Boundaries of Operation for Refurbished Parallel AC–DC Reconfigurable Links in Distribution Grids

Abstract

Parallel ac-dc reconfigurable link technology can find interesting applications in medium voltage power distribution. A given system can operate in different configurations while maintaining equivalent capacity during (n-1) contingencies. It is proved that within the defined operating boundaries, a parallel ac-dc configuration has higher efficiency as compared to pure ac or pure dc power delivery. Using sensitivity analysis, the variations in these efficiency boundaries with power demand, power factor, grid voltages, link lengths, conductor areas and converter efficiency is described. It is shown that parallel ac-dc system can have smaller payback time as compared to a purely dc power transmission for the same capacity due to lower investment cost in converter station and superior efficiency. As compared to a purely ac system, the payback of a refurbished parallel acdc configuration can be less than 5 years for a 10 km, 10 kV distribution link within the specified assumptions and operating conditions.

Reliability, Efficiency and Cost Trade-offs for Medium Voltage Distribution Network Expansion using Refurbished AC-DC Reconfigurable Links

“…On the other hand, the converter losses vary for each configuration due to different ratio of dc and ac power flow in the system to deliver the required demand at RSS. Consequently, the system efficiency vary with link length, ac-dc power share and the power factor at RSS as derived in [25]. The findings in [25] suggest that parallel ac-dc operation such as Case C may offer some efficiency benefits as compared to fully ac or dc operation within the defined boundary of operation.…”

Comparisons of MVAC and MVDC Systems in Dynamic Operation, Fault Protection and Post-Fault Restoration

“…The main breaker CB 3 is tripped at t = t2 to isolate the fault. The interval between t1 and t2 is used for fault detection, location and isolation which can be hundreds of milliseconds [9], [11]. The AC fault currents through the CB 3 reach to 8.71 p.u.…”

Voltage Source Converter Control under Distorted Grid Voltage for Hybrid AC-DC Distribution Links

“…Parallel AC-DC re-configurable link system can implement purely DC, AC and hybrid AC-DC power delivery. Parallel AC-DC operation (as depicted in Fig.1) is a special configuration [4]. In this operation, the main grid delivers power to loads (P and Q) in part by both AC and DC links using the power steering capability of the B2B system.…”

“…Recent studies indicate that hybrid AC-DC distribution links as depicted in Fig.1 have a potential application in capacity enhancement and efficient power redirection under specific operating conditions, particularly for high power, medium voltage level and moderate distribution distances, e.g. 5....20 km, [1]- [4]. Back-To-Back (B2B) Voltage Source Converters (VSCs) with long DC buried cables in-between the transmitting-and receiving-end substations can be a feasible refurbishment strategy to such parallel AC-DC link architectures [5], [6].…”