Seamless Switching Research Articles

The Suppression of Voltage Overshoot and Oscillation During the Fast Recovery Process From Load Short-Circuit Fault for Three-Phase Stand-Alone Inverter

When a three-phase stand-alone inverter feeds several loads simultaneously, to ensure high reliability and continuity of power supply for the large load network, the inverter needs to operate continuously, even during faulty conditions. Moreover, the inverter should provide large enough current by switching from the voltage control mode (VCM) to the current control mode (CCM) to trigger the circuit breaker connecting the short-circuit fault branch to recover the power supply. Therefore, when a load short-circuit fault occurs, the inverter will switch from VCM to CCM. In CCM, the short-circuit currents can be controlled by the current-limiting strategy. Once the fault is cleared, to quickly supply the remaining loads, the output voltages should be restored to the rated voltage as soon as possible. However, the fast recovery process from the load short-circuit fault may cause significant voltage overshoot and oscillation. The voltage overshoot may lead to load damage, and the voltage oscillation may extend fault recovery time. To effectively solve the above problems, the voltage overshoot introduced by large fault current and postfault load impedance after fault clearance is first analyzed in this article, and then the suppression strategy based on the parallel virtual impedance is proposed. Second, the voltage oscillation introduced by the initial phase difference between the voltage references and the output voltages when the inverter switches from CCM to VCM is analyzed, and then the effective suppression strategy which can achieve seamless mode switching after fault clearance is proposed. The experimental results have been carried to verify the effectiveness of the proposed strategies.

A DLL-Based Quadrature Clock Generator With a 3-Stage Quad Delay Unit Using the Sub-Range Phase Interpolator for Low-Jitter and High-Phase Accuracy DRAM Applications

In an effort to keep pace with bandwidth growth, DRAM employes the quad data rate (QDR) to transfer four data in one clock cycle. In recent graphic memories, QDR is being implemented by a phase-locked loop (PLL). However, it is hard to apply a PLL to main and mobile memories for its high power dissipation and hardware cost. Therefore, we propose a new delay-locked loop-based quadrature clock generator (DLL-QCG) to replace a PLL. A sub-range technique is adopted for a phase interpolator (PI) to achieve a very fine resolution with low power and small area. A tiny resolution mitigates the jitter accumulation effect of the conventional all-digital DLL-QCG and reduces a phase error. With the introduction of the sub-range PI, the delay line structure is changed from two-stage (coarse-fine) to three-stage (coarse-fine-finer). To control this, we also develop a new controller, which ensures clock quality through seamless boundary switching at the fine-to-finer. The circuit is fabricated using a 28 nm CMOS FDSOI technology with a 1 V supply voltage and an area of 0.0072 mm2. It operates from 1.8 to 2.5 GHz and achieves a phase error of 3.35° to 6.35° without a quadrature-phase collector. In addition, the measured RMS and peak-to-peak jitters at operating bandwidth are 1.05 to 1.71 ps and 8.4 to 12 ps, respectively.

Design of Downhole Automatic Power Supply Device based on TPS2121

Maintaining a consistent power supply for downhole drilling devices has proved to be very problematic. For that reason, a downhole automatic power supply device was designed. In the case of the MWD instrument powered by disposable high-temperature lithium battery, the problem of seamless switching of multiple power sources in power supply could only be addressed by selecting an appropriate power multiplexing method for a series-parallel battery pack, thus the downhole automatic power supply device was designed. After analyzing the shortcomings of the original power supply method, it was found that the battery utilization rate of the diode power multiplexing method was low. Further, the microcontroller-based power supply technology failed to cope with the instantaneous voltage loss of battery and occupied the microcontroller resources. Through comprehensive comparison, the priority power supply multiplexer chip TPS2121 was used to realize the seamless switching between multiple power sources, and the DC/DC converter was designed by using the LM5166 synchronous step-down converter to form an automatic downhole power supply device. The indoor test and field test demonstrated that this downhole automatic power supply device could achieve the automatic switching of multiple battery packs, improved the battery utilization rate by using each battery pack in sequence, and achieved the seamless power supply of MWD instrument by cooperating with the DC/DC converter. In addition, this device presented high reliability and economic benefits.

Energy management and control strategy for DC microgrid based on DMPPT technique

In a conventional photovoltaic (PV) DC microgrid system, mismatches among the PV modules due to partial shading will cause power loss. The distributed maximum power point tracking (DMPPT) can effectively solve the mismatch problem and achieve high-efficiency power output. This study proposes a maximum power range estimation method based on the DMPPT technique, which can provide guidance for designing parameters. Moreover, in order to realise seamless switching between different operation modes and ensure the stability of the DC microgrid, this study proposes a modified energy management and control strategy based on the hierarchical method. Simulation and experiment results indicate that the proposed control strategy for the DC microgrid based on the DMPPT technique can switch flexibly among different operation modes of the system, with a variation of environmental conditions and battery states, ensuring the stable bus voltage as well as safe operation.

Voltage control strategy of microgrid for multi inverters

Microgrid technology can solve the large-scale access problem of distributed energy, the key problem to be solved is how to realize multiple distributed electricity. In the work, the integrated control method for droop control and droop control is adopted to realize the microgrid without communication lines. The seamless switching of two modes of grid connection and isolated operation improves the stability and reliability of the system and realizes the control of distributed power supply.

Research on Operation Status and Switching Strategy of AC/DC Control Device

The AC/DC hybrid distribution network is large in scale and high in voltage level, and contains more sources and loads, and the degree of control is more complicated. Therefore, the disconnection of the line in the AC/DC hybrid distribution network, the AC/DC fault of the system, and the change of the operating state of the flexible DC device may cause the operating mode of the system to change. In this paper, the corresponding system operation mode is proposed for the typical hand-hand AC/DC hybrid distribution network. The operating mode of the flexible DC device, the switching conditions of the flexible DC device, and the switching strategy are studied. The influence of the hot standby operation on the distribution network is analyzed, and the seamless switching of the flexible DC device is realized.

Research on VSG Control Strategy of Microgrid

In order to solve the low inertia problem and damping effect brought by the large-scale integration of Distributed Generators (DGs) into the grid, the Virtual Synchronous Generator (VSG) control strategy is introduced, The VSG control strategy is applied to the distributed generators grid-connected inverter to make it have the characteristics of synchronous generator, which can provide voltage and frequency support for the grid.Based on the established model, a detailed and complete VSG parameter calculation process is given,and aiming at the problem of seamless switching operation of microgrid based on VSG control, a simplified presynchronization control method is presented, which can simplify the operation and improve the safety and stability of the microgrid. The simulation results based on Real-Time Digital Simulator prove that the proposed method can effectively improve the safety and stability and has good practicability.

Optimizing Engine Start Systems with Application to Sailing/Coasting and Mild Hybridization

Engine start systems are key to providing a good customer experience for today’s drivers. Considerable effort goes into ensuring a smooth and quiet engine start, especially in vehicles equipped with start/stop systems. We present two novel mechatronic starters that are designed to improve start quality by enabling faster and quieter engine starts. In the first proposed concept, the traditional alternator is replaced with a motor/generator unit that is capable of exerting positive torque on the engine as needed, in addition to the conventional power generation function. The motor/generator is selectively connected to the crankshaft via a selectable geared or belted connection to enable different operating modes. This starter executes a 400 ms faster start for a typical engine when compared to a conventional 12V starter. We also present a second starter that uses an integrated two-speed gear train to crank the engine. The cranking gear ratio is changed from the initial high ratio to a lower ratio once the engine starts to spin. This ratio change allows the starter motor to continue to operate in a favorable torque-speed zone and push the engine to a higher pre-ignition rpm than a conventional starter, resulting in a quieter, smoother start.
 We also present results from incorporating the belted/geared starter concept in vehicles with sailing/coasting mode as well as in mild hybrid propulsion systems. Sailing/coasting mode of operation is enabled by the quick engine re-start capability of this starter allowing seamless switching between fuelled and unfuelled engine operation. Such an operation could reduce fuel consumption by about 3-6% on the NEDC driving cycle, without regenerative braking. One may further hybridize the propulsion system by adding a battery for storing regenerative braking energy. Using such an architecture, a 6-8% fuel economy improvement on the WLTP certification driving cycle may be achieved, depending on voltage and power levels implemented, as well as energy storage systems included.

Research on Seamless Switching Method between Grid and Island

The seamless switching control strategy between grid-connected microgrid and island operation mode is an important factor to ensure its safe and stable operation. The new master-slave control strategy and the peer-to-peer control strategy are combined to control the switching process of the grid-connected mode of the micro-grid to the island mode. A microgrid simulation model combining photovoltaic cells and batteries was built on the DigSILENT/PowerFactory platform to verify the correctness of the proposed control strategy and ensure the stability of the active, reactive, voltage and frequency of the microgrid.

An Implementation of Solar PV Array Based Multifunctional EV Charger

In this article, an implementation of solar photovoltaic (PV) array powered grid-connected residential electric vehicle (EV) charger is presented, which caters the need of an EV, household loads, and the grid. The charger is enabled to operate autonomously using a PV array for providing an uninterruptible charging and power to household loads. However, in the absence of the PV array or insufficient PV array generation, the grid-connected mode of operation is presented. Moreover, the charger is supported with the synchronization and seamless mode switching control, so that the charger automatically connects/disconnects from the grid without disturbing the EV charging and household supply. The charger is also enabled with the vehicle-to-grid active/reactive power support to the grid and vehicle-to-home power transfer for supporting the local loads in an islanded condition. The charger is also controlled to operate as an active power filter for achieving the unity power factor operation and total harmonic distortion of the grid current within 5%. Moreover, for achieving energy management, a dc-link voltage regulation based energy management strategy is used and a sliding mode control is used for regulating the dc-link voltage. For satisfactory operation under distorted voltage condition, a second-order generalized integrator frequency-locked loop with dc offset rejection is used to generate the sinusoidal reference grid current. The charger is designed for a single-phase 230-V, 50-Hz grid and it is experimentally validated in the laboratory.

Study of A Bus Voltage Control Strategy for Two-Way AC/DC Current Converter in DC Microgrid

In an isolated DC microgrid consisting of photovoltaic cells, an energy storage unit and load, reasonable control of grid-connected two-way AC/DC converter can effectively realize coordinated power distribution and bus voltage stabilization of the microgrid. A mathematical model of grid-connected converter was established first in this paper, followed by a simulation analysis of the grid-connected converter under direct voltage control. In consideration of the fact that the ideal dynamic voltage response could not be realized by conventional control of the grid-connected converter, a seamless switching control strategy of inhibiting voltage fluctuation was proposed based on the voltage fluctuation analysis of the AC/DC converter, which improved the robust stability of the DC microgrid. The effectiveness and feasibility of the proposed control strategy were verified through the simulation results.

A novel control strategy for mode seamless switching of PV converter in DC microgrid based on double integral sliding mode control

With the photovoltaic (PV) penetration increases in dc microgrid, the traditional PV converters with maximum power point tracking (MPPT) control, which are equivalent to current sources, can hardly meet the needs of coordinated operation. The PV converter should operate in both MPPT and constant voltage control (CVC) modes. When the operation mode changes, the PV converter needs to switch between current and voltage sources. Inevitably, the bus voltage instability would be caused. This paper presents a novel switching strategy for the smooth and seamless operation of the PV converter between MPPT and CVC modes. The PV converter under these two modes is always controlled as a voltage source, and its control variables are both the output voltage of PV arrays. When its operation mode changes from MPPT to CVC, a small offset signal based on DC bus voltage would be introduced to the reference voltage of inner loop of the PV converter, so as to shift the maximum power point (MPP) voltage. Meanwhile in the voltage inner loop, a double integral sliding mode controller (DISMC) is used to improve the performance and anti-interference ability of the PV converter. This method unifies MPPT and bus voltage adjustment strategy without any communication and changing any hardware structure and control parameters. When mode switching occurs, only the reference value of voltage inner loop would be slightly adjusted near the maximum photovoltaic power point, so the seamless transition for PV converter between the two modes can be ensured. Finally, the effectiveness of the mode seamless switching control strategy is demonstrated by the simulation and experimental tests.

Decentralized Bidirectional Voltage Supporting Control for Multi-Mode Hybrid AC/DC Microgrid

A hybrid ac/dc microgrid consists of alternating current (ac) subgrid(s), direct current (dc) subgrid(s) and intermediate bidirectional power converters (BPCs). The presence of dc distribution networks complicates the operation and corresponding control of the hybrid ac/dc microgrid. This paper proposes a decentralized bidirectional voltage supporting control scheme for the multi-mode hybrid ac/dc microgrid, which can provide uninterruptable ac and dc voltages in case of unintentional ac and dc islanding events. An ac phase angle – dc voltage inverse droop control with virtual impedance are designed and implemented in BPCs, which can support the ac and dc voltages and enable seamless mode switching without additional voltage sources. Proper power sharing between ac and dc subgrids is realized without frequency deviation in the ac islanded mode. The stability of proposed control is analyzed under different modes, and its performance is verified by real-time hardware-in-loop (HIL) tests.

DSL-Based Hardware Generation with Scala

We present a hardware generator for computations with regular structure including the fast Fourier transform (FFT), sorting networks, and others. The input of the generator is a high-level description of the algorithm; the output is a token-based, synchronized design in the form of RTL-Verilog. Building on prior work, the generator uses several layers of domain-specific languages (DSLs) to represent and optimize at different levels of abstraction to produce a RAM- and area-efficient hardware implementation. Two of these layers and DSLs are novel. The first one allows the use and domain-specific optimization of state-of-the-art streaming permutations. The second DSL enables the automatic pipelining of a streaming hardware dataflow and the synchronization of its data-independent control signals. The generator including the DSLs are implemented in Scala, leveraging its type system, and uses concepts from lightweight modular staging (LMS) to handle the constraints of streaming hardware. Particularly, these concepts offer genericity over hardware number representation, including seamless switching between fixed-point arithmetic and FloPoCo generated IEEE floating-point operators, while ensuring type-safety. We show benchmarks of generated FFTs, sorting networks, and Walsh-Hadamard transforms that outperform prior generators.

A Doubly-Fed Induction Generator Adaptive Control Strategy and Coordination Technology Compatible with Feeder Automation

The extensive connection of distributed generation (DG) with the distribution network (DN) is one of the core features of a smart grid, but in case of a large number, it may result in problems concerning the DN-DG compatibility during fault isolation and service restoration, for which no efficient and economic solutions have been developed. This paper proposes a doubly-fed induction generator (DFIG) adaptive control strategy (ACS) and a coordination technology to be compatible with the typical feeder automation (FA) protection logics in the ring distribution system. First of all, an ACS simulating the inertia/damping characteristics and excitation principles of synchronous generators is developed to achieve seamless switching between DFIG grid-connection/island modes, and make distant synchronization possible. Next, a technology coordinating the DFIG islands controlled by ACS and the remote tie-switches based on local inspection of synchronization conditions for closing is developed to achieve the safety grid-connection of DFIG islands in the absence of DN-DG communication. At the last, a detailed simulation scenario with a ring DN accessed by five DFIGs is used to validate the effectiveness of ACS and coordination technology compatible with FA in various faults scenes.

Scalable and customizable arbitrary waveform generator for superconducting quantum computing

Superconducting quantum processors are manufactured based on a semiconductor process, which makes qubit integration possible. At the same time, this kind of qubit exhibits high-performance fidelity and decoherence time and requires a programmable arbitrary waveform generator (AWG). This paper presents the implementation of an AWG with a sampling rate of two-gigabit samples per second as well as 16-bit vertical resolution digital-to-analog converters. The AWGs are designed for a scaled-up usage scenario by integrating them with separate microwave devices onto a single backplane. A special waveform sequence output controller is designed to realize seamless waveform switching and arbitrary waveform generation. The jitter of multiple AWG channels is around 10 ps, and the integral nonlinearity and differential nonlinearity are both about 2 least significant bits. This customizable AWG has been used in several superconducting quantum processors, and the result of multiple qubits’ measurement verifies that the AWG is qualified for controlling tens of superconducting qubits.

Control Strategy of Energy Storage Inverter Based on Virtual Synchronous Generator Technology

In the microgrid system, the power supply quality of sensitive loads is directly affected by the grid-connected and off-grid operation states of the energy storage power supply as well as the dynamic switching process between the two states. To solve this problem, this paper adopts a control method of energy storage inverter based on virtual synchronous generator, which makes the energy storage inverter equivalent to a controlled voltage source with functions of inertia simulation, frequency modulation and voltage regulation. Besides, a seamless switching control strategy of energy storage inverter is proposed, which can realize the automatic smooth switching of the grid-connected state, off-grid state and state between the two.

Broadcast Channel Origination As a Service: From Concept to Operational Implementation

<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Historically, broadcasters have used on-premises channel origination systems requiring periodic replacement, capital expense planning, and asset depreciation. With a shortening replacement cycle caused by rapid technology advances, coupled with the difficulty in accurately forecasting future storage, processing, and networking requirements, the traditional channel origination approach has become unacceptable. Channel origination as a service allows broadcasters to overcome many of the pitfalls of traditional approaches by leveraging a virtualized architecture for all channel functions, each of which is implemented in the cloud. This approach can reliably support frame-accurate and seamless switching between file-based, linear, and live content. Managed security can be provided across all platforms and network infrastructure and can be implemented in world-class data centers and networks. Channel origination, as a service, yields lower recurring operating costs per channel. Control of traffic, master control, and operations may be handled using traditional staffing configurations and workflows, shared across multiple stations, or outsourced to service providers.</i>

Shared Coded Picture Technique for Tile-Based Viewport-Adaptive Streaming of Omnidirectional Video

Tile-based viewport-adaptive streaming methods have been used in delivering omnidirectional video for virtual reality applications. In these methods, the 360° video is encoded in multiple quality versions by using the motion constrained tile set (MCTS) technique. A set of high-quality and low-quality tiles, corresponding to viewport and non-viewport areas, respectively, are selected and transmitted to the user. However, these methods require frequent intra random access points to ensure seamless viewport switching capability, very high decoding complexity, or a multi-layer coding scheme. The frequent intra random access points include very high bitrate in viewport switching points. The high decoding complexity and multi-layer decoder requirements are not aligned with the omnidirectional media format (OMAF) standard. Such requirements make these methods sub-optimal or impractical for streaming the omnidirectional video. This paper studies the current tile-based solutions for delivering the omnidirectional content. Moreover, the OMAF-compliant shared coded picture (SCP)-based scheme is proposed in this paper for streaming the omnidirectional video. The core concept of the SCP-based method is to manipulate the switching point pictures in a way that the frequent intra-coded pictures are no longer required for the viewport switching operations between different quality versions of the content. The experiments illustrated that the SCP-based method outperforms the MCTS-based method on average by 11% to 14% in terms of streaming bitrate reduction with only 4% extra decoding complexity.

Bumpless Optimal Control over Multi-Objective Microgrids with Mode-Dependent Controllers

To avoid transient jumps at the switching time between two operating modes in microgrids, this paper proposes a linear quadratic-based optimal bumpless controller with two degrees of freedom (DOF) to suppress the transient disturbance and realize seamless switching between mode-dependent controllers. By minimizing the transient performance criteria, which contains both the reference tracking error and the controller tracking error, this bumpless algorithm not only effectively forces the latent controller to track the active controller, but also guarantees the plant output track the reference as close as possible. For the different control objectives of the two modes, a current-based networked PI controller is proposed in islanded mode to achieve power sharing, as well as suppressing circulating current, and a power-based PI controller is designed in grid connected mode to supply required P and Q, as well as effectively synchronize f and v safely with the main grid. A microgrid test system with two operation modes was built in Matlab/Simulink. Several operating cases were executed to verity the feasibility and effectiveness of this optimal bumpless control strategy.