Abstract: A synchronous machine system comprising a synchronous motor including a stator, stator winding, rotor, and field winding; an AC power supply circuit structured to transmit current to or from the stator winding of the synchronous motor at a controlled frequency and transmit current to or from a power source at a controlled frequency; a DC exciter unit structured to receive power from a power source, convert the received power to DC power at a desired voltage, and supply the converted power across a DC bus to the field winding of the synchronous motor; and an energy storage circuit coupled to the DC bus of the DC exciter unit having at least one ultracapacitor, and structured to receive power from a power source, to charge the ultracapacitor, and to provide power to the field winding of the synchronous motor following a power failure.

Abstract: A synchronous machine system comprising a synchronous motor including a stator, stator winding, rotor, and field winding; an AC power supply circuit structured to transmit current to or from the stator winding of the synchronous motor at a controlled frequency and transmit current to or from a power source at a controlled frequency; a DC exciter unit structured to receive power from a power source, convert the received power to DC power at a desired voltage, and supply the converted power across a DC bus to the field winding of the synchronous motor; and an energy storage circuit coupled to the DC bus of the DC exciter unit having at least one ultracapacitor, and structured to receive power from a power source, to charge the ultracapacitor, and to provide power to the field winding of the synchronous motor following a power failure.

Abstract: An arrangement which includes two or more energy storage units for electrical energy connected in series, and two or more balancing resistor units. Each balancing resistor unit is connected in parallel with one of the energy storage units. The arrangement also includes means for determining a voltage over all of the series-connected energy storage units and means for determining the energy storage unit voltages between poles of the energy storage units. One or more of the balancing resistor units include a base resistor unit and a control resistor unit connected in series and a switching device connected in parallel with the control resistor units.

Abstract: A method and an arrangement of measuring inverter current, where the inverter is connected to and supplied by a DC intermediate circuit having two or more parallel capacitor branches connected between the positive and negative rail of the DC intermediate circuit, and the capacitance of the capacitor branches being known. The method comprises the steps of measuring the current of one of the parallel capacitor branches, and determining from the measured current the magnitude of the inverter current.

Abstract: A method of controlling a brake chopper and a control arrangement, the brake chopper being connected between the positive and the negative rails of an intermediate voltage circuit feeding an inverter bridge, wherein current measurement means are arranged between a DC voltage source and the brake chopper and adapted to measure DC current flowing in the intermediate voltage circuit, which method comprises steps of forming with the inverter bridge an output voltage to a load connected to the output of the inverter bridge, determining a time instant when the DC current of the intermediate circuit is sampled, and preventing the use of the brake chopper at the determined time instant.

Abstract: An arrangement which includes two or more energy storage units for electrical energy connected in series, and two or more balancing resistor units. Each balancing resistor unit is connected in parallel with one of the energy storage units. The arrangement also includes means for determining a voltage over all of the series-connected energy storage units and means for determining the energy storage unit voltages between poles of the energy storage units. One or more of the balancing resistor units include a base resistor unit and a control resistor unit connected in series and a switching device connected in parallel with the control resistor units.

Abstract: A method and an arrangement of measuring inverter current, where the inverter is connected to and supplied by a DC intermediate circuit having two or more parallel capacitor branches connected between the positive and negative rail of the DC intermediate circuit, and the capacitance of the capacitor branches being known. The method comprises the steps of measuring the current of one of the parallel capacitor branches, and determining from the measured current the magnitude of the inverter current.

Abstract: A method in connection with a frequency converter, which frequency converter comprises output phases and switches of the output phases, the output phases being switched to feed a load, and the main circuit of the frequency converter being provided with common-mode inductance. The method comprises a step where, in case of earth fault, switches of the output phase having an earth fault are modulated in such a way that the average potential of this phase corresponds to the ground potential.