| 摘要 |
When measuring fault currents in an inverter, in which controlled semiconductor switches are pulse width modulated, PWM-VSI, to convert a DC voltage from an intermediary circuit to a 3-phase AC voltage, DC currents are measured in the positive and the negative rail of the inverter, so that it is possible to detect faults originating from both short-circuits and earthing faults, maintaining a high sensitivity when reconstructing phase currents, which can be made by a so-called vector modulation, called (SFAVM), in which the states of the individual transistor switches are defined in a vector room (SFAVM) having six active states in which current flows in the inverter and two active states in which no current flows in the inverter. On the basis of the DC current measurements the phase currents can be reconstructed, and all faults can be detected. As mentioned, the measurement takes place as a measurement of DC currents, and for this purpose two transducers are used, which are constructed in a way that at the same current they give two different physical values, so that if there is no fault on the inverter, the phase current can still be reconstructed. The invention is especially expedient in connection with motor controls, active inverters, active filters, compensators, etc. |
