Design of switching control systems for ventilated greenhouses

K. Chao, R. S. Gates

Research output: Contribution to journalArticlepeer-review


A state-space averaging method was employed in the design of a switching control system for a conventional single-phase, two-speed ventilation fan with time-averaged temperature feedback. The unique state-space averaging method allows the switched, i.e., discontinuous, system to be approximated as a continuous system; thus direct digital control design techniques can be applied for designing the switching controller. Dynamic simulation of the controller action and greenhouse air temperature indicated that the root- mean-square temperature could closely match the set point temperature, and that the switching period affected fluctuations about the set point. The validity of the designed switching controller was confirmed through field tests and compared to a conventional staging control strategy in research greenhouses. The proposed design method shows promise as an alternative to conventional PID systems and stage controllers, and is applicable to any discontinuous switched system. Detailed design development is provided.

Original languageEnglish (US)
Pages (from-to)1513-1523
Number of pages11
JournalTransactions of the American Society of Agricultural Engineers
Issue number4
StatePublished - Oct 31 1996


  • Computer simulation
  • Controlled environment
  • Digital control system
  • Thermal response
  • Ventilation

ASJC Scopus subject areas

  • Agricultural and Biological Sciences (miscellaneous)


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