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SUMMARY:Distributed schemes for stability and optimality in power networks
  - Andreas Kasis\, University of Cambridge
DTSTART:20170525T130000Z
DTEND:20170525T140000Z
UID:TALK71064@talks.cam.ac.uk
CONTACT:Tim Hughes
DESCRIPTION:The generation\, transmission and distribution of electricity 
 underpins modern technology and constitutes a necessary element for our de
 velopment\, economic functionality and prosperity. In the recent years\, a
 s a result of environmental concerns and technological advances\, private 
 and public investment have been steadily turning towards renewable sources
  of energy\, resulting in a growing penetration of those in the power netw
 ork. This poses additional challenges in the control of power networks\, s
 ince renewable generation is in general intermittent\, and a large penetra
 tion may cause frequent deviations between generation and demand\, which c
 an harm power quality\, damage equipment and even cause blackouts.\n \nLoa
 d side participation in the power grid is considered by many a means to co
 unterbalance intermittent generation\, due to its ability to provide fast 
 response at urgencies. Industrial loads as well as household appliances\, 
 such as refrigerators and air-conditioners\, may respond to frequency devi
 ations adjusting their demand accordingly in order to support the network.
  This is backed by the development of relevant sensing and computation tec
 hnologies.\n\nThe increasing numbers of local renewable sources of generat
 ion along with the introduction of controllable loads dramatically increas
 es the number of active elements in the power network\, making traditional
 ly implemented\, centralised control difficult and costly. This shows the 
 need for the employment of highly distributed schemes in the control of ge
 neration and demand. Such schemes need to ensure the smooth and stable ope
 ration of the network. Furthermore\, an issue of fairness among controllab
 le loads needs to be considered\, such that it is ensured that all load pa
 rticipants share the burden to support the network evenly and with minimum
  disruption.\n\nWe consider the dynamic behaviour of power networks within
  the primary and secondary frequency control timeframes. Using tools from 
 linear and non-linear control and optimisation\, we present methods to des
 ign distributed control schemes for generation and demand that guarantee s
 tability and fairness in power allocation. Our analysis provides relaxed s
 tability conditions in comparison with current literature and allows the i
 nclusion of practically relevant classes of generation and demand dynamics
  that have not been considered within this setting\, such as of higher ord
 er dynamics. Furthermore\, fairness in the power allocation between loads 
 is guaranteed by ensuring that the equilibria of the system are solutions 
 to appropriately constructed optimisation problems. It is evident that a s
 ynchronising variable is required for optimality to be achieved and freque
 ncy is used as such in primary control schemes whereas for secondary frequ
 ency control a synchronising variable that follows from a 'primal-dual' co
 ntrol scheme is adopted. For the latter case\, the requirements of the syn
 chronising feedback scheme have been relaxed with the use of an appropriat
 e observer\, showing that stability and optimality guarantees are retained
 .\n \nThe problem of secondary frequency regulation where ancillary servic
 es are provided from switching loads is also considered. Such loads switch
  on and off when some prescribed frequency threshold is reached in order t
 o support the power network at urgencies. To study their behaviour\, tools
  from discontinuous and hybrid systems analysis have been employed. We sho
 w that the presence of switching loads does not compromise the stability o
 f the power network and reduces the frequency overshoot\, potentially savi
 ng the network from collapsing. Furthermore\, we explain that when the on 
 and off switching frequencies are equivalent\, then arbitrarily fast switc
 hing phenomena might occur\, something undesirable in practical implementa
 tions. As a solution to this problem\, hysteresis schemes where the switch
  on and off frequencies differ are proposed and stability guarantees are p
 rovided within this setting.\n\nAll our analytic results are distributed a
 nd network independent and have been verified with realistic simulations o
 n well accepted benchmarks.
LOCATION: Cambridge University Engineering Department\, LR6
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