OPF for an HVDC feeder solution for railway power supply systems

Abstract

With increasing railway traffic, the demand for electrical power increases. However, railway power systems are often weak causing high transmission losses and large voltage drops.One possible method to strengthen the railway power supply system is to implement a High Voltage Direct Current (HVDC) feeder in parallel to the Overhead Contact Line (OCL). The HVDC feeder is connected to the OCL by converters.The paper describes different properties and characteristics of such an HVDC feeder solution. An AC/DC unified Optimal Power Flow (OPF) model and unit commitment is used to obtain proper control of the converters.The non-linear load flow and converter loss equations, and the binary variables for the unit commitment, lead to an optimization problem of Mixed Integer Non-Linear Programming (MINLP) type. The optimization problem is formulated in the software GAMS, and is solved by the solver BONMIN. In each case, the objective has been to minimize the total active power losses.

AC cables strengthening low frequency AC railway with purely active power loads

“…The line, transformer, and cable [7] data are listed in Table I. Line and transformer data are representative, and in line with [5].…”

“…Technically, VSC-HVDC transmission for railway [5] is preferable to AC cables, as it also offers a large variety In relation to [2], a more robust and reliable computational approach was presented and used in [6]. This paper studies the same system as [6], but there thyristor-based trains with DC motors were considered.…”

Medium‐voltage DC electric railway systems: A review on feeding arrangements and power converter topologies

“…Ref. [10] has further evaluated the above proposal using a unified AC‐DC optimal power flow model and an on/off control of DC‐AC converters feeding the overhead line. In comparison to a 16 2/3 Hz, 15 kV MVAC system, a MVDC feeder would reduce the voltage drop of the catenary and reduce transmission losses.…”

“…In comparison to a 16 2/3 Hz, 15 kV MVAC system, a MVDC feeder would reduce the voltage drop of the catenary and reduce transmission losses. Furthermore, an optimisation problem has been formulated to determine the optimal control of the converters [11] to minimise total active power losses. The performance of MVDC feeder solution has been compared with both centralised and decentralised 16 2/3 Hz 15 kV MVAC systems, showing better voltage regulation and less power losses in the MVDC system.…”

AC cables strengthening railway low frequency AC power supply systems — A deepened study

“…Transformers are cheaper than DC-AC converters, and the control and protection is simpler and thus cheaper with an AC solution. Technically, the fourth option of VSC-HVDC transmission [12] is preferable to AC cables, in terms of control options.…”