RESONANCE CHARACTERISTICS OF DISTRIBUTED SOLAR COLLECTOR FIELDS

In practice the outlet temperature of a distributed collector field is usually regulated by a feedforward controller combined with a simple PI based feedback loop. Such systems give oscillatory performance, even though the controller design is aimed to give aperiodic responses. Through the use of a nonlinear computer model of a distributed collector field, the performance of simple PI based controllers on such systems is analyzed and investigated. Using experimental results obtained from both the computer model and the plant in question, the dynamics of the collector field are found to contain resonance characteristics. It is demonstrated that the main reason for the oscillatory performance of PI based control schemes are these characteristics and not, as previously thought, the variability of system dynamics. Furthermore, it is shown that these simple controllers are wholly inadequate for the purpose of achieving fast well-damped responses on this system.