| 摘要 |
PURPOSE:To protect a power switch element from thermal breakdown with high accuracy in the low-frequency operation mode of an inverter. CONSTITUTION:Data alpha on the output current io of an inverter, power switch element temperature Tc, element junction temperature TiMAX, and margin temperature are fetched (S1), and the loss P(io) to io is deduced from the table of the total power loss P of io vs. element being gotten in advance (S2), and it is sought by the formula of the allowable maximum transient heat impedance theta(tA)={TJMAX-(Tc+alpha)}/P(io) of the element. The time tA of its reaching Q (tA) is deduced from the table of t Vs. (tA) being gotten beforehand (S4), and it is compared with half cycle 1/(2Xfo), thus when current application time tA continues for tA or more (S5 and S6), the inverter is tripped to prevent the thermal breakdown of the element. |
