Abstract: A method in connection with a network converter, and a network converter, the network converter comprising two or more network converter modules coupled in parallel, and first control means for controlling the network converter modules. The method comprises the steps of controlling the network converter modules by the first control means, preventing or allowing use of one or more network converter modules in order to reconfigure the network converter during operation of the network converter.

Abstract: A method in connection with a network inverter, an LCL network filter (3) being connected between the network inverter (1) and network (2), and the network inverter being arranged to operate as an active converter of harmonic components of electricity, and the method comprises the steps of forming a current reference (i1, ref) for the network inverter (1) for producing a desired voltage, selecting a harmonic electric component (v), the proportion of which needs to be changed, forming a current reference (i1, refv) altering the selected harmonic component (v), summing the generated current reference (i1, refv) altering the selected harmonic component with the current reference (i1, ref) of the network inverter to produce a summed current reference (i1, ref, tot), and controlling the network inverter with the summed current reference (i1, ref, tot) in a coordinate system bound to the virtual flux linkage of the network inverter by using DTC control.

Abstract: A method and arrangement for charging an intermediate circuit of a frequency converter, the intermediate circuit of the frequency converter comprising one or more capacitors, and the frequency converter having means for charging the intermediate circuit, the means comprising a rectifier bridge, a direct current choke, a direct-current transformer, a zero diode, and a semiconductor switch and a control circuit arranged to control the switch. The method comprises the steps of defining in advance high and low current limits, controlling the semi-conductor switch alternately to conductive and non-conductive states depending on the magnitude of a charging current, and stopping the controlling of the semiconductor switch when the charging current remains below the high current limit.

Abstract: A method in connection with a network inverter, an LCL network filter (3) being connected between the network inverter (1) and network (2), and the network inverter being arranged to operate as an active converter of harmonic components of electricity, and the method comprises the steps of forming a current reference (i1, ref) for the network inverter (1) for producing a desired voltage, selecting a harmonic electric component (v), the proportion of which needs to be changed, forming a current reference (i1, refv) altering the selected harmonic component (v), summing the generated current reference (i1, refv) altering the selected harmonic component with the current reference (i1, ref) of the network inverter to produce a summed current reference (i1, ref, tot), and controlling the network inverter with the summed current reference (i1, ref, tot) in a coordinate system bound to the virtual flux linkage of the network inverter by using DTC control

Abstract: A method and arrangement for charging an intermediate circuit of a frequency converter, the intermediate circuit of the frequency converter comprising one or more capacitors, and the frequency converter having means for charging the intermediate circuit, the means comprising a rectifier bridge, a direct current choke, a direct-current transformer, a zero diode, and a semiconductor switch and a control circuit arranged to control the switch. The method comprises the steps of defining in advance high and low current limits, controlling the semiconductor switch alternately to conductive and non-conductive states depending on the magnitude of a charging current, and stopping the controlling of the semiconductor switch when the charging current remains below the high current limit.