The principle of minimum dissipation rate is applied to tokamak plasmas with energy and helicity balances imposed as two constraints. The analytical solution on toroidal current distribution are derived from the resul...The principle of minimum dissipation rate is applied to tokamak plasmas with energy and helicity balances imposed as two constraints. The analytical solution on toroidal current distribution are derived from the resulting Euler-Lagrangian equation. Three typical forms of current profiles are found for low-aspect-ratio tokamaks like NSTX. One of them decreases with r on equatorial plane, the second peaks in the inner half part on equatorial plane and the third may have a hole or reverse in the central part.展开更多
1. IntroductionA large number of networks for realizing first and second order transfer functions using a currentconveyor have been reported in the literature. Especially, the networks that can offer highinput impedan...1. IntroductionA large number of networks for realizing first and second order transfer functions using a currentconveyor have been reported in the literature. Especially, the networks that can offer highinput impedance attract attention, for high input impedance has the advantage that the networksmay be used in cascade without requiring impedance matching device. In the Higashimura and展开更多
针对双有源桥(dual active bridge,DAB)电路在电动汽车充放电能量转换过程中存在的传输效率低的问题,文中提出一种结合微分极值法与分段控制的最小电流应力优化控制策略。该策略在满足软开关约束的前提下,优化电流应力与抑制回流功率,...针对双有源桥(dual active bridge,DAB)电路在电动汽车充放电能量转换过程中存在的传输效率低的问题,文中提出一种结合微分极值法与分段控制的最小电流应力优化控制策略。该策略在满足软开关约束的前提下,优化电流应力与抑制回流功率,从而有效提升传输效率。首先,以功率正向传输为例,推导拓展移相(extended phase shift,EPS)控制在两种工作模态下实现开关管软开关的条件,并分析回流功率的产生机理,阐述减小电流应力对抑制回流功率的作用;然后,基于微分极值法推导最小电流应力的最优移相比组合,并结合不同模态下软开关范围进行分段控制;最后,实验结果表明,在电压传输比大于1时,该最小电流应力优化策略在全功率范围内实现所有开关管软开关的同时,可以有效降低电流应力、抑制回流功率、提升传输效率。在电压传输比小于1时,该策略虽仍可降低电流应力,但并不能实现所有开关管零电压开通。展开更多
在设计和研发大功率宽输出电压范围的双有源桥(dual active bridge,DAB)变换器时,传统的电流应力优化策略往往只关注移相比优化,忽略了电感量变化对电流应力的影响,这可能导致在大功率应用中电流应力超出理论预期,从而降低开关管的可靠...在设计和研发大功率宽输出电压范围的双有源桥(dual active bridge,DAB)变换器时,传统的电流应力优化策略往往只关注移相比优化,忽略了电感量变化对电流应力的影响,这可能导致在大功率应用中电流应力超出理论预期,从而降低开关管的可靠性。因此,在大功率应用场景下,为使变换器在全功率范围内获得最小电流应力,首先提出了考虑电感量随电流应力变化的动态关系,并基于此关系选择在恰当电感量下的优化三移相控制方法;其次,通过分析三移相控制并建立相应的数学模型,利用KKT(Karush-Kuhn-Tucker)条件寻求最优移相比组合,以实现电流应力优化;最后,搭建额定功率为100 kW的DAB变换器仿真模型及样机实验平台进行验证。实验结果表明,与传统三移相控制方法相比,所提方法在仿真和实验中都表现出较高的有效性,确保了变换器在整个运行过程中电流应力始终保持在理论预期范围内,保证了变换器在稳定运行时开关管的可靠性。展开更多
文摘The principle of minimum dissipation rate is applied to tokamak plasmas with energy and helicity balances imposed as two constraints. The analytical solution on toroidal current distribution are derived from the resulting Euler-Lagrangian equation. Three typical forms of current profiles are found for low-aspect-ratio tokamaks like NSTX. One of them decreases with r on equatorial plane, the second peaks in the inner half part on equatorial plane and the third may have a hole or reverse in the central part.
文摘1. IntroductionA large number of networks for realizing first and second order transfer functions using a currentconveyor have been reported in the literature. Especially, the networks that can offer highinput impedance attract attention, for high input impedance has the advantage that the networksmay be used in cascade without requiring impedance matching device. In the Higashimura and
文摘针对双有源桥(dual active bridge,DAB)电路在电动汽车充放电能量转换过程中存在的传输效率低的问题,文中提出一种结合微分极值法与分段控制的最小电流应力优化控制策略。该策略在满足软开关约束的前提下,优化电流应力与抑制回流功率,从而有效提升传输效率。首先,以功率正向传输为例,推导拓展移相(extended phase shift,EPS)控制在两种工作模态下实现开关管软开关的条件,并分析回流功率的产生机理,阐述减小电流应力对抑制回流功率的作用;然后,基于微分极值法推导最小电流应力的最优移相比组合,并结合不同模态下软开关范围进行分段控制;最后,实验结果表明,在电压传输比大于1时,该最小电流应力优化策略在全功率范围内实现所有开关管软开关的同时,可以有效降低电流应力、抑制回流功率、提升传输效率。在电压传输比小于1时,该策略虽仍可降低电流应力,但并不能实现所有开关管零电压开通。
文摘在设计和研发大功率宽输出电压范围的双有源桥(dual active bridge,DAB)变换器时,传统的电流应力优化策略往往只关注移相比优化,忽略了电感量变化对电流应力的影响,这可能导致在大功率应用中电流应力超出理论预期,从而降低开关管的可靠性。因此,在大功率应用场景下,为使变换器在全功率范围内获得最小电流应力,首先提出了考虑电感量随电流应力变化的动态关系,并基于此关系选择在恰当电感量下的优化三移相控制方法;其次,通过分析三移相控制并建立相应的数学模型,利用KKT(Karush-Kuhn-Tucker)条件寻求最优移相比组合,以实现电流应力优化;最后,搭建额定功率为100 kW的DAB变换器仿真模型及样机实验平台进行验证。实验结果表明,与传统三移相控制方法相比,所提方法在仿真和实验中都表现出较高的有效性,确保了变换器在整个运行过程中电流应力始终保持在理论预期范围内,保证了变换器在稳定运行时开关管的可靠性。
