INITIAL RESIDUAL OUTPUT WAVEFORM REMOVING METHOD FOR OUTPUT WAVEFORM SENSOR

摘要

PURPOSE:To obtain an accurate zero-phase output by storing an initial residual output waveform due to three-phase unbalance from a voltage sensor in a storage means and subtracting a signal based upon the stored data from a signal with the initial residual output waveform due to the present three-phase unbalance. CONSTITUTION:Detection signals from voltage sensors are inputted to input terminals 6-8 and an initial residual voltage due to the three-phase unbalance from a voltage sensor is applied to the output-side point A of an operational amplifier OP1. Then the initial residual output waveforms at output points B and C of operational amplifiers OP1 and OP3 are set to the same shape and the output waveform from the point C is stored as initial residual voltage data in a RAM 13 by a CPU 11. Then the initial residual voltage data of one cycle stored in the RAM 13 is inputted from the CPU 11 to the uninverted input terminal of an operation amplifier OP6 through a D/A converter 6 and an operational amplifier OP5. Further, the output waveform from the operational amplifier OP2 is inputted from the uninverted input terminal of the amplifier OP6 and subtracted by the amplifier OP6 to obtain a zero-phase output which contains no initial residual voltage at an output terminal K.