Design and testing of an armature-reaction-compensated permanent magnet synchronous generator for island operation

摘要

At present, permanent magnet synchronous generators (PMSGs) are of great interest.Since they do not have electrical excitation losses, the highly efficient, lightweight andcompact PMSGs equipped with damper windings work perfectly when connected to anetwork. However, in island operation, the generator (or parallel generators) alone isresponsible for the building up of the network and maintaining its voltage and reactivepower level. Thus, in island operation, a PMSG faces very tight constraints, which aredifficult to meet, because the flux produced by the permanent magnets (PMs) isconstant and the voltage of the generator cannot be controlled. Traditional electricallyexcited synchronous generators (EESGs) can easily meet these constraints, because thefield winding current is controllable. The main drawback of the conventional EESG isthe relatively high excitation loss.This doctoral thesis presents a study of an alternative solution termed as a hybridexcitation synchronous generator (HESG). HESGs are a special class of electricalmachines, where the total rotor current linkage is produced by the simultaneous actionof two different excitation sources: the electrical and permanent magnet (PM)excitation. An overview of the existing HESGs is given. Several HESGs are introducedand compared with the conventional EESG from technical and economic points of view.In the study, the armature-reaction-compensated permanent magnet synchronousgenerator with alternated current linkages (ARC-PMSG with ACL) showed a betterperformance than the other options. Therefore, this machine type is studied in moredetail. An electromagnetic design and a thermal analysis are presented. To verify theoperation principle and the electromagnetic design, a down-sized prototype of 69 kVAapparent power was built. The experimental results are demonstrated and comparedwith the predicted ones. A prerequisite for an ARC-PMSG with ACL is an even numberof pole pairs (p = 2, 4, 6, …) in the machine. Naturally, the HESG technology is notlimited to even-pole-pair machines. However, the analysis of machines with p = 3, 5, 7,… becomes more complicated, especially if analytical tools are used, and is outside thescope of this thesis. The contribution of this study is to propose a solution where an ARC-PMSG replaces anEESG in electrical power generation while meeting all the requirements set forgenerators given for instance by ship classification societies, particularly as regardsisland operation.The maximum power level when applying the technology studied here is mainly limitedby the economy of the machine. The larger the machine is, the smaller is the efficiencybenefit. However, it seems that machines up to ten megawatts of power could benefitfrom the technology. However, in low-power applications, for instance in the 500 kWrange, the efficiency increase can be significant.