【作者】 贾鹏宇；

【导师】 郑琼林；

【作者基本信息】 北京交通大学 ， 电气工程， 2014， 博士

【摘要】 摘要：随着电源、负载特性需求的不同,越来越多的DC-DC变换器采用高阶化拓扑或者采用分布式级联方式相互连接形成高性能的直流变换器系统,以满足不同的设计要求。直流变换器系统的稳定性一直以来是人们研究的热点。变换器的小信号模型参数是影响变换器系统稳定性的重要因素,本文针对影响变换器系统稳定性的关键参数：被控对象模型传递函数、音频敏感率、输入阻抗以及输出阻抗进行分析,并提出相应的优化方法以改善变换器系统的稳定性。目前已有大量文献对基本的二阶变换器拓扑进行了深入分析,已解决了稳定性问题,但是在包含太阳能电池板、蓄电池等装置的场合,为了满足输入输出电流连续的要求,往往需要加入额外的滤波器或者采用含有多个电感电容元件的高阶变换器。高阶变换器的模型中含有多个零极点,尤其当模型中存在右半平面零点时,被控对象传递函数的相频曲线容易较早穿越.180。,限制反馈环路增益的带宽。本文归纳了优化高阶变换器被控对象的阻尼设计方法,针对广泛应用于航天电源系统的Superbuck变换器拓扑,提出一种RC阻尼设计方法,从而避免其被控对象传递函数中存在右半平面零点,保证其模型满足最小相位系统的条件,从而提高变换器的稳定性。采用输入电压前馈的方法可以在理论上实现变换器的音频敏感率(输入电压扰动.输出电压扰动传递函数,audio susceptibility)等于零。但是当变换器模型的阶次较高时,理论所需的前馈控制器传递函数较为复杂且计算过程繁琐。为了简化求解过程,本文提出一种简化变换器电路模型的方法,而不会影响所得前馈控制器的准确性。此外,本文提出采用比例控制器代替理论所需的前馈控制器进行控制的方法,并分析了在这种控制方式下音频敏感率能够大幅度衰减的有效频率范围与主电路参数之间的关系,指出了比例前馈控制器仅取决于变换器的稳态电压增益比的规律。在级联系统中,即使变换器单独能够稳定工作,级联时也未必稳定,这是由于级联的前后级变换器阻抗存在相互作用。为了提高级联系统的稳定性,需要减小前后级变换器的阻抗交截范围,对于DC-DC变换器而言,一方面希望降低前级变换器的输出阻抗,另一方面希望增大后级变换器的输入阻抗。本文基于DC.DC变换器的一般性小信号模型,提出了以平均输入电流环为内环、输出电压环为外环的双环控制方法,分析了在这种控制方式下影响变换器输入阻抗的因素,并给出了改变内环电流采样系数前后变换器输入阻抗的量化计算过程。分析表明,当电流内环的截止频率大于电压外环截止频率时,增大电流采样系数,能够提高电流内环环路增益,有效增大变换器的输入阻抗。从而在级联系统中,能够有效减小负载变换器的输入阻抗与源变换器输出阻抗的交集,提高级联系统的稳定性。同样的,为了优化变换器的输出阻抗,提出了一种在变换器输出端口模拟出并联虚拟电阻的控制方法,可以适用于模型中不含右半平面零点的变换器拓扑。这种控制方法在不改变变换器稳态工作点的基础上仅改变了交流小信号模型,因此不会带来额外的功率损耗。通过采用有源阻尼控制器的方法,可以有效降低变换器输出阻抗的谐振峰值,改善品质因数,达到优化变换器输出阻抗特性的目的。更多还原

【Abstract】 With different demands of source and load, high order topologies and cascaded connection are widely used in DC-DC converter system to realize high performance. The stability issues of DC-DC converter system are always focused on. The small signal model parameters are the important factors which affect the stability of DC-DC converter system. In this paper the key parameters, which are summarized as controlled object, audio susceptibility, input impedance and output impedance, are analyzed and the corresponding improvements are proposed.Many literatures have focused on the basic second-order converters and the stability problems have been solved. But when these converters are used as the interface connected with the solar array and battery, the extra filter should be added into the topologies to meet the continuous current demand. The high-order converter topology with continuous input or output current is another solution. By these means, there are many poles and zeros in the model. Especially when there are right-half-plane (RHP) zeros, the phase of bode plots may pass through-180°in low frequency, therefore the bandwidth of closed-loop system may be limited. In this paper, the damping optimizations for controlled object in high-order converter topologies are summarized. A simple parameter design method for damping networks of Superbuck topology to avoid right-half-plane (RHP) zeros is presented. By this method the controlled object can be considered as a minimum phase system.The feedforward control can realize zero audio-susceptibility in converters. But when the order of the model is high, the desired feedforward controller is complicated and the derivation is redundancy. A method for simplification of the converter when computing the feedforward controller is presented so that the related components of the circuit can be easily established. In this paper, the proportional feedforward controller instead of the accurate form is used to realize zero audio susceptibility in certain frequency range. It shows that the proportional feedforward controller only depends on the DC gain of the converter.Because of the impedance interaction of source converter and load converter, the cascaded system may be not stable when the converters are stable independently. To improve the stability of cascaded system, the intersection range of output impedance and input impedance should be decreased. One side, the output impedance of source converter should be decreased, the other, the input impedance of load converter should be increased.Based on the unified small signal model of DC-DC converter, the double loop control method with input current inner loop and output voltage outer loop is proposed. The input impedance is analyzed under this situation and the paper gives the quantization of the input impedance when the current sampling factor is changed. It is shown that when the cross over frequency of current loop is larger than that of the voltage loop, the input impedance can be significant increased when the current sampling factor is increased. Therefore the impedance intersection of source and load converters can be decreased so to improve the stability.Similarly, to improve the output impedance of the converter, an active damping method to emulate a virtual resistor, which is connected in parallel with the output of the converter’s small signal model, is presented. This method can be applied into the converter whose model has no RHP zeros. The small signal model is improved but the steady-state operating point is not affected. By this means, the resonant peaks of output impedance can be decreased and the output impedance can be improved.更多还原