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 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 for controlling brake resistors and a brake chopper, the number of brake resistors being two or more and the brake resistors being connected in series with switches to be controlled, the series connection being connected between a positive and a negative rail of a DC voltage intermediate circuit, the method comprising the step of determining a magnitude for a voltage of the DC intermediate circuit; and determining a first voltage limit and a second voltage limit. The method further comprises the steps of switching brake resistors to the intermediate circuit in a periodically alternating manner, each switch being switched during a switching period and the on-period of each switch in a switching period being responsive to the magnitude of the voltage in the DC voltage intermediate circuit when the voltage is above the first predetermined limit and below the second predetermined limit.

Abstract: A method and an arrangement for charging capacitors of a direct-voltage intermediate circuit of a frequency converter. The arrangement comprises a charging circuit (CCA) comprising a first diode (D1) and a second diode (D2) connected in series with the first diode (D1) and a current-limiting component (AA) connected in parallel with the series connection of the diodes (D1, D2), whereby said capacitors may be charged through a main switch (K1b, K2b, . . . , Knb) of the capacitor, the first diode (D1) and the current-limiting component (AA).

Abstract: This publication discloses a switching device combination for capacitive loads (3) connected to a direct voltage. The switching device combination includes an actual switch component (1) for connecting voltage to the capacitive load (3), a charging switch component (2) for connecting charging voltage to the capacitive load in the initial stage, which charging switch component is dimensioned for a lower current than the actual switch component (1), a controller component (4), by means of which the actual switch component (1) is controlled from an open state to a closed state and vice versa, with the aid of a mechanical lever (5), which is connected to a first shaft (6), and delay elements (11) for delaying the connection of the actual switch component (1), so that the closed charging switch component (2) will have time to charge the capacitive load (3) before the connection of the actual switch component (1).

Abstract: A method and an arrangement for protecting a frequency converter in a system comprising a motor and a frequency converter supplying it via a bipolar or multipolar supply connection, the arrangement comprising first connecting means adapted to couple poles of the supply connection mutually substantially into short-circuit in response to a detection of a fault in the frequency converter.

Abstract: A method for operating parallel-connected inverter modules, wherein two or more inverter modules (A, B, C) are connected in parallel to feed the same load. Each inverter module has two or more output phases (u, v, w) for supplying electric power into a two or more phase load by determining the temperature (TAu, TAv, TAw, TBu, TBv, TBw, TCu, TCv, TCw) of each output phase (Au, Av, Aw, Bu, Bv, Bw, Cu, Cv, Cw) in each inverter module, comparing the temperatures of the output phases in each inverter module with the temperatures of the same output phase in other parallel-connected modules, and generating an alarm signal if the temperature of the output phase in an inverter module differs from the temperatures of the same output phase of the other inverter modules more than allowed by a predetermined limit.

Abstract: A choke arrangement and a method in conjunction with an inverter, the phase output of the inverter being configured to be composed of two or more parallel branches, each of which comprises an upper (V1, V3, V5) and a lower (V2, V4, V6) power semiconductor component at the output, the upper one of which being coupled to a positive voltage of a direct voltage intermediate circuit and the lower to a negative voltage, the components being in series, the output of each branch being composed of a point between the components. The arrangement comprises branch-specific single-phase chokes (L1, L2, L3), the first ends of which chokes are arranged to be coupled to the outputs of the power semiconductor components and the second ends together to form the phase output of the inverter.