Power transistor-assisted Sen Transformer: a novel approach to power flow control

Abstract

The importance of flexible power flow control in electric power transmission networks is increasing owing to many factors that have arisen. Sen Transformer (ST) is one of the attractive power flow controllers. It has a wide control range, independent active and reactive power flow control capability, and is economically attractive. However, it operates in stepwise mode, has limited operating points, relatively slow response rate, and suffers from compensation error. Motivated by the limitations of the ST, power transistor assisted ST (TAST) as a novel power flow controller is proposed in this paper. The TAST consists of a highly-rated ST and a lowly-rated AC chopper based transistorized ST (TST). This paper first points to the importance of transmission lines' power flow control and reviews available power flow control devices. It then introduces the proposed TAST, determines the ratings of the TST and the switching pattern of its choppers. Next, it demonstrates the steady-state performance of the TAST, determines its control limits, compares the TAST to the ST and the unified power flow controller (UPFC), and the different control strategies of the TAST. In this paper, the TAST is modeled in MATLAB/SIMULINK and tested in an equivalent two bus system and in the IEEE-14 bus test system. The work also demonstrates improvement of the response rate of the ST. Cost analysis of the TAST is also done and is compared to that of the equivalent UPFC. Based on the results, the TAST realizes continuous, error-free, more flexible operation, improved response rate, and low cost. Moreover, the TAST provides 14.62% wider power flow control range. In conclusion, the TAST's operational characteristics are closely comparable to that of the UPFC with the advantage of lower cost and extended control area.

Power flow control capability of the power transistor‐assisted Sen transformer and the unified power flow controller: a close comparison

“…Nonetheless, most technically effective and economically attractive ones need to be used. Among most competent flexible AC transmission systems (FACTS) controllers are the unified PFC (UPFC) [12], the Sen transformer (ST) [13], and the power transistor-assisted ST (TAST) [14]. The UPFC, while it is the most flexible FACTS controller, requires the high installation and operating costs [14,15].…”

“…Among most competent flexible AC transmission systems (FACTS) controllers are the unified PFC (UPFC) [12], the Sen transformer (ST) [13], and the power transistor-assisted ST (TAST) [14]. The UPFC, while it is the most flexible FACTS controller, requires the high installation and operating costs [14,15]. The ST, while is closely comparable to the UPFC at a far lower installation cost, has some technical drawbacks such as its step-wise operation, limited operating points, existence of control-error, and slow response [14].…”

“…The UPFC, while it is the most flexible FACTS controller, requires the high installation and operating costs [14,15]. The ST, while is closely comparable to the UPFC at a far lower installation cost, has some technical drawbacks such as its step-wise operation, limited operating points, existence of control-error, and slow response [14]. The recently introduced TAST eliminates the technical drawbacks of the ST at an additional cost.…”

“…The recently introduced TAST eliminates the technical drawbacks of the ST at an additional cost. The TAST, similar to the UPFC, operates continuously, has no limitation among its control range, suffers no control-error, and has improved response rate [14]. Additionally, the TAST has a wider power flow control range, yet, at a cost that is less than half of the comparable UPFC [14].…”

“…The TAST, similar to the UPFC, operates continuously, has no limitation among its control range, suffers no control-error, and has improved response rate [14]. Additionally, the TAST has a wider power flow control range, yet, at a cost that is less than half of the comparable UPFC [14]. The continuous control enables the smooth move from a steady operating point to another, ensures optimum operation [16], and prevents systems collapse [7].…”