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Battery energy storage systems (BESS) based on modular multilevel converters (MMCs) allow battery packs to be integrated into the electrical grid in a modular fashion. Inherent to the operation of the MMC, the module's dc-link capacitor voltage experiences oscillations at grid frequency and its harmonics. This article investigates the close relation between this voltage oscillation and the battery current ripple. The precise capacitor energy requirements for various operations of BESS-MMC, which include arm/phase power balancing and state-of-charge balancing are analyzed in this article. Furthermore, this article also explores the relation between the controller design and the submodule's (SMs) capacitor sizing in terms of its energy requirements. Design guidelines for the SM level voltage control to attenuate battery ripple and detailed analysis for the capacitor energy requirement in each operating mode are presented. The control and capacitor sizing design are validated in real-time using embedded microprocessors in a Typhoon-based controller hardware-in-the-loop environment. [ABSTRACT FROM AUTHOR]

An isolated multilevel bidirectional dc–dc converter is presented in this article to interface the low-voltage (LV) battery and the high-voltage (HV) propulsion inverter in electric vehicles. The proposed topology achieves a HV step-up ratio in the motoring mode by reconfiguring two split capacitor half-bridge circuits in series/parallel through the symmetrical modulation of a voltage bidirectional, two quadrant switch. This reconfiguration generates a high-frequency multilevel voltage output at the dc-bus side of the inverter, which reduces the output filter volume. The dc-bus voltage is regulated by the duty cycle modulation of the intermediary switch in the motoring mode, simplifying the sensing and control. During regenerative braking, the converter is operated with phase shift modulation between the HV half bridges and the LV full bridge to regulate the battery voltage. The presented modulation strategies achieve zero voltage switching for the full-bridge devices over a wide load range. A comprehensive analysis of the proposed multilevel converter in motoring and braking modes along with the design constraints and soft switching boundary conditions is presented in this article. Detailed experimental results on a 1.5-kW laboratory prototype are presented to verify the design approach and illustrate the converter performance. [ABSTRACT FROM AUTHOR]

High voltage direct current (HVdc) power transmission systems do not encounter any natural zero crossing unlike the ac systems, and hence, the dc circuit breakers employed should be fast-acting and reliable to ensure safe operation. Circuit breakers (CBs) that have fast response time with lower energy loss dissipation are required for subsea HVdc transmission systems. This article investigates the performance of various CB topologies, including ultrafast coupled inductor hybrid CB (CIHCB) topology without and with the integration of resistive-type superconducting fault current limiter (R-SFCL) for a 100-kV, 100-MW HVdc transmission systems. It is found that the addition of R-SFCL with 1.7-ms response time decreases the peak current through the breaker and, hence, the power dissipated in the CB during short-circuit fault conditions. Thus, the rating of CB can be significantly decreased with the proposed topology. Furthermore, a comparison of power loss in CIHCB with the existing topologies, such as mechanical CB, resonant CB, and HVdc-hybrid CB, are also presented in this article. [ABSTRACT FROM AUTHOR]

This article proposes a multilevel dc–dc converter topology for fast charging of electric and plug-in hybrid electric vehicles (EVs and PHEVs). The proposed dc–dc converter topology converts the front end ac–dc converter output and provides regulated supply to the EV propulsion battery. The proposed topology consists of full-bridge converter at the primary, while the secondary side consists of voltage doubler rectifier units and combination of diodes and mosfet for reconfiguration of the voltage doubler rectifiers to generate the multilevel voltage. The multilevel voltage at the output helps in reducing the output filter size and increases the power density of the converter. The topology utilizes the resonance between leakage inductor of high frequency transformer, parasitic output capacitors of full-bridge mosfets and voltage doubler capacitors to achieve soft switching (ZVS turn-on) for all the full-bridge devices and soft turn-offfor the rectifier diodes. The load limited ZVS turn on capability of conventional full-bridge topologies is mitigated through the use of resonance between magnetizing inductance of transformer and mosfet output capacitors. The converter is designed for 650 V dc bus input and 200–400 V EV battery output at 100 kW rated charging power. The analysis of the proposed converter in continuous and discontinuous modes of operation, soft switching operation, and the component design guidelines are presented in this article. The proposed converter is validated through detailed PLECS simulation results for 100 kW charging power. Experimental results from laboratory prototype of 500 W power are also presented to validate the design methodology and converter performance. [ABSTRACT FROM AUTHOR]

Direct electrical heating (DEH) is a well-established method for preventing hydrate formation inside subsea oil transfer pipelines. However, poor efficiency and high reactive power requirement of the existing line-frequency DEH systems have necessitated high-frequency power processing along with reactive power compensation. To meet these design objectives, a dc–ac converter using an LCCL resonant tank is presented in this article to function as a high-frequency alternating current source. The LCCL resonant tank is tuned at the frequency of the maximum tank current gain to maximize the heat generation and reduce the VA rating of the tank. The maximum tank current gain operation also ensures zero-voltage switching of the bridge inverter devices. Detailed frequency domain analysis and design guidelines are presented for the proposed LCCL resonant inverter (RI). Experimental results on a 10-A laboratory prototype and controller hardware-in-the-loop results for a 350-A system illustrate the advantages of the LCCL RI in DEH application. [ABSTRACT FROM AUTHOR]

This paper proposes a soft-switched modulation technique with synchronous rectification for an isolated single-stage single-phase matrix-type dc–ac converter. The dc side consists of a full bridge inverter, and the ac side is a 2×2 matrix converter-based cycloconverter. The proposed unipolar modulation strategy provides zero current switching/zero voltage switching (ZVS) for the ac side devices and ZVS-on for the dc side devices. It also allows natural commutation of the current flowing through the secondary side leakage inductor of the isolation transformer and the grid inductor during unity power factor (UPF) condition, thus eliminates the requirement of snubber circuit. An improved soft-switched flyback-based regenerative snubber circuit is also presented for non-UPF operation. Proposed snubber circuit recycles the energy stored in the snubber capacitors in every switching cycle. A guideline to design snubber circuit along with a comparative study is discussed in this paper. Performance of the proposed hybrid modulation technique is evaluated in an SiC mosfet based 1.2-kW dc–ac converter prototype. A detailed analysis of the converter performance has been presented in this paper considering the circuit non-idealities. [ABSTRACT FROM AUTHOR]

This paper presents a nine-level inverter topology for an open-end induction motor drive requiring only eight switches per phase, using two three-level inverters with two isolated dc links in a 3:1 ratio. A space-vector-based formulation is used to determine pole voltages such that both inverters supply power to the load over the full modulation range, eliminating the possibility of dc bus overcharging. Proper selection of switching states ensures that all floating capacitor voltages are kept tightly balanced. A digital state machine is used to select sequences of switching states in order to eliminate deadtime-induced pole voltage transients, further improving the output-voltage quality. A level-shifted carrier-based pulse width modulation scheme is used. The steady-state and transient performance of this topology were verified and the experimental results are included. [ABSTRACT FROM AUTHOR]

This paper proposes a novel multiple-input bidirectional dc–dc power converter to interface more than two dc sources of different voltage levels. This finds applications in hybrid electric/fuel cell vehicles (FCVs), where different dc sources of unequal voltage levels need to be connected with bidirectional power flow capability. The converter can be used to operate in both the buck and boost modes with bidirectional power control. It is also possible to independently control power flow between any two sources when more than two sources are actively transferring power in either directions. The operation, analysis, and design of the converter are presented with different modes of power transfer. The proposed converter is demonstrated for FCV application using real-time hardware-in-the-loop system. Experimental results for a 5-kW system are presented, validating the theoretical analysis. [ABSTRACT FROM PUBLISHER]

Efficient power conversion technologies are strategic to the advancement of fuel cell vehicles (FCVs). This paper presents an overview of power conditioning system (PCS) architectures for an FCV propulsion system. Two new power conversion topologies to obtain variable ac from the fuel cell system are proposed. The switching of the power devices are based on the proposed hybrid modulation technique that minimizes the switching losses in the inverter. The proposed converters do not use the dc-link filter capacitors. Elimination of the dc-link capacitor not only reduces the size and volume but also helps in retaining the sine wave modulated information at the input of a three-phase inverter. Bidirectional converter topologies are proposed for interfacing low-voltage battery and fuel cell dc bus. Experimental results are presented for the proposed topologies. [ABSTRACT FROM AUTHOR]