Single-Phase Bi-directional Ćuk Inverter for Battery Applications

Bidirectional inverters are widely applied in photovoltaic and wind systems that require battery power backup. They are advantageous over unidirectional inverters because of their ability to convert DC power into AC power and then AC power back into DC power to recharge for storage purposes. Generally, bidirectional inverters are designed to have multiple power stages and/or make use of transformers for isolation and voltage/current gain. This usually increases the cost of production and oftentimes reduces the efficiency of the system. At the same time, attempts at eliminating usage of transformers and reduction in the number of power stages limits the range of bidirectional inverters’ capabilities. This is because battery applications today require low voltage DC-AC inverters with AC-DC power flow capability to store energy for later use. As such, only buck-boost based topologies are majorly being proposed and used for this functionality. The buck boost converter is the most widely used in such applications because of its higher efficiency, low component count and simple structure. It has drawbacks, however, such as: pulsating input and output currents - this leads to lower high electromagnetic interference; lower power factor during AC-DC power flow rectification when the batteries are being recharged; and external filter is also required during this power flow to keep the charging voltage constant. This research proposes a bidirectional inverter that attempts to overcome the drawbacks of the widely used buck-boost converter-based topology. The bidirectional inverter proposed in this work is based on a bidirectional Ćuk converter. The Ćuk converter has both continuous input and output currents. A galvanic isolation option on a Ćuk converter is simpler than a buck boost converter - this is important for grid tied systems. The inverter is based on a pseudo DC-link architecture - it uses a front end Ćuk converter cascaded with an unfolding bridge to convert DC power into AC power. The switches in the converter stage are switched at high frequency, while the switches in the unfolding stage are switched slower at the grid frequency. This configuration is desirable over the two-stage topologies because the switching losses in the unfolding bridge are lower because of this low switching frequency used. This configuration also ensures good switch utilization at the unfolding stage by lowering the parasitic effects on the power transfer. The proposed inverter has 4 modes of operation: during modes I and II the power is positive, and it converts DC power into AC power; during modes III and IV the power is negative, and it converts AC power back into DC power. The inverter is designed such that during DC-AC power flow, the input and output inductor currents and coupling capacitor voltage are continuous for improved efficiency. During the AC-DC power flow, the coupling capacitor voltage is discontinuous to achieve a higher input power factor by improving the AC line current, thereby simultaneously increasing the efficiency. The inverter was analysed in terms of: the dead time inserted into the switches to avoid shoot through and shortcircuiting switches; the parasitic effects on the power transfer ratio. Because the Cúk inverter is a high order system, several robust control strategies, such as sliding mode and current control have been proposed. These control methods require complex theory and present practical challenges to be reviewed. As such a new nested loop control strategy was proposed based on the dynamics of the coupling capacitor as the primary energy storage in the Cúk inverter. The control strategy uses 2 loops: an inner current loop and an outer voltage loop. Lead compensators were designed for both the current and voltage loops to achieve good dynamic response at a high bandwidth. Both simulated and experimental results showed that the bidirectional inverter was able to meet the design specifications. The control strategy showed good dynamic response and disturbance rejection under several inverter variations. Although the efficiency during simulations was above 96%, the experimental efficiency dropped significantly because the inverter was built on a Vero board for easy manipulation. The AC input power factor was > 0.95 for both simulated and experimental results

Dynamic modeling of a dual active bridge DC to DC converter with average current control and load-current feed-forward

Bidirectional power flow is needed in many power conversion systems like energy storage systems, regeneration systems, power converters for improvement of the power quality and some DC-DC applications where bidirectional high power conversion and galvanic isolation are required. The dual active bridge (DAB) is an isolated, high voltage ratio DC-DC converter suitable for high power density and high power applications, being a key interface between renewable energy sources and energy storage devices. This paper is focused on the modeling and control design of a DC-DC system with battery storage based on a DAB converter with average current mode control of the output current and output voltage control. The dynamic response of the output voltage to load steps is improved by means of an additional load-current feed-forward control loop. An analytical study of the load-current feed-forward is presented and validated by means of both simulations and experimental results.This work was supported by the Spanish Ministry of Economy and Competitiveness under grant ENE2012-37667-C02-01.Guacaneme Moreno, JA.; Gabriel Garcerá; Figueres Amorós, E.; Patrao Herrero, I.; González Medina, R. (2015). Dynamic modeling of a dual active bridge DC to DC converter with average current control and load-current feed-forward. International Journal of Circuit Theory and Applications. 43(10):1311-1332. https://doi.org/10.1002/cta.2012S131113324310Vazquez, S., Lukic, S. M., Galvan, E., Franquelo, L. G., & Carrasco, J. M. (2010). Energy Storage Systems for Transport and Grid Applications. IEEE Transactions on Industrial Electronics, 57(12), 3881-3895. doi:10.1109/tie.2010.2076414De Doncker, R. W. A. A., Divan, D. M., & Kheraluwala, M. H. (1991). A three-phase soft-switched high-power-density DC/DC converter for high-power applications. IEEE Transactions on Industry Applications, 27(1), 63-73. doi:10.1109/28.67533Kheraluwala, M. N., Gascoigne, R. W., Divan, D. M., & Baumann, E. D. (1992). Performance characterization of a high-power dual active bridge DC-to-DC converter. IEEE Transactions on Industry Applications, 28(6), 1294-1301. doi:10.1109/28.175280Chang, Y.-H., & Wu, K.-W. (2012). A gain/efficiency-enhanced bidirectional switched-capacitor DC-DC converter. International Journal of Circuit Theory and Applications, 42(5), 468-493. doi:10.1002/cta.1863Li H Liu D Peng FZ Gui-Jia S Small Signal Analysis of A Dual Half Bridge Isolated ZVS Bi-directional DC-DC converter for Electrical Vehicle Applicat 36th IEEE Power Electronics Specialists Conference 2005 2777 2782Chiu, H.-J., Yao, C.-J., & Lo, Y.-K. (2009). A DC/DC converter topology for renewable energy systems. International Journal of Circuit Theory and Applications, 37(3), 485-495. doi:10.1002/cta.475Doishita K Hashiwaki M Aoki T Kawagoe Y Murakami N Highly reliable uninterruptible power supply using a bi-directional converter The 21st International Telecommunication Energy Conference (INTELEC '99), Copenhagen 1999 10.1109/INTLEC.1999.794066Krismer F Biela J Kolar JW A comparative evaluation of isolated bi-directional DC/DC converters with wide input and output voltage range 40th IAS Annual Meeting Industry Applications Conference 2005 1 599 606Aggeler D Biela J Inoue S Akagi H Kolar JW Bi-Directional Isolated DC-DC Converter for Next-Generation Power Distribution - Comparison of Converters using Si and SiC Devices Power Conversion Conference-Nago 2007 510 517Krishnamurthy HK Ayyanar R Building Block Converter Module for Universal (AC-DC, DC-AC, DC-DC) Fully Modular Power Conversion Architecture IEEE Power Electronics Specialists Conference 2007 483 489Romero-Cadaval, E., Spagnuolo, G., Franquelo, L. G., Ramos-Paja, C. A., Suntio, T., & Xiao, W. M. (2013). Grid-Connected Photovoltaic Generation Plants: Components and Operation. IEEE Industrial Electronics Magazine, 7(3), 6-20. doi:10.1109/mie.2013.2264540Yu, X., She, X., Ni, X., & Huang, A. Q. (2014). System Integration and Hierarchical Power Management Strategy for a Solid-State Transformer Interfaced Microgrid System. IEEE Transactions on Power Electronics, 29(8), 4414-4425. doi:10.1109/tpel.2013.2289374Liserre, M., Sauter, T., & Hung, J. (2010). Future Energy Systems: Integrating Renewable Energy Sources into the Smart Power Grid Through Industrial Electronics. IEEE Industrial Electronics Magazine, 4(1), 18-37. doi:10.1109/mie.2010.935861Mi, C., Bai, H., Wang, C., & Gargies, S. (2008). Operation, design and control of dual H-bridge-based isolated bidirectional DC–DC converter. IET Power Electronics, 1(4), 507. doi:10.1049/iet-pel:20080004Friedemann A Krismer F Kolar JW Design of a Minimum Weight Dual Active Bridge Converter for an Airborne Wind Turbine System Proceedings of the 27th Applied Power Electronics Conference and Exposition (APEC) 2012Krismer, F., & Kolar, J. W. (2010). Accurate Power Loss Model Derivation of a High-Current Dual Active Bridge Converter for an Automotive Application. IEEE Transactions on Industrial Electronics, 57(3), 881-891. doi:10.1109/tie.2009.2025284Hengsi Qin, & Kimball, J. W. (2012). Generalized Average Modeling of Dual Active Bridge DC–DC Converter. IEEE Transactions on Power Electronics, 27(4), 2078-2084. doi:10.1109/tpel.2011.2165734Segaran D McGrath B Holmes DG Adaptive dynamic control of a Bidirectional DC-DC converter IEEE Proceedings Energy Conversion Congress 2010 1442 1449Bai H Mi C Wang C Gargies S The dynamic model and hybrid phase-shift control of a dual-active-bridge converter Proceedings IECON 2008 2840 2845Segaran, D., Holmes, D. G., & McGrath, B. P. (2013). Enhanced Load Step Response for a Bidirectional DC–DC Converter. IEEE Transactions on Power Electronics, 28(1), 371-379. doi:10.1109/tpel.2012.2200505Tang W Lee FC Ridley RB Small-signal modeling of average current-mode control APEC'92. Seventh Annual Conference Proceedings 1992 747 755Kheraluwala MH High-Power High frequency DC-DC converters PhD thesis 1991Fang, C.-C. (2011). Sampled-data poles, zeros, and modeling for current-mode control. International Journal of Circuit Theory and Applications, 41(2), 111-127. doi:10.1002/cta.790Redl, R., & Sokal, N. O. (1986). Near-Optimum Dynamic Regulation of DC-DC Converters Using Feed-Forward of Output Current and Input Voltage with Current-Mode Control. IEEE Transactions on Power Electronics, PE-1(3), 181-192. doi:10.1109/tpel.1986.4766303Qin H Kimball JW Closed-loop control of DC-DC dual active bridge converters driving single-phase inverters IEEE Energy Conversion Congress and Exposition (ECCE) 2012 173 17

High-power three-port three-phase bidirectional DC-DC converter

This paper proposes a three-port three-phase bidirectional dc-dc converter suitable for high-power applications. The converter combines a slow primary source and a fast storage to power a common load (e.g., an inverter). Since this type of system is gaining popularity in sustainable energy generation systems and electrical vehicles, the proposed topology is of practical interest. The proposed converter consists of three high-frequency inverter stages operating in a six-step mode, and a high-frequency three-port three-phase symmetrical transformer. The converter provides galvanic isolation and supports bidirectional power flow for all the three ports. An arbitrary power flow profile in the system can be achieved by phase shifting the three inverter stages. Thanks to the three-phase structure, the current handling capability of the circuit is larger and the ripple currents at the dc sides are much lower owing to the interleaving effect of the threephase, and thus the VA rating of the filter capacitors is much lower. The operating principle and, in particular, the transformer design which is based on conventionally and coaxially wound structures are presented. Circuit simulation results are included to verify the proposed converter topology and the dual-PI-loop control strategy

Modeling And Design Of Multi-port Dc/dc Converters

In this dissertation, a new satellite platform power architecture based on paralleled three-port DC/DC converters is proposed to reduce the total satellite power system mass. Moreover, a fourport DC/DC converter is proposed for renewable energy applications where several renewable sources are employed. Compared to the traditional two-port converter, three-port or four-port converters are classified as multi-port converters. Multi-port converters have less component count and less conversion stage than the traditional power processing solution which adopts several independent two-port converters. Due to their advantages multi-port converters recently have attracted much attention in academia, resulting in many topologies for various applications. But all proposed topologies have at least one of the following disadvantages: 1) no bidirectional port; 2) lack of proper isolation; 3) too many active and passive components; 4) no softswitching. In addition, most existing research focuses on the topology investigation, but lacks study on the multi-port converter’s control aspects, which are actually very challenging since it is a multi-input multi-output control system and has so many cross-coupled control loops. A three-port converter is proposed and used for space applications. The topology features bidirectional capability, low component count and soft-switching for all active switches, and has one output port to meet certain isolating requirements. For the system level control strategy, the multi-functional central controller has to achieve maximal power harvesting for the solar panel, the battery charge control for the battery, and output voltage regulation for the dc bus. In order to design these various controllers, a good dynamic model of the control object should be obtained first. Therefore, a modeling procedure based on a traditional state-space averaging method is v proposed to characterize the dynamic behavior of such a multi-port converter. The proposed modeling method is clear and easy to follow, and can be extended for other multi-port converters. In order to boost the power level of the multi-port converter system and allow redundancy, the three-port converters are paralleled together. The current sharing control for the multi-port converters has rarely been reported. A so called “dual loop” current sharing control structure is identified to be suitable for the paralleled multi-port converters, since its current loop and the voltage loop can be considered and designed independently, which simplifies the multi-port converter’s loop analysis. The design criteria for that dual loop structure are also studied to achieve good current sharing dynamics while guaranteeing the system stability. The renewable energy applications are continuously demanding the low cost solution, so that the renewable energy might have a more competitive dollar per kilowatt figure than the traditional fossil fuel power generation. For this reason, the multi-port converter is a good candidate for such applications due to the low component count and low cost. Especially when several renewable sources are combined to increase the power delivering certainty, the multi-port solution is more beneficial since it can replace more separate converters. A four-port converter is proposed to interface two different renewable sources, such as the wind turbine and the solar panel, one bidirectional battery device, and the galvanically isolated load. The four-port converter is based on the traditional half-bridge topology making it easy for the practicing power electronics engineer to follow the circuit design. Moreover, this topology can be extended into n input ports which allow more input renewable sources. vi Finally, the work is summarized and concluded, and references are listed

Performance analysis of DC/DC bidirectional converter with sliding mode and pi controller

A sliding mode controller for a non-isolated DC/DC, bidirectional converter is presented and comparative study with PI controller is done along with ISE analysis, in order to do performance analysis. The proposed system can be utilized in many applications such as electrical vehicle, distributed power generation or small grids. Second theorem of Lyapunov is utilized and stability of the closed loop system is mathematically proven. The adopted control strategy achieves effective output voltage regulation and good dynamic stability. Rejection of disturbance is also an inherent characteristic of this technique. Furthermore, it is illustrated that the system can successfully follow changes of load demand and compensates sudden disturbances in operating condition. The design is evaluated and verified using Matlab/Simulink. Results of Matlab simulation are provided to show the feasibility of the proposed system and effectiveness of control method. Simulation results show that this technique can provide a considerable edge over control techniques which are presently available (applied) over this type of converter

Design and simulation of cascaded H-bridge multilevel inverter with energy storage

Stand-alone power system provides a solution for the user in rural areas that are disconnected from the utility grid which requires power electronics device for the power conversion. This work proposes a design of 5-level cascaded H-bridge inverter with energy storage to realize DC-AC power conversion for such system. The DC-DC bidirectional converter is designed to control the charging and discharging of current into/from the battery during the buck and boost mode of operation. At the DC side, dual-loop control strategy using PI controllers is designed to control the current and voltage. The inner loop current controller controls the recharging/discharging of current for the battery, while the outer voltage controller controls the DC link voltage at 200 V for each of the H-bridge unit. At the AC side, multiple feedback loop control strategy regulates the inverter output voltage at 240 Vrms under various load change. The modelling and design of the system is implemented under Matlab Simulink environment. From the results, the battery storage unit works well with the DC link voltage to achieve a balance power transfer within the system between the PV source, load and battery storage under variation of PV power and loading condition

A new bidirectional AC-DC converter using matrix converter and Z-source converter topologies

This thesis proposes a new bidirectional three-phase AC-DC power converter using matrix converter and Z-source inverter topologies. Advantages of the AC-DC matrix converter are the inherently controllable power factor, the tight DC voltage regulation, the wide bandwidth with quick response to load variation, the single-stage buck-voltage AC-to-DC power conversion; advantages of the z-source inverter are the increased reliability by allowing the shoot-through between upper and lower power switches of one inverter leg, insensitivity to DC bus voltage due to the extra freedom of controlling DC-link voltage. The proposed Matrix-Z-source converter (MZC) marries up both advantages of AC-DC matrix converter and Z-source inverter. It can achieve voltage-boost DC-AC inversion capable of variable voltage variable frequency (VVVF) AC output; it can achieve voltage-buck AC-DC rectification capable of inherent control over AC current phase angle and DC output regulation with a (VVVF) AC source supply. Both foresaid performance in DC-AC inversion and AC-DC rectification can be implemented in a simple open-loop control manner. Three constraints of VSI, in the bidirectional AC-DC power conversion, are the peak AC voltages are always less than DC-link voltage, closed-loop control has to be employed when DC regulation and/or AC current phase angle control are required, and AC voltage is sensitive to the variation of the DC-link voltage in DC-AC inversion. The voltage-boost inversion and/or voltage-buck rectification of MZC overcomes the first constraint; thus MZC enables the AC machine voltage increased higher than DC-link voltage hence advantages of running AC machine at relatively high voltages are enabled. The direct DC voltage regulation and inherent AC-current-phase-angle control of MZC overcomes the second constraint in an open-loop manner; hence a simplified system design is obtained with sufficient room for the further improvement by closed-loop control schemes. The extra freedom in controlling DC-link voltage of MZC overcomes the third constraint hence a DC source voltage adaptable inverter is obtained. This thesis focuses on the study of the feasibility of the proposed MZC through theoretical analysis and experimental verification. At first, the proposed MZC is conceptually constructed by examining the quadrant operation of AC-DC matrix converter and Z-source inverter. After the examination of the operating principles of both AC-DC matrix converter and Z-source inverter, the configuration of MZC is then proposed. The MZC has two operating modes: DC-AC inversion and AC-DC rectification. Circuit analysis for both operating modes shows that the new topology does not impose critical conflict in circuit design or extra restriction in parameterization. On the contrary, one version of the proposed MZC can make full advantage of Z-source network components in both operating modes, i.e. a pair of Z-source inductor and capacitor can be used as low-pass filter in AC-DC rectification. The modulation strategy, average modeling of system, and features of critical variables for circuit design of the proposed MZC were examined for each operating mode. Simulations of the proposed MZC and its experimental verification have been presented. Analytical models of conduction and switching losses of the power-switch network in different operating mode have shown that the losses in the MZC compare favorably with conventional VSI for a range of power factor and modulation indices

Topologies for Battery and Supercapacitor Interconnection in Residential Microgrids with Intermittent Generation

Context:This paper presents a comparative study of the performance of three topologies for interconnecting Lithium ion batteries and supercapacitors in a hybrid energy storage system for use in electric residential microgrids with intermittent generation. The hybrid system’s main purpose is to prolong battery life, using the supercapacitor to handle the dynamic component of current from a pulsed current load. This work builds upon a preliminary simulation-based study, in which two semi-active topologies were compared and evaluated. Here, we add an active topology to the study and describe the operational benefits of each topology. Method:For every topology in this study, a non-isolated half-bridge bidirectional DC converter was used, and a proportional–integral (PI) double-loop linear ACC control algorithm was designed for controlling the converters. In the active topology an additional optimisation-based real-time frequencydecoupling control strategy was employed. Results:A parallel active topology allows better management of stored energy in the SC by supporting variation of SC terminal voltages with a DC converter as interface to the DC bus. Conclusions: Semi-active topologies are easier to design and control, but the operational benefits of supercapacitors require voltage variation at the terminals. This variation is made possible with an active topology. Acknowledgements: First author thanks Universidad Distrital Francisco Jos´e de Caldas for the financial support in his doctoral studies through the study commission contract N° 000101-2016

A Bidirectional Soft-Switched DAB-Based Single-Stage Three-Phase AC–DC Converter for V2G Application

In vehicle-to-grid applications, the battery charger of the electric vehicle (EV) needs to have a bidirectional power flow capability. Galvanic isolation is necessary for safety. An ac-dc bidirectional power converter with high-frequency isolation results in high power density, a key requirement for an on-board charger of an EV. Dual-active-bridge (DAB) converters are preferred in medium power and high voltage isolated dc-dc converters due to high power density and better efficiency. This paper presents a DAB-based three-phase ac-dc isolated converter with a novel modulation strategy that results in: 1) single-stage power conversion with no electrolytic capacitor, improving the reliability and power density; 2) open-loop power factor correction; 3) soft-switching of all semiconductor devices; and 4) a simple linear relationship between the control variable and the transferred active power. This paper presents a detailed analysis of the proposed operation, along with simulation results and experimental verification