Multi-port DC Research Articles

Multi-Port DC-AC Converter With Differential Power Processing DC-DC Converter and Flexible Power Control for Battery ESS Integrated PV Systems

Due to the unpredictable and fluctuating nature of solar photovoltaic (PV), energy storage systems (ESS), such as batteries, are always integrated with PV systems to smooth the power supply. In this article, a multiport dc–ac converter (MPC) with differential power processing dc–dc converter (DPPC) is proposed for battery ESS integrated PV systems. The MPC is capable of regulating most of active power among PV, battery and ac grid, and only the differential power (partial power) needs to be handled by the dc-dc converter. Hence, the major merits of higher integration, higher efficiency, and lower cost can be achieved by the proposed configuration. A new cooperative control scheme for the MPC and DPPC is investigated, aiming at realizing flexible active power flow. Besides, a modified space vector pulsewidth modulation is developed for the MPC, taking into the consideration of the voltage variation of both PV and battery. The active power controllability of the MPC and the power rating of the DPPC are quantitatively analyzed. The effectiveness of the proposed configuration, control and modulation schemes is validated by experimental results.

A switching capacitor based multi‐port bidirectional DC–DC converter

This paper introduces a novel bidirectional multi-port DC–DC converter recommended for electric vehicle applications. The proposed structure has three ports with bidirectional features which can be operated in both step-up and step-down modes. This converter can supply the load from two independent voltage sources and can obtain a high voltage conversion ratio in both step-up and step-down operations. The low voltage stress throughout the power switches, high efficiency, and low components count are the characteristics of the proposed topology. For demonstrating the proposed structure's performance, the principle of operation modes, steady-state analysis, and comparison results with other similar works are provided. Finally, an experimental prototype is built with a 120 W power level at 50 kHz operating, which validates the suggested converter's effectiveness and bidirectional trait. The suggested converter's efficiency in boost and buck mode is obtained about 94.2% and 94.37%, respectively that makes this converter to be used in renewable energy systems and electric vehicles with hybrid energy sources.

An Integrated Multiport DC - DC Converter for Renewable Energy System

An Integrated Multiport DC - DC Converter for Renewable Energy System

A Multi-port DC Solid-state Transformer for MVDC Integration Interface of Multiple Distributed Energy Sources and DC Loads in Distribution Network

In traditional DC distribution networks with both a low-voltage DC (LVDC) and a medium-voltage DC (MVDC) bus, DC units are connected to the LVDC bus through LVDC converters. In this approach no galvanic isolation is provided and two power conversion stages are needed between the DC units and the MVDC grid, hence leading to a high number of converters and higher costs. To address these shortcomings, this paper proposes a novel multi-port DC solid-state transformer (MDCSST) to interface DC units directly to the MVDC bus. Multiple modules are connected in series on the medium voltage side to the MVDC bus, whereas DC units are independently connected on the low-voltage side of the MDCSST. Compared to a traditional DC distribution network, the proposed scheme connects DC units to the MVDC bus without an extra converter or an LVDC bus, therefore saving cost and reducing the number of converters. In addition, DC units are galvanically isolated by high-frequency transformers. The main challenge of the MDCSST is to resolve the voltage-imbalance problem on the MVDC side which is caused by the DC units power differences. An LC-branch is used to balance the voltages among the modules and to transfer their differential powers.

Multiport bidirectional DC–DC converter for PV powered electric vehicle equipped with battery and supercapacitor

This study presents a novel quasi-Z-source converter integrated isolated multiport bidirectional DC–DC converter topology for a photovoltaic (PV) powered and battery/supercapacitor buffered electric vehicle (EV). The proposed topology can provide uninterrupted power to the electric motor of EV and regain the braking energy with the capability of bidirectional power flow. The system integrates quasi-Z-source and H-bridge converters with an existing switch. Thus, a four-port converter is achieved without any need for individual converters or additional switches. Besides, the high-gain quasi-Z-source converter allows the reduction of the rated voltages of the battery and supercapacitor packs, as well as allows using a high-frequency transformer (HFT) with a low turn ratio. The isolation between ports is provided by a secondary centre-tapped HFT. The secondary side of the HFT is equipped with a controlled full-wave rectifier to provide bidirectional power flow. In addition, a power flow management and corresponding control scheme are suggested. The performance of the proposed system has been evaluated for different operational changes. Results show that it properly performs the power flow between the ports under steady-state and transient conditions. The power flow capabilities and efficiency values validate the viability and effectiveness of the proposed system.

Multicell Reconfigurable Multi-Input Multi-Output Energy Router Architecture

This article presents a multicell reconfigurable multi-input multi-output (MR-MIMO) power conversion architecture for multiport applications such as multisource energy router, battery balancer, and photovoltaic optimizer. The MR-MIMO architecture couples a large number of modular dc–ac cells with a single magnetic core which processes multiway bidirectional power flow. The system voltage and current ratings can be linearly extended and reconfigured by connecting the dc–ac cells in series or parallel. The MR-MIMO architecture decouples the voltage rating and current rating of the basic cells, and offers much lower device stress than traditional wide-operation range multiport dc–dc converters. The key contributions of this article include: 1) a multicell reconfigurable 12-winding MIMO converter with high performance across a wide range; 2) a hybrid time-sharing and phase-shift control strategy; and 3) a systematic method of designing multiwinding PCB transformers. The MR-MIMO architecture allows one power converter being used for multiple purposes through software reconfiguration. The work presented in this article proved that it is possible to gain significantly design flexibility in a multicell reconfigurable architecture without sacrificing the efficiency or power density. A 500-W 4-port energy router with 12 modular cells and a 12-winding transformer has been built and tested to verify the effectiveness of the proposed MR-MIMO architecture. The energy router maintains over 95% efficiency across a wide range of input and output voltage options.

Soft-Switching Solid-State Transformer With Reduced Conduction Loss

Solid-state transformers (SSTs) are a promising solution photovoltaic (PV), wind, traction, data center, battery energy storage system (BESS), and fast charging electric vehicle (EV) applications. The traditional SSTs are typically three-stage, i.e., hard-switching cascaded multilevel rectifiers and inverters with dual active bridge (DAB) converters, which leads to bulky passives, low efficiency, and high electromagnetic interference (EMI). This article proposes a new soft-switching solid-state transformer (S4T). The S4T has full-range zero-voltage switching (ZVS), electrolytic capacitor-less dc link, and controlled dv/dt, which reduces EMI. The S4T comprises two reverse-blocking current-source inverter (CSI) bridges, auxiliary branches for ZVS, and transformer magnetizing inductor as a reduced dc link with 60% ripple. Compared with the prior S4T, an effective change on the leakage inductance diode is made to reduce the number of the devices on the main power path by 20% for significant conduction loss saving and retain the same functionality of damping the resonance between the leakage and resonant capacitors and recycling trapped leakage energy. The conduction loss saving is crucial, being the dominating loss mechanism in SSTs. Importantly, the proposed single-stage SST not only holds the potential for high power density and high efficiency but also has full functionality, e.g., multiport dc loads integration, voltage regulation, and reactive power compensation, unlike the traditional single-stage matrix SST. The S4T can achieve single-stage isolated bidirectional dc-dc, ac-dc, dc-ac, or ac-ac conversion. It can also be configured input-series output-parallel (ISOP) in a modular way for medium-voltage (MV) grids. Hence, the S4T is a promising candidate for the SST. The full functionality, e.g., voltage buck-boost, multiport, etc., and the universality of the S4T for the dc-dc, dc-ac, and ac-ac conversion are verified through the simulations and experiments of two-port and three-port MV prototypes based on 3.3 kV SiC mosfets in dc-dc, dc-ac, and ac-ac modes at 2 kV.

Integrated Multiport DC Power Flow Controller With DC Circuit Breaker

Power flow controllers and circuit breakers are important devices in a DC grid, and combining them and expanding their ports can save many components. This paper proposes an integrated multiport DC power flow controller with a DC circuit breaker that can achieve power flow control and fault removal on multiple DC lines during steady and fault states, respectively. First, the device's topology based on modular multilevel converters is proposed, and the principles of power flow control and self-power balance based on bridge arm voltage are introduced. Second, it is improved by adding a fault removal capability. The equivalent circuit and fault currents in different time sequences are analyzed, and the component parameter selection method is designed. Third, in the PSCAD/EMTDC, the power flow control and fault removal capabilities are verified using three conditions: flow control, line fault, and bus fault. Finally, the number of components and steady-state losses are analyzed. Overall, the proposed device has power flow control and fault removal functions as well as a certain limiting effect on the fault current, which greatly reduces the system construction cost.

A Multi-Port Current-Limiting Hybrid DC Circuit Breaker

Recently the hybrid multi-port DC circuit breaker (MP-DCCB) is becoming popular in protecting HVDC grids, thanks to their reduction of power electronics devices. In this paper, an enhanced multi-port current-limiting DCCB (MP-CLCB) for multiple line protection is proposed. The integrated fault current limiter (FCL) inside the MP-CLCB can clear the fault faster with slightly increased costs. To reduce the energy dissipation requirement for the surge arresters caused by the newly added current-limiting path, an energy transfer path which provides a loop with the inductors during the current decay stage is designed. The theoretical analysis of the pre-charging, current-limiting, fault interruption and energy dissipation of the MP-CLCB is carried out. Moreover, the design principles of the energy dissipation and the key parameters of the MP-CLCB are provided. The proposed approaches are verified through simulations in PSCAD/EMTDC. The results show that the MP-CLCB can replace multiple DCCBs, accelerate the fault current interruption and reduce the energy dissipation requirement for the surge arresters.

RETRACTED ARTICLE: An AC–DC/DC–DC hybrid multi-port embedded energy router based steady-state power flow optimizing in power system using substantial transformative energy management strategy

Novel and flexible interconnected architecture for micro grids and their associated energy the management strategy proposes to respond to the increase in renewable energy sources power generation. The key idea of the system is improve the renewable energy generation capacity using a multi-port DC–DC converter, the energy flow between the generation source and the micro grid system can be analyzed with the energy routers. The consumption methods can be used to compensate immediate energy shortage energy production. A multi-port based AC–DC and DC–DC converter and the, power routers are used as energy centers, are improve the stabilize energy flow between micro grids and the main grid. The power generation of the each and every renewable sources are monitored and controlled by the proposed substantial transformative energy management (STEM) strategy also the energy flow variation of the grid system is analyzed with the. This work demonstrates the role of energy routers in optimizing the efficient and flexible way of energy stabilization in grid system. This analysis model establishes the entire system, including power routers, interconnected microcircuits, and the main grid. Interconnected microcircuits were analyzed by various operating systems facilitated by power routers, and corresponding control strategies were developed. The simulation is performed on Mat lab/Simulink simulation platforms, and the results show the effectiveness especially in THD 2.52% is achieved and reliability of the control strategy for micro-grid interconnection and flexible energy flow correspondence.

Active Damping Control of Multiport DC Power Flow Controller for MMC-MTDC With Unbalanced AC Grid

Multiport dc power flow controller (M-DCPFC) has become one of the most attractive solutions to regulate the power flow in the modular multilevel converter-based multiterminal dc (MMC-MTDC) transmission system. However, the current studies on the M-DCPFC mainly focus on the power flow control under the normal operation in the transmission system. To eliminate the impact of the power oscillation which frequently happens because of the unbalanced ac grid, this article proposes an integration to calibrate the active damping control into the M-DCPFC. It introduces the complementary virtual damping to the transmission lines in order to reduce the dc current fluctuations, which suppresses the dc-side power oscillations. In this article, the influence of the unbalanced ac grid on the MMC-MTDC transmission system is investigated and the active damping control of M-DCPFC is presented in detail. A four-terminal MMC-MTDC transmission system is developed as the test platform in the real-time model-in-the-loop (MIL) simulation. The proposed active damping control is validated and shows its effectiveness under different unbalanced conditions.

Small Signal Modeling and Decoupled Controller Design for a Triple Active Bridge Multiport DC–DC Converter

This article proposes modeling and two controller design techniques for a triple active bridge (TAB) three-port dc-dc converter comprising of fuel cell, battery, and load. The sources are integrated, employing boost interleaved full-bridge converters in order to get smoother source current profile. The converter is a nonlinear multi-input multi-output (MIMO) system with a large number of control variables. Moreover, a high degree of coupling among the control variables makes its modeling and control system design quite cumbersome and complex. To overcome the complexity of analysis in a higher order system like TAB, a generalized frequency-domain modeling technique is introduced in this article. A new decoupling matrix-based proportional-integral controller design method is also proposed. It reduces the design complexity and improves the system dynamic performance (lower settling time, overshoot/undershoot in the controlled variables) in comparison to similar three-port converters reported in the literature. Further, the performance of the proposed controller is compared by simulation with another popular MIMO system controller design technique, namely the state feedback control. A 1-kW laboratory prototype is built and tested to verify the system performance during dynamic load changes, source current variation, and battery charging/discharging operation.

Bidirectional multi‐port dc–dc converter with low voltage stress on switches and diodes

In this study, a new transformer-less multi-port dc–dc converter with bidirectional capability is proposed. The proposed converter has dual inputs and dual outputs in which one of the inputs is considered energy storage (ES) such as a battery. Owing to the bidirectional capability, charging and discharging of the ES are provided. In the charging mode, the energy of the regenerative braking can charge the battery. These features make the proposed converter suitable for hybrid energy systems. Continuous charging and discharging current of the battery, low normalised peak voltage stress (NPVS) on semiconductors, and step-up capability are other advantages of the proposed converter. Reduced NPVS causes the semiconductors with low turn-on resistance and reduced rating voltage to be utilised. The performance analysis of the proposed converter in charging and discharging modes is described. Finally, the performance of the converter and mathematical analysis are validated by experimental results.

High Step-Up Non-isolated DC–DC Converter Using Diode–Capacitor Cells

The objective of this paper is to propose a new topology for high step-up multiport DC–DC converter. The proposed converter has two-input single-output ports, and its voltage gain is significantly increased using diode–capacitor cells, which are modified Dickson’s charge pump. Moreover, the voltage stress on the switching devices is reduced. Thus, this converter is very useful for high-power applications. The voltage gain of the proposed converter can be further increased by increasing the number of diode–capacitor cells. The main advantage of this expandable structure is the use of only two inductors in its structure, which considerably decreases the losses and even the size of the converter. The conversion ratios, voltage stress on switches and diodes, as well as the average current of switches and diodes, are formulated, and the theoretical analysis of the converter is proposed. In order to experimentally validate the performance of the proposed converter and theoretical calculations, a converter with the first input voltage source of 10 V and the second input voltage source of 15 V is designed and the output voltage level of 312.5 V is measured, which confirm the simulation results. Moreover, the maximum efficiency occurred at 100 W and full load efficiency is 93.5%, which are all noticeable achievements.

Multiport DC–DC Converter With Step-Up Capability and Reduced Voltage Stress on Switches/Diodes

This article aims to propose a new nonisolated step-up multiport dc–dc converter. The proposed topology is a dual-input dual-output dc–dc converter with different output voltages levels. This makes it possible to be used in hybrid energy systems with different input sources as well as in electric vehicles to supply the traction motor and auxiliary loads. The proposed converter is capable of providing high voltage gains with small values of duty cycles and low normalized peak voltage stress across the semiconductor devices. Therefore, the switches with small turn- on resistance and the diodes with a reduced nominal voltage can be used, which in turn reduces the switching and conduction losses. The operation principles of the proposed converter are explained and steady-state analysis is carried out. Then, the circuit performance is compared with other related step-up multiport dc–dc converters in the literature. Eventually, the performance of the proposed converter is validated with experimental results.

A High Gain Multiport DC–DC Converter for Integrating Energy Storage Devices to DC Microgrid

Interfacing multiple low-voltage energy storage devices with a high-voltage dc bus efficiently has always been a challenge. In this article, a high gain multiport dc–dc converter is proposed for low voltage battery-supercapacitor based hybrid energy storage systems. The proposed topology utilizes a current-fed dual active bridge structure, thus providing galvanic isolation of the battery from the dc bus, wide zero voltage switching (ZVS) range of all the switches, and bidirectional power flow between any two ports. The dc bus side bridge uses voltage multiplier cells to achieve a high voltage conversion ratio between the supercapacitor (SC) and the dc bus. Moreover, as the proposed topology employs only one two-winding transformer to achieve a three-port interface, the number of control variables are reduced, which decreases control complexities. The operation of the proposed converter is analyzed in detail, including the derivation of ZVS conditions for the switches and transformer power flow equations. A decoupled closed-loop control strategy is implemented for the dc bus voltage control and energy management of the storage devices under different operating conditions. A 1-kW laboratory prototype is built to verify the effectiveness of the proposed converter, along with the control scheme.

A Reduced-Switch-Count Family of Soft-Switched High-Frequency Inductive AC-Link Converters

This article introduces a new family of partial-resonance high-frequency ac-link converters with a reduced number of switches, which contributes to enhanced reliability and reduced size. The proposed family of converters can be configured to interface various number of single-/multiport dc and/or single-/multiphase ac systems of sources and loads through a partial-resonance parallel LC link. The LC link is composed of a small inductor and a very small ac capacitor without the use of bulky and short life-cycle electrolytic capacitors. The high-frequency ac link is responsible for transferring power between different ports of the system entirely or partially as well as realizing zero voltage switching for all the power switches/diodes over the full load range, which results in minimized stress over the switches as well as low electromagnetic interference (EMI). This class of converters, which only employs two-quadrant switches, is inherently bidirectional with voltage step-up/step-down capability. It allows variable frequencies and power factors between the input and output terminals in one stage of power conversion. The proposed converters can function in buck–boost, buck, and/or boost modes of operation to step up and/or step down the input voltage. Functioning in buck or boost modes of operation can significantly reduce the link peak current and voltage, contributing to reduced power loss, size of components, voltage/current stress of power switches/diodes, and EMI. Furthermore, the proposed converters are robust against the open-circuit/short-circuit problems of input, output, and link inductors/capacitors, which place emphasis on improved reliability of the system. They are also capable of minimizing poor recovery issues and related losses of the body diodes of switches by using external fast recovery diodes in series with the main switching devices. In view of these features, this class of converters is expected to exhibit improved reliability, efficiency, power density, functionality, and flexibility compared to most existing power converters. A current modulation approach is also developed for each function to regulate the input and output currents on a switching cycle-by-cycle basis. A detailed performance analysis to investigate the challenges of each function in terms of frequency, power factor, and voltage amplitude is presented. The effectiveness of the proposed configurations along with the modulation schemes is verified theoretically using simulation software and experimentally via a low-power laboratory prototype at different operating conditions.

An Integrated Multiport Dc – Dc Converter for Renewable Energy Applications

As conventional energy sources are steadily depleting n nature due to human activities, renewable energy sources are the need of the hour. Renewable energy source delivers environmental friendly, sustainable power. Due to the intermittent nature of these source, the power produced cannot be used directly by the consumers. So the output power is conditional to meet the grid requirements by using semiconductor devices.In the present system, wind energy output is coupled with back to back power converter and solar energy output with dc to ac converter. The output from the two systems are separately interfaced with the power grid. This has the disadvantages of higher components count, increased cost and inefficient power flow management. The proposed system consists of four ports among which one port is for solar point input, one port is for wind energy input, one bi-directional battery port and an isolated load port. Zero voltage switching is adopted for all main switches in the converter. The integrated four port converter has the advantages of interfacing two sources and controlling them with low cost, compact structure that allow and intelligent power flow management between the household users, the electric distribution grid and the distributed generation units. This converter provides the facilities to combine two or more generation sources. Solar power and wind power are given as input to the two input ports of the converter. The converters use four main switches for this conversion. The output voltage will be a DC voltage. This voltage can be used to derive any DC load or can be converted to AC voltage using inverter to drive an AC load.

Synthesis of Integrated Multiport DC–DC Converters With Reduced Switches

With the increasing demand of different voltage levels in industrial applications, multiport dc–dc converters have been widely employed owing to their low-cost merits. Aiming to provide more multiport topologies so that engineers can select out a preferred one for the specified application, this article proposes a novel principle to systematically implement topology derivation by replacing switches in original converters with pulsating current source cells. This principle is simple and effective, with which multiple new integrated multiport converters having a low number of switches are easily evolved. The advantage of reduced switches is very beneficial for the low-power applications with relatively less switches since the overall cost can be effectively improved. And in order to achieve a comprehensive understanding of the proposed converters, an example single-input dual-output converter that integrates the asymmetrical half-bridge flyback converter with the buck converter is analyzed in detail. It operates similarly with the two separate converters, but with favorable advantages of reduced switches and improved switching operation. Finally, an experimental prototype is built to verify the theoretical analysis.

A Versatile Family of Partial-Resonance Inductive-AC-Link Universal Converters

In this paper, a new class of bidirectional partial-resonance power converters is presented. The proposed family can be configured to interface single- or multi-port dc, single- or multi-phase ac systems at input-side and/or output-side. The proposed family offers a very modular structure, which can lead to cost reduction from a common designed module. In this converter, which accomplishes power conversion in a single stage, a small inductor placed in series with the input and output switch-bridges forms the link. This small link inductor is responsible for transferring power between different ports of the system. The proposed topologies can operate in buck, boost, and buck–boost modes of operation to step up and/or step down the voltage. In buck–boost mode of operation, the converter is controlled such that the power is entirely transferred through the link inductor; whereas, in buck or boost modes of operation only a fraction of the power is transferred through the link inductor, and the remaining power is directly transferred from input phases to the output phases. Galvanic isolation, which is typically a prominent factor contributing to power density of a converter, can be provided by means of a compact and lightweight single-phase high-frequency transformer added to the link. In comparison with earlier generations of partial-resonance inductive-link power converters, in the proposed converter, the level of link peak current and consequently power-loss, as well as voltage and current stress of switches are dramatically decreased. A very small film capacitor can be placed in parallel with the link inductor to facilitate zero-voltage-switching (ZVS) operation for all the switches/diodes. Apart from increasing the overall efficiency, minimized dv/dt stress and improvement in power density are achieved by adding the link capacitor. The proposed converter employs four-quadrant switches, i.e., bidirectional-conducting bidirectional-blocking switches, and charges the link inductor in both positive and negative directions in each cycle. In view of this, better utilization of the link inductor and lower total harmonic distortion (THD) are offered. Furthermore, two distinct switching algorithms are developed for the proposed family of converters. In this paper, the detailed behavior of the proposed family is investigated analytically, and simulation and experimental results are presented to evaluate the performance and effectiveness of the proposed converter. A low-power proof-of-concept prototype with input voltage of 59 V/161 V, load voltage of 178 V/73.5 V, maximum switching frequency of 4.9 kHz/3.65 kHz at 215 W/450 W in a step-up/step-down operation is considered for the experimental verification.