METHOD FOR CONTROLLING NEUTRAL POINT POTENTIAL OF INVERTER OF NEUTRAL POINT CLAMPING TYPE

摘要

A method for controlling the neutral point potential of an inverter of neutral point clamping type irrespective of the power factor by measuring or predicting the phase current in a simple way. The output state taken by an inverter of three-phase neutral point clamping type is represented by a vector. Depending on the phase state where the voltage vector outputted from the invcrter is contained between which vectors, the occurrence time ratio of a specific vector corresponding to the voltage vector is changed to stabilize the neutral point voltage. The time of the three-phase output voltage when six switched states where the positive bus (P), the negative bus (N), and the neutral line (O) are connected to respective three-phase output terminals are set up is controlled below a first preset value. The shortage of the output voltage due to the control is compensated by the six switched states except the two switched states where the three-phase output terminals are all connected to the positive bus (P) or IMAGE