On the protection of compact DC power systems with high-power energy storage

  • Puran Rakhra

Student thesis: Doctoral Thesis


High-power energy storage systems (ESS) are being considered for future aerospace platforms and other compact DC power system applications to improve the overall transient performance of electrical power distribution systems. These sources are being integrated with advanced bidirectional power electronic converter interfaces with high bandwidth control systems and current limiting functionality. To date, the literature has primarily focused on the control and behaviour of high-power ESS during normal operating conditions with an emphasis on the systems level benefits they offer. Little consideration has been given to their response during network fault conditions.Through simulation and hardware experimentation, this thesis demonstrates that an ESS, by design, can contribute significant levels of current to a fault as it attempts to sustain the network voltage. This behaviour inadvertently reduces the fault current contribution from the primary source of power on the network, reducing the effectiveness of associated protection devices (protection blinding).The impact of several key DC power system design and operation parameters on the ESS fault response is quantified and a new critical fault impedance term, beyond which protection blinding can be expected to occur, is introduced. Building upon this new knowledge, enhancements to typical compact DC power system protection schemes which more effectively account for the presence of ESS are proposed and evaluated.Differential protection schemes are shown to eliminate protection blinding whilst offering the greatest flexibility in increasing protection speed and fault discrimination, and maximising ESS availability. Adaptive protection schemes are shown to be a reliable backup option where a consistent protection system response can be obtained despite the potentially intermittent nature of the ESS fault current contribution. A novel control strategy that actively modifies the fault response of the ESS to facilitate the use of conventional overcurrent schemes is also proposed and demonstrated for applications where communications-based protection is unfavourable. The thesis concludes by proposing a framework to guide protection engineers in the selection of appropriate protection and control strategies when considering the integration of high-power ESS within compact DC power systems.
Date of Award5 Jun 2017
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)

Cite this