基于简化统一模型的DC-DC开关变换器数字优化控制策略

A Novel Digital Optimal Control for DC-DC Converters Based on Simplified Unified Model

在DC-DC开关变换器大信号运行过程中,变换器的运行模式并不是唯一的。为得到适用于电感电流连续导通模式(CCM)和不连续导通模式(DCM)下DC-DC开关变换器易于实现的数字控制策略,提出了一种基于变换器简化统一离散模型的数字优化控制策略。通过将基于两种运行模式的统一离散模型系数矩阵中的幂指数函数进行线性化处理,得到变换器简化的统一离散模型;基于简化模型的电压电流特性,设计优化目标函数;根据模型的递推状态,最小化目标函数进行优化控制决策;由模型根据递推状态和优化控制进行模型运行模式决策,模型的输出为实际系统提供优化轨迹;根据实际变换器系统与模型输出的偏差来修正优化控制,以补偿实际系统中因寄生参数引起的控制偏差。以Boost变换器为例,建立了变换器的简化统一离散模型,求取了优化控制量,采用数字PI控制器调节控制修正量。仿真和实验结果验证了控制策略能在启动过程中实现对变换器输出电压的快速、无过冲控制,及各种扰动工作条件下对变换器输出电压准确、快速的控制。

Operating on big signal condition, the work mode of DC-DC switching converter isn＇t only one, so, a novel optimal control strategy based on the simplified unified discrete model is presented, which is easy to be realized adopting digital way for DC-DC converter operating in CCM and DCM. The power-exponent functions in model coefficient matrix are linearized to simplify the unified discrete model based on CCM and DCM. According to the voltage and current characteristics of simplified model, the objective function is designed. Optimal control strategy is deduced by substituting model states into objective function and minimizing the objective function. According to the recursion states and optimal control, the operation mode of simplified model is decided by itself and the output of model provides the optimization output track. For compensating the control error caused by parasitic parameters in actual converter system, the optimal control is modified according to the output error of actual system and model. In this paper, the simplified unified discrete model of Boost converter is founded, optimal control is obtained, and digital PI is adopted to adjust control error. Simulation and experimental results validate that the output voltage of converter can be controlled with fast response and without impulse voltage in starting period, and the output voltage of converter can be controlled accurately and quickly on various work conditions.