BALANCE OFFSET CONTROL DEVICE FOR NEUTRAL-POINT VOLTAGE CONTROL IN NEUTRAL POINT CLAMPED CONVERTER

摘要

The purpose of the present invention is to provide balance offset control device and method for controlling a neutral-point voltage in a neutral point clamped (NPC) converter, which resolve DC-link voltage imbalance occurring in the NPC converter by adding an output value of a balance offset controller to a three-phase reference voltage for pulse width modulation (PWD) to calculate a final reference voltage. According to the present invention, the balance offset control device for controlling a neutral-point voltage in a NPC converter comprises: a voltage control unit for reducing a voltage difference between an upper end capacitor and a lower end capacitor that are arranged across the neutral point, to a permissible limit; a sign determining unit for determining a sign by calculating the direction of a current flowing at the neutral point by each sector; a voltage limiting unit for limiting the level of a balance offset voltage, thereby resolving DC-link voltage imbalance by adding an output value of a balance offset controller to a three-phase reference voltage for PWD. [Reference numerals] (AA) Synchronous 2 phase/stationary 2 phase transformation formula (2); (BB) Stationary 2 phase/stationary 3 phase transformation formula (3); (CC) Offset voltage calculation formula (5) or (10); (DD) SVPWM reference voltage calculation formula (7) or (10); (EE) Final reference voltage calculation formula (23); (FF) Balance switch On/Off (13); (GG) Sign_bal formula (16)~(22); (HH) Controller (14) or (15); (II) Limit value (24)