Abstract: A method and an arrangement are disclosed for balancing load between parallel connected inverter modules, which inverter modules are arranged to supply a common load. The method can include providing similar switching instructions for parallel connected inverter modules, determining on the basis of phase currents of each parallel inverter module a first time period for each output phase of each inverter module for correcting current imbalance by advancing or delaying turn-on or turn-off time instants of switch components of the inverter modules, and advancing or delaying the turn-on or turn-off time instants of the switching instructions based on the first time period.

Abstract: A method and an arrangement for determining the rotation speed of a motor fed by an inverter, the arrangement comprising means for determining the rotation speed of the motor in at least two alternative manners, whereby the means for determining the rotation speed of the motor comprise one of the at least two alternative manners of performance: means for measuring the frequency of the voltage fed to the motor by the inverter; and means for estimating the rotation speed of the motor on the basis of the measured frequency.

Abstract: A method and arrangement for controlling a doubly-fed induction machine by a frequency converter including a rotor side converter (INU) connected to a rotor circuit of a doubly-fed induction machine (DFIG) and having a control system with rotor flux as a feedback variable, a grid side converter (ISU) connected to an AC power network, and a direct voltage intermediate circuit (DC) connected between the rotor side converter (INU) and the grid side converter (ISU). The method includes forming a rotor flux reference (?r,ref), forming a damping signal (?ref,D), summing the damping signal and the rotor flux reference for obtaining a modified rotor flux reference (?ref), and feeding the modified rotor flux reference to a controller of the rotor side converter (INU) for damping sub-synchronous resonances.

Abstract: An exemplary electric drive system has a plural number of electric drive subsystems. Each subsystem having a fault diagnostics arrangement, where the arrangement includes a respective control board for each subsystem. Event data of each subsystem is recorded on the respective control board, and one of the respective control boards of the electric drive system is a main control board of the electric drive system. Event data of a subsystem is transferred from the respective control board to the main control board through a data transfer medium.

Abstract: A method and an arrangement are disclosed for balancing load between parallel connected inverter modules, which inverter modules are arranged to supply a common load. The method can include providing similar switching instructions for parallel connected inverter modules, determining on the basis of phase currents of each parallel inverter module a first time period for each output phase of each inverter module for correcting current imbalance by advancing or delaying turn-on or turn-off time instants of switch components of the inverter modules, and advancing or delaying the turn-on or turn-off time instants of the switching instructions based on the first time period.

Abstract: A method and an arrangement for determining the rotation speed of a motor fed by an inverter, the arrangement comprising means for determining the rotation speed of the motor in at least two alternative manners, whereby the means for determining the rotation speed of the motor comprise one of the at least two alternative manners of performance: means for measuring the frequency of the voltage fed to the motor by the inverter; and means for estimating the rotation speed of the motor on the basis of the measured frequency.

Abstract: A protection configuration for converter means which comprise a plurality of controllable switches, the protection configuration comprising a protection circuit coupled to the alternating voltage side of the converter means, which protection circuit comprises at least one protective switch configured to short-circuit the alternating voltage side of the converter means, wherein the protection configuration, in predetermined failure situations, is configured to close the protective switch and thus to short-circuit the alternating voltage side of the converter means. After the failure situation has cleared up, the protection configuration is configured to short-circuit the alternating voltage side of the converter means by means of the controllable switches to enhance commutation of the protective switch.

Abstract: A method for operating a doubly-fed machine by determining its rotational speed (nact), forming a rotational speed reference (nref), measuring network voltage and current, and calculating network active power (Pact) and reactive power (Qact). Thereafter, calculating shaft torque (T) based on active power (Pact) and rotating speed (nact), forming a frequency reference (Fref) for the inverter based on machine rotating speed (nact), rotating speed reference (nref), shaft torque (T), and the known pole pair number and network frequency, forming a reactive power reference (Qref) for the machine.

Abstract: A protection configuration for converter means which comprise a plurality of controllable switches, the protection configuration comprising a protection circuit coupled to the alternating voltage side of the converter means, which protection circuit comprises at least one protective switch configured to short-circuit the alternating voltage side of the converter means, wherein the protection configuration, in predetermined failure situations, is configured to close the protective switch and thus to short-circuit the alternating voltage side of the converter means. After the failure situation has cleared up, the protection configuration is configured to short-circuit the alternating voltage side of the converter means by means of the controllable switches to enhance commutation of the protective switch.

Abstract: A method for operating a doubly-fed machine by determining its rotational speed (nact), forming a rotational speed reference (nref), measuring network voltage and current, and calculating network active power (Pact) and reactive power (Qact). Thereafter, calculating shaft torque (T) based on active power (Pact) and rotating speed (nact), forming a frequency reference (Fref) for the inverter based on machine rotating speed (nact), rotating speed reference (nref), shaft torque (T), and the known pole pair number and network frequency, forming a reactive power reference (Qref) for the machine.

Abstract: A method in connection with a synchronous machine, the method comprising the steps of determining phase currents (iu, iv, iw) of a stator in the synchronous machine, determining phase voltages (uu, uv, uw) of a stator in the synchronous machine and estimating a position angle (&ggr;). The method also comprises the steps of generating estimates for stator flux vector components (&psgr;i&agr;, &psgr;i&bgr;) of the determined phase currents (iu, iv, iw) of the stator and the estimated rotor angle (&ggr;) using a current model (2) of the synchronous machine, generating estimates for the stator flux vector components (&psgr;i&agr;, &psgr;i&bgr;), comparing the generated stator flux vector estimates (&psgr;i&agr;, &psgr;i&bgr;; &psgr;&agr;, &psgr;&bgr;) with the phase difference of the estimates in order to achieve a proportional quantity, and adjusting the estimate (&ggr;) of the rotor position angle on the basis of the quantity proportional to the phase difference.