Optimal Current Observer for Predictive Current Controlled Buck DC-DC Converter

Abstract

In digital current mode controlled DC-DC converter, the conventional current sensor is either costly or has low accuracy. Thus, current observer, which could be realized based on digital circuit itself, is an ideal substitute for conventional current sensors. However, the observed current may diverge because of parasitic parameters. In this paper, an optimal current observer is proposed to solve the problem. Employing the optimal current observer based predictive current control, a buck converter, which shows preferable transient response than PID controlled converter is implemented. The effectiveness of the optimal current observer is experimentally demonstrated.

Performance improvement of a buck converter using Kalman filtering

“…Step load response time: the proposed algorithm transient response after a load change is about 200 µs, showing a similar response time to the methods presented in [21,5], showing a better step response than the regular voltage mode control method using a PI in the control loop;…”

“…• The estimation error considering all the operation time is about 1 % and in steady state an error less than 1 %. The error in the estimation achieved in [5] is of 5 % in steady state,…”

“…To eliminate the need for the current sensing hardware, prediction techniques have been developed for the estimation of parameters of the buck converter. For the prediction of the inductor current, current observers can be used [5]. However, for typically noisy systems such as non-isolated converters, estimation based on Kalman filtering (KF) is preferable [6].…”

“…A similar method is presented in [5], proposing a current observer for predictive current control of a buck converter. In the first implementation the current observer is based in the equations of the inductor current slopes, without considering any parasitics in the system.…”

“…The author observes that with the ideal equations the method would diverge and proposes an optimal current observer, having into consideration the parasitic parameters of the circuit, such as the freewheel diode voltage drop and the inductor series resistance, achieving the desired convergence of the method. The control loop used in [5] applies controls the valley current with trailing edge modulation, claiming that it can eliminate the current error in less than two switching cycles. Figure 2.4: Boost converter control algorithm.…”