| 摘要 |
<p>The invention refers to an automatic dephasing method with the phaseφ= kx360 degrees/N, where k = 0,1,...N-1, in a narrow frequency band and with a dephasing circuit with 120 degrees, with application of the method for the case N=3, k=1. The method is based on an automatic control loop of the phase, where the control is made in order to maintain a constant dephasing of 0 degree between frequency multiples of order N of the inlet signal and the dephased signal.The 120-degree dephaser, achieved with a voltage controlled dephasing circuit (cell with "low pass" type transfer function and with TEC used with variable resistance), uses two identical PLL circuits for the multiplication by 3 of the frequency and the phases of the inlet and outlet signals. The correction signal from the phase sensitive detector ("with 3 states") amplified and integrated, commands the dynamic resistance of TEC and thus the dephasing inserted by the circuit, so that the frequency multiples of order 3 of the inlet and outlet signals to be in phase. The working domain of frequency of the dephaser is limited by the capture band of the PLL circuits.The circuit is not modifying the outlet signal amplitude and allows the maintenance of a constant dephasing (120 degree) between the inlet and outlet signals, independent of the frequency fluctuations of the signal or of the variation of the parameters, with temperature or in time, of the components, thus eliminating the need of control.The 120 degree dephased circuit can be used within the frame of devices which are measuring with precision the symmetrical components of voltage and current in a three-phased system with asymmetric sinusoidal magnitudes, for example in a wattmeter for three-phased alternating current in the range 35...75 Hz.</p> |
