A special kind of control technique is said to be effective at eliminating voltage ripple in the output of buck converters that see a wide range of inputs.
The design comes from scientists at Golestan University in Iran, Concordia University in Canada, and Delft University of Technology in the Netherlands. The researchers published their study in IEEE/CAA Journal of Automatica Sinica (JAS), a joint publication of the IEEE and the Chinese Association of Automation.
The researchers apply what’s called a sliding-mode control technique to a buck converter as a way of managing widely ranging input and output conditions. Sliding-mode control is a nonlinear control method that uses a discontinuous control signal. The idea is that the system “slides” along a cross-section of the system’s normal behavior. So feedback control is not a continuous function of time. Instead, it can switch from one structure to another based on the current conditions. The classic problem with sliding-mode control schemes, however, is high-frequency voltage ripple in the output, called chatter in sliding-mode parlance. The new design described in JAS is said to overcome the chatter problem.
The chatter problem arises from the fact that control equations for the technique involve time derivatives of the system that are higher than the first derivative. The approach the researchers took was to make the sliding line parameter changeable.
The result is a series of second-order equations. But the circuit for implementing the control scheme is relatively simple. It consists of an ordinary buck converter with a pass transistor operated by a PC through an opto-isolated driver.
Researchers ran simulations and obtained experimental results from their prototype and checked the results for different operating points. They found the twisting method, a special kind of sliding-mode, could efficiently deal with steady state error and produce the least amount of settling time in the output voltage in the presence of load disturbances.