A Bidirectional Dual Buck-Boost Voltage Balancer with Direct Coupling Based on a Burst-Mode Control Scheme for Low-Voltage Bipolar-Type DC Microgrids

Abstract

DC microgrids are considered as prospective systems because of their easy connection of distributed energy resources (DERs) and electric vehicles (EVs), reduction of conversion loss between dc output sources and loads, lack of reactive power issues, etc. These features make them very suitable for future industrial and commercial buildings' power systems. In addition, the bipolar-type dc system structure is more popular, because it provides two voltage levels for different power converters and loads. To keep voltage balanced in such a dc system, a bidirectional dual buck-boost voltage balancer with direct coupling is introduced based on P-cell and N-cell concepts. This results in greatly enhanced system reliability thanks to no shoot-through problems and lower switching losses with the help of power MOSFETs. In order to increase system efficiency and reliability, a novel burst-mode control strategy is proposed for the dual buck-boost voltage balancer. The basic operating principle, the current relations, and a small-signal model of the voltage balancer are analyzed under the burst-mode control scheme in detail. Finally, simulation experiments are performed and a laboratory unit with a 5kW unbalanced ability is constructed to verify the viability of the bidirectional dual buck-boost voltage balancer under the proposed burst-mode control scheme in low-voltage bipolar-type dc microgrids.

Design and Performance Evaluation of SMC-Based DC–DC Converters for Microgrid Applications

“…In the past few years, microgrids (MGs) have appeared as favorable means of unifying and synchronizing the task of distributed power resources [3]. These MGs are often deemed appropriate for increasing the flexibility of distribution systems, as well as integrating several RESs [4], making them suitable for a wide range of applications [5].…”

Voltage unbalances mitigation in bipolar DC microgrids using a novel three‐port multidirectional buck–boost converter

“…In [21][22][23][24][25][26][27][28][29][30], various non-isolated DC-DC voltage balancing converters have been introduced, which can be adapted with BDCMG applications. In [21], non-isolated ICs have been introduced.…”

“…As mentioned in [14], the main disadvantages of the ICs are reduction of system reliability, significant voltage transient by changing the connection mode to the main grid, and the neutral line current in unbalanced voltage states. To compensate these disadvantages, an INC based on buck-boost has been introduced in [28]. However, these types of converters are not able to compensate the voltage drop because they are not connected to an active voltage source.…”

“…Therefore, in [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], various isolate and non-isolate converters have been proposed by different authors. In general, these topologies can be classified into three categories, that is, interlink converters (ICs), internal converters (INCs) and threeport multidirectional DC-DC converters (TMCs) [14].…”

Modeling, control, and implementation of the soft switching dc-dc converter for battery charging/discharging applications

“…The interleaved buck boost converter is described to reduce switching losses, current and voltage ripples and reduction of switches and diodes by connecting switching capacitor in [17]. In order to obtain high conversion ratio, cascade connection of a magnetically coupled interleaved buck boost converter is employed to reduce input and output ripple currents [18][19][20][21]. Pulsewidth-modulation (PWM) and adaptive-conversion-ratio (ACR) phase generator are proposed to achieve high gain and efficiency to the cascaded boost converter [22].In order to realize a high accuracy and quick response for suitable design and control; it is required to have an accurate model of the bidirectional converter.…”