Motor control apparatus with phase related detector

Abstract

A microprocessor controlled motor starter is utilized in which the sign values of two phases of voltage are sampled and stored prior to actual motor startup to determine if a phase reversal, a phase imbalance, or a phase loss exists. If any of the preceding conditions exist, the motor start operation is aborted. This generally requires sampling the signs of the appropriate voltages three times during each voltage cycle at approximately equal intervals of 120.degree., give or take 10.degree. or so, and then forming a matrix of voltage signs versus sampling intervals. By comparing diagonal measurements of the sign values in the matrix for three diagonals in a direction of advancing time, phase loss or imbalance can be determined. The determining factor is that each diagonal must contain two values which should be equal, that is, both should be digital ones or both should be digital zeros. If such is the case for the three diagonal measurements, then no phase imbalance or loss exists. By using the same matrix and measuring appropriate two memory location diagonals against time in an appropriate manner, phase reversal can also be detected. Only signl values are utilized and only digital sign values are utilized with a digital one arbitrarily representing positive half cycle of voltage and a digital zero representing a negative half cycle of voltage. A calculating routine is provided whereby a measurement of the degree of phase imbalance can be determined by comparing the total number of diagonal measurements made over a large number of cycles with the number of failed diagonal measurements.