Abb Stromberg Drives Oy

Olavi Kangasaho

Matti Mard

Vesa Vauhkonen

This invention relates to a method for controlling the torque of a synchronous machine supplied by a frequency converter, wherein starting from measured variables (i.sub.R, i.sub.S, i.sub.T, i.sub.f) representing the state of the machine the direct axis flux component (.psi..sub.d), the quadrature axis flux component (.psi..sub.q) and the pole angle (.delta.) for the machine are determined, and set values are produced for the flux (.psi. set value), excitation current (i.sub.fo set value) and current building the torque (i.sub.2 set value). To prevent the 'pull out' of the drive in the method of the invention, from the determined pole angle (.delta.) there is formed, by means of a limiting block for the pole angle, a limited pole angle (.delta..sub.r) that equals the pole angle (.delta.) if the pole angle has an absolute value smaller than a separately adjustable limit (.delta..sub.max), but equals the limit (.delta..sub.max) if the pole angle has an absolute value equal to or greater than the limit (.delta..sub.max), the set value (i.sub.2 set value) of the current building the torque, being perpendicular to the direction forming the limited pole angle (.delta..sub.r) with the direct axis (d) of the rotor, is projected as the set value (i.sub.do set value) for the direct stator current and as the set value for the quadrature stator current (i.sub.qo set value) and for maintaining the direct flux (.psi..sub.d) at a value corresponding to the limited pole angle (.delta..sub.r) and the flux set value (.psi. set value), the set value (i.sub.fo set value) for the excitation current is calculated on the basis of the limited pole angle (.delta..sub.r), the flux set value (.psi.set value) and the set value for the direct stator current (i.sub.do set value) so that the set value for the excitation current (i.sub.fo set value) compensates for the direct stator set value (i.sub.do set value).

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Kauniainen, Finland

Olavi Kangasaho