Study On The Transient Performance Of The Digital Control Switching DC-DC Converters

This paper proposes the digital peak voltage control of switching DC-DC converters, and it is developed. The creative point can be summarized as the following. The first one is that the digital peak voltage algorithm is proposed on different modulation methods. The second one is that the algorithm to overcome time delay is introduced and improved digital peak voltage is then proposed. The third one is that the multi-sample technique is proposed to be used in switching DC-DC converter to improve the transient performance. The fourth one is that the nonlinear compensation of power function is used in the PID of the digital control loop. The fifth one is that the algorithm to eliminate the sub-harmonic oscillation, with digital slope compensation and digital respostion of duty ratio compent proposed.In the digital control technique of switching DC-DC converter, the digital algorithm is an important topic. At present time, it is urgent to digitize the control methods, and it is also the inevitable and important step to develop the digital control technique in switching DC-DC converters.The status of digital control technique of switching DC-DC converters is briefly introduced in this paper. Digital implementations of PWM with various modulation methods are discussed and compared with analog implemenations. Based on the modulation methods, the digital peak voltage control technique with different modulation methods is studied on Buck converter topology.In the digital control loop of switching converter, the time for digital operations is inevitable and it is at least one switching cycle. As the result, one-switching-cycle delay exists between the sampling and the output of the result duty ratio. There is no doubt that the delay will degrade the transient performance of the switching DC-DC converter. The phenomenon has been noted but no effective method is proposed for DC-DC converters till now. The algorithm to overcome this time delay is presented and comprehensively studied. Simulation and experiment results provide evidence to compare the transient performanc, and it shows the improvement brought by the algorithm to overcome this time delay.For the study of transient performance of switching converter, we usually assume that the perturbation is applied at the beginning of switching cycle. In fact, the perturbation is located during the whole switching cycle at random. To study the effects, multi-sample technique is presented in this paper to sample the perturbations as soon as it happens. Multi-sample technique leads to the dynamic reference voltage, which acts as the calibration of the transient waveforms. In this way, the perturbations can be sampled in time to improve the load transient performance.Nonlinear control technique has been adopted in switching converter to improve the transient performance. In the traditional implementation, nonlinear is usually restricted by the complex circuits in analog platform. This paper utilizes the flexibility of the digital control techniques to realize nonlinear compensation. According to the error partitions, the nonlinear coefficients of the proportional item are presented, and they will decrease the impact of the delay effect brought by integral item to improve the transient performance of switching DC-DC converters.By Tustin method, the model of Buck converter is digitized. By synthesizing the small signal model of control algorithms, the model of the whole system is obtained. The canonical model provides the way to verify the analysis in the transient performance.In the paper, buck converter is taken as an example for the study.