Digital Voltage-mode Controller Research Articles

A Novel Modular Radiation Hardening Approach Applied to a Synchronous Buck Converter

Radiation and extreme temperature are the main inhibitors for the use of electronic devices in space applications. Radiation challenges the normal and stable operation of DC-DC converters, used as power supply for onboard systems in satellites and spacecrafts. In this situation, special design techniques known as radiation hardening or radiation tolerant designs have to be employed. In this work, a module level design approach for radiation hardening is addressed. A module in this sense is a constituent of a digital controller, which includes an analog to digital converter (ADC), a digital proportional-integral-derivative (PID) controller, and a digital pulse width modulator (DPWM). As a new Radiation Hardening by Design technique (RHBD), a four module redundancy technique is proposed and applied to the digital voltage mode controller driving a synchronous buck converter, which has been implemented as hardware-in-the-loop (HIL) simulation block in MATLAB/Simulink using Xilinx system generator based on the Zynq-7000 development board (ZYBO). The technique is compared, for reliability and hardware resources requirement, with triple modular redundancy (TMR), five modular redundancy (FMR) and the modified triplex–duplex architecture. Furthermore, radiation induced failures are emulated by switching all duplicated modules inputs to different signals, or to ground during simulation. The simulation results show that the proposed technique has 25% and 30%longer expected life compared to TMR and FMR techniques, respectively, and has the lowest hardware resource requirement compared to FMR and the modified triplex–duplex techniques.

A Highly Integrated Series–Parallel Switched-Capacitor Converter With 12 V Input and Quasi-Resonant Voltage-Mode Regulation

This paper presents an integrated circuit (IC) implementation of a hybrid switched capacitor converter based on a modified series-parallel architecture. The converter operates in a quasi-resonant mode to regulate a nominal 3.7 V output from a 12 V supply. The design uses zero-current detection and nested 1-b regulation to autotune the zero-current switching state, simplify the design of a digital voltage-mode control scheme, and achieve partial zero-voltage switching. The modified architecture is able to operate with single-voltage rated devices without degrading the voltage times current product of the converter. This paper discusses details of level shifting, gate driving, and bootstrapping for an all n-channel powertrain, including a precharge circuit, to facilitate safe startup. The converter IC was designed in 180-nm bulk CMOS with a 5 V option for power devices. It was tested in a flip-chip assembly with a 36 nH 0402 inductor to deliver up to 4.6 W at 87.5% efficiency at a power density of 0.23 W/mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Analysis of Minimum-Phase Fourth-Order Buck DC–DC Converter

A new fourth-order buck converter exhibiting better dynamic performance (no right-half-plane zeros) and voltage gain identical to the buck converter with input filter is proposed. Converter design expressions are formulated through time-domain analysis. The proposed converter performance is compared with other buck topologies reported in literature. State-space and discrete-time analysis is established, and then small-signal models are obtained. These transfer functions reveal that there is no right half of $s$ -plane zero in the control-to-output transfer function. A digital voltage-mode controller is designed, and then enhanced dynamic performance features of the proposed converter are brought out through analysis and then compared with other fourth-order converters reported. A 42- to 28-V 75-W converter prototype is made for simulation and experimental investigation. The distinct features of the proposed converter are demonstrated through analytical computer simulations and experimental results.

Systematic selection of analogue redesign method for forward-type digital power converters

This article proposes a systematic approach to determine the most suitable analogue redesign method to be used for forward-type converters under digital voltage mode control. The focus of the method is to achieve the highest phase margin at the particular switching and crossover frequencies chosen by the designer. It is shown that at high crossover frequencies with respect to switching frequency, controllers designed using backward integration have the largest phase margin; whereas at low crossover frequencies with respect to switching frequency, controllers designed using bilinear integration with pre-warping have the largest phase margins. An algorithm has been developed to determine the frequency of the crossing point where the recommended discretisation method changes. An accurate model of the power stage is used for simulation and experimental results from a Buck converter are collected. The performance of the digital controllers is compared to that of the equivalent analogue controller both in simulation and experiment. Excellent closeness between the simulation and experimental results is presented. This work provides a concrete example to allow academics and engineers to systematically choose a discretisation method.

Design of Robust Digital Stabilizing Controller for Fourth-Order Boost DC–DC Converter: A Quantitative Feedback Theory Approach

In this paper, we have proposed a quantitative feedback theory based robust digital voltage mode controller for a fourth-order boost dc-dc converter operating in continuous conduction mode. Discrete-time models of the converter are established for triangular trailing-edge modulation, which is then used in the compensator design. It is observed that an up-down glitch is present in the frequency response of control-to-output transfer functions of higher order dc-dc converters, and because of this, gain margin (GM) and phase margin (PM) alone are unable to give correct information about closed-loop stability. Therefore, in this paper, we have introduced a safety margin as an additional design specification, which along with GM and PM information reflects the actual stability of the higher order dc-dc converters. A simplification in loop-shaping approach is also proposed, which considerably reduces the time and effort involved in loop-shaping as compared to present trial-and-error-based approach and also results in a robust compensator of feasible order. Robustness of the designed controllers is analyzed in frequency and time domains through computer simulations and is then verified experimentally on a 28-V 30-W laboratory prototype converter. The experimental results are in line with the analytical design studies and demonstrate that the controller, which is directly designed through a discrete-time model, is more robust than an average model-based digitally redesigned controller.

Robust Digital Voltage-Mode Controller for Fifth-Order Boost Converter

In this paper, a robust digital voltage-mode controller (DVMC) is proposed for a fifth-order boost point-of-load converter. Salient features of the proposed topology are compared with a conventional boost converter. Mathematical models are formulated using a discrete-time modeling technique and then employed in the compensator design, which uses the digital direct design approach. The DVMC is designed to ensure load voltage regulation. Robustness theory is applied directly in the digital domain, and then, various robust stability criteria describing sensitivity functions are formulated. The controller is designed to satisfy robustness criteria and then evaluated over a range of disturbances in spite of the fact that it maintains regulation. To confirm this, design simulations have been carried out on a 25-W 12-36-V converter system. Experimental results are provided to validate the concept and also to verify the range over which the designed controller is robust.

Digital Hysteretic Voltage-Mode Control for DC–DC Converters Based on Asynchronous Sampling

This paper investigates a digital voltage-mode controller for dc-dc converters based on hysteresis modulation. The control structure implements a high-bandwidth hysteretic differentiator as its main building block, and realizes a nonconventional structure of PID compensation with performances comparable to analog hysteretic controls, thus breaking the bandwidth and dynamic limitations commonly encountered in typical digital control arrangements. The employment of an asynchronous A/D converter based on the threshold inverter quantization concept dramatically shrinks the average delay time that separates the sampling instant from the corrective control action. Moreover, the hysteretic nature of the derivative action results in an inherent nonlinear response to large signal load variations, which translates into fast control intervention and reduced settling times. The hysteretic differentiator employs a ring-oscillator-based modulator, which ensures resolution up to 390 ps without asking for a high-frequency clock. Both the 6-bit asynchronous A/D converter and the ring-oscillator-based modulator are designed and manufactured in the same IC using a standard 0.35 mum CMOS process. Analytical modeling, computer simulations, and experimental results on a synchronous buck converter confirm the validity of the approach and the dynamic performances achievable by the proposed control architecture.

Mixed-Signal Voltage-Mode Control for DC–DC Converters With Inherent Analog Derivative Action

This paper investigates a mixed-signal fixed frequency digital voltage-mode controller for dc-dc converters. Switch turn-on is determined by system clock, while switch turn-off is determined asynchronously by comparing a signal proportional to the derivative of the output voltage and the voltage ramp driven by the digital-to-analog converter (DAC). One of the most important features is that the derivative action of the proportional-integral-derivative (PID) voltage-mode controller is inherently obtained by a combination of the analog front-end and the hard-wired digital logic, without requiring the numerical computation of the derivative action nor analog reactive elements (capacitors), which are usually needed for the derivative action in the analog domain and which are critical for the IC controller integration. Moreover, as compared to conventional digital approaches based on analog-to-digital converters (ADCs) and digital pulsewidth modulators (DPWMs), the phase-lag due to the uniformly sampled DPWM and due to the output voltage sampling is avoided, thus improving phased margin at the crossover frequency where the derivative contribution is usually prevailing. This property potentially enables faster controllers with improved dynamic response, breaking bandwidth limitation of conventional digital control architectures. The proposed control architecture is also effective from the IC point of view, since it is based on a DAC, a simple analog front-end, including a sample and hold, a comparator and an operational amplifier, and low digital signal-processing requirement ( gates). Simulation and experimental results on a 1.2 V-20 A synchronous buck converter confirm the properties of the proposed solution.

Synchronous–Asynchronous Digital Voltage-Mode Control for DC–DC Converters

This paper investigates a mixed synchronous/asynchronous digital voltage-mode controller for DC-DC converters. In the proposed control architecture, the turn-on switching event is determined asynchronously by comparing the converter output voltage and a synchronously generated voltage ramp driven by the digital control using a low-resolution digital-to-analog converter. Switch turn-off is determined synchronously by the system clock. In the proposed approach, the derivative action of the proportional-integral-derivative voltage-mode controller is inherently obtained by the frequency modulation, without requiring the digital computation of the derivative action. A simplified small-signal model is also derived in order to analyze the performance achievable by the proposed solution. This control architecture features good dynamic performance, and frequency modulation during transients. Simulation and experimental results on a synchronous buck converter, where the digital control has been implemented in field programmable gate array, confirm the effectiveness of the proposed solution.