Seamless Mode Transition Research Articles

Robust control for improving performance of grid-synchronized solar PV-BES-wind based microgrid

An integration of hybrid renewable energy systems (HRESs) to the grid results in power quality issues at the point of interconnection. This paper proposes an approach to investigate and mitigate power quality issues and uncertainties associated with integration of a HRES that includes a solar photovoltaic (PV) array, a wind generator, and battery energy storage (BES). The system functions in grid tied mode, standalone mode and seamless mode transition between these modes. Primary objective of proposed control approach is to ensure stable and reliable operation while mitigating effects of power quality issues. To achieve this objective, proposed control approach employs advanced control strategies, including generalized fourth order filter (GFOF) for grid tied mode and phase angle estimation. An off-grid mode uncertainty and disturbances are overcome by proportional resonant based control. GFOF addresses multiple power quality issues associated with grid-connected mode, including robust performance during voltage unbalance, harmonics suppression, DC offset removal, weak grid conditions, and evaluation of unit templates. GFOF extracts fundamental load currents and voltages for evaluation of reference grid currents and phase angle. This precisely estimates frequency and phase angle for seamless synchronization. It provides adaptive mode transition. Power quality of currents is enhanced in both islanded and grid-connected modes through utilization of GFOF control, ensuring that total harmonic distortions (THDs) of grid currents remain below 5% (simulated THD is 1.77% and experimental THD is 3.80%), as specified by the IEEE-1547and 519 standards. A comparative analysis has justified efficacy of control. Simulated and experimental results confirm effectiveness of proposed controllers in various scenarios, demonstrating their ability to provide a favourable solution for controlling unfavourable grid conditions with technical strength and precision.

A Wide-Input-/Output-Voltage-Range Buck Converter With Adaptive Light-Load Efficiency Improvement and Seamless Mode Transition

A Wide-Input-/Output-Voltage-Range Buck Converter With Adaptive Light-Load Efficiency Improvement and Seamless Mode Transition

A Dual-Mode Buck Converter with Light-Load Efficiency Improvement and Seamless Mode Transition Technique

A Dual-Mode Buck Converter with Light-Load Efficiency Improvement and Seamless Mode Transition Technique

Improved Sensorless Operation of Double Inverter Fed Wound Rotor Induction Machine With Seamless Mode Transitions

The performance of a sensorless induction motor drive depends on the accuracy in estimating the flux position from the supply voltage and machine parameters. Accurate estimation of flux position at low speed operation is difficult due to the low supply frequency. In a double inverter fed induction motor drive, the low speed operation can be obtained by maintaining the relative frequency between stator and rotor supply <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">voltage</b> without reducing the individual supply frequency to a very low value. In this paper, a novel frequency profile for the stator and rotor supplies of a DFIM drive is proposed, in which the minimum supply frequency of any side inverter is around 0.5 p.u. for the whole speed range of operation. With this proposed scheme, the zero speed operation of the drive is obtained by maintaining both the stator and rotor supply frequencies as 1.0 p.u.. To achieve this, the DFIM is required to be operated as a squirrel cage induction motor for certain speed range. The control scheme for both the stator and rotor side inverters along with seamless mode transitions are also presented. In this DFIM drive, the required motor power is only 50 % of the rated load power and the total <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">volt-ampere (VA)</b> rating of the two inverters is same as that of a conventional squirrel cage induction motor drive. Experimental studies are carried out on a 45 <bold xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">kW</b> wound rotor induction machine to validate the control scheme with the proposed frequency profile and results are presented.

Coordinated Power Management of a Laboratory Scale Wind Energy Assisted LVDC Microgrid With Hybrid Energy Storage System

The present work proposes a coordinated power management scheme (CPMS) of wind energy-fed self-excited induction generator (SEIG) based low-voltage direct current (LVDC) autonomous microgrid. The battery and supercapacitor (SC) based hybrid energy storage system (HESS) is interfaced with the common 48 V LVDC bus using a parallel-active configuration through two bidirectional converters. The central idea of hybridization is to mitigate the instantaneous surge current demand and alleviate the charge/discharge stress during transients, thus ultimately enhancing the cycle life of the battery. The experimental validation of the autonomous LVDC microgrid equipped with the CPMS is conducted for various operating modes. The dSPACE DS1103 digital controller is used for the real-time implementation of the complete system. The effectiveness of the proposed CPMS is supported by the analysis of comparative experimental results demonstrates its ability to incorporate seamless mode transition. The developed 48 V LVDC microgrid can be a promising solution for powering consumer electronics in homes/office spaces or other small-scale applications.

An On-/Off-Time Sensing-Based Load-Adaptive Mode Control of Triple Mode Buck Converter for Implantable Medical Devices.

Wireless power transfer (WPT) technology applied to implantable medical devices (IMDs) significantly reduces the need for battery replacement surgery health conditions. This paper presents an on-/off-time sensing-based load-adaptive mode control of triple mode buck converter for implantable medical devices; the converter can adjust the control mode for low power consumption and achieve high power conversion efficiency (PCE) under a small active area. The three modes in the proposed system are the pulse width modulation (PWM), pulse frequency modulation (PFM), and ultra-low power (ULP) modes. The on-time sensor can be used to adjust the system from PWM to PFM modes, and the off-time sensor can be used to adjust the system from PFM to ULP modes. It is fabricated using TSMC 0.18 µm CMOS technology. The input voltage lies in the range 2.2-5.0 V, the output voltage is 1.8 V, and the load current lies in the range 0.05-200 mA (x4000). The experimental results demonstrate the seamless mode transition under the step up/down load transient response. The peak PCE is approximately 94.3% at the 80 mA and the minimum PCE is approximately 65.4% within the load current range.

Control Strategy for Multiple Residential Solar PV System in Distribution Network With Improved Power Quality

This paper presents a modified power control (MPC) for a grid-interfaced autonomous microgrid connecting multiple solar photovoltaic inverter (SPI) units. An MPC provides the automatic transition capability between grid-tied mode (GTM) and an islanding mode (IAM) for a microgrid consisting of multiple parallel-operated SPIs. In GTM, SPIs extract PV power to fulfil the load demand, and the rest power is fed to the grid at the unity power factor (UPF) by working in the current control mode (CCM). Upon grid failure, the main SPI unit inherently changes from CCM in GTM to voltage control mode (VCM) in the IAM state to achieve an uninterruptable power supply to loads. When the grid restores, the main SPI unit near the point of common coupling (PCC) re-synchronizes the PCC voltage with grid voltage in the microgrid and control shifts back to GTM. A seamless mode transition in the microgrid is achieved without rearrangement of control formation, and power distribution between the parallel SPI units is achieved without communication setup. This reduces the cost of remote communication setup for resynchronization and saves the complexity. Moreover, MPC accurately regulates the reference grid current of SPIs when the load demand fluctuates. The MPC method combines the adaptive integrator filter (AIF), which attenuates the harmonics from the input signal to strictly control the power factor at PCC and maintains the total harmonics distortion (THD) of grid current and PCC voltage according to the IEEE stand. 519. The performance of the presented MPC method is evaluated via a simulation and test results.

Self-Synchronizing Control Enabling Disruption-Free Operation and Seamless Mode Transitions in Wind–Solar Based Hybrid AC/DC Microgrid

This paper introduces a novel self-synchronizing control architecture for the power converters in a hybrid AC/DC microgrid (HMG), wherein, the doubly fed induction generator (DFIG) and the solar photovoltaic (SPV) array are utilized for wind and solar generation, respectively. The self-synchronizing control enables the HMG to remain functional and provides a disruption-free power at all the four identified operation modes. Different operation modes are enforced due to grid islanding or DFIG wind generator disconnection scenarios. Meanwhile, the shifting among these four operation modes culminate into eight possible transition phases. The HMG's self-synchronizing control is devised to achieve seamless operation at all possible transition phases, and avoids any voltage spikes or transient overcurrents. Such a seamless transition functionality becomes increasingly vital in case of the DFIG-SPV based HMG. This is due to the direct interconnection of DFIG stator with the utility grid that renders the system largely vulnerable to any un-synchronized transition. Therefore, major research emphasis of this work is on the development of a novel methodology for ensuring a disruption-free operation and seamless mode transitions in a DFIG-SPV based HMG. The HMG control is based on a new affine projection sign algorithm (APSA), which supplements the HMG with unity power factor operation and load unbalance/harmonics mitigation. The viability of the HMG and its self-synchronizing control at various mode transition phases and system dynamics are extensively tested on an experimental rig developed in the laboratory. Test results endorse the feasibility of the self synchronizing control, while, a comparative analysis demonstrates the superiority of the APSA scheme over other state-of-art approaches.

Subject-Independent Continuous Locomotion Mode Classification for Robotic Hip Exoskeleton Applications.

Autonomous lower-limb exoskeletons must modulate assistance based on locomotion mode (e.g., ramp or stair ascent) to adapt to the corresponding changes in human biological joint dynamics. However, current mode classification strategies for exoskeletons often require user-specific tuning, have a slow update rate, and rely on additional sensors outside of the exoskeleton sensor suite. In this study, we introduce a deep convolutional neural network-based locomotion mode classifier for hip exoskeleton applications using an open-source gait biomechanics dataset with various wearable sensors. Our approach removed the limitations of previous systems as it is 1) subject-independent (i.e., no user-specific data), 2) capable of continuously classifying for smooth and seamless mode transitions, and 3) only utilizes minimal wearable sensors native to a conventional hip exoskeleton. We optimized our model, based on several important factors contributing to overall performance, such as transition label timing, model architecture, and sensor placement, which provides a holistic understanding of mode classifier design. Our optimized DL model showed a 3.13% classification error (steady-state: 0.80 ± 0.38% and transitional: 6.49 ± 1.42%), outperforming other machine learning-based benchmarks commonly practiced in the field (p<0.05). Furthermore, our multi-modal analysis indicated that our model can maintain high performance in different settings such as unseen slopes on stairs or ramps. Thus, our study presents a novel locomotion mode framework, capable of advancing robotic exoskeleton applications toward assisting community ambulation.

Natural Boundary Transition and Inherent Dynamic Control of a Hybrid-Mode-Modulated Dual-Active-Bridge Converter

This article proposes a hybrid-mode modulation strategy for the single-phase dual-active-bridge (DAB) dc–dc converter that realizes soft switching in the whole operating range. Different from existing modulation methods that are usually dependent on complex mathematical optimization processes, the presented article reveals that the simple trapezoidal continuous conduction mode and triangular discontinuous conduction mode inspired by a quasi-single-active-bridge operation can naturally and sequentially extend the soft-switching boundary of the conventional single-phase-shift (SPS) modulation to the full range in both the buck and boost modes. Meanwhile, the transformer rms current is also reduced. Moreover, a fast-dynamic control with inherent seamless mode transitions is realized by introducing the predictive-current SPS modulation. The proposed hybrid-mode modulation strategy with closed-form solutions can be easily implemented in a generalized closed-loop controller, which enables an ultrawide-voltage-range operation of the DAB converter with significantly elevated efficiency and fast transient responses. The effectiveness of the proposed method is validated by comprehensive experimental results from a small-scale DAB prototype.

An Ultra-Low Quiescent Current Tri-Mode DC-DC Buck Converter With 92.1% Peak Efficiency for IoT Applications

An ultra-low quiescent current tri-mode DC-DC buck converter is presented in this paper, which is able to handle a 100,000X load range. In pulse width modulation (PWM) and pulse frequency modulation (PFM) mode, adaptive on-time (AOT) V² control is utilized to achieve seamless mode transition and constant switching frequency in PWM mode. A deep green mode (DGM) is proposed for light load, where both the switching loss and the power of control circuitry are minimized. By reducing the comparator current, a delay-based hysteresis window adaptive to load current is generated, reducing the switching frequency and the loss. Meanwhile, the average current of zero current detector (ZCD) and AOT controller are reduced significantly by dynamic biasing. As a result, the efficiency of the converter is improved while maintaining a reasonable output ripple. The proposed converter is implemented in a 0.18μ m BCD technology. Experimental results show that the converter can provide a 1.6 V output from a 2.7 to 4.7V input for 1μ A to 100 mA load, while consuming only 490nA quiescent current. The proposed converter achieves a 92.1% peak efficiency and efficiency can be maintained above 80% in a load range of 20μ A to 60 mA.

A Dual Active Bridge DC–DC-Based Single Stage AC–DC Converter With Seamless Mode Transition and High Power Factor

In this article, a dual active bridge (DAB) based single-stage isolated ac–dc converter is studied. By analyzing the root mean square value of the leakage inductor current, the high-frequency transformer turns ratio is optimized for higher conversion efficiency. Three operating modes of the DAB converter are utilized in the control strategy. The current and the voltage waveforms of these operating modes are analyzed. The control variables, including the phase-shift ratio <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ϕ</i> , the primary side duty cycle <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , and the secondary side duty cycle <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> are combined based on instantaneous calculation according to achieve boundary zero voltage switching (ZVS). The mode transition is seamless while the switching frequency is constant. Furthermore, the magnetizing inductor of the transformer is designed to help the secondary side switches to achieve ZVS. ZVS conditions and parameter design are given in this article. Besides, a 1 kW prototype was fabricated to verify the effectiveness of the design and the control strategy.

CAPSA Based Control for Power Quality Correction in PV Array Integrated EVCS Operating in Standalone and Grid Connected Modes

In this article, a solar photo voltaic (PV) array and a storage battery integrated three phase electric vehicle charging station (EVCS) is presented, which uses a convex combined affine projection sign algorithm (APSA) for improving the power quality at the grid. This algorithm convexly combines the output of two APSA with large step size and small step size. Therefore, this algorithm achieves fast convergence and low steady-state error in abruptly changing input conditions. Therefore, this algorithm is suitable for an EVCS, where the charging current of EV changes frequently. The EVCS provides both ac and dc charging to EVs. In the daytime, the CS operates in standalone mode to charge the EV connected at the point of common interconnection (PCI). However, the EV requiring dc power can take power from the dc link through a bidirectional dc-dc converter. Whereas, in the absence of PV array generation, the CS takes power from the grid. Moreover, while connecting the CS to the grid, the PCI voltage is synchronized to the grid voltage for achieving the seamless mode transition. Various steady-state and dynamic condition results have been taken on the experimental prototype developed in the laboratory for demonstrating its satisfactory behavior.

Decentralized PV–BES Coordination Control With Improved Dynamic Performance for Islanded Plug-n-Play DC Microgrid

In this article, a decentralized photovoltaic (PV)-battery energy storage (BES) coordination control method for Plug-n-Play (PnP) dc microgrid (MG) is proposed. With the proposed control method, PV units can operate under dc bus voltage control when BES units are saturated due to state-of-charge (SoC) limit or charging/discharging power limit. The mode transition and power sharing are based on a communication-less manner. By bypassing communication, the MG system can become more flexible and reliable. The proposed control system contains controllers for PV converter and BES converter, respectively. The PV converter controller can achieve seamless mode transition between maximum power point tracking (MPPT) control and droop control. The BES converter controller has a decoupled feature that a high-pass-filter (HPF) path could improve MG dynamic performance under generation-dominating mode. The BES HPF compensation overcomes the issue of poor dynamic performance under PV-dominating mode and makes the system more resistive to PV parameter variation. The detailed design, analysis, and implementation of the proposed PV-BES coordination control are provided in this article. The simulation and experimental results have been provided to verify the concept and analytical study.

A 1-A 6-MHz Digitally Assisted Buck–Boost Converter With Seamless Mode Transitions and Fast Dynamic Performance for Mobile Devices

A 1-A 6-MHz buck-boost converter with seamless mode transitions and fast dynamic operation is proposed for extending the useable voltage range of Li-ion batteries in mobile devices, and thereby their battery life. The proposed converter employs a proportional-integral peak-current-mode pulsewidth modulation controller with a digital adaptive slew-rate control scheme that minimizes output undershoots, overshoots, and settling time during mode transitions and dynamic events, such as load and output voltage steps. Additionally, hysteretic mode detection is proposed to prevent falsely triggering the converter to transition between the various operation modes (i.e., buck, boost, and buck-boost) and negatively impacting the performance of the circuit loads. The converter is fabricated in 0.13-μm CMOS technology, and supports 2.3-5 V input and 1.5-3.6 V output. The converter achieves 91.7% peak efficiency and over 80% efficiency at 1-mA load across all conditions. The output voltage ripple is less than 10 mV with a 220-nH inductor and a 10-μF output capacitor.

A 470-nA Quiescent Current and 92.7%/94.7% Efficiency DCT/PWM Control Buck Converter With Seamless Mode Selection for IoT Application

An ultra-low quiescent current dual-mode buck converter system is designed for IoT application, which includes a double clock time (DCT) and a pulse-width-modulation (PWM) control modes. The proposed DCT mode can reduce the conversion loss over a wide loading range from nA-to-mA and achieve seamless mode transition from DCT to PWM control. Implemented in a $0.18\mu \text{m}$ CMOS, this converter achieves a peak efficiency of 92.7%/94.7% in DCT/PWM and >80% efficiency from $10~\mu $ A to 50 mA (5000x), with a wide input voltage from 2 V to 5 V. A quiescent current of 470 nA including bandgap voltage reference and internal oscillator is achieved. The DCT-to-PWM mode selection mechanism achieves an undershoot of 80 mV at $11~\mu \text{s}$ recovery time when load current jumps from $6.67~\mu \text{A}$ to 50 mA.

A 7.4-MHz Tri-Mode DC-DC Buck Converter With Load Current Prediction Scheme and Seamless Mode Transition for IoT Applications

The growth of IoT applications requires DC-DC converters to have small printed circuit board (PCB) areas and high efficiency over a wide load range. A multi-mode operation of DC-DC converters, therefore, is often necessary to achieve this high efficiency over a wide load range. This paper introduces a tri-mode DC-DC buck converter for IoT applications. The tri-mode operation with PWM, PFM, and multiple-sawtooth PWM (MSPWM) modes helps to retain the high efficiency over the wide load range. The MSPWM mode also enhances a noise margin of the converter, ensuring a regular switching operation at an ultra-light load condition. With a load current prediction scheme, the proposed tri-mode converter requires neither additional load current sensor nor multiple mode controllers. In addition, a soft-start operation is employed to prevent an in-rush current. The proposed tri-mode buck converter has been fabricated through a 0.18- $\mu \text{m}$ CMOS process with a chip area of 0.97 mm $\times0.88$ mm. A load-dependent seamless mode transition is realized, and a maximum converter efficiency of 91% has been measured with a 7.4-MHz switching frequency.

계통연계형 인버터의 끊김 없는 모드 전환을 위한 전압 제어 기능이 포함된 통합 전류 제어기에 대한 연구

본 논문에서는 계통연계형 3상 인버터의 끊김 없는 모드 전환을 위해 전압 제어 기능이 포함된 통합 전류 제어기를 제안한다. 단독운전 및 계통연계 모드 모두에서 자연스럽고 끊김 없는 모드 전환을 위해 완전히 동일한 제어 알고리즘과 제어기가 사용된다. 제안된 전류 제어기를 사용하면 정상 상태에서의 필터 회로들의 전압, 전류 값이 전향 보상되어 빠른 응답을 기대할 수 있다. 여러 보상 요소들이 포함되어 있음에도 불구하고 제안된 제어기 구조는 단일 제어루프로 구성되어 있으므로 제어기를 쉽게 설계할 수 있다. 전류 지령에 부하 전류를 포함하여 부하 변경에 관계없이 과도 전류가 최소화된다. 회로 파라미터의 불일치 및 낮은 제어 대역폭으로 인한 전압 오류를 보상하는 정전압 컨트롤러도 포함되어 있다. 제안된 방법은 중요 부하가 실시간으로 변화하는 경우에도 부하 및 계통에 안정적인 전력을 제공할 수 있을 것으로 예상된다. 제안된 통합 전류 제어기는 55 kVA 급 계통연계 3상 인버터에 대한 시뮬레이션으로 검증되었다.

Wide Input Voltage DC Electronic Load Architecture With SiC MOSFETs for High Efficiency Energy Recycling

A SiC three-stage converter architecture of energy recycling dc electronic load with high frequency isolation is proposed. With interleaving boost converters and a LLC-DCX using 1200-V SiC MOSFETs as high frequency isolation pre-regulation stage, the proposed architecture can adapt to wide input voltage of 150-750 V with high efficiency. As the bus voltage is 780 V, a T-type three-level inverter is accepted as grid-connected stage for low leakage current, small grid current harmonics and high conversion efficiency. The transfer mechanism of second harmonic component of the input current ripple is analyzed and is well suppressed by proposed current program control. An overshoot-free soft-start control is proposed to minimize resonant current peak using the inverter reverse operation. The switching frequency reduction modulation control is proposed to solve the extremely low duty-cycle problem under high input voltage and low load condition. A seamless mode transition digital control of three-stage load is proposed with smoothly switched capability between the input current loop and input voltage loop to solve the duty-cycle mutation problem during mode transition. A 5-kW, 300-kHz SiC prototype with 150-750 V input was built. The peak full-load efficiency of three-stage architecture is 95% at 750 V input. The power density is 12.6 W/in <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> .

Optimised adaptive control methodology for mode transition of hybrid electric vehicle based on the dynamic characteristics analysis

Mode transition plays an important role in the operation of hybrid electric vehicles. The clutch is a key actuator for mode transition, but friction resulting from its use makes it difficult to achieve seamless mode transition. Moreover, as is usual in an electromechanical coupling system, the hybrid powertrain may exhibit complex dynamic behaviours as operating parameters change during mode transition. This paper considered changes in the clutch friction coefficient, and established a mathematical model of the hybrid powertrain in a parallel-series hybrid electric vehicle (PSHEV) during mode transition. The Routh-Hurwitz criterion and bifurcation theory are introduced to analyse the influence of speed difference on the dynamic characteristics of the hybrid powertrain, and the corresponding instability threshold were given. Furthermore, an optimised adaptive control methodology was proposed to control the dynamic behaviours, and tests on PSHEV were carried out. The results show that the variations of speed difference may lead to the occurrence of Fold and Hopf bifurcations, and that once the speed difference reaches the instability threshold, it may cause the system to enter a chaotic state and exhibit random oscillation. The proposed control methodology can effectively expand the security domain and suppress the oscillation to improve smoothness of mode transition.