Mono-inverter multi-machine systems have been subject of researches for many decades. Nowadays, they are interesting for manufacturers of fan arrays which usually consist of permanent magnet synchronous motors (PMSM). The main aim of this thesis is to explore different configurations of multi-connected PMSM controlled by single frequency converter (FC) which can be used in fan drive systems and to develop a control method which will ensure stable operation of the system when different load torque is applied to each PMSM. The main subject of analysis is mono-inverter dual serial-connected PMSM system.
In the opening part, fan array concept, FC and basic drive control methods are presented. Then control solutions for parallel-connected PMSM are summed up from other authors' research papers. We focused on master/slave and average technique methods. The latter can be used in serial-connected PMSM system without being modified.
In the main part, stability of dual serial-connected PMSM system is analysed analytically and with the help of Simulink Linear Analysis Tool. The analysis results showed that change of magnetization is needed to stabilise the system. In order to reduce the additional losses magnetizing current controller is proposed. Simulation models consisting of two, three and four serial-connected PMSM were used to test its behaviour. Adding an average angular speed observer to the simulation model causes extra stability problems. Despite that, some simulations have shown possibility of stable operating of the drive with sensorless angular speed control.
In the final part, limitations of using commercial FC in dual connected PMSM system are discussed and substantiated with experimental results. Additionally, the comparison between serial and parallel connection of PMSM is made where the pros and cons of each solution are highlighted.