Low-voltage Port Research Articles

A Coupled Inductor-Based Bidirectional DC-DC Converter with Step-Up Step-Down Operation for Electric Vehicle Applications

A coupled-inductor-based high step-up high step-down DC-DC converter with bidirectional capability suitable for electric vehicle (EV) applications is proposed in this paper. The voltage gain in both step-up and step-down operations is increased by a two-winding coupled inductor. The current ripple in the low-voltage port is low making it suitable for renewable energy sources. In addition, the low number of components causes the efficiency of the proposed converter to be competitive with similar topologies in the literature. Due to the use of only three bidirectional switches with low voltage stress, the cost and volume of the converter are reduced. To demonstrate the performance of the proposed bidirectional converter, an analysis of the operation modes in the steady state is presented. Also, a comparison between the suggested converter and other similar converters in the literature is provided. The results of these comparisons show that the proposed converter has a lower number of components and higher efficiency than the others. In addition, lower voltage stress and noticeable voltage gain in comparison with others are further results of these comparisons. Eventually, the experimental results in step-up and step-down operations are presented. In step-up operation, the experimental prototype is tested under fs = 50 kHz, VLow = 20 V, VHigh = 110 V, rated power = 120 W, with 94.60% efficiency. Furthermore, VHigh is considered 100 V with VLow = 33 V and 94.43% efficiency at 50 W rated power in step-down mode operation.

A Novel Fault Ride-Through Topology With High Efficiency and Fast Fault Clearing Capability for MVdc PV System

The multiport dc/dc converter with input independent output series structure is simple and efficient for photovoltaic (PV) applications. Through the cascade of sub-modules (SM), the converter has a high step-up ratio to connect MVdc bus. However, it has many ports which increase the risk of short-circuit faults. Therefore, this article proposes a fault ride-through (FRT) topology for multiport converter. When low-voltage ports are short-circuited, they can be isolated by blocking the switches of their own. The FRT topology can support the output voltage of faulty SMs to avoid the disconnection from MVdc bus. Other healthy ports can still generate power to MVdc bus. When the medium-voltage port is short-circuited, the FRT topology can quickly clear the fault current to prevent devices from being damaged. Due to the zero voltage switching, the proposed topology has higher efficiency. For medium-voltage fault, the FRT topology has faster fault clearing speed because more capacitors are reused. Finally, the proposed topology is verified by simulation and experiment.

Control of a Hybrid Modular Solid-State Transformer for Uninterrupted Power Supply Under MVdc Short-Circuit Fault

Modular multilevel converter (MMC)-based solid-state transformers (M-SSTs) show promise in hybrid ac/dc distribution grids where there is need for a medium-voltage dc (MVdc) interface. It can be used to interconnect several distribution networks with different voltage forms and levels and enable flexible power flow among them. In an M-SST, the MVdc short-circuit fault is a critical issue due to the rapidity of the fault current, which can cause device damage and power failure of the low-voltage (LV) grids. Aiming at addressing this issue, this article proposes a fault-mode control strategy applied to a hybrid M-SST topology for uninterrupted power supply of its LV ports. The topology consists of a hybrid MMC with both half- and full-bridge submodules and isolated bidirectional dc–dc converters. Through the proposed control, the fault current is eliminated when an MVdc short-circuit fault occurs. The hybrid M-SST can keep uninterrupted power interaction between the MVac port and the LVdc port during the fault, thereby improving power supply reliability. Moreover, an improved capacitor voltage balance control and an optimized modulation scheme are developed and included in the uninterrupted operation scheme to maintain the harmonic performance of the ac port. The feasibility and effectiveness of the proposed topology and control are verified by simulation and experimental results.

Split Duty Cycle Coupled Multiphase Boost–Buck Converter

The classic boost and buck cascaded converter has inductors at the input and output ports of the converters, which makes it ideal interface for bidirectional battery charging applications where accurate current control and low ripple currents are required. This paper proposes a split duty cycle coupled multi-phase variant applied to the cascaded boost-buck converter and utilizing coupled inductor features to achieve very lower current ripples at the output,lower power losses, reduction in magnetic component volume. Moreover, current sharing between each phase is inherently implemented, making it suitable for high conversion ratio bidirectional operation in a systematic energy storage applications where the low voltage port has very high current. The paper covers split duty cycle converter operation principle using coupled inductors between input and the multi-phase output. Magnetic component design and selection guidelines are presented. The proposed control method and coupled inductor structure are validated by simulation and experimental results.

Three-Port Series-Resonant DC/DC Converter for Automotive Charging Applications

In the energy distribution grid of electric vehicles (EVs), multiple different voltage potentials need to be interconnected, to allow arbitrary power flow between the various energy sources and the different electrical loads. However, between the different potentials, galvanic isolation is absolutely necessary, either due to safety reasons and/or due to different grounding schemes. This paper presents an isolated three-port DC/DC converter topology, which, in combination with an upstream PFC rectifier, can be used as combined EV charger for interconnecting the single-phase AC mains, the high-voltage (HV) battery and the low-voltage (LV) bus in EVs. The proposed topology comprises two synergetically controlled and magnetically coupled converter parts, namely, a series-resonant converter between the PFC-sided DC-link capacitor and the HV battery, as well as a phase-shifted full-bridge circuit equivalent in the LV port, and is mainly characterized by simplicity in terms of control and circuit complexity. For this converter, a simple soft switching modulation scheme is proposed and comprehensively analyzed, in consideration of all parasitic components of a real converter implementation. Based on this analysis, the design of a 3.6 kW, 500 V/500 V/15 V prototype is discussed, striving for the highest possible power density and as low as possible manufacturing costs, by using PCB-integrated windings for all magnetic components. The hardware demonstrator achieves a measured full-load efficiency in charge mode of 96.5% for nominal operating conditions and a power density of 16.4 kWL−1.

SIDO coupled inductor‐based high voltage conversion ratio DC–DC converter with three operations

Here, a single-input, dual output (SIDO) coupled inductor-based high voltage conversion ratio DC–DC converter is proposed. The proposed converter has the capability of operating as a SIDO converter in a way that the terminal of the input voltage source is exchangeable among the three ports. Therefore, there are three different operation modes for the proposed converter. The voltage conversion ratios of the high voltage ports over the low voltage port can be improved by increasing the turn ratio of the coupled inductors. The main advantage of the proposed converter is achieving high voltage gains with lower number of components for the whole range of duty cycles comparing to the conventional multi-port high voltage gain converters. Moreover, two output voltages of the proposed converter can be simultaneously regulated on different constant levels with a good precision. In this study, the voltage conversion ratios, the inductors’ average currents, the voltage and current stress on the switches are calculated theoretically. Finally, an experimental prototype of 30 V input and 410, 260 V outputs with the power 510 W is implemented and the results are verifying the theoretical ones.

Short-Circuit Fault-Tolerant Topology for Multiport Cascaded DC/DC Converter in Photovoltaic Power Generation System

A multiport dc/dc converter with cascaded submodules (SMs) can be employed in a photovoltaic (PV) power generation system for its high step-up ratio. Consisting of multiple low-voltage (LV) input ports and one high-voltage (HV) output port, the multiport converter is more likely to suffer short-circuit faults than a two-port converter. To ensure reliable operation of the converter, its short-circuit fault-tolerant capability should be necessarily considered. In this article, a short-circuit fault-tolerant topology for multiport cascaded dc/dc converter in the PV power generation system is proposed to satisfy the requirements of fault tolerance ability. When one or more short-circuit faults occur at LV ports, the proposed topology guarantees the normal operation of other fault-free SMs. When a short-circuit fault occurs at the HV port, the short-circuit fault current can be interrupted rapidly by the fault-tolerant topology, which protects the converter from a large current surge. The fault-tolerant ability of the proposed topology is verified by both simulation and experimental results.

A New Hybrid Structure of a Bidirectional DC-DC Converter With High Conversion Ratios for Electric Vehicles

In this paper, a new bidirectional dc-dc converter that is based on the quadratic and switched-capacitor structures is proposed for Electric Vehicle applications. The proposed converter has high voltage conversion ratios, low voltage stress on the semiconductor devices, constant potential difference between the grounds of its low voltage and high voltage ports, and continuous current at its low voltage port. Synchronous rectification is utilized to enhance the efficiency of the converter. In addition, an extended version of the proposed converter is discussed in this paper. Finally, the experimental results obtained from a 2-kW/800-V scaled-down prototype validate the feasibility of the proposed topology and the correctness of its theoretical analysis.

Non‐isolated high step‐up three‐port converter with single magnetic element for photovoltaic systems

A new non-isolated high-voltage gain three-port converter for standalone photovoltaic systems is proposed. The magnetic element of this converter is only one coupled inductor. The primary winding of the coupled inductor is shared between battery charger circuit and main converter. Leakage inductance energy of the coupled inductor is either transferred to battery or is regenerated via the passive-clamp circuit. Using switched capacitor and voltage lift techniques, the voltage gain is significantly increased for both low-voltage ports. Single magnetic element, high-voltage gain with reasonable duty cycle, low-voltage stress on the switches, low winding turn ratio of coupled inductor and high efficiency are the merits of this converter. The operation principles and the steady-state analysis are described for the three modes of: single-input single-output, single-input dual-output and dual-input single-output. To verify the theoretical analysis, a laboratory prototype with 28 V input, 48 V battery voltage and 380 V output voltage is implemented and tested.

Novel Three-Port Converter With High-Voltage Gain

In this paper, a novel three-port converter (TPC) with high-voltage gain for stand-alone renewable power system applications is proposed. This converter uses only three switches to achieve the power flow control. Two input sources share only one inductor. Thus, the volume can be reduced. Besides, the conversion ratio of the converter is higher than other TPCs. Thus, the degree of freedom of duty cycle is large. The converter can have a higher voltage gain for both low-voltage ports with a lower turns ratio and a reasonable duty ratio. The voltage stress of switches is low; thus, conduction loss can be further improved by adopting low Rds(on) switches. Therefore, the converter can achieve a high conversion ratio and high efficiency at the same time. The operation principles, steady-state analysis, and control method of the converter are presented and discussed. A prototype of the proposed converter with a low input voltage 24 V for photovoltaic source, a battery port voltage 48 V, and an output voltage 400 V is implemented to verify the theoretical analysis. The power flow control of the converter is also built and tested with a digital signal processor.

Efficiency-Optimized High-Current Dual Active Bridge Converter for Automotive Applications

An efficiency-optimized modulation scheme and design method are developed for an existing hardware prototype of a bidirectional dual active bridge (DAB) dc/dc converter. The DAB being considered is used for an automotive application and is made up of a high-voltage port with port voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , 240 V ≤ V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ≤ 450 V, and a low-voltage port with port voltage V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , 11 V ≤ V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ≤ 16 V; the rated output power is 2 kW. A much increased converter efficiency is achieved with the methods detailed in this paper: The average efficiency, calculated for different voltages V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> and V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> , different power levels, and both directions of power transfer, rises from 89.6% (conventional phase shift modulation) to 93.5% (proposed modulation scheme). Measured efficiency values, obtained from the DAB hardware prototype, are used to verify the theoretical results.

Accurate Small-Signal Model for the Digital Control of an Automotive Bidirectional Dual Active Bridge

The derivation of an accurate small-signal model for a galvanically isolated, bidirectional dc-dc converter and the implementation of a corresponding controller on a DSP as well as key methods and functions required for the digital implementation are detailed in this paper. The investigated dc-dc converter, an automotive dual active bridge (DAB) system, enables power transfer between a low-voltage port (ranging from 11 to 16 V) and an HV port (240 to 450 V). The nominal power rating is 2 kW. The developed small-signal model yields highly accurate results for the DAB system, but the proposed modeling procedure could also be applied to arbitrary resonant power converters with unidirectional or bidirectional power transfer.