Input-series-output-parallel Research Articles

Analysis and control design for input‐series output‐parallel multi‐channel inductive power transfer system

AbstractTo realize high‐power inductive power transfer (IPT) for fast charging of electric vehicles (EVs), an input‐series output‐parallel (ISOP) multi‐channel IPT system is analysed in this paper, and an output control strategy based on single neuron controller is proposed to improve the stability of the system. Firstly, the steady‐state operating conditions of ISOP‐IPT system is analysed based on different compensation networks which shows that the constant‐voltage‐output compensation networks are more suitable for the proposed circuit structure. Then, to improve the voltage equalization between channels, an open‐loop control method combining parameter design and phase‐shift control is proposed against different coil misalignments. At the same time, based on the single neuron controller, the system output closed‐loop control is realized without the need of accurate system modelling. Finally, a three‐channel ISOP‐IPT experimental system was constructed, which operated stably at 2.9 kW with a power efficiency of 93.38%. The system closed‐loop control with control time of 22 ms is realized. The voltage equalization control offset is less than 1%.

A new winding structure with low common‐mode current in input series output parallel planar transformer LLC converter

AbstractMHz switches and integrated magnetic planar transformers (PT) promote the high density and miniaturization of DC/DC converters. The parasitic parameters of the PT at high frequency significantly affect the performance of converters, resulting in severe electromagnetic interference (EMI) problems. Firstly, this paper proposes a new common‐mode (CM)‐suppression winding structure for the input series output parallel (ISOP) matrix transformer LLC converter. The sources and conduction principle of CM noise are analyzed. Furthermore, this optimization based on winding shape and position is simple and feasible, suppressing the CM noise significantly. Compared with conventional multilayer winding structure, this optimization increases the current‐carrying area by 2.8%–5.9%, effectively improving the primary current distribution. In addition, the proposed structure makes the best planar windings in footprint with expanded windings, bringing the simplest layout in the primary winding. Finally, a 1 MHz 400 V/12 V 300 W LLC converter is constructed to verify the effect of this winding structure. The results show that a 40% reduction in CM current can be achieved while maintaining the current balance.

An Input-Series Output-Parallel DC–DC Converter Based on Fuzzy PID Three-Loop Control Strategy

In order to achieve high and low voltage isolation transformation in DC transmission and distribution networks, a multi module input-series output-parallel (ISOP) system consisting of a buck/boost converter and a CLLLC resonant converter as submodules was studied. This system can ensure that the CLLLC converter operates in the optimal state during frequency changes, achieves a soft switching function, and maintains a high conversion efficiency. This article establishes a mathematical model of a cascaded converter, analyzes its gain characteristics, and proposes a fuzzy PID three-loop control strategy to achieve good input voltage and output current sharing in the ISOP system. A simulation model is built on the MATLAB(R2023a)/Simulink platform to verify the effectiveness and superiority of the proposed control strategy. Finally, by building a prototype platform, the feasibility of the ISOP system and the effectiveness of fuzzy PID three-loop control were verified through experiments.

Input-parallel output-series Si-SiC hybrid inverter with fractional harmonic elimination

This paper proposes an input-parallel output-series (IPOS) Si-SiC hybrid inverter with dual-frequency harmonic elimination modulation strategy. The proposed topology composed of two power conversion cells and a three-phase five-column medium-frequency step-down transformer, the low-frequency power conversion cell (LFPC-C, 1 kHz) leverages strong current-carrying capacity of silicon-based devices for dealing with the system main power, and the high-frequency power conversion cell (HFPC-C, 30 kHz) based on wide-bandgap semiconductor SiC devices is used to addressing the fractional harmonics compensation power. This topology combines the strong current carrying capability of Si devices with the low switching loss of SiC devices at high frequency and achieves high quality power conversion at low cost and low loss. Compared to existing “IPOP” Si-SiC hybrid inverters, this topology adopts a coupling step-down transformer on the output side of both LFPC-C and HFPC-C, which can effectively reduce current stress of HFPC-C SiC devices. Additionally, a dual-frequency harmonic elimination modulation strategy based on the topology is proposed to solve the fractional harmonics caused by the LFPC-C. The paper establishes a mathematical model according to the harmonic distribution characteristics of the LFPC-C and HFPC-C, and designs the system control schedules. Building upon the derivation of the voltage ripple model and the design of hardware parameters, Si IGBT and SiC MOSFET were selected for constructing a 7.5 kW prototype for testing, and the experimental results validate the feasibility of this topology and the accuracy of theoretical analysis.

Research on Hybrid Rectifier for High Power Electrolytic Hydrogen Production Based on Modular Multilevel Converter

Aiming at the problem that silicon-controlled rectifiers (SCR) and pulse width modulation (PWM) rectifiers cannot balance high power levels, high hydrogen production efficiency, and high grid connected quality in the current research on rectifier power supplies for electrolytic hydrogen production, a new hybrid rectifier topology based on a modular multilevel converter (MMC) is proposed. The hybrid topology integrates a silicon-controlled rectifier (SCR) with an auxiliary power converter, wherein the SCR is designated as the primary power source for electrolytic hydrogen production. The auxiliary converter employs a cascaded modular multilevel converter (MMC) and an input-series-output-parallel (ISOP) phase-shifted full-bridge (PSFB) arrangement. This configuration allows the auxiliary converter to effectively mitigate AC-side harmonics and minimize DC-side ripple, concurrently transmitting a small amount of power. The effectiveness of the hybrid rectifier in achieving low ripple and harmonic distortion outputs was substantiated through hardware-in-the-loop experiments. Notably, the hybrid topology is characterized by its enhanced electric-to-hydrogen conversion efficiency, elevated power density, cost efficiency, and improved grid compatibility.

The Study of Multi-Terminal DC Systems in an Offshore Wind Environment: A Focus on Cable Ripple Analysis

This paper studies the THD and AC losses on the DC cables of offshore wind farm-based multi-terminal HVDC systems when they extract and deliver power from and to more than one connection point. In the paper, the study of a full system PLECS + Simulink model with two branches, including a wind resource, a wind turbine, a Permanent Magnet Synchronous Generator (PMSG), a Pulse Width Modulation (PWM) rectifier, a Single Active Bridge (SAB) DC–DC converter, an Input Parallel Output Series (IPOS) DC–DC converter, HVDC cables, and a simplified onshore system, is presented. It focuses on the investigation of the output ripple content of multiple DC–DC converters on DC cables under different wind conditions with different voltage and power ratings. The importance of the study is providing a general understanding of the operation of the innovative offshore wind farm-based DC system, as well as the interaction between different DC–DC converters and their influence on cable ripple content under different situations.

Novel Series-Parallel Phase-Shifted Full-Bridge Converters with Auxiliary LC Networks to Achieve Wide Lagging-Leg ZVS Range

Under light load conditions, the phase-shifted full-bridge (PSFB) converter often has difficulty in realizing the zero-voltage switching (ZVS) of the lagging-leg by relying on the energy of its resonant inductor; however, for the series-parallel PSFB converter applied in high-power applications, the lagging-leg still has the problem of difficult realization of ZVS. Based on this, the paper analyzes the reasons why the series-parallel PSFB converter has difficulty in achieving ZVS for the lagging-leg under light and heavy loads. Under interleaved control, the ZVS of the lagging-leg over the full load range is realized by adding an auxiliary LC branch at the midpoint of the lagging-leg of both submodules. Based on the double-bridge input-parallel-output-series (IPOS) PSFB converter, analyzing the working principle of the circuit after adding the auxiliary LC branch and extending it to the series-parallel PSFB converter. The design requirements of the LC auxiliary branch of the dual-bridge series-parallel PSFB converter are given and the effects of the LC auxiliary branch on the module operating state and device stress are analyzed. On this basis, an extension is carried out to give the working principle and design method of the auxiliary LC branch of the N-bridge series-parallel PSFB converter. Finally, a 100 kW Matlab/Simulink simulation model verifies the superior performance of the proposed LC auxiliary branch to realize the lagging-leg ZVS of the series-parallel PSFB converter under light and heavy loads and achieves a 1.09% peak efficiency improvement at rated load.

Review of DC-DC Partial Power Converter Configurations and Topologies

The Partial Power Processing (PPP) concept has garnered attention as it enables the down-sizing of converter and component ratings. Unlike conventional power processing, PPP addresses a portion of the transferred power, leading to a reduction in conversion losses. Throughout this paper, the state of the art of isolated and non-isolated DC-DC converter topologies will be revised. Partial Power Converter (PPC) systems represent one of the main streams of PPP, which, based on isolation requirements and converter connections, can further be divided into isolated converters, such as: Input-Parallel-Output-Series (IPOS), Input-Series-Output-Parallel (ISOP), and, Input-Series-Output-Series (ISOS), or non-isolated converters. This work intends to evaluate and differentiate the characteristics of each type of topology while developing analytically possible connections that may require further research and reviewing metrics that help in fair comparisons of different PPC arrangements, operating under different conditions. A thorough revision is provided for DC-DC converter topologies due to their increased importance in present-day applications, such as energy storage, Electric Vehicles (EVs), and Photo-Voltaics (PVs).

An open-circuit fault diagnosis strategy for input series output parallel dual active bridge DC/DC converter based on the mean of AC voltages and currents

An open-circuit fault diagnosis strategy for input series output parallel dual active bridge DC/DC converter based on the mean of AC voltages and currents

Modelling for Multiport Converter-based Hybrid Power supply for Renewable Energy Source Application

This research work deals with the design, modeling and technical evaluation of multiport modular converter based hybrid Power supply using solar PV for small village. The village’s maximum power demand is 50kvA, consisting of demands of twenty (20) households. The first converter in the proposed multiport system is a high frequency isolated DC-DC converter fed with HVDC link yielding an output voltage of 700vDC. The isolated DC-DC converter uses a medium frequency transformer with primary and secondary side converters in input-series output-parallel (ISOP) configuration. Also, the output of first converter is connected to a solar PV and battery system through a buck-boost converter. The second converter in the system is solar PV fed three phase modular inverter designed to have output AC line voltage of 0.415 kV. The three phase inverter is based on modular multilevel converter (MMC) with interleaved modulation techniques. A silicon carbide power MOSFETs, with model numbers CPM3-10000-0270(CREE) and SD11703 (Solitron) are used as a building blocks for isolated DC-DC converter. On the other hand, SiC -MOSFET with part number SCT3017AL (RHOM) is used as basic building block for modular inverter. A solar PV module with open circuit voltage of 85V and maximum power rating of 415W is used to feed the inverter. Different scenarios such as changes in load and changes in solar irradiance are used for critically evaluating the performances of the system under question. The output voltage THD, current distortions, changes in the converter output voltage, current magnitude and converter efficiency are used for performance evaluation of the system under consideration. Simulink/ PLECS (Piecewise Linear Electrical Circuit Simulation) combo simulation platform is used to model and simulate the system in question. Simulation results showed that the proposed multiport converter system can be a viable alternative to low frequency distribution transformer.
 Keywords: Multiport converter, MMC, DC-DC converter, Hybrid power Supply, Solar PV.

Unified Real-Time Simulation Method for DC/DC Conversion Systems Consisting of Cascaded Dual-Port Submodules

The DC/DC conversion systems are constructed from multiple cascaded dual-port submodules in series and/or parallel at both the input port and output port. The complexity of the series-parallel structures brings great challenges to real-time simulation. This paper proposes a unified real-time simulation method of series-parallel DC/DC conversion systems, which unifies the input-series-output-series (ISOS), input-series-output- parallel (ISOP), input-parallel-output-parallel (IPOP) and input-parallel-output-series (IPOS) structures. First, based on the nodal analysis method, the dual-port equivalent model of each submodule in the series-parallel DC/DC conversion system is obtained. Second, by cascading each submodule, the unified form of the system dual-port equivalent model of the series-parallel DC/DC conversion system is constructed. For the series connection, the port is equivalent to Thevenin's equivalent circuit. For the parallel connection, the port is equivalent to Norton's equivalent circuit. The real-time simulation model of a specific series-parallel DC/DC conversion system can be obtained by combining the input/output port equivalent circuits. Besides, the high-frequency waveforms of the internal circuit can also be obtained through parallel calculation steps. The real-time simulation of the proposed unified model is carried out with a 250ns time-step on Xilinx K-7 Series FPGA, which verifies the accuracy and simulation efficiency of the unified model.

A Hybrid Interleaved DC-DC Converter Based on Buck-Boost topologies for Medium Voltage Applications

DC-DC power converters with high voltage gain are primary components for renewable energy generation such as offshore wind farms. As the DC-DC converters installed in these farms should have limited size and weight, the non-isolated DC-DC converters are the most suitable choose for the offshore wind farms. Although, several DC-DC converters with high voltage gain have been developed for offshore wind farms. Most of them includes large count of semiconductors or experiences high voltage stresses. In this paper, a reduced components count converter is proposed for the collector system of offshore wind farms. The proposed topology is a modular input parallel output series non-isolated DC-DC converter. It is a hybrid interleaved structure which combines two buck-boost topologies into a single converter. The proposed converter aims to offer high voltage gain with reduced voltage and current stress on the converter's components. Moreover, the interleaved PWM offers limited output voltage ripple and supply current ripple. The operation modes and the steady-state performance of the proposed converter are analysed. In addition, a small signal model based on the state space averaged method is developed for the proposed converter. The accuracy of the developed model is verified using the converter's switching model. Furthermore, the output voltage control scheme utilizing a simple PI controller for the proposed converter is presented.

Decentralized Control Strategy for Switching Harmonic Elimination of Modularized Input Parallel Output Series Dual Active Bridge Converter

Decentralized Control Strategy for Switching Harmonic Elimination of Modularized Input Parallel Output Series Dual Active Bridge Converter

Experimental Validation of 40 kW EV Charger Based on Vienna Rectifier and Series-Resonant Dual Active Bridge

This work presents the experimental validation of a 40 kW electric vehicle (EV) charger. The proposed system comprises two 20 kW modules connected in parallel at the input and output. Each module has two stages—as a grid converter Vienna Rectifier (VR) was chosen, and as an isolated DC/DC stage, two Series-Resonant Dual-Active-Bridges (SRDABs) in input-series-output-parallel (ISOP) configurations were applied. The AC/DC and DC/DC stages were enclosed in 2U rack standard housing. A bipolar DC-link with ±400 V DC voltage was employed to connect both stages of the charger module while the charger’s output is dedicated to serving 800 V batteries. VRs operated at 66 kHz switching frequency and the SRDABs operated at 100 kHz. The converters used in the charger structure were based on silicon carbide (SiC) power devices. The description and parameters of the built hardware prototypes of both—AC/DC and DC/DC—converters are provided. Moreover, the experimental validation of each stage and the whole charging system, including oscilloscope waveforms and power analyzer measurements at nominal power, are included. Such a configuration enables energy conversion with high efficiency without a negative impact on the grid and high-quality grid waveforms.

Magnetic Integration for Multiple Resonant Converters

A universal integration method for the magnetic components (MCs) of multiple resonant converters is proposed in this article. Two rules for integration of multiple independent MCs are summarized, one of which is to keep functional independent of MCs after integration, while the other is to achieve lower loss and volume through integration. Following the proposed rules and by dividing an MC into winding-part and nonwinding-part, integration is achieved by sharing the nonwinding-part of the MCs. An input-series output-parallel (ISOP) resonant converter is taken as an example to show how integration is accomplished step by step. It is shown that, both volume and loss of the magnetic cores are reduced after integration of all the high frequency transformers and inductors. Detailed theoretical analysis, finite element analysis simulations and comparisons have been presented. A 600 V–800 V input, 28 V/2000 W-output ISOP resonant converter was built. Experimental results have been provided to verify the effectiveness and feasibility of the proposed integration methods.

On the Impedance and Stability Analysis of Dual-Active-Bridge-Based Input-Series Output-Parallel Converters in DC Systems

Dual-active-bridge-based (DAB-based) input-series output-parallel (ISOP) converters have become increasingly popular due to their promising features made up of the advantages of the modular power electronics and the DAB converter. The modeling of the DAB converter and the DAB-based ISOP converter has been widely explored for control design in order to analyze the stability and improve the performance of the converter itself such as the voltage balancing and power sharing of DAB submodules. However, the modeling on the impedance of the DAB-based ISOP converter, which can be quite useful for system-level stability analysis and optimization, has not been addressed sufficiently so far. To solve this issue, this paper presents comprehensive impedance modeling of the DAB-based ISOP converter, where the output voltage control and the input voltage balancing control are applied to the converter to achieve the equal power sharing of the submodules. The proposed input impedance model and output impedance model of the DABbased ISOP converter are validated through the frequencydomain sweep in simulation and experiment. With the validated impedance models, the instability phenomenon and the frequency of the main harmonic component in oscillating waveforms can be accurately predicted at the source side and at the load side of the converter respectively.

Analysis and Design of a Partial Power Processing Architecture for High Step-Up Applications

Combining the advantageous features of the traditional two-stage and input-parallel-output-series (IPOS) structure, this paper proposes a partial power connection method for step-up applications with the advantages of wide input voltage range, galvanic isolation and partial power voltage regulation. In the proposed structure, the non-isolated DC-DC converter handles a small portion of the total power to regulate the system output voltage by simple PWM control. The latter stage should be a full bridge structure and the partial power processing is realized with different input voltages of the two bridge arms, which is beneficial to reduce the total number and cost of components, and two connection architectures are achieved in this way. The operation characteristics of the two architectures are analyzed in detail in this paper, and an optimal structure is obtained from the perspective of fewer components and better partial power processing capacity. Further, an isolated full bridge DC-DC converter with secondary resonance is selected to operate at the unregulated state as an application case to verify the feasibility and advantages of the proposed structure. An experimental prototype with 32-40V input voltage range and 400V/ 0.5A output is built with 1MHz switching frequency. The peak measured efficiency at 40V full load is 95.3%.

Minimizing Input Current Ripple for Four-Phase Input-Parallel Output-Series DC–DC Converter With Phase-Shift Modulation

This paper proposes a PWM scheme based on phase-shift modulation (PSM) for the four-phase input-parallel output-series (4P-IPOS) converter. And operation with dual-output configuration is investigated. The natural output voltages and inductor currents balancing can be achieved even without any extra components or dedicated control. In addition, compared with the conventional PWM scheme, performance improves. The input current ripple is reduced significantly at high voltage gain. An 800-W prototype of the 4P-IPOS converter was built and tested to verify the performance of the suggested scheme.

Isolated Cascaded DAB DC-DC Converter to Boost Medium DC Voltage to HVDC

The offshore wind farms typically use ac system to collect power from each generator, with the voltage increased by means of high, heavy step-up transformers. DC collection grids have also recently been taken into consideration as solution to simplify and minimize the offshore windfarm platforms. DC collection grids offer an additional method to reduce complexity of offshore windfarms. However, to increase the DC voltage for HVDC transmission requires the development of high-power and high voltage converters, which presents a technical challenge. This research makes use of an isolated cascaded dual active bridge (DAB) DC-DC converter to boost medium DC voltage to HVDC. Isolated Cascaded DAB DC-DC Converters are connected in series on the output side and in parallel on the input side to obtain a high transformation ratio and high power. The bidirectional DAB DC-DC converters cab be designed with power densities in the variability of tens to hundreds of kilowatts, depending on the components used and the switching frequency at which the converters function most effectively. The input parallel output series (IPOS) topology, 225 kV HVDC can be generated from a 5 kV MVDC input by cascading DAB DC-DC up to 30 stages. This converter family is useful due to its scalability and flexibility, since the power and voltage ratings can be increased while still using the same cells. MATLAB Simulink simulations are performed and verified the elementary operating characteristics of the system.

Analysis and Suppression of Rectifier Diode Voltage Oscillation Mechanism in IPOS High-Power PSFB Converters

Parasitic oscillations in the rectifier diode voltage of phase-shifted-full-bridge (PSFB) converters limit their application in high-voltage and high-power situations. The conventional analysis method for parasitic oscillation in rectifier diode voltage in PSFB converters treats the filter inductor as a constant current source and fails to consider the impact of changes in filter inductor current on the rectifier diode’s parasitic oscillation. Consequently, this approach does not apply when analyzing the rectifier diode voltage’s parasitic oscillations in high-power PSFB converters employing an input-parallel output-series (IPOS) configuration with interleaved drive. This research paper introduces an innovative equivalent circuit model for analyzing the parasitic oscillations of rectifier diode voltage in IPOS high-power PSFB converters. The model takes into account the mutual influence of rectifier diode voltage oscillations between submodules under interleaved control, considering the influence of changes in filter inductor current on rectifier diode parasitic oscillation. Based on the circuit model, we explain the mechanism of multiple oscillations of the rectifier diode voltage and the reason for the high peak of the first oscillation. Consequently, the interplay of rectifier diode voltage oscillations in IPOS high-power k-module PSFB converters under interleaved control is analyzed. To mitigate the adverse effects of rectifier diode voltage parasitic oscillation, a buffering strategy involving the connection of a resistor capacitor diode (RCD) circuit in parallel after the rectifier bridge is adopted, considering the structure of the IPOS high-power PSFB converter. The study provides a detailed analysis of the circuit’s operation mechanism upon incorporating the RCD buffer circuit and establishes the relationship between buffer capacitance, resistance, and spike voltage. Furthermore, a design method for buffer capacitors and discharge resistors in buffer circuits is presented. Finally, a 100 kW prototype is tested to verify the rectifier diode voltage oscillation mechanism of the IPOS high-power PSFB converter and the rationality of the buffer capacitor and discharge resistor design method under the interleaved drive approach.