This paper presents a novel inter-cluster direct current(DC)capacitor voltage balancing control scheme for the single-star configured modular multilevel cascaded converter(MMCC)-based static synchronous compensator(ST...This paper presents a novel inter-cluster direct current(DC)capacitor voltage balancing control scheme for the single-star configured modular multilevel cascaded converter(MMCC)-based static synchronous compensator(STATCOM)under unbalanced grid voltage.The negative-sequence component of grid voltage at the point of common connection(PCC)causes unbalanced active power flow in the phase limbs of converter.This leads to the imbalance of DC voltages of the sub-module capacitors across the MMCC phases,and consequently,the malfunction of converter.The proposed solution is to inject both negative-sequence current(NSC)and zero-sequence voltage(ZSV)into the phase limbs of MMCC.A quantification factor Qf is used to achieve the sharing of inter-cluster active pow-er between the NSC and ZSV injection methods.Accurate determination of the quantification factor has been presented.In addition to maintaining the DC voltages of sub-module capacitor across the MMCC phases balanced,it also prevents the overcurrent and overvoltage of converter by injecting NSC and ZSV with the right proportion.The control scheme is validated on a 3.54 kV 1.2 MVA power system using MMCC-based STATCOM with 3-level bridge cells as sub-modules.The results show that the proposed scheme provides superior effectiveness in eliminating the voltage imbalance of DC capacitor in the phase limb while maintaining low voltage and current ratings.展开更多
The hybrid cascaded HVDC system employs a line commutated converter(LCC)as the rectifier and an LCC in series with multiple paralleled modular multilevel converters(MMCs)as the inverter.MMC arms are susceptible to ove...The hybrid cascaded HVDC system employs a line commutated converter(LCC)as the rectifier and an LCC in series with multiple paralleled modular multilevel converters(MMCs)as the inverter.MMC arms are susceptible to overcurrent following a severe AC fault at the receiving end,however,its fundamental mechanism has not been totally revealed.Therefore,this article explores the overcurrent characteristics on MMC arms,in terms of both the DC and AC components.Apart from the DC overcurrent component induced by the commutation failure(CF)of the inverter LCC,the AC overcurrent component is also significant.It dramatically depends on the coupling effects among the AC systems of the inverter side.Further,corresponding suppression strategies are proposed,which are applicable to different receiving-end AC fault scenarios.Eventually,the time-domain simulation results from PSCAD/EMTDC validate the effectiveness of the proposed overcurrent suppression control.It is also demonstrated that the presented methods can not only suppress overcurrent for MMC arms,but also reduce the imbalanced power between two sides,as well as improve the dynamic performances of the entire system.展开更多
文摘This paper presents a novel inter-cluster direct current(DC)capacitor voltage balancing control scheme for the single-star configured modular multilevel cascaded converter(MMCC)-based static synchronous compensator(STATCOM)under unbalanced grid voltage.The negative-sequence component of grid voltage at the point of common connection(PCC)causes unbalanced active power flow in the phase limbs of converter.This leads to the imbalance of DC voltages of the sub-module capacitors across the MMCC phases,and consequently,the malfunction of converter.The proposed solution is to inject both negative-sequence current(NSC)and zero-sequence voltage(ZSV)into the phase limbs of MMCC.A quantification factor Qf is used to achieve the sharing of inter-cluster active pow-er between the NSC and ZSV injection methods.Accurate determination of the quantification factor has been presented.In addition to maintaining the DC voltages of sub-module capacitor across the MMCC phases balanced,it also prevents the overcurrent and overvoltage of converter by injecting NSC and ZSV with the right proportion.The control scheme is validated on a 3.54 kV 1.2 MVA power system using MMCC-based STATCOM with 3-level bridge cells as sub-modules.The results show that the proposed scheme provides superior effectiveness in eliminating the voltage imbalance of DC capacitor in the phase limb while maintaining low voltage and current ratings.
文摘The hybrid cascaded HVDC system employs a line commutated converter(LCC)as the rectifier and an LCC in series with multiple paralleled modular multilevel converters(MMCs)as the inverter.MMC arms are susceptible to overcurrent following a severe AC fault at the receiving end,however,its fundamental mechanism has not been totally revealed.Therefore,this article explores the overcurrent characteristics on MMC arms,in terms of both the DC and AC components.Apart from the DC overcurrent component induced by the commutation failure(CF)of the inverter LCC,the AC overcurrent component is also significant.It dramatically depends on the coupling effects among the AC systems of the inverter side.Further,corresponding suppression strategies are proposed,which are applicable to different receiving-end AC fault scenarios.Eventually,the time-domain simulation results from PSCAD/EMTDC validate the effectiveness of the proposed overcurrent suppression control.It is also demonstrated that the presented methods can not only suppress overcurrent for MMC arms,but also reduce the imbalanced power between two sides,as well as improve the dynamic performances of the entire system.
