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NOVEL PARTIALLY INSULATED MULTIPORT DC-DC CONVERTER WITH PARALLEL OPERATION TECHNIQUE
Abstract
This study presents a new partially insulated multiport DC-DC converter topology for photovoltaic (PV) powered battery buffered DC-Microgrid systems. The challenging problem due to their intermittent nature of PVs is eliminated by batteries controlled with the existing H-bridge converters. The input ports are operated in parallel. The proposed converter provides more power transfer by connecting PV arrays and batteries in parallel form. The isolation between the input and output ports is provided by a multi-winding high-frequency transformer (HFT). The primary side of the multi-winding HFT is equipped with individual H-bridge converters for each PVs while the secondary side is endowed with a bridge rectifier circuit. The proposed converter makes it possible to charge batteries in addition to provide power transfer towards the loads. Besides, the proposed converter also allows power transfer from batteries to loads. In order to meet the control objectives of maximum power point tracking (MPPT), battery constant current (CC) / constant voltage (CV) charging and phase shift, a control scheme that includes multi-control loops is suggested. The performance of the proposed converter has been evaluated for different operating modes. In this manner, the viability and the effectiveness of the proposed method have been validated.
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This paper presents a new consensus-based control method for hybrid energy storage system (HESS) with a cascaded multiport converter in the DC microgrid. The cascaded multiport converter has two stages, where the first stage is for the supercapacitor and the second stage is for the batteries. The two-stage structure can reduce the component rating of the second stage since the batteries are indirectly connected to the DC bus via the supercapacitor at the first stage. Additionally, the second stage with multiple ports is able to integrate multiple batteries. The HESS balances the power mismatch between the generation of the photovoltaics (PV) and the dissipation of the loads, as well as maintains the bus voltage of the DC microgrid. To solve the state-of-charge (SOC) imbalance of multiple batteries for the long lifespan of HESS, a consensus-based control method is developed in this paper to equalize the SOCs among multiple batteries. The consensus-based method can accommodate a varying number of batteries, which enables the plug-and-play operation. A hardware-in-loop (HIL) setup is adopted to implement the DC microgrid, including the HESS using the cascaded multiport converter and the PV. The HIL experimental results demonstrate the effectiveness of the proposed consensus-based control method.
Photovoltaic (PV)/battery hybrid power units have attracted vast research interests in recent years. For the conventional distributed power generation systems with PV/battery hybrid power units, two independent power converters, including a unidirectional dc–dc converter and a bidirectional converter, are normally required. This paper proposes an energy management and control strategy for the PV/battery hybrid distributed power generation systems with only one integrated three-port power converter. As the integrated bidirectional converter shares power switches with the full-bridge dc–dc converter, the power density and the reliability of the system is enhanced. The corresponding energy management and control strategy are proposed to realize the power balance among three ports in different operating scenarios, which comprehensively takes both the maximum power point tracking (MPPT) benefit and the battery charging/discharging management into consideration. The simulations are conducted using the Matlab/Simulink software to verify the operation performance of the proposed PV/battery hybrid distributed power generation system with the corresponding control algorithms, where the MPPT control loop, the battery charging/discharging management loop are enabled accordingly in different operating scenarios.
In this paper, a family of three-port three-level converters (TPTLC) composed of asymmetrical bidirectional half-bridge modules is proposed, which offers the benefits in terms of a simple control scheme, extended soft switching over a wide range of operating conditions, and reduced voltage stress across switches. The proposed converters take advantage of a pulse-width-modulation plus phase-shift control technique to regulate the output voltage as well as control the power flow between different ports independently. A stacked TPTLC is taken as an example to be introduced in detail to gain a thorough insight into the proposed family of converters. The stacked TPTLC can provide a high voltage-gain along with a wide voltage-gain range without using any transformer, resulting in the improvement in the power density. In order to minimize the conduction loss and reduce the current stress of switches, the root-mean-square current of the inductor and the boundary condition of the phase-shift controller in different operation scenarios are studied. Finally, the feasibility of the proposed concept and effectiveness of the design approach are validated based on the experimental results of a 1 kW, 100 kHz prototype of the stacked TPTLC using gallium nitride switches.
A three-port bidirectional multi-element resonant converter is developed in this paper. It contains multiple resonant components, which leads to various resonant frequencies. Due to the appropriate placement of these frequencies, the transfer of the fundamental and the third order harmonic active power is guaranteed. Besides, a non-ideal isolated transformer is considered, as the parasitic leakage inductor is often ignored for the multi-port resonant converter. A systematic design procedure is proposed to reduce the coupling power between two input ports. It turns out to be instructive for the decoupled power flow management of the multi-element resonant converters. Preferred parameters are easily selected by means of the small signal model established in this paper. It contributes to the improvement of degree of control freedom consequently, with respect to the complex decoupling matrices. In the end, a 750W prototype is built in the laboratory. The feasibility of theoretical analyses is verified by experimental results. In addition, zero-voltage-switching characteristics for all the power switches of three ports are achieved. The highest conversion efficiency is 96.3%.
This paper presents a comprehensive review of multiport converters for integrating solar energy with energy storage systems. With recent development of battery as a viable energy storage device, the solar energy is transforming into a more reliable and steady source of power. Research and development of multiport converters is instrumental in enabling this transformation in an efficient manner. The high efficiency of conversion in comparatively smaller footprint makes a multiport converter very attractive in this application. Most of the recently reported multiport converter topologies are discussed here. A breakdown of isolated and non-isolated topologies is presented along with comparison of converter architectures and features such as operating conditions, device count, efficiency etc. Each group of multiport converters are subdivided into different smaller groups based on their architecture. Detailed specification are presented for important topologies. Finally, a performance comparison is carried out featuring the advantages and disadvantages of the various topologies leading to suggestions for the direction of future research.
Interfacing multiple low voltage energy storage devices with a high voltage DC bus efficiently has always been a challenge. In this paper, 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 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 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.
Photovoltaic (PV) systems having rechargeable batteries are prone to be complex and costly because multiple converters are necessary to individually regulate a load, PV panel, and battery. This paper proposes novel nonisolated multiport converters (MPCs) integrating a bidirectional PWM converter and phase-shift switched capacitor converter (PS-SCC) for standalone PV systems. A PWM converter and PS-SCC are integrated with reducing the total switch count, realizing the simplified system and circuit. In the proposed MPCs, two control freedoms of duty cycle and phase shift angle are manipulated to individually regulate the load, PV panel, and/or battery. The detailed operation analysis was performed to mathematically derive gain characteristics and ZVS operation boundaries. For the battery discharging mode, in which the PV panel is not available and the MPC behaves as a single-input-single-output converter with two control freedoms available, the optimized control scheme achieving the lowest RMS current is also proposed to maximize power conversion efficiencies. Various kinds of experimental verification tests using a 200-W prototype were performed to verify the theoretical analysis and to demonstrate the performance of the proposed MPC.
Bipolarity in dc microgrids is desirable as it enhances the system reliability and efficiency. However, a bipolar dc microgrid (BDCMG) demands multiple conventional dc-dc converters to feed power to both the poles of the bipolar dc grid. To handle this requirement and to maintain high efficiency, a new four-port, dual-input-dual-output (DIDO) dc-dc converter topology is proposed for interfacing the solar PV and fuel cell (FC) sources to a low-voltage BDCMG. The proposed topology is unidirectional, efficient, and compact. It has fewer circuit elements with only one inductor as compared to the conventional nonisolated dc-dc converters. The proposed converter regulates one of the pole voltages of the dc bus and also ensures MPPT of the PV source. Further, the converter can be operated as a single-inputdual- output (SIDO) converter. The control complexity of the proposed converter is low as it can be operated in various modes with only one set of controllers. To design the control system for the proposed converter, a small-signal model is derived for each operating mode. Loss modelling and efficiency analysis of the proposed converter are carried out and its efficacy and performance are validated by detailed simulation and experimental results under various operating conditions.
A systematic method for deriving soft-switching three-port converters (TPCs), which can interface multiple energy, is proposed in this paper. Novel full-bridge (FB) TPCs featuring single-stage power conversion, reduced conduction loss and low voltage stress are derived. Two non-isolated bidirectional power ports and one isolated unidirectional load port are provided by integrating an interleaved bidirectional Buck/Boost converter and a bridgeless Boost rectifier via a high frequency transformer. The switching bridges on the primary side are shared, hence the number of active switches is reduced. Primary-side pulse width modulation and secondary-side phase shift control strategy are employed to provide two control freedoms. Voltage and power regulations over two of the three power ports are achieved. Furthermore, the current/voltage ripples on the primary-side power ports are reduced due to the interleaving operation. Zero-voltage-switching and zero-current-switching are realized for the active switches and diodes, respectively. A typical FB-TPC with voltage-doubler rectifier developed by the proposed method is analyzed in detail. Operation principles, control strategy and characteristics of the FB-TPC are presented. Experiments have been carried out to demonstrate the feasibility and effectiveness of the proposed topology derivation method.
In this study, a novel multi-port CLL resonant converter with an asymmetrical duty cycle control is analyzed. The proposed asymmetrical duty cycle manages the output voltage for various load conditions. Series connected transformers at the secondary side enable to split the power in each port and reduce the voltage stresses on the switches compared to the parallel connected transformers. Even under the unbalanced input conditions, the current sharing between ports is preserved because of the magnetizing inductance of the CLL resonant converter that can be as large as needed. In order to investigate the proposed control in the converter, two different isolated DC sources and a variable load are used. The converter operation is tested at 120 V inputs with the output of 200 V at a full power of 1 kW with a maximum efficiency of 97.4%. The experimental results show that the multi-port CLL resonant converter with the proposed controller is an appropriate topology for sustainable energy platforms which are supplied by different type of energy sources such as photovoltaic, fuel-cell, wind, etc., at various power capacities.
In order to interface one photovoltaic (PV) port, one bidirectional battery port, and one load port of a PV-battery dc power system, a novel nonisolated three-port dc/dc converter named boost bidirectional buck converter (B3C) and its control method based on three-domain control are proposed in this paper. The power flow and operating principles of the proposed B3C are analyzed in detail, and then, the dc voltage relation between three ports is deduced. The proposed converter features high integration and single-stage power conversion from both PV and battery ports to the load port, thus leading to high efficiency. The current of all three ports is continuous; hence, the electromagnetic noise can be reduced. Furthermore, the control and modulation method for B3C has been proposed for realizing maximum power point tracking (MPPT), battery management, and bus voltage regulation simultaneously. The operation can be transited between conductance mode and MPPT mode automatically according to the load power. Finally, experimental verifications are given to illustrate the feasibility and effectiveness of the proposed topology and control method.
This paper proposes a new isolated, three-port, bidirectional, DC-DC converter for simultaneous power management of multiple energy sources. The proposed converter has the advantage of using the least number of switches and soft switching for the main switch, which is realized by using a LCL-resonant circuit. The converter is capable of interfacing sources of different voltage-current characteristics with a load and/or a DC microgrid. The proposed converter is constructed for simultaneous power management of a photovoltaic (PV) panel, a rechargeable battery, and a load. Simulation and experimental results show that the proposed converter is capable of maximum power point tracking control for the PV panel when there is solar radiation and controlling the charge and discharge of the battery when there is surplus energy and power deficiency with respect to the load, respectively.
A novel multiport isolated bidirectional dc-dc converter for hybrid battery and supercapacitor applications is presented, which can achieve zero voltage switching for all switches in the whole load range. The bidirectional power flow between any two of the ports is free, and the circulating power is low for the well matching of the transformer voltages of all time regardless of the voltage variations of the battery and supercapacitor. Moreover, the current ripples are greatly decreased by interleaved control, which is good for battery and supercapacitor. The converter topology and the operation principle are introduced. Detailed analysis on soft-switching of all switches is given. On the basis of theoretical analysis, the principle and method for parameter designing are provided. A hybrid energy management strategy combining bus voltage control and energy management of the energy storage devices is proposed and the control scheme is presented. Moreover, detailed parameter design of a prototype converter is given for a 380-V dc-bus microgrid lab system. Effectiveness of the control strategy, correctness of the analysis on soft-switching, and the parameter design methods are verified by the simulation and experimental results.
Soft-Switched Nonisolated High Step-Up Three-Port
- R Faraji
R. Faraji, "Soft-Switched Nonisolated High Step-Up Three-Port," IEEE Trans. Power
Electron., vol. 33, no. 12, pp. 10101-10111, 2018.