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A two-stage hybrid isolated dc–dc boost converter for high power and wide input voltage range applications is proposed. It can be used as a front-end dc–dc converter that can boost variable low voltage from a power source [battery (home/industrial inverter/industrial UPS application), fuel-cell or solar-PV] and interface it to a high-voltage dc-ink, which typically feeds an inverter. A detailed comparison among the different family of converter topologies for isolated dc–dc boost application is carried out that can prove to be useful for power electronics engineers to choose the correct topology for a given input voltage range. The quantitative comparison takes into account the power device utilization, transformer utilization, capacitance utilization, and inductive energy requirement. Based on the comparison, it is shown that with input voltage variation greater than ±20%, two-stage hybrid isolated dc–dc boost converter is superior compared to other family of converters. Design details for the two-stage converter are provided. The converter is developed and tested for a 5 KW inverter application with an input dc voltage range of 90–170 V and output ac voltage of 230 V. Theoretical analysis for loss calculations is also provided which closely matches the experimental results. [ABSTRACT FROM AUTHOR]

Several applications such as power supplies for electric precipitators, ozone generation, partial discharge, etc., require ac superimposed dc (ACsDC) voltage supply. Most of such applications use intransigent systems for producing ACsDC voltages. In this paper, three different kinds of flexible power electronic converters are proposed for producing ACsDC voltages. These converters have two power conversion stages: input and output. In the input stage, two isolated dc voltages are obtained by using an isolated three-port dc–dc converter or two isolated two-port dc–dc converters. In the output stage, one of the input-stage dc voltages is used to generate an ac voltage and the obtained ac voltage is added to the remaining input-stage dc voltage to obtain an ACsDC voltage. Based on the converters used in the input stage, the proposed ACsDC converters are named as a dual active bridge (DAB) converter-based ACsDC converter (DAB-ACsDC), triple port active bridge (TAB) converter-based ACsDC converter (TAB-ACsDC), and dual transformer-based asymmetrical triple port active bridge (DT-ATAB) converter-based ACsDC converter (DTATAB-ACsDC). A detailed analysis of these ACsDC converters and their verifications using simulations and experimental studies are presented, which depict that the proposed converters can be used effectively for producing ACsDC voltages. [ABSTRACT FROM AUTHOR]

The current-source modular multilevel converter (CSMMC) is a good alternative for high-power applications with medium-voltage and high-current requirements. In such applications, to obtain the multilevel current output and for current scaling, a large number of submodules are required in CSMMC. The detailed representation of such systems in electromagnetic transient-type simulation programs brings computational complexity with a large computing burden. This paper presents a computationally efficient equivalent model of CSMMC based on the Norton equivalents. Each arm of the converter is represented by a two-node Norton equivalent in this model, which eliminates the internal intermediate nodes and, hence, significantly reduces computing time. The proposed model is implemented in PSCAD/EMTDC by using the module component coded in FORTRAN and results are validated with the full-size traditional model in PSCAD/EMTDC. Moreover, hybrid models are presented and validated for the submodule level studies such as fail-safe functionality with redundant submodules. This paper also focuses on the control method and dynamic studies of the CSMMC-based back-to-back system. The results of these studies are compared with the proposed equivalent model, and accurate matching of the results confirms the usefulness of the proposed model in such studies. [ABSTRACT FROM AUTHOR]

The hybrid modular multilevel converter with cascaded full bridges (HMMC-CFB) is a recently proposed dc fault tolerant converter topology for high-power applications. It has a director part (DP) consisting of a series of connected half-bridge submodules, and a wave-shaping part (WSP) composed of a series of connected full-bridge submodules (FBSMs). The submodules in DP avoid high voltage stresses and improve synchronization between DP and WSP by slowing down the change rate of DP output voltage. This slowdown is achieved by using a trapezoidal reference signal for DP. The WSP attenuates the voltage harmonics produced by DP. However, the energy exchanged by WSP changes with modulation index, which may cause improper voltage regulation of the submodule capacitors. This paper proposes a new control technique to regulate the energy exchanged by WSP, which uses a variable slope trapezoidal reference signal of DP. To obtain this slope, the feedforward and feedback controllers are used. The feedforward controller gives the value of slope depending on the modulation index (mv) to keep the energy exchanged by WSP nearly equal to zero, whereas the losses and nonideality of the converter are taken care of by the feedback controller. This technique guarantees proper voltage regulation of the submodule capacitors for all modulation indices. The efficacy of the proposed technique is confirmed using simulations and experimentations. This paper also presents a circulating current suppressing controller for HMMC-CFB. The proposed control schemes and dc fault tolerant capability of HMMC-CFB are tested on a grid-connected model built in PSCAD. [ABSTRACT FROM AUTHOR]

The fault-tolerant multilevel converters are gaining increased interests for high-voltage direct current (HVDC) applications due to their ability to suppress the fault current during dc-side faults. However, most of these topologies use full-bridge submodules (FBSMs) resulting in the requirement of a large number of semiconductor switches. In this paper, a new generalized cross-connected SM (GX-SM) structure is presented, which requires lesser number of switching devices and provides the same functionality as the FBSM. A comparison of the switches required in the different converter topologies using FBSMs and GX-SMs is performed. The performance evaluation of two of the dc-side fault-tolerant converter topologies, namely alternate arm modular multilevel converter (AAMMC) and hybrid cascaded modular multilevel converter (HCMC) with the GX-SM, is performed using simulation studies done in PSCAD/EMTDC. The modulation and control schemes for these GX-SMs-based converters are presented. A new mixed-SM configuration of AAMMC is proposed which utilizes an optimal combination of GX-SMs and half-bridge SMs. The study results demonstrate the effectiveness of the proposed GX-SM structure, and satisfactory responses of the GX-SMs-based AAMMC and HCMC systems controlled using the presented modulation and control strategies under various system conditions. [ABSTRACT FROM PUBLISHER]

Multilevel current source converters are a smart choice for the high-power applications with low-voltage and high-current requirements. This paper presents the detailed analysis of a current source modular multilevel converter (CSMMC) and its application as a STATCOM. Various properties of CSMMC are compared with the voltage-source modular multilevel converter (VSMMC). The submodule inductance selection method and a sorting-based algorithm for inductor current balancing are proposed for CSMMC. The validity of the inductance selection method and the inductor current balancing algorithm are confirmed by the simulation of a three-phase CSMMC using PSCAD/EMTDC. The carrier phase-shifted sinusoidal pulsewidth modulation is used as the switching technique. The performance of a converter is analyzed with interleaved and noninterleaved carrier signals for the upper and lower arms. Results show that CSMMCs and corresponding VSMMCs have analogous features. Hence, the development on VSMMCs can be used for reference to CSMMCs and vice-versa. Furthermore, the control designs for CSMMC-based STATCOM are presented and verified using simulations. The obtained results of the proposed STATCOM show that the steady-state and transient performance of the system are quite satisfactory. This makes the CSMMC suitable for HVDC and flexible ac transmission systems applications. [ABSTRACT FROM PUBLISHER]