Showing papers by "Dragan Maksimovic published in 2009"
TL;DR: In this article, a hardware-description-language-coded autotuning algorithm for digital PID-controlled DC-DC power converters based on online frequency-response measurement is presented.
Abstract: This paper describes a hardware-description-language-coded autotuning algorithm for digital PID-controlled DC-DC power converters based on online frequency-response measurement. The algorithm determines the PID controller parameters required to maximize the closed-loop bandwidth of the feedback control system while maintaining user-specified stability margins and integral-based no-limit-cycling criteria, as well as ensuring single-crossover-frequency operation and sufficiently high loop gain magnitude at low frequencies. Experimental results are provided for five different pulsewidth-modulated DC-DC converters, including a well-damped synchronous buck, a lightly damped synchronous buck with and without a poorly damped input filter, a boost operating in continuous-conduction mode, and a boost operating in discontinuous-conduction mode.
171 citations
TL;DR: In this article, an online adaptive tuning technique for digitally controlled switched-mode power supplies (SMPS) is presented, which is based on continuous monitoring of the system crossover frequency and phase margin.
Abstract: This letter presents an online adaptive tuning technique for digitally controlled switched-mode power supplies (SMPS). The approach is based on continuous monitoring of the system crossover frequency and phase margin, followed by a multi-input-multi-output (MIMO) control loop that continuously and concurrently tunes the compensator parameters to meet crossover frequency and phase margin targets. Continuous stability margin monitoring is achieved by injecting a small digital square-wave signal between the digital compensator and the digital pulsewidth modulator. The MIMO loop adaptively adjusts the compensator parameters to minimize the error between the desired and measured crossover frequency and phase margin. Small-signal models are derived, and the MIMO control loop is designed to achieve stability and performance over a wide range of operating conditions. Using modest hardware resources, the proposed approach enables adaptive tuning during normal SMPS operation. Experimental results demonstrating system functionality are presented for a synchronous buck SMPS.
137 citations
TL;DR: In this article, a hybrid digital adaptive (HDA) controller is proposed for step-load transient responses in synchronous buck DC-DC converters, which results in near-time-optimal step load transient responses even when the output voltage is sampled using a relatively low-resolution, narrow-range window A/D converter.
Abstract: This paper presents a hybrid digital adaptive (HDA) control for fast step-load transient responses in synchronous buck DC-DC converters. The proposed HDA controller results in near-time-optimal step-load transient responses even when the output voltage is sampled using a relatively low-resolution, narrow-range window A/D converter. The controller is a combination of a standard constant-frequency pulsewidth-modulated (PWM) control in the vicinity of steady-state operating point and a bank of switching surface controllers (SSCs) away from the reference. The switching surface slope is adaptively selected by a supervisor based on an inductor current estimate. Furthermore, the controller is capable of taking into account a maximum inductor current limitation. A large-signal stability analysis is presented for all possible cases during transients when one of the SSCs is active. Experimental results demonstrate fast transient responses for a 1.3 V, 10 A synchronous buck converter over a wide range of step-load transients.
117 citations
TL;DR: In this paper, an approach to adaptive tuning of voltage-mode digital controllers for switched-mode power supplies in the presence of large signal changes from discontinuous conduction mode (DCM) to continuous conduction modes (CCM) and vice versa is presented.
Abstract: This paper presents an approach to adaptive tuning of voltage-mode digital controllers for switched-mode power supplies in the presence of large signal changes from discontinuous conduction mode (DCM) to continuous conduction mode (CCM) and vice versa. The approach is capable of maintaining a high-performance control loop without the stability issues related to DCM-to-CCM mode transitions. The adaptive tuner, modeled as a multiple-input-multiple-output (MIMO) controller, is designed to continuously adjust the parameters of a PID compensator such that crossover frequency and phase margin measured by the digital controller match desired values. A simplified design procedure for the adaptive tuning system is proposed that reduces the small-signal MIMO design into two independent single-input, single-output control loops. Simulation results are given showing that despite wide uncertainty in the power stage, the adaptive tuning system still converges to the desired stability margins. Experimental results are given using an 11- to 5-V, 45-W, DCM/CCM buck converter as a test bed.
71 citations
06 Nov 2009
TL;DR: In this paper, the authors proposed an alternative modulation approach for digitally controlled DC-DC switching converters, which exploits the natural jittering activity of a digital hysteretic feedback loop in order to provide an effective increase in resolution.
Abstract: This paper presents an alternative modulation approach for digitally controlled DC-DC switching converters, which exploits the natural jittering activity of a digital hysteretic feedback loop in order to provide an effective increase in resolution. The proposed structure replaces conventional high-resolution digital pulse-width modulators (DPWM) or sigma-delta based (ΣΔ-DPWM) solutions with a single, fully-digital block featuring reduced complexity, high resolution, and improved noise performance and small-signal dynamic characteristics, enabling the design of accurate, high-bandwidth digital feedback loops with minimum hardware resources. A stochastic modeling approach is developed for the proposed structure, which allows the derivation of a simple and effective switching frequency control criterion. Analysis, simulation and experimental tests are shown to validate the properties of the proposed digital hysteretic modulator.
58 citations
06 Nov 2009
TL;DR: In this article, the authors analyzed the general problem of inductor current limitation in the time-optimal load transient response of a DC-DC buck converter and derived the minimum number of switching actions required to handle a generic current-limited TOC, leading to the formulation of a minimum switch CL-TOC concept.
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 current-limited, time-optimal control (CL-TOC) is introduced and compared to the previously reported unconstrained time-optimal 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 minimum-switch CL-TOC concept. Two distinct approaches for minimum-switch 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.
40 citations
TL;DR: In this paper, a digital square-wave signal is injected into the feedback loop and the injection signal frequency is adjusted while monitoring loop signals to obtain the system crossover frequency and phase margin online, i.e., during normal closed loop SMPS operation.
Abstract: This paper presents a practical injection-based method for continuous monitoring of the crossover frequency and phase margin in digitally controlled switched-mode power supplies (SMPS). The proposed approach is derived from Middlebrook's loop-gain measurement technique, adapted to a digital controller implementation. A digital square-wave signal is injected into the feedback loop and the injection signal frequency is adjusted while monitoring loop signals to obtain the system crossover frequency and phase margin online, i.e., during normal closed loop SMPS operation. The approach does not require open loop or steady-state SMPS operation and is capable of convergence in the presence of load transients or other disturbances. A method for designing the stability margin monitor, based on small-signal models derived using an envelope modeling approach, is also presented. Experimental results are given for multiple power stage configurations demonstrating close matches between monitored and expected crossover frequencies and phase margins.
36 citations
21 Mar 2009
TL;DR: A current sharing technique for digitally controlled two-phase buck DC-DC converters where pulse width and resistance mismatches are digitally compensated to achieve approximately equal current sharing without sensing currents is described.
Abstract: This paper describes a current sharing technique for digitally controlled two-phase buck DC-DC converters where pulse width and resistance mismatches are digitally compensated to achieve approximately equal current sharing without sensing currents. Effects of various non-idealities on the current sharing performance are discussed and corresponding mitigation techniques are presented. An extension to converters with more than two phases is discussed. Experimental results are shown for a two-phase synchronous buck converter with 6V input voltage, and 1.3 V, 0 - 20 A output.
31 citations
Patent•
12 Jun 2009TL;DR: In this article, the adaptive tuning controller uses the phase, gain, and/or frequency measurements to adjust the digital feedback signal and compares the operating measurements with desired values and generates adjusted operating attributes.
Abstract: A digital controller configured to inject a signal into a digital feedback path that facilitates regulation of a power converter and measure the corresponding phase, gain, or frequency. The digital controller may also include an adaptive tuning controller for adjusting power converter operating attributes based in part on the measurements. In an exemplary embodiment, the adaptive tuning controller uses the phase, gain, and/or frequency measurements to adjust the digital feedback signal. In an exemplary embodiment, the adaptive tuning controller compares the operating measurements with desired values and generates adjusted operating attributes. In accordance with an exemplary embodiment, the monitoring and adjusting of the digital feedback signal occurs while the digital controller is regulating a power signal in the power converter.
27 citations
21 Mar 2009
TL;DR: In this paper, an extension to the predictive current control law leads to improved current regulation over wide load range in both continuous conduction mode (CCM) and in DCM.
Abstract: This paper addresses control techniques aimed at improving light-load efficiency and reducing harmonic distortion in digitally controlled single-phase boost power factor correction (PFC) rectifiers. Based on a discontinuous conduction mode (DCM) detection circuit, it is shown how an extension to the predictive current control law leads to improved current regulation over wide load range in both continuous conduction mode (CCM) and in DCM. Furthermore, adaptive switching and adaptive switching frequency techniques are introduced to reduce switching losses and improve efficiency at light loads. Experimental results are shown for a 300W boost PFC rectifier.
22 citations
21 Mar 2009
TL;DR: In this paper, a buck-boost converter supplying an adjustable DC voltage to a WCDMA RF power amplifier (RFPA) in order to improve the system efficiency under different transmitted RF power levels is presented.
Abstract: This paper focuses on the non-inverting buck-boost converter supplying an adjustable DC voltage to a WCDMA RF power amplifier (RFPA) in order to improve the system efficiency under different transmitted RF power levels. It is shown that precise output voltage positioning and low output voltage ripple over a wide output voltage range, including buck, boost and buck/boost transition modes, can be accomplished using Σ-Δ modulation in combination with a small, low-power, low-resolution DPWM core. A two-mode digital controller is presented, in which the compensator parameters are changed upon buck/ boost mode transitions in order to improve closed-loop dynamic performance. Results are verified on an experimental test bed that consists of a prototype 0.5 μm CMOS chip that integrates power MOSFETs, drivers and dead-time control logic, and the digital controller implemented on an FPGA. The worst case output voltage ripple over buck, boost and mode transition region is within 35mV and the output voltage transients meet the WCDMA RFPA settling time requirements.
21 Mar 2009
TL;DR: An approach to continuous adaptive tuning of digitally controlled switched-mode power supply (SMPS) feedback loops via a multiple-input, multiple-output (MIMO) control loop that adjusts compensator parameters such that crossover frequency and phase margin measured by the digital controller match desired values.
Abstract: This paper presents an approach to continuous adaptive tuning of digitally controlled switched-mode power supply (SMPS) feedback loops. Tuning is performed via a multiple-input, multiple-output (MIMO) control loop that adjusts compensator parameters such that crossover frequency and phase margin measured by the digital controller match desired values. A design procedure for the adaptive tuning system is proposed which simplifies the small-signal MIMO design into two independent single-input, single-output (SISO) control loops. The adaptive tuning algorithm is further extended to account for large-signal changes from continuous conduction mode (CCM) to discontinuous conduction mode (DCM) and viceversa. Experimental results are given using an 11 V-to-5 V, 45 W, DCM/CCM buck converter as a test-bed.
06 Nov 2009
TL;DR: In this paper, a digital output voltage sensing method for power factor correction (PFC) rectifiers that requires only a single analog comparator and a small amount of digital hardware is proposed.
Abstract: This paper proposes a digital output voltage sensing method for power factor correction (PFC) rectifiers that requires only a single analog comparator and a small amount of digital hardware Using this method a digital estimation of the output error voltage can be obtained at a rate of twice the line frequency (2f line ) without the use of a traditional analog to digital converter (A/D) The proposed method effectively implements a windowed A/D around the output reference voltage with a window range equal to the magnitude of the ac output voltage ripple When used in combination with a nonlinear-carrier (NLC) current controller, a power feedforward function is inherently embedded in the operation of the single-comparator A/D (SCA/D), which simplifies the voltage loop design and reduces voltage loop gain variation due to operating power level Experimental results are reported comparing load transient responses using the SCA/D or a traditional A/D in a digitally controlled 300W boost PFC
06 Nov 2009
TL;DR: A distributed master-slave multiphase DC-DC converter architecture and related digital control and communication techniques to remove the voltage sensing mismatch and to accomplish active current sharing among the modules.
Abstract: This paper describes a distributed master-slave multiphase DC-DC converter architecture and related digital control and communication techniques. In the distributed master-slave architecture, all converter modules are identical, but one module operates as the master. The master module communicates its voltage error and current data over a single-wire serial bus to remove the voltage sensing mismatch and to accomplish active current sharing among the modules. Experimental results are shown for a 5 V-to-12 V input, 1.3 V, 20 A output two-phase synchronous buck converter.
21 Mar 2009
TL;DR: In this article, the authors investigate input power measurement techniques that use data already available from the digital PFC controller or downstream DC-DC controllers, and short calibration routines resulting in accurate input power measurements are outlined.
Abstract: Accurate input power measurements for off-line power supplies are required for both time-of-use billing and system power management purposes. When a digitally controlled PFC is utilized at the front end of the power supply much if not all the information necessary to calculate the input power has already been sensed as digital control data. This paper investigates input power measurement techniques that use data already available from the digital PFC controller or downstream DC-DC controllers. Speci cally, three techniques are considered and short calibration routines resulting in accurate input power measurements are outlined.
01 Jan 2009
TL;DR: This chapter provides a review of system-level and circuit-level implementation aspects of strategic adaptive power management techniques which require wideband efficient power amplification, and that are crucial for power demanding loads in portable devices, such as envelope tracking for polar RF power transmitters, and on-chip line drivers for power line communications.
Abstract: This chapter provides a review of system-level and circuit-level implementation aspects of strategic adaptive power management techniques which require wideband efficient power amplification, and that are crucial for power demanding loads in portable devices, such as envelope tracking for polar RF power transmitters, and on-chip line drivers for power line communications. The stringent specifications of such amplifiers pose relevant challenges both to assess the system-level impact of the amplifier limitations, as well as to design the power converter both in terms of converter topology and control. A discussion on advanced topologies aiming miniaturization and wideband low-distortion operation, both multi-level conversion and linear-assisted scheme, is presented. Details of advanced modulation and control methods are shown, namely low-oversampling ratio sigma-delta modulation with high-order filter, and digital predistortion of output filter dynamics built-in in PWM modulation.