The grid-connected converter(GCC) is widely used as the interface between various distributed generations and the utility grid. To achieve precise power control for GCC, this paper presents a model predictive direct p...The grid-connected converter(GCC) is widely used as the interface between various distributed generations and the utility grid. To achieve precise power control for GCC, this paper presents a model predictive direct power control(MPDPC)with consideration of the unbalanced filter inductance and grid conditions. First, the characteristics of GCC with unbalanced filter inductance are analyzed and a modified voltage control function is derived. On this basis, to compensate for the power oscillation caused by unbalanced filter inductance, a novel power compensation method is proposed for MPDPC to eliminate the DC-side current ripple while maintaining sinusoidal grid current. Besides, to improve the control robustness against mismatched filter inductance, a filter inductance identification scheme is proposed. Through this scheme, the estimated value of filter inductance is updated in each control period and applied in the proposed MPDPC. Finally, simulation results in PSCAD/EMTDC confirm the validity of the proposed MPDPC and the filter inductance identification scheme.展开更多
Fast and accurate acquisition of positive sequence components of unbalanced grid voltage is an essential requirement to ensure the safety operation of the grid-connected inverter.To improve the extraction speed of pos...Fast and accurate acquisition of positive sequence components of unbalanced grid voltage is an essential requirement to ensure the safety operation of the grid-connected inverter.To improve the extraction speed of positive sequence components of unbalanced voltage,this study proposes a sampling period delay filter(SPDF)to quickly separate positive and negative sequence components by delaying two sampling periods of grid voltage in dq frame.With the SPDF method,only one coordinate transformation is required and the computational burden can be reduced apparently.Then,the noise immunity performance of the proposed SPDF algorithm is investigated;and the corresponding solution,operation period delay filter(OPDF),can guarantee the desired fast response performance under the premise of limiting the amplified noise within the acceptable range.Finally,the feasibility and priority of the above two algorithms have been verified by the simulation and experimental results.展开更多
A doubly-fed induction generator(DFIG)based configuration is still preferred by wind turbine manufacturers due to the cost-effective power converter and independent control of the active power and reactive power.To co...A doubly-fed induction generator(DFIG)based configuration is still preferred by wind turbine manufacturers due to the cost-effective power converter and independent control of the active power and reactive power.To cope with stricter grid codes(e.g.reactive power compensation,low voltage ride-through operation,as well as steady and safe operation during long-term distorted grid),control strategies are continuously evolving.This paper starts with a control strategy using the combined reactive power compensation from both the back-to-back power converters for their optimized lifetime distribution under normal grid conditions.Afterwards,an advanced demagnetizing control is proposed to keep the minimum thermal stress of the rotor-side converter in the case of the short-term grid fault.A modularized control strategy of the DFIG system under unbalanced and distorted grid voltage is discussed,with the control targets of the smooth active and reactive power or the balanced and sinusoidal current of the rotor-side converter and the grid-side converte。Finally,a bandwidth based repetitive controller is evaluated to improve the DFIG system's robustness against grid frequency deviation.展开更多
基金supported by the Science and Technology Projects of State Grid Corporation of China “Key Technologies and Demonstration Application of Distributed Power Clusters Regulation”(No. 52153220000U)。
文摘The grid-connected converter(GCC) is widely used as the interface between various distributed generations and the utility grid. To achieve precise power control for GCC, this paper presents a model predictive direct power control(MPDPC)with consideration of the unbalanced filter inductance and grid conditions. First, the characteristics of GCC with unbalanced filter inductance are analyzed and a modified voltage control function is derived. On this basis, to compensate for the power oscillation caused by unbalanced filter inductance, a novel power compensation method is proposed for MPDPC to eliminate the DC-side current ripple while maintaining sinusoidal grid current. Besides, to improve the control robustness against mismatched filter inductance, a filter inductance identification scheme is proposed. Through this scheme, the estimated value of filter inductance is updated in each control period and applied in the proposed MPDPC. Finally, simulation results in PSCAD/EMTDC confirm the validity of the proposed MPDPC and the filter inductance identification scheme.
基金The work was supported by the National Natural Science Foundation of China(51707091).
文摘Fast and accurate acquisition of positive sequence components of unbalanced grid voltage is an essential requirement to ensure the safety operation of the grid-connected inverter.To improve the extraction speed of positive sequence components of unbalanced voltage,this study proposes a sampling period delay filter(SPDF)to quickly separate positive and negative sequence components by delaying two sampling periods of grid voltage in dq frame.With the SPDF method,only one coordinate transformation is required and the computational burden can be reduced apparently.Then,the noise immunity performance of the proposed SPDF algorithm is investigated;and the corresponding solution,operation period delay filter(OPDF),can guarantee the desired fast response performance under the premise of limiting the amplified noise within the acceptable range.Finally,the feasibility and priority of the above two algorithms have been verified by the simulation and experimental results.
文摘A doubly-fed induction generator(DFIG)based configuration is still preferred by wind turbine manufacturers due to the cost-effective power converter and independent control of the active power and reactive power.To cope with stricter grid codes(e.g.reactive power compensation,low voltage ride-through operation,as well as steady and safe operation during long-term distorted grid),control strategies are continuously evolving.This paper starts with a control strategy using the combined reactive power compensation from both the back-to-back power converters for their optimized lifetime distribution under normal grid conditions.Afterwards,an advanced demagnetizing control is proposed to keep the minimum thermal stress of the rotor-side converter in the case of the short-term grid fault.A modularized control strategy of the DFIG system under unbalanced and distorted grid voltage is discussed,with the control targets of the smooth active and reactive power or the balanced and sinusoidal current of the rotor-side converter and the grid-side converte。Finally,a bandwidth based repetitive controller is evaluated to improve the DFIG system's robustness against grid frequency deviation.