A Ćuk-Based Modular DC–DC Converter For Medium Voltage Direct Current (MVDC) Applications

Abstract

EDIUM-Voltage (MV) grid is typically used as an interface between various renewable energy sources and different loads. MV grids, as depicted in Fig. 1, may also be used as a link between renewable energy sources and high-voltage direct-current (HVDC) transmission system [1]. There are two main approaches for stepping up the low input voltages to medium voltages in MV grid: The first approach establishes Medium Voltage AC (MVAC) grids by using low frequency transformers with large turn-ratios, as shown in Fig. 1(a) [2-5]. However, high-voltage transformers that have large turn ratios are costly and have low power density. The second approach forms a Medium Voltage DC (MVDC) grid by employing DC-DC converters with high voltage gains, as represented in Fig. 1 (b). This approach eliminates the need for large low frequency transformers. High-power efficient DC-DC converters that can offer large voltage gains are one of the key components of the MVDC grid [6,7]. Different types of DC-DC converters have been proposed and studied for MVDC application. Some of these converters are single module configurations [4,[7][8][9][10][11][12][13][14]. Soft-switching techniques are typically used in these converters to minimize the switching losses. However, in these converters power switches typically suffer from extremely high voltage stress. Considering the limitations of commercially available semiconductor devices, series connection of switches seems inevitable in most of these topologies. However, the voltage balancing across series switches is challenging. Additionally, the series connection of the switches can lead to more complex gate driver design [15]. Another category of DC-DC converters used in MVDC grid are modular converters, which are formed by several low power converters with series or parallel input/output terminals [16]. Modular converters are excellent candidates for MVDC grid application. Modular DC-DC converters allow the development of high-power rating converters using commercially available switches that have lower voltage/current ratings than input or output voltages/currents. These converters decrease the voltage stress (dv/dt) and problems associated with the electromagnetic interference (EMI). They also reduce the total harmonic distortion [17][18][19][20][21][22][23][24]. Another major merit of modular DC-DC converters is the redundancy feature that allows them to operate under fault conditions, as each power module or power cell can work independently [25]. Additionally, maintenance of modular converters is expected to be easier [15]. Different modular DC-DC converter topologies are proposed in literature for MVDC

An Ultra-High Gain Compact Module Bidirectional DC–DC Converter for Energy Storage System

“…Therefore, they are not suitable for the HES, to integrate with electric vehicles. With a threelevel DC-DC, the stress caused by the voltage on the switches is significantly reduced, however, the voltage gain is relatively low because of parasitic parameters [11], [12]. The voltage gain (Vout/Vin) of multilevel BDDC achieves high gain, but their control strategy and other hardware circuits must maintain a balance between the switch's reliability occurring at the time of implementation in real-time [13].…”