Grundfos wants to supply their MQ-3 pump with a frequency converter, which will
release its rotor speed from the grid frequency. This makes it possible to control the
angular velocity of the rotor and hence makes it possible to provide a constant pressure.
To analyze how the improved MQ-3 pump "Squba" must be controlled so it delivers a
constant pressure, a prototype model of Squba is developed in Matlab Simulink. The
model is set up with Affinity and ideal gas equations; the model is afterwards verified
with experimental data from the lab. Afterward the model is converted into the real
Squba model by providing it with real Squba pump data from Grundfos. To determine
the volume of the pressure tank there is carried out a series of analysis for the system's
four-parameters (flow, volume, pre-charge and reference pressure). After which they are
used to calculate the pressure tanks volume and pre-charge level. Subsequently, the nonlinear
model is linearized and block reduced, in order to obtain the transfer function of
Squba so the technical tools for regulation could be used to design a controller. In
addition, the stability of the system is analyzed, to determine the linearization point of
Squba transfer function. The non-linear pump model and the transfer function in
linearization point match sufficiently, so the transfer function can be considered to be
verified. Then there is designed a PI controller, using the Root Locus method, as the P
alone couldn’t fulfill the task. Finally the PI controller is implemented in the non-linear
pump model, where the assessed that the controller does not fulfill the task.