Abstract: A frequency converter (100) comprises a processor (102), memory (104) and basic software (106) in the memory, the execution of which software implements the basic functionality of the frequency converter. For application-specific customization, the memory of the frequency converter is arranged to include application software (108) that contains callable functions (210) and is installable separately from the basic software. The frequency converter is arranged to execute the basic software (106) and the application software (108) with the same processor (102). The basic software (106) calls a function of the application software and/or provides functions of its own to be called by the application software indirectly via a link (240k) in a call table (240), the location of the link in the call table being independent of the location of the function (210) corresponding to the link in the memory.

Abstract: A frequency converter (100) comprises a processor (102), memory (104) and basic software (106) in the memory, the execution of which software implements the basic functionality of the frequency converter. For application-specific customization, the memory of the frequency converter is arranged to include application software (108) that contains callable functions (210) and is installable separately from the basic software. The frequency converter is arranged to execute the basic software (106) and the application software (108) with the same processor (102). The basic software (106) calls a function of the application software and/or provides functions of its own to be called by the application software indirectly via a link (240k) in a call table (240), the location of the link in the call table being independent of the location of the function (210) corresponding to the link in the memory.

Abstract: The invention relates to a method of determining the estimate of the stator flux of an electric machine, comprising the determination of a stator flux estimate (.PHI..sub.sest) of the electric machine as a time integral of the difference between the voltage (u.sub.s) supplied to the stator and the product of the stator current (i.sub.s) and the stator resistance estimate (R.sub.sest), whereby the stator resistance estimate (R.sub.sest) of the electric machine is determined by correcting the initial value or another earlier value of the stator resistance on the basis of the stator current component (i.sub.d.sup.s, i.sub.d.sup..delta., i.sub.d.sup.r) parallel to the stator flux estimate (.PHI..sub.sest), the air gap flux estimate (.PHI..sub..delta.est) or the rotor flux estimate (.PHI..sub.rest). To be able to follow changes in the stator resistance of the electric machine in different operational conditions of the machine, said current component (i.sub.d.sup.s, i.sub.d.sup..delta., i.sub.d.sup.