Bidirectional AC-DC Converter Research Articles

Bidirectional H8 AC–DC Topology Combining Advantages of Both Diode-Clamped and Flying-Capacitor Three-Level Converters

A three-level bidirectional ac–dc converter with H8 topology is proposed to combine the advantages of both neutral-point clamped and flying-capacitor (FC) three-level converters for medium-voltage (MV) ac–dc solid-state transformer (SST) applications. The innovative H8 converter features self-balanced capacitor voltage, common-mode voltage elimination, and small capacitance of the FCs. The proposed carrier-based modulation enables the H8 converter to operate under both active and reactive power conditions. A 10-kVA ac–dc converter prototype with 1.7-kV SiC MOSFETs and 3.3-kV SiC diodes verifies the feasibility and advantages of the proposed topology and the modulation method. The capacitance of the FCs in the H8 converter is reduced by 45 times compared to that of the FC converters. The H8 converter efficiency is tested up to 99% at 2-kV dc voltage. The proposed H8 converter is suitable for the next-generation PV inverter, grid-forming inverter, MV fast charger, and SST applications.

A Single-Stage Bidirectional AC–DC Converter Feasible for Onboard Battery Chargers

This article proposes a novel topology of a single-stage single-phase bidirectional ac–dc converter with high-frequency isolation feasible for onboard chargers. Its structure uses the interleaving concept associated with an autotransformer that is responsible for sharing the current stresses and increasing the current ripple frequency, as well as obtaining a five-level voltage waveform. A theoretical study of the structure, the operation principle, and a detailed loss analysis are performed. The mathematical analysis and control strategy are validated through simulations and a 1-kW small-scale experimental prototype. The topology is also redesigned to 6.6 kW and a comparison with a traditional two-stage solution usually employed in onboard chargers is presented, thus demonstrating that the proposed structure is competitive with other similar counterparts. Despite the proposed converter presents higher capacitive losses, when operating at 200 kHz, it has reduced volume of magnetics, resulting in an efficiency of 95.71%. If the proposed converter is designed for the operation at 80 kHz, a similar magnetic volume results when compared with the two-stage solution, but with a higher efficiency of 96.36% and avoiding the volume of resonant capacitors.

An autonomous flexible power management for hybrid AC/DC microgrid with multiple subgrids under the asymmetric AC side faults

In this paper, an autonomous flexible power management is proposed for hybrid AC/DC microgrid with multiple subgrids under the asymmetric AC side faults. First, based on the double-frequency disturbance of the DC common bus (DCB) voltage caused by asymmetric AC side faults, this paper analyzes the characteristics of the transmission power of bi-directional DC/DC converters (BDCs) and bi-directional AC/DC converters (BACs) adopt the normalized droop control (NDC). Then, interactive relationships between DCB voltage and DC subgrids bus voltage, AC subgrids bus frequency are derived. According the interactive relationships, suppression links combined with virtual component adjustment coefficients are designed for BDCs and BACs to eliminated the double-frequency disturbance of the transmission power. Meanwhile, the support links is added to the power control of BACs to maintain the frequency automatically once the energy storage (ES) in faulty AC subgrid becomes unavailable due to the line protection. Furthermore, with the autonomous flexible power management, the total load demand proportionally shared among the remaining subgrids can be accordingly attained when faulty AC subgrid or its local ES quit the operation. Finally, the system stability analysis is given and the results of Hardware-In-Loop tests verify the correctness and effectiveness of the proposed autonomous flexible power management.

A Control Strategy to Smooth Power Ripple of a Single-Stage Bidirectional and Isolated AC-DC Converter for Electric Vehicles Chargers

This paper proposes a single-stage AC-DC rectifier with power factor correction (PFC), high-frequency isolation and bidirectional power conversion capability for on-board battery charger (OBC) applications. The proposed converter is based on the interleaving technique and the Dual Active Bridge (DAB) operation, applying the phase-shift control to regulate the power flow. In addition to topology, this article presents a control strategy for reducing low-frequency power ripples transferred to the secondary side without any additional component and hence maintaining overall size and cost. The single-phase OBC can interchange active power with the grid to charge batteries while performing grid-to-vehicle (G2V) functionality or transferring energy back to the grid via vehicle-to-grid (V2G) mode. The theoretical analysis of the converter including modulation strategy and feedback control scheme are presented. The proposed topology and control strategy have been verified by experimental results of a 650 W SiC-based prototype.

A Bidirectional Grid-Connected DC–AC Converter for Autonomous and Intelligent Electricity Storage in the Residential Sector

Controlling the cost of electricity consumption remains a major concern, particularly in the residential sector. Smart home electricity management systems (HEMS) are becoming increasingly popular for providing uninterrupted power and improved power quality, as well as for reducing the cost of electricity consumption. When power transfer is required between a storage system and the AC grid, and vice versa, these HEMS require the use of a bidirectional DC–AC converter. This paper emphasizes the potential value of an almost unexplored topology, the design of which was based on the generation of sinusoidal signals from sinusoidal half waves. A DC–DC stage, which behaved as a configurable voltage source, was in series with a DC–AC stage, i.e., an H-bridge, to achieve an architecture that could operate in both grid and off-grid configurations. Wide bandgap power switches (silicon carbide metal-oxide-semiconductor field-effect transistors [MOSFETs]), combined with appropriate control strategies, were the keys to increasing compactness of the converter while ensuring good performance, especially in terms of efficiency. The converter was configured to automatically change the operating mode, i.e., inverter or rectifier in power factor correction mode, according to an instruction issued by the HEMS; the latter being integrated in the control circuit with automatic duty cycle management. Therefore, the HEMS set the amount of energy to be injected into the grid or to be stored. The experimental results validate the operating modes of the proposed converter and demonstrate the relevance of such a topology when combined with an HEMS, especially in the case of an AC grid connection. The efficiency measurements of the bidirectional DC–AC converter, performed in grid-connected inverter mode, show that we exceeded the efficiency target of 95% over the entire output power range studied, i.e., from 100 W to 1.5 kW.

A simplified methodology for renewable energy integration and harmonic current reduction in hybrid micro grid

ABSTRACT Due to advancements in power electronics devices and the support of improvements on both the power supply and load sides, Distributed Energy (DG) is rapidly being connected to the grid in the form of AC/DC Hybrid Micro-Grid (HMG). The development will result in a substantial change in the network topology, new design problems for the micro-grid control unit, and new requirements for the simulation testing laboratory. The Bidirectional AC-DC converter (BAC) is necessary for hybrid microgrids to provide voltage stableness and power equilibrium between the AC and DC grids. To suppress the harmonic current control approach, an enhanced Fryze-Buchholz Depenbrock (FBD) current harmonic detection technique is integrated with droop control in this paper. This proposed system not only performs the power transformation but also minimizes harmonics. While considering non-linear load, the proposed system yields the control ability for regulating the converter to eliminate the harmonics of 74.41% in the grid current. While incorporating the HMG in the proposed system, the control strategy decreases 90.3% and 89.4% of reactive power in both linear and non-linear loads. The obtained simulation results are used to confirm the feasibility and effectiveness of the control scheme.

Performance Evaluation of Single-Phase On-Board Charger with Advanced Controller

Abstract: The increasing mobility of electric vehicles has inspired vehicle growth to power grid technology. Such as vehicle to grid technology allows to transfer the power from the electric vehicle battery to the power grid. This enable speak load shaving, load leveling, voltage regulation, and improved stability of the power system. To develop the vehicle to grid technology requires a specialized EV battery charger, which permits the bi-directional energy transfer between the power grid and the electric vehicle battery. There is a specific control strategy used for a bi-directional battery charger. The proposed control strategy is used for charge and discharge battery of EV. The charger strategy has two parts: 1) Bidirectional AC-DC Converter in two-way Communication System. 2) Bidirectional DC-DC Buck-Boost Converter. There are two modes of operation for a bidirectional ac-dc converter: for G2V, rectifying mode is used, and for V2G, inverter mode is used. The suggested charge strategy not only allows for two-directional power flow but also provides power quality management of the power grid. Fuzzy logic controller (FLC) transforms linguistic control topology evaluations knowledge into an automated control topology using FLC. The FLC is more stable, has less overshoot, and responds quickly. The operation of a standard PI controller and a FLC was compared in this study using MATLAB and Simulink, and different time domain characteristics were compared as toshow that the FLC had a smaller overshoot and a faster response than the PI controller. Keywords: Bi-directional AC-DC converter, bi-directional DC-DC Buck-Boost converter, electric vehicles (EVs), on-board battery charger (OBC), grid to vehicle (G2V), vehicle to grid (V2G).

Design of power quality enhanced sustainable bidirectional electric vehicle charging station in distribution grid

Integration of electric vehicle charging stations with the distribution grid rises the grid current harmonics. In this article, a sustainable bidirectional electric vehicle charging station in the distribution grid is designed. The quality of the charging station is improved by employing an adaptive neuro-fuzzy controlled distribution static compensator. The proposed sustainable bidirectional electric vehicle charging station comprises a 3-phase bidirectional ac-dc converter, bidirectional chopper, distribution static compensator and a lithium-ion battery. The bidirectional converters facilitate power flow from grid to vehicle and vice-versa. The decoupled current and dc voltage control method has been implemented for a 3-phase bidirectional converter. A multi-step current control strategy is exploited to control the bidirectional chopper. Distribution static compensator alleviates the grid current harmonics. The proposed system performance is evaluated with two kinds of controllers such as proportional – integral and adaptive neuro-fuzzy controller based on the distribution static compensator dc-side voltage and grid current harmonics. The proposed system has been modelled in MATLAB/Simulink and validated through software in the loop setup comprising of dSPACE (DS1202) hardware. The validated results show that the adaptive neuro-fuzzy controller provides better performance.

Grid Management through Vehicle-To-Grid Technology

This research paper is based on a project which is a prototype on a smaller level of integrating vehicle-to-grid technology at the residential and commercial levels which can be expanded in future with the help of bi-directional AC-DC power converters and Control systems. Vehicle-to-Grid is a technology that allows energy to be supplied back to the power grid from the battery of an electric car for fulfilling the excess demand on the grid. It is depicted in the prototype with the help of TP charging module and embedded system i.e. Arduino to manage the ever-increasing energy demand from the grid. With the increasing environmental problems, modern automobile technology is innovating in the field of Electric Vehicles (EV) with lesser pollution and better efficiency. This has attracted a lot of attention, but the major hindrance faced is the availability of energy required to maintain the grid is resonance. We can overcome this by vehicle-to-grid technology in smart parking systems. When the EV is parked, energy may be drawn out or supplied to the EV through the grid depending upon the requirements of the grid and the vehicle’s battery. The implementation of this technology enables the stored energy in the electric vehicle to be transferred to the power grid and vice-versa.

An adjustable gain three port converter for battery and grid integration in remote location microgrid systems

The battery-grid integration (BGI) is the crux of microgrid systems that not only performs the energy management but also coordinates distributed energy resources and loads. The prevailing BGIs are either individual power converters based, which cause low efficiency and high cost, or multiport converter (MPC) based, which involve a higher component count and/or the lower voltage limit restriction in the DC port. With the increased penetration of distributed energy resources, the demand for MPCs with a wider buck-boost voltage gain capability is unavoidable. They can be used to interface low voltage sources like fuel cells, photovoltaic panels, batteries, etc. To perform the basic functionalities in BGI converters, like the power transfer from the storage to the grid and vice versa at different working conditions, the bidirectional capability in DC and AC ports is mandatory. This paper proposes a high voltage gain, bidirectional buck-boost port based hybrid MPC, called as an energy cushion multiport converter (ECMPC), for the integration of batteries with the single-phase AC microgrid (SPACMG). The ECMPC has three ports, among them one is the bidirectional AC port for the grid, the second one is the bidirectional DC port for the battery, and the last one is a DC output port for the common usage. The modes of operation with an appropriate switching sequence is detailed and a control scheme is also suggested. The performed comprehensive simulation analysis guides the component selection and the design of the converter. The critical comparison of the suggested converter with the prevailing single-phase bidirectional DC-AC converters being employed in the BGI is also presented. The theoretical study is supported by a laboratory corroboration. The system is managed for a minimal energy wastage through anew suggested minimal wastage energy management system (MWEMS). The system in the entirety is implemented and controlled by an ALTERA field-programmable gate array, ALTERA QUARTUS II 12.0SP2 processor.

Experimental Validation of an Advanced Load-Shift System Operating as Shunt Active Power Filter

This paper presents a load-shift system with advanced functionalities for the power grid. When compared with the conventional approach, an advanced load-shift system allows the compensation of power quality problems on the power grid side, namely problems related to current harmonics, current imbalances, and low power factor. The advanced load-shift system is composed by a bidirectional ac-dc converter to interface the power grid and by a bidirectional dc-dc converter to interface an energy storage system. Since the main innovation is related with the power grid interface, the focus of this work is on the analysis of the ac-dc converter, which is based on a three-phase four-leg voltage source converter. A theoretical study and the details concerning the control algorithm are presented and discussed along the paper. A laboratory prototype of the advanced load-shift system was developed, and the main details of implementation are described in the paper. Experimental results obtained with the developed prototype prove that the advanced load-shift system contributes for the technology progress in this area, validating a new operation concept concerning the power quality on the power grid side. For all the operation modes, the system operates with high power factor and the currents on the power grid side are balanced with a low total harmonic distortion and in phase with the respective power grid voltages.

Integrated DC-AC and AC-DC converter using H-converter for wide range voltage applications

PurposeThis paper aims to propose Hidden Converter (H-Converter) combined with dual port 3Ø inverter for energy storage application to produce wide range of voltage. Some of the application required wide range of voltages, but problem from E-chopper is either boost or buck mode of operations, both modes are not possible. To overcome this drawback, H-Converter is combined with dual port 3Ø inverter controlled by carrier-based pulse width modulation (CB-PWM) technique is added with zero sequence injection.Design/methodology/approachHidden converter is a bidirectional DC-DC chopper used to convert fixed DC to variable DC and vice versa in both buck and boost modes of operations. Dual port inverter is combined with hidden DC-DC converter can produce wide range of voltages.FindingsThe bidirectional DC-AC converter requires less power for processing and consumes less power losses by using modest carrier built- pulse width modulation scheme through proposed zero structure addition.Originality/valueBy using this proposed strategy H-Converter can produce wide range of voltage in both the sides and mostly power is processed in the 3Ø inverter with a one stage conversion with less power loss. As a result, with one stage power conversion has more efficiency because of less power loss. This proposed converter has designed by analysis, and the real time result is tested in an experiment.

A Common DC-Bus-Configured Traction Motor Emulator Using a Virtually Isolated Three-Phase AC-DC Bidirectional Converter

An industrial drive testing, with a `real-machine' can pave way, for some serious issues to test-bench and motor. A slight disturbance in control logic amid testing, can damage the physical machine or drive. Such dangerous testing conditions can be avoided by supplanting real motor with a power electronic converter based `Motor Emulator' (ME) test-bench system. The conventional ME comprises of two-stage three-phase AC-DC-AC conversion with first-stage AC-DC as emulator and second-stage DC-AC as regenerating unit. This two-stage power conversion, require independent control algorithm, burdening control complexity as well as the number of power electronic switches are quite significant. Hence, to economize and downsize conventional multistage ME system, this paper experimentally validates a common DC-bus-configured ME system with only the AC-DC regenerative emulator stage. A virtually isolated bidirectional two-level three-phase AC-DC converter is proposed as the regenerative emulator converter in a common DC-Bus-configured ME system. The Proposed converter's operating principle along with mathematical design and control strategy are also presented. To validate the operation of the proposed converter as a common DC-bus-configured emulator, a permanent magnet synchronous motors (PMSM) of 7.5 kW is emulated and its experimental results are presented here.

A Bidirectional Isolated Integrated AC–DC Converter Based on an Interleaved 3-Level T-Type Power Converters

This paper presents an integrated single-phase bidirectional ac–dc converter based on a dual-active-bridge (DAB) topology. The primary side is based on a multi-state switching cell (MSSC) with a T-type (TNPC) cell, which is composed of two three-level interleaved legs and coupled inductor, while the secondary side is a single-phase full-bridge (FB). Moreover, a comparative analysis between an isolated ac–dc converter with a neutral point clamped (NPC) converter on the primary side is presented. The basic converter operating principles and experimental results of a 850 W prototype are presented in order to validate the theoretical analysis. The control strategy is implemented on the TMS320F28379D DSP. The proposed topology achieves a maximum efficiency of 91.40% at 300 W output power, and 89.40% at rated power. From the experimental results, it can be stated that the converter based on the T-type topology is more efficient than the structure based on the NPC.

Design and Implementation of an Energy-Management System for a Grid-Connected Residential DC Microgrid

The design and implementation of an energy-management system (EMS) applied to a residential direct current microgrid (DC-µG) is presented in this work. The proposed residential DC-µG is designed to provide a maximum power of one kilowatt by using two photovoltaic arrays (PAs) of 500 W, a battery bank (BB) of 120 V–115 Ah, a supercapacitor module of 0.230 F and a bidirectional DC–AC converter linked to the AC main grid (MG). The EMS works as a centralized manager and it defines the working operation mode for each section of the DC-µG. The operation modes are based on: (1) the DC-link bus voltage, (2) the generated or demanded power to each section of the DC-µG and (3) the BB’s state of charge. The proposed EMS—during the several working operation modes and at the same time—can obtain the maximum energy from the PAs, reduce the energy consumption from the main grid and keep the DC-link bus voltage inside a range of 190 V ± 5%. The EMS and local controllers are implemented by using LabVIEW and NI myRIO-1900 platforms. Moreover, experimental results during connection and disconnection of each DC-µG sections and different on-the-fly transitions are reported, these results focus on the behavior of the DC bus, which shows the DC bus robustness and stability. The robustness of the DC-µG is demonstrated by maintaining a balance of energy between the sources and loads connected to the DC bus under different scenarios.

Study on Novel Bidirectional AC-DC Converter Circuit of the Wireless Charging for Portable Devices

In this paper, a novel symmetrical topology for the small power high frequency bidirectional AC-DC converter has been proposed, which is applied to the bi-directional wireless power transmission system based on the magnetic coupling resonance. It has dual functions of the inverter and rectifier. The research is mainly reflected in the following aspects: First, based on analyzing the principle of the wireless power bidirectional transmission technology, the operation mechanism of the topology circuit is analyzed emphatically. Second, the feasibility of the designed converter is verified by the simulation of the PSPICE software. Third, the hardware system has been operated at 200 kHz in the modes of the constant current, the constant voltage and the constant resistance, respectively. The results show the maximal output power of the designed circuit is 7.8 W, meeting the design requirement. This circuit has the advantages of the simple circuit structure and simple control. It's suitable for the bidirectional wireless power charging of the small power portable devices.

Bidirectional DC–AC Converter-Based Communication Solution for Microgrid

Abstract The communication system of a microgrid can transfer the information of electricity price, power consumption and so on between users and the control centre. This capability is of great significance to improve the efficiency and sustainability of power facilities. In this paper, a bidirectional DC–AC converter topology is proposed to achieve the composite transmission of power and signals in microgrids. Since the transmitted signals are modulated by power switches of converters and integrated into the currents, the cost of signal couplers can be saved and the circuit structure can be simplified. In order to verify the feasibility of the proposed method, a simulation model of the proposed converter is implemented in MATLAB/Simulink. With the power supply frequency of 50 Hz, when the converter operates in the inverter mode and rectifier mode, the data transmission rate can reach 120 bit/s and 48 bit/s, respectively.

Research and Simulation of DC Microgrid Three-Phase AC-DC Converter Control Strategy Based on Double Loop

The new voltage and current double loop control strategy is proposed to solve the DC microgrid bus voltage fluctuation caused by loads fluctuation, parameters perturbation and unbalanced three-phase power supply. Firstly, the $dq$ axis mathematical model of three-phase AC-DC bidirectional converter in DC microgrid is analyzed and established, and then the controllers are designed according to the $dq$ axis mathematical model. The outer loop is a voltage loop based on variable gain linear extended state observer (VGLESO) and sliding mode theory. VGLESO can not only effectively overcome the problem of peak output of traditional high-gain LESO in the initial stage of operation, and ensure that the system has good startup characteristics, but also quickly track and compensate the total disturbance of the system without additional current sensors. The inner loop is a current loop based on adaptive PI, which can eliminate the influence of system parameters perturbation on bus voltage and improve the system’s adaptability. Under the action of the inner and outer loops, the system has good dynamic and static characteristics. Finally, the feasibility and correctness of the control strategy are verified by Matlab/Simulink.

Stability Investigation of Bidirectional AC-DC Converter Considering Operating Conditions

This paper investigates the stability performances of bidirectional ac-dc converters considering operating conditions based on the small-signal impedance model. It finds that the converter has different stability margins when working in different operating conditions (including inverter mode and rectifier mode, as well as generating/absorbing reactive power), which should be taken into account in the design of the converter for bidirectional energy conversions. To have an intuitive understanding of the instability mechanisms of bidirectional converters in different operating conditions, the concept of positive feedback is used. It finds that with phase-lock loop (PLL) and dc-link voltage control loop (VCL), positive feedback effects appear when the converter operating in different conditions; and the influencing mechanisms of the parameters, including control parameters of PLL, inner current and outer voltage controllers and power ratings, on the converter's stability can be explicitly identified by the positive feedback gains. And it indicates that reducing the values of the parameters along the positive feedback paths will be a practical way to enhance the converter's stability. The theoretical stability analysis results are verified by simulations and experiments.

Critical-Conduction-Mode-Based Soft-Switching Modulation for Three-Phase PV Inverters With Reactive Power Transfer Capability

In this article, an improved critical-conduction-mode-based soft-switching modulation technique is proposed for three-phase photovoltaic (PV) inverter applications under not only the unity power factor operating condition, but also nonunity power factor operating condition in order to reduce switching loss. With the proposed improvements, for the typical power factor range from the 0.8 lagging condition to the 0.8 leading condition in PV applications, zero-voltage-switch turn- on or valley drain–source voltage turn- on is achieved, which is especially beneficial for silicon carbide (SiC)-based systems at a high switching frequency operation to achieve not only high power density but also high efficiency. The proposed modulation technique is digitally implemented with one low-cost microcontroller. The capability of reactive power transfer and benefits of the improved modulation for achieving soft switching under nonunity power factor conditions are experimentally verified on a SiC-based three-phase bidirectional ac–dc converter prototype. The tested peak efficiency is 98.9% under the unity power factor operation, and above 98.0% within the aforementioned typical power factor range in PV applications, at above 300 kHz switching frequency operation.