An Evaluation Method for Voltage Dips in a Shipboard Microgrid under Quasi-balanced and Unbalanced Voltage Conditions

High power motor loads are widely used in shipboard microgrids (SMGs) consuming about 70% of the generated electrical power. Voltage dips, which are usually caused by the starting current of high-power motors, are one of the main causes of onboard sensitive electrical equipment dropout. This phenomenon must be considered in design of SMGs to comply with maritime standards. In this paper, an evaluation method is proposed to estimate the expected severity of voltage dips and also generator current transient surges due to the onboard motor startups under real sea-going conditions. This is based on the Riemann-summation-principle evaluation method. The quasi-balanced and unbalanced ac bus voltage cases are carefully selected to present the actual impact of the voltage dips in real SMG. The evaluations are validated by measurements gathered from the ballast pump motor startup in the SMG. The proposed method can provide ship engineers with necessary information about the actual magnitude/depth of voltage dips. Accordingly, the allowable capacities of high-power motors can be estimated, which is beneficial to determine proper motor starter designs and improve the power quality in real SMGs.