Tight Output Voltage Regulation Research Articles

O Splines-Based Fixed-Frequency Integral Sliding-Mode Controller for PFC Rectifier

This paper proposes a fast-response sliding mode controller (SMC) for a semi-bridgeless boost converter under large and quick load fluctuations to ensure tight output voltage regulation and unity power factor correction (PFC) at the line side. In this sense, a novel approach for estimating the reference current profile is presented focusing on the real-time phasor estimation via the O-splines of the discrete-time Taylor-Fourier transform (DTTFT). This method allows for improving the computational efficiency and dynamic performance of the estimations of amplitude, frequency and phase of the network voltage used for the generation of the reference current profile. Several aspects of the controller design are discussed, including the choice of the sliding surface, the existence and stability conditions, and the implementation of an adaptive hysteresis band to fix the switching frequency and reduce zero-crossing distortion. Experimental results of a GaN-based prototype validate the theoretical predictions, exhibiting a PF close to 1 and a total harmonic distortion lower than 3.2% in presence of load changes of up to 50% and changes in the output voltage set point. Several comprehensive experimental comparisons between the proposed framework and the most widely used methods recently reported in the literature are accomplished in terms of transitory and steady-state responses. The robustness of the proposed control approach is experimentally demonstrated under sag conditions and a wide operating range of the input voltage.

Observer and Nonlinear Control Design of VSC-HVDC Transmission System

This paper deals with the problem of controlling power systems that contain Voltage Source converters based on High Voltage Direct Current (VSC-HVDC). Specifically, the system under study consists of two power grids and two VSC stations connected via a long HVDC cable. Using the backstepping design technique, we design a nonlinear controller that meets three control objectives: (i) tight output voltage regulation of the HVDC cable; (ii) guarantee the power factor correction (PFC) at both sides of the HVDC system; (iii) regulation of the active power at the inverter station. Furthermore, we design a high-gain observer that provides the controller with online estimates of all states based on the measurements of the HVDC input voltage and current in the cable. Finally, one provides a stability analysis of the output feedback controller and simulation results highlighting its performances.

Bidirectional CLLC Resonant Converter Employing PLC Capability and EM Noise Reduction Technique for Small-Sized ESS Application

An energy storage system (ESS) requires high reliability with low electromagnetic (EM) interference, communication capability between ESS applications, and bidirectional power conversion for charging and discharging operations. However, a conventional ESS separately has power converters, communication devices, and large-sized EM interference filters for its stable operation. In this article, a current-fed capacitor-inductor-inductor-capacitor (CLLC) resonant converter employing asymmetric pulsewidth modulation and spread spectrum modulation is proposed to obtaining three functions, bidirectional power conversion with tight output voltage regulation, EM noise mitigation, and power line communication capability among ESSs, simultaneously. It can improve the cost-effectiveness, system's form factor, and communication flexibility. The proposed integration of three functionalities has design constraints on the implementation of each function. Design methodologies of power stage and control algorithm are also proposed for achieving the simultaneous operation of each function. The performance of the proposed converter and control algorithm are verified through a 20-W prototype converter.

A Comprehensive Overview in Control Algorithms for High Switching-Frequency LLC Resonant Converter

An LLC resonant converter has been widely used in various industrial applications because of its high cost-effectiveness, high power conversion efficiency, simple design methodology, and simple control algorithms using a pulse frequency modulation (PFM). In addition, the soft switching capability of the LLC resonant converter is good to obtain high switching frequency operations, which can get the high-power density of the power converter. Over the past years, several studies have been conducted to improve the performance of a high switching frequency LLC resonant converter with resonant tank design, optimal power stage design, and enhanced control algorithms. This paper is the review paper in terms of the control algorithms for the LLC resonant converter. It focuses on the overview of the high switching-frequency LLC resonant converter in terms of the control algorithms. The advanced control algorithm can improve power conversion efficiency, dynamic performance, tight output voltage regulation, and small electro-magnetic interference. The operational principles of the control algorithms are briefly explained to show their own characteristics and advantages. Thereafter, the research issues for the future works will be discussed in the conclusion.

Input Filter-Based Ripple Injection for Mitigating Limit Cycling in Buck Converters Driving CPL

In a two-stage dc-dc intermediate bus architecture (IBA), an LC input filter with a series parasitic resistance is often used in an intermediate bus converter (IBC) because of its discontinuous input current, which is designed using Middlebrook's impedance criteria. Using the ripple voltage of the input filter capacitor, this article proposes a closed-loop pulsewidth modulation (PWM) control method in the IBC to mitigate limit-cycle oscillations (LCOs) in an IBA. This ripple voltage is shown to indirectly carry inductor current information of the IBC and offers a virtual damping in the closed-loop system. Small-signal models are derived, and stability conditions are established. A simple PI controller is shown to be sufficient to achieve tight output voltage regulation and fast transient response. The proposed technique is extended to a multiphase IBC to achieve equal current sharing among the phases. Hardware prototypes are developed, and the analytical claims are verified using experimental results.

A Power Management System for Electromagnetic Energy Harvesters in Battery/Batteryless Applications

This article presents a miniaturized and cost-effective power management system (PMS) for low-voltage electromagnetic energy harvesters (EMEHs) operating in both battery-powered and batteryless applications. The PMS consists of two converters and their associated controllers. The first converter converts EMEH’s ac voltage into a dc one in a single step and provides a maximum efficiency point tracking (MEPT) feature to maximize the harvested energy and can be used alone in battery-powered applications. The second converter provides tight output voltage regulation for batteryless applications. The MEPT converter utilizes a topology that uses a single inductor shared between the positive and negative half cycles of the EMEH voltage, unlike the majority of existing solutions, hence achieving system’s cost and size reductions. In addition, its control architecture is based on low-power comparators and does not require zero-crossing detection (ZCD) block, in contrast to many existing solutions, allowing for further reduction in cost, losses, and size. Moreover, the shared inductor is not only used by the power stage but also as a key element of the bias supply scheme allowing for voltage stepping up and hence providing sufficient voltage to supply the control circuits. The voltage regulation converter features a highly integrated dc–dc converter where the power inductor serves as normal inductor and a substrate for the converter. Experimental results show the effectiveness of the PMS with an EMEH that has a damped ac voltage characteristics ranging from 1.0 V to 10 mV for battery and batteryless applications. The presented MEPT converter, switching at 40 kHz, achieves 32.3-mm3 magnetics volume, which is the biggest contributor to the real estate of the PMS. Also, it can harvest up to 17 mJ out of 20 mJ available energy while achieving a BOM cost less than 0.7€. Moreover, the highly integrated buck converter, switching at 4 MHz, provides a tight regulated voltage of 1.2 V at 5 mA for a group of wireless sensors while achieving efficiency of 80% for load currents between $100~\mu \text{A}$ and 200 mA.

Sliding Mode Control Scheme for a CLLC Resonant Converter

In this paper, a comprehensive sliding mode control (SMC) loop design for a CLLC resonant converter is proposed. The major objectives of the proposed SMC are to improve the converter dynamics and to achieve a tight output voltage regulation with respect to any parameter variations and external disturbances. The sliding surface coefficients are selected to ensure both large- and small-signal stability for the robustness of the converter under different operating conditions. Furthermore, system dynamic performances considering the error dynamics and overshoots are investigated. To validate the proposed algorithm, a hardware prototype of a bi-directional CLLC resonant converter for plug-in electric vehicle applications is developed and tested up to 1 kW, and the effectiveness of the proposed control solution is verified by the load transients and start-up tests. At a 100% step-change in load power, the SMC achieves 1 ms settling time, which is approximately 0.9 ms faster than the conventional proportional integral control strategy.

Spread Spectrum Technique for Decreasing EM Noise in High-Frequency APWM HB Resonant Converter With Reduced EMI Filter Size

A spread spectrum technique (SST) has been proposed as a solution to mitigate electromagnetic (EM) interference in power converters. In the previous research, the SST has been widely applied to the power converters that have insensitive voltage gain according to switching frequency variation, such as buck, boost and flyback topologies. However, resonant converters have sensitive voltage gain according to the switching frequency variation, which cannot regulate the output voltage with the SST. In this paper, a high-frequency (HF) half-bridge (HB) resonant converter employing the SST is developed for power supply applications with 100-W power capability. The design methodology of its resonant tank and the SST is proposed to obtain the tight output voltage regulation performance and the EM noise reduction. In addition, the size reduction of EM noise filters is analyzed by employing the SST. The output voltage regulation performance and the filter size reduction will be experimentally verified using a 100-W prototype HF HB resonant converter.

Microfabricated Magnetics on Silicon for Point of Load High-Frequency DC–DC Converter Applications

This paper presents the design, fabrication, and characterization on silicon integrated magnetics for high-frequency power applications. The presented device achieves superior characteristics in terms of energy density, electrical resistance, current capability, and inductance versus frequency stability. In order to demonstrate the effectiveness of use of the presented device for high-frequency power applications, it is tested with two different buck point of load (PoL) dc–dc converters, one of them is off-shelf chipset and the other is designed specifically for the microdevice. Experimental measurements show that the microdevices achieve a maximum inductance of about 50 nH, electrical resistance of 300 mΩ, rated current capabilities up to 1 A, and stable L versus f characteristics up to 100 MHz. Also, the PoL buck converters with the microdevices achieve a peak efficiency of up to 82% with a flat efficiency curve at switching frequencies up to 30 MHz while providing tight output voltage regulation (<0.2%) and low temperature rise (40 °C) at the rated current.

Design Methodology of Tightly Regulated Dual-Output LLC Resonant Converter Using PFM-APWM Hybrid Control Method

A dual-output LLC resonant converter using pulse frequency modulation (PFM) and asymmetrical pulse width modulation (APWM) can achieve tight output voltage regulation, high power density, and high cost-effectiveness. However, an improper resonant tank design cannot achieve tight cross regulation of the dual-output channels at the worst-case load conditions. In addition, proper magnetizing inductance is required to achieve zero voltage switching (ZVS) of the power MOSFETs in the LLC resonant converter. In this paper, voltage gain of modulation methods and steady state operations are analyzed to implement the hybrid control method. In addition, the operation of the hybrid control algorithm is analyzed to achieve tight cross regulation performance. From this analysis, the design methodology of the resonant tank and the magnetizing inductance are proposed to compensate the output error of both outputs and to achieve ZVS over the entire load range. The cross regulation performance is verified with simulation and experimental results using a 190 W prototype converter.

Spread-Spectrum Technique Employing Phase-Shift Modulation to Reduce EM Noise for Parallel–Series LLC Resonant Converter

A spread-spectrum technique (SST) has been developed to mitigate an electromagnetic interference in power converters. However, for resonant converters using a pulse-frequency modulation, it is difficult to regulate its output voltage with the SST, because the switching-frequency variation according to the spread spectrum induces large output-voltage fluctuation. In this letter, an enhanced phase-shift algorithm of the frequency modulation of the SST and a parallel–series structure for an LLC resonant converter are proposed to obtain a tight output-voltage regulation under the spread-spectrum operation. The performance of the proposed methods is experimentally verified using a 600-W prototype parallel–series LLC resonant converter.

Sliding Mode Control of Single-Phase Interleaved Totem-Pole PFC for Electric Vehicle Onboard Chargers

In this paper, a comprehensive sliding mode control (SMC) loop design for single-phase interleaved totem pole (ILTP) power factor correction (PFC) converters in electric vehicle onboard charger applications is proposed. The major objectives of the proposed SMC are to improve the converter dynamics, ensure a tight output voltage regulation under fast load fluctuations, and maintain a unity power factor. The sliding mode coefficients are selected to ensure both small signal and large signal stability for the robustness of the converter in wide operating conditions. As verification to the proof-of-concept, a hardware prototype of a single-phase ILTP PFC is developed and tested to validate the effectiveness of loop design by the load transient tests. The steady state results exhibit a power factor >0.995 and total harmonic distortion <3% at 800 W load power. At a 25% step-change in load power, SMC achieves 80 ms settling time, which is approximately 200 ms faster than the conventional PI control.

Fully Integrated Digital Average Current-Mode Control Voltage Regulator Module IC

This paper introduces a fully integrated 12-to-1.xV voltage regulator module IC. A fully synthesizable digital two-loop controller has been realized through hardware description language tools. Several new IP blocks have been developed and described in detail: a window delay-line-based analog to digital converter (DL-ADC), two independent PI compensators with shared hardware for calculations, high-resolution digital pulsewidth modulation (PWM), and a programmable dead-time module. To fully exploit the benefits of digital electronics, reduce power consumption, and save area, all units of the digital controller have been designed through asynchronous architecture, eliminating the need of high-speed clock. High-performance synchronized, fixed frequency, PWM operation is enabled by a digital programmable time-base generator and system governor, which has been developed as well. In addition, to extend the capabilities of the window DL-ADC to support the full range of the load with minimal hardware penalty, adaptive reference of the current compensation is introduced. The mixed-signal IC has been fabricated on a 0.18- $\mu \text{m}$ 5-V CMOS process. It incorporates the digital controller and periphery as well as a synchronous buck power stage, including a drive circuitry that enables operation up to several megahertz from a 12-V input. The digital core has been realized by an automated synthesis process and place-and-route tools, resulting in an effective silicon area of 0.16 mm2. Experimental results of the fabricated IC operating in closed loop are provided, demonstrating the performance and benefits of the new controller for meeting the requirements of tight output voltage regulation over wide load range.

Spread Spectrum Technique to Reduce EMI Emission for an LLC Resonant Converter Using a Hybrid Modulation Method

A spread spectrum technique has been introduced to mitigate electromagnetic interference (EMI) in power converters. However, this technique is difficult to apply to resonant converters that use a pulse frequency modulation (PFM), because the spread spectrum can induce large output voltage fluctuations by PFM's switching frequency variations. In this letter, a hybrid control method using the PFM and phase shift modulation is proposed to obtain tight output voltage regulation under the spread spectrum operation of an LLC resonant converter. The performance of the proposed hybrid control method is experimentally verified using a 500 W prototype LLC resonant converter.

Fixed-Frequency Sliding-Mode Control Scheme Based on Current Control Manifold for Improved Dynamic Performance of Boost PFC Converter

This paper deals with the switching regulation of boost power factor correction (PFC) converter under large and quick load fluctuation to ensure tight output voltage regulation and unity PF (UPF) at line side. In this sense, the sliding-mode control (SMC) technique based on current-controlled manifold is proposed. Input current distortion is limited even during light loading condition. In addition, the dead-zone issue related to light load near to the crossover of input current is resolved in this paper. To execute the proposed SMC algorithm, equivalent control approach is used for the selection of sliding coefficients, ensuring the system stability. The control operation manipulates both inner SM current controller to frame input current and an outer PI controller to maintain desired regulated output voltage. For experimental validation, a 500-W, 390 V/dc boost PFC prototype, controlled by dSPACE 1104 signal processor is framed. The presented simulation and experimental results infer that the proposed converter controller offers UPF, tight output voltage regulation, and percentage total harmonic distortion standard even under fluctuating load behavior. In this paper, the performance of the proposed control scheme is experimentally verified with different load behaviors and external references, which explains the robustness and effectiveness of the proposed system.

An Integrated High-Density Power Management Solution for Portable Applications Based on a Multioutput Switched-Capacitor Circuit

This paper introduces a novel power management architecture (PMA) and its on-chip implementation, designed for battery-powered portable applications. Compared to the conventional two-stage PMA, consisting of a front-end inductive converter followed by a set of point-of-load buck converters, the presented PMA has drastically improved power density. The new architecture, named multioutput switched-capacitor convertor–differential-input buck (MSC–DB) convertor, is based on a novel hybrid converter topology that combines a fixed ratio MSC and a set of DB converters, to achieve low volume and high power processing efficiency. The front-end switched-capacitor stage has a higher power density than the conventionally used inductive converters. The downstream DB converters enable tight output voltage regulation, and allow for up to four times reduction of output filter inductors without the need for increasing switching frequency, hence limiting switching losses and improving the efficiency of the system. Furthermore, the new PMA is able to balance the state-of-charge of the input battery cells, a feature not existing in conventional systems. The PMA architecture is implemented both as a discrete prototype and as an application-specific integrated circuit (IC) module. The on-chip implemented architecture is fabricated in a standard 0.13-μm CMOS process and operates at 9.3-MHz switching frequency. Experimental comparisons with a conventional two-cell battery input architecture, providing 15 W of total power in three different voltage outputs, demonstrate up to two times reduction in the inductances of the downstream converter stages and more than two times reduction in losses, equivalent to the improvement of the power processing efficiency of a 12%. Moreover, the fabricated IC module is copackaged with low-profile thin-film inductors to demonstrate the effectiveness of the introduced architecture in reducing the volume of PMAs for portable applications.

Self-Synchronized Universal Droop Controller

In this paper, a self-synchronization mechanism is embedded into the universal droop controller (UDC), which is applicable to inverters having an impedance angle between $-{\pi }/{2}$ rad and ${\pi }/{2}$ rad, to form a self-synchronized UDC (SUDC). Both the voltage loop and the frequency loop of the UDC are modified to facilitate the standalone and grid-connected operation of inverters. Importantly, the dedicated phase-locked-loop that is often needed for grid-connected or parallel-operated converters is removed. The inverter is able to achieve synchronization before and after connection without the need of a dedicated synchronization unit. Since the original structure of the UDC is kept in the SUDC, the properties of the UDC, such as accurate power sharing and tight output voltage regulation, are well maintained. Extensive experimental results are presented to demonstrate the performance of the proposed SUDC for a grid-connected single-phase inverter.

Fuzzy Gain Scheduling of PI Plus Derivative Controller to Improve the Transient Response of Boost DC/DC Converter

This paper illustrates a fuzzy gain scheduling of PI plus derivative controller. The proposed control technique improves the transient response of a DC/DC converter. The proposed control system is easy to implement based on an STM32F4 microcontroller. The performance evaluation was done by an experiment through a boost DC/DC converter, with a 24W load, a 12V input voltage, and a 24V output voltage, respectively. The system operation achieves tight output voltage regulation, both for the steady-state and transient responses.

Field‐programmable gate array‐based linear–non‐linear control with high‐resolution digital pulse width modulator and high‐speed embedded analogue‐to‐digital converter for multi‐phase voltage regulator modules

Power converters for applications with high switching frequency and tight output voltage regulation such as voltage regulator modules (VRM) for microprocessors power supplies require fast dynamic response to meet the specifications. An existing control technique known as linear-non-linear (LnL) control strategy allows improving the transient converter response by means of an easy rule for the saturation of the duty cycle. The use of a digital implementation can optimise the transient response of the multi-phase VRM with LnL. However, digital control leads to other problems derived from time discretisation and finite word length effects. The limited resolution and the sampling delay are critical issues for digital control implementation of multi-phase VRM with LnL control. As a result, a high-resolution digital pulse width modulator (DPWM) and high-speed analogue-to-digital (A/D) converter are required to obtain proper performance of the converter. This study is focused on the digital implementation of the well-known LnL control in a multi-phase VRM taking advantage of low-cost field-programmable gate array resources. A detailed description of the digital implementation of the main converter control blocks, which are the A/D converter, the compensator and the DPWM, is provided in the paper.

Applying Reduced General Direct Space Vector Modulation Approach of AC–AC Matrix Converter Theory to Achieve Direct Power Factor Controlled Three-Phase AC–DC Matrix Rectifier

This paper presents a novel approach to achieve both tight dc voltage regulation and direct power factor control by applying general direct space vector modulation (G-SVM) of matrix converter theory to a three-phase ac–dc matrix rectifier. The reduced form of G-SVM and the derivation of the three-phase ac–dc matrix rectifier from a three-phase ac–ac matrix converter are described and theoretically justified. The proposed matrix converter features intrinsic buck conversion, tight output voltage regulation via modulation, inherent capability of four-quadrant operation, elimination of the bulky storage component on the dc bus, and sinusoidal input current. Moreover, the reduced G-SVM-controlled three-phase ac–dc matrix rectifier can achieve leading, lagging, or unity input power factor by simple and direct control of the input current displacement angle. This significantly benefits the potential application of the reduced G-SVM-controlled three-phase matrix rectifier to automotive, aircraft, ship, and other three-phase standby dc supplies. In these applications, the unity power factor control is indispensable when the dc load widely changes. Simulated and experimental verification for this strategy has been presented and discussed in this paper.