Input-series Output-parallel Connection Research Articles

Decoupling Control of Cascaded Power Electronic Transformer Based on Feedback Exact Linearization

This article addresses the decoupling control design for the cascaded power electronic transformer (PET) in input-series–output-parallel connection. Due to the coupling and interaction between the submodules and between substages, in essence it is a complex nonlinear system. A nonlinear control strategy based on feedback exact linearization (FEL) is developed to decouple all the control objectives so as to realize the dc-link and output voltages fast stabilizing and the submodule balancing without coupling and interactions. Based on the separation of the ac current time-scale and dc voltage time-scale, the FEL control law is derived, and the specific tuning process of control parameters is given for desired control bandwidths. Taken the dynamic influences of the current-loop, filter, and delay into account, further analyses are made and compared with a dual active bridge (DAB) balancing control-based strategy to show the improvement on decoupling effect and dynamic performance of the proposed control. Finally, the simulation and experimental results verify the theoretical analysis, which exhibit better dynamic features and minimal coupling effect under the condition of bidirectional power changes and parameter inconsistency and uncertainty.

Comprehensive sharing control strategy for input‐series output‐parallel connected modular DC–DC converters

The systems consisting of multiple DC–DC converters with input-series output-parallel (ISOP) connection are widely used in high-power applications. In the ISOP connection, the total input voltage and output current should be divided equally between the converters. However, in order to achieve this purpose, a proper control scheme should be used. This study proposes two control schemes: (i) output current feedback (OCF) and (ii) input voltage feedback (IVF). Based on the power balance, in the IVF scheme, the total output current, and in the OCF scheme, the total input voltage are divided automatically between the converters, and there is no need to use an extra control loop. The IVF and the OCF control schemes consist of two control loops: a common output voltage regulator (OVR) loop and individual input voltage sharing loops in the IVF scheme or individual output current sharing loops in the OCF scheme. The proposed control scheme can effectively improve the stability and dynamic characteristics of system. Finally, both the results of the simulation and laboratory prototype of an ISOP system consisting two forward converters have verified the performance of the IVF and OCF control schemes.

Modular Dual-Active Bridge Converter Architecture

This paper describes a modular architecture based on the dual-active bridge (DAB) converter in input-series–output-parallel (ISOP) connection. This work is focused on the input voltage sharing to ensure a proper operation of each module by means of an active control of input and output voltages. A small-signal model of the modular architecture is proposed and a decoupled control loops’ scheme is used to implement the control strategy. An experimental setup has been built in order to validate the model of the DAB converter in ISOP connection and the proposed control strategy, taking different operating conditions and constructive parameter values into account.

Input-Series–Output-Parallel-Connected Buck Rectifiers for High-Voltage Applications

This paper presents input-series-output-parallel (ISOP) configuration for single-phase front-end buck rectifiers (BRs). The configuration is especially suitable for traction applications, where the complete rectification system needs to withstand high ac voltages and supply medium-power loads. The primary rectification module of the proposed configuration is based on pulsewidth-modulated BR (current source inverter topology). The desired isolation, mandatory for ISOP connection, is provided at the dc stage through a medium-frequency/high-frequency transformer. Equal power sharing by modules is achieved from the ac side through input voltage and current sharing. The proposed control scheme is configured using two loops. While the outer loop regulates the output dc voltage and active wave shaping of the source current, the inner loop ensures stable voltage sharing. The performance of the proposed ISOP configuration is verified using numerical simulation. Experimental verification is achieved through a 2-kW grid-connected laboratory prototype.