دانلود رایگان ترجمه مقاله مبدل DC-DC کلیدزنی نرم دوطرفه توده شده غیرایزوله (نشریه اسپرینگر 2017)

مبدل DC-DC کلیدزنی نرم دوطرفه توده شده غیرایزوله دارای PWM همراه با طرح کنترل تغییر فاز

Non-isolated stacked bidirectional soft-switching DC-DC converter with PWM plus phase-shift control scheme

Abstract

In this paper, a non-isolated stacked bidirectional DC-DC converter with zero-voltage-switching (ZVS) is introduced for the high step-up/step-down conversion systems. The extremely narrow turn-on and/or turn-off duty cycle existing in the conventional bidirectional buck-boost converters can be extended due to the stacked module configuration for large voltage conversion ratio applications. Furthermore, the switch voltage stress is halved because of the series connection of half bridge modules. The PWM plus phase-shift control strategy is employed, where the duty cycle is adopted to regulate the voltages between the input and output sides and the phaseshift angle is applied to achieve the power flow regulation. This decoupled control scheme can not only realize seamless bidirectional transition operation, but also achieve adaptive voltage balance for the power switches. In addition, ZVS soft-switching operation for all active switches is realized to minimize the switching losses. Finally, a prototype of 1 kW operating at 100 kHz is built and tested to demonstrate the effectiveness of the proposed converter and the control strategy.

1 Introduction

Energy storage systems (ESS) with bidirectional DC-DC converters are essential in renewable energy based microgrids, electric vehicles (EVs), transportations, et al [1–5]. Bidirectional DC-DC converters play the role of converting and transferring the electrical energy of the storage elements, which conduct both charge and discharge operation. As a result, the bidirectional DC-DC converters are the key interfaces for efficient energy management. Generally, the voltage of the storage elements is relatively low due to safety issues. Meanwhile, the bus voltage of the DC-based micro-grid, electric EVs and plug-in hybrid EVs (PHEVs) is relatively high in order to improve the system power level. Consequently, a step-up and step-down bidirectional converter is required to link the low voltage storage elements and high voltage bus. How to derive high efficiency DC-DC converters with large conversion ratio is still challengeable in the power electronics community.

Isolated bidirectional DC-DC converters with high-frequency transformer, such as the Flyback-based [6, 7], Forward-Flyback based [8], boost integrated Flyback rectifier/energy (BIFRED) based [9], dual half-bridge based [10, 11], dual active bridge (DAB) based converters [12–15] and their counterparts [16–22], can easily achieve high step-up/step-down conversion because the turns ratio of the transformer provides another control freedom for the voltage regulation. However, the conduction losses and transformer losses are a little high because the whole delivered energy will flow through the power switches and windings of primary and secondary sides.

If the passive diodes in buck or boost converters are replaced by active switches, the conventional bidirectional Buck-Boost converters are formed. They suffer from large switching losses due to the hard switching operation. In order to solve this problem, some active and/or passive components are inserted to achieve zero-voltage-switching (ZVS) or zero-current-switching (ZCS) performance [12, 23–26]. However, the additional active switches may increase the control complexity and the passive components may bring extra voltage or current stress on the power switches. More importantly, extreme duty cycle and high voltage stress for the power switches are inevitable in large conversion ratio and high voltage applications, which would limit the converter efficiency and dynamic response.

In order to avoid the extreme duty cycle operation, multi-level converters are attractive candidates [27, 28]. Three level bi-directional converters are proposed by introducing the three-level tank into the conventional bidirectional converters. The switch voltage stress is only half of the high-side voltage [29]. And the inductor is reduced to improve the dynamic response due to the reduced voltage step.

An advanced non-isolated stack bidirectional DC-DC converter is proposed in [30], which has a high step-up/ step-down conversion ratios. This converter is controlled by an optimized PWM method, which is divided into forward and reverse modes according to the power flow. Seamless mode change is realized by introducing an intermediate switching pattern. However, the PWM plus phase-shift control (PPS) control scheme, which is widely adopted in the isolated converters [31–33], can be employed in this non-isolated stack converter to improve the circuit performance. The duty cycle and phase shift angle of the PPS control strategy can not only balance the voltage of the high and low voltage side sources, but also regulate the power flow independently and smoothly, which eliminates the requirement of switching pattern change. Furthermore, due to the stack structure and PPS control method, the voltage stress of power switches is reduced to half of the high-side voltage and the extreme duty cycle operation is avoided in high step-up/step-down conversion systems. Moreover, ZVS soft switching operation is achieved for all the power switches without any additional active or passive components.

The outline of this paper is highlighted as follows. The brief introduction of the non-isolated stack converter with PPS control and the steady-state operation analysis are illustrated in Section 2. The performance characteristics of the converter are specified in Section 3. Besides, the phaseshift angle selection analysis is implied in Section 4. The performance of the introduced converter is verified by a 1 kW prototype in Section 5. The main contributions of this paper are summarized in the last section.