thermal generators and wind farms is developed.The probability of stochastic wind power based on the Weibull distribution is included in the CEED model.The model is tested on a standard system involving six thermal units and two wind farms.A set of numerical case studies are reported.The performance of the hybrid computational method is validated by comparing with other solvers on the test system.展开更多
When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by g...When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by grid voltage phase shifting and the integration effect of the phase-locked loop(PLL)in the converter.The system may exhibit an undesirable transient process with expanded current which is harmful for the converter devices.In this paper,a transient current estimation method is proposed for the scenario of converter-grid phase difference caused by the frequency shifting of the grid side.A piecewise phase calculation model is established to determine the transient phase difference of the system.Then,according to the maximum phase difference calculated by the model,the system stability is assessed and the maximum value of system transient current can be estimated after comparing the maximum phase difference with the critical phase difference and π,Finally,the current estimation results are verified by detailed circuit simulations of a 21-level MMC-HVDC system built in PSCAD.展开更多
With the advent of distributed energy sources in low voltage distribution systems,direct power supply through these sources to local loads as microgrids is becoming a reality.Different microgrid architectures will app...With the advent of distributed energy sources in low voltage distribution systems,direct power supply through these sources to local loads as microgrids is becoming a reality.Different microgrid architectures will appear in near future.Microgrids can be operated in an islanded or grid connected modes.Different control techniques will be implemented for smooth operation of microgrids.展开更多
基金supported in part by Australian Research Council (ARC) Discovery Project (No. DP170104426)
文摘This paper proposes a novel high-efficiency generation technique for photovoltaic(PV) system,named maximum power point capturing(MPPC) technique. This is an aperiodic perturbation MPPC technique compared to the conventional periodic perturbation maximum power point tracking technique. Firstly, under a closed-loop circuit and an open-loop circuit,the complete I-V curves and P-V curves are defined. Secondly, the proposed MPPC technique is based on the complete I-V curves and a practical model of solar PV systems.The proposed method realizes that maximum power point(MPP) is captured online, and its control strategy is designed to set a steady operating area around MPP. The duty cycle keeps constant when the operating point is within the steady operating area, i.e., aperiodic perturbation, and when the operating point is outside the steady operating area, MPPC is triggered to capture a new MPP with an updated steady operating area. Simulation results demonstrate that no oscillations exist in steady-state;dynamic performances are improved;and only two perturbations are required to capture the new MPP. Using the proposed MPPC method,low voltage ride through and high voltage ride through can be prevented.
基金This work was supported by the National Natural Science Foundation of China(51877159,51637007,U1866601).
文摘When the power grid suffers from grid faults that cause phase disturbances,the grid-connected converter becomes destabilized by the interaction between the phase-locked loop(PLL)and the control loop.In this paper,the stability of the PLL affected by the control loop under transient grid faults is studied.First,the equivalent model of the PLL under the influence of the control loop is established.Then,different response processes of PLLs under the ground fault with various control parameters are qualitatively analyzed.Furthermore,a small-signal model is proposed to assess the stability of the PLL under different control loop parameters.The system poles can be calculated to show the physical origin of the instability.Finally,simulations of a three-phase 21-level modular multilevel converter(MMC)built in PSCAD and a down-scale experiment is performed to verify the parameter influence of the control loop on the PLL.
文摘In this paper,a computation framework for addressing combined economic and emission dispatch(CEED)problem with valve-point effects as well as stochastic wind power considering unit commitment(UC)using a hybrid approach connecting sequential quadratic programming(SQP)and particle swarm optimization(PSO)is proposed.The CEED problem aims to minimize the scheduling cost and greenhouse gases(GHGs)emission cost.Here the GHGs include carbon dioxide(CO_(2)),nitrogen dioxide(NO_(2)),and sulphur oxides(SO_(x)).A dispatch model including both thermal generators and wind farms is developed.The probability of stochastic wind power based on the Weibull distribution is included in the CEED model.The model is tested on a standard system involving six thermal units and two wind farms.A set of numerical case studies are reported.The performance of the hybrid computational method is validated by comparing with other solvers on the test system.
基金supported by the National Natural Science Foundation of China under Grants 51877159,51637007the Fundamental Research Funds for Central Universities Program 2042019kf0195。
文摘When a modular multilevel converter based high voltage direct current(MMC-HVDC)system operates under grid faults,there will be a phase difference between the grid voltage and the converter output.It can be caused by grid voltage phase shifting and the integration effect of the phase-locked loop(PLL)in the converter.The system may exhibit an undesirable transient process with expanded current which is harmful for the converter devices.In this paper,a transient current estimation method is proposed for the scenario of converter-grid phase difference caused by the frequency shifting of the grid side.A piecewise phase calculation model is established to determine the transient phase difference of the system.Then,according to the maximum phase difference calculated by the model,the system stability is assessed and the maximum value of system transient current can be estimated after comparing the maximum phase difference with the critical phase difference and π,Finally,the current estimation results are verified by detailed circuit simulations of a 21-level MMC-HVDC system built in PSCAD.
文摘With the advent of distributed energy sources in low voltage distribution systems,direct power supply through these sources to local loads as microgrids is becoming a reality.Different microgrid architectures will appear in near future.Microgrids can be operated in an islanded or grid connected modes.Different control techniques will be implemented for smooth operation of microgrids.
