Bidirectional Power Transmission Research Articles

Multi-Terminal DC Transformer for Renewable Energy Cluster Grid Connection

An AC (alternative current) power integration of distributed energies faces multi-fold challenges such as synchronization and weak grid-induced instability. In this study, a multi-terminal DC transformer is proposed for renewable energy clusters grid connection. The DC transformer provides multiple DC input ports for renewable energy collection, while the load port is connected to the medium-voltage DC grid via a modular multilevel converter (MMC). The multi-port topology enables flexible power transfer between multiple input sources to the load without additional components. The carrier layer modulation strategy is implemented to balance the MMC module voltage; bidirectional power transmission between multiple input sources is achieved through the phase shift modulation (PSM) method. First, we provided a detailed introduction of the proposed topology and working principle. A simulation model was built using the SIMULINK, and the simulation results verified the effectiveness of the proposed converter modulation strategy and phase shift modulation method. A corresponding hardware experimental platform was designed and built, and the modulation and voltage equalization functions of modular multilevel rectifiers were presented as well as the measured results of power transmission modulation of the converter under single-input and multi-input conditions. The results indicate that the proposed transformer can achieve multiple DC inputs and has multi-channel power transmission capabilities, making it suitable for renewable energy clusters grid connection.

A Bidirectional Direct AC-AC Resonant SCC

A direct ac-ac resonant switched-capacitor converter (SCC) for both noninverting and inverting output voltages is proposed here, which is suitable for bidirectional power transmission including different applications such as dynamic voltage restorer (DVR), constant voltage regulator (CVR), and constant current regulator (CCR). Zero voltage switching (ZVS) and zero current switching (ZCS) operation conditions are easily realized for its power switches, which effectively reduce the switching losses, as well as the electromagnetic interference (EMI) noise. Consequently, high-frequency operation is possible, which improves the converter power density, in practice. Continuous voltage-gain, transformerless connection of the converter output port to the gird, no commutation problems without using extra components, and improving the electrical specifications are some other advantages of the given resonant SCC. The converter operation principles, its key waveforms and different operational states, its mathematical analysis and normalized state-plane trajectories, simulation results, as well as its design procedure, are also given here, in detail. To verify the given theoretical analyses and simulation results, a 500 W prototype converter for a 2 kW DVR with 220 V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">rms</sub> nominal output voltage has been implemented successfully, which realizes 96.55% efficiency at its rating power value.

Design and Implementation of Novel Rotor Side Brushless Controller With Bidirectional Wireless Power Transmission for Doubly-Fed Machine

This paper proposes a novel rotor side brushless controller (RSBC) with bidirectional wireless power transmission (WPT) for a doubly-fed motor (DFM), which can realize the brushless DFM without changing the stator and rotor structures. The WPT-RSBC consists of a grid side converter, a series–series compensated resonant converter, and a rotor side converter. According to the operational characteristics of DFMs, the design requirements of the WPT-RSBC are given in this paper. The systematic selection method for four-quadrant operations of the DFM is introduced, and the variable bus voltage control strategy is proposed to improve its transmission efficiency. The mathematical model and small-signal model of each subsystem in the WPT-RSBC are given, and the stability of the primary and secondary DC bus is analyzed. An experimental platform is implemented to verify the feasibility of the WPT-RSBC. For the prototype, the air-gap length is 1 mm, and the RSBC's transmission efficiency can be up to 92%.

A segmented‐region optimum EPS modulation scheme based on unified parameter algorithm in DAB‐based EV charger circuit

AbstractDue to galvanic isolation, bidirectional power transmission and extensive voltage adjustment, dual active bridge (DAB) exerts significant interface between renewable sources and electric vehicle (EV) storage port. However, for DAB operations, under light load or high voltage gain conditions, minimization of root‐mean‐square (RMS) current (MRMS) causes a restricted soft‐switching range. With variations of output power and operation modes, maintenance for all switches ZVS operation is difficult to maintain. Therefore, here, a segmented‐region optimum modulation (SROM) scheme based on extended‐phase‐shift (EPS) control is proposed to solve the aforementioned problems and solve complicated coupled relationship among different optimization methods. Firstly, based on voltage gain and transmission power, all EPS modes are divided clearly. Then, for switching loss reduction, fully‐power‐range ZVS (FZVS) is realized through transitions among EPS modes. Thirdly, either all semiconductors ZVS or not, most suitable optimization method is selected for different EPS regions by SROM. Further, to establish accurate boundaries among these optimization methods, relationship between inner phase‐shift ratio D1 and outer phase‐shift ratio D2 are quantified by unified parameter algorithm with unified parameter m. Therefore, for any EPS modes, efficiency is promoted comprehensively. A DAB‐based prototype is established and experimental results verify correctness and effectiveness of proposed method.

Bidirectional Atmospheric Channel Reciprocity-Based Adaptive Power Transmission

In atmosphere free-space optical communication (FSO) systems, the scintillation effect produced by turbulence effects increases the bit error rate (BER) of the communication system and reduces the system’s performance. However, a high correlation of turbulent noise occurs in the two transmission channels when a signal transmitted in the bidirectional atmospheric channel with channel reciprocity. The performance of the FSO system can be increased by extracting channel state information (CSI) in forward transmission and using adaptive power technology to reduce turbulence in inverse transmission. In this research, we propose a bidirectional atmospheric channel reciprocity-based adaptive power transmission (CR-APT) technique that lowers the bit error rate of the transmitted signal by using the CSI of the relevant channel. To verify the effectiveness of the technique, a bidirectional atmospheric channel with various turbulence intensities is built in the simulation program, along with various background sounds to vary the channel reciprocity, and the impact of reciprocity on signal transmission is examined. The simulation findings demonstrate that adaptive power transmission with high reciprocity is excellent under the weak turbulence condition, and its future development is promising.

Control Algorithms for a Bidirectional Wireless Power Transmission System at the Redistribution of Energy Resources in a Group of Ground Robots

Redistributing energy resources within a group of ground robots allows for an increase in the reachable workspace area and expands its functional capabilities. The use of wireless energy transfer systems for exchanging energy resources between ground robots reduces the requirements for positioning accuracy and enhances the reliability of the robotic system. This study examines control and management algorithms for a bidirectional wireless energy transfer system when operating as part of a ground robot. A structural diagram of the bidirectional wireless energy transfer module is proposed for integration into the robot’s control system, built on distributed principles. The developed algorithms take into account the specific features of the circuitry solutions of the bidirectional wireless energy transfer system, implemented using an uncontrolled resonant generator. The proposed solutions are tested on a robotics platform. The experiments focus on the process of replenishing the energy resources of one robot with another robot. Energy is transmitted between robots equipped with the same Li-ion battery, which has a nominal voltage of 7.4 V and a capacity of 5 A•h. The battery is charged from 50 % to 90 % capacity with different positioning accuracies of the robots. When there is a displacement of 4 mm and a distance of 4 mm between the receiving and transmitting coils, the charging time was 48 minutes, which is 5 % longer than the wired charging method. The maximum charging time reached 57 minutes with a distance of 15 mm between the robots. The use of bidirectional wireless power transfer for energy exchange between ground robots or for charging robots at a charging station enhances the autonomy of the group’s operation, as energy transfer can be successfully achieved even with low positioning accuracy. The proposed solutions can be used for battery charging and resource redistribution processes in groups of ground and underwater robots.

Topologies and Operations of Hybrid-Type DC–DC Converters Interfacing DC-Current Bus and DC-Voltage Bus

Along with the application of current source converter (CSC), there will be more and more dc-current bus (DCB) for supporting power conversion. The DCB usually provides a common current, and the bidirectional voltage is employed to realize the bidirectional power transmission. In current power system, the dc-voltage bus (DVB) is most widely used DC terminal. Then, it will be foreseeable that topologies which can connect the DCB and the DVB will be urgently needed in the future grid system, such as the dc grid and electric vehicle. However, to connect these two dc terminals, the middle ac power stage is usually required since the power transfer characteristics of these two dc terminals are incompatible. So, the hybrid-type dc-dc converter concept interfacing the DCB and the DVB will be discussed, and the potential hybrid dc-dc converters without or with electric isolation are presented in this paper. Moreover, for these hybrid dc-dc converters, the basic principle for the modulation operation is proposed and analyzed. In addition, by using a non-isolated two-level bidirectional hybrid dc-dc converter and an isolated full-bridge hybrid dc-dc converter as examples, the modulation methods for bidirectional transferred power are illustrated in detail. Finally, simulation and experiment results of the isolated full-bridge hybrid dc-dc converter are used to verify the effectiveness of the proposed hybrid dc-dc converter idea and the corresponding modulation methods.

An Optimized Power-Efficiency Coordinated Control Method for EVs Charging and Discharging Applications

Recently, bidirectional wireless power transmission (BD-WPT) technology has been increasingly used in electric vehicles (EVs) charging and discharging applications to realize interactive energy feedback between EVs and the power grid. Although the efficiency of BD-WPT system has been impressively improved, it still heavily relies on complex control methods. This paper proposes a simple but effective control method to achieve maximum efficiency with zero reactive power. Specifically, a resonance judgment and phase synchronization (RJ&amp;PS) network is employed to ensure the resonance performance and synchronization of the bilateral control signals, which realizes the stead auto-starting of the secondary side and guarantees the disentanglement between power control processes as well. With the help of voltage ratio design and symmetric phase shift between bilateral inverters, the optimization efficiency is well achieved. The results of the experiment and simulation match well, showing the effectiveness of the proposed method in this paper.

Research on Multiple Duty Modulation Scheme in Dual-Active-Bridge-Based Energy Storage System

To ensure efficient energy charging process inside energy storage system, dual-active-bridge (DAB) becomes significant interface circuit because of its bidirectional power transmission ability and simple modulation scheme. In order to achieve DAB efficiency promotion, lower root-mean-square (RMS) current stress and wider soft-switching region are required. Therefore, a multiple duty modulation (MDM) is proposed to achieve aforementioned goals. In this article, detailed derivations of mathematical models for typical MDM modes are demonstrated. Power characteristics and soft-switching performance are also depicted in detailed. RMS current is selected as optimization objective which is implemented by fmincon function in MATLAB. To substantiate the effectiveness of the proposed modulation scheme, a comprehensive comparison among existing works in terms of RMS current and soft-switching region are implemented under different conditions. Finally, a DAB-based experimental prototype is built and effectiveness under proposed modulation scheme is verified.

A Novel Phase-Shift Pulsewidth Modulation Method for Light-Load Bidirectional Resonant Converter

For the bidirectional full-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converter, soft switching of primary side and secondary side switches and bidirectional power transmission are its obvious advantages. However, in the pulse frequency modulation control under light-load conditions, the converter will have the disadvantages of output voltage imbalance and low transmission efficiency. In order to improve the range of voltage regulation and efficiency of <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converter under light-load conditions, a novel phase-shift pulsewidth modulation method is proposed in this article. There is low voltage gain regulation and low operation losses can be achieved under light load. Considering the parasitic parameters and dead time of the switches, the voltage gain of the proposed control method under light load is precise research by using the time domain analysis method. Finally, an experimental prototype of a bidirectional full-bridge <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converter with 200 V input voltage, 200 V output voltage, and a rated power of 800 W is designed. According to the simulation and experimental results, it can be shown that the proposed control method is effective under light-load operation.

Research on optimum extended phase-shift control with minimum peak-to-peak current of DAB converter applied to small DC power grid

The Dual Active Bridge (DAB) DC-DC converter has the ability of bidirectional power transmission and the modulation scheme that is easy to implement, which can ensure the efficient transmission of energy in the system. Therefore, it is often used in various scenarios of small DC grid, such as energy storage, photovoltaic system, electric vehicle charging and so on. The main methods to improve the efficiency of dual active bridge include reducing the effective value of current and widening the soft switching area. Based on the above idea, an optimized extended phase-shift (EPS) modulation strategy is proposed in this paper. The modulation strategy achieves the goal of reducing the effective value of the current through the constraint optimization of the corresponding variables, and then improves the efficiency of the converter. In this paper, the working principles of several typical modulation strategies are introduced in detail, and then the power characteristics and soft-switching characteristics of the new method and other commonly used modulation schemes are analyzed and compared. Finally, the effectiveness of the optimization method for extended phase-shift modulation strategy is verified by the dual active bridge experimental prototype.

A multi-shift phase angle control strategy for bidirectional wireless power transmission system

Using the charging and discharging capability of battery-based loads and a two-way wireless energy transmission system, grid-load balancing can be achieved in both directions. The system can be applied to many locations by deploying power flow in real time. In the scenario of vehicle network interconnection, it realizes peak-shaving and valley-filling to optimize grid dispatching capability; in the scenario of modular satellite interconnection, it realizes load balancing and effectively improves energy utilization. Therefore, a suitable control strategy is needed to precisely change the output power flow and the output power magnitude. A method to coordinate multiple phase shifting angles in the system hierarchy to achieve power flow regulation is proposed for a bidirectional wireless power transmission system with a dual full-bridge topology. In this paper, we first model the bidirectional transmission system and analyze the relationship between each phase shift angle and active and reactive power. The traditional control strategy is optimized by reducing the number of control loop variables and using the system power factor angle instead of the difficult-to-control external phase shift angle, while ensuring the voltage gain for optimal system efficiency. Finally, only two control loops are used to control the direction and magnitude of the output power respectively, and the effectiveness and correctness of the control strategy are verified by using the corresponding simulation experiments to achieve smooth switching of the bidirectional electric power transmission power flow.

Inertia emulation with the concept of virtual supercapacitor based on SOC for distributed storage systems in islanded DC microgrid

One of the main crises that the world will face is the over pollution of the environment due to the use of fossil fuels. This problem will be solved by replacing renewable energy sources (RESs). DC microgrids (DCMGs) provide the ability to exploit all the potential of RESs. But, high penetration of these sources reduces the inertia and damping of the DCMGs. Therefore, it makes DCMG vulnerable to fluctuations and disturbances. This challenge can be addressed by using distributed energy storage systems (DESS) in DCMGs and inertial simulations. To improve the inertia as well as to balance the charge/discharge of the DESS, the concept of a virtual supercapacitor based on the state of charge (SOC) is introduced. Under the proposed control strategy, DCMG inertia is provided and the SOC balance is maintained in charge and discharge mode. Due to the bidirectional power transmission capability, symmetrical structure and considering the protection purposes of dual half-bridge converter (DHB) can be selected. A small signal has also been investigated to analyse the role of virtual inertia in stability. The simulation results in MATLAB/Simulink show the correct performance dynamics and high impact of the proposed scheme compared to conventional schemes.

Backward Step-Up Control Strategy for Bidirectional LLC Resonant Converter

An LLC resonant converter has the advantages of simple structure and soft switching. It can enable bidirectional power transmission, but it is difficult to realize a normalized gain greater than one under backward mode (backward step-up mode). Cascaded dc/dc converters or topological changes can solve this problem, but additional switches and components are required and losses are added. Without changing the LLC resonant converter’s basic topology, this paper proposes a variable duty-cycle control strategy of primary side switches for backward step-up mode. Using variable duty-cycle control, the LC resonant tank can be charged, and then the backward step-up mode can be realized. Soft switching characteristics of some primary side switches and all secondary side switches are guaranteed. In this study, the working principle of an LLC resonant converter under bidirectional control strategy was analyzed, and the backward step-up control was analyzed in detail. The voltage gain and the boundary of continuous conduction mode (CCM) and discontinuous conduction mode (DCM) were derived. A synchronous rectification method related to the backward step-up control is proposed. The control strategy was verified by experiments.

A Novel Bidirectional Five-Level Multimode CLLC Resonant Converter

In order to widen voltage gain of bidirectional on-board charger to meet requirements of electric vehicle with different voltage levels, a novel bidirectional five-level multimode <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant converter is proposed by combining the <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">CLLC</i> resonant tank module (RTM) with the five-level cascaded neutral-point clamp active bridge which is composed of two three-level neutral-point clamp (3L-NPC) bridge arms. Furthermore, the converter can, respectively, establish three voltage gain modes of high, medium, and low to effectively widen voltage gain adjustment capabilities through the fixed-frequency plus phase-shift hybrid modulation independently adopted in each 3L-NPC bridge arm, while soft-switching is realized by phase control between resonant current and input voltage of RTM. Meanwhile, the key parameters of RTM would be symmetrically designed to make bidirectional power transmission characteristics, which become consistent based on soft-switching and monotonic voltage gain control. Finally, according to the simulation platform and experimental prototype, it can be shown that the practical voltage gain is close to the theoretical design gain and converter has good dynamic performances after realizing soft-switching in each mode.

A Sharing-Branch Modular Multilevel DC Transformer With Wide Voltage Range Regulation for DC Distribution Grids

As the key equipment in dc distribution grids, dc transformer (DCT) suffers from low power density caused by a large number of submodules (SMs). Hence, this article proposes a novel DCT for the interconnection of medium-voltage dc (MVdc) and low-voltage dc (LVdc) distribution grids, which adopts a series-connected half-bridge SM branch (SSB) on MV-side to achieve low voltage stress of devices and reduce the number of SMs. Quasi square wave modulation strategy and phase-shifted control are employed to realize bidirectional power transmission control and zero-voltage switching (ZVS) for all switches. Furthermore, in order to ensure low current stress and ZVS within wide voltage range, a certain number of SMs are constantly inserted or bypassed to achieve voltage matching. Besides, smooth transition control strategy is employed to avoid current spikes caused by abruptly bypassing or inserting SMs. Based on the theoretical analysis, design consideration and control strategy are elaborated. Finally, a 500&#x00A0;kW&#x002F;6&#x2013;12&#x00A0;kV&#x002F;750&#x00A0;V simulation model and a 2&#x00A0;kW prototype are built to verify the proposed DCT.

Unified Modeling, Analysis, and Design of Isolated Bidirectional CLLC Resonant DC–DC Converters

Due to the bidirectional power transmission, high power density, and high efficiency, bidirectional CLLC resonant converters are attracting more and more research attention in electric vehicles and energy storage systems. However, the existing models are difficult to unify the bidirectional circuits to analyze and design the circuit factors, and thus the parameter design approach and bidirectional synchronous rectification (SR) become rather complex and cumbersome. Especially in asymmetric parameter design, a lot of calculations or iterations are needed, which seriously increase the difficulty of design. To address this concern, a bidirectional unified modeling, analysis, and design method is proposed in this article. By selecting appropriate and quantitative bidirectional circuit factors, this model unifies the forward and reverse circuits and establishes the relationship between them, which greatly simplifies the calculation or iteration of the parameter design and the complexity of bidirectional SR. In addition, this parameter design method makes the bidirectional gain reach a higher range and reduces the range of bidirectional switching frequency. Finally, this unified modeling, analysis, and design method is verified in bidirectional CLLC resonant converters including symmetrical full-bridge, asymmetrical full-bridge, symmetrical half-bridge, and asymmetrical half-bridge CLLC, respectively.

Toward integrating bidirectional multiband data and power transmission using double clad optical fibers for the next generation disaster resilient managing communication systems

AbstractDuring the cyclones and floods, all through the nation, the telecommunication network services were the most hit, leaving numerous individuals stripped from the ability to contact their precious ones. This paper is to demonstrate potential communications during such power blackouts. The double clad fiber is used for optically powering, transmitting and receiving the data to and from the remote antenna units by the Bidirectional method. The RoF multiband signals such as baseband, millimeter wave, and microwave, are transmitted and received bidirectionally by the single mode core, and power in outer clad to the Remote Antenna Unit. By the proposed RoF link transmission of 1 Gbps over a 100‐Km DCF with an optical power of about12.0 W is achieved.

Multitime Scale Frequency Regulation of a General Resonant DC Transformer in a Hybrid AC/DC Microgrid

The high-frequency resonant dc transformer (DCT) becomes popular in hybrid ac/dc microgrids, thanks to its good bidirectional power transmission (PT) ability and high power density. However, its application is limited by either the complex systematic control or the complicated parameter design. To solve this problem, in this article, a multitime scale frequency regulation approach is put forward for a general CLLC-DCT (GCLLC-DCT). By establishing the general model of the resonant DCT, the relationship between the transmitted power and the resonant frequency is derived at first. Afterward, the power trigger mechanism is introduced to assist the implementation of the proposed approach. If the long-time scale control is triggered, only once calculation based on the PT requirement will be introduced to avoid redundant computations. If the short-time scale control is triggered, the frequency regulation based on the voltage conversion gain feature of GCLLC-DCT will be executed till it reaches a new steady state, which is beneficial to ensure the real-time control precision. The cooperation of the short-time and long-time scale control is also presented to make the proposed approach easily implement at hybrid ac/dc microgrids. The lab-scale prototype of GCLLC-DCT has been set up based on a hybrid ac/dc microgrid to verify the superiority of the proposed approach.

Battery Charger with Bidirectional Power Transmission

The gradual reduction in price of electric batteries contributes to their wider use in autonomous and centralized power supply systems as a backup source of electricity and increase the share of electric vehicles. In the paper the conditions for increasing the efficiency of electric vehicle batteries, in particular in the framework of the concept of V2G (Vehicle to Grid) as a drive for the organization of autonomous power supply systems are analyzed. It is shown that this is possible only with the simple integration of batteries into the system, flexibility, and a wide range of modes that have to be provided by unified charge-discharge devices. Such charging devices have to have such features: a wide range of input and output voltage parameters; correction of the input power factor; the ability to take the maximum power from renewable energy sources; high energy efficiency. A review of possible topologies for a charger with bidirectional power transmission and a bridge converter with soft switching of transistors at zero voltage, which has a high efficiency, galvanic isolation and the ability to correct the shape of the current. The modes of operation of the converter are analyzed and conditions of soft switching is obtained. It is shown that soft switching is valid for current that is not less than minimal one. Efficiency of the converter with soft commutation is compared with a similar converter with rigid commutation of transistors. It is shown that static losses in converter with soft commutation it higher than in the rigid one. So, the proposed converter should be used if the increase in static losses is compensated by the lack of dynamic losses. Additional feature of the converter is that the regulation of the output voltage of the converter with soft switching is carried out according to the law of frequency-pulse modulation with a constant pause duration, where the pause duration is determined by the period of resonant processes of the converter. The model of the converter in Matlab Simulink is built and it is shown that the efficiency of the proposed converter topology is 10-15% higher, which together with the possibility of sinusoidal current with THD ≈ 20% and two-way transmission energy indicates the feasibility of its use as a charger for electric vehicles under the concept of V2G. However, it should be noted that the use of LCL filter creates a phase shift between voltage and current and degrades the THD value. To improve the shape, it is possible to use specialized laws of modulation [or to use modular converters, which allow to obtain a continuous current shape and reduce the volume of the filter.