Abstract: The invention relates to an inverter arrangement for simultaneous control of a stator flux and a torque of an electric machine (M). In the invention, the inverter of the inverter arrangement is controlled on the basis of a stator voltage reference (u.sub.sref) defined on the basis of the error variables (T.sub.err, .PSI..sub.err) of the torque and the stator flux; on the basis of the stator voltage reference, in turn, are defined reference values for the phase voltages (u.sub.aref, u.sub.bref, u.sub.cref) of the stator voltage. The phase voltages (u.sub.a, u.sub.b, u.sub.c) of the stator voltage supplied to the electric machine (M) are controlled by a feedback voltage controller (VAC) to correspond to the defined reference values (u.sub.aref, u.sub.bref, u.sub.cref) of the phase voltages.

Abstract: The invention relates to a connector and a manufacturing method thereof for a three-phase cable including concentric, segmentally disposed phase conductors (1) with surrounding insulation structures (11) and a concentric earth conductor (8) enclosing the phase conductors. According to the invention, the phase conductors (1) inside the connector are isolated from each other by a star-shaped dividing insulation piece (3) keeping the phase conductors (1) separate in their segments. Phase terminals (2) of the connector are disposed on the segment bottoms of the dividing insulation piece (3). The connector further incorporates a clamp (5, 7) suited for pressing the phase conductors (1) against the phase terminals (2) and a ferrule (10) on which the earth conductor (8) can be bent backward to mechanically lock a receptacle.

Abstract: The invention relates to a method of ensuring the stability of a synchronous machine in controlling the synchronous machine on the basis of direct control of flux and torque, in which the torque generated by the synchronous machine is increased/decreased by increasing/decreasing the instantaneous angular velocity of the stator flux. In accordance with the invention, the method comprises the steps of determining the direction of the stator flux vector (.psi.s) in rotor coordinates (dq), and forcing the stator flux vector (.psi.s) to remain in quadrants I and IV (Q1, Q4) of the rotor coordinates by rotating the stator flux in the rotor coordinates to a necessary degree.

Abstract: The present invention relates to a method for controlling the power to be transferred via a mains inverter, the mains inverter (VVS) being arranged to transfer electric power in both directions between the n-phase AC main system (U) and the DC intermediate circuit (1).

Abstract: A method of producing a rotor structure for an electrical machine includes heating a plurality of annular plates and then placing the heated plates around an axle such that the plates shrink and attach to the axle, the plates buckling into the general shape of a truncated cone as they cool. The heated plates can be positioned on the axle individually or as a group, thus forming a rotor core packet of stampings around the axle.

Abstract: The present invention relates to a mount structure for supporting an electric motor comprising a rotor and a stator frame, such an electric motor being preferably a marine engine rotating a propeller, on a ground base, such as a hull of a ship. The mount structure comprises at least one vibration damping unit, which comprises a vibration damping rail, which is arranged to receive and damp the vibration of the electric motor and which is secured to the stator frame.

Abstract: A load-commutated synchronous motor drive has a line-commutated network-side converter (3), a current-source dc intermediate link (PL, NL, 5) and a load-commutated machine-side converter (2) for connection to a synchronous machine (1). The motor drive comprises control members adapted, to ensure the commutation, in connection with commutation of the machine-side converter (2), to switch the network-side converter (3) for operation with a lower pulse number than the natural pulse number of the network-side converter.

Abstract: The invention relates to a method for damping the load swing of a crane during the traversing motion of a load-carrying trolley and/or a trolley-carrying bridge. The method comprises determining substantially continuously the acceleration of the trolley/bridge and the instantaneous swing time constant, swing velocity (v) and deviation (s) from equilibrium of the pendulum formed by the load. When the velocity reference changes, the acceleration providing the desired change in velocity is determined, said acceleration being switched on immediately, and the acceleration compensating for the swing prevailing at the moment of change of the velocity reference is determined, said acceleration being switched on either immediately or, if the compensating acceleration exceeds the maximum acceleration permissible to the traversing drive when switched on immediately, when the pendulum formed by the load has reached its extreme position.

Abstract: The invention relates to a method of starting an asynchronous machine irrespective of whether the rotor of the machine is rotating or not when the machine is supplied by an inverter provided with a separate moment and flux or moment and magnetizing current control, which is faster than the time constants of the asynchronous machine. According to the invention, zero moment is set as a target for the control, a voltage is supplied to the stator of the machine by the inverter, a stator current vector and a stator flux generated by the voltage is determined, an estimate of that vector or some other quantity comparable to the stator flux is determined, a moment caused by the stator flux vector and the stator current vector is determined and information of the moment is supplied to the control, which tries to zero the caused moment by making the stator flux and a rotor flux generated thereby cophasal, thus synchronizing the supply frequency of the inverter with a possible rotation of the machine rotor.

Abstract: An electric apparatus mounted in sliding bearings includes an end N at which is located a fan, an end D at which is located a shaft, a rotor journalled at one end by means of a first sliding bearing at the end N and the opposite end journalled by means of a second sliding bearing at the end D, the end N being provided with a first bearing housing with an oil sump for the first sliding bearing and the end D being provided with a second bearing housing with an oil sump for the second sliding bearing, and a passage system which interconnects the oil sumps to enable oil to circulate therebetween and limit the warm up of the slide bearing at end D. Limiting the warm up of the slide bearing at end D enables the rotational speed of the electric apparatus to be increased or allows the electric apparatus to be used in warmer environments than previously possible.

Abstract: The invention relates to a method of monitoring a temperature rise of a stator winding of a squirrel cage induction motor, in which method a stator current I of the motor is measured and the temperature rise of the motor at each moment is determined on the basis of this current I, when a rated temperature rise .theta..sub.N of the motor at a rated current I.sub.N, the rated current I.sub.N and a temperature rise time constant .tau. of the motor are known. The method comprises steps of determining the stator current I of the motor as discrete moments separated by .DELTA.t long time periods, determining the temperature rise .theta..sub.n(1) of the motor during one time period n from the equation ##EQU1## determining a cooling .theta..sub.n(2) of the motor during the same time period n from the equation.theta..sub.n(2) =.theta..sub.n-1 e.sup.-.DELTA.t/.tau.,where .theta..sub.n-1 is the temperature rise of the motor at the end of the preceding time period, and summing the temperature rise .theta..sub.

Abstract: The invention relates to a propeller drive system for a vessel or the like for operating two contra-rotating propellers (1,2) disposed on two coaxial shafts (3,4) in succession. The power supplies of two electric motors (5,6) rotating the propellers (1,2) comprise a first and second frequency converter (7,8) and their control unit comprises means for controlling the frequency converters (7,8) so that the direction of rotation of the motors (5,6) and their rotational speed from zero up to the nominal speed can be chosen freely.

Abstract: Apparatus for determining an estimate for the stator flux of an asynchronous machine when the supply frequency .omega..sub.s, stator inductance L.sub.s, at least one of stator resistance R.sub.s and an estimate R.sub.se therefor, and short-circuit inductance .sigma.L.sub.s are known, is carried out by structure for measuring the stator current 1.sub.s and stator voltage u.sub.s, calculating a difference voltage by subtracting at least one of the product of the stator resistance and the estimate thereof and the stator current from the stator voltage, integrating the difference voltage in relation to time to give a stator flux estimate .psi..sub.se, subtracting, prior to integrating a correction term based on the feedback stator flux estimate .psi..sub.se and being proportional to the product of the difference variable and the direction vector C given therefor, from the difference voltage, determining the difference variable from the equation:(.psi..sub.se -L.sub.s 1.sub.s).multidot.(.psi..sub.se -.sigma.L.sub.

Abstract: The invention relates to a method for braking an alternating-current motor when the alternating-current motor (1) is supplied by a frequency converter (4) comprising an intermediate circuit (2). In accordance with the invention, when the voltage (uc) of the intermediate circuit (4) reaches a predetermined value during braking, the magnetization of the motor (1) is increased to increase the thermal losses of the motor, and, once the voltage (uc) of the intermediate circuit drops below said predetermined value, the increased magnetization is removed.

Abstract: The invention relates to a control circuit for a semiconductor switch, comprising a transformer coupling (T1, T2) for generating AC voltage signals including both control energy and control information, a rectification coupling (DB1, DB2) for rectifying the AC voltage signals generated by the transformer coupling (T1, T2) for generating DC voltage levels (U1, U2, U3) appropriate for turning on and turning off a semiconductor switch (SW1), a first resistor (R2) connected at its first end to a driving electrode of the semiconductor switch (SW1), a second resistor (R1) connected between the driving electrode and the emitter or source electrode of the semiconductor switch, and a booster semiconductor switch (V1) provided between the driving electrode of the semiconductor switch (SW1) and an DC voltage output (U3) generated by the rectification coupling and intended for turning off the semiconductor switch, the driving electrode of the booster semiconductor (V1) being connected to a DC voltage output (U2) generate

Abstract: A method of determining a short-circuit inductance in an asynchronous machine even during operation of the machine includes the steps of causing a step change in the stator voltage (u.sub.s); measuring both the stator voltage (u.sub.s) and the stator current derivative (i'.sub.s) both before and after the step change in the stator voltage; determining the difference between the measured stator voltages (u.sub.s (t.sub.1), u.sub.s (t.sub.2)) and the difference between the measured stator current derivatives (i'.sub.s (t.sub.1), i'.sub.s (t.sub.2)); and determining the quotient of the difference between the stator voltages and the difference between the stator current derivatives for obtaining a short-circuit inductance (.sigma.L.sub.s).

Abstract: The invention relates to a method for slip compensation in a squirrel cage induction motor when the motor (2) is fed by an inverter (1) without feedback at a supply frequency less than 20% of the rated supply frequency of the motor after the motor has first been fed at a frequency more than 50% of the rated frequency for a period of time at least equal to a mechanical time constant of a combination formed by the motor and a load device, wherein a term (kT) proportional to the torque of the motor is determined and added to the set value of the rotation speed (n) to effect slip compensation. To improve the compensation accuracy, the value of said compensation term is stored in a memory before transition from the frequency more than 50% of the rated frequency to a frequency less than 50% of the rated frequency, and the stored compensation term is used as such for slip compensation when the supply frequency of the motor is less than 20% of the rated frequency.