基于传统虚拟同步机(Virtual Synchronous Generator,VSG)控制的储能型模块化多电平换流器(Modular Multilevel Converter,MMC)在不平衡网压下输出电流不平衡且存在功率二倍频脉动.为避免过大的有功功率纹波影响网侧频率支撑性能,针对...基于传统虚拟同步机(Virtual Synchronous Generator,VSG)控制的储能型模块化多电平换流器(Modular Multilevel Converter,MMC)在不平衡网压下输出电流不平衡且存在功率二倍频脉动.为避免过大的有功功率纹波影响网侧频率支撑性能,针对改进型MMC超级电容对称储能系统(Improved MMC based on Symmetrical Super Capacitor Energy Storage System,IMMC-SSCESS)数学模型,分析其在不平衡网压下电流不平衡与功率脉动产生机理,提出基于电流参考指令修正和负序电压补偿的改进VSG控制.研究结果表明:改进VSG控制能实现输出电流平衡、有功脉动抑制和无功脉动抑制3种控制目标,各控制目标下IMMC-SSCESS有功功率纹波显著降低或抑制为0,有效改善了其不平衡网压下的频率支撑性能.展开更多
在网压不平衡工况下,模块化多电平储能系统(modular multilevel converter energy storage system,MMCESS)如果以并网电流平衡为控制目标,虽然可以保证交流系统安全运行,但是会引起各相放电速度不同,导致子模块储能电池荷电状态(state o...在网压不平衡工况下,模块化多电平储能系统(modular multilevel converter energy storage system,MMCESS)如果以并网电流平衡为控制目标,虽然可以保证交流系统安全运行,但是会引起各相放电速度不同,导致子模块储能电池荷电状态(state of charge,SOC)的不均衡。为解决上述问题,首先对比分析了传统MMC和MMC-ESS的内部环流特性;然后分析了以并网电流平衡为目标的不平衡网压控制对电池SOC的影响;针对这一问题,提出了利用注入直流环流的控制策略,有效地实现了相间功率均衡,并论述了直流环流控制器参数对系统稳定性的影响;以各相电压跌落度为变量,绘制各相注入的直流环流占额定桥臂电流比例的三维图,针对不同跌落度分析了各相桥臂电流的变化,为设备器件选型提供了依据;最后,通过仿真和实验验证了理论分析的正确性及控制策略的可行性。展开更多
To determine the interdependence of intracranial pressure(ICP) and intraocular pressure(IOP) and how it affects optic nerve pressures, eight normal dogs were examined using pressure-sensing probes implanted into the l...To determine the interdependence of intracranial pressure(ICP) and intraocular pressure(IOP) and how it affects optic nerve pressures, eight normal dogs were examined using pressure-sensing probes implanted into the left ventricle, lumbar cistern, optic nerve subarachnoid space in the left eye, and anterior chamber in the left eye. This allowed ICP, lumbar cistern pressure(LCP), optic nerve subarachnoid space pressure(ONSP) and IOP to be simultaneously recorded. After establishing baseline pressure levels, pressure changes that resulted from lowering ICP(via shunting cerebrospinal fluid(CSF) from the ventricle) were recorded. At baseline, all examined pressures were different(ICP>LCP>ONSP), but correlated(P<0.001). As ICP was lowered during CSF shunting, IOP also dropped in a parallel time course so that the trans-lamina cribrosa gradient(TLPG) remained stable(ICP-IOP dependent zone). However, once ICP fell below a critical breakpoint, ICP and IOP became uncoupled and TLPG changed as ICP declined(ICP-IOP independent zone). The optic nerve pressure gradient(ONPG) and trans-optic nerve pressure gradient(TOPG) increased linearly as ICP decreased through both the ICP-IOP dependent and independent zones. We conclude that ICP and IOP are coupled in a specific pressure range, but when ICP drops below a critical point, IOP and ICP become uncoupled and TLPG increases. When ICP drops, a rise in the ONPG and TOPG creates more pressure and reduces CSF flow around the optic nerve. This change may play a role in the development and progression of various ophthalmic and neurological diseases, including glaucoma.展开更多
文摘基于传统虚拟同步机(Virtual Synchronous Generator,VSG)控制的储能型模块化多电平换流器(Modular Multilevel Converter,MMC)在不平衡网压下输出电流不平衡且存在功率二倍频脉动.为避免过大的有功功率纹波影响网侧频率支撑性能,针对改进型MMC超级电容对称储能系统(Improved MMC based on Symmetrical Super Capacitor Energy Storage System,IMMC-SSCESS)数学模型,分析其在不平衡网压下电流不平衡与功率脉动产生机理,提出基于电流参考指令修正和负序电压补偿的改进VSG控制.研究结果表明:改进VSG控制能实现输出电流平衡、有功脉动抑制和无功脉动抑制3种控制目标,各控制目标下IMMC-SSCESS有功功率纹波显著降低或抑制为0,有效改善了其不平衡网压下的频率支撑性能.
文摘在网压不平衡工况下,模块化多电平储能系统(modular multilevel converter energy storage system,MMCESS)如果以并网电流平衡为控制目标,虽然可以保证交流系统安全运行,但是会引起各相放电速度不同,导致子模块储能电池荷电状态(state of charge,SOC)的不均衡。为解决上述问题,首先对比分析了传统MMC和MMC-ESS的内部环流特性;然后分析了以并网电流平衡为目标的不平衡网压控制对电池SOC的影响;针对这一问题,提出了利用注入直流环流的控制策略,有效地实现了相间功率均衡,并论述了直流环流控制器参数对系统稳定性的影响;以各相电压跌落度为变量,绘制各相注入的直流环流占额定桥臂电流比例的三维图,针对不同跌落度分析了各相桥臂电流的变化,为设备器件选型提供了依据;最后,通过仿真和实验验证了理论分析的正确性及控制策略的可行性。
基金supported by the National Natural Science Foundation of China (81271005, 81300767)Beijing Natural Science Foundation (7122038)+3 种基金two separate donations by the China Health and Medical Development FoundationB.A.S. was supported by the BMBF network ERA-net Neuron “Restoration of Vision after Stroke (REVIS)” (BMBF 01EW1210)by the “Hai-ju” Beijing Overseas Talents ProgramRuowu Hou was supported by the Beijing Tongren Hospital Foundation (2015-YJJ-GGL-013)
文摘To determine the interdependence of intracranial pressure(ICP) and intraocular pressure(IOP) and how it affects optic nerve pressures, eight normal dogs were examined using pressure-sensing probes implanted into the left ventricle, lumbar cistern, optic nerve subarachnoid space in the left eye, and anterior chamber in the left eye. This allowed ICP, lumbar cistern pressure(LCP), optic nerve subarachnoid space pressure(ONSP) and IOP to be simultaneously recorded. After establishing baseline pressure levels, pressure changes that resulted from lowering ICP(via shunting cerebrospinal fluid(CSF) from the ventricle) were recorded. At baseline, all examined pressures were different(ICP>LCP>ONSP), but correlated(P<0.001). As ICP was lowered during CSF shunting, IOP also dropped in a parallel time course so that the trans-lamina cribrosa gradient(TLPG) remained stable(ICP-IOP dependent zone). However, once ICP fell below a critical breakpoint, ICP and IOP became uncoupled and TLPG changed as ICP declined(ICP-IOP independent zone). The optic nerve pressure gradient(ONPG) and trans-optic nerve pressure gradient(TOPG) increased linearly as ICP decreased through both the ICP-IOP dependent and independent zones. We conclude that ICP and IOP are coupled in a specific pressure range, but when ICP drops below a critical point, IOP and ICP become uncoupled and TLPG increases. When ICP drops, a rise in the ONPG and TOPG creates more pressure and reduces CSF flow around the optic nerve. This change may play a role in the development and progression of various ophthalmic and neurological diseases, including glaucoma.
