Active Power Tracking Control for DC-Link Voltage Suppression of MVDC System with Voltage-Sourced Converter

Abstract

The newly increased electrical energy is needed around the metropolitan area, and therefore, the transmission system is needed to be reorganized. MVDC (medium voltage direct current) system is an attractive one for constructing these new systems. This MVDC system, which is composed of two or more VSCs (voltage-sourced converters), prevents the degradation of system reliability due to renewable energy resource and is contributed to making it more stable for power supplying companies to supply the electrical power. Furthermore, to connect the increased renewable energy resource with larger capacity into the main grid through this MVDC system, the regulations such as FRT (fault ride through) for the grid have been more and more required. According to the FRT, the VSC system is required to supply the reactive current to grid when the grid voltage drops below the allowed voltage range. However, the FRT operation can cause the DC-link voltage in the MVDC system to increase. If the DC-link voltage exceeds the nominal voltage, the damage to the DC-related application may occur. In this paper, as the method to solve this problem, the application of the APTC (active power tracking control) into the MVDC system was proposed. The APTC is based on the principle that the DC-link voltage is determined by the power balance between the incoming and the outgoing active powers into the DC-link. If the outgoing active power decreases due to the short circuit in grid side, the DC-link voltage rises with the constant incoming active power. However, if the incoming active power is controlled to be reduced by the APTC performance of the MVDC system at the same time, the DC-link voltage is expected to be maintained at a constant level. The effectiveness of the suggested APTC application was verified through the PSCAD (power system computer aided design)/EMTDC (electro magnetic transient design and control) simulation.