PWM-PD multiple output DC/DC converters: operation and control-loop modeling

In this paper, PWM-PD multiple output dc/dc converters are presented. Operation analysis and power block design are shown. Furthermore, a small-signal model is developed for the PWM-PD multiple output dc/dc converters working in continuous conduction mode. The control-block is presented and the closed-loop circuit performances, such as the line, load and cross regulation, are obtained analytically. Finally, experimental results for a PWM-PD converter, with three fully regulated outputs and with transformer, are shown.     

Output feedback and dynamical sliding-mode control of power converters

Using the underlying idea of the most widely accepted controller for power converters, the current-mode control, a new dynamical and sliding-mode control for dc–dc power converters, is proposed. The controller requires only voltage measurements; is easy to design; is robust under load and input voltage variations, exhibits fast response and does not depend on the load (although a knowledge of the load range is necessary to tune the controller). In spite of these features, it can be easily implemented using standard electronics components. The stability analysis is carried out using the discontinuous (large signal) nonlinear model. This analysis provides a set of controller admissible parameters to keep closed-loop system stability.     

Resonant converters: nonlinear analysis and control

The current trends in development and deployment of advanced switching converters have facilitated the unified activities in topology design, nonlinear analysis, optimization, and control. In this paper, by using nonlinear models of resonant converters, bounded controllers are designed to ensure a spectrum of performance objectives required. To attain high efficiency and power density, new converter topologies were developed. It is recognized that advanced closed-loop configurations must be designed to guarantee a spectrum of specifications and requirements imposed on the converter dynamics. The output voltage of converters is regulated by changing the duty ratio, which is constrained by lower and upper limits. In this paper, to approach design tradeoffs and analyze converter performance (settling time, overshoot, stability margins, and other quantities), the constraints and nonlinearities are thoroughly examined. Innovative controllers are synthesized to ensure performance improvements. To illustrate the control laws designed and to validate these algorithms, analytical and experimental results are presented and discussed. In particular, nonlinear analysis and design with experimental verification are performed and documented for a resonant converter with zero-current-switching     

Stabilizing the Frequency of Hysteretic Current-Mode DC/DC Converters

A systematic investigation of methods to stabilize the operating frequency of hysteretic current-mode dc/dc converters through control of the current hysteresis is presented. The control laws for every power stage are derived, and two open-loop and two closed-loop circuits are shown and analized in detail. The interaction of the major voltage control loop and the frequency control circuitry is also investigated for buck converters. It is shown that, if the average inductor current is programmed, the two mechanisms are independent, while if the peak inductor current is programmed, they are not. The frequency control circuitry in the latter case decreases the phase margin of the voltage control loop and can lead to instability. Simple circuits are developed to implement the superior average inductor-current programming. As a consequence of being controlled via the current hysteresis, the operating frequency cannot be stabilized in the light mode, where VO/RL < IH/2. In the special case, where the frequency of the converter is stabilized by a phase-locked loop, a method and circuit are shown to solve this problem and achieve constant frequency operation at any load.     

Granular control of photovoltaic arrays by means of a multi‐output Maximum Power Point Tracking algorithm

In this paper, a Distributed Maximum Power Point Tracking (D‐MPPT) approach in photovoltaic (PV) applications is discussed. The proposed control method is suitable for the granular control of the PV generator at a module level or even at a sub‐module level. D‐MPPT is usually implemented by means of independent converters, each one of them running its own MPPT algorithm. Instead, the architecture proposed in this paper consists of only one digital controller, implementing a multivariable MPPT algorithm based on the Perturb and Observe approach, acting on a number of dc/dc converters, each one of them dedicated to a single PV module. The proposed control strategy reduces the number of current sensors with respect to the classical D‐MPPT architecture and tracks the maximum power evaluated at the dc/dc converters' output. Planar solid immersion mirror simulations and experimental results confirm the validity of the approach and of the design guidelines proposed in the paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Development of a fuzzy logic controller for DC/DC converters:design, computer simulation, and experimental evaluation

The design of a fuzzy logic controller for DC/DC power converters is described in this paper. A brief review of fuzzy logic and its application to control is first given. Then, the derivation of a fuzzy control algorithm for regulating DC/DC power converters is described in detail. The proposed fuzzy control scheme is evaluated by computer simulations as well as experimental measurements of the closed-loop performance of simple DC/DC power converters in respect of load regulation and line regulation     

Positive output multiple-lift push-pull switched-capacitor Luo-converters

Micro-power-consumption technique requires high-power-density dc/dc converters and power supply source. Voltage lift technique is a popular method to apply in electronic circuit design. Since a switched capacitor can be integrated into a power IC chip, its size is small. Combining switched-capacitor and voltage lift technique can construct dc/dc converters with small size, high power density, high-voltage transfer gain, high power efficiency, and low electromagnetic interference. This paper introduces a new series of dc/dc converters-positive output multiple-lift push-pull switched-capacitor dc/dc Luo-converters.     

Stability Analysis, Design, and Simulation of a Closed-Loop Converter-Controlled DC Drive

A method for the design of controllers for closed-loop converter-controlled dc drives is given. Popov's stability criterion has been applied for analyzing stability in the large of the drive system. The paper includes experimental and digital simulation results of a dc drive.     

Active Damping in DC/DC Power Electronic Converters: A Novel Method to Overcome the Problems of Constant Power Loads

Multi-converter power electronic systems exist in land, sea, air, and space vehicles. In these systems, load converters exhibit constant power load (CPL) behavior for the feeder converters and tend to destabilize the system. In this paper, the implementation of novel active-damping techniques on dc/dc converters has been shown. Moreover, the proposed active-damping method is used to overcome the negative impedance instability problem caused by the CPLs. The effectiveness of the new proposed approach has been verified by PSpice simulations and experimental results.     

Limits of the neutral-point balance in back-to-back-connected three-level converters

This paper explores the limits of neutral-point current control in back-to-back connected three-level converters. The theoretical analysis used is based on a mathematical neutral-point current model, which can be extended to apply to converters with higher numbers of levels. The low-frequency ripple, which appears in the neutral-point voltage for some operation conditions, can be removed for an extended operating area when two converters are connected back to back to the same dc bus. As a consequence, a lower voltage is applied to the devices, and the value of the capacitors can also be significantly reduced. Some practical graphics are given to represent the design according to the specifications of the application.     

A family of high power density unregulated bus converters

This paper begins by reviewing current bus converters and exploring their limitations. Next, a family of inductor-less bus converters is proposed to overcome the limitations. In the new bus converters, magnetizing current is used to achieve zero-voltage-switching (ZVS) turn-on for all switches. The resonant concept is used to achieve nearly zero-current-switching (ZCS) turn-off for the primary switches and no body diode loss for the synchronous rectifiers (SRs). Meanwhile, the self-driven method can be easily applied to save drive loss of SRs. Based on these concepts, a full-bridge bus converter is built in the quarter-brick size to verify the analysis. The experimental results indicate that it can achieve 95.5% efficiency at 500-W, 12-V/45-A output. Compared with industry products, this topology can dramatically increase the power density. These concepts are also applied to nonisolated dc/dc converters. As an example, a resonant Buck converter is proposed and experimentally demonstrated.     

Steady-state and large-signal design of current-programmed DC-DCconverters

A new method for steady-state design of current-programmed-mode (CPM) DC-DC converters is presented. The method uses a set of equations derived based on the relationships between line voltage, load current, control current, and the stabilizing artificial ramp. The set of normalized equations are verified by a fast large-signal simulation and experimental measurement. These equations are plotted on the converter DC output plane (a graph of output current versus output voltage) in which characteristic curves related to different artificial ramps and boundaries of different operating modes are indicated. A general design procedure is presented for a CPM converter with both input voltage and output resistive load varied. By this means, the design time can be significantly reduced, and systematic design trade-offs can be made to ensure correct converter operation over the desired range of line and load variation     

A Complete Harmonic Elimination Approach to DC Link Voltage Balancing for a Cascaded Multilevel Rectifier

This paper presents a complete method that is used to balance dc link voltages in a cascaded H-Bridge (CHB) multilevel rectifier. Recently, such converters have been the subject of extensive research due to their suitability for high-power applications. One requirement in using a multilevel active rectifier at high levels of power is to limit the switching losses by reducing the switching frequency to a minimum. Another requirement for these converters is to ensure that individual dc link capacitor voltages for each cell of the converter are always balanced to ensure controllability and to limit stress on the converter cells. This paper presents a complete method in solving both of these problems using a selective-harmonic-elimination pulsewidth-modulation scheme. The scheme utilizes a simple controller to track each cell dc link capacitor voltage magnitude and accordingly biases the power flowing into each cell to ensure that the voltages across each cell capacitor converge. This is the case even when the loads attached to the individual cells are not balanced. The theory is supported by both simulated results from Saber and by experimental results from a seven-level CHB single-phase multilevel rectifier.     

A Three-Level Full-Bridge Zero-Voltage Zero-Current Switching Converter With a Simplified Switching Scheme

Multilevel dc–dc converters making use of high-frequency transformers are suitable for integration in solid-state solutions for applications in electric power distribution systems. This paper presents a simplified switching scheme for three-level full-bridge dc–dc converters that enables zero-voltage and zero-current switching of all the main power devices. It describes the main operational modes and design equations of the converter as well as provides simulation and experimental results to demonstrate the feasibility of the proposed ideas.      

Buck-boost converter feedback controller design via evolutionary search

Buck-boost converters are switched power converters. The model of the converter system varies from the ON state to the OFF state and hence traditional methods of controller design based on approximate transfer function models do not yield good dynamic response at different operating points of the converter system. This article attempts to design a feedback controller for a buck-boost type dc–dc converter using a genetic algorithm. The feedback controller design is perceived as an optimisation problem and a robust controller is estimated through an evolutionary search. Extensive simulation and experimental results provided in the article show the effectiveness of the new approach.     

Analysis and design of a low-stress buck-boost converter in universal-input PFC applications

In converters for power-factor-correction (PFC), the universal-input capability, i.e., the ability to operate from any ac line voltage world-wide, comes with a heavy penalty in terms of component stresses and losses, and with restrictions on the dc output voltage. In this paper, we propose a new two-switch topology, boost-interleaved buck-boost (BoIBB) converter, which can offer significant performance improvements over single-switch buck-boost converters (including flyback, SEPIC, or Cuk topologies) or other two-switch buck-boost converters in universal-input PFC applications. The paper presents an analysis of the converter operation and component stresses, as well as design guidelines. High efficiency (over 93%) throughout the universal-input ac line voltage range is demonstrated on an experimental 100-W, 200-V dc output, universal-input BOIBB PFC rectifier.     

Control strategy for single-phase PWM ac/dc voltage-source converters based on Lyapunov's direct method

Several methods for dc voltage control of single-phase pulse width modulation ac/dc voltage-source converters are known. They differ in their performance and the complexity of the hardware and software they use. One of the basic requirements of the control method is a nearly sinusoidal input current with unity power factor. However, global stability of the converter is not guaranteed by the methods proposed so far. This paper describes a new control method based on Lyapunov's direct method. It is shown that the converter can be stabilized globally to handle large signal disturbances. The closed-loop system not only ensures stability, but also exhibits excellent transient response for abrupt changes in the load. More importantly, the proposed control method can keep the advantages and remove the disadvantages of the existing methods. Computer simulations and experiments are presented to show the effectiveness and applicability of the proposed control method for the converter.     

A prognostic method for predicting failure of dc/dc converter

The failure of dc/dc converters can directly result in electronic systems working unconventionally or significant downtime. To pre-determine time to failure and generate substantial safety and cost benefits, it is necessary to assess the extent of deviation of dc/dc converters from its expected state of health in real time and predict time to failure in advance. This paper presents a novel prognostic method for predicting the time to failure of dc/dc converters. The process involves identifying precursor parameters, determining prognostic of failure, and determining a criterion for predicting time to failure. The output voltage is used as a precursor parameter and directly monitored when the converter with a given load periodically operates at different temperature stresses. The phenomenon that the differences of output voltages collected at different temperature stresses begin to increase with a large (or small) fluctuation is detected in collected output voltages. This phenomenon is identified as a prognostic of failure. A percentage of the initial difference is used as the criterion for predicting time to failure. A case study is given to illustrate the procedure that how to monitor output voltages, detect prognostic and predict time to failure. The results show the health state could be assessed in real time and the time to failure could be predicted in advance. Furthermore, the deviation of the predicted time to failure from the actual time to failure could meet the demand of a considered acceptable range in engineering practice.     

Robust feedforward compensation scheme with AC booster for high frequency low voltage buck DC–DC converters

Today and in the future, high frequency low voltage DC–DC converters are an effective power-management solution for fast transient response and small profile in portable electronic systems. This paper presents a robust feedforward compensation scheme with AC booster. An ac amplifier is added in parallel with the main path to compensate the high-frequency gain reduction, which improves gain-bandwidth (GBW) product and slew rate significantly. This approach takes the multistage error amplifier (EA) as an element in the compensation circuit instead of using passive elements used in traditional proportional-plus-integral-and-derivative (PID) compensation circuits. The positive phase shift of left-half-phase (LHP) zeros caused by the feedforward path and ac boosting path in the multistage EA is used to cancel the negative phase shift by the resonant poles of the power stage of buck DC–DC converter in order to compensate the DC–DC converters. A graphical loop-gain method is used to design the feedback compensation and analyze the closed-loop performances of the converter for the complexion arising from the presence of multiple poles of EA before crossover frequency in high frequency converters. The high gain, wide bandwidth, and high slew rate are achieved by the absence of traditional pole-splitting effect and the added ac booster. In addition, the design guidelines for this feedback compensation network realized by robust feedforward with AC booster compensation (RFACBC) scheme and multistage EA are established. When the proposed compensation networks were employed in 100 MHz buck DC–DC converter implemented in SMIC 0.18 μm CMOS process, the simulation results validate the feasibility and functionality of the RFACBC scheme and design guidelines. The closed-loop dc gain achieves over 60 dB with over 20 MHz GBW and 61° phase margin under wide range loads. Furthermore, the settling time is improved due to the advanced frequency compensation.     

PCB integrated inductors for low power DC/DC converter

This paper discusses the use of printed circuit board (PCB) integrated inductors for low power DC/DC buck converters. Coreless, magnetic plates and closed core structures are compared in terms of achievable inductance, power handling and efficiency in a footprint of 10 /spl times/ 10 mm/sup 2/. The magnetic layers consist of electroplated NiFe, so that the process is fully compatible with standard PCB process. Analytic and finite element method (FEM) methods are applied to predict inductor performance for typical current waveforms encountered in a buck converter. Conventional magnetic design procedures are applied to define optimum winding and core structures for typical inductor specifications. A 4.7 /spl mu/H PCB integrated inductor with dc current handling of up to 500 mA is presented. This inductor is employed in a 1.5 W buck converter using a commercial control integrated circuit (IC). The footprint of the entire converter measures 10 /spl times/ 10 mm/sup 2/ and is built on top of the integrated inductor to demonstrate the concept of integrated passives in power electronic circuits to achieve ultra flat and compact converter solutions.