Development of models to study VSC response to AC system faults and the potential impact on network protection

Abstract

As the utilization of renewable energy sources (RES) and HVDC links is growing rapidly, many characteristics of the resulting power system can be seriously changed. HVDC links, as well as RES using converters as an interface with the main grid, can be all treated as non-synchronous sources. These sources are different from the traditional synchronous generators in many ways and bring significant challenges to the existing protection systems. Therefore, the aim of this paper is to explore power system protection performance issues under the context of the main characteristics of future power networks. In this paper the operating principles of converters is investigated. Initial equivalent models of Voltage Source Converters (VSC) in response to both symmetrical and unsymmetrical faults in the AC power systems are introduced and developed. Such models explain the characteristics of the future power networks with focuses on protection system performance. The VSC models will investigate system performance under fault conditions taking into account of European HVDC Grid Code requirements proposed by the European Network of Transmission System Operators for Electricity (ENTSO-E)[1]

Impact of low (zero) carbon power systems on power system protection: a new evaluation approach based on a flexible modelling and hardware testing platform

“…The outer controller is applied to generate reference signals for the current controller. This process can be manipulated to manage the converter's P , Q , , or any other desired output [30].…”

A systematic evaluation of network protection responses in future converter-dominated power systems

“…The value of the current is calculated using an outer controller. The detailed operating principles of this model are explained in more detail in [6].…”

“…In order to implement an accurate and flexible representation of a converter source for use in protection studies, a comprehensive Voltage Source Converter (VSC) model has been developed [6]. The model has been further refined [7] to allow the user to modify its responses during fault conditions.…”

Protection challenges in future converter dominated power systems: demonstration through simulation and hardware tests

“…For the outer controllers, the VSC output current control can be transformed into other forms for regulating P, Q, V DC or V AC , and flexible combinations for the outer controllers can be selected to achieve various objectives. Detailed operating principles for such controllers can be found in [7]. In this system, a dual sequence control scheme is implemented as this permits the VSC to output both balanced and unbalanced three phase currents, facilitates stable, non-oscillating real and reactive power control and outputs, and minimises DC link voltage ripples during unbalanced network conditions [7].…”

“…Detailed operating principles for such controllers can be found in [7]. In this system, a dual sequence control scheme is implemented as this permits the VSC to output both balanced and unbalanced three phase currents, facilitates stable, non-oscillating real and reactive power control and outputs, and minimises DC link voltage ripples during unbalanced network conditions [7]. The scheme can also enable the response of the converter to be similar to a synchronous generator, albeit with a lesser relative magnitude of fault current, during unbalanced fault conditions [8], which obviously is desirable in terms of complying with various grid code requirements.…”