The Virtual Resistor based Active Damping(VR-AD) is widely employed in converters connected to the grid via LCL filters in order to mitigate the inherent resonance of the filters. Nevertheless, in digitally controlled...The Virtual Resistor based Active Damping(VR-AD) is widely employed in converters connected to the grid via LCL filters in order to mitigate the inherent resonance of the filters. Nevertheless, in digitally controlled systems, the PWM and the calculating delays modify the system characteristics in terms of frequency and phase, thus destabilizing the system and degrading the VR-AD performances, mainly in low switching frequencies. Moreover, the stability of the system is greatly affected under weak grid operation characterized by large grid impedance variation. This paper solves these problems by proposing a systematic, robust and optimized design procedure of voltage oriented PI control(VOC) with VRAD. The considered design procedure ensures robust control(sufficient stability margins) and high quality of grid current(reduced steady-state error and minimized THD value) despite the negative impact of digital time delay, grid impedance variation and filter parameters change. Simulation and experimental results are presented to show robustness and efficiency of the suggested design procedure.展开更多
In order to reduce the switching frequency harmonics caused by the grid-connected converter,the LCL filter is adopted.However the third-order LCL filter,as an undamped system,is not stable.In order to overcome this pr...In order to reduce the switching frequency harmonics caused by the grid-connected converter,the LCL filter is adopted.However the third-order LCL filter,as an undamped system,is not stable.In order to overcome this problem,a damping resistor and the active damping method are often used;but the damping resistor will result in the power consumption,and the method of active damping needs more sensors compared to the standard control.展开更多
The paper presents a successful design and good result of grid voltage feed-forward control strategy with no damping regulator of LCL filter applied in Three-phase Pulse Width Modulation( PWM) rectifier under unbalanc...The paper presents a successful design and good result of grid voltage feed-forward control strategy with no damping regulator of LCL filter applied in Three-phase Pulse Width Modulation( PWM) rectifier under unbalance grid condition for renewable energy processing. It is demonstrated that the closed-loop current control is decoupled with the grid voltage feed-forward control,and good waveform of grid current with low order harmonics is obtained under unbalance grid condition. This novel strategy is simple and reliable,applied with PI regulator but no resonant controller in α,β two-phase stationary frame. Moreover,the results of experiment and simulation are also illustrated to validate the novel strategy well applied in the closed-loop current control system under unbalanced grid condition.展开更多
As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, dampin...As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, damping resistance was virtualized, mathematical model under the DQ frame that can realize decoupling control was established, a dual-loop control strategy for grid-connected inverter with LCL filter was proposed, the system stability was analyzed and the design method of controller was given. The proposed method overcame the flaws of loss increase, efficiency reduce and cost increase which were caused by damping resistance in LCL type grid-connected inverter, the system efficiency and power supply quality of the output were improved. Feasibility and effectiveness of the new method were validated by simulation and experimental results.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 application of LCL filters has become popular for inverters connected to the power grid due to their advantages in harmonic current reductions. However,the power grid in a distribution system is non-ideal, present...The application of LCL filters has become popular for inverters connected to the power grid due to their advantages in harmonic current reductions. However,the power grid in a distribution system is non-ideal, presenting itself as a voltage source with significant impedance. This means that an inverter using an LCL filter may interact with other grid-connected inverters via the nonideal grid. In this paper, damping optimization of LCLfilters to reduce this interaction is studied for a three-phase voltage source inverter(VSI). Simulation results show that resonant oscillation occurs in a distributed power grid, even if the VSI with an LCL filter is well designed for standalone applications. A small-signal analysis is performed to predict this stability problem and to locate the boundary of the instability using an impedance approach. Based on these analytical results, optimized damping of the LCLfilter can be designed. The oscillation phenomena and optimized damping design are verified by simulations and experimental measurements.展开更多
基金supported by the Tunisian Ministry of High Education and Research under Grant LSE-ENIT-LR11ES15
文摘The Virtual Resistor based Active Damping(VR-AD) is widely employed in converters connected to the grid via LCL filters in order to mitigate the inherent resonance of the filters. Nevertheless, in digitally controlled systems, the PWM and the calculating delays modify the system characteristics in terms of frequency and phase, thus destabilizing the system and degrading the VR-AD performances, mainly in low switching frequencies. Moreover, the stability of the system is greatly affected under weak grid operation characterized by large grid impedance variation. This paper solves these problems by proposing a systematic, robust and optimized design procedure of voltage oriented PI control(VOC) with VRAD. The considered design procedure ensures robust control(sufficient stability margins) and high quality of grid current(reduced steady-state error and minimized THD value) despite the negative impact of digital time delay, grid impedance variation and filter parameters change. Simulation and experimental results are presented to show robustness and efficiency of the suggested design procedure.
文摘In order to reduce the switching frequency harmonics caused by the grid-connected converter,the LCL filter is adopted.However the third-order LCL filter,as an undamped system,is not stable.In order to overcome this problem,a damping resistor and the active damping method are often used;but the damping resistor will result in the power consumption,and the method of active damping needs more sensors compared to the standard control.
文摘The paper presents a successful design and good result of grid voltage feed-forward control strategy with no damping regulator of LCL filter applied in Three-phase Pulse Width Modulation( PWM) rectifier under unbalance grid condition for renewable energy processing. It is demonstrated that the closed-loop current control is decoupled with the grid voltage feed-forward control,and good waveform of grid current with low order harmonics is obtained under unbalance grid condition. This novel strategy is simple and reliable,applied with PI regulator but no resonant controller in α,β two-phase stationary frame. Moreover,the results of experiment and simulation are also illustrated to validate the novel strategy well applied in the closed-loop current control system under unbalanced grid condition.
文摘As to the concrete topology of three-phase LCL type grid-connected inverter with damping resistance, mathematical model was deduced in detail, using method of equivalent transformation to the structure diagram, damping resistance was virtualized, mathematical model under the DQ frame that can realize decoupling control was established, a dual-loop control strategy for grid-connected inverter with LCL filter was proposed, the system stability was analyzed and the design method of controller was given. The proposed method overcame the flaws of loss increase, efficiency reduce and cost increase which were caused by damping resistance in LCL type grid-connected inverter, the system efficiency and power supply quality of the output were improved. Feasibility and effectiveness of the new method were validated by simulation and experimental results.
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.51507118)by Open Fund of State Key Laboratory of Operation and Control of Renewable Energy and Storage Systems,China Electric Power Research Institute(Research on renewable energy power generation grid-connected converter fault tolerance evaluation method
文摘The application of LCL filters has become popular for inverters connected to the power grid due to their advantages in harmonic current reductions. However,the power grid in a distribution system is non-ideal, presenting itself as a voltage source with significant impedance. This means that an inverter using an LCL filter may interact with other grid-connected inverters via the nonideal grid. In this paper, damping optimization of LCLfilters to reduce this interaction is studied for a three-phase voltage source inverter(VSI). Simulation results show that resonant oscillation occurs in a distributed power grid, even if the VSI with an LCL filter is well designed for standalone applications. A small-signal analysis is performed to predict this stability problem and to locate the boundary of the instability using an impedance approach. Based on these analytical results, optimized damping of the LCLfilter can be designed. The oscillation phenomena and optimized damping design are verified by simulations and experimental measurements.
