Near time-optimal transient response in DC-DC buck converters taking into account the inductor current limit

Abstract

This paper analyzes the general problem of inductor current limitation in the time-optimal load transient response of a DC-DC buck converter. The concept of currentlimited, time-optimal control (CL-TOC) is introduced and compared to the previously reported unconstrained timeoptimal solutions. A fundamental tradeoff between maximum allowed current overshoot and voltage recovery time is recognized, and a set of design equations is developed which provide the engineer with the necessary analytical tools for the controller design. Furthermore, the minimum number of switching actions required to handle a generic current-limited TOC is determined, leading to the formulation of a minimumswitch CL-TOC concept. Two distinct approaches for minimumswitch digital CL-TOC are then introduced. The first method, which is an extension of a charge-balance approach, has the advantage of achieving the time-optimal switching sequence without the need for a prior knowledge of the output filter LC parameters. The second approach implements a near CL-TOC employing the switching surface concept and defining the current limitation in the state-space. Simulation and experimental results are provided to demonstrate the effectiveness of the approaches.Index Terms--Time optimal control, inductor current limit, digital control, switching surface control, charge balance principle.

Voltage-Based Charge Balance Controller Suitable for Both Digital and Analog Implementations

“…Another CBC controller is proposed and implemented using FPGA in [7], taking advantage of continuous time concept; however, the robustness of algorithm is limited and complex calculation is needed in real time to decide the t on and t off time for optimal control. The optimal control algorithm proposed in [6]- [12] is implemented also using FPGA and it applies similar geometric equation as [5] to derive the algorithm, but the time instants are determined by output voltage information instead of time intervals. However, a high-speed ADC or an asynchronous ADC is required to detect the voltage peak/valley, resulting in high cost of the implementation.…”

“…2, the output voltage at t 3 can be calculated in (12) and the inductor current is reaching the new load current level at the same time…”

“…An analog implementation is presented in [19] to reduce the reaction time and improve the performance. Using field-programmable gate array (FPGA), extensive work has been conducted in designing digital charge balance control (CBC) controllers that further improves robustness [6], [8]- [12], [18], practical performance [6], [11], [12], and simplicity of the control system [6], [22]. However, all the previous schemes are not able to address at least one of the following limitations, resulting in high cost, power consumption, and long development time for controlled products: 1) Complex real-time calculation is embedded in the algorithm, like division and square root [5], [7], which requires high-speed digital control devices for working out operations in a limited time interval.…”

Second order sliding mode controlled point of load power supply

“…To improve the large-signal dynamics in point-of-load (POL) power supplies such as the buck converter shown in Fig.1, several nonlinear solutions, including charge balance principles [2], nonlinear state feedback [3][4], or more advanced nonlinear digital time optimal control techniques [5][6][7][8][9][10], have been reported. These approaches are either sensitive to power stage component parameters (e.g., output filter inductor and output capacitor) or face difficulty making transitions between controller modes in real time.…”

Frequency response analysis of proposed digital control system for DPWM-POL

“…For the control purpose, pulse width modulation (PWM) control is a one of appropriate technique. Digital control or DPWM can accomplish robust and flexible power control with soft-tuned parameters and will become popular control technique [1][2][3][4][5][6][7][8][9][10][11][12]. Although, there are some disadvantages in cost and speed, against analog control circuit.…”