A systematic approach is proposed for the derivation of nonisolated three-port converter (TPC) topologies based on dual-input converters (DIC) and dual-output converters (DOC), which serves as an interface for a renewable source, a storage battery, and a load simultaneously. The power flow in a TPC is analyzed and compared with that in a DIC or a DOC, respectively. Beginning with building the power flow paths of a TPC from a DIC or a DOC, the general principles and detailed procedures for the generation and optimization of TPC topologies are presented. Based on these works, a family of nonisolated TPC topologies is developed. The derived TPCs feature single-stage power conversion between any two of the three ports, and result in high integration and high efficiency. One of the proposed TPCs, named Boost-TPC, is taken as an example for verifying the performance of its circuit topology with related operational methods. Pulsewidth modulation and power management methods, used in this circuit, are analyzed in detail. Experiments have been carried out on a 1-kW prototype of the Boost-TPC, which demonstrate the feasibility and effectiveness of the proposed topology derivation method.

Topology Derivation of Nonisolated Three-Port DC–DC Converters From DIC and DOC

Power electronics DC–DC converters are being widely used in various applications like hybrid energy systems, hybrid vehicles, aerospace, satellite applications and portable electronics devices. In the recent past, a lot of research and development has been carried out to enhance the reliability, efficiency, modularity and cost effectiveness of these converters. A number of new topologies have been proposed and new characteristics of power conversion have been defined. DC–DC converters have made a successful transition from single input–single output to multiinput–multioutput converters. These converters are now able to interface different level inputs and combine their advantages to feed the different level of outputs. Research is continued to bring down the cost and reduce the number of components while keeping the continuous improvement in the areas like reliability and efficiency of the overall system. The study of different multiinput DC–DC converter topologies suggests that there is no single topology which can handle the entire goals of cost, reliability, flexibility, efficiency and modularity single handed. This paper presents some of the recent trends in the development of multiinput and multioutput DC–DC converters. Methods to synthesize multiinput converters, their operational principles, merits and demerits are studied.

Multiinput DC–DC converters in renewable energy applications – An overview

Single-inductor multiple-output (SIMO) dc-dc switching regulators are potentially very good replacement to multiple parallel converters in today's power management units for portable applications where multiple supplies are required. The outputs in these converters being coupled, cross-regulation among the outputs plays a major role in deciding the performance of the system. This paper proposes a control scheme that ensures good load and line regulation and stable system dynamics and reduces cross-regulation effect significantly. In designing a control scheme, proper analysis of the system is an important factor, and SIMO class of converters being driven by a ripple in the inductor current, conventional modeling does not hold good. Consequently, a ripple-based modeling approach that accurately judges the system performance is adopted. A cross-derivative state feedback control methodology has been proposed so as to completely decouple the outputs. Finally, a single-inductor dual-output SIMO converter has been built on a printed circuit board using discrete components, and the test results presented validate the modeling technique proposed. The simulation and experimental results show that the proposed control scheme significantly reduces cross-regulation at the outputs.

Control Scheme for Reduced Cross-Regulation in Single-Inductor Multiple-Output DC–DC Converters

This paper presents a new digital current-mode control technique for single-inductor multiple-output converters in continuous-conduction mode. This predictive control method can calculate all the required duty cycles corresponding to the outputs for the next switching cycle. Since the calculation is based on every current reference representing the load current, all current control loops corresponding to different outputs are theoretically independent, which can greatly reduce the cross regulation. To avoid subharmonic oscillation, proper predictive digital current control is adopted. Inductor current estimation is used to remove the current sensing circuit, and corresponding calibration techniques are presented. Simulation and experimental results are given to verify the effectiveness of this control technique.

Predictive Digital Current Control of Single-Inductor Multiple-Output Converters in CCM With Low Cross Regulation

This paper presents a model predictive voltage control (MPVC) method for the single-inductor multiple-output (SIMO) dc–dc converter. The proposed MPVC method is able to solve the cross-regulation problem, which is a critical issue in SIMO dc–dc converters. The design of the proposed method including augmented state-space model, cost function, enumerated algorithm, and constraints for the SIMO dc–dc converter is discussed. Simulation for the influences of predict horizon $N_{P}$ , control horizon $N_{C}$ , and Lagrange multiplier $\lambda$ on the voltage ripple is conducted to guide the control parameters’ setting for hardware implementation. Steady-state operation and dynamic performance of the proposed MPVC method are conducted in simulation and experiment based on the single-inductor dual-output (SIDO) buck converter to verify the proposed MPVC method. In addition, the comparison between the proposed method and state-of-art methods for the SIMO dc–dc converters is presented. Simulation and experimental results demonstrate that the MPVC method guarantees low cross regulation for the SIMO dc–dc converter in continuous-conduction mode (CCM) and has a fast response speed to variations in load and reference.

Model Predictive Voltage Control for Single-Inductor Multiple-Output DC–DC Converter With Reduced Cross Regulation

Single-inductor dual-output (SIDO) switching converters always suffer from large ripple and severe cross-regulation problem, when a large inductor current is switched between two outputs. This paper proposes a novel fly capacitor method for SIDO converters to reduce the output ripple and spike. An adaptive common-mode control is presented to suppress the cross-regulation problem. A duty-ratio-based current estimation method is proposed to detect the load current, and the converter can automatically switch between pulsewidth modulation and pulse-frequency modulation modes. The two outputs of the converter are specified for 1.2 V/400 mA and 1.8 V/200 mA with input voltage ranging from 2.7 to 5 V. The chip has been fabricated on a 0.25-? m CMOS mixed-signal process. The conversion efficiency is 82% at a total output power of 840 mW, while the output ripple is about 20 mV and spike is less than 40 mV. The maximum overshot voltage during load response is 50 mV.

A Dual-Mode Single-Inductor Dual-Output Switching Converter With Small Ripple

Improving battery longevity in portable devices usually requires the use of different voltage levels with a wide range of load capability for various functional blocks. Since a single-inductor-multiple-output (SIMO) converter can support multiple output voltages while using only one inductor, it is an excellent candidate to minimize the component count and thus the production cost. However, the cross-regulation and power consumption are two main issues of the previously reported SIMO converters [1-5]. Although pseudo-continuous conduction-mode (PCCM) control with a freewheel period [1] tries to augment power density and eliminate cross-regulation, associated power dissipation of freewheel switch exacerbates its overall efficiency. The charge-control technique with energy recovery presented [2] decouples the output channels between each switching cycle, at the expense of additional switching loss and slow response. The comparator-based controlled SIMO converters are investigated in [3, 4] and the cross-regulation in most channels is improved due to the fast response of the comparator. However, since the channel that is last connected to inductor is inevitably regulated by the accumulative error of all channels to balance the overall inductor current, every load transition at other outputs will introduce serious cross-regulation [3] and load-regulation problem [4] in the channel. In addition, cross-regulation and slow response also limit the application of dynamic voltage scaling (DVS) technique, which is widely used in single-output converters to improve the system power efficiency by providing variable voltage with fast reference tracking.

4.3 An 87%-peak-efficiency DVS-capable single-inductor 4-output DC-DC buck converter with ripple-based adaptive off-time control

Power management in portable devices demands small size, low cost as well as long battery lifetime, which in turn drive the development of single-inductor multiple-output (SIMO) converters [1–5]. Due to the battery voltage variation during usage and the wide-range dynamic voltage scaling (DVS) applied for power reduction, high-efficiency buck-boost conversion is required to extend the battery lifetime. The buck-boost converter in [6] selects the operation mode by comparing the output with the supply voltage, which is not suitable for multioutput converters. The reported single-inductor dual-output (SIDO) buck-boost converter in [4] uses a state machine with sophisticated current sense for mode selection and requires a freewheeling state that dissipates energy. The converter in [3] uses one additional auxiliary inductor for step-up/down mode adjustment. This paper proposes an extended-PWM (EPWM) control which automatically selects buck or boost mode and facilitates smooth mode transition. It is suitable for flexible outputs and maintains a high efficiency in buck and in boost converters.

A 90% peak efficiency single-inductor dual-output buck-boost converter with extended-PWM control

A low-power process-independent programmable transconductance rail-to-rail operational amplifier (OpAmp) is proposed. It employs an improved transconductance feedback loop that senses the transconductance (gmT) accurately and enforces it to be equal to the conductance of a reference resistor. Experimental results in a 0.13- μm standard CMOS technology under a 1-V power supply demonstrate a continuous programmable gmT range from 87 to 165 μA/V with minimum fluctuation of ±2.4% and programmable deviation less than 4.5% from the reference value. The OpAmp achieves a unity-gain bandwidth of 3.7 MHz with a 95-pF load while only consuming 187 μA of quiescent current. The figure of merit of the proposed OpAmp is 1879 MHz·pF/mA.

1-V Low-Power Programmable Rail-to-Rail Operational Amplifier With Improved Transconductance Feedback Technique

An average current mode controlled single-inductor dual-output (SIDO) buck converter is presented. The outputs are specified with 1.2 V/400 mA and 1.8 V/200 mA. The proposed decoupling model helps to analyze the multi-loop system and to design the on-chip compensators. The converter has been fabricated in 0.25-mum mixed-signal process. Simulation and measurement results confirm the proposed analysis. The power efficiency is 86% at a total output power of 840 mW while the output ripples are about 40 mV at an oscillator frequency of 600 KHz.

Zhiliang Hong

Papers

A Dual-Mode Single-Inductor Dual-Output Switching Converter With Small Ripple

4.3 An 87%-peak-efficiency DVS-capable single-inductor 4-output DC-DC buck converter with ripple-based adaptive off-time control

A 90% peak efficiency single-inductor dual-output buck-boost converter with extended-PWM control

1-V Low-Power Programmable Rail-to-Rail Operational Amplifier With Improved Transconductance Feedback Technique

Design of single-inductor dual-output switching converters with average current mode control