摘要 |
PROBLEM TO BE SOLVED: To enable the detection of service interruption in a predetermined time regardless of whether input is of 50 Hz or 60 Hz. SOLUTION: Input commercial electro power is rectified and smoothed (23) and is captured in a control part 25 (S1) as a digital value Vin (24). Then the zero-cross point of the input alternating current is detected (27), and an adjacent zero-cross interval is measured to determine whether it is of 50 Hz or 60 Hz (S2). A reference value Vs is set to 50 Hz. In the case that it is determined as 50 Hz, Vin/2=Vin' (S3). In the case that it is determined as 60 Hz, it is corrected as (Vin-Vc)/2=Vin' (S4), and it is determined whether Vin'<Vs or not (S5) to determined whether a service interruption or not. |