Elimination of limit cycles in HVAC systems using the describing function method

In heating, ventilating and air conditioning systems, the presence of undesirable limit cycles is a common problem. This paper outlines the application of the well known describing function method to the analysis and synthesis of a temperature control system used for air-conditioning an office room. PI-controllers are most commonly used in this field of application. In the present case, an existing standard controller leads to limit cycles around the desired room temperature. The so-called inward approach in combination with the describing function method proves to be an innovative tool for eliminating oscillations while preserving desired performance specifications.