Input-series And Output-parallel Research Articles

A H-Bridge-Multiplexing-Based Novel Power Electronic Transformer

Cascaded H-bridge power electronic transformers (CHB-PET) play a pivotal role in distribution grids and their efficient operation. The input series and output parallel (ISOP) configurations result in a huge number of power switching devices, high-frequency transformers (HFT), and capacitors in high-voltage, high-capacity CHB-PET, leading to the need for high hardware costs and huge-sized CHB-PET, which further poses a significant challenge to the engineering feasibility and marketability of the CHB-PET. To address these issues, a CHB-PET topology is proposed in this paper. The novel topology exploits the concept of multi-frequency modulation to achieve power decoupling and power unit multiplexing through reasonable LC resonant frequency selection, which optimizes the ISOP structure and ultimately reduces the hardware cost and size of the CHB-PET. In this study, the effectiveness of reducing the number of power switching devices and HFT is firstly analyzed, and after describing its working principle, the control strategy of each power conversion link of PET is discussed before the correctness and effectiveness of the CHB-PET topology and control strategy proposed in this paper are verified via simulation.

A Modular Non-Inverting Buck-Boost DC-DC Converter

DC-DC power converters with high voltage gain play a critical role in DC power collection topologies for offshore wind farms and their HVDC transmission systems. This paper proposes a modular DC-DC converter with high voltage gain based on a non-inverting buck-boost topology for high-power applications. The proposed converter consists of three non-inverting buck-boost modules connected as input-parallel and output series (IPOS). The reduced voltage stress on power devices, the increased voltage gain, and enhanced power conversion efficiency are all advantages of the proposed IPOS cascaded converters. However, IPOS cascaded DC-DC converters have a voltage balancing issue on the output side. The operation modes and the dynamic performance of the proposed converter are studied in both cases of identical and non-identical converter modules. Moreover, a novel state-space model for the proposed converter with non-identical modules and different control signals is developed. This model has been verified using the converter's switched model, and the result reveals that the developed model is accurate. Furthermore, output capacitors voltage balancing control scheme based on simple PI controllers for the proposed DC-DC converter is presented. The capacitor voltages are hence perfectly balanced. In addition, the presented controller system achieves a fast response with negligible oscillations and steady-state error. MATLAB/Simulink software package is used to simulate the proposed converter, investigate its operation, and examine the converter's dynamic behaviour.

A New Coupled-Inductor-Based High-Gain Interleaved DC-DC Converter With Sustained Soft Switching

This paper presents a new soft switching high voltage gain interleaved dc-dc converter with a three-windings coupled inductor for a fuel cell vehicle. Two interleaved and intercoupled boost cells are connected by the input parallel and output series (IPOS) configuration, realizing low input current ripple and high voltage gain simultaneously. All power switches can operate under soft switching conditions by only adding a simple auxiliary circuit composed of one auxiliary inductor and one power switch. Besides, the auxiliary inductor is coupled with the main inductors, which results in a rapid zero convergence of the auxiliary current and a small conduction loss of the auxiliary circuit. The operating principle, steady state characteristic, comparison with other converters, and parameter design are analyzed in this paper. Finally, the main characteristics of the proposed converter are verified by a 1-kW laboratory prototype.

15 kV SiC MOSFET: An Enabling Technology for Medium Voltage Solid State Transformers

Due to much higher achievable blocking voltage and faster switching speed, power devices based on wide bandgap (WBG) silicon carbide (SiC) material are ideal for medium voltage (MV) power electronics applications. For example, a 15 kV SiC MOSFET allows a simple and efficient two-level converter configuration for a 7.2 kV solid state transformer (SST) for smart grid applications. Compared with multilevel input series and output parallel (ISOP) solution, this approach offers higher efficiency and reliability, reduced system weight and cost by operating at medium to high switching frequency. However, the main concern is how to precisely implement this device in different MV applications, achieving highest switching frequency while maintaining good thermal performance. This paper reviews the characteristics of 15 kV SiC MOSFET and offers a comprehensive guideline of implementing this device in practical MV power conversion scenarios such as AC-DC, DC-DC and AC-AC in terms of topology selection, loss optimization and thermal management.

Fault Tolerant Operation of ISOP Multicell Dc-Dc Converter Using Active Gate Controlled SiC Protection Switch

An active gate controlled semiconductor protection switch using SiC-MOSFET is proposed to achieve the fault tolerant operation of ISOP (Input Series and Output Parallel) connected multicell dc-dc converter. The SiC-MOSFET with high temperature capability simplifies the configuration of the protection circuit, and its on-resistance control by the active gate controller realizes the smooth protection without the voltage and the current surges. The first laboratory prototype of the protection switch is fabricated by using a SiC-MOSFET with a high frequency buck chopper for the active gate controller. The effectiveness of the proposed protection switch is verified, taking the impact of the volume reduction into account.

Design Consideration for High Power Density GaN Buck-Rectifier in ISOP-IPOS Converter based dc Distribution System

GaN (gallium nitride) buck-rectifier has been proposed to realize high power density ISOP (input series and output parallel)-IPOS (input parallel and output series) converter-based dc distribution system. The ultra-low loss bi-directional switch can be developed by the GaN power device because of the low on-resistance, the high-speed switching behavior and its own device structure. The buck-rectifier using the GaN bi-directional switches has the potential to achieve higher power density than the commonly utilized boost-rectifier. Availability of the GaN-HEMT (high electron mobility transistor) for the buck rectifier has been verified taking the theoretical limit of the on-resistance and the switching loss energy into account. Design consideration for a high power density buck-rectifier has been also conducted and the application effect of the GaN bidirectional switches has been evaluated quantitatively. The ISOP-IPOS converter-based dc (direct current) distribution system takes full advantage of the buck-rectifier and the rectifier using GaN devices contributes to realizing higher power density dc distribution system.

Feed-Forward Control of Input-Series and Output-Parallel DC Transformer

The input-series and output-parallel (ISOP) DC transformer, which has no output filter, runs under near 100% duty ratio, and is easily achieve zero voltage switching (ZVS) conditions and higher efficiency, is more and more attractive in the high input voltage and high power applications. In order to achieving input voltages sharing in ISOP DC transformer based on two non-resonant DC transformer modules, the feed-forward control method is proposed in this paper. And the principle of the proposed control is analyzed in detail. Finally, experimental results are given to verify the proposed control method to have a good ability of sharing the input voltages.

Master/Slave Control of Input-Series- and Output-Parallel-Connected Converters: Concept for Low-Cost High-Voltage Auxiliary Power Supplies

This paper deals with low-cost high input voltage auxiliary power supplies. The objective of the paper is to give an overview of the existing solutions, and then present a new, efficient, and cost-effective solution. The proposed solution is based on input-series- and output-parallel (ISOP)-connected converters topology and simple decoupled master/slave control strategy. The main output voltage is controlled by the master converter, while the input voltages and output currents are controlled and balanced by the slave converter. The ISOP topology has two important advantages, namely the use of two series-connected rated for lower voltage converters gives a significant reduction of the switch-mode power supply overall cost and size, and loss free balancing of the voltages of the input serially connected filter capacitors. The proposed solution is theoretically analyzed and experimentally verified on a laboratory setup. The experimental results are presented and discussed.

Common-duty-ratio control of input-series connected modular DC-DC converters with active input voltage and load-current sharing

This paper proposes a simple control method to achieve active sharing of input voltage and load current among modular converters that are connected in series at the input and in parallel at the output. The input-series connection enables a fully modular power-system architecture, where low voltage and low power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for very low R/sub DSON/, thus, resulting in lower conduction losses. In the proposed scheme, the duty ratio to all the converter modules connected in input-series and output-parallel (ISOP) configuration is made common. This scheme does not require a dedicated input-voltage or load-current-share controller. It relies on the inherent self-correcting characteristic of the ISOP connection when the duty ratio of all the converters is the same. The proposed scheme is analyzed using the average model of a forward converter. The stability and performance of the scheme are verified through numerical simulation, both in frequency domain and in time domain. The proposed control method is also validated on an experimental prototype ISOP system comprising of two forward converters.

Active Input–Voltage and Load–Current Sharing in Input-Series and Output-Parallel Connected Modular DC–DC Converters Using Dynamic Input-Voltage Reference Scheme

This paper explores a new configuration for modular DC/DC converters, namely, series connection at the input, and parallel connection at the output, such that the converters share the input voltage and load current equally. This is an important step toward realizing a truly modular power system architecture, where low-power, low-voltage, building block modules can be connected in any series/parallel combination at input or at output, to realize any given system specifications. A three-loop control scheme, consisting of a common output voltage loop, individual inner current loops, and individual input voltage loops, is proposed to achieve input voltage and load current sharing. The output voltage loop provides the basic reference for inner current loops, which is modified by the respective input voltage loops. The average of converter input voltages, which is dynamically varying, is chosen as the reference for input voltage loops. This choice of reference eliminates interaction among different control loops. The input-series and output-parallel (ISOP) configuration is analyzed using the incremental negative resistance model of DC/DC converters. Based on the analysis, design methods for input voltage controller are developed. Analysis and proposed design methods are verified through simulation, and experimentally, on an ISOP system consisting of two forward converters.