PWM CONTROL METHOD FOR THREE-PHASE MULTILEVEL INVERTER, AND CONTROL DEVICE

PROBLEM TO BE SOLVED: To solve the problem that, when providing an inhibition band in PWM gate signal generation, there is a period in which switching is not generated, as long as or longer than 1.5 cycle of a carrier signal in accordance with zero-phase offset.SOLUTION: When a voltage command of one phase or more in voltage commands of three phases is present in the inhibition band, a minimum zero-phase offset amount which makes the voltage commands of all the three phases get out of the inhibition band is calculated. The calculated zero-phase offset discriminates whether a code is positive or negative with respect to a boundary of a voltage level region and inhibits for each cycle of voltage command update a change of positive→negative→positive or negative→positive→negative for each cycle. From a state where the voltage commands of all the three phases do not exist within the inhibition band during the inhibition, a code which is discriminated when the voltage command of one or more of the three phases exists within the inhibition band is held until the voltage commands of all the three phases do not exist in the inhibition band any more, and during the holding, the zero-phase offset amount is calculated sing the held positive or negative code.SELECTED DRAWING: Figure 1 【課題】ＰＷＭゲート信号生成時に禁止帯を設ける場合、零相オフセットによってはキャリア信号の１．５周期以上スイッチングが発生しない期間がある。【解決手段】三相の電圧指令うち１相以上の電圧指令が前記禁止帯内に存在したとき、三相全ての電圧指令が禁止帯外に脱出する最小の零相オフセット量を演算し、且つ算出された零相オフセットは前記電圧レベル領域の境界に対し正か負かの符号を判定し、電圧指令更新の周期毎に正→負→正、若しくは負→正→負へと周期毎の変化を禁止する。また、その禁止において三相全ての電圧指令が禁止帯内に存在しない状態から、三相のうち１相以上の電圧指令が前記禁止帯内に存在したときに判定された符号を、三相全ての電圧指令が禁止帯内に存在しなくなるまで保持し、その間の零相オフセット量の演算は保持された正または負の符号を用いて行う。【選択図】 図１