Optimal design and decoupling control of series DC-link voltages for quadruple-active-bridge based UPQC

Analysis and validations of operation behaviors for dual active bridge‐based unified power quality conditioner under different working conditions

“…After integrating the battery bank, to avoid the voltage or current shock issues caused by the switching of control modes, the SC and PC are controlled as a sinusoidal current source and a sinusoidal voltage source, respectively, which is different from Han et al 17,18 in control strategy. Specifically, the SC is employed to control the grid input current i G and stabilize the low-voltage u dcl of dc link; the PC is employed to control the load voltage u L to be stable and sinusoidal; and the DAB is employed to control the high-voltage u dch of dc link.…”

“…For this reason, the researches on LFT‐less UPQC (LFTL‐UPQC) have received more attention in the recent years. According to the system's topology, LFTL‐UPQC can be mainly divided into four types as follows: two‐leg UPQC, 9–11 three‐leg UPQC, 12–14 cross‐phase UPQC, 15,16 and dual active bridge‐based UPQC (DAB‐UPQC) 17,18 …”

“…According to the system's topology, LFTL-UPQC can be mainly divided into four types as follows: two-leg UPQC, [9][10][11] three-leg UPQC, [12][13][14] cross-phase UPQC, 15,16 and dual active bridge-based UPQC (DAB-UPQC). 17,18 In Cheung et al, 9 the single-phase two-leg UPQC consists of two half-bridge converters, and only four switches are used in this structure, so its economy is very attractive. However, since the midpoint of dc link is directly connected to the ac bus, it will inevitably lead to line-frequency voltage fluctuations in the dc link.…”

“…Although the LFTL-UPQC topologies in above articles [9][10][11][12][13][14] are simple, since the SC and PC share the same dc link, the electrical isolation should be implemented between the grid and the UPQC from the perspective of safe operation, so as to prevent the short circuit between two converters and capacitor shoot-through at the dc link. For this consideration, the DAB is introduced into UPQC's dc link to achieve electrical isolation in Han et al 17,18 Compared with the traditional method of using LFT to achieve isolation, the DAB has the advantage of lightweight due to its high-frequency operation characteristics, which can greatly reduce the size and weight of UPQC system. However, almost all the grid current flows through the SC in DAB-UPQC, and this current may even be larger than the load current when the grid voltage fluctuates, which is a prominent feature different from the conventional UPQC.…”

“…However, almost all the grid current flows through the SC in DAB-UPQC, and this current may even be larger than the load current when the grid voltage fluctuates, which is a prominent feature different from the conventional UPQC. As a result, the current stress of switches in the SC will be increased, so it is necessary to pay special attention to the change of current stress in the process of designing SC, which is a key issue ignored by Han et al 17,18 Additionally, the study on the working principle and soft-switching implementation for the DAB plays an important role in controlling the bidirectional power transmission and improving the operation efficiency, which is another key issue ignored by Han et al 17,18 In this paper, the above two issues are analyzed and discussed to clarify the operation behaviors of DAB-UPQC. Moreover, to provide continuous power for the load, the battery bank is integrated in the DAB-UPQC.…”