双有源桥直流变换器三电平扩展移相控制下电感电流有效值最优跟踪控制策略

Optimal Tracking Control Strategy of Inductive Current RMS for Dual-Active Bridge DC Converter with Three-Level Extended Phase-Shift Control

多电平双有源桥直流变换器广泛应用于电压传输范围宽的场合,能够减小功率开关电压应力,并提供更多自由度,优化变换器性能。首先,该文提出基于三电平扩展移相控制的三电平双有源桥直流变换器最小电感电流有效值跟踪控制策略,建立三电平扩展移相控制策略下各工作模式下的数学模型,根据拉格朗日乘数法得到各可行域内部最优极值点处移相比之间的相互关系;然后,分析边界最优点,通过比较内部最优极值点和边界最优点处电感电流有效值,得到全局最优工作点;最后,根据传输功率与全局最优工作点处移相比的变化关系,得到全局最优工作点跟踪控制策略,克服寄生电阻和开关损耗对最优工作点的影响。将三电平扩展移相优化调制策略与两电平扩展移相控制、单移相控制以及峰值电流优化控制进行对比实验,实验结果验证了所提该优化策略能够有效减小电感电流有效值并提高变换效率。

A two-level dual active bridge(DAB)converter cannot reach high efficiency in wide voltage transmission range occasions.Therefore,a multilevel structure is applied to DAB to optimize converter efficiency and reduce the voltage stress of power switching.A tracking control strategy for minimum inductance current RMS value based on three-level extended phase shift(3-EPS)control is proposed when a large mismatch exists between input and output voltages.Firstly,the relationship between the phase-shift ratios D0=f0(D2)and D1=f1(D2)at several optimal extreme points in different power regions is obtained by the Lagrange multiplier method.Different extreme points can achieve different power ranges.The inductance current RMS value of each optimal extreme point is compared in the power overlap range,and the global optimum extreme points in different power ranges are obtained.Secondly,the optimal boundary points are analyzed and compared with global optimum extreme points.Because the inductance current RMS values of global optimum extreme points are always smaller than those of boundary points in each power range,the global optimum extreme points are the final global optimal operating points.Finally,the positive PI controller or negative PI controller is chosen based on the partial derivative polarity of the power to D2 to track the global optimal operating points.Besides,based on the switching point current,the zero-voltage switch(ZVS)of most switches can be realized under ideal conditions.However,the ZVS range is compressed,considering that the inductance energy is enough to discharge the parasitic capacitance fully.Experimental results show that when voltage transmission ratio k equals 1.6 or 2.6,the efficiency of optimal 3-EPS control is higher than optimal two-level extended phase shift(2-EPS)control and single phase shift(SPS)control in low to medium power range.However,the efficiencies of the above three controls are very close when the per unit power reaches 0.8.When per unit power equals 0.5 and k is between 1.1 and 1.2,the advantage of 3-EPS is not apparent.When k is between 1.2 and 2,the advantage is evident again.Compared with 2-EPS,when k is larger than 2,the effect of 3-EPS decreases as k increases.When k equals 4,the efficiencies of 3-EPS and 2-EPS are very close.The efficiency of the minimum inductance current RMS value tracking control strategy is higher than the peak current optimal control.The following conclusions can be drawn from analysis and experiment results.(1)The optimal control strategy proposed achieves lower inductance current RMS value under a wide input voltage range,and the efficiency is higher than 90%in most power ranges.(2)When k is kept unchanged,compared with 2-EPS and SPS,the effect of 3-EPS decreases as the unitary power increases.(3)When power is kept unchanged,the effect of 3-EPS is not apparent if k is larger than 1 but close to 1 because the mismatch between input and output voltages is minor.When k is between 1 and 2 and away from 1,the effect of 3-EPS is obvious.(4)When k is larger than 2,compared with 2-EPS,the effect of 3-EPS decreases as k increases.When k reaches 4,the effect of 3-EPS is almost vanished.