开关磁阻发电机(Switched Reluctance Generator,SRG)具有良好的电机本体特性,且发出直流电,适合用于风力发电且容易实现并网运行。提出一种新型开关磁阻风力发电并网系统整体控制策略,机侧SRG功率变换器采用基于励磁电流扰动控制法的...开关磁阻发电机(Switched Reluctance Generator,SRG)具有良好的电机本体特性,且发出直流电,适合用于风力发电且容易实现并网运行。提出一种新型开关磁阻风力发电并网系统整体控制策略,机侧SRG功率变换器采用基于励磁电流扰动控制法的最大风能跟踪(Maximum Power Point Tracking,MPPT)控制策略,网侧三相逆变器采用基于电网电压定向的双闭环矢量控制,以实现无需测量风速及无需知道风力机机械特性下系统的最大风能跟踪并网运行,提高风能利用效率。建立开关磁阻风力发电并网运行系统仿真模型,仿真结果验证了所提控制策略的正确性和有效性,具有一定的工程应用价值。展开更多
Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation metho...Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation method.The results show two types of optimal initial perturbations of sea surface salinity,one associated with freshwater and the other with salinity.Both types of perturbations excite decadal variability of the THC.Under the same amplitude of initial perturbation,the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation,suggesting that the THC is more sensitive to freshwater than salinity perturbation.As the amplitude of initial perturbation increases,the decadal variations become stronger for both perturbations.For salinity perturbations,recovery time of the THC to return to steady state gradually saturates with increasing amplitude,whereas this recovery time increases remarkably for freshwater perturbations.A nonlinear(advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability excitation.The results are consistent with previous ones from simple box models,and highlight the importance of nonlinear feedback in decadal THC variability.展开更多
The decadal variability of the North Atlantic thermohaline circulation(THC) is investigated within a three-dimensional ocean circulation model using the conditional nonlinear optimal perturbation method. The results s...The decadal variability of the North Atlantic thermohaline circulation(THC) is investigated within a three-dimensional ocean circulation model using the conditional nonlinear optimal perturbation method. The results show that the optimal initial perturbations of temperature and salinity exciting the strongest decadal THC variations have similar structures: the perturbations are mainly in the northwestern basin at a depth ranging from 1500 to 3000 m. These temperature and salinity perturbations act as the optimal precursors for future modifications of the THC, highlighting the importance of observations in the northwestern basin to monitor the variations of temperature and salinity at depth. The decadal THC variation in the nonlinear model initialized by the optimal salinity perturbations is much stronger than that caused by the optimal temperature perturbations, indicating that salinity variations might play a relatively important role in exciting the decadal THC variability. Moreover, the decadal THC variations in the tangent linear and nonlinear models show remarkably different characteristics, suggesting the importance of nonlinear processes in the decadal variability of the THC.展开更多
文摘开关磁阻发电机(Switched Reluctance Generator,SRG)具有良好的电机本体特性,且发出直流电,适合用于风力发电且容易实现并网运行。提出一种新型开关磁阻风力发电并网系统整体控制策略,机侧SRG功率变换器采用基于励磁电流扰动控制法的最大风能跟踪(Maximum Power Point Tracking,MPPT)控制策略,网侧三相逆变器采用基于电网电压定向的双闭环矢量控制,以实现无需测量风速及无需知道风力机机械特性下系统的最大风能跟踪并网运行,提高风能利用效率。建立开关磁阻风力发电并网运行系统仿真模型,仿真结果验证了所提控制策略的正确性和有效性,具有一定的工程应用价值。
基金Supported by the National Basic Research Program of China(973 Program)(No.2012CB417404)
文摘Nonlinear development of salinity perturbations in the Atlantic thermohaline circulation(THC) is investigated with a three-dimensional ocean circulation model,using the conditional nonlinear optimal perturbation method.The results show two types of optimal initial perturbations of sea surface salinity,one associated with freshwater and the other with salinity.Both types of perturbations excite decadal variability of the THC.Under the same amplitude of initial perturbation,the decadal variation induced by the freshwater perturbation is much stronger than that by the salinity perturbation,suggesting that the THC is more sensitive to freshwater than salinity perturbation.As the amplitude of initial perturbation increases,the decadal variations become stronger for both perturbations.For salinity perturbations,recovery time of the THC to return to steady state gradually saturates with increasing amplitude,whereas this recovery time increases remarkably for freshwater perturbations.A nonlinear(advective) feedback between density and velocity anomalies is proposed to explain these characteristics of decadal variability excitation.The results are consistent with previous ones from simple box models,and highlight the importance of nonlinear feedback in decadal THC variability.
基金supported by the National Basic Research Program of China(973 Program,Grant No.2012CB417404)
文摘The decadal variability of the North Atlantic thermohaline circulation(THC) is investigated within a three-dimensional ocean circulation model using the conditional nonlinear optimal perturbation method. The results show that the optimal initial perturbations of temperature and salinity exciting the strongest decadal THC variations have similar structures: the perturbations are mainly in the northwestern basin at a depth ranging from 1500 to 3000 m. These temperature and salinity perturbations act as the optimal precursors for future modifications of the THC, highlighting the importance of observations in the northwestern basin to monitor the variations of temperature and salinity at depth. The decadal THC variation in the nonlinear model initialized by the optimal salinity perturbations is much stronger than that caused by the optimal temperature perturbations, indicating that salinity variations might play a relatively important role in exciting the decadal THC variability. Moreover, the decadal THC variations in the tangent linear and nonlinear models show remarkably different characteristics, suggesting the importance of nonlinear processes in the decadal variability of the THC.
