Buck变换器扰动补偿控制算法及实现

农业装备中普遍存在多种扰动,这些扰动对Buck变换器的输出电压影响很大,传统的比例积分PI(proportional integral)控制方法较难取得满意的控制效果。针对这一问题,该文基于扰动观测理论,提出了一种抗扰动控制方法。首先,采用变参数PI控制器代替传统PI控制器,作为改进的PI控制器。该变参数PI控制器不仅具有传统PI稳定简便的特点,而且通过实时调整PI参数可使系统在不同阶段都具有较高的性能。然后,设计扰动观测器(disturbance observer,DOB)观测出参数摄动与负载变化所带来的系统扰动,将其作为补偿量补偿到前馈通道,形成复合控制器,提高系统的收敛速度与抗扰动能力。最后,通过仿真和试验,分别验证了该算法的有效性。试验证明,采用这种基于扰动补偿的复合控制器可使Buck变换器在负载突变时,恢复时间缩短了71.4%,输出电压误差减小了20.8%。在输入突变时,恢复时间缩短了58.3%,输出电压误差减小了30.0%,有效地提高了Buck变换器的稳定性和抗扰动性。该研究为提高Buck变换器的控制性能提供了参考。

Disturbance compensation controller algorithm and implementation for buck converters

Abstract: There are a variety of disturbances wide existing in the agricultural devices, including uncertain parameters, input voltage variations and load changes and these perturbations heavily affect the output voltage of the Buck converter. The traditional proportional integral (PI) control methods are difficult to obtain satisfactory performance. To solve this problem, many nonlinear theories have been applied to the Buck converter for obtaining better control performance. However, the implementation of these nonlinear controllers, such as adaptive controller and fuzzy-neural controller, generally requires complex hardware circuit or advanced processor, which increases the cost of the production and reduces the reliability of the control circuit. In this paper, based on the disturbance observation theory, a new control method for disturbance attenuation is proposed. First of all, the conventional PI controller is replaced with the variable-parameter PI (VAPI) controller, which not only possesses the easy-implementation characteristic the conventional PI holds, but also guarantees that the closed loop system will have a better performance in different control stages by online tuning the PI parameters. Then, a linear disturbance observer (DOB) is constructed to estimate the exact value of the disturbance which is caused by input voltage variations and load changes. The disturbance is estimated through the information of output voltage and the structure of control system, and the estimated value is used to compensate the disturbance in forward channel, which will significantly improve the convergence and disturbance rejection property of the closed loop system. With the above improvements, a new composite controller can thus be obtained. The composite controller in the paper is implemented by using a semi-physical experimental platform. The platform is mainly based on a data acquisition card and a buck circuit. When the system of the Buck converter is running, the output voltage can be collected by the data acquisition card. By calculating these voltage data, the control output signal can be obtained directly. Later, the data acquisition card will transmit the obtained control signal to the buck converter circuit. The advantages of this semi-physical experimental platform are making the implementation of the algorithm more flexibly and the modification of controller parameters more conveniently. Based on the experiment platform, the implementation of the composite controller can be summarized as three steps. Firstly, the continuous composite controller is constructed in frequency domain. Secondly, the continuous composite control strategy is discretized so that the data can be processed by computer. Finally, the discrete controller is implemented directly by using the LabVIEW program. Experimental results obtained from the semi-physical experiment platform show that after replacing PI controller with the composite controller, when the load varies, the recovery time of the Buck converter can be shortened by 71.4% and the output voltage error can be reduced by 20.8%. When the input voltage varies, the recovery time can be shortened by 58.3% and the output voltage error can be reduced by 30.0%. According to these comparative results, it is obvious that the proposed new composite controller can effectively improve the convergence and anti-disturbance performance of the Buck converter. Meanwhile, considering the property of easy-implementation, the composite control method has potential applications in engineering area.